Hydrogen Production Step Research Articles

Thermodynamic viability of a new three step high temperature Cu-Cl cycle for hydrogen production

A new three step high temperature Cu-Cl thermochemical cycle for hydrogen production is presented. The performance of the proposed cycle is investigated through energy and exergy approaches. Furthermore, the effects of various parameters, such as the temperatures of the steps of the cycle and power plant efficiency, on various energy and exergy efficiencies are assessed with parametric studies. The results show that the exergy and energy efficiencies of the proposed cycle are 68.3% and 32.0%, respectively. In addition, the exergy analysis results reveal that the hydrogen production step has the maximum specific exergy destruction with a value of 150.9 kJ/mol. The results suggest that proposed cycle may provide enhanced options for high temperature thermochemical cycles by improving thermal management without causing a sudden temperature jump/fall between the hydrogen production step and other steps.

Performance analysis of a water–gas shift membrane reactor for integrated coal gasification combined cycle plant

In integrated gasification combined cycle (IGCC) systems, the water–gas shift reaction, which promotes the conversion of CO present in syngas mixtures into hydrogen, is an important step for hydrogen production. Application of the water–gas shift membrane reactor (WGSMR) in IGCC systems is an attractive option for CO2 capture compared with conventional methods because of smaller heat loss in gas purification and high CO conversion by selectively removing hydrogen from the reaction zone through the membrane. In this study, we proposed and evaluated commercial-scale WGSMR models combined with IGCC using reported laboratory-scale experimental data to optimize their operational parameters. Various models were developed using the Aspen Plus® Ver. 8.6 process simulator to investigate the impacts of hydrogen separation, pressure loss, and the flow direction between the sweep gas on the permeate side and syngas on the retentate side on the WGSMR performance with respect to CO conversion, H2 yield, and reactor temperature. The membrane reactor model gave approximately 20% higher CO conversion than a reactor model without H2 separation and approximately 4% lower CO conversion than a membrane reactor model with a pressure drop. A counter-current membrane reactor model gave approximately 2% higher CO conversion than a co-current model; the H2 yield on the permeate side was 9.3% higher in the counter-current model by separation of H2 through the membrane. A sensitivity analysis indicated that a high flow rate and low pressure of sweep gas are advantageous for H2 recovery, and high catalyst loading and high syngas inlet temperature are preferable for higher CO conversion.

Uranium thermochemical cycle: hydrogen production demonstration

ABSTRACTIn hydrogen production industry, thermochemical cycle technology for converting thermal energy into chemical storage energy of hydrogen owns absolute advantages. Compared with other thermochemical cycles, thermochemical cycle technology based on uranium (UTC) is safer and more efficient. This technology consists of three steps, where only the hydrogen production step is unique. In this paper, the verification has been done for this step. Solid products were characterized by XRD and Raman spectroscopy, which were confirmed to be α-Na2U2O7. Gas chromatographic analyses were performed for gas samples, in which hydrogen output was obtained using an internal standard method.

Solar hybrid photo-thermochemical sulfur-ammonia water-splitting cycle: Photocatalytic hydrogen production stage

One of the main limitations of existing solar thermochemical water-splitting cycles (WSC) are that they utilize only thermal component of the solar irradiation neglecting its photonic component. A new hybrid photo-thermochemical sulfur–ammonia (HySA) WSC developed at the Florida Solar Energy Center allows circumventing this shortcoming. In the HySA cycle, water splitting occurs by means of solar beam splitting which enables utilization of the quantum (UV–Vis) portion of the solar spectrum in the hydrogen production stage and the thermal (IR) portion in the oxygen production stage. Present work investigates the photocatalytic hydrogen production step using narrow band gap CdS and CdSZnS composite photocatalysts, and ammonium sulfite as an electron donor. The choice of the electron donor was determined by the considerations of its regenerability in the thermal stages of the HySA cycle. This article examines the impact of photocatalyst and cocatalyst loading, temperature, and light intensity on hydrogen production rates. Photocatalysts, cocatalysts and photoreaction products were analyzed by a number of materials characterization (XRD, SEM, TEM, EDS) and analytical (GC and IC) methods. The experimental data obtained provide guidance for the improved solar photoreactor design.

