A method for preparing a single-multiple valence anion selective electric nanofiltration membrane

Abstract

The application provides a preparation method of a single-multivalent anion selective electrodialysis membrane, which comprises the following steps: constructing a polyamide functional layer on the surface of an ultrafiltration membrane through an interfacial polymerization method, and then soaking the polyamide functional layer in a mixed solution of sodium poly(styrenesulfonate) (PSS) and 4,4'-diazidostilbene-2,2'-disulfonic acid disodium salt (DAS) and performing cross-linking modification through ultraviolet irradiation, so as to prepare the electrodialysis membrane with high single-multivalent anion selectivity. The application can effectively regulate the negative charge density on the membrane surface, and the obtained electrodialysis membrane exhibits excellent separation performance for chloride ions and sulfate ions, and is simple and convenient to operate, stable in effect, suitable for the selective separation of single-multivalent anions in high-salt wastewater, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention belongs to the field of separation membrane preparation, specifically relating to a method for preparing a monovalent and multivalent anion selective electrofiltration membrane. Background Technology

[0002] High-salinity wastewater is a typical and difficult-to-treat wastewater generated during industrial production and water resource recycling. It mainly contains inorganic ions such as chloride, sulfate, sodium, calcium, and magnesium ions. Direct discharge can cause environmental problems such as water mineralization and soil salinization, making its resource recovery and zero-discharge treatment a necessity for the industry. Among existing salt separation technologies, membrane separation is the mainstream technology due to its simple separation process, good economy, low energy consumption, and ability to operate at room temperature, making it suitable for the concentration and separation of medium- to high-salinity wastewater. Currently, the most widely used salt separation technologies include nanofiltration and selective electrodialysis. Nanofiltration is highly effective in separating monovalent and multivalent ions, but its separation process requires high-pressure drive, resulting in high energy consumption. While selective electrodialysis has relatively low energy consumption, its separation selectivity is often inferior to nanofiltration.

[0003] Electrofiltration is a novel separation process that combines electrodialysis and nanofiltration. It uses an electric field as the primary driving force and improves separation performance by replacing traditional ion exchange membranes with nanofiltration membranes. It offers the dual advantages of low energy consumption and high selectivity, making it a promising direction for the desalination of high-salt wastewater.

[0004] Existing research directly replaces traditional anion exchange membranes with unmodified nanofiltration membranes in electro-driven separation processes. While this achieves higher selective separation than traditional ion exchange membranes, the overall separation performance remains unsatisfactory. It lacks sufficient selectivity for monovalent and polyvalent anions, making it difficult to achieve high-precision salt separation and failing to meet the practical requirements of industrial high-salt wastewater desalination. Furthermore, the limited surface charge density and insufficient functional layer structure control of unmodified nanofiltration membranes further restrict the engineering application of electro-nanofiltration technology. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a method for preparing a monovalent / multivalent anion-selective electro-nanofiltration membrane, which yields an electro-nanofiltration membrane with higher monovalent / multivalent anion selectivity.

[0006] The present invention discloses a method for preparing a monovalent or multivalent anion-selective electrofiltration nanofiltration membrane, comprising the following steps: (1) Take out the ultrafiltration membrane that has been soaked in pure water for a predetermined time, immerse it in an aqueous solution containing polyamine for a predetermined time, and then remove the residual liquid on the membrane surface; (2) Pour the organic solution of polyacryl chloride into the ultrafiltration membrane treated in step (1). After the ultrafiltration membrane is immersed in the organic solution of polyacryl chloride for a predetermined time, rinse the surface of the ultrafiltration membrane with n-hexane several times. (3) Place the ultrafiltration membrane after step (2) into an oven for heat treatment, take it out and rinse the membrane surface several times with deionized water to wash away the unreacted solution. (4) Immerse the membrane reacted in step (3) in a mixture of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) for a predetermined time and then remove it. (5) Place the membrane reacted in step (4) under ultraviolet light for a predetermined time to promote the cross-linking reaction on the membrane surface; (6) Take out the membrane after the reaction in step (5), wash it with deionized water to remove the residual liquid that did not participate in the crosslinking reaction on the membrane, and then immerse it in deionized water for storage to obtain an electrofiltration membrane.

[0007] Furthermore, in step (1), the ultrafiltration membrane material is polyethersulfone.

[0008] Furthermore, in step (1), the concentration of the aqueous solution of the polyamine is 1 wt%, wherein the polyamine is selected from piperazine.

