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

A series of solid catalysts were prepared in order to solve the problems such as the separation of product, the recovery and recycle of catalyst brought by homogeneous catalysis. The conditions in the preparation of the catalysts were investigated, the structures of the catalysts were characterized, and the catalytic activity in the reaction of synthesizing propylene carbonate (PC) from urea and 1,2-propylene glycol (PG) was also evaluated.Zinc-iron oxide catalysts were prepared by co-precipitation method. The effect of the kind of precipitator, precipitation end-point pH, calcination temperature, and adding manner of the precipitator on the catalytic performance of the catalysts was investigated. The suitable preparation conditions were as follows: zinc nitrate and iron nitrate as the precursors, molar ratio of Zn/Fe 1:2, ammonia as the precipitator, normal mixing manner of the precipitator, precipitation end-point pH 8.04, and calcination temperature 450 ℃. Then the catalytic activity of zinc-iron oxides for synthesis of PC via urea and PG was studied. The optimal reaction conditions are as follows: reaction temperature 170 ℃, reaction time 2 h, catalyst concentration 1.4%(wt), molar ratio of urea to PG 1:4. The highest yield of PC was 78.6%. XRD, CO_<sup>2-TPD and XPS were employed for the catalyst characterization. Two kinds of crystal phase, ZnO and ZnFe₂O₄, were detected. ZnO acts as the main active component, and the synergistic effect of ZnO and ZnFe₂O₄ promotes the catalytic performance.A series of supported Pb catalysts were prepared by impregnation method and their catalytic behavior was investigated in the reaction for synthesizing PC. After the reduction temperature was determined by TPR technique, the effect of different supports, loading and reduction manner on the activity of the catalysts was evaluated. The suitable preparation conditions were as follows: support SiO₂, loading of Pb 10%, and the reduction atmospere pure hydrogen. PbO and Pb were detected in XRD characterization, and the synergistic effect of PbO and Pb promoted the catalytic performance. Under the optimal reaction conditions: reaction temperature 180 ℃, reaction time 2 h, catalyst concentration 0.9%(wt), and molar ratio of urea to PG 1:4, the highest yield of PC was 86.9%.Pb/Fe₃O₄/SiO₂ magnetic particles were prepared by Sol-Gel method. The suitable preparation conditions were as follows: temperature for gelatin 60℃, and pH value in Sol-Gel process 4.When the reaction conditions are as follows: reaction temperature 180℃, reaction time 2 h, catalyst concentration 1.7%(wt), and molar ratio of urea to PG 1:4, the yield of PC is 87.7%. Besides the Pb/Fe₃O₄/SiO₂ catalyst showed a good magnetism.