Composite membrane for treating coal chemical wastewater and preparation method thereof

Abstract

The application discloses a kind of composite membrane for coal chemical industry wastewater treatment and preparation method thereof, belong to coal chemical industry wastewater treatment technical field, preparation steps are as follows: base film is placed in cold plasma processor and is handled, then it is transferred to pyridine and deionized water mixture, temperature 65-75 ℃, 3-chloro-2-hydroxypropyl methyl diallyl ammonium chloride is added, and heat preservation treatment 2-3h, obtain pretreatment film;Acrylic acid, acrylamide are added to acetic acid solution, after stirring, modified chitosan, potassium persulfate and N,N'-methylene bisacrylamide are added, continue stirring 2-3h, obtain treatment liquid;Pretreatment film is soaked in treatment liquid, nitrogen atmosphere, 60 ℃ is handled 2h, the application composite membrane can overcome the problem that existing treatment film is poor in use effect in treating wastewater containing oxidant, and stable performance, with high hydrophilicity, pollution resistance, adsorption, preparation method is simple, easy to scale production.

Description

Technical Field

[0001] This invention belongs to the field of coal chemical wastewater treatment technology, specifically relating to a composite membrane for coal chemical wastewater treatment and its preparation method. Background Technology

[0002] Coal chemical wastewater is a type of water collected in the final stage of the production process. It mainly consists of wastewater from circulating water, ion-crosslinked acid and alkali water from desalination, and wastewater from other process units. The main characteristics of the water source are: (1) high salt content: salt content is 5000mg / L-6000mg / L; (2) large fluctuations in water quality, the wastewater is composed of multiple streams of wastewater with large differences in water quality; (3) many types of pollutants: organic matter, bacteria, ammonia nitrogen, inorganic salts, Ca 2+ Mg 2+ Ba 2+ SO4 2- SiO2, F - In particular, the sewage has a high content of organic matter; (4) it has poor biodegradability and contains toxic, harmful and difficult-to-degrade organic matter such as phenolic compounds, polycyclic aromatic hydrocarbons, naphthalene, pyridine, biphenyl, and oil.

[0003] Currently, advanced chemical oxidation technology is widely used in coal chemical wastewater treatment because it overcomes the problems of weak capacity, low selectivity, and high initial investment associated with ordinary chemical oxidation. For example, Chinese patent CN101781039B discloses a combination of catalytic oxidation and membrane separation technology for coking wastewater. Ultrafiltration and reverse osmosis membranes are used to treat the coking wastewater after catalytic oxidation, achieving considerable social benefits. However, the wastewater after catalytic oxidation contains oxidants, which can damage the CF bonds of ultrafiltration and reverse osmosis membranes (most existing ultrafiltration and reverse osmosis membranes are made of polyvinylidene fluoride), causing a deterioration in the fouling removal capacity of the ultrafiltration and reverse osmosis membranes, requiring frequent replacement and increasing treatment costs. Summary of the Invention

[0004] The purpose of this invention is to provide a composite membrane for treating coal chemical wastewater and its preparation method, thereby solving the problem of poor performance of existing composite membranes in treating wastewater containing oxidants.

[0005] The objective of this invention can be achieved through the following technical solutions:

[0006] A method for preparing a composite membrane for treating coal chemical wastewater includes the following steps:

[0007] Step 1: Place the base membrane in a cold plasma treatment instrument with a power of 250W and treat it for 200s under an oxygen atmosphere to obtain a hydroxylated base membrane. Transfer the hydroxylated base membrane to a mixture of pyridine and deionized water, add 3-chloro-2-hydroxypropylmethyldiallylammonium chloride at a temperature of 65-75℃, and keep it at this temperature for 2-3 hours. Remove the membrane, rinse it with methanol and deionized water, and vacuum dry it at 60℃ to obtain a pretreated membrane.

[0008] Step 2: Add acrylic acid and acrylamide to acetic acid solution, stir, then add modified chitosan, potassium persulfate and N,N'-methylenebisacrylamide, and continue stirring for 2-3 hours to obtain the treatment solution;

[0009] The third step involves immersing the pretreated membrane in the treatment solution, treating it at 60°C for 2 hours under a nitrogen atmosphere, then removing it and rinsing it sequentially with methanol and deionized water for 10-30 minutes each, followed by complete drying at 50°C to obtain the composite membrane for coal chemical wastewater treatment.

