A method for preparing a reverse osmosis membrane for seawater desalination and the resulting reverse osmosis membrane

Abstract

The application provides a preparation method of a reverse osmosis membrane for seawater desalination and the obtained reverse osmosis membrane, and the preparation method comprises the following steps: step one, preparing a polysulfone support layer; step two, preparing a cyclodextrin nanoporous intermediate layer on the polysulfone support layer through a chemical cross-linking reaction; and step three, preparing a polyamide layer on the cyclodextrin nanoporous intermediate layer to obtain the reverse osmosis membrane. The reverse osmosis membrane obtained through the preparation method provided by the application adopts the cyclodextrin to prepare the cyclodextrin nanoporous intermediate layer on the basis of the polysulfone support layer, so that the surface pore size of the support layer is reduced, the thickness, compactness and surface roughness of the subsequent polyamide layer are improved, and then the desalination rate and water flux are improved.

Description

Technical Field

[0001] This invention relates to the field of reverse osmosis membrane technology, and specifically to a method for preparing a reverse osmosis membrane for seawater desalination and the resulting reverse osmosis membrane. Background Technology

[0002] Currently, freshwater scarcity has become a growing concern, and seawater desalination is a crucial way to address the global water crisis. Reverse osmosis is a highly efficient, low-cost, and widely used seawater desalination technology, and the reverse osmosis membrane is one of the most critical components in the process. However, current reverse osmosis membranes used for seawater desalination suffer from problems such as difficulty in exceeding the upper limit of selective permeability equilibrium and poor long-term operational stability (poor high-pressure resistance).

[0003] The selectivity of the reverse osmosis membrane depends primarily on the structure of the membrane material and the properties of the polyamide layer. Existing technologies often use a polysulfone layer coated on a nonwoven fabric as a support layer, and then improve the functionality of the polyamide layer by controlling the concentration of the aqueous and oil phase solutions, adding additives, and using interfacial polymerization processes. However, the above methods have drawbacks such as a large difference in pore size between the support layer and the functional layer, poor high-pressure resistance, poor long-term operational stability, and limited improvement in the performance of the functional layer.

[0004] In summary, there is an urgent need for a reverse osmosis membrane for seawater desalination to address the problems existing in current technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a reverse osmosis membrane for seawater desalination and its preparation method, aiming to solve the problems of low selective permeability and poor high-pressure resistance of existing reverse osmosis membranes. The specific technical solution is as follows:

[0006] A method for preparing a reverse osmosis membrane for seawater desalination includes the following steps:

[0007] Step 1: Fabricate the polysulfone support layer;

[0008] Step 2: A cyclodextrin nanoporous intermediate layer is fabricated on the polysulfone support layer through a chemical cross-linking reaction;

[0009] Step 3: Fabricate a polyamide layer on the cyclodextrin nanoporous intermediate layer to obtain a reverse osmosis membrane.

[0010] Preferably, step two specifically involves: contacting the polysulfone support layer with a cyclodextrin aqueous solution for 5-20 minutes, and then heat-treating it at a temperature of 50℃-100℃ to obtain a cyclodextrin nanoporous intermediate layer; the cyclodextrin aqueous solution is an aqueous solution containing 0.5-10% cyclodextrin, 0.1-5% crosslinking agent, and 0.1-0.5% catalyst by mass concentration.

[0011] Preferably, the cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; the crosslinking agent is at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexamethylenedialdehyde, ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentanediamine, and hexamethylenediamine; and the catalyst is at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride.

[0012] Preferably, the fabrication of the polyamide layer on the cyclodextrin nanoporous interlayer includes the following steps:

[0013] Coating with polyamine aqueous solution: Contact the nanoporous intermediate layer containing cyclodextrin with polyamine aqueous solution for 1-10 minutes;

[0014] Coating with polyacryl chloride solution: Contact with polyacryl chloride solution for 15-60 seconds;

[0015] Heat treatment: Heat treatment at a temperature of 60℃-80℃ to obtain a reverse osmosis membrane.

