A cation exchange membrane having a zwitterionic functional layer on the surface thereof and a method for producing the same

Abstract

The application discloses a cation exchange membrane with a zwitterionic functional layer on the surface and a preparation method thereof. The cation exchange membrane with the zwitterionic functional layer on the surface is prepared by taking a sulfonated polyether ether ketone cation exchange membrane as a base film, taking trimesoyl chloride as an oil-phase monomer, and taking zwitterionic polyethylene imine ZPEI as a water-phase monomer, and then forming a zwitterionic functional layer on the surface of the base film through an interfacial polymerization reaction, so that the cation exchange membrane with the zwitterionic functional layer on the surface is obtained. The zwitterionic functional layer is formed on the surface of the base film without changing the structure of the negative charge group of the main body of the cation exchange membrane, the surface polyelectrolyte layer structure is introduced, a new functional layer with zwitterions is formed on the surface of the membrane, and the membrane has high one / two-valent cation selective permeability and high total cation flux.

Description

Technical Field

[0001] This invention relates to the field of composite materials, and more specifically to a cation exchange membrane with a zwitterionic functional layer on its surface and its preparation method. Background Technology

[0002] Lithium, as the lightest metal on Earth with the highest redox potential and the largest specific heat capacity, has wide applications in batteries, ceramics and specialty glass industries, nuclear industry, and pharmaceutical industry. A previous report indicated that nearly 70% of the world's lithium reserves are found in brine (approximately 21.6 Mt). Recovering lithium from brine has become a trend in the lithium recycling industry. Electrodialysis is a separation process based on electrochemical membranes. A typical electrodialysis device mainly consists of a pair of anode and cathode electrodes and several pairs of cation and anion exchange membranes. It uses a fixed voltage as the driving force to selectively transport certain anions or cations, thereby achieving the purpose of ion separation and enrichment. It has significant advantages in reducing harmful wastewater [8-11] (Sep. Purif. Technol. 172 (2017) 388–403.; Ore Geol. Rev. 48 (2012) 55–69; Desalination 356 (2015) 129–139). Ion exchange membrane technology can be divided into diffusion dialysis process driven by concentration difference and membrane electrolysis, electrodialysis and bipolar membrane electrodialysis processes driven by potential difference, depending on the driving force. Furthermore, ion exchange membrane technology is an economical, environmentally friendly, and highly selective method for ion separation, enabling the selective separation of corresponding ions from concentrated aqueous solutions containing chemically similar ions (J.Mem br.Sci.632(2021)119355; Sep.Purif.Technol.240(2020)116600).

[0003] The preparation of electro-driven membranes with targeted ion selectivity emphasizes the use of key fundamental properties, including the transport characteristics of hydrated ions (theoretical size of hydrated ions, ion hydration energy, ion hydration entropy) and the membrane mechanism of ion selectivity. The mechanisms for preparing electro-driven membranes with targeted ion selectivity mainly include membrane pore size sieving, electrostatic repulsion, and binding affinity. In recent years, some new selection mechanisms for preparing electro-driven membranes with targeted ion selectivity have been developed, including bio-driven ion channels and quantum mechanical theory (Prog. Mater. Sci. 128(2022)100958).

[0004] Polyelectrolytes have wide applications in various fields. Specifically, polyelectrolyte multilayer membranes prepared through layer-by-layer assembly possess selective layers with opposite charges and small pore size distribution. Furthermore, porous structures and porous thin-layer selective cation exchange membranes (CEMs) reduce mass transfer resistance and increase limiting current density. In addition, several methods have been developed to modify the surface of conventional cation exchange membranes by introducing charged polyelectrolytes through interfacial polymerization to enhance ion selectivity. The polyelectrolyte formed on the surface of nanofiltration after interfacial polymerization strongly repels divalent cations, while the negative charge of the bottom membrane ensures cation flux. Therefore, introducing nanofiltration interfacial polymerization into CEMs is a promising method to improve ion selectivity. Given this, introducing this charged polyelectrolyte onto the surface of ion exchange membranes, while maintaining ion exchange membrane flux, is beneficial for increasing the selectivity for monovalent / divalent cations. Summary of the Invention

