Crown ether derivative for electrodialysis, electrodialysis membrane and treatment method

Abstract

The invention belongs to the technical field of electrodialysis membranes, and discloses a crown ether derivative for electrodialysis, an electrodialysis membrane and a treatment method. The crown ether derivative has good hydrophilicity, not only can enhance the transmission rate of monovalent cations, but also has the characteristic of specifically complexing and adsorbing bivalent or higher cations. The crown ether derivative is used for modifying an electrodialysis cation exchange membrane, and the obtained modified cation exchange membrane has high performance and high selectivity, can efficiently separate monovalent metal salt and divalent metal salt, and can realize efficient treatment of strong brine when being applied to strong brine treatment.

Description

Technical Field

[0001] The present invention relates to the technical field of electrodialysis membranes, and particularly to a crown ether derivative for electrodialysis, an electrodialysis membrane, and a treatment method. Background Art

[0002] As a kind of electrodialysis membrane, a bipolar membrane is composed of an anode membrane, an intermediate layer, and a cathode membrane, and has anion and cation selectivity. Under the action of a direct current electric field, H2O between the bipolar membranes is dissociated into H + and OH - . H + passes through the cation membrane; OH - passes through the anion membrane. Therefore, bipolar membranes have important application prospects in fields such as acid-base production, resource recovery, and electrolytic water hydrogen production. And an electrodialysis device chamber is a device composed of bipolar membranes, cation exchange membranes, and anion exchange membranes, which can be used for the treatment of concentrated brine. Electrodialysis is a membrane separation technology in which ions in a concentrated brine solution migrate directionally through ion exchange membranes under the action of a potential difference to achieve desalination, concentration, and separation and purification, and is widely used in fields such as seawater desalination, wastewater treatment, and chemical production. With the development of industry, the application fields of electrodialysis have gradually expanded, which also puts forward higher requirements for the separation performance of electrodialysis.

[0003] In the prior art, the ion selectivity of the cation exchange membrane in the electrodialysis device is low, and the separation of monovalent metal salts and divalent metal salts cannot be effectively achieved. Therefore, the need to develop an electrodialysis membrane capable of efficiently separating monovalent salts and divalent salts is extremely urgent. Summary of the Invention

[0004] In view of the above technical problems, the present invention provides a crown ether derivative for electrodialysis, an electrodialysis membrane, and a treatment method. The crown ether derivative has good hydrophilicity, and can not only enhance the transport rate of monovalent cations, but also specifically complex and adsorb cations with a valence of more than two. Using the crown ether derivative of the present invention for the modification treatment of an electrodialysis cation exchange membrane, the obtained modified cation exchange membrane has high performance and high selectivity, can efficiently separate monovalent metal salts and divalent metal salts, and applying it to the treatment of concentrated brine is expected to achieve the efficient treatment of concentrated brine.

[0005] To solve the above technical problems, the present invention adopts the following technical solutions:

[0006] In a first aspect, the present invention provides a crown ether derivative for an electrodialysis membrane, and the structure of the crown ether derivative is shown in formula (I),

[0007]

[0008] The crown ether derivative of the present invention not only contains a hydrophilic group side chain but also contains an oxygen atom with an unshared electron pair. Among them, the hydrophilic group side chain endows the crown ether derivative with good hydrophilicity. The hydrophilic group side chain can also form hydrogen bonds with water molecules, which can enhance the transport rate of monovalent cations; the oxygen atom endows the crown ether derivative with specific complexation and adsorption of cations with a valence of more than two, and transports monovalent cations. When the crown ether derivative of the present invention is used to prepare a cation exchange membrane, the separation of monovalent cations (Na + 、K + etc.) and cations with a valence of more than two (Mg 2+ 、Ca 2 +、Ba 2+ 、Cu 2+ 、Fe 3+ etc.) can be achieved, and it is expected to obtain a cation exchange membrane capable of efficiently separating monovalent metal salts and divalent metal salts.

[0009] In a second aspect, the present invention also provides a preparation method of the above crown ether derivative, including: dissolving L-DOPS, an organic ester compound, and a catalyst in a solvent, and heating to obtain the crown ether derivative.

