Equation of state composition dependence: I. Implications from experimental binary PVTx data. II. Application of hybrid composition dependence for representing vapor-liquid equilibria of nonideal mixtures

This work addresses the equation of state composition dependence. The effects of various plausible approximations which can be introduced into the statistical mechanical expressions for fluid mixture thermodynamic properties are investigated. The resultant composition dependence is compared with that observed for experimental data. A modified mean density approximation (MMDA) is suggested for further investigation.; Hybrid Mixing Rules (HMR) based on the composition dependence of the virial equation combined with the van der Waals one fluid theory of mixing have been developed. The virial equation is truncated to third order composition dependence and for the remaining terms of the equation of state, classical mixing rules or conformal solution mixing rules are used. Two different types of equations of state are tested with the new mixing rules. Vapor-liquid equilibrium calculations for a number of binaries and ternaries show good agreement with experimental data. The new mixing rules referred to as the Hybrid Mixing Rules (HMR), give better results than the conformal solution mixing rules for most of the systems studied irrespective of the type of equation of state (BWR or cubic type) used. Thus the HMR model can be used to improve any corresponding states or cubic type equations of state for mixtures.; The new mixing rules require two binary interaction parameters for all types of systems, which are determined by regressing binary vapor-liquid equilibrium (VLE) data. VLE predictions for multicomponent systems are made with the interaction parameters obtained from the binary data. Calculations without the use of any binary interaction parameters are made for both binary and ternary VLE data which show reasonable predictions for nonpolar systems.