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
posted on 2005-05-18, 00:00authored byShaokuan 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.