Influence of dynamic damage of deformed coal molecular structure on methane adsorption

To reveal the dynamic damage caused by tectonic stress on aromatic lamellae in coal and its influence on methane adsorption, the samples of deformed coal with different deformation degrees in Pingdingshan mining area were collected. The characteristics of lattice fringes and the types of defects of deformed coal were obtained by HRTEM and Raman spectroscopy. By means of molecular simulation, the differences of formation energy and adsorption energy of defects of deformed coal were compared, and the formation mechanism of defects was dis-cussed. Meanwhile, the adsorption behavior of methane molecules on different defects was simulated by using GCMC method. Its results show that SW and vacancy-like defects widely present in deformed coals, including SV, DV and MV. According to the formation mechanism and formation energy of the defects, the brittle deformation coal is mainly composed of SV and DV defects, and the ductile deformation coal contains mainly SW, MV1 and MV2 defects. Compared with the carbon-carbon bond and the aromatic ring center in the defect, the higher electron density above the carbon atom in the defect is more conducive to the adsorption of methane molecules. From the methane density distribution, the methane molecules are more easily enriched near the defects. The adsorption isotherms of methane molecules on the different defects surface are consistent with the characteristics of type I adsorption curve. The adsorption capacity of methane molecules with different defects is shown as follows: the size order of VL is MV1>MV2>DV>SW>SV, and the size order of PL is SW>SV>DV>MV2>MV1. The research shows that the defects from the internal structure of the deformed coal under the action of geological tectonic dynamics are conducive to increase the methane storage space. © 2020, Editorial Office of Journal of China Coal Society. All right reserved.