Adsorption-selective carbon membrane for gas separation

The preparation and characterisation of adsorption-selective microporous carbon membranes is described. The prepared membranes can separate the components of a gas mixture depending on their adsorption properties instead of the molecular size. Thus, these membranes are suitable to separate non-adsorbable or weakly adsorbable components (i.e. N2, H2, O2, etc.) from the more strongly adsorbable components (i.e. hydrocarbons) in a gas mixture. The membrane is prepared from deposition of a thin film of a phenolic resin on the inner face of an alumina tube. After carbonisation (under vacuum at 700°C) and air oxidation (300–400°C), a carbon membrane with the described characteristics is obtained. The prepared membrane shows high permeabilities and selectivities towards separation of gas mixtures formed by hydrocarbons and N2. As an example, the values of permeability and selectivity (hydrocarbon/N2) for the separation of a complex gas mixture formed by 16.3% CH4, 16.1% C2H6, 16.2% C3H8, 20% C3H6 and 31.4% N2 are: CH4, 320 Barrer (α=2.6); C2H6, 1104 Barrer (α=9.1); C3H6, 2930 Barrer (α=23.4); C3H8, 2850 Barrer (α=22.8).