Low-temperature oxidation of brown coal. 3. Reaction with molecular oxygen at temperatures close to ambient

Abstract

Yallourn brown coal was oxidized with pure molecular oxygen at temperatures of 35 and 70 °C until, after about 45 days, no further gain in mass occurred. At this stage, despite the loss of considerable quantities of carbon and hydrogen from the coal as carbon dioxide, carbon monoxide and water, the coal had gained in mass by 15 g per kg of dry coal. Virtually all the gain was accounted for by increases in the content of carboxyl, carbonyl and phenolic groups. These functional groups, which subsequently break down to yield the stable products already mentioned, are formed apparently by attack on the aliphatic structures of the coal. At 35 °C, reactions leading to the formation of functional groups such as phenolic groups, and their breakdown to water, predominated; however, at 70 °C, the formation of carboxyl groups and their breakdown to carbon dioxide became more important, the amount of water formed being less than that at 35 °C. The general course of these reactions was qualitatively similar to that observed by other workers using bituminous coals, but the extent of the reactions was an order of magnitude greater.