| In the process of oil and gas exploitation, the presence of carbon dioxide will lead to severe acidic corrosion of carbon steels. Among numerous corrosion inhibition measurements, the injection of corrosion inhibitors is one of the most effective and economic ways. In terms of carbon dioxide corrosion, imidazolines and imidazoline derivatives are notable corrosion inhibitors, but the dosage and cost limit their further application. Mercapoethanols are capable of self-assembling onto metals and have rarely been applied to corrosion protection field. In this paper,4 kinds of mercapoethanols have been chosen as the experimental objects. Weight-loss measurement, electrochemical method, scanning electronic microscopy and X-ray photoelectron spectroscopy have been used to investigate the corrosion inhibition performance of mercapoethanols in 3.5% NaCl solution saturated with carbon dioxide at 65?. Then the synergistic inhibition effect between mercapoethanols and imidazoline has also been studied. In addition, to get a further insight into the adsorption thermodynamics and kinetics mechanism, the adsorption model of synergistic inhibitors was established. Through above experiments, the following conclusions are made.1) Mercapoethanols are capable of good corrosion inhibition performance, in terms of the corrosion of carbon steels under carbon dioxide environment. Weight-loss study shows that carbon steels severely corroded in 3.5% NaCl solution saturated with carbon dioxide at 338 K. The addition of 2×10-4 mol·L-1 mercaptoethanols can effectively retards the corrosion of carbon steels. And with the increase in the length of carbon chains in the molecular structure of mercaptoethanols, the corrosion inhibition performance generally increases. Potentiodynamic polarization curves reveals that mercaptoethanols with short carbon chains, such as 2ME and 3ME, have predominant influence on the cathodic evolution reaction of carbon steels. While mercaptoethanols with long carbon chains, such as 6ME and 9ME, can retard both the anodic and cathodic reaction, and have a predominant influence on the cathodic reaction.2) There is notable synergistic inhibition effect between mercaptoethanol (2ME) and imidazoline (OIM). Weight-loss and electrochemical measurement reveals that there is notable synergistic inhibition effect between mercaptoethanol and imidazoline. At 338 K, OIM-2ME mixture could strongly inhibit the corrosion of carbon steels in 3.5% NaCl solution saturated with carbon dioxide. With trace level of 5×10-5 mol·L-1 addition, the inhibition efficiency can reach up to 90%. When OIM:2ME equals 1:3, OIM-2ME exhibits best synergistic inhibition effect. And OIM-2ME is a mixed type corrosion inhibitor, which can inhibit both the anodic dissolving reaction and cathodic hydrogen evolution reaction. In addition, based on electrochemical impedance spectroscopy and XPS surface analysis, a bilayer adsorption model has been established to illustrate the synergistic inhibition effect of OIM and 2ME. In the bilayer adsorption model,2ME molecules adsorbs onto the surface of carbon steels with priority to form the first protective layer; then the protonated OIM molecules link to ME molecules by hydrogen bonds, forming the second inhibitor film.3) The experiment results reveal the adsorption thermodynamics and kinetics behaviour of 2ME, OIM and OIM-2ME. Weight-loss studies show that the corrosion inhibition performance of OIM-2ME increase with the increase of its concentration, influencing the charge transfer process and retarding the corrosion of carbon steels. Electrochemical measurements show that OIM-2ME is capable of excellent temperature adaptability and has excellent corrosion inhibition performance among 308 K and 353 K. Adsorption kinetics study suggests that the addition of OIM-2ME increases the energy barrier of corrosion, retarding the corrosion of carbon steels. Adsorption thermodynamics suggests that OIM,2ME and OM-2ME can spontaneously adsorb onto carbon steel and obey Langmuir adsorption. |
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