Study On Basic Reaction Engineering Of Methanol Synthesis Over New Catalyst And Mathematical Simulation Of Methanol Reactor

Methanol is a kind of clean fuel with good combustion performance, which can be directly used as vehicle fuel or blended with gasoline. Methanol is also an important organic chemical raw material and an important C1product which is widely used in pharmaceutical, chemical and other fields. Large scale methanol synthesis and methanol to olefin are the trend of the methanol industry in the world, which put forward new requirements on the performance of methanol synthesis catalyst and the production capacity of methanol reactor.The present work established an intrinsic kinetics model for a new methanol synthesis catalyst. Based on the intrinsic kinetics model, a diffusion-reaction model was established. Heat transfer in the fixed-bed was experimentally investigated. A mathematical model for1800,000t/a methanol synthesis reactor was established and the influences of the operating conditions were investigated. It can provide the basic research data for the design of the reactor and optimal operation.The intrinsic kinetics of methanol synthesis over new methanol synthesis catalyst SC309was experimentally investigated in an isothermal integral reactor, with the range of catalyst size0.154-0.198mm, temperature180～260℃, pressure4-8MPa and space velocity4000～10000h-1. According to the experimental results, the influence of operating conditions was investigated and there exists an optimum reaction temperature at about240℃. Under the experimental conditions, the conversions of CO and CO2increased with the rising pressure and decreased with the increasing space velocity. The intrinsic kinetic model of Langmuir-Hinshelwood type was derived in form of the reactant fugacity. The parameters of the models were obtained through Levenberg-Marquardt method. Residual analysis and statistical test indicated that the intrinsic kinetic models were suitable.A diffusion-reaction model of methanol synthesis over catalyst SC309was established. The calculation method was obtained for internal effectiveness factors of industrial granularity catalyst with the zise of Φ5mm×5mm. The internal effectiveness factors were obtained by using numerical integration shooting method to solve the diffusion-reaction model. The model was verified by the global reaction rate obtained in a gradientless reactor at temperature180～260℃, pressure4-8MPa and space velocity4000～10000h-1. The absolute values of the relative error between model calculation values and experimentcal data were less than10%. The model calculation values agreed well with the experimentcal data. Thus the diffusion-reaction model can be used for the calculation of internal diffusion effectiveness factor of SC309. The effects of the catalyst particle size and operating conditions were investigated based on the model. The relationship between internal effectiveness factors and different operating conditions was obtained, which can provide basis for the reactor design.The temperature distributions in the fixed-bed packing with industrial granularity catalyst SC309were measured at air flow rate2.4～7m3/h, air temperature160～200℃of preheater outlet and heating tube temperature210～270℃. The effects of operating conditions on temperature distribution in the fixed-bed were investigated. A two-dimensional heat transfer model with no chemical reactions was established to describe the heat transfer in the fixed-bed. Orthogonal collocation method and Levenberg-Marquardt method were adopted to solve the equations and then effective radial thermal conductivity and effective wall heat transfer coefficient were obtained. The correlations of parameters and particle Reynolds numbers were obtained by correlating effective radial thermal conductivity and effective wall heat transfer coefficient with particle Reynolds number. The influence of the particle Reynolds number on the temperature distribution inside the bed was discussed and the result showed that improving particle Reynolds number conduced to radial temperature uniformly distributed in the fixed-bed.The technique of1800,000t/a methanol synthesis was proposed, which used two water-cooled reactors operating in parallel. The shell side was filled with catalyst, and the tube side of the reactor was fed by boiling water to remove the reaction heat. By simplifying the section of the catalyst bed surrounded by cooling-tubes reasonably and combining with intrinsic kinetics model, diffusion-reaction model and heat transfer model, a mathematical model for methanol synthesis reactor was established. The effect of operating conditions on reactor performance was studied based on the mathematical model. The results indicated that the reactor inlet temperature mainly influenced the temperature of the inlet section of the catalyst bed, but it had little effect on methanol concentration distribution in the bed and methanol yield. The temperature and the methanol concentration in the catalyst bed increased with the rising boiling water temperature. Both the pressure and the hydrogen-carbon ratio of syngas had little effect on the temperature distribution of catalyst bed. The methanol yield and methanol concentration in catalyst bed were increased obviously with the increasing pressure. While the hydro gen-carbon ratio of syngas was decreased, the methanol yield and methanol concentration in catalyst bed correspondingly decreased.