Volumetric Adsorption Measurements of N2, CO2, CH4, and a CO2 + CH4 Mixture on a Natural Chabazite from (5 to 3000) kPa

We report here measured adsorption capacities for a natural chabazite zeolite at pressures ranging from (5 to 3000) kPa, at temperatures of (244 and 305) K, for pure N-2, CH4, and CO2, and for gas mixtures of CH4 + CO2. The pure gas data sets from this work and from the literature were in good agreement (10 %) and were regressed to Toth models over a wide range of pressure and temperature. We show that extrapolation of models that were fit only to low pressure data (below 120 kPa) can lead to a 30 % deviation in adsorption capacities predicted at high pressures. Similarly, models fit only to high pressure pure fluid data resulted in unreliable predictions for mixture adsorption capacities particularly when the component's partial pressure was low. The experimental results indicate that, while the chabazite is unlikely to be useful for N-2/CH4 separation, it may have potential for removing bulk CO2 from natural gas, particularly at low temperatures. A feed gas mixture of 0.95CH(4) + 0.05CO(2) placed in contact with the chabazite resulted in equilibrium vapor phases with CO2 mole fractions of about (0.0013 and 0.0002) at (305 and 244) K, respectively. The ideal adsorbed solution theory was used to successfully describe the observed mixture behavior, although it was found to be sensitive to the data range over which the pure fluid models were regressed.