[0010] Preferably, the specific preparation method of the crown ether derivative includes:

[0011] Under an inert gas atmosphere, add L-DOPS and the catalyst sodium hydroxide to dimethyl sulfoxide, reflux at 100-120 °C for 30-40 min to obtain a first reaction solution;

[0012] Add the organic ester compound to dimethyl sulfoxide and stir evenly to obtain a second reaction solution;

[0013] Drop half of the second reaction solution into the first reaction solution at a rate of 1-5 d / min. After refluxing at 50-70 °C for 1-2 h, then continue to drop the remaining amount of the second reaction solution at a rate of 1-5 d / min, and continue to reflux at 50 °C - 70 for 12-16 h to obtain a crude product;

[0014] Then add concentrated hydrochloric acid to the crude product, remove dimethyl sulfoxide by steam distillation, perform solid-liquid separation, and wash the filter cake with water, acetone, and dry it to obtain crystals, which are the crown ether derivative.

[0015] The present invention uses L-DOPS containing a hydrophilic group side chain and an organic ester compound in a dimethyl sulfoxide solution of a sodium hydroxide catalyst, and refluxes under a nitrogen atmosphere to prepare a crude product, which is separated and purified to obtain a crown ether derivative containing a rich hydrophilic group side chain. It not only contains a crown ether structure but also contains rich hydrophilic groups hydroxyl -OH, carboxyl -COOH, and amino -NH2. Among them, the oxygen atoms rich in the crown ether structure in the crown ether derivative can specifically adsorb metal cations alkali metal ions, alkaline earth metal ions, transition metal ions (Be2+ , Mg 2+ , Ca 2 +, Ba 2+ , Cu 2+ , Fe 2+ , Fe 3+ , Zn 2+ , Al 3+ etc.) to form a complex. Using the crown ether derivative to prepare a cation exchange membrane is expected to achieve the separation of polyvalent metal ions and monovalent metal ions in a metal ion-containing solution by the cation exchange membrane.

[0016] Preferably, the inert gas atmosphere is N2 or helium;

[0017] The molar ratio of the L-DOPS to the organic ester compound is (1 - 2):1;

[0018] The organic ester compound is diethylene glycol bis(p-toluenesulfonate) (CAS No.: 7460 - 82 - 4); the L-DOPS is (2S,3R)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropionic acid, with the molecular formula C9H 11 NO5 (CAS No.: 23651 - 95 - 8);

[0019] The L-DOPS in the first reaction solution accounts for 0.1 - 0.2 mol / 100 ml of the volume of the solvent dimethyl sulfoxide;

[0020] The sodium hydroxide in the first reaction solution accounts for 0.2 - 0.3 mol / 100 ml of the volume of the solvent dimethyl sulfoxide;

[0021] The organic ester compound in the second reaction solution accounts for 0.05 - 0.15 mol / 30 ml of the volume of the solvent dimethyl sulfoxide.

[0022] Thirdly, the present invention also provides a treatment method for an electrodialysis membrane, including the following steps:

[0023] S1. Add the crown ether derivative, the organosilicon solution and the two-dimensional MXene material with a mass ratio of (2 - 3):(1 - 1.5):(0.2 - 0.5) to a good solvent, stir evenly to obtain a modified solution;

[0024] S2. After mixing the modified solution with a film-forming agent evenly, coat it on the surface of the cation exchange membrane, and perform heat treatment in an inert atmosphere, then cool to room temperature to obtain a modified cation exchange membrane.

[0025] The modified solution prepared from the crown ether derivative, organosilicon solution and two-dimensional MXene material with the above-mentioned ratios is dissolved in a film-forming agent and coated on the surface of the cation exchange membrane to prepare a modified cation exchange membrane. Among them, the hydrophilic side chain of the crown ether derivative forms a hydrogen bond with water molecules, enhancing the transport rate of monovalent cations. At the same time, the oxygen atoms of the crown ether derivative specifically complex and adsorb cations with a valence of more than two, and transport monovalent cations, endowing the modified cation exchange membrane with the ability to separate monovalent cations (Na + 、K + 、etc.) from cations with a valence of more than two (Mg 2+ 、Ca 2 +、Ba 2+ 、Cu 2+ 、Fe 3+ 、etc.) in wastewater; the organosilicon solution endows the modified cation exchange membrane with high mechanical strength, high temperature resistance, oxidation stability, corrosion resistance and other characteristics; the two-dimensional MXene material can provide ion transport channels for monovalent ions (Na + 、K + 、etc.), intercept divalent cations, do not retain beneficial monovalent cations, and also has anti-pollution properties, extending the service life of the cation exchange membrane.

