An EIS study of the effect of the pedant group in imidazolines as corrosion inhibitors for carbon steel in CO2 environments

Electrochemical impedance spectroscopy (EIS) measurements were carried out to study the corrosion inhibition of carbon steel in 3 % NaCl with and without diesel saturated with CO2 at 50 °C. The inhibitors examined were hydroxyethyl (HEI‐18), amino ethyl (AEI‐18), and amide ethyl imidazolines (AMEI‐18). When the oily phase, i.e diesel, is absent, the inhibition efficiency of the imidazolines is low, around 80 %. It was found, however, that the inhibition dramatically increased with the presence of the oily phase, because the imidazolines are able to act as both emulsifiers and corrosion inhibitors. Experimental results showed an increase in the film resistance (Rf), charge transfer resistance (Rct), capacitance of the film and the capacitance of the double layer values with the addition of inhibitor in presence of the oily phase also in several orders of magnitude. The most effective inhibitor in presence of diesel is a solution of AMEI‐18, as the oily phase is carried to the surface also. This is due to the presence of two large alkyl groups than the only chain present in the HEI‐18 and AEI‐18 imidazolines with better hydrophobic properties associated with the formation of a protective film that reduces drastically the corrosion process. The effects of the interaction of inhibitors with hydrocarbons and the correlation on the performance of inhibitor films have been examined.