Adsorption equilibria of two ternary systems involving m-xylene, p-xylene, and either toluene or isopropylbenzene on zeolite K-Y have been studied. Due to nonideal behavior of the adsorbed phase, m-and p-xylene selectivity is strongly dependent upon composition. In particular, it is found that the addition of a third component can either enhance or depress such selectivity values. Ternary experimental data are well predicted by the developed equilibrium model, whose parameters can be estimated based only on experimental data relative to pure and binary mixtures. Finally, the role of these nonidealities in the equilibrium behavior on the dynamics of adsorption separation columns is discussed.

A new approach is developed for applying ideal and real adsorbed solution theory models to the description of multicomponent adsorption equilibria at fixed pressure. This allows ignoring single-component behavior in the Henry's law region, P -0, but introduces new parameters that must be evaluated from binary equilibrium data. Comparisons with various sets of experimental data show that the new approach gives results as good as the classical one, but without requiring knowledge of the single component behavior in the Henry's law region; moreover, it removes the sensitivity to the type of model adopted in fittingsingle-component equilibrium data.

The statistical thermodynamic approach to multicomponent adsorption equilibria on zeolites has been extended to nonideal systems, through the correction of cross coefficients characterizing the interaction between unlike molecules. Estimation of the model parameters requires experimental binary equilibrium data. Comparisons with the classical model based on adsorbed solution theory are reported for three nonideal ternary systems. The two approaches provide comparable results in the simulation of binary and ternary adsorption equilibrium data at constant temperature and pressure.

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The use of adsorption devices for large-scale bulk separations is becoming quite common. Most of such units operate by displacement chromatography, which requires conditions very close to the sorbent saturation. A well known example is provided by the separation of paraxylene from the hydrocarbon fraction C,, which can be performed by adsorption on zeolites from either liquid or vapor phase. The key problem in the mathematical simulation of adsorption separation units is the evaluation of the multicomponent adsorption equilibria (Paludetto et al., 1987).When strongly adsorbable compounds are involved, the high surface coverage can induce deviations from ideality in the adsorbed phase. Nonideal behaviors, such as selectivity values depending on the mixture composition, are quite common and cannot be accounted for by simple equilibrium correlations. For instance, the well known multicomponent Langmuir isotherm is not able to reproduce such behaviors. Moreover, for strongly adsorbable compounds, the investigation of the region at very low surface coverages (the so-called Henry region), with the accuracy required by many classical equilibrium models, can be quite difficult and cumbersome due to the very high values of the Henry constants characterizing these compounds. However, for such compounds it is quite easy to measure vapor mixtures equilibrium data at a fixed temperature and pressure by using, for example, the device presented by Paludetto et al. (1987). Thus, when dealing with strongly adsorbable compounds, particularly when the main goal is to evaluate the multicomponent adsorption equilibria at a fixed temperature and pressure (as it is Correspondence concerning this paper should be addresssd to M. Morbidclli. 1736November 1990 often the case for industrial separations), it is convenient to base the equilibrium model on binary-mixture equilibrium data at fixed temperature and pressure values.The aim of this paper is to test the reliability of two equilibrium relationships valid at the saturation limit by comparison with two sets of nonideal experimental data, namely toluene/ benzene/ parachlorotoluene and benzene/ parachlorotoluene/chlorobenzene on zeolite K-Ca X at 200OC. Singlecomponent, binary, and ternary-mixture data are reported. The aforementioned models, which originate from the adsorbed solution theory (Myers and Prausnitz, 1965) and the simplified statistical model (Ruthven and Wong, 1985), provide suitable approximations that are reasonable when dealing with strongly adsorbable compounds. They allow us to compute multicomponent equilibria using only information from experiments performed at the same conditions of temperature and pressure, even though they refer to binary, rather than to single-component systems.Finally, the comparison has been extended to sets of experimental data involving para-and metaxylene, as previously reported in the literature. Multicomponent Equilibrium ModelsThe first model considered is the ideal adsorbed solution theory (IAST), which was originally developed by Myers ...