High-Pressure Adsorption: The Adsorption of Methane on Porasil at Low Temperatures and Elevated Pressures by Gas Chromatography

The adsorption of methane on fused silica beads has been studied by gas chromatography from 5 to 120 atm for − 91.9 to 31.4°C. Only a few investigations of adsorption at high pressure have been reported due to the severe experimental difficulties. The “Hypothetical Perfect Gas” perturbation technique has been revised for application at high pressure to obtain the free gas volume. Two modifications in analysis are required: one for the steric effect of the perturbation gas and the second for the adsorption of the perturbation gas on the adsorbed phase. A second method of calculation based on solubility theory has been developed to correct for the solution of the perturbation gas in the adsorbed phase at high pressures. In addition to the usually measured differential or Gibbs adsorption, the gas chromatographic technique yields the absolute or total adsorption. This distinction is not observable at low pressures. A region of constant absolute adsorption in isotherms with increasing pressure was observed above the critical temperature of methane corresponding to a practically constant gas-phase fugacity. Application of limiting conditions to the measurements of Gibbs adsorption at high pressure gave the same value for the constant region of absolute adsorption isotherm, as well as the same value for the adsorbed phase density, which was evaluated from the dependence of the gas-phase volume upon the amount of absolute adsorption. This agreement substantiates the calculation method developed here.