A UNIFAC model for phase equilibrium calculations in aqueous and nonaqueous sugar solutions

Abstract

A UNIFAC type model is proposed to describe and predict phase equilibria in aqueous and nonaqueous sugar solutions. One new main UNIFAC group, CHOH sugar, has been introduced to describe all monosaccharides. This main group contains three different subgroups, CH 2OH, CHOH axial and CHOH equatorial, which are introduced based on considerations of the actual saccharide ring forms in solution. UNIFAC interaction parameters between the new group and the CH 2; OH; H 2O; CH 2–O groups have been estimated from the solubility data of monosaccharides in water, alcohol and their binary solvent mixtures. Another UNIFAC main group, CH–O–CH, has been introduced to describe the disaccharide osidic bond. Interaction parameters between the new group and the CH 2; OH; H 2O; CH 2–O; CHOH sugar groups have been estimated too. The model gives very satisfactory correlation and prediction of solute activity properties (i.e. solubility and i-butanol/water partition coefficients of sugars are determined by the activity of the solute) as well as satisfactory prediction of solvent activity properties (i.e. bubble and freezing points are determined by the activity of the solvent). A comparison with the UNIFAC model developed recently by Peres and Macedo [Fluid Phase Equil. 139 (1997) 47–74], which is the only other predictive model applicable to nonaqueous sugar solutions, suggests that both models provide similar results for aqueous sugar solutions, but the proposed model is more suitable for the prediction of phase equilibrium of sugar solutions involving also nonaqueous solvents as well as in such two-phase systems.