Increased H2 Production Research Articles

On the energy efficiency of hydrogen production processes via steam reforming using membrane reactors

The novel paradigm of distributed energy production foresees the production of hydrogen from methane and biomasses in small plants, which may take advantage from membrane-based processes. By means of a modeling approach, this paper compares the energy efficiency of two membrane-based processes to produce H2 from methane steam reforming. The two-step process (TS) envisages a high temperature classical reactor and a following WGS stage in a membrane reactor, while the alternative process uses a simple packed-bed membrane reactor (MR). Both processes show a general increase of H2 production and energy efficiency with the pressure and a maximum energy efficiency for S/C of 4, while the increase of the space velocity reduces the performances of the MR. The results show that the TS process performs better than the studied MR and that the maximum energy efficiency of both processes is between 30 and 40%. A comparison with the literature shows that the TS process may achieve similar performances respect to an intensified MR.

Microbiota stability in healthy individuals after single-dose lactulose challenge-A randomized controlled study.

Background and aimsLactulose is a common food ingredient and widely used as a treatment for constipation or hepatic encephalopathy and a substrate for hydrogen breath tests. Lactulose is fermented by the colon microbiota resulting in the production of hydrogen (H2). H2 is a substrate for enteropathogens including Salmonella Typhimurium (S. Typhimurium) and increased H2 production upon lactulose ingestion might favor the growth of H2-consuming enteropathogens. We aimed to analyze effects of single-dose lactulose ingestion on the growth of intrinsic Escherichia coli (E. coli), which can be efficiently quantified by plating and which share most metabolic requirements with S. Typhimurium.Methods32 healthy volunteers (18 females, 14 males) were recruited. Participants were randomized for single-dose ingestion of 50 g lactulose or 50 g sucrose (controls). After ingestion, H2 in expiratory air and symptoms were recorded. Stool samples were acquired at days -1, 1 and 14. We analyzed 16S microbiota composition and abundance and characteristics of E. coli isolates.ResultsLactulose ingestion resulted in diarrhea in 14/17 individuals. In 14/17 individuals, H2-levels in expiratory air increased by ≥20 ppm within 3 hours after lactulose challenge. H2-levels correlated with the number of defecations within 6 hours. E. coli was detectable in feces of all subjects (2 x 102–109 CFU/g). However, the number of E. coli colony forming units (CFU) on selective media did not differ between any time point before or after challenge with sucrose or lactulose. The microbiota composition also remained stable upon lactulose exposure.ConclusionIngestion of a single dose of 50 g lactulose does not significantly alter E. coli density in stool samples of healthy volunteers. 50 g lactulose therefore seems unlikely to sufficiently alter growth conditions in the intestine for a significant predisposition to infection with H2-consuming enteropathogens such as S. Typhimurium (www.clinicaltrials.gov NCT02397512).

PH and a mixed carbon-substrate spectrum influence FocA- and FocB-dependent, formate-driven H2 production in Escherichia coli.

Escherichia coli encodes two formate channels, FocA and FocB, that either export formate or import it for further disproportionation by the formate hydrogenlyase (FHL) complex to H2 and CO2. We show that FocA/B appear to change their substrate-translocation direction depending on pH and electron donor. When cells were grown on glucose and glycerol at pH 7.5, formate accumulated in focB or focA-focB mutants when glucose or formate was used as electron donor because H2 production increased ∼2- and ∼1.5-fold, respectively. Moreover, addition of external formate to the growth medium increased H2 production in a focA-focB mutant. This indicates that in the wild type, formate is preferentially exported at pH 7.5 and that another FocA/B-independent uptake system exists. At pH 6.5 and 5.5, the formate channel mutants showed reduced H2 production, suggesting that formate is usually imported by them to produce H2 at acidic pH. Addition of formate to the growth medium increased H2 production at these pHs. Notably, glycerol failed to act as an effective electron donor for formate production. Taken together, our results suggest that regulation of formate translocation direction by FocA/FocB channels is important for maintaining internal pH and proton motive force by modulating H2 production.

Boosting Hydrogen Production by Anodic Oxidation of Primary Amines over a NiSe Nanorod Electrode.

