산성 이온성 액체 촉매를 이용한 대두유의 에스터화 및 에스터 교환 반응에 관한 연구

Abstract

The objectives of this study are to prepare supported- and unsupported-acidic ionic liquid catalysts, to investigate the characteristic with FT-IR and 1H-NMR measurements, and to explore suitable catalysts for the esterification and transesterification of soybean oil to produce high yield of fatty acid methyl esters(FAMEs). As the first step, the esterification of free fatty acid with methanol to biodiesel was investigated in a batch reactor using various solid acid catalysts, such as polymer cation-exchanged resins with sulfuric acid functional group (Amberlyst-15, Dowex 50Wx8), acidic ionic liquids (ILs)-modified silica gels respectively with -SO3H and -SO2Cl functional group (SiO2-[ASBI][HSO4], SiO2-[ASCBI][HSO4]) and grafted silica gels respectively with -SO3H and -SO2Cl functional group (SiO2-R-SO3H, SiO2-R-SO2Cl). The effects of reaction time, temperature, reactant concentration (molar ratio of methanol to oleic acid), and catalyst amount were studied. Allylimidazolium-based ILs on modified silica gels were superior to other tested solid acid catalysts. Especially, the performance of SiO2-[ASBI][HSO4] (immobilized by grafting of 3-allyl-1-(4-sulfobutyl) imidazolium hydrogen sulfate on silica gel) was better than that of a widely known Amberlyst-15 catalyst at the same reaction conditions. A high conversion yield of 96% was achieved in the esterification reaction of the simulated cooking oil at 353 K for 2 h. The high catalytic activity of SiO2-[ASBI][HSO4] was attributed to the presence of strong Brønsted acid sites from the immobilized functional groups. The catalyst was recovered and the biodiesel product was separated by simple processes such as decantation and filtration. In the second step, the production of biodiesel from soybean oil catalyzed by Lewis acidic ionic liquids (ILs) containing metal chloride salts was investigated. Metal chloride salts, such as SnCl2, ZnCl2, AlCl3, FeCl3, and CuCl, were screened for oil transesterification in the range of 363-423 K. Among these metal chlorides, tin chloride showed particularly high catalytic property for the oil transesterification. Similarly, among these Lewis acidic ionic liquid catalysts [Me3NC2H4OH]Cl-2SnCl2 resulted in a high FAMEs content of 91.1% under the following reaction conditions: 403 K, 14 h, and a molar ratio of 1:12:0.9 (oil:methanol:catalyst). Unlike the pure tin chloride catalysts, Lewis acidic ILs containing tin chloride [Me3NC2H4OH]Cl-2SnCl2 catalyst could be recycled up to five times without any significant loss of activity by separating from the FAMEs with simple decantation. The Lewis acidity and high moisture-stability of this catalyst appeared to be responsible for the excellent catalytic performance. The effects of reaction time and the molar ratio of methanol/catalyst to oil on the FAMEs production were also studied in this work.