Synthesis Of Amino Acid Amide Corrosion Inhibitors And Their Influence On The Pitting Corrosion Sensitivity Of Carbon Steel

Carbon steel,as an economical and easily manufactured industrial material,is widely used in surface facilities and underground wells in oil/gas fields.However,CO2,H2S,chloride ions and other corrosion medium are normally found in oil field development,which corrodes the carbon steel easily in such an environment,especially at low pH and high concentration of chloride ions.It may result,in serious damage and a huge economic loss,if the corrosion control measures are not followed.The use of inhibitor is one of the most economical and effective measures to prevent the corrosion in oil field facilities.Carbon steel is widely used for pipeline and storage tanks in the oil/gas fields.At present,the mainly organic corrosion inhibitor includes:imidazoline,fatty amine,quaternary ammonium slates.However,inhibitors have drawbacks such as a high required concentration and poor control of pitting corrosion.Therefore,it is necessary to develop new kinds of inhibitors with improved performance against pitting resistance of Carbon Steel.In this thesis,three amide inhibitors were synthesized by the reaction of methionine(Met),L-cysteine(Cys)and thiourea(TU)with oleic acid,all of which contain Sulphur as a precursors.The structure of these new inhibitors was identified by IR&NMR techniques and their corrosion resistance characteristics were evaluated.Methionine derivative(Met-D)found most effective among all the new inhibitors.The relationship of pitting corrosion and inhibitors was studied by using the methionine derivative(Met-D),thiourea(TU)and mixture of methionine derivative(Met-D)&thiourea inhibitors.The inhibitor mixture was tested in a gas field in China,and the inhibition efficiency be found higher than 90%.The well casing corrosion have been controlled by the inhibitor mixture1.Two novel environmentally firendly amino acid amide derivatives were synthesized by using oleic acid,methionine and cysteine as raw materials.The latter two compounds contain sulfur element.The inhibition efficiencies of the two amino acids and their derivatives were evaluated by weight loss,potentiodynamic polarization,electrochemical Impedance Spectroscopy,Electrochemical Noise and Wire Beam Electrode methods.The results show that the inhibition efficiencies of amino acid amide derivatives are higher than amino acids.In addition,thiourea amide derivative with a similar structure was synthesized.The inhibition performance of the three corrosion inhibitors were studied in CO2-saturated with 3%NaCl solution.The results showed that these three inhibitors efficiencies are in the order of methionine derivative>thiourea derivative>cysteine derivative.The inhibition efficiency is 92%when methionine derivative is used at 50mg·L-1.As the concentration increases,the increasing tendency of inhibition efficiency slows down,likely due to the agglomeration of the inhibitor molecules in the solution.Quantum chemical calculations shows that methionine amide derivative is adsorbed on the surface of carbon steel,both through C=C bond and O&N atoms.While cysteine and thiourea derivatives are adsorbed only by S and N atoms.This means that the methionine amide derivative has a more adsorbed center than the other two inhibitors.Therefore,its corrosion inhibition ability is better than the others.2.The effect of methionine amide derivatives and thiourea on the pitting corrosion sensitivity of carbon steel in CO2 saturated saline solution was studied through the polarization curve,electrochemical noise,and wire beam electrode(WBE).It was found that the pitting sensitivity would increase,when low concentration of methionine amide(50mg·L-1)was added;no impact on pitting at higher concentrations(100mg.L-1 and 200mg.L-1).When the concentration of thiourea was only 50mg.L-1,the pitting sensitivity of carbon steel decreased.If thiourea concentration was higher,then the pitting sensitivity increased.3.The inhibition effect of the combined use of thiourea and methionine amide derivative on pitting corrosion of N80 steel was studied.When different proportions of the corrosion inhibitor were added,the increase in pitting potential of carbon steel is was observed,indicating that the inhibitor film is more compact and stable caused by interaction between different types of inhibitors on the steel surface.The fluctuation of current and potential noise is more moderate than each of the two inhibitors.The PSD current is reduced to 10-21,which shows that the general corrosion is slight.The PI index is also reduced and the slope of the potential(PSD)shows that the system is in uniform corrosion stage.Based on the results of WEB galvanic current,corrosion potential,and lower localized corrosion intensity index,it was found that the corrosion inhibitors mixture reduces not only the overall corrosion but also the pitting corrosion.Fractional Free Volume(FFV)values of different inhibitor films were calculated by using molecular dynamics simulation.The results showed that the porosity of the composite inhibitor film decreases by the corrosion inhibitor's mixture,indicating that the more compact inhibitor film is formed.Therefore,local corrosion caused by uneven adsorption of corrosion inhibitors can be controlled by rational compounds of corrosion inhibitors.4.The Met-D and TU were mixed as MetTF and tested in the oil field.The test results showed that MetTF is effective for general and pitting corrosion control of Carbon Steel.According to the GB/T 21605 chemical acute oral toxicity LD50 test method,Mixed MetTF is with low toxicity.