Imidazoline schiff base corrosion inhibitor and preparation method and application thereof

Abstract

This invention discloses an imidazoline Schiff base corrosion inhibitor, its preparation method, and its application, relating to the field of anti-corrosion coatings for oil well metal pipes. The method involves reacting a heterocyclic carboxylic acid with an organic polyamine to obtain an imidazoline reactant; reacting the imidazoline reactant with iodobutane to obtain a quaternized modified reactant; and reacting the quaternized modified reactant with cinnamaldehyde to obtain the corrosion inhibitor. The three molecular groups present in the corrosion inhibitor of this invention can exert a synergistic effect, exhibiting good corrosion inhibition performance under strong acid and high-temperature conditions. The corrosion inhibitor of this invention can be applied to protect oil and gas field casing materials from corrosion during oil and gas field development, thereby ensuring the smooth production and development of oil and gas resources at a lower economic cost.

Description

Technical Field

[0001] This invention relates to the field of anti-corrosion coatings for oil well metal pipes, specifically to an imidazoline Schiff base corrosion inhibitor, its preparation method, and its application. Background Technology

[0002] During oil and gas field production and development, casing and tubing frequently face complex corrosive environments. Corrosion failure of casing and tubing materials often leads to severe economic losses and even safety accidents and ecological problems. According to joint research data from the Chinese Society for Corrosion and Protection, the China Petroleum Society, and the Chemical Industry and Engineering Society of China, corrosion-related losses in various sectors in China account for approximately 3% of the total GDP.

[0003] Currently, common methods for corrosion protection of oil casing materials, both domestically and internationally, include selecting materials with superior performance, applying surface coatings, electrochemical protection, and adding corrosion inhibitors. Among these methods, adding corrosion inhibitors is widely adopted by many oilfields due to its ease of use, low cost, and synergistic effects. In China's oil and gas fields, organic corrosion inhibitors (imidazoline and quaternary ammonium salts) suitable for high-temperature acid fracturing and complex operating conditions dominate. Imidazolline corrosion inhibitors, in particular, possess excellent physicochemical properties and significantly inhibit CO2 and H2S corrosion, leading to their widespread application and research.

[0004] However, current imidazoline corrosion inhibitors have drawbacks such as poor film density, weak adaptability to extreme environments, and insufficient long-term effectiveness and temperature resistance, requiring modification.

[0005] Therefore, there is an urgent need for an imidazoline Schiff base corrosion inhibitor and its preparation method. Summary of the Invention

[0006] One objective of this invention is to provide a method for preparing an imidazoline Schiff base corrosion inhibitor. The method involves quaternizing imidazoline with n-butane iodide, and then reacting the modified quaternized product with cinnamaldehyde to form the final corrosion inhibitor. This simple preparation method provides corrosion protection suitable for strong acid environments and high-temperature environments.

[0007] Another objective of this invention is to provide an imidazoline Schiff base corrosion inhibitor and its application. The sulfur atoms and a large number of nitrogen atoms in the corrosion inhibitor of this invention have a significant effect on inhibiting the corrosion of corrosive ions such as hydrogen ions and chloride ions, and can be effectively applied to the corrosion protection of oil casing materials in the production and development of oil and gas fields.

[0008] The first objective of the invention is a method for preparing an imidazoline-based Schiff base corrosion inhibitor, comprising the following steps:

[0009] Heterocyclic carboxylic acids are reacted with organic polyamines to obtain imidazoline reactants;

[0010] The imidazoline reactant was reacted with iodobutane to obtain the quaternized modified reactant;

[0011] The quaternized modified reactant was reacted with cinnamaldehyde to obtain a corrosion inhibitor.

[0012] This invention modifies imidazoline reactants by quaternization to introduce quaternary ammonium salt groups, and then modifies the quaternized reactants by Schiff base reaction to introduce Schiff base structures. This not only significantly enhances the water solubility and adsorption capacity of the corrosion inhibitor, but also improves the corrosion inhibition capacity, stability and temperature resistance of the corrosion inhibitor.

[0013] This invention uses iodobutane to quaternize imidazoline, and then reacts the modified quaternized reactant with cinnamaldehyde to form the final corrosion inhibitor molecule.

