INFRARED-SPECTROSCOPY OF THERMALLY TREATED LOW-RANK COALS .2. MID-INFRARED AND NEAR-INFRARED PHOTOACOUSTIC SPECTRA OF COALS HEATED IN OXIDIZING AND INERT ATMOSPHERES

Mid- and near-infrared photoacoustic spectra of three Western Canadian low-rank coals (high volatile bituminous, sub-bituminous and lignite) which were treated at temperatures up to 500 degrees C in oxidizing o r inert atmospherres show that the rank of each coal was upgraded by t he treatment. Intensification of both mod-infrared aromatic CH bands a nd near-infrared electronic absorption implies an increase in aromatic ity. Decarboxylation occurs at higher treatment temperatures, as does an increase in C-O functionality. ASTM rank determinations of the feed and treated coals show a systematic increase with thermal treatment.