Rosin imidazoline as an eco-friendly corrosion inhibitor for the carbon steel in CO₂-containing solution and its synergistic effect with thiourea

Rosin is known as an eco-friendly raw material from natural plants. The main component of rosin is abietic acid. Abietic acid has a carboxyl and a tricyclic phenanthrene skeleton in which conjugated double bonds are present. Conjugation structure will lead to local enrichment of electrons, thereby creating sites that can be used for adsorption. In this case, it is expected that a better performance could be obtained if an inhibitor is synthesized from rosin. In this work, rosin was used to synthesize an imidazoline derivative as a corrosion inhibitor, then the corrosion inhibition performance and synergistic effect with thiourea (TU) of rosin imidazoline (RI) for carbon steel in test solution were studied using weight loss measurement, electrochemical techniques and surface characterization. The results show that the inhibition efficiency of RI reaches 83.8% at 200 mg/L. A further increase in RI concentration does not effectively improve the inhibition performance since the critical micelle concentration of RI is present at around 200 mg/L. The molecular characteristics of RI was analyzed by quantum chemical calculations. It clearly shows that multiple adsorption sites exists in the RI molecular structure, hence RI could offer a good inhibition performance. With the compounding of 200 mg/L RI and 10 mg/L TU, the inhibition efficiency could increase as high as 89.8%, demonstrating a good synergistic effect between RI and TU. The corresponding synergistic mechanisms are also proposed.