A terpolymer, a low-phosphorus scale inhibitor and a preparation method thereof

Abstract

This invention discloses a ternary copolymer, a low-phosphorus scale inhibitor, and a method for preparing the same, belonging to the field of water treatment materials technology. The ternary copolymer has the following structural formula: This invention also proposes a low-phosphorus scale inhibitor comprising one or more of the above-mentioned ternary copolymers. Furthermore, this invention provides a method for preparing the above-mentioned ternary copolymer, comprising the following steps: S1, mixing chitosan solution and 2-phosphonobutane-1,2,4-tricarboxylic acid, then adding a dehydrating agent, followed by dropwise addition of an acetaminoiminoacetic acid solution to obtain a reaction solution; S2, heating the reaction solution to 70℃~85℃ to react and obtain the ternary copolymer. The ternary copolymer proposed in this invention exhibits good dispersibility and scale inhibition properties.

Description

Technical Field

[0001] This invention relates to the field of water treatment materials technology, specifically to a terpolymer, a low-phosphorus scale inhibitor, and a method for preparing the same. Background Technology

[0002] In oilfield extraction, water injection is typically used to balance formation pressure; produced water is commonly used to improve oil extraction efficiency. However, produced water originates from the formation and, in addition to a large amount of water, contains many metal ions, such as calcium ions. 2+ Mg 2+ Ba 2+ 、Sr 2+ These are metal ions. These ions are the main scale-forming ions, and they react with CO32-. 2- SO4 2- After they combine and undergo a precipitation reaction, scale is formed.

[0003] Oilfield scale is mostly classified into two categories: the first is carbonate scale, such as CaCO3 and BaCO3, which can be removed with inorganic acids. The principle behind this is that H+... + With CO3 2- The first type is scale that produces H2O and CO2, but the cleaning process can easily cause equipment corrosion, which is not conducive to equipment maintenance. The second type is sulfate scale, such as CaSO4 and BaSO4. This type of scale has a small solubility product and does not react with acid, so acid washing is not feasible. It can only be removed by replacing pipes or physical methods, but the cleaning process requires production to be stopped, which will inevitably seriously affect oilfield production.

[0004] Currently, the most common and effective method to prevent scale formation is to add chemical scale inhibitors to the produced water injected into oil fields. Most mainstream scale inhibitors are phosphorus-based, but their excessive use can lead to eutrophication, which is detrimental to environmental protection. With the development of water treatment technology and the continuous improvement of chemical scale inhibitor materials, and in response to global environmental protection initiatives, there is a growing preference for low-phosphorus or phosphorus-free "green scale inhibitors." As the country places increasing emphasis on environmental protection, developing a green, environmentally friendly scale inhibitor with excellent scale-inhibiting performance is essential. Summary of the Invention

[0005] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a terpolymer, a low-phosphorus scale inhibitor and its preparation method, thereby solving the technical problem of how to develop a green and environmentally friendly scale inhibitor with excellent scale inhibition performance in the prior art.

[0006] To achieve the above-mentioned technical objectives, the present invention provides a terpolymer having the following structural formula:

[0007]

[0008] In the formula, m, n, and q represent the molar amounts of the monomer chitosan, the monomer acetaminoiminoacetic acid, and the monomer 2-phosphonobutane-1,2,4-tricarboxylic acid, respectively, and m:n:q = 1:(0.2~0.5):(0.1~0.3).

[0009] In any embodiment, the terpolymer is formed by grafting three monomers: chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0010] The present invention also proposes a low-phosphorus scale inhibitor comprising one or more of the above-mentioned terpolymers.

[0011] Furthermore, the present invention also proposes a method for preparing the above-mentioned terpolymer, comprising the following steps:

[0012] S1. Mix chitosan solution and 2-phosphonobutane-1,2,4-tricarboxylic acid, then add a dehydrating agent, and then add acetaminoiminoacetic acid solution dropwise to obtain the reaction solution;

[0013] S2. The reaction solution is heated to 70°C to 85°C to obtain the terpolymer.

[0014] In any embodiment, in step S1, the chitosan solution is prepared by the following steps: mixing chitosan with an acetic acid solution with a volume concentration of 5-8%, heating to 45-55°C, and stirring to obtain the chitosan solution.

[0015] In any embodiment, in step S1, the chitosan and the 2-phosphonobutane-1,2,4-tricarboxylic acid are mixed at a mass ratio of 1:(1-7).

[0016] In any embodiment, in step S1, the dehydrating agent is N,N'-dicyclohexylcarboimide.

