SD membrane sheet based on interfacial polymerization of synergistic alcohol phase system and preparation method thereof

Abstract

The application relates to the technical field of membrane separation materials, and discloses an SD membrane sheet based on synergistic alcohol phase system interfacial polymerization and having high flux, controllable desalination rate and excellent operation stability and a preparation method thereof. The preparation method comprises the following steps: (1) adding a polymer into an organic solvent to obtain a mixed solution; (2) continuously adding a pore former to obtain a precursor solution; (3) performing vacuum defoaming treatment on the precursor solution and then scraping and coating the precursor solution on a carrier to obtain a base film; and (4) sequentially immersing the base film in a synergistic alcohol phase system solution and an oil phase solution to perform polyamide treatment, so that the SD membrane sheet is obtained; the synergistic alcohol phase system solution comprises interfacial polymerization amine monomers, a diffusion regulator, a network builder and functional copolymer monomers; the diffusion regulator comprises monohydric alcohol with carbon atoms less than or equal to 3; the network builder comprises polyhydric alcohol with carbon atoms less than or equal to 3 or a polymer thereof; the functional copolymer monomers comprise alcohol amine compounds with carbon atoms less than or equal to 4; and the oil phase solution comprises interfacial polymerization acid chloride monomers.

Description

Technical Field

[0001] This invention relates to the technical field of membrane separation materials, and more specifically, to SD membranes based on synergistic alcohol phase interfacial polymerization and their preparation methods. Background Technology

[0002] In typical zero-discharge processes, high-salinity wastewater, after pretreatment and concentration using conventional membrane methods (such as reverse osmosis), produces concentrated brine with extremely high total dissolved solids (TDS) (salt concentrations typically range from 10 to 80 g / L or even higher). This type of high-salinity brine has a complex composition, containing high concentrations of inorganic salts, recalcitrant organic matter, and scale inhibitors. Direct discharge of such brine would severely damage the ecological environment.

[0003] Currently, the final concentration of concentrated brine mainly relies on thermal evaporation (such as multi-effect evaporation (MED) and mechanical vapor recompression (MVR)) and special membrane methods (such as ultra-high pressure reverse osmosis (DTRO) and electrodialysis (ED). While MVR technology can achieve complete separation of water and salt, it has extremely high energy consumption and operating costs. To reduce the load on the evaporation section, membrane pre-concentration is usually performed before the brine enters the evaporator to improve the overall system recovery rate. However, when treating extremely high salinity feedwater, traditional reverse osmosis (RO) membranes, due to their extremely high desalination rate (typically >98%), cause a sharp deterioration in concentration polarization at the membrane interface. The system must overcome extremely high osmotic pressure and is highly susceptible to membrane scaling and fouling, severely limiting the concentration limit.

[0004] To overcome the aforementioned bottlenecks, the industry has proposed a novel process route: after the conventional reverse osmosis concentration stage, a specific desalination membrane with a moderate desalination rate (e.g., 30%–70%) is introduced for cyclic concentration. This type of membrane allows some monovalent salts to permeate, thereby effectively controlling the local salt concentration on the membrane surface and significantly reducing operating osmotic pressure and scaling tendency. The concentrated water after pre-concentration by the desalination membrane then enters the evaporator, which can significantly reduce the evaporation volume and energy consumption costs. However, in current commercial membrane products, RO membranes focus on extremely high desalination rates, while nanofiltration (NF) membranes focus on the selective retention of divalent ions (the desalination rate for monovalent salts such as NaCl is typically <30%). There is a significant product and technology gap in the moderate desalination rate range of 30–70%, especially for the concentration of high-salt wastewater from monovalent salt systems.

