Statistical thermodynamic approach to the prediction of vapor-liquid equilibria of multi-component mixtures

Abstract

A Hard Sphere Expansion ( HSE) conformal solution theory, which is a result of the application of statistical mechanics, is developed in order to predict the vapor-liquid equilibria properties of multicomponent mixtures. The HSE mixing rules are derived with consideration of the Kihara spherical-core function as the pair potential together with the 3-body potential function. Based on this HSE conformal solution theory, an equation of state for multi-component fluid is developed. In this conformal solution theory perturbation equation of state of pure fluids is used as the reference equation of state. The vapor-liquid equilibria properties of several properly chosen binary and ternary non-polar mixtures are predicted. These mixtures include: argon-krypton, argon-methane, methane-krypton, nitrogen-methane, nitrogen-argon, argon-neopentane, methane-neopentane, methane-perfluoromethane, carbon dioxideethylene, carbon dioxide-ethane, nitrogen-argon-oxygen, and nitrogen-argon-methane. The predicted results obtained in the present investigation compare quite favorably with the experimental vapor-liquid equilibria values. Furthermore, the present approach, being a purely molecular theory of fluid mixtures, provides detailed insight into the peculiar behavior of the azeotropic fluid mixture. It is shown that the vapor-liquid equilibria properties of multicomponent fluid systems may be predicted correctly through the present statistical mechanic approach provided that like- and unlike-interaction parameters of the species of the mixtures are known a priori. Generally, the present investigation shows that the use of the molecular theory of fluid mixtures in predicting the mixture properties is very promising.