Monovalent selective composite membrane and preparation method thereof

Abstract

The invention discloses a monovalent selective composite membrane and a preparation method thereof.The composite membrane comprises a supporting layer and an active functional layer, the active functional layer comprises a polymerization layer and a deposition layer, and the polymerization layer is formed by polymerizing a water phase and an organic phase on the surface interface of the supporting layer; the deposition layer is formed by co-depositing a phenolic compound and an amino polymer on the surface of the polymerization layer. By regulating the concentration of the amino polymer in the deposition process and changing the sequence of the polymerization layer and the deposition layer, the composite membrane has efficient Cl <-> / SO4 < 2-> separation capacity in an electrodialysis test.

Description

Technical Field

[0001] The present invention relates to the technical field of composite membranes, and particularly to a monovalent selective composite membrane and a preparation method thereof. Background Art

[0002] A composite membrane is a membrane composed of two or more layers of materials with different properties, aiming to combine the advantages of each layer of materials to achieve specific functions or performances. Usually, one layer serves as a support layer to provide mechanical strength, and the other layer has a separation function, such as selectively permeating certain molecules or ions. Composite membranes can be classified into various types according to their structures, functions, and application fields. According to the structure classification, they include asymmetric membranes, thin-film composite membranes, etc.; according to the function classification, they include nanofiltration membranes, reverse osmosis membranes, ultrafiltration membranes, etc.; according to the application scenario classification, they include gas separation membranes, electrodialysis membranes, etc.

[0003] Although composite membranes have advantages such as good mechanical properties and chemical resistance, they still have deficiencies in terms of permeability, desalination performance, etc. For the above problems, many membrane modification methods have been proposed in the prior art. For example, Chinese Patent CN111097294B discloses a preparation method of a nanofiltration membrane for reclaimed water treatment. The steps are as follows: adding polyvalent acyl chloride into an oil-phase solvent to prepare an oil-phase solution; adding polyamine and a water-soluble additive into deionized water to prepare an aqueous solution; respectively contacting and reacting the support substrate membrane with the aqueous solution and the oil-phase solution to obtain a pretreated membrane sheet; cleaning the pretreated membrane sheet, soaking it in glycerol, and drying it to obtain a nanofiltration membrane. The obtained nanofiltration membrane can effectively improve the water flux while ensuring the rejection rate of organic matter polyethylene glycol. Chinese Patent CN106422812B discloses a preparation method of a dopamine nanofiltration membrane, including the following steps: preparing a mixed solution of dopamine and a nucleophilic reagent, immersing the substrate membrane into the mixed solution of dopamine and the nucleophilic reagent, taking it out after shaking, rinsing it with water to remove the mixed solution on the surface, and drying it; soaking the dried membrane sheet in a cross-linking agent solution for reaction, taking it out, putting it in a vacuum oven, and taking it out after heat treatment to obtain a dopamine nanofiltration membrane. The obtained dopamine nanofiltration membrane has good separation performance.

[0004] The above preparation methods can improve the permeability of the composite membrane and the separation performance for the substances to be separated to a certain extent, but they perform poorly in distinguishing different types of anions, which limits their use effects in high-selectivity application scenarios. Therefore, how to further improve the separation effect of the composite membrane for anions is the focus of subsequent research. Summary of the Invention

[0005] The purpose of the present invention is to provide a monovalent selective composite membrane and a preparation method thereof to solve the problem of poor separation effect of the composite membrane for anions.

[0006] To achieve the above object, a first aspect of the present invention provides a monovalent selective composite membrane, which includes a support layer and an active functional layer. The active functional layer includes a polymerization layer and a deposition layer. The polymerization layer is formed by interfacial polymerization of an aqueous phase and an organic phase on the surface of the support layer, and the deposition layer is formed by co-deposition of a phenolic compound and an amino polymer on the surface of the polymerization layer.

[0007] A second aspect of the present invention provides a method for preparing a monovalent selective composite membrane, which includes the following steps:

[0008] S1: Prepare an aqueous phase solution and an organic phase solution respectively;

[0009] S2: Pour the aqueous phase solution and the organic phase solution onto the support layer in sequence, and an interfacial polymerization reaction occurs. After drying, a thin film is obtained;

[0010] S3: Add a phenolic compound and an amino polymer to a solvent to dissolve and form a mixed solution, and then add a buffer to the mixed solution to obtain a deposition solution;

[0011] S4: Pour the deposition solution onto the thin film. After the deposition reaction is completed, a composite membrane is obtained.

