Maximum Methane Conversion Research Articles

Effects of non-uniform porosity on thermochemical performance of solar driven methane reforming

As one of the effective methods for solving the greenhouse problem, methane reforming has received increasing attention. The performance of a reactor is strongly influenced by the foam structure with different parameters. In this study, the idea of non-uniform partition design of porosity (an expansion kind of hierarchical porous structure) in a porous media reactor was put forward and investigated. The heat and mass transfer phenomena and thermochemical properties of methane reforming under high convergence solar radiation were numerically studied. Finite volume method coupled with thermochemical kinetics is considered to solve this problem. Based on a constant pore size, the porosity of the porous medium is divided into two layers and combined in different forms in an axial direction. The effects of non-uniform porosity on thermochemical performance of solar driven methane reforming are analyzed and an optimization method for non-uniform porosity is proposed. The results show that methane conversion in a reactor with uniform porous media increases with growth up of the porosity. In addition, a reactor with non-uniform porous media exhibits better thermochemical performance and reforming performance compared to one with uniform porous media. Finally, different non-uniform partitions have an impact on methane conversion. When the porosity is constant, methane conversion decreases with an increase of the length of the first layer of porous media, and the maximum methane conversion (82.42%) was achieved at L1 = 0.01 m with φ1 = 0.75, φ2 = 0.9.

Process simulation and thermodynamic analysis of a chemical looping combustion system using methane as fuel and NiO as the oxygen carrier in a moving-bed reactor

This study provides a comprehensive evaluation and sensitivity analysis of the methane chemical looping combustion process in Aspen Plus, using a micro-reactor system and nickel oxide supported by alumina as the oxygen carrier. The effect of various parameters and limitations was investigated and thermodynamic evaluations made so that the outcomes of this study should be beneficial for scaling up the CLC process using a nickel-based oxygen carrier. By varying the fuel reactor temperature from 700 °C to 1200 °C, the maximum achievable conversion of methane to carbon dioxide was estimated to be 61.19%. The effect of the fuel reactor pressure (20 bar to 40 bar) on the conversion of methane remained constant. However, the reduction of oxygen carrier with hydrogen was slower than methane when the fuel reactor pressure varied from 20 bar to 40 bar. Once the entering carriers flow rate varied (1 ×10-8 kmol/s to 1 kmol/s), methane conversion decreased from 100% to nearly 50%. However, this study’s results showed a good agreement with the reported experimental results in the literature.

Combined methane reforming with a mixture of methane combustion products and steam over a Ni-based catalyst: An experimental and thermodynamic study

Combined methane reforming with a mixture of methane combustion products and steam over a commercial Ni-based catalyst is studied both experimentally and theoretically. The 7-holes cylinder of NiO-αAl2O3 catalysts is used as the pellets. The thermodynamic analysis of the reforming process was carried out by total Gibbs free energy minimization to determine the maximum achievable methane conversion in the reformer. The reforming performances were determined for various amount of extra steam in inlet reaction mixture (from 0 to 2 mol of H2O per mole of CH4). The methane conversion is increasing when steam is added to the reaction mixture at a fixed temperature. The methane conversion reaches a maximum value (about 1) at the temperature range above 800∘C. Based on experimental results, the approximation functions of the methane conversion versus the residence time for the various temperatures and methane-to-oxidizer ratio were obtained. The methane conversion reaches the value that is close to equilibrium at the residence time above 4.0 kgcat⋅s/mol. The effect of pressure (in the pressure range from 1 to 5 bar) on methane conversion is insignificant and is no more than 1–2%. The values of the methane conversion can be used for the energy analysis of the thermochemical recuperation system by methane reforming with steam and flue gases.

