High-separation-selectivity nanofiltration membrane and preparation method thereof

Abstract

The invention provides a nanofiltration membrane with high separation selectivity and a preparation method thereof. The nanofiltration membrane comprises a base membrane layer and a separation layer formed on the base membrane layer, wherein the separation layer is prepared from a water phase containing a first water-phase monomer, a second water-phase monomer and a humectant and an organic phase containing trimesoyl chloride through an interfacial polymerization reaction. The bivalent ion desalination rate of the nanofiltration membrane reaches up to 99.5%, the monovalent ion desalination rate of the nanofiltration membrane is lower than 15%, and meanwhile, the rolling qualification rate of a membrane element is also improved.

Description

Technical Field

[0001] The invention belongs to the technical field of water treatment membranes, and in particular relates to a high separation selectivity nanofiltration membrane and a preparation method thereof. Background Art

[0002] The current new energy market is extremely hot, especially in the field of new energy electric vehicles, where the domestic market is far ahead. Lithium batteries, as an important component of new energy electric vehicles, are being identified by major companies as the first track for research and development. Among them, the salt lake lithium extraction industry that provides lithium resources for lithium batteries is closely related to membrane technology. This industry uses a large number of highly selective nanofiltration membranes as an important part of magnesium-lithium separation. The application of membrane technology has rapidly improved the efficiency of salt lake lithium extraction. On the other hand, the municipal water treatment industry is also undergoing technological iteration and upgrading, and the original ultrafiltration membrane filtration is being upgraded to nanofiltration membrane filtration. In the field of municipal water treatment, nanofiltration membranes are not only required to have a high flux, but also to have high selectivity to effectively remove soluble solutes, organic matter, colloids, bacteria, microorganisms and other impurities in water, while retaining some ions required by the human body. Therefore, it is crucial to develop a nanofiltration membrane with high selectivity.

[0003] There are many types of nanofiltration membranes on the market, among which polyamide composite nanofiltration membranes have received extensive attention and use due to their excellent physical and chemical properties. Most commercial nanofiltration membranes on the market use piperazine as the aqueous phase monomer and glycerol as the pore retainer in the manufacturing process. However, the polyamide composite nanofiltration membrane prepared by the above method has some disadvantages. For example, glycerol as a pore retainer has a swelling effect on the nanofiltration membrane, resulting in poor product stability. Long-term storage will cause a serious decrease in the desalination rate, which is not conducive to product storage and use; using piperazine as a monomer, the polyamide layer formed is relatively dense. Although it has a high divalent ion removal rate, its monovalent ion removal rate is relatively high, 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 membrane selectivity resulting in low separation efficiency of monovalent and divalent ions, which needs to be solved urgently. Summary of the invention

[0005] In view of the above problems existing in the prior art, one of the purposes of the present invention is to provide a high separation selectivity nanofiltration membrane, which has a divalent ion desalination rate of up to 99.5% and a monovalent ion desalination rate of less than 15%, while also improving the winding qualification rate of the membrane element.

[0006] Another object of the present invention is to provide a method for preparing the above-mentioned high separation selectivity nanofiltration membrane.

[0007] In order to achieve the above-mentioned invention object, the technical solution adopted by the present invention is as follows:

[0008] On the one hand, the present invention 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 made by interfacial polymerization reaction 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 invention, the first aqueous phase monomer is selected from piperazine and its derivatives, preferably one or more of piperazine, homopiperazine and aminoethylpiperazine, more preferably one or more of piperazine and homopiperazine.

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

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

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

[0013] The above-mentioned high separation selectivity nanofiltration membrane of the present invention adopts two aqueous phase monomers, and the two aqueous phase monomers react with the organic phase monomers at the same time to form a separation layer with an interpenetrating network structure. On the one hand, due to its surface charge effect, it can ensure that divalent ions (such as calcium ions / magnesium ions / sulfate ions, etc.) have a high removal rate. 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 to make up for the large holes formed in the initial 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 that of conventional nanofiltration membranes, and monovalent ions (such as sodium ions / lithium ions / chloride ions, etc.) are more easily permeable, so its removal rate is lower, which effectively ensures the high selective separation performance of the nanofiltration membrane.

[0014] In the above-mentioned high separation selectivity nanofiltration membrane of the present invention, in a preferred embodiment provided, the moisturizing agent in the water phase is further limited to DL-tryptophan ethyl ester hydrochloride. In the traditional process, glycerol is usually used as a moisturizing agent. The residual glycerol in the membrane will swell the polyamide separation layer, resulting in an increase in the flux of the membrane, a decrease in the desalination rate, and a large fluctuation in the performance of the membrane. However, the use of a salt solution as a moisturizing agent will not swell the polyamide separation layer. Therefore, the moisturizing agent can ensure the stability of the desalination rate of the nanofiltration membrane, which is conducive to long-term storage and use. In addition, adding the moisturizing agent to the water phase can reduce the post-processing process and improve the production efficiency of the membrane. At the same time, the salt solution moisturizing agent will not cause the membrane surface to adhere due to humidity fluctuations, and the friction with the water inlet grid is small, which improves the qualified rate of membrane element rolling.

