A high-pressure reverse osmosis membrane and a preparation method thereof

Abstract

The application relates to a high-pressure reverse osmosis membrane and a preparation method thereof, and relates to the technical field of membrane separation, wherein the high-pressure reverse osmosis membrane is sequentially provided with a polyester non-woven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer and a self-lubricating protective layer from bottom to top. The desalination layer of the reverse osmosis membrane of the application is not only firmly combined with the support layer initially, but also can self-repair the bonding interface after suffering from repeated impacts and causing slight damage, and has better resistance to scratching and bending during the disassembly process, thereby further prolonging the service life of the membrane element, reducing the replacement frequency and guaranteeing the system operation.

Description

Technical Field

[0001] This invention relates to the field of membrane separation technology, and in particular to a high-pressure reverse osmosis membrane and its preparation method. Background Technology

[0002] Reverse osmosis membranes are the core components of seawater desalination and pure water production. Most reverse osmosis membranes have a three-layer composite structure: a sturdy non-woven fabric bottom layer provides support, a porous polysulfone layer in the middle, and an extremely thin polyamide desalination layer on top that performs the actual filtration. During normal use, water passes through the desalination layer under high pressure, while salt and impurities are retained.

[0003] However, in actual plant operation, reverse osmosis systems frequently encounter situations such as sudden start-up or shutdown of high-pressure pumps and excessively rapid valve opening and closing. These operations cause violent oscillations in the water flow within the pipeline, generating impact forces similar to water hammer. Sometimes, the pressure on the permeate side of the membrane becomes abnormally higher than that on the feed side, creating reverse pressure, or back pressure. Both of these situations cause physical damage to the membrane; the uppermost desalination layer may blister and peel, similar to damp wall plaster, or even detach entirely from the underlying support layer. Once the desalination layer peels off, the membrane's desalination capacity drops drastically, the permeate water quality deteriorates, and the entire membrane element must be replaced, resulting in significant economic losses.

[0004] To address the issue of easy peeling of the desalination layer, the factory currently mainly adopts external protection measures such as installing buffer tanks and optimizing valve opening and closing procedures. While these methods have some effect, they do not fundamentally improve the adhesion between the desalination layer and the support layer. Peeling can still occur if there is operational error or excessive impact.

[0005] In membrane material research, some techniques attempt to chemically bond the desalination layer and support layer more tightly by coating the support layer with a layer such as polyethyleneimine or dopamine, or by adding anchoring molecules during interfacial polymerization. While these methods do increase the initial tensile force required for peeling, they essentially create a one-time, irreparable bond. Once subjected to repeated impacts or bending, this bond will crack and cannot be re-bonded. Reverse osmosis membranes withstand thousands of water hammer and start-up / shutdown shocks during actual service. This repeated fatigue gradually breaks the chemical bonds, causing damage to accumulate and ultimately leading to large-area desalination layer peeling.

[0006] In addition, there is a long-overlooked problem: when membrane elements need to be removed from the pressure vessel for cleaning or replacement, operators have to pull the wet membrane, which is up to 1 meter long and weighs more than 20 kilograms, out of the narrow shell. During this process, the membrane surface will inevitably scrape against the shell wall or bend due to uneven stress. These mechanical actions can also cause micro-peeling of the desalination layer.

[0007] Therefore, there is an urgent need in this field to develop a new type of reverse osmosis membrane to solve the problem that the desalination layer and the support layer in the reverse osmosis membrane are not firmly bonded and cannot self-repair the bonding interface after being subjected to repeated impacts that cause minor damage. Summary of the Invention

[0008] To address the aforementioned technical problems, this invention provides a high-pressure reverse osmosis membrane and its preparation method. The reverse osmosis membrane of this invention not only exhibits a strong initial bond between the desalination layer and the support layer, but also possesses the ability to self-repair the bonding interface after suffering minor damage from repeated impacts. Furthermore, it demonstrates better resistance to scratches and bends during disassembly, further extending the service life of the membrane element, reducing replacement frequency, and ensuring system operation.

[0009] In a first aspect, the present invention provides a high-pressure reverse osmosis membrane, wherein the high-pressure reverse osmosis membrane is provided with a polyester non-woven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer, and a self-lubricating protective layer from bottom to top. The porous polymer support layer is made of polysulfone, polyethersulfone, or polyvinylidene fluoride; the dynamic buffer layer comprises polymer A containing catechol groups and polymer B containing boric acid groups in a mass ratio of 1:0.5-2; the self-lubricating protective layer is a blend of polyacrylic acid and polyvinyl alcohol in a mass ratio of 1:2-2:1, with a coating thickness of 50-200 nm.

