Analysis of wood vacuum pyrolysis solid residues by diffuse reflectance infrared Fourier transform spectrometry

Vacuum pyrolysis of wood furnishes high yields of oils which are a source of liquid fuels and chemicals. Wood charcoal is a solid residual by-product. Solid residues produced at 200, 263, 327, 363, 401, and 448 °C in a Process Development Unit were analyzed using wet chemical methods and chromatography and infrared spectrometry.A Diffuse Reflectance Infrared Fourier Transform (DRIFT) study of the solid residues which contained various proportions of organic polymeric constituents consisting of unconverted lignin, polysaccharides, and recondensed materials was performed. Polysaccharide contents were determined by hydrolysis in trifluoroacetic acid followed by derivatization and gas-chromatographic analysis. The DRIFT study showed that the solid residue retained its wood nature below 263 °C. Significant degradation, decomposition, and recondensation reactions occurred with increasing temperature and coal-like nature prevailed above 327 °C. Occurrence of a new band at 1700 cm−1 in samples produced at 363 °C and above was found to be indicative of a new carbonyl group, presumably in recondensed material.A series of equations were also developed to predict semiquantitatively Klason residue, glucose and xylose content of the solid residues. The usefulness of each equation is discussed in the article. Keywords: wood, vacuum pyrolysis, solid residue, DRIFT, spectrometry.