Elucidation of elemental and structural changes in high-volatile bituminous coal during thermal treatment by X-ray diffraction and terahertz time-domain spectroscopy

Abstract Research on the chemical composition and structure of coal is fundamental for understanding chemical reactivity in combustion, pyrolysis, and gasification processes. In this work, X-ray diffraction (XRD) and terahertz time-domain spectroscopy (THz-TDS) are used to investigate both the chemical structural characteristics and thermal evolution of high-volatile bituminous coal subjected to different heat treatments. The XRD spectra indicate that aromaticity (fa) and coal rank (I26/I20) increase with temperature, which is consistent with elemental analysis. However, the structural parameters, such as interlayer spacing (d002), lateral size (La), and stacking height (Lc), show weak changes. Combined with the element analysis and XRD results, THz-TDS is carried out to characterize the above samples more precisely and further elucidate their chemical and structural changes. The study demonstrates the capability of the THz technique to determine and characterize the structural parameters and chemical compositions to evaluate coal rank and classification.