Ionic liquids as extractants in extractive distillation: A review of advances in screening methods and their mechanisms of action

Extractive distillation (ED), in which the selection of the extractant is particularly important, is a common method for separating azeotropic mixtures. Ionic liquids (ILs) have been used as extractants in ED processes owing to their low melting point, stable physical and chemical properties, and non-volatilization. These advantages improve the efficiency and performance of azeotrope separation by ED and have wide application prospects. In this review, the types of extractants used in ED are described, and screening methods, including experimental and model prediction methods, for ILs as extractants are introduced. The separation mechanisms of the extractants are discussed with respect to typical polar–polar, polar–nonpolar, and nonpolar–nonpolar azeotropic systems. Furthermore, several outlooks are presented regarding the preparation of novel ILs and their screening and mechanisms of action. This review provides new insights into and research directions for using ILs as extractants in ED.