The inhibition mechanism of five 1-(2-aminoethyl)-2-alkyl-imidazoline compounds [(NH₂)C₂H₄-C₃H₄N₂-CH₂(CH₂)_nCH₃, n＝5, 7, 9, 11, 13] against CO₂ corrosion was investigated by molecular dynamics simulation method. Diffusion coefficient of four corrosive medium particles (H₂O, H₃O^＋, Cl^－ and HCO) in inhibitor membranes was calculated and the diffusion mechanism was studied by analyzing free volume fractional, interaction energy and self-diffusion coefficient of membranes. Results of diffusion coefficient showed that the membranes could restrict the diffusion of corrosive medium particles effectively so as to slow down the corrosion processes, and the diffusion of H₃O^＋, Cl^－ and HCO was hindered more strongly than that of H₂O. As the alkyl chain length increased, the ability of the membrane to hinder the diffusion of particles enhanced. With the help of the theoretical results, the inhibitor had preferable inhibition performance with the increase of alkyl chain length, which accorded well with experimental results.

Key words: imidazoline, corrosion inhibitor membrane, diffusion coefficient, molecular dynamics simulation