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.     

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 ] …     

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     

Transient behaviour of dense catalytic membranes based on Cu- and Co-doped Bi4V2O11 (BIMEVOX) in the oxidation of propene and propane

ME-doped γ-Bi₄V₂O₁₁ (BIMEVOX) oxides are highly oxide ion conducting materials and this property may be profitably used in selective oxidation of hydrocarbons. The catalytic properties of BICUVOX and BICOVOX when shaped as dense membranes displayed in catalytic dense membrane reactor are examined in the oxidation of propene and of propane. Mirror-polished BICUVOX and BICOVOX membranes studied previously were poorly active for propene oxidation because of a small number of active sites but showed an excellent stability and reproducibility (lasting more than 1 month) during which products of mild oxidation (acrolein, hexadiene) and CO were formed. Membranes with depolished surfaces exhibit high conversions of propene (up to 60 mol%), and also of propane (up to 20 mol%) but – contrary to mirror-polished membranes – a complex transient behaviour is observed during which syngas production occurs. The membrane polarisation followed by in situ solid electrolyte potentiometry shows that the oxygen reservoir is far higher than expected on the reaction side which is separated (by the membrane) from the oxidising side where (diluted) oxygen is reduced to O²⁻ specie. The influence of oxygen partial pressure on the catalytic performance suggests that the electronic conductivity of the material is limiting the oxygen flux through the membrane, and thus is determining the catalytic properties and transient behaviours of depolished membranes.     

Zeolites-catalyzed Alkylation of Isobutane with 2-butene: Influence of Acidic Properties

Mixed-conducting SrFe_0.7Al_0.3O_3- (SFA) exhibits substantial catalytic activity towards partial oxidation of methane and can thus be considered as a component of monolithic ceramic reactors for synthesis gas generation, where the dense membrane and porous catalyst at the permeate-side surface are made of similar compositions. Surface modification of SFA powder and membranes with Pt has no essential effect on the performance of a model reactor, suggesting that the catalytic behavior of SFA is mainly determined by the surface states of iron and oxygen ions in the catalyst. The Mössbauer spectroscopy shows that reduction of SrFe_0.7Al_0.3O_3-, having cubic perovskite lattice in air, leads to the co-existence of perovskite- and brownmillerite-like domains, whilst the concentrations of metallic Fe and even Fe²⁺ under typical operation conditions are lower than the detection limits. The amount of vacancy-ordered phase increases with decreasing oxygen content, the estimations of which were confirmed by coulometric titration data. The catalytic activity of ferrite-based materials may thus be associated with lattice instability characteristic of morphotropic phase transformations.     

Nanostructured catalytic membrane reactors of the new generation

Studied in this work were the industrially important processes (partial oxidation of methane, oxidation of methanol to formaldehyde, reduction of oxygen in aqueous media, oxidation of CO to CO₂) involving the use of nanostructured catalytic membrane reactors of the new generation. The membrane reactors were prepared according to various methods: sol-gel, molecular layering, magnetron sputtering, chemical deposition, etc. Subject to study were also the structure of the catalytic membranes and the kinetics of the reactions occurring in the gaseous and liquid phases. It was demonstrated that the deposition of a nanostructured catalytic layer to nonselective porous membranes could give rise to, or enhance, the selectivity of both their gas permeability and catalytic activity. In the case of the application of hybrid membranes, an “asymmetry effect” was discovered and explained. Some of the membranes studied can be considered as specific nanoreactors.     

Analysis of oxygen permeation through dense ceramic membranes with chemical reactions of finite rate

The oxygen permeation through oxygen ionic or mixed-conducting ceramic membranes under reaction conditions was examined with a model taking into account of different electrical transport mechanisms (p-type and n-type transports) and finite reaction rate. It was demonstrated that with a reaction consuming oxygen in one side of the membrane, the oxygen partial pressure in the reaction side decreases and the oxygen permeation flux increases with the increase in the reaction rate for both the p-type and the n-type transport dominated mechanism. The increase in reaction rate causes a transition of the transport mechanism from p-type to n-type. This transition leads to an increase in the permeation flux by up to 30 times. This effect offers one explanation for the large discrepancies in published permeation data for membrane reactors of partial oxidation reaction employing an oxygen permeable dense ceramic membrane. For a membrane with a specific transport mechanism, the increase in the reactant partial pressure causes an increase in the reaction rate and oxygen permeation flux. However, the increase in the inlet inert gas amount has a complicated effect on the oxygen permeation flux because it lowers both oxygen partial pressure and the reaction rate at the same time.     