[0010] In the above technical solution, the dynamic buffer layer forms a dynamic cross-linked network through reversible borate ester bonds between the catechol groups of polymer A and the boric acid groups of polymer B. When the membrane is subjected to water hammer or back pressure impact, the borate ester bonds in this dynamic cross-linked network preferentially undergo reversible breakage, dissipating impact energy and preventing stress from being directly transmitted to the polyamide separation layer. After the impact is eliminated, the broken borate ester bonds can spontaneously recombine in the presence of moisture, restoring the integrity of the cross-linked network, thereby endowing the interface with self-healing ability for micro-damage. In this way, even if the membrane is subjected to countless micro-impacts during long-term use, the dynamic buffer layer can continuously self-repair, preventing damage accumulation that could lead to large-scale detachment of the desalination layer.

[0011] Optionally, the polymer A containing catechol groups is dopamine-modified polyethylene glycol or dopamine-modified polyethyleneimine; the polymer B containing boric acid groups is phenylboronic acid-modified polyvinyl alcohol.

[0012] In the above technical solution, the preparation method of dopamine-modified polyethylene glycol or dopamine-modified polyethyleneimine is as follows: polyethylene glycol or polyethyleneimine is dissolved in 2-(N-morpholino)ethanesulfonic acid buffer at pH 5.5 to prepare an 8wt% solution. 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide are added for activation for 30 min. Then, dopamine hydrochloride is added (the molar ratio of polyethylene glycol to dopamine is 1:2, and the molar ratio of polyethyleneimine to dopamine is 1:0.3). The mixture is stirred at room temperature for 24 h. The reaction solution is dialyzed with deionized water for 48 h and then freeze-dried to obtain dopamine-modified polyethylene glycol.

[0013] The preparation method of phenylboronic acid modified polyvinyl alcohol is as follows: Polyvinyl alcohol is dissolved in dimethyl sulfoxide to prepare an 8 wt% solution. 4-Carboxyphenylboronic acid (the molar ratio of hydroxyl to 4-carboxyphenylboronic acid in dimethyl sulfoxide is 1:0.1), 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride, and 4-dimethylaminopyridine are added, and the mixture is stirred at 70 °C for 48 h. The reaction solution is poured into excess anhydrous ethanol to precipitate the polyvinyl alcohol. After filtration, the precipitate is washed three times with ethanol. The precipitate is then dissolved in deionized water, dialyzed for 48 h, and freeze-dried to obtain phenylboronic acid modified polyvinyl alcohol with a grafting rate of 10 mol.

[0014] Dopamine-modified polyethylene glycol or dopamine-modified polyethyleneimine can achieve efficient energy dissipation and interface self-healing in a room temperature water environment by forming borate ester bonds between its catechol structure and the phenylboronic acid groups of phenylboronic acid-modified polyvinyl alcohol.

[0015] Optionally, the dynamic buffer layer further includes cyclic oligosaccharides at a mass of 10-20% of the total mass of polymer A and polymer B, wherein the cyclic oligosaccharides are any one of α-cyclodextrin, β-cyclodextrin, or γ-cyclodextrin.

[0016] In the above technical solution, cyclic oligosaccharides, acting as slip ring molecules, are embedded in the molecular chains of polymer A or polymer B, forming a polyquasi-rotaxane structure. When the membrane is subjected to bending or tensile stress during disassembly, the cyclic oligosaccharides slip along the polymer chains, dispersing locally concentrated stress over a wider area through intramolecular friction, thus preventing stress concentration from causing microcracks in the polyamide separation layer. This slip ring effect complements the self-healing function of the dynamic borate ester bonds, respectively addressing mechanical damage during disassembly and pressure impact damage during operation.

[0017] Optionally, the self-lubricating protective layer may further contain 0.3-0.8% by weight of nano-silica or nano-titanium dioxide.

[0018] In the above technical solution, nano-silica or nano-titanium dioxide particles are uniformly dispersed in polyacrylic acid and polyvinyl alcohol matrix. On the one hand, this improves the surface hardness and wear resistance of the coating. On the other hand, when the membrane element is pulled out of the pressure vessel, the ball bearing effect of the nanoparticles further reduces the coefficient of friction and reduces mechanical damage to the polyamide separation layer caused by scratching.

