Preparation And Characterization Of Large Pore Volume Pseudo-boehmite With High Specific Surface Area

Fluidized catalytic cracking(FCC)is an important method of secondary processing of crude oil,and the catalyst is the core technology of catalytic cracking.With the domestic crude oil is increasingly heavy and inferior,refineries are faced with the problem of mixing more heavy oil and residual oil.Heavy oil is difficult to enter the interior of the zeolite because of its large molecular size,and its cracking mainly occurs on the catalyst support.At present,the active support of the domestic catalytic cracking catalyst is mainly provided by alumina,and the precursor for preparing alumina is mainly pseudo-boehmite.The pore volume and specific surface area of the pseudo-boehmite widely used in industry is respectively about 0.4cm~3/g,400m~2/g,and the average pore diameter is about 3 to 4nm.The pore structure of the pseudo-boehmite unable to satisfy the requirement of processing heavy crude oil.In addition,improving the pore structure of FCC catalyst is beneficial to improve the diffusion efficiency of oil and gas molecules in the catalyst,prevent excessive cracking and reduce coke production.Therefore,it is of great significance to improve the pore structure of pseudo-boehmite with high specific surface area and large pore volume to improve the heavy oil conversion ability of the catalytic cracking catalyst.In this paper,the pseudo-boehmite was prepared by acid method,alkali method and double aluminum method.The effects of different raw materials and the order of gelation on the preparation of pseudo-boehmite were studied in detail.Further study of using ammonium bicarbonate and urea as pore expanding agents respectively to prepared pseudo-boehmite by double aluminum method.The pseudo-boehmite was characterized by XRD,nitrogen physisorption-desorption,Py-FTIR and SEM.The results show that compared with acid method and alkali method,the pore structure of the pseudo-boehmite prepared by double aluminum method which used sodium aluminate and industrial aluminum sulfate as a raw material is more advantageous compared with the industrial pseudo-boehmite,it has higher pore volume and larger average pore size.Using sodium aluminate as alkaline aluminum source,aluminum chloride,aluminum nitrate and aluminum sulfate are used as acid aluminum source respectively,the result of preparation of pseudo-boehmite by double aluminum method showed that the specific surface area of the products prepared by three acid aluminum sources had little difference,but the pseudo-boehmite prepared with industrial aluminum sulfate as raw material has higher pore volume and average pore diameter compared with aluminum chloride and aluminum nitrate.With industrial aluminum sulfate and sodium aluminate as raw materials,the preparation of pseudo-boehmite by methods of acid drop alkali,alkali drop acid,flow titration and fast flow titration show that the pseudo-boehmite can be prepared by three other ways except that the acid drop alkali which product is gibbsite,among which the product prepared by the flow titration method has high specific surface area,pore volume and average pore size.The addition of ammonium bicarbonate and urea in the double aluminum method can regulate the pore structure of the pseudo-boehmite.After adding a certain amount of ammonium bicarbonate in the preparation of the pseudo-boehmite,the specific surface area of the product increased,the pore size is more concentrated,but the pore volume is reduced;After adding a certain amount of urea as the pore expanding agent,the specific surface area,the pore volume and the average pore size of the product increased.The results show that with the increase of urea addition,the specific surface area,pore volume and average pore size of the product increase first and then decrease.When the amount of urea is 5.0%,the high specific surface area,pore volume and average pore size of pseudo-boehmite with the specific surface area 467.3m~2/g,pore volume1.03cm~3/g,and the average pore size 8.81nm was prepared.In the process of catalyst preparation,high specific surface area and large pore volume pseudo-boehmite was added to replace the industrial pseudo-boehmite.The ACE evaluation of the catalyst showed that,under the condition of 3000ppmNi and 5000ppmV,the gasoline yield increased by 1.56%,the yield of heavy oil decreased by 0.69%,the coke yield decreased by 0.74%and the total liquid yield increased by 1.46%after the introduction of the high specific surface area and large pore volume of the pseudo-boehmite,which showed good heavy oil conversion ability and coke selectivity.