High desulfurization rate reverse osmosis membrane, preparation method and application thereof

Abstract

The application relates to the technical field of membrane separation and seawater desalination, in particular to a high-desalination-rate reverse osmosis membrane and a preparation method and application thereof. The polyamide reverse osmosis membrane with at least 70% nodular regions on the surface is prepared by introducing ethylenediaminetetraacetic acid metal salt as a complexing additive in an aqueous solution, and the polyamide reverse osmosis membrane can improve the desalination rate of the membrane on the basis of ensuring the membrane interception rate and flux.

Description

Technical Field

[0001] This invention relates to the field of membrane separation and seawater desalination technology, specifically to a high boron removal rate reverse osmosis membrane, its preparation method, and its application. Background Technology

[0002] With global population growth and industrial development, freshwater resources are becoming increasingly scarce, and seawater desalination technology has become an important way to obtain usable freshwater. Among them, reverse osmosis (RO) membrane technology has become the mainstream technology for seawater desalination due to its advantages such as low energy consumption, high-quality produced water, and stable operation.

[0003] Most existing commercial reverse osmosis membranes are aromatic polyamide film composite membranes, which form a separation layer through an interfacial polymerization reaction between an aqueous aromatic diamine monomer (such as m-phenylenediamine, MPD) and an organic polyacrylamide chloride (such as trimesoyl chloride, TMC). These membranes have achieved salt rejection rates exceeding 99.5%, but their performance in removing neutral small-molecule boric acid (H3BO3) from seawater is insufficient. Therefore, improving the boron removal capacity of reverse osmosis membranes has been an important research direction in this field.

[0004] In existing technologies, inorganic salts or small-molecule solvents are added to the aqueous or organic phase to improve membrane performance, thereby regulating MPD diffusion behavior or reducing interfacial tension and improving membrane morphology and structure. However, because these additives have a single function, they are prone to interfacial instability or structural defects, making it difficult to balance flux and selectivity, and they also fail to solve the problem of low boron removal rate. Therefore, how to improve the boron removal rate of polyamide reverse osmosis membranes while ensuring the rejection rate and flux is an urgent problem to be solved. Summary of the Invention

[0005] To address the aforementioned problems, this invention prepares a polyamide reverse osmosis membrane with a nodular region covering at least 70% of the surface area by adding ethylenediaminetetraacetic acid metal salt to the aqueous phase, thereby improving the deboron removal rate of the membrane while ensuring membrane rejection rate and flux.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a high boron removal rate reverse osmosis membrane involves sequentially contacting a porous base membrane with an aqueous solution and an organic solution containing a complexing additive to form a polyamide reverse osmosis membrane via interfacial polymerization. The complexing additive is an ethylenediaminetetraacetic acid (EDTA) metal salt, and neither the aqueous solution nor the organic solution contains any additives that react with the EDTA metal salt. The surface of the reverse osmosis membrane has at least 70% nodular regions.

[0008] Preferably, the aqueous solution contains a polyamine monomer, and the concentration of the polyamine monomer in the aqueous solution is 0.5-5 wt%; the polyamine monomer is selected from one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, diaminotoluene, ethylenediamine, propylenediamine, butanediamine, diaminocyclohexane, and piperazine.

[0009] Preferably, the complexing additive is selected from one or more of the following: disodium ethylenediaminetetraacetate, dipotassium ethylenediaminetetraacetate, trisodium ethylenediaminetetraacetate, tripotassium ethylenediaminetetraacetate, tetrasodium ethylenediaminetetraacetate, tetrapotassium ethylenediaminetetraacetate, calcium disodium ethylenediaminetetraacetate, magnesium disodium ethylenediaminetetraacetate, aluminum disodium ethylenediaminetetraacetate, zinc disodium ethylenediaminetetraacetate, barium disodium ethylenediaminetetraacetate, manganese disodium ethylenediaminetetraacetate, cobalt disodium ethylenediaminetetraacetate, copper disodium ethylenediaminetetraacetate, nickel disodium ethylenediaminetetraacetate, iron disodium ethylenediaminetetraacetate, lead disodium ethylenediaminetetraacetate, silver disodium ethylenediaminetetraacetate, and cadmium disodium ethylenediaminetetraacetate; the concentration of the complexing additive in the aqueous solution is 0.01-5 wt%.

