Synthesis of some quaternary ammonium gemini surfactants and evaluation of their performance as corrosion inhibitors for carbon steel in oil well formation water containing sulfide ions

Abstract

Three quaternary ammonium gemini surfactants were synthesized, characterized, and evaluated as corrosion inhibitors for carbon steel in oil well formation water containing sulfide ions. The corrosion inhibition efficiency was measured by using electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization techniques. The data obtained from EIS were analyzed to model the corrosion inhibition process through an equivalent circuit. The Tafel polarization results indicate that the inhibitors act as mixed type inhibitors. The nature of the protective film formed on the carbon steel surface was studied using scanning electron microscopy (SEM) and energy dispersive analysis of X-rays (EDX). The effect of molecular structure on the inhibition efficiency was investigated by quantum chemical calculations. It was found that the inhibition efficiency increased with increasing length of the alkyl group attached to the tertiary nitrogen atom. The values of standard adsorption equilibrium constant and free energy of adsorption for the three inhibitors were calculated and discussed. The adsorption of the inhibitor molecules on carbon steel surface was found to follow the Langmuir adsorption isotherm.