Chemical Modification Of Soybean Oil By Solid Catalysts

Chemical modification is the premise to industrial application of plant oils.Transesterification and epoxidation are two fundamental reactions of chemical modification whichare dependent on moleculer structure of plant oils. Synthesis and application of novel solidcatalysts is the core to improve the two chemical modification reactions. In the thesis, solid basecatalysts for transesterification were synthesized using layered double hydroxides （LDHs） as theprecursor and its catalytic behavior in the transesterification of soybean oil by ethylene glycol wasstudied. Two supported catalysts for epoxidation were prepared via immobilization of peroxophosphotungstic acid and methyltrioxorhenium （MTO） onto halloysite nanotubes （HNTs） and itscatalytic behaviors in epoxidation of soybean oil using H₂O₂as oxidant were studied. The relatedexperiments and results are summarized as follow:For solid base catalysts, crystalline Li-Al LDHs was synthesized through coprecipitation andLi-Al layered double oxide （Li-Al LDO） with larger specific area and pore size was obtained aftercalcining of Li-Al LDHs. To suppress the memory effect of Li-Al LDHs, Li-Al LDO was furthermodified with silane coupling agent Z6020and the modification caused increasing of pore size.Both Li-Al LDO （Cat-1） and modified Li-Al LDO （Cat-2） as catalysts can catalyze thesolvent-free transesterification of soybean oil by ethylene glycol and can be used for4circles.Modification with Z6020can obviously decrease the temperature for regeneration of the catalysts,from450℃for Cat-1to120℃for Cat-2. After three times regeneration, both Cat-1and Cat-2still can catalyze the transesterification of soybean oil. Reaction at160℃for2h at1000rpmstirring rate,10:1ethylene glycol to soybean oil molar ratio, and5wt%catalyst, the yield reachedmore than93%for both Cat-1and Cat-2, respectively.The immobilization of peroxo phosphotungstic acid ({PO₄[W（O）（O₂）₂]₄}^3-) onto HNTsincluded three steps. First, amine groups were anchored onto HNTs through modification with Z-6020. Then amine groups were quaternary-ammonated with CH3I and CH2Br（CH2）4CH3toproduce cationic ions. Finally,{PO₄[W（O）（O₂）₂]₄}^3-was immobilized onto HNTs via ion exchange.In solvent-free epoxidation of soybean oil catalyzed by supported {PO₄[W（O）（O₂）₂]₄}^3-, thecombination of mechanical stirring and ultrasonication was helpful to accelerate the mass transferamong soybean oil-H₂O₂-supported {PO₄[W（O）（O₂）₂]₄}^3-catalysts three phases. The introductionof phase transfer agent （methyl tri-n-octyl ammonium chloride） during immobliztion of{PO₄[W（O）（O₂）₂]₄}^3-was also helpful to increase the catalytic efficiency. The supported{PO₄[W（O）（O₂）₂]₄}^3-still had good catalytic activity after three circles and the deactivated catalystcan be reloaded with {PO₄[W（O）（O₂）₂]₄}^3-to recover the activity.In immobilization of MTO, Poly （4-vinylpyridine）（P-4VP） brushes of different length wasgrafted onto HNTs by living surface-initiated atom transfer radical polymerization （SI-ATRP） andthen MTO was immobilized via coordination of MTO with N in pyridine. As the length of P-4VPbrushes can be adjusted by varying the polymerization time, and the coordination of MTO with Nin pyridine was stoichiometric, controlled immobilization of MTO was realized. Thus resultedsupported MTO is effective for epoxidation of soybean oils. The conversion of soybean oilincreased with MTO loadings, keeping the high selectivity.