Propylene synthesis via isomerization–metathesis of 1-hexene and FCC olefins

Abstract

Conversion of 1-hexene or olefins obtained by fluid catalytic cracking (FCC) to propylene via isomerization–metathesis (ISOMET) was investigated using ethylene as a cross-coupling agent. Zeolite H-beta (HBEA) was applied as an isomerization catalyst. The olefin metathesis (OM) catalysts were about 12 wt% molybdena, supported on zeolite beta (MoO₃/HBEA), and γ-alumina (MoO₃/Al₂O₃). HBEA-supported catalyst with a lower molybdena content (6 wt%) was also investigated. The catalysts were characterized by X-ray diffractometry (XRD), H₂-temperature-programmed reduction (H₂-TPR), and Fourier transform infrared (FT-IR), visible Raman, in situ ultraviolet-visible (UV/VIS) and XPS spectroscopy. It was shown that HBEA is a highly active and robust catalyst of double-bond isomerization. Applying a physical mixture of HBEA and 12MoO₃/Al₂O₃ catalyst at 150 °C and 3 bar ethylene pressure, 60% conversion of 1-hexene to propylene was attained. Interestingly, quantitative conversion to propylene was achieved after reactivation of the deactivated catalyst in an argon atmosphere at 550 °C. It was found that the pre-treatment of the catalyst with olefins such as ethylene before inert gas activation resulted in significant catalyst activity improvement. This suggests that the adsorbed olefins may play a key role in the formation of active metal centers during the catalyst reactivation process. The catalyst mixture also had good performance in the conversion of FCC olefins to propylene. The MoO₃/HBEA catalysts have rendered reasonable activity; however, the catalysts showed a significantly shorter lifetime than the alumina-containing catalyst mixture.