Thiophene-imidazoline derivatives with varying chain lengths modified by organic acids as corrosion inhibitors for carbon steel in the CO-saturated oilfield produced water.

The dissolution of CO in oilfield produced water causes severe pipeline corrosion and economic losses, highlighting the critical need for medium-high temperature corrosion inhibitors for carbon steel protection. Imidazoline derivative corrosion inhibitors S4-C7 (thiophene-imidazoline octanamide), S4-C9 (thiophene-imidazoline decanamide), S4-C11 (thiophene-imidazoline lauramide) and S4-C13 (thiophene-imidazoline myristamide) with different carbon chain lengths were synthesized by modifying thiophene-imidazoline with different organic acids. At medium-high temperatures, weight loss measurements, electrochemical tests, surface morphology analysis, and theoretical calculations were employed to investigate their inhibition performances and mechanisms in CO-containing solutions. The findings indicate that S4-C11 exhibits excellent corrosion inhibition performance. Specifically, when its concentration reaches 100 mg L, it can attain an inhibition efficiency of 87.55%. In addition, the investigation was carried out to elucidate the underlying factors contributing to the disparities in the corrosion inhibition efficiencies among corrosion inhibitors with varying carbon chain lengths. One of the reasons is that the carbon chain length affects the hydrophobicity of the corrosion inhibitors. Through quantum chemical calculations and molecular dynamics simulations, it has been firmly established that, in comparison with S4-C7, S4-C11 exhibits a more remarkable electron-donating ability. Moreover, S4-C11 shows lower adsorption energy on carbon steel surfaces and forms a more compact protective film, which collectively contributes to its superior performance. These combined properties more effectively limit contact between the steel surface and corrosive species, thereby inhibiting further corrosion.