Surface engineering on a microporous metal-organic framework to boost ethane/ethylene separation under humid conditions

Recently, examples of metal-organic frameworks (MOFs) have been identified displaying ethane (C₂H₆) over ethylene (C₂H₄) adsorption selectivity. However, it remains a challenge to construct MOFs with both large C₂H₆ adsorption capacity and high C₂H₆/C₂H₄ adsorption selectivity, especially under humid conditions. Herein, we reported two isoreticular MOF-5 analogues (JNU-6 and JNU-6-CH₃) and their potential applications in one-step separation of C₂H₄ from C₂H₆/C₂H₄ mixtures. The introduction of CH₃ groups not only reduces the pore size from 5.4 Å in JNU-6 to 4.1 Å in JNU-6-CH₃ but also renders an increased electron density on the pyrazolate N atoms of the organic linker. JNU-6-CH₃ retains its framework integrity even after being immersed in water for six months. More importantly, it exhibits large C₂H₆ adsorption capacity (4.63 mmol g⁻¹) and high C₂H₆/C₂H₄ adsorption selectivity (1.67) due to the optimized pore size and surface function. Breakthrough experiments on JNU-6-CH₃ demonstrate that C₂H₄ can be directly separated from C₂H₆/C₂H₄ (50/50, v/v) mixtures, affording benchmark productivity of 22.06 and 18.71 L kg⁻¹ of high-purity C₂H₄ (≥99.95%) under dry and humid conditions, respectively.