Development of Energy-Efficient Biphasic Solvents for Co2 Capture and Their Absorption Performance and Reaction Mechanism

Abstract

Biphasic solvent garnered growing attention for CO2 capture, owing to their considerable potential in reducing energy consumption. This study presents a novel liquid-liquid phase-change absorption system (AEEA-DEHA-H2O), constructed using a tertiary amine with a hydroxylamine group, N, N-diethyl hydroxylamine (DEHA), as a co-absorbent. In this system, the hydroxyl group in DEHA is directly bonded to the nitrogen atom, which enhances the system's hydrophilicity and consequently reduces its viscosity. The phase-change absorbent composed of 30wt%AEEA+40wt% DEHA+30wt% H2O (30A40D30H) exhibited the best absorption and desorption performance, with a CO2 absorption capacity of 0.93 mol/mol and a desorption efficiency of 76.3%. After CO2 saturation, 99% of the absorbed CO2 was found in the CO2-rich phase, which accounted for 57% of the total volume. Furthermore, the viscosity of the system at 40°C after saturation was 78 mPa·s. Biphasic absorbent 30A30D40H afforded the minimum regeneration heat of 2.38 GJ/tCO2, which was 37.4 % lower than that of the aqueous 30wt % MEA absorbent. Analysis by 13C NMR and quantum chemical calculations indicates that the primary amine nitrogen on the AEEA molecule is more reactive with CO2 than the secondary amine nitrogen, forming zwitterions. The polarity difference between the reactants and products may lead to phase separation, with the highly polar reaction products aggregating in the lower phase (CO2-rich phase) and unreacted, low-polarity substances like DEHA accumulating in the upper phase. Therefore, the AEEA-DEHA-H2O biphasic solvent system provides a theoretical basis for the development of new liquid-liquid biphasic solvents.

Keywords: CO2 capture, Biphasic solvent, AEEA, Reaction Mechanism, phase change mechanism