For electrocatalytic water splitting, the sluggish anodic oxygen evolution reaction (OER) restricts the cathodic hydrogen evolution reaction (HER). Therefore, developing an alternative anodic reaction with accelerating kinetics to produce value-added chemicals, especially coupled with HER, is of great importance. Now, a thermodynamically more favorable primary amine (-CH2 -NH2 ) electrooxidation catalyzed by NiSe nanorod arrays in water is reported to replace OER for enhancing HER. The increased H2 production can be obtained at cathode; meanwhile, a variety of aromatic and aliphatic primary amines are selectively electrooxidized to nitriles with good yields at the anode. Mechanistic investigations suggest that NiII /NiIII may serve as the redox active species for the primary amines transformation. Hydrophobic nitrile products can readily escape from aqueous electrolyte/electrode interface, avoiding the deactivation of the catalyst and thus contributing to continuous gram-scale synthesis.

Boosting Hydrogen Production by Anodic Oxidation of Primary Amines over a NiSe Nanorod Electrode

AbstractFor electrocatalytic water splitting, the sluggish anodic oxygen evolution reaction (OER) restricts the cathodic hydrogen evolution reaction (HER). Therefore, developing an alternative anodic reaction with accelerating kinetics to produce value‐added chemicals, especially coupled with HER, is of great importance. Now, a thermodynamically more favorable primary amine (−CH2−NH2) electrooxidation catalyzed by NiSe nanorod arrays in water is reported to replace OER for enhancing HER. The increased H2 production can be obtained at cathode; meanwhile, a variety of aromatic and aliphatic primary amines are selectively electrooxidized to nitriles with good yields at the anode. Mechanistic investigations suggest that NiII/NiIII may serve as the redox active species for the primary amines transformation. Hydrophobic nitrile products can readily escape from aqueous electrolyte/electrode interface, avoiding the deactivation of the catalyst and thus contributing to continuous gram‐scale synthesis.

Alkaline zirconates as effective materials for hydrogen production through consecutive carbon dioxide capture and conversion in methane dry reforming

In this work, H2 production was evaluated using different carbonation conditions and two alkaline zirconates. For this purpose, Li2ZrO3 and Na2ZrO3 were synthesized, characterized and tested on a consecutive process composed of initial CO2 capture, followed by methane dry reforming (MDR). Thermogravimetric results showed that under the four gas mixtures tested (diluted and saturated CO2, CO and CO-O2), both ceramics are able to chemisorb CO2, with Na2ZrO3 having the highest capture with saturated CO2. In catalytic tests, ceramics carbonated with saturated CO2 or CO-O2 gas flows were able to act as sorbents and catalysts, producing H2 at T > 750 °C through the partial oxidation of methane. This reaction was produced because CO2 desorption did not occur, thus avoiding the MDR process. On the other hand, carbonated ceramics under a CO-O2 gas mixture presented an outstanding catalytic performance. Between 450 and 750 °C, H2 was formed through the MDR process promoted by CO2 desorption from both ceramics. This result is in line with CO2 desorption results, where a weaker CO2–solid interaction was observed in comparison with saturated CO2. Afterward, both ceramics presented a similar catalytic behavior, good regeneration and cyclability after the double process proposed (CO2 capture-MDR reaction). Lithium zirconate also presented high thermal stability during cycle tests; meanwhile, sodium zirconate showed an important H2 production increase as a function of cycles. Finally, both materials are feasible options for producing a clean energy source in a moderate temperature range through the catalytic conversion of two greenhouse gases (CO2 and CH4).

Highly Efficient Visible-Light-Induced Photocatalytic Production of Hydrogen for Magnetically Retrievable Fe3O4@SiO2@MoS2/g-C3N4 Hierarchical Microspheres

A new multifunctional compound containing hierarchical microspheres of Fe3O4@SiO2@MoS2/g-C3N4 (FSMG) was created. The microspheres comprised Fe3O4@SiO2 as a magnetic component and a heterostructure of MoS2/g-C3N4 as an outer shell, and both elements are compounded by an effective and applicable method and can be used in photocatalytic applications. Highly efficient separation of the photodriven pairs of electron/hole pairs (e–/h+) was exhibited with the as-synthesized FSMG structures under visible light. The photocatalytic activities of Fe3O4@SiO2@MoS2, g-C3N4, and FSMG are assessed by surveying the hydrogen (H2) production and rhodamine B (RhB) photodegradation from water. These contrasting studies show that microspheres of FSMG show promising visible-light-induced photocatalytic activity and exhibit 1.99-fold and 3.38-fold increased activity over that of Fe3O4@SiO2@MoS2 and g-C3N4 mechanisms, respectively, in RhB degradation and a 4.13-fold and 11.09-fold increase in H2 production from water, respective...

