A Novel Phase Change Absorbent for CO2 Capture with Low Viscosity and Effective Absorption–Desorption Properties

Excessive carbon dioxide (CO₂) emissions can lead to environmental problems, and the use of phase change absorbents for CO₂ capture has received much attention due to their excellent absorption and desorption properties. Herein, a novel liquid–liquid phase change absorbent consisting of N-aminoethylpiperazine (AEP), diethylene glycol dimethyl ether (DEGDME), and H₂O is utilized. Under the optimal absorption conditions, the absorption capacity is 1.23 mol CO₂·mol⁻¹ amine. The rich-phase viscosity of the AEP/DEGDME/H₂O solution is only 6.2 mPa s⁻¹, and the rich phase-to-volume ratio is 52.7%, which is suitable for industrial applications. After five cycles of absorption–desorption experiments, the cyclic capacity reaches 0.62 mol CO₂·mol⁻¹ amine. However, it should be noted that this leads to an increase in the viscosity of the solution with time. The ¹³C Nuclear Magnetic Resonance characterization is used to analyze the material distribution and phase separation mechanism, and it is found that during the absorption process, the carbamate and carbonate products generated by the reaction of the amino group in the AEP with CO₂ are mainly located in the rich phase, while the DEGDME and H₂O mainly remain in the lean phase. In the desorption process, most of the absorbed products are decomposed, and the regeneration efficiency is 66.8%. Through the regeneration energy consumption experiment, when the regeneration efficiency is 56%–67%, the total regeneration energy consumption is 2.71–2.89 GJ t⁻¹ CO₂, which is 0.91–1.09 GJ t⁻¹ CO₂ lower than that of the regeneration efficiency of 30 wt% MEA solution at 63%, which indicates that this absorbent has certain energy-saving advantages.