Alkali-resistant film for pulp waste liquid treatment and preparation method thereof

Abstract

The application belongs to the technical field of membrane separation, and particularly relates to an alkali-resistant membrane for paper pulp waste liquid treatment and a preparation method thereof. The alkali-resistant membrane for paper pulp waste liquid treatment is a nanofiltration membrane, which comprises a base film and a functional layer. The functional layer is obtained by polymerization reaction of a cationic urea-based pyrimidone monomer containing a double bond and 1-vinylimidazole. The alkali-resistant membrane for paper pulp waste liquid treatment provided by the application has high water flux, lignin retention rate and cellulose retention rate, and still has high water flux, lignin retention rate and cellulose retention rate after being soaked in paper pulp waste liquid with a pH of 14 for 3 months.

Description

Technical Field

[0001] This invention belongs to the field of membrane separation technology, specifically relating to an alkali-resistant membrane for pulp waste liquid treatment and its preparation method. Background Technology

[0002] The paper industry plays a vital role in the national economy. Traditionally, the paper industry uses high-temperature alkaline washing of pulp to dissolve lignin, hemicellulose, and pigments into the alkaline solution, resulting in high-purity cellulose. However, after multiple cycles of use, the hemicellulose and pigments accumulate, turning the solution black – this is known as black liquor. This alkaline black liquor contains large amounts of suspended solids and organic pollutants, which not only affect the quality of paper products but also cause significant resource waste and environmental pollution. Traditionally, these alkaline waste liquors are treated by acid neutralization for recovery. This method is not only costly and energy-intensive but also prone to secondary pollution and resource waste, failing to meet the demands of sustainable development.

[0003] Membrane separation technology is considered an ideal alternative due to its high efficiency and energy saving. However, its large-scale application in pulp black liquor treatment still faces several technical obstacles: Firstly, pulp black liquor has extremely high alkalinity (pH typically reaches 12-14), and traditional polyamide nanofiltration membranes are easily degraded by OH radicals in strongly alkaline environments. - Ion attack leads to structural hydrolysis and performance degradation. Secondly, pulp black liquor contains a large amount of complex components such as lignin, hemicellulose, pigments, and inorganic salts. These substances are easily adsorbed and deposited on the membrane surface during membrane separation, forming a dense fouling layer, which causes a sharp drop in membrane flux.

[0004] There are few reports on alkali-resistant membranes for pulp wastewater treatment in the prior art. Chinese patent CN 120479222 A discloses a ZnO / PES mixed matrix ultrafiltration membrane and a polyaniline-ZnO / PES mixed matrix nanofiltration membrane, along with their preparation methods and applications. This technical solution uses PES as an organic polymer, PEG1500 as a pore-forming agent, and ZnO as a nanofiller. The ZnO / PES composite ultrafiltration membrane is prepared via a solvent-inducible phase inversion method. A polyaniline-coated ZnO nanocomposite material is synthesized, and zinc nitrate hexahydrate is mixed with ammonia water to form a nanocomposite structure. The synthesized nanocomposite particles are then used as fillers to prepare the polyaniline-ZnO / PES mixed matrix nanofiltration membrane. However, the retention rates of lignin and hemicellulose are low, and long-term performance is not considered. Summary of the Invention

[0005] The purpose of this invention is to provide an alkali-resistant membrane for pulp waste liquor treatment and its preparation method. The alkali-resistant membrane for pulp waste liquor treatment provided by this invention has high water flux, lignin rejection rate and cellulose rejection rate. Even after soaking in pulp waste liquor at pH 14 for 3 months, it still has high water flux, lignin rejection rate and cellulose rejection rate.

[0006] To achieve the above objectives, the present invention provides the following technical solution: The first aspect of the present invention provides an alkali-resistant membrane for pulp wastewater treatment, the alkali-resistant membrane being a nanofiltration membrane comprising a base membrane and a functional layer; the functional layer being obtained by polymerization of a cationic ureidopyrimidinone monomer containing double bonds and 1-vinylimidazolium.

