Structural Transformations of Coal at Low Temperature Oxidation via In-situ FTIR

ABSTRACT

Structural transformations in different coal ranks during low temperature oxidation (≤ 210°C) are crucial to understand the spontaneous combustion of coal and related environmental problems. The in-situ Fourier transform infrared (FTIR) technique was used to highlight the variations of aromatic, aliphatic, oxygen functional groups, and hydrogen bonds of different coal ranks spanning from lignite to anthracite. Chemical changes were observed at real-time experimental conditions. Characteristic temperature points were selected as the point where obvious gas changes occurred. Structural parameters were determined by fitting FTIR spectra. The band of highly substituted aromatic rings had a direct correlation with low rank coals. The degree of substitution (DOS) of aromatic sites with alkyl groups showed a good power function correlation with fixed carbon content. Aliphatic carbon changes displayed similar trends with different coal ranks. Moreover, increasing coalification decreased the oxygen functional parameter ‘C’. The ‘C’ value of samples with high oxygen content increased with temperature, caused due to the oxidation of aliphatic structures. The fitting areas of the 3600–3000 cm⁻¹ region reduced with increasing coal rank. The aromatic structures changed more significantly with temperature in low-rank coal than in high-rank coal.

KEYWORDS:

• Aromatic
• aliphatic
• oxygen functional groups
• hydrogen bonds
• low temperatures oxidation

Data Availability

All data included in this study are available in the submitted article.

Disclosure statement

The authors declare no competing financial interest.

Additional information

Funding

This work is supported by the National Natural Science Foundation of China [Nos. 41672153 and 41430640] and the Scientific Research Foundation of Key Laboratory of Coalbed Methane Resource & Reservoir Formation Process, Ministry of Education [No. 2017-002].