Increase In Hydrogen Yield Research Articles

The integrated process for hydrogen production from biomass: Study on the catalytic conversion behavior of pyrolytic vapor in gas–solid simultaneous gasification process

The gas–solid simultaneous conversion in the integrated process means the biomass pyrolysis products, pyrolytic vapor and biochar, can be comprehensively converted for hydrogen production from biomass in the presence of steam. In order to study the catalytic conversion behavior of biomass pyrolytic vapor in this gasification process, the influence of bio-char on the conversion of model pyrolytic vapor (MPV) was investigated in a fixed bed reactor. The results showed that biochar enhanced the conversion of MPV, resulting in the increase of carbon conversion and potential hydrogen yield from 68.46% to 86.88% and 42.16% to 82.76% respectively. The catalytic activities of different metal elements in biochar were found with the following sequence: K > Ca > Mg > Fe > Zn > Al. Meanwhile, the alkali and alkaline earth metals (AAEM) like K, Ca, and Mg were found to play the dominating roles in the conversion of MPV, and especially, the catalytic effect of K was the most obvious among the metals in bio-char. Finally, the effects of temperature (750–900 °C) and steam to MPV ratio (2–5 g/g) on the catalytic conversion of MPV in the presence of biochar were investigated. The carbon conversion and potential hydrogen yield of model pyrolytic vapor were improved by increasing temperature and steam to MPV ratio (S/MPV).

Catalytic activity of LiZr2(PO4)3 nasicon-type phosphates in ethanol conversion process in conventional and membrane reactors

In this paper synthesis and catalytic properties of new catalysts based on double lithium-zirconium phosphate (LiZr2(PO4)3) with monoclinic NASICON-type structure, doped by indium, niobium and molybdenum are discussed. The obtained samples with particle size of 50–300nm were characterized by X-ray diffraction, scanning electron microscopy and X-ray microanalysis. The synthesized samples exhibit catalytic activity in the dehydration and dehydrogenation reactions of ethanol conversion. The main products were acetaldehyde, diethyl ether, hydrogen, C2- and C4-hydrocarbons. Indium- and molibdenum-doped samples were characterized by high activity in dehydrogenation processes, while niobium-doped was more active in dehydration processes. The highest selectivity in diethyl ether formation was achieved for LiZr2(PO4)3 and Nb-doped samples (90 and 60% at 300°C). The highest hydrogen yield (up to 60%) was obtained with the use of In-doped catalyst. LiZr2(PO4)3 and Mo-doped samples are also noticeable for high C4-hydrocarbons formation, selectivity to which reaches 60% at 390°C. Use of a 100% hydrogen selective palladium-ruthenium alloy membrane increases hydrogen yield by 20%.

Methane steam reforming at low temperatures in a BaZr0.7Ce0.2Y0.1O2.9 proton conducting membrane reactor

The feasibility of Methane steam reforming (MSR) at low temperatures (450–650°C) was studied in a Ni-BZCY72/BZCY72/Cu proton conducting membrane reactor, which allowed for the simultaneous separation of hydrogen. The cell reactor was first tested under open-circuit conditions, i.e., with the reactor operating as a catalytic reformer. The impact of several parameters, such as steam to carbon feed ratio, the operating temperature and the total flow rate was evaluated. The Ni-BZCY72 electrode exhibited high catalytic activity with methane conversion close to thermodynamic equilibrium, which was attributed to the high nickel content (45wt.% after full reduction), as well as to the presence of ceria and zirconia in the support. Carbon dioxide was the main carbonaceous product with a molar ratio to carbon monoxide higher than 9, indicating that the Water Gas Shift reaction was predominant in the process. When hydrogen was electrochemically transported from the Ni-BZCY72 anode to the Cu cathode, a significant increase in methane conversion and hydrogen yield was observed. The methane conversion and hydrogen yield were improved by up to 50% in the temperature range of 550–650°C over their corresponding open-circuit values. The BZCY72 perovskite exhibited satisfying proton fluxes and transference numbers at all temperatures and applied cell voltages examined. Finally, the Ni-BZCY72 reactor cell showed excellent chemical stability and durability, as well as coke tolerance for 24h on stream.

