Preparation method and application of a selective ion exchange membrane

Abstract

The application discloses a preparation method and application of a selective ion exchange membrane. The method comprises the following steps: coating a mixed solution containing a polyphenol compound, a crosslinking agent and an interfacial catalyst on the surface of a base film to obtain a base film with a functional precursor assembly layer; and coating an oil phase solution composed of an acyl chloride compound and a non-polar organic solvent on the functional precursor assembly layer to induce a single-step in-situ polymerization reaction, so as to obtain an anion selective membrane. The selective anion exchange membrane prepared by the method is used for monovalent and multivalent anion screening, electrodialysis salt concentration or zero discharge of high-salt wastewater. The selective anion exchange membrane obtained by the application can realize efficient separation between monovalent anions and multivalent anions in an electrodialysis process.

Description

Technical Field

[0001] This invention relates to the field of ion exchange membrane preparation and application technology, and in particular to a method for preparing and applying a selective ion exchange membrane. Background Technology

[0002] Currently, electrodialysis, due to its significant advantages such as high concentration ratio, low operating pressure, and ease of automation, has been widely applied in seawater salt production, salt concentration and purification, and zero discharge of high-salinity wastewater, making it a core technology for achieving high-concentration brine preparation and resource utilization. However, the ion exchange membranes used in conventional electrodialysis can only selectively permeate ions, with limited separation capabilities for monovalent / polyvalent ions. This makes it difficult to achieve fine separation in mixed salt systems, and membrane fouling and scaling frequently occur in high-salinity or complex water systems. Therefore, with the increasing demand for seawater desalination and bittern refining, the need for monovalent selective anion exchange membranes is becoming increasingly urgent. These membranes need to possess high selectivity, high flux, low resistivity, and good chemical, thermal, and mechanical stability. Although there has been progress in domestic research on commercial monovalent selective anion exchange membranes, reports of productization are scarce, and breakthroughs in membrane performance bottlenecks are urgently needed.

[0003] To improve the performance of monovalent selective anion exchange membranes, researchers have developed various modification methods, mainly including direct preparation methods and surface modification methods. Direct preparation methods refer to the introduction of nanoparticles or polymers (such as doped polyaniline or inorganic fillers or small molecules containing specific functional groups) into the membrane matrix to regulate the membrane's density and hydrophilicity / hydrophobicity, thereby improving the pore size sieving effect, but this can easily lead to an increase in membrane resistance. Surface modification methods include impregnation, electrodeposition, layer-by-layer self-assembly, and chemical grafting. Impregnation methods involve immersing the membrane in a modifier solution, using electrostatic attraction or free diffusion to form a functional layer on the membrane surface, such as using dopamine self-polymerization to form a polydopamine layer. However, the modified layer has poor stability and is prone to detachment. Electrodeposition and layer-by-layer self-assembly methods use an electric field to drive the deposition of modifiers, forming multiple layers with alternating positive and negative charges, improving monovalent selectivity. However, these methods are complex and require sophisticated equipment. Chemical grafting methods form covalent bonds on the membrane surface through redox systems or Menshutkin reactions, such as using butynedioic acid or sulfonic acid groups to enhance the membrane's hydrophilicity and electronegativity. However, these methods have harsh reaction conditions and low yields. Although these methods can partially improve the selectivity and durability of membranes, they generally suffer from reduced flux, high cost, or insufficient stability, and cannot fully meet the needs of industrial applications.

[0004] CN105646924A discloses a monovalent anion-selective ion exchange membrane and its preparation method. This method first prepares a positively charged base membrane, and then, through a traditional liquid-liquid interface polymerization process, utilizes an acyl chloride organic phase and an acidic amine aqueous phase to construct a negatively charged layer on the base membrane surface. The optimal Cl... -SO4 2- The separation coefficient was chosen to be 11.2. However, due to the difficulty in controlling the diffusion of active monomers in liquid-liquid interfacial polymerization, monomers easily penetrate into the pores and cause blockage, and the interfacial reaction density is insufficient, making it difficult to meet the industrial requirements of high throughput and ultra-high selectivity.

