Synthesis Of Propylene Carbonate From Urea Aicoholysis Catalyzed By Manganese Oxide

Propylene carbonate （PC） is an excellent organic solvent, and alsowidely used as a chemical material. Generally, the methods for the synthesisof PC include cycloaddition of propylene oxide, phosgene and ureaalcoholysis. The alcoholysis, in which urea and1,₂-propylene glycol areused as raw materials, has the advantages of cheap and easily availablematerials, being friendly to the environment, and safe operation under mildreaction conditions. Moreover, it can effectively avoid the dependence uponpetrochemical industries in the cycloaddition of propylene oxide and the useof toxic phosgene, so it is considered a green route for the synthesis of PC.Many catalysts have been reported, but their performances are difficult forindustrialization. Therefore, the performances of catalysts need to be furtherimproved.Based on the previous work, MnO₂/γ-Al₂O₃, MnO₂/SiO₂and LaMnO₃were prepared and characterized by X-ray diffraction （XRD）, N₂adsorption（BET） and CO₂temperature-programmed desorption （CO₂-TPD）. Thepreparation conditions and the reason for affecting the catalytic activitieswere discussed. Further, the above catalysts were modified, and the effect ofpreparation methods and conditions on the mechanism was studied as well.Influence of the reaction temperature, reaction time and concentration of thecatalyst on the PC synthesis from Urea alcoholysis were investigated indetail in a batch reactor.1. The effect of different manganese sources as the precursor on thesynthesis of PC was investigated. MnO₂, which was prepared by theMn（NO₃）₂as the manganese source, has the strongest alkali intensity and themost quantity on its surfaces, and the catalytic activity was the highest witha8₃.9%yield of PC.₂. Compared with the physical mixing method and the impregnation method, the ultrasonic impregnation method was the best. WhenMnO₂/γ-Al₂O₃was prepared by the ultrasonic impregnation under theconditions of₃0%loading amount, calcination temperature of400℃andcalcination time of₂h, the yield of PC reached65.0%due to the strongestalkali intensity and the most quantity on its surfaces.₃. MnO₂/γ-Al₂O₃was modified by bases and salts on the basis of theultrasonic impregnation method. It was found that the alkali intensity andthe quantity on the surfaces of MnO₂/γ-Al₂O₃, which was modified by asmall amount of NaOH, were further enhanced according to the result ofCO₂-TPD, and the yield of PC increased from65.0%to81.6%.4. MnO₂/SiO₂was prepared with manganous nitrate as the precursorand SiO₂as the support, and its activity in the Urea alcoholysis wasinvestigated. When the alcoholysis was carried out at170℃with reactiontime of₂h, molar ratio of urea to1,₂-propylene of1:4and₃.₃%catalystamount （based on the weigh of urea）, the yield of PC was up to81.6%. Thedecrease of the activity of the recycled catalyst was caused by loss of activecomponent.5. The LaBO₃（B=Cr, Mn, Fe, Co, Ni, Cu） perovskite catalysts wereprepared by the sol-gel method. Among them, LaMnO₃and LaCuO₃exhibited the high activities, and the yield of PC was over85.0%.6. Although LaMnO₃prepared by the sol-gel method had small particlesize compared with the precipitation method, the activity was improved only₂.1%, and it was necessary for a lot of citric acid, long calcination time andhigh calcination temperrature. Therefore, the precipitation method waschose to prepare LaMnO₃. When LaMnO₃was prepared under the optimalconditions of pH value of9¹0, calcination temperature of700℃andcalcinations time of₂h, the yield of PC arrived to8₃.9%.