A kinetic model for the hexane cracking reaction over H-ZSM-5

Abstract

A kinetic model for the n-hexane cracking reaction over H-ZSM-5 has been developed. This model describes hydrocarbon transformations in the following reaction steps: protolytic cracking of n-hexane, hydrogen transfer between n-hexane and light olefins, oligomerization, and cracking of olefins. The activation energy of the protolytic cracking steps is 75.6–152.4 kJ/mol, depending on the reaction products, and that of the hydrogen transfer steps is 4.1–8.9 kJ/mol, depending on the olefin involved in the reaction step. It is demonstrated that a considerable contribution from hydrogen transfer to n-hexane cracking manifests itself in the autocatalytic character for the reaction at 400°C. At 538°C (the temperature of the α-test) hydrogen transfer does not play an appreciable role in hexane cracking over H-ZSM-5 zeolites.