Selective separation of CO2 is becoming one of the key technologies in the (petro-) chemical industry. This study focuses on the adsorption and separation of CO2 from CH4 on a new low-silica (LS) type of the eight-membered ring KFI zeolite. A series of alkali (Li, Na, K) and alkaline-earth (Mg, Ca, Sr) exchanged samples of the new LS KFI were synthesized and characterized. LS Li-KFI showed the largest pore volume, whereas LS Na-KFI and LS K-KFI were inaccessible for Argon at 87 K. Adsorption of CO2 at 303 K demonstrated the dominant quadrupolar interaction on alkali-exchanged LS KFI samples. LS Li-KFI showed the largest capacities upon high pressure isotherm measurements of CO2 (4.8 mmol/g), CH4 (2.6 mmol/g), and N2 (2.2 mmol/g) up to 40 bar at 303 K. The performance of the new LS KFI was compared to a KFI sample (ZK-5) with a higher Si/Al ratio. Isotherm measurements and dynamic breakthrough experiments demonstrated that ZK-5 samples show larger working capacities for CO2/CH4 separations at low pressure. Li-ZK-5 and Na-ZK-5 show the highest capacities and high selectivities (similar to benchmark 13X).

This study investigates the potential of the well-known metal− organic framework (MOF) Mg-MOF-74 for low-pressure CO 2 separations under dynamic conditions. We developed a technique to make pellets of Mg-MOF-74 without large capacity loss and measured CO 2 and CH 4 isotherms on these pellets up to 40 bar in the temperature range of 293−338 K. Dynamic breakthrough separation experiments with mixtures of CO 2 and CH 4 on a column packed with Mg-MOF-74 pellets at 308 K and 1 bar indicated a higher CO 2 capacity and separation efficiency for the MOF with respect to the benchmark 13X zeolite. The MOF regains 81% of its original capacity when purging with helium at 308 K during 10 min and can be fully regenerated at 353 K, which indicates the facile desorption of CO 2 on this material. However, the performance of Mg-MOF-74 severely deteriorates upon long-term exposure to relevant impurities in CO 2 separations at low pressures such as water and oxygen.

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Kinetic separation of CO2from CH4over rubidium or cesium-exchanged ZK-5 (KFI) zeolites for upgrade of biogas to renewable fuels.