The Research On The Corrosion Inhibition Of N80Steel In Acid Solution By Quaternary Ammonium Inhibitors From Cotton-seed Oil

The process of oil well acidizing is a technology which has been widely used in most oil fields at home and abroad. However, high concentration of acid use can bring about serious corrosion. In order to diminish metal dissolution and acid consumption, corrosion inhibitors were widely used in this process. The developed inhibitors which fitting well with the practicality of the produce are very important. For this reason, there is a very important theoretical and practical meaning to test the property and explore the mechanism of the corrosion inhibitors. For improving economic performance and controlling of costs, the study of the synergistic effect of corrosion inhibitors has been a very hot subject in recent years.Meanwhile, environmental pollution and ecological damage caused by corrosion inhibitor has been realized by industrial community and academic interests. It is of great significance to research organic inhibitors which are more friendly to the environment. Cotton-seed oil, a kind of natural and renewable resource. which is also extremely abundant in Xinjiang. Therefore, developing low toxicity and efficient cotton-seed oil inhibitor is a significant research project worthy of carrying out deeply study.In this paper, three series of cotton-seed oil corrosion inhibitors were synthesized. The corrosion inhibition and their synergistic inhibition with the surfactants to the mild steel in15%HCl solution were investigated. Moreover, the adsorption mechanism of corrosion inhibitor was also proposed. The main contents and results of the present work are as follows.1. Using cotton-seed oil and diethylenetriamine, triethylenetetramine, tetraethylenepentamine as raw materials, three series cotton-seed oil imidazoline quaternary ammonium corrosion inhibitors were synthesized. The molecular structure of imidazoline corrosion inhibitors was carried out using the infrared spectrometry. Near the1610cm-1and700cm-1were ascribed to the characteristic absorption peak of imidazoline ring and the characteristic absorption peak of benzene ring, respectively. The results confirmed that the synthesized products are the target product.2. The inhibiting effect of these compounds on the corrosion of mild steel in15%HCl solutions have been studied using weight loss measurement, and the adsorption behavior on the metal surface is simulated. The results show that the inhibition efficiency increases and the corrosion rate decreases with the increasing concentration of the inhibitors, and the inhibition efficiency can reach above90%. The increasing temperature decreaes the inhibition efficiency, and accelerates the corrosion rate. At the same time, the adsorption behavior of the inhibitors on the metal surface fits well with Langmuir adsorption isotherm. The adsorption free energy values locate in the range of20-40kJ/mol, which indicates that the adsorption of inhibitors includes the physisorption and chemsorption.3. The electrochemical behavior of the mild steel electrode in the blank and containing the inhibitors is studied by electrochemical method. The polarization curves results indicate that the inhibitors suppress anodic processes mostly of electrode corrosion at different degree. and the inhibitors the mixed-type inhibitors; the Tafel slopes increase at different degree. Furthermore, the research finds that the increasing temperature decreases the inhibition efficiency.4. This work investigates the corrosion inhibition of the inhibitors and their synergistic inhibition with PEG400.TW-80and CTAB.By weight loss method and Tafel polarization curves.lt found that PKG400,TW-80have a good synergistic effect with the inhibitors,the efficiency of imidazoline inhibitors improved great by combining with them. In this way we can reduce the dosage of corrosion inhibitors and control of costs.5. This part provides quantum chemical studies on the reactive sites and the relationship between the inhibition efficiency and the theoretical parameters for the five models of imidazolines. The structures, the frontier molecular orbital energies and distributions, dipole moments, atom charges, and the reactive descriptors, like the Fukui function, chemical potentials, hardness and softness as well as electrophilicity have been calculated and discussed. It has been found that the main reactive site is the N atom near the outer side of the imidazole ring. Because B2showed the strongest electrophilic power, it is logic to have the highest inhibition efficiency. These results provide useful information and guidelines about the reactive sites suitable for bonding with metal surfaces, the relationship between the theoretical parameters and inhibition efficiency, as well as the corrosion inhibition mechanism.