Coupled Membrane Reactor Research Articles

Enhancement of simultaneous hydrogen production and methanol synthesis in thermally coupled double-membrane reactor

Coupling the methanol synthesis with the dehydrogenation of cyclohexane to benzene in a co-current flow, catalytic fixed-bed double-membrane reactor configuration in order to simultaneous pure hydrogen and methanol production was considered theoretically. The thermally coupled double-membrane reactor (TCDMR) consists of two Pd/Ag membranes, one for separation of pure hydrogen from endothermic side and another one for permeation of hydrogen from feed synthesis gas side (inner tube) into exothermic side. A steady-state heterogeneous model is developed to analyze the operation of the coupled methanol synthesis. The proposed model has been used to compare the performance of a TCDMR with conventional reactor (CR) and thermally coupled membrane reactor (TCMR) at identical process conditions. This comparison shows that TCDMR in addition to possessing advantages of a TCMR has a more favorable profile of temperature and increased productivity compared with other reactors. The influence of some operating variables is investigated on hydrogen and methanol yields. The results suggest that utilizing of this reactor could be feasible and beneficial. Experimental proof of concept is needed to establish the validity and safe operation of the recuperative reactor.

A comparison of hydrogen and methanol production in a thermally coupled membrane reactor for co-current and counter-current flows

This work considers three concentric tube reactors to prepare pure hydrogen, especially applicable in fuel cell technologies, with zero CO2 emission. Hydrogen and methanol production rates are compared in a thermally coupled exothermic and endothermic reactor for co-current and counter-current modes. Synthesis of methanol is coupled with dehydrogenation of cyclohexane as a high content hydrogen carrier (7.1 wt%). The efficient coupling of exothermic and endothermic reactions increases the profitability of operation of the reactor, reduces the size of reactor and decreases the operational and capital costs. By inserting a hydrogen-perm selective membrane into the reactor configuration, hydrogen can permeate selectively into the membrane, and hence, the third tube receives hydrogen. The simulation results are compared with the corresponded results for an industrial methanol fixed-bed reactor, which operates under the same feed conditions. The influence of some operating variables is investigated on methanol and hydrogen yields during the performance of reactor. The results show higher methanol conversion, as the same as conventional reactor, and hydrogen for co-current flow. Copyright © 2010 John Wiley & Sons, Ltd.

Multiobjective Optimization of a Porous Ceramic Membrane Reactor for Oxidative Coupling of Methane

Multiobjective optimization of a porous ceramic membrane reactor for oxidative coupling of methane has been studied with the elitist nondominated sorting genetic algorithm with jumping genes (NSGA-...

A novel configuration for hydrogen production from coupling of methanol and benzene synthesis in a hydrogen-permselective membrane reactor

Coupling energy intensive endothermic reaction systems with suitable exothermic reactions improve the thermal efficiency of processes and reduce the size of the reactors. One type of reactor suitable for such a type of coupling is the heat-exchanger reactor. In this work, a distributed mathematical model for thermally coupled membrane reactor that is composed of three sides is developed for methanol and benzene synthesis. Methanol synthesis takes place in the exothermic side and supplies the necessary heat for the endothermic dehydrogenation of cyclohexane reaction. Selective permeation of hydrogen through the Pd/Ag membrane is achieved by co-current flow of sweep gas through the permeation side. A steady-state heterogeneous model of the two fixed beds predicts the performance of this novel configuration. The co-current mode is investigated and the simulation results are compared with corresponding predictions for an industrial methanol fixed-bed reactor operated at the same feed conditions. The results show that although methanol productivity is the same as conventional methanol reactor, but benzene is also produced as an additional valuable product in a favorable manner, and auto-thermal conditions are achieved within the both reactors and also pure hydrogen is produced in permeation side. This novel configuration can increase the rate of methanol synthesis reaction and shift the thermodynamics equilibrium. The performance of the reactor is numerically investigated for various key operating variables such as inlet temperatures, molar flow rates of exothermic and endothermic streams, membrane thickness and sweep gas flow rate. The reactor performance is analyzed based on methanol yield, cyclohexane conversion and hydrogen recovery yield. The results suggest that coupling of these reactions in the presence of membrane could be feasible and beneficial. Experimental proof-of-concept is needed to establish the validity and safe operation of the novel reactor.

Oxidative coupling of methane using catalyst modified dense perovskite membrane reactors

A comparative study modifying an ionic oxygen conducting membrane reactor for the oxidative coupling of methane to higher hydrocarbons with 3 different catalytic surface modifications is presented. Dense Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCFO) membrane disks were wash-coated with a Pt/MgO model catalyst as well as with more efficient Sr/La 2O 3 and LaSr/CaO catalysts. The role of the catalyst is underlined by the fact that the LaSr/CaO shows that highest yield between 900 and 1000 °C while yields decline for the Sr/La 2O 3 catalyst at temperatures above 900 °C. The latter observation agrees well with observations on conventional catalytic reactors using hydrocarbon/oxygen co-feeding at lower temperature and seems to relate to the formation of highly reactive oxygen species formed at the La 2O 3 surface. Operating a LaSr/CaO modified membrane reactor at 950 °C with a CH 4 concentration of 34%, a C 2-hydrocarbon yield of more than 18% was achieved (at a selectivity of more than 65%). Given the interesting performance, it is obvious that future membrane reactors should employ efficient catalyst systems and development should focus on maximizing the exposure of catalytically modified membrane surfaces.