[0017] In any embodiment, in step S1, the acetaminoiminoacetic acid solution is prepared by dissolving acetaminoiminoacetic acid in a NaOH solution with a mass concentration of 2-3%.

[0018] In any embodiment, in step S1, the mass ratio of chitosan to acetaminoiminoacetic acid in the acetaminoiminoacetic acid solution is (1-2):1.

[0019] In any embodiment, the reaction time in step S2 is 3-5 hours.

[0020] In any embodiment, in step S1, the amount of the dehydrating agent is 10-12% of the total mass of chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0021] Compared with the prior art, the beneficial effects of the present invention include: the ternary copolymer proposed in this invention is a ternary copolymer formed by the dehydration condensation of three monomers: chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid. Chitosan itself has a large number of hydroxyl and amino groups, and after being linked with the other two monomers, it simultaneously possesses carboxyl groups and a small amount of phosphonic acid groups. Carboxyl groups are the most important groups for inhibiting calcium scale formation, and the oxygen and hydroxyl groups in the small amount of phosphonic acid groups can react with calcium (Ca) in water. 2 Metal ions such as Mg2+ and magnesium (Mg2+) form stable soluble complexes. Hydroxyl and amino groups can disperse scale particles in water by adsorbing onto the surface of the scale particles, and can also improve the solubility of the scale inhibitor by forming hydrogen bonds, thus giving the terpolymer good dispersion and scale inhibition properties.

[0022] From a green and environmentally friendly perspective, the present invention provides a terpolymer that not only has a significantly lower phosphorus content than traditional phosphorus-based scale inhibitors, but also has scale inhibition performance that is comparable to traditional scale inhibitors. It is particularly effective against CaCO3 and its biodegradability allows it to be degraded more quickly in the environment. Attached Figure Description

[0023] Figure 1 This is the infrared spectrum of the scale inhibitor (i.e., CTS-PBTCA-ADA) prepared in Example 3 of this invention. Detailed Implementation

[0024] The "range" disclosed in this application is defined by a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60–120 and 80–110 are listed for a specific parameter, it is understood that ranges of 60–110 and 80–120 are also expected. Furthermore, if minimum range values ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are listed, then the following ranges are all expected: 1–3, 1–4, 1–5, 2–3, 2–4, and 2–5. In this application, unless otherwise stated, the numerical range "a–b" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0~5" indicates that all real numbers between "0~5" have been listed in this article; "0~5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0025] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0026] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0027] This specific embodiment provides a ternary copolymer having the following structural formula:

[0028]

[0029] In the formula, m, n, and q represent the molar numbers of the monomers chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid, respectively, and m:n:q = 1:(0.2~0.5):(0.1~0.3); the terpolymer is formed by grafting three monomers: chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0030] This specific embodiment also proposes a low-phosphorus scale inhibitor, comprising one or more of the above-mentioned terpolymers.

[0031] This specific embodiment also proposes a method for preparing the above-mentioned terpolymer, including the following steps:

[0032] S1. Chitosan and 2-phosphonobutane-1,2,4-tricarboxylic acid are mixed at a mass ratio of 1:(1-7), followed by the addition of the dehydrating agent N,N'-dicyclohexylcarboimide, and then the addition of an acetaminophen-acetic acid solution to obtain a reaction solution. The chitosan solution is prepared by the following steps: mixing chitosan with an acetic acid solution with a volume concentration of 5-8%, heating to 45-55°C, and stirring to obtain the chitosan solution. The acetaminophen-acetic acid solution is prepared by the following steps: dissolving acetaminophen-acetic acid in a NaOH solution with a mass concentration of 2-3%. The mass ratio of acetaminophen-acetic acid in the chitosan and the acetaminophen-acetic acid solution is (1-2):1. The amount of the dehydrating agent is 10-12% of the total mass of chitosan, acetaminophen-acetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

[0033] S2. The reaction solution is heated to 70℃~85℃ and reacted for 3-5 hours to obtain the terpolymer.

[0034] This specific embodiment uses an N,N'-dicyclohexylcarboimide dehydration condensation initiation system to obtain a ternary copolymer scale inhibitor by removing one molecule of water between monomers. The relevant reaction mechanism is as follows:

[0035] During the reaction, the amino groups on the chitosan molecule and the carboxyl groups on the 2-phosphonobutane-1,2,4-tricarboxylic acid and acetaminoiminoacetic acid molecules each lose a mole of water. The latter two monomers are then repeatedly introduced into the chitosan molecule through dehydration condensation in this manner. The reaction equation is as follows:

[0036]

[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 the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0038] In this invention, the terms "some embodiments," "this embodiment," and examples are used to describe a subset of all possible embodiments. However, it is understood that "some embodiments" can be the same subset or different subsets of all possible embodiments and can be combined with each other without conflict.

