Corrosion inhibition of mild steel by expired clindamycin in optimised HCl concentrations via central composite design-response surface methodology

Abstract

Findings tailored towards adsorption and corrosion inhibition of metal addressed limitations in describing the interaction between the inhibitor and metal surface, utilising kinetics, thermodynamics, and isotherm models through a central composite design-response surface methodology (CCD-RSM). Expired clindamycin (ECLI) was employed as an anti-corrosion agent to stampede the corrosion of mild steel in the oil and gas industries in optimised HCl concentration using the weight loss method. From the analysis of variance (ANOVA), the significance of process parameters was ascertained. The regression coefficients (R²) of the developed models and validation experiment conducted at optimum conditions insinuate that the predicted values are in excellent agreement with the experimental values. The change in enthalpy was positive and less than the 100 kJ/mol threshold, which indicates an endothermic reaction. The experimental data fit the Langmuir, Freundlich, Temkin, El-Awady, Frumkin, and Flory-Huggins isotherms, but the Langmuir isotherm best expresses the adsorption mechanism. The corrosion rate constant was evaluated using zero-order, first-order, and second-order kinetics; hence, the corrosion process followed zero-order kinetics. The adsorption of ECLI on mild steel in varying HCl media is plausible, spontaneous, and exhibits both physisorption and chemisorption according to Gibbs’ free energy threshold.