Escherichia coli (XL1-BLUE) for continuous fermentation of bioH2 and its separation by polyimide membrane

In this work continuous hydrogen production by Escherichia coli (XL1-BLUE) and its purification by membrane gas separation were studied. Firstly, a kinetic investigation was performed on formate supplemented broth in order to determine exponential growth phase (5–7 h) while the most intense hydrogen fermentation takes place. Furthermore, important process design parameters such as saturation constant and maximal growth rate were calculated (K_S = 0.77 g l⁻¹, μ_max = 0.39 h⁻¹). Afterward, based on the kinetic study, continuous hydrogen fermentations using cultures of E. coli (XL1-BLUE) were carried out in a CSTR reactor configuration applying various hydraulic retention times (HRT) related to both exponential and stationary growth period (5 h, 7 h, 9 h). The results indicated that highest hydrogen yield (0.26 mmol H₂/mmol formate added) and productivity (5.1 mmol H₂ l⁻¹ d⁻¹) could be achieved by applying HRT = 7 h that does not allow the living cells to reach stationary phase. In addition to hydrogen production, the concentration of bioH₂ by polyimide membrane under different operational circumstances was investigated using pure and mixed gases, as well. The results of single gas experiments indicated that increasing the temperature has positive effect on separation efficiency. Moreover, the influence of retentate and feed flow ratio (Q_R/Q_F) was studied applying binary H₂/CO₂ gaseous mixture and it was found that polyimide membrane has high potential for H₂ purification since 18% increase in H₂ concentration and 22% decrease in CO₂ content could be attained in the permeate by a one-step separation process.     

H2 production via water gas shift in a composite Pd membrane reactor prepared by the pore-plating method

In this work, H₂ production via catalytic water gas shift reaction in a composite Pd membrane reactor prepared by the ELP “pore-plating” method has been carried out. A completely dense membrane with a Pd thickness of about 10.2 μm over oxidized porous stainless steel support has been prepared. Firstly, permeation measurements with pure gases (H₂ and N₂) and mixtures (H₂ with N_2, CO or CO₂) at four different temperatures (ranging from 350 to 450 °C) and trans-membrane pressure differences up to 2.5 bar have been carried out. The hydrogen permeance when feeding pure hydrogen is within the range 2.68–3.96·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5, while it decreases until 0.66–1.35·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5 for gas mixtures. Furthermore, the membrane has been also tested in a WGS membrane reactor packed with a commercial oxide Fe–Cr catalyst by using a typical methane reformer outlet (dry basis: 70%H₂–18%CO–12%CO₂) and a stoichiometric H₂O/CO ratio. The performance of the reactor was evaluated in terms of CO conversion at different temperatures (ranging from 350 °C to 400 °C) and trans-membrane pressures (from 2.0 to 3.0 bar), at fixed gas hourly space velocity (GHSV) of 5000 h⁻¹. At these conditions, the membrane maintained its integrity and the membrane reactor was able to achieve up to the 59% of CO conversion as compared with 32% of CO conversion reached with conventional packed-bed reactor at the same operating conditions.     

Hydrogen production from soft-drink wastewater in an upflow anaerobic packed-bed reactor

The production of hydrogen from soft-drink wastewater in two upflow anaerobic packed-bed reactors was evaluated. The results show that soft-drink wastewater is a good source for hydrogen generation. Data from both reactors indicate that the reactor without medium containing macro- and micronutrients (R2) provided a higher hydrogen yield (3.5 mol H₂ mol⁻¹ of sucrose) as compared to the reactor (R1) with a nutrient-containing medium (3.3 mol H₂ mol⁻¹ of sucrose). Reactor R2 continuously produced hydrogen, whereas reactor R1 exhibited a short period of production and produced lower amounts of hydrogen. Better hydrogen production rates and percentages of biogas were also observed for reactor R2, which produced 0.4 L h⁻¹ L⁻¹ and 15.8% of H₂, compared to reactor R1, which produced 0.2 L h⁻¹ L⁻¹ and 2.6% of H₂. The difference in performance between the reactors was likely due to changes in the metabolic pathway for hydrogen production and decreases in bed porosity as a result of excessive biomass growth in reactor R1. Molecular biological analyses of samples from reactors R1 and R2 indicated the presence of several microorganisms, including Clostridium (91% similarity), Enterobacter (93% similarity) and Klebsiella (97% similarity).     

