Optimized Separation of Acetylene from Carbon Dioxide and Ethylene in a Microporous Material

Abstract

Selective separation of acetylene (C 2 H 2 ) from carbon dioxide (CO 2 ) or ethylene (C 2 H 4 ) needs specific porous materials whose pores can realize sieving effects while pore surfaces can differentiate their recognitions for these molecules of similar molecular sizes and physical properties. We report a microporous material [Zn(dps) 2 (SiF 6 )] ( UTSA-300, dps = 4,4′-dipyridylsulfide) with two-dimensional channels of about 3.3 Å, well-matched for the molecular sizes of C 2 H 2 . After activation, the network was transformed to its closed-pore phase, UTSA-300a, with dispersed 0D cavities, accompanied by conformation change of the pyridyl ligand and rotation of SiF 6 2– pillars. Strong C–H···F and π–π stacking interactions are found in closed-pore UTSA-300a, resulting in shrinkage of the structure. Interestingly, UTSA-300a takes up quite a large amounts of acetylene (76.4 cm 3 g –1 ), while showing complete C 2 H 4 and CO 2 exclusion from C 2 H 2 under ambient conditions. Neutron powder diffraction and molecular modeling studies clearly reveal that a C 2 H 2 molecule primarily binds to two hexafluorosilicate F atoms in a head-on orientation, breaking the original intranetwork hydrogen bond and subsequently expanding to open-pore structure. Crystal structures, gas sorption isotherms, molecular modeling, experimental breakthrough experiment, and selectivity calculation comprehensively demonstrated this unique metal–organic framework material for highly selective C 2 H 2 /CO 2 and C 2 H 2 /C 2 H 4 separation.