[0005] To prepare membranes with moderate desalination rates, existing techniques typically focus on adjusting the interfacial polymerization process of the polyamide functional layer. The functional layer of traditional polyamide composite membranes is often prepared by reacting m-phenylenediamine with trimesoyl chloride. Due to the extremely fast reaction rate and the highly dense cross-linked network formed, it is difficult to stably prepare a separation layer that combines both "moderate desalination rate" and "high water flux" simply by fine-tuning conventional process parameters. Therefore, existing techniques often attempt to achieve low desalination rates by reducing the cross-linking degree and density of the polyamide separation layer. Specific methods include: replacing m-phenylenediamine with sterically hindered monomers such as piperazine, directly reducing the concentration of monomers in the aqueous / oil phases, shortening the reaction time, or performing surface etching post-treatment. However, these improvements, which only address formulation and reaction conditions, generally suffer from the following insurmountable technical drawbacks in practical applications: The inherent contradiction between mechanical strength and flux stability: Simply reducing the degree of crosslinking to achieve a low desalination rate will severely weaken the mechanical strength of the polyamide functional layer. Under the high operating pressure required for actual high brine concentration, this loose membrane with low crosslinking is prone to severe compaction, which not only leads to a rapid decline in water flux and makes long-term stable operation impossible, but is also often accompanied by the loss of membrane separation selectivity, resulting in a dual dilemma of "flux-selectivity" and "low desalination-high pressure resistance".

[0006] The functional layer structure is difficult to control precisely and carries a high risk of defects: On traditional homogeneous, hydrophilic polysulfone substrates, the interfacial polymerization reaction is extremely fast and uniformly distributed. Simply changing the monomer formulation or reducing the reactant concentration can easily lead to non-selective pores or structural defects in the polyamide layer, resulting in extremely poor batch-to-batch stability of membrane performance. More importantly, due to the homogeneous nature of traditional substrates, existing processes are simply unable to induce the formation of a non-uniform polyamide network structure on the substrate that possesses both "loose pores (for low desalination)" and "high compressive strength framework (for high stability)". Summary of the Invention

[0007] This invention provides an SD membrane based on synergistic alcohol-phase interfacial polymerization, which combines high throughput, controllable desalination rate, and excellent operational stability, as well as its preparation method. The technical solution is as follows: The method for preparing SD films based on synergistic alcohol phase interfacial polymerization includes the following steps: (1) Add the polymer to the organic solvent under heating and stirring conditions. After the addition is completed, stir for a period of time to obtain a mixture; (2) After cooling the mixture, continue to add the pore-forming agent. After the addition is completed, stir for a period of time to obtain the precursor solution; (3) Vacuum degassing treatment is performed on the precursor solution to obtain the casting solution; the casting solution is coated onto the carrier and then subjected to gel bath treatment to obtain the base film; (4) The base film is sequentially immersed in a synergistic alcohol phase solution and an oil phase solution for polyamidation treatment to obtain the SD film; The synergistic alcohol phase system solution comprises an interfacial polymerizable amine monomer, a diffusion modifier, a network building agent, and a functional comonomer; the diffusion modifier comprises a monohydric alcohol with ≤3 carbon atoms; the network building agent comprises a polyhydric alcohol or its polymer with ≤3 carbon atoms; and the functional comonomer comprises an alcohol amine compound with ≤4 carbon atoms. The oil phase solution includes interfacial polymerized acyl chloride monomers.

[0008] The SD membrane based on synergistic alcohol phase interfacial polymerization of the present invention has the following advantages: (1) The diffusion regulator (monohydric alcohol) can effectively reduce the surface tension of the aqueous phase and regulate the diffusion rate of amine monomers to the oil phase, slowing down the interfacial polymerization rate, thereby accurately constructing a loose channel that achieves a moderate desalination rate. (2) The network building agent (polyhydric alcohol) increases the viscosity of the aqueous phase, which not only further regulates the diffusion process, but also induces the formation of a tough, high-compression-strength skeleton in the functional layer, effectively overcoming the mechanical strength weakening and compaction phenomenon under high pressure caused by simply reducing the degree of crosslinking, and ensuring the long-term stability of water flux. (3) The functional comonomer (alcoholic amine) participates in the interfacial polymerization reaction, introducing a large number of hydrophilic hydroxyl groups into the polyamide network, significantly improving the water flux of the membrane. (4) The synergistic effect of the diffusion regulator, network building agent and functional comonomer breaks through the bottleneck of the difficulty in accurately controlling the non-uniform polyamide network structure by simply fine-tuning the conventional formula, and realizes the comprehensive improvement of the overall performance of the SD membrane.

