DEVELOPMENT OF MOLECULAR-SIEVING PROPERTIES IN MICROPOROUS CARBONS

Molecular Sieving properties of microporous carbons were investigated by adsorption and diffusion of Ar, N2 and O2. Modification of the pore structure of these carbons to a molecular sieve type was made by thermal treatment, controlled gasification or carbon deposition from pyrolysis of organics. Sieving behavior was improved in the case of carbons containing a significant distribution of micropores of narrow size (approximately 0.5 nm). Carbon deposition from cracking of propylene on a carbon containing an appropriate pore structure improved its sieving properties for kinetic separation of O2 from Ar. Deposition of a controlled amount of carbon can be achieved from chemisorption of propylene. Similar treatment of activated carbons showed no useful improvement in selectivity for separation. The basic pore structure of the precursor carbon was found to be critical for the development of molecular sieving properties.