[0005] Existing modification technologies, such as impregnation and traditional liquid-liquid interfacial polymerization, lack control over the diffusion path of the modifier and the stability of the active layer, resulting in problems such as easy shedding of the modified layer, pore blockage caused by the infiltration of active monomers into the membrane pores, and insufficient skin layer density. Furthermore, the kinetics of traditional uncatalyzed interfacial polymerization are slow, making it difficult to construct a dense sieving skin layer sufficient for ultra-high monovalent selectivity in a short time. Therefore, how to precisely control the polymerization reaction to occur only on the membrane surface without clogging the pores, while significantly improving the density of the separation layer, is a key challenge that urgently needs to be solved. Summary of the Invention

[0006] This invention addresses the problems of insufficient selectivity, low flux, and poor stability in existing monovalent selective anion exchange membranes by providing a method for preparing and applying selective ion exchange membranes. This method introduces an interfacial catalyst into the reaction system, utilizing an organic base catalyst with nucleophilic function to significantly lower the reaction energy barrier and accelerate the interfacial polymerization kinetics. Simultaneously, polyphenolic compounds are selected to construct the active framework, replacing traditional single amine monomers. Furthermore, a key drying step is introduced to transform the liquid deposition layer into a semi-solid / solid-phase precursor assembly layer, physically locking the surface active sites and effectively avoiding the blockage caused by monomer penetration into the membrane pores in traditional interfacial polymerization processes. Ultimately, a monovalent selective separation layer with both high flux and high density is rapidly constructed on the base membrane surface.

[0007] The present invention adopts the following technical solution:

[0008] A method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0009] (1) The anion exchange membrane is pretreated to obtain the base membrane;

[0010] (2) Coat the mixed solution onto the surface of the base film at a rate of 0.5~2.0 mL / cm². 2 The substrate is contacted at 25–45°C for 10 min–24 h to obtain a base film with an active deposition layer, and then dried at 30–60°C for 10–120 min to obtain a base film with a functionalized precursor assembly layer.

[0011] The mixed solution is an aqueous solution containing active substances, crosslinking agents, and interfacial catalysts; the mass ratio of each component is: active substances: crosslinking agents: interfacial catalysts = 1:(0.1~4.0):(0.01~0.5);

[0012] The total concentration of solute in the mixed solution is 0.5–15.0 g / L;

[0013] The active substance is a polyphenolic compound, and the crosslinking agent includes any one or more of metal ligands, organic crosslinking agents, or oxidation inducing agents.

[0014] The interfacial catalyst is one or more of 4-dimethylaminopyridine, 1-methylimidazolium, or triethylenediamine.

[0015] (3) Coat the surface of the base film with the functionalized precursor assembly layer obtained in step (2) with the oil phase solution, the coating amount being 0.5~2.0 mL / cm. 2 The membrane is contacted at 25–45°C for 0.5–10 min, followed by heat treatment at 60–95°C for 2–15 min to obtain anion-selective membrane.

[0016] The oil phase solution is composed of acyl chloride compounds and nonpolar organic solvents; the acyl chloride compounds account for 0.05 to 1.0 wt% of the total mass of the oil phase solution.

[0017] The acyl chloride compounds include one or more of pyromellitic terephthaloyl chloride, isophthaloyl chloride, or terephthaloyl chloride;

[0018] The nonpolar organic solvent includes n-hexane, n-heptane, or isoalkanes.

[0019] The polyphenolic compound in step (2) is any one or a combination of at least two of catechol compounds or complex polyphenolic compounds.

[0020] The catechol compound is any one or a combination of at least two of catechol, dopamine, 3,4-dihydroxyphenylalanine, or caffeic acid; the complex polyphenol compound includes any one or a combination of at least two of tannic acid, gallic acid, or proanthocyanidins; preferably dopamine or tannic acid.

[0021] The metal ligand includes any one or a combination of at least two of ferric chloride, ferric sulfate, copper chloride, or copper sulfate.

[0022] The organic crosslinking agent includes one or a combination of at least two of piperazine, polyethyleneimine, ethylenediamine, or polylysine, preferably piperazine.

[0023] The oxidation inducer includes one or at least two of tris(hydroxymethyl)aminomethane hydrochloric acid, sodium periodate, or ammonium persulfate.

[0024] The drying process described in step (2) is natural air drying, thermal radiation drying, or vacuum drying.

[0025] The selective ion exchange membrane prepared by the method is used for monovalent and multivalent anion sieving, electrodialysis salt concentration, or zero discharge of high-salt wastewater.

[0026] The aforementioned monovalent and polyvalent anions include monovalent anions and polyvalent anions; the monovalent anions include Cl... - NO3 - or F - One or more of the following; the multivalent anions include SO42-. 2- Or PO4 3- One or more;

[0027] The salt is one or more of NaCl, LiCl, or Na2SO4.

