Molecular Sturacture Model Building And Study Of Adsorption Mechanism

The macromolecular structure of coals has the complexity and heterogeneity. The further study of coal macromlecular has great significance for sedimentary and burial mechanism and energy efficiencies.Based on proximate and ultimate analysis,13C CP/MAS NMR data of Ximing-8 coal, a macromolecular structural model was constructed. In this model, phenanthrene, anthracene is the main aromatic compound;aliphatic structure exists mainly in the forms of aliphatic side chains, cycloalkanes and hydrogenated aromatic rings.O atoms are present as carboxyl, carbonyl and hydroxyl groups and two N atoms exist in the forms of pyridine and pyrrole, while two S atoms in the form of thiophenic. Molecular mechanics (MM) and molecular dynamics (MD) techniques were used to carry out energy minimization simulations on this model. The simulation results indicate that stabilization of the macromolecular structure is due to the energies of van derWaals, torsion, angle, bond and inversion in descending order of importance, and intramolecularπ-πinteractions between aromatic layers enables their quasi-parallel arrangement.Then through the density functional theory (DFT)calculations, the interactions between methane and coal surfaces have been investigated.Several adsorption sites and orientations of methane (CH4) on Ximing-8 were systematically considered.It turned out that:2-B-UP is most favorable system, the adsorption energy is -38.37 kcal/mol;on aromatic unit structures phenanthrene is the most favorable system;on heterocyclic unit structures thiophenic is the most favorable system;for Up orientation of CH4, the adsorption energy is smallest;CH4 molecule prefers to be adsorbed in the middle of C-C bond and X-C bond, and tends to be adsorbed on aromatic unit structures;compared with graphite the adsorption energy of coal is smaller than graphite.