Comparative Study of Corrosion Inhibition In Carbon Steel Using Non Ionic Surfactants In Acidic Medium

Abstract

The use of surfactants is one of the numerous ways of protecting a metallic surface from electrochemical oxidation or corrosion. The amphiphilic nature of these surfactants leads to the formation of a protective layer on the metallic surface, effectively minimizing the area of contact between the fluids and the metal, thus inhibiting corrosion. Cationic surfactant like CTAB (Cetyltrimethylammonium bromide) has been most commonly used as a corrosion inhibitor, but since it is not environment-friendly, its use has been discouraged. As an alternative, the use of non-ionic surfactants like TritonX100 (Polyoxyethylene octyl phenyl ether), Tween 20 (Polyoxyethylene (20) sorbitan monolaurate), Tween 80 (Polyoxyethylene (20) sorbitan monooleate) and Brij35 (Polyoxyethylene (23) lauryl ether), which are much more environment-friendly were studied as inhibitors. Carbon steel, a common material of construction of industrial vessels and equipment, in contact with hydrochloric acid (HCl) was used to study their action. The non-ionic surfactants showed inhibition efficiencies around 91-92%, which is very close to that of CTAB (97%) at concentrations of 300-500 ppm with 1M HCl at 30°C. The efficiency held steady with increase in further concentration of the surfactants. Increase in immersion time of carbon steel, did not affect the inhibition efficiency by a large factor. As the temperature of the setup was increased, inhibition efficiency was found to decrease substantially, down to almost 30% at 80°C. The inhibition efficiency decreased to 50% with increase in acid concentration up to 4M HCl. Tween20 and Tween80 showed results much closer to CTAB, closely followed by TritonX100, while Brij35 lagged. Since the concentrations of the non-ionic surfactants used are in the order of ppm, their use in coatings for carbon steel equipment is highly economical and is a very good alternative to CTAB.

Keywords: surfactant, inhibition efficiency, nonionic, environment friendly, corrosion