Preparation method of modified imidazoline quaternary ammonium salt and modified imidazoline corrosion inhibitor

Abstract

The invention relates to a preparation method of modified imidazoline quaternary ammonium salt and a modified imidazoline corrosion inhibitor, and belongs to the technical field of oil and gas field chemicals. The preparation method comprises the following steps: carrying out amidation dehydration reaction on citric acid and polyamine, then carrying out cyclization dehydration reaction to generate an imidazoline intermediate, and sequentially carrying out substitution reaction, coupling reaction and quaternization reaction on the imidazoline intermediate to generate modified imidazoline quaternary ammonium salt; the substitution reaction is that the imidazoline intermediate reacts with haloid acid; the coupling reaction is that a substitution product reacts with a Grignard reagent; the quaternization reaction is that a coupling reaction product reacts with benzyl halide. The prepared modified imidazoline type quaternary ammonium salt can be more firmly adsorbed on the surface of a metal material, the oxidation-reduction potential of H < + > is changed, and meanwhile the potential can be reduced to achieve the corrosion inhibition purpose; in addition, a hydrophobic long-chain group in the modified imidazoline quaternary ammonium salt can also improve the corrosion inhibition performance of the compound.

Description

Technical Field

[0001] The invention relates to a preparation method of a modified imidazoline type quaternary ammonium salt and a modified imidazoline corrosion inhibitor, belonging to the technical field of oil and gas field chemicals. Background Art

[0002] Metal corrosion is a widespread problem in all industries. It not only causes economic losses but also damages the ecological environment. Therefore, adding corrosion inhibitors is a long-term and effective measure to prevent metal corrosion in environmental media. In oil and gas field production systems, the pH value of water media is generally between 5.5 and 6.5, with high mineralization and a large amount of CO2, which leads to widespread and serious corrosion of pipelines and equipment in the production system.

[0003] At present, the main measure for controlling corrosion on site in oil and gas fields is to add corrosion inhibitors to the wellbore. Reasonable dosing cycle and dosage can effectively slow down the corrosion of oil and water pipeline equipment. The corrosion inhibition mechanism of corrosion inhibitors added in major oil and gas fields is mostly based on chemical adsorption. The hydrophilic polar groups of highly electronegative elements such as O, N, P, S in the corrosion inhibitors are adsorbed on the active points of the metal surface or the entire surface, changing the charge state and interface properties of the metal surface, making the energy state of the metal surface tend to be stable, increasing the activation energy of the corrosion reaction, and slowing down the corrosion rate. At present, imidazoline corrosion inhibitors are commonly used in major oil and gas fields, and there are many studies on the synthesis and corrosion inhibition mechanism of imidazoline corrosion inhibitors.

[0004] The Chinese invention patent application with application publication number CN115710229A discloses a water-soluble bisimidazoline corrosion inhibitor and its preparation method, which is to react an organic acid and a polyamine at 140-160°C for 2 hours under the condition of xylene as a water-carrying agent, and then continue to heat up to 200-220°C for cyclization reaction for 6 hours to obtain an imidazoline intermediate; then react with a quaternary ammonium agent at 80-90°C for 5 hours to obtain a water-soluble bisimidazoline corrosion inhibitor. The corrosion inhibitor of the invention has a bisimidazoline structure, has double functional groups, has good water solubility and high surface activity, has stronger adsorption on the metal surface than ordinary monocyclic imidazoline corrosion inhibitors, and has a high corrosion inhibition rate. However, the symmetrical bisimidazoline hydrophobic group is easy to fold, which affects the corrosion inhibition of the agent, and the single imidazoline corrosion inhibitor has poor pitting resistance and high temperature resistance in high-mineralization oil and gas wells.

[0005] The Chinese invention patent application with application publication number CN115820237A discloses a corrosion inhibitor for carbon dioxide flooding and its preparation method, which is compounded with a modified imidazoline derivative, a surfactant, hexamethylenetetramine, an iodide, propargyl alcohol and a solvent. The invention provides a modified imidazoline derivative for use as a corrosion inhibitor, but the adsorption performance and corrosion inhibition performance of the corrosion inhibitor are relatively low, and propargyl alcohol is a highly toxic substance, which poses a great safety hazard during preparation, transportation and on-site filling. Summary of the invention

[0006] The first object of the present invention is to provide a method for preparing a modified imidazoline quaternary ammonium salt, so as to solve the problems of poor adsorption performance, pitting resistance and high temperature resistance of imidazoline corrosion inhibitors in the prior art.