Effect of pretreatment techniques on food waste solubilization and biogas production during thermophilic batch anaerobic digestion

The purpose of this study was to optimize the alkaline, ultrasonication, and thermal pretreatment in order to enhance the solubilization of food waste (FW) for the production of volatile fatty acids, hydrogen, and methane in thermophilic batch anaerobic digestion. Initially, the effect of pretreatment techniques in the acidogenic phase was studied, and the optimal combinations of different conditions were determined. It was found that each pretreatment technique affected food waste solubilization differently. Alkaline pretreatment increased hydrogen yield in the acidogenic sludge by four times over control. COD solubilization was increased by 47 % when FW pre-heated at 130 °C for 60 min. Ultrasonication at 20 kHz and 45 min reduced processing time to 38 h from the 60–80 h needed in normal operation. Response surface methodology (RSM) was used to optimize a combination of alkaline, ultrasonication, and thermal pretreatment. Optimized conditions were applied to methanogenic single-stage thermophilic AD process, and their impact on biogas production was monitored. Results showed that FW heated at 130 °C for 50 min geminates biogas production compared to control experiment. In conclusion, a short thermal pretreatment regime could significant affect biogas production in single-stage thermophilic AD.

Improvement of bioelectrochemical property and energy recovery by acylhomoserine lactones (AHLs) in microbial electrolysis cells (MECs)

Quorum sensing (QS) has been extensively studied as a cell–cell communication system, where small chemical signal molecules (acylhomoserine lactones, AHLs) can regulate the bacterial communications in bioelectrochemical systems via chemical signaling and electric signaling. In this study, electrochemical activity of bio-anode is substantially promoted by adding two kinds of AHLs with different chain length at the stage of community formation in microbial electrolysis cells (MECs). Hydrogen yield increase is observed by adding of two chain length AHLs, 3-oxo-hexanoyl-homoserine lactone (3OC6-HSL) and 3-oxo-dodecanoyl homoserine lactone (3OC12-HSL). A higher MEC current is acquired with addition of 3OC6-HSL than 3OC12-HSL at a fixed voltage of 0.8 V (vs. SHE). The highest yield is up to 3.8 ± 0.2 mol H2 mol−1 acetate at 10 μM 3OC6-HSL, which is increased 29% over control MECs. Evaluated on applied voltage, energy efficiency is increased to 171.6 ± 21.3% with short chain AHL, however, no significant improvement is performed on energy efficiency and coulombic efficiency with long-chain AHL. The study shows that bioelectrochemical characteristics of MECs varied on the chain length of AHL signal molecules and short-chain AHLs have a more positive effect on electron transfer and energy recovery in MECs.

Hydrogen production from high temperature steam catalytic gasification of bio-char

Hydrogen production from the catalytic steam gasification of bio-char derived from the pyrolysis of sugar cane bagasse has been investigated in relation to gasification temperature up to 1050 °C, steam flow rate from 6 to 25 ml h−1 and type of Nickel catalyst. The catalysts used were Ni-dolomite, Ni–MgO and Ni–Al2O3, all with 10% nickel loading. The hydrogen yield in the absence of a catalyst at a gasification temperature of 950 °C was 100.97 mmol g−1 of bagasse char. However, the presence of the Ni–MgO and Ni–Al2O3 catalysts produced significantly improved hydrogen yields of 178.75 and 187.25 mmol g−1 of bagasse char respectively at 950 °C. The hydrogen yield from the char with the Ni-dolomite only showed a modest increase in hydrogen yield. The influence of gasification temperature showed that the optimum temperature to obtain the highest hydrogen yield was 950 °C. Increase in gasification temperature from 750 to 950 °C significantly increased hydrogen yield from 45.30 to 187.25 mmol g−1 of bagasse char at 950 °C, but was followed by a decrease in yield at 1050 °C. The influence of steam flow rate showed that with the increase in steam flow rate from 6 to 15 ml h−1 hydrogen yield was increased from 187.25 to 208.41 mmol g−1 of bagasse char. Further increase in steam flow rate resulted in a decrease in hydrogen yield.

