METHANE COUPLING USING CATALYTIC MEMBRANE REACTORS

The purpose of this review article is to provide readers with an extensive account on methane-coupling reactions performed in membrane reactors available in literature up to 2000. The principles, advantages or disadvantages, and crucial problems of all kinds of membrane reactors used in methane coupling are discussed. Some areas such as solid oxide membrane reactors for methane oxidative coupling are treated less extensively, as it has always been reviewed by other researchers. More emphasis has been placed in catalytic proton or mixed proton and electron-hole conducting membrane reactors, as they have greater potentials and have received less attention in the literature.     

Design of mixed conducting ceramic membranes/reactors for the partial oxidation of methane to syngas

The performance of mixed conducting ceramic membrane reactors for the partial oxidation of methane (POM) to syngas has been analyzed through a two‐dimensional mathematical model, in which the material balance, the heat balance and the momentum balance for both the shell and the tube phase are taken into account. The modeling results indicate that the membrane reactors have many advantages over the conventional fixed bed reactors such as the higher CO selectivity and yield, the lower heating point and the lower pressure drop as well. When the methane feed is converted completely into product in the membrane reactors, temperature flying can take place, which may be restrained by increasing the feed flow rate or by lowering the operation temperature. The reaction capacity of the membrane reactor is mainly determined by the oxygen permeation rate rather than by the POM reaction rate on the catalyst. In order to improve the membrane reactor performance, reduction of mass transfer resistance in the catalyst bed is necessary. Using the smaller membrane tubes is an effective way to achieve a higher reaction capacity, but the pressure drop is a severe problem to be faced. The methane feed velocity for the operation of mixed conducting membrane reactors should be carefully regulated so as to obtain the maximum syngas yield, which can be estimated from their oxygen permeability. The mathematical model and the kinetic parameters have been validated by comparing modeling results with the experimental data for the La_0.6Sr_0.4Co_0.2Fe_0.8O_3‐α (LSCF) membrane reactor. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

The effects of kinetics, hydrodynamics and feed conditions on methane coupling using fluidized bed reactor

A previously developed model describing bubbling fluidized bed reactors is used in this investigation to study the effect of various important hydrodynamic, operating and design parameters on the performance of a large scale fluidized bed reactor used in oxidative coupling of methane. Three kinetic schemes obtained from the literature have been used in this study. The model predicted fairly well the experimental results reported recently under different reaction conditions. The simulation results revealed that increasing the ratio of methane to oxygen in the feed leads to lower methane conversion but higher C₂ selectivity. As the ratio is decreased the system loses its fixed-point stability to a periodic stability. Higher methane conversion and product selectivity are obtained upon decreasing the feed flow rate and particle diameter.     

Solid electrolyte membrane reactors: Status and trends

A survey of recently published research work on solid electrolyte (SE) membrane reactors is given, with focus on high-temperature oxygen ion conductors, high-temperature proton conductors and low-temperature proton conductors. In these three material classes, the current status and the future trends of membrane reactor development are briefly elucidated. SE membrane reactor principles are realized in gas sensors, fuel cells, electrolyzers and reactors for partial oxidation. In all these fields SE membranes are in contact with porous electrolyte layers at which anodic or cathodic electrochemical reactions take place. In the area of membrane reactors using high-temperature oxygen ion conductors, there is a trend towards lower operating temperatures on order to ensure stable long-term operation of the membrane materials, and to match the optimal temperature window of the applied catalysts. As a younger generation of ion conducting ceramics, high-temperature proton conductors offer new possibilities for the implementation of electrochemical membrane reactors. Finally, current trends in the application of low-temperature proton conductors being based on polymeric materials are discussed. These materials can not only be used for fuel cells but also as membranes in hydrogenation or oxidation reactors.     

Application of membrane separation processes in petrochemical industry: a review

In this paper a general review on different membrane processes and membrane reactors was done. As the main aim of this paper is to review the application of membrane processes in petrochemical industry, processes such as olefin/paraffin separation, light solvent separation, solvent dewaxing, phenol and aromatic recovery, dehydrogenation, oxidative coupling of methane and steam reforming of methane were discussed in detail. Besides, separation using polymer-inorganic nano composite membranes and wastewater treatment using membrane bio-reactors were reviewed.     

Reaction engineering studies of methane coupling in fluidised-bed reactors

The oxidative coupling of methane has been conducted in 30 and 60mm dia. fluidised-bed reactors. Methane conversions as high as 40% were achieved at isothermal conditions using methane/oxygen mixtures without diluents. At the same contact time the two reactors had similar selectivities to hydrocarbons. At 850°C the hydrocarbon selectivity decreased dramatically with increasing contact time but this effect was much less severe at lower temperatures. Axial gas concentration profiles through the catalyst bed in the 60mm reactor indicated that at 850°C there was a rapid consumption of oxygen and formation of products in the bottom section of the bed followed by a net loss of hydrocarbon in the oxygen-free zone. This loss was due to carbon formation on the catalyst which was circulated back to the oxygen-containing zone of the bed where the carbon was combusted.     