Biomass gasification integrated with CO2 capture processes for high-purity hydrogen production: Process performance and energy analysis

The performance of an integrated biomass gasification and CO2 capture process to produce H2-rich gas satisfying a PEMFC specification is investigated. Wood residue and CaO are used as a biomass feedstock and a CO2 sorbent, respectively. Modeling of such an integrated process is performed by using ASPEN Plus. The effect of change in major parameters, i.e., gasifying temperature, carbonation temperature and CaO/C ratio, on the product gas composition is investigated. The H2 concentration of the product gas leaving the gasifier is found to increase as the gasifying temperature increases and reaches its maximum value when the gasifying temperature is higher than 700 °C. For the integrated process, the H2 concentration significantly decreases as the carbonation temperature increases to higher than 500 °C. Moreover, the result indicates that the CaO/C ratio should be maintained at a value higher than 3.17 to ensure that the generated CO2 is completely captured. The energetic and exergetic performances, as well as the environmental impact of the integrated process at various amounts of recycled CO2, are also investigated. The energy conversion efficiency and the exergy efficiency based on H2 production increase as the CO2/C ratio increases, whereas the CO2 emission shows the opposite trend. The maximum exergy efficiency of 69.65%, based on the hydrogen production and the heat generation, is achieved at CO2/C and CaO/C ratios of 0.6 and 4.48, respectively. At this condition, a specific emission of CO2 of 4.4 g CO2 - eqMJ- 1 and an energy conversion efficiency of 88.09% are achieved.

Single pot bioconversion of prairie cordgrass into biohydrogen by thermophiles

The aim of the present work was to use a thermophilic consortium for H2 production using lignocellulosic biomass in a single pot. The thermophilic consortium, growing at 60 °C utilized both glucose and xylose, making it an ideal source of microbes capable of utilizing and fermenting both hexose and pentose sugars. The optimization of pH, temperature, and substrate concentration increased the H2 production from 1.07 mmol H2/g of prairie cordgrass (PCG) to 2.2 mmol H2/g PCG by using the thermophilic consortium. A sequential cultivation of a thermostable lignocellulolytic enzyme producing strain Geobacillus sp. strain WSUCF1 (aerobic) with the thermophilic consortium (anaerobic) further increased H2 production with PCG 3-fold (3.74 mmol H2/g PCG). A single pot sequential culturing of aerobic and anaerobic microbes can be sustainable and advantageous for industrial scale production of biofuels.

Hydrogen and syngas production from catalytic steam gasification of char derived from ion-exchangeable Na- and Ca-loaded coal

Catalytic steam gasification of char derived from low-rank coal possesses substantial potential as a source of hydrogen energy and syngas feedstocks, and its performances are largely associated with the employed catalysts. Therein, ion-exchangeable Na or Ca species are always regarded as excellent in-situ catalysts in low-rank coal. In this paper, gasification of Na-Char, Ca-Char and a Na/Ca-Char mixture with different partial pressures of steam was performed within a temperature range of 700–900 °C using a micro fluidized bed reaction analyzer. The results indicate that Na and Ca species could accelerate the gas release rate during gasification and even significantly increase H2 production, in sharp contrast to non-catalytic gasification. Variations in the product gases during Na-Char and Ca-Char gasification were completely different, which associated with the different deactivation pathways and catalytic reaction mechanisms of Na and Ca catalysts. With an increasing gasification temperature, the decreasing trend of H2 production for Na-Char gasification was mainly due to the loss of Na during gasification. Conversely, the enhancement of Ca activity promoted the H2 production. The H2/CO ratio of Ca-Char gasification at 700 °C approximately ranged from 1.0 to 2.0 as a function of the partial pressure of steam, which suggested catalytic gasification can be suitable for hydrogen-rich production and subsequent synthesis reactions. In addition, gasification of Na/Ca-Char mixture produced a higher hydrogen content in the product gases than that of Na-Char or Ca-Char gasification alone, particularly for the 30%Na/70%Ca-Char mixture. It implies that the high H2 production of 70%Ca30%Na-Char mixture was attributed to the cooperative effects of the Na and Ca species on the catalytic activity. This study provides comprehensive information regarding the effects of ion-exchangeable Na, Ca and a Na/Ca mixture on the hydrogen production and syngas composition during steam gasification, which provides new insight into the utilization of low-rank coal.

