Cellulose-based anion exchange membrane and preparation method thereof

Abstract

The invention discloses a cellulose-based anion exchange membrane and a preparation method thereof, and the preparation method comprises the following steps: (1) freezing a mixture containing alkali, urea, cellulose and water to obtain an alkali-urea solution of cellulose; (2) mixing the alkali-urea solution of cellulose with a cross-linking agent, and stirring to obtain a cellulose solution mixed with the cross-linking agent; (3) adding a poly (diallyldimethylammonium chloride) aqueous solution into the cellulose solution mixed with the cross-linking agent, and uniformly mixing; then, casting and dehydrating the mixed solution to obtain a cross-linked hydrogel film; thirdly, inorganic ions in the cross-linked hydrogel membrane are removed, drying is conducted, and the halogen type anion exchange membrane is obtained; and finally, carrying out ion exchange on the halogen type anion exchange membrane and an alkali solution to obtain the anion exchange membrane. The anion exchange membrane prepared by the method has the characteristics of low swelling rate, high ionic conductivity, high mechanical property and high alkali-resistant stability.

Description

Technical Field

[0001] The present invention belongs to the technical field of anion exchange membranes, and more specifically, relates to a cellulose-based anion exchange membrane and a preparation method thereof. Background Art

[0002] Anion exchange membrane (AEM) is a type of polymer electrolyte composed of cations fixed on the polymer backbone and free-moving anions. It plays the role of conducting ions and isolating positive and negative electrodes in electrochemical devices, and it is required to have high ionic conductivity, high mechanical properties and high alkali resistance stability.

[0003] The main chain of AEM is generally selected from engineering plastics, such as polysulfone, polyarylsulfone, polyethersulfone, polyetheretherketone, polyvinyl alcohol, polyolefin, etc.; or it is synthesized from monomers through condensation polymerization, free radical polymerization and other methods. The advantage of engineering plastics is high strength, but studies have shown that the short-range grafting of cations to the ether-containing main chain will make the polymer main chain susceptible to attack by hydroxide and then chain degradation. The synthesis of ether-free main chains from monomers is the current mainstream strategy, such as the preparation of polyaryl piperidine by superacid polymerization, and then the reaction of iodomethane with tertiary amine to obtain cationic polyaryl piperidine. Although the anion exchange membrane prepared from this type of ionic polymer has good comprehensive properties, the synthesis process requires the consumption of a large amount of organic acid and organic solvent. It is very important to prepare anion exchange membranes in a more environmentally friendly way.

[0004] In addition, since high ion content will cause excessive water absorption and swelling of AEM, which will lead to a decrease in the mechanical properties of the wet film, in order to make AEM have both high ionic conductivity and high mechanical properties, it is usually necessary to introduce additional strategies to limit swelling, such as introducing hydrophobic fluorinated side chains on the polymer main chain, covalent crosslinking, organic-inorganic material blending, and reinforcing the substrate. However, these strategies to limit swelling usually lead to a decrease in ion concentration and sacrifice some ion conductivity. For example, covalent crosslinking and the introduction of hydrophobic side chains will occupy some functional sites, resulting in a decrease in the reaction sites available for cationic grafting; organic-inorganic material blending and reinforcing the substrate will introduce additional non-ionic components, which will lead to a decrease in the ion exchange capacity of AEM.

[0005] In summary, the existing problems are: the reported AEM preparation methods are not green and environmentally friendly, and the methods for limiting the swelling of AEM usually lead to a decrease in ionic conductivity. Therefore, it is necessary to develop a green and environmentally friendly anion exchange membrane and a preparation method thereof that effectively limits the swelling rate. Summary of the invention

[0006] The purpose of the present invention is to provide a cellulose-based anion exchange membrane and a preparation method thereof. The anion exchange membrane prepared by the method of the present invention has the characteristics of low swelling rate and high ion conductivity, high mechanical properties, and high alkali resistance and stability. In addition, the method of the present invention synthesizes chemically cross-linked cellulose as a polymer network in an organic solvent-free system to bind polydiallyldimethylammonium chloride ion polymers, so the present invention provides a green and environmentally friendly path to prepare anion exchange membranes.

