Pore Engineering for One-Step Ethylene Purification from a Three-Component Hydrocarbon Mixture

Ethylene production from C2 hydrocarbon mixtures through one separation step is desirable but challenging because of the similar size and physical properties of acetylene, ethylene, and ethane. Herein, we report three new isostructural porous coordination networks (NPU-1, NPU-2, NPU-3; NPU represents Northwestern Polytechnical University) that are sustained by 9-connected nodes based upon a hexanuclear metal cluster of composition [Mn₆(μ₃-O)₂(CH₃COO)₃]⁶⁺. NPU-1/2/3 exhibit a dual cage structure that was systematically fine-tuned in terms of cage size to realize selective adsorption of C₂H₂ and C₂H₆ over C₂H₄. Dynamic breakthrough experiments demonstrated that NPU-1 produces ethylene in >99.9% purity from a three-component gas mixture (1:1:1 C₂H₂/C₂H₄/C₂H₆). Molecular modeling studies revealed that the dual adsorption preference for C₂H₂ and C₂H₆ over C₂H₄ originates from (a) strong hydrogen-bonding interactions between electronegative carboxylate O atoms and C₂H₂ molecules in one cage and (b) multiple non-covalent interactions between the organic linkers of the host network and C₂H₆ molecules in the second cage.