Influence of gaseous end-products inhibition and nutrient limitations on the growth and hydrogen production by hydrogen-producing fermentative bacterial B49

The effect of hydrogen and carbon dioxide partial pressure on the growth of the extremely thermophilic archaebacterium Pyrodictium brockii at 98 degrees C was investigated. Previous work with this bacterium has been done using an 80:20 hydrogen-carbon dioxide gas phase with a total pressure of 4 atm; no attempt has been made to determine if this mixture is optimal. It was found in this study that reduced hydrogen partial pressures affected cell yield, growth rate, and sulfide production. The effect of hydrogen partial pressure on cell yield and growth rate was less dramatic when compared to the effect on sulfide production, which was not found to be growth-associated. Carbon dioxide was also found to affect growth but only at very low partial pressures. The relationship between growth rate and substrate concentration could be correlated with a Monod-type expression for either carbon dioxide or hydrogen as the limiting substrate. The results from this study indicate that a balance must be struck between cell yields and sulfide production in choosing an optimal hydrogen partial pressure for the growth of P. brockii.

Biohydrogen production behavior of moderately thermophile Thermoanaerobacterium thermosaccharolyticum W16 under different gas-phase conditions

Methane hydrate exists in huge amounts in certain locations, in sea sediments and the geological structures below them, at low temperature and high pressure. Production methods are in development to produce the methane to a floating platform. There it can be reformed to produce hydrogen and carbon dioxide, in an endothermic process. Some of the methane can be burned to provide heat energy to develop all needed power on the platform and to support the reforming process. After separation, the hydrogen is the valuable and transportable product. All carbon dioxide produced on the platform can be separated from other gases and then sequestered in the sea as carbon dioxide hydrate. In this way, hydrogen is made available without the release of carbon dioxide to the atmosphere, and the hydrogen could be an enabling step toward a world hydrogen economy.

Hydrogen is a promising clean energy source replacing largely consumed fossil fuels which emit greenhouse gases such as carbon dioxide causing global warming because water is the only substance after hydrogen burning and a wide variety of energies can be utilized for stable supply of hydrogen. However, hydrogen has serious drawbacks, low energy density and explosive nature, which promotes the use of hydrogen carriers to realize hydrogen storage and transportation with efficiency. Though some hydrogen carriers such as ammonia, liquid hydrogen, and methylcyclohexane have been reported, formic acid is increasingly attractive among them since it can be synthesized from carbon dioxide and hydrogen produced by water-splitting and is a nontoxic organic acid.A number of studies on hydrogen production from formic acid with metal complex catalysts have been developed[1], where a strong acidic solution is needed to decompose formic acid into hydrogen and carbon dioxide efficiently. Moreover, the reaction control is mainly conducted by pH, temperature and pressure. Thus, a simple reaction control alternative to these factors under mild condition is desirable in terms of safety and sustainability.We report herein hydrogen production based on formate decomposition using hybrid catalytic system composed of enzyme (FDH: formate dehydrogenase), photosensitizer (ZnTPPS: Zn (II) meso-tetra(4-sulfonatophenyl)porphyrin), hydrogen evolution catalyst (Pt-PVP: platinum nanoparticles dispersed by polyvinylpyrrolidone), NAD+ and methyl viologen (MV) as electron mediators as shown in Figure 1. By using this system, hydrogen production in neutral pH region was controlled with visible light irradiation.A mixed solution of 200 mM phosphate buffer (4.9 mL, pH 7.0) containing HCOONa (50 µmol), NAD+ (25 µmol), ZnTPPS (50 nmol), MV (250 nmol) and Pt-PVP (250 nmol) was deaerated by freeze-pump-thaw cycle repeated six times, and then gas phase was replaced by argon. 0.10 mL FDH (0.95U) was added to the solution. Finally, the solution was irradiated with 250 W halogen lamp at 30.5 oC. Gas phase was analyzed by gas chromatography to qualify and quantify produced hydrogen and carbon dioxide. Formate in the solution was also analyzed with ion chromatography.In this condition, hydrogen production and formate consumption were on the increase constantly and nearly equal, while apparent carbon dioxide production was half of them. The possible cause is that a part of the produced carbon dioxide which induces global warming was captured in the reaction solution as pH of the solution had been adjusted to 7.0. After 25-hour-irradiation, formate was converted into hydrogen completely. This result illustrates hydrogen production was derived from formate decomposition. In addition, the optimum pH for hydrogen production was investigated in this system ranging from pH 6.0 to pH 8.0. The highest catalytic activity was observed at pH 7.0 because formate oxidation catalyzed by FDH proceeded the most smoothly in the region of pH 7.0-8.0 and more adequate protons to be reduced were in this system at pH 7.0 than pH 8.0. Finally, Figure 2 shows the visible light response of gas production and formate consumption. Hydrogen was produced only in the presence of visible light irradiation whereas carbon dioxide production and formate consumption increased consistently. This means formate oxidation proceeded regardless of the visible light irradiation or non-irradiation producing carbon dioxide while photocatalytic hydrogen production from NADH regenerated by formate dehydrogenation was driven by visible light irradiation.A hybrid catalytic system for visible light-controlled hydrogen production from formate in neutral pH range was constructed successfully, leading to the unharmful and green utilization of formic acid as a useful hydrogen carrier.In this hybrid catalytic system, MV is used as an electron mediator for charge separation, which has been known to inhibit light absorption of photosensitizer due to the absorption overlap between MV• and ZnTPPS[2]. As a result, this system becomes slightly complicated including four redox reactions. Hence, hybrid photocatalytic system without MV will be constructed in the future for efficient and simple hydrogen evolution.Reference[1] W. H. Wang, Y. Himeda, J. T. Muckerman, G. F. Manbeck, E. Fujita, Chem. Rev. 2015, 115, 12936.[2] M. E. El-Khouly, E. El-Mohsnawy, S.Fukuzumi, J. Photochem. Photobiol. C. 2017, 31, 36. Figure 1

