(374ar) Liquid Phase Serial Filtration of Pine and Cottonwood Pyrolysis Oils and Observed Effects On Aging

Pyrolysis oil produced from biomass undergoes chemical and/or physical aging processes over time and at elevated temperatures resulting in viscosity, molecular weight, and water content increases and sometimes phase separation. Instability during storage is a major barrier in the utilization of pyrolysis oil as a viable alternative fuel. It has been theorized that char particles entrained in the oil during pyrolysis catalyze polymerization reactions which result in the observed viscosity increase. To investigate the impacts of filtration, a serial filtration of four pyrolysis oils was performed prior to an accelerated aging study at 80 °C. The pyrolysis oils used in this study were produced from ground timber biomass, clear-wood cottonwood, clear-wood pine, bark pine, and bark cottonwood, using an auger reactor under vacuum and both total and fractionated oils were investigated. The serial filtration included 20-25 µm vacuum filtration, 2.5 µm vacuum filtration, and then 0.2 µm centrifugal filtration. Filtered and non-filtered samples were then aged at 80 °C for up to 3 weeks. The aged pyrolysis oil was characterized by pH, density, water content (Karl Fischer titration), viscosity (rheology), Fourier transform infrared (FTIR), gel permeation chromatography, and combined gas chromatography-mass spectroscopy (GC/MS). The filtered solids were analyzed using FTIR, optical microscopy, and the determination of methanol insoluble materials (MIM) content. Building upon our previous research, it was found that the post-condensation removal of char prevented a viscosity increase but not other changes typically observed during aging including water content and molecular weight increase. In addition, rather than esterification or etherification -- once thought to cause the viscosity increase -- the GC/MS and FTIR data indicate an increase in phenolic compounds suggesting a different mechanism.