[0028] The essential features of this invention are:

[0029] In-situ interfacial polymerization (ISIP) has emerged as a highly efficient and simple surface modification technique. This method introduces active functional groups in situ onto the membrane surface and carries out polymerization reactions under the promotion of a catalyst to form a thin and dense charged composite layer. This invention uses polyphenolic compounds (such as tannic acid) with rigid frameworks to construct the active layer, utilizing the large steric hindrance structure of benzene rings to replace the flexible and disordered entanglement structure of traditional amine monomers. This rigid framework ensures the formation of a porous structure and physically confines the space for subsequent polymerization reactions. Simultaneously, using nucleophilic organic base catalysts (such as those containing pyridine rings), the nucleophilic nitrogen atoms actively attack acyl chlorides to generate highly active N-acylpyridine salt intermediates, significantly reducing the reaction energy barrier and inducing rapid crosslinking of acyl chlorides with phenolic hydroxyl groups on the solid surface. This effectively controls the pore size distribution and dimensions of the membrane, overcoming the bottleneck of slow reaction rates and incomplete reactions associated with polyphenolic substances. Ultimately, this invention achieves dual control over the membrane's chemical structure and physical pore size through the above mechanism, significantly improving the selectivity of monovalent anions by utilizing the synergistic effect of size sieving principle and Donnan repulsion.

[0030] The beneficial effects of this invention are as follows:

[0031] This invention induces in-situ interfacial polymerization of trimesoyl chloride within a confined space by constructing an active layer consisting of a polyphenol framework, a crosslinking agent, and an interfacial catalyst. Subsequent coating with an oil-phase solution enhances the charge-to-weight ratio of the membrane surface, forming a dense and ultrathin negatively charged composite skin. Simultaneously, the nucleophilic catalytic effect of the interfacial catalyst significantly improves the reaction kinetics, enabling the formation of a highly crosslinked, dense sieve layer on the base membrane surface. This allows the monovalent selective anion exchange membrane to achieve monovalent anion exchange (such as Cl-) during electrodialysis. - NO3 - F - (etc.) and polyvalent anions (such as SO42-) 2- PO43- Highly efficient separation between (etc.), especially for Cl - and SO4 2- It has strong separation ability, Cl - SO4 2- A separation coefficient of 37.6 can be selected, corresponding to a chloride ion flux of 5.65 × 10⁻⁶. -8 mol·cm -2 ·s -1 The concentration of NaCl is significantly higher than that of commercial membranes (Comparative Example 1), reaching 3.2 (significantly better than the 2.1 times of commercially available products), with a final NaCl concentration of 2.88 mol / L in the concentration chamber. This achieves low-energy salt concentration while solving the problem of resource recovery from high-salt wastewater. The membrane preparation method involves first coating with an aqueous solution, which facilitates better affinity between the catalyst-containing aqueous phase and the hydrophilic crosslinking layer; then coating with an oil phase solution, which increases the charge on the membrane surface, thereby enhancing the anion selectivity of the modified layer. Detailed Implementation

[0032] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0033] This method is based on commercial anion exchange membranes. First, an active deposition layer is constructed on the surface of the base membrane to enhance adhesion and provide active sites for cross-linking reactions. Then, a negatively charged composite separation layer is formed through a single in-situ interfacial polymerization to achieve efficient separation of single high-valence anions. This method is applied to the electrodialysis salt concentration process.

[0034] The mechanism is as follows: (1) A commercial anion exchange membrane is selected as the base membrane and pretreated; (2) An active deposition layer mixed aqueous solution is prepared and coated on the surface of the base membrane; (3) Then an oil phase solution is prepared and a single in-situ interfacial polymerization is carried out to form a negatively charged composite separation layer; finally, a monovalent selective anion exchange membrane is obtained by heat treatment and curing. The active deposition layer constructed in step (2) utilizes the assembly of rigid polyphenols and crosslinking agents to form a semi-solid / solid phase precursor that is insoluble in the oil phase. Coating with an aqueous solution followed by an oil solution not only optimizes the hydrophilicity and roughness of the base membrane surface but also blocks monomer penetration into the membrane pores, thus ensuring the unobstructed flow of the original ion transport channels of the base membrane. Subsequently, during in-situ interfacial polymerization, a nucleophilic catalyst is innovatively introduced to induce rapid cross-linking of trimesoyl chloride at the solid-liquid interface, constructing a dense active skin. The carboxyl groups generated by the hydrolysis of unreacted acyl chloride and the phenolic hydroxyl groups inherent in the polyphenol skeleton together provide a negative potential environment. Thus, through the dual synergistic mechanism of pore size sieving and strong electrostatic Donnan repulsion, efficient retention of anions with large hydration radii and high valence states is achieved, ultimately resulting in a simultaneous improvement in high throughput and high selectivity.

