ADSORPTION OF CO2 AND XENON BY POROUS-GLASS OVER A WIDE-RANGE OF TEMPERATURE AND PRESSURE - APPLICABILITY OF THE LANGMUIR CASE-VI EQUATION

Data on the adsorption of CO2 and Xe by Vycor porous glass have been analyzed in terms of Langmuir's case VI equation. Measurements over a wide range of temperature and pressure enable a thermodynamic analysis to be made which identifies the parameters of the equation with those postulated in its theoretical derivation. The monolayer capacities in both instances are independent of temperature over a range of 100 K. The curves of isosteric enthalpy against coverage can be accounted for quantitatively in terms of the shift from monolayer to multilayer adsorption as the pressure is increased, and for the two adsorptives the curves can be correlated by a corresponding states procedure. The enthalpy and entropy curves show that the grounds on which case VI has been rejected in the past are false. A striking empirical relation is found between one of the parameters of the equation and the molar volume of the bulk liquid.