Selective separation of acetylene (C2H2) from carbon dioxide (CO2) and ethylene (C2H4) mixtures is critical in the petrochemical industry due to their similar size and physicochemical properties. Developing three-dimensional porous covalent organic frameworks (3D COFs) remains challenging in this context. In this work, a non-symmetrical 2-phenyl pyridine based three-dimensional covalent organic framework (COF-PPy) has been synthesized, which features a rare dia-C9 fold interpenetrated structure as suggested by computational simulations. COF-PPy exhibits high acetylene (C2H2) adsorption capacity (4.5 mmol g-1 at 298 K), as well as excellent separation and purification performance for C2H2/CO2 and C2H2/C2H4 mixtures. The in situ-FTIR studies suggest that the multi-point interactions between nitrogen centers of COF-PPy and H-C≡CH (COF-Pyridine-N···H-C≡C-H and COF-imine-N··H-C≡CH) account for the higher affinities for C2H2 over other gases. Furthermore, dynamic breakthrough studies reveal that COF-PPy can be employed as an effective adsorbent for the efficient separation of C2H2 from CO2 and C2H4. In addition, COF-PPy exhibits lower heat of adsorption (Qst) values with high adsorption capacity for C2H2 as compared to previously reported C2H2-selective adsorbents, indicating less regeneration energy. Our work therefore provides some new avenues for the design and construction of 3D COFs for efficient C2H2 capture and separation.
Keywords: dynamic breakthrough; gas separation; in situ FTIR; three dimensional COFs.
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