American Chemical Society
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In Situ High-Temperature Electron Paramagnetic Resonance (EPR) Investigation of the Charring of Cellulose and Cellulose/Na2CO3 Mixtures and the O2-Induced and H2O-Induced Behaviors of These Chars

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journal contribution
posted on 2005-05-18, 00:00 authored by Shaokuan Zheng, Ji-Wen Feng, Gary E. Maciel
In situ high-temperature electron paramagnetic resonance (EPR) has been used to study the pyrolysis (under a helium atmosphere) of cellulose and cellulose/Na2CO3 mixtures, as well as changes in the resulting chars under exposure to O2 and H2O after quenching to room temperature. It has been found that the addition of Na2CO3 not only dramatically changes the pyrolysis behavior, but also has substantial effects on the subsequent exposure behaviors of the resulting chars to O2 and H2O. The presence of Na2CO3 substantially narrows the EPR lines of cellulose chars at all charring temperatures used in this study. For low-temperature (≤350 °C) pure-cellulose chars and for cellulose/Na2CO3 mixture chars prepared at all but the highest temperature (550 °C) of this study, short-term (≤120 min) exposure to O2 has no obvious effect on the spin concentration and the line width; however, decreases in the spin concentration and increases in the line width are observed for high-temperature (≥400 °C) pure-cellulose chars. Effects of H2O introduction into the He/O2 gas stream are most dramatic for lower-temperature cellulose/Na2CO3 chars and for higher-temperature chars of pure cellulose. The results are discussed in terms of a complex array of possible free-radical reactions.