Highly Efficient Propyne/Propylene Separation in a "Flexible-Robust" and Hydrolytically Stable Cu(II)-MOF.

Propyne/propylene separation is important in the petrochemical industry but challenging due to their similar physical properties and close molecular sizes. Metal-organic frameworks (MOFs) are a class of promising adsorbents for light hydrocarbon separations. Among them, the so-called "flexible-robust" MOFs combine the advantages of flexibility and rigidity in structure and could show enhanced gas separation selectivity as well as improved gas uptake at low pressure. Interpenetrated MOFs offer a platform to explore the "flexible-robust" feature of MOFs based on their subnetwork displacement in the process of gas adsorption. Herein, we present two hydrolytically stable MOFs ( BUT-308 and BUT-309 ) with interpenetrated structures and fascinating propyne/propylene separation performance. BUT-308 is composed of interpenetrated 2D Cu(BDC-NH 2 )BPB layers (H 2 BDC-NH 2 = 2-aminobenzene-1,4-dicarboxylic acid; BPB = 1,4-bis(4-pyridyl)benzene), while BUT-309 consists of twofold interpenetrated 3D pillared-layer Cu 2 (BDC-NH 2 ) 2 (BPB-CF 3 ) nets (BPB-CF 3 = 2-trifluoromethyl-1,4-bis(4-pyridyl)benzene). Gas adsorption measurements showed that BUT-309 was a "flexible-robust" adsorbent with multistep adsorption isotherms for C 3 H 4 rather than C 3 H 6 at a wide temperature range. The guest-dependent pore-opening behavior endows BUT-309 with high potential in the C 3 H 4 /C 3 H 6 separation. The C 3 H 4 adsorption measurements of BUT-309 at 273-323 K showed that the lowering of the temperature induced the pore-opening action at lower pressure. Column breakthrough experiments further confirmed the capability of BUT-309 for the efficient removal of C 3 H 4 from a C 3 H 4 /C 3 H 6 binary gas, and the C 3 H 6 processing capacity at 273 K (15.7 cm 3 g -1 ) was higher than that at 298 K (35.2 cm 3 g -1 ). This work shows a rare example of "flexible-robust" MOFs and demonstrated its high potential for C 3 H 4 /C 3 H 6 separation.