[0007] In order to achieve the above object, one aspect of the present invention provides a method for preparing a cellulose-based anion exchange membrane, the preparation method comprising:

[0008] (1) freezing a mixture containing alkali, urea, cellulose and water to obtain an alkali-urea solution of cellulose;

[0009] (2) mixing the cellulose alkali-urea solution and the cross-linking agent and stirring to obtain a cellulose solution mixed with the cross-linking agent;

[0010] (3) Adding a polydiallyldimethylammonium chloride aqueous solution to the cellulose solution mixed with a cross-linking agent and mixing them evenly; then, casting and dehydrating the mixed solution to obtain a cross-linked hydrogel membrane; then, removing inorganic ions from the cross-linked hydrogel membrane and drying it to obtain a halogen-type anion exchange membrane; finally, exchanging ions between the halogen-type anion exchange membrane and an alkaline solution to obtain the anion exchange membrane.

[0011] In the present invention, in step (1), the mixture containing alkali, urea, cellulose and water is preferably prepared by a method comprising the following steps: dissolving alkali and urea in water to obtain an alkali-urea solution; then, uniformly mixing cellulose and the alkali-urea solution to obtain the mixture containing alkali, urea, cellulose and water.

[0012] In the present invention, since the anion exchange membrane prepared by the present invention has a high ion exchange capacity, and cellulose is a polysaccharide containing a large number of active hydroxyl groups, the prepared anion exchange membrane has a high water content, and the hydroxyl groups assist the hydroxide ion conduction, so the AEM prepared by the present invention has a high ion conductivity. Since the ion component is composed of diallyldimethylammonium chloride structural units, it does not contain other polar groups except cations, and the cross-linked cellulose firmly binds the ionic polymer, so the AEM prepared by the present invention has high alkali resistance stability. Since the cross-linked cellulose has high mechanical properties, the AEM prepared by the present invention has a large tensile strength.

[0013] According to the present invention, preferably, in step (1), the alkali comprises sodium hydroxide (NaOH) and / or potassium hydroxide (KOH).

[0014] According to the present invention, preferably, in step (1), the mass ratio of the alkali, urea and cellulose is (0.7-1.2): (1.2-2): 0.3;

[0015] The solid-liquid ratio of the cellulose to water is 0.3:(7.8-10) g / mL.

[0016] According to the present invention, preferably, in step (1), the freezing temperature is -20°C to -60°C, and the freezing time is 4 to 12 hours.

[0017] In the present invention, preferably, in step (1), the freezing temperature is independently selected from any value of -20°C, -30°C, -40°C, -50°C, -60°C, or a range between any two of the above. The freezing time is independently selected from any value of 4h, 6h, 8h, 10h, 12h, or a range between any two of the above.

[0018] According to the present invention, preferably, in step (2), the cross-linking agent is epichlorohydrin;

[0019] The solid-liquid ratio of the cellulose to the cross-linking agent is 0.3:(1-2) g / mL.

[0020] According to the present invention, preferably, in step (2), the stirring temperature is 5° C. to 15° C., and the stirring time is 2 to 4 hours.

[0021] In the present invention, preferably, in step (2), the stirring temperature is independently selected from any value of 5°C, 10°C, 15°C, or a range between any two of the above. The stirring time is independently selected from any value of 2h, 3h, 4h, or a range between any two of the above.

[0022] According to the present invention, preferably, in step (3), the mass fraction of the polydiallyldimethylammonium chloride aqueous solution is 20% to 40%;

[0023] The mass dosage ratio of the cellulose to the polydiallyldimethylammonium chloride aqueous solution is 0.3:(0.3-2.5).