[0010] Preferably, the organic phase solution contains a polyacrylamide chloride monomer, and the concentration of the polyacrylamide chloride monomer in the organic phase solution is 0.01-5 wt%; the polyacrylamide chloride monomer is selected from one or more of the following: trimesoyl chloride, terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylate chloride, biphenyl tricarboxylate chloride, biphenyl tetracarboxylate chloride, naphthalene dicarboxylate chloride, naphthalene tricarboxylate chloride, naphthalene tetracarboxylate chloride, malonyl chloride, succinicoyl chloride, glutaryl chloride, and adipyl chloride.

[0011] Preferably, the organic phase solution contains an alkane solvent, which is selected from one or more of hexaane, heptane, octane, nonane, decane, undecane, dodecane, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M.

[0012] Preferably, the contact time between the surface of the porous base membrane and the aqueous solution is 1-300 s; the contact time between the surface of the porous base membrane and the organic solution is 1-300 s.

[0013] Preferably, the porous base membrane is made of one of the following materials: polysulfone, polyethersulfone, polyphenylsulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyetherimide, polyacrylonitrile, polyphenylene ether, polyphenylene sulfide, polyether ketone, and polyarylether ketone.

[0014] Preferably, after the polyamide reverse osmosis membrane is formed by interfacial polymerization, the polyamide separation layer is further subjected to post-treatment, wherein the post-treatment is selected from one or more of diazotization, acylation, amination or surface grafting modification.

[0015] The present invention also provides a high boron removal rate reverse osmosis membrane prepared according to the above preparation method, wherein the surface has at least 70% nodular regions.

[0016] The high boron removal rate reverse osmosis membrane provided by this invention can be used in water treatment.

[0017] Compared with the prior art, the present invention has the following advantages:

[0018] First, this invention introduces ethylenediaminetetraacetic acid (EDTA) metal salt as a complexing additive into an aqueous solution to prepare a polyamide reverse osmosis membrane with at least 70% nodular region on its surface. This membrane can improve the boron removal rate while maintaining the membrane rejection rate and flux, increasing the boric acid rejection rate by approximately 7%-12%. Second, the addition of EDTA metal salt significantly inhibits the diffusion of amine monomers into the organic phase, making the diffusion uniform and controllable, which helps to form a homogeneous and dense polyamide layer. Specifically, the metal cation effectively inhibits the cross-interface diffusion of amine monomers, reducing the reaction zone and enhancing the controllability of the reaction; simultaneously, the EDTA anion, by adjusting the interfacial polarity and solvation state, causes an incremental enrichment of amine monomers at the interface, thereby achieving controllable inhibition of amine monomer migration. Attached Figure Description

[0019] Figure 1 These are scanning electron microscope (SEM) images of the surface and cross-section of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Example 1, wherein the SEM images of the surface of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Example 1 are magnified to 50,000; and the SEM images of the cross-section of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Example 1 are magnified to 10,000. Detailed Implementation

[0020] The following is a further detailed description of the present invention in conjunction with specific preferred embodiments, and it should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention. Specific conditions not specified in the embodiments are performed according to conventional conditions or conditions recommended by the manufacturer. Unless otherwise specified, all reagents or instruments used are conventional products obtained through commercial channels.

[0021] Example 1

[0022] This embodiment provides a method for preparing a reverse osmosis membrane, and the specific preparation process is as follows:

[0023] (1) Preparation of aqueous solution

[0024] m-phenylenediamine, camphor sulfonic acid, triethylamine, and tetrasodium ethylenediaminetetraacetate were added sequentially to deionized water to prepare a homogeneous and transparent aqueous solution. The concentrations of each component in the aqueous solution were as follows: 4 wt% m-phenylenediamine, 3 wt% camphor sulfonic acid, 2 wt% triethylamine, and 0.01 wt% tetrasodium ethylenediaminetetraacetate.

