Preparation method of ammonia nitrogen interception type reverse osmosis membrane based on amination degree controllable supporting layer

Abstract

The invention discloses a preparation method of an ammonia nitrogen interception type reverse osmosis membrane based on an amination degree controllable supporting layer, and relates to a preparation method of a reverse osmosis membrane. The invention aims to solve the problem that a reverse osmosis membrane prepared based on an inert support layer is poor in ammonia nitrogen selective separation performance. The method comprises the following steps: 1, synthesizing an APAEPO polymer with a controllable amination degree; 2, preparing a polymer supporting layer with a controllable amination degree by adopting a non-solvent induced phase inversion method; and 3, preparing the ammonia nitrogen interception type reverse osmosis membrane by adopting an interfacial polymerization method. By adjusting the amination degree (0-80%) of the supporting layer, the ammonia nitrogen retention rate (92.2%-99.1%) and water flux of the membrane can be flexibly regulated and controlled, the requirements of different reclaimed water treatment scenes (such as low-ammonia-nitrogen sewage reuse and high-ammonia-nitrogen wastewater deep purification) are met, and the application range is wide. The preparation process of the aminated polymer does not need to introduce a toxic modifier, the polymerization reaction condition is mild, the secondary pollution is small, and the aminated polymer can be directly industrially popularized.

Description

Technical Field

[0001] The invention relates to a method for preparing a reverse osmosis membrane. Background Art

[0002] Water shortages have become a core challenge to global sustainable development. High-quality reuse of recycled water, a vital unconventional water resource, is a key approach to alleviating the imbalance between water supply and demand. Reverse osmosis membrane technology, due to its efficient separation of salt ions and small molecule pollutants, has become a core technology for deep purification of recycled water. However, in recycled water treatment scenarios requiring efficient retention of ammonia and nitrogen, conventional reverse osmosis membranes still face a critical bottleneck. Reverse osmosis membranes based on inert support layers (such as polysulfone and polyethersulfone) exhibit poor selective separation performance for ammonia and nitrogen.

[0003] Ammonia nitrogen (NH3 / NH4 + Because it is close in size to water molecules and has similar polarity, and easily forms hydrogen bonds with the polyamide functional layer, it can easily penetrate traditional reverse osmosis membranes, causing the ammonia nitrogen concentration in the produced water to exceed the standard, limiting the application of recycled water in scenarios with high water quality requirements (such as industrial circulating cooling, groundwater recharge, and high-quality domestic sewage reuse). Traditional modification strategies often focus on surface modification (such as surface grafting) or matrix doping (such as nanomaterial doping) of the polyamide functional layer, but ignore the regulatory effect of the support layer on the structure of the separation layer: the inert support layer lacks active functional groups, making it difficult to directionally control the interfacial polymerization process, resulting in an uneven structure and insufficient cross-linking of the polyamide layer, further weakening the ammonia nitrogen retention capacity.

[0004] Existing research indicates that the structure and surface chemistry of the support layer directly influence the formation of the polyamide separation layer. The pore size distribution and surface functional groups of the support layer can regulate the adsorption and diffusion behavior of aqueous monomers, thereby determining the micromorphology, thickness, cross-linking degree, and other structural characteristics of the polyamide layer. Therefore, developing a functional support layer with a controllable degree of amination, and enhancing the ammonia nitrogen retention performance of reverse osmosis membranes by regulating the synergistic effect between the support layer and the polyamide layer, has become a key approach to breaking through the bottlenecks of traditional technologies. Summary of the Invention

[0005] The purpose of the present invention is to solve the problem that reverse osmosis membranes prepared based on an inert support layer have poor selective separation performance for ammonia nitrogen, and to provide a method for preparing an ammonia nitrogen retaining reverse osmosis membrane based on a support layer with controllable amination degree.

