Imidazolate of 1-butyl-3-ethyl imidazole as corrosion inhibitor on API 5L X52 steel in NaCl saturated with CO2

Abstract

Imidazolate of 1-butyl-3-ethyl imidazole (IBPI3) is studied as a corrosion inhibitor on API 5L-X52 steel in NaCl at 3% (m/v) saturated with CO2 at room temperature. The inhibition efficiency was determined throughout: 1) electrochemical methods, 2) polarization curves (Tafel Extrapolation) (CP) and 3) Electrochemical Impedance Spectroscopy (EIS). For all cases, it was determinate that inhibition efficiency increases with the concentration increase of IBPI3. The best efficiency was 94.9 % at a concentration of 50 ppm and room temperature. The thermodynamic analysis demonstrated that a combined adsorption process occurs, according to Langmuir isotherm at different rotation rates. The inhibiting effect of ionic liquids over the metallic surface was corroborated through SEM-EDS. Density functional theory (DFT) calculations, with an implicit solvation model, are carried out to bring light to the adsorption mechanism of IBPI3 species and its stability. Global parameters within the HSAB theoretical framework support the experimental results of the good corrosion inhibition properties found for the ionic liquid. The mixed physisorption-chemisorption is mainly accounted by the chemical bond arising between the anionic part of IBPI3 and the metal surface. Charge transference occurs from imidazolate to the nearest iron surface atoms, leading to a stronger electrostatic interaction between the cationic fragment of IBPI3 and these negatively charged metal atoms, which is the physical contribution to the adsorption process. The charge transference weakens the binding of the IBPI3 inhibitor to the metal surface. Condensed Fukui indices reveal that the layer formed on the metal surface, composed by IBPI3 molecules, is almost inert against nucleophilic and electrophilic attacks.