Theoretical Study On The Mechanism Of The Inhibition Efficiency Of 1-(2-hydroxyethyl)-2-alkyl Imidazoline Inhibitor

As an economic and effective technique to inhibit corrosion, organic corrosion inhibitor has been widely applied in various industrial departments, such as chemical cleaning, industrial water, mechanical equipment, which has become an indispensable industrial anti-corrosion material. Most organic corrosion can adsorb onto the metal surface and form a protective film, which block corrosive medium diffusion to metal surface, and thus slow down corrosion rate. However, the inhibition mechanism of inhibitor is still need to further research in order to guide designing newly-type inhibitor. In this paper, 1-(2-hydroxyethyl)-2-alkyl imidazoline inhibitors with various alkyl chain lengths were chosen to investigate corrosion inhibition mechanism for carbon steel in H2S corrosion environment by combination of quantum chemical method and molecular dynamics simulation.The HOMO and LUMO of six inhibitor molecules had the same distribution center. All three reactivity centers (N(4),N(7),C(8)) were located on imidazole ring, indicating the head of imidazoline molecule was preferred to adsorb on metal surface. As a result, alkyl chain was favored to form hydrophobic film.In liquid phase, the adsorption behavior of six kinds of inhibitors on Fe surface was studied by molecular dynamics simulation, and the adsorption mechanism was also investigated. The head group of inhibitor molecule parallely attached to the Fe surface, while the alkyl chain stretched out into liquid phase with a certain angle. With the elongthment of alkyl chain, adsorption angle increased. Also the binding strength of inhibitor molecules with the Fe surface enhanced with the increased of alkyl chain length. Corrosion inhibitors could form corrosion inhibitors membrane on the metal surface. The compactness and stabilization of membrane strengthened as the alkyl chain increased.The diffusion behavior of four corrosive particles (H2O, H3O+, HS-, and Cl-) in membranes was investigated through molecular dynamics simulation. The inhibition performance of inhibitor membranes was analyzed by calculating diffusion coefficient, fractional free volume and the interaction energy. The results showed that all inhibior membranes could effectively prevent the corrosive particles diffuse to the metal surface. With the elongation of alkyl chain length, the inhibitor membranes showed increased capacity for prevention of diffusion of corrosive particles. The inhibition ability of cations or anions (H3O+, HS-, and Cl-) was stronger that that of neutral molecule (H2O).