SOLUBILITY PREDICTION IN NONIDEAL LIQUID MIXTURES (UNIFAC, HEXYLRESORCINOL)

Theories which predict solubility of a new or existing chemical species solely from pure component data are unsuccessful in the prediction of the solubility of solids in highly nonideal liquid mixtures. For such systems, a semiempirical approach can be used.;One part of this study determined the predictive ability of UNIFAC in a strongly interacting system involving hydrogen bonding and one in which the components differed in size and shape: the solubility of hexylresorcinol in 21 mixtures of ethyl acetate, ethyl myristate and hexane at 10.0(DEGREES), 14.9(DEGREES), 20.3(DEGREES) and 25.6(DEGREES)C. Experimental partial molar excess enthalpies and entropies of hexylresorcinol were compared with those predicted by UNIFAC to investigate the physical significance of the theory.;UNIFAC was an excellent predictor of the solubility of hexylresorcinol in these solvent mixtures with an error of greater than 15% seen in only one out of every seven solvent mixtures. The experimental partial molar excess enthalpies and entropies of hexylresorcinol, on the other hand, were not predicted well.;In a second study, mixture response surface methodology was tested as an efficient statistical method to empirically predict solubility in nonideal mixed solvent systems. In this method, a minimum number of experimentally determined solubilities are used to generate empirical equations relating solubility to solvent composition which can then be used to predict solubility in any solvent mixture. The method was used to predict xanthine solubilities in dioxane/water mixtures and was shown to be superior to the extended Hildebrand method. (Abstract shortened with permission of author.).;For the purpose of semi-empirically predicting solubility in a previously untested solvent mixture, a group-contribution approach is attractive. A group-contribution approach, UNIFAC, which is based on a quasi-chemical model for activity coefficients, has been used to predict liquid phase activity coefficients and naphthalene solubility in several polar and nonpolar solvents. For the purpose of predicting solubility, UNIFAC does not require any solubility experimentation. UNIFAC only requires that each component's structure and the enthalpy of fusion of the solid be known. Therefore, from a practical standpoint, UNIFAC would have considerable advantage over other methods.