Abstract: Model isotherms are derived considering a two site hypothesis, one for the alpha cage [or large cage], and one for the beta cage. Two simple model isotherms, one a dual site Toth isotherm and one a dual site Langmuir isotherm are fitted to the data using the optimization package Solver in EXCEL. Both dual site Toth or Langmuir isotherm models fit the data satisfactorily.

The optimized standard enthalpy and entropy of adsorption parameters are surprising for the beta cage, The enthalpy of the beta cage is 1/3rd of that observed calorimetrically, and the standard entropy of adsorption is positive, a physical impossibility. Substituting the calorimetric enthalpy of adsorption corrected the standard differential entropy of sorption values resulting in these values varying significantly with temperature. This variation is postulated to be due to the formation of clusters of water.

KEYWORDS: Adsorption, water, 3A, 4A, 5A or 13X zeolite, Langmuir isotherm, Toth isotherm, dual site isotherms, standard enthalpy of adsorption, standard entropy of adsorption, solver in EXCEL.