Inhibitive Effect of Some Natural Naphthenates as Corrosion Inhibitors on the Corrosive Performance of Carbon Steel in CO2-Saturated Brine

Abstract. Two surfactants [sodium and potassium salts of naphthenic acids] were synthesized by liquid-phase oxidation process of the naphtha fraction of the Baku crude oil and their chemical structure was confirmed by FT-IR spectroscopy. The surface tension at 298K was measured; the critical micelle concentration (CMC) and some surface active parameters were calculated. The inhibition efficiency (η%) of these surfactants has been studied by both Linear polarization resistance corrosion rate and Potentiodynamic polarization measurements at 50 °C. The data showed that, the presence of investigated inhibitors results a high decrease in the corrosion rate. The inhibition efficiency increases with an increase in the inhibitor dose, getting maximum inhibition efficiency 99.48% at 100 ppm of potassium salt. The Tafel polarization results indicate that the inhibitors act as mixed inhibitors. Tafel slopes are approximately constant and independent on the inhibitor concentration. The adsorption of the inhibitors on the carbon steel surface obeys Langmuir's adsorption isotherm. The thermodynamic parameters of adsorption revealed a strong interaction between the inhibitors and the corroding carbon steel surface.