Study on evolution characteristics of thermal contribution functional groups in low temperature oxidation process of bituminous coal

In order to study the key functional groups that play a major role in heat during the low-temperature oxidation of bituminous coal, this paper takes three kinds of bituminous coals with different degrees of metamorphism as the research objects, analyzes the variation law of thermal effect parameters during low-temperature oxidation of coal by C80 microcalorimetry experiment, and calculates and analyzes the activation energy of different oxidation stages by oxidation kinetics method. The change rule of functional groups during low temperature oxidation was analyzed by Fourier transform infrared experiment. The correlation between heat and functional groups was comparatively analyzed by using the grey correlation degree and frequency ratio model method, and the key functional groups of bituminous coal that play a major role in heat at different oxidation stages were identified. The results showed that with the deepening of metamorphism degree, the heat flow curve and exotherm gradually decrease, while the characteristic temperature and activation energy gradually increase. Among them, from Caojiatan's long-flame coal to Dongtan's gas coal, the exotherm decreased by 35.5 %, and the maximum endothermic rate temperature and heat balance temperature increased by 3.43 °C and 13.32 °C respectively. With the deepening of metamorphism degree, the content of hydroxyl groups keeps increasing, the content of aliphatic hydrocarbons, aromatic functional groups and fatty ethers first decreases and then increases, and the content of carboxyl groups first increases and then decreases. The correlation analysis between the gray correlation method and the frequency ratio model method shows that as the degree of metamorphic deepened, the key functional groups that play a major role in heat change from COOH to OH in the rapid endothermic stage, from-CH2- to COC in the slow endothermic stage, and from OH to COOH in the rapid exothermic stage. The key functional groups of bituminous coal, which play a major role in heat, follow the evolution of OH → CH2, COC → COOH as the oxidation stage advances.