Molecular theory of phase equilibria in model associated mixtures. I. Binary mixtures of water and a simple fluid

摘要

The phase equilibrium behavior of a basic statistical mechanical model of a binary mixture of water and a simple fluid are investigated. For water we use a primitive model which incorporates no attractive forces other than hydrogen bonds within a hardhyphen;sphere core, and the simple fluid is modeled by a fluid of hard spheres with an attractive meanhyphen;field term. The qualitative behavior of the phase equilibria andPminus;Tcritical lines of this model are calculated using an accurate theoretical equation of state for primitive water obtained in analytical form using the Wertheim thermodynamic perturbation theory, for a range of values of the mixturersquo;s two underlying parameters, the hardhyphen;sphere size ratio and the mean field strength. The model exhibits type IIId and type IVast; phase behavior of three qualitatively different types, characterized by the existence of either one or two threehyphen;phase lines. The model exhibits a range of phenomena, including tricritical points and double critical end points. The implications of the model results for corresponding real fluid mixtures are also discussed.