Ca-based Solid Base Catalyzed Transesterification Of Propylene Carbonate And Methanol For Preparation Of Dimethyl Carbonate Research

Dimethyl carbonate（DMC）is a green chemical intermediate widely used in organic synthesis,fuel additives and electrolytes.Transesterification has become the mainstream method for industrial production of DMC because of its mild reaction conditions,simple process flow and co-production of propylene glycol（PG）with high added value.Traditional transesterification method often uses sodium methoxide as catalyst,which has high catalytic efficiency and DMC yield.However,the catalytic process belongs to homogeneous reaction,which inevitably increases the cost of separating product from catalyst.In this paper,heterogeneous Ca-based solid base catalyst with low temperature,high activity and easy separation was studied,which has basic research significance in the application field of transesterification synthesis of DMC.In this paper,a series of Ca-Co solid base catalysts with different molar ratio were prepared.Their catalytic performances of transesterification of methanol and PC were investigated.The reaction conditions such as catalyst dosage,feed ratio,reaction temperature and reaction time were optimized,and the physicochemical properties of the catalysts were analyzed by XRD,N₂ adsorption,FT-IR,CO₂-TPD,SEM,TEM,XPS,TG and other characterization methods,the reasons for the reduction of catalyst activity were deduced.The details are as follows:（1）Benson,Joback,Ma Peisheng and other group contribution methods were adopted to estimate the thermodynamic parameters of the reaction of methanol and PC to produce DMC.The calculated values ofΔrH andΔrG of the reaction at 298.15 K are-3.81 and-11.40 k J/mol respectively.The reaction is likely to be spontaneous and slightly exothermic,and the equilibrium constant is basically maintained around 1 in the temperature range of 273.15-338.15 K,indicating that the temperature change has little effect on the progress of the reaction.（2）Solid base catalysts with different Ca/Co molar ratios were prepared by sol-gel method.It was found that 0.9Ca0.1Co catalyst has relatively good catalytic performance.When the feed ratio was 8,the reaction was conducted at 65℃ for 30 min,the conversion rate of PC and DMC yield were 71.6% and 72.9%.The characterization results show that the amounts of moderately basic sites on the catalyst surface plays a decisive role in the transesterification process,the 0.9Ca0.1Co catalyst possessed the large amount of basic sites and showed the highest activity.In addition,it is found that the increase of Co content can reduce the binding energy of O1 s in Ca-O in the catalyst,promote the formation of methoxyl anion,and improve the reaction performance.It is worth noting that when the molar ratio of calcium to cobalt changes,the valence distribution of Co in Ca₂CoO₃ layer in Ca₃Co₄O₉ phase will change,and the catalytic activity sequence is in good agreement with the relative concentration of Co³⁺ and Co⁴⁺ in the catalyst.Optimization of reaction conditions showed that when the amount of catalyst was 4.1wt% of PC,n（Me OH）: n（PC）= 8,the reaction temperature 30℃ and the reaction time 30 min,the relatively good conversion rate of PC and DMC yield were 68.7% and 71.0%,respectively.Characterization of fresh catalyst and catalyst reused for 5 timesshowed that the organic matter adsorbed by the catalyst and the loss of Ca were the main reasons for the decrease of activity.（3）The 0.9Ca0.1Co catalysts with calcium nitrate,calcium acetate and calcium chloride as calcium sources were prepared by sol-gel method,and their catalytic transesterification performances were investigated.when calcium chloride is used as the calcium source,the introduced Cl element is difficult to remove,and due to the strong electronegativity of Cl element,it is easy to absorb water and deteriorate to form Ca Cl OH phase.When calcium acetate is used as the calcium source,the specific surface area and pore volume of the catalyst was the smallest,led to the decreased the amount of moderately basic sites which resulted in the decreased catalytic activity.The 0.9Ca0.1Co catalyst prepared with calcium nitrate as the calcium source has more moderately basic sites and the highest activity.In addition,the 0.9Ca0.1Co catalyst prepared by the sol-gel method has larger number of surface base sites,and its transesterification activity is higher than the catalysts prepared by the coprecipitation and the direct calcination methods.