[0014] Compared with existing technologies, the three molecular groups present in the corrosion inhibitor of this invention can exert a synergistic effect, maintaining good corrosion inhibition performance even under strong acid and high temperature environments. It can be applied to the corrosion protection of oil and gas casing materials during oil and gas field development, thereby ensuring the smooth production and development of oil and gas resources at a lower economic cost.

[0015] Specifically, the reaction of heterocyclic carboxylic acids with organic polyamines includes the following steps:

[0016] Under a nitrogen atmosphere, heterocyclic carboxylic acids and xylene were placed in a three-necked flask. An organic polyamine was slowly added dropwise to the flask, and the temperature was raised to 140-150 °C. After reacting for 4 hours, the temperature was increased to 210-230 °C, and the mixture was refluxed for 4 hours to obtain the reactants. The reactants were then purified to obtain the imidazoline reactants. Xylene was used as the solvent.

[0017] The heterocyclic carboxylic acid is one or more of furanoic acid, 2-thiophenic acid, and pyrrolic acid; the organic polyamine is tetraethylenepentamine or diethylenetriamine.

[0018] Preferably, the heterocyclic carboxylic acid is 2-thiophenecarboxylic acid, and the organic polyamine is diethylenetriamine. The sulfur atom in 2-thiophenecarboxylic acid carries a lone pair of electrons, which can combine with the 3d orbital of Fe to form a coordinate bond, ensuring that the synthesized corrosion inhibitor has a good corrosion inhibition effect. The primary amino group of diethylenetriamine and the carboxyl group of 2-thiophenecarboxylic acid undergo a condensation cyclization reaction, which introduces a thiophene group containing an sulfur atom, thereby endowing the product with unique electronic properties and adsorption capacity.

[0019] The imidazoline reactants prepared by the above method have more active sites, which is beneficial for the introduction of more active groups.

[0020] Furthermore, the reaction of the imidazoline reactant with iodobutane includes the following steps:

[0021] Under a nitrogen atmosphere, the imidazoline reactant and anhydrous ethanol were placed in a three-necked flask and heated to 60-90°C. Iodobutane was slowly added dropwise to the flask, and the mixture was heated to reflux and maintained for 4 hours. After the reaction was complete, the mixture was cooled to room temperature to obtain the quaternized modified reactant. Anhydrous ethanol was used as the solvent.

[0022] Iodobutane can introduce positively charged quaternary ammonium groups to improve the water solubility of the synthesized corrosion inhibitor. At the same time, the introduced n-butyl chain length is moderate, which avoids precipitation caused by excessively long alkyl groups and maintains the uniform dispersion of molecules in solution. Furthermore, the iodide ions of iodobutane have an anodic passivation effect, which can form a synergistic protective effect with other groups, further enhancing the corrosion inhibition ability of the final synthesized corrosion inhibitor.

[0023] The imidazoline reacts with n-iodobutane to convert the tertiary amine nitrogen (N) on the imidazoline ring into a quaternary ammonium salt group (N) via alkylation. + This can give corrosion inhibitors stronger corrosion inhibition performance and environmental adaptability.

[0024] Furthermore, the quaternized modified product reacts with cinnamaldehyde, including the following steps:

[0025] Under a nitrogen atmosphere, the quaternization-modified reactant was placed in a three-necked flask, and cinnamaldehyde was slowly added dropwise to the flask. The mixture was heated to reflux and reacted for 4 hours. After that, it was cooled to room temperature and subjected to vacuum distillation to obtain the corrosion inhibitor.

[0026] Cinnamaldehyde is modified with a Schiff base. The large π bond in the phenyl group of cinnamaldehyde and the π bond in the C=C group have a high electron cloud density, which can be adsorbed onto the surface of N80 steel through electrostatic attraction, further enhancing the corrosion inhibition ability of the corrosion inhibitor. The imidazoline is further modified with a Schiff base by condensation and dehydration of the primary amino group at the end of the imidazoline with the aldehyde group of cinnamaldehyde, generating a conjugated enamine structure. This significantly enhances the adsorption and corrosion inhibition efficiency of the corrosion inhibitor.

[0027] Another object of the present invention is an imidazoline Schiff base corrosion inhibitor and its application. Specifically, the corrosion inhibitor comprises the following components in parts by weight: 120-140 parts of heterocyclic carboxylic acid, 113-155 parts of organic polyamine, 202-276 parts of iodobutane, 145-198 parts of cinnamaldehyde, 172-215 parts of xylene, and 95-142 parts of anhydrous ethanol.

