Removal of 2- and 3-methylthiophene from their mixtures with n-heptane using tetrahexylammonium bromide-based deep eutectic solvents as extractive desulfurization agents

Deep eutectic solvents (DESs) have previously been proven to be potential extractive desulfurization agents. However, so far, only the recovery of thiophene, benzothiophene and dibenzothiophene from aliphatic mixtures have been assessed. In this work, two other sulfur-containing hydrocarbons (i.e., 2-methylthiophene and 3-methylthiophene) were for the first time recovered from their mixtures with n-heptane using two DESs as extracting agents: (i) tetrahexylammonium bromide:ethylene glycol with molar ratio 1:2 (DES 1) and (ii) tetrahexylammonium bromide:glycerol with molar ratio1:2 (DES 2). First, the binary solubilities of n-heptane and 2- and 3-methylthiophene in both DESs at 298 K and atmospheric pressure were measured. Thereafter, the liquid–liquid equilibrium (LLE) data for the four pseudo-ternary systems consisting of n-heptane + 2-methylthiophene/3-methylthiophene + DES 1/DES 2 were determined at 298 K and atmospheric pressure. On the basis of the experimental data, the distribution ratios and selectivities were calculated and used to determine the viability of both DESs for the industrial extractive desulfurization process. The experimental data were also succesfully correlated using the non-random two-liquid (NRTL) model. Both DESs were found to be able to extract 2- and 3-methylthiophene from n-heptane, with DES 1 being more preferable over DES 2.