Multiscale Simulation and Mechanism Analysis of Cyclohexane/Ethanol Separation by Ionic Liquid Extractive Distillation

Abstract

Ionic liquids (ILs) excel in extractive distillation (ED) for the separation of binary azeotropes due to their unique physical and chemical properties. However, the mechanism of action of ILs in azeotropes is unclear, and the present-day mechanistic studies have been conducted at specific concentrations. In this work, the formation and separation process of azeotropes and the phase behavior of each component at different component concentrations were studied microscopically by quantum chemistry (QC) calculations, molecular dynamics (MD) simulation, and process simulation. The hydrogen-bond donor− acceptor connection between solvents was outlined using the COSMO-SAC model. By using QC to evaluate the hydrogen-bond interaction between ethanol and ILs, the optimal extractant [Dmim][Ac] was chosen. The phase behavior of different concentrations of ILs with ethanol and cyclohexane was further investigated by MD. The two-dimensional atomic number density distribution (ANDD) instinctively indicates the mixing behavior and structural distribution of the cyclohexane−ethanol−ILs ternary system at the atomic level. The radial distribution function (RDF) and spatial distribution function (SDF) showed that the interaction between anions and ethanol in ILs was the strongest, and the amount of ILs had a significant impact on the cations throughout the separation procedure. Although anions have a strong attraction to cyclohexane and ethanol, this effect is not sensitive to the concentration of ILs. Aspen Plus V12 was used to simulate the separation of the cyclohexane−ethanol azeotropic system in the industrial process, and the feasibility of ILs as an extractant was verified. This work provides theoretical guidance for the study of the ED mechanism and solvent selection.