Study of the Kinetics of Adsorption and Desorption of Water Vapor on Low-Silica Zeolites

Granular LTA and SOD zeolites have been synthesized, characterized, and further used to study the kinetics of water adsorption and desorption. It has been shown that LTA zeolite in a static mode provides adsorption of water vapor at the level of ~30 wt % for LTA and ~20 wt % for SOD. It has been found that during water adsorption from the gas phase on the LTA or SOD zeolite in a flow-through unit, the dew point reaches –50 or –9°С, respectively. The kinetics of adsorption of water vapor on zeolite granules has been studied; the values of apparent activation energy of the adsorption process have been calculated, which amount to about 50 kJ mol–1; and the rate order of the process has been determined (0.2 for LTA and 0.9 for SOD). The apparent activation energies for water desorption from the zeolites have been calculated by isoconversional analysis in terms of the Friedman, Ozawa–Flynn–Wall, and Kissinger–Akahira–Sunose models. It has been shown that all three models give similar results. It has been found that at given degree of conversion, the activation energies are not higher than 60 kJ mol–1, a value that corresponds to desorption of physically bound water. The increase in activation energy to 110 kJ mol–1 (for SOD) or 80 kJ mol–1 (for LTA) is associated with the removal of water from the α- and β-cages of zeolites.