The influence of reaction temperature on the cracking mechanism of n-hexane over H-ZSM-48

Abstract

The cracking of n-hexane at different temperatures over H-ZSM-48 has been analyzed using an established kinetic model. The model includes a monomolecular cracking path based on Langmuir adsorption isotherm as well as a bimolecular path following Rideal kinetics which accounts for the possibility of a chain mechanism being involved. Catalyst decay is accounted by using a time on stream decay function. The scrutiny of the optimal parameters for the model describing n-hexane conversion suggests that the catalyst surface composition is sensitive to temperature owing to the difference in the enthalpy of absorption between the reactant and the average product of the cracking. As the temperature increases, the reactant competes more successfully for the active sites. The average activation energy for protolytic cracking of n-hexane on H-ZSM-48 was found to be 20.2 kcal mol^-1. Steric inhibition during hydrogen transfer between n-hexane and C₄ and C₃ olefins is also observed.