Home About us Contact
|
Home About us Contact | ||
|
|
||
Hydrogen Yield (hydrogen + yield)
Selected AbstractsEnhanced bio-hydrogen production from sweet sorghum stalk with alkalization pretreatment by mixed anaerobic culturesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 8 2010Xiang-Xing Shi Abstract Bio-hydrogen production from sweet sorghum stalk using mixed anaerobic sludge was reported in this paper. Batch tests were carried out to analyze influences of several environmental factors on yield of H2 from sweet sorghum stalk under constant mesophillic temperature (36±1°C). The experimental results showed that, for the raw stalk, the cumulative hydrogen yield was 52.1,ml,g,1·TVS with utilization percentages of sugars, hemi-cellulose and cellulose in the stalk being 89.12, 15.23 and 13.89% respectively; whereas for the stalk pretreated by 0.4% NaOH solution at room temperature for 24,h, the cumulative hydrogen yield was 127.26,ml,g,1·TVS with utilization percentages of sugars, hemi-cellulose and cellulose being 99.17, 53.64, 41.56%, respectively. The hydrogen content in the biogas was about 53% while the methane content was less than 4% throughout the study. Besides hydrogen and methane, the main metabolic products detected were ethanol, propionate and butyrate. The experimental results suggested that the alkalization pretreatment of the substrate plays a crucial role in the conversion of the sweet sorghum stalk wastes into bio-hydrogen by the mixed anaerobic sludge. Copyright © 2009 John Wiley & Sons, Ltd. [source] Bio-hydrogen production from acetic acid steam-exploded corn straws by simultaneous saccharification and fermentation with Ethanoligenens harbinense B49INTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 5 2010Ji-Fei Xu Abstract Bio-hydrogen produced from acetic acid steam-exploded corn straw (ASCS) by simultaneous saccharification and fermentation (SSF) with Ethanoligenes harbinense 49. The effects of acetic acid concentration and enzyme loading were investigated with respect to the maximum specific hydrogen production rate and hydrogen productivity. The hydrogen yield increased with increasing of acetic acid concentration, increased and then decreased with increasing of enzyme loading. The effect of enzyme loading for hydrogen production was more crucial than that of the acetic acid concentration. At acetic acid concentration of 16% and enzyme loading of 120 and 180,U/g, the maximum hydrogen yield and maximum specific hydrogen production rate was 72,ml/g ASCS and 103,ml/g VSS·d, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Thermodynamic analysis of two-step solar water splitting with mixed iron oxidesINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 10 2009Martin Roeb Abstract A two-step thermochemical cycle for solar production of hydrogen from water has been developed and investigated. It is based on metal oxide redox pair systems, which can split water molecules by abstracting oxygen atoms and reversibly incorporating them into their lattice. After successful experimental demonstration of several cycles of alternating hydrogen and oxygen production, the present work describes a thermodynamic study aiming at the improvement of process conditions and at the evaluation of the theoretical potential of the process. In order to evaluate the maximum hydrogen production potential of a coating material, theoretical considerations based on thermodynamic laws and properties are useful and faster than actual tests. Through thermodynamic calculations it is possible to predict the theoretical maximum output of H2 from a specific redox-material under certain conditions. Calculations were focussed on the two mixed iron oxides nickel,iron-oxide and zinc,iron-oxide. In the simulation the amount of oxygen in the redox-material is calculated before and after the water-splitting step on the basis of laws of thermodynamics and available material properties for the chosen mixed iron oxides. For the simulation the commercial Software FactSage and available databases for the required material properties were used. The analysis showed that a maximum hydrogen yield is achieved if the reduction temperature is raised to the limits of the operation range, if the temperature for the water splitting is lowered below 800°C and if the partial pressure of oxygen during reduction is decreased to the lower limits of the operational range. The predicted effects of reduction temperature and partial pressure of oxygen could be confirmed in experimental studies. The increased hydrogen yield at lower splitting temperatures of about 800°C could not be confirmed in experimental results, where a higher splitting temperature led to a higher hydrogen yield. As a consequence it can be stated that kinetics must play an important role especially in the splitting step. Copyright © 2009 John Wiley & Sons, Ltd. [source] Effects of butyric acid stress on anaerobic sludge for hydrogen production from kitchen wastesJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 6 2010Mingxing Zhao Abstract BACKGROUND: Anaerobic digestion is an alternative technology to achieve the dual benefits of hydrogen production and waste stabilization from kitchen wastes. In this work, the