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

Abstract

A highpressure volumetric gas adsorption system Rev. Sci. Instrum. 62, 2186 (1991; 10.1063/1.1142336 Apparatus for creep rupture testing in highpressure hydrogen at elevated temperatures Rev. Sci. Instrum. 53, 86 (1982); 10.1063/1.1136822 Isothermal, isobaric, elevated temperature, highpressure, flow calorimeter Rev. Sci. Instrum. 52, 1226 (1981);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.

Study of a Fluid/Solid Interface over a Wide Density Range Including the Critical Region. I. Surface Excess of Ethylene/Graphite

“…Physical adsorption of gases near their critical region has been investigated previously by other authors but these studies were made o n ill-defined surfaces like fused silica [ 5 ] , silica gel, alumina [6], or on highly porous solids like activated carbon and molecular sieving carbon [7]. In these cases adsorption is mainly a process of pore-filling and depends mainly on the pore size distribution of the adsorbent.…”

Thermodynamic Properties of the Adsorbate for High-Pressure Multilayer Adsorption

“…Unless one can measure the adsorbed phase volume, it is impossible to know the amount of buoyancy correction. Only series perturbation gas chromatography (Hori and Kobayashi, 1971; Masukawa and Kobayashi, 1968) can yield the value of V so that the experimental value of the absolute adsorption can be determined. The value of Cg is small at low pressures, and VCE is negligible in eq 1.…”

“…^Xdsorption at high pressure has been reported (Hori and Kobayashi, 1971) in terms of two definitions: absolute adsorption and Gibbs adsorption. The adsorbed phase volume is determined by the surface area of the adsorbent and the intermolecular forces between the adsorbate and the adsorbent.…”

Chromatographic Study of Mixed Gas Adsorption by the Step and Pulse Method

“…By measuring the retention time as a function of the concentration of the vapor in the mobile phase the whole adsorption isotherm can be determined [2,3].…”