Supercritical Fluid Adsorption to Weakly Attractive Solids: Universal Scaling Laws

Adsorption of light hydrocarbons (C1–C3) confined in the pores of silica aerogel (nominal density 0.2 g/cm3) was studied experimentally and by computer simulation. Five isotherms of ethane (25.0, 32.0, 32.3, 33.0, and 35.0 °C) were obtained over a temperature range including the critical temperature of the bulk fluid (Tc = 32.18 °C) to ∼220 bar by the vibrating tube densimetry (VTD) method, which yields unique information impossible to obtain by excess sorption measurements. Two isotherms (35 and 50 °C) of methane adsorption in SiO2 aerogel were measured far above its critical temperature, Tc = −82.59 °C, at 0–150 bar using a gravimetric method. The experimental pore fluid properties of methane, ethane, propane, and CO2 (obtained earlier by VTD for the same SiO2 aerogel sample) show behavior conforming to the principle of corresponding states over the entire covered reduced temperature ranges from Tr = 0.976 to Tr = 1.696. The magnitudes of the excess adsorption maxima and the reduced fluid densities wher...