Exploring molecular structure characteristics and chemical index of Qinghua bituminous coal: A comprehensive insight from single molecule of macerals to particles with various sizes

Understanding the relationship between the coal structure and its reactive behaviour is of great significance to achieve clean coal conversion and its efficient utilisation. One of the key tasks is to elucidate the molecular structure and chemical bonding information of coal. Owing to the complexity of the chemical structure of coal, studies on the molecular structure of coal, especially coal models with complex particle structures of different sizes for bituminous coal from northwest China, are highly warranted. In this work, the molecular structure characteristics and chemical index of a Qinghua bituminous coal sample collected from the Ningdong area, China, were assessed. Using a combination of material characterization, computation, and molecular modelling methods, a standard method for modelling complex coal structures from single molecules of macerals to particles of various sizes was developed. The single molecular structure of vitrinite and inertinite present in Qinghua coal can be expressed as C₂₆₉H₁₉₆N₄O₁₃S and C₂₅₅H₁₇₉N₃O₁₄S, respectively. Then, a series of complex particle models of various sizes were established based on the single molecular structure models of vitrinite and inertinite. Among these models, the size of the complex particles was as large as 11 nm, with the total atomic number approaching 60,000. Furthermore, the energetic and structural features of the complex coal particle structures were also explored based on their energy decomposition and radial distribution function analysis. In addition, the chemical structure index analysis was performed for different coal macerals to further understand the internal relationship between its structure and application.