钙钛矿型致密膜透氧过程的模拟研究

由于钙钛矿型致密膜的透氧机理十分复杂,影响因素较多,因此对过程进行数学模拟是实现其工业化应用的一个重要步骤,本文将影响其高温透氧过程的主体扩散和表面交换反应有机结合起来,同时考虑膜表面气固相交界层内的传递阻力,建立了钙钛矿型致密膜透氧过程的数学模型,并对模型的适用范围进行了理论分析,以便为钙钛矿型致密膜透氧过程的实验研究提供前瞻性预测。     

New Integrated Catalytic Membrane Processes for Enhanced Propylene and Polypropylene Production

Newly reported integrated processes are discussed for aliphatic (paraffin) hydrocarbon dehydrogenation into olefins and subsequent polymerization into polyolefins (e.g., propane to propylene to polypropylene, ethane to ethylene to polyethylene). Catalytic dehydrogenation membrane reactors (permreactors) made by inorganic or metal membranes are employed in conjunction with fluid bed polymerization reactors using coordination catalysts. The catalytic propane dehydrogenation is considered as a sample reaction in order to design an integrated process of enhanced propylene polymerization. Related kinetic experimental data of the propane dehydrogenation in a fixed bed type catalytic reactor is reviewed which indicates the molecular range of the produced C₁-C₃ hydrocarbons. Experimental membrane reactor conversion and yield data are also reviewed. Experimental data were obtained with catalytic membrane reactors using the same catalyst as the non-membrane reactor. Developed models are discussed in terms of the operation of the reactors through computational simulation, by varying key reactor and reaction parameters. The data show that it is effective for catalytic permreactors to provide streams of olefins to successive polymerization reactors for the end production of polyolefins (i.e., polypropylene, polyethylene) in homopolymer or copolymer form. Improved technical, economic, and environmental benefits are discussed from the implementation of these processes.     

A novel porous‐dense dual‐layer composite membrane reactor with long‐term stability

A porous‐dense dual‐layer composite membrane reactor was proposed. The dual‐layer composite membrane composed of dense 0.5 wt % Nb₂O₅‐doped SrCo_0.8Fe_0.2O_3‐δ (SCFNb) layer and porous Ba_0.3Sr_0.7Fe_0.9Mo_0.1O_3‐δ (BSFM) layer was prepared. The stability of SCFNb membrane reactor was improved significantly by the porous‐dense dual‐layer design philosophy. The porous BSFM surface‐coating layer can effectively reduce the corrosion of the reducing atmosphere to the membrane, whereas the dense SCFNb layer permeated oxygen effectively. Compared with single‐layer dense SCFNb membrane reactor, no degradation of performance was observed in the dual‐layer membrane reactor under partial oxidation of methane during continuously operating for 1500 h at 850°C. At 900°C, oxygen flux of 18.6 mL (STP: Standard Temperature and Pressure) cm^?2 min^?1, hydrogen production of 53.67 mL (STP) cm^?2 min^?1, CH₄ conversion of 99.34% and CO selectivity of about 94% were achieved. © 2013 American Institute of Chemical Engineers AIChE J, 59: 4355–4363, 2013     

Modellbildung und Rechnersimulation als Werkzeug der sicheren Reaktionsführung

Model formation and computer simulation as tools for safe reaction engineering . The possibilities and problems of the simulation of the transient operating behaviour of reactors are discussed for the example of a catalytic fixed bed reactor. A survey of the development of mathematical models for the study of reactor stability and dynamics and a terse discussion of problems of digital calculation of model equations are followed by three examples of the application of available methods in practice: an example of section-wise temperature profile control and two examples of the study of the dynamics and control of cooled tube bank reactors for partial oxidation reactions.     