[0007] Furthermore, the base film is selected from at least one of polyetheretherketone, polyethersulfone, polysulfone, and polyacrylonitrile.

[0008] Furthermore, the cationic ureidopyrimidinone monomer containing double bonds is obtained by reacting isocyanate-terminated ureidopyrimidinone with a bis-quaternary ammonium salt compound containing hydroxyl groups and double bonds.

[0009] Furthermore, the isocyanate-terminated ureidopyrimidinone is obtained by reacting 2-amino-4-hydroxy-6-methylpyrimidine with diisocyanate.

[0010] Furthermore, the preparation method of the isocyanate-terminated ureidopyrimidinone includes: mixing 2-amino-4-hydroxy-6-methylpyrimidine and diisocyanate, stirring and reacting at 90-110℃ for 12-24h under nitrogen protection, adding petroleum ether to precipitate after the reaction, filtering, washing with acetone, and drying to obtain the product.

[0011] Furthermore, the diisocyanate is selected from at least one of hexamethylene diisocyanate, isophorone diisocyanate, and diphenylmethane diisocyanate.

[0012] Furthermore, the molar ratio of 2-amino-4-hydroxy-6-methylpyrimidine to diisocyanate is 1:3-8.

[0013] Furthermore, the hydroxyl-containing and double-bonded quaternary ammonium salt compound is obtained by reacting epoxidized eugenol with tetramethylpropanediamine.

[0014] Furthermore, the preparation method of the hydroxyl-containing and double-bonded quaternary ammonium salt compound includes: mixing epoxidized eugenol, tetramethylpropanediamine and ethanol, adding hydrochloric acid, reacting at 60-70℃ for 8-10 h, distilling after the reaction, recrystallizing from acetone, and drying to obtain the compound.

[0015] Furthermore, the molar ratio of epoxidized eugenol, tetramethylpropanediamine, and hydrochloric acid is 2-2.4:1:2.2-2.5.

[0016] Furthermore, the amount of ethanol added is 2-3 times the total mass of epoxidized eugenol and tetramethylpropanediamine.

[0017] The structural formula of the tetramethylpropanediamine is as follows: .

[0018] Furthermore, the preparation method of the epoxidized eugenol includes: mixing eugenol, epichlorohydrin and benzyltriethylammonium chloride, reacting under nitrogen protection at 118-122℃ for 2-3 hours, cooling to 50-60℃, adding sodium hydroxide solution dropwise over 40-60 minutes, maintaining the temperature for 3-5 hours, and extracting the organic phase after the reaction to obtain epoxidized eugenol.

[0019] Furthermore, the molar ratio of eugenol, epichlorohydrin, benzyltriethylammonium chloride and sodium hydroxide is 1:1-1.2:0.3-0.5:1.05-1.2.

[0020] Furthermore, the preparation method of the cationic ureidopyrimidinone monomer containing double bonds includes: mixing isocyanate-terminated ureidopyrimidinone, a quaternary ammonium salt compound containing hydroxyl and double bonds and dichloromethane, adding dibutyltin dilaurate, and stirring the reaction at 40-45℃ for 2-3 hours under nitrogen protection. After the reaction is completed, rotary evaporation and recrystallization are performed to obtain the product.

[0021] Furthermore, the mass ratio of the isocyanate-terminated ureidopyrimidinone, the hydroxyl- and double-bonded quaternary ammonium salt compound, dibutyltin dilaurate, and dichloromethane is 1:2-3:0.02-0.04:200-400.

[0022] A second aspect of the present invention provides a method for preparing an alkali-resistant membrane for pulp waste liquor treatment, comprising the following steps: The base film is immersed in an aqueous ethanol solution with a volume concentration of 45-55% for 1-3 hours and then air-dried to obtain a pretreated base film. A double-bonded cationic ureidopyrimidinone monomer, 1-vinylimidazole, and water were mixed evenly, and an initiator was added to obtain a functional layer solution. The pretreated base membrane was immersed in the functional layer solution and heated under nitrogen protection to carry out the polymerization reaction. After the reaction was completed, the base membrane was removed, washed, and dried to obtain the alkali-resistant membrane. The alkali-resistant membrane was then stored in deionized water.

