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 bee n measured at 20 degreesC using a glass high-vacuum volumetric apparatus. T he X-ray diffraction pattern of Cp showed that the main crystalline phases correspond to clinoptilolite-heulandite and minor amounts of mordenite, cri stobalite, feldspar (albite), quartz, smectite, and opal. The adsorption ra tes of gases in the initial period (t < 180 s) were measured with a custom acquisition data card capable of registering pressure and time data five ti mes per second, simultaneously. The influence of cation exchange on adsorpt ion kinetics of the gases depended on the gas-adsorbent contact time (t). I n the initial period, the adsorption rate of all gases on all samples decre ased in the order Ca-Cp > K-Cp > Cp > Na-Cp, and the affinity decreased in the order CO2 much greater than N-2 > O-2 > CH4, whereas at equilibrium (t --> infinity s) the adsorption uptake decreased in the sequence CO2 much gr eater than CH4 > N-2 > O-2. The slow adsorption of methane in Na-Cp was pro bably 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 se paration of N-2/O-2, N-2/CH4, and CO2/CH4 mixtures.