Chemical Gas Generators Based on Mechanically Alloyed Al·Mg Powder

ABSTRACTBecause of the high energy density, easy ignition, and good storability, mechanically alloyed Al·Mg powder has the potential to improve the performance characteristics of various energetic and gas-generating materials. Here, the use of this powder in combustible mixtures for generation of oxygen and hydrogen is explored. The mixtures for oxygen generation consisted of sodium chlorate, nanoscale cobalt oxide catalyst, and Al·Mg powder, while those for hydrogen generation included water, polyacrylamide as a gellant, and Al·Mg powder. To increase hydrogen yield, ammonia borane (NH3BH3) was also added to Al·Mg − water mixtures. Combustion experiments were conducted in an argon environment, using laser ignition. The thermal wave propagation over the oxygen-generating mixtures was studied using infrared video recording. It has been shown that mechanically alloyed Al·Mg material is a promising alternative to currently used iron because significantly smaller amounts of this additive are needed for a steady propagation of the combustion wave. The hydrogen generation experiments have shown that mixtures of mechanically alloyed Al·Mg powder with 10−60 wt% gelled water are combustible, with the front velocities exceeding the values obtained for the mixtures of water with nanoscale Al. Hydrogen yield was measured using mass-spectrometry. In the mixtures that included ammonia borane, D2O was used instead of H2O. Measurements of H2, D2, and HD concentrations in the product gas provided insight into the reaction mechanisms. The isotopic tests have shown that AB participates in two parallel processes − thermolysis and hydrolysis, thus increasing hydrogen yield.

Hydrogen production by Enterobacter cloacae isolated from sugar refinery sludge

Hydrogen is recognized as a promising fuel for the future because it is renewable, environmentally harmless and cost-effective. Systematic research on the process of hydrogen production is important for increasing hydrogen yield and identification of suitable strains of bacteria. We investigated the hydrogen production pathways of Enterobacter cloacae. The maximum hydrogen yield was ∼707 ml L−1, the H2 content of the gas-phase was in the range 30–35% and the overall rate of hydrogen production was ∼70.70 ml h−1 L−1. Ethyl alcohol and 2,3-butanediol were the major fermentative products, indicating the hydrogen-producing fermentation pathway of E. cloacae was the 2,3-butanediol pathway. Proteins and enzymes involved in the 2,3-butanediol pathway were generally detected by proteomics analysis, providing further evidence for the presence of the 2,3-butanediol pathway in E. cloacae. Both 13C labeling experiments and proteomics analysis indicated the Embden-Meyerhof-Parnas (EMP) pathway was the major pathway and the hexose monophosphate (HMP) pathway had a weaker role, or did not participate, in glucose catalysis in E. cloacae.

Key factors for biohydrogen production by dark fermentation

AbstractAmong biological ways of hydrogen production, the dark fermentation process gives important prospects. One of the key factors of bioreactor operation is the biogas extraction. Thus, this work gives a parametric optimization of the bioreactor as a function of the sweep gas nature and flow rate.The bacterial inoculum was activated sludge of wastewater treatment plant, which was thermally treated to inhibit the activity of hydrogenotrophic and non‐hydrogen producing micro‐organisms. The fermentation was performed in a semi‐batch bioreactor with a model substrate. Biogas was analyzed online by GC‐TCD and metabolites (volatile fatty acids and alcohols) were analyzed by GC‐FID. Kinetics parameters of hydrogen production were obtained by modelling.Increase the sweep gas (N2) flow rate in the bioreactor results in an increase of hydrogen yield and cumulative production of 35 %. In the purpose of recycling the CO2 produced by fermentation, the addition of CO2 to N2 as sweep gas gives a yield improvement from 2.10 molH2/molhexose with N2 alone, to 2.37 molH2/molhexose with a mixture of CO2:N2 (75:25). In order to reduce the amount of suspended matter in initial biomass, filtration tests show an equivalent hydrogen yield but with a higher lag time than with unfiltered biomass (30 h towards 4.4 h). The presence of hydrogen producing bacteria mainly stick with the solid part of sludge was highlighted.

