Carbon molecular sieving membranes derived from condensed polynuclear aromatic (COPNA) resins for gas separations

Condensed polynuclear aromatic (COPNA) compounds were synthesized from pyrene, phenanthrene, and 1,4-benzenedimethanol. Each COPNA compound was dissolved in tetrahydrofuran, and the solution was used as a coating on the outer surface of a porous alpha-alumina support tube. The resulting green films were carbonized at 400-1000 degrees C. The permeances of the COPNA-based carbon membranes were largest for a carbonization temperature of 600 degrees C, where the mesopore structure was most developed. This optimum carbonization temperature was 50-100 degrees C lower than that found for polyimide films synthesized from 3,3'4,4'-biphenyltetracarboxylic dianhydride and 4,4'-oxydianiline. The mesopores of the COPNA-based carbon membranes did not penetrate through the total thickness of each membrane and served as channels which increased permeances by linking the micropores. The permselectivities of the COPNA-based carbon membranes were similar to those of the polyimide-based carbon membranes, which contained only micropores.