Robust carbazole-based covalent triazine frameworks with defective ultramicropore structure for efficient ethane-selective ethane-ethylene separation

Abstract The selective adsorption of ethane (C2H6) in the separation process of C2H6 and ethylene (C2H4) is of great importance for obtaining polymer-grade C2H4 in industry, yet it is still challenging task to develop suitable adsorbents with large adsorption capacity, high selectivity and excellent stability for efficient separation of C2H6/C2H4. Herein, carbazole-based covalent trazine frameworks (CTFs) prepared by ionothermal strategy are proposed for C2H6/C2H4 for the first time. By changing the preparation conditions, the obtained CTF-DCTC-500 shows defective ultramicropore structure while CTF-DCTC-400 does not. Compared with CTF-DCTC-400, the introduction of defective ultramicropore in CTF-DCTC-500 not only increases the adsorption capacity of C2H6, but also exhibits obviously C2H6/C2H4 separation behavior. Surprisingly, the adsorption selectivity of C2H6/C2H4 in CTF-DCTC-500 at 298 K and 1 bar is up to 2.08, exceeding all reported COF materials. To the best of our knowledge, this is first reported CTF material with preferential C2H6 adsorption over C2H4. Breakthrough experiments on CTF-DCTC-500 reveal that the polymer-grade C2H4 with 99.95 % purity can be directly obtained from the C2H6/C2H4 mixture in the practical application. Furthermore, CTF-DCTC-500 possesses the high chemical stability and excellent cycling stability and regeneration for C2H6/C2H4 separation, indicating it is a promising material for C2H6/C2H4 separation. This work not only provides a highly stable carbazole-based CTF with high C2H6/C2H4 separation selectivity, but also emphasizes the important role of defective ultramicropore structure on C2H6/C2H4 separation.