A pyridine derivative 2-(2-Methylaminoethyl)pyridine (MAEP) as a ‘green’ corrosion inhibitor for low-carbon steel in hydrochloric acid media

Abstract

2-(2-Methylaminoethyl)pyridine (MAEP) was investigated as a corrosion inhibitor for carbon steel (CS) in aqueous HCl at various MAEP concentrations, temperatures, pH levels, HCl concentrations and immersion times. The maximum corrosion inhibition efficiency was found to be around 91% at an inhibitor concentration of 25 mM. The corresponding corrosion resistance values, measured by impedance spectroscopy and polarization resistance, were 407± 41 and 422±52 Ω cm2, respectively, and the Tafel technique measured a corrosion current density of 52±5 μA cm−2. MAEP also efficiently protected CS at relatively higher temperatures, HCl concentrations and at low pH levels. The adsorption of MAEP on CS was found to obey the modified-Langmuir isotherm. The standard Gibbs free energy of adsorption was −18.1 kJ mol−1 with an adsorption affinity constant of 29 M−1. The MAEP adsorption kinetics was found to be relatively fast. MAEP was found to effectively protect CS from corrosion over a period of one month of immersion of the material in the very corrosive electrolyte. The interaction of MAEP with the CS surface was found to occur through the nitrogen atom in the heterocyclic ring of MAEP.