Response characteristics of molecular active structure of coal of different metamorphic degree to extractant

To explore the distribution characteristics of the molecular active structure of different metamorphic coal samples and their response characteristics to extractants, four extraction reagents (cyclohexane, cellulase, tea polyphenols, and tetrahydrofuran) were selected to extract three different coals of different metamorphic degrees (smokeless, bituminous, and lignite coal). In combination with FTIR test analysis results, the differences of infrared spectrum distribution characteristics and active functional group contents before and after extraction of different metamorphic coal samples and the response characteristics of key active structures to extractants were studied. The results showed that the extraction effect of extractant on the active structure of coal samples of different metamorphic degrees is different. Under the same extraction conditions, the solvent extraction efficiency increases with decrease of coal rank. Owing to the relatively more stable structure of high metamorphic coal samples, the overall extraction difficulty of lignite molecular active structure is lower than those of smokeless and bituminous coal groups. This research preliminarily determined the optimal extraction reagent for the key active structure of coal molecules of different metamorphic degrees. The results provide a theoretical basis for subsequent research on the targeted stripping of specific active structures in the process of coal spontaneous combustion.