Calculation of Complex Phase Equilibria in the Critical Region of Fluid Mixture Based on Multi-Fluid Lattice Equation of State

Quantitative correlation of critical loci and multiphase behaviors has received considerable attention because the increased industrial importance of processes operating within the high-pressure region such as supercritical fluid extraction. However, in the critical region, classical thermodynamic models such as equations of state (EOS) frequently fail to correlate phase equilibrium properties. Recently, the present authors proposed a new lattice-hole EOS based on the multi-fluid approximation of the nonrandom lattice theory. The model requires only two molecular parameters reflecting size and interaction energy for a pure fluid and one additional interaction parameters for a binary mixture. In this work, the reliable applicability of the EOS was demonstrated to various phase equilibria of complex mixtures in the critical region. Demonstration of the EOS was made to calculate multiphase behaviors such as solid-liquid-vapor (SLV) equilibria and critical loci of binary complex mixtures at high pressure. For P-T, P-x, and T-p phase diagrams tested, the model agrees well with experimental data.