Studies and Prevention of Carbon Steel Corrosion and Solvent Degradation During Amine-Based CO2 Capture from Industrial Gas Streams

Abstract

This research is focused on simultaneous inhibition of carbon steel (1020) corrosion and oxidative monoethanolamine (MEA) degradation in a carbon dioxide (CO2) capture process from simulated post-combustion coal-fired flue gas, where components typically present in the flue gas partly contribute to such problems. Therefore, in this work, various additives were selected to study in the effects of flue gas composition on both carbon steel (1020) corrosion and oxidative MEA degradation. Sodium chloride (NaCl), ferrous chloride (FeCl2), and hydrochloric acid (HCl) were selected to represent different sources of chlorides in the flue gas. Sulphurous acid (H2SO3), sulphuric acid (H2SO4), and nitric acid (HNO3) were selected to represent the aqueous solutions of sulphur dioxide (SO2), sulphur trioxide (SO3), and nitrogen dioxide (NO2), respectively. In addition, sodium bisulfite (NaHSO3), sodium sulfite (Na2SO3), sodium sulphate (Na2SO4), and ferrous sulphate heptahydrate (FeSO4·7H2O) were additionally selected in the study of corrosion. All the experiments were conducted under the base-case conditions containing MEA, CO2, and O2. In the carbon steel (1020) corrosion study, the results illustrate that NaCl, HCl, Na2SO4, FeSO4·7H2O, H2SO4, and HNO3 all accelerated the corrosion process, while FeCl2 slowed down metal corrosion. Surprisingly, H2SO3, NaHSO3, and Na2SO3, either behaved as corrosion promoters or corrosion inhibitors depending strongly on their concentrations. Finally, the mixed additives were studied by mixing HCl, H2SO3, H2SO4, and HNO3. The modified power law rate equation of the systems containing all four additives provided an acceptable percentage of average absolute deviations (%AAD) of 8.6%. In the oxidative MEA degradation study, FeCl2, HCl, H2SO4, and HNO3 essentially accelerated oxidative solvent degradation. On the other hand, NaCl and H2SO3 (below 250 ppm) appeared to prevent MEA degradation. Finally, the mixed additives study was performed by mixing HCl, H2SO3, H2SO4, and HNO3 in the concentration ranges equivalent to the mixed additives in the corrosion study. The modified power law rate equation of the systems containing all four additives provided an acceptable %AAD of 9.4%. In the inhibition study, both carbon steel corrosion and oxidative solvent degradation were inhibited simultaneously by introducing various inhibitors. Inhibitor A prevented carbon steel corrosion and oxidative MEA degradation by behaving as a hydrogen ion (H+) scavenger. It provided the maximum efficiency of 88.9% inhibition on carbon steel corrosion and 97.3% inhibition on oxidative solvent degradation. Inhibitor B behaved primarily as an oxygen scavenger where it minimized carbon steel corrosion at the maximum of 92.4% inhibition and 59.9% inhibition on solvent degradation. Inhibitor C behaved as a free radical scavenger where it provided the maximum efficiency only at 42.7% inhibition on carbon steel corrosion but 92.6% inhibition on oxidative MEA degradation. Finally, the mixed inhibitors (A and C) were performed where the mixed inhibitors ratio III provided the best overall inhibitors’ performance at 90.2% inhibition for carbon steel corrosion and 65.2% inhibition for oxidative MEA degradation. In conclusion, this work helped to establish “ultimate” inhibitors that were able to inhibit corrosion and solvent degradation simultaneously, which was essentially a successful achievement.