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Sample records for hydrogen sorption kinetics

  1. Understanding the role of few-layer graphene nanosheets in enhancing the hydrogen sorption kinetics of magnesium hydride.

    PubMed

    Liu, Guang; Wang, Yijing; Jiao, Lifang; Yuan, Huatang

    2014-07-23

    The catalytic effects of few-layer, highly wrinkled graphene nanosheet (GNS) addition on the dehydrogenation/rehydrogenation performance of MgH2 were investigated. It was found that MgH2-5 wt %GNSs nanocomposites prepared by ball milling exhibit relatively lower sorption temperature, faster sorption kinetics, and more stable cycling performance than that of pure-milled MgH2. The dehydrogenation step confirms that the Avrami exponent n increases from 1.22 to 2.20 by the Johnson-Mehl-Avrami (JMA) formalism when the desorption temperature is reduced from 350 °C to 320 °C and 300 °C, implying that a change in the decomposition temperature can alter the mechanism during the dehydrogenation process. For rehydrogenation, the Avrami value n is close to 1; further study by several models coincident with n = 1 reveals that the absorption process of the MgH2-5 wt %GNSs sample conforms to the Mampel equation formulated through the random nucleation approach and that the nature of the absorption mechanism does not change within the temperature range studied. Furthermore, microstructure analysis demonstrated that the defective GNSs are distributed uniformly among the MgH2 particles and that the grain size of the MgH2-5 wt %GNSs nanocomposite is approximately 5-9 nm. The efficient metal-free catalytic dehydrogenation/rehydrogenation of MgH2 can be attributed to the coupling of the nanosize effect and defective GNSs.

  2. Hydrogen peroxide modified sodium titanates with improved sorption capabilities

    SciTech Connect

    Nyman, May D.; Hobbs, David T.

    2009-02-24

    The sorption capabilities (e.g., kinetics, selectivity, capacity) of the baseline monosodium titanate (MST) sorbent material currently being used to sequester Sr-90 and alpha-emitting radioisotopes at the Savannah River Site are significantly improved when treated with hydrogen peroxide; either during the original synthesis of MST, or, as a post-treatment step after the MST has been synthesized. It is expected that these peroxide-modified MST sorbent materials will have significantly improved sorption capabilities for non-radioactive cations found in industrial processes and waste streams.

  3. Fast hydrogen sorption from MgH2-VO2(B) composite materials

    NASA Astrophysics Data System (ADS)

    Milošević, Sanja; Kurko, Sandra; Pasquini, Luca; Matović, Ljiljana; Vujasin, Radojka; Novaković, Nikola; Novaković, Jasmina Grbović

    2016-03-01

    The hydrogen sorption kinetics of MgH2‒VO2(B) composites synthesised by mechanical milling have been studied. The microstructural properties of composites were characterized by means of X-ray diffraction (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Particle size analysis (PSD), while sorption behaviour was followed by differential scanning calorimetry (DSC) and Sievert measurements. Results have shown that although desorption temperature reduction is moderate; there is a substantial improvement in hydrogen sorption kinetics. The complete desorption of pure MgH2 at elevated temperature takes place in more than 30 min while the composite fully desorbs in less than 2 min even at lower temperatures. It has been shown that the metastable γ-MgH2 phase and the point defects have a decisive role in desorption process only in the first sorption cycle, while the second and the subsequent sorption cycles are affected by microstructural and morphological characteristics of the composite.

  4. Sorption Enhanced Reaction Process (SERP) for production of hydrogen

    SciTech Connect

    Anand, M.; Hufton, J.; Mayorga, S.

    1996-10-01

    Sorption Enhanced Reaction Process (SERP) is a novel process that is being developed for the production of lower cost hydrogen by steam-methane reforming (SMR). In this process the reaction of methane with steam is carried out in the presence of an admixture of a catalyst and a selective adsorbent for carbon dioxide. The key consequences of SERP are: (i) reformation reaction is carried out at a significantly lower temperature (300-500{degrees}C) than that in a conventional SMR reactor (800-1100{degrees}C), while achieving the same conversion of methane to hydrogen, (ii) the product hydrogen is obtained at reactor pressure (200-400 psig) and at 98+% purity directly from the reactor (compared to only 70-75% H{sub 2} from conventional SMR reactor), (iii) downstream hydrogen purification step is either eliminated or significantly reduced in size. The first phase of the program has focused on the development of a sorbent for CO{sub 2} which has (a) reversible CO{sub 2} capacity >0.3 mmol/g at low partial pressures of CO{sub 2} (0.1 - 1.0 atm) in the presence of excess steam (pH{sub 2}O/pCO{sub 2}>20) at 400-500{degrees}C and (b) fast sorption-desorption kinetics for CO{sub 2}, at 400-500{degrees}C. Several families of supported sorbents have been identified that meet the target CO{sub 2} capacity. A few of these sorbents have been tested under repeated sorption/desorption cycles and extended exposure to high pressure steam at 400-500{degrees}C. One sorbent has been scaled up to larger quantities (2-3 kg) and tested in the laboratory process equipment for sorption and desorption kinetics of CO{sub 2}. The CO{sub 2}, sorption and desorption kinetics are desirably fast. This was a critical path item for the first phase of the program and now has been successfully demonstrated. A reactor has been designed that will allow nearly isothermal operation for SERP-SMR. This reactor was integrated into an overall process flow diagram for the SERP-SMR process.

  5. Sorption kinetics of heavy oil into porous carbons.

    PubMed

    Nishi, Yoko; Iwashita, Norio; Sawada, Yoshihiro; Inagaki, Michio

    2002-12-01

    Sorption kinetics of heavy oil into porous carbons was evaluated by a concept of liquid sorption coefficient obtained from the weight increase of heavy oil with sorption time, which was measured by a wicking test. Exfoliated graphite, carbonized fir fibers and carbon fiber felts were used as porous materials. It was found that the liquid sorption coefficient of fibrous carbons was twice larger than that of exfoliated graphite. Such a difference in the liquid sorption coefficient between the exfoliated graphite and two fibrous carbons was caused by a difference in effective sorption porosity and tortuosity between them. For the exfoliated graphite and carbonized fir fibers, the liquid sorption coefficient and the effective sorption porosity were strongly dependent on their density. The maximum values of both liquid sorption coefficient and effective sorption porosity of the exfoliated graphite were shown at the bulk density around 16 kg/m3. The liquid sorption coefficient of the carbonized fir fibers increased with increasing the density in the range from 6 to 30 kg/m3. When the carbonized fir fibers were densified above 30 kg/m3, the sorption rate was saturated. On the other hand, the sorption kinetics into the carbon fiber felt was almost independent of the bulk density, because the density of the carbon fiber felt is not effective for the pore structure. The effect of bulk density on the sorption kinetics could be supported from an analysis of pore structure of the porous carbons with different densities, which was measured by mercury porosimeter. PMID:12448551

  6. Effect of sorption on flocculation kinetics: Experimental studies

    SciTech Connect

    Subramaniam, K.; Yiacoumi, S.; Tsouris, C.

    1997-11-01

    Sorption of copper and cadmium ions from aqueous solutions by ferric oxide particles was studied using batch equilibrium and kinetic experiments. The sorption process was found to be pH dependent, with the uptake increasing at high pH values. An increase in equilibrium pH was observed when the initial pH was in the acidic range and a decrease from initial values was observed in the basic range, in the case of both copper and cadmium sorption. The former phenomenon is due to competition between metal and proton binding and the latter is due to precipitation mechanisms at high initial pH values. A large increase in the zeta potential of the particles from baseline values was observed during equilibrium sorption. This increase occurs as a result of surface charge neutralization due to metal ion uptake. Particle destabilization appears to occur as a result of metal ion sorption. Kinetic experiments indicate that the uptake of copper by ferric oxide particles is a slow process. pH histories were similar to those obtained in the sorption equilibrium experiments. Changes in the size distribution of the ferric oxide particles due to aggregate formation during uptake of ions is observed in the kinetic studies. These findings indicate a potential role of metal ion uptake in particle flocculation kinetics through alteration of the surface electrostatic potential.

  7. Kinetics of the sorption of triterpene saponin by hypercrosslinked polystyrene

    NASA Astrophysics Data System (ADS)

    Mironenko, N. V.; Brezhneva, T. A.; Selemenev, V. F.

    2013-03-01

    The kinetics of sorption of triterpene saponin by the polymer sorbent NM-200 is considered. The influence of the surface activity of glycoside on the rate of formation and structure of the adsorption layer on the sorbent's surface is established. The rate-determining step of sorption is found to be diffusion into the sorbent grain. The value of the activation energy demonstrates the determining role of dispersion forces in the interaction between triterpene saponin and the polymer sorbent MN-200.

  8. Hydrogen sorption studies of materials used in Li(Si)/FeS/sub 2/ thermal batteries

    SciTech Connect

    Assink, R.A.; Schneider, D.A.; Guidotti, R.A.

    1988-06-01

    Hydrogen formation occurs during long-term storage of Li(Si)/FeS/sub 2/ thermal batteries as a result of residual moisture reacting with the Li(Si) anode. A study of the rates of hydrogen sorption by materials used in Li(Si)/FeS/sub 2/ thermal batteries was undertaken in order to obtain a measure of their reactivity to hydrogen in the thermal battery environment. The sorption of hydrogen by pellets of the anode material, separator mix, catholyte mix, and heat powder was monitored for periods of up to a month at a temperature of 60/degree/C. The anode material was 44% Li/56% Si alloy; the separator was 65% LiCl-KCl eutectic/35% MgO; the catholyte was 75% FeS/sub 2//25% electrolyte binder mix (with the composition 88% LiCl-KCl eutectic/12% SiO/sub 2/; and the heat powder was 88% Fe/12% KClO/sub 4/. Individual components of the mixes exhibiting significant sorption of hydrogen were examined, and the FeS/sub 2/ was the only material found to be actively sorbing hydrogen. The kinetics of the sorption process were enhanced by a smaller particle size of FeS/sub 2/, a higher hydrogen pressure, and a higher level of oxidized iron impurities. The hydrogen was not removed by vacuum heating at 200/degree/C. A hydrogen sorption study of the insulation materials used in the battery showed the ceramic-fiber blanket to be a significant sorbent for hydrogen. 7 refs., 10 figs., 5 tabs.

  9. Hydrogen sorption studies of materials used in Li(Si)/FeS2 thermal batteries

    NASA Astrophysics Data System (ADS)

    Assink, Roger A.; Schneider, Duane A.; Guidotti, Ronald A.

    1988-06-01

    Hydrogen formation occurs during long-term storage of Li(Si)/FeS2 thermal batteries as a result of residual moisture reacting with the Li(Si) anode. A study of the rates of hydrogen sorption by materials used in Li(Si)/FeS2 thermal batteries was undertaken in order to obtain a measure of their reactivity to hydrogen in the thermal battery environment. The sorption of hydrogen by pellets of the anode material, separator mix, catholyte mix, and heat powder was monitored for periods of up to a month at a temperature of 60 C. The anode material was 44 percent Li/56 percent Si alloy; the separator was 65 percent LiCl-KCl eutectic/35 percent MgO; the catholyte was 75 percent FeS2/25 percent electrolyte binder mix (with the composition 88 percent LiCl-KCl eutectic/12 percent SiO2; and the heat powder was 88 percent Fe/12 percent KClO4. Individual components of the mixes exhibiting significant sorption of hydrogen were examined, and the FeS2 was the only material found to be actively sorbing hydrogen. The kinetics of the sorption process were enhanced by a smaller particle size of FeS2, a higher hydrogen pressure, and a higher level of oxidized iron impurities. The hydrogen was not removed by vacuum heating at 200 C. A hydrogen sorption study of the insulation materials used in the battery showed the ceramic-fiber blanket to be a significant sorbent for hydrogen.

  10. Dependence of methane sorption kinetics on coal structure

    SciTech Connect

    B. Kovaleva; E.A. Solov'eva

    2006-01-15

    The data of experimental laboratory studies into the methane sorption kinetics in samples of mineral coals of different metamorphism grade and petrographic composition are presented. Their relation to the character of gas emission from gas-saturated coal seams is considered. The dependence of the gas emission type on the size of undisturbed fragment of coal and methane diffusion coefficient is revealed.

  11. Kinetic Study of Denatonium Sorption to Smectite Clay Minerals.

    PubMed

    Crosson, Garry S; Sandmann, Emily

    2013-06-01

    The denatonium cation, as a benzoate salt, is the most bitter cation known to modern society and is frequently added to consumer products to reduce accidental and intentional consumption by humans and animals. Denatonium can enter the environment by accidental discharges, potentially rendering water supplies undrinkable. Interactions of denatonium with soil components (i.e., smectite minerals) ultimately control the environmental fate of denatonium, but the current literature is devoid of studies that evaluate denatonium sorption to smectite minerals. This study investigated the mechanism and kinetics of denatonium sorption to smectite clay minerals as a function of smectite type, temperature, pH and ionic strength. Uptake by synthetic mica montmorillonite (Syn-1), Wyoming montmorillonite (SWy-2), and Texas montmorillonite (STx-1b) at 305K was rapid, with equilibrium being reached within 2 min for all clays. Complete removal of denatonium was observed for STx-1b at pH 6.9, while partial removal was observed for Syn-1 and SWy-2. Kinetic behavior of SWy-2 and Syn-1 is consistent with a pseudo-second-order model at 305K. An activation energy of +25.9 kJ/mol was obtained for sorption to Syn-1 and was independent of temperature between 286K and 338K. Activation-free energy (ΔG*), activation enthalpy (ΔH*), and activation entropy (ΔS*) for Syn-1 were found to be +62.91 kJ/mol, +23.36 kJ/mol, and -0.130 kJ/(K·mol), respectively. Sorption capacities at pH 3.6, 6.9, and 8.2 were constant at 1.3×10(-2) g denatonium/g clay; however, the kinetic rate constant increased by 56%, going from acidic to basic solution conditions. Distribution coefficients were negatively correlated with ionic strength, suggesting cation exchange. Collectively, results suggested that smectite minerals can serve as efficient sinks for denatonium cations. This is much-needed information for agencies developing regulations regarding denatonium usage and for water treatment professionals who may

  12. Kinetic Study of Denatonium Sorption to Smectite Clay Minerals

    PubMed Central

    Crosson, Garry S.; Sandmann, Emily

    2013-01-01

    Abstract The denatonium cation, as a benzoate salt, is the most bitter cation known to modern society and is frequently added to consumer products to reduce accidental and intentional consumption by humans and animals. Denatonium can enter the environment by accidental discharges, potentially rendering water supplies undrinkable. Interactions of denatonium with soil components (i.e., smectite minerals) ultimately control the environmental fate of denatonium, but the current literature is devoid of studies that evaluate denatonium sorption to smectite minerals. This study investigated the mechanism and kinetics of denatonium sorption to smectite clay minerals as a function of smectite type, temperature, pH and ionic strength. Uptake by synthetic mica montmorillonite (Syn-1), Wyoming montmorillonite (SWy-2), and Texas montmorillonite (STx-1b) at 305K was rapid, with equilibrium being reached within 2 min for all clays. Complete removal of denatonium was observed for STx-1b at pH 6.9, while partial removal was observed for Syn-1 and SWy-2. Kinetic behavior of SWy-2 and Syn-1 is consistent with a pseudo–second-order model at 305K. An activation energy of +25.9 kJ/mol was obtained for sorption to Syn-1 and was independent of temperature between 286K and 338K. Activation-free energy (ΔG*), activation enthalpy (ΔH*), and activation entropy (ΔS*) for Syn-1 were found to be +62.91 kJ/mol, +23.36 kJ/mol, and −0.130 kJ/(K·mol), respectively. Sorption capacities at pH 3.6, 6.9, and 8.2 were constant at 1.3×10−2 g denatonium/g clay; however, the kinetic rate constant increased by 56%, going from acidic to basic solution conditions. Distribution coefficients were negatively correlated with ionic strength, suggesting cation exchange. Collectively, results suggested that smectite minerals can serve as efficient sinks for denatonium cations. This is much-needed information for agencies developing regulations regarding denatonium usage and for water treatment

  13. Application of green seaweed biomass for MoVI sorption from contaminated waters. Kinetic, thermodynamic and continuous sorption studies.

    PubMed

    Bertoni, Fernando A; Medeot, Anabela C; González, Juan C; Sala, Luis F; Bellú, Sebastián E

    2015-05-15

    Spongomorpha pacifica biomass was evaluated as a new sorbent for Mo(VI) removal from aqueous solution. The maximum sorption capacity was found to be 1.28×10(6)±1×10(4) mg kg(-1) at 20°C and pH 2.0. Sorption kinetics and equilibrium studies followed pseudo-first order and Langmuir adsorption isotherm models, respectively. FTIR analysis revealed that carboxyl and hydroxyl groups were mainly responsible for the sorption of Mo(VI). SEM images show that morphological changes occur at the biomass surface after Mo(VI) sorption. Activation parameters and mean free energies obtained with Dubinin-Radushkevich isotherm model demonstrate that the mechanism of sorption process was chemical sorption. Thermodynamic parameters demonstrate that the sorption process was spontaneous, endothermic and the driven force was entropic. The isosteric heat of sorption decreases with surface loading, indicating that S. pacifica has an energetically non-homogeneous surface. Experimental breakthrough curves were simulated by Thomas and modified dose-response models. The bed depth service time (BDST) model was employed to scale-up the continuous sorption experiments. The critical bed depth, Z0 was determined to be 1.7 cm. S.pacifica biomass showed to be a good sorbent for Mo(VI) and it can be used in continuous treatment of effluent polluted with molybdate ions.

  14. Application of green seaweed biomass for MoVI sorption from contaminated waters. Kinetic, thermodynamic and continuous sorption studies.

    PubMed

    Bertoni, Fernando A; Medeot, Anabela C; González, Juan C; Sala, Luis F; Bellú, Sebastián E

    2015-05-15

    Spongomorpha pacifica biomass was evaluated as a new sorbent for Mo(VI) removal from aqueous solution. The maximum sorption capacity was found to be 1.28×10(6)±1×10(4) mg kg(-1) at 20°C and pH 2.0. Sorption kinetics and equilibrium studies followed pseudo-first order and Langmuir adsorption isotherm models, respectively. FTIR analysis revealed that carboxyl and hydroxyl groups were mainly responsible for the sorption of Mo(VI). SEM images show that morphological changes occur at the biomass surface after Mo(VI) sorption. Activation parameters and mean free energies obtained with Dubinin-Radushkevich isotherm model demonstrate that the mechanism of sorption process was chemical sorption. Thermodynamic parameters demonstrate that the sorption process was spontaneous, endothermic and the driven force was entropic. The isosteric heat of sorption decreases with surface loading, indicating that S. pacifica has an energetically non-homogeneous surface. Experimental breakthrough curves were simulated by Thomas and modified dose-response models. The bed depth service time (BDST) model was employed to scale-up the continuous sorption experiments. The critical bed depth, Z0 was determined to be 1.7 cm. S.pacifica biomass showed to be a good sorbent for Mo(VI) and it can be used in continuous treatment of effluent polluted with molybdate ions. PMID:25660712

  15. Kinetics and Equilibrium Sorption Models: Fitting Plutonium, Strontium, Uranium and Neptunium Loading on Monosodium Titanate (MST)

    SciTech Connect

    Fondeur, F

    2006-03-08

    The Dubinin-Astashov (DA) isotherm parameters for U, Pu, Sr and Np have been updated to include additional data obtained since the original derivation. The DA isotherms were modified to include a kinetic function derived by Rahn to describe sorbate loading from the beginning of sorption up to steady state. The final functions describe both kinetic and thermodynamic sorption.

  16. Development of a 15 K Hydrogen-Based Sorption Cooler

    NASA Astrophysics Data System (ADS)

    Burger, J. F.; Holland, H. J.; Meijer, R. J.; Linder, M.; ter Brake, H. J. M.

    2010-04-01

    At the University of Twente, a 15 K hydrogen-based sorption cooler is under development, which has no moving parts and, therefore, is essentially vibration-free. Moreover, it has the potential of a very long life. Although the cooler may operate standalone, it is designed to precool a helium-based sorption cooler thats establishes 5 mW at 4.5 K, requiring a cooling power of 25 mW at the hydrogen stage. Both coolers use microporous activated carbon as the adsorption material. The combination of these two cooler stages needs a total of 5.4 W of input power and is heat sunk at two passive radiators at temperatures of about 50 K and 90 K (1.9 W and 3.5 W, respectively). We developed and built a demonstrator of the helium cooler under a previous ESA-TRP contract, and in 2008 we started a new ESA-sponsored project aiming at the development of the hydrogen stage. In the paper, the preliminary design of this hydrogen-cooler is presented, along with introductory experiments on its Joule-Thomson cold stage.

  17. AFFECTS OF MECHANICAL MILLING AND METAL OXIDE ADDITIVES ON SORPTION KINETICS OF 1:1 LiNH2/MgH2 MIXTURE

    SciTech Connect

    Erdy, C.; Anton, D.; Gray, J.

    2010-12-08

    The destabilized complex hydride system composed of LiNH{sub 2}:MgH{sub 2} (1:1 molar ratio) is one of the leading candidates of hydrogen storage with a reversible hydrogen storage capacity of 8.1 wt%. A low sorption enthalpy of {approx}32 kJ/mole H{sub 2} was first predicted by Alapati et al. utilizing first principle density function theory (DFT) calculations and has been subsequently confirmed empirically by Lu et al. through differential thermal analysis (DTA). This enthalpy suggests that favorable sorption kinetics should be obtainable at temperatures in the range of 160 C to 200 C. Preliminary experiments reported in the literature indicate that sorption kinetics are substantially lower than expected in this temperature range despite favorable thermodynamics. Systematic isothermal and isobaric sorption experiments were performed using a Sievert's apparatus to form a baseline data set by which to compare kinetic results over the pressure and temperature range anticipated for use of this material as a hydrogen storage media. Various material preparation methods and compositional modifications were performed in attempts to increase the kinetics while lowering the sorption temperatures. This paper outlines the results of these systematic tests and describes a number of beneficial additions which influence kinetics as well as NH{sub 3} formation.

  18. PCB Congener Sorption To Carbonaceous Sediment Components: Macroscopic Comparison And Characterization Of Sorption Kinetics And Mechanism

    EPA Science Inventory

    Sorption of polychlorinated biphenyls (PCBs) to sediment is a key process in determining their mobility, bioavailability, and chemical decomposition in aquatic environments. In order to examine the validity of currently used interpretation approaches for PCBs sorption, comparati...

  19. Concurrent Co2+ and Sr2+ sorption from binary mixtures using aluminum industry waste: Kinetic study

    NASA Astrophysics Data System (ADS)

    Milenković, A.; Smičiklas, I.; Šljivić-Ivanović, M.; Vukelić, N.

    2015-12-01

    Multi-component sorption studies are essential to identify the applicability of red mud as a lowcost sorbent for the simultaneous removal of metal ions from wastewaters. Sorption kinetics of Co2+ and Sr2+ ions was investigated, at different total concentrations of mixtures and different molar ratios of two cations. Kinetics of metal sorption from binary systems was found to be well described by pseudo-second order rate model. Equilibrium sorbed amounts and equilibrium times for Co2+ sorption increased with the increase of its total concentration in the mixture, whereas pseudo-second order rate constants exhibited the opposite trend. Sr2+ sorption was strongly suppressed in the presence of Co2+ ions, and the removal efficiency decreased with increasing concentration and mole fraction of Co2+. Red mud can be used for simultaneous Co2+ and Sr2+ removal from mixtures of lower initial concentration, otherwise Co2+ sorption is dominant.

  20. Mechanism and kinetics of aluminum dissolution during copper sorption by acidity paddy soil in South China.

    PubMed

    Liu, Peiya; Li, Yujiao; Wen, Qinliang; Dong, Changxun; Pan, Genxing

    2015-08-01

    Soil aggregates were prepared from a bulk soil collected from paddy soil in the Taihu Lake region and aluminum (Al) dissolution, solution pH changes during copper (Cu(2+)) sorption were investigated with static sorption and magnetic stirring. Kinetics of Cu(2+) sorption and Al dissolution were also studied by magnetic stirring method. No Al dissolution was observed until Cu(2+) sorption was greater than a certain value, which was 632, 450, 601 and 674 mg/kg for sand, clay, silt, and coarse silt fractions, respectively. Aluminum dissolution increased with increasing Cu(2+) sorption and decreasing solution pH. An amount of dissolved Al showed a significant positive correlation with non-specific sorption of Cu(2+) (R(2)>0.97), and it was still good under different pH values (R(2)>0.95). Copper sorption significantly decreased solution pH. The magnitude of solution pH decline increased as Cu(2+) sorption and Al dissolution increased. The sand and clay fraction had a less Al dissolution and pH drop due to the higher ferric oxide, Al oxide and organic matter contents. After sorption reaction for half an hour, the Cu(2+) sorption progress reached more than 90% while the Al dissolution progress was only 40%, and lagged behind the Cu(2+) sorption. It indicated that aluminum dissolution is associated with non-specific sorption.

  1. Effects of sorption kinetics on the fate and transport of pharmaceuticals in estuaries.

    PubMed

    Liu, Dong; Lung, Wu-Seng; Colosi, Lisa M

    2013-08-01

    Many current fate and transport models based on the assumption of instantaneous sorption equilibrium of contaminants in the water column may not be valid for certain pharmaceuticals with long times to reach sorption equilibrium. In this study, a sorption kinetics model was developed and incorporated into a water quality model for the Patuxent River Estuary to evaluate the effect of sorption kinetics. Model results indicate that the assumption of instantaneous sorption equilibrium results in significant under-prediction of water column concentrations for some pharmaceuticals. The relative difference between predicted concentrations for the instantaneous versus kinetic approach is as large as 150% at upstream locations in the Patuxent Estuary. At downstream locations, where sorption processes have had sufficient time to reach equilibrium, the relative difference decreases to roughly 25%. This indicates that sorption kinetics affect a model's ability to capture accumulation of pharmaceuticals into riverbeds and the transport of pharmaceuticals in estuaries. These results offer strong evidence that chemicals are not removed from the water column as rapidly as has been assumed on the basis of equilibrium-based analyses. The findings are applicable not only for pharmaceutical compounds, but also for diverse contaminants that reach sorption equilibrium slowly.

  2. INFLUENCE OF ORGANIC COSOLVENTS ON THE SORPTION KINETICS OF HYDROPHOBIC ORGANIC CHEMICALS

    EPA Science Inventory

    A quantitative examination of the kinetics of sorption of hydrophobic organic chemicals by soils from mixed solvents reveals that the reverse sorption rate constant (k2) increases log-linearly with increasing volume fraction of organic cosolvent (fc). This relationship was expec...

  3. Sorption enhanced reaction process (SERP) for production of hydrogen

    SciTech Connect

    Sircar, S.; Anand, M.; Carvill, B.

    1995-09-01

    Sorption Enhanced Reaction (SER) is a novel process that is being developed for the production of lower cost hydrogen by steam-methane reforming (SMR). In this process, the reaction of methane with steam is carried out in the presence of an admixture of a catalyst and a selective adsorbent for carbon dioxide. The consequences of SER are: (1) reformation reaction at a significantly lower temperature (300-500{degrees}C) than conventional SMR (800-1100{degrees}C), while achieving the same conversion of methane to hydrogen, (2) the product hydrogen is obtained at reactor pressure (200-400 psig) and at 99+% purity directly from the reactor (compared to only 70-75% H{sub 2} from conventional SMR reactor), (3) downstream hydrogen purification step is either eliminated or significantly reduced in size. The early focus of the program will be on the identification of an adsorbent/chemisorbent for CO{sub 2} and on the demonstration of the SER concept for SMR in our state-of-the-art bench scale process. In the latter stages, a pilot plant will be built to scale-up the technology and to develop engineering data. The program has just been initiated and no significant results for SMR will be reported. However, results demonstrating the basic principles and process schemes of SER technology will be presented for reverse water gas shift reaction as the model reaction. If successful, this technology will be commercialized by Air Products and Chemicals, Inc. (APCI) and used in its existing hydrogen business. APCI is the world leader in merchant hydrogen production for a wide range of industrial applications.

  4. Sorption kinetics of uranium-238 and neptunium-237 on a glacial sediment

    NASA Astrophysics Data System (ADS)

    Braithwaite, A.; Richardson, S.; Moyes, L. N.; Livens, F. R.; Bunker, D. J.; Hughes, C. R.; Smith, J. T.; Hilton, J.

    2000-02-01

    Studies of uptake of radionuclides by natural materials have shown that sorption may occur via fast equilibrium exchange and/or slow kinetic processes, which can be described using a series of box models. This paper describes the use of such models to evaluate the solid-solution partitioning of 238U and 237Np on a clay rich sediment. Experimental data are obtained using the batch sorption technique, which are then analysed using 1, 2, and 3 box kinetic models. Uptake of 238U is initially rapid, with approximately 90% sorbed within the first 30 minutes. Sorption continues, but at a slower rate. Uptake of 237Np is initially slower than U, with approximately 30% sorbed within the first 30 minutes. Sorption again continues, at a slower rate. Analysis of the experimental data indicates that sorption can be described using 2 and 3 box kinetic models. The results demonstrate that sorption of uranium and neptunium on clay rich sediments occurs via equilibrium and kinetically controlled pathways, with neptunium being controlled by kinetics to a greater extent than uranium. The 2 or 3 box model can describe sorption of neptunium, uranium requires the 3 box model.

  5. Kinetic analysis of strontium and potassium sorption onto sands and gravels in a natural channel.

    USGS Publications Warehouse

    Bencala, K.E.; Jackman, A.P.; Kennedy, V.C.; Avanzino, R.J.; Zellweger, G.W.

    1983-01-01

    A kinetic, first-order mass transfer model was used to describe the sorption of strontium onto sand-and gravel-sized streambed sediments. Rate parameters, empirically determined for strontium, allowed for the prediction of potassium sorption with moderate success. The model parameters varied significantly with particle size. The sorption data were collected during an experimental injection of several elements into a small mountain pool-and- riffle stream. The sorption process onto sand- and gravel-sized sediment was relatively slow compared to changes in the dissolved concentrations. -Authors

  6. Kinetics of cadmium ion sorption on ion exchange and chelating resins

    SciTech Connect

    Bilba, D.; Bilba, N.; Albu, M.

    1999-11-01

    Cadmium sorption from aqueous solutions on sulfonic (C-150) and iminodiacetic (S-930) Purolite macroporous resins was investigated. The influence of operating variables such as initial pH, Cd(II) concentration, time and temperature on the equilibrium parameters was measured. The ion preference and sorption ability of resins, i.e., binding constant (b) and saturation capacity (x{sub m}), derived from sorption isotherm, depend on the functional group structure. The Cd(II) uptake is only particle diffusion controlled. The kinetic parameters, i.e., t{sub 1/2} values for 50% attainment of equilibrium sorption, rate constant ({bar K}) and diffusion coefficient ({bar D}) are higher on the sulfonic resin. The moving boundary particle diffusion model fits the entire ion sorption process on chelating resin, but only the initial sorption on the sulfonic resin, confirming the difference in chemistry between chelation and ion exchange.

  7. Optimization of Nano-Carbon Materials for Hydrogen Sorption

    SciTech Connect

    Yakobson, Boris I

    2013-08-02

    Research undertaken has added to the understanding of several critical areas, by providing both negative answers (and therefore eliminating expensive further studies of unfeasible paths) and positive feasible options for storage. Theoretical evaluation of the early hypothesis of storage on pure carbon single wall nanotubes (SWNT) has been scrutinized with the use of comprehensive computational methods (and experimental tests by the Center partners), and demonstrated that the fundamentally weak binding energy of hydrogen is not sufficiently enhanced by the SWNT curvature or even defects, which renders carbon nanotubes not practical media. More promising direction taken was towards 3-dimensional architectures of high porosity where concurrent attraction of H2 molecule to surrounding walls of nano-scale cavities can double or even triple the binding energy and therefore make hydrogen storage feasible even at ambient or somewhat lower temperatures. An efficient computational tool has been developed for the rapid capacity assessment combining (i) carbon-foam structure generation, (ii) accurate empirical force fields, with quantum corrections for the lightweight H2, and (iii) grand canonical Monte Carlo simulation. This made it possible to suggest optimal designs for carbon nanofoams, obtainable via welding techniques from SWNT or by growth on template-zeolites. As a precursor for 3D-foams, we have investigated experimentally the synthesis of VANTA (Vertically Aligned NanoTube Arrays). This can be used for producing nano-foams. On the other hand, fluorination of VANTA did not show promising increase of hydrogen sorption in several tests and may require further investigation and improvements. Another significant result of this project was in developing a fundamental understanding of the elements of hydrogen spillover mechanisms. The benefit of developed models is the ability to foresee possible directions for further improvement of the spillover mechanism.

  8. Kinetic modeling of antimony(III) oxidation and sorption in soils.

    PubMed

    Cai, Yongbing; Mi, Yuting; Zhang, Hua

    2016-10-01

    Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model.

  9. Kinetic modeling of antimony(III) oxidation and sorption in soils.

    PubMed

    Cai, Yongbing; Mi, Yuting; Zhang, Hua

    2016-10-01

    Kinetic batch and saturated column experiments were performed to study the oxidation, adsorption and transport of Sb(III) in two soils with contrasting properties. Kinetic and column experiment results clearly demonstrated the extensive oxidation of Sb(III) in soils, and this can in return influence the adsorption and transport of Sb. Both sorption capacity and kinetic oxidation rate were much higher in calcareous Huanjiang soil than in acid red Yingtan soil. The results indicate that soil serve as a catalyst in promoting oxidation of Sb(III) even under anaerobic conditions. A PHREEQC model with kinetic formulations was developed to simulate the oxidation, sorption and transport of Sb(III) in soils. The model successfully described Sb(III) oxidation and sorption data in kinetic batch experiment. It was less successful in simulating the reactive transport of Sb(III) in soil columns. Additional processes such as colloid facilitated transport need to be quantified and considered in the model. PMID:27214003

  10. Kinetics of neptunium(V) sorption and desorption on goethite: An experimental and modeling study

    NASA Astrophysics Data System (ADS)

    Tinnacher, Ruth M.; Zavarin, Mavrik; Powell, Brian A.; Kersting, Annie B.

    2011-11-01

    Various sorption phenomena, such as aging, hysteresis and irreversible sorption, can cause differences between contaminant (ad)sorption and desorption behavior and lead to apparent sorption 'asymmetry'. We evaluate the relevance of these characteristics for neptunium(V) (Np(V)) sorption/desorption on goethite using a 34-day flow-cell experiment and kinetic modeling. Based on experimental results, the Np(V) desorption rate is much slower than the (ad)sorption rate, and appears to decrease over the course of the experiment. The best model fit with a minimum number of fitting parameters was achieved with a multi-reaction model including (1) an equilibrium Freundlich site (site 1), (2) a kinetically-controlled, consecutive, first-order site (site 2), and (3) a parameter ψ, which characterizes the desorption rate on site 2 based on a concept related to transition state theory (TST). This approach allows us to link differences in adsorption and desorption kinetics to changes in overall reaction pathways, without assuming different adsorption and desorption affinities (hysteresis) or irreversible sorption behavior a priori. Using modeling as a heuristic tool, we determined that aging processes are relevant. However, hysteresis and irreversible sorption behavior can be neglected within the time-frame (desorption over 32 days) and chemical solution conditions evaluated in the flow-cell experiment. In this system, desorption reactions are very slow, but they are not irreversible. Hence, our data do not justify an assumption of irreversible Np(V) sorption to goethite in transport models, which effectively limits the relevance of colloid-facilitated Np(V) transport to near-field environments. However, slow Np(V) desorption behavior may also lead to a continuous contaminant source term when metals are sorbed to bulk mineral phases. Additional long-term experiments are recommended to definitely rule out irreversible Np(V) sorption behavior at very low surface loadings and

  11. Liquefaction chemistry and kinetics: Hydrogen utilization studies

    SciTech Connect

    Rothenberger, K.S.; Warzinski, R.P.; Cugini, A.V.

    1995-12-31

    The objectives of this project are to investigate the chemistry and kinetics that occur in the initial stages of coal liquefaction and to determine the effects of hydrogen pressure, catalyst activity, and solvent type on the quantity and quality of the products produced. The project comprises three tasks: (1) preconversion chemistry and kinetics, (2) hydrogen utilization studies, and (3) assessment of kinetic models for liquefaction. The hydrogen utilization studies work will be the main topic of this report. However, the other tasks are briefly described.

  12. Kinetics of sorption of lead on bed sediments of River Hindon, India.

    PubMed

    Sharma, M K; Jain, C K; Singhal, D C; Choubey, V K

    2009-10-01

    A number of low cost waste sorbent have been used for removal of heavy metals, however, few studies have been carried out on the sorption process on riverbed sediments in their natural state of occurrence. Stream sediments adsorb certain solutes from streams, thereby significantly changing the solute composition, but little is known about quantitatively describing sorption phenomena and rates of these processes. In the present investigation, sorption of lead ions on river bed sediments of river Hindon, a tributary of river Yamuna, India has been studied to demonstrate the role of bed sediments in controlling metal pollution. The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time and particle size has been studied. The sorption of lead ions increased with respect to pH and sorbent dose and decreased with sorbent particle size. Two important geochemical phases, iron and manganese oxide, also play important role in the sorption process. The sorption data were analysed using Langmuir and Freundlich isotherm models to determine the mechanistic parameters related to the sorption process. Further, although lead ions have more affinity for the fine fraction of the sediment, but the overall contribution of coarser fraction to sorption is more as compared to clay and silt fraction. The kinetic data suggest that the sorption of lead on bed sediments is an endothermic process, which is spontaneous at low temperature. The uptake of lead is controlled by both bulk and intraparticle diffusion mechanism. PMID:18791802

  13. Kinetics of sorption of lead on bed sediments of River Hindon, India.

    PubMed

    Sharma, M K; Jain, C K; Singhal, D C; Choubey, V K

    2009-10-01

    A number of low cost waste sorbent have been used for removal of heavy metals, however, few studies have been carried out on the sorption process on riverbed sediments in their natural state of occurrence. Stream sediments adsorb certain solutes from streams, thereby significantly changing the solute composition, but little is known about quantitatively describing sorption phenomena and rates of these processes. In the present investigation, sorption of lead ions on river bed sediments of river Hindon, a tributary of river Yamuna, India has been studied to demonstrate the role of bed sediments in controlling metal pollution. The effect of various operating variables, viz., initial concentration, solution pH, sediment dose, contact time and particle size has been studied. The sorption of lead ions increased with respect to pH and sorbent dose and decreased with sorbent particle size. Two important geochemical phases, iron and manganese oxide, also play important role in the sorption process. The sorption data were analysed using Langmuir and Freundlich isotherm models to determine the mechanistic parameters related to the sorption process. Further, although lead ions have more affinity for the fine fraction of the sediment, but the overall contribution of coarser fraction to sorption is more as compared to clay and silt fraction. The kinetic data suggest that the sorption of lead on bed sediments is an endothermic process, which is spontaneous at low temperature. The uptake of lead is controlled by both bulk and intraparticle diffusion mechanism.

  14. Effect of dissolved organic matter on ammonium sorption kinetics and equilibrium to Chinese clinoptilolite.

    PubMed

    Zhang, Ying; Bi, Erping

    2012-01-01

    In the in-situ remediation of ammonium (NH4+) in groundwater by a sequential reactive barrier filled with zeolite, it is of great importance to understand the mechanisms of NH4+ sorption to zeolite. In this study, the effect of dissolved natural organic matter on NH4+ sorption to natural Chinese clinoptilolite was studied by batch experiments taking humic acid (HA) as a model substance. The surface of clinoptilolite was characterized by scanning electronic microscopy (SEM). A needle cluster of sorbed HA could be observed on the surface of the clinoptilolite. The negative effect of HA on NH4+ sorption is thought to be their competition for sorption sites, the surface coverage and blockage of the pores of clinoptilolite by HA. The fitting results of kinetic sorption data indicated that the rate-controlling step for NH4+ sorption by clinoptilolite in both NH4+ and NH4+ + HA systems is the heterogeneous chemisorption. The existence of HA (10 mg/L) significantly reduced the initial sorption rate of NH4+, but the effect of a further concentration increase of HA was slight. The effect of HA on maximum sorption capacity was found to be insignificant in the experiments. A high aqueous Ca2+ concentration can decrease the negative effect of HA on NH4+ sorption by precipitation of calcium humate.

  15. Synergistic role of different soil components in slow sorption kinetics of polar organic contaminants.

    PubMed

    Zhang, Dongmei; Hou, Lei; Zhu, Dongqiang; Chen, Wei

    2014-01-01

    We observed that the sorption kinetics of nitrobenzene and 2,4-dinitrotoluene (two model polar compounds) was significantly slower than that of 1,4-dichlorobenzene and phenanthrene (two model apolar compounds). The difference was attributable to the strong non-hydrophobic interactions between the polar molecules and soil. Interestingly, sorption kinetics of the polar sorbates to the soil organic matter-free soil, humic/fulvic acid-free soil, and extracted humic acids was very fast, indicating that different soil components played a synergetic role in the observed slow kinetics. We propose that slow sorption kinetics of highly polar sorbates stems mainly from the strong specific interactions (H-bonding, electron donor-acceptor interactions, etc.) with humic/fulvic acids; such specific interactions occur when sorbate molecules diffuse through humic/fulvic acids coiled, in relatively compressed confirmations, within the complex, tortuous, and porous soil matrices formed by mineral grains/particles and soil organic matter.

  16. Characterization, kinetics and thermodynamics of Ag(I) sorption using novel sorbent: Dry wheatgrass.

    PubMed

    Shah, Kruti R; Tipre, Devayani R; Dave, Shailesh R

    2016-12-01

    In the present study, dried wheatgrass (DWG), an available and renewable biomass, was investigated as a novel Ag(I) sorbent. Sorption data was modeled to 11 different kinetic and diffusion models at different DWG concentration. Pseudo-second-order model fits the data most appropriately among these. Diffusion was not the sole mechanism controlling Ag(I) sorption by DWG. The enthalpy and entropy for Ag(I) sorption by DWG are 10.511 kJ mol(-1) and 0.065 kJ mol(-1) K(-1), respectively. Gibbs free energy decreases with rise in temperature. Ag(I) sorption by DWG is spontaneous, endothermic with increased randomness at the interface. Characterization of DWG suggested the presence of diverse functional groups. Ag(I) sorption by DWG involved mechanisms such as physisorption and chemisorptions. DWG can be efficiently used to remediate and recover Ag(I) from solution in an eco-friendly manner. PMID:27260662

  17. Materials Down Select Decisions Made Within the Department of Energy Hydrogen Sorption Center of Excellence

    SciTech Connect

    Simpson, Lin

    2009-11-30

    Technical report describing DOE's Hydrogen Sorption Center of Excellence investigation into various adsorbent and chemisorption materials and progress towards meeting DOE's hydrogen storage targets. The report presents a review of the material status as related to DOE hydrogen storage targets and explains the basis for the down select decisions.

  18. Mg-based nanocomposites with high capacity and fast kinetics for hydrogen storage.

    PubMed

    Yao, Xiangdong; Wu, Chengzhang; Du, Aijun; Lu, Gao Qing; Cheng, Huiming; Smith, Sean C; Zou, Jin; He, Yinghe

    2006-06-22

    Magnesium and its alloys have shown a great potential in effective hydrogen storage due to their advantages of high volumetric/gravimetric hydrogen storage capacity and low cost. However, the use of these materials in fuel cells for automotive applications at the present time is limited by high hydrogenation temperature and sluggish sorption kinetics. This paper presents the recent results of design and development of magnesium-based nanocomposites demonstrating the catalytic effects of carbon nanotubes and transition metals on hydrogen adsorption in these materials. The results are promising for the application of magnesium materials for hydrogen storage, with significantly reduced absorption temperatures and enhanced ab/desorption kinetics. High level Density Functional Theory calculations support the analysis of the hydrogenation mechanisms by revealing the detailed atomic and molecular interactions that underpin the catalytic roles of incorporated carbon and titanium, providing clear guidance for further design and development of such materials with better hydrogen storage properties.

  19. Sorption/desorption kinetics of contaminants on mobile particles: Modeling and experimental evidence

    NASA Astrophysics Data System (ADS)

    Bold, Steffen; Kraft, Siegfried; Grathwohl, Peter; Liedl, Rudolf

    2003-12-01

    In this study the impact of sorption/desorption kinetics between organic contaminants and mobile particles suspended in subsurface water is analyzed. TCE migration through a granular activated carbon column is investigated at different transport velocities with lignite and activated carbon particles as mobile carriers. The measured breakthrough characteristics of TCE can be reproduced by a reactive transport model simulating sorption/desorption kinetics applying an intraparticle diffusion approach for mobile particles and the packed bed of granular activated carbon. Model predictions are based on independently measured physicochemical parameters, i.e., no calibration of TCE sorption/desorption is required. The close matches of experimental data to predicted data validate the exclusively process-based model assumptions and indicate that this approach has large predictive capabilities. Extending these findings, a sensitivity study is presented in order to specify under which conditions sorption/desorption of contaminants in mobile particles has to be modeled as a kinetic process. It is found that sorption/desorption kinetics are of major importance for Damköhler numbers between 0.01 and 100.

  20. SORPTION KINETICS OF PAHS IN METHANOL-WATER SYSTEMS

    EPA Science Inventory

    The objectives of this study were to evaluate the relationships between the equilibrium sorption constant (Kp), the first-order desorption rate coefficient (k2), and the volumetric fraction of water miscible solvent (fc); and to utilize SPARC-calculated (SPARC Performs Automatic ...

  1. Abamectin in soils: Analytical methods, kinetics, sorption and dissipation.

    PubMed

    Dionisio, Andreza Camilotti; Rath, Susanne

    2016-05-01

    Abamectin is a broad-spectrum antiparasitic agent that has been widely employed in veterinary medicine and has also been used as a pesticide in agriculture. Veterinary drugs may reach the soil and may be transported to surface and ground waters, posing risks to terrestrial and aquatic organisms. Sorption, transformation and transport processes are primarily responsible for the fate of these substances in the environment. In this study, the sorption and the aerobic dissipation of abamectin in Brazilian soils (sand, clay and sandy-clay) were evaluated. For sorption studies, batch equilibrium experiments were performed. Sorption and desorption isotherms were fitted to the Freundlich model. Abamectin showed a high affinity to soil particles, with Freundlich sorption and desorption coefficients ranging from 44 to 138 μg(1-1/n) (cm(3))(1/n) g(-1) and from 89 to 236 μg(1-1/n) (cm(3))(1/n) g(-1), respectively. Dissipation of abamectin was evaluated in sterile and non-sterile soils in an aerobic and dark environment under controlled temperature and humidity. The time required for a 50% reduction of the amount of abamectin present in non-sterile soils was up to 4 days, and the time period for 90% dissipation was up to 12 days. In sterilized soils, there was no reduction in the concentration of abamectin over 37 days of exposure, suggesting that aerobic microbial degradation must have been the primary mechanism responsible for the dissipation of abamectin in soils. PMID:26923238

  2. Sorption of selenate on soils and pure phases: kinetic parameters and stabilisation.

    PubMed

    Loffredo, N; Mounier, S; Thiry, Y; Coppin, F

    2011-09-01

    This study was conducted to identify the principle selenate carrier phases for two selected soils, by comparing their reactivity with selenate to that of pure phases of the solids. Silica, calcium carbonate, aluminium hydroxide, goethite, bentonite and humic acid were selected as the main soil carrier phases. Comparisons were made first on the parameter values obtained with the best fit of a kinetic sorption model which can discriminate instantaneous sorption from kinetically limited sorption. Then comparisons were made of the ability for each solid to stabilise selenate by measuring the ratio of the partition coefficient for sorption (Kd(sorption)) over that of the desorption (Kd(desorption)). Kinetics and stabilisation were used to help elucidate the nature of interactions with the test solid phases for a large range of selenate concentrations. The experiments were conducted over 165 h in batch reactors, the solid being isolated from the solution by dialysis tubing, at two pH (5.4 and 8) and three selenate concentrations (1 × 10(-3), 1 × 10(-6) and 1 × 10(-8) mol L(-1)). The results obtained showed that only aluminium hydroxide can sorb selenate throughout the studied pH range (pH 5.4 to 8.0). The sorption capacity on this mineral was high (Kd(sorption) > 100 to 1 × 10(4) L kg(-1)) and the selenate was mainly stabilized by the formation of inner sphere complexes. The sorption on goethite occurred at pH 5.4 (Kd(sorption) 52 L kg(-1)), mainly as outer sphere complexes, and was null at pH 8. On silica, a weak sorption was observed only at pH 5.4 and at 165 h (Kd(sorption) 4 L kg(-1)). On bentonite, calcium carbonate and humic acid no significant sorption was observed. Concerning the two soils studied, different behaviours were observed for selenate. For soil Ro (pH 5.4), Kd(sorption) was low (8 L kg(-1)) compared to soil Bu (pH 8) (70 L kg(-1)). The sorption behaviour of selenate on soil Ro was mainly due to outer sphere complexes, as for

  3. Sorption enhanced reaction process (SERP) for the production of hydrogen

    SciTech Connect

    Hufton, J.; Mayorga, S.; Gaffney, T.; Nataraj, S.; Rao, M.; Sircar, S.

    1998-08-01

    The novel Sorption Enhanced Reaction Process has the potential to decrease the cost of hydrogen production by steam methane reforming. Current effort for development of this technology has focused on adsorbent development, experimental process concept testing, and process development and design. A preferred CO{sub 2} adsorbent, K{sub 2}CO{sub 3} promoted hydrotalcite, satisfies all of the performance targets and it has been scaled up for process testing. A separate class of adsorbents has been identified which could potentially improve the performance of the H{sub 2}-SER process. Although this material exhibits improved CO{sub 2} adsorption capacity compared to the HTC adsorbent, its hydrothermal stability must be improved. Single-step process experiments (not cyclic) indicate that the H{sub 2}-SER reactor performance during the reaction step improves with decreasing pressure and increasing temperature and steam to methane ratio in the feed. Methane conversion in the H{sub 2}-SER reactor is higher than for a conventional catalyst-only reactor operated at similar temperature and pressure. The reactor effluent gas consists of 90+% H{sub 2}, balance CH{sub 4}, with only trace levels (< 50 ppm) of carbon oxides. A best-case process design (2.5 MMSCFD of 99.9+% H{sub 2}) based on the HTC adsorbent properties and a revised SER process cycle has been generated. Economic analysis of this design indicates the process has the potential to reduce the H{sub 2} product cost by 25--31% compared to conventional steam methane reforming.

  4. Hydrogen sorption in titanium alloys with a symmetric {Sigma}5(310) tilt grain boundary and a (310) surface

    SciTech Connect

    Kulkova, S. E.; Bakulin, A. V.; Kulkov, S. S.; Hocker, S.; Schmauder, S.

    2012-09-15

    The hydrogen sorption in intermetallic B2 TiM (M = Ni, Co, Pd) with a symmetric {Sigma}5(310) tilt grain boundary and a (310) surface is studied by density functional theory methods. The effect of hydrogen on the electronic characteristics of the alloys is analyzed as a function of a sorption position at the interfaces. The hydrogen sorption energy is shown to depend on the local environment of hydrogen; on the whole, hydrogen at the interfaces prefers titanium-rich positions. The hydrogen sorption energy in metal-rich positions decreases when the d shell of the second alloy component is filled with electrons. The grain-boundary energy, the surface energy, and the hydrogen segregation energies to the interfaces are calculated. Hydrogen sorption in titanium alloys is shown to decrease Griffith work and to favor brittle fracture along tilt grain boundaries.

  5. Chemical Kinetic Modeling of Hydrogen Combustion Limits

    SciTech Connect

    Pitz, W J; Westbrook, C K

    2008-04-02

    A detailed chemical kinetic model is used to explore the flammability and detonability of hydrogen mixtures. In the case of flammability, a detailed chemical kinetic mechanism for hydrogen is coupled to the CHEMKIN Premix code to compute premixed, laminar flame speeds. The detailed chemical kinetic model reproduces flame speeds in the literature over a range of equivalence ratios, pressures and reactant temperatures. A series of calculation were performed to assess the key parameters determining the flammability of hydrogen mixtures. Increased reactant temperature was found to greatly increase the flame speed and the flammability of the mixture. The effect of added diluents was assessed. Addition of water and carbon dioxide were found to reduce the flame speed and thus the flammability of a hydrogen mixture approximately equally well and much more than the addition of nitrogen. The detailed chemical kinetic model was used to explore the detonability of hydrogen mixtures. A Zeldovich-von Neumann-Doring (ZND) detonation model coupled with detailed chemical kinetics was used to model the detonation. The effectiveness on different diluents was assessed in reducing the detonability of a hydrogen mixture. Carbon dioxide was found to be most effective in reducing the detonability followed by water and nitrogen. The chemical action of chemical inhibitors on reducing the flammability of hydrogen mixtures is discussed. Bromine and organophosphorus inhibitors act through catalytic cycles that recombine H and OH radicals in the flame. The reduction in H and OH radicals reduces chain branching in the flame through the H + O{sub 2} = OH + O chain branching reaction. The reduction in chain branching and radical production reduces the flame speed and thus the flammability of the hydrogen mixture.

  6. Kinetics of Ni sorption in soils: roles of soil organic matter and Ni precipitation.

    PubMed

    Shi, Zhenqing; Peltier, Edward; Sparks, Donald L

    2012-02-21

    The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times.

  7. Kinetics of Ni sorption in soils: roles of soil organic matter and Ni precipitation.

    PubMed

    Shi, Zhenqing; Peltier, Edward; Sparks, Donald L

    2012-02-21

    The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times. PMID:22283487

  8. Kinetics of Ni Sorption in Soils: Roles of Soil Organic Matter and Ni Precipitation

    SciTech Connect

    Shi, Zhenqing; Peltier, Edward; Sparks, Donald L.

    2012-12-10

    The kinetics of Ni sorption to two Delaware agricultural soils were studied to quantitatively assess the relative importance of Ni adsorption on soil organic matter (SOM) and the formation of Ni layered double hydroxide (Ni-LDH) precipitates using both experimental studies and kinetic modeling. Batch sorption kinetic experiments were conducted with both soils at pH 6.0, 7.0, and 7.5 from 24 h up to 1 month. Time-resolved Ni speciation in soils was determined by X-ray absorption spectroscopy (XAS) during the kinetic experiments. A kinetics model was developed to describe Ni kinetic reactions under various reaction conditions and time scales, which integrated Ni adsorption on SOM with Ni-LDH precipitation in soils. The soil Ni speciation (adsorbed phases and Ni-LDH) calculated using the kinetics model was consistent with that obtained through XAS analysis during the sorption processes. Under our experimental conditions, both modeling and XAS results demonstrated that Ni adsorption on SOM was dominant in the short term and the formation of Ni-LDH precipitates accounted for the long-term Ni sequestration in soils, and, more interestingly, that the adsorbed Ni may slowly transfer to Ni-LDH phases with longer reaction times.

  9. Sorption kinetic studies of ammonium from aqueous solution on different inorganic and organic media.

    PubMed

    Kucić, Dajana; Cosić, Ivana; Vuković, Marija; Briski, Felicita

    2013-01-01

    In this study, the sorption of ammonium from aqueous solution onto activated carbon, natural zeolite, peat and potting soil was studied by performing batch kinetic sorption experiments. The activated carbon wasn't efficiently removing ammonium at concentrations higher than 50 mg L(-1). Sorption isotherms of ammonium on zeolite, peat and potting soil were determined at 25 degrees C and 200 rpm with the initial concentration of 50-7000 mg L(-1). Equilibrium data were fitted by Freundlich, Langmuir and Temkin isotherm and parameters were evaluated according these models. Langmuir model gives better fit to experimental data than Freundlich and Temkin models. Maximum adsorption capacities were for activated carbon 0.631 mg g(-1), zeolite 58 mg g(-1), peat 595 mg g(-1) and for potting soil 575 mg g(-1). The equilibrium kinetic data were analyzed using adsorption kinetic models: the pseudo-first and second-order equations and were found to follow the pseudo-second-order kinetic model. A comparison between linear and non-linear regression method for estimating the adsorption and kinetics parameters was examined. The obtained results showed that non-linear method may be a better way to determine the kinetic parameters. Thermodynamic studies showed exothermic and endothermic nature of the adsorption of NH4(+) on inorganic and organic adsorbents, respectively. From present results it can be seen that zeolite, peat and potting soil are good adsorbents for removal ammonium from aqueous solution.

  10. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite.

    PubMed

    Tinnacher, Ruth M; Begg, James D; Mason, Harris; Ranville, James; Powell, Brian A; Wong, Jennifer C; Kersting, Annie B; Zavarin, Mavrik

    2015-03-01

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu-FA-mineral complexes could enhance colloid-facilitated Pu transport. However, more representative natural conditions need to be investigated to quantify the relevance of these findings. PMID:25607800

  11. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite

    SciTech Connect

    Tinnacher, Ruth M.; Begg, James D.; Mason, Harris; Ranville, James; Powell, Brian A.; Wong, Jennifer C.; Kersting, Annie B.; Zavarin, Mavrik

    2015-01-21

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu–FA–mineral complexes could enhance colloid-facilitated Pu transport. In conclusion, more representative natural conditions need to be investigated to quantify the relevance of these findings.

  12. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite

    DOE PAGES

    Tinnacher, Ruth M.; Begg, James D.; Mason, Harris; Ranville, James; Powell, Brian A.; Wong, Jennifer C.; Kersting, Annie B.; Zavarin, Mavrik

    2015-01-21

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presencemore » of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu–FA–mineral complexes could enhance colloid-facilitated Pu transport. In conclusion, more representative natural conditions need to be investigated to quantify the relevance of these findings.« less

  13. Effect of fulvic acid surface coatings on plutonium sorption and desorption kinetics on goethite.

    PubMed

    Tinnacher, Ruth M; Begg, James D; Mason, Harris; Ranville, James; Powell, Brian A; Wong, Jennifer C; Kersting, Annie B; Zavarin, Mavrik

    2015-03-01

    The rates and extent of plutonium (Pu) sorption and desorption onto mineral surfaces are important parameters for predicting Pu mobility in subsurface environments. The presence of natural organic matter, such as fulvic acid (FA), may influence these parameters. We investigated the effects of FA on Pu(IV) sorption/desorption onto goethite in two scenarios: when FA was (1) initially present in solution or (2) found as organic coatings on the mineral surface. A low pH was used to maximize FA coatings on goethite. Experiments were combined with kinetic modeling and speciation calculations to interpret variations in Pu sorption rates in the presence of FA. Our results indicate that FA can change the rates and extent of Pu sorption onto goethite at pH 4. Differences in the kinetics of Pu sorption were observed as a function of the concentration and initial form of FA. The fraction of desorbed Pu decreased in the presence of FA, indicating that organic matter can stabilize sorbed Pu on goethite. These results suggest that ternary Pu-FA-mineral complexes could enhance colloid-facilitated Pu transport. However, more representative natural conditions need to be investigated to quantify the relevance of these findings.

  14. Sorption kinetics of zinc and nickel on modified chitosan.

    PubMed

    Tripathi, Nimisha; Choppala, Girish; Singh, Raj S; Srivastava, Prashant; Seshadri, Balaji

    2016-09-01

    This study was conducted to evaluate the effect of equilibration time on adsorption of zinc [Zn(II)] and nickel [Ni(II)] on pure and modified chitosan beads. The initial adsorption of Zn(II) was high on molybdenum (Mo)-impregnated chitosan beads (MoCB) during the initial 60 min. However, after 240 min, Zn(II) adsorption occurred more on single super phosphate chitosan beads (SSPCB), followed by monocalcium phosphate chitosan beads (MCPCB), untreated pure chitosan beads (UCB), and MoCB. Similarly, Ni(II) adsorption was greatest on MoCB during the initial 60 min. At the conclusion of the experiment (at 240 min), the greatest adsorption was occurred on MCPCB, followed by MoCB, UCB, and SSPCB. Chemical sorption and intra-particle diffusion were probably the dominant processes responsible for Zn(II) and Ni(II) sorption onto chitosan beads. The results demonstrated that modified chitosan beads were effective in adsorbing Zn and Ni and hence, could be used for the removal of these toxic metals from soil. PMID:27497960

  15. Kinetics and equilibrium of the sorption of bisphenol A by carbon nanotubes from wastewater.

    PubMed

    Bohdziewicz, J; Kamińska, G

    2013-01-01

    The aim of this study was to determine the sorption potential of carbon nanotubes (CNTs) to bisphenol A (BPA) contained in synthetic wastewater whose composition corresponds to biologically treated effluents. These nanotubes differed in their outer diameter, the number of graphene layers and the presence of modifying functional groups. Based on the nitrogen adsorption-desorption isotherms, mensuration of the specific surface area and pore size distribution was undertaken. The porous structure of the CNTs was bidispersive; the majority consisted of micropores, there was an average fraction of mesopores, and macropores did not occur. On the basis of common kinetics models (pseudo-first-order and pseudo-second-order models), a trial of modelling the kinetics of BPA sorption onto nanotubes was undertaken. The experimental data were well fitted only to the pseudo-second-order models. The kinetics study indicated that adsorption of BPA on CNTs proceeded very fast, with the majority of the adsorbate being adsorbed in the first few seconds. The sorption capacity of nanotubes to BPA was the highest for single-walled CNTs. A decrease in the sorption potential of the nanotubes for higher pH values occurred as a result of the deprotonation of the BPA and formation of bisphenolate anions, consequently leading to a decrease of π-π (hydrophobic) interaction and enhancing electrostatic repulsion. Overall, these results unequivocally confirm the ideal performance and potential of nanotubes for removal of micropollutants from synthetic wastewater. Replicating the conditions occurring in real wastewater allows us to expect a high sorption of BPA in real competitive sorption systems. PMID:24056428

  16. Kinetics and equilibrium of the sorption of bisphenol A by carbon nanotubes from wastewater.

    PubMed

    Bohdziewicz, J; Kamińska, G

    2013-01-01

    The aim of this study was to determine the sorption potential of carbon nanotubes (CNTs) to bisphenol A (BPA) contained in synthetic wastewater whose composition corresponds to biologically treated effluents. These nanotubes differed in their outer diameter, the number of graphene layers and the presence of modifying functional groups. Based on the nitrogen adsorption-desorption isotherms, mensuration of the specific surface area and pore size distribution was undertaken. The porous structure of the CNTs was bidispersive; the majority consisted of micropores, there was an average fraction of mesopores, and macropores did not occur. On the basis of common kinetics models (pseudo-first-order and pseudo-second-order models), a trial of modelling the kinetics of BPA sorption onto nanotubes was undertaken. The experimental data were well fitted only to the pseudo-second-order models. The kinetics study indicated that adsorption of BPA on CNTs proceeded very fast, with the majority of the adsorbate being adsorbed in the first few seconds. The sorption capacity of nanotubes to BPA was the highest for single-walled CNTs. A decrease in the sorption potential of the nanotubes for higher pH values occurred as a result of the deprotonation of the BPA and formation of bisphenolate anions, consequently leading to a decrease of π-π (hydrophobic) interaction and enhancing electrostatic repulsion. Overall, these results unequivocally confirm the ideal performance and potential of nanotubes for removal of micropollutants from synthetic wastewater. Replicating the conditions occurring in real wastewater allows us to expect a high sorption of BPA in real competitive sorption systems.

  17. Moisture sorption kinetics of switchgrass, big bluestem, and bromegrass biomass

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Moisture status in biomass is the most influential factor of biomass storage, and hydration kinetics control the dynamic moisture condition of the biomass, thus affecting biomass storage and processing operations and final utilization applications. Moisture hydration characteristics of switchgrass, ...

  18. Synthesis, characterization, and reversible hydrogen sorption study of sodium-doped fullerene

    NASA Astrophysics Data System (ADS)

    Knight, Douglas A.; Teprovich, Joseph A., Jr.; Summers, Andrew; Peters, Brent; Ward, Patrick A.; Compton, Robert N.; Zidan, Ragaiy

    2013-11-01

    Herein is presented a novel, straightforward route to the synthesis of an alkali metal-doped fullerene as well as a detailed account of its reversible and enhanced hydrogen sorption properties in comparison to pure C60. This work demonstrates that a reaction of sodium hydride with fullerene (C60) results in the formation of a sodium-doped fullerene capable of reversible hydrogen sorption via a chemisorption mechanism. This material not only demonstrated reversible hydrogen storage over several cycles, it also showed the ability to reabsorb over three times the amount of hydrogen (relative to the hydrogen content of NaH) under optimized conditions. The sodium-doped fullerene was hydrogenated on a pressure composition temperature (PCT) instrument at 275 ° C while under 100 bar of hydrogen pressure. The hydrogen desorption behavior of this sodium-doped fullerene hydride was observed over a temperature range up to 375 ° C on the PCT and up to 550 ° C on the thermogravimetric analysis (TGA). Powder x-ray diffraction verifies the identity of this material as being Na6C60. Characterization of this material by thermal decomposition analysis (e.g. PCT and TGA methods), as well as FT-IR and mass spectrometry, indicates that the hydrogen sorption activity of this material is due to the reversible formation of a hydrogenated fullerene (fullerane). However, the reversible formation of fullerane was found to be greatly enhanced by the presence of sodium. It was also demonstrated that the addition of a catalytic amount of titanium (via TiO2 or Ti(OBu)4) further enhances the hydrogen sorption process of the sodium-doped fullerene material.

  19. Analysis of the importance of sorption kinetics to PCB fate modeling

    SciTech Connect

    Connolly, J.; Dean, M.

    1995-12-31

    A considerable amount of literature exists describing the importance of slow kinetics and resistantly bound fractions to the sorption process for hydrophobic organics such as PCBs. The frequently observed deviations of field measured partition coefficients from the presumed relationship between the organic carbon normalized partition coefficient (K{sub oc}) and octanol-water partition coefficient (K{sub ow}) may be evidence of slow sorption kinetics. Of note are the observations in Green Bay and New Bedford Harbor of increases in PCB partition coefficients along a gradient from high concentration to low concentration. These changes in partitioning were evaluated by incorporating a kinetic model derived from experiments with Hudson River sediment into a model of PCB fate in lower Green Bay. The kinetic model successfully described the observed changes in PCB partition coefficient. The results of this work support the conclusion that sorption kinetics are important to the transport and fate of PCBs. An implication of these results is that the resistant fraction of the sorbed PCBs increases with time. This may result in a decrease in bioavailability that could be significant to the use of models to protect future concentrations and ecological or human health risk.

  20. Kinetics of water vapor sorption on porous glass as a method of porometry

    NASA Astrophysics Data System (ADS)

    Kreisberg, V. A.; Rakcheev, V. P.

    2014-09-01

    Equilibrium low temperature nitrogen adsorption and a new method based on the kinetics of water vapor sorption at room temperature are used for a comparative study of pore morphology of high-silica porous glass. The values of the total pore volume, the specific surfaces, the effective mesopore diameters, and the fraction of each mode in the total mesopore volume are established using both techniques. It is found that the rate of water vapor sorption at constant pressure grows in inverse ratio to the diameter of cylindrical menisci in pores. The time dependence of the volume of adsorbed water is linear, while the characteristic time of filling for each pore mode varies directly with the square of the effective pore mode diameter. The proposed new kinetic porometry technique based on analyzing water vapor adsorption kinetics at room temperature is quite simple as it requires no complicated vacuum equipment and allows the simultaneous examination of large numbers of porous material samples.

  1. THE AFFECTS OF HALIDE MODIFIERS ON THE SORPTION KINETICS OF THE LI-MG-N-H SYSTEM

    SciTech Connect

    Erdy, C.; Gray, J.; Lascola, R.; Anton, D.

    2010-12-16

    In this present work, the affects of different transition metal halides (TiCl{sub 3}, VCl{sub 3}, ScCl{sub 3} and NiCl{sub 2}) on the sorption properties of the 1:1 molar ratio of LiNH{sub 2} to MgH{sub 2} are investigated. The modified mixtures were found to contain LiNH{sub 2}, MgH{sub 2} and LiCl. TGA results showed that the hydrogen desorption temperature was reduced with the modifier addition in this order: TiCl{sub 3}>ScCl{sub 3}>VCl{sub 3}>NiCl{sub 2}. Ammonia release was not significantly reduced resulting in a weight loss greater than the theoretical hydrogen storage capacity of the material. The isothermal sorption kinetics of the modified systems showed little improvement after the first dehydrogenation cycle over the unmodified system but showed drastic improvement in rehydrogenation cycles. XRD and Raman spectroscopy identified the cycled material to be composed of LiH, MgH{sub 2}, Mg(NH{sub 2}){sub 2} and Mg{sub 3}N{sub 2}.

  2. THE EFFECTS OF HALIDE MODIFIERS ON THE SORPTION KINETICS OF THE LI-MG-N-H SYSTEM

    SciTech Connect

    Anton, D.; Gray, J.; Price, C.; Lascola, R.

    2011-07-20

    The effects of different transition metal halides (TiCl{sub 3}, VCl{sub 3}, ScCl{sub 3} and NiCl{sub 2}) on the sorption properties of the 1:1 molar ratio of LiNH{sub 2} to MgH{sub 2} are investigated. The modified mixtures were found to contain LiNH{sub 2}, MgH{sub 2} and LiCl. TGA results showed that the hydrogen desorption temperature was reduced with the modifier addition in this order: TiCl{sub 3} > ScCl{sub 3} > VCl{sub 3} > NiCL{sub 2}. Ammonia release was not significantly reduced resulting in a weight loss greater than the theoretical hydrogen storage capacity of the material. The isothermal sorption kinetics of the modified systems showed little improvement after the first dehydrogenation cycle over the unmodified system but showed drastic improvement in rehydrogenation cycles. X-ray diffraction and Raman spectroscopy identified the cycled material to be composed of LiH, MgH{sub 2}, Mg(NH{sub 2}){sub 2} and Mg{sub 3}N{sub 2}.

  3. Influence of phosphorus on Cu sorption kinetics: stirred flow chamber experiments.

    PubMed

    Pérez-Novo, C; Fernández-Calviño, D; Bermúdez-Couso, A; López-Periago, J E; Arias-Estévez, M

    2011-01-15

    A stirred flow reactor was used to study the influence of phosphorus on the adsorption and desorption kinetics of copper in two acid soils on granite and amphibolite. The presence of P was found to significantly increase Cu adsorption in both soils, albeit at different types of sites (mainly in slow adsorption sites in the soil on granite, and both in fast and slow adsorption sites in that on amphibolite). The increased Cu sorption at fast sites in the amphibolite soil was due to its high content in Fe oxyhydroxides, which bound P and released OH(-) as a result, thereby raising the pH and leading to a higher sorption capacity during fast reactions. On the other hand, the increased Cu sorption at slow adsorption sites was due to Cu(2+) acting as a bridging element between P and organic matter.

  4. Sorption kinetics of arsenic on laterite soil in aqueous medium.

    PubMed

    Maji, Sanjoy K; Pal, Anjali; Pal, Tarasankar; Adak, Asok

    2007-06-01

    The efficiency of a locally available laterite soil in removing both arsenite and arsenate from aqueous medium by adsorption was evaluated. It was observed that in batch experiment conducted at 0.5 mg/L initial concentration of arsenic, laterite soil could remove up to 98% of arsenite and 95% of arsenate under optimized conditions. The kinetic profiles under various conditions were developed. Both arsenite and arsenate removal followed pseudo--second order reaction kinetic model. Pore and film diffusion coefficients were determined from the half-time equation and film diffusion appeared to be the rate-limiting. This was further supported by multiple interruption tests. PMID:17558779

  5. Sorption kinetics of arsenic on laterite soil in aqueous medium.

    PubMed

    Maji, Sanjoy K; Pal, Anjali; Pal, Tarasankar; Adak, Asok

    2007-06-01

    The efficiency of a locally available laterite soil in removing both arsenite and arsenate from aqueous medium by adsorption was evaluated. It was observed that in batch experiment conducted at 0.5 mg/L initial concentration of arsenic, laterite soil could remove up to 98% of arsenite and 95% of arsenate under optimized conditions. The kinetic profiles under various conditions were developed. Both arsenite and arsenate removal followed pseudo--second order reaction kinetic model. Pore and film diffusion coefficients were determined from the half-time equation and film diffusion appeared to be the rate-limiting. This was further supported by multiple interruption tests.

  6. Influence of nonlinear sorption kinetics on the slow-desorbing organic contaminant fraction in soil

    SciTech Connect

    Schlebaum, W.; Schraa, G.; Van Riemsdijk, W.H.

    1999-05-01

    Release rates of hydrophobic organic compounds (HOCs) from the soil matrix influence the availability of HOCs in soils or sediments for microbial degradation or removal by physical means (e.g., soil washing or soil venting). In this study it was shown that the initial contaminant concentration influences the desorption rate. This was attributed to the presence of a limited number of high affinity sites that cause nonlinear sorption behavior. The experimental results could be described with a kinetic model composed of two separate compartments. One compartment was described with a Freundlich isotherm and corresponding kinetics and was assumed to represent sorption to high affinity sites. The second compartment was described with a linear sorption isotherm and first-order kinetics. The model was used to simulate the influence of purging strategies on removal of QCB. The simulations showed that after removal of a fast-desorbing fraction, the slow-desorbing fraction could be efficiently removed at very low purging rates. Intermittent purging reduced the total purging time but the simulations showed large fluctuations in the aqueous pentachlorobenzene concentration. For each subsequent purging interval, the purging efficiency decreased due to the nonlinear desorption kinetics of the slow-desorbing fraction of pentachlorobenzene.

  7. Relation of organic contaminant equilibrium sorption and kinetic uptake in plants

    USGS Publications Warehouse

    Li, H.; Sheng, G.; Chiou, C.T.; Xu, O.

    2005-01-01

    Plant uptake is one of the environmental processes that influence contaminant fate. Understanding the magnitude and rate of plant uptake is critical to assessing potential crop contamination and the development of phytoremediation technologies. We determined (1) the partition-dominated equilibrium sorption of lindane (LDN) and hexachlorobenzene (HCB) by roots and shoots of wheat seedlings, (2) the kinetic uptake of LDN and HCB by roots and shoots of wheat seedlings, (3) the kinetic uptake of HCB, tetrachloroethylene (PCE), and trichloroethylene (TCE) by roots and shoots of ryegrass seedlings, and (4) the lipid, carbohydrate, and water contents of the plants. Although the determined sorption and the plant composition together suggest the predominant role of plant lipids for the sorption of LDN and HCB, the predicted partition with lipids of LDN and HCB using the octanol-water partition coefficients is notably lower than the measured sorption, due presumably to underestimation of the plant lipid contents and to the fact that octanol is less effective as a partition medium than plant lipids. The equilibrium sorption or the estimated partition can be viewed as the kinetic uptake limits. The uptakes of LDN, PCE, and TCE from water at fixed concentrations increased with exposure time in approach to steady states. The uptake of HCB did not reach a plateau within the tested time because of its exceptionally high partition coefficient. In all of the cases, the observed uptakes were lower than their respective limits, due presumably to contaminant dissipation in and limited water transpiration by the plants. ?? 2005 American Chemical Society.

  8. Metal-anion sorption by chitosan beads: Equilibrium and kinetic studies

    SciTech Connect

    Guibal, E.; Milot, C.; Tobin, J.M.

    1998-04-01

    Chitosan is a well-known biopolymer, whose high nitrogen content confers remarkable ability for the sorption of metal ions from dilute effluents. However, its sorption performance in both equilibrium and kinetic terms is controlled by diffusion processes. Gel bead formation allows an expansion of the polymer network, which improves access to the internal sorption sites and enhances diffusion mechanisms. Molybdate and vanadate recovery using glutaraldehyde cross-linked chitosan beads reaches uptake capacities as high as 7--8 mmol/g, depending on the pH. The optimum pH (3--3.5) corresponded to the predominance range of hydrolyzed polynuclear metal forms and optimum electrostatic attraction. While for beads, particle size does not influence equilibrium, for flakes, increasing sorbent radius significantly decreases uptake capacities to 1.5 mmol/g. Sorption kinetics are mainly controlled by intraparticle diffusion for beads, while for flakes the controlling mechanisms are both external and intraparticle diffusion. The gel conditioning increases the intraparticle diffusivity by 3 orders of magnitude: intraparticle diffusivities range between 10{sup {minus}13} and 10{sup {minus}10} m{sup 2}/min, depending on the sorbent size and the conditioning.

