Separation Of Polyunsaturated Fatty Acids By Liquid-liquid Extraction

It is a big challenge to separate those compounds with pretty similar structure, for example, the polyunsatured fatty acids (PUFA) with long chain. Due to the highly beneficial health effects of PUFAs, especially Ω-3PUFAs, such as EPA and DHA, therefore, it is of great meaningfulness to obtain high-purity PUFAs. The difference in the chemical structures of FAs are the chain length with16,18,20,22or more carbons, and the degree of unsaturation with or without double bonds. The longer the chain lenth is, the higher hydrophobicity is, leading to small solubility of PUFAs in polar organic solvents. However, the double bonds can cause a bit positive effect for the afficity to polor organic solvents. Now, the effective method to obtain high-purity PUFAs should be chromatography separation. But it consumes large amount of organic solvents, such as acetonitrile, methonal and THF. Besides, the throughput are small, and the cost is high. The other methods, such as urea complexation and molecular distillation, ontains low-purity EPA+DHA, which is always smaller than75%. So, it is in great demand to develop a efficient and ecomonic method to seprate PUFAs. Recently, a great number of research have shown that ionic liquid-based liquid-liquid extraction is a promising, economic, efficient mehod to separate bioactive homologues.Thus, In this paper, liquid-liquid extraction experiments was selected as the method to obtain high-purity PUFAs. Before the experimental performation, fast screening of extractants including organic solvents and ionic liquids had been finished efficiently by COSMO-RS, which was used to calculation the sepation selectivity, and the correlationship betwwen the selectivity and interaction energies was discussded deeply.As far as the liquid-liquid extraction experiments, two model systems, the mixture of fatty acids and the mixture of fatty acids methyl esters with different chain lengths and unsaturation degrees, was used to evaluate the extractive separation. The polar organic solvents-hexane biphasic systems was selected to be applied into the separation of the mixture of Fas and the mixture of FAMEs, respectively. The results reveal that DMSO exhibited high separation selectivity for both FA mixture and FAME mixture systems, whose values of C20:5to C18:3could even be larger than1.8. But the distribution coefficients of FAMEs (DC20:5<0.15) was far smaller than those of Fas (DEPA=11.54). Therefore, DMSO is perfect extractant for the separation of polyunsaturated fatty acids, not for polyunsaturated fatty acid methyl esters.By evalutating the separation performance of the ionic liquids/diluent-hexane biphasic systems, the mixture of FAMEs was used for the experiments, and the result were compared with that of pure organic solvent as extractant. The result shows that the [EMIm][N(CN)2]/DMF demonstrated higher sepatation selectivity (1.83) than pure DMF (1.51). But the distribution coefficient of C20:5was small (0.3), even3times smller than that of pure DMF as extractant (1.12), while the mole fraction of IL was10%. The imidazolium and pyridiniumium ionic liquids showed highest seaparation selectivity among all the ILs, because of the π-π interactions with PUFAMEs. However, the small distribution coefficients of FAMEs might because higher polarity of ILs/DMF mixed extractants than pure DMF. In general, the experimental results were in accordance with the predicted separation selectivity by COSMO-RS.In order to evaluate the feasibility of liquid-liquid extraction for paracticle application, the multi-stage fractional extraction was performed by the process calculation. The result showed that both high purity and high recovery of products could be obtained by adjusting the process parameters.