[0025] (2) Preparation of organic phase solution

[0026] Tristyroyl chloride was added to Isopar G organic solvent to prepare a homogeneous and transparent organic phase solution. The concentration of the components in the organic phase solution was as follows: 0.25 wt% tristyroyl chloride.

[0027] (3) Contact the surface of the polysulfone membrane with the aqueous solution prepared in step (1) for 10s, remove the excess aqueous solution on the surface, and contact the membrane layer formed by the aqueous solution with the organic solution prepared in step (2) to undergo interfacial polymerization reaction for 10s. After the reaction is completed, remove the excess organic solution on the surface to obtain the nascent reverse osmosis membrane.

[0028] (4) Heat-treat the nascent reverse osmosis membrane in a 90℃ oven for 6 minutes.

[0029] (5) Rinse the reverse osmosis membrane prepared in step (4) with deionized water.

[0030] Example 2

[0031] This embodiment provides a method for preparing a reverse osmosis membrane, and the specific preparation process is as follows:

[0032] (1) Preparation of aqueous solution

[0033] m-phenylenediamine, camphor sulfonic acid, triethylamine, and tetrasodium ethylenediaminetetraacetate were added sequentially to deionized water to prepare a homogeneous and transparent aqueous solution. The concentrations of each component in the aqueous solution were as follows: 4 wt% m-phenylenediamine, 3 wt% camphor sulfonic acid, 2 wt% triethylamine, and 0.5 wt% tetrasodium ethylenediaminetetraacetate.

[0034] (2) Preparation of organic phase solution

[0035] Tristyroyl chloride was added to Isopar G organic solvent to prepare a homogeneous and transparent organic phase solution. The concentration of the components in the organic phase solution was as follows: 0.25 wt% tristyroyl chloride.

[0036] (3) Contact the surface of the polysulfone membrane with the aqueous solution prepared in step (1) for 10s, remove the excess aqueous solution on the surface, and contact the membrane layer formed by the aqueous solution with the organic solution prepared in step (2) to undergo interfacial polymerization reaction for 10s. After the reaction is completed, remove the excess organic solution on the surface to obtain the nascent reverse osmosis membrane.

[0037] (4) Heat-treat the nascent reverse osmosis membrane in a 90℃ oven for 6 minutes.

[0038] (5) Rinse the reverse osmosis membrane prepared in step (4) with deionized water.

[0039] Example 3

[0040] This embodiment provides a method for preparing a reverse osmosis membrane, and the specific preparation process is as follows:

[0041] (1) Preparation of aqueous solution

[0042] m-phenylenediamine, camphor sulfonic acid, triethylamine, and tetrasodium ethylenediaminetetraacetate were added sequentially to deionized water to prepare a homogeneous and transparent aqueous solution. The concentrations of each component in the aqueous solution were as follows: 4 wt% m-phenylenediamine, 3 wt% camphor sulfonic acid, 2 wt% triethylamine, and 5 wt% tetrasodium ethylenediaminetetraacetate.

[0043] (2) Preparation of organic phase solution

[0044] Tristyroyl chloride was added to Isopar G organic solvent to prepare a homogeneous and transparent organic phase solution. The concentration of the components in the organic phase solution was as follows: 0.25 wt% tristyroyl chloride.

[0045] (3) Contact the surface of the polysulfone membrane with the aqueous solution prepared in step (1) for 10s, remove the excess aqueous solution on the surface, and contact the membrane layer formed by the aqueous solution with the organic solution prepared in step (2) to undergo interfacial polymerization reaction for 10s. After the reaction is completed, remove the excess organic solution on the surface to obtain the nascent reverse osmosis membrane.

[0046] (4) Heat-treat the nascent reverse osmosis membrane in a 90℃ oven for 6 minutes.

[0047] (5) Rinse the reverse osmosis membrane prepared in step (4) with deionized water.

