Carbon molecular sieve gas separation membranes based on poly(vinylidene chloride-co-vinyl chloride)

The preparation of a composite carbon membrane from Poly(vinylidene chloride-co-vinyl chloride) is described. The membrane is formed by a thin microporous carbon layer (Thickness, 0.8 mu m) obtained by pyrolysis of a polymeric film supported over a macroporous carbon substrate (Pore size, 1 mu m; Porosity, 30%). Single gas permeation experiments with pure gases of different molecular size (He, CO2, O-2, N-2 and CH4) were performed at different temperatures between 25 degrees C and 150 degrees C. It has been observed that the microporous carbon layer exhibits molecular sieving properties and it allows the separation of gases depending on their molecular size. The carbon membrane shows high selectivities for the separation of permanent gases like O-2/N-2 system (Selectivity approximate to 14 at 25 degrees C). Air preoxidation at 200 degrees C for 6 h improves the permselectivity but a loss in gas permeance is observed. (C) 2000 Elsevier Science Ltd. All rights reserved.