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

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 kJ mol−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.

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• The ZSM-5 zeolites with different crystal size were synthesized.
• n-Hexane cracking over ZSM-5 zeolites was carried out.
• Effect of crystal size was investigated using Thiele modulus.
• Cracking reaction over nano-zeolite proceeded under reaction limiting condition.
• The nano-zeolite effective in the stabilization of the catalytic activity.