[0010] To address the problems of poor hydrophilicity, susceptibility to fouling, and poor performance in treating wastewater containing oxidants, polyvinylidene fluoride (PVDF) membranes are introduced. First, oxygen plasma is used to treat the base membrane, generating active hydroxyl groups on its surface. This improves the hydrophilicity of the base membrane and imparts reactivity. Then, in a pyridine aqueous solution, 3-chloro-2-hydroxypropylmethyldiallylammonium chloride undergoes an elimination reaction with the hydroxyl groups on the membrane surface, introducing quaternary ammonium salt and allyl structures to obtain a pretreated membrane. Finally, under the action of an initiator, the allyl groups on the pretreated membrane undergo a copolymerization reaction with acrylic acid, acrylamide, modified chitosan, and N,N'-methylenebisacrylamide, forming a chemically bonded gel layer on the pretreated membrane surface. This enhances the membrane material's hydrophilicity, adsorption capacity, fouling resistance, and antioxidant properties.

[0011] Furthermore, the mass ratio of the hydroxylated membrane, pyridine, and deionized water is 1:1-2.5:15-20, and the amount of 3-chloro-2-hydroxypropylmethyldiallylammonium chloride used is 5-15% of the mass of the hydroxylated membrane.

[0012] Furthermore, the ratio of acrylic acid, acrylamide, and acetic acid solution is 0.05 mol: 0.05 mol: 60-80 mL, the mass fraction of acetic acid solution is 2%, the amount of modified chitosan is 3% of the total mass of acrylic acid and acrylamide, the amount of potassium persulfate is 2% of the total mass of acrylic acid and acrylamide, and the amount of N,N'-methylenebisacrylamide is 1% of the total mass of acrylic acid and acrylamide.

[0013] Furthermore, the modified chitosan is prepared through the following steps:

[0014] S1. At room temperature, sodium hydroxide and deionized water were added to a three-necked flask and stirred to dissolve. L-glutamic acid was then added, and the mixture was heated to 50°C and stirred for 30 min. Then, an ethanol solution of allyl isothiocyanate was added dropwise. The mixture was stirred at 50°C for 6 h and then cooled to room temperature. The reaction product was placed in a separatory funnel and extracted with diethyl ether until the upper ether layer was colorless. The lower alcohol-water solution was collected, and hydroquinone was added to the pure aqueous solution. The solvent was removed by rotary evaporation. The rotary evaporation product was washed with anhydrous ethanol by centrifugation, and the precipitate was dried under vacuum at 50°C to constant weight to obtain the glutamic acid derivative.

[0015] S2. Chitosan was dispersed in deionized water and transferred to a flask. Glutamic acid derivative, EDC, and NHS were added. The pH was adjusted to 5 with 0.1 mol / L hydrochloric acid solution. After stirring for 30-60 min, the reaction was carried out at 30℃ for 12 h. After the reaction was completed, the pH was adjusted to 8 with 0.5 mol / L sodium hydroxide solution. The reaction product was placed in a dialysis bag with a molecular cutoff of 8000-14000 Da and dialyzed in distilled water for five days, with the distilled water being changed every 6 h. The dialyzed product was freeze-dried to obtain modified chitosan.

[0016] Based on the hydrophilicity, biodegradability, biocompatibility, non-toxicity, chelating properties, and high adsorption capacity for pollutants of chitosan, this invention modifies it to enhance its water solubility and adsorption performance while giving it cross-linking activity. Specifically, L-glutamic acid and allyl isothiocyanate are used as substrates to prepare a glutamic acid derivative that integrates dicarboxylate, thiourea, and allyl structures. Then, under acidic conditions, the amino groups of chitosan and the carboxyl groups of the glutamic acid derivative are linked through an amide reaction to introduce carboxyl, thiourea, and allyl structures into the chitosan molecular chain, thus obtaining modified chitosan.

[0017] Furthermore, in S1, the ratio of sodium hydroxide, deionized water, L-glutamic acid, allyl isothiocyanate, and hydroquinone is 0.2 mol: 80-100 mL: 0.1 mol: 0.11-0.13 mol: 0.1 g, and the ethanol solution of allyl isothiocyanate is composed of allyl isothiocyanate and anhydrous ethanol in a ratio of 0.11-0.13 mol: 20 mL.

[0018] Furthermore, the ratio of chitosan, deionized water, glutamic acid derivative, EDC and NHS in S2 is 2g:100mL:2.5-3.1g:0.9-1.0g:0.4-0.6g, the degree of deacetylation of chitosan is 85-95%, EDC is 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride, and NHS is N-hydroxysuccinimide.

