Development of environmentally friendly corrosion inhibitors combined with experimental and DFT calculations: Synergistic protective effects of PASP and LPHA in H ₂ S environment

The development of environmentally friendly corrosion inhibitors is crucial for ensuring the safety and longevity of pipeline steel in environments rich in hydrogen sulfide (H
2
S). This study investigates the synergistic protective effects of polyaspartic acid (PASP) and L-phenylalanine (LPHA) on X65MS pipeline steel in a simulated H
2
S corrosion environment. Electrochemical techniques, including electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, and electrochemical noise (EN) analysis, were employed to evaluate the corrosion inhibition performance. Additionally, density functional theory (DFT) calculations and molecular dynamics (MD) simulations were utilized to elucidate the adsorption mechanisms at the atomic level. The results demonstrated that the composite inhibitor system (0.1 mol/L LPHA+0.2 mol/L PASP) achieved an outstanding inhibition efficiency of 92.95%, significantly outperforming the individual components. The synergistic effect was attributed to the complementary roles of PASP and LPHA: PASP formed a chemisorption layer through carboxylate-Fe coordination, while LPHA enhanced adsorption via amino groups and hydrophobic benzene rings, effectively filling gaps in the protective film. DFT calculations revealed strong electron-donating capabilities for PASP (highest occupied molecular orbital (HOMO): -7.231 eV) and LPHA (HOMO: -5.453 eV), while MD simulations confirmed a higher binding energy (-122.54 Kcal/mol) for the composite system. Surface analysis (scanning electron microscopy (SEM)-energy dispersive spectroscopy (EDS)) showed an 85% reduction in sulfur content on the treated steel, validating the efficacy of the inhibitor. This study provides a green and efficient solution for mitigating H
2
S-induced corrosion, combining experimental and theoretical insights to advance sustainable corrosion protection technologies within the oil and gas industry.