Mild oxidation of brown coal at relatively low temperature was examined as one of the methods to suppress the spontaneous combustibility of the brown coal. Two brown coals were heated up to 260, 280 or 300 °C in a helium stream containing 22 % oxygen and kept for 0 - 120 min. Pyrolysis was also tested for comparison purpose, in which the coals were heated to 300, 400 or 500 °C in a helium stream and kept for 10 min. The spontaneous combustibility of the treated coals was evaluated by gasification rate of the coals measured in 22 % oxygen-containing helium at elevated temperature or the amount of oxygen adsorbed on the coals from gaseous oxygen at 100 °C. The gasification rate of the coals treated by low temperature oxidation was lowered with the increase of gaseous oxygen consumption during the treatment, suggesting that spontaneous combustibility of the coals was successfully suppressed by the treatment. Pyrolysis treatment, on the other hand, had little effect on spontaneous combustibility. In-situ FT-IR analysis showed that aliphatic C-H groups of the coal were selectively oxidized to form esters, anhydrides, or CO_2 during low temperature oxidation.
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