A mixed electronic and protonic conducting hydrogen separation membrane with asymmetric structure

In this work, highly doped ceria with lanthanum, La_0.5Ce_0.5O_2−δ (LDC), are developed as hydrogen separation membrane material. LDC presents a mixed electronic and protonic conductivity in reducing atmosphere and good stability in moist CO₂ environment. LDC separation membranes with asymmetrical structure are fabricated by a cost-saving co-pressing method, using NiO + LDC + corn starch mixture as substrate and LDC as top membrane layer. Hydrogen permeation properties are systemically studied, including the influence of operating temperature, hydrogen partial pressure in feed stream and water vapor in both sides of the membrane on hydrogen permeating fluxes. Hydrogen permeability increases as the increasing of temperature and hydrogen partial pressure in feed gas. Using 20% H₂/N₂ (with 3% of H₂O) as feed gas and dry high purity argon as sweep gas, an acceptable flux of 2.6 × 10⁻⁸ mol cm⁻² s⁻¹ is achieved at 900 °C. The existing of water in both sides of membrane has significant effect on hydrogen permeation and the corresponding reasons are analyzed and discussed.     

Bio-hydrogen production during acidogenic fermentation in a multistage stirred tank reactor

The objective of this study was to evaluate the production of hydrogen in a two-stage CSTR system – both reactors having the same volume – and compare its performance with a conventional one-stage process. The lab-scale two-stage and one-stage systems were operated at five pHs and five hydraulic retention time (HRTs). The maximum volumetric hydrogen productivity and yield obtained with the two-stage system were 5.8 mmol L⁻¹ h⁻¹ and 2.7 mol H₂ mol glucose⁻¹, respectively, at an HRT of 12 h and pH 5.5. Overall, the two-stage system showed, at steady state, a better performance that the one-stage system for all the evaluated pHs. However, a comparison between the one-stage system, operating at 6 h of HRT, and the first reactor of the two-stage system at the same HRT did not show any significant difference, highlighting the positive impact of having a two-stage process. The determination of the ratio between the experimental measured H₂ in the gas phase and the theoretical H₂ generated in the liquid phase (discrepancy factor) indicated that an important part of the hydrogen produced in the first reactor was transferred into the second reactor instead of being desorbed in the headspace. Therefore, the improving of hydrogen production in the two-stage system is rather attributed to the increased transfer of hydrogen from liquid to gas than an actual total hydrogen production increase.     

A novel tubular oxygen-permeable membrane reactor for partial oxidation of CH4 in coke oven gas to syngas

Dense BaCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFNO) membrane tubes were prepared by slip casting and readily brazed to 310S stainless steel supports using a silver-based alloy. A novel tubular membrane reactor was constructed by placing a cylindrical Ni-based monolithic catalyst coaxially around the tubular membrane and a conventional Ni-based catalyst-bed apart from the membrane tube. The novel membrane reactor was successfully applied to partial oxidation of CH₄ in coke oven gas (COG). At 850 °C, 94% of CH₄ conversion, 93% of H₂ and as high as 11.3 cm³ cm⁻² min⁻¹ of oxygen permeation flux were obtained. The experimental H₂ and CO selectivity and CH₄ conversion were close to the thermodynamically predicated ones. There was a good match in the coefficient of thermal expansion (CTE) among BCFNO membrane, Ag-based alloy and 310S metal support. Long-term operation test results indicate that the novel tubular BCFNO membrane reactor exhibited not only high activity but also good stability for the partial oxidation of CH₄ in COG to syngas.     

Sulfate-reducing bacteria as new microorganisms for biological hydrogen production

Sulfate-reducing bacteria (SRB) have an extremely high hydrogenase activity and in natural habitats where sulfate is limited, produce hydrogen fermentatively. However, the production of hydrogen by these microorganisms has been poorly explored. In this study we investigated the potential of SRB for H₂ production using the model organism Desulfovibrio vulgaris Hildenborough. Among the three substrates tested (lactate, formate and ethanol), the highest H₂ production was observed from formate, with 320 mL L⁻¹_medium of H₂ being produced, while 21 and 5 mL L⁻¹_medium were produced from lactate and ethanol, respectively. By optimizing reaction conditions such as initial pH, metal cofactors, substrate concentration and cell load, a production of 560 mL L⁻¹_medium of H₂ was obtained in an anaerobic stirred tank reactor (ASTR). In addition, a high specific hydrogen production rate (4.2 L g⁻¹_dcw d⁻¹; 7 mmol g⁻¹_dcw h⁻¹) and 100% efficiency of substrate conversion were achieved. These results demonstrate for the first time the potential of sulfate reducing bacteria for H₂ production from formate.     