[0009] As a further improvement to the above-mentioned method for preparing SD film: in step (1), the polymer is polysulfone; the organic solvent is N,N-dimethylformamide; the polymer is added when the temperature reaches 50-80°C, and the mixture is stirred for 24-36 hours after the addition is completed.

[0010] As a further improvement to the above-mentioned method for preparing SD film: in step (2), the pore-forming agent is added when the mixture is cooled to 20-40°C, and the mixture is stirred for 12-24 hours after the addition is completed; the pore-forming agent is polyvinylpyrrolidone-K30 or polyethylene glycol; the mass ratio of organic solvent, polymer and pore-forming agent is (75-85):(15-25):(1-5).

[0011] As a further improvement to the above-mentioned method for preparing SD film: in step (3), the precursor solution is vacuum degassed at 50°C for 6 to 12 hours; using non-woven fabric as a carrier, the casting solution at 30 to 60°C is scraped onto the non-woven fabric with a thickness of 150 to 300 μm, evaporated in the air for 10 to 30 seconds, and then immersed in pure water at 10 to 25°C for 5 to 30 minutes for gel bath treatment.

[0012] As a further improvement to the above-mentioned method for preparing the SD membrane: In step (3), after the gel bath treatment, the membrane is first immersed in an aqueous solution of tannic acid with a concentration of 0.5-2 g / L for 1-3 minutes, then drained and immersed in an aqueous solution containing Ti with a concentration of 0.1-0.5 g / L. 4+ or Fe 3+ The reaction was carried out in an aqueous solution of metal salt for 1-2 minutes. After the reaction was completed, the sample was removed and washed with pure water. Thus, a metal-polyphenol network layer was constructed on the surface of the base film through the coordination reaction of tannic acid and metal ions. This modified layer can significantly improve the hydrophilicity and smoothness of the base film surface, providing an excellent reaction platform for subsequent interfacial polymerization. It not only reduces structural defects in the functional layer, but also greatly enhances the interfacial bonding force between the base film and the separation layer.

[0013] As a further improvement to the above-mentioned method for preparing SD films: in step (4), the interfacial polymeric amine monomer includes m-phenylenediamine and / or piperazine; the diffusion modifier includes ethanol and / or isopropanol; the network building agent includes glycerol and / or polyethylene glycol with an average molecular weight of 200 to 800; and the functional comonomer includes ethanolamine and / or diethanolamine.

[0014] As a further improvement to the above-mentioned method for preparing SD films: in the synergistic alcohol phase system solution, the mass ratio of interfacial polymeric amine monomer, diffusion regulator, network builder, functional comonomer and water is (0.5-2.5):(20-60):(1-10):(0.1-1):(30-70); the pH value of the synergistic alcohol phase system solution is adjusted to 10±0.5 using triethylamine; after immersing in the synergistic alcohol phase system solution for 30-90 seconds, the film is removed and the surface of the base film is swept with compressed air.

[0015] As a further improvement to the above-mentioned method for preparing SD film: in step (4), the interfacial polymerized acyl chloride monomer in the oil phase solution is trimesoyl chloride, and the solvent is n-hexane, isoparaffin, or cyclohexane; the mass fraction of trimesoyl chloride in the oil phase solution is 0.05-0.2 wt.%; after immersing in the oil phase solution for 20-60 seconds, it is taken out and heat-treated at 50-80°C for 1-5 minutes, and then the surface of the base film is rinsed with deionized water.

[0016] As a further improvement to the above-mentioned method for preparing SD membranes, the method includes immersing the membrane in a weakly alkaline aqueous solution containing 0.1–1 wt.% aminoethyl sulfobetaine or aminopropyl sulfobetaine at a temperature of 40–50°C and a pH of 8–9 for 2–5 minutes before heat treatment. After the reaction is complete, the membrane is removed and subjected to heat treatment. This utilizes the reaction of unreacted acyl chloride groups with sulfobetaine compounds to graft zwitterions onto the surface of the polyamide functional layer, endowing the membrane surface with extremely strong hydrophilicity and excellent antifouling properties (especially against organic and biological fouling), effectively mitigating flux decline during operation and extending the membrane's service life.

[0017] The SD film is prepared by the above-described preparation method.

