Relationship between Molecular Structure of Imidazoline and Its Corrosion Inhibition Behaviors for Carbon Steel in 3%NaCl Solution Saturated by CO2 under Flowing Conditions
The inhibition performances of imidazolines with different hydrophilic groups under static condition were investigated in 3% NaCl solution. The results showed that: the inhibition efficiency of inhibitors follows the order: 2 - undecyl - carboxymerhy1 - imidazoline (CMI-11)＞2-undecyl - hydroxyethyl –imidazoline (HEI-11)＞2-undecyl- aminoethyl- imidazoline(AEI-11)＞2-undecyl -imidazoline (IM-11). The presence of the hydrophilic group improves the corrosion inhibition performance.
In order to study the relationship between the molecular structure and inhibition properties of imidazoline inhibitors, quantum chemical calculations have been also applied. The calculated quantum chemical parameters support that the lower the LUMO-HOMO energy gap of different inhibitors, the higher the inhibition efficiency of inhibitors. The property of inhibitor can be well correlated with its hardness and electronegativity. The lower the hardness, and the larger the electronegativity, the better the inhibition efficiency.
The inhibition performances of imidazolines with different hydrophobic groups under static condition were investigated in 3%NaCl solution. The results showed that: the inhibition efficiency of inhibitors follows the order: 2 – nonyl – aminoethyl – imidazoline (IM-9)＞2 – butyl – aminoethyl - imidazoline (IM-4)＞2 – undecyl – aminoethyl - imidazoline (IM-11)＞2-heptadecyl– aminoethyl-imidazoline( IM-17). The inhibition behavior was affected by the length of carbon chain and solubility of the inhibitors. The inhibition efficiency at 5m/s decreased in the order of IM-9 > IM-11 > IM-17 > IM-4, and solution flow (5m/s) dramatically worsened the inhibition performance of imidazolines. Whenever under static or flowing condition, the presence of the double bond in hydrophobic group improves the corrosion inhibition performance.
The inhibition performances of quaternary ammonium salt of imidazolines were investigated in 3%NaCl solution under static and flowing condition. Under static condition, 2 – undecyl – 1 - hydroxyethyl -1- hydroxyethyl quaternary imidazoline (HQI) exhibited better inhibition performance than 2 – undecyl -1- aminoethyl-1- hydroxyethyl quaternary imidazoline(AQI) did in 3%NaCl solution; in contrast, at 5m/s inhibition performance of AQI was better than that of HQI. Whenever under static or flowing condition, quaternary ammonium salt showed better inhibition behavior than that of imidazoline. The inhibition efficiency was decreased under single phase flowing condition, and the inhibition efficiency was further decreased by the entrained sand in the multiphase flowing condition. As a result, for inhibitors used in flowing condition, the successful selection of inhibitors depends on polycentric adsorption and synergistic effect.
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