Hydrogen Production via Synthetic Biogas Reforming in Atmospheric-Pressure Microwave (915\xa0MHz) Plasma at High Gas-Flow Output

This paper is a contribution to the development of microwave plasma-based technology for hydrogen (H2) production from a so-called synthetic biogas, considered as a mixture of methane (CH4) and carbon dioxide (CO2). The efficiency of hydrogen production via reforming of CH4 in the synthetic biogas flowing through a waveguide-supplied metal cylinder-based microwave plasma source (MPS) operating at atmospheric pressure was tested experimentally. The MPS operated at a frequency of 915 MHz. The working plasma-forming gas was a mixture of CH4:CO2 of volume ratios from 0 to 1. Its flow rate was varied from 3 to 12 m3/h. The microwave power absorbed by the plasma was up to 7.5 kW. The experiment showed that using this kind of MPS, the plasma processing of the synthetic biogas can be run stably at high flow rates (up to 12 m3/h). The optimal CH4:CO2 ratio in terms of high energy efficiency of the microwave plasma reforming of CH4 was found to be 40:60. The maximum achieved hydrogen production rate was 156 g(H2)/h at a microwave absorbed power of 7.5 kW (at a flow rate of 6 m3/h) with the energy efficiency of hydrogen production of 21 g(H2)/kWh. The maximum energy yield of hydrogen production of 24 g(H2)/kWh was achieved at 4.5 kW of the microwave absorbed power (the hydrogen production rate was 108 g(H2)/h in this condition). The maximum methane conversion degree and maximum hydrogen selectivity were 86.5% and 73.3%, respectively at an absorbed microwave power of 6.5 kW (at 3 m3/h).

Experimental investigation of reforming and flow characteristics of a steam methane reformer filled with nickel catalyst of various shapes

An experimental investigation of the steam methane reforming process in a cylindrical packed bed filled with the Ni-αAl2O3 catalysts was performed to understand the effect of particle shapes of catalyst on a pressure drop and a methane conversion. Four particle shapes such as a simple cylinder, a Raschig ring, a 7-holes cylinder, and a 7-holes sphere were tested. Moreover, the simple cylinders and the Raschig rings were tested for various end-to-end dimensions (5 mm, 10 mm, 15 mm, 20 mm, 25 mm). The present study showed that the methane conversion is increasing with an increase in the geometric surface of the packed at a constant packed bed length (600 mm). Two quantities are proposed for evaluating the effectiveness of the packed beds filled with a catalyst of various shape: a weight residence time (kgcat·s/mol) and a surface residence time (m2·s/mol). The maximum methane conversion is observed for the 7-holes spheres. The catalytic activity of the surface unit of all investigated catalyst shapes is approximately the same. A characteristic quadratic dependence of a pressure drop versus velocity ΔP=f(u2) is observed for all catalyst types. The minimum pressure drops are taking place in a packed bed filled with the 7-holes cylinders, while the maximum pressure drops are occurring for the simple cylinders. The linear (1/mm) and volumetric (1/m3) drag coefficient were calculated. The drag coefficient is decreasing when the velocity decreases, especially in the velocity range up to 1 m/s.

Absorptive Hydrogen Scavenging for Enhanced Aromatics Yield During Non‐oxidative Methane Dehydroaromatization on Mo/H‐ZSM‐5 Catalysts

Addition of Zr metal particles to MoCx /ZSM-5 in interpellet mixtures (2:1 weight ratio) resulted in maximum single-pass methane conversion of 27 % for dehydroaromatization at 973 K (in significant excess of the equilibrium prescribed circa 10 % conversion at these conditions) and a concurrent 1.4-5.6-fold increase in aromatic product yields due to circumvention of thermodynamic equilibrium limitations by absorptive H2 removal by Zr while retaining cumulative aromatic product selectivity. The absorptive function of the polyfunctional catalyst formulation can be regenerated by thermal treatment in He flow at 973 K, yielding above-equilibrium methane conversion in successive regeneration cycles. H2 uptake experiments demonstrate formation of bulk ZrH1.75 on hydrogen absorption by Zr at 973 K. Cooperation between absorption and catalytic centers distinct in location and function enables circumvention of persistent thermodynamic challenges in non-oxidative methane dehydrogenation.

