Molecular Modeling and Reactivity of Thermally Altered Coals by Molecular Simulation Techniques

In this study, the chemical structure characteristics and reactivity features of three thermally altered coals with different ranks were analyzed by combining molecular modeling and molecular simulation methods to reveal and predict their chemical behaviors and properties. First, 2D molecular models of the three thermally altered coals were constructed based on X-ray photoelectron spectroscopy (XPS), solid-state 13C nuclear magnetic resonance spectroscopy (13C NMR), high-resolution transmission electron microscopy (HRTEM), and ultimate analysis data. 2D molecular models of the three thermally altered coals show different structural characteristics. 3D molecular models of the three thermally altered coals and their potential energy distributions were obtained by geometry optimization and anneal dynamics simulations. For exploring the reactivity of the three thermally altered coals with different ranks, the frontier molecular orbitals and Mulliken bond orders of the three molecular models were calculated based on quantum chemistry calculations. The frontier orbital (HOMO and LUMO) analysis results indicated that compared with the other two thermally altered coals, the thermally altered coal with Ro of 8.32% had higher reactivity in electrophilic or nucleophilic reactions. The bond order results provided detailed information on the active sites of the three thermally altered coal molecules, thereby predicting the thermal behaviors of the three thermally altered coals. These works can provide a theoretical basis for the industrial utilization of thermally altered coal. Meanwhile, these three models will be used in the future to study the combustion, pyrolysis, and graphitization mechanisms of thermally altered coals by reactive molecular dynamics methods.