[0016] Preferably, the polyamine aqueous solution is an aqueous solution containing 3.0-5.0% m-phenylenediamine, 0.5-1.5% 1,3,5-triaminobenzene, 1.0-1.5% triethylamine, and 1.5-2.5% camphorsulfonic acid by mass concentration.

[0017] Preferably, the polyacrylamide chloride solution is an organic solution containing 0.15-0.3% trimesoyl chloride and 0.05-0.1% isophthaloyl chloride by mass; the organic solution is a hexane solution or an ISOPARG solution.

[0018] A reverse osmosis membrane for seawater desalination, prepared by the above method, comprises a polysulfone support layer, a cyclodextrin nanoporous intermediate layer, and a polyamide layer arranged sequentially.

[0019] Preferably, the polysulfone support layer has a thickness of 40-80 μm, the cyclodextrin nanoporous intermediate layer has a thickness of 50-200 nm, and the polyamide layer has a thickness of 200-400 nm.

[0020] Preferably, the reverse osmosis membrane is a flat sheet membrane, a hollow fiber membrane, or a tubular membrane.

[0021] The application of the technical solution of the present invention has the following beneficial effects:

[0022] This invention employs a cyclodextrin nanoporous intermediate layer, constructed using cyclodextrin on top of a polysulfone support layer. This reduces the surface pore size of the support layer, increases the thickness and density of the subsequent polyamide layer, and decreases surface roughness, thereby improving desalination rate and water flux. The mechanism is as follows: the cyclodextrin nanoporous intermediate layer forms a host-guest interaction with the aqueous monomers, which can control the orderly release of the aqueous monomers during the interfacial polymerization process, regulate the thickness, density, and surface roughness of the polyamide functional layer, and significantly improve the permeate selectivity and antifouling performance of the membrane material. Meanwhile, conventional polysulfone support layers, after being directly polymerized at the interface to form a dense functional layer, are prone to collapse and damage under high pressure. However, the cyclodextrin nanoporous intermediate layer formed by chemically cross-linking cyclodextrin has a smaller pore size. As a connecting layer between the functional layer and the support layer of the reverse osmosis membrane, it can enhance the connection strength with the functional layer and improve the membrane material's pressure resistance and desalination rate. Furthermore, cyclodextrin has a slightly conical hollow cylindrical three-dimensional ring structure with a large number of hydroxyl groups on its outer side, making it hydrophilic. The cavity is shielded by CH bonds, forming a hydrophobic region. Therefore, the cyclodextrin nanoporous intermediate layer can increase the water permeation rate and improve the water flux of the reverse osmosis membrane.

[0023] In addition to the objectives, features, and advantages described above, the present invention has other objectives, features, and advantages. The invention will now be described in further detail with reference to the figures. Attached Figure Description

[0024] The accompanying drawings, which form part of this application, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings:

[0025] Figure 1 This is a cross-sectional electron microscope image of the reverse osmosis membrane prepared in Comparative Example 1 of this invention;

[0026] Figure 2 This is a cross-sectional electron microscope image of the reverse osmosis membrane prepared in Example 1 of the present invention;

[0027] Figure 3 This is a surface electron microscope image of the reverse osmosis membrane prepared in Comparative Example 1 of this invention;

[0028] Figure 4 This is a surface electron microscope image of the reverse osmosis membrane prepared in Example 1 of the present invention. Detailed Implementation

[0029] To facilitate understanding of the present invention, a more comprehensive description is provided below, along with preferred embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a thorough and complete understanding of the disclosure of the present invention.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention.

[0031] Example 1:

[0032] Rinse the surface of the polysulfone support layer repeatedly with deionized water, and then purge the film surface with nitrogen until there are no droplets.

