Adsorption Equilibria of Light Organics on Single-Walled Carbon Nanotube Heterogeneous Bundles: Thermodynamical Aspects

Abstract

Single-component adsorption equilibria of five different hydrocarbons (CH4, C2H6, C2H4, C3H8, and C3H6) on a high-purity sample of single-walled carbon nanotube heterogeneous bundles were measured using a static gravimetric method. The physicochemical properties and morphology of the bundles were thoroughly characterized to obtain information about the tube diameter distribution; the latter is shown to be well approximated by a Gaussian function with a mean diameter of 14.1 ± 1.4 A. The adsorption measurements were performed at room temperature (T ≈ 300 K) and pressures from 2 × 10−3 up to 80 bar corresponding to reduced temperatures, T/Tc, from 0.81 to 1.59 and relative pressures, p/p0, in the range 1.4 × 10−5 to 0.89, where Tc and p0 are, respectively, the critical temperature and saturation vapor pressure of the adsorptive fluid. The excess adsorption isotherms exhibit an overall type-II shape, except that of supercritical CH4 which is type-I; none of the isotherms yield a hysteresis loop at the studie...