Phase Diagram of Ethylene Carbonate–Sulfolane System

Abstract

Phase equilibria in the ethylene carbonate (EC)–sulfolane (SL) binary system were investigated using differential scanning calorimetry in a temperature range from –150 to +50°C to construct a phase diagram of the system. The EC–SL system belongs to a simple eutectic type, with a eutectic point of –16°C at 70 wt % of SL. It was noted that the EC-SL solutions have a tendency to supercooling in the composition range from 50 to 75 wt % of SL; the metastable liquid phase is characterized by a glass transition temperature Tg = –105°C. Reaching of an equilibrium state is hindered in the middle region of compositions; this can be explained in terms of strong dipole-dipole interactions between EC and SL molecules, whose intensity increases with decreasing temperature. Quantum-chemical calculations of the Gibbs energy of the formation of isolated dimers of various types, performed by the M052X method based on density-functional theory, confirm this assumption.