Study On The Catalytic Reaction Of 1-Hexene Over Nano-ZSM-5

Worldwide environment protection has made fuel quality standards more and morestringent. In China, one of the most obvious problems of fuel quality is redundant olefinfraction of gasoline. So, to decrease the olefin content of FCC gasoline is an important andeconomic way to solve the problem of high olefin content in commercial gasoline in China.Isoalkanes can evidently promote the octane value and reduce the sensitivity of gasoline.Simultaneously, higher calorific value and cleaner exhaust gas are given when they arecombusting. So, isoalkanes are ideal components of blended gasoline.Nano-scale ZSM-5 zeolite, due to its specialties of higher activity, specific selectivity,stronger ability to resist coking and excellent abilities for aromatization, isomerization andalkylation, can be used to reduce the olefin fraction in the gasoline, while the RON preserved.In this paper, variation characteristics of the content of isoalkanes in the products of1-hexene cracking were investigated in a pulse injection micro-reactor and a micro-fixed bed,based on which we reached the following conclusions:(1) Under the reaction temperature of 643K, the content of isoalkanes correlated wellto the aromatics in the products of 1-hexene cracking over HZSM-5. Hydrogen transferreaction was the main way in which isoalkanes were generated.(2) Ni oxide modification to nano-HZSM-5 could efficiently recover the aromatizationactivity which was reduced by hydrothermal treatment, while La oxide modification did notwork. The content Of isoalkanes decreased when NiSO₄ was loaded, for supported Ni oxidecould promote the dehydrogenation of the precursors of aromatics by unimolecular reactionwhich did not generate negative hydrogen ions, and the carbonium ions could not obtainsufficient negative hydrogen ions to promote hydrogen transfer reaction. The ability ofisomerization and aromatization of ZSM-5 changed little when the Ni oxide loading capacityreached 3wt%. The cracking activity disappeared when the BrÇ’sted acid centers were totallypoisoned by 2, 6-dimethypyridine, which showed that NiO could not crack 1-hexene aloneand only assistant-catalysis was afforded.(3) High reaction temperature was benefit to the generation of aromatics, but notisoalkanes. The content of isoalkanes was cut down at high temperature through thedehydrogenation to inhibit hydrogen transfer reaction and the fortified cracking reaction ofisoalkanes. This effect was more evident over NiZSM-5 because of the double inhibition of high reaction temperature and dehydrogenation of L acid centers. Otherwise, the bondbreaking capability of Ni was negative to the generation of alkanes.