[0018] In summary, the preparation method of SD membrane based on synergistic alcohol phase interfacial polymerization of the present invention has a simple process and low material cost. The obtained SD membrane can not only achieve appropriate concentration of high salt concentration water, but also has significantly improved mechanical strength. It can operate stably and continuously at high throughput under high pressure conditions, has a wider range of applications, and is highly practical.

[0019] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0020] The accompanying drawings, which form part of this invention, are used to aid in understanding the invention. The contents provided in the drawings and their descriptions in relation to the invention can be used to explain the invention, but do not constitute an improper limitation of the invention.

[0021] Figure 1 This is a low-magnification SEM image of the SD film based on synergistic alcohol phase interfacial polymerization in Example 9.

[0022] Figure 2 This is a high-magnification SEM image of the SD film based on the synergistic alcohol phase system interfacial polymerization of Example 9. Detailed Implementation

[0023] The present invention will now be clearly and completely described in conjunction with the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Before describing the present invention in conjunction with the accompanying drawings, it should be particularly noted that: The technical solutions and features provided in the various parts of this invention, including the following description, can be combined with each other without conflict.

[0024] Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0025] Regarding the terminology and units used in this invention: The terms "comprising," "having," and any variations thereof in the specification, claims, and related parts of this invention are intended to cover non-exclusive inclusion.

[0026] Example 1

[0027] The method for preparing SD films based on synergistic alcohol phase interfacial polymerization in this embodiment includes the following steps: (1) Add N,N-dimethylformamide to a three-necked flask, place the three-necked flask in an electric heating mantle and heat it while stirring. When the temperature reaches 60°C, add polysulfone to the N,N-dimethylformamide. After the addition is complete, stir for 24 hours to obtain a mixture.

[0028] (2) When the temperature of the mixture is lowered to 25°C, polyvinylpyrrolidone-K30 is added and the mixture is stirred for 12 hours to obtain the precursor solution; wherein, the mass ratio of N,N-dimethylformamide, polysulfone and polyvinylpyrrolidone-K30 is 80:17:3.

[0029] (3) The precursor solution was vacuum degassed at 50°C for 12 hours to obtain the casting solution; the casting solution at 40°C was coated onto the nonwoven fabric with a scraper with a blade spacing of 150 μm and a moving speed of 10 m / min. After pre-evaporation in the air for 30 seconds, it was placed in pure water at 25°C for 10 minutes for gel bath treatment, so that N,N-dimethylformamide and pure water could be exchanged and solidified into a film to obtain the base film.

[0030] (4) Polyamidation treatment of the base film, specifically: First, the base film is immersed in a synergistic alcohol phase system solution for 50 seconds. After immersion, it is removed and the surface of the base film is cleaned with compressed air. The synergistic alcohol phase system solution includes an interfacial polymeric amine monomer, a diffusion regulator, a network builder, and a functional comonomer. The solvent is water, and the pH is adjusted to 10±0.5 using triethylamine. The interfacial polymeric amine monomer is m-phenylenediamine, the diffusion regulator is ethanol, the network builder is glycerol, and the functional comonomer is ethanolamine. The mass ratio of the interfacial polymeric amine monomer, diffusion regulator, network builder, functional comonomer, and water is 1.8:30:2:0.6:60. The base film is first immersed in an oil phase solution for 30 seconds and then removed. The oil phase solution is a hexane solution of trimesoyl chloride with a mass fraction of 0.1 wt.%. Then, it is heat-treated at 50°C for 5 minutes and then rinsed with deionized water to obtain the SD film.

[0031] Tests showed that the flux of the SD membrane in this embodiment was 44.1 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 41.5%.

[0032] Example 2

[0033] Compared with Example 1, the difference in the preparation method of the SD film in this example is that the mass ratio of N,N-dimethylformamide, polysulfone, and polyvinylpyrrolidone-K30 is 75:15:1.

[0034] Tests showed that the flux of the SD membrane in this embodiment was 41.2 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 40.1%.

[0035] Example 3

[0036] Compared with Example 1, the difference in the preparation method of the SD film in this example is that the mass ratio of N,N-dimethylformamide, polysulfone, and polyvinylpyrrolidone-K30 is 85:25:5.

