Molecular model for the VLE p-T-x relationships of binary mixtures

An analytical expression for the pressure-temperature-composition relations in the vapour-liquid equilibrium of con-polar binary mixtures is proposed. The model is based on a simple analytical expression for the vapour pressu re of pure non-polar fluids, which, for a given temperature, requires as in put only the Lennard-Jones molecular parameters and the acentric factor of the substance. The equilibrium mixture pressure is then expressed as a func tion of the vapour pressure of each component and of a mixture contribution . The molecular parameters required for this mixture contribution are relat ed to the molecular parameters of the pure component through a modified Lor entz-Berthelot mixing rule, where the interaction parameters are given as s imple functions of the temperature and composition, with eight appropriate constants for each binary mixture. We show that the model permits one to re produce or predict in a simple way the pressure (for a given liquid mole fr action) or the liquid composition (for a given pressure).