Study Of Corrosion Inhibitors In Acetic Acid And CO₂ Mediums

Acetic acid is an important component of acidizing fluids in oil and gas production industry and a lower molecular organic acid as associated products in producing fluids of gas and oil fields, which coexists mostly with CO₂, Cl^- containing in the producing fluids. So, three molecular structures as corrosion inhibitors, such as symmetrical N,N'- disubstituted thioureido imidazolines, substituted thioureido imidazolines and a new imidazolyl thioureas derivative, were designed.Symmetrical N,N'-disubstituted thioureido imidazolines were synthesized from oleic acid, lauric acid, diethylenetriamine and carbon disulfide. Substituted thioureido imida zolines were synthesized by oleic acid,diethylenetriamine and thiourea. A new imidazolyl thioureas derivative was prepared from thiourea, tetraethylene pentamine, organic acid, and the optimum synthesis condition was investigated.Their inhibiting behavior on X52 steel in saturated CO₂, 0.1mol/LCH3COOH and 0.5%NaCl solutions were investigated by weight loss, potentiodynamic polarization and electrochemical hydrogen permeation measurement. The results showed that symmetrical N,N'-disubstituted thioureido imidazolines's adsorption behavior obeyed Langmuir equation, and which worked mainly by changing the anodic process of corrosion reaction; amido imidazolyl thiourea is a good inhibitor for inhibiting corrosion and hydrogen permeation even at a low concentration. It also mainly controlled the anodic process of corrosion reaction, and it's adsorption behavior obeyed Langmuir equation too.The inhibition synergistic effect between amino imidazolyl thiourea and some inhibitors, such as hexamethylenamine, potassium iodide, butynol, trisodium phosphate and organic phosphate, was investigated by potentiodynamic polarization and weight-loss method. The results showed that there was synergistic effect between amino imidazolyl thiourea and KI.