An extended regular solution model with local volume fraction

The regular solution model (the Hildebrand-Scatchard equation) coupled with the Flory-Huggins equation has been extended by using the local volume fraction proposed by Wilson so that it can be applied to polar mixtures. From the extended regular solution model, activity coefficient equations can be derived. Pair energy parameters required to evaluate local volume fractions can be estimated by solubility parameters and molar volumes predicted from the molecular structures of constituent pure components by using additive methods. The applicability of the present regular solution model is examined by correlating vapor-liquid equilibria of several ethanol + hydrocarbon binary systems, and it is found that the proposed model can be adopted for polar mixtures.

Regular Solution

Local Volume Fraction

Activity Coefficient

Vapor-Liquid Equilibrium

Ethanol

Hydrocarbon