[0026] In short, under the synergistic effect of the crown ether derivative, organosilicon solution and two-dimensional MXene material, a modified cation exchange membrane with high performance and high ion selectivity is obtained. This modified cation exchange membrane can be used for the treatment of concentrated brine, efficiently separate monovalent cations and divalent cations, realize the separation of monovalent salts and divalent salts, and thus achieve zero discharge of concentrated brine.

[0027] Preferably, in step S1, the mass ratio of the crown ether derivative, organosilicon solution and two-dimensional MXene material is (2-3):(1-1.5):(0.2-0.5); the modified cation exchange membrane prepared from the crown ether derivative, organosilicon solution and two-dimensional MXene material with this mass ratio has the characteristics of high mechanical strength, corrosion resistance, high performance and good ion selectivity, and can achieve efficient separation of monovalent cations and divalent cations.

[0028] Preferably, the two-dimensional MXene material is a 5mg / ml - 10mg / ml monolayer Ti3C2Tx dispersion. The MXene material is obtained by removing A atoms from the MAX phase ceramic through methods such as liquid-phase etching to obtain a two-dimensional transition metal carbon or carbide, which has good electrical conductivity and rich surface chemical properties.

[0029] The organosilicon solution is tetramethylsilane or epoxy group-modified silicone oil.

[0030] The good solvent includes any one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide. The crown ether derivative, the organosilicon solution, and the two-dimensional MXene material account for 5%-10% of the mass of the good solvent.

[0031] The good solvent of the present invention can dissolve the crown ether derivative, the organosilicon solution, and the two-dimensional MXene material into a modified solution with uniform composition.

[0032] Preferably, in step S2, the modified solution accounts for 10%-25% of the mass of the film-forming agent;

[0033] The film-forming agent includes: 1,3,5-benzenetricarbonyl chloride or polyvinylpyrrolidone, both of which are in liquid form; under the action of the film-forming agent of the present invention, the modified solution is uniformly coated and cured on the surface of the cation exchange membrane to form a modified cation exchange membrane. The hydrogen bond sites in the pore channels on the modified cation exchange membrane can form specific interactions with water molecules, which can force water molecules to conduct through the proton channels, and can significantly enhance the conduction efficiency of water molecules. The thickness of the modified cation exchange membrane layer is 20-50 μm.

[0034] The heat treatment in an inert atmosphere is: in an N2 or helium atmosphere, heat treatment is carried out at 80-150 °C for 15-36 h;

[0035] The cation exchange membrane includes: a standard membrane (commercial CSE membrane) or a blend crosslinked proton exchange membrane (commercial CMB membrane), both of which are commercially available. The types of CSE membrane and CMB membrane are both strongly acidic Na, and the materials are both perfluorosulfonic acid.

[0036] Preferably, the modified cation exchange membrane is treated with a mixed gas by low-temperature plasma to introduce hydrophilic groups. The mixed gas is 50% O2 and 50% NH; the power of the plasma is 80-100 W, the plasma treatment time is 90-120 s; the low temperature is 10-15 °C; the hydrophilic groups are -OH, -COOH, -NH2. When the present invention uses a mixed gas containing O2 and NH for treatment, the active particles in the plasma can react with the surface of the modified cation exchange membrane to introduce functional groups such as oxygen-containing (-OH, -COOH) and nitrogen-containing (-NH2). These functional groups can enhance the hydrophilicity and ion conductivity of the membrane.

[0037] Fourthly, the present invention also provides an electrodialysis membrane prepared by the above treatment method of the electrodialysis membrane.

[0038] Fifth aspect, an electrodialysis device, comprising: an anode, a cathode, an electrodialysis membrane assembly, a sensor and a current controller; wherein, the anode is a titanium electrode, and a rare metal layer with a thickness of 10-20 nm is provided on the surface of the titanium electrode, and the rare metal is at least one of cerium, platinum, dysprosium, and ruthenium to improve the conductivity, anti-corrosion and other effects of the electrode; the cathode is a stainless steel electrode;

[0039] The above-mentioned treatment method of the electrodialysis membrane or the above-mentioned modified cationic exchange membrane is used to make an electrodialysis membrane assembly; the structure of the electrodialysis membrane assembly is: -│anion exchange membrane│bipolar membrane│modified cation exchange membrane│anion exchange membrane│bipolar membrane│modified cation exchange membrane│anion exchange membrane│+ arranged in this structure.

