Potential of Eucalyptus globulus industrial bark as a biorefinery feedstock: Chemical and fuel characterization

Eucalyptus globulus bark is a residue from the pulp industry, traditionally used for energy production. This work aims at a more comprehensive knowledge of this industrial bark providing alternative possible uses based on its chemical and thermal characteristics. Bark and wood (18.3% of the total) were separated and bark was fractionated into fine (B-1, Phi < 0.180 mm) medium (B-3, 0.450 < Phi < 0.850 mm) and coarse (B-6, 2 < Phi < 10 mm) fractions. B-1 showed a higher inorganic (21%), extractives (12.2%) and lignin (23.4%) contents than B-3/B-6 (3.7/5.1%, 8.9/9.8% and 21.6/22.8%, respectively) and much lower polysaccharide content (44% vs 63/62%). B-6 presented the highest contents of total phenolics (TFC, 271 mgGAE/g(Ext)), flavonoids (FC, 106 mgCE/g(Ext)) and condensed tannins (CTC, 65 mgCE/g(Ext)) as well as antioxidant activities for Ferric Reducing Antioxidant Power (FRAP, 5.8 mmolFe(2+)/g(Ext)) and 2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay (DPPH, 4.3 and 2.5 antioxidant activity index for ethanol and water extracts). B-3 and B-6 fractions showed similar proximate and ultimate analysis with higher High Heating Value (HHV close to 18 MJ/kg) and lower volatiles-to-fixed-carbon ratio (4.4) than B-1 (15.2 MJ/kg and 6.3 respectively). Bark has some detrimental thermal characteristics, such as high amounts of ash and chlorine (0.35%), presenting chemical features that point to their possible use in the food and pharmaceutical industries (high extractive content, phytochemical composition and antioxidant potential) or polysaccharides valorization (polyols, hemicellulose-derived oligomers, ethanol production).