Imidazoline Schiff base corrosion inhibitor as well as preparation method and application thereof

Abstract

The invention discloses an imidazoline Schiff base corrosion inhibitor and a preparation method and application thereof, and relates to the field of oil well metal pipe anticorrosive coatings. Heterocyclic carboxylic acid reacts with organic polyamine to obtain an imidazoline reactant; reacting the imidazoline reactant with iodo-n-butane to obtain a quaternization modified reactant; and reacting the quaternization modified reactant with cinnamyl aldehyde to obtain the corrosion inhibitor. Three molecular groups in the corrosion inhibitor can play a synergistic effect, and the corrosion inhibitor has a good corrosion inhibition effect under strong acid environment and high temperature environment conditions. The corrosion inhibitor can be applied to corrosion protection of oil casing materials in the development process of oil and gas fields, so that smooth production and development of oil and gas resources are guaranteed with low economic cost.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of oil well metal pipe anticorrosion coating, in particular to an imidazoline Schiff base corrosion inhibitor and its preparation method and application. BACKGROUND

[0002] In the production and development process of oil and gas fields, oil casing often faces complex corrosion environment, and corrosion failure of oil casing material often causes serious economic losses, and even leads to safety accidents and ecological problems. According to the joint research data of China Corrosion and Protection Society, China Petroleum Society and China Chemical Society, the loss caused by corrosion in various fields accounts for about 3% of the total GDP.

[0003] At present, when facing the corrosion protection problem of oil casing material, the commonly used methods are to select materials with better performance, material surface coating, electrochemical protection and adding corrosion inhibitor protection. Among the many corrosion protection methods, adding corrosion inhibitor is widely used by many oilfields because of its convenience, low cost and synergistic effect. Among the commonly used corrosion inhibitors in domestic oil and gas fields, organic corrosion inhibitors (imidazoline, quaternary ammonium salt) suitable for high temperature acidizing and fracturing and complex working conditions are dominant. Among them, imidazoline corrosion inhibitor has excellent physical and chemical properties, and has significant inhibiting effect on CO2 and H2S corrosion, and has been widely applied and studied.

[0004] However, the current imidazoline corrosion inhibitor has the shortcomings of poor film densification, weak adaptability to extreme environment, and insufficient long-term effect and temperature resistance, which needs to be modified.

[0005] Therefore, an imidazoline Schiff base corrosion inhibitor and its preparation method are urgently needed. SUMMARY

[0006] One object of the present application is to provide a preparation method of an imidazoline Schiff base corrosion inhibitor, which modifies imidazoline by iodinated n-butane quaternary amination, and forms the final corrosion inhibitor by Schiff base reaction between the modified quaternary amination reactant and cinnamaldehyde. Through a simple preparation method, corrosion protection suitable for strong acid environment and high temperature environment conditions is obtained.

[0007] Another object of the present application is to provide an imidazoline Schiff base corrosion inhibitor and its application. The sulfur atom and a large number of nitrogen atoms in the corrosion inhibitor have obvious corrosion inhibition effect on hydrogen ions, chloride ions and other corrosive ions, and can be effectively applied to the corrosion protection of oil casing material in the production and development process of oil and gas fields.

[0008] The first object of the application is a preparation method of an imidazoline Schiff base corrosion inhibitor, comprising the following steps:

[0009] reacting the heterocyclic carboxylic acid with an organic polyamine to obtain an imidazoline reactant;

[0010] reacting the imidazoline reactant with iodine n-butane to obtain a quaternary amination modified reactant;

[0011] reacting the quaternary amination modified reactant with cinnamaldehyde to obtain the corrosion inhibitor.

[0012] The imidazoline reactant is modified by quaternary amination in the application, and a quaternary ammonium salt group is introduced, and then the quaternary amination modified reactant is modified by Schiff base reaction, and a Schiff base structure is introduced, which can not only significantly enhance the water solubility and adsorption capacity of the corrosion inhibitor, but also improve the corrosion inhibition capacity, stability and temperature resistance of the corrosion inhibitor.