[0040] The cathode of the electrodialysis membrane assembly is connected to the negative pole of the DC power supply through a wire, and the anode is connected to the positive pole of the DC power supply through a wire; a sensor and a current controller are connected to the wire between the whole machine of the DC power supply and the anode of the electrodialysis membrane assembly of the electrodialysis membrane assembly. The current sensor is a Hall current sensor for detecting the magnitude of the current of the electrodialysis device; the current controller can monitor and record current data in real time, and accurately control and adjust the magnitude of the current passing through the membrane group to prevent excessive current from causing damage to the membrane group and the electrode, improve the efficiency of electrodialysis, ensure the safety of the electrodialysis device, and extend the service life. Description of the Drawings

[0041] Figure 1 It is a schematic structural diagram of the electrodialysis device of the present invention;

[0042] Figure 2 It is an infrared spectrum diagram of the crown ether derivative of the present invention. Detailed Embodiments

[0043] In order to make the objectives, technical solutions and advantages of the present invention clearer, the following further describes the present invention in detail with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention. The "upper", "lower", "left", and "right" defined in the present invention are only limited to the views shown in the drawings of the specification of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0044] The preparation method of the Ti3C2Tx dispersion of two-dimensional MXene material is as follows: MAX phase Ti3AlC2 and TiC powders with a molar ratio of 1:1 are calcined at 1350 °C in an argon atmosphere to obtain a Ti3AlC2 precursor. Then, the Ti3AlC2 precursor is soaked in 70% hydrofluoric acid for 3 h to obtain a crude product Ti3C2Tx. The crude product is washed with deionized water and centrifuged at 4000 r / min for 15 min to remove residual hydrofluoric acid. This operation is repeated until the pH value of the supernatant is about 7. After discarding the supernatant, the MXene material Ti3C2Tx is obtained through filtration and drying. Ti3C2Tx is dissolved in deionized water and ultrasonicated for 2 h in an argon atmosphere, and then centrifuged at 4000 r / min for 1 h to obtain a 5 mg / ml - 10 mg / ml monolayer Ti3C2Tx dispersion.

[0045] The reaction mechanism of the crown ether derivative is as follows: Using L-DOPS under the action of a base catalyst, two oxygen anions are generated, and only the carbocation connected to ethylene glycol bis(p-toluenesulfonate) undergoes cyclization to form a crown ether derivative. The reaction mechanism is shown in Formula (II).

[0046]

[0047] Formula (II).

[0048] The specific preparation method of the crown ether derivative is as follows:

[0049] In a 250 ml three-necked flask equipped with a reflux device, 0.15 mol of L-DOPS, 100 ml of dimethyl sulfoxide, and 0.30 mol of sodium hydroxide are successively added in an N2 atmosphere, and refluxed at 115 °C for 30 min to ensure that all the sodium hydroxide is dissolved, obtaining a first reaction solution;

[0050] 0.075 mol of ethylene glycol bis(p-toluenesulfonate) is diluted with 30 ml of dimethyl sulfoxide to prepare an ethylene glycol bis(p-toluenesulfonate) / dimethyl sulfoxide solution as a second reaction solution;

[0051] Add 15 ml of the obtained diethylene glycol bis(p-toluenesulfonate) / dimethyl sulfoxide solution dropwise to the above first reaction solution at a rate of 5 drops per minute. Then, after refluxing at 60 °C for 1 h, continue to drop in the remaining 15 ml of the diethylene glycol bis(p-toluenesulfonate) / dimethyl sulfoxide solution at 5 drops per minute. Then reflux at 60 °C for 16 h (track with the color reaction of FeCl3 solution to judge whether the conversion of L-DOPS is complete. If no purple color appears, it indicates that the reaction is complete). Add 1.5 ml of concentrated hydrochloric acid, remove the dimethyl sulfoxide solvent by steam distillation, filter, wash the filter cake with water and drain it. The obtained solid is dispersed in 100 ml of acetone for recrystallization. After stirring for 30 min, filter, wash with acetone again and dry to obtain a crystal yield of up to 75%. That is, a crown ether derivative with hydrophilic -OH, -COOH, and -NH2 groups in the side chain. Compared with n-butanol, a commonly used solvent for the preparation of crown ethers, dimethyl sulfoxide as a solvent can better dissolve L-DOPS, sodium hydroxide, and diethylene glycol bis(p-toluenesulfonate), improving the product yield.

