Gasification characteristics and kinetics of pyrolysis-derived coal chars under a CH4-containing atmosphere

The CO₂ gasification technology of char represents a crucial approach for achieving environmentally sustainable and effective utilization of low-rank coal. Thermogravimetric analysis (TGA) was applied to investigate the CO₂ gasification properties and kinetics of chars prepared by low-rank coal pyrolyzed in the N₂ and CH₄-containing atmospheres. The physicochemical properties of the chars were analyzed through Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS), micro-Raman spectroscopy, and CO₂ adsorption techniques. The gasification activation energy (E_α) of chars was determined by the Flynn-Wall-Ozawa (FWO) approach, and the gasification reaction mechanisms were elucidated through the Malek method. The findings suggest that the CH₄-containing atmosphere significantly increased the proportion of graphitic carbon (C-C) structures and enhanced the graphitization degree (A_G/A_All) in char, while reducing its specific surface area. Further analysis revealed that the C-C structure proportion, volatile matter content, A_G/A_All, and specific surface area of char-CH₄ showed strong linear correlations (R² > 0.9) with its gasification reactivity and activation energy. The CH₄-containing atmosphere reduced the gasification activity of char. Additionally, the CO₂ gasification processes of char could be described by the two-dimensional diffusion mechanism (α = 0.2–0.5) and the three-dimensional diffusion model (α = 0.6–0.9), respectively.