Hydrolyzed polyacrylonitrile salt copolymer and method for preparing the same

Abstract

The present application relates to the technical field of oil field fluid loss additive, and particularly relates to a hydrolytic polyacrylonitrile salt copolymer and a preparation method thereof, which comprises the following raw materials in parts by weight: 15-20 parts of composite slurry, 5-8 parts of modified chitosan, 0.1-0.12 parts of ethylenediaminetetraacetic acid and 0.12-0.15 parts of zinc acetate through an oxidative degradation system; the hydrolysis process of polyacrylonitrile is improved, so that small molecular structures are formed, and the modified chitosan with grafting segments is compounded, covalent and non-covalent actions are used to form a copolymer, so that the fluid loss performance of the copolymer under high temperature and high salt conditions is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of oil field fluid loss additive, and particularly relates to a hydrolyzed polyacrylonitrile salt copolymer and a preparation method thereof. BACKGROUND

[0002] In the drilling operation of oil and gas fields, the fluid loss additive as the core component of the drilling fluid treatment agent plays a key role in maintaining the stability of the well wall and controlling the invasion of the filtrate into the formation. Although the traditional hydrolyzed polyacrylonitrile salt fluid loss additive has good fluid loss reduction effect, it is still prone to molecular chain curling under high temperature and high salt conditions, resulting in a decrease in adsorption stability. In particular, in complex formations, the conventional hydrolyzed polyacrylonitrile salt is prone to cross-linking and precipitation with high-valence metal ions, significantly reducing the fluid loss control effect. For example, the patent CN102994055B “Preparation method of drilling fluid fluid loss additive hydrolyzed polyacrylonitrile ammonium salt” uses refined cotton and acrylic as raw materials, and obtains the drilling fluid fluid loss additive hydrolyzed polyacrylonitrile ammonium salt treatment agent through alkalization, etherification and hydrolysis reaction. However, the problem of performance decrease of the fluid loss additive under high temperature and high salt conditions has not been solved. SUMMARY

[0003] The present application aims to provide a hydrolyzed polyacrylonitrile salt copolymer and a preparation method thereof. The hydrolysis process of polyacrylonitrile is improved by an oxidative degradation system, so that small molecular structures are formed, and the modified chitosan with grafting segments is compounded, and the copolymer is formed through covalent and non-covalent interactions, thereby improving the fluid loss reduction performance under high temperature and high salt conditions.

[0004] The object of the present application can be achieved by the following technical solution: a preparation method of a hydrolyzed polyacrylonitrile salt copolymer, comprising the following steps: weighing the following raw materials: 15-20 parts of a composite slurry, 5-8 parts of modified chitosan, 0.1-0.12 parts of ethylenediaminetetraacetic acid and 0.12-0.15 parts of zinc acetate, mixing the composite slurry, the modified chitosan, the ethylenediaminetetraacetic acid and the zinc acetate, stirring at a temperature of 65-70℃ for 2-3h, and obtaining a hydrolyzed polyacrylonitrile salt copolymer.

[0005] The composite slurry is prepared by the following steps:

[0006] Step A1: polyacrylonitrile chopped fibers, Tween 80 and deionized water are mixed, stirred and sodium hydroxide is added, and the stirring speed is 240-300rpm and the temperature is 85-90℃, and the reaction is carried out for 3-4h to obtain a hydrolyzed polyacrylonitrile;

[0007] Step A2: hydrolyzed polyacrylonitrile is added with hydrochloric acid solution to adjust pH value to 3, then hydrogen peroxide and ferric sulfate solution are added, and the reaction is carried out at a stirring speed of 200-240 rpm and a temperature of 75-80℃ for 1.5-2 h, then the temperature is lowered to 50℃, and sodium hydroxide solution is added to adjust pH value to 9, and the stirring is continued for 15-20 min, then calcium chloride is added, and the stirring is continued for 1.5-2 h to prepare the composite slurry;

[0008] Further, in step A1, the dosage ratio of polyacrylonitrile cut fiber, Tween 80, deionized water and sodium hydroxide is 1.9-2.4 g: 0.1-0.12 g: 15-20 mL: 2.2-2.5 g;

[0009] Further, in step A2, the dosage ratio of hydrolyzed polyacrylonitrile, hydrogen peroxide, ferric sulfate solution and calcium chloride is 1.2-1.5 g: 2.5-3 mL: 0.5-0.8 mL: 0.3-0.4 g, the mass fraction of hydrochloric acid solution is 15%, the volume fraction of hydrogen peroxide is 10%, the molar concentration of ferric sulfate solution is 0.1 mol / L, and the mass fraction of sodium hydroxide solution is 15%;

[0010] Further, during the reaction, under the action of alkaline conditions and surfactant Tween 80, hydrolyzed polyacrylonitrile is prepared, then under acidic conditions, hydrogen peroxide and ferric sulfate solution system is used for oxidative degradation to form small molecular structure, and ion exchange is carried out by using calcium chloride to form calcium salt compound, and the composite slurry is prepared.