Hydrogen generation from ammonia borane and water through combustion reactions with mechanically alloyed Al·Mg powder

It is known that ammonia borane (AB) forms combustible mixtures with gelled water and nanoscale aluminum powder. The reaction of nanoaluminum with water serves as a source of heat for ammonia borane thermolysis and hydrolysis, also releasing additional hydrogen from water. Nanoaluminum, however, has drawbacks such as high cost and reduced amount of free metallic aluminum. The present paper investigates a feasibility of using a mechanically alloyed Al·Mg powder instead of nanoaluminum in these mixtures. Initial experiments showed that mixtures of mechanically alloyed Al·Mg powder with gelled water are combustible. The velocities of combustion front propagation exceed those obtained for mixtures of nano-Al powder with gelled water. Then, combustion experiments were conducted with mixtures of AB, mechanically alloyed Al·Mg powder, and gelled heavy water (D2O). Heavy water was used to investigate the reaction mechanisms through mass-spectroscopy of released H2, HD, and D2 gases. The isotopic tests have shown that AB participates in two parallel processes – thermolysis and hydrolysis, thus increasing hydrogen yield.

Investigation on hydrogen production by catalytic steam reforming of maize stalk fast pyrolysis bio-oil

Hydrogen production via catalytic steam reforming of maize stalk fast pyrolysis bio-oil over the nickel/alumina supported catalysts promoted with cerium was studied using a laboratory scale fixed bed coupled with Fourier transform infrared spectroscopy/thermal conductivity detection analysis (FTIR/TCD). The effects of nickel loading, reaction temperature, water to carbon molar ratio (WCMR) and bio-oil weight hourly space velocity (WbHSV) on hydrogen production were investigated. The highest hydrogen yield of 71.4% was obtained over the 14.9%Ni-2.0%Ce/A12O3 catalyst under the reforming conditions of temperature = 900 °C, WCMR = 6 and WbHSV = 12 h−1. Increasing reaction temperature from 600 to 900 °C resulted in the significant increase of hydrogen yield. The hydrogen yield was significantly enhanced by increasing the WCMR from 1 to 3, whereas it increased slightly by further increasing WCMR. The hydrogen yield decreased with the increase of WbHSV. Meanwhile, the coke deposition percentage changed little with increasing WbHSV up to 12 h−1 and then it increased by 4.5% with the further increase of WbHSV from 12 to 24 h−1.

Tri-reforming of methane over Ni@SiO2 catalyst

A nickel-silica core@shell catalyst was applied for a methane tri-reforming process in a fixed-bed reactor. To determine the optimal condition of the tri-reforming process for production of syngas appropriate for methanol synthesis the effect of reaction temperature (550–750 °C), CH4:H2O molar ratio (1:0–3.0) and CH4:O2 molar ratio (1:0–0.5) in the feedstock was investigated. CH4 conversion rate and H2/CO ratio in the produced syngas were influenced by the feedstock composition. Increasing the amount of steam above the proportion of CH4:H2O 1:0.5 reduced the H2:CO molar ratio in produced syngas to ∼1.5. Increasing oxygen partial pressure improved methane conversion to 90% at 750 °C. At low ∼550 °C reaction temperature the tri-reforming process was not effective with low hydrogen production (H2 yield ∼20%) and very low <5% CO2 conversion. Increasing reaction temperature increased hydrogen yield to ∼85% at 750 °C. From all the tested reaction conditions the optimal for tri-reforming over the 11%Ni@SiO2 catalyst was: feed composition with molar ratio CH4:CO2:H2O:O2:He 1:0.5:0.5:0.1:0.4 at T = 750 °C. The results were explained in the context of characterisation of the catalysts used. The obtained results showed that the tri-reforming process can be applied for production of syngas with composition suitable for methanol synthesis.