[0024] According to the present invention, preferably, in step (3), the temperature of mixing the cellulose solution mixed with the crosslinking agent and the polydiallyldimethylammonium chloride aqueous solution is 5° C. to 15° C., and the time is 4 to 6 hours;

[0025] The temperature of dehydration is 40° C. to 55° C., and the relative humidity of dehydration is 40% to 60%.

[0026] In the present invention, preferably, in step (3), the mixing temperature is independently selected from any value of 5°C, 10°C, 15°C, or a range between any two of the above. The mixing time is independently selected from any value of 4h, 5h, 6h, or a range between any two of the above.

[0027] In the present invention, preferably, in step (3), the dehydration temperature is independently selected from any value of 40°C, 50°C, 55°C, or a range between any two of the above. The dehydration relative humidity is independently selected from any value of 40%, 50%, 60%, or a range between any two of the above.

[0028] In the present invention, preferably, the casting is casting on a glass plate.

[0029] According to the present invention, preferably, in step (3), the drying temperature is 40°C to 55°C and the drying time is 4 to 6 hours;

[0030] The alkaline solution includes a NaOH aqueous solution and / or a KOH aqueous solution, and the concentration of the alkaline solution is 0.5-2.0 mol / L.

[0031] In the present invention, preferably, in step (3), the hydrogel is soaked in deionized water for 12 to 24 hours to remove inorganic ions, and fresh deionized water is preferably replaced 3 to 5 times during the soaking period.

[0032] In the present invention, preferably, in step (3), the drying temperature is independently selected from any value of 40°C, 45°C, 50°C, 55°C, or a range between any two of the above. The drying time is independently selected from any value of 4h, 5h, 6h, or a range between any two of the above.

[0033] In the present invention, the ion exchange between the halogen-type anion exchange membrane and the alkaline solution is performed by immersing the halogen-type anion exchange membrane in the alkaline solution. Preferably, the temperature of the alkaline solution is 30 to 80°C; for example, the temperature of the alkaline solution is independently selected from any value of 30°C, 40°C, 50°C, 60°C, 70°C, 80°C or a range between any two of the above. The soaking time is preferably 12-24h, for example, the soaking time is independently selected from any value of 12h, 14h, 16h, 18h, 20h, 22h, 24h or a range between any two of the above. It is preferred to replace the fresh alkaline solution 3-5 times during the soaking period.

[0034] Another aspect of the present invention provides a cellulose-based anion exchange membrane prepared by the above preparation method.

[0035] The technical solution of the present invention has the following beneficial effects:

[0036] (1) The anion exchange membrane prepared by the present invention has the characteristics of low planar swelling rate and high water content.

[0037] (2) The anion exchange membrane prepared by the present invention has the characteristics of high dimensional stability and high ionic conductivity.

[0038] (3) The anion exchange membrane prepared by the present invention has the characteristic of high tensile strength.

[0039] (4) The anion exchange membrane prepared by the present invention has the characteristics of high alkali resistance and stability.

[0040] (5) The method for preparing anion exchange membrane of the present invention is green and environmentally friendly, and does not involve any organic solvents and highly corrosive and toxic substances.

[0041] (6) The raw material cellulose for preparing the anion exchange membrane of the present invention is widely available and inexpensive.

[0042] Other features and advantages of the present invention will be described in detail in the following detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] The above and other objects, features and advantages of the present invention will become more apparent through a more detailed description of exemplary embodiments of the present invention in conjunction with the accompanying drawings, wherein like reference numerals generally represent like components throughout the exemplary embodiments of the present invention.

[0044] Figure 1 An optical photograph of a cellulose-based anion exchange membrane according to Example 3 of the present invention is shown.

[0045] Figure 2 The linear sweep voltammetry (LSV) curve of the cellulose-based anion exchange membrane according to Example 4 of the present invention at 50° C. is shown.