[0028] The corrosion inhibitor of this invention has good application in the field of anti-corrosion coatings for oil well metal pipes under strong acid and high temperature environments.

[0029] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0030] This invention discloses an imidazoline Schiff base corrosion inhibitor, its preparation method, and its application. The invention involves an amidation and dehydration cyclization reaction of 2-thiophenecarboxylic acid and diethylenetriamine to obtain an imidazoline reaction product. This imidazoline product undergoes a nucleophilic substitution reaction with iodobutane in an ethanol solution, thereby achieving quaternization modification. The quaternization-modified product is then modified with a Schiff base by introducing cinnamaldehyde, and purified to obtain the corrosion inhibitor. The production process of the corrosion inhibitor of this invention is simple and requires no special equipment.

[0031] The three molecular groups present in the corrosion inhibitor of this invention can exert a synergistic effect. The sulfur atoms and abundant nitrogen atoms in the corrosion inhibitor have a significant inhibitory effect on corrosive ions such as hydrogen ions and chloride ions, and exhibit good corrosion inhibition effects under strong acid and high temperature environments. The corrosion inhibitor of this invention can be applied to protect oil casing materials during oil and gas field development, thereby ensuring the smooth production and development of oil and gas resources at a lower economic cost. Attached Figure Description

[0032] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 The infrared spectrum of the corrosion inhibitor prepared in Example 1.

[0034] Figure 2 The 1H NMR spectrum of the corrosion inhibitor prepared in Example 1.

[0035] Figure 3 The carbon NMR spectrum of the corrosion inhibitor prepared in Example 1.

[0036] Figure 4 The graphs show the electrochemical polarization curves obtained from the corrosion inhibitors in Examples 1-5. Detailed Implementation

[0037] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and accompanying drawings. However, this does not limit the invention to the scope of the embodiments described. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0038] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0039] Example 1

[0040] The corrosion inhibitor comprises the following components in parts by weight: 120-140 parts of 2-thiophenecarboxylic acid, 113-155 parts of diethylenetriamine, 202-276 parts of iodobutane, 145-198 parts of cinnamaldehyde, 172-215 parts of xylene, and 95-142 parts of anhydrous ethanol.

[0041] A method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0042] Step 1: Under a nitrogen atmosphere, 135 parts of 2-thiophenecarboxylic acid and 210 parts of xylene were placed in a three-necked flask. 125 parts of diethylenetriamine were slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature was raised to 145 °C and the reaction time was 4 h. Then the temperature was raised to 220 °C and the mixture was refluxed for 4 h to obtain the reactant. The reactant was purified to obtain the imidazoline reactant.

[0043] Step 2: Under a nitrogen atmosphere, the imidazoline reactant and 130 parts of anhydrous ethanol are placed in a three-necked flask and heated to 80°C. 260 parts of iodobutane are slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The mixture is heated to reflux and maintained for 4 hours. After the reaction is completed, it is cooled to room temperature to obtain the quaternized modified reactant.

[0044] Step 3: Under a nitrogen atmosphere, place the quaternization modified reactant into a three-necked flask, and slowly add 165 parts of cinnamaldehyde dropwise into the three-necked flask through a constant pressure dropping funnel. Heat to reflux, react for 4 hours, cool to room temperature, and perform vacuum distillation to obtain the corrosion inhibitor.

[0045] The molecular structure of the corrosion inhibitor prepared in Example 1 is shown in Formula I below:

[0046] I.

[0047] The infrared spectrum of the corrosion inhibitor in Example 1 is as follows: Figure 1 As shown, Figure 1 The x-axis represents wavenumber / cm -1 The vertical axis represents transmittance. Figure 1 3380.0cm -1 (N-Hstr.), 2960.0 cm-1 (CH str.), 1530.0 cm -1 (C=N str.), 1380.0cm -1 (phenyl str.) and 1030.0 cm -1 The characteristic absorption peak of the corrosion inhibitor molecule (CN str.).

