Effects of Crystal Size and Si/Al Ratio of MFI-type Zeolite Catalyst on n-Hexane Cracking for Light Olefin Synthesis

Catalytic cracking of n-hexane over MFI-type zeolite catalysts was examined at a reaction temperature of 823 K under atmospheric pressure. Conversion of n-hexane depended on the Si/Al ratio of the MFI-type zeolite catalyst, so the relationships between the product yields and n-hexane conversion could be fitted as single, smooth curves. To investigate the effect of crystal size of MFI-type zeolite on the catalytic activity, light olefin yield and product composition, nano- and macro-sized MFI-type zeolites with crystal sizes of approximately 150-200 nm and 1.5 μm, respectively, were prepared. The nano-sized zeolite exhibited a high n-hexane conversion with stable activity for 18 h compared with the macro-sized zeolite. The high activity of the nano-sized MFI-type zeolite is considered to be due to rapid diffusion of the produced light olefins out of the intracrystalline pores of the nano-zeolite due to the low diffusion resistance. Accordingly, the nano-sized zeolite achieved high yield of light olefins (approximately 35 %) and long catalyst lifetime.