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.     

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.     

Transient reaction and exergy analysis of catalytic partial oxidation of methane in a Swiss-roll reactor for hydrogen production

Catalytic partial oxidation of methane (CPOM) is a promising method for hydrogen production with autothermal reaction. To figure out the unsteady reaction characteristics of CPOM in a Swiss-roll reactor along with heat recirculation, a numerical method is employed to simulate the transient reaction dynamics, with emphasis on energy recovery using exergy analysis. Three different gas hourly space velocities (GHSVs) of 5000, 10,000 and 50,000 h⁻¹ with the condition of atomic O/C ratio of 1 are considered. The predictions indicate that increasing GHSV substantially shortens the transient period of chemical reactions; however, it also reduces the methane conversion, as results of more reactants sent into the reactor and shorter residence time of the reactants in the catalyst bed. Within the investigated range of GHSV, the methane conversion with energy recovery at the steady state is larger than 80%, much higher than the reaction without heat recovery. The selectivities of H₂ and CO in the product gas are always larger than 90%. The exergy recovery is in the range of 66–80%, implying that over two-third useful work contained in the product gas can be reused to preheat the reactants in the reactor, thereby enhancing the performance of CPOM.     

Effect of ruthenium addition on molybdenum catalysts for syngas production via catalytic partial oxidation of methane in a monolithic reactor

Hydrogen is mainly produced from hydrocarbon resources. Natural gas, mostly composed of methane, is widely used for hydrogen production. As a valuable feedstock for ‘Fischer–Tropsch’ (FT) process and ‘Gas to Liquids’ (GTL) technology, syngas production from catalytic partial oxidation of methane (CPOM) is gaining prominence especially owing to its more desirable H₂/CO ratio; relatively less energy consumption, and lower investment, compared to steam reforming processes (SMR), the leading technology.In the present study, effect of ruthenium (Ru) addition on molybdenum (Mo) catalysts for syngas production from methane (CH₄) via partial oxidation in a monolithic reactor was investigated. Mo based catalysts supported on Nickel (Ni) and Cobalt (Co) metal oxides and Ni-Co bimetallic oxides and their Ru added versions were developed, characterized, and tested for performance in a monolithic type reactor system. Catalyst activity was investigated in terms of H₂ and CO selectivity, CH₄ conversion; and CO₂ emission and it is concluded that addition of Ru over the structure led to increase in catalytic activity and reduction in carbon deposition over the catalyst surface.     

Hydrogen production through partial oxidation of methane in a new reactor configuration

Performance of the side feeding (SF) air injection in the process of partial oxidation of methane (POM) has been investigated by means of developing a one-dimensional steady-state non-isothermal model. A fixed bed reactor (FBR), a one-side feeding reactor (One-SF), and a membrane reactor (MR) has been compared for the conversion of methane, selectivity of hydrogen and reactor temperature. The results of the model revealed that the One-SF can operate within FBR and MR, and increasing the number of air injections of SF could achieve to the performance of the MR. The performance of the two to five-SF was studied according to the hydrogen selectivity, methane conversion, temperature profile and H₂/CH₄ ratio. It was observed that increasing the number of injections up to the three, increased the selectivity of hydrogen from 0.496 to 0.530 and decreased the outlet temperature from 1269 K to 1078 K. These results lead to creating of a process with controllable operating temperature and enhancing the selectivity of hydrogen. Consequently, decreasing the problems of high operating temperature in FBR and reduction of the process cost compared with MR.     

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.     