[0006] A method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree is specifically completed by the following steps:

[0007] 1. Synthesis of APAEPO polymers with controllable degree of amination:

[0008] ①, using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as basic monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as an amination monomer; mixing the basic monomers, the amination monomer and anhydrous potassium carbonate, and dissolving the mixture in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution;

[0009] ②. Under nitrogen atmosphere, the mixed solution is first heated to reflux temperature and refluxed at constant temperature for a certain period of time to remove any moisture in the system. After the toluene is evaporated, the temperature is raised to the polycondensation reaction temperature and the polycondensation reaction is carried out at constant temperature for a certain period of time to obtain the reaction product;

[0010] ③. Add the reaction product to deionized water and immerse it at a constant temperature for a certain period of time; repeat several times, filter, and then dry the solid matter at a constant temperature to obtain APAEPO polymers with different degrees of amination;

[0011] Second, a non-solvent-induced phase inversion method was used to prepare a polymer support layer with controllable degree of amination;

[0012] ①, APAEPO polymers with different degrees of amination are mixed with an organic solvent, heated and stirred at a constant temperature for a period of time, and then allowed to stand and degas for a certain period of time to obtain a casting solution;

[0013] ②. Under constant temperature and humidity conditions, the casting solution is applied to the non-woven fabric with deionized water as a coagulation bath to obtain a polymer support layer with a controllable degree of amination;

[0014] 3. Preparation of ammonia nitrogen retention reverse osmosis membrane by interfacial polymerization:

[0015] ① Dissolve the polyamine monomer in deionized water and stir evenly to obtain an aqueous solution;

[0016] ② Dissolve the polyacyl chloride monomer in a hydrocarbon organic solvent and stir evenly to obtain an oil phase solution;

[0017] ③ Immerse the polymer support layer with controllable degree of amination in an aqueous solution for a certain period of time, and then purge the residual aqueous solution on the surface with nitrogen gas after taking it out;

[0018] ④. Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to cause an amide polymerization reaction, thereby preparing a polyamide functional layer on the surface of the support layer. After taking it out, clean the surface with a hydrocarbon organic solvent. After the residual hydrocarbon organic solvent evaporates naturally, place it in a constant temperature oven for heat treatment. After taking it out, cool it to room temperature to obtain an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree.

[0019] The "controllable amination degree support layer" described in this invention is based on poly(arylene ether phosphine oxide) (PAEPO), a polymer synthesized from 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide. By introducing varying proportions of amino functional groups (-NH2) through a polycondensation reaction, the aminated poly(arylene ether phosphine oxide) (APAEPO) support layer is prepared. The amination degree (ratio of amino functional groups) can be precisely controlled by adjusting the proportion of amino-containing polycondensation monomers (e.g., 0%, 20%, 40%, 60%). By varying the amination degree of the support layer, the support layer's regulatory effect on the interfacial polymerization reaction is adjusted, and the micro-nanostructure and physicochemical properties of the polyamide separation layer are optimized, achieving highly selective separation of ammonia and nitrogen by the reverse osmosis membrane.

[0020] Advantages of the present invention:

[0021] (1) The casting solution system of the aminated polymer has enhanced thermodynamic stability and slowed phase separation rate, which helps to induce the formation of a support layer structure with smaller pore size and more uniform distribution; the amino group exhibits a surface segregation effect during the film formation process, causing the hydrophilic amino group to be enriched on the surface of the support layer, resulting in a support layer with higher hydrophilicity and surface amino group density;

[0022] (2) The amino active groups on the surface of the aminated support layer can regulate the adsorption and diffusion behavior of the polyamine monomer during the interfacial polymerization reaction, thereby regulating the micro-nanostructure of the polyamide functional layer, obtaining a thinner and more highly cross-linked functional layer, and enhancing its size screening effect;

[0023] (3) The amino functional groups (-NH2) on the surface of the aminated support layer are protonated in aqueous solution to form a positively charged layer (-NH3 + ), and the negatively charged surface of the polyamide functional layer (-COO - ) forms a "double-layer electrostatic barrier" and enhances the resistance of the reverse osmosis membrane to NH4 through the Donan effect. + of exclusion;

[0024] (4) The support layer with controllable degree of amination has a more uniform pore size distribution and moderate porosity, which can effectively reduce the "funnel effect" that hinders the transmission of water molecules. While strengthening the screening, it ensures the ideal water flux and achieves the synergistic optimization of "high selectivity-high flux", which helps to ensure the water production efficiency;

[0025] (5) By adjusting the degree of amination of the support layer (0-80%), the ammonia nitrogen retention rate (92.2%~99.1%) and water flux of the membrane can be flexibly controlled to meet the needs of different recycled water treatment scenarios (such as low ammonia nitrogen wastewater reuse and high ammonia nitrogen wastewater deep purification), with a wide range of applications;

