Selective Synthesis Of Glycerol Carbonate From Glycerol And Urea Catalyzed By Mixed Oxides

Glycerol,as a renewable biomass source,is one of the important platform chemicals for biological derivatives.Among all kinds of glycerol derivatives,as a five-membered cyclic carbonate,glycerol carbonate has a wide reactive range because of hydroxyl and cyclic carbonate,leading to important applications in various fields.In this thesis,we synthesized glycerol carbonate by carbonylation of glycerol and urea using mixed metal oxide as a catalyst.The properties of the catalysts were characterized by various characterization techniques,and the reaction conditions were optimized.At first,four mixed metal oxide catalysts(M²⁺:N³⁺=3,M²⁺and N³⁺represent divalent and trivalent metal cations respectively),Mg-La,Mg-Ce,Ni-La,and Ni-Ce,which were prepared by coprecipitation method,were used for carbonylation of glycerol and urea,respectively.The results showed that MgLa-O catalyst had the best catalytic performance at the reaction conditions of 140℃,0.01MPa for 3 hours.In order to further improve the yield of glycerol carbonate,the MgLa-O catalysts with Mg/La ratios of 3,2,1 and 0.5 were prepared.The results showed that the selectivity of glycerol carbonate reached 75%using the catalyst with Mg/La of 1.Then,the calcination temperature of the catalyst Mg/La of 1 was investigated.The catalyst calcined at 500℃had the highest lattice oxygen ratio,which provided enough alkaline sites for the reaction and was beneficial to glycerol adsorption.Finally,the deposition temperature of MgLa-O catalyst（Mg/La of 1）was studied.The results showed that different deposition temperatures had great influence on the ctalyst acid-base properties.The catalyst deposited at 60℃was more alkaline and had better carbonylation performance.At last,,the reaction conditions were optimized over the MgLa-O catalyst（Mg:La of 1,deposited at 60℃,calcined at 500℃）.The highest glycerol carbonate yield of 46.5%was obtained at 140℃,the molar ratio of urea to glycerol of 1:1.5,with the catalyst loading of 0.65g after 4 hours.Furthermore,the reusability of the catalyst was evaluated,and the results showed that its stability and reusability needed to be further improved.