Superhydrophobic Molecular Selector for Efficient Separation of Ethane over Ethylene under Dry and Humid Conditions

Abstract

Exploring humidity-resistant, ethane-selective adsorbents for the one-step purification of polymer-grade (>99.95%) ethylene from ethane-ethylene mixtures is of great importance, yet remains a significant challenge. To address this challenge, we present a novel strategy for constructing a "superhydrophobic molecular selector" (SMS) based on a porous organic cage (POC), which features a superhydrophobic outer surface and an inner cavity with multiple ethane-selective functional sites. The resulting SMS-POC-1 demonstrates excellent C₂H₆ adsorption capacity (97 cm³ g^-1 at 298 K) and C₂H₆/C₂H₄ selectivity (<i>S</i>_ads = 2.40 at 298 K), offering a superior trade-off between ethane adsorption capacity and C₂H₆/C₂H₄ adsorption selectivity among all C₂H₆-selective adsorbents. Especially, breakthrough experiments demonstrate that SMS-POC-1 efficiently produces polymer-grade C₂H₄ from C₂H₆/C₂H₄ mixtures at 60% relative humidity (RH), making it the highest-selectivity adsorbent reported to date that can stably operate in a humid environment. The combination of experimental results and theoretical calculations reveals that the coexistence of a superhydrophobic outer surface and synergistic C-H···π interactions and hydrogen-bonding sites accounts for the high C₂H₆/C₂H₄ separation performance under humid conditions for SMS-POC-1. Our work thus not only demonstrates a general strategy for guiding the design of humidity-resistant adsorption-separation materials but also presents a promising candidate for potential applications in hydrocarbon separation.