[0019] Furthermore, the base membrane is a polyvinylidene fluoride microporous filter membrane with a pore size of 0.22 μm.

[0020] Furthermore, a composite membrane for treating coal chemical wastewater is prepared by the above-mentioned method.

[0021] The beneficial effects of this invention are:

[0022] (1) This invention provides a composite membrane for treating coal chemical wastewater, which overcomes the problem of poor performance of existing treatment membranes in treating wastewater containing oxidants. It has stable performance, high hydrophilicity, pollution resistance and adsorption, and the preparation method is simple and easy to scale up.

[0023] (2) The composite membrane for treating coal chemical wastewater provided by the present invention contains a variety of hydrophilic groups on its surface, such as hydroxyl, amino, carboxyl, amide, and quaternary ammonium salt groups. This not only improves the hydrophilicity of the composite membrane and reduces membrane fouling, but also has good adsorption performance for metal ions and organic pollutants in wastewater, thus improving the retention performance of the composite membrane. In addition, it also contains a thiourea structure. Thiourea salt has excellent scavenging ability for hydroxyl radicals and can protect the composite membrane from the action of oxidants in wastewater by eliminating free radicals. Furthermore, it has good antibacterial properties and excellent chelation performance for metal ions. On the one hand, it plays a synergistic antibacterial role with the quaternary ammonium salt structure, and on the other hand, it improves the retention performance of the composite membrane for metal ions. Detailed Implementation

[0024] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. 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 of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0025] In the following examples and comparative examples, the chitosan was purchased from Xianju Chemical Products Co., Ltd., with a degree of deacetylation of 88% and a viscosity-average molecular weight of 550,000.

[0026] Example 1

[0027] A modified chitosan is prepared by the following steps:

[0028] S1. At room temperature, add 0.2 mol sodium hydroxide and 80 mL deionized water to a three-necked flask, stir to dissolve, then add 0.1 mol L-glutamic acid, heat to 50 °C and stir for 30 min. Then add dropwise a solution consisting of 0.11 mol allyl isothiocyanate and 20 mL anhydrous ethanol. Stir the reaction at 50 °C for 6 h and cool to room temperature. Place the reaction product in a separatory funnel and extract with diethyl ether until the upper ether layer is colorless. Collect the lower alcohol-water solution, add 0.1 g hydroquinone to the pure water solution, remove the solvent by rotary evaporation, wash the rotary evaporation product with anhydrous ethanol by centrifugation, and dry the precipitate under vacuum at 50 °C to constant weight to obtain the glutamic acid derivative.

[0029] S2. Disperse 2g of chitosan in 100mL of deionized water and transfer it to a flask. Add 2.5g of glutamic acid derivative, 0.9g of EDC and 0.4g of NHS. Adjust the pH to 5 with 0.1mol / L hydrochloric acid solution. Stir for 30min and then react at 30℃ for 12h. After the reaction is complete, adjust the pH to 8 with 0.5mol / L sodium hydroxide solution. Place the reaction product in a dialysis bag with a molecular cutoff of 8000-14000Da and dialyze it in distilled water for five days, changing the distilled water every 6h. Freeze-dry the dialyzed product to obtain modified chitosan.

[0030] Example 2

[0031] A modified chitosan is prepared by the following steps:

[0032] S1. At room temperature, add 0.2 mol sodium hydroxide and 100 mL deionized water to a three-necked flask, stir to dissolve, then add 0.1 mol L-glutamic acid, heat to 50 °C and stir for 30 min, then add dropwise a solution consisting of 0.13 mol allyl isothiocyanate and 20 mL anhydrous ethanol, stir at 50 °C for 6 h and cool to room temperature, place the reaction product in a separatory funnel, extract with diethyl ether until the upper ether layer is colorless, collect the lower alcohol-water solution, add 0.1 g hydroquinone to the pure water solution, remove the solvent by rotary evaporation, wash the rotary evaporation product with anhydrous ethanol by centrifugation, and dry the precipitate under vacuum at 50 °C to constant weight to obtain the glutamic acid derivative;

[0033] S2. Disperse 2g of chitosan in 100mL of deionized water and transfer it to a flask. Add 3.1g of glutamic acid derivative, 1.0g of EDC and 0.6g of NHS. Adjust the pH to 5 with 0.1mol / L hydrochloric acid solution. Stir for 60min and then react at 30℃ for 12h. After the reaction is complete, adjust the pH to 8 with 0.5mol / L sodium hydroxide solution. Place the reaction product in a dialysis bag with a molecular cutoff of 8000-14000Da and dialyze it in distilled water for five days, changing the distilled water every 6h. Freeze-dry the dialyzed product to obtain modified chitosan.

