Inhibition of N80 steel corrosion in impure supercritical CO2 and CO2-saturated aqueous phases by using imino inhibitors

Steel corrosion has been widely investigated during supercritical CO2 phase with various impurities in carbon capture and storage system; however, the use of inhibitors to suppress steel corrosion has been rarely studied. This work investigated the corrosion inhibition effect of imidazoline and piperazine on N80 steel in watersaturated supercritical CO2 phase and supercritical CO2-saturated aqueous phase with impurities (SO2, NO2, and O-2). Results showed that the inhibition efficiency of piperazine increased from 64% to 86% in the aqueous phase when the piperazine concentration increased from 300 ppm to 1000 ppm. In all cases, the inhibition efficiency in the supercritical CO2 phase was lower than that in the aqueous phase under the same test conditions. By contrast, the inhibition effect of imidazoline was negligible, and severe localized attacks were found within deep pits in supercritical CO2 and aqueous phases. Based on the pH measurement results, piperazine exhibited remarkable neutralization effect and thus could be a potential pH stabilizer. Fe3C possibly resided on the steel surface, and Fe-2(SO4)(3) was confirmed in the product scale. Nevertheless, steel corrosion inhibition in impure supercritical CO2 phase remains challenging.