The Synergistic Effect between Imidazoline-Based Dissymmetric bis-Quaternary Ammonium Salts and Thiourea Against CO₂ Corrosion at High Temperature

Imidazoline-based dissymmetric bis-quaternary ammonium salt (DBA), a type of environmentally friendly surfactant, was compounded with thiourea (TU). The inhibition properties of the compound inhibitor for Q235 steel in a simulated oil field that produced water saturated with CO₂ at high temperature were studied by weight loss measurement, polarization curves, cyclic voltammetry, electrochemical impedance spectroscopy, and observation of surface morphology. Weight loss measurements show that DBA alone has poor inhibition efficiency at high temperature, and TU has a narrow inhibition concentration range. However, DBA and TU together show a synergistic effect, which not only overcomes the short comings when used individually, but also significantly reduces the corrosion rate at reduced dosage. DBA-TU acts as a mixed prohibition inhibitor, and can rapidly form a protective film. The inhibition efficiency decreased slowly with soaking time, which shows it has good substantivity. In conclusion, DBA-TU can be used as high temperature corrosion inhibitor against CO₂ corrosion.