A composite membrane with high boron removal rate and its preparation method

Abstract

This invention belongs to the field of polymer separation membrane technology for water treatment, specifically relating to a composite membrane with a high boron removal rate and its preparation method. The method includes: contacting a base membrane with an aqueous solution to form an aqueous liquid layer, followed by contacting it with an oil solution to perform an interfacial polymerization reaction, forming a polyamide functional layer on the base membrane; wherein the aqueous solution comprises m-phenylenediamine, pyromellitic triamine, camphor sulfonic acid, triethylamine, and water; and the oil solution comprises pyromellitic tricarboxylate chloride, toluene diisocyanate, and naphtha; the resulting base membrane containing the polyamide functional layer is then sequentially contacted with a solution containing aldehydes and a sodium nitrite solution for post-treatment to obtain a polyamide functional layer with a high cross-linking density; after treatment with NaHSO3 solution, it is then immersed in a glycerol solution for protection. This composite membrane not only has a high boron removal rate but also ensures a high desalination rate and flux. The method of this invention is simple to operate and has good application prospects in the large-scale production of high boron removal rate reverse osmosis membranes.

Description

Technical Field

[0001] This invention belongs to the field of polymer separation membrane technology for water treatment, specifically relating to a composite membrane with high boron removal rate and its preparation method. Background Technology

[0002] Boron concentration in seawater is approximately 5 ppm. Repeated ingestion of water containing boron concentrations exceeding 0.5 ppm has been reported to cause health problems. Therefore, a sufficiently high boron removal rate is crucial when using reverse osmosis technology for seawater desalination. Early reverse osmosis membranes achieved only about 50% boron removal, far lower than their removal rate for sodium salts (>99%). The difficulty in removing boron from seawater is primarily due to the fact that boron does not dissociate in seawater (it generally exists as boric acid), a non-charged protic acid that can bind to the effective portion of the membrane via hydrogen bonds, diffusing into solutions with low ion concentrations in the same manner as water. Another reason is that the molecular diameter of boric acid is less than 2.72 angstroms, while the pores of reverse osmosis membranes consist of a network of 1-3 angstroms and aggregated pores of 3.5-4.5 angstroms. The boric acid molecule is close to the radius of the network pores but smaller than the radius of the aggregated pores, making boron removal by reverse osmosis membranes even more challenging. Currently, most reverse osmosis processes for deboring boron from seawater reduce boron concentration by using two-stage filtration. While these processes can reduce boron concentration to some extent, they also increase costs and energy consumption. Therefore, there is a need to develop composite membranes with high boron removal rates.

[0003] Patent CN102380318A discloses a reverse osmosis membrane with a high boron removal rate and its manufacturing method. It utilizes a polymer gel coating or an organic / inorganic hybrid gel coating to improve the boron removal capacity of reverse osmosis membranes used for seawater desalination. However, the boron removal rate does not exceed 95%, and the water flux is low. Other methods improve the membrane by modifying the composition of the aqueous / oil phase solution. For example, patent CN113856483A discloses adding cyclopropylamine molecules to an aqueous solution containing m-phenylenediamine. This reduces the pore size of the reverse osmosis membrane, increases the permeation resistance of boric acid molecules, and simultaneously reduces the hydrogen bonding between boric acid and water molecules. Patent CN114345149A further adjusts the membrane's micro / nano structure by introducing flexible polyisobutyleneamine polymers into the organic phase, adjusting the pore size and filling defects in the reverse osmosis membrane. However, the boron removal rate does not exceed 95%, and the water flux is also low. Patent CN101053787 discloses that membranes treated with compounds containing iodine atoms show a significant boron removal rate, up to 97%, but it is still difficult to achieve an average boron removal rate of over 95%, and the water flux is severely reduced.

