Revisiting the Classic Activity Coefficient Models

A link, established between the classic excess Gibbs free energy expressions and conventional mixture models, allowed the extension of the Margules and van Laar models to multicomponent mixtures. It is shown that the multicomponent form of the classic van Laar model features only one parameter per component in the mixture. It is also a special case of several other models including those due to Wassiljewa and Scatchard. This means that the latter can be seen to be a more general Scatchard–van Laar expression. It is also proven that the composition dependence of the Porter, Margules, van Laar, NRTL, and Wilson are all obtainable as special cases of the weighted double power mean mixture model. The ability of the models to accurately predict ternary performance from knowledge of binary behavior was tested using nine isothermal vapor–liquid data sets. The Wilson-type models performed best in this regard. The extended Scatchard–van Laar model also proved to be effective despite being particularly parameter-sparse.