Inverse Adsorption Separation of CO₂/C₂H₂ Mixture in Cyclodextrin-Based Metal–Organic Frameworks

The demand for CO2/C2H2 separation, especially the removal of CO2 impurity, continues to grow because of the high-purity C2H2 required for various industrial applications. The adsorption separation of C2H2 and CO2 via porous materials is gaining a considerable attention as it is more energy-efficient compared with cryogenic distillation. The ideal porous materials are those that preferentially adsorb CO2 over C2H2; however, very few adsorbents meet such requirement. Herein, two isostructural cyclodextrin-based CD-MOFs (CD-MOF-1 and CD-MOF-2) were demonstrated to have an inverse ability to selectively capture CO2 from C2H2 by single-component adsorption isotherms and dynamic breakthrough experiments. These two MOFs showed excellent adsorption capacity and benchmark selectivity (118.7) for CO2/C2H2 mixture at room temperature, enabling the pure C2H2 to be obtained in only one step. This work revealed that these materials were promising adsorbents for obtaining high-purity C2H2 via selectively capturing CO2 from C2H2.