[0007] The second object of the present invention is to provide a modified imidazoline corrosion inhibitor to solve the problem in the prior art that the liquid corrosion inhibitor for oil and water wells is not tightly bonded to the surface of the pipe and is easily eroded.

[0008] In order to achieve the above purpose, the first technical solution of the present invention is:

[0009] A method for preparing a modified imidazoline quaternary ammonium salt comprises the following steps: citric acid and polyamine undergo an amidation dehydration reaction, followed by a cyclization dehydration reaction to generate an imidazoline intermediate, and the imidazoline intermediate undergoes a substitution reaction, a coupling reaction and a quaternization reaction in sequence to generate a modified imidazoline quaternary ammonium salt;

[0010] The substitution reaction is a reaction between an imidazoline intermediate and a hydrohalic acid; the coupling reaction is a reaction between a substitution product and a Grignard reagent; and the quaternization reaction is a reaction between a coupling reaction product and a benzyl halide.

[0011] The invention carries out an amidation dehydration reaction on citric acid and polyamine, and then carries out a cyclization dehydration reaction to generate an imidazoline intermediate, wherein the intermediate contains three five-membered rings, and then the intermediate reacts with a hydrohalic acid, wherein the halogen group replaces the hydroxyl group of the intermediate, and then the obtained substance carries out a coupling reaction with a Grignard reagent, wherein the alkyl group in the Grignard reagent replaces the halogen group (i.e., the hydrophobic long-chain group) in the intermediate, and finally the five-membered ring of the imidazoline type quaternary ammonium salt is modified by using a benzyl halide to obtain a modified imidazoline type quaternary ammonium salt.

[0012] The modified imidazoline quaternary ammonium salt of the present invention has three five-membered rings, and the C=N double bond on the ring and the lone pair of electrons on the N atom undergo covalent adsorption on the metal surface, and can be more firmly adsorbed on the surface of the metal material, changing the H + The redox potential of the metal can be increased, and at the same time, some oxidants in the protective medium can be complexed to reduce their potential to achieve the purpose of corrosion inhibition. In addition, the hydrophobic long-chain groups (R groups) in the modified imidazoline quaternary ammonium salts are oriented on the metal surface to form a dense hydrophobic layer, which can not only hinder the diffusion and migration of corrosion products, but also improve the corrosion inhibition performance of the compound.

[0013] In order to promote the occurrence of the amidation dehydration reaction, preferably, the citric acid and the polyamine undergo an amidation dehydration reaction in a solvent, and the solvent is xylene. Xylene not only acts as a solvent in the reaction, but also acts as a water-carrying agent to promote the reaction.

[0014] More preferably, the molar ratio of citric acid to xylene is (1-1.05):(0.5-0.8).

[0015] In order to improve the efficiency of the amidation dehydration reaction and the substitution reaction, preferably, the molar ratio of the citric acid to the polyamine is (1-1.05):(3.5-4), and the molar ratio of the hydrohalic acid to the citric acid is (0.5-0.7):(1-1.05).

[0016] More preferably, the hydrohalic acid is one or more of hydroiodic acid, hydrobromic acid and hydrochloric acid. The substitution reaction activities of the three hydrohalic acids with the hydroxyl group on the imidazoline intermediate are hydroiodic acid>hydrobromic acid>hydrochloric acid.

[0017] In order to facilitate the substitution reaction, preferably, the hydrohalic acid is hydroiodic acid.

[0018] In order to ensure the synthesis of modified imidazoline quaternary ammonium salt, preferably, the molar ratio of the Grignard reagent to citric acid is (1.1-1.3):(1-1.05), and the molar ratio of the benzyl halide to citric acid is (3.5-4.0):(1-1.05).

[0019] More preferably, the Grignard reagent is R-Mg-X, R is a C6-C8 n-alkyl group, and X is bromine or iodine, such as heptylmagnesium bromide.

[0020] More preferably, the benzyl halide is benzyl chloride. The chlorine in benzyl chloride has a strong electronegativity and a strong reaction activity, which is more conducive to the reaction.