[0012] Preferably, in step S1, the solute in the aqueous phase solution is an amine monomer with an amino group, the solvent is water, and the mass concentration of the solute in the aqueous phase solution is 0.15 - 0.25%; the solute in the organic phase solution is a substance containing an acyl chloride group, the solvent is an organic solvent, and the mass concentration of the solute in the organic phase solution is 0.1 - 0.2%.

[0013] Preferably, in step S1, the amine monomer is at least one of polyethyleneimine, piperazine, m-phenylenediamine, and ethylenediamine, the substance containing an acyl chloride group is at least one of trimesoyl chloride, phthaloyl chloride, terephthaloyl chloride, and isophthaloyl chloride, and the organic solvent is n-hexane.

[0014] Preferably, in step S2, pour the aqueous phase solution onto the surface of the support layer first. The contact time of the aqueous phase solution with the support layer is 3 - 8 min. After the contact of the aqueous phase solution is completed, remove the aqueous phase solution on the surface of the support layer, and then pour the organic phase solution. The contact time of the organic phase solution with the aqueous phase on the surface of the support layer is 1 - 3 min. During this process, an interfacial polymerization reaction occurs between the organic phase and the aqueous phase.

[0015] Preferably, in step S3, the mass concentration of the phenolic compound in the mixed solution is 0.15 - 0.25%, the mass concentration of the amino polymer is 0.1 - 0.4%, the solvent is water, and the addition amount of the buffer is 0.005 - 0.008 g / ml.

[0016] Preferably, the addition amount of the buffer is 0.0065 g / ml, that is, 0.0065 g of the buffer is added to every 1 ml of the mixed solution.

[0017] Preferably, in step S3, the phenolic compound is at least one of dopamine and gallic acid, the amino polymer is polyethyleneimine, and the buffer is tris(hydroxymethyl)aminomethane.

[0018] Preferably, in step S4, the deposition reaction time is 20 - 30 h.

[0019] The third aspect of the present invention provides an application of a monovalent-selective composite membrane, the application of the monovalent-selective composite membrane in the separation of monovalent chloride ions and divalent sulfate ions.

[0020] Therefore, by adopting the above-mentioned monovalent-selective composite membrane and its preparation method, the present invention has the following beneficial effects:

[0021] (1) By using two techniques of interfacial polymerization and co-deposition, the present invention not only realizes the effective separation of monovalent ions but also broadens the application scope of the membrane.

[0022] (2) By adjusting the concentration of the aqueous phase and the reaction sequence, the present invention helps to optimize the microstructure of the membrane, thereby improving its mechanical strength and chemical stability.

[0023] (3) By introducing amino groups into the composite membrane, the present invention increases the positive charge density on the membrane surface, making the membrane particularly suitable for the selective separation of anions during electrodialysis, especially for Cl - and SO4 2- and other ions with similar charges but different sizes. The separation process can be precisely controlled by adjusting the membrane pore size and charge distribution, improving the purity of the target substance.

[0024] (4) The preparation method of the composite membrane in the present invention has the advantages of simple process, simple equipment, flexible operation, and almost no secondary pollution, and is easy to realize industrial production.

[0025] (5) The electrodialysis technology of the present invention has the advantages of no need to add chemical reagents, high selectivity, and low energy consumption, and has good economic benefits.

[0026] The technical solutions of the present invention will be further described in detail below through the drawings and examples. Description of the Drawings

[0027] Figure 1 is a graph showing the changes in salt concentrations in the concentration chamber and dilution chamber of different membranes;

[0028] Figure 2 is the desalination efficiency and water flux after different membranes operate for 5 h;

[0029] Figure 3 is for different membranes to separate Cl - and SO4 2-Graph of transmission rate varying with time;

[0030] Figure 4 For different membranes separating Cl - and SO4 2- Graph of ion flux varying with time;

[0031] Figure 5 For different membranes separating Cl - and SO4 2- Graph of separation coefficient varying with time;

[0032] Figure 6 For the variation of ion flux and selectivity of ENA - 0.2 with cycles. Specific implementation manner

[0033] The present invention will be further described below. It should be noted that this embodiment is based on this technical solution and gives detailed implementation manners and specific operation processes, but the present invention is not limited to this embodiment.