butyric acid stress on anaerobic sludge was investigated in order to improve the tolerance of sludge against organic acids, and to enhance hydrogen accumulation. RESULTS: The tolerance of butyric acid in anaerobic sludge increased with the stress concentration, however, it decreased at concentrations greater than of 4.0 g L,1. The maximum hydrogen yield reached 63.72 mL g,1 VS at 4.0 g L,1 stress, representing an increase of 114% compared with the control group. The concentration of volatile solids (VS) of the sludge and SCOD increased steadily with time up to 20 h. At 4.0 g L,1 butyric acid stress, the maximum activity of ,-glucosidase, BAA-hydrolysing protease and dehydrogenase enzyme were 14912.1 µmol PNP g,1 TS h,1, 134.14 µmol NH4 -N g,1 TS h,1 and 7316.42 µg TF g,1 TS h,1, which were 2.78, 1.90 and 2.01 times that of the control, respectively. CONCLUSIONS: The feasibility of butyric acid stress on anaerobic sludge to increase hydrogen production from kitchen wastes was demonstrated. Remarkably, 4.0 g L,1 butyric acid stress was found to be favorable for improving the tolerance of butyric acid in sludge as well as hydrogen yield in the experiment. Copyright © 2010 Society of Chemical Industry [source] Hydrogen generation in a reverse-flow microreactor: 1.AICHE JOURNAL, Issue 8 2005Model formulation, scaling Abstract A 1-D model for methane partial oxidation in a tubular microreactor is considered. This work is motivated by a recent report by Kikas et al. that experimentally demonstrated the possibility of autothermal generation of hydrogen by partial oxidation of methane in a tubular microreactor. The reactor consists of four cylindrical channels, each 500 microns in diameter, containing Pt/13%,Rh catalyst. Autothermal generation of hydrogen was possible in both unidirectional (UD) and reverse-flow (RF) operations of the reactor, with the RF operation providing better hydrogen yield and lower temperatures than those of the UD operation. Critical comparison of methane oxidation and reforming kinetics from the literature is performed. An analysis of the timescales of individual processes within the reactor is presented to gain fundamental insight into the reactor operation. Finally, the effect of radiation heat transfer is also considered, and it is found to play an important role for a shorter-size reactor. © 2005 American Institute of Chemical Engineers AIChE J, 2005 [source] Simulation of autothermal reforming in a staged-separation membrane reactor for pure hydrogen productionTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2008Anwu Li Abstract Steam methane reforming with oxygen input is simulated in staged-separation membrane reactors. The configuration retains the advantage of regular membrane reactors for achieving super-equilibrium conversion, but reaction and membrane separation are carried out in two separate units. Equilibrium is assumed in the models given the excess of catalyst. The optimal pure hydrogen yield is obtained with 55% of the total membrane area allocated to the first of two modules. The performance of the process with pure oxygen input is only marginally better than with air. Oxygen must be added in split mode to reach autothermal operation for both reformer modules, and the oxygen input to each module depends on the process conditions. The effects of temperature, steam-to-carbon ratio and pressure of the reformer and the area of the membrane modules are investigated for various conditions. Compared with a traditional reformer with an ex situ membrane purifier downstream, the staged reactor is capable of much better pure hydrogen yield for the same autothermal reforming operating conditions. Le reformage du méthane à la vapeur avec apport d'oxygène est simulé dans des réacteurs à membranes de séparation étagés. Cette configuration conserve l'avantage des réacteurs à membranes réguliers pour la conversion en sur-équilibre, mais la réaction et la séparation par membranes sont réalisées dans deux unités séparées. L'équilibre est supposé dans les modèles selon l'excès en catalyseur. Le rendement optimal en hydrogène pur est obtenu avec 55% de la surface totale des membranes affectée au premier des deux modules. La performance du procédé avec apport d'oxygène pur n'est que marginalement meilleure par rapport à l'air. De l'oxygène peut être ajouté en mode fractionné pour atteindre un fonctionnement autothermique pour les deux modules reformeurs, et l'apport d'oxygène de chaque module dépend des conditions de procédé. Les effets de la température, du rapport vapeur-carbone et de la pression du reformeur et de la surface des modules membranaires sont étudiés pour diverses conditions. Comparativement au reformeur traditionnel avec, en aval, un purificateur à membranes ex-situ, le réacteur étagé peut donner un bien meilleur rendement en hydrogène pur pour les mêmes conditions opératoires de reformage autothermique. [source] Production of hydrogen via glycerol steam reforming in a Pd-Ag membrane reactor over Co-Al2O3 catalystASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010A. Iulianelli Abstract Generally, biodiesel fuel, when converted from vegetables oils, produces around 10 wt% of glycerol as a byproduct, which