SPECTROSCOPIC STUDIES OF CARBONS .18. THE CHARRING OF RICE HULLS

Rice hulls were pyrolyzed in vacuo at various temperatures up to 800°C and infrared spectra of the chars were recorded using FT phototherma l beam deflection spectroscopy. There was a substantial weight loss in the 200-400°C range during which the SiO2 content rose from an initial 28 wt.% to near 50 wt.%. The residues consisted of an intimate mixture of finely-divided char and silica; the char itself was a mixture of aromatics derived from the lignin and aliphatics derived from the cellulosic components. Above 400°C the aliphatics decreased, and aromatization and polyaromatization proceeded. Overall, the pyrolysis was not significantly different than one which might be expected of a mixture of lignin and cellulosic material. The SiO2·H2O aggregates within the char changed in composition and structure, but had no significant effect on the pyrolysis. Reaction of the char with oxygen can burn off char and expose the underlying silica, so that a dual surface results. © 1990.