[0005] The purpose of this invention is to provide a cation exchange membrane with a zwitterionic functional layer on its surface and its preparation method. By interfacial polymerization on the surface of the cation exchange membrane, without changing the negatively charged group structure of the cation exchange membrane substrate, a surface polyelectrolyte layer structure is introduced to form a new zwitterionic functional layer on the membrane surface, so that the membrane has high selective permeability to mono / divalent cations and high total cation flux.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] In a first aspect, the present invention provides a cation exchange membrane with a zwitterionic functional layer on its surface, which uses a sulfonated polyether ether ketone (SPEEK) cation exchange membrane as a base membrane, pyromellitic trimethylol chloride as an oil phase monomer, and zwitterionic polyethyleneimine ZPEI as an aqueous phase monomer, and forms a zwitterionic functional layer on the surface of the base membrane through an interfacial polymerization reaction, thereby obtaining a cation exchange membrane with a zwitterionic functional layer on its surface.

[0008] The structural formula of the amphoteric polyethyleneimine (ZPEI) described in this invention is shown in formula (I), and it can be prepared by referring to the methods reported in existing literature, for example, according to literature [Science Advances, 2019, 5(6), 9562-9572]. Specifically, the amphoteric polyethyleneimine (ZPEI) can be prepared by the following steps: Deionized water is added to a reaction vessel, and diethylenetriaminepentaacetic acid is added to it. The mixture is heated and stirred until the white powder is completely dissolved. Then, an appropriate amount of 30% hydrogen peroxide solution is slowly added to the reaction vessel, and the reaction solution is continuously heated to 50-80°C. Subsequently, oxygen is slowly purged into the reaction solution. Then, an appropriate amount of polyethyleneimine (PEI) is dissolved in deionized water and slowly poured into the reaction solution. The mixture is heated at 50-80°C (with continuous oxygen purging) for 5-8 hours. The obtained product is rotary evaporated at 30-50°C to remove the solvent water, resulting in a pale yellow viscous liquid. This liquid is dissolved in ethanol and purified by column chromatography. The eluent is collected and the solvent is removed by rotary evaporation to obtain amphoteric polyethyleneimine (ZPEI). Preferably, the mass ratio of the diethylenetriaminepentaacetic acid, the 30% hydrogen peroxide solution, and the polyethyleneimine (PEI) is 0.5-0.8:3-6:8-10, more preferably 0.5-0.8:3-6:10.

[0009]

[0010] The sulfonated polyether ether ketone (SPEEK) cation exchange membrane of the present invention can also be prepared according to the methods reported in existing literature. Specifically, the sulfonated polyether ether ketone (SPEEK) cation exchange membrane can be prepared by the following method: take polyether ether ketone (PEEK), add a certain volume of concentrated sulfuric acid, stir, and react at 40-60°C for 10-14 hours; pour the resulting solution into cold water, wash with deionized water until neutral, and then vacuum dry at 50-80°C for 12-36 hours to obtain polymer sulfonated polyether ether ketone (SPEEK); then use the polymer sulfonated polyether ether ketone (SPEEK) to form a homogeneous cation exchange membrane using solution casting.

[0011] Preferably, the concentration of the concentrated sulfuric acid is 90-98 wt%, and the feeding ratio of the polyether ether ketone to the concentrated sulfuric acid is 10-20 g: 80-120 mL, more preferably 10-20 g: 100 mL.

[0012] Preferably, the solvent used in the solution casting method is one of NMP, DMF, or DMSO.

[0013] In a second aspect, the present invention provides a method for preparing a cation exchange membrane with a zwitterionic functional layer on its surface as described in the first aspect, comprising the following steps:

[0014] Step 1: Obtain amphoteric polyethyleneimine ZPEI;

[0015] Step 2: Obtain a sulfonated polyether ether ketone (SPEEK) cation exchange membrane;

[0016] Step 3: Dissolve the pyromellitic chloride solid powder in n-hexane to prepare an oil phase solution;

[0017] Step 4: Immerse the sulfonated polyether ether ketone cation exchange membrane obtained in Step 2 in the oil phase solution prepared in Step 3 for a certain period of time to allow pyromellitic trimethylol chloride to be uniformly attached to the membrane surface, while storing part of the solution inside the membrane.