Hydrogen production by non-catalytic partial oxidation of coal in supercritical water: The study on reaction kinetics

Supercritical water gasification (SCWG) has attracted great attention for efficient and clean coal conversion recently. A novel kinetic model of non-catalytic partial oxidation of coal in supercritical water (SCW) that describes formation and consumption of gas products (H2, CO, CH4 and CO2) is reported in this paper. The model comprises 7 reactions, and the reaction rate constants are obtained by fitting the experimental data. Activation energy analysis indicates that steam reforming of fixed carbon (FC) is the rate-determining step for the complete gasification of coal. Once CH4 is produced by pyrolysis of coal, steam reforming of CH4 will be the rate-determining step for directional hydrogen production.

Strained graphitic carbon nitride for hydrogen purification

Hydrogen purification from a mixture of gas is a critical step in hydrogen production as an energy source and other clean energy applications. Recently gas purification using membranes with sub-nanometer pores, such as porous graphene has offered an attractive option which purifies the targeted gas from other impurity gases based on size exclusion exploiting the differences in the gases' molecular size. Using a combination of density functional theory (DFT) and molecular dynamic (MD) simulations, we demonstrate that graphitic carbon nitride (g-C3N4), a graphene like 2-dimensional nanomaterial can effectively purify H2 from CO2 and CH4. However, under neutral conditions the H2 flux across the membrane is comparatively weak, and our theoretical analysis shows that the flux can be significantly improved by widening the pore area via applying biaxial strains as low as 2.5% and 5% on the membrane. Interestingly, the strain tuning only improves the membranes H2 permeability, while its excellent H2/CO2 and H2/CH4 selectivity is not compromised.

Nanosized manganese oxide supported on carbon black: A new, cheap and green composite for water oxidation

Water splitting is a very promising method to produce hydrogen. However, water oxidation is a crucial step for hydrogen production since it can provide cheap electrons for proton reduction. Herein a nanosized Mn oxide immobilized on carbon black as a reasonable catalyst for water oxidation is reported. The composites were synthesized by a simple, low-cost procedure using different ratios of carbon black and Mn oxide. Catalysts were characterized by scanning electron microscopy, energy-dispersive spectroscopy (EDX), scanning electron microscope (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), electronic spectroscopy, Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) and atomic absorption spectroscopy (AAS). In the next step, the water-oxidizing activities of the composites were observed in the presence of cerium(IV) ammonium nitrate. The composites were reasonable catalysts with turnover frequencies of ∼0.07 (mmol O2/mol Mn s). In addition to the water-oxidizing activity, the self-healing for this composite in the experimental condition was also studied.

Biohydrogen and methane production via a two-step process using an acid pretreated native microalgae consortium

A native microalgae consortium treated under thermal-acidic hydrolysis was used to produce hydrogen and methane in a two-step sequential process. Different acid concentrations were tested, generating hydrogen and methane yields of up to 45mLH2gVS−1 and 432mLCH4gVS−1, respectively. The hydrogen production step solubilized the particulate COD (chemical oxygen demand) up to 30%, creating considerable amounts of volatile fatty acids (up to 10gCODL−1). It was observed that lower acid concentration presented higher hydrogen and methane production potential. The results revealed that thermal acid hydrolysis of a native microalgae consortium is a simple but effective strategy for producing hydrogen and methane in the sequential process. In addition to COD removal (50–70%), this method resulted in an energy recovery of up to 15.9kJ per g of volatile solids of microalgae biomass, one of the highest reported.

Energy and exergy analyses of hydrogen production step in boron based thermochemical cycle for hydrogen production

This study deals with a thermodynamic assessment of hydrogen production step of the boron based thermochemical cycle. In addition, this step is assessed for its merits and demerits in terms of energetic and exergetic performances for various reference environment temperatures. In this regard, the energy and exergy efficiencies of this step are calculated as 11.00% and 20.34% and also the hydrogen production step of the cycle inlet, outlet exergy rates and exergy destruction are calculated as 1653.32 kJ/mol, 336.31 kJ/mol and 317.02 kJ/mol while the reference environment temperature is kept constant at 298 K, respectively. The technical and economic problems of the hydrogen storage and transportation find a possible solution provided that the hydrogen production step of this cycle is performed on-board of a vehicle.

