Numerical Study On The Preparation Of Zinc Acetate/Activated Carbon Catalyst In Fluidized Bed

Vinyl acetate is a kind of important organic chemical raw material, with a good prospect of application. Zinc acetate/activated carbon is the catalyst in the synthetic process of vinyl acetate, and there is a very large demand for this catalyst in the domestic vinyl acetate industry. At present, our country usually use the technology of eights last century to make zinc acetate/activated carbon catalyst, there are some disadvantages in uniformity and output. This paper carries out the following work centering on the above mentioned problems.(1)Applying the particle dynamics theory, considering the interaction between the gas and particles, particles component, the mathematical model of the gas-solid two phase flow, the gas-liquid-solid three phase flow and the gas-solid-solid three phase flow in fluidized bed was established. In the model, the gas phase is the first phase (continuous phase), liquid phase and solid phase are the second phase (particle phase), for the compound mixed by two different solid particles with different density, they were regarded as two phases respectively, and each component was signified by corresponding particle size, density and other parameters such as elastic recovery coefficient and volume fraction.(2)Based on the preparation of zinc acetate/activated carbon catalyst in the fluidized bed reactor, using the PC-SIMPLE algorithm and the Eulerian multiphase flow model in FLUENT software, the gas-solid flow hydrodynamic characteristics under different conditions were simulated. The simulation results show the formation, growth and disappearance of bubbles, and provide the basis for optimizing the operating conditions of the fluidized bed reactor.(3)Using the Eulerian multiphase flow model of FLUENT software, the gas-liquid-solid three phase flow and the gas-solid-solid three phase flow in the preparation of vinyl acetate catalyst were simulated. The simulation results show that, the spraying droplets of zinc acetate present an uneven distribution in the bed due to the resistance of the air and the activated carbon particles, so the upper activated carbon particles in the fluidized bed contact with more zinc acetate solution, and the lower activated carbon particles contact with relatively less solution, and the density of the upper part particles larger than that of the lower part, which leads to the density stratification. Based on this conclusion, a new technology is put forward in order to produce catalysts with uniform loads:the spraying operation and the drying operation in the fluidized bed is conducted alternately by stages. Considering the density stratification of particles and the new operation mode, the inversion of light and heavy particles is simulated. The simulation results show that, for the two kinds of particles with large difference of density, the light particles on the bottom gradually rise while the heavier particles on the top gradually sink, and the inversion of particles ultimately realize, but for the two kinds of particles with small difference of density, the inversion is not obvious, and larger gas velocity can not improve the effect of inversion.(4)Analysing the theory of the drying process of zinc acetate/activated carbon catalyst, discussing the different situations during the different phases in drying process, combined with the dynamic fluidized drying operation method, the absorption quantity of zinc acetate and water content can be suitable. The balance calculation of material and heat in the preparation of zinc acetate/activated carbon catalyst is done, and the temperature distribution in the fluidized bed is simulated by FLUENT.