[0052] Figure 2 This is the infrared spectrum of the crown ether derivative of the present invention. As can be seen from Figure 2 it that strong absorption peaks appear near 3610 cm -1 , 3406 cm -1 , 3390 cm -1 , 2910 cm -1 , 2894 cm -1 , 1703 cm -1 , 1590 cm -1 , 1413 cm -1 , 1370 cm -1 , 1250 cm -1 , 1080 cm -1 , 906 cm -1 , 815 cm -1 , 730 cm -1 etc. The stretching vibration of -OH is at 3610 cm-1; two absorption peaks appear near 3406 cm -1 and 3390 cm -1 , which are the stretching vibration absorption peaks of -NH2; the stretching vibration peaks of C-H are at 2910 cm -1 and 2894 cm -1 ; the characteristic vibration peak of -COOH is near 1703 cm -1 ; the skeletal vibrations of the benzene ring are near 1590 cm -1 , 1413 cm -1 , and 1370 cm -1 ; and the absorption peaks at 906 cm -1 , 815 cm -1 , and 730 cm -1is the vibration peak in the fingerprint region of the benzene ring; 1250 cm -1 and 1080 cm -1 nearby are the stretching vibration peaks of the ether bond (C-O-C); among them, 1250 cm -1 is the characteristic vibration of the aromatic ether bond; the above results indicate that the molecular structure of the crown ether derivative contains groups such as -CH, -NH2, -COOH, C-O-C, and benzene ring, which is consistent with the above molecular structure.

[0053] The present invention will be further elaborated in detail below in conjunction with specific embodiments.

[0054] Example 1

[0055] I. Add the crown ether derivative, organosilicon solution (tetramethylsilane, CAS: 75-76-3), and monolayer Ti3C2Tx of two-dimensional MXene material with a mass ratio of 2:1.5:0.5 to N,N-dimethylformamide and stir evenly to obtain a modified solution. Among them, the crown ether derivative, organosilicon solution, and monolayer Ti3C2Tx of two-dimensional MXene material account for 5% of the mass of N,N-dimethylformamide.

[0056] II. After mixing the modified solution with a polyvinylpyrrolidone film-forming agent evenly (the modified solution accounts for 10% of the mass of polyvinylpyrrolidone), coat it on the surface of the cation exchange membrane: commercial CSE membrane, and heat-treat it at 80-150 °C for 15-36 h in an N2 atmosphere, and then cool it to room temperature to obtain the modified cation exchange membrane.

[0057] Example 2

[0058] I. Add the crown ether derivative, organosilicon solution (epoxy group-modified silicone oil, model: BSM-204), and monolayer Ti3C2Tx of two-dimensional MXene material with a mass ratio of 3:1:0.2 to N,N-dimethylacetamide and stir evenly to obtain a modified solution. Among them, the crown ether derivative, organosilicon solution, and monolayer Ti3C2Tx of two-dimensional MXene material account for 7% of the mass of N,N-dimethylformamide.

[0059] II. After mixing the modified solution with a 1,3,5-benzenetricarbonyl chloride film-forming agent evenly (the modified solution accounts for 20% of the mass of 1,3,5-benzenetricarbonyl chloride), coat it on the surface of the cation exchange membrane: commercial CMB membrane, and heat-treat it at 80-150 °C for 15-36 h in an N2 atmosphere, and then cool it to room temperature to obtain the modified cation exchange membrane.

[0060] Example 3

[0061] 1. Add a crown ether derivative, an organosilicon solution (epoxy-modified silicone oil, model: BSM-204), and a monolayer of Ti3C2Tx of two-dimensional MXene material with a mass ratio of 2.5:1:0.3 to N,N-dimethylformamide, stir evenly to obtain a modified solution. Among them, the crown ether derivative, the organosilicon solution, and the monolayer of Ti3C2Tx of two-dimensional MXene material account for 10% of the mass of N,N-dimethylformamide.

