Vapor–liquid equilibrium behavior and quantum chemical calculations for bioethanol + water + choline chloride:urea + potassium acetate

Abstract

Extractive distillation is an effective method for separating azeotropic mixtures, and its success depends on the careful selection of distillation entrainers. Recently, deep eutectic solvents (DESs) have emerged as a novel and environmentally friendly class of entrainers. However, most research has focused on on pure DES entrainers. Developing new DESs remains a challenging task that requires significant time to identify suitable components and mixing ratios that form low freezing points. In this study, the well-known azeotropic mixture of biomass fuel ethanol and water was used as the model system. The distillation efficiency of the pure DES (choline chloride:urea 1:2, mol/mol) was significantly enhanced by adding just 5 wt% potassium acetate, leading to a 40 % reduction in the usage of single DES. It was found that increasing the hybrid entrainer content from 0 to 34.8 wt% significantly raised the relative volatility of ethanol/water mixture near the azeotropic point from 0.99 to 3.29. To gain a deeper understanding of ethanol/water separation across the entire concentration range, the pseudobinary and pseudoternary vapor–liquid equilibria (VLE) of the ethanol/water + hybrid entrainer system were investigated, and the binary energy parameters of the Non-Random-Two-Liquid (NRTL) model were regressed. Lastly, quantum chemical calculations of the separation mechanism were conducted, covering several aspects: geometry optimizations of the individual components and complexes, electrostatic potential calculations, interaction energy assessments, analysis of hydrogen-bond donors and acceptors, examination of the location and bond lengths of intermolecular hydrogen bonds, evaluation of the influence on vibrational frequencies, and natural bond orbital analysis (NBO).