  9. The kinetics of fluoride sorption by zeolite: Effects of cadmium, barium and manganese.

    PubMed

    Cai, Qianqian; Turner, Brett D; Sheng, Daichao; Sloan, Scott

    2015-01-01

    Industrial wastewaters often consist of a complex chemical cocktail with treatment of target contaminants complicated by adverse chemical reactions. The impact of metal ions (Cd(2+), Ba(2+) and Mn(2+)) on the kinetics of fluoride removal from solution by natural zeolite was investigated. In order to better understand the kinetics, the pseudo-second order (PSO), Hill (Hill 4 and Hill 5) and intra-particle diffusion (IPD) models were applied. Model fitting was compared using the Akaike Information Criterion (AIC) and the Schwarz Bayesian Information Criterion (BIC). The Hill models (Hill 4 and Hill 5) were found to be superior in describing the fluoride removal processes due to the sigmoidal nature of the kinetics. Results indicate that the presence of Mn (100 mg L(-1)) and Cd (100 mg L(-1)) respectively increases the rate of fluoride sorption by a factor of ~28.3 and ~10.9, the maximum sorption capacity is increased by ~2.2 and ~1.7. The presence of Ba (100 mg L(-1)) initially inhibited fluoride removal and very poor fits were obtained for all models. Fitting was best described with a biphasic sigmoidal model with the degree of inhibition decreasing with increasing temperature suggesting that at least two processes are involved with fluoride sorption onto natural zeolite in the presence of Ba.

  10. The kinetics of fluoride sorption by zeolite: Effects of cadmium, barium and manganese.

    PubMed

    Cai, Qianqian; Turner, Brett D; Sheng, Daichao; Sloan, Scott

    2015-01-01

    Industrial wastewaters often consist of a complex chemical cocktail with treatment of target contaminants complicated by adverse chemical reactions. The impact of metal ions (Cd(2+), Ba(2+) and Mn(2+)) on the kinetics of fluoride removal from solution by natural zeolite was investigated. In order to better understand the kinetics, the pseudo-second order (PSO), Hill (Hill 4 and Hill 5) and intra-particle diffusion (IPD) models were applied. Model fitting was compared using the Akaike Information Criterion (AIC) and the Schwarz Bayesian Information Criterion (BIC). The Hill models (Hill 4 and Hill 5) were found to be superior in describing the fluoride removal processes due to the sigmoidal nature of the kinetics. Results indicate that the presence of Mn (100 mg L(-1)) and Cd (100 mg L(-1)) respectively increases the rate of fluoride sorption by a factor of ~28.3 and ~10.9, the maximum sorption capacity is increased by ~2.2 and ~1.7. The presence of Ba (100 mg L(-1)) initially inhibited fluoride removal and very poor fits were obtained for all models. Fitting was best described with a biphasic sigmoidal model with the degree of inhibition decreasing with increasing temperature suggesting that at least two processes are involved with fluoride sorption onto natural zeolite in the presence of Ba. PMID:25909159

  11. Kinetics, equilibrium and thermodynamics of the sorption of p-nitrophenol on two variable charge soils of Southern China

    NASA Astrophysics Data System (ADS)

    Zhang, Jiyang; Wu, Chunde; Jia, Aiyin; Hu, Bing

    2014-04-01

    The sorption of p-nitrophenol (PNP) on two variable charge soils was studied under a series of batch experimental conditions of solution pH, contact time, and temperature. Their kinetic and equilibrium parameters were assessed. The optimum pH for sorption of PNP was 5.0 for Xuwen soil and 5.4 for Guangzhou soil, respectively. Langmuir and Freundlich models were successfully used to describe the sorption isotherms. Results implied that monolayer sorption and heterogeneous energetic distribution of active sites on the surface of the soils were possible. The kinetic data were fitted with pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. The sorption process was well described by pseudo-second-order kinetic model, and the intra-particle diffusion was not the sole rate-controlling step. The negative standard Gibbs free energy (ΔrGm0) values of the sorption implied that the sorption of PNP on soils was spontaneous, and the changes of the standard enthalpy (ΔrHm0) showed that the sorption as endothermic. In addition, the soils were characterized by surface area, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy.

  12. Sorption kinetics of Cs and Sr in sediments of a Savannah River Site reservoir

    SciTech Connect

    Stephens, J.A.

    1997-07-01

    Laboratory measurements of the sorption and desorption of {sup 134}Cs and {sup 85}Sr to sediments were conducted. These sediments were sampled from the profundal zone of Par Pond at the Savannah River Site, Aiken, South Carolina. The isotopes {sup 134}Cs and {sup 85}Sr were used to trace the sorption properties of the main contaminants found in the reservoir which are {sup 137}Cs and {sup 90}Sr respectively. The sorption behavior of these two elements was studied using spiked sediment/water slurries of a known mass to volume ratio. The results reveal that Sr undergoes significant reversible sorption while a fraction of Cs irreversibly sorbs to the sediment. The calculated distribution coefficient Kd at equilibrium was (3 {+-} 0.6) x 10{sup 3} for {sup 134}Cs after 60 d and (1 {+-} 0.2) x 10{sup 3} for {sup 85}Sr after 7 d at pH {approx} 6 and slurry ratio of 1:1000 g/ml. The K{sub d} for {sup 134}Cs ranged from 2 x 10{sup 2} to 3 x 10{sup 4} depending on pH and conductivity. The {sup 85}Sr reached equilibrium in a few days, while {sup 134}Cs reached an apparent equilibrium in 1--2 months. The K{sub d} for {sup 134}Cs was a function of the slurry ratio, pH, conductivity, and contact time. These factors were interrelated since the sediments released ions to the slurry mixture which decreased the pH and increased the conductivity. A sorption isotherm measured for {sup 134}Cs was linear at water concentrations from 60 mBq/ml to 20 Bq/ml. A kinetic model was proposed to describe the basic sorption of {sup 134}Cs to Par Pond sediments under homogeneous laboratory conditions.

  13. Carbon and hydrogen isotope fractionation of benzene and toluene during hydrophobic sorption in multistep batch experiments.

    PubMed

    Imfeld, G; Kopinke, F-D; Fischer, A; Richnow, H-H

    2014-07-01

    The application of compound-specific stable isotope analysis (CSIA) for evaluating degradation of organic pollutants in the field implies that other processes affecting pollutant concentration are minor with respect to isotope fractionation. Sorption is associated with minor isotope fractionation and pollutants may undergo successive sorption-desorption steps during their migration in aquifers. However, little is known about isotope fractionation of BTEX compounds after consecutive sorption steps. Here, we show that partitioning of benzene and toluene between water and organic sorbents (i.e. 1-octanol, dichloromethane, cyclohexane, hexanoic acid and Amberlite XAD-2) generally exhibits very small carbon and hydrogen isotope effects in multistep batch experiments. However, carbon and hydrogen isotope fractionation was observed for the benzene-octanol pair after several sorption steps (Δδ(13)C=1.6 ± 0.3‰ and Δδ(2)H=88 ± 3‰), yielding isotope fractionation factors of αC=1.0030 ± 0.0005 and αH=1.195 ± 0.026. Our results indicate that the cumulative effect of successive hydrophobic partitioning steps in an aquifer generally results in insignificant isotope fractionation for benzene and toluene. However, significant carbon and hydrogen isotope fractionation cannot be excluded for specific sorbate-sorbent pairs, such as sorbates with π-electrons and sorbents with OH-groups. Consequently, functional groups of sedimentary organic matter (SOM) may specifically interact with BTEX compounds migrating in an aquifer, thereby resulting in potentially relevant isotope fractionation.

  14. [Sorption mechanism of ofloxacin by carbon nanotubes].

    PubMed

    Zhao, Xing-Xing; Yu, Shui-Li; Wang, Zhe

    2014-02-01

    Sorption of ofloxacin (OFL) by carbon nanotubes is an effective method to control its fate in aquatic environment. The sorption process of OFL by mixed acid-treated and non-treated multi-walled carbon nanotubes was discussed. Sorption kinetics, sorption isotherm, desorption, sorption thermodynamics and effect of pH were investigated. The results indicated that the sorption kinetics followed the pseudo-second order kinetics model. The equilibrium sorption capacity of OFL on MWCNTs-O was higher. The sorption isotherm could be fitted by both the Langmuir and Freundlich models. The equilibrium sorption capacity dropped when the pH of aqueous solution was in the range of 6.0 to 10.0. Obvious desorption hysteresis was observed during the desorption experiments, especially on MWCNTs-O. Sorption thermodynamics analysis showed that the interactions between the OFL and sorbents were mainly between molecules. More oxygen-containing functional groups introduced on MWCNTs provided OFL molecules with more sorptive sites, which facilitated the generation of hydrogen bonds, a relatively strong interaction. The hydrogen bonds dominated the sorption process of OFL by MWCNTs/MWCNTs-O, explaining the experimental phenomena.

  15. Kinetic modeling of pH-dependent antimony (V) sorption and transport in iron oxide-coated sand.

    PubMed

    Cai, Yongbing; Li, Lulu; Zhang, Hua

    2015-11-01

    Understanding the mechanisms and kinetics controlling the retention and transport of antimony (Sb) is prerequisite for evaluating the risk of groundwater contamination by the toxic element. In this study, kinetic batch and saturated miscible displacement experiments were performed to investigate effects of protonation-deprotonation reactions on sorption-desorption and transport of Sb(V) in iron oxide-coated sand (IOCS). Results clearly demonstrated that Sb(V) sorption was highly nonlinear and time dependent, where both sorption capacity and kinetic rates decreased with increasing solution pH. Breakthrough curves (BTCs) obtained at different solution pH exhibited that mobility of Sb(V) were higher under neutral to alkaline condition than under acidic condition. Because of the nonlinear and non-equilibrium nature of Sb(V) retention and transport, multi-reaction models (MRM) with equilibrium and kinetic sorption expressions were utilized successfully to simulate the experiment data. Equilibrium distribution coefficient (Ke) and reversible kinetic retention parameters (k1 and k2) of both kinetic sorption and transport experiment showed marked decrease as pH increased from 4.0 to 7.5. Surface complexation is suggested as the dominant mechanism for the observed pH-dependent phenomena, which need to be incorporated into the kinetic models to accurately simulate the reactive transport of Sb(V) in vadose zone and aquifers.

  16. Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: a stirred flow-through reactor study.

    PubMed

    Garcia-Sanchez, L; Loffredo, N; Mounier, S; Martin-Garin, A; Coppin, F

    2014-12-01

    This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred flow-through reactor experiments were conducted on samples of a silty clay soil (pH = 8, Eh = 240-300 mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989), were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1 L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17 h and 191 h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the Kd approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters. PMID:25151638

  17. Kinetics of selenate sorption in soil as influenced by biotic and abiotic conditions: a stirred flow-through reactor study.

    PubMed

    Garcia-Sanchez, L; Loffredo, N; Mounier, S; Martin-Garin, A; Coppin, F

    2014-12-01

    This study (i) quantified the kinetics of selenate sorption and (ii) measured the influence of biotic processes in soil selenate stabilisation. Stirred flow-through reactor experiments were conducted on samples of a silty clay soil (pH = 8, Eh = 240-300 mV) from Bure (France) in both non-sterile and sterile conditions. Parameters of the proposed two-site sorption model (EK), adapted from van Genuchten and Wagenet (1989), were estimated by nonlinear regression. Fast selenate sorption on type-1 sites was moderate, with an equilibrium constant of 25.5 and 39.1 L/kg for non-sterile and sterile conditions. Rate-limited sorption on type-2 sites increased with time, and was predominant for longer periods of time in non-sterile conditions. At equilibrium, it would represent over 96% of the sorbed inventory, with mean sorption times of 17 h and 191 h for non-sterile and sterile conditions. Our results showed for Bure soil that (i) selenate sorption in flowing and mildly-oxidising conditions was strongly kinetically controlled, especially in non-sterile conditions, (ii) selenate desorption was much slower than sorption, which suggests its pseudo-irreversible stabilisation, and (iii) microbial activity increased the contribution of rate-limited sorption on type-2 sites, for which it increased sorption rate by a factor 7 but also facilitated its reversibility. This work stresses the limits of the Kd approach to represent selenate sorption in flowing conditions and supports an alternative formulation like the EK model, but also points out that biotic conditions are significant sources of variability for sorption parameters.

  18. Nanotube-derived carbon foam for hydrogen sorption.

    PubMed

    Ding, Feng; Lin, Yu; Krasnov, Pavel O; Yakobson, Boris I

    2007-10-28

    A new kind of carbon foam, which is based on the welding of single-walled carbon nanotubes, is built in a computer simulation. Its precisely defined architecture and all atomic positions allow one to perform detailed theoretical analysis of the properties. Such foam is as light as 19 of steel, while its stiffness is similar and nearly isotropic, and it represents a strong three-dimensional material with various possible applications. Furthermore, its nanoporous structure is accessible to molecular hydrogen and the potential surface analysis indicates that it should be an excellent hydrogen storage medium. Importantly, such foam is a feasible structure that can be produced based on the known tube/fullerene welding techniques.

  19. Kinetics studies of uranium sorption by powdered corn cob in batch and fixed bed system

    PubMed Central

    Mahmoud, Mohamed A.

    2015-01-01

    Sorption of uranium (VI) from aqueous solution onto powdered corn cob has been carried out using batch and fixed-bed technique. The experimental results in batch technique were fitted well with pseudo second-order kinetics model. In the fixed bed technique, Thomas and Bohart–Adams models were evaluated by linear regression analysis for U(VI) uptake in different flow rates, bed heights and initial concentrations. The column experimental data were fitted well with Thomas mode (r2 = 0.999), but the Bohart–Adams model (r2 = 0.911), predicted poor performance of fixed-bed column. PMID:26843973

  20. Kinetics studies of uranium sorption by powdered corn cob in batch and fixed bed system.

    PubMed

    Mahmoud, Mohamed A

    2016-01-01

    Sorption of uranium (VI) from aqueous solution onto powdered corn cob has been carried out using batch and fixed-bed technique. The experimental results in batch technique were fitted well with pseudo second-order kinetics model. In the fixed bed technique, Thomas and Bohart-Adams models were evaluated by linear regression analysis for U(VI) uptake in different flow rates, bed heights and initial concentrations. The column experimental data were fitted well with Thomas mode (r (2) = 0.999), but the Bohart-Adams model (r (2) = 0.911), predicted poor performance of fixed-bed column. PMID:26843973

  1. Kinetics of catalytic transfer hydrogenation of soybean lecithin

    SciTech Connect

    Naglic, M.; Smidovnik, A.; Koloini, T.

    1997-12-01

    Catalytic transfer hydrogenation of soybean lecithin has been studied using aqueous sodium formate solution as hydrogen donor and palladium on carbon as catalyst. Kinetic constants and selectivity have been determined at intensive stirring. Hydrogenation reactions followed the first-order kinetics with respect to fatty acids. In addition to short reaction time, this method offers safe and easy handling. Hydrogenated soybean lecithin provides products with increased stability with respect to oxidation.

  2. Biodegradation kinetic constants and sorption coefficients of micropollutants in membrane bioreactors.

    PubMed

    Fernandez-Fontaina, Eduardo; Pinho, Ines; Carballa, Marta; Omil, Francisco; Lema, Juan M

    2013-04-01

    In order to elucidate the capability of biomass developed in membrane bioreactors (MBR) to degrade and sorb emerging micropollutants, biodegradation (kbiol) and sorption (ksor) kinetic constants as well as solid-liquid partition coefficients (Kd) of 13 selected pharmaceutical and personal care products (PPCPs) were determined with MBR heterotrophic biomass adding a pulse (100 ppb of each compound) and following the liquid and solid phase concentrations over time. The results obtained were compared to literature data referring to conventional activated sludge (CAS) systems. Two experiments were performed: one in the MBR itself and the second one in a batch reactor with the same type and concentration of biomass as in the MBR. Overall, both biodegradation and sorption coefficients were in the same range as previously reported by other studies in CAS systems, indicating that MBR biomass does not show better capabilities for the biological degradation and/or sorption of PPCPs compared to the biomass developed in CAS reactors. Therefore, the higher PPCPs removal efficiencies found in MBRs are explained by the high biomass concentrations obtained at the long sludge retention times at which this type of reactors are usually operated. PMID:22773131

  3. Hydrogen desorption kinetics for aqueous hydrogen fluoride and remote hydrogen plasma processed silicon (001) surfaces

    SciTech Connect

    King, Sean W. Davis, Robert F.; Carter, Richard J.; Schneider, Thomas P.; Nemanich, Robert J.

    2015-09-15

    The desorption kinetics of molecular hydrogen (H{sub 2}) from silicon (001) surfaces exposed to aqueous hydrogen fluoride and remote hydrogen plasmas were examined using temperature programmed desorption. Multiple H{sub 2} desorption states were observed and attributed to surface monohydride (SiH), di/trihydride (SiH{sub 2/3}), and hydroxide (SiOH) species, subsurface hydrogen trapped at defects, and hydrogen evolved during the desorption of surface oxides. The observed surface hydride species were dependent on the surface temperature during hydrogen plasma exposure with mono, di, and trihydride species being observed after low temperature exposure (150 °C), while predominantly monohydride species were observed after higher temperature exposure (450 °C). The ratio of surface versus subsurface H{sub 2} desorption was also found to be dependent on the substrate temperature with 150 °C remote hydrogen plasma exposure generally leading to more H{sub 2} evolved from subsurface states and 450 °C exposure leading to more H{sub 2} desorption from surface SiH{sub x} species. Additional surface desorption states were observed, which were attributed to H{sub 2} desorption from Si (111) facets formed as a result of surface etching by the remote hydrogen plasma or aqueous hydrogen fluoride treatment. The kinetics of surface H{sub 2} desorption were found to be in excellent agreement with prior investigations of silicon surfaces exposed to thermally generated atomic hydrogen.

  4. Synthesis and characterization of MnPS{sub 3} for hydrogen sorption

    SciTech Connect

    Ismail, N.; Temerk, Y.M.; El-Meligi, A.A.; Badr, M.A.; Madian, M.

    2010-05-15

    Single phase MnPS{sub 3} powder was prepared by solid state reaction between Mn, S and P carried out at 650 deg. C in evacuated silica tube. The structure, morphology and sorption characteristics of the prepared solid were investigated. The results revealed that the obtained MnPS{sub 3} compound was capable of adsorbing 3.5 wt% hydrogen at -193 deg. C and a pressure of 30 bar. Little amount of hydrogen (0.07 wt%) was adsorbed at room temperature. The hydrogen adsorption/desorption cycles at various temperatures did not result in irreversible chemical structural changes of the MnPS{sub 3} compound, but the microstructure after hydrogen cycling diminished and became finer. - Graphical abstract: Atomic building of MPS{sub 3}

  5. Imidacloprid sorption kinetics, equilibria, and degradation in sandy soils of Florida.

    PubMed

    Leiva, Jorge A; Nkedi-Kizza, Peter; Morgan, Kelly T; Qureshi, Jawwad A

    2015-05-27

    Imidacloprid (IMD) is a neonicotinoid insecticide soil-drenched on sandy soils of southwest Florida for the control of Diaphorina citri Kuwayama or Asian citrus psyllid (ACP). The ACP vectors causal pathogens of a devastating citrus disease called citrus greening. Understanding the behavior of IMD in these soils and plants is critical to its performance against target pests. Samples from Immokalee fine sand (IFS) were used for sorption kinetics and equilibria experiments. IMD kinetics data were described by the one-site mass transfer (OSMT) model and reached equilibrium between 6 and 12 h. Batch equilibrium and degradation studies revealed that IMD was weakly sorbed (K(OC) = 163-230) and persistent, with a half-life of 1.0-2.6 years. Consequently, IMD has the potential to leach below the citrus root zone after the soil-drench applications. PMID:25938475

  6. Modeling of kinetics of Cr(VI) sorption onto grape stalk waste in a stirred batch reactor.

    PubMed

    Escudero, Carlos; Fiol, Nuria; Poch, Jordi; Villaescusa, Isabel

    2009-10-15

    Recently, Cr(VI) removal by grape stalks has been postulated to follow two mechanisms, adsorption and reduction to trivalent chromium. Nevertheless, the rate at which both processes take place and the possible simultaneity of both processes has not been investigated. In this work, kinetics of Cr(VI) sorption onto grape stalk waste has been studied. Experiments were carried out at different temperatures but at a constant pH (3+/-0.1) in a stirred batch reactor. Results showed that three steps take place in the process of Cr(VI) sorption onto grape stalk waste: Cr(VI) sorption, Cr(VI) reduction to Cr(III) and the adsorption of the formed Cr(III). Taking into account the evidences above mentioned, a model has been developed to predict Cr(VI) sorption on grape stalks on the basis of (i) irreversible reduction of Cr(VI) to Cr(III) reaction, whose reaction rate is assumed to be proportional to the Cr(VI) concentration in solution and (ii) adsorption and desorption of Cr(VI) and formed Cr(III) assuming that all the processes follow Langmuir type kinetics. The proposed model fits successfully the kinetic data obtained at different temperatures and describes the kinetics profile of total, hexavalent and trivalent chromium. The proposed model would be helpful for researchers in the field of Cr(VI) biosorption to design and predict the performance of sorption processes.

  7. Sorption kinetics and leachability of heavy metal from the contaminated soil amended with immobilizing agent (humus soil and hydroxyapatite).

    PubMed

    Chaturvedi, Pranav Kumar; Seth, Chandra Shekhar; Misra, Virendra

    2006-08-01

    Release of heavy metals onto the soil as a result of agricultural and industrial activities may pose a serious threat to the environment. This study investigated the kinetics of sorption of heavy metals on the non-humus soil amended with (1:3) humus soil and 1% hydroxyapatite used for in situ immobilization and leachability of heavy metals from these soils. For this, a batch equilibrium experiment was performed to evaluate metal sorption in the presence of 0.05 M KNO(3) background electrolyte solutions. The Langmuir isotherms applied for sorption studies showed that the amount of metal sorbed on the amended soil decreased in the order of Pb(2+)>Zn(2+)>Cd(2+). The data suggested the possibility of immobilization of Pb due to sorption process and immobilization of Zn and Cd by other processes like co-precipitation and ion exchange. The sorption kinetics data showed the pseudo-second-order reaction kinetics rather than pseudo-first-order kinetics. Leachability study was performed at various pHs (ranging from 3 to 10). Leachability rate was slowest for the Pb(2+) followed by Zn(2+) and Cd(2+). Out of the metal adsorbed on the soil only 6.1-21.6% of Pb, 7.3-39% of Zn and 9.3-44.3% of Cd leached out from the amended soil.

  8. Radiochemical study of hydroxide films. V. Effect of carbonate ion on statics and kinetics of sorption of microamounts of uranium by thin-layer titanium hydroxide

    SciTech Connect

    Nedobukh, T.A.; Kaftailov, V.V.; Betenekov, N.D.

    1988-07-01

    The effect of carbonate ion on the statics and kinetics of sorption of microamounts of uranium from artificial seawater has been studied. It was found experimentally that with increase of carbonate concentration in the solution the distribution coefficient diminishes due to formation of uranyltricarbonate complex not amenable to sorption by titanium hydroxide. It has been shown that dissociation of the tricarbonate form of uranyl is the limiting stage of sorption. The principal kinetic parameters of the process have been determined.

  9. Drug release and its relationship with kinetic and thermodynamic parameters of drug sorption onto starch acetate fibers.

    PubMed

    Xu, Weijie; Yang, Yiqi

    2010-03-01

    Drug release and its relationship with kinetic and thermodynamic parameters of drug sorption onto starch acetate (SA) fibers have been studied using Diclofenac, 5-Fluorouracil (5-Fu), and Metformin as model drugs. The sorption method is more flexible and can avoid limitations or problems which occur with molten or dissolution methods. To understand drug release of sorption loading, kinetic and apparent thermodynamic parameters, such as diffusion coefficient, activation energy for diffusion, affinity, and sorption enthalpy and entropy, have been investigated. The quantitative relationship between drug release and drug-loading concentration, affinity, and activation energy for diffusion has been established to predict the initial burst and subsequent release of the drugs. Up to 12% of Diclofenac, based on the weight of SA, can be loaded onto fibers using the sorption method. Drugs with higher activation energy for diffusion, lower diffusion coefficients, and higher affinity for SA fiber, such as Diclofenac, are more suitable for sorption loading. It has also been found that elevated temperatures will achieve higher loading capacity and a more constant release rate.

  10. Hydrogen storage materials discovery via high throughput ball milling and gas sorption.

    PubMed

    Li, Bin; Kaye, Steven S; Riley, Conor; Greenberg, Doron; Galang, Daniel; Bailey, Mark S

    2012-06-11

    The lack of a high capacity hydrogen storage material is a major barrier to the implementation of the hydrogen economy. To accelerate discovery of such materials, we have developed a high-throughput workflow for screening of hydrogen storage materials in which candidate materials are synthesized and characterized via highly parallel ball mills and volumetric gas sorption instruments, respectively. The workflow was used to identify mixed imides with significantly enhanced absorption rates relative to Li2Mg(NH)2. The most promising material, 2LiNH2:MgH2 + 5 atom % LiBH4 + 0.5 atom % La, exhibits the best balance of absorption rate, capacity, and cycle-life, absorbing >4 wt % H2 in 1 h at 120 °C after 11 absorption-desorption cycles.

  11. Hydrogen sorption characteristics of nanostructured Pd–10Rh processed by cryomilling

    SciTech Connect

    Yang, Nancy; Yee, Joshua K.; Zhang, Zhihui; Kurmanaeva, Lilia; Cappillino, Patrick; Stavila, Vitalie; Lavernia, Enrique J.; San Marchi, Chris

    2014-10-03

    Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanical milling is commonly used to process complex powder systems for solid-state hydrogen storage; however, milling can also be used to evolve nanostructured powder to modify hydrogen sorption characteristics. In the present study, cryomilling (mechanical attrition milling in a cryogenic liquid) is used to produce nanostructured palladium-rhodium alloy powder. Characterization of the cryomilled Pd-10Rh using electron microscopy, X-ray diffraction, and surface area analysis reveals that (i) particle morphology evolves from spherical to flattened disk-like particles; while the (ii) crystallite size decreases from several microns to less than 100 nm and (iii) dislocation density increases with increased cryomilling time. Hydrogen absorption and desorption isotherms as well as the time scales for absorption were measured for cryomilled Pd-10Rh, and correlated with observed microstructural changes induced by the cryomilling process. In short, as the microstructure of the Pd-10Rh alloy is refined by cryomilling: (i) the maximum hydrogen concentration in the α-phase increases, (ii) the pressure plateau becomes flatter, and (iii) the equilibrium hydrogen capacity at 760 Torr increases. In addition, the rate of hydrogen absorption was reduced by an order of magnitude compared to non-cryomilled (atomized) powder.

  12. Hydrogen sorption characteristics of nanostructured Pd–10Rh processed by cryomilling

    DOE PAGES

    Yang, Nancy; Yee, Joshua K.; Zhang, Zhihui; Kurmanaeva, Lilia; Cappillino, Patrick; Stavila, Vitalie; Lavernia, Enrique J.; San Marchi, Chris

    2014-10-03

    Palladium and its alloys are model systems for studying solid-state storage of hydrogen. Mechanical milling is commonly used to process complex powder systems for solid-state hydrogen storage; however, milling can also be used to evolve nanostructured powder to modify hydrogen sorption characteristics. In the present study, cryomilling (mechanical attrition milling in a cryogenic liquid) is used to produce nanostructured palladium-rhodium alloy powder. Characterization of the cryomilled Pd-10Rh using electron microscopy, X-ray diffraction, and surface area analysis reveals that (i) particle morphology evolves from spherical to flattened disk-like particles; while the (ii) crystallite size decreases from several microns to less thanmore » 100 nm and (iii) dislocation density increases with increased cryomilling time. Hydrogen absorption and desorption isotherms as well as the time scales for absorption were measured for cryomilled Pd-10Rh, and correlated with observed microstructural changes induced by the cryomilling process. In short, as the microstructure of the Pd-10Rh alloy is refined by cryomilling: (i) the maximum hydrogen concentration in the α-phase increases, (ii) the pressure plateau becomes flatter, and (iii) the equilibrium hydrogen capacity at 760 Torr increases. In addition, the rate of hydrogen absorption was reduced by an order of magnitude compared to non-cryomilled (atomized) powder.« less

  13. In-situ Hydrogen Sorption 2D-ACAR Facility for the Study of Metal Hydrides for Hydrogen Storage

    NASA Astrophysics Data System (ADS)

    Legerstee, W. J.; de Roode, J.; Anastasopol, A.; Falub, C. V.; Eijt, S. W. H.

    We developed a dedicated hydrogen sorption setup coupled to a positron 2D-ACAR (two-dimensional Angular Correlation of Annihilation Radiation) setup employing a 22Na-source, which will enable to collect 2D-ACAR momentum distributions in-situ as a function of temperature, hydrogen pressure and hydrogen content. In parallel, a dedicated glovebox was constructed for handling air-sensitive metal and metal hydride samples, with a special entrance for the 2D-ACAR sample insert. The 2D-ACAR setup was tested in first measurements on a Pd0.75Ag0.25 foil and on a ball-milled MgH2 powder in both the hydrogen loaded and desorbed states. The hydrogen loaded Pd0.75Ag0.25Hx sample was kept under a 1 bar hydrogen pressure to prevent partial desorption during measurements at room temperature. The collected 2D-ACAR distributions of Pd0.75Ag0.25 and Pd0.75Ag0.25Hx showed similar features as observed in previous studies. The broadening of the ACAR distributions observed for the Mg to MgH2 metal-insulator transition was compared in a quantitative manner to ab-initio calculations reported in the literature.

  14. Thermodynamic, kinetic and conformational analysis of proteins diffusion-sorption on a solid surface.

    PubMed

    Sanfeld, Albert; Royer, Catherine; Steinchen, Annie

    2015-08-01

    In this paper we examine particularly some of the more fundamental properties of protein conformational changes at a solid surface coupled with diffusion from the bulk of an aqueous solution and with the adsorption-desorption processes. We focus our attention on adsorbed protein monolayers upon a solid surface using a thermodynamic and kinetic analytical development. Account is also taken of the effects on the overall rate of the conformational change on a solid surface of deviation from ideality, of protein flexibility, of surface free energy and of interaction with reactive solid sites. Our theory applied to steady states is illustrated by examples such as folding-misfolding-unfolding of RNase and SNase on a solid surface after diffusion and adsorption from an aqueous solution. For this purpose, we put forward the determining steps which shall lead to the steady state. The existence of three situations is highlighted according to the values of the typical constants relevant for the protein considered: reaction rate determining step, diffusion and sorption determining steps, mixed adsorption diffusion and reaction rate. Finally, we have tried to link the developments of our theories to a large literature based on experimental results encountered during proteins diffusion-sorption-reaction processes, fundamental topics that has been since long investigated by Miller's team in MPKG.

  15. Quantum effects in the sorption kinetics of 4He by mesoporous materials

    NASA Astrophysics Data System (ADS)

    Dolbin, A. V.; Khlistyuck, M. V.; Esel'son, V. B.; Gavrilko, V. G.; Vinnikov, N. A.; Basnukaeva, R. M.; Danchuk, V. V.

    2016-02-01

    Sorption and desorption of 4He by a mesoporous silicate material MCM-41 was studied in the temperature range of 1.5-290 K. It was shown that for T = 25-290 K the thermal activation mechanism is dominant in the sorption kinetics of 4He atoms by an MCM-41 sample. Its activation energy was estimated as Ea ≈ 164.8 K. For T = 12-23 K, the diffusion of 4He atoms in the MCM-41 was practically independent of temperature, which typically occurs when the tunnelling mechanism of diffusion dominates over the thermally activated one. A change in the mobility of 4He atoms in MCM-41 channels was observed at T = 6-12 K, which may be indicative of the formation upon cooling (or decay upon heating) of a 4He monolayer and subsequent multilayers on the inner surfaces of the channels. Below 6 K, the diffusion coefficients of 4He are only weakly temperature dependent, which may be attributed to the behavior of quantum 4He liquid in the MCM-41 channels covered with several layers of 4He atoms.

  16. Sorption of methylene blue on treated agricultural adsorbents: equilibrium and kinetic studies

    NASA Astrophysics Data System (ADS)

    Tiwari, D. P.; Singh, S. K.; Sharma, Neetu

    2015-03-01

    Agricultural adsorbents are reported to have a remarkable performance for adsorption of dyes. In the present study, formaldehyde and sulphuric acid treated two agricultural adsorbents; potato peel and neem bark are used to adsorb methylene blue. On the whole, the acid-treated adsorbents are investigated to have high sorption efficiency compared to HCHO treated adsorbents. The percentage removal efficiency of H2SO4 treated potato peel (APP) increases considerably high from 75 to 100 % with increase in adsorbent dose, whereas the removal efficiency of H2SO4 treated neem bark (ANB) is found to be 98 % after adding the first dose only. The monolayer sorption behaviour of HCHO treated potato peel (PP) and APP is well defined by Langmuir, whereas the chemisorptions behaviour of HCHO treated neem bark (NB) and ANB is suggested by Temkin's isotherm model. The maximum adsorption capacity measured is highest in ANB followed by NB, PP and APP with the values of 1000, 90, 47.62 and 40.0 mg/g, respectively. The pseudo-second-order kinetic model fitted well with the observed data of all the four adsorbents. The results obtained reveal that NB and ANB both are good adsorbents compared to PP and APP.

  17. Herbicide sorption by immersed soils: stoichiometry and the law of mass action in support of predictive kinetics.

    PubMed

    Gamble, Donald S

    2009-03-15

    The stoichiometry of labile herbicide sorption on immersed soils has been determined for a few herbicides and a number of soils (Gamble, D. S.; Khan, S. U. Atrazine in organic soil: Chemical speciation during heterogeneous catalysis. J. Agric. Food Chem. 1990, 38, 297-308; Gamble, D. S.; Ismaily, L. A. Atrazine in mineral soil: The analytical chemistry of speciation. Can. J. Chem. 1992, 70, 1590-1596; Gamble, D. S.; Khan, S. U. Atrazine in mineral soil: Chemical species and catalysed hydrolysis. Can. J. Chem. 1992, 70, 1597-1603; Gilchrist, G. F. R.; Gamble, D. S.; Khan, S. U. Atrazine interactions with clay minerals: Kinetics and equilibria of sorption. J. Agric. Food Chem. 1993, 41, 1748-1755; Gamble, D. S. Physical chemistry parameters that control pesticide persistence and leaching in watershed soils. Final report submitted to the Great Lakes Water Quality Program Committee, Guelph, Ontario, June, 1994; Li, J.; Langford, C. H.; Gamble, D. S. Atrazine sorption by a mineral soil: Processes of labile and nonlabile uptake. J. Agric. Food Chem. 1996, 44, 3672-3679; Li, J.; Langford, C. H.; Gamble, D. S. Atrazine sorption by a mineral soil: The effects of size fractions and temperature. J. Agric. Food Chem. 1996, 44, 3680-3684; Gamble, D. S. Pesticide-soil research for the behaviour of chlorothalonil and its metabolite SD-3701 in soil. Final report submitted to Ricerca Inc., Sept 15, 1998; Gamble, D. S. Atrazine sorption kinetics in a characterized soil: Predictive calculations. Environ. Sci. Technol. 2008, 42, 1537-1541). This was done by using equilibrium titrations forthe measurement of labile sorption capacities thetaC. The titrations were made possible by resolving total sorption into its labile and unrecovered fractions. But equilibrium was not also necessary for unrecovered fractions. The site saturation at titration plateaus defined thetaC. The first purpose of determining the stoichiometry is to permitthe use of second-order kinetics instead of unpredictive

  18. Sorption kinetics of TNT and RDX in anaerobic freshwater and marine sediments: Batch studies.

    PubMed

    Ariyarathna, Thivanka; Vlahos, Penny; Tobias, Craig; Smith, Richard

    2016-01-01

    Examination of the partitioning of explosives onto sediment in marine environments is critical to predict the toxicological impacts of worldwide explosive-contaminated sites adjacent to estuaries, wetlands, and the coastal ocean. Marine sediments have been identified as sites of enhanced munitions removal, yet most studies addressing these interactions focus on soils and freshwater sediments. The present study measured the kinetics of 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) sorption onto 2 marine sediments of varying grain sizes (silt vs sand) and organic carbon (OC) content. Abiotic sediment sorption tests were performed at 23 °C, 15 °C, and 4 °C by spiking TNT and RDX solutions directly into anaerobic sediment slurries. Marine sediments showed significantly higher compound uptake rates (0.30-0.80 h(-1) ) than freshwater silt (0.0046-0.0065 h(-1) ) for both compounds, probably because of lower compound solubilities and a higher pH in marine systems. Equilibrium partition constants are on the same order of magnitude for marine silt (1.1-2.0 L kg(-1) sediment) and freshwater silt (1.4-3.1 L kg(-1) sediment) but lower for marine sand (0.72-0.92 L kg(-1) sediment). Total organic carbon content in marine sediments varied linearly with equilibrium partition constants for TNT and was moderately linear for RDX. Uptake rates and equilibrium constants of explosives are inversely correlated to temperature regardless of sediment type because of kinetic barriers associated with low temperatures.

  19. Interfacial thermodynamics and kinetics of sorption of diclofenac on prepared high performance flower-like MoS2.

    PubMed

    Zhang, Yalei; Yin, Zengfu; Dai, Chaomeng; Zhou, Xuefei; Chen, Wen

    2016-11-01

    Flower-like MoS2 with numerous wrinkled nanosheets was prepared via a facile hydrothermal method. The surface morphology and microstructure of the obtained materials were characterized using X-ray diffraction data (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the compositions of the flower-like MoS2 were further revealed by an energy dispersion spectrometer (EDX) and X-ray photoelectron spectrometry (XPS). The obtained MoS2 was used as an adsorbent to remove diclofenac (DCF, C14H10Cl2NO2Na) from aqueous solutions and presented excellent performance for removing DCF. The sorption kinetics, isotherms and effect of solution pH on the sorption were evaluated in batch sorption experiments. The sorption characteristics of the interactions between DCF and MoS2 in water were analyzed using a pseudo-second-order model, an intraparticle diffusion model and Boyd model to determine the sorption rate-determining steps. It was concluded that the sorption of DCF on MoS2 was fitted better by the pseudo-second-order model and that external diffusion governed the sorption process of DCF onto the MoS2. The interfacial interaction free energies between DCF and MoS2 in the sorption process can be calculated based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO). The flower-like MoS2 presenting excellent performance for removing DCF, could be a better choice of treating DCF-containing wastewaters.

  20. Interfacial thermodynamics and kinetics of sorption of diclofenac on prepared high performance flower-like MoS2.

    PubMed

    Zhang, Yalei; Yin, Zengfu; Dai, Chaomeng; Zhou, Xuefei; Chen, Wen

    2016-11-01

    Flower-like MoS2 with numerous wrinkled nanosheets was prepared via a facile hydrothermal method. The surface morphology and microstructure of the obtained materials were characterized using X-ray diffraction data (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Additionally, the compositions of the flower-like MoS2 were further revealed by an energy dispersion spectrometer (EDX) and X-ray photoelectron spectrometry (XPS). The obtained MoS2 was used as an adsorbent to remove diclofenac (DCF, C14H10Cl2NO2Na) from aqueous solutions and presented excellent performance for removing DCF. The sorption kinetics, isotherms and effect of solution pH on the sorption were evaluated in batch sorption experiments. The sorption characteristics of the interactions between DCF and MoS2 in water were analyzed using a pseudo-second-order model, an intraparticle diffusion model and Boyd model to determine the sorption rate-determining steps. It was concluded that the sorption of DCF on MoS2 was fitted better by the pseudo-second-order model and that external diffusion governed the sorption process of DCF onto the MoS2. The interfacial interaction free energies between DCF and MoS2 in the sorption process can be calculated based on the extended Derjaguin-Landau-Verwey-Overbeek (XDLVO). The flower-like MoS2 presenting excellent performance for removing DCF, could be a better choice of treating DCF-containing wastewaters. PMID:27475708

  1. Hydrogen production from glucose and sorbitol by sorption-enhanced steam reforming: challenges and promises.

    PubMed

    He, Li; Chen, De

    2012-03-12

    Concerning energy and environmental sustainability, it is appealing to produce hydrogen from sugars or sugar alcohols that are readily obtained from the hydrolysis of cellulosic biomass. Nevertheless, the conversion of such compounds for hydrogen production poses great technical challenges. In this paper, we report that hydrogen purity and yield can be significantly improved by integrating in situ CO(2) capture into the steam reforming reaction of the model compounds-glucose and sorbitol. The experimental assessment was conducted at a steam-to-carbon ratio of 1.8 for sorbitol and 6 for glucose from 450-625 °C. As predicted by thermodynamic analysis, combining CO(2) capture and reforming reactions at favorable operating conditions yielded very high purity hydrogen, for instance, 98.8 mol % from sorbitol and 99.9 mol % from glucose. However, there are trade-offs between hydrogen purity and yield in practice. The lower operating temperatures in the examined range helped to increase the hydrogen purity and reduce the CO content in the gas product, whereas a high hydrogen yield was more likely to be obtained at higher temperatures. Coupling CO(2) capture lowered the risk of coke formation during the steam reforming of glucose. Coke accumulated in the reactor for the sorption-enhanced steam reforming of glucose was mostly from the slow pyrolysis of glucose before it came into contact with the catalyst-acceptor bed. This problem may be solved by improving heat transfer or reconstructing the reactor, for instance, by using a fluidized-bed reactor.

  2. Preparation, microstructure and hydrogen sorption properties of nanoporous carbon aerogels under ambient drying

    NASA Astrophysics Data System (ADS)

    Tian, H. Y.; Buckley, C. E.; Mulè, S.; Paskevicius, M.; Dhal, B. B.

    2008-11-01

    Organic aerogels are prepared by the sol-gel method from polymerization of resorcinol with furfural. These aerogels are further carbonized in nitrogen in order to obtain their corresponding carbon aerogels (CA); a sample which was carbonized at 900 °C was also activated in a carbon dioxide atmosphere at 900 °C. The chemical reaction mechanism and optimum synthesis conditions are investigated by means of Fourier transform infrared spectroscopy and thermoanalyses (thermogravimetric/differential thermal analyses) with a focus on the sol-gel process. The carbon aerogels were investigated with respect to their microstructures, using small angle x-ray scattering (SAXS), transmission electron microscopy (TEM) and nitrogen adsorption measurements at 77 K. SAXS studies showed that micropores with a radius of gyration of <0.35 ± 0.07 to 0.55 ± 0.05 nm were present, and TEM measurements and nitrogen adsorption showed that larger mesopores were also present. Hydrogen storage properties of the CA were also investigated. An activated sample with a Brunauer-Emmett-Teller surface area of 1539 ± 20 m2 g-1 displayed a reasonably high hydrogen uptake at 77 K with a maximum hydrogen sorption of 3.6 wt% at 2.5 MPa. These results suggest that CA are promising candidate hydrogen storage materials.

  3. Kinetics of sorption of Cu(II)-ethylenediaminetetraacetic acid chelated anions on cross-linked, polyaminated chitosan beads

    SciTech Connect

    Juang, R.S.; Ju, C.Y.

    1998-08-01

    Rates of sorption of Cu(II)-ethylenediaminetetraacetic acid (EDTA) chelated anions from aqueous solutions on cross-linked, poly(ethylenimine) (PEI)-modified chitosan beads were measured in a batch stirred vessel. All experiments were carried out in an equimolar solution of Cu(II) and EDTA (0.47--3.15 mol/m{sup 3}). It was shown that the rates of sorption increased with an increase in the initial concentration of Cu(II), pH, and temperature but decreased with an increase in the molecular weight of PEI introduced in the beads. The widely used homogeneous diffusion model based on Fick`s law and the shrinking core model cannot describe the sorption process. On the contrary, the kinetic data were well fit by the Elovich equation. The apparent activation energies evaluated (3.5--8.4 kcal/mol at pH 3) indicated the combined film and particle diffusion mechanism.

  4. Hydrogen diffusion kinetics and structural integrity of superhigh pressure Mg-5 wt%Ni alloys with dendrite interface

    NASA Astrophysics Data System (ADS)

    Fu, Hui; Wu, Wenshi; Dou, Yang; Liu, Baozhong; Li, Hanning; Peng, Qiuming

    2016-07-01

    A strategy of low-angle orientation dendrite interface-high index planes-which prepared by super-high pressure (SHP) technique, is proposed and successfully improved the hydrogen storage properties of Mg based materials for the first time, wherein a simple binary Mg-Ni alloy is used as a sample to elucidate its related mechanisms. The phase composition, morphology variation and hydrogen storage properties of the as-cast and SHP Mg-5Ni alloys in the temperature range of 1100-1600 °C are systemically investigated. The reversible hydrogen storage capacities and plateau hydrogen pressure of the as-cast and SHP alloys are close due to the same hydrogen storage phases (Mg and Mg2Ni). Note that although SHP treatment at 1600 °C has a large weight fraction of Mg6Ni compound, it still effectively reduces the onset temperature of dehydriding (∼262 °C), as well as improves the hydrogen desorption kinetics at low temperatures and structural integrity. The low onset temperature and outstanding hydrogen sorption/desorption kinetics are mainly associated with the formation of a large number of dendrite interface, in which the hydrogen atoms readily occur "zig-zag" jumps along {11-20} prismatic planes. This dendrite interface of high index planes which prepared by SHP technique paves a new pathway to enhance the hydrogen storage performances of magnesium based alloys.

  5. Kinetics of hydrogen release from lunar soil

    NASA Astrophysics Data System (ADS)

    Bustin, Roberta

    1990-10-01

    With increasing interest in a lunar base, there is a need for extensive examination of possible lunar resources. Hydrogen will be needed on a lunar base for many activities including providing fuel, making water, and serving as a reducing agent in the extraction of oxygen from its ores. Previous studies have shown the solar wind has implanted hydrogen in the lunar regolith and that hydrogen is present not only in the outer layer of soil but to considerable depths, depending on the sampling site. If this hydrogen is to be mined and used on the lunar surface, a number of questions need to be answered. How much energy must be expended in order to release the hydrogen from the soil. What temperatures must be attained, and how long must the soil be heated. This study was undertaken to provide answers to practical questions such as these. Hydrogen was determined using a Pyrolysis/GC technique in which hydrogen was released by heating the soil sample contained in a quartz tube in a resistance wire furnace, followed by separation and quantitative determination using a gas chromatograph with a helium ionization detector. Heating times and temperatures were varied, and particle separates were studied in addition to bulk soils. The typical sample size was 10 mg of lunar soil. All of the soils used were mature soils with similar hydrogen abundances. Pre-treatments with air and steam were used in an effort to find a more efficient way of releasing hydrogen.

  6. Kinetics of hydrogen release from lunar soil

    NASA Technical Reports Server (NTRS)

    Bustin, Roberta

    1990-01-01

    With increasing interest in a lunar base, there is a need for extensive examination of possible lunar resources. Hydrogen will be needed on a lunar base for many activities including providing fuel, making water, and serving as a reducing agent in the extraction of oxygen from its ores. Previous studies have shown the solar wind has implanted hydrogen in the lunar regolith and that hydrogen is present not only in the outer layer of soil but to considerable depths, depending on the sampling site. If this hydrogen is to be mined and used on the lunar surface, a number of questions need to be answered. How much energy must be expended in order to release the hydrogen from the soil. What temperatures must be attained, and how long must the soil be heated. This study was undertaken to provide answers to practical questions such as these. Hydrogen was determined using a Pyrolysis/GC technique in which hydrogen was released by heating the soil sample contained in a quartz tube in a resistance wire furnace, followed by separation and quantitative determination using a gas chromatograph with a helium ionization detector. Heating times and temperatures were varied, and particle separates were studied in addition to bulk soils. The typical sample size was 10 mg of lunar soil. All of the soils used were mature soils with similar hydrogen abundances. Pre-treatments with air and steam were used in an effort to find a more efficient way of releasing hydrogen.

  7. Kinetics of cadmium, chromium, and lead sorption onto chemically modified sugarcane bagasse and wheat straw.

    PubMed

    Mahmood-ul-Hassan, M; Suthar, V; Rafique, E; Ahmad, R; Yasin, M

    2015-07-01

    In this study, cadmium (Cd), chromium (Cr), and lead (Pb) adsorption potential of unmodified and modified sugarcane bagasse and ground wheat straw was explored from aqueous solution through batch equilibrium technique. Both the materials were chemically modified by treating with sodium hydroxide (NaOH) alone and in combination with nitric acid (HNO3) and sulfuric acid (H2SO4). Two kinetic models, pseudo-first order and pseudo-second order were used to follow the adsorption process and reaction fallowed the later model. The Pb removal by both the materials was highest and followed by Cr and Cd. The chemical treatment invariably increased the adsorption capacity and NaOH treatment proved more effective than others. Langmuir maximum sorption capacity (q m) of Pb was utmost (12.8-23.3 mg/g of sugarcane bagasse, 14.5-22.4 mg/g of wheat straw) and of Cd was least (1.5-2.2 mg/g of sugarcane bagasse, 2.5-3.8 mg/g of wheat straw). The q m was in the order of Pb > Cr > Cd for all the three adsorbents. Results demonstrate that agricultural waste materials used in this study could be used to remediate the heavy metal-polluted water.

  8. Photosynthetic hydrogen and oxygen production - Kinetic studies

    NASA Astrophysics Data System (ADS)

    Greenbaum, E.

    1982-01-01

    The simultaneous photoproduction of hydrogen and oxygen was measured in a study of the steady-state turnover times of two biological systems, by driving them into the steady state with repetitive, single-turnover flash illumination. The systems were: (1) in vitro, isolated chloroplasts, ferredoxin and hydrogenase; and (2) the anaerobically-adapted green alga Chlamydomonas reinhardtii. It is found that the turnover times for production of both oxygen and hydrogen in photosynthetic water splitting are in milliseconds, and either equal to, or less than, the turnover time for carbon dioxide reduction in intact algal cells. There is therefore mutual compatibility between hydrogen and oxygen turnover times, and partial compatibility with the excitation rate of the photosynthetic reaction centers under solar irradiation conditions.

  9. HYGROSCOPIC MOISTURE SORPTION KINETICS MODELING OF CORN STOVER AND ITS FRACTIONS

    SciTech Connect

    Igathinathane, C.; Pordesimo, L. O.; Womac, A.R.; Sokhansanj, Shahabaddine

    2009-01-01

    Corn stover, a major crop-based lignocellulosic biomass feedstock, is required to be at an optimum moisture content for efficient bioconversion processes. Environmental conditions surrounding corn stover, as in storage facilities, affect its moisture due to hygroscopic sorption or desorption. The measurement and modeling of sorption characteristics of corn stover and its leaf, husk, and stalk fractions are useful from utilization and storage standpoints, hence investigated in this article. A benchtop low-temperature humidity chamber provided the test environments of 20 C, 30 C, and 40 C at a constant 95% relative humidity. Measured sorption characteristics with three replications for each fraction were obtained from instantaneous sample masses and initial moisture contents. Observed sorption characteristics were fitted using exponential, Page, and Peleg models. Corn stover fractions displayed a rapid initial moisture uptake followed by a slower sorption rates and eventually becoming almost asymptotic after 25 h. Sorption characteristics of all corn stover fractions were significantly different (P < 0.0001) but not the effect of temperature (P > 0.05) on these fractions. The initial 30 min of sorption was found to be critical due to peak rates of sorption from storage, handling, and processing standpoints. The Page and Peleg models had comparable performance fitting the sorption curves (R2 = 0.995), however the exponential model (R2 = 0.91) was not found suitable because of patterned residuals. The Arrhenius type relationship (P < 0.05; R2 = 0.80) explained the temperature variation of the fitted sorption model parameters. The Peleg model fitted constants, among the sorption models studied, had the best fit (R2 = 0.93) with the Arrhenius relationship. A developed method of mass proportion, involving individual corn stover fraction dry matter ratios, predicted the whole corn stover sorption characteristics from that of its individual fractions. Sorption

  10. Characterization of hot hydrogen-atom reactions by kinetic spectrography.

    NASA Technical Reports Server (NTRS)

    Tomalesky, R. E.; Sturm, J. E.

    1971-01-01

    The flash photolysis of hydrogen iodide in the presence of nitrous oxide, carbon dioxide, and water has been investigated by kinetic spectroscopy. Although the fraction of hydrogen iodide dissociated was very large, the only observable intermediate was imidogen. It was demonstrated that the rapid removal of imidogen and the apparent absence of hydroxyl radicals in each case is a result of the following two reactions, respectively: (1) NH + HI yields NH2 + I; and (2) OH + HI yields H2O + I.

  11. Dual-mode modeling of competitive and concentration-dependent sorption and desorption kinetics of polycyclic aromatic hydrocarbons in soils

    NASA Astrophysics Data System (ADS)

    Zhao, Dongye; Pignatello, Joseph J.; White, Jason C.; Braida, Washington; Ferrandino, Francis

    2001-08-01

    A radial dual-mode diffusion model is proposed for mass transfer of hydrophobic compounds in soil organic matter (SOM) that is able to predict competitive and concentration effects on sorption and desorption rates. On the basis of dual-mode sorption theory for glassy polymers the model assumes a population of specific adsorption sites ("holes") interspersed uniformly in the dissolution (partition) domain of SOM. It further assumes Fickian diffusion in the dissolution domain and immobilization in the holes, with microscopic local equilibrium between the two domains. The model is solved numerically (Crank-Nicolson implicit method). Using parameters from single-solute equilibrium and kinetic experiments, the model adequately predicts batch transient sorption and desorption of phenanthrene (primary solute) as a function of pyrene (cosolute) concentration, and batch transient sorption of phenanthrene as a function of its own concentration, in two soils. The model shows that phenanthrene sorption approaches equilibrium faster with increasing cosolute or self-concentration owing to the concentration dependence of the apparent diffusivity, as predicted by a simple hole-plugging mechanism (i.e., fewer and fewer holes are available). Simulations show the effect to be greatest under infinite bath uptake conditions. Under finite bath conditions this positive effect on rate may be opposed by a batch process temporal bias present when the water:soil ratio is kept constant in a series of experiments. The bias is due to gradient driving force effects that slow the rate as a result of the decrease in percent of solute finally taken up by the solid as cosolute or concentration increases.

  12. Sorption behavior of nonylphenol (NP) on sewage-irrigated soil: kinetic and thermodynamic studies.

    PubMed

    Liao, Xiaoping; Zhang, Caixiang; Yao, Linlin; Li, Jiale; Liu, Min; Xu, Liang; Evalde, Mulindankaka

    2014-03-01

    The reuse of wastewater for irrigation of agricultural land is a well established resources management practice but has the disadvantage of inputting various forms of contaminants into the terrestrial environment including nonylphenol (NP), a well known endocrine disrupting substance. To elucidate the environmental fate and transport of NP, the sorption behavior on sewage-irrigated soil was studied by batch experiment. It was found that sorption processes of NP on different sorbents (soil, humic acid (HA) and silica) could be expressed well using two compartment pseudo first-order model, where both surface and intra-particle diffusion were probable rate-controlling processes. Linear model could better express the sorption of NP on soil, black carbon (BC) and mineral (e.g., SiO2) except HA than Freundlich model. The large value of distribution coefficients of normalized organic carbon (Koc) on soils indicated that NP was limited to migrate to deep soil. The higher desorption partition coefficient of NP on soil showed enhanced hysteresis. According to the experimental data, the calculated thermodynamic parameters implied that the sorption reaction on sewage-irrigation was spontaneous, exothermic and entropy decreasing process. The amount of soil organic matter (SOM) dominated the sorption capacity, whereas the sorption behavior of NP on soil showed no significant correlation with ionic strength.

  13. Kinetics of hydrogen peroxide decomposition by catalase: hydroxylic solvent effects.

    PubMed

    Raducan, Adina; Cantemir, Anca Ruxandra; Puiu, Mihaela; Oancea, Dumitru

    2012-11-01

    The effect of water-alcohol (methanol, ethanol, propan-1-ol, propan-2-ol, ethane-1,2-diol and propane-1,2,3-triol) binary mixtures on the kinetics of hydrogen peroxide decomposition in the presence of bovine liver catalase is investigated. In all solvents, the activity of catalase is smaller than in water. The results are discussed on the basis of a simple kinetic model. The kinetic constants for product formation through enzyme-substrate complex decomposition and for inactivation of catalase are estimated. The organic solvents are characterized by several physical properties: dielectric constant (D), hydrophobicity (log P), concentration of hydroxyl groups ([OH]), polarizability (α), Kamlet-Taft parameter (β) and Kosower parameter (Z). The relationships between the initial rate, kinetic constants and medium properties are analyzed by linear and multiple linear regression.

  14. Kinetics of hydrogen peroxide decomposition by catalase: hydroxylic solvent effects.

    PubMed

    Raducan, Adina; Cantemir, Anca Ruxandra; Puiu, Mihaela; Oancea, Dumitru

    2012-11-01

    The effect of water-alcohol (methanol, ethanol, propan-1-ol, propan-2-ol, ethane-1,2-diol and propane-1,2,3-triol) binary mixtures on the kinetics of hydrogen peroxide decomposition in the presence of bovine liver catalase is investigated. In all solvents, the activity of catalase is smaller than in water. The results are discussed on the basis of a simple kinetic model. The kinetic constants for product formation through enzyme-substrate complex decomposition and for inactivation of catalase are estimated. The organic solvents are characterized by several physical properties: dielectric constant (D), hydrophobicity (log P), concentration of hydroxyl groups ([OH]), polarizability (α), Kamlet-Taft parameter (β) and Kosower parameter (Z). The relationships between the initial rate, kinetic constants and medium properties are analyzed by linear and multiple linear regression. PMID:22565543

  15. Interaction between chitosan and uranyl ions. Role of physical and physicochemical parameters on the kinetics of sorption

    SciTech Connect

    Piron, E. |; Accominotti, M.; Domard, A.

    1997-03-19

    This work corresponds to the first part of our studies on the interactions between chitosan particles dispersed in water and uranyl ions. The measurements were obtained by ICP, and we considered the role of various physical and physicochemical parameters related to chitosan. We showed that the crystallinity, the particle dimensions, and the swelling in water of chitosan are parameters which are connected together and govern the kinetic laws of metal diffusion and sorption. The molecular mobility of the polymer chains is then essential parameter. 31 refs., 5 figs., 3 tabs.

  16. Biosorption kinetics, thermodynamics and isosteric heat of sorption of Cu(II) onto Tamarindus indica seed powder.

    PubMed

    Chowdhury, Shamik; Saha, Papita Das

    2011-12-01

    Biosorption of Cu(II) by Tamarindus indica seed powder (TSP) was investigated as a function of temperature in a batch system. The Cu(II) biosorption potential of TSP increased with increasing temperature. The rate of the biosorption process followed pseudo second-order kinetics while the sorption equilibrium data well fitted to the Langmuir and Freundlich isotherm models. The maximum monolayer Cu(II) biosorption capacity increased from 82.97 mg g(-1) at 303 K to 133.24 mg g(-1) at 333 K. Thermodynamic study showed spontaneous and endothermic nature of the sorption process. Isosteric heat of sorption, determined using the Clausius-Clapeyron equation increased with increase in surface loading showing its strong dependence on surface coverage. The biosorbent was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy. The results of FTIR analysis of unloaded and Cu(II)-loaded TSP revealed that -NH(2), -OH, -C=O and C-O functional groups on the biosorbent surface were involved in the biosorption process. The present study suggests that TSP can be used as a potential, alternative, low-cost biosorbent for removal of Cu(II) ions from aqueous media.

  17. Biosorption kinetics, thermodynamics and isosteric heat of sorption of Cu(II) onto Tamarindus indica seed powder.

    PubMed

    Chowdhury, Shamik; Saha, Papita Das

    2011-12-01

    Biosorption of Cu(II) by Tamarindus indica seed powder (TSP) was investigated as a function of temperature in a batch system. The Cu(II) biosorption potential of TSP increased with increasing temperature. The rate of the biosorption process followed pseudo second-order kinetics while the sorption equilibrium data well fitted to the Langmuir and Freundlich isotherm models. The maximum monolayer Cu(II) biosorption capacity increased from 82.97 mg g(-1) at 303 K to 133.24 mg g(-1) at 333 K. Thermodynamic study showed spontaneous and endothermic nature of the sorption process. Isosteric heat of sorption, determined using the Clausius-Clapeyron equation increased with increase in surface loading showing its strong dependence on surface coverage. The biosorbent was characterized by scanning electron microscopy (SEM), surface area and porosity analyzer, X-ray diffraction (XRD) spectrum and Fourier transform infrared (FTIR) spectroscopy. The results of FTIR analysis of unloaded and Cu(II)-loaded TSP revealed that -NH(2), -OH, -C=O and C-O functional groups on the biosorbent surface were involved in the biosorption process. The present study suggests that TSP can be used as a potential, alternative, low-cost biosorbent for removal of Cu(II) ions from aqueous media. PMID:21872453

  18. The influence of nickel layer thickness on microhardness and hydrogen sorption rate of commercially pure titanium alloy

    NASA Astrophysics Data System (ADS)

    Kudiiarov, V. N.; Kashkarov, E. B.; Syrtanov, M. S.; Yugova, I. S.

    2016-02-01

    The influence of nickel coating thickness on microhardness and hydrogen sorption rate by commercially pure titanium alloy was established in this work. Coating deposition was carried out by magnetron sputtering method with prior ion cleaning of surface. It was shown that increase of sputtering time from 10 to 50 minutes leads to increase coating thickness from 56 to 3.78 μm. It was established that increase of nickel coating thickness leads to increase of microhardness at loads less than 0.5 kg. Microhardness values for all samples are not significantly different at loads 1 kg. Hydrogen content in titanium alloy with nickel layer deposited at 10 and 20 minutes exceeds concentration in initial samples on one order of magnitude. Further increasing of deposition time of nickel coating leads to decreasing of hydrogen concentration in samples due to coating delamination in process of hydrogenation.

  19. Data Analysis of Plutonium Sorption on Colloids in a Minimal Kinetics Model

    SciTech Connect

    Wittman, Richard S.; Buck, Edgar C.; Hanson, Brady D.

    2005-08-15

    We considered a sorption model containing the minimal dynamic features of the system to fit plutonium adsorption data similar to that developed by Painter et al. (2002). Global fits to recent data favored nonzero values of reversible sorption, allowing the definition of equilibrium distribution coefficients in all cases except the synthetic form of montmorillonite. In most cases, the two-site model was adequate to fit the data. The model represents a mathematic simplification of the time-dependent sorption process and takes no account for pH-dependent surface charge changes and actinide-mineral surface interfacial chemistry. However, this allows the model to be readily incorporated into existing performance assessment codes when applied to repository environment relevant data sets.

  20. Kinetics of Platinum-Catalyzed Decomposition of Hydrogen Peroxide

    NASA Astrophysics Data System (ADS)

    Vetter, Tiffany A.; Colombo, D. Philip, Jr.

    2003-07-01

    CIBA Vision Corporation markets a contact lens cleaning system that consists of an AOSEPT disinfectant solution and an AOSEPT lens cup. The disinfectant is a buffered 3.0% m/v hydrogen peroxide solution and the cup includes a platinum-coated AOSEPT disc. The hydrogen peroxide disinfects by killing bacteria, fungi, and viruses found on the contact lenses. Because the concentration of hydrogen peroxide needed to disinfect is irritating to eyes, the hydrogen peroxide needs to be neutralized, or decomposed, before the contact lenses can be used again. A general chemistry experiment is described where the kinetics of the catalyzed decomposition of the hydrogen peroxide are studied by measuring the amount of oxygen generated as a function of time. The order of the reaction with respect to the hydrogen peroxide, the rate constant, and the energy of activation are determined. The integrated rate law is used to determine the time required to decompose the hydrogen peroxide to a concentration that is safe for eyes.

  1. Polynuclear aromatic hydrocarbons hydrogenation. 1: Experimental reaction pathways and kinetics

    SciTech Connect

    Korre, S.C.; Klein, M.T. . Dept. of Chemical Engineering); Quann, R.J. . Paulsboro Research Lab.)

    1995-01-01

    The relationship between molecular structure and hydrogenation reactivity in heavy oil hydroprocessing was sought via the elucidation of the controlling reaction pathways and kinetics of one-, two-, three-, and four-fused ring compounds. Hydrogenation reactions of o-xylene, tetralin, naphthalene, phenanthrene, anthracene, pyrene, and chrysene and their multicomponent mixtures were studied in cyclohexane solvent using a presulfided CoMo/Al[sub 2]O[sub 3] catalyst in a 1-liter batch autoclave at P[sub H[sub 2

  2. Effects and Mechanisms of Mechanical Activation on Hydrogen Sorption/ Desorption of Nanoscale Lithium Nitrides

    SciTech Connect

    Shaw, Leon, L.; Yang, Gary, Z.; Crosby, Kyle; Wwan, Xufei. Zhong, Yang; Markmaitree, Tippawan; Osborn, William; Hu, Jianzhi; Kwak, Ja Hun

    2012-04-26

    The objective of this project is to investigate and develop novel, mechanically activated, nanoscale Li3N-based and LiBH4-based materials that are able to store and release {approx}10 wt% hydrogen at temperatures near 100 C with a plateau hydrogen pressure of less than 10 bar. Four (4) material systems have been investigated in the course of this project in order to achieve the project objective. These 4 systems are (i) LiNH2+LiH, (ii) LiNH2+MgH2, (iii) LiBH4, and (iv) LiBH4+MgH2. The key findings we have obtained from these 4 systems are summarized below. *The thermodynamic driving forces for LiNH2+LiH and LiBH4 systems are not adequate to enable H2 release at temperatures < 100 C. *Hydrogen release in the solid state for all of the four systems is controlled by diffusion, and thus is a slow process. *LiNH2+MgH2 and LiBH4+MgH2 systems, although possessing proper thermodynamic driving forces to allow for H2 release at temperatures < 100 C, have sluggish reaction kinetics because of their diffusion-controlled rate-limiting steps. *Reducing particles to the nanometer length scale (< 50 nm) can improve the thermodynamic driving force to enable H2 release at near ambient temperature, while simultaneously enhancing the reaction kinetics as well as changing the diffusion-controlled rate-limiting step to gas desorption-controlled rate-limiting step. This phenomenon has been demonstrated with LiBH4 and offers the hope that further work along this direction will make one of the material systems, i.e., LiBH4, LiBH4+MgH2 and LiNH2+MgH2, possess the desired thermodynamic properties and rapid H2 uptake/release kinetics for on-board applications. Many of the findings and knowledge gained from this project have been published in archival refereed journal articles [1-15] and are accessible by general public. Thus, to avoid a bulky final report, the key findings and knowledge gained from this project will be succinctly summarized, particularly for those findings and knowledge

  3. Mechanisms and kinetics of high-temperature cadmium sorption by packed bed of calcined kaolin.

    PubMed

    Yang, H C; Yun, J S; Kang, M J; Kang, Y; Kim, J H

    2001-01-01

    Sorption experiments by passing CdCl2-carrying flue gas through the packed bed of calcined macro-porous kaolin particles were performed over a temperature range of 973-1173K and a CdCl2 partial pressure range of 8-16.1 Pa. The observed structural change of the sorbent mineral at the stage of sorption and the results of desorption tests revealed the characteristics of an irreversible chemical reaction as a major cadmium capturing mechanism. In the fully saturated kaolin sorbent, CdO x Al2O x 2SiO2 is present as a sorption reaction product together with a smaller amount of 2CdO x Al2O x 2SiO2. The increase in sorbent bed temperature resulted in an increase in the rate of sorption, but it had no effect on maximum cadmium uptake. The gas-phase CdCl2 diffusion into the macro pores of calcined kaolin had a negligible effect on the overall sorption rate. The reaction between gaseous CdCl2 and solid Al2O3 x 2SiO2 is very sensitive to the concentration of CdCl2 but relatively insensitive to the temperature of the sorbent bed. The order of reaction with respect to the CdCl2 vapor concentration was determined to be 3.26. The activation energy, Ea, was estimated as 5.56 kcal/mol according to the Arrhenius relationship. PMID:11688684

  4. The kinetic and thermodynamic sorption and stabilization of multiwalled carbon nanotubes in natural organic matter surrogate solutions: the effect of surrogate molecular weight.

    PubMed

    Li, Tingting; Lin, Daohui; Li, Lu; Wang, Zhengyu; Wu, Fengchang

    2014-03-01

    Styrene sulfonate (SS) and polystyrene sulfonates (PSSs) were used as surrogates of natural organic matter to study the effect of molecular weight (from 206.2 to 70,000 Da) on their sorption by a multiwalled carbon nanotube (MWCNT) and an activated carbon (AC) and on their stabilization of MWCNT suspension. Results indicate that surface-diffusion through the liquid-sorbent boundary was the rate-controlling step of the kinetic sorption of both MWCNTs and AC, and surface-occupying and pore-filling mechanisms respectively dominated the thermodynamic sorption of MWCNTs and AC. Sorption rates and capacities of MWCNTs and AC in molecular concentration of SS and PSS decreased with increasing molecular weight. The PSSs but not SS facilitated the stabilization of MWCNT suspension because of the increased electrosteric repulsion. The PSSs with more monomers had greater capabilities to stabilize the MWCNT suspension, but the capabilities were comparable after being normalized by the total monomer number.

  5. Kinetic modelling of molecular hydrogen transport in microporous carbon materials.

    SciTech Connect

    Hankel, M.; Zhang, H.; Nguyen, T. X.; Bhatia, S. K.; Gray, S. K.; Smith, S. C.

    2011-01-01

    The proposal of kinetic molecular sieving of hydrogen isotopes is explored by employing statistical rate theory methods to describe the kinetics of molecular hydrogen transport in model microporous carbon structures. A Lennard-Jones atom-atom interaction potential is utilized for the description of the interactions between H{sub 2}/D{sub 2} and the carbon framework, while the requisite partition functions describing the thermal flux of molecules through the transition state are calculated quantum mechanically in view of the low temperatures involved in the proposed kinetic molecular sieving application. Predicted kinetic isotope effects for initial passage from the gas phase into the first pore mouth are consistent with expectations from previous modeling studies, namely, that at sufficiently low temperatures and for sufficiently narrow pore mouths D{sub 2} transport is dramatically favored over H{sub 2}. However, in contrast to expectations from previous modeling, the absence of any potential barrier along the minimum energy pathway from the gas phase into the first pore mouth yields a negative temperature dependence in the predicted absolute rate coefficients - implying a negative activation energy. In pursuit of the effective activation barrier, we find that the minimum potential in the cavity is significantly higher than in the pore mouth for nanotube-shaped models, throwing into question the common assumption that passage through the pore mouths should be the rate-determining step. Our results suggest a new mechanism that, depending on the size and shape of the cavity, the thermal activation barrier may lie in the cavity rather than at the pore mouth. As a consequence, design strategies for achieving quantum-mediated kinetic molecular sieving of H{sub 2}/D{sub 2} in a microporous membrane will need, at the very least, to take careful account of cavity shape and size in addition to pore-mouth size in order to ensure that the selective step, namely passage

  6. Sorption kinetics during macropore transport of organic contaminants in soils: Laboratory experiments and analytical modeling

    NASA Astrophysics Data System (ADS)

    Rahman, M. Mokhlesur; Liedl, Rudolf; Grathwohl, Peter

    2004-01-01

    Preferential solute transport coupled with diffusion into the surrounding matrix region has been examined in a silty loam soil by conducting macropore column experiments for various hydrophobic organic compounds (phenanthrene, 1, 2-DCB, TCE, carbofuran) representing the polycyclic aromatic hydrocarbons, chlorobenzenes, chlorinated solvents, and pesticides. A new and ready-to-use analytical solution was developed for this setting to model the breakthrough curves. The model accounts for advection in the macropore region, diffusion into the matrix region, and linear sorption in both regions. In this setting, hydrodynamic dispersion is negligible as proved by a comparison of an advection-dispersion model of finite pulse input. Conservative tracer experiments were predicted very well with independently determined transport parameters except for the tortuosity factor, which was used as a fitting parameter for the pore diffusion coefficient in the matrix. In case of sorbing solutes the sorption coefficient (Kd) was used as additional fitting parameter. The fitted Kd was 65% smaller for less sorbing compounds, e.g., carbofuran, and 80% less for strongly sorbing compounds, e.g., phenanthrene compared to the independently determined Kd from batch experiments. This indicates that sorption equilibrium was not obtained completely during the matrix diffusion at the timescale of the macropore flow experiment.

  7. The effects of iron(II) on the kinetics of arsenic oxidation and sorption on manganese oxides.

    PubMed

    Wu, Yun; Li, Wei; Sparks, Donald L

    2015-11-01

    In this study, As(III) oxidation kinetics by a poorly-crystalline phyllomanganate (δ-MnO2) in the presence and absence of dissolved Fe(II) was investigated using stirred-flow and batch experiments. Chemically synthetic δ-MnO2 was reacted with four influent solutions, containing the same As(III) concentration but different Fe(II) concentrations, at pH 6. The results show an initial rapid As(III) oxidation by δ-MnO2, which is followed by an appreciably slow reaction after 8h. In the presence of Fe(II), As(III) oxidation is inhibited due to the competitive oxidation of Fe(II) as well as the formation of Fe(III)-(hydr)oxides on the δ-MnO2 surface. However, the sorption of As(III), As(V) and Mn(II) are increased, for the newly formed Fe(III)-(hydr)oxides provide additional sorption sites. This study suggests that the competitive oxidation of Fe(II) and consequently the precipitation of Fe(III) compounds on the δ-MnO2 surface play an important role in As(III) oxidation and As sequestration. Understanding these processes would be helpful in developing in situ strategies for remediation of As-contaminated waters and soils.

  8. The role of sorption and biodegradation in the removal of acetaminophen, carbamazepine, caffeine, naproxen and sulfamethoxazole during soil contact: A kinetics study.

    PubMed

    Martínez-Hernández, Virtudes; Meffe, Raffaella; Herrera López, Sonia; de Bustamante, Irene

    2016-07-15

    In countries like Spain, where water is a limited resource, reusing effluents from wastewater treatment plants may imply the introduction of incompletely eliminated pollutants into the environment. Therefore, this work identified the role of sorption and biodegradation in attenuating pharmaceutical compounds (acetaminophen, carbamazepine, caffeine, naproxen and sulfamethoxazole) in natural soil. It also determined which sorption and removal ("sorption+biodegradation") kinetics models describe the behaviour of these substances in the water-soil system. Presence of potential transformation products (TPs) as a result of pharmaceuticals biodegradation was also studied. To this end, serial batch-type experiments were performed with a soil:water ratio of 1:4 and an initial pharmaceutical concentration of 100μgL(-1). Despite results are dependent on soil characteristics, they revealed that, for those substances with a higher affinity to the soil used (loamy sand), sorption seems to play a key role during the first 48h of contact with soil, and gives way to biodegradation afterwards. The sorption of the pharmaceuticals studied follows a pseudo second-order kinetics. Caffeine and sulfamethoxazole displayed the fastest initial sorption velocities (h=2055 and h=228μgkg(-1)h(-1), respectively). The removal kinetics experiments, satisfactorily simulated by the first-order kinetics model, indicated the presence of potential microbial adaptation to degradation. Indeed, half-lives decreased from 1.6- to 11.7-fold with respect to initial values. The microbial capacity to degrade sulfamethoxazole could be a matter of concern if bacteria have developed resistance to this antibiotic. Caffeine, acetaminophen and sulfamethoxazole were mitigated to a greater extent, whereas the removal of naproxen and carbamazepine was more limited. The appearance of epoxy-carbamazepine and N4-acetyl-sulfamethoxazole as possible TPs of carbamazepine and sulfamethoxazole, respectively, indicated that

  9. The role of sorption and biodegradation in the removal of acetaminophen, carbamazepine, caffeine, naproxen and sulfamethoxazole during soil contact: A kinetics study.

