Adsorption Kinetics of CO2 ,O 2 ,N 2, and CH4 in Cation-Exchanged Clinoptilolite

The rate of adsorption of pure CO2 ,O 2 ,N 2, and CH4 on natural untreated clinoptilolite-rich volcanic tuff (Cp) from Tehuacan (Puebla, Mexico), and on cation-exchanged clinoptilolite samples (Ca-Cp, K-Cp, and Na-Cp) has been measured at 20 °C using a glass high-vacuum volumetric apparatus. The X-ray diffraction pattern of Cp showed that the main crystalline phases correspond to clinoptilolite-heulandite and minor amounts of mordenite, cristobalite, feldspar (albite), quartz, smectite, and opal. The adsorption rates of gases in the initial period (t K-Cp > Cp > Na-Cp, and the affinity decreased in the order CO2 . N2 > O2 > CH4, whereas at equilibrium (t f ∞ s) the adsorption uptake decreased in the sequence CO2 . CH4 > N2 > O2. The slow adsorption of methane in Na-Cp was probably due to diffusional difficulties as a result of channel blockage by Na + cations. By cation exchange of Cp an adsorbent can be tailored for the separation of N 2/O2 ,N 2/CH4, and CO2/CH4 mixtures.