Compositional Characterization and Pyrolysis of Loblolly Pine and Douglas-fir Bark

Abstract

Two potential biofuel resources, Douglas-fir and Loblolly pine bark, were subjected to extensive chemical and compositional analysis. The barks were initially extracted with dichloromethane, and the resulting extracted compounds were characterized by gas chromatography coupled with mass spectrometric analysis. Characterization of the major bark biocomponents indicated that Douglas-fir and Loblolly pine bark contained 22.5 and 13.2 % tannins, 44.2 and 43.5 % lignin, 16.5 and 23.1 % cellulose, and 7.6 and 14.1 % hemicellulose, respectively. Of particular interest is the high content of tannins and lignin, which make these barks excellent potential precursors for bio-oils and/or other value-added chemicals. 13C nuclear magnetic resonance (NMR) was used to characterize the chemical structure of the lignin and tannins. These samples were also analyzed by 31P NMR after phosphitylation of the hydroxyl groups in lignin and tannins. The NMR spectral data indicated that the lignin in both barks contained p-hydroxyphenyl (h) and guaiacyl (g) of lignin monomers with an h/g ratio of 10:90 and 22:78 for Douglas-fir and Loblolly pine bark, respectively. Gel permeation chromatography was used to analyze the molecular weight distributions of extracted tannins, isolated cellulose, and ball-milled lignin. The pyrolysis of Douglas-fir and pine bark at 500°C in a tubular reactor generated 48.2 and 45.2 % of total oil, of which the light oil contents are 14.1 and 20.7 % and heavy oil are 34.1 and 24.4 %. Similarly, fast pyrolysis at 375°C yielded 56.1 and 49.8 % of total oil for Douglas-fir and pine bark, respectively.