Effect of the addition of glycerol on hydrogen production from industrial municipal solid waste

The purpose of this study was to investigate the effect of glycerol supplementation (1% v/v) on the hydrogen production (HP) steps in thermophilic-dry dark fermentation of industrial municipal solid waste (IMSW) in batch mode. For this purpose, physicochemical and microbiological parameters were considered. The rates of HP and specific hydrogen production (SHP) almost doubled when adding 1% v/v crude glycerol to the IMSW. This result was in keeping with the high values of hydrolysis yield (75±4%) and microbial activity (7.3∗10−12±0.9∗10−12lH2/cell). Microbiological studies showed that the percentages of Eubacteria decreased slightly after the dark fermentation process. Archaea contents were not significant and the biogas produced was methane-free.

Hydrogen and methane production from cassava wastewater using two-stage upflow anaerobic sludge blanket reactors (UASB) with an emphasis on maximum hydrogen production

The objective of this study was to produce hydrogen and methane from cassava wastewater using two steps of upflow anaerobic sludge blanket reactors (UASB), emphasizing maximum hydrogen production. For the first hydrogen production stage, the UASB system was operated at 37 °C and pH 5.5 at different COD loading rates. A maximum specific H2 production rate of 0.39 l H2/l d and a maximum H2 yield of 39.83 l H2/kg COD removed were found at a COD loading rate of 25 kg/m3d and the gas produced contained 36.4% H2, and 63.6% CO2 without methane. For the second methane production stage, the UASB was fed by the effluent produced from the hydrogen production step operated at the optimum COD loading rate. A maximum specific CH4 production rate of 0.91 l CH4/l d and a maximum CH4 yield of 115.23 l CH4/kg COD removed were found at a COD loading rate of 8 kg/m3d. The inhibition levels of organic acids to acidogens and methanogens were found to be 10,000 and 400 mg/l as acetic acid, respectively.

Structural Insight into the Complex of Ferredoxin and [FeFe] Hydrogenase from Chlamydomonas reinhardtii.

The transfer of photosynthetic electrons by the ferredoxin PetF to the [FeFe] hydrogenase HydA1 in the microalga Chlamydomonas reinhardtii is a key step in hydrogen production. Electron delivery requires a specific interaction between PetF and HydA1. However, because of the transient nature of the electron-transfer complex, a crystal structure remains elusive. Therefore, we performed protein-protein docking based on new experimental data from a solution NMR spectroscopy investigation of native and gallium-substituted PetF. This provides valuable information about residues crucial for complex formation and electron transfer. The derived complex model might help to pinpoint residue substitution targets for improved hydrogen production.

Decoupled catalytic hydrogen evolution from a molecular metal oxide redox mediator in water splitting.

The electrolysis of water using renewable energy inputs is being actively pursued as a route to sustainable hydrogen production. Here we introduce a recyclable redox mediator (silicotungstic acid) that enables the coupling of low-pressure production of oxygen via water oxidation to a separate, catalytic hydrogen production step outside the electrolyzer that requires no post-electrolysis energy input. This approach sidesteps the production of high-pressure gases inside the electrolytic cell (a major cause of membrane degradation) and essentially eliminates the hazardous issue of product gas crossover at the low current densities that characterize renewables-driven water-splitting devices. We demonstrated that a platinum-catalyzed system can produce pure hydrogen over 30 times faster than state-of-the-art proton exchange membrane electrolyzers at equivalent platinum loading.

