Effect of air oxidation on gas separation properties of adsorption-selective carbon membranes

Molecular sieve carbon membranes (MSCM) obtained by carbonisation of a phen olic resin film can be transformed into adsorption-selective carbon membran es (ASCM) by means of air oxidation at temperatures between 100 and 450 deg reesC. ASCM can separate the components of a gas mixture depending on their adsorption properties instead of the size of the gas molecules as occurs f or MSCM. In this work ASCM are prepared according to the following steps: ( a) deposition of a thin film of a phenolic resin on the inner face of an al umina tube, (b) carbonisation (under vacuum at 700 degreesC) and (c) air ox idation at temperatures above 100 degreesC, The influence of oxidation temp erature (between 100 and 475 degreesC) and oxidation time (between 0.5 and 6 h) on the separation characteristics of the prepared carbon membranes is analysed. The membranes show high permeances and selectivities towards the separation of multicomponent gas mixtures formed by hydrocarbons and N-2. A s an example, a carbon membrane oxidised at 250 degreesC (0.5 h) shows the following values of permeances tin mol m(-2) s(-1) Pa-1 x 10(-10)) and sele ctivities (alpha =hydrocarbon/N-2) for the separation of a complex gas mixt ure formed by 16.3% CH4, 16.1% C2H6, 16.2% C3H8, 20% n-C4H10 and 31.4% N-2 are: CH4, 172 (alpha =3); C2H6, 700 (alpha = 12); C3H6, 1730 (alpha =30); n -C4H10, 4270 (alpha =74). (C) 2001 Published by Elsevier Science Ltd.