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

Abstract

Molecular sieve carbon membranes (MSCM) obtained by carbonisation of a phenolic resin film can be transformed into adsorption-selective carbon membranes (ASCM) by means of air oxidation at temperatures between 100 and 450°C. ASCM can separate the components of a gas mixture depending on their adsorption properties instead of the size of the gas molecules as occurs for 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 alumina tube, (b) carbonisation (under vacuum at 700°C) and (c) air oxidation at temperatures above 100°C. The influence of oxidation temperature (between 100 and 475°C) 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. As an example, a carbon membrane oxidised at 250°C (0.5 h) shows the following values of permeances (in mol m −2 s −1 Pa −1×10 −10) and selectivities ( α=hydrocarbon/N 2) for the separation of a complex gas mixture formed by 16.3% CH 4, 16.1% C 2H 6, 16.2% C 3H 8, 20% n-C 4H 10 and 31.4% N 2 are: CH 4, 172 ( α=3); C 2H 6, 700 ( α=12); C 3H 6, 1730 ( α=30); n-C 4H 10, 4270 ( α=74).