Preparation of carbon molecular sieve membranes and their gas separation properties

Carbon molecular sieve (CMS) membranes were prepared by pyrolyzing flat membranes of 3,3',4,4'-diphenylhexafluoroisopropylidene tetracarboxylic dianhydride (6FDA)-based polyimide and polypyrrolone and composite membranes of phenolic resin coated on alumina tubes at 500-800 degrees C in N-2. The gas permeability and selectivity depended significantly on the precursor polymers and pyrolysis conditions. With increasing pyrolysis temperature, the permeability decreased and the selectivity increased, because the membranes became denser and the effective pore size for molecular sieving became smaller, whereas gas adsorption increased. CMS membranes from the polyimide and polypyrrolone displayed high performance for gas separation applications such as CO2/CH4, O-2/N-2, and propylene/propane. CMS membranes made from a phenolic resin displayed high performance for CO2/N-2 separation.