Effect of oxidation on gas permeation of carbon molecular sieving membranes based on BPDA-pp'ODA polyimide

A BPDA-pp'ODA polyimide film was formed on the outer surface of a porous alumina support tube and was then carbonized in an inert atmosphere at 600-900 degrees C. The resulting carbon molecular sieving (CMS) membranes were oxidized in O-2-N-2 mixtures at 300 degrees C or in CO2 at 800-900 degrees C, and the permeation properties were determined. The O-2 oxidation increased both permeances and permselectivities. The CMS membranes were exposed to air at 100 degrees C for 1 month, and their resistance to oxidation was determined. The results show that permeance was decreased in the initial stage of exposure, while permselectivity was increased. Both properties were largely restored by heat-treatment in nitrogen at 600 degrees C for 1-4 h. This suggests that CMS membranes would be stable at 100 degrees C for months, when used in an atmosphere which contained only a small fraction of oxidants.