An analytical method of predicting Lee-Kesler-Plöcker equation-of-state binary interaction coefficients

Abstract

An analytical method is proposed for finding numerical values of binary interaction coefficients for the Lee-Kesler-Plocker (LKP) equation of state. The method is based on solving simultaneous equations from Plocker's mixing rules for pseudocritical parameters of a mixture and the Lee-Kesler equation for the saturation line. For mixtures of hydrocarbons containing from two to nine carbon atoms, the divergence between calculated and experimentally based interaction coefficients (ICs) is no more than ±0.4%. The method is extended to mixtures of polar substances. For polar mixtures, aneffective molar composition concept is introduced which takes into account the impact of dipole moments on the process of molecular associations. Formulas for finding the effective molar composition of mixtures containing polar and/or nonpolar constituents and the binary interaction coefficient (κij) based on this effective composition and pure component properties are shown. Calculatedκij values for 12 binary mixtures of polar substances differ by 0.4 % or less from correspondingκij values obtained by processing experimental data on saturated pressure (Ps) and saturated temperature (Ts) lines for these same mixtures. A simplified alternativeκij approximation method with an error (2–5 %) is also given for mixtures of polar substances.