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

A UNIFAC type model is proposed to describe and predict phase equilibria in aqueous and nonaqueous sugar solutions. One new main UNIFAC group, CHOHsug ar, has been introduced to describe all monosaccharides. This main group co ntains three different subgroups, CH2OH, CHOHaxial and CHOHequatorial, whic h are introduced based on considerations of the actual saccharide ring form s in solution. UNIFAC interaction parameters between the new group and the CH2; OH; H2O; CH2-O groups have been estimated from the solubility data of monosaccharides in water, alcohol and their binary solvent mixtures. Anothe r UNIFAC main group, CH-O-CH, has been introduced to describe the disacchar ide osidic bond. Interaction parameters between the new group and the CH2; OH; H2O; CH2-O; CHOHsugar groups have been estimated too. The model gives v ery satisfactory correlation and prediction of solute activity properties ( i.e. solubility and i-butanol/water partition coefficients of sugars are de termined by the activity of the solute) as well as satisfactory prediction of solvent activity properties (i.e. bubble and freezing points are: determ ined by the activity of the solvent). A comparison with the UNIFAC model de veloped recently by Peres and Macedo [Fluid Phase Equil. 139 (1997) 47-74], which is the only other predictive model applicable to nonaqueous sugar so lutions, suggests that both models provide similar results for aqueous suga r 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. (C) 2000 Elsevier Science B.V. All right s reserved.