[0062] 2. After mixing the modified solution evenly with a polyvinylpyrrolidone film-forming agent (the modified solution accounts for 10% of the mass of polyvinylpyrrolidone), coat it on the surface of a cation exchange membrane: a commercial CSE membrane, and heat-treat it at 80-150 °C for 15-36 h in an N2 atmosphere, then cool it to room temperature to obtain a modified cation exchange membrane.

[0063] 3. Use a mixed gas with a volume ratio of 50% O2 and 50% NH3 to perform low-temperature plasma treatment on the modified cation exchange membrane at 12 °C, with a power of 100 W and a pressure of 1 Pa for 100 s, and a gas flow rate of 3 L / min. Introducing O2 and argon Ar during plasma surface treatment can cause chemical reactions on the surface of the modified cation exchange membrane, thereby introducing new hydrophilic groups -OH, -COOH, -NH2. Plasma surface etching can also roughen the surface of the modified layer of the modified cation exchange membrane without penetrating the modified layer. Without damaging the crown ether derivative, it can increase the contact area between the membrane layers, thereby improving the performance of the bipolar membrane.

[0064] Comparative Example 1

[0065] A commercially available cation exchange membrane, product model: commercial CSE membrane, with a material of perfluorosulfonic acid.

[0066] Comparative Example 2

[0067] Compared with Example 2, the modified solution in this example only contains a crown ether derivative.

[0068] Specifically: After mixing the modified solution evenly with a 1,3,5-benzenetricarbonyl chloride film-forming agent (the modified solution accounts for 20% of the mass of 1,3,5-benzenetricarbonyl chloride), coat it on the surface of a cation exchange membrane: a commercial CSE membrane, and heat-treat it at 80-150 °C for 15-36 h in an N2 atmosphere, then cool it to room temperature to obtain a modified cation exchange membrane.

[0069] Comparative Example 3

[0070] Compared with Example 2, the modified solution in this example is only a dispersion of an organosilicon solution and a monolayer of Ti3C2Tx of two-dimensional MXene material with a mass ratio of 1:0.2.

[0071] Specifically:

[0072] A silicone solution with a mass ratio of 1:0.2 and monolayer Ti3C2Tx of two-dimensional MXene material are dispersed and added to N,N-dimethylacetamide, and stirred evenly to obtain a modified solution. Among them, the silicone solution and the dispersed monolayer Ti3C2Tx of two-dimensional MXene material account for 5% of the mass of N,N-dimethylacetamide;

[0073] After uniformly mixing the modified solution with 1,3,5-benzenetricarbonyl chloride film-forming agent (the modified solution accounts for 20% of the mass of 1,3,5-benzenetricarbonyl chloride), it is coated on the surface of the cation exchange membrane: commercial CSE membrane, and heat-treated at 80-150 °C for 15-36 h in an N2 atmosphere, and then cooled to room temperature to obtain the modified cation exchange membrane.

[0074] Application Example 1

[0075] The present invention provides an electrodialysis device, as Figure 1 shown. Figure 1 is a schematic structural diagram of the electrodialysis device of the present invention.

[0076] Figure 1 The electrodialysis device in includes: an anode, a cathode, an electrodialysis membrane assembly, a sensor and a current controller; among them, the anode is a titanium electrode, and a 20-nm-thick cerium metal layer is provided on the surface of the titanium electrode to improve the conductivity, anti-corrosion and other effects of the electrode; the cathode is a stainless steel electrode. The cathode is connected to the negative electrode of the DC power supply through a wire, the anode is connected to the positive electrode of the DC power supply through a wire, and a Hall current sensor and a current controller are sequentially connected on the wire between the positive electrode of the DC power supply and the anode of the electrodialysis membrane assembly. The Hall current sensor is used to detect the current magnitude of the electrodialysis device; the current controller can monitor and record the current data in real time, and accurately control and adjust the current magnitude passing through the electrodialysis membrane group to prevent excessive current from causing damage to the membrane group and the electrode, ensuring the safety of the electrodialysis device and extending its service life.

[0077] Figure 1 The structure of the electrodialysis membrane assembly in is: -│anion exchange membrane│bipolar membrane│cation exchange membrane│anion exchange membrane│bipolar membrane│cation exchange membrane│anion exchange membrane│+, Figure 1 In, A is an anion exchange membrane, C is a cation exchange membrane, and BP is a bipolar membrane. The left side of the bipolar membrane is an acid chamber, the right side is an alkali chamber, and the concentrated brine chamber is between the cation exchange membrane and the anion exchange membrane. All anion exchange membranes in the electrodialysis membrane assembly are commercial AMX, and the bipolar membrane is commercial HP-BP-02.

