Monolayer capacity estimation by inverse gas chromatography at finite concentrations

Abstract

Using inverse gas chromatography data, a method of monolayer capacity calculation by analysis of specific retention volume vs. partial pressure dependence is presented. Three porous polymers were chosen as adsorbents to test the robustness of the calculation: microporous styrene-divinylbenzene copolymer Dowex L-285, microporous hypercross-linked polystyrene MN-200 and macroporous styrene-divinylbenzene copolymer Polysorb-1. It was shown that the change of retention volume as a function of partial pressure approaches zero when the formation of the second layer of adsorbate starts; the point at which this occurs indicates the monolayer capacity. By integrating the retention volume vs. partial pressure dependence up to the partial pressure at which the retention volume becomes constant, the monolayer capacity was obtained. A comparison of the calculated monolayer capacities, the gas-solid interface areas (specific surface areas), and the differential isosteric free energies of adsorption using the proposed method against calculations using classical Langmuir, Brunauer/Emmett/Teller (BET) and Dubinin-Radushkevich (DR) approaches suggest the reliability of the proposed method.