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

Abstract

The separation of ethane (C₂H₆) from ethylene (C₂H₄) is of prime importance in the production of polymer-grade C₂H₄ for industrial manufacturing. It is very challenging and still remains unexploited to fully realize efficient C₂H₆/C₂H₄ 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 m² g^-1, exhibiting the preferential binding of C₂H₆ over C₂H₄ and thus highly selective separation of C₂H₆/C₂H₄. 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 C₂H₆ molecule than the planar C₂H₄, thus affording overall stronger multipoint van der Waals interactions with C₂H₆. The exceptional separation performance of HOF-76a for C₂H₆/C₂H₄ 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) C₂H₆/C₂H₄ 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.