Neutralization and Adsorption Effects of Various Alkanolamines on the Corrosion Behavior of N80 Steel in Supercritical CO₂ with Impurities

The use of alkanolamines is regarded as the most commonly used way in carbon capture, utilization, and storage system for carbon dioxide capture owing to several advantages compared with other methods. This work investigated the effect of monoethanolamine (MEA), diethanolamine (DEA), and N-methyldiethanolamine (MDEA) on the corrosion behavior of N80 steel in supercritical CO₂ phase and aqueous phase with impurities (SO₂, NO₂, and O₂). The results by weight-loss measurements showed that all of the tested alkanolamines inhibited corrosion, and the inhibition efficiency of the three alkanolamines at a concentration of 300 ppmv was between 55% and 67% in the aqueous phase, whereas the inhibition efficiencies were low in supercritical CO₂ phase. The electrochemical experiments were used to study the corrosion inhibition mechanism of MEA, DEA, and MDEA at atmospheric pressure and high-pressure of CO₂/SO₂/NO₂/O₂ amines environment. Results showed that adsorption phenomenon was obvious under atmospheric pressure condition, while this phenomenon was not found under high-pressure condition. The off-line pH measurements indicated that alkanolamines could increase the pH value of the solution. Results imply that the primary cause of decrease of corrosion rate is the neutralization effect of alkanolamines. Surface analytical methods were used to observe the surface morphology and chemical compositions.