Yttrium-stabilized zirconia-promoted metallic nickel catalysts for the partial oxidation of methane to hydrogen

A metallic Ni catalyst has been prepared with nickel sponge and further promoted with YSZ (yttrium-stabilized zirconia) by an impregnation method. The catalysts are characterized by ICP, BET, SEM, XRD and H₂-TPR, and then studied for the partial oxidation of methane to hydrogen. The influences of reaction temperature, CH₄/O₂ ratios and gas hourly space velocity on the reaction rate are investigated. The catalyst characterization results show that the YSZ-promoted metallic Ni catalysts have high specific surface area; there is more NiO phase in the YSZ-promoted catalysts than in the metallic Ni catalyst; a mutual diffusion of Ni²⁺ and Zr⁴⁺ ions might happen between the NiO and YSZ phases. The reaction results show that the YSZ promotion increases the CH₄ conversion and the selectivities to H₂ and CO.     

Design of a methane processing system producing high-purity hydrogen

Design of a catalytic methane-to-proton exchange membrane fuel cell (PEMFC) grade hydrogen conversion system consisting of indirect partial oxidation (IPOX), water–gas shift (WGS) and preferential carbon monoxide oxidation (PROX) reactors is investigated using modeling and simulation techniques. Steady-state simulation, design and sizing of reactors, which are considered to be packed-bed tubular type, are carried out for twelve different feed composition and PEMFC power output configurations, namely (CH₄/O₂, H₂O/CH₄) = (2.24, 1.17), (1.89, 1.56) and (10, 50, 100, 500, 1000, 1500 W). For every configuration, material balance calculations are executed to obtain the flow rates of each species at each stream. These results are then used as boundary conditions to estimate the catalyst weights in each reactor via simulations conducted using a one-dimensional pseudo-homogeneous reactor model. Finally, reactor and catalyst particle dimensions are estimated by considering pressure drop and a set of criteria to quantify interfacial heat and intraparticle mass transfer resistances and fluid flow characteristics in packed beds. The total catalyst quantity is found to increase almost linearly with the PEMFC power output at both feed compositions. Total system volume, excluding piping, pumping, heat exchange and other peripheral units, is estimated to be 6.3, 40.3, 83.4, 488, 985 and 1527 cm³ for 10, 50, 100, 500, 1000 and 1500 W operations, respectively. WGS unit requires the highest space corresponding to ca. 50% of the total reactor volume, followed by IPOX (ca. 39%) and PROX (ca. 11%) reactors. Power densities, based on the weight and volume of the reactors are estimated as 1.1 kW/kg and 1.2 kW/l, respectively.     

Partial oxidation of methane on neodymium and lanthanium chromate based perovskites for hydrogen production

Perovskite-type mixed oxides LaCrO₃ and Nd_0.95CrO₃ were synthesized by the polymerization complex method. The perovskites were characterized by different techniques aiming to evaluate the influence of the non-stoichiometry and the nature of site A on the catalytic properties for the POM reaction. The non-stoichiometry and A sites did not affect the methane conversion, but the selectivity. The methane conversion with the neodymium catalyst Nd_0.95CrO₃ (N95) was 34%, and of the mixed La_0.95CrO₃ (L95) catalyst 38%, under these conditions. The rate of the Nd_0.95CrO₃ (N95) perovskite was equal to 3.50 mol.g⁻¹.h⁻¹ at 700 °C, which suggests higher activity compared to cobaltate perovskites. Although the hydrogen selectivity was similar the selectivity to CO and CO₂ were different. Catalysts did not suffer structure changes during the POM reaction and negligible deactivation.     

A two-step process for hydrogen production from vacuum residue

A two-step process has been developed for the conversion of vacuum residue to hydrogen. The first step involves oxidation of the vacuum residue in liquid phase at 373-423 K using ozone. The partially oxygenated products are utilized for hydrogen production by catalytic oxidative steam reforming over 2 wt% Pt/Al₂O₃-La₂O₃-CeO₂ catalyst. This two-step process reduces the formation of coke on the catalyst surface. Results show that it is a viable and technically feasible method for production of hydrogen from vacuum residue.     

Hydrogen production by non-catalytic partial oxidation of coal in supercritical water: Explore the way to complete gasification of lignite and bituminous coal

Supercritical water gasification (SCWG) of coal is a promising technology for clean coal utilization. In this paper, hydrogen production by non-catalytic partial oxidation of coal was systematically investigated in supercritical water (SCW) with quartz batch reactors for the first time. The influences of the main operating parameters including residence time, temperature, oxidant equivalent ratio (ER) and feed concentration on the gasification characteristics of coal were investigated. The experimental results showed that H₂ yield and carbon gasification efficiency (CE) increased with increasing temperature and decreasing feed concentration. CE increased with increasing ER, and H₂ yield peaked when ER equaled 0.1. CE increased quickly within 1 min and then tended to be stable between 2 and 3 min. In particular, complete gasification of lignite was obtained at 950 °C when ER equaled 0.1, as for bituminous coal, at a higher temperature of 980 °C when ER equaled 0.2.     

