Gemini cationic pyridinium surfactants based on palm kernel oil mucilage as novel green corrosion inhibitors for pipeline steel in aerated 0.5 wt% NaCl solution under dynamic conditions: Experimental and computational studies

Abstract

Pipeline steel is specifically designed for long-distance fluid transportation. It is prone to corrosion caused by pitting and cracking due to its exposure to hostile operating environments. Because of this, it is challenging to administer low doses of potent inhibitors. In this study, a series of Gemini surfactants (GSS-2, −4, −6) based on palm kernel oil mucilage as novel green corrosion inhibitors was eco-friendly prepared and characterized, then tested as a green corrosion inhibitor for pipeline steel in an aerated 0.5 wt% NaCl solution. The results showed that GSS surfactants act as excellent inhibitors in the tested conditions, with inhibition efficiency reaching 97.06, 98.02, and 98.66 % after three days by weight loss measurements for the optimum concentration (10^-5M) of GSS-2, GSS-4, and GSS-6, respectively. Additionally, it was approved that these surfactants obey Langmuir adsorption isotherm and exhibit physico-chemical adsorption properties, with ΔG_ads values ranged from −51.31 to −56.48 kJ/mol. The pipeline steel corrosion showed lower entropy, lower enthalpy, and lower activation energy with the GSS inhibitors. The most effective GSS-6 surfactant lowered the reaction entropy, enthalpy and activation energy from −163.51 to −199.51 J.mol⁻¹.K⁻¹, from 23.71 to 18.24 kJ.mol⁻¹ and from 26.38 to 20.91 kJ.mol⁻¹, respectively. Both SEM-EDX and XPS analyses proved the interaction of GSS molecules with the pipeline steel surface. The molecular geometries and inhibitory effectiveness of corrosion inhibitors GSS-2, GSS-4, and GSS-6 were investigated through density functional theory (DFT) calculations and Monte Carlo (MC) simulations. Monte Carlo simulations confirm that adsorption is driven by interactions with chloride ions, oxygen, and nitrogen atoms, with GSS-6 demonstrating the highest adsorption energy. The results obtained from theoretical calculations establish GSS-6 as the most effective inhibitor, which consists of experimental data.