Time-dependent electrochemical behavior of carbon steel in MEA-based CO2 capture process

Time-dependent electrochemical behavior of carbon steel was evaluated in CO2-loaded monoethanolamine (MEA) solutions in simulated carbon capture environments. Tests were conducted in 30 wt.% MEA solution with different combinations of controlling factors (oxygen [O2], heat stable salts [HSS], flow and temperature) for 7 days. Corrosion behavior of carbon steel was evaluated by using electrochemical techniques (linear polarization resistance [LPR] and potentiodynamic polarization measurements), weight loss method and surface analytical techniques. Solution pH and ferrous/ferric ion concentration were also measured to monitor the change of water chemistry with time. The results showed that the corrosion rate of carbon steel decreased with time and then stabilized to very low values in the MEA/CO2 condition. XPS characterization revealed formation of a very thin protective FeCO3 layer on the surface, as well as adsorption of MEA. However, when O2 was present in the system, the corrosion rates remained at relatively high values, further increasing with flow. The presence of HSS resulted in a higher corrosion rate at the initial stage, but had a minimal effect on the corrosion rate for longer time exposure. Temperature had a slight effect on the corrosion rate because the solubility of CO2 and O2 decreases with increasing temperature.