Use of molecular shape factors in vapor‐liquid equilibrium calculations with the corresponding states principle

Abstract

AbstractCalculation of fugacities of components in a gaseous or liquid solution directly from the corresponding states principle requires an improvement in the pseudo‐critical constants for the mixture. The derivation of the pseudo‐criticals must take into account deviations from the simple two parameter corresponding states principle which require additional parameters incorporated into the definition of the pseudo‐criticals. In this work parameters called molecular shape factors are introduced into the pseudo‐criticals. A generalized correlation for these shape factors is presented.Use of the shape factors greatly improves the calculation of vapor‐liquid equilibrium ratios for nonpolar hydrocarbon mixtures with large differences in molecular size and shape. Excellent results are obtained both in the low pressure and in the retrograde region when the pseudo‐reduced properties of the vapor and liquid lie within the range of accurately known properties of a reference fluid and the reduced temperatures for each component is greater than approximately 0.6.