Simulation Of Eggshell Catalyst For Fischer-Tropsch Synthesis

Cobalt-based catalysts for Fischer-Tropsch synthesis were simulated by COMSOL Multiphysics software based on lumped kinetic model.A more reasonable mathematical and geometric model of three catalysts with different geometrical structures was established from the point of view of single particle and this model was verified.The effects of catalyst structure on fluid flow,mass transfer,and heat transfer and reaction rate were investigated.The effect of catalyst active component thickness on the reaction results was investigated.The CO and H2 mole fraction distribution,temperature distribution and product selectivity distribution were obtained by using COMSOL software at 498K?3MPa?1000h-1.The results show that H/C ratio and temperature increases gradually from outside to inside.The effects of fluid flow pattern,temperature and pressure on Fischer-Tropsch synthesis was simulated by COMSOL software.Turbulent flow is conducive to the formation of heavy hydrocarbons and the reduction of catalyst temperature rise;the increase of reaction temperature increases the diffusivity of reactants and products in catalyst particles,which increases the hydrogen-carbon ratio in catalyst particles and significantly improves the selectivity of CH4,the temperature in catalyst particles increases.The increase of reaction pressure decreases the concentration of CO and H2 in catalyst particles.At the same time,the temperature inside the catalyst particles rises.The simulation results of spherical,strip and clover catalysts under laminar and turbulent conditions show that the turbulent conditions improve the flow field distribution of clover and clover catalysts,which is more conducive to heat transfer.The clover catalyst has the best catalytic performance with a selectivity of 85%for C5+.It was found that the cross-sectional area of contact with fluids was higher at the oblique inlet of clover catalyst under laminar flow conditions,and the average consumption rate of CO was 0.055 mol/(g· h)at the oblique inlet of clover catalyst and 0.041 mol/(g ·h)at the oblique outlet of the cylinder in turbulent flow.The influence of active component thickness of spherical catalyst on the reaction results was investigated.With the increase of active component thickness of catalyst,CO conversion increased gradually,C5-(methane and low carbon hydrocarbons)selectivity increased gradually,while the selectivity of C10H22 and C22H46 decreased gradually.The temperature rise of catalyst particles increased and the peak temperature moved gradually to the catalyst particles,which was not conducive to the transfer of reaction heat.The optimum active component thickness of eggshell spherical catalyst is 10%.