Application of an Ionic Liquid-Functionalized Metal-Organic Framework in N₂/He and O₂/He Adsorptive Separation:...

In order to satisfy the demand for natural gas helium recovery, an ionic liquid-MOF composite, [C₂mim][Val]@PCN-250(Fe), is produced by an impregnation method. The adsorption and separation behaviors of N₂/He and O₂/He mixtures on both pristine and modified PCN-250(Fe) are examined through experiments and molecular simulations at ambient and sub-ambient temperatures. Adsorption isotherms for N₂, O₂, and He are determined at 298 and 200 K, with ideal adsorbed solution theory (IAST) used to calculate selectivity. Breakthrough experiments with different helium contents assess the separation performance. Molecular simulations reveal adsorption heats, adsorbate probability density, and adsorption energy distributions, as well as binding energies, clarifying competitive adsorption mechanisms. Both pristine and modified PCN-250(Fe) preferentially adsorb N₂ and O₂ over He, with selectivity enhanced at lower temperatures. The introduction of the ionic liquid significantly enhances the N₂/He and O₂/He separation performance at ambient temperature, especially under lower pressures and higher helium content. Breakthrough experiments confirm that reduced temperatures greatly enhance separation efficiency. Overall, ionic liquid modification significantly improves the helium enrichment performance of PCN-250(Fe), particularly in helium-rich mixtures under ambient conditions.