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G.A. Mansoori, S.F. Aghamiri, H. Modarress
A Generalized Chemical Associating Theory of Mixtures
In this report a generalized chemical association theory is introduced for calculation of thermodynamic properties of mixtures of associating fluids. In the development of this theory every associating component is considered as a mixture of various associated i-mer species. The concepts of analytic and true mole fractions are re-examined and general expressions relating the two sets of compositions are derived. Generalized sets of equilibrium association reactions and the related equilibrium constants are introduced. Generalized equations describing the composition of associating species with respect to the equilibrium constants, orders of reactions, and state variables are derived. The resulting equations are analytically solved for cases of a pure associating fluid obeying the monomer-dimer model, the monomer-dimer-trimer model, and the infinite equilibria model. The generalized form of the theory is solved for binary associating fluid mixtures when both of the components are associating. For the three special cases when there exist only self association, solvation, and the case when only one of the components is associating, the resulting equations are shown to produce simple analytic results. The theory is also solved for a generalized multi-component mixtures. It is shown that when only one of the components is associating the working equations simplify to analytic expressions. Expressions for the excess thermodynamic functions and activity coefficients of associated fluid mixtures are derived. The theory is applied to derive general distribution function expressions for the associated species. Application of the theory to the van der Waals mixture model is introduced in order to calculate thermodynamic properties of associating solutions. The resulting associated mixture model is used for vapor-liquid equilibrium calculations of fifteen different binary mixtures in which one or both components are associating and when only solvation exists. The calculations are shown to be consistently improving the prediction over the non-associating case.
Zeitschrift für Physikalische Chemie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0942-9352
Volume: 205, 02/1998
Pages: 211