A molecular simulation study of propane and propylene adsorption onto single-walled carbon nanotube bundles

We have carried out configurational-bias Grand Canonical Monte Carlo simulations of propane and propylene adsorption onto homogeneous bundles of single-walled carbon nanotubes, at ambient temperature (T = 298.15 K) and over a pressure range of 0.1 bar ≤ p ≤ 10.4 bar. The distinct contributions from external sites (grooves and external surface) and endohedral volume (inter- and intra-tubular) are individually addressed for bundles with nanotube diameters (D) within the range 11.0 Å ≤ D ≤ 18.1 Å. The different contributions from the various adsorption sites are interpreted from a molecular perspective, which takes into account both the skeletal geometry of the bundle and individual tube diameter. The resulting microscopic picture is then related to a macroscopic measurable isotherm by modeling the nanotube bundles, as a function of a characteristic hydraulic diameter (D _h) over the range 100 Å ≤ D _h ≤ 310 Å. A previously unobserved anisotropic behavior of the adsorption isotherm for the peripheral surface of the bundles as a function of hydraulic diameter is reported.