Global phase diagrams of model and real binary fluid mixtures Part II. Non-Lorentz–Berthelot mixtures of attractive hard spheres

Abstract

The global phase diagram of a binary mixture of attractive hard spheres described by the Boublík–Mansoori–Carnahan–Starling–Leland equation of state with a van der Waals mean field attractive term is investigated in its dependence on the ratio of the hard-sphere diameters and the strength of the attraction. Two values of the energetic combining rule parameter k₁₂, determining the deviation from the geometric mean rule, are considered. In addition to phenomena reported recently for k₁₂=1, the shield region of quadruple points is investigated for k₁₂=0.8, along with its associated azeotropic phenomena. For k₁₂=1.15, the mixture exhibits a rich set of low-temperature azeotropic phenomena: cusps on the p–T projections of azeotropic lines, exchange of branches of azeotropic lines, zero-temperature limited azeotropy, and double critical azeotropic points. Some of these azeotropic phenomena are described here for the first time.