Study on Molecular Model Construction and Gas Adsorption Simulation of Anthracite in the Qinshui Basin
Zhihui Wen, Yanping Wang, Jianping Wei, Jianwei Wang, Leilei Si, Qi Wang
Abstract
Uncovering gas adsorption characteristics of coal at the molecular scale is of great theoretical significance for the study of gas occurrence, coalbed methane exploitation, and carbon dioxide sequestration. In this study, based on proximate analysis, ultimate analysis, 13 C nuclear magnetic resonance, and Fourier-transform infrared spectroscopy experiments, the existence forms and relative contents of elements of anthracite in the Qinshui Basin were tested and analyzed, and a macromolecular structure model was constructed. Besides, three types of acidic oxygen-containing functional groups, namely, carboxyl groups, phenolic hydroxyl groups, and lactone groups, were added to the molecular model. Furthermore, CH 4 adsorption simulation was conducted on the original molecular model of anthracite and models with three types of acidic functional groups added. The following research results were obtained. The molecular formula of the constructed macromolecular model of anthracite in the Qinshui Basin is C 193 H 138 N 2 O 7 . The molecular structure of coal becomes more compact and curved after structural optimization and annealing optimization. For the four models, the CH 4 adsorption characteristics of coal molecules all conform to the Langmuir equation under the same simulation conditions. Among them, the original model has the largest CH 4 adsorption capacity, while the addition of oxygen-containing functional groups reduces the CH 4 adsorption capacity to varying extents. The reduction of CH 4 adsorption capacity follows the order: adding carboxyl groups > adding phenolic hydroxyl groups > adding lactone groups, which is mainly attributed to the different adsorption heats and adsorptive potential wells triggered by the addition of acidic functional groups in molecules.