Submitted to: Fuel
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/24/2013
Publication Date: 6/21/2013
Citation: Mullen, C.A., Boateng, A.A., Reichenbach, S.E. 2013. Hydrotreating of fast pyrolysis oils from protein-rich pennycress seed presscake. Fuel. 111, 797-804. Interpretive Summary: In order to meet the renewable fuels standards set by the US government, 21 billion gallons of advanced bio-fuels will need to be produced by 2022. Accomplishing this will require the use of several different types of feedstocks including crop residuals, forest residuals and purposely grown energy crops and also the use of many different technologies to convert these feedstocks to liquid fuel. One promising process is fast pyrolysis which can convert biomass to a liquid called pyrolysis oil which could be refined to “green” gasoline and diesel fuels that are indistinguishable from those produced from petroleum. An important step in their upgrading or refining is the catalytic addition of hydrogen to remove oxygen as water to produce a hydrocarbon product that is more like petroleum. We recently discovered that utilizing feedstocks with high levels of protein as part of their composition produces pyrolysis oil with a lower amount of oxygen as a result of chemical substitution of nitrogen for oxygen. We therefore tested the pyrolysis oil of pennycress presscake, a high protein biomass in the next step of fuel synthesis, catalytic hydrogenation. We tested three precious metals, ruthenium, palladium and platinum as catalyst for this process and compared the results with those from pyrolysis oils from non-protein containing biomass (wood) undergoing the same process. Results showed that after both pyrolysis and an upgrading step the materials derived from pennycress presscake had a higher energy content, less oxygen content and more hydrocarbon (petroleum-like) content than did liquids produced from wood. This information will be useful to help select feedstocks for those producing or considering producing bio-fuels via a fast pyrolysis process, those considering producing energy crops, and those refining biomass pyrolysis oils.
Technical Abstract: 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 ~2000 psi H2 and 320 °C over five precious metal on charcoal catalysts: two Ru/C catalysts, two Pd/C catalysts, and on Pt/C catalyst. The liquid products were characterized by elemental analysis, GCxGC/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 hydrodentirogenation 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 overall heteroatom (O, N, 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.