[0019] Secondly, the present invention provides a method for preparing a high-pressure reverse osmosis membrane, the method comprising the following steps: (1) The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer containing 1-3 g / L of dopamine at pH 8.0-8.8 and reacted at room temperature for 1-2 h to form an initial adhesive layer. (2) Dissolve polymer A and polymer B in deionized water in proportion, adjust the pH to 8.0-9.0, and prepare a buffer layer solution with a total solid content of 0.5-2 wt%. Immerse the substrate obtained in step (1) into the solution and react for 1-3 h under the conditions of 50-100 W power and 40-60℃ temperature to form a dynamic buffer layer. (3) The substrate obtained in step (2) is immersed in an aqueous solution containing 2-4 wt% m-phenylenediamine and 2-4 wt% camphor sulfonic acid with pH 9-11 for 60-120 s. After being taken out and rolled dry, it is immersed in an organic solution containing 0.1-0.3 wt% trimesoyl chloride for 30-90 s. Then it is heat-cured at 80-100℃ for 5-10 min to form a polyamide release layer. (4) Dissolve polyacrylic acid and polyvinyl alcohol in deionized water in proportion to prepare a coating solution of 0.1-0.5 wt%, coat it on the surface of the polyamide separation layer, and dry it at 80-100℃ for 5-10 min to form a self-lubricating protective layer. (5) Immerse the obtained membrane in a protective solution containing 10-25 vol% glycerol, remove and dry it to obtain a high-pressure reverse osmosis membrane.

[0020] In the above technical solution, ultrasonic-assisted reaction is used in step (2). The cavitation effect of ultrasonic waves promotes the uniform mixing of polymer A and polymer B in the solution, while accelerating the formation of slip ring structure by cyclic oligosaccharides on polymer chains, thereby improving the crosslinking uniformity of the dynamic buffer layer and the dispersion density of slip ring molecules.

[0021] Optionally, step (2) further includes dissolving polymer A and polymer B in deionized water in proportion, adding cyclic oligosaccharides, adjusting the pH to 8.0-9.0, and preparing a buffer layer solution with a total solid content of 0.5-2 wt%.

[0022] In the above technical solution, cyclic oligosaccharides can spontaneously attach to polymer chains under alkaline conditions without the need for additional catalysts or complex grafting reactions, making the process simple and controllable. The amount of cyclic oligosaccharides added is controlled within the range of 5-20% of the total mass of polymers A and B, ensuring sufficient slip ring effect while avoiding excessive hydrophilicity of the buffer layer due to excessive cyclodextrin, which could affect the interfacial bonding strength.

[0023] Optionally, step (4) further includes dissolving polyacrylic acid and polyvinyl alcohol in deionized water in a certain proportion, and then adding nano-silica or nano-titanium dioxide to prepare a coating solution of 0.1-0.5 wt%.

[0024] In the above technical solution, nanoparticles are uniformly suspended in the coating solution by ultrasonic dispersion. After coating and drying, the nanoparticles are anchored in the polyacrylic acid and polyvinyl alcohol matrix by a hydrogen bond network. The addition of nanofillers not only improves the scratch resistance of the self-lubricating protective layer, but the abundant hydroxyl groups on their surface can also form additional hydrogen bonds with the carboxyl groups on the surface of the polyamide release layer, enhancing the adhesion of the protective layer.

[0025] Thirdly, the present invention provides an application of a high-pressure reverse osmosis membrane in seawater desalination and pure water preparation.

[0026] In summary, the present invention has at least one of the following beneficial technical effects: 1. By constructing a dynamic buffer layer containing reversible borate bonds, the membrane can dissipate impact energy and repair micro-damage through the reversible fracture-recombination mechanism of borate bonds when subjected to cyclic impacts such as water hammer and back pressure, thus significantly improving the peel fatigue life of the desalination layer.

[0027] 2. By introducing cyclic oligosaccharides as slip ring molecules into the dynamic buffer layer, the bending and tensile stresses generated during disassembly are dispersed by their sliding motion on the polymer chain, avoiding local micro-peeling caused by stress concentration, and improving the membrane's tolerance to operational damage.

[0028] 3. By setting a self-lubricating protective layer of polyacrylic acid / polyvinyl alcohol containing nanofillers, the coefficient of friction and the risk of scratch damage during membrane element disassembly are reduced. At the same time, the nanofillers enhance the wear resistance of the coating and further protect the structural integrity of the polyamide separation layer.

[0029] 4. The preparation method of this invention is simple, highly controllable, and suitable for large-scale industrial application. Detailed Implementation

[0030] The present invention will be further described in detail below with reference to the embodiments.

[0031] All materials used in the following examples are available for purchase on the market.