    PubMed

    Martínez-Hernández, Virtudes; Meffe, Raffaella; Herrera López, Sonia; de Bustamante, Irene

    2016-07-15

    In countries like Spain, where water is a limited resource, reusing effluents from wastewater treatment plants may imply the introduction of incompletely eliminated pollutants into the environment. Therefore, this work identified the role of sorption and biodegradation in attenuating pharmaceutical compounds (acetaminophen, carbamazepine, caffeine, naproxen and sulfamethoxazole) in natural soil. It also determined which sorption and removal ("sorption+biodegradation") kinetics models describe the behaviour of these substances in the water-soil system. Presence of potential transformation products (TPs) as a result of pharmaceuticals biodegradation was also studied. To this end, serial batch-type experiments were performed with a soil:water ratio of 1:4 and an initial pharmaceutical concentration of 100μgL(-1). Despite results are dependent on soil characteristics, they revealed that, for those substances with a higher affinity to the soil used (loamy sand), sorption seems to play a key role during the first 48h of contact with soil, and gives way to biodegradation afterwards. The sorption of the pharmaceuticals studied follows a pseudo second-order kinetics. Caffeine and sulfamethoxazole displayed the fastest initial sorption velocities (h=2055 and h=228μgkg(-1)h(-1), respectively). The removal kinetics experiments, satisfactorily simulated by the first-order kinetics model, indicated the presence of potential microbial adaptation to degradation. Indeed, half-lives decreased from 1.6- to 11.7-fold with respect to initial values. The microbial capacity to degrade sulfamethoxazole could be a matter of concern if bacteria have developed resistance to this antibiotic. Caffeine, acetaminophen and sulfamethoxazole were mitigated to a greater extent, whereas the removal of naproxen and carbamazepine was more limited. The appearance of epoxy-carbamazepine and N4-acetyl-sulfamethoxazole as possible TPs of carbamazepine and sulfamethoxazole, respectively, indicated that

  10. Kinetic Method for Hydrogen-Deuterium-Tritium Mixture Distillation Simulation

    SciTech Connect

    Sazonov, A.B.; Kagramanov, Z.G.; Magomedbekov, E.P.

    2005-07-15

    Simulation of hydrogen distillation plants requires mathematical procedures suitable for multicomponent systems. In most of the present-day simulation methods a distillation column is assumed to be composed of theoretical stages, or plates. However, in the case of a multicomponent mixture theoretical plate does not exist.An alternative kinetic method of simulation is depicted in the work. According to this method a system of mass-transfer differential equations is solved numerically. Mass-transfer coefficients are estimated with using experimental results and empirical equations.Developed method allows calculating the steady state of a distillation column as well as its any non-steady state when initial conditions are given. The results for steady states are compared with ones obtained via Thiele-Geddes theoretical stage technique and the necessity of using kinetic method is demonstrated. Examples of a column startup period and periodic distillation simulations are shown as well.

  11. Kinetic, equilibrium and thermodynamic studies on sorption of uranium and thorium from aqueous solutions by a selective impregnated resin containing carminic acid.

    PubMed

    Rahmani-Sani, Abolfazl; Hosseini-Bandegharaei, Ahmad; Hosseini, Seyyed-Hossein; Kharghani, Keivan; Zarei, Hossein; Rastegar, Ayoob

    2015-04-01

    In this work, the removal of uranium and thorium ions from aqueous solutions was studied by solid-liquid extraction using an advantageous extractant-impregnated resin (EIR) prepared by loading carminic acid (CA) onto Amberlite XAD-16 resin beads. Batch sorption experiments using CA/XAD-16 beads for the removal of U(VI) and Th(IV) ions were carried out as a function of several parameters, like equilibration time, metal ion concentration, etc. The equilibrium data obtained from the sorption experiments were adjusted to the Langmuir isotherm model and the calculated maximum sorption capacities in terms of monolayer sorption were in agreement with those obtained from the experiments. The experimental data on the sorption behavior of both metal ions onto the EIR beads fitted well in both Bangham and intra-particle diffusion kinetic models, indicating that the intra-particle diffusion is the rate-controlling step. The thermodynamic studies at different temperatures revealed the feasibility and the spontaneous nature of the sorption process for both uranium and thorium ions. PMID:25576783

  12. Kinetic, equilibrium and thermodynamic studies on sorption of uranium and thorium from aqueous solutions by a selective impregnated resin containing carminic acid.

    PubMed

    Rahmani-Sani, Abolfazl; Hosseini-Bandegharaei, Ahmad; Hosseini, Seyyed-Hossein; Kharghani, Keivan; Zarei, Hossein; Rastegar, Ayoob

    2015-04-01

    In this work, the removal of uranium and thorium ions from aqueous solutions was studied by solid-liquid extraction using an advantageous extractant-impregnated resin (EIR) prepared by loading carminic acid (CA) onto Amberlite XAD-16 resin beads. Batch sorption experiments using CA/XAD-16 beads for the removal of U(VI) and Th(IV) ions were carried out as a function of several parameters, like equilibration time, metal ion concentration, etc. The equilibrium data obtained from the sorption experiments were adjusted to the Langmuir isotherm model and the calculated maximum sorption capacities in terms of monolayer sorption were in agreement with those obtained from the experiments. The experimental data on the sorption behavior of both metal ions onto the EIR beads fitted well in both Bangham and intra-particle diffusion kinetic models, indicating that the intra-particle diffusion is the rate-controlling step. The thermodynamic studies at different temperatures revealed the feasibility and the spontaneous nature of the sorption process for both uranium and thorium ions.

  13. Processes and kinetics of Cd2+ sorption by a calcareous aquifer sand

    USGS Publications Warehouse

    Fuller, C.C.; Davis, J.A.

    1987-01-01

    The rate of Cd2+ sorption by a calcareous aquifer sand was characterized by two reaction steps, with the first step reaching completion in 24 hours. The second step proceeded at a slow and nearly constant rate for at least seven days. The first step includes a fast adsorption reaction which is followed by diffusive transport into either a disordered surface film of hydrated calcium carbonate or into pore spaces. After 24 hours the rate of Cd2+ sorption was constant and controlled by the rate of surface coprecipitation, as a solid solution of CdCO3 in CaCO3 formed in recrystallizing material. Desorption of Cd2+ from the sand was slow. Clean grains of primary minerals, e.g. quartz and aluminosilicates. sorbed much less Cd2+ than grains which had surface patches of secondary minerals, e.g. carbonates, iron and manganese oxides. Calcite grains sorbed the greatest amount of Cd2+ on a weight-normalized basis despite the greater abundance of quartz. A method is illustrated for determining empirical binding constants for trace metals at in situ pH values without introducing the experimental problem of supersaturation. The binding constants are useful for solute transport models which include a computation of aqueous speciation. ?? 1987.

  14. Removal of divalent heavy metals (Cd, Cu, Pb, and Zn) and arsenic(III) from aqueous solutions using scoria: kinetics and equilibria of sorption.

    PubMed

    Kwon, Jang-Soon; Yun, Seong-Taek; Lee, Jong-Hwa; Kim, Soon-Oh; Jo, Ho Young

    2010-02-15

    Kinetic and equilibrium sorption experiments were conducted on removal of divalent heavy metals (Pb(II), Cu(II), Zn(II), Cd(II)) and trivalent arsenic (As(III)) from aqueous solutions by scoria (a vesicular pyroclastic rock with basaltic composition) from Jeju Island, Korea, in order to examine its potential use as an efficient sorbent. The removal efficiencies of Pb, Cu, Zn, Cd, and As by the scoria (size=0.1-0.2mm, dose=60gL(-1)) were 94, 70, 63, 59, and 14%, respectively, after a reaction time of 24h under a sorbate concentration of 1mM and the solution pH of 5.0. A careful examination on ionic concentrations in sorption batches suggested that sorption behaviors of heavy metals onto scoria are mainly controlled by cation exchange. On the other hand, arsenic appeared to be sensitive to specific sorption onto hematite (a minor constituent of scoria). Equilibrium sorption tests indicated that the removal efficiency for heavy metals increases with increasing pH of aqueous solutions, which is resulted from precipitation as hydroxides. Similarly, multi-component systems containing heavy metals and arsenic showed that the arsenic removal increases with increasing pH of aqueous solutions, which can be attributed to coprecipitation with metal hydroxides. The empirically determined sorption kinetics were well fitted to a pseudo-second order model, while equilibrium sorption data for heavy metals and arsenic onto scoria were consistent with the Langmuir and Freundlich isotherms, respectively. Natural scoria studied in this work is an efficient sorbent for concurrent removal of divalent heavy metals and arsenic.

  15. Hydrogen recombination kinetics and nuclear thermal rocket performance prediction

    SciTech Connect

    Wetzel, K.K.; Solomon, W.C.

    1994-07-01

    The rate constants for the hydrogen three-body collisional recombination reaction with atomic and molecular hydrogen acting as third bodies have been determined by numerous investigators during the past 30 yr, but these rates exhibit significant scatter. The discrepancies in the rate constants determined by different investigators are as great as two orders of magnitude in the temperature range of interest for nuclear thermal rocket (NTR) operation, namely, 2000-3300 K. The impact of this scatter on our ability to predict the specific impulse (I(sub sp)) delivered by a 30-klbf NTR has been determined for chamber pressures and temperatures from, respectively, 20-1000 psia and 2700-3300 K. The variation in I(sub sp) produced by using the different rate constants is as great as 10%, or 100 s. This variation also obscures the influence of chamber pressure on I(sub sp); using fast kinetics, low pressures yield significantly improved performance, while using slow or nominal kinetics, the pressure dependence of I(sub sp) is negligible. Because the flow composition freezes at very small area ratios, optimization of the nozzle contour in the near-throat region maximizes recombination. Vibrational relaxation is found to produce negligible losses in I(sub sp). 36 refs.

  16. Hydrogen recombination kinetics and nuclear thermal rocket performance prediction

    NASA Astrophysics Data System (ADS)

    Wetzel, Kyle K.; Solomon, Wayne C.

    1994-07-01

    The rate constants for the hydrogen three-body collisional recombination reaction with atomic and molecular hydrogen acting as third bodies have been determined by numerous investigators during the past 30 yr, but these rates exhibit significant scatter. The discrepancies in the rate constants determined by different investigators are as great as two orders of magnitude in the temperature range of interest for nuclear thermal rocket (NTR) operation, namely, 2000-3300 K. The impact of this scatter on our ability to predict the specific impulse (I(sub sp)) delivered by a 30-klbf NTR has been determined for chamber pressures and temperatures from, respectively, 20-1000 psia and 2700-3300 K. The variation in I(sub sp) produced by using the different rate constants is as great as 10%, or 100 s. This variation also obscures the influence of chamber pressure on I(sub sp); using fast kinetics, low pressures yield significantly improved performance, while using slow or nominal kinetics, the pressure dependence of I(sub sp) is negligible. Because the flow composition freezes at very small area ratios, optimization of the nozzle contour in the near-throat region maximizes recombination. Vibrational relaxation is found to produce negligible losses in I(sub sp).

  17. Hydrogen-rich gas production via CaO sorption-enhanced steam gasification of rice husk: a modelling study.

    PubMed

    Beheshti, Sayyed Mohsen; Ghassemi, Hojat; Shahsavan-Markadeh, Rasoul; Fremaux, Sylvain

    2015-01-01

    Gasification is a thermochemical process in which solid or liquid fuels are transformed into synthesis gas through partial oxidation. In this paper, a kinetic model of rice husk gasification has been developed, which is interesting for the applications of the syngas produced. It is a zero-dimensional, steady-state model based on global reaction kinetic, empirical correlation of pyrolysis and is capable of predicting hydrogen yield in the presence of sorbent CaO. The model can also be used as a useful tool to investigate the influence of process parameters including steam/biomass ratio, CaO/fuel ratio (CaO/Fuel), and gasification temperature on hydrogen efficiency, CO2 capture ratio (CCR), and average carbonation conversion (Save). Similar to hydrogen formation, CCR also increases with increasing CaO/Fuel, but an opposite trend is exhibited in Save. Model predictions were compared with available data from the literature, which showed fairly good agreement.

  18. Equilibrium, kinetics and mechanism modeling and simulation of basic and acid dyes sorption onto jute fiber carbon: Eosin yellow, malachite green and crystal violet single component systems.

    PubMed

    Porkodi, K; Vasanth Kumar, K

    2007-05-01

    Batch experiments were carried out for the sorption of eosin yellow, malachite green and crystal violet onto jute fiber carbon (JFC). The operating variables studied are the initial dye concentration, initial solution pH, adsorbent dosage and contact time. Experimental equilibrium data were fitted to Freundlich, Langmuir and Redlich-Peterson isotherm by non-linear regression method. Langmuir isotherm was found to be the optimum isotherm for eosin yellow/JFC system and Freundlich isotherm was found to be the optimum isotherm for malachite green/JFC and crystal violet/JFC system at equilibrium conditions. The sorption capacities of eosin yellow, malachite green and crystal violet onto JFC according to Langmuir isotherm were found to 31.49 mg/g, 136.58 mg/g, 27.99 mg/g, respectively. A single stage batch adsorber was designed for the adsorption of eosin yellow, malachite green and crystal violet onto JFC based on the optimum isotherm. A pseudo second order kinetic model well represented the kinetic uptake of dyes studied onto JFC. The pseudo second order kinetic model successfully simulated the kinetics of dye uptake process. The dye sorption process involves both surface and pore diffusion with predominance of surface diffusion at earlier stages. A Boyd plot confirms the external mass transfer as the rate limiting step in the dye sorption process. The influence of initial dye concentration on the dye sorption process was represented in the form of dimensionless mass transfer numbers (Sh/Sc(0.33)) and was found to be agreeing with the expression:

  19. Kinetic release of hydrogen peroxide from different whitening products.

    PubMed

    da Silva Marques, Duarte Nuno; Silveira, Joao Miguel; Marques, Joana Rita; Amaral, Joao Almeida; Guilherme, Nuno Marques; da Mata, António Duarte

    2012-01-01

    The objective of this in vitro study was to evaluate the kinetics of hydrogen peroxide (HP) release from five different bleaching products: VivaStyle® 10% fitted tray gel, VivaStyle® 30% in-office bleaching gel, VivaStyle® Paint-On Plus paint-on bleaching varnish, Opalescence PF® 10% carbamide peroxide gel and Trèswhite Supreme™ 10% HP gel. Each product was firstly titrated for its HP content by a described method. HP release kinetics was assessed by a modified spectrophotometric technique. One sample t test was performed to test for differences between the manufacturers' claimed HP concentrations and the titrated HP content in the whitening products. Analysis of variance plus Tamhane's post hoc tests and Pearson correlation analysis were used as appropriate. Values of P < 0.05 were taken as significant. Titrated HP revealed an increased content when compared to the manufacturer's specifications for all the products tested (P < 0.05), although only products from one manufacturer produced significantly higher results. All products presented a significant (P < 0.05) and sustained release of HP. However, the product with paint-on cellulose-based matrix resulted in significantly (P < 0.05) faster kinetics when compared to other products tested. These results are consistent with manufacturers' reduced recommended application times. The results of this study suggest that modifying the matrix composition may be a viable alternative to HP concentration increase, since this may result in faster release kinetics without exposure to high HP concentrations. PMID:22908081

  20. Optimization, equilibrium, kinetic, thermodynamic and desorption studies on the sorption of Cu(II) from an aqueous solution using marine green algae: Halimeda gracilis.

    PubMed

    Jayakumar, R; Rajasimman, M; Karthikeyan, C

    2015-11-01

    The aptitude of marine green algae Helimeda gracilis for sorption of Cu(II) ions from an aqueous solution was studied in batch experiments. The effect of relevant parameters such as function of pH, sorbent dosage, agitation speed and contact time was evaluated by using Response surface methodology (RSM). A maximum percentage removal of Cu (II) by Halimeda gracilis occurs at pH-4.49, sorbent dosage-1.98g/L, agitation speed-119.43rpm and contact time-60.21min. Further, the sorbent was characterized by using Fourier Transform Infrared Spectroscopy (FTIR) and Scanning electron microscope (SEM) analysis. Experimental data were analyzed in terms of pseudo-first order, pseudo-second order, intraparticle diffusion, power function and elovich kinetic models. The results showed that the sorption process of Cu(II) ions followed well pseudo-second order kinetics. The sorption data of Cu(II) ions at 308.15K are fitted to Langmuir, Freundlich, Dubinin-Radushkevich (D-R), Temkin, Sips and Toth isotherms. Sorption of Cu(II) onto marine green algae Helimeda gracilis followed the Langmuir and Toth isotherm models (R(2)=0.998 and R(2)=0.999) with the maximum sorption capacity of 38.46 and 38.07mg/g. The calculated thermodynamic parameters such as ΔG°, ΔH° and ΔS° showed that the sorption of Cu(II) ions onto Helimeda gracilis biomass was feasible, spontaneous and endothermic. Desorption study shows that the sorbent could be regenerated using 0.2M HCl solution, with up to 89% recovery.

  1. U(VI) sorption and reduction kinetics on the magnetite (111) surface.

    PubMed

    Singer, David M; Chatman, Shawn M; Ilton, Eugene S; Rosso, Kevin M; Banfield, Jillian F; Waychunas, Glenn A

    2012-04-01

    Sorption of contaminants onto mineral surfaces is an important process that can restrict their transport in the environment. In the current study, uranium (U) uptake on magnetite (111) was measured as a function of time and solution composition (pH, [CO(3)](T), [Ca]) under continuous batch-flow conditions. We observed, in real-time and in situ, adsorption and reduction of U(VI) and subsequent growth of UO(2) nanoprecipitates using atomic force microscopy (AFM) and newly developed batch-flow U L(III)-edge grazing-incidence X-ray absorption spectroscopy near-edge structure (GI-XANES) spectroscopy. U(VI) reduction occurred with and without CO(3) present, and coincided with nucleation and growth of UO(2) particles. When Ca and CO(3) were both present no U(VI) reduction occurred and the U surface loading was lower. In situ batch-flow AFM data indicated that UO(2) particles achieved a maximum height of 4-5 nm after about 8 h of exposure, however, aggregates continued to grow laterally after 8 h reaching up to about 300 nm in diameter. The combination of techniques indicated that U uptake is divided into three-stages; (1) initial adsorption of U(VI), (2) reduction of U(VI) to UO(2) nanoprecipitates at surface-specific sites after 2-3 h of exposure, and (3) completion of U(VI) reduction after ~6-8 h. U(VI) reduction also corresponded to detectable increases in Fe released to solution and surface topography changes. Redox reactions are proposed that explicitly couple the reduction of U(VI) to enhanced release of Fe(II) from magnetite. Although counterintuitive, the proposed reaction stoichiometry was shown to be largely consistent with the experimental results. In addition to providing molecular-scale details about U sorption on magnetite, this work also presents novel advances for collecting surface sensitive molecular-scale information in real-time under batch-flow conditions.

  2. Kinetic modeling of α-hydrogen abstractions from unsaturated and saturated oxygenate compounds by hydrogen atoms.

    PubMed

    Paraskevas, Paschalis D; Sabbe, Maarten K; Reyniers, Marie-Françoise; Papayannakos, Nikos G; Marin, Guy B

    2014-10-01

    Hydrogen-abstraction reactions play a significant role in thermal biomass conversion processes, as well as regular gasification, pyrolysis, or combustion. In this work, a group additivity model is constructed that allows prediction of reaction rates and Arrhenius parameters of hydrogen abstractions by hydrogen atoms from alcohols, ethers, esters, peroxides, ketones, aldehydes, acids, and diketones in a broad temperature range (300-2000 K). A training set of 60 reactions was developed with rate coefficients and Arrhenius parameters calculated by the CBS-QB3 method in the high-pressure limit with tunneling corrections using Eckart tunneling coefficients. From this set of reactions, 15 group additive values were derived for the forward and the reverse reaction, 4 referring to primary and 11 to secondary contributions. The accuracy of the model is validated upon an ab initio and an experimental validation set of 19 and 21 reaction rates, respectively, showing that reaction rates can be predicted with a mean factor of deviation of 2 for the ab initio and 3 for the experimental values. Hence, this work illustrates that the developed group additive model can be reliably applied for the accurate prediction of kinetics of α-hydrogen abstractions by hydrogen atoms from a broad range of oxygenates. PMID:25209711

  3. Metal sorption by peat and algae treated peat: kinetics and factors affecting the process.

    PubMed

    Lourie, Elena; Gjengedal, Elin

    2011-10-01

    The article presents a new approach that can be used for the purification of water contaminated by heavy metals. The treatment of peat with microalgae showed to be an effective way of increasing metal uptake by peat. Metal sorption was studied for a multimetal solution containing Cu, Cd, Ni, Zn, Cd, and Pb. Cu and Pb were found to be the metals having the highest affinity to peat. Water hardness has a strong effect on the uptake of borderline metals (Cd, Ni, Zn, Cd) from a solution. The use of algae for peat treatment resulted in less time to reach an equilibrium (24 h vs. 72 h for pure peat), and the effect of water hardness (Ca²⁺) on metal uptake was considerably reduced. Both peat and algal-treated peat were able to take up metals from rather acidic solutions (pH 3.0). pH had less influence on the metal uptake compared with water hardness. The affinity of heavy metals to peat was the following: Pb>Cu>Ni>Cd>Zn>Co. It slightly changed to Pb>Cu>Ni>Cd≈Co≈Zn when the combined sorbent, peat treated with microalga, was applied.

  4. Description of gas/particle sorption kinetics with an intraparticle diffusion model: Desorption experiments

    USGS Publications Warehouse

    Rounds, S.A.; Tiffany, B.A.; Pankow, J.F.

    1993-01-01

    Aerosol particles from a highway tunnel were collected on a Teflon membrane filter (TMF) using standard techniques. Sorbed organic compounds were then desorbed for 28 days by passing clean nitrogen through the filter. Volatile n-alkanes and polycyclic aromatic hydrocarbons (PAHs) were liberated from the filter quickly; only a small fraction of the less volatile ra-alkanes and PAHs were desorbed. A nonlinear least-squares method was used to fit an intraparticle diffusion model to the experimental data. Two fitting parameters were used: the gas/particle partition coefficient (Kp and an effective intraparticle diffusion coefficient (Oeff). Optimized values of Kp are in agreement with previously reported values. The slope of a correlation between the fitted values of Deff and Kp agrees well with theory, but the absolute values of Deff are a factor of ???106 smaller than predicted for sorption-retarded, gaseous diffusion. Slow transport through an organic or solid phase within the particles or preferential flow through the bed of particulate matter on the filter might be the cause of these very small effective diffusion coefficients. ?? 1993 American Chemical Society.

  5. Sorption kinetics of Hg and HgCl[sub 2] on Kirkwood-Cohansey aquifer sediments from the New Jersey Coastal Plain

    SciTech Connect

    MacLeod, C.; Peterson, J. . Dept. of Geological and Geophysical Sciences)

    1992-01-01

    Anomalously high Hg concentrations have been detected from domestic wells in the Kirkwood-Cohansey Aquifer System, New Jersey Coastal Plain. Mercury concentrations ranging from 0.2--83.0 [mu]g/l in relatively shallow wells ([lt] 100 feet) have been detected. Concentrations in excess of 2.0 [mu]g/l, (the USEPA Drinking Water Standard) have been detected in wells where the Cohansey Sand is overlain by the Bridgeton Formation; a fluvial iron-rich sand with some gravelly channel deposits containing goethite and gibbsite nodules. In this study, Bridgeton Fm. sediments were used to determine the sorption kinetics for solutions containing HgCl[sub 2] and for solutions containing dissolved elemental Hg in order to assess the potential for the Bridgeton sediments to act as a conduit for Hg mobilized from the surface. Results of batch equilibrium experiments suggest that dissolved elemental Hg sorbs to Bridgeton sediments by a risk-order kinetic process. Sorption of the Hg proceeded exponentially and equilibrium was reached within 14 hours. The sorption kinetics for the HgCl[sub 2] solutions, however, appear to be of a second or higher order. For this compound sorption to the sediments begins exponentially, but after 6 hours desorption into the water begins to predominate followed by a slower exponential sorption step that requires nearly 36 hours to reach equilibrium. These experiments illustrate the necessity of determining the distribution coefficients of possible source compounds when attempting to evaluate mobilization potential of a contaminant in the unsaturated zone. Moreover, these data also suggest that HgCl[sub 2], a seed dressing for corn, medial bacteriacide, and embalming fluid ingredient, is more mobile in the environment than dissolved elemental Hg. Consequently, the ground water contamination potential appears to be greater for HgCl[sub 2] than for elemental Hg.

  6. Sorption-desorption kinetics for powdered and non-powered coal

    SciTech Connect

    Romanov, V.; Soong, Y.

    2007-05-01

    Diffusion through macro- and meso-pores with the subsequent filling of open micropores is a relatively fast process and the manometric measurements with fifteen minute pressure stabilization steps provide a good estimate of excess (ad)sorption. This can be followed by a much slower processes of the penetrant diffusion into the macromolecular network, accompanied by its structural relaxation, with or without free volume changes. The “free volume” effect is a change of the sample’s excluded volume because of the penetrant molecules mixing within the formerly excluded volume of the network or because of contraction (either reversible or semi-permanent) due to external pressure. If the resulting swelling of the sample leads to the mixture’s volume equal to the sum of the initial volumes of the components, there is no apparent change to the void volume and no pressure relaxation is observed (b). On the other hand, if the external forces (either macroscopic pressure or microscopic molecular interaction forces) change the excluded volume of the network (its density), without exchange of the sorbent molecules between the sample and the free fluid phase, such change causes a corresponding change in the void volume, which constitutes a pure free volume effect (c). In this case, no post-decompression exodus of the sorbent out of the sample is observed. As a special case, we consider an incorporation of the penetrant molecules into the network without any change in the volume of the mixture (d), though mathematically this can be written as a superposition of the previous two cases

  7. Study of sorption behavior, shelf life and colour kinetics of vacuum puffed honey powder at accelerated storage conditions.

    PubMed

    Devi, K Deepika; Paul, Sanjib Kr; Sahu, Jatindra K

    2016-05-01

    In the study, the storage life of vacuum puffed honey powder at accelerated storage environment (90 % relative humidity and 36 °C) was computed by determining the sticky-point moisture content as the critical parameter of the honey powder. The value of monolayer moisture content in the GAB model was calculated to be 0.081 kg water/kg dry solids by fitting water activity and moisture sorption data. Shelf life of the honey powder was predicted to be 222 days when the powder was packaged in aluminum foil-laminated polyethylene pouches with permeability value of 5.427X10(-8) kg/m(2)//day/Pa. Actual shelf life of honey powder was experimentally determined as 189 days and analysis of mean relative percent derivation modulus (Rd) and root mean square (RMS) established the accuracy and acceptability of the technique for the prediction of shelf life of honey powder. Overall colour deviation pattern followed first order reaction kinetics with rate constant (k1) as 0.037 day(-1). This study revealed overall colour difference of 18.1 till the end of shelf life with drastic change during initial storage period. PMID:27407199

  8. Study of sorption behavior, shelf life and colour kinetics of vacuum puffed honey powder at accelerated storage conditions.

    PubMed

    Devi, K Deepika; Paul, Sanjib Kr; Sahu, Jatindra K

    2016-05-01

    In the study, the storage life of vacuum puffed honey powder at accelerated storage environment (90 % relative humidity and 36 °C) was computed by determining the sticky-point moisture content as the critical parameter of the honey powder. The value of monolayer moisture content in the GAB model was calculated to be 0.081 kg water/kg dry solids by fitting water activity and moisture sorption data. Shelf life of the honey powder was predicted to be 222 days when the powder was packaged in aluminum foil-laminated polyethylene pouches with permeability value of 5.427X10(-8) kg/m(2)//day/Pa. Actual shelf life of honey powder was experimentally determined as 189 days and analysis of mean relative percent derivation modulus (Rd) and root mean square (RMS) established the accuracy and acceptability of the technique for the prediction of shelf life of honey powder. Overall colour deviation pattern followed first order reaction kinetics with rate constant (k1) as 0.037 day(-1). This study revealed overall colour difference of 18.1 till the end of shelf life with drastic change during initial storage period.

  9. Trapping of hydrogen atoms in X-irradiated salts at room temperature and the decay kinetics

    NASA Technical Reports Server (NTRS)

    May, C. E.; Philipp, W. H.; Marsik, S. J.

    1974-01-01

    The salts (hypophosphites, formates, a phosphite, a phosphate, and an oxalate) were X-irradiated, whereby hydrogen formed chemically by a radiolytic process becomes trapped in the solid. By room temperature vacuum extraction, the kinetics for the evolution of this trapped hydrogen was studied mass spectrometrically. All salts except two exhibited second-order kinetics. The two exceptions (NaH2PO2(H2O) and K2HPO4) showed first-order kinetics. Based on experimental results, the escape of hydrogen involves three steps: the diffusion of hydrogen atoms from the bulk to the surface, association of these atoms on the surface (rate controlling step for second-order hydrogen evolution), and the desorption of molecular hydrogen from the surface. The hydrogen does not escape if the irradiated salt is stored in air, apparently because adsorbed air molecules occupy surface sites required in the escape mechanism.

  10. Tailoring Thermodynamics and Kinetics for Hydrogen Storage in Complex Hydrides towards Applications.

    PubMed

    Liu, Yongfeng; Yang, Yaxiong; Gao, Mingxia; Pan, Hongge

    2016-02-01

    Solid-state hydrogen storage using various materials is expected to provide the ultimate solution for safe and efficient on-board storage. Complex hydrides have attracted increasing attention over the past two decades due to their high gravimetric and volumetric hydrogen densities. In this account, we review studies from our lab on tailoring the thermodynamics and kinetics for hydrogen storage in complex hydrides, including metal alanates, borohydrides and amides. By changing the material composition and structure, developing feasible preparation methods, doping high-performance catalysts, optimizing multifunctional additives, creating nanostructures and understanding the interaction mechanisms with hydrogen, the operating temperatures for hydrogen storage in metal amides, alanates and borohydrides are remarkably reduced. This temperature reduction is associated with enhanced reaction kinetics and improved reversibility. The examples discussed in this review are expected to provide new inspiration for the development of complex hydrides with high hydrogen capacity and appropriate thermodynamics and kinetics for hydrogen storage.

  11. Structural study of Ni- or Mg-based complexes incorporated within UiO-66-NH{sub 2} framework and their impact on hydrogen sorption properties

    SciTech Connect

    Žunkovič, E.; Mazaj, M.; Mali, G.; Rangus, M.; Devic, T.; Serre, C.; Logar, N. Zabukovec

    2015-05-15

    Nickel and magnesium acetylacetonate molecular complexes were post-synthetically incorporated into microporous zirconium-based MOF (UiO-66-NH{sub 2}) in order to introduce active open-metal sites for hydrogen sorption. Elemental analysis, nitrogen physisorption and DFT calculations revealed that 5 molecules of Ni(acac){sub 2} or 2 molecules of Mg(acac){sub 2} were incorporated into one unit cell of UiO-66-NH{sub 2}. {sup 1}H–{sup 13}C CPMAS and {sup 1}H MAS NMR spectroscopy showed that, although embedded within the pores, both Ni- and Mg-complexes interacted with the UiO-66-NH{sub 2} framework only through weak van der Waals bonds. Inclusion of metal complexes led to the decrease of hydrogen sorption capacities in Ni-modified as well as in Mg-modified samples in comparison with the parent UiO-66-NH{sub 2}. The isosteric hydrogen adsorption enthalpy slightly increased in the case of Ni-modified material, but not in the case of Mg-modified analogue. - Graphical abstract: A post-synthesis impregnation of Mg- and Ni-acetylacetonate complexes performed on zirconium-based MOF UiO-66-NH{sub 2} does influence the hydrogen sorption performance with respect to the parent matrix. The structural study revealed that Mg- and Ni-acetylacetonate molecules interact with zirconium-terephthalate framework only by weak interactions and they are not covalently bonded to aminoterephthalate ligand. Still, they remain confined into the pores even after hydrogen sorption experiments. - Highlights: • Mg- and Ni-acetylacetonate molecules embedded in the pores of UiO-66-NH{sub 2} by PSM. • Molecules of complexes interact with framework only by van der Waals interactions. • Type/structure of deposited metal-complex impact hydrogen enthalpy of adsorption.

  12. Spectroscopic study on sorption of hydrogen sulfide by means of red soil.

    PubMed

    Ko, T H; Chu, H

    2005-07-01

    This paper reports the results of the characterization of red soils in relation to the sorption of H2S from coal gas at 500 degrees C by spectroscopic techniques in order to provide more information on red soils' structural change both before and after reaction. In addition, by-products analysis has also been studied using Fourier transform infrared (FTIR) spectroscopy. Before and after the experiments the red soils were characterized with X-ray powder diffraction (XRPD), energy dispersion spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and FTIR spectroscopy. XRPD results indicate that iron oxide species disappear from the original to reacted red soil. EDS analysis shows that a significant amount of sulfur is present in the reacted red soil, which is in agreement with the results of the elemental analysis and the calculated value based on breakthrough curve. XPS regression fitting results further indicate that sulfur retention may be associated with the iron oxides. S 2p XPS fittings point out that the major sulfur species present in the reacted red soil are composed of S(-2), elemental sulfur, polysulfide, sulfite and sulfate. Additionally, the binding energy of iron shifts to a lower position for the reacted red soil, which indicates that iron oxides in the original red soil have been converted into iron sulfide. Appreciable amounts of the by-products CO2, SO2 and COS are detected by on-line FTIR spectroscopy during the initial and later stages of the sorption process. The formation of CO2 is related to the water-shift reaction, and SO2 is probably attributable to the reaction of organic matters and H2S. The concentration of COS is quantified by GC/FPD and found it to be about 350 ppm, which is close to the equilibrium concentration of the reaction of inlet CO and H2S at a temperature of 500 degrees C.

  13. Kinetics of sorption and abiotic oxidation of arsenic(III) by aquifer materials

    USGS Publications Warehouse

    Amirbahman, A.; Kent, D.B.; Curtis, G.P.; Davis, J.A.

    2006-01-01

    The fate of arsenic in groundwater depends largely on its interaction with mineral surfaces. We investigated the kinetics of As(III) oxidation by aquifer materials collected from the USGS research site at Cape Cod, MA, USA, by conducting laboratory experiments. Five different solid samples with similar specific surface areas (0.6-0.9 m2 g-1) and reductively extractable iron contents (18-26 ??mol m-2), but with varying total manganese contents (0.5-3.5 ??mol m-2) were used. Both dissolved and adsorbed As(III) and As(V) concentrations were measured with time up to 250 h. The As(III) removal rate from solution increased with increasing solid manganese content, suggesting that manganese oxide is responsible for the oxidation of As(III). Under all conditions, dissolved As(V) concentrations were very low. A quantitative model was developed to simulate the extent and kinetics of arsenic transformation by aquifer materials. The model included: (1) reversible rate-limited adsorption of As(III) onto both oxidative and non-oxidative (adsorptive) sites, (2) irreversible rate-limited oxidation of As(III), and (3) equilibrium adsorption of As(V) onto adsorptive sites. Rate constants for these processes, as well as the total oxidative site densities were used as the fitting parameters. The total adsorptive site densities were estimated based on the measured specific surface area of each material. The best fit was provided by considering one fast and one slow site for each adsorptive and oxidative site. The fitting parameters were obtained using the kinetic data for the most reactive aquifer material at different initial As(III) concentrations. Using the same parameters to simulate As(III) and As(V) surface reactions, the model predictions were compared to observations for aquifer materials with different manganese contents. The model simulated the experimental data very well for all materials at all initial As(III) concentrations. The As(V) production rate was related to the

  14. Kinetics Study of Solid Ammonia Borane Hydrogen Release – Modeling and Experimental Validation for Chemical Hydrogen Storage

    SciTech Connect

    Choi, Yong-Joon; Ronnebro, Ewa; Rassat, Scot D.; Karkamkar, Abhijeet J.; Maupin, Gary D.; Holladay, Jamelyn D.; Simmons, Kevin L.; Brooks, Kriston P.

    2014-02-24

    Ammonia borane (AB), NH3BH3, is a promising material for chemical hydrogen storage with 19.6 wt% gravimetric hydrogen capacity of which 16.2 wt% hydrogen can be utilized below 200°C. We have investigated the kinetics of hydrogen release from AB and from an AB-methyl cellulose (AB/MC) composite at temperatures of 160-300°C using both experiments and modeling. The purpose of our study was to show safe hydrogen release without thermal runaway effects and to validate system model kinetics. AB/MC released hydrogen at ~20°C lower than neat AB and at a rate that is two times faster. Based on the experimental results, the kinetics equations were revised to better represent the growth and nucleation process during decomposition of AB. We explored two different reactor concepts; Auger and fixed bed. The current Auger reactor concept turned out to not be appropriate, however, we demonstrated safe self-propagation of the hydrogen release reaction of solid AB/MC in a fixed bed reactor.

  15. Kinetics of hydrogenation of acetophenone to methylphenylcarbinol on KGA-43 copper-chromium catalyst

    SciTech Connect

    Ziyatdinov, A.Sh.; Stepanenko, V.V.; Chernykh, I.S.; Leonova, E.B.; Pisarenko, V.N.; Kafarov, V.V.

    1988-08-20

    The purpose of this investigation was to study the kinetics of the hydrogenation of acetophenone on KGA-43 catalyst, to establish a kinetic model for it, and to test the adequacy of the kinetic model for experiment. The kinetic studies of the hydrogenation of acetophenone on the new KGA-43 catalyst were conducted on a laboratory unit. Using the theory of steady-state reactions a kinetic model incorporating 10 unknown parameters was constructed. To determine the point estimates of the kinetic constants they used the method of maximum probability. The results of five repeated experiments were used to calculate the elements of a dispersion-covariation matrix of the reproducibility of the observations.

  16. Reaction kinetics for the oxygen hydrogenation process on Pt(111) derived from temperature-programmed XPS

    NASA Astrophysics Data System (ADS)

    Näslund, Lars-Åke

    2013-12-01

    Oxygen hydrogenation under ultra high vacuum conditions at the platinum surface was explored using temperature-programmed X-ray photoelectron spectroscopy. Through modeling of the oxygen consumption, information on the reaction kinetics was obtained indicating that the reaction rate of the oxygen hydrogenation process depends on the hydrogen diffusion and on the lifetime of hydroxyl intermediates. The reaction rate is, however, enhanced when an autocatalytic process stabilizes the hydroxyl intermediates through hydrogen bonding to neighboring water molecules. The overall activation energy for the hydrogenation of atomic oxygen to form water was determined to be 0.20 eV with a frequency factor of only 103 s- 1.

  17. Sorption of water alkalinity and hardness from high-strength wastewater on bifunctional activated carbon: process optimization, kinetics and equilibrium studies.

    PubMed

    Amosa, Mutiu K

    2016-08-01

    Sorption optimization and mechanism of hardness and alkalinity on bifunctional empty fruit bunch-based powdered activation carbon (PAC) were studied. The PAC possessed both high surface area and ion-exchange properties, and it was utilized in the treatment of biotreated palm oil mill effluent. Batch adsorption experiments designed with Design Expert(®) were conducted in correlating the singular and interactive effects of the three adsorption parameters: PAC dosage, agitation speed and contact time. The sorption trends of the two contaminants were sequentially assessed through a full factorial design with three factor interaction models and a central composite design with polynomial models of quadratic order. Analysis of variance revealed the significant factors on each design response with very high R(2) values indicating good agreement between model and experimental values. The optimum operating conditions of the two contaminants differed due to their different regions of operating interests, thus necessitating the utility of desirability factor to get consolidated optimum operation conditions. The equilibrium data for alkalinity and hardness sorption were better represented by the Langmuir isotherm, while the pseudo-second-order kinetic model described the adsorption rates and behavior better. It was concluded that chemisorption contributed majorly to the adsorption process.

  18. Sorption of water alkalinity and hardness from high-strength wastewater on bifunctional activated carbon: process optimization, kinetics and equilibrium studies.

    PubMed

    Amosa, Mutiu K

    2016-08-01

    Sorption optimization and mechanism of hardness and alkalinity on bifunctional empty fruit bunch-based powdered activation carbon (PAC) were studied. The PAC possessed both high surface area and ion-exchange properties, and it was utilized in the treatment of biotreated palm oil mill effluent. Batch adsorption experiments designed with Design Expert(®) were conducted in correlating the singular and interactive effects of the three adsorption parameters: PAC dosage, agitation speed and contact time. The sorption trends of the two contaminants were sequentially assessed through a full factorial design with three factor interaction models and a central composite design with polynomial models of quadratic order. Analysis of variance revealed the significant factors on each design response with very high R(2) values indicating good agreement between model and experimental values. The optimum operating conditions of the two contaminants differed due to their different regions of operating interests, thus necessitating the utility of desirability factor to get consolidated optimum operation conditions. The equilibrium data for alkalinity and hardness sorption were better represented by the Langmuir isotherm, while the pseudo-second-order kinetic model described the adsorption rates and behavior better. It was concluded that chemisorption contributed majorly to the adsorption process. PMID:26752149

  19. Sorption of arsenite, arsenate, and thioarsenates to iron oxides and iron sulfides: a kinetic and spectroscopic investigation.

    PubMed

    Couture, R-M; Rose, J; Kumar, N; Mitchell, K; Wallschläger, D; Van Cappellen, P

    2013-06-01

    Sorption to iron (Fe) minerals determines the fate of the toxic metalloid arsenic (As) in many subsurface environments. Recently, thiolated As species have been shown to dominate aqueous As speciation under a range of environmentally relevant conditions, thus highlighting the need for a quantitative understanding of their sorption behavior. We conducted batch experiments to measure the time-dependent sorption of two S-substituted arsenate species, mono- and tetrathioarsenate, and compared it to the sorption of arsenite and arsenate, in suspensions containing 2-line ferrihydrite, goethite, mackinawite, or pyrite. All four As species strongly sorbed to ferrihydrite. For the other sorbents, binding of the thiolated As species was generally lower compared to arsenate and arsenite, with the exception of the near instantaneous and complete sorption of monothioarsenate to pyrite. Analysis of the X-ray absorption spectroscopy (XAS) spectra of sorbed complexes implied that monothioarsenate binds to Fe oxides as a monodentate, inner-sphere complex. In the presence of Fe sulfides, mono- and tetrathioarsenate were both unstable and partially reduced to arsenite. Adsorption of the thiolated As species to the Fe sulfide minerals also caused the substitution of surface sulfur (S) atoms by As and the formation of As-Fe bonds.

  20. Graphene CVD growth on copper and nickel: role of hydrogen in kinetics and structure.

    PubMed

    Losurdo, Maria; Giangregorio, Maria Michela; Capezzuto, Pio; Bruno, Giovanni

    2011-12-14

    Understanding the chemical vapor deposition (CVD) kinetics of graphene growth is important for advancing graphene processing and achieving better control of graphene thickness and properties. In the perspective of improving large area graphene quality, we have investigated in real-time the CVD kinetics using CH(4)-H(2) precursors on both polycrystalline copper and nickel. We highlighted the role of hydrogen in differentiating the growth kinetics and thickness of graphene on copper and nickel. Specifically, the growth kinetics and mechanism is framed in the competitive dissociative chemisorption of H(2) and dehydrogenating chemisorption of CH(4), and in the competition of the in-diffusion of carbon and hydrogen, being hydrogen in-diffusion faster in copper than nickel, while carbon diffusion is faster in nickel than copper. It is shown that hydrogen acts as an inhibitor for the CH(4) dehydrogenation on copper, contributing to suppress deposition onto the copper substrate, and degrades quality of graphene. Additionally, the evidence of the role of hydrogen in forming C-H out of plane defects in CVD graphene on Cu is also provided. Conversely, resurfacing recombination of hydrogen aids CH(4) decomposition in the case of Ni. Understanding better and providing other elements to the kinetics of graphene growth is helpful to define the optimal CH(4)/H(2) ratio, which ultimately can contribute to improve graphene layer thickness uniformity even on polycrystalline substrates. PMID:22006173

  1. Sorption Kinetics Of Selected Heavy Metals Adsorption To Natural And Fe(III) Modified Zeolite Tuff Containing Clinoptilolite Mineral

    NASA Astrophysics Data System (ADS)

    Sirotiak, Maroš; Lipovský, Marek; Bartošová, Alica

    2015-06-01

    In the research described in this paper, studied was sorption capacity of natural and ferric modification of zeolite tuff containing mineral clinoptilolite from the Nižný Hrabovec deposit to remove potentially toxic metals (ionic forms of chromium, nickel, copper and aluminium) from their water solutions. We reported that the Fe (III) zeolite has an enhanced ability to sorption of Cu (II), and a slight improvement occurs in the case of Cr (VI) and Ni (II). On the other hand, the deterioration was observed in the case of Al (III) adsorption.

  2. Thermodynamics and Kinetics of Phase Transformations in Hydrogen Storage Materials

    SciTech Connect

    Ceder, Gerbrand; Marzari, Nicola

    2011-08-31

    The aim of this project is to develop and apply computational materials science tools to determine and predict critical properties of hydrogen storage materials. By better understanding the absorption/desorption mechanisms and characterizing their physical properties it is possible to explore and evaluate new directions for hydrogen storage materials. Particular emphasis is on the determination of the structure and thermodynamics of hydrogen storage materials, the investigation of microscopic mechanisms of hydrogen uptake and release in various materials and the role of catalysts in this process. As a team we have decided to focus on a single material, NaAlH{sub 4}, in order to fully be able to study the many aspects of hydrogen storage. We have focused on phase stability, mass transport and size-dependent reaction mechanisms in this material.

  3. Sorption kinetics of superabsorbent polymers (SAPs) in fresh Portland cement-based pastes visualized and quantified by neutron radiography and correlated to the progress of cement hydration

    SciTech Connect

    Schroefl, Christof; Mechtcherine, Viktor; Vontobel, Peter; Hovind, Jan; Lehmann, Eberhard

    2015-09-15

    Water sorption of two superabsorbent polymers in cement-based pastes has been characterized by neutron radiography. Cement pastes with W/C of 0.25 and 0.50 and one additionally containing silica fume (W/C = 0.42) were investigated. The SAPs differed in their inherent sorption kinetics in extracted cement pore solution (SAP 1: self-releasing; SAP 2: retentive). Desorption from SAP 1 started very early after paste preparation. Hence, its individual non-retentiveness governs its behavior only. SAP 2 released water into all matrices, but its kinetics were different. In the paste with the highest W/C, some moderate water release was recorded from the beginning. In the other two pastes, SAP 2 retained its stored liquid during the dormant period, i.e., up to the percolation threshold. Intense desorption then set in and continued throughout the acceleration period. These findings explain the pronouncedly higher efficiency of SAP 2 as internal curing admixture as compared to SAP 1.

  4. [Sorption Characteristics of Phenanthrene and 1, 1-Dichloroethene onto Reed Straw Biochar in Aquatic Solutions].

    PubMed

    Wu, Qing-wen; Meng, Liang; Zhang, Zhi-hao; Luo, Qi-shi; Yang, Jie

    2016-02-15

    The purpose of this study was to investigate the sorption characteristics of phenanthrene (PHE) and 1, 1-dichloroethene (1, 1-DCE) onto reed straw biochar at 500 degrees C in aquatic solutions. The sorption mechanisms and effects of solution pH and biochar mass on sorption intensity were discussed. The results showed that the time required to reach sorption equilibrium was 60 min and 480 min for PHE and 1, 1-DCE, respectively, with maximum removal rates of 81, 87% and 90.18%. The sorption kinetics of both PHE and 1, 1-DCE fitted the pseudo-second-order model well, but the pseudo-second-order reaction rate of PHE was higher than that of 1, 1-DCE. Furthermore, the sorption processes were controlled by both membrane diffusion and intra-particle diffusion, and the latter was found to be the rate-controlling step. Sorption isotherms of the two organic pollutants fitted well with the Freundlich equation, and the sorption affinity of 1, 1-DCE onto biochar was greater than that of PHE. The total sorption mechanism of biochar was the combination of partition and adsorption, and dominated by adsorption. The adsorption capacity of 1, 1-DCE was greater than that of PHE, but its partition capacity was much smaller, indicating that pollutants' molecular volume and relative polarity would mainly affect the total sorption. Analysis of Fourier transform infrared spectroscopy (FTIR) demonstrated that oxygen- and hydrogen-containing functional groups and pi--pi interaction were important for PHE and 1, 1-DCE sorption onto biochar. The solution pH value had no significant effect on the sorption intensity of PHE and 1, 1-DCE, however, with biochar mass increasing from 5 mg to 50 mg, the equilibrium sorption amount of PHE and 1, 1-DCE decreased by 6.78 times and 2.18 times, and the removal rate increased by 20.21% and 15.78%, respectively. PMID:27363160

  5. Kinetic and Prediction of Hydrogen Outgassing from Lithium Hydride

    SciTech Connect

    Dinh, L N; Schildbach, M A; Smith, R A; Balazs, B; McLean II, W

    2006-08-31

    In most industrial or device applications, LiH is placed in either an initially dry or a vacuum environment with other materials that may release moisture slowly over many months, years, or even decades. In such instances, the rate of hydrogen outgassing from the reaction of LiH with H{sub 2}O can be reasonably approximated by the rate at which H{sub 2}O is released from the moisture containing materials. In a vacuum or dry environment, LiOH decomposes slowly with time into Li{sub 2}O even at room temperature according to: 2LiOH(s) {yields} Li{sub 2}O(s) + H{sub 2}O(g) (1). The kinetics of the decomposition of LiOH depends on the dryness/vacuum level and temperature. It was discovered by different workers that vacuum thermal decomposition of bulk LiOH powder (grain sizes on the order of tens to hundreds of micrometers) into Li{sub 2}O follows a reaction front moving from the surface inward. Due to stress at the LiOH/vacuum interface and defective and missing crystalline bonding at surface sites, lattice vibrations at the surfaces/interfaces of most materials are at frequencies different than those in the bulk, a phenomenon observed in most solids. The chemical reactivity and electronic properties at surfaces and interfaces of materials are also different than those in the bulk. It is, therefore, expected that the amount of energy required to break bonds at the LiOH/vacuum interface is not as large as in the bulk. In addition, in an environment where there is a moisture sink or in the case of a continuously pumped vacuum chamber, H{sub 2}O vapor is continuously removed and LiOH decomposes into Li{sub 2}O from the LiOH/vacuum interface (where it is thermally less stable) inward according to reaction (1) in an effort to maintain the equilibrium H{sub 2}O vapor pressure at the sample/vacuum interface. In a closed system containing both LiH and LiOH, the H{sub 2}O released from the decomposition of LiOH reacts with LiH to form hydrogen gas according to the following

  6. A study of spin isomer conversion kinetics in supercritical fluid hydrogen for cyrogenic fuel storage technologies

    NASA Astrophysics Data System (ADS)

    Matthews, Manyalibo J.; Petitpas, Guillaume; Aceves, Salvador M.

    2011-08-01

    A detailed kinetic study of para-ortho hydrogen conversion under supercritical conditions using rotational Raman scattering is presented. Isochoric measurements of initially low ortho concentrations over temperatures 32 < T < 280 K and densities 0.014 < ρ < 0.060 g/cm3 were used to derive kinetic rate constants k(ρ, T) by solving an autocatalytic kinetic rate equation. At low ortho concentrations and T < 100 K, k is found to be ˜2× higher than previous results based on thermal conductivity measurements, decreasing weakly with temperature, similar to Wigner's original paramagnetic theory. Accurate modeling of k(ρ, T) is critical in predicting cryogenic hydrogen fuel tank dormancy performance for hydrogen-power vehicles.

  7. Solid-State Hydrogen Storage: Storage Capacity,Thermodynamics and Kinetics

    SciTech Connect

    Osborn, William; Markmaitree, Tippawan; Shaw, Leonard D.; Ren, Ruiming; Hu, Jian Z.; Kwak, Ja Hun; Yang, Zhenguo

    2009-04-01

    Solid-state reversible hydrogen storage systems hold great promise for on-board applications. The key criteria for a successful solid-state reversible storage material are high storage capacity, suitable thermodynamic properties, and fast hydriding and dehydriding kinetics. The LiNH2 + LiH system has been utilized as an example system to illustrate these critical issues that are common among other solid-state reversible storage materials. The progress made in thermodynamic destabilization and kinetic enhancements via various approaches have been emphasized. The implications of these advancements in the development of future solid-state reversible hydrogen storage materials are discussed.

  8. An investigation of the kinetics for hydrogen chemisorption on iron metal surfaces

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1980-01-01

    A quasi-isothermal approach was used to study the kinetics of hydrogen and hydrogen sulfide chemisorption onto iron film in an effort to understand the environmental degradation of steels. The coverage of chemisorbed hydrogen or chemisorbed sulfur was observed as a function of time for fixed conditions of substrate temperature. Auger electron spectroscopy was used to observe the sulfur and chemisorption-induced resistance change was employed to monitor hydrogen coverage. To compare the results obtained from studying the kinetics by two different techniques, the kinetics of oxygen chemisorption onto iron films was also studied. A reaction model utilized to interpret the H2/Fe2 chemisorption kinetics was applied to data from an earlier study on the desorption kinetics for H2 chemisorbed onto nicket films in the vicinity of the Curie temperature of the film. This analysis permitted a separation of the gross desorption process into individual components so that the influence of the magnetic phase transition on the rate constants could be determined.

  9. Sorption kinetics and equilibrium of the herbicide diuron to carbon nanotubes or soot in absence and presence of algae.

    PubMed

    Schwab, Fabienne; Camenzuli, Louise; Knauer, Katja; Nowack, Bernd; Magrez, Arnaud; Sigg, Laura; Bucheli, Thomas D

    2014-09-01

    Carbon nanotubes (CNT) are strong sorbents for organic micropollutants, but changing environmental conditions may alter the distribution and bioavailability of the sorbed substances. Therefore, we investigated the effect of green algae (Chlorella vulgaris) on sorption of a model pollutant (diuron, synonyms: 3-(3,4-Dichlorophenyl)-1,1-dimethylurea, DCMU) to CNT (multi-walled purified, industrial grade, pristine, and oxidized; reference material: Diesel soot). In absence of algae, diuron sorption to CNT was fast, strong, and nonlinear (Freundlich coefficients: 10(5.79)-10(6.24) μg/kgCNT·(μg/L)(-n) and 0.62-0.70 for KF and n, respectively). Adding algae to equilibrated diuron-CNT mixtures led to 15-20% (median) diuron re-dissolution. The relatively high amorphous carbon content slowed down ad-/desorption to/from the high energy sorption sites for both industrial grade CNT and soot. The results suggest that diuron binds readily, but - particularly in presence of algae - partially reversibly to CNT, which is of relevance for environmental exposure and risk assessment. PMID:24949853

  10. Kinetics of liquid-phase hydrogenation of phenol on a palladium catalyst

    SciTech Connect

    Kotova, V.G.; Kul'kova, N.V.; Temkin, M.I.

    1988-08-01

    The kinetics of liquid-phase hydrogenation of phenol into cyclohexanone on a Pd catalyst were studied. At atmospheric pressure, the reaction rate is described by the equation previously obtained for liquid-phase hydrogenation of benzoic acid. At pressures of 0.7-4 MPa, the rate obeys a zero-order equation. The preexponential factor of the Arrhenius equation for the number of rotations in the zero-order region correspond to a transmission coefficient of /kappa/ << 1.

  11. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, Mickey R.

    1993-01-01

    The goal of this program was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of degradation. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. The interaction of hydrogen with the surfaces of alpha-2(Ti3Al) titanium aluminide, gamma(TiAl) titanium aluminide, and beryllium were studied.

  12. Cr(VI) sorption behavior from aqueous solutions onto polymeric microcapsules containing a long-chain quaternary ammonium salt: kinetics and thermodynamics analysis.

    PubMed

    Barassi, Giancarlo; Valdés, Andrea; Araneda, Claudio; Basualto, Carlos; Sapag, Jaime; Tapia, Cristián; Valenzuela, Fernando

    2009-12-15

    This work studies the adsorption of Cr(VI) ions from an aqueous acid solution on hydrophobic polymeric microcapsules containing a long-chain quaternary ammonium salt-type extractant immobilized in their pore structure. The microcapsules were synthesized by adding the extractant Aliquat 336 during the in situ radical copolymerization of the monomers styrene (ST) and ethylene glycol dimethacrylate (EGDMA). The microcapsules, which had a spherical shape with a rough surface, behaved as efficient adsorbents for Cr(VI) at the tested temperatures. The results of kinetics experiments carried out at different temperatures showed that the adsorption process fits well to a pseudo-second-order with an activation energy of 82.7 kJ mol(-1), confirming that the sorption process is controlled by a chemisorption mechanism. Langmuir's isotherms were found to represent well the experimentally observed sorption data. Thermodynamics parameters, namely, changes in standard free energy (DeltaG(0)), enthalpy (DeltaH(0)), and entropy (DeltaS(0)), are also calculated. The results indicate that the chemisorption process is spontaneous and exothermic. The entropy change value measured in this study shows that metal adsorbed on microcapsules leads to a less chaotic system than a liquid-liquid extraction system.

  13. GEOMETRY, HEAT REMOVAL AND KINETICS SCOPING MODELS FOR HYDROGEN STORAGE SYSTEMS

    SciTech Connect

    Hardy, B

    2007-11-16

    It is recognized that detailed models of proposed hydrogen storage systems are essential to gain insight into the complex processes occurring during the charging and discharging processes. Such insight is an invaluable asset for both assessing the viability of a particular system and/or for improving its design. The detailed models, however, require time to develop and run. Clearly, it is much more efficient to begin a modeling effort with a good system design and to progress from that point. To facilitate this approach, it is useful to have simplified models that can quickly estimate optimal loading and discharge kinetics, effective hydrogen capacities, system dimensions and heat removal requirements. Parameters obtained from these models can then be input to the detailed models to obtain an accurate assessment of system performance that includes more complete integration of the physical processes. This report describes three scoping models that assess preliminary system design prior to invoking a more detailed finite element analysis. The three models address the kinetics, the scaling and heat removal parameters of the system, respectively. The kinetics model is used to evaluate the effect of temperature and hydrogen pressure on the loading and discharge kinetics. As part of the kinetics calculations, the model also determines the mass of stored hydrogen per mass of hydride (in a particular reference form). As such, the model can determine the optimal loading and discharge rates for a particular hydride and the maximum achievable loading (over an infinite period of time). The kinetics model developed with the Mathcad{reg_sign} solver, runs in a mater of seconds and can quickly be used to identify the optimal temperature and pressure for either the loading or discharge processes. The geometry scoping model is used to calculate the size of the system, the optimal placement of heat transfer elements, and the gravimetric and volumetric capacities for a particular

  14. A Chemical Kinetic Mechanism for the Ignition of Silane/Hydrogen Mixtures

    NASA Technical Reports Server (NTRS)

    Jachimowski, C. J.; Mclain, A. G.

    1983-01-01

    A chemical kinetic reaction mechanism for the oxidation of silane/hydrogen mixtures is presented and discussed. Shock-tube ignition delay time data were used to evaluate and refine the mechanism. Good agreement between experimental results and the results predicted by the mechanism was obtained by adjusting the rate coefficient for the reaction SiH3 + O2 yields SiH2O + OH. The reaction mechanism was used to theoretically investigate the ignition characteristics of silane/hydrogen mixtures. The results revealed that over the entire range of temperature examined (800 K to 1200 K), substantial reduction in ignition delay times is obtained when silane is added to hydrogen.

  15. Fundamental studies on kinetic isotope effect (KIE) of hydrogen isotope fractionation in natural gas systems

    USGS Publications Warehouse

    Ni, Y.; Ma, Q.; Ellis, G.S.; Dai, J.; Katz, B.; Zhang, S.; Tang, Y.

    2011-01-01

    Based on quantum chemistry calculations for normal octane homolytic cracking, a kinetic hydrogen isotope fractionation model for methane, ethane, and propane formation is proposed. The activation energy differences between D-substitute and non-substituted methane, ethane, and propane are 318.6, 281.7, and 280.2cal/mol, respectively. In order to determine the effect of the entropy contribution for hydrogen isotopic substitution, a transition state for ethane bond rupture was determined based on density function theory (DFT) calculations. The kinetic isotope effect (KIE) associated with bond rupture in D and H substituted ethane results in a frequency factor ratio of 1.07. Based on the proposed mathematical model of hydrogen isotope fractionation, one can potentially quantify natural gas thermal maturity from measured hydrogen isotope values. Calculated gas maturity values determined by the proposed mathematical model using ??D values in ethane from several basins in the world are in close agreement with similar predictions based on the ??13C composition of ethane. However, gas maturity values calculated from field data of methane and propane using both hydrogen and carbon kinetic isotopic models do not agree as closely. It is possible that ??D values in methane may be affected by microbial mixing and that propane values might be more susceptible to hydrogen exchange with water or to analytical errors. Although the model used in this study is quite preliminary, the results demonstrate that kinetic isotope fractionation effects in hydrogen may be useful in quantitative models of natural gas generation, and that ??D values in ethane might be more suitable for modeling than comparable values in methane and propane. ?? 2011 Elsevier Ltd.

  16. Isotope effects on desorption kinetics of hydrogen isotopes implanted into stainless steel by glow discharge

    SciTech Connect

    Matsuyama, M.; Kondo, M.; Noda, N.; Tanaka, M.; Nishimura, K.

    2015-03-15

    In a fusion device the control of fuel particles implies to know the desorption rate of hydrogen isotopes by the plasma-facing materials. In this paper desorption kinetics of hydrogen isotopes implanted into type 316L stainless steel by glow discharge have been studied by experiment and numerical calculation. The temperature of a maximum desorption rate depends on glow discharge time and heating rate. Desorption spectra observed under various experimental conditions have been successfully reproduced by numerical simulations that are based on a diffusion-limited process. It is suggested, therefore, that desorption rate of a hydrogen isotope implanted into the stainless steel is limited by a diffusion process of hydrogen isotope atoms in bulk. Furthermore, small isotope effects were observed for the diffusion process of hydrogen isotope atoms. (authors)

  17. Sorption kinetic study of selenite and selenate onto a high and low pressure aged iron oxide nanomaterial

    PubMed Central

    Gonzalez, Christina M.; Hernandez, Jeffrey; Peralta-Videa, Jose R.; Botez, Cristian E.; Parsons, Jason G.; Gardea-Torresdey, Jorge L.

    2015-01-01

    The sorption of selenite (SeO32−) and selenate (SeO42−) onto Fe3O4 nanomaterials produced by non microwave-assisted or microwave-assisted synthetic techniques was investigated through use of the batch technique. The phase of both synthetic nanomaterials was determined to be magnetite by X-ray diffraction. The average grain sizes of non microwave-assisted and microwave-assisted synthetic Fe3O4 were determined to be 27 and 25 nm, respectively through use of the Scherrer's equation. Sorption of selenite was pH independent in the pH range of 2-6, while sorption of selenate decreased at pH 5 and 6. The addition of Cl− had no significant effect on selenite or selenate binding, while the addition of NO3− only affected selenate binding to the microwave assisted Fe3O4. A decrease of selenate binding to both synthetic particles was observed after the addition of SO42− while selenite binding was not affected. The addition of PO43− beginning at concentrations of 0.1 ppm had the most prominent effect on the binding of both selenite and selenate. The capacities of binding, determined through the use of Langmuir isotherm, were found to be 1923 and 1428 mg Se/kg of non microwave-assisted Fe3O4 and 2380 and 2369 mg Se/kg of microwave-assisted Fe3O4 for selenite and selenate, respectively. PMID:21907486

  18. Kinetics studies of d-glucose hydrogenation over activated charcoal supported platinum catalyst

    NASA Astrophysics Data System (ADS)

    Ahmed, Muthanna J.

    2012-02-01

    The kinetics of the catalytic hydrogenation of d-glucose to produce d-sorbitol was studied in a three-phase laboratory scale reactor. The hydrogenation reactions were performed on activated charcoal supported platinum catalyst in the temperature range 25-65°C and in a constant pressure of 1 atm. The kinetic data were modeled by zero, first and second-order reaction equations. In the operating regimes studied, the results show that the hydrogenation reaction was of a first order with respect to d-glucose concentration. Also the activation energy of the reaction was determined, and found to be 12.33 kJ mole-1. A set of experiment was carried out to test the deactivation of the catalyst, and the results show that the deactivation is slow with the ability of using the catalyst for several times with a small decrease in product yield.

  19. Kinetics of the reaction of nitric oxide with hydrogen

    NASA Technical Reports Server (NTRS)

    Flower, W. L.; Hanson, R. K.; Kruger, C. H.

    1974-01-01

    Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The reaction kinetics were studied in the temperature range 2400-4500 K using a shock-tube technique. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principle result of the study was the determination of the rate constant for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k sub 1 were obtained for each test through comparisons of measured and numerically predicted NO profiles.

  20. Kinetics of Hydrogen-Transfer Isomerizations of Butoxyl Radicals

    SciTech Connect

    Zheng, J.; Truhlar, D. G.

    2010-01-01

    Five isomerization reactions involving intramolecular hydrogen-transfer in butoxyl radicals have been studied using variational transition state theory with small curvature tunneling. A set of best estimates of barrier heights and reaction energies for these five reactions was obtained by using coupled cluster theory including single and double excitations with a quasiperturbative treatment of connected triple excitations and a basis set extrapolated to the complete basis set limit plus core–valence correlation contributions and scalar relativistic corrections. This work predicts high-pressure limiting rate constants of these five reactions over the temperature range 200–2500 K and clarifies the available experimental data from indirect measurements. This study shows the importance of performing rate calculations with proper accounting for tunneling and torsional anharmonicity. We also proposed two new models for use in fitting rate constants over wide ranges of temperature.

  1. Kinetics of the oxidation of hydrogen sulfite by hydrogen peroxide in aqueous solution:. ionic strength effects and temperature dependence

    NASA Astrophysics Data System (ADS)

    Maaß, Frank; Elias, Horst; Wannowius, Klaus J.

    Conductometry was used to study the kinetics of the oxidation of hydrogen sulfite, HSO -3, by hydrogen peroxide in aqueous non-buffered solution at the low concentration level of 10 -5-10 -6 M, typically found in cloud water. The kinetic data confirm that the rate law reported for the pH range 3-6 at higher concentration levels, rate= kH·[H +]·[HSO -3]·[H 2O 2], is valid at the low concentration level and at low ionic strength Ic. At 298 K and Ic=1.5×10 -4 M, third-order rate constant kH was found to be kH=(9.1±0.5)×10 7 M -2 s -1. The temperature dependence of kH led to an activation energy of Ea=29.7±0.9 kJ mol -1. The effect of the ionic strength (adjusted with NaCl) on rate constant kH was studied in the range Ic=2×10 -4-5.0 M at pH=4.5-5.2 by conductometry and stopped-flow spectrophotometry. The dependence of kH on Ic can be described with a semi-empirical relationship, which is useful for the purpose of comparison and extrapolation. The kinetic data obtained are critically compared with those reported earlier.

  2. Kinetics of the reaction of nitric oxide with hydrogen

    NASA Technical Reports Server (NTRS)

    Flower, W. L.; Hanson, R. K.; Kruger, C. H.

    1975-01-01

    The reaction of nitric oxide with hydrogen has been studied in the temperature range 2400-4500 K using a shock-tube technique. Mixtures of NO and H2 diluted in argon or krypton were heated by incident shock waves, and the infrared emission from the fundamental vibration-rotation band of NO at 5.3 microns was used to monitor the time-varying NO concentration. The decomposition of nitric oxide behind the shock was found to be modeled well by a fifteen-reaction system. A principal result of the study was the determination of the rate constant k1 for the reaction H + NO yields N + OH, which may be the rate-limiting step for NO removal in some combustion systems. Experimental values of k1 were obtained for each test through comparisons of measured and numerically predicted NO profiles. The data are fit closely by the expression k1 = 1.34 times 10 to the fourteenth power exp(-49 200/RT) cu cm/mole-sec. These data appear to be the first available for this rate constant.

  3. Kinetics and capacities of phosphorus sorption to tertiary stage wastewater alum solids, and process implications for achieving low-level phosphorus effluents.

    PubMed

    Maher, Chris; Neethling, J B; Murthy, Sudhir; Pagilla, Krishna

    2015-11-15

    The role of adsorption and/or complexation in removal of reactive or unreactive effluent phosphorus by already formed chemical precipitates or complexes has been investigated. Potential operational efficiency gains resulting from age of chemically precipitated tertiary alum sludge and the recycle of sludge to the process stream was undertaken at the Iowa Hill Water Reclamation Facility which employs the DensaDeg(®) process (IDI, Richmond, VA) for tertiary chemical P removal to achieve a filtered final effluent total phosphorus concentration of <30 μg/L. The effect of sludge solids age was found to be insignificant over the solids retention time (SRT) of 2-8 days, indicating that the solids were unaffected by the aging effects of decreasing porosity and surface acidity. The bulk of solids inventory was retained in the clarifier blanket, providing no advantage in P removal from increased solids inventory at higher SRTs. When solids recycle was redirected from the traditional location of the flocculation reactor to a point just prior to chemical addition in the chemical mixing reactor, lower effluent soluble P concentrations at lower molar doses of aluminum were achieved. At laboratory scale, the "spent" or "waste" chemical alum sludge from P removal showed high capacity and rapid kinetics for P sorption from real wastewater effluents. Saturation concentrations were in the range of 8-29 mg soluble reactive P/g solids. Higher saturation concentrations were found at higher temperatures. Alum sludge produced without a coagulant aid polymer had a much higher capacity for P sorption than polymer containing alum sludge. The adsorption reaction reached equilibrium in less than 10 min with 50% or greater removal within the first minute.

  4. Time-dependent gas phase kinetics in a hydrogen diluted silane plasma

    SciTech Connect

    Nunomura, S.; Kondo, M.; Yoshida, I.

    2009-02-16

    The gas phase kinetics in a high-pressure hydrogen diluted silane plasma has been studied at time scales of 10{sup -2}-6x10{sup 2} s. The time-resolved gas phase composition shows the following kinetics at different time scales: silane decomposition and polysilane generation in < or approx. 2x10{sup -1} s, nanoparticle formation and plasma density reduction in 10{sup -1}-10{sup 0} s, polysilane accumulation in 10{sup 0}-10{sup 2} s, and silane depletion and electrode heating in > or approx. 10{sup 1} s. Disilane radicals are implied to be the dominant film precursors in addition to silyl radicals.

  5. Thermodynamics, Kinetics, and Activation energy Studies of the sorption of chromium(III) and chromium(VI) to a Mn3O4 nanomaterial

    PubMed Central

    Cantu, Yvette; Remes, Abril; Reyna, Alejandra; Martinez, Denise; Villarreal, Jahaziel; Ramos, Hilda; Trevino, Samantha; Tamez, C.; Martinez, A.; Eubanks, T.; Parsons, J. G.

    2014-01-01

    In this study, a manganese oxide, Mn3O4 was used to remove chromium(III) and chromium(VI) from aqueous solutions. The Mn3O4 nanomaterial was synthesized through a precipitation method, and was characterized using XRD, which confirmed the material had a crystal structure similar to hausmannite. In addition, using Scherrer’s equation it was determined that the nanomaterial had an average grain size of 19.5 ± 1.10 nm. A study of the effects of pH on the binding of chromium(III) and chromium(VI) showed that the optimum binding pH was 4 and 3 respectively. Batch isotherm studies were performed to determine the binding capacity of chromium(III), which was determined to be 18.7 mg/g, 41.7 mg/g, and 54.4 mg/g respectively for 4°C, 21°C, and 45°C. Chromium(VI) on the other hand had lower binding capacities of 2.5 mg/g, 4.3 mg/g, and 5.8 mg/g for 4°C, 21°C, 45°C, respectively. Thermodynamic studies performed indicated the sorption process was for the most part controlled by physisorption. The ΔG for the sorption of chromium(III) and Chromium(VI) ranged from −0.9 to −13 kJ/mol, indicating a spontaneous reaction was occurring. The enthalpy indicated a endothermic reaction was occurring during the binding and show ΔH values of 70.6 and 19.1 kJ.mol for chromium(III) and Chromium(VI), respectively. In addition, ΔS for the reaction had positive values of 267 and 73 J/mol for chromium(III) and chromium(VI) which indicate a spontaneous reaction. In addition, the sorption process was found to follow pseudo second order kinetic and the activation energy studies indicated the binding process occurred through chemisorption. PMID:25097453

  6. Polymer-induced surface modifications of Pd-based thin films leading to improved kinetics in hydrogen sensing and energy storage applications.

    PubMed

    Ngene, Peter; Westerwaal, Ruud J; Sachdeva, Sumit; Haije, Wim; de Smet, Louis C P M; Dam, Bernard

    2014-11-01

    The catalytic properties of Pd alloy thin films are enhanced by a thin sputtered PTFE coating, resulting in profound improvements in hydrogen adsorption and desorption in Pd-based and Pd-catalyzed hydrogen sensors and hydrogen storage materials. The remarkably enhanced catalytic performance is attributed to chemical modifications of the catalyst surface by the sputtered PTFE leading to a possible change in the binding strength of the intermediate species involved in the hydrogen sorption process.

  7. Process development for hydrogen production with Chlamydomonas reinhardtii based on growth and product formation kinetics.

    PubMed

    Lehr, Florian; Morweiser, Michael; Rosello Sastre, Rosa; Kruse, Olaf; Posten, Clemens

    2012-11-30

    Certain strains of microalgae are long known to produce hydrogen under anaerobic conditions. In Chlamydomonas reinhardtii the oxygen-sensitive hydrogenase enzyme recombines electrons from the chloroplast electron transport chain with protons to form molecular hydrogen directly inside the chloroplast. A sustained hydrogen production can be obtained under low sulfur conditions in C. reinhardtii, reducing the net oxygen evolution by reducing the photosystem II activity and thereby overcoming the inhibition of the hydrogenases. The development of specially adapted hydrogen production strains led to higher yields and optimized biological process preconditions. So far sustainable hydrogen production required a complete exchange of the growth medium to establish sulfur-deprived conditions after biomass growth. In this work we demonstrate the transition from the biomass growth phase to the hydrogen production phase in a single batch culture only by exact dosage of sulfur. This eliminates the elaborate and energy intensive solid-liquid separation step and establishes a process strategy to proceed further versus large scale production. This strategy has been applied to determine light dependent biomass growth and hydrogen production kinetics to assess the potential of H₂ production with C. reinhardtii as a basis for scale up and further process optimization.

  8. Process development for hydrogen production with Chlamydomonas reinhardtii based on growth and product formation kinetics.

    PubMed

    Lehr, Florian; Morweiser, Michael; Rosello Sastre, Rosa; Kruse, Olaf; Posten, Clemens

    2012-11-30

    Certain strains of microalgae are long known to produce hydrogen under anaerobic conditions. In Chlamydomonas reinhardtii the oxygen-sensitive hydrogenase enzyme recombines electrons from the chloroplast electron transport chain with protons to form molecular hydrogen directly inside the chloroplast. A sustained hydrogen production can be obtained under low sulfur conditions in C. reinhardtii, reducing the net oxygen evolution by reducing the photosystem II activity and thereby overcoming the inhibition of the hydrogenases. The development of specially adapted hydrogen production strains led to higher yields and optimized biological process preconditions. So far sustainable hydrogen production required a complete exchange of the growth medium to establish sulfur-deprived conditions after biomass growth. In this work we demonstrate the transition from the biomass growth phase to the hydrogen production phase in a single batch culture only by exact dosage of sulfur. This eliminates the elaborate and energy intensive solid-liquid separation step and establishes a process strategy to proceed further versus large scale production. This strategy has been applied to determine light dependent biomass growth and hydrogen production kinetics to assess the potential of H₂ production with C. reinhardtii as a basis for scale up and further process optimization. PMID:22750091

  9. Sorption of radionuclides on Yucca Mountain tuffs

    SciTech Connect

    Meijer, A.; Triay, I.; Knight, S.; Cisneros, M.