[0013] The imidazoline is modified by quaternary amination using iodine n-butane in the application, and the modified quaternary amination modified reactant and cinnamaldehyde form the final corrosion inhibitor molecule through Schiff base reaction.

[0014] Compared with the prior art, the three molecular groups existing in the corrosion inhibitor of the application can play a synergistic effect, and can still maintain good corrosion inhibition effect in a strong acid environment and a high temperature environment. It can be applied to corrosion protection of oil casing materials in the development process of oil and gas fields, so as to ensure the smooth production and development of oil and gas resources at a low economic cost.

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

[0016] The heterocyclic carboxylic acid and dimethylbenzene are put into a three-necked flask under a nitrogen atmosphere, the organic polyamine is slowly dropped into the three-necked flask, and the temperature is raised to 140-150 DEG C. After 4h of reaction, the temperature is raised to 210-230 DEG C, and sufficient reflux is carried out for 4h to obtain the reactant. The reactant is purified to obtain the imidazoline reactant. The dimethylbenzene is used as a solvent.

[0017] The heterocyclic carboxylic acid is one or more of furan carboxylic acid, 2-thiophene carboxylic acid and pyrrole carboxylic acid; and the organic polyamine is tetraethylene pentaamine or diethylene triamine.

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

[0019] The imidazoline reactant prepared by the above method has more active sites, which is conducive to the introduction of more active groups.

[0020] Further, the imidazoline reactant is reacted with n-butyl iodide, comprising the following steps:

[0021] Under a nitrogen atmosphere, the imidazoline reactant and anhydrous ethanol are placed in a three-necked flask, heated to 60-90 DEG C, the n-butyl iodide is slowly dropped into the three-necked flask, heated to reflux, and kept for 4 hours, after the reaction is completed, cooled to room temperature, to obtain the quaternary ammonium modified reactant, wherein the anhydrous ethanol is a solvent.

[0022] The n-butyl iodide can introduce a positively charged quaternary ammonium group to improve the water solubility of the synthesized corrosion inhibitor, meanwhile, the introduced n-butyl chain length is moderate, which avoids the precipitation caused by too long alkyl group, and maintains the uniform dispersion of the molecule in the solution, and the iodine ion of the n-butyl iodide has an anodic passivation effect, which can form a cathode and anode synergistic protection effect with other groups, further enhancing the corrosion inhibition capacity of the finally synthesized corrosion inhibitor.

[0023] The imidazoline reactant is reacted with n-butyl iodide, through the alkylation reaction, the tertiary amine nitrogen (N) on the imidazoline ring is converted into a quaternary ammonium salt group (N + ), which can give the corrosion inhibitor stronger corrosion inhibition performance and environmental adaptability.

[0024] Further, the quaternary ammonium modified reactant is reacted with cinnamaldehyde, comprising the following steps:

[0025] Under a nitrogen atmosphere, the quaternary ammonium modified reactant is placed in a three-necked flask, the cinnamaldehyde is slowly dropped into the three-necked flask, heated to reflux, after the reaction for 4 hours, cooled to room temperature, and subjected to vacuum rectification, to obtain the corrosion inhibitor after purification.

[0026] Through the Schiff base modification of cinnamaldehyde, the benzene group of cinnamaldehyde contains a large pi bond and a pi bond in C=C, which has a high electron cloud density, can be adsorbed on the surface of N80 steel through electrostatic attraction, further improving the corrosion inhibition capacity of the corrosion inhibitor. Through the condensation and dehydration of the primary amino group at the end of the imidazoline and the aldehyde group of cinnamaldehyde, the Schiff base modified imidazoline with a conjugated enamine structure is generated, which can significantly enhance the adsorption and corrosion inhibition efficiency of the corrosion inhibitor.

[0027] Another object of the present application is an imidazoline Schiff base corrosion inhibitor and 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 n-butyl iodide, 145-198 parts of cinnamaldehyde, 172-215 parts of dimethylbenzene and 95-142 parts of anhydrous ethanol.

