A Nonclassical Model of a Type 2 Mixture with Vapor–Liquid, Liquid–Liquid, and Three-Phase Equilibria

A model with nonclassical exponents is developed for phase equilibria of a Type 2 mixture with vapor liquid equilibrium (VLE) and liquid liquid equilibrium (LLE). Starting with a Leung Griffiths model for a Type 1 mixture with only VLE, the model adds a Schofield parametric construction to describe LLE and a three-phase locus. Care is taken to suppress a spurious and artificial phase boundary. The model is applied to VLE data of carbon dioxide+methane. It is conjectured that this mixture upon cooling would undergo liquid liquid separa- tion, but it freezes before such ``virtual LLEʹʹ can be observed. Experimental bubble curves and the LLE structure from a classical equation of state are accurately modeled.