Synergistic Effect Between Halide Ions And Azole Corrosion Inhibitors:a Molecular Simulation Study

Corrosion inhibitor has been widely used in the field of oil well aciding and pickling,because of its low dosage,low cost and high universality.In practical application,inhibitor molecules will undergo the diffusion process,and then adsorb onto the metal surface and form inhibitor film to protect metal surface.However,when the corrosive medium is the acidic environment,the corrosion inhibitors are easily protonated,and the experimental study found that when the metal is located in an acidic environment,the metal surface has a positive charge.So under the acidic environment,it is difficult to adsorb to the metal surface for the protonated inhibitor molecules,but when the Cl~-,Br~-and I~-ions are present in the solution,the corrosion inhibition performance of the inhibitor can be effectively improved.However,due to the limitations of experimental methods and conditions,it is difficult to reveal the mechanism of the effect of halide ions on the adsorption of the protonated inhibitor molecules on metal surface.Therefore,three halide ions(Cl~-,Br~-and I~-)and three inhibitor molecules(MBO,MBI and MBT)were considered as research object in this paper.By using both quantum chemistry and molecular dynamics simulations,the synergistic mechanism between halogen ion and corrosion inhibitor was discussed.Firstly,the reaction activity of three kinds of inhibitors was studied by the quantum chemistry method.the study of rontier orbital distribution showed that the the frontier orbitals of three kinds of inhibitors are distributed in a ring structure,and almost all of heavy atoms in molecules are covered,according to the parameters of both global reaction activity and local reaction activity,the inhibition efficiency of the three kinds of corrosion inhibitors follows the order MBT>MBI>MBO.Then,the molecular dynamics method was used to study the influence of the concentration and type of halogen ions on the corrosion inhibition performance.According to the results of equilibrium structure,concentration distribution,diffusion coefficient and interaction energy parameters,it is can be seen that the corrosion inhibition efficiency increases with the increasing concentration of halogen ions in a certain range,and after the concentration up to a critical value,the inhibition efficiency decreased.Three kinds of halogen ions can effectively promote the adsorption of corrosion inhibitors on the metal surface with the orderof I~->Br~->Cl~-.Finally,the effect of the concentration and headgroup type of the corrosion inhibitor on corrosion inhibition performance was studied.It can be seen that at a low concentration of inhibitors,increasing the concentration of corrosion inhibitor is beneficial to the inhibitor adsorption on the metal surface and forming a complete and dense corrosion inhibitor membrane.However,when the concentration exceeds the critical value,continuing to increase the corrosion inhibitor concentration has very few effect on the adsorption and membrane forming behavior.The inhibition efficiency of the inhibitors follows the order MBT>MBI>MBO.