[0023] Furthermore, the mass ratio of the double-bonded cationic ureidopyrimidinone monomer, 1-vinylimidazole, initiator, and water is 8-12:3-6:0.1-0.5:100.

[0024] Furthermore, the initiator is selected from at least one of potassium persulfate, ammonium persulfate, and sodium persulfate.

[0025] Furthermore, the temperature for the polymerization reaction is 60-80℃, and the time is 2-4 hours.

[0026] Compared with the prior art, the advantages and beneficial effects of the present invention are as follows: The functional layer of the alkali-resistant membrane provided by this invention is obtained by polymerization of a cationic ureidopyrimidinone monomer containing double bonds and 1-vinylimidazolium. This improves the retention rate of lignin and hemicellulose while exhibiting excellent service life. Even after soaking in pulp waste liquor at pH 14 for 3 months, it still maintains high water flux, lignin retention rate, and cellulose retention rate. Specifically, the cationic ureidopyrimidinone monomer containing double bonds is obtained by reacting isocyanate-terminated ureidopyrimidinone with a hydroxyl- and double-bond-containing quaternary ammonium salt compound. The ureidopyrimidinone containing four hydrogen bonds... The combined action of quaternary ammonium salt and 1-vinylimidazole not only enables the functional layer to efficiently adsorb and retain negatively charged lignin and hemicellulose in pulp wastewater through electrostatic interactions, but also provides strong antifouling properties, preventing the adsorption and deposition of pollutants on the membrane surface. The network structure formed by the cross-linking of 1-vinylimidazole and cationic ureidopyrimidinone monomers containing double bonds further effectively improves the retention rate of lignin and hemicellulose. At the same time, the rigid groups it contains can effectively improve the structural stability of nanofiltration membranes in alkaline pulp wastewater. Attached Figure Description

[0027] Figure 1 The infrared spectrum of the cationic ureidopyrimidinone monomer containing double bonds prepared in Example 1. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1 Preparation of alkali-resistant membrane for pulp waste liquor treatment The polyether ether ketone nanofiltration membrane was immersed in a 50% ethanol aqueous solution for 2 hours and then dried to obtain a pretreated membrane. Mix 10 parts of a cationic ureidopyrimidinone monomer containing double bonds, 5 parts of 1-vinylimidazole and 100 parts of water evenly, and add 0.3 parts of potassium persulfate to obtain a functional layer solution. The pretreated base film was immersed in the functional layer solution and heated to 70°C for 3 hours under nitrogen protection. After the reaction was completed, the base film was removed, washed, and dried to obtain the alkali-resistant film. The alkali-resistant film was stored in deionized water.

[0030] The method for preparing the cationic ureidopyrimidinone monomer containing double bonds is as follows: 1 part of isocyanate-terminated ureidopyrimidinone, 2.5 parts of a quaternary ammonium salt compound containing hydroxyl groups and double bonds, and 350 parts of dichloromethane are mixed, and 0.035 parts of dibutyltin dilaurate are added. Under nitrogen protection, the mixture is stirred and reacted at 45°C for 2 hours. After the reaction is completed, the mixture is rotary evaporated and recrystallized to obtain the product.

[0031] The isocyanate-terminated ureidopyrimidinone is prepared by mixing 1 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 5 mol of hexamethylene diisocyanate, stirring at 100°C for 16 h under nitrogen protection, adding petroleum ether to precipitate after the reaction, filtering, washing with acetone, and drying to obtain the final product.

