Kinetics of n-hexane cracking over ZSM-5 zeolites – Effect of crystal size on effectiveness factor and catalyst lifetime

Abstract

The catalytic cracking of n-hexane over ZSM-5 zeolite (MFI-type zeolite, Si/Al = 150 and 240) catalysts was examined at reaction temperatures ranging from 823 to 923 K under atmospheric pressure. The reaction rate constants and activation energies of n-hexane cracking over ZSM-5 zeolites with various crystal sizes and Si/Al ratios were evaluated. The catalytic cracking of n-hexane was first order with respect to the n-hexane concentration, and the activation energies of n-hexane cracking over ZSM-5 zeolites were found to be approximately 123-128 kJmol -1 . Compared with the macro-sized zeolite, the nano-sized zeolites exhibited high n-hexane conversion with stable activity for 50 h. This is because the cracking reaction with nano-sized zeolite proceeded under reaction-limiting conditions, whereas the reaction with macro-sized zeolite proceeded under transition conditions between reaction-and diffusion-limiting conditions. As a result, the application of nano-zeolite to the catalytic cracking of n-hexane was effective and gave light olefins with high yield and excellent stable activity.

Influence of crystal size of HZSM-5 on hydrodeoxygenation of eugenol in aqueous phase

“…For example, when using zeolite as catalyst in hydrodeoxygenation reactions, the rate-determining step tends to be the diffusion of reactant/product molecules within the micropores of zeolites [14]. With the decrease in crystal size, a significant increase in the catalytic stability can be obtained in the reactions catalyzed by ZSM-5 [14,15].…”

Maximizing propylene production via FCC technology

“…In ZSM-5 there exists a remarkable molecular sieving effect for light hydrocarbons and this has been widely used as shape selective catalysts in various hydrocarbon processes; however, because the crystal sizes of ZSM-5 are usually much larger than the sizes of the micropores, the rate limiting step of the reaction tends to be the diffusion of the reactant/product molecules within the micropores [40,54,101]. Moreover, carbon solid (coke) readily forms near the external surface of the crystal under diffusion controlled conditions, thereby, rapidly plugging the pores, leading to a short catalyst lifetime.…”

“…Konno et al [54], studied the effect of zeolite crystal size on the catalytic stability using ZSM-5 zeolites (Si/ Al = 150) in n-hexane cracking. Their results are summarized in Fig.…”

Synthesis and characterization of hierarchical nanoporous HY zeolites from acid-activated kaolin

“…This shows that the HY zeolite samples have high numbers of mildly acidic sites. These sites can suppress catalyst deactivation in catalytic cracking, as reported by Konno et al [24,25]. Mesoporosity can improve the properties of zeolites by preventing secondary reactions by decreasing the diffusion path length; this aids selectivity.…”