Hydrogen production from fossil and renewable sources using an oxygen transport membrane

Oxygen transport membranes (OTMs) made of mixed ion-electron conductors can be used to increase the production of hydrogen from fossil and renewable sources. This study describes two methods for producing hydrogen with La_0.7Sr_0.3Cu_0.2Fe_0.8O_3−δ (LSCF7328), an OTM material that is easily prepared, exhibits good mechanical properties, and is stable in severe gas conditions. In tests with thin-film (thickness ≈22 μm) LSCF7328 membranes, hydrogen was produced by flowing simulated product streams from CO₂ gasification of coal on one side of the OTM and steam on the other side. In this method, the so-called coal gas on the oxygen-permeate side drives the removal of oxygen from the other side of the OTM, where hydrogen and oxygen are produced by water splitting. With CO (99.5% purity) flowing on the oxygen-permeate side, the hydrogen production rate was measured to be ≈4.7 cm³/min-cm² at 900 °C, indicating that hydrogen can be produced at a significant rate by using product streams from coal gasification. This process also yields a CO₂-rich product stream that is ready for sequestration. In another test, a tubular LSCF7328 was found to increase the hydrogen production from ethanol reforming by supplying high-purity oxygen from air.     

Hydrogen production by redox of bimetal cation-modified iron oxide

Pure hydrogen can be stored and supplied directly to polymer electrolyte fuel cell by the redox of iron oxide: Fe₃O₄ + 4H₂ → 3Fe + 4H₂O and 4H₂O + 3Fe → Fe₃O₄ + 4H₂. Four bimetal-modified samples were prepared by impregnation. The hydrogen storage properties of the samples were investigated. The result shows that the Fe₂O₃–Mo–Al sample presented the most excellent catalytic activity and cyclic stability. H₂ forming temperature and H₂ forming rate could be surprisingly decreased and enhanced, respectively. The average H₂ forming temperature at the rate of 250 μmol min⁻¹·Fe-g⁻¹ for Fe₂O₃–Mo–Al in the first 4 cycles could be decreased from 469 °C before the addition of Mo–Al to 273 °C after the addition of Mo–Al. The reason for it may be that the Mo–Al additive in the sample can prevent from the sintering of the particles and accelerate the H₂O decomposition due to Mo taking part in the redox reaction. The average storage capacity of Fe₂O₃–Mo–Al was up to 4.68 wt%.     

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).     

Synthesis and electrochemistry of Li3MnO4: Mn in the +5 oxidation state

Computational and experimental work directed at exploring the electrochemical properties of tetrahedrally coordinated Mn in the +5 oxidation state is presented. Specific capacities of nearly 700 mAh g⁻¹ are predicted for the redox processes of Li_xMnO₄ complexes based on two two-phase reactions. One is topotactic extraction of Li from Li₃MnO₄ to form LiMnO₄ and the second is topotactic insertion of Li into Li₃MnO₄ to form Li₅MnO₄. In the experiments, it is found that the redox behavior of Li₃MnO₄ is complicated by disproportionation of Mn⁵⁺ in solution to form Mn⁴⁺ and Mn⁷⁺ and by other irreversible processes; although an initial capacity of about 275 mAh g⁻¹ in lithium cells was achieved. Strategies based on structural considerations to improve the electrochemical properties of MnO₄ⁿ⁻ complexes are given.     

Biohydrogen production from ricebran using Clostridium saccharoperbutylacetonicum N1-4

