Trends and research progresses on the recycling of ionic liquids

Ionic liquids (ILs), comprised entirely of cations and anions, are classified as property-tunable and green solvents. Due to their special properties, such as high thermal stability, low volatility, as well as outstanding physical and chemical nature, ILs have shown great application prospects in many fields and become a research hotspot in recent years. However, the inevitable loss during the use of ILs and the problem of relatively high cost, the recycling and reuse of ILs have drawn great attentions with the scaling up of the ionic liquid-based technologies. Before the large-scale industrial application of ILs, the problem of IL recycling must be solved. This review aims to introduce methods of recycling ionic liquids, which have been investigated widely in recent years. We mainly discussed five methods applied in recycling and reuse of ILs, i. e. distillation, extraction, membrane separation, adsorption and phase separation. The advantages and disadvantages were summarized and analyzed. The results indicated that the recycling and reuse of ILs will greatly enlarge the application range of ILs, while there are still some other challenges need to be resolved. For example, the recycling scale is yet small and the methods reported in the literature are still in their infancy stage. Finally, the review puts forward the future research direction for recycling and reuse of ILs. © 2019, Chemical Industry Press. All right reserved.