Preparation and characterization of adsorption-selective carbon membranes for gas separation

The preparation and characterisation of adsorption-selective carbon membranes (ASCMs) is described. ASCMs can separate the components of a gas mixture depending on their adsorption strength. These membranes allow the separation of non-adsorbable or weakly adsorbable components (e.g. N-2, H-2, O-2, etc) from the more strongly adsorbable components (e.g. hydrocarbons) in a gas mixture. They are prepared from the deposition of a thin film of a phenolic resin on the inner face of an alumina tube. Air oxidative treatment at temperatures in the range of 300-400 degreesC, prior to carbonisation (pre-oxidation) or after carbonisation (under vacuum at 700 degreesC) (post-oxidation) gives rise to an adsorption-selective carbon membrane. This membrane shows a high permeability and selectivity towards the separation of gas mixtures formed by hydrocarbons and N-2. Taking into account the permeation and separation properties of the membranes, post-oxidation treatment is shown to be more effective than pre-oxidation. The separation characteristics of the carbon membranes are dependent on the composition of the gas mixture (i.e. proportion of more strongly adsorbable components) and temperature.