[0018] Step 5: Dissolve a certain amount of amphoteric polyethyleneimine ZPEI in deionized water to prepare an aqueous solution;

[0019] Step 6: Slowly pour the aqueous solution prepared in Step 5 onto the membrane obtained in Step 4 to initiate interfacial polymerization, causing pyromellitic tricarboxylate chloride and amphoteric polyethyleneimine ZPEI to react for a period of time, forming an amphoteric surface functional layer containing the chemical structure shown in formula (II):

[0020]

[0021] Step 7: After drying and cleaning the membrane obtained in step S6, a cation exchange membrane with a zwitterionic functional layer on its surface is obtained.

[0022] Preferably, the thickness of the cation exchange membrane with the zwitterionic functional layer on its surface is 400–500 μm.

[0023] Preferably, in step 3, the mass concentration of pyromellitic chlorobenzene chloride in the oil phase solution is 0.1% to 5%, more preferably 0.8% to 1.5%.

[0024] Preferably, in step 4, the immersion time of the sulfonated polyether ether ketone cation exchange membrane in a hexane solution of trimesoyl chloride is 5 to 15 minutes, more preferably 10 minutes.

[0025] Preferably, in step 5, the mass concentration of amphoteric polyethyleneimine (ZPEI) in the aqueous solution is 0.1% to 5%, more preferably 0.8% to 1.5%.

[0026] Preferably, the duration of the interfacial polymerization reaction in step 6 is 5 to 15 minutes, more preferably 10 minutes.

[0027] Preferably, in step 7, the membrane is dried at a temperature of 20–40°C, and then the unreacted residue on the membrane surface is cleaned with deionized water.

[0028] Compared with the prior art, the advantages of this invention are:

[0029] (1) The method for preparing a cation exchange membrane with a zwitterionic functional layer on its surface as described in this invention introduces interfacial polymerization, a traditional method of nanofiltration, into the preparation of ion exchange membranes. This results in ion exchange membranes with high selectivity for monovalent / divalent cations and high ion flux. It has excellent application prospects in the field of ion selective separation.

[0030] (2) Compared with traditional interfacial polymerization that reacts between an aqueous phase and an organic phase, the interfacial polymerization described in this invention reacts only in a single phase and does not require special equipment. Therefore, it has the advantages of being more convenient and faster than traditional interfacial polymerization.

[0031] (3) The cation exchange membrane with zwitterionic functional layer on the surface obtained by the present invention has a zwitterionic functional layer, which introduces electrostatic repulsion, increases the selectivity of mono / divalent cations while ensuring ion flux. Attached Figure Description

[0032] Appendix Figure 1 This is a surface SEM image of the cation exchange membrane with a zwitterionic functional layer prepared in Example 2 of the present invention;

[0033] Appendix Figure 2 This is a cross-sectional SEM image of the cation exchange membrane with a zwitterionic functional layer prepared in Example 2 of the present invention;

[0034] Appendix Figure 3 This is an appearance diagram of the cation exchange membrane with a zwitterionic functional layer prepared in Example 2 of the present invention;

[0035] Appendix Figure 4 The Li-based cation exchange membranes prepared in Examples 1-3 of this invention + Permeation flux.

[0036] Appendix Figure 5 The Li-based cation exchange membranes prepared in Examples 1-3 of this invention + and Mg 2+ Osmosis selectivity. Detailed Implementation

[0037] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0038] Example 1:

[0039] Preparation of sulfonated polyether ether ketone (SPEEK) cation exchange membrane: 15g of polyether ether ketone was weighed and added to 100mL of 98% concentrated sulfuric acid. The mixture was stirred and reacted at 50℃ for 12 hours. The resulting solution was poured into cold water, washed with deionized water until neutral, and then vacuum dried at 80℃ for 24 hours to obtain the polymer sulfonated polyether ether ketone (SPEEK). The obtained SPEEK polymer was dissolved in 100mL of NMP to obtain a clear, transparent yellow casting solution. This solution was poured into a glass mold and placed in a vacuum drying oven at 100℃ for 24 hours to obtain the ion exchange membrane.

