Nano-hzsm-5 Zeolite Modified And Catalytic Properties Of The Study

In China, one of the most obvious problems of fuel quality is redundant olefin fraction of gasoline, which is attributed to the high proportion of FCC gasoline with ample olefins in gasoline pool. At the present time, it is difficult to largely change the gasoline pool composition, for the lack of the catalytic reforming unit, alkylation unit, isomerization and production units of oxygenous compounds. So, to decrease the olefin content of FCC gasoline is an important and economic way to solve the problem of high olefin content in commercial gasoline in China.ZSM-5 zeolite has been widely applied in hydrocarbons transformation processes due to its excellent ability for aromatization, isomerization and alkylation. Based on these abilities, the olefins in gasoline can be transformed into iso-paraffins and aromatics with high RON. In this way, olefins content in gasoline could be reduced greatly, while the RON preserved. In this paper, the parent nano-scale ZSM-5 zeolites (20～50nm) was chosen as matrix of catalyst for reducing olefins content and its super ability and stability had been found.The modification of the used nano-HZSM-5 zeolite has been done by several methods such as hydrothermal treatment, different metal oxide impregnation and combined methods tailored for nano-HZSM-5. To make a thorough understanding of the reaction mechanism, special concern was given to the monitoring of the modification effects and the physiochemical properties of catalysts, namely adsorptivity and diffusivity, total acidity distribution and acid type distribution. The uptake rates of normal hexane (n-h) and cyclohexane (c-h), the relative diffusivity of n-h and c-h, viz, Dn/Dc were used to characterize its diffusivity property. In terms of acidity characterization, both NH3-TPD and FT-IR techniques were employed to describe the total acid content and acid type distribution.1,Hydrothermal treatment modificationThe effects of hydrothermal treatment conditions on physiochemical properties and catalytic properties were investigated. The results indicated that hydrothermal treatment mainly passivated the strong acid sites of nano-HZSM-5, and caused minor influence on crystalline and diffusive property. The suitable hydrothermal treatment conditions were: temperature 500℃, time 3h and 0.5mol/L NH3-H2O as medium.2,Metal oxides impregnation modificationThe impregnation modification effects of mix rare earth, nickel oxide on the physiochemical properties and catalytic properties of nano-HZSM-5 catalyst were investigated. The obtained catalyst by impregnating mix rare earth oxide had strong isomerization activity, moderate aromatization activity and stable activity. The catalyst by loading 2~3%(wt) mix rare earth had more stable activity. The olefins content in gasoline decreased from 65.9% to about 25%, and the ratio of iso-/n-paraffins content increased from 3.0 to 7.0, and the aromatics content retained 35 %, and the RON was maintained. The total acid amount of the attained catalysts by loading suitable nickel oxide decreased lightly, L acid sites increased obviously, and B acid sites declined. Enhancement of aromatization activity by synergistic function of B acid and L acid resulted in the increase of aromatics content in gasoline. However.3,The combined modificationBy combining alkaline medium hydrothermal treatment and loading mix rare earth oxide, loading nickel oxide, respectively, the HZnm-C1a catalyst was prepared. The characterization results showed that the acid properties of nano-HZSM-5 catalyst were adjusted effectively, viz. L acid sites increased obviously, B acid sites decreased lightly and the ratio of L/B sites increased by 1.5 or so. The catalytic test results indicated that the HZnm-C1a catalyst exhibited strong ability to reduce olefins content in gasoline and stable activity. During test period, the olefins content in gasoline decreased from 56.3% to below 23%, the olefins content of product gasoline only increased by 4%. The components of product gasoline were ideal, thereinto, the paraffins content increased to 53%, the aromatics content maintained about 25%, the ratio of iso-/n-paraffins increased from 3.2 to 6.5, the RON was retained above 90.From the above research, we had further recognized the effects of different modification methods on the physiochemical and catalytic performance of nano-HZSM-5 catalyst. Then, the feasible pathways to decrease catalyst cost for upgrading gasoline preparation costs were provided and the new approach about preparation catalyst was developed. The research work is practically significant to promote gasoline cleanness and environmental protection.