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

Physisorption-driven removal of acetylene (C2H2) from ethylene (C2H4) is a promising pathway to produce polymer-grade C2H4. However, advances have been constrained by the compromise needed between selectivity and adsorption capacity. Herein, physisorption-mediated separation of trace C2H2 from C2H4 was carefully examined over pillared metal–organic frameworks (MOFs) through a combination of experiments and theoretical calculations, disclosing that concurrent enhancement of C2H2 uptake capacity and selectivity under low C2H2 pressure conditions was observed due to pore-environment engineering of MOFs. Compared to its counterparts including −H and −NH2, the −CH3-functionalized MOF, named ZU-901, could achieve the highest separation performance, delivering a C2H2 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 C2H2 and C2H4 with a volumetric ratio of 1:99 (1% C2H2/99% C2H4 (V/V)) at 298 K. Their efficiency for C2H2/C2H4 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% C2H2/99% C2H4 (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 C2H2 via the synergetic effect of O···H(HC≡) and H(H2pzdc, −CH3)···C(C≡) interactions between C2H2 molecules and frameworks. This work presents an example of pore-environment optimization to break the selectivity-capacity trade-off toward the purification of C2H4 by the removal of C2H2.