Unveiling pore size contributions and host-guest interactions in methane adsorption under varying pressure conditions: a semi-empirical adsorption model

Natural gas, primarily composed of methane (CH₄), offers a greener alternative to conventional fuels. Efficient storage through adsorbed natural gas technology necessitates an understanding of CH₄–adsorbent interactions. This study explored CH₄ adsorption on activated carbons at 1–35 bar and 298 K, determining an efficiency factor (φ) as an indicator of optimal pore size. In the given system, φ ranged from 2.0 at 1 bar to 2.5 at 35 bar, indicating an increasing trend with pressure. To gain further insights, quantitative contributions (kx) were established based on different micropore sizes (di < 0.76 nm, 0.76 nm < dii < 1.14 nm, and 1.14 nm < diii < 2 nm). At 1 bar, ki, kii, and kiii contributed 91, 9, and 1%, respectively. These contribution values shifted to 35, 54, and 11% at 35 bar, suggesting that effective pore sizes increase with increasing pressure. Notably, CH₄ capacity directly correlated with dii in the high-pressure adsorption. Atomistic computations were used to elucidate the role of pore sizes in facilitating CH₄ accessibility at different pressures. This comprehensive model provides valuable insights for designing optimal adsorbents, specifically targeting pore size-dependent applications such as gas adsorption and separation, as well as catalyst supports.