[0037] Tests showed that the flux of the SD membrane in this embodiment was 39.8 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 40.8%.

[0038] Example 4

[0039] Compared with Example 1, the difference in the preparation method of the SD film in this example is that the interfacial polymeric amine monomer is replaced with piperazine, and the mass ratio of interfacial polymeric amine monomer, diffusion regulator, network builder, functional comonomer and water is 0.5:20:1:0.1:30.

[0040] Tests showed that the flux of the SD membrane in this embodiment was 45.6 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 36.5%.

[0041] Example 5

[0042] Compared with Example 1, the difference in the preparation method of the SD film in this example is that the interfacial polymeric amine monomer is replaced with m-phenylenediamine and piperazine (mass ratio of 1:1), and the mass ratio of interfacial polymeric amine monomer, diffusion regulator, network building agent, functional comonomer and water is 2.5:60:10:1:70.

[0043] Tests showed that the flux of the SD membrane in this embodiment was 36.5 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 43.2%.

[0044] Example 6

[0045] Compared with Example 1, the difference in the preparation method of the SD film in this example is that the diffusion regulator is replaced with isopropanol; the network builder is replaced with polyethylene glycol 400; and the functional comonomer is still ethanolamine.

[0046] Tests showed that the flux of the SD membrane in this embodiment was 42.5 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 39.5%.

[0047] Example 7

[0048] Compared with Example 1, the difference in the preparation method of the SD film in this example is that: the diffusion regulator is still ethanol; the network builder is replaced with polyethylene glycol 400; and the functional comonomer is replaced with diethanolamine.

[0049] Tests showed that the flux of the SD membrane in this embodiment was 43.1 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 39.2%.

[0050] Example 8

[0051] Compared with Example 1, the difference in the preparation method of the SD membrane in this example is that: in step (3), after the gel bath treatment, the membrane is first immersed in a tannic acid aqueous solution with a concentration of 1 g / L for 2 minutes, then taken out and drained, and then immersed in a ferric chloride aqueous solution with a concentration of 0.3 g / L for 2 minutes. After the reaction is completed, it is taken out and washed with pure water.

[0052] Tests showed that the flux of the SD membrane in this embodiment was 54.5 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 (·h), the sodium chloride desalination rate is 38.6%.

[0053] Example 9

[0054] Compared with Example 8, the difference in the preparation method of the SD membrane in this example is that: in step (4), before heat treatment, the membrane is immersed in a weakly alkaline aqueous solution containing 0.5 wt.% aminoethyl sulfobetaine, at a temperature of 40-50°C and a pH of 8-9 for 4 minutes, and then taken out for heat treatment after the reaction is completed.

[0055] Tests showed that the flux of the SD membrane in this embodiment was 58.2 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 The sodium chloride desalination rate was 37.5%, and the flux after 48 hours of continuous operation was 56.8 L / (m³). 2 (·h), the sodium chloride desalination rate is 37.2%.

[0056] Compare with Example 1 Compared with Example 1, the difference in the preparation method of the SD film in this comparative example is that the synergistic alcohol phase system solution does not contain a diffusion modifier.

[0057] The flux of the SD membrane in this control example was tested to be 20.3 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 The sodium chloride desalination rate was 68.5%. Due to the absence of a diffusion modifier, the diffusion rate of amine monomers from the aqueous phase to the oil phase during interfacial polymerization was not effectively suppressed, resulting in an excessively rapid reaction rate. This led to highly cross-linked and dense polyamide functional layers, causing the desalination rate to rise sharply to 68.5%. Although still below 70%, the water flux decreased significantly to 20.3 L / (m³). 2 The ·h) is no longer sufficient to meet engineering requirements, indicating that diffusion regulators play a key role in slowing down the interfacial polymerization rate and accurately constructing loose channels to achieve a controllable moderate desalination rate.

[0058] Compare with Example 2 Compared with Example 1, the difference in the preparation method of the SD film in this comparative example is that the synergistic alcohol phase system solution does not contain a network building agent.

