A KINETIC-MODEL FOR THE HEXANE CRACKING REACTION OVER H-ZSM-5

A kinetic model for the n-hexane cracking reaction over H-ZSM-5 has be en developed. This model describes hydrocarbon transformations in the following reaction steps: protolytic cracking of n-hexane, hydrogen tr ansfer between n-hexane and light olefins, oligomerization, and cracki ng 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 it self in the autocatalytic character for the reaction at 400-degrees-C. At 538-degrees-C (the temperature of the alpha-test) hydrogen transfe r does not play an appreciable role in hexane cracking over H-ZSM-5 ze olites. (C) 1994 Academic Press, Inc.