Study on the transformation characteristics of microstructure in Shengli lignite during low-temperature oxidation

A Shengli lignite from Inner Mongolia was selected as the research object, with which the low-temperature oxidation experiments were carried out at different temperatures (200-300℃) in a fixed bed reactor. The structure of coal samples after oxidation treatment was characterized by FT-IR, Raman and XPS. The effects of low-temperature oxidation at different temperatures on the microstructure and mass change of lignite were investigated and the combustion performance was determined by TGA. The results show that the temperature has a significant influence on mass change rate of Shengli lignite during low-temperature oxidation. The mass change rate of lignite is very limited when temperature is below 220℃ and it changes obviously when the temperature is higher than 220℃. Especially at 220-230℃, the mass change rate of coal samples is changed from 5.80% (220℃) to 42.55% (230℃). The FT-IR/Raman/XPS characterization results show that the analogous benzoquinone structure forms after oxidized at 220℃, and these lead to the stretching vibration absorption peak of the aromatic C=C shift to lower wavenumber. In Raman spectra, the position of the D peak shifts, and the distance between the peaks of D and G increases. The content of C-O-and C=O on the surface of coal samples increases at oxidation temperature lower than 220℃. It is speculated that the jump of mass change rate of coal samples at 220-230℃ is mainly related to the oxidative decomposition of analogous benzoquinone structure.