[0021] Preferably, the temperature of the amidation dehydration reaction is 140-160°C, and the reaction time is 2.5-3h; at this temperature, citric acid and polyamines are prone to undergo amidation dehydration reaction, which is convenient for the formation of intermediates; the temperature of the substitution reaction is 20-40°C, and the reaction time is 0.5-2h. When the substitution reaction is carried out at this temperature, the substitution efficiency is relatively high.

[0022] Preferably, the coupling reaction temperature is 145-160°C, and the reaction time is 3-4 hours; the quaternization reaction temperature is 100-120°C, and the reaction time is 3-5 hours. Reaction at this temperature facilitates the modification of the five-membered ring.

[0023] In order to make the amino groups in the polyamine form a five-membered ring, preferably, the temperature of the cyclodehydration reaction is 200-230° C., and the reaction time is 4-6 hours.

[0024] In order to improve the adsorptivity of the modified imidazoline type quaternary ammonium salt, preferably, the polyamine is polyethylene polyamine. Polyethylene polyamine contains more than two vinyl groups and more than three amino groups. The polyethylene polyamine is one or more of diethylene triamine, triethylene tetramine, and tetraethylene pentamine. More preferably, triethylene tetramine is used. The modified imidazoline type quaternary ammonium salt obtained by triethylene tetramine has a better sustained release effect and a high sustained release rate.

[0025] The second technical solution of the present invention is:

[0026] A modified imidazoline corrosion inhibitor, comprising the following components: modified imidazoline quaternary ammonium salt, pyridine, hexamethylenetetramine, thiourea, and water;

[0027] The modified imidazoline type quaternary ammonium salt is prepared by the above-mentioned preparation method of the modified imidazoline type quaternary ammonium salt.

[0028] The modified imidazoline corrosion inhibitor of the present invention is obtained by compounding modified imidazoline quaternary ammonium salt, pyridine, urotropine, thiourea and water. Among them, the three five-membered rings and hydrophobic long-chain groups of the modified imidazoline quaternary ammonium salt improve the adsorption capacity and slow-release effect of the corrosion inhibitor on the surface of metal materials; the nitrogen atom on the six-membered heterocyclic ring in the pyridine molecular structure forms a coordination bond with the iron atom on the surface of steel and is adsorbed on the surface of steel; the lone pair of electrons on the nitrogen atom in the tetranitrogen heterocyclic structure of urotropine forms a coordination bond with the iron atom on the surface of steel and is adsorbed on the surface of steel; the sulfur atom and nitrogen atom in the molecular structure of thiourea form a coordination bond with the iron atom on the surface of steel to inhibit the corrosion reaction of the metal surface. The three auxiliary agents can all play a synergistic adsorption role with the modified tri-imidazoline quaternary ammonium salt, prevent the adsorption film from falling off at high temperature, and improve the corrosion inhibition performance. The modified imidazoline corrosion inhibitor of the present invention has the advantages of high corrosion inhibition rate, good economy and strong safety.

[0029] In order to make the modified imidazoline corrosion inhibitor have better corrosion inhibition performance, preferably, it is composed of the following components in parts by mass: 15-20 parts of modified imidazoline quaternary ammonium salt, 1-3 parts of pyridine, 1-3 parts of urotropine, 3-8 parts of thiourea, and 18-22 parts of water. DETAILED DESCRIPTION

[0030] The preparation method of the modified imidazoline type quaternary ammonium salt of the present invention adopts the following steps:

[0031] (1) Mixing citric acid and polyamine in a solvent, heating to 140-160° C., stirring, condensing and refluxing for 2.5-3 hours, and performing an amidation dehydration reaction;

[0032] (2) heating to 200-230°C and carrying out cyclodehydration reaction for 4-6 hours;

[0033] (3) cooling to 135-145° C. and distilling for 0.5-1 h to evaporate excess solvent and polyamine to obtain a tris-imidazoline intermediate;

[0034] (4) mixing the triimidazoline intermediate with a hydrohalic acid, maintaining the temperature at 20 to 40° C., and stirring for 0.5 to 2 hours to carry out a substitution reaction to obtain a substituted product;

[0035] (5) mixing the substituent with the Grignard reagent R-Mg-X, heating to 145-160° C., reflux for 3-4 hours to carry out coupling reaction, and then cooling to room temperature to obtain a conjugate;

[0036] (6) The conjugate is mixed with a benzyl halide, heated to 100-120° C., refluxed for 3-5 hours, and subjected to a quaternization reaction. After cooling, a modified triimidazoline quaternary ammonium salt is obtained.