Entropy generation from hydrogen production of catalytic partial oxidation of methane with excess enthalpy recovery

Catalytic partial oxidation of methane (CPOM) is an important route for producing hydrogen and it is featured by autothermal reaction. To recognize the reaction characteristics of CPOM, H₂ production and entropy generation from CPOM in Swiss-roll reactors are studied numerically. The considered parameters affecting the performance of CPOM include the excess enthalpy recovery, gas hourly space velocity (GHSV), number of turns and atomic O/C ratio. The impact of chemical reactions, heat transfer and friction on entropy generation is also analyzed. The results indicate that preheating reactants through waste heat recovery as well as increasing GHSV or number of turns is conducive to enhancing H₂ yield, whereas the maximum H₂ yield develops at O/C = 1.2. A higher H₂ yield is always accompanied by a higher value of entropy generation, and chemical reactions are the main source of entropy generation, especially from steam methane reforming. In contrast, viscous dissipation almost plays no part on entropy generation, compared to heat transfer and chemical reactions. From the analysis of entropy generation, detailed mechanisms of H₂ production from CPOM can be figured out.     

Production of hydrogen by partial oxidation with thermal plasma

The purpose of this paper is to investigate the characteristics and optimum operating conditions of the plasmatron-assisted CH₄ reforming reaction for the hydrogen-rich gas production. In order to increase the hydrogen production and the methane conversion rate, parametric screening study was conducted at various CH₄ flow ratio and steam flow ratio and with and without adding catalyst in the reactor. High-temperature plasma flame was made with air and arc discharge, and the air flow rate and the input power were set to 5.1  L/min and 6.4 kW, respectively.When the steam flow ratio was 30.2%, the hydrogen production was maximized and the optimal methane conversion rate was 99.7%. Under these optimal conditions, the following syngas concentrations were determined: H₂, 50.4%; CO, 5.7%; CO₂, 13.8%; and C₂H₂, 1.1%. H₂/CO ratio was 9.7 and the hydrogen yield was 93.7%.     

Large eddy simulation of premixed hydrogen/methane/air flame propagation in a closed duct

In this paper, large eddy simulation (LES) is performed to investigate the propagation characteristics of premixed hydrogen/methane/air flames in a closed duct. In LES, three stoichiometric hydrogen/methane/air mixtures with hydrogen fractions (volume fractions) of 0, 50% and 100% are used. The numerical results have been verified by comparison with experimental data. All stages of flame propagation that occurred in the experiment are reproduced qualitatively in LES. For fuel/air mixtures with hydrogen fractions of 0 and 50%, only four stages of “tulip” flame formation are observed, but when the hydrogen fraction is 100%, the distorted “tulip” flame appears after flame front inversion. In the acceleration stage, the LES and experimental flame speed and pressure dynamic coincide with each other, except for a hydrogen fraction of 0. After “tulip” flame formation, all LES and experimental flame propagation speeds and pressure dynamics exhibit the same trends for hydrogen fractions of 0 and 100%. However, when the hydrogen fraction is 50%, a slight periodic oscillation appears only in the experiment. In general, the different structures displayed in the flame front during flame propagation can be attributed to the interaction between the flame front, the vortex and the reverse flow formed in the unburned and burned zones.     

Numerical simulation of nano-carbon deposition in the thermal decomposition of methane

A comparison of various hydrogen production processes indicates that the thermal decomposition of methane (TDM) provides an attractive option from both economical and technical points of view. The main problem for this process is the deposition of the nano-carbon particles on the reactor wall (or catalyst surface). This research concentrates on the numerical simulation of the TDM process without use of a catalyst to find a technique that decreases the carbon accumulation in a tubular reactor. In this model, the produced carbon particles are tracked with the Lagrangian method under thermophoretic, Brownian, van der Waals, Basset, drag, lift, gravity, pressure and virtual mass forces. In additional to experimental studies, numerical simulation also shows some carbon particle deposit around and especially downstream of the reaction zone. The results indicate that the main cause of the separation of particles from the wall is the thermophoretic force, and that downstream of the reactor, where the temperature gradient has decreased, the particles are trapped on the wall under van der Waals and Brownian forces. Two methods are investigated to decrease carbon deposition on the wall. The first is to increase the wall temperature to use the thermophoretic effect, which is rejected because in addition to the increase of thermophoretic force, the probability of particle generation increases nearly 10 times. The second method is the application of a wall jet as a sweeping flow to generate a buffer gas and to decrease particle generation near the wall. This design provides good results in producing a clean reactor.     

