A method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree.

Abstract

A method for preparing an ammonia nitrogen-rejecting reverse osmosis membrane based on a support layer with controllable amination degree is disclosed. This invention aims to address the problem of poor selective separation performance of ammonia nitrogen in reverse osmosis membranes prepared based on inert support layers. The method comprises: 1. Synthesizing APAEPO polymer with controllable amination degree; 2. Preparing a polymer support layer with controllable amination degree using a solvent-inducible phase inversion method; 3. Preparing an ammonia nitrogen-rejecting reverse osmosis membrane using interfacial polymerization. This invention allows for flexible control of the membrane's ammonia nitrogen rejection rate (92.2%~99.1%) and water flux by adjusting the amination degree of the support layer (0-80%), meeting the needs of different reclaimed water treatment scenarios (such as low-ammonia nitrogen wastewater reuse and high-ammonia nitrogen wastewater deep purification), thus having a wide range of applications. The preparation process of the amination polymer in this invention does not require the introduction of toxic modifiers, the polymerization reaction conditions are mild, secondary pollution is minimal, and it can be directly industrialized.

Description

Technical Field

[0001] This invention relates to a method for preparing a reverse osmosis membrane. Background Technology

[0002] Water scarcity has become a core challenge for global sustainable development. Reclaimed water, as an important unconventional water resource, is crucial for alleviating the water supply-demand imbalance through high-quality reuse. Reverse osmosis membrane technology, due to its highly efficient separation of salt ions and small molecule pollutants, has become a core technology for deep purification of reclaimed water. However, in reclaimed water treatment scenarios requiring efficient ammonia nitrogen removal, traditional reverse osmosis membranes still face key bottlenecks; reverse osmosis membranes based on inert support layers (such as polysulfone and polyethersulfone) exhibit poor selective separation performance for ammonia nitrogen.

[0003] Ammonia nitrogen (in the form of NH3 / NH4) + Because polyamide molecules are similar in size and polarity to water molecules and readily form hydrogen bonds with the polyamide functional layer, they easily penetrate traditional reverse osmosis membranes, leading to excessive ammonia nitrogen concentrations in the produced water. This limits the application of reclaimed water in high-quality water-retention scenarios (such as industrial circulating cooling, groundwater recharge, and high-quality reuse of domestic sewage). 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 neglect the regulatory role of the support layer on the separation layer structure: the inert support layer, lacking active functional groups, makes it difficult to directionally regulate the interfacial polymerization process, resulting in an uneven polyamide layer structure and insufficient cross-linking, 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 microstructure, thickness, and crosslinking degree of the polyamide layer. Therefore, developing functional support layers with controllable amination degree, and improving the ammonia nitrogen rejection performance of reverse osmosis membranes by regulating the synergistic effect between the support layer and the polyamide layer, has become a key direction for overcoming traditional technical bottlenecks. Summary of the Invention

[0005] The purpose of this invention is to solve the problem of poor selective separation performance of ammonia nitrogen in reverse osmosis membranes prepared based on inert support layers, 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-retaining reverse osmosis membrane based on a support layer with controllable amination degree is specifically carried out according to the following steps:

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

[0008] ① Using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as base monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as amination monomer; the base monomer, amination monomer and anhydrous potassium carbonate are mixed and dissolved in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution;

[0009] ② Under nitrogen atmosphere protection, the mixed solution is first heated to the reflux temperature and kept at the reflux temperature for a certain time to remove any water that may exist in the system. After the toluene evaporates, the temperature is raised to the polycondensation reaction temperature and kept at the reflux temperature for a certain time to obtain the reaction product.

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

[0011] II. Preparation of polymer support layer with controllable amination degree using a solvent-inducible phase inversion method;

[0012] ① Mix APAEPO polymers with different degrees of amination with organic solvents, then heat and stir at a constant temperature for a period of time, and then let stand to degas for a certain period of time to obtain casting solution;

[0013] ② Under constant temperature and humidity conditions, the casting solution is scraped onto the nonwoven fabric, and deionized water is used as the coagulation bath to obtain a polymer support layer with controllable amination degree.

