Kinetic studies on isobutylene cracking to propylene over a HZSM-5 catalyst in a mixed flow reactor

Abstract

The kinetics of isobutylene cracking to propylene was studied in a mixed flow reactor with high-velocity spinning rate over a HZSM-5 catalyst. The experiment was carried out at temperatures from 500 to 575 °C, in the absence of the influences of external and internal mass transfer. According to the kinetic model established, the kinetic parameters for each step were calculated. The estimated intrinsic activation energies for the forward and reverse reactions were 157.8 and 184.3 kJ/mol, respectively. The adsorption enthalpy of isobutylene was also calculated, with a value of −106.1 kJ/mol. The heats of cracking reactions for octylcation and pentylcation are 107.2 and 137.2 kJ/mol, respectively. The validity of the kinetic model was verified by the good agreement on the yield of propylene between experimental results and model predictions. According to the analysis of the rate of propylene formation, an optimal temperature and a proper conversion must be selected to maximize the yield of propylene.