The Application Of Ionic Liquids In The Synthesis Of Biodiesel

Biodiesel （long-chain monoalkyl fatty acid esters）, a renewable and green energy, isproduced from vegetable oils and animal fats. At present, the production of biodiesel isgenerally performed by chemical method, which not only has difficulty in post-processingand has a high demanding on raw materials, but also is unfriendly to environment. Comparedwith chemical method, enzymatic process seems to be a promising alternative because of itsmild reaction conditions, low demanding on raw materials, which makes it possible to usewaste oils as feedstocks for enzymatic production of biodiesel. However, enzymatic reactionscurrently use organic solvent as reaction medium, which not only is volatile but also isflammable and explosive, limiting its further application. To solve these problems, thepossibility of ionic liquids used as environment-friendly solvents and liquid acid catalysts forbiodiesel synthesis was explored in this dissertation. The effects of different acidic ILs ascatalysts on the synthesis of biodiesel from the esterification of oleic acid with methanol wereexamined, and the use of the IL which exhibited the best catalytic efficiency for biodieselsynthesis from glycerol trioleate and waste oils with high acid value was further examined.On the other hand, the possibility of transesterification of soybean oil with methanol forbiodiesel production with lipase in the IL-containing system was explored. Moreover, use ofwaste oils with high acid value as feedstocks for biodiesel synthesis with lipase in aIL-containing system was further investigated to reduce production cost.Of all the seven acidic ILs tested, the IL1-sulfobutyl-3-methylimidazolium hydrosulfate（[BHSO₃MIM][HSO₄]） exhibited the best catalytic efficiency. In addition, the[BHSO₃MIM][HSO₄]-catalyzed esterification of oleic acid with methanol was systematicallyexplored. The optimum molar ratio of methanol to oleic acid, catalyst amount, reactiontemperature and reaction time were4/1,10%（based on the mass of oleic acid）,120oC and4h,respectively, under which the obtained yield of methyl oleate （biodiesel） reached97.3%. Also,[BHSO₃MIM]HSO₄as a catalyst still retained around95%of its original catalytic activityafter successive re-use of10batches （4h per batch）, showing the excellent operationalstability.The use of [BHSO₃MIM]HSO₄for biodiesel synthesis from glycerol trioleate was examined, and the optimum molar ratio of methanol to glycerol trioleate, catalyst amount,reaction time and reaction temperature were10/1,10%（based on the mass of glyceroltrioleate）,8h and120oC, respectively, under which the obtained yield of biodiesel reached51.3%. Also,[BHSO₃MIM]HSO₄as a catalyst still retained around98%of its originalcatalytic activity after successive re-use of5batches （8h per batch）.The use of [BHSO₃MIM]HSO₄for biodiesel synthesis from waste oils containing72%of free fatty acids was examined, and the optimum molar ratio of methanol to oil, catalystamount, reaction time and reaction temperature were8/1,10%（based on the mass of oils）,6h and140oC, respectively, under which the obtained yield of biodiesel reached94.9%.Obviously, the acidic IL [BHSO₃MIM]HSO₄was able to efficiently catalyze conversions ofwaste oils with different amount of FFAs into biodiesel, and showed tremendous applicationpotential. Also,[BHSO₃MIM]HSO₄as a catalyst still retained around97%of its originalcatalytic activity after successive re-use of5batches （6h per batch）.Moreover, the transesterification of soybean oil to biodiesel catalyzed by LipozymeTLIM （a low-cost immobilized lipase） was further explored with ILs as solvents. Among thetested ten ILs,[BMIM]PF₆was found to be the most suitable reaction medium for thetransesterification. The optimal mass ratio of IL to oil, molar ratio of methanol to oil, enzymeamount, water addition, reaction temperature and shaking rate were1/1,3/1,10%（based onthe mass of oil）,0.3%（based on the mass of oil）,40oC and150r/min, respectively, underwhich the obtained yield of biodiesel （methyl esters of fatty acids） reached95.1%afterreaction time of4h.The lipase-catalyzed synthesis of biodiesel in the [BMIM]PF₆-containing system wasfurther opimized using response surface methodology. The design of3level3factor wasadopted to evaluate the effects of various key variables on the reaction. A correspondingstatistic mathematical model was established based on the experimental data, and then by theresponse surface analysis, the optimum mass ratio of IL to oil, molar ratio of methanol to oiland enzyme amount were1.1/1,3.1/1and10%, respectively, under which a high yield of98.3%was obtained after reaction for4h at40oC. The lipase still maintained around95%ofits original activity after being repeatedly used for5batches （4h per batch） combined withthe re-use of [BMIM]PF₆, and gave a relatively high yield of methyl ester （93%）, showing quite a good operational stability in the presence of [BMIM]PF₆.This work forms the theoretical foundation for developing a novel route to and loweringthe cost for biodiesel production.