Preparation Of Spherical Alumina With Larger Pore Size And Its Performance On Propane Dehydrogenation

In this paper,pseudo-boehmite was firstly prepared by the hydrolysis of aluminum isopropoxide.Then the pseudo-boehmite was used as the precursor to prepare spherical alumina granules with alginic acid.The macroporous alumina granules were used as carrier to make catalysts.The catalysts were characterized by N₂ adsorption-desorption,SEM,TEM,NH₃-TPD and XRD.The catalytic performance of propane dehydrogenation was investigated and the following is conclusions:Synthesis of pseudo-bohmite from aluminium isopropoxide.Pseudo-bohmite was obtained from hydrolysis of aluminium isopropoxide.Hydrolysis conditions including ratio of water to aluminium isopropoxide,ratio of water to isopropoxide in the hydrolysis solution and additive were found to be key factors in determining quality and property of pseudobohmite.Finally,the hydrolysis temperature was 60°C,the ratio of hydrolyzed solution was isopropanol:water:isopropoxide aluminum=40:8:1,the additive was 1.5 ml of ammonia,the solution was hydrolyzed for 6hours under the condition of pH 11.1.After aging for 12 hours,drying at 100°C for 5hours we got pseudo-boehmite powder with a specific surface area of 458.6 m²·g^-1,a pore volume of 1.218 cm³·g^-1,an average pore size of 10.62 nm and a bulk density of0.1771 g·cm^-3.Synthesis of alumina spheres granules from pseudo-boehmite and ammonium alginate.It was found that soaking in the acid solution can enhance the strength of the spheres granules while the pore size,pore volume and specific surface area of the spheres granules were reduced;The increasing calcining temperature could largen the pore size and pore volume while the specific surface area and the mechanical strength of the granules was decrease;When the alumina spheres granules were made by using heat-treated pseudo-boehmite powder,the pore size,specific surface area,and pore volume of the alumina spheres granules were increased as the temperature increasing.Alumina spheres granules with different contents of carbon could be made by ammonium alginate solution of 1.2%-2.5%when the calcination temperature is 500°C.Finally,the pseudo-boehmite pretreated at 150°C to make alumina spheres granules,with calcining temperature of 850?,no acid soaking,we obtained the alumina spheres granules with specific surface area of 165m²·g^-1,the pore volume of0.635cm³·g^-1,and the average pore size of 17.4nm,the strength of 20.3 N.The catalyst with Pt content of 0.3%,Sn content of 0.3%,K content of 0.6%was prepared by the method of co-impregnation using the above alumina spheres granules.The activity was higher when the acid content in the impregnating solution became higher.The carrier with different carbon content was made by different concentrations of ammonium alginate solution with the calcining temperature of 500?.Using the carrier to make PtSnK catalyst and the results showed us that the carbon could increase the stability of catalyst.After reaction 100 hours,the propane conversion rate could still reach 30%.