The evolution law of functional groups during the heating of coal in oxygen and oxygen‐free atmospheres

There is a change in both the quantity and type of functional groups due to the fact that they become oxidized and pyrolyzed during the spontaneous coal combustion process. In order to study the oxidation and pyrolysis mechanisms that are at play during the evolution of these functional groups, in situ Fourier transform infrared (FTIR) spectroscopy was employed to test the real‐time evolution of these functional groups in both air and argon atmospheres. The differences found between functional groups when under an oxygen oxygen‐free environment were analyzed. The results show that when the temperature exceeds 200 °C, the changes in functional groups steadily increase and that regardless of whether the atmosphere is made up of argon or air, the oxygen‐containing functional groups change significantly. In this situation, −OH, −CH3, and −CH2‐ are important reactants in the whole heating process; −COOH and −C=O are reactants during the low temperature oxidation stage, but when reaching the high temperature stage, they become the products; C‐O‐C and C=C is a stable reaction product. During the coal spontaneous combustion process, oxidation and pyrolysis work as two coupling reactions: The heat released by the oxidation reaction pyrolyzes the macromolecular structure and coal‐oxygen complexes, while a large number of active groups are produced during pyrolysis, which then provides the reactants for the oxidation reaction. These results reveal the changes that functional groups go through during the process of oxidation and pyrolysis, and provide a theoretical basis for the development of efficient fire‐fighting materials. © 2021 Society of Chemical Industry and John Wiley & Sons, Ltd.