[0009] Furthermore, in step (2), the concentration of the organic solution of polyacryl chloride is 0.1 w / v%, wherein the polyacryl chloride is selected from trimesoyl chloride.

[0010] Furthermore, in step (2), the ultrafiltration membrane is immersed in an organic solution of polyacryl chloride for more than 2 minutes.

[0011] Furthermore, in step (4), the concentrations of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidostyrene-2,2′-disulfonate (DAS) are 1 g / L and 2 g / L, respectively.

[0012] Furthermore, in step (1), the ultrafiltration membrane is soaked in pure water for more than 24 hours and in a polyamine aqueous solution for more than 2 minutes.

[0013] Furthermore, in step (3), the temperature of the oven is set to 60°C and the heat treatment time is 10 minutes.

[0014] Furthermore, in step (4), the predetermined soaking time is set to 8 minutes.

[0015] Furthermore, in step (5), the predetermined duration of ultraviolet irradiation is set to 45 seconds.

[0016] Compared with the prior art, the present invention has the following advantages: This invention employs interfacial polymerization to construct a polyamide functional layer on the surface of an ultrafiltration membrane. The functional layer is then crosslinked and enhanced by immersion in a mixture of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) followed by ultraviolet irradiation. This preparation method is simple to operate, can effectively adjust the negative charge density of the functional layer, and the electro-nanofiltration membrane prepared by this invention exhibits high selective separation performance for monovalent and polyvalent anions, showing promising application prospects. Attached Figure Description

[0017] Figure 1 This is a schematic diagram of the electro-nanofiltration device of the present invention; Figure 2 This is a schematic diagram showing the change of anion content in the dilute chamber over time in Example 1; Figure 3 This is a schematic diagram showing the change in the selectivity coefficient of monovalent and polyvalent anions with the concentration of sodium poly(p-)styrene sulfonate (PSS); Figure 4 This is a schematic diagram showing the change in the selectivity coefficient of monovalent and polyvalent anions with the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS). Specific implementation methods

[0018] This invention proposes a method for preparing a monovalent and multivalent anion selective electrofiltration nanofiltration membrane, comprising the following steps: (1) Take out the ultrafiltration membrane that has been soaked in pure water for 24 hours, immerse it in an aqueous solution containing polyamines for 2 minutes. Then use a rubber roller to remove the residual liquid on the membrane surface; (2) Pour the organic solution of polyacryl chloride into the ultrafiltration membrane treated in step (1), immerse it in the organic solution for 2 minutes, and rinse the membrane surface with n-hexane 2-3 times; (3) Place the membrane after step (2) in a 60°C oven for 10 minutes for heat treatment, then take it out and rinse the membrane surface with deionized water 3-5 times to remove the unreacted solution. (4) Immerse the membrane reacted in step (3) in a mixture of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) for 8 minutes and then remove it. (5) Place the membrane reacted in step (4) under ultraviolet light for 45 seconds to promote the cross-linking reaction on the membrane surface; (6) Take out the membrane after the reaction in step (5), wash it with deionized water to remove the residual liquid that did not participate in the crosslinking reaction on the membrane, and then immerse it in deionized water for storage to obtain an electrofiltration membrane.

[0019] Furthermore, the concentration of the aqueous solution of the polyamine in (1) is 1 wt%, wherein the polyamine is selected from piperazine.

[0020] Furthermore, the concentration of the organic solution of the polyacryl chloride in (2) is 0.1 w / v%, wherein the polyacryl chloride is selected from trimesoyl chloride.

[0021] Furthermore, in (4), the concentrations of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidostyrene-2,2′-disulfonate (DAS) are 1 g / L and 2 g / L, respectively.

[0022] Furthermore, the ultrafiltration membrane material is polyethersulfone.

[0023] The preparation method of the monovalent and multivalent anion selective electrofiltration membrane provided by the present invention will be further described below with reference to the embodiments. Example 1

[0024] Preparation of nanofiltration membrane: (1) Take out the ultrafiltration membrane that has been soaked in pure water for 24 hours, immerse it in an aqueous solution of 1 wt% polyamine for 2 minutes. Then remove the residual liquid on the membrane surface with a rubber roller; (2) Pour the organic solution of 0.1 w / v% polyacryl chloride into the ultrafiltration membrane treated in step (1), soak it in the organic solution for 2 min, and rinse the membrane surface with n-hexane 2-3 times; (3) Place the membrane after step (2) in a 60°C oven for 10 minutes for heat treatment, then take it out and rinse the membrane surface with deionized water 3-5 times to remove the unreacted solution. (4) Immerse the membrane reacted in step (3) in a mixture of 1 g / L sodium poly(p-)styrene sulfonate (PSS) and 2 g / L disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) for 8 min and then remove it. (5) Irradiate the membrane reacted in step (4) under ultraviolet light for 45 seconds; (6) Take out the membrane after the reaction in step (5), wash it with deionized water to remove the residual liquid that did not participate in the crosslinking reaction on the membrane, and then immerse it in deionized water to obtain an electrofiltration membrane.

