Configurations of Dense Ceramic Membrane Reactors

There are three main types of dense ceramic membranes disk/flat sheet, tubular, and hollow fibers. The disk/flat sheet membranes are applied mostly in research work because they can be fabricated easily in laboratories with a small amount of membrane material. Comparatively, the hollow fiber membranes can provide the largest membrane area per volume but low mechanical strength, while the tubular membranes possess a satisfactory specific membrane area, high mechanical strength, and are easy to assemble in membrane reactors. Dense ceramic MRs can be constructed and operated in either packed bed MR or catalytic MR configurations. 

This configuration is applied mostly in practical use of dense ceramic MRs. The reactions take place in the catalyst bed while the membrane functions mainly as an oxygen distributor or extractor. Since the catalyst is separated physically from the membrane, the separation function of the membrane and the catalytic properties of catalysts can be modulated separately so that the MR performance will be optimized. 

It is well established that MIECs are inherently catalytic to oxidation reactions. Therefore, MIEC-derived membranes may serve as both catalyst and oxygen separator, and no other catalysts are used in the dense ceramic MRs. Since chemical reactions take place on the membrane surface, it is required to have a much more porous membrane surface so as to contain a sufficient quantity of active sites. This can be achieved in the membrane preparation process, or by coating a porous membrane material after preparation. The main potential problems for this configuration are that the membrane may not have sufficient catalytic activity and the catalytic selectivity cannot he modulated with respect to the reactions considered. 

In order to overcome this problem, an additional catalyst can be coated on the membrane surface to form a new catalytic dense membrane [36, 37]. The catalyst layer is generally porous and integrated with the membrane into a single body. The catalyst layer can also be formed together with the membrane in a single step as shown by Wu et al. [39]. 

DENSE CERAMIC OXYGEN-PERMEABLE MEMBRANE REACTORS 

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