High‐Pressure Molecular Sieving of High‐Humidity C2H4/C2H6 Mixture by a Hydrophobic Flexible Metal–Organic Framework

Molecular sieving is an ideal separation mechanism, but controlling pore size, restricting framework flexibility, and avoiding strong adsorption are all very challenging. Here, we report a flexible adsorbent showing molecular sieving at ambient temperature and high pressure, even under high humidity. While typical guest-induced transformations are observed, a high transition pressure of 16.6 atm is observed for C₂H₄ at 298 K because of very weak C₂H₄ adsorption (~16 kJ mol^-1). Also, C₂H₆ is completely excluded below the pore-opening pressure of 7.7 atm, giving single-component selectivity of ca. 300. Quantitative high-pressure column breakthrough experiments using 1 : 1 C₂H₄/C₂H₆ mixtures at 10 atm as input confirm molecular sieving with C₂H₄ adsorption of 0.73 mmol g^-1 or 32 cm³(STP) cm^-3 and negligible C₂H₆ adsorption of 0.001(2) mmol g^-1, and the adsorbent can be completely regenerated by inert gas purging. Furthermore, it is highly hydrophobic with negligible water adsorption, and the C₂H₄/C₂H₆ separation performance is unaffected at high humidity.