Phase-Change CO2 Absorption Using Novel 3‑Dimethylaminopropylamine with Primary and Tertiary Amino Groups

Phase-change solvents exhibit the promising potential to reduce the regeneration energy for CO2 capture. In this paper, 3-dimethylaminopropylamine (DMAPA) with intramolecular primary and tertiary amino groups was mixed with solvent NHD and water for phase-change absorption of CO2 in the model flue gas. The results show that the homogeneous mixture changes into two phases after CO2 absorption when NHD/H2O ranges from 9:1 to 5:5 and 90% of CO2 is enriched in the lower phase with only 23% of the total volume. The absorption loading reaches 1.06 mol CO2/mol amine, the phase separation time for DMAPA–NHD–H2O is only 14% of that for MEA–SA–H2O, and the viscosity of the lower phase is only 37.14 mPa·s when DMAPA and NHD/H2O are 1 M and 8:2, respectively. Analysis of the reaction mechanism shows that the primary amino group of DMAPA initially reacts with CO2 and the tertiary amino group captures proton of zwitterionic intermediate as an acceptor. The mixed-amine effect is suggested to explain the high absorption performance of the DMAPA–NHD–H2O mixture. The energy estimation shows that the regeneration energy is reduced by 42% compared with that of the 5 M MEA solution, which confirms the advantage of phase-change absorption using DMAPA–NHD–H2O.