Prediction of vapour-liquid equilibrium: Theory, computer techniques and application to permanent gas mixtures at pressures in excess of 5 bar

Abstract

A technique for calculating the composition of two coexisting phases in equilibrium at a given temperature and pressure is described. The method is applicable, in principle, to any one-fluid model and any two- parameter closed equation of state. The philosophy of the technique is similar to that used in previous work on critical points.    Values of (∂G/∂x₂)_T,P are calculated for mole fraction compositions ranging from zero to unity in small steps in order to locate (∂G/∂x₂)_T,P loops. Around each loop there is a region of phase separation and the compositions of coexisting phases are found by the usual equal-area line technique.     The use of the method is briefly illustrated by comparison with the experimental results for simple gas mixtures. The agreement between theory and experiment is satisfactory.