Study On The Biodiesel Production Via Transesterification Using CaO-based Catalysts

Biodiesel production via transesterification of animal and vegetable oils with alcohol using suitable catalysts is of significance,in terms of both resolving energy shortage and environmental protection.CaO is the most used catalyst in current biodiesel production,however,there are still some different viewpoints about the actual active species of CaO in the transesterification,especially for the reason why the reaction accelerates after an induction period.In addition,the catalytic performance of commercial CaO in the transesterification also needs to be improved.The work in this thesis is focused on these two aspects.At first,the active species change of CaO during the transesterification of soybean oil with methanol was investigated,the formation of induction period and active species for various reaction stages was analyzed;then several reproducible plant templates were used to prepare noval CaO/C solid base materials,in order to obtain good catalysts for biodiesel production.The main progresses of this thesis are:(1)There is an induction period in the transesterification of soybean oil with methanol using commercial CaO catalyst,and catalytic activity has a significant change in different reaction stages.The active species are mainly CaO and Ca(OH)2 at the initial and middle stages,and Ca(C3H7O3)2 is mainly responsible for the active specie at the later stage or in recycled catalyst.The recycled and fresh CaO mixed catalyst showed higher catalytic activity,which may be related to the formation of CaC3H6O3 in the reaction process.The formation of induction period comes mainly from the effect of mass transfer.The accelerateion of reaction after the induction period is derived from the formation of monoglycerides and diglycerides,a kind of surfactants,in liquid phase.The presence of such surfactants can improve the solubility of methanol in soybean oil and promote the formation of microemulsion.It is advantaged for the contact between two reactants and solid base.The mass transfer resistance is reduced,and thus reaction accelerates apparently.The catalytic performance of commercial CaO is significantly improved by treating with H2O or HOAc at room temperature followed by cacining at 973 K.This modification can reduce the particle size of CaO,significantly increase the bulk volume and the surface area,therefore the modified CaO exhibited higher catalytic performance.(2)A novel CaO(C)solid base material has been synthesized by means of a "gel template" using corn starch as the template agent and the carbon precursor.The CaO particles are dispersed on the carbon surfaces.The CaO(C)material possesses both microporous and mesoporous structures,with a specific surface area higher than 200 m2/g.It exhibited good catalytic activity in transesterification of soybean oil with methanol.(3)A new "in-situ steaming" route was developed to prepare shaped CaO/C solid base catalyst.In this route,self-raising flour was used as template and carbon precursor,and the porous structure was generated with the aid of CO2 escaping from the fermented flour during the steaming process.It is a convenient shaping route,the resulting catalyst has higher specifi c surface area,and exhibites good catalytic activity in transesterification of soybean oil with methanol.