Study On Preparation Of 2-naphthaldehyde By Gas-solid Phase Catalytic Oxidation

2-Naphthaldehyde（2-NA）is an organic chemical intermediate,which has important applications in the fields of drug synthesis and material preparation.The gas-solid catalytic oxidation of 2-methylnaphthalene（2-MN）to 2-NA is an economical and efficient process route,which can utilize 2-MN resources effectively to solve the problems of serious pollution and insufficient production capacity of the traditional processes.The preparation of 2-NA by gas-solid phase catalytic oxidation is a complex reaction process.The activity of the catalyst and the reaction conditions have an important influence on the yield and selectivity of the target product.This paper mainly studied the preparation and modification of V₂O₅ catalysts to produce 2-NA,optimization of reaction conditions,reaction kinetics,and the ternary solid-liquid equilibria of the catalytic reaction products.On the basis of the preliminary work of our laboratory,V₂O₅ was used as the active component to prepare the catalysts by impregnation method.The effects of catalyst support,vanadium loading amount,calcination condition,molar ratio of potassium to vanadium and promoter on the activity of the catalyst were investigated.The results showed that the catalyst had a better yield for 2-naphthaldehyde after calcined at 450℃for 2h,using anatase phase TiO₂ as the support.Meanwhile,the vanadium loading was5.77%of the mass of TiO₂ and the molar ratio of potassium to vanadium was 1.97:1.The preferred catalyst was characterized by N2 adsorption-desorption,which has a specific surface area of 5.4 m²?g^-1 and an average pore diameter of 37 nm.The performance of the preferred V₂O₅/TiO₂ catalyst was enhanced by doping molybdenum and tungsten.The effects of molybdenum doping amount,tungsten doping amount and co-doping of molybdenum and tungsten on the activity of the catalyst were investigated.The results indicated that the doping of molybdenum reduced the pore size and pore volume of V₂O₅/TiO₂ catalyst,and diffraction peak intensity of KVO₃,changed the ratio of V⁵⁺/V⁴⁺and the morphology of surface vanadium oxygen species（VO_x）,and decreased the number of strong acid sites and weak acid sites on the catalyst surface.When the molar ratio of vanadium to molybdenum was 1:1,the catalytic performance of Mo-V₂O₅/TiO₂ catalyst was better than that of V₂O₅/TiO₂ catalyst,and the yield of 2-naphthaldehyde on Mo-V₂O₅/TiO₂catalyst was higher.Doping of tungsten reduced the pore size,pore volume and surface acidity of the catalyst,and decreased the oxidation strength of the catalyst.Co-doping of molybdenum and tungsten changed the distribution of acid sites on the catalyst surface and improved the activity of the catalyst.The mechanism of molybdenum promotional effect was proposed.Molybdenum replaced potassium or titanium atoms to form new Mo-O-V bond and Mo-O-Ti bond,which affected the activity of V₂O₅/TiO₂ catalyst.For the catalyst with a molar ratio of vanadium to molybdenum of 1:1,the effects of reaction conditions on the performance of the catalyst were studied by single-factor and response surface methodology.The optimized reaction conditions were as follows:reaction temperature 390℃,space velocity 11000 h^-1 and feed flow rate 3.87×10^-4mol?h^-1.Under the optimized reaction conditions,the conversion of 2-MN and the yield of 2-NA were 68.6%and 37.7%,respectively.The catalyst still maintained high activity after continuous operation of 180 h.The reaction kinetics of the catalytic oxidation of 2-MN to 2-NA was studied in a fixed bed reactor.The kinetic model was established by taking 2-MN,2-NA,phthalic anhydride（PA）,2-methyl-1,4-naphthoquinone（2-MNQ）,and 4-methylphthalic anhydride（4-MA）as the key component.The kinetic equations to describe the catalytic oxidation of 2-MN to 2-NA were obtained.Residual analysis and statistical tests showed that the kinetic model was suitable.The products of the catalytic reaction system mainly include 2-NA,PA and 4-MA.In order to effectively separate 2-NA,the solid-liquid phase equilibria of the ternary system of the reaction products were studied.The solubilities of 2-NA,4-MA,and PA in ethyl acetate were determined in the range of 283.15 K to 313.15 K by the equilibrium method.The solid-liquid phase equilibria of 2-NA+PA+ethyl acetate,2-NA+4-MA+ethyl acetate and PA+4-MA+ethyl acetate at 288.15 K,298.15 K,and308.15 K were studied by the wet residue method of Schreinemaker,respectively.The density values of the equilibrium liquid phase and ternary system phase diagrams were obtained.The solubility data of three systems were correlated by NRTL model and Wilson model.For 2-NA+4-MA+ethyl acetate system,NRTL model has a better correlation result.For PA+4-MA+ethyl acetate system and 2-NA+PA+ethyl acetate system,Wilson model has a better correlation result.