Study On The Diffusion Inside Porous Materials With Hierarchical Pores

Diffusion in porous materials is the most common mass transfer process in chemical engineering processes,such as,heterogeneous catalytic reaction,adsorption separation,ion exchange.In these processes,the performances of porous materials are influenced by the molecular diffusion inside the pores of porous materials.Therefore,it is very important to study the diffusion behavior of molecules in the pores of porous materials to enhance mass transfer in pores,optimize the pore structure,and design efficient porous materials.In the previous reports,the porous materials used for study of the molecular diffusion inside the pores of these porous materials have complex and random pore structures,so that one could not obtain accurate research results using such materials.In order to describe the molecular diffusion in the pores of porous materials accurately,in this work,some model porous materials with narrow pore size and uniform pore structure were prepared through orderly self-assembly of monodisperse SiO₂ nanospheres.The main contents of the thesis are as follows:1.The self-assembly of monodisperse SiO₂ microspheres in n-octanol and silicone oil was studied.It was found that the self-assembled aggregates obtained in n-octanol and in silicone oil were all compact clusters or supraparticles when the concentration of monodisperse SiO₂ microspheres in the emulsion droplets was low.When the concentration of the monodisperse SiO₂microspheres in the emulsion droplets was high,hollow structured aggregates of supraballs were obtained in n-octanol,while in silicone oil solid structured aggregates of supraballs were obtained.2.Intrinsic pore diffusivity and intrinsic surface diffusivity of dibenzothiophene inside model porous materials with uniform pore structure were determined.It was found that the intrinsic pore diffusivity increased with increasing pore size.When the pore diameter was larger than 35 nm,the diffusion became unrestricted.The ratio of the amount transferred by the surface diffusion to the total amount increased with decreasing pore size.The intrinsic surface diffusivity on the pore surface having strong adsorption force was smaller than that on the pore surface having weak adsorption force.3.The uptakes of dibenzothiophene in bidisperse porous materials were investigated and a bidisperse pore diffusion model was established.The experimental values of uptakes fitted well with the established bidisperse pore model.Based on the model,an equation for calculating the effective diffusivity in porous material with bidisperse pores was established.The established equation could predict well the effective diffusivity reported in some literatures.4.A model was proposed to describe the molecular diffusion inside porous materials with hierarchical pores of ternary pores.Based on the model,a correlation formula for calculating effective diffusivity in porous material with ternary pores was established.Some porous materials with ternary pores of micro-,meso-and macropores were prepared and effective diffusivity was obatined over these prepared porous materials using isobutane as the probe molecule through zero length column(ZLC)technique.It was found that the established formula could predict the experimental values of effective diffusivity well.