The Extraction and Characterization of Bio-oils from Woody Biomass and Investigation of Their Use as Antioxidants in Model Biodiesel

Currently, antioxidants used in biodiesel to prevent degradation by autoxidation are synthesized from petroleum, which is non-renewable and has had a volatile price in recent years. Therefore, this thesis examines the possibility of using phenolic species from bio-oils derived from woodchips as antioxidants to protect biodiesel.
Crude bio-oil (18.5% w/w of woodchips) was obtained by microwave-enhanced pyrolysis of spruce woodchips (picea abies). Characterization by multiple analytical techniques shows that a noticeable portion of the bio-oil consisted of aromatics (mostly phenols) and sugars. The phenolic content of the bio-oil was quantified and identified by GC-FID & GC-MS and was found to be ca. 6% (w/w), while the total phenolic content was determined by Folin-Ciocalteu (FC) assay was ca. 23% (w/w). To isolate these phenols, the crude bio-oil was further fractionated by supercritical CO2, and by two multi-solvent fractionation methods, namely: water-insoluble phase and water-soluble phase. The extract obtained with the highest phenolic content was a diethyl ether extract isolated from the water-soluble phase of crude bio-oil, at ca. 56% (w/w) by FC assay, with ca. 9% (w/w) identified and quantified by GC-MS & FID.
The effectiveness of these renewable phenols in a model biodiesel was examined using methyl linoleate autoxidation in 1 bar of oxygen at 120 ○C. Addition of low amounts of crude bio-oil to methyl linoleate was sufficient to increase its induction time, and was comparable with a commercial antioxidant (butylated hydroxy-toluene). Further examination of methyl linoleate with bio-oil isolated extracts indicated that these were less effective than the parent crude bio-oil. This was striking because some of the isolated extracts contained higher phenolic concentrations than the bio-oil. The antioxidancy of a chemical model of the crude bio-oil phenol consisting of six representative components at appropriate concentrations was approximately three times less active than the crude bio-oil, suggesting that components with noticeable antioxidancy remain to be identified.