[0025] Electro-nanofiltration experiment: Install the electrofiltration membrane obtained in the above steps into the electrofiltration device. Figure 1 The installation shown is such that the functional layer of the electrofiltration membrane faces the cathode to ensure that the functional layer of the electrofiltration membrane makes initial contact during anion transport. Both the anode and cathode of the device are titanium-coated ruthenium electrodes. Figure 1 The CEM in this example is a cation exchange membrane with an effective membrane area of ​​63 cm². 2The solutions in each compartment were as follows: both electrode compartments contained 0.2 mol / L Na₂SO₄ solution; the dilute compartment contained a mixed solution of Na₂SO₄ and NaCl, both with a concentration of 0.05 mol / L; and the concentrated compartment contained 0.05 mol / L NaCl solution. Each compartment had a volume of 500 ml. The device was connected to a power source at both ends and operated for 60 minutes at a current density of 5 mA / cm². 2 Determination of Cl in the dilute chamber - SO4 2- The concentration was determined, and the selectivity coefficients for monovalent and polyvalent anions were calculated. The results are as follows: Figure 2 As shown.

[0026] Monovalent and multivalent ion selectivity coefficients: Example 2

[0027] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of sodium poly(p-)styrene sulfonate (PSS) in step (4) is adjusted to 0 g / L. Then, the modified electro-nanofiltration membrane is subjected to electro-nanofiltration performance testing. After running for 60 minutes, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 3 As shown. Example 3

[0028] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of sodium poly(p-)styrene sulfonate (PSS) in step (4) is adjusted to 0.5 g / L. Then, the modified electro-nanofiltration membrane is subjected to electro-nanofiltration performance testing. After running for 60 minutes, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 3 As shown. Example 4

[0029] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of sodium poly(p-)styrene sulfonate (PSS) in step (4) is adjusted to 1.5 g / L. Then, the modified electro-nanofiltration membrane is subjected to electro-nanofiltration performance testing. After running for 60 minutes, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 3 As shown. Example 5

[0030] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of sodium poly(p-)styrene sulfonate (PSS) in step (4) is adjusted to 2.0 g / L. Then, the modified electro-nanofiltration membrane is subjected to electro-nanofiltration performance testing. After running for 60 minutes, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 3 As shown. Example 6

[0031] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of sodium poly(p-)styrene sulfonate (PSS) in step (4) is adjusted to 2.5 g / L. Then, the modified electro-nanofiltration membrane is subjected to electro-nanofiltration performance testing. After running for 60 minutes, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 3 As shown.

[0032] Depend on Figure 3 The optimal concentration of sodium poly(p-)styrene sulfonate (PSS) can be determined to be 1 g / L. Example 7

[0033] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) in step (4) is adjusted to 0.5 g / L. Then, an electro-nanofiltration experiment is conducted on the modified membrane. After running for 60 min, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 4 As shown. Example 8

[0034] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) in step (4) is adjusted to 1.0 g / L. Then, an electro-nanofiltration experiment was conducted on the modified membrane. After running for 60 min, the Cl in the device was measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 4 As shown. Example 9

[0035] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) in step (4) is adjusted to 1.5 g / L. Then, an electro-nanofiltration experiment is conducted on the modified membrane. After running for 60 min, the Cl in the device is measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 4 As shown. Example 10

[0036] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) in step (4) is adjusted to 2.5 g / L. Then, an electro-nanofiltration experiment was conducted on the modified membrane. After running for 60 min, the Cl in the device was measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 4 As shown. Example 11

[0037] The preparation of the electro-nanofiltration membrane in this embodiment is largely the same as in Example 1, except that the concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) in step (4) is adjusted to 3.0 g / L. Then, an electro-nanofiltration experiment was conducted on the modified membrane. After running for 60 min, the Cl in the device was measured. - SO4 2- Concentration, and calculate the selectivity coefficients for monovalent and polyvalent anions, the results are as follows: Figure 4 As shown.

