ZSM Catalyst Preparation And The Application In Hexene Oligomerization

In recent years,low carbon olefin resourceshave become more and more abundant.The petroleum catalytic cracking FCC,Fischer-Tropsch synthesis and other by-products also produce a large number of olefin.Chinahas been implementing the adjustment of energy structure to advocate the development and production of clean fuel routes.Due to the increasing awareness of environmental protection and the increasingly strict regulations,the olefins content in gasoline is strictly controlled.As an important category of synthetic liquid fuel routes,olefin oligomerization reaction to producehigh-quality liquid fuelhas attracted extensive attention from the industry and academia.In recent years,the rapid development of China’s aviation industry makes the consumption of aviation kerosene increasing day by day.The demand of C₉-C₁₆ as the ideal component of aviation fuel is also on the rise in the future.The by-product C₆ olefin can be realized through oligomerization reaction.To sum up,the comprehensive utilization of C₅/C₆olefins raw materials to improve economic benefits,and the selection of appropriate catalysts is the most priority.In this paper,the topological structure of the MFI zeolite molecular sieve was selected as the catalyst to investigate its catalytic activity in the oligomerization of 1-hexene.The relationship between the structure of the catalyst and the catalytic performance of olefins was studied by adjusting the acidity,pore and introducing metal active site of molecular sieve.ZSM-5 zeolites with different Si/Al ratios were prepared by functionalization of primary zeolites.The catalytic performance of ZSM-5zeolites with different Si/Al ratios for the oligomerization of 1-hexene was evaluated.The results show that the ZSM-5 molecular sieves with low Si/Al ratio are difficult to synthesize（the silicon to aluminum molecular ratio is66）,while the ZSM-5 molecular sieves withhigh acidityhave the same pore structure,and the low Si/Al ratio molecular sieves withhigh acidity are more conducive to the olefin oligomerization.With the increase of Si/Al ratio,the conversion ofhexene increases,and the selectivity of dimer reaches thehighest of 78.7%.Thehierarchical ZSM-5 molecular sieves with different acidity were prepared by changing the addition amount of silanization reagent.The application of reaction temperature and space velocity inhexene oligomerization reaction was investigated.The results show that with the increase of reaction temperature,the conversion ofhexene increases while the selectivity of dimer decreases slightly.With the temperature reach to260°C,the initial conversion rate of 1-hexene is 49.3%and the selectivity of dimer is 67.8%.Under the conditions of mass space velocity was 1.51h^-1,temperature was 260°C,pressure was 4MPa and reaction time was 12h,the maximum average space-time yield of 698mgg_cath^-1 was obtained.Finally,Ni/ZSM-5 samples with different Ni content on the same acidic support and samples with the same Ni content on different acidic support were prepared by ion exchange method.The effects of SBA-15 introduced by mechanical mixing and NH₄HF₂ treatment on the oligomerization ofhexene were investigated.The results show that the synergistic effect of Ni active site and protic acid site makes the catalyst obtain better catalytic activity in olefins oligomerization.The improvement of mass transfer efficiency also improved the catalytic activity to some extent.