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Methane Conversion (methane + conversion)
Selected AbstractsChemical-looping combustion process: Kinetics and mathematical modelingAICHE JOURNAL, Issue 4 2010Ion Iliuta Abstract Chemical Looping Combustion technology involves circulating a metal oxide between a fuel zone where methane reacts under anaerobic conditions to produce a concentrated stream of CO2 and water and an oxygen rich environment where the metal is reoxidized. Although the needs for electrical power generation drive the process to high temperatures, lower temperatures (600,800°C) are sufficient for industrial processes such as refineries. In this paper, we investigate the transient kinetics of NiO carriers in the temperature range of 600 to 900°C in both a fixed bed microreactor (WHSV = 2-4 g CH4/h/g oxygen carrier) and a fluid bed reactor (WHSV = 0.014-0.14 g CH4/h per g oxygen carrier). Complete methane conversion is achieved in the fluid bed for several minutes. In the microreactor, the methane conversion reaches a maximum after an initial induction period of less than 10 s. Both CO2 and H2O yields are highest during this induction period. As the oxygen is consumed, methane conversion drops and both CO and H2 yields increase, whereas the CO2 and H2O concentrations decrease. The kinetics parameter of the gas,solids reactions (reduction of NiO with CH4, H2, and CO) together with catalytic reactions (methane reforming, methanation, shift, and gasification) were estimated using experimental data obtained on the fixed bed microreactor. Then, the kinetic expressions were combined with a detailed hydrodynamic model to successfully simulate the comportment of the fluidized bed reactor. © 2010 American Institute of Chemical Engineers AIChE J, 2010 [source] Computational study of staged membrane reactor configurations for methane steam reforming.AICHE JOURNAL, Issue 1 2010Abstract This article and Part II report a computational study carried out to analyze the performance achievable using a staged membrane reactor in the methane steam reforming process to produce high purity hydrogen. A reaction/separation unit in which reactive stages are laid out in series to permeative stages already proposed in literature (Caravella et al., J Memb Sci. 2008;321:209,221) is modified here to increase its flexibility. The improvement includes the consideration of the Pd-based membrane along the entire length. Two- and ten-staged reactors are examined in terms of methane conversion, hydrogen recovery factor and hydrogen recovery yield, considering co- and counter-current flow configurations. Individual stage lengths are obtained by maximizing either methane conversion or hydrogen recovery yield, comparing the results to the ones of an equivalent traditional reactor and a conventional membrane reactor. The analysis allows demonstrating that the counter-current configuration leads to significant improvements in the hydrogen recovery, but proves almost irrelevant with respect to methane conversion. The influence of the number of stages and the amount of catalyst is quantified in the accompanying part II article. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] Computational study of staged membrane reactor configurations for methane steam reforming.AICHE JOURNAL, Issue 1 2010Abstract The present work complements part I of this article and completes a computational analysis of the performances of staged membrane reactors for methane steam reforming. The influence of the number of stages and catalyst amount is investigated by comparing the methane conversion and hydrogen recovery yield achieved by an equisized-staged reactor to those of an equivalent conventional membrane reactor for different furnace temperatures and flow configurations (co- and counter-current). The most relevant result is that the proposed configuration with a sufficiently high number of stages and a significantly smaller catalyst amount (up to 70% lower) can achieve performances very close to the ones of the conventional unit in all the operating conditions considered. This is equivalent to say that the staged configuration can compensate and in fact substitute a significant part of the catalyst mass of a conventional membrane reactor. To help the interpretation of these results, stage-by-stage temperature and flux profiles are examined in detail. Then, the quantification of the performance losses with respect to the conventional reactor is carried out by evaluating the catalyst amount possibly saved and furnace temperature reduction. © 2009 American Institute of Chemical Engineers AIChE J, 2010 [source] A C1 