    1989-11-01

    A substantial database of sorption coefficients for important radionuclides on Yucca Mountain tuffs has been obtained by Los Alamos National Laboratory over the past ten years. Current sorption studies are focussed on validation questions and augmentation of the existing database. Validation questions concern the effects of the use of crushed instead of solid rock samples in the batch experiments, the use of oversaturated stock solutions, and variations in water/rock ratios. Sorption mechanisms are also being investigated. Database augmentation activities include determination of sorption coefficients for elements with low sorption potential, sorption on psuedocolloids, sorption on fracture lining minerals, and sorption kinetics. Sorption can provide an important barrier to the potential migration of radionuclides from the proposed repository within Yucca Mountain to the accessible environment. In order to quantify this barrier, sorption coefficients appropriate for the Yucca Mountain groundwater system must be obtained for each of the important radionuclides in nuclear waste. Los Alamos National Laboratories has conducted numerous batch (crushed-rock) sorption experiments over the past ten years to develop a sorption coefficient database for the Yucca Mountain site. In the present site characterization phase, the main goals of the sorption test program will be to validate critical sorption coefficients and to augment the existing database where important data are lacking. 11 refs., 1 fig., 3 tabs.

  10. Analytical chemical kinetic investigation of the effects of oxygen, hydrogen, and hydroxyl radicals on hydrogen-air combustion

    NASA Technical Reports Server (NTRS)

    Carson, G. T., Jr.

    1974-01-01

    Quantitative values were computed which show the effects of the presence of small amounts of oxygen, hydrogen, and hydroxyl radicals on the finite-rate chemical kinetics of premixed hydrogen-air mixtures undergoing isobaric autoignition and combustion. The free radicals were considered to be initially present in hydrogen-air mixtures at equivalence ratios of 0.2, 0.6, 1.0, and 1.2. Initial mixture temperatures were 1100 K, 1200 K, and 1500 K, and pressures were 0.5, 1.0, 2.0, and 4.0 atm. Of the radicals investigated, atomic oxygen was found to be the most effective for reducing induction time, defined as the time to 5 percent of the total combustion temperature rise. The reaction time, the time between 5 percent and 95 percent of the temperature rise, is not decreased by the presence of free radicals in the initial hydrogen-air mixture. Fuel additives which yield free radicals might be used to effect a compact supersonic combustor design for efficient operation in an otherwise reaction-limited combustion regime.

  11. SEDIMENT-ASSOCIATED REACTIONS OF AROMATIC AMINES: 1. ELUCIDATION OF SORPTION MECHANISMS

    EPA Science Inventory

    Sorption of aromatic amines to sediments and soils can occur by both reversible physical processes and irreversible chemical processes. To elucidate the significance of these sorption pathways, the sorption kinetics of aniline and pyridine were studied in resaturated pond sedimen...

  12. Oxygen atom kinetics in silane-hydrogen-nitrous oxide mixtures behind reflected shock waves

    NASA Astrophysics Data System (ADS)

    Javoy, S.; Mével, R.; Dupré, G.

    2010-11-01

    Resonance Absorption Spectroscopy has been used to study the O-atom dynamics behind reflected shock waves in highly argon diluted silane-hydrogen-nitrous oxide mixtures in the temperature range 1606-2528 K and at total pressures from 234 to 584 kPa. The absorptions at 130.5 nm of N 2O, SiH 4 and Si have been taken into account to compare simulated and experimental absorption profiles. A detailed kinetic model has been also used to interpret the results and reaction pathway and sensitivity analyses have been performed to underline important elementary reactions. A comparison with the O-atom kinetic in silane-nitrous oxide and hydrogen-nitrous oxide mixtures is also proposed.

  13. First-passage kinetic Monte Carlo on lattices: Hydrogen transport in lattices with traps

    NASA Astrophysics Data System (ADS)

    von Toussaint, U.; Schwarz-Selinger, T.; Schmid, K.

    2015-08-01

    A new algorithm for the diffusion in 2D and 3D discrete simple cubic lattices based on a recently proposed technique, Green-functions or first-passage kinetic Monte Carlo has been developed. It is based on the solutions of appropriately chosen Greens functions, which propagate the diffusing atoms over long distances in one step (superhops). The speed-up of the new approach over standard kinetic Monte Carlo techniques can be orders of magnitude, depending on the problem. Using this new algorithm we simulated recent hydrogen isotope exchange experiments in recrystallized tungsten at 320 K, initially loaded with deuterium. It was found that the observed depth profiles can only be explained with 'active' traps, i.e. traps capable of exchanging atoms with activation energies significantly lower than the actual trap energy. Such a mechanism has so far not been considered in the modeling of hydrogen transport.

  14. Synthesis, X-ray crystal structures, and gas sorption properties of pillared square grid nets based on paddle-wheel motifs: implications for hydrogen storage in porous materials.

    PubMed

    Chun, Hyungphil; Dybtsev, Danil N; Kim, Hyunuk; Kim, Kimoon

    2005-06-01

    A systematic modulation of organic ligands connecting dinuclear paddle-wheel motifs leads to a series of isomorphous metal-organic porous materials that have a three-dimensional connectivity and interconnected pores. Aromatic dicarboxylates such as 1,4-benzenedicarboxylate (1,4-bdc), tetramethylterephthalate (tmbdc), 1,4-naphthalenedicarboxylate (1,4-ndc), tetrafluoroterephthalate (tfbdc), or 2,6-naphthalenedicarboxylate (2,6-ndc) are linear linkers that form two-dimensional layers, and diamine ligands, 4-diazabicyclo[2.2.2]octane (dabco) or 4,4'-dipyridyl (bpy), coordinate at both sides of Zn(2) paddle-wheel units to bridge the layers vertically. The resulting open frameworks [Zn(2)(1,4-bdc)(2)(dabco)] (1), [Zn(2)(1,4-bdc)(tmbdc)(dabco)] (2), [Zn(2)(tmbdc)(2)(dabco)] (3), [Zn(2)(1,4-ndc)(2)(dabco)] (4), [Zn(2)(tfbdc)(2)(dabco)] (5), and [Zn(2)(tmbdc)(2)(bpy)] (8) possess varying size of pores and free apertures originating from the side groups of the 1,4-bdc derivatives. [Zn(2)(1,4-bdc)(2)(bpy)] (6) and [Zn(2)(2,6-ndc)(2)(bpy)] (7) have two- and threefold interpenetrating structures, respectively. The non-interpenetrating frameworks (1-5 and 8) possess surface areas in the range of 1450-2090 m(2)g(-1) and hydrogen sorption capacities of 1.7-2.1 wt % at 78 K and 1 atm. A detailed analysis of the sorption data in conjunction with structural similarities and differences concludes that porous materials with straight channels and large openings do not perform better than those with wavy channels and small openings in terms of hydrogen storage through physisorption.

  15. Reduced kinetic mechanism of ignition for nonpremixed hydrogen/air in a supersonic mixing layer

    SciTech Connect

    Ju, Y.; Niioka, T. . Inst. of Fluid Science)

    1994-11-01

    Transient ignition processes in a two-dimensional spatially evolving supersonic mixing layer consisting of a parallel nonpremixed airstream and a hydrogen stream both with temperatures higher than 1,000 K were investigated numerically by using the full chemistry and its reduced chemistry. A phenomenon different from that examined in previous studies, in which ignition of hydrogen/oxygen mixtures was considered, was found in the nonpremixed case examined here. It was shown that the concentration of O was greater than that of OH before ignition, but became smaller with the development of ignition process. Fourteen important reactions for ignition were obtained and verified using sensitivity analyses of ignition delay time and radical concentrations. Several different four-step and three-step reduced kinetic mechanisms were then deduced by introducing the steady-state approximation to different species. Comparison of these reduced kinetic mechanisms with the full chemistry showed that the steady-state approximation of O used in previous studies caused serious errors in the prediction of ignition delay time in supersonic flow, in which nonpremixed character is predominant and the transport phenomenon is important. Ignition locations predicted with the proper four-step and three-step reduced kinetic mechanisms were within 5% and 20% of those predicted with the full chemistry. Finally, these two reduced mechanisms were used to evaluate the effect of viscous dissipation on ignition in the supersonic shear layer. Good agreements between the results of the present reduced kinetic mechanisms and those of the full chemistry were obtained.

  16. In situ oxidation remediation technologies: kinetic of hydrogen peroxide decomposition on soil organic matter.

    PubMed

    Romero, Arturo; Santos, Aurora; Vicente, Fernando; Rodriguez, Sergio; Lafuente, A Lopez

    2009-10-30

    Rates of hydrogen peroxide decomposition were investigated in soils slurries. The interaction soil-hydrogen peroxide was studied using a slurry system at 20 degrees C and pH 7. To determine the role of soil organic matter (SOM) in the decomposition of hydrogen peroxide, several experiments were carried out with two soils with different SOM content (S1=15.1%, S2=10%). The influence of the oxidant dosage ([H2O2](o) from 10 to 30 g L(-1) and soil weight to liquid phase volume ratio=500 g L(-1)) was investigated using the two calcareous loamy sand soil samples. The results showed a rate dependency on both SOM and hydrogen peroxide concentration being the H2O2 decomposition rate over soil surface described by a second-order kinetic expression r(H2O2) = -dn(H2O2) / W(SOM) dt = kC(H2O2) C(SOM). Thermogravimetric analysis (TGA) was used to evaluate the effect caused by the application of this oxidant on the SOM content. It was found a slightly increase of SOM content after treatment with hydrogen peroxide, probably due to the incorporation of oxygen from the oxidant (hydrogen peroxide).

  17. In situ hydrogen consumption kinetics as an indicator of subsurface microbial activity

    USGS Publications Warehouse

    Harris, S.H.; Smith, R.L.; Suflita, J.M.

    2007-01-01

    There are few methods available for broadly assessing microbial community metabolism directly within a groundwater environment. In this study, hydrogen consumption rates were estimated from in situ injection/withdrawal tests conducted in two geochemically varying, contaminated aquifers as an approach towards developing such a method. The hydrogen consumption first-order rates varied from 0.002 nM h-1 for an uncontaminated, aerobic site to 2.5 nM h-1 for a contaminated site where sulfate reduction was a predominant process. The method could accommodate the over three orders of magnitude range in rates that existed between subsurface sites. In a denitrifying zone, the hydrogen consumption rate (0.02 nM h-1) was immediately abolished in the presence of air or an antibiotic mixture, suggesting that such measurements may also be sensitive to the effects of environmental perturbations on field microbial activities. Comparable laboratory determinations with sediment slurries exhibited hydrogen consumption kinetics that differed substantially from the field estimates. Because anaerobic degradation of organic matter relies on the rapid consumption of hydrogen and subsequent maintenance at low levels, such in situ measures of hydrogen turnover can serve as a key indicator of the functioning of microbial food webs and may be more reliable than laboratory determinations. ?? 2007 Federation of European Microbiological Societies.

  18. Hydrogen atom abstraction from organometallic hydrogen sources: First kinetics of H atom abstraction by benzyl radical from `Mo-S-H`

    SciTech Connect

    Birbaum, J.C.; Franz, J.A.; Linehan, J.C.

    1997-12-31

    Hydrogen transfers are very important in catalytic and stoichiometric organometallic reaction schemes, yet few kinetic studies of the transfers from a metal hydride to an organic radical have been performed. To our knowledge there are no kinetic studies of hydrogen atom transfers from atoms attached to metals such as sulfur or oxygen. We present the first study with the extremely fast hydrogen atom transfer from (CpMoSSH){sub 2} to benzyl radical. The rate constant for this reaction was found to be greater than 10{sup 6} M{sup -1}s{sup -1} at room temperature.

  19. Kinetic measurement and prediction of the hydrogen outgassing from the polycrystalline LiH/LiOH system

    SciTech Connect

    Dinh, L N; Grant, D M; Schildbach, M A; Smith, R A; Leckey, J H; Siekhaus, W J; Balazs, B; McLean II, W

    2005-03-09

    In this report, we present the use of temperature programmed reaction/decomposition (TPR) in the isoconversion mode to measure outgassing kinetics and to make kinetic prediction concerning hydrogen release from the polycrystalline LiH/LiOH system in the absence of any external H{sub 2}O source.

  20. A kinetic study on the adsorption and reaction of hydrogen over silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide

    SciTech Connect

    VanderWiel, D.P.

    1999-02-12

    Although the catalytic hydrogenation of carbon monoxide has been a subject of considerable investigation for many years, its increasing economical attractiveness as an industrial source of hydrocarbons has recently led to a search for more active and selective catalysts. A fundamental problem in the development of such catalysts is an incomplete knowledge of the operative surface processes, due in large part to the inability to accurately measure surface concentrations of reactant species during reaction. Specifically, the concentration of surface hydrogen proves difficult to estimate using normally revealing techniques such as transient isotopic exchange due to kinetic isotope effects. Knowledge of such concentrations is essential to the determination of the mechanisms of adsorption and reaction, since many kinetic parameters are concentration dependent. It is the aim of this research to investigate the mechanism and kinetics of the adsorption and reaction of hydrogen on silica-supported ruthenium and silver-ruthenium catalysts during the hydrogenation of carbon monoxide. By preadsorbing carbon monoxide onto the surface of ruthenium and silver-ruthenium catalysts, the kinetics of hydrogen adsorption and reaction can be monitored upon exposure of this surface to ambient hydrogen gas. This is accomplished by conducting identical experiments on two separate systems. First, the formation of methane is monitored using mass spectroscopy, and specific reaction rates and apparent activation energies are measured. Next, in situ {sup 1}H-NMR is used to monitor the amount of hydrogen present on the catalyst surface during adsorption and reaction. The results for these two sets of experiments are then combined to show a correlation between the rate of reaction and the surface hydrogen concentration. Finally, transition state theory is applied to this system and is used to explain the observed change in the apparent activation energy. The structure sensitivity of hydrogen

  1. Sorption enhanced CO2 methanation.

    PubMed

    Borgschulte, Andreas; Gallandat, Noris; Probst, Benjamin; Suter, Riccardo; Callini, Elsa; Ferri, Davide; Arroyo, Yadira; Erni, Rolf; Geerlings, Hans; Züttel, Andreas

    2013-06-28

    The transformation from the fatuous consumption of fossil energy towards a sustainable energy circle is most easily marketable by not changing the underlying energy carrier but generating it from renewable energy. Hydrocarbons can be principally produced from renewable hydrogen and carbon dioxide collected by biomass. However, research is needed to increase the energetic and economic efficiency of the process. We demonstrate the enhancement of CO2 methanation by sorption enhanced catalysis. The preparation and catalytic activity of sorption catalysts based on Ni particles in zeolites is reported. The functioning of the sorption catalysis is discussed together with the determination of the reaction mechanism, providing implications for new ways in catalysis. PMID:23673365

  2. Fundamental Kinetics of Supercritical Coal Liquefaction: Effect of Catalysts and Hydrogen-Donor Solvents

    SciTech Connect

    McCoy, Ben J; Madras, Girodhar; Smith, J M; Kodera, Yoichi

    1997-04-16

    This is the quarterly report on our recent progress toward the overall objective to understand the supercritical fluid extraction of hydrocarbons from coal. Our strategy is to simulate coal as a high molecular-weight polymeric material by studying the degradation of polymers under various conditions. The hypothesis we are testing is that degradation of such macromolecules is applicable to the decomposition (depolymerization) of the coal network. Polymer degradation and coal liquefaction are influenced strongly by the solvent in the reaction. This motivated our investigation of the effect of hydrogen donor solvents on polymer degradation. In particular, we obtained new experimental data to show how a hydrogen donor, 6-hydroxy tetralin, influences the degradation rate of polystyrene. We also developed a detailed radical mechanism for hydrogen donation based on the Rice-Herzfeld chain reaction concept with the elementary steps of initiation, depropagation, hydrogen abstraction, and termination. Expressions for the degradation rate parameters were obtained by applying continuous distribution kinetics to the MWD of the reacting polymer. The theory explains the different influences of the hydrogen donor solvent on the degradation rate coefficients for different polymers. Though developed for the degradation of polymers, the mechanism and the theory are potentially applicable for chain scission and addition reactions among distributions of paraffins, olefins, and radicals of all chain lengths. The concepts can, in principle, be extended to examine the effect of hydrogen donors on coal liquefaction and on the complex mixture of liquefaction compounds. Based on this work, a research paper titled "Effect of Hydrogen Donors on Polymer Degradation", has been submitted for publication. Our research paper entitled, "Molecular weight effect on the dynamics of polystyrene degradation", has been accepted for publication by the journal, Industrial and Engineering Chemistry Research.

  3. An Experimental and Chemical Kinetics Study of the Combustion of Syngas and High Hydrogen Content Fuels

    SciTech Connect

    Santoro, Robers; Dryer, Frederick; Ju, Yiguang

    2013-09-30

    An integrated and collaborative effort involving experiments and complementary chemical kinetic modeling investigated the effects of significant concentrations of water and CO2 and minor contaminant species (methane [CH4], ethane [C2H6], NOX, etc.) on the ignition and combustion of HHC fuels. The research effort specifically addressed broadening the experimental data base for ignition delay, burning rate, and oxidation kinetics at high pressures, and further refinement of chemical kinetic models so as to develop compositional specifications related to the above major and minor species. The foundation for the chemical kinetic modeling was the well validated mechanism for hydrogen and carbon monoxide developed over the last 25 years by Professor Frederick Dryer and his co-workers at Princeton University. This research furthered advance the understanding needed to develop practical guidelines for realistic composition limits and operating characteristics for HHC fuels. A suite of experiments was utilized that that involved a high-pressure laminar flow reactor, a pressure-release type high-pressure combustion chamber and a high-pressure turbulent flow reactor.

  4. Ab Initio Kinetics of Hydrogen Abstraction from Methyl Acetate by Hydrogen, Methyl, Oxygen, Hydroxyl, and Hydroperoxy Radicals.

    PubMed

    Tan, Ting; Yang, Xueliang; Krauter, Caroline M; Ju, Yiguang; Carter, Emily A

    2015-06-18

    The kinetics of hydrogen abstraction by five radicals (H, O((3)P), OH, CH3, and HO2) from methyl acetate (MA) is investigated theoretically in order to gain further understanding of certain aspects of the combustion chemistry of biodiesels, such as the effect of the ester moiety. We employ ab initio quantum chemistry methods, coupled cluster singles and doubles with perturbative triples correction (CCSD(T)) and multireference averaged coupled pair functional theory (MRACPF2), to predict chemically accurate reaction energetics. Overall, MRACPF2 predicts slightly higher barrier heights than CCSD(T) for MA + H/CH3/O/OH, but slightly lower barrier heights for hydrogen abstraction by HO2. Based on the obtained reaction energies, we also report high-pressure-limit rate constants using transition state theory (TST) in conjunction with the separable-hindered-rotor approximation, the variable reaction coordinate TST, and the multi-structure all-structure approach. The fitted modified Arrhenius expressions are provided over a temperature range of 250 to 2000 K. The predictions are in good agreement with available experimental results. Abstractions from both of the methyl groups in MA are expected to contribute to consumption of the fuel as they exhibit similar rate coefficients. The reactions involving the OH radical are predicted to have the highest rates among the five abstracting radicals, while those initiated by HO2 are expected to be the lowest. PMID:25974050

  5. Kinetic Isotope Effects as a Probe of Hydrogen Transfers to and from Common Enzymatic Cofactors

    PubMed Central

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2013-01-01

    Enzymes use a number of common cofactors as sources of hydrogen to drive biological processes, but the physics of the hydrogen transfers to and from these cofactors is not fully understood. Researchers study the mechanistically important contributions from quantum tunneling and enzyme dynamics and connect those processes to the catalytic power of enzymes that use these cofactors. Here we describe some progress that has been made in studying these reactions, particularly through the use of kinetic isotope effects (KIEs). We first discuss the general theoretical framework necessary to interpret experimental KIEs, and then describe practical uses for KIEs in the context of two case studies. The first example is alcohol dehydrogenase, which uses a nicotinamide cofactor to catalyze a hydride transfer, and the second example is thymidylate synthase, which uses a folate cofactor to catalyze both a hydride and a proton transfer. PMID:24161942

  6. Decomposition Kinetics of Hydrogen Peroxide: Novel Lab Experiments Employing Computer Technology

    NASA Astrophysics Data System (ADS)

    Abramovitch, Dorota A.; Cunningham, Latrice K.; Litwer, Mitchell R.

    2003-07-01

    The quantitative catalytic decomposition of hydrogen peroxide has been used in many general chemistry experiments. The typical procedure involves measuring the volume of oxygen generated in the reaction under constant pressure using a displacement method and calculating the necessary data. A pressure sensor interfaced with a computer using LabWorks II software allowed us to modify this reaction and to measure the change in pressure, at constant volume. Since the software allows the collection and display of real-time data and the ability to import the data to Excel, we re-examined the kinetics of this reaction. Using different concentrations of hydrogen peroxide and catalase enzyme and graphing initial concentrations versus initial rates, we determined the rate and the order of the decomposition.

  7. Computation of Kinetics for the Hydrogen/Oxygen System Using the Thermodynamic Method

    NASA Technical Reports Server (NTRS)

    Marek, C. John

    1996-01-01

    A new method for predicting chemical rate constants using thermodynamics has been applied to the hydrogen/oxygen system. This method is based on using the gradient of the Gibbs free energy and a single proportionality constant D to determine the kinetic rate constants. Using this method the rate constants for any gas phase reaction can be computed from thermodynamic properties. A modified reaction set for the H/O system is determined. A11 of the third body efficiencies M are taken to be unity. Good agreement was obtained between the thermodynamic method and the experimental shock tube data. In addition, the hydrogen bromide experimental data presented in previous work is recomputed with M's of unity.

  8. Kinetic isotope effects as a probe of hydrogen transfers to and from common enzymatic cofactors.

    PubMed

    Roston, Daniel; Islam, Zahidul; Kohen, Amnon

    2014-02-15

    Enzymes use a number of common cofactors as sources of hydrogen to drive biological processes, but the physics of the hydrogen transfers to and from these cofactors is not fully understood. Researchers study the mechanistically important contributions from quantum tunneling and enzyme dynamics and connect those processes to the catalytic power of enzymes that use these cofactors. Here we describe some progress that has been made in studying these reactions, particularly through the use of kinetic isotope effects (KIEs). We first discuss the general theoretical framework necessary to interpret experimental KIEs, and then describe practical uses for KIEs in the context of two case studies. The first example is alcohol dehydrogenase, which uses a nicotinamide cofactor to catalyze a hydride transfer, and the second example is thymidylate synthase, which uses a folate cofactor to catalyze both a hydride and a proton transfer.

  9. Isosteric heat of hydrogen adsorption on MOFs: comparison between adsorption calorimetry, sorption isosteric method, and analytical models

    NASA Astrophysics Data System (ADS)

    Kloutse, A. F.; Zacharia, R.; Cossement, D.; Chahine, R.; Balderas-Xicohténcatl, R.; Oh, H.; Streppel, B.; Schlichtenmayer, M.; Hirscher, M.

    2015-12-01

    Isosteric heat of adsorption is an important parameter required to describe the thermal performance of adsorptive storage systems. It is most frequently calculated from adsorption isotherms measured over wide ranges of pressure and temperature, using the so-called adsorption isosteric method. Direct quantitative estimation of isosteric heats on the other hand is possible using the coupled calorimetric-volumetric method, which involves simultaneous measurement of heat and adsorption. In this work, we compare the isosteric heats of hydrogen adsorption on microporous materials measured by both methods. Furthermore, the experimental data are compared with the isosteric heats obtained using the modified Dubinin-Astakhov, Tóth, and Unilan adsorption analytical models to establish the reliability and limitations of simpler methods and assumptions. To this end, we measure the hydrogen isosteric heats on five prototypical metal-organic frameworks: MOF-5, Cu-BTC, Fe-BTC, MIL-53, and MOF-177 using both experimental methods. For all MOFs, we find a very good agreement between the isosteric heats measured using the calorimetric and isosteric methods throughout the range of loading studied. Models' prediction on the other hand deviates from both experiments depending on the MOF studied and the range of loading. Under low-loadings of less than 5 mol kg-1, the isosteric heat of hydrogen adsorption decreases in the order Cu-BTC > MIL-53 > MOF-5 > Fe-BTC > MOF-177. The order of isosteric heats is coherent with the strength of hydrogen interaction revealed from previous thermal desorption spectroscopy measurements.

  10. Microscopic Observation of Kinetic Molecular Sieving of Hydrogen Isotopes in a Nanoporous Material

    SciTech Connect

    Nguyen, T. X.; Bhatia, S. K.; Jobic, H.

    2010-08-20

    We report quasielastic neutron scattering studies of H{sub 2}-D{sub 2} diffusion in a carbon molecular sieve, demonstrating remarkable quantum effects, with the heavier isotope diffusing faster below 100 K, confirming our recent predictions. Our transition state theory and molecular dynamics calculations show that while it is critical for this effect to have narrow windows of size comparable to the de Broglie wavelength, high flux requires that the energy barrier be reduced through small cages. Such materials will enable novel processes for kinetic molecular sieving of hydrogen isotopes.

  11. Gas cleaning and hydrogen sulfide removal for COREX coal gas by sorption enhanced catalytic oxidation over recyclable activated carbon desulfurizer.

    PubMed

    Sun, Tonghua; Shen, Yafei; Jia, Jinping

    2014-02-18

    This paper proposes a novel self-developed JTS-01 desulfurizer and JZC-80 alkaline adsorbent for H2S removal and gas cleaning of the COREX coal gas in small-scale and commercial desulfurizing devices. JTS-01 desulfurizer was loaded with metal oxide (i.e., ferric oxides) catalysts on the surface of activated carbons (AC), and the catalyst capacity was improved dramatically by means of ultrasonically assisted impregnation. Consequently, the sulfur saturation capacity and sulfur capacity breakthrough increased by 30.3% and 27.9%, respectively. The whole desulfurizing process combined selective adsorption with catalytic oxidation. Moreover, JZC-80 adsorbent can effectively remove impurities such as HCl, HF, HCN, and ash in the COREX coal gas, stabilizing the system pressure drop. The JTS-01 desulfurizer and JZC-80 adsorbent have been successfully applied for the COREX coal gas cleaning in the commercial plant at Baosteel, Shanghai. The sulfur capacity of JTS-01 desulfurizer can reach more than 50% in industrial applications. Compared with the conventional dry desulfurization process, the modified AC desulfurizers have more merit, especially in terms of the JTS-01 desulfurizer with higher sulfur capacity and low pressure drop. Thus, this sorption enhanced catalytic desulfurization has promising prospects for H2S removal and other gas cleaning.

  12. Gas cleaning and hydrogen sulfide removal for COREX coal gas by sorption enhanced catalytic oxidation over recyclable activated carbon desulfurizer.

    PubMed

    Sun, Tonghua; Shen, Yafei; Jia, Jinping

    2014-02-18

    This paper proposes a novel self-developed JTS-01 desulfurizer and JZC-80 alkaline adsorbent for H2S removal and gas cleaning of the COREX coal gas in small-scale and commercial desulfurizing devices. JTS-01 desulfurizer was loaded with metal oxide (i.e., ferric oxides) catalysts on the surface of activated carbons (AC), and the catalyst capacity was improved dramatically by means of ultrasonically assisted impregnation. Consequently, the sulfur saturation capacity and sulfur capacity breakthrough increased by 30.3% and 27.9%, respectively. The whole desulfurizing process combined selective adsorption with catalytic oxidation. Moreover, JZC-80 adsorbent can effectively remove impurities such as HCl, HF, HCN, and ash in the COREX coal gas, stabilizing the system pressure drop. The JTS-01 desulfurizer and JZC-80 adsorbent have been successfully applied for the COREX coal gas cleaning in the commercial plant at Baosteel, Shanghai. The sulfur capacity of JTS-01 desulfurizer can reach more than 50% in industrial applications. Compared with the conventional dry desulfurization process, the modified AC desulfurizers have more merit, especially in terms of the JTS-01 desulfurizer with higher sulfur capacity and low pressure drop. Thus, this sorption enhanced catalytic desulfurization has promising prospects for H2S removal and other gas cleaning. PMID:24456468

  13. Hydrogen release kinetics during reactive magnetron sputter depostion of a-Si:H: An isotope labeling study

    NASA Astrophysics Data System (ADS)

    Abelson, J. R.; Mandrell, L.; Doyle, J. R.

    1994-08-01

    The release of moleculear hydrogen from the growing surface of hydrogenated amorphous silicon films is determined using an isotope labeling technique. The results demonstrate that surface-bonded H atoms are readily abstracted by atomic hydrogen arriving from the gas phase. The films are deposited by dc reactive magnetron sputtering of a silicon target in an argon-hydrogen atmosphere. To achieve isotope labeling, we first deposit a deuterated amorphous silicon film, then commence growth of hydrogenated amorphous silicon and measure the transient release of HD and D2 from the growing surface using mass spectrometry. Release occurs when the supply of reactive hydrogen in the growth flux exceeds the incorporation rate into the film, and is observed under all experimental conditions. The net rate of H incorporation is known from ex situ measurments of film growth and hydrogen content. We combine the H release and incorporation data in a mass balance argument to determine the H-surface kinetics. Under conditions which produce electronically useful films, (1) 0.5-1.0 hydrogen atoms react with the growing surface per incorporated silicon atom, (2) the near surface of the growing film contains 1-3 x 10(exp 15)/sq cm pf excess hydrogen, the dominant hydrogen release mechanism is by direct abstraction to form H2 molecules, and the kinetics of H release and incorportation can be described by constant rate coefficients. These data are supported by studies of H interactions with single-crystal silicon and amorphous carbon surfaces.

  14. Role of point defects and additives in kinetics of hydrogen storage materials

    NASA Astrophysics Data System (ADS)

    van de Walle, Chris

    2010-03-01

    First-principles computational studies of hydrogen interactions with storage materials can provide direct insight into the processes of H uptake and release, and may help in developing guidelines for designing storage media with improved storage capacity and kinetics. One important conclusion is that the defects involved in kinetics of semiconducting or insulating H-storage materials are charged, and hence their formation energy is Fermi-level dependent and can be affected by the presence of impurities that change the Fermi level [1,2]. This provides an explanation for the role played by transition-metal impurities in the kinetics of NaAlH4 and related materials. Desorption of H and decomposition of NaAlH4 requires not only mass transport of H but also of Al and/or Na. This process is mediated by native defects. We have investigated the structure, stability, and migration enthalpy of native defects based on density functional theory. The results allow us to estimate diffusion activation energies for the defects that may be involved in mass transport. Most of the relevant defects exist in charge states other than neutral, and consideration of these charge states is essential for a proper description of kinetics. We propose specific new mechanisms to explain the observed activation energies and their dependence on the presence of impurities. We have also expanded our studies to materials other than NaAlH4. In the case of LiBH4 and Li4BN3H10 we have found that the calculations have predictive power in terms of identifying which impurities will actually enhance kinetics. Other complex hydrides that we are currently investigating include Li2NH and LiNH2. [4pt] [1] A. Peles and C. G. Van de Walle, Phys. Rev. B 76, 214101 (2007). [0pt] [2] C. G. Van de Walle, A. Peles, A. Janotti, and G. B. Wilson-Short, Physica B 404, 793 (2009).

  15. Kinetic and Thermodynamic Investigation of Hydrogen Release from Ethane 1,2-di-amineborane

    SciTech Connect

    Neiner, Doinita; Karkamkar, Abhijeet J.; Bowden, Mark; Choi, Young Joon; Luedtke, Avery T.; Holladay, Jamelyn D.; Fisher, Allison M.; Szymczak, Nathaniel; Autrey, Thomas

    2011-07-18

    The thermodynamics and kinetics of hydrogen (H2) release from ethane 1,2-di-amineborane (EDAB, BH3NH2CH2CH2NH2BH3) were measured using Calvet and differential scanning calorimetry (DSC), pressure-composition isotherms, and volumetric gas-burette experiments. The results presented here indicate that EDAB releases ~ 9 wt.% H2 at temperatures ranging from 100 °C to 200 °C in two moderately exothermic steps, approximately -10±1 kJ/mol H2 and -3.8±1 kJ/mol H2. Isothermal kinetic analysis shows that EDAB is more stable than ammonia borane (AB) at temperatures lower than 100°C; however, the rates of hydrogen release are faster for EDAB than for AB at temperatures higher than 120°C. In addition, no volatile impurities in the H2 released by EDAB were detected by mass spectrometry upon heating with 1°C/min to 200°C in a calorimeter.

  16. Kinetic study of the reactions between chloramine disinfectants and hydrogen peroxide: temperature dependence and reaction mechanism.

    PubMed

    McKay, Garrett; Sjelin, Brittney; Chagnon, Matthew; Ishida, Kenneth P; Mezyk, Stephen P

    2013-09-01

    The temperature-dependent kinetics for the reaction between hydrogen peroxide and chloramine water disinfectants (NH2Cl, NHCl2, and NCl3) have been determined using stopped flow-UV/Vis spectrophotometry. Rate constants for the mono- and dichloramine-peroxide reaction were on the order of 10(-2)M(-1)s(-1) and 10(-5)M(-1)s(-1), respectively. The reaction of trichloramine with peroxide was negligibly slow compared to its thermal and photolytically-induced decomposition. Arrhenius expressions of ln(kH2O2-NH2Cl)=(17.3±1.5)-(51500±3700)/RT and ln(kH2O2-NHCl2)=(18.2±1.9)-(75800±5100)/RT were obtained for the mono- and dichloramine peroxide reaction over the temperature ranges 11.4-37.9 and 35.0-55.0°C, respectively. Both monochloramine and hydrogen peroxide were first-order in the rate-limiting kinetic step and concomitant measurements made using a chloride ion selective electrode showed that the chloride was produced quantitatively. These data will aid water utilities in predicting chloramine concentrations (and thus disinfection potential) throughout the water distribution system.

  17. Surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process: N2 sorption and XPS studies

    NASA Astrophysics Data System (ADS)

    Nikolova, D.; Krstić, J.; Spasov, L.; Simeonov, D.; Lončarević, D.; Stefanov, Pl.; Jovanović, D.

    2011-12-01

    The effect of the type of the silica gel pore structure on the surface properties of the Ni-silica gel catalyst precursors for the vegetable oil hydrogenation process has been examined applying N2 sorption and X-ray photoelectron spectroscopy techniques. The nickel catalyst precursors with identical composition (SiO2/Ni = 1.0) has been synthesized by precipitation of Ni(NO3)2 · 6H2O solution with Na2CO3 solution on the three types of silica gel with different pore structures. It is shown that the usage of the silica gel supports with different texture as source of SiO2 causes different location of Ni-species into the support pores and on the external surface area. The XPS data confirm the formation of surface species with different strength of interaction and different dispersion. These surface characteristics of the precursors will predetermine the formation of the active nickel metallic phase as well as the mass transfer of the reactants and products to and from the catalytic sites.

  18. Chromium(VI) reduction by hydrogen sulfide in aqueous media: stoichiometry and kinetics.

    PubMed

    Kim, C; Zhou, Q; Deng, B; Thornton, E C; Xu, H

    2001-06-01

    The objective of this work was to investigate the reaction stoichiometry, kinetics, and mechanism for Cr(VI) reduction by hydrogen sulfide in the aqueous phase. Batch experiments with excess [Cr(VI)] over [H2S]T indicated that the molar amount of sulfide required for the reduction of 1 M Cr(VI) was 1.5, suggesting the following stoichiometry: 2CrO4(2-) + 3H2S + 4H+-->2Cr(OH)3(s) + 3S(s) + 2H2O. Further study with transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS) confirmed that chromium hydroxide and elemental sulfur were the stable products. The kinetics of Cr(VI) reduction by hydrogen sulfide was measured under various initial concentrations of Cr(VI) and sulfide as well as pH values controlled by HEPES, phosphate, and borate buffers. Results showed that the overall reaction was second-order, i.e., first-order with respect to Cr(VI) and first-order to sulfide. The reaction rate increased as pH was decreased, and the pH dependence correlated well with the fraction of fully protonated sulfide (H2S) in the pH range of 6.5-10. The nature of buffers did not influence the reaction rate significantly in the homogeneous system. The reaction kinetics could be interpreted by a three-step mechanism: formation of an inner-sphere chromate-sulfide intermediate complex ((H2O4CrVIS)2-), intramolecular electron transfer to form Cr(IV) species, and subsequent fast reactions leading to Cr(III).

  19. COSOLVENT EFFECTS ON SORPTION ISOTHERM LINEARITY

    EPA Science Inventory

    Sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic polymers associated with soils and sediments. In this study, aqueous and mixed solvent systems were used t...

  20. Carbon-coated Li3 N nanofibers for advanced hydrogen storage.

    PubMed

    Xia, Guanglin; Li, Dan; Chen, Xiaowei; Tan, Yingbin; Tang, Ziwei; Guo, Zaiping; Liu, Huakun; Liu, Zongwen; Yu, Xuebin

    2013-11-20

    3D porous carbon-coated Li3 N nanofibers are successfully fabricated via the electrospinning technique. The as-prepared nanofibers exhibit a highly improved hydrogen-sorption performance in terms of both thermodynamics and kinetics. More interestingly, a stable regeneration can be achieved due to the unique structure of the nanofibers, over 10 cycles of H2 sorption at a temperature as low as 250 °C.

  1. Metastable olivine provides regional constraints on hydrogen content based on transformation kinetics

    NASA Astrophysics Data System (ADS)

    Du Frane, W. L.; Sharp, T. G.; Mosenfelder, J. L.; Leinenweber, K. D.

    2009-12-01

    187 +/- 40 kJ/mol. These rates are similar to rates for olivine with 300 ppm D2O: 2.1x10-9 m/s at 900 °C, 18 GPa with activation enthalpy of 232 kJ/mol [Diedrich, et al., 2009]. The similarity of growth rates for olivine containing a range of H2O (75-300 ppm) suggests that even a small amount of hydrogen can significantly enhance olivine growth rates as long as enough hydrogen partitions to the rim to hydrolytically weaken it, and prevent the buildup of elastic strain energy. Nominally anhydrous olivine may also transform at a similar rate if the growth rims have sufficiently high viscoelastic relaxation rates in Earth. Without the effects of elastic strain energy, growth rates of this magnitude have been demonstrated by thermo-kinetic models to be incompatible with formation of a metastable olivine wedge [Marton, et al., 2006]. Therefore if metastable olivine exists within subducting slabs, olivine must contain less than 75 ppm H2O and transformation rates must be reduced by elastic strain energy. Evidence of metastable olivine in subducting slabs would thus produce regional constraints on hydrogen content in earth’s transition zone.

  2. Modeling of hydrogen production methods: Single particle model and kinetics assessment

    SciTech Connect

    Miller, R.S.; Bellan, J.

    1996-10-01

    The investigation carried out by the Jet Propulsion Laboratory (JPL) is devoted to the modeling of biomass pyrolysis reactors producing an oil vapor (tar) which is a precursor to hydrogen. This is an informal collaboration with NREL whereby JPL uses the experimentally-generated NREL data both as initial and boundary conditions for the calculations, and as a benchmark for model validation. The goal of this investigation is to find drivers of biomass fast-pyrolysis in the low temperature regime. The rationale is that experimental observations produce sparse discrete conditions for model validation, and that numerical simulations produced with a validated model are an economic way to find control parameters and an optimal operation regime, thereby circumventing costly changes in hardware and tests. During this first year of the investigation, a detailed mathematical model has been formulated for the temporal and spatial accurate modeling of solid-fluid reactions in biomass particles. These are porous particles for which volumetric reaction rate data is known a priori and both the porosity and the permeability of the particle are large enough to allow for continuous gas phase flow. The methodology has been applied to the pyrolysis of spherically symmetric biomass particles by considering previously published kinetics schemes for both cellulose and wood. The results show that models which neglect the thermal and species boundary layers exterior to the particle will generally over predict both the pyrolysis rates and experimentally obtainable tar yields. An evaluation of the simulation results through comparisons with experimental data indicates that while the cellulose kinetics is reasonably accurate, the wood pyrolysis kinetics is not accurate; particularly at high reactor temperatures. Current effort in collaboration with NREL is aimed at finding accurate wood kinetics.

  3. Kinetic Analysis of Competitive Electrocatalytic Pathways: New Insights into Hydrogen Production with Nickel Electrocatalysts.

    PubMed

    Wiedner, Eric S; Brown, Houston J S; Helm, Monte L

    2016-01-20

    The hydrogen production electrocatalyst Ni(P(Ph)2N(Ph)2)2(2+) (1) is capable of traversing multiple electrocatalytic pathways. When using dimethylformamidium, DMF(H)(+), the mechanism of H2 formation by 1 changes from an ECEC to an EECC mechanism as the potential approaches the Ni(I/0) couple. Two electrochemical methods, current-potential analysis and foot-of-the-wave analysis (FOWA), were performed on 1 to measure detailed kinetics of the competing ECEC and EECC pathways. A sensitivity analysis was performed on the methods using digital simulations to understand their strengths and limitations. Chemical rate constants were significantly underestimated when not accounting for electron-transfer kinetics, even when electron transfer was fast enough to afford a reversible noncatalytic wave. The EECC pathway of 1 was faster than the ECEC pathway under all conditions studied. Buffered DMF:DMF(H)(+) mixtures afforded an increase in the catalytic rate constant (k(obs)) of the EECC pathway, but k(obs) for the ECEC pathway did not change when using buffered acid. Further kinetic analysis of the ECEC path revealed that base increases the rate of isomerization from exo-protonated Ni(0) isomers to the catalytically active endo-isomers, but decreases the rate of protonation of Ni(I). FOWA did not provide accurate rate constants, but FOWA was used to estimate the reduction potential of the previously undetected exo-protonated Ni(I) intermediate. Comparison of catalytic Tafel plots for 1 under different conditions reveals substantial inaccuracies in the turnover frequency at zero overpotential when the kinetic and thermodynamic effects of the conjugate base are not accounted for properly.

  4. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, Mickey R.

    1991-01-01

    The goal was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of the degradation process. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. Modern advanced aerospace applications often require the use of structural materials in high pressure hydrogen environments at temperatures which range from low cryogenic temperatures to very high temperatures (1300 K and greater). Materials proposed for these applications, such as the titanium aluminides, beta-titanium alloys, nickel- and cobalt-based superalloys, molybdenum-rhenium alloys, beryllium, and various beryllides, need to possess a high degree of immunity from hydrogen induced degradation of mechanical properties. In the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak, in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in

  5. DOE Hydrogen Sorption Center of Excellence: Synthesis and Processing of Single-Walled Carbon Nanohorns for Hydrogen Storage and Catalyst Supports

    SciTech Connect

    David B. Geohegan; Hui Hu; Mina Yoon; Alex A. Puretzky; Christopher M. Rouleau; Norbert Thonnard; Gerd Duscher; Karren More

    2011-05-24

    The objective of the project was to exploit the unique morphology, tunable porosity and excellent metal supportability of single-walled carbon nanohorns (SWNHs) to optimize hydrogen uptake and binding energy through an understanding of metal-carbon interactions and nanoscale confinement. SWNHs provided a unique material to understand these effects because they are carbon nanomaterials which are synthesized from the 'bottom-up' with well-defined, sub-nm pores and consist of single-layer graphene, rolled up into closed, conical, horn-shaped units which form ball-shaped aggregates of {approx}100-nm diameter. SWNHs were synthesized without metal catalysts by the high-temperature vaporization of solid carbon, so they can be used to explore metal-free hydrogen storage. However, SWNHs can also be decorated with metal nanoparticles or coatings in post-processing treatments to understand how metals augment hydrogen storage. The project first explored how the synthesis and processing of SWNHs could be modified to tailor pore sizes to optimal size ranges. Nanohorns were rapidly synthesized at 20g/hr rates by high-power laser vaporization enabling studies such as neutron scattering with gram quantities. Diagnostics of the synthesis process including high-speed videography, fast pyrometry of the graphite target, and differential mobility analysis monitoring of particle size distributions were applied in this project to provide in situ process control of SWNH morphology, and to understand the conditions for different pore sizes. We conclude that the high-temperature carbon-vaporization process to synthesize SWNHs is scalable, and can be performed by electric arc or other similar techniques as economically as carbon can be vaporized. However, the laser vaporization approach was utilized in this project to permit the precise tuning of the synthesis process through adjustment of the laser pulse width and repetition rate. A result of this processing control in the project was to

  6. Synthetic use of the primary kinetic isotope effect in hydrogen atom transfer: generation of α-aminoalkyl radicals.

    PubMed

    Wood, Mark E; Bissiriou, Sabine; Lowe, Christopher; Norrish, Andrew M; Sénéchal, Katell; Windeatt, Kim M; Coles, Simon J; Hursthouse, Michael B

    2010-10-21

    The extent to which deuterium can act as a protecting group to prevent unwanted 1,5-hydrogen atom transfer to aryl and vinyl radical intermediates was examined in the context of the generation of α-aminoalkyl radicals in a pyrrolidine ring. Intra- and intermolecular radical trapping following hydrogen atom transfer provides an illustration of the use of the primary kinetic isotope effect in directing the outcome of synthetic C-C bond-forming processes.

  7. Hybrid electrodynamics and kinetics simulation for electromagnetic wave propagation in weakly ionized hydrogen plasmas.

    PubMed

    Chen, Qiang; Chen, Bin

    2012-10-01

    In this paper, a hybrid electrodynamics and kinetics numerical model based on the finite-difference time-domain method and lattice Boltzmann method is presented for electromagnetic wave propagation in weakly ionized hydrogen plasmas. In this framework, the multicomponent Bhatnagar-Gross-Krook collision model considering both elastic and Coulomb collisions and the multicomponent force model based on the Guo model are introduced, which supply a hyperfine description on the interaction between electromagnetic wave and weakly ionized plasma. Cubic spline interpolation and mean filtering technique are separately introduced to solve the multiscalar problem and enhance the physical quantities, which are polluted by numerical noise. Several simulations have been implemented to validate our model. The numerical results are consistent with a simplified analytical model, which demonstrates that this model can obtain satisfying numerical solutions successfully.

  8. Dual Studies on a Hydrogen-Deuterium Exchange of Resorcinol and the Subsequent Kinetic Isotope Effect.

    PubMed

    Giles, Richard; Kim, Iris; Chao, Weyjuin Eric; Moore, Jennifer; Jung, Kyung Woon

    2014-08-12

    An efficient laboratory experiment has been developed for undergraduate students to conduct hydrogen-deuterium (H-D) exchange of resorcinol by electrophilic aromatic substitution using D2O and a catalytic amount of H2SO4. The resulting labeled product is characterized by (1)H NMR. Students also visualize a significant kinetic isotope effect (k H/k D ≈ 3 to 4) by adding iodine tincture to solutions of unlabeled resorcinol and the H-D exchange product. This method is highly adaptable to fit a target audience and has been successfully implemented in a pedagogical capacity with second-year introductory organic chemistry students as part of their laboratory curriculum. It was also adapted for students at the advanced high school level. PMID:25132687

  9. Spectroscopic application of an iterative kinetic cathode sheath model to high voltage hollow cathode glow discharge in hydrogen

    NASA Astrophysics Data System (ADS)

    Spasojević, Dj.; Mijin, S.; Šišović, N. M.; Konjević, N.

    2016-02-01

    We present a simple one-dimensional iterative kinetic model of the cathode sheath region of high voltage, low-pressure hydrogen hollow cathode discharge. The model's convenience as a supplemental diagnostic tool is demonstrated by determining the most relevant discharge parameters through an analysis of the spectral shape of the hydrogen Balmer alpha line recorded along the axis of a cylindrically symmetrical high voltage low-pressure hollow cathode glow discharge in hydrogen. Thus, an effectively one-dimensional approach is tested and shown to give satisfactory spectral lines fits with reasonable values for discharge parameters, most notably the gas temperature.

  10. Chemical kinetic analysis of hydrogen-air ignition and reaction times

    NASA Technical Reports Server (NTRS)

    Rogers, R. C.; Schexnayder, C. J., Jr.

    1981-01-01

    An anaytical study of hydrogen air kinetics was performed. Calculations were made over a range of pressure from 0.2 to 4.0 atm, temperatures from 850 to 2000 K, and mixture equivalence ratios from 0.2 to 2.0. The finite rate chemistry model included 60 reactions in 20 species of the H2-O2-N2 system. The calculations also included an assessment of how small amounts of the chemicals H2O, NOx, H2O2, and O3 in the initial mixture affect ignition and reaction times, and how the variation of the third body efficiency of H2O relative of N2 in certain key reactions may affect reaction time. The results indicate that for mixture equivalence ratios between 0.5 and 1.7, ignition times are nearly constant; however, the presence of H2O and NO can have significant effects on ignition times, depending on the mixture temperature. Reaction time is dominantly influenced by pressure but is nearly independent of initial temperature, equivalence ratio, and the addition of chemicals. Effects of kinetics on reaction at supersonic combustor conditions are discussed.

  11. Hydrogen donor-acceptor fluctuations from kinetic isotope effects: a phenomenological model.

    PubMed

    Roston, Daniel; Cheatum, Christopher M; Kohen, Amnon

    2012-08-28

    Kinetic isotope effects (KIEs) and their temperature dependence can probe the structural and dynamic nature of enzyme-catalyzed proton or hydride transfers. The molecular interpretation of their temperature dependence requires expensive and specialized quantum mechanics/molecular mechanics (QM/MM) calculations to provide a quantitative molecular understanding. Currently available phenomenological models use a nonadiabatic assumption that is not appropriate for most hydride and proton-transfer reactions, while others require more parameters than the experimental data justify. Here we propose a phenomenological interpretation of KIEs based on a simple method to quantitatively link the size and temperature dependence of KIEs to a conformational distribution of the catalyzed reaction. This model assumes adiabatic hydrogen tunneling, and by fitting experimental KIE data, the model yields a population distribution for fluctuations of the distance between donor and acceptor atoms. Fits to data from a variety of proton and hydride transfers catalyzed by enzymes and their mutants, as well as nonenzymatic reactions, reveal that steeply temperature-dependent KIEs indicate the presence of at least two distinct conformational populations, each with different kinetic behaviors. We present the results of these calculations for several published cases and discuss how the predictions of the calculations might be experimentally tested. This analysis does not replace molecular QM/MM investigations, but it provides a fast and accessible way to quantitatively interpret KIEs in the context of a Marcus-like model.

  12. Coal desulfurization in oxidative acid media using hydrogen peroxide and ozone: a kinetic and statistical approach

    SciTech Connect

    F.R. Carrillo-Pedroza; A. Davalos Sanchez; M. Soria-Aguilar; E.T. Pecina Trevino

    2009-07-15

    The removal of pyritic sulfur from a Mexican sub-bituminous coal in nitric, sulfuric, and hydrochloric acid solutions was investigated. The effect of the type and concentration of acid, in the presence of hydrogen peroxide and ozone as oxidants, in a temperature range of 20-60{sup o}C, was studied. The relevant factors in pyrite dissolution were determined by means of the statistical analysis of variance and optimized by the response surface method. Kinetic models were also evaluated, showing that the dissolution of pyritic sulfur follows the kinetic model of the shrinking core model, with diffusion through the solid product of the reaction as the controlling stage. The results of statistical analysis indicate that the use of ozone as an oxidant improves the pyrite dissolution because, at 0.25 M HNO{sub 3} or H{sub 2}SO{sub 4} at 20{sup o}C and 0.33 g/h O{sub 3}, the obtained dissolution is similar to that of 1 M H{sub 2}O{sub 2} and 1 M HNO{sub 3} or H{sub 2}SO{sub 4} at 40{sup o}C. 42 refs., 9 figs., 3 tabs.

  13. On the mean kinetic energy of the proton in strong hydrogen bonded systems.

    PubMed

    Finkelstein, Y; Moreh, R; Shang, S L; Shchur, Ya; Wang, Y; Liu, Z K

    2016-02-01

    The mean atomic kinetic energies of the proton, Ke(H), and of the deuteron, Ke(D), were calculated in moderate and strongly hydrogen bonded (HB) systems, such as the ferro-electric crystals of the KDP type (XH2PO4, X = K, Cs, Rb, Tl), the DKDP (XD2PO4, X = K, Cs, Rb) type, and the X3H(SO4)2 superprotonic conductors (X = K, Rb). All calculations utilized the simulated partial phonon density of states, deduced from density functional theory based first-principle calculations and from empirical lattice dynamics simulations in which the Coulomb, short range, covalent, and van der Waals interactions were accounted for. The presently calculated Ke(H) values for the two systems were found to be in excellent agreement with published values obtained by deep inelastic neutron scattering measurements carried out using the VESUVIO instrument of the Rutherford Laboratory, UK. The Ke(H) values of the M3H(SO4)2 compounds, in which the hydrogen bonds are centro-symmetric, are much lower than those of the KDP type crystals, in direct consistency with the oxygen-oxygen distance ROO, being a measure of the HB strength. PMID:26851916

  14. Fundamental Kinetics of Supercritical Coal Liquefaction: Effect of Catalysts and Hydrogen-Donor Solvents.

    SciTech Connect

    McCoy, B.J.; Smith, J.M.

    1997-07-21

    Most research on polymer degradation is for single polymers, even though the thermal decomposition of polymer mixtures is of interest both practically and theoretically. Polymer degradation rates depend on the mixture type, and adding a polymer can increase, decrease, or leave unchanged the degradation rate of the first polymer. We show how distribution-kinetics theory, based on molecular-weight distributions (MWDs), provides expressions for degradation rates of binary polymer mixtures. The approach accounts for initiation, termination, hydrogen abstraction, and radical chain scission in the governing equations for MWDS. Molecular-weight moments yield expressions for molar and mass concentrations and rate coefficients for combinations of random and chain-end scission. Experimental data show the concentration effect of poly((x-methyl styrene)) (PAMS) on the degradation of polystyrene dissolved in mineral oil at 275 {degrees}C in a batch reactor. Samples analyzed by gel permeation chromatography yielded the time evolution of the MD. The results indicated that, owing to the interaction of mixed radicals with polymer by hydrogen abstraction, polystyrene degradation rate decreases with increasing PAMS concentration.

  15. Capacitively coupled radio-frequency hydrogen discharges: The role of kinetics

    NASA Astrophysics Data System (ADS)

    Marques, L.; Jolly, J.; Alves, L. L.

    2007-09-01

    This paper presents a systematic characterization of capacitively coupled radio-frequency hydrogen discharges, produced within a parallel plate cylindrical setup at different rf applied voltages (Vrf=50-600V), frequencies (f=13.56-40.68MHz), and pressures (p=0.2-1torr). A two-dimensional, time-dependent fluid model for charged particle transport is self-consistently solved coupled to a homogeneous kinetic model for hydrogen, including vibrationally excited molecular species and electronically excited atomic species. Numerical simulations are compared with experimental measurements of various plasma parameters. A good quantitative agreement is found between simulations and experiment for the coupled electrical power and the plasma potential. The model underestimates the values of the electron density, the self-bias potential, and the H(n =1) atom density with respect to measurements, but agrees with experiment when predicting that all these parameters increase with either Vrf, f, or p. The dissociation degree is about 10-3 for the work conditions considered. Simulations adopt a wall recombination probability for H atoms that was experimentally measured, thus accounting for surface modification with discharge operating conditions. Results show the key role played by the atomic wall recombination mechanism in plasma description.

  16. Synthetic use of the primary kinetic isotope effect in hydrogen atom transfer 2: generation of captodatively stabilised radicals.

    PubMed

    Wood, Mark E; Bissiriou, Sabine; Lowe, Christopher; Windeatt, Kim M

    2013-04-28

    Using C-3 di-deuterated morpholin-2-ones bearing N-2-iodobenzyl and N-3-bromobut-3-enyl radical generating groups, only products derived from the more stabilised C-3, rather than the less stabilised C-5 translocated radicals, were formed after intramolecular 1,5-hydrogen atom transfer, suggesting that any kinetic isotope effect present was not sufficient to offset captodative stabilisation.

  17. The influence of pH on the kinetics, reversibility and mechanisms of Pb(II) sorption at the calcite-water interface

    NASA Astrophysics Data System (ADS)

    Rouff, Ashaki A.; Elzinga, Evert J.; Reeder, Richard J.; Fisher, Nicholas S.

    2005-11-01

    Pb(II) sorption experiments with calcite powders were conducted in suspensions equilibrated at atmospheric PCO 2(g) and ambient temperature at pH 7.3, 8.2 and 9.4. Pb fractional sorption was low at pH 7.3 and 9.4 relative to pH 8.2, and correlated well with PbCO 30(aq) speciation. Desorption experiments conducted for initial sorption times ranging from 0.5 h to 12 d reveal an almost completely reversible process at pH 8.2, attributed to the dominance of an adsorption mechanism, with slight and pronounced irreversibility at pH 7.3 and 9.4 respectively. Similarities in X-ray absorption near edge spectra (XANES) for 24 h and 12 d pH 7.3 and 9.4 sorption samples indicate no effect of initial sorption time. Results from linear combination (LC) fits of XANES spectra for samples sorbed at pH 9.4 confirm ˜75% adsorbed and ˜25% coprecipitated components. The coprecipitated fraction was attributed to the non-exchangeable metal observed in desorption experiments. At pH 7.3, ˜95% adsorbed and ˜5% coprecipitated components were obtained. A comparison of results from desorption experiments and LC-XANES alludes to an irreversibly bound adsorbed component for the pH 9.4 12 d sorption sample. Extended X-ray absorption fine structure spectroscopy (EXAFS) analysis of pH 7.3 and 9.4 12 d sorption samples confirms the presence of both adsorbed and coprecipitated metal. At pH 7.3 a first-shell Pb-O bond length of 2.38 Å is intermediate between that of adsorbed (2.34 Å) and coprecipitated (2.51 Å) Pb. At pH 9.4, two first-shell Pb-O distances at 2.35 Å and 2.51 Å were obtained, indicative of the occurrence of both adsorption and coprecipitation and a larger coprecipitated fraction relative to that at pH 7.3, consistent with LC-XANES results. We propose that the disparity in the fraction of coprecipitated metal with pH may be linked to the ability of sorbed Pb to inhibit near-surface dynamic exchange of Ca and CO 3 species, which dictates step advance and retreat. Less effective

  18. Structural and kinetic studies of metal hydride hydrogen storage materials using thin film deposition and characterization techniques

    NASA Astrophysics Data System (ADS)

    Kelly, Stephen Thomas

    Hydrogen makes an attractive energy carrier for many reasons. It is an abundant chemical fuel that can be produced from a wide variety of sources and stored for very long periods of time. When used in a fuel cell, hydrogen emits only water at the point of use, making it very attractive for mobile applications such as in an automobile. Metal hydrides are promising candidates for on-board reversible hydrogen storage in mobile applications due to their very high volumetric storage capacities---in most cases exceeding even that of liquid hydrogen. The United States Department of Energy (DOE) has set fuel system targets for an automotive hydrogen storage system, but as of yet no single material meets all the requirements. In particular, slow reaction kinetics and/or inappropriate thermodynamics plague many metal hydride hydrogen storage materials. In order to engineer a practical material that meets the DOE targets, we need a detailed understanding of the kinetic and thermodynamic properties of these materials during the phase change. In this work I employed sputter deposited thin films as a platform to study materials with highly controlled chemistry, microstructure and catalyst placement using thin film characterization techniques such as in situ x-ray diffraction (XRD) and neutron reflectivity. I observed kinetic limitations in the destabilized Mg2Si system due to the slow diffusion of the host Mg and Si atoms while forming separate MgH2 and Si phases. Conversely, I observed that the presence of Al in the Mg/Al system inhibits hydrogen diffusion while the host Mg and Al atoms interdiffuse readily, allowing the material to fall into a kinetic and/or thermodynamic trap by forming intermetallic compounds such as Mg17Al 12. By using in situ XRD to analyze epitaxial Mg films grown on (001) oriented Al2O3 substrates I observed hydride growth consistent with a model of a planar hydride layer growing into an existing metal layer. Subsequent film cycling changes the hydrogen

  19. Kinetic and mechanistic studies of carbon-to-metal hydrogen atom transfer involving Os-centered radicals: evidence for tunneling.

    PubMed

    Lewandowska-Andralojc, Anna; Grills, David C; Zhang, Jie; Bullock, R Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-01

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene, and 1,4-cyclohexadiene to Cp(CO)2Os(•) and (η(5)-(i)Pr4C5H)(CO)2Os(•) radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons are in the range 1.5 × 10(5) M(-1) s(-1) to 1.7 × 10(7) M(-1) s(-1) at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary deuterium kinetic isotope effects of 13.4 ± 1.0 and 16.8 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (η(5)-(i)Pr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 °C temperature range were carried out to obtain the difference in activation energies (E(D) - E(H)) and the pre-exponential factor ratio (A(H)/A(D)). For hydrogen atom transfer from xanthene to (η(5)-(i)Pr4C5H)(CO)2Os(•), the (E(D) - E(H)) = 3.3 ± 0.2 kcal mol(-1) and A(H)/A(D) = 0.06 ± 0.02 values suggest a quantum mechanical tunneling mechanism.

  20. Thermodynamics of cationic surfactant sorption onto natural clinoptilolite

    SciTech Connect

    Sullivan, E.J.; Bowman, R.S.; Carey, J.W.

    1998-10-15

    Sorption enthalpies of hexadecyltrimethylammonium bromide (HDTMA) as monomers and micelles and tetraethylammonium bromide (TEA) were used with surfactant, counterion, and co-ion sorption isotherms to infer the conformation, sorption mechanism, and relative stability of the sorbed surfactants on natural clinoptilolite. The average value of the sorption enthalpy was {minus}10.38 kJ/mol for monomers, {minus}11.98 kJ/mol for micelles, and +3.03 kJ/mol for TEA. Sorption of monomers produced a lower sorption plateau than equivalent micelle sorption (maxima 145 mmol/kg, 225 mmol/kg). Analysis of the sorption data demonstrated a change in the sorption mechanism at the external cation exchange capacity (ECEC) of clinoptilolite. Sorption data from below and above the ECEC were fit to a simple polynomial model and the Gibbs free energy of sorption ({Delta} G{sub m}{sup 0}) and sorption entropies were calculated. Resultant values of {Delta} G{sub m}{sup 0} were {minus}9.27 and {minus}14.38 kJ/mol for HDTMA monomers and micelles, respectively, for sorption below the ECEC, and {minus}16.11 and {minus}23.10 kJ/mol, respectively, for sorption above the ECEC. The value for TEA was {minus}1.04 kJ/mol, indicating weaker sorption than for HDTMA. Monomer sorption to clinoptilolite exceeded the ECEC, even when the solution concentration was below the critical micelle concentration. Hydrophobic (tail-tail) components of {Delta} G{sub m}{sup 0} were the driving force for sorption of HDTMA, both below and above the ECEC. A significant kinetic effect was observed in the sorption isotherms with a period of rapid sorption followed by slow equilibration requiring 7 days to achieve steady state for HDTMA; TEA equilibration occurred within 24 h.

  1. [Sorption behaviors of BDE-28 on natural soils].

    PubMed

    Liu, Wen-Xin; Ling, Xi; Chen, Jiang-Lin; Li, Wei-Bo; Dou, Han; Tao, Shu

    2011-03-01

    The sorption kinetics and isotherms of BDE-28 on three natural soils with different soil organic matter fractions (f(oc)) were investigated. The results indicated that a two (fast and slow)-compartment first-order model was more appropriate for describing the sorption kinetic data, compared to a one-compartment first-order model, especially in the initial sorption stage within 25 h. The fast sorption was predominant during the whole sorption process from beginning to the apparent sorption equilibrium; while the contribution of the slow sorption to the total sorption amount gradually increased and then achieved a plateau at 49 h or 55 h. The approaching time to the individual sorption capacity for the fast sorption was much shorter than that for the slow sorption. The contribution of the fast sorption to the increase in the total sorption amount of BDE-28 was prevailing at the beginning of sorption process from 2.5 h to 4.5 h; whereas the fraction of the slow sorption became primary at the subsequent stage of sorption process. The fitting results by the Dubinin-Ashtakhov (DA) model were comparable with those by the Freundlich model in the range of apparent equilibrium concentration studied. As for the Freundlich model, the nonlinear exponent (n) values of BDE-28 for the two samples with lower f(oc) (0.72%) or higher f(oc) (7.90%) approached to 1.0 (1.03 +/- 0.05 and 1.00 +/- 0.05, respectively), suggesting the linear sorption characteristics in the studied range of apparent equilibrium concentrations of BDE-28; while the nonlinear behavior of BDE-28 for the left sample with medium f(oc) (4.42%) was indicated by its n value less than 1.0 (0.89 +/- 0.04). PMID:21634174

  2. Thermodynamic and kinetic properties of hydrogen defect pairs in SrTiO3 from density functional theory.

    PubMed

    Bork, Nicolai; Bonanos, Nikolaos; Rossmeisl, Jan; Vegge, Tejs

    2011-09-01

    A density functional theory investigation of the thermodynamic and kinetic properties of hydrogen-hydrogen defect interactions in the cubic SrTiO(3) perovskite is presented. We find a net attraction between two hydrogen atoms with an optimal separation of ∼2.3 Å. The energy gain is ca. 0.33 eV compared to two non-interacting H defects. The main cause of the net attractive potential is elastic defect interactions through lattice deformation. Two possible diffusion paths for the hydrogen defect pair are investigated and are both determined to be faster than the corresponding diffusion path for single hydrogen atoms. Finally, we set up a simple model to determine the contribution from the double hydrogen defect to the total hydrogen flux, and find the double defect to be the main diffusing species at temperatures below ca. 400 °C. Post submission infrared absorption experiments show excellent agreement with the proposed properties of the double hydrogen defect. PMID:21769355

  3. Mechanisms and Kinetics of Boron Removal from Silicon by Humidified Hydrogen

    NASA Astrophysics Data System (ADS)

    Safarian, Jafar; Tang, Kai; Olsen, Jan Erik; Andersson, Stefan; Tranell, Gabriella; Hildal, Kjetil

    2016-04-01

    The removal of boron from silicon by top blowing of humidified hydrogen has been studied in the present work through experimental work, thermodynamic calculations, computational fluid dynamic modeling, and quantum chemistry calculations. The effect of process parameters; temperature, lance diameter, lance distance from the melt surface, gas flow rate, and crucible material on the kinetics of boron removal were studied. It has been shown that the rate of boron removal is decreased with increasing temperature due to the competitive reactions between silicon and oxygen as well as boron and oxygen, which can be confirmed with the increases of p SiO/ p HBO in the system. The rate of boron removal is increased with increasing the gas flow rate due mainly to the better supply and transport of the gas over the melt surface, as confirmed by the CFD modeling. Moreover, the rate of boron removal in alumina crucible is the highest followed by that in quartz and graphite crucibles, respectively. Faster B removal in quartz crucible than that in graphite crucible can be attributed to more oxygen dissolves in silicon melts. The fastest boron removal in alumina crucible is attributed to the additional boron gasification through aluminum borate (AlBO2) formation on the melt surface. Thermodynamic properties of the AlBO2 species have thus been revised by quantum chemistry calculations, which were more accurate to describe the formation of gaseous AlBO2 than those in the JANAF Thermochemical Tables. The main chemical reactions for boron gasification from silicon melts are proposed as In graphite, quartz and alumina crucible:quad \\underline{{B}} + \\underline{{H}} + \\underline{{O}} = {{ HBO}}( {{g}} ) {{In alumina crucible}}:\\underline{{Al}} + \\underline{{B}} + \\underline{{O}} = {{ AlBO}}2 ( {{g}} ) Based on the obtained results, it has been proposed that boron removal from silicon melt by humidified hydrogen is controlled both by the chemical reaction for boron gasification and

  4. Biomimetic Kinetic Resolution: Highly Enantio- and Diastereoselective Transfer Hydrogenation of Aglain Ketones To Access Flavagline Natural Products

    PubMed Central

    2015-01-01

    We have previously reported asymmetric syntheses and absolute configuration assignments of the aglains (+)-ponapensin and (+)-elliptifoline and proposed a biosynthetic kinetic resolution process to produce enantiomeric rocaglamides and aglains. Herein, we report a biomimetic approach for the synthesis of enantiomerically enriched aglains and rocaglamides via kinetic resolution of a bridged ketone utilizing enantioselective transfer hydrogenation. The methodology has been employed to synthesize and confirm the absolute stereochemistries of the pyrimidone rocaglamides (+)-aglaiastatin and (−)-aglaroxin C. Additionally, the enantiomers and racemate of each metabolite were assayed for inhibition of the heat-shock response, cytotoxicity, and translation inhibition. PMID:25514979

  5. Modulation of the thermodynamic, kinetic, and magnetic properties of the hydrogen monomer on graphene by charge doping.

    PubMed

    Huang, Liang Feng; Ni, Mei Yan; Zhang, Guo Ren; Zhou, Wang Huai; Li, Yong Gang; Zheng, Xiao Hong; Zeng, Zhi

    2011-08-14

    The thermodynamic, kinetic, and magnetic properties of the hydrogen monomer on doped graphene layers were studied by ab initio simulations. Electron doping heightens the diffusion potential barrier, while hole doping lowers it. However, both kinds of dopings heighten the desorption potential barrier. The underlying mechanism was revealed by investigating the effect of charge doping on the bond strength of graphene and on the electron transfer and the coulomb interaction between the hydrogen monomer and graphene. The kinetic properties of H and D monomers on doped graphene layers during both the annealing process (annealing time t(0) = 300 s) and the constant-rate heating process (heating rate α = 1.0 K/s) were simulated. Macroscopic diffusion of hydrogen monomers on graphene can be achieved when the doping-hole density reaches 5.0 × 10(13) cm(-2). Both electron and hole dopings linearly reduce the total magnetic moment and exchange splitting, which was explained by a simple exchange model. The laws found in this work had been generalized to explain many phenomena reported in literature. This study can further enhance the understanding of the interaction between hydrogen and graphene and was expected to be helpful in the design of hydrogenated-graphene-based devices. PMID:21842947

  6. USING METHANOL-WATER SYSTEMS TO INVESTIGATE PHENANTHRENE SORPTION-DESORPTION ON SEDIMENT

    EPA Science Inventory

    Sorption isotherm nonlinearity, sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic matter (NOM) polymers associated with soils and sediments. A conceptualizat...

  7. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, Mickey R.

    1994-01-01

    The goal of this program has been to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. During the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak. Weak in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in hydrogen while gamma titanium aluminide exhibits less degradation and beryllium essentially no degradation. The interaction of oxygen with the surface of several of these materials was studied. More recently, preliminary hydrogen permeation studies were completed for three high temperature alloys, Incoloy 909, Mo-47.5Re (wt. %), and this past year, Haynes 188.

  8. Kinetics of hydrogen isotope exchange in β-phase Pd-H-D

    SciTech Connect

    Luo, Weifang; Cowgill, Donald F.

    2015-07-22

    Hydrogen isotope gas exchange within palladium powders is examined using a batch-type reactor coupled to a residual gas analyzer (RGA). Furthermore, the exchange rates in both directions (H2 + PdD and D2 + PdH) are measured in the temperature range 178–323 K for the samples with different particle sizes. The results show this batch-type exchange is closely approximated as a first-order kinetic process with a rate directly proportional to the surface area of the powder particles. An exchange rate constant of 1.40 ± 0.24 μmol H2/atm cm2 s is found for H2 + PdD at 298 K, 1.4 times higher than that for D2 + PdH, with an activation energy of 25.0 ± 3.2 kJ/mol H for both exchange directions. Finally, a comparison of exchange measurement techniques shows these coefficients, and the fundamental exchange probabilities are in good agreement with those obtained by NMR and flow techniques.

  9. Kinetics of hydrogen isotope exchange in β-phase Pd-H-D

    DOE PAGES

    Luo, Weifang; Cowgill, Donald F.

    2015-07-22

    Hydrogen isotope gas exchange within palladium powders is examined using a batch-type reactor coupled to a residual gas analyzer (RGA). Furthermore, the exchange rates in both directions (H2 + PdD and D2 + PdH) are measured in the temperature range 178–323 K for the samples with different particle sizes. The results show this batch-type exchange is closely approximated as a first-order kinetic process with a rate directly proportional to the surface area of the powder particles. An exchange rate constant of 1.40 ± 0.24 μmol H2/atm cm2 s is found for H2 + PdD at 298 K, 1.4 times highermore » than that for D2 + PdH, with an activation energy of 25.0 ± 3.2 kJ/mol H for both exchange directions. Finally, a comparison of exchange measurement techniques shows these coefficients, and the fundamental exchange probabilities are in good agreement with those obtained by NMR and flow techniques.« less

  10. A probabilistic approach to the effect of water hydrogen bonds on the kinetics of protein folding and protein denaturation.

    PubMed

    Djikaev, Y S; Ruckenstein, E

    2010-02-26

    Previously, we presented a review of our kinetic models for the nucleation mechanism of protein folding and for the protein thermal denaturation in a barrierless way. A protein was treated as a random heteropolymer consisting of hydrophobic, hydrophilic, and neutral beads. As a crucial idea of the model, an overall potential around the cluster of native residues wherein a residue performs a chaotic motion was considered as the combination of the average dihedral, effective pairwise, and confining potentials. The overall potential as a function of the distance from the cluster has a double well shape. This allowed one to develop kinetic models for the nucleation mechanism of protein folding (NMPF) and barrierless protein denaturation (BPD) by using the mean first passage time analysis. In the original models, however, hydrogen bonding effects were taken into account only indirectly which affected the accuracy of the models because hydrogen bonding does play a crucial role in the folding, stability, and denaturation of proteins. To improve the NMPF and BPD models and explicitly take into account the hydrogen bonding "water-water" and "water-protein residue", we have developed a probabilistic hydrogen bond (PHB) model for the effect of hydrogen bond networks of water molecules around two solute particles (immersed in water) on their interaction, and have then combined the PHB model with the NMPF and BPD models. In this paper, that can be regarded as sequel of our previous review, we analyze the modified NMPF and BPD models that explicitly take into account the effect of water-water hydrogen bonding on these processes. As expected, the application of the modified models to the folding/unfolding of two model proteins (one short, consisting of 124 residues and the other large, consisting of 2500 residues) demonstrate that the hydrogen bond networks play a very important role in the protein folding/unfolding phenomena.

  11. Kinetic model for photoinduced and thermally induced creation and annihilation of metastable defects in hydrogenated amorphous silicon

    NASA Astrophysics Data System (ADS)

    Abdulhalim, I.

    1995-03-01

    A microscopic many-body model is proposed for the kinetics of metastable defects (MSDs) in hydrogenated amorphous silicon (a-Si:H). It is based on the existence of short-lived large energy fluctuations which induce transient traps for carriers that release their energy and enhance the creation or annihilation of MSDs. The expressions found for the photoinduced and thermally induced creation and annihilation rates' coefficients explain the dependence on the variety of parameters.

  12. METAL HYDRIDE HYDROGEN COMPRESSORS: A REVIEW

    SciTech Connect

    Bowman Jr, Robert C; Yartys, Dr. Volodymyr A.; Lototskyy, Dr. Michael V; Pollet, Dr. B.G.

    2014-01-01

    Metal hydride (MH) thermal sorption compression is an efficient and reliable method allowing a conversion of energy from heat into a compressed hydrogen gas. The most important component of such a thermal engine the metal hydride material itself should possess several material features in order to achieve an efficient performance in the hydrogen compression. Apart from the hydrogen storage characteristics important for every solid H storage material (e.g. gravimetric and volumetric efficiency of H storage, hydrogen sorption kinetics and effective thermal conductivity), the thermodynamics of the metal-hydrogen systems is of primary importance resulting in a temperature dependence of the absorption/desorption pressures). Several specific features should be optimized to govern the performance of the MH-compressors including synchronisation of the pressure plateaus for multi-stage compressors, reduction of slope of the isotherms and hysteresis, increase of cycling stability and life time, together with challenges in system design associated with volume expansion of the metal matrix during the hydrogenation. The present review summarises numerous papers and patent literature dealing with MH hydrogen compression technology. The review considers (a) fundamental aspects of materials development with a focus on structure and phase equilibria in the metal-hydrogen systems suitable for the hydrogen compression; and (b) applied aspects, including their consideration from the applied thermodynamic viewpoint, system design features and performances of the metal hydride compressors and major applications.

