Thermodynamic, Adsorption and Optimization Studies on Carbon Steel in Hydrochloric Acid Environment using Okro Leaf Extract as Corrosion Inhibitor

Abstract

This present study seeks to exploit the use of eco-friendly, Okro leaf extract as an inhibitor in mitigating corrosion on carbon steel metal in acidic environment Gravimetric method was used to study the corrosion process. It was revealed that the inhibition efficiency of the extract on carbon steel decreases as temperature increases. This trend confirmed the physical adsorption mechanism for the corrosion process that resulted in a high rate of corrosion of the carbon steel. Activation energy Ea, enthalpy (ΔHº), and entropy (ΔSº) calculated showed good interactions. The rise in activation energy with inhibitor concentration confirmed the physical (physisorption) adsorption mechanism for the corrosion of a carbon steel surface. The positive value of adsorption enthalpy (ΔHº) obtained confirmed the endothermic nature of the corrosion process. The activation entropy (ΔSº) values obtained were all negatives which show that the activated complex in the rate-determining step represents association rather than dissociation step. Corrosion inhibition occurred by an attribute of inhibitor molecules adsorption on the surface of carbon steel which is seen to be in conformity with Langmuir, Freundlich, and El-Awady adsorption isotherm models. To obtain the least weight loss of carbon steel, optimization of the process variables affecting the corrosion process was carried out using Response Surface Methodology (RSM). Three parameters were varied viz; inhibitor concentration, contact time and temperature, and their effects on weight loss of carbon steel were established. The obtained data fitted well to the quadratic model which was also validated. The model predicted the lowest weight loss of 0.045 g with the optimal condition of inhibitor concentration of 198.71 ppm, 2.04 hrs of contact time, and 40.29°C of temperature.