[0039] If the application documents contain similar descriptions such as "first / second", the following explanation shall be added: In the following description, the terms "first / second / third" are used only to distinguish similar objects and do not represent a specific ordering of objects. It is understood that "first / second / third" may be interchanged in a specific order or sequence where permitted, so that the embodiments described herein can be implemented in an order other than that illustrated or described herein.

[0040] In this embodiment, the term "and / or" is merely a description of the relationship between related objects, indicating that there can be three relationships. For example, object A and / or object B can represent three situations: object A exists alone, object A and object B exist simultaneously, and object B exists alone.

[0041] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0042] Example 1

[0043] This embodiment presents a low-phosphorus terpolymer scale inhibitor, which is prepared by the following steps:

[0044] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, a certain amount of chitosan and 5% acetic acid solution are added. The mixture is heated to 50°C and stirred until the chitosan is completely dissolved. Then, 2-phosphonobutane-1,2,4-tricarboxylic acid is added and stirred for 30 minutes. The mass ratio of chitosan to 2-phosphonobutane-1,2,4-tricarboxylic acid is 1:1. Next, the dehydrating agent N,N'-dicyclohexylcarboimide is added. Then, a certain amount of acetaminophenacetic acid is dissolved in 2% NaOH solution and slowly added dropwise to the reactor to obtain the reaction solution. The mass ratio of chitosan to acetaminophenacetic acid is 1:1, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0045] S2. After raising the temperature of the reaction solution to 70°C and stabilizing the temperature, heat the reaction for another 4 hours. After the reaction time is reached, cool to room temperature to obtain a reaction solution. Precipitate the solid product by passing it through anhydrous ethanol. After filtration, washing, and vacuum drying, obtain the purified terpolymer scale inhibitor.

[0046] Example 2

[0047] This embodiment presents a low-phosphorus terpolymer scale inhibitor, which is prepared by the following steps:

[0048] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, a certain amount of chitosan and 5% acetic acid solution are added. The mixture is heated to 50°C and stirred until the chitosan is completely dissolved. Then, 2-phosphonobutane-1,2,4-tricarboxylic acid is added and stirred for 30 minutes. The mass ratio of chitosan to 2-phosphonobutane-1,2,4-tricarboxylic acid is 1:3. The dehydrating agent N,N'-dicyclohexylcarboimide is added. Then, a certain amount of acetaminophenacetic acid is dissolved in 2% NaOH solution and slowly added dropwise to the reactor to obtain the reaction solution. The mass ratio of chitosan to acetaminophenacetic acid is 1:1, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0049] S2. After raising the temperature of the reaction solution to 85°C and stabilizing the temperature, heat the reaction for 3 hours. After the reaction time is reached, cool to room temperature to obtain the reaction solution. Precipitate the solid product by passing it through anhydrous ethanol. After filtration, washing, and vacuum drying, the purified terpolymer scale inhibitor is obtained.

[0050] Example 3

[0051] This embodiment presents a low-phosphorus terpolymer scale inhibitor, which is prepared by the following steps:

[0052] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, a certain amount of chitosan and 5% acetic acid solution are added. The mixture is heated to 50°C and stirred until the chitosan is completely dissolved. Then, 2-phosphonobutane-1,2,4-tricarboxylic acid is added and stirred for 30 minutes. The mass ratio of chitosan to 2-phosphonobutane-1,2,4-tricarboxylic acid is 1:5. The dehydrating agent N,N'-dicyclohexylcarboimide is added. Then, a certain amount of acetaminophenacetic acid is dissolved in 2% NaOH solution and slowly added dropwise to the reactor to obtain the reaction solution. The mass ratio of chitosan to acetaminophenacetic acid is 1:1, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0053] S2. After raising the temperature of the reaction solution to 70°C and stabilizing the temperature, heat the reaction for another 4 hours. After the reaction time is reached, cool to room temperature to obtain a reaction solution. Precipitate the solid product by passing it through anhydrous ethanol. After filtration, washing, and vacuum drying, obtain the purified terpolymer scale inhibitor.

