Molecular simulations on diameter effect of carbon nanotube for separation of CO₂/CH₄

Biomethane route has large potential in emission reduction and energy saving. One of the key issues is separation of biogas in operating conditions of 333 K and 0.1 MPa. Grand canonical Monte Carlo (GCMC) and equilibrium molecular dynamics simulations (EMD) were used to compute adsorption loadings and self-diffusivities of CH₄/CO₂ at various diameters of carbon nanotube (CNT) bundles. Single component and equimolar gases were simulated. CO₂ always had larger adsorption loading and diffusion coefficient than CH₄ as the result of relatively strong interaction between CO₂ molecules and tube walls, due to the confined capacity. The permselectivity reached a maximum in closely 1 nm, and under such conditions the separation process was controlled by adsorption rather than diffusion.