In-situ Raman spectroscopy study on coal pyrolysis and subsequent char low temperature oxidation and gasification

Thermal conversion is pivotal for clean and efficient coal utilization. Evolution of solid structure profoundly affects the gasification mechanism. However, in-situ study on coal structure evolution during gasification is limited. In this study, in-situ Raman spectroscopy was used to investigate the carbon structure evolution during thermal conversion. Results revealed two stages in coal pyrolysis: polycondensation and aromatic ring fusion. During polycondensation, numerous side chain groups break, while aromatic compounds condensed and rings fused in the aromatic ring fusion stage, increasing molecular size. In char gasification, larger particles required more time to achieve stable shrinkage, thus delaying coal char graphitization process. Low temperature oxidation led to decreased order due to oxygen-containing structure formation, evolving into a graphite-like structure as disordered carbon diminished. In addition, oxygen-containing groups acted as active oxidation sites. The insights into real-time structure evolution enhance understanding of the particle behavior during thermal conversion of coal.