New model for S-shaped isotherm data and its application to process modeling using IAST

Abstract

Recently S-shaped (sigmoidal-shaped) adsorption isotherms have attracted much attention as having potential for reduced energy use in pressure or temperature swing based separations. Despite a wide variety of such isotherm data reported in the literature, convenient mathematical representations of S-shaped isotherms are not yet available. The absence of such models relating pressure and uptake values hinders the evaluation of many potentially promising adsorbents in separation and storage. Herein, a new mathematical model is proposed that parameterizes S-shaped isotherm data. The model provides a basis for deriving analytical expressions for the spreading pressures, to achieve a dramatic computational cost reduction in the ideal adsorption solution theory (IAST) calculation for multi-component isotherms. Then, the proposed model is generalized for its broader application. To consider the temperature effect based on isotherm data distributed at varying temperatures, a method is suggested to use such distributed data in fitting a single isotherm model. Each of the models and methods is illustrated with their application examples to facilitate the understanding and clarifying the advantages of the proposed model. Among them, a practical example with simulations of breakthrough experiments is provided. © 2020 Elsevier B.V.