The inhibition mechanism of six corrosion inhibitors against H2S corrosions has been theoretically studied using quantum chemistry calculations, molecular dynamics simulations and molecular mechanics, and the inhibition performance was also evaluated. Front orbital distributions and Fukui indexes indicate that active reaction zones of the molecules are located in the imidazoline ring, which possesses three reactive sites of N(4), N(7) and C(8), enabling the ring to be multicenteredly adsorbed on metal surface. The calculated mono-molecular adsorption energies, membrane cohesive energies, distance of alkyl chains, and adsorption angles suggest that the stability and binding ability of the inhibiting membrane be enhanced with the increase of the alkyl length. When the number of carbon atoms in the alkyl chain is more than 13, the inhibitors can form a dense and high coverage hydrophobic membrane on metal surface, which can prevent efficiently the corrosive media in solutions from diffusing to the surface so as to slow down or even check the corrosion processes.

Key words: imidazoline, inhibition mechanism, quantum chemistry calculation, molecular dynamics simulation, molecular mechanics