microkinetic model for methane conversion to syngas on Rh/Al2O3AICHE JOURNAL, Issue 4 2009Matteo Maestri Abstract A microkinetic model capable of describing multiple processes related to the conversion of natural gas to syngas and hydrogen on Rh is derived. The parameters of microkinetic models are subject to (intrinsic) uncertainty arising from estimation. It is shown that intrinsic uncertainty could markedly affect even qualitative model predictions (e.g., the rate-determining step). In order to render kinetic models predictive, we propose a hierarchical, data-driven methodology, where microkinetic model analysis is combined with a comprehensive, kinetically relevant set of nearly isothermal experimental data. The new, thermodynamically consistent model is capable of predicting several processes, including methane steam and dry reforming, catalytic partial oxidation, H2 and CO rich combustion, water-gas shift and its reverse at different temperatures, space velocities, compositions and reactant dilutions, using the measured Rh dispersion as an input. Comparison with other microkinetic models is undertaken. Finally, an uncertainty analysis assesses the effect of intrinsic uncertainty and catalyst heterogeneity on the overall model predictions. © 2009 American Institute of Chemical Engineers AIChE J, 2009 [source] Methane steam reforming at microscales: Operation strategies for variable power output at millisecond contact timesAICHE JOURNAL, Issue 1 2009Georgios D. Stefanidis Abstract The potential of methane steam reforming at microscale is theoretically explored. To this end, a multifunctional catalytic plate microreactor, comprising of a propane combustion channel and a methane steam reforming channel, separated by a solid wall, is simulated with a pseudo 2-D (two-dimensional) reactor model. Newly developed lumped kinetic rate expressions for both processes, obtained from a posteriori reduction of detailed microkinetic models, are used. It is shown that the steam reforming at millisecond contact times is feasible at microscale, and in agreement with a recent experimental report. Furthermore, the attainable operating regions delimited from the materials stability limit, the breakthrough limit, and the maximum power output limit are mapped out. A simple operation strategy is presented for obtaining variable power output along the breakthrough line (a nearly iso-flow rate ratio line), while ensuring good overlap of reaction zones, and provide guidelines for reactor sizing. Finally, it is shown that the choice of the wall material depends on the targeted operating regime. Low-conductivity materials increase the methane conversion and power output at the expense of higher wall temperatures and steeper temperature gradients along the wall. For operation close to the breakthrough limit, intermediate conductivity materials, such as stainless steel, offer a good compromise between methane conversion and wall temperature. Even without recuperative heat exchange, the thermal efficiency of the multifunctional device and the reformer approaches ,65% and ,85%, respectively. © 2008 American Institute of Chemical Engineers AIChE J, 2009 [source] Catalytic Effects of Metals on the Conversion of Methane in Gliding DischargesPLASMA PROCESSES AND POLYMERS, Issue 7-8 2007Krzysztof Schmidt-Sza, owski Abstract Plasma-catalytic methane conversion was studied under gliding-discharge conditions using a mobile (spouted) catalytic bed of fine particles. A new model of the GD reactor was tested for the non-oxidative methane coupling using alumina-supported catalysts containing Cu, Ni, Ag or Pt resistant against the plasma action. C2 hydrocarbons, besides hydrogen, were the main products, with some amounts of non-volatile substances (mainly soot). With Cu/Al2O3, Ni/Al2O3, Ag/Al2O3, and alumina beds, acetylene was mainly produced from the CH4,+,H2 mixture with none or a minor share of other C2 hydrocarbons. Using Pt/Al2O3, an increased ethylene and ethane content was found with lower acetylene content. [source] Oxidative Coupling of Methane in a Negative DC Corona Reactor at Low TemperatureTHE CANADIAN JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2003Faezeh Bagheri-Tar Abstract Oxidative coupling of methane (OCM) in the presence of DC corona is reported in a narrow glass tube reactor at atmospheric pressure and at temperatures below 200°C. The corona is created by applying 2200V between a tip and a plate electrode 1.5 mm apart. The C2 selectivity as well as the methane conversion are functions of methane-to-oxygen ratio, gas residence time, and electric current. At CH4/O2 ratio of 5 and the