Two isostructural pillar-layered metal-organic frameworks with hydrophobic properties for efficient C2H6/C2H4 separation under humid conditions

The development of ethane (C 2 H 6 )-selective porous materials for the direct production of polymer-grade ethylene (C 2 H 4 ) from a C 2 H 6 /C 2 H 4 mixture in a single energy-efficient adsorption step is of crucial importance. However, it remains a considerable challenge, particularly due to the potential detrimental effect of moisture impurities on material performance. Hence, there is an urgent need to design durable hydrophobic C 2 H 6 -selective adsorbents suitable for industrial applications. In this study, two isostructural ultramicroporous metal–organic frameworks (M−BTTB−BPY) featuring fsc topology and two-fold interpenetrated structures were synthesized via a pillar-layered method using tetradentate carboxylic ligands along with bipyridine and Zn(II) or Co(II) ions. Both frameworks demonstrated remarkable water stability, with pore environments enriched by low-polarity aromatic groups that facilitated strong interactions with C 2 H 6 molecules. Experimental adsorption isotherms further revealed excellent separation efficiency for the C 2 H 6 /C 2 H 4 gas mixture, attributed to the unique C 2 H 6 uptake capacity of Zn-BTTB-BPY (3.1 mmol/g) and a high C 2 H 6 /C 2 H 4 selectivity of 2.3 at 298 K and 1 bar. Furthermore, GCMC and DFT calculations indicated that the cooperative van der Waals interactions between the MOFs and C 2 H 6 enhanced the efficient separation of the C 2 H 6 -C 2 H 4 mixture. Notably, both MOFs exhibited significant hydrophobicity with minimal water adsorption, enabling them to effectively produce polymer-grade C 2 H 4 (≥99.9 %) directly from the C 2 H 6 /C 2 H 4 mixture, even under conditions of 100 % relative humidity.