Conversion of Lignin-derived Ketonic Intermediate to Fuel Products: Syngas-assisted vs. Conventional Hydrotreating

A new strategy for the transformation of an intermediate of the lignin conversion process, namely cyclohexanone, to fuel-grade products is assessed in this study. In this regard, the conventional hydrodeoxygenation process (with pure hydrogen) was compared to an innovative one with a simulated lignin-derived syngas stream in a wide range of reaction conditions (300–400 °C, 1–15 bar, and small-to-large feed-to-catalyst ratios) and over commercial molybdenum-based (nickle‑molybdenum (NiMo) and cobalt‑molybdenum(CoMo)) catalysts. Cyclohexanone conversion, product distribution, deoxygenation efficacy, and heating value were compared in each case. Cyclohexanone was transformed into cyclohexane, cyclohexene, benzene, cresols, phenol, toluene, and bi-cyclic compounds, which are beneficial in jet-fuel processing. Increasing the reaction temperature and pressure intensified the conversion of cyclohexanone (up to 87.8% conversion at 400 °C and 15 bar over both NiMo and CoMo catalysts), whereas increasing the feed-to-catalyst ratio reduced it. Operating conditions and the reducing gas (pure hydrogen or syngas) had major impacts on the conversion of cyclohexanone, deoxygenation efficiency, product distribution, and the heating value of the final product blend. The results of this study claim that cyclohexanone conversion to fuel-grade hydrocarbons (up to 97.61% over NiMo and 74.71% over CoMo catalysts) is a beneficial route and the conventional hydrodeoxygenation process can be replaced with the syngas-assisted one with a small change in production capacity, still large positive impact on the sustainability and environmental footprints of lignin conversion to biofuels.