Effect of chemical structure of hydroxyethyl imidazolines inhibitors on the CO2 corrosion in water–oil mixtures

The corrosion inhibition of oleic, coconut, and stearic acid modified hydroxyethyl imidazolines on 1018 carbon steel was evaluated by using potenthiodynamic polarization curves, linear polarization resistance, and electrochemical impedance spectroscopy techniques. Solutions included deaerated CO2 saturated 3% NaCl with and without Diesel at 50 °C. Regardless of the presence of diesel, the corrosion rate was decreased with the addition of the inhibitors, but the time to reach a steady state was longer than when the oily part, i.e., diesel, was present. This was because the inhibitors are oil soluble, and with diesel, they are more easily transported towards the metal surface. With diesel, the formed film seems to be more stable and protective, not allowing the electrolyte to corrode the sample increasing the efficiency values up to 87 and 94%. The most efficient inhibitors were the coconut type fatty acid hidroxyethyl imidazoline because the formed film was much more stable from the beginning of the test, whereas the least efficient was the stearic acid modified hydroxyethyl imidazoline.