| The utilization of Q235 carbon steel is extensively prevalent in oil and gas pipelines at present,which usual services environment contains organic acid corrosive media（such as formic acid）that will cause serious corrosion and great impact on pipeline security.Besides,with the rise of green energy,methanol fuel has become the most standardized alternative to petroleum.A large number of methanol fuels have been used in the process of industrial production or life in order to diminish the exploitation and utilization of petroleum,among which,small organic acids such as formic acid and acetic acid also are inevitably brought into the methanol fuel giving rise to the corrosion problem.Hence,it is exigent to stem and battle against the corrosion.This thesis mainly aimed to investigate the corrosion inhibition in 10 mol·L-1 methanol/0.1mol·L-1 formic acid medium using the single organic compounds,based on imidazole derivative,pyridine derivative and rosin amino acid surfactants,namely 1-dodecyl-3-methyimidazolium chloride（DMIC）,dodecylpyridinium chloride（DPC）and hexadecylpyridinium chloride monohydrate（HDPC）and dehydroabietic acylamino sodium（6-DAS）,more than that,the corrosion inhibition performance of Q235 steel by the new combination system of low concentration（DPC,HDPC and 6-DAS）compounded with 6-DAS was studied,which utilized weight loss measurements and electrochemical techniques such as polarization plots and electrochemical impedance spectroscopy（EIS）to evaluate inhibition performance.Also,the morphologies and compositions of the surface of Q235steel were investigated by contact angle test,atomic force microscope（AFM）,scanning electron microscopy（SEM）,energy dispersive X-ray spectroscopy（EDX）,Raman spectroscopy（Raman）and X-ray photoelectron spectroscopy（XPS）.Besides,the adsorption behavior of single corrosion inhibitor molecules was studied by isothermal adsorption model.Ultimately,quantum chemical calculation and molecular dynamics simulation were available to illustrate the inhibition mechanism.The main experimental results are as follows:（1）The static weight loss method and electrochemical experiments showed that the concentration of DMIC,DPC and HDPC was 6×10-2 mol·L-1,the inhibition rates were88.81%,90.97%and 92.07%,respectively.As the concentration of 6-DAS was 1×10-2mol·L-1,the inhibition rate can reach at 92.23%.Compared with the other three corrosion inhibitors,the dosage of 6-DAS was the smallest,thus,the inhibition effect of the four corrosion inhibitors should be as follows:6-DAS>HDPC>DPC>DMIC.Meanwhile,the adsorption isotherm showed that the adsorptions of four single corrosion inhibitors were consistent with Langmuir isothermal adsorption and it was attributed to the result of the simultaneous action of physical adsorption and chemical adsorption.In addition,when the fixed concentration of 6-DAS was 1×10-3 mol·L-1,the inhibition efficiency of 6-DAS-DMIC,6-DAS-DPC and 6-DAS-HDPC with different concentration ratios（1:1,1:2,1:4 and 1:8）was all above 90%.Besides,four single corrosion inhibitors and compound corrosion inhibitors were regarded as the mixed-type corrosion inhibitors dominated with anode.（2）The surface analysis showed that the metal surface treated with corrosion inhibitor was smoother than that without corrosion inhibitor,and the surface of carbon steel immersed with,6-DAS-HDPC inhibitor was the smoothest.Meanwhile,the element changed on the surface of carbon steel before and after immersion showed that four single corrosion inhibitors and compound corrosion inhibitors can be well adsorbed on the metal surface.（3）Quantum chemical calculations showed that 6-DAS molecules had smallest orbital energy gap,and it was easier to supply/receive iron electrons to form chemical bonds and adsorb reactions than the other three molecules（DMIC,DPC and HDPC）.The corresponding Fukui index also showed that all the four inhibitors have active sites that react with metals.The electrostatic potential distribution（MEP）of these inhibitors revealed that the negatively charged red regions distributed in the benzene ring,hexatomic ring and the heteroatoms such as oxygen（O）and nitrogen（N）,which would be preferred centers for adsorption to metal surfaces.（4）MD simulation showed that high concentration of DMIC,DPC,HDPC and 6-DAS were absorbed on the metal surface,and their hydrophobic carbon chains formed waterproof film to protect the metal.However,when the content of corrosion inhibitor was unsaturated,the hydrophobic carbon chain will repel each other due to the steric hindrance effect,which will produce more pores and make the corrosion particles diffuse into the pore structure.After compounding,the two inhibitors filled in for each other,which made the protective film denser and improved the acid resistance of the metal.From all above,it was proved that the single corrosion inhibitors（DMIC,DPC,HDPC and 6-DAS）with higher concentration and compound corrosion inhibitors（6-DAS-DMIC,6-DAS-DPC and 6-DAS-HDPC）all had good corrosion inhibition effect on carbon steel in organic acids environment through corrosion inhibition measurement and theoretical analysis.More importantly,the compounding of corrosion inhibitors not only reduces the dosage and cost to a great extent,but also reduces the environmental pollution,which also provides theoretical guidance for the development and research of new compound corrosion inhibitors. |
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