Synthesis Of Diphenyl Carbonate By Oxidative Carbonylation With Phenol Over Magnetic Manganese Oxide Supported Palladium Catalysts

Diphenyl Carbonate （DPC） is an important “green” precursor forproducing high-quality polycarbonates. There are three main methods tosynthesize DPC: phosgene method, transesterification and oxidativecarbonylation. Among them, the one-step oxidative carbonylation of phenol toDPC without using the highly toxic phosgene and high atom efficiencyconform to the requirements of green chemical and sustainable low carboneconomy. It has become the hot subject in all over the world.The researchs of oxidative carbonylation process mainly focus on thechoice of catalytic systems （including main catalyst and promoter）, andcatalytic reaction mostly was carried out in a fixed bed reactor or slurry bedreactor, The catalytic properties in these reactors were not satisfactory due tothe inherent disadvantages such as high-pressure drops and insufficient flowrates. It is necessary to study the correlation between the reaction efficiencyand the different reactors. According to the characteristics of this catalyticreaction system, developing a novel reactor may tend to increase theefficiency of heat and mass transfer and enhance the reaction. So we attemptto apply the magnetically stabilized bed （MSB） to intensify this process. Themainly preliminary works of this research is the design and preparation ofmagnetic catalysts.In this thesis, the perovskite-type oxide and ferric oxides with excellentredox ability and magnetic properties were used as the supports to prepare themagnetic catalysts. The phase and physical structures of support and catalystswere characterized by XRD, SEM, BET, VSM, H2-TPR techniques. Theinfluence of magnetic properties and catalytic activity by different dopingmetals or sites with support and the preparation condition had been alsostudied. At last, the suitable catalysts were chosen, which meet therequirements of magnetic performance and possess better catalytic activity. The relevant conclusions were listed as follow:（1） Pb doping at A-site affect the amount of oxygen vacancies，theconcentration and mobility of oxygen species. The Pd/LaXPb1-XMnO₃in rangeof x=0.4⁰.5possesses the relatively higher amount of oxygen vacancies,better mobility and activity of the lattice oxygen, which promote the rate ofregeneration of the active palladium. These catalysts had better activity withDPC yield of10.4¹1.2%. Meanwhile, due to greater value of saturationmagnetization and soft magnetic properties, they could be used in the MSB.（2） Different metal doping into the B sites of La0.5Pb0.5Mn0.9M_0.1O₃makedifferent effect on the amount of the lattice oxygen and the mobility ofoxygen species. The samples with the Co and Ni as doping cation obtain thelarger amount of lattice oxygen. After partial substitution of Mn³⁺with Cu²⁺,the oxygen vacancy concentration increases significantly. Ni co-dopingefficiently enhance the flow ability of oxygen species in support.All thesefeatures can improve the catalytic activity. All the samples obtain the softmagnetic properties. But the doping metal broken the double exchangebetween Mn metal ion，the values of saturation magnetization of dopedcatalysts were decreased. Combining with the catalytic performance andmagnetic properties, the sample with Co and Cu metal ions were chosen asbetter catalysts in the application of the MSB.（3） The amount of lattice oxygen in La0.5Pb0.5Mn1-XCoXO₃can beincreased effectively by Co metal ion doping into B-site. The sample withx=0.1obtain higher content of lattice oxygen, relatively better flowability andsuitable surface area, which had better activity with a DPC yield of12.4%.（4）Among the different MFe₂O₄support, the sample of MnFe₂O₄has theexcellent redox ability and the presence of Mn⁴⁺is beneficial to the electrontransfer of the support. These characteristics can promote the regeneration ofthe active palladium, Thus, Pd/MnFe₂O₄had shown best catalyticperformance. The optimal calcination temperature and time of support was at 500℃and2h, respectively. At this preparation condition, the correspondingcatalyst achieves a higher activity with the DPC yield of5.15%. This catalystwith high value of saturation magnetization (43.3emu g^-1) and low coercivitymay be suitable for operation in the magnetically stabilized bed （MSB）reactor.（5）The optimum reaction condition of oxidative carbonylation of phenolto produce DPC by Pd/MnFe₂O₄total pressure5.0MPa, partial pressure ofoxygen0.35MPa, reaction temperature75℃, reaction time6h, the yield ofDPC could reach7.4%.