Corrosion mitigation via a pH stabilization method in monoethanolamine-based solutions for post-combustion CO₂ capture

A pH stabilization method was investigated to mitigate corrosion in aqueous 5 M monoethanolamine for post-combustion CO₂ capture. The room temperature pH of a naturally aerated CO₂-loaded solution (i.e., 9.7) was adjusted with NaHCO₃ powders to 9.3 and 9.1, and its effect on corrosion of A106 carbon steel was studied. Lower pH initially accelerated corrosion but promoted protective FeCO₃ layer formation and subsequently A106 passivation (i.e., Fe₃O₄ formation). Dissolved oxygen also played a pivotal role by functioning as an additional oxidizer, retarding FeCO₃ formation via preferentially oxidizing Fe²⁺ to form rust, and promoting passivation of A106 under the FeCO₃ layer.