Development of a reaction mechanism for predicting hydrogen production from homogeneous decomposition of methane

In this paper, a reaction mechanism is developed to model the kinetics of hydrogen production from decomposition of methane. The pyrolysis of hydrocarbons from several combustion mechanisms is compared with experiment to obtain the elementary reactions of this mechanism. Some modifications are then made to reduce the large errors observed at a high residence time. Sensitivity analysis is performed to find the reactions with the highest effect on hydrogen production and their rate constants are changed by using other mechanisms to obtain the lowest error in hydrogen production compared to experimental data. This study shows that modifying the rate constants of the reactions of dissociation of methane to hydrogen and methyl radicals, and the formation of benzene from propargyl radicals have the highest effect on improving the results. The new mechanism reduces the error introduced from existing models for predicting the amount of hydrogen production up to 15%, depending on residence time and temperature levels.     

An evaluation of detailed reaction mechanisms for hydrogen combustion under gas turbine conditions

Chemical kinetics in hydrogen combustion for elevated pressures have recently become more relevant because of the implementation of hydrogen as a fuel in future gas turbine combustion applications, such as IGCC or IRCC systems. The aim of this study is to identify a reaction mechanism that accurately represents H₂/O₂ kinetics over a large range of conditions, particularly at elevated pressures as present in a gas turbine combustor. Based on a literature review, six mechanisms of different research groups have been selected for further comparisons within this study. Reactor calculations of ignition delay times show that the mechanisms of Li et al. and Ó Conaire et al. yield the best agreement with data from shock tube experiments at pressures up to 33 bar. The investigation of one-dimensional laminar hydrogen flames indicate that these two mechanisms also yield the best agreement with experimental data of laminar flame speed, particularly for elevated pressures. The present study suggests that the Li mechanism is best suited for the prediction of H₂/O₂ chemistry since it includes more up-to date data for the range of interest.     

Reduction of a detailed reaction mechanism for hydrogen combustion under gas turbine conditions

The aim of this study is to find a reduced mechanism that accurately represents chemical kinetics for lean hydrogen combustion at elevated pressures, as present in a typical gas turbine combustor. Calculations of autoignition, extinction, and laminar premixed flames are used to identify the most relevant species and reactions and to compare the results of several reduced mechanisms with those of a detailed reaction mechanism. The investigations show that the species OH and H are generally the radicals with the highest concentrations, followed by the O radical. However, the accumulation of the radical pool in autoignition is dominated by HO₂ for temperatures above, and by H₂O₂ below the crossover temperature. The influence of H₂O₂ reactions is negligible for laminar flames and extinction, but becomes significant for autoignition. At least 11 elementary reactions are necessary for a satisfactory prediction of the processes of ignition, extinction, and laminar flame propagation under gas turbine conditions. A 4-step reduced mechanism using steady-state approximations for HO₂ and H₂O₂ yields good results for laminar flame speed and extinction limits, but fails to predict ignition delay at low temperatures. A further reduction to three steps using a steady-state approximation for O leads to significant errors in the prediction of the laminar flame speed and extinction limit.     

High-purity hydrogen gas production by catalytic thermal decomposition using mechanochemical treatment

The objectives of this work, were to produce high-purity hydrogen gas from rice husk by two-step process and to study the effect of nickel hydroxide/nickel acetate/sodium acetate and calcium hydroxide on the concentration of gaseous products. The samples were characterized by X-ray diffraction (XRD) and thermogravimetry-mass spectroscopy (TG/MS). The gaseous products were analyzed by gas chromatography (GC). The results indicated that hydrogen gas was produced from the milled samples by heating at 400–600 °C with the low concentrations of methane, carbon monoxide and carbon dioxide. The highest concentration of hydrogen gas from milled samples with the catalyst, was approximately 95–97 %mol. Furthermore, the milled samples with the carbon dioxide capture agent gave the carbon dioxide concentration, was below 2 %mol.     

Hydrogen production by splitting water on solid acid materials by thermal dissociation

Conventionally, there have been three basic ways of research on H₂ production from H₂O-splitting with solar energy: photo-catalytic, photo-electrochemical and thermochemical. Among them the thermal dissociation of H₂O has been considered the most efficient, because it is a single step energy conversion process and gives much higher conversion efficiency than those resulted from other methods. However, the major stumbling block of thermal dissociation of H₂O has been the requirement of a high dissociation temperature which causes problems both with materials for the reactor and with energy conversion efficiency for the process. In this study, we show that the dissociation temperature can be drastically lowered when H₂O is thermally dissociated on solid acid materials. A probable mechanism of the thermal H₂O-splitting on solid acid materials is also presented, based on some experimental results of this study and reports in the literature.     

