Multi-Scale Investigation Of Mass Transfer In Porous Media For Catalytic Distillation Process

Catalytic distillation combines the catalytic reaction with the distillation,which has more advantages,such as enhancing the rate of conversion and selectivity of the reaction,reducing the energy consumption of the equipment as well as decreasing the cost of the equipment.It is undeniable that catalytic distillation has a potential industrial prospect in process intensification field.What should be pointed out is that the catalytic packing is the core component of catalytic distillation process.However,catalytic packing that includes two different processes,mass transfer and reaction,which makes catalytic distillation process become very complicated.Besides that,the catalytic packing is a multi-scale structure that includes two kinds of porous media in different scales.The larger one is composed of catalyst particles in random arrangement,and the smaller one consist of pores inside the catalyst particles.In this paper,multi-scale investigation of mass transfer in catalytic packing was carried out to enhance catalyst performance.The porous media structure formed by catalyst particles was taken as the macroscopic scale.And the other one was used as the microscopic scale.Lattice Boltzmann method was used to investigate mass transfer behavior at the above two scales.At the macroscopic scale,a lattice Boltzmann model was developed to study the mass transfer behavior,and the longitudinal dispersion coefficient in the porous media composed of catalyst particles was calculated.The study showed that mass transfer behavior under this scale can be mainly divided into three categories.There are the mechanical dispersion,the boundary layer dispersion and holdup dispersion,of which the boundary layer dispersion and holdup dispersion can also be expressed as non-mechanical dispersion.According to the research,it has been found that in the range of high Peclet number,non-mechanical dispersion is dominant than mechanical dispersion.Moreover,intraparticle diffusion behavior plays an influence on mass transfer process in macroscale.After that,a new correlation of longitudinal mass dispersion was established,which can predict longitudinal mass dispersion in larger ranges of porosity(?bed=0.3 to 0.7).At the microscopic scale,mass transfer process inside catalyst has been studied.The resin catalyst is widely used in catalytic distillation.There are two major mass transfer behaviors inside resin catalyst,which are pore diffusion and surface diffusion,respectively.It is should be mentioned that pore diffusion mainly exists in larger pores such as macropores or mesopores,while surface diffusion mainly happens in the micropores.According to analyze commercial resin catalysts,it has been found that resin catalyst only has macropores and mesopores,so pore diffusion is the main mass transfer behavior inside resin catalyst.The research showed that the effect of the number of mesopores on the mass transfer is different in different porosity ranges.At the same time,an optimal value for the effect of the ratio of average diameter for macropore and mesopore on mass transfer was determinded.Besides that,the growth direction of the pores plays a significant role on mass transfer inside resin catalysts.