Evolution of Microscopic Groups in Coal Under Air Leakage Disturbance and in-Situ Temperature Increase

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ABSTRACT Currently, research on coal spontaneous combustion (CSC) mostly focuses on its macroscopic behavioral characteristics. However, there is still a significant research gap in exploring the role, pathways, and mechanisms of micro functional groups in the spontaneous combustion process of coal under complex conditions. Therefore, this paper utilizes the VERTEX 70 V in-situ Fourier Transform Infrared (FTIR) Spectroscopy to investigate the impact of air leakage (AL) disturbance and the increase in in-situ temperature affects the microscopic groups within coal, further revealing the microscopic mechanism of CSC under these conditions. The results indicate that, based on alterations in the primary microscopic groups, the in-situ process can be categorized into three phases. During the initial and final stages of the reaction, there is a relatively minor overall alteration in the quantity of oxygen-containing functional groups, accompanied by a slight decrease in the quantity of aromatic hydrocarbons. The content of aliphatic hydrocarbons follows a pattern of initial increase followed by a subsequent decrease. As the AL rate rises, the contents of both oxygen-containing functional groups and aromatic hydrocarbons first decrease and then increase, reaching a minimum at 150 mL/min. In contrast, the quantity of aliphatic hydrocarbons experiences an initial rise followed by a subsequent decline, reaching its peak when the AL is set at 150 mL/min. The experimental results confirm at the microscopic level that during the in-situ oxidation process of coal, when the AL rate is 150 mL/min, the reaction activity of coal reaches its highest, the chemical stability drops to its lowest, and the coal oxygen reaction rate shows the fastest state.