Study on model construction and optimization of molecular structure

Understanding the structural characteristics of coal molecules at the molecular scale is of significance to realize rational utilization and efficient transformation of coal.The macromolecule structure of coal sample, from Qingdong Coal Mine of Huaibei Mining Group, was studied using the methods of proximate analysis, elemental analysis, carbon nuclear magnetic resonance ( 13 C-NMR) and X-ray photoelectric spectrometry (XPS).The results showed that the aromatic structure in the macromolecular structure of Qingdong coal was mainly composed of naphthalene and anthracene, and the aliphatic carbon existed mainly in the form of —CH3 , —CH2 and cycloalkanes.The ratio of aromatic bridge carbon to aromatic peripheral carbon was 0.35.The oxygen and nitrogen atom were in the form of carbonyl group and phenolic hydroxyl group, and pyridine and pyrrole, respectively.Sulfur atom was too low to considered in the model.Based on this, the average macromolecular structure model of Qingdong coal was established.Its molecular formula was C142 H128 N2O3 , and its molecular weight was 1 910.60.The aromatic structural units in the macromolecular structure of coal sample included 2 benzene rings, 2 naphthalene and 4 anthracene.The heteroatoms in the molecular structure of coal were in the form of 2 carbonyl groups, 1 phenolic hydroxyl group, 1 pyridine group and 1 pyrrole group.Optimization and annealing molecular dynamics simulations of a single constructed model were performed.The chemical bonds such as bridge bonds and fat bonds were obviously twisted.The intramolecular π -π interactions between aromatic layers enabled their quasi-parallel arrangement.The total energy decreased from 2 121.14 kJ/mol to 1 255.85 kJ/mol, in which bond stretch energy and van der Waals energy played a key role in energy.Eighteen macromolecular models of Qingdong coal were constructed into an aggregation structure.After the optimization of molecular mechanics and molecular dynamics simulations, the macromolecules in the aggregated structure model were constrained by the surrounding molecules, and the originally parallel-arranged flaky aromatic carbon structures were bent and twisted, aromatic carbon layers in the structure were disorderly.In the study, the Qingdong coal macromolecular structure model was constructed to provide a model basis for further flotation reagent selection.