Buoyancy effect correction on high pressure pure gas adsorption gravimetric measurements

In this paper, we present a theoretical treatment which makes possible the calculation of real adsorption isotherms from the corresponding excess adsorption data obtained by experimental means. We studied the adsorption of N₂, CH₄, Ar, C₃H₈ and n-C ₄H₁₀ on an activated carbon (F30/470 - Chemviron Carbon) for pressures ranging from 0 to 10 000 kPa and temperatures ranging from 303 to 383 K. For subcritical temperatures, the maximum pressure was the saturation pressure at the isotherm temperature. The correction method is based on the potential theory adapted for high pressure and high temperature conditions. It is based on a Dubinin-Radushkevich treatment of the excess adsorption data in the low pressure area. The Dubinin-Radushkevich model was adapted so that it may be used both for subcritical and supercritical conditions. As a consequence, the treatment procedure can be used in a wide temperature range and does not require any assumption on the adsorbed phase density. This study has shown that the buoyancy effect on the adsorbed phase could be neglected for subcritical conditions but could be quite important for high pressure supercritical conditions.