Response mechanism of dominant reactive functional groups in lignite under hypoxic conditions: a study combining phased microstructural and energy changes

High moisture and volatile of lignite make it easy to spontaneous combustion. It is important to study energy changes and phased microstructural in oxidation process for prevention and control of coal fire. Therefore, by analyzing the characteristics of lignite microstructure, combined with Pearson correlation analysis, this study investigates the influence of hypoxic conditions on low-temperature oxidation characteristics of lignite, and phased mechanism of groups. The results indicate that during dehydration and degassing stage, lignite surface exhibits a granular structure. The activation energy exhibits significantly increased sensitivity to O₂ concentration. The reduction in O₂ concentration intensifies the self-reaction of groups and restricts the chemisorption between lignite and oxygen. During dynamic equilibrium stage, a scale-like structure forms on the lignite surface. The high-temperature effect expands the reaction pathways of groups, while hypoxic condition suppresses the formation of active structures and volatile. Correlation analysis reveals that –OH and –CH₂/CH₃ are the primary heat-producing groups, and –CHO and –COOH are the primary heat-absorbing groups. When O₂ concentration rises from 5 % to 21 %, the main reaction groups of low-temperature oxidation are –CH₂/CH₃ → –OH → –CH₂/CH₃. Furthermore, hypoxic condition inhibits the reactions of –OH and –COOH, while exerting minimal influence on –CHO and –CH₂/CH₃.