Precise multicomponent isotherms are usually required to properly analyze the dynamic behavior of adsorption separation processes (for example, Frey, 1992). Among the most accurate and versatile isotherms for this purpose are those resulting from ideal adsorbed solution (IAS) theory (Myers and Prausnitz, 1965; Valenzuela and Myers, 1989). In most cases, however, the equations resulting from IAS theory must be solved iteratively, which makes it inconvenient to incorporate those equations into numerical simulations of column dynamics.
In this study, two formulations for IAS theory are developed which yield explicit relations for the adsorbed concentrations for arbitrary numbers of components. The first method involves fitting the relation between the spreading pressure and the gas-phase pressure for each individual component to a three-parameter Pad6 approximation which is the ratio of firstand second-order polynomials. This method can be applied to a variety of single-component isotherms, including those which deviate significantly from Langmuir isotherms. The second method is an extension to any number of adsorbates of the Taylor series solution for two adsorbates developed by LeVan and Vermeulen (1981). The second method applies when the single-component isotherms correspond closely to Langmuir isotherms and when the maximum adsorption capacities for the various adsorbates are not too dissimilar.
Although this study considers only the use of IAS theory on a homogeneous surface, the methods discussed here can also be employed in certain types of heterogeneous IAS theories, such as those in which the adsorbent surface is postulated to consist of several types of uniform surface patches, and IAS theory is used to determine the amounts adsorbed on each type of surface patch (Myers, 1987). Correspondence concerning this work should be addressed to D . D. Frey, who IS currently at the Dept. of Chemical and Biochemical Engineering, University of Maryland.