[0014] III. Preparation of ammonia nitrogen-retaining reverse osmosis membranes using interfacial polymerization:

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

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

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

[0018] ④ Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to allow it to undergo amide polymerization reaction, thereby obtaining a polyamide functional layer on the surface of the support layer. After removal, 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 removal, cool it to room temperature to obtain an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree.

[0019] The "controllable amination degree support layer" described in this invention uses polyarylene ether phosphine oxide (PAEPO) as the substrate. PAEPO is a polymer synthesized from 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide. Amination-modified PAEPO support layers are prepared by introducing different proportions of amino functional groups (-NH2) through a polycondensation reaction. The amination degree (proportion of amino functional groups) can be precisely controlled by adjusting the proportion of amino-containing polycondensation monomers (e.g., 0%, 20%, 40%, 60%). By changing the amination degree of the support layer, the regulatory effect of the support layer on the interfacial polymerization reaction is adjusted, optimizing the micro / nano structure and physicochemical properties of the polyamide separation layer, and achieving high selectivity separation of ammonia nitrogen by the reverse osmosis membrane.

[0020] Advantages of this invention:

[0021] (1) The casting solution system of amination 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; amino groups exhibit surface segregation effect during film formation, which enriches hydrophilic amino groups on the surface of the support layer, resulting in a support layer with higher hydrophilicity and surface amino density.

[0022] (2) The amino active groups on the surface of the amination support layer can regulate the adsorption and diffusion behavior of polyamine monomers during the interfacial polymerization reaction, thereby regulating the micro-nano structure of the polyamide functional layer, obtaining a thinner functional layer with higher cross-linking degree, and strengthening its size sieving effect.

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

[0024] (4) The support layer with controllable amination degree has a more uniform pore size distribution and moderate porosity, which can effectively reduce the "funnel effect" from hindering the transport 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 water production efficiency.

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

[0026] (6) The preparation process of amination polymer does not require the introduction of toxic modifiers, the polymerization reaction conditions are mild (180℃-200℃), and there is little secondary pollution. The preparation process of the support layer and polyamide functional layer with controllable amination degree based on it is compatible with the existing reverse osmosis membrane production line and can be directly promoted to the industrial level. Attached Figure Description

[0027] Figure 1 Image (a) is a cross-sectional scanning electron microscope image of the polymer support layer APAEPO-0 with an amination degree of 0 prepared in step 2 ② of Example 1; Figure 1 Image (b) is a cross-sectional scanning electron microscope image of the polymer support layer APAEPO-20 with an amination degree of 20% prepared in step 2② of Example 3;

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

[0029] Figure 3 Image (a) is a cross-sectional transmission electron microscope image of the polyamide reverse osmosis membrane prepared in step three of Example 1, section ④. Figure 3 Image (b) is a cross-sectional transmission electron microscope image of the ammonia nitrogen-retaining reverse osmosis membrane prepared in step three of Example 3, section 4, based on a polymer support layer with an amination degree of 20%. Detailed Implementation

[0030] Specific Implementation Method 1: This implementation method describes a method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree. The method is specifically completed according to the following steps:

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

[0032] ① Using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as base monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as amination monomer; the base monomer, amination monomer and anhydrous potassium carbonate are mixed and dissolved in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution;

[0033] ② Under nitrogen atmosphere protection, the mixed solution is first heated to the reflux temperature and kept at the reflux temperature for a certain time. After the toluene evaporates, the temperature is raised to the polycondensation reaction temperature and kept at the reflux temperature for a certain time to obtain the reaction product.

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

[0035] II. Preparation of polymer support layer with controllable amination degree using a solvent-inducible phase inversion method;

[0036] ① Mix APAEPO polymers with different degrees of amination with organic solvents, then heat and stir at a constant temperature for a period of time, and then let stand to degas for a certain period of time to obtain casting solution;

[0037] ② Under constant temperature and humidity conditions, the casting solution is scraped onto the nonwoven fabric, and deionized water is used as the coagulation bath to obtain a polymer support layer with controllable amination degree.

[0038] III. Preparation of ammonia nitrogen-retaining reverse osmosis membranes using interfacial polymerization:

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

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

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

[0042] ④ Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to allow it to undergo amide polymerization reaction, thereby obtaining a polyamide functional layer on the surface of the support layer. After removal, 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 removal, cool it to room temperature to obtain an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree.