[0034] Comparative Example 1

[0035] Compared with Example 1, the glutamic acid derivative in Example 1 was replaced with L-glutamic acid, while the other raw materials and preparation process remained unchanged.

[0036] Example 3

[0037] A method for preparing a composite membrane for treating coal chemical wastewater includes the following steps:

[0038] Step 1: Place the 0.22μm polyvinylidene fluoride microporous filter membrane in a cold plasma treatment instrument at a power of 250W and under an oxygen atmosphere for 200s to obtain a hydroxylated membrane. Transfer the hydroxylated membrane to a mixture of 1 part pyridine and 15 parts deionized water at a temperature of 65℃, add 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride, and keep it at this temperature for 2 hours. Remove the membrane, rinse it with methanol and deionized water, and vacuum dry it at 60℃ to obtain a pretreated membrane. The amount of 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride used is 5% of the mass of the hydroxylated membrane.

[0039] Step 2: Add 3.63 kg of acrylic acid and 3.55 kg of acrylamide to 60 L of 2 wt% acetic acid solution, stir for 5 min, then add the modified chitosan, potassium persulfate and N,N'-methylenebisacrylamide from Example 1, and continue stirring for 2 h to obtain the treatment solution. The amount of modified chitosan is 3% of the total mass of acrylic acid and acrylamide, the amount of potassium persulfate is 2% of the total mass of acrylic acid and acrylamide, and the amount of N,N'-methylenebisacrylamide is 1% of the total mass of acrylic acid and acrylamide.

[0040] The third step involves immersing the pretreated membrane in the treatment solution, treating it at 60°C for 2 hours under a nitrogen atmosphere, then removing it and rinsing it sequentially with methanol and deionized water for 10 minutes each, followed by complete drying at 50°C to obtain a composite membrane for coal chemical wastewater treatment.

[0041] Example 4

[0042] A method for preparing a composite membrane for treating coal chemical wastewater includes the following steps:

[0043] Step 1: Place the 0.22 μm polyvinylidene fluoride microporous filter membrane in a cold plasma treatment instrument at a power of 250 W under an oxygen atmosphere for 200 s to obtain a hydroxylated membrane. Transfer the hydroxylated membrane to a mixture of 2 times the mass of pyridine and 18 times the mass of deionized water. Add 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride at a temperature of 70 °C and keep it at this temperature for 2.5 h. Remove the membrane, rinse it with methanol and deionized water, and vacuum dry it at 60 °C to obtain a pretreated membrane. The amount of 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride used is 10% of the mass of the hydroxylated membrane.

[0044] Step 2: Add 3.63 kg of acrylic acid and 3.55 kg of acrylamide to 70 L of 2 wt% acetic acid solution, stir for 8 min, then add the modified chitosan, potassium persulfate and N,N'-methylenebisacrylamide from Example 2, and continue stirring for 2.5 h to obtain the treatment solution. The amount of modified chitosan is 3% of the total mass of acrylic acid and acrylamide, the amount of potassium persulfate is 2% of the total mass of acrylic acid and acrylamide, and the amount of N,N'-methylenebisacrylamide is 1% of the total mass of acrylic acid and acrylamide.

[0045] The third step involves immersing the pretreated membrane in the treatment solution, treating it at 60°C for 2 hours under a nitrogen atmosphere, then removing it and rinsing it sequentially with methanol and deionized water for 20 minutes each, followed by complete drying at 50°C to obtain a composite membrane for coal chemical wastewater treatment.

[0046] Example 5

[0047] A method for preparing a composite membrane for treating coal chemical wastewater includes the following steps:

[0048] Step 1: Place the 0.22 μm polyvinylidene fluoride microporous filter membrane in a cold plasma treatment instrument at a power of 250 W under an oxygen atmosphere for 200 s to obtain a hydroxylated membrane. Transfer the hydroxylated membrane to a mixture of 2.5 times the mass of pyridine and 20 times the mass of deionized water. Add 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride at a temperature of 75 °C and keep it at this temperature for 3 h. Remove the membrane, rinse it with methanol and deionized water, and vacuum dry it at 60 °C to obtain a pretreated membrane. The amount of 3-chloro-2-hydroxypropylmethyldiallyl ammonium chloride used is 15% of the mass of the hydroxylated membrane.

