Synthesis of Jet Fuels from Propenyl-Substituted Phenolic Monomers of Lignin

Production of jet fuels from renewable biomass is key to decarbonizing the aviation sector. In this work, valorization of the aromatic macromolecule lignin in plant biomass toward monocyclic and fused bicyclic alkanes was proposed. The lignin was first depolymerized toward prop-1-enyl-substituted monomers with high selectivity (>70%) using ethanol as the solvent in the absence of external H2. Alkylation of these monomers with hemicellulose-derived 2-methylfuran using solid acids such as Amberlyst 35 generated alkylation products (yield >80%) along with a small amount of dimers. The alkylation products can be hydrodeoxygenated toward monocyclic alkanes using Ru/C and zeolites, where the product distribution can be controlled by the microporosity of the zeolite. C14 is the major product using Ru/C and mordenite (MOR). The Friedel–Crafts dealkylation of the alkylation products can occur by using Beta and Y zeolites, leading to the formation of more C9. Using the same acid catalyst (i.e., Amberlyst 35) can almost quantitatively convert these monomers toward dimers, which can be hydrodeoxygenated toward fused bicyclic alkanes in the presence of hydrogenation catalysts and zeolites. However, the product distribution can be determined by the activity of the hydrogenation catalyst. C18 was obtained with high yield (>90%) using Pd/C and zeolites such as MOR and alkaline-treated Beta zeolite (Beta-AT). However, C12 was the dominant product (yield of 77.5%) using Raney Ni and alkaline-treated Beta-AT. This work paves a new way for the production of high-density cycloalkanes from recalcitrant lignin.