A high separation selectivity nanofiltration membrane and a preparation method thereof

Abstract

The application provides a high separation selectivity nanofiltration membrane and a preparation method thereof. The nanofiltration membrane comprises a base film layer and a separation layer formed on the base film layer; wherein the separation layer is prepared by interfacial polymerization of a water phase containing a first water phase monomer, a second water phase monomer and a humectant and an organic phase containing trimesoyl chloride. The nanofiltration membrane has a divalent ion desalination rate of up to 99.5%, a monovalent ion desalination rate of less than 15%, and meanwhile, the roll qualified rate of the membrane element is improved.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of water treatment membranes, and particularly relates to a high-separation-selectivity nanofiltration membrane and a preparation method thereof. BACKGROUND

[0002] The current new energy market is extremely hot, especially in the field of new energy electric vehicles. The domestic market is far ahead, and lithium batteries, as an important part of new energy electric vehicles, are being developed by major enterprises as the first track. The salt lake lithium extraction industry, which is closely related to membrane technology, is an important part of the lithium resource provided for lithium batteries. The industry applies a large number of high-selectivity nanofiltration membranes as an important part of magnesium-lithium separation. The application of membrane technology rapidly improves the efficiency of salt lake lithium extraction. On the other hand, the municipal water treatment industry is also undergoing technology iteration and upgrading, from the original ultrafiltration membrane filtration to nanofiltration membrane filtration. In the field of municipal water treatment, not only is it required that the nanofiltration membrane has a high flux, but it is also required that it has high selectivity to effectively remove impurities such as dissolved solutes, organic matter, colloids, bacteria, and microorganisms in water, while retaining part of the ions needed by the human body. Therefore, it is crucial to develop a nanofiltration membrane with high selectivity.

[0003] At present, there are many types of nanofiltration membranes on the market, among which polyamide composite nanofiltration membranes have attracted widespread attention and use due to their excellent physicochemical properties. Commercial nanofiltration membranes mostly use piperazine as the water phase monomer and glycerol as the pore stabilizer in the manufacturing process. However, the polyamide composite nanofiltration membranes prepared by the above method have some disadvantages, such as the swelling effect of glycerol as the pore stabilizer on the nanofiltration membrane, which leads to poor product stability and a significant decrease in desalination rate during long-term storage, which is not conducive to product storage and use. The use of piperazine as a monomer forms a dense polyamide layer, which has a high divalent ion removal rate but a high monovalent ion removal rate, which is not conducive to the separation of monovalent and divalent ions in practical applications.

[0004] In summary, the current nanofiltration membrane field still has the problem of low selectivity of the membrane sheet, which leads to low separation efficiency of monovalent and divalent ions, which needs to be solved urgently. SUMMARY

[0005] In view of the above problems existing in the prior art, one of the purposes of the present application is to provide a high-separation-selectivity nanofiltration membrane. The divalent ion desalination rate of the nanofiltration membrane is as high as 99.5%, the monovalent ion desalination rate is less than 15%, and the roll qualification rate of the membrane element is also improved.

[0006] Another purpose of the present application is to provide a preparation method of the above-mentioned high-separation-selectivity nanofiltration membrane.

[0007] To achieve the above-mentioned purposes, the technical solutions adopted by the present application are as follows:

[0008] In one aspect, the present application provides a high separation selectivity nanofiltration membrane, comprising a base membrane layer and a separation layer formed on the base membrane layer; wherein the separation layer is prepared by interfacial polymerization of an aqueous phase containing a first aqueous phase monomer, a second aqueous phase monomer and a humectant, and an organic phase containing trimesoyl chloride.

[0009] In one embodiment of the present application, the first aqueous phase monomer is selected from piperazine and derivatives thereof, preferably one or more of piperazine, homopiperazine, aminoethylpiperazine, more preferably one or more of piperazine and homopiperazine.

[0010] In one embodiment of the present application, the second aqueous phase monomer is selected from N-acetyl-5-methoxytryptamine.

