CO2 Capture with NaX Zeolite

Cation exchanged zeolites are of potential use in pressure swing adsorption (PSA) technologies for CO2 capture applications. Published experimental data for CO2/CH4, CO2/N2, and CO2/C3H8 mixture adsorption in NaX zeolite, also commonly referred to by its trade name 13X, have demonstrated that the Ideal Adsorbed Solution Theory (IAST) fails to provide adequately accurate estimates of mixture adsorption equilibrium. In particular, the IAST estimates of CO2/CH4 and CO2/N2 selectivities are significantly higher than those realized in experiments.
The experimental data of CO2 capture from humid gases in CALF-20 also indicate strong deviations from the IAST.
In this presentation, Configurational-Bias Monte Carlo (CBMC) simulations are employed to provide confirmation of the observed thermodynamic non-idealities in adsorption of CO2/CH4, CO2/N2, mixtures in NaX zeolite. The CBMC simulations provide valuable insights into the root cause of the failure of the IAST, whose applicability mandates a homogeneous distribution of adsorbates within the pore landscape. By sampling 100000 equilibrated spatial locations of individual guest molecules within the cages of NaX zeolite, the radial distribution functions (RDF) of each of the pairs of guest molecules are determined. Examination of the RDFs clearly reveals congregation effects wherein the CO2 guests occupy positions in close proximity of the Na+ cations. The positioning of the partner molecules (CH4, N2) is further removed from the CO2 guest molecules; consequently, the competition in mixture adsorption faced by the partner molecules is less severe than that anticipated by the IAST. The important message to emerge from this article is the need for quantification of thermodynamic non-ideality effects in mixture adsorption.
For theoretical background consult:
Krishna, R.; Van Baten, J. M. How Reliable is the Ideal Adsorbed Solution Theory for Estimation of Mixture Separation Selectivities in Microporous Crystalline Adsorbents? ACS Omega 2021, 6, 15499-15513. doi.org/10.102....
R. Krishna, J.M. Van Baten, Using Molecular Simulations for Elucidation of Thermodynamic Non-Idealities in Adsorption of CO2-containing Mixtures in NaX Zeolite, ACS Omega 5 (2020) 20535-20542. doi.org/10.102...
Watch also presentations: Adsorption vs Diffusion in FAU Zeolite, The IAST for Mixture Adsorption, The RAST for Mixture Adsorption Equilibrium on my UA-cam channel www.youtube.co...

[@ladyalexander2003]

Trees are fantastic at removing CO2 from the atmosphere and giving us back oxygen to breathe! 🤷‍♀️