Improve Hydrogen Yield Research Articles

Improvement of biohydrogen production with novel augmentation strategy using different organic residues

Biohydrogen has been regarded as carbon neutral fuel. Thus it possesses tremendous potential in energy sector. The present study deals with the potentiality of bio-augmented facultative anaerobic bacteria with obligate anaerobe for the improvement of H2 production. The co-culture strategy of Klebsellia pneumoniae and Clostridium acetobutylicum improved hydrogen yield by 37% and 18% respectively as compared to individual organism. COD removal efficiency was also observed higher in case of co-culture. Maximum H2 yield by this augmented system using cane molasses, starchy wastewater and distillery effluent were 9.47, 8.72 and 7.78 mol H2 kg−1 CODreduced respectively. The COD removal efficiency using different organic residues were in the range of 50–70%. Highest H2 production rate of 1125, 642 and 790 mL L−1 h−1 were observed by using cane molasses, starchy wastewater and distillery effluent respectively in CSTR. So, bio-augmented system could be helpful in realizing the goal of “waste to energy” concept.

Directional regulation of the metabolic heterogeneity in anaerobic mixed culture to enhance fermentative hydrogen production by adaptive laboratory evolution

In this study, an adaptive laboratory evolution strategy was originally developed to enhance fermentative hydrogen production by directionally regulating the metabolic heterogeneity in anaerobic mixed culture. The results indicated that the co-introduction of 4-methylpyrazole and oxamate could redistribute the metabolic flux to butyrate-type hydrogen fermentation. Subsequently, a synergistic evolutionary pressure, combining exogenous butyrate stress with 4-methylpyrazole and oxamate, was employed to evolve hydrogen-producing mixed culture with continuous fermentation system. The metabolic engineering strategy could directionally regulate the metabolic heterogeneity through efficiently shaping powerful butyrate-type hydrogen-producing community, by which evolved culture acquired a significantly improved hydrogen yield and productivity. Furthermore, compared with original culture, evolved culture possessed much higher activities of pyruvate-ferredoxin oxidoreductase and hydrogenase but a much lower ferredoxin-NAD+ oxidoreductase activity, and these enzymatic evolutionary mechanisms were crucially important for the enhanced hydrogen fermentation.

Study of Cyclic Ni3Al Catalyst Pretreatment Process for Uniform Carbon Nanotubes Formation and Improved Hydrogen Yield in Methanol Decomposition

The 50μm thick Ni3Al thin foils were investigated as the solid-state catalyst. In this study, a cyclic Ni3Al catalysts pretreatment process was performed to obtain more uniform carbon nanotubes and gradual fragmentation of Ni nanoparticles. In temperature about 500oC the cyclic methanol decomposition was conducted. The change of hydrogen yield in methanol decomposition over tested catalysts in following cyclic pretreatment was analyzed in details. The carbon nanostructures formed during methanol decomposition was investigated by SEM, BET, XRD and Raman spectroscopy. It has been proven that the Ni nanoparticles agglomerated with following consecutive cycles, caused gradual decrease of methanol conversion and hydrogen yield in every next cycle.

Effect of salts addition on the hydrogen generation of Al–LiH composite elaborated by ball milling

Hydrogen generation from ball milled Al–LiH-salts mixture is studied. Different salts are used to test their effects on the hydrolysis properties of Al–LiH composite. KCl is found to be more effective than other salts and shows the best performance. Raising initial reaction temperature can effectively improve hydrogen yield and HG (hydrogen generation) rate of the Al–LiH–KCl mixture. Optimizing the milling conditions is necessary to improve the hydrogen generation performances of the composites. The addition amounts of KCl and LiH are varied and 10 mol% proves to be the optimum value for both of them in this work. Too much addition of LiH or KCl will cause the decrease of the hydrogen yield. A proper milling time of 10 h is discovered in this work which is beneficial for the decrease of grain size and improvement of reactivity. The 10 h milled Al-10 mol%LiH-10 mol% KCl mixture reaches a hydrogen yield of 97.1% in 10 min at 60 °C. Preliminary mechanism for the improvement has been discussed.