[0037] The reaction process involved in the above preparation method is as follows:

[0038]

[0039]

[0040] The technical solution of the present invention is further described below in conjunction with specific implementation methods.

[0041] 1. Embodiment of the preparation method of the modified imidazoline quaternary ammonium salt of the present invention

[0042] Example 1

[0043] The preparation method of the modified imidazoline type quaternary ammonium salt of the present embodiment adopts the following steps:

[0044] (1) 1 mol of citric acid, 3.5 mol of triethylenetetramine, and 0.5 mol of xylene were added to a reaction kettle, heated to 145° C., stirred, condensed and refluxed for 3 h to carry out an amidation dehydration reaction;

[0045] (2) Heating to 210°C and carrying out cyclodehydration reaction for 4 hours;

[0046] (3) Cooling to 140° C. and distilling for 40 min to distill off excess xylene and triethylenetetramine to obtain a trisimidoline intermediate.

[0047] (4) adding 0.5 mol of hydroiodic acid to the triimidazoline intermediate obtained in step (3), maintaining the temperature at 25° C., stirring for 0.5 h to carry out a substitution reaction, and obtaining a mixture I;

[0048] (5) adding 1.1 mol of hexylmagnesium bromide to the mixture I of step (4), heating to 150° C., reflux for 3.5 h, performing a coupling reaction, and then cooling to room temperature to obtain a mixture II;

[0049] (6) Add 3.5 mol of benzyl chloride to the mixture II of step (5), heat to 100° C., reflux for 3 h, and cool to obtain a reddish brown viscous liquid, which is the modified triimidazoline quaternary ammonium salt, with an active ingredient content of 76%.

[0050] Example 2

[0051] The preparation method of the modified imidazoline type quaternary ammonium salt of the present embodiment adopts the following steps:

[0052] (1) 1 mol of citric acid, 3.7 mol of triethylenetetramine, and 0.5 mol of xylene were added to a reaction kettle, heated to 150° C., stirred, and refluxed under condensation for 2.5 hours to carry out an amidation dehydration reaction;

[0053] (2) The temperature was raised to 220°C and the cyclodehydration reaction was carried out for 4.5 hours;

[0054] (3) cooling to 140° C. and distilling for 0.5 h to distill off excess xylene and triethylenetetramine to obtain a trisimidoline intermediate;

[0055] (4) adding 0.6 mol of hydroiodic acid to the triimidazoline intermediate obtained in step (3), maintaining the temperature at 30° C., and stirring for 1 h to carry out a substitution reaction to obtain a mixture I;

[0056] (5) adding 1.1 mol of heptylmagnesium bromide to the mixture I of step (4), heating to 150° C., reflux for 3 h, performing a coupling reaction, and then cooling to room temperature to obtain a mixture II;

[0057] (6) Add 3.8 mol of benzyl chloride to the mixture II of step (5), heat to 110° C., reflux for 3.5 h, and cool to obtain a reddish brown viscous liquid, which is the modified triimidazoline quaternary ammonium salt, with an active ingredient content of 76%.

[0058] Embodiment 3-8

[0059] The preparation method of the modified imidazoline quaternary ammonium salt of Examples 3-8 adopts the following steps:

[0060] (1) adding citric acid, triethylenetetramine and xylene into a reaction kettle in proportion, heating to a certain temperature, stirring, condensing and refluxing for a certain period of time, and performing an amidation dehydration reaction;

[0061] (2) heating to a certain temperature and performing cyclodehydration reaction for a certain period of time;

[0062] (3) cooling to a certain temperature for distillation, distilling for a certain time to distill off excess xylene and triethylenetetramine to obtain a triimidazoline intermediate;

[0063] (4) adding hydroiodic acid to the triimidazoline intermediate obtained in step (3) in proportion, heating to a certain temperature, and refluxing for a certain time to carry out a substitution reaction to obtain a mixture I;

[0064] (5) adding the Grignard reagent R-Mg-X to the mixture I of step (4) in proportion, heating to a certain temperature, refluxing for a certain time, performing a coupling reaction, and then cooling to room temperature to obtain a mixture II;

[0065] (6) Adding benzyl chloride to the mixture II of step (5) in proportion, heating to a certain temperature, refluxing for a certain time, carrying out a quaternization reaction, and cooling to obtain a modified triimidazoline quaternary ammonium salt.