[0046] Figure 3 The Fourier transform infrared (FTIR) spectrum of the cellulose-based anion exchange membrane according to Example 5 of the present invention is shown; wherein Wavenumber represents the wave number. DETAILED DESCRIPTION

[0047] The preferred embodiments of the present invention will be described in more detail below. Although the preferred embodiments of the present invention are described below, it should be understood that the present invention can be implemented in various forms and should not be limited by the embodiments set forth herein. On the contrary, these embodiments are provided to make the present invention more thorough and complete, and to fully convey the scope of the present invention to those skilled in the art.

[0048] The present invention is further illustrated by the following examples.

[0049] In the following examples, the cellulose used was α-cellulose (particle size 25 μm) purchased from MacLean. The epichlorohydrin and polydiallyldimethylammonium chloride aqueous solution (mass fraction 20%, Mw 200,000-350,000) used were purchased from MacLean.

[0050] The corresponding performance test methods in the test data of the following embodiments and comparative examples are as follows:

[0051] (1) Ion exchange capacity:

[0052] The Mohr titration method was used to test the ion exchange capacity of AEM, and the calculation formula is as follows: (AgNO3) is the concentration of AgNO3 solution, v (AgNO3) is the volume of AgNO3 solution consumed, m dry(Cl) is the dry weight of the AEM.

[0053]

[0054] IEC is the ion exchange capacity.

[0055] (2) Dimensional stability:

[0056] First record the dry film size x dry(OH) , then the test anion is OH - The size of AEM after full swelling with water at different temperatures is recorded as x hyd(OH) , the formula for calculating dimensional stability is as follows:

[0057]

[0058] SD is the swelling rate, the rate of change of the plane dimension (length or width) is the plane swelling rate, and the rate of change of the thickness is the longitudinal swelling rate.

[0059] (3) Water content:

[0060] Take the anion as OH - AEM, wipe the water on its surface with filter paper, and weigh its mass W in the saturated water state hyd The membrane was then placed in a vacuum drying oven at 65°C and fully dried for 12 hours until the mass of the membrane no longer decreased, and then its mass W was measured. dry , the formula for calculating the moisture content is as follows:

[0061]

[0062] (4) Ionic conductivity: The present invention uses the AC impedance method to measure the ionic resistance of the anion exchange membrane. The measurement frequency range is 1 Hz-4 MHz, the potential amplitude is 5 mV, and the measured resistance Nyquist curve is fitted. The intersection of the curve and the real axis Z' is the ionic resistance value R of the anion exchange membrane.

[0063] The formula for calculating conductivity is as follows:

[0064]

[0065] σ is the ionic conductivity, l is the distance between the two electrodes, R is the ionic resistance of the sample being measured, and S is the cross-sectional area of ​​the membrane.

[0066] (5) Mechanical strength: The mechanical property test includes the tensile strength and elongation at break of the polymer to be tested. The operating rate of the instrument stretching is 5 mm / min.

[0067] (6) Alkali resistance stability: The stability test conditions of the embodiment are 80° C. and immersion in 1 mol / L KOH aqueous solution for 360 hours.

[0068] (7) Water electrolysis performance

[0069] The cathode uses a Pt / C catalyst, the anode uses a NiFe2O4 catalyst, the membrane electrode ionomer uses a QAPPT ion polymer prepared by the method of the literature Journal of Power Sources 390 (2018) 165-167, and the anion exchange membrane prepared in the embodiment is used as the electrolyte diaphragm in the water electrolyzer. The electrolyte solution in the electrolyzer is a 1 mol / L KOH aqueous solution. The LSV scanning speed is 10 mV / s, the scanning range is 1.2-2.0 V, and the test temperature is 50°C.

