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

Abstract

• Effective separation of toluene from n -heptane was achieved with EmimCl:DMU. • Quantum chemistry calculation was used to verify the feasibility of separation. • The proposed DES showed very good stability and reusability. • Othmer–Tobias correlation was used to check the reliability of experimental data. • The experimental LLE data were modeled by using the NRTL thermodynamic model. 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.