Measurement and Prediction of the Heat of Adsorption and Equilibrium Concentration of CO 2 on Zeolite 13X

Adsorption isotherms are reported for pure carbon dioxide on zeolite 13X (also called zeolite NaX) pellets over a temperature range of 0 to 200 °C and a pressure range of 0.001 to 100 kPa. These pure-component equilibria are fit with Langmuir, Toth, two-site Langmuir, and three-site Langmuir models, both with and without temperature dependence being included in the saturation capacity. The agreement between fitted and measured isotherms is shown to increase with increasing number of available fitting parameters in the model, with the constant-saturation, two-site Langmuir isotherm providing the best balance between agreement with the measurements and model complexity. The isosteric heats of adsorption are measured across a temperature range from 10 to 200 °C using differential scanning calorimetry. The measured heats of adsorption decrease with increasing CO 2 loading but show little variation with temperature. The measurements are shown to agree with predicted heats of adsorption derived from the fitted Langmuir and Toth isotherms (via the Clausius–Clapeyron equation); the heats of adsorption predicted using the more complex multisite Langmuir models suffer from nonphysical artifacts.