A hybrid adsorbent-membrane reactor (HAMR) system for hydrogen production

Design characteristics and performance of a novel reactor system, termed a hybrid adsorbent-membrane reactor (HAMR), have been investigated for hydrogen production. The recently proposed HAMR concept couples reactions and membrane separation steps with adsorption on the membrane feed-side or permeate-side. Performance of conventional reactors has been significantly improved by this integrated system. In this paper, an HAMR system has been studied involving a hybrid-type packed-bed catalytic membrane reactor undergoing methane steam reforming through a porous ceramic membrane with a CO₂ adsorption system. This HAMR system is of potential interest to pure hydrogen production for fuel cells for various mobile and stationary applications. Reactor behaviors have been investigated for a range of temperature and pressure conditions. The HAMR system shows enhanced methane conversion, hydrogen yield, and product purity, and provides good promise for reducing the hostile operating conditions of conventional reformers, and for meeting the product purity requirements.     

Oxyfuel combustion using a catalytic ceramic membrane reactor

Membrane catalytic combustion (MCC) is an environmentally friendly technique for heat and power generation from methane. This work demonstrates the performances of a MCC perovskite hollow fibre membrane reactor for the catalytic combustion of methane. The ionic–electronic La_0.6Sr_0.4Co_0.2Fe_0.8O₃₋ (LSCF6428) mixed conductor, in the form of an oxygen-permeable hollow fibre membrane, has been prepared successfully by means of a phase-inversion spinning/sintering technique. For this process polyethersulfone (PESf) was used as a binder, N-methyl-2-pyrrollidone (NMP) as solvent and polyvinylpyrrolidone (PVP, K16-18) as an additive. With the prepared LSCF6428 hollow fibre membranes packed with catalyst, hollow fibre membrane reactors (HFMRs) have been assembled to perform the catalytic combustion of methane. A simple mathematical model that combines the local oxygen permeation rate with approximate catalytic reaction kinetics has been developed and can be used to predict the performance of the HFMRs for methane combustion. The effects of operating temperature and methane and air feed flow rates on the performance of the HFMR have been investigated both experimentally and theoretically. Both the methane conversion and oxygen permeation rate can be improved by means of coating platinum on the air side of the hollow fibre membranes.     

MODELING AND SIMULATION OF A NONISOTHERMAL CATALYTIC MEMBRANE REACTOR

A two-dimensional nonisothermal mathematical model has been developed to simulate a tube-and-shell configuration, catalytic membrane reactor. The three-layer membrane consists of an inert large-pore support, an o₂ semipermeable dense perovskite layer and a porous catalytic layer. The model is applied to the simulation of the partial oxidation or methane to syngas (oxyreforming). The membrane reactor simultaneously supplies oxygen to the catalytic reaction along the reactor length, and separates oxygen from the air feed, using a dense perovskite layer which is a mixed conductor, thus allowing rapid oxygen permeation without the use of an external circuit. Two configurations of catalytic membrane reactors are simulated, for both bench-scale and industrial-scale conditions. Comparisons are made to the conventional fixed-bed reactor, and to membrane reactors which are isothermal, adiabatic or wall-cooled. The simulation results imply that the temperature rise in exothermic partial oxidation reactions may be mitigated substantially by the use of a dense membrane reactor,     

Advanced reactor concepts for oxidative coupling of methane

Oxidative coupling of methane (OCM) has been investigated as an interesting way to obtain higher hydrocarbons from natural gas. The aim of this article is to evaluate the reactor concepts for oxidative coupling of methane, from the 1980s through the current state of the art, giving a general insight into the reactor engineering possibilities and perspectives of application of OCM in large scale reactors. The concepts were classified according to the type of reactor bed, the heat management system, the oxygen feeding policy, the degree of integration with separation units, the relative cost, and the current demonstration on industrial scale.     

Catalytic Membrane Reactors – Lab Curiosity or Key Enabling Technology?

Two industrially interesting partial oxidations have been performed in catalytic membrane reactors with oxygen‐transporting membrane: aromatization of natural gas and oxidation of ammonia to nitric oxide. In both reactions, the oxygen used has been separated from air through a perovskite membrane, which also is the catalyst for the ammonia oxidation. When conducting the methane aromatization in an oxygen‐transporting membrane reactor, coke deposition is reduced and the aromatics yield is higher than that of a reference non‐oxidative fixed‐bed reactor.     

Conversion of methane through dielectric-barrier discharge plasma

Methane coupling to produce C₂ hydrocarbons through a dielectric-barrier discharge (DBD) plasma reaction was studied in four DBD reactors. The effects of high voltage electrode position, different discharge gap, types of inner electrode, volume ratio of hydrogen to methane and air cooling method on the conversion of methane and distribution of products were investigated. Conversion of methane is obviously lower when a high voltage electrode acts as an outer electrode than when it acts as an inner electrode. The lifting of reaction temperature becomes slow due to cooling of outer electrode and the temperature can be controlled in the expected range of 60°C–150°C for ensuring better methane conversion and safe operation. The parameters of reactors have obvious effects on methane conversion, but it only slightly affects distribution of the products. The main products are ethylene, ethane and propane. The selectivity of C₂ hydrocarbons can reach 74.50% when volume ratio of hydrogen to methane is 1.50.     

