Influence of inert gas atmosphere on the oxidation reaction of active groups in coal: Experimental and simulation studies

To study the influence and inerting mechanism of inert gas atmosphere on the oxidation of active groups in coal, Shuiyu (SY) bituminous coal and model compounds were taken as the objects of the research. A combination of temperature-programmed and Fourier transform infrared spectroscopy (FT-IR) experiments and quantum chemical calculations was used to compare the differences in the inhibition effects of CO₂ and N₂ on different active groups from both experimental and simulation perspectives and to reveal the inerting mechanisms of CO₂ and N₂ on the reaction of active groups with O₂ in coal. The results showed that CO₂ was more effective than N₂ in inerting the oxidation reaction of active functional groups in coal and reducing the generation of oxygen-containing functional groups in coal. The higher the temperature, the more consistent the inerting effect of two atmospheres on the oxidation reaction of active groups. The difference between the two atmospheres on the inerting effect on the oxidative process of oxygen-containing functional groups in coal was large, and the difference on the inerting effect on the oxidative process of aliphatic hydrocarbons in coal was smaller. The reactivity of the active H atoms in the groups was decreased by both CO₂ and N₂, which changed the positions of the nucleophilic reactive sites for individual active groups, and CO₂ was more significant than N₂ in decreasing the reactivity of the active H atoms. Among them, the influence of N₂ on the chemical adsorption of alkanes with O₂ was greater, while CO₂ on the chemical adsorption of oxygen-containing functional groups with O₂ was greater. Whether the two atmospheres inhibit or promote the oxidation reaction of the active group, the possibility and heat release of the oxidation reaction for the system after the interaction of CO₂ with the active group was lower than that of N₂. The effect of inert gas type on the chemical adsorption and oxidation reaction of oxygen-containing functional groups with O₂ was more significant, and the effect on aliphatic hydrocarbons was smaller. Therefore, the difference of inerting effect between CO₂ and N₂ on coal spontaneous combustion was closely related to the type of functional groups in coal and temperature. In the technology for fire prevention of inert gases in underground coal mines, the type of inert gas should be comprehensively evaluated according to the type and composition of functional groups in coal and the field temperature.