Modulating isomers distribution of n-dodecane hydroisomerization by ZSM-22/ZSM-48 composite zeolite

ZSM-22 and ZSM-48 zeolites with different topological structures showed distinct catalytic performance in the hydroisomerization of n-alkanes, especially in the distribution of isomers. In this paper, ZSM-22/ZSM-48 composite zeolites were synthesized by the mechanical mixing method and the secondary hydrothermal synthesis, and the samples were characterized by XRD, SEM, NH₃-TPD and N₂ adsorption/desorption. The results show that ZSM-22/ZSM-48 composite zeolites show the combined properties of the two individual zeolites, such as the specific surface area, micropore volume, micropore area and acidity are between the single ZSM-22 and ZSM-48 zeolites. By using n-dodecane as the model reactant, the effects of topological structure on hydroisomerization properties and product distribution are investigated. In Pt/ZSM-22/ZSM-48-S, the percentage of 2-methylundecane in the monobranched iso-dodecane product is 19%−44%, which is about 20% higher than the percentage of 2-methylundecane product in Pt/ZSM-48, and about 10% lower than the percentage of 2-methylundecane product in Pt/ZSM-22. And the percentage of 5-methylundecane in the monobranched iso-dodecane products is 23%−42%, which is about 8% higher than Pt/ZSM-22 and about 13% lower than Pt/ZSM-48. The results show that the distribution ratio of the isomer products can be regulated by adjusting the topological ratio of the two molecular sieves, ZSM-22 and ZSM-48, in the Pt/ZSM-22/ZSM-48 composite molecular sieve catalyst.