[0043] Specific Implementation Method Two: This implementation method differs from Specific Implementation Method One in that: the amount of 4,4'-dihydroxybiphenyl mentioned in step one ① is in the ratio of the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide to 1:(1-3); the amount of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide mentioned in step one 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 in Specific Implementation Method One.

[0044] Specific Implementation Method 3: This implementation method differs from Specific Implementation Method 1 or 2 in that: the molar ratio of 4,4'-dihydroxybiphenyl to anhydrous potassium carbonate in step 1① is 1:(1~2); the molar ratio of the amount of 4,4'-dihydroxybiphenyl to the volume ratio of the organic solvent containing toluene in step 1① is 1 mmol:(1.5 mL~2 mL). Other steps are the same as in Specific Implementation Method 1 or 2.

[0045] Specific Implementation Method Four: This implementation method differs from Specific Implementation Methods One to Three in that the volume ratio of toluene to N,N-dimethylacetamide in the mixed solution of toluene and N,N-dimethylacetamide mentioned in step one ① is 1:(1-2.5). The other steps are the same as in Specific Implementation Methods One to Three.

[0046] Specific Implementation Method Five: This implementation method differs from Specific Implementation Methods One to Four in that: the reflux temperature in step one (②) is 120℃~160℃, and the isothermal reflux time is 3h~6h; the polycondensation reaction temperature in step one (②) is 180℃~200℃, and the isothermal polycondensation reaction time is 12h~16h. Other steps are the same as in Specific Implementation Methods One to Four.

[0047] Specific Implementation Method Six: This implementation method differs from Specific Implementation Methods One to Five 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 to 6 times; the constant temperature drying temperature is 100℃~120℃, and the drying time is 24h~36h. Other steps are the same as in Specific Implementation Methods One to Five.

[0048] Specific Implementation Method Seven: This implementation method differs from Specific Implementation Methods One to Six in that: the organic solvent mentioned in step two ① is one or more of N,N-dimethylformamide, N,N-dimethylacetamide, N-methylpyrrolidone, and tetrahydrofuran; the mass percentage concentration of the casting solution mentioned in step two ① is 10% to 30%; the constant temperature heating and stirring temperature in step two ① is 60℃ to 100℃, the constant temperature heating and stirring time is 24h to 36h, and the standing degassing time is 6h to 12h. Other steps are the same as in Specific Implementation Methods One to Six.

[0049] Specific Implementation Method Eight: This implementation method differs from Specific Implementation Methods One to Seven in that: in step two ②, the temperature range is 20℃~40℃ and the relative humidity range is 30%~60% under constant temperature and humidity conditions; and in step two ②, the blade gap is controlled to be 100μm~400μm during the coating process. Other steps are the same as in Specific Implementation Methods One to Seven.

[0050] Specific Embodiment Nine: This embodiment differs from Specific Embodiments One to Eight in that: the polyamine monomer mentioned in step three 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 mentioned in step three ① is 0.5% to 4.0%; the polyacrylamide chloride monomer mentioned in step three ② is one or more of 1,3-phenylenediamide chloride, 1,3,5-phenyltricarboxyamide chloride, and 1,2,4,5-phenyltetracarboxyamide chloride; the mass percentage concentration of the oil phase solution mentioned in step three ② is 0.05% to 0.50%; and the hydrocarbon organic solvent mentioned in step three ② is one or more of cyclohexane, n-hexane, Isopar G, toluene, and benzene. The other steps are the same as in Specific Embodiments One to Eight.

[0051] Specific Implementation Method Ten: This implementation method differs from Specific Implementation Methods One to Nine in the following ways: In step three ③, the polymer support layer with controllable amination degree is immersed in the aqueous phase solution for 30s to 300s, and after removal, the surface residual aqueous phase solution is purged with nitrogen gas at a pressure of 0.1MPa to 1.0MPa; in step three ④, the nitrogen-purged support layer is immersed in the oil phase solution for 15s to 300s; the hydrocarbon organic solvent mentioned in step three ④ is one or more of cyclohexane, n-hexane, Isopar G, toluene, and benzene; the heat treatment temperature mentioned in step three ④ is 50℃ to 90℃, and the heat treatment time is 3min to 20min. Other steps are the same as in Specific Implementation Methods One to Nine.

