Synergistic Effects between 2-mercaptoethanol and 2-methyl-imidazoline as Corrosion Inhibitors in CO2-saturated brine: DFT and Experiments (C2026-00338)

Dharmendr Kumar, Venkata Muralidhar K, Vinay Jain, Jeremy Moloney

CO2 corrosion of steel components is a problem faced by practically all oil & gas companies. Synergistic blending of corrosion inhibitors is one of the common methods extensively employed to combat this problem. However, the mechanisms behind synergism, although important for coming up with new blends, are very less understood.
In this work, we have investigated the individual and combined effects of 2-mercapthoethanol (ME) and 2-methyl-2-imidazoline (MI) on CO2 corrosion inhibition using both density functional theory (DFT) and experiments. We have modeled the adsorption of ME and MI on cementite (Fe3C) surface using DFT. While the adsorption energy magnitudes for stand-alone molecules suggest MI to be adsorbing stronger, on increasing the surface coverage ME appears to be offering a stronger and more compact protective layer. A (1:1) ratio of ME-MI leads to an even improved adsorption energy suggesting a synergistic effect, as also seen in experimental bubble tests. Projected density of states (PDOS) and electron density difference (EDD) plots calculations indicate intermolecular interactions provide further insights into the synergism. By combining molecular-level DFT and empirical data, this work lays a rational foundation for designing synergistic inhibitor mixtures with improved cost-efficiency and film cohesion under sweet corrosion environments.