Synthesis Of Dimethyl Carbonate From Catalytic Alcoholysis Of Methyl Carbamate Over Hydrotalcite-like Based Composite Oxides

Dimethyl carbonate（DMC）,a low toxicity and environment-friendly organic compound,has been applied in many fields due to its unique physical and chemical properties.Its synthetic methods have been attracted extensive attention of many researchers.The technology of urea synthesis by CO₂ and NH₃ has been industrialized,so the route of the alcoholysis of urea synthesis DMC is very popular among numerous methods because of its a series of advantages,such as the low raw materials price,easy separation and so on.The successful development of CO₂-urea-DMC industrial chain could not only solve the current problem over urea production capacity in China but also accomplish the conversion of CO₂ to high value-added chemical products,and enrich CO₂ utilization path.The synthesis of DMC by urea alcoholysis is divided into two steps:urea-Methyl carbamate（MC）and MC-DMC.The former is spontaneous and the latter is non-spontaneous.In this paper,the second step of the synthesis of DMC by urea alcoholysis was studied.The mixed oxides were screened in a miniature high-pressure reactor with methanol and MC as raw materials under the same reaction condition.Finally,the characterization and condition optimization of Zn/Al LDO catalysts were determined.We found the optimal reaction conditions of Zn/Al LDO catalyst calcination temperature was 600^o C,n _Methanol:n _MCC equaled to 15,the mass percent of the catalyst and reactant was 1%,reaction temperature was 180^o C and reaction time was 10 h.The yield and selectivity of DMC were 16.5%and 58.25%,respectively.The results showed that the yield of DMC was positively correlated with the alkaline site on the catalyst.The selectivity and yield of DMC decreased with the increase of catalyst reuse times.In order to explore the mechanism of Zn/Al LDO catalyzing this reaction,we compared Zn/Al LDO with single ZnO,Al₂O₃ and ZnO-Al₂O₃（physical mixture of ZnO and Al₂O₃ with same proportion and mass as ICP results）and found that Zn/Al LDO has the best catalytic performance,indicating that ZnO and Al₂O₃ have synergistic effect on Zn/Al LDO and its structure is better than ZnO-Al₂O₃.Finally,the crystal complexes generated in the reaction process was characterized and the synthesis path was proposed so as to study the reaction mechanism.