[0004] Therefore, although some technical solutions have been provided in the existing technology to improve the boron removal effect of polyamide reverse osmosis membranes, they all lead to a reduction in other membrane properties to varying degrees when improving the boron removal effect. In particular, it is difficult to balance membrane separation and permeation performance. The technical solutions need to be further improved. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a composite membrane with a high boron removal rate and its preparation method. By adjusting the aqueous and oil phase membrane formulations and improving the post-processing technology, the crosslinking density of the composite membrane separation layer is increased, thereby improving the boron removal rate and achieving better flux and desalination rate.

[0006] The primary objective of this invention is to provide a method for preparing a composite membrane with a high deboronization rate.

[0007] The present invention achieves the above objectives through the following technical solutions:

[0008] A method for preparing a composite membrane with a high boron removal rate includes the following steps:

[0009] S1. The base film is brought into contact with an aqueous solution to form an aqueous liquid layer, and then brought into contact with an oil solution to carry out an interfacial polymerization reaction, forming a polyamide functional layer on the base film.

[0010] The aqueous phase solution comprises m-phenylenediamine, pyromellitic triamine, camphor sulfonic acid, triethylamine, and water; the oil phase solution comprises pyromellitic tricarboxylate chloride, toluene diisocyanate, and naphtha.

[0011] S2. The polyamide functional layer base film obtained in step S1 is sequentially contacted with a solution containing aldehydes and a sodium nitrite solution to obtain a polyamide functional layer with high crosslinking density.

[0012] S3. The base film containing the high cross-linking density polyamide functional layer obtained in step S2 is treated with NaHSO3 solution and then immersed in glycerol solution for protection to obtain the composite film with high deboronization rate.

[0013] Compared with previous studies, this invention employs a simplified formulation, avoiding the use of alcohols and surfactants. Surfactants can generate foam during membrane formation, affecting the compactness of interfacial polymerization; alcohols can increase membrane flux, but their volatilization can also affect flux, requiring continuous replenishment and increasing costs. However, in the system of this invention, the same flux effect can still be achieved without the presence of alcohols.

[0014] This invention achieves this by scientifically and rationally adjusting the formulations of the aqueous and oil phases. In the aqueous phase, m-phenylenediamine and pyromellitic triamine are used in combination, while toluene diisocyanate is added to the oil phase to regulate flux and improve boron removal rate. Because pyromellitic triamine has three reactive groups, the resulting polyamide crosslinking density is high, and toluene diisocyanate can react again with unreacted amino groups to fill gaps. Furthermore, by improving the post-treatment process, it was discovered that while aldehyde solution treatment increases the crosslinking density of the composite membrane separation layer, it also leads to a decrease in flux. Post-treatment with sodium nitrite solution balances the flux, ultimately achieving a better flux effect while improving the boron removal rate.

[0015] Preferably, the base membrane in step S1 is a non-woven fabric supported ultrafiltration membrane, and the ultrafiltration membrane is a polysulfone membrane, a polyethersulfone membrane, or a sulfonated polysulfone membrane.

[0016] Preferably, the aqueous phase solution components in step S1, by mass percentage, are: 1.0%–1.4% m-phenylenediamine, 1.0%–1.4% pyromellitic triamine, 1%–1.4% camphor sulfonic acid, 0.5%–0.7% triethylamine, and the balance being water; the oil phase solution components, by mass percentage, are: 0.25%–0.35% pyromellitic tricarboxylate chloride, 0.05%–0.2% toluene diisocyanate, and the balance being naphtha.

[0017] Preferably, the contact time with the aqueous solution in step S1 is 30-90 seconds, and the contact time with the oil solution is 30-90 seconds.

[0018] Preferably, the aldehydes mentioned in step S2 include butyraldehyde, pentanaldehyde, hexanal, furfural, and glutaraldehyde.

[0019] Preferably, the mass concentration of the aldehyde solution in step S2 is 0.35% to 1.0%, and the treatment time is 30 to 90 seconds.

[0020] Preferably, the mass concentration of the sodium nitrite solution in step S2 is 0.2% to 0.5%, and the treatment time is 30 to 90 seconds.

