The inhibiting effect of sophorolipids on the corrosion of X65 steel in the simulated oilfield produced water saturated with CO2 was investigated by weight-loss measurement, polarization, electrochemical impedance spectroscopy, and scanning electronic microscope analysis. Results demonstrated that sophorolipids showed good inhibition performance for X65 steel corrosion in simulated oilfield produced water saturated with CO2 and was found to be an anodic-type inhibitor.

In order to enhance the solubility of chitosan in water and its corrosion inhibition performance on Q235 steel in 1 M HCl solution, N-vanillyl-O-2′-hydroxypropyltrimethylammonium chloride chitosan (VHTC) was synthesized. The structure of VHTC was characterized by FT-IR and 1H-NMR spectroscopy. The corrosion inhibition performance of VHTC on Q235 steel in 1 M HCl solution was studied by weight loss, polarization, electrochemical impedance spectroscopy (EIS) and stereo microscope analysis. Experimental results indicate that VHTC shows better inhibition efficiency compared to chitosan. When the concentration of VHTC increases to 200 mg L−1, the inhibition efficiency reaches 90 %, which is almost equal to the conventional corrosion inhibitors (e.g., imidazoline). The polarization study demonstrates that VHTC is a mixed-type inhibitor caused by a geometrical blanketing effect. The charge transfer resistance is proportional to the inhibitor concentration as revealed by the EIS results, indicating that the protective film on the Q235 steel surface is formed by adsorption of the inhibitor molecules. The inhibition efficiency of VHTC achieves the maximum value within 24 h when the concentration of VHTC is 200 mg L−1. The morphology observation of the corroded steel surface indicates that the corrosion of Q235 steel in 1 M HCl solution is significantly inhibited after introducing VHTC into the acidic solution.

Imidazoline-based dissymmetric bis-quaternary ammonium salt (DBA), a type of environmentally friendly surfactant, was compounded with thiourea (TU). The inhibition properties of the compound inhibitor for Q235 steel in a simulated oil field that produced water saturated with CO2 at high temperature were studied by weight loss measurement, polarization curves, cyclic voltammetry, electrochemical impedance spectroscopy, and observation of surface morphology. Weight loss measurements show that DBA alone has poor inhibition efficiency at high temperature, and TU has a narrow inhibition concentration range. However, DBA and TU together show a synergistic effect, which not only overcomes the short comings when used individually, but also significantly reduces the corrosion rate at reduced dosage. DBA–TU acts as a mixed prohibition inhibitor, and can rapidly form a protective film. The inhibition efficiency decreased slowly with soaking time, which shows it has good substantivity. In conclusion, DBA–TU can be used as high temperature corrosion inhibitor against CO2 corrosion.

In this paper, the inhibition performance of a novel dissymmetric bis-quaternary ammonium salt with an imidazoline ring and an ester group (DBAS) for Q235 steel in 2 % NaCl solution saturated with CO2 was investigated using weight loss, the polarization curve, electrochemical impedance spectroscopy methods and the quantum chemistry calculation. The results show that DBAS, which is good for the environment and have many activated centers and low ELUMO, has a high inhibition performance for Q235 steel in 2 % NaCl solution saturated with CO2. The inhibition efficiency of the studied corrosion inhibitor increased with increasing inhibitor concentrations. The inhibitor is a mixed-type inhibitor which inhibits both anodic and cathodic reactions.

The inhibition performance of two imidazoline inhibitors, 1-(2-thioureaethyl)-2-alkyl-imidazoline (TAI) and chloride-1-(2,3-dihydroxylpropyl)-1-(2-thioureaethyl)-2-alkyl-imidazoline sodium phosphate (TAIP), for Q235 steel in saltwater saturated with CO2 was studied by using molecular dynamics simulations and quantum chemistry calculations. The conclusions were experimentally verified by weight loss, polarization curves, electrochemical impedance spectroscopy (EIS) and surface analysis techniques. The theoretical results suggest that imidazoline ring and heteroatoms are the active site and the adsorption stability weakens gradually in the order of TAIP, TAI. Experimental results show that the two inhibitors act as mixed type inhibitors and can inhibit the corrosion of Q235 in CO2 saturated saltwater solution.

The surface properties of a series of imidazoline-based dissymmetric bis-quaternary ammonium (DBA) salts with different hydrophobic chain lengths DBA-12, DBA-14 and DBA-16 were determined. The adsorption behaviors of these compounds in 1 M HCl solution and their inhibitive effect on Q235 steel (U12350) were investigated using the weight-loss method, polarization, and electrochemical impedance spectroscopy. Results indicate that the three inhibitors all showed good inhibition performance for Q235 Steel in 1 M HCl solution and were found to be mixed-type inhibitors. The adsorption behavior of the three inhibitors can fit the Langmuir isotherm equation and the values of \( \Updelta G_{\text{ads}}^{0} \) are around or lower than 40 kJ mol−1, indicating that there is a stronger chemical adsorption.

The inhibition effect and adsorption behavior of a novel dissymmetric bisquaternary ammonium salt (DBAL) for Q235 steel in 1 M hydrochloric acid medium were investigated using weight loss method, polarization and electrochemical impedance spectroscopy (EIS). The result of weight loss method indicates that the inhibition efficiency increased with DBAL concentration and temperature in the studied range. The inhibition efficiency is above 90% at a concentration of 3.28 × 10−4 M in the temperature range of 298–328 K. The polarization measurements reveal that DBAL is a mix-type inhibitor which mainly inhibits cathodic process. EIS results show that changes in the impedance parameters (Rct and Cd) were due to the formation of a protective layer on the Q235 steel surface by the adsorption of inhibitor molecules. Adsorption follows the Langmuir isotherm via chemical adsorption on the Q235 steel surface. Thermodynamic and kinetic parameters were evaluated from the effect of temperature on corrosion and inhibition processes to discuss the adsorption mechanism.Highlights► The dissymmetric bisquaternary ammonium gemini surfactant as HCl corrosion inhibitors. ► The studied bis-quaternary ammonium salt is a mixed-type inhibitor. ► The inhibition efficiency increases with temperature. ► Adsorption of the inhibitor follow Langmuir isotherm and is chemical adsorption.