  13. Effects of pH and ORP on microbial ecology and kinetics for hydrogen production in continuously dark fermentation.

    PubMed

    Song, Jiaxiu; An, Dong; Ren, Nanqi; Zhang, Yongming; Chen, Ying

    2011-12-01

    The microbial structure and kinetic characteristics of the hydrogen producing strains in two fermentative continuous stirred-tank reactors (CSTRs) were studied by controlling pH and oxidation and reduction potential (ORP). The fluorescence in situ hybridization (FISH) tests were conducted to investigate the fermentative performance of Clostridium histolyticum (C. histolyticum), Clostridium lituseburense (C. lituseburense) and Enterobacteriaceae. The experimental results showed that in ethanol-type reactor 1#, the relative abundance of the strains was 48%, 30% and 22%. Comparatively, the relative abundance in butyric acid-type reactor 2# was 24%, 55% and 19% with butyric acids and hydrogen as the main products. The kinetic results indicated that the hydrogen yield coefficients YP/X in both reactors were 8.357 and 5.951 l-H2/g, while the coefficients of the cellular yield were 0.0268 and 0.0350 g-Cell/g, respectively. At the same biomass, the hydrogen yield in ethanol-type reactors was more than that in butyric acid reactors. However, the cellular synthesis rate in ethanol-type reactors was low when the same carbon source was used.

  14. A Kinetic Platform to Determine the Fate of Hydrogen Peroxide in Escherichia coli

    PubMed Central

    Adolfsen, Kristin J.; Brynildsen, Mark P.

    2015-01-01

    Hydrogen peroxide (H2O2) is used by phagocytic cells of the innate immune response to kill engulfed bacteria. H2O2 diffuses freely into bacteria, where it can wreak havoc on sensitive biomolecules if it is not rapidly detoxified. Accordingly, bacteria have evolved numerous systems to defend themselves against H2O2, and the importance of these systems to pathogenesis has been substantiated by the many bacteria that require them to establish or sustain infections. The kinetic competition for H2O2 within bacteria is complex, which suggests that quantitative models will improve interpretation and prediction of network behavior. To date, such models have been of limited scope, and this inspired us to construct a quantitative, systems-level model of H2O2 detoxification in Escherichia coli that includes detoxification enzymes, H2O2-dependent transcriptional regulation, enzyme degradation, the Fenton reaction and damage caused by •OH, oxidation of biomolecules by H2O2, and repair processes. After using an iterative computational and experimental procedure to train the model, we leveraged it to predict how H2O2 detoxification would change in response to an environmental perturbation that pathogens encounter within host phagosomes, carbon source deprivation, which leads to translational inhibition and limited availability of NADH. We found that the model accurately predicted that NADH depletion would delay clearance at low H2O2 concentrations and that detoxification at higher concentrations would resemble that of carbon-replete conditions. These results suggest that protein synthesis during bolus H2O2 stress does not affect clearance dynamics and that access to catabolites only matters at low H2O2 concentrations. We anticipate that this model will serve as a computational tool for the quantitative exploration and dissection of oxidative stress in bacteria, and that the model and methods used to develop it will provide important templates for the generation of comparable

  15. Thermodynamic and kinetic considerations for the reaction of semiquinone radicals to form superoxide and hydrogen peroxide

    PubMed Central

    Song, Yang; Buettner, Garry R.

    2010-01-01

    The quinone/semiquinone/hydroquinone triad (Q/SQ•−/H2Q) represents a class of compounds that has great importance in a wide range of biological processes. The half-cell reduction potentials of these redox couples in aqueous solutions at neutral pH, E°′, provide a window to understanding the thermodynamic and kinetic characteristics of this triad and their associated chemistry and biochemistry in vivo. Substituents on the quinone ring can significantly influence the electron density “on the ring” and thus modify E°′ dramatically. E°′ of the quinone governs the reaction of semiquinone with dioxygen to form superoxide. At near-neutral pH the pKa's of the hydroquinone are outstanding indicators of the electron density in the aromatic ring of the members of these triads (electrophilicity) and thus are excellent tools to predict half-cell reduction potentials for both the one-electron and two-electron couples, which in turn allow estimates of rate constants for the reactions of these triads. For example, the higher the pKa's of H2Q, the lower the reduction potentials and the higher the rate constants for the reaction of SQ•− with dioxygen to form superoxide. However, hydroquinone autoxidation is controlled by the concentration of di-ionized hydroquinone; thus, the lower the pKa's the less stable H2Q to autoxidation. Catalysts, e.g., metals and quinone, can accelerate oxidation processes; by removing superoxide and increasing the rate of formation of quinone, superoxide dismutase can accelerate oxidation of hydroquinones and thereby increase the flux of hydrogen peroxide. The principal reactions of quinones are with nucleophiles via Michael addition, for example, with thiols and amines. The rate constants for these addition reactions are also related to E°′. Thus, pKa's of a hydroquinone and E°′ are central to the chemistry of these triads. PMID:20493944

  16. Kinetic and Mechanistic Studies of Carbon-to-Metal Hydrogen Atom Transfer Involving Os-Centered Radicals: Evidence for Tunneling

    SciTech Connect

    Lewandowska-Androlojc, Anna; Grills, David C.; Zhang, Jie; Bullock, R. Morris; Miyazawa, Akira; Kawanishi, Yuji; Fujita, Etsuko

    2014-03-05

    We have investigated the kinetics of novel carbon-to-metal hydrogen atom transfer reactions, in which homolytic cleavage of a C-H bond is accomplished by a single metal-centered radical. Studies by means of time-resolved IR spectroscopic measurements revealed efficient hydrogen atom transfer from xanthene, 9,10-dihydroanthracene and 1,4-cyclohexadiene to Cp(CO)2Os• and (n5-iPr4C5H)(CO)2Os• radicals, formed by photoinduced homolysis of the corresponding osmium dimers. The rate constants for hydrogen abstraction from these hydrocarbons were found to be in the range 1.54 × 105 M 1 s 1 -1.73 × 107 M 1 s-1 at 25 °C. For the first time, kinetic isotope effects for carbon-to-metal hydrogen atom transfer were determined. Large primary kinetic isotope effects of 13.4 ± 1.0 and 16.6 ± 1.4 were observed for the hydrogen abstraction from xanthene to form Cp(CO)2OsH and (n5-iPr4C5H)(CO)2OsH, respectively, at 25 °C. Temperature-dependent measurements of the kinetic isotope effects over a 60 -C temperature range were carried out to obtain the difference in activation energies and the pre-exponential factor ratio. For hydrogen atom transfer from xanthene to (n5-iPr4C5H)(CO)2Os•, the (ED - EH) = 3.25 ± 0.20 kcal/mol and AH/AD = 0.056 ± 0.018 values are greater than the semi-classical limits and thus suggest a quantum mechanical tunneling mechanism. The work at BNL was carried out under contract DE-AC02-98CH10886 with the U.S. Department of Energy and supported by its Division of Chemical Sciences, Geosciences & Biosciences, Office of Basic Energy Sciences. RMB also thanks the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences for support. Pacific Northwest National Laboratory is operated by Battelle for the U.S. Department of Energy.

  17. Cosolvent effects on sorption isotherm linearity.

    PubMed

    Bouchard, Dermont C

    2002-06-01

    Sorption-desorption hysteresis, slow desorption kinetics, and other nonideal phenomena have been attributed to the differing sorptive characteristics of the natural organic polymers associated with soils and sediments. In this study, aqueous and mixed solvent systems were used to investigate the effects of a cosolvent, methanol, on sorption isotherm linearity with natural organic matter (NOM), and to evaluate whether these results support, or weaken, the rubbery/glassy polymer conceptualization of NOM. All of the sorption isotherms displayed some nonlinear character. Our data indicates that all of the phenanthrene and atrazine isotherms were nonlinear up to the highest equilibrium solution concentration to solute solubility in water or cosolvent ratios (Ce/Sw,c) used, approximately 0.018 and 0.070, respectively. Isotherm linearity was also observed to increase with volumetric methanol content (fc). This observation is consistent with the NOM rubbery/glassy polymer conceptualization: the presence of methanol in NOM increased isotherm linearity as do solvents in synthetic polymers, and suggests that methanol is interacting with the NOM, enhancing its homogeneity as a sorptive phase so that sorption is less bimodal as fc increases. When the equilibrium solution concentration was normalized for solute solubility in water or methanol-water solutions, greater relative sorption magnitude was observed for the methanol-water treatments. This observation, in conjunction with the faster sorption kinetics observed in the methanol-water sediment column systems, indicates that the increase in relative sorption magnitude with fc may be attributed to the faster sorption kinetics in the methanol-water systems, and hence, greater relative sorptive uptake for the rubbery polymer fraction of NOM at similar time scales.

  18. Variations in protein/flavin hydrogen bonding in a LOV domain produce non-Arrhenius kinetics of adduct decay†

    PubMed Central

    Zoltowski, Brian D.; Nash, Abigail I.; Gardner, Kevin H.

    2011-01-01

    Light Oxygen Voltage (LOV) domains utilize a conserved blue light-dependent mechanism to control a diverse array of effector domains in biological and engineered proteins. Variations in the kinetics and efficiency of LOV photochemistry fine tune various aspects of the photic response. Characterization of the kinetics of a key aspect of this photochemical mechanism in EL222, a blue-light responsive DNA binding protein from Erythrobacter litoralis HTCC2594, reveals unique non-Arrhenius behavior in the rate of dark state cleavage of the photochemically-generated adduct. Sequence analysis and mutagenesis studies establish that this effect stems from a Gln to Ala mutation unique to EL222 and homologous proteins from marine bacteria. Kinetic and spectroscopic analyses reveal that hydrogen bonding interactions between the FMN N1, O2 and ribityl hydroxyls with the surrounding protein regulate photocycle kinetics and stabilize the LOV active site from temperature-induced alteration in local structure. Substitution of residues interacting with the N1-O2 locus modulates adduct stability, structural flexibility and sequestration of the active site from bulk solvent without perturbation of light-activated DNA binding. Together, these variants link non-Arrhenius behavior to specific alteration of an H-bonding network, while affording tunability of photocycle kinetics. PMID:21923139

  19. Radionuclide sorption on drill core material from the Canadian Shield

    SciTech Connect

    Vandergraat, T.T.; Abry, D.R.

    1982-06-01

    The sorption of four radionuclides, /sup 90/Sr, /sup 137/Cs, /sup 144/Ce, and /sup 237/Pu, on drill core material from two rock formations in the Canadian Shield has been studied as part of the Canadian Nuclear Fuel Waste Management Program. For all four radionuclides, sorption increased with increased mafic mineral content of the rock. Autoradiographic investigations showed enhanced sorption on dark, or mafic, minerals and high sorption on chlorite infilling material in a closed fracture. Desorption was less complete than sorption after the same equilibration time, indicating a degree of irreversible sorption, or slower desorption kinetics. The effect of surface roughness (measured by mercury porosimetry) on sorption was not as great as that of the chemical and mineral composition of the rock.

  20. Distillation Kinetics of Solid Mixtures of Hydrogen Peroxide and Water and the Isolation of Pure Hydrogen Peroxide in Ultrahigh Vacuum

    NASA Technical Reports Server (NTRS)

    Teolis, B. D.; Baragiola, R. A.

    2006-01-01

    We present results of the growth of thin films of crystalline H2O2 and H2O2.2H2O (dihydrate) in ultrahigh vacuum by distilling an aqueous solution of hydrogen peroxide. We traced the process using infrared reflectance spectroscopy, mass loss on a quartz crystal microbalance, and in a few cases ultraviolet-visible reflectance. We find that the different crystalline phases-water, dihydrate, and hydrogen peroxide-have very different sublimation rates, making distillation efficient to isolate the less volatile component, crystalline H2O2.

  1. Pyrolytic temperatures impact lead sorption mechanisms by bagasse biochars.

    PubMed

    Ding, Wenchuan; Dong, Xiaoling; Ime, Inyang Mandu; Gao, Bin; Ma, Lena Q

    2014-06-01

    The characteristics and mechanisms of Pb sorption by biochars produced from sugarcane bagasse at 250, 400, 500, and 600 °C were examined. The Pb sorption isotherms, kinetics and desorption were investigated. All biochars were effective in Pb sorption and were well described by Langmuir isotherm model and pseudo-second-order kinetic model. The maximum sorption capacity decreased from 21 to 6.1 mg g(-1) as temperature increased from 250 to 600 °C. The Pb sorption was rapid initially, probably controlled by cation exchange and complexation and then slowed down, which might be due to intraparticle diffusions. FTIR data and kinetic models suggested that oxygen functional groups were probably responsible for the high Pb sorption onto low temperature biochars (250 and 400 °C) whereas intraparticle diffusion was mainly responsible for low Pb sorption onto high temperature biochars (500 and 600 °C). Decreased phosphorus concentration indicated that P-induced Pb precipitation was also responsible for Pb sorption. Pyrolysis temperature significantly affected biochar properties and played an important role in Pb sorption capacity and mechanisms by biochars. PMID:24393563

  2. Time dependent sorption behavior of dinotefuran, imidacloprid and thiamethoxam.

    PubMed

    Kurwadkar, Sudarshan T; Dewinne, Dustan; Wheat, Remington; McGahan, Donald G; Mitchell, Forrest L

    2013-01-01

    Dinetofuran (DNT), imidacloprid (IMD) and thiamethoxam (THM) are among the neonicotinoid insecticides widely used for managing insect pests of agricultural and veterinary importance. Environmental occurrence of neonicotinoid in post-application scenario poses unknown issues to human health and ecology. A sorption kinetic study provides much needed information on physico-chemical interaction of neonicotinoid with soil material. In this research study, time-dependent sorption behavior of DNT, IMD and THM in vineyard soil was studied. Sorption kinetics studies were conducted over a period of 96 hours with sampling duration varying from 0, 2, 4, 8, 12, 24, 60 and 96 hours. All three neonicotinoids exhibited very low sorption potential for the soil investigated. Overall percent sorption for all three neonicotinoids was below 20.04 ± 2.03% with highest percent sorption being observed for IMD followed by DNT and THM. All three neonicotinoids are highly soluble with solubility increasing with IMD < THM < DNT. Although, DNT has the highest solubility among all three neonicotinoids investigated, it exhibited higher percent sorption compared to THM, indicating factors other than solubility influenced the sorption kinetics. Low sorption potential of neonicotinoids indicates greater leaching potential with regard to groundwater and surface water contamination.

  3. Gas-Phase Hydrogen-Deuterium Exchange Labeling of Select Peptide Ion Conformer Types: a Per-Residue Kinetics Analysis

    NASA Astrophysics Data System (ADS)

    Khakinejad, Mahdiar; Kondalaji, Samaneh Ghassabi; Tafreshian, Amirmahdi; Valentine, Stephen J.

    2015-07-01

    The per-residue, gas-phase hydrogen deuterium exchange (HDX) kinetics for individual amino acid residues on selected ion conformer types of the model peptide KKDDDDDIIKIIK have been examined using ion mobility spectrometry (IMS) and HDX-tandem mass spectrometry (MS/MS) techniques. The [M + 4H]4+ ions exhibit two major conformer types with collision cross sections of 418 Å2 and 446 Å2; the [M + 3H]3+ ions also yield two different conformer types having collision cross sections of 340 Å2 and 367 Å2. Kinetics plots of HDX for individual amino acid residues reveal fast- and slow-exchanging hydrogens. The contributions of each amino acid residue to the overall conformer type rate constant have been estimated. For this peptide, N- and C-terminal K residues exhibit the greatest contributions for all ion conformer types. Interior D and I residues show decreased contributions. Several charge state trends are observed. On average, the D residues of the [M + 3H]3+ ions show faster HDX rate contributions compared with [M + 4H]4+ ions. In contrast the interior I8 and I9 residues show increased accessibility to exchange for the more elongated [M + 4H]4+ ion conformer type. The contribution of each residue to the overall uptake rate showed a good correlation with a residue hydrogen accessibility score model calculated using a distance from charge site and initial incorporation site for nominal structures obtained from molecular dynamic simulations (MDS).

  4. Sorption of microconstituents onto primary sludge.

    PubMed

    Ying, Zhu; Droste, R L

    2015-01-01

    The presence of microconstituents (MCs) in the environment has become an emerging concern to scientists and engineers. Sorption is one of the important removal mechanisms for MCs in wastewater treatment plants (WWTPs) since there is significant sludge production. The purpose of this study is to explore sorption kinetics and isotherms of MCs onto primary sludge. Three MCs, bisphenol-A (BPA), 17-α-ethinylestradiol (EE2) and triclosan (TCS), were chosen for this study. They are hydrophobic and have low vapor pressure, which makes sorption a potential removal mechanism. Both sorption kinetics and isotherm experiments were conducted using primary sludge collected from a local municipal WWTP. The time to equilibrium was around 7 h for all chosen MCs. A pseudo second-order rate model was better at describing the sorption rate than a pseudo first-order rate model. Linear sorption isotherm models were found to fit the experimental data, and the solid-liquid partitioning coefficients for BPA, EE2 and TCS were 81, 728 and 6,407 L/kg. PMID:26287837

  5. Kinetics and mechanisms of heterogeneous reaction of gaseous hydrogen peroxide on mineral oxide particles.

    PubMed

    Zhao, Yue; Chen, Zhongming; Shen, Xiaoli; Zhang, Xuan

    2011-04-15

    Recent studies have shown that heterogeneous reactions of hydrogen peroxide (H(2)O(2)) on aerosol surfaces may play an important role in tropospheric chemistry. The data concerning the kinetics and mechanisms of these reactions, however, are quite scarce so far. Here, we investigated, for the first time, the heterogeneous reactions of gaseous H(2)O(2) on SiO(2) and α-Al(2)O(3) particles, two major components of mineral dust aerosol, using transmission-Fourier Transform Infrared (T-FTIR) spectroscopy, and high-performance liquid chromatography (HPLC). It is found that H(2)O(2) molecularly adsorbs on SiO(2), and a small amount of molecularly adsorbed H(2)O(2) decomposes due to its thermal instability. For α-Al(2)O(3), catalytic decomposition of H(2)O(2) evidently occurs, but there is also a small amount of H(2)O(2) molecularly adsorbed on the particle surface. The BET uptake coefficients of H(2)O(2) on both particles appear to be independent of gaseous H(2)O(2) concentration (1.27-13.8 ppmv) and particle sample mass (2.8-6.5 mg for SiO(2) and 8.6-18.9 mg for α-Al(2)O(3)), but are strongly dependent on relative humidity with the values ranging from (1.55 ± 0.14) × 10(-8) and (1.21 ± 0.04) × 10(-7) at 2% RH to (0.61 ± 0.06) × 10(-8) and (0.76 ± 0.09) × 10(-7) at 76% RH for SiO(2) and α-Al(2)O(3), respectively. On the basis of the experimental results and literature data, the potential mechanisms for heterogeneous decomposition of H(2)O(2) were proposed, and the atmospheric implications of these reactions were discussed. It is found that heterogeneous reaction of H(2)O(2) on both mineral oxides plays a significant role in processing mineral aerosols, although its role as a sink for ambient H(2)O(2) is probably limited.

  6. Sorption-desorption of aminocyclopyrachlor in selected Brazilian soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Aminocyclopyrachlor sorption and desorption was investigated in 14 soils from Brazil, representing a range of pH, and organic carbon (OC) and clay contents. Sorption kinetics demonstrated that soil-solution equilibrium was attained in a 24-h period. Freundlich equation adequately described behavior ...

  7. Sorption-desorption of indaziflam in selected agricultural soils

    Technology Transfer Automated Retrieval System (TEKTRAN)

    Sorption and desorption of indaziflam in 6 soils from Brazil and 3 soils from the USA, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in a 24-h period. The Freundlich equa...

  8. LEAD SORPTION ON RUTHENIUM OXIDE: A MACROSCOPIC AND SPECTROSCOPIC STUDY

    EPA Science Inventory

    The sorption and desorption of Pb on RuO2 xH2O were examined kinetically and thermodynamically via spectroscopic and macroscopic investigations. X-ray absorption spectroscopy (XAS) was employed to determine the sorption mechanism with regard to identity of nearest atomic neighbo...

  9. Influence of different types of effectors on the kinetic parameters of suicide inactivation of catalase by hydrogen peroxide.

    PubMed

    Ghadermarzi, M; Moosavi-Movahedi, A A

    1999-04-12

    The effects of cyanide and azide ions (class A), sodium-n-dodecyl sulphate (SDS) and 2-mercaptoethanol (class B), 3-aminotriazole (class C) and NADPH (class D) on the initial activity (ai), inactivation rate constant (ki) and the partition ratio (r) of bovine liver catalase reaction with its suicide substrate, hydrogen peroxide, were studied in 50 mM sodium phosphate buffer, pH 7.0 at 27 degrees C. The above kinetic parameters were determined by processing the progress curve data. In class A, which contains fast and reversible inhibitors of catalase, a proportional decrease in ai and ki was observed by inhibitors, so that the r remained constant. In class B, which contains slow and irreversible inactivators, a decrease in ai and constancy of ki and r were observed when catalase was incubated in the presence of such inactivators for a determined time. In class C, containing effector which can combine with intermediate compound I, ai was relatively unchanged but an increase in ki and a decrease in r were observed. In class D, containing effector which reduces compound I to ferricatalase, ai was not affected significantly but some decrease in ki was detected which was linked with an increase in r. These results demonstrate that different classes of effectors affect the determined kinetic parameters of catalase in various ways. Thus, determination of such parameters by simple kinetic experiments can be carried out for classification of the agents which have an effect on the kinetics of catalase. PMID:10209276

  10. Mixed-Gas Sorption Joule-Thomson Refrigerator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Petrick, S. Walter; Bard, Steven

    1991-01-01

    Proposed mixed-gas sorption Joule-Thomson refrigerator provides cooling down to temperature of 70 K. Includes only one stage and no mechanical compressor. Simpler, operates without vibrating, and consumes less power in producing same amount of cooling. Same sorption principle of operation applicable in compressor that chemisorbs oxygen or hydrogen from mixture with helium, neon, and/or other nonreactive gases.

  11. Theoretical and kinetic study of the hydrogen atom abstraction reactions of unsaturated C6 methyl esters with hydroxyl radical

    NASA Astrophysics Data System (ADS)

    Wang, Quan-De; Ni, Zhong-Hai

    2016-04-01

    This work reports a systematic ab initio and chemical kinetic study of the rate constants for hydrogen atom abstraction reactions by hydroxyl radical (OH) on typical isomers of unsaturated C6 methyl esters at the CBS/QB3 level of theory. The high-pressure limit rate constants at different reaction sites for all the methyl esters in the temperature range from 500 to 2000 K are calculated via transition-state theory with the Wigner method for quantum tunneling effect and fitted to the modified three parameters Arrhenius expression using least-squares regression. Further, a branching ratio analysis for each reaction site has been performed.

  12. Growth kinetics of hydrogen sulfide oxidizing bacteria in corroded concrete from sewers.

    PubMed

    Jensen, Henriette Stokbro; Lens, Piet N L; Nielsen, Jeppe L; Bester, Kai; Nielsen, Asbjørn Haaning; Hvitved-Jacobsen, Thorkild; Vollertsen, Jes

    2011-05-30

    Hydrogen sulfide oxidation by microbes present on concrete surfaces of sewer pipes is a key process in sewer corrosion. The growth of aerobic sulfur oxidizing bacteria from corroded concrete surfaces was studied in a batch reactor. Samples of corrosion products, containing sulfur oxidizing bacteria, were suspended in aqueous solution at pH similar to that of corroded concrete. Hydrogen sulfide was supplied to the reactor to provide the source of reduced sulfur. The removal of hydrogen sulfide and oxygen was monitored. The utilization rates of both hydrogen sulfide and oxygen suggested exponential bacterial growth with median growth rates of 1.25 d(-1) and 1.33 d(-1) as determined from the utilization rates of hydrogen sulfide and oxygen, respectively. Elemental sulfur was found to be the immediate product of the hydrogen sulfide oxidation. When exponential growth had been achieved, the addition of hydrogen sulfide was terminated leading to elemental sulfur oxidation. The ratio of consumed sulfur to consumed oxygen suggested that sulfuric acid was the ultimate oxidation product. To the knowledge of the authors, this is the first study to determine the growth rate of bacteria involved in concrete corrosion with hydrogen sulfide as source of reduced sulfur. PMID:21440988

  13. Growth kinetics of hydrogen sulfide oxidizing bacteria in corroded concrete from sewers.

    PubMed

    Jensen, Henriette Stokbro; Lens, Piet N L; Nielsen, Jeppe L; Bester, Kai; Nielsen, Asbjørn Haaning; Hvitved-Jacobsen, Thorkild; Vollertsen, Jes

    2011-05-30

    Hydrogen sulfide oxidation by microbes present on concrete surfaces of sewer pipes is a key process in sewer corrosion. The growth of aerobic sulfur oxidizing bacteria from corroded concrete surfaces was studied in a batch reactor. Samples of corrosion products, containing sulfur oxidizing bacteria, were suspended in aqueous solution at pH similar to that of corroded concrete. Hydrogen sulfide was supplied to the reactor to provide the source of reduced sulfur. The removal of hydrogen sulfide and oxygen was monitored. The utilization rates of both hydrogen sulfide and oxygen suggested exponential bacterial growth with median growth rates of 1.25 d(-1) and 1.33 d(-1) as determined from the utilization rates of hydrogen sulfide and oxygen, respectively. Elemental sulfur was found to be the immediate product of the hydrogen sulfide oxidation. When exponential growth had been achieved, the addition of hydrogen sulfide was terminated leading to elemental sulfur oxidation. The ratio of consumed sulfur to consumed oxygen suggested that sulfuric acid was the ultimate oxidation product. To the knowledge of the authors, this is the first study to determine the growth rate of bacteria involved in concrete corrosion with hydrogen sulfide as source of reduced sulfur.

  14. Electrochemical studies of kinetic properties of titanium- and vanadium-hydrogen systems at intermediate temperatures using molten salt techniques

    SciTech Connect

    Liaw, B.Y.; Deublein, G.; Huggins, R.A.

    1995-07-01

    A novel molten salt technique for studying hydrogen transport in Ti an V metals is described. The molten-salt electrolytes were eutectic mixtures of alkali halides dissolved with excess LiH, operating in temperature ranges typically above 300 C, to which electrochemical techniques were difficult to apply conventionally. The authors used the molten salt technique to investigate the thermodynamic properties of the Ti-H system previously. In this work, they determined composition-dependent diffusion and permeation data of hydrogen in Ti and in binary hydride phases using a galvanostatic intermittent titration technique (GITT). The results are in accordance with the best values reported by others using different techniques. They also reported some preliminary results regarding the kinetic properties of hydrogen in V and its hydride measured by more conventional time-lag and steady-state permeation techniques. The successful application of this molten salt technique in the metal hydrogen systems opened a new arena for potential application in energy conversion and storage.

  15. Kinetic and spectroscopic studies of the [palladium(Ar-bian)]-catalyzed semi-hydrogenation of 4-octyne.

    PubMed

    Kluwer, Alexander M; Koblenz, Tehila S; Jonischkeit, Thorsten; Woelk, Klaus; Elsevier, Cornelis J

    2005-11-01

    The kinetics of the stereoselective semi-hydrogenation of 4-octyne in THF by the highly active catalyst [Pd{(m,m'-(CF(3))(2)C(6)H(3))-bian}(ma)] (2) (bian = bis(imino)acenaphthene; ma = maleic anhydride) has been investigated. The rate law under hydrogen-rich conditions is described by r = k[4-octyne](0.65)[Pd][H(2)], showing first order in palladium and dihydrogen and a broken order in substrate. Parahydrogen studies have shown that a pairwise transfer of hydrogen atoms occurs in the rate-limiting step. In agreement with recent theoretical results, the proposed mechanism consists of the consecutive steps: alkyne coordination, heterolytic dihydrogen activation (hydrogenolysis of one Pd-N bond), subsequent hydro-palladation of the alkyne, followed by addition of N-H to palladium, reductive coupling of vinyl and hydride and, finally, substitution of the product alkene by the alkyne substrate. Under hydrogen-limiting conditions, side reactions occur, that is, formation of catalytically inactive palladacycles by oxidative alkyne coupling. Furthermore, it has been shown that (Z)-oct-4-ene is the primary reaction product, from which the minor product (E)-oct-4-ene is formed by an H(2)-assisted, palladium-catalyzed isomerization reaction.

  16. Estimation of kinetic parameters related to biochemical interactions between hydrogen peroxide and signal transduction proteins

    PubMed Central

    Brito, Paula M.; Antunes, Fernando

    2014-01-01

    The lack of kinetic data concerning the biological effects of reactive oxygen species is slowing down the development of the field of redox signaling. Herein, we deduced and applied equations to estimate kinetic parameters from typical redox signaling experiments. H2O2-sensing mediated by the oxidation of a protein target and the switch-off of this sensor, by being converted back to its reduced form, are the two processes for which kinetic parameters are determined. The experimental data required to apply the equations deduced is the fraction of the H2O2 sensor protein in the reduced or in the oxidized state measured in intact cells or living tissues after exposure to either endogenous or added H2O2. Either non-linear fittings that do not need transformation of the experimental data or linearized plots in which deviations from the equations are easily observed can be used. The equations were shown to be valid by fitting to them virtual time courses simulated with a kinetic model. The good agreement between the kinetic parameters estimated in these fittings and those used to simulate the virtual time courses supported the accuracy of the kinetic equations deduced. Finally, equations were successfully tested with real data taken from published experiments that describe redox signaling mediated by the oxidation of two protein tyrosine phosphatases, PTP1B and SHP-2, which are two of the few H2O2-sensing proteins with known kinetic parameters. Whereas for PTP1B estimated kinetic parameters fitted in general the present knowledge, for SHP-2 results obtained suggest that reactivity toward H2O2 as well as the rate of SHP-2 regeneration back to its reduced form are higher than previously thought. In conclusion, valuable quantitative kinetic data can be estimated from typical redox signaling experiments, thus improving our understanding about the complex processes that underlie the interplay between oxidative stress and redox signaling responses. PMID:25325054

  17. Estimation of kinetic parameters related to biochemical interactions between hydrogen peroxide and signal transduction proteins

    NASA Astrophysics Data System (ADS)

    Brito, Paula; Antunes, Fernando

    2014-10-01

    The lack of kinetic data concerning the biological effects of reactive oxygen species is slowing down the development of the field of redox signaling. Herein, we deduced and applied equations to estimate kinetic parameters from typical redox signaling experiments. H2O2-sensing mediated by the oxidation of a protein target and the switch-off of this sensor, by being converted back to its reduced form, are the two processes for which kinetic parameters are determined. The experimental data required to apply the equations deduced is the fraction of the H2O2 sensor protein in the reduced or in the oxidized state measured in intact cells or living tissues after exposure to either endogenous or added H2O2. Either non-linear fittings that do not need transformation of the experimental data or linearized plots in which deviations from the equations are easily observed can be used. The equations were shown to be valid by fitting to them virtual time courses simulated with a kinetic model. The good agreement between the kinetic parameters estimated in these fittings and those used to simulate the virtual time courses supported the accuracy of the kinetic equations deduced. Finally, equations were successfully tested with real data taken from published experiments that describe redox signaling mediated by the oxidation of two protein tyrosine phosphatases, PTP1B and SHP-2, which are two of the few H2O2-sensing proteins with known kinetic parameters. Whereas for PTP1B estimated kinetic parameters fitted in general the present knowledge, for SHP-2 results obtained suggest that reactivity towards H2O2 as well as the rate of SHP-2 regeneration back to its reduced form are higher than previously thought. In conclusion, valuable quantitative kinetic data can be estimated from typical redox signaling experiments, thus improving our understanding about the complex processes that underline the interplay between oxidative stress and redox signaling responses.

  18. Estimation of kinetic parameters related to biochemical interactions between hydrogen peroxide and signal transduction proteins.

    PubMed

    Brito, Paula M; Antunes, Fernando

    2014-01-01

    The lack of kinetic data concerning the biological effects of reactive oxygen species is slowing down the development of the field of redox signaling. Herein, we deduced and applied equations to estimate kinetic parameters from typical redox signaling experiments. H2O2-sensing mediated by the oxidation of a protein target and the switch-off of this sensor, by being converted back to its reduced form, are the two processes for which kinetic parameters are determined. The experimental data required to apply the equations deduced is the fraction of the H2O2 sensor protein in the reduced or in the oxidized state measured in intact cells or living tissues after exposure to either endogenous or added H2O2. Either non-linear fittings that do not need transformation of the experimental data or linearized plots in which deviations from the equations are easily observed can be used. The equations were shown to be valid by fitting to them virtual time courses simulated with a kinetic model. The good agreement between the kinetic parameters estimated in these fittings and those used to simulate the virtual time courses supported the accuracy of the kinetic equations deduced. Finally, equations were successfully tested with real data taken from published experiments that describe redox signaling mediated by the oxidation of two protein tyrosine phosphatases, PTP1B and SHP-2, which are two of the few H2O2-sensing proteins with known kinetic parameters. Whereas for PTP1B estimated kinetic parameters fitted in general the present knowledge, for SHP-2 results obtained suggest that reactivity toward H2O2 as well as the rate of SHP-2 regeneration back to its reduced form are higher than previously thought. In conclusion, valuable quantitative kinetic data can be estimated from typical redox signaling experiments, thus improving our understanding about the complex processes that underlie the interplay between oxidative stress and redox signaling responses.

  19. First-principles-based kinetic Monte Carlo studies of diffusion of hydrogen in Ni–Al and Ni–Fe binary alloys

    SciTech Connect

    Tafen, De Nyago

    2015-02-14

    The diffusion of dilute hydrogen in fcc Ni–Al and Ni–Fe binary alloys was examined using kinetic Monte Carlo method with input kinetic parameters obtained from first-principles density functional theory. The simulation involves the implementation of computationally efficient energy barrier model that describes the configuration dependence of the hydrogen hopping. The predicted hydrogen diffusion coefficients in Ni and Ni89.4Fe10.6 are compared well with the available experimental data. In Ni–Al, the model predicts lower hydrogen diffusivity compared to that in Ni. Overall, diffusion prefactors and the effective activation energies of H in Ni–Fe and Ni–Al are concentration dependent of the alloying element. Furthermore, the changes in their values are the results of the short-range order (nearest-neighbor) effect on the interstitial diffusion of hydrogen in fcc Ni-based alloys.

  20. First-principles-based kinetic Monte Carlo studies of diffusion of hydrogen in Ni–Al and Ni–Fe binary alloys

    DOE PAGES

    Tafen, De Nyago

    2015-02-14

    The diffusion of dilute hydrogen in fcc Ni–Al and Ni–Fe binary alloys was examined using kinetic Monte Carlo method with input kinetic parameters obtained from first-principles density functional theory. The simulation involves the implementation of computationally efficient energy barrier model that describes the configuration dependence of the hydrogen hopping. The predicted hydrogen diffusion coefficients in Ni and Ni89.4Fe10.6 are compared well with the available experimental data. In Ni–Al, the model predicts lower hydrogen diffusivity compared to that in Ni. Overall, diffusion prefactors and the effective activation energies of H in Ni–Fe and Ni–Al are concentration dependent of the alloying element.more » Furthermore, the changes in their values are the results of the short-range order (nearest-neighbor) effect on the interstitial diffusion of hydrogen in fcc Ni-based alloys.« less

  1. Reduced and Validated Kinetic Mechanisms for Hydrogen-CO-sir Combustion in Gas Turbines

    SciTech Connect

    Yiguang Ju; Frederick Dryer

    2009-02-07

    Rigorous experimental, theoretical, and numerical investigation of various issues relevant to the development of reduced, validated kinetic mechanisms for synthetic gas combustion in gas turbines was carried out - including the construction of new radiation models for combusting flows, improvement of flame speed measurement techniques, measurements and chemical kinetic analysis of H{sub 2}/CO/CO{sub 2}/O{sub 2}/diluent mixtures, revision of the H{sub 2}/O{sub 2} kinetic model to improve flame speed prediction capabilities, and development of a multi-time scale algorithm to improve computational efficiency in reacting flow simulations.

  2. Equilibrium, Thermodynamics, and Kinetic Sorption Studies for the Removal of Coomassie Brilliant Blue on Wheat Bran as a Low-Cost Adsorbent

    PubMed Central

    Ata, Sadia; Imran Din, Muhammad; Rasool, Atta; Qasim, Imran; Ul Mohsin, Ijaz

    2012-01-01

    The sorption studies of coomassie brilliant blue (CBB) from aqueous solution have been carried out on wheat bran (WB). Coomassie brilliant blue on wheat bran was used to study the adsorption behavior under various parameters such as pH, dosage amount, and contact time. It was observed that under optimized conditions up to 95.70% dye could be removed from solution onto WB. Langmuir and Freundlich adsorption isotherms were used to elaborate the results. Freundlich model was found to be fitted well and favored multilayer adsorption. The Freundlich constants n and KF were determined as 0.53 and 2.5 × 10−4. Thermodynamic parameters such as ΔG, ΔH, and ΔS studied were taking into account, showed spontaneous and favorable reaction for coomassie brilliant blue on wheat bran. The maximum adsorption capacity qm was found to be 6.410 mg/g. The investigations show that non treated WB is a low-cost adsorbent for the removal of dyes from textile industry effluents. PMID:22567559

  3. Proton-transfer mechanism for dispersed decay kinetics of single molecules isolated in potassium hydrogen phthalate.

    PubMed

    Bott, Eric D; Riley, Erin A; Kahr, Bart; Reid, Philip J

    2009-08-25

    The excited-state decay kinetics of single 2',7'-dichlorofluorescein (DCF) molecules oriented and overgrown within crystals of potassium acid phthalate (KAP) are reported. Time-correlated single-photon counting measurements (TCSPC) of 56 DCF molecules in KAP reveal that single-exponential decay is exhibited by roughly half of the molecules. The remainder demonstrates complex excited-state decay kinetics that are well fit by a stretched exponential function consistent with dispersed kinetics. Histograms of single-molecule luminescence energies revealed environmental fluctuations and distinct chemical species. The TCSPC results are compared to Monte Carlo simulations employing a first-passage model for excited-state decay. Agreement between experiment and theory, on both bulk and single-molecule levels, suggests that a subset of the DCF molecules in KAP experience fluctuations in the surrounding environment that modify the energy barrier to proton transfer leading to dispersed kinetics.

  4. Hydrogen tunneling in adenosylcobalamin-dependent glutamate mutase: evidence from intrinsic kinetic isotope effects measured by intra-molecular competition †

    PubMed Central

    Yoon, Miri; Song, Hangtian; Håkansson, Kristina; Marsh, E. Neil G.

    2010-01-01

    Hydrogen atom transfer reactions between substrate and coenzyme are a key mechanistic feature of all AdoCbl-dependent enzymes. For one of these enzymes, glutamate mutase, we have investigated whether hydrogen tunneling makes a significant contribution to the mechanism by examining the temperature-dependence of the deuterium kinetic isotope effect associated with hydrogen atom transfer from methylaspartate to the coenzyme. To do this we designed a novel intra-molecular competition experiment that allowed us to measure the intrinsic kinetic isotope effect, even though hydrogen transfer may not be rate determining. From the Arrhenius plot of the kinetic isotope effect, the ratio of the pre-exponential factors AH/AD was 0.17 ± 0.04 and the isotope effect on the activation energy, ΔEa(D – H) was 1.94 ± 0.13 kcal/mol. The results imply that significant degree of hydrogen tunneling occurs in glutamate mutase, even though the intrinsic kinetic isotope effects are well within the semi-classical limit and are much smaller than those measured for other AdoCbl enzymes and model reactions for which hydrogen tunneling has been implicated. PMID:20225826

  5. Modeling the reaction kinetics of a hydrogen generator onboard a fuel cell -- Electric hybrid motorcycle

    NASA Astrophysics Data System (ADS)

    Ganesh, Karthik

    Owing to the perceived decline of the fossil fuel reserves in the world and environmental issues like pollution, conventional fuels may be replaced by cleaner alternative fuels. The potential of hydrogen as a fuel in vehicular applications is being explored. Hydrogen as an energy carrier potentially finds applications in internal combustion engines and fuel cells because it is considered a clean fuel and has high specific energy. However, at 6 to 8 per kilogram, not only is hydrogen produced from conventional methods like steam reforming expensive, but also there are storage and handling issues, safety concerns and lack of hydrogen refilling stations across the country. The purpose of this research is to suggest a cheap and viable system that generates hydrogen on demand through a chemical reaction between an aluminum-water slurry and an aqueous sodium hydroxide solution to power a 2 kW fuel cell on a fuel cell hybrid motorcycle. This reaction is essentially an aluminum-water reaction where sodium hydroxide acts as a reaction promoter or catalyst. The Horizon 2000 fuel cell used for this purpose has a maximum hydrogen intake rate of 28 lpm. The study focuses on studying the exothermic reaction between the reactants and proposes a rate law that best describes the rate of generation of hydrogen in connection to the surface area of aluminum available for the certain reaction and the concentration of the sodium hydroxide solution. Further, the proposed rate law is used in the simulation model of the chemical reactor onboard the hybrid motorcycle to determine the hydrogen flow rate to the fuel cell with time. Based on the simulated rate of production of hydrogen from the chemical system, its feasibility of use on different drive cycles is analyzed. The rate of production of hydrogen with a higher concentration of sodium hydroxide and smaller aluminum powder size was found to enable the installation of the chemical reactor on urban cycles with frequent stops and starts

  6. Systematic evaluation of nitrate and perchlorate bioreduction kinetics in groundwater using a hydrogen-based membrane biofilm reactor.

    PubMed

    Ziv-El, Michal C; Rittmann, Bruce E

    2009-01-01

    To evaluate the simultaneous reduction kinetics of the oxidized compounds, we treated nitrate-contaminated groundwater (approximately 9.4 mg-N/L) containing low concentrations of perchlorate (approximately 12.5 microg/L) and saturated with dissolved oxygen (approximately 8 mg/L) in a hydrogen-based membrane biofilm reactor (MBfR). We systematically increased the hydrogen availability and simultaneously varied the surface loading of the oxidized compounds on the biofilm in order to provide a comprehensive, quantitative data set with which to evaluate the relationship between electron donor (H(2)) availability, surface loading of the electron acceptors (oxidized compounds), and simultaneous bioreduction of the electron acceptors. Increasing the H(2) pressure delivered more H(2) gas, and the total H(2) flux increased linearly from approximately 0.04 mg/cm(2)-d for 0.5 psig (0.034 atm) to 0.13 mg/cm(2)-d for 9.5 psig (0.65 atm). This increased rate of H(2) delivery allowed for continued reduction of the acceptors as their surface loading increased. The electron acceptors had a clear hydrogen-utilization order when the availability of hydrogen was limited: oxygen, nitrate, nitrite, and then perchlorate. Spiking the influent with perchlorate or nitrate allowed us to identify the maximum surface loadings that still achieved more than 99.5% reduction of both oxidized contaminants: 0.21 mg NO(3)-N/cm(2)-d and 3.4 microg ClO(4)/cm(2)-d. Both maximum values appear to be controlled by factors other than hydrogen availability.

  7. Electrical and mechanical controlling of the kinetic and magnetic properties of hydrogen atoms on free-standing silicene.

    PubMed

    Podsiadły-Paszkowska, Agata; Krawiec, Mariusz

    2016-07-20

    Effects of strain, charge doping and external electric field on kinetic and magnetic properties of hydrogen atoms on a free-standing silicene layer are investigated by first-principles density functional theory. It was found that the charge doping and strain are the most effective ways of changing the hydrogen-silicene binding energy, but they can only raise its value. The perpendicular external electric field can also lower it albeit in a narrower range. The strain has also the strongest impact on diffusion processes, and the diffusion barrier can be modified up to 50% of its unstrained value. The adsorption of hydrogen atoms results in a locally antiferromagnetic ground state with the effective exchange constant of approximately 1 eV. The system can easily be driven into a nonmagnetic phase by the charge doping and strain. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in fields of modern nanoelectronics and spintronics. PMID:27228502

  8. Electrical and mechanical controlling of the kinetic and magnetic properties of hydrogen atoms on free-standing silicene

    NASA Astrophysics Data System (ADS)

    Podsiadły-Paszkowska, Agata; Krawiec, Mariusz

    2016-07-01

    Effects of strain, charge doping and external electric field on kinetic and magnetic properties of hydrogen atoms on a free-standing silicene layer are investigated by first-principles density functional theory. It was found that the charge doping and strain are the most effective ways of changing the hydrogen-silicene binding energy, but they can only raise its value. The perpendicular external electric field can also lower it albeit in a narrower range. The strain has also the strongest impact on diffusion processes, and the diffusion barrier can be modified up to 50% of its unstrained value. The adsorption of hydrogen atoms results in a locally antiferromagnetic ground state with the effective exchange constant of approximately 1 eV. The system can easily be driven into a nonmagnetic phase by the charge doping and strain. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in fields of modern nanoelectronics and spintronics.

  9. Electrical and mechanical controlling of the kinetic and magnetic properties of hydrogen atoms on free-standing silicene.

    PubMed

    Podsiadły-Paszkowska, Agata; Krawiec, Mariusz

    2016-07-20

    Effects of strain, charge doping and external electric field on kinetic and magnetic properties of hydrogen atoms on a free-standing silicene layer are investigated by first-principles density functional theory. It was found that the charge doping and strain are the most effective ways of changing the hydrogen-silicene binding energy, but they can only raise its value. The perpendicular external electric field can also lower it albeit in a narrower range. The strain has also the strongest impact on diffusion processes, and the diffusion barrier can be modified up to 50% of its unstrained value. The adsorption of hydrogen atoms results in a locally antiferromagnetic ground state with the effective exchange constant of approximately 1 eV. The system can easily be driven into a nonmagnetic phase by the charge doping and strain. The obtained results are very promising in view of the silicene functionalization and potential applications of silicene in fields of modern nanoelectronics and spintronics.

  10. Transport and sorption of volatile organic compounds and water vapor in porous media

    SciTech Connect

    Lin, Tsair-Fuh

    1995-07-01

    To gain insight on the controlling mechanisms for VOC transport in porous media, the relations among sorbent properties, sorption equilibrium and intraparticle diffusion processes were studied at the level of individual sorbent particles and laboratory columns for soil and activated carbon systems. Transport and sorption of VOCs and water vapor were first elucidated within individual dry soil mineral grains. Soil properties, sorption capacity, and sorption rates were measured for 3 test soils; results suggest that the soil grains are porous, while the sorption isotherms are nonlinear and adsorption-desorption rates are slow and asymmetric. An intragranular pore diffusion model coupled with the nonlinear Freundlich isotherm was developed to describe the sorption kinetic curves. Transport of benzene and water vapor within peat was studied; partitioning and sorption kinetics were determined with an electrobalance. A dual diffusion model was developed. Transport of benzene in dry and moist soil columns was studied, followed by gaseous transport and sorption in activated carbon. The pore diffusion model provides good fits to sorption kinetics for VOCs to soil and VOC to granular activated carbon and activated carbon fibers. Results of this research indicate that: Intraparticle diffusion along with a nonlinea sorption isotherm are responsible for the slow, asymmetric sorption-desorption. Diffusion models are able to describe results for soil and activated carbon systems; when combined with mass transfer equations, they predict column breakthrough curves for several systems. Although the conditions are simplified, the mechanisms should provide insight on complex systems involving transport and sorption of vapors in porous media.

  11. Sorption of Thiobacillus ferrooxidans to particulate material

    SciTech Connect

    Dispirito, A.A.; Dugan, P.R.; Tuovinen, O.H.

    1983-04-01

    Iron-oxidizing thiobacilli oxidize many sulfide minerals. It has been suggested that one mechanism of the oxidation involves a mineral surface attack by the bacteria, thereby catalyzing chemical reactions that normally proceed at slow rates. Evidence for a direct surface attack by acidophilic thiobacilli has been obtained from scanning electron microscope studies in which organisms have been shown to colonize mineral surfaces, eventually resulting in pitting and corrosion of the substratum. Scanning electron microscopic characterization of bacterial-mineral interactions is limited in that the technique is not readily suitable to estimate the kinetics of the bacterial sorption to particles. In a search for suitable methods for evaluating bacterial sorption, autoradiographic techniques have been investigated; similarly, measurements of biomass have been used to examine the time course of bacterial sorption. In the present work, cell protein was used as a measure of monitoring the sorption of Thiobacillus ferrooxidans to various fine-grain particulates. The materials chosen for the study include both oxidizable substrates and inert particles that were not chemically altered during their exposure to the bacteria suspensions. In the present communication, the term ''sorption'' is used without regard to the electrochemical properties, charge effects, and biological mechanism of attachment, all of which influence the bacterial sorption on solids.

  12. FUNDAMENTAL KINETICS OF SUPERCRITICAL COAL LIQUEFACTION: EFFECT OF CATALYSTS AND HYDROGEN-DONOR SOLVENTS

    SciTech Connect

    Benjamin J. McCoy; J.M. Smith

    1998-08-01

    This report outlines a distribution kinetics approach to macromolecular reactions that has been applied to several processes. The objective was to develop an understanding of high-temperature, dense-phase thermolytic processes for complex macromolecular systems, such as coal. Experiments and theory are described for chemical models that simulate depolymerization of coal. The approach has been exceptionally successful for the model macromolecular systems. Development of a novel chemical reaction engineering analysis, based on distribution kinetics, was a major accomplishment of the current research.

  13. An investigation of the kinetics of hydrogen chemisorption on iron metal surfaces

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1982-01-01

    The isothermal kinetics of H2, H2S, and O2 chemisorption onto epitaxially grown (III) oriented Fe films were studied. The measurements were made using the techniques of chemisorption induced resistance change and Auger electron spectroscopy (for adsorbed sulfur and oxygen). Also the origin of the chemisorption induced resistance change for these systems and its applicability to kinetic measurements were established. The chemisorption kinetics were interpreted as dissociative chemisorption via an adsorbed molecular species. The applicable rate constants were established. In none of the studies were the rate constants observed to be coverage dependent. By comparing the temperature dependence of the rate constants with absolute rate theory, the binding energies and activation energies of all the kinetic processes were obtained for the H2/Fe system. The initial sticking coefficient was pressure dependent for both the H2/Fe and H2S/Fe systems. This results from the step between the adsorbed molecular state and the dissociated chemisorbed state being the rate limiting step for absorption at certain pressures and temperatures. Estimates were obtained for the temperature dependence of the rate constants for the O2/Fe system.

  14. Enhanced fluoride sorption by mechanochemically activated kaolinites.

    PubMed

    Meenakshi, S; Sundaram, C Sairam; Sukumar, Rugmini

    2008-05-01

    Kaolinite clay obtained from the mines was processed and studied for its fluoride sorption capacity. The surface area of the clay mineral was increased from 15.11 m(2)/g (raw) to 32.43 m(2)/g (activated) by mechanochemical activation. Batch adsorption studies were conducted to optimize various equilibrating conditions like the effect of contact time, dosage, pH for both raw and micronized kaolinites (RK and MK). The effect of other interfering anions on the defluoridation capacity (DC) of the sorbents was studied. Sorption of fluoride by the sorbents was observed over a wide pH range of 3-11. The studies revealed there is an enhanced fluoride sorption on MK. FTIR and XRD were used for the characterization of the sorbent. The surface morphology of the clay material was observed using SEM. The adsorption of fluoride was studied at three different temperatures, viz., 303, 313 and 323 K. The sorption data obtained at optimized conditions were subjected to Freundlich and Langmuir isotherms. Sorption intensity (1/n) (0.770-0.810) has been evaluated using Freundlich isotherm, whereas the values of sorption capacity Q(0) (0.609, 0.714 and 0.782 mg/g) and binding energy b (0.158, 0.145 and 0.133 L/mg) at three different temperatures have been estimated using Langmuir isotherm. Adsorption process was found to be controlled by both Freundlich and Langmuir isotherms. Thermodynamic studies revealed that the sorption of fluoride on MK is endothermic and a spontaneous process. The kinetic studies indicate that the sorption of fluoride on MK follows pseudo-first-order and intraparticle diffusion models.

  15. Competitive sorption of cadmium and lead in acid soils of central Spain

    SciTech Connect

    Serrano, S.; Garrido, F.; Campbell, C.G.; Garcia-Gonzolez, Maria Teresa

    2004-01-30

    The bioavailability and ultimate fate of heavy metals in the environment are controlled by chemical sorption. To assess competitive sorption of Pb and Cd, batch equilibrium experiments (generating sorption isotherms) and kinetics sorption studies were performed using single and binary metal solutions in surface samples of four soils from central Spain. For comparisons between soils, as well as, single and binary metal solutions, soil chemical processes were characterized using the Langmuir equation, ionic strength, and an empirical power function for kinetic sorption. In addition, soil pH and clay mineralogy were used to explain observed sorption processes. Sorption isotherms were well described by the Langmuir equation and the sorption kinetics were well described by an empirical power function within the reaction times in this study. Soils with higher pH and clay content (characterized by having smectite) had the greatest sorption capacity as estimated by the maximum sorption parameter (Q) of the Langmuir equation. All soils exhibited greater sorption capacity for Pb than Cd and the presence of both metals reduced the tendency for either to be sorbed although Cd sorption was affected to a greater extent than that of Pb. The Langmuir binding strength parameter (k) was always greater for Pb than for Cd. However, these k values tended to increase as a result of the simultaneous presence of both metals, that may indicate competition for sorption sites promoting the retention of both metals on more specific sorption sites. The kinetic experiments showed that Pb sorption is initially faster than Cd sorption from both single and binary solutions although the simultaneous presence of both metals affected the sorption of Cd at short times while only a minor effect was observed on Pb. The estimated exponents of the kinetic function were in all cases smaller for Pb than for Cd, likely due to diffusion processes into micropores or interlayer space of the clay minerals which

  16. Dual Studies on a Hydrogen-Deuterium Exchange of Resorcinol and the Subsequent Kinetic Isotope Effect

    ERIC Educational Resources Information Center

    Giles, Richard; Kim, Iris; Chao, Weyjuin Eric; Moore, Jennifer; Jung, Kyung Woon

    2014-01-01

    An efficient laboratory experiment has been developed for undergraduate students to conduct hydrogen-deuterium (H-D) exchange of resorcinol by electrophilic aromatic substitution using D[subscript 2]O and a catalytic amount of H[subscript 2]SO[subscript 4]. The resulting labeled product is characterized by [superscript 1]H NMR. Students also…

  17. Regenerative Sorption Refrigerator

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.; Wen, Liang-Chi; Bard, Steven

    1991-01-01

    Two-stage sorption refrigerator achieves increased efficiency via regenerative-heating concept in which waste heat from praseodymium/cerium oxide (PCO) chemisorption compressor runs charcoal/krypton (C/Kr) sorption compressor. Waste heat from each PCO sorption compressor used to power surrounding C/Kr sorption compressor. Flows of heat in two compressor modules controlled by gas-gap thermal switches. Has no wearing moving parts other than extremely long life, room-temperature check valves operating about twice per hour. Virtually no measurable vibration, and has potential operating life of at least ten years.

  18. Kinetics of hydrogen consumption by rumen fluid, anaerobic digestor sludge, and sediment.

    PubMed

    Robinson, J A; Tiedje, J M

    1982-12-01

    Michaelis-Menten kinetic parameters for H(2) consumption by three methanogenic habitats were determined from progress curve and initial velocity experiments. The influences of mass transfer resistance, endogenous H(2) production, and growth on apparent parameter estimates were also investigated. Kinetic parameters could not be determined for undiluted rumen fluid and some digestor sludge from gas-phase measurements of H(2), since mass transfer of H(2) across the gas-liquid interface was rate limiting. However, accurate values were obtained once the samples were diluted. H(2) consumption by digestor sludge with a long retention time and by hypereutrophic lake sediment was not phase transfer limited. The K(m) values for H(2) uptake by these habitats were similar, with means of 5.8, 6.0, and 7.1 muM for rumen fluid, digestor sludge, and sediment, respectively. V(max) estimates suggested a ratio of activity of approximately 100 (rumen fluid):10 (sludge):1 (sediment); their ranges were as follows: rumen fluid, 14 to 28 mM h; Holt sludge, 0.7 to 4.3 mM h; and Wintergreen sediment, 0.13 to 0.49 mM h. The principles of phase transfer limitation, studied here for H(2), are the same for all gaseous substrates and products. The limitations and errors associated with gas phase determination of kinetic parameters were evaluated with a mathematical model that combined mass transport and Michaelis-Menten kinetics. Three criteria are described which can be used to evaluate the possibility that a phase transfer limitation exists. If it does not exist, (i) substrate consumption curves are Michaelis-Menten and not first order, (ii) the K(m) is independent of initial substrate concentration, and (iii) the K(m) is independent of biomass (V(max)) and remains constant with dilution of sample. Errors in the Michaelis-Menten kinetic parameters are caused by endogenously produced H(2), but they were <15% for rumen fluid and 10% for lake sediment and digestor sludge. Increases in V

  19. Mechanochemistry of lithium nitride under hydrogen gas.

    PubMed

    Li, Z; Zhang, J; Wang, S; Jiang, L; Latroche, M; Du, J; Cuevas, F

    2015-09-14

    Hydrogen uptake during the mechanochemistry of lithium nitride under 9 MPa hydrogen pressure has been analyzed by means of in situ solid-gas absorption and ex situ X-ray diffraction (XRD) measurements. In situ hydrogenation curves show two H-sorption steps leading to an overall hydrogen uptake of 9.8 wt% H after 3 hours of milling. The milled end-products consist of nanocrystalline (∼10 nm) LiNH2 and LiH phases. The first reaction step comprises the transformation of the polymorph α-Li3N (S.G. P6/mmm) into the β-Li3N (S.G. P63/mmc) metastable phase and the reaction of the latter with hydrogen to form lithium imide: β-Li3N + H2→ Li2NH + LiH. Reaction kinetics of the first step is zero-order. Its rate-limiting control is assigned to the collision frequency between milling balls and Li3N powder. In the second absorption step, lithium imide converts to lithium amide following the reaction scheme Li2NH + H2→ LiNH2 + LiH. Reaction kinetics is here limited by one-dimensional nucleation and the growth mechanism, which, in light of structural data, is assigned to the occurrence of lithium vacancies in the imide compound. This study provides new insights into the reaction paths and chemical kinetics of light hydrogen storage materials during their mechanochemical synthesis.

  20. Structure of chitosan gels mineralized by sorption

    NASA Astrophysics Data System (ADS)

    Modrzejewska, Z.; Skwarczyńska, A.; Douglas, T. E. L.; Biniaś, D.; Maniukiewicz, W.; Sielski, J.

    2015-10-01

    The paper presents the structural studies of mineralized chitosan hydrogels. Hydrogels produced by using sodium beta-glycerophosphate (Na-β-GP) as a neutralizing agent. Mineralization was performed method "post loading", which consisted in sorption to the gels structure Ca ions. In order to obtain - in the structure of gels - compounds similar to the hydroxyapatites present naturally in bone tissue, gels after sorption were modified in: pH 7 buffer and sodium hydrogen phosphate. In order to determine the structural properties of the gels, the following methods were used: infrared spectroscopy with Fourier transformation, FTIR, X-ray diffractometry, XRD, scanning electron microscopy, SEM.

  1. The kinetics of iodide oxidation by hydrogen peroxide in acid solution

    NASA Astrophysics Data System (ADS)

    Milenković, M. C.; Stanisavljev, D. R.

    2011-12-01

    The kinetics of the complex reaction between I- and H2O2 in acid media was investigated. The particular attention was focused on the determination of the rate constant of the reaction between HIO and H2O2 involved in the investigated complex process. The examination of the whole kinetics was performed by simultaneously monitoring the evolution of O2 pressure, I{3/-} and I- concentrations. We modeled the behavior of experimentally followed components based on Liebhafsky's research. Our preliminary results suggest a significantly higher rate constant (3.5 × 107 M-1 s-1) of the reaction between HIO and H2O2 as those proposed in the literature.

  2. Nonlinear dynamics of hydrogen-air detonations with detailed kinetics and diffusion

    NASA Astrophysics Data System (ADS)

    Powers, Joseph; Romick, Christopher; Aslam, Tariq

    2014-11-01

    We consider the calculation of unsteady detonation in a mixture of calorically imperfect ideal gases with detailed kinetics. The use of detailed kinetics introduces multiple reaction length scales, and their interaction gives rise to complex dynamics. These are predicted using a wavelet-based adaptive mesh refinement technique and includes multi-component species, momentum, and energy diffusion, as well as DuFour and Soret effects. In the one-dimensional limit, we predict a transition from stability to unstable limit cycles as a driving piston velocity is lowered. At low overdrive, energy is partitioned into a variety of high frequency oscillatory modes. For weak low frequency instabilities, the dynamics are largely explained by a competition between advection and reaction time scales, with diffusion serving to perturb the dynamics. For higher frequency instabilities, the influence of diffusion is larger. We present new extensions to two-dimensional dynamics.

  3. Enantiodivergent Atroposelective Synthesis of Chiral Biaryls by Asymmetric Transfer Hydrogenation: Chiral Phosphoric Acid Catalyzed Dynamic Kinetic Resolution.

    PubMed

    Mori, Keiji; Itakura, Tsubasa; Akiyama, Takahiko

    2016-09-12

    Reported herein is an enantiodivergent synthesis of chiral biaryls by a chiral phosphoric acid catalyzed asymmetric transfer hydrogenation reaction. Upon treatment of biaryl lactols with aromatic amines and a Hantzsch ester in the presence of chiral phosphoric acid, dynamic kinetic resolution (DKR) involving a reductive amination reaction proceeded smoothly to furnish both R and S isomers of chiral biaryls with excellent enantioselectivities by proper choice of hydroxyaniline derivative. This trend was observed in wide variety of substrates, and various chiral biphenyl and phenyl naphthyl adducts were synthesized with satisfactory enantioselectivities in enantiodivergent fashion. The enantiodivergent synthesis of synthetically challenging, chiral o-tetrasubstituted biaryls were also accomplished, and suggests high synthetic potential of the present method. PMID:27491630

  4. An Investigation of the Effect of Surface Impurities on the Adsorption Kinetics of Hydrogen Chemisorbed onto Iron

    NASA Technical Reports Server (NTRS)

    Shanabarger, M. R.

    1997-01-01

    The original goal of this program was to investigate the effect surface impurities have on the heterogeneous kinetic processes of those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. However, shortly after the initiation of the original program, the program's NASA Technical Monitor, Dr. Howard Nelson, requested that the effort supported by this Co-operative Agreement be redirected to study more pressing materials issues associated to the development of the National Aero-Space Plane (NASP). The results of these efforts are outlined in this report. Detailed discussions of specific work, including experimental techniques and procedures, will be found in the publications listed with the subsection discussing that specific work as well and in Section 5. No inventions were generated or disclosed within this Agreement.

  5. Impact of Materials Processing on Microstructural Evolution and Hydrogen Isotope Storage Properties of Pd-Rh Alloy Powders.

    SciTech Connect

    Yee, Joshua K

    2015-02-01

    Cryomilled Pd - 10Rh was investiga ted as potential solid - state storage material of hydrogen. Pd - 10Rh was first atomized, and then subsequently cryomilled. The cryomilled Pd - 10Rh was then examined using microstructural characterization techniques including op tical microscopy, electron microscopy, and X - ray diffraction. Pd - 10Rh particles were significantly flattened, increasing the apparent surface area. Microstructural refinement was observed in the cryomilled Pd - 10Rh, generating grains at the nanom etric scale through dislocation - based activity. Hydrogen sorption properties were also characterized, generating both capacity as well as kinetics measurements. It was found that the microstructural refinement due to cryomilling did not play a significant role on hyd rogen sorption properties until the smallest grain size (on the order of %7E25 nm) was achieved. Additionally, the increased surface area and other changes in particle morphology were associated with cryomilling changed the kinetics of hydrogen absorption.

  6. Kinetic study of the effects of calcium ions on cationic artichoke (Cynara scolymus L.) peroxidase: calcium binding, steady-state kinetics and reactions with hydrogen peroxide.

    PubMed

    Hiner, Alexander N P; Sidrach, Lara; Chazarra, Soledad; Varón, Ramón; Tudela, José; García-Cánovas, Francisco; Rodríguez-López, José Neptuno

    2004-01-01

    The apparent catalytic constant (k(cat)) of artichoke (Cynara scolymus L.) peroxidase (AKPC) with 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) increased 130-fold in the presence of calcium ions (Ca2+) but the affinity (K(m)) of the enzyme for ABTS was 500 times lower than for Ca2+-free AKPC. AKPC is known to exhibit an equilibrium between 6-aquo hexa-coordinate and penta-coordinate forms of the haem iron that is modulated by Ca2+ and affects compound I formation. Measurements of the Ca2+ dissociation constant (K(D)) were complicated by the water-association/dissociation equilibrium yielding a global value more than 1000 times too high. The value for the Ca2+ binding step alone has now been determined to be K(D) approximately 10 nM. AKPC-Ca2+ was more resistant to inactivation by hydrogen peroxide (H(2)O(2)) and exhibited increased catalase activity. An analysis of the complex H(2)O(2) concentration dependent kinetics of Ca2+-free AKPC is presented.

  7. Implementation of steady state approximation for modelling of reaction kinetic of UV catalysed hydrogen peroxide oxidation of starch

    NASA Astrophysics Data System (ADS)

    Kumoro, Andri Cahyo; Retnowati, Diah Susetyo; Ratnawati, Budiyati, Catarina Sri

    2015-12-01

    With regard to its low viscosity, high stability, clarity, film forming and binding properties, oxidised starch has been widely used in various applications specifically in the food, paper, textile, laundry finishing and binding materials industries. A number of methods have been used to produce oxidised starch through reactions with various oxidizing agents, such as hydrogen peroxide, air oxygen, ozone, bromine, chromic acid, permanganate, nitrogen dioxide and hypochlorite. Unfortunately, most of previous works reported in the literatures were focused on the study of reaction mechanism and physicochemical properties characterization of the oxidised starches produced without investigation of the reaction kinetics of the oxidation process. This work aimed to develop a simple kinetic model for UV catalysed hydrogen peroxide oxidation of starch through implementation of steady state approximation for the radical reaction rates. The model was then verified using experimental data available in the literature. The model verification revealed that the proposed model shows its good agreement with the experimental data as indicated by an average absolute relative error of only 2.45%. The model also confirmed that carboxyl groups are oxidised further by hydroxyl radical. The carbonyl production rate was found to follow first order reaction with respect to carbonyl concentration. Similarly, carboxyl production rate also followed first order reaction with respect to carbonyl concentration. The apparent reaction rate constant for carbonyl formation and oxidation were 6.24 × 104 s-1 and 1.01 × 104 M-1.s-1, respectively. While apparent reaction rate constant for carboxyl oxidation was 4.86 × 104 M-1.s-1.

  8. Thermochemical and kinetics studies of the CH3SH+S (3P) hydrogen abstraction and insertion reactions.

    PubMed

    Cardoso, Daniely V V; Cunha, Leonardo A; Spada, Rene F K; Ferrão, Luiz F A; Roberto-Neto, Orlando; Machado, Francisco B C

    2014-09-01

    Sulfur-containing molecules have a significant impact on atmosphere and biosphere. In this work we studied, from the point of view of electronic structure and chemical kinetics methods, the elementary reactions between a methanethiol molecule and a sulfur atom leading to hydrogen abstraction C-S bond cleavage (CH(3)SH+S; R1:→ CH(3)S+SH; R2: → CH(2)SH+SH; R3:→ CH(3)+HS(2)). The geometrical structures of the reactants, products, and saddle points for the three reaction paths were optimized using the BB1K method with the aug-cc-pV(T+d)Z basis set. The thermochemical properties were improved using single point coupled-cluster (CCSD(T)) calculations on the BB1K geometries followed by extrapolation to the complete basis set (CBS) limit. This methodology was previously applied and has given accurate values of thermochemical and kinetics properties when compared to benchmark calculations and experimental data. For each reaction, the thermal rate constants were calculated using the improved canonical variational theory (ICVT) including the zero-curvature (ICVT/ZCT) and small-curvature (ICVT/SCT) tunneling corrections. For comparison, the overall ICVT/SCT reaction rate constant at 300 K obtained with single-point CCSD(T)/CBS calculations for the CH(3)SH+S reaction is approximately 1400 times lower than the isovalent CH(3)SH+O reaction, obtained with CVT/SCT. The reaction path involving the hydrogen abstraction from the thiol group is the most important reactive path in all temperatures.

  9. In-situ neutron investigation of hydrogen absorption kinetics in La(FexSi1-x)13 magnetocaloric alloys for room-temperature refrigeration application

    NASA Astrophysics Data System (ADS)

    Hai, Xueying; Mayer, Charlotte; Colin, Claire V.; Miraglia, Salvatore

    2016-02-01

    Promising magnetocaloric material La(Fe,Si)13 with a first-order magnetic transition has been widely investigated. The observed instability of hydrogen in the material is detrimental for its industrial upscale and a better control of the hydrogen absorption/desorption is necessary to optimize its application potential. In this article, the hydrogen absorption kinetics is studied through an in-situ neutron diffraction experiment. The results allow us to have an inside look at the structure "breathing" to accommodate the interstitial atoms and compare the effect of hydrides with carbohydrides.

  10. Ab initio study of the kinetics of hydrogen abstraction reactions on toluene and tetralin

    SciTech Connect

    Beste, Ariana; Britt, Phillip F; Buchanan III, A C; Harrison, Robert J; Hathorn, Bryan C

    2008-01-01

    Hydrogen abstraction reactions play a key role in many thermal and catalytic processes involved in the production of fuels and chemicals. In this paper, the reaction barriers and rate constants for the hydrogen abstraction reactions on toluene and tetralin by the benzyl radical are calculated by ab initio methods. These reactions are representatives of similar reactions occurring in the thermolysis of lignin model compounds containing the phenethyl phenyl ether (PPE) structural moiety. Thermolysis of PPE occurs by a free radical chain mechanism in which the product selectivity arises from competitive hydrogen abstraction at the benzylic and nonbenzylic methylen sites by chain carrying benzyl and phenoxyl radicals. The title reactions serve to calibrate the theoretical methods to be used in the study of PPE through comparison of the rate constants and the reaction enthalpies with reliable experimental values. In this study, we used two different hybrid density functionals (BHandHLYP, B3LYP) and second-order perturbation theory to obtain equilibrium and transition state geometries. Multiple transition states were found for both reactions. BHandHLYP underestimates and second-order perturbation theory overestimates the reaction barriers; B3LYP energy barriers agree well with experiment. Absolute and relative rate constants were calculated using transition state theory. We found that the relative rate constant using the B3LYP functional agrees within a factor of 2.0 with experiment at the experimental temperature of 333 K, indicating that the B3LYP functional will be successful in predicting relative rate constants for hydrogen abstraction reactions participating in the pyrolysis of PPE.

  11. One-step reduced kinetics for lean hydrogen-air deflagration

    SciTech Connect

    Fernandez-Galisteo, D.; Sanchez, A.L.; Linan, A.; Williams, F.A.

    2009-05-15

    A short mechanism consisting of seven elementary reactions, of which only three are reversible, is shown to provide good predictions of hydrogen-air lean-flame burning velocities. This mechanism is further simplified by noting that over a range of conditions of practical interest, near the lean flammability limit all reaction intermediaries have small concentrations in the important thin reaction zone that controls the hydrogen-air laminar burning velocity and therefore follow a steady state approximation, while the main species react according to the global irreversible reaction 2H{sub 2} + O{sub 2} {yields} 2H{sub 2}O. An explicit expression for the non-Arrhenius rate of this one-step overall reaction for hydrogen oxidation is derived from the seven-step detailed mechanism, for application near the flammability limit. The one-step results are used to calculate flammability limits and burning velocities of planar deflagrations. Furthermore, implications concerning radical profiles in the deflagration and reasons for the success of the approximations are clarified. It is also demonstrated that adding only two irreversible direct recombination steps to the seven-step mechanism accurately reproduces burning velocities of the full detailed mechanism for all equivalence ratios at normal atmospheric conditions and that an eight-step detailed mechanism, constructed from the seven-step mechanism by adding to it the fourth reversible shuffle reaction, improves predictions of O and OH profiles. The new reduced-chemistry descriptions can be useful for both analytical and computational studies of lean hydrogen-air flames, decreasing required computation times. (author)

  12. Degradation kinetics and mechanism of trace nitrobenzene by granular activated carbon enhanced microwave/hydrogen peroxide system.

    PubMed

    Tan, Dina; Zeng, Honghu; Liu, Jie; Yu, Xiaozhang; Liang, Yanpeng; Lu, Lanjing

    2013-07-01

    The kinetics of the degradation of trace nitrobenzene (NB) by a granular activated carbon (GAC) enhanced microwave (MW)/hydrogen peroxide (H202) system was studied. Effects of pH, NB initial concentration and tert-butyl alcohol on the removal efficiency were examined. It was found that the reaction rate fits well to first-order reaction kinetics in the MW/GAC/H202 process. Moreover, GAC greatly enhanced the degradation rate of NB in water. Under a given condition (MW power 300 W, H202 dosage 10 mg/L, pH 6.85 and temperature (60 +/- 5)degrees C), the degradation rate of NB was 0.05214 min-1when 4 g/L GAC was added. In general, alkaline pH was better for NB degradation; however, the optimum pH was 8.0 in the tested pH value range of 4.0-12.0. At H202 dosage of 10 mg/L and GAC dosage of 4 g/L, the removal of NB was decreased with increasing initial concentrations of NB, indicating that a low initial concentration was beneficial for the degradation of NB. These results indicated that the MW/GAC/H202 process was effective for trace NB degradation in water. Gas chromatography-mass spectrometry analysis indicated that a hydroxyl radical addition reaction and dehydrogenation reaction enhanced NB degradation. PMID:24218864

  13. Hydrogen peroxide release kinetics into saliva from different whitening products: a double-blind, randomized clinical trial.

    PubMed

    Marques, Duarte Nuno da Silva; da Mata, António Duarte Sola Pereira; Silveira, João Miguel Lourenço; Marques, Joana Rita Oliveira Faria; Amaral, João Pedro de Almeida Rato; Guilherme, Nuno Filipe Rito Parada Marques

    2012-02-01

    The objective of this study is to compare salivary hydrogen peroxide (HP) release kinetics and potential toxicity of systemic exposure of four different whitening products. A double-blind, randomized controlled trial was conducted in a Portuguese dental faculty clinic. Two hundred forty volunteers were randomized to eight intervention groups. Participants were randomly assigned to receive active or placebo applications of one of four different products: Opalescence 10% PF™ (OPL), Vivastyle® 10%™ (VS10%), Vivadent Paint On Plus™ (PO+), and Trés White Supreme™ (TWS). Saliva collection was obtained by established methods at different times. The HP salivary content was determined by a photometric method. Salivary HP variations, total amount of salivary HP, and counts of subjects above the safe daily HP dose were the main outcome measures. All whitening systems significantly released HP to the saliva when compared to placebo, and all showed different release kinetics. The adaptable tray system (TWS) presented a risk increase of 37% [20-54%, 95% confidence interval] when compared to the other systems. The use of an adaptable tray whitening system with higher concentration of HP increases the toxicity potential.

  14. Sorption of fibronectin to human root surfaces in vitro

    SciTech Connect

    Mendieta, C.; Caravana, C.; Fine, D.H. )

    1990-05-01

    The purpose of this study was to determine the conditions that favor the sorption and retention of human plasma fibronectin to cementum. Rectangular root segments prepared from teeth extracted for orthodontic reasons were mounted on a capillary pipette and immersed in solutions of {sup 125}I fibronectin for assay of cementum sorption under various conditions. Kinetic studies showed sorption to be rapid, with 77% of the maximum fibronectin sorption occurring within 1 minute. Fibronectin sorption was reduced when added in conjunction with serum and was inhibited by monovalent ions (such as sodium), but enhanced in the presence of divalent cations (such as calcium). Exposure of cementum to serum partially blocked subsequent sorption of fibronectin, while cementum bound fibronectin was eluted by subsequent exposure to serum. Treatment of cementum with citric acid pH 1.1 (4 minutes) followed by 5% sodium hypochlorite (5 minutes) caused a significant increase in fibronectin sorption with maximum retention upon subsequent exposure to serum (P less than 0.05). Fibronectin sorption to cementum was: rapid, electrostatic in nature, competitive, reversible, Ca+(+)-facilitated, and maximized by prior treatment of the root with citric acid and sodium hypochlorite. It is concluded that sorption of fibronectin to cementum can be achieved for clinical gain; however, conditions of application can significantly influence both accumulation and subsequent release of root sorbed material.

