Research on a Tertiary Amine-Based CO₂ Biphasic Absorbent: DEEA/PZ/DEGDE/H₂O

This study investigated a biphasic absorbent based on tertiary amines, in which diethylethanolamine (DEEA) was used as the primary absorbent, piperazine (PZ) served as an activator to enhance DEEA’s absorption performance, and diethylene glycol diethyl ether (DEGDE) was employed as the phase splitter. The optimal formulation, determined through absorption and desorption experiments, was found to be 3 M DEEA/1 M PZ/50% DEGDE/50% H2O. The biphasic absorbent achieved a cyclic CO2 loading of 3.01 mol CO2/kg, which is 3.2 times higher than the conventional 5 M MEA absorbent, with the CO2-rich phase volume accounting for only 50% of the total solution. The average absorption rate during the second cycle reached 0.046 mol CO2 kg–1 min–1, comparable to that of 5 M MEA (0.043 mol CO2 kg–1 min–1), effectively addressing the issue of the inherently low absorption rate of tertiary amines. The reaction heat, measured by differential scanning calorimetry, was 1.32 GJ/t CO2, and the total regeneration energy was 1.95 GJ/t CO2, representing just 44.8% of the regeneration energy required for 5 M MEA (4.35 GJ/t CO2). Mechanism analysis showed that the reaction product of PZ, PZ(COO)22–, undergoes a critical interaction with DEEA, forming a zwitterionic intermediate, DEEACOO–, while simultaneously regenerating PZ. The DEEACOO– complex then rapidly reacts with water to generate bicarbonate and carbonate species, which are easily desorbed, significantly reducing the regeneration energy.