[0052] The beneficial effects of the present invention are verified using the following embodiments:

[0053] Example 1: A method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree, specifically completed according to the following steps:

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

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

[0056] ② Under nitrogen atmosphere protection, the mixed solution is first heated to 150℃ and kept at 150℃ for 4 hours to remove any water that may be present in the system. After the toluene evaporates, the temperature is raised to 180℃ and kept at 180℃ for 12 hours to obtain the reaction product.

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

[0058] The constant temperature drying in step 1③ is 100℃, and the drying time is 24 hours;

[0059] II. Preparation of polymer support layer with controllable amination degree using a solvent-inducible phase inversion method;

[0060] ① Mix the polymer APAEPO-0 with a degree of amination of 0 and N-methylpyrrolidone, then heat and stir at 80℃ for 36 hours, and then let it stand to degas for 8 hours to obtain the casting solution.

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

[0062] ② Under constant temperature and humidity conditions, the casting solution is scraped onto the nonwoven fabric, and deionized water is used as the coagulation bath to obtain a polymer support layer APAEPO-0 with an amination degree of 0.

[0063] In step 2②, the constant temperature and humidity conditions refer to a temperature range of 25℃ and a relative humidity range of 35%.

[0064] In step 2②, the gap between the scraper blades is controlled to be 150μm during the scraping process.

[0065] III. Preparation of ammonia nitrogen-retaining reverse osmosis membranes using interfacial polymerization:

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

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

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

[0069] The polyacryl chloride monomer mentioned in step 3② is 1,3,5-benzenetricarboxyl chloride;

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

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

[0072] Test conditions: The pure water flux of the reverse osmosis membrane was tested under the conditions of 1.0 MPa pressure, 25℃ temperature, and pH 7.0. Subsequently, the salt rejection rate of the membrane was tested using a 2000 mg / L sodium chloride solution, and the ammonia nitrogen rejection efficiency was tested using a 100 mg N / L ammonium chloride solution. Under the same preparation conditions, at least three parallel experiments were conducted, and the average value of the experimental results was taken to improve the accuracy and reliability of the experimental data. The test data are recorded in Table 1.

[0073] Example 2: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 45 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 5 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-10 with an amination degree of 10%; step two ② yielded a polymer support layer APAEPO-10 with an amination degree of 10%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with an amination degree of 10%. Other steps and parameters were the same as in Example 1.

[0074] The test data were recorded in Table 1 using the test method described in Example 1.

[0075] Example 3: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 40 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 10 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-20 with a degree of amination of 20%; step two ② yielded a polymer support layer APAEPO-20 with a degree of amination of 20%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with a degree of amination of 20%. Other steps and parameters were the same as in Example 1.

[0076] The test data were recorded in Table 1 using the test method described in Example 1.

[0077] Example 4: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 30 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 20 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-40 with a degree of amination of 40%; step two ② yielded a polymer support layer APAEPO-40 with a degree of amination of 40%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with a degree of amination of 40%. Other steps and parameters were the same as in Example 1.

[0078] The test data were recorded in Table 1 using the test method described in Example 1.

[0079] Example 5: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 25 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 25 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-50 with a degree of amination of 50%; step two ② yielded a polymer support layer APAEPO-50 with a degree of amination of 50%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with a degree of amination of 50%. Other steps and parameters were the same as in Example 1.

[0080] The test data were recorded in Table 1 using the test method described in Example 1.

[0081] Example 6: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 20 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 30 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-60 with a degree of amination of 60%; step two ② yielded a polymer support layer APAEPO-60 with a degree of amination of 60%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with a degree of amination of 60%. Other steps and parameters were the same as in Example 1.

[0082] The test data were recorded in Table 1 using the test method described in Example 1.

