Influences of channel morphology and Brønsted acidity on ETS-10, ZSM-5, and SSZ-13 for xenon and krypton separation

Abstract

Developing an efficient and economical technology to separate radioactive gas from used nuclear fuel is crucial for preventing nuclear pollution and the recycle of Xe and Kr. In this study, ETS-10, ZSM-5, and SSZ-13 zeolites were selected to investigate the effects of channel morphology and the Brønsted acidity for noble gas separation. The pore structures of as-synthetic zeolites were characterized by N2 physisorption, XRD, SEM, TG, and FT-IR analyses. The Adsorption isotherms revealed that the maximum adsorption amounts of Xe and Kr (mmol g−1) followed the sequence of ZSM-5 (Xe: 1.69, Kr: 0.72) > ETS-10 (Xe: 1.61, Kr: 0.66) > SSZ-13 (Xe: 1.55, Kr: 0.53), reaching the advance of most reported porous materials. ZSM-5 exhibited excellent Henry’s selectivity of Xe/Kr at 14.8, better than ETS-10 (12.8) and SSZ-13 (9.7), owing to its higher Qst(Xe-Kr) energy gaps resulting from its stronger coordination defects and stronger Brønsted acidity associating with the Debye force interactions. An extremely high Xe/Kr selectivity at 56 for ZSM-5 below 10 kPa through IAST calculation (Xe: Kr = 20:80) was observed, insuring efficient Xe separation from the used radioactive gas. In addition, ZSM-5 also possessed remarkable Xe/N2, Xe/O2, and Xe/Ar selectivities of more than 60 from Henry’s selectivity, and more than 160 below 10 kPa from IAST selectivity (Xe/N2, Xe/O2, and Xe/Ar = 1:99), further ensuring the efficient Xe capture from cryogenic air separation. The experimental results revealed that the abundant coordination defects and the strong Brønsted acidity contributing to the Debye force interactions were essential for Xe or Kr separation.