Evolution of functional groups during in-situ pyrolysis of tar-rich coal using synchrotron infrared spectroscopy

The key dissociation mechanism for optimizing the tar yield and conversion efficiency of tar-rich coal pyrolysis lies in the evolution of functional groups during the thermochemical process. This study utilizes synchrotron infrared spectroscopy to explore the evolution of functional groups during the pyrolysis of tar-rich coal, in conjunction with thermogravimetric experiments, to clarify the influence of pyrolysis stages on these functional groups. Results show that at low temperatures (100–250 °C), most functional groups remain stable, with -OH group cleavage initiating at 200 °C. In the medium-temperature range (250–500 °C), functional groups such as C=O, C-O-C, and C=C exhibit accelerated decomposition starting from 300 °C. NH group cleavage significantly intensifies between 350 and 400 °C, while -CH₃ and -CH₂ groups show marked breakdown beyond 400 °C. At higher temperatures (500–700 °C), continued decomposition of -CH₃, C-O, and = C-H groups occurs, becoming nearly undetectable above 600 °C. These findings offer fundamental insights into the transformations of functional groups that govern tar formation and volatile release, providing essential data for refining pyrolysis processes.