Study On C₅ Fraction Hydrogenation Catalyst And Reaction Process

C₅ fraction contains a large amount of olefins.When it is directly returned as ethylene cracking raw material,it will lead to too high aromatics yield and coking in the reaction furnace,which needs to be fully hydrogenated to alkanes.At present,C₅ fraction hydrogenation in industry generally uses high nickel catalyst with nickel content of 35 wt%.The two-stage hydrogenation process is of great significance to develop a new and efficient catalyst for one-stage hydrogenation.In this paper,by inspecting the affect of nickel content,preparation patterns and additives type,a new catalyst which can realize one-stage total hydrogenation at low temperature was prepared.Ni/Al₂O₃ catalyst with Ni content of 15～40 wt%was prepared by co-precipitation method,and isoprene was used as a model compound for hydrogenation performance evaluation.Under the condition of temperature180～200℃,pressure 1.5～2 MPa,hydrogen/oil molar ratio 11～12,and the space velocity at heavy time was less than 5 h^-1,the yield of isopentane was 100%when the nickel content was 25 wt%.The activity of the catalyst remained unchanged after 60 hours of reaction,and the yield of isopentane was more than90%at 100 hours.Ni/Al₂O₃ catalyst with 25 wt%loading was prepared by different methods such as coprecipitation,deposition precipitation,equal volume impregnation,total impregnation and multiple impregnation.The hydrogenation performance of the catalyst prepared by total impregnation was evaluated by simulating C₅fraction.It was found that the hydrogenation performance of the catalyst prepared by total impregnation method was the best.Under the condition of temperature 145℃,pressure 2 MPa,hydrogen/oil molar ratio 11,and the space velocity at heavy time was less than 7 h^-1,all olefins in the simulated fraction could be transformed into alkanes.Then,different contents of K,Mg,W and Mo additives were added to modify the catalyst,it is found that the properties of K and W are better.Ni₂₅-K₁-W₂/Al₂O₃ catalyst prepared by total impregnation method can convert all olefins into alkanes at about 110℃,which is 10～20℃lower than other catalysts,XRD,H₂-TPR and other structural characterization showed that the addition of additives had an effect on the acid regulation of the catalyst and the dispersion of active substances.The service life of Ni₂₅-K₁-W₂/Al₂O₃ catalyst was evaluated,and the reasons for its deactivation were studied.It was found that the activity began to decline at 50 h.At this time,there was a large amount of carbon deposition in the catalyst and the pore structure changed.It was found that oxidation at 500℃for 6 h could restore the activity of the catalyst to a level close to that of the fresh catalyst.