Mixed-conducting perovskite reactor

Mixed-Conducting Perovskite Reactor for High-Temperature Applications Control of Microstructure and Architecture... 

J.E. ten Elshof, H.J.M. Bouwmeester and H. Verweij, Oxidative Coupling of Methane in a Mixed-Conducting Perovskite Membrane Reactor , Appl. Catal. A, 130 195-212 (1995). 

Catalysts are usually applied to activate methane dissociation and hydrogen combination. Such catalysts may be of Pt, Ag or other specially designed oxides. It is worth noting that several mixed conducting perovskites (e.g., strontium cerates) are very efficient methane coupling catalysts and have been used as such in regular catalytic reactors. Studies on the methane... 

Our research is focused on the control of both the microstructure and the architecture of perovskite-type mixed-conducting reactors for high temperature applications, especially for oxygen separation from air and syngas production. 

Since the membrane conducts oxygen ions, in the great majority of the cases through a mechanism involving anion vacancy diffusion, an equivalent counterflux of electrons should take place for charge neutrality membrane materials should be mked conductors. Perovskite-type mixed-conducting materials are considered suitable candidates for use in dense membrane reactor chemical looping processes, since they fulfill most of the required characteristics. 

Some perovskite-type oxides having transition elements at B sites exhibit mixed conduction at elevated temperatures. A typical example is doped lanthanum cobaltite, in which oxide ions and holes are charge carriers. The electronic conductivity is a few orders of magnitudes higher than that of the oxide-ionic although the ionic conductivity itself is sufficiently high (>10 S cm at several 100°Q. This kind of mixed conductor is a promising candidate for the electrode materials of SOFCs and ceramic membrane reactors and is described in Chapters 7 and 8 in detail. 

Some of the many different types of catalysts which have good catalytic properties for the OCM reaction qualify as membrane materials. Membrane reactors for OCM were designed and tested by Nozaki et al. (1992). Three kinds of reactors were developed the first one consisted of a porous membrane covered with a thin film of catalyst (type I) the second one, a dense ionic-conducting membrane (non porous) with catalytic layer (type II) and the third one was a membrane made of perovskite-type mixed oxides which was active for OCM (type III). Figure 11 presents the diagram for the membrane reactor system and table 13 shows the different materials used for supports and coated catalysts. 

Key words membrane reactor, perovskite, proton conducting membrane, mixed ionic-electronic conductor (MIEC), partial oxidation of methane... 

Continuous air separation by an oxygen-conducting membrane which constitutes the wall of a CPO reactor is another approach which has received much interest, also from industry. Two types of membrane materials have been studied zirkonia-based membranes, which are efficient oxygen ion conductors but require electrodes to transfer electrons to the reduction interface, and perovskites (of general formula ABO3, with dopants in the A and/or B site), which are mixed ionic/electronic conductors (MIEC). ... 

Abstract Dense ceramic membrane reactors are made from composite oxides, usually having perovskite or fluorite structure with appreciable mixed ionic (oxygen ion and/or proton) and electronic conductivity. They combine the oxygen or hydrogen separation process with the catalytic reactions into a single step at elevated temperatures (>700°C), leading to significantly improved yields, simplified production processes and reduced capital costs. This chapter mainly describes the principles of various types of dense ceramic membrane reactors, and the fabrication of the membranes and membrane reactors. 

Key words membrane reactors, mixed ionic-electronic conductors (MIECs), perovskite, oxygen permeable membrane, proton conducting membrane. 

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