Pore-Environment Engineering of Pillared Metal–Organic Frameworks for Boosting the Removal of Acetylene from Ethylene

Abstract

Physisorption-driven removal of acetylene (C 2 H 2 ) from ethylene (C 2 H 4 ) is a promising pathway to produce polymer-grade C 2 H 4 . However, advances have been constrained by the compromise needed between selectivity and adsorption capacity. Herein, physisorption-mediated separation of trace C 2 H 2 from C 2 H 4 was carefully examined over pillared metal–organic frameworks (MOFs) through a combination of experiments and theoretical calculations, disclosing that concurrent enhancement of C 2 H 2 uptake capacity and selectivity under low C 2 H 2 pressure conditions was observed due to pore-environment engineering of MOFs. Compared to its counterparts including −H and −NH 2, the −CH 3 -functionalized MOF, named ZU-901, could achieve the highest separation performance, delivering a C 2 H 2 uptake capacity of 0.57 mmol·g –1 at 0.01 bar and an ideal adsorbed solution theory selectivity of ca. 83 for a mixture of C 2 H 2 and C 2 H 4 with a volumetric ratio of 1:99 (1% C 2 H 2 /99% C 2 H 4 (V/V)) at 298 K. Their efficiency for C 2 H 2 /C 2 H 4 separation, especially in the low-pressure range, was demonstrated by dynamical breakthrough experiments, where the breakthrough time reached 220 min·g –1 under a 1% C 2 H 2 /99% C 2 H 4 (V/V) flow rate of 2 mL min –1 . Theoretical calculations pointed out that ZU-901 with ligand functionalization has the optimized pore environment and aperture size, boosting the selectively accommodated C 2 H 2 via the synergetic effect of O···H(HC≡) and H(H 2 pzdc, −CH 3 )···C(C≡) interactions between C 2 H 2 molecules and frameworks. This work presents an example of pore-environment optimization to break the selectivity-capacity trade-off toward the purification of C 2 H 4 by the removal of C 2 H 2 .