CO2 capture performance of an AEP/DEEA/n-butanol/H2O phase change absorbent synergistically regulated by a multi-site amine and a tertiary amine

A liquid-liquid AEP/DEEA/n-butanol/H 2 O absorbent is developed. • Multi-variable optimization of absorption and desorption is performed. • NMR reveals carbamate and bicarbonate/carbonate absorption pathways. • Desorption energy AEP/DEEA/n-butanol/H 2 O is 66% of that of 30 wt% MEA/H 2 O. High regeneration energy remains a major obstacle to the practical application of alkanolamine-based absorbents for CO 2 capture. To reduce the regeneration energy demand, a liquid-liquid phase-change absorbent composed of polyamine 1-(2-aminoethyl)piperazine (AEP), 2-(diethylamino)ethanol (DEEA), n-butanol and H 2 O was developed. The effects of composition and operating conditions on the absorption–desorption performance were systematically investigated, identifying 1.8:1.2 AEP/DEEA, 4:3 n-butanol/H 2 O, 30 wt% total amine, and 303.15 K as suitable microchannel absorption conditions. 13 C and 1 H NMR analyses showed that AEP mainly absorbed CO 2 via the carbamate pathway, whereas the tertiary amine site of AEP and DEEA mainly promoted CO 2 hydration to form HCO 3 − /CO 3 2− . Under the optimal composition of 18 wt% AEP, 12 wt% DEEA, 40 wt% n-butanol, and 30 wt% H 2 O, the volume fraction and CO 2 loading of the rich phase reached 48.68% and 3.42 mol CO 2 ·kg −1 solution, respectively. Under desorption at 363.15 K with 2 mL lean-phase addition for 60 min, the desorption efficiency and cyclic capacity reached 58.91% and 1.95 mol CO 2 ·kg −1 solution, respectively, while the apparent desorption energy consumption was only 66% of that of 30 wt% MEA. Overall, this phase-change absorbent achieved effective synergy among rapid absorption, reversible regeneration, and phase-separation intensification, demonstrating its potential for low-energy CO 2 capture.