Binding corrosion promoters from aqueous solutions by Benzalkonium chloride

Corrosion inhibition in aqueous environments is essential for extending the operational lifespan of oilfield infrastructure. In this study, we present a novel density functional theory (DFT)-based framework to investigate the molecular interactions between benzalkonium chloride (BAC) and six corrosion promoters commonly encountered in oilfield operations: FeCl₂, NaHCO₃, NaCl, acetic acid, dissolved CO₂, and CaCl₂. Our simulations reveal that BAC exhibits strong binding affinities with FeCl₂ (ΔG = −18.88 kJ/mol), NaCl (ΔG = +14.39 kJ/mol), and NaHCO₃ (ΔG = +22.21 kJ/mol), while interactions with acetic acid, CO₂, and CaCl₂ are thermodynamically less favorable (e.g., ΔG for CaCl₂ = +62.50 kJ/mol). These findings are supported by detailed electronic structure analysis, including HOMO-LUMO gaps and NBO interactions, which show significant π–cation stabilization in the BAC-FeCl₂ complex (E² = 40.95 kcal/mol). The results provide a valuable insight into BAC's selective inhibition behavior and suggest that combining BAC with complementary inhibitors could enhance protection against a broader range of corrosive species. This work offers a predictive methodology for designing advanced corrosion inhibition systems with direct relevance to chemical engineering applications in the oil and gas industry.