The Separation Of Polyunsaturated Fatty Acid Methyl Ester

ω-3 polyunsaturated fatty acids have important physiological functions for human body and are widely used in medicine, cosmetics and dietary supplement industry. Thus, it is significant to purify ω-3 polyunsaturated fatty acid. The fatty acid composition of vegetable oil is complex. It is difficult to separate polyunsaturated fatty acids with similar molecular structure. The study focuses on two parts: Firstly, the exaction conditions of linolenic acid methyl ester from tallow catalpa oil methyl ester by silver nitrate were investigated, the extraction process and equipments were designed. Secondly, according to the action principle between silver ion and polyunsaturated fatty acids, lewis acid ionic liquid was used as the extractant, and the extraction performance of ionic liquid for fatty acid methyl esters(FAMEs) was researched.Silver ions can form reversible π-bonded complexes with double bonds. This reversible interaction between silver ions and double bonds can be employed to selective separate ω-3 polyunsaturated fatty acids. In this work, silver nitrate was dissolved in methanol aqueous solution as extractant to extract linolenic acid methyl ester from tallow catalpa oil methyl ester. The influences of extraction temperature, concentration of silver ion and content of methanol on extraction equilibrium and extraction selectivity of inolenic acid methyl ester were investigated. The results indicated at lower extraction temperature, the extractant with higher concentration of silver ion and methanol had better extraction performance for linolenic acid methyl ester. Linolenic acid methyl ester had better separation effect under the conditions of at 10℃, 1 mol/L AgNO3 and 60% methanol in the extractant and 20℃, 1.8 mol/L AgNO3 and 50% methanol in the extractant. The selectivity of linolenic acid methyl ester can reach to 33.65 and 35.44, respectively, and the extraction equilibrium constant of linolenic acid methyl ester can reach to 1.7969 and 1.272, respectively. This paper chose 20℃ as extraction temperature, aqueous solution with 1.8 mol/L AgNO3 and 50% methanol as extractant after comprehensive considering the operation temperature, the extraction rate and selectivity of linolenic acid methyl ester.The extraction equilibrium constants were measured. The complex heat between linolenic acid methyl ester and silver ion was calculated through the linear fitting of Van’t Hoff equation, the complex heat was-59.07 kJ/mol. And one linolenic acid methyl ester molecule can complex with 2.5 silver ions. Under the determinate extraction condition, the impacts of extraction stage and reverse extraction on the separation of linolenic acid methyl ester were researched. The results showed that, the purity of linolenic acid methyl ester can be over 95%, and the yield of linolenic acid methyl ester was 80.1% after three steps extraction and three steps reverse extraction. The study also found that the extractant can be recycled after reverse extraction. Based on experiment results, the extraction process was constructed, and the extraction tower with 0.8 m diameter and 6 m packing layer was designed to produce 11 000 tons of linolenic acid methyl ester annually.According to the action principle between silver ion and polyunsaturated fatty acids, lewis acid ionic liquid was used as the extractant, the influences of ionic liquid anion type, carbon chain length and unsaturation degree of FAMEs on separation were investigated. The type of ionic liquid anion had impacts on lewis acidity of ionic liquid. The extraction performance of lewis acid ionic liquid was better than normal ionic liquid. And the ionic liquid with stronger lewis acidity had better extraction capacity. Moreover, the extraction capacity of ionic liquid for FAMEs was influenced by the molecular structure of FAMEs. The FAMEs with more double bonds and shorter carbon chain have higher extraction rate and extraction equilibrium constant. There existed interplay between different FAMEs.The impact of phase ratio on the extraction capacity of ionic liquid for FAMEs was also studied. The result showed that phase ratio had few influence on the extraction rate of PUFAMEs, but great influence on SFAMEs. With the increase of oil phase volume, the extraction rate of SFAMEs was decreased and the extraction selectivity of PUFAMEs was improved. What’s more, the extraction rate of SFAMEs declined rapidly with decrease of the carbon chain. The polarity of oil phase and extract phase would be changed after adding polar solvents, which will affect the extraction performance of ionic liquid for FAMEs. The impacts of the dose of ethyl acetate and ethanol on extraction rate of ionic liquid for FAMEs were studied. The results indicated that the addition of polar solvent could reduce the extraction rate. That will contribute to reverse extraction FAMEs from ionic liquid.