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

Alwehaibi, Abdulrahman (2016) The Extraction and Characterization of Bio-oils from Woody Biomass and Investigation of Their Use as Antioxidants in Model Biodiesel. PhD thesis, University of York.

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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.

Item Type: Thesis (PhD)
Academic Units: The University of York > Chemistry (York)
Depositing User: Mr Abdulrahman Alwehaibi
Date Deposited: 06 Sep 2018 08:58
Last Modified: 06 Sep 2018 08:58
URI: http://etheses.whiterose.ac.uk/id/eprint/21369

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