Experimental study of ultra-rich thermal partial oxidation of methane using a reticulated porous structure

Performance of SiC porous burner used in a non-catalytic partial oxidation reformer for syngas production was experimentally investigated in this study. Premixed combustion of ultra-rich methane-oxygen mixtures was conducted at thermal loads of 6 and 8 kW. In order to have a comprehensive analysis, temperature distribution along the burner and product compositions were measured. Moreover, a thermodynamic analysis was performed using Gibbs free energy minimization method to calculate equilibrium concentrations prior to the experimental work. The results showed that the highest syngas mole fraction of 0.67 and H₂/CO ratio of 1.86 can be achieved at higher power. The CH₄ conversions were found to be in the range of 79–96%, while the equilibrium data indicated complete consumption of methane.Eventually, this study proved high reforming efficiency of partial oxidation process within SiC porous burner, with a good methane conversion and syngas purity. Therefore, due to highly efficient characteristics of this burner, it may be a good solution in development of reformers, particularly for small-scale applications.     

A comparative study of molybdenum phosphide catalyst for partial oxidation and dry reforming of methane

Molybdenum phosphide (MoP) was firstly used as a catalyst for partial oxidation of methane (POM) and its catalytic performance for POM was compared with that for dry reforming of methane (DRM). It was found that the MoP phase was the dominant active site in POM and DRM reactions, and the activity would gradually decrease when more and more MoP was converted to Mo₂C phase (non-dominant active site) and then rapid deactivation would occur due to bulk oxidation of catalyst. The redox type mechanism over MoP catalyst was vitally important to keep its structure reasonably well during methane reforming reactions. The MoP catalyst revealed a higher catalytic stability in POM than in DRM, attributing to the higher H₂ yield obtained in POM, which can promote and maintain the redox cycle of catalyst.     

Catalytic partial oxidation of methane for the production of syngas using microreaction technology: A computational fluid dynamics study

Catalytic partial oxidation of methane in high temperature environments under extremely short contact time conditions has emerged as a very promising reaction pathway for the production of syngas. This paper addresses the issues related to the favorable operating conditions for the process. Computational fluid dynamics simulations were performed to gain insight into the underlying mechanism and the key factors affecting primary reaction products. Particular emphasis was given to the role of homogenous and heterogeneous reaction pathways in determining the distribution of reaction products. The effect of preheating temperature, pressure, feed composition, and reactor dimension was investigated in order to identify conditions that will maximize the yield of syngas. Comparisons were made between air-feed and oxygen-feed systems. The relative importance of homogeneous and heterogeneous reactions was assessed, and the reaction pathways responsible for the production of syngas were identified. It was shown that there is a strong interplay between gas-phase and surface chemistry due to the competitive oxidation reactions occurring simultaneously in the system. The contribution of homogeneous and heterogeneous reaction pathways is highly dependent on the operating conditions. Gas-phase chemistry is favored at high preheating temperatures, high pressures, and large reactors, whereas surface chemistry is favored at low preheating temperatures, low pressures, and small reactors, with a tendency to shift towards higher syngas yields. It is particularly beneficial to utilize air instead of oxygen as the oxidant, especially at industrially relevant pressures, thereby inhibiting or avoiding the onset of undesired gas-phase chemistry.     

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.     

Catalytic DBD plasma reactor for low temperature partial oxidation of methane: Maximization of synthesis gas and minimization of CO2

In this study, room temperature synthesis gas production from partial oxidation of methane through a dielectric barrier discharge plasma reactor was investigated experimentally. In this case, operating conditions including applied voltage and Ar flow rate were evaluated to obtain the best operating conditions for the purpose of enhancing CH₄ conversion and selective synthesis gas production. In addition, plasma alone system was compared with the catalytic system (NiO–CaO/Al₂O₃), revealing great improvement of synthesis gas selectivity through utilization of the catalyst. The maximum CH₄ conversion of 99.9% with the synthesis gas module of 1.84 and energy efficiency of 3.2% was gained in the catalytic system where the applied voltage was 10 kV. Besides, synthesis gas module of almost 2, which is in favor of commercial applications including methanol production, was achievable at the applied voltage of 8 kV in the catalytic system. Finally, the obtained results were compared with the similar previous studies.     