[0048] The corrosion inhibitor prepared in Example 1 was subjected to detection of the resonance of hydrogen nuclei in a magnetic field, and the proton nuclear magnetic resonance spectrum of the corrosion inhibitor prepared in Example 1 was obtained, as shown below. Figure 2 As shown. From Figure 2 According to the 1H NMR spectrum, δ (7.39) is the characteristic absorption peak of the benzene ring, δ (6.80) is the characteristic absorption peak of -C-CH=C, δ (3.20) is the characteristic absorption peak of =N-CH-CN, and δ (1.07) is the characteristic absorption peak of -CCCCC-.

[0049] The corrosion inhibitor prepared in Example 1 was subjected to carbon NMR spectroscopy based on the principle of nuclear magnetic resonance, and the carbon NMR spectrum of the corrosion inhibitor prepared in Example 1 was obtained, as follows: Figure 3 As shown. Figure 3 Carbon NMR spectroscopy revealed that δ(165.3) is the characteristic absorption peak of NC=N, δ(128.0) is the characteristic absorption peak of the benzene ring, δ(40.4) is the characteristic absorption peak of -NCCN-, and δ(56.5, 28.3, 19.8, and 14.0) are the characteristic absorption peaks of -CCCC-. In summary, the infrared spectroscopy and NMR results jointly confirmed the synthesis of the quaternized imidazoline Schiff base corrosion inhibitor.

[0050] Example 2

[0051] Based on the above embodiments, a method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0052] Step 1: Under a nitrogen atmosphere, 135 parts of 2-thiophenecarboxylic acid and 210 parts of xylene were placed in a three-necked flask. 125 parts of diethylenetriamine were slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature was raised to 145 °C and the reaction time was 4 h. Then the temperature was raised to 220 °C and the mixture was refluxed for 4 h to obtain the reactant. The reactant was purified to obtain the imidazoline reactant.

[0053] Step 2: Under a nitrogen atmosphere, the imidazoline reactant is placed in a three-necked flask. 165°C cinnamaldehyde is slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature is raised to reflux and reacted for 4 hours. After cooling to room temperature, the mixture is purified by vacuum distillation to obtain the corrosion inhibitor.

[0054] Example 3

[0055] Based on the above embodiments, a method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0056] Step 1: Under a nitrogen atmosphere, 135 parts of 2-thiophenecarboxylic acid and 210 parts of xylene were placed in a three-necked flask. 125 parts of diethylenetriamine were slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature was raised to 145 °C and the reaction time was 4 h. Then the temperature was raised to 220 °C and the mixture was refluxed for 4 h to obtain the reactant. The reactant was purified to obtain the imidazoline reactant.

[0057] Step 2: Under a nitrogen atmosphere, place the imidazoline reactant and 130 parts of anhydrous ethanol into a three-necked flask, heat to 80°C, and slowly add 260 parts of iodobutane dropwise into the three-necked flask through a constant pressure dropping funnel. Heat to reflux and maintain for 4 hours. After the reaction is complete, cool to room temperature to obtain the corrosion inhibitor.

[0058] Example 4

[0059] A method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0060] Step 1: Under a nitrogen atmosphere, 125 parts of 2-thiophenecarboxylic acid and 185 parts of xylene were placed in a three-necked flask. 135 parts of diethylenetriamine were slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature was raised to 145 °C and the reaction time was 4 h. Then the temperature was raised to 220 °C and the mixture was refluxed for 4 h to obtain the reactant. The reactant was purified to obtain the imidazoline reactant.

[0061] Step 2: Under a nitrogen atmosphere, the imidazoline reactant and 105 parts of anhydrous ethanol are placed in a three-necked flask and heated to 80°C. 230 parts of iodobutane are slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The mixture is heated to reflux and maintained for 4 hours. After the reaction is completed, it is cooled to room temperature to obtain the quaternized modified reactant.

[0062] Step 3: Under a nitrogen atmosphere, the quaternization-modified reactant is placed in a three-necked flask. 0.13 mol of cinnamaldehyde is slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature is raised to reflux, and after reacting for 4 hours, it is cooled to room temperature and subjected to vacuum distillation to obtain the corrosion inhibitor.

[0063] Example 5

[0064] A method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0065] Step 1: Under a nitrogen atmosphere, 140 parts of 2-thiophenecarboxylic acid and 180 parts of xylene were placed in a three-necked flask. 120 parts of diethylenetriamine were slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The temperature was raised to 145 °C and the reaction time was 4 h. Then the temperature was raised to 220 °C and the mixture was refluxed for 4 h to obtain the reactant. The reactant was purified to obtain the imidazoline reactant.

