Dimer Indolizine Derivatives of Quaternary Salt Corrosion Inhibitors: Enlightened High-Effective Choice for Corrosion Prevention of Steel in Acidizing
Authors: Yang Zhen , Wang Yefei , Finšgar Matjaž , Zhan Fengtao , Hu Huayou , Wu Jiajia , Ding Wengang , Ding Mingchen , Chen Wuhua 
Published: October 2020

Summary
For decades, increasingly severe downhole conditions call for superior and less-expensive corrosion inhibitors (CIs) for acidizing in petroleum production. Inhibitors that exhibit satisfactory protective ability at relatively low concentration are of great interest to most scholars in this area. In this work, two newly obtained dimer indolizine derivatives that were derived from the conventional quaternary quinolinium salts were introduced as potential highly efficient acidizing CIs. The indolizine derivatives could perform well alone, even without any synergistic component, in concentrated hydrochloric acid (HCl).
Two quinoline ammonium salts, ethyl acetate quinolinium chloride (EAQC) and n-butyl quinolinium chloride (BuQC), were synthesized in advance by means of the quaternarization process. Afterward, in the presence of alkali, the ammonium salts could then get converted into the corresponding novel dimer indolizine derivatives easily by means of a 1,3-dipolar cycloaddition reaction in a relatively high yield. The derivatives were purified and their accurate chemical structures were confirmed by elementary analysis, nuclear magnetic resonance (NMR), and mass spectrometry (MS). Dimer derivatives of two quinoline salts were prepared successfully and characterized separately as C26H23N2O4Cl and C26H27N2Cl. Corrosion-inhibition performance of the quaternary quinoline salts as well as the related dimer indolizine derivatives in concentrated HCl for N80 steel was investigated by gravimetric research, electrochemical method, and scanning electron microscopy (SEM) energy dispersive X-ray analysis. The thermodynamic aspect of the inhibition was also discussed.
The structure of EAQC and BuQC are very close to the quinolinium salt inhibitors that are commonly used as key components in commercially accessible acid CI products. However, under alkaline condition, EAQC and BuQC would easily be transformed to dimer indolizine derivatives that possess a general “indolizine” structure. That is the reason why the targeted molecules are recognized as “dimer indolizine derivatives.” Both the derivatives have good thermal stability at approximately 248°F and are easily soluble in acid solution. The surprising difference in the anticorrosion effect between the original quinoline salts and their dimer derivatives was proved by weight-loss experiments in 15 wt% HCl at 194 and 248°F with dosage ranges from 0.01 to 0.5 wt%. The derivatives could retard the corrosion of steel considerably at a much lower concentration compared with their precursors. A 0.1-wt% dosage of indolizine derivatives could increase the inhibition efficiency (IE) of N80 steel remarkably, to approximately 99.0% in 15 wt% HCl at 194°F. Results obtained from gravimetric tests and electrochemical methods are in good agreement and confirmed the well-behaved inhibition of the derivatives.
We predict that the inhibition will be enhanced apparently when similar quinoline or pyridine ammonium salt are converted via the similar 1,3-dipolar cycloaddition mechanism. We have determined that the use of dimer indolizine derivatives provides a creative new choice for low-cost corrosion prevention, and the protective compounds can be applied as main component of acidizing CIs in the coming years.