Impedance spectroscopic measurements of pure gas adsorption equilibria on zeolites

Abstract

Physisorption equilibria of gases on inert porous solids like activated carbon or molecular sieves can be characterized by measuring the (frequency dependent) capacitance of a capacitor filled with a sample adsorbent. This quantity strongly depends not only on the physico-chemical structure of the empty adsorbent in vacuum, but also on the permanent or induced dipole moments of the molecules adsorbed and of the fluid phase. Consequently, it should be possible to determine the excess mass being adsorbed on the internal surface of a highly porous solid by measurements of the dielectric constant. The aim of this work is to show for various pure gases and adsorbents that the change of the capacitance of an adsorption system depends on the adsorbed mass. Therefore, this effect can be used to characterize porous solids and their adsorbates and, for example, to check the state or the quality of industrial adsorbents during a process on site if calibration measurements have been taken.