Selecting layer material for reverse osmosis membrane and its preparation method and application
Self-polymerized microporous polyimide materials were prepared by copolymerization of aromatic diamines and dianhydrides, which solved the problems of chemical stability and chlorine resistance of reverse osmosis membranes, achieving highly selective and efficient water treatment effects, and are suitable for seawater desalination, food equipment and medical fields.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- SUZHOU INST OF NANO TECH & NANO BIONICS CHINESE ACEDEMY OF SCI
- Filing Date
- 2023-03-27
- Publication Date
- 2026-05-12
AI Technical Summary
Existing reverse osmosis membranes suffer from insufficient chemical stability, poor chlorine resistance, and poor oxidation resistance in water treatment, which affects their application performance.
A self-polymerized microporous polyimide material was prepared by copolymerization of aromatic diamine and dianhydride through dehydration condensation reaction as a selective layer to form a highly selective reverse osmosis membrane. A dense selective layer was then formed on the substrate membrane using a rotary evaporation coating method.
It improves the chemical stability and mass transfer rate of reverse osmosis membranes, significantly enhances chlorine resistance, and achieves a selectivity of 99%, making it suitable for seawater desalination, food processing equipment, and medical applications.
Smart Images
Figure CN116272428B_ABST
Abstract
Description
Technical Field
[0001] This invention relates to a reverse osmosis membrane material, specifically to a highly selective selective layer material for reverse osmosis membranes, its preparation method, and its application, belonging to the technical field of reverse osmosis membrane materials. Background Technology
[0002] Polyamide reverse osmosis (RO) membranes have achieved commercial success in desalination, but inherent defects in the material, such as poor resistance to active chlorine, hinder their application in water treatment. Improving chemical stability is crucial for membrane separation. For many years, extensive research has focused on enhancing the permeation selectivity and chemical stability of polyamide membranes through monomer selection, interfacial polymerization process control, post-treatment, and nanomaterial composites. However, these efforts are limited by their chemical composition and preparation methods. Cellulose acetate and polyester materials, another widely used type, also suffer from poor selectivity and acid / alkali resistance. Finding membrane materials with excellent chemical stability and selectivity, moving beyond existing material systems, remains a significant challenge in membrane separation modification. Therefore, designing the molecular structure of microporous polymer materials to fundamentally address the poor chlorine resistance, oxidation resistance, and acid / alkali resistance of existing reverse osmosis membranes, thereby leveraging their superior chemical stability, high specific surface area, and high free volume, and developing novel oxidation-resistant and acid / alkali-resistant polymer desalination membranes with excellent permeability and selectivity, has been a long-standing research direction in the field. Summary of the Invention
[0003] The main objective of this invention is to provide a highly selective selective layer material for reverse osmosis membranes and a method for preparing the same, so as to overcome the problem of insufficient chemical stability of reverse osmosis membranes in the prior art.
[0004] Another object of the present invention is to provide a method for preparing a reverse osmosis membrane using the selected layer material.
[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:
[0006] This invention provides a selective layer material for reverse osmosis membranes, which is a self-polymerizing microporous polymer obtained by copolymerization of aromatic diamines and dianhydrides (also known as "tetracarboxylic anhydride substances") via a dehydration condensation reaction. The dianhydrides include any one or a combination of two or more of 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, and 4,4′-(hexafluoroisopropylidene)phthalic anhydride.
[0007] This invention provides a method for preparing a selective layer material for a reverse osmosis membrane, comprising:
[0008] A mixed reaction system containing aromatic diamine, dianhydride and solvent is first prepolymerized, and then heated to carry out a dehydration condensation reaction to obtain a selector layer material for reverse osmosis membranes.
[0009] This invention also provides a method for preparing a reverse osmosis membrane, comprising:
[0010] The aforementioned selective layer material for reverse osmosis membranes is mixed with a casting solution solvent to form a polymer casting solution;
[0011] The polymer casting solution is applied to the substrate membrane for film formation treatment to obtain a reverse osmosis membrane with a selective layer.
[0012] Accordingly, embodiments of the present invention also provide a reverse osmosis membrane with a selective layer prepared by the aforementioned preparation method.