[0035] The anion exchange membrane involved in this invention is a commercially available and known material. The following embodiments specifically use product 5330 from Hebei Langfang Yadeshi Environmental Protection Co., Ltd., with a thickness of 0.180 mm. However, it is not limited to this.

[0036] Example 1:

[0037] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0038] (1) The base membrane is a commercially available anion exchange membrane. Pretreatment: Soak the base membrane in deionized water for 24 hours, then remove it and drain the surface moisture.

[0039] (2) Prepare an aqueous solution containing 2.0 g / L tannic acid, 1.0 g / L ferric chloride, and 0.2 g / L 4-dimethylaminopyridine, using deionized water as the solvent; place the base film obtained in step (1) horizontally in a mold, and coat the base film surface with the aqueous solution at a coating amount of 1.0 mL / cm. 2 The reaction was carried out at 25°C for 15 minutes. During this process, Fe... 3+ The tannic acid is rapidly coordinated and assembled into a metal-polyphenol network, in which 4-dimethylaminopyridine is uniformly dispersed. Then, the excess aqueous solution is removed with a silica gel roller, and the base film is taken out and placed in a hot air drying environment at 40°C for 15 min to transform the liquid deposition layer into a solid precursor assembly layer containing the catalyst.

[0040] (3) Prepare a heptane solution containing 0.15 wt% trimesoyl chloride as the oil phase solution; place the dried base film from step (2) horizontally in the mold, and coat the oil phase solution onto the surface of the solid precursor assembly layer with a coating amount of 1.5 mL / cm. 2 The solid precursor assembly layer and the oil phase solution were reacted at 25°C for 2 min; pyromellitic methyl chloride and -OH / -NH2 on the surface of the assembly layer under restricted interfacial crosslinking were carried out. After the reaction was completed, the oil phase was discarded, and the membrane was placed in hot air drying at 80°C for 5 min to obtain the finished membrane. The prepared membrane was stored in deionized water for later use.

[0041] Example 2:

[0042] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0043] (1) The base membrane is a commercially available anion exchange membrane. Pretreatment: Soak the base membrane in deionized water for 24 hours, then remove it and drain the surface moisture.

[0044] (2) Prepare an aqueous solution containing 2.0 g / L tannic acid, 1.0 g / L ferric chloride, and 0.2 g / L 1-methylimidazole, using deionized water as the solvent; place the base film obtained in step (1) horizontally in a mold, and coat the base film surface with the aqueous solution at a coating amount of 1.0 mL / cm. 2 The reaction was carried out at 25°C for 15 minutes. During this process, Fe... 3+ The tannic acid is rapidly coordinated and assembled into a metal-polyphenol network, in which 1-methylimidazole is uniformly dispersed. Then, the excess aqueous solution is removed with a silica gel roller, and the base film is taken out and placed in a hot air drying environment at 40°C for 15 min to transform the liquid deposited layer into a solid precursor assembly layer containing the catalyst.

[0045] (3) Prepare a heptane solution containing 0.1 wt% trimesoyl chloride as the oil phase solution; place the dried base film from step (2) horizontally, and coat the oil phase solution onto the surface of the solid precursor assembly layer with a coating amount of 1.5 mL / cm. 2 The solid-phase precursor assembly layer and the oil phase solution were reacted at 25°C for 2 min; trimesoyl chloride and -OH / -NH2 on the surface of the assembly layer underwent restricted interfacial crosslinking. After the reaction was completed, the oil phase was discarded, and the membrane was heat-treated at 80°C for 5 min to obtain the finished membrane. The prepared membrane was stored in deionized water for later use.

[0046] Example 3:

[0047] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0048] (1) Same as step (1) in Example 1.

[0049] (2) Prepare a tris(hydroxymethyl)aminomethane-hydrochloric acid buffer solution (pH=8.5) containing 2.0 g / L dopamine and 0.1 g / L 4-dimethylaminopyridine (wherein the concentration of tris(hydroxymethyl)aminomethane-hydrochloric acid) is 4.0 g / L). Place the base film obtained in step (1) horizontally in the mold, and coat the surface of the base film with the aqueous solution at a coating amount of 1.0 mL / cm. 2 The reaction was carried out in an open environment at 25°C for 10 hours. The alkaline environment provided by tris(hydroxymethyl)aminomethane and the assisting effect of 4-dimethylaminopyridine induced the oxidative polymerization of dopamine. After the reaction, the surface pigment was rinsed with deionized water and allowed to air dry naturally in a ventilated area for 30 minutes. At this point, the moist deposited layer transformed into a dark brown solid precursor assembly layer.