[0032] The composite substrate consists of a polyester nonwoven fabric coated with a polysulfone porous polymer layer, with a molecular weight cutoff of 50,000 Da (Guochu Technology (Xiamen) Co., Ltd.); dopamine hydrochloride (DA, purity ≥98%); Tris buffer: 50 mM tris(hydroxymethyl)aminomethane, pH adjusted with hydrochloric acid; Polymer A: dopamine-modified polyethylene glycol (PEG-DA), weight-average molecular weight 10,000 Da, prepared according to the previous preparation example; Polymer A2: dopamine-modified polyethyleneimine (PEI-DA), weight-average molecular weight 8,000 Da, prepared according to the previous preparation example; Polymer B: phenylboronic acid-modified polyvinyl alcohol (PVA-PBA), phenylboronic acid grafting rate 10 mol%, prepared according to the previous preparation example; m-phenylenediamine (MPD, purity ≥99%); camphor sulfonic acid (CSA, purity ≥99%); trimesoyl chloride (TMC, purity ≥98%); Isopar G (isoparaffin solvent); polyacrylic acid (PAA, weight average molecular weight 5,000 Da); polyvinyl alcohol (PVA, degree of hydrolysis 98%, weight average molecular weight 30,000 Da); β-cyclodextrin (β-CD, purity ≥98%); nano silica (SiO2, particle size 20 nm); glycerol (purity ≥99%).

[0033] Example 1: This example provides a high-pressure reverse osmosis membrane #1 and its preparation method.

[0034] The high-pressure reverse osmosis membrane is composed of a polyester nonwoven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer, and a self-lubricating protective layer from bottom to top.

[0035] The preparation method steps are as follows: S1. Preparation of the initial bonding layer: The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer solution containing 1 g / L dopamine at pH 8.5 and reacted at room temperature for 1 h. After being taken out, it is rinsed 3 times with deionized water to form the initial bonding layer. S2. Preparation of dynamic buffer layer: Dopamine-modified polyethylene glycol and phenylboronic acid-modified polyvinyl alcohol with a mass ratio of 1:0.5 were dissolved in deionized water to prepare a buffer layer solution with a total solid content of 0.5 wt%. The pH was adjusted to 8 with 0.1 M NaOH. The substrate obtained in step S1 was immersed in the solution and placed in an ultrasonic cleaner. It was reacted for 3 h at a power of 50 W and a temperature of 60 °C. After removal, it was rinsed twice with deionized water and dried at 60 °C for 10 min to form a dynamic buffer layer. S3. Preparation of polyamide separation layer: The substrate obtained in step S2 is immersed in an aqueous solution containing 2 wt% m-phenylenediamine and 4 wt% camphor sulfonic acid at pH 9 for 120 s. After being taken out and rolled dry, it is immersed in an organic solution containing 0.1 wt% trimesoyl chloride for 90 s. Then it is heat-cured at 80℃ for 10 min to form a polyamide separation layer. S4. Preparation of self-lubricating protective layer: Polyacrylic acid and polyvinyl alcohol in a mass ratio of 1:2 are dissolved in deionized water to prepare a 0.1 wt% coating solution, which is then coated on the surface of the polyamide separation layer and dried at 80℃ for 10 min to form a self-lubricating protective layer with a coating thickness of 60 nm. S5. Post-treatment: Immerse the obtained membrane in a protective solution containing 10 vol% glycerol, soak at room temperature for 30 min, remove and air dry to obtain high-pressure reverse osmosis membrane #1.

[0036] Example 2: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0037] The high-pressure reverse osmosis membrane is composed of a polyester nonwoven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer, and a self-lubricating protective layer from bottom to top.

[0038] The preparation method steps are as follows: S1. Preparation of the initial bonding layer: The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer solution containing 3g / L dopamine at pH 8.8 and reacted at room temperature for 2 h. After being taken out, it is rinsed 3 times with deionized water to form the initial bonding layer. S2. Preparation of dynamic buffer layer: Dopamine-modified polyethyleneimine and phenylboronic acid-modified polyvinyl alcohol with a mass ratio of 1:2 were dissolved in deionized water to prepare a buffer layer solution with a total solid content of 2wt%. The pH was adjusted to 9 with 0.1 M NaOH. The substrate obtained in step S1 was immersed in the solution and placed in an ultrasonic cleaner. It was reacted for 1 hour at a power of 100 W and a temperature of 40℃. After removal, it was rinsed twice with deionized water and dried at 60℃ for 10 min to form a dynamic buffer layer. S3. Preparation of polyamide separation layer: The substrate obtained in step S2 is immersed in an aqueous solution containing 4 wt% m-phenylenediamine and 2 wt% camphor sulfonic acid at pH 11 for 30 s. After being taken out and rolled dry, it is immersed in an organic solution containing 0.3 wt% trimesoyl chloride for 30 s. Then it is heat-cured at 100℃ for 5 min to form a polyamide separation layer. S4. Preparation of self-lubricating protective layer: Polyacrylic acid and polyvinyl alcohol in a mass ratio of 2:1 are dissolved in deionized water to prepare a 0.5 wt% coating solution, which is then coated on the surface of the polyamide separation layer and dried at 100℃ for 5 min to form a self-lubricating protective layer with a coating thickness of 200 nm. S5. Post-treatment: Immerse the obtained membrane in a protective solution containing 25 vol% glycerol, soak at room temperature for 30 min, remove and air dry to obtain high-pressure reverse osmosis membrane #2.