[0013] The embodiments of the present invention also provide the application of the aforementioned selective layer material for reverse osmosis membranes or reverse osmosis membranes in the fields of seawater desalination equipment, food processing equipment, preparation of porous adsorption materials, membrane separation, or medical and pharmaceutical applications.
[0014] Compared with the prior art, the beneficial effects of the present invention are as follows:
[0015] 1) The selective layer material provided by this invention is a self-polymerizing microporous polyimide polymer with a rigid main chain. The polymer's amide bonds lack hydrogen atoms, thus lacking sites for attack by active chlorine. The rigid main chain exhibits strong chemical stability and its resistance to active chlorine is far superior to that of commercial polyamide reverse osmosis membranes. The self-polymerizing microporous polyimide generates a large number of micropores through main chain stacking, resulting in a very high mass transfer rate as a separation membrane material.
[0016] 2) This invention uses a rotary evaporation coating method to quickly form a dense selective layer with good adhesion on the substrate membrane. It does not have special requirements for the substrate membrane and can easily and conveniently prepare a stable reverse osmosis membrane.
[0017] 3) The reverse osmosis membrane provided by this invention can achieve a selectivity of 99% for sodium chloride and a chlorine resistance of over 12,000 ppm·h. This reverse osmosis membrane with good selectivity and outstanding oxidation resistance has important applications in seawater desalination, food and other high-purity water equipment, membrane separation, and medical fields. Attached Figure Description
[0018] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0019] Figure 1 This is a partial cross-sectional SEM image of the reverse osmosis membrane obtained in Example 1 of the present invention;
[0020] Figure 2 This is a partial surface SEM image of the reverse osmosis membrane obtained in Example 1 of the present invention;
[0021] Figure 3 This is a cross-sectional SEM image of the reverse osmosis membrane obtained in Example 1 of the present invention;
[0022] Figure 4 This is a SEM image of the overall surface of the reverse osmosis membrane obtained in Example 1 of the present invention;
[0023] Figure 5 The graph shows the NaCl retention of polymers prepared by different molar ratios of 3,5-diaminobenzoic acid and 2,3,5,6-tetramethyl-1,4-phenylenediamine in Example 1 of this invention (the amount of anhydride monomer added is the molar sum of the diamines).
[0024] Figure 6 This is a chlorine resistance test diagram for the ratio of 3,5-diaminobenzoic acid and 2,3,5,6-tetramethyl-1,4-phenylenediamine in Example 1 of the present invention, when the ratio is 2:3. Detailed Implementation
[0025] In view of the problems of existing technology, the inventors of this case, through long-term research and extensive practice, have proposed the technical solution of this invention. The main method involves preparing a reverse osmosis membrane by polymerizing aromatic diamines and tetracarboxylic anhydride to obtain self-polymerized microporous polyimide, which serves as the selective layer material. The rigidity of the main chain and the lack of active chlorine attack sites significantly improve its stability and oxidation resistance. Based on this result, the inventors of this case have proposed a method for preparing reverse osmosis membrane materials. The technical solution of this invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of this invention, not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.
[0026] One aspect of the present invention provides a selective layer material for a reverse osmosis membrane, which is a self-polymerized microporous polymer obtained by copolymerization of aromatic diamine and dianhydride via a dehydration condensation reaction.
[0027] In some embodiments, the aromatic diamine includes any one or a combination of two or more of 2,3,5,6-tetramethyl-1,4-phenylenediamine, bis(4-aminophenyl)sulfone, 3,5-diaminobenzoic acid, telrogalodiamine monomer, etc., but is not limited thereto.
[0028] In some embodiments, the dianhydride includes any one or a combination of two or more of 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, and 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, but is not limited thereto.
[0029] The selective layer material provided by the above technical solution of this invention is a self-polymerizing microporous polyimide polymer with a rigid main chain. The polymer amide bonds lack hydrogen atoms, thus lacking sites for attack by active chlorine. The rigid main chain exhibits strong chemical stability and its resistance to active chlorine is far superior to that of commercial polyamide reverse osmosis membranes. This self-polymerizing microporous polyimide generates a large number of micropores through main chain stacking, resulting in a very high mass transfer rate as a separation membrane material.