[0034] Example 1

[0035] A preparation method of a monovalent - selective composite membrane, comprising the following steps:

[0036] S1: Prepare an aqueous solution and an organic solution respectively;

[0037] Dissolve polyethyleneimine in water to form an aqueous solution with a mass concentration of 0.2%, and dissolve trimesoyl chloride in n - hexane to form an organic solution with a mass concentration of 0.15%;

[0038] S2: The support layer is a porous membrane. The porous membrane is fixed on an acrylic device as a base membrane. Pour the aqueous solution onto the base membrane, let the aqueous solution contact the base membrane for 5 min, pour out the excess aqueous solution and wipe the residual solution. Then pour the organic solution onto the base membrane, let the aqueous solution and the organic solution contact for 2 min, then wash with n - hexane and put it in an oven at 60°C for drying for 15 min to obtain a polyamide film;

[0039] S3: Add dopamine and polyethyleneimine to water and dissolve to form a mixed solution. The mass concentration of dopamine is 0.2% and the mass concentration of polyethyleneimine is 0.1%. Then add 0.65 g of tris(hydroxymethyl)aminomethane to 100 mL of the mixed solution to obtain a deposition solution;

[0040] S4: Pour the deposition solution onto the polyamide film. After the deposition reaction for 24 h, obtain a composite membrane, denoted as ENA - 0.1.

[0041] Example 2

[0042] The difference between this example and Example 1 is that the mass concentration of polyethyleneimine in step S3 is different. In this example, the mass concentration of polyethyleneimine is 0.2%, and the composite membrane is denoted as ENA-0.2.

[0043] Example 3

[0044] The difference between this example and Example 1 is that the mass concentration of polyethyleneimine in step S3 is different. In this example, the mass concentration of polyethyleneimine is 0.4%, and the composite membrane is denoted as ENA-0.4.

[0045] Example 4

[0046] The difference between this example and Example 2 is that the preparation order of the polymerization layer and the deposition layer is different. In this example, the deposition layer is prepared first, and then the polymerization layer is prepared. The preparation process of the composite membrane in this example is as follows:

[0047] S1: Dopamine and polyethyleneimine are added to water and dissolved to form a mixed solution. The mass concentration of dopamine is 0.2%, and the mass concentration of polyethyleneimine is 0.2%. Then, 0.65 g of tris(hydroxymethyl)aminomethane is added to 100 mL of the mixed solution to obtain a deposition solution.

[0048] S2: The support layer is a porous membrane. The porous membrane is fixed on an acrylic device as a base membrane. The deposition solution is poured onto the base membrane. After a deposition reaction for 24 h, a deposited thin film is obtained.

[0049] S3: An aqueous solution and an organic solution are respectively prepared.

[0050] Polyethyleneimine is dissolved in water to form an aqueous solution with a mass concentration of 0.2%, and trimesoyl chloride is dissolved in n-hexane to form an organic solution with a mass concentration of 0.15%.

[0051] S4: The aqueous solution is poured onto the deposited thin film, and the aqueous solution is allowed to contact the deposited thin film for 5 min. The excess aqueous solution is poured off and the residual solution is wiped. Then, the organic solution is poured onto the deposited thin film, and the aqueous solution and the organic solution are allowed to contact for 2 min. Then, after washing with n-hexane, it is placed in an oven at 60 °C and dried for 15 min to obtain a composite membrane, which is denoted as ERNA.

[0052] Example 5

[0053] The difference between this example and Example 2 is that the composite membrane only includes a base membrane and a deposition layer. The preparation process of the composite membrane in this example is as follows:

[0054] S1: Dissolve dopamine and polyethyleneimine in water to form a mixed solution with the mass concentration of dopamine being 0.2% and that of polyethyleneimine being 0.2%. Then, add 0.65 g of tris(hydroxymethyl)aminomethane to 100 mL of the mixed solution to obtain a deposition solution;

[0055] S2: The support layer is a porous membrane, which is fixed on an acrylic device as a base membrane. Pour the deposition solution onto the base membrane. After a deposition reaction for 24 h, a deposited thin film, i.e., a composite membrane, is obtained and denoted as EUA.

[0056] Example 6

[0057] The difference between this example and Example 2 is that the composite membrane only includes a base membrane and a polymerization layer. The preparation process of the composite membrane in this example is as follows:

[0058] S1: Prepare an aqueous solution and an organic solution respectively;

[0059] Dissolve polyethyleneimine in water to form an aqueous solution with a mass concentration of 0.2%, and dissolve trimesoyl chloride in n - hexane to form an organic solution with a mass concentration of 0.15%.

