Mechanistic Insights into 2-Mercaptoethanol and Thioglycolic Acid Corrosion Inhibitor Chemistries for Mild Steel: DFT and Experimental Investigations

Abstract Sulfur-containing corrosion inhibitors (CIs), such as 2-mercaptoethanol (2ME), thioglycolic acid (TGA), and sodium thiosulfate (STS), are extensively used in oilfield formulations, often in conjunction with other chemistries like quaternary ammonium compounds, imidazolines, and aromatic amines, to mitigate steel corrosion in carbon dioxide environments. These sulfur-based CIs are favored for their effectiveness, low cost, and synergy with other chemistries. To optimize these formulations—by improving performance, reducing costs, and enhancing sustainability—there is a need to better understand their interactions with metal surfaces and other chemistries to discover/design more effective solutions. In this work, the inhibition effects of 2ME and TGA have been investigated using density functional theory (DFT) and corrosion experiments. Results reveal that both 2ME and TGA form strong inhibitor films on the cementite (Fe3C) surface, creating Fe—S and Fe—O bonds. 2ME shows higher adsorption energy than TGA which is further supported by extensive surface coverage studies. Experimental bubble cell tests on C1018 carbon steel at 80°C in a carbon dioxide-saturated 3% sodium chloride environment support these findings. Additionally, the inhibition trends over time for both 2ME and TGA are similar, suggesting a similar mechanism of inhibition. These results underscore the utility of computational techniques like DFT in accelerating the discovery of novel corrosion inhibitor chemistries.