[0026] (6) The preparation process of aminated polymers does not require the introduction of toxic modifiers, the polymerization reaction conditions are mild (180℃-200℃), and the secondary pollution is small. The preparation process of the support layer and polyamide functional layer with controllable amination degree based on the aminated polymers is compatible with the existing reverse osmosis membrane production line and can be directly promoted industrially. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1 (a) is a cross-sectional scanning electron micrograph of the polymer support layer APAEPO-0 having a degree of amination of 0 prepared in step 2② of Example 1; Figure 1 (b) is a cross-sectional SEM image of the polymer support layer APAEPO-20 with a degree of amination of 20% prepared in step 2② of Example 3;

[0028] Figure 2 (a) is a scanning electron microscope image of the polyamide reverse osmosis membrane prepared in step 3④ of Example 1, Figure 2 (b) is a scanning electron microscope image of an ammonia nitrogen retention reverse osmosis membrane based on a polymer support layer with a degree of amination of 20% prepared in step 3 (4) of Example 3;

[0029] Figure 3 (a) is a cross-sectional transmission electron micrograph of the polyamide reverse osmosis membrane prepared in step 3④ of Example 1, Figure 3 (b) is a cross-sectional transmission electron micrograph of an ammonia nitrogen retention reverse osmosis membrane based on a polymer support layer with an amination degree of 20%, prepared in step 3 (4) of Example 3. DETAILED DESCRIPTION

[0030] Specific embodiment 1: This embodiment is a method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree, which is specifically completed by the following steps:

[0031] 1. Synthesis of APAEPO polymers with controllable degree of amination:

[0032] ①, using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as basic monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as an amination monomer; mixing the basic monomers, the amination monomer and anhydrous potassium carbonate, and dissolving the mixture in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution;

[0033] ②. Under nitrogen atmosphere, heat the mixed solution to reflux temperature, keep reflux at constant temperature for a certain time, and after the toluene is evaporated, raise the temperature to the polycondensation reaction temperature, keep the polycondensation reaction at constant temperature for a certain time to obtain the reaction product;

[0034] ③. Add the reaction product to deionized water and immerse it at a constant temperature for a certain period of time; repeat several times, filter, and then dry the solid matter at a constant temperature to obtain APAEPO polymers with different degrees of amination;

[0035] Second, a non-solvent-induced phase inversion method was used to prepare a polymer support layer with controllable degree of amination;

[0036] ①, APAEPO polymers with different degrees of amination are mixed with an organic solvent, heated and stirred at a constant temperature for a period of time, and then allowed to stand and degas for a certain period of time to obtain a casting solution;

[0037] ②. Under constant temperature and humidity conditions, the casting solution is applied to the non-woven fabric with deionized water as a coagulation bath to obtain a polymer support layer with a controllable degree of amination;

[0038] 3. Preparation of ammonia nitrogen retention reverse osmosis membrane by interfacial polymerization:

[0039] ① Dissolve the polyamine monomer in deionized water and stir evenly to obtain an aqueous solution;

[0040] ② Dissolve the polyacyl chloride monomer in a hydrocarbon organic solvent and stir evenly to obtain an oil phase solution;

[0041] ③ Immerse the polymer support layer with controllable degree of amination in an aqueous solution for a certain period of time, and then purge the residual aqueous solution on the surface with nitrogen gas after taking it out;

[0042] ④. Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to cause an amide polymerization reaction, thereby preparing a polyamide functional layer on the surface of the support layer. After taking it out, clean the surface with a hydrocarbon organic solvent. After the residual hydrocarbon organic solvent evaporates naturally, place it in a constant temperature oven for heat treatment. After taking it out, cool it to room temperature to obtain an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree.

[0043] Specific embodiment 2: This embodiment differs from specific embodiment 1 in that the ratio of the amount of 4,4'-dihydroxybiphenyl described in step 1 (1) to the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is 1:(1-3); the amount of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide described in step 1 (1) accounts for 0-80% of the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide. The other steps are the same as specific embodiment 1.

[0044] Specific embodiment 3: This embodiment differs from either specific embodiment 1 or 2 in that the molar ratio of 4,4'-dihydroxybiphenyl to anhydrous potassium carbonate in step 1 (1) is 1:(1-2); and the volume ratio of 4,4'-dihydroxybiphenyl to the organic solvent containing toluene in step 1 (1) is 1 mmol:(1.5 mL-2 mL). Other steps are the same as those in specific embodiment 1 or 2.

