An amine functionalized carbazolic porous organic framework for selective adsorption of CO2 and C2H2 over CH4

A new microporous organic polymer (PCBNH2) has been synthesized based on amine functionalized carbazole derivative by oxidative coupling polymerization with anhydrous FeCl3. Polymer PCB-NH2 exhibits microporous nature with a BET surface area of 542.4 m2 g−1, and shows moderately high CO2 and C2H2 adsorption capacities, 51.6 cm3 g−1 (10.3 wt%), 58.4 cm3 g−1 (7.5 wt%) at 278 K, 1 atm, respectively. Remarkably, at 278 K, the predicted IAST selectivities of PCB-NH2 are 16.7–5.8 for a CO2/CH4 (5:95 v/v) gas mixture and 34.3–21.0 for a C2H2/CH4 (50:50 v/v) gas mixture at pressures varying from 0 to 1 atm, respectively. More interesting, PCB-NH2 displays higher CO2/CH4 selectivity than its matrix polymer PCB. The isosteric heats of CO2 adsorption (Qst) for PCB-NH2 and PCB further indicate that the amine group may facilitate the interaction between the polarizable CO2 molecules and the polymer by local dipole−quadrupole interactions, subsequently favors selective gas separation for these gas molecules. The high selectivity of CO2/CH4 and C2H2/CH4 makes PCB-NH2 possible candidate for future natural gas upgrading and acetylene purification.