Comparative of thermokinetic behaviors and four functional groups variations from spontaneous combustion of coal and its pre-oxidized

In China, coal spontaneous combustion (CSC) is seriously disasters in gobs during coal seam groups mining, the secondary or multiple oxidation processes of residual coal occur inevitably, severely increasing the risk of coal fires. This paper focused on the thermal reaction behavior of two samples of raw coal and degrees of pre-oxidized (Oxi-80 °C, Oxi-130 °C, and Oxi-180 °C), we determined their characteristics of physical and chemical via thermogravimetric-Fourier transform infrared spectroscopy (TG-FTIR) with the heating rates being 1.0, 2.0, 5.0, and 10.0 °C min⁻¹. According to the characteristic temperature, the CSC process could be divided into three stages of oxidation (stage I), combustion (stage II), and thermal residual (stage III). The results indicated that for pre-oxidized coal the length of aliphatic side chains was shorter, and the number of branched aliphatic side chains was lower than that of the raw coal. The kinetic models revealed the mechanism category was changed between raw coal and pre-oxidized coal. However, the heating rate exerted little influence on the mechanism category of each stage, particularly in stage I. The average values of apparent activation energy for the pre-oxidized coal samples were lower than that of raw coal. Therefore, the pre-oxidized coal samples required less energy to activate and more readily caused spontaneous combustion than raw coal at certain stages.