Theoretical Study On The Synergistic Effect Of Imidazoline Oleate And L-cysteine On Corrosion Inhibition

Corrosion of materials is a worldwide problem facing the oil and gas industry.Currently,adding corrosion inhibitors is one of the main countermeasures of corrosion protection.The addition of corrosion inhibitors is widely used because of its low cost,quick effect,and simple operation.In order to further improve the efficiency of the corrosion inhibitors and reduce the costs,two or more corrosion inhibitors are usually mixed use in industrial production.The main propose of this thesis is to study the synergistic mechanism of corrosion inhibitors from a theoretical perspective and provide theoretical support for the compounding of corrosion inhibitors.The synergistic effects of two green inhibitors,oleic acid imidazoline(OIM)and L-cysteine(CYS).were studied by experiments and molecular simulation techniques to analyze the synergistic mechanism.Firstly,the corrosion inhibition performances of OIM and CYS on carbon steel were studied by weight loss method and electrochemical technique.Then the active sites of OIM and CYS molecule were studied by density functional theory.Finally,molecular mechanics and molecular dynamics methods were used to study the kinetic adsorption process of OIM and CYS on Fe(110)surface,and the synergistic mechanism was discussed.The main conclusions drawn from the study are as follows:1.The results of weightlessness test and electrochemical experiment show that the corrosion inhibition efficiency the of mixture corrosion inhibitor OIM and CYS on Q235 carbon steel in 3.5 wt.%NaCl solution containing saturated CO2 is up to 91.14%.The corrosion inhibition efficiency is obviously higher than that of OIM and CYS used individually.The significant synergistic effect was observed when the two corrosion inhibitors are mixed used.The synergistic index S is 2.45.The electrochemical analysis results show that the corrosion inhibitors of OIM and CYS was a double-layer adsorption mechanism.2.Density functional calculations show that the active region of OIM molecule is distributed on the cephalic imidazole ring,and the active region of CYS molecule is located on the polar group of-SH,and the reaction activity of OIM is stronger than that of CYS,which is consistent with the experimental results.3.Molecular dynamics simulation results show that the two inhibitors take the parallel adsorption configurations on the metal surface.The absolute value of adsorption energy of OIM molecule is 120.95 kcal·mol-1,which is higher than that of CYS molecule by 65.68 kcal·mol-1.With the increase of the number of the same inhibitor molecule,the film compactness and the interaction energy with metal surface increase.The optimum number of adsorption molecule of OIM and CYS are 12 and 36,respectively.A double-layer mixed adsorption inhibitor film is formed when the mixture corrosion inhibitor are used.OIM is the host body of the corrosion inhibitor film,and the CYS molecule fills in the voids of the film making the film layer denser.The corrosion inhibition effect is the best when the proportion of OIM and CYS is 3 to 1,which is consistent with the experimental result.