Enchancing corrosion resistance of carbon steel using expired pharmaceutical drug sulpuren: a response surface methodology approach in acidic media

Abstract

The anticorrosion potency of Sulpuren drug for carbon steel in a 0.5 M H2SO4 solution was studied using the weight loss method and response surface methodology (RSM). From the weight loss results, the inhibition efficiency (IE) increased when increasing Sulpuren's concentration and decreased at elevated temperatures. The data reveal that at a constant concentration of Sulpuren drug, as the temperature increases from 293 K to 333 K, the corrosion rate of carbon steel generally increases. At the highest concentration, 1.25% v/v, the protection reaches 96.03% after 6 hours of soaking at 303 K, and the maximum inhibition efficiency of 100% was achieved after 72 hours with a Sulpuren concentration of 1% v/v. The anticorrosion activity of Sulpuren drug was interpreted based on its adsorption on the carbon steel surface. The adsorption occurred according to the Langmuir isotherm model. The inhibition process was conducted by a complex mechanism involving mixed-mode interactions, including both physical and chemical adsorption, taking place simultaneously between the inhibitor molecules and the metal surface. The process of corrosion is entropically favorable, and the corrosion process follows a unimolecular reaction pathway. The second-order polynomial statistical model for corrosion IE formed using RSM is found to be favorable. It is shown that this model could successfully explain the experimental data with R2 and R2adj values close to unity and at a 95% confidence level.