Optimization of hydrogen production from organic fraction of municipal solid waste (OFMSW) dry anaerobic digestion with analysis of microbial community

Summary Effect of mixed culture bacteria (MCB) addition, initial substrate concentration to inoculum (So/Xo), carbon to nitrogen (C/N) ratio on the hydrogen production (HP) from organic fraction of municipal solid waste (OFMSW) via dry anaerobic digestion was investigated. The results showed that supplementation of OFMSW with MCB substantially improved hydrogen yield (HY) and HP. HYs were 306.2 ± 33.0, 149.8 ± 16.6, and 155.3 ± 22.9 mlH2/gCODremoved for OFMSW supplemented with MCB, OFMSW, and MCB, respectively. HP at So/Xo ratio of 9.2 gCOD/gVSS was 3.1 times higher than those obtained at So/Xo ratio of 1.7 gCOD/gVSS. The maximum HY of 338.4 ± 18.9 mlH2/gCODremoved was achieved at So/Xo ratio of 9.2 gCOD/gVSS. The HP and HY were substantially increased from 169.7 ± 17.1 to 524.2 ± 34.4 ml and from 163.1 ± 23.6 to 338.4 ± 18.9 mlH2/gCODremoved with increasing the C/N from 16 to 25, respectively. However, HP and HY decreased at C/N ratio exceeding 26.6. The modified Gompertz equation model was highly fitted to the experimental data with correlation coefficient (R2 > 0.984). The 16S rRNA sequences showed the dominance of Pseudomonas fulva with similarity of 99%. Copyright © 2015 John Wiley & Sons, Ltd.

Low emission hydrogen generation through carbon assisted electrolysis

The conventional electrolysis process for hydrogen generation offers many advantages such as on-site on-demand generation, pure hydrogen that can be stored for latter use directly in fuel cells, and potential of direct coupling to a renewable source of energy. However, the process is very energy intensive. Therefore, at present hydrogen is produced mainly by Natural Gas reforming and coal gasification at temperatures in the vicinity of 800 °C. This method of hydrogen production involves the steps of reforming/gasification, shift reaction and gas separation at high temperatures to improve hydrogen yield and purity based on its application. This paper investigates the thermodynamic and practical energy benefits of single step water electrolysis process assisted by carbon, where part of the energy can come from the chemical energy of carbon. The process has been demonstrated in a solid state electrolytic cell operating at near room temperature. The paper also discusses the technology status and challenges to achieve high hydrogen generation rates.

Improvement of hydrogen yield of lba-transgenic Chlamydomonas reinhardtii caused by increasing respiration and impairing photosynthesis

The transgenic alga lba of Chlamydomonas reinhardtii yielded H2 with 50%–180% higher than the control strain. Further experiments showed that photosynthetic rates and photosynthetic reaction center II's photochemical capacities of the transgenic algae obviously decreased 33.4%–85.9% and 30.0%–51.7%, respectively, compared with those of the control. On the contrary, respiration rates of the transgenic algae significantly increased, with 40.0%–200.0% higher than those of the control. Furthermore, starch contents of the transgenic algae were also improved significantly by 79.1%–592.8% compared with the control. Therefore, the reason of H2 yield improvement of the transgenic alga lba is not only due to its decrease of photosynthetic capacity and increase of the respiration rate, but also due to the metabolic changes related to starch metabolism, photosynthesis and respiration which is possibly caused by hetero-expression of lba gene in chloroplasts of C. reinhardtii, indicating the potential of utilization of lba gene to improve hydrogen yield of micro-green algae.

Optimization and sensitivity analysis of a photovoltaic-electrolyser direct-coupling system in Beijing

