Kinetic and thermodynamic study of n-pentane adsorption on activated carbons modified by either carbonization or impregnation with ammonium hydroxide

This study investigates the n-pentane adsorption performances on different activated carbons both as raw and modified by means of either chemical (amination with ammonium hydroxide) or thermal (carbonization at 1273 K) treatments. The raw, chemically and physically modified activated carbons were tested for n-pentane adsorption at 261 K in a volumetric apparatus. Maximum adsorption capacity values of 13, 11.7 and 9.1 μmol g−1 were obtained for the thermally, chemically and raw activated carbons, respectively, thus testifying the effectiveness of the treatment methods in improving the n-pentane adsorption capacity of the parent sorbent, due to an increase in the content of both acidic and basic functional groups. On the other hand, at low n-pentane partial pressures the volume of ultramicropores appears the ruling faction in determining a higher sorbent capture capacity. Kinetic adsorption data were successfully modelled according to the fractal-like Vermeulen model, and the outcomes suggested a more marked time-dependence of the intraparticle diffusivity for the chemically treated sample, likely related to a greater surface heterogeneity of this sample. Immersion enthalpy data also suggested that weaker adsorbate-adsorbent interactions promote a faster diffusion process.