residence time of about 30 ms, a C2 yield of 23.1% has been achieved. The main products of this process are ethane, ethylene, acetylene as well as CO and CO2 with CO/CO2 ratios as high as 25. It is proposed that methane is activated by electrophilic oxygen species to form methyl radicals and C2 products are produced by a consecutive mechanism, whereas COx is formed during parallel reactions. On décrit le couplage oxydant du méthane (OCM) en présence d'une couronne CC dans un réacteur tubulaire étroit en verre à la pression atmosphérique et à des températures en dessous de 200°C. La couronne est créée en appliquant 2200 V entre une pointe et une électrode plate distantes de 1,5 mm. La sélectivité du C2 ainsi que la conversion du méthane sont des fonctions du rapport méthane-oxygène, du temps de séjour du gaz et du courant électrique. À un rapport de CH4/O2 de 5 et un temps de séjour d'environ 30 ms, un rendement de C2 de 23,1 % est obtenu. Les principaux produits de ce procédé sont l'éthane, l'éthylène, l'acétylène, ainsi que le CO et le CO2 avec des rapports de CO/CO2 aussi élevés que 25. On propose l'idée que le méthane est activé par des espèces d'oxygène électrophiles pour former des radicaux de méthyle et que les produits du C2 sont produits par un mécanisme consécutif, tandis que les COx se forment lors de réactions parallèles. [source] Solar membrane natural gas steam-reforming process: evaluation of reactor performanceASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010M. De Falco Abstract In this work, the performance of an innovative plant for efficient hydrogen production using solar energy for the process heat duty requirements has been evaluated via a detailed 2D model. The steam-reforming reactor consists of a bundle of coaxial double tubes assembled in a shell. The annular section of each tube is the reaction zone in which Ni-based catalyst pellets are packed, whereas the inner tube is a dense Pd-based selective membrane that is able to remove hydrogen from the reaction zone. By coupling reaction and hydrogen separation, equilibrium constrains inside the reactor are circumvented and high methane conversions at relatively low temperatures are achieved. The heat needed for the steam-reforming reaction at this low operating temperature can be supplied by using a molten salt stream, heated up to 550 °C by a parabolic mirror solar plant, as heating fluid. The effects on membrane reactor performance of some operating conditions, as gas mixture residence time, reaction pressure and steam-to-carbon ratio, are assessed together with the enhancement of methane conversion with respect to the traditional process, evaluated in the range 40.5,130.9% at the same operating conditions. Moreover, owing to the use of a solar source for chemical process heat duty requirements, the greenhouse gases (GHG) reduction is estimated to be in the range 33,67%. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of surface defects in Pd-based membranes on the performance of a membrane reactorASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010Alessio Caravella Abstract In this work, the influence of superficial defects over the surface of a Pd-based membrane is analyzed in a membrane reactor for the methane steam-reforming process. In order to include the presence of defects in the permeation, a previous model of a defect-free Pd-based membrane reactor is extended and integrated to include a variable portion of area with defects in the form of pinholes. As a consequence, two different permeation mechanisms are taken into account, one through the Pd-based surface and the other one through the pinholes, where a Knudsen-like transport is considered to occur. The presence of the Knudsen transport causes the membrane separation factor between the hydrogen and the other species involved in the process to decrease, affecting the reactor performances significantly. Three reactor performance indices are investigated as functions of the fraction of the defected area and the mean pore diameter of defects, namely methane conversion, the hydrogen recovery factor, the hydrogen recovery yield and the net purity of hydrogen in the permeate. The results show that the hydrogen recovery factor is positively influenced by the decrease in hydrogen selectivity, whilst methane conversion and hydrogen net purity decrease significantly with it. On the contrary, regarding the hydrogen recovery yield, it is shown that in certain conditions (low furnace temperature, , 550 °C) it decreases with hydrogen selectivity. However, it increases again at higher furnace temperatures (,650 °C). Globally, this investigation helps in identifying acceptable defect levels on a Pd-based membrane for methane steam-reforming applications and highlights that even a very small defect level (in terms of the pinhole diameter and/or amount of the defected area) can importantly compromise the reactor performances. