Catalytic Cracking of n-Hexane and n-Heptane over ZSM-5 Zeolite: Influence of SiO2/Al2O3 Ratio

Resumo

The performance of two types of ZSM-5 zeolite catalysts (MFI-type zeolite, SiO₂/Al₂O₃ = 50 and 300) was studied in the catalytic cracking of n-hexane and n-heptane as a model compound of light naphtha for production of light olefins at 500, 550, and 600°C. The physicochemical properties of ZSM-5 catalysts were characterized by means of XRD, BET, SEM and NH₃-TPD. The influence of SiO₂/Al₂O₃ molar ratio was investigated on conversion and product selectivity. ZSM-5 zeolite yielded higher conversion in the cracking of n-hexane compared to n-heptane and maximum conversion was achieved over ZSM-5(50) at 600°C. ZSM-5(50) showed higher alkane selectivity rather than olefins. It was found that ZSM-5(300) was more desirable in terms of having significant selectivity to light olefins as well as producing high propylene to ethylene ratio. The maximum propylene to ethylene ratio of 2.7 and 2.48 was observed over ZSM-5(300) at 500°C for n-hexane and n-heptane cracking, respectively.