[0015] On the other hand, the present invention provides a method for preparing a nanofiltration membrane with high separation selectivity. In the embodiments of the present invention, the membrane can be prepared by conventional methods in the art, for example, by interfacial polymerization of aqueous phase monomers and oil phase monomers.

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

[0017] S1: Mixing the first aqueous phase monomer, the second aqueous phase monomer and the moisturizer with water to prepare an aqueous phase solution, immersing the base film in the aqueous phase solution, and then removing excess aqueous phase from 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 membrane of S1 therein to carry out an interfacial polymerization reaction, and drying to obtain the nanofiltration membrane.

[0019] In the above-mentioned preparation method of the present invention, S1, the first aqueous phase monomer, the second aqueous phase monomer, the moisturizing agent, and the base membrane, are selected in accordance with the raw material selection mentioned in the above-mentioned high separation selectivity nanofiltration membrane, and are not further limited. The preparation process can select the corresponding raw materials within the range as needed.

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

[0021] Specifically, in the aqueous phase 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 thereof, the content of the second aqueous phase 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 thereof, and the content of the moisturizer 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 thereof.

[0022] In one embodiment of the present invention, the immersion time in step S1 is 50-120 s, including but not limited to 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 120 s or a range between any two of them.

[0023] In one embodiment of the present invention, in the oil phase solution of step S2, the content of trimesoyl chloride 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 the range composed of any two thereof.

[0024] In one embodiment of the present invention, the organic solvent in step S2 is selected from one or more of alkane solvents and cycloalkane solvents, preferably one or more of n-hexane, ethylcyclohexane, n-decane, n-heptane and isoalkane solvents, more preferably one or more of n-decane and n-heptane.

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

[0026] In one embodiment of the present invention, the drying in step S2, the drying temperature is 60-90°C, including but not limited to 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C or a range composed of any two thereof, and the drying time is 60-120s, including but not limited to 60s, 70s, 80s, 90s, 100, 110s, 120s or a range composed of any two thereof.

[0027] The high separation selectivity nanofiltration membrane of the present invention can be prepared by the above method. 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 invention has a qualified rate of membrane element rolling up to over 99.2%.

[0029] The high separation selectivity nanofiltration membrane of the present invention can be applied to fields such as lithium extraction from salt lakes and municipal water treatment.

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

[0031] (1) It has high selective separation performance, with a divalent ion desalination rate of up to 99.5% and a monovalent ion desalination rate of less than 15%, providing strong technical support for more salt separation scenarios.

[0032] (2) Adding a moisturizer to the aqueous phase solution can reduce the post-processing process, improve production efficiency, and prevent the separation layer from swelling during storage, thereby ensuring the stability of the separation layer.

[0033] (3) During the membrane element rolling process, there will be no wrinkles on the membrane element end surface due to membrane adhesion or high friction, which improves the operability and pass rate of membrane element rolling. DETAILED DESCRIPTION

[0034] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments, but the protection scope of the present invention is not limited to the described contents.

[0035] The raw materials of the present invention are all purchased from the market. The sources of the main raw materials in the comparative examples and embodiments are as follows in Table 1:

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

[0037]

[0038]

[0039] 2. Performance evaluation method used by the nanofiltration membrane of the present invention:

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

[0041] Desalination rate calculation formula: R = (1 – C p / C f )×100%, where R represents the desalination rate, C f and C p are the salt concentrations (ppm) in the feed solution and the permeate, respectively.

[0042] The calculation formula of desalination rate change rate: △R=R0-R 30 , where R 30 represents the initial desalination rate, R 30 It indicates the desalination rate of the membrane after being stored at room temperature for 30 days.

[0043] Test method for membrane element rolling qualification rate: use the prepared nanofiltration membrane sheets to roll membrane elements, roll 500 pieces, and calculate the membrane element rolling qualification rate based on this base number.

[0044] Example 1

[0045] An aqueous solution was prepared by mixing 1.5% piperazine, 0.1% N-acetyl-5-methoxytryptamine, 3.5% DL-tryptophan ethyl ester hydrochloride and 94.9% water in a mass percentage. The polysulfone base membrane was immersed in the aqueous solution for 100 seconds. After taking it out, a roller was used to remove the aqueous phase on the base membrane surface.

