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 C 2 H 6 -selective porous materials can directly produce high-purity C 2 H 4 in a single operation but suffers from poor selectivity. Here, we report an approach to boost the separation of C 2 H 6 over C 2 H 4, 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 C 2 H 6 over C 2 H 4 . Under ambient conditions, the prototypical compound shows a very small uptake difference and selectivity for C 2 H 6 /C 2 H 4, whereas its smaller-pore isoreticular analogue exhibits a quite large uptake ratio of 237% (60.0/25.3 cm 3 cm –3 ), remarkably increasing the C 2 H 6 /C 2 H 4 selectivity. Neutron powder diffraction studies clearly reveal that the latter material shows self-adaptive sorption behavior for C 2 H 6, which enables it to continuously maintain close van der Waals contacts with C 2 H 6 molecules in its optimized pore structure, thus preferentially binds C 2 H 6 over C 2 H 4 . Gas sorption isotherms, crystallographic analyses, molecular modeling, selectivity calculation, and breakthrough experiment comprehensively demonstrate this unique MOF material as an efficient C 2 H 6 -selective adsorbent for C 2 H 4 purification.