[0083] Example 7: The difference between this example and Example 1 is as follows: In step one ①, 50 mmol of 4,4'-dihydroxybiphenyl and 10 mmol of bis(4-fluorophenyl)phenylphosphine oxide were used as the base monomers; 40 mmol of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide was used as the amination monomer; the base monomer, the amination monomer, and 55 mmol of anhydrous potassium carbonate were mixed and dissolved in a mixed solvent of 35 mL of toluene and 65 mL of N,N-dimethylacetamide to obtain a mixed solution; step one ③ yielded a polymer APAEPO-80 with an amination degree of 80%; step two ② yielded a polymer support layer APAEPO-80 with an amination degree of 80%; step three ④ yielded an ammonia nitrogen-retaining reverse osmosis membrane based on a polymer support layer with an amination degree of 80%. Other steps and parameters were the same as in Example 1.

[0084] The test data were recorded in Table 1 using the test method described in Example 1.

[0085] Comparative Example 1:

[0086] A conventional polyamide reverse osmosis membrane was prepared using a commercial polysulfone ultrafiltration membrane as a support layer;

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

[0088] The test data were recorded in Table 1 using the test method described in Example 1.

[0089] Table 1. Reverse osmosis membrane performance of different embodiments and Comparative Example 1

[0090]

[0091]

[0092] As can be seen from the data in Table 1, the measured amination degree (9.87%–79.36%) deviated little from the expected amination degree (10%–80%) in the experiment. This indicates that the amination degree of the support layer can be precisely controlled by adjusting the monomer ratio, providing a reliable basis for the targeted optimization of reverse osmosis membrane performance. The amination degree adjustment has the most significant effect on enhancing ammonia nitrogen rejection. Example 3, with an amination degree of 21.30%, achieved an ammonia nitrogen rejection rate as high as 99.13%, which is 8.81 percentage points higher than the traditional membrane (Comparative Example 1, 91.32%), and 7.01 percentage points higher than the unaminated membrane (Example 1, 92.12%). This is also significantly higher than the approximately 93% ammonia nitrogen rejection level of traditional polyamide reverse osmosis membranes in the prior art. Even when the degree of amination increased to 58.42% (Example 6), the ammonia nitrogen rejection rate remained stable at 98.04%, indicating that the amination support layer achieved targeted and efficient rejection of ammonia nitrogen through the synergistic effect of the "double 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 rejection in traditional membranes.

[0093] Amination modification of the support layer significantly improved desalination performance while enhancing ammonia nitrogen retention. Example 3 (amination degree 21.30%) achieved a NaCl retention rate of 99.22%, an increase of 1.61 percentage points compared to Comparative Example 1 (97.61%), and an increase of 2.48 percentage points compared to the unaminated Example 1 (96.74%). This result demonstrates that the amination support layer, by regulating the interfacial polymerization process, promotes the formation of a more cross-linked and uniform structure in the polyamide layer, thereby enhancing both ammonia nitrogen retention and salt ion sieving capacity, achieving synergistic and efficient separation of ammonia nitrogen and salt ions.

[0094] Furthermore, the amination modification of the support layer improves the water permeability of the reverse osmosis membrane. The water permeability coefficient of Example 3 is 2.93 LMH / bar, an increase of 49.5% compared to Comparative Example 1 (1.96 LMH / bar) and 38.9% compared to Example 1 without amination (2.11 LMH / bar). This is attributed to the more uniform pore distribution of the support layer due to moderate amination (around 20%) and the ultra-thin structure of the polyamide layer. While ensuring high selectivity, it effectively reduces the resistance to water molecule transport, meeting the urgent need for "high selectivity and high water flux" in practical applications. Excessive amination (e.g., 79.36%) will lead to a slight decline in various properties due to excessive reduction in the pore size of the support layer and a decrease in the crosslinking degree of the polyamide layer.

[0095] Figure 1 Image (a) is a cross-sectional scanning electron microscope image of the polymer support layer APAEPO-0 with an amination degree of 0 prepared in step 2 ② of Example 1; Figure 1 Image (b) is a cross-sectional scanning electron microscope image of the polymer support layer APAEPO-20 with an amination degree of 20% prepared in step 2② of Example 3;

[0096] Combination Figure 1 It can be seen that the support layer prepared in both embodiments exhibits an asymmetric structure composed of a dense skin and finger-like pores. As the degree of amination increases, the size of the finger-like macropores in the support layer decreases, the average pore size on its surface decreases, and the pore size distribution becomes narrower, which is beneficial for controlling the storage and diffusion behavior of aqueous monomers during interfacial polymerization.