[0048] Example 4

[0049] This embodiment provides a method for preparing a high-performance boron-removing reverse osmosis membrane. The specific preparation process is as follows:

[0050] (1) Preparation of aqueous solution

[0051] m-phenylenediamine, camphor sulfonic acid, triethylamine, and tetrasodium ethylenediaminetetraacetate were added sequentially to deionized water to prepare a homogeneous and transparent aqueous solution. The concentrations of each component in the aqueous solution were as follows: 4 wt% m-phenylenediamine, 3 wt% camphor sulfonic acid, 2 wt% triethylamine, and 0.5 wt% tetrasodium ethylenediaminetetraacetate.

[0052] (2) Preparation of organic phase solution

[0053] Tristyroyl chloride was added to Isopar G organic solvent to prepare a homogeneous and transparent organic phase solution. The concentration of the components in the organic phase solution was as follows: 0.25 wt% tristyroyl chloride.

[0054] (3) Contact the surface of the polysulfone membrane with the aqueous solution prepared in step (1) for 10s, remove the excess aqueous solution on the surface, and contact the membrane layer formed by the aqueous solution with the organic solution prepared in step (2) to undergo interfacial polymerization reaction for 10s. After the reaction is completed, remove the excess organic solution on the surface to obtain the nascent reverse osmosis membrane.

[0055] (4) Heat-treat the nascent reverse osmosis membrane in a 90℃ oven for 6 minutes.

[0056] (5) Soak the nascent reverse osmosis membrane in 0.4wt% sodium nitrite (pH 2-5) for 60s, drain, and then soak in 1.0wt% sodium bisulfite for 60s.

[0057] Example 5

[0058] This embodiment provides a method for preparing a reverse osmosis membrane, and the specific preparation process is as follows:

[0059] (1) Preparation of aqueous solution

[0060] m-phenylenediamine, camphor sulfonic acid, triethylamine, and zinc disodium ethylenediaminetetraacetate were sequentially added to deionized water to prepare a homogeneous and transparent aqueous solution. The concentrations of each component in the aqueous solution were as follows: 4 wt% m-phenylenediamine, 3 wt% camphor sulfonic acid, 2 wt% triethylamine, and 0.5 wt% zinc disodium ethylenediaminetetraacetate.

[0061] (2) Preparation of organic phase solution

[0062] Tristyroyl chloride was added to Isopar G organic solvent to prepare a homogeneous and transparent organic phase solution. The concentration of the components in the organic phase solution was as follows: 0.25 wt% tristyroyl chloride.

[0063] (3) Contact the surface of the polysulfone membrane with the aqueous solution prepared in step (1) for 10s, remove the excess aqueous solution on the surface, and contact the membrane layer formed by the aqueous solution with the organic solution prepared in step (2) to undergo interfacial polymerization reaction for 10s. After the reaction is completed, remove the excess organic solution on the surface to obtain the nascent reverse osmosis membrane.

[0064] (4) Heat-treat the nascent reverse osmosis membrane in a 90℃ oven for 6 minutes.

[0065] (5) Rinse the reverse osmosis membrane prepared in step (4) with deionized water.

[0066] Comparative Example 1

[0067] The difference between this comparative example and Example 1 is that no tetrasodium ethylenediaminetetraacetate was added to the aqueous solution; otherwise, they are the same as in Example 1.

[0068] Comparative Example 2

[0069] The difference between this comparative example and Example 2 is that 0.5 wt% ethylenediaminetetraacetic acid (EDTA) was added to the aqueous solution instead of sodium EDTA, while the rest remained the same as in Example 1.

[0070] Comparative Example 3

[0071] The difference between this comparative example and Example 4 is that no tetrasodium ethylenediaminetetraacetate was added to the aqueous solution; otherwise, they are the same as in Example 4.

[0072] Comparative Example 4

[0073] The difference between this comparative example and Example 2 is that 0.5 wt% sodium citrate was added to the aqueous solution instead of sodium ethylenediaminetetraacetate, while the rest remained the same as in Example 1.

