Effect Of Hydrophobic Base Structure On Corrosion Inhibition Performance Of Imidazoline Quaternary Ammonium Salt

The problems of carbon oxide corrosion have become increasingly prominent in petroleum and natural gas industry. To solve the problem of protection in carbon dioxide corrosion is a primary concern for more and more oil field. The use of corrosion inhibitor is the most common, convenient, effective and economical way, wherein Imidazoline Corrosion Inhibitor has been one of the most widely used.In the article, based on the characteristic of corrosion in carbon dioxide, with xylene as water-carrying agent, five kinds of imidazoline which contains different hydrophobic group structure were synthesized by oleic acid, naphthenic acid, benzoic acid, stearic acid, lauric acid, and diethylene-triamine through amidation and cyclization reaction. Using the vacuum distillation to remove the excess sovent which is unreacted completely.Then corresponding imidazoline quaternary ammonium salt was synthesized with benzyl chloride and imidazoline. Then was purfied by recrystallization. Infrared spectroscopy was used to characterize the structure of the synthesized product.At the same time, according to the SY/T5273-2000standard, the results show that imidazoline quaternary ammonium salt has good water solubility.Using the weight loss method and electrochemical test to evaluate the inhibitor performance for N80steel in CO2-saturated stimulating oilfield water, and to study the effect of the corrosion time, temperature and concentration. The result of the static weight loss method investigated that:1) imidazoline quaternary ammonium salt corrosion inhibitor has timeliness, the inhibitor performance was the best in48h;2) the inhibitor performance decreased with the increase of temperature, when the temperature was40℃,the performance was better;3) the inhibitor performance firstly increased with the increase of concentration, and then the inhibitor performance was stable, even it could fall. At the different temperatures, the concentration of d inhibitor was not the same when the inhibition efficiency achieved the best. The results of the dynamic weight loss showed that the corrosion rate accelerated with the increase of the fluid velocity, but in the certain velocity, the inhibition performance was still good. The obtained result by the polarization curve test was consistent with the static weight loss, and there appeared an optimum inhibitor performance with the variation of inhibitor’s concentration. Above methods indicated that the inhibition performance of the oleic acid and naphthenic imidazoline quaternary ammonium salt were better, however, lauryl imidazoline quaternary ammonium salt was the worst, which showed that the carbon chain length and structure of the hydrophobic group in the molecule of inhibitors had certain influence on the inhibition performance. The inhibition mechanisms of imidazoline quaternary ammonium salt were studied by polarization curves, electrochemical impedance, SEM. The conclusions showed that the inhibitor mechanism of imidazoline quaternary ammonium salt was adsorption effect. The structure of the electric double layer was changed by the adsorption film of inhibitor molecular on the surface of wild steel, which was the principal cause of inhibitor performance. The inhibitor mechanism of imidazoline quaternary ammonium salt was negative catalytic effect.