Corrosion Behavior of Iron in Aqueous Amine Solvents Containing Carbon Dioxide

Introduction

The escalating severity of climate change effects calls for mitigation strategies to curb greenhouse gas emissions, particularly CO2. Post combustion CO2 capture (PCCC) through amine scrubbing is a potential near term mitigation strategy. Amine scrubbing has been used for decades in the natural gas sweetening process (DuPart, Bacon & Edwards, 1993) and can be easily retrofitted to key CO2 emission sources, namely fossil fuel based power generation plants, steel and cement production facilities.

CO2 corrosion
Figure 1: Schematic of Post Combustion Capture Process

Despite decades of successful implementation for natural gas sweetening (DuPart, Bacon & Edwards, 1993) corrosion remains a technical limitation of the amine scrubbing process. Stainless steel is therefore used as a primary infrastructure material for this process however this material is costly and is susceptible to corrosion in these systems, both of which escalate capital and operational costs.  Demonstration of the suitability of relatively inexpensive materials (e.g. carbon steel) and/or reliable corrosion control strategies could advance wide-scale PCCC deployment.

Amines are not inherently corrosive however such behaviour results from CO2 absorption. Primary (1 º, e.g. monoethanolamine (MEA)) and secondary (2 º) amines, absorb CO2 in a direct, kinetically fast reaction, forming carbamates in the process. These amine types have been found to exhibit corrosive attack on iron (Fe) substrates(DuPart, Bacon & Edwards, 1993). While some studies have attributed solution corrosivity to hydrogen-carbonate species (Veawab & Aroonwilas, 2002), others hold amine carbamates responsible (DuPart, Bacon & Edwards, 1993; Guo & Tomoe, 1999).

Tertiary amines (3 º, e.g. methyldiethanolamine (MDEA)) react with CO2 in an indirect manner requiring CO2 hydrolysis and subsequent capture. This capture process results in formation of hydrogen-carbonate which can in turn react with Fe ions (present due to Fe oxidation) to form FeCO3 (Zheng et al., 2016; Sedransk Campbell, Yu & Williams, 2017). Iron carbonate film are thought to provide protection to the underlying substrate by acting as a physical barrier to limit the ingress of corrosive solution (Crolet, Thevenot & Nešić, 1998; Han et al., 2009). Moreover, 3 ° amines have been reported as the least corrosive solvent type for amine scrubbing (DuPart, Bacon & Edwards, 1993).

Project Objectives

This project will investigate the active corrosion of iron substrates in different aqueous amine solvents loaded with carbon dioxide to establish the relationship between amine type and iron corrosion. Electrochemical techniques, surface characterisation analyses and mathematical modelling will be conducted to identify the corroding agents present in the different test aqueous amine solvents. Corrosion product formation and stability will also be investigated to determine the relationship between product formation and aqueous amine type. A developed understanding of the corrosion mechanism and product formation will then facilitate corrosion control strategy proposals through amine selection.

Reactor
Figure 2: Experimental Set-up for Electrochemical Studies of Iron in Aqueous Amine Solvent Saturated with Carbon Dioxide

References

  1. Crolet, J.L., Thevenot, N. & Nešić, S. (1998) Role of Conductive Corrosion Products in the Protectiveness of Corrosion Layers. Corrosion. [Online] 54 (3), 194–203. Available from: doi:10.5006/1.3284844.
  2. DuPart, M.S., Bacon, T.R. & Edwards, D.J. (1993) Understanding corrosion in alkanolamine gas treating plants. Hydrocarbon Processing. 72 (5), 89–94.
  3. Guo, X.P. & Tomoe, Y. (1999) The effect of corrosion product layers on the anodic and cathodic reactions of carbon steel in CO2 saturated MDEA solutions at 100oC. Corrosion science. 41 (di), 1391–1402.
  4. Han, J., Young, D., Colijn, H., Tripathi, A., et al. (2009) Chemistry and Structure of the Passive Film on Mild Steel in CO2 Corrosion Environments. Industrial and Engineering Chemistry Research. [Online] 48 (13), 6296–6302. Available from: doi:10.1021/ie801819y.
  5. Sedransk Campbell, K.L., Yu, L.C. & Williams, D.R. (2017) Siderite corrosion protection for carbon steel infrastructure in post-combustion capture plants. International Journal of Greenhouse Gas Control. [Online] 58, 232–245. Available from: doi:10.1016/j.ijggc.2017.01.018.
  6. Veawab, A. & Aroonwilas, A. (2002) Identification of oxidizing agents in aqueous amine-CO2 systems using a mechanistic corrosion model. Corrosion Science. [Online] 44 (5), 967–987. Available from: doi:10.1016/S0010-938X(01)00125-1.
  7. Zheng, L., Landon, J., Matin, N.S. & Liu, K. (2016) FeCO 3 Coating Process toward the Corrosion Protection of Carbon Steel in a Postcombustion CO 2 Capture System. Industrial & Engineering Chemistry Research. [Online] 55 (14), 3939–3948. Available from: doi:10.1021/acs.iecr.5b04145.