| Abstract
| - We investigate possible usage of single-walled carbon nanotubes (SWNTs) as an efficient storage and separationdevice of hydrogen−methane mixtures at room temperature. The study has been done using Grand CanonicalMonte Carlo simulations for modeling storage and separation of hydrogen−methane mixtures in idealizedSWNTs bundles. These mixtures have been studied at several pressures, up to 12 MPa. We have found thatthe values of the stored volumetric energy and equilibrium selectivity greatly depend on the chiral vector(i.e., pore diameter) of the nanotubes. The bundle formed by [5,4] SWNTs (nanotube diameter of 6.2 Å) canbe regarded as a threshold value. Below that value the densification of hydrogen or methane is negligible.Bundles with wider nanotube diameter (i.e., 12.2, 13.6, 24.4 Å) seem to be promising nanomaterials forhydrogen−methane storage and separation at 293 K. SWNTs with pore diameters greater than 24.4 Å (i.e.,[18,18]) are less efficient for both on-board vehicle energy storage and separation of hydrogen−methanemixture at 293 K with pressures up to 12 MPa. SWNTs comprised of cylindrical pores of 8.2 and 6.8 Å indiameter (equivalent chiral vector [6,6] and [5,5], respectively) are the most promising for separation of thehydrogen−methane mixture at room temperature, with the former selectively adsorbing methane and thelatter selectively adsorbing hydrogen. We observed that inside the pores of [6,6] nanotubes absorbed methaneforms a quasi-one-dimensional crystal when the system has thermalized. The average intermolecular distanceof such a crystal is smaller than the one of liquid methane in bulk at 111.5 K, therefore exhibiting the quasi-one-dimensional system clear compression characteristics. On the other hand, for a smaller nanotube diameterof 6.8 Å the hydrogen can enter into the tubes and methane remaining in bulk. We found that in the interiorof [5,5] nanotubes adsorbed/compressed hydrogen forms a quasi-one-dimensional crystal.
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