[0032] The preparation method of the hydroxyl-containing and double-bonded quaternary ammonium salt compound is as follows: 2.2 mol of epoxidized eugenol, 1 mol of tetramethylpropanediamine and ethanol (the amount added is twice the total mass of epoxidized eugenol and tetramethylpropanediamine) are mixed, 2.3 mol of hydrochloric acid is added, and the mixture is reacted at 70℃ for 10 h. After the reaction is completed, the mixture is distilled, recrystallized from acetone, and dried to obtain the compound.

[0033] The method for preparing epoxidized eugenol is as follows: 1 mol of eugenol, 1.2 mol of epichlorohydrin and 0.4 mol of benzyltriethylammonium chloride are mixed and reacted at 120℃ for 2 h under nitrogen protection. The temperature is then lowered to 60℃, and 20 wt% sodium hydroxide solution (containing 1.1 mol of sodium hydroxide) is added dropwise over 50 min. The reaction is maintained at this temperature for 3 h. After the reaction is completed, the organic phase is extracted to obtain epoxidized eugenol.

[0034] The infrared spectrum of the cationic ureidopyrimidinone monomer containing double bonds prepared in this embodiment is shown below. Figure 1 As shown, from Figure 1 It can be seen that 3331cm -1 With 1549cm -1 The peak at 1650 cm⁻¹ is a characteristic peak for NH. -1 The peak at 2923 cm⁻¹ is a characteristic peak of C=C. -1 The characteristic peak of -CH3 is at 2850 cm⁻¹. -1 The characteristic peak of -CH2 is located at 2280 cm⁻¹. -1 No characteristic peak of -NCO was found nearby, indicating that the isocyanate has reacted completely. This invention successfully synthesized a cationic ureidopyrimidinone monomer containing a double bond.

[0035] Example 2 Preparation of alkali-resistant membrane for pulp waste liquor treatment The polyether ether ketone nanofiltration membrane was immersed in a 50% ethanol aqueous solution for 2 hours and then dried to obtain a pretreated membrane. Mix 8 parts of a cationic ureidopyrimidinone monomer containing double bonds, 3 parts of 1-vinylimidazole and 100 parts of water evenly, and add 0.2 parts of potassium persulfate to obtain a functional layer solution. The pretreated base film was immersed in the functional layer solution and heated to 70°C for 3 hours under nitrogen protection. After the reaction was completed, the base film was removed, washed, and dried to obtain the alkali-resistant film. The alkali-resistant film was stored in deionized water.

[0036] The method for preparing the cationic ureidopyrimidinone monomer containing double bonds is as follows: 1 part of isocyanate-terminated ureidopyrimidinone, 2.5 parts of a quaternary ammonium salt compound containing hydroxyl groups and double bonds, and 350 parts of dichloromethane are mixed, and 0.035 parts of dibutyltin dilaurate are added. Under nitrogen protection, the mixture is stirred and reacted at 45°C for 2 hours. After the reaction is completed, the mixture is rotary evaporated and recrystallized to obtain the product.

[0037] The isocyanate-terminated ureidopyrimidinone is prepared by mixing 1 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 5 mol of hexamethylene diisocyanate, stirring at 100°C for 16 h under nitrogen protection, adding petroleum ether to precipitate after the reaction, filtering, washing with acetone, and drying to obtain the final product.

[0038] The preparation method of the hydroxyl-containing and double-bonded quaternary ammonium salt compound is as follows: 2.2 mol of epoxidized eugenol, 1 mol of tetramethylpropanediamine and ethanol (the amount added is twice the total mass of epoxidized eugenol and tetramethylpropanediamine) are mixed, 2.3 mol of hydrochloric acid is added, and the mixture is reacted at 70℃ for 10 h. After the reaction is completed, the mixture is distilled, recrystallized from acetone, and dried to obtain the compound.

[0039] The method for preparing epoxidized eugenol is as follows: 1 mol of eugenol, 1.2 mol of epichlorohydrin and 0.4 mol of benzyltriethylammonium chloride are mixed and reacted at 120℃ for 2 h under nitrogen protection. The temperature is then lowered to 60℃, and 20 wt% sodium hydroxide solution (containing 1.1 mol of sodium hydroxide) is added dropwise over 50 min. The reaction is maintained at this temperature for 3 h. After the reaction is completed, the organic phase is extracted to obtain epoxidized eugenol.

