Effects of temperature, concentration and synergism on green Schiff bases synthesized from vanillin in applications as corrosion inhibitors for carbon steel in well stimulation

Mild carbon steel is widely used in construction materials owing to its relatively low price, ease of manufacture and high tensile strength. When it is subjected to an aggressive environment, the use of efficient corrosion inhibitors is required. The offshore oil and gas industry apply well stimulation techniques employing strong acids (5-35 wt%), which severely damage metallic structures. Conventional inhibitors may result in environmental and human health problems. In order to avoid that, green compounds have been widely investigated. However in certain applications, such as materials for offshore installations, protection is afforded by multi-component formulations. The synergistic effect of formulations is achieved by the active compounds, intensifiers, surfactants and solvents. Thus the performance of three Schiff bases synthesized from vanillin, a green aldehyde, and aromatic amines was investigated in corrosion inhibition of carbon steel. Weight loss measurements were made in 2 M and 15% HCl over a 313K-353K temperature range in concentrations between 0.4%wt./v and 1.0%wt./v. Effects of binary and ternary mixtures in 15% HCl revealed an increased efficiency for isolated inhibitors at higher concentrations. The addition of potassium iodide enhanced efficiency to 97.78% in 15% HCl at 333 K. Electrochemical tests indicated mixed-type inhibitors. Surface analysis confirmed the presence of a protective film as well as reduced carbon steel roughness. Density-functional theory (DFT) calculations revealed the effects of a substituent on structural and electronic properties in the neutral and acid phases. The role of a sulfur atom in preventing corrosion was also addressed by DFT calculations.

Automated summary

Mild carbon steel is commonly used in construction, but requires efficient corrosion inhibitors in aggressive environments. Green compounds and multi-component formulations have been investigated for better protection.