An energy-efficient cyclic amine system developed for carbon capture from both flue gas and air

High energy consumption is a major barrier to the large-scale deployment of carbon capture processes from flue gases or air (direct air capture, DAC). The non-aqueous amines reported in literature possess a high energy efficiency for CO₂ capture from flue gases, they struggle with gas streams containing ultra-dilute CO₂, like air, due to poor absorption kinetics. This study developed novel 2-PE (2-piperidineethanol)/APZ (Aminoethylpiperazine) based CO₂ absorbents to address these problems. The experiments and MD simulation results showed that the 2-PE/APZ-based absorbents possessed a superior absorption performance both in flue gas and air. Among the developed absorbents, when 2-PE/APZ mixed with DMF (Dimethylformamide), the CO₂ loading reached to 1.004 mol/mole, as the theoretical maximum. In DAC tests, 87.31 % CO₂ from the air was captured in 24 h experiments. The regeneration heat duty of 2-PE/APZ/DMF decreased to 1.694 KJ/g CO₂, a 55.89 % reduction compared to the benchmark 30 wt% MEA. The CO₂ absorption/desorption mechanism was analysed by NMR, In-situ FT-IR, and DFT calculation. It indicated that this significant improvement in CO₂ absorption performance and the reduction in energy consumption are due to the synergistic effect of 2-PE and APZ. During CO₂ absorption, CO₂ reacts with APZ forming APZ zwitterion rapidly, then deprotonation to the 2-PE. The formation of protonated 2-PEH⁺ ion pairs with APZCOO^- reduces hydrogen bonds and van der Waals forces among the amine-CO₂ complex, facilitating easy regeneration at mild conditions while maintaining high reactivity. The combination of theoretical and experimental results indicates that 2-PE/APZ-based absorbents can serve as a promising alternative for carbon capture from flue gas to air with low energy usage.