Using sodium thiosulphate for carbon steel corrosion protection against monoethanolamine and 2-amino-2-methyl-1-propanol

The corrosion performance of carbon steel (C1018) with inhibitor sodium thiosulphate (STS) has been compared to C1018 (without an inhibitor) and stainless steel (SS316 L) at 80 and 120 °C to determine the feasibility of use in a post-combustion CO2 capture plant (PCCC). The corrosivity of variable ratio monoethanolamine (MEA) and 2-amino-2-methyl-1-propanol (AMP) aqueous solvent blends were assessed after seven days using a gravimetric method for mass change, Fe ion solution concentration (ICP-OES), surface imaging (SEM) and analytical techniques (EDX and XRD). At low concentrations of MEA (25%), the use of the corrosion inhibitor is ineffective as it prevents the formation of protective films naturally developed by AMP. The performance of the inhibitor with MEA-AMP blends was noteworthy at higher MEA concentrations of 50 and 75%. In these cases, reduced corrosion rates were observed through gravimetric and ICP analyses. Imaging by SEM showed reduced surface corrosion and adsorption of STS-derived species. Since these higher MEA concentration solutions offer better CO2 loadings, but still some exhibit corrosive effects when used alone on carbon steel, the use of STS can facilitate an economical usage of carbon steel for PCCC plants.