[0011] In one embodiment of the present application, the humectant is selected from DL-tryptophan ethyl ester hydrochloride.

[0012] In one embodiment of the present application, the base membrane layer is selected from a polysulfone base membrane.

[0013] The high separation selectivity nanofiltration membrane described above in the present application uses two aqueous phase monomers, which simultaneously react with the organic phase monomer to form a separation layer with an interpenetrating network structure. On the one hand, due to the surface charge effect, it can ensure a high removal rate of divalent ions (such as calcium ions / magnesium ions / sulfate ions, etc.), and on the other hand, due to the relatively slow reaction speed of the second aqueous phase monomer, it can continue to react with the organic phase monomer to form a cross-linked structure in the later stage of the reaction, making up for the large cavities formed in the early stage of the reaction. At the same time, the interpenetrating network structure formed by the reaction of the two aqueous phase monomers with the organic phase monomer has a larger pore size than conventional nanofiltration membranes, and monovalent ions (such as sodium ions / lithium ions / chloride ions, etc.) are more likely to pass through, so its removal rate is lower, effectively ensuring the high selectivity separation performance of the nanofiltration membrane.

[0014] In one preferred scheme of the high separation selectivity nanofiltration membrane described above in the present application, the humectant in the aqueous phase is further limited to DL-tryptophan ethyl ester hydrochloride. In traditional processes, glycerol is usually used as a humectant. The residual glycerol in the membrane can swell the polyamide separation layer, resulting in a larger membrane flux, a lower desalination rate, and a larger fluctuation in membrane performance. However, using a salt solution as a humectant will not swell the polyamide separation layer, so this humectant can ensure the stability of the desalination rate of the nanofiltration membrane, which is beneficial for long-term storage and use. Adding the humectant to the aqueous phase can reduce the post-processing process and improve the efficiency of membrane production. At the same time, the salt solution humectant will not cause the membrane surface to stick due to humidity fluctuations, and the friction with the water inlet grid is smaller, which improves the qualification rate of the membrane element roll.

[0015] In another aspect, the present application provides a method for preparing a high separation selectivity nanofiltration membrane. In an embodiment of the present application, the method can be prepared by using conventional methods in the art, for example, by using an aqueous monomer and an oil monomer to prepare an interfacial polymerization reaction.

[0016] Specifically, a method for preparing a high separation selectivity nanofiltration membrane, the method comprising the following steps:

[0017] S1: mixing the first aqueous monomer, the second aqueous monomer and the humectant with water to prepare an aqueous solution, immersing a base film therein, and then removing the excess aqueous phase on the surface of the base film;

[0018] S2: dissolving trimesoyl chloride in an organic solvent to prepare an oil phase solution, and then placing the base film of S1 in the oil phase solution to perform an interfacial polymerization reaction, and drying to obtain the nanofiltration membrane.

[0019] In the above-mentioned preparation method of the present application, the first aqueous monomer, the second aqueous monomer, the humectant and the base film of S1 are selected in accordance with the selection of the raw materials mentioned above for the high separation selectivity nanofiltration membrane, and no further limitation is made. The corresponding raw materials can be selected within the scope according to the needs.

[0020] In an embodiment of the present application, in the aqueous solution of step S1, the content of the first aqueous phase is 0.5-2wt%, the content of the second aqueous monomer is 0.05-0.15wt%, and the content of the humectant is 3-5wt%.

[0021] Specifically, in the aqueous solution of step S1, the content of the first aqueous phase includes but is not limited to 0.5wt%, 0.7wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt% or a range consisting of any two of them, the content of the second aqueous monomer includes but is not limited to 0.05wt%, 0.05wt%, 0.07wt%, 0.09wt%, 0.1wt%, 0.12wt%, 0.14wt%, 0.15wt% or a range consisting of any two of them, and the content of the humectant includes but is not limited to 3wt%, 3.2wt%, 3.5wt%, 3.7wt%, 4wt%, 4.2wt%, 4.5wt%, 4.7wt%, 5wt% or a range consisting of any two of them.

