Carbon molecular sieve membranes: Preparation, characterization, and gas permeation properties

Gas permeation properties of a series of carbon molecular sieve (CMS) membranes prepared by pyrolysis of a Kapton polyimide precursor were investigated. Pyrolysis at high temperatures and low heating rates produced the most selective membranes. The experimental observation that gas permeabilities were not always in the order of the kinetic gas diameters originated from differences in sorption and/or diffusivity. Kapton-based CMS membranes whose pore openings were slightly enlarged by moderate activation or those prepared from other polyimide precursor types provided a series of CMS membranes that had different permeation properties. Some of the membranes were effective even for alkene/alkane separation. Imidization and pyrolysis of capillary polyamic acid membranes resulted in CMS membranes with an asymmetric structure, which also exhibited excellent performance.