Separation of toluene from a toluene/n-heptane mixture using ethylene glycol containing deep eutectic solvents

Abstract

Deep eutectic solvents (DESs) were synthesized and used to separate toluene from n-heptane. DES3 and DES4 were synthesized using choline chloride, urea, and ethylene glycol with a molar ratio of 1: 2: 1 and methyltriph-enylphosphonium bromide and ethylene glycol with a 1: 3 ratio, respectively. While dynamic viscosity of DES2 ranged from 575.9 to 73.8 over temperatures 293.2 to 323.2 K, respectively, that of DES3 ranged from 219.5 to 39.44 [mPa·s]. The viscosity of both DES3 and DES4 follows the Arrhenius equation with respect to temperature from 293.2 to 323.2 K. The liquid-liquid equilibrium (LLE) of the pseudoternary system of toluene, n-heptane, and DES3 were performed at temperature of 303.2 K at ambient pressure. Another LLE of the pseudoternary system of toluene, n-heptane, and DES4 were was obtained over a temperature range of 298.2–313.2 K with a 10 K interval at atmospheric pressure. The experimental LLE data were correlated using the non-random two-liquid (NRTL) model. DESs were not detected in the raffinate phase, and as a result no further separation process for DES was necessary in the toluene separation process. The values of selectivity in the presence of DES 4 changed in a range from 24.4 to 147.5, however, those in the presence of DES3 from 4.1 to 18.7 at 313.2 K. The values of selectivity of toluene with DES applied in this study were far higher than those with other conventional solvents.