[0066] Step 2: Under a nitrogen atmosphere, the imidazoline reactant and 140 parts of anhydrous ethanol are placed in a three-necked flask and heated to 80°C. 270 parts of iodobutane are slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The mixture is heated to reflux and maintained for 4 hours. After the reaction is completed, it is cooled to room temperature to obtain the quaternized modified reactant.

[0067] Step 3: Under a nitrogen atmosphere, the quaternization-modified reactant is placed in a three-necked flask. Cinnamaldehyde at 190°C is slowly added dropwise to the three-necked flask through a constant-pressure dropping funnel. The temperature is raised to reflux, and after reacting for 4 hours, it is cooled to room temperature and subjected to vacuum distillation to obtain the corrosion inhibitor.

[0068] Example 6

[0069] A method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0070] Step 1: Add lauric acid and boric acid to a three-necked flask in a certain proportion, heat with a heating mantle and stir, raise the temperature to 40℃~50℃, and then add xylene in a certain proportion to obtain mixture I;

[0071] Step 2: When the temperature of the heating mantle rises to 100-120°C, diethylenetriamine is added dropwise to mixture I using a constant pressure dropping funnel to carry out the reaction. The temperature is then raised to 160-180°C to carry out the amidation and dehydration reaction, and then the cyclization reaction is carried out at 240-260°C for 3-3.5 hours to obtain the imidazoline oil-soluble corrosion inhibitor.

[0072] Step 3: After the temperature drops to 60-80℃, add the quaternization reagent in proportion and carry out a water bath reaction to obtain a brownish-black viscous imidazoline quaternary ammonium salt corrosion inhibitor.

[0073] Example 7

[0074] A method for preparing an imidazoline Schiff base corrosion inhibitor includes the following steps:

[0075] In a 1000ml three-necked round-bottom flask equipped with an electric stirrer, temperature controller, condenser, and water separator, 1 mol (282.5 g) of oleic acid, 1.2 mol (123.6 g) of diethylenetriamine, 0.6 g of alumina, and 120 g of xylene were added. The mixture was stirred continuously, heated to 160℃, and reacted at this temperature for 2 hours. The temperature was then increased to 200℃ and reacted at this temperature for 3 hours. The temperature was then increased to 240℃ and reacted at this temperature until no more droplets were produced in the water separator. The temperature was then lowered to 90℃, and 1 mol (126.5 g) of benzyl chloride was slowly added dropwise to the reactor using a constant-pressure dropping funnel. After the addition was complete, the reaction was maintained at this temperature for 2 hours. The temperature was then lowered to 90℃, and 68.4 g of thiourea was added to the reactor. The temperature was increased to 110℃ and reacted at this temperature for 1.5 hours. The mixture was then cooled to 80℃ and poured out to obtain an oil-based thioamide-benzylimidazoline cationic compound.

[0076] Example 8

[0077] (1) Corrosion inhibition performance test

[0078] Referring to the standard SY / T 5405-1996 "Performance Test Method and Evaluation Index of Corrosion Inhibitors for Acidizing", a high-temperature and high-pressure autoclave was used to simulate the complex working environment downhole. Formation water from a certain oilfield in Bohai was used as the experimental medium. The static weight loss method was used to evaluate the corrosion inhibitors in Examples 1-6. The experimental results are shown in Table 1.

[0079] Table 1:

[0080]

[0081] As shown in Table 1, at a temperature of 150℃ and a CO2 partial pressure of 1.5 MPa, the corrosion inhibitor obtained in Example 1 can effectively reduce the corrosion rate when added to the corrosive medium. When the amount added is 50 mg / L, the corrosion inhibition efficiency is 90.12%.

[0082] The corrosion inhibitor in Example 2 was not modified with quaternization. When the corrosion inhibitor in Example 2 was added to the corrosive medium, although it could reduce the corrosion rate, the corrosion inhibition ability was weak. When the amount added was 50 mg / L, the corrosion inhibition efficiency was only 64.53%.

[0083] The corrosion inhibitor in Example 3 did not undergo the Schiff base reaction. When the corrosion inhibitor in Example 3 was added to the corrosive medium, the corrosion rate was reduced, but the corrosion inhibition ability was weak. When the amount added was 50 mg / L, the corrosion inhibition efficiency was only 58.82%.