[0078] The membranes obtained in Examples 1-3 and Comparative Examples 1-3 are used to replace the cation exchange membrane in the above electrodialysis membrane assembly to make an electrodialysis membrane assembly, and are used for the treatment of concentrated brine.

[0079] Among them, the structures of the electrodialysis membrane modules of Examples 1-3 and Comparative Examples 2-3 are as follows: -│Anion exchange membrane│Bipolar membrane│Modified cation exchange membrane│Anion exchange membrane│Bipolar membrane│Modified cation exchange membrane│Anion exchange membrane│+.

[0080] While the structure of the electrodialysis membrane module of Comparative Example 1 is: -│Anion exchange membrane│Bipolar membrane│Cation exchange membrane│Anion exchange membrane│Bipolar membrane│Cation exchange membrane│Anion exchange membrane│+.

[0081] The specific test process for the electrodialysis device to treat concentrated brine is as follows: First, soak the membrane to be tested in a 0.1 mol / L -1 NaCl / MgCl2 solution for 24 h to reach equilibrium, then install the membrane to be tested in the electrodialysis device. Add 100 ml of 0.1 mol / L NaCl / MgCl2 solution to the concentrated brine chamber of the electrodialysis device through a pipeline, add 100 ml of 0.3 mol / L NaCl solution to the electrode chamber, add HCl to the acid chamber, and add NaOH to the alkali chamber. The initial acid concentration in the acid chamber and the initial alkali concentration in the alkali chamber are both 0.01 mol / L. All solutions in the experiment are circulated by a peristaltic pump. The current density of the electrodialysis device is 25-30 mA / cm -2 . After running for 1 h, samples are taken from the acid chamber, alkali chamber, and concentrated brine chamber, and the ion concentrations in each chamber are measured by inductively coupled plasma spectroscopy. The results are shown in Table 1.

[0082] Table 1

[0083]

[0084]

[0085] As can be seen from Table 1, the concentration of HCl in the acid chamber of Examples 1-3 is above 0.987 mol / L, and the concentration of NaOH in the alkali chamber is above 0.979 mol / L, both of which are better than those of Comparative Examples 1-3; the ion concentrations of MgCl2 and NaCl in the concentrated brine chamber of Examples 1-3 are lower than those in the concentrated brine chamber of Comparative Examples 1-3. This shows that only the electrodialysis device composed of the membranes obtained by the modification method of Examples 1-3 of the present invention can achieve the efficient separation of Mg 2+ and Na + in concentrated brine, and the membranes obtained in Comparative Examples 1-3 are inferior to those of Examples 1-3.

[0086] In summary, the modified cation exchange membrane obtained by the treatment method of the electrodialysis membrane of the present invention has high performance and high selectivity, can efficiently separate monovalent salts and divalent salts, and when used for treating concentrated brine, can efficiently separate monovalent cations and divalent cations, realize the separation of monovalent salts and divalent salts, and thus achieve zero discharge of concentrated brine.

[0087] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims

1. A crown ether derivative for an electrodialysis membrane, characterized in that, The structure of the crown ether derivative is shown in formula (I), 2. The preparation method of the crown ether derivative according to claim 1, characterized in that, including: Dissolve droxidopa, organic ester compound, and catalyst in a solvent, and obtain the crown ether derivative by heating.

3. The preparation method of the crown ether derivative according to claim 2, characterized in that Under an inert gas atmosphere, add droxidopa and sodium hydroxide catalyst to the solvent dimethyl sulfoxide, reflux at 100 - 120 °C for 30 - 40 min to obtain a first reaction solution; Add the organic ester compound to the solvent dimethyl sulfoxide and stir evenly to obtain a second reaction solution; Drop half of the second reaction solution into the first reaction solution at a rate of 1 - 5 d / min, reflux at 50 - 70 °C for 1 - 2 h, then continue to drop the remaining amount of the second reaction solution at a rate of 1 - 5 d / min, and continue to reflux at 50 - 70 °C for 12 - 16 h to obtain a crude product; Then add concentrated hydrochloric acid to the crude product, remove dimethyl sulfoxide by steam distillation, perform solid-liquid separation, wash the filter cake with water, wash with acetone, and dry to obtain crystals, which are the crown ether derivative.