Methane dehydroaromatization – A study on hydrogen use for catalyst reduction, role of molybdenum, the nature of catalyst support and significance of Bronsted acid sites

Abstract Methane dehydroaromatization was studied over Mo/SiO2 and Mo/HZSM-5 with different Mo loadings (2, 5, 10 wt%) at 973 K and 1023 K in a recirculating batch reactor. H2 pretreatment at 1023 K prior to methane activation has significantly improved the catalyst activity with increase in Mo loading and reduced the induction time on benzene formation in both Mo/SiO2 and Mo/HZSM-5. 10 wt% Mo/HZSM-5 gave a maximum methane conversion of 19% and ∼67% benzene selectivity at 1023 K. The XRD analysis of used catalysts revealed that the MoO3 species were converted to β-Mo2C phase. Studies on Mo/SiO2 catalysts showed that benzene was formed even in the absence of acidic zeolite sites. Reactions of ethylene in the presence of pure silica, HZSM-5 and in a blank reactor revealed that conversion of ethylene to aromatics was similar in case of the blank reactor and silica. Thus, it is believed that molybdenum carbide sites act as active sites only for C–H bond activation of methane and ethylene formation. Even though, ethylene can undergo subsequent oligomerization without any catalytic aid to form benzene at 973 K and above addition of acidic zeolites improved the selectivity of benzene.

Thermal Fluid Analysis of Cold Plasma Methane Reformer

One of the most important methods of methane utilization is the conversion to synthesis gas (syngas). However, conventional ways of reforming methane usually require very high temperature, therefore non-thermal (non-equilibrium) plasma methane reforming is an attractive alternative. In this study, a novel plasma based reformer named 3D Gliding Arc Vortex Reformer (3D-GAVR) was investigated for partial oxidation of methane to produce syngas. The tangential input creates a vortex in the plasma zone and an expanded plasma presides within the entire area between the two electrodes. Using this method, the experimental results show that hydrogen can be produced for as low as $ 4.45 per kg with flow rates of around 1 L per minute. The maximum methane conversion percentage which is achieved by this technology is up to 62.38%. In addition, a computational fluid dynamics (CFD) modeling is conducted for a cold plasma reformer chamber named reverse vortex flow gliding arc reactor (RVF-GA) to investigate the effects of geometry and configuration on the reformer performance. In this modified reformer, an axial air input port is added to the top of the reaction vessel while the premixed reactants can enter the cylindrical reaction zone through tangential jets. The CFD results show that a reverse vortex flow (RVF) scheme can be created which has an outer swirling rotation along with a low pressure area at its center with some component of axial flow. The reversed vortex flow utilizes the uniform temperature and heat flux distribution inside the cylinder, and enhances the gas mixtures leading to expedition of the chemical reaction and the rate of hydrogen production.

Ni/Ce0.95M0.05O2−d (M = Zr, Pr, La) for methane steam reforming at mild conditions

Methane obtained from renewable resources such as biogas or biomass gasification may be reformed to produce hydrogen, an important and environmentally friendly energy vector. In the present work, nickel based catalysts supported on either pure or doped ceria (5 at% of Zr, Pr or La doping) were studied for this purpose. Catalysts were obtained by impregnation of 5 wt% nickel of ceria based supports prepared by coprecipitation by the urea method. Catalysts were calcined at three temperatures (600, 750 or 900 °C), characterized by different techniques (XRD, H2-TPR, TPO, OSC-OSCC, H2-Chemisorption) and evaluated at different feed conditions and temperatures for methane steam reforming. Catalysts calcined at 900 °C were tested at three different reaction temperatures (600, 700 and 800 °C). Higher temperatures favored methane conversion and CO selectivity. For catalysts tested at 600 °C, increasing vapor/methane ratio caused an increase in hydrogen yield and lowered carbon formation. However, high vapor pressure was seen to favor nickel sintering. Intermediate calcination temperature (750 °C) enhanced nickel-support interaction leading to maximum methane conversion.