[0097] Figure 2 Image (a) is a scanning electron microscope image of the polyamide reverse osmosis membrane prepared in step three, section four of Example 1. Figure 2 (b) is a scanning electron microscope image of the ammonia nitrogen-retaining reverse osmosis membrane prepared in step three of Example 3, section ④, based on a polymer support layer with an amination degree of 20%.

[0098] Combination Figure 2 It can be seen that the reverse osmosis membranes prepared in both embodiments exhibit the typical "ridge-valley" structure of polyamide membranes. Among them, the reverse osmosis membrane prepared with the unaminated support layer has a higher number of leaf-like protrusions on its surface. Figure 2 (a)) The uniformity is not good; while the "ridge" structure and "valley" structure of the ammonia nitrogen-retaining reverse osmosis membrane made of a support layer with a 20% amination degree are more evenly distributed, which increases the effective filtration area and is conducive to the improvement of water flux. At the same time, its cross-linking is more dense, which lays the structural foundation for improving the selectivity of ammonia nitrogen.

[0099] Figure 3 Image (a) is a cross-sectional transmission electron microscope image of the polyamide reverse osmosis membrane prepared in step three of Example 1, section ④. Figure 3 Image (b) is a cross-sectional transmission electron microscope image of the ammonia nitrogen-retaining reverse osmosis membrane prepared in step three of Example 3, section 4, based on a polymer support layer with an amination degree of 20%.

[0100] Combination Figure 3 It is known that the polyamide functional layer of the reverse osmosis membrane made of a support layer with a higher degree of amination has a smaller apparent thickness. This is due to the reduced diffusion rate of polyamine monomers during the interfacial polymerization process caused by the strong affinity between the aqueous monomer and the amination support layer, thus forming a thinner functional layer. This demonstrates the regulatory role of the amination support layer in the interfacial bonding process. This thin and dense functional layer is beneficial to overcoming the trade-off between selectivity and permeability, and simultaneously achieving high selectivity and high water flux.

[0101] This invention designs a support layer with controllable amination degree and constructs an ammonia nitrogen-rejecting reverse osmosis membrane based on it, increasing the ammonia nitrogen rejection rate to over 99% (a core breakthrough). At the same time, it enhances desalination performance and maintains an ideal water permeability coefficient, providing an innovative solution with selectivity, stability, and water production rate for high ammonia nitrogen reclaimed water treatment scenarios, and significantly expanding the application potential of reverse osmosis membranes in the field of efficient ammonia nitrogen separation.

[0102] The applicant declares that the present invention illustrates the ammonia nitrogen-retaining reverse osmosis membrane based on a controllable amination degree support layer and its preparation method through the above embodiments. However, the application of the present invention is not limited to the above examples. Those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims. Furthermore, the present invention is not limited to the embodiments shown, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A preparation method of an ammonia-nitrogen interception type reverse osmosis membrane based on an amine degree of control support layer, characterized by The preparation method is specifically carried out according to the following steps: I. Synthesis of Amination-Controllable Polyarylether Oxyphosphorus Polymers: ① Using 4,4'-dihydroxybiphenyl and bis(4-fluorophenyl)phenylphosphine oxide as base monomers and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide as amination monomer; the base monomer, amination monomer and anhydrous potassium carbonate are mixed and dissolved in a mixed solution of toluene and N,N-dimethylacetamide to obtain a mixed solution; ② Under nitrogen atmosphere protection, the mixed solution is first heated to the reflux temperature and kept at the reflux temperature for a certain time. After the toluene evaporates, the temperature is raised to the polycondensation reaction temperature and kept at the reflux temperature for a certain time to obtain the reaction product. ③ Add the reaction product to deionized water and soak it at a constant temperature for a certain period of time; repeat several times, filter, and then dry the solid material at a constant temperature to obtain amination polyarylene ether oxyphosphorus polymers with different degrees of amination. II. Preparation of polymer support layers with controllable amination degree using a solvent-inducible phase inversion method; ① Mix amination polyarylene ether oxyphosphorus polymers with different degrees of amination with organic solvents, then heat and stir at a constant temperature for a period of time, and then let stand to degas for a certain period of time to obtain casting solution; ② Under constant temperature and humidity conditions, the casting solution is scraped onto the nonwoven fabric, and deionized water is used as the coagulation bath to obtain a polymer support layer with controllable amination degree. III. Preparation of ammonia nitrogen-retaining reverse osmosis membranes using interfacial polymerization: ① Dissolve the polyamine monomer in deionized water and stir until homogeneous to obtain an aqueous solution; ② Dissolve the polyacryl chloride monomer in a hydrocarbon organic solvent and stir until homogeneous to obtain an oil phase solution; ③ Immerse the polymer support layer with controllable amination degree in an aqueous solution for a certain period of time, and then remove it and purge the surface of residual aqueous solution with nitrogen gas. ④ Immerse the nitrogen-purged support layer in an oil phase solution for a certain period of time to allow it to undergo amide polymerization reaction, thereby obtaining a polyamide functional layer on the surface of the support layer. After removal, 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 removal, cool it to room temperature to obtain an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree.