[0084] When the corrosion inhibitor product obtained in Example 4 is added to the corrosive medium, the corrosion rate can be effectively reduced. When the amount added is 100 mg / L, the corrosion inhibition efficiency is 92.53%.

[0085] When the corrosion inhibitor product obtained in Example 5 is added to the corrosive medium, the corrosion rate can be effectively reduced. When the amount added is 200 mg / L, the corrosion inhibition efficiency is 95.88%.

[0086] When the corrosion inhibitor product obtained in Example 6 is added to the corrosive medium, it has a certain corrosion inhibition effect, but it is worse than that of Example 1. When the corrosion inhibitor product obtained in Example 7 is added to the corrosive medium, it has a certain corrosion inhibition effect, but it is worse than that of Example 1. Therefore, compared with Example 6, the corrosion inhibitor of the present invention has a better corrosion inhibition effect at a temperature of 150°C and a CO2 partial pressure of 1.5 MPa.

[0087] Example 6 uses traditional lauric acid and boric acid. The S atom in the thiophene structure of 2-thiophene carboxylic acid in Example 1 can form a more stable coordinate bond with the 3d orbital of Fe and form a stable protective film on the carbon steel surface. It is more stable than the physical adsorption of lauric acid (long-chain fatty acid). In addition, the use of 2-thiophene carboxylic acid is more environmentally friendly than the boric acid used in Example 6.

[0088] Furthermore, the sulfur-containing heteroatoms and π electrons in the thiophene structure of 2-thiophenecarboxylic acid react with the amino group of diethylenetriamine to form sulfur-containing polyamides. These polyamides can form bidentate coordination bonds (such as Fe-S and Fe-N bonds) with the metal surface through S / N atoms, and their adsorption strength is far greater than that of the monocarboxyl physical adsorption of oleic acid. At the same time, compared with the corrosion inhibitor of Example 7, the corrosion inhibitor synthesized in Example 1 has better corrosion protection for metal materials in acidic media. The corrosion inhibitor of Example 7, that is, the corrosion inhibitor synthesized from oleic acid, will become ineffective when pH < 5.

[0089] In Example 7, the quaternizing agent was benzyl chloride. The enhancement abilities of the corrosion inhibitors in Examples 6 and 7 for improving the corrosion inhibitor adsorption capacity were similar, with benzyl chloride showing a slightly higher enhancement. However, the iodobutane used in Example 1 had a greater advantage in improving the high-temperature stability of the corrosion inhibitor molecules. Firstly, iodobutane has a lower risk of high-temperature decomposition, and after amination, it produces butyltrimethylammonium iodide, whose alkyl chain (C4) is a saturated aliphatic chain with high thermal stability (decomposition temperature >250℃). Furthermore, the alkyl chain has low thermal motion and strong membrane recombination ability, resulting in a higher adsorption retention rate of the corrosion inhibitor molecules modified with iodobutane at high temperatures.

[0090] Apart from the differences in the structure of the raw materials mentioned above, neither Example 6 nor Example 7 included a Schiff base modification process in the synthesis of the corrosion inhibitors. However, Example 1 used cinnamaldehyde to modify the quaternized corrosion inhibitor with a Schiff base. The large π bond in the phenyl group of cinnamaldehyde and the π bond in C=C have a high electron cloud density, which can be adsorbed onto the carbon steel surface by electrostatic attraction. Furthermore, the large π conjugated system formed by the α,β-unsaturated aldehyde group and benzene ring of cinnamaldehyde can form a rigid conjugated skeleton, which can enhance thermal stability. Therefore, the adsorption capacity and stability of the corrosion inhibitor are enhanced by the thiophene structure and the phenyl structure, so that the corrosion inhibitor can also have a good corrosion inhibition effect on carbon steel at high temperature.

[0091] Furthermore, in Example 7, thiourea modification was performed to enhance the corrosion inhibition ability of the corrosion inhibitor molecules. Although this reaction process can introduce thiourea groups with unique structures, the thermal stability of the thiourea groups is worse than that of the sulfur-containing structure in thiophene of Example 1. At high temperatures, thiourea may decompose to produce corrosive H2S.

