The hydroconversion of waste cooking oil into hydrocarbon fuel was investigated over the hierarchical USY zeolite-supported NiMo catalysts which were prepared by dealumination ((NH₄)₂SiF₆)/desilication (NaOH). The physical and acidity properties of the hierarchical catalysts were characterized by X-ray diffraction (XRD), the Brunauer-Emmett-Teller (BET) infrared spectroscopy of adsorbed pyridine (Py-IR), ammonia temperature-programmed desorption (NH₃-TPD), and H₂ temperature-programmed reduction (H₂-TPR). The Brønsted/Lewis (B/L) acid distribution was little affected by dealumination and the acid density decreased significantly. However, the highly-desilicated catalysts decreased the B/L ratio obviously. Therefore, many more Mo species in the NiMoO₄⁻ and MoO₃ phases were produced in the AHFS-treated catalysts, while more high-valence-state Mo species in the NiMoO₄⁻ phase were formed in the NaOH-treated catalysts. The AHFS-treated catalysts showed higher catalytic activity and better DCO₂ selectivity and selective cracking for jet fuel. The 42.3% selectivity of jet fuel and 13.5% selectivity of jet-range aromatics was achieved over the 8 wt % (NH₄)₂SiF₆-treated catalyst with 67% DCO₂ selectivity.

A hierarchical SBUY-MCM-41 catalyst was prepared by sacrificing USY (a microporous molecular sieve) to synthesize the MCM-41 zeolite via a hydrothermal method. The hydroconversion of waste cooking oil into hydrocarbon fuel over a NiMo/SBUY-MCM-41 catalyst was investigated. The micropores of the Y building units were inherited by the SBUY-MCM-41 zeolite, in which a special hierarchical structure was formed and the accessibility of reactants to the micropore active sites was improved. The hierarchical SBUY-MCM-41 showed high acidity and hydrothermal stability. Compared with mesoporous Al-MCM-41 and microporous USY zeolites, the SBUY-MCM-41-supported NiMo catalyst significantly enhanced the selective cracking of waste cooking oil for the production of jet-fuel-range hydrocarbons (37.3%), with the highest selectivity for the formation of C₁₀–C₁₄ hydrocarbons and a satisfactory selectivity for the formation of jet-fuel-range aromatics (7.6%), as well as a few cyclic compounds. The improved selectivity is the result of the special hierarchical structure and acid distribution of SBUY-MCM-41. This work provides a new strategy to synthesize a hierarchical catalyst for producing alternative jet fuel from waste cooking oil and vegetable oils.

A life-cycle assessment of bio-jet fuel from waste cooking oil (WCO) produced by hydrotreatment was performed and compared with petroleum-derived jet fuel. This study aimed to evaluate the sustainability and find out the bottleneck restricting the development of WCO-based jet fuel production. The carbon intensity of the WCO-based bio-jet fuel was 63.7% lower compared to the conventional jet fuel, and the proportion of greenhouse gas (GHG) emissions caused by hydrogen in the WCO was 18.7%. The feedstock stage proportion of GHG emissions of first-, second-, and third-generation biofuels increased. A sensitivity analysis found that the transportation distance of WCO was more sensitive to GHG emissions, and it is important to develop a detailed plan for feedstock collection. A scenario analysis was also performed according to China’s energy structure and hydrogen sources. Although the electric power structure derived from renewable energy will increase GHG emissions in the immediate future, it will eventually reduce emissions due to technical progress by 2050. The preparation of jet fuel from WCO can not only recycle waste but can also contribute to emission reduction for the aviation industry, which is a potential sustainable and feasible aviation fuel route.