Closed-loop liquid-liquid equilibria and the global phase behaviour of binary mixtures involving hard-sphere plus van der Waals interactions

Calculations of the critical properties of binary mixtures of components of equal size are reported using the Guggenheim equation of state. The calcul ations are used to determine the global phase diagram of binary mixtures. T ype VI phase behaviour is predicted successfully indicating that closed-loo p liquid-liquid equilibria can be obtained from hard-sphere + van der Waals interactions. Closed-loop liquid-liquid equilibria occur in the region of the global phase diagram characterized by moderately strong unlike interact ions and components with very dissimilar critical temperatures. The Guggenh eim equation can predict all experimentally known phase behaviour types. Tn addition, other hypothetical phase behaviour types are also predicted.