Hydrolysis of imidazoline based corrosion inhibitor and effects on inhibition performance of X65 steel in CO2 saturated brine

The molecular characteristics of a TOFA/DETA based imidazoline inhibitor were evaluated by analysing the inhibitor protonation profile, the CMC and micelle size and the rate of acid-catalysed hydrolysis of the inhibitor to improve understanding of the corrosion inhibition performance of the main imidazoline component and its hydrolysis products. The ability of the TOFA/DETA imidazoline based corrosion inhibitor and its products of hydrolysis in retarding both uniform and localized corrosion were assessed and compared on wet-ground X65 carbon steel at 80 °C in CO2 saturated 3 wt % NaCl brines. The findings indicate that the imidazoline based inhibitor forms micellar solutions, with a characteristic micelle size of 18 ± 9 nm at the CMC (10 ± 1 ppm) in CO2 saturated 3 wt % NaCl brines, and that under such conditions (pH~4.1), the inhibitor is fully protonated which increases inhibitor solubility/dispersibility and enhances molecular adsorption of the positively charged imidazoline on the metal surface thereby improving inhibition performance. Hydrolysis of the imidazoline and amido-amine is acid-catalysed and the consumption of imidazoline follows a pseudo-first-order reaction mechanism with an activation energy of 72.0 ± 2.9 kJ mol-1. The study concludes that the pre-aged inhibitor has different effects on uniform and localized corrosion behavior of X65 carbon steel.