A comparative study between operability of fluidized-bed and fixed-bed reactors to produce synthesis gas through tri-reforming

Fluidized-bed reactor has been suggested as a suitable candidate for syngas production due to its special advantages such as elimination of pressure drop problem and bad temperature profile distribution. In this study the fixed-bed and fluidized-bed tri-reformer configurations to produce syngas are modeled heterogeneously based on the conservation mass and energy balances. The obtained data are validated by a pilot plant. Then the operability and performance of considered configurations is compared at steady state condition. This comparison reveals 1.2% and 6% enhancement in the methane conversion and CO2 consumption in fluidized-bed tri-reformer reactor, respectively, which mainly result from the fact that fluidized-bed reactor presents more effective temperature management and smaller pressure drop in comparison with the fixed-bed reactor. An increase in methane conversion, hydrogen yield and CO2 consumption as well as a decline in hot spot temperature in the catalytic bed shows the superiority of fluidized-bed tri-reformer reactor for producing synthesis gas.

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 in a UASB reactor and bacterial quantification under non-sterile conditions

Biohydrogen production from crude glycerol by immobilized Klebsiella sp. TR17 was investigated in an up-flow anaerobic sludge blanket (UASB) reactor. The reactor was operated under non-sterile conditions at 40○C and initial pH 8.0 at different hydraulic retention times (HRTs) (2–12 h) and glycerol concentrations (10–30 g/L). Decreasing the HRT led to an increase in hydrogen production rate (HPR) and hydrogen yield (HY). The highest HPR of 242.15 mmol H2/L/d and HY of 44.27 mmol H2/g glycerol consumed were achieved at 4 h HRT and glycerol concentrations of 30 and 10 g/L, respectively. The main soluble metabolite was 1,3-propanediol, which implies that Klebsiella sp. was dominant among other microorganisms. Fluorescence in situ hybridization (FISH) revealed that the microbial community was dominated by Klebsiella sp. with 56.96, 59.45, and 63.47% of total DAPI binding cells, at glycerol concentrations of 10, 20, and 30 g/L, respectively.

Optimization of hydrogen production by filtration combustion of natural gas by water addition

The effect of adding steam during filtration combustion of natural gas–air mixtures was studied with the aim to evaluate the optimization of hydrogen production. Temperature, velocity, chemical products of combustion waves, and conversion from fuel to H2 and CO were evaluated in the range of equivalence ratio (φ) from stoichiometric (φ = 1.0) to φ = 3.0 and steam content in the mixture from 0% to 39%, at filtration velocities from 12 to 25 cm/s. Numerical simulation was carried out using GRI-MECH 3.0. Results suggest that H2 and CO concentrations, dominant for rich and ultrarich combustion, are products from partial oxidation and steam natural gas reforming processes. Experimental and numerical results show that hydrogen yield increase with an increase of steam content in the natural gas–air mixtures.

Enhanced ultraclean hydrogen production by multi-stage reformers

The performance of multi-stage circulating fast fluidized bed membrane reformers (CFFBMRs) for production of ultraclean hydrogen is investigated in comparison to a single circulating fast fluidized bed membrane reformer (CFFBMR). The two-stage reformer configuration gives significant increase in the methane conversion of 27.46% and ultraclean hydrogen yield of 29.61% compared to the single CFFBMR. The concept of the multi-stage short reformers policy is introduced. Impressively, substantial increase of ultraclean hydrogen yield of 83.91% is achieved.

