Effect of Co‐Adsorbed Guest Adsorbates on the Separation of Ethylene/Ethane Mixtures on Metal‐Organic Frameworks with Open Metal Sites

Abstract

AbstractDirect determination of the equilibrium adsorption and spectroscopic observation of adsorbent‐adsorbate interaction is crucial to evaluate the olefin/paraffin separation performance of porous adsorbents. However, the experimental characterization of competitive adsorption of various adsorbates at atomic‐molecular level in the purification of multicomponent gas mixtures is challenging and rarely conducted. Herein, solid‐state NMR spectroscopy is employed to examine the effect of co‐adsorbed guest adsorbates on the separation of ethylene/ethane mixtures on Mg‐MOF‐74, Zn‐MOF‐74 and UTSA‐74. 1H MAS NMR facilitates the determination of equilibrium uptake and adsorption selectivity of ethylene/ethane in ternary mixtures. The co‐adsorption of H2O and CO2 significantly leads to the degradation of ethylene uptake and ethylene/ethane selectivity. The detailed host‐guest and guest‐guest interactions are unraveled by 2D 1H−1H spin diffusion homo‐nuclear correlation and static 25Mg NMR experiments. The experimental results verify H2O coordinated on open metal sites can supply a new adsorption site for ethylene and ethane. The effects of guest adsorbates on the adsorption capacity and adsorption selectivity of ethylene/ethane mixtures are in the following order: H2O>CO2>O2. This work provides a direct approach for exploring the equilibrium adsorption and detailed separation mechanism of multicomponent gas mixtures using MOFs adsorbents.