Continuous Synthesis of Cyclic Jet Fuel Precursors from Phenolics and Cyclohexanone

Producing jet fuel-range cycloalkanes from renewable lignin oil is a promising way to replace petroleum-based jet fuels and reduce greenhouse gas emissions. Recent studies have focused on converting lignin-derived phenolics into cyclic jet fuels using metal–acid bifunctional catalysts, primarily in batch reactors. Here, we report the continuous synthesis of bi- and tricyclic jet fuel precursors using lignin-derived phenolics and cyclohexanone, catalyzed by metal–acid bifunctional catalysts composed of Pd and HUSY under H₂ in a fixed-bed reactor. First, we investigated the reaction network of acid-catalyzed C–C coupling reactions in the system of phenol and cyclohexanone. And then, we explored the effect of the integration manner of metal–acid catalysts on performance. A series of catalysts composed of Pd and HUSY with different proximities initially exhibited similar carbon yields of target products (bi- and tricyclic compounds generated via C–C coupling reactions), reaching 91.37% for 0.2Pd/Y (Pd supported on HUSY), 91.17% for 0.2Pd/Al|Y (grinding and granulation of Pd/Al₂O₃ with the HUSY powder), and 88.53% for 0.2Pd/Al–Y (physical mixture of Pd/Al₂O₃ granules with HUSY granules). However, their deactivation rates varied over time on stream. Among them, Pd/Al|Y exhibited the best stability. Furthermore, the influences of the metal-to-acid ratio and reaction conditions on catalytic performance were also investigated. In addition, the substrates were expanded from phenol to guaiacol, 2,6-dimethoxyphenol, eugenol, and two mimics of real lignin oil. Overall, this study presents a viable method for the efficient synthesis of polycyclic jet fuels from lignin-derived phenolics and cyclohexanone.