ON THE THERMODYNAMIC FACTORS GOVERNING THE ADSORPTION OF P-XYLENE AND M-XYLENE ONTO FAUJASITE ZEOLITE CONTAINING NA+ AND K+ CATIONS

A partly hydrated faujasite zeolite can selectively adsorb p- or m-xylene from a mixture of both isomers according to the nature of its cations (Na+ or K+). Microcalorimetric and Raman laser spectroscopic studies of the adsorption interactions enable us to explain the observed selectivity. The Na+ faujasite selectivity for m-xylene is due to the difference in enthalpy of adsorption in favor of m-xylene which is not compensated by the difference in entropy of adsorption, the latter in favor of p-xylene. With K+ faujasite the difference in enthalpy of adsorption is not great enough and it is now the difference in entropy of adsorption, always favoring p-xylene, which determines the selectivity. © 1980 by Academic Press, Inc.