[0028] The corrosion inhibitor of the present application has good application in the field of anticorrosion coating of oil well metal pipes in strong acid environment and high temperature environment.

[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, the quaternization-modified reactant is placed in a three-necked flask. 165 parts of cinnamaldehyde are slowly added dropwise to the three-necked flask through a constant pressure dropping funnel. The mixture is heated to reflux and reacted for 4 hours. Then, it is cooled to room temperature and purified by 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 The 1H NMR spectrum shows that 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. Cinnamaldehyde at 165°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.

[0054] Example 3

[0055] On the basis of the above-mentioned embodiments, a preparation method of the imidazoline Schiff base corrosion inhibitor comprises the following steps:

[0056] Step 1, under the nitrogen atmosphere, 135 parts of 2-thiophene carboxylic acid and 210 parts of dimethylbenzene are put into a three-necked flask, 125 parts of diethylene triamine is slowly dropped into the three-necked flask through a constant pressure dropping funnel, and the temperature is raised to 145 DEG C, after 4 hours of reaction, the temperature is raised to 220 DEG C, and is fully refluxed for 4 hours, to obtain a reactant; the reactant is purified to obtain an imidazoline reactant.

[0057] Step 2, under the nitrogen atmosphere, the imidazoline reactant and 130 parts of anhydrous ethanol are put into a three-necked flask, the temperature is raised to 80 DEG C, 260 parts of iodine n-butane is slowly dropped into the three-necked flask through a constant pressure dropping funnel, the temperature is raised to reflux, and is kept for 4 hours, after the reaction is completed, the temperature is cooled to room temperature, to obtain the corrosion inhibitor.

[0058] Example 4

[0059] A preparation method of the imidazoline Schiff base corrosion inhibitor comprises the following steps:

[0060] Step 1, under the nitrogen atmosphere, 125 parts of 2-thiophene carboxylic acid and 185 parts of dimethylbenzene are put into a three-necked flask, 135 parts of diethylene triamine is slowly dropped into the three-necked flask through a constant pressure dropping funnel, and the temperature is raised to 145 DEG C, after 4 hours of reaction, the temperature is raised to 220 DEG C, and is fully refluxed for 4 hours, to obtain a reactant; the reactant is purified to obtain an imidazoline reactant.

[0061] Step 2, under the nitrogen atmosphere, the imidazoline reactant and 105 parts of anhydrous ethanol are put into a three-necked flask, the temperature is raised to 80 DEG C, 230 parts of iodine n-butane is slowly dropped into the three-necked flask through a constant pressure dropping funnel, the temperature is raised to reflux, and is kept for 4 hours, after the reaction is completed, the temperature is cooled to room temperature, to obtain the corrosion inhibitor.

[0062] Step 3, under the nitrogen atmosphere, the quaternary ammonium modified reactant is put into a three-necked flask, 0.13 mol of cinnamyl aldehyde is slowly dropped into the three-necked flask through a constant pressure dropping funnel, the temperature is raised to reflux, after 4 hours of reaction, the temperature is cooled to room temperature, and is subjected to vacuum rectification, to obtain the corrosion inhibitor after purification.

[0063] Example 5

[0064] A preparation method of the imidazoline Schiff base corrosion inhibitor comprises the following steps:

[0065] Step 1, under the atmosphere of nitrogen, 140 parts of 2-thiophene carboxylic acid and 180 parts of xylene are put into a three-necked flask, 120 parts of diethylene triamine is slowly dropped into the three-necked flask through a constant pressure dropping funnel, and the temperature is raised to 145 ℃, the reaction time is 4 h, then the temperature is raised to 220 ℃, and the reaction is refluxed for 4 h to obtain a reactant; the reactant is purified to obtain an imidazoline reactant.

[0066] Step 2, under the atmosphere of nitrogen, the imidazoline reactant and 140 parts of anhydrous ethanol are put into a three-necked flask, the temperature is raised to 80 ℃, 270 parts of iodine n-butane is slowly dropped into the three-necked flask through a constant pressure dropping funnel, the temperature is raised to reflux, and the reaction is kept for 4 h, then the reaction is cooled to room temperature to obtain a quaternary amination modified reactant.