[0011] The modified chitosan is prepared by the following steps:

[0012] Step B1: chitosan and acetic acid solution are mixed, and stirring is carried out at a stirring speed of 240-300 rpm and a temperature of room temperature, and then methanol and acetic anhydride are added, and the reaction is carried out for 3-4 h, then sodium hydroxide solution is added, and filtration and drying are carried out to prepare acetylated chitosan, and then acetylated chitosan and N,N-dimethylformamide are mixed, and stirring is carried out at a stirring speed of 240-300 rpm and a temperature of room temperature, and then 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine are added, and the reaction is carried out for 24 h, and then dialysis filtration and freeze-drying are carried out to prepare a macromolecular initiator;

[0013] Step B2: The macromolecular initiator and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 120-150 rpm and a temperature of 60℃, and then ammonium persulfate, acrylic acid and acrylamide were added, reacted for 24 h, precipitated with diethyl ether, dialyzed and filtered, and freeze-dried to obtain the grafted chitosan. The grafted chitosan and tetrahydrofuran were mixed, stirred at a stirring rate of 120-150 rpm and a temperature of 30℃, and then tributylphosphine and sodium borohydride were added, reacted for 24 h, dialyzed and filtered, and freeze-dried to obtain the terminal thiol group grafted chitosan;

[0014] Step B3: The triethanolamine, allyl chloride and N,N-dimethylformamide were mixed, reacted for 12 h at a stirring rate of 240-300 rpm and a temperature of 45-50℃, filtered, washed, and dried to obtain the unsaturated quaternary ammonium salt. The terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 120-150 rpm and a temperature of room temperature, and then benzoin dimethyl ether was added, reacted for 50-60 min under ultraviolet irradiation, dialyzed and filtered, and freeze-dried to obtain the modified grafted chitosan.

[0015] Further, in the step B1: the chitosan, acetic acid solution, methanol, acetic anhydride and sodium hydroxide solution were used in a ratio of 4.5-5 g: 200-240 mL: 200-240 mL: 1-1.5 mL: 15-20 mL, the mass fraction of the acetic acid solution was 1%, the mass fraction of the sodium hydroxide solution was 10%, and the acetylated chitosan, N,N-dimethylformamide, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine were used in a ratio of 0.45-0.48 g: 8-10 mL: 0.32-0.35 g: 0.2-0.21 g: 0.012-0.015 g;

[0016] Further, in the step B2: the macromolecular initiator, N,N-dimethylformamide, ammonium persulfate, acrylic acid and acrylamide were used in a ratio of 0.28-0.3 g: 5-6 mL: 0.1 g: 4.5-5 g: 5.5-6 g; and the grafted chitosan, tetrahydrofuran, tributylphosphine and sodium borohydride were used in a ratio of 3.1-3.2 g: 8-10 mL: 0.012-0.015 g: 0.008-0.01 g;

[0017] Further, in the step B3: the triethanolamine, allyl chloride and N,N-dimethylformamide were used in a ratio of 1.5-1.6 g: 0.8-0.9 g: 50-60 mL; and the terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt, N,N-dimethylformamide and benzoin dimethyl ether were used in a ratio of 4.2-4.5 g: 2.1-2.3 g: 50-60 mL: 0.12-0.15 g.

[0018] Further, during the reaction process, the chitosan is acetylated and modified by acetic anhydride to obtain acetylated chitosan, then the carboxyl group in 2-(dodecyltrithiocarbonate)-2-methylpropionic acid reacts with the amino group in the acetylated chitosan under the catalysis of dicyclohexyl carbodiimide and 4-dimethylaminopyridine to form an amide structure, thereby obtaining a macromolecular initiator, then the trithiocarbonate group in the macromolecular initiator reacts with the double bond in acrylic acid and acrylamide under the catalysis of ammonium persulfate to obtain grafted chitosan, then the trithiocarbonate group is broken by a tributylphosphine and sodium borohydride system to expose the mercapto group, thereby obtaining a terminal mercapto group grafted chitosan, and the terminal mercapto group grafted chitosan undergoes a click reaction with an unsaturated quaternary ammonium salt to obtain modified grafted chitosan.