[0040] Performance of cation exchange membranes without surface functional layers: The thickness, water content, and swelling ratio of the prepared ion exchange membranes were tested. Specific testing methods are described in the literature: Journal of Membrane Science 581(2019)150–157; Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164. The sheet resistance and mono / divalent cation permeation selectivity of the ion exchange membranes were also tested. and ion flux For specific testing methods, please refer to the literature reports: Journal of Membrane Science 574(2019)181–195; Journal of Membrane Science 577(2019)153–164; Journal of Membrane Science 582(2019)236–245. Specific parameters are shown in Table 1 and the appendix. Figure 4-5 .

[0041] Example 2:

[0042] Preparation of amphoteric polyethyleneimine (ZPEI): 30 mL of deionized water was added to a 100 mL three-necked flask, followed by 529.40 mg (1.34 mmol) of diethylenetriaminepentaacetic acid. The mixture was heated and stirred until the white powder was completely dissolved. Then, 3.17 g of a 30% hydrogen peroxide solution was slowly added to the flask, and the reaction was continuously heated to 70 °C. Subsequently, oxygen was slowly purged into the solution. Then, 10 g (0.02 mol) of polyethyleneimine (PEI, molecular weight 1800 Da) was dissolved in 30 mL of deionized water and slowly poured into the solution. The mixture was heated at 70 °C (with continuous oxygen purging) for 6 h. The product was rotary evaporated at 45 °C to remove the solvent water, yielding a pale yellow viscous liquid. This liquid was dissolved in ethanol and purified by column chromatography (ethanol as the eluent). The solution was collected and rotary evaporated to remove the ethanol, yielding the product, amphoteric polyethyleneimine (ZPEI).

[0043] Preparation of sulfonated polyether ether ketone (SPEEK) cation exchange membrane: The same preparation process as in Example 1 was used.

[0044] Preparation of a cation exchange membrane with a zwitterionic functional layer on its surface: 1.2 g of trimesoyl chloride solid powder was dissolved in n-hexane to prepare a 1% (w / w) solution. A sulfonated polyether ether ketone (PEEK) cation exchange membrane was first immersed in the prepared trimesoyl chloride n-hexane solution for 10 min, allowing the trimesoyl chloride to adhere uniformly to the membrane surface while partially storing the solution inside the membrane. 2 g of ZPEI solid powder was dissolved in water to prepare a 1% (w / w) solution. The prepared ZPEI aqueous solution was slowly poured onto the membrane obtained after immersing the trimesoyl chloride, initiating interfacial polymerization. This reaction between the trimesoyl chloride and ZPEI lasted for 10 min, forming a zwitterionic surface separation layer containing an aromatic framework. The resulting membrane was dried at 30°C for 24 h, and then the unreacted residue on the membrane surface was washed with deionized water to obtain a cation exchange membrane with a zwitterionic functional layer.

[0045] Performance of cation exchange membranes with zwitterionic functional layers on the surface: The thickness, water content, and swelling ratio of the prepared cation exchange membranes with positively charged functional layers on the surface were tested; the sheet resistance, monovalent / divalent cation permeation selectivity, and ion flux of the ion exchange membranes were also tested. The specific test methods were the same as in Example 1, and the specific test results are shown in Table 1 and the attached figures.

[0046] Example 3:

[0047] Preparation of sulfonated polyether ether ketone (SPEEK) cation exchange membrane: The same preparation process as in Example 1 was used.

[0048] Preparation of cation exchange membrane with a positively charged polyelectrolyte functional layer on the surface: The same preparation process as in Example 1 was used. The only difference was that ZPEI was replaced with polyethyleneimine (PEI, molecular weight 1800 Da), resulting in a cation exchange membrane with a positively charged functional layer on the surface.

[0049] Performance of cation exchange membranes with positively charged polyelectrolyte functional layers on the surface: The thickness, ion exchange capacity, water content, and swelling ratio of the prepared cation exchange membranes with positively charged functional layers on the surface were tested; and the sheet resistance, permeation selectivity, and ion flux of the ion exchange membranes were also tested. The specific test methods were the same as in Example 1, and the specific test results are shown in Table 1 and the attached figures.