[0040] Example 3 Preparation of alkali-resistant membrane for pulp waste liquor treatment The polyether ether ketone nanofiltration membrane was immersed in a 50% ethanol aqueous solution for 2 hours and then dried to obtain a pretreated membrane. Mix 12 parts of a cationic ureidopyrimidinone monomer containing double bonds, 6 parts of 1-vinylimidazole and 100 parts of water evenly, and add 0.5 parts of potassium persulfate to obtain a functional layer solution. The pretreated base film was immersed in the functional layer solution and heated to 70°C for 3 hours under nitrogen protection. After the reaction was completed, the base film was removed, washed, and dried to obtain the alkali-resistant film. The alkali-resistant film was stored in deionized water.

[0041] The method for preparing the cationic ureidopyrimidinone monomer containing double bonds is as follows: 1 part of isocyanate-terminated ureidopyrimidinone, 2.5 parts of a quaternary ammonium salt compound containing hydroxyl groups and double bonds, and 350 parts of dichloromethane are mixed, and 0.035 parts of dibutyltin dilaurate are added. Under nitrogen protection, the mixture is stirred and reacted at 45°C for 2 hours. After the reaction is completed, the mixture is rotary evaporated and recrystallized to obtain the product.

[0042] The isocyanate-terminated ureidopyrimidinone is prepared by mixing 1 mol of 2-amino-4-hydroxy-6-methylpyrimidine and 5 mol of hexamethylene diisocyanate, stirring at 100°C for 16 h under nitrogen protection, adding petroleum ether to precipitate after the reaction, filtering, washing with acetone, and drying to obtain the final product.

[0043] The preparation method of the hydroxyl-containing and double-bonded quaternary ammonium salt compound is as follows: 2.2 mol of epoxidized eugenol, 1 mol of tetramethylpropanediamine and ethanol (the amount added is twice the total mass of epoxidized eugenol and tetramethylpropanediamine) are mixed, 2.3 mol of hydrochloric acid is added, and the mixture is reacted at 70℃ for 10 h. After the reaction is completed, the mixture is distilled, recrystallized from acetone, and dried to obtain the compound.

[0044] The method for preparing epoxidized eugenol is as follows: 1 mol of eugenol, 1.2 mol of epichlorohydrin and 0.4 mol of benzyltriethylammonium chloride are mixed and reacted at 120℃ for 2 h under nitrogen protection. The temperature is then lowered to 60℃, and 20 wt% sodium hydroxide solution (containing 1.1 mol of sodium hydroxide) is added dropwise over 50 min. The reaction is maintained at this temperature for 3 h. After the reaction is completed, the organic phase is extracted to obtain epoxidized eugenol.

[0045] Comparative Example 1 Preparation of alkali-resistant membrane for pulp waste liquor treatment: The only difference from Example 1 is that 1-vinylimidazole is replaced with acrylic acid, otherwise the same.

[0046] Comparative Example 2 Preparation of alkali-resistant membrane for pulp waste liquor treatment: The only difference from Example 1 is that the cationic ureidopyrimidinone monomer containing double bonds is replaced with methacryloyloxyethyltrimethylammonium chloride, and all other aspects are the same.

[0047] Comparative Example 3 Preparation of alkali-resistant membranes for pulp waste liquor treatment: The only difference from Example 1 is that the cationic ureidopyrimidinone monomer containing double bonds is replaced with a bisquaternary ammonium salt compound containing hydroxyl groups and double bonds; all other aspects are the same.

[0048] Comparative Example 4 Preparation of alkali-resistant membrane for pulp waste liquor treatment: The only difference from Example 1 is that the hydroxyl and double bond-containing quaternary ammonium salt compound is replaced with (3-hydroxypropyl)trimethylammonium chloride-2-hydroxycrotonate, otherwise the same.

