Ultrasound-Enhanced Transesterification Of Fish Oil With Ethanol Catalyzed By Acidic Ionic Liquids

Fish oil has positive effects on lowering blood fat and promoting brain development for containing eieosapentacnoic acid(EPA)and docosahexanoic acid(DHA).However,both EPA and DHA in natural fish oil exist in the form of glycerides,which are low in content and high in boiling point.The fatty acid ethyl ester obtained by transesterification of fish oil with ethanol,which is easily absorbed,can facilitate the purification of EPA and DHA.In this work,the physicochemical properties and composition of raw fish oil were determined.The results showed that the acidic value of fish oil is high because of the existence of free fatty acid,which determined the choice of acidic catalysts.Sulfonic acid functionalized imidazole/pyridine ionic liquids([PSMim][HSO4],[BSMim][HSO4],[PSpy][HSO4],and[BSpy][HSO4]),and amino acid ionic liquids([Pro][HSO4],[Gly][HSO4]and[Ala][HSO4])were synthesized.The structures were characterized by 1H-NMR,13C-NMR,IR,and the water content and Hammett acidity were determined by Karl Fischer Moisture Analyzer and Hammett indicator-UV spectrum method,respectively.The Bronsted acidic ionic liquids(BILs)were used to catalyze the transesterification,in which most sulfonic acid functionalized ionic liquids,except[BSpy][HSO4],result in less side reactions and more excellent product quality than H2SO4.Amino acid ionic liquids showed worse yield due to its low acidity and short carbon chain.The transesterification of fish oil with ethanol is a heterogeneous process under experimental conditions of this work,and ultrasound can speed up the reaction rate by the emulsification of liquid-liquid phase to increase the reaction interfacial area.The optimum reaction conditions were determined as ultrasonic mixing power of 700 W,ethanol/fish oil mass ratio of 0.4,catalyst[PSMim][HSO4]dosage of fish oil of 9%,reaction temperature of 75?,and reaction time of 180 min.MD simulation revealed the obvious density enhancement of the BILs at the interface,in which the ester group on fatty acid glyceride tends to be located at the outmost position of the interface and approach the catalyst phase.Hopefully,the results obtained in this work may bring new insights into the understanding of the promoting effects of BILs as catalysts and ultrasonic methods on the transesterification reactions.