Core-scale experimental and numerical study of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si1.svg" display="inline" id="d1e1431"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub><mml:mo linebreak="goodbreak" linebreakstyle="after">−</mml:mo><mml:msub><mml:mrow><mml:mi mathvariant="normal">CO</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math> mixture separation in coal: A three-component system investigation

The role of co ₂ in improving sonic hydrogen production

Improved hydrogen production under microaerophilic conditions by overexpression of polyphosphate kinase in Enterobacter aerogenes

We have investigated hydrogen (H2) production by the cellulose-degrading anaerobic bacterium, Clostridium thermocellum. In the following experiments, batch-fermentations were carried out with cellobiose at three different substrate concentrations to observe the effects of carbon-limited or carbon-excess conditions on the carbon flow, H2-production, and synthesis of other fermentation end products, such as ethanol and organic acids. Rates of cell growth were unaffected by different substrate concentrations. H2, carbon dioxide (CO2), acetate, and ethanol were the main products of fermentation. Other significant end products detected were formate and lactate. In cultures where cell growth was severely limited due to low initial substrate concentrations, hydrogen yields of 1 mol H2/mol of glucose were obtained. In the cultures where growth ceased due to carbon depletion, lactate and formate represented a small fraction of the total end products produced, which consisted mainly of H2, CO2, acetate, and ethanol throughout growth. In cultures with high initial substrate concentrations, cellobiose consumption was incomplete and cell growth was limited by factors other than carbon availability. H2-production continued even in stationary phase and H2/CO2 ratios were consistently greater than 1 with a maximum of 1.2 at the stationary phase. A maximum specific H2 production rate of 14.6 mmol g dry cell(-1) h(-1) was observed. As cells entered stationary phase, extracellular pyruvate production was observed in high substrate concentration cultures and lactate became a major end product.

Solid Acid Electrochemical Cell for the Production of Hydrogen from Ammonia

In phase II of a feasibility study on commercialized fast reactor cycle system of Japan Nuclear Cycle Development Institute, we are finding a concept of a multi-purpose small sized fast reactor with various requirements, such as, safety and improved economical competitiveness. In this study, a membrane reforming hydrogen production plant using a small sized sodium cooled reactor was designed as one of promising concepts. In the membrane reformer, methane and steam are reformed into carbon dioxide and hydrogen with sodium heat at a temperature 500deg-C. In the equilibrium condition, steam reforming proceeds with catalyst at a temperature more than 800deg-C. Using membrane reformers, the steam reforming temperature can be decreased from 800 to 500deg-C because the hydrogen separation membrane remove hydrogen selectively from catalyst area and the partial pressure of hydrogen is kept much lower than equilibrium condition. In this study, a hydrogen and electric co-production plant has been designed. The reactor thermal output is 375MW and 25% of the thermal output is used for hydrogen production (70000Nm3/h). The hydrogen production cost is estimated but it is still higher than the economical goal. The major reason of the high cost comes from the large size of hydrogen separation reformers because of the limit of hydrogen separation efficiency of palladium membrane. A new highly efficient hydrogen separation membrane is needed to reduce the cost of hydrogen production using membrane reformers. There is possibility of multi-tube failure in the membrane reformers. In future study, a design of measures against tube failure and elemental experiments of reaction between sodium and reforming gas will be needed.

