Mechanistic study and performance enhancement of CO2 absorption using DEHA as a viscosity modifier in biphasic solvent systems

Biphasic absorbents have garnered increasing attention in CO₂ capture due to their potential for reducing energy consumption. However, the high viscosity of the CO₂-rich phase after phase separation often leads to challenges such as increased flow resistance, reduced heat transfer efficiency, and instability of phase separation. To address these issues, this study proposes a novel phase-change capture system comprising AEEA-DEHA-H₂O (AEEA: 2-(2-aminoethylamino)ethanol, DEHA: N, N-diethylhydroxylamine). The experimental results revealed that a biphasic absorbent composed of 30wt% AEEA, 40wt% DEHA, and 30wt% H₂O achieved an absorption capacity of 0.93 mol CO₂·mol⁻¹ amine, with a desorption efficiency of 75.3 % at 110 °C and a viscosity of 58 mPa·s after saturation at 40 °C. The energy consumption of this system was 20.5 % lower than that of the conventional MEA solvent. Quantum chemical calculations indicated that the hydroxyl group in the DEHA structure was directly bonded to the nitrogen atom, which enhanced the hydrophilicity of the system. This structural feature allowed DEHA molecules to form strong hydrogen bonds with water, thereby increasing their water solubility and reducing the viscosity of the system. Furthermore, the strong affinity of AEEA-derived products for other CO₂ capture products and H₂O resulted in their aggregation into a CO₂-rich phase. In contrast, the relatively low polarity of DEHA led to a weaker affinity for AEEA-derived products, allowing DEHA to separate from the solution and form a CO₂-lean phase.