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Antioxidants from slow pyrolysis bio-oil of birch wood: Application for biodiesel and biobased lubricants

Sriraam R. Chandrasekaran, Dheeptha Murali, Karen A. Marley, Richard A. Larson, Kenneth M. Doll, Bryan R. Moser, John Scott, Brajendra K. Sharma
ACS sustainable chemistry & engineering 2016 v.4 no.3 pp. 1414-1421
Betula, additives, antioxidant activity, antioxidants, biochar, biodiesel, biolubricants, boiling point, butylated hydroxytoluene, distillation, elemental composition, gas chromatography-mass spectrometry, green chemistry, lignin, molecular weight, oxidative stability, particle size, phenols, pyrolysis, soybean oil, temperature, wood
Birch wood was slowly pyrolyzed to produce bio-oil and biochar. Slow pyrolysis conditions including reaction temperature, residence time, and particle size of the feed were optimized to maximize bio-oil yield. Particle size had an insignificant effect, whereas yields of up to 56% were achieved using an optimized reaction temperature of 450 °C and a residence time of 2 h. Bio-oil was also produced from commercial Kraft lignin and was compared to the bio-oil obtained from birch wood. These bio-oils were characterized for elemental composition, phenolic compound identification using GC-MS, boiling point distribution using GC-FID, and molecular weight distribution using GPC. Simulated distillation indicated that a majority of the bio-oil compounds were found in the fraction between 200 and 300 °C, followed by fractions <200 °C and 300-400 °C. Phenolic fractions extracted from bio-oil using an alkali method were evaluated as antioxidant additives in soy biodiesel using Mihaljevic, Rancimat, and PDSC test methods. The phenolic extract showed similar antioxidant activity as the commercial antioxidant butylated hydroxytoluene (BHT) typically used in biodiesel. These phenolic extracts were also evaluated as antioxidants in soybean oils for formulating biolubricants and exhibited improved oxidation stability similar to what was observed in soy biodiesel. It was found that many of the monomeric constituents of the phenolic mixture showed little or no antioxidant activity. However, a series of phenols present in the bio-oils exhibited molecular weights (MWs) of 302, 316, 330, and 344 corresponding to a group of dimers which may be responsible for the observed antioxidant properties.