Radiation-Resistant Kr-Selective MOF With Record Kr/Xe Selectivity at Elevated Pressure

Area of Science:

• Materials Science
• Chemical Engineering
• Nuclear Engineering

Background:

• Separating krypton (Kr) and xenon (Xe) from spent nuclear fuel off-gas is essential but challenging due to co-adsorption issues with current materials at high pressures.
• Industrial pressure swing adsorption (PSA) processes are hindered by the limited performance of existing adsorbents for Kr/Xe separation.

Purpose of the Study:

• To engineer and evaluate a metal-organic framework (MOF), CALF-20M-w, for efficient molecular sieving separation of Kr/Xe under industrial pressure conditions.
• To demonstrate the material's capability for high-purity xenon (Xe) recovery and radioactive Kr removal from nuclear fuel reprocessing streams.

Main Methods:

• Utilized a metal-organic framework, CALF-20M-w, with a specific pore size (3.7 Å) tailored for Kr/Xe kinetic diameter differences.
• Employed GCMC simulations to understand gas adsorption mechanisms and steric exclusion effects.
• Conducted dynamic breakthrough separation experiments and PSA simulations to assess performance.

Main Results:

• CALF-20M-w achieved a record Kr/Xe uptake ratio of 52.2 and selectivity of 4424 at 195 K and 5 bar.
• GCMC simulations confirmed steric exclusion of Xe in CALF-20M-w channels within the 1-30 bar pressure range.
• Dynamic experiments yielded >99.9% pure Xe, demonstrating effective Kr removal.
• CALF-20M-w exhibited superior radiation resistance compared to benchmark materials like UiO-66 and ZIF-8.

Conclusions:

• CALF-20M-w establishes new benchmarks for high-pressure Kr/Xe molecular sieving, surpassing existing materials.
• The MOF's performance and radiation stability make it a highly promising candidate for nuclear waste management and rare gas purification.
• This engineered MOF offers a viable solution for radioactive Kr removal from spent nuclear fuel off-gases.