[0021] Preferably, in step S3, the NaHSO3 solution has a mass concentration of 6% to 10% and a treatment time of 3 to 6 minutes; the glycerol solution has a mass concentration of 5% to 8% and an immersion time of 3 to 10 minutes.

[0022] The present invention also provides a composite membrane with a high deboronization rate prepared by the above method.

[0023] The present invention also provides the application of the above-mentioned composite membrane in improving the boron removal rate in water treatment.

[0024] Compared with the prior art, the beneficial effects of the present invention are:

[0025] This invention increases the crosslinking density of the composite membrane separation layer by adjusting the aqueous and oil phase membrane formulations and improving the post-processing technology, thereby improving the boron removal rate to over 95%, while also ensuring good desalination rate and water flux. This provides a new solution for improving boron removal rate in seawater desalination. Detailed Implementation

[0026] The technical solution of the present invention will be clearly and completely described below with reference to embodiments and comparative examples. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0027] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0028] The polysulfone-based membrane used in this embodiment of the invention is prepared using a conventional method. The specific steps are as follows: 15%-17% polysulfone by mass is dissolved in N,N-dimethylformamide and stirred to form a uniform casting solution with a viscosity range of 400-470 mPa·s. After standing to remove bubbles, the casting solution is scraped onto a nonwoven fabric and then cured into a film in a coagulation bath, thereby forming a polymer porous support layer on the nonwoven fabric.

[0029] Example 1

[0030] A method for preparing a composite membrane with a high boron removal rate includes the following steps:

[0031] S1. The nonwoven fabric-supported polysulfone membrane is contacted with an aqueous solution (1.0% m-phenylenediamine, 1.0% pyromellitic triamine, 1.0% camphor sulfonic acid, 0.5% triethylamine, balance water) for 60 seconds, and then dried until there are no obvious water droplets. Then, an oil phase solution (0.25% pyromellitic trimethylol chloride, 0.05% toluene diisocyanate, balance naphtha) is poured onto the surface of the porous support layer for 60 seconds, and then heat-treated at 50°C for 2 minutes to form a polyamide functional layer on the polymer porous support layer.

[0032] S2. The polysulfone film with a polyamide functional layer obtained in step S1, supported by nonwoven fabric, is sequentially contacted with 0.5% butyraldehyde solution for 60s and 0.35% sodium nitrite solution for 60s to obtain a polyamide functional layer with high crosslinking density.

[0033] S3. Then, treat with 8% NaHSO3 solution for 3 minutes, and then immerse in 8% glycerol solution for 3 minutes to obtain a composite membrane with high boron removal rate.

[0034] Example 2

[0035] A method for preparing a composite membrane with a high boron removal rate includes the following steps:

[0036] S1. The nonwoven fabric-supported polysulfone membrane is contacted with an aqueous solution (1.4% m-phenylenediamine, 1.4% pyromellitic triamine, 1.4% camphor sulfonic acid, 0.7% triethylamine, balance water) for 60 seconds, and then dried until there are no obvious water droplets. Then, an oil phase solution (0.35% pyromellitic tricarboxylate chloride, 0.2% toluene diisocyanate, balance naphtha) is poured onto the surface of the porous support layer for 60 seconds, and then heat-treated at 50°C for 2 minutes to form a polyamide functional layer on the polymer porous support layer.

[0037] S2. The polysulfone film with a polyamide functional layer obtained in step S1, supported by nonwoven fabric, is sequentially contacted with 0.5% glutaraldehyde solution for 60s and 0.35% sodium nitrite solution for 60s to obtain a polyamide functional layer with high crosslinking density.

[0038] S3. After treatment with 8% NaHSO3 solution for 5 min, the composite membrane with high boron removal rate is obtained by immersion in 8% glycerol solution for 5 min.

