Microstructural Changes and Kinetic Analysis of Oxidation Reaction in Coal–Oil Symbiosis

During the coal mining process, fractures generated can lead to crude oil infiltrating into coal seams, forming coal–oil symbiosis (COS). The complex three-phase interaction of coal–oil–oxygen makes the mechanism of COS spontaneous combustion filled with uncertainties. This study utilized synchronous thermal analysis to analyze the physico-chemical behavior of raw coal and COS at different heating rates. Additionally, detailed characterization of their surface morphology and functional groups was conducted using scanning electron microscopy (SEM) and in situ FTIR technology. The findings suggest that the coverage of crude oil on the surface of coal inhibits the adsorption of oxygen by the coal, leading to the disappearance of the stage where COS absorbs oxygen and gains weight. Moreover, the continuous decline of –OH groups and aliphatic hydrocarbons in the later stages suggests that crude oil acts as a catalyst for combustion during the latter stages of the reaction. The Kissinger–Akahira–Sunose, Starink, and Flynn–Wall–Ozawa methods showed that the apparent activation energy of COS is 23.3 and 19.7% lower than that of raw coal in thermal decomposition and combustion stages, respectively.