Thermodynamics of liquid-liquid equilibria including the critical region. Transformation to non-classical coordinates using revised scaling

Abstract

Classical or mean-field models for equilibrium properties of fluids and fluid mixtures are inaccurate near a critical point. To improve the performance of such models near the critical point of a pure fluid, Fox proposed a method of transforming the coordinates of a classical equation of state to non-classical coordinates. Recently, we have extended the method of Fox to binary liquid mixtures at constant pressure and to ternary liquid mixtures at constant pressure and temperature. However, our previous extension has used simple scaling, where transformation to non-classical coordinates is symmetric with respect to the critical point. In this work, our extension is applied to binary and ternary liquid mixtures in a revised-scaling context that allows for the asymmetry found in real systems. Results are shown for binary and ternary liquid mixtures. For a few illustrative examples, good agreement is obtained between experimental and calculated coexistence curves.