[0050] (3) Prepare a heptane solution containing 0.15 wt% trimesoyl chloride as the oil phase solution; place the dried base film from step (2) horizontally, and coat the oil phase solution onto the surface of the solid precursor assembly layer with a coating amount of 1.5 mL / cm.2 The solid precursor assembly layer and the oil phase solution were reacted at 25°C for 1 min; pyromellitic methyl chloride and -OH / -NH2 on the surface of the assembly layer underwent restricted interfacial crosslinking. After the reaction was completed, the oil phase was discarded, and the membrane was heat-treated at 80°C for 7 min to obtain the finished membrane. The prepared membrane was stored in deionized water for later use.

[0051] Example 4:

[0052] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0053] (1) Same as step (1) in Example 1.

[0054] (2) Prepare an aqueous solution containing 2.0 g / L gallic acid, 0.5 g / L copper sulfate, and 0.2 g / L 4-dimethylaminopyridine. Place the base film obtained in step (1) horizontally in a mold, and coat the base film surface with the aqueous solution at a coating amount of 1.0 mL / cm. 2 The reaction was carried out at 25°C for 10 min. Gallic acid deposition was rapidly catalyzed using a Fenton-like reaction. After the reaction, excess aqueous solution was removed with a silica gel roller, and the base film was removed and placed in a 40°C hot air drying environment for 15 min to transform the liquid deposition layer into a solid precursor assembly layer containing the catalyst.

[0055] (3) Prepare a heptane solution containing 0.1 wt% trimesoyl chloride as the oil phase solution; place the dried base film from step (2) horizontally, and coat the oil phase solution onto the surface of the solid precursor assembly layer with a coating amount of 1.5 mL / cm. 2 The solid-phase precursor assembly layer and the oil phase solution were reacted at 25°C for 2 min; trimesoyl chloride and -OH / -NH2 on the surface of the assembly layer underwent restricted interfacial crosslinking. After the reaction was completed, the oil phase was discarded, and the membrane was heat-treated at 80°C for 5 min to obtain the finished membrane. The prepared membrane was stored in deionized water for later use.

[0056] Example 5:

[0057] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0058] (1) Same as step (1) in Example 1.

[0059] (2) Prepare an aqueous solution containing 2.0 g / L catechol, 1.0 g / L sodium periodate, and 0.1 g / L 4-dimethylaminopyridine. Place the base film obtained in step (1) horizontally in a mold, and coat the base film surface with the aqueous solution at a coating amount of 1.0 mL / cm. 2The reaction was carried out at 25°C for 10 min. After the reaction, excess aqueous solution was removed with a silicone roller, and the base film was taken out and placed in a hot air drying environment at 40°C for 15 min to transform the liquid deposition layer into a solid precursor assembly layer containing the catalyst.

[0060] (3) Step (3) is the same as step (3) in Example 1.

[0061] Example 6:

[0062] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0063] (1) Same as step (1) in Example 1.

[0064] (2) Prepare an aqueous solution containing 2.0 g / L tannic acid, 1.0 g / L piperazine, and 0.2 g / L 4-dimethylaminopyridine, using deionized water as the solvent. Place the base film obtained in step (1) horizontally in a mold, and coat the base film surface with the aqueous solution at a coating amount of 1.0 mL / cm². 2 The reaction was carried out at 25°C for 20 min. A Michael addition reaction was performed between the amino groups of piperazine and oxidized tannic acid to form a cross-linked network. After the reaction, excess aqueous solution was removed using a silica gel roller, and the base film was removed and placed in a 40°C hot air drying environment for 15 min to transform the liquid-deposited layer into a solid-phase precursor assembly layer containing the catalyst.

[0065] (3) Prepare a heptane solution containing 0.1 wt% trimesoyl chloride as the oil phase solution; place the dried base film from step (2) horizontally, and coat the oil phase solution onto the surface of the solid precursor assembly layer with a coating amount of 1.5 mL / cm. 2 The solid precursor assembly layer and the oil phase solution were reacted at 25°C for 1 min; pyromellitic methyl chloride and -OH / -NH2 on the surface of the assembly layer underwent restricted interfacial crosslinking. After the reaction was completed, the oil phase was discarded, and the membrane was heat-treated at 80°C for 10 min to obtain the finished membrane. The prepared membrane was stored in deionized water for later use.

[0066] Example 7:

[0067] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0068] (1) Same as step (1) in Example 1.

[0069] (2) Except for adjusting the concentration of the aqueous solution to 0.5 g / L tannic acid, 0.25 g / L ferric chloride and 0.1 g / L 4-dimethylaminopyridine, the other operations are the same as step (2) in Example 1.

[0070] (3) is the same as step (3) in Example 1.

