Water activity in polyol systems

Water activities of binary and ternary mixtures containing polyols were mea sured using an electronic hygrometer with temperature ranging from (10 to 3 5) degrees C. The concentrations of the mixtures varied according to the so lubility limit for each polyol (D-sorbitol, D-mannitol, xylitol, meso-eryth ritol, and glycerol). Results were compared with the group contribution-bas ed models ASOG and UNIFAC. The predictions using parameters from the litera ture were poor, probably as a consequence of the strongly polar hydroxyl gr oups bounded to consecutive carbon atoms in the polyol molecule. Better agr eement was obtained by readjusting some of the interaction parameters. The data bank used in this procedure included water activity data as well as po lyol solubility data taken from the literature. The best results were achie ved using the UNIFAC-Larsen model with an average relative deviation of 0.9 % for water activity and solubility data.