Molecular sieving selectivity of active carbons and active carbon fibers improved by chemical vapour deposition of benzene

Modification of the pore size of several types of carbon adsorbents by chemical vapour deposition of carbon from benzene at 1000 K was examined. The carbons included commercial molecular sieve carbon (MSC), pitch based active carbon fiber (ACF), super and commercial active carbon (S-AC, AC). Greatly improved selectivity for the separation of CO2 and CH4 was achieved by this method for MSC and ACF. ACF is expected to exhibit rapid adsorption and desorption rates during molecular sieving separations. Carbon adsorbents which contain micropores of uniform size appear to have the highest potential for improvement in selectivity by CVD. Saturation of benzene CVD was observed in such carbons, indicating the deposition in the pore. In contrast, carbons which contain micropores in combination with large concentrations of mesopores lose adsorption capacity by filling of the mesopores with deposited carbon. The concentration of benzene and deposition temperature are key factors in achieving homogeneous carbon deposition on the pore wall but not on the outer surface which leads to improved selectivity. Copyright (C) 1996 Elsevier Science Ltd