[0070] Example 1

[0071] (1) Dissolve 1.2 g of sodium hydroxide and 2 g of urea in 10 mL of deionized water to obtain an alkali-urea solution. Disperse 0.3 g of cellulose in the alkali-urea solution, mix well, and freeze in a -20°C ultra-low temperature refrigerator for 12 h to obtain an alkali-urea solution of cellulose;

[0072] (2) mixing all the cellulose alkali-urea solution prepared in step (1) with 1 mL of epichlorohydrin, and stirring at 15° C. for 2 hours to obtain a cellulose solution mixed with a crosslinking agent;

[0073] (3) Add 0.3 g of polydiallyldimethylammonium chloride aqueous solution to the entire cellulose solution mixed with a crosslinking agent prepared in step (2), mix thoroughly at 15°C for 4 hours, cast the mixed solution on a glass plate, dehydrate at 40°C and 40% relative humidity to obtain a crosslinked hydrogel membrane, soak the crosslinked hydrogel membrane in deionized water for 20 hours to remove inorganic ions in the crosslinked hydrogel membrane, and replace fresh deionized water 3 times during the soaking period. Then place the crosslinked hydrogel membrane on a heating platform at 50°C and bake for 5 hours to obtain a dry halogen-type anion exchange membrane. Soak the obtained halogen-type anion exchange membrane in a 1 mol / L potassium hydroxide aqueous solution at 80°C for 12 hours, replace fresh alkali solution 3 times during the period, and then rinse the residual floating alkali on the membrane surface with deionized water until the pH of the aqueous solution is 7 to obtain an anion exchange membrane with hydroxide as the anion.

[0074] The ion exchange capacity of the anion exchange membrane was measured to be 0.99 mmol g -1 ; The plane swelling rate at 80℃ is 5.5%, the longitudinal swelling rate at 80℃ is 50.2%, the water content at 80℃ is 103.6%, and the ionic conductivity at 80℃ is 61.8mS cm -1 The tensile strength of the dry film is 66.5MPa, and the elongation at break is 2.71%. After being immersed in 1mol / L KOH aqueous solution at 80℃ for 360h, the retention rate of ionic conductivity at 80℃ is 86.2%.

[0075] Example 2

[0076] (1) Dissolve 1.2 g of sodium hydroxide and 2 g of urea in 10 mL of deionized water to obtain an alkali-urea solution. Disperse 0.3 g of cellulose in the alkali-urea solution, mix well, and freeze in a -20°C ultra-low temperature refrigerator for 12 h to obtain an alkali-urea solution of cellulose;

[0077] (2) mixing all the cellulose alkali-urea solution prepared in step (1) with 1 mL of epichlorohydrin, and stirring at 15° C. for 2 hours to obtain a cellulose solution mixed with a crosslinking agent;

[0078] (3) Add 0.6g of polydiallyldimethylammonium chloride aqueous solution to the whole cellulose solution mixed with the crosslinking agent prepared in step (2), mix thoroughly at 15°C for 4h, cast the mixed solution on a glass plate, dehydrate at 40°C and 40% relative humidity to obtain a crosslinked hydrogel membrane, soak the crosslinked hydrogel membrane in deionized water for 20h to remove inorganic ions in the crosslinked hydrogel membrane, and replace fresh deionized water 3 times during the soaking period. Then place the crosslinked gel membrane on a heating platform at 50°C and bake for 5h to obtain a dry halogen-type anion exchange membrane. Soak the obtained halogen-type anion exchange membrane in a 1mol / L potassium hydroxide aqueous solution at 80°C for 12h, replace fresh alkali solution 3 times during the period, and then rinse the residual floating alkali on the membrane surface with deionized water until the pH of the aqueous solution is 7 to obtain an anion exchange membrane with hydroxide as the anion.

[0079] The ion exchange capacity of the anion exchange membrane was measured to be 1.62 mmol g -1 ; The plane swelling rate at 80℃ is 9.0%, the longitudinal swelling rate at 80℃ is 75.5%, the water content at 80℃ is 277.1%, and the ionic conductivity at 80℃ is 101.1mS cm -1 The tensile strength of the dry film is 59.9 MPa, and the elongation at break is 3.22%. After being immersed in 1 mol / L KOH aqueous solution at 80°C for 360 hours, the retention rate of ionic conductivity at 80°C is 85.3%.

