Creation Of Hierarchical Pore In The Molecular Sieve System

Microporous zeolites are widely used in petrochemical catalysis due to their unique pore structure,specific acid sites and large specific surface area.However,there are still the following disadvantages:Firstly,due to the small pore size of microporous molecular sieves,macromolecular reactants cannot enter molecular sieve pores,larger volumes of products cannot diffuse out of the molecular sieve channels,and occupy active sites,tend to deposit carbon and reduce catalyst life.Secondly,the cost of synthesizing molecular sieves with chemical reagents is high.The introduction of some mesopores in the molecular sieve can promote the circulation of macromolecules,reduce carbon deposition,and increase catalyst life.Moreover,Fabrication of mesoporosity in low-cost method remains a great challenge.Based on the above problems,Kaolin/NaY molecular sieves with higher crystallinity were synthesized using kaolin and directing agent.The relative crystallinity of the obtained molecular sieve was 82%.Due to the connectivity of molecular sieves and kaolinite,hierarchical meso-micropores were obtained.The total specific surface area,external specific surface area,the total pore volume and the mesoporous volume of the product are 691.7m2·g-1,75.5m2·g-1,0.38 cm3·g-1 and 0.06 cm3·g-1.Kaolin instead of some raw materials provides all aluminum sources and some silicon sources.Using kaolin and seed crystals,seed crystals are dissolved under alkaline conditions to provide nucleation,and the kaolin active component is connected with-Si-O-Si-or-Si-O-Al-to synthesize kaolin/ZSM-5 molecular sieve.The crystallization temperature was 170? and the crystallization time was 18 h.The total specific surface area,extermal specific surface area and the total pore volume of the product are 256.1m2·g-1,53.3 m2·g-1 and 0.16 cm3·g-1.Kaolin as raw material,TPABr and TPHAc were used as template to synthesize kaolin/ZSM-5 composite hierarchical molecular sieves.TPABr induced the synthesis of microporous structure due to charge-matching,and the hydrophilic group of TPHAc was hydrolyzed to-Si-(OH)3.-Si-O-Si-or-Si-O-Al-is formed with the silica-alumina gel in the system,hydrophilic long-chain self-assembled are introduced into the molecular sieve and calcined to form mesopores.The crystallization temperature was 170? and the crystallization time was 36 h.The total specific surface area,external specific surface area,microporous specific surface area,the total pore volume and the mesoporous volume of the product are 443.9 m2·g-1,151.1 m2·g1,292.8 m2·g-1,0.26 cm3·g-1 and 0.12 cm3·g-1.The kaolin was preliminarily treated with 6 mol/L HCl to remove some of the aluminum,the molecular sieve with high silica-alumina ratio was obtained.The total specific surface area?external specific surface area?the total pore volume and the mesoporous volume of the product respectively are 326.5 m2·g-1,163.7 m2·g-1,0.33 cm3·g-1 and 0.23 cm3·g-1.