[0033] A cyclodextrin nanoporous intermediate layer was prepared on a polysulfone support layer by a chemical crosslinking reaction: the polysulfone support layer was contacted with a cyclodextrin aqueous solution (containing 2.5% α-cyclodextrin, 1% 1,3-propanediamine, and 0.5% N,N'-diisopropylcarbodiimide solution) for 10 minutes, and then heat-treated at 65°C to obtain a membrane containing a cyclodextrin nanoporous intermediate layer.

[0034] Prepare a polyamine aqueous solution (containing 3.5% m-phenylenediamine, 1.0% 1,3,5-triaminobenzene, 1.2% triethylamine, and 2.4% camphor sulfonic acid by mass concentration). Contact the membrane surface containing the cyclodextrin nanoporous intermediate layer with the above polyamine aqueous solution for 60 seconds, and then purge the membrane surface with nitrogen gas until no droplets remain.

[0035] A polyacrylamide chloride solution (containing 0.25% trimesoyl chloride and 0.05% isophthaloyl chloride in hexane) was prepared. The surface of a cyclodextrin nanoporous interlayer membrane immersed in a polyamine aqueous solution was contacted with the polyacrylamide chloride solution for 20 seconds. After the organic solvent evaporated, the membrane was heat-treated at 70°C to obtain a reverse osmosis membrane. (See [link to relevant documentation]). Figure 2 and Figure 4 .

[0036] Example 2: The difference from Example 1 is that the cyclodextrin aqueous solution is a solution of 10% α-cyclodextrin, 5% glyoxal, and 0.5% hydrochloric acid; the polyamine aqueous solution is a solution of 3.5% m-phenylenediamine, 1.0% 1,3,5-triaminobenzene, 1.2% triethylamine, and 2.4% camphor sulfonic acid; the polyacrylamide chloride solution is a solution of 0.3% trimesoyl chloride and 0.05% isophthaloyl chloride in hexane; and other aspects not mentioned are the same as in Example 1.

[0037] Example 3: The difference from Example 1 is that the cyclodextrin aqueous solution is 0.5% β-cyclodextrin, 0.1% glutaraldehyde and 0.1% sulfuric acid solution, the polyamine aqueous solution is 3.0% m-phenylenediamine, 1.5% 1,3,5-triaminobenzene, 1.2% triethylamine and 2.4% camphor sulfonic acid, the polyacrylamide chloride solution is 0.25% trimesoyl chloride and 0.1% isophthaloyl chloride in hexane solution, and other aspects not mentioned are the same as in Example 1.

[0038] Comparative Example 1:

[0039] Rinse the surface of the polysulfone support layer repeatedly with deionized water, and then purge the film surface with nitrogen until there are no droplets.

[0040] Prepare an aqueous solution of polyamine containing 3.5% m-phenylenediamine, 1.0% 1,3,5-triaminobenzene, 1.2% triethylamine, and 2.4% camphor sulfonic acid. Contact the surface of the polysulfone support layer with the above aqueous solution of polyamine for 60 seconds, and then purge the film surface with nitrogen until there are no droplets.

[0041] A hexane solution containing 0.25% (w / w) trimesoyl chloride and 0.05% (w / w) isophthaloyl chloride was prepared. The surface of a polysulfone support layer impregnated with an aqueous solution of a polyamine was contacted with the polyacrylamide chloride solution for 20 seconds. After the organic solvent evaporated, the membrane was heat-treated at 70°C to obtain a reverse osmosis membrane. (See [link to relevant documentation]). Figure 1 and Figure 3 .

[0042] Comparative Example 2: The difference from Example 1 is that the cyclodextrin aqueous solution is a solution of 0.1% γ-cyclodextrin, 1% 1,3-propanediamine, and 0.5% N,N'-diisopropylcarbodiimide; the polyamine aqueous solution is a solution of 3.6% m-phenylenediamine, 0.8% 1,3,5-triaminobenzene, 1.2% triethylamine, and 2.4% camphor sulfonic acid; and the polyacrylamide chloride solution is a solution of 0.28% trimesoyl chloride and 0.05% isophthaloyl chloride in hexane. Other aspects not mentioned are the same as in Example 1.