Electro-hydrolysis of cheese whey solution for hydrogen gas production and chemical oxygen demand (COD) removal using photo-voltaic cells (PVC)

Diluted cheese whey (CW) solution was used for hydrogen gas production by electro-hydrolysis using photo-voltaic cells (PVC) as source of electricity. Effects of initial chemical oxygen demand (COD) concentration on the rate and yield of hydrogen gas production were investigated using a completely mixed and sealed reactor with aluminum electrodes. Cumulative hydrogen gas formation (CHF) increased with increasing initial COD concentration. The highest cumulative hydrogen gas volume (26472 mL), hydrogen gas production rate (4553 mL d⁻¹), hydrogen yield (7004 mL H₂ g⁻¹ COD), and percent COD removal (21.5%) were obtained with initial COD of 35172 mg L⁻¹. H₂ gas formation from water control was only 5365 mL. pH of the CW solution increased with decreasing conductivities during the course of experiments. Gas phase contained more than 99% H₂ at the end of experiments. The highest energy efficiency (20.4%) was also obtained with the highest COD content. Nearly pure hydrogen gas formation by electro-hydrolysis of cheese whey using PVC panels was proven to be an effective method.     

Hydrogen permeation behavior of Nb30Ti35Ni35−xCox (x = 0…35) alloys containing high fractions of eutectic

The hydrogen permeability of cast Nb₃₀Ti₃₅Ni_35−xCo_x (x = 0…35) alloys is found to increase with the Co content, induced by the tailored microstructures containing high fractions of eutectic and less primary phase. Among the cast alloys, Nb₃₀Ti₃₅Co₃₅ consisting entirely of eutectic exhibits the highest permeability, particularly 2.65 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 at 673 K. This permeability is further increased to 3.58 × 10⁻⁸ mol H₂ m⁻¹ s⁻¹ Pa^−0.5 by aligning eutectic grains perpendicularly to the membrane surface using directional solidification. The high permeability is attributed to the high hydrogen solubility and diffusivity in alloys. Our work demonstrates that hydrogen permeable alloys containing high fractions of eutectic may exhibit high permeability by adequately optimizing morphology, volume fraction and alignment of the bcc-Nb phase in the eutectic as the pathways for hydrogen permeation.     

High pressure palladium membrane reactor for the high temperature water-gas shift reaction

The water-gas shift (WGS) catalytic membrane reactor (CMR) incorporating a composite Pd-membrane and operating at elevated temperatures and pressures can greatly contribute to the efficiency enhancement of several methods of H₂ production and green power generation. To this end, mixed gas permeation experiments and WGS CMR experiments have been conducted with a porous Inconel supported, electroless plated Pd-membrane to better understand the functioning and capabilities of those processes. Binary mixtures of H₂/He, H₂/CO₂, and a ternary mixture of H₂, CO₂ and CO were separated by the composite membrane at 350, 400, and 450 °C, 14.4 bar (P_tube = 1 bar), and space velocities up to 45,000 h⁻¹. H₂ permeation inhibition caused by reversible surface binding was observed due to the presence of both CO and CO₂ in the mixtures and membrane inhibition coefficients were estimated. Furthermore, WGS CMR experiments were conducted with a CO and steam feed at 14.4 bar (P_tube = 1 bar), H₂O/CO ratios of 1.1-2.6, and GHSVs of up to 2900 h⁻¹, considering the effect of the H₂O/CO ratio as well as temperature on the reactor performance. Experiments were also conducted with a simulated syngas feed at 14.0 bar (P_tube  = 1 bar), and 400-450 °C, assessing the effect of the space velocity on the reactor performance. A maximum CO conversion of 98.2% was achieved with a H₂ recovery of 81.2% at 450 °C. An optimal operating temperature for high CO conversion was identified at approximately 450 °C, and high CO conversion and H₂ recovery were achieved at 450 °C with high throughput, made possible by the 14.4 bar reaction pressure.     

Bio-hydrogen production from cheese whey powder (CWP) solution: Comparison of thermophilic and mesophilic dark fermentations

Cheese whey powder (CWP) solution was used as the raw material for hydrogen gas production by mesophilic (35 °C) and thermophilic (55 °C) dark fermentations at constant initial total sugar and bacteria concentrations. Thermophilic fermentation yielded higher cumulative hydrogen formation (CHF = 171 mL), higher hydrogen yield (111 mL H₂ g⁻¹ total sugar), and higher hydrogen formation rate (3.46 mL H₂ L⁻¹ h⁻¹) as compared to mesophilic fermentation. CHF in both cases were correlated with the Gompertz equation and the constants were determined. Despite the longer lag phase, thermophilic fermentation yielded higher specific H₂ formation rate (2.10 mL H₂ g⁻¹cells h⁻¹). Favorable results obtained in thermophilic fermentation were probably due to elimination of H₂ consuming bacteria at high temperatures and selection of fast hydrogen gas producers.     

