Moderately polarized carborane-MOF with inverse C2 selectivity for one-step polymer-grade ethylene purification

Abstract

Ethylene purification from ternary C₂ mixtures (C₂H₂/C₂H₄/C₂H₆) typically requires multi-step processes due to competing adsorption mechanisms in conventional adsorbents. Herein, we report a carborane-based metal–organic framework (CB-Zn-DPG) featuring moderately polarized pore surfaces that inverts traditional selectivity trends. Unlike polar MOFs (C₂H₂ > C₂H₄ > C₂H₆) or nonpolar MOFs (C₂H₆ > C₂H₄ > C₂H₂), CB-Zn-DPG simultaneously captures both C₂H₂ (61.5 cm³ g⁻¹) and C₂H₆ (44.0 cm³ g⁻¹) preferentially over C₂H₄ (42.4 cm³ g⁻¹) at 298 K and 1.0 bar, with higher isosteric heats for impurities (C₂H₂ 31.5 kJ mol⁻¹; C₂H₆ 29.8 kJ mol⁻¹vs. C₂H₄ 25.9 kJ mol⁻¹). DFT calculations reveal multi-site van der Waals interactions at the channel centers for C₂H₂/C₂H₆, while C₂H₄ adsorbs weakly at the pore corners. Dynamic breakthroughs confirm direct production of >99.99% polymer-grade C₂H₄ from equimolar C₂H₄/C₂H₆ (50/50) and ternary C₂H₂/C₂H₄/C₂H₆ (1/90/9) mixtures in a single column operation. This work establishes pore-surface polarity engineering as a paradigm for challenging hydrocarbon separations.