Study On the effects of surfactants on CH 4 -CO 2 competitive adsorption of jincheng anthracite based on molecular simulation

Surfactant-assisted modification of coal surfaces offers a potential strategy for enhancing CO2 storage and CH4 recovery in CO2-enhanced coalbed methane, but the molecular mechanisms underlying competitive CH42 adsorption remian unclear. In the present study, a Jincheng anthracite model with a 5-nm slit pore was constructed in Materials Studio. Grand Canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations were used to evaluate three surfactants sharing the same hydrophobic tail but different head groups (Brij-58, CPC, and SHS) in terms of gas adsorption, interaction energies, and diffusion under varying pressures. The results indicate that coal naturally has a stronger affinity for CO2 than for CH4, and surfactant modification further amplifies this adsorption selectivity. Surfactants regulate interfacial adsorption structures, weaken CH4–coal interactions, and enhance CO2 adsorption stability, thereby promoting CH4 displacement and CO2 enrichment. Overall performance follows the order Brij-58 > CPC > SHS. Brij-58 enhances CO2 enrichment through ether oxygen groups in its polyoxyethylene head group, whereas CPC stabilizes the interfacial adsorption layer through electrostatic interactions. SHS shows the weakest effect on selectivity. These findings clarify how surfactants regulate CH4/CO2 competitive adsorption and provide a theoretical reference for surfactant selection in high-rank coal seams.