[0066] The process parameters and Grignard reagents involved in the examples are shown in Table 1.

[0067] Table 1 Reagents and process parameters involved in the examples

[0068]

[0069]

[0070] 2. Embodiments of the modified imidazoline corrosion inhibitor of the present invention

[0071] Example 9

[0072] The modified imidazoline corrosion inhibitor of this embodiment is composed of the following components in parts by mass: 16 parts of the modified imidazoline quaternary ammonium salt prepared in Example 1, 2 parts of pyridine, 1 part of urotropine, 5 parts of thiourea, and 19 parts of water.

[0073] The specific method is to stir and mix the above ingredients.

[0074] Example 10

[0075] The modified imidazoline corrosion inhibitor of this embodiment is composed of the following components in parts by mass: 16.2 parts of the modified imidazoline quaternary ammonium salt prepared in Example 2, 2.1 parts of pyridine, 1.1 parts of urotropine, 5.1 parts of thiourea, and 19.1 parts of water.

[0076] Examples 11-16

[0077] The modified imidazoline corrosion inhibitors of Examples 11-16 were compounded with the modified imidazoline quaternary ammonium salts prepared in Examples 3-8 in sequence, and the specific compositions are shown in Table 2.

[0078] Table 2 Modified imidazoline corrosion inhibitors of Examples 8-13

[0079]

[0080] 3. Comparison

[0081] Comparative Example 1

[0082] The modified imidazoline corrosion inhibitor of this comparative example is composed of the following components in parts by mass: 40 parts of modified imidazoline derivatives, 15 parts of OP-10, 5 parts of urotropine, 3 parts of cuprous iodide, 6 parts of propargyl alcohol, 10 parts of water, and 30 parts of isopropanol.

[0083] The preparation method of the modified imidazoline derivative of this comparative example adopts the following steps:

[0084] (1) 2 mol of oleic acid and 2.2 mol of tetraethylenepentamine were mixed and reacted at 180° C. for 4.5 hours to obtain a first mixture;

[0085] (2) cooling the first mixture obtained in step (1) to 50° C., adding 2 mol of carbon disulfide, heating to 60° C. and reacting for 3 h, then adding 90 g of a 20% formaldehyde solution, stirring and mixing until no heat is released, to obtain a second mixture;

[0086] (3) Add 1.2 mol of phosphorous acid to the second mixture obtained in step (2), mix and then perform a third reaction to obtain a modified imidazoline derivative.

[0087] Comparative Example 2

[0088] The preparation method of the imidazoline corrosion inhibitor of this comparative example adopts the following steps: under the condition of 20% xylene as a water-carrying agent, lauric acid and ethylenediamine are mixed in a molar ratio of 1:1.2, and an amidation reaction is carried out at 150°C for 2 hours, and the temperature is continuously raised to 220°C for a cyclization reaction for 6 hours to obtain an imidazoline intermediate; then the imidazoline intermediate and 1,6-dichlorohexane are mixed in a molar ratio of 2:0.8, and the mixture is reacted at 80°C for 5 hours to obtain a water-soluble bisimidazoline corrosion inhibitor.

[0089] Comparative Example 3

[0090] The preparation method of the corrosion inhibitor of this comparative example adopts the following steps: 1 mol of benzoic acid and 2.6 mol of xylene are added to an ethanol solution, and then 1.6 g of catalyst boric acid and a few grains of zeolite are added, and the solution is heated to 100°C, and 0.6 mol of diethylenetriamine is added dropwise, and the temperature is adjusted to 90°C, and 0.05 g of AMSD as a chain transfer agent is added, and then 1 mol of acrylic acid is added dropwise, and the reaction is continued for 3.5 hours to obtain the terpolymer corrosion inhibitor.

[0091] V. Experimental Examples

[0092] In this experimental example, the corrosion inhibition performance of the corrosion inhibitors of Examples 1-16, Comparative Examples 2 and 3 and the imidazoline derivative in Comparative Example 1 was tested. The results are shown in Tables 3 and 4.