[0071] Example 8:

[0072] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0073] (1) Same as step (1) in Example 1.

[0074] (2) Except for adjusting the concentration of the aqueous solution to 8.0 g / L tannic acid, 4.0 g / L ferric chloride and 0.5 g / L 4-dimethylaminopyridine, the other operations are the same as step (2) in Example 1.

[0075] (3) is the same as step (3) in Example 1.

[0076] Example 9:

[0077] This embodiment provides a method for preparing a selective ion exchange membrane, the method comprising the following steps:

[0078] (1) Same as step (1) in Example 1.

[0079] (2) Except for adjusting the concentration of 4-dimethylaminopyridine in the aqueous solution to 0.5 g / L, the other operations are the same as step (2) in Example 1.

[0080] (3) is the same as step (3) in Example 1.

[0081] Comparative Example 1:

[0082] This comparative example provides commercially available monovalent anion exchange membranes; the remaining operations are not performed.

[0083] Comparative Example 2:

[0084] This comparative example provides a method for preparing a selective ion exchange membrane, which differs from Example 1 only in that no 4-dimethylaminopyridine catalyst is added; all other aspects are the same as in Example 1.

[0085] Comparative Example 3:

[0086] This comparative example provides a method for preparing a selective ion exchange membrane, which differs from Example 1 only in that: 4-dimethylaminopyridine is not added to the aqueous phase in step (2), but 0.2 g / L of 4-dimethylaminopyridine is dissolved in the oil phase solution in step (3).

[0087] Comparative Example 4:

[0088] This comparative example uses a traditional interfacial polymerization process (wet two-step method): the base film is first immersed in a chitosan (CTS) aqueous solution, and after being taken out, it is directly immersed in a polyethyleneimine (PEI) aqueous solution without drying. After being taken out, it is then contacted with a trimesoyl chloride (TMC) oil phase solution.

[0089] Comparative Example 5:

[0090] This comparative example provides a method for preparing a selective ion exchange membrane, which differs from Example 1 only in that step (3) is omitted.

[0091] Performance testing:

[0092] Selective electrodialysis testing procedure: First, the prepared monovalent selective anion exchange membrane and commercial cation exchange membrane are cut into 5cm × 5cm square membrane sheets. These membrane sheets are then fixed between the compartments of the electrodialysis device, which consists of an anode compartment, a desalination compartment, a concentration compartment, and a cathode compartment arranged sequentially. The effective membrane area is 16cm². 2 The compartments and membranes were then secured with screws. Next, 120 mL of 0.15 mol / L Na₂SO₄ solution was poured into the cathode and anode chambers, respectively; 120 mL of 0.01 mol / L NaNO₃ solution was poured into the concentration chamber; and 120 mL of a mixed solution of 0.1 mol / L NaCl and 0.1 mol / L Na₂SO₄ was poured into the desalination chamber. Then, a titanium-coated ruthenium electrode was placed in the electrode chamber, and the peristaltic pump was turned on, setting the flow rate to 120 mL / min. Finally, the power supply was turned on at 5 mA / cm². 2 The experiment was run in constant current mode, with samples taken every 0.5 hours and the experiment ended after 1 hour. The ambient temperature was 20℃.

[0093] The overall operation steps of the electrodialysis concentration and salt production process are similar to those of the selective electrodialysis process. The difference is that the concentration chamber contains 500 mL of simulated concentrated seawater, the desalination chamber contains 100 mL of simulated concentrated seawater, and the current density is 20 mA / cm². 2 .

[0094] Ion flux definition: J = (C t -C0)·V / (A·t), where J represents the ion flux, C0 and C t Represents the ion concentration (mol / L) in the concentration chamber at initial time 0 and time t, respectively, and A represents the effective area of ​​the membrane (cm²). 2 V represents the volume of the solution in the concentration chamber (L), and t represents the operation time (s).

[0095] Choose the definition of the separation coefficient: P=J M - ·C N 2- / (J N2- ·C M - In the formula, P represents the selection separation coefficient, and J... M - and J N 2- These represent the fluxes of monovalent and divalent anions (mol·cm⁻¹), respectively. -2 ·s -1 ), C M - and C N 2- These represent the initial concentrations (mol / L) of monovalent and divalent anions in the desalination chamber.

