Study On Preparation And Catalytic Properties Of The New Catalyst For Isobutene Conversion To Methyl Methacrylate By Two-Stage

Methyl methacrylate (MMA) is a monomer that is used to polymerize the organic glass and the MBS resin. MMA is produced by the method of acetone-cyanhydrin(ACH) mainly in our country. The synthetic route is complex, the technical line is long, and the yield is low with high cost after many steps. Hydrocyanic acid (seriously poisonous) is used as raw material, the treatment of numerous waste acid is difficult . Furthermore, concentrated sulfuric acid consumed in this method corrodes equipments and pollutes the environment seriously. Considering all of these, it is greatly necessary to develop a new chemical technology of MMA. Recently, in many countries isobutene is used as raw material to produce MMA and the method already is industrialized. The process of isobutene to be oxidized and esterified into methyl methacrylate is realized through three stages: First, isobutene is oxidized to methacrolein(MAL).Then MAL is converted into methylacrylic acid (MAA) through oxidation. At last, MAA is esterified to MMA with methanol. In Japan, XuHuaCheng company uses isobutene as stock to get MAL, then acquires the product through direct oxidation and esterification. However, the technological process is being developed.This article simplifies the three-stage method described above to two-stage method. The method merges the oxidation and esterification into one step. That is to say, MAL is resolved in methanol, the air is inputed, in order for oxidation and esterification. This is a new synthetic method, and the preparation of catalyst is the key technique of this essay. In the first stage of reaction, the main catalyst is Mo-Bi or Mo-V mixed oxide, rare earth element is added as promoter. In the fixed bed reactor we checked some factors which can influence the conversion of isobutene and the selectivity of methacrolein. These factors include the temperature of the reaction, the concentration of isobutene , the flowing rate of raw material gas and the addition of rare earthelement. We've synthesized 50 kinds of new molybdenum-vanadium catalyst, characterized them, and selected 2 kinds of them with high activity. Furthermore, We've characterized them by means of measuring specific surface, Infrared spectrum, X-ray diffraction, Scanning electron microscope and Raman spectrum. The activity of catalyst prepared by coprecipitation is mainly decided by its chemical components, and it is influenced by the preparation conditions at the same time. The composition of main phase of the optimum catalyst is a -Bi₂Mo₃O₁₂, Er₂Mo₃O₁₂; Mo₄V₆O₂₄, YbVO₄). The reaction mechanism is discussed and the relation between the reaction and structure of catalyst is found, which can provide theoretical foundation for improving the catalyst.In the second stage, the main catalyst is palladium. Adding palladium to the catalyst can improve the selectivity of MMA. When the content of water in the reaction system is lower than 3.5 percent, it can prevent the reduction of catalyst's activity and restrain production of the by-product-methacrylic acid. We mainly study some factors which influence the conversion of raw materials and the selectivity of the main product. Such factors include the molar ratio of raw materials, the temperature of the reaction and the composition of the catalyst. With the development of the separation technique of by-products, an economical technological route is hoped to be established. We added the rare earth so as to improve the composition and structure of the catalyst and adjust the performance of the catalyst. Adding Ln to the catalyst Pd₅Pb₁Fe₁ can improve not only the conversion of MAL, but also the selectivity of MMA.Experimental results indicate: adding suitable rare earth element Ln to Mo-Bi-O or Mo-V-O catalyst can adjust the previous crystal structure and it is advantageous to activate and regenerate the active sites. It can improve the conversion of isobutene and the selectivity of the production of methacrolein. Because this method substitutes the traditional two techno...