Modeling and simulation of methane steam reforming in a thermally coupled membrane reactor

A distributed mathematical model for thermally coupled membrane reactor that is composed of three channels is developed for methane steam reforming. Methane combustion takes place in the first channel on a Pt / δ – Al 2 O 3 catalyst layer that supplies the necessary heat for the endothermic steam reforming reaction. In the second channel, catalytic steam reforming reactions take place in the presence of Ni/MgO–Al 2O 3 catalyst. The combustion catalyst forms a thin layer next to the reactor wall to minimize the heat transfer resistance. Selective permeation of hydrogen through the palladium membrane is achieved either by co-current or counter-current flow of sweep gas through the third channel. The burner is modeled as a monolith reactor and the reformer is assumed to behave as a pseudo-homogenous reactor. The mass and energy balance equations for the thermally coupled membrane reactor form a set of 22 coupled ordinary differential equations. With the application of appropriate boundary conditions, the distributed reactor model for steady-state operation is solved as a boundary value problem. The model equations are discretized using spline collocation on finite elements. The discretized nonlinear modeling equations, along with the boundary conditions, form a system of algebraic equations that are solved using the trust region dogleg method. The performance of the reactor is numerically investigated for various key operating variables such as inlet fuel concentration, inlet steam/methane ratio, inlet reformer gas temperature and inlet reformer gas velocity. Simulations for both the co-current and the countercurrent flow modes are also performed using different sweep gas flow rates. For each case, the reactor performance is analyzed based on methane conversion and hydrogen recovery yield.

Oxidative Coupling of Methane in a Perovskite Hollow-Fiber Membrane Reactor

A La0.6Sr0.4Co0.2Fe0.8O3-α (LSCF) perovskite hollow-fiber membrane with an asymmetric structure has been prepared via a combined phase inversion/sintering technique where poly(ether sulfone) is employed as a polymeric binder, N-methyl-2-pyrrolidone as a solvent, and poly(vinylpyrrolidone) as an additive, respectively. The prepared LSCF hollow-fiber membranes are gastight and have been further fabricated into a hollow-fiber membrane reactor (HFMR) for oxidative coupling of methane (OCM). The experimental results indicate that the newly developed LSCF hollow-fiber membrane exhibits good oxygen permeation rate, methane conversion, and C2 yield compared to conventional disk-shaped membranes. A C2 yield of 15.3% with a corresponding selectivity of 43.8% has been achieved in the HFMR at 950 °C with feed flow rates of a CH4−Ar mixture and air of 17.2 and 32.9 cm3(STP)/min, respectively. The results further indicate that the operating temperature for OCM in the HFMR should not be higher than 950 °C. However, high...

Oxidative coupling of methane in Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ tubular membrane reactors

A dense membrane tube made of Ba 0.5Sr 0.5Co 0.8Fe 0.2O 3− δ (BSCF) was prepared by plastic extrusion from BSCF oxide synthesized by the complexing EDTA-citrate method. The membrane tube was used in a catalytic membrane reactor for oxidative coupling of methane (OCM) to C 2 without an additional catalyst. At high methane concentration (93%), about 62% C 2 selectivity was obtained, which is higher than that achieved in a conventional reactor using the BSCF as a catalyst. The dependence of the OCM reaction on temperature and methane concentration indicates that the C 2 selectivity in the BSCF membrane reactor is limited by high ion recombination rates. If an active OCM catalyst (La-Sr/CaO) was packed in the membrane tube, C 2 selectivity and CH 4 conversion increased compared to the blank run. The highest C 2 yield in the BSCF membrane reactor in presence of the La-Sr/CaO catalyst was about 15%, similar to that in a packed-bed reactor with the same catalyst under the same conditions. However, the ratio of C 2H 4/C 2H 6 in the membrane reactor was much higher than that in the packed-bed reactor, which is an advantage of the membrane reactor.

Oxygen-permeable dense membrane reactor for the oxidative coupling of methane

A perovskite material (BaCe 0.8Gd 0.2O 3) in powder form, with both electronic and ionic conductivity, was synthesized by the ethylene glycol method. A dense membrane tube was fabricated using a plastic extrusion technique. The oxygen permeances of the dense membrane tube were measured as functions of temperature and oxygen partial pressure on the feed side. In the temperature range of 688–955°C, the oxygen flux showed an approximately exponential dependence on temperature. The oxygen flux increased proportionally to the natural logarithm of the ratio of oxygen partial pressures across the membrane. Experimental results for the oxidative coupling of methane (OCM) to C 2 hydrocarbons, in the absence of additional catalyst, showed that this material has fairly good catalytic activity for the OCM reaction. The maximum yield to C 2 hydrocarbons that was obtained was 16%, which compares favorably to prior dense membrane studies.

