THE CHAIN MECHANISM IN CATALYTIC CRACKING - THE KINETICS OF 2-METHYLPENTANE CRACKING

The cracking of 2-methylpentane on USHY at 300, 400, 450, and 500°C is interpreted in detail in terms of a chain mechanism. The kinetic equation developed from this mechanism fits the experimental data very well. The contribution of chain processes to the overall rate of conversion depends on the kinetic chain length, which in turn depends on the surface coverage by carbenium ions and their reactivities. Kinetic parameters were obtained at all four temperatures. A detailed examination of the kinetics shows that chain processes are more important at low reaction temperatures, whereas protolytic cracking dominates at higher temperatures. The parameters also show that both competitive inhibition by products and the rate of catalyst decay increase with increasing reaction temperature. Furthermore, they show that carbenium ions formed on Brønsted sites are more stable than carbonium ions. © 1993 Academic Press, Inc.