低共熔溶剂：一种应用在混合物分离过程中的绿色溶剂

低共熔溶剂(DESs)因具有合成容易、价格低廉、环境友好、挥发性低、溶解能力强、可生物降解、结构可设计等特点，被认为是一种绿色溶剂。近年来，研究者通过深入研究低共熔溶剂的性质，结合低共熔溶剂的特点，将其替代传统的有机溶剂，在混合物分离过程中开展了大量的研究工作，包括：酸性气体(如CO₂、CO₂和H₂S)吸收、生物活性物质萃取、燃料油品中含硫和含氮化合物的脱除、油酚混合物分离、芳烃和脂肪烃混合物的分离、醇水混合物分离、生物柴油合成过程中甘油的脱除等。本文分析了低共熔溶剂的结构、性质和特点，综述了低共熔溶剂在分离领域的最新研究成果，探讨了低共熔溶剂在混合物分离应用中存在的问题，展望了低共熔溶剂的发展趋势。

Deep Eutectic Solvents: Green Solvents for Separation Applications

Deep eutectic solvents (DESs) are regarded as a new class of green solvents because of their unique properties such as easy synthesis, low cost, environmental friendliness, low volatility, high dissolution power, high biodegradability, and feasibility of structural design. DESs have been widely applied for the separation of mixtures as alternatives to conventional solvents. A DES usually consists of a hydrogen bond donor (HBD) and a hydrogen bond acceptor (HBA). HBAs include amides, thiourea, amines, imidazole, azole, alcohols, acids and phenol. HBAs include quaternary ammonium salts, quaternary phosphonium salts, imidazolium-based salts, dication based salts, inner salts, and molecular imidazole and its analogues. Therefore, there are numerous DESs available for use in different applications. With an in-depth understanding of the common and novel properties of DESs, researchers have prepared and applied DESs to various types of separations. We first introduce the composition of DESs, including various HBDs and HBAs frequently used in the literature. Second, the properties of DESs, including phase diagrams, melting points, density, viscosity, and conductivity, are summarized. Third, recent applications of DESs in the separation of mixtures are reviewed, including the absorption of acidic gases (CO₂, SO₂ and H₂S), the extraction of bioactive compounds, extraction of sulfur-and nitrogen-containing compounds from fuel oils, extraction of phenolic compounds from oils, separation of mixtures of aromatic and aliphatic compounds, separation of alcohol and water mixtures, removal of glycerol from biodiesel, separation of alcohol and ester mixtures, removal of radioactive nuclear contaminants, and separation of isomer mixtures of benzene carboxylic acids. DESs are used in two ways for the separation of mixtures. (1) A DES prepared in advance is used as a solvent to separate a component from a mixture by selective dissolution or absorption of specific compound(s), such as the absorption of SO₂ using betaine+ethylene glycol DES. Here, DESs are used like traditional solvents. (2) A DES is formed in situ during the separation of mixtures by adding a HBA to a mixture containing one or more HBDs, such as the removal of phenol from an oil mixture using choline chloride, where a phenol+choline chloride DES is formed during the separation process and the formed DES does not dissolve in the oil phase. Although various DESs have been broadly developed for the separation of mixtures, research continues in the field of DESs, including analysis of the physicochemical properties of DES, especially during extraction or absorption, development of functional DESs for high-efficiency separations, development of efficient methods to regenerate DESs, and combined use of DESs with other techniques to improve separation processes. This article describes general trends in the development of DESs for separation and evaluates the problematic or challenging aspects of DESs in the separation of mixtures.