COMPARISON OF THE PERFORMANCE OF ZSM-5, BETA-ZEOLITE, Y, USY, AND THEIR COMPOSITES IN THE CATALYTIC CRACKING OF N-OCTANE, 2,2,4-TRIMETHYLPENTANE, AND 1-OCTENE

The cracking of n-octane, 2,2,4-trimethylpentane, and 1-octene was examined over ZSM-5, beta zeolite, Y, USY, and the composites of any of the two former zeolites as additives to the latter two traditional cracking zeolites, under high-severity conditions, namely relatively high temperatures (500-degrees-C) and high conversions. The behaviors of these catalysts under the above conditions are very different from those already studied in the literature, which have been at low conversion and lower temperature. While for the latter conditions the selectivities for olefins were higher and for aromatics lower over ZSM-5 than over Y faujasite, in the present conditions the above trends are inverted. The shifting in the rates of primary cracking, hydrogen transfer, oligomerization, and bimolecular condensation-cracking reactions produced by the changes in the zeolite employed and conditions are responsible for this behavior. For the composites of Y faujasite with either ZSM-5 or beta zeolite the C3 and C4 paraffin selectivities can be calculated as the weighted averages of those for the individual zeolites. In contrast, for the USY zeolite based composites, the additivity rule is not always obeyed, and the selectivities for C3 and C4 paraffins can be larger than those over the individual zeolites.