Catalytic conversion of light hydrocarbons to propylene over MFI-zeolite/metal-oxide composites

• Fe–Ga–Al-MFI gave high selectivity to propylene in catalytic hydrocarbon-cracking.
• Fe–Ga–Al-MFI/aluminum-oxide composites exhibited excellent catalytic performance.
• Propylene yield (18 wt%) was kept for 80 h in n-hexane cracking over the composite.

Zeolite-based composite catalysts for producing propylene efficiently by cracking of light hydrocarbons were developed in the present study to meet future demand for propylene and utilize various light hydrocarbons (e.g., light-naphtha, condensates recovered from natural gas and olefinic hydrocarbons obtained from GTL-process). The composite catalysts, consisting of Al-MFI zeolites containing iron and gallium atoms (Fe–Ga–Al-MFI) at optimized ratio and aluminum-oxide binder (Al2O3), were employed for cracking of n-hexane or 1-hexene using fixed-bed-type reactor at around 550 °C. Since the Fe–Ga–Al-MFI zeolites caused acidity suitable for generating light olefins selectively, high propylene yields (18–41 wt%) were obtained by suppressing formation of aromatics at mild temperatures. The present catalyst exhibited high propylene productivity and catalytic stability simultaneously in the steam-cracking of hydrocarbons at suitable steam ratio. Moreover, in the cracking of n-hexane without dilution over the present catalyst, high propylene yields of ca. 18 wt% were maintained for at least 80 h due to its high resistance to coke formation in spite of severe conditions, suggesting that simplified cracking process for on-purpose propylene production from light hydrocarbons is feasible in fixed-bed mode by using the present composite catalysts.

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