Study On The Preparation Of 2-Methyl-1,4-Naphthoquinone By Gas-Solid Catalytic Oxidation

The gas-solid catalytic oxidation of 2-MN to 2-MNQ is a series of coexistence complex high exothermic with phthalic anhydride and other by-products producing, which has a main drawback of small selectivity of 2-MNQ restricting its applications. It is critical to modulate the catalyst activity and control reaction conditions, which is important to improve the yield of target product 2-MNQ. This paper mainly focus on the preparation of the catalyst, the operation problems, reaction kinetics and some issues on thermodynamics of products separation.The catalyst was prepared by impregnations, with V2O5 as active component. Activity and selectivity of the catalysts are shown to the process of 2-MNQ via gas-solid oxidation of 2-MN over air in the present of composited vanadium catalyst. With respect to the course of the reaction, the conversion of 2-MN and the yield of 2-MNQ were considered as testing goal. The support of the catalyst, the amount of catalyst additives and the acidity or alkaline of the catalyst makes a great influence on the activity of catalyst. The results indicated that, Si O2 was better than Ti O2 as support, with the quality of NH4VO3 as 5.77wt% of support of Si O2. The catalyst calcination temperature was 400~450℃ and the calcination time was 2 h,which was determined by the thermal analysis. The promoter of catalyst K2SO4 has certain adjustment effect on the distribution of vanadium valence, and its quality directly affects the selectivity of 2-MNQ. The yield of 2-MNQ reached a higher value with the ratio of n(K2SO4): n(NH4VO3) =1:1. The acidity or alkaline of the catalyst affects the oxidation function of the catalyst.The acid catalysts were more likely to make oxidation deeper. The catalysts were characterized by XRD, BET, SEM and so on, which indicated that the active components V2O5 is highly fragmented on the support of Si O2 and specific surface area of the catalyst is 10.01 m2 · g-1 with the average pore diameter of 10 nm.The activity of the catalyst was tested in a fixed-type bed reactor by the selective oxidation of 2-MN to 2-MNQ, and the process conditions were optimized by single factor experiment and response surface methodology. The reaction temperature was 390℃, space velocity was 200 m L·(g· min)-1 and the material flow was 13.04×10-4mol·h-1. Under the optimum conditions, the conversion rate of 2-MN was 80.01%, and the yield of 2-MNQ was 46.53 %. Besides, the catalyst was a satisfactory for its long working hours still with high activity. This finding demonstrates that the composited vanadium catalyst is a promising heterogeneous catalyst in gas-solid selectivity oxidation of 2-MN to 2-MNQ process.In this paper, the dynamics on the gas-solid catalytic oxidation of 2-MN to 2-MNQ in the present of catalyst was studied. The process is a series of parallel and consecutive reaction network. By simplifying the reaction network and establishing dynamic model, four functions were used to describe the process of the catalytic oxidation of 2-MN to 2-MNQ:Residual analysis and statistical test results showed that the intrinsic kinetics model is appropriate.The study can be used for design of industrial reactors.The gas-solid catalytic oxidation of 2-MN to 2-MNQ is a series of complex and high exothermic process. In order to reduce the effect of reaction heat, the industrial catalyst were coated into porcelain annulus catalyst with thin layer. The classical Wicke-Kallenbach was modified to determine diffusion in radial direction of porcelain annulus catalyst with thin layer by a steady-state method. The tortuosity factors of gases through N2-CO2 and Ar-CO2 gas pairs were determined, and the experiment was carried out at different temperatures ranging from 303.15 K to 343.15 K under atmospheric pressure of 0.1MPa. The dependences of the effective diffusivity on temperature and different gas pairs were experimentally determined and the tortuosity factors were evaluated by a parallel path pore dimensional model. The ratio of diffusion flux between two components at each point agreed well with the theory of Graham. Results demonstrated that the improved Wicke-Kallenbach cell is reasonable, good stability and the data achieved by the experimental equipment is reliable. The tortuosity factor estimated for the catalyst is 2.6.The reaction target product is 2-methyl-1,4-naphthoquinone, with the main side product 2-naphthaldehyde and phthalic anhydride included. In order to effectively separate products, the reaction product of quaternary system of 2-MNQ + 2-MA + PA + 1,4-dioxane and its ternary and binary systems solid-liquid equilibrium need to be studied. The solubility of 2-naphthaldehyde in six pure solvents(methanol, ethanol, isopropanol, n-butyl alcohol, n-heptane and n-hexane) and binary mixtures(methanol +ethanol) were determined experimentally by the equilibrium methods at different temperatures. The temperature dependence of solubility of 2-naphthaldehyde were correlated by the Van’t Hoff equation, the modified Apelblat equation and λh equation. The solid-liquid phase equilibrium and the solubility of the ternary system of 2-MNQ + PA + 1,4-dioxane, 2-NA +PA + 1,4-dioxane, 2-MNQ + 2-NA +1,4-dioxane at(283.15, 293.15 and 303.15) K were measured and the corresponding ternary phase diagrams were constructed, meanwhile the density of equilibrium liquid phase were determined. The ternary phase diagram for solid-liquid phase equilibrium data were calculated using the NRTL model and the corresponding binary interaction parameters were obtained, and the model give acceptable results for the investigated systems. Based on the ternary phase diagrams, phase diagram of the quaternary of 2-MNQ + 2-MA + PA + 1,4-dioxane was studied at 283.15 K. The phase diagrams were constructed. It is important to investigate the phase diagrams for designing and optimizing the process of the 2-MNQ from mixed compounds.