PHASE BEHAVIOR AND THERMODYNAMIC PROPERTIES FOR NONPOLAR AND POLAR MIXTURES (EQUATION OF STATE, VAPOR-LIQUID EQUILIBRIUM)

Pseudocritical rules have been developed which enable the calculation of vapor-liquid equilibrium (VLE) values and thermodynamic properties for nonpolar, polar, and quadrupolar mixtures for wide ranges of temperatures and pressures. Interaction constants of mixtures are obtained by procedures for the calculation of the interaction second virial coefficient with relationships for the Kihara spherical core potential for nonpolar fluids and of Lin-Stiel for a pre-averaged potential function for polar fluids. The only input data required for these procedures are the critical temperature and pressure and acentric factor for nonpolar components and an additional parameter, the polarity factor for polar components. The approaches of this study are effective for nonpolar, polar, and quadrupolar mixtures considered.; For nonpolar mixtures, the Lee-Kesler equation of state is employed with the pseudocritical constants of the system to determine the fugacities of the components in the gaseous and liquid phases. Excellent results are obtained for VLE values for nonpolar mixtures, particularly for mixtures containing dissimilar components such as the methane-n-heptane and methane-n-octane systems.; For polar mixtures, the procedures of this study enable the calculation of thermodynamic properties and phase behavior. The Wu-Stiel equation of state for polar fluids is required for the thermodynamic properties of mixtures such as PVT behavior and heats of mixing. The results of this study for polar mixtures indicated that the developed pseudocritical relationships enable the prediction of the correct azeotropic behavior and limited miscibility behavior. Because of the intrinsic sensitivity for the limited miscibility mixtures, the VLE calculations are very difficult for these polar systems.; A nonlinear relationship for the effective acentric factor for mixtures is necessary for accurate VLE calculations for nonpolar-quadrupolar mixtures. Good results are obtained for carbon dioxide, nitrogen, benzene, and ethylene with hydrocarbons, particularly for higher asymmetric mixtures, such as the carbon dioxide-n-decane and nitrogen-n-heptane systems.; The approach of this study is not only simple for the calculation of phase behavior and thermoydnamic properties of mixtures, but also provides insight into the molecular interactions of mixtures.