[0043] Comparative Example 3: The difference from Example 1 is that the cyclodextrin aqueous solution is a solution of 12% β-cyclodextrin, 1% 1,3-propanediamine, and 0.5% N,N'-diisopropylcarbodiimide; the polyamine aqueous solution is a solution of 3.5% m-phenylenediamine, 1.0% 1,3,5-triaminobenzene, 1.2% triethylamine, and 2.4% camphor sulfonic acid; and the polyacrylamide chloride solution is a solution of 0.28% trimesoyl chloride and 0.05% isophthaloyl chloride in hexane. Other aspects not mentioned are the same as in Example 1.

[0044] Comparative Example 4: The difference from Comparative Example 1 is that it also includes a cyclodextrin nanoporous intermediate layer on the polyamide layer: the reverse osmosis membrane is contacted with a cyclodextrin aqueous solution (containing 2.5% α-cyclodextrin, 1% 1,3-propanediamine, and 0.5% N,N'-diisopropylcarbodiimide solution) for 10 minutes, and then heat-treated at 65°C to obtain a reverse osmosis membrane containing a cyclodextrin nanoporous intermediate layer.

[0045] The reverse osmosis membranes obtained in Examples 1-3 and Comparative Examples 1-4 were tested on a cross-flow membrane test bench. Under the test conditions of 32000ppm NaCl aqueous solution, 800psi operating pressure, 25℃ temperature, and pH 7-8, the water flux and desalination rate of the membranes were tested. The membranes were then run at 1500psi pressure for 4 hours, and the above conditions were tested again. The results are shown in Table 2.

[0046] Table 2. Experimental results of Examples 1-3 and Comparative Examples 1-4

[0047]

[0048] The experimental results of Examples 1-3 and Comparative Examples 2-3 show that by adjusting the appropriate cyclodextrin concentration, it is possible to maintain a high water flux while maintaining a high desalination rate, and even after high-pressure operation, it is still possible to ensure both high water flux and high desalination rate.

[0049] When the cyclodextrin concentration is too low, the water flux decreases due to the thinness of the cyclodextrin nanoporous interlayer. Furthermore, the reverse osmosis membrane is prone to damage under high pressure, resulting in a sharp increase in water flux and a decrease in desalination rate. When the cyclodextrin concentration is too high, the water flux inevitably decreases due to the excessive thickness of the cyclodextrin nanoporous interlayer and the excessively long water channels. Even though the cyclodextrin nanoporous interlayer can increase the water permeation rate, the water flux will inevitably decrease.

[0050] As can be seen from Example 1 and Comparative Example 1, on the one hand, the cyclodextrin nanoporous intermediate layer formed by cyclodextrin of appropriate concentration can increase the water flux of the reverse osmosis membrane. The mechanism is that cyclodextrin has a slightly conical hollow cylindrical three-dimensional ring structure, which contains a large number of hydroxyl groups on the outside and is hydrophilic, while the cavity is shielded by CH bonds and forms a hydrophobic region. Therefore, the cyclodextrin nanoporous intermediate layer formed by cyclodextrin can increase the water permeation rate and improve the water flux of the reverse osmosis membrane.

[0051] On the other hand, the cyclodextrin nanoporous interlayer can enhance the high pressure resistance of the reverse osmosis membrane. For example, the anti-permeation membrane in Comparative Example 1, which does not have a cyclodextrin nanoporous interlayer, has a large increase in water flux and a decrease in desalination rate after high pressure operation. This may be due to damage to the reverse osmosis membrane during high pressure operation.

