Studies On The Diffusion Of Asphaltene In Residue Hydrotreating Catalysts

The adsorption and deposition of asphaltene is the main reason for coking of the hydrotreating catalysts,so the studies on diffusion of asphaltene in catalyst are receiving more and more attention.In this paper,the diffusion experiment is carried out with Tahe atmospheric pressure residual asphaltene as material and toluene as solvent.The diffusion experiment is carried out under different experiment conditions,and a program is compiled to fit the experimental data and diffusion data to get the parameters with the MATLAB technology,to investigate the effect of different experimental conditions on the effective diffusion coefficient of the asphaltene aggregation in hydrotreating catalyst.Combined the experimental data and calculated parameters with the equations of hindered diffusion to calculate the hindered diffusion factor,to study the hindered diffusion factor in the different reaction conditions and the degree of diffusion obstruction of asphaltene in different catalysts.The effects of different experiment conditions on the effective diffusion coefficients of the asphaltene in hydrotreating catalyst are different.The effective diffusion coefficient decreases with the solution initial concentration increase and the scope of decreasing decreases significantly.With the increasing of operation time,the effective diffusion coefficient decrease and the decreasing speed is quicker and quicker.When the catalyst pores decease,the effective diffusion coefficient decrease and the scope of change is big because the effect of catalyst pores on the diffusion of the asphaltene aggregation in catalyst is large.The obstruction of catalyst pores is increasingly serious,further diffusion of asphaltene aggregation is hindered,and the effective diffusion coefficient decreases with the increasing of operation time,so the increasing speed of asphaltene penetration depth decreases in the same time.The hindered diffusion factor of asphaltene in hydrotreating catalyst is affected by different experiment conditions.With the increasing of solution initial concentration,the degree of obstruction of asphaltene aggregation in the pores of hydrotreating catalyst increases,and the hindered diffusion factor calculated by both of the diffusion experiment data and the corresponding math models decreases.With the increasing of time,the deposition and adsorption of the asphaltene aggregation on the surface and in the pores of catalyst are increasingly serious,so the pore diameter and porosity of catalyst decrease and lead to the hindered diffusion factor of the asphaltene aggregation in catalyst decreases.With the decreasing of the catalyst pore diameter,the degree of obstruction of asphaltene aggregation in catalyst increases,the hindered diffusion factor decrease.The diffusion of asphaltene aggregation in the catalyst whose average pore radius is 4.7nm is severely hindered,and its hindered diffusion factor F(λ) is very small.