The multiple equilibrium model for characterizing porous materials

Abstract

In this work, a multiple-process equilibrium model was used to analyze gas-solid adsorption equilibria in the porous carbonaceous material, BPL. Methane was used as a non-polar gaseous probe molecule to study the adsorption process. This analysis provided adsorption capacities, n_i, along with the associated equilibrium constants, K_i, for the three processes needed to fit the isotherms. The temperature dependence of the K_i allowed determination of the enthalpies of the adsorption processes, ΔH_i. These enthalpies were greater than the heat of vaporization for methane but less than that usually associated with chemisorption processes. Simulated adsorption data were generated based on the methane analysis to determine the effect of pore size distribution on the analysis. It is concluded that, given a continuous distribution of pore sizes, a large number of adsorption processes is necessary to describe accurately the total adsorption. For heterogeneous distributions, as is observed in activated carbon materials, it is possible to resolve discontinuities in the distribution.