Modeling and optimization of synthesis parameters in nanostructure La 1 − x Ba x Ni 1 − y Cu y O 3 catalysts used in the reforming of methane with CO 2

Abstract To achieve an efficient catalyst for the production of synthesis gas by dry reforming of methane a series of LaxBa1 − xNiyCu1 − yO3 perovskite-type oxides were synthesized with the sol−gel auto-combustion method. The reaction was carried out under continuous flow of feed stream which included CO2, CH4 and Argon as an internal standard, under atmospheric pressure. In order to design the modified catalysts and to optimize the methane conversion, an artificial neural network (ANN) model linked with genetic algorithm (GA) was applied. A high R2 value was obtained for training, validation and test sets of data: 0.99, 0.97 and 0.96 respectively. The model predicted that the maximum methane conversion was achieved via La0.996Ba0.004Ni0.6Cu0.4O3 (Tca = 700 °C). The catalysts were characterized by XRD and FE-SEM.

Steam methane reforming at low S/C ratios for power-to-gas applications

Steam reforming is a well-established industrial process for the production of hydrogen from hydrocarbon fuels, in most cases from natural gas. High steam to carbon ratios are applied to gain maximum methane conversion. Since steam reforming of natural gas is a highly endothermic reaction it may also be applied as a chemical storage of renewable energy. For this power-to-hydrogen application milder conditions and shorter operating times are characteristic. However process efficiency declines with increasing S/C ratio for storage applications. Though, when lowering S/C ratios one of the major challenges lies in coke formation due to unwanted reactions. On this reason, experiments with different hydrocarbon feedstock, including methane and a synthetic natural gas mixture were conducted in a laboratory test rig to investigate the influence of very low S/C ratios in the range of 0.1–0.4 and reaction temperatures between 450 and 500 °C at atmospheric pressure. Measurements showed drastic decrease of catalyst life times when small amounts of ethane and propane were added to the hydrocarbon feedstock. Long-term tests showed that catalyst deactivation led to flattening of the temperature profile, changes in dry product gas composition and rising pressure drop over fixed bed. Increase of reaction temperature, lowering of S/C and use of higher hydrocarbons in the feed led to intense carbon lay down.

CO2 Reforming of CH4 on Co-Containing Supported Catalysts

<p>Mono- and bimetallic cobalt-containing catalysts supported on alumina have been investigated in the reaction of interaction between carbon dioxide and methane at variation of experiment temperature and pressure. It was shown, that the bimetallic catalysts have a high activity in this reaction in compare with monometallic ones. The main reaction products are carbon oxide, hydrogen, water and oxygenates. The yield of latter reaches 30% at certain conditions (P > 0.5 MPa, T < 853K). The maximum conversion of both methane (100%) and carbon dioxide (94%) is reached at lower pressure (0.1MPa) and 1023 K. In these conditions the synthesis-gas is a main reaction product. One of the advantages of the bimetallic catalysts is their resistance to coke formation.</p>

Calcium promoted Fe/Al2O3 oxygen carrier for hydrogen production via cyclic chemical looping steam methane reforming process

