Thermodynamic properties of high-pressure liquid mixtures containing supercritical components

A method was developed for describing liquid-phase fugacities in order to predict high-pressure vapor-liquid equilibrium of systems containing supercritical components. A solution theory is formulated to provide expressions for the change in fugacity of components of a multicomponent fluid due to any change in the state of the system in terms of integrals of the statistical mechanical direct correlation function. The method not only provides an excellent description of the nonideality of gas-solvent liquid mixtures including even those with highly polar solvents but also yields good predictions of vapor-liquid equilibrium at elevated pressures and relates Henry's constants of a solute in two different solvents. A method is proposed to calculate phase equilibrium by treating the solvent mixture as a pseudo-component. This is very useful for gas solubility in uncharacterized, complex solvent mixtures. Investigations of the n-butane-n-decane-methane ternary indicate that this is likely to be a viable approach.