On the nature of elementary reactions from methane to hydrogen over transition metals

Elementary reactions that are relevant to catalytic hydrogen production have been evaluated over a wide range of transition metals. The UBI-QEP formalism was used to estimate heats of chemisorption and activation energies. The reactions were evaluated on a clean surface with the primary purpose of illustrating relative differences of intrinsic properties. The results were supportive of what is typically observed experimentally, in particular with respect to the relative difference between classical combustion catalysts (Pt, Pd) and state-of-art reforming catalysts (Ni, Rh). The likely scrambling of CH_x species was also predicted which is in accordance with isotopic tracer studies in the literature.     

Effective suppression of deactivation by utilizing Ni-doped ordered mesoporous alumina-supported catalysts for the production of hydrogen and CO gas mixture from methane

Several different kinds of ordered mesoporous alumina (OMA)-supported and Ni-doped OMA-supported Ni catalysts have been prepared for catalytic partial oxidation of methane (CPOM) to produce hydrogen and CO gas mixture. The Ni metal was incorporated in various ways of the impregnation, the doping, and the partial doping followed by impregnation. The prepared OMA-supported catalysts showed a wormhole-like, pseudo-hexagonal structure. By incorporating Ni in the OMA matrix during synthesis of supports, the resulting catalysts showed better-distributed and less-sintered nanocrystals even after CPOM at elevated temperature for over 100 h. By employing the partial doping of Ni followed by impregnation of Ni, the prepared CPOM catalyst was found more productive due to the well-distributed and well-anchored Ni nanocrystals inside the OMA matrix and the confined ordered mesopores as well. Through the test under non-stoichiometric feed ratio, the catalyst prepared only by impregnation was found vulnerable to carbon deposition and deactivated more rapidly. Even worse, the formation rate of carbon deposition was so fast that the test could not be conducted due to the increased pressure difference. In contrast, the highly distributed Ni nanocrystals partially or fully utilizing doping were found to have stronger resistance to carbon deposition.     

Calcium silicate-based catalytic filters for partial oxidation of methane and biogas mixtures: Preliminary results

Development and testing of catalytic filters for partial oxidation of methane to increase hydrogen production in a biomass gasification process constitute the subject of the present study. Nickel, iron and lanthanum were coated on calcium silicate filters via co-impregnation technique, and catalytic filters were characterized by ICP-MS, XPS, XRD, TEM, TGA, TPR and BET techniques. The influences of varying reaction temperature and addition of Fe or La to Ni-based catalytic filters on methane conversion, and hydrogen selectivity have been investigated in view of preliminary results obtained from reactions with 6% methane-nitrogen mixture, and catalytic filters were tested with model biogas mixtures at optimum reaction temperature of each filter which were 750 °C or 850 °C. Approximately 93% methane conversion was observed with nearly 6% methane-nitrogen mixture, and 97.5% methane conversion was obtained with model biogas containing CH₄ which is 6%, CO₂, CO, and N₂ at 750 °C. These results indicate that calcium silicate provides a suitable base material for catalytic filters for partial oxidation of methane and biogas containing methane.     

Partial oxidation of methane over CeO2 loaded hydrotalcite (MgNiAl) catalyst for the production of hydrogen rich syngas (H2, CO)

In this work, partial oxidation of methane (POM) was investigated using Mg-Ni-Al (MNA) hydrotalcite promoted CeO₂ catalyst in a fixed bed reactor. MNA hydrotalcite was synthesized using the co-precipitation process, while CeO₂ was incorporated via the wetness impregnation technique. The CeO₂@MNA samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDS), thermal gravimetric analysis (TGA), Fourier transform infrared spectroscopy (FTIR), and Brunauer-Emmett-Teller (BET) technique. The catalytic activity of CeO₂ promoted MNA (CeO₂@MNA) for POM reaction was evaluated for various CeO₂ loading kept the feed ratio CH₄/O₂ = 2 at 850 °C. The catalyst containing 10 wt% cerium loading (10%CeO₂@MNA) showed 94% CH₄ conversion with H₂/CO ratio above 2.0, that is more suitable for FT synthesis. The performance of catalyst is attributed to highly crystalline stable CeO₂@MNA with better Ce-MNA interactions withstand for 35 h time on stream. Furthermore, the spent catalyst was examined by TGA, SEM-EDS, and XRD to evaluate the carbon formation and structural changes during the span of reaction time.     

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.     