The use of OCM reactors for ignition enhancement of natural gas combustion for practical applications: Reactor design aspects

The major goal of the study is the improvement of the ignition characteristics of lean, premixed natural gas (NG) combustion under engine-like conditions. A new process is investigated involving the oxidative coupling of methane reaction (OCM) for the in situ production of C₂ hydrocarbons to be used as ignition enhancers during lean combustion of methane in internal combustion (IC) engines. Addition of the OCM product mixture enhances the ignition characteristics of lean methane/air mixtures, the beneficial effect resulting from the C₂H₄/C₂H₆ components. OCM in both conventional plug flow and packed-bed membrane reactors is modelled and optimised with respect to reactor conditions and ignition characteristics. An additional ignition technique that includes flowing a jet of a fuel/air stream against a hot inert surface has been implemented for quantifying the effect of the proposed ignition enhancers.     

固体电解质电化学反应器中甲烷氧化偶联反应的模拟

建立了固体电解质电化学反应器的数学模型,采用修正的Newton-Raphson法求解模型方程.利用该模型对以质量浓度为1%Sr/La_2O_3-Ag为催化电极的固体电解质电化学反应器中的电能与目的产物乙烯、乙烷共生进行了研究.考察了外加负载、反应温度、进料组成等因素对甲烷氧化偶联(OCM)反应和输出电流的影响,并将计算结果与实验结果进行了比较,得到了令人满意的结果.     

Li~+/MgO上交叉偶联作用的研究

采用Li+/MgO催化剂研究了Li含量、反应温度、原料气组成对甲烷和甲苯催化氧化交叉偶联成乙苯或苯乙烯 (即C8)反应的影响 ,对几种Li含量催化剂上各影响因素引起的差异进行了考察。结果表明 ,其活性中心也主要是Li+O- ,合适的L酸点是本交叉偶联反应中反应物的吸附中心 ,Li+O- 和L酸点是决定偶联反应产物C2 和C8的主要因素。偶联可能主要按游离基机理进行     

膜催化技术用于甲烷转化反应的研究进展

介绍了膜催化技术在甲烷转化反应中的应用,这些过程包括甲烷氧化偶联反应制乙烯,甲烷部分氧化制甲醇,甲烷水蒸气重整制合成气等,通过膜催化反应与传统催化反应的比较,揭示了膜催化技术的优点。     

Optimal conditions of isobutane dehydrogenation in radial flow moving bed hydrogen-permselective membrane reactors to enhance isobutene and hydrogen production

In the isobutane dehydrogenation process, coupling reaction and separation and optimization of the intensified process can improve the isobutane conversion and selectivity, reduce operational costs and lets to produce pure hydrogen. In this research, the radial flow moving bed reactors in the Olefex technology have been supported by Pd–Ag membrane plate to remove hydrogen from the reaction zone. The reactions occur in the tube side and the hydrogen is permeated from the reaction zone to the sweep gas stream. The proposed configuration has been modeled heterogeneously based on the mass and energy conservation laws considering reaction networks. To prove the accuracy of the considered model, the simulation results of the conventional process have been compared against available plant data. The Genetic algorithm as an effective method in the global optimization has been considered to optimize the operating condition of membrane reactors to enhance isobutene productivity. In this optimal configuration, the isobutene production has been enhanced about 3.7%.     

Process intensification aspects for steam methane reforming: An overview

Steam methane reforming (SMR) is the most widely used process in industry for the production of hydrogen, which is considered as the future generation energy carrier. Having been perceived as an important source of H₂, there are abundant incentives for design and development of SMR processes mainly through the consideration of process intensification and multiscale modeling; two areas which are considered as the main focus of the future generation chemical engineering to meet the global energy challenges. This article presents a comprehensive overview of the process integration aspects for SMR, especially the potential for multiscale modeling in this area. The intensification for SMR is achieved by coupling with adsorption and membrane separation technologies, etc., and using the concept of multifunctional reactors and catalysts to overcome the mass transfer, heat transfer, and thermodynamic limitations. In this article, the focus of existing and future research on these emerging areas has been drawn. © 2009 American Institute of Chemical Engineers AIChE J, 2009     

致密透氧膜用于甲烷部分氧化制合成气的实验研究

引　言钙钛矿型致密透氧膜在高温下具有氧离子、电子混合导电性 .当膜两侧存在氧分压梯度时 ,高压侧的氧在膜表面经化学吸附解离成氧离子、电子 ,于膜主体内扩散至另一侧 ,并重新结合、脱附至低氧压体系 .将致密透氧膜反应器用于甲烷部分氧化制合成气反应为天然气利用开辟了一条崭新的路径 ,近年来受到普遍关注 .该过程集空分与反应于一体 ,降低了大量的操作成本 ,通过膜壁控制氧气的进料有效控制了反应进程 .提高膜的透氧量 ,解决还原性气氛下膜的稳定性等问题 ,是该过程实现工业化的关键 .Ｂａｌａｃｈａｎｄｒａｎｄ[1] 、Ｔｓａｉ[2 ] …