(135a) Biomass Pretreatment to Improve Bio-Oil Stability

Storage stability is one of the most important properties of a fuel. Bio-oil produced from biomass by the fast pyrolysis process is known for its poor storage stability which makes it a less convenient fuel. The aldehydes and carboxylic acids contained in the bio-oil react with each other and with other species that causes the instability of the oil. Pretreatments are the first opportunity to improve the quality of bio-oil by selectively controlling the impurities in the feedstock that influence the pyrolysis reactions. Potential biomass pretreatment techniques were studied in order to understand their effect on the stability of the bio-oil produced from the treated feedstocks. Switchgrass was pretreated by washing with hot water and dilute acids separately, and also by infusing various acids at different concentrations. Pyrolysis-GC-MS set up was used to analyze the composition of the bio-oil produced from these treated feedstocks. For the purpose of predicting the stability of the oil produced, the pyrolysis products were categorized broadly into anhydrosugars, light oxygenates, furans and phenolics. Hot water and dilute acid wash improved the yield of levoglucosan and reduced the yield of carboxylic acids and aldehydes while the acid wash increased the yield of furans. However, the overall effects were not good enough to justify the extra energy spent on drying the washed feedstock. In order to avoid the need for drying, acids were infused into switchgrass and tested. It was found that phosphoric acid at 2 wt% of the biomass produced the maximum yield of anhydrosugars and lowest yield of light oxygenates. Sulfuric acid was slightly better than phosphoric acid while nitric and hydrochloric acids were less effective. Acetic and formic acids were not effective at all.

This work was funded by the U.S. Department of Energy and the ConocoPhillips Company