A highly stable microporous covalent imine network adsorbent for natural gas upgrading and flue gas CO2 capture

Abstract The feasible capture and separation of CO 2 and N 2 from CH 4 is an important task for natural gas upgrading and the control of greenhouse gas emissions. Here, we studied the microporous covalent imine networks (CIN) material prepared through Schiff base condensation and exhibited superior chemical robustness under both acidic and basic conditions and high thermal stability. The material possesses a relatively uniform nanoparticle size of approximately 70–100 nm. This network featured permanent porosity with a high surface area (722 m 2 /g) and micropores. A single-component gas adsorption study showed enhanced CO 2 and CH 4 uptakes of 3.32 mmol/g and 1.14 mmol/g, respectively, at 273 K and 1 bar, coupled with high separation selectivities for CO 2 /CH 4 , CH 4 /N 2 , and CO 2 /N 2 of 23, 11.8 and 211, respectively. The enriched Lewis basicity in the porous skeletons favours the interaction of quadrupolar CO 2 and polarizable CH 4 , resulting in enhanced CH 4 and CO 2 uptake and high CH 4 /N 2 , CO 2 /CH 4 and CO 2 /N 2 selectivities. Breakthrough experiments showed high CO 2 /CH 4 , CH 4 /N 2 and CO 2 /N 2 selectivities of 7.29, 40 and 125, respectively, at 298 K and 1 bar. High heats of adsorption for CH 4 and CO 2 (Qst CH4 ; 32.61 kJ mol −1 and Qst CO2 ; 42.42 kJ mol −1 ) provide the ultimate validation for the high selectivity. To the best of our knowledge, such a versatile adsorbent material that displays both enhanced uptake and selectivity for a variety of binary gas mixtures, including CO 2 /CH 4 , CO 2 /N 2 and CH 4 /N 2 , has not been extensively explored.