Transport diffusivity of propane and propylene inside SWNTs from equilibrium molecular dynamics simulations

The gas transport of two model gases (propane and propylene) inside the single-walled nanotubes (SWNTs) of various diameters was systematically investigated using the molecular dynamics (MD) simulations. The thermodynamic factor can be obtained directly from equilibrium MD simulations following the newly-minted method proposed by Schnell et al. (Chem. Phys. Lett., 2011, 504, 199-201). This process eliminates the need to implement the tedious and challenging Monte Carlo simulations for the adsorption isotherm, from which the thermodynamic factor is usually extracted. The satisfactory agreement between simulation and the literature is found for self-diffusivity, corrected diffusivity and transport diffusivity, as well as for the thermodynamic factor. The ideal selectivity for a propane-propylene mixture through SWNT membranes could be optimized through adjusting the concentration gradient. This method can be readily extended to the binary and multiple-component systems.