One of the major challenges in the conversion of biomass pyrolysis to high value products and fuels is the poor stability of the oils. Biomass pyrolysis oils have shown increases in viscosity during storage at ambient conditions and when heated above ambient temperature. The poor stability of the biomass pyrolysis oils have been attributed to the high intrinsic oxygen content of the oils. Researchers have been working on stabilizing the oils for various applications. In order to demonstrate the role of oxygen in the stability of biomass pyrolysis oils, we prepared three pyrolysis oil samples using catalysts and no catalysts. Two of the oils prepared with different catalysts were stored at room temperature for several months and were also subjected to distillation. The two catalyst oils (catalyst #1 oil and catalyst #2 oil) had oxygen content of 21 wt% whereas the non-catalytic oil had oxygen content of 43 wt%. The viscosities of the two oils were measured when fresh and after storage. The viscosity of catalyst #1 oil remained almost constant after 18 months of storage whereas the catalyst #2 oil sample almost solidified after 5 months of storage at ambient conditions. A sample the catalyst #1 oil whose viscosity did not change after 18 months of was stored without lid for six months and its viscosity measured. After six months storage without lid, the viscosity of catalyst #1 oil also increased but at a less rate compared to the non-catalyst oil and the catalyst #2 oil. The catalyst #1 oil sample could be completely distilled both in vacuum and atmospheric pressure whereas catalyst #2 oil and the non-catalyst oil formed solid after 45wt% of the material was distilled. The results clearly showed the intrinsic oxygen content of biomass pyrolysis oil is not a good measure of the stability of the oil instead, the distillation of the oil may be a better measure of the oil stability. Further, atmospheric oxygen also contributes significantly towards the destabilization of the biomass pyrolysis oils. Specific oxygenated functional d groups in the biooils are responsible for the for poor stability which is not measured by the total oxygen content of the biooils.
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