The effects of seed sludge and hydraulic retention time on the production of hydrogen from a cassava processing wastewater and glucose mixture in an anaerobic fluidized bed reactor

The potential for co-fermentation of a cassava processing wastewater and glucose mixture was studied in anaerobic fluidized bed reactors. The effects of different hydraulic retention times (HRTs) (10–2 h) and varying sources of inoculum are reported. The sludge from a UASB reactor that had been used to treat poultry slaughterhouse wastewater (SP) resulted in the highest yields of hydrogen (HY) and ethanol (EtOHY) of 1.0 mmol H₂ g⁻¹ COD (10 h) and 3.0 mmol EtOH g⁻¹ COD (6 h). The sludge from a UASB reactor used for the treatment of swine wastewater (SW) resulted in a maximum HY of 0.65 mmol H₂ g⁻¹ COD (6 h) and EtOHY of 2.1 mmol g⁻¹ COD (10 and 8 h). Methane was produced with a maximum production of 9.68 L CH₄ d⁻¹ L⁻¹. Based on phylogenetic analysis of 16S rRNA, bacteria and methanogenic archaea similar to Lactobacillus and Methanobacterium, respectively, were identified.     

Single-step synthesized dual-layer hollow fiber membrane reactor for on-site hydrogen production through ammonia decomposition

On-site hydrogen production via catalytic ammonia decomposition presents an attractive pathway to realize H₂ economy and to mitigate the risk associated with storing large amounts of H₂. This work reports the synthesis and characterization of a dual-layer hollow fiber catalytic membrane reactor for simultaneous NH₃ decomposition and H₂ permeation application. Such hollow fiber was synthesized via single-step co-extrusion and co-sintering method and constitutes of 26 μm-thick mixed protonic-electronic conducting Nd_5.5Mo_0.5W_0.5O_11.25-δ (NMW) dense H₂ separation layer and Nd_5.5Mo_0.5W_0.5O_11.25-δ-Ni (NMW-Ni) porous catalytic support. This dual-layer NMW/NMW-Ni hollow fiber exhibited H₂ permeation flux of 0.26 mL cm⁻² min⁻¹ at 900 °C when 50 mL min⁻¹ of 50 vol% H₂ in He was used as feed gas and 50 mL min⁻¹ N₂ was used as sweep gas. Membrane reactor based on dual-layer NMW/NMW-Ni hollow fiber achieved NH₃ conversion of 99% at 750 °C, which was 24% higher relative to the packed-bed reactor with the same reactor volume. Such higher conversion was enabled by concurrent H₂ extraction out of the membrane reactor during the reaction. This membrane reactor also maintained stable NH₃ conversion and H₂ permeation flux as well as structure integrity over 75 h of reaction at 750 °C.     

Enhanced bio-hydrogen production by immobilized Clostridium sp. T2 on a new biological carrier

Biological mycelia pellets, which are formed spontaneously in the process of Aspergillus niger Y3 fermentation, were explored as carrier for immobilization of Clostridium sp. T2 to improve hydrogen production. Batch fermentation tests showed that optimal dosage and size of mycelia pellets for hydrogen production were 0.350 g 150 ml⁻¹ medium and 1.5 mm. Under these conditions, hydrogen production with immobilized cells on mycelia pellets was further investigated in continuous stirred-tank reactor (CSTR) with hydraulic retention time (HRT) ranging from 12 to 8 h. It obtained that the maximum hydrogen production rate reached 2.76 mmol H₂ L⁻¹ h⁻¹ at 10 h HRT, which was 40.8% higher than the carrier-free process, but slightly lower than the counterpart immobilized in sodium alginate with the value of 3.15 mmol H₂ L⁻¹ h⁻¹. SEM observation showed that abundant cells were closely adhered to mycelia pellets. The present results indicate the potential of using mycelia pellets as biological carrier for enhancing hydrogen production.     

