Study On Calcium-based Solid Base Catalyst For Biodiesel Production

CaO-ZnO solid base catalysts were prepared by co-precipitation method and sol-gel method respectively.The catalytic performance of catalysts was evaluated by using soybean oil and methanol as feeds.The preparation conditions of CaO-ZnO solid base catalysts were systematically investigated.The effects of reaction conditions such as methanol/oil molar ratio and catalyst/oil mass ratio on the transesterification were investigated.The effects of catalysts modification,activation and regeneration were also studied.The results of the catalyst preparation show that the suitable preparation conditions of co-precipitation method are as follows,NaOH/Na₂CO₃ molar ratio=0.75:1,Ca/Zn molar ratio=1:1,calcination temperature 850?,calcination time 5 h.Using citric acid as complexing agent,the suitable conditions of sol-gel method for the CaO-ZnO solid base catalyst preparation are as follows,V?Water?/n(?Mⁿ⁺)=320 mL?mol^-1,V?Ammonia?/n(?Mⁿ⁺)=5 mL?mol^-1,Ca/Zn molar ratio 1:1,calcination temperature 750?,calcination time 4 h.The CaO-ZnO solid base catalyst prepared under the above conditions exhibits high catalytic performance.The relative surface area of the catalyst prepared by the two methods is relatively small,and in comparison,the catalyst prepared by the sol-gel method has a little larger specific surface area,which is beneficial to the reactants easily contacting with the catalyst.The results of the catalyst evaluation and SEM,BET and CO₂-TPD characterizations indicates that there is no obvious relation between the alkali amount the catalytic performance of the catalyst for the reaction.The presence of larger pores in the catalyst is favorable to the vegetable oil molecules into the pores,and the active site of the catalyst can be effectively utilized.The optimization results showed that the suitable reaction conditions were as follows,methanol/oil molar ratio=30:1,catalyst/oil mass ratio=0.06:1,reaction temperature 70?,and reaction time 90min.Under these conditions,the yield of glycerol over the catalysts prepared by the two methods is higher than 90%.Compared with the catalyst prepared by the co-precipitation method,the catalyst prepared by the sol-gel method has a relatively high catalytic activity.After used repeatedly 5 times,the catalytic performance decreasing of the catalyst was not observed,it implies that the CaO-ZnO solid base catalyst has excellent stability.The results of the catalyst modification showed that the activation of the catalyst with a mixed solution of 10 wt%glycerol-methanol can effectively shorten the reaction induction period.No significant difference between the catalytic performance of the regenerated catalyst and the fresh catalyst was observed.Under the conditions of reaction temperature 65?,methanol/oil molar ratio=42:1 and LHSV 3 h^-1,the yield of glycerol was over 90%for the continuous transesterification process.