[0092] Secondly, at high temperatures, the molecular thermal motion is intense, and corrosion inhibitors with stronger adsorption capacity have better corrosion inhibition effects. The adsorption capacity of the corrosion inhibitors synthesized in Examples 6 and 7 is poor at high temperatures. Although quaternization modification can improve the adsorption capacity of corrosion inhibitor molecules to some extent, it cannot improve their thermal stability in high-temperature environments. Example 1 uses cinnamaldehyde to modify the corrosion inhibitor with a Schiff base, which can improve the stability of the corrosion inhibitor molecules at high temperatures. The high-temperature stability of Example 1 is better than that of Examples 6 and 7. In addition to using molecules with better stability at high temperatures, such as cinnamaldehyde and iodobutane, for the corresponding reaction, the 2-thiophenecarboxylic acid in the raw materials of Example 1 itself has a rigid aromatic structure, which has better adaptability and stability in high-temperature environments compared with the other two corrosion inhibitor synthesis materials.

[0093] In summary, based on the weight loss data test results in Table 1, it can be found that the quaternized imidazoline Schiff base corrosion inhibitor has excellent corrosion inhibition performance and can effectively inhibit the corrosion of oil casing materials under high temperature and CO2 environments. The imidazoline derivative products that have not undergone quaternization modification or Schiff base reaction only have a certain corrosion inhibition effect in oil and gas field working environments, and the corrosion inhibition ability of the quaternized imidazoline Schiff base corrosion inhibitor will be further enhanced with the increase of the amount of corrosion inhibitor added.

[0094] (2) Electrochemical polarization curve

[0095] The corrosion inhibition performance of the corrosion inhibitors in Examples 1-5 of this invention was evaluated using electrochemical testing methods. A saturated calomel electrode was used as the reference electrode, and a platinum electrode as the auxiliary electrode. Polarization curves were obtained using potentiodynamic scanning. The test conditions were the same as the corrosion environment. The test results are as follows: Figure 4 As shown.

[0096] Depend on Figure 4 Electrochemical test results show that after adding the quaternized modified imidazoline Schiff base corrosion inhibitor, the cathodic and anodic Tafel slopes of the polarization curves are increased compared with those without the corrosion inhibitor. Furthermore, the currents of both the cathodic and anodic polarization curves shift towards lower currents, the corrosion current density decreases, and the corrosion potential shifts towards the more positive polarization potential. Therefore, it is determined that the prepared imidazoline Schiff base corrosion inhibitor mainly inhibits the anodic reaction of the metal and belongs to the mixed type corrosion inhibitor that mainly inhibits the anode.

[0097] The above description is only some specific embodiments of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing an imidazoline-based Schiff base corrosion inhibitor, characterized in that, Includes the following steps: Under a nitrogen atmosphere, heterocyclic carboxylic acids were placed in a three-necked flask, and organic polyamines were slowly added dropwise to the three-necked flask. The temperature was raised to 140-150 °C and the reaction time was 4 h. Then the temperature was raised to 210-230 °C and the mixture was refluxed for 4 h to obtain the reactants. The reactants were purified to obtain imidazoline reactants; Under a nitrogen atmosphere, the imidazoline reactant was placed in a three-necked flask and heated to 60-90°C. Iodobutane was slowly added dropwise to the three-necked flask, and the mixture was heated to reflux and maintained for 4 hours. After the reaction was completed, the mixture was cooled to room temperature to obtain the quaternized modified reactant. Under a nitrogen atmosphere, the quaternization-modified reactant was placed in a three-necked flask, and cinnamaldehyde was slowly added dropwise to the three-necked flask. The mixture was heated to reflux and reacted for 4 hours. After cooling to room temperature, the mixture was subjected to vacuum distillation to obtain a corrosion inhibitor after purification. The heterocyclic carboxylic acid is 2-thiophenecarboxylic acid; the organic polyamine is diethylenetriamine.

2. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, Place the heterocyclic carboxylic acid and xylene into a three-necked flask.

3. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, Place the imidazoline reactant and anhydrous ethanol into a three-necked flask.

4. The corrosion inhibitor prepared by any one of the preparation methods according to claims 1-3.

5. The application of the corrosion inhibitor prepared by any one of the preparation methods according to claims 1-3 in the anti-corrosion coating of oil well metal pipes.

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