In Situ FTIR Study of the Out-of-Plane Deformation Vibration Region in Metallurgical Coals during Coking

Coking coal is an essential feedstock for coke production, and its thermoplastic properties are the primary determinant of coke quality. Thermoplastic behavior is influenced by the coal rank, maceral composition, and rheological properties. Understanding these thermoplastic characteristics is essential for optimizing coke production processes. This work extends our previous publication on in situ FTIR/MS spectroscopy, in which spectra were acquired at 10 °C intervals at a heating rate of 5 °C/min from 30 to 600 °C. However, this study focused exclusively on the 900–700 cm–1 region─the spectral region most relevant to aromatic substitution patterns. In situ FTIR was used to characterize and quantify structural changes in three Australian metallurgical coals during coking. The findings showed that as the coking temperature increases beyond the plastic region, fused aromatic C-ring structures become progressively ordered and more condensed, and aromatic clusters grow due to aromatic carbon hybridization. Thus, the degree of substitution (DOS) of aromatic rings increased with coal rank and vitrinite composition, and the maximum fluidity in mid-ranked coal also contributed, as exhibited by coal B. The methodology and techniques employed in this work can be applied to coal and coal maceral blends to provide further insights into the chemistry underlying the transformation of coal to metallurgical coke. This will guide coal experts and marketers in selecting optimal coal blends for producing high-quality coke─critical for the iron and steel industries. More samples with distinct properties will be considered in future work.