Adsorption of binary liquid mixtures on heterogeneous adsorbents

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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.

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