[0039] Example 3: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0040] The high-pressure reverse osmosis membrane is composed of a polyester nonwoven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer, and a self-lubricating protective layer from bottom to top.

[0041] The preparation method steps are as follows: S1. Preparation of the initial bonding layer: The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer solution containing 1.5 g / L dopamine at pH 8.5 and reacted at room temperature for 1.5 h. After removal, it is rinsed 3 times with deionized water to form the initial bonding layer. S2. Preparation of dynamic buffer layer: Dopamine-modified polyethylene glycol and phenylboronic acid-modified polyvinyl alcohol with a mass ratio of 1:1 were dissolved in deionized water to prepare a buffer layer solution with a total solid content of 1.0 wt%. The pH was adjusted to 8.5 with 0.1 M NaOH. The substrate obtained in step S1 was immersed in the solution and placed in an ultrasonic cleaner. The reaction was carried out at a power of 80 W and a temperature of 50℃ for 2 h. After removal, the substrate was rinsed twice with deionized water and dried at 60℃ for 10 min to form a dynamic buffer layer. S3. Preparation of polyamide separation layer: The substrate obtained in step S2 is immersed in an aqueous solution containing 3 wt% m-phenylenediamine and 3 wt% camphor sulfonic acid at pH 10 for 90 s. After being taken out and rolled dry, it is immersed in an organic solution containing 0.2 wt% trimesoyl chloride for 60 s. Then it is heat-cured at 90℃ for 8 min to form a polyamide separation layer. S4. Preparation of self-lubricating protective layer: Polyacrylic acid and polyvinyl alcohol in a mass ratio of 1:1 are dissolved in deionized water to prepare a 0.3 wt% coating solution, which is then coated on the surface of the polyamide separation layer and dried at 90℃ for 8 min to form a self-lubricating protective layer with a coating thickness of 100 nm. S5. Post-treatment: Immerse the obtained membrane in a protective solution containing 20 vol% glycerol, soak at room temperature for 30 min, remove and air dry to obtain high-pressure reverse osmosis membrane #3.

[0042] Example 4: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0043] This embodiment is the same as Embodiment 3, except that step S2 further includes adding 10% of the total mass of dopamine-modified polyethylene glycol and phenylboronic acid-modified polyvinyl alcohol to the buffer layer solution as α-cyclodextrin.

[0044] Example 5: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0045] This embodiment is the same as embodiment 3, except that step S2 further includes adding 20% ​​of the total mass of dopamine-modified polyethylene glycol and phenylboronic acid-modified polyvinyl alcohol as γ-cyclodextrin to the buffer layer solution.

[0046] Example 6: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0047] This embodiment is the same as Embodiment 3, except that step S2 further includes adding 15% of the total mass of dopamine-modified polyethylene glycol and phenylboronic acid-modified polyvinyl alcohol as β-cyclodextrin to the buffer layer solution.

[0048] Example 7: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0049] This embodiment is the same as embodiment 3, except that step S4 further includes dissolving polyacrylic acid and polyvinyl alcohol in deionized water in a certain proportion, and then adding 0.3% of nano titanium dioxide by the total mass of the coating to prepare a 0.3wt% coating solution.

[0050] Example 8: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0051] This embodiment is the same as embodiment 3, except that step S4 further includes dissolving polyacrylic acid and polyvinyl alcohol in deionized water in a certain proportion, and then adding 0.5% of nano-silica by the total mass of the coating to prepare a 0.3wt% coating solution.

[0052] Example 9: This example provides a high-pressure reverse osmosis membrane and its preparation method.

[0053] This embodiment is the same as embodiment 6, except that step S4 further includes dissolving polyacrylic acid and polyvinyl alcohol in deionized water in a certain proportion, and then adding 0.5% of nano-silica by the total mass of the coating to prepare a 0.3wt% coating solution.

[0054] Comparative Example 1: This comparative example provides a comparative reverse osmosis membrane, the preparation method of which includes the following steps: S1. The composite substrate with a polysulfone porous polymer layer on a polyester nonwoven fabric is used directly as the raw material, without any coating treatment.

[0055] S2. Preparation of aqueous solution: Dissolve 3.0 wt% m-phenylenediamine and 3.0 wt% camphor sulfonic acid in deionized water, adjust the pH to 10.0 with triethylamine, and stir until completely dissolved.

