Corrosion inhibition of carbon steel in diethanolamine–H 2 O–CO 2 system by some organic sulphur compounds

Abstract

This paper presents an electrochemical investigation of the corrosion inhibition of carbon steel in diethanolamine–water–carbon dioxide systems by four sulphur-containing organic compounds: 2-mercaptobenzothiazole, 2-mercaptobenzimidazole, diethyl thiourea and dimethyl sulfoxide which were found to be effective in the same order as introduced. Potentiodynamic polarisation revealed their cathodic mechanism of action. The adsorption–desorption behaviour of the inhibitors was studied using capacitance-potential and the constant phase element exponent-potential profiles obtained from dynamic electrochemical impedance spectroscopy measurements. Furthermore, quantum chemical calculations at the density functional theory level were performed to help in the analysis of the experimental results. The inhibition power of mercaptobenzazoles was found regardless to whether they were dissociated or not. The double layer capacitance values showed a rather consistent increasing trend with some theoretical parameters namely, the fraction of transferred electrons, the highest occupied molecular orbital energy level, and the permanent dipole moments of the inhibitor molecules.