Hydrogen gas production from food wastes by electrohydrolysis using a statical design approach

Hydrogen gas production was investigated by electrohydrolysis of food waste due to its high organic content. Different voltages generated by DC power supply were applied to food waste in order to produce hydrogen gas. Effects of the DC voltage, reaction time and initial solid content on cumulative hydrogen gas production, hydrogen gas content in the gas phase and total organic carbon (TOC) removal were investigated by using a Box-Behnken statistical experiment design approach. The most suitable voltage/reaction time/solid content values resulting in the highest hydrogen gas content (99%), the highest cumulative hydrogen gas formation (7000 mL) and total organic carbon removal (33%) were determined as 5 V/75 h/20%. The results indicated that food wastes constitute a good source for H₂ gas production by electrohydrolysis. Hydrogen gas produced by electrohydrolysis of food waste can be directly used in fuel cells due to its high putrity.     

Hydrogen generation from formic acid decomposition at room temperature using a NiAuPd alloy nanocatalyst

Formic acid has been widely regarded as a safe and sustainable hydrogen storage material. Despite tremendous efforts, developing low-noble-metal-loading material with high activity for the dehydrogenation of formic acid remains a great challenge. Here, carbon supported highly homogeneous trimetallic NiAuPd alloy nanoparticles are prepared and employed as catalyst for the selective dehydrogenation of formic acid. Unexpectedly, at Ni molar contents as high as 40%, the resultant Ni_0.40Au_0.15Pd_0.45/C exhibits high activity and 100% hydrogen selectivity for hydrogen generation from formic acid aqueous solution without any additives even at 298 K. Such a low-noble-metal-loading catalyst with high activity may greatly encourage the practical application of formic acid as a hydrogen storage material.     

Hydrogen production from methane and natural gas steam reforming in conventional and microreactor reaction systems

Ni-based (over MgO and Al₂O₃) and noble metal-based (Pd and Pt over Al₂O₃) catalysts were prepared by wet impregnation method and thereafter impregnated in microreactors. The catalytic activity was measured at several temperatures, atmospheric pressure and different steam to carbon, S/C, ratios. These conditions were the same for conventional, fixed bed reactor system, and microreactors. Weight hourly space velocity, WHSV, was maintained equal in order to compare the activity results from both reaction systems. For microreactor systems, similar activities of Ni-based catalyst were measured in the steam methane reforming (SMR) activity tests, but not in the case of natural gas steam reforming tests. When noble metal-based catalysts were used in the conventional reaction system no significant activity was measured but all catalysts showed some activity when they were tested in the microreactor systems. The analysis by SEM and TEM revealed a carbon-free surface for Ni-based catalyst as well as carbon filaments growth in case of noble metal-based catalysts.     

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.     

Hydrogen production from biogas using hot slag

Possibility of hydrogen production from biogas using hot slag has been studied, in which decomposition rate of _CO2${\mathrm{CO}}_2$–_CH4${\mathrm{CH}}_4$ in a packed bed of granulated slag was measured at constant flow-rate and pressure. The molten slag, discharged at high temperature over 1700 K from smelting industries such as steelmaking or municipal waste incineration. It has enough potential for replacing energy required for hydrogen production due to the catalytic steam reforming or carbon decomposition of hydrocarbon. However, heat recovery of hot slag has never been established. Therefore, the objective of this work is to generate hydrogen from methane using heated slag particles as catalyst, in which the effect of temperature on the hydrogen generation was mainly investigated at range from 973 to 1273 K. In the experiments a mixed gas of _CH4${\mathrm{CH}}_4$ and _CO2${\mathrm{CO}}_2$ was continuously introduced into the packed bed of hot slag at constant flow-rate and atmospheric pressure and then the outlet gas was monitored by gas chromatography. The results indicate that slag acted as not only thermal media but also good catalyst, for promoting decomposition. The product gases were mainly hydrogen and carbon monoxide with/without solid carbon deposition on the surface of slag, depending on the reaction temperature. Increasing temperature led to large hydrogen generation with decreasing un-reacted methane in the outlet gas, at when the largest methane conversion was about 96%. The results suggested a new energy-saving process of hydrogen production, in which the waste heat from molten slag can replace the energy required for hydrogen production, reducing carbon dioxide emission.     

Hydrogen production from solid sodium borohydride with hydrogen peroxide decomposition reaction

This study investigates hydrogen production from solid sodium borohydride with hydrogen peroxide decomposition reaction for a fuel cell based air-independent propulsion system in space and underwater applications. Sodium borohydride in the solid state was used as a hydrogen source in the present study. Pure hydrogen could be generated by a catalytic hydrolysis reaction in which the water source was obtained from the hydrogen peroxide decomposition. Hydrogen peroxide was selected as an oxidizer, being decomposed catalytically to generate oxygen and water. The pure oxygen was provided to a fuel cell and the water was stored separately for the hydrolysis reaction. A fuel cell system was fabricated to validate the fuel cell based air-independent power system proposed in the present study. Two catalytic reactors were prepared; one for the solid sodium borohydride hydrolysis reaction and the other for the hydrogen peroxide decomposition reaction. The hydrogen and oxygen generation rate were measured based on the various conditions. The performance evaluation of a fuel cell system proposed in the present study was carried out.     

