Mechanistic insight into separation of benzene and cyclohexane by extractive distillation using deep eutectic solvent as entrainer

Abstract

In this work, a technical scheme for separation of benzene and cyclohexane by extractive distillation using deep eutectic solvent (DESs) as entrainer was proposed. Acetic acid (AA) was selected as hydrogen bond donor (HBD), tetraethylammonium bromide (TEAB) and tetraethylammonium chloride (TEAC) were selected as hydrogen bond acceptors (HBA), and two kinds of DESs were successfully prepared (i.e., DES1 is TEAC : AA = 1:3, DES2 is TEAB : AA = 1:3). Vapor liquid equilibrium experiments show that the relative volatility of benzene cyclohexane system can be significantly improved by using DESs as an entrainer, so that the separation of the target system can be achieved by extractive distillation. Further, quantitative calculations and molecular dynamics simulations were performed to explore the separation mechanism at the molecular level. The interaction sites between molecules were revealed by ESP analysis, and the interaction types between molecules were further elaborated by IGMH analysis. The results show that the Br atom of TEAB and the Cl atom of TEAC have hydrogen bonding with benzene, while there is π - π interaction between AA and benzene. The intermolecular interaction energy and spatial distribution function (SDF) further proved that the interaction between DES and benzene was stronger than that with cyclohexane. In conclusion, DES as entrainer for azeotrope separation has broad industrial application prospects.