[0049] Step 2: Add 3.63 kg of acrylic acid and 3.55 kg of acrylamide to 80 L of 2 wt% acetic acid solution, stir for 10 min, then add the modified chitosan, potassium persulfate and N,N'-methylenebisacrylamide from Example 2, and continue stirring for 3 h to obtain the treatment solution. The amount of modified chitosan is 3% of the total mass of acrylic acid and acrylamide, the amount of potassium persulfate is 2% of the total mass of acrylic acid and acrylamide, and the amount of N,N'-methylenebisacrylamide is 1% of the total mass of acrylic acid and acrylamide.

[0050] The third step involves immersing the pretreated membrane in the treatment solution, treating it at 60°C for 2 hours under a nitrogen atmosphere, then removing it and rinsing it sequentially with methanol and deionized water for 30 minutes each, followed by complete drying at 50°C to obtain a composite membrane for coal chemical wastewater treatment.

[0051] Comparative Example 2

[0052] Compared with Example 3, the modified chitosan in Example 3 was replaced with the substance in Comparative Example 1, and the other raw materials and preparation process were the same as in Example 3.

[0053] Comparative Example 3

[0054] Compared with Example 3, the modified chitosan in Example 3 was replaced with chitosan, and the other raw materials and preparation process were the same as in Example 3.

[0055] Comparative Example 4

[0056] This comparative example is the pretreated membrane obtained in the first step of Example 3.

[0057] The composite membranes obtained in Examples 3-5 and Comparative Examples 2-4 were subjected to performance tests, and the test items are as follows:

[0058] (a) Contact Angle Test:

[0059] Each composite membrane was cut, and the cut samples were fixed on a glass slide with double-sided tape. 5 μL of deionized water was drawn up with a microsyringe and dropped onto the membrane surface. The water contact angle of the deionized water on the membrane surface was measured by taking a picture with a video contact angle meter. The experiment was repeated 3 times and the average value of the results was taken.

[0060] The membrane was fixed to the bottom of the culture dish with double-sided tape. The culture dish was filled with deionized water. 5 μL of dichloromethane was absorbed with a microsyringe and dropped onto the membrane surface. The photograph was taken to test the underwater oil contact angle of dichloromethane on the membrane surface. The experiment was repeated 3 times and the average value of the results was taken.

[0061] (ii) Separation efficiency

[0062] Toluene, water, and Tween 80 were ultrasonically mixed at a volume ratio of 1:99:0.1 for 30 min to obtain an oil-in-water emulsion; copper sulfate pentahydrate was dissolved in deionized water to prepare a 10 g / L metal ion solution; methylene blue was dissolved in deionized water to prepare a 50 mg / L organic dye solution.

[0063] Each group of membrane samples (circular with a diameter of 5 cm) was placed in a sand core filter device, and the above solution was injected into the device. Filtration was carried out under vacuum pump pressure of 0.5 bar, and the filtrate was collected. The absorbance standard curve of the solution before and after separation was tested using a UV spectrophotometer. Then the absorbance of the filtrate was tested. The concentration of the solution after separation was determined by substituting the test results into the standard curve. The experiment was repeated 3 times, and the average value of the results was taken. The separation efficiency (%) = (C0-C1) / CO×100%, where CO is the concentration of the solution before separation, g / L; C1 is the concentration of the filtrate after separation, g / L.

[0064] (III) Antibacterial properties

[0065] Referring to the American Association of Textile Chemicals and Finishing Manufacturers (AATCC) 100-2004 testing standard, each group of membranes was cut into 40mm × 40mm samples. These samples were then contacted with 100 μL of *E. coli* (ATCC 25922) bacterial suspension and incubated at 37°C for 120 min. The samples were then repeatedly washed with 10 mL of PBS buffer. The wash solution was appropriately diluted and used for viable cell culture and counting. The sterilization rate was calculated as follows:

[0066] Sterilization rate (%) = ((AB) / A) × 100, where A is the number of bacteria before contact and B is the number of residual bacteria.

[0067] (iv) Antioxidant properties

[0068] Each group of membranes was placed in a 0.1% KMnO4 solution for 6 hours, then removed, washed three times with pure water, and the separation efficiency was tested.

