Model construction and optimization of coal molecular structure

Understanding the structural characteristics of coal molecular at the molecular level is of paramount importance for the effective utilization of coal. In this work, the molecular structure of coal sample, from Liuzhuang(LZ) Coal Mine in Anhui Province, China, is investigated using modern analytical techniques, such as elemental analysis, X-ray photoelectron spectroscopy (XPS),Fourier Transform Infrared Spectroscopy(FT-IR) and Solid 13C nuclear magnetic resonance spectroscopy (13C NMR). It is found that the aromatic compounds of LZ coal are mainly in the form of 2 and 3 rings, with an aromaticity of 40.99% and the ratio of aromatic bridge carbon to aromatic peripheral carbon is 0.232. sulfur element is too low to considered in the model. Based on the above analysis, the molecular formula of LZ coal is inferred as C158H143O35N7. The experimental 13C NMR is consistent with the simulated spectrum, which indicates the accuracy of LZ molecular structure model. The molecular structure model is constructed and optimized by using classical molecular dynamics and the density functional based tight-binding method to obtain the lowest energy and most stable conformation, respectively. The optimized model has a more prominent steric configuration, but the lamellar structure of the aromatic layer is arranged in a more disordered manner. The experimental FT-IR spectra of the model are in preferably good agreement with the simulated results, which proves the correctness of LZ molecular structure. The molecular structure of LZ mine coal established in this paper can provide basic scientific data for further investigation of gas adsorption and resolution in coal seams at the atomic and molecular scales. Overall, Compared to contemporary technologies, these results show a good comparability among the different techniques and therefore provide comprehensive, accurate analytical technique to analyze the molecular structure of coal.