Study On The Catalysts And Synthetic Process For The Synthesis Of Diphenyl Carbonate By Transesterification

The Hydrotalcite-like catalysts and the transesterification-disproportionation two-step synthetic technology for the synthesis of diphenyl carbonate by transesterification from phenol and dimethyl carbonate were studied in this paper.The catalytic performance of hydrotalcite-like catalysts for transesterification between phenol and dimethyl carbonate was investigated under normal pressure. Based on the group’s former research work, various effects affecting the selectivity of hydrotalcite-like catalyst for transesterification products were investigated. It was found that the basic strength of the interlayer organic anions has little influence on the selectivity of hydrotalcite-like catalysts. The main effect affecting the selectivity of hydrotalcite-like catalyst for transesterification productsis is the remained basic co-precipitation agent (NaOH) in the catalyst preparation process. Therefore, by improvement of the hydrotalcite-like catalyst’s preparation procedure, the catalyst selectivity for transesterification products reached about 95%, at least 12% higher than the group’s former result.Various hydrotalcite-like catalysts with different combinations of cations were synthsized under the optimal preparation procedure, and characterized by XRD, TG-DTA, FT-IR and BET method. The catalytic performances of these synthtic hydrotalcite-like catalysts were tested for the transesterification reaction between dimethyl carbonate and phenol. It was found that the Mg/Fe-CO3 hydrotalcite-like catalysts (Pyroaurite) with the atomic ratio n(M2+)/n(M3+)=3 had the best catalytic performance. Under the optimal reaction condition of Mg/Fe atomic ratio of 3:1, n(phenol):n(DMC)=2:1, the mole of phenol=0.5, w(cat.)=1.5% of the total mass of phenol and DMC, time=9h, the conversion of DMC reached 61.5%, and the yields of diphenyl carbonate and methyl phenyl carbonate were 13.9% and 43.7%, respectively. The catalyst’s reuse experiment indicates that Pyroaurite catalyst can be recycled, seperated and regenerated easily within the scope of this study (4 runs).The relation between the catalytic performance and the structure and components of the hydrotalcite-like catalysts were investigated. It was found that the catalytic performance of the hydrotalcite-like catalysts is related to the character of involved cations. While the catalytic activity was influenced by trivalent cations, the life time of catalysts was influenced by divalent cations. From the investigation of the reason for the deactivation of hydrotalcite-like catalysts, it was found that the characteristic layered structure of the hydrotalcite-like catalysts was the key factor to their catalytic activities. Once the layered structure collapsed, the activities were lost. But the catalytic activity can be recovered by the structure reconstruction of the hydrotalcite-like compounds. These research results provide a theoretical foundation for the advancement of the catalytic performance of hydrotalcite-like catalysts.Based on the group’s former research, the transesterification-disproportionation two-step synthetic technology was studied using the self-made pressured reactive distillation reactor. Applying two-step process to the synthesis of diphenyl carbonate by the dimethyl carbonate’s phenolic transesterification, under the optimal reaction condition of 180℃, 1.0MPa, w%(cat./phenol)=3,6 h, the conversion per pass of phenol reached 82%, and the isolated yield per pass of diphenyl carbonate reached 44%. The catalyst’s reuse experiment shows that Ti(OBu)4 is a stable, recyclable catalyst for the synthesis of diphenyl carbonate using the transesterification-disproportionation two-step process.