Impact of the Desilication Treatment of Y Zeolite on the Catalytic Cracking of Bulky Hydrocarbon Molecules

Mesoporosity was induced on a USY zeolite by means of an alkaline leaching process. Samples were immersed in 0.05, 0.10 and 0.20 M NaOH solutions during 15 min at room temperature and then were exchanged with NH₄ ⁺ ions and calcined to yield the acid forms. The formation of mesopores with size ranging from 20 to 100 Å increased with the concentration of NaOH. The modified zeolites were used at 30 wt% to formulate cracking catalysts with an inert SiO₂ matrix. The catalytic performance of these catalysts in the conversion of 1,3,5-tri-isopropylbenzene was evaluated in a batch, fluidized bed reactor at 450, 500 and 530 °C, with a catalyst to oil relationship of 4.7 and contact times up to 16 s. The catalysts with the modified zeolites were more active in the cracking of these bulky molecules than the one with the parent, unmodified zeolite; moreover, the selectivity to the products of primary cracking reactions increased. These results reveal an enhanced diffusion of the reactant molecules to the zeolite active sites and of the products out of the catalyst particles.