[0069] The results are shown in Table 1:

[0070] Table 1

[0071]

[0072]

[0073] As shown in Table 1, compared with Comparative Examples 2, 3, and 4, the hydrophilicity of the composite membranes obtained in Examples 3, 4, and 5 is significantly improved, making it easier for bacteria to be adsorbed onto the membrane surface, thereby increasing the probability of contact between the membrane surface coating and bacteria. The modified coating contains thiourea, quaternary ammonium salt, and chitosan. Under the antibacterial effect of these three substances, the bacteria are killed, giving the composite membrane excellent antifouling properties. In addition, the separation efficiency and antioxidant properties of the composite membrane are also improved.

[0074] It should be noted that, in this document, relational terms such as "first" and "second" are used only to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such process, method, article, or apparatus.

[0075] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite membrane for treating coal chemical wastewater, characterized in that, The steps are as follows: Step 1: The base membrane is treated in a cold plasma treatment instrument to obtain a hydroxylated base membrane. The hydroxylated base membrane is then transferred to a mixture of pyridine and deionized water. 3-chloro-2-hydroxypropylmethyldiallylammonium chloride is added at a temperature of 65-75℃ and the mixture is kept at this temperature for 2-3 hours. After treatment, the membrane is removed, rinsed, and dried to obtain a pretreated membrane. The base membrane is a polyvinylidene fluoride microporous filter membrane. Step 2: Add acrylic acid and acrylamide to acetic acid solution, stir, then add modified chitosan, potassium persulfate and N,N'-methylenebisacrylamide, and continue stirring for 2-3 hours to obtain the treatment solution; The third step is to immerse the pretreated membrane in the treatment solution, treat it at 60°C for 2 hours under a nitrogen atmosphere, then take it out, rinse it, and dry it to obtain a composite membrane for coal chemical wastewater treatment. Modified chitosan is prepared through the following steps: S1. At room temperature, sodium hydroxide and deionized water were added to a three-necked flask and stirred until dissolved. L-glutamic acid was then added and stirred at 50°C. An ethanol solution of allyl isothiocyanate was added dropwise. After reacting for 6 hours, the mixture was cooled to room temperature. The reaction product was placed in a separatory funnel and extracted with diethyl ether until the upper ether layer was colorless. The lower alcohol-water solution was collected, and hydroquinone was added to the alcohol-water solution. The solvent was removed by rotary evaporation. The rotary evaporation product was washed with anhydrous ethanol by centrifugation, and the precipitate was dried under vacuum at 50°C to constant weight to obtain the glutamic acid derivative. S2. Chitosan was dispersed in deionized water and transferred to a flask. Glutamic acid derivative, EDC and NHS were added, and the pH was adjusted to 5. After stirring for 30-60 min, the mixture was stirred at 30 °C for 12 h. After the reaction was completed, the pH was adjusted to 8, and the reaction product was placed in a dialysis bag. After dialysis, the product was freeze-dried to obtain modified chitosan.

2. The method for preparing a composite membrane for coal chemical wastewater treatment according to claim 1, characterized in that, The mass ratio of hydroxylated membrane, pyridine, and deionized water is 1:1-2.5:15-20, and the amount of 3-chloro-2-hydroxypropylmethyldiallylammonium chloride used is 5-15% of the mass of the hydroxylated membrane.

3. The method for preparing a composite membrane for coal chemical wastewater treatment according to claim 1, characterized in that, The ratio of acrylic acid, acrylamide, and acetic acid solution is 0.05 mol: 0.05 mol: 60-80 mL. The mass fraction of acetic acid solution is 2%. The amount of modified chitosan is 3% of the total mass of acrylic acid and acrylamide. The amount of potassium persulfate is 2% of the total mass of acrylic acid and acrylamide. The amount of N,N'-methylenebisacrylamide is 1% of the total mass of acrylic acid and acrylamide.

4. The method for preparing a composite membrane for coal chemical wastewater treatment according to claim 1, characterized in that, In S1, the ratio of sodium hydroxide, deionized water, L-glutamic acid, allyl isothiocyanate, and hydroquinone is 0.2 mol: 80-100 mL: 0.1 mol: 0.11-0.13 mol: 0.1 g.

5. The method for preparing a composite membrane for coal chemical wastewater treatment according to claim 1, characterized in that, The ratio of chitosan, deionized water, glutamic acid derivative, EDC and NHS in S2 is 2g:100mL:2.5-3.1g:0.9-1.0g:0.4-0.6g.

6. A composite membrane for treating coal chemical wastewater, characterized in that, It is prepared by the preparation method described in any one of claims 1-5.

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