Fabrication Of Mesopores In ZSM-5 Zeolite

ZSM-5 zeolite with hierarchical mesopores would overcome the diffusion resistance caused by micropores of conventional ZSM-5 zeolite,which made it accessible to reach the active centers of catalysts for heavy oil molecules and improve the catalytic efficiency.Therefore,it has a good application potential in heavy oil fluid catalytic cracking.It's a general way to employ organic amine in synthesizing hierarchical ZSM-5 zeolite.However,two problems remain unaddressed in this method:(1)Conditional quaternary ammonium cation templates are characterized by high price,lower productivity and environmental pollution;(2)Synthesis procedure is complicated,no easy to fabricate the uniform mesopores and prone to produce phase separation.In order to solve the issues above,amphiphilic organosilane and seed-assisted method can be used for the synthesis of hierarchical ZSM-5 zeolite.The seed induced the crystallization of micropores,the hydrophilic moieties of organosilane TPHAC condensate with the aluminosilicate species or external hydroxyl of dissolved seed crystals via chemical bonding.The hydrophobic moieties like long-chain alkyl can self-assembly to form the micelles and template the formation of mesopores.The scale-up synthesis of 10 liters is conducted at the optimized condition:crystallization temperature 170 ?,crystallization time 18 h,contents of mesoporous template 3.12 g,the water-bath temperature 50 ?,the stirring speed 500 rpm.The BET surface area,mesoporous surface area,total pore volume and mesoporous volume of the zeolite are 367.3 m2/g,110.1 m2/g,0.312 cm3/g,0.178 cm3/g,respectively.Dual-template of TPHAC/TPABr was employed to prepare hierarchical ZSM-5 zeolite.It is found that the ethanol contents in the TPHAC solution played certain impact on the critical micelle concentration(CMC)of organosilane micelles.With increase of ethanol contents,the CMC value of TPHAC micelles would increased and micellar size would decreased.As a result,the pore size distribution became more uniform.This result indicated using an adequate amount of ethanol has a synergetic effect with the structure-directing effect of template to a degree.Excessive ethanol amounts would hinder the self-assembly of micelles and interaction with seed crystal,which had an influence on the state of TPHAC micelles,like the pore size distribution became broader owing to the increase of TPHAC oligomers with larger size.The optimal conditions were the crystallization temperature 170 ?,the crystallization time 36 h,TPHAC mass 6.15 g,and the ethanol mass 3.15 g.Accordingly,the BET surface area,mesoporous surface area,total pore volume and mesoporous volume of the zeolite are 368.7 m2/g,106.1 m2/g,0.367 cm3/g,and 0.246 cm3/g,respectively.Gemini-type surfactant with dual functional groups is synthesized.Enhancement of the interaction between the gel and surfactant favor the fabrication of the mesopores in ZSM-5 zeolite.The BET surface area,mesoporous surface area,total pore volume and mesoporous volume of the zeolite are 378.5 m2/g,92.5 m2/g,0.35 cm3/g,and 0.24 cm3/g,respectively.