Tandem hydroalkylation and deoxygenation of lignin-derived phenolics to synthesize high-density fuels

Lignin is the most abundant naturally phenolic biomass, and the synthesis of high-performance renewable fuel from lignin has attracted significant attention. We propose the efficient synthesis of high-density fuels using simulated lignin cracked oil in tandem with hydroalkylation and deoxygenation reactions. First, we investigated the reaction pathway for the hydroalkylation of phenol, which competes with the hydrodeoxygenation form cyclohexane. And then, we investigated the effects of metal catalyst types, the loading amount of metallic, acid dosage, and reactant ratio on the reaction results. The phenol hydroalkylation and hydrodeoxygenation were balanced when 180°C and 5 MPa H2 with the alkanes yield of 95%. By extending the substrate to other lignin-derived phenolics and simulated lignin cracked oil, we obtained the polycyclic alkane fuel with high density of 0.918 g·ml−1 and calorific value of 41.2 MJ·L−1. Besides, the fuel has good low-temperature properties (viscosity of 9.3 mm2·s−1 at 20°C and freezing point below −55°C), which is expected to be used as jet fuel. This work provides a promising way for the easy and green production of high-density fuel directly from real lignin oil.