Development,Corrosion Inhibition Performance And Theoretical Calculation Of Novel High-efficient Pyrimidine Inhibitors

The development of environmentally friendly high-performance corrosion inhibitors is one of the important ways to solve the corrosion problem in the process of oil and gas exploitation,thereby reducing production costs,and dealing with the energy crisis and environmental pollution problems.Pyrimidine compounds have attracted extensive attention in the field of corrosion inhibitors research due to their low toxicity and wide sources of raw materials.However,due to the high corrosivity and complexity of the environments in the oil and gas production process,the development of high-efficiency pyrimidine corrosion inhibitors is still a great challenge,and their corresponding corrosion inhibition mechanism needs to be deeply revealed.With the development of theoretical calculation methods,such as quantum chemistry calculations,the application of more accurate and efficient calculation methods with considering various environmental factors will help to deeply understand the inhibition mechanism of corrosion inhibitors in the complicated environment of practical application.In order to deal with the problem of material corrosion failure in the process of oil and gas exploitation,especially in the process of enhanced oil recovery(EOR),several high-efficiency pyrimidine corrosion inhibitors were designed and developed in this work.Their corrosion inhibition performance was evaluated by electrochemical tests and surface analysis.Moreover,theoretical calculations were performed to explore the effects of environmental factors and the interactions between corrosive species and inhibitor molecules on the inhibition performance,and then deeply reveal the inhibition mechanism of corrosion inhibitors.The main research content of this work includes the following four parts:1.Three pyrimidine derivatives,6-amino-2-(benzylthio)-4(3H)-pyrimidinone(BTP-1),6-amino-3-benzyl-2-(benzylthio)-4(3H)-pyrimidinone(BTP-2)and 6-(benzyloxy)-2-(benzylthio)-4-pyrimidinamine(BTP-3),were developed as corrosion inhibitors to control the corrosion of carbon steel in HCl environment during the acidification of oil and gas well.The results of weight loss measurement,electrochemical tests and surface analysis show that these three inhibitors can effectively inhibit the corrosion of carbon steel,especially for BTP-3 which exhibits the highest inhibition performance.The quantum chemistry calculations reveal that benzyl substituents can enhance the adsorption strength of these three inhibitor molecules on the Fe surface and improve their hydrophobicity and coverage area,and then enhance their inhibition performance.Due to the differences in the site and number of benzyl substituents and the steric hindrance in these inhibitor molecules,there are obvious differences in their adsorption capacity and adsorption configuration on the Fe surface,then leading to the difference in their corrosion inhibition performance.2.With 2-Mercaptopyrimidine(MP)as precursor,2-benzylthiopyrimidine(BTP)was synthesized through a simple method,and both MP and BTP were evaluated as inhibitors for the corrosion of carbon steel in CO₂ environment.Electrochemical measurements show that both MP and BTP have high corrosion inhibition performance,especially for BTP with an inhibition efficiency of 99.82%,corresponding to the corrosion rate of carbon steel of0.0027 mm/y.The thermodynamic parameters determined by quantum chemical calculations indicate that both MP and BTP are almost not protonated in the solution.MP molecules undergo a tautomeric transformation of thiol(MP-thiol)and thione(MP-thione).However,due to the introduction of benzyl group,this tautomeric transformation does not occur in the BTP molecules.Quantum chemical calculations show that the S and N atoms of MP and BTP molecules act as the coordination atoms for their adsorption on the Fe surface.The introduction of benzyl substituent in BTP leads to the difference in the inhibition performance of MP and BTP in many aspects,including inhibition of the thiol/thione tautomeric transformation,improvement of hydrophobicity,and enhancement of the adsorption capacity of BTP on the Fe surface.3.Under the guidance of the above research ideas and experimental results,an inhibitor for the corrosion of carbon steel in supercritical CO₂ environment,4,6-diamino-2-(benzylthio)pyrimidine(DABTP),was further developed.The electrochemical tests and surface analysis indicate that DABTP exhibits high inhibition performance under static and dynamic conditions.Meanwhile,the flow of fluid under dynamic conditions leads to the decrease in the corrosion inhibition performance of DABTP.The electron localization function(ELF)of DABTP molecule suggests that the S and N atoms in DABTP molecule act as the coordination atoms for the adsorption on Fe surface.In addition,DABTP molecules exhibit high polarity and hydrophilicity.Therefore,DABTP molecules are not easy to be extracted by supercritical CO₂ phase and then can maintain a high effective concentration in water phase.The calculation of the intermolecular interaction reveals that DABTP molecules can combine with each other through hydrogen bonds,which may enhance their adsorption stability on Fe surface.The decrease in the inhibition performance of DABTP under dynamic conditions could be attributed to the desorption of DABTP molecules,the destruction of the intermolecular hydrogen bond structure,and the acceleration of the mass transfer process of corrosive species.4.The influence of the corrosion product film formed on the carbon steel surface in supercritical CO₂ environment on the corrosion inhibition performance of DABTP was explored.Electrochemical measurements show that the formed Fe₃C and Fe CO₃ corrosion product films will reduce the corrosion inhibition performance of DABTP.The calculations based on the GFN-x TB method indicate that DABTP could adsorb on the surface of Fe,Fe₃C and Fe CO₃ by forming coordination bonds with the order of adsorption strength of Fe CO₃>Fe>Fe₃C.Since the insulating Fe CO₃ could not act as the electrochemical reaction interface,the adsorbed DABTP molecules on Fe CO₃ surface cannot directly exert corrosion inhibition performance.Meanwhile,the adsorption strength of DABTP molecules on Fe₃C surface is weak.Therefore,the directly adsorbed DABTP molecules on Fe surface can exert better corrosion inhibition performance.The corrosion product film will hinder the diffusion of DABTP molecules to the surface of Fe substrate,leading to the decrease in the corrosion inhibition performance.However,after the formation of dense Fe CO₃ film,the corrosion rate of carbon steel is small under the joint inhibition of Fe CO₃ film and DABTP.