High-temperature reactor for hydrogen production by partial oxidation of hydrocarbons

Today, conversion of hydrocarbons is one of the most common hydrogen production technologies. This paper presents a design of a high-temperature reactor — the main component of a hydrogen production unit using partial oxidation of hydrocarbons — as well as a physical model of gas generation. It also presents a schematic diagram of an experimental setup as well as results of experimental studies on steady-state modes of partial oxidation in the combustion chamber of a high-temperature reactor for various hydrocarbon feed/oxidant combinations. In the course of the study, we identified patterns that describe how the excess oxidant ratio affects the composition of products of incomplete combustion of hydrocarbons to obtain hydrogen-containing gas of the required composition and parameters for hydrogen production. We propose a method to calculate nominal geometric dimensions of a high-temperature reactor, which makes it possible to estimate its weight and size at the design stage. The paper presents results of experimental studies confirming the adequacy of the proposed method.     

Partial oxidative gasification of phenol for hydrogen in supercritical water

The paper reports partial oxidative gasification of phenol for hydrogen in supercritical water (SCW) at lower temperature (<753 K), at which cleavages of aromatic ring occur difficultly and tend to undesirable polymerization. The results showed that O₂ is effective to gasification of phenol in SCW. ∼76% of phenol was gasified and 2.7 mol/mol of hydrogen was produced within 180 s with Na₂CO₃ as catalyst at the selected process conditions, a molar ratio of oxygen-to-phenol, 7.5–1, 723 K, and 24 MPa. It was found that unstable opening-rings products oxalic and maleic acid and stable dimmerization compounds in liquid water were formed during partial oxidation process. The process also indicated phenol was rapidly converted, and some opening-rings products were slowly gasified, which also confirmed oxygen served as effective reactant for ring-opening. Based on the given reaction conditions, a treatment process using a real wastewater from coking industry was performed. The data showed that the present technology provides an effective way to gasification of phenol wastewater for high-value energy utilization.     

Enhancement of hydrogen production rates in reformation process of methane using permeable Ni tube and chemical heat pump

Enhancement of the overall conversion efficiency from CH₄ to H₂ using a permeable-membrane Ni tube and temperature rise by a chemical heat pump system packed with hydrogen-absorbing alloys have been investigated in order to produce H₂ more efficiently using a high-temperature heat source. The two feasibilities to enhance the conversion efficiency are tested using their respective experimental apparatuses. Two things are experimentally proved that (1) Ni permeable-membrane tubes can provide measures to convert CH₄ to H₂ continuously without any deterioration in the course of partial oxidation or steam reformation and (2) two Zr(V_1−xFe_x)₂ alloys with different Fe displacement ratios can comprise a chemical heat-pump system working at higher-temperature conditions.     

Effective hydrogen production from partial oxidation of propane over composite Ni/Al2O3SiC catalyst

In this work, hydrogen production from partial oxidation (POX) of propane over composite Ni/Al₂O₃SiC catalyst was investigated. In order to utilize the high thermal conductivity and chemical stability of SiC, the composite Al₂O₃SiC support of the catalyst was synthesized by precipitation technique, then Ni component was loaded using impregnation method. The as-prepared samples were characterized by X-ray diffraction, BET, scanning electron microscopy (SEM) and transmission electron microscopy (TEM) measurements. As observed, stacking porous structures were appeared after calcination process by doping SiC with certain ratios. According to the stiochiometric ratio, a C₃H₈O₂ (1:1.5) gas mixture was used to study the catalytic activity for hydrogen production from POX of propane. From the results, local overheat of the catalyst bed generated by the exothermic reactions was relieved by doping SiC and Ni/Al₂O₃SiC (30 wt%) catalyst performed a higher hydrogen production. Aggregation and carbon deposition of Ni/Al₂O₃SiC (30 wt%) catalyst were reduced compared to Ni/Al₂O₃ from the observation of SEM and TEM with H₂ production up to around 236 μmol/g_cat·s and kept stable for 26 h at 600 °C. By means of TGA, non-isothermal oxidative decarburizations of the spent catalysts were studied. It was found that less carbon deposit and lower activation energy for oxidative decarburization were found by doping SiC to Ni/Al₂O₃.     

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 by partial oxidation of methane: Modeling and simulation

A one-dimensional non-isothermal model for oxygen permeable membrane reactor has been developed to simulate the partial oxidation of methane to produce hydrogen. The performance of two fixed bed reactors (FBRs) viz. one with pure O₂ in feed (FBR1), other with air in feed (FBR2), and a membrane reactor (MR) having air in non-reaction side have been studied at various feed conditions and inlet temperatures in order to investigate the effect of these parameters on conversion of methane and yield of hydrogen. The fixed bed reactor with pure O₂ in feed has been found to provide better performance as compared to fixed bed reactor with air and membrane reactor.