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Reformer and membrane modules plant to optimize natural gas conversion to hydrogenASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 3 2009M. De Falco Abstract Membrane technology may play a crucial role in the efficient production of hydrogen from natural gas and heavy hydrocarbons. The present work assesses the performance of a hydrogen production plant utilizing by reformer and membrane modules (RMM), by which the hydrogen produced in reaction units is separated by Pd-based membranes. A major advantage of RMM architecture is the shift of chemical equilibria favoring hydrogen production due to the removal of hydrogen through membranes at each reaction step, thus improving hydrogen yield while simultaneously allowing methane conversion at temperatures below 650 °C. Lower operating temperatures allow location of the modules downstream of a gas turbine, achieving an efficient hybrid system producing electric power and hydrogen with a significant reduction in energy consumption of approximately 10% relative to conventional systems. Fundamental concepts are analyzed and integrated into a process scheme. Effects of variables including reactor temperature outlet, steam-to-carbon ratio and recycle ratio throughout pinch and sensitivity analysis are described. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] Effect of Oxygen on Methane Steam Reforming in a Sliding Discharge ReactorCHEMICAL ENGINEERING & TECHNOLOGY (CET), Issue 5 2006F. Ouni Abstract Hydrogen-rich gas can be efficiently produced in compact plasma reformers by the conversion of a variety of hydrocarbon fuels, including natural gas and gasoline. This article describes experimental and modeling progress in plasma reforming of methane using a sliding discharge reactor (SDR). Experiments have been carried out in a compact device operating at low consumed power (1,2,kW). Previous studies of methane steam reforming using a SDR at atmospheric pressure show promising results (H2 concentration higher than 55,%). In order to study the effect of oxygen on the methane conversion and thus hydrogen production, a small amount of oxygen in the range of 7,20,% was added to the CH4 -H2O mixture. An unexpected result was that under our experimental conditions in the SDR oxygen did not have any influence on the methane conversion. Almost the totality of added oxygen is recovered intact. Moreover, part of the H2 produced was transformed into water by reaction with O2. A model describing the chemical processes based on classical thermodynamics is also proposed. The results indicate that the reactor design has to be improved in order to increase conversion and hydrogen production. [source] Solar membrane natural gas steam-reforming process: evaluation of reactor performanceASIA-PACIFIC JOURNAL OF CHEMICAL ENGINEERING, Issue 1 2010M. De Falco Abstract In this work, the performance of an innovative plant for efficient hydrogen production using solar energy for the process heat duty requirements has been evaluated via a detailed 2D model. The steam-reforming reactor consists of a bundle of coaxial double tubes assembled in a shell. The annular section of each tube is the reaction zone in which Ni-based catalyst pellets are packed, whereas the inner tube is a dense Pd-based selective membrane that is able to remove hydrogen from the reaction zone. By coupling reaction and hydrogen separation, equilibrium constrains inside the reactor are circumvented and high methane conversions at relatively low temperatures are achieved. The heat needed for the steam-reforming reaction at this low operating temperature can be supplied by using a molten salt stream, heated up to 550 °C by a parabolic mirror solar plant, as heating fluid. The effects on membrane reactor performance of some operating conditions, as gas mixture residence time, reaction pressure and steam-to-carbon ratio, are assessed together with the enhancement of methane conversion with respect to the traditional process, evaluated in the range 40.5,130.9% at the same operating conditions. Moreover, owing to the use of a solar source for chemical process heat duty requirements, the greenhouse gases (GHG) reduction is estimated to be in the range 33,67%. Copyright © 2009 Curtin University of Technology and John Wiley & Sons, Ltd. [source] | ||||||||||