Preparation of supported carbon molecular sieve membranes

Carbon molecular sieve membranes were prepared by carbonization of a polymeric him supported on a macroporous carbon substrate. Disk-shaped macroporous carbon supports (35 mm in diameter and 2.5 mm in thickness) were obtained by carbonization of fine particles of graphite blended with a phenolic resin. The polymeric precursor of the selective carbon him was a polyamic acid commercially available in solution that after imidization led to formation of BPDA-pPDA polyimide. The support coated with the polymeric solution was heated following the sequence: (i) drying at 150 degrees C during 1 h in air (heating rate: 3 degrees C/min); (ii) imidization under vacuum at 380 degrees C (heating rate: 1 degrees C/min); (iii) carbonization under vacuum at temperatures ranging between 550 degrees C and 700 degrees C (heating rate: 0.5 degrees C/min). This procedure provided one-coat membranes. It was repeated to produce two- and three-coat carbon membranes. At 25 degrees C the resulting carbon membranes showed selectivity O-2/N-2 of 14 and He/N-2 of 136 and permeation rate of pure He and O-2 of 27.2 x 10(-10) and 2.8 x 10(-10) mol/m(2) s Pa, respectively. (C) 1999 Elsevier Science Ltd. All rights reserved.