[0054] Figure 1 The infrared spectrum of the scale inhibitor prepared in this example. From Figure 1 It was found to be 1629.1cm. -1 1531.8cm -1 1192.0cm -1 1072.2cm -1 776.5cm -1The characteristic absorption peak is at 1192.0 cm⁻¹. -1 It is the peak of the P=O bond stretching vibration, 1072.2 cm⁻¹. -1 The peak is the stretching vibration peak of the PO bond, indicating that the product contains a phosphate group. (1629.1 cm⁻¹) -1 It is the stretching vibration peak of C=O, 1531.8 cm⁻¹ -1 This is caused by the coupling of the bending vibration of NH and the stretching vibration of CN, 776.5cm -1 This is caused by out-of-plane bending vibration of the NH4+, and also at 3000 cm. -1 The presence of two peaks on both sides, combined with the above, indicates that the product's molecular formula contains an R-CONH2 structure. Therefore, the dehydration condensation reaction between monomers was successful.

[0055] Example 4

[0056] This embodiment presents a low-phosphorus terpolymer scale inhibitor, which is prepared by the following steps:

[0057] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, a certain amount of chitosan and 5% acetic acid solution are added. The mixture is heated to 50°C and stirred until the chitosan is completely dissolved. Then, 2-phosphonobutane-1,2,4-tricarboxylic acid is added and stirred for 30 minutes. The mass ratio of chitosan to 2-phosphonobutane-1,2,4-tricarboxylic acid is 1:7. The dehydrating agent N,N'-dicyclohexylcarboimide is added. Then, a certain amount of acetaminophenacetic acid is dissolved in 2% NaOH solution and slowly added dropwise to the reactor to obtain the reaction solution. The mass ratio of chitosan to acetaminophenacetic acid is 1:1, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0058] S2. After raising the temperature of the reaction solution to 75°C and stabilizing the temperature, heat the reaction for another 5 hours. After the reaction time is reached, cool to room temperature to obtain a reaction solution. Precipitate the solid product by passing it through anhydrous ethanol. After filtration, washing, and vacuum drying, obtain the purified terpolymer scale inhibitor.

[0059] Comparative Example 1

[0060] The preparation method of the copolymer scale inhibitor proposed in this comparative example differs from that in Example 3 only in that 2-phosphonobutane-1,2,4-tricarboxylic acid is not added, and an equal amount of acetaminoiminoacetic acid is used to replace 2-phosphonobutane-1,2,4-tricarboxylic acid in Example 3. The specific preparation steps are as follows:

[0061] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, a certain amount of chitosan and 5% acetic acid solution are added. The temperature is raised to 50°C and stirred until the chitosan is completely dissolved. Then, the dehydrating agent N,N'-dicyclohexylcarboimide is added. Next, a certain amount of acetaminophenacetic acid is dissolved in 2% NaOH solution and then slowly added dropwise to the reactor to obtain the reaction solution. The mass ratio of chitosan to acetaminophenacetic acid is 1:6, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0062] S2. After raising the temperature of the reaction solution to 70°C, heat the reaction for 4 hours after the temperature stabilizes, and keep the pH acidic during the reaction. After the reaction time is reached, cool to room temperature to obtain the reaction solution. Precipitate the solid by passing the product through anhydrous ethanol. After filtration, washing, and vacuum drying, the purified terpolymer scale inhibitor is obtained.

[0063] Comparative Example 2

[0064] The preparation method of the copolymer scale inhibitor proposed in this comparative example differs from that in Example 3 only in that acetaminoiminoacetic acid is not added, and an equal amount of 2-phosphonobutane-1,2,4-tricarboxylic acid is used to replace the acetaminoiminoacetic acid in Example 3. The specific preparation steps are as follows:

[0065] S1. In a three-necked flask equipped with a constant pressure funnel, thermometer, and stirrer, add a certain amount of chitosan and 5% acetic acid solution. Heat to 50°C and stir until the chitosan is completely dissolved. Then add 2-phosphonobutane-1,2,4-tricarboxylic acid and stir for 30 minutes. The mass ratio of chitosan to 2-phosphonobutane-1,2,4-tricarboxylic acid is 1:6. Add dehydrating agent N,N'-dicyclohexylcarboimide to obtain the reaction solution. The dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of the monomers.

[0066] S2. After raising the temperature of the reaction solution to 70°C, heat it for another 4 hours after the temperature stabilizes, and keep the pH acidic during the reaction. After the reaction time is reached, cool it to room temperature to obtain the reaction solution. Precipitate the solid by passing the product through anhydrous ethanol. After filtration, washing, and vacuum drying, the purified copolymer scale inhibitor is obtained.

