Thermal Stability of Phase-Change Absorbents MEA-NHD-H ₂ O and DMAPA-NHD-H ₂ O in CO ₂ Capture Process

The stability of absorbents is critical for carbon capture applications. This study investigates the thermal degradation of two low-energy phase-change absorbents in the CO2 absorption process: monoethanolamine (MEA)-polyethylene glycol dimethyl ether (NHD)-H2O and 3-(dimethylamino)propylamine (DMAPA)-NHD-H2O. The results show that both amines and NHD are stable at 110 °C for 14 days. But the degradation of amines accelerates after CO2 absorption at 110 °C, with carbamate or protonated amines as key degradation intermediates. The addition of NHD reduces the water content in the system, accelerating carbamate polymerization and thereby decreasing amine stability in CO2-loaded systems. Thermal degradation lowers the density and viscosity of MEA and DMAPA solutions via carbamate cyclization. Despite degradation ratios reaching 36.3% (MEA) and 45.0% (DMAPA), the CO2 absorption capacity decreases only by 15.1 and 23.4%, as degradation products (nitrogen-containing heterocycles/aliphatic amines) retain proton-accepting ability. These findings provide insights for optimizing phase-change absorbents for industrial-scale applications.