[0050] Table 1

[0051]

Claims

1. A cation exchange membrane with a zwitterionic functional layer on its surface, characterized in that: The cation exchange membrane with a zwitterionic functional layer on its surface is formed by interfacial polymerization of sulfonated polyether ether ketone cation exchange membrane as base membrane, pyromellitic tricarboxylate chloride as oil phase monomer, and zwitterionic polyethyleneimine ZPEI as aqueous phase monomer to form a zwitterionic functional layer on the surface of the base membrane. The method for preparing the cation exchange membrane with a zwitterionic functional layer on its surface includes the following steps: Step 1: Obtain amphoteric polyethyleneimine ZPEI; Step 2: Obtain a homogeneous sulfonated polyether ether ketone cation exchange membrane by solution casting. Step 3: Dissolve the pyromellitic chloride solid powder in n-hexane to prepare an oil phase solution; Step 4: Immerse the sulfonated polyether ether ketone cation exchange membrane obtained in Step 2 in the oil phase solution prepared in Step 3 for a certain period of time to allow pyromellitic trimethylol chloride to be uniformly attached to the membrane surface, while storing part of the solution inside the membrane. Step 5: Dissolve a certain amount of amphoteric polyethyleneimine ZPEI in deionized water to prepare an aqueous solution; Step 6: Slowly pour the aqueous solution prepared in step 5 onto the membrane obtained in step 4 to initiate interfacial polymerization, so that pyromellitic tricarboxylate chloride and amphoteric polyethyleneimine ZPEI react for a period of time to form an amphoteric surface functional layer. Step 7: After drying and cleaning the membrane obtained in step S6, a cation exchange membrane with a zwitterionic functional layer on its surface is obtained. The structural formula of the amphoteric polyethyleneimine ZPEI is shown in formula (I): (I)。 2. A method for preparing a cation exchange membrane with a zwitterionic functional layer on its surface as described in claim 1, characterized in that: The preparation method includes the following steps: Step 1: Obtain amphoteric polyethyleneimine ZPEI; Step 2: Obtain the sulfonated polyether ether ketone cation exchange membrane; Step 3: Dissolve the pyromellitic chloride solid powder in n-hexane to prepare an oil phase solution; Step 4: Immerse the sulfonated polyether ether ketone cation exchange membrane obtained in Step 2 in the oil phase solution prepared in Step 3 for a certain period of time to allow pyromellitic trimethylol chloride to be uniformly attached to the membrane surface, while storing part of the solution inside the membrane. Step 5: Dissolve a certain amount of amphoteric polyethyleneimine ZPEI in deionized water to prepare an aqueous solution; Step 6: Slowly pour the aqueous solution prepared in step 5 onto the membrane obtained in step 4 to initiate interfacial polymerization, so that pyromellitic tricarboxylate chloride and amphoteric polyethyleneimine ZPEI react for a period of time to form an amphoteric surface functional layer. Step 7: After drying and cleaning the membrane obtained in step S6, a cation exchange membrane with a zwitterionic functional layer on its surface is obtained.

3. The preparation method according to claim 2, characterized in that: In step 3, the mass concentration of pyromellitic chlorobenzene chloride in the oil phase solution is 0.1%~5%.

4. The preparation method according to claim 3, characterized in that: In step 3, the mass concentration of pyromellitic chlorobenzene chloride in the oil phase solution is 0.8-1.5%.

5. The preparation method according to any one of claims 2-4, characterized in that: In step 4, the sulfonated polyether ether ketone cation exchange membrane is immersed in the oil phase solution for 5 to 15 minutes.

6. The preparation method according to claim 5, characterized in that: In step 4, the sulfonated polyether ether ketone cation exchange membrane is immersed in the oil phase solution for 10 minutes.

7. The preparation method according to claim 2, characterized in that: In step 5, the mass concentration of amphoteric polyethyleneimine ZPEI in the aqueous solution is 0.1% to 5%.

8. The preparation method according to claim 7, characterized in that: In step 5, the mass concentration of amphoteric polyethyleneimine ZPEI in the aqueous solution is 0.8-1.5%.

9. The preparation method according to claim 2, characterized in that: The duration of the interfacial polymerization reaction described in step 6 is 5 to 15 minutes.

10. The preparation method according to claim 9, characterized in that: The duration of the interfacial polymerization reaction described in step 6 is 10 minutes.

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