Selective Liquid-liquid Extraction Of Natural Phenolic Compounds Using Ionic Liquids

Natural phenolic compounds are important resource for functional food and medicine. The separation of them has great value but the current separation methods like adsorption have problems such as low capacity, large solvent consumption and significant energy consumption. Basing on the unique properties of ILs such as task-specific tunability and good ability to form liquid-liquid biphasic systems, a novel method was developed mediated by amino acid ionic liquids (AAILs) through liquid-liquid extraction process in this dissertation, for the separation of tocopherols as the representative of natural phenols. The effect of ILs on the selectively extraction was investigated in the model system consisting of a-tocopherol and methyl linoleate. The great potential of this method was demonstrated.Firstly, seven ILs with common anions were investigated for the partitioning of a-tocopherol and methyl linoleate in IL-diluent/hexane biphasic system at30℃with the initial component concentration of1.5mg/mL. The study of different ILs used for the extraction showed that, the selectivity of a-tocopherol to methyl linoleate was higher obtained by the ILs with stronger hydrogen-bonding basity. The selectivity of a-tocopherol to methyl linoleate was5.6obtained by [bmim]Cl-DMF mixture in which the mole fraction of [bmim]Cl, with the strongest basity among ILs investigated, here was5%.Five AAILs were synthesized using1-ethyl-3-methylimidazolium ([emim]+) as cation. The phase equilibria and the physicochemical properties of AAIL-molecular solvent binary mixtures were studied. AAILs could form liquid-liquid biphasic systems with non-polar solvents such as hexane and octane with low mutual-solubility. At30℃, the solubility of [emim]Ala in hexane was only0.017mg/g. Added with2%of AAIL, the value of hydrogen-bonding basity (β) for AAIL-polar solvent mixture was increased by20%.The partition of a-tocopherol and methyl linoleate in the AAIL-diluent/hexane biphasic system was investigated at30℃with the initial component concentration of 1.5mg/mL. Several impact factors on the extraction such as type of AAILs, the concentration of AAIL in the AAIL-diluent mixture, temperature, and concentration of components in the feedstock, were studied. Through adding small amount of AAILs in the AAIL-diluent mixture, a good match could be achieved between the distribution coefficient and the selectivity of a-tocopherols. When using [emim]Ala-dimethylformamide (DMF) as extractant with the mole fraction of IL5%, the distribution coefficient of a-tocopherol was2.46, which was1.4times higher than the data obtained by [bmim]Cl-DMF or pure DMF under the same condition, and the selectivity to methyl linoleate reached to14.3, which was2times higher than that obtained by [bmim]Cl-DMF and4times higher than that of pure DMF.The mechanism of a-tocopherol extracted by ILs was investigated. A linear relationship was found between the distribution coefficient of a-tocopherol and the β values of IL-DMF extractant, and also between selectivity and (3values. The IR measurement offered a direct evidence of the hydrogen-bonding interaction between a-tocopherol and AAIL. So the selectivity separation of a-tocopherol and methyl linoleate by ILs could probably be ascribed to the hydrogen-bonding interaction between the IL and a-tocopherol.