[0019] The hydrolyzed polyacrylonitrile salt copolymer and the preparation method thereof have the following beneficial effects: the hydrolysis process of polyacrylonitrile is improved by an oxidative degradation system, so that the polyacrylonitrile forms a small molecule structure, and is compounded with modified chitosan having a grafting segment, and a copolymer is formed through covalent and non-covalent interactions, so that the filtration loss performance of the copolymer under high-temperature and high-salt conditions is improved.

[0020] In the preparation process of the composite slurry, the hydrolyzed polyacrylonitrile is subjected to oxidative degradation under acidic conditions by a hydrogen peroxide and iron sulfate solution system to form a calcium salt compound having a small molecule structure, and due to the fact that the modified chitosan has a segment containing acrylic acid and acrylamide introduced through reversible addition-fragmentation chain transfer polymerization and a large number of hydroxyl groups and quaternary ammonium salt structures introduced at the grafting chain end through a click reaction, and in the preparation process of the hydrolyzed polyacrylonitrile salt copolymer, ethylenediaminetetraacetic acid and zinc acetate are added, so that the composite slurry contains a large number of calcium salt compounds, and through the complexation of calcium ions and zinc ions with the modified chitosan and ethylenediaminetetraacetic acid, a copolymer is formed, so that the filtration loss performance of the hydrolyzed polyacrylonitrile salt copolymer under high-temperature and high-salt conditions is greatly improved. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below, obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the protection scope of the present application.

[0022] Embodiment 1 A method for preparing a hydrolyzed polyacrylonitrile salt copolymer, comprising the following steps: weighing the following raw materials: 15 parts of a composite slurry, 5 parts of modified chitosan, 0.1 parts of ethylenediaminetetraacetic acid, and 0.15 parts of zinc acetate, mixing the composite slurry, the modified chitosan, the ethylenediaminetetraacetic acid, and the zinc acetate, stirring at a temperature of 65 DEG C for 2 h, and obtaining a hydrolyzed polyacrylonitrile salt copolymer.

[0023] The composite slurry is prepared by the following steps:

[0024] Step A1: mixing polyacrylonitrile chopped fibers, Tween 80, and deionized water, stirring, and adding sodium hydroxide, reacting at a stirring speed of 240 rpm and a temperature of 85 DEG C for 3 h, and obtaining a hydrolyzed polyacrylonitrile;

[0025] Step A2: adding a hydrochloric acid solution to the hydrolyzed polyacrylonitrile to adjust the pH value to 3, then adding hydrogen peroxide and ferric sulfate solutions, reacting at a stirring speed of 200 rpm and a temperature of 75 DEG C for 1.5 h, then cooling to 50 DEG C, adding a sodium hydroxide solution to adjust the pH value to 9, continuing to stir for 15 min, then adding calcium chloride, and continuing to stir for 1.5 h, and obtaining a composite slurry;

[0026] Further, in Step A1, the amount ratio of the polyacrylonitrile chopped fibers, Tween 80, deionized water, and sodium hydroxide is 1.9 g:0.1 g:15 mL:2.2 g;

[0027] Further, the polyacrylonitrile chopped fibers are from Haosong Engineering Fiber, and the specification is 5-6 mm;

[0028] Further, in Step A2, the amount ratio of the hydrolyzed polyacrylonitrile, hydrogen peroxide, ferric sulfate solution, and calcium chloride is 1.2 g:2.5 mL:0.5 mL:0.3 g, the mass fraction of the hydrochloric acid solution is 15%, the volume fraction of the hydrogen peroxide is 10%, the molar concentration of the ferric sulfate solution is 0.1 mol / L, and the mass fraction of the sodium hydroxide solution is 15%;

[0029] The modified chitosan is prepared by the following steps:

[0030] Step B1: mixing chitosan and an acetic acid solution, stirring at a stirring speed of 240 rpm and a temperature of room temperature, adding methanol and acetic anhydride, reacting for 4 h, adding a sodium hydroxide solution, filtering, drying, obtaining acetylated chitosan, mixing the acetylated chitosan and N,N-dimethylformamide, stirring at a stirring speed of 300 rpm and a temperature of room temperature, adding 2-(dodecyltrithio carbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide, and 4-dimethylamino pyridine, reacting for 24 h, dialysis filtering, freeze-drying, and obtaining a macromolecular initiator;

