Parameter prediction of factors influencing methane adsorption for coal macromolecules under different water molecular morphologies

Gas (methane) is a major hazard in coal mines, coexisting with coal seams and often adsorbed within them. The presence of moisture and pre-adsorption forms significantly affects methane adsorption. To optimize and predict key influencing factors, this study used molecular simulation and orthogonal analysis to construct cluster water coal macromolecular models (CY-CW-CMM) and random water coal macromolecular models (CY-RW-CMM) for Chiyu Mine (CY) coal. The intrinsic relationship between the two models and their absolute methane adsorption behaviors were analyzed under varying water content, temperature, and pressure. Fourier transform infrared (FTIR) spectroscopy experiments further verified the functional group changes before methane adsorption. Results showed that as water molecules increased, the maximum electrostatic potential energy of CY-RW-CMM was slightly lower than CY-CW-CMM due to dispersed water molecules occupying high-energy adsorption sites, reducing adsorption space. After methane adsorption, CY-RW-CMM exhibited weaker capacity due to the “roughness” of water molecules in pore structures and strong fusion effects with coal macromolecules. The optimal conditions for methane adsorption were determined as 1% water molecular content, 10 MPa pressure, and 283.15 K temperature, with water content being the dominant factor in both models. FTIR tests showed soaked coal had more oxygen-containing functional groups, including OH-OH hydrogen bonding, -CH
2
asymmetric stretching, and increased C=O and benzene ring tertiary substituents, all of which reduced methane adsorption capacity. This study provides valuable insights into improving gas extraction efficiency and understanding coal adsorption mechanisms.