Pore-Environment Engineering of Pillared Metal–Organic Frameworks for Boosting the Removal of Acetylene from Ethylene
Zhengdong Guo, Lifeng Yang, Yijian Li, Jiyu Cui, Xiaofei Lü, Liyuan Chen, Xian Suo, Xili Cui, Huabin Xing
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 .