[0031] Step B2: The macromolecular initiator and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 120 rpm and a temperature of 60℃, and then ammonium persulfate, acrylic acid and acrylamide were added, reacted for 24 h, precipitated with diethyl ether, dialyzed and filtered, freeze-dried to obtain the grafted chitosan. The grafted chitosan and tetrahydrofuran were mixed, stirred at a stirring rate of 150 rpm and a temperature of 30℃, and then tributylphosphine and sodium borohydride were added, reacted for 24 h, dialyzed and filtered, freeze-dried to obtain the terminal thiol group grafted chitosan;

[0032] Step B3: The triethanolamine, allyl chloride and N,N-dimethylformamide were mixed, reacted for 12 h at a stirring rate of 300 rpm and a temperature of 45℃, filtered, washed, dried to obtain the unsaturated quaternary ammonium salt. The terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 150 rpm and a temperature of room temperature, and then benzoin dimethyl ether was added, reacted for 50 min under ultraviolet irradiation, dialyzed and filtered, freeze-dried to obtain the modified grafted chitosan.

[0033] Further, in the step B1: the amount ratio of chitosan, acetic acid solution, methanol, acetic anhydride and sodium hydroxide solution was 5g: 200mL: 240mL: 1.5mL: 15mL, the mass fraction of acetic acid solution was 1%, the mass fraction of sodium hydroxide solution was 10%, and the amount ratio of acetylated chitosan, N,N-dimethylformamide, 2- (dodecyltrithiocarbonate) -2-methylpropionic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine was 0.48g: 8mL: 0.35g: 0.2g: 0.012g;

[0034] Further, the chitosan was from Shanghai Zheyanchuang Biological Technology Co., Ltd., and the item number was ZT6356;

[0035] Further, in the step B2: the amount ratio of macromolecular initiator, N,N-dimethylformamide, ammonium persulfate, acrylic acid and acrylamide was 0.3g: 5mL: 0.1g: 5g: 5.5g; and the amount ratio of grafted chitosan, tetrahydrofuran, tributylphosphine and sodium borohydride was 3.2g: 8mL: 0.015g: 0.008g;

[0036] Further, in the step B3: the amount ratio of triethanolamine, allyl chloride and N,N-dimethylformamide was 1.6g: 0.8g: 50mL; and the amount ratio of terminal thiol group grafted chitosan, unsaturated quaternary ammonium salt, N,N-dimethylformamide and benzoin dimethyl ether was 4.5g: 2.1g: 60mL: 0.12g.

[0037] Example 2 A method for preparing a hydrolyzed polyacrylonitrile salt copolymer, comprising the following steps: weighing the following raw materials in parts by weight: 20 parts of composite slurry, 5 parts of modified chitosan, 0.12 parts of ethylenediaminetetraacetic acid and 0.12 parts of zinc acetate; mixing the composite slurry, modified chitosan, ethylenediaminetetraacetic acid and zinc acetate; stirring at 70°C for 2 hours to obtain a hydrolyzed polyacrylonitrile salt copolymer.

[0038] The composite slurry is prepared through the following steps:

[0039] Step A1: Mix chopped polyacrylonitrile fibers, Tween 80 and deionized water, stir and add sodium hydroxide. React for 4 hours at a stirring rate of 300 rpm and a temperature of 85°C to obtain hydrolyzed polyacrylonitrile.

[0040] Step A2: Add hydrochloric acid solution to hydrolyzed polyacrylonitrile to adjust the pH value to 3, then add hydrogen peroxide and ferric sulfate solution. React for 1.5 hours at a stirring speed of 200 rpm and a temperature of 80°C. Then cool down to 50°C and add sodium hydroxide solution to adjust the pH value to 9. Continue stirring for 15 minutes, then add calcium chloride and continue stirring for 2 hours to obtain the composite slurry.

[0041] Furthermore, in step A1, the ratio of chopped polyacrylonitrile fibers, Tween 80, deionized water, and sodium hydroxide is 2.4g:0.1g:15mL:2.5g;

[0042] Furthermore, the chopped polyacrylonitrile fibers are derived from Haosong Engineering Fibers and have a specification of 5-6mm;

[0043] Furthermore, in step A2, the ratio of hydrolyzed polyacrylonitrile, hydrogen peroxide, ferric sulfate solution, and calcium chloride is 1.2g:3mL:0.5mL:0.4g, the hydrochloric acid solution has a mass fraction of 15%, the hydrogen peroxide has a volume fraction of 10%, the ferric sulfate solution has a molar concentration of 0.1mol / L, and the sodium hydroxide solution has a mass fraction of 15%.

