Preparation Of Mesoporous Spherical Alumina Support By Sol-Gel Method—Structure And Performance

Alumina is widely used as catalyst support due to its excellent properties.The pore structure of the alumina support has an important influence on the activity,selectivity and other properties of the catalyst.The study of the relationship between the alumina support structure and the catalytic performance and the regulation of the catalyst support structure are important for the preparation of high-quality and stable catalysts.In this paper,spherical alumina support was prepared by sol-gel method using pseudo-boehmite as raw material,and the structure changes during the preparation of spherical alumina supports and their effects on the catalytic performance were mainly studied.The main research results are as follows:(1)The sol viscosity and surface tension are important factors in the drop-ball process.When the viscosity of the sol is too high and the surface tension is small,the sol ball will appear tailing;when the viscosity of the sol is too small and the surface tension is high,the sol ball cannot pass through the two-phase liquid surface.Therefore,it is necessary to optimize the sol-making process to obtain a sol with stable performance and easy to drop balls.Experiments show that when the temperature is 40°C,the solid content is 20%,and the molar ratio of aluminum to acid is 0.0325,the sol viscosity is 698 m Pa·s and the surface tension is 43.93 m N/m,which meets the requirements of the drop ball process.(2)Different spherical alumina support was prepared by changing the amount of acid added,calcination temperature,rare earth(X and Y),additives a-d,and post-treatment.The detection and analysis of its structure and properties show that:increasing the amount of acid and calcination temperature,adding Y or additive b will increase the strength of the spherical support.Increasing the amount of acid added,adding X or additives a,c,d and post-treatment can increase the surface area of the spherical support.Adding rare earth,additives a-d and post-treatment will increase the pore volume of the spherical support.Adding rare earth or additive d,increasing the calcination temperature and post-treatment will increase the average pore size of the spherical support.The structure and properties of spherical alumina support can be regulated by changing the above preparation conditions.(3)Spherical alumina supports Y1-Y4 and R1 with different pore structures were prepared,and propane dehydrogenation experiments were carried out after the self-made and commercial spherical supports were loading with the catalyst to explore the effect of support pore structure on the catalytic performance.the result shows:It was found that the deactivation rate of Y3 within 24h was only 4.38%,and the yield reached28.86%,which is comparable to the performance of commercially available spherical supports.The surface area of Y3 is 190.8m~2/g,the pore volume is 0.55cc/g,and the average pore diameter is 11.60nm.The large surface area,pore volume and average pore diameter are the reasons for its excellent catalytic stability.(4)The pore structure and thermogravimetric analysis of the catalyst after the catalysis experiment were carried out.The results showed that the pore volume of the catalyst decreased by 32.50%to 45.83%during the catalytic reaction.Carbon is an important reason for the reduction of catalyst pore volume.Adding rare earth and increasing the calcination temperature can reduce the coke deposition of the catalyst and reduce the degree of graphitization of the coke deposition.