Biomass pyrolysis oils can be potential transportation fuels if they could be successfully upgraded and refined. Conventional pyrolysis oils or bio-oils are usually acidic , have high viscosity , low energy density , and are very reactive. Catalytic biomass pyrolysis oils are much more stable but also have acidic properties. In this paper we investigated the fractions of the biooil that are responsible for the aging of the oils through polarity-based fractionation. In this approach column chromatography method was used to fractionate the biooil employing hexane , toluene , chloroform and methanol as eluents. The viscosity of the fractions increased in this order; hexane<toluene<chloroform<methanol. The methanol fraction in most cases was a solid at room temperature and the least viscous oils were the toluene and hexane fractions. Some portions of the chloroform and methanol fractions were also soluble in water. When the water soluble fractions were removed , although the residues were soluble in DMSO and chloroform , they did not produce any signals when subjected to liquid state 13C-nmr analysis. MALDI-TOF analyses revealed that these materials were mostly lignin and carbohydrate oligomers that were soluble in methanol. The increase in viscosity of the biooils was attributed to association of the oligomers and crystallization of levoglucosan in the oil fractions. However , when about 10 wt% methanol was added to the oils the viscosity aging process was reduced because the methanol dissolved the oligomers and prevented the association reaction.
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