[0045] Specific embodiment 4: This embodiment differs from Specific embodiments 1 to 3 in that the volume ratio of toluene to N,N-dimethylacetamide in the mixed solution of toluene and N,N-dimethylacetamide in step 1 (1) is 1:(1-2.5). The other steps are the same as Specific embodiments 1 to 3.

[0046] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that the reflux temperature in step 1 (2) is 120°C to 160°C, and the constant temperature reflux time is 3 to 6 hours; the polycondensation reaction temperature in step 1 (2) is 180°C to 200°C, and the constant temperature polycondensation reaction time is 12 to 16 hours. The other steps are the same as specific embodiments 1 to 4.

[0047] Specific embodiment 6: This embodiment differs from specific embodiments 1 to 5 in that: the constant temperature immersion in step 1 (3) is performed at 60°C to 90°C for 5 to 10 hours; step 1 (3) is repeated 3 to 6 times; the constant temperature drying is performed at 100°C to 120°C for 24 to 36 hours. The other steps are the same as specific embodiments 1 to 5.

[0048] Specific embodiment 7: This embodiment differs from Specific embodiments 1 to 6 in that the organic solvent in step 2 (1) is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and tetrahydrofuran; the mass percent concentration of the casting solution in step 2 (1) is 10% to 30%; the constant temperature heating and stirring in step 2 (1) is at a temperature of 60°C to 100°C, the constant temperature heating and stirring time is 24 hours to 36 hours, and the static degassing time is 6 hours to 12 hours. The other steps are the same as Specific embodiments 1 to 6.

[0049] Specific Embodiment 8: This embodiment differs from Specific Embodiments 1 to 7 in that the constant temperature and humidity conditions described in step 2 (2) are set to a temperature range of 20°C to 40°C and a relative humidity range of 30% to 60%. The scraper gap during the coating process described in step 2 (2) is controlled to be 100 μm to 400 μm. Other steps are the same as Specific Embodiments 1 to 7.

[0050] Specific Embodiment 9: This embodiment differs from Specific Embodiments 1 to 8 in that: the polyamine monomer in step 3 (1) is one or more of 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, piperazine, 2-methylpiperazine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene, and polyethyleneimine; the mass percentage concentration of the aqueous phase solution in step 3 (1) is 0.5% to 4.0%; the polyacyl chloride monomer in step 3 (2) is one or more of 1,3-phthaloyl chloride, 1,3,5-benzenetricarboxylic acid chloride, and 1,2,4,5-pyromellitotetracarboxylic acid chloride; the mass percentage concentration of the oil phase solution in step 3 (2) is 0.05% to 0.50%; and the hydrocarbon organic solvent in step 3 (2) is one or more of cyclohexane, n-hexane, Isopar G, toluene, and benzene. Other steps are the same as Specific Embodiments 1 to 8.

[0051] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that: in step 3 (3), the polymer support layer with a controllable degree of amination is immersed in an aqueous solution for 30 to 300 seconds, and after removal, the residual aqueous solution on the surface is purged with nitrogen at a nitrogen pressure of 0.1 MPa to 1.0 MPa; in step 3 (4), the nitrogen-purged support layer is immersed in an oil solution for 15 to 300 seconds; the hydrocarbon organic solvent in step 3 (4) is one or more of cyclohexane, n-hexane, Isopar G, toluene, and benzene; and the heat treatment temperature in step 3 (4) is 50° C. to 90° C., and the heat treatment time is 3 to 20 minutes. The other steps are the same as those in specific embodiments 1 to 9.

[0052] The following examples are used to verify the beneficial effects of the present invention:

[0053] Example 1: A method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable degree of amination, which is specifically completed by the following steps:

[0054] 1. Synthesis of APAEPO polymers with controllable degree of amination:

[0055] ①, using 50 mmol of 4,4'-dihydroxybiphenyl and 50 mmol of bis(4-fluorophenyl)phenylphosphine oxide as base monomers; mixing the base monomers with 55 mmol of anhydrous potassium carbonate, and dissolving the mixture in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution;

[0056] ②. Under nitrogen atmosphere, heat the mixed solution to 150°C and maintain the temperature at 150°C for 4 hours to remove any moisture in the system. After the toluene is evaporated, heat the solution to 180°C and conduct polycondensation at 180°C for 12 hours to obtain the reaction product.

