Molecular dynamic simulation and experimental investigation on the synergistic mechanism and synergistic effect of oleic acid imidazoline and l-cysteine corrosion inhibitors

Abstract

The synergistic mechanism and the synergistic effect of oleic imidazoline (OIM) and l-cysteine (CYS) as carbon steel corrosion inhibitors were studied by experimental and theoretical methods in 3.5 wt.% NaCl solution saturated by CO2 at 60 ℃. The results of the weight-loss and the electrochemistry experiment show that the inhibition performance of the mixture corrosion inhibitors is better than that of the individual inhibitor. The inhibition efficiency of the mixture corrosion inhibitors is high up to 95.08 % when the ratio of OIM and CYS 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. The molecular dynamic simulation results also indicate that OIM is preferentially adsorbed onto the surface of the carbon steel. The adsorbed OIM molecules form a film with voids and CYS molecules fill in the voids forming a bilayer film. The bilayer film becomes the most condensed and the thickest when the proportion of OIM and CYS is 3 to 1 in both aqueous solution and NaCl solution saturated by CO2. So the synergistic inhibition mechanism of OIM and CYS is a bilayer adsorption mechanism. The smallest diffusion coefficient of the corrosive particle Cl− is 0.2294 when the ratio of OIM and CYS is 3 to 1. Therefore, the film can effectively prevent the carbon steel from corrosion. As a result, the mixture corrosion inhibitors of OIM and CYS with the ration of 3 to 1 present the best synergistic effect. The results can provide a helpful guideline for further studying the synergistic inhibition effect of the mixture inhibitors of OIM and other chemicals.