Effects of carbon nanotube size and carbon dioxide concentration on the diffusion properties and local structure of mixed systems: A molecular dynamics simulation

We utilized molecular dynamics simulations to investigate the adsorption, diffusion, and local structural evolution of CH4, CO2, SO2, and H2O mixtures in carbon nanotube (CNT) models with varying CO2 concentrations (10-80 %) and CNT chiralities ((5, 5) to (22, 22)). All four components exhibited significant adsorption onto the CNT surfaces, with adsorption patterns varying substantially as tube diameter increased. CH4 and CO2 diffusion were more influenced by CNT size, whereas SO2 and H2O diffusion showed weaker dependence. Significant differences in diffusion coefficients among the mixture components demonstrated the feasibility of using CNT systems for adsorption-based separation. Chirality (7, 7) was found to be most favorable for CH4 and CO2 diffusion. Additionally, a moderate increase in CO2 concentration enhanced CH4 and CO2 diffusion, improving separation efficiency. The optimal separation conditions for CH4 were identified at CO2 concentrations of 20-50 % and CNT chiralities ranging from (5, 5) to (7, 7) at low temperatures.