Study on the reaction mechanism of olefins on FCC catalyst

With the increasing attentions to global environment, it becomes a new subject to reduce the olefin content in catalytic cracking gasoline, and to increase the content of iso-paraffin and naphthene at the same time. As the mid-product of the FCC process, olefin will undergo various reactions, and its reaction mechanism is quite complex. A series of cracking experiments of pure olefin compounds and FCC gasoline under different reaction conditions have been carried out in the self-made instrument of subminiature reactor-chromatograph united apparatus. The reaction mechanism of pure olefin compounds and that of olefins in gasoline under different conditions were analyzed. In the reactions of pure olefin molecules, the olefins with carbon number less than six mainly isomerize, and no cracking and H-transformation reactions take place. 95% of olefins with carbon number more than seven directly crack to produce C_3, C_4 at high reaction temperatures. Compared with the rules of pure olefin compounds cracking, the conversion of olefins in gasoline mainly occurs among olefins with carbon number more than seven, and the content of C_5, C_6 olefins in upgraded gasoline is hardly reduced. Though some interactions of olefin compounds in the gasoline upgrading process are observed, the mechanism and rules of pure olefins can be used to predict the conversion of olefins in gasoline. Therefore, under FCC conditions, it is difficult to transform C5, C6 olefins, and this is also the key problem of olefin reduction. Conversions of olefins over spent catalyst and regenerated catalyst with a small quantity of coke deposition were compared. It is found that the route of the conversion of olefins in gasoline is hardly influenced by the type of coke on catalyst.