On the Azeotropic Behaviour of Adsorption Systems

This paper addresses the azeotropic behaviour of adsorption occurring on a heterogeneous solid, which is composed of patches of different adsorption energies. One of the adsorbates is excluded from adsorption onto one or more patches. If such species is the weaker adsorbing species, then the azeotropic behaviour does not occur. On the other hand, if that species is the stronger adsorbing species then the azeotropic phenomenon might occur. The occurrence of the azeotropic depends on the relative affinities of all species and the total pressure must be greater than a threshold pressure. We shall illustrate this theory with two systems exhibiting azeotropic behaviour: isobutane/ethylene/13X and propane/carbon dioxide/mordenite.