[0039] Example 3

[0040] A method for preparing a composite membrane with a high boron removal rate includes the following steps:

[0041] S1. The nonwoven fabric-supported polysulfone membrane is contacted with an aqueous solution (1.2% m-phenylenediamine, 1.2% pyromellitic triamine, 1.2% camphor sulfonic acid, 0.6% triethylamine, balance water) for 60 seconds, and then dried until no obvious water droplets are visible. Then, an oil phase solution (0.30% pyromellitic trimethylol chloride, 0.1% toluene diisocyanate, balance naphtha) is poured onto the surface of the porous support layer for 60 seconds, and then heat-treated at 50°C for 2 minutes to form a polyamide functional layer on the polymer porous support layer.

[0042] S2. The polysulfone film with a polyamide functional layer obtained in step S1, supported by nonwoven fabric, is sequentially contacted with 0.5% hexanal solution for 60s and 0.35% sodium nitrite solution for 60s to obtain a polyamide functional layer with high crosslinking density.

[0043] S3. After treatment with 8% NaHSO3 solution for 4 min, the composite membrane with high boron removal rate is obtained by immersion in 8% glycerol solution for 4 min.

[0044] Comparative Example 1

[0045] The difference between Comparative Example 1 and Example 1 is that the oil phase solution in step S1 is 0.25% pyromellitic acid chloride and the balance is naphtha. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0046] Comparative Example 2

[0047] The difference between Comparative Example 2 and Example 1 is that the aqueous solution in step S1 consists of 2.0% m-phenylenediamine, 1.0% camphor sulfonic acid, 0.5% triethylamine, and the remainder water. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0048] Comparative Example 3

[0049] The difference between Comparative Example 3 and Example 1 is that step S2 is omitted. The other preparation steps and conditions are the same as those in Example 1, and will not be repeated here.

[0050] Comparative Example 4

[0051] The difference between Comparative Example 4 and Example 1 is that the oil phase solution in step S1 consists of 0.25% trimesoyl chloride, 0.05% tributyl phosphate, and the remainder is naphtha. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0052] Comparative Example 5

[0053] The difference between Comparative Example 5 and Example 1 is that the aqueous solution in step S1 consists of 1.0% m-phenylenediamine, 1.0% ethylenediamine, 1.0% camphorsulfonic acid, 0.5% triethylamine, and the remainder water. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0054] Comparative Example 6

[0055] The difference between Comparative Example 6 and Example 1 is that the 0.5% butyraldehyde solution treatment in step S2 is not performed. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0056] Comparative Example 7

[0057] The difference between Comparative Example 7 and Example 1 is that the 0.35% sodium nitrite solution treatment in step S2 is not performed. The other preparation steps and conditions are the same as in Example 1, and will not be repeated here.

[0058] Performance testing and analysis

[0059] The composite membranes prepared in the embodiments and comparative examples of the present invention were subjected to performance tests in accordance with GB / T32373-2015. The test conditions were as follows: temperature: 25℃; pressure: 5.5MPa / 800psi; NaCl concentration: 32000ppm; 30ppm boric acid (5ppm boron); the test results are shown in Table 1.

[0060] Table 1

[0061]

[0062]

[0063] As shown in Table 1, the embodiments of the present invention achieve high levels in flux, sodium chloride removal efficiency, and boron removal rate. Comparative Example 1, lacking toluene diisocyanate, shows a significant decrease in flux and a boron removal rate of only 79.07%, indicating that toluene diisocyanate plays a role in regulating flux and improving the boron removal rate. Furthermore, Comparative Example 4 demonstrates that the commonly used flux-improving additive, tributyl phosphate, is far less effective than toluene diisocyanate and cannot simultaneously improve the boron removal efficiency, suggesting that a certain degree of compatibility between the aqueous and oil phase components is required for the prepared composite membrane to function effectively. Comparative Examples 2 and 5 illustrate the influence of the selection and matching of aqueous phase amines on the composite membrane performance. The present invention uses other aliphatic amines, such as ethylenediamine / propylenediamine / 1,2-diaminocyclohexane, which not only reduces the sodium chloride removal rate but also significantly decreases flux and boron removal rate. This may be because aliphatic amines lack benzene rings, have fewer rigid structures, and the resulting membrane pores are prone to collapse, leading to a decrease in both flux and desalination rate. Furthermore, comparative examples 3, 6, and 7 demonstrate the impact of post-treatment on membrane performance. The post-treatment combining aldehyde treatment and sodium nitrite treatment enables the composite membrane to possess both good flux and boron removal rate.

