The preparation and characteristics of supported carbon membranes from comm
ercial polyimides are reported here. Carbon molecular sieve membranes (CMSM
) with asymmetric and symmetric structures have been obtained in only one c
asting step by the phase inversion technique. The precursors were polyimide
-type polymers available commercially: Allotherm(R) 610-16 (BASF) and Matri
mid(R) 5218 (Ciba Specialty Chemicals). The preparation method involved coa
ting of the macroporous carbon supports with a polymeric solution and subse
quent gellation of the polymeric film by immersion in a coagulant bath. The
carbon membranes were obtained by heat treatment (450-700 degrees C) of th
e resulting devices under vacuum. The permeability and selectivity data ind
icate that the resulting carbon membranes possess molecular sieve propertie
s and that they are suitable for the separation of permanent gases of indus
trial interest (O-2/N-2, CO2/CH4, CO2/N-2, etc.). Kapton(R) carbon membrane
s are more permeable than those derived from Matrimid(R). The permeability
and permselectivity measured at 25 degrees C for Kapton(R)-derived CMSM wer
e: permeability (CO2) = 92 Barrer, permselectivity (CO2/CH4) = 16, permsele
ctivity (CO2/N-2 = 9; permeability (O-2)=45 Barrer, permselectivity (O-2/N-
2)=4. By contrast, the materials obtained from Matrimid(R) are, in general,
less permeable but more selective: permeability (CO2)=12 Barrer, permselec
tivity (CO2/CH4)=33, permselectivity (CO2/N-2)=15; permeability (O-2)=5 Bar
rer, permselectivity (O-2/N-2)=6. (C) 1999 Elsevier Science B.V. All rights
reserved.