[0057] ③. Add the reaction product to deionized water and immerse at 80°C for 6 hours; repeat 4 times, filter, and then dry the solid matter at a constant temperature to obtain a polymer APAEPO-0 with a degree of amination of 0;

[0058] The constant temperature drying temperature of step 1 (3) is 100°C and the drying time is 24 hours;

[0059] Second, a non-solvent-induced phase inversion method was used to prepare a polymer support layer with controllable degree of amination;

[0060] ①, the polymer APAEPO-0 with a degree of amination of 0 and N-methylpyrrolidone were mixed, and then heated and stirred at 80°C for 36 hours, and then allowed to stand and degas for 8 hours to obtain a casting solution;

[0061] The mass percentage concentration of the casting solution described in step 2① is 20%;

[0062] ②. Under constant temperature and humidity conditions, the casting solution was applied on a non-woven fabric, and deionized water was used as a coagulation bath to obtain a polymer support layer APAEPO-0 with a degree of amination of 0;

[0063] The constant temperature and humidity conditions described in step 2② are as follows: the temperature range is 25°C and the relative humidity range is 35%;

[0064] During the scraping process described in step 2②, the scraper gap is controlled to be 150μm;

[0065] 3. Preparation of ammonia nitrogen retention reverse osmosis membrane by interfacial polymerization:

[0066] ① Dissolve the polyamine monomer in deionized water and stir evenly to obtain an aqueous solution with a mass percentage concentration of 2.0%;

[0067] The polyamine monomer described in step 3① is 1,3-phenylenediamine;

[0068] ② Dissolve the polyacyl chloride monomer in n-hexane and stir evenly to obtain an oil phase solution with a mass percentage concentration of 0.1%;

[0069] The polyacyl chloride monomer described in step 3② is 1,3,5-benzenetricarboxylic acid chloride;

[0070] ③ Immerse the polymer support layer APAEPO-0 with a degree of amination of 0 into the aqueous solution for 120 seconds. After taking it out, purge the residual aqueous solution on the surface with nitrogen at a pressure of 0.6 MPa.

[0071] ④. Immerse the nitrogen-purged support layer in the oil phase solution for 30 seconds to cause an amide polymerization reaction, thereby obtaining a polyamide functional layer on the surface of the support layer. After removing the support layer, clean the surface with n-hexane. After the residual n-hexane evaporates naturally, place the support layer in a constant temperature oven at 80°C for heat treatment for 3 minutes. After removing the support layer, cool it to room temperature to obtain a polyamide reverse osmosis membrane.

[0072] Test conditions: The reverse osmosis membrane's pure water flux was tested at a pressure of 1.0 MPa, a temperature of 25°C, and a pH of 7.0. The membrane's salt rejection was then tested using a 2000 mg / L sodium chloride solution, and its ammonia nitrogen retention was tested using a 100 mg / L ammonium chloride solution. At least three parallel tests were conducted under the same preparation conditions, and the results were averaged to improve the accuracy and reliability of the experimental data. The test data are recorded in Table 1.

[0073] Example 2: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 45 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 5 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-10 having an amination degree of 10%; step 2 (2) obtains a polymer support layer APAEPO-10 having an amination degree of 10%; and step 3 (4) obtains an ammonia-nitrogen-retaining reverse osmosis membrane based on the polymer support layer having an amination degree of 10%. All other steps and parameters are the same as those in Example 1.

[0074] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0075] Example 3: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 40 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 10 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-20 with a degree of amination of 20%; step 2 (2) obtains a polymer support layer APAEPO-20 with a degree of amination of 20%; and step 3 (4) obtains an ammonia-nitrogen-retaining reverse osmosis membrane based on the polymer support layer with a degree of amination of 20%. All other steps and parameters are the same as those in Example 1.

[0076] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0077] Example 4: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 30 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 20 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and the amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-40 having an amination degree of 40%; step 2 (2) obtains a polymer support layer APAEPO-40 having an amination degree of 40%; and step 3 (4) obtains an ammonia nitrogen-retaining reverse osmosis membrane based on the polymer support layer having an amination degree of 40%. All other steps and parameters are the same as those in Example 1.

[0078] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0079] Example 5: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 25 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 25 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and the amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-50 having a degree of amination of 50%; step 2 (2) obtains a polymer support layer APAEPO-50 having a degree of amination of 50%; and step 3 (4) obtains an ammonia-nitrogen-retaining reverse osmosis membrane based on the polymer support layer having a degree of amination of 50%. All other steps and parameters are the same as those in Example 1.