Effect of the membrane activity on the performance of a catalytic membrane reactor

AbstractA mathematical model for a catalytic membrane reactor for oxidative coupling of methane (OCM), in which the membrane acts as an oxygen distributor to a bed of catalyst, is presented. From experimental data obtained using several silica membranes impregnated with Li and/or Na, which were prepared by the sol–gel method using alumina supports, the catalytic activity of the membrane was included in the so‐called real membrane reactor (RMR) model. Then, the RMR performance was compared with that of the ideal membrane reactor (IMR), whose membrane was supposed to have no activity for the OCM and with experimental data obtained in membrane reactors. Since the membrane activity was implemented in the RMR model, for the first time in the literature, maxima in the hydrocarbon selectivity–methane conversion curves were predicted in agreement with previous experimental trends. Besides, the IMR performance was compared with that of the fixed‐bed reactor (FBR), giving the maximum improvement of a membrane reactor over the FBR. Key factors for the future improvement of the performance in this kind of membrane reactor are deduced from these simulations.

Catalytic membrane reactor for oxidative coupling of methane. Part 1: preparation and characterisation of LaOC1 membranes

The sol-gel process was investigated in order to prepare LaOC1 inorganic membranes on commercial alumina tubular supports which were catalytically active for the oxidative coupling of methane. The preparation of LaOCI meso and microporous membranes is described on the basis of the fundamental phenomena occurring during the sol preparation and thermal treatment. Membranes were synthesised from LaC1 3 precursor in aqueous media. Important parameters, mastering the sol formation and consequently the final material textural characteristics, were the molar ratio [aceta]/La],[NH 3/La] and the total concentration of lanthanum in the sol. Without any acetate addition, turbid sols were obtained leading at 800°C to mesoporous membranes. The effect of acetate ions is shown to be of prime importance in order to limit the polycondensation reactions in the sol and to prepare microporous materials. Under these conditions, quite dense membranes were obtained at 200°C due to lanthanum acetate polymerisation. The formation of carbonates and their decomposition at 600°C explain the maximum micro-porosity observed at this temperature. When these membranes were treated at 800°C, the microporous volume decreased.

Catalytic membrane reactor for oxidative coupling of methane. Part II —Catalytic properties of LaOCl membranes

This work presents the potential of a LaOCI porous membrane reactor for the reaction of oxidative coupling of methane. The sol-gel method provided LaOCl membranes supported on alumina tubes which presented mesoporous texture. Actually, the severe operating conditions of this reaction caused textural instability which restricted any transport effects to the macroporous domain. However, despite moderate separation effects between methane and oxygen, beneficial effects of the membrane reactor have been observed, subject to surface composition, structural and feeding configuration requirements.

Simulation of a catalytic membrane reactor for oxidative coupling of Methane

There is considerable interest in direct and indirect conversion of methane to more valuable products such as basic feedstock and liquid fuel. However, total oxidation of methane leading to useless carbon dioxide and water is thermodynamically favored over the formation of ethane and ethylene, and in addition the desired C{sub 2} products tend to undergo further oxidation. Considerable efforts screening a large number of mainly metal oxide-based catalysts have been made to obtain a suitable one active and especially selective toward the desired C{sub 2} products, and the C{sub 2} yield of up to 30% has been reported. There are few studies regarding the potential advantages of using membrane reactors in the conversion of methane. The authors report here a simulation study showing that using a catalytic membrane reactor would greatly improve the selectivity and yield to C{sub 2} compounds, compared with the conventional cofeed operation.

Membrane reactor for oxidative coupling of CH4with an oxide ion–electron hole mixed conductor

A membrane reactor for the oxidative coupling of CH4 has been constructed with an oxide ion–electron hole mixed conductor, BaCe0.8Gd0.2O3–α. 10% CH4 diluted with Ar and an O2–Ar mixture at a given ratio were fed into opposite sides of the membrane at 1173 K. The formation rate of C2–hydrocarbons (ethane and especially ethene) in the CH4 compartment increased with Po2 in the O2–Ar compartment. This enhancement was due to electrochemical oxygen permeation, causing the conductor to short-circuit itself, resulting form the mixed conduction. For comparison, 10% CH4 and a small amount of O2 were co-fed into one side of the membrane. The membrane operation gave a C2 selectivity two times that of the co-feed operation for all CH4 conversions. From a catalytic study using BaCe1–xGdxO3 –α powders as catalyst, it was found that increasing both the oxide-ion and electron-hole conductivities enhanced the formation of C2 hydrocarbons, but reduced that of CO2. On the basis of these results, a mechanism for the oxidative coupling of CH4 of the mixed-conductor membrane was proposed.