Study On The Diffusion Behavior Of Solute Molecules In Porous Materials

The diffusion behavior of molecules in the porous materials pores is significantly affected by the pore structure.While the pore structure of the traditional porous materials is complex,which brings some difficulties to the study of molecular diffusion in pores.In this study,monodisperse silica microspheres were assembled into silica particles with millimeter size,which pore size,pore volume and pore tortuosity factor can be determined.Meanwhile,there are no block pores and dead holes in the particles.The silica particles with uniform pore structure can be used as model porous materials,where the diffusion behavior of dibenzothiophene(DBT,one main component of petroleum)can be studied.The research content and methods are as follows:Firstly,to investigate the assembly conditions of monodisperse silica microspheres into colloidal crystal microspheres,monodisperse silica microspheres of 30 nm,50 nm,194 nm and 300 nm were assembled in different solvents(n-octanol,silicine oil and castor oil).Hollow colloidal crystal microspheres were obtained in n-octanol,while solid colloidal crystal microspheres obtained in silicine oil and in castor oil.The colloidal crystal microspheres were on the micrometer scale.And its morphology was not affected by the mass fraction and size of primary silica particles in droplets,mass ratio of silica sol to solvent.However,silicone oil could clog the pores of colloidal crystal microspheres.Secondly,in order to obtain silica particles that can be used as model porous materials,it is necessary to synthesize solid particles with millimeter size and transfixion pores.Therefore,based on the experiments above,monodisperse silica microspheres(30 nm,50 nm,90 nm,300nm)were assembled in castor oil to obtain millimeter silica particles.A drop of silica-water suspension was injected into a glass tube which was full of castor oil and formed into silica sol droplets.Then the glass tube was rotated by an electromotor and heated by water vapor to remove the water from the drop of silica-water suspension.In an hour later,the drop of silica-water suspension was transferred to a polytetrafluoroethylene(PTFE)container and water in the drop of silica-water suspension was further removed.Finally millimeter-sized silica particles with high-ordered packing of silica nanospheres were obtained.Thirdly,a solution of 1,3,5-trimethylbenzene and n-octane and 2,6-dimethyl pyridine was used as solvent and dibenzothiophene(DBT)was used as diffusion compound to study the diffusion behavior and regularity of DBT.The diffusion behavior of DBT in silica model porous materials were studied by adsorption-diffusion method.Then,the effective pore diffusivity D_p,intrinsic surface diffusion coefficient D_s~*and intrinsic diffusion coefficient D_i of DBT were obtained.And so was the diffusion restrictive factor F(?)of BDT.Finally,based on the calculated intrinsic diffusion coefficient D_i and intrinsic surface diffusion coefficient D_s~*,the mass ratio of DBT molecules diffusion on porous materials surface to total DBT molecules diffusion(RST)was calculated.It showed that the RST increased remarkably with decreasing catalyst pore size.