[0064] Application examples

[0065] The high boron removal rate composite membrane prepared in Example 1, the feed water grid, and the product water grid were rolled around the product water central tube and encapsulated with end caps and a shell to form an SW-8040 membrane element. The element was tested according to the conditions specified in GB / T34241-2017: temperature: 25℃; pressure: 5.5MPa / 800psi; NaCl concentration: 32000ppm, with an additional 5ppm boron (30ppm boric acid). The tested product water flow rate was 35.8m³. 3 / d, desalination rate 99.71%, boron removal rate 94.40% (GB / T34241-2017 SW-8040 performance requirements: water production ≥22.7m³ / d). 3 / d, desalination rate ≥99.6%.

[0066] Obviously, the above embodiments of the present invention are merely examples to clearly illustrate the technical solution of the present invention, and are not intended to limit the specific implementation of the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the claims of the present invention should be included within the protection scope of the claims of the present invention.

Claims

1. A method for preparing a composite membrane with high boron removal rate, characterized in that, Includes the following steps: S1. The base film is brought into contact with an aqueous solution to form an aqueous liquid layer, and then brought into contact with an oil solution to carry out an interfacial polymerization reaction, forming a polyamide functional layer on the base film. The aqueous phase solution comprises m-phenylenediamine, pyromellitic triamine, camphor sulfonic acid, triethylamine, and water; the oil phase solution comprises pyromellitic tricarboxylate chloride, toluene diisocyanate, and naphtha. S2. The polyamide functional layer base film obtained in step S1 is sequentially contacted with a solution containing aldehydes and a sodium nitrite solution to obtain a polyamide functional layer with high crosslinking density. S3. The base film containing the high cross-linking density polyamide functional layer obtained in step S2 is treated with NaHSO3 solution and then immersed in glycerol solution for protection to obtain the composite film with high deboronization rate. The base membrane mentioned in step S1 is a non-woven fabric supported ultrafiltration membrane, which is a polysulfone membrane, a polyethersulfone membrane, or a sulfonated polysulfone membrane.

2. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, The aqueous phase solution components in step S1, by mass percentage, are: 1.0%–1.4% m-phenylenediamine, 1.0%–1.4% pyromellitic triamine, 1%–1.4% camphor sulfonic acid, 0.5%–0.7% triethylamine, and the balance being water; the oil phase solution components, by mass percentage, are: 0.25%–0.35% pyromellitic tricarboxylate chloride, 0.05%–0.2% toluene diisocyanate, and the balance being naphtha.

3. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, The contact time with the aqueous solution in step S1 is 30-90 seconds, and the contact time with the oil solution is 30-90 seconds.

4. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, The aldehydes mentioned in step S2 include butyraldehyde, pentanaldehyde, hexanal, furfural, and glutaraldehyde.

5. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, The mass concentration of the aldehyde solution in step S2 is 0.35% to 1.0%, and the treatment time is 30 to 90 seconds.

6. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, The sodium nitrite solution in step S2 has a mass concentration of 0.2% to 0.5% and a treatment time of 30 to 90 seconds.

7. The method for preparing a composite membrane with high boron removal rate according to claim 1, characterized in that, In step S3, the NaHSO3 solution has a mass concentration of 6% to 10% and a treatment time of 3 to 6 minutes; the glycerol solution has a mass concentration of 5% to 8% and an immersion time of 3 to 10 minutes.

8. A composite membrane with high boron removal rate, characterized in that, Prepared by the method described in any one of claims 1-7.

9. The application of the composite membrane according to claim 8 in improving boron removal rate in water treatment.

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