SrFe0.6Cu0.3Ti0.1O3-δ透氧膜反应器中甲烷部分氧化反应工艺及膜稳定性考察

采用SrFe_0.6Cu_0.3Ti_0.1O_3-δ混合导体透氧膜组装成膜催化反应器,进行甲烷部分氧化制合成气反应,考察了反应温度、空速、催化剂粒径等条件的影响,并分析了反应气氛引起的透氧膜结构变化情况。结果表明,在膜反应器内,催化反应与透氧过程存在相互制约和相互促进的关系。在膜反应器内进行甲烷部分氧化反应后,透氧膜的两侧表面均发生蚀刻现象,结晶度显著降低,反应侧蚀刻现象较为严重,膜表面形成了疏松的多孔层,反应气氛使膜表面晶体结构发生了较大改变,Sr容易从钙钛矿结构中析出并与CO₂结合形成SrCO₃,Sr的析出导致组成不平衡,促进了钙钛矿结构分解及其他物相的产生。     

Catalytic dense membranes of doped Bi4V2O11 (BIMEVOX) for selective partial oxidation: chemistry of defects versus catalysis

A catalytic dense membrane reactor (CDMR) is used to physically separate the reaction step from the reoxidation of the catalyst. By decoupling the redox mechanism prevailing in mild oxidation of hydrocarbons, the operating conditions may be optimized resulting in an increase of selectivity. The membranes are made up of BIMEVOX oxides, obtained by partial substitution of V in γ-Bi₄V₂O₁₁ by ME (Co, Cu, Ta). Experiments performed on BIMEVOX dense membranes using propene and propane are described in terms of, (i) active sites on polished or unpolished surfaces, (ii) operating conditions (T, pO₂ in the high oxygen partial pressure compartment), which determine the selectivity, either to mild oxidation products (acrolein, hexadiene, CO), or to partial oxidation products (CO, H₂), and, (iii) nature of ME cations and relative properties. The discussion deals with the respective role of electronic versus oxide ion conductivities which depend on defects in the structure as well as on the redox properties of cations.     

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.     

Catalytic wet oxidation of phenol using membrane reactors: A comparative study with slurry-type reactors

The wet air oxidation of phenol over cerium mixed oxides has been carried in autoclave slurry-type reactor and also in a contactor type membrane reactor to assist about the benefits provided by the employment of the mesoporous top layer of a ceramic tubular membrane as catalyst (Ce mixed oxides) support. The effect of mixed oxide composition and use of Pt as dopant onto the phenol removal rate and selectivity towards mineralization have been studied on both types of reactor. For slurry-type reactors, two different autoclave reactors were used: one mechanically stirred highly pressurized, and the other magnetically stirred containing a porous stainless steel membrane as gas diffuser in an attempt to attain higher gas–liquid interfacial area. The performances of these reactors have been compared under similar reaction conditions (i.e. catalyst loading/liquid volume, temperature, phenol concentration) although the way in which reactants are fed to the reaction vessel (different among each other configuration) is clearly affecting the CWO phenol degradation route. From the catalytic systems studied, Pt doped Ce–Zr mixed oxides exhibit the best reaction performance in spite of the achieved phenol conversion levels are below 50%. For autoclave reactors, the gas feeding to the liquid volume by a membrane diffuser has almost no effect on phenol removal for the reaction conditions tested; whereas the catalytic membrane contactor type reactor clearly outperform autoclave reactor provided with membrane diffuser.     

Investigation on the partial oxidation of methane to syngas in a tubular Ba0.5Sr0.5Co0.8Fe0.2O3−δ membrane reactor

A perovskite material of Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ (BSCF), with both electronic and ionic conductivity, was synthesized by a combined citrate–EDTA complexing method. The dense membrane tube made of BSCF was fabricated using the plastic extrusion method. The partial oxidation of methane (POM) to syngas was performed in the tubular BSCF membrane reactor packed with a LiLaNiO/γ–Al₂O₃ catalyst. The reaction performance of the membrane reactor was investigated as functions of temperature, air flow rate in the shell side and methane concentration in the tube side. The mechanism of POM in the membrane reactor was discussed in detail. It was found that in the tubular membrane reactor, combustion reaction of methane with permeated oxygen took place in the reaction zone close to the surface of the membrane, then followed by steam and CO₂ reforming of methane in the middle zone of the tube side. The membrane tube can be operated steadily for 500 h in pure methane with 94% methane conversion and higher than 95% CO selectivity, and higher than 8.0 ml/cm² min oxygen permeation flux.     