[0030] Compared to ordinary polyimide materials, the polyimide of this invention uses monomers that, in addition to reactive functional groups, possess torsion centers and rigid main chain structures. Therefore, these rigid torsion centers and rigid main chains are also present in the polymer. During the stacking process, due to the rigidity of the main chain, the polymer cannot effectively encapsulate and stack, resulting in a large number of micropores. Thus, it is superior to ordinary polyimide in terms of micropore structure, and also brings higher mass transfer performance. The specific surface area of the self-polymerizing microporous polymer is 200 m² / g. 2 g -1 The above pore size distribution is as follows In terms of high selectivity, the rejection rate for NaCl reaches 99%, and the rejection rate for boric acid under neutral conditions reaches 83.4%.
[0031] Another aspect of the present invention provides a method for preparing the aforementioned selective layer material for reverse osmosis membranes, comprising:
[0032] A mixed reaction system containing aromatic diamine, dianhydride and solvent is first prepolymerized, and then heated to carry out a dehydration condensation reaction to obtain a selector layer material for reverse osmosis membranes.
[0033] In some embodiments, the selective layer material for reverse osmosis membranes is obtained through a two-step reaction. The preparation method may specifically include: prepolymerizing a mixed reaction system containing aromatic diamine, dianhydride and solvent at 50-80°C for 8-18 hours, and then heating to 200-250°C for a dehydration condensation reaction for at least 4 hours, preferably 4-6 hours, until the system becomes viscous, thereby obtaining the selective layer material for reverse osmosis membranes.
[0034] Furthermore, after the reaction is complete, a solvent phase inversion and washing are required. Specifically, this may include: pouring the completed reaction system into a methanol solution for phase inversion, and then washing away the reaction solvent with methanol-ethanol solutions multiple times.
[0035] In some embodiments, the aromatic diamine includes any one or a combination of two or more of bis(4-aminophenyl) sulfone, 3,5-diaminobenzoic acid, telrogalodiamine monomer, etc., but is not limited thereto.
[0036] In some embodiments, the tetracarboxylic anhydride includes any one or a combination of two or more of 3,3',4,4'-diphenylsulfone tetracarboxylic anhydride, 3,3',4,4'-benzophenone tetracarboxylic anhydride, and pyromellitic tetracarboxylic anhydride, but is not limited thereto.
[0037] In some embodiments, the proportion of monomers is determined according to the ratio of functional group anhydride to amino group, wherein the molar ratio of the anhydride functional group in the tetracarboxylic anhydride to the amino group in the aromatic diamine is 1:1.
[0038] Furthermore, the solvent is selected from those with a boiling point above 200°C and good solubility, such as ultra-dry N,N-dimethylpyrrolidone, but not limited thereto. The entire reaction process of the selective layer material of this invention must ensure that the system is dry and anhydrous. Moreover, the raw materials used in polymerization need to be thoroughly dried, and a water separator containing toluene is required during the reaction to azeotropically remove water from the reaction products.
[0039] Another aspect of the present invention provides a method for preparing a reverse osmosis membrane, comprising:
[0040] Mix any of the aforementioned selective layer materials for reverse osmosis membranes with a casting solution solvent to form a polymer casting solution;
[0041] The polymer casting solution is applied to the substrate membrane for film formation treatment to obtain a reverse osmosis membrane with a selective layer.
[0042] In some embodiments, the casting solution solvent may be any one or a combination of two of tetrahydrofuran, N,N-dimethylformamide, etc., but is not limited thereto.
[0043] Furthermore, the concentration of the selective layer material (i.e., polymer) for the reverse osmosis membrane in the polymer casting solution is 2–6 wt%.
[0044] Furthermore, the substrate membrane can be a commercial ultrafiltration membrane, but is not limited to this.
[0045] In some embodiments, the film-forming process is performed at a temperature of 20–30°C.
[0046] Furthermore, the film-forming process includes a rotary evaporation coating method with a rotation speed of 3000–5000 r / min and a rotary evaporation coating time of 20–50 s.
