Mechanistic Modeling of Carbon Steel Corrosion in a Methyldiethanolamine (MDEA)-Based Carbon Dioxide Capture Process

A predictive model was developed for corrosion of carbon steel in carbon dioxide (CO₂)-loaded aqueous methyldiethanolamine (MDEA) systems, based on modeling of thermodynamic equilibria and electrochemical reactions. The concentrations of aqueous carbonic and amine species (CO₂, bicarbonate [HCO₃⁻], carbonate [CO₃²⁻], MDEA, and protonated MDEA [MDEAH⁺]) as well as pH values in the MDEA solution were calculated. The water chemistry model showed a good agreement with experimental data for pH and CO₂ loading, with an improved correlation upon use of activity coefficients. The electrochemical corrosion model was developed by modeling polarization curves based on the given species's concentrations. The required electrochemical parameters (e.g., exchange current densities, Tafel slopes, and reaction orders) for different reactions were determined from experiments conducted in glass cells. Iron oxidative dissolution, HCO₃⁻ reduction, and MDEAH⁺ reduction reactions were implemented to build a comprehensive model for corrosion of carbon steel in an MDEA-CO₂-water (H₂O) environment. The model is applicable to uniform corrosion when no protective films are present. A solid foundation is provided for corrosion model development for other amine-based CO₂ capture processes.