[0059] The flux of the SD membrane in this control example was tested to be 18.5 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 The sodium chloride desalination rate was 35.2%. Due to the absence of a network building agent, although the diffusion regulator in the synergistic alcohol phase system gave the functional layer a certain degree of porosity (low desalination rate), the functional layer underwent severe compaction at a high operating pressure of 70 bar due to the lack of a high-compression-strength framework constructed by polyols. This resulted in a sharp decline in flux to the lowest value among all samples, indicating that the network building agent plays a key role in maintaining high-pressure stability.

[0060] Compare with Example 3 Compared with Example 1, the difference in the preparation method of the SD film in this comparative example is that the synergistic alcohol phase system solution does not contain functional comonomers.

[0061] The flux of the SD membrane in this control example was tested to be 26.4 L / (m²) under conditions of 70 bar and 70,000 ppm. 2 The sodium chloride desalination rate was 45.1%. Due to the absence of functional comonomers, the polyamide network lacked hydrophilic hydroxyl groups introduced by alkanolamine compounds, resulting in a significant decrease in the overall hydrophilicity of the functional layer and a water flux reduction to 26.4 L / (m²). 2 ·h); Meanwhile, due to the lack of a moderate disruption effect of monofunctional alcohol amines on the crosslinking network, the degree of crosslinking of the functional layer is slightly improved, and the desalination rate increases to 45.1%, indicating that the functional comonomer plays a key role in improving the hydrophilicity of the membrane surface, increasing the flux, and synergistically regulating the desalination rate.

[0062] Figure 1 This is a low-magnification SEM image of the SD film from Example 9. Figure 2 This is a high-magnification SEM image of the SD film from Example 9. (See image for details.) Figure 1-2 As shown, the SD film has a smooth surface and contains pores of uniform size and distribution.

[0063] The flux and sodium chloride desalination rate of the SD membranes in the above examples and control examples were tested according to the "Test Methods for Reverse Osmosis Membranes" (GB / T 32373-2015), as follows: 1. Take several (no fewer than 4) samples. The samples should be free of obvious defects such as wrinkles and damage. The size of the samples should meet the requirements of completely covering the sealing ring of the evaluation cell. The effective membrane area of ​​the samples in the evaluation cell should not be less than 2.5 × 10⁻⁶. -3 m 2 Prepare a 70,000 ppm sodium chloride solution and adjust the pH to 7.5 ± 0.5.

[0064] 2. Immerse the sample in deionized water or distilled water for 30 minutes; 3. Place the sample into the evaluation cell, turn on the booster pump, and slowly adjust the operating pressure to 70 bar for cross-flow filtration. Maintain the temperature at 25℃±0.5℃ and run stably for 30 minutes. Collect the permeate produced after passing through the sample using a measuring cup (no less than 30 ml per sample), and use a stopwatch to calculate the required time. Determine the total dissolved solids (TDS) content of the original solution (sodium chloride solution) and the permeate separately according to GB / T 5750.4.

[0065] 4. After the test is completed, slowly reduce the operating pressure to below 0.05MPa and turn off the booster pump.

[0066] Flux is calculated using the following formula:

[0067] In the formula, J Flux, in L / (m 2 h); V The volume of the graduated cylinder sample is in liters (L). T Sampling time, in hours; A The effective area of ​​the sample is expressed in m². 2 .

[0068] The sodium chloride desalination rate is calculated using the following formula:

[0069] In the formula, R The desalination rate of sodium chloride is expressed as % (%). C P The TDS of the permeate is expressed in mg / L. C f The TDS of the stock solution is expressed in mg / L.

[0070] In this invention, the symbol "SD" is an abbreviation for Super Degree, which indicates high-concentration of ultra-high concentration liquids.

[0071] The foregoing has described the relevant content of the present invention. Those skilled in the art will be able to implement the present invention based on these descriptions. All other embodiments obtained by those skilled in the art based on the above description of the present invention without inventive effort should fall within the scope of protection of the present invention.

