Enhanced SO₂Resistance of Tetraethylenepentammonium Nitrate Protic Ionic Liquid-Functionalized SBA-15 during CO₂Capture from Flue Gas

Post-combustion carbon capture using amine-based adsorbents is a highly competitive approach to control CO2 emissions from fossil fuel-fired power plants. However, it is well known that amine-based adsorbents suffer from long-term stability issues due to amine poisoning by flue gas contaminants. Minor contaminants, such as SO2, can preferably react with amine sites to form irreversible sulfonamides. This work investigated the effect of nitrates on the SO2 resistance of tetraethylenepentammonium nitrate protic ionic liquid-functionalized SBA-15 for CO2 capture. The tetraethylenepentamine-functionalized SBA-15 without nitrates was prepared as the control. The CO2 adsorption capacity was measured over multiple capture cycles in the presence of 500 ppm SO2. The CO2 capture capacities of the sorbent without nitrates decreased by 1.48 mmol g-1 (50.3%) over 11 capture cycles. After introducing nitrates into the sorbent, the CO2 adsorption capacities only decreased by 0.55 mmol g-1 (21.8%). In addition, the nitrates restricted the reaction between amine groups and SO2 leading to reversible sulfonamide products. The significant improvement in SO2 resistance was further explained with density functional theory (DFT) calculations, which revealed that the binding energy and net charge transfer between SO2 and amine groups were decreased after introducing the nitrate group into the amine. To further investigate the regenerability and structural stability of tetraethylenepentammonium nitrate-functionalized SBA-15 for CO2 capture under realistic conditions, the long-term operating performance was evaluated in a gas mixture of 150 ppm SO2, 150 ppm NO, 100% RH, 15% CO2, and balance N2. The CO2 adsorption capacities and the structural properties of nitrate-containing sorbents were nearly unchanged over eight adsorption/regeneration cycles.