Hydrotreatment of Fast Pyrolysis Oil Using Heterogeneous Noble-Metal Catalysts

TLDR

Fast pyrolysis oils from lignocellulosic biomass are promising second‑generation biofuels, yet their high acidity (pH≈2.5) and diverse oxygen functionalities limit their application without upgrading. This study investigates upgrading fast pyrolysis oil through catalytic hydrotreatment. The authors evaluated heterogeneous noble‑metal catalysts (Ru/C, Ru/TiO2, Ru/Al₂O₃, Pt/C, Pd/C) against conventional sulfided NiMo/Al₂O₃ and CoMo/Al₂O₃ catalysts at 250–350 °C and 100–200 bar. Ru/C achieved the best performance, yielding up to 60 wt % oil with 90 wt % deoxygenation, producing less acidic, drier products with a higher HHV (~40 MJ kg⁻¹) and a shift toward phenolics, aromatics, and alkanes as shown by NMR and GC analyses.

Abstract

Fast pyrolysis oils from lignocellulosic biomass are promising second-generation biofuels. Unfortunately, the application range for such oils is limited because of the high acidity (pH∼2.5) and the presence of oxygen in a variety of chemical functionalities, and upgrading of the oils is required for most applications. Herein, we report an experimental study on the upgrading of fast pyrolysis oil by catalytic hydrotreatment. A variety of heterogeneous noble-metal catalysts were tested for this purpose (Ru/C, Ru/TiO2, Ru/Al2O3, Pt/C, and Pd/C), and the results were compared to those obtained with typical hydrotreatment catalysts (sulfided NiMo/Al2O3 and CoMo/Al2O3). The reactions were carried out at temperatures of 250 and 350 °C and pressures of 100 and 200 bar. The Ru/C catalyst was found to be superior to the classical hydrotreating catalysts with respect to oil yield (up to 60 wt %) and deoxygenation level (up to 90 wt %). The upgraded products were less acidic and contained less water than the original fast pyrolysis oil. The HHV was about 40 MJ/kg, which is about twice the value of pyrolysis oil. Analyses of the products by 1H NMR spectroscopy and 2D GC showed that the upgraded pyrolysis oil had lower contents of organic acids, aldehydes, ketones, and ethers than the feed, whereas the amounts of phenolics, aromatics, and alkanes were considerably higher.