Modification of Pore Structure in Carbon Molecular Sieve Films Prepared from Polyimide

Abstract

It has been found that carbon molecular sieve (CMS) film prepared from Kapton-type polyimide shows a high selectivity in permeation of gases. For example, carbon dioxide permeates through the film 50 times faster than nitrogen. Since the property is governed by the micropore structure, modification of micropore size distribution was studied on this CMS film. The micropore size varies with heat-treatment temperature; as a result, polyimide film with the thickness of 25μm gave CMS films having sieving property comparable to zeolite 4A or 5A. CMS films prepared from polyimide film of 125μm had smaller size and volume of micropore than the thinner films treated at the same temperatures. On the other hand, change in molecular orientation in pristine film, which influences the graphitizability remarkably, was not effective for modifying the pore structure in CMS film.