New Insights into the Effect of CO2 and NaCl Aqueous Solution on the Adsorption Behavior of Corrosion Inhibitors through Molecular Simulations

  • Seba Al-Areeqi

Student thesis: Master's Thesis

Abstract

Corrosion inhibitors well-rooted their presence in the industry to combat internal metal deterioration. Nevertheless, their successful implementation in different conditions is based in most of the cases on a trial-and-error testing approach [1]. Molecular simulations can be used to tailor organic corrosion inhibitors structures to provide relationship between their chemical structures and their protectiveness ability [2]. However, seldom attempts have focused on simulation of corrosion inhibitors in industrial rigorously encountered conditions, such as sweet corrosion (in the presence of CO2) and saline aqueous phase. Hence, the goal of this work is to model corrosion inhibitor molecules near the metal surface in diverse environments with the purpose of designing ad-hoc corrosion inhibitor formulations for industrial applications. Three amine-based and imidazoline-based inhibitors abbreviated: TEPA, iTEPA and IEDA were selected for this MSc thesis study via implementing classical molecular dynamics (MD) simulations. Results of single inhibitors adsorption showed that CO2-saturated saline media lead to severe alteration of the three inhibitors spatial conformation on iron surface. Interestingly, water dominated the competing interactions by forming a highly ordered structural double adsorption layer placed in direct contact with the surface. Quantitative results of the adsorption energies went downward by 48% and 82% for TEPA and iTEPA inhibitors after addition of NaCl ions and dissolved CO2 gas to the aqueous phase. On the contrary, enhancement by 36% in IEDA adsorption performance on the iron surface was revealed in the same applied condition. The molecular-level insights of the multi-inhibitor adsorption near the aqueous-metal interface revealed the following: 1) TEPA and iTEPA manifested organized assembled inhibition films on the iron surface detected by ordered density profile peaks. 2) Inhibition films adsorbed on the iron surface on top of the CO2 that was held in place by strong surface interactions. 3) Radial distribution function g(r) evident strong hydrogen bonding tendency at 1.7 Å distant peaks in the g(r) plots between donor-acceptor IEDA functional groups and water atoms that hindered IEDA adsorption process. Finally, the synergistic effect of hybrid inhibitor mixture1 resulted in triple the adsorption energy compared to pure multiple inhibitor films.
Date of AwardOct 2019
Original languageAmerican English

Keywords

  • corrosion inhibitors
  • molecular simulations
  • adsorption
  • imidazoline derivatives
  • synergistic/dispersive effect
  • multi-inhibitor adsorption.

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