ANALYSIS OF THE UNIFAC-TYPE GROUP-CONTRIBUTION MODELS AT THE HIGHLY DILUTE REGION .1. LIMITATIONS OF THE COMBINATORIAL AND RESIDUAL EXPRESSIONS

An analysis of the behavior of UNIFAC-type group-contribution models a t the infinite-dilution region is presented. It is shown that the modi fied UNIFAC and Entropic-FV combinatorial expressions account satisfac torily for the combinatorial effects, but not the Flory-Huggins and or iginal UNIFAC ones. It is also shown that available residual terms fai l to account sufficiently for the residual effects, performing actuall y better when combined with the aforementioned poorer Flory-Huggins an d original UNIFAC combinatorial expressions. The ensuing implications of these limitations of the residual terms on the accuracy of infinite -dilution activity coefficient correlation are then demonstrated.