[0047] In some more specific embodiments, the present invention obtains a self-polymerizing microporous polymer by polymerizing an aromatic diamine and tetracarboxylic anhydride, which is used as a selective layer material, and a highly selective reverse osmosis membrane is prepared by rotary evaporation coating on a supporting substrate membrane.
[0048] In a more preferred embodiment, the main steps of the reverse osmosis membrane preparation method are as follows:
[0049] Step 1: Dissolve the selective layer material (i.e., polymer) for the reverse osmosis membrane into the casting solution solvent to prepare the casting solution;
[0050] Step 2: Select an ultrafiltration cross-linked substrate membrane, allow it to dry thoroughly and keep it flat;
[0051] Step 3: Lay the base film flat on the spin coater, control the temperature at 20-30℃, take 3-5ml of casting solution, control the rotation speed at 3000-5000r / min, and spin evaporate the film for 20-50s.
[0052] Step 4: Immerse the composite membrane coated by rotary evaporation in pure water for preservation to obtain a reverse osmosis membrane with a highly selective selective layer thickness of 200–700 nm.
[0053] In summary, this invention uses a rotary evaporation coating method to quickly form a dense selective layer with good adhesion on the substrate membrane, without requiring special substrate membrane, and can easily and conveniently prepare a stable reverse osmosis membrane.
[0054] Accordingly, another aspect of the present invention provides a reverse osmosis membrane prepared by the aforementioned preparation method, wherein the thickness of the selective layer is 200–700 nm.
[0055] Furthermore, the selective layer material prepared by the present invention through a simple polycondensation reaction can be spin-coated to obtain a thin film composite membrane structure with an ultra-thin selective layer. The selectivity of this reverse osmosis membrane to NaCl reaches more than 90%, preferably more than 95%, and it can withstand more than 12,000 ppm·h of chlorine at an active chlorine concentration of 500 ppm. It has high mass transfer efficiency and good separation effect. The preparation method and materials are universal.
[0056] Another aspect of the present invention provides the aforementioned selective layer material for reverse osmosis membranes, or reverse osmosis membranes with good selectivity and outstanding oxidation resistance, for important applications in seawater desalination, high-purity water equipment for food processing, preparation of porous adsorption materials, membrane separation, and medical applications.
[0057] The following describes the technical solution of the present invention in more detail with reference to several preferred embodiments. The specific embodiments described below are only for further illustration and explanation of the present invention and are not intended to limit the present invention. In the embodiments described below, the base membrane is exemplified by cross-linked P84 or PAN ultrafiltration membrane; the diamine monomers are exemplified by 2,3,5,6-tetramethyl-1,4-phenylenediamine, bis(4-aminophenyl)sulfone, 3,5-diaminobenzoic acid, and telregrudiamine; the dianhydride monomers are exemplified by 4,4′-(hexafluoroisopropylidene)diphthalic anhydride, and tetracarboxylic anhydrides including 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, and pyromellitic tetracarboxylic dianhydride; the polymerization reaction solvent is exemplified by ultra-dry N,N-dimethylpyrrolidone; and the casting solution solvent is exemplified by tetrahydrofuran and N,N-dimethylformamide. Any simple modifications based on the method of the present invention should be within the scope of protection of the claims.
[0058] Example 1
[0059] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0060] Step 1: Add diamine monomers (2,3,5,6-tetramethyl-1,4-phenylenediamine and 3,5-diaminobenzoic acid in a molar ratio of 2:3-3:2), and add 4,4′-(hexafluoroisopropylidene) phthalic anhydride in the same amount as the sum of the molar amounts of the diamine monomers, and dissolve in ultra-dry N,N-dimethylpyrrolidone.
[0061] Step 2: After dissolution, heat to 60℃, stir evenly, and allow to pre-react for 10 hours;
[0062] Step 3: Add a water separator containing toluene to the condenser, heat to 200°C, and react for 6 hours;
[0063] Step 4: Slowly pour the obtained solution into methanol to carry out phase inversion, wash and dry to obtain PI-COOH polymer;
[0064] Step 5: Dissolve the polymer in tetrahydrofuran to prepare a 2wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater. Control the temperature at 30℃. Take 5ml of the casting solution and control the rotation speed at 3000r / min. Rotary evaporate the membrane for 50s.
