Ultradeep Removal of Moisture in Gases to Parts-per-Billion Levels: The Exploration of Adsorbents

Owing to the rigid standards of manufacturing semiconductor components, decrease of the moisture to parts-per-billion (ppb), at a global level, is always vital but extremely nerve-racking in the production of high-purity gases. Herein, typical adsorbents including oxides (SiO₂ and γ-Al₂O₃), zeolites (4A and NaX), and metal-organic frameworks (MOFs; HKUST-1, UiO-66, and ZIF-8) are investigated with respect to the abilities of ultradeep dewatering from N₂. Compared with other adsorbents, NaX performs much better on both dewatering efficiency (DE, from 2750 to 66 ppb) and the adsorption capacity (AC, 1.55 × 10⁴ L N₂·g^-1). Moreover, it is for the first time experimentally and theoretically proved that the dewatering ability of X zeolite mainly depends on its cation species (Na⁺, Li⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺, Sr²⁺, or Ba²⁺), the forces between the zeolite and H₂O, and the number of H₂O molecules per cell of the zeolite. CaX thus shows a fascinating DE from 2750 to 33 ppb, a huge AC of 9.08 × 10⁴ L N₂·g^-1, and an ideal reusability, compared with results of the scarce contributions reported to date.