The Study On Trivalent Manganese Metal Oxide Catalysts System For Ortho-methylation Of 4-chlorophenol

4-chloro-2-cresol is an important fine organic chemical raw material.It is mainly used for preservatives,disinfectants,bactericides and intermediates of plant growth regulators,etc.The traditional synthesis method of 4-chlorophenol derivatives was the chlorination of phenols.There were some problems in the production process,such as low utilization of chlorine atoms,serious pollution of by-products and high maintenance cost of equipments.China is rich in coal resources.The methanol capacity of production is large and the price is steadiness.The gas-phase ortho-methylation of 4-chlorophenol with methanol to produce 4-chloro-2-cresol has the advantages of low production cost,beneficial to further expanding production,environmental friendly synthesis process and high atom utilization rate,which can replace the traditional chlorination process and become a new choice for mass synthesis of 4-chloro-2-cresol.Therefore,the key to realize the industrialization of this process is to design and develop catalysts with high raw material conversion,high mono ortho selectivity,long cycle life time and long catalysis life time.In this paper,a series of Mn₂O₃ catalysts were synthesized by different methods.And their reaction activity in vapor-phase ortho-methylation of 4-chlorophenol with methanol was evaluated.The catalysts were characterized by X-ray diffraction,X-ray photoelectron spectroscopy,N₂ adsorption/desorption,field-emission scanning electron microscopy,NH₃/CO₂ temperature programmed desorption,H₂ temperature programmed reduction,solid visible ultraviolet spectra,thermogravimetry and differential thermal analysis.These results were correlated with the catalytic activity and product selectivity of this reaction.The mechanism of dechlorination was interpreted.The effects of different reaction conditions on catalytic activity and product selectivity were investigated.The main contents and results are as follows:Part 1:The study on Mn₂O₃ catalyst prepared by precipitation method in vapor-phase ortho-methylation of 4-chlorophenol with methanol.Mn₂O₃ catalyst was synthesized by ammonia precipitation method.The catalyst samples with different crystallinity,the number of acid-base sites,specific surface area,pore size and pore volume were prepared by calcination under different temperatures.The reaction performance was evaluated in a fixed bed reactor.The product distribution showed that dechlorination was the main side reaction.We have studied dechlorination effect in detail.By changing the carrier gas from N₂ to H₂/Ar mixture,it was proved that H₂ produced by methanol decomposition could not dechlorinate 4-chlorophenol.The dechlorination of 4-chlorophenols was inhibited by changing the methylating reagent from methanol to formaldehyde solution,which indicated that methanol was the main reason for the dechlorination of 4-chlorophenols.XRD,XPS and TG-MS characterization showed that Mn³⁺was reduced to Mn²⁺during the reaction.And the oxygen species distribution on the catalyst surface was changed.After summarizing the reaction mechanism of 4-chlorophenol with methanol,a mechanism of dechlorination of 4-chlorophenol by methanol was proposed.XRD and TG-DTA were used to characterize the crystal phase and the carbon deposition on the surface of the catalyst.The reaction conditions such as reaction temperature,ratio of phenol to alcohol and liquid hourly space velocity were optimized.The reasons of the reaction conditions affected the catalytic activity and the selectivity of the products were discussed.Part 2:The study of ?-Mn₂O₃ nanowires in the gas phase ortho-methylation of 4-chlorophenol with methanol.?-Mn₂O₃ nanowires were synthesized by hydrothermal method and calcined under different temperatures for the prepartion with different crystallinity,the number of acid-base sites,specific surface area,pore size and pore volume samples.The catalytic performance was evaluated in a fixed bed reactor.SEM showed that the mesoporous structure of the catalyst originated from the sintering and stacking of?-Mn₂O₃ nanowires.The sintering and stacking effect intensed with the increase of calcination temperature.XRD,N₂ adsorption-desorption and NH₃/CO₂-TPD results showed that the structure of the nanowires catalyst was stable and the crystalline phase did not change in the investigation calcination temperature range.Mn₂O₃synthesized by hydrothermal method had larger specific surface area and more active sites than the synthesized by precipitation method.XRD,XPS and TG-MS characterization showed that Mn³⁺was reduced to Mn²⁺and the surface oxygen species distribution was changed during the reaction.Characterization of H₂-TPR indicated that the lattice oxygen in bulk phase of Mn₂O₃ nanowire catalyst was easier to migrate to the surface of the catalyst.XRD and TG-DTA were used to characterize the crystal phase and surface carbon species deposition of the catalysts.At the same time,the reaction conditions such as reaction temperature,phenol alcohol ratio and liquid hourly space velocity were optimized.The reason why?-Mn₂O₃ nanowires have high activity at high liquid hourly space velocity was discussed.Part 3:The study of spinel Zn_1-xCu_xMn₂O₄ catalyst in the gas phase ortho-methylation of 4-chlorophenol with methanol.A series of Zn_1-xCu_xMn₂O₄(x=0,0.25,0.5,0.75,1)spinel catalysts with different zinc and copper contents were synthesized by coprecipitation method.The structure and surface properties of the catalysts were characterized by XRD,solid UV-vis spectra,XPS,SEM,N₂ adsorption-desorption,H₂-TPR,NH₃/CO₂-TPD and TG-DTA.The effects of Zn/Cu atomic ratio and calcination temperature on the structure and reaction activity of the catalyst were investigated.The optimum reaction conditions were as follows:x=0.25,reaction temperature 390 ^oC,phenol alcohol ratio1:20.The single-pass yield of 4-chloro-2-cresol reached up to 46.8%.Although the specific surface area of spinel structure Zn_1-xCu_xMn₂O₄ catalyst was small,it can maintain high conversion at high space velocity due to its high surface oxygen species activity.Part 4:The study of perovskite structure Sr²⁺doped lanthanum manganate catalyst in gas phase ortho-methylation of 4-chlorophenol with methanol.Lanthanum manganate catalysts with different Mn content(LM₁,LM₂,LM₃)were prepared by sol-gel method.On the basis of LM₃,a series of perovskite catalysts were prepared by introducing different amounts of Sr²⁺.The catalyst was characterized and the reaction of ortho-methylation of 4-chlorophenol with methanol was evaluated.The results showed that when the content of Mn was large(LM₂,LM₃),amorphous manganese oxide would be formed due to cation enrichment effect.The higher the Mn content,the lower crystallinity and average valence of Mn.The introduction of Sr²⁺could distort the lattice of perovskite and form oxygen vacancies.In the reaction process,the migration rate of lattice oxygen in the catalyst would be accelerated.However,the surface properties(acidity and basicity,specific surface area)of the catalyst would not be greatly affected.The addition of Sr²⁺made the lattice oxygen of the catalyst more easily migrate to the surface of the catalyst,promoting the oxidation process of methanol to formaldehyde,and made the catalyst maintain excellent activity in a certain period.