  15. Sorption of radionuclides by cement-based barrier materials

    SciTech Connect

    Li, Kefei Pang, Xiaoyun

    2014-11-15

    This paper investigates the sorption of radionuclide ions, {sup 137}Cs{sup +} and {sup 90}Sr{sup 2+}, by cement-based barrier materials for radioactive waste disposal. A mortar with ternary binder is prepared and powder samples are ground from the hardened material following a predetermined granulometry. After pre-equilibrium with an artificial pore solution, the sorption behaviors of powder samples are investigated through single sorption and blended sorption. The results show that: (1) no systematic difference is observed for single and blended sorptions thus the interaction between {sup 137}Cs{sup +} and {sup 90}Sr{sup 2+} sorptions must be weak; (2) the sorption kinetics is rapid and all characteristic times are less than 1d; (3) the sorption capacity is enhanced by C–A–S–H hydrates and the measured K{sub d} values can be predicted from C–S–H sorption data with Ca/Si ratio equal to Ca/(Si + Al) ratio.

  16. High-yield hydrogen production from biomass by in vitro metabolic engineering: Mixed sugars coutilization and kinetic modeling

    SciTech Connect

    Rollin, Joseph A.; Martin del Campo, Julia; Myung, Suwan; Sun, Fangfang; You, Chun; Bakovic, Allison; Castro, Roberto; Chandrayan, Sanjeev K.; Wu, Chang-Hao; Adams, Michael W. W.; Senger, Ryan S.; Zhang, Y. -H. Percival

    2015-04-06

    The use of hydrogen (H2) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H2 and CO2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H2 with a yield of two H2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was used to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H2 productivity was increased 3-fold to 32 mmol H2∙L₋1∙h₋1. The productivity was further enhanced to 54 mmol H2∙L₋1∙h₋1 by increasing reaction temperature, substrate, and enzyme concentrations—an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production.

  17. High-yield hydrogen production from biomass by in vitro metabolic engineering: Mixed sugars coutilization and kinetic modeling

    DOE PAGES

    Rollin, Joseph A.; Martin del Campo, Julia; Myung, Suwan; Sun, Fangfang; You, Chun; Bakovic, Allison; Castro, Roberto; Chandrayan, Sanjeev K.; Wu, Chang-Hao; Adams, Michael W. W.; et al

    2015-04-06

    The use of hydrogen (H2) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H2 and CO2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H2 with a yield of two H2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was usedmore » to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H2 productivity was increased 3-fold to 32 mmol H2∙L₋1∙h₋1. The productivity was further enhanced to 54 mmol H2∙L₋1∙h₋1 by increasing reaction temperature, substrate, and enzyme concentrations—an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production.« less

  18. High-yield hydrogen production from biomass by in vitro metabolic engineering: Mixed sugars coutilization and kinetic modeling.

    PubMed

    Rollin, Joseph A; Martin del Campo, Julia; Myung, Suwan; Sun, Fangfang; You, Chun; Bakovic, Allison; Castro, Roberto; Chandrayan, Sanjeev K; Wu, Chang-Hao; Adams, Michael W W; Senger, Ryan S; Zhang, Y-H Percival

    2015-04-21

    The use of hydrogen (H2) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H2 and CO2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H2 with a yield of two H2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was used to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H2 productivity was increased 3-fold to 32 mmol H2⋅L(-1)⋅h(-1). The productivity was further enhanced to 54 mmol H2⋅L(-1)⋅h(-1) by increasing reaction temperature, substrate, and enzyme concentrations--an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production.

  19. High-yield hydrogen production from biomass by in vitro metabolic engineering: Mixed sugars coutilization and kinetic modeling

    PubMed Central

    Rollin, Joseph A.; Martin del Campo, Julia; Myung, Suwan; Sun, Fangfang; You, Chun; Bakovic, Allison; Castro, Roberto; Chandrayan, Sanjeev K.; Wu, Chang-Hao; Adams, Michael W. W.; Senger, Ryan S.; Zhang, Y.-H. Percival

    2015-01-01

    The use of hydrogen (H2) as a fuel offers enhanced energy conversion efficiency and tremendous potential to decrease greenhouse gas emissions, but producing it in a distributed, carbon-neutral, low-cost manner requires new technologies. Herein we demonstrate the complete conversion of glucose and xylose from plant biomass to H2 and CO2 based on an in vitro synthetic enzymatic pathway. Glucose and xylose were simultaneously converted to H2 with a yield of two H2 per carbon, the maximum possible yield. Parameters of a nonlinear kinetic model were fitted with experimental data using a genetic algorithm, and a global sensitivity analysis was used to identify the enzymes that have the greatest impact on reaction rate and yield. After optimizing enzyme loadings using this model, volumetric H2 productivity was increased 3-fold to 32 mmol H2⋅L−1⋅h−1. The productivity was further enhanced to 54 mmol H2⋅L−1⋅h−1 by increasing reaction temperature, substrate, and enzyme concentrations—an increase of 67-fold compared with the initial studies using this method. The production of hydrogen from locally produced biomass is a promising means to achieve global green energy production. PMID:25848015

  20. Analysis of the lifetime and spatial localization of hydrogen peroxide generated in the cytosol using a reduced kinetic model.

    PubMed

    Lim, Joseph B; Huang, Beijing K; Deen, William M; Sikes, Hadley D

    2015-12-01

    Hydrogen peroxide (H2O2) acts as a signaling molecule via its reactions with particular cysteine residues of certain proteins. Determining the roles of direct oxidation by H2O2 versus disulfide exchange reactions (i.e. relay reactions) between oxidized and reduced proteins of different identities is a current focus. Here, we use kinetic modeling to estimate the spatial and temporal localization of H2O2 and its most likely oxidation targets during a sudden increase in H2O2 above the basal level in the cytosol. We updated a previous redox kinetic model with recently measured parameters for HeLa cells and used the model to estimate the length and time scales of H2O2 diffusion through the cytosol before it is consumed by reaction. These estimates were on the order of one micron and one millisecond, respectively. We found oxidation of peroxiredoxin by H2O2 to be the dominant reaction in the network and that the overall concentration of reduced peroxiredoxin is not significantly affected by physiological increases in intracellular H2O2 concentration. We used this information to reduce the model from 22 parameters and reactions and 21 species to a single analytical equation with only one dependent variable, i.e. the concentration of H2O2, and reproduced results from the complete model. The reduced kinetic model will facilitate future efforts to progress beyond estimates and precisely quantify how reactions and diffusion jointly influence the distribution of H2O2 within cells.

  1. Impact of coal structural heterogeneity on the nonideal sorption of organic contaminants.

    PubMed

    Shi, Xin; Fu, Heyun; Li, Yuan; Mao, Jingdong; Zheng, Shourong; Zhu, Dongqiang

    2011-06-01

    Carbonaceous geosorbents (black carbon, coal, and humin/kerogen) play a primary role in the nonideal sorption (isotherm nonlinearity, hysteresis, and multiphasic kinetics) of hydrophobic organic chemicals by soils and sediments. The present study investigated the impact of coal structural heterogeneity on sorption/desorption of two model monoaromatic compounds (1,3-dichlorobenzene and 1,3-dinitrobenzene). Due to the higher degree of aromaticity and condensation, anthracite showed stronger sorption affinity and nonlinearity and slower sorption kinetics than lignite. Removal of humic substances by alkali extraction and/or mineral fraction by acidification did not much affect organic carbon-normalized sorption coefficient to the coal, suggesting nearly complete accessibility of adsorption sites on the condensed organic carbon. However, the treatments greatly increased sorption kinetics and meanwhile alleviated hysteresis of 1,3-dinitrobenzene, as compared with the original lignite. These observations were attributed to the enhanced exposure of high-energy adsorption sites on the condensed organic carbon after exfoliating the surface coverage by humic substances and minerals. An empirical biphasic pseudo-second-order model consisting of a fast sorption phase and a slow sorption phase adequately quantified the overall sorption kinetics for the coal sorbents. The results indicated that the condensed organic carbon, in combination with other structural components, controls the nonideal sorption of unburned coal.

  2. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    SciTech Connect

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Bornath, T.; Bredow, R.; Doppner, T.; Fennel, T.; Fletcher, L. B.; Forster, E.; Gode, S.; Gregori, G.; Harmand, M.; Hilbert, V.; Laarmann, T.; Lee, H. J.; Ma, T.; Meiwes-Broer, K. H.; Mithen, J. P.; Murphy, C. D.; Nakatsutsumi, M.; Neumayer, P.; Przystawik, A.; Skruszewicz, S.; Tiggesbaumker, J.; Toleikis, S.; White, T. G.; Glenzer, S. H.; Redmer, R.; Tschentscher, T.

    2015-09-25

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of ${10}^{15}-{10}^{16}\\;$ W cm–2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about $25$ and $40\\;\\mathrm{eV}$ for simulated delay times up to $+70\\;\\mathrm{fs}$ after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and $30\\;$eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. In conclusion, we resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.

  3. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    NASA Astrophysics Data System (ADS)

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Becker, A.; Bornath, T.; Bredow, R.; Döppner, T.; Fennel, T.; Fletcher, L. B.; Förster, E.; Göde, S.; Gregori, G.; Harmand, M.; Hilbert, V.; Laarmann, T.; Lee, H. J.; Ma, T.; Meiwes-Broer, K. H.; Mithen, J. P.; Murphy, C. D.; Nakatsutsumi, M.; Neumayer, P.; Przystawik, A.; Skruszewicz, S.; Tiggesbäumker, J.; Toleikis, S.; White, T. G.; Glenzer, S. H.; Redmer, R.; Tschentscher, T.

    2015-11-01

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities of {10}15-{10}16 W cm-2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about 25 and 40 {eV} for simulated delay times up to +70 {fs} after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8-18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and 30 eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. We resolved the time-scale for laser-heating of hydrogen, and PIC results for laser-matter interaction were successfully tested against the experiment data.

  4. Kinetics and mechanisms of iron sulfide reductions in hydrogen and in carbon monoxide

    USGS Publications Warehouse

    Wiltowski, T.; Hinckley, C.C.; Smith, Gerard V.; Nishizawa, T.; Saporoschenko, Mykola; Shiley, R.H.; Webster, J.R.

    1987-01-01

    The reduction of iron sulfides by hydrogen and by carbon monoxide has been studied using plug flow and thermogravimetric methods. The reactions were studied in the 523-723??K temperature range and were found to be first-order processes. Plug flow studies were used to correlate reaction rates between pyrite and the gases as a function of the surface area of the pyrite. The rate of H2S formation increases with the surface area of the pyrite sample. The results of thermogravimetric experiments indicate that the reactions consist of several steps. Rate constants for the pyrite reduction by H2 and by CO were obtained. The activation energies increased with degree of reduction. Values of Ea were 113.2 (step I) and 122.5 kJ/mole (step II) for pyrite reduction with CO and 99.4 (step I), 122.4 (step II), 125.2 (step III), and 142.6 kJ/mole (step IV) for pyrite reduction with hydrogen. ?? 1987.

  5. A model of redox kinetics implicates the thiol proteome in cellular hydrogen peroxide responses.

    PubMed

    Adimora, Nnenna J; Jones, Dean P; Kemp, Melissa L

    2010-09-15

    Hydrogen peroxide is appreciated as a cellular signaling molecule with second-messenger properties, yet the mechanisms by which the cell protects against intracellular H(2)O(2) accumulation are not fully understood. We introduce a network model of H(2)O(2) clearance that includes the pseudo-enzymatic oxidative turnover of protein thiols, the enzymatic actions of catalase, glutathione peroxidase, peroxiredoxin, and glutaredoxin, and the redox reactions of thioredoxin and glutathione. Simulations reproduced experimental observations of the rapid and transient oxidation of glutathione and the rapid, sustained oxidation of thioredoxin on exposure to extracellular H(2)O(2). The model correctly predicted early oxidation profiles for the glutathione and thioredoxin redox couples across a range of initial extracellular [H(2)O(2)] and highlights the importance of cytoplasmic membrane permeability to the cellular defense against exogenous sources of H(2)O(2). The protein oxidation profile predicted by the model suggests that approximately 10% of intracellular protein thiols react with hydrogen peroxide at substantial rates, with a majority of these proteins forming protein disulfides as opposed to protein S-glutathionylated adducts. A steady-state flux analysis predicted an unequal distribution of the intracellular anti-oxidative burden between thioredoxin-dependent and glutathione-dependent antioxidant pathways, with the former contributing the majority of the cellular antioxidant defense due to peroxiredoxins and protein disulfides.

  6. Ultrafast electron kinetics in short pulse laser-driven dense hydrogen

    DOE PAGES

    Zastrau, U.; Sperling, P.; Fortmann-Grote, C.; Becker, A.; Bornath, T.; Bredow, R.; Doppner, T.; Fennel, T.; Fletcher, L. B.; Forster, E.; et al

    2015-09-25

    Dense cryogenic hydrogen is heated by intense femtosecond infrared laser pulses at intensities ofmore » $${10}^{15}-{10}^{16}\\;$$ W cm–2. Three-dimensional particle-in-cell (PIC) simulations predict that this heating is limited to the skin depth, causing an inhomogeneously heated outer shell with a cold core and two prominent temperatures of about $25$ and $$40\\;\\mathrm{eV}$$ for simulated delay times up to $$+70\\;\\mathrm{fs}$$ after the laser pulse maximum. Experimentally, the time-integrated emitted bremsstrahlung in the spectral range of 8–18 nm was corrected for the wavelength-dependent instrument efficiency. The resulting spectrum cannot be fit with a single temperature bremsstrahlung model, and the best fit is obtained using two temperatures of about 13 and $$30\\;$$eV. The lower temperatures in the experiment can be explained by missing energy-loss channels in the simulations, as well as the inclusion of hot, non-Maxwellian electrons in the temperature calculation. In conclusion, we resolved the time-scale for laser-heating of hydrogen, and PIC results for laser–matter interaction were successfully tested against the experiment data.« less

  7. Sorption behavior of fluoride ions from aqueous solutions by hydroxyapatite.

    PubMed

    Jiménez-Reyes, M; Solache-Ríos, M

    2010-08-15

    The effects of pH, contact time, fluoride-ion concentration, and the dose of sorbent on the sorption of fluoride ions by hydroxyapatite were studied. Equilibrium was reached in 16 h of contact time and the maximum sorption of fluoride ions was in the pH(eq) range between 5 and 7.3. The highest efficiency in the sorption system was determined by using 0.01 g of hydroxyapatite and 25 mL of solution. The pseudo-second order model described the kinetic sorption processes, and the Freundlich model, the sorption isotherm process. These results indicated that the mechanism was chemisorption on a heterogeneous material. Fluoride ions were partially desorbed using an alkaline solution.

  8. Promising gaseous and electrochemical hydrogen storage properties of porous Mg-Pd films under mild conditions.

    PubMed

    Xin, Gongbiao; Yuan, Huiping; Jiang, Lijun; Wang, Shumao; Liu, Xiaopeng; Li, Xingguo

    2015-05-28

    In this paper, the gaseous and electrochemical hydrogen storage properties of 200 nm Mg-Pd thin films with different morphologies have been investigated. The results show that Mg-Pd films become porous with the increase of substrate temperature. Porous Mg-Pd films exhibit superior gaseous and electrochemical hydrogen storage behaviors under mild conditions, including rapid hydrogen sorption kinetics, a large hydrogen storage amount, high electrochemical discharge capacity, and a fast hydrogen diffusion rate. The excellent behaviors of porous Mg-Pd films might be ascribed to the significantly shortened hydrogen diffusion paths and the large contact areas between the hydrogen gas and the solid Mg phases, which are elucidative for the development and applications of thick Mg-Pd films.

  9. Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

    PubMed

    Zhang, Xin; Liu, Yongfeng; Wang, Ke; Li, You; Gao, Mingxia; Pan, Hongge

    2015-12-21

    A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability. PMID:26632764

  10. Ultrafine Nanocrystalline CeO2@C-Containing NaAlH4 with Fast Kinetics and Good Reversibility for Hydrogen Storage.

    PubMed

    Zhang, Xin; Liu, Yongfeng; Wang, Ke; Li, You; Gao, Mingxia; Pan, Hongge

    2015-12-21

    A nanocrystalline CeO2@C-containing NaAlH4 composite is successfully synthesized in situ by hydrogenating a NaH-Al mixture doped with CeO2@C. Compared with NaAlH4 , the as-prepared CeO2@C-containing NaAlH4 composite, with a minor amount of excess Al, exhibits significantly improved hydrogen storage properties. The dehydrogenation onset temperature of the hydrogenated [NaH-Al-7 wt % CeO2@C]-0.04Al sample is 77 °C lower than that of the pristine sample because of a reduced kinetic barrier. More importantly, the dehydrogenated sample absorbs ∼4.7 wt % hydrogen within 35 min at 100°C and 10 MPa of hydrogen. Compositional and structural analyses reveal that CeO2 is converted to CeH2 during ball milling and that the newly formed CeH2 works with the excess of Al to synergistically improve the hydrogen storage properties of NaAlH4. Our findings will aid in the rational design of novel catalyst-doped complex hydride systems with low operating temperatures, fast kinetics, and long-term cyclability.

  11. Picosecond kinetics of excited state decay processes in internally hydrogen-bonded polymer photostabilizers

    NASA Technical Reports Server (NTRS)

    Huston, A. L.; Scott, G. W.

    1982-01-01

    A construction of economically practical solar energy conversion devices could be based on the employment of inexpensive, visible-radiation transparent, durable, light-fast materials. Difficulties arise in connection with the availability of such materials. Plastics which are not particularly susceptible to solar ultraviolet degradation are, in general, expensive, while less expensive optically transparent films are susceptible to deterioration when exposed to solar radiation. However, techniques are known for protecting polymers from photochemical degradation. According to these techniques, the composition or structure of polymeric material is modified by incorporation of photostabilizers. Two classes of ultraviolet absorbers are used as commercial photostabilizers. These classes include 2-hydroxybenzophenone (HB) and 2-(2-prime -hydroxyphenyl)benzotriazole (HPB). The present investigation is concerned with the results of spectroscopic and kinetics measurements related to the study of the mechanism of excited-state relaxation of polymer photostabilizers in the class HB and HPB.

  12. Gastrointestinal distribution and kinetic characterization of the sodium-hydrogen exchanger isoform 8 (NHE8).

    PubMed

    Xu, Hua; Chen, Huacong; Dong, Jiali; Lynch, Ronald; Ghishan, Fayez K

    2008-01-01

    NHE8 is a newly identified NHE isoform expressed in rat intestine. To date, the kinetic characteristics and the intestinal segmental distribution of this NHE isoform have not been studied. This current work was performed to determine the gene expression pattern of the NHE8 transporter along the gastrointestinal tract, as well as its affinity for Na(+), H(+), and sensitivity to known NHE inhibitors HOE694 and S3226. NHE8 was differentially expressed along the GI tract. Higher NHE8 expression was seen in stomach, duodenum, and ascending colon in human, while higher NHE8 expression was seen in jejunum, ileum and colon in adult mouse. Moreover, the expression level of NHE8 is much higher in the stomach and jejunum in young mice compared with adult mice. To evaluate the functional characterictics of NHE8, the pH indicator SNARF-4 was used to monitor the rate of intra-cellular pH (pH(i)) recovery after an NH(4)Cl induced acid load in NHE8 cDNA transfected PS120 cells. The NHE8 cDNA transfected cells exhibited a sodium-dependent proton exchanger activity having a Km for pH(i) of approximately pH 6.5, and a Km for sodium of approximately 23 mM. Low concentration of HOE694 (1 microM) had no effect on NHE8 activity, while high concentration (10 microM) significantly reduced NHE8 activity. In the presence of 80 microM S3226, the NHE8 activity was also inhibited significantly. In conclusion, our work suggests that NHE8 is expressed along the gastrointestinal tract and NHE8 is a functional Na(+)/H(+) exchanger with kinetic characteristics that differ from other apically expressed NHE isoforms.

  13. Iridium Catalyzed Dehydrogenation of Substituted Amine Boranes: Kinetics, Thermodynamics and Implications for Hydrogen Storage.

    SciTech Connect

    Dietrich, Brandon L.; Goldberg, Karen I.; Heinekey, D. M.; Autrey, Thomas; Linehan, John C.

    2008-10-06

    Dehydrogenation of ammonia borane (AB) and methylamine-borane (MeAB) is catalyzed efficiently by the iridium pincer complex (η3-1,3-(OPtBu2)2C6H3)Ir(H)2 (1). With MeAB and with MeAB/AB mixtures, rapid release of one equivalent of H2 is observed to yield soluble oligomeric products at rates similar to those previously reported for the dehydrogenation of AB catalyzed by 1. The rapid dehydrogenation reaction has allowed the experimental determination of the reaction enthalpy (ΔH) for the dehydrogenation of AB, MeAB, and AB/MeAB mixtures by calorimetry. The reactions are significantly more exothermic than suggested by some computational studies. This work was supported by the U.S. Department of Energy (DOE) as part of the Center of Excellence for Chemical Hydrogen Storage. PNNL is operated by Battelle for DOE.

  14. Reduction of ferrylmyoglobin by hydrogen sulfide. Kinetics in relation to meat greening.

    PubMed

    Libardi, Silvia H; Pindstrup, Helene; Cardoso, Daniel R; Skibsted, Leif H

    2013-03-20

    The hypervalent meat pigment ferrylmyoglobin, MbFe(IV)═O, characteristic for oxidatively stressed meat and known to initiate protein cross-linking, was found to be reduced by hydrogen sulfide to yield sulfmyoglobin. Horse heart myoglobin, void of cysteine, was used to avoid possible interference from protein thiols. For aqueous solution, the reactions were found to be second-order, and an apparent acid catalysis could be quantitatively accounted for in terms of a fast reaction between protonated ferrylmyoglobin, MbFe(IV)═O,H(+), and hydrogen sulfide, H2S (k2 = (2.5 ± 0.1) × 10(6) L mol(-1) s(-1) for 25.0 °C, ionic strengh 0.067, dominating for pH < 4), and a slow reaction between MbFe(IV)═O and HS(-) (k2 = (1.0 ± 0.7) × 10(4) L mol(-1) s(-1) for 25.0 °C, ionic strengh 0.067, dominating for pH > 7). For meat pH, a reaction via the transition state {MbFe(IV)═O···H···HS}([symbol: see text]) contributed significantly, and this reaction appeared almost independent of temperature with an apparent energy of activation of 2.1 ± 0.7 kJ mol(-1) at pH 7.4, as a result of compensation among activation energies and temperature influence on pKa values explaining low temperature greening of meat.

  15. Utilization of optical polarization microscopy in the study of sorption characteristics of wound dressing host materials.

    PubMed

    Devetak, Miha; Peršin, Zdenka; Stana-Kleinschek, Karin; Maver, Uroš

    2014-04-01

    Polarization microscopy was used for evaluation of kinetics of diclofenac sorption in three different wound dressing materials. The sorption kinetics can be evaluated by radii change and intensity of the light traveling through the fiber. The most frequently used host materials for drugs in wound dressings are alginate, polyesters such as polyethylene terephthalate, and viscose. We studied sorption of diclofenac as an example drug. Effective, but rather simple in vitro simulation of diclofenac sorption gives insight into the applicability of the mentioned materials for development of wound healing materials.

  16. Molecular Scale Assessment of Methylarsenic Sorption on Aluminum Oxide

    SciTech Connect

    Shimizu, M.; Ginder-Vogel, M; Parikh, S; Sparks, D

    2010-01-01

    Methylated forms of arsenic (As), monomethylarsenate (MMA) and dimethylarsenate (DMA), have historically been used as herbicides and pesticides. Because of their large application to agriculture fields and the toxicity of MMA and DMA, the sorption of methylated As to soil constituents requires investigation. MMA and DMA sorption on amorphous aluminum oxide (AAO) was investigated using both macroscopic batch sorption kinetics and molecular scale extended X-ray absorption fine structure (EXAFS) and Fourier transform infrared (FTIR) spectroscopic techniques. Sorption isotherm studies revealed sorption maxima of 0.183, 0.145, and 0.056 mmol As/mmol Al for arsenate (As{sup V}), MMA, and DMA, respectively. In the sorption kinetics studies, 100% of added As{sup V} was sorbed within 5 min, while 78% and 15% of added MMA and DMA were sorbed, respectively. Desorption experiments, using phosphate as a desorbing agent, resulted in 30% release of absorbed As{sup V}, while 48% and 62% of absorbed MMA and DMA, respectively, were released. FTIR and EXAFS studies revealed that MMA and DMA formed mainly bidentate binuclear complexes with AAO. On the basis of these results, it is proposed that increasing methyl group substitution results in decreased As sorption and increased As desorption on AAO.

  17. Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide.

    PubMed

    Huang, Liubin; Zhao, Yue; Li, Huan; Chen, Zhongming

    2015-09-15

    Heterogeneous reaction of SO2 on mineral dust seems to be an important sink for SO2. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H2O2) in this reaction. Here, we investigated the uptake kinetics of SO2 on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H2O2 at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γc). We found that with increasing RH, the γc decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H2O2 can promote the uptake of SO2 on mineral dust at different RHs. The probable explanations are that H2O2 rapidly reacts with SO2 on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H2O2 on the mineral dust, immediately react with adsorbed SO2 as well. Our results suggest that the removal of SO2 via the heterogeneous reaction on mineral dust is an important sink for SO2 and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere. PMID:26281003

  18. Kinetics of Heterogeneous Reaction of Sulfur Dioxide on Authentic Mineral Dust: Effects of Relative Humidity and Hydrogen Peroxide.

    PubMed

    Huang, Liubin; Zhao, Yue; Li, Huan; Chen, Zhongming

    2015-09-15

    Heterogeneous reaction of SO2 on mineral dust seems to be an important sink for SO2. However, kinetic data about this reaction on authentic mineral dust are scarce and are mainly limited to low relative humidity (RH) conditions. In addition, little is known about the role of hydrogen peroxide (H2O2) in this reaction. Here, we investigated the uptake kinetics of SO2 on three authentic mineral dusts (i.e., Asian mineral dust (AMD), Tengger desert dust (TDD), and Arizona test dust (ATD)) in the absence and presence of H2O2 at different RHs using a filter-based flow reactor, and applied a parameter (effectiveness factor) to the estimation of the effective surface area of particles for the calculation of the corrected uptake coefficient (γc). We found that with increasing RH, the γc decreases on AMD particles, but increases on ATD and TDD particles. This discrepancy is probably due to the different mineralogy compositions and aging extents of these dust samples. Furthermore, the presence of H2O2 can promote the uptake of SO2 on mineral dust at different RHs. The probable explanations are that H2O2 rapidly reacts with SO2 on mineral dust in the presence of adsorbed water, and OH radicals, which can be produced from the heterogeneous decomposition of H2O2 on the mineral dust, immediately react with adsorbed SO2 as well. Our results suggest that the removal of SO2 via the heterogeneous reaction on mineral dust is an important sink for SO2 and has the potential to alter the physicochemical properties (e.g., ice nucleation ability) of mineral dust particles in the atmosphere.

  19. Effects of protein-ligand interactions on hydrogen/deuterium exchange kinetics: canonical and noncanonical scenarios.

    PubMed

    Sowole, Modupeola A; Konermann, Lars

    2014-07-01

    Hydrogen/deuterium exchange (HDX) methods are widely used for monitoring protein-ligand interactions. This approach relies on the fact that ligand binding can modulate the extent of protein structural fluctuations that transiently disrupt hydrogen bonds and expose backbone amides to the solvent. It is commonly observed that ligand binding causes a reduction of HDX rates. This reduction can be restricted to elements adjacent to the binding site, but other regions can be affected as well. Qualitatively, ligand-induced HDX protection can be rationalized on the basis of two-state models that equate structural dynamics with global unfolding/refolding. Unfortunately, such models tend to be unrealistic because the dynamics of native proteins are dominated by subglobal transitions and local fluctuations. Ligand binding lowers the ground-state free energy. It is not obvious why this should necessarily be accompanied by a depletion of excited-state occupancies, which would be required for a reduction of HDX rates. Here, we propose a framework that implies that ligand binding can either slow or accelerate amide deuteration throughout the protein. These scenarios are referred to as "type 1" and "type 2", respectively. Evidence for type 1 binding is abundant in the literature, whereas the viability of type 2 interactions is less clear. Using HDX mass spectrometry (MS), we demonstrate that the oxygenation of hemoglobin (Hb) provides a dramatic example of a type 2 scenario. The observed behavior is consistent with cooperative T → R switching, where part of the intrinsic O2 binding energy is reinvested for destabilization of the ground state. This destabilization increases the Boltzmann occupancy of unfolded conformers, thereby enhancing HDX rates. Surprisingly, O2 binding to myoglobin (Mb) also induces elevated HDX rates. These Mb data reveal that type 2 behavior is not limited to cooperative multisubunit systems. Although enhanced protection from deuteration is widely

  20. Inhibition of Tafel Kinetics for Electrolytic Hydrogen Evolution on Isolated Micron Scale Electrocatalysts on Semiconductor Interfaces.

    PubMed

    Coridan, Robert H; Schichtl, Zebulon G; Sun, Tao; Fezzaa, Kamel

    2016-09-21

    Semiconductor-liquid junctions are ubiquitous in photoelectrochemical approaches to artificial photosynthesis. By analogy with the antennae and reaction centers in natural photosynthetic complexes, separating the light-absorbing semiconductor and electrocatalysts can improve catalytic efficiency. A catalytic layer can also impair the photovoltage-generating energetics of the electrode without appropriate microscopic organization of catalytically active area on the surface. Here, we have developed a method using high-speed X-ray phase contrast imaging to study in situ electrolytic bubble growth on semiconductor electrodes fabricated with isolated, micron-scale platinum electrocatalysts. X-rays are a nonperturbative probe by which gas evolution dynamics can be studied under conditions relevant to solar fuels applications. The self-limited growth of a bubble residing on the isolated electrocatalyst was measured by tracking the evolution of the gas-liquid boundary. Contrary to observations on macroscopic electrodes, bubble evolution on isolated, microscopic Pt pads on Si electrodes was insensitive to increasing overpotential. The persistence of the bubble causes mass transport limitations and inhibits the expected Tafel-like kinetics. The observed scaling of catalytic current densities with pad size implies that electrolysis is occurring predominantly on the perimeter of the active area. PMID:27575549

  1. Water gas shift reaction kinetics and reactor modeling for fuel cell grade hydrogen

    NASA Astrophysics Data System (ADS)

    Choi, Yongtaek; Stenger, Harvey G.

    The kinetics of the water gas shift reaction was studied to evaluate existing reaction mechanisms, test various rate expressions and simulate the performance in a methanol fuel processor for fuel cell applications. The reaction was carried out in a micro reactor testing unit using a commercial Sud-Chemie Cu/ZnO/Al 2O 3 catalyst between 120 and 250 °C with a range of feed rates and compositions. Using non-linear least squares optimization, the parameters in five rate expressions were fit to the experimental data. Based on a review of published work on the WGS reaction mechanism, our study found that a rate expression derived from a regenerative mechanism and another rate expression derived from adsorptive mechanism fit the experimental data equally well. Numerical integration of a one-dimensional PFR model was used for this parameter fitting. An empirical rate expression, rCO= kPCOPH 2O (1- β) with activation energy of 47.4 kJ/mol was also obtained from the experimental data. Reactor performance was simulated to determine catalyst loadings required to achieve specific CO conversions as a function of temperature and water feed rate. These results are useful in studying the design trade offs available to reformer systems.

  2. Modeling kinetic processes controlling hydrogen and acetate concentrations in an aquifer-derived microcosm.

    PubMed

    Watson, Ian A; Oswald, Sascha E; Mayer, K Ulrich; Wu, Youxian; Banwart, Steven A

    2003-09-01

    Groundwater contaminants may degrade via fermentation to intermediate species, which are subsequently consumed by terminal electron-accepting processes (TEAPs). A numerical model of an aquifer-derived laboratory microcosm is developed to simulate the dynamic behavior of fermentation and respiration in groundwater by coupling microbial growth and substrate utilization kinetics with a formulation that also includes aqueous speciation and other geochemical reactions including surface complexation, mineral dissolution, and precipitation. The model is used to test approaches that currently make use of H2(aq) to diagnose prevalent TEAPs in groundwater. Competition between TEAPs is integral to the conceptual model of the simulation, and the results indicate that competitive exclusion is significant but with some overlap found in the temporal sequence of TEAPs. Steady-state H2(aq) concentrations observed during different TEAPs do not differ significantly. The results are not consistent with previous applications of the partial equilibrium approach since most TEAP redox pairs exhibit free energies that suggest a particular process is able to proceed, yet observations here show that this process does not proceed.

  3. Effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene.

    PubMed

    Wang, Peng; Hua, Zulin; Cai, Yunjie; Shen, Xia; Li, Qiongqiong; Liu, Xiaoyuan

    2015-08-01

    The sorption behaviors of pollutants affected by hydrodynamic conditions were confirmed in natural water environment. The effects of hydrodynamic conditions on the sorption behaviors of aniline on sediment with coexistence of nitrobenzene were investigated. The particle entrainment simulator (PES) was used to simulate varied bottom shear stresses. The batch equilibrium method was applied to the experiments with the stress levels and the action time controlled at 0.2-0.5 N/m(2) and 24 h, respectively. The findings indicated that apparent partition coefficient of aniline on sediment increased with the shear stress significantly, while decreased with nitrobenzene concentration. On the contrary, both the sorption amount of aniline on suspended particulate matter (Q s) and the effect of nitrobenzene concentration on Q s declined as the shear stress increased. The sorption kinetic results showed that the sorption process followed the pseudo-second-order kinetics equation, and the process included two stages: fast sorption stage and slow sorption stage, among which the average sorption rate of fast stage was 7.5-9.5 times that of slow one. The effect of shear stress on the average sorption rate of aniline was enhanced with the increase of nitrobenzene concentration. And shear stress weakened the disturbance of cosolute on main solute sorption process. In addition, experiment results of sorption kinetic show that only the initial sorption rate was affected by shear stress and cosolute concentration. In the first 5 min, shear stress had positive effects on the sorption rate. After that, the sorption rate barely changed with shear stress and cosolute concentration.

  4. Reaction kinetics of hydrogen peroxide with copper and iron in sea water

    SciTech Connect

    Moffett, J.W.; Zika, R.G.

    1987-08-01

    The oxidation of Fe(II) and Cu(I) and the reduction of Fe(III) and Cu(II) by hydrogen peroxide in sea water have been studied to understand their mechanisms and probable significance in the upper marine water column. At 10/sup -7/ M H/sub 2/O/sub 2/, a level commonly found in surface sea water, reaction with H/sub 2/O/sub 2/ is the dominant oxidation pathway for Fe(II). Reduction of Fe(III) by peroxide was not observed in the pH range 7-8. Reduction of Cu(II) and oxidation of Cu(I) by H/sub 2/O/sub 2/ contribute to a dynamic redox cycling of that element in the upper water column. Calculations based on these data indicate that CU(I) oxidation and FE(II) oxidation by H/sub 2/O/sub 2/ are at least as important as nitrite photolysis as a source of OH radicals in the ocean. 47 references, 6 figures, 2 tables.

  5. Sorption of Lincomycin by Manure-Derived Biochars from Water.

    PubMed

    Liu, Cheng-Hua; Chuang, Ya-Hui; Li, Hui; Teppen, Brian J; Boyd, Stephen A; Gonzalez, Javier M; Johnston, Cliff T; Lehmann, Johannes; Zhang, Wei

    2016-03-01

    The presence of antibiotics in agroecosystems raises concerns about the proliferation of antibiotic-resistant bacteria and adverse effects to human health. Soil amendment with biochars pyrolized from manures may be a win-win strategy for novel manure management and antibiotics abatement. In this study, lincomycin sorption by manure-derived biochars was examined using batch sorption experiments. Lincomycin sorption was characterized by two-stage kinetics with fast sorption reaching quasi-equilibrium in the first 2 d, followed by slow sorption over 180 d. The fast sorption was primarily attributed to surface adsorption, whereas the long-term slow sorption was controlled by slow diffusion of lincomycin into biochar pore structures. Two-day sorption experiments were performed to explore effects of biochar particle size, solid/water ratio, solution pH, and ionic strength. Lincomycin sorption to biochars was greater at solution pH 6.0 to 7.5 below the dissociation constant of lincomycin (7.6) than at pH 9.9 to 10.4 above its dissociation constant. The enhanced lincomycin sorption at lower pH likely resulted from electrostatic attraction between the positively charged lincomycin and the negatively charged biochar surfaces. This was corroborated by the observation that lincomycin sorption decreased with increasing ionic strength at lower pH (6.7) but remained constant at higher pH (10). The long-term lincomycin sequestration by biochars was largely due to pore diffusion plausibly independent of solution pH and ionic composition. Therefore, manure-derived biochars had lasting lincomycin sequestration capacity, implying that biochar soil amendment could significantly affect the distribution, transport, and bioavailability of lincomycin in agroecosystems.

  6. Sorption of Lincomycin by Manure-Derived Biochars from Water.

    PubMed

    Liu, Cheng-Hua; Chuang, Ya-Hui; Li, Hui; Teppen, Brian J; Boyd, Stephen A; Gonzalez, Javier M; Johnston, Cliff T; Lehmann, Johannes; Zhang, Wei

    2016-03-01

    The presence of antibiotics in agroecosystems raises concerns about the proliferation of antibiotic-resistant bacteria and adverse effects to human health. Soil amendment with biochars pyrolized from manures may be a win-win strategy for novel manure management and antibiotics abatement. In this study, lincomycin sorption by manure-derived biochars was examined using batch sorption experiments. Lincomycin sorption was characterized by two-stage kinetics with fast sorption reaching quasi-equilibrium in the first 2 d, followed by slow sorption over 180 d. The fast sorption was primarily attributed to surface adsorption, whereas the long-term slow sorption was controlled by slow diffusion of lincomycin into biochar pore structures. Two-day sorption experiments were performed to explore effects of biochar particle size, solid/water ratio, solution pH, and ionic strength. Lincomycin sorption to biochars was greater at solution pH 6.0 to 7.5 below the dissociation constant of lincomycin (7.6) than at pH 9.9 to 10.4 above its dissociation constant. The enhanced lincomycin sorption at lower pH likely resulted from electrostatic attraction between the positively charged lincomycin and the negatively charged biochar surfaces. This was corroborated by the observation that lincomycin sorption decreased with increasing ionic strength at lower pH (6.7) but remained constant at higher pH (10). The long-term lincomycin sequestration by biochars was largely due to pore diffusion plausibly independent of solution pH and ionic composition. Therefore, manure-derived biochars had lasting lincomycin sequestration capacity, implying that biochar soil amendment could significantly affect the distribution, transport, and bioavailability of lincomycin in agroecosystems. PMID:27065399

  7. Hydrogenation of the alpha,beta-Unsaturated Aldehydes Acrolein, Crotonaldehyde, and Prenal over Pt Single Crystals: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    SciTech Connect

    Kliewer, C.J.; Somorjai, G.A.

    2008-11-26

    Sum-frequency generation vibrational spectroscopy (SFG-VS) and kinetic measurements using gas chromatography have been used to study the surface reaction intermediates during the hydrogenation of three {alpha},{beta}-unsaturated aldehydes, acrolein, crotonaldehyde, and prenal, over Pt(111) at Torr pressures (1 Torr aldehyde, 100 Torr hydrogen) in the temperature range of 295K to 415K. SFG-VS data showed that acrolein has mixed adsorption species of {eta}{sub 2}-di-{sigma}(CC)-trans, {eta}{sub 2}-di-{sigma}(CC)-cis as well as highly coordinated {eta}{sub 3} or {eta}{sub 4} species. Crotonaldehyde adsorbed to Pt(111) as {eta}{sub 2} surface intermediates. SFG-VS during prenal hydrogenation also suggested the presence of the {eta}{sub 2} adsorption species, and became more highly coordinated as the temperature was raised to 415K, in agreement with its enhanced C=O hydrogenation. The effect of catalyst surface structure was clarified by carrying out the hydrogenation of crotonaldehyde over both Pt(111) and Pt(100) single crystals while acquiring the SFG-VS spectra in situ. Both the kinetics and SFG-VS showed little structure sensitivity. Pt(100) generated more decarbonylation 'cracking' product while Pt(111) had a higher selectivity for the formation of the desired unsaturated alcohol, crotylalcohol.

  8. Hydrogen exchange kinetics and the mechanism of reaction B of yeast tryptophan synthase.

    PubMed

    Turner, P D; Loughrey, H C; Bailey, C J

    1985-12-20

    It has been shown that yeast tryptophan synthase (L-serine hydro-lyase (adding indoleglycerol-phosphate) EC 4.2.1.20) catalyses tritium exchange reactions between protons on the alpha-carbon of L-serine of L-tryptophan, and water. The absolute rates of these reactions and indole-serine condensation (reaction B), all of which are pyridoxal phosphate-dependent, were measured. L-Serine exchange was resolved into two components, a high-affinity, slow, Michaelian reaction (KmS,H = 0.06 mM, kcats,H 3 X 10(-3) s-1) and a faster reaction (kcat greater than 2.5 S-1) which was not saturated even at 100 mM L-serine. Hydrogen exchange by tryptophan was a Michaelian process (KmT,H = 2.9 mM; kcatT,H = 0.6 s-1). Indole did not inhibit either exchange reaction. A plausible explanation of the results, that reaction B has a ping-pong mechanism with serine as first substrate and water and L-tryptophan as first and second products, respectively, was inadequate because of the observations that L-tryptophan is as first and second products, respectively, was inadequate because of the observations that L-tryptophan is synthesised with less than 1 mol of exchanged proton per mol amino acid, and that the ratio kcat/Km for serine changes between enzyme reactions. A branched modification with two enzyme-serine complexes, only one of which will exchange protons with water, will fit all the results. PMID:3935173

  9. Sorption and Release of Organics by Primary, Anaerobic, and Aerobic Activated Sludge Mixed with Raw Municipal Wastewater

    PubMed Central

    Modin, Oskar; Saheb Alam, Soroush; Persson, Frank; Wilén, Britt-Marie

    2015-01-01

    New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215–230 nm were also rapidly removed. PMID:25768429

  10. Sorption and release of organics by primary, anaerobic, and aerobic activated sludge mixed with raw municipal wastewater.

    PubMed

    Modin, Oskar; Saheb Alam, Soroush; Persson, Frank; Wilén, Britt-Marie

    2015-01-01

    New activated sludge processes that utilize sorption as a major mechanism for organics removal are being developed to maximize energy recovery from wastewater organics, or as enhanced primary treatment technologies. To model and optimize sorption-based activated sludge processes, further knowledge about sorption of organics onto sludge is needed. This study compared primary-, anaerobic-, and aerobic activated sludge as sorbents, determined sorption capacity and kinetics, and investigated some characteristics of the organics being sorbed. Batch sorption assays were carried out without aeration at a mixing velocity of 200 rpm. Only aerobic activated sludge showed net sorption of organics. Sorption of dissolved organics occurred by a near-instantaneous sorption event followed by a slower process that obeyed 1st order kinetics. Sorption of particulates also followed 1st order kinetics but there was no instantaneous sorption event; instead there was a release of particles upon mixing. The 5-min sorption capacity of activated sludge was 6.5±10.8 mg total organic carbon (TOC) per g volatile suspend solids (VSS) for particulate organics and 5.0±4.7 mgTOC/gVSS for dissolved organics. The observed instantaneous sorption appeared to be mainly due to organics larger than 20 kDa in size being sorbed, although molecules with a size of about 200 Da with strong UV absorbance at 215-230 nm were also rapidly removed.

  11. Departures of the electron energy distribution from a Maxwellian in hydrogen. I - Formulation and solution of the electron kinetic equation. II - Consequences

    NASA Technical Reports Server (NTRS)

    Shoub, E. C.

    1977-01-01

    The problem of calculating the steady-state free-electron energy distribution in a hydrogen gas is considered in order to study departures of that distribution from a Maxwellian at sufficiently low degrees of ionization. A model kinetic equation is formulated and solved analytically for the one-particle electron distribution function in a steady-state partially ionized hydrogen gas, and it is shown that the formal solution can be accurately approximated by using the WKB method. The solutions obtained indicate that the high-energy tail of the distribution is susceptible to distortion by imbalanced inelastic collisions for ionization fractions not exceeding about 0.1 and that such departures from a Maxwellian can lead to significant changes in the collisional excitation and ionization rates of ground-state hydrogen atoms. Expressions for the electron-hydrogen collision rates are derived which explicitly display their dependence on the hydrogen departure coefficients. The results are applied in order to compare self-consistent predictions with those based on the a priori assumption of a Maxwellian distribution for models of the thermal ionization equilibrium of hydrogen in the optically thin limit, spectral-line formation by a gas consisting of two-level atoms, and radiative transfer in finite slabs by a gas of four-level hydrogen atoms.

  12. Improved hydrogen-storage thermodynamics and kinetics for an RbF-doped Mg(NH2)2-2 LiH system.

    PubMed

    Li, Chao; Liu, Yongfeng; Gu, Yingjie; Gao, Mingxia; Pan, Hongge

    2013-09-01

    The introduction of RbF into the Mg(NH2)2-2 LiH system significantly decreased its (de-)hydrogenation temperatures and enhanced its hydrogen-storage kinetics. The Mg(NH2)2-2 LiH-0.08 RbF composite exhibits the optimal hydrogen-storage properties as it could reversibly store approximately 4.76 wt % hydrogen through a two-stage reaction with the onset temperatures of 80 °C for dehydrogenation and 55 °C for hydrogenation. At 130 °C, approximately 70 % of hydrogen was rapidly released from the 0.08 RbF-doped sample within 180 min, and the fully dehydrogenated sample could absorb approximately 4.8 wt % of hydrogen at 120 °C. Structural analyses revealed that RbF reacted readily with LiH to convert to RbH and LiF owing to the favorable thermodynamics during ball-milling. The newly generated RbH participated in the following dehydrogenation reaction, consequently resulting in a decrease in the reaction enthalpy change and activation energy.

  13. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron. Annual status report, 1 January-31 December 1994

    SciTech Connect

    Shanabarger, M.R.

    1994-12-01

    The goal of this program has been to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. During the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak. Weak in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K. These results correlate well with other recent studies which show that the mechanical properties for alpha-2 titanium aluminide are readily degraded in hydrogen while gamma titanium aluminide exhibits less degradation and beryllium essentially no degradation. The interaction of oxygen with the surface of several of these materials was studied. More recently, preliminary hydrogen permeation studies were completed for three high temperature alloys, Incoloy 909, Mo-47.5Re (wt. %), and this past year, Haynes 188.

  14. Measurement and decomposition kinetics of residual hydrogen peroxide in the presence of commonly used excipients and preservatives.

    PubMed

    Towne, Victoria; Oswald, C Brent; Mogg, Robin; Antonello, Joseph; Will, Mark; Gimenez, Juan; Washabaugh, Michael; Sitrin, Robert; Zhao, Qinjian

    2009-11-01

    Quantitation of residual hydrogen peroxide (H(2)O(2)) and evaluation of the impact on product stability is necessary as unwanted H(2)O(2) can potentially be introduced during the manufacturing of pharmaceuticals, biologics, and vaccines. A sensitive and convenient microplate-based method with fluorescence detection for H(2)O(2) quantitation was recently reported (Towne et al., 2004, Anal Biochem 334: 290-296). This method was found to be highly robust and reproducible, with a level of detection of 0.015 ppm and a level of quantitation of 0.025 ppm (in water). The relatively small sample requirements and amenability for automation make this assay an attractive tool for detecting residual H(2)O(2) levels. Without additional manipulation, the assay can be conducted on heterogeneous solutions with significant degree of turbidity, such as the presence of suspensions or aluminum-containing adjuvants. The quantitation of H(2)O(2) and its decomposition kinetics was also studied in presence of two common vaccine preservatives (thimerosal and phenol) and eight commonly used excipients (polyols). Over time, there is a distinct, temperature dependent decrease in H(2)O(2) recovered in thimerosal and phenol containing samples versus non-preservative containing controls. Based on the half-life of spiked H(2)O(2), the decay rates in eight polyols tested were found to be: ribose > sucrose > (glycerol, glucose, lactose, mannitol, sorbitol, and xylose).

  15. Exposure of Microcystis aeruginosa to Hydrogen Peroxide under Light: Kinetic Modeling of Cell Rupture and Simultaneous Microcystin Degradation.

    PubMed

    Huo, Xiangchen; Chang, De-Wei; Tseng, Jing-Hua; Burch, Michael D; Lin, Tsair-Fuh

    2015-05-01

    The effect of hydrogen peroxide on the cell integrity of a cyanobacterium, Microcystis aeruginosa, and on the release and degradation of microcystins (MCs) under simulated sunlight was investigated. The cyanobacterium was exposed to H2O2 in the range of 0-60 mg·L(-1) for 3.5 h. Production of OH radical in the solution was estimated by a chemical probe method. More than 99% (2 log) of the M. aeruginosa cells were ruptured or damaged by 3 h for all the treatments. Loss of cell integrity over time revealed two distinct phases. Cells retained their integrity during the initial lag phase and rapidly ruptured following first-order reaction afterward. A linear relationship was found between the duration of the lag phase and the steady-state concentration of OH radical. Release of MCs was closely correlated with the loss of cell integrity. Sequential reaction models were developed to simulate the release and degradation of MCs. These models were able to quantitatively describe the kinetics of all reactions under different H2O2 doses and extended exposure time. In particular, the models successfully predicted the concentration change of MCs using independently measured parameters. These models provide a simple and quantitative means to estimate the interaction of oxidants and cells and the consequent release of metabolites during oxidation treatment of cyanobacterium-laden waters.

  16. Evaluation of Tafel-Volmer kinetic parameters for the hydrogen oxidation reaction on Pt(1 1 0) electrodes

    NASA Astrophysics Data System (ADS)

    Mann, R. F.; Thurgood, C. P.

    2011-05-01

    Modelling of PEM fuel cells has long been an active research area to improve understanding of cell and stack operation, facilitate design improvements and support simulation studies. The prediction of activation polarization in most PEM models has concentrated on the cathode losses since anode losses are commonly much smaller and tend to be ignored. Further development of the anode activation polarization term is being undertaken to broaden the application and usefulness of PEM models in general. Published work on the kinetics of the hydrogen oxidation reaction (HOR) using Pt(h k l) electrodes in dilute H2SO4 has been recently reassessed and published. Correlations for diffusion-free exchange current densities were developed and empirical predictive equations for the anode activation polarization were proposed for the experimental conditions of the previously published work: Pt(1 0 0), Pt(1 1 0) and Pt(1 1 1) electrodes, pH2 of 1 atm, and temperatures of 1, 30 and 60 °C. It was concluded that the HOR on Pt(1 1 0) electrodes followed a Tafel-Volmer reaction sequence. The aim of the present paper is to generalize these Tafel-Volmer correlations, apply them to published data for Pt(1 1 0) electrodes and further develop the modelling of anode activation polarization over the range of operating conditions found in PEMFC operation.

  17. Hydrogen sorption from the Mg(NH2)2-KH system and synthesis of an amide-imide complex of KMg(NH)(NH2).

    PubMed

    Wang, Jianhui; Wu, Guotao; Chua, Yong Shen; Guo, Jianping; Xiong, Zhitao; Zhang, Yao; Gao, Mingxia; Pan, Hongge; Chen, Ping

    2011-11-18

    The interaction between KH and Mg(NH(2))(2) is investigated. Results from temperature-programmed desorption measurements on samples of [Mg(NH(2))(2)][KH](x) (x=0.5, 1.0, and 2.0) indicated that dehydrogenation from [Mg(NH(2))(2)][KH] occurred through a two-step reaction with an onset temperature as low as 60 °C. Accompanied by hydrogen release, K(2)Mg(NH(2))(4) and MgNH successively developed at lower temperatures, whereas KMg(NH)(NH(2)) developed at higher temperatures. However, when dehydrogenation was conducted under isothermal and near-equilibrium conditions, a single-step reaction that led to the formation of KMg(NH)(NH(2)) was observed. KMg(NH)(NH(2)) is a new amide-imide complex. The synthesis of KMg(NH)(NH(2)) can be achieved either by dehydrogenation of the [Mg(NH(2))(2)][KH] mixture or by thermal decomposition of the [K(2)Mg(NH(2))(4)][Mg(NH(2))(2)] mixture. PMID:22083869

  18. Size-dependent mechanical properties of Mg nanoparticles used for hydrogen storage

    SciTech Connect

    Yu, Qian; Qi, Liang; Mishra, Raja K.; Zeng, Xiaoqin; Minor, Andrew M.

    2015-06-29

    Magnesium (Mg) hydride is a promising hydrogen storage material, yet its application has been limited by the slow hydrogen sorption kinetics. Recently, Mg nanoparticles have shown significant improvement of hydrogen storage properties in terms of dimensional stability upon cycling with the trend that the smaller the particle, the better the sorption kinetics. Since the volume change during sorption generates stress, leading to plastic deformation, the fundamentals of the mechanical deformation of the Mg particles are a significant issue. By using in situ transmission electron microscope compression tests and atomistic simulations on Mg nanoparticles, it was observed that deformation in the larger particles was dominated by the nucleation of 〈a〉-type dislocations from stress concentrations at the contact surface, while the smaller particles deformed more homogeneously with greater distribution of multiple types of dislocation sources. Importantly, this improvement of plastic deformation with decrease in size is orientation-independent. First-principles calculations suggest that this improved plasticity can be explained by the nearly-isotropic ideal shear strength for Mg, which becomes more important in smaller nanoparticles. As a result, the smaller Mg nanoparticles demonstrated better plastic stability to accommodate volume change upon hydrogen storage cycling.

  19. A nanoscale demonstration of hydrogen atom spillover and surface diffusion across silica using the kinetics of CO2 methanation catalyzed on spatially separate Pt and Co nanoparticles.

    PubMed

    Beaumont, Simon K; Alayoglu, Selim; Specht, Colin; Kruse, Norbert; Somorjai, Gabor A

    2014-08-13

    Hydrogen spillover is of great importance to understanding many phenomena in heterogeneous catalysis and has long been controversial. Here we exploit well-defined nanoparticles to demonstrate its occurrence through evaluation of CO2 methanation kinetics. Combining platinum and cobalt nanoparticles causes a substantial increase in reaction rate, but increasing the spatial separation between discrete cobalt and platinum entities results in a dramatic ∼ 50% drop in apparent activation energy, symptomatic of H atom surface diffusion limiting the reaction rate. PMID:25026434

  20. The dynamics of sorption of sulfuric acid by weakly basic polyacrylic anion exchangers

    NASA Astrophysics Data System (ADS)

    Mamchenko, A. V.; Kushnir, T. V.

    2009-05-01

    The nonequilibrium dynamics of sorption of sulfuric acid by free base forms of Amberlite IRA-67 and Lewatite VP.OC.1072 weakly basic anion exchangers is studied. It is established that, in hydrodynamic regimes of filtration, which are typical of OH filters of the first stage of water-desalting plants, the limiting stage of sorption kinetics is inside diffusion. It is concluded that the process is correctly described by an asymptotic solution to the inside-diffusion model of sorption dynamics.

  1. Sorption of roxarsone onto soils with different physicochemical properties.

    PubMed

    Fu, Qing-Long; He, Jian-Zhou; Blaney, Lee; Zhou, Dong-Mei

    2016-09-01

    Elevated roxarsone (ROX) concentrations in soils, caused by land application of ROX-bearing poultry litter, mandate investigation of ROX sorption onto soils. Equilibrium and kinetic studies of ROX sorption onto five soils were carried out to explore the relationship between sorption parameters and soil properties, and to reveal the effects of coexisting humic acid (HA), P(V), As(V), and As(III) on ROX transport. Experimental results indicated that ROX sorption reached equilibrium within 24 h, with pseudo-second order rate constants of 5.74-5.26 × 10(2) g/(mg h); film and intra-particle diffusion were the rate-limiting processes. ROX sorption to soils involved partitioning and adsorption phenomena; however, their relative contributions varied for different soils. The maximum ROX sorption varied with soil type, ranging from 0.59 to 4.12 mg/g. Results from correlation analysis and multiple linear regressions revealed that the maximum sorption capacities, partition coefficients, and desorption percentages were correlated with soil properties, especially iron content, total organic carbon, and dissolved organic carbon. ROX sorption to soils was affected more by soil pH than the initial pH of ROX-containing solutions. Carboxylic and amide functional groups were determined to be responsible for ROX sorption to soils. ROX sorption capacities decreased in the presence of HA, P(V), As(V), and As(III), indicating that ROX mobility in soils was facilitated by dissolved organic matter (DOM) and competing anions. PMID:27281543

  2. Reaction kinetics of hydrogen abstraction reactions by hydroperoxyl radical from 2-methyltetrahydrofuran and 2,5-dimethyltetrahydrofuran.

    PubMed

    Chakravarty, Harish Kumar; Fernandes, Ravi X

    2013-06-20

    Highly accurate rate parameters for H-abstraction reactions by HO2 radicals are needed for development of predictive chemical kinetic models for ignition. In this article, we report the rate coefficients for reaction of hydroperoxyl radical (HO2) with 2-methyltetrahydrofuran (MTHF) and 2,5-dimethyltetrahydrofuran (DMTHF) computed employing CBS-QB3 and CCSD(T)/cc-pVTZ//B3LYP/cc-pVTZ level of theory in the temperature range of 500-2000 K. Conventional transition state theory (CTST) with hindered rotor approximation for low frequency torsional modes and RRHO (rigid-rotor harmonic oscillator) approximation for all other vibrational modes is employed to evaluate the high pressure rate constants as a function of temperature. Rate constant of each individual hydrogen abstraction channel is taken into account to calculate the overall rate constant. Three-parameter Arrhenius expressions have been obtained by fitting to the computed rate constants of all abstraction channels between 500 and 2000 K. Eight transition states have been identified for MTHF and four for slightly more stable trans-DMTHF. Intrinsic reaction coordinates (IRC) calculations were performed to verify the connectivity of all the transition states (TSs) with reactants and products. One dimensional Eckart's asymmetrical method has been used to calculate quantum mechanical tunneling effect. Results of the theoretically calculated rate coefficients indicate that the hydrogen abstraction by HO2 from the C2 carbon of both MTHF and DMTHF is the most dominant path among all reaction pathways attributed to its lowest barrier height. The total rate coefficients of the MTHF and DMTHF with HO2 at CCSD(T)/cc-pVTZ//B3LYP/cc-pVTZ level of theory are k(T) = 8.60T(3.54) exp(-8.92/RT) and k(T)= 3.17T(3.63) exp(-6.59/RT) cm(3) mol(-1) s(-1), respectively. At both the level of theories, the predicted total abstraction rate constant for DMTHF is found to be higher as compared to that of MTHF over an entire temperature range

  3. Modeling temperature dependent kinetic isotope effects for hydrogen transfer in a series of soybean lipoxygenase mutants: The effect of anharmonicity upon transfer distance

    PubMed Central

    Meyer, Matthew P.; Klinman, Judith P.

    2010-01-01

    Soybean lipoxygenase-1 (SLO) catalyzes the oxidation of linoleic acid. The rate-limiting step in this transformation is the net abstraction of the pro-S hydrogen atom from the center of the 1,5-pentadienyl moiety in linoleic acid. The large deuterium kinetic isotope effect (KIE) for this step appears in the first order rate constant (Dkcat = 81 ± 5 at T = 25 °C). Furthermore, the KIE and the rate for protium abstraction are weakly temperature dependent (EA,D − EA,H = 0.9 ± 0.2 kcal/mol and EA,H = 2.1 ± 0.2 kcal/mol, respectively). Mutations at a hydrophobic site about 13 Å from the active site Fe(III), Ile553, induce a marked temperature dependence that varies roughly in accordance with the degree to which the residue is changed in bulk from the wild type Ile. While the temperature dependence for these mutants varies from the wild type enzyme, the magnitude of the KIE at 25 °C is on the same order of magnitude. A hydrogen tunneling model [Kuznetsov, A.M., Ulstrup, J. Can. J. Chem. 77 (1999) 1085–1096] is utilized to model the KIE temperature profiles for the wild type SLO and each Ile553 mutant. Hydrogenic wavefunctions are modeled using harmonic oscillators and Morse oscillators in order to explore the effects of anharmonicity upon computed kinetic observables used to characterize this hydrogen transfer. PMID:21132078

  4. New approach in modeling Cr(VI) sorption onto biomass from metal binary mixtures solutions.

    PubMed

    Liu, Chang; Fiol, Núria; Villaescusa, Isabel; Poch, Jordi

    2016-01-15

    In the last decades Cr(VI) sorption equilibrium and kinetic studies have been carried out using several types of biomasses. However there are few researchers that consider all the simultaneous processes that take place during Cr(VI) sorption (i.e., sorption/reduction of Cr(VI) and simultaneous formation and binding of reduced Cr(III)) when formulating a model that describes the overall sorption process. On the other hand Cr(VI) scarcely exists alone in wastewaters, it is usually found in mixtures with divalent metals. Therefore, the simultaneous removal of Cr(VI) and divalent metals in binary mixtures and the interactive mechanism governing Cr(VI) elimination have gained more and more attention. In the present work, kinetics of Cr(VI) sorption onto exhausted coffee from Cr(VI)-Cu(II) binary mixtures has been studied in a stirred batch reactor. A model including Cr(VI) sorption and reduction, Cr(III) sorption and the effect of the presence of Cu(II) in these processes has been developed and validated. This study constitutes an important advance in modeling Cr(VI) sorption kinetics especially when chromium sorption is in part based on the sorbent capacity of reducing hexavalent chromium and a metal cation is present in the binary mixture.

  5. A FAMILY OF PEROXO-TITANATE MATERIALS TAILORED FOR OPTIMAL STRONTIUM ANDACTINIDE SORPTION

    SciTech Connect

    Hobbs, D

    2006-08-07

    Achieving global optimization of inorganic sorbent efficacy, as well as tailoring sorbent specificity for target sorbates would facilitate increased wide-spread use of these materials in applications such as producing potable water or nuclear waste treatment. Sodium titanates have long been known as sorbents for radionuclides; {sup 90}Sr and transuranic elements in particular. We have developed a related class of materials, which we refer to as peroxo-titanates: these are sodium titanates or hydrous titanates synthesized in the presence of or treated post-synthesis with hydrogen peroxide. Peroxo-titanates show remarkable and universal improved sorption behavior with respect to separation of actinides and strontium from Savannah River Site (SRS) nuclear waste simulants. Enhancement in sorption kinetics can potentially result in as much as an order of magnitude increase in batch processing throughput. Peroxo-titanates have been produced by three different synthetic routes: post-synthesis peroxide-treatment of a commercially produced monosodium titanate, an aqueous-peroxide synthetic route, and an isopropanol-peroxide synthetic route. The peroxo-titanate materials are characteristically yellow to orange, indicating the presence of protonated or hydrated Ti-peroxo species; and the chemical formula can be generally written as H{sub v}Na{sub w}Ti{sub 2}O{sub 5}-(xH{sub 2}O)[yH{sub z}O{sub 2}] where (v+w) = 2, z = 0-2, and total volatile species accounts for 25-50 wt % of the solid. Further enhancement of sorption performance is achieved by processing, storing and utilizing the peroxo-titanate as an aqueous slurry rather than a dry powder, and post-synthesis acidification. All three synthesis modifications; addition of hydrogen peroxide, use of a slurry form and acidification can be applied more broadly to the optimization of other metal oxide sorbents and other ion separations processes.

  6. Evaluation of recycling the effluent of hydrogen fermentation for biobutanol production: kinetic study with butyrate and sucrose concentrations.

    PubMed

    Chen, Wen-Hsing; Jian, Zih-Ce

    2013-10-01

    Butyrate in the effluent of hydrogen-producing bioreactor is a potential feed for biobutanol production. For recycling butyrate, this study investigated the kinetics of biobutanol production by Clostridium beijerinckii NRRL B592 from different paired concentrations of butyrate and sucrose in a series of batch reactors. Results show that the lag time of butanol production increased with higher concentration of either sucrose or butyrate. In regression analyses, the maximum specific butanol production potential of 6.49 g g(-1) of dry cell was projected for 31.9 g L(-1) sucrose and 1.3 g L(-1) butyrate, and the maximum specific butanol production rate of 0.87 g d(-1) g(-1) of dry cell was predicted for 25.0 g L(-1) sucrose and 2.6 g L(-1) butyrate. The specific butanol production potential will decrease if more butyrate is added to the reactor. However, both sucrose and butyrate concentrations are weighted equally on the specific butanol production rate. This observation also is true on butanol yield. The maximum butanol yield of 0.49 mol mol(-1) was projected for 25.0 g L(-1) sucrose and 2.3 g L(-1) butyrate. In addition, a confirmation study found butanol yield increased from 0.2 to 0.3 mol mol(-1) when butyrate addition increased from 0 to 1 g L(-1) under low sugar concentration (3.8 g L(-1) sucrose). The existence of butyrate increases the activity of biobutanol production and reduces the fermentable sugar concentration needed for acetone-butanol-ethanol fermentation.

  7. Theoretical and kinetic study of the hydrogen atom abstraction reactions of esters with H(O.)2 radicals.

    PubMed

    Mendes, Jorge; Zhou, Chong-Wen; Curran, Henry J

    2013-12-27

    This work details an ab initio and chemical kinetic study of the hydrogen atom abstraction reactions by the hydroperoxyl radical (HȮ2) on the following esters: methyl ethanoate, methyl propanoate, methyl butanoate, methyl pentanoate, methyl isobutyrate, ethyl ethanoate, propyl ethanoate, and isopropyl ethanoate. Geometry optimizations and frequency calculations of all of the species involved, as well as the hindrance potential descriptions for reactants and transition states, have been performed with the Møller-Plesset (MP2) method using the 6-311G(d,p) basis set. A validation of all of the connections between transition states and local minima was performed by intrinsic reaction coordinate calculations. Electronic energies for all of the species are reported at the CCSD(T)/cc-pVTZ level of theory in kcal mol(-1) with the zero-point energy corrections. The CCSD(T)/CBS (extrapolated from CCSD(T)/cc-pVXZ, in which X = D, T, Q) was used for the reactions of methyl ethanoate + HȮ2 radicals as a benchmark in the electronic energy calculations. High-pressure limit rate constants, in the temperature range 500-2000 K, have been calculated for all of the reaction channels using conventional transition state theory with asymmetric Eckart tunneling corrections. The 1-D hindered rotor approximation has been used for the low frequency torsional modes in both reactants and transition states. The calculated individual and total rate constants are reported for all of the reaction channels in each reaction system. A branching ratio analysis for each reaction site has also been investigated for all of the esters studied in this work. PMID:24175616

  8. Spatial Moment Equations for a Groundwater Plume with Degradation and Rate-Limited Sorption

    EPA Science Inventory

    In this note, we analytically derive the solution for the spatial moments of groundwater solute concentration distributions simulated by a one-dimensional model that assumes advective-dispersive transport with first-order degradation and rate-limited sorption. Sorption kinetics...

  9. Gas Diffusion in Metals: Fundamental Study of Helium-Point Defect Interactions in Iron and Kinetics of Hydrogen Desorption from Zirconium Hydride

    NASA Astrophysics Data System (ADS)

    Hu, Xunxiang

    The behavior of gaseous foreign species (e.g., helium and hydrogen), which are either generated, adsorbed or implanted within the structural materials (e.g., iron and zirconium) exposed to irradiation environments, is an important and largely unsolved topic, as they intensively interact with the irradiation-induced defects, or bond with the lattice atoms to form new compounds, and impose significant effects on their microstructural and mechanical properties in fission and fusion reactors. This research investigates two cases of gas diffusion in metals (i.e., the helium-point defect interactions in iron and kinetics of hydrogen desorption from zirconium hydride) through extensive experimental and modeling studies, with the objective of improving the understanding of helium effects on the microstructures of iron under irradiation and demonstrating the kinetics of hydrogen diffusion and precipitation behavior in zirconium that are crucial to predict cladding failures and hydride fuel performance. The study of helium effects in structural materials aims to develop a self-consistent, experimentally validated model of helium---point defect, defect cluster and intrinsic defects through detailed inter-comparisons between experimental measurements on helium ion implanted iron single crystals and computational models. The combination of thermal helium desorption spectrometry (THDS) experiment with the cluster dynamic model helps to reveal the influence of impurities on the energetics and kinetics of the He-defect interactions and to realize the identification of possible mechanisms governing helium desorption peaks. Positron annihilation spectroscopy is employed to acquire additional information on He-vacancy cluster evolution, which provides an opportunity to validate the model qualitatively. The inclusion of He---self-interstitial clusters extends the cluster dynamic model while MD simulations explore the effects of dislocation loops on helium clustering. In addition, the

  10. Sorption of cesium ions by nanostructured calcium aluminosilicates

    NASA Astrophysics Data System (ADS)

    Gordienko, P. S.; Shabalin, I. A.; Yarusova, S. B.; Suponina, A. P.; Zhevtun, I. G.

    2016-10-01

    Data on the sorption properties of synthetic calcium aluminosilicates (CASes) with Al: Si ratios of 2: 2, 2: 6, and 2: 10, fabricated within the multicomponent system CaCl2-AlCl3-KOM-SiO2-H2O, are presented. Isotherms of the sorption of Cs+ ions from aqueous solutions with Cs+ concentrations of 0.2 to 6.0 mmol L-1 are analyzed. The CAS maximum sorption capacity and the Langmuir constants are determined. Kinetic data are obtained, and the energy of cation-exchange activation upon the sorption of Cs+ ions is determined. The effect of a salt background (1% KCl + 6% NaCl) has on the values of distribution coefficient ( K d) and the degree of Cs+ ion removal is established.

  11. Status Of Sorption Cryogenic Refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, Jack A.

    1988-01-01

    Report reviews sorption refrigeration. Developed for cooling infrared detectors, cryogenic research, and other advanced applications, sorption refrigerators have few moving parts, little vibration, and lifetimes of 10 years or more. Describes types of sorption stages, multistage and hybrid refrigeration systems, power requirements, cooling capacities, and advantages and disadvantages of various stages and systems.

  12. Sorption vacuum trap

    NASA Technical Reports Server (NTRS)

    Barrington, A. E.; Caruso, A. J.

    1970-01-01

    Modified sorption trap for use in high vacuum systems contains provisions for online regeneration of sorbent material. Trap is so constructed that it has a number of encapsulated resistance heaters and a valving and pumping device for removing gases from heated sorbing material. Excessive downtime is eliminated with this trap.

  13. Carbon Aerogels for Hydrogen Storage

    SciTech Connect

    Baumann, T F; Worsley, M; Satcher, J H

    2008-08-11

    This effort is focused on the design of new nanostructured carbon-based materials that meet the DOE 2010 targets for on-board vehicle hydrogen storage. Carbon aerogels (CAs) are a unique class of porous materials that possess a number of desirable structural features for the storage of hydrogen, including high surface areas (over 3000 m{sup 2}/g), continuous and tunable porosities, and variable densities. In addition, the flexibility associated with CA synthesis allows for the incorporation of modifiers or catalysts into the carbon matrix in order to alter hydrogen sorption enthalpies in these materials. Since the properties of the doped CAs can be systematically modified (i.e. amount/type of dopant, surface area, porosity), novel materials can be fabricated that exhibit enhanced hydrogen storage properties. We are using this approach to design new H{sub 2} sorbent materials that can storage appreciable amounts of hydrogen at room temperature through a process known as hydrogen spillover. The spillover process involves the dissociative chemisorption of molecular hydrogen on a supported metal catalyst surface (e.g. platinum or nickel), followed by the diffusion of atomic hydrogen onto the surface of the support material. Due to the enhanced interaction between atomic hydrogen and the carbon support, hydrogen can be stored in the support material at more reasonable operating temperatures. While the spillover process has been shown to increase the reversible hydrogen storage capacities at room temperature in metal-loaded carbon nanostructures, a number of issues still exist with this approach, including slow kinetics of H{sub 2} uptake and capacities ({approx} 1.2 wt% on carbon) below the DOE targets. The ability to tailor different structural aspects of the spillover system (i.e. the size/shape of the catalyst particle, the catalyst-support interface and the support morphology) should provide valuable mechanistic information regarding the critical aspects of the

  14. Is It Homogeneous or Heterogeneous Catalysis Derived from [RhCp*Cl2]2? In Operando-XAFS, Kinetic and Crucial Kinetic Poisoning Evidence for Subnanometer Rh4 Cluster-Based Benzene Hydrogenation Catalysis

    SciTech Connect

    Bayram, Ercan; Linehan, John C.; Fulton, John L.; Roberts, John A.; Szymczak, Nathaniel; Smurthwaite, Tricia D.; Ozkar, Saim; Balasubramanian, Mahalingam; Finke, Richard G.

    2011-11-23

    Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl2]2 (Cp* = [{eta}5-C5(CH3)5]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based 'homogeneous' from polymetallic, 'heterogeneous' catalysis. The reason, this study will show, is the previous failure to use the proper combination of (i) operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, plus then and crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being a 'wholly kinetic phenomenon' as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in this case subnanometer Rh4 cluster-based catalysis from larger, polymetallic Rh(0)n nanoparticle catalysis, at least under favorable conditions. The combined operando-XAFS (X-ray absorption fine structure) spectroscopy and kinetic evidences provide a compelling case for Rh4-based, with average stoichiometry 'Rh4Cp*2.4Cl4Hc', benzene hydrogenation catalysis in 2-propanol with added Et3N and at 100 C and 50 atm initial H2 pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)n had formed nanoparticles, then those Rh(0)n nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)n nanoparticles as a model system). The results 'especially the poisoning methodology developed and employed' are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions. The results are also of fundamental

  15. Is it homogeneous or heterogeneous catalysis derived from [RhCp*Cl2]2? In operando XAFS, kinetic, and crucial kinetic poisoning evidence for subnanometer Rh4 cluster-based benzene hydrogenation catalysis.

    PubMed

    Bayram, Ercan; Linehan, John C; Fulton, John L; Roberts, John A S; Szymczak, Nathaniel K; Smurthwaite, Tricia D; Özkar, Saim; Balasubramanian, Mahalingam; Finke, Richard G

    2011-11-23

    Determining the true, kinetically dominant catalytically active species, in the classic benzene hydrogenation system pioneered by Maitlis and co-workers 34 years ago starting with [RhCp*Cl(2)](2) (Cp* = [η(5)-C(5)(CH(3))(5)]), has proven to be one of the most challenging case studies in the quest to distinguish single-metal-based "homogeneous" from polymetallic, "heterogeneous" catalysis. The reason, this study will show, is the previous failure to use the proper combination of: (i) in operando spectroscopy to determine the dominant form(s) of the precatalyst's mass under catalysis (i.e., operating) conditions, and then crucially also (ii) the previous lack of the necessary kinetic studies, catalysis being a "wholly kinetic phenomenon" as J. Halpern long ago noted. An important contribution from this study will be to reveal the power of quantitiative kinetic poisoning experiments for distinguishing single-metal, or in the present case subnanometer Rh(4) cluster-based catalysis, from larger, polymetallic Rh(0)(n) nanoparticle catalysis, at least under favorable conditions. The combined in operando X-ray absorption fine structure (XAFS) spectroscopy and kinetic evidence provide a compelling case for Rh(4)-based, with average stoichiometry "Rh(4)Cp*(2.4)Cl(4)H(c)", benzene hydrogenation catalysis in 2-propanol with added Et(3)N and at 100 °C and 50 atm initial H(2) pressure. The results also reveal, however, that if even ca. 1.4% of the total soluble Rh(0)(n) had formed nanoparticles, then those Rh(0)(n) nanoparticles would have been able to account for all the observed benzene hydrogenation catalytic rate (using commercial, ca. 2 nm, polyethyleneglycol-dodecylether hydrosol stabilized Rh(0)(n) nanoparticles as a model system). The results--especially the poisoning methodology developed and employed--are of significant, broader interest since determining the nature of the true catalyst continues to be a central, often vexing issue in any and all catalytic reactions

  16. SORPTION OF VINCLOZOLIN AND ATRAZINE ON FOUR GEOSORBENTS

    EPA Science Inventory

    The objectives of this study were to evaluate the magnitude and kinetics of vinclozolin and atrazine sorption on one surface soil and three freshwater sediments using batch and column techniques. Data from miscible displacement column studies were analyzed using a two-domain, fir...