[0060] S2: The support layer is a porous membrane, which is fixed on an acrylic device as a base membrane. Pour the aqueous solution onto the base membrane, allow the aqueous solution to contact the base membrane for 5 min, pour off the excess aqueous solution and wipe the residual solution. Then, pour the organic solution onto the base membrane, allow the aqueous solution and the organic solution to contact for 2 min. After washing with n - hexane, place it in an oven at 60 °C and dry for 15 min to obtain a polyamide thin film, i.e., a composite membrane, denoted as ENA.

[0061] Example 7

[0062] The difference between this example and Example 2 is that the deposition layer only includes dopamine and tris(hydroxymethyl)aminomethane. The preparation process of the composite membrane in this example is as follows:

[0063] S1: Prepare an aqueous solution and an organic solution respectively;

[0064] Dissolve polyethyleneimine in water to form an aqueous solution with a mass concentration of 0.2%, and dissolve trimesoyl chloride in n - hexane to form an organic solution with a mass concentration of 0.15%;

[0065] S2: The support layer is a porous membrane, which is fixed on an acrylic device as a base membrane. Pour the aqueous solution onto the base membrane, allow the aqueous solution to contact the base membrane for 5 min, pour off the excess aqueous solution and wipe the residual solution. Then, pour the organic solution onto the base membrane, allow the aqueous solution and the organic solution to contact for 2 min. After washing with n - hexane, place it in an oven at 60 °C and dry for 15 min to obtain a polyamide thin film;

[0066] S3: Dissolve dopamine in water to form a mixed solution with the mass concentration of dopamine being 0.2%, and then add 0.65 g of tris(hydroxymethyl)aminomethane to 100 mL of the mixed solution to obtain a deposition solution;

[0067] S4: Pour the deposition solution onto a polyamide film, and after 24 h of deposition reaction, a composite film is obtained.

[0068] Comparative Example 1

[0069] In this comparative example, the performance of an anion exchange membrane (SYMA-1) was tested. The above-mentioned anion exchange membrane (SYMA-1) was purchased from Zhongke Xinyang Membrane Technology Co., Ltd.

[0070] Comparative Example 2

[0071] In this comparative example, the performance of a univalent anion exchange membrane (AXP-D) was tested. The above-mentioned univalent anion exchange membrane (AXP-D) was purchased from ASTOM Co., Ltd. of Japan.

[0072] Test Example

[0073] (1) The desalination performance and ion separation performance of the membranes in the examples and comparative examples were tested. The test method was as follows:

[0074] An electrodialysis device was used to test the desalination performance and ion separation performance of the membranes. The test system included an electrodialysis device, a programmable DC power supply, a multi-channel peristaltic pump, and peristaltic tubes. The electrodialysis device consisted of an electrode chamber, a desalination chamber, a concentration chamber, and electrode plates. The test membrane area was 20 cm 2 , and the current density for desalination performance test was 250 A / m 2 , and the circulation flow rate was 500 mL / min. 12 g / L NaCl solutions were added to the desalination chamber and the concentration chamber respectively, and 0.3 M NaCl solution was added to the electrode solution.

[0075] The formula for calculating the membrane desalination efficiency is where γ is the desalination efficiency (%), C in is the initial concentration of NaCl in the desalination chamber (g / L), and C 5h is the concentration of NaCl in the desalination chamber after 5 h (g / L).

[0076] The formula for calculating the water flux is where V in and V 5h are the initial volume and the volume after 5 h of the NaCl solution in the desalination chamber respectively (L), A is the effective membrane area of the experiment (0.002 m 2 ), and t is the running time (h).

[0077] The current density for the separation performance test is 50 - 200 A / m 2 , and the circulation flow rate is 250 mL / min. A 0.1 M NaCl and Na2SO4 solution is added to the desalination chamber, a 0.01 M NaNO3 solution is added to the concentration chamber, and a 0.3 M Na2SO4 solution is added to the electrode solution.

[0078] The formula for the transport rate is where T i is the ion transport rate (%), and C0 and C t are the concentrations of ions in the desalination chamber at the initial and t moments (mol·L -1 ), respectively. V0 and V t are the volumes of the desalination chamber at the initial and t moments (L), respectively.

[0079] The formula for the ion flux is where J X represents the ion flux (mol·(cm 2 ·min) -1 ), V is the volume of the concentration chamber (L), A m is the effective area of the membrane (cm 2 ), and t is the experimental running time (min).