[0049] Comparative Example 5: Preparation of Alkali-Resistant Membranes for Pulp Waste Liquor Treatment The polyether ether ketone nanofiltration membrane was immersed in a 50% ethanol aqueous solution for 2 hours and then dried to obtain a pretreated membrane. Mix 1 part of isocyanate-terminated ureidopyrimidinone, 2.5 parts of a quaternary ammonium salt compound containing hydroxyl groups and double bonds, and 350 parts of dichloromethane, and add 0.035 parts of dibutyltin dilaurate to obtain a functional layer solution. The pretreated base membrane was immersed in the functional layer solution and stirred at 45°C for 2 hours under nitrogen protection. After the reaction was completed, the base membrane was removed, washed, and dried to obtain the alkali-resistant membrane. The alkali-resistant membrane was stored in deionized water; the rest were the same.

[0050] Performance testing 1. Using the above-mentioned alkali-resistant membrane at room temperature, pulp waste liquor (a composite solution containing lignin and hemicellulose) was filtered. After pre-compression at 7.5 bar for 0.5 h, the permeate was obtained under conditions of 25℃ and 7.5 bar. The retention rates of lignin and hemicellulose and the water flux of the alkali-resistant membrane were tested: Retention rate = (1-ρ p / ρ f )×100%, where ρ f ρ represents the concentration of lignin or hemicellulose in pulp waste liquor. p This represents the concentration of lignin or hemicellulose in the corresponding permeate. Water flux = V / (A×t×△P), where V is the volume of the collected permeate; A is the effective area of ​​the test membrane; t is the test time; and △P is the test pressure.

[0051] Table 1

[0052] Note: The effective area of ​​the alkali-resistant membrane is 50×10. -4 m 2 .

[0053] 2. After soaking the above-mentioned alkali-resistant membranes in pulp waste liquor with a pH of 14 for 3 months, their water flux and retention rates of lignin and hemicellulose were tested.

[0054] Table 2

[0055] Note: The effective area of ​​the alkali-resistant membrane is 50×10. -4 m 2 .

[0056] As can be seen from Tables 1 and 2, the alkali-resistant membranes provided in Examples 1-3 of the present invention have high water flux, lignin rejection rate and cellulose rejection rate, and still have high water flux, lignin rejection rate and cellulose rejection rate after being soaked in pulp waste liquor at pH 14 for 3 months. Comparative Example 1 uses a functional layer obtained by polymerizing acrylic acid with a cationic ureidopyrimidinone monomer containing double bonds. The resulting alkali-resistant film has a decreased lignin and cellulose retention rate. After soaking in pulp waste liquor at pH 14 for 3 months, the lignin and cellulose retention rates also decreased. Comparative Example 2 uses a functional layer obtained by polymerization of methacryloyloxyethyltrimethylammonium chloride and 1-vinylimidazolium. The resulting alkali-resistant membrane has decreased lignin and cellulose rejection rates. After soaking in pulp waste liquor at pH 14 for 3 months, the water flux, lignin rejection rate, and cellulose rejection rate have decreased significantly. Comparative Example 3 uses a functional layer obtained by polymerizing a quaternary ammonium salt compound containing hydroxyl groups and double bonds with 1-vinylimidazolium. The resulting alkali-resistant membrane exhibits decreased lignin and cellulose retention rates. After soaking in pulp waste liquor at pH 14 for 3 months, the water flux, lignin and cellulose retention rates decreased significantly. In Comparative Example 4, the double-bonded quaternary ammonium salt compound was replaced with (3-hydroxypropyl)trimethylammonium chloride-2-hydroxycrotonate. The lignin and cellulose retention rates of the resulting alkali-resistant membrane decreased. After soaking in pulp waste liquor at pH 14 for 3 months, the lignin and cellulose retention rates also decreased. Comparative Example 5 uses isocyanate-terminated ureidopyrimidinone and a quaternary ammonium salt compound containing hydroxyl and double bonds to polymerize a functional layer. The resulting alkali-resistant membrane has a decreased lignin and cellulose retention rates. After soaking in pulp waste liquor at pH 14 for 3 months, the lignin and cellulose retention rates also decreased.

