Study On The Preparation Of Catalyst And Reaction Mechanism For Aromatization Of FCC Gasoline

FCC gasoline accounts for the highest proportion in Chinese gasoline pool,and the cumulative output is significantly higher than the consumption.With the improvement of vehicle gasoline standards and the tightening of fuel vehicle market in the future,refining and chemical enterprises have realized the transformation from pure fuel to fuel head incarnation.FCC gasoline aromatization route is an effective way to solve the problem of gasoline surplus and aromatics production shortage.In this paper,by adjusting the temperature and time of ZSM-5 molecular hydrothermal treatment and Zn/Ni metal loading,the preparation method of deep aromatization catalyst was formed,and the reaction conditions were optimized.The reaction mechanism of FCC gasoline aromatization and the relationship between catalyst acid properties and aromatization reaction performance were deeply understood.The effect of hydrothermal treatment conditions on the aromatization performance of ZSM-5 zeolite was investigated,and the structure-activity relationship between acidity and aromatization performance of ZSM-5 zeolite was deeply understood.The results show that the amount of L-acid increases with the increase of hydrothermal treatment temperature when the hydrothermal treatment temperature is higher than 600℃ The increase of hydrothermal treatment temperature will lead to the decrease of aromatics yield,the decrease of BTX selectivity and the increase of C9~+aromatics.Prolonging the hydrothermal treatment time can transform tetrahedral framework aluminum into partial octahedral non framework aluminum,reduce cracking activity,increase liquid yield,selectivity of C9~+aromatics and C8~+alkanes,and decrease total aromatics yield and BTX selectivity.The effects of Zn and Ni loading on the aromatization performance of the catalysts were investigated.It was found that the main forms of Zn on the catalysts were Zn O and[Zn(OH)]~+The presence of[Zn(OH)]~+increased the L-acid content of the catalyst,promoted the aromatization reaction,significantly enhanced the yields of C8 and C10 aromatics,and inhibited the formation of low-carbon hydrocarbons.However,the Zn O formed after over loading of Zn covered part of L-acid sites,resulting in the weakening of aromatization reaction.Furthermore,it was found that the addition of Ni increased the amount of L-acid,increased the yield of C8 aromatics,and decreased the hydrogen transfer index significantly,which indicated that the introduction of Ni enhanced the alkylation reaction on the benzene ring and promoted the transition from hydrogen transfer aromatization to dehydroaomatization.Based on the evaluation results of 1-hexene aromatization catalyzed by Zn/Ni,the reaction network of olefin aromatization was constructed,and the reaction mechanism on acidic catalyst was elucidated.The effect of reaction conditions on aromatization performance of FCC gasoline was investigated by using the optimized catalyst.It was found that Zn/Ni Bimetallic Catalyst significantly promoted the formation of aromatics above C8-10 and the cyclization reaction of carbocation.The increase of temperature significantly promoted the conversion of C6 and C7olefins.Olefin conversion and aromatics yield increased with the increase of temperature,while BTX yield and olefin saturation decreased with the increase of temperature..