Hydrogen rich gas production by thermocatalytic decomposition of kenaf biomass

Kenaf (Hibiscus cannabinus L.), a well known energy crop and an annual herbaceous plant grows very fast with low lodging susceptibility was used as representative lignocellulosic biomass in the present work. Thermocatalytic conversions were performed by aqueous phase reforming (APR) of kenaf hydrolysates and direct gasification of solid biomass of kenaf using 5% Pt on activated carbon as catalyst. Hydrolysates used in APR experiments were prepared by solubilization of kenaf biomass in subcritical water under CO₂ gas pressure.     

Hydrogen production by using manganese ferrite: Evidences and benefits of a multi-step reaction mechanism

Hydrogen production by water splitting with _MnFe2O4/_Na2CO3${\mathrm{MnFe}}_2{\mathrm{O}}_4/{\mathrm{Na}}_2{\mathrm{CO}}_3$ system was studied at 973 K. An intermediate phase, resulting from decarbonatation of _MnFe2O4/_Na2CO3${\mathrm{MnFe}}_2{\mathrm{O}}_4/{\mathrm{Na}}_2{\mathrm{CO}}_3$ mixture in inert atmosphere, proved to be effective in hydrogen reduction from water with stoichiometric yield. The presence of a highly reactive intermediate phase suggests the feasibility of a high efficiency, three-step, thermochemical cycle for hydrogen production. In fact, the possibility of obtaining _CO2${\mathrm{CO}}_2$ separately from the gases mixture dramatically enhances process efficiency.     

Experimental and numerical study of detailed reaction mechanism optimization for syngas (H2 + CO) production by non-catalytic partial oxidation of methane in a flow reactor

The National Institute of Standards and Technology (NIST) detailed reaction mechanism of methane combustion was optimized based on a flow reactor experiment to obtain syngas (H₂ + CO). The experimental methane partial oxidation was conducted with pre-mixed gas in a flow reactor. Specifically, 0.2% methane and 0.1% oxygen were diluted with 99.7% argon, restraining the exothermic effect. The experiment was conducted from 1223 K to 1523 K under pressure. Through a comparison of the experimental results with calculated values, the NIST mechanism was selected as a starting point. Rate coefficients of O + OH = O₂ + H, CH₃ + O₂ = CH₃O + O, and C₂H₂ + O₂ = HCCO + OH were replaced with results from other studies. The replaced rate coefficient for CH₃ + O₂ = CH₃O + O was again optimized, within its reported uncertainty of 3.16, based on the experimental results of this study. The revised value of the rate coefficient for CH₃ + O₂ = CH₃O + O was k₃₇ = 7.92 × 10¹³ × e^{(−31400/RT)}. The optimized mechanism showed better performance in predicting the results of other studies, as well as this study. The optimization reduced the RMS error for the results of this study from 6.7 to 1.18.     

Hydrogen production from dairy wastewater using catalytic supercritical water gasification: Mechanism and reaction pathway

The supercritical water gasification (SCWG) of real dairy wastewater (cheese-based or whey) was performed in a batch reactor in presence of two catalysts (MnO₂, MgO) and one additive (formic acid). The operational conditions of this work were at a temperature range of 350–400 C and the residence time of 30–60 min. The catalysts and formic acid were applied in 1 wt%, 3 wt%, and 5 wt% to determine their effect on hydrogen production. The concentrations of catalysts and formic acid were calculated based on the weight of feedstock without ash. The results showed that increased temperature and prolonged residence time contributed to the hydrogen production (HP) and gasification efficiency (GE). The gas yield of hydrogen in the optimum condition (400 C and 60 min) was achieved as 1.36 mmol/gr DAF (dry ash free). Formic acid addition was favored towards enhancing hydrogen content while the addition of metal oxides (MnO₂ and MgO) had an apex in their hydrogen production and they reached the highest hydrogen in 1 wt% concentration then ebbed. Moreover, GE was increased by the addition of the catalysts and formic acid concentrations. The highest hydrogen content (35.4%) was obtained in 1 wt% MnO₂ and the highest GE (32.22%) was attained in the 5 wt% formic acid concentration. A reaction pathway was proposed based on the GC-MS data of feedstock and produced liquid phase at different condition as well as similar studies.     

