(648f) Molecular Simulations of Corrosion Inhibitors on Metal Surface at Operating Conditions

Corrosion is a massive problem that results in extensive damage to facilities and infrastructure, and in extreme cases can cause fatalities [1]. The total cost of corrosion has been estimated to be US$2.5 trillion, which corresponds to around 3% of the global GDP [2]. In this regard, corrosion inhibitors (CI) synthesized from organic compounds are one the many tools that industry uses, increasing the lifetime of equipment while also ensuring a safe operation. They have been applied in various fields such as petroleum extraction and refining, pipelines transportation and industrial water [3].Research in the study of CI chemicals have been growing in the past few years, with new families of compounds being discovered and new techniques being used [4],[5],[6],[7].

In specific, depending on the application and the operating conditions, the process stream can contain small amount of acid gases, such as CO₂, which alter the environment of the internal wall of the pipeline, causing the so-called sweet corrosion, and leading to the formation of FeCO₃ oxides on the metal surface. Therefore, the corrosion mechanism also changes since the effect of CO₂ with water on the metal is different compared to just water and other fluids [8]. Tackling this internal corrosion requires the understanding of the environment in the pipes during flow, where the metal is in contact with different molecules in multiphase flow conditions at varying temperatures.

Little is understood regarding how is the mechanism of the formation of the protective film of corrosion inhibitors on the metal surface. In recent times, molecular simulation has raised as a modern tool to complement the adsorption characterization of these chemicals, while providing insights of the experimental results by observing the molecular interactions through a microscopic picture of the system under investigation. Although extensive research has been made to model the behavior of corrosion inhibitors on metallic surfaces [3],[9],[10], simulations are mostly done with only one inhibitor chemical molecule on the surface, and in vacuum and aqueous conditions, with scarce evaluation of the presence of electrolyte molecules and acid gases on the inhibitors mechanism.

Thus, this contribution is devoted to study the corrosion inhibitor film on the metal surface in brine systems saturated with CO₂. We have performed Molecular Dynamics simulations to help in the understanding of the inhibitor adsorption on the substrate, complemented with electrochemical experiments, such as linear polarization resistance (LPR) and electrochemical impedance spectroscopy (EIS). The presence of CO₂ enriched environment, electrolyte molecules and inhibitor formulations in the simulation box was inspected in order to quantify their influence on the inhibition performance at different operating conditions. Results show that a decrease of around 30% in the adsorption energy for inhibitors is obtained after the addition of water molecules. Interestingly, the presence of water leads to the formation of an electric double layer where H₂O molecules form an inner layer through strong chemical bonds with the top layer of the metal surface, that hinders the inhibitor molecule adsorption, but that can be broken by CO2 molecules in most of the cases.

This work has been partially supported by ADNOC Gas Processing and its stakeholders (Shell, Total and Partex) through the Gas Research Center (project GRC-2017)

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