  17. Sorption behavior of dibutyl phthalate and dioctyl phthalate by aged refuse.

    PubMed

    Fang, Cheng-ran; Long, Yu-yang; Shen, Dong-sheng

    2014-06-01

    Sorption is a fundamental process controlling the transformation, fate, degradation, and biological activity of hydrophobic organic contaminants in the environment. We investigated the kinetics, isotherms, and potential mechanisms for the sorption of two phthalic acid esters (PAEs), dibutyl phthalate (DBP) and dioctyl phthalate (DOP), on aged refuse. A two-compartment first-order model performed better than a one-compartment first-order model in describing the kinetic sorption of PAEs, with a fast sorption process dominating. Both the Freundlich and Dubinin-Astakhov (DA) models fit the sorption isotherms of DBP and DOP, with the DA model being of a better fit over the range of apparent equilibrium concentrations. The values of the fitting parameters (n, b, E) of the PAEs suggest nonlinear sorption characteristics. Higher predicted partition coefficient values and saturated sorption capacity existed in refuse containing larger quantities of organic matter. The sorption capacity of DOP was significantly higher than that of DBP. PAE sorption was dependent on liquid phase pH. Desorption hysteresis occurred in PAE desorption experiments, especially for the long-chain DOP. PAEs may therefore be a potential environmental risk in landfill.

  18. Sorption of carbamazepine from water by magnetic molecularly imprinted polymers based on chitosan-Fe₃O₄.

    PubMed

    Zhang, Ya-Lei; Zhang, Juan; Dai, Chao-Meng; Zhou, Xue-Fei; Liu, Shu-Guang

    2013-09-12

    A novel magnetic-molecularly imprinted polymer (MMIP) based on chitosan-Fe₃O₄ has been synthesized for fast separation of carbamazepine (CBZ) from water. During polymerization, the modified chitosan-Fe₃O₄ was used not only as supporter but also as functional monomer. The properties of obtained MMIP were characterized by scanning electron and transmission electron microscopy, X-ray diffraction, Fourier transform infrared spectra, thermo-gravimetric analysis and so on. The sorption equilibrium data was well described by Freundlich isotherm model and the increase in the temperature generated an increase in the sorption amount, indicating endothermic nature of adsorption process. Sorption kinetics followed the pseudo-second-order model. The feasibility of selective sorption of CBZ from real water by the MMIP was analyzed by using spiked real water samples. The result showed that the sorption capacity of MMIP has no obvious decrease in different water samples whereas there was obvious decline in the sorption amount of the MNIP.

  19. Kinetics of Mo, Ni, V and Al leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide.

    PubMed

    Szymczycha-Madeja, Anna

    2011-02-28

    The kinetics of molybdenum, nickel, vanadium and aluminium leaching from a spent hydrodesulphurization catalyst in a solution containing oxalic acid and hydrogen peroxide was investigated. The effects of temperature and particle size were examined. In addition, the reaction mechanism for the dissolution of the spent catalyst was discussed. The results of the kinetic analysis for various experimental conditions indicated that the reaction rate of leaching process is controlled by chemical reaction at the particle surface. The values of the activation energies of 31±2, 36±4, 30±4 and 57±3 kJ mol(-1) for Mo, Ni, V and Al, respectively, are characteristic for mechanism controlled by chemical reaction. PMID:21167639

  20. Kinetics and mechanisms of the oxidation of alcohols and hydroxylamines by hydrogen peroxide, catalyzed by methyltrioxorhenium, MTO, and the oxygen binding properties of cobalt Schiff base complexes

    SciTech Connect

    Zauche, Timothy

    1999-02-12

    Catalysis is a very interesting area of chemistry, which is currently developing at a rapid pace. A great deal of effort is being put forth by both industry and academia to make reactions faster and more productive. One method of accomplishing this is by the development of catalysts. Enzymes are an example of catalysts that are able to perform reactions on a very rapid time scale and also very specifically; a goal for every man-made catalyst. A kinetic study can also be carried out for a reaction to gain a better understanding of its mechanism and to determine what type of catalyst would assist the reaction. Kinetic studies can also help determine other factors, such as the shelf life of a chemical, or the optimum temperature for an industrial scale reaction. An area of catalysis being studied at this time is that of oxygenations. Life on this earth depends on the kinetic barriers for oxygen in its various forms. If it were not for these barriers, molecular oxygen, water, and the oxygenated materials in the land would be in a constant equilibrium. These same barriers must be overcome when performing oxygenation reactions on the laboratory or industrial scale. By performing kinetic studies and developing catalysts for these reactions, a large number of reactions can be made more economical, while making less unwanted byproducts. For this dissertation the activation by transition metal complexes of hydrogen peroxide or molecular oxygen coordination will be discussed.

  1. Activatino of Erbium Films for Hydrogen Storage

    SciTech Connect

    M Brumbach; j Ohlhausen; K Zavadil; C Snow; J Woicik

    2011-12-31

    Hydriding of metals can be routinely performed at high temperature in a rich hydrogen atmosphere. Prior to the hydrogen loading process, a thermal activation procedure is required to promote facile hydrogen sorption into the metal. Despite the wide spread utilization of this activation procedure, little is known about the chemical and electronic changes that occur during activation and how this thermal pretreatment leads to increased rates of hydrogen uptake. This study utilized variable kinetic energy X-ray photoelectron spectroscopy to interrogate the changes during in situ thermal annealing of erbium films, with results confirmed by time-of-flight secondary ion mass spectrometry and low energy ion scattering. Activation can be identified by a large increase in photoemission between the valence band edge and the Fermi level and appears to occur over a two stage process. The first stage involves desorption of contaminants and recrystallization of the oxide, initially impeding hydrogen loading. Further heating overcomes the first stage and leads to degradation of the passive surface oxide leading to a bulk film more accessible for hydrogen loading.

  2. Activation of erbium films for hydrogen storage

    NASA Astrophysics Data System (ADS)

    Brumbach, Michael T.; Ohlhausen, James A.; Zavadil, Kevin R.; Snow, Clark S.; Woicik, Joseph C.

    2011-06-01

    Hydriding of metals can be routinely performed at high temperature in a rich hydrogen atmosphere. Prior to the hydrogen loading process, a thermal activation procedure is required to promote facile hydrogen sorption into the metal. Despite the wide spread utilization of this activation procedure, little is known about the chemical and electronic changes that occur during activation and how this thermal pretreatment leads to increased rates of hydrogen uptake. This study utilized variable kinetic energy X-ray photoelectron spectroscopy to interrogate the changes during in situ thermal annealing of erbium films, with results confirmed by time-of-flight secondary ion mass spectrometry and low energy ion scattering. Activation can be identified by a large increase in photoemission between the valence band edge and the Fermi level and appears to occur over a two stage process. The first stage involves desorption of contaminants and recrystallization of the oxide, initially impeding hydrogen loading. Further heating overcomes the first stage and leads to degradation of the passive surface oxide leading to a bulk film more accessible for hydrogen loading.

  3. Efficient Estimators for Quantum Instanton Evaluation of theKinetic Isotope Effects: Application to the Intramolecular HydrogenTransfer in Pentadiene

    SciTech Connect

    Vanicek, Jiri; Miller, William H.

    2007-06-13

    The quantum instanton approximation is used to compute kinetic isotope effects for intramolecular hydrogen transfer in cis-1,3-pentadiene. Due to the importance of skeleton motions, this system with 13 atoms is a simple prototype for hydrogen transfer in enzymatic reactions. The calculation is carried out using thermodynamic integration with respect to the mass of the isotopes and a path integral Monte Carlo evaluation of relevant thermodynamic quantities. Efficient 'virial' estimators are derived for the logarithmic derivatives of the partition function and the delta-delta correlation functions. These estimators require significantly fewer Monte Carlo samples since their statistical error does not increase with the number of discrete time slices in the path integral. The calculation treats all 39 degrees of freedom quantum-mechanically and uses an empirical valence bond potential based on a modified general AMBER force field.

  4. Superior dehydrogenation/hydrogenation kinetics and long-term cycling performance of K and Rb cocatalyzed Mg(NH(2))(2)-2LiH system.

    PubMed

    Li, Chao; Liu, Yongfeng; Ma, Ruijun; Zhang, Xin; Li, You; Gao, Mingxia; Pan, Hongge

    2014-10-01

    The coaddition of KH and RbH significantly improves the hydrogen storage properties of the Mg(NH2)2-2LiH system. An Mg(NH2)2-2LiH-0.04KH-0.04RbH composite was able to reversibly store 5.2 wt % H2 when the dehydrogenation operates at 130 °C and the hydrogenation operates at 120 °C. The isothermal dehydrogenation rate at 130 °C was approximately 43 times that of a pristine sample. During ball-milling, KH reacts with RbH to form a K(Rb)H solid solution. Upon heating, RbH first separates from the K(Rb)H solid solution and participates in the first step of dehydrogenation reaction, and then the remaining KH participates in the second dehydrogenation reaction. The presence of RbH and KH provide synergetic effects, which improve the thermodynamics and kinetics of hydrogen storage in the Mg(NH2)2-2LiH system. In particular, more than 93% of the hydrogen storage capacity (4.4 wt %) remains after cycling a sample with 0.04 mol of KH and RbH for 50 cycles, indicating notably better cycling stability compared with any presently known Li-Mg-N-H systems. PMID:25230404

  5. TECHNETIUM SORPTION MEDIA REVIEW

    SciTech Connect

    DUNCAN JB; KELLY SE; ROBBINS RA; ADAMS RD; THORSON MA; HAASS CC

    2011-08-25

    This report presents information and references to aid in the selection of 99Tc sorption media for feasibility studies regarding the removal of 99Tc from Hanford's low activity waste. The report contains literature search material for sorption media (including ion exchange media) for the most tested media to date, including SuperLig 639, Reillex HPQ, TAM (Kruion), Purolite A520E and A530E, and Dowex 1X8. The U.S. Department of Energy (DOE), Office of River Protection (ORP) is responsible for management and completion of the River Protection Project (RPP) mission, which comprises both the Hanford Site tank farms and the Waste Treatment and Immobilization Plant (WTP). The RPP mission is to store, retrieve and treat Hanford's tank waste; store and dispose of treated wastes; and close the tank farm waste management areas and treatment facilities in a safe, environmentally compliant, cost-effective and energy-effective manner.

  6. Sorption-desorption of indaziflam in selected agricultural soils.

    PubMed

    Alonso, Diego G; Koskinen, William C; Oliveira, Rubem S; Constantin, Jamil; Mislankar, Suresh

    2011-12-28

    Indaziflam, a new alkylazine herbicide that inhibits cellulose biosynthesis, is under current development for soil applications in perennial crops and nonagricultural areas. Sorption and desorption of indaziflam in six soils from Brazil and three soils from the United States, with different physical chemical properties, were investigated using the batch equilibration method. Sorption kinetics demonstrated that soil-solution equilibrium was attained in <24 h. The Freundlich equation described the sorption behavior of the herbicide for all soils (R(2) > 0.99). K(f) values of the Brazilian oxisols ranged from 4.66 to 29.3, and 1/n values were ≥ 0.95. Sorption was positively correlated to %OC and clay contents. U.S. mollisol K(f) values ranged from 6.62 to 14.3; 1/n values for sorption were ≥ 0.92. K(f) values from mollisols were also positively correlated with %OC. These results suggest that indaziflam potential mobility, based solely on its sorption coefficients, would range from moderate to low in soil. Desorption was hysteretic on all soils, further decreasing its potential mobility for offsite transport.

  7. The kinetic and mechanical aspects of hydrogen-induced failure in metals. Ph.D. Thesis, 1971

    NASA Technical Reports Server (NTRS)

    Nelson, H. G.

    1972-01-01

    Premature hydrogen-induced failure observed to occur in many metal systems involves three stages of fracture: (1) crack initiation, (2) stable slow crack growth, and (3) unstable rapid crack growth. The presence of hydrogen at some critical location on the metal surface or within the metal lattice was shown to influence one or both of the first two stages of brittle fracture but has a negligible effect on the unstable rapid crack growth stage. The relative influence of the applied parameters of time, temperature, etc., on the propensity of a metal to exhibit hydrogen induced premature failure was investigated.

  8. The batch study of Sr(2+) sorption by bone char.

    PubMed

    Smiciklas, I; Dimovic, S; Sljivic, M; Plecas, I

    2008-02-01

    Considering the excellent sorption properties of synthetic calcium hydroxyapatite (HAP) towards many divalent cations, the potential application of bone char, the natural source of HAP, for sequestering Sr(2+)ions from aqueous solutions has been studied in batch conditions. Contact time, initial solution pH and initial Sr(2+) concentrations were varied to examine the effect of these process parameters on the amount of Sr(2+) sorbed. The kinetics of Sr(2+) sorption was found to be a 2-step process, with contact time of 24 h required for attaining equilibrium. The sorption isotherm was well fitted with Langmuir and DKR theoretical models. Sorption of Sr(2+) on bone char was found to be a favorable, thermodynamically feasible and spontaneous process, with the maximum sorption capacity of 0.271 mmol/g and sorption energy of 11.09 kJ/mol. The sorption was pH-independent in the initial pH range 4-10, as a result of excellent buffering properties of bone char (constant final pH), while for pH > 10 sorbed amounts of Sr(2+) increased due to attractive electrostatic forces between negatively charged sorbent surface and positively charged metal ions. On the basis of the amount of Ca(2+) released and final pH decrease in respect to the point of zero charge of bone char (pH(PZC)), two possible mechanisms of Sr(2+) sorption were identified: ion-exchange and the formation of complex compounds with HAP and carbon active surface sites. The amounts of Sr(2+) leached from bone char increased with the increase of Ca(2+) content and the decrease of solution pH. In comparison with synthetic HAP, bone char represents a cost-effective alternative for Sr(2+) sequestering. PMID:18172814

  9. Combined capillary electrophoresis and high performance liquid chromatography studies on the kinetics and mechanism of the hydrogen peroxide-thiocyanate reaction in a weakly alkaline solution.

    PubMed

    Hu, Ying; Song, Yanan; Horváth, Attila K; Cui, Yin; Ji, Chen; Zhao, Yuemin; Gao, Qingyu

    2014-03-01

    The hydrogen peroxide-thiocyanate reaction has been reinvestigated by means of capillary electrophoresis and high performance liquid chromatography under weakly alkaline conditions at 25.0±0.1 °C. Concentration-time series of thiocyanate, sulfate and cyanate have been followed by capillary electrophoresis as well as that of thiocyanate and hydrogen peroxide by HPLC. It has been clearly demonstrated that OxSCN(-) (where x=1, 2 and 3) cannot be accumulated in detectable amount in contrast to the results of Christy and Egeberg, hence these species can only be regarded as short-lived intermediates. It has been shown that the overall rate law is first-order with respect to both reactants, but no pH-dependence was observed within the pH range of 8.86-10.08. A simple kinetic model has been proposed to fit all the concentration-time curves simultaneously at five different pHs demonstrating the powerful combination of the experimental techniques CE and HPLC with simultaneous evaluation of kinetic curves. It is also enlightened that the quality of the buffer strongly affects the rate of the overall reaction that increases in the order of application of ammonia, phosphate, carbonate and borate, respectively at a constant ionic strength and pH.

  10. Characteristics of the mass transfer of phosphatidylcholine during its sorption on mesoporous composites based on MCM-41

    NASA Astrophysics Data System (ADS)

    Sinyaeva, L. A.; Karpov, S. I.; Belanova, N. A.; Roessner, F.; Selemenev, V. F.

    2015-12-01

    The kinetic parameters of sorption of phosphatidylcholine on mesoporous composites based on MCM-41 are considered. It is noted that the possibility of both the diffusion and adsorption rate limitations of the process should be taken into account in the description of the kinetics of sorption of non-polar fat-soluble physiologically active compounds (PACs) from hexane solutions onto mesoporous materials of MCM- 41 type. The adequacy of using the Boyd diffusion model and the Lagergren, Ho and McKay, and Elovich models to describe the kinetics of sorption of phosphatidylcholine on mesoporous composites based on MCM-41 is shown. The contributions from diffusion limitation (internal and external) and the rate of the chemical step of adsorption to the overall rate of the sorption process are determined. It is found that the sorption of the phospholipid is a mixed diffusion process.

  11. A turbulent Eulerian multi-fluid reactive flow model and its application in modelling sorption enhanced steam methane reforming

    NASA Astrophysics Data System (ADS)

    Chao, Zhongxi; Wang, Yuefa; Jakobsen, Jana P.; Fernandino, Maria; Jakobsen, Hugo A.

    2011-12-01

    A turbulent multi-fluid reactive fluid model is presented in the paper, which is a combination of a kinetic theory granular flow multi-fluid model(Chao et al., 2011) and the reaction kinetics description(Lindborg, 2008). A two dimensional in-house code was developed to simulate the gas-catalyst-sorbent three-phase reactive flow in the sorption enhanced steam methane reforming fluidized bed reactor. In the simulation, Ca-based sorbents and Ni/MgAl2O3 catalysts are used. The simulation results show that a high production of hydrogen in SE-SMR is obtained compared with the conventional SMR process. The increase of the gas fluidization velocity does not affect the purity of the product hydrogen apparently,while it can shorten the time to get to the breakthrough apparently. The increase of the steam/carbon ratio can increase the purity of the product hydrogen. A homogeneous gas temperature distribution is found which is due to the gas, particle turbulent flows and the heat balance of the SMR-CO2 adsorption reactions. These simulation results are in good agreement with the experimental results from Johnsen et al. (2006a).

  12. Catechol and humic acid sorption onto a range of laboratory-produced black carbons (biochars).

    PubMed

    Kasozi, Gabriel N; Zimmerman, Andrew R; Nkedi-Kizza, Peter; Gao, Bin

    2010-08-15

    Although the major influence of black carbon (BC) on soil and sediment organic contaminant sorption is widely accepted, an understanding of the mechanisms and natural variation in pyrogenic carbon interaction with natural organic matter (NOM) is lacking. The sorption of a phenolic NOM monomer (catechol) and humic acids (HA) onto BC was examined using biochars made from oak, pine, and grass at 250, 400, and 650 degrees C. Catechol sorption equilibrium occurred after 14 d and was described by a diffusion kinetic model, while HA required only 1 d and followed pseudo-second-order kinetics. Catechol sorption capacity increased with increasing biochar combustion temperature, from pine < oak < grass and from coarse < fine particle size. At lower catechol concentrations, sorption affinity (Freundlich constant, K(f)) was directly related to micropore surface area (measured via CO(2) sorptometry) indicating the predominance of specific adsorption. In contrast, HA exhibited an order of magnitude less sorption (0.1% versus 1%, by weight) due to its exclusion from micropores. Greater sorption of both catechol and HA occurred on biochars with nanopores, i.e. biochars made at higher temperatures. These findings suggest that addition of BC to soil, via natural fires or biochar amendments, will sequester abundant native OM through sorption. PMID:20669904

  13. Kinetics of hydrogen consumption by methanogenic consortia and cultures of hydrogen-consuming anaerobes. [Methanospirillum PM1, M. hungatei JF-1, Methanosarcina barkeri MS, Methanobacterium PM2, Desulfovibrio G11 and PS1

    SciTech Connect

    Robinson, J.A.

    1982-01-01

    Hydrogen plays a central role in the breakdown of organic matter in anaerobic habitats, influencing the nature of the fermentation end products and possibly, rates at which the initial substrates are degraded. The kinetics were examined for H/sub 2/ consumption by samples from natural anaerobic habitats, pure cultures of H/sub 2/-consuming anaerobes, and co-cultures comprised of methanogenic and sulfate-reducing bacteria. These kinetic studies were performed using a gas-recirculation system that allowed precise measurements of gaseous phase H/sub 2/ and CH/sub 4/. Uptake and growth kinetic parameters were estimated for the natural samples and suspensions of H/sub 2/-consumers by fitting H/sub 2/ depletion (progress curve) data to integrated forms of Michaelis-Menten and Monod equations. Samples included eutrophic lake sediments, anaerobic digestor sludge, and rumen fluid. The bacteria studied were methanospirillum PM1, Methanosarcina barkeri MS, Methanospirillum hungatei JF-1, Methanohbacterium PM2, and Desulfovibrio strains G11 and PS1.

  14. Hydrogen storage in sodium aluminum hydride.

    SciTech Connect

    Ozolins, Vidvuds; Herberg, J.L. (Lawrence Livermore National Laboratories, Livermore, CA); McCarty, Kevin F.; Maxwell, Robert S. (Lawrence Livermore National Laboratories, Livermore, CA); Stumpf, Roland Rudolph; Majzoub, Eric H.

    2005-11-01

    Sodium aluminum hydride, NaAlH{sub 4}, has been studied for use as a hydrogen storage material. The effect of Ti, as a few mol. % dopant in the system to increase kinetics of hydrogen sorption, is studied with respect to changes in lattice structure of the crystal. No Ti substitution is found in the crystal lattice. Electronic structure calculations indicate that the NaAlH{sub 4} and Na{sub 3}AlH{sub 6} structures are complex-ionic hydrides with Na{sup +} cations and AlH{sub 4}{sup -} and AlH{sub 6}{sup 3-} anions, respectively. Compound formation studies indicate the primary Ti-compound formed when doping the material at 33 at. % is TiAl{sub 3} , and likely Ti-Al compounds at lower doping rates. A general study of sorption kinetics of NaAlH{sub 4}, when doped with a variety of Ti-halide compounds, indicates a uniform response with the kinetics similar for all dopants. NMR multiple quantum studies of solution-doped samples indicate solvent interaction with the doped alanate. Raman spectroscopy was used to study the lattice dynamics of NaAlH{sub 4}, and illustrated the molecular ionic nature of the lattice as a separation of vibrational modes between the AlH{sub 4}{sup -} anion-modes and lattice-modes. In-situ Raman measurements indicate a stable AlH{sub 4}{sup -} anion that is stable at the melting temperature of NaAlH{sub 4}, indicating that Ti-dopants must affect the Al-H bond strength.

  15. Methanol Synthesis from CO2 Hydrogenation over a Pd4/In2O3 Model Catalyst: A Combined DFT and Kinetic Study

    SciTech Connect

    Ye, Jingyun; Liu, Changjun; Mei, Donghai; Ge, Qingfeng

    2014-08-01

    Methanol synthesis from CO2 hydrogenation on Pd4/In2O3 has been investigated using density functional theory (DFT) and microkinetic modeling. In this study, three possible routes in the reaction network of CO2 + H2 → CH3OH + H2O have been examined. Our DFT results show that the HCOO route competes with the RWGS route whereas a high activation barrier kinetically blocks the HCOOH route. DFT results also suggest that H2COO* + H* ↔ H2CO* +OH* and cis-COOH* + H* ↔CO* + H2O* are the rate limiting steps in the HCOO route and the RWGS route, respectively. Microkinetic modeling results demonstrate that the HCOO route is the dominant reaction route for methanol synthesis from CO2 hydrogenation. We found that the activation of H adatom on the small Pd cluster and the presence of H2O on the In2O3 substrate play important roles in promoting the methanol synthesis. The hydroxyl adsorbed at the interface of Pd4/In2O3 induces the transformation of the supported Pd4 cluster from a butterfly structure into a tetrahedron structure. This important structure change not only indicates the dynamical nature of the supported nanoparticle catalyst structure during the reaction but also shifts the final hydrogenation step from H2COH to CH3O.

  16. Oxidation of vanadium(III) by hydrogen peroxide and the oxomonoperoxo vanadium(V) ion in acidic aqueous solutions: a kinetics and simulation study.

    PubMed

    Du, Guodong; Espenson, James H

    2005-07-25

    The reaction between vanadium(III) and hydrogen peroxide in aqueous acidic solutions was investigated. The rate law shows first-order dependences on both vanadium(III) and hydrogen peroxide concentrations, with a rate constant, defined in terms of -d[H(2)O(2)]/dt, of 2.06 +/- 0.03 L mol(-)(1) s(-)(1) at 25 degrees C; the rate is independent of hydrogen ion concentration. The varying reaction stoichiometry, the appreciable evolution of dioxygen, the oxidation of 2-PrOH to acetone, and the inhibition of acetone formation by the hydroxyl radical scavengers, dimethyl sulfoxide and sodium benzoate, point to a Fenton mechanism as the predominant pathway in the reaction. Methyltrioxorhenium(VII) does not appear to catalyze this reaction. A second-order rate constant for the oxidation of V(3+) by OV(O(2))(+) was determined to be 11.3 +/- 0.3 L mol(-)(1) s(-)(1) at 25 degrees C. An overall reaction scheme consisting of over 20 reactions, in agreement with the experimental results and literature reports, was established by kinetic simulation studies.

  17. Hydrogen kinetics in a-Si:H and a-SiC:H thin films investigated by real-time ERD

    NASA Astrophysics Data System (ADS)

    Halindintwali, S.; Khoele, J.; Nemroaui, O.; Comrie, C. M.; Theron, C. C.

    2015-04-01

    Hydrogen effusion from hydrogenated amorphous silicon (a-Si:H) and amorphous silicon carbide (a-Si1-xCx:H) thin films during a temperature ramp between RT and 600 °C was studied by in situ real-time elastic recoil detection analysis. Point to point contour maps show the hydrogen depth profile and its evolution with the ramped temperature. This paper proposes a diffusion limited evolution model to study H kinetic properties from total retained H contents recorded in a single ramp. In a compact a-Si:H layer where H predominantly effuses at high temperatures between 500 and 600 °C, an activation energy value of ∼1.50 eV and a diffusion pre-factor of 0.41 × 10-4 cm2/s were obtained. Applied to an non-stoichiometric a-Si1-xCx:H film in the same range of temperature, the model led to reduced values of activation energy and diffusion prefactor of ∼0.33 eV and 0.59 × 10-11 cm2/s, respectively.

  18. Theoretical analysis of kinetic effects on the quantitative comparison of K(d) values and contaminant retardation factors.

    PubMed

    Tinnacher, Ruth M; Honeyman, Bruce D

    2010-10-21

    Distribution coefficients (K(d) values) describe contaminant partitioning between liquids and solids for linear sorption at equilibrium conditions. If experimentally-determined K(d) values do not represent sorption equilibria, errors are introduced in contaminant transport models. These errors may be further propagated when K(d) values are used to compare contaminant mobility under different chemical solution conditions. Our theoretical analysis based on pseudo-first order sorption kinetics shows that, independent if two systems have the same or different sorption kinetics, relative comparisons of K(d) values and retardation factors are always affected by sorption times under non-equilibrium conditions. The time-frames required for attaining constant K(d) values are not only dependent on kinetic sorption characteristics, but also the equilibrium K(d) values approached. The type of kinetic errors introduced is affected by the specific differences in sorption kinetics and equilibrium K(d) values between the two systems. For systems with the same sorption kinetics, relative increases or decreases in contaminant velocities are always underestimated. In case of different kinetics, either an under- or overestimation of relative differences seems possible. Experimental sorption times should aim to equilibrate the system with the highest K(d) value for systems with comparable kinetics, and the system with the slowest sorption kinetics for different kinetics. PMID:20864208

  19. Sorption compressor/mechanical expander hybrid refrigeration

    NASA Technical Reports Server (NTRS)

    Jones, J. A.; Britcliffe, M.

    1987-01-01

    Experience with Deep Space Network (DSN) ground-based cryogenic refrigerators has proved the reliability of the basic two-stage Gifford-McMahon helium refrigerator. A very long life cryogenic refrigeration system appears possible by combining this expansion system or a turbo expansion system with a hydride sorption compressor in place of the usual motor driven piston compressor. To test the feasibility of this system, a commercial Gifford-McMahon refrigerator was tested using hydrogen gas as the working fluid. Although no attempt was made to optimize the system for hydrogen operation, the refrigerator developed 1.3 W at 30 K and 6.6 W at 60 K. The results of the test and of theoretical performances of the hybrid compressor coupled to these expansion systems are presented.

  20. Divacancies and the hydrogenation of Mg-Ti films with short range chemical order

    SciTech Connect

    Leegwater, H.; Schut, H.; Eijt, S. W. H.; Egger, W.; Baldi, A.; Dam, B.

    2010-03-22

    We obtained evidence for the partial chemical segregation of as-deposited and hydrogenated Mg{sub 1-y}Ti{sub y} films (0<=y<=0.30) into nanoscale Ti and Mg domains using positron Doppler-broadening. We exclusively monitor the hydrogenation of Mg domains, owing to the large difference in positron affinity for Mg and Ti. The electron momentum distribution broadens significantly upon transformation to the MgH{sub 2} phase over the whole compositional range. This reveals the similarity of the metal-insulator transition for rutile and fluorite MgH{sub 2}. Positron lifetime studies show the presence of divacancies in the as-deposited and hydrogenated Mg-Ti metal films. In conjunction with the relatively large local lattice relaxations we deduce to be present in fluorite MgH{sub 2}, these may be responsible for the fast hydrogen sorption kinetics in this MgH{sub 2} phase.

  1. Capacity and mechanisms of ammonium and cadmium sorption on different wetland-plant derived biochars.

    PubMed

    Cui, Xiaoqiang; Hao, Hulin; Zhang, Changkuan; He, Zhenli; Yang, Xiaoe

    2016-01-01

    The objective of this study was to investigate the relationship between Cd(2+)/NH4(+) sorption and physicochemical properties of biochars produced from different wetland plants. Biochars from six species of wetland plants (i.e., Canna indica, Pennisetum purpureum Schum, Thalia dealbata, Zizania caduciflora, Phragmites australis and Vetiveria zizanioides) were obtained at 500°C and characterized, and their sorption for ammonium and cadmium was determined. There were significant differences in elemental composition, functional groups and specific surface area among the biochars derived from different wetland plant species. Sorption of ammonium and cadmium on the biochars could be described by a pseudo second order kinetic model, and the simple Langmuir model fits the isotherm data better than the Freundlich or Temkin model. The C. indica derived biochar had the largest sorption capacity for NH4(+) and Cd(2+), with a maximum sorption of 13.35 and 125.8mgg(-1), respectively. P. purpureum Schum derived biochar had a similar maximum sorption (119.3mgg(-1)) for Cd(2+). Ammonium sorption was mainly controlled by cation exchange, surface complexation with oxygen-containing functional groups and the formation of magnesium ammonium phosphate compounds, whereas for Cd(2+) sorption, the formation of cadmium phosphate precipitates, cation exchange and binding to oxygen-containing groups were the major possible mechanisms. In addition, the sorption of ammonium and cadmium was not affected by surface area and microporosity of the biochars. PMID:26386447

  2. A Microscale Approach to Chemical Kinetics in the General Chemistry Laboratory: The Potassium Iodide Hydrogen Peroxide Iodine-Clock Reaction

    ERIC Educational Resources Information Center

    Sattsangi, Prem D.

    2011-01-01

    A microscale laboratory for teaching chemical kinetics utilizing the iodine clock reaction is described. Plastic pipets, 3 mL volume, are used to store and deliver precise drops of reagents and the reaction is run in a 24 well plastic tray using a total 60 drops of reagents. With this procedure, students determine the rate of reaction and the…

  3. Dehydrogenation kinetics, reversibility, and reaction mechanisms of reversible hydrogen storage material based on nanoconfined MgH2-NaAlH4

    NASA Astrophysics Data System (ADS)

    Plerdsranoy, Praphatsorn; Meethom, Sukanya; Utke, Rapee

    2015-12-01

    Studies of dehydrogenation kinetics, reversibility, and reaction mechanisms during de/rehydrogenation of nanoconfined MgH2-NaAlH4 into carbon aerogel scaffold (CAS) for reversible hydrogen storage material are for the first time proposed. Two different MgH2:NaAlH4 molar ratios (1:1 and 2:1) of hydride composite are melt infiltrated into CAS under 1:1 (CAS:hydride composite) weight ratio. Successful nanoconfinement is confirmed by N2 adsorption-desorption. Multiple-step dehydrogenation of milled samples is reduced to two-step reaction due to nanoconfinement. Peak temperatures corresponding to main dehydrogenation of nanoconfined samples significantly reduce as compared with those of milled samples, i.e., ∆T=up to 50 and 34 °C for nanoconfined sample with 1:1 and 2:1 (MgH2:NaAlH4) molar ratios, respectively. Hydrogen content released (the 1st cycle) and reproduced (the 2nd, 3rd, and 4th cycles) of nanoconfined samples enhance up to 80% and 68% with respect to theoretical hydrogen storage capacity, respectively, while those of milled samples are 71% and 38%, respectively. Remarkable hydrogen content reproduced after nanoconfinement is due to the fact that metallic Al obtained after dehydrogenation (T=300 °C under vacuum) of nanoconfined samples prefer to react with MgH2 and produces Al12Mg17, favorable for reversibility of MgH2-NaAlH4 system, whereas that of milled samples stays in the form of unreacted Al under the same temperature and pressure condition.

  4. Can soil drying affect the sorption of pesticides in soil?

    NASA Astrophysics Data System (ADS)

    Chaplain, Véronique; Saint, Philippe; Mamy, Laure; Barriuso, Enrique

    2010-05-01

    The sorption of pesticides in soils mainly controls their further dispersion into the environment. Sorption is usually related to the physico-chemical properties of molecules but it also depends on the hydrophobic features of soils. However, the hydrophobicity of soils changes with wetting and drying cycles and this can be enhanced with climate change. The objective of this study was to measure by using controlled artificial soils the influence of the hydrophobic characteristic of soils on the retention of a model pesticide. Artificial soils consisted in silica particles covered by synthetic cationic polymers. Polymers were characterized by the molar ratio of monomers bearing an alkyl chain of 12C. Two polymers were used, with 20 and 80 % ratios, and the same degree of polymerization. In addition, porous and non-porous particles were used to study the accessibility notion and to measure the influence of diffusion on pesticide sorption kinetics. Lindane was chosen as model molecule because its adsorption is supposed mainly due to hydrophobic interactions. Results on polymers adsorption on silica showed that it was governed by electrostatic interactions, without any dependency of the hydrophobic ratio. Polymers covered the entire surface of porous particles. Kinetic measurements showed that lindane sorption was slowed in porous particles due to the molecular diffusion inside the microporosity. The adsorption of lindane on covered silica particles corresponded to a partition mechanism described by linear isotherms. The slope was determined by the hydrophobic ratio of polymers: the sorption of lindane was highest in the most hydrophobic artificial soil. As a result, modification in soil hydrophobicity, that can happen with climate change, might affect the sorption and the fate of pesticides. However additional experiments are needed to confirm these first results. Such artificial soils should be used as reference materials to compare the reactivity of pesticides, to

  5. Non-linear dynamics of stable carbon and hydrogen isotope signatures based on a biological kinetic model of aerobic enzymatic methane oxidation.

    PubMed

    Vavilin, Vasily A; Rytov, Sergey V; Shim, Natalia; Vogt, Carsten

    2016-06-01

    The non-linear dynamics of stable carbon and hydrogen isotope signatures during methane oxidation by the methanotrophic bacteria Methylosinus sporium strain 5 (NCIMB 11126) and Methylocaldum gracile strain 14 L (NCIMB 11912) under copper-rich (8.9 µM Cu(2+)), copper-limited (0.3 µM Cu(2+)) or copper-regular (1.1 µM Cu(2+)) conditions has been described mathematically. The model was calibrated by experimental data of methane quantities and carbon and hydrogen isotope signatures of methane measured previously in laboratory microcosms reported by Feisthauer et al. [ 1 ] M. gracile initially oxidizes methane by a particulate methane monooxygenase and assimilates formaldehyde via the ribulose monophosphate pathway, whereas M. sporium expresses a soluble methane monooxygenase under copper-limited conditions and uses the serine pathway for carbon assimilation. The model shows that during methane solubilization dominant carbon and hydrogen isotope fractionation occurs. An increase of biomass due to growth of methanotrophs causes an increase of particulate or soluble monooxygenase that, in turn, decreases soluble methane concentration intensifying methane solubilization. The specific maximum rate of methane oxidation υm was proved to be equal to 4.0 and 1.3 mM mM(-1) h(-1) for M. sporium under copper-rich and copper-limited conditions, respectively, and 0.5 mM mM(-1) h(-1) for M. gracile. The model shows that methane oxidation cannot be described by traditional first-order kinetics. The kinetic isotope fractionation ceases when methane concentrations decrease close to the threshold value. Applicability of the non-linear model was confirmed by dynamics of carbon isotope signature for carbon dioxide that was depleted and later enriched in (13)C. Contrasting to the common Rayleigh linear graph, the dynamic curves allow identifying inappropriate isotope data due to inaccurate substrate concentration analyses. The non-linear model pretty adequately described experimental

  6. Hydrogen storage by physisorption on Metal Organic Frameworks

    NASA Astrophysics Data System (ADS)

    Dailly, Anne

    2008-03-01

    Cryo-adsorption systems based on materials with high specific surface areas have the main advantage that they can store and release hydrogen with fast kinetics and high reversibility over multiples cycles. Recently Metal Organic Frameworks (MOFs) have been proposed as promising adsorbents for hydrogen. These crystallographically well organized hybrid solids resulting from the three dimensional connection of inorganic clusters using organic linkers show the largest specific surface areas of all known crystalline solids. The determination of the relationships between physical properties (chemistry, structure, surface area ) of the MOFs and their hydrogen storage behavior is a key step in the characterization of these materials, if they are to be designed for hydrogen storage applications. Excess hydrogen sorption measurements for different MOFs will be presented. We show that maximum hydrogen uptake at high pressure and 77K does not always scale with the specific surface area. A linear correlation trend only apply within a class of specific materials and breaks down when the surface area measurement does not represent the surface sites that are available to H2. The influence of pore size and shape will also be discussed by comparing several MOFs with different structure types. The hydrogen adsorption and binding energy at low pressure are strongly dependent on the metal ions and the pore size.

  7. Chitosan sorbents for platinum sorption from dilute solutions

    SciTech Connect

    Guibal, E.; Larkin, A.; Vincent, T.; Tobin, J.M.

    1999-10-01

    Chitosan has proved efficient at removing platinum in dilute effluents. The maximum uptake capacity reaches 300 mg/g (almost 1.5 mmol/g). The optimum pH for sorption is pH 2. A glutaraldehyde cross-linking pretreatment is necessary to stabilize the biopolymer in acidic solutions. Sorption isotherms have been studied as a function of pH, sorbent particle size, and the cross-linking ratio. Surprisingly, the extent of the cross-linking (determined by the concentration of the cross-linking agent in the treatment bath) has no significant influence on uptake capacity. Competitor anions such as chloride or nitrate induce a large decrease in the sorption efficiency. Sorption kinetics show also that uptake rate is not significantly changed by increasing either the cross-linking ratio or the particle size of the sorbent. Mass transfer rates are significantly affected by the initial platinum concentration and by the conditioning of the biopolymer. Gel-bead conditioning appears to reduce the sorption rate. While for molybdate and vanadate ions, mass transfer was governed by intraparticle mass transfer, for platinum, both external and intraparticle diffusion control the uptake rate. In contrast with the former ions, platinum does not form polynuclear hydrolyzed species, which are responsible for steric hindrance of diffusion into the polymer network.

  8. Thallium(I) sorption using Prussian blue immobilized in alginate capsules.

    PubMed

    Vincent, Thierry; Taulemesse, Jean-Marie; Dauvergne, Agnès; Chanut, Thomas; Testa, Flaviano; Guibal, Eric

    2014-01-01

    Prussian blue (PB) was immobilized in alginate capsules. The composite sorbent was used for the recovery of Tl(I) ions from slightly acidic solutions: optimum pH being close to 4. The sorption isotherm can be described by the bi-site Langmuir sorption isotherm. This means that the metal ion can be bound through two different sorption sites: one having a strong affinity for Tl(I) (probably PB), the other having a lower affinity (probably the encapsulating material). The kinetics are described by either the pseudo-second order rate equation or the Crank's equation (resistance to intraparticle diffusion). The ionic strength (increased by addition of NaCl, KCl or CaCl₂) slightly decreased sorption capacity. The SEM-EDX analysis of PB-alginate capsules (before and after Tl(I) sorption) shows that the PB is homogeneously distributed in the capsules and that all reactive groups remain available for metal binding.

  9. Electrochemical Surface Interrogation of a MoS2 Hydrogen-Evolving Catalyst: In Situ Determination of the Surface Hydride Coverage and the Hydrogen Evolution Kinetics.

    PubMed

    Ahn, Hyun S; Bard, Allen J

    2016-07-21

    The hydrogen evolution reaction (HER) on an electrodeposited a-MoS2 electrode was investigated by a surface-selective electrochemical titration technique by application of surface interrogation scanning electrochemical microscopy. In a mildly acidic (pH 4.6) environment, the saturated surface hydride coverage of MoS2 was determined to be 31%, much higher than that expected for a crystalline nanoparticle. The HER rate constant of a surface molybdenum atom was measured for the first time in situ to be 3.8 s(-1) at a 600 mV overpotential. At high Mo-H coverages, a change in the nature of the active sites was observed upon consumption of Mo-H by HER.

  10. Electrochemical Surface Interrogation of a MoS2 Hydrogen-Evolving Catalyst: In Situ Determination of the Surface Hydride Coverage and the Hydrogen Evolution Kinetics.

    PubMed

    Ahn, Hyun S; Bard, Allen J

    2016-07-21

    The hydrogen evolution reaction (HER) on an electrodeposited a-MoS2 electrode was investigated by a surface-selective electrochemical titration technique by application of surface interrogation scanning electrochemical microscopy. In a mildly acidic (pH 4.6) environment, the saturated surface hydride coverage of MoS2 was determined to be 31%, much higher than that expected for a crystalline nanoparticle. The HER rate constant of a surface molybdenum atom was measured for the first time in situ to be 3.8 s(-1) at a 600 mV overpotential. At high Mo-H coverages, a change in the nature of the active sites was observed upon consumption of Mo-H by HER. PMID:27383727

  11. An investigation of the effect of surface impurities on the adsorption kinetics of hydrogen chemisorbed onto iron. Annual Status Report, 1 Jan. - 31 Dec. 1991. [titanium aluminides and beryllium

    SciTech Connect

    Shanabarger, M.R.

    1991-12-01

    The goal was to develop an understanding of heterogeneous kinetic processes for those molecular species which produce gaseous hydrogen degradation of the mechanical properties of metallic structural materials. Although hydrogen degradation of metallic materials is believed to result from dissolved protonic hydrogen, the heterogeneous hydrogen interface transport processes often dominate the kinetics of the degradation process. The initial step in the interface transport process is the dissociative chemisorption of the molecular species at the metal surface followed by hydrogen absorption into and transport through the bulk. Modern advanced aerospace applications often require the use of structural materials in high pressure hydrogen environments at temperatures which range from low cryogenic temperatures to very high temperatures (1300 K and greater). Materials proposed for these applications, such as the titanium aluminides, beta-titanium alloys, nickel- and cobalt-based superalloys, molybdenum-rhenium alloys, beryllium, and various beryllides, need to possess a high degree of immunity from hydrogen induced degradation of mechanical properties. In the present program, the interaction of hydrogen with the surfaces of alpha-2 (Ti3Al) titanium aluminide, gamma (TiAl) titanium aluminide, and beryllium were studied. The interaction of low pressure hydrogen with gamma titanium aluminide and beryllium was found to be relatively weak, in the sense that adsorption leads to a low surface concentration of dissociated hydrogen, i.e., the chemisorption process is reversible at room temperature (300 K) for gamma titanium aluminide and the sticking coefficient for chemisorption is extremely small for beryllium. Hydrogen was found to interact readily with alpha-2 titanium aluminide to form a stable surface hydride at 300 K.

  12. Characteristics of and sorption to biochars derived from waste material

    NASA Astrophysics Data System (ADS)

    Sun, Huichao; Kah, Melanie; Sigmund, Gabriel; Hofmann, Thilo

    2015-04-01

    /kg). Sorption generally increased with increasing pyrolysis temperature but there was no effect of particle size on sorption affinity. For mineral phase rich biochars, sorption generally increased after acid demineralization. When considering all materials together, the sorbent aromaticity (hydrogen-carbon ratio) was the most important factor controlling sorption of pyrene. Overall, the study demonstrates that biochars derived from human and animal waste material and exhibiting high mineral contents have potential for remediation applications.

  13. Superior hydrogen desorption kinetics of Mg(NH{sub 2}){sub 2} hollow nanospheres mixed with MgH{sub 2} nanoparticles

    SciTech Connect

    Xie Lei; Li Yaoqi; Yang Rong; Liu Yang; Li Xingguo

    2008-06-09

    Mg{sub 3}N{sub 2} nanocubes were prepared by vaporized bulk magnesium in ammonia atmosphere associated with plasma metal reaction. Then the product transformed to Mg(NH{sub 2}){sub 2} hollow nanospheres after it was reacted with NH{sub 3} based on the Kirkendall effect. The electron microscopy results suggested that the obtained hollow nanospheres were around 100 nm and the shell thickness was about 10 nm. Because of its short distance for Mg{sup 2+} diffusion and large specific surface area for interaction between Mg(NH{sub 2}){sub 2} and MgH{sub 2}, the structure dramatically enhanced the hydrogen desorption kinetics of Mg(NH{sub 2}){sub 2}-2MgH{sub 2}.

  14. Two-stage hydrotreating of a bitumen-derived middle distillate to produce diesel and jet fuels, and kinetics of aromatics hydrogenation

    SciTech Connect

    Yui, S.M.

    1994-12-31

    The middle distillate from a synthetic crude oil derived from Athabasca bitumen was further hydrotreated in a downflow pilot unit over a typical NiMo catalyst at 330 to 400 C, 7 to 11 MPa and 0.63 to 1.39 h{sup {minus}1} LHSV. Feed and liquid products were characterized for aromatics, cetane index (CI) and other diesel specification items. Aromatics were determined by a supercritical fluid chromatography method, while CI was determined using the correlation developed at Syncrude Canada Ltd. Also feed and selected products were distilled into a jet fuel cut (150/260 C) by spinning band distillation for the determination of smoke point and other jet fuel specification items. A good relationship between aromatics content and CI was obtained. Kinetics of aromatics hydrogenation were investigated, employing a simple-first order reversible reaction model.

  15. Kinetic study of terahertz generation based on the interaction of two-color ultra-short laser pulses with molecular hydrogen gas

    NASA Astrophysics Data System (ADS)

    Soltani Gishini, M. S.; Ganjovi, A.; Saeed, M.

    2016-06-01

    In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, interaction of two-color ultra-short laser pulses with the molecular hydrogen gas (H2) is examined. The operational laser parameters, i.e., its pulse shape, duration, and waist, are changed and, their effects on the density and kinetic energy of generated electrons, THz electric field, intensity, and spectrum are studied. It is seen that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse, and the intensity of generated THz radiation is increased at the higher pulse durations and waists. For all the operational laser parameters, the maximum value of emitted THz signal frequency always remains lower than 5 THz. The intensity of applied laser pulses is taken about 1014 w/cm2, and it is observed that while a small portion of the gaseous media gets ionized, the radiated THz signal is significant.

  16. Kinetic isotope effect of proton-coupled electron transfer in a hydrogen bonded phenol-pyrrolidino[60]fullerene.

    PubMed

    Ravensbergen, Janneke; Brown, Chelsea L; Moore, Gary F; Frese, Raoul N; van Grondelle, Rienk; Gust, Devens; Moore, Thomas A; Moore, Ana L; Kennis, John T M

    2015-12-01

    Proton-coupled electron transfer (PCET) plays a central role in photosynthesis and potentially in solar-to-fuel systems. We report a spectroscopy study on a phenol-pyrrolidino[60]fullerene. Quenching of the singlet excited state from 1 ns to 250 ps is assigned to PCET. A H/D exchange study reveals a kinetic isotope effect (KIE) of 3.0, consistent with a concerted PCET mechanism.

  17. Sorption of thallium(I) ions by peat.

    PubMed

    Robalds, Artis; Klavins, Maris; Dreijalte, Liga

    2013-01-01

    The increasing industrial use of thallium has raised the need for removal of this highly toxic element from wastewater. Thallium is more toxic than cadmium, copper, zinc, lead and mercury and as it is easily accumulated in humans, animals and plants, it poses a threat to both the environment and human health. Peat has been used as an effective, relatively cheap and easily available sorbent to treat waters containing heavy metals. In this study, peat was characterized and used as sorbent for the removal of Tl(I) ions from aqueous solution. The effect of initial Tl(I) concentration, pH, contact time, temperature and ionic strength was studied in batch mode. The maximum sorption capacity of peat reached 24.14 mg/g at 20 °C and initial Tl(I) concentration of 500 mg/L. Sorption capacity was found to be pH dependent and maximum uptake occurred at pH 10. Kinetic data revealed that sorption was relatively rapid - 82.8% of Tl(I) ions were sorbed in the first 10 min. The kinetics of sorption was analyzed using pseudo-first order and pseudo-second order models. Results show that peat can be used as an effective sorbent to remove Tl(I) ions from aqueous solutions.

  18. The dynamics of reductive sorption of oxygen by a granular bed of electron-ion exchangers with different copper dispersities

    NASA Astrophysics Data System (ADS)

    Konev, D. V.; Kravchenko, T. A.; Kalinichev, A. I.; Kipriyanova, E. S.

    2009-05-01

    The behavior of an immobile granular sorbent bed in one-component sorption in a column reactor is described in terms of the kinetic model of redox sorption taking into consideration the dispersity of metal particles, their radial distribution, peculiarities of chemical oxidation, and the relation of the overall rate of the process to the properties of the ion exchange matrix. The mathematical problem is formulated and solved numerically; the solution is analyzed theoretically in relation to the basic parameters of the sorption system. A satisfactory agreement is obtained between the experimental and calculated data on the reductive sorption of molecular oxygen from water on a copper-containing electron-ion exchanger.

  19. Kinetic measurement and prediction of the hydrogen outgassing from the polycrystalline LiH/Li2O/LiOH system

    SciTech Connect

    Dinh, L N; Grant, D M; Schildbach, M A; Smith, R A; Siekhaus, W J; Balazs, B; Leckey, J H; Kirkpatrick, J; McLean II, W

    2005-04-06

    Due to the exothermic reaction of lithium hydride (LiH) salt with water during transportation and handling, there is always a thin film of lithium hydroxide (LiOH) present on the LiH surface. In dry or vacuum storage, this thin LiOH film slowly decomposes. We have used temperature-programmed reaction/decomposition (TPR) in combination with the isoconversion method of thermal analysis to determine the outgassing kinetics of H{sub 2}O from pure LiOH and H{sub 2} and H{sub 2}O from this thin LiOH film. H{sub 2} production via the reaction of LiH with LiOH, forming a lithium oxide (Li{sub 2}O) interlayer, is thermodynamically favored, with the rate of further reaction limited by diffusion through the Li{sub 2}O and the stability of the decomposing LiOH. Lithium hydroxide at the LiOH/vacuum interface also decomposes easily to Li{sub 2}O, releasing H{sub 2}O which subsequently reacts with LiH in a closed system to form H{sub 2}. At the onset of dry decomposition, where H{sub 2} is the predominant product, the activation energy for outgassing from a thin LiOH film is lower than that for bulk LiOH. However, as the reactions at the LiH/Li{sub 2}O/LiOH and at the LiOH/vacuum interfaces proceed, the overall activation energy barrier for the outgassing approaches that of bulk LiOH decomposition. The kinetics developed here predicts a hydrogen evolution profile in good agreement with hydrogen release observed during long term isothermal storage.

  20. Elucidating hydrogen oxidation/evolution kinetics in base and acid by enhanced activities at the optimized Pt shell thickness on the Ru core

    SciTech Connect

    Elbert, Katherine; Hu, Jue; Ma, Zhong; Zhang, Yu; Chen, Guangyu; An, Wei; Liu, Ping; Isaacs, Hugh S.; Adzic, Radoslav R.; Wang, Jia X.

    2015-10-05

    Hydrogen oxidation and evolution on Pt in acid are facile processes, while in alkaline electrolytes, they are 2 orders of magnitude slower. Thus, developing catalysts that are more active than Pt for these two reactions is important for advancing the performance of anion exchange membrane fuel cells and water electrolyzers. Herein, we detail a 4-fold enhancement of Pt mass activity that we achieved using single-crystalline Ru@Pt core–shell nanoparticles with two-monolayer-thick Pt shells, which doubles the activity on Pt–Ru alloy nanocatalysts. For Pt specific activity, the two- and one-monolayer-thick Pt shells exhibited enhancement factors of 3.1 and 2.3, respectively, compared to the Pt nanocatalysts in base, differing considerably from the values of 1 and 0.4, respectively, in acid. To explain such behavior and the orders of magnitude difference in activity on going from acid to base, we performed kinetic analyses of polarization curves over a wide range of potential from –250 to 250 mV using the dual-pathway kinetic equation. From acid to base, the activation free energies increase the most for the Volmer reaction, resulting in a switch of the rate-determining step from the Tafel to the Volmer reaction, and a shift to a weaker optimal hydrogen binding energy. Furthermore, the much higher activation barrier for the Volmer reaction in base than in acid is ascribed to one or both of the two catalyst-insensitive factors: slower transport of OH than H+ in water and a stronger O–H bond in water molecules (HO–H) than in hydrated protons (H2O–H+).

  1. Elucidating hydrogen oxidation/evolution kinetics in base and acid by enhanced activities at the optimized Pt shell thickness on the Ru core

    DOE PAGES

    Elbert, Katherine; Hu, Jue; Ma, Zhong; Zhang, Yu; Chen, Guangyu; An, Wei; Liu, Ping; Isaacs, Hugh S.; Adzic, Radoslav R.; Wang, Jia X.

    2015-10-05

    Hydrogen oxidation and evolution on Pt in acid are facile processes, while in alkaline electrolytes, they are 2 orders of magnitude slower. Thus, developing catalysts that are more active than Pt for these two reactions is important for advancing the performance of anion exchange membrane fuel cells and water electrolyzers. Herein, we detail a 4-fold enhancement of Pt mass activity that we achieved using single-crystalline Ru@Pt core–shell nanoparticles with two-monolayer-thick Pt shells, which doubles the activity on Pt–Ru alloy nanocatalysts. For Pt specific activity, the two- and one-monolayer-thick Pt shells exhibited enhancement factors of 3.1 and 2.3, respectively, compared tomore » the Pt nanocatalysts in base, differing considerably from the values of 1 and 0.4, respectively, in acid. To explain such behavior and the orders of magnitude difference in activity on going from acid to base, we performed kinetic analyses of polarization curves over a wide range of potential from –250 to 250 mV using the dual-pathway kinetic equation. From acid to base, the activation free energies increase the most for the Volmer reaction, resulting in a switch of the rate-determining step from the Tafel to the Volmer reaction, and a shift to a weaker optimal hydrogen binding energy. Furthermore, the much higher activation barrier for the Volmer reaction in base than in acid is ascribed to one or both of the two catalyst-insensitive factors: slower transport of OH– than H+ in water and a stronger O–H bond in water molecules (HO–H) than in hydrated protons (H2O–H+).« less

  2. Modeling and Uncertainty Quantification of Vapor Sorption and Diffusion in Heterogeneous Polymers

    SciTech Connect

    Sun, Yunwei; Harley, Stephen J.; Glascoe, Elizabeth A.

    2015-08-13

    A high-fidelity model of kinetic and equilibrium sorption and diffusion is developed and exercised. The gas-diffusion model is coupled with a triple-sorption mechanism: Henry’s law absorption, Langmuir adsorption, and pooling or clustering of molecules at higher partial pressures. Sorption experiments are conducted and span a range of relative humidities (0-95 %) and temperatures (30-60 °C). Kinetic and equilibrium sorption properties and effective diffusivity are determined by minimizing the absolute difference between measured and modeled uptakes. Uncertainty quantification and sensitivity analysis methods are described and exercised herein to demonstrate the capability of this modeling approach. Water uptake in silica-filled and unfilled poly(dimethylsiloxane) networks is investigated; however, the model is versatile enough to be used with a wide range of materials and vapors.

  3. Environmental fatigue of an Al-Li-Cu alloy. Part 1: Intrinsic crack propagation kinetics in hydrogenous environments

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1991-01-01

    Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness by aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl, and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075.

  4. Environmental fatigue of an Al-Li-Cu alloy. I - Intrinsic crack propagation kinetics in hydrogenous environments

    NASA Technical Reports Server (NTRS)

    Piascik, Robert S.; Gangloff, Richard P.

    1991-01-01

    Deleterious environmental effects on steady-state, intrinsic fatigue crack propagation (FCP) rates (da/dN) in peak aged Al-Li-Cu alloy 2090 are established by electrical potential monitoring of short cracks with programmed constant delta K and K(sub max) loading. The da/dN are equally unaffected by vacuum, purified helium, and oxygen but are accelerated in order of decreasing effectiveness of aqueous 1 percent NaCl with anodic polarization, pure water vapor, moist air, and NaCl with cathodic polarization. While da/dN depends on delta K(sup 4.0) for the inert gases, water vapor and chloride induced multiple power-laws, and a transition growth rate 'plateau'. Environmental effects are strongest at low delta K. Crack tip damage is ascribed to hydrogen embrittlement because of the following: (1) accelerated da/dN due to part-per-million levels of H2O without condensation; (2) impeded molecular flow model predictions of the measured water vapor pressure dependence of da/dN as affected by mean crack opening; (3) the lack of an effect of film-forming O2; (4) the likelihood for crack tip hydrogen production in NaCl; and (5) the environmental and delta K-process zone volume dependencies of the microscopic cracking modes. For NaCl, growth rates decrease with decreasing loading frequency, with the addition of passivating Li2CO3, and upon cathodic polarization. These variables increase crack surface film stability to reduce hydrogen entry efficiency. The hydrogen environmental FCP resistance of 2090 is similar to other 2000 series alloys and is better than 7075.

  5. Preparation of Pt/Al2O3 catalyst in CTAB microemulsion and kinetics of m-chloronitrobenzene hydrogenation

    NASA Astrophysics Data System (ADS)

    Li, Feng; Cao, Bo; Ma, Rui; Song, Hualin; Song, Hua

    2016-02-01

    Pt/Al2O3 catalyst was prepared successfully by a microemulsion method using cetyltrimethylammonium bromide (CTAB) as the surfactant and N2H5OH as the reducing agent. Selective hydrogenation of m-chloronitrobenzene ( m-CNB) was used as a probe to investigate how parameters affect the preparation of catalysts via the microemulsion method. Transmission electron microscope (TEM) and selected-area electron diffraction (SAED) show that Pt particles (mean size 3 nm) were distributed uniformly on the catalyst and were in polycrystalline structure. Experiments on m-CNB selective hydrogenation show that at 303 K and hydrogen pressure of 0.1 MPa, the turnover frequency (TOF) was 0.216 s-1, the m-CNB conversion was 99.6% and the m-CAN selectivity was 98.9%, indicating high dechlorination inhibition effect. The reaction was an approximately first-order process with apparent activation energy of 26.92 kJ mol-1.

  6. Kinetic measurements of the reactivity of hydrogen peroxide and ozone towards small atmospherically relevant aldehydes, ketones and organic acids in aqueous solutions

    NASA Astrophysics Data System (ADS)

    Schöne, L.; Herrmann, H.

    2014-05-01

    Free radical reactions are an important degradation process for organic compounds within the aqueous atmospheric environment. Nevertheless, non-radical oxidants such as hydrogen peroxide and ozone also contribute to the degradation and conversion of these substances (Tilgner and Herrmann, 2010). In this work, kinetic investigations of non-radical reactions were conducted using UV / Vis spectroscopy (dual-beam spectrophotometer and stopped flow technique) and a capillary electrophoresis system applying pseudo-first order kinetics to reactions of glyoxal, methylglyoxal, glycolaldehyde, glyoxylic, pyruvic and glycolic acid as well as methacrolein (MACR) and methyl vinyl ketone (MVK) with H2O2 and ozone at 298 K. The measurements indicate rather small rate constants at room temperature of k2nd < 3 M-1 s-1 (except for the unsaturated compounds exposed to ozone). Compared to radical reaction rate constants the values are about 10 orders of magnitude smaller (kOH • ~109 M-1 s-1). However, when considering the much larger non-radical oxidant concentrations compared to radical concentrations in urban cloud droplets, calculated first-order conversion rate constants change the picture towards H2O2 reactions becoming more important, especially when compared to the nitrate radical. For some reactions mechanistic suggestions are also given.

  7. Kinetic measurements on the reactivity of hydrogen peroxide and ozone towards small atmospherically relevant aldehydes, ketones and organic acids in aqueous solution

    NASA Astrophysics Data System (ADS)

    Schöne, L.; Herrmann, H.

    2013-10-01

    Within the aqueous atmospheric environment free radical reactions are an important degradation process for organic compounds. Nevertheless, non-radical oxidants like hydrogen peroxide and ozone also contribute to the degradation and conversion of this substance group (Tilgner und Herrmann, 2010). In this work kinetic investigations of non-radical reactions were conducted using UV/Vis spectroscopy (dual-beam spectrophotometer and Stopped Flow technique) and a capillary electrophoresis system applying pseudo-first order kinetics of glyoxal, methylglyoxal, glycolaldehyde, glyoxylic, pyruvic and glycolic acids as well as methacrolein (MACR) and methyl vinyl ketone (MVK) towards H2O2 and ozone. The measurements indicate rather small rate constants at room temperature of k2nd < 3 M-1 s-1 (except for the unsaturated compounds exposed to ozone). Compared to radical reaction rate constants the values are about 10 orders of magnitude smaller (kOH· ~ 109 M-1 s-1). However, when considering the much larger non-radical oxidant concentrations compared to radical concentrations in urban cloud droplets, calculated turnovers change the picture to more important H2O2 reactions especially when compared to the nitrate radical. For some reactions also mechanistic suggestions are given.

  8. Hydrogen/Deuterium Exchange Kinetics Demonstrate Long Range Allosteric Effects of Thumb Site 2 Inhibitors of Hepatitis C Viral RNA-dependent RNA Polymerase.

    PubMed

    Deredge, Daniel; Li, Jiawen; Johnson, Kenneth A; Wintrode, Patrick L

    2016-05-01

    New nonnucleoside analogs are being developed as part of a multi-drug regimen to treat hepatitis C viral infections. Particularly promising are inhibitors that bind to the surface of the thumb domain of the viral RNA-dependent RNA polymerase (NS5B). Numerous crystal structures have been solved showing small molecule non-nucleoside inhibitors bound to the hepatitis C viral polymerase, but these structures alone do not define the mechanism of inhibition. Our prior kinetic analysis showed that nonnucleoside inhibitors binding to thumb site-2 (NNI2) do not block initiation or elongation of RNA synthesis; rather, they block the transition from the initiation to elongation, which is thought to proceed with significant structural rearrangement of the enzyme-RNA complex. Here we have mapped the effect of three NNI2 inhibitors on the conformational dynamics of the enzyme using hydrogen/deuterium exchange kinetics. All three inhibitors rigidify an extensive allosteric network extending >40 Å from the binding site, thus providing a structural rationale for the observed disruption of the transition from distributive initiation to processive elongation. The two more potent inhibitors also suppress slow cooperative unfolding in the fingers extension-thumb interface and primer grip, which may contribute their stronger inhibition. These results establish that NNI2 inhibitors act through long range allosteric effects, reveal important conformational changes underlying normal polymerase function, and point the way to the design of more effective allosteric inhibitors that exploit this new information. PMID:27006396

  9. Mechanisms of some hydrogen-transfer reactions: temperature dependence of the kinetic isotope effect and intramolecular C-H insertion: synthesis of (+/-)-pentalenolactone E methyl ester

    SciTech Connect

    Schuchardt, J.L.

    1985-01-01

    The mechanisms of three familiar organic hydrogen transfer reactions have been investigated by a study of the temperature dependence of the kinetic isotope effect. The Oppenauer oxidation of benzhydrol to benzophenone resulted in relatively small isotope effects (k/sub H//k/sub D/ = 2.3 10/sup 0/C), which are consistent with either a linear, unsymmetrical or a nonlinear H-transfer. The temperature dependence of k/sub H//k/sub D/ is in doubt due to an unanticipated isotopic scrambling effect. The Grignard reduction of benzophenone by isobutylmagnesium bromide shows significant temperature dependence of the kinetic isotope effect. The less-than-maximum isotope effects and activation energy difference suggest an unsymmetrical linear H-transfer mechanism. There is no evidence of tunneling in either the Oppenauer oxidation of the Grignard reduction with the system investigated. The reduction of benzyl bromide by tri-n-butyltin hydride gives temperature-dependent isotope effects and activation parameters consistent with an unsymmetrical linear H-transfer. The results for cyclohexyl bromide were less illuminating. (+/-)-Pentalenolactone E methyl ester was synthesized in 12 steps from 4,4-dimethylcyclohexanone. Disconnection of the target molecule at a unveils substantial molecular symmetry. The key to the analysis is the synthetic step which allows bond formation to an unfunctionalized carbon atom. The key step, rhodium-mediated intramolecular C-H insertion successfully generated the tricyclic skeleton of pentalenolactone via a sterically congested transition state.

  10. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    SciTech Connect

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-21

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53–75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  11. Quantitative analysis of desorption and decomposition kinetics of formic acid on Cu(111): The importance of hydrogen bonding between adsorbed species

    NASA Astrophysics Data System (ADS)

    Shiozawa, Yuichiro; Koitaya, Takanori; Mukai, Kozo; Yoshimoto, Shinya; Yoshinobu, Jun

    2015-12-01

    Quantitative analysis of desorption and decomposition kinetics of formic acid (HCOOH) on Cu(111) was performed by temperature programmed desorption (TPD), X-ray photoelectron spectroscopy, and time-resolved infrared reflection absorption spectroscopy. The activation energy for desorption is estimated to be 53-75 kJ/mol by the threshold TPD method as a function of coverage. Vibrational spectra of the first layer HCOOH at 155.3 K show that adsorbed molecules form a polymeric structure via the hydrogen bonding network. Adsorbed HCOOH molecules are dissociated gradually into monodentate formate species. The activation energy for the dissociation into monodentate formate species is estimated to be 65.0 kJ/mol at a submonolayer coverage (0.26 molecules/surface Cu atom). The hydrogen bonding between adsorbed HCOOH species plays an important role in the stabilization of HCOOH on Cu(111). The monodentate formate species are stabilized at higher coverages, because of the lack of vacant sites for the bidentate formation.

  12. Kinetic evidence for the formation of discrete 1,4-dehydrobenzene intermediates. Trapping by inter- and intramolecular hydrogen atom transfer and observation of high-temperature CIDNP

    SciTech Connect

    Lockhart, Thomas P.; Comita, Paul B.; Bergman, Robert G.

    1981-07-01

    Upon heating, alkyl-substituted cis-1,2-diethynyl olefins undergo cyclization to yield reactive 1,4-dehydrobenzenes; the products isolated may be derived from either unimolecular or bimolecular reactions of the intermediate. (Z)-4,5-Diethynyl-4-octene (4) undergoes rearrangement to yield 2,3-di-n-propyl-1,4-dehydrobenzene (17). Solution pyrolysis of 4 in inert aromatic solvents produces three unimolecular products, (Z)-dodeca-4,8-diyn-6-ene (7), benzocyclooctene (9), and o-allyl-n-propylbenzene (10), in high yield. When 1,4-cyclohexadiene is added to the pyrolysis solution as a trapping agent, high yields of the reduced product o-di-n-propylbenzene (12) are obtained. The kinetics of solution pyrolysis of 4 in the presence and absence of trapping agent establish that 2,3-di-n-propyl-1,4-dehydrobenzene is a discrete intermediate on the pathway leading to products. When the reaction was run in the heated probe of an NMR spectrometer, CIDNP was observed in 10. This observation, along with kinetic and chemical trapping evidence, indicates the presence of two additional intermediates, formed from 17 by sequential intramolecular [1,5] hydrogen transfer, on the pathway to products. The observation of CIDNP, coupled with the reactivity exhibited by 17 and the other two intermediates, implicate a biradical description of these molecules. Biradical 17 has been estimated to have a lifetime of about 10-9 s at 200°C and to lie in a well of about 5 kcal/mol with respect to the lowest energy unimolecular pathway ([1,5] hydrogen transfer). Ring opening (expected to be the lowest energy process for 1,4-dehydrobenzenes in which intramolecular hydrogen transfer is unlikely) to the isomeric diethynyl olefin 7 appears to have an activation enthalpy of about 10 kcal/moL Upon thermal reaction in the gas phase (400°C) or in solution in inert solvents (Z)-hexa-2,3-diethyl-1,5-diyn-3-ene (5) rearranges in good yield to the isomeric diethynyl olefin (Z)-deca-3,7-diyn-5-ene (8

  13. Pyrrole Hydrogenation over Rh(111) and Pt(111) Single-Crystal Surfaces and Hydrogenation Promotion Mediated by 1-Methylpyrrole: A Kinetic and Sum-Frequency Generation Vibrational Spectroscopy Study

    SciTech Connect

    Kliewer, Christopher J.; Bieri, Marco; Somorjai, Gabor A.

    2008-03-04

    Sum-frequency generation (SFG) surface vibrational spectroscopy and kinetic measurements using gas chromatography have been used to study the adsorption and hydrogenation of pyrrole over both Pt(111) and Rh(111) single-crystal surfaces at Torr pressures (3 Torr pyrrole, 30 Torr H{sub 2}) to form pyrrolidine and the minor product butylamine. Over Pt(111) at 298 K it was found that pyrrole adsorbs in an upright geometry cleaving the N-H bond to bind through the nitrogen evidenced by SFG data. Over Rh(111) at 298 K pyrrole adsorbs in a tilted geometry relative to the surface through the p-aromatic system. A pyrroline surface reaction intermediate, which was not detected in the gas phase, was seen by SFG during the hydrogenation over both surfaces. Significant enhancement of the reaction rate was achieved over both metal surfaces by adsorbing 1-methylpyrrole before reaction. SFG vibrational spectroscopic results indicate that reaction promotion is achieved by weakening the bonding between the N-containing products and the metal surface because of lateral interactions on the surface between 1-methylpyrrole and the reaction species, reducing the desorption energy of the products. It was found that the ring-opening product butylamine was a reaction poison over both surfaces, but this effect can be minimized by treating the catalyst surfaces with 1-methylpyrrole before reaction. The reaction rate was not enhanced with elevated temperatures, and SFG suggests desorption of pyrrole at elevated temperatures.

  14. Catalyzed light hydride nanomaterials embedded in a micro-channels hydrogen storage container.

    PubMed

    Dehouche, Zahir; Peretti, Hernán A; Yoo, Yeong; Belkacemi, Khaled; Goyette, Jacques

    2009-01-01

    Activated alloys synthesized by arc-melting were examined as catalysts for improving the hydrogen sorption characteristics of nanostructured magnesium hydride, proposed as a reversible hydrogen storage material. The MgH(2)-catalyst absorbing materials were prepared by ball milling of pure MgH(2) with hydrided Zr(47)Ni(53), Zr(9)Ni(11), and other alloys investigated. The nanostructured MgH(2)-intermetallic systems were tested at 250 degrees C and catalyst addition of eutectoid Zr(47)Ni(53) resulted in the fastest desorption time and highest initial desorption rate. The catalyzed Mg-hydride with activated Zr(9)Ni(11) and Zr(7)Ni(10) phases showed fast desorption kinetics. Moreover, the results demonstrated that the composition of dispersed Zr(x)Ni(y)catalysts has a strong influence on the amount of accumulated hydrogen and desorption rate of Mg-nanocomposite. Part two covers advanced micro-channels hydrogen storage module design based on the results of semi-empirical computer simulations of heat and mass transfers in the container. The micro-channels reservoir concept offers many advantages over the conventional metal hydride hydrogen storage system. It is a micro-structured system that can pack a lot of power into a small space and dissipate effectively the heat of the sorption reactions. This review summarizes recent patents related to CNTS.

  15. Surface response of tungsten to helium and hydrogen plasma flux as a function of temperature and incident kinetic energy

    NASA Astrophysics Data System (ADS)

    Sukumar, Harikrishnan

    Tungsten is a leading candidate material for the diverter in future nuclear fusion reactors. Previous experiments have demonstrated that surface defects and bubbles form in tungsten when ex- posed to helium and hydrogen plasmas, even at modest ion energies. In some regimes, between 1000K and 2000K, and for He energies below 100eV, "fuzz" like features form. The mechanisms leading to these surfaces comprised of nanometer sized tungsten tendrils which include visible helium bubbles are not currently known. The role of helium bubble formation in tendril morphology could very likely be the starting point of these mechanisms. Using Molecular dynamics (MD) simulations, the role of helium and hydrogen exposure in the initial formation mechanisms of tungsten "fuzz" are investigated. Molecular dynamics simulations are well suited to describe the time and length scales associated with initial formation of helium clusters that eventually grow to nano-meter sized helium bubbles. MD simulations also easily enable the modeling of a variety of surfaces such as single crystals, grain boundaries or "tendrils". While the sputtering yield of tungsten is generally low, previous observations of surface modification due to plasma exposure raise questions about the effects of surface morphology and sub-surface helium bubble populations on the sputtering behavior. Results of computational molecular dynamics are reported that investigate the influence of sub-surface helium bubble distributions on the sputtering yield of tungsten (100) and (110) surfaces induced by helium ion exposure in the range of 300 eV to 1 keV. The calculated sputtering yields are in reasonable agreement with a wide range of experimental data; but do not show any significant variation as a result of the pre-existing helium bubbles. Molecular dynamics simulations reveal a number of sub-surface mechanisms leading to nanometer- sized "fuzz" in tungsten exposed to low-energy helium plasmas. We find that during the bubble

  16. EFFECT OF TEMPERATURE ON THE SORPTION OF CHELATED RADIONUCLIDES.

    USGS Publications Warehouse

    Maest, Ann S.; Crerar, David A.; Dillon, Edward C.; Trehu, Stephen M.; Rountree, Tamara N.; ,

    1985-01-01

    Temperature effects in the near-field radioactive waste disposal environment can result in changes in the adsorptive capacity and character of the substrate and the chemistry of the reacting fluids. This work examines the effect of temperature on 1) the kinetics of radionuclide sorption onto clays from 25 degree -75 degree C and 2) the degradation and metal-binding ability of two organic complexing agents found in chelated radioactive wastes and natural groundwaters.

  17. Sorption isotherms and isosteric heats of sorption of Malaysian paddy.

    PubMed

    Mousa, Wael; Ghazali, Farinazleen Mohamad; Jinap, S; Ghazali, Hasanah Mohd; Radu, Son

    2014-10-01

    Understanding the water sorption characteristics of cereal is extremely essential for optimizing the drying process and ensuring storage stability. Water relation of rough rice was studied at 20, 30, 40 and 50 °C over relative humidity (RH.) between 0.113 and 0.976 using the gravimetric technique. The isotherms displayed the general sigmoid, Type II pattern and exhibited the phenomenon of hysteresis where it was more pronounced at lower temperatures. The sorption characteristics were temperature dependence where the sorption capacity of the paddy increased as the temperature was decreased at fixed (RH). Among the models assessed for their ability to fit the sorption data, Oswin equation was the best followed by the third order polynomial, GAB, Smith, Chung-Pfost, and Henderson models. The monolayer moisture content was higher for desorption than adsorption and tend to decrease with the increase in temperature. Given the temperature dependence of the sorption isotherms the isosteric heats of sorption were calculated using Claussius-Clapeyron equation. The net isosteric heats decreased as the moisture content was increased and heats of desorption were greater than that of adsorption. PMID:25328208

  18. Excellent catalytic effects of highly crumpled graphene nanosheets on hydrogenation/dehydrogenation of magnesium hydride.

