Effect of sulfonate anions on the performance of triethylmethylammonium-derived ionic liquids as corrosion inhibitors

Three novel ionic liquids (ILs) derived from trimethylammonium were evaluated as corrosion inhibitors (CIs) of API-X52 steel in 1 M HCl within a temperature interval ranging from 25 to 40 °C. The ILs were: triethylmethylammonium amino-1-propanesulfate (TEAP), triethylmethylammonium sulfanilate (TES) and triethylmethylammonium 2-aminobenzenesulfonate (TEAS). The inhibition efficiency (η) of these compounds was obtained by the polarization resistance (R_p) and Tafel polarization electrochemical techniques. The electrochemical results revealed that these compounds can be classified as mixed-type CIs. The η increased with the temperature within the studied interval, being the maximal η equal to 88%. Furthermore, the adsorption mechanism was of physicochemical type, which was related to the chemical structure of the anion and cation in the ILs. The XPS analysis indicated the presence of chemical bonds characteristic of sulfates, hydrocarbon chains, and the IL amino group, thus confirming the adsorption of the CIs on the metal surface. The theoretical computations allowed elicit the location of the HOMO and LUMO and their relationship with the η, which were in good agreement with the electrochemical outcomes based on the chemical structure of the assessed ILs.