[0038] Depend on Figure 4 The optimal concentration of disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) can be determined to be 2 g / L.

[0039] This invention uses sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4'-diazidostyrene-2,2'-disulfonate (DAS) as modifying agents, and employs a UV-initiated covalent crosslinking method to modify the surface of a nanofiltration membrane, constructing an electro-nanofiltration membrane with high selectivity for monovalent and multivalent anions. The electro-nanofiltration membrane prepared under optimal modification conditions exhibits high selectivity for Cl... - SO4 2- The monovalent and polyvalent anion selectivity coefficient is as high as 30.51, which is significantly higher than that of the unmodified base film for Cl. - SO4 2- The selectivity coefficient for monovalent and polyvalent anions is 9.4 times that of (3.25).

[0040] The results of static electrofiltration experiments showed that, in simulated high-salinity wastewater with a salinity of 1% and Cl... - SO4 2- Concentration ratio 1:1, operating current density 5mA / cm³ 2 Under these conditions, the monovalent and polyvalent anion selectivity coefficient of the modified electro-nanofiltration membrane of this invention can reach 35.26. After operating under these conditions for 120 minutes, the monovalent and polyvalent selectivity coefficient of the modified electro-nanofiltration membrane can reach 16.8 times that of commercial anion exchange membranes, demonstrating a very significant modification effect.

[0041] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited to the above embodiments. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions, including combining the various technical features in other suitable ways; such simple modifications and equivalent substitutions should all be considered as the content disclosed in the present invention and fall within the protection scope of the present invention.

Claims

1. A method for preparing a monovalent or multivalent anion-selective electrofiltration nanofiltration membrane, characterized in that, Includes the following steps: (1) Take out the ultrafiltration membrane that has been soaked in pure water for a predetermined time, immerse it in an aqueous solution containing polyamine for a predetermined time, and then remove the residual liquid on the membrane surface; (2) Pour the organic solution of polyacryl chloride into the ultrafiltration membrane treated in step (1). After the ultrafiltration membrane is immersed in the organic solution of polyacryl chloride for a predetermined time, rinse the surface of the ultrafiltration membrane with n-hexane several times. (3) Place the ultrafiltration membrane after step (2) into an oven for heat treatment, take it out and rinse the membrane surface several times with deionized water to wash away the unreacted solution. (4) Immerse the membrane reacted in step (3) in a mixture of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidisostyrene-2,2′-disulfonate (DAS) for a predetermined time and then remove it. (5) Place the membrane reacted in step (4) under ultraviolet light for a predetermined time to promote the cross-linking reaction on the membrane surface; (6) Take out the membrane after the reaction in step (5), wash it with deionized water to remove the residual liquid that did not participate in the crosslinking reaction on the membrane, and then immerse it in deionized water for storage to obtain an electrofiltration membrane.

2. The preparation method according to claim 1, characterized in that, The ultrafiltration membrane material in step (1) is polyethersulfone.

3. The preparation method according to claim 1, characterized in that, In step (1), the concentration of the aqueous solution of the polyamine is 1 wt%, wherein the polyamine is selected from piperazine.

4. The preparation method according to claim 1, characterized in that, In step (2), the concentration of the organic solution of polyacryl chloride is 0.1 w / v, wherein the polyacryl chloride is selected from trimesoyl chloride.

5. The preparation method according to claim 4, characterized in that, In step (2), the ultrafiltration membrane is immersed in an organic solution of polyacryl chloride for more than 2 minutes.

6. The preparation method according to claim 1, characterized in that, In step (4), the concentrations of sodium poly(p-)styrene sulfonate (PSS) and disodium 4,4′-diazidostyrene-2,2′-disulfonate (DAS) are 1 g / L and 2 g / L, respectively.

7. The preparation method according to claim 1, characterized in that, In step (1), the ultrafiltration membrane is soaked in pure water for more than 24 hours and in a polyamine aqueous solution for more than 2 minutes.

8. The preparation method according to claim 1, characterized in that, In step (3), the temperature of the oven is set to 60°C and the heat treatment time is 10 minutes.

9. The preparation method according to claim 1, characterized in that, In step (4), the soaking time is set to 8 minutes.

10. The preparation method according to claim 1, characterized in that, In step (5), the predetermined duration of ultraviolet irradiation is set to 45 seconds.

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