PERLAKUAN ETHYL METHANE SULFONATE (EMS) PADA ENTEROBACTER AEROGENES AY-2 DARI LIMBAH METAN FERMENTASI UNTUK PENINGKATAN PRODUKSI GAS HIDROGEN

Enterobacter aerogenes AY-2 mutant is known for hydrogen gas producer which ws obtained from the sludge of methane fermentation and the yield is 1.5 fold higher than wildtype. Hydrogen gas production can be gain via NADH oxidation in anaerobic metabolic pathway by blocking organic acid production. Metabolic pathway can be changed by mutagenesis. Enterobacter aerogenes AY-2 mutated with ethyl methane sulfonate in logarithmic phase with consentration 10, 11, 12,13, 14 and 15 μl/ml cell suspention during 120 minute. Mutation that result lowest survival ratio (0,01%) was 14 μl EMS/ml cell suspention is repeated with variation incubation time, 30, 60, 90 and 120 minute. 166 double mutant colony has been collected and choosen randomly. The choosen 43 colony was fermented in glycerol complex medium for determining ten double mutant with the highest H2 production. Double mutant AD-H43 is a highest H2 producer that increase 20% H2 production from AY-2 and has a decrease lactid acid production, 31% less from AY-2. Increasing H2 production in double mutant AD-H43 is caused by lactate dehydrogenase defficient.Keywords: Enterobacter aerogenes AY-2, ethyl methane sulfonate (EMS), H2 and methanesludge

PERLAKUAN ETHYL METHANE SULFONATE (EMS) PADA ENTEROBACTER AEROGENES AY-2 DARI LIMBAH METAN FERMENTASI UNTUK PENINGKATAN PRODUKSI GAS HIDROGEN

Enterobacter aerogenes AY-2 mutant is known for hydrogen gas producer which ws obtained from the sludge of methane fermentation and the yield is 1.5 fold higher than wildtype. Hydrogen gas production can be gain via NADH oxidation in anaerobic metabolic pathway by blocking organic acid production. Metabolic pathway can be changed by mutagenesis. Enterobacter aerogenes AY-2 mutated with ethyl methane sulfonate in logarithmic phase with consentration 10, 11, 12, 13, 14 and 15 μl/ml cell suspention during 120 minute. Mutation that result lowest survival ratio (0,01%) was 14 μl EMS/ml cell suspention is repeated with variation incubation time, 30, 60, 90 and 120 minute. 166 double mutant colony has been collected and choosen randomly. The choosen 43 colony was fermented in glycerol complex medium for determining ten double mutant with the highest H2 production. Double mutant AD-H43 is a highest H2 producer that increase 20% H2 production from AY-2 and has a decrease lactid acid production, 31% less from AY-2. Increasing H2 production in double mutant AD-H43 is caused by lactate dehydrogenase deffi cient.Keywords: Enterobacter aerogenes AY-2, ethyl methane sulfonate (EMS), H2 and methane sludge

Effects of current density, bicarbonate and humic acid on electrochemical induced calcium phosphate precipitation

Phosphorus (P) removal and recovery from sewage as calcium phosphate (CaP) by chemical precipitation is a widely used method. To avoid the addition of chemicals to increase the pH of the bulk solution and the need for a further separation step in conventional chemical precipitation process, we developed an electrochemical method, which can locally increase the pH near a Ti cathode. The separation of product and liquid then happens simultaneously by accumulating CaP at the electrode surface. The current density plays a crucial role in this system. A current density of 19 A/m2 results in the formation of crystalline CaP rather than amorphous CaP, but it does not enhance the removal of P in 24 h. Moreover, the current efficiency decreases with increasing current density. Furthermore, the increased H2 production at high current density may push the precipitated CaP back to the bulk solution, resulting in its dissolution. In the presence of bicarbonate (1–5 mM) or humic acid (1–20 mg/L), the removal of P was higher. This is probably due to the inhibited CaP precipitation in the bulk solution which in turn leaves more Ca and P ions available for the local precipitation on the cathode. However, bicarbonate at high concentration (10 mM) dropped P removal from 52 to 25%. This is caused by competition of carbonate and phosphate with the free Ca2+ ions and also by buffering the producted hydroxide ions at the cathode. The study shows that P can be removed as CaP by electrochemical precipitation at low current densities at common concentrations of bicarbonate and humic acid.

