Adsorption Kinetics-Driven Humidity-Resistant C₂H₂/CO₂ Separation by a Hydrophilic Metal–Organic Framework

The separation of C 2 H 2 /CO 2 under highly humid conditions by using metal–organic frameworks (MOFs) is extremely challenging because water vapor would reduce the C 2 H 2 adsorption capacity or even degrade the structure of MOFs. In this work, a zirconium zeolitic metal–organic framework ( NNM-5 ) with a small aperture and large cavities exhibits commendable C 2 H 2 /CO 2 selectivity (16.6 at 298 K and 1 bar) and a high uptake ratio (3.13 at 298 K and 1 bar). More importantly, NNM-5 could maintain at least five breakthrough cycles under highly humid conditions (around 100% RH) without performance degradation compared to that under dry conditions. Our studies indicate that the kinetic mechanism is the key to excellent separation performance under highly humid conditions based on the fact that the material is hydrophilic with a high water uptake, but the diffusion rate of H 2 O is 2 orders slower than that of C 2 H 2 and CO 2 in NNM-5 .