Treated ricebran hydrolysate was fermented anaerobically using Clostridium saccharoperbutylacetonicum N1-4 at an initial pH of 6 ± 0.2 and an operating temperature of 30 °C for production of hydrogen. The effects of different pretreatment methods on the liberation of sugar from 100 g of ricebran per litre of medium (distilled water) were investigated. In addition, the effects of the pretreatment method on ricebran hydrolysates of different initial ricebran concentrations on liberated sugar as well as the effects of the initial inoculum concentration, ricebran (substrate) concentration, and FeSO₄·7H₂O concentration on the yield as well as the productivity of hydrogen were investigated. The combination of enzymatic hydrolysis and a boiling pretreatment method produced the most fermentable sugar, 29.03 ± 0.0 g/L from 100 g of ricebran per litre of medium (distilled water), while the amount of sugar liberated by ricebran hydrolysates of different initial ricebran concentrations upon pretreatment monotonically increased with the initial ricebran concentration. The increment in substrate, inoculum, and FeSO₄·7H₂O concentrations had a significantly positive effect (p < 0.05) on both the yield and productivity of hydrogen. The maximum hydrogen gas yield (Y_P/S) and productivity of 3.37 mol-H₂ per mol-sugar consumed and 7.58 mmol/(L h), respectively, were obtained from ricebran hydrolysate with a 100 g/L ricebran concentration (equivalent to 28.59 ± 1.27 g sugar/L). In other experiments, 0.03 g/L FeSO₄·7H₂O and 1.5 g/L inoculum resulted in the best hydrogen gas yield and productivity from ricebran hydrolysates.     

Statistical optimization of dilute acid pretreatment of pinus needles to be used as substrate for biofuel production

In this study response surface methodology (RSM) was applied to study the effect of H₂SO₄ concentration, temperature, and time on the production of reducing sugars, total sugars, and total phenolic compounds from pine needles. Three variables with three levels showed that maximum release of total phenolic compounds (31.20 ± 0.002 mM) was observed at 1% H₂SO₄ concentration, 130°C temperature for 75 min of residence time. Under these conditions, the predicted value of total phenolic compounds was 31.27 mM, which indicated that the model is valid, having negligible variation in observed and predicted values. These results suggested that this substrate could be potentially used as substrate for bioethanol production.     

Biohydrogen production by Rhodobacter capsulatus Hup mutant in pilot solar tubular photobioreactor

In this study, a pilot solar tubular photobioreactor was successfully implemented for fed batch operation in outdoor conditions for photofermentative hydrogen production with Rhodobacter capsulatus (Hup⁻) mutant. The bacteria had a rapid growth with a specific growth rate of 0.052 h⁻¹ in the batch exponential phase and cell dry weight remained in the range of 1–1.5 g/L throughout the fed batch operation. The feeding strategy was to keep acetic acid concentration in the photobioreactor at the range of 20 mM by adjusting feed acetate concentration. The maximum molar productivity obtained was 0.40 mol H₂/(m³ h) and the yield obtained was 0.35 mol H₂ per mole of acetic acid fed. Evolved gas contained 95–99% hydrogen and the rest was carbon dioxide by volume.     

Comparative study on the production of biohydrogen from rice mill wastewater

This study presents the production of biohydrogen from rice mill wastewater. The acid hydrolysis and enzymatic hydrolysis operating conditions were optimized, for better reducing sugar production. The effect of pH and fermentation time on biohydrogen production from acid and enzymatic hydrolyzed rice mill wastewater was investigated, using Enterobacter aerogenes and Citrobacter ferundii. The enzymatic hydrolysis produced the maximum reducing sugar (15.8 g/L) compared to acid hydrolysis (14.2 g/L). The growth data obtained for E. aerogenes and C. ferundii, fitted well with the Logistic equation. The hydrogen yields of 1.74 mol H₂/mol reducing sugar, and 1.40 mol H₂/mol reducing sugar, were obtained from the hydrolyzate obtained from enzymatic and acid hydrolysis, respectively. The maximum hydrogen yield was obtained from E. aerogenes compared to C. ferundii, and the optimum pH for better hydrogen production was found to be in the range from 6.5 to 7.0. The chemical oxygen demand (COD) reduction obtained was around 71.8% after 60 h of fermentation.     

