Study on Carbon Steel Corrosion in Mixed Amine Absorbents for CO ₂ Capture

To address the severe corrosion caused by 30% monoethanolamine (MEA) in carbon capture, this study developed mixed amine absorbents (30 wt % total) by combining MEA with 2-amino-2-methyl-1-propanol (AMP), piperazine (PZ), N-methyldiethanolamine (MDEA), 2-(2-aminoethylamino)ethanol (AEEA), or diethylenetriamine (DETA). The corrosion behavior on 20# carbon steel was evaluated through novel dynamic immersion tests, electrochemical analysis, and multitechnique characterization. Results revealed the corrosion rate order as 20% DETA + 10% MEA ≫ 20% AEEA + 10% MEA > 30%MEA > 20% MEA + 10% PZ/AMP/MDEA > 20% PZ/AMP/MDEA + 10% MEA. AMP, MDEA, and PZ promoted protective FeCO3 film formation via HCO3– generation, whereas AEEA and DETA intensified corrosion, forming nonprotective green rust (Fe6(OH)12CO3·2H2O). The work further clarifies the competitive regulatory mechanism of degradation products─corrosion-accelerating heat-stable salts (e.g., formate) and corrosion-inhibiting degradation product N-hydroxyethyl-2-imidazolidinone (HEIA). The absorption–degradation–corrosion interrelationship was systematically elucidated. These findings provide a mechanistic basis for designing efficient, low-corrosion amine solvents for carbon capture.