[0044] The modified chitosan was prepared through the following steps:

[0045] Step B1: Chitosan and acetic acid solution were mixed and stirred at 240 rpm and room temperature, while methanol and acetic anhydride were added. The mixture was reacted for 3 hours, followed by the addition of sodium hydroxide solution. The mixture was then filtered and dried to obtain acetylated chitosan. Acetylated chitosan and N,N-dimethylformamide were mixed and stirred at 240 rpm and room temperature, while 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexylcarbodiimide and 4-dimethylaminopyridine were added. The mixture was reacted for 24 hours, dialyzed and filtered, and then freeze-dried to obtain a macromolecular initiator.

[0046] Step B2: The macromolecular initiator and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 120 rpm and a temperature of 60℃, and then ammonium persulfate, acrylic acid and acrylamide were added, reacted for 24 h, precipitated with ether, dialyzed and filtered, and freeze-dried to obtain the grafted chitosan. The grafted chitosan and tetrahydrofuran were mixed, stirred at a stirring rate of 120 rpm and a temperature of 30℃, and then tributylphosphine and sodium borohydride were added, reacted for 24 h, dialyzed and filtered, and freeze-dried to obtain the terminal thiol group grafted chitosan;

[0047] Step B3: The triethanolamine, allyl chloride and N,N-dimethylformamide were mixed, reacted for 12 h at a stirring rate of 240 rpm and a temperature of 45℃, filtered, washed, and dried to obtain the unsaturated quaternary ammonium salt. The terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 120 rpm and a temperature of room temperature, and then benzoin dimethyl ether was added, reacted for 50 min under ultraviolet irradiation, dialyzed and filtered, and freeze-dried to obtain the modified grafted chitosan.

[0048] Further, in the step B1, the amount ratio of chitosan, acetic acid solution, methanol, acetic anhydride and sodium hydroxide solution was 4.5 g: 200 mL: 200 mL: 1 mL: 15 mL, the mass fraction of the acetic acid solution was 1%, the mass fraction of the sodium hydroxide solution was 10%, and the amount ratio of acetylated chitosan, N,N-dimethylformamide, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine was 0.45 g: 8 mL: 0.32 g: 0.2 g: 0.012 g;

[0049] Further, the chitosan was from Shanghai Zheyanchuang Biological Technology Co., Ltd., and the product code was ZT6356;

[0050] Further, in the step B2, the amount ratio of the macromolecular initiator, N,N-dimethylformamide, ammonium persulfate, acrylic acid and acrylamide was 0.28 g: 5 mL: 0.1 g: 4.5 g: 5.5 g; and the amount ratio of the grafted chitosan, tetrahydrofuran, tributylphosphine and sodium borohydride was 3.1 g: 8 mL: 0.012 g: 0.008 g;

[0051] Further, in the step B3, the amount ratio of triethanolamine, allyl chloride and N,N-dimethylformamide was 1.5 g: 0.8 g: 50 mL; and the amount ratio of the terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt, N,N-dimethylformamide and benzoin dimethyl ether was 4.2 g: 2.1 g: 50 mL: 0.12 g.

[0052] Example 3 A method for preparing a hydrolyzed polyacrylonitrile salt copolymer, comprising the following steps: weighing the following raw materials: 20 parts of a composite slurry, 8 parts of modified chitosan, 0.12 parts of ethylenediaminetetraacetic acid, and 0.15 parts of zinc acetate, mixing the composite slurry, modified chitosan, ethylenediaminetetraacetic acid, and zinc acetate, stirring at a temperature of 70°C for 3h, to obtain a hydrolyzed polyacrylonitrile salt copolymer.

[0053] The composite slurry is prepared by the following steps:

[0054] Step A1: mixing polyacrylonitrile chopped fibers, Tween 80, and deionized water, stirring and adding sodium hydroxide, stirring at a speed of 300rpm and a temperature of 90°C for 4h, to obtain a hydrolyzed polyacrylonitrile;

[0055] Step A2: adding hydrochloric acid solution to the hydrolyzed polyacrylonitrile to adjust the pH value to 3, then adding hydrogen peroxide and ferric sulfate solution, stirring at a speed of 240rpm and a temperature of 80°C for 2h, then cooling to 50°C and adding sodium hydroxide solution to adjust the pH value to 9, continuing to stir for 20min, then adding calcium chloride and continuing to stir for 2h, to obtain a composite slurry;

[0056] Further, in step A1, the amount ratio of polyacrylonitrile chopped fibers, Tween 80, deionized water, and sodium hydroxide is 2.4g:0.12g:20mL:2.5g;

