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

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 N2. 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/N2) for the separation of a complex gas mixture formed by 16.3% CH4, 16.1% C2H6, 16.2% C3H8, 20% n-C4H10 and 31.4% N2 are: CH4, 172 (α=3); C2H6, 700 (α=12); C3H6, 1730 (α=30); n-C4H10, 4270 (α=74).