Theoretical design of new benzimidazole derivatives as steel corrosion inhibitors in CO₂ corrosive environment: DFT and Monte Carlo approaches

The interaction of steel with some benzimidazoles namely mercaptobenzimidazole (MBI), 2-(4-thiazolyl)benzimidazole (2-TBI), 2-(2-bromophenyl)-1H-benzimidazole (2-BPBI), 2-(2-pyridyl)benzimidazole (2-PBI) and 2-(2-bromophenyl-1-methyl-1H-benzimidazole (2-BPMBI) for CO₂ corrosion was investigated using density functional theory (DFT) and Monte Carlo (MC) simulation techniques. The BLYP functional together with the generalized gradient approximation (GGA) with double zeta plus polarization function (DNP) basis set was adopted for the DFT computation while the simulated annealing methodology which uses a Monte Carlo sampling of the search space to locate the low energy configuration of the adsorbate-substrate interaction was used for the MC technique. The simulation box consisting of Fe (110), inhibitor, CO₂, NaCI and H₂O was fabricated to simulate oilfield sweet corrosion system at low temperatures. DFT results obtained from this study indicate that the nitrogen atoms of the benzimidazole ring, the aromatic rings, S and the Br atoms are the major active sites for the adsorption of the inhibitors on steel surface. The adsorption energy values for the low adsorption configurations of the adsorbate-surface interactions are high and negative indicating a strong and stable interaction of all the studied molecules with steel in the presence of the corrosive agents. The adsorption strength of the studied molecules on Fe (110) surface in the presence of the corrosive system follows the trend: 2-BPMBI > 2BPBI > 2-PBI > 2TBI > MBI. From the ranking, 2-BPMBI could serve as a new corrosion inhibitor for steel in CO₂-brine environment and could replace MBI which has been reported as a good corrosion inhibitor. In view of the above, our approach will be helpful for quick prediction of a potential inhibitor from a lot of similar inhibitors and subsequently in their rational design and synthesis for corrosion inhibition application.