A predictive model was developed for corrosion of carbon steel in CO2-loaded aqueous methyldiethanolamine (MDEA) systems, based on modeling of thermodynamic equilibria and electrochemical reactions. The concentrations of aqueous carbonic and amine species (CO2, HCO3-, CO32-, MDEA and 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 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 (Fe) oxidative dissolution, bicarbonate (HCO3-) reduction and protonated alkanolamine (MDEAH+) reduction reactions were implemented to build a comprehensive model for corrosion of carbon steel in an MDEA-CO2-H2O environments. 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.

Subject
Steel surfaces, Hydrogen concentration, Corrosion rate, Electrochemical reactions, Corrosion reactions, Cathodic polarization curves, Partial pressures, Anodic reactions, Corrosion modeling, Carbon steel, Risk reduction, Tafel slope, Corrosion potential
Keywords:
MDEA, corrosion model, CO2 capture, carbon steel, carbon capture and storage
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2012
Association for Materials Protection and Performance (AMPP)
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