2. The preparation method of the ammonia-nitrogen interception type reverse osmosis membrane based on the amine degree of polymerization controllable support layer according to claim 1, characterized in that The amount of 4,4'-dihydroxybiphenyl mentioned in step 1① is in the ratio of the total amount of bis(4-fluorophenyl)phenylphosphine oxide and bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide to 1:(1~3); the amount of bis(4-fluorophenyl)-(3-aminophenyl)phosphine oxide mentioned 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 interception type reverse osmosis membrane based on an amine degree of control support layer according to claim 1, characterized in that The molar ratio of 4,4'-dihydroxybiphenyl to anhydrous potassium carbonate in step 1① is 1:(1~2); the molar ratio of the amount of 4,4'-dihydroxybiphenyl to the volume ratio of the organic solvent containing toluene in step 1① is 1 mmol:(1.5 mL~2 mL).

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

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

6. The method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that... The temperature for constant temperature immersion washing in step 1③ is 60℃~90℃, and the immersion time is 5h~10h; step 1③ is repeated 3~6 times; the temperature for constant temperature drying is 100℃~120℃, and the drying time is 24h~36h.

7. The method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that... The organic solvent mentioned 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 mentioned in step 2① is 10%~30%; the temperature of the constant temperature heating and stirring in step 2① is 60℃~100℃, the time of constant temperature heating and stirring is 24h~36h, and the standing degassing time is 6h~12h.

8. The method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that... In step 2②, the temperature range is 20℃~40℃ and the relative humidity range is 30%~60% under constant temperature and humidity conditions; in step 2②, the gap between the scraper blades is controlled to be 100μm~400μm during the scraping process.

9. The method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a support layer with controllable amination degree according to claim 1, characterized in that... The polyamine monomer mentioned 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 mentioned in step 3① is 0.5%~4.0%; the polyacrylamide chloride monomer mentioned in step 3② is one or more of 1,3-phenylenediamide chloride, 1,3,5-phenyltricarboxyamide chloride, and 1,2,4,5-phenyltetracarboxyamide chloride; the mass percentage concentration of the oil phase solution mentioned in step 3② is 0.05%~0.50%; the hydrocarbon organic solvent mentioned in step 3② is one or more of cyclohexane, n-hexane, Isopar G, toluene, and benzene.

10. The method for preparing an ammonia nitrogen-retaining reverse osmosis membrane based on a controllable amination degree support layer according to claim 1, characterized in that... In step 3.③, the polymer support layer with controllable amination degree is immersed in the aqueous phase solution for 30s~300s, and after removal, the surface residual aqueous phase solution is purged with nitrogen gas at a pressure of 0.1MPa~1.0MPa; in step 3.④, the nitrogen-purged support layer is immersed in the oil phase solution for 15s~300s; the hydrocarbon organic solvent mentioned in step 3.④ is one or more of cyclohexane, n-hexane, Isopar G, toluene and benzene; the heat treatment temperature mentioned in step 3.④ is 50℃~90℃, and the heat treatment time is 3min~20min.

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