Hydrogen as a clean energy carrier for solar energy can be produced by using photovoltaic-electrolyser (PVE) direct-coupling system that is well known as a kind of simple and low investment but unstable system for solar energy conversion. The key to improve hydrogen yield of a direct-coupling system is to keep its working points around maximum power point (MPP) of photovoltaic (PV) modules. The coupling of three different connection patterns of six PV modules with one electrolyser were investigated in summer, autumn and winter, three typical seasons in a year, to seek the optimum arrangement for higher system efficiency in Beijing (116°E, 40°N). A corresponding mathematics model of the system is applied to simulate and analyze the instantaneous efficiency of the system, which agreed well with the experimental results. The variation rate of the system instantaneous efficiency varies with the solar irradiation intensity, the ambient temperature and the resistance of the electrolyser. The working point that distinguishes the variation trends of the system efficiency is called the efficiency changing point (ECP). The author use a parameter V/Vm, the ratio between the voltage of the working point to the voltage of the maximum power point, to analyze the respective ECP of each factor above. It can be concluded that the variation rate of system instantaneous efficiency changes little with the above factors when the value of V/Vm of working point is smaller than that of the ECP and is sensitive to those factors when the value of V/Vm is larger than that of the ECP. Following the annual historical climate data in Beijing, the result of the annual analysis is that the best scheme for the experiment system with a 1 m2 PV panel covering 1.05 m2 areas of ground can convert 78.4 kWh of solar energy to hydrogen energy in 2012.

Improvement of the energy conversion efficiency of Chlorella pyrenoidosa biomass by a three-stage process comprising dark fermentation, photofermentation, and methanogenesis

The effects of pre-treatment methods on saccharification and hydrogen fermentation of Chlorella pyrenoidosa biomass were investigated. When raw biomass and biomass pre-treated by steam heating, by microwave heating, and by ultrasonication were used as feedstock, the hydrogen yields were only 8.8-12.7 ml/g total volatile solids (TVS) during dark fermentation. When biomass was pre-treated by steam heating with diluted acid and by microwave heating with diluted acid, the dark hydrogen yields significantly increased to 75.6 ml/g TVS and 83.3 ml/g TVS, respectively. Steam heating with diluted acid is the preferred pre-treatment method of C. pyrenoidosa biomass to improve hydrogen yield during dark fermentation and photofermentation, which is followed by methanogenesis to increase energy conversion efficiency (ECE). A total hydrogen yield of 198.3 ml/g TVS and a methane yield of 186.2 ml/g TVS corresponding to an overall ECE of 34.0% were obtained through the three-stage process (dark fermentation, photofermentation, and methanogenesis).

A genetic and metabolic approach to redirection of biochemical pathways of Clostridium butyricum for enhancing hydrogen production

Clostridium butyricum, a well known H(2) producing bacterium, produces lactate, butyrate, acetate, ethanol, and CO(2) as its main by-products from glucose. The conversion of pyruvate to lactate, butyrate and ethanol involves oxidation of NADH. It was hypothesized that the NADH could be increased if the formation of these by-products could be eliminated, resulting in enhancing H(2) yield. Herein, this study aimed to establish a genetic and metabolic approach for enhancing H(2) yield via redirection of metabolic pathways of a C. butyricum strain. The ethanol formation pathway was blocked by disruption of aad (encoding aldehyde-alcohol dehydrogenase) using a ClosTron plasmid. Although elimination of ethanol formation alone did not increase hydrogen production, the resulting aad-deficient mutant showed approximately 20% enhanced performance in hydrogen production with the addition of sodium acetate. This work demonstrated the possibility of improving hydrogen yield by eliminating the unfavorable by-products ethanol and lactate.

Engineering the pentose phosphate pathway to improve hydrogen yield in recombinant Escherichia coli

Among various routes for the biological hydrogen production, the NAD(P)H-dependent pentose phosphate (PP) pathway is the most efficient for the dark fermentation. Few studies, however, have focused on the glucose-6-phosphate 1-dehydrogenase, encoded by zwf, as a key enzyme activating the PP pathway. Although the gluconeogenic activity is essential for activating the PP pathway, it is difficult to enhance the NADPH production by regulating only this activity because the gluconeogenesis is robust and highly sensitive to concentrations of glucose and AMP inside the cell. In this study, the FBPase II (encoded by glpX), a regulation-insensitive enzyme in the gluconeogenic pathway, was activated. Physiological studies of several recombinant, ferredoxin-dependent hydrogenase system-containing Escherichia coli BL21(DE3) strains showed that overexpression of glpX alone could increase the hydrogen yield by 1.48-fold compared to a strain with the ferredoxin-dependent hydrogenase system only; the co-overexpression of glpX with zwf increased the hydrogen yield further to 2.32-fold. These results indicate that activation of the PP pathway by glpX overexpression-enhanced gluconeogenic flux is crucial for the increase of NAD(P)H-dependent hydrogen production in E. coli BL21(DE3).

