Liquid–Liquid Equilibrium for Thiophene Extraction from Coal Tar Model Mixture with Ionic Liquid-Based Deep Eutectic Solvents

Coal tar is a valuable resource for clean coal utilization due to its rich chemicals, however, its sulfur compounds can cause environmental pollution through SO x emissions during combustion. Therefore, two ionic liquid-based deep eutectic solvents (IL-DESs) composed of 1-ethyl-3-methylimidazolium chloride with monoethanolamine ([EMIM]Cl/MEA) and diethanolamine ([EMIM]Cl/DEA) in a molar ratio of 1:2 were formulated as extractants for extracting thiophene from a model coal tar mixture by extraction. The liquid–liquid equilibrium for two quaternary mixtures ( n -hexane + toluene + thiophene + IL-DESs) was explored at three temperatures of 298.15 K, 308.15 K, and 318.15 K. The extractive performance of the two IL-DESs was assessed based on the indicators of selectivity and partition ratio. The results showed that [EMIM]Cl/MEA demonstrated superior performance for thiophene extraction compared with that of [EMIM]Cl/DEA. The non-random two-liquid (NRTL) model was utilized for correlating the experimental tie-line results with the root mean square deviation ( RMSD ) values lower than 0.01. Furthermore, molecular dynamics simulation was conducted to elucidate molecular interactions between thiophene and the IL-DESs. The results of the spatial distribution function and radial distribution function demonstrated that hydrogen bonding and van der Waals forces have been identified as the primary interactions between thiophene and the IL-DESs.