Study On Modified Hydrotalcite Catalyst For Synthesis Of Diphenyl Carbonate By Transesterification

Diphenyl carbonate (DPC) is an important carbonic ester, an important precursor for the synthesis of polycarbonate without using phosgene. In synthesis paths for DPC, the transesterification of dimethyl carbonate (DMC) with phenol is considered to be the most promising process due to the use of nontoxic feedstock and no hazard to environment. An easy and effective gas chromatographic method for quantitatively analyzing DPC and MPC was set up by studying and exploring the process of DPC synthesis from the transesterification of DMC with phenol over modified hydrotalcite.A series of organic anion-pillared hydrotalcite (org- LDHs) were synthesized by ion exchange method, and the catalysts were characterized by XRD, FT-IR and TG-DTA. The catalytic performance of hydrotalcite and pillared hydrotalcite with different anions were tested in transesterification of dimethyl carbonate (DMC) with phenol. The results showed that the catalytic selectivity of this transesterification reaction over these organic anion-pillared hydrotalcite was significantly improved. The catalytic selectivity of Mg/Al-C4H4O4, Mg/Al-C6H8O4, Mg/Al-C10H16O4, Mg/Al-1, 4-C8H4O4, Mg/Al-C7H5O2 et al pillared hydrotalcite for transesterified products (DPC and MPC) were all greater than 90%, at least 10% higher than that of the hydrotalcite. Under the condition of n (Phenol)/n (DMC)=4, amount of catalyst=1.5%(wt), time=8h, Mg/Al-C6H8O4 and Mg/Al-4-CH3- C7H4SO3 pillared hydrotalcite presented the best catalytic performance, the conversion of phenol reached 12.9% and 13.0%, respectively.Using Mg/Al-C6H8O4 pillared hydrotalcite with the highest activity, the experimental conditions of transeserification such as reaction temperature, reactant ratio, catalyst concentration, and reaction time were optimised. When the reaction had been carried out for 12h, at reaction temperature 150~185℃, molar ratio of phenol to DMC 3:1, and catalyst concentration 1.5 wt%, the conversion of phenol and the transesterification selectivity reached 24.0% and 92.5% respectively.The effect of the structure and chemical components of org- LDHs on the catalytic activity has been investigated. The lamellar structure of org- LDHs showed significant effect on the transesterification, and the catalytic activity of org- LDHs was related to the components.The reaction mechanism for transesterification over org- LDHs was studied.