Kinetic Study of Subcritical Steam Gasification of Coal Using Calcium-Based Carbon Dioxide Sorbent

The subcritical steam gasification of coal was performed with a calcium-based CO2 sorbent (Ca(OH)2) in a laboratory-scale batch reactor to examine the gasification kinetics with respect to the effects of partial pressure of steam and coal quality. The study was intended to support the hydrogen production by a reaction-integrated novel gasification (HyPr-RING) process in which coal is gasified with subcritical steam in a fluidized bed containing Ca(OH)2. Conducting subcritical steam gasification at 600–727 °C and 3–20 MPa produced zero emissions of CO2 because the rate of CO2 sorption by Ca(OH)2 was faster than that of CO2 generation by gasification. The gasification reaction mechanism was represented by a parallel first-order reaction model of the components of volatiles and char in coal. Hydrogen was mainly produced via tar from volatiles. The optimal partial pressure of steam preferred for hydrogen generation was 3 MPa, rather than 20 MPa. More volatiles in coal increased hydrogen yield in the gasificat...

NADPH fluorescence as an indicator of hydrogen production in the green algae Chlamydomonas reinhardtii

This study investigated cellular Nicotinamide Adenine Dinucleotide Phosphate (NADPH) fluorescence as a potential indicator of biohydrogen production in Chlamydomonas reinhardtii and a β-NADPH standard. NADPH fluorescence profiles of cultures grown in TAP-S (Tris-acetate phosphate minus sulphur) media, TAP (Tris-acetate phosphate) media and TAP + 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) were subsequently compared. Hydrogen production induced from sulphur depletion was found to correlate directly (r = 0.941) with NADPH over the ten day period. The addition of leachate was used to increase hydrogen yields, and subsequently increased the NADPH concentration by 50%–70%. A direct correlation was observed (r = 0.929) between NADPH and hydrogen when the leachate supplemented media was used. As NADPH is the terminal electron acceptor in the photosynthetic chain, results show that NADPH has a pivotal role in hydrogen production as a carrier molecule. Under sulphur depletion, cellular NADPH fluorescence can be used as an indicator of hydrogen production.

Improving hydrogen generation from kitchen wastes by microbial acetate tolerance response

The microbial acid tolerance response (ATR) was adopted to improve the hydrogen yield by relieving the organic acids inhibition. The results indicated that the hydrogen generation from kitchen wastes could be enhanced with the acetic acid stress of 6.0g/L, and it reached 68.3mL/gVS, which was 2.09 times of the control. The improvement was due to the increase of acetic acid tolerance with more ATR induction, since the increase of hydrogen yield was positive correlation with the concentration of acetic acid. H+-ATPase activity system played an important role in the ATR. It reached maximum of 132.4U/gTS at 6.0g/L stress, which was 45.2% higher than the control. Dehydrogenase enzyme in 6.0g/L group improved of 50.6% than the control, and it could indicate the microbial activity during hydrogen generation process.

CdO–CdS nanocomposites with enhanced photocatalytic activity for hydrogen generation from water

Nanocomposites of CdO–CdS have been prepared in ethylene glycol water mixture followed by heating at 300 °C. TEM and XRD studies confirmed the atomic scale mixing of CdO and CdS nanoparticles, leading to the formation of CdSO3 phase at the interfacial region between CdO and CdS. Photocatalytic studies for hydrogen generation from water show an enhanced activity for CdO–CdS composites compared to individual components namely CdO or CdS nanoparticles. Based on optical absorption, surface area measurements, steady state and time resolved fluorescence studies, it is established that, enhanced absorption in the visible region, higher surface area and increase in lifetime of the charge carriers are responsible for the observed increase in hydrogen yield from water when composite sample was used as the photocatalyst compared to individual components. The composite sample when combined with Pt as co-catalyst exhibit a large increase in the photocatalytic activity.