Effective separation of toluene from n-heptane with imidazolium-based deep eutectic solvents

In this work, the selective extraction of toluene from toluene/n-heptane mixtures by using a series of deep eutectic solvents (DESs) with imidazolide-based ionic liquids as the hydrogen bond acceptor (HBA) and lactams as the hydrogen bond donor (HBD) was assessed. Investigation of the HBA alkyl chain length, HBA:HBD molar ratio, and HBD structure showed that the optimum extraction agent was EmimCl:1,3-dimethylurea (2:1). The feasibility of using DESs to separate toluene and n-heptane was confirmed by quantum chemistry calculations. The effects of toluene concentration, operating temperature, and DES:toluene volume ratio on the toluene selectivity were determined. The DES was recovered by distillation and reused. The Othmer-Tobias correlation was used to check the reliability of the experimentally obtained liquid-liquid extraction data. The liquid-liquid equilibrium data for the ternary system {toluene + n-heptane + DES} were obtained and fitted to a non-random two-liquid model.