Influence of impregnation with lactic acid on sugar yields from steam pretreatment of sugarcane bagasse and spruce, for bioethanol production

Lignocellulosic biomass can be utilized to produce ethanol, a promising alternative energy source produced through fermentation of sugars. However, in order to achieve high sugar and ethanol yields, the lignocellulosic material must be pretreated before the enzymatic hydrolysis and fermentation. Dilute acid pretreatment, using SO₂, is one of the most promising methods of pretreatment for softwood and agricultural residues. However, handling the high acidity of the slurry obtained from pretreatment and difficulty in recycling/degradation of the impregnating agent are some of the drawbacks of the dilute acid processes. In the present study the influence of utilization of a weak organic acid (lactic acid), as impregnating agent, on the sugar yield from pretreatment, with and without addition of SO₂, was investigated. The efficiency of pretreatment was assessed by enzymatic hydrolysis of the slurry obtained by pretreatment, using sugarcane bagasse and spruce, stored for one and two months in the presence of lactic acid separately, as feedstocks. Pretreatment of bagasse after storage with 0.5% lactic acid resulted in an overall glucose yield, i.e. after enzymatic hydrolysis, of 79% of theoretical based on the amount available in the raw material. This was as good as pretreatment using SO₂ as impregnating agent. However, storage of spruce with lactic acid before pretreatment, with and without addition of SO₂, was not efficient and resulted in lower sugar yields than pretreatment using SO₂ only.     

Biohydrogen production by Anabaena sp. PCC 7120 wild-type and mutants under different conditions: Light, nickel, propane, carbon dioxide and nitrogen

Increasing awareness of environmental problems caused by the current use of fossil fuel-based energy, has led to the search for alternatives. Hydrogen is a good alternative and the cyanobacterium Anabaena sp. PCC 7120 is naturally able to produce molecular hydrogen, photosynthetically from water and light. However, this H₂ is rapidly consumed by the uptake hydrogenase.This study evaluated the hydrogen production of Anabaena sp. PCC 7120 wild-type and mutants: hupL⁻ (deficient in the uptake hydrogenase), hoxH⁻ (deficient in the bidirectional hydrogenase) and hupL⁻/hoxH⁻ (deficient in both hydrogenases) on several experimental conditions, such as gas atmosphere (argon and propane with or without N₂ and/or CO₂ addition), light intensity (54 and 152 ??Em⁻²s⁻¹), light regime (continuous and light/dark cycles 16 h/8 h) and nickel concentrations in the culture medium.In every assay, the hupL⁻ and hupL⁻/hoxH⁻ mutants stood out over wild-type cells and the hoxH⁻ mutant. Nevertheless, the hupL⁻ mutant showed the best hydrogen production except in an argon atmosphere under 16 h light/8 h dark cycles at 54 ??Em⁻²s⁻¹ in the light period, with 1 ??M of NiCl₂ supplementation in the culture medium, and under a propane atmosphere.In all strains, higher light intensity leads to higher hydrogen production and if there is a daily 1% of CO₂ addition in the gas atmosphere, hydrogen production could increase 5.8 times, related to the great increase in heterocysts differentiation (5 times more, approximately), whereas nickel supplementation in the culture medium was not shown to increase hydrogen production. The daily incorporation of 1% of CO₂ plus 1% of N₂ did not affect positively hydrogen production rate.     

Hydrogen cycle with sodium borohydride

In this paper, we review production of NaBH₄ as hydrogen storage material. Linking this with other processes, we create a system to recycle hydrogen. Difficulties and advantages of NaBH₄ synthesis by natural available boron source colemanite and borax minerals were discussed. We show that basic chemicals suffice for NaBH₄ production in a procedure designed to work below 275 °C. This procedure may be used to compensate for the loss of materials during the recycle. In this procedure, hydrogen including substances have been used to remove oxygen and bond remaining hydrogen to the by-product NaBO₂ of dehydrogenation reaction. The wet and dry applications of producing NaBH₄ have been also discussed. Moreover, a shorter procedure can be proposed to directly obtain NaBH₄ from borax mineral. Among these processes, dehydrogenation is critical but it requires plenty of water. Hence, new types of catalyst are important to reduce the amount of water required during dehydrogenation.     

