Catalytic hydroreforming of the polyethylene thermal cracking oil over Ni supported hierarchical zeolites and mesostructured aluminosilicates

Abstract

The hydroreforming of the liquid product resulting from LDPE thermal cracking at 400°C (C5–C40) has been studied using Ni supported hierarchical zeolites (Ni/h-ZSM-5, Ni/h-Beta) and mesostructured materials (Ni/Al-MCM-41 and Ni/Al-SBA-15) as catalysts. Hydroreforming experiments were carried out at 310°C under 20bar of hydrogen. All the catalysts were synthesized with a Si/Al atomic ratio of 30 and a Ni content of 7wt%. According to XRD, TPR and TEM data, the activated catalysts displayed Ni particles both over the external surface and inside the catalyst pores in different percentages depending on their porous structure and nature. Complete hydrogenation of the olefins was observed over both mesostructured catalysts (Ni/Al-SBA-15 and Ni/Al-MCM-41) and hierarchical Ni/h-Beta. In contrast, over Ni/h-ZSM-5, there is always left about 30% of olefins, due to an imbalance in the acid and metal function. Ni/h-ZSM-5 led towards significant amounts of gases (∼18%) while gasoline range hydrocarbons were the main products (55%) over Ni/h-Beta, at the expense of diesel fractions. In contrast, the hydrocracking extent was far lower over Ni/Al-MCM-41 and Ni/Al-SBA-15, the latter showing additionally the appearance of a slight degree of oligomerization, which led towards an increase in the heavy diesel fraction (C19–C40). Hydroisomerization reactions also occur, mostly in the case of Ni supported hierarchical zeolites. Likewise, aromatics were formed over these catalysts in a large extent. The RON number of the gasolines obtained at 310°C was within 81–89 depending on the chosen catalysts while the cetane index (CCI) of the diesel fraction was around 70–80. On the other hand, Ni leaching was not detected.