Structural Characterization and Molecular Simulation of Baoqing Lignite

The molecular structure of Baoqing lignite was analyzed by ultimate analysis, Fourier transform infrared spectroscopy, X-ray diffraction spectroscopy, ¹³C solid-state nuclear magnetic resonance, and X-ray photoelectron spectroscopy. The results revealed that the aromaticity of Baoqing lignite is 27.64%, and the aromatic structure mainly contains benzene and naphthalene. The aliphatic structure consists of alkyl side chains and cycloalkyl. Oxygen atoms are present in phenol, ether, carbonyl, and carboxyl groups; nitrogen atoms are chiefly in pyridine and pyrrole; sulfur atoms mainly exist in sulfoxide sulfur. The molecular structure model of Baoqing lignite was constructed based on experimental data, and the molecular formula is C₁₈₄H₁₉₉O₅₀N₂S. The molecular configuration was optimized by adopting the M06-2X basis set in the framework of density functional theory. Moreover, the simulated FTIR spectrum was in good agreement with the experimental spectra, proving the accuracy of the molecular structure. The molecular model of Baoqing lignite contains a majority of aliphatic structures and aromatic rings with a poor condensation degree. Moreover, the aromatic layers irregularly arrange in space.