(365e) Preliminary Studies of pH and Char Particle Content On Bio-Oil Aging

Bio-oil produced by biomass pyrolysis has been shown to degrade over time and at elevated temperatures resulting in increased viscosity that makes processing and handling difficult. It has been theorized that char particles remaining in the bio-oil after pyrolysis and condensation catalyze polymerization reactions leading to the viscosity increases during bio-oil aging. Additionally, pyrolysis bio-oil has a low pH as produced (pH ~2-3) and the effect of the low pH on the polymerization reactions is unknown. In this study, the effects of particulate filtration and pH adjustment are investigated on pyrolysis bio-oil samples produced from ground clear wood cottonwood and pine biomass using an auger reactor under vacuum. The bio-oil control samples were aged up to 21 days at 80 °C and 28 days at 50 °C. For the filtration experiments, pine whole tree fractionated bio-oil was filtered in series by vacuum filtration at 20 µm followed by centrifugal filtration at 0.2 µm and then aged at 80 °C up to 21 days. For the pH adjustment experiments, the pH of pine clear wood fractionated bio-oil was adjusted by the addition of KOH to obtain nominal pH values of 5, 7 and 9 and these pH-adjusted samples were aged at 80 °C up to 14 days. All bio-oil samples were characterized with Fourier transform infrared (FTIR) spectroscopy, gel permeation chromatography (GPC), and combined gas chromatography-mass spectroscopy (GC/MS); select samples were analyzed by light microscopy and electrospray ionization mass spectroscopy (ESI-MS). GPC analysis showed an increase in molecular weight and PDI during aging. The ESI-MS results revealed a polymeric pattern in several of the bio-oil samples, including the aged samples. Light microscopy verified that a large amount of the char particles were removed by centrifugal filtration.