Creation and Generation Mechanism of Macromolecular Representation for Dongsheng Coal Vitrinite

Insights into macromolecules of coal were critical for improving the understanding of the coal upgrading and coalification process. Here, the creation and generation of macromolecular representation for Dongsheng coal vitrinite was clarified using industry analysis, elemental analysis, and the peak fitting technology of 13C nuclear magnetic resonance (13C NMR), Fourier transform infrared spectrum, and X-ray diffraction. The structural parameters and macromolecular representation (C167H148N2O27) were innovatively calculated and created based on these characterization results and chemical shift correction, finally obtaining the plane macromolecular models whose 13C NMR spectrum was close to the experimental spectrum. The property parameters of basic structural units were La (average lateral sizes) = 19.917 Å, Lc (stacking heights) = 24.776 Å, d002 (interlayer spacing) = 3.488 Å, N (number of stacking layers) = 5.6213, and La/Lc < 1. Suffering from the dynamic metamorphism effects, the length of intermolecular aromatic lamellae for Dongsheng coal vitrinite was 7-8 aromatic rings in size. The aromatic clusters were dominated by benzene, naphthalene, and anthracene, and their numbers were 2, 4, and 2 per vitrinite model, respectively. Hydrogenated aromatic rings, ether bonds, and oxygen-methylene serve as the main bridge bonds to connect the aromatic clusters, where the short aliphatic chains were distributed around the edge of aromatic rings. Oxygen atoms exist in the form of hydroxyl, ether bond, carbonyl, and carboxyl groups, and their numbers were 2, 7, 4, and 8 per vitrinite model, respectively. The nitrogen atoms exist in the form of pyridine and pyrrole. The entropy weighting method was used to estimate the rationality of the macromolecular representation of long frame coal vitrinite, providing a new mathematical evaluation method for molecular simulation. Comparison of various macromolecular models from different geological conditions indicates that tectonic stress can promote the degree of aromatization and ring condensation. The thermal history and tectonic stress have a compensation effect for promoting the aromatization process. Aliphatic carbons were the most unstable units under thermal history and tectonic stress, and they are more easily removed from the aliphatic structure, followed by methyl. This finding of this paper can provide significance for coal liquefaction engineering in Dongsheng coalfield.