[0080] Example 3

[0081] (1) Dissolve 0.7 g of sodium hydroxide and 1.2 g of urea in 7.8 mL of deionized water to obtain an alkali-urea solution. Disperse 0.3 g of cellulose in the alkali-urea solution, mix well, and freeze in a -40°C ultra-low temperature refrigerator for 8 h to obtain an alkali-urea solution of cellulose;

[0082] (2) mixing all the cellulose alkali-urea solution prepared in step (1) with 1.5 mL of epichlorohydrin, and stirring at 10° C. for 4 hours to obtain a cellulose solution mixed with a crosslinking agent;

[0083] (3) Add 0.9g of polydiallyldimethylammonium chloride aqueous solution to the whole cellulose solution mixed with the crosslinking agent prepared in step (2), mix thoroughly at 5°C for 6h, cast the mixed solution on a glass plate, dehydrate at 55°C and 60% relative humidity to obtain a crosslinked hydrogel membrane, soak the crosslinked hydrogel membrane in deionized water for 20h to remove inorganic ions in the crosslinked hydrogel membrane, and replace fresh deionized water 3 times during the soaking period. Then place the crosslinked hydrogel membrane on a heating platform at 50°C and bake for 5h to obtain a dry halogen-type anion exchange membrane. Soak the obtained halogen-type anion exchange membrane in a 1mol / L potassium hydroxide aqueous solution at 80°C for 12h, replace fresh alkali solution 3 times during the period, and then rinse the residual floating alkali on the membrane surface with deionized water until the pH of the aqueous solution is 7 to obtain an anion exchange membrane with hydroxide as the anion.

[0084] The ion exchange capacity of the anion exchange membrane was measured to be 2.01 mmol g -1 ; The plane swelling rate at 80℃ is 10.6%, the longitudinal swelling rate at 80℃ is 84.4%, the water content at 80℃ is 304.9%, and the ionic conductivity at 80℃ is 121.1mS cm -1 The tensile strength of the dry film is 55.0MPa, and the elongation at break is 4.93%. After being immersed in 1mol / L KOH aqueous solution at 80℃ for 360h, the retention rate of ionic conductivity at 80℃ is 83.0%.

[0085] The optical morphology of the anion exchange membrane prepared in this example is as follows Figure 1 As shown. Figure 1 The results show that the anion exchange membrane prepared in this example is smooth, uniform and transparent, indicating that the ionic components and the cross-linked cellulose have significant compatibility.

[0086] Example 4

[0087] (1) Dissolve 0.7 g of sodium hydroxide and 1.2 g of urea in 7.8 mL of deionized water to obtain an alkali-urea solution. Disperse 0.3 g of cellulose in the alkali-urea solution, mix well, and freeze in a -40°C ultra-low temperature refrigerator for 8 h to obtain an alkali-urea solution of cellulose;

[0088] (2) mixing all the cellulose alkali-urea solution prepared in step (1) with 1.5 mL of epichlorohydrin, and stirring at 10° C. for 4 hours to obtain a cellulose solution mixed with a crosslinking agent;

[0089] (3) Add 1.5 g of polydiallyldimethylammonium chloride aqueous solution to the entire cellulose solution mixed with the crosslinking agent prepared in step (2), mix thoroughly at 5°C for 6 h, cast the mixed solution on a glass plate, dehydrate at 55°C and 60% relative humidity to obtain a crosslinked hydrogel membrane, soak the crosslinked hydrogel membrane in deionized water for 20 h to remove inorganic ions in the crosslinked hydrogel membrane, and replace fresh deionized water 3 times during the soaking period. Then place the crosslinked hydrogel membrane on a heating platform at 55°C and bake for 5 h to obtain a dry halogen-type anion exchange membrane. Soak the obtained halogen-type anion exchange membrane in a 1 mol / L potassium hydroxide aqueous solution at 80°C for 12 h, replace fresh alkali solution 3 times during the period, and then rinse the residual floating alkali on the membrane surface with deionized water until the pH of the aqueous solution is 7 to obtain an anion exchange membrane with hydroxide as the anion.

