| Extractive separation of acidic compounds from water solution is an important process, which is widely applied for the preparation of water-soluble chemicals, environmental governance, and so on. However, the existing hydrophobic extractant have problems such as limited variety, weak recognition ability of hydrogen-bond and over-rely on acid-alkali chemical reaction to improve the extraction performance. Based on the unique properties of ionic liquids such as task-specific tunability and good ability to form liquid-liquid biphasic systems, a novel ionic liquid-molecular solvent composite extractant with good hydrophobicity and strong recognition ability of hydrogen-bond was developed, which can be used to separation the water-soluble acidic compounds efficiently by physical extraction.The performance of Br--based hydrophobic ionic liquid-molecular solvent composite extractant for selective separation of L-ascorbic acid (AA) and ascorbyl glucoside (AA-2G) was systematically studied. Efficient separation of AA and AA-2G was achieved by tuning the species or ratio of ionic liquids or molecular solvent. The distribution coefficient of AA can reach up to 1.362 when the extractant was tetradecyltrihexylphosphonium bromide ([P66614]Br)-ethyl acetate mixture (xIL=10%), which was 60～680 times larger than using regular hydrophobic ionic liquids or ethyl acetate as extractant, and the selectivity of AA to AA-2G was more than 60. Besides, Br--based hydrophobic ionic liquid-molecular solvent composite extractant also have strengths such as large extraction capacity, low mutual solubility with water and good recycle ability. The purity of AA-2G can be increased from 50% to 96.2% after five stages countercurrent extraction, and the yield coefficient maintained more than 98%.The extraction mechanism of AA and AA-2G was systematically studied by quantum chemistry calculation, conductor-like screening model for real solvent (COSMO-RS) calculation, determination of solubility, design of extraction experiments, and so on. The results showed that the mechanism of extraction of AA by Br--based hydrophobic ionic liquid-molecular solvent composite extractant was physical extraction. There were strong hydrogen-bond interactions between AA and Br-, which drives AA into the Br--based hydrophobic ionic liquid-rich phase with molecule form or ion pair form. The hydrogen-bond interaction between AA and [P66614]Br was stronger than those between AA and regular hydrophobic molecular solvent or regular hydrophobic ionic liquids, and larger solubility or distribution of AA in Br--based hydrophobic ionic liquid-molecular solvent mixtures was thus obtained. The solubility difference between AA and AA-2G in extractant led to the larger selectivity of AA to AA-2G. AA was likely to be preferentially dissolved by the Br--based hydrophobic ionic liquid in composite extractant.Br--based hydrophobic ionic liquid-molecular solvent composite extractant was also applied to the remove of weakly acidic phenol compounds from water. The results showed that [P66614]Br-ethyl acetate mixtures could not only decrease the viscosity of extractant notably, but also have good affinity to phenols. The distribution coefficient of phenol in [P66614]Br-ethyl acetate-water biphasic system ([P66614]Br: ethyl acetate=1:4) reached up to 345, which was 5.3 times larger than that using pure ethyl acetate as extractant,9-60 times larger than those using several common hydrophobic ionic liquids and only 25.3% smaller than that using pure [P66614]Br. The viscosity of 20 mol%[P66614]Br mixture was only 1% of pure [P66614]Br. |
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