Intermolecular Electron Transfer Promotion On The Adsorption Of Mixed Inhibitors:An Investigation Of Synergistic Mechanism

Oil and gas gathering pipelines are suffering severe corrosion,which threaten the safety,properties and environment of public.Among those corrosion and protection methods,adding inhibitor is an easy operated way,low concentration of inhibitors will show high inhibition efficiency,such the method is widely used in industry field and daily lives.Organic surfactants are typically composed of a hydrophilic group and a hydrophobic group,the easily aggregation and adsorption of organic surfactant at interface will change the composition and structure of the interface,surface tension,interfacial free energy,iron or electron transfer at interface and other properties,making them play an important role in scientific area,industrial field and ordinary lives.Previous research have shown that the complex formulation of different surfactants showed better properties than single component while they were mixed in an appropriate condition,that is synergistic effect,therefore,the study of synergistic mechanisms became an important problem which has been attracting much attention of researchers.Accordingly,in this paper,imidazoline quaternary ammonium salts?IM?was chosen as inhibitor agent,octyl phenol ethoxylates?OP?and benzotriazole?BTAH?were chosen as added additives,the working mechanism for the enhanced adsorption of inhibitors on Fe/H₂O by the electron transfer and bonging process was studied.Then synergistic effect mechanism of mixed inhibitors was studied.Finally,the following detailed results were achieved:Electrochemical results indicated that both IM+BTAH and IM+OP shows good inhibition performance,but the inhibition efficency of IM+OP is higher than that of IM+BTAH.Calculation results indicated that the synergistic effect of mixed inhibitors have close relationship with the frontier orbital energies of single component.The EHOMO and ELUMO of OP molecule are lower that that of IM molecule,therefore,OP and BTAH molecules prefer to donate electrons to the metal surface while IM molecule prefer to accept electrons from metal surface in IM+BTAH and IM+OP system,the electron transfer and bonging with metal surface are enhanced.Water molecules will be displaced by inhibitor molecules and the displacement of water molecules was enhanced after they were mixed together,interfacial capacitance decreases and interfacial charge transfer resistance increased,thus the migrate of corrosive particles to the metal surface was hindered greatly than single component,mixed inhibitors show good synergistic effect.The adsorption procedure of IM+BTAH and IM+OP mixed system were studied.IM and BTAH mixed system were studied.Results showed that the inhibition efficency of IM+BTAH and IM+OP system increased with temperature,mixed inhibitor molecules can adsorbed on metal surface spontaneously.Under the same condition,the inhibition efficiency of IM+OP is higher than that of IM+BTAH,the adsorption of inhibitor follows Langmuir adsorption isotherm.Mixed inhibitors shows better synergistic effect with the increasing difference between accepting-donating abilities.What's more,IM and KL were chosen as inhibitor agent,BTAH,SIK and OP were chosen as added additives,the inhibition performance of mixed inhibitors were studied.Electrochemical measurements and weight-loss tests results indicated that all the mixed inhibitors show good inhibition performance than single component,and the inhibition efficiency order is KL+OP > IM+OP > IM+SIK > IM+BTAH.The tendency of the calculated frontier orbital energies of inhibitor molecules is the same with the results as we have obtained in the experimental tests,that is the tendency of the enhanced adsorption of mixed inhibitors is KL+OP>IM+OP>IM+SIK>IM+BTAH.Surface morphologies observation found that L245 steel will suffer pitting corrosion only when IM was added in the test solution.The phenomenon attributes to the desorption of inhibitors on metal surface,there exiht film desorption and readsorption process,the partial film desorption area is easy to suffer the corrosion of the test solution.The surface potential distribution of the chorine located area is low,the surface potential of the surrounding area is high,which forming a small anode – large cathod area ratio and the anode dissolved first,thus pits formed on L245 steel surface.Under the work of the occlusion cell and its autocatalysis,pits continue to grow and Fe²⁺ accumulated in the pits,local electric field formed and the field point to the outside of the pit,the positively charged IM molecules can't migrate to the inside of the pit and the pit expanded continuously.Furthermore,the outside of the pit where inhibitor molecules adsorbed shows higher surface potential,the surface potential of the inside of the pit is lower,small anode and large cathode area ratio formed and pit grow continously.