[0074] Comparative Example 5

[0075] The difference between this comparative example and Example 1 is that tetrasodium ethylenediaminetetraacetate (EDTA) is not added to the aqueous phase, but instead added to the organic phase solution; otherwise, it remains the same as in Example 1. In this comparative example, because ETA is insoluble in the organic phase solution, the resulting membrane is defective and cannot be used as a reverse osmosis membrane.

[0076] Characterization

[0077] The performance of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Examples 1-4 was tested under the following conditions: sodium chloride concentration of 32000 ppm, boric acid concentration of 5 ppm, test temperature of 25°C, and test pressure of 5.5 MPa. The results of water flux, salt and boron rejection of each reverse osmosis membrane are shown in Table 1.

[0078] Table 1 Performance test results of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Examples 1-4

[0079]

[0080] The addition of EDTA-4Na regulates the interfacial rate of MPD in the water-organic cross-phase. Through the synergistic effect of carboxylate ions and metal ions, the interfacial polymerization rate becomes controllable, resulting in a denser polyamide reverse osmosis membrane with improved desalination and deboronization performance.

[0081] Test Example 2

[0082] The surfaces of the reverse osmosis membranes obtained in Examples 1-5 and Comparative Example 1 were observed using a scanning electron microscope. The SEM images of the surfaces of the reverse osmosis membranes in Examples 1-5 and Comparative Example 1 were taken at a magnification of 50,000; the SEM images of the cross-sections of the reverse osmosis membranes in Examples 1-5 and Comparative Example 1 were taken at a magnification of 10,000. The results are as follows: Figure 1 As shown.

[0083] based on Figure 1 As can be seen, the surface of the reverse osmosis membrane obtained in the aqueous phase of Comparative Example 1 without the addition of complexing additives consists of typical tightly packed fine "nodular" structures and "blade" shapes, exhibiting the wrinkled state characteristic of polyamide reverse osmosis membranes. The "nodular" structures exhibit a spherical configuration with ridge-valley undulations, while the "blades" appear as smooth, extended, sheet-like blades. (Observation) Figure 1 As shown in Example 1, the polyamide structure with a "nodular" structure on the surface of the reverse osmosis membrane obtained by adding a complexing additive to the aqueous phase gradually replaces the original "leaf" structure, transforming the surface into a more uniform and smooth nodular structure. Furthermore, with increasing concentration and enhanced regulatory effect, the surface structure of Examples 2 and 3 shows a more significant improvement, and Example 3 shows almost no "leaf" structure on the membrane surface. Example 4 demonstrates that diazotization treatment also rearranges and adjusts the membrane surface structure, and the "leaf" structure on the membrane surface is reduced. This reduction in the "leaf" structure verifies the increased density of the separation layer structure, indicating that the present invention improves the reduction of pore size distribution and enhances the degree of crosslinking of the separation layer through the participation of complexing additives in interface regulation.

[0084] Test Example 3

[0085] use Figure 1 The SEM images of Examples 1-5 and Comparative Example 1 were analyzed using ImageJ software to determine the area ratio of the "leaf-like structure" and "nodular structure" regions. The results of the structural area test are shown in Table 2 (due to the incompleteness of the interfacial polymerization reaction, small oligomers will appear during the reverse osmosis membrane formation process, so the sum of the area ratios of the "leaf-like structure" and "nodular structure" regions is less than 100%).

[0086] Table 2. Percentage of each region on the surface of the reverse osmosis membrane samples obtained in Examples 1-5 and Comparative Example 1

[0087]

[0088] As shown in Table 2, the addition of complexing additives to the aqueous phase reduces the "leaf-like" structure on the surface of the separation layer and transforms it into a more uniform and dense "nodular" structure.

[0089] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them. The basic principles and main features of the present invention have been described above with specific implementation schemes. Based on the present invention, some modifications or substitutions can be made, but these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of protection claimed by the present invention.

Claims

1. A method for preparing a high boron removal rate reverse osmosis membrane, characterized in that, A porous base membrane is sequentially contacted with an aqueous phase solution and an organic phase solution to form a polyamide reverse osmosis membrane through interfacial polymerization. The aqueous phase solution contains a complexing additive, which is an ethylenediaminetetraacetic acid (EDTA) metal salt. Neither the aqueous phase solution nor the organic phase solution contains any additives that react with the EDTA metal salt. The surface of the reverse osmosis membrane has at least 70% nodular regions.

