Molecular Dynamics Simulation on the Adsorption Behavior of Toluene and Ethyl Acetate and Pore Structure Effects in Activated Carbon Synergistically Regulated by Pyridinic/Pyrrolic Nitrogen

To address the challenge of competitive adsorption and separation arising from the coexistence of nonpolar hydrocarbons (TL-toluene) and polar solvents (EAC-ethyl acetate) in oilfield associated gas and produced-water treatment, this study employs grand canonical Monte Carlo (GCMC) and molecular dynamics (MD) simulations to systematically investigate the adsorption mechanisms and pore-confinement effects of pyridinic-N and pyrrolic-N doped activated carbons toward toluene and ethyl acetate. The results demonstrate that nitrogen doping induces electronic cloud redistribution and constructs polar adsorption sites, thereby enhancing π–π interactions with toluene and electrostatic attraction with ethyl acetate, respectively. As a consequence, the capacity retention of the polar component is significantly improved under competitive adsorption conditions.In-depth analysis based on slit-pore models reveals a distinctive pore-size effect. At a critical micropore width of 1.0 nm, an anomalous “selectivity reversal” is observed, wherein the adsorption amount of the polar component surpasses that of the nonpolar component. Mechanistic investigations confirm that this phenomenon originates from a “competition-induced structural reconstruction” process: toluene preferentially occupies the pore walls, forcing ethyl acetate molecules to retreat toward the pore center, where they self-assemble into a high-density sandwich-like cluster with a “Wall–Toluene–EAC–Toluene–Wall” configuration. Energy analyses indicate that the penetrative long-range electrostatic field generated by the N-doped surface acts synergistically with physical squeezing effects imposed by spatial confinement, effectively stabilizing the polar molecular clusters at the pore center.The proposed “sub-nanometer physical squeezing–chemical field stabilization” mechanism provides a theoretical foundation for the rational design of adsorption materials targeting complex multicomponent VOC systems.