Extraction of CH4 from natural gas and inverse C3H6/C3H8 separation in an ultramicroporous covalent triazine framework

The purification of CH4 from natural gas and the separation of C3H8/C3H6 are of great importance for the chemical industry. Nonetheless, the development of adsorbents that exhibit superior adsorption separation efficiency and robust stability remains a significant challenge. In this research, a novel carbazole-based covalent triazine framework (CTF) with nitrogen-rich binding sites and microporous structures was prepared to achieve the efficient separation of C3H8/CH4, C3H6/CH4 and C3H8/C3H6 mixtures. The prepared CTF-DCTCs exhibit an exceptional adsorption capacity for both C3H8 (61.6-98.8 cm3/g) and C3H6 (67.2-87.9 cm3/g) at 298 K and 1 bar, and excellent separation selectivities for C3H8/CH4 (83.3-166.1) and C3H6/CH4 (120.0-145.2). It is noteworthy that CTF-DCTC-500 with defective ultramicroporous structure shows the characteristic of preferentially adsorbing C3H8 in the C3H8/C3H6 separation, achieving a separation selectivity of 2.03 at 298 K. This is the first report of a COF material exhibiting C3H8-selective adsorption in the C3H8/C3H6 separation. Furthermore, breakthrough experiments have confirmed that CTF-DCTC-500 is capable of achieving a complete separation of the C3H8/C3H6/CH4 mixture and exhibits commendable cyclic stability. This work introduces an outstanding COF adsorbent for the purification of natural gas and C3H6.