Synthesis Of Hierarchical ZSM-5 Zeolite And Application On Oligomerization Of Isobutene

The dimers of isobutene oligomerization products isooctene are used as gasoline blending components after hydrogenation,which can increase the octane number of gasoline and reduce the lead content.At the same time,isobutene dimer is the raw material for synthesizing several chemicals.Therefore,the oligomerization of isobutene has received more and more attention.ZSM-5 molecular sieve catalyst has many unparalleled advantages because of its unique structure,and it shows good catalytic performance in the reaction of isobutene.However,the trapping of the conventional microporous molecular sieve is limited to a large internal diffusion resistance,and is easily deactivated due to clogged pores.Replacing the conventional microporous ZSM-5 molecular sieve with a hierarchical ZSM-5 molecular sieve is an effective method to improve its internal diffusion performance.In this paper,the nano-hierarchical ZSM-5 molecular sieve was synthesized by a relatively concise method,and its catalytic performance was evaluated in the isobutene oligomerization reaction.The target product was a dimer.The specific work is as follows:(1)Using tetrapropylammonium bromide(TPABr)as a single template,sodium silicate as a silicon source,and aluminum sulfate 18-hydrate as an aluminum source,a multilevel pore ZSM-5 was synthesized by hydrothermal crystallization Molecular sieve.The influencing factors in the synthesis of ZSM-5 were investigated.The results showed that the optimal dosage of template agent was b=2n,the optimal crystallization time was4d,and the optimal crystallization temperature was 150?.(2)Under this optimized condition,a series of hierarchical ZSM-5 with different Si O₂/Al₂O₃ ratios were synthesized which Si O₂/Al₂O₃=27,50,72,93,114.The performance of catalytic isobutene oligomerization reaction was evaluated.The sample that Si O₂/Al₂O₃=72 showed the best performance.(3)On the basis of single template synthesis,C_14-3-14 and TPABr were introduced to form a double template,and the effect of different C_14-3-14 addition was investigated.The results showed that the double template method effectively increased the mesopore volume,Where C_14-3-14/Si O₂=2q the best sample properties.The sample was synthesized with a single template method with a similar ratio of silicon to aluminum and the conventional microporous ZSM-5 was used to evaluate the isobutene oligomerization reaction.The sample synthesized with the double template method performed best.(4)The process conditions have a significant impact on the catalytic performance.This article examines the three important factors of reaction temperature,reaction space velocity,and reaction pressure.The results show that:the optimal reaction temperature is110?,the optimal reaction space velocity is 3h^-1.The optimal reaction pressure is 2MPa.Under the optimized process conditions,the long-term reaction evaluation of the synthesized hierarchical ZSM-5 molecular sieve showed its excellent catalytic performance.After 72 hours,the yield of C8 can still reach 64.7%.