Ultrasonic extraction of active groups in coal spontaneous combustion and their gas release patterns

To investigate the release patterns of CO and C₂H₄ as spontaneous combustion indicator gases during anthracite oxidation,Fourier transform infrared (FTIR) spectroscopy was used to characterize the surface functional groups of the anthracite. Four optimal extractants:ethylenediamine,N-methylpyrrolidone(NMP),petroleum ether,and toluene were selected for targeting hydroxyl,carbon-oxygen,aliphatic,and aromatic groups,respectively. These extractants were employed in ultrasound -assisted solvent extraction to isolate and simplify the complex structural units of anthracite. The microstructural changes of coal samples before and after extraction were further examined using FTIR and thermogravimetry-mass spectrometry (TG-MS), aiming to elucidate the generation mechanisms of CO and C₂H₄ during coal spontaneous combustion. The results indicate that different functional groups contribute differently to the formation of various gases,and the influence of the same group varies across different temperature stages. Specifically, carbon-oxygen functional groups significantly affect CO generation before 300℃, but their impact diminishes at higher temperatures. Aliphatic hydrocarbons primarily influence the production of C₂H₄ and the combined CO+C₂H₄ gases above 300℃, and a reduction in aliphatic hydrocarbons leads to a decrease in gas concentrations. This study provides theoretical support at the level of functional group reaction pathways for early gas warning in coal spontaneous combustion.