| Recently, the corrosion caused by small molecular organic acids has appeared in the atmospheric and vacuum distillation units. These corrosion can not only cause serious economic losses for the enterprises, but also can effect the long-term safety operation of the equipment. Therefore, studying on the corrosion and the protection of the metal in the small molecule organic acids systems has great significance. The water-soluble imidazoline amide which prepared by our laboratory independently refers to(N-(2-octyl-2-imidazoline)triethylene tetraamide. It has some special features, like good inhibition performance, safety,and environment-friendly. According to the preliminary work, it was found that the water-soluble imidazoline amide had better inhibition efficiency in the small molecule organic acids.The physical and chemical properties of the water-soluble imidazoline amide are studied in this paper. And how the dosage of water-soluble imidazoline amide, the temperature of the system, the pH of the system, and the velocity of flow effect on the film-forming inhibition performance of the water-soluble imidazoline amide are studied.Low temperature kinematic viscosity and density meter were used to study the density and pour point of the water-soluble imidazoline amide and its complex inhibitor; the static anti-foaming method and static suds method were used to study the anti-foaming and suds suppressing properties of the defoamers for the water-soluble imidazoline amide; and AC impedance test methods, atomic force microscopy(AFM) and scanning electron microscopy(SEM) were used to study the film-forming inhibition performance of the water-soluble imidazoline amide in the small molecular organic acids.The studies showed that after the water-soluble imidazoline amide mixed with the ethylene glycol and methanol, the pour point of the mixed system can be reduced to below-40℃. The dosage of the water-soluble imidazoline amide and the blistering volume of the mixed system were directly related. For the water-soluble imidazoline amide, the block polyether-modified silicone oil was better than ultra silicone defoamers and silicone-free defoamers in the aspects of anti-foaming and foam suppression. And when m(block polyether-modified silicone oil):m(water-soluble imidazoline amide) is 15:50, the antifoaming rate and the foam suppression rate of block polyether-modified silicone were 87.5%and75%. When the dosage of water-soluble imidazoline amide was 15μg?g-1, AC impedance test results showed the inhibition film formed on the surface of Q235-B steel had larger membrane resistance and lesser degree of phase separation; AFM observation results showed the inhibition film was smooth and uniform, and the adhesion between the inhibition film and the sample was 7.0nN. When the pH of the system was 7.0-7.5, AC impedance test results showed both the film resistance and the charge transfer resistance of the inhibition film formed on the surface of Q235-B steel were larger; and the electric double layer capacitor was smaller, it meant more water-soluble imidazoline amide molecules adsorbed on the surface of carbon steel Q235-B; AFM observations results showed the inhibition film was more complete and dense, and the inhibition efficiency was better. When the temperature of the system was 30℃-50℃, AFM observation results showed the adhesion of the inhibition film formed on the surface of Q235-B steel had no big difference, the SEM observation showed there was no significant corrosion on the surface of Q235-B steel, but as the temperature continued to rise, the adhesion values are decreasing, the surface of Q235-B steel appeared corrosion. Along with the velocity of flow increasing, AFM observation results showed the adhesion of inhibition film decreased, and the inhibition efficiency of water-soluble imidazoline amide on the Q235-B steel reduced; and SEM observation results showed that when the velocity of flow was greater than 1.15m·s-1, the surface of the Q235-B steel had a tendency to become loose. |
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