[0057] Further, the polyacrylonitrile chopped fibers are from Haosong Engineering Fiber, with a specification of 5-6mm;

[0058] Further, in step A2, the amount ratio of hydrolyzed polyacrylonitrile, hydrogen peroxide, ferric sulfate solution, and calcium chloride is 1.5g:3mL:0.8mL:0.4g, the mass fraction of hydrochloric acid solution is 15%, the volume fraction of hydrogen peroxide is 10%, the molar concentration of ferric sulfate solution is 0.1mol / L, and the mass fraction of sodium hydroxide solution is 15%;

[0059] The modified chitosan is prepared by the following steps:

[0060] Step B1: mixing chitosan and acetic acid solution, stirring at a speed of 300rpm and a temperature of room temperature, adding methanol and acetic anhydride, reacting for 4h, then adding sodium hydroxide solution, filtering, drying, to obtain acetylated chitosan, mixing the acetylated chitosan and N,N-dimethylformamide, stirring at a speed of 300rpm and a temperature of room temperature, adding 2-(dodecyltrithio carbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide, and 4-dimethylamino pyridine, reacting for 24h, dialysis filtering, freeze-drying, to obtain a macromolecular initiator;

[0061] Step B2: The macromolecular initiator and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 150 rpm and a temperature of 60℃, and then ammonium persulfate, acrylic acid and acrylamide were added, reacted for 24 h, precipitated with diethyl ether, dialyzed and filtered, and freeze-dried to obtain the grafted chitosan. The grafted chitosan and tetrahydrofuran were mixed, stirred at a stirring rate of 150 rpm and a temperature of 30℃, and then tributylphosphine and sodium borohydride were added, reacted for 24 h, dialyzed and filtered, and freeze-dried to obtain the terminal thiol group grafted chitosan;

[0062] Step B3: The triethanolamine, allyl chloride and N,N-dimethylformamide were mixed, reacted for 12 h at a stirring rate of 300 rpm and a temperature of 50℃, filtered, washed, and dried to obtain the unsaturated quaternary ammonium salt. The terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt and N,N-dimethylformamide were mixed, stirred under nitrogen protection at a stirring rate of 150 rpm and a temperature of room temperature, and then benzoin dimethyl ether was added, reacted for 60 min under ultraviolet irradiation, dialyzed and filtered, and freeze-dried to obtain the modified grafted chitosan.

[0063] Further, in the step B1, the amount ratio of chitosan, acetic acid solution, methanol, acetic anhydride and sodium hydroxide solution was 5 g:240 mL:240 mL:1.5 mL:20 mL, the mass fraction of the acetic acid solution was 1%, the mass fraction of the sodium hydroxide solution was 10%, and the amount ratio of acetylated chitosan, N,N-dimethylformamide, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexyl carbodiimide and 4-dimethylamino pyridine was 0.48 g:10 mL:0.35 g:0.21 g:0.015 g;

[0064] Further, the chitosan was from Shanghai Zheyanchuang Biological Technology Co., Ltd., and the product code was ZT6356;

[0065] Further, in the step B2, the amount ratio of the macromolecular initiator, N,N-dimethylformamide, ammonium persulfate, acrylic acid and acrylamide was 0.3 g:6 mL:0.1 g:5 g:6 g, and the amount ratio of the grafted chitosan, tetrahydrofuran, tributylphosphine and sodium borohydride was 3.2 g:10 mL:0.015 g:0.01 g;

[0066] Further, in the step B3, the amount ratio of triethanolamine, allyl chloride and N,N-dimethylformamide was 1.6 g:0.9 g:60 mL, and the amount ratio of the terminal thiol group grafted chitosan, the unsaturated quaternary ammonium salt, N,N-dimethylformamide and benzoin dimethyl ether was 4.5 g:2.3 g:60 mL:0.15 g.

[0067] Comparative Example 1 This comparative example is compared with Example 3, the hydrogen peroxide and ferric sulfate solution in the preparation process of the composite slurry of Example 3 is removed, and the other steps are the same.

[0068] Comparative Example 2 This comparative example is compared with Example 3, the modified chitosan in the preparation process of the hydrolyzed polyacrylonitrile salt copolymer of Example 3 is replaced by the grafted chitosan of Example 3, and the other steps are the same.