[0052] As can be seen from Example 1 and Comparative Example 4, the arrangement order of the polysulfone support layer, the cyclodextrin nanoporous intermediate layer, and the polyamide layer in the reverse osmosis membrane is very important. When the reverse osmosis membrane obtained by the preparation method described in Comparative Example 4 is implemented, its water flux under standard test is low, while its water flux increase after high-pressure operation is large. The mechanism is that the cyclodextrin nanoporous layer on the polyamide layer prolongs the water channel, resulting in a decrease in water flux. After high-pressure operation, due to the large pore size of the polysulfone support layer, the polyamide layer collapses and is damaged at the large pores, and the cyclodextrin nanoporous layer on the upper layer cannot play a reinforcing role, resulting in a large increase in water flux and a decrease in desalination rate after high-pressure operation.

[0053] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a reverse osmosis membrane for seawater desalination, characterized in that, Includes the following steps: Step 1: Fabricate the polysulfone support layer; Step 2: A cyclodextrin nanoporous intermediate layer is fabricated on the polysulfone support layer through a chemical cross-linking reaction; Step 3: Fabricate a polyamide layer on the cyclodextrin nanoporous intermediate layer to obtain a reverse osmosis membrane; Step two specifically involves contacting the polysulfone support layer with a cyclodextrin aqueous solution for 5-20 minutes and then heat-treating it at a temperature of 50℃-100℃ to obtain a cyclodextrin nanoporous intermediate layer; the cyclodextrin aqueous solution is an aqueous solution containing 0.5-10% cyclodextrin, 0.1-5% crosslinking agent, and 0.1-0.5% catalyst by mass concentration. The cyclodextrin includes at least one of α-cyclodextrin, β-cyclodextrin, and γ-cyclodextrin; the crosslinking agent is at least one of glyoxal, malondialdehyde, succinaldehyde, glutaraldehyde, hexamethylenedialdehyde, ethylenediamine, 1,2-propanediamine, 1,3-propanediamine, 1,4-butanediamine, pentanediamine, and hexamethylenediamine; the catalyst is at least one of hydrochloric acid, sulfuric acid, phosphoric acid, nitric acid, dicyclohexylcarbodiimide, N,N'-diisopropylcarbodiimide, and 1-(3-dimethylaminopropyl)-3-ethylcarbodiimide hydrochloride. Step three includes the following steps: Coating with polyamine aqueous solution: Contact the nanoporous intermediate layer containing cyclodextrin with polyamine aqueous solution for 1-10 minutes; Coating with polyacryl chloride solution: Contact with polyacryl chloride solution for 15-60 seconds; Heat treatment: Heat treatment at a temperature of 60℃-80℃ to obtain a reverse osmosis membrane.

2. The preparation method according to claim 1, characterized in that, The polyamine aqueous solution contains 3.0-5.0% m-phenylenediamine, 0.5-1.5% 1,3,5-triaminobenzene, 1.0-1.5% triethylamine, and 1.5-2.5% camphorsulfonic acid by mass concentration.

3. The preparation method according to claim 1, characterized in that, The polyacrylamide chloride solution is an organic solution containing 0.15-0.3% trimesoyl chloride and 0.05-0.1% isophthaloyl chloride by mass; the organic solution is a hexane solution or an ISOPAR G solution.

4. A reverse osmosis membrane for seawater desalination, characterized in that, The preparation method described in any one of claims 1-3 is used to prepare the product, which includes a polysulfone support layer, a cyclodextrin nanoporous intermediate layer and a polyamide layer arranged sequentially.

5. The reverse osmosis membrane for seawater desalination according to claim 4, characterized in that, The polysulfone support layer has a thickness of 40-80 μm, the cyclodextrin nanoporous intermediate layer has a thickness of 50-200 nm, and the polyamide layer has a thickness of 200-400 nm.

6. The reverse osmosis membrane for seawater desalination according to claim 4, characterized in that, The reverse osmosis membrane can be a flat sheet membrane, a hollow fiber membrane, or a tubular membrane.

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