Understanding competitive adsorption of water and trichloroethylene in a high-silica Y zeolite

In this study, the adsorption of trichloroethylene (TCE) and water was investigated on a hydrophobic Y zeolite with an Si to Al ratio of 80. Single adsorbate isotherms for water or TCE, and TCE isotherms under conditions of 100% relative humidity (RH) were measured over the temperature range from 5 to 47 °C. Water adsorption isotherms were well described by the Freundlich isotherm model with isotherm exponents of 1.5. Isosteric heats for water adsorption were less exothermic than the enthalpy for water condensation, and ranged from -34 to -39 kJ/mol. Entropy changes associated with water adsorption were less negative than those for condensation of bulk water, indicating that the adsorbed phase had less structure than bulk water. Type V isotherms were observed for TCE adsorption under conditions of 0% RH. Isosteric heats for TCE adsorption on the dry zeolite ranged from -40 to -56 kJ/mol, and showed regions where the heats of adsorption both increased and decreased with increasing TCE loading. The Henry's law asymptote for TCE adsorption on the dry zeolite was not experimentally accessible at the lowest vapor concentrations investigated. Type V isotherms with a linear region were observed for TCE adsorption under conditions of 100% RH. The isosteric heats for TCE adsorption on the wet zeolite depended strongly on the adsorbed phase concentration, and ranged from -35 to -64 kJ/mol. At adsorbed phase TCE concentrations below 0.01 g/g, the presence of water increased TCE uptake by the zeolite. However, at all other TCE loadings the presence of water decreased TCE adsorption by up to 83%.