[0080] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0081] Example 6: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 20 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 30 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-60 with a degree of amination of 60%; step 2 (2) obtains a polymer support layer APAEPO-60 with a degree of amination of 60%; and step 3 (4) obtains an ammonia-nitrogen-retaining reverse osmosis membrane based on the polymer support layer with a degree of amination of 60%. All other steps and parameters are the same as those in Example 1.

[0082] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0083] Example 7: This example differs from Example 1 in that: in step 1 (1), 50 mmol of 4,4'-dihydroxybiphenyl and 10 mmol of bis(4-fluorophenyl)phenylphosphine oxide are used as base monomers; 40 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is used as an amination monomer; the base monomer and the amination monomer are mixed with 55 mmol of anhydrous potassium carbonate and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step 1 (3) obtains a polymer APAEPO-80 having an amination degree of 80%; step 2 (2) obtains a polymer support layer APAEPO-80 having an amination degree of 80%; and step 3 (4) obtains an ammonia nitrogen-retaining reverse osmosis membrane based on the polymer support layer having an amination degree of 80%. All other steps and parameters are the same as those in Example 1.

[0084] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0085] Comparative Example 1:

[0086] Conventional polyamide reverse osmosis membrane prepared using commercial polysulfone ultrafiltration membrane as the support layer;

[0087] The difference from Example 1 lies in the source of the support layer.

[0088] The test method in Example 1 was used, and the test data are recorded in Table 1.

[0089] Table 1 Reverse osmosis membrane performance of different embodiments and comparative example 1

[0090]

[0091] As can be seen from the data in Table 1, the experimentally measured degrees of amination (9.87%–79.36%) deviated closely from the expected degrees of amination (10%–80%). This demonstrates that precise control of the support layer's degree of amination can be achieved through monomer ratio adjustment, providing a reliable foundation for targeted optimization of reverse osmosis membrane performance. Controlling the degree of amination has the most significant effect on enhancing ammonia nitrogen rejection. Example 3, with a degree of amination of 21.30%, achieved an ammonia nitrogen rejection rate of 99.13%, an 8.81 percentage point increase over the conventional membrane (Comparative Example 1, 91.32%) and a 7.01 percentage point increase over the unaminated membrane (Example 1, 92.12%). This performance significantly surpasses the approximately 93% ammonia nitrogen rejection achieved by conventional polyamide reverse osmosis membranes in the prior art. Even when the degree of amination increased to 58.42% (Example 6), the ammonia nitrogen retention rate remained stable at 98.04%, indicating that the aminated support layer achieved targeted and efficient retention of ammonia nitrogen through the synergistic effect of the "double-layer electrostatic barrier" (protonated amino groups in the support layer and negative charges in the polyamide layer) and the dense structure of the polyamide layer, fundamentally solving the bottleneck of insufficient ammonia nitrogen retention in traditional membranes.

[0092] Amination of the support layer significantly improves desalination performance while enhancing ammonia nitrogen retention. Example 3 (degree of amination 21.30%) achieved a NaCl retention rate of 99.22%, a 1.61 percentage point increase over Comparative Example 1 (97.61%) and a 2.48 percentage point increase over the unaminated Example 1 (96.74%). This result demonstrates that the amination of the support layer, by regulating the interfacial polymerization process, promotes a more cross-linked and uniform structure in the polyamide layer. This enhances ammonia nitrogen retention while simultaneously improving the screening capacity for salt ions, achieving a synergistic and efficient separation of ammonia nitrogen and salt ions.

[0093] Furthermore, amination of the support layer significantly improves the water permeability of the reverse osmosis membrane. The water permeability coefficient of Example 3 is 2.93 LMH / bar, a 49.5% increase over Comparative Example 1 (1.96 LMH / bar) and a 38.9% increase over the unaminated Example 1 (2.11 LMH / bar). This is due to the more uniform pore distribution of the support layer and the ultra-thin structure of the polyamide layer, which effectively reduces the resistance to water molecule transport while ensuring high selectivity, meeting the urgent need for "high selectivity and high water flux" in practical applications. However, an excessively high degree of amination (e.g., 79.36%) can lead to a slight decline in various performance characteristics due to excessively reduced support layer pore size and decreased crosslinking of the polyamide layer.