[0067] Scale inhibition performance evaluation

[0068] The scale inhibition ability of the polymer scale inhibitors prepared in Examples 1-4 and Comparative Examples 1-2 on calcium sulfate was tested using the following methods:

[0069] Accurately weigh 0.50g of scale inhibitor, dissolve it in a small amount of pure water, and transfer it to a 250mL volumetric flask. Dilute to the mark to obtain the scale inhibitor solution. Take 200mL of pure water into a 250mL volumetric flask, add 6.00mL of pre-prepared CaCl2 solution, and dilute to the mark. 2+ The content is 4000 mg·L -1 Accurately add 3.75 ml of scale inhibitor solution, let stand for 10 minutes, then add the pre-prepared Na2CO3 solution while shaking, so that the CO32-... 2- The content is 6280 mg·L -1 Dilute with pure water to the mark, pour into a ground glass joint Erlenmeyer flask, place in a water bath at 50℃±1℃ for 30 minutes, and then let stand for 16 hours.

[0070] After the reaction was complete, the solution was cooled to room temperature and filtered using quantitative filter paper. The filtrate of CaCO3 was titrated with a standard solution of ethylenediaminetetraacetic acid (EDTA) to determine the Ca2+ content. 2+ The concentration was determined. A blank test was conducted simultaneously. The test results are recorded in Table 1.

[0071] Table 1. Scale inhibition performance test results of the scale inhibitors in Examples 1-4 and Comparative Examples 1-2.

[0072]

[0073] As shown in Table 1, this invention uses chitosan, 2-phosphonobutane-1,2,4-tricarboxylic acid, and acetaminoiminoacetic acid as raw materials, and adopts an N,N'-dicyclohexylcarboimide dehydration condensation initiation system to remove one molecule of water between monomers to obtain a ternary copolymer scale inhibitor with good scale inhibition performance for calcium carbonate; when the scale inhibitor dosage is 30 mg / L, a scale inhibition efficiency of 99.53% can be achieved.

[0074] Furthermore, the results above show that the scale inhibition effect of Example 3 of the present invention is better, indicating that when the mass ratio of chitosan, 2-phosphonobutane-1,2,4-tricarboxylic acid and acetaminoiminoacetic acid is 1:5:1, and the dehydrating agent N,N'-dicyclohexylcarboimide accounts for 10% of the total mass of monomers, the scale inhibition rate of the obtained product is higher.

[0075] The specific embodiments of the present invention described above do not constitute a limitation on the scope of protection of the present invention. Any other corresponding changes and modifications made in accordance with the technical concept of the present invention should be included within the scope of protection of the claims of the present invention.

Claims

1. A terpolymer, characterized in that, It has the following structural formula: In the formula, m:n:q=1:(0.2~0.5):(0.1~0.3).

2. The terpolymer according to claim 1, characterized in that, The terpolymer is formed by grafting chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

3. A low-phosphorus scale inhibitor, characterized in that, It includes one or more of the terpolymers described in claim 1 or 2.

4. A method for preparing the terpolymer according to claim 1 or 2, characterized in that, Includes the following steps: S1. Mix chitosan solution and 2-phosphonobutane-1,2,4-tricarboxylic acid, then add a dehydrating agent, and then add acetaminoiminoacetic acid solution dropwise to obtain the reaction solution; S2. The reaction solution is heated to 70°C to 85°C to obtain the terpolymer.

5. The method for preparing the terpolymer according to claim 4, characterized in that, In step S1, the chitosan solution is prepared by the following steps: mixing chitosan with an acetic acid solution with a volume concentration of 5-8%, heating to 45-55°C, and stirring to obtain the chitosan solution.

6. The method for preparing the terpolymer according to claim 4, characterized in that, In step S1, the chitosan and the 2-phosphonobutane-1,2,4-tricarboxylic acid are mixed at a mass ratio of 1:(1-7).

7. The method for preparing the terpolymer according to claim 4, characterized in that, In step S1, the dehydrating agent is N,N'-dicyclohexylcarboimide.

8. The method for preparing the terpolymer according to claim 4, characterized in that, In step S1, the acetaminoiminoacetic acid solution is prepared by dissolving acetaminoiminoacetic acid in a NaOH solution with a mass concentration of 2-3%.

9. The method for preparing the terpolymer according to claim 4, characterized in that, In step S1, the mass ratio of chitosan to acetaminoiminoacetic acid in the acetaminoiminoacetic acid solution is (1-2):1; and / or, in step S1, the amount of the dehydrating agent is 10-12% of the total mass of chitosan, acetaminoiminoacetic acid, and 2-phosphonobutane-1,2,4-tricarboxylic acid.

10. The method for preparing the terpolymer according to claim 4, characterized in that, In step S2, the reaction time is 3-5 hours.

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