Kinetics of coupling cracking of butene and pentene on modified HZSM-5 catalyst

The cracking of butene and pentene is an effective route for MTO process to sufficiently utilize these olefin byproducts. Butene and pentene can be efficiently converted to propylene and ethylene over HZSM-5 catalyst modified by Fe and P. In the coupling cracking of butene and pentene, butene mainly cracked through bimolecular pathway, while pentene cracked via both monomolecular and bimolecular pathways. Moreover, propylene was an intermediate product and might involve other type reactions besides cracking. Based on the effect of operating conditions, a six-lump (butene, pentene, propylene, ethylene, C1-5 alkanes and C6+ hydrocarbons) kinetic model is proposed for the coupling cracking of butene and pentene. Different cracking mechanisms were taken into account, and different reaction orders were obtained for reaction steps in the kinetic model. The experimental data were measured in an isothermal fixed-bed reactor under a wide range of operating conditions (at 490-610 °C; space time of 0.93-4.67 (g of catalyst) h (mol CH2)−1; steam ratio of 0.18-0.9 (g of steam) (g of feed)−1 range), and the kinetic parameters were estimated through Levenberg-Marquardt algorithm. A good parity between calculated and experimental data was attained, indicating the applicability of the model to quantify the distribution of product lumps.