[0067] Step 3, under the atmosphere of nitrogen, the quaternary amination modified reactant is put into a three-necked flask, 190 parts of cinnamyl aldehyde is slowly dropped into the three-necked flask through a constant pressure dropping funnel, the temperature is raised to reflux, the reaction is kept for 4 h, then the reaction is cooled to room temperature, and the product is purified by vacuum rectification to obtain the corrosion inhibitor.

[0068] Example 6

[0069] A preparation method of an imidazoline Schiff base corrosion inhibitor, comprising the following steps:

[0070] Step 1, lauric acid and boric acid are added into a three-necked flask according to a certain proportion, a heating jacket is heated and stirred, the temperature is raised to 40-50 ℃, then xylene is added according to a certain proportion to obtain a mixture I;

[0071] Step 2, when the temperature of the heating jacket is raised to 100-120 ℃, diethylene triamine is added dropwise into the mixture I through a constant pressure dropping funnel to react, the temperature is continuously raised to 160-180 ℃ to perform an amide dehydration reaction, then a cyclization reaction is performed at 240-260 ℃ for 3-3.5 h to obtain an imidazoline oil-soluble corrosion inhibitor;

[0072] Step 3, when the temperature is reduced to 60-80 ℃, a quaternary amination reagent is added according to a certain proportion to perform a water bath reaction, and a brown-black viscous imidazoline quaternary ammonium salt corrosion inhibitor is obtained.

[0073] Example 7

[0074] A preparation method of an imidazoline Schiff base corrosion inhibitor, comprising the following steps:

[0075] In a 1000ml three-necked round bottom flask equipped with an electric stirrer, temperature controller, condenser and water separator, 1mol (282.5g) of oleic acid, 1.2mol (123.6g) of diethylenetriamine, 0.6g of aluminum oxide and 120g of dimethylbenzene were added, and the temperature was raised to 160°C under constant stirring, and the reaction was kept at this temperature for 2 hours, then the temperature was raised to 200°C, and the reaction was kept at this temperature for 3 hours, then the temperature was raised to 240°C, and the reaction was kept at this temperature until no liquid drops were generated in the water separator; then the temperature was lowered to 90°C, 1mol (126.5g) of benzyl chloride was slowly added into the reactor through a constant pressure dropping funnel, and the reaction was kept at this temperature for 2 hours after the addition was completed, then the temperature was lowered to 90°C, 68.4g of thiourea was added into the reactor, the temperature was raised to 110°C, and the reaction was kept at this temperature for 1.5 hours, then the temperature was lowered to 80°C, and the product was poured out, thereby obtaining the oil-based sulfamide benzyl imidazoline cationic compound.

[0076] Example 8

[0077] (1) Inhibition performance test

[0078] According to the standard SY / T 5405-1996 "Performance test method and evaluation index of corrosion inhibitor for acidification", the high-temperature and high-pressure kettle was used to simulate the complex working condition environment in the well, the formation water of an oilfield in Bohai was used as the experimental medium, the static hanging piece weight loss method was used to evaluate the corrosion inhibitors of examples 1-6, and the experimental results are shown in Table 1.

[0079] Table 1:

[0080]

[0081] As shown in Table 1, when the corrosion inhibitor obtained in example 1 was added to the corrosion medium under the conditions of temperature 150°C and CO2 partial pressure 1.5Mpa, the corrosion rate could be effectively reduced, and when the addition amount was 50mg / L, the corrosion inhibition efficiency was 90.12%.

[0082] The corrosion inhibitor of example 2 was not modified by quaternary amination, and when the corrosion inhibitor of example 2 was added to the corrosion medium, the corrosion rate could be reduced, but the corrosion inhibition ability was weak, and when the addition amount was 50mg / L, the corrosion inhibition efficiency was only 64.53%.

