Model construction and molecular dynamics simulation of coal group component skeleton structure

In order to further understand the internal mechanism of the structure formation of coal macromolecular network from molecular aspect,the group components including heavy component (HC),loose medium component (LMC),dense medium component (DMC),and light component (LC) were respectively extracted from the all-group component of coal and the skeleton structure of group components and small organic molecules were collected.The molecular models of group component skeletons (HC-S,LMC-S,and DMC-S) were constructed based on the parameters deduced from the results of XPS,13C NMR,FTIR,and ultimate analysis.The configurations with the lowest potential energy and densities of simulated models were acquired using molecular mechanics and molecular dynamics simulations.Then,the molecular and energy mechanisms of the formation of multi-molecular stable aggregate were further explored.The results indicate that the molecular formulas of HC-S,LMC-S and DMC-S were C246H186N4O15,C216H183N5O5 S and C195H179N3O4S respectively.The LMC-S model has the highest density,followed by HC-S and DMC-S.The density of the simulated models has a good agreement with the experiments values.In the case of the unit cell containing 12 DMC-S macromolecules,a stable aggregate with the size about 50×10-10 m can be formed due to the interactions between nitrogen and hydrogen in the structural unit of different molecules.However,the stable aggregate (LMC-S-25) with the size about 70×10-10m was formed via the - conjugation effects.The stable aggregates of HC-S were not formed when the molecules number less than 20.The mechanisms are consistent with the experimental results.Besides,the LMC-S has the largest gyration radius,followed by DMC-S and HC-S,indicating the smallest flexibility of LMC-S and the incompact formed aggregates.On the other hand,HC-S has the highest flexibility and will become compact as for the formed aggregates.These analysis results coincide with the experimental phenomenon well.Finally,the comparison table between the simulation calculation and experimental results of skeleton monomers and their aggregates were given.