Manganese doped cadmium sulfide nanocrystal for hydrogen production from water under visible light

A series of Mn 2+ doped CdS photocatalysts were prepared by a co-precipitation method and characterized by XRD, DRS, TEM, and XPS techniques. While the band gap, crystal phase and the morphology of CdS nanocrystal were not found to be affected noticeably by Mn 2+ doping, there was an optimal Mn 2+ doping content of wt 0.5% where the hydrogen production was more than doubled compared to pure CdS. Calculations of density functional theory (DFT) with plane waves and pseudopotentials were used to characterize the doping effect of Mn in cubic CdS. It is assumed that Mn 2+ serving as shallow trapping sites can separate e−/h + pairs at surface of nanosized CdS, so as to greatly reduce their surface recombination and which in turn leads to improved hydrogen yield.

Pyrolysis of wood at high temperature: The influence of experimental parameters on gaseous products

The pyrolysis of wood was carried out in an Entrained Flow Reactor at high temperature (650 to 950°C) and under rapid heating conditions (>103Ks−1). The influence of the diameter and initial moisture of the particle, reactor temperature, residence time and the nature of the gaseous atmosphere on the composition of the gaseous products has been characterised. Particle size, between 80–125 and 160–200μm, did not show any impact. Pyrolysis and tar cracking essentially happen in very short time period: less than 0.6s; the products yields are only slightly modified after 0.6s in the short residence times (several seconds) of our experiments. Higher temperatures improve hydrogen yield in the gaseous product while CO yield decreases. Under nitrogen atmosphere, after 2s at 950°C, 76% (daf) of the mass of wood is recovered as gases: CO, CO2, H2, CH4, C2H2, C2H4 and H2O. Tests performed under steam partial pressure showed that hydrogen production is slightly enhanced.

Catalytic hydrothermal conversion of cellulose over SnO2 and ZnO nanoparticle catalysts

The hydrothermal conversion of cellulose in the presence of nanometal oxide particles (SnO2 and ZnO) was investigated in this study. Both catalysts were synthesized hydrothermally and characterized using TEM, FESEM-EDX, X-ray diffraction spectroscopy and BET (Brunauer, Emmett and Teller) methods. In order to reveal the effect of nano-scale catalysts, experiments were conducted using bulk (non-nano) metal oxide and pure cellulose without any catalyst. The hydrothermal conversion experiments were carried out in a micro autoclave at 300, 400, 500, 600°C and 1h reaction time. The compositions of the gaseous products and the aqueous phase were determined with various analytical techniques (GC, ion chromatography, HPLC, UV–vis). Contribution of carbon containing products to the carbon mass balance was also represented. The results indicated both nano and bulk ZnO and SnO2 to have an effect on the water–gas shift reaction at varying temperatures. The water–gas shift reaction (WGS) proceeded fast at 300°C in the presence of ZnO, while the rate of WGS was lower at 300°C in the presence of SnO2. Nano ZnO led to improved hydrogen yield, while ethane and propane were formed as a result of side reactions in the presence of nano and bulk SnO2.

Hydrogen production by mixed bacteria through dark and photo fermentation

Mixed bacteria were used to improve hydrogen yield from cassava starch in combination of dark and photo fermentation. In dark fermentation, mixed anaerobic bacteria (mainly Clostridium species) were used to produce hydrogen from cassava starch. Substrate concentration, fermentation temperature and pH were optimized as 10.4 g/l, 31 °C and 6.3 by response surface methodology (RSM). The maximum hydrogen yield and production rate in dark fermentation were 351 ml H 2/g starch (2.53 mol H 2/mol hexose) and 334.8 ml H 2/l/h, respectively. In photo fermentation, immobilized mixed photosynthetic bacteria (PSB, mainly Rhodopseudomonas palustris species) were used to produce hydrogen from soluble metabolite products (SMP, mainly acetate and butyrate) of dark fermentation. The maximum hydrogen yield in photo fermentation was 489 ml H 2/g starch (3.54 mol H 2/mol hexose). The total hydrogen yield was significantly increased from 402 to 840 ml H 2/g starch (from 2.91 to 6.07 mol H 2/mol hexose) by mixed bacteria and cell immobilization in combination of dark and photo fermentation.

