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

Abstract

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.