[0056] S3. Preparation of organic phase solution: Dissolve 0.2 wt% of trimesoyl chloride in Isopar G organic solvent and stir until completely dissolved.

[0057] S4. Interfacial polymerization to form a polyamide separation layer: Lay the composite substrate flat with the porous polymer support layer facing upwards. Pour the aqueous solution evenly onto the substrate surface to completely cover it, maintaining contact for 90 seconds. Then tilt the substrate and use a rubber roller to roll and remove excess aqueous droplets from the surface until there is no obvious liquid film on the surface. Immediately pour the organic solution evenly onto the treated substrate surface, maintaining contact for 60 seconds. Then tilt the substrate and use a rubber roller to roll and remove excess organic phase. Place the coated substrate in an oven and heat-treat at 90°C for 8 minutes to form a polyamide separation layer.

[0058] S5. Post-treatment: Immerse the obtained membrane in a 20% (v / v) glycerol aqueous solution for 30 min at room temperature, then remove and air dry to obtain the control reverse osmosis membrane D1.

[0059] Comparative Example 2: This comparative example provides a comparative reverse osmosis membrane, excluding the dynamic buffer layer and the self-lubricating protective layer. The specific preparation steps are as follows: S1. Formation of the initial adhesive layer: The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer solution containing 1.5 g / L dopamine at pH 8.5 and reacted at room temperature for 1.5 h. After removal, it is rinsed 3 times with deionized water to form the initial adhesive layer.

[0060] S2. Interfacial polymerization to form a polyamide release layer: The substrate obtained in step (1) is laid flat with the initial adhesive layer facing upward. An aqueous solution (containing 3.0 wt% m-phenylenediamine and 3.0 wt% camphor sulfonic acid, with the pH adjusted to 10.0 using triethylamine) is prepared. The aqueous solution is poured evenly onto the substrate surface and kept in contact for 90 s. The solution is then rolled dry. Immediately, an organic solution (containing 0.2 wt% Isopar G solution of pyromellitic methyl chloride) is poured in and kept in contact for 60 s. The solution is then rolled dry. Finally, the solution is heat-cured at 90°C for 8 min to form a polyamide release layer.

[0061] S3. Post-treatment: Immerse the obtained membrane in a 20% glycerol aqueous solution at room temperature for 30 min, then remove and air dry to obtain the control reverse osmosis membrane D2.

[0062] Comparative Example 3: This comparative example provides a comparative reverse osmosis membrane, which is prepared in the same way as in Example 9, except that the dopamine-modified polyethylene glycol in step S2 is replaced with unmodified polyethylene glycol.

[0063] Comparative Example 4: This comparative example provides a comparative reverse osmosis membrane, which is prepared in the same way as in Example 9, except that the phenylboronic acid modified polyvinyl alcohol in step S2 is replaced with unmodified polyvinyl alcohol.

[0064] The reverse osmosis membranes of Examples 1-9 and Comparative Examples 1-4 were subjected to basic separation performance tests, single back pressure tolerance tests, cyclic back pressure impact tests, and anti-disassembly and scratch simulation tests. The test results are shown in Table 1.

[0065] One of them is the basic separation performance test.

[0066] A high-pressure flat-sheet membrane testing device was used, with an operating pressure of 5.5 MPa, a feed solution of 32,000 mg / L NaCl aqueous solution, and an operating temperature of 25℃. The effective test area of ​​the membrane was 15.79 cm². Before testing, the membrane was pre-pressed at 4 MPa for 4 h to stabilize the flux. The mass of the permeate was measured using an electronic balance and converted to volume. The conductivity of the feed solution and permeate was measured using a conductivity meter. The water flux J [L / (m²·h)] and NaCl rejection rate R (%) were calculated. In the formula, V is the permeate volume (L), t is the collection time (h), A is the effective membrane area (m²), and C... p To achieve the desired liquid salt concentration, C f This represents the salt concentration in the feed solution. Each sample group was tested in triplicate, and the average value was taken.

[0067] II. Single back pressure tolerance test.

[0068] After completing the basic performance tests, the high-pressure pump was shut off, and a reverse pressure of 0.3 MPa was applied to the permeate side of the membrane (the permeate side pressure was 0.3 MPa higher than the feed side) for 10 minutes, after which the pressure was released. The membrane was then returned to normal operating conditions (5.5 MPa, 32,000 mg / L NaCl, 25℃), and after stabilizing for 30 minutes, the desalination rate was tested again. The desalination rate decay was calculated as: initial desalination rate - desalination rate after back pressure. Simultaneously, the membrane surface was visually inspected for bubbling or peeling.

[0069] III. Cyclic back pressure impact test.