多孔膜反应器中丙烷催化脱氢制丙烯的模拟研究

针对丙烷高效脱氢制丙烯的多孔膜反应器构建了无量纲数学模型并进行了模拟研究,考察了催化剂活性、透氢膜性能、操作条件对多孔膜反应器中丙烷脱氢的转化率、丙烯收率、氢气收率和纯度的影响。结果表明,移走产物氢气可以有效提升膜反应器的性能,其性能的提升程度由不同温压条件下催化剂和透氢膜性能共同决定。高活性催化剂是丙烷高效转化的基础,催化剂活性越高,膜反应器内的产氢速率越快;其次,膜的选择性和渗透通量越高,氢气的移除效率越高,可在最大程度上打破热力学平衡的限制,使反应向生成丙烯的方向移动。当多孔透氢膜的氢气渗透率在10^-7~10^-6 mol·m^-2·s^-1·Pa^-1,H₂/C₃H₈选择性达到100时,其丙烷转化率可以与Pd膜反应器内的转化率相当,但分离的氢气纯度低于Pd膜反应器。与传统的固定床反应器相比,膜反应器由于促进了化学平衡的移动,可以在较低的反应温度下获得相当高的丙烷转化率,且丙烷转化率随着反应压力的增加呈现出一个最大值。该模拟研究可为实际生产过程中膜反应器用于PDH反应的高效强化提供有益的技术指导。     

The aromatic enhancement in the axial‐flow spherical packed‐bed membrane naphtha reformers in the presence of catalyst deactivation

Because of some disadvantages of conventional tubular reactors (CTRs), the concept of spherical membrane reactors is proposed as an alternative. In this study, it is suggested to apply hydrogen perm‐selective membrane in the axial‐flow spherical packed‐bed naphtha reformers. The axial flow spherical packed‐bed membrane reactor (AF‐SPBMR) consists of two concentric spheres. The inner sphere is supposed to be a composite wall coated by a thin Pd‐Ag membrane layer. Set of coupled partial differential equations are developed for the AF‐SPBMR model considering the catalyst deactivation, which are solved by using orthogonal collocation method. Differential evolution optimization technique identifies some decision variables which can manipulate the input parameters to obtain the desired results. In addition to lower pressure drop, the enhancement of aromatics yield by the membrane layer in AF‐SPBMR adds additional superiority to the spherical reactor performance in comparison with CTR. © 2011 American Institute of Chemical Engineers AIChE J, 2011     

APPLICATIONS OF A NON-PERMSELECTIVE, CATALYTICALLY ACTIVE MEMBRANE, A MODEL STUDY

A theoretical investigation has been presented for applications and features of a non-permselective, catalytic membrane reactor with separated feed of reactors [12-14, 17, 18]. Transmembrane fluxes were calculated from the dusty gas model as a function of a great number of parameters and operation conditions. This study shows that the non-permselective, catalytic membrane reactor with separated feed of reactants (CMRSR) has attractive features to use this reactor in fast and highly exothermic reactions and selectivity improvement in multiple reactions.

When the CMRSR is operated in the transport controlled regime, the process is easy to control and even possesses some self-controllability. Due to the transport conversion, thermal runaway cannot occur which allows operation with concentrated feed of reactants. Furthermore, a transmembrane pressure difference increases both the fluxes and the selectivity, because the reaction products are preferentially directed towards one side of the membrane. The simultaneous increase of both selectivity and fluxes is a remarkable feature of a CMRSR which is in contrast with conventional reactors.     

Simulation of a catalytic membrane reactor for the oxidative dehydrogenation of butane

A two-dimensional model has been used to simulate the oxidative dehydrogenation of butane on a two-layer catalytic membrane (diffusion layer and V/MgO active layer) operating with segregated reactant feeds. The model considers plug flow on both sides of the membrane, uses an extended Fick's law expression to describe multi-component diffusion in the radial direction, and a complex kinetic scheme to account for the reaction network. The simulation study shows that different feed configurations lead to marked differences on the partial pressure profiles of the different species across the membrane, and explains the performance order (in terms of the selectivity-conversion behaviour) that was observed experimentally. Similarly, the behaviour observed for membranes with catalytic layers of different width was justified by taking into account the variation of the oxygen partial pressure across the active zone of the membrane.