Molecular hydrogen is an environmentally clean source of energy, but it is not available on Earth. Steam reforming of bio-derived compounds represents a valuable route for the generation of molecular hydrogen and has the advantage that it is CO2-neutral and it requires a limited amount of additional infrastructure for implementation. At present, suitable catalysts for selective bio-alcohol and dimethyl ether reforming into hydrogen and carbon dioxide are being developed, but their use on structured wall reactors for practical application is still under way. Among them, aerogel-based coated structures appear very promising due to their very high mass transfer rates and their ability to disperse highly active metal nanoparticles. The performance of these systems improves considerably by using microreaction technologies. Microreactors based on silicon micromonoliths together with integrated downstream carbon monoxide selective oxidation hold a promising futurefor the effective on-site and on-demand generation of hydrogen from renewable fuels in portable fuel cell applications.

Significant progress has been made in the past two years in improving the understanding of acid consumption and catalytic hydrogen generation during the Defense Waste Processing Facility (DWPF) processing of waste sludges in the Sludge Receipt and Adjustment Tank (SRAT) and Slurry Mix Evaporator (SME). This report reviews issues listed in prior internal reviews, describes progress with respect to the recommendations made by the December 2006 external review panel, and presents a summary of the current understanding of catalytic hydrogen generation in the DWPF Chemical Process Cell (CPC). Noble metals, such as Pd, Rh, and Ru, are historically known catalysts for the conversion of formic acid into hydrogen and carbon dioxide. Rh, Ru, and Pd are present in the DWPF SRAT feed as by-products of thermal neutron fission of {sup 235}U in the original waste. Rhodium appears to become most active for hydrogen as the nitrite ion concentration becomes low (within a factor of ten of the Rh concentration). Prior to hydrogen generation, Rh is definitely active for nitrite destruction to N{sub 2}O and potentially active for nitrite to NO formation. These reactions are all consistent with the presence of a nitro-Rh complex catalyst, although definite proof for the existence of this complex during Savannah River Site (SRS) waste processing does not exist. Ruthenium does not appear to become active for hydrogen generation until nitrite destruction is nearly complete (perhaps less nitrite than Ru in the system). Catalytic activity of Ru during nitrite destruction is significantly lower than that of either Rh or Pd. Ru appears to start activating as Rh is deactivating from its maximum catalytic activity for hydrogen generation. The slow activation of the Ru, as inferred from the slow rate of increase in hydrogen generation that occurs after initiation, may imply that some species (perhaps Ru itself) has some bound nitrite on it. Ru, rather than Rh, is primarily responsible for the hydrogen generation in the SME cycle when the hydrogen levels are high enough to be noteworthy. Mercury has a role in catalytic hydrogen generation. Two potentially distinct roles have been identified. The most dramatic effect of Hg on hydrogen generation occurs between runs with and without any Hg. When a small amount of Hg is present, it has a major inhibiting effect on Rh-catalyzed H{sub 2} generation. The Rh-Ru-Hg matrix study showed that increasing mercury from 0.5 to 2.5 wt% in the SRAT receipt total solids did not improve the inhibiting effect significantly. The next most readily identified role for Hg is the impact it has on accelerating NO production from nitrite ion. This reaction shifts the time that the ideal concentration of nitrite relative to Rh occurs, and consequently causes the most active nitro-Rh species to form sooner. The potential consequences of this shift in timing are expected to be a function of other factors such as amount of excess acid, Rh concentration, etc. Graphical data from the Rh-Ru-Hg study suggested that Hg might also be responsible for partially inhibiting Ru-catalysis initially, but that the inhibition was not sustained through the SRAT and SME cycles. Continued processing led to a subsequent increase in hydrogen generation that was often abrupt and that frequently more than doubled the hydrogen generation rate. This phenomenon may have been a function of the extent of Hg stripping versus the initial Ru concentration in these tests. Palladium is an active catalyst, and activates during (or prior to) nitrite destruction to promote N{sub 2}O formation followed by a very small amount of hydrogen. Pd then appears to deactivate. Data to date indicate that Pd should not be a species of primary concern relative to Rh and Ru for hydrogen generation. Pd was a very mild catalyst for hydrogen generation compared to Rh and Ru in the simulated waste system. Pd was comparable to Rh in enhancing N{sub 2}O production when present at equal concentration. Pd, however, is almost always present at less than a quarter of the Rh concentration in SRS sludge waste. Ag did not appear to ever become active for hydrogen generation. Data from two tests spiked with silver were comparable to the data from two tests with no noble metals. All significant technical gaps and inconsistencies with historical data in the prior two internal reviews of catalytic hydrogen generation work at SRS have been resolved. About 90% of the recommended work from the external technical review panel has been completed. Work planned or in progress could bring progress on the review panel recommendations up to about 95% by the end of calendar 2009. This primarily covers the sludge simulant matrix study on bulk compositional factors plus some follow-up work on X-ray absorption spectroscopy and improved acid equations.

