Inverse CO<sub>2</sub>/C<sub>2</sub>H<sub>2</sub> Separation with MFU‐4 and Selectivity Reversal via Postsynthetic Ligand Exchange
Qiao Liu, Sung Gu Cho, Jordon S. Hilliard, Ting‐Yuan Wang, Szu‐Chia Chien, Li‐Chiang Lin, Anne C. Co, Casey R. Wade
Abstract
Abstract Although many porous materials, including metal–organic frameworks (MOFs), have been reported to selectively adsorb C 2 H 2 in C 2 H 2 /CO 2 separation processes, CO 2 ‐selective sorbents are much less common. Here, we report the remarkable performance of MFU‐4 (Zn 5 Cl 4 (bbta) 3 , bbta=benzo‐1,2,4,5‐bistriazolate) toward inverse CO 2 /C 2 H 2 separation. The MOF facilitates kinetic separation of CO 2 from C 2 H 2 , enabling the generation of high purity C 2 H 2 (>98 %) with good productivity in dynamic breakthrough experiments. Adsorption kinetics measurements and computational studies show C 2 H 2 is excluded from MFU‐4 by narrow pore windows formed by Zn−Cl groups. Postsynthetic F − /Cl − ligand exchange was used to synthesize an analogue ( MFU‐4‐F ) with expanded pore apertures, resulting in equilibrium C 2 H 2 /CO 2 separation with reversed selectivity compared to MFU‐4 . MFU‐4‐F also exhibits a remarkably high C 2 H 2 adsorption capacity (6.7 mmol g −1 ), allowing fuel grade C 2 H 2 (98 % purity) to be harvested from C 2 H 2 /CO 2 mixtures by room temperature desorption.