InterPore2024

Dynamic separation of CO2 from N2 using alkali-metal forms of nanosized chabazite

16 May 2024, 14:50

15m

Oral Presentation (MS01) Porous Media for a Green World: Energy & Climate MS01

Speaker

Dr Sajjad Ghojavand (LCS, ENSICAEN)

Description

Due to the rising atmospheric concentration of CO2 from human activities, the separation of CO2 from N2, commonly referred to as flue gas, has become a crucial priority.[1] There are four prevalent technologies used for CO2 capture: (i) adsorption with amine-based solvents, (ii) adsorption by nanoporous solids, (iii) cryogenic distillation, and (iv) membrane separation. Zeolites, among the materials considered for CO2 adsorption, offer the advantage of being inorganic, non-toxic substances with high thermal stability and selectivity, which can be adjusted by their framework structure and chemical composition.[1] Moreover, recent findings indicate that zeolites exhibit flexible structures.[2] This flexibility in zeolites is observable as a response to the adsorption or desorption of guest molecules. It can manifest as changes in the zeolite lattice parameters (framework dynamics) or by the relocation of extra-framework cations within zeolite pores (extra-framework dynamics).[1,2] Traditional zeolites face diffusion limitations of guest molecules through their pore networks due to their typical existence as micron-sized polycrystalline powders.[3] To overcome these limitations, various methods have been developed to increase the surface area/volume ratio. Among these approaches, nanozeolites consisting of discrete nanoparticles that result in a greater external surface area and a higher number of available active sites.[3]
We have successfully demonstrated the outstanding CO2 capture capabilities of nanosized chabazite (CHA) zeolites in various alkali forms (Na+, K+, and Cs+).[1,3,4] In this study, we initially estimated CO2 and N2 equilibrium adsorption isotherms through Grand Canonical Monte Carlo (GCMC) calculations at 298 K. Subsequently, utilizing molecular dynamics simulations, we determined the self-diffusivities of CO2 molecules at different loadings for various CHA nanocrystals. The experimental validation of dynamic CO2/N2 separation was conducted through breakthrough measurements, simulating a 17/83 (CO2/N2) mixed-component gas mixture package at 298 K (molar basis).
Based on the breakthrough results, we obtained dynamic saturation CO2 loadings of 2.48, 1.72, and 0.57 mmol g-1 for Na-CHA, K-CHA, and Cs-CHA nanosized zeolites, respectively, with CO2/N2 molar selectivity at saturation of 62, 46, and 23. Comparing the nanosized (60 nm) Cs-CHA zeolite with its micron-sized (3 μm) counterpart, we observed significantly faster CO2 breakthrough kinetics for the nanosized Cs-CHA zeolite. Ultimately, this accelerated kinetic behavior led to a remarkable over 150% improvement in dynamic CO2 removal.
In summary, different alkali forms of nanosized CHA zeolites prove to be exceptional materials for effectively separating CO2 from N2.

Acknowledgments: The support of the Centre for Zeolites and Nanoporous Materials, Label of Excellence, Normandy Region (CLEAR). IRN Zeolites and TotalEnergies is acknowledged.