Hydrotreating of fast pyrolysis oils from protein-rich pennycress seed presscake
The fast pyrolysis oils produced from proteinaceous biomass, such as pennycress presscake differ significantly from those produced from biomass with mostly lignocellulosic composition. Those from proteinaceous biomass tend to be deoxygenated, contain more nitrogen, be less acidic and be more stable. Because their composition is different, their behavior in and products from upgrading via hydrotreating will be different. We studied the mild batch hydrogenation of the pyrolysis oil produced from pennycress presscake at ∼13.8 MPa (138 bar) H2 and 320 °C over five precious metal on charcoal catalysts: two Ru/C catalysts, two Pd/C catalysts, and one Pt/C catalyst. The liquid products were characterized by elemental analysis, GC × GC/MS and NMR. The Ru catalysts were most effective at further deoxygenating the pyrolysis oils, with the Pd catalyst slightly less effective, and the Pt catalyst the least effective. None of the catalysts were highly effective for hydrodenitrogenation, though among them Pt removed the most nitrogen from the liquids. Using the best catalysts, an upgraded pyrolysis oil containing <15 wt% total heteroatom content (O + N + S) with an HHV of 37.0 MJ/mg was realized. Compared with wood pyrolysis oils upgraded at similar conditions, the upgraded pyrolysis oils from pennycress presscake had lower oxygen and total heteroatom (O, N, and S) content, had higher energy content and were closer compositionally to petroleum. The products were very rich in long aliphatic hydrocarbon chains; these large aliphatic moieties were present in both purely hydrocarbon compounds and in heteroatom containing compounds especially alkyl amides.