Modeling and analysis of flow distribution in an A-type microchannel reactor

Flow distribution among microchannels is a fatal factor affecting the performance of laminated microchannel reactors for hydrogen production. Homogeneous flow strongly depends on the structural design of the microchannel reactor. The present work concentrates on improving the flow distribution in microchannel reactors for hydrogen production by optimization of the structural design. An innovative A-type microchannel reactor for hydrogen production with one inlet/two outlets was developed and analyzed. The equivalent electrical resistance network model was used to calculate the flow distribution in the microchannel reactor which was validated by computational fluid dynamics (CFD). The influences of structural parameters on flow distribution in the A-type were investigated quantitatively. The calculated results showed that longer microchannels with a higher aspect ratio and a small side length in the manifolds were beneficial for attaining uniform flow distribution in the A-type microchannel reactor. Furthermore, it was found that flow distributions among the microchannels in the A-type were much more uniform than those in the conventional Z-type microchannel reactor with one inlet/one outlet. Finally, an optimization strategy was proposed to optimize the manifold geometries to obtain a comparatively even flow distribution among microchannels.     

Minimization of hot spot in a microchannel reactor for steam reforming of methane with the stripe combustion catalyst layer

Hot spot formation is inevitable in a heat exchanger microchannel reactor used for steam reforming of methane because of the local imbalance between the generated and absorbed heat. A stripe configuration of the combustion catalyst layer was suggested to make the catalytic combustion rate uniform in order to minimize the hot spot near the inlet. The stripe configuration was optimized by response surface methodology with computational fluid dynamics. With the optimal catalyst layer, the hot spot was not observed near the inlet and the maximum temperature decreased by 130 K from that of the uniform catalyst layer without any conversion loss. The maximum relative particle diameters of the uniform and the optimal stripe catalyst layer were about 3.68 and 2.51, respectively, and the surface-averaged particle diameter of the optimal stripe catalyst layer was 7.64% less than that of the uniform stripe catalyst layer.     

Increased hydroxyl concentration by tungsten oxide modified h-BN promoted catalytic performance in partial oxidation of methane

Hexagonal boron nitride (h-BN) as a layered inorganic nonmetallic material has been widely used. Hydrogen peroxide (H₂O₂) modification can trigger exfoliation and afford abundant B–OH active sites at edge of h-BN, which can enhance methane activation ability. Introducing tungsten oxide (WO₃) to h-BN produces a similar effect, because doping WO₃ into h-BN resulted in electron transfer to N, inducing fracture of B–N bond, resulting in N vacancy (triboron center), exposing more B sites and promoting the generation of B–OH. Significantly, the introduction of WO₃ on the modified h-BN dramatically increased the concentration of B–OH compared with the unmodified h-BN, because H₂O₂ modification weakened B–N bond. By means of XRD, TEM, XPS,EPR, FT-IR, it is proved that the high concentration of B–OH active sites contributed to activating C–H bond, thus methane conversion and CO and H₂ selectivity were significantly improved.     

A performance study of methanol steam reforming in an A-type microchannel reactor

The methanol steam reforming (MSR) performance in a microchannel reactor is directly related to the flow pattern design of the microchannel reactor. Hydrogen production improvements can be achieved by optimal design of the flow pattern. In this study, an A-type microchannel reactor with a flow pattern design of one inlet and two outlets was applied to conduct the MSR for hydrogen production. The MSR performance of the A-type microchannel reactor was investigated through numerical analysis by establishing a three-dimensional simulation model and compared with that of the conventional Z-type microchannel reactor. Experiments were also conducted to test the MSR performance and validate the accuracy of the simulation model. The results showed that compared with the conventional Z-type microchannel reactor, the species distributions in the A-type microchannel reactor were more homogeneous. In addition, compared with the Z-type microchannel reactor, the A-type microchannel reactor was shown to effectively increase the methanol conversion rate by up to 8% and decrease the pressure drop by about 20%, regardless of a slightly higher CO mole fraction. It was also noted that with various quantities of microchannels and microchannel cross sections, the A-type microchannel reactor was still more competitive in terms of a higher methanol conversion rate and a lower pressure drop.     

