Investigation on the synergistic effects and mechanism of oleic imidazoline and mercaptoethanol corrosion inhibitors by experiment and molecular dynamic simulation

• Mercaptoethanol was used as the synergist of Oleic imidazoline • When combined with OIM and ME, the inhibition performance was further improved • The adsorption sites of OIM and ME were determined by molecular simulation • The adsorption of OIM and ME on the surface of carbon steel conforms to the bilayer adsorption mechanism The synergistic effect and the synergistic mechanism of oleic imidazoline (OIM) and mercaptoethanol (ME) as carbon steel corrosion inhibitors were studied by the weight-loss and electrochemistry theoretical methods in 3.5wt.% NaCl aqueous solution saturated by CO 2 at 60°C. Both the weight-loss and the electrochemistry experiment results show that the synergistic effect between OIM and ME greatly improves the corrosion inhibition performance of the mixture corrosion inhibitors. The inhibition efficiency of the mixture corrosion inhibitors is high up to 96.56% when the ratio of OIM and ME is 3 to 1. The quantum chemical parameters calculated at the B3LYP/6-311++G(d,p) level show that OIM can be preferentially adsorbed for its low energy gap. The molecular dynamic simulation results also indicate that OIM is preferentially adsorbed onto the Fe(110) surface with a adsorption energy of -1583.7 kcal·mol −1 . The adsorbed OIM molecules form a film with voids and ME molecules fill in the voids forming a bilayer film. The bilayer film becomes the most condensed and the thickest when the molar ratio of OIM and ME is 3 to 1 in NaCl aqueous solution saturated by CO 2 . The film can effectively prevents the carbon steel from corrosion because the corrosive medium is blocked by the film. As a result, the mixture corrosion inhibitors of OIM and ME with the ration of 3 to 1 presents the best synergistic effect and the synergistic mechanism is a bilayer adsorption mechanism. The results can provide a helpful guideline for further studying the synergistic effect of the mixture inhibitors of OIM and other chemicals.