Imidazole Based-Polyethylene Glycol Monomethyl Ether Green Carbon Steel Corrosion Inhibitors

The use of carbon steel is vulnerable in corrosive environment,especially in hydrochloric acid pickling solutions,because of its low corrosion resistance.This leads to enormous economic losses and hazards.Add corrosion inhibitors is proved to be an efficient way for protecting the carbon steel from corrosion in corrosive medium.Recently,most organic inhibitors containπ-electron(s)centers and functional groups(with N,O,S and P atoms)were reported in literature.Nevertheless,a large number of organic inhibitors offer environmental toxicity,which may cause harm to human health.Therefore,alternative nontoxic,biodegradable and green corrosion inhibitors will be the best candidate as corrosive agents.Firstly,Carboxymethylation by Chloroacetic acid and polyethylene glycol monomethyl ether(MPEGn)with different molecular weight(M=200,350,750,1500)as raw materials to obtain polyethylene glycol monomethyl ether carboxylic acid(MPECn).Then,imidazole(IMI)and MPECn were performed to get the imidazole based-polyethylene glycol monomethyl ether carboxylic acid-MPECn-IMI(MPEC-IMI(200),MPEC-IMI(350),MPEC-IMI(750),MPEC-IMI(1500)).The structures of MPECn-IMI molecules were characterized by FTIR spectroscopy and ~1H NMR;the inhibitive effect and mechanism of MPECn-IMI molecules in 0.5M HCl solution for Q235 carbon steel were evaluated by static weight loss,electrochemical techniques(Tafel and EIS),scanning electron microscopy(SEM)measures,quantum chemical and molecular dynamics(MD).Results show that MPECn-IMI molecules play an important role in protecting carbon steel,and the corrosion inhibition efficiencies of four inhibitors are increased with the increase of polyethylene glycol chain(molecular weight).Under the optimum conditions of their own,the inhibition efficiencies can reach up to 88.85%for MPEC-IMI(200)(70mg/L),89.07%for MPEC-IMI(350)(70mg/L),91.35%for MPEC-IMI(750)(70mg/L)and 92.88%for MPEC-IMI(1500)(50mg/L)in 0.5M HCl solution at 318K,respectively.The mechanism of retarding corrosion for carbon steel mainly involves the formation of the absorptive protective film on carbon steel surface,and the type of adsorption for four inhibitors basically obeys the Langmuir monolayer adsorption.Adsorption behavior analysis reveals that both physisorption and chemisorption exist during the corrosion inhibition process;moreover,the adsorption gets stronger with the increase of molecular chain in MPECn-IMI molecules.By virtue of quantum chemical calculations and molecular dynamics simulations,results further confirm that MPECn-IMI molecules all possess high reactivity and strong interaction with the carbon steel surface;furthermore,the interaction increases with the increase of the chain length for four inhibitors,which commendably corresponds to the experimental results.