Synthesis Of Hierarchical Zeolite Y

Fluid catalytic cracking(FCC)is one of the most important technologies to process heavy oil.Zeolite Y is the main active component in catalyst.However,zeolite Y suffers from narrow microporous channel(0.74 nm),which limits its application in large molecules conversion.Fortunately,hierarchical zeolite Y with graded pores was characterized with high crystallinity,large specific surface area,and strong acidity.As a result of this,zeolite Y overcomes the shortage of the diffusion restriction of heavy oil large molecules.Moreover,it also enhances the mass transfer of the catalyst.As the direct consequence,large molecules could easily contacte with the active sites,thereby improving the catalytic conversion efficiency of large molecules.As a typical example,our group reported the synthesis of zeolite Y with TPOAC([(CH30)3SiC3H6N(CH3)2C18H37]Cl)as the mesotemplate to synthesize hierarchical zeolite Y to solve the problem of large molecules conversion.In spite of this,high cost of TPOAC still an obstacle for its industrial application.Hierarchical zeolite Y by using amphiphilic siliane couping agent(named as MT-16)with a shorter hydrophobic chain was synthesized by our group as the mesotemplate in this paper.In this novel strategy,the hydrophilic group-Si-(OCH3)3 in the MT-16 was hydrolyzed to-Si-(OH)3 in alkaline mediam.The mesotemplate was anchored in the molecular sieve framework by the convalent bond of-Si-O-Si(Al).In the subsequent process,the hydrophilic long-chain alkyl group(-C16H33)self-assembled and occupied a certain space.Zeolite Y with graded pores was obtained after calcination.The relative crystallinity of hierarichical Y was 92%,with the total surface area 677 m2·g-1,the external surface area 139 m2·g-1,the total pore volume 0.55 cm3·g-1,and the average pore size 3.6 nm.Zeolite Y with graded pores was obtained by in-situ crystallization by using kaolin as raw material.Calcination at high temperature would lead to the collapse of kaolin and the removal of hydroxyl groups,resulting in the activation of natural kaolin.In the subsequent process,the silica-alumina species could be obtained from the activated kaolin.Zeolite Y could be grown in the activated kaolin by in-situ crystallization and composite with macro-meso-micopores would be obtained by this novel strategy.The using of kaolin could replace some chemical reagents,and provided part of silicon source and the total aluminum source required in synthesis progress,so that could reduce the cost of synthesis.The novel composites obtained in this paper were characterized with the enhanced thermal stability,improved wear resiitance,and graded pores.In addition,Zeolite Y was synthesized by using Suzhou and Maoming kaolin as raw materials respectively.The total surface area of the molecular sieve synthesized by Suzhou kaolin calcined at 850?reached 727 m2·g-1,the external specific surface area was 74 m2·g-1,the total pore volume was 0.37 cm3·g-1,and the average pore diameter was 3.1 nm.The total specific surface area of molecular sieve synthesized by Maoming kaolin calcined at 950? was 755 m2·g-1,,the external specific surface area was 95 m2·g-1,the total pore volume was 0.42 cm3·g-1,and the average pore diameter was 3.8 nm.