| The processing capacity of crude oil reached 750 million t/a in China, with further refining industry scale, integration, many of the expansion of the atmospheric and vacuum distillation unit was bigger and bigger in processing capacity, there were 23 refinery which was ten million tons of device in the refinery. Refining production was a high degree of automation of continuous production process, atmospheric and vacuum distillation unit was the first step of refinery crude oil processing, called the "leading" device, it could provide the downstream secondary processing equipment with high quality raw materials. Therefore, the unit directly affected the normal operation of the whole refinery. In recent years, poor quality of refining crude oil with high sulfur, high acid and high salt, there was a series of serious corrosion problems in the process of crude oil processing, atmospheric and vacuum distillation unit at the top of condensing cooling system of low temperature corrosion (<120℃) was common. Because of leak, the unit was forced to stop to repair or reduce quantity processing, brought the huge economic losses for the production of oil refining, and easily led to disastrous consequences such as safety accidents and environmental pollution. Adding inhibitors technology was the most commonly method with economic and effective for oil refining process and adding a small amount of inhibitors could reduce the corrosion of metal. The type of imidazoline inhibitors was a kind of excellent performance and has been widely used, which could satisfy the requirement of environmental protection and had no adverse effect on product quality. But the oil was solvent and neutralizing agent must be used separately, both reducing the security and making the filling process complicated. Therefore, the development of new more green, environmental protection and efficient corrosion inhibitor was a very meaningful work. The water-soluble imidazoline amide was attention to low cost and safety, it could compound with neutralizing agent and convenient to use.(1) From the molecular design, the introduction of Aceticacid as a water-soluble groups, and Tetraethylenepentamine, pelargonic acid, methylbenzene synthesized water-soluble imidazoline amide which had more adsorption center and water-soluble.End group of Tetraethylenepentamine was amidated by pelargonic acid, all of the other amidogens were amidated by Aceticacid, it get water-soluble imidazoline amide inhibitors with closing ring and dehydration. Reaction raw material mole ratio of n (Tetraethylenepentamine):n (pelargonic acid):n (Aceticacid)= 1:1:4.5, the reaction temperature of amidation was 135℃, the reaction temperature of closing ring was 230℃; the reaction time of amidation was 4 h, the reaction time of closing ring was 4 h. The water-soluble imidazoline amide was characterized using gas liquid chromatography, infrared spectroscopy, nuclear magnetic resonance (NMR), mass spectrometry. Quantum chemical was used to studying laws between inhibitors efficiency and the molecular structure. The results showed that the activity region of synthetic product was mainly distributed in imidazoline ring and hydrophilic chain, △E significantly reduced and activity of inhibitors increased after amidation. The activity of inhibitors molecules increased with the hydrophilic group chain length, adsorption of the metal surface increased and more stable, corrosive medium was more difficult to close to the metal surface reaction with Fe. The water-soluble imidazoline amide had good water solubility, concentrations of 10-50 aqueous solution placed a year without stratification and precipitation, compound with Ethylenediamine, Monoethanolamine, Ammonium Hydroxide together were better solubility.(2) The inhibition performance was evaluated by means of the static mass loss method, polarization curves, scanning electron microscope and atomic force microscopy. The results showed that the inhibition effect of the corrosion inhibitor was improved when it was added 15-20mg/L in HCl/NH4Cl-H2O, H2S/NH4HS-H2O and HCl/NH4Cl-H2S/NH4HS-H2O. Microscopy results demonstrated that inhibitors could be formed on the surface of the carbon steel specimen to protect it from corrosion, The surface roughness decreased, adhesion strength increased obviously between AFM probe and the sample surface.The water-soluble imidazoline amide corrosion inhibitor molecules through the "active position covering effect" inhibit the corrosion of carbon steel, its adsorption behavior conforms to Flory Huggins isothermal model, each water-soluble imidazoline averagely replaced 0.31 water molecules and it was multilayer adsorption. Through the theoretical calculation and AFM analysis, corrosion inhibitor molecule could be formed on the surface of Q235 carbon steel with 15 to 20 nm thick film.From thermodynamics, the adsorption process was spontaneous and endothermic process, rised temperature conducive to the adsorption reaction, every molecule of water stripping caused adsorption entropy increase was greater than the multiple of inhibitors molecules caused by entropy decreases, the whole process was process of entropy increase. From kinetics, adsorption reaction rate was affected by the concentration of inhibitors and diffusion rate, increased the concentration of inhibitors or temperature could increase adsorption rate and inhibition efficiency.(3) The problem of low molecular organic corrosion and the performance of water-soluble imidazoline amide were studied. Corrosion reaction rate of Q235 carbon steel was affected by the reaction conditions, prolonged the reaction time in HCOOH-CH3COOH-H2O, increased the concentration and the reaction temperature would increase the degree of corrosion. Uniform corrosion characteristic was observed on Q235 carbon steel surface and corrosion products was mainly Fe2O3, Fe (HCOO) 2 and Fe (CH3COO)2.Corrosion dynamic model was established according to the theory of multiphase reaction kinetics, dynamics process was controlled by corrosion reaction rate of surface.The total apparent reaction of low molecular organic acids corrosion kinetics was first level from the experiment and reaction activated energy was 25.06kJ/mol. The corrosion reaction dynamics equation is r(mol/1·h)=306.13(h-1)e T(K) CHCOOH/CH3COOH(mol/1)-The equation showed that concentration of low molecular organic was 10 mg/L, the temperature< 367 K (95℃), the corrosion rate< 0.2 mm/a, corrosion was lighter; but when the concentration was 100 mg/L, temperature> 287 K (14℃), the corrosion rate was more than 0.2 mm/a of technical requirements, made more severe corrosion in the tower cooling system and the whole line produces.The water-soluble imidazoline amide had a good inhibitory effect in HCOOH-CH3COOH-H2O. The research results showed that when adding to 15 mg/L, corrosion rate was only 0.015 mm/a, inhibition efficiency was 97.1%. Inhibitors was inhibiting anode type corrosion inhibitor, because of inhibitors adsorption on the surface of reactivity of metal, it increased the activation energy of corrosion reaction and reduced pre-exponential factors, corrosion rate was reduced. Inhibitors could be formed on the surface of the carbon steel specimen to protect it from corrosion, the surface roughness decreased under 7nm.When adding to 20 mg/L, adhesion of measured value reached 8.9 nN between the AFM probe and the sample surface. |
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