Electrolysis of humidified methane to hydrogen and carbon dioxide at low temperatures and voltages

Hydrogen production from water-splitting has attracted significant interest because of its use in refining, chemicals’ production and as an alternative fuel. A promising technology for hydrogen production through water-splitting at moderate temperatures is the use of mixed ionic-electronic conducting (MIEC) membranes [1-2]. Using an inert gas on the oxygen-lean side, oxygen permeation rates are slow unless vacuum is used (or higher pressure on the feed side). Fuel addition in the oxygen-lean stream raises the oxygen chemical potential difference and hence the oxygen permeation and hydrogen production rate increase significantly [1-5]. One such fuel is ethane whose partial dehydrogenation leads to a valuable chemical, namely ethylene. Coupling water-splitting and ethane dehydrogenation using a MIEC membrane can reduce the complexity and capital cost of producing both (process intensification). This study investigated the co-production of hydrogen and ethylene using BaFe0.9Zr0.1O3- δ membranes. Experimental measurements performed in a button-cell reactor showed significant oxygen permeation, ethane conversion and selectivity to ethylene. The performance of a 1.1 mm thick membrane operating at inlet XH2O=50% at the steam side (balance is nitrogen) was investigated as a function of temperature and inlet ethane mole fraction at the oxygen-lean side (balance is helium). At T=900 °C and XC2H6=10%, the oxygen permeation flux (JO2) was ≈ 2.0 μmole/cm2/sec, while the ethane conversion and selectivity to ethylene were 95% and 83%, respectively. At these conditions, the combination of gas-phase and surface reactions lead to the production of other products, such as hydrogen, methane, acetylene, carbon monoxide and carbon dioxide. When using ethane, the oxygen permeation through BaFe0.9Zr0.1O3- δ increases due to electrochemical reactions of these products with oxygen ions on the membrane surface, while the electron transfer process takes place through a redox mechanism that involves iron and its different oxidation states [5]. Lowering the temperature to T=850 °C decreased the oxygen permeation flux to ≈ 1.0 μmole/cm2/sec and conversion of ethane to 79% while ethylene selectivity increased to 93%. Under long-term operation, BaFe0.9Zr0.1O3- δ shows good stability. To further increase the performance of the material, we investigated the limitations imposed by surface reactions and charged species diffusion in an effort to identify the rate-limiting step in the overall oxygen permeation process.

The production of molecular hydrogen (H2) from water by hydrogenase of thermophilic cyanobacterium Synechococcus sp. strain H-1 has been studied by following the time courses of the hydrogen concentration in the gas-phase, cell mass concentration and cellular content of D-glucose in dark batch reactions at temperatures ranging from 313 to 333 K. An anaerobic, dark, NO3− starvation, neutral or alkaline pH and shaking condition was found to be a prerequisite for H2 production. Strain H-1 could multiply and produce hydrogen at all temperatures studied. A linear relation between hydrogen production and glucose consumption was observed and the yield coefficient of hydrogen in terms of D-glucose consumption was 71, 115 and 146 at initial concentrations of cell mass of 0.75, 2.5 and 9.5 g · L−1, respectively. The activation energies for the maximum specific rates of cell mass growth, D-glucose consumption and hydrogen production were found to be 62, 12.6 and 122 kJ · mol−1, respectively. The maximum specific hydrogen production rate was found to be 0.09 μmol · mg-chl a−1 · h−1 at 328 K, which is comparable to that reported in non-nitrogen-fixing unicellular cyanobacteria. It is concluded that utilization of thermophilic Synechococcus sp. strain H-1 for hydrogen production is beneficial since the contamination risk of mesophilic bacteria is low.