[0065] The partial cross-sectional SEM image of the reverse osmosis membrane obtained in this embodiment is shown below. Figure 1 As shown, the SEM image reveals the thickness and morphology of the reverse osmosis membrane, with a selective layer thickness of approximately 350-450 nm; a local surface SEM image of the reverse osmosis membrane is shown below. Figure 2 As shown in the SEM image, the prepared membrane is a dense, smooth, and defect-free separation membrane. The overall cross-section and surface image of the reverse osmosis membrane are shown below. Figure 3 andFigure 4 As shown. For data on NaCl retention of polymers prepared by different molar ratios (the amount of anhydride monomer added is the molar sum of the diamines) of 3,5-diaminobenzoic acid and 2,3,5,6-tetramethyl-1,4-phenylenediamine in the reverse osmosis membrane, please refer to [reference needed]. Figure 5 The selectivity for NaCl is over 99%, and the chlorine resistance is as follows when the ratio of 3,5-diaminobenzoic acid and 2,3,5,6-tetramethyl-1,4-phenylenediamine is 2:3. Figure 6 As shown, this indicates that a rejection rate of over 95% can be maintained at 14000 ppm·h.
[0066] Example 2
[0067] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0068] Step 1: Add diamine monomers (the molar ratio of telrogallodiamine and 3,5-diaminobenzoic acid is 4:1), and the amount of 4,4′-(hexafluoroisopropylidene) phthalic anhydride added is the sum of the molar amounts of the diamine monomers, and dissolve in ultra-dry N,N-dimethylpyrrolidone.
[0069] Step 2: After dissolution, heat to 70℃, stir evenly, and allow to pre-react for 15 hours;
[0070] Step 3: Add a water separator containing toluene to the condenser, heat to 220°C, and react for 5 hours;
[0071] Step 4: Slowly pour the obtained solution into methanol for phase inversion, wash and dry to obtain PI-TB polymer;
[0072] Step 5: Dissolve the polymer in tetrahydrofuran to prepare a 5wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater. Control the temperature at 20℃. Take 3-5ml of the casting solution. Control the rotation speed at 5000r / min. Rotary evaporate the membrane for 20s.
[0073] The cross-sectional SEM image and surface SEM image of the reverse osmosis membrane obtained in this embodiment are consistent with... Figures 1-4 Similarly, tests showed that the reverse osmosis membrane exhibits a selectivity of over 98% for NaCl and can withstand chlorine concentrations of over 12,000 ppm·h at an active chlorine concentration of 500 ppm.
[0074] Example 3
[0075] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0076] Step 1: Add dianhydride (the molar ratio of pyromellitic dianhydride to 3,3',4,4'-diphenylsulfone tetracarboxylic acid dianhydride is 1:1), add diamine monomer (the molar ratio of telrogallodiamine to 3,5-diaminobenzoic acid is 1:4), the total amount of dianhydride and diamine monomer added in the end is the same, and dissolve in ultra-dry N,N-dimethylpyrrolidone;
[0077] Step 2: After dissolution, heat to 50°C, stir evenly, and allow to pre-react for 18 hours;
[0078] Step 3: Add a water separator containing toluene to the condenser, heat to 250°C, and react for 4 hours;
[0079] Step 4: Slowly pour the obtained solution into methanol for phase inversion, wash and dry to obtain PI-SDBA polymer;
[0080] Step 5: Dissolve the polymer in tetrahydrofuran to prepare a 4wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater, control the temperature at 25℃, measure 3-5ml of the casting solution, control the rotation speed at 4000r / min, and spin-evaporate the membrane for 30s.
[0081] The cross-sectional SEM image and surface SEM image of the reverse osmosis membrane obtained in this embodiment are consistent with... Figures 1-4 Similarly, tests showed that the reverse osmosis membrane exhibits a selectivity of over 95% for NaCl and can withstand chlorine concentrations exceeding 12,000 ppm·h at an active chlorine concentration of 500 ppm.
