(625c) Thermodynamic Modeling of Adsorption Equilibria of Water + Ethanol Liquid Mixture on Silica DDR Zeolite

Bioresource derived ethanol is environmentally safe, economical, an important product for biorefineries and has wide applications in various industries. Hence, concentrating dilute ethanol from the fermentation broths to obtain fuel-grade ethanol is important, while the highly nonideal mixture of water and ethanol makes it a challenging process. As an alternative to thermal separations, adsorption separation is energy-efficient and widely practiced in industry. In this work, we studied the water + ethanol mixture adsorption on silica DDR zeolite (Deca-Dodecasil 3 Rhombohedral) at 300K [ACS omega, 6(23), 15499-15513] using the recently developed generalized Brunauer-Emmett-Teller (gBET) isotherm model [Industrial & Engineering Chemistry Research, 63(31), 13853-13863]. We modified the gBET model developed for the mixed-gas multilayer adsorption to account for the multicomponent multilayer liquid adsorption. The pressure term in gBET is replaced with species fugacity to properly describe the adsorption driving force as affected by the non-ideality of the mixture in both adsorbed and bulk phases. The interactions between the adsorbate and adsorbent in the monolayer adsorbed phase are represented with adsorption nonrandom two-liquid (aNRTL) activity coefficient model, while the interactions between water and ethanol in the bulk liquid and the condensed phase are represented with the classical NRTL model. The gBET model results for the single components and binary systems are compared with those from the classical Langmuir and BET isotherm models for the single components, as well as Ideal Adsorbed Solution Theory and Real Adsorbed Solution Theory for the binary systems. The proposed gBET model is much simpler than the others, and it accurately represents the adsorption equilibrium behavior as functions of bulk liquid composition and system pressure.