[0096] NaCl recovery rate: In electrodialysis, the NaCl recovery rate is defined as the percentage of NaCl that migrates to the concentration chamber at a certain time t compared to the initial amount of NaCl in the desalination chamber. The calculation formula is: R NaCl (%) = V ct ·(C ct -C c0 )×100 / (V d0 C d0 C d0 V is the initial NaCl concentration (mol / L) in the desalination chamber; d0 It is the initial volume (L) of the solution in the desalination chamber; C c0 The initial concentration of NaCl in the concentration chamber (mol / L); C ct V is the NaCl concentration (mol / L) in the concentration chamber at a certain moment; ct It is the volume (L) of the solution in the concentration chamber at a certain moment.

[0097] The monovalent selective anion exchange membranes prepared in Examples 1-9 and Comparative Examples 1-4 have Cl - Flux, SO4 2- The flux and selective separation coefficients are shown in Table 1. Electrodialysis concentration experiments were conducted on the monovalent selective anion exchange membranes prepared in Example 1 and Comparative Example 1. The initial NaCl concentration in the concentration chamber, the final NaCl concentration in the concentration chamber, and the NaCl concentration factor are shown in Table 2.

[0098] Table 1

[0099]

[0100] The following conclusions can be drawn from Table 1:

[0101] (1) As can be seen from the comparison of data from Examples 1-9 and Comparative Example 4, the membranes prepared by different polyphenol systems provided by the present invention have Cl - The flux remained at a high level (4.80-6.25×10).-8 mol·cm -2 ·s -1 The result was significantly higher than that of Comparative Example 4, which used a traditional wet interfacial polymerization process (only 2.30 × 10⁻⁶). -8 mol·cm -2 ·s -1 This strongly demonstrates that the "precursor solidification followed by in-situ catalytic interfacial polymerization" step proposed in this invention has strong universality and effectiveness. By transforming the liquid deposition layer into a semi-solid / solid phase layer, the blockage caused by monomers penetrating into the membrane pores is successfully avoided, thereby significantly reducing membrane resistance and solving the problem of flux decay in traditional modification methods.

[0102] (2) As can be seen from Example 1 and Comparative Example 2, the selective separation coefficient of the membrane was increased by more than 40% after the introduction of the catalyst.

[0103] Because the reaction kinetics between phenolic hydroxyl groups in the polyphenol backbone and acyl chlorides are slow, the resulting skin layer under catalytic conditions is relatively loose and has a low degree of cross-linking, making it difficult to effectively retain divalent anions with large hydration radii. This invention utilizes 4-dimethylaminopyridine as a highly efficient nucleophilic catalyst to accelerate the interfacial polymerization rate, significantly lower the reaction energy barrier, and induce a highly efficient esterification and cross-linking reaction between acyl chlorides and phenolic hydroxyl groups on the solid surface. This constructs a dense skin layer with a high degree of cross-linking, thereby improving the sieving performance of monovalent / polyvalent ions.

[0104] (3) As can be seen from Example 1 and Comparative Example 3, the selectivity of the membrane can be improved as long as a catalyst is present. However, the performance of Example 1 is significantly better than that of Comparative Example 3. This is because the solid-phase locking process used in this invention physically anchors the catalyst to the solid-phase precursor assembly layer, creating a local high concentration of catalyst at the solid-liquid reaction interface. Compared with the method in Comparative Example 3 where the catalyst is dispersed in the oil phase and needs to diffuse to the interface, this invention (Example 1) can more efficiently induce the interfacial polymerization reaction, thereby constructing a separation skin with fewer defects and higher cross-linking degree, achieving precise sieving of monovalent anions.

[0105] (4) As can be seen from Example 1 and Comparative Example 4, the liquid amine monomer diffuses outward from the base membrane pores and reacts with the oil phase. Due to the lack of solid phase locking, the liquid monomer can easily penetrate and block the base membrane pores, resulting in a thick and uneven reaction layer, which exhibits high resistance, low flux and poor selectivity.

[0106] (5) As can be seen from Example 1 and Comparative Example 5, the solid active layer alone cannot provide sufficient pore size sieving effect. It is necessary to form a dense skin layer through in-situ interfacial polymerization in order to achieve selective permeation of monovalent anions.

[0107] (6) Example 1 achieved the highest selectivity (37.6) using a rigid metal-polyphenol coordination network with the aid of a catalyst, which is far superior to commercial membranes (Comparative Example 1); while Example 6 (tannic acid / piperazine) achieved the highest flux (6.10 × 10⁻⁶) using organic amine crosslinking. -8 mol·cm -2 ·s -1 This demonstrates that the present invention can flexibly control the flux and selectivity of the membrane by selecting different polyphenol backbones to meet the needs of different industrial application scenarios.

[0108] Table 2

[0109]

[0110] (7) The salt concentration factor (3.2) of Example 1 is higher than that of conventional commercial membrane salt concentration factor.

