Novel High-Efficient Key Component of Steel Corrosion Inhibitors Formulation for Acidification: Indolizine Derivatives of the Conventional N-Heterocyclic Quaternary Ammonium Salts

Acidizing, the widely used technique for well stimulation, requires a great consumption of effective Corrosion Inhibitors (CIs), due to the severe and fast corrosion of metallic equipment caused by strong hot acid as soon as the acidizing fluids are pumping down to reservoir. This paper presents a new concept of indolizine derivative inhibitors with remarkable inhibition effectiveness for steel under acidizing condition, which will reduce the cost and environmental burden of acidizing CIs significantly. Indolizine derivatives of several quinolinium salts (serves as main component of currently used acidizing CIs) were synthesized respectively through an optimized mild procedure from quinoline and different halides. The inhibition of the new inhibitors for N80 steel were evaluated in hot 15 wt.% HCl by gravimetric and electrochemical analysis, while their corrosion prevention mechanism were studied. Surface adsorption and thermodynamic aspect of inhibition process were also investigated. Synergistic inhibition performances of the indolizine derivatives with surfactant, KI and other additives were examined. For the synthesis step, a relatively high yield of the crude products were reported. Inhibition assessment results showed that compared with their quinolinium salt precursors, the dimer derivative can dramatically mitigate the corrosion speed and exhibit considerable inhibition efficiencies even at an extremely low dosage. The results obtained from gravimetric tests, electrochemical methods as well as the surface analysis are in good agreement and confirmed the well-behaved anti-corrosion properties of the derivatives. Conclusion from biotoxicity experiments showed that compared with their precursor quinolinium salts, both the indolizine derivatives and the original quinolinium salts share almost the same EC50 values, revealing the advantages in eco-friendly aspect. Mechanism study reveals that the new compounds can be characterized as cationic "mixed type" and the special molecular structure (conjugated aromatic moiety) may contribute a lot to their remarkable inhibition. Besides, the studied dimer derivatives also presents a good solubility and thermo-stability in acid solution. The amazing synergistic inhibition of indolizine derivative obviously shows that the inhibitive mixture could be utilized as new effective CI for acidizing. The inhibition of conventional quinoline salts CIs would get greatly updated after been converted to their indolizine dimer derivatives. This provides a smart solution for exploring innovative acidizing CI with better protection efficiency. The use of indolizine derivatives may largely minimize the total amount as well as the total expenses of CIs in acidizing fluids and showing good prospects in replacement of the current main components of acidizing CIs in the near future.