Effects of Char Particles On the Aging of Bio-Oil Produced From Timber Biomass Pyrolysis

The viscosity of bio-oil created from biomass pyrolysis has been found to generally increase as the bio-oil ages. This viscosity increase is accelerated by the addition of heat. It is theorized that a major mechanism for this viscosity increase is a polymerization reaction catalyzed by char particles. To test this hypothesis, bio-oil samples created from pine whole tree biomass were aged at 80C for 3 weeks. Prior to aging, a subset of these samples were vacuum filtered (20-25 micrometer pore size) followed by centrifugal filtration (0.2 micrometer pore size). The filtered solids and bio-oil were analyzed using Fourier transform infrared (FTIR) spectroscopy, diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS), gel permeation chromatography (GPC), and combined gas chromatography-mass spectroscopy (GC/MS). Particle size distribution data was obtained using optical microscopy and Image-Pro Plus software on both the removed solids and unfiltered bio-oil. Measured particle size distributions confirmed a significant decrease in particle density and size after filtering. Removed solids showed very similar FTIR spectra as the unfiltered bio-oil. It was theorized that this was due to a thin coating of bio-oil remaining on the particles. A methanol and acetone washing procedure was developed; this method allowed for the true FTIR spectra of the removed particles to be collected. The filtered solids FTIR spectra showed marked similarity to the char produced during pyrolysis.