[0083] The corrosion inhibitor of example 3 was not subjected to Schiff base reaction, and when the corrosion inhibitor of example 3 was added to the corrosion medium, the corrosion rate was reduced, but the corrosion inhibition ability was weak, and when the addition amount was 50mg / L, the corrosion inhibition efficiency was only 58.82%.

[0084] When the corrosion inhibitor product obtained in example 4 was added to the corrosion medium, the corrosion rate could be effectively reduced, and when the addition amount was 100mg / L, the corrosion inhibition efficiency was 92.53%.

[0085] The corrosion inhibitor product obtained in Example 5 can effectively reduce the corrosion rate when added to a corrosion medium, and the corrosion inhibition efficiency is 95.88% when the addition amount is 200 mg / L.

[0086] The corrosion inhibitor product obtained in Example 6 has a certain corrosion inhibition effect when added to a corrosion medium, but is poorer than the corrosion inhibition of Example 1. The corrosion inhibitor product obtained in Example 7 has a certain corrosion inhibition effect, but is poorer than the corrosion inhibition of Example 1. Therefore, compared with Example 6, the corrosion inhibitor of the present application has 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 coordination bond with the 3d orbital set of Fe and form a stable protective film on the surface of carbon steel, which 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 use of boric acid in Example 6.

[0088] In addition, the sulfur-containing heteroatom and π electron in the thiophene structure of 2-thiophene carboxylic acid react with the amine group of diethylenetriamine to form a sulfur-containing polyamide. The S / N atom can form a bidentate coordination bond (such as Fe-S and Fe-N bond) with the metal surface, and the adsorption strength is much higher than that of the single carboxyl physical adsorption of oleic acid. At the same time, the corrosion inhibitor synthesized in Example 1 has better corrosion protection ability for metal materials in acidic medium than the corrosion inhibitor synthesized in Example 7. The corrosion inhibitor synthesized in Example 7, i.e. the corrosion inhibitor synthesized from oleic acid, will be invalid when PH < 5.

[0089] The quaternary amine reagent in Example 7 is benzyl chloride. The strengthening ability of the corrosion inhibitors in Example 6 and Example 7 to the adsorption ability of the corrosion inhibitor is not much different, and benzyl chloride is slightly higher. However, the use of iodobutane in Example 1 has greater advantages in improving the high-temperature stability of the corrosion inhibitor molecule. First, iodobutane has a low risk of high-temperature decomposition, and after amination, it generates butyl trimethyl ammonium iodide, which has a saturated aliphatic chain (C4) and high thermal stability (decomposition temperature > 250°C). In addition, the alkyl chain has small thermal motion and strong film reorganization ability. The adsorption retention rate of the corrosion inhibitor molecule modified by iodobutane is higher in a high-temperature environment.

[0090] In addition to the structural differences of the above-mentioned synthetic raw materials, the synthesis process of the corrosion inhibitors in Examples 6 and 7 does not include a Schiff base modification process, while the Schiff base modification of the quaternary amine modified corrosion inhibitor in Example 1 is carried out using cinnamaldehyde. The phenyl group of cinnamaldehyde contains a large pi bond and a pi bond in C=C, which has a high electron cloud density, can be adsorbed on the surface of carbon steel by electrostatic attraction, and the alpha, beta-unsaturated aldehyde group of cinnamaldehyde + benzene ring forms a rigid conjugated skeleton to strengthen the thermal stability. Therefore, the adsorption capacity and stability of the corrosion inhibitor are enhanced by the thiofene structure and phenyl structure, so that the corrosion inhibitor can also have good corrosion inhibition effect on carbon steel at high temperature.

[0091] In addition, Example 7 is also modified by thiourea to improve the corrosion inhibition ability of the corrosion inhibitor molecule. Although this reaction process can also introduce a thiourea group with a unique structure, the thermal stability of the thiourea group is poorer than that of the sulfur-containing structure in the thiofene of Example 1. At high temperatures, thiourea may decompose to produce corrosive H2S.