[0057] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An alkali-resistant membrane for treating pulp waste liquor, characterized in that, The alkali-resistant membrane is a nanofiltration membrane, comprising a base membrane and a functional layer; the functional layer is obtained by polymerization of a cationic ureidopyrimidinone monomer containing double bonds and 1-vinylimidazolium. The cationic ureidopyrimidinone monomer containing double bonds is obtained by reacting isocyanate-terminated ureidopyrimidinone with a quaternary ammonium salt compound containing hydroxyl groups and double bonds. The hydroxyl- and double-bonded quaternary ammonium salt compound is obtained by reacting epoxidized eugenol with tetramethylpropanediamine; The structural formula of the tetramethylpropanediamine is as follows: .

2. The alkali-resistant membrane for pulp waste liquor treatment according to claim 1, characterized in that, The base film is selected from at least one of polyetheretherketone, polyethersulfone, polysulfone, and polyacrylonitrile.

3. The alkali-resistant membrane for pulp waste liquor treatment according to claim 2, characterized in that, The isocyanate-terminated ureidopyrimidinone is obtained by reacting 2-amino-4-hydroxy-6-methylpyrimidine with diisocyanate.

4. The alkali-resistant membrane for pulp waste liquor treatment according to claim 3, characterized in that, The method for preparing the isocyanate-terminated ureidopyrimidinone includes: mixing 2-amino-4-hydroxy-6-methylpyrimidine and diisocyanate, stirring and reacting at 90-110℃ for 12-24h under nitrogen protection, adding petroleum ether to precipitate after the reaction, filtering, washing with acetone, and drying to obtain the product.

5. The alkali-resistant membrane for pulp waste liquor treatment according to claim 4, characterized in that, The preparation method of the hydroxyl-containing and double-bonded quaternary ammonium salt compound includes: mixing epoxidized eugenol, tetramethylpropylenediamine and ethanol, adding hydrochloric acid, reacting at 60-70℃ for 8-10 h, distilling after the reaction, recrystallizing from acetone, and drying to obtain the compound.

6. The alkali-resistant membrane for pulp waste liquor treatment according to claim 5, characterized in that, The method for preparing epoxidized eugenol includes: mixing eugenol, epichlorohydrin and benzyltriethylammonium chloride, reacting under nitrogen protection at 118-122℃ for 2-3 hours, cooling to 50-60℃, adding sodium hydroxide solution dropwise over 40-60 minutes, maintaining the temperature for 3-5 hours, and extracting the organic phase after the reaction to obtain epoxidized eugenol.

7. The alkali-resistant membrane for pulp waste liquor treatment according to claim 1, characterized in that, The method for preparing the cationic ureidopyrimidinone monomer containing double bonds includes: mixing isocyanate-terminated ureidopyrimidinone, a quaternary ammonium salt compound containing hydroxyl and double bonds, and dichloromethane; adding dibutyltin dilaurate; and stirring the mixture at 40-45°C for 2-3 hours under nitrogen protection. After the reaction is completed, the mixture is rotary evaporated and recrystallized to obtain the monomer.

8. The method for preparing an alkali-resistant membrane for pulp waste liquor treatment according to any one of claims 1-7, characterized in that, Includes the following steps: The base film is immersed in an aqueous ethanol solution with a volume concentration of 45-55% for 1-3 hours and then air-dried to obtain a pretreated base film. A double-bonded cationic ureidopyrimidinone monomer, 1-vinylimidazole, and water were mixed evenly, and an initiator was added to obtain a functional layer solution. The pretreated base membrane was immersed in the functional layer solution and heated under nitrogen protection to carry out the polymerization reaction. After the reaction was completed, the base membrane was removed, washed, and dried to obtain the alkali-resistant membrane. The alkali-resistant membrane was then stored in deionized water.

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