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

The global phase diagram of a binary mixture of attractive hard spheres des cribed by the Boublik-Mansoori-Carnahan-Starling-Leland equation of state w ith a van der Waals mean field attractive term is investigated in its depen dence on the ratio of the hard-sphere diameters and the strength of the att raction. Two values of the energetic combining rule parameter k(12), determ ining the deviation from the geometric mean rule, are considered. In additi on to phenomena reported recently for k(12)=1, the shield region of quadrup le points is investigated for k(12)=0.8, along with its associated azeotrop ic phenomena. For k(12)=1.15, the mixture exhibits a rich set of low-temper ature azeotropic phenomena: cusps on the p-T projections of azeotropic line s, exchange of branches of azeotropic lines, zero-temperature limited azeot ropy, and double critical azeotropic points. Some of these azeotropic pheno mena are described here for the first time.