Thermal stability and effect of typical water gas shift reactant composition on H2 permeability through a Pd-YSZ-PSS composite membrane

This work comprises a study of hydrogen separation with a composite Pd-YSZ-PSS membrane from mixtures of H₂, N₂, CO and CO₂, typical of a water gas shift reactor. The Pd layer is extended over a tubular porous stainless steel support (PSS) with an intermediate layer of yttria-stabilized-zirconia (YSZ). YSZ and Pd layers were incorporated over the PSS using Atmospheric Plasma Spraying and Electroless Plating techniques, respectively. The Pd and YSZ thickness values are 13.8 and 100 μm, respectively, and the Pd layer is fully dense. Permeation measurements with pure, binary and ternary gases at different temperatures (350–450 °C), trans-membrane pressures (0–2.5 bar) and gas composition have been carried out. Moreover, thermal stability of the membrane was also checked by repeating permeation measurements after several cycles of heating and cooling the system. Membrane hydrogen permeances were calculated using Sieverts' law, obtaining values in the range of 4·10⁻⁵–4·10⁻⁴ mol m⁻² s⁻¹ Pa^−0.5. The activation energy of the permeance was also calculated using Arrhenius' equation, obtaining a value of 16.4 kJ/mol. In spite of hydrogen selectivity being 100% for all experiments, the hydrogen permeability was affected by the composition of feed gas. Thus, a significant depletion in H₂ permeate flux was observed when other gases were in the mixture, especially CO, being also more or less significant depending on gas composition.     

Hydrogen production from acid hydrolyzed molasses by the hydrogen overproducing Escherichia coli strain HD701 and subsequent use of the waste bacterial biomass for biosorption of Cd(II) and Zn(II)

This study was devoted to investigate production of hydrogen gas from acid hydrolyzed molasses by Escherichia coli HD701 and to explore the possible use of the waste bacterial biomass in biosorption technology. In variable substrate concentration experiments (1, 2.5, 5, 10 and 15 g L⁻¹), the highest cumulative hydrogen gas (570 ml H₂ L⁻¹) and formation rate (19 ml H₂ h⁻¹ L⁻¹) were obtained from 10 g L⁻¹ reducing sugars. However, the highest yield (132 ml H₂ g⁻¹ reducing sugars) was obtained at a moderate hydrogen formation rate (11 ml H₂ h⁻¹ L⁻¹) from 2.5 g L⁻¹ reducing sugars. Subsequent to H₂ production, the waste E. coli biomass was collected and its biosorption efficiency for Cd²⁺ and Zn²⁺ was investigated. The biosorption kinetics of both heavy metals fitted well with the pseudo second-order kinetic model. Based on the Langmuir biosorption isotherm, the maximum biosorption capacities (q_max) of E. coli waste biomass for Cd²⁺ and Zn²⁺ were 162.1 and 137.9 (mg/g), respectively. These q_max values are higher than those of many other previously studied biosorbents and were around three times more than that of aerobically grown E. coli. The FTIR spectra showed an appearance of strong peaks for the amine groups and an increase in the intensity of many other functional groups in the waste biomass of E. coli after hydrogen production in comparison to that of aerobically grown E. coli which explain the higher biosorption capacity for Cd²⁺ or Zn²⁺ by the waste biomass of E. coli after hydrogen production. These results indicate that E. coli waste biomass after hydrogen production can be efficiently used in biosorption technology. Interlinking such biotechnologies is potentially possible in future applications to reduce the cost of the biosorption technology and duplicate the benefits of biological H₂ production technology.     

Bio-hydrogen production from acid hydrolyzed waste ground wheat by dark fermentation

Waste ground wheat was subjected to acid hydrolysis (pH = 3.0) at 90 °C for 15 min using an autoclave. The sugar solution obtained from acid hydrolysis was subjected to dark fermentation for hydrogen gas production after neutralization. In the first set of experiments, initial total sugar concentration was varied between 3.9 and 27.5 g L⁻¹ at constant biomass (cell) concentration of 1.3 g L⁻¹. Biomass concentration was varied between 0.28 g L⁻¹ and 1.38 g L⁻¹ at initial total sugar concentration of 7.2 ± 0.2 g L⁻¹ in the second set of experiments. The highest hydrogen yield (1.46 mol H₂ mol⁻¹ glucose) and the specific formation rate (83.6 ml H₂ g⁻¹ cell h⁻¹) were obtained with 10 g L⁻¹ initial total sugar concentration. Biomass (cell) concentration affected the specific hydrogen production rate yielding the highest rate (1221 ml H₂ g⁻¹ cell h⁻¹) and the yield at the lowest (0.28 g L⁻¹) initial biomass concentration. The most suitable X_o/S_o ratio, maximizing the yield and specific rate of hydrogen gas formation was X_o/S_o = 0.037. Dark fermentation of acid hydrolyzed ground wheat was found to be more beneficial as compared to simultaneous bacterial hydrolysis and fermentation.     

