Effect of organic carboxylates in coal on the production of active sites and coal self-ignition behavior

The heat release of coal oxidation lead to the thermal decomposition of carboxylic groups, which include carboxylic acid and carboxylate. However, few researchers have studied the effect of the decomposition of intrinsic carboxylate structure on coal self-ignition process. In this work, different coal samples were selected and treated with alkali solutions to form organic carboxylate structures, and the thermal decomposition of the raw and alkali-treated coals followed by the room temperature oxidation process were analyzed. The effect of the carboxylate structures on the thermal behavior, elemental distribution, and functional groups of coal was also studied by means of TGA, FTIR, XPS and EPR. The results showed that the carboxylic groups in coal were transformed into carboxylate structures by ion exchange. In addition, highly reactive free radical active sites were produced and accumulated along with the decomposition of carboxylates, thus accelerating the self-heating of coal. In the room-temperature oxidation experiment, the temperature of alkali-treated Wulan coal was spontaneously raised by 13.9℃, while that of raw coal was 4.3 ℃. The results showed that the thermal decomposition of organic carboxylate played an important role in promoting the spontaneous combustion of coal, and acid pretreatment could be a potential method to effectively inhibit the coal self-ignition process.