Chemical-looping steam methane reforming (CL-SMR) is known as an innovated method for the generation of high purity H2 or synthesis gas. This process is based on reduction–oxidation cycles through a gas–solid reaction with a catalyst as oxygen carrier. In this study, the effect of Fe metal loading in Fe/Al2O3 oxygen carrier and its preparation method were investigated in CL-SMR process under different reaction temperatures of 550–800 °C. The results revealed that 15 wt.%Fe/γ-Al2O3 oxygen carrier synthesized by an impregnation method has the best activity in this process. Afterwards, the effect of calcium promoter on the performance of optimized oxygen carrier (15 wt.%Fe/γ-Al2O3) was studied via various impregnation methods. The results showed 15 wt.%Fe–5 wt.%Ca/γ-Al2O3 oxygen carrier synthesized by co-impregnation method exhibited the highest catalytic activity of 100% methane conversion and 83% hydrogen production yield at a low temperature of about 700 °C. Moreover, this oxygen carrier revealed the maximum methane conversion and the lowest activity reduction during 17 oxidation–reduction cycles between the other samples. The prepared samples were characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), energy dispersive X-ray spectroscopy (EDS) analysis, and BET techniques.

Performance assessment of packed bed reactor and catalytic membrane reactor for steam reforming of methane through metal foam catalyst support

A kinetic model for the methane steam reforming has been investigated. The performances are compared between the packed bed reactor and catalytic membrane reactor with metal foam catalyst support. The effects of various variables such as pressure, temperature of the reaction, ratio of methane to steam in feed, thickness of membrane and sweep gas on the total methane conversion and hydrogen production were investigated qualitatively. The comparison between these two types of reactors was carried out in the temperature range of 350 °C–750 °C and pressure range of 2–30 bar. Isothermal modeling has been performed and showed a higher performance of the membrane reactor rather than the packed bed reactor. Methane conversion can be reached 100% for lower temperatures than used with industrial PBR, and better performances are reached with an increase of the operating pressure. The maximum conversion of methane for the CMR is quickly reached while the conversion evolution observed for the PBR is smoother.

Steam Reforming of Methane Over Catalyst Derived from Ordered Double Perovskite: Effect of Crystalline Phase Transformation

La2NiTiO6 double perovskite was synthesized by modified Pechini method. The catalyst activity for steam reforming of methane was investigated at temperatures from 450 to 950 °C, under different reduction conditions. By reducing La2NiTiO6 with 10 % H2/N2 at 1,000 °C, the crystalline phase changed to mainly Ni0 and La2TiO5, which decreases the onset temperature of methane conversion to 550 °C and provides a maximum methane conversion of 95 % at 950 °C. This activity is higher when compared to that achieved with La2NiTiO6 reduced with 1.8 % H2/Ar, which is composed of Ni0 supported on both non-stoichiometric La2NiTiO6 and La2O3, and also to those of unreduced La2NiTiO6 and Ni/La2O3 formed by reduction of LaNiO3. Activity improvement is related to the increased number of active sites and/or metal-support interaction.

CH4/H2 Ratio Effect on Methane Pyrolysis on Resistive Molybdenum Catalyst

The aim of this study is to examine the methane conversion into C2 hydrocarbons at resistive metal catalyst – electrically heated molybdenum plate - and to determine the effect of H2 content in the reaction gas mixture on the process characteristics. For hydrogen-free pyrolysis the maximum methane conversion reaches 60% at temperature plate of 1300°C and the product selectivity has clearly defined maxima: for ethane it is at a temperature of 1050°C (6%), for ethylene it is at a temperature of 1150°C (10%) and for acetylene it is in the temperature range of 1250-1300°C (28%). With further temperature increase the selectivity for acetylene drops significantly due to intensive decomposition of methane into carbon and hydrogen. The hydrogen addition into the reaction mixture positively effects the selectivity of unsaturated hydrocarbon C2 (ethylene and acetylene) and negatively effects on the selectivity for conversion of ethane and methane.

