Applications of deep eutectic solvents for hard-to-separate liquid systems

Abstract

• Three types of hard-to-separate systems are classified by solute polarity. • Three extraction approaches using DESs in separation are introduced. • Applications of DESs in various separation systems are reviewed. • Separation mechanism and guideline for DES screening are analyzed. • DES stability and methods for recycling of DESs after separation are discussed. Deep eutectic solvents (DESs) are low-freezing mixtures formed by hydrogen bond donor (HBD) and acceptor (HBA). The change of HBA and HBD type or their ratio gives rise to a variation of the formed DES structure and properties. Such designable features make DESs meet the specific separation requirement for various systems. This work overviews the applications of DESs in three typical hard-to-separate liquid systems classified based on the solute polarity, namely non-polar solute, mildly polar solute, and polar solute systems. For each type of hard-to-separate system, the features and problems are addressed, and the requirement for DESs are analyzed. Moreover, the separation mechanism and the guideline for screening DES are introduced, and the methods for recycling of DESs after separation are discussed. Finally, further research trends of using DESs in hard-to-separate systems are prospected.