Study On Synthesis Of Propylene Carbonate From Urea And 1,2-Propylene Glycol

The route of urea alcoholysis from urea and 1,2-propylene glycol is the trend of synthesis of propylene carbonate(PC), because of cheap and easily available feedstock,mild reaction condition and safe operation. A series of single metal oxides, metal carbonates, basic zinc carbonate and composite catalysts had been prepared and used on PC synthesis. By using X ray diffraction technique, the catalysts had been characterized. In addition, the process conditions were optimized.Among single metal oxides, ZnO gave the highest catalytic performance, At the optimal reaction conditions:the reaction time at 2hours, the reaction temperature at 180℃and the catalyst concentration at 0.6wt%, the yield of PC is 92.5%. Recycled four times, PC yield is still greater than 85%. Zinc carbonate prepared through coprecipitation method among single metal carbonate catalysts has the highest activity.The experiment results showed that the activity of basic zinc carbonate catalyst calcined at 240℃for 2h was highest. The optimal reaction conditions are as follows:reaction temperature of 170℃for 2h,0.06Mpa of vacuity, n(PG):n(urea)=2.5, the dosage of the catalyst 1%(based on mass of material). The highest yield of PC is 94.5% and 94.7%. XRD showed that there were two kinds of crystal phase, ZnO and Zn4CO3(OH)6·H2O in the catalyst. ZnO acted as the main active component, and the synergistic effect of ZnO and Zn4CO3(OH)6·H2O promotes the catalytic performance.In addition, a series of composite catalysts had been prepared, the Zn/Al hydrotalcite calcine had the highest catalytic activity, at the optimization of process conditions, PC yield reached 94.7%, the best reaction conditions as follow: 1,2-propylene glycol and urea in a molar ratio of 1.5, reaction time was 2h, reaction temperature 170℃, concentration of catalyst for 0.7%,0.06MPa reaction degree of vacuum. After the catalyst repeatedly used for four times, the yield could reach about 90%. XRD showed that, the main cause of decrease of catalyst activity is that catalyst crystal was destroyed.