High-performance Ni–BaZr0.1Ce0.7Y0.1Yb0.1O3−δ (BZCYYb) membranes for hydrogen separation

Cermet membranes composited of Ni and doped barium cerate have been widely studied for hydrogen separation; however, their practical application is limited primarily by the relatively low permeation rate and instability of doped barium cerate in H₂O and CO₂ containing gases. Here we report our findings on the development of a thin-film cermet membrane consisting of Ni and BaZr_0.1Ce_0.7Y_0.1Yb_0.1O_3−δ (BZCYYb), supported on a porous Ni–BZCYYb substrate. High fluxes of 1.12 and 0.49 ml min⁻¹ cm⁻² have been demonstrated at 900 °C and 700 °C, respectively, when hydrogen was used as the feed gas on one side and N₂ as the sweep gas on the other side. Most importantly, the high-performance membrane can be easily fabricated by a cost-effective particle-suspension coating/co-firing process, offering great promise for large scale hydrogen separation applications.     

A truncated antenna mutant of Chlamydomonas reinhardtii can produce more hydrogen than the parental strain

Photoproduction of H₂ gas was examined in the Chlamydomonas reinhardtii tla1 strain, CC-4169, containing a truncated light-harvesting antenna, along with its parental CC-425 strain. Although enhanced photosynthetic performance of truncated antenna algae has been demonstrated previously (Polle et al. Planta 2003; 217:49-59), improved H₂ photoproduction has yet to be reported. Preliminary experiments showed that sulfur-deprived, suspension cultures of the tla1 mutant could not establish anaerobiosis in a photobioreactor, and thus, could not photoproduce H₂ gas under conditions typical for the sulfur-deprived wild-type cells (Kosourov et al. Biotech Bioeng 2002; 78:731-40). However, they did produce H₂ gas when deprived of sulfur and phosphorus after immobilization within thin (∼300 μm) alginate films. These films were monitored for long-term H₂ photoproduction activity under light intensities ranging from 19 to 350 μE m⁻² s⁻¹ PAR. Both the tla1 mutant and the CC-425 parental strain produced H₂ gas for over 250 h under all light conditions tested. Relative to the parental strain, the CC-4169 mutant had lower maximum specific rates of H₂ production at low and medium light intensities (19 and 184 μE m⁻² s⁻¹), but it exhibited a 4-times higher maximum specific rate at 285 μE m⁻² s⁻¹ and an 8.5-times higher rate at 350 μE m⁻² s⁻¹ when immobilized at approximately the same cell density as the parental strain. As a result, the CC-4169 strain accumulated almost 4-times more H₂ than CC-425 at 285 μE m⁻² s⁻¹ and over 6-times more at 350 μE m⁻² s⁻¹ during 250-h experiments. These results are the first demonstration that truncating light-harvesting antennae in algal cells can increase the efficiency of H₂ photoproduction in mass culture at high light intensity.     

Preparation of a novel bimodal catalytic membrane reactor and its application to ammonia decomposition for COx-free hydrogen production

A novel bimodal catalytic membrane reactor (BCMR) consisting of a Ru/γ-Al₂O₃/α-Al₂O₃ bimodal catalytic support and a silica separation layer was proposed. The catalytic activity of the support was successfully improved due to enhanced Ru dispersion by the increased specific surface area for the γ-Al₂O₃/α-Al₂O₃ bimodal structure. The silica separation layer was prepared via a sol–gel process, showing a H₂ permeance of 2.6 × 10⁻⁷ mol Pa⁻¹ m⁻² s⁻¹, with H₂/NH₃ and H₂/N₂ permeance ratios of 120 and 180 at 500 °C. The BCMR was applied to NH₃ decomposition for CO_x-free hydrogen production. When the reaction was carried out with a NH₃ feed flow rate of 40 ml min⁻¹ at 450 °C and the reaction pressure was increased from 0.1 to 0.3 MPa, NH₃ conversion decreased from 50.8 to 35.5% without H₂ extraction mainly due to the increased H₂ inhibition effect. With H₂ extraction, however, NH₃ conversion increased from 68.8 to 74.4% due to the enhanced driving force for H₂ permeation through the membrane.