Study On The Synthesis Of Propylene Carbonate By Urea Method

Propylene carbonate has the characteristics of low toxicity and low pollution,it is excellent solvent and chemical products,and has wide application prospect in many fields.With the strengthening of the world’s environmental awareness,PC production and application by the attention at home and abroad,has a huge attraction and market potential.Urea alcoholysis method has the advantages of low cost,mild condition,reusable byproduct,good production safety,remarkable economic benefit and so on,and has strong competitiveness.In this paper,mesoporous composite metal oxides and magnetic supported catalysts were prepared.The effects of catalyst preparation conditions such as catalyst dosage,molar ratio of raw materials,reaction time and reaction temperature on the synthesis of urea were studied.TEM,BET,FT-IR,XRD and TG-DSC were used to characterize the catalyst.The main research contents are as follows:（1）MgO has the highest catalytic efficiency in the single metal oxide catalyst in the synthesis of urea by alcoholysis.In the composite metal oxide catalyst,the catalytic activity of magnesium-zinc composite metal oxide is the best.（2）Magnesium-zinc composite metal oxide catalysts with mesoporous structure prepared by template method and hydrothermal method were used to catalyze the synthesis of PC reaction.The catalytic activity of the mesoporous magnesium-zinc composite metal oxide prepared by the metal atom ratio n(Mg²⁺):n(Zn²⁺)=4:1,the oven temperature of 180℃and the calcination temperature of 500℃is higher than that of the ordinary Magnesium-zinc composite metal oxide.The yield of PC was93.01%under the optimum reaction conditions with the catalyst mass fraction of1.5%,n（PG）:n（urea）=2.5:1,reaction time of 3h and reaction temperature of 190℃.Through characterization analysis,the catalyst is prepared by stacking a sheet-like cube with uniform particle size and spherical particles having a particle size of about 20μm,the specific surface area of 76.577m²/g,pore volume of 0.3402cm³/g,the average pore size of 12.4715nm,with a clear mesoporous structure.（3）A porous SiO₂/Fe₃O₄ carrier with magnetic properties was prepared by template method and sol-gel method.The supported magnetic magnesium oxide catalyst was prepared by impregnation method.The catalyst prepared by calcination at 600℃was the best in the catalytic reaction.Catalyst magnetic response performance is better,easy recycling.The optimum conditions for the synthesis of PC were as follows:the mass fraction of catalyst was 1.0%,n（PG）:n（urea）=2:1,the reaction time was 3h,the reaction temperature was 180℃,reaching 89.49%.Through characterization analysis,the catalyst carrier is a sphere having a particle size of about 400nm and a uniform size.Fe3O4 particles coated on the surface of SiO2 with mesoporous structure.the specific surface area of the carrier was866.196 m²/g,the pore volume was 0.1259 cm³/g,the average pore size was 3.417 nm.The specific surface area of the carrier is large,the pore size is also suitable,it is beneficial to load the active component and improve the catalytic efficiency.MgO is supported on the SiO2 surface of the carrier and is highly dispersed.