[0069] Take the hydrolyzed polyacrylonitrile salt copolymer prepared in Example 1, Example 2, Example 3, Comparative Example 1 and Comparative Example 2, mix 300 mL of deionized water and 15 g of sodium bentonite, stir at a stirring rate of 2500 rpm for 20 min, scrape the clay adhered to the wall of the container, and seal and stand for 24 h to prepare a fresh water-based slurry. Mix 300 mL of deionized water, 75 g of sodium bentonite, 15 g of sodium chloride and 2.5 g of sodium carbonate, stir at a stirring rate of 2500 rpm for 20 min, scrape the clay adhered to the wall of the container, and seal and stand for 24 h to prepare a salt water-based slurry. Add 3 g of hydrolyzed polyacrylonitrile salt copolymer to the fresh water-based slurry and the salt water-based slurry respectively, stir at a stirring rate of 2000 rpm for 20 min, stand for 24 h, and then stir for 5 min. The filtration loss of the slurry at room temperature is measured. Pour the slurry into an aging tank and age at a temperature of 150°C for 16 h. Stir for 5 min and measure the filtration loss after high-temperature aging. The filtration loss is measured according to GB / T 16783.1-2014. The test results are shown in Table 1.

[0070] Table 1 Test results table

[0071] Test item Example 1 Example 2 Example 3 Comparative Example 1 Comparative Example 2 Fresh water-based filtration loss (mL) 11.64 11.50 11.25 14.64 12.32 Salt water-based filtration loss (mL) 24.17 23.68 23.17 27.95 24.76 Fresh water-based filtration loss after aging (mL) 12.07 11.83 11.49 17.26 15.57 Salt water-based filtration loss after aging (mL) 24.07 23.82 23.78 30.70 31.21

[0072] As shown in the table, comparing Example 1, Example 2 and Example 3 with Comparative Example 1 and Comparative Example 2, Comparative Example 1 removes the hydrogen peroxide and ferric sulfate solution in the preparation process of the composite slurry of Example 3. Due to the lack of an oxidative degradation system, it cannot form small molecular structures, and thus cannot form copolymers with modified chitosan. Moreover, it cannot avoid the situation of molecular chain curling under high temperature and high salt conditions, resulting in a decrease in filtration loss performance. Comparative Example 2 replaces the modified chitosan in the preparation process of the hydrolyzed polyacrylonitrile salt copolymer of Example 3 with the grafted chitosan of Example 3. Due to the lack of quaternary ammonium structures and a large number of hydroxyl structures introduced at the chain ends, the covalent and non-covalent interactions are reduced, thereby affecting the filtration loss performance under high temperature and high salt conditions.

[0073] In the description, references to "one embodiment," "an example," "certain examples" etc. mean that the particular feature, structure, material, or characteristic being described is included in at least one embodiment or example of the application. The appearances of an item in various examples or embodiments is not necessarily indicative of a frequency of occurrence in the various examples or embodiments. Moreover, descriptions of well-known methods associated are omitted so as not to obscure the disclosure.

[0074] The foregoing merely illustrates the principles of the application. Various modifications and adaptations will occur to those skilled in the art after consideration of the preceding description. All such modifications and adaptations employing the principles of the application are intended to be within the scope of the claims.

Claims

1. A method for preparing a hydrolyzed polyacrylonitrile salt copolymer, characterized in that: The process includes the following steps: Weigh the following raw materials by weight: 15-20 parts of composite slurry, 5-8 parts of modified chitosan, 0.1-0.12 parts of ethylenediaminetetraacetic acid (EDTA) and 0.12-0.15 parts of zinc acetate. Mix the composite slurry, modified chitosan, EDTA and zinc acetate, and stir for 2-3 hours at a temperature of 65-70℃ to obtain a hydrolyzed polyacrylonitrile salt copolymer. The composite slurry is prepared through the following steps: Step A1: Mix chopped polyacrylonitrile fibers, Tween 80 and deionized water, stir and add sodium hydroxide. React for 3-4 hours at a stirring rate of 240-300 rpm and a temperature of 85-90℃ to obtain hydrolyzed polyacrylonitrile. Step A2: Add hydrochloric acid solution to hydrolyzed polyacrylonitrile to adjust the pH to 3, then add hydrogen peroxide and ferric sulfate solution. React for 1.5-2 hours at a stirring speed of 200-240 rpm and a temperature of 75-80℃. Then cool down to 50℃ and add sodium hydroxide solution to adjust the pH to 9. Continue stirring for 15-20 minutes, then add calcium chloride and continue stirring for 1.5-2 hours to obtain the composite slurry. In step A2: the ratio of hydrolyzed polyacrylonitrile, hydrogen peroxide, ferric sulfate solution, and calcium chloride is 1.2-1.5g: 2.5-3mL: 0.5-0.8mL: 0.3-0.4g; the mass fraction of hydrochloric acid solution is 15%; the volume fraction of hydrogen peroxide is 10%; the molar concentration of ferric sulfate solution is 0.1mol / L; and the mass fraction of sodium hydroxide solution is 15%.

