Application of pyrene-derived benzimidazole-linked polymers to CO ₂ separation under pressure and vacuum swing adsorption settings

Pyrene-derived benzimidazole-linked polymers (BILPs) have been prepared and evaluated for selective CO₂ uptake and separation under pressure and vacuum swing conditions. Condensation of 1,3,6,8-tetrakis(4-formylphenyl)pyrene (TFPPy) with 2,3,6,7,10,11-hexaaminotriphenylene, 2,3,6,7,14,15 hexaaminotriptycene, and 3,3′-diaminobenzidine afforded BILP-11, BILP-12 and BILP-13, respectively, in good yields. BILP-12 exhibits the highest specific surface area (SA_BET = 1497 m² g^-1) among all known BILPs and it also has very high CO₂ uptake 5.06 mmol g ^-1 at 273 K and 1.0 bar. Initial slope selectivity calculations indicate that BILP-11 has high selectivity for CO₂/N₂ (103) and CO₂/CH₄ (11) at 273 K. IAST selectivity calculations of BILPs at 298 K also showed high CO₂/N₂ (31-56) and CO₂/CH₄ (6.6-7.6) selectivity levels. The isosteric heats of adsorption for CO₂ fall in the range of 32 to 36 kJ mol^-1 and were considerably higher than those of CH₄ (16.1-21.7 kJ mol^-1). More importantly, the performance of pyrene-based BILPs in CO₂ removal from flue gas and methane-rich gases (natural gas and landfill gas) under different industrial conditions was investigated according to evaluation criteria suggested recently by Bae and Snurr. The outcome of this study revealed that BILPs are among the best known porous materials in the field; they exhibit high working capacity, regenerability, and sorbent selection parameters. Collectively, these properties coupled with the remarkable physicochemical stability of BILPs make this class of polymers very promising for CO₂ separation applications. This journal is