Simultaneous Production of Hydrogen and Methane from Cassava Wastewater Using a Two Stage Upflow Anaerobic Sludge Blanket System Under Thermophilic Operation

The objective of this study was to investigate the hydrogen and methane production from cassava wastewater by using a two stage upflow anaerobic sludge blanket (UASB) system under thermophillic operation (55 °C). The recycle ratio of the effluent from the methane bioreactor-to-the feed flow rate was fixed at 1:1 and the solution pH in the hydrogen bioreactor was maintained at 5.5 by a pH controller while the solution pH of the methane bioreactor was not controlled. The liquid working volumes of the hydrogen and methane bioreactors were 4 and 24 L, respectively. The two stage UASB system was operated at different COD loading rates (30, 60, 90, 120, and 150 kg/m 3 d based on the hydrogen bioreactor volume). Under the optimum COD loading rate of 90 kg/m 3 d based on the hydrogen bioreactor volume corresponding to 15 kg/m 3 d based on the methane bioreactor volume for the hydrogen bioreactor, the produced gas contained 40 % H2, 52 % CO2 and 8 % CH4 and the system provided a maximum hydrogen yield and specific hydrogen production rate of 18 mL/g COD removed and 520 mL/L d, respectively. Under this optimum COD loading rate, the produced gas of the methane bioreactor contained 65 % CH4 and 35 % CO2 without hydrogen and the system provided a maximum methane yield and specific methane production rate of 115 mL/g COD removed and 650 mL/L d, respectively. The operation of recycling from methane bioreactor to hydrogen bioreactor optimized the use of NaOH for pH control in the hydrogen production step.

Hydrothermal synthesis of CuV2O6 supported on mesoporous SiO2 as SO3 decomposition catalysts for solar thermochemical hydrogen production

Hydrothermal synthesis of CuV2O6 supported on 3-D ordered mesoporous SiO2 (CuV/SiO2) was studied to evaluate the catalytic activity for SO3 decomposition, which is a key step in solar thermochemical hydrogen production. A composite oxide hydrate, Cu3O(V2O7)·H2O, and an oxide hydroxide hydrate, Cu3(OH)2V2O7·(H2O)2, were formed at lower hydrothermal temperatures (≤200 °C). The oxide hydrate phase mainly yielded Cu2V2O7 after calcination at 600 °C in air. By contrast, the hydrothermal synthesis at 250 °C (CuV/SiO2@250) directly crystallized CuV2O6 from the oxide hydroxide hydrate, although its very large particle size (∼5 μm) is not suitable for the catalytic application. The SO3 decomposition activity measured at 600 °C was associated with the yield as well as the dispersion of CuV2O6, giving rise to the maximum for the hydrothermal synthesis at 200 °C. CuV/SiO2@250 achieved the highest catalytic activity at the reaction temperature of 650 °C, because the melting phase of CuV2O6 penetrated mesoporous SiO2 and thus improved the dispersion of the active phase.

Plastidial Expression of Type II NAD(P)H Dehydrogenase Increases the Reducing State of Plastoquinones and Hydrogen Photoproduction Rate by the Indirect Pathway in Chlamydomonas reinhardtii1.

Biological conversion of solar energy into hydrogen is naturally realized by some microalgae species due to a coupling between the photosynthetic electron transport chain and a plastidial hydrogenase. While promising for the production of clean and sustainable hydrogen, this process requires improvement to be economically viable. Two pathways, called direct and indirect photoproduction, lead to sustained hydrogen production in sulfur-deprived Chlamydomonas reinhardtii cultures. The indirect pathway allows an efficient time-based separation of O2 and H2 production, thus overcoming the O2 sensitivity of the hydrogenase, but its activity is low. With the aim of identifying the limiting step of hydrogen production, we succeeded in overexpressing the plastidial type II NAD(P)H dehydrogenase (NDA2). We report that transplastomic strains overexpressing NDA2 show an increased activity of nonphotochemical reduction of plastoquinones (PQs). While hydrogen production by the direct pathway, involving the linear electron flow from photosystem II to photosystem I, was not affected by NDA2 overexpression, the rate of hydrogen production by the indirect pathway was increased in conditions, such as nutrient limitation, where soluble electron donors are not limiting. An increased intracellular starch was observed in response to nutrient deprivation in strains overexpressing NDA2. It is concluded that activity of the indirect pathway is limited by the nonphotochemical reduction of PQs, either by the pool size of soluble electron donors or by the PQ-reducing activity of NDA2 in nutrient-limited conditions. We discuss these data in relation to limitations and biotechnological improvement of hydrogen photoproduction in microalgae.

