ESR SPECTROSCOPIC STUDY ON THE CHEMISTRY OF COAL OXIDATION

To better understand the chemistry of coal weathering and the influence of pre-oxidation on subsequent devolatilization, in situ electron spin resonance (e.s.r.) spectroscopic studies were performed on coal, weathered coal and on the corresponding untreated and preoxidized fractions (extract and residue). In this technique, pyrolysis is performed in an e.s.r. cavity and the concentration of free radicals is followed as the sample is pyrolyzed. Elemental analysis of the pre-oxidized and untreated samples indicated that H/C ratio of the extract and the coal sample was reduced slightly during 48 h of oxidation at 150°C in air whereas the H/C ratio of the residue was essentially unchanged. The influence of pre-oxidation (48 h at 150°C) was to increase the e.s.r. spin concentration of the weathered coal slightly compared to the raw coal when devolatilized.