| Summary: | 碩士 === 國立中正大學 === 化學工程研究所 === 107 === Biodiesel can be prepared from vegetable oil and methanol by transesterification, and the alkaline catalyst is usually added to catalyze the reaction. Its reaction is influenced by water in reactants because the triglyceride were be hydrolyzed to form long carbon chain free acids, then it can make saponification reaction with alkaline catalyst. Therefore, the conversion and the yield of biodiesel were be reduced, and the produce emulsification cause a problem in products that are difficult to separate and purify. In this study, the alkaline pellet catalysts, MgO/SiO2(Q30), were prepared by incorporating Mg(NO3)2 into granular SiO2(Q30) followed by calcination in air at 500℃. These catalysts were tested by soybean-oil transesterification with methanol at 200℃ with methanol to oil ratio (mole) of 6:1, respectively. Cycling test results indicated that conversion at 2nd cycle is at 87.6% and that at 5th cycle is 78.7% and the MgO leached amont is 41.8mg/kg. Catalyst deactivation is mainly caused by MgO leached in reaction, because MgO is easily dissociated, resulting in defects of the catalyst structure and degrad the activity. The catalyst deactivation, however, can be suppressed by the addition of B(OCH3)3 to reaction. From previous studies, we know that B(OCH3)3 contribute to the formation of the product FAME and can be recovered by azeotropy. Experiment result showed that the addition of 5Wt% of B(OCH3)3 to reaction system, no catalyst deactivation was observed, while only 0.1Wt% was added, conversion decreased about 87.2% at the 2nd cycle, because B(OCH3)3 can effectively reduce the Mg2+ loss from the catalyst MgO/SiO2 (Q30). Synchrotron XRPD and FT-IR showed that -OCH3 from B(OCH3)3 react with Mg2+ to form Mg(OCH3)2 on catalyst surface ,which increases catalyst hydrophobicity thereby greatly inhibiting the formation of Mg(OH)2 and the corresponding Mg2+ leaching.
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