[0022] In an embodiment of the present application, the immersion of step S1 is for 50-120s, including but not limited to 50s, 60s, 70s, 80s, 90s, 100s, 110s, 120s or a range consisting of any two of them.

[0023] In an embodiment of the present application, the content of trimesoyl chloride in the oil phase solution of step S2 is 0.1-0.3wt%, including but not limited to 0.1wt%, 0.12wt%, 0.15wt%, 0.17wt%, 0.2wt%, 0.22wt%, 0.25wt%, 0.27wt%, 0.3wt% or a range consisting of any two of them.

[0024] In an embodiment of the present application, the organic solvent of step S2 is selected from one or more of alkanes solvents, cycloalkanes solvents, preferably one or more of n-hexane, ethylcyclohexane, n-decane, n-heptane and isomeric alkane solvents, more preferably one or more of n-decane, n-heptane.

[0025] In an embodiment of the present application, the interfacial polymerization reaction of step S2 has no special requirements for temperature, and can be carried out at room temperature, and the time is 60-100s, including but not limited to 60s, 65s, 70s, 75s, 80s, 85, 90s, 95s, 100s or a range consisting of any two of them.

[0026] In an embodiment of the present application, the drying of step S2 is carried out at a temperature of 60-90℃, including but not limited to 60℃, 65℃, 70℃, 75℃, 80℃, 85℃, 90℃ or a range consisting of any two of them, and the drying time is 60-120s, including but not limited to 60s, 70s, 80s, 90s, 100, 110s, 120s or a range consisting of any two of them.

[0027] The high separation selectivity nanofiltration membrane of the present application can be prepared by the above method, and the divalent ion desalination rate of the nanofiltration membrane is as high as 99.5%, and the monovalent ion desalination rate is less than 15%.

[0028] The nanofiltration membrane of the present application has a qualified rate of membrane element winding of more than 99.2%.

[0029] The high separation selectivity nanofiltration membrane of the present application can be applied to the fields of salt lake lithium extraction and municipal water treatment.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] (1) It has high selective separation performance, the divalent ion desalination rate is as high as 99.5%, and the monovalent ion desalination rate is less than 15%, which provides strong technical support for more desalination scenarios.

[0032] (2) The moisturizing agent is added in the aqueous solution, the post-processing process is reduced, the production efficiency is improved, and the separation layer will not swell during storage, ensuring the stability of the separation layer.

[0033] (3) In the process of rolling the membrane element, the end surface folding problem of the membrane element caused by adhesion or large friction of the membrane sheet does not occur, and the operability and the qualified rate of the membrane element rolling are improved. DETAILED DESCRIPTION

[0034] The technical solutions of the present application will be further described in detail below in combination with specific embodiments, but the protection scope of the present application is not limited to the content described.

[0035] The raw materials of the present application are all purchased from the market, and the main raw material sources in the comparative examples and the examples are as shown in Table 1:

[0036] Table 1 Main raw materials in comparative examples and examples

[0037]

[0038]

[0039] Secondly, the performance evaluation method of the nanofiltration membrane of the present application:

[0040] The test conditions of the desalination rate (i.e. the separation performance of the membrane sheet for divalent ions) are as follows: the feed liquid is respectively 500 ppm of sodium chloride solution and 2000 ppm of MgSO4, the temperature of the feed liquid is 25℃, the pH of the feed liquid is 6.8-7.2, and the operating pressure is 0.69 MPa.

[0041] The desalination rate calculation formula is: R = (1-C p / C f ) × 100%, wherein R represents the desalination rate, C f and C p respectively represent the concentrations (ppm) of the salt in the feed liquid and the permeate liquid.

[0042] The desalination rate change rate calculation formula is: ΔR = R0-R 30 , wherein R 30 represents the initial desalination rate, and R 30 represents the desalination rate of the membrane sheet after being stored at room temperature for 30 days.

