Phase equilibria of d-glucose and sucrose in mixed solvent mixtures: Comparison of UNIQUAC 1-based models

Solid-liquid equilibrium measurements of ternary sucrose-mixed solvent mixtures at 25, 40, and 60 °C are carried out, using a simple and accurate analytical method. A search for a reliable activity coefficient model for sugar liquid mixtures is performed: three UNIQUAC based models are investigated—modified UNIQUAC, entropic free-volume and original Flory-Huggins. New UNIQUAC interaction parameters are estimated based on the aqueous and non-aqueous experimental data presented in this work together with those available in the literature. The solubility calculations were carried out using an equation based on fusion enthalpy data for the sugars. Although the UNIQUAC-based models investigated give in general a quite satisfactory representation of different thermodynamic properties of aqueous solutions containing d-glucose, d-fructose, and/or sucrose, it is shown that only the modified UNIQUAC model is able to accurately describe the ternary solubility data of d-glucose and sucrose in mixed solvent mixtures. Various UNIQUAC-based procedures were applied to ternary sucrose-mixed solvent mixtures. A modified UNIQUAC model was able to describe the ternary solubility data of d-glucose and sucrose in mixed solvents.