[0082] Example 4
[0083] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0084] Step 1: Add diamine monomers (the molar ratio of bis(4-aminophenyl) sulfone and 3,5-diaminobenzoic acid can be 1:4-4:1), and the amount of 3,3′,4,4′-benzophenone tetracarboxylic dianhydride added is the sum of the molar amounts of the diamine monomers, and dissolve in ultra-dry N,N-dimethylpyrrolidone.
[0085] Step 2: After dissolution, heat to 80℃, stir evenly, and allow to pre-react for 8 hours;
[0086] Step 3: Add a water separator containing toluene to the condenser, heat to 230°C, and react for 5 hours;
[0087] Step 4: Slowly pour the obtained solution into methanol for phase inversion, wash and dry to obtain PI-MPD polymer;
[0088] Step 5: Dissolve the polymer in tetrahydrofuran to prepare a 3wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater. Control the temperature at 30℃. Take 3-5 ml of the casting solution. Control the rotation speed at 5000 r / min. Rotary evaporate the membrane for 40 seconds.
[0089] The cross-sectional SEM image and surface SEM image of the reverse osmosis membrane obtained in this embodiment are consistent with... Figures 1-4 Similarly, tests showed that the reverse osmosis membrane exhibits a selectivity of over 95% for NaCl and can withstand chlorine concentrations exceeding 12,000 ppm·h at an active chlorine concentration of 500 ppm.
[0090] Example 5
[0091] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0092] Step 1: Add diamine monomer (the molar ratio of bis(4-aminophenyl)sulfone and 3,5-diaminobenzoic acid is 2:1), the amount of pyromellitic dianhydride added is the sum of the molar amounts of the diamine monomer, and dissolve in ultra-dry N,N-dimethylpyrrolidone.
[0093] Step 2: After dissolution, heat to 70℃, stir evenly, and allow to pre-react for 12 hours;
[0094] Step 3: Add a water separator containing toluene to the condenser, heat to 200°C, and react for 6 hours;
[0095] Step 4: Slowly pour the obtained solution into methanol to carry out phase inversion, wash and dry to obtain PI-PMDA polymer;
[0096] Step 5: Dissolve the polymer in tetrahydrofuran to prepare a 4wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater. Control the temperature at 20℃. Take 3-5ml of the casting solution. Control the rotation speed at 3500r / min. Rotary evaporate the membrane for 50s.
[0097] The cross-sectional SEM image and surface SEM image of the reverse osmosis membrane obtained in this embodiment are consistent with... Figures 1-4 Similarly, tests showed that the reverse osmosis membrane exhibits a selectivity of over 95% for NaCl and can withstand chlorine concentrations exceeding 12,000 ppm·h at an active chlorine concentration of 500 ppm.
[0098] Example 6
[0099] The specific steps for preparing the reverse osmosis membrane in this embodiment are as follows:
[0100] Step 1: Add dianhydride monomers (the molar ratio of pyromellitic dianhydride and 4,4′-(hexafluoroisopropylidene) phthalic anhydride is 4:1), and the amount of 3,5-diaminobenzoic acid added is the sum of the molar amounts of the dianhydride monomers, and dissolve in ultra-dry N,N-dimethylpyrrolidone.
[0101] Step 2: After dissolution, heat to 60℃, stir evenly, and allow to pre-react for 18 hours;
[0102] Step 3: Add a water separator containing toluene to the condenser, heat to 240℃, and react for 5 hours;
[0103] Step 4: Slowly pour the obtained solution into methanol to carry out phase inversion, wash and dry to obtain PI-COOH polymer;
[0104] Step 5: Dissolve the polymer in N,N-dimethylformamide to prepare a 3wt% casting solution. Spread the cross-linked P84 ultrafiltration membrane on a spin coater, control the temperature at 28℃, measure 3-5ml of the casting solution, control the rotation speed at 4500r / min, and spin-evaporate the membrane for 35s.
[0105] The cross-sectional SEM image and surface SEM image of the reverse osmosis membrane obtained in this embodiment are consistent with... Figures 1-4 Similarly, tests showed that the reverse osmosis membrane exhibits a selectivity of over 95% for NaCl and can withstand chlorine concentrations exceeding 12,000 ppm·h at an active chlorine concentration of 500 ppm.