2. The method for preparing a hydrolyzed polyacrylonitrile salt copolymer according to claim 1, characterized in that: In step A1: the ratio of chopped polyacrylonitrile fibers, Tween 80, deionized water and sodium hydroxide is 1.9-2.4g: 0.1-0.12g: 15-20mL: 2.2-2.5g.

3. The method for preparing a hydrolyzed polyacrylonitrile salt copolymer according to claim 1, characterized in that: The modified chitosan was prepared through the following steps: Step B1: Chitosan and acetic acid solution are mixed and stirred at 240-300 rpm and room temperature. Methanol and acetic anhydride are added and the mixture is reacted for 3-4 hours. Sodium hydroxide solution is then added, filtered, and dried to obtain acetylated chitosan. Acetylated chitosan and N,N-dimethylformamide are mixed and stirred at 240-300 rpm and room temperature. 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine are added and the mixture is reacted for 24 hours. The mixture is then dialyzed, filtered, and freeze-dried to obtain a macromolecular initiator. Step B2: Mix the macromolecular initiator and N,N-dimethylformamide under nitrogen protection, stirring at 120-150 rpm and 60°C, and add ammonium persulfate, acrylic acid and acrylamide. React for 24 h, precipitate with diethyl ether, dialyze and filter, and freeze dry to obtain grafted chitosan. Mix the grafted chitosan with tetrahydrofuran, stirring at 120-150 rpm and 30°C, and add tributylphosphine and sodium borohydride. React for 24 h, dialyze and filter, and freeze dry to obtain thiol-terminated grafted chitosan. Step B3: Triethanolamine, allyl chloride, and N,N-dimethylformamide are mixed and reacted at a stirring rate of 240-300 rpm and a temperature of 45-50℃ for 12 h. After filtration, washing, and drying, an unsaturated quaternary ammonium salt is obtained. Terminal thiol-grafted chitosan, the unsaturated quaternary ammonium salt, and N,N-dimethylformamide are mixed and stirred under nitrogen protection at a stirring rate of 120-150 rpm and a temperature of room temperature. Benzoin dimethyl ether is added and the mixture is reacted under ultraviolet irradiation for 50-60 min. After dialysis and filtration, the mixture is freeze-dried to obtain modified grafted chitosan.

4. The method for preparing a hydrolyzed polyacrylonitrile salt copolymer according to claim 3, characterized in that: In step B1: the ratio of chitosan, acetic acid solution, methanol, acetic anhydride, and sodium hydroxide solution is 4.5-5g: 200-240mL: 200-240mL: 1-1.5mL: 15-20mL, the mass fraction of acetic acid solution is 1%, the mass fraction of sodium hydroxide solution is 10%, and the ratio of acetylated chitosan, N,N-dimethylformamide, 2-(dodecyltrithiocarbonate)-2-methylpropionic acid, dicyclohexylcarbodiimide, and 4-dimethylaminopyridine is 0.45-0.48g: 8-10mL: 0.32-0.35g: 0.2-0.21g: 0.012-0.015g.

5. The method for preparing a hydrolyzed polyacrylonitrile salt copolymer according to claim 3, characterized in that: In step B2: the ratio of macromolecular initiator, N,N-dimethylformamide, ammonium persulfate, acrylic acid and acrylamide is 0.28-0.3g: 5-6mL: 0.1g: 4.5-5g: 5.5-6g; the ratio of grafted chitosan, tetrahydrofuran, tributylphosphine and sodium borohydride is 3.1-3.2g: 8-10mL: 0.012-0.015g: 0.008-0.01g.

6. The method for preparing a hydrolyzed polyacrylonitrile salt copolymer according to claim 3, characterized in that: In step B3: the ratio of triethanolamine, allyl chloride, and N,N-dimethylformamide is 1.5-1.6g: 0.8-0.9g: 50-60mL; the ratio of terminal thiol-grafted chitosan, unsaturated quaternary ammonium salt, N,N-dimethylformamide, and benzoin dimethyl ether is 4.2-4.5g: 2.1-2.3g: 50-60mL: 0.12-0.15g.

7. A hydrolyzed polyacrylonitrile salt copolymer, characterized in that: It is prepared according to any one of the preparation methods described in claims 1-6.