Application of the Unified Functional Activity Coefficient (UNIFAC) and Analytical Solution of Groups (ASOG) for the Calculation of Mutual Solubilities in Water Systems of Alkanes, Arenes, and Alkanols

The recommended solubilities taken from the International Union of Pure and Applied Chemistry/National Institute of Standards and Technology (IUPAC-NIST) Solubility Data Series were used as testing data for the prediction of the solubilities in water systems of alkanes, arenes, and alkanols with various versions of unified functional activity coefficient (UNIFAC) and analytical solution of groups (ASOG) methods. It was strongly confirmed that parameters aimed at the prediction of vapor liquid equilibria (VLE) are not applicable for predictions of liquid liquid equilibria (LLE) in the water systems. The average relative error of the predicted solubility for alkane water systems is equal to hundreds or even thousands of percent. For arene water and alkanol water systems it is usually about 100 %. Much better accuracy can be obtained with parameters adjusted to the solubility data. The UNIFAC version developed by Voutsas and Tassios, VT-UNIFAC, predicts mutual solubilities in alkane water systems with an average relative error equal to about 40 %. This modification supplemented with temperature-dependent parameters for a pair of groups, ACCH(2)-H(2)O, predicts the mutual solubilities in alkylbenzene water systems with 20 % accuracy. For alkanol water systems, the VT-UNIFAC was not applied because of lack of group-interaction parameters for the OH group.