could be used for producing hydrogen by a steam-reforming reaction. Different scientific works have been realized in conventional reactors on the steam reforming of glycerol (GSR) in the aqueous or the gas phase. High reaction pressure and a relatively small catalyst deactivation are noticed when GSR is carried out in an aqueous phase, whereas the catalyst deactivation is the main disadvantage in the gas phase. In this work, GSR reaction was performed in a perm-selective Pd-Ag membrane reactor (MR) packed with a Co-Al2O3 commercial catalyst in order to extract a CO-free hydrogen stream and also enhance the performances in terms of glycerol conversion and hydrogen yield with respect to a traditional reactor (TR), both working at weight hourly space velocity (WHSV) = 1.01 h,1, 400 °C and H2O/C3H8O3 = 6/1. In MR, a maximum glycerol conversion of around 45.0% was achieved at 1.0 bar as reaction pressure, whereas it was around 94% at 4.0 bar. Moreover, as best value, more than 60.0% of CO-free hydrogen recovery was achieved in the MR at 4.0 bar and 22.8 of sweep factor (sweep gas to glycerol ratio). Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Reformer and membrane modules plant to optimize natural gas conversion to hydrogenASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009M. De Falco Abstract Membrane technology may play a crucial role in the efficient production of hydrogen from natural gas and heavy hydrocarbons. The present work assesses the performance of a hydrogen production plant utilizing by reformer and membrane modules (RMM), by which the hydrogen produced in reaction units is separated by Pd-based membranes. A major advantage of RMM architecture is the shift of chemical equilibria favoring hydrogen production due to the removal of hydrogen through membranes at each reaction step, thus improving hydrogen yield while simultaneously allowing methane conversion at temperatures below 650 °C. Lower operating temperatures allow location of the modules downstream of a gas turbine, achieving an efficient hybrid system producing electric power and hydrogen with a significant reduction in energy consumption of approximately 10% relative to conventional systems. Fundamental concepts are analyzed and integrated into a process scheme. Effects of variables including reactor temperature outlet, steam-to-carbon ratio and recycle ratio throughout pinch and sensitivity analysis are described. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Water gas shift reaction via Pd-based membranesASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009Silvano Tosti Abstract The water gas shift reaction has been studied in tubular Pd-based membranes: a thin walled dense tube and a composite Pd-ceramic tube have been considered. A computer code based on a finite element model has been developed for modelling the membrane reactor. The model accounts for the reaction kinetic, the hydrogen diffusion through the porous ceramic support and permeation through the PdAg membrane and for the partial pressure gradients of hydrogen generated at the permeate side of the membrane when a flow of purge gas is introduced. The code has been used to assess the influence of temperature, lumen pressure, presence of wall effects and sweep gas mode on the reaction conversion and hydrogen yield of the membrane reactors. At 200 kPa of lumen pressure and counter-current sweep mode, it was found that both reaction conversion and hydrogen yield increase with temperature: the dense and the composite membranes exhibit very close values of conversion (more than 99% at 400 °C) and hydrogen yield (96,97% at 400 °C). In co-current mode, the highest values of both reaction conversion and hydrogen yield have been assessed at 350 °C, while it was demonstrated that the beneficial effects of increasing the lumen pressure up to 400 kPa are maximum at 300 °C. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Continuous fermentative hydrogen production from a wheat starch co-product by mixed microfloraBIOTECHNOLOGY & BIOENGINEERING, Issue 6 2003I. Hussy Abstract For the transition to the hydrogen economy, hydrogen must be produced sustainably, e.g., by the fermentation of agricultural material. Continuous fermentative production of hydrogen from an insoluble substrate in nonsterile conditions is yet to be reported. In this study hydrogen production using mixed microflora from heat-treated digested sewage sludge in nonsterile conditions from a particulate co-product of the wheat flour industry (7.5 g L,1 total hexose) at 18- and 12-hour hydraulic retention times, pH 4.5 and 5.2, 30°C and 35°C was examined. In continuous operation, hydrogen yields of approximately 1.3 moles hydrogen/mole hexose consumed were obtained, but decreased if acetate or propionate levels rose, indicating metabolism shifted towards hydrogen consumption by homoacetogenesis or propionate producers. These shifts occurred both at pH 4.5 and 5.2. Sparging the reactor with nitrogen to reduce hydrogen in the off-gas from 50% to 7% gave stable operation with a hydrogen yield of 1.9 moles hydrogen /mole hexose consumed over an 18-day period. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng84: 619,626, 2003. [source] | ||||||||||