[0111] Example 1, as a preferred technical solution of the present invention, describes a monovalent selective anion exchange membrane comprising a support, a polyphenol solid-phase intermediate layer, and an in-situ polymerized active layer; the in-situ polymerized active layer is anchored to the intermediate layer via ester or amide bonds; the monovalent selective anion exchange membrane is effective for Cl... - SO4 2- The selection separation coefficient can reach 37.6.

[0112] In summary, this invention provides a method for preparing and applying a selective ion exchange membrane. By constructing a negatively charged dense layer through in-situ induced interfacial polymerization, the membrane exhibits high selectivity and high flux for monovalent and polyvalent anions. This effectively optimizes the membrane's separation performance for monovalent and polyvalent ions and the concentration and salt production process. Furthermore, the membrane demonstrates good stability, and the preparation method is simple and easy to operate.

[0113] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

[0114] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing a selective ion exchange membrane, characterized in that, The method includes the following steps: (1) The anion exchange membrane is pretreated to obtain the base membrane; (2) Coat the mixed solution onto the surface of the base film at a rate of 0.5~2.0 mL / cm². 2 The substrate is contacted at 25–45°C for 10 min–24 h to obtain a base film with an active deposition layer, and then dried at 30–60°C for 10–120 min to obtain a base film with a functionalized precursor assembly layer. The mixed solution is an aqueous solution containing active substances, crosslinking agents, and interfacial catalysts; the mass ratio of each component is: active substances: crosslinking agents: interfacial catalysts = 1:(0.1~4.0):(0.01~0.5); The active substance is a polyphenolic compound, and the crosslinking agent includes any one or more of metal ligands, organic crosslinking agents, or oxidation inducing agents. The interfacial catalyst is one or more of 4-dimethylaminopyridine, 1-methylimidazolium, or triethylenediamine. (3) Coat the surface of the base film with the functionalized precursor assembly layer obtained in step (2) with the oil phase solution, the coating amount being 0.5~2.0 mL / cm. 2 The membrane is contacted at 25–45°C for 0.5–10 min, followed by heat treatment at 60–95°C for 2–15 min to obtain anion-selective membrane. The oil phase solution is composed of acyl chloride compounds and nonpolar organic solvents; the acyl chloride compounds account for 0.05 to 1.0 wt% of the total mass of the oil phase solution.

2. The method for preparing the selective ion exchange membrane as described in claim 1, characterized in that, The total concentration of solute in the mixed solution in step (2) is 0.5 to 15.0 g / L.

3. The method for preparing the selective ion exchange membrane as described in claim 1, characterized in that, The acyl chloride compounds mentioned in step (3) include one or more of pyromellitic methyl methacrylate (PMMA), isophthaloyl chloride (IMMA), or terephthaloyl chloride (THC). The nonpolar organic solvent includes n-hexane, n-heptane, or isoalkanes.

4. The method for preparing the selective ion exchange membrane as described in claim 1, characterized in that, The polyphenolic compound in step (2) is any one or a combination of at least two of catechol compounds or complex polyphenolic compounds.

5. The method for preparing the selective ion exchange membrane as described in claim 4, characterized in that, The catechol compounds are any one or a combination of at least two of catechol, dopamine, 3,4-dihydroxyphenylalanine, or caffeic acid; the complex polyphenol compounds include any one or a combination of at least two of tannic acid, gallic acid, or proanthocyanidins.

6. The method for preparing the selective ion exchange membrane as described in claim 1, characterized in that, In step (2), the metal ligand includes any one or a combination of at least two of ferric chloride, ferric sulfate, copper chloride, or copper sulfate; The organic crosslinking agent includes one or a combination of at least two of piperazine, polyethyleneimine, ethylenediamine, or polylysine. The oxidation inducer includes one or at least two of tris(hydroxymethyl)aminomethane hydrochloric acid, sodium periodate, or ammonium persulfate.

7. The method for preparing the selective ion exchange membrane as described in claim 1, characterized in that, The drying process described in step (2) is natural air drying, thermal radiation drying, or vacuum drying.

8. The application of the selective ion exchange membrane prepared by the method according to any one of claims 1-7, characterized in that, It is used for screening monovalent and polyvalent anions, electrodialysis salt concentration, or zero discharge of high-salt wastewater.

9. The application as described in claim 8, characterized in that, The aforementioned monovalent and polyvalent anions include monovalent anions and polyvalent anions; the monovalent anions include Cl... - NO3 - or F - One or more of the following; the multivalent anions include SO42-. 2- Or PO4 3- One or more; The salt is one or more of NaCl, LiCl, or Na2SO4.

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