Adsorption of binary liquid mixtures on heterogeneous adsorbents

Abstract

An analytic equation to describe surface excess isotherm for adsorption of a non-ideal binary liquid mixture on a heterogeneous adsorbent is derived. The model assumes that the adsorbent heterogeneity can be described by a gamma distribution of selectivities and that the adsorbed phase is ideal. The parameters of the model are m, the total number of moles adsorbed, (A/RT)(σ°2–σ°1)*, the difference between the Gibbs free energy of the two pure components of the liquid mixture on the heterogeneous adsorbent, and n, a distribution parameter. The heterogeneous model was successfully used to describe experimental surface excess isotherms for adsorption of various binary liquid hydrocarbon mixtures on silica gel and Graphon.A parametic study of the effect of surface heterogeneity on the shape of the surface excess isotherm, Gibbs free energy and the heat of immersion of a binary liquid mixture is carried out. Criteria for the formation of U- and S-shaped isotherms are derived. A method for estimation of the adsorbent surface area for heterogeneous adsorbents from the surface excess isotherm is proposed and tested.