A Porous Coordination Polymer with an Interdigitated Structure for Enhanced Inverse Separation of C2H6 and C2H4

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.