[0070] Repeat the cycle of "0.3 MPa reverse pressure for 10 min → pressure release → normal operation at 5.5 MPa for 30 min, then test the desalination rate" three times. Calculate the desalination rate recovery rate after three cycles = (desalination rate after the third cycle ÷ initial desalination rate) × 100%. A recovery rate ≥ 95% is considered to have significant self-healing ability.

[0071] IV. Anti-disassembly and scratch simulation test.

[0072] Lay the membrane flat and fix it in place with the polyamide separation layer facing upwards. Apply a 500 g weight to a slider wrapped with 400-grit sandpaper (contact area 2 cm × 2 cm) and scratch the membrane surface 10 times in one direction at a speed of 10 cm / s. After scratching, test the desalination rate under standard conditions and calculate the desalination rate retention rate after scratching = (desalination rate after scratching ÷ initial desalination rate) × 100%.

[0073] Table 1 As shown in Table 1, the initial desalination rates of all reverse osmosis membranes in Examples 1-9 and Comparative Examples 1-4 were above 99.4%, with initial water fluxes ranging from 47.9 to 51.2 L / (m²·h). Among them, the comparative reverse osmosis membrane in Comparative Example 1, without any coating, had the highest water flux (51.2 L / (m²·h)) because it had no intermediate layer mass transfer resistance. The water fluxes of Examples 1-9 were slightly lower, but still within the typical range for high-performance reverse osmosis membranes, indicating that the introduction of the dynamic buffer layer and self-lubricating protective layer did not significantly sacrifice the membrane's permeability performance.

[0074] Examples 1-3 showed a single back pressure attenuation of only 0.1-0.2%, and a recovery rate of 99.6%-99.8% after three cycles, with no blistering on the surface. Example 3 exhibited the lowest attenuation and a recovery rate of 99.8%, superior to Examples 1 and 2. This indicates that a moderate cross-linking density of borate ester bonds at equal mass ratios results in the best self-healing effect.

[0075] The performance of the reverse osmosis membranes in Examples 4-6 was further improved after the addition of cyclic oligosaccharides to the dynamic buffer layer. Examples 4 and 5 showed a single back pressure decrease of 0.1% and a recovery rate of 99.8%. Example 6 showed a single back pressure decrease of 0.0% and a recovery rate as high as 99.9%. Cyclodextrin, as a slip ring molecule, is embedded in the polymer chain and further disperses stress through slip motion during impact, synergistically enhancing shock resistance and self-healing ability with dynamic borate ester bonds. Among these, Example 6 showed the best effect after the addition of β-cyclodextrin.

[0076] Examples 7-8 show that the addition of nanofillers to the self-lubricating protective layer resulted in single-cycle back pressure attenuation of 0.1% and 0.0%, respectively, with recovery rates of 99.8% and 99.9%. The introduction of nanofillers slightly improved back pressure tolerance and enhanced the coating's density and wear resistance.

[0077] Example 9 exhibited the best overall performance. It achieved an initial desalination rate of 99.6%, a water flux of 47.9 L / (m²·h), no decrease in back pressure after a single cycle (0.0%), and maintained a desalination rate of 99.5% and a recovery rate of 99.9% after three cycles. This indicates that the synergistic effect of the cyclodextrin slip ring effect and the nano-reinforcement in the self-lubricating protective layer further enhances the membrane's shock resistance and self-healing capabilities.

[0078] Comparative Example 1, lacking an initial tack layer, dynamic buffer layer, and self-lubricating protective layer, showed a sharp drop in desalination rate from 99.4% to 90.5% after a single back pressure cycle, a decrease of 8.9%. After three cycles, the desalination rate was only 80.3%, with a recovery rate of 80.8%. Visual inspection revealed large-area blistering and desalination layer peeling. This indicates that the conventional polyamide film, relying solely on physical adhesion to the support layer, is completely unable to withstand back pressure impacts, and the damage is irreversible.

[0079] Comparative Example 2 only had a dopamine initial adhesion layer, lacking a dynamic buffer layer and a self-lubricating layer. Its back pressure decayed by 3.3% in a single cycle, and its recovery rate after three cycles was 92.0%, showing a significant improvement over Comparative Example 1. However, slight blistering at the edges still occurred. The dopamine initial adhesion layer improved the initial bonding force through adhesion, but lacked a dynamic reversible cross-linking structure, and therefore could not self-repair after accumulated damage.

[0080] In Comparative Example 3, unmodified polyethylene glycol was used instead of modified polyethylene glycol in the dynamic buffer layer. The single back pressure decay was 4.6%, and the recovery rate after three cycles was 89.4%. Since unmodified polyethylene glycol does not contain catechol groups, it cannot form borate bonds with phenylboronic acid-modified polyvinyl alcohol. As a result, the dynamic buffer layer loses its dynamic crosslinking and self-healing functions, and its performance is worse than that of Comparative Example 2.