[0043] The membrane element rolling qualified rate test method is as follows: the prepared nanofiltration membrane sheet is used for rolling the membrane element, 500 pieces are rolled, and the qualified rate of the membrane element rolling is calculated based on this basis.

[0044] Example 1

[0045] The water phase solution is prepared by mixing 1.5% of piperazine, 0.1% of N-acetyl-5-methoxy tryptamine, 3.5% of DL-tryptophan ethyl ester hydrochloride and 94.9% of water in the mass percentage ratio, the polysulfone-based membrane is immersed in the water phase solution for 100s, and the water phase on the surface of the base membrane is removed after taking out by using a press roller.

[0046] Trimesoyl chloride was dissolved in n-decane to prepare an oil phase solution with a mass fraction of 0.16%, and the above-mentioned base film was placed in the oil phase solution for interfacial polymerization for 80 s, dried at 80 °C for 100 s to obtain a high separation selectivity nanofiltration membrane dry film piece. The desalination rate, desalination rate change rate, and membrane element rolling qualified rate of the nanofiltration membrane for monovalent ions (Na + ), divalent ions (Mg 2+ ) were evaluated, and the evaluation results are recorded in Table 2.

[0047] Example 2

[0048] A water phase solution was prepared by mixing 2.0% of homopiperazine, 0.05% of N-acetyl-5-methoxy tryptamine, 3.0% of DL-tryptophan ethyl ester hydrochloride, and 94.95% of water by mass percentage, and the polysulfone base film was immersed in the water phase solution for 50 s. After taking out, the water phase on the surface of the base film was removed by using a press roller.

[0049] Trimesoyl chloride was dissolved in n-heptane to prepare an oil phase solution with a mass fraction of 0.3%, and the above-mentioned base film was placed in the oil phase solution for interfacial polymerization for 100 s, dried at 90 °C for 120 s to obtain a high separation selectivity nanofiltration membrane dry film piece. The desalination rate, desalination rate change rate, and membrane element rolling qualified rate of the nanofiltration membrane for monovalent ions (Na + ), divalent ions (Mg 2+ ) were evaluated, and the evaluation results are recorded in Table 2.

[0050] Example 3

[0051] A water phase solution was prepared by mixing 0.5% of homopiperazine, 0.15% of N-acetyl-5-methoxy tryptamine, 5% of DL-tryptophan ethyl ester hydrochloride, and 94.35% of water by mass percentage, and the polysulfone base film was immersed in the water phase solution for 120 s. After taking out, the water phase on the surface of the base film was removed by using a press roller.

[0052] Trimesoyl chloride was dissolved in n-decane to prepare an oil phase solution with a mass fraction of 0.1%, and the above-mentioned base film was placed in the oil phase solution for interfacial polymerization for 60 s, dried at 60 °C for 60 s to obtain a high separation selectivity nanofiltration membrane dry film piece. The desalination rate, desalination rate change rate, and membrane element rolling qualified rate of the nanofiltration membrane for monovalent ions (Na + ), divalent ions (Mg 2+ ) were evaluated, and the evaluation results are recorded in Table 2.

[0053] Comparative Example 1

[0054] Comparative Example 1 is different from Example 1 in that the water phase solution only contains 1.5% of homopiperazine by mass fraction, without adding N-acetyl-5-methoxy tryptamine and DL-tryptophan ethyl ester hydrochloride.

[0055] The evaluation results are recorded in Table 2.

[0056] Comparative Example 2

[0057] Comparative Example 2 differs from Example 1 in that the aqueous phase solution contains 1.5% by mass of piperazine and 0.1% of N-acetyl-5-methoxytryptamine, and no DL-tryptophan ethyl ester hydrochloride is added.

[0058] The evaluation results are recorded in Table 2.

