CARBON MOLECULAR-SIEVE GAS SEPARATION MEMBRANES .1. PREPARATION AND CHARACTERIZATION BASED ON POLYIMIDE PRECURSORS

Carbon molecular sieving membranes are new, high-performance materials for gas separations. The selectivities of these membranes are much hi gher than those typically found with polymeric materials, and the sele ctivities are achieved without sacrificing productivity. Ultramicropor ous carbon membranes can be produced by pyrolyzing various thermosetti ng polymeric materials under a variety of pyrolysis conditions. The me mbranes described in this paper were produced from the pyrolysis of a hollow-fiber polyimide precursor under conditions found to yield membr anes with good air separation properties. Membranes were produced by t wo different temperature protocols, and were evaluated with mixed gas feeds at pressures ranging up to 200 psig (1.48 MPa). The lower temper ature protocol yielded membranes with O-2/N-2 selectivities ranging fr om 8.5 to 11.5, and a higher temperature pyrolysis yielded membranes w ith selectivities ranging from 11.0 to 14.0. These membranes were foun d to be quite stable over time periods of several days with high-purit y, dry feeds. Limited studies also showed that these membranes were hi ghly effective for the separation of other mixed gas pairs, including CO2/N-2, CO2/CH4, and H-2/CH4.