Prepraration Of Calcium Oxide Solid Base And Study On The Synthesis Of Biodiesel

The catalytic performances of calcium oxides in the transesterification reaction of methanol and refined soybean oil have been evaluated in this study. The species of precursors and the loading amount of solid base catalysts were studied to obtain the best catalytic activity and reusability.The transesterification reaction parameters were investigated to assess the best FAME yield, including the reaction temperature, the reaction time, mass of catalyst, acid value of raw material, molar ratio of methanol and oil, the emulsification and cosolvent effect.Besides, some instrumental methods, such as XRD, RAMAN, BET, SEM, TG, CO₂-TPD were used to reveal the matrix structure, the specific surface area, the thermo stability and the base strength of catalysts. Both the poisoning mechanism in the air atmosphere and the catalytic mechanism in the transesterification reaction of calcium oxides catalysts were also detailedly investigated to study the poison effect.Finally, the solid-acid catalyzed esterification reaction and the solid-base catalyzed transesterification reaction were combined together as a whole process. And a series of raw materials, including soybean oil, palm oil, soybean oil- fatty acid mixture and waste cooking oil, were tested to evaluate the reliability and stability of the process.The main results and observations from these studies are summarized as follow: The catalytic transesterification activities and the base strength both increase in the order CaO-N< Ara-N < Cal-N. When the Li loading was 1.25%, Li/CaO performed the highest catalytic activity which could maintain activity even after being reused for 7 cycles. In the late of the transesterificaiton reaction, calcium oxides reacted with glycerol by-product, and calcium glycerin was formed. Calcium glycerin could dissolve in the reaction medium and acted as a homogeneous catalyst.Various impacts of reaction conditions have been studied and the optimized reaction conditions were summarized as follow: the acid value of raw material was no more than 1mgKOH/g; the mass ratio of catalyst to soybean oil was 1%; mole ratio of methanol and oil was 6:1; the speed of emulsifying machine was 6000 r/min; and 5% FAME was added as cosolvent.Compared with Ara-N, Cal-N showed higher tolerance to the poison of air, which may be due to its quickly formed amorphous structure of calcium carbonate on the surface. Therefore, further carbonation of bulk CaO could be effectively prevented. Whereas, Ara-N is inclined to form a compact calcite-CaCO₃ phase on the surface, and thus the catalytic transesterification reaction is blocked.