Boosting Ethane/Ethylene Separation within Isoreticular Ultramicroporous Metal–Organic Frameworks

Abstract

The separation of ethane from its analogous ethylene is of great importance in the petrochemical industry, but very challenging and energy intensive. Adsorptive separation using C₂H₆-selective porous materials can directly produce high-purity C₂H₄ in a single operation but suffers from poor selectivity. Here, we report an approach to boost the separation of C₂H₆ over C₂H₄, involving the control of pore structures in two isoreticular ultramicroporous metal-organic framework (MOF) materials with weakly polar pore surface for strengthened binding affinity toward C₂H₆ over C₂H₄. Under ambient conditions, the prototypical compound shows a very small uptake difference and selectivity for C₂H₆/C₂H₄, whereas its smaller-pore isoreticular analogue exhibits a quite large uptake ratio of 237% (60.0/25.3 cm³ cm^-3), remarkably increasing the C₂H₆/C₂H₄ selectivity. Neutron powder diffraction studies clearly reveal that the latter material shows self-adaptive sorption behavior for C₂H₆, which enables it to continuously maintain close van der Waals contacts with C₂H₆ molecules in its optimized pore structure, thus preferentially binds C₂H₆ over C₂H₄. Gas sorption isotherms, crystallographic analyses, molecular modeling, selectivity calculation, and breakthrough experiment comprehensively demonstrate this unique MOF material as an efficient C₂H₆-selective adsorbent for C₂H₄ purification.