4. The preparation method of the crown ether derivative according to claim 3, characterized in that, The inert gas atmosphere is N2 or helium; and / or The molar ratio of droxidopa to the organic ester compound is (1 - 2):1; and / or The organic ester compound is diethylene glycol bis(p-toluenesulfonate), and droxidopa is (2S,3R)-2-amino-3-(3,4-dihydroxyphenyl)-3-hydroxypropanoic acid; and / or The droxidopa in the first reaction solution accounts for 0.1 - 0.2 mol / 100 ml of the volume of the solvent dimethyl sulfoxide; and / or The sodium hydroxide in the first reaction solution accounts for 0.2 - 0.3 mol / 100 ml of the volume of the solvent dimethyl sulfoxide; and / or The organic ester compound in the second reaction solution accounts for 0.05 - 0.15 mol / 30 ml of the volume of the solvent dimethyl sulfoxide.

5. A treatment method for an electrodialysis membrane, characterized in that, including the following steps: S1. Use the crown ether derivative described in claim 1 or the crown ether derivative obtained by the preparation method described in any one of claims 2 - 4 for the treatment method of the electrodialysis membrane. The specific method is: add the crown ether derivative, organosilicon solution, and two-dimensional MXene material with a mass ratio of (2 - 3):(1 - 1.5):(0.2 - 0.5) to a good solvent, stir evenly to obtain a modified solution; S2. After mixing the modified solution and the film-forming agent evenly, coat it on the surface of the cation exchange membrane, and perform heat treatment in an inert atmosphere, and cool to room temperature to obtain a modified cation exchange membrane.

6. The treatment method of the electroosmotic membrane according to claim 5, characterized in that, In step S1, The two-dimensional MXene material is a monolayer Ti3C2Tx dispersion with a concentration of 5 mg / ml - 10 mg / ml; and / or The organosilicon solution is tetramethylsilane or epoxy group-modified silicone oil; and / or The good solvent includes any one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; and / or The crown ether derivative, organosilicon solution, and two-dimensional MXene material account for 5% - 10% of the mass of the good solvent.

7. The treatment method of the electrodialysis membrane according to claim 1, characterized in that In step S2, the modified solution accounts for 10% - 25% of the mass of the film-forming agent; and / or The film-forming agent includes: 1,3,5-benzenetricarbonyl chloride or polyvinylpyrrolidone; and / or The heat treatment under an inert atmosphere is as follows: under the atmosphere of N2 or helium, heat treatment is carried out at 80 - 150 °C for 15 - 36 h with heat preservation; The cation exchange membrane includes: a standard membrane or a blended cross-linked proton exchange membrane.

8. The treatment method of the electrodialysis membrane according to any one of claims 5-7, characterized in that, Including: The obtained modified cation exchange membrane of S2 is subjected to low-temperature plasma treatment with a mixed gas to introduce hydrophilic groups; Among them, the mixed gas is 50% O2 and 50% NH by volume ratio; the power of the plasma is 80 - 100 W, under 0.1 - 10 Pa, the plasma treatment is carried out for 90 - 120 s; the low temperature is 10 - 15 °C; and / or The hydrophilic groups are -OH, -COOH, -NH2.

9. An electrodialysis membrane, characterized in that, It is prepared by the treatment method of the electrodialysis membrane according to any one of claims 5 - 8.

10. An electrodialysis device, characterized in that, Including: An anode, a cathode, an electrodialysis membrane assembly, a sensor and a current controller; wherein, The electrodialysis membrane assembly is made by using the treatment method of the electrodialysis membrane according to any one of claims 5 - 8 or the modified cationic exchange membrane obtained in claim 9; The anode is a titanium electrode, and a rare metal layer is arranged on the surface of the titanium electrode, and the rare metal is at least one of cerium, platinum, dysprosium, ruthenium; The cathode is a stainless steel electrode; The structure of the electrodialysis membrane assembly is made by arranging in the structure of -│anion exchange membrane│bipolar membrane│modified cation exchange membrane│anion exchange membrane│bipolar membrane│modified cation exchange membrane│anion exchange membrane│+.

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