Study On Corrosion Inhibition Performance Of Imidazoline Amide For Atmospheric And Vacuum Distillation Unit In The Low-temperature Section

The atmospheric and vacuum distillation unit receives the serious corrosion as the acidvalue and sulfur content of mining or imported crude oil is higher and higher. Not onlyaffects the economic benefit of refineries, but also more harmful to people’s life. The lowtemperature corrosion of atmospheric and vacuum distillation unit refinery mainly refers tothe corrosion below120℃, corrosion system is mainly due to the sulfide and chloride incrude oil decomposition of S2-and Cl-under high temperature and combined with theformation of condensation water and tower HCl-H2S-H2O system. Due to the injection ofammonia and oil acidizing fluid, crude oil pretreatment additives made of ammoniumchloride and small molecule organic acid content increased. Water soluble imidazoline amideis a kind of good performance corrosion inhibitor and has good corrosion inhibition effect onHCl-H2S-H2O system.Based on the previous research, this paper further evaluate the corrosion inhibitionperformance of water soluble imidazoline amide in hydrogen sulfide, hydrogen chloride,small molecule organic acid and ammonium chloride. Weight-loss method, electrochemicalpolarization and scanning electron microscope were used to study the corrosion inhibitionperformance and film-forming performance of water soluble imidazoline amide in hydrogensulfide, hydrogen chloride, ammonium chloride and small molecule organic acid, and theoptimum amount of water soluble imidazoline amide were investigated.The research results show that the water soluble imidazoline amide can form chemicaladsorption film on the metal surface, and effectively prevent the metal surface in contactwith corrosive medium, has a good corrosion inhibition. The results of weight loss methodshow that, with the concentration of inhibitor increasing, the inhibition performanceimproved when the concentration of inhibitor was15mg/L, the weight loss of Q235carbensteel was minimum, inhibition rate was the highest, up to97.1%. Electrochemicalpolarization curve test showed that water soluble imidazoline amide had little influence onthe cathode, but can formation the passivation range in the anode region, and this instructedthat the water soluble imidazoline amide was an anodic inhibitor can be adsorbed to theisolation effect on the metal surface, when the inhibitor addition amount was15mg/L, thelongest passivation interval and can reach-0.02V~1.30V, the minimum passive current only 49μA·cm-2. Electrochemical impedance spectroscopy to present a single capacitive reactancearc, and with the increase of concentration of corrosion inhibitor, impedance arc radiusincreases gradually. Scanning electron microscope showed that the increase of the amount ofcorrosion inhibitor， the corrosion surface of Q235carbon steel gradually reduced, when theinhibitor adding amount of15mg/L, Q235steel surface was smooth, there was almost nocorrosion.Water soluble imidazoline amide suitable for constant pressure relief device "top three"system, can play a good role in the corrosion of hydrogen sulfide, hydrogen chloride,ammonium chloride and small molecule organic acid corrosion medium, when the inhibitoraddition amount was15mg/L, the inhibition rate reached the highest.