Interaction of coals with oxygen at temperatures up to 600°C

Abstract

Coking and combustion properties of coals alter on oxidation. The carbonyl or ether groups which are formed during oxidation apparently cause these changes or are transient oxidation intermediates. In the present work we investigated the oxidation of six coals, ranking from lignite to anthracite, in molecular oxygen at temperatures up to 600 °C. The original coals and coals extracted with benzene-alcohol or pyridine were examined. A differential scanning calorimetry system (DSC) was utilized to determine the oxidation thermograms of the coals. The residual material obtained after the DSC experiments was further investigated by Fourier transform infrared spectroscopy (FTIR) to determine the structural changes which had occurred. We found that coals contained relatively few structural groups which indicated different oxidation temperatures. The oxidation temperatures of similar structures in different coals increased with increasing rank. Extraction of coals with simple solvents, i.e., benzene-alcohol or pyridine, rendered coals more susceptible to oxidation. The resistance of coals to oxidation increased as the rank of the coal was increased. At oxidation temperatures up to 350 °C both carbonyl and ether groups formed in the coal structure. As the temperature of oxidation was raised to 600°C, i.e., low-temperature controlled combustion, the carbonyl groups disappeared and generally the ether groups dominated in the oxidized product.