A Semi-theoretical van der Waals Equation for Calculation of Vapor-Liquid Equilibria at High Pressures

Abstract

An equation of the van der Waals type is derived and applied to the calculation of vapor–liquid equilibria at elevated pressures. For the hard-sphere part of the equation the theoretical relation of Carnahan–Starling is used. The effect of intermolecular forces is represented by the usual van der Waals term but the "constant a" is permitted to vary with temperature and density as dictated by the experimental PVT data for argon; this variation of the "constant a" is generalized for other simple fluids through corresponding states. While this treatment is of little interest for representing the configurational properties of pure fluids, it is useful for calculating the properties of simple fluid mixtures. Illustrative vapor–liquid equilibrium calculations are performed for binary and ternary mixtures of nitrogen, argon, and oxygen at 6 and 18 atm.