Claims

1. A method for preparing SD films based on synergistic interfacial polymerization of an alcohol phase system, characterized in that: Includes the following steps: (1) Add the polymer to the organic solvent under heating and stirring conditions. After the addition is completed, stir for a period of time to obtain a mixture; (2) After cooling the mixture, continue to add the pore-forming agent. After the addition is completed, stir for a period of time to obtain the precursor solution; (3) Vacuum degassing treatment is performed on the precursor solution to obtain the casting solution; the casting solution is coated onto the carrier and then subjected to gel bath treatment to obtain the base film; (4) The base film is sequentially immersed in a synergistic alcohol phase solution and an oil phase solution for polyamidation treatment to obtain the SD film; The synergistic alcohol phase system solution comprises an interfacial polymerizable amine monomer, a diffusion modifier, a network building agent, and a functional comonomer; the diffusion modifier comprises a monohydric alcohol with ≤3 carbon atoms; the network building agent comprises a polyhydric alcohol or its polymer with ≤3 carbon atoms; and the functional comonomer comprises an alcohol amine compound with ≤4 carbon atoms. The interfacial polymeric amine monomer includes m-phenylenediamine and / or piperazine; the diffusion modifier includes ethanol and / or isopropanol; the network builder includes glycerol and / or polyethylene glycol with an average molecular weight of 200-800; the functional comonomer includes ethanolamine and / or diethanolamine; In the synergistic alcohol phase system solution, the mass ratio of interfacial polymeric amine monomer, diffusion regulator, network builder, functional comonomer and water is (0.5-2.5):(20-60):(1-10):(0.1-1):(30-70); the pH value of the synergistic alcohol phase system solution is adjusted to 10±0.5 using triethylamine. The oil phase solution includes interfacial polymerized acyl chloride monomers.

2. The method for preparing the SD film as described in claim 1, characterized in that: In step (1), the polymer is polysulfone; the organic solvent is N,N-dimethylformamide; the polymer is added when the temperature reaches 50-80°C, and the mixture is stirred for 24-36 hours after the addition is completed.

3. The method for preparing the SD film as described in claim 1, characterized in that: In step (2), the mixture is cooled to 20-40°C before the pore-forming agent is added. After the addition is completed, the mixture is stirred for 12-24 hours. The pore-forming agent is polyvinylpyrrolidone-K30 or polyethylene glycol. The mass ratio of organic solvent, polymer and pore-forming agent is (75-85):(15-25):(1-5).

4. The method for preparing an SD film as described in claim 1, characterized in that: In step (3), the precursor solution is vacuum degassed at 50°C for 6 to 12 hours; using non-woven fabric as a carrier, the casting solution at 30 to 60°C is scraped onto the non-woven fabric with a thickness of 150 to 300 μm, evaporated in the air for 10 to 30 seconds, and then immersed in pure water at 10 to 25°C for 5 to 30 minutes for gel bath treatment.

5. The method for preparing the SD film as described in claim 4, characterized in that: Step (3) further includes, after gel bath treatment, immersing the membrane in a tannic acid aqueous solution with a concentration of 0.5–2 g / L for 1–3 minutes, draining it, and then immersing it in a solution containing Ti with a concentration of 0.1–0.5 g / L. 4+ or Fe 3+ React in an aqueous solution of a metal salt for 1-2 minutes. After the reaction is complete, remove the sample and wash it with pure water.

6. The method for preparing the SD film as described in claim 1, characterized in that: After immersing in the synergistic alcohol phase solution for 30–90 seconds, remove the film and clean the surface of the base film with a compressed air knife.

7. The method for preparing an SD film as described in claim 1, characterized in that: In step (4), the interfacial polymerized acyl chloride monomer in the oil phase solution is trimesoyl chloride, and the solvent is n-hexane, isoparaffin, or cyclohexane; the mass fraction of trimesoyl chloride in the oil phase solution is 0.05–0.2 wt.%; after immersing in the oil phase solution for 20–60 seconds, the substrate is removed, heat-treated at 50–80°C for 1–5 minutes, and then rinsed with deionized water.

8. The method for preparing an SD film as described in claim 7, characterized in that: This also includes immersing the membrane in a weakly alkaline aqueous solution containing 0.1–1 wt.% aminoethyl sulfobetaine or aminopropyl sulfobetaine at a temperature of 40–50°C and a pH of 8–9 for 2–5 minutes before heat treatment, and then removing it for heat treatment after the reaction is complete.

9. An SD film, characterized in that: It is prepared by the preparation method according to any one of claims 1-8.

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