A Porous Coordination Polymer with an Interdigitated Structure for Enhanced Inverse Separation of C ₂ H ₆ and C ₂ H ₄

Ethylene (C₂H₄) is primarily produced for polyethylene manufacturing, where trace amounts of ethane (C₂H₆) impurities can seriously affect the ethylene polymerization process. However, due to the similar molecular size and physical properties of ethane and ethylene, it is extremely challenging to deeply remove low-concentration ethane impurities from ethylene. Herein, a new coordination polymer with an interdigitated framework, termed [Cu(4-OH-ipa)(bpa)] (CID-32), was synthesized specifically for the inverse separation of C₂H₆/C₂H₄. CID-32 possesses 1D narrow corrugated channels, and its large microporous cavities and narrow pore windows may enhance its discrimination between ethane and ethylene. Experimental results demonstrate that CID-32 exhibits a stronger affinity for ethane over ethylene, and its separation selectivity of C₂H₆/C₂H₄ (50/50, v/v) is 3.47 at 298 K and 0.1 bar. Breakthrough experiments further confirmed the excellent C₂H₆/C₂H₄ separation performance of CID-32. Molecular simulations revealed that ethane tends to be adsorbed near the CID layers, and the C-H···π interactions between ethane and the framework are stronger than those of ethylene, which is consistent with the preferential adsorption behavior of ethane in CID-32. The tunable dipyridyl-like ligands and carboxylic layers in CIDs may provide the possibility for designing new adsorbents with different microporous environments and enhanced C₂H₆/C₂H₄ separation performance.