2. The preparation method according to claim 1, characterized in that, The aqueous solution contains a polyamine monomer, and the concentration of the polyamine monomer in the aqueous solution is 0.5-5 wt%; the polyamine monomer is selected from one or more of o-phenylenediamine, m-phenylenediamine, p-phenylenediamine, 1,3,5-triaminobenzene, diaminotoluene, ethylenediamine, propylenediamine, butanediamine, diaminocyclohexane, and piperazine.

3. The preparation method according to claim 1, characterized in that, The complexing additive is selected from one or more of the following: disodium ethylenediaminetetraacetate (EDTA), dipotassium ethylenediaminetetraacetate (EDTA), trisodium ethylenediaminetetraacetate (EDTA), tripotassium ethylenediaminetetraacetate (EDTA), tetrasodium ethylenediaminetetraacetate (EDTA), tetrapotassium ethylenediaminetetraacetate (EDTA), calcium disodium ethylenediaminetetraacetate (EDTA), magnesium disodium ethylenediaminetetraacetate (EDTA), aluminum disodium ethylenediaminetetraacetate (EDTA), zinc disodium ethylenediaminetetraacetate (EDTA), barium disodium ethylenediaminetetraacetate (EDTA), manganese disodium ethylenediaminetetraacetate (EDTA), cobalt disodium ethylenediaminetetraacetate (EDTA), copper disodium ethylenediaminetetraacetate (EDTA), nickel disodium ethylenediaminetetraacetate (EDTA), iron disodium ethylenediaminetetraacetate (EDTA), lead disodium ethylenediaminetetraacetate (EDTA), silver disodium ethylenediaminetetraacetate (EDTA), and cadmium disodium ethylenediaminetetraacetate (EDTA); the concentration of the complexing additive in the aqueous solution is 0.01-5 wt%.

4. The preparation method according to claim 1, characterized in that, The organic phase solution contains a polyacrylamide chloride monomer, and the concentration of the polyacrylamide chloride monomer in the organic phase solution is 0.01-5 wt%; the polyacrylamide chloride monomer is selected from one or more of the following: pyromellitic terephthaloyl chloride, isophthaloyl chloride, biphenyl dicarboxylate chloride, biphenyl tricarboxylate chloride, biphenyl tetracarboxylate chloride, naphthalene dicarboxylate chloride, naphthalene tricarboxylate chloride, naphthalene tetracarboxylate chloride, malonyl chloride, succinic acid chloride, glutaryl chloride, and adipyl chloride.

5. The preparation method according to claim 1, characterized in that, The organic phase solution contains an alkane solvent, which is selected from one or more of hexaane, heptane, octane, nonane, decane, undecane, dodecane, Isopar C, Isopar E, Isopar G, Isopar H, Isopar L, and Isopar M.

6. The preparation method according to claim 1, characterized in that, The contact time between the surface of the porous base membrane and the aqueous solution is 1-300 s; the contact time between the surface of the porous base membrane and the organic solution is 1-300 s.

7. The preparation method according to claim 1, characterized in that, The porous base membrane is made of one of the following materials: polysulfone, polyethersulfone, polyphenylsulfone, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene, polypropylene, polyimide, polyetherimide, polyacrylonitrile, polyphenylene ether, polyphenylene sulfide, polyether ketone, and polyarylether ketone.

8. The preparation method according to claim 1, characterized in that, After the polyamide reverse osmosis membrane is formed by interfacial polymerization, the polyamide separation layer is further subjected to post-treatment, which is selected from one or more of diazotization, acylation, amination or surface grafting modification.

9. A high boron removal rate reverse osmosis membrane prepared by the preparation method according to claim 1, characterized in that, The surface of the reverse osmosis membrane has at least 70% nodular regions.

10. The application of the high boron removal rate reverse osmosis membrane according to claim 9 in water treatment.

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