[0081] In Comparative Example 4, unmodified polyvinyl alcohol was used instead of phenylboronic acid-modified polyvinyl alcohol in the dynamic buffer layer. The single back pressure decay was 4.9%, and the recovery rate after three cycles was 88.8%, similar to Comparative Example 3. Again, the lack of boronic acid groups prevented the formation of reversible boronic acid ester bonds, verifying the necessity of dynamic covalent bonds.

[0082] The above are all preferred embodiments of the present invention and are not intended to limit the scope of protection of the present invention. Therefore, all equivalent changes made in accordance with the structure, shape and principle of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A high-pressure reverse osmosis membrane, characterized in that, The high-pressure reverse osmosis membrane is provided with a polyester non-woven fabric layer, a porous polymer support layer, a dynamic buffer layer, a polyamide separation layer, and a self-lubricating protective layer from bottom to top. The porous polymer support layer is made of polysulfone, polyethersulfone, or polyvinylidene fluoride. The dynamic buffer layer comprises polymer A containing catechol groups and polymer B containing boric acid groups in a mass ratio of 1:0.5-2. The self-lubricating protective layer is a blend of polyacrylic acid and polyvinyl alcohol with a mass ratio of 1:2 to 2:1, and the coating thickness is 50-200 nm.

2. The high-pressure reverse osmosis membrane according to claim 1, characterized in that, The polymer A containing catechol groups is dopamine-modified polyethylene glycol or dopamine-modified polyethyleneimine; the polymer B containing boric acid groups is phenylboronic acid-modified polyvinyl alcohol.

3. A high-pressure reverse osmosis membrane according to claim 2, characterized in that, The dynamic buffer layer also includes cyclic oligosaccharides at a mass of 10-20% of the total mass of polymer A and polymer B, wherein the cyclic oligosaccharides are any one of α-cyclodextrin, β-cyclodextrin or γ-cyclodextrin.

4. A high-pressure reverse osmosis membrane according to claim 1, characterized in that, The self-lubricating protective layer also contains 0.3-0.8% nano-silica or nano-titanium dioxide by weight of the coating.

5. A method for preparing a high-pressure reverse osmosis membrane as described in any one of claims 1-4, characterized in that, The preparation method includes the following steps: (1) The composite substrate of polyester nonwoven fabric and porous polymer support layer is immersed in Tris buffer solution containing 1-3 g / L of dopamine at pH 8.0-8.8 and reacted at room temperature for 1-2 h to form an initial adhesive layer. (2) Dissolve polymer A and polymer B in deionized water in proportion, adjust the pH to 8.0-9.0, and prepare a buffer layer solution with a total solid content of 0.5-2 wt%. Immerse the substrate obtained in step (1) into the solution and react for 1-3 h at a power of 50-100 W and a temperature of 40-60℃ to form a dynamic buffer layer. (3) The substrate obtained in step (2) is immersed in an aqueous solution containing 2-4 wt% m-phenylenediamine and 2-4 wt% camphor sulfonic acid with pH 9-11 for 60-120 s. After being taken out and rolled dry, it is immersed in an organic solution containing 0.1-0.3 wt% trimesoyl chloride for 30-90 s. Then it is heat-cured at 80-100℃ for 5-10 min to form a polyamide separation layer. (4) Dissolve polyacrylic acid and polyvinyl alcohol in deionized water in proportion to prepare a coating solution of 0.1-0.5 wt%, coat it on the surface of the polyamide separation layer, and dry it at 80-100℃ for 5-10 min to form a self-lubricating protective layer. (5) Immerse the obtained membrane in a protective solution containing 10-25 vol% glycerol, remove and dry it to obtain a high-pressure reverse osmosis membrane.

6. The method for preparing a high-pressure reverse osmosis membrane according to claim 5, characterized in that, Step (2) further includes dissolving polymer A and polymer B in deionized water in a certain proportion, adding cyclic oligosaccharides, adjusting the pH to 8.0-9.0, and preparing a buffer layer solution with a total solid content of 0.5-2 wt%.

7. The method for preparing a high-pressure reverse osmosis membrane according to claim 5, characterized in that, Step (4) further includes dissolving polyacrylic acid and polyvinyl alcohol in deionized water in a certain proportion, and then adding nano-silica or nano-titanium dioxide to prepare a coating solution of 0.1-0.5 wt%.

8. An application of a high-pressure reverse osmosis membrane in seawater desalination and pure water preparation, characterized in that, High-pressure reverse osmosis membranes prepared using any one of the high-pressure reverse osmosis membranes as described in claims 1-4 or the preparation methods as described in claims 5-7.

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