A PHYSICAL-CHEMICAL UNIFAC MODEL FOR AQUEOUS-SOLUTIONS OF SUGARS

A new physical chemical model is proposed to describe the thermodynamic properties of binary water-carbohydrate mixtures. The chemical part of the model takes into account the conformational equilibria of sugars and the solvation equilibria between water and sugars. The physical part of the model is a modified UNIFAC model where three new main groups (pyranose ring, furanose ring and osidic bond) are introduced to describe carbohydrate molecules. The coefficients of the model (six interaction parameters and one parameter describing the partial molar Gibbs energy of the hydrogen bond, all temperature dependent) are adjusted on seven binary water-sugar systems (glucose, mannose, galactose, fructose, sucrose, lactose, maltose). The experimental data include water activity, osmotic coefficients, activity coefficients, freezing and boiling temperatures, excess Gibbs energy and excess enthalpy. The model allows carbohydrate isomers to be distinguished and the excess Gibbs energy of systems not used in the coefficients estimation (xylose, raffinose) to be predicted.