Boosting\nEthane/Ethylene Separation within Isoreticular Ultramicroporous Metal–Organic\nFrameworks

Abstract

The separation of ethane from its\nanalogous ethylene is of great importance in the petrochemical industry,\nbut very challenging and energy intensive. Adsorptive separation using\nC₂H₆-selective porous materials can directly\nproduce high-purity C₂H₄ in a single operation\nbut suffers from poor selectivity. Here, we report an approach to\nboost the separation of C₂H₆ over C₂H₄, involving the control of pore structures in two isoreticular\nultramicroporous metal–organic framework (MOF) materials with\nweakly polar pore surface for strengthened binding affinity toward\nC₂H₆ over C₂H₄. Under\nambient conditions, the prototypical compound shows a very small uptake\ndifference and selectivity for C₂H₆/C₂H₄, whereas its smaller-pore isoreticular analogue exhibits\na quite large uptake ratio of 237% (60.0/25.3 cm³ cm^–3), remarkably increasing the C₂H₆/C₂H₄ selectivity. Neutron powder diffraction\nstudies clearly reveal that the latter material shows self-adaptive\nsorption behavior for C₂H₆, which enables it\nto continuously maintain close van der Waals contacts with C₂H₆ molecules in its optimized pore structure, thus preferentially\nbinds C₂H₆ over C₂H₄.\nGas sorption isotherms, crystallographic analyses, molecular modeling,\nselectivity calculation, and breakthrough experiment comprehensively\ndemonstrate this unique MOF material as an efficient C₂H₆-selective adsorbent for C₂H₄ purification.