Equilibrium adsorption of gases and liquids on heterogeneous adsorbents — A practical viewpoint

Abstract

The equilibrium characteristics of industrial adsorbents are determined primarily by the energetic heterogeneity of fluid-solid interactions. This heterogeneity is caused by thedetailed structural and chemical properties of the solid; it is modeled as a distribution of sites of different energy levels so that an overall extensive property of a heterogeneous adsorbent is the sum of individual contributions from each type of site. The energy distribution of an adsorbent is estimated from its experimental adsorption isotherms using a model of surface heterogeneity. Alternatively, theories of energetic heterogeneity provide a basis for generating analytical adsorption isotherm equations that cover wide ranges of pressure and temperature and are therefore useful for process design calculations. Although the energetic heterogeneity of solid adsorbents is usually very complex, models containing two or three constants for the energy distribution are adequate for practical purposes. The heterogeneous model is particularly successful in predicting multicomponent adsorption equilibria from single-gas adsorption isotherms.