Radiolytic Dissolution of Calcite under Gamma and Helium Ion Irradiation

Samples of calcite have been irradiated using both the 60.7 MeV helium ion beam of the ARRONAX (Nantes, France) cyclotron and 661.7 keV gamma radiations. The irradiation of calcite pellets results mainly in radiolytically generated gas (H2, CO2). The presence of superficial water during the calcite irradiation in a humid atmosphere is a key factor for the production of radiolysis gases. Besides, the irradiation of calcite–water biphasic media was performed. The gas released after these irradiations is quantified. No significant amount of CO2 has been detected, whereas carbonate ions act as OH• scavengers, thus inducing an increase of H2 production. The amount of hydrogen peroxide created confirms this scavenging mechanism. Finally, ionic chromatography experiments with irradiated solutions allow us to quantify the organic anions (formate HCOO–, acetate CH3COO–, propionate CH3-CH2COO–, and oxalate C2O42–) formed by calcite and/or carbonate ion radiolysis and study the variation of calcium carbonate solubil...

Increasing Hydrogen Production Efficiency of N2-Fixing Cyanobacterium Anabaena siamensis TISTR 8012 by Cell Immobilization

H2 produced by cyanobacteria is one of the interesting alternative energy carriers for the future. The filamentous N2-fixing cyanobacterium Anabaena siamensis TISTR 8012 is a potential microorganism for H2 production. It can produce H2 via both photosynthesis and nitrogen fixation processes. This study aimed to increase the efficiency of H2 production by immobilization of A. siamensis cells. The result showed that H2 production rate by A. siamensis grown in BG110 medium was higher than that in BG11 and Allen-Arnon media due to an increase of the heterocyst cells. The sulfur deprivation during adaptation period for 24 hours increased its H2 production rate. The optimal conditions for H2 production by immobilized cells were immobilization with alginate and using 150 gel beads in 20 mL glass vial. In immobilized cells, an addition of 0.5% fructose resulted in a 2-fold increase of H2 production rate. Finally, the reducing agents β–mercaptoethanol and methylviologen enhanced H2 production rate with 3.092 and 2.426 µmolH2 mg chl a-1 h-1, respectively, in A. siamensis immobilized cells whereas NADH, dithiothreitol and sodium dithionite were not capable of increasing H2 production rate.

Characterization of light-dependent hydrogen production by new green microalga Parachlorella kessleri in various conditions

Nowadays, hydrogen (H2) production by green microalgae seems to be a very perspective, as stocks of water and solar energy are practically inexhaustible and renewable. The aim of this study was the optimization of conditions (organic carbon sources and lighting regime), which can provide light-dependent H2 production by green microalga Parachlorella kessleri RA-002 newly isolated in Armenia. The results indicated that carbon sources and lighting regimes affected H2 production. In the presence of used carbon sources H2 production was observed, but the highest yield of H2 was obtained in the presence of acetate. It was 2-fold higher than the H2 yield determined in the presence of glucose. The increase of H2 production might be connected with the stimulation of H2-producing enzyme – [Fe]-hydrogenase synthesis. The data obtained show that acetate can be used as an effective carbon source in H2 production. H2 production by microalga (in the presence of acetate and glucose) was enhanced by 1.5–2.5-fold in comparison with continuously illuminated algal cells, when P. kessleri was illuminated during 24h, and then was moved in the darkness. H2 yield increase is possible due to hydrogenase activation and the creation of anaerobic conditions. This study was significant to find out available effective substrates and optimal lighting regime to provide with light-dependent H2 production by microalgae.

