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In this paper representative samples of four differing types of biomass char are studied and contrasted in terms of their solid state char chemistry and liberated organic compounds on rapid heating by laser pyrolysis. Specifically, we investigate Avicel cellulose, citrus peel pectin, birch wood xylan and organosolv lignin. These substrates are studied in their uncharred form as well as after charring for 1/2 and 1 h at 200 and 375 °C. Char yields and CHO analyses are reported. Diffuse reflectance infrared spectroscopy, DRIFTS, is used to contrast and follow the progress of charring. DRIFTS of the biomass char reveals similarities between lignin and cellulose chars and between pectin and xylan chars based on hydroxyl and carbonyl stretches. Laser pyrolysis molecular beam mass spectroscopy, LPMBMS, is used to probe both the solid state chemistry of the chars and the organic compounds released on rapid heating. The stability of the biomasses to charring is lignin>cellulose>xylan>pectin. On charring for longer times cellulose produces larger molecular weight PAH, whereas lignin, pectin and xylan produce smaller molecular weight PAH, however, xylan and pectin produce somewhat larger molecular weight PAH in smaller quantities at intermediate temperatures. These differences are rationalized in terms of the ability of the aromatic structures in the chars to anneal into larger condensed ring structures, and the possible influence of hydrogen bonding, both in the biomass and in the char, on this annealing. |
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