ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios as fluid catalytic cracking catalyst additives for residue cracking

Three proton-type ZSM-5 zeolites with different SiO₂/Al₂O₃ ratios (SARs) of 33, 266, and 487 were characterized and examined as fluid catalytic cracking catalyst additives for residue oil cracking. The catalytic performance of the ZSM-5 additives was evaluated using an ultra-stable Y-zeolite (USY)-based fluid catalytic cracking catalyst in a fixed fluid bed unit. As observed, the cracking of primary olefins over the hybrid catalysts consisting of USY-based catalyst and ZSM-5 additive was considerably inhibited by increasing the SAR of the ZSM-5 zeolite, thus avoiding substantial loss of gasoline paraffins. The introduction of ZSM-5 additives led to higher liquid petroleum gas yields as well as higher isobutane and isopentane yields. The improved yields were attributed to the combined effects of the ZSM-5 additives and USY-based catalyst. The variations of gasoline paraffins and aromatics both accounted for the enhancement in the octane number values. The use of ZSM-5 with higher SARs (266 and 487) led to an enhancement in the octane number with minimal loss of gasoline. This enhancement was mainly attributed to the moderate aromatization and isomerization reactivity of the ZSM-5 additives that mainly originated from their relatively small pores and suitable acidic properties with higher SARs.