[0090] The ion exchange capacity of the anion exchange membrane was measured to be 2.90 mmol g -1 ; The plane swelling rate at 80℃ is 15.3%, the longitudinal swelling rate at 80℃ is 95.6%, the water content at 80℃ is 427.4%, and the ionic conductivity at 80℃ is 143.7mS cm -1 The tensile strength of the dry film is 41.0 MPa, and the elongation at break is 5.36%. After being immersed in 1 mol / L KOH aqueous solution at 80°C for 360 hours, the retention rate of ionic conductivity at 80°C is 80.1%.

[0091] The water electrolysis performance test results of the anion exchange membrane prepared in this embodiment in a zero-gap electrolyzer are shown in the attached figure. Figure 2 As shown. Figure 2 It can be seen that the performance of water electrolysis in 1 mol / L KOH aqueous solution at 50°C is a current density of 0.50 A / cm 2 The corresponding voltage is 1.8V and the current density is 1.07A / cm 2 The corresponding voltage is 2.0V.

[0092] Example 5

[0093] (1) Dissolve 0.7 g of sodium hydroxide and 1.2 g of urea in 7.8 mL of deionized water to obtain an alkali-urea solution. Disperse 0.3 g of cellulose in the alkali-urea solution, mix well, and freeze in a -40°C ultra-low temperature refrigerator for 8 h to obtain an alkali-urea solution of cellulose;

[0094] (2) mixing all the cellulose alkali-urea solution prepared in step (1) with 2 mL of epichlorohydrin, and stirring at 5° C. for 4 hours to obtain a cellulose solution mixed with a crosslinking agent;

[0095] (3) Add 2.25g of polydiallyldimethylammonium chloride aqueous solution to the whole cellulose solution mixed with the crosslinking agent prepared in step (2), mix thoroughly at 5°C for 6h, cast the mixed solution on a glass plate, dehydrate at 55°C and 60% relative humidity to obtain a crosslinked hydrogel membrane, soak the crosslinked hydrogel membrane in deionized water for 20h to remove inorganic ions in the crosslinked hydrogel membrane, and replace fresh deionized water 3 times during the soaking period. Then place the crosslinked hydrogel membrane on a heating platform at 55°C and bake for 5h to obtain a dry halogen-type anion exchange membrane. Soak the obtained halogen-type anion exchange membrane in a 1mol / L potassium hydroxide aqueous solution at 80°C for 12h, replace fresh alkali solution 3 times during the period, and then rinse the residual floating alkali on the membrane surface with deionized water until the pH of the aqueous solution is 7 to obtain an anion exchange membrane with hydroxide as the anion.

[0096] The Fourier transform infrared spectroscopy results of the anion exchange membrane prepared in this example are as follows: Figure 3 As shown. Figure 3 The results show that the anion exchange membrane prepared in this embodiment has a -1 The peak observed at 3000-3700 cm -1 The strong broad peaks between 3425cm and 3425cm are mainly caused by the stretching vibration of bound water molecules during the measurement process. -1 is the stretching vibration peak of -OH in cellulose, 2924 cm -1 and 2880cm -1 It is the CH symmetric and asymmetric stretching vibration peak of methyl and methylene groups; 1060cm -1 Corresponding to CO stretching vibration, 1113cm -1 The absorption peak at is the COC stretching vibration. The infrared spectrum analysis shows that the prepared anion exchange membrane contains the COC stretching vibration peak. This indicates that under alkaline conditions, cellulose and epichlorohydrin undergo a cross-linking chemical reaction and bind polydiallyldimethylammonium chloride in the cellulose polymer network.

[0097] The ion exchange capacity of the anion exchange membrane was measured to be 3.20 mmol g -1 ; The plane swelling rate at 80℃ is 27.3%, the longitudinal swelling rate at 80℃ is 131.7%, the water content at 80℃ is 620.1%, and the ionic conductivity at 80℃ is 107.8mS cm -1 The tensile strength of the dry film is 36.7MPa, and the elongation at break is 14.2%. After being immersed in 1mol / L KOH aqueous solution at 80℃ for 360h, the retention rate of ionic conductivity at 80℃ is 76.1%.

