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

The reaction system of synthesizing propylene carbonate from urea and 1,2-propylene glycol has been analyzed thermodynamically. The conclusion is drawn that Gibbs free energy and enthalpy of the reaction are -3.7671kJ/mol and 52.210kJ/mol at 298.15K respectively. Increasing reaction temperature can not only increase reaction rate but also enhance equillibrium conversion.The catalytic performances of zinc acetate, metal oxide and metal have been investigated for this reaction system.The homogeneous synthesis of propylene carbonate (PC) has been studied over Zn(OAc)2 catalyst; PC yield is 93.7% under the suitable conditions.According to the result of GC/MS, some side-reactions has been supposed. In addition, it is found that Zn(OAc)2 catalyst has taken part in the reaction. Supported zinc acetate catalyst has been prepared, and the effect of support and loads on PC yield has been studied. The stability of 15% Zn(OAc)2/AC catalyst has been reseached; the yield of PC decreases to 66.1% of used catalyst from 78.2% of fresh catalyst. According to the analysis result of XRD, XPS and atomic absorption spectroscopy of both used and fresh catalysts, as well as the result of GC/MS of the solution after reaction, the reason for deactivation of Zn(OAc)2/AC has been determined.The catalytic performance of metal oxide catalysts on sythesis of PC has been estimated; MgO shows the best activity. The best calcination temperature of magnesium bicarbonate, 750℃ has been reached. The suitable reaction conditions have been been determined by orthogonal experiment over MgO calcined from magnesium bicarbonate; the highest yield of PC is 91.5%. Supported MgO on silica has been prepared. The effect of precursor, loads and calcination temperature on catalyst activity hase been studied; the highest yield of PC is 86.3%.A series of compound metal oxide catalysts have been prepared by different methods.Among those, Mg-Al compound oxide has better catalyst activity. That Mg-Al precursor can be decomposed completely at 400℃ is determined by both TG-DTA and XRD analysis of catalysts at different calcination temperature.The effect of titration manner. Mg/Al molar ratio, NaOH/Na2CO3 molar ratio and aging temperature has been investigated. The yieldof PC is 81.0% at the suitable preparation condtions. Introducing thulium cation has decreased the catalytic activity.Metal catalysts have been applied to this reaction system. Mg, Zn, Pb and Fe shows certain catalytic activity. Within the range of the experiment temperature, the optimal reaction temperature of Mg and Zn is 180℃ and the yield of PC is 73.5% and 69.2% respectively.The optimal reaction temperature of Pb and Fe is 175℃ and the yield of PC is 60.1% and 64.7% respectively. The recovered catalyst has been characterized by XRD, new crystal substances have been found in both Mg and Zn catalysts while nothing but Pb and Fe catalyst.