[0094] Figure 1 (a) is a cross-sectional scanning electron micrograph of the polymer support layer APAEPO-0 having a degree of amination of 0 prepared in step 2② of Example 1; Figure 1(b) is a cross-sectional SEM image of the polymer support layer APAEPO-20 with a degree of amination of 20% prepared in step 2② of Example 3;

[0095] Combine Figure 1 It can be seen that the support layers prepared in the two embodiments both present an asymmetric structure consisting of a dense cortex and finger-like pores. As the degree of amination increases, the size of the finger-like macropores formed in the support layer decreases, the average pore size on the surface decreases, and the pore size distribution becomes narrower, which is conducive to controlling the storage and diffusion behavior of the aqueous phase monomer during the interfacial polymerization process.

[0096] Figure 2 (a) is a scanning electron microscope image of the polyamide reverse osmosis membrane prepared in step 3④ of Example 1, Figure 2 (b) is a scanning electron microscope image of an ammonia nitrogen retention reverse osmosis membrane based on a polymer support layer with a degree of amination of 20% prepared in step 3 (4) of Example 3;

[0097] Combine Figure 2 It can be seen that the surface of the reverse osmosis membranes prepared in the two examples showed the typical "ridge-valley" structure of polyamide membranes. Among them, the surface leaf-like protrusions of the reverse osmosis membrane prepared by the unaminated support layer were higher ( Figure 2 (a)), the uniformity is poor; while the "ridge" structure and "valley" structure of the ammonia nitrogen retention reverse osmosis membrane made of a support layer with a degree of amination of 20% are more evenly distributed with each other, which increases the effective filtration area and is beneficial to the improvement of water flux. At the same time, its cross-linking is denser, laying a structural foundation for the improvement of ammonia nitrogen selectivity.

[0098] Figure 3 (a) is a cross-sectional transmission electron micrograph of the polyamide reverse osmosis membrane prepared in step 3④ of Example 1, Figure 3 (b) is a cross-sectional transmission electron micrograph of an ammonia nitrogen retention reverse osmosis membrane based on a polymer support layer with an amination degree of 20%, prepared in step 3 (4) of Example 3.

[0099] Combine Figure 3 It can be seen that the apparent thickness of the polyamide functional layer of the reverse osmosis membrane prepared by the support layer with a higher degree of amination is smaller. This is because the strong affinity between the aqueous phase monomer and the aminated support layer leads to a decrease in the diffusion rate of the polyamine monomer during the interfacial polymerization, thereby forming a thinner functional layer. This reflects the regulatory effect of the aminated support layer on the interfacial bonding process. This thin and dense functional layer is conducive to overcoming the trade-off effect between selectivity and permeability, and simultaneously achieving high selectivity and high water flux.

[0100] The present invention designs a support layer with a controllable degree of amination and constructs an ammonia-nitrogen-retaining reverse osmosis membrane based on it, thereby increasing the ammonia-nitrogen retention rate to over 99% (a core breakthrough), while simultaneously enhancing the desalination performance and maintaining an ideal water permeability coefficient. This provides an innovative solution that combines selectivity, stability, and water production rate for high-ammonia-nitrogen recycled water treatment scenarios, significantly expanding the application potential of reverse osmosis membranes in the field of efficient ammonia-nitrogen separation.

[0101] The applicant states that the present invention uses the above-described embodiments to illustrate the ammonia-nitrogen-retaining reverse osmosis membrane based on a support layer with a controllable degree of amination and its preparation method. However, the application of the present invention is not limited to the above-described examples. Those skilled in the art may make modifications or variations based on the above description, and all such modifications and variations are intended to fall within the scope of protection of the appended claims. Furthermore, the present invention is not limited to the embodiments shown herein, but is intended to conform to the broadest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree, characterized in that The preparation method is specifically completed according to the following steps:

1. Synthesis of APAEPO polymers with controllable degree of amination: ①, using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as basic monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as an amination monomer; mixing the basic monomers, the amination monomer and anhydrous potassium carbonate, and dissolving the mixture in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution; ②. Under nitrogen atmosphere, heat the mixed solution to reflux temperature, keep reflux at constant temperature for a certain time, and after the toluene is evaporated, raise the temperature to the polycondensation reaction temperature, keep the polycondensation reaction at constant temperature for a certain time to obtain the reaction product; ③. Add the reaction product to deionized water and immerse it at a constant temperature for a certain period of time; repeat several times, filter, and then dry the solid matter at a constant temperature to obtain APAEPO polymers with different degrees of amination; Second, a non-solvent-induced phase inversion method was used to prepare a polymer support layer with controllable degree of amination; ①, APAEPO polymers with different degrees of amination are mixed with an organic solvent, heated and stirred at a constant temperature for a period of time, and then allowed to stand and degas for a certain period of time to obtain a casting solution; ②. Under constant temperature and humidity conditions, the casting solution is applied to the non-woven fabric with deionized water as a coagulation bath to obtain a polymer support layer with a controllable degree of amination; 3. Preparation of ammonia nitrogen retention reverse osmosis membrane by interfacial polymerization: ① Dissolve the polyamine monomer in deionized water and stir evenly to obtain an aqueous solution; ② Dissolve the polyacyl chloride monomer in a hydrocarbon organic solvent and stir evenly to obtain an oil phase solution; ③ Immerse the polymer support layer with controllable degree of amination in an aqueous solution for a certain period of time, and then purge the residual aqueous solution on the surface with nitrogen gas after taking it out; ④. Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to cause an amide polymerization reaction, thereby preparing a polyamide functional layer on the surface of the support layer. After taking it out, clean the surface with a hydrocarbon organic solvent. After the residual hydrocarbon organic solvent evaporates naturally, place it in a constant temperature oven for heat treatment. After taking it out, cool it to room temperature to obtain an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree.

2. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The amount of 4,4'-dihydroxybiphenyl described in step 1① to the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide is 1:(1-3); the amount of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide described in step 1① accounts for 0-80% of the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide.

3. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The molar ratio of 4,4'-dihydroxybiphenyl described in step 1① to anhydrous potassium carbonate is 1:(1~2); the volume ratio of the amount of 4,4'-dihydroxybiphenyl described in step 1① to the organic solvent containing toluene is 1mmol:(1.5mL~2mL).

4. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The volume ratio of toluene to N,N-dimethylacetamide in the mixed solution of toluene and N,N-dimethylacetamide described in step 1① is 1: (1~2.5).

5. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The reflux temperature in step 1 ② is 120 ℃ ~ 160 ℃, and the constant temperature reflux time is 3h ~ 6h; the polycondensation reaction temperature in step 1 ② is 180 ℃ ~ 200 ℃, and the constant temperature polycondensation reaction time is 12h ~ 16h.

6. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The constant temperature immersion temperature in step 1 ③ is 60 ℃ ~ 90 ℃, and the constant temperature immersion time is 5h ~ 10h; step 1 ③ is repeated 3 times to 6 times; the constant temperature drying temperature is 100 ℃ ~ 120 ℃, and the drying time is 24h ~ 36h.

7. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The organic solvent described in step 2① is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone and tetrahydrofuran; the mass percentage concentration of the casting solution described in step 2① is 10%~30%; the temperature of the constant temperature heating and stirring described in step 2① is 60℃~100℃, the time of constant temperature heating and stirring is 24h~36h, and the static degassing time is 6h~12h.

8. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The constant temperature and humidity conditions described in step 2② are in the range of 20°C to 40°C and in the range of 30% to 60% relative humidity; the scraper gap is controlled to be 100 μm to 400 μm during the coating process described in step 2②.

9. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that The polyamine monomer described in step 3① is one or more of 1,2-phenylenediamine, 1,3-phenylenediamine, 1,4-phenylenediamine, piperazine, 2-methylpiperazine, 1,3,5-triaminobenzene, 1,2,4-triaminobenzene and polyethyleneimine; the mass percentage concentration of the aqueous phase solution described in step 3① is 0.5%~4.0%; the polyacyl chloride monomer described in step 3② is one or more of 1,3-phthaloyl chloride, 1,3,5-benzenetricarboxylic acid chloride and 1,2,4,5-benzenetetracarboxylic acid chloride; the mass percentage concentration of the oil phase solution described in step 3② is 0.05%~0.50%; the hydrocarbon organic solvent described in step 3② is one or more of cyclohexane, n-hexane, Isopar G, toluene and benzene.

10. The method for preparing an ammonia nitrogen retention reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that In step 3③, the polymer support layer with controllable degree of amination is immersed in an aqueous solution for 30s to 300s, and after being removed, the residual aqueous solution on the surface is purged with nitrogen at a nitrogen pressure of 0.1MPa to 1.0MPa; in step 3④, the nitrogen-purged support layer is immersed in an oil solution for 15s to 300s; the hydrocarbon organic solvent described in step 3④ is one or more of cyclohexane, n-hexane, Isopar G, toluene and benzene; the heat treatment temperature in step 3④ is 50°C to 90°C, and the heat treatment time is 3min to 20min.

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