[0106] Comparative Example 1
[0107] The preparation process of this comparative example is basically the same as that of Example 1, except that the aromatic diamine (3,5-diaminobenzoic acid) is replaced with ethylenediamine.
[0108] Since the polyimide prepared in this invention is an inherently microporous polymer, it must have a rigid main chain and a torsion center. Therefore, if ethylenediamine is used instead, the polymer will lose its microporous properties and become an ordinary polyimide material. Its selectivity for NaCl and its chlorine resistance at an active chlorine concentration of 500 ppm are also significantly worse than those in Example 1.
[0109] Comparative Example 2
[0110] The preparation process of this comparative example is basically the same as that of Example 1, the main difference being that tetracarboxylic anhydride is replaced with other aromatic materials. This will affect the pore size distribution, specific surface area, and hydrophilicity, and the separation effect of salt will fluctuate.
[0111] In addition, the inventors of this case also conducted experiments with other raw materials, process operations, and process conditions described in this specification, referring to the aforementioned embodiments, and obtained relatively ideal results in all cases.
[0112] It should be understood that the above are merely specific application examples of the present invention and do not constitute any limitation on the scope of protection of the present invention. All technical solutions formed by equivalent transformations or equivalent substitutions fall within the scope of protection of the present invention.
Claims
1. A method for preparing a reverse osmosis membrane, characterized in that, include: A selective layer material for reverse osmosis membranes is mixed with a casting solution solvent to form a polymer casting solution. The selective layer material is a self-polymerizing microporous polymer obtained by copolymerization of aromatic diamines and dianhydrides via a dehydration condensation reaction. The dianhydride is selected from any one or a combination of two or more of 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride, 3,3',4,4'-benzophenone tetracarboxylic dianhydride, pyromellitic dianhydride, and 4,4'-(hexafluoroisopropylidene)diphthalic anhydride. The aromatic diamine is selected from any one or a combination of two or more of 2,3,5,6-tetramethyl-1,4-phenylenediamine, bis(4-aminophenyl)sulfone, 3,5-diaminobenzoic acid, and telroglycan diamine monomers, and different types of dianhydride and aromatic diamine are considered as one type. The specific surface area of the self-polymerizing microporous polymer is 200 m² / g. 2 g -1 The pore size distribution is 4-7 Å. The preparation method of the selective layer material includes: prepolymerizing a mixed reaction system containing an aromatic diamine, a dianhydride, and a solvent at 50-80°C for 8-18 h, and then heating to 200-250°C for a dehydration condensation reaction for more than 4 h to obtain the selective layer material; the molar ratio of the anhydride functional group in the dianhydride to the amino group in the aromatic diamine is 1:
1. The polymer casting solution is applied to the substrate membrane for film formation treatment to obtain a reverse osmosis membrane with a selective layer. The thickness of the selective layer is 200~700nm, the selectivity of the reverse osmosis membrane to NaCl is above 90%, and it can withstand chlorine concentrations of 500ppm for more than 12000ppm·h.
2. The preparation method according to claim 1, characterized in that: The casting solution solvent is selected from any one or a combination of two of tetrahydrofuran and N,N-dimethylformamide.
3. The preparation method according to claim 1, characterized in that: The concentration of the polymer casting solution is 2~6wt%.
4. The preparation method according to claim 1, characterized in that: The film-forming process is performed at a temperature of 20~30℃.
5. The preparation method according to claim 1, characterized in that: The film-forming process includes a rotary evaporation coating method with a rotation speed of 3000~5000 r / min and a rotary evaporation coating time of 20~50 s.
6. The preparation method according to claim 1, characterized in that: The bottom membrane is an ultrafiltration membrane.
7. The preparation method according to claim 1, characterized in that: The reverse osmosis membrane has a selectivity of over 95% for NaCl.
8. The preparation method according to claim 1, characterized in that: The dehydration condensation reaction takes 4 to 6 hours.
9. The preparation method according to claim 1, characterized in that: The solvent is ultra-dry N,N-dimethylpyrrolidone.
10. The reverse osmosis membrane prepared by any one of claims 1-9 is used in seawater desalination equipment, food processing equipment, preparation of porous adsorption materials, membrane separation, or in the fields of medicine and healthcare.