[0093] In order to evaluate the corrosion inhibition performance of the modified imidazoline quaternary ammonium salts of Examples 1-8 and the modified imidazoline liquid corrosion inhibitors of Examples 9-16, the static uniform corrosion inhibition rate, indoor dynamic uniform corrosion inhibition rate, and pitting corrosion inhibition rate of the modified imidazoline quaternary ammonium salts of Examples 1-8, the modified imidazoline liquid corrosion inhibitors of Examples 9-16, the corrosion inhibitors of Comparative Examples 2 and 3, and the imidazoline derivative in Comparative Example 1 were tested respectively. The corrosion inhibition rate test method is carried out according to the corrosion inhibition rate evaluation steps in the standard SY / T 5273-2014 "Performance Indicators and Evaluation Methods for Corrosion Inhibitors for Oilfield Produced Water Treatment".

[0094] As shown in Table 3, the static uniform corrosion inhibition rate, indoor dynamic uniform corrosion inhibition rate, and pitting corrosion inhibition rate of the modified imidazoline quaternary ammonium salts of Examples 1-8 of the present invention are better than the inhibitors of Comparative Examples 2 and 3 and the imidazoline derivative in Comparative Example 1, and have excellent corrosion inhibition performance. The evaluation concentrations of Examples 1-8 in Table 3 refer to the concentrations of the effective ingredients of the modified imidazoline quaternary ammonium salts.

[0095] It can be seen from Table 4 that the modified imidazoline corrosion inhibitors of Examples 9 to 16 of the present invention have excellent static uniform corrosion inhibition rate, indoor dynamic uniform corrosion inhibition rate and pitting corrosion inhibition rate.

[0096] Table 3 Corrosion inhibition performance test results

[0097]

[0098]

[0099] Table 4 Corrosion inhibition performance test results of corrosion inhibitors

[0100]

Claims

1. A method for preparing a modified imidazoline type quaternary ammonium salt, characterized in that: The following steps are involved: Citric acid and polyamine undergo an amidation dehydration reaction, and then undergo a cyclization dehydration reaction to generate an imidazoline intermediate, and the imidazoline intermediate undergoes a substitution reaction, a coupling reaction, and a quaternization reaction in sequence to generate a modified imidazoline type quaternary ammonium salt; The substitution reaction is a reaction between an imidazoline intermediate and a hydrohalic acid; the coupling reaction is a reaction between a substitution product and a Grignard reagent; and the quaternization reaction is a reaction between a coupling reaction product and a benzyl halide.

2. The method for preparing a modified imidazoline type quaternary ammonium salt according to claim 1, wherein The molar ratio of the citric acid to the polyamine is (1-1.05):(3.5-4), and the molar ratio of the hydrohalic acid to the citric acid is (0.5-0.7):(1-1.05).

3. The preparation method of modified imidazoline type quaternary ammonium salt according to claim 1, characterized in that, The molar ratio of the Grignard reagent to the citric acid is (1.1-1.3):(1-1.05), and the molar ratio of the benzyl halide to the citric acid is (3.5-4.0):(1-1.05).

4. The preparation method of the modified imidazoline type quaternary ammonium salt according to claim 1 or 2, characterized in that, The temperature of the amidation dehydration reaction is 140-160° C., and the reaction time is 2.5-3 h; the temperature of the substitution reaction is 20-40° C., and the reaction time is 0.5-2 h.

5. The preparation method of the modified imidazoline type quaternary ammonium salt according to claim 1 or 3, characterized in that, The temperature of the coupling reaction is 145-160° C., and the reaction time is 3-4 hours; the temperature of the quaternization reaction is 100-120° C., and the reaction time is 3-5 hours.

6. The method for preparing a modified imidazoline type quaternary ammonium salt according to claim 1, wherein The temperature of the cyclodehydration reaction is 200-230° C., and the reaction time is 4-6 hours.

7. The preparation method of the modified imidazoline type quaternary ammonium salt according to claim 1 or 2, characterized in that, The polyamine is polyethylene polyamine.

8. A modified imidazoline corrosion inhibitor, characterized in that: It is composed of the following components: modified imidazoline type quaternary ammonium salt, pyridine, urotropine, thiourea and water; The modified imidazoline quaternary ammonium salt is prepared by the preparation method of the modified imidazoline quaternary ammonium salt according to any one of claims 1 to 7.

9. The modified imidazoline corrosion inhibitor according to claim 8, characterized in that The invention is composed of the following components in parts by mass: 15 to 20 parts of modified imidazoline quaternary ammonium salt, 1 to 3 parts of pyridine, 1 to 3 parts of urotropine, 3 to 8 parts of thiourea and 18 to 22 parts of water.

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