Effect of active functional groups in coal on the release behavior of small molecule gases during low-temperature oxidation

The low-temperature oxidation of active groups in coal plays an important role in the release of small molecule gases during coal spontaneous combustion. In this paper, under the temperature of 30 °C–350 °C, the formation and release of small molecule gases and changes of active functional groups were investigated via TG-DSC, TG-IR and in-situ FTIR measurement on low-rank coal. The relationship between the gases and the active functional groups of coal were explored by grey correlation analysis. The methyl/methylene content in coal sample 1 is significantly higher than that in coal sample 2 and the initial content of OH–OH in the two coal samples is similar. The initial contents of oxygen-containing functional groups in coal sample 1 are higher. According to the grey correlation analysis, CO was mainly responsible for the formation of CO2 and CO. And methyl/methylene groups made a great contribution to producing CH4. 100 °C–200 °C is the key temperature for producing gases. The research results establish the relationship between microscopic changes and macroscopic phenomena of low-rank coal during low-temperature oxidation process, and provide research ideas for understanding low-rank coal low-temperature oxidation process and revealing low-temperature oxidation mechanism.