(364f) Rheology and Stability Considerations in Processing of Bio-Oils

Understanding the rheology and stability of biofuels has been identified as a major need in the large-scale production and use of these materials. A particularly challenging problem has been quantifying and eliminating the dramatic viscosity increase that can occur upon storage of biofuels. Here, we report results on the viscosity, microstructure, and chemical composition of bio-oils prepared by a fast pyrolysis approach, upon aging these fuels at high temperatures for periods of several days. Our preliminary results suggest that the viscosity increase is not correlated with any microstructural change. In addition, while there have been significant efforts on removing chars as a means of stabilizing biofuels, our results show that removal of neither large nor small char particles has any significant impact on the rate of viscosity increase. The viscosity increase appears to be due to formation of high molecular weight polymeric species over time. Even small amounts of these species (~1 wt%) have a dramatic effect on the rheology. Our work also suggests that hydrogenation of the samples may be beneficial in eliminating the viscosity increase. Overall, these studies help identify the major issues that must be addressed in order for bio-oils to be produced, stored, and transported efficiently in large volumes.