Activity coefficients at infinite dilution of various organic solutes in the deep eutectic solvent (tetramethylammonium chloride + 1,6 hexanediol in the 1:1 molar ratio)

Abstract

Deep eutectic solvents (DESs) have emerged as potential green and low-cost substitutes to ionic liquids in various chemical processes. In this study, experimental activity coefficients at infinite dilution for 22 organic solutes were measured in the DES consisting of tetramethylammonium chloride and 1,6 hexanediol (1:1 molar ratio) by gas-liquid chromatography at four temperatures within the range of (313.15–343.15) K at 101.3 kPa. The effect of the molecular structure of the solute on limiting activity coefficient was also examined. From infinite dilution activity coefficients, limiting partial molar excess enthalpies, entropies and Gibbs free energies were calculated to gain insight into solute-DES interactions. It emerged that the strongest soulte-DES interactions were associated with pyridine, thiophene and methyl acetate. Subsequently, limiting selectivities and capacities were calculated for various separation problems to evaluate the potential use of the DES as a separation agent. The best separation performance of the investigated DES was obtained for mixtures consisting of n-alkanes and thiophene or pyridine. For this reason, it was concluded that the DES (tetramethylammonium chloride + 1,6 hexanediol in the 1:1 molar ratio) is a credible candidate to be considered for the denitrogenation as well as the desulphurisation of transportation fuels.