Construction of Lean Coal Molecular Structure Model Based on Spectroscopic Characterization

ABSTRACT The chemical structure of coal exerts a profound influence on its properties and utilization pathways. A comprehensive analysis of coal's molecular structure is crucial for mitigating environmental pollution arising from coal combustion and improving the efficiency of coal utilization. This study investigated relatively scarce lean coal. Fourier transform infrared spectroscopy (FTIR), Carbon‐13 nuclear magnetic resonance ( 13 C NMR), and X‐ray photoelectron spectroscopy (XPS) techniques were employed to characterize the chemical forms of carbon, hydrogen, oxygen, nitrogen, and sulfur within the coal. Additionally, the chemical structural parameters were calculated, and a macromolecular model of lean coal was constructed. The results indicate that the aromatic structures in Shanxi lean coal are dominated by trisubstituted and tetrasubstituted benzene rings and exhibit a relatively high degree of aromatic condensation. In the aliphatic hydrocarbon structures of the coal, the proportions of ‐CH 3 , ‐CH 2 , and ‐CH groups are 48.85%, 29.38%, and 21.77%, respectively, indicating that the aliphatic carbon chains are relatively short. The oxygen‐containing functional groups in the coal are dominated by carbonyl groups (‐C=O) and hydroxyl groups (‐OH). Among these, hydroxyl π hydrogen bonds are the most abundant hydroxyl structure in the coal, with a relative content of 73.00%. The relative content of aryl ethers in the coal is 8.80%, while the carboxyl group content is only 1.02%, indicating a low degree of oxidation of the coal. The aromatic hydrogen ratio, aromatic carbon ratio, and aromatic cluster size of the coal are 0.42, 0.80, and 0.49, respectively. The molecular formula of the constructed lean coal structural model is C 121 H 98 O 11 N 3 S, with a molecular weight of 1800. The molecular model consists of three pyrene units, one anthracene unit, one phenanthrene unit, and one naphthalene unit. With respect to nitrogen‐containing groups, there is one nitrogen oxide, one protonated pyridine, and one pyrrole, respectively. In addition, one thiophene sulfur atom is also present in the structure. This model offers a foundational understanding of lean coal at the molecular level, which can inform its efficient and clean utilization.