Synergistic corrosion inhibition effect of quinoline quaternary ammonium salt and Gemini surfactant in H2S and CO2 saturated brine solution

•A synergistic effect of QB and 12-3OH-12 is found in our research system.•We discuss the relationship between addition and adsorption quantity of inhibitors.•There is a competitive adsorption between QB and 12-3OH-12.•A simple adsorption model is proposed based on the obtained results.

Corrosion inhibition of a quinolinium quaternary ammonium salt and a Gemini surfactant, 1,3-bis(dodecyldimethylammonium chloride)-2-propanol, for mild steel in H2S and CO2 saturated brine solution was investigated by using polarization test, EIS and XPS. The synergistic effect is found between these two compounds when the Gemini concentration is less than 50 mg L−1 in the solution containing 100 mg L−1 quinolinium quaternary ammonium salt, and it disappears when the Gemini concentration is larger than 50 mg L−1. The synergistic mechanism is explained by competitive adsorption of these two compounds on steel surface.