(594f) Molecular Simulations Study of Corrosion Inhibitors Performance on Different Surface Morphologies in CO2-Saline Aqueous Phase

Corrosion inhibitors (CIs) well-rooted their presence in the oil and gas industry to combat internal metal deterioration. The global market of corrosion inhibitors has reported 7.2 billion US$ in 2017 and forecasting to reach US$10.1 by the end of 2025 [1]. Despite the extensive application of CIs in industrial applications, their successful implementation is based in most cases on a trial-and-error testing approach. A deep understanding of the atomistic interactions near the aqueous-solid interface is the key answer to achieving improved CIs performance on metallic substrates that are in continuous contact with aqueous harsh media [2]. Computational quantum mechanics (QM) and molecular simulations can be implemented as powerful tools to screen the effectiveness of organic inhibitors prior to experimental validation. Several studies in the literature have focused on extracting CIs adsorption insights using quantum mechanics and molecular simulations with vacuum or pure water conditions of single inhibitor adsorption [3] -[5]. However, inhibitor adsorption in CO₂-saline solution conditions have not been reported nor considerably examined the multiple CIs aggregation behavior [6]. Besides, the adsorption of such organic compounds not only depends on the competitive adsorbate environment, but is significantly influenced by the metallic surface morphological properties [7] -[8].

This work belongs to a long-term project on using computational tools to design ad-hoc corrosion inhibitors for their practical implementation, providing a relationship between their structural properties and their surface protectiveness ability in different environments. We have recently published results concerning all-atom molecular simulations and chemical quantum calculations to understand the effect of the environment on the surface adsorption of corrosion inhibitor (CI) molecules on iron surfaces [9]. Three CIs abbreviated: TEPA, iTEPA and HC-iTEPA studied were selected to systematically investigate the influence of the alkyl tail, N-pendant group, imidazoline and benzene rings, on the CIs adsorption behavior. The quantum molecular parameters in water solvation anticipated higher electron transfer ability of iTEPA in aqueous conditions compared to TEPA and iTEPA, thus, leading to stronger adsorption on the iron surface, corroborated by the molecular dynamics (MD) classical simulations. MD simulations showed nearly 53%, 39%, 59% reduction in adsorption energies for single inhibitor molecule of TEPA, iTEPA, and HC-iTEPA when shifting from water to CO₂-saline media, respectively. The formation of water double adsorption layer contributed to decreasing the CIs adsorption energies. Nevertheless, the multi-inhibitors study revealed strong adsorption of TEPA and iTEPA on the iron surface, while HC-iTEPA neglected cooperative adsorption and aggregated as a spherical-like micelle with lower surface coverage propensity.

In the present contribution, building on previous work, we will present and discuss for the first time predictions concerning the adsorption behavior of CI molecules with different amine and imidazoline-based groups on different surface morphologies in dense CO₂-saline aqueous phase. MD and DFT calculations revealed that defected wide-groove surfaces significantly enhanced the multi-inhibitors cooperative adsorption behavior. Results of multi-inhibitors adsorption energy (E_ads) followed the order of rough2>rough1>smooth substrates. Furthermore, iTEPA/HC-iTEPA binary multi-inhibitor synergistic effect supported the multi-inhibitor surface interactions. DFT calculations complemented the MD simulation findings, revealing the most preferential sites responsible for the inhibitors electron donation\acceptance ability towards/from the iron surface.

We acknowledge financial support for this work from Khalifa University of Science and Technology (project RC2-2019-007)

KEY WORDS: corrosion inhibitors, adsorption, molecular simulations, surface roughness.

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