Selective Ethane/Ethylene Separation in a Robust Microporous Hydrogen-Bonded Organic Framework.

The separation of ethane (C ₂ H ₆ ) from ethylene (C ₂ H ₄ ) is of prime importance in the production of polymer-grade C ₂ H ₄ for industrial manufacturing. It is very challenging and still remains unexploited to fully realize efficient C ₂ H ₆ /C ₂ H ₄ separation in the emerging hydrogen-bonded organic frameworks (HOFs) due to the weak nature of hydrogen bonds. We herein report the benchmark example of a novel ultrarobust HOF adsorbent (termed as HOF-76a) with a Brunauer-Emmett-Teller surface area exceeding 1100 m ² g ^-1 , exhibiting the preferential binding of C ₂ H ₆ over C ₂ H ₄ and thus highly selective separation of C ₂ H ₆ /C ₂ H ₄ . Theoretical calculations indicate the key role of the nonpolar surface and the suitable triangular channel-like pores in HOF-76a to sterically "match" better with the nonplanar C ₂ H ₆ molecule than the planar C ₂ H ₄ , thus affording overall stronger multipoint van der Waals interactions with C ₂ H ₆ . The exceptional separation performance of HOF-76a for C ₂ H ₆ /C ₂ H ₄ separation was clearly demonstrated by gas adsorption isotherms, ideal adsorbed solution theory calculations, and simulated and experimental breakthrough curves. Breakthrough experiments on HOF-76a reveal that polymer-grade ethylene gas can be straightforwardly produced from 50/50 (v/v) C ₂ H ₆ /C ₂ H ₄ mixtures during the first adsorption cycle with a high productivity of 7.2 L/kg at 298 K and 1.01 bar and 18.8 L/kg at 298 K and 5.0 bar, respectively.