[0080] The formula for the selectivity coefficient is where P represents the selectivity of Cl - and SO4 2- , J Cl- represents the flux of chloride ions (mol·(cm 2 ·min) -1 ), J SO42- represents the flux of sulfate ions (mol·(cm 2 ·min) -1 ), C SO42- is the initial concentration of SO4 2- in the desalination chamber (mol·L -1 ), and C Cl- represents the initial concentration of Cl - in the desalination chamber (mol·L -1 ).

[0081] The test results are shown in Table 1 and Figures 1 to 5 .

[0082] Table 1 Membrane performance test results of the examples and comparative examples

[0083]

[0084] (2) The membrane of Example 2 was tested for its membrane stability performance under the above separation system, and seven consecutive cycle experiments were carried out, with each experiment running for 2 h. The test results are shown in Figure 6 , and it can be seen from Figure 6 that after seven cycles, the ion flux and selectivity of the ENA-0.2 membrane did not change significantly, indicating that the composite membrane prepared by the present invention has good stability.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that they can still modify or equivalently replace the technical solutions of the present invention, and these modifications or equivalent replacements do not enable the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A monovalent selective composite membrane, characterized in that: It includes a support layer and an active functional layer. The active functional layer includes a polymerization layer and a deposition layer. The polymerization layer is formed by interfacial polymerization of an aqueous phase and an organic phase on the surface of the support layer, and the deposition layer is formed by co-deposition of a phenolic compound and an amino polymer on the surface of the polymerization layer.

2. The preparation method of a single-valence selective composite membrane according to claim 1, wherein: It includes the following steps: S1: Prepare an aqueous phase solution and an organic phase solution respectively; S2: Pour the aqueous phase solution and the organic phase solution onto the support layer in sequence, an interfacial polymerization reaction occurs, and a film is obtained after drying; S3: Add a phenolic compound and an amino polymer into a solvent to dissolve and form a mixed solution, and then add a buffer to the mixed solution to obtain a deposition solution; S4: Pour the deposition solution onto the film, and a composite film is obtained after the deposition reaction is completed.

3. The preparation method of a unit price selective composite membrane according to claim 2, characterized in that: In step S1, the solute in the aqueous phase solution is an amine monomer with an amino group, the solvent is water, and the mass concentration of the solute in the aqueous phase solution is 0.15 - 0.25%; the solute in the organic phase solution is a substance containing an acyl chloride group, the solvent is an organic solvent, and the mass concentration of the solute in the organic phase solution is 0.1 - 0.2%.

4. The preparation method of a unit price selective composite membrane according to claim 3, characterized in that: In step S1, the amine monomer is at least one of polyethyleneimine, piperazine, m-phenylenediamine, and ethylenediamine, the substance containing an acyl chloride group is at least one of trimesoyl chloride, phthaloyl chloride, terephthaloyl chloride, and isophthaloyl chloride, and the organic solvent is n-hexane.

5. The preparation method of a monovalent selective composite membrane according to claim 2, characterized in that: In step S2, first pour the aqueous phase solution onto the surface of the support layer, the contact time between the aqueous phase solution and the support layer is 3 - 8 min. After the contact of the aqueous phase solution is completed, remove the aqueous phase solution on the surface of the support layer, and then pour the organic phase solution. The contact time between the organic phase solution and the aqueous phase on the surface of the support layer is 1 - 3 min. During this process, an interfacial polymerization reaction occurs between the organic phase and the aqueous phase.

6. The preparation method of a unit price selective composite membrane according to claim 2, characterized in that: In step S3, the mass concentration of the phenolic compound in the mixed solution is 0.15 - 0.25%, the mass concentration of the amino polymer is 0.1 - 0.4%, the solvent is water, and the addition amount of the buffer is 0.005 - 0.008 g / ml.

7. The preparation method of a unit price selective composite membrane according to claim 2, characterized in that: In step S3, the phenolic compound is at least one of dopamine and gallic acid, the amino polymer is polyethyleneimine, and the buffer is tris(hydroxymethyl)aminomethane.

8. The preparation method of a monovalent-selective composite membrane according to claim 2, characterized in that: In step S4, the deposition reaction time is 20 - 30 h.

9. Use of a monovalent selective composite membrane according to claim 1, characterized in that: Application of the monovalent selective composite membrane in the separation of monovalent chloride ions and divalent sulfate ions.

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