Investigation of POD - Oil steel corrosion inhibitor as surfactant

Abstract

Waste of the caprolactam production that is the POD-oil (Product of Oxidizing and Dehydrogenation) is investigated by electrochemical impedance spectroscopy technique as a corrosion inhibitor of carbon steel in 20% hydrochloric solution. The inhibitor is investigated also as surfactant at the solution - air interface by means of the maximum bubble pressure technique. It is shown that the Langmuir adsorption of inhibitor takes place at solution - air and solution - steel interfaces. Equilibrium adsorption constant values make (2.2±0.5)x102 M-1 and (2.4±0.5)x102 M-1 respectively. Free adsorption energy was estimated as -(23±0.5) kJxmol-1 for both interfaces. The closeness of the adsorption constant and the agreement of the free adsorption energy values suggest that the inhibitor adsorption on steel is caused basically by the hydrophobic interaction of inhibitor with the solution and less depends on the interaction with steel.