Isosteric heats of adsorption of gases and vapors on a microporous carbonaceous material

Abstract

High-resolution, multiple temperature adsorption isotherms of ten adsorptives classified into highly polar (1.7 ± 0.1 D) and nonpolar (0 D) probes with increasing kinetic diameters were measured on a well-characterized poly(furfuryl alcohol)-based microporous carbon. The Clausius–Clapeyron equation was applied to each, resulting in isosteric heats of adsorption. Fluid–fluid interactions, nonspecific fluid–solid interactions, and specific fluid–high energy site interactions were identified and discussed as variables contributing to the total isosteric heat of adsorption. Each isosteric heat was compared against its position relative to adsorption heat by a flat surface, twice this heat, and adsorptive latent heat of condensation. The shape of each curve was analyzed via the contribution of each interaction to the total across the fractional filing range, leading to identification of fillings as Zero Coverage, Low Coverage, and High Coverage. This systematic investigation provided a detailed analysis of the influences of adsorptive size, its conformation, and polarity effects on micropore filling, and tabulation of the analyses gave a clear and comprehensive insight into the adsorption mechanisms.