Hydrogen gas production from electrohydrolysis of industrial wastewater organics by using photovoltaic cells (PVC)

Electrical current generated by a photovoltaic cell (PVC) was supplied to wastewater in a mechanically mixed and sealed reactor using stainless steel electrodes. Hydrogen gas was generated by reaction of protons released from decomposition of organic compounds and electrons provided by electrical current. Gas phase was composed of 75–99% H₂ gas.     

Hydrogen evolution reaction of low carbon steel electrode in hydrochloric acid as a source for hydrogen production

The hydrogen evolution reaction (HER) (cathodic reaction) of low carbon steel electrode immersed in hydrochloric acid was investigated as a source for hydrogen production. Corrosion rate, hydrogen evolution rate, and current density increase with the increase of HCl concentration. Theoretically and practically, every 1 g of iron produces about 0.036 g of hydrogen. Therefore, the hydrogen production efficiency over the immersion period is about 100%. High correlation coefficient (close to +1) statistically indicates that there is a strong relation between loss in weight and the amount of evolved hydrogen (as dependent variable) and both time of immersion and acid concentrations (as independent variables). Application of the hydrogen produced by low carbon steel electrode has been performed on storage material. The tested material absorbs about 6 wt.% of hydrogen under atmospheric pressure and room temperature.     

Hydrogen production from water gas shift reaction in a high gravity (Higee) environment using a rotating packed bed

Hydrogen production via the water gas shift reaction (WGSR) was investigated in a high gravity environment. A rotating packed bed (RPB) reactor containing a Cu–Zn catalyst and spinning in the range of 0–1800 rpm was used to create high centrifugal force. The reaction temperature and the steam/CO ratio ranged from 250 to 350 °C and 2 to 8, respectively. A dimensionless parameter, the G number, was derived to account for the effect of centrifugal force on the enhancement of the WGSR. With the rotor speed of 1800 rpm, the induced centrifugal force acting on the reactants was as high as 234 g on average in the RPB. As a result, the CO conversion from the WGSR was increased up to 70% compared to that without rotation. This clearly revealed that the centrifugal force was conducive to hydrogen production, resulting from intensifying mass transfer and elongating the path of the reactants in the catalyst bed. From Le Chatelier’s principle, a higher reaction temperature or a lower steam/CO ratio disfavors CO conversion; however, under such a situation the enhancement of the centrifugal force on hydrogen production from the WGSR tended to become more significant. Accordingly, a correlation between the enhancement of CO conversion and the G number was established. As a whole, the higher the reaction temperature and the lower the steam/CO ratio, the higher the exponent of the G number function and the better the centrifugal force on the WGSR.     

Hydrogen production by steam reforming of acetic acid using hydrotalcite type precursors

Acetic acid can be used as a model compound in the study of the steam reforming of the hydrophilic phase of bio-oil. In order to perform acetic acid reforming reactions, low cost catalysts with high catalytic activity and selectivity are required. Thus, NiMgAl hydrotalcite derived catalysts emerge as a good alternative. In this work, four NiMgAl hydrotalcite type precursors were prepared, with different Ni/Mg molar ratios (0.3, 0.4, 0.5, and 0.6). Various characterization tests have been performed for the prepared hydrotalcite type precursors. The stability of the catalytic activity was evaluated during 24 h and the used samples were submitted to a thermogravimetric analysis to evaluate carbon accumulation. Characterization tests proved that Ni/Mg ratios had a direct influence in the reducibility of the precursors. The Temperature-programmed surface reaction analysis showed that the steam reforming of acetic acid occurred majorly when the temperature reached 873 K. Stability test showed that precursors 04NiMg and 05NiMg had the best catalytic performance. It was also seen that sample 06NiMg suffered from deactivation by carbon deposition, which was confirmed by the thermogravimetric analysis.     

Hydrogen production and End-Uses from combined heat,hydrogen and power system by using local resources

To address the problem of fossil fuel usage at the Missouri University of Science and Technology campus, using of alternative fuels and renewable energy sources can lower energy consumption and hydrogen use. Biogas, produced by anaerobic digestion of wastewater, organic waste, agricultural waste, industrial waste, and animal by-products is a potential source of renewable energy. In this work, we have discussed Hydrogen production and End-Uses from CHHP system for the campus using local resources. Following the resource assessment study, the team selects FuelCell Energy DFC1500™ unit as a molten carbonate fuel cell to study of combined heat, hydrogen and power (CHHP) system based on a molten carbonate fuel cell fed by biogas produced by anaerobic digestion. The CHHP system provides approximately 650 kg/day. The total hydrogen usage 123 kg/day on the university campus including personal transportation applications, backup power applications, portable power applications, and other mobility applications are 56, 16, 29, 17, and 5 respectively. The excess hydrogen could be sold to a gas retailer. In conclusion, the CHHP system will be able to reduce fossil fuel usage, greenhouse gas emissions and hydrogen generated is used to power different applications on the university campus.