**5. Conclusions**

In this study, proximate analysis, ultimate analysis, 13C-NMR, XPS, and XRD were performed on Huainan gas coal to quantify its structure. The macromolecular structure model of coal was constructed and optimized based on the quantitative analysis results. The model was verified and optimized by NMR carbon spectroscopy and MS software to obtain the correct molecular model. The following conclusions were drawn.

The results showed that XBP was 0.407. The aromatic structures were mostly anthracene and phenanthrene, followed by naphthalene and benzene rings. The molecule model contained five ether−oxygen bonds, two carbonyl groups, one carboxyl group, two pyridine nitrogen, and one pyrrole nitrogen. Its molecular formula was determined to be C181H150O9N3.

The minimum energy value of the optimized molecules was 684.560 KJ/mol. The van der Waals energy was the main component of non-bond energy, which was the main factor to stabilize the coal molecular structure and change the energy. The changes including the bond length, angle, torsion, and inversion were the basis of coal molecules with stereoscopic configuration. The intermolecular aromatic lamellae were arranged in an approximately parallel manner by the π−π interaction. The short-range order of the highgrade coal structure was determined by the directional arrangement of the intermolecular aromatic lamellae.

The coal molecular crystal unit was constructed by adding periodic boundary conditions to the optimized structure, and it was used for the density simulation. The result showed that the simulative density of the coal molecular crystal unit was 1.0 g/cm3 when the total energy reached the lowest value of 562.944 kcal/mol, which was close to the real density measured by the experiment. At the same time, the predicted carbon spectrum obtained by the MestReNova software agreed well with the experimental spectrum, which suggests that the construction of the gas coal macromolecular model is reasonable and effective.

**Author Contributions:** Funding acquisition, L.Q.; investigation, J.C.; methodology, L.L.; project administration, L.Q.; resources, L.Q.; supervision, L.Q.; validation, L.L.; visualization, J.C.; writing original draft, L.L. and Z.W.; writing—review and editing, L.Q. and L.L. All authors have read and agreed to the published version of the manuscript.

**Funding:** This work is supported by the National Science Foundation of China (51804355).

**Data Availability Statement:** Not applicable.

**Conflicts of Interest:** The authors declare no conflict of interest.
