Reaction pathway and kinetics of C3–C7 olefin transformation over high-silicon HZSM-5 zeolite at 400–490 °C

Abstract

The pathway and kinetics of C3–C7 olefin transformation reactions were investigated in a fixed-bed reactor over a high-silicon HZSM-5 catalyst at 400–490°C in this work. The main reaction pathway was identified on the observations of the product distribution when the individual olefin was fed alone. The results show that C7= proceeds dominantly through a monomolecular cracking, whereas C4= and C3= through a bi- and trimolecular cracking, respectively, and both mono- and bimolecular cracking for C5= and C6=. On the basis of the proposed reaction pathway, the kinetic model was developed for each olefin, with the corresponding parameters correlated using the experimental data. Despite the fact that olefin cracking proceeds by a rather complex pathway, a fairly satisfactory agreement between the calculated and experimental data was achieved over the test temperature range of 400–490°C, and a phenomenon of the minus observed activation energy for both bi- and trimolecular cracking can be well interpreted by the combination of the reaction and adsorption steps on the catalyst surface.