Study Of Highly Effective Anti-sulfur Corrosion Inhibitors And Their Inhibition Mechanism For Gathering And Transportation Pipeline

The contents of this thesis belonged to the national "Eleventh Five-Year" plan major science and technology issues. Five kinds of corrosion inhibitors of imidazoline derivatives, Mannich bases, pyridine and quinoline and a new nitrogen-containing fused heterocyclic quaternary ammonium salts were synthetized for harsh corrosive environment of PuGuang gas gathering and transportation system, in which the partial pressure of hydrogen sulfide was more than 1.5 MPa, partial pressure of carbon dioxide was more than 1.0 MPa and the average salinity was 159 000mg/l. Synthesis conditions of various inhibitors were optimized by orthogonal experimental design and selected its'handsome synergist which had synergistic inhibition with it. After complexed with various surface active agents and solvents, the finished product inhibitors were gotten. Those inhibitors were evaluated through weight loss methods which saturated with H₂S/CO₂ and high pressure of H₂S/CO₂ at the static and dynamic conditions respectively. And the methods of Anti-hydrogen sulfide stress corrosion cracking, Atomic Force Microscope (AFM) and Environmental Scanning Electron Microscopy (SEM) were taken to evaluate the performance of corrosion resistance to sulfur. Inhibition mechanism and the relationship between molecular structure and anti-sulfur property were researched through composition analysis of the sample surface of product films obtained by X Energy Dispersive Diffraction Spectra (EDX) and quantum chemical paramaters obtained by Density Functional Theory (DFT).The results showed that the optimized synthesis of orthogonal test were the best synthetic inhibitors. Imidazoline derivatives and Mannich bases, respectively, worked in coordination with phenyl thiourea, propargyl alcohol and quaternary ammonium salts had a good synergistic anti-sulfur effect with synergist Y1(a compound containing S and N elements). Corrosion inhibitive properties were weaker when improve water-soluble of all corrosion inhibitors. Five corrosion inhibitors all had some certain anti-sulfur properties in the corrosion environment containing H₂S/CO₂.The order of advantages and disadvantages was: New nitrogen-containing fused heterocyclic quaternary ammonium salt > quinoline quaternary ammonium salt > pyridine quaternary ammonium salt > imidazoline derivatives> Mannich base. The mechanism of corrosion inhibitor which have better inhibitive property of sulfur corrosion was mainly inhibit the corrosion of CO₂/Cl^-in the environment of H₂S/CO₂/Cl^-, and promoted dense carbide and sulfide protective film on the specimen surface.The anti-sulfur performance was closely related to the molecular structure of corrosion inhibitors. Corrosion inhibitors were more efficient in the sulfur-containing environment that their molecules are higher polarity, smaller the E_LUMO, greater the E_HOMO and smaller theΔE which stand for the energy gap of E_LUMO and E_HOMO. In general, corrosion inhibitors, which have stronger electrostatic adsorption, smaller the steric effect, and larger the electron density of central adatom, would have better corrosion resistance to sulfur.