Study of the hydrogen production step of the Mn2O3/MnO thermochemical cycle

In this work, a complete study of the second step of the Mn2O3/MnO thermochemical cycle for solar hydrogen production has been performed. It includes a complete thermodynamic calculation of the equilibrium phases between MnO, NaOH and H2, which shows that the reaction takes place theoretically at temperatures above 75 °C. However, the experimental results demonstrate that it is necessary at least 450 °C to achieve a satisfactory reaction rate. It indicates a dramatic influence of chemical kinetics and diffusion process, displacing the reaction to higher temperatures than those predicted by thermodynamics. The resultant solid of the reaction exhibits a phases distribution highly dependent on the temperature and the NaOH:MnO ratio and this is of great influence in the overall rate of the process. The kinetic study shows that the overall process involves not only the chemical reaction between MnO and NaOH, but also a number of physical processes (heat and mass transfer) and solid phase transformations. The apparent activation energy calculated is a composite value determined by the activation energies of those elementary processes.

Status of the Solar Sulfur Ammonia Thermochemical Hydrogen Production System for Splitting Water

A sulfur ammonia (SA) cycle for splitting water to produce hydrogen with solar energy was evaluated using the Aspen Plus® chemical process modeling tool. The hydrogen production step consists of electrolytic oxidation of ammonium sulfite and the oxygen evolution side is a molten salt sub-cycle. Laboratory testing for the thermochemistry of molten salts and electrolysis has indicated that the cycle is viable. The solar field, reactor configurations and continuous operation with storage have been evaluated. The SA cycle is an all-fluid cycle and the solar receiver operates below 1073K. All of the electricity needed by the process is generated internally from waste heat. Using thermal energy storage, the system will operate continuously with no shut downs required due to the variability of solar energy.

Dark fermentation from real solid waste. Evolution of microbial community

The purpose of this paper was to study the evolution of microbial community and its relation to the hydrogen production (HP) steps in thermophilic-dry dark fermentation from real organic fraction of municipal solid waste (OFMSW). Nine organic loading rates (OLRs) (from 9 to 220 g TVS/l/d) were investigated. Population dynamics study showed that increasing OLR (between 9 and 110 g TVS/l/d) resulted in an increase in the relations between Eubacteria:Archaea and hydrolytic-acidogenic bacteria (HABs):acetogens. This was strongly influenced by the microbial content of the OFMSW. The presence of acetogens and Archaea was due to contribution of these microorganisms in the substrate (the biogas produced was methane-free). The maximum value of hydrolysis (63±7%) was observed at 110 g TVS/l/d OLR according to maximum HP and HAB activity. The highest average values of acidification yields (57-60%) were achieved for OLR between 28 and 43 g TVS/l/d.

A zinc nanoparticles-dispersed multi-scale web of carbon micro-nanofibers for hydrogen production step of ZnO/Zn water splitting thermochemical cycle

Water splitting via the two-step ZnO/Zn thermochemical cycle is a promising and environmentally benign method for producing hydrogen from steam. In this study, we focus on the second step of the cycle, which is the exothermic hydrolysis reaction of Zn nanoparticles with steam. The unique Zn nanoparticle-dispersed carbon micro-nanofibers (Zn-CNFs) were prepared by impregnating carbon microfibers (ACFs) with a sodium dodecyl sulfate (SDS)-mediated mono-dispersed aqueous solution of Zn(II), followed by calcinations and reduction. The surfactant increased the metal (average crystal size∼25nm) loading by approximately two-fold on the ACFs. The CNFs were grown on Zn-ACF at 700°C by catalytic chemical vapor deposition (CCVD) using acetylene as the carbon source. Zn has dual roles in this system, one as a catalyst for CNF growth and the other as a reactant in the hydrolysis reaction. The water-splitting reaction was performed at different steam and N2 flow rates and reaction temperatures. The production rate and yield of H2 at a reaction temperature of 600°C were calculated as 1.66×10−6mol/gs and 80%, respectively, which are comparable to or higher than results reported in the literature. The Zn-CNFs prepared in this study are a potential candidate for the H2 production step of the ZnO/Zn thermochemical cycle.