Carbon molecular sieve membranes were prepared by crbonization of a polymeric film supported on a macroporous carbon substrate. Disk-shaped macroporous carbon supports (35 mm in diamter and 2.5 mm in thickness) were obtained by carbonizaton of fine particles of graphite blended with a phenolic resin. The polymeric precursor of the selective carbon film was a polymic 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 deg C during 1 h in air (heating rate:3 degC/min);(ii) imidization under cacuum at 380 deg C (heating rate: 1 deg C/min);(iii) carbonization under vacuum at temperatures ranging between 550 deg C and 700 deg C (heating rate: 0.5 deg C/min).This procedure provided one-coat membranes. It was repeated to produce two-and three-coat carbon membranes.At 25 deg 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*10~(-10) MOL/M~2 s Pa, respectively.
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