Investigation of physicochemical properties of deep eutectic solvent and sulfolane mixtures

The relatively high freezing point of pristine sulfolane compared to that of conventional aprotic organic solvents poses practical limitations in industrial applications. Tailoring the physicochemical properties of sulfolane via mixtures with deep eutectic solvent (DES) systems may be a feasible approach to reducing its freezing point and expanding its usability. In this study, DES mixtures (DESM) comprising sulfolane, choline chloride and ethylene glycol were prepared and characterized in terms of its physicochemical properties, including freezing temperature, density, viscosity, surface tension and refractive index. The prepared DESMs exhibited moderate densities (1.223–1.233 g·cm –3 and low viscosities (12.01–17.30 cP) at 303.15 K. COSMO-RS calculations were performed to elucidate the intermolecular interactions among the DESM components, while experimental density data were used to validate COSMO-RS density predictions, yielding an average absolute relative deviation (AARD) of 3.07%. The Vogel-Fulcher-Tamman (VFT) model was found to be the most suitable for describing the temperature dependence of DESM viscosities. Notably, introducing ethylene glycol as the hydrogen bond donor component lowered the freezing point from that of pristine sulfolane (ca. 301.55 K) to as low as 249.63 K in the DESM system. The enhanced physicochemical properties of sulfolane demonstrate the potential of these systems as tuneable solvents for future industrial applications.