Flat Supported and Unsupported Carbon Membranes

Porous carbon films have been prepared fiom Kapton-type polyimide (PI) to produce supported and unsupported caibon membranes by Hattori et al. [2-4]. They reported that the carbon molecular sieve (CMS) film used for gas separation should be as thin as possible in order to enhance the separation efficiency. However, the thin film should be supported by a porous plate for handling convenience. The flat homogeneous carbon films prepared by pyrolysis at 800°C yielded selectivi-ties of 4.2 [4], 

Rao and Sircar [5-7] introduced nanoporous supported carbon membranes which were prepared by pyrolysis of PVDC layer coated on a macroporous graphite disk support. The diameter of the macropores of the dried polymer film was reduced to the order of nanometer as a result of a heat treatment at 1,000°C for 3 h. These membranes with mesopores could be used to separate hydrogen-hydrocarbon mixtures by the surface diffusion mechanism, in which gas molecules were selectively adsorbed on the pore wall. This transport mechanism is different from the molecular sieving mechanism. Therefore, these membranes were named as selective sitrface flow (SSF ) membranes. It consists of a thin (2-5 pm) layer of nanoporous carbon (effective pore diameter in the range of 5-6 A) supported on a mesoporous inert support such as graphite or alumina (effective pore diameter in the range of 0.3-1.0 pm). The procedures for making the selective surface flow membranes were described in [5, 7]. In particular, the requirements to produce a surface diffusion membrane were shown clearly in [7]. 

A solution to overcome reproducibility problems of nanoporous carbon (NPC) membranes has been introduced by Acharya and Foley [8], They have used spray 

Flat Tube Capillary Flollow fiber Flat 

Chen and Yang [9] prepared a large, crack-free carbon molecular sieve membrane (CMSM) supported on a macroporous substrate by coating a layer of PFA followed by controlled pyrolysis. Diffusion of binary mixtures was measured and the results were compared with the kinetic theory for predicting binary dififusivities from pure component dififusivities. Good agreement was obtained between theoretical predictions and experimental data for binary diffusion, as shown in Chap. 2. 

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