Design And Synthesis Of Corrosion Inhibitors In Oil And Gas Fields With High H₂S And CO₂

H₂S and CO₂ corrosion, is a common corrosion type in the world oil industry, also is one of the prominent problems which plagued the development of petroleum industry of China. In the H₂S and CO₂ corrosion protection, the use of inhibitor is a significant measure at home and abroad. At present, the inhibitor which resists high concentration of H₂S and CO₂ is reported rarely, and highly priced, and also has high pertinence, depending on the further development. In this paper, 15 kinds of undecyl imidazoline corrosion inhibitors commonly used in oil field were chosen to be research objects.The quantitative structure-activity relationship (QSAR) of undecyl imidazoline corrosion inhibitors for anti-corrosion behavior towards hydrogen sulfide and carbon dioxide was studied using density functional theory (DFT) and regression analysis methods. A stepwise regression analysis was used to determine the main independent factors that affect the activity of the compounds and a QSAR model was established. We found that the electron transfer parameter (ΔN), the electrostatic charge of non-hydrogen atoms in the imidazole ring (ΣQring) and the mean molecular polarizability (α) were the main independent factors that contribute to corrosion inhibition. Based on the QSAR model, combination of hard and soft acid-base theory and intramolecular synergistic effect, via modifying substituent R2 structures to improve the values of the three parameters, such asΔN,ΣQring, andα, we have theoretically designed 4 new compounds. The predicted results by QSAR model show that the four inhibitors all have excellent anti-corrosion of hydrogen sulfide and carbon dioxide The method of quantitative structure-activity relationship which used for design drug molecules was applied to the inhibitor molecular designing, through theoretical and experimental methods to verify the design results . The systemic research results are as follows: activities.According to the results of previous studies, alkyl chain lengths of four new imidazoline corrosion inhibitor molecules were revised, and its inhibition performance was theorectically filtered and evaluated using molecular dynamic simulations (MD) and quantum chemistry calculations (QC). MD result shows that the corrosion inhibitor molecule with alkyl chain length of 15 has better adsorption energy than the molecules whose alkyl chain length is 11 or 17 when hydrophilic groups are the same. When the adsorption process occurs, the ring of imidazole and the hydrophilic chain were firstly adsorbed to the metal surface, and the non-polar alkyl chain deviated from the surface and self-assemblies into a compactly-arranged hydrophobic membrance. The adsorption stability weakens gradually in the order of D, C, A and B. Quantum chemistry calculation results indicated that the reaction activity sites mainly concentrated in the imidazole ring and heteroatoms. D bore the highest reaction activity among the four molecules. The reaction activity weakens gradually in the order of D, C, A and B.The first three molecules we designed were synthesized by solvent method and the corrosion inhibition performance for mild steel corrosion under the condition of H₂S and CO₂ coexistence were investigated by weight loss method, polarization curve and electrochemical impedance spectroscopy (EIS). The results indicated that the three inhibitors all have excellent corrosion inhibition performance. The average highest inhibition efficiencies of the three corrosion inhibitors are 92.96%, 90.72% and 94.36%, respectively. The best added concentration is 100mg/L, which verified the correctness of molecular design by computer simulation method.The synergetic adsorption and corrosion inhibition properties of 1-(2-methyl- thioureaethyl)-2-pentadecyl-imidazoline (B) and 2-aminothiazole (AT) for Q235 steel corrosion under H₂S and CO₂ coexistence were investigated by weight loss method. Results showed that the combined inhibitor strongly inhibited the corrosion of Q235 steel. The corrosion inhibition efficiency using 50mg/L B was 97.63%. The inhibition efficiency increases with increasing in inhibitor concentration but decrease with the temperature, and it has good and high temperature performance. Adsorption obeyed Langmuir isotherm. It was spontaneous and exothermic, and belonged to mix-type adsorption which mainly dominated by chemisorptions.