Various thermodynamic models have been proposed for systems containing hydrogen bonding compounds (Economou and Donohue, 1991b). The most widely used theory is based on the assumption that hydrogen bonding results in the formation of new species in the system and is referred to as chemical theory. The associated-perturbed-anisotropic-chain theory (APACT) (Ikonomou and Donohue, 1986), an equation of state that accounts for hydrogen bonding using chemical theory, was recently generalized to treat compounds that can self-associate and solvate with other compounds in the mixture (Economou et al., 1990). The resulting equations for hydrogenbonding interactions were solved analytically for three types of binary mixtures. The first one contains an amphoteric component, which is both acidic and basic (that is, an alcohol), and a component that is only acidic (that is, chloroform) or only basic (that is, a ketone). The second type of binary mixtures contains an amphoteric component and a component that does not self-associate nor solvate (a diluent). The third type of binary mixtures contains one basic and one acidic component. However, for the general case of two or more self-associating components, the resulting expressions contained coupled infinite series so that these expressions could not be written in a closed form and were not solved analytically. Thus, approximate or numerical solutions have been proposed (Economou et al., 1990;Panayiotou, 1990;Anderko, 1991;Economou and Donohue, 1991a).In this work, we derive expressions for the mole fraction of the monomeric species and the ratio n,/no, that is a measure of the extent of the association, using an approach introduced by Nagata and Ohtsubo (1986). This approach accounts explicitly for all the different configurations of the association species of the system. We present here the closed-form equations for the general case of an associating binary mixture. These expressions are believed to be general and reduce to the analytic equations for the special cases described above. However, the need of an approximate or numerical solution for Correspondence concerning this work should be addressed to M. D. Donohue. the general case of a multicomponent associating system remains.
TheoryIn the ABPACT (acid-base-perturbed-anisotropic-chain theory) equation of state and in many other theories for associating systems (Economou and Donohue, 1991b), the assumption is made that hydrogen bonding results in the formation of new species. For the specific case of two bonding sites per molecule, linear chains (such as dimers and trimers) are formed. For systems where more than one associating compound is present, linear chains can contain monomer molecules from only one of the compounds or from different compounds. Specifically, for a binary mixture of components M and N where both components have one acidic (electron acceptor) site and one basic (electron donor) site, hydrogen bonding is described through the following chemical equilibria:The first two equilibria account for the self-...