Examination of a Novel Hydrazone Derivative as a Corrosion Inhibitor of Mild Steel Exposed to Oil Field Water

Abstract

A novel hydrazone derivative, [(1E,8E)-9-(3-bromo-4-methoxyphenyl)-1,8-bis(2-(2,4-dinitrophenyl) hydrazone)-3,3,6,6-tetramethyl-1,2,3,4,5,6,7,8,9,10-decahydroacridine], with the molecular formula C₃₆H₃₆BrN₉O₉, was evaluated as a corrosion inhibitor for mild steel in oil-field water collected from the Niger Delta region of Nigeria. The oil-field water was characterised for pH, conductivity, total dissolved solids, dissolved oxygen, and chloride and sulphate ion contents. The medium was slightly acidic (pH 6.8) and had a conductivity of 54,000 μS/cm, indicating a highly conductive corrosive environment. Corrosion rate and inhibition efficiency were determined by weight-loss measurements as functions of inhibitor concentration, exposure time, and temperature. The maximum inhibition efficiency during the 30-day exposure test was 35.11% at 10 ppm. Inhibition efficiency decreased as the temperature increased above room temperature, whereas the corrosion rate increased. Adsorption data were evaluated using the Langmuir isotherm. The reported enthalpy and entropy of adsorption were −47.82 kJ mol⁻¹ and −170.09 J mol⁻¹ K⁻¹, respectively. The reported standard Gibbs free energies of adsorption at 303, 313, 323, and 333 K were −99.65, −101.05, −102.78, and −104.46 kJ mol⁻¹, respectively. These findings demonstrate concentration-dependent inhibition and reduced inhibitor performance at elevated temperatures. The thermodynamic and adsorption results were interpreted as evidence of spontaneous adsorption; however, further electrochemical and surface-characterisation studies are required to confirm the inhibition mechanism.