Thermodynamic analysis and experimental investigation of a unique photoelectrochemical hydrogen production system

In this study, we thermodynamically analyze and experimentally investigate a continuous type hybrid photoelectrochemical H2 generation reactor. This system enhances solar spectrum use by employing photocatalysis and PV/T. Additionally, by replacing electron donors with electrodes to drive the photocatalysis, the potential of pollutant emissions are minimized. In this study, the present reactor is tested under electrolysis operation during which the present reactor is investigated under three different inlet mass flow rates (0.25, 0.50, and 0.75 g/s) and four different operating temperatures (20, 40, 60, and 80 °C). Some parametric studies are run by varying the environmental temperature between 0 and 40 °C. In addition, the impact of coating the membrane electrode assembly of the reactor with Cu2O is investigated. The present results show that the highest energy and exergy efficiencies occur at the environmental temperature of 20 °C which is about 60% and 50%, respectively. The Cu2O coated membrane gives a lot higher current readings, meaning that the coating makes the membrane more conductive and increases H2 production by permitting ions at a higher rate.

Impact of selectively enriched microbial communities on long-term fermentative biohydrogen production

The effect of selectively enriched inoculum for biohydrogen production and shifts in microbial communities was observed using anaerobic sequencing batch reactor (AnSBR). Significantly, combined pretreatment using acid and iodopropane resulted 3 fold increase in H2 production (8.65mol/kgCODR) over untreated control (2.63mol/kgCODR). Pretreatment showed significant shifts in the microbial communities which are thus accounted for enhanced H2 production. The high-throughput pyrosequence analysis depicted shifts in phylum Firmicutes and Proteobacteria. In the case of Proteobacteria, there was an increase in Betaproteobacterial, decrease in Epsilonproteobacterial and compositional variation in Alphaproteobacterial species. The decreased OTU number after pretreatment indicate, reduction of undesirable microbial populations while favouring conditions for microbiome that are involved in acidogenic, acetogenic and H2 production.

Metabolic pathway and flux analysis of H2 production by an anaerobic mixed culture

A metabolic model is proposed for H2 production from a mixed culture growing on glucose. The model based on the metabolism of Firmicutes, predominant phylum, includes substantial changes compared with previous models. Full TCA cycle and a bifurcating dehydrogenase that uses ferredoxin and participates in the reduction of crotonyl-coenzyme-A are introduced. Pathway analysis suggests that H2 yields greater than those reported are possible redirecting the flow of glucose to the pentose phosphate pathway instead of glycolysis. H2 yield as high as 10 mol H2/mol glucose is metabolically possible if the H2 pressure is sufficiently low. The adequacy was determined by metabolic flux analysis. Experimental yield of 2.23 mol H2/mol glucose are contained in the solution space and shows that growth is suboptimal for the mixed culture used. Data suggest that H2 yields can be improved by knocking out both competing reactions and the phosphoglucose isomerase. Higher NADPH2 production could increase H2 production even though it would reduce growth rate.

Response Surface Methodology and Aspen Plus Integration for the Simulation of the Catalytic Steam Reforming of Ethanol

The steam reforming of ethanol (SRE) on a bimetallic RhPt/CeO2 catalyst was evaluated by the integration of Response Surface Methodology (RSM) and Aspen Plus (version 9.0, Aspen Tech, Burlington, MA, USA, 2016). First, the effect of the Rh–Pt weight ratio (1:0, 3:1, 1:1, 1:3, and 0:1) on the performance of SRE on RhPt/CeO2 was assessed between 400 to 700 °C with a stoichiometric steam/ethanol molar ratio of 3. RSM enabled modeling of the system and identification of a maximum of 4.2 mol H2/mol EtOH (700 °C) with the Rh0.4Pt0.4/CeO2 catalyst. The mathematical models were integrated into Aspen Plus through Excel in order to simulate a process involving SRE, H2 purification, and electricity production in a fuel cell (FC). An energy sensitivity analysis of the process was performed in Aspen Plus, and the information obtained was used to generate new response surfaces. The response surfaces demonstrated that an increase in H2 production requires more energy consumption in the steam reforming of ethanol. However, increasing H2 production rebounds in more energy production in the fuel cell, which increases the overall efficiency of the system. The minimum H2 yield needed to make the system energetically sustainable was identified as 1.2 mol H2/mol EtOH. According to the results of the integration of RSM models into Aspen Plus, the system using Rh0.4Pt0.4/CeO2 can produce a maximum net energy of 742 kJ/mol H2, of which 40% could be converted into electricity in the FC (297 kJ/mol H2 produced). The remaining energy can be recovered as heat.