Aromatization-free strategy for sustainable aviation fuel: Co-upcycling waste oils and polystyrene plastics into alkanes and aromatics

Abstract

Sustainable aviation fuel (SAF) is a promising solution for reducing aviation-related carbon emissions. However, conventional SAF production methods such as waste oil aromatization face challenges like complex processing requirements and the generation of unwanted polycyclic aromatic hydrocarbons (PAHs). This study presents a novel, aromatization-free approach to SAF production by co-upcycling waste oils and polystyrene (PS) plastics. The inherent aromatic ring structures in PS plastics are utilized to directly form aromatic hydrocarbons, bypassing the need for traditional aromatization. A two-stage pressurized fixed-bed reactor was employed, where waste oils and PS underwent co-hydropyrolysis to generate intermediates, followed by gas-phase catalytic hydrogenation. Under optimized conditions (0.15 MPa H₂, 480 °C for co-hydropyrolysis, 350 °C for hydrogenation, and 5 mg Pd/SBA-15 catalyst), this process yielded 71.0 wt% C₈-C₁₆ jet fuel components, with 84.5 % selectivity. In comparison, catalysts with higher acidity, such as Pd/HZSM-5 and Pd/USY, promoted side reactions like cracking, leading to lower liquid yields (35.7 wt% and 18.1 wt%, respectively) and a more complex product mixture. Additionally, Pd/SBA-15 catalyst demonstrated excellent stability, maintaining consistent catalytic performance over 10 repeated cycles, and showed potential for scalability with a variety of waste plastics and oils. The study underscores the feasibility of co-upcycling waste oils and PS plastics, offering an efficient, sustainable pathway to streamline SAF production while reducing the environmental impacts associated with conventional methods.