Simulating and Optimizing Auto-Thermal Reforming of Methane to Synthesis Gas Using a Non-Dominated Sorting Genetic Algorithm II Method

Conventional synthesis gas production plants consist of a natural gas steam reforming to CO + 3H2 on Ni catalysts in a furnace. An alternative method for highly endothermic steam reforming is auto-thermal reforming. In this work, synthesis gas production by auto-thermal reforming was simulated based on a heterogeneous and one-dimensional model in two cases. The first case was the auto-thermal reformer of Dias and Assaf's study. The present work was validated by the reported experimental results. The second case was the fixed-bed catalytic auto-thermal reactor operated at high pressure, which was suitable for methanol production and Fischer–Tropsch reactions (baseline case). Then, the effect of operating variables on the system behavior was studied. Finally, Pareto-optimal solutions were determined by non-dominated sorting genetic algorithm II. The objectives included obtaining a H2/CO ratio of 2 in the produced synthesis gas and the maximum methane conversion. The adjustable parameters were the feed temperature, mass flux, and O2/CH4 and H2O/CH4 ratios in the feed.

Direct conversion of methane with methanol toward higher hydrocarbon over Ga modified Mo/H-ZSM-5 catalyst

Methane conversion to higher hydrocarbons was studied over gallium modified Mo/HZSM-5 catalyst. It was demonstrated that the small amount of methanol addition in the methane stream improves the catalyst activity and selectivity toward aromatics hydrocarbon. The calcined catalysts were characterized using BET surface area, pore volume distribution, TPR, TPD, XRD, FTIR and SEM analysis. A maximum methane conversion (up to 15.5% with 88.7% aromatic selectivity) was achieved over 2%Ga-5%Mo/HZSM-5 catalyst. The catalytic activity over 5%Mo/HZSM-5 and 2%Ga-5%Mo/HZSM-5 catalyst revealed that 2%Ga-5%Mo/HZSM-5 leads to better methane conversion. This was attributed to aromatization property of gallium which facilitated the hydrogen transfer reaction with methane.

Critical Damkhöler number for the thermal decomposition of methane gas in a fluid-wall aerosol flow reactor

In this work, a theoretical analysis is carried out to predict the thermal decomposition of methane to hydrogen and carbon black occurring in a fluid-wall aerosol flow reactor. The mathematical formulation takes into account that the involved physical properties in the thermal decomposition process are temperature-dependent. The governing equations (mass, momentum, energy and species conservation) were nondimensionalized and simplified in order to be solved numerically. We show that the maximum conversion of methane to hydrogen occurs for a well-defined reactor length, which can be found in dimensionless form, as a characteristic Damkhöler number. This dimensionless parameter represents the competition between residence to reactive times and for the present formulation is an eigenvalue of the problem. In addition, the numerical results show that considering thermal-dependent properties modify the evolution of the thermal decomposition process in a substantial manner.

Methane steam reforming operation and thermal stability of new porous metal supported tubular palladium composite membranes

In 2009 cooperation between Plansee SE, Austria (PSE), Karlsruhe Institute of Technology, Germany (KIT) and the Engineering Division of Linde AG, Germany (LE) was set up with the aim to develop new tubular palladium composite membranes and a membrane reformer system for small scale on-site hydrogen production.This paper presents for the first time in detail KIT and LE laboratory results of the new membranes. They are composed of a porous metal support, a porous ceramic diffusion barrier and a dense Pd layer which was produced by physical vapor deposition (PVD) as an activation step and two additional methods: electroless plating (ELP) and electro plating (EP).Ideal H2/N2-permselectivities between 700 and almost 10,000 were measured at 600 °C and hydrogen transport kinetic parameters were determined for both membrane types. PVD/ELP-membranes reached a 15% higher H2-permeability than PVD/EP-membranes. Moreover, stability tests were carried out indicating that the membranes are resistant to temperature and feed gas changes, to thermal cycling in N2-atmosphere between room temperature and 650 °C, and to short-term high-temperature methane steam reforming (MSR) at 700 °C. Long-term operation for several hundred hours at realistic operating conditions proved that MSR can be performed without degradation of the membranes. Without optimizing membrane area versus feed load, a maximum methane conversion of 60% was achieved at a H2-recovery of 70% at 650 °C, 16 bar(a) and a S/C of 3 without the use of sweep gas.