Improvement of the hard sphere expansion conformal solution theory

An improved corresponding states procedure for accurate prediction of thermodynamic properties for simple Lennard-Jones and real hydrocarbon mixtures is developed. For simple Lennard-Jones fluids, a "blip function method" of determining the hard sphere diameters for the perturbation theory developed by Weeks, Chandler and Andersen (6) is incorporated with the hard sphere expansion conformal solution theory of Mansoori and Leland (4). The mixture properties are obtained by the sum of the difference between the hard sphere properties of the mixture and the reference systems, and the total reference properties. Several Lennard-Jones mixtures of different combinations of force parameters have been studied. Significant improvement over the methods previously developed such as Van der Waals one-fluid theory and the original HSE theory on excess volumes, excess enthalpies and excess Gibbs free energies of mixing are obtained. For the real hydrocarbon fluids with unknown intermolecular potentials, a novel approach in which the hard sphere diameters are approximated by their high-temperature-limit values developed by Hsu and Leland (5) is studied in detail. Satisfactory results for the compressibility factors of a binary mixture of methane and propane at a wide range of temperature and pressure further demonstrate the applicability of the HSE method. The HSE method is then extended to polar fluids by separating the polar and asymmetric interaction contributions from the total thermodynamic properties. A carefully selected parameter is used to represent each polar and asymmetric interaction. Sample calculation on several mixtures of light normal paraffins and a quadrapolar fluid, carbon dioxide, has been carried out. Results show definite improvement over the CSP procedure previously developed. This work shed the light toward better understanding of the polar fluid mixtures