MEASUREMENT AND PREDICTION OF BINARY ADSORPTION EQUILIBRIA OF VAPORS ON DEALUMINATED Y-ZEOLITES (DAY)

Adsorption equilibria of toluene, 1-propanol and their binary mixtures have been measured on Y-zeolites with three different silicon to alum inum ratios: 13, 55 and 100 at 318.15 K. The partial pressures of the pure components were varied between 0.04 and 2.20 kPa. The total press ures for the binary mixtures were adjusted to 0.35 and 1.05 kPa, respe ctively. The surface of zeolites usually exhibits polar and nonpolar a dsorption behavior depending on the degree of dealumination. For examp le, highly dealuminated zeolites preferably adsorb nonpolar compounds from mixtures of adsorptives with different polarities. Therefore, in the binary mixture of toluene and 1-propanol, Y-zeolites with a Si/Al- ratio greater than 100 adsorb approximately four times more toluene th an 1-propanol and show nearly ideal adsorption behavior, which can be predicted fairly well with the ideal adsorbed solution theory (IAS). A t lower Si/Al-values the binary adsorption isotherms show strong nonid eal behavior with an adsorption azeotropic point. This behavior-caused by intermolecular and molecule-surface interactions-cannot be predict ed successfully by using the IAS-theory. Adsorbate phase activity coef ficients have to be considered to take into account the real behavior. In this paper a new method for predicting these adsorbate phase activ ity coefficients to describe ideal and nonideal multicomponent adsorpt ion equilibria is proposed. This model is called predictive real adsor bed component isotherms (PRAST). Based on the IAS-theory, this model i ncludes adsorbate phase activity coefficients derived from pure isothe rm data. It will be shown that real mixture behavior, caused by surfac e heterogeneity, e.g. the molecule-surface interactions is predicted w ith PRAST. (C) 1998 Published by Elsevier Science S.A. All rights rese rved.