The predictive accuracy for estimating infinite dilution activity coefficients by γ^∞-based UNIFAC

Abstract

The predictive accuracy for estimating infinite dilution activity coefficients γ^∞ by a modification of the UNIFAC method wherein the group interaction parameters were based on only γ^∞ data (referred to as ‘γ^∞-based UNIFAC’) has been studied. Estimates and measured values were compared for six prototypical solutes in a series of homologous n-alkanes, l-alcohols and alkanenitrile solvents. Despite the fact that the interaction parameters were derived using only γ^∞ data, this approach still gave serious errors due to several inherent problems in the original UNIFAC model. Its performance is sometimes even poorer than that of the original UNIFAC method. For example for nitromethane in alcohols and p-dioxane in nitriles γ^∞ values predicted by the γ^∞-based UNIFAC are essentially zero. The large errors for these systems are most likely due to inaccurate interaction parameters in the γ^∞-based UNIFAC method.