[0098] Comparative Example

[0099] The authors of the literature (European Polymer Journal 221(2024)113543; https: / / doi.org / 10.1016 / j.eurpolymj.2024.113543) synthesized three different cross-linked anion exchange membranes by chloromethylation and cross-linking quaternization of polysulfone. The synthesis process involves organic reagents such as chloroform and N,N-dimethylacetamide. The three cross-linking agents are tris(1-methylpiperidine) (BMP), N,N,N',N'-tetramethyl-1,6-hexanediamine (TMHDA) and 1,4-diazobicyclo[2.2.2]octane (DABCO). Among them, the anion exchange membrane BMP-c-CMPSF cross-linked by BMP has the best ion conductivity. The optimal test example BMP-c-CMPSF was selected as the comparative example of the present invention.

[0100] The optimized comparative example BMP-c-CMPSF has an ion exchange capacity of 1.58 mmol / g.

[0101] The ionic conductivity of the optimized comparative example BMP-c-CMPSF at 80°C is 53.7 mS / cm.

[0102] The swelling ratio of the optimized comparative example BMP-c-CMPSF at 80° C. is 23%.

[0103] The optimized comparative example BMP-c-CMPSF has a water content of 50% at 80°C.

[0104] The optimized comparative example BMP-c-CMPSF has a tensile strength of 32.8 MPa and an elongation at break of 4.2%.

[0105] The optimized comparative example BMP-c-CMPSF has a water electrolysis performance of 0.38 A / cm in a 1 mol / L KOH aqueous solution at 50 °C. 2 The corresponding voltage is 1.8V and the current density is 0.81A / cm 2 The corresponding voltage is 2.0V.

[0106] Unfortunately, the authors did not clearly point out the degradation rate of the anion exchange membrane backbone and the degradation rate of ionic conductivity in the article.

[0107] Table 1 shows the test data summary of the anion exchange membranes prepared in the above Examples 1 to 5 and the optimized comparative example BMP-c-CMPSF, as follows:

[0108] The swelling ratio, water content, ion conductivity and water electrolysis performance test temperature of the comparative example and the exemplary embodiment are the same.

[0109] Table 1 Test results comparison table

[0110]

[0111]

[0112] ——Indicates not measured.

[0113] It can be seen from the performance data in Table 1 and the anion exchange membrane preparation method of the embodiment that: compared with the comparative example, the cellulose-based anion exchange membrane prepared in Examples 1 to 5 of the present invention has the characteristics of high ion exchange capacity, high dimensional stability, high water content, high ion conductivity, high mechanical properties, good alkali resistance and stability, high water electrolysis performance, and a green and mild preparation process.

[0114] A cellulose-based anion exchange membrane prepared in Examples 1 to 5 of the present invention comprises cross-linked cellulose as a polymer network and polydiallyldimethylammonium chloride as an ion component. Since alkali-urea is used to dissolve cellulose at low temperature, the preparation process does not involve any organic solvent, and the preparation method is green and gentle. Since cellulose is not grafted with ions, and the ion components are composed of highly stable five-membered heterocyclic cations, the prepared anion exchange membrane has the characteristics of high alkali resistance and stability. Since the cross-linked fibers have anisotropic swelling behavior, the low planar swelling rate can effectively limit the swelling of the ion components, and the high longitudinal swelling rate ensures that the anion exchange membrane has a high water content. Since cross-linked cellulose is used as a polymer skeleton, the anion exchange membrane prepared by the present invention has the characteristics of high tensile strength. Since the prepared anion exchange membrane has a high ion exchange capacity and a high water content, the prepared anion exchange membrane has a high ion conductivity, so the embodiment shows better water electrolysis performance.

[0115] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and changes will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments.

Claims

1. A method for preparing a cellulose-based anion exchange membