IN-SITU EXAMINATION OF COAL MACERALS OXIDATION BY MICRO-FT-IR SPECTROSCOPY

Two heterogeneous coals, from the Mahakam delta (HY 158) and the Campine basin (SP 1), have been selected for an in situ study of individual maceral oxidation. HY 158 is vintrinite rich (80%) but also contains resinite and bituminite, while SP 1 is a cannel coal composed of spores, vitrinite and inertinite. Doubly-polished thin-sections have been prepared and photographed in order to select the appropriate individual maceral areas. The thin-sections were oxidized at 140-degrees-C in a ventilated oven for 1 to 384 h. Between each oxidation step the selected areas were analysed by Fourier transform micro-infrared spectroscopy (micro-FT-i.r.). Aliphatic CH consumption, carbonyl, carboxyl and ether content increases are observed. However, results indicate that macerals behave differently when submitted to increasing oxidation: (1) extents and rates of oxidative alteration strongly depend on the nature of the maceral; (2) two different vitrinites can exhibit contrasting behaviour; (3) slight differences in the chemical composition of the unoxidized macerals can induce significant chemical variations during the oxidation process. Comparison with global FT-i.r. data obtained on powdered and oxidized parent coal has been carried out (HY 158) and although there are similarities, variation in the extent of the oxidative alteration occurs.