Hydrogen production over Ni/ceria-supported catalysts by partial oxidation of methane

The catalytic performance of Ni dispersed on ceria-doped supports, (Ce_0.88La_0.12) O_2-x, (Ce_0.91Gd_0.09) O_2-x, (Ce_0.71Gd_0.29) O_2-x, (Ce_0.56Zr_0.44) O_2-x and pure ceria, was tested for the catalytic partial oxidation of Methane (CPOX). The catalysts were characterized by Brunauer Emmett Teller (BET), X-ray diffraction (XRD), temperature programmed reduction (TPR) and temperature programmed oxidation (TPO). Ni/ (Ce_0.56Zr_0.44) O_2-x showed higher Hydrogen production than the Ni/Gadolinium-doped catalysts, which may be due to its higher reducibility and surface area. By enhancing the support reducibility in Ni/doped-ceria catalysts, their catalytic activity is promoted because the availability of surface lattice oxygen is increased, which can participate in the formation of CO and H₂. It was also found that Ni/(Ce_0.56Zr_0.44) O_2-x showed higher catalytic performance after redox pretreatments. Similarly, a higher amount of H₂ or O₂ was consumed during hydrogenation and oxidation pretreatments, respectively. This may be correlated to re-dispersion of metallic particles and changes on the metal-support interface. In addition, it was observed that the ionic conductivity of Ni/(Ce_0.56Zr_0.44) O_2-x had an effect on the amount of carbon formed during the CPOX reaction at oxygen concentrations lower than the stoichiometric required, O/C ratios lower than 0.6. Its high oxygen mobility may have accelerated the surface oxidation reactions of carbon by reactive oxygen species, thus, inhibiting carbon growth on the catalyst surface.     

Study of partial oxidation reforming of methane to syngas over self-sustained electrochemical promotion catalyst

A self-sustained electrochemical promotion (SSEP) catalyst is synthesized for partial oxidation reforming (POXR) of CH₄ to produce syngas (H₂ and CO) at a relatively low temperature ranging from 350 to 650 °C. The SSEP catalyst is comprised of 4 components: microscopic Ni/Cu/CeO₂ anode, La_0.9Sr_0.1MnO₃ cathode, copper as electron conductor, and yttria-stabilized-zirconia as oxygen ion conductor, which form microscopic electrochemical cells to enable the self-sustained electrochemical promotion for the POXR process. The SSEP catalyst exhibited much better catalytic performance in POXR of CH₄ than a Ni–Cu–CeO₂ catalyst and a commercial Pt–CeO₂ catalyst. The CH₄ conversion over the SSEP catalyst is 29.4% at 350 °C and reaches 100% at 550 °C and the maximum selectivity to H₂ is on the level of 90% at 450–650 °C under a GHSV of 42,000 h⁻¹. The mechanism of the SSEP is discussed.     

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.     

A novel tubular oxygen-permeable membrane reactor for partial oxidation of CH4 in coke oven gas to syngas

Dense BaCo_0.7Fe_0.2Nb_0.1O_3−δ (BCFNO) membrane tubes were prepared by slip casting and readily brazed to 310S stainless steel supports using a silver-based alloy. A novel tubular membrane reactor was constructed by placing a cylindrical Ni-based monolithic catalyst coaxially around the tubular membrane and a conventional Ni-based catalyst-bed apart from the membrane tube. The novel membrane reactor was successfully applied to partial oxidation of CH₄ in coke oven gas (COG). At 850 °C, 94% of CH₄ conversion, 93% of H₂ and as high as 11.3 cm³ cm⁻² min⁻¹ of oxygen permeation flux were obtained. The experimental H₂ and CO selectivity and CH₄ conversion were close to the thermodynamically predicated ones. There was a good match in the coefficient of thermal expansion (CTE) among BCFNO membrane, Ag-based alloy and 310S metal support. Long-term operation test results indicate that the novel tubular BCFNO membrane reactor exhibited not only high activity but also good stability for the partial oxidation of CH₄ in COG to syngas.