Vanillin-derived non-ionic surfactants as green corrosion inhibitors for carbon steel in acidic environments

Abstract

Four eco-friendly ('green') non-ionic surface active agents were synthesized via reaction of fatty acids obtained from hydrolysis of castor oil with vanillin. The products were then reacted with monoethanol amine to form a vanillin ester Schiff base. The vanillin ester Schiff base was ethoxylated using ethylene oxide gas in the presence of tri-ethyl amine as a catalyst to give the desired non-ionic surfactants. The chemical structures of the obtained surfactants were characterized using FTIR and 1HNMR spectroscopy. The inhibition effect of the four synthesized non-ionic surfactants derived from vanillin (VE15, VE20, VE40, and VE60) on the corrosion of carbon steel in acidic media of 0.5-M HCl was studied by weight loss, potentiodynamic and electrochemical impedance spectroscopy measurements. The results show that the synthesized inhibitors are effective inhibitors even at very low concentrations, and the adsorption on carbon steel surface obeys the Langmuir adsorption isotherm. Potentiodynamic polarization curves reveal that the synthesized inhibitors behave as mixed-type inhibitors. Adsorption of used inhibitors led to a reduction in the double layer capacitance and an increase in the charge transfer resistance. Calculated ΔG ads o values indicated that the mechanism by which these inhibitors adsorb onto carbon steel in 0.5-M HCl solution is chemical adsorption. The surface activities of the synthesized surfactants were determined using surface tension measurements. The biodegradability of these surfactants indicates that the compounds readily degrade in the environment and can be considered as green corrosion inhibitors.