Dual protonation reactions in biphasic absorbents facilitate efficient capture of low-concentration CO2 from gas-fired power plants

Abstract

To efficiently capture low concentrations of CO₂ from gas-fired flue gas, a novel binary amine-based biphasic absorbent, 3-Dimethylaminopropylamine (DMPDA)-N,N-Dimethylcyclohexylamine (DMCA)–H₂O, has been proposed. To further optimize the absorbent’s reaction conditions, its absorption, desorption, and phase separation performances were investigated at different temperatures. Compared to single amine-based biphasic absorbents, this absorbent demonstrates higher absorption capacity (2.23 mol/kg at 313 K), faster absorption rate (1.2 × 10^-4 mol/(s·mol)), greater cyclic capacity (1.94 mol/kg at 383 K), and comparable viscosity (40.30 mPa·s). Furthermore, it exhibits an appropriate phase split loading (0.31 mol/kg), low rich phase volume percentage (44.35 %), and good adaptability to process conditions. The optimal absorption temperature was found to be 313 K, and the absorbent’s ability to return to a homogeneous phase after desorption at 383 K ensures recyclability. Additionally, experimental and theoretical analyses indicate that the superior performance of the absorbent is attributed to the dual protonation reactions, which also elucidate the phase separation mechanism. The synergy between the internal and external tertiary amines promotes the reaction between primary amines and CO₂, while the strong molecular interactions among the products and the significant polarity difference with the phase splitter trigger phase separation. Compared to 30 wt% MEA, the estimated regeneration energy for the DMPDA/DMCA/H₂O system is reduced by 36 %, with lower corrosive characteristics. This study offers promising prospects for practical applications in gas-fired power plants and provides theoretical support for the development of novel biphasic absorbents.