    PubMed

    Liu, Guang; Wang, Yijing; Xu, Changchang; Qiu, Fangyuan; An, Cuihua; Li, Li; Jiao, Lifang; Yuan, Huatang

    2013-02-01

    Highly crumpled graphene nanosheets (GNS) with a BET surface area as high as 1159 m(2) g(-1) was fabricated by a thermal exfoliation method. A systematic investigation was performed on the hydrogen sorption properties of MgH(2)-5 wt% GNS nanocomposites acquired by ball-milling. It was found that the as-synthesized GNS exhibited a superior catalytic effect on hydrogenation/dehydrogenation of MgH(2). Differential Scanning Calorimetry (DSC) and isothermal hydrogenation/dehydrogenation measurements indicated that both hydrogen sorption capacity and dehydrogenation/hydrogenation kinetics of the composites improved with increasing milling time. The composites MgH(2)-GNS milled for 20 h can absorb 6.6 wt% H(2) within 1 min at 300 °C and 6.3 wt% within 40 min at 200 °C, even at 150 °C, it can also absorb 6.0 wt% H(2) within 180 min. It was also demonstrated that MgH(2)-GNS-20 h could release 6.1 wt% H(2) at 300 °C within 40 min. In addition, microstructure measurements based on XRD, SEM, TEM as well as Raman spectra revealed that the grain size of thus-prepared MgH(2)-GNS nanocomposites decreased with increasing milling time, moreover, the graphene layers were broken into smaller graphene nanosheets in a disordered and irregular manner during milling. It was confirmed that these smaller graphene nanosheets on the composite surface, providing more edge sites and hydrogen diffusion channels, prevented the nanograins from sintering and agglomerating, thus, leading to promotion of the hydrogenation/dehydrogenation kinetics of MgH(2). PMID:23254449

  19. Sludge-Derived Biochar for Arsenic(III) Immobilization: Effects of Solution Chemistry on Sorption Behavior.

    PubMed

    Zhang, Weihua; Zheng, Juan; Zheng, Pingping; Tsang, Daniel C W; Qiu, Rongliang

    2015-07-01

    Recycling sewage sludge by pyrolysis has attracted increasing attention for pollutant removal from wastewater and soils. This study scrutinized As(III) sorption behavior on sludge-derived biochar (SDBC) under different pyrolysis conditions and solution chemistry. The SDBC pyrolyzed at a higher temperature showed a lower As(III) sorption capacity and increasingly nonlinear isotherm due to loss of surface sites and deoxygenation-dehydrogenation. The Langmuir sorption capacity on SDBC (3.08-6.04 mg g) was comparable to other waste-derived sorbents, with the highest As(III) sorption on SDBC pyrolyzed at 400°C for 2 h. The As(III) sorption kinetics best fit with the pseudo-second-order equation, thus suggesting the significance of the availability of surface sites and initial concentration. Sorption of As(III) was faster than that of Cr(VI) but slower than that of Pb(II), which was attributed to their differences in molar volume (correlated to diffusion coefficients) and sorption mechanisms. The X-ray photoelectron spectra revealed an increase of oxide oxygen (O) with a decrease of sorbed water, indicative of ligand exchange with hydroxyl groups on SDBC surfaces. The As(III) sorption was not pH dependent in acidic-neutral range (pH < 8) due to the buffering capacity and surface characteristics of the SDBC; however, sorption was promoted by increasing pH in the alkaline range (pH > 8) because of As(III) speciation in solution. An increasing ionic strength (0.001-0.1 mol L) facilitated As(III) sorption, indicating the predominance of ligand exchange over electrostatic interactions, while high concentrations (0.1 mol L) of competing anions (fluoride, sulfate, carbonate, and phosphate) inhibited As(III) sorption. These results suggest that SDBC is applicable for As(III) immobilization in most environmentally relevant conditions. PMID:26437093

  20. Sorption-desorption and biosorption of bisphenol A, triclosan, and 17α-ethinylestradiol to sewage sludge.

    PubMed

    Banihashemi, Bahman; Droste, Ronald L

    2014-07-15

    To better understand the fate of microconstituents (MCs) in an activated sludge (AS) system, sorption, biosorption, and desorption studies were investigated at μg/L range for 17α-ethinylestradiol (EE2), bisphenol A (BPA), and triclosan (TCS). Batch experiments with activated and deactivated sludge originating from continuous flow porous pot reactors operating at solid retention times (SRTs) of 5, 10, and 15 days were conducted in order to investigate the sorption kinetics and distinguish physicochemical sorption and biosorption. The effect of SRT and the biomass concentration on sorption kinetics were also studied. Selected MCs showed high sorption affinity to the non-viable biomass during the first 30 min of the experiment, which was gradually reduced until equilibrium was reached. Desorption results showed two distinct stages, a very rapid desorption within 20 min followed by a slow desorption stage. Biosorption study indicated that the soluble concentrations of target compounds decreased rapidly for selected MCs similar to the sorption study; however, the soluble and solid phase concentrations continued to decrease slowly during the length of the experiment which indicates the possible biodegradation of these compounds in both phases. Finally, mathematical models were applied to describe the sorption mechanism and Freundlich sorption isotherms with values of 1/n close to 1 were found to best fit the results which demonstrate that all tested concentrations result on the linear part of the Freundlich isotherm. Calculation of the Freundlich constant, KF and distribution coefficient, Kd exhibited the greater tendency of EE2 and TCS for sorption, compared to BPA. The results of this study indicated that the SRT had a clear effect on the sorption kinetics where the highest sorption rate constant was achieved for a SRT of 10 days for all three target substances. This could be due to change of the morphology of the biomass from reactors operating at different SRTs

  1. Silica Precipitation and Lithium Sorption

    SciTech Connect

    Jay Renew

    2015-09-20

    This file contains silica precipitation and lithium sorption data from the project. The silica removal data is corrected from the previous submission. The previous submission did not take into account the limit of detection of the ICP-MS procedure.

  2. Comparison of the sorption behaviors and mechanisms of perfluorosulfonates and perfluorocarboxylic acids on three kinds of clay minerals.

    PubMed

    Zhao, Lixia; Bian, Jingna; Zhang, Yahui; Zhu, Lingyan; Liu, Zhengtao

    2014-11-01

    The sorption of four perfluoroalkyl acids (PFAAs) [perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA)] on three typical minerals [montmorillonite (MM), kaolinite (KL) and hematite (HM)] was studied. The sorption of PFOS and PFHxS was much stronger than PFOA and PFHxA. The sorption of each PFAA on the minerals followed an order of HM>KL>MM, even though MM was positively while KL and HM were negatively charged, implying that the sorption is driven by some other interactions besides electrostatic attraction. The sorption decreased with an increase in pH and a decrease in ionic strength of the solution, and their impacts on PFOS were much stronger than other three PFAAs. Surface complexing and hydrogen-bonding could make great contributions to the sorption of PFOS on the minerals. The results are important for understanding the transport and fate of PFAAs in sediment and ground water. PMID:25113183

  3. Comparison of the sorption behaviors and mechanisms of perfluorosulfonates and perfluorocarboxylic acids on three kinds of clay minerals.

    PubMed

    Zhao, Lixia; Bian, Jingna; Zhang, Yahui; Zhu, Lingyan; Liu, Zhengtao

    2014-11-01

    The sorption of four perfluoroalkyl acids (PFAAs) [perfluorooctane sulfonate (PFOS), perfluorohexane sulfonate (PFHxS), perfluorooctanoic acid (PFOA) and perfluorohexanoic acid (PFHxA)] on three typical minerals [montmorillonite (MM), kaolinite (KL) and hematite (HM)] was studied. The sorption of PFOS and PFHxS was much stronger than PFOA and PFHxA. The sorption of each PFAA on the minerals followed an order of HM>KL>MM, even though MM was positively while KL and HM were negatively charged, implying that the sorption is driven by some other interactions besides electrostatic attraction. The sorption decreased with an increase in pH and a decrease in ionic strength of the solution, and their impacts on PFOS were much stronger than other three PFAAs. Surface complexing and hydrogen-bonding could make great contributions to the sorption of PFOS on the minerals. The results are important for understanding the transport and fate of PFAAs in sediment and ground water.

  4. Heavy metal sorption by calcium alginate beads from Laminaria digitata.

    PubMed

    Papageorgiou, Sergios K; Katsaros, Fotios K; Kouvelos, Evangelos P; Nolan, John W; Le Deit, Herve; Kanellopoulos, Nick K

    2006-10-11

    Alginate with a high M/G ratio, extracted from Laminaria digitata, was evaluated for Cu(2+), Cd(2+) and Pb(2+) sorption in acidic solutions, in the form of calcium cross-linked beads. The high M/G ratio of alginate extracted from this algal species is most likely the determining factor for the increased adsorption capacity of the investigated metals, indicating that the mannuronic acid is responsible for the ion exchange mechanism. The data obtained from the batch experiments have been interpreted with Langmuir, Freundlich and Sips models. The Sips equation provided the best fit with the experimental results, indicating sorption sites heterogeneity for the material. The pH was found to have a significant effect on the process, with sorption capacity reaching a maximum at pH 4.5, indicating a competition mechanism between H(+) and metal ions. Kinetic experiments were performed at the optimum pH. For the interpretation of the kinetic experiments the Linear Adsorption Model was employed and diffusion coefficients were determined. The model fits the experimental data at higher concentrations, where the adsorbed quantity remains almost constant. Finally, a simplified expression of the batch kinetic adsorption model was employed. The model, predicts adequately, not only the diffusivity values, but also the concentration profiles inside the spherical particles.

  5. Study of the dissociation of molecular hydrogen

    NASA Technical Reports Server (NTRS)

    Vessot, R. F. C.

    1981-01-01

    Dissociators used to obtain an RF plasma discharge for hydrogen masers and the test system used for operation and evaluation of the dissociators are described. A compact sorption cartridge using a graphite matrix is tested as part of a hydrogen scavenging system. Testing of a vacuum enclosed hydrogen dissociator suitable for long term operation in space is described.

  6. Electrochemical kinetic performances of electroplating Co-Ni on La-Mg-Ni-based hydrogen storage alloys

    NASA Astrophysics Data System (ADS)

    Li, Yuan; Tao, Yang; Ke, Dandan; Ma, Yufei; Han, Shumin

    2015-12-01

    Electroplating Co-Ni treatment was applied to the surface of the La0.75Mg0.25Ni3.48 alloy electrodes in order to improve the electrochemical and kinetic performances. The Scanning electron microscope-Energy dispersive spectroscopy and X-ray diffraction results showed that the electrodes were plated with a homogeneous Co-Ni alloy film. The alloy coating significantly improved the high rate dischargeability of the alloy electrode, and the HRD value increased to 57.5% at discharge current density 1875 mA/g after the Co-Ni-coating. The exchange current density I0, the limiting current density IL and the oxidation peak current also increased for the coated alloy. The improvement of overall electrode performances was attributed to an enhancement in electro-catalytic activity and conductivity at the alloy surface, owing to the precipitation of the Co-Ni layer.

  7. THERMOCHEMICAL AND PHOTOCHEMICAL KINETICS IN COOLER HYDROGEN-DOMINATED EXTRASOLAR PLANETS: A METHANE-POOR GJ436b?

    SciTech Connect

    Line, Michael R.; Yung, Yuk L.; Vasisht, Gautam; Chen, Pin; Angerhausen, D. E-mail: gv@s383.jpl.nasa.gov

    2011-09-01

    We introduce a thermochemical kinetics and photochemical model. We use high-temperature bidirectional reaction rates for important H, C, O, and N reactions (most importantly for CH{sub 4} to CO interconversion), allowing us to attain thermochemical equilibrium, deep in an atmosphere, purely kinetically. This allows the chemical modeling of an entire atmosphere, from deep-atmosphere thermochemical equilibrium to the photochemically dominated regime. We use our model to explore the atmospheric chemistry of cooler (T{sub eff} < 10{sup 3} K) extrasolar giant planets. In particular, we choose to model the nearby hot-Neptune GJ436b, the only planet in this temperature regime for which spectroscopic measurements and estimates of chemical abundances now exist. Recent Spitzer measurements with retrieval have shown that methane is driven strongly out of equilibrium and is deeply depleted on the day side of GJ436b, whereas quenched carbon monoxide is abundant. This is surprising because GJ436b is cooler than many of the heavily irradiated hot Jovians and thermally favorable for CH{sub 4}, and thus requires an efficient mechanism for destroying it. We include realistic estimates of ultraviolet flux from the parent dM star GJ436, to bound the direct photolysis and photosensitized depletion of CH{sub 4}. While our models indicate fairly rich disequilibrium conditions are likely in cooler exoplanets over a range of planetary metallicities, we are unable to generate the conditions for substantial CH{sub 4} destruction. One possibility is an anomalous source of abundant H atoms between 0.01 and 1 bars (which attack CH{sub 4}), but we cannot as yet identify an efficient means to produce these hot atoms.

  8. Kinetics study of fermentative hydrogen production from liquid swine manure supplemented with glucose under controlled pH.

    PubMed

    Wu, Xiao; Zhu, Jun; Miller, Curtis

    2013-01-01

    Kinetics of H2 production from liquid swine manure supplemented with glucose by mixed anaerobic cultures was investigated using batch experiments under four different pH conditions (4.4, 5.0, 5.6, and uncontrolled). The temperature for the experiments was controlled at 37 ± 1°C and the length of experiments varied between 50 and 120 hours, depending upon the time needed for completion of each individual experiment. The modified Gompertz model was evaluated for its suitability for describing the H2 production potential, H2 production rate, and substrate consumption rate for all the experiments. The results showed that the Gompertz model could adequately fit the experimental results. The effect of pH was significant on all kinetic parameters for H2 production including yield, production rate and lag time, and the substrate utilization rate. The optimal pH was found to be 5.0, at which a maximum H2 production rate (0.64 L H2/h) was obtained, and deviation from the optimal pH could result in substantial reductions in H2 production rate (0.32 L H2/h for pH 4.0 and 0.43 L H2/h for pH 5.6). The results also showed that if pH was not controlled for the batch fermentation process, the substrate utilization efficiency could steeply decrease from 98.8% to 33.7%.

  9. Sorption of organophosphorous pesticides onto chickpea husk from aqueous solutions.

    PubMed

    Akhtar, Mubeena; Iqbal, Shahid; Bhanger, M I; Zia-Ul-Haq, Muhammad; Moazzam, Muhammad

    2009-02-15

    The sorption efficiency of chickpea husk of black gram variety (BGH), for the removal of organophosphorous pesticides (OPPs), i.e. triazophos (TAP) and methyl parathion (MP) from aqueous media has been investigated. Optimization of operating sorption parameters, i.e. particle size, sorbent dose, agitation time, pH, initial concentration of sorbates, and temperature has been studied. The sorption data fitted well to Freundlich, Langmuir and Dubinin-Radushkevich (D-R) sorption isotherms. The maximum sorption capacities of BGH for TAP and MP were calculated to be 3.5+/-0.45 and 10.6+/-0.83 mmol g(-1) by Freundlich, 0.0077+/-0.021 and 0.025+/-0.0094 mmol g(-1) by Langmuir and 0.48+/-0.037 and 0.15+/-0.077 mmol g(-1) by D-R isotherms respectively, employing 0.2g of sorbent, at pH 6, 90 min agitation time and at 303 K. Application of first order Lagergren and Morris-Weber equations to the kinetic data yielded correlation coefficients, close to unity and showed partial intra-particle diffusion. The negative values of thermodynamic parameters, i.e. DeltaH (kJ mol(-1)), DeltaS (J mol(-1) K(-1)) and DeltaG (kJ mol(-1)) indicate the exothermic and spontaneous nature of the sorption process. The sorbed pesticides were recovered by sonication with methanol, making the regeneration and reutilization of the sorbents promising. The investigated sorbent exhibited potential applications in water decontamination, treatments of industrial and agricultural waste waters and thus productively demonstrated viable use of agricultural waste material.

  10. Linearity of iodine sorption and sorption capacities for seven soils

    SciTech Connect

    Sheppard, M.I.; Hawkins, J.L.; Smith, P.A.

    1996-11-01

    Iodine, a soluble and prevalent element in spent nuclear fuel and a pivotal element in the assessment of Canada`s nuclear fuel waste disposal option, sorbs to soils rich in organics and hydrous oxides. Biotic factors, such as microbes, enzymes and plant exudates, have been implicated in the retention of I to soils. Anion exchange of I{sup {minus}} or IO{sub 3}{sup {minus}} and chemical or biological oxidation to I{sub 2} followed by reactions with the soil organic matter are possible retention mechanisms. We have carried out sorption and desorption studies across a wide range of soil solution concentrations (10{sup {minus}7} to 10{sup 5} mg I/L, 10{sup {minus}12} to 1 M) for seven soils typical of upland and lowland soils of the Canadian Precambrian Shield. Soil solid-liquid partition values (K{sub d}), required for impact assessments, varied from 60 to 1800 L/kg and were significantly correlated with extractable Al oxide content, and background I and organic matter content. Freundlich isotherm fits show that sorption of I across our intentionally large concentration range is nonlinear; however, sorption of I across our intentionally large concentration range is nonlinear; however, sorption of I at environmental concentrations (<0.1 mg I/L soil solution) is linear and can be described by the K{sub d} model. Sorption of I was not related to peroxidase enzyme activity. Desorption percentages were small implying sorption was not easily reversed, even with a strong electrolyte, KNO{sub 3}. Desorption results and simple correlations of I sorption to soil properties suggest that the oxidation of I{sup {minus}} to I{sub 2} and complexation to organic functional groups or oxides are the major processes for I retention in Shield soils. 52 refs., 2 figs., 2 tabs.

  11. Combining experimental techniques with non-linear numerical models to assess the sorption of pesticides on soils

    NASA Astrophysics Data System (ADS)

    Magga, Zoi; Tzovolou, Dimitra N.; Theodoropoulou, Maria A.; Tsakiroglou, Christos D.

    2012-03-01

    The risk assessment of groundwater pollution by pesticides may be based on pesticide sorption and biodegradation kinetic parameters estimated with inverse modeling of datasets from either batch or continuous flow soil column experiments. In the present work, a chemical non-equilibrium and non-linear 2-site sorption model is incorporated into solute transport models to invert the datasets of batch and soil column experiments, and estimate the kinetic sorption parameters for two pesticides: N-phosphonomethyl glycine (glyphosate) and 2,4-dichlorophenoxy-acetic acid (2,4-D). When coupling the 2-site sorption model with the 2-region transport model, except of the kinetic sorption parameters, the soil column datasets enable us to estimate the mass-transfer coefficients associated with solute diffusion between mobile and immobile regions. In order to improve the reliability of models and kinetic parameter values, a stepwise strategy that combines batch and continuous flow tests with adequate true-to-the mechanism analytical of numerical models, and decouples the kinetics of purely reactive steps of sorption from physical mass-transfer processes is required.

  12. Sorption and transformation of the reactive tracers resazurin and resorufin in natural river sediments

    NASA Astrophysics Data System (ADS)

    Lemke, D.; González-Pinzón, R.; Liao, Z.; Wöhling, T.; Osenbrück, K.; Haggerty, R.; Cirpka, O. A.

    2014-08-01

    Resazurin (Raz) and its reaction product resorufin (Rru) have increasingly been used as reactive tracers to quantify metabolic activity and hyporheic exchange in streams. Previous work has indicated that these compounds undergo sorption in stream sediments. We present laboratory experiments on Raz and Rru transport, sorption, and transformation, consisting of 4 column and 72 batch tests using 2 sediments with different physicochemical properties under neutral (pH = 7) and alkaline (pH = 9) conditions. The study aimed at identifying the key processes of reactive transport of Raz and Rru in streambed sediments and the experimental setup best suited for their determination. Data from column experiments were simulated by a travel-time-based model accounting for physical transport, equilibrium and kinetic sorption, and three first-order reactions. We derived the travel-time distributions directly from the breakthrough curve (BTC) of the conservative tracer, fluorescein, rather than from fitting an advective-dispersive transport model, and inferred from those distributions the transfer functions of Raz and Rru, which provided conclusive approximations of the measured BTCs. The most likely reactive transport parameters and their uncertainty were determined by a Markov chain-Monte Carlo approach. Sorption isotherms of both compounds were obtained from batch experiments. We found that kinetic sorption dominates sorption of both Raz and Rru, with characteristic timescales of sorption in the order of 12 to 298 min. Linear sorption models for both Raz and Rru appeared adequate for concentrations that are typically applied in field tracer tests. The proposed two-site sorption model helps to interpret transient tracer tests using the Raz-Rru system.

  13. Hydrogen interaction kinetics of Ge dangling bonds at the Si0.25Ge0.75/SiO2 interface

    NASA Astrophysics Data System (ADS)

    Stesmans, A.; Nguyen Hoang, T.; Afanas'ev, V. V.

    2014-07-01

    The hydrogen interaction kinetics of the GePb1 defect, previously identified by electron spin resonance (ESR) as an interfacial Ge dangling bond (DB) defect occurring in densities ˜7 × 1012 cm-2 at the SiGe/SiO2 interfaces of condensation grown (100)Si/a-SiO2/Ge0.75Si0.25/a-SiO2 structures, has been studied as function of temperature. This has been carried out, both in the isothermal and isochronal mode, through defect monitoring by capacitance-voltage measurements in conjunction with ESR probing, where it has previously been demonstrated the defects to operate as negative charge traps. The work entails a full interaction cycle study, comprised of analysis of both defect passivation (pictured as GePb1-H formation) in molecular hydrogen (˜1 atm) and reactivation (GePb1-H dissociation) in vacuum. It is found that both processes can be suitably described separately by the generalized simple thermal (GST) model, embodying a first order interaction kinetics description based on the basic chemical reactions GePb1 + H2 → GePb1H + H and GePb1H → GePb1 + H, which are found to be characterized by the average activation energies Ef = 1.44 ± 0.04 eV and Ed = 2.23 ± 0.04 eV, and attendant, assumedly Gaussian, spreads σEf = 0.20 ± 0.02 eV and σEd = 0.15 ± 0.02 eV, respectively. The substantial spreads refer to enhanced interfacial disorder. Combination of the separately inferred kinetic parameters for passivation and dissociation results in the unified realistic GST description that incorporates the simultaneous competing action of passivation and dissociation, and which is found to excellently account for the full cycle data. For process times ta ˜ 35 min, it is found that even for the optimum treatment temperature ˜380 °C, only ˜60% of the GePb1 system can be electrically silenced, still far remote from device grade level. This ineffectiveness is concluded, for the major part, to be a direct consequence of the excessive spreads in the activation energies, ˜2

  14. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    DOE PAGES

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in themore » total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. In conclusion, these multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.« less

  15. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    PubMed Central

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-01-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments. PMID:26902901

  16. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage.

    PubMed

    Cho, Eun Seon; Ruminski, Anne M; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J

    2016-02-23

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  17. Graphene oxide/metal nanocrystal multilaminates as the atomic limit for safe and selective hydrogen storage

    NASA Astrophysics Data System (ADS)

    Cho, Eun Seon; Ruminski, Anne M.; Aloni, Shaul; Liu, Yi-Sheng; Guo, Jinghua; Urban, Jeffrey J.

    2016-02-01

    Interest in hydrogen fuel is growing for automotive applications; however, safe, dense, solid-state hydrogen storage remains a formidable scientific challenge. Metal hydrides offer ample storage capacity and do not require cryogens or exceedingly high pressures for operation. However, hydrides have largely been abandoned because of oxidative instability and sluggish kinetics. We report a new, environmentally stable hydrogen storage material constructed of Mg nanocrystals encapsulated by atomically thin and gas-selective reduced graphene oxide (rGO) sheets. This material, protected from oxygen and moisture by the rGO layers, exhibits exceptionally dense hydrogen storage (6.5 wt% and 0.105 kg H2 per litre in the total composite). As rGO is atomically thin, this approach minimizes inactive mass in the composite, while also providing a kinetic enhancement to hydrogen sorption performance. These multilaminates of rGO-Mg are able to deliver exceptionally dense hydrogen storage and provide a material platform for harnessing the attributes of sensitive nanomaterials in demanding environments.

  18. Direct Observation of the Kinetically Relevant Site of CO Hydrogenation on Supported Ru Catalyst at 700 K by Time-Resolved FT-IR Spectroscopy

    SciTech Connect

    Frei, Heinz; Wasylenko, Walter; Frei, Heinz

    2008-06-04

    Time-resolved FT-IR spectra of carbon monoxide hydrogenation over alumina-supported ruthenium particles were recorded on themillisecond time scale at 700 K using pulsed release of CO and a continuous flow of H2/N2 (ratio 0.067 or 0.15, 1 atm total pressure). Adsorbed carbon monoxide was detected along with gas phase products methane (3016 and 1306 cm-1), water (1900 +- 1300 cm-1), and carbon dioxide (2348 cm-1). Aside from adsorbed CO, no other surface species were observed. The rate of formation of methane is 2.5 +- 0.4 s-1 and coincides with the rate of carbon dioxide growth (3.4 +- 0.6 s-1), thus indicating that CH4 and CO2 originate from a common intermediate. The broad band of adsorbed carbon monoxide has a maximum at 2010 cm-1 at early times (36 ms) that shifts gradually to 1960 cm-1 over a period of 3 s as a result of the decreasing surface concentration of CO. Kinetic analysis of the adsorbed carbon monoxide reveals that surface sites absorbing at the high frequency end of the infrared band are temporally linked to gas phase product growth. Specifically, a (linear) CO site at 2026 cm-1 decays with a rate constant of 2.9 +- 0.1 s-1, which coincides with the rise constant of CH4. This demonstrates that the linear CO site at 2026 cm-1 is the kinetically most relevant one for the rate-determining CO dissociation step under reaction conditions at 700 K.

  19. A statistical mechanical theory of proton transport kinetics in hydrogen-bonded networks based on population correlation functions with applications to acids and bases.

    PubMed

    Tuckerman, Mark E; Chandra, Amalendu; Marx, Dominik

    2010-09-28

    Extraction of relaxation times, lifetimes, and rates associated with the transport of topological charge defects in hydrogen-bonded networks from molecular dynamics simulations is a challenge because proton transfer reactions continually change the identity of the defect core. In this paper, we present a statistical mechanical theory that allows these quantities to be computed in an unbiased manner. The theory employs a set of suitably defined indicator or population functions for locating a defect structure and their associated correlation functions. These functions are then used to develop a chemical master equation framework from which the rates and lifetimes can be determined. Furthermore, we develop an integral equation formalism for connecting various types of population correlation functions and derive an iterative solution to the equation, which is given a graphical interpretation. The chemical master equation framework is applied to the problems of both hydronium and hydroxide transport in bulk water. For each case it is shown that the theory establishes direct links between the defect's dominant solvation structures, the kinetics of charge transfer, and the mechanism of structural diffusion. A detailed analysis is presented for aqueous hydroxide, examining both reorientational time scales and relaxation of the rotational anisotropy, which is correlated with recent experimental results for these quantities. Finally, for OH(-)(aq) it is demonstrated that the "dynamical hypercoordination mechanism" is consistent with available experimental data while other mechanistic proposals are shown to fail. As a means of going beyond the linear rate theory valid from short up to intermediate time scales, a fractional kinetic model is introduced in the Appendix in order to describe the nonexponential long-time behavior of time-correlation functions. Within the mathematical framework of fractional calculus the power law decay ∼t(-σ), where σ is a parameter of the

  20. The kinetics and mechanism of methanol synthesis by hydrogenation of CO 2 over a Zn-deposited Cu(111) surface

    NASA Astrophysics Data System (ADS)

    Fujitani, T.; Nakamura, I.; Uchijima, T.; Nakamura, J.

    1997-07-01

    The hydrogenation of CO 2 over a Zn-deposited Cu(111) surface has been studied using an X-ray photoelectron spectroscopy (XPS) apparatus combined with a high-pressure flow reactor. It was shown that the turnover frequency (TOF) for methanol formation linearly increased with Zn coverage below ϑZn=0.19 and decreased above ϑZn=0.20. The optimum TOF obtained at ϑZn=0.19 was thirteen-fold larger than that of the Zn-free Cu(111) surface. On the other hand, the TOF for CO formation started to decrease at ϑZn=0.10 and approached zero at ϑZn=0.5. No promotional effect of Zn was thus observed for the reverse water-gas shift (RWGS) reaction on Cu(111). Post-reaction surface analysis by XPS showed the formation of formate species (HCOO a) on the Cu(111) surfaces. The formate coverage linearly increased with the Zn coverage below ϑZn=0.15, suggesting that the formation of the formate species was stabilized by the Zn species. The relation between ϑHCOO and ϑZn is similar to that between TOF and ϑZn; thus, the formate species is considered to be the reaction intermediates during methanol formation, and the amount of the formate species should determine the rate of the reaction. It was found that the surface chemistry of the Zn-deposited Cu surface drastically changed at ϑZn=0.15. At higher Zn coverages ( ϑZn>0.15), Zn on Cu(111) was readily oxidized to ZnO during the CO 2 hydrogenation reaction. On the other hand, at low Zn coverages below ϑZn=0.15, Zn was partially oxidized in the absence of oxygen in ZnO or O a on the Cu surface under the reaction conditions. It was suggested that the Zn on Cu(111) was directly bound to the oxygen in the surface formate species as the role of the active sites.

  1. Changes in the kinetic behaviour of threonine transport into Trypanosoma brucei elicited by variation in hydrogen ion concentration

    PubMed Central

    Voorheis, H. Paul

    1977-01-01

    1. The dependence of V and V/Km for threonine transport into Trypanosoma brucei upon the external concentration of H+ was studied. 2. Two ionizing groups, the α-amino group of the substrate and a group at the substrate-binding site of the carrier, were found to influence the observed kinetic behaviour of transport. 3. The pK of the group at the substrate-binding site on the free carrier was found to be 6.95 at 30°C and to be temperature-dependent; its heat of ionization was −63.8kJ, which is outside the range for most proton dissociations and suggests a significant contribution from some other source, possibly the remainder of the carrier or the membrane environment. 4. Binding of substrate caused the pK of its α-amino group to shift to a higher value, whereas that of the carrier group shifted to a lower value (6.65 at 30°C). 5. The ionic interaction between substrate and carrier appeared to be involved in the stabilizing of the protonated substrate and the species of the carrier–substrate complex required for the membrane-translocation step. 6. The same ionic species of carrier–substrate complex is required for both substrate dissociation and translocation of the substrate through the membrane. 7. H+ symport or antiport did not occur during threonine uptake. PMID:18141

  2. Sorption and solubility of ofloxacin and norfloxacin in water-methanol cosolvent.

    PubMed

    Peng, Hongbo; Li, Hao; Wang, Chi; Zhang, Di; Pan, Bo; Xing, Baoshan

    2014-05-01

    Prediction of the properties and behavior of antibiotics is important for their risk assessment and pollution control. Theoretical calculation was incorporated in our experimental study to investigate the sorption of ofloxacin (OFL) and norfloxacin (NOR) on carbon nanotubes and their solubilities in water, methanol, and their mixture. Sorption for OFL and NOR decreased as methanol volume fractions (fc) increased. But the log-linear cosolvency model could not be applied as a general model to describe the cosolvent effect on OFL and NOR sorption. We computed the bond lengths of possible hydrogen bonds between solute and solvent and the corresponding interaction energies using Density Functional Theory. The decreased OFL solubility with increased fc could be attributed to the generally stronger hydrogen bond between OFL and H2O than that between OFL and CH3OH. Solubility of NOR varied nonmonotonically with increasing fc, which may be understood from the stronger hydrogen bond of NOR-CH3OH than NOR-H2O at two important sites (-O18 and -O21). The interaction energies were also calculated for the solute surrounded by solvent molecules at all the possible hydrogen bond sites, but it did not match the solubility variations with fc for both chemicals. The difference between the simulated and real systems was discussed. Similar sorption but different solubility of NOR and OFL from water-methanol cosolvent suggested that sorbate-solvent interaction seems not control their sorption.

  3. Modeling depth-variant and domain-specific sorption and biodegradation in dual-permeability media

    NASA Astrophysics Data System (ADS)

    Ray, Chittaranjan; Vogel, Tomas; Dusek, Jaromir

    2004-05-01

    A dual-permeability model (S_1D_DUAL) was developed to simulate the transport of land-applied pesticides in macroporous media. In this model, one flow domain was represented by the bulk matrix and the other by the preferential flow domain (PFD) where water and chemicals move at faster rates. The model assumed the validity of Darcian flow and the advective-dispersive solute transport in each of the two domains with inter-domain transfer of water and solutes due to pressure and concentration gradients. It was conceptualized that sorption and biodegradation rates vary with soil depth as well as in each of the two flow domains. In addition to equilibrium sorption, kinetic sorption was simulated in the PFD. Simulations were conducted to evaluate the combined effects of preferential flow, depth- and domain-variant sorption, and degradation on leaching of two pesticides: one with strong sorption potential (trifluralin) and the other with weak sorption potential (atrazine). Simulation results for a test case showed that water flux in the PFD was three times more than in the matrix for selected storm events. When equilibrium sorption was considered, the simulated profile of trifluralin in each domain was similar; however, the atrazine profile was deeper in the PFD than in the bulk matrix under episodic storm events. With an assumption of negligible sorption in the PFD, both the atrazine and the trifluralin profiles moved twice deeper into the PFD. The simulated concentrations of the chemicals were several orders higher in the PFD than in the matrix, even at deeper depths. The volume fraction of the macropores and the sorption and biodegradation properties of the chemicals could also affect the amount of pesticides leaving the root zone. For an intense storm event, slow sorption reaction rates in the PFD produced higher breakthrough concentrations of atrazine at the bottom of the simulated soil profile, thus posing the risk for breakthrough of chemicals from the root zone.

  4. Structural analysis of kinetic folding intermediates for a TIM barrel protein, indole-3-glycerol phosphate synthase, by hydrogen exchange mass spectrometry and Gō model simulation.

    PubMed

    Gu, Zhenyu; Rao, Maithreyi K; Forsyth, William R; Finke, John M; Matthews, C Robert

    2007-11-23

    The structures of partially folded states appearing during the folding of a (betaalpha)(8) TIM barrel protein, the indole-3-glycerol phosphate synthase from Sulfolobus solfataricus (sIGPS), was assessed by hydrogen exchange mass spectrometry (HX-MS) and Gō model simulations. HX-MS analysis of the peptic peptides derived from the pulse-labeled product of the sub-millisecond folding reaction from the urea-denatured state revealed strong protection in the (betaalpha)(4) region, modest protection in the neighboring (betaalpha)(1-3) and (betaalpha)(5)beta(6) segments and no significant protection in the remaining N and C-terminal segments. These results demonstrate that this species is not a collapsed form of the unfolded state under native-favoring conditions nor is it the native state formed via fast-track folding. However, the striking contrast of these results with the strong protection observed in the (betaalpha)(2-5)beta(6) region after 5 s of folding demonstrates that these species represent kinetically distinct folding intermediates that are not identical as previously thought. A re-examination of the kinetic folding mechanism by chevron analysis of fluorescence data confirmed distinct roles for these two species: the burst-phase intermediate is predicted to be a misfolded, off-pathway intermediate, while the subsequent 5 s intermediate corresponds to an on-pathway equilibrium intermediate. Comparison with the predictions using a C(alpha) Gō model simulation of the kinetic folding reaction for sIGPS shows good agreement with the core of the structure offering protection against exchange in the on-pathway intermediate(s). Because the native-centric Gō model simulations do not explicitly include sequence-specific information, the simulation results support the hypothesis that the topology of TIM barrel proteins is a primary determinant of the folding free energy surface for the productive folding reaction. The early misfolding reaction must involve aspects of

  5. Changes in the hydrogen exchange kinetics of Escherichia coli aspartate transcarbamylase produced by effector binding and subunit association.

    PubMed Central

    Lennick, M; Allewell, N M

    1981-01-01

    Large changes in solvent accessibility to aspartate transcarbamylase (aspartate carbamoyltransferase, carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2), as monitored by tritium exchange, result from binding of substrates and substrate analogs to the catalytic subunit (c3), binding of nucleoside triphosphates to the regulatory subunit (r2), and subunit association. Rates of exchange are reduced in each of these cases, although to different degrees. Succinate, in the presence of carbamoyl phosphate, retards exchange from c3 no more than carbamoyl phosphate alone, and less than N-phosphonacetyl-L-aspartate, a bisubstrate analog. Larger changes in rates of exchange from r2 are produced by CTP than by ATP; however, both CTP and ATP accelerate exchange from c3 to the same extent. The changes in the kinetics of exchange that result from binding of both substrate analogs and nucleoside triphosphates to the native enzyme (c6r6) are much smaller. Carbamoyl phosphate, with or without succinate, retards exchange only slightly, while the bisubstrate analog has a somewhat larger effect. Experiments with reconstituted enzyme, in which only c3 is tritium labeled, indicate that changes in solvent accessibility produced by active site ligands are largely confined to c3. Neither CTP nor ATP alters the overall rate of exchange from c6r6 significantly. The possibility of opposing changes in the two types of subunits was ruled out in experiments in which only one subunit was labeled. The nonadditive effects of ligation and subunit association imply a set of responsive protons common to both processes and suggest that they are linked not only thermodynamically and functionally but also dynamically. PMID:7031660

  6. Sorption of graphites at high temperatures. Final report, February 1, 1977-June 30, 1978. [800 to 1100/sup 0/C; pseudo-isopiestic method

    SciTech Connect

    Kazi, N.I.; Pyecha, T.D.; Zumwalt, L.R.

    1980-06-30

    This report include: (1) corrected data and new data on cesium sorption by bulk graphite (H-451) with a discussion of anomalies and a comparison of the data; (2) a review of the exponential (Freundlich) isotherm theory and a derivation of the modified-exponential isotherm; (3) a report on a study by the pseudo-isopiestic method of cesium by H-451 graphite powder (size range 44 to 74 ..mu..m) of the type used in the Knudsen cell mass spectrometer method; (4) a comparison of the results on particulate graphite (powder) obtained by the Knudsen cell method and also a comparison of cesium sorption results obtained with the bulk graphite; (5) development of a theory for the kinetics of sorption of a system (cesium and graphite) which shows an exponential (Freundlich) type of sorption; (6) comparison of theoretical with observed kinetics for sorption of cesium by graphite (H-451) powder and a comparison of bulk graphite vs. particulate graphite sorption kinetics; (7) report of a study of the effects of barium on cesium sorption by H-451 graphite at 1000/sup 0/C; and (8) a thermodynamic treatment of mixed sorption and its application to mixed barium-cesium and strontium-cesium sorption by graphite.

  7. Arsenic Sorption in Dried Leaves

    NASA Astrophysics Data System (ADS)

    Silva, Gabriela C.; de Carvalho, Regina P.; Duarte, Grazielle; Santos, Mércia H.

    2005-10-01

    Biosorption is the retention of metal ions from aqueous solutions by biomasses. This phenomenon can be helpful in the design of alternative filters for the depollution of industrial and mining waste waters. The recovery of filtered metal ions can also be commercially interesting. Although many studies about the sorptive capacity of biomasses have been done for different metals, few have investigated sorption sites and mechanisms in these systems. We studied the retention of arsenic ions from aqueous solutions using dried lettuce leaves (L. sativa) as biomass. The toxic arsenic forms As(III) and As(V) are commonly found in mining waste waters. Early studies have shown that lettuce leaves have a good sorptive capacity for copper and iron ions, comparable to other sorbents such as activated carbon or ionic-exchange resins. Arsenic sorption by lettuce dried leaves was not found to be effective when in natura biomass was used. Sorptive capacity was improved and became comparable to the sorption of the other ions studied when the biomass was charged with Fe(III). The sorption mechanism of arsenic in Fe-charged biomass must be similar to the one proposed for As sorption by mineral clays, where As ions bind to Fe(III) atoms in the clay structure.

  8. [Sorption behavior of Triton X-100 on loess and affecting factors].

    PubMed

    Zhong, Jin-Kui; Zhao, Bao-Wei; Zhu, Kun; Qian, Xiao-Long; Zhang, Jie-Xi

    2013-03-01

    Batch experiments involving soil-aqueous systems were conducted to determine sorption of Triton X-100 onto natural loess as a function of equilibrium time, Triton X-100 concentration, ionic strength, and pH value. The results showed that the equilibration time for sorption of Triton X-100 onto loess was about 30 min. The sorption kinetics of Triton X-100 fitted well to the pseudo-first-order kinetic model and the corresponding parameters Q(e), k1, and r2 were 3.041 mg x g(-1), 0.102 min(-1), and 0.9934, respectively. Sorption isotherm was found to be distinctly nonlinear. The Sips model provided the best fitting to the experimental data among the four isothermal models tested. Q(max) and r2 of Sips model were 3.202 mg x g(-1) and 0.998 7, respectively. It was found that the ionic strength and the pH of the solution had a significant influence on the sorption of Triton X-100 onto loess. The amount of Triton X-100 sorbed onto the loess increased significantly with increasing concentration of NaCl. Sorption of Triton X-100 onto loess was influenced greatly by pH, the amount of Triton X-100 sorbed decreased as the pH increased.

  9. Sorption and biodegradation characteristics of the selected pharmaceuticals and personal care products onto tropical soil.

    PubMed

    Foolad, Mahsa; Hu, Jiangyong; Tran, Ngoc Han; Ong, Say Leong

    2016-01-01

    In the present study, the sorption and biodegradation characteristics of five pharmaceutical and personal care products (PPCPs), including acetaminophen (ACT), carbamazepine (CBZ), crotamiton (CTMT), diethyltoluamide (DEET) and salicylic acid (SA), were studied in laboratory-batch experiments. Sorption kinetics experimental data showed that sorption systems under this study were more appropriately described by the pseudo second-order kinetics with a correlation coefficient (R2)>0.98. Sorption equilibrium data of almost all target compounds onto soil could be better described by the Freundlich sorption isotherm model. The adsorption results showed higher soil affinity for SA, following by ACT. Results also indicated a slight effect of pH on PPCP adsorption with lower pH causing lower adsorption of compounds onto the soil except for SA at pH 12. Moreover, adsorption of PPCPs onto the soil was influenced by natural organic matter (NOM) since the higher amount of NOM caused lower adsorption to the soil. Biodegradation studies of selected PPCPs by indigenous microbial community present in soil appeared that the removal rates of ACT, SA and DEET increased with time while no effect had been observed for the rest. This study suggests that the CBZ and CTMT can be considered as suitable chemical sewage indicators based on their low sorption affinity and high resistance to biodegradation.

  10. Sorption and biodegradation characteristics of the selected pharmaceuticals and personal care products onto tropical soil.

    PubMed

    Foolad, Mahsa; Hu, Jiangyong; Tran, Ngoc Han; Ong, Say Leong

    2016-01-01

    In the present study, the sorption and biodegradation characteristics of five pharmaceutical and personal care products (PPCPs), including acetaminophen (ACT), carbamazepine (CBZ), crotamiton (CTMT), diethyltoluamide (DEET) and salicylic acid (SA), were studied in laboratory-batch experiments. Sorption kinetics experimental data showed that sorption systems under this study were more appropriately described by the pseudo second-order kinetics with a correlation coefficient (R2)>0.98. Sorption equilibrium data of almost all target compounds onto soil could be better described by the Freundlich sorption isotherm model. The adsorption results showed higher soil affinity for SA, following by ACT. Results also indicated a slight effect of pH on PPCP adsorption with lower pH causing lower adsorption of compounds onto the soil except for SA at pH 12. Moreover, adsorption of PPCPs onto the soil was influenced by natural organic matter (NOM) since the higher amount of NOM caused lower adsorption to the soil. Biodegradation studies of selected PPCPs by indigenous microbial community present in soil appeared that the removal rates of ACT, SA and DEET increased with time while no effect had been observed for the rest. This study suggests that the CBZ and CTMT can be considered as suitable chemical sewage indicators based on their low sorption affinity and high resistance to biodegradation. PMID:26744934

  11. Kinetic schemes of chemical transformations and particle morphology upon interaction between Ln2(SO4)3 (Ln = La, Pr, Nd, Sm) and hydrogen

    NASA Astrophysics Data System (ADS)

    Andreev, P. O.; Sal'nikova, E. I.; Andreev, O. V.; Kovenskii, I. M.

    2016-01-01

    The phase compositions of samples obtained during the treatment of anhydrous sulfates Ln2(SO4)3 (Ln = La, Pr, Nd, Sm) in a stream with an excess of hydrogen in the temperature range of 400 to 1100°C at exposures of up to 420 min are determined. Kinetic schemes are compiled for the chemical transformations and changes of phase composition of the mixtures in coordinates of temperature and time that have six fields of the phase combinations: Ln2(SO4)3, Ln2(SO4)3 + Ln2O2SO4, Ln2O2SO4, Ln2O2SO4 + Ln2O2S, Ln2O2S, and Ln2O2S + Ln2O3. Single-phase samples of Ln2O2SO4 compounds are obtained at temperatures (°C) of 540-560 (La), 460-520 (Pr), 470-520 (Nd), and 480-520 (Sm). The temperatures (°C) of Ln2O2S compounds are 580-920 (La), 600-900 (Pr), 600-900 (Nd), and 600-800 (Sm). It is shown via electron microscopy that particles of La2(SO4)3 in the shape of cylinders are converted into flakes of Ln2O2SO4, predominantly flat Ln2O2S crystallites.

  12. Human Salivary Aldehyde Dehydrogenase: Purification, Kinetic Characterization and Effect of Ethanol, Hydrogen Peroxide and Sodium Dodecyl Sulfate on the Activity of the Enzyme.

    PubMed

    Alam, Md Fazle; Laskar, Amaj Ahmed; Choudhary, Hadi Hasan; Younus, Hina

    2016-09-01

    Human salivary aldehyde dehydrogenase (hsALDH) enzyme appears to be the first line of defense in the body against exogenous toxic aldehydes. However till date much work has not been done on this important member of the ALDH family. In this study, we have purified hsALDH to homogeneity by diethylaminoethyl-cellulose (DEAE-cellulose) ion-exchange chromatography in a single step. The molecular mass of the homodimeric enzyme was determined to be approximately 108 kDa. Four aromatic substrates; benzaldehyde, cinnamaldehyde, 2-naphthaldehyde and 6-methoxy-2-naphthaldehyde were used for determining the activity of pure hsALDH. K m values for these substrates were calculated to be 147.7, 5.31, 0.71 and 3.31 μM, respectively. The best substrates were found to be cinnamaldehyde and 2-naphthaldehyde since they exhibited high V max /K m values. 6-methoxy-2-naphthaldehyde substrate was used for further kinetic characterization of pure hsALDH. The pH and temperature optima of hsALDH were measured to be pH 8 and 45 °C, respectively. The pure enzyme is highly unstable at high temperatures. Ethanol, hydrogen peroxide and SDS activate hsALDH, therefore it is safe and beneficial to include them in mouthwashes and toothpastes in low concentrations. PMID:27324040

  13. Kinetics and Mechanism of the Hydrogenation of CpCr(CO)3•/[CpCr(CO)3]2 Equilibrium to CpCr(CO)3H

    SciTech Connect

    Norton, Jack R.; Spataru, Tudor; Camaioni, Donald M.; Lee, Suh-Jane; Li, Gang; Choi, Jongwook; Franz, James A.

    2014-05-26

    The kinetics of the hydrogenation of 2 CpCr(CO)3•/[CpCr(CO)3]2 to CpCr(CO)3H has been investigated. The reaction is second-order in Cr and first-order in H2, with a rate constant of 45 M 2s 1 at 25 °C in benzene. DFT calculations rule out an H2 complex as an intermediate, and suggest (a) end-on approach of H2 to one Cr of [CpCr(CO)3]2 as the Cr-Cr bond undergoes heterolytic cleavage, (b) heterolytic cleavage of the coordinated H2 between O and Cr, and (c) isomerization of the resulting O-protonated CpCr(CO)2(COH) to CpCr(CO)3H. The work at Pacific Northwest National Laboratory (PNNL) was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences and Biosciences; Battelle operates PNNL for DOE.

  14. [Surface Property and Sorption Characteristics of Phosphorus onto Surface Sediments in Sanggou Bay].

    PubMed

    Zhu, Jia-mei; Cao, Xiao-yan; Liu, Su-mei; Wang, Li-sha; Yang, Gui-peng; Ge, Cheng-feng; Lu, Min

    2016-02-15

    Kinetic curves and isotherms were investigated to study the sorption mechanism of phosphorus onto the sediments of Sanggou Bay, together with the surface charge properties of sediments and the forms of phosphorus studied. The results showed that the sorption including a fast process and a slow one, and could be described by a two-compartment first order equation. The thermodynamic isotherms were well fitted with a modified Langmuir equation. The maximum adsorption capacity was larger in summer than in spring, and the smaller particle size was favorable to the sorption. The maximum adsorption capacities (Qm) were 0.0471-0.1230 mg x g(-1), and the zero equilibrium phosphorus concentration (EPC0) of the sediments ranged from 0.0596 mg x L(-1) to 0.1927 mg x L(-1), which indicated that the sediments from Sanggou Bay were sources of phosphorus. Inorganic phosphorus (IP) was the main form of total phosphorus (TP). The contents of exchangeable or loosely absorbed P and Fe-bound P increased significantly in the samples after sorption. The sorption process involved physical sorption and chemical sorption, with the former being the predominant.

  15. Hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions.

    PubMed

    Baumgartner, Rebekka; McNeill, Kristopher

    2012-09-18

    Fluorinated organic compounds are increasingly used in many applications, and their release to the environment is expected. It is therefore important to find suitable methods for degradation of fluorinated compounds under environmentally relevant conditions. In this study, a simple heterogeneous rhodium-based catalytic system (Rh/Al(2)O(3) and H(2)) for hydrodefluorination and hydrogenation of fluorobenzene under mild aqueous conditions (1 atm of H(2), ambient temperature) was developed and the underlying reaction mechanism was investigated. Fluorobenzene degraded rapidly (t(1/2) ≈ 0.2 h) to form cyclohexane and fluoride (F(-)) as the stable end products, with benzene and cyclohexene observed as intermediates. Cyclohexadiene intermediates were not observed but were expected to form during the hydrogenation of benzene. Three postulated but unobserved fluorinated intermediates were subjected to the catalytic reaction conditions, and it was concluded that they most likely do not form during the fluorobenzene degradation reaction. Isotope labeling experiments showed that the unsaturated intermediates undergo rapid and reversible hydrogenation/dehydrogenation under the reaction conditions and also that fully saturated compounds are unreactive in the catalytic system. Both molecular hydrogen and water were sources of hydrogen in the final cyclohexane product. Kinetic fitting indicated that sorption/desorption of fluorobenzene onto the catalyst surface plays an important role in the mechanism. PMID:22871102

  16. Sorption behavior of Pb(II) and Cd(II) on iron ore slime and characterization of metal ion loaded sorbent.

    PubMed

    Mohapatra, M; Rout, K; Mohapatra, B K; Anand, S

    2009-07-30

    The present investigation evaluates the sorption effectiveness of Pb(II) and Cd(II) ions on iron ore slime (IOS) obtained from Jindal Steel Ltd., Vijayanagaram, India. The sorption followed pseudo-second-order kinetics for both the cations. Pb(II) and Cd(II) sorption increased with the increase in pH from 2 to 4.5. The sorption data fitted well to Freundlich model as compared to Langmuir model. Synergistic effect of Pb(II) and Cd(II) on their sorption on IOS sample showed that Pb(II) sorption increases in presence of Cd(II) whereas Cd(II) sorption decreases. Presence of chloride or sulphate resulted in increased Pb(II) sorption but adversely affected Cd(II) sorption. The XRD patterns of Pb(II) adsorbed on IOS sample showed disappearance of some silica peaks and shifting of hematite peaks corresponding to 104 and 110 plane. For Cd(II) sorbed IOS sample, only peak shift for hematite of 104 and 110 plane was observed. Shifting of IR bands indicated that the Pb(II) sorption occurred through an inner sphere mechanism where as Cd(II) sorption occurred through outer sphere mechanism. EPMA studies showed that Pb(II) form a uniform thin layer and Cd(II) concentrate only on iron oxide phase. Regeneration and stability data on metal ion loaded IOS sample has been included.

  17. Kinetics and Catalysis Demonstrations.

    ERIC Educational Resources Information Center

    Falconer, John L.; Britten, Jerald A.

    1984-01-01

    Eleven videotaped kinetics and catalysis demonstrations are described. Demonstrations include the clock reaction, oscillating reaction, hydrogen oxidation in air, hydrogen-oxygen explosion, acid-base properties of solids, high- and low-temperature zeolite reactivity, copper catalysis of ammonia oxidation and sodium peroxide decomposition, ammonia…

  18. Dynamics of Rear Stagnant Cap formation at the surface of spherical bubbles rising in surfactant solutions at large Reynolds numbers under conditions of small Marangoni number and slow sorption kinetics.

    PubMed

    Dukhin, S S; Kovalchuk, V I; Gochev, G G; Lotfi, M; Krzan, M; Malysa, K; Miller, R

    2015-08-01

    On the surface of bubbles rising in a surfactant solution the adsorption process proceeds and leads to the formation of a so called Rear Stagnant Cap (RSC). The larger this RSC is the stronger is the retardation of the rising velocity. The theory of a steady RSC and steady retarded rising velocity, which sets in after a transient stage, has been generally accepted. However, a non-steady process of bubble rising starting from the initial zero velocity represents an important portion of the trajectory of rising, characterized by a local velocity profile (LVP). As there is no theory of RSC growth for large Reynolds numbers Re » 1 so far, the interpretation of LVPs measured in this regime was impossible. It turned out, that an analytical theory for a quasi-steady growth of RSC is possible for small Marangoni numbers Ma « 1, i.e. when the RSC is almost completely compressed, which means a uniform surface concentration Γ(θ)=Γ(∞) within the RSC. Hence, the RSC angle ψ(t) is obtained as a function of the adsorption isotherm parameters and time t. From the steady velocity v(st)(ψ), the dependence of non-steady velocity on time is obtained by employing v(st)[ψ(t)] via a quasi-steady approximation. The measurement of LVP creates a promising new opportunity for investigation of the RSC dynamics and adsorption kinetics. While adsorption and desorption happen at the same localization in the classical methods, in rising bubble experiments desorption occurs mainly within RSC while adsorption on the mobile part of the bubble surface. The desorption flux from RSC is proportional to αΓ(∞), while it is usually αΓ. The adsorption flux at the mobile surface above RSC can be assumed proportional to βC0, while it is usually βC0(1-Γ/Γ(∞)). These simplifications may become favorable in investigations of the adsorption kinetics for larger molecules, in particular for globular proteins, which essentially stay at an interface once adsorbed.

  19. Dynamics of Rear Stagnant Cap formation at the surface of spherical bubbles rising in surfactant solutions at large Reynolds numbers under conditions of small Marangoni number and slow sorption kinetics.

    PubMed

    Dukhin, S S; Kovalchuk, V I; Gochev, G G; Lotfi, M; Krzan, M; Malysa, K; Miller, R

    2015-08-01

    On the surface of bubbles rising in a surfactant solution the adsorption process proceeds and leads to the formation of a so called Rear Stagnant Cap (RSC). The larger this RSC is the stronger is the retardation of the rising velocity. The theory of a steady RSC and steady retarded rising velocity, which sets in after a transient stage, has been generally accepted. However, a non-steady process of bubble rising starting from the initial zero velocity represents an important portion of the trajectory of rising, characterized by a local velocity profile (LVP). As there is no theory of RSC growth for large Reynolds numbers Re » 1 so far, the interpretation of LVPs measured in this regime was impossible. It turned out, that an analytical theory for a quasi-steady growth of RSC is possible for small Marangoni numbers Ma « 1, i.e. when the RSC is almost completely compressed, which means a uniform surface concentration Γ(θ)=Γ(∞) within the RSC. Hence, the RSC angle ψ(t) is obtained as a function of the adsorption isotherm parameters and time t. From the steady velocity v(st)(ψ), the dependence of non-steady velocity on time is obtained by employing v(st)[ψ(t)] via a quasi-steady approximation. The measurement of LVP creates a promising new opportunity for investigation of the RSC dynamics and adsorption kinetics. While adsorption and desorption happen at the same localization in the classical methods, in rising bubble experiments desorption occurs mainly within RSC while adsorption on the mobile part of the bubble surface. The desorption flux from RSC is proportional to αΓ(∞), while it is usually αΓ. The adsorption flux at the mobile surface above RSC can be assumed proportional to βC0, while it is usually βC0(1-Γ/Γ(∞)). These simplifications may become favorable in investigations of the adsorption kinetics for larger molecules, in particular for globular proteins, which essentially stay at an interface once adsorbed. PMID:25455807

  20. Sorption and desorption studies of a reactive azo dye on effective disposal of redundant material.

    PubMed

    Çelekli, Abuzer; Bozkurt, Hüseyin

    2013-07-01

    The effective disposal of redundant elephant dung (ED) is important for environmental protection and utilization of resource. The aim of this study was to remove a toxic-azo dye, Reactive Red (RR) 120, using this relatively cheap material as a new adsorbent. The FTIR-ATR spectra of ED powders before and after the sorption of RR 120 and zero point charge (pHzpc) of ED were determined. The sorption capacity of ED for removing of RR 120 were carried out as functions of particle size, adsorbent dose, pH, temperature, ionic strength, initial dye concentration, and contact time. Sorption isotherm, kinetic, activation energy, thermodynamic, and desorption parameters of RR 120 on ED were studied. The sorption process was found to be dependent on particle size, adsorbent dose, pH, temperature, ionic strength, initial dye concentration, and contact time. FTIR-ATR spectroscopy indicated that amine and amide groups have significant role on the sorption of RR 120 on ED. The pHzpc of ED was found to be 7.3. Sorption kinetic of RR 120 on ED was well described by sigmoidal Logistic model. The Langmuir isotherm was well fitted to the equilibrium data. The maximum sorption capacity was 95.71 mg g(-1). The sorption of RR 120 on ED was mainly physical and exothermic according to results of D-R isotherm, Arrhenius equation, thermodynamic, and desorption studies. The thermodynamic parameters showed that this process was feasible and spontaneous. This study showed that ED as a low-cost adsorbent had a great potential for the removal of RR 120 as an alternative eco-friendly process.

  1. Dynamic design of gas sorption J-T refrigerator

    NASA Technical Reports Server (NTRS)

    Chan, C. K.

    1986-01-01

    A long-life Joule-Thomson refrigerator which is heat powered, involves no sealing, and has few mechanical parts is desirable for long-term sensor cooling in space. In the gas-sorption J-T refrigerator, cooling is achieved by gas sorption (either adsorption or absorption) processes. Currently, a modular, single-stage refrigerator is being designed and built to be operated at 20 K. The design was analyzed using a dynamic model, which is described here. The model includes the kinetics of the compressors and the heat switches, the heat transfer of the pre-coolers and the heat exchangers, the on/off ratio of the check valves, and the impedance of the J-T valve. The cooling power, the cycle time, and the operating conditions were obtained in terms of the power input, the heat sink temperature, and the J-T impedance.

  2. Sorption Properties of Iron-Magnesium and Nickel-Magnesium Mg2FeH6 and Mg2NiH4 Hydrides

    NASA Astrophysics Data System (ADS)

    Matysina, Z. A.; Zaginaichenko, S. Yu.; Shchur, D. V.; Gabdullin, M. T.

    2016-06-01

    Based on molecular-kinetic representations, theory of hydrogen absorption-desorption processes in binary Mg-Fe and Mg-Ni alloys is developed. Free energies of hydrides of these alloys are calculated. Equations of their thermodynamically equilibrium state determining the P-T-c diagrams are derived. A temperature dependence of the desorbed hydrogen concentration is established. A maximal desorption temperature is estimated. The state diagrams determining the concentration dependence of the maximal desorption temperature are constructed. Isopleths and isotherms of hydrogen solubility in the alloys are calculated. The possibility of manifestation of the hysteresis effect in hydrogen solubility isotherms is revealed and the decrease of the width and length of a hysteresis loop with increasing temperature is demonstrated together with the influence of the magnesium hydrate MgH2 in Mg2FeH6 samples and running of chemical reactions on the behavior of the isotherms and the occurrence of bends and jumps in them. All established functional dependences of the sorption properties of the examined alloys are compared with experimental data available from the literature.

  3. Effects of oil dispersant on solubilization, sorption and desorption of polycyclic aromatic hydrocarbons in sediment-seawater systems.

    PubMed

    Zhao, Xiao; Gong, Yanyan; O'Reilly, S E; Zhao, Dongye

    2015-03-15

    This work investigated effects of a prototype oil dispersant on solubilization, sorption and desorption of three model PAHs in sediment-seawater systems. Increasing dispersant dosage linearly enhanced solubility for all PAHs. Conversely, the dispersant enhanced the sediment uptake of the PAHs, and induced significant desorption hysteresis. Such contrasting effects (adsolubilization vs. solubilization) of dispersant were found dependent of the dispersant concentration and PAH hydrophobicity. The dual-mode models adequately simulated the sorption kinetics and isotherms, and quantified dispersant-enhanced PAH uptake. Sorption of naphthalene and 1-methylnaphthalene by sediment positively correlated with uptake of the dispersant, while sorption of pyrene dropped sharply when the dispersant exceeded its critical micelle concentration (CMC). The deepwater conditions diminished the dispersant effects on solubilization, but enhanced uptake of the PAHs, albeit sorption of the dispersant was lowered. The information may aid in understanding roles of dispersants on distribution, fate and transport of petroleum PAHs in marine systems. PMID:25616532

  4. Determination of soil–water sorption coefficients of volatile methylsiloxanes

    PubMed Central

    Kozerski, Gary E; Xu, Shihe; Miller, Julie; Durham, Jeremy

    2014-01-01

    The sorption behaviors of 4 cyclic and linear volatile methyl siloxane (VMS) compounds between water and organic matter in 3 United Kingdom soils were studied by a batch equilibrium method using13C-enriched sorbates. Sorption and desorption kinetics and isotherms were determined for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), octamethyltrisiloxane (L3), and decamethyltetrasiloxane (L4). Concentrations of [13C]-VMS in the soil and aqueous phases were measured directly by extraction and gas chromatography–mass spectrometry techniques. All VMS compounds were sorbed rapidly, reaching constant distributions in all soils by 24 h. Desorption kinetics were very rapid, with reattainment of equilibrium within 1 h. In the main, linear isotherms were observed for aqueous concentrations at or below 4% of the solubility limits. The average sorption organic carbon partition coefficient (log KOC) values across soils were 4.23 for D4, 5.17 for D5, 4.32 for L3, and 5.13 for L4, with standard deviations of 0.09 to 0.34. Desorption KOC values were systematically greater by 0.1 log units to 0.3 log units. The linear isotherms and low variation in KOC values across soils suggested partitioning-dominated sorption of the VMS. Compared with traditional hydrophobic organic compounds, KOC values for the VMS compounds were significantly lower than expected on the basis of their octanol–water partition coefficients. A linear free energy relationship analysis showed that these differences could be rationalized quantitatively in terms of the inherent characteristics of the VMS compounds, combined with the differences in solvation properties of organic matter and octanol. Environ Toxicol Chem 2014; 33:1937–1945. PMID:24862578

  5. Copper Sorption Mechanisms on Smectites

    SciTech Connect

    Strawn, Daniel G.; Palmer, Noel E.; Furnare, Luca J.; Goodell, Carmen; Amonette, James E.; Kukkadapu, Ravi K.

    2004-06-22

    Abstract– Due to the importance of clay minerals in metal sorption many studies have attempted to derive mechanistic models that describe adsorption processes. These models often include several different types of adsorption sites, including permanent charge sites and silanol and aluminol functional groups on the edges of clay minerals. The edge sites have similar pH-dependent adsorption properties as many oxide minerals. To provide a basis for development of adsorption models it is critical that molecular level studies be done to characterize sorption processes. In this study we conducted XAFS and ESR spectroscopic experiments on copper (II) sorbed on smectite clays using suspension pH and ionic strength as variables. At low ionic strength, results suggest that Cu is sorbing in the interlayers and maintains its hydration sphere. At high ionic strength Cu atoms are excluded from the interlayer and sorb primarily on the silanol and aluminol functional groups of the montmorillonite or beidellite structures. Interpretation of the XAFS and ESR spectroscopy results provides evidence that multinuclear complexes are forming on the edge sites. Fitting of EXAFS spectra revealed that the Cu-Cu atoms in the multinuclear complexes are 2.65 Å apart, and have coordination numbers near one. This structural information suggests that small Cu dimers are sorbing on the surface. These complexes are consistent with observed sorption on mica and amorphous silicon dioxide, as well as the Cu-bearing silicate minerals plancheite and shattuckite, yet are inconsistent with previous spectroscopic results for Cu sorption on montmorillonite. We hypothesize that the differences in sorption mechanisms on the edges of the montmorillonite are due to loading level. The results reported in this paper provide mechanistic data that will be valuable for modeling surface interactions of Cu with clay minerals, and predicting the geochemical cycling of Cu in the environment.

  6. HGMS: Glasses and Nanocomposites for Hydrogen Storage.

    SciTech Connect

    Lipinska, Kris; Hemmers, Oliver

    2013-02-17

    directly address any hydrogen storage technical barriers or targets in terms of numbers. Specifically, hydrogen sorption and desorption tests or kinetics measurements were not part of the project scope. However, the insights gained from these studies could help to answer fundamental questions necessary for considering glass-based materials as hydrogen storage media and could be applied indirectly towards the DOE hydrogen storage technical targets such as system weight and volume, system cost and energy density. Such questions are: Can specific macro-crystals, proven to attract hydrogen when in a macroscopic form (bulk), be nucleated in glass matrices as nanocrystals to create two-phased materials? What are suitable compositions that enable to synthetize glass-based, two-phase materials with nanocrystals that can attract hydrogen via surface or bulk interactions? What are the limits of controlling the microstructure of these materials, especially limits for nanocrystals density and size? Finally, from a technological point of view, the fabrication of glass-derived nanocomposites that we explore is a very simple, fast and inexpensive process that does not require costly or specialized equipment which is an important factor for practical applications.

  7. The effects of temperature and pH on the kinetics of reactions between catalase and its suicide substrate hydrogen peroxide.

    PubMed

    Ghadermarzi, M; Moosavi-Movahedi, A A

    1997-12-01

    Variation of initial (intact) activity (ai), inactivation rate constant (ki) and the partition ratio (r) of bovine liver catalase in the reaction with its suicide substrate, hydrogen peroxide, were determined in workable ranges of temperature (17-42 degrees C) or pH (5-10.5), using the data of progress curves. The changes of temperature had a slight effect on ai, giving a Q10 of 1.15 for the enzymatic breakdown of H2O2, corresponding to an improved value for its activation energy of 8.8 +/- l kJ.mol-1. In contrast, the ki was greatly increased by elevation of temperature, giving a Q10 of 2.1 for the suicide inactivation reaction of catalase. Consequently, a significant decrease of r was observed by increasing of temperature. In pH studies, decreasing of pH from 7.0 to 5.0 led to reduction of ai whereas the ki value was not effected significantly, possibly due to the parallel changes in affinities to free catalase and compound I for H2O2. Reduction of ki and alpha i were observed at pH > 9.5, where reversible dissociation of tetrameric enzyme into catalytically inactive subunits is possible. The r had a maximum value at pH around 7.5, similar to that of catalase activity. The effect of ionic strength on the above kinetic parameters was studied. There was not an observable influence when the ammonium sulfate concentration was below l M. PMID:9541866

  8. Role of hydrogen abstraction acetylene addition mechanisms in the formation of chlorinated naphthalenes. 2. Kinetic modeling and the detailed mechanism of ring closure.

    PubMed

    McIntosh, Grant J; Russell, Douglas K

    2014-12-26

    The dominant formation mechanisms of chlorinated phenylacetylenes, naphthalenes, and phenylvinylacetylenes in relatively low pressure and temperature (∼40 Torr and 1000 K) pyrolysis systems are explored. Mechanism elucidation is achieved through a combination of theoretical and experimental techniques, the former employing a novel simplification of kinetic modeling which utilizes rate constants in a probabilistic framework. Contemporary formation schemes of the compounds of interest generally require successive additions of acetylene to phenyl radicals. As such, infrared laser powered homogeneous pyrolyses of dichloro- or trichloroethylene were perturbed with 1,2,4- or 1,2,3-trichlorobenzene. The resulting changes in product identities were compared with the major products expected from conventional pathways, aided by the results of our previous computational work. This analysis suggests that a Bittner-Howard growth mechanism, with a novel amendment to the conventional scheme made just prior to ring closure, describes the major products well. Expected products from a number of other potentially operative channels are shown to be incongruent with experiment, further supporting the role of Bittner-Howard channels as the unique pathway to naphthalene growth. A simple quantitative analysis which performs very well is achieved by considering the reaction scheme as a probability tree, with relative rate constants being cast as branching probabilities. This analysis describes all chlorinated phenylacetylene, naphthalene, and phenylvinylacetylene congeners. The scheme is then tested in a more general system, i.e., not enforcing a hydrogen abstraction/acetylene addition mechanism, by pyrolyzing mixtures of di- and trichloroethylene without the addition of an aromatic precursor. The model indicates that these mechanisms are still likely to be operative.

  9. Hydrogen interaction kinetics of Ge dangling bonds at the Si{sub 0.25}Ge{sub 0.75}/SiO{sub 2} interface

    SciTech Connect

    Stesmans, A. Nguyen Hoang, T.; Afanas'ev, V. V.

    2014-07-28

    The hydrogen interaction kinetics of the GeP{sub b1} defect, previously identified by electron spin resonance (ESR) as an interfacial Ge dangling bond (DB) defect occurring in densities ∼7 × 10{sup 12} cm{sup −2} at the SiGe/SiO{sub 2} interfaces of condensation grown (100)Si/a-SiO{sub 2}/Ge{sub 0.75}Si{sub 0.25}/a-SiO{sub 2} structures, has been studied as function of temperature. This has been carried out, both in the isothermal and isochronal mode, through defect monitoring by capacitance-voltage measurements in conjunction with ESR probing, where it has previously been demonstrated the defects to operate as negative charge traps. The work entails a full interaction cycle study, comprised of analysis of both defect passivation (pictured as GeP{sub b1}-H formation) in molecular hydrogen (∼1 atm) and reactivation (GeP{sub b1}-H dissociation) in vacuum. It is found that both processes can be suitably described separately by the generalized simple thermal (GST) model, embodying a first order interaction kinetics description based on the basic chemical reactions GeP{sub b1} + H{sub 2} → GeP{sub b1}H + H and GeP{sub b1}H → GeP{sub b1} + H, which are found to be characterized by the average activation energies E{sub f} = 1.44 ± 0.04 eV and E{sub d} = 2.23 ± 0.04 eV, and attendant, assumedly Gaussian, spreads σE{sub f} = 0.20 ± 0.02 eV and σE{sub d} = 0.15 ± 0.02 eV, respectively. The substantial spreads refer to enhanced interfacial disorder. Combination of the separately inferred kinetic parameters for passivation and dissociation results in the unified realistic GST description that incorporates the simultaneous competing action of passivation and dissociation, and which is found to excellently account for the full cycle data. For process times t{sub a} ∼ 35 min, it is found that even for the optimum treatment temperature ∼380 °C, only ∼60% of the GeP{sub b1} system

  10. Sorption of boron trifluoride by activated carbons

    SciTech Connect

    Polevoi, A.S.; Petrenko, A.E.

    1988-01-10

    The sorption of born trifluoride on AG-3, SKT, SKT-3, SKT-7, SKT-4A, SKT-6A, and SKT-2B carbons was investigated. The sorption isotherms for both vapors and gas were determined volumetrically. The coefficients of two equations described the sorption of BF/sub 3/ in the sorption of BF/sub 3/ on active carbons. Heats of sorption of BF/sub 3/ on the activated carbons are shown and the sorption isotherms and temperature dependences of the equilibrium pressure of BF/sub 3/ for activated carbons were presented. The values of the heats of sorption indicated the weak character of the reaction of BF/sub 3/ with the surface of the carbons. The equations can be used for calculating the phase equilibrium of BF/sub 3/ on carbons in a wider range of temperatures and pressures.

  11. Mechanisms of plutonium sorption to mineral oxide surfaces: new insights with implications for colloid-enhanced migration

    SciTech Connect

    Schwantes, J. M.; Santschi, Peter H.

    2010-11-01

    New equilibrium and kinetic models have been developed to describe rate-limited sorption and desorption of Pu onto and off of mineral oxide surfaces using a generic approach to estimate sorption constants that require minimal laboratory calibrations. Equilibrium reactions describing a total of six surface species were derived from a combination of empirical relationships previously described in the literature and generated as part of this work.

  12. Measurement of clay surface areas by polyvinylpyrrolidone (PVP) sorption and its use for quantifying illite and smectite abundance

    USGS Publications Warehouse

    Blum, A.E.; Eberl, D.D.

    2004-01-01

    A new method has been developed for quantifying smectite abundance by sorbing polyvinylpyrrolidone (PVP) on smectite particles dispersed in aqueous solution. The sorption density of PVP-55K on a wide range of smectites, illites and kaolinites is ???0.99 mg/m2, which corresponds to ???0.72 g of PVP-55K per gram of montmorillonite. Polyvinylpyrrolidone sorption on smectites is independent of layer charge and solution pH. PVP sorption on Si02, Fe 2O3 and ZnO normalized to the BET surface area is similar to the sorption densities on smectites. ??-Al 2O3, amorphous Al(OH)3 and gibbsite have no PVP sorption over a wide range of pH, and sorption of PVP by organics is minimal. The insensitivity of PVP sorption densities to mineral layer charge, solution pH and mineral surface charge indicates that PVP sorption is not localized at charged sites, but is controlled by more broadly distributed sorption mechanisms such as Van der Waals' interactions and/or hydrogen bonding. Smectites have very large surface areas when dispersed as single unit-cell-thick particles (???725 m2/g) and usually dominate the total surface areas of natural samples in which smectites are present. In this case, smectite abundance is directly proportional to PVP sorption. In some cases, however, the accurate quantification of smectite abundance by PVP sorption may require minor corrections for PVP uptake by other phases, principally illite and kaolinite. Quantitative XRD can be combined with PVP uptake measurements to uniquely determine the smectite concentration in such sample. ?? 2004, The Clay Minerals Society.

  13. MODELING THE RATE-CONTROLLED SORPTION OF HEXAVALENT CHROMIUM.

    USGS Publications Warehouse

    Grove, D.B.; Stollenwerk, K.G.

    1985-01-01

    Sorption of chromium VI on the iron-oxide- and hydroxide-coated surface of alluvial material was numerically simulated with rate-controlled reactions. Reaction kinetics and diffusional processes, in the form of film, pore, and particle diffusion, were simulated and compared with experimental results. The use of empirically calculated rate coefficients for diffusion through the reacting surface was found to simulate experimental data; pore or particle diffusion is believed to be a possible rate-controlling mechanism. The use of rate equations to predict conservative transport and rate- and local-equilibrium-controlled reactions was shown to be feasible.

  14. Improved Mg-based alloys for hydrogen storage

    SciTech Connect

    Sapru, K.; Ming, L.; Stetson, N.T.; Evans, J.

    1998-08-01

    The overall objective of this on-going work is to develop low temperature alloys capable of reversibly storing at least 3 wt.% hydrogen, allowing greater than for 2 wt.% at the system level which is required by most applications. Surface modification of Mg can be used to improve its H-sorption kinetics. The authors show here that the same Mg-transition metal-based multi-component alloy when prepared by melt-spinning results in a more homogeneous materials with a higher plateau pressure as compared to preparing the material by mechanical grinding. They have also shown that mechanically alloyed Mg{sub 50}Al{sub 45}Zn{sub 5} results in a sample having a higher plateau pressure.

  15. Mixed refrigerant Joule-Thomson sorption cryocoolers

    NASA Astrophysics Data System (ADS)

    Tzabar, Nir; Grossman, Gershon

    2014-01-01

    Joule-Thomson (JT) sorption cryocooling is the most mature technology for cooling from a normal Room-Temperature (RT) down to temperatures below 100 K in the absence of moving parts. Therefore, high reliability and no vibrations are attainable, in comparison with other cryocoolers. Cooling to 80 - 100 K with JT cryocoolers is often implemented with pure nitrogen. Alternatively, mixed refrigerants have been suggested for reducing the operating pressures to enable closed cycle cryocooling. There is a variety of publications describing nitrogen sorption cryocoolers with different configurations of sorption compressors. In the present research we suggest a novel sorption JT cryocooler that operates with a mixed refrigerant. Merging of sorption cryocooling and a mixed refrigerant enables the use of a simple, single stage compressor for cooling to 80 - 100 K, lower operating temperatures of the sorption cycle, and thus - reduced power consumption. In previous studies we have analyzed sorption compressors for mixed gases and mixed refrigerants for JT cryocoolers, separately. In this paper the option of mixed refrigerant sorption JT cryocoolers is explored. The considerations for developing mixed refrigerants to be driven by sorption compressors and to be utilized with JT cryocoolers are provided. It appears that, unlike with pure nitrogen, mixed refrigerants can be suitable fo