Siderite corrosion protection for carbon steel infrastructure in post-combustion capture plants

To mitigate CO2 release, large-scale post-combustion capture with amine solvents is essential. To achieve capital cost savings, carbon steel infrastructure can replace stainless steel if corrosion by CO2-loaded amine solvents is controlled. A coating, to protect the carbon steel, formed using an amine (or additive) is beneficial because it can be regenerated. Siderite has been shown to form a protective crystalline product layer, created when Fe oxidised at the surface reacts with carbonate ions. Tertiary or sterically-hindered CO2-loaded amine solutions can form this layer. Herein siderite was prepared on carbon steel substrates from 5 M methyldiethanolamine (MDEA), 5 M 2-amino-2-methyl-1-propanol (AMP), and 1 M K2CO3 at 40 and 80 °C. At 40 °C, K2CO3 produced the most successful protective siderite layer; by contrast, the amine solutions developed layers with interlocking crystals at 80 °C. After siderite formation, these substrates were tested in 2.5 M MEA and AEPZ, both highly corrosive but with more desirable capture kinetics. At 80 °C, substrates pre-treated with MDEA or AMP showed good resistance against the corrosive actions of MEA and AEPZ for four weeks. The siderite layer reduced Fe oxidation at the surface and ingress of solution species thereby ceasing contact and corrosion.