Influence Of Surface States Of Steels On Inhibition Performance Of An Imidazoline-based Inhibitor In CO₂ Environments

With the development and application of Carbon Capture and Storage（CCS）and enhanced oil/gas recovery（EOR/EGR）by CO₂ injection,CO₂ corrosion was found widely existed on the corresponding engineering structure materials and devices,which caused serious negative effect on their service life and production safety.The employment of imidazoline and its derivatives is considered the simplest way to minimize the CO₂ corrosion because of their high inhibition effectiveness and environmental friendliness.The researchers have made progress in corrosion inhibitor,such as molecular design,synthesis,synergistic effect and inhibition performance.However,it still exsists serious probems in practical applications when employs the corrosion inhibitors.So far,the reports of effects on inhibitor inhibition performance by material surface conditions are rather few,and the mechanism is not clear.The influence of microstructure on localized corrosion in the presence of inhibitor has not been reported.In addition,the inhibitors used in vapor and liquid phases to against CO₂ corrosion mainly in an atmosphere environment,and the studies on the inhibitors employed in the harsh CO₂ corrosion environments（high temperature and high pressure）are few.In this PhD thesis,an imidazoline-based inhibitor was synthesized.Weight loss and electrochemical experiments were carried out to investigate the influence of surface states on the inhibitor inhibition performance in liquid phase of CO₂ containing environment.The Scanning electron microscopy（SEM）,X-ray diffraction（XRD）,Raman spectroscopy,Laser scanning confocal microscope and SKPFM technics were employed to analyze the morphology and chemical composition of the corrosion products,the depth of the localized corrosion and the Volta potentials of the samples.A vapor-liquid phases corrosion inhibitor was obtained to against the steels’ corrosion in high temperature and high pressure CO₂ environments.The inhibition mechanism of the inhibitors was studied by quantum chemical calculations.The results are expected to provide theoretical support to predict the employment of the inhibitors in CO₂ environments,guide the practical applications.The main research results are as the follows:（1）The inhibitor acted as a mixed-type inhibitor.The adsorption process of the inhibitor on freshly abraded samples was chemisorption and followed Langmuir isotherm.Compared to X70 steel,Q235 steel has a larger amount and more homogeneous distribution of carbides,therefore the inhibitor had stronger power to adsorb onto the Q235 surface,and the inhibition efficiencies for Q235 steel were larger than that for X70 steel.（2）Pre-corrosion had a detrimental effect on the inhibitor performance.The differences in inhibition efficiency of the inhibitor for samples pre-corroded for different time were related to the different corrosion products after pre-corrosion.In order to obtain an excellent corrosion inhibition effect,it is necessary to increase the inhibitor concentration after pre-corrosion.（3）Surface roughness had an influence on the inhibitor inhibition performance.The smoother surfaces exhibited higher inhibition efficiencies compared to the rougher surfaces.The thermodynamic and kinetics parameters indicated that the inhibitor molecules would be more preferentially absorbed on smoother surfaces and the adsorption ability was stronger than those on the rougher surfaces.Compared to rougher surface,the smoother surface with a higher EWF was more attractive to react with the inhibitor to form an adsorption film which had a higher protective ability,leading to the larger inhibition efficiency.（4）Carbon steels with different microstructures were liable to suffer localized corrosion in the presence of inhibitor.H steel（coarse laminar pearlite+ferrite）suffered more severe localized corrosion compared to T steel（globular and short rod shaped cementite+ferrite）.SKPFM results found that,in the presence of inhibitor,H steel had a larger driving force for galvanic corrosion between the pearlite and ferrite compared to that of T steel.The localized corrosion on H steel mainly distributed on the laminar pearlite area.（5）Imidazoline-based inhibitor complexed with morpholine and p-toluidine could efficiently inhibit the corrosion of CO₂ vapor-liquid two phases（333 K、10 MPa）.Results showed that S atom acted as the adsorption center cite of the imidazoline-based inhibitor.The synergistic inhibition effect of the imidazoline-based inhibitor and morpholine was obvious in the vapor phase.P-toluidine could adsorb on the corrosion products to inhibit the localized corrosion.