The effect of different washing processes on fuel properties in camelina methyl ester

The present study was conducted to examine the effect of different washing processes on fuel properties in biodiesel produced from camelina oil through transesterification. For this purpose, dry washing with Magnesol, washing with Na₂SO₄, washing with water, and unwashing methods were compared. In dry washing with Magnesol, density, KV, CP, CFPP, PP, FP, and heating value (HV) were found to be 0.887 g/cm³, 5.090 mm²/s, 1°C, –4°C, –7°C, 165°C, and 41 MJ/kg, respectively. The effect of flash point (FP), density and kinematic viscosity (KV) on heating value (HV) was investigated and the regression among these values was determined. The r² was 0.953 and corrected r² was found to be 0.810. The effect of cloud point (CP), CFPP, and kinematic viscosity (KV) on PP (pour point) values was examined and the regression among these values was determined. The r² was found to be 0.999 and corrected r² was found to be 0.995.     

Hydrogen production by flue gas through sulfur–iodine thermochemical process: Economic and energy evaluation

The use of low quality fossil fuel with high sulfur content is becoming more frequent and probably will play a very important role in the future, due to the depletion of reserves.     

Effect of H2O2 on Pt electrode dissolution in H2SO4 solution based on electrochemical quartz crystal microbalance study

The effect of H₂O₂ on the Pt dissolution in 0.5 mol dm⁻³ H₂SO₄ was investigated using an electrochemical quartz crystal microbalance (EQCM). For the potential cycling at 50 mV s⁻¹, the Pt weight irreversibly decreases in a N₂ atmosphere with H₂O₂, while only a negligible Pt weight-loss is observed in the N₂ and O₂ atmospheres without H₂O₂. The EQCM data measured by the potential step showed that the Pt dissolution in the presence of H₂O₂ depends on the electrode potential and the H₂O₂ concentration. For the stationary electrolysis, the Pt dissolution occurs at 0.61–1.06 and 1.06–1.36 V vs. RHE. It should be noted that the Pt dissolution phenomenon in the presence of H₂O₂ is also affected by the potential scanning time. Based on these results, H₂O₂ is considered not only to contribute to the formation of Pt-oxide causing the cathodic Pt dissolution, but also to participate in the anodic Pt dissolution and the chemical Pt dissolution.     

Hydrogen evolution from pure water over a new advanced photocatalyst Sm2GaTaO7

In this work, a new oxide Sm₂GaTaO₇ with pyrochlore-related structure was successfully synthesized by conventional solid state reaction. RuO₂ nanoparticles were loaded as cocatalyst onto Sm₂GaTaO₇ surface. X-ray powder diffraction (XRD) and Rietveld refinement characterization results revealed that Sm₂GaTaO₇ crystallized into a monoclinic system with space group C2/c. The band gap (E_g) was calculated by Kubelka–Munk formula, obtaining a value in the order of 4.1 eV. The Sm₂GaTaO₇ oxide showed a particle size around 2–3 μm and a specific surface area of 0.5 m²/g. The photocatalytic results revealed that Sm₂GaTaO₇ was able to produce hydrogen from pure water. The hydrogen evolution activity was enhanced by using 0.2 wt.% of RuO₂ amount, which exceeded 2.4 times compared with the base photocatalyst, Sm₂GaTaO₇.     

Hydrogen production using Pt-loaded TiO2 photocatalysts

A series of synthesised TiO₂-based and commercial photocatalysts were modified by Pt photodeposition and a study made of their photocatalytic activity in hydrogen production. The modified commercial photocatalysts were Evonik P25, Kronos vlp7000 and Hombikat UV-100, and the other modified photocatalysts were synthesised by our group using sol–gel and sol–gel hydrothermal processes (SG400, SG750 and HT). Pt weight percentages used in the study were 0.5, 1.0 and 2.1 wt.% (Pt/TiO₂). The photocatalysts were extensively characterised by X-ray diffraction (XRD), UV–vis diffuse reflectance, Brunauer–Emmett–Teller (BET) surface area measurement, transmission electron microscopy (TEM), scanning electron microscopy (SEM–EDX), Fourier transform infrared spectroscopy (FTIR) and laser light dispersion. Methanol (25% vol.) was used as sacrificial agent over the 8 h of the hydrogen production tests and measurements were taken of the final concentrations of formaldehyde and formic acid as well as initial and final TOC. Photoactivity of all photocatalysts increased in the presence of Pt. The most efficient of the synthesised photocatalysts was SG750 and of the commercial photocatalysts P25. Maximum production of SG750 was 1846 μmol h⁻¹ at 1.0 wt.% Pt and its production per surface unit was notably higher than that of P25.     