[0092] Secondly, at high temperatures, the thermal motion of molecules is intense, and the corrosion inhibitor with stronger adsorption capacity has better corrosion inhibition effect. The adsorption capacity of the corrosion inhibitors synthesized in Examples 6 and 7 is poor at high temperatures. Although the quaternary amine modification can improve the adsorption capacity of the corrosion inhibitor molecule to a certain extent, it cannot improve the thermal stability of the corrosion inhibitor in a high-temperature environment. The Schiff base modification of the corrosion inhibitor in Example 1 using cinnamaldehyde can improve the stability of the corrosion inhibitor molecule at high temperatures. The high-temperature stability of Example 1 is better than that of Examples 6 and 7. In addition to using cinnamaldehyde and iodine n-butane, which have better stability at high temperatures, to carry out the corresponding reaction, the 2-thiophene carboxylic acid in the raw materials of Example 1 itself has a rigid aromatic structure, which has better adaptability and stability in a high-temperature environment than the synthesis materials of the other two corrosion inhibitors.

[0093] In summary, according to the weight loss data test results in Table 1, it can be found that the imidazoline Schiff base corrosion inhibitor after quaternary amine modification has excellent corrosion inhibition performance and can have good corrosion inhibition effect on oil casing materials in a high-temperature and CO2 environment. The imidazoline derivative products without quaternary amine modification or Schiff base reaction only have certain corrosion inhibition effect in the working environment of oil and gas fields, and the corrosion inhibition ability of the imidazoline Schiff base corrosion inhibitor after quaternary amine modification is further enhanced with the increase of the amount of the corrosion inhibitor.

[0094] (2) Electrochemical polarization curve

[0095] The electrochemical test method is used to evaluate the corrosion inhibition performance of the corrosion inhibitors in Examples 1-5. The saturated mercury-mercury electrode is used as the reference electrode, the platinum electrode is used as the auxiliary electrode, the potentiodynamic scanning method is used to measure the polarization curve, the test conditions are the same as the corrosion environment, and the test results are shown in Table 1. Figure 4 ​

[0096] By Figure 4 The electrochemical test results show that after adding the quaternary amine modified imidazoline Schiff base corrosion inhibitor, the cathode and anode Tafel slope of the polarization curve are increased compared with no addition of the corrosion inhibitor, the current of the cathode and anode polarization curve is offset to the low current direction, the corrosion current density is reduced, and the corrosion potential moves to the positive direction of the polarization potential, so it is determined that the prepared imidazoline Schiff base corrosion inhibitor mainly inhibits the anodic reaction of the metal, and belongs to a mixed type inhibitor mainly inhibiting the anode.

[0097] The above only describes some specific embodiments of the present application, and is not used to limit the present application, and any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application should be included in the protection scope of the present application.

Claims

1. A method for preparing an imidazoline-based Schiff base corrosion inhibitor, characterized in that, Includes the following steps: Heterocyclic carboxylic acids are reacted with organic polyamines to obtain imidazoline reactants; The imidazoline reactant was reacted with iodobutane to obtain the quaternized modified reactant; The quaternized modified reactant was reacted with cinnamaldehyde to obtain a corrosion inhibitor.

2. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, The reaction of heterocyclic carboxylic acids with organic polyamines 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.

3. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, The reaction of imidazoline reactants with n-butane iodide includes the following steps: 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.

4. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, The reaction of the quaternized modified product with cinnamaldehyde includes the following steps: 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.

5. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, The corrosion inhibitor comprises the following components in parts by weight: 120-140 parts heterocyclic carboxylic acid, 113-155 parts organic polyamine, 202-276 parts iodobutane, and 145-198 parts cinnamaldehyde.

6. The method for preparing an imidazoline Schiff base corrosion inhibitor according to claim 1, characterized in that, The heterocyclic carboxylic acid is one or more of furanoic acid, 2-thiophenic acid, and pyrrolic acid; the organic polyamine is tetraethylenepentamine or diethylenetriamine.

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

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

9. The corrosion inhibitor prepared by any one of the preparation methods according to claims 1-8.

10. The application of the corrosion inhibitor prepared by any one of the preparation methods according to claims 1-8 in the anti-corrosion coating of oil well metal pipes.

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