Phase Equilibria In Fluid Mixtures At High Pressures

Abstract

The six types of phase behaviour observed in binary mixtures are described briefly. Liquid-liquid immiscibility in Type II and Type III phase behaviour is discussed in terms of pressure-temperature-composition diagrams. The conditions for the coexistence of two phases and the conditions for a critical point in both binary and ternary mixtures are presented. The criticality conditions are given in terms of both the Gibbs and Helmholtz functions. Methods for calculating high pressure equilibrium in fluid mixtures using these conditions together with a one fluid model are discussed. The use of empirical and theoretically based equations of state to calculate the Helmholtz function are briefly reviewed and the need for caution when using this approach is pointed out. Finally the need for a classification for the phase behaviour of ternary mixtures and for liquid-liquid equilibrium data of higher accuracy are considered. © 1986 IUPAC