Electrochemical Model of CO_2 Corrosion in the Presence of Quaternary Ammonium Corrosion Inhibitor Model Compounds

摘要

The oil and gas industry utilizes surfactant-type organic corrosion inhibitors to mitigate internal pipeline corrosion. Changes in corrosion rates due to inhibitor addition have been related to adsorption isotherms as a function of the inhibitor concentration. However, the question as to how a corrosion inhibitor affects the electrochemical reactions governing CO_2 corrosion remains unclear. This research proposed to investigate the issue by using a systematic approach: four different corrosion inhibitor model compounds, synthesized in-house, were utilized to determine the effect of the tail length on the kinetics of the electrochemical process underlying the corrosion of a UNS K03014 steel in CO_2 corrosion at pH 4. The corrosion inhibitors all contained the same head group (dimethyl-benzyl-ammonium) with four different alkyl tail lengths (C4, C8, C12, and C16). A theoretical model of the increase in the activation energy of the electrochemical process underlying CO_2 corrosion due to the presence of the corrosion inhibitors led to the development of a modified Butler-Volmer equation. Such an equation describes the retardation in charge transfer rates of the electrochemical reactions associated with the corrosion of mild steel. The model was compared with experimental potentiodynamic sweeps for each system containing the corrosion inhibitor model compounds. As a result, the corrosion model predicts the corrosion rate and the open circuit potential in the presence of a corrosion inhibitor with a high degree of accuracy.