Solvent pre-selection for binary mixtures based on the activity coefficient at infinite dilution in deep eutectic solvent: Tetraethylammonium chloride+ Ethylene glycol

The values of activity coefficient at infinite dilution (γ12∞) were reported for 27 solutes in tetraethylammonium chloride + ethylene glycol deep eutectic solvent (DES) system at a molar ratio of 1.000:1.997 by inverse gas chromatography (IGC) method at intervals of 10 K from 303.15 to 333.15 K. Then the measured γ12∞ values were used to determine the thermodynamic functions (ΔH1E,∞, ΔS1E,∞, and ΔG1E,∞). The values of selectivity (Sij∞) and capacity (kj∞) for six extraction problems (that is, heptane/toluene, benzene/methanol, heptane/thiophene, acetone/ethanol, cyclohexane/benzene, and cyclohexane/ethanol.) were calculated from experimental γ12∞ values and compared with literature values of other solvents under the same separation conditions. The results indicate that the studied DES is a potential extractant for separation of cyclohexane/ethanol and heptane/thiophene systems. The Flory-Huggins interaction parameters (χ12∞) were used to evaluate the miscibility between DES and organic probes, and the results reveal that alcohols exhibited the best solubility in tested DES. Furthermore, the Hildebrand solubility parameters (δ2) were calculated for tested DES, and the values of δ2 decreased with the increase of temperature.