The Effect of Benzimidazole Derivatives as Corrosion Inhibitors for Carbon Steel in Hydrochroric Acid Solution

Carbon steel has been widely used in oil and petro-chemical industries, and thus, its corrosion is one of the serious problems encountered in these industries. Application of corrosion inhibitors can be considered as an effective way to reduce the degradation of equipment in these industries. Benzimidazole derivatives are heterocyclic organic compounds, which can be used successfully as corrosion inhibitors for carbon steel in acidic media. In this study, the inhibitive properties and adsorption ability of two derivatives of benzimidazole, namely 2-mercaptobenzimidazole and 2- methylbenzimidazole, as well as their effect on corrosion resistance of carbon steel in 1M HCl solution was investigated. The potentiodynamic polarization readings were carried out in HCl solution containing inhibitor concentrations of 0, 50, 100, 150, 200 and 250 ppm. The results showed that the 2-mercaptobenzimidazole was more efficient than 2-methylbenzimidazole. The 2-mercaptobenzimidazole decreased the corrosion rate of carbon steel 88% at 250 ppm, while this value was 54% for 2- methylbenzimidazole at the same concentration. The adsorption of both inhibitors obeys the Langmuir isotherm. The standard free energy of adsorption calculated for both derivatives indicated on physical adsorption. By considering the Tafel slops and equilibrium potentials, the inhibition mechanism of both inhibitors was estimated to be of mixed type