Shaped natural and synthetic zeolites for CO2 capture in a wide temperature range

The CO2 adsorption performances of a Linde-Type A (LTA) zeolite and a natural Clinoptilolite (Clino) zeolite, both in shaped form, were investigated as such or after an ion-exchange procedure and compared to assess their potential application as solid adsorbents for Carbon Capture and Storage (CCS). The samples were characterized following a multi-technique approach. Their structural and textural properties were evaluated to investigate the accessibility of the different ions present inside the microporous structure and the strength of their interaction with the adsorbates. The CO2 adsorption tests were carried out performing pure CO2 adsorption/desorption isotherms and dynamic breakthrough measurements in a wide range of temperature (298-423 K). The ion -exchange enhanced the adsorption capacity of the synthetic zeolite, while no significant increment in the CO2 adsorption performances is observed for the natural one. Nonetheless, the CO2 adsorption reversibility is affected by the cation exchange process in both synthetic and natural zeolites. The CO2 adsorption capacities of LTA zeolites are higher at lower temperatures, whereas the CO2 adsorption performances of natural Clino are interesting also at medium-high temperature, being the most performant material at 423 K. By performing IR experiments with specific probe molecules, the presence of a consistent number of Fe2+ ions in the framework of natural Clino, responsible for the capacity of this material to strongly interact with CO2 also at medium-high temperatures, was proved. The peculiar adsorption behavior of natural Clino, its low cost and availability in shaped form are some of the essential features for its possible implementation in real CCS technologies.