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

[0047] Example 2

[0048] An aqueous solution was prepared by mixing 2.0% homopiperazine, 0.05% N-acetyl-5-methoxytryptamine, 3.0% DL-tryptophan ethyl ester hydrochloride and 94.95% water in a mass percentage. The polysulfone base membrane was immersed in the aqueous solution for 50 seconds. After taking it out, a roller was used to remove the aqueous phase on the base membrane surface.

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

[0050] Example 3

[0051] An aqueous solution was prepared by mixing 0.5% piperazine, 0.15% N-acetyl-5-methoxytryptamine, 5% DL-tryptophan ethyl ester hydrochloride and 94.35% water in a mass percentage. The polysulfone base membrane was immersed in the aqueous solution for 120 seconds. After taking it out, a roller was used to remove the aqueous phase on the surface of the base membrane.

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

[0053] Comparative Example 1

[0054] The difference between Comparative Example 1 and Example 1 is that the aqueous phase solution contains only 1.5% by mass of piperazine, and no N-acetyl-5-methoxytryptamine or DL-tryptophan ethyl ester hydrochloride is added.

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

[0056] Comparative Example 2

[0057] The difference between Comparative Example 2 and Example 1 is that the aqueous phase solution contains 1.5% by mass of piperazine and 0.1% by mass 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] The difference between Comparative Example 3 and Example 1 is that the aqueous phase solution contains 1.5% by mass of piperazine and 3.5% by mass 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 Nanofiltration membrane performance evaluation results of the embodiments and comparative examples

[0063] Comparative Example 1 Comparative Example 2 Comparative Example 3 Example 1 Example 2 Example 3 <![CDATA[R(Mg 2+ ),%]]> 99.3 99.2 99.3 99.5 99.6 99.5 <![CDATA[R(Na + ),%]]> 45.0 20.5 40.2 14.6 14.0 13.7 Desalination rate change rate, △R 1.2％ 0.91％ 0.97％ 0.19％ 0.21％ 0.21％ Rolling qualified rate, % 97 97.8 97.6 99.0 99.1 99.0

[0064] It can be seen from the data in Table 2 that the embodiment of the present invention uses two monomers to react with the organic phase monomer at the same time, and its removal rate is lower, which effectively ensures the high selective separation performance of the nanofiltration membrane.

[0065] The embodiment of the present invention adds a moisturizer to the water phase, which can improve the qualified rate of component rolling. In particular, when DL-tryptophan ethyl ester hydrochloride is used as a moisturizer, the stability of the nanofiltration membrane desalination rate can be guaranteed, which is conducive to long-term storage and use.

[0066] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A high separation selectivity nanofiltration membrane, characterized in that: It comprises a base film layer and a separation layer formed on the base film layer; wherein the separation layer is made by an interfacial polymerization reaction between an aqueous phase containing a first aqueous phase monomer, a second aqueous phase monomer and a moisturizer and an organic phase containing trimesoyl chloride.

2. The high separation selectivity nanofiltration membrane according to claim 1, characterized in that: The first aqueous phase monomer is selected from piperazine and its derivatives, preferably one or more of piperazine, homopiperazine, and aminoethylpiperazine, more preferably one or more of piperazine and homopiperazine; and / or The second aqueous phase monomer is selected from N-acetyl-5-methoxytryptamine.

3. The high separation selectivity nanofiltration membrane according to claim 1, characterized in that: The moisturizing agent is selected from DL-tryptophan ethyl ester hydrochloride; and / or The base membrane layer is selected from polysulfone base membrane.

4. A method for preparing a nanofiltration membrane with high separation selectivity according to any one of claims 1 to 3, characterized in that: The following steps are included: S1: Mix the first aqueous phase monomer, the second aqueous phase monomer and the moisturizer with water to prepare an aqueous phase solution, and immerse the base film in the aqueous phase solution. Then, the excess water phase on the surface of the basement membrane is removed; S2: dissolving trimesoyl chloride in an organic solvent to prepare an oil phase solution, and then placing the base membrane of S1 therein to carry out an interfacial polymerization reaction, 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 0.5-2wt%, the content of the second aqueous phase monomer is 0.05-0.15wt%, and the content of the moisturizer is 3-5wt%.

6. The preparation method according to claim 4, characterized in that: The dipping time in step S1 is 50-120 seconds.

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 alkane solvents and cycloalkane solvents, preferably one or more of n-hexane, ethylcyclohexane, n-decane, n-heptane and isoalkane solvents, more preferably one or more of n-decane and n-heptane.

9. The preparation method according to claim 4, characterized in that: The interfacial polymerization reaction in step S2 takes 60-100 seconds.

10. The preparation method according to claim 4, characterized in that: In step S2, the drying temperature is 60-90° C. and the drying time is 60-120 seconds.

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