Kinetic and Thermodynamic Study of Corrosion Inhibition of Carbon Steel in Acidic Media by Extracts of Parkia biglobosa Pod: Application to Oilfield Pickling Operations

Acid pickling is a standard industrial cleaning process in oilfield operations in Nigeria that causes significant corrosion of carbon steel equipment, necessitating the use of corrosion inhibitors. This study investigates the kinetic and thermodynamic parameters governing the corrosion inhibition of carbon steel in one molar hydrochloric acid solution by extracts of Parkia biglobosa pod, a widely available agricultural by-product in North Central Nigeria. Inhibition efficiency was evaluated by weight loss, hydrogen evolution, and electrochemical methods including electrochemical impedance spectroscopy and potentiodynamic polarisation at temperatures of 30, 40, 50, and 60 degrees Celsius. Thermodynamic activation parameters including activation energy, enthalpy, and entropy of adsorption were calculated from temperature-dependent corrosion rate data. The effect of immersion time, inhibitor concentration, and acid concentration was systematically evaluated. Surface morphology of inhibited and uninhibited steel coupons was examined by scanning electron microscopy. Results show that inhibition efficiency increased from 71 to 94 percent as inhibitor concentration increased from 100 to 500 milligrams per litre, but decreased with rising temperature, suggesting a physisorption mechanism. Negative adsorption enthalpy and entropy values are consistent with spontaneous, exothermic physical adsorption. Electrochemical data indicate that the extract functions as a mixed-type inhibitor affecting both anodic and cathodic reactions. Langmuir adsorption isotherm was obeyed. FTIR analysis confirmed the presence of nitrogen and oxygen-containing functional groups responsible for metal coordination. The study supports the potential application of Parkia biglobosa pod extract as a biodegradable oilfield pickling inhibitor. Keywords: corrosion inhibition, carbon steel, Parkia biglobosa, hydrochloric acid, thermodynamics