Design and use of ionic liquids in separation processes for azeotropic mixtures

Abstract

Separation of azeotrope and close-boiling mixtures is a challenge in several industries. Ionic liquids (ILs) have been recently determined as alternative entrainers in the extractive distillation (ED) owing to the flexibility in their tailor-made molecular structures and properties for a specific work. A systematic methodology of selection and design of the best IL-based separation process was developed to investigate the viability of the azeotropic separation process using ILs through five different mixtures as case studies including the mixtures of ethanol + water, ethanol + hexane, benzene + hexane, toluene + methyl cyclohexane (MCH), and ethylbenzene (EB) + p-xylene (PX). The Hildebrand solubility Group Contribution parameter along with the capacity and selectivity of ILs are the key parameters for selecting the suitable ILs as entrainers. All first four azeotropic mixtures were successfully demonstrated and four best ILs were identified, i.e. [MMIM][DMP] from ethanol + water, [EMIM][BTI] from ethanol + hexane mixture, [EMIM][EtSO4] from benzene + hexane mixture, and [HMIM][TCB] from toluene + methyl cyclohexane (MCH) mixture. However, the proposed screening criteria cannot effectively demonstrate the isomer mixture, i.e. EB + PX mixture, due to the similarity of these isomers causing no differences in the calculated Hildebrand solubility parameter, selectivity and capacity. A simulation process of ILs was carried out successfully, which a minimum energy requirement and a solvent usage were determined and compared with the conventional solvent process. In order to get a supported decision-making in an investment, economic evaluation was determined and compared between the IL and conventional solvent processes.