New Technology On Synthesis Of Diphenyl Carbonate With Pd/MnO_x-PbO_x Catalytic Reaction-Preparation And Characterization Of Catalyst

Diphenyl carbonate(DPC) is an important precursor for producing polycarbonates by a melt-transesterification process.As a very promising safer technology,the direct oxidative carbonylation method for DPC,which is friendly and sustainable to environment,not only simplifies technical process but also avoids using of the toxic phosgene.Numerous catalytic systems that include Pd have been reported,however,the catalytic efficiency is still far from the commercially feasible level.Thus,the study of process for the DPC synthesis mainly focus on seeking a novel catalytic system with high efficiency.The catalytic mechanism for the oxidative carbonylation of phenol to diphenyl carbonate showed that diphenyl carbonate was produced by the insertion of CO into Pd-O bond and subsequent reductive elimination of intermediate Pd(COOPh)(OPh).The aggregation of Pd⁰ and the regeneration rate of active Pd²⁺ from Pd⁰ could be well improved to accelerate the catalytic recycle by the addition of redox promoters into palladium catalyst.The goal is to find a high oxidation active support for synthesis DPC under low O₂ content and less the volume of Pd, which has two function of support and redox promoters,develope a novel efficient supported catalyst and improve the hetergenerous catalytic system to be applied in the industrial process on the bases of former research.In this paper,a new supported catalyst Pd/MnO_x-PbO_x with high activity for direct synthesis of diphenyl carbonate is prepared.The effects of the carrier preparation methods,calcination temperature of carrier,precursor and molar ratio of Mn/Pb on catalytic activity were investigated.The characterization of catalysts and support properties were investigated by XRD,SEM,XPS and BET.The effects of reaction temperature,time,solvent and volume of catalysts were discussed in the batch slurry reactor through the synthesis of DPC.The main conclusions are as follows: 1.Some metal oxide such as ZrO₂,TiO₂,γ-Al₂O₃,MnO_x,PbO,MgO, CuO were selected as cocatalyst and the carrier of Pd catalyst for direct synthesis of diphenyl carbonate(DPC),then NaOH was used as a precipitating agent to prepare catalyst,high active MnO_x cocatalyst was screened out by the activity test of the catalyst,high efficient catalyst Pd/MnO_x also have been developed and the preparation way of carrier is decomposing manganese carbonate.2.The study results shows that the MnO₂ in the Pd/MnO_x an be a efficient cocatalyst to recovery the Pd⁰ to active Pd²⁺ and the activity increased with the proportion of the MnO₂ in the support.The Pd/MnO_x supported on MnO_x decomposed by MnCO₃ at 370℃showed the highest activity and the DPC yield and TON can reach 10.7%and 260 respectively.3.The catalytic active of Pd/MnO_x-PbO_x is best among manganese oxid and differernt metal oxid.The Pd/MnO_x-PbO_x supported on MnO_x-PbO_x decomposed by MnCO₃ and PbCO₃(W_pbco3/W_Mnco3+Pbco3=30%)at 370℃showed the highest activity and the DPC yield and TON can reach 15.9%and 387 respectively.It can be obtain combine the results of characterization,the reason why MnO_x-PbO_x has high oxidation active is the co-oxidation and co-redox of MnO_x and PbO_x.4.The cocatalytic active of carrier is correlative to the component and microstructure of carrier.The carrier prepared by Compleximetry precipitation when the molar ratio of Mn/Pb is 6:1 shows the highest catalytic activity and the DPC yield and TON can reach 22.3%and 543 respectively under total pressure 5 MPa,O₂ content 7%,reaction temperature 65℃,time 5 h,Phenl 25 g,CH₂C1₂75 g,catalyst 1 g,Pd loading content(mass fraction) 0.5%,4 A molecularsiece 3g, TBAB 0.998g.