[0059] Comparative Example 3

[0060] Comparative Example 3 differs from Example 1 in that the aqueous phase solution contains 1.5% by mass of piperazine and 3.5% of DL-tryptophan ethyl ester hydrochloride, and no N-acetyl-5-methoxytryptamine is added.

[0061] The evaluation results are recorded in Table 2.

[0062] Table 2 Evaluation results of nanofiltration membrane performance of examples and comparative examples

[0063] Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Example 3 [R(Mg 2+ ), %]] 99.3 99.2 99.3 99.5 99.6 99.5 [R(Na + ), %]] 45.0 20.5 40.2 14.6 14.0 13.7 Desalination rate change rate, ΔR 1.2％ 0.91％ 0.97％ 0.19％ 0.21％ 0.21％ Coil forming qualification rate, % 97 97.8 97.6 99.0 99.1 99.0

[0064] From the data in Table 2, it can be seen that the removal rate of the examples of the present application is lower when two monomers are simultaneously reacted with the organic phase monomer, which effectively ensures the high selective separation performance of the nanofiltration membrane.

[0065] The moisturizing agent is added to the aqueous phase in the examples of the present application, which can improve the element rolling pass rate. Especially when DL-tryptophan ethyl ester hydrochloride is used as the moisturizing agent, the stability of the nanofiltration membrane desalination rate can be ensured, which is conducive to long-term storage and use.

[0066] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. For those skilled in the art, the present application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A high separation selectivity nanofiltration membrane, characterized in that, The nanofiltration membrane comprises a base membrane layer and a separation layer formed on the base membrane layer; wherein the separation layer is prepared by interfacial polymerization of an aqueous phase containing a first aqueous phase monomer, a second aqueous phase monomer and a humectant, and an organic phase containing trimesoyl chloride; The first aqueous phase monomer is selected from piperazine and derivatives thereof; the second aqueous phase monomer is selected from N-acetyl-5-methoxytryptamine; and the humectant is selected from DL-tryptophan ethyl ester hydrochloride.

2. The high-separation-selectivity nanofiltration membrane according to claim 1, wherein, The first aqueous phase monomer is selected from one or more of piperazine, homopiperazine and aminoethylpiperazine.

3. The high-separation-selectivity nanofiltration membrane according to claim 1, wherein, The base membrane layer is selected from a polysulfone base membrane.

4. A method for producing the high-separation-selectivity nanofiltration membrane according to any one of claims 1 to 3, characterized by, The method comprises the following steps: S1: mixing the first aqueous phase monomer, the second aqueous phase monomer and the humectant with water to prepare an aqueous phase solution, and immersing a base membrane in the aqueous phase solution, then removing the excess aqueous phase on the surface of the base membrane; S2: dissolving trimesoyl chloride in an organic solvent to prepare an oil phase solution, and then immersing the base membrane of S1 in the oil phase solution to perform interfacial polymerization, and drying to obtain the nanofiltration membrane.

5. The preparation method according to claim 4, characterized in that, In the aqueous phase solution of step S1, the content of the first aqueous phase is 0.5-2 wt%, the content of the second aqueous phase monomer is 0.05-0.15 wt%, and the content of the humectant is 3-5 wt%.

6. The preparation method according to claim 4, characterized in that, The immersion in step S1 is performed for 50-120 s.

7. The preparation method according to claim 4, characterized in that, In the oil phase solution of step S2, the content of trimesoyl chloride is 0.1-0.3 wt%.

8. The preparation method according to claim 4, characterized in that, The organic solvent in step S2 is selected from one or more of alkanes and cycloalkanes.

9. The preparation method according to claim 8, characterized in that, The organic solvent is selected from one or more of n-hexane, ethylcyclohexane, n-decane, n-heptane and isomeric alkane solvents.

10. The method of claim 4, wherein, The interfacial polymerization in step S2 is performed for 60-100 s.

11. The preparation method according to claim 4, characterized in that, The drying in step S2 is performed at a temperature of 60-90℃ for 60-120 s.

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