Microscopic characteristics and gas generation patterns of spontaneous combustion oxidation in deep high-temperature coal seams of the Juye mining area

• Gray relational analysis linked functional groups to gas products in different coals. • Microporous structure and staged pore volume revealed via pore characteristic tests. • Oxygenated functional groups strongly link to gas products in Tangkou and Xinjulong coal. • –CH and substituted aromatics showed highest association in Zhaolou coal. The microscopic characteristics of coal molecules form the foundation to study on coal oxidation process and its mechanisms. Within this study, the pore characteristics and gas product variations of three coal samples were analyzed using liquid nitrogen adsorption, mercury intrusion testing, and programmed temperature experiments. Using in-situ infrared spectroscopy, the transformation patterns of the principal functional groups within coal samples were studied. Subsequently, gray relational analysis was implemented to examine the association patterns between dominant functional groups and their related gases. The analytical findings demonstrate that the tested coal specimens exhibit a significant abundance of microporous, and the cumulative pore volume exhibits a staged pattern as a function of pore diameter. The oxygen consumption rate shows a similar trend to the variations in CO and CO 2 , while the oxygen concentration exhibits an opposite trend. The CH 4 , C 2 H 6 and C 2 H 4 gases exhibit a positive correlation with temperature elevation. While the hydroxyl content in Tangkou and Zhaolou coals decreases before increasing, Xinjulong coal displays a unique pattern of initial ascend, decline, and secondary increase. The methyl and methylene contents initially increase and then decrease. The quantity of aromatic compounds and oxygenated functional groups demonstrate a positive correlation with temperature elevation. Grey relational analysis reveals strong associations between oxygenated functional groups and characteristic gases in Tangkou and Xinjulong coals, while Zhaolou coal shows strongest correlations with –CH and substituted aromatic hydrocarbons. This research provides important insights for understanding the combustion properties and fire risk management of the Juye coal mine.