Study on synthesis of hierarchical flower-like ZSM-5 zeolite and its catalytic performance for n-octane cracking
The research and development of high activity catalysts has been a hot topic in the field of catalytic cracking of naphtha to produce light olefins.In this paper,the flower-like ZSM-5 zeolite was synthesized by using the Gemini quater-nary ammonium surfactant[C18H37-N+(CH3)2-C6H12-N+(CH3)2-C6H13]Br2 as structure-directing agent.The effects of crys-tallization temperature,n(Si)/n(Al),n(H2O)/n(SiO2)and n(Na2O)/n(SiO2)on the physicochemical properties of the ZSM-5 zeolite were investigated by XRD,SEM,N2 adsorption-desorption and NH3-TPD characterization techniques,and the catalytic cracking performance of n-octane on ZSM-5 zeolite was investigated.The research results showed that forma-tion of flower ZSM-5 zeolite was optimized preparation conditions is the raw material molar composition of n(Na2O)∶n(Al2O3)∶n(SiO2)∶n(C18-6-6Br2)∶n(H2O)=5∶1∶100∶10∶4 000,crystallization time of 72 h,the crystallization temperature of 175℃.With the increase of n(Si)/n(Al),the flower-like ZSM-5 particles tended to agglomerate more.When the feeding n(Na2O)/n(SiO2)was higher than 0.05,other heterophase appeared in the zeolite samples.With the increase of n(H2O)/n(SiO2),the layer morphology of ZSM-5 zeolite gradually became less obvious.In the catalytic cracking of n-octane to eth-ylene and propylene,the conversion of n-octane on the flower-like ZSM-5 zeolite remained stable after 30 h continuous testing,and the total yield of ethylene and propylene was gradually increased from the initial 62.0%to 64.4%.The high cata-lytic activity and excellent anti-carbon stability of the flower-like ZSM-5 zeolite were mainly attributed to its unique layered morphology and hierarchical structure.
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