Perturbation of formate pathway for hydrogen production by expressions of formate hydrogen lyase and its transcriptional activator in wild Enterobacter aerogenes and its mutants

Abstract To examine perturbation effects of formate pathway on hydrogen productivity in Enterobacter aerogenes (Ea), formate dehydrogenase FDH-H gene (fdhF) and formate hydrogen lyase activator protein FHLA gene (fhlA) originated from Escherichia coli, were overexpressed in the wild strain Ea, its hycA-deleted mutant (A) by knockout the formate hydrogen lyase repressor and hybO-deleted mutant (O) by knockout of the uptake hydrogenase, respectively. Overexpression of fdhF and fhlA promoted cell growth and volumetric hydrogen production rates of all the strains, and the hydrogen production per gram cell dry weight (CDW) for Ea, A and O was increased by 38.5%, 21.8% and 5.25%, respectively. The fdhF and fhlA overexpression improved the hydrogen yield per mol glucose of strains Ea and A, but declined that of strain O. The increase of hydrogen yield of the strain Ea with fdhF and fhlA expression was mainly attributed to the increase of formate pathway, while for the mutant A, the improved hydrogen yield with fdhF and fhlA expression was mainly due to the increase of NADH pathway. Analysis of the metabolites and ratio of ethanol-to-acetate showed that the cellular redox state balance and energy level were also changed for these strains by fdhF and fhlA expression. These findings demonstrated that the hydrogen production was not only dependent on the hydrogenase genes, but was also affected by the regulation of the whole metabolism. Therefore, fdhF and fhlA expression in different strains of E. aerogenes could exhibit different perturbation effects on the metabolism and the hydrogen productivity.

Modeling of fluidized bed membrane reactors for hydrogen production from steam methane reforming with Aspen Plus

Hydrogen production via steam methane reforming with in situ hydrogen separation in fluidized bed membrane reactors was simulated with Aspen Plus. The fluidized bed membrane reactor was divided into several successive steam methane sub-reformers and membrane sub-separators. The Gibbs minimum free energy sub-model in Aspen Plus was employed to simulate the steam methane reforming process in the sub-reformers. A FORTRAN sub-routine was integrated into Aspen Plus to simulate hydrogen permeation through membranes in the sub-separator based on Sieverts' law. Model predictions show satisfactory agreement with experimental data in the literature. The influences of reactor pressure, temperature, steam-to-carbon ratio, and permeate side hydrogen partial pressure on reactor performances were investigated with the model. Extracting hydrogen in situ is shown to shift the equilibrium of steam methane reactions forward, removing the thermodynamic bottleneck, and improving hydrogen yield while neutralizing, or even reversing, the adverse effect of pressure.

Reformer and membrane modules plant to optimize natural gas conversion to hydrogen

AbstractMembrane 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.

Hydrogen production by immobilized R. faecalis RLD-53 using soluble metabolites from ethanol fermentation bacteria E. harbinense B49

In order to increase the hydrogen yield from glucose, hydrogen production by immobilized Rhodopseudomonas faecalis RLD-53 using soluble metabolites from ethanol fermentation bacteria Ethanoligenens harbinense B49 was investigated. The soluble metabolites from dark-fermentation mainly were ethanol and acetate, which could be further utilized for photo-hydrogen production. Hydrogen production by B49 was noticeably affected by the glucose and phosphate buffer concentration. The maximum hydrogen yield (1.83 mol H 2/mol glucose) was obtained at 9 g/l glucose. In addition, we found that the ratio of acetate/ethanol (A/E) increased with increasing phosphate buffer concentration, which is favorable to further photo-hydrogen production. The total hydrogen yield during dark- and photo-fermentation reached its maximum value (6.32 mol H 2/mol glucose) using 9 g/l glucose, 30 mmol/l phosphate buffers and immobilized R. faecalis RLD-53. Results demonstrated that the combination of dark- and photo- fermentation was an effective and efficient process to improve hydrogen yield from a single substrate.