Influence of Cu concentration on the biohydrogen production of continuous stirred tank reactor

In this paper, the effect of hydraulic retention time (HRT, 16 h–4 h) on fermentative hydrogen production by mixed cultures was firstly investigated in a sucrose-fed anaerobic continuous stirred tank reactor (CSTR) at 35 °C and initial pH 8.79. After stable operations at HRT of 16–6 h, the bioreactor became unstable when the HRT was lowered to 4 h. The maximum hydrogen yield reached 3.28 mol H₂/mol-Sucrose at HRT 4 h. Supplementation of Cu²⁺ at HRT 4 h improved the operation stability through enhancement of substrate degradation efficiency. The effect of Cu²⁺ concentration ranging from 1.28 to 102.4 mg/L on fermentative hydrogen production was studied. The results showed that Cu²⁺ was able to enhance the hydrogen production yield with increasing Cu²⁺ concentration from 1.28 to 6.4 mg/L. The maximum hydrogen yield of 3.31 mol H₂/mol-Sucrose and the maximum hydrogen production rate of 14.44 L H₂/Day/L-Reactor were obtained at 6.4 mg/L Cu²⁺ and HRT 4 h Cu²⁺ at much higher concentration could inhibit the hydrogen production, but it could increase substrate degradation efficiency (12.8 and 25.6 mg/L Cu²⁺). The concentration of Cu²⁺ had effect on the distribution of soluble metabolite.     

Hydrogen production performance by Enterobacter cloacae KBH3 isolated from termite guts

Two out of six bacterial isolates obtained from the guts of Globitermes sp. termites were identified as hydrogen-producing bacteria. One isolate, Enterobacter cloacae KBH3, was characterised using the BIOLOG identification system and 16S rRNA gene analysis. In a batch fermentation study to evaluate its growth in defined medium, E. cloacae KBH3 produced 154 ml H₂ per litre medium with approximately 50% hydrogen content. The carbon utilisation results suggest that E. cloacae KBH3 have the potential to be a good hydrogen producer. This strain is also able to produce hydrogen within a wide range of temperatures (28–40 °C) and pH (4.5–8). In several fermentation runs, the pH of the culture dropped from 6.5 to 5.36 within the first 3 h, which was mostly due to the biosynthesis of formate. An increase of cumulative hydrogen production was recorded as well as a decrease in the concentration of formate, indicating the importance of the formate pathway for hydrogen production. The highest rate of hydrogen production of 180.74 ml H₂/l/h was achieved when lactate and acetate were at their highest concentrations. Most of the hydrogen gas was produced during the exponential growth phase, and the biogas continued to be produced during the stationary phase. The specific growth rate was calculated to be 0.224 per hour while the hydrogen yield was 1.8 mol of hydrogen per mol of glucose. At the end of the batch study, the highest cumulative hydrogen production was 2404 ml H₂ per litre of fermentation medium.     

Hydrogen production by catalytic processing of renewable methane-rich gases

Biomass-derived methane-rich gases such as landfill gas (LFG), biogas and digester gas are promising renewable resources for near-future production of hydrogen. The technical and economical feasibility of hydrogen production via catalytic reforming of LFG and other methane-rich gases is evaluated in this paper. The thermodynamic equilibrium calculations and experimental measurements of reformation of methane-rich CH₄–CO₂ mixtures over Ni-based catalyst were conducted. The problems associated with the catalyst deactivation due to carbon lay down and effects of steam and oxygen on the process sustainability were explored. Two technological approaches distinguished by the mode of heat input to the endothermic process (i.e., external vs autothermal) were modeled using AspenPlus^TM${\mathrm{AspenPlus}}^{\mathrm{TM}}$ chemical process simulator and validated experimentally. A 5 kW_th pilot unit for hydrogen production from LFG-mimicking CH₄–CO₂ mixture was fabricated and operated. A preliminary techno-economic assessment indicates that the liquid hydrogen production costs are in the range of $3.00–$7.00 per kilogram depending upon the plant capacity, the process heat input option and whether or not carbon sequestration is included in the process.