Cumene cracking on a diffusion-limited aging catalyst

Abstract

The Campbell-Wojciechowski mechanism of cumene cracking is applied to conversion data obtained using a series of LaY zeolite catalysts of various particle sizes. A study of the parameters obtained by fitting the model to data for each particle size allows a qualitative interpretation of the effects of intraparticle diffusion in an aging catalyst to be made. As a result of such considerations a new test to evaluate the significance of intra-particle diffusion in this reaction is introduced. Using this test it is shown that LaY catalyst particles as small as 70 80 mesh are diffusion limited for cumene cracking. Nonetheless, the activation energy for the cracking reaction using the diffusion limited 70 80 mesh catalyst was found to be 22.1 kcal/mole, in disconcertingly good agreement with previously reported values. It is also shown that if site poisoning proceeds by the dimerization of adsorbed species cumene, not propylene as previously suspected, is the probable poisoning agent in the cumene cracking reaction. At the same time “coke on catalyst” is shown not to be directly related to catalyst activity.