Novel Catalytic Materials For Gasoline Olefin Reduction In Catalytic Cracking Processes

Fuel quality standards become more and more stringent worldwidely for environment protection. One of the most obvious problems of fuel quality is from redundant olefin fraction of gasoline in China, 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 pooi composition, because of the lack of the units for catalytic reforming, alkylation, isomerization and production of oxygenous compounds. So, It is an important and economic way to decrease the olefin content of FCC gasoline to solve the problem of high olefin content in commercial gasoline in China.The cracking catalyst is a very important part of FCC technology. The change of it's characteristics is one of usefhl methods to adjust the product composition in catalytic cracking. In FCC process dedicated to reduce the olefm content of gasoline, a matching catalyst is also needed. Because of the relationship between the olefin content of gasoline and hydrogen transfer reaction in FCC process, it is necessary to discover and develop catalytic materials that can reduce olefins through hydrogen transfer reactions. Meanwhile, coke yield increase and octane number loss should be considered when reducing olefins through hydrogen transfer reactions.In this paper, the composition of typical FCC gasoline in China is labored. The results showed that FCC gasoline contains mainly C4-C 10 hydrocarbons. And most olefins were distributed between C4-C8, especially C5 and C6, contributing greatly to gasoline octane number. The decrease of olefin content will lower the octane number of gasoline. Thermodynamics analysis was performed on reactions that can decrease olefins while increasing octane number of gasoline. The results showed that increase ofiso-paraffin and aromatics could be achieved by increasing the skeleton isomerization, eye lization and hydrogen transfer reactions of olefins.Hydrogen transfer activity of different zeolites has been studied in the catalytic cracking of dodecane. The catalytic experiments were carried out in a micro fixed bed reactor. The ratio of paraffins to olefins in liquid product was defined as Hydrogen Transfer Index(HIT). The experimental results showed that Y zeolite had the best hydrogen transfer activity among HZSM-5, H ~ and HY due to it's characteristics that are more proper for bimolecular reactions than the other two zeolites. Lower Si02/A1203 and higher content of rare earth element are useful for hydrogen transfer reactions over zeolites, but the activity changes increased the coke yield. The addition of phosphorus could optimize the acidity of the zeolite, maintain lower coke yield while increasing hydrogen transfer reactions. This kind of hydrogen transfer reactions were defined as "selective hydrogen transfer reactions". The acidity characterization results showed that the amount of B acidity increased after modification by phosphorus, at the same time, the strength of the acidity became weak. The acidity weakening altered the adsorption of different hydrocarbons on the surface of catalytic materials, decreased the adsorption and formation of coke precursor, alleviated the formation of coke while increasing hydrogen transfer reactions. The increase of B acidity increases hydrogen transfer reaction. The change of acidity by phosphorus modification concerned with interaction between phosphorus and aluminium atom on the zeolite surface. The characterization results of 31p MAS-NMIR and 2'Al MAS-NMR showed that the addition of different amount of phosphorus led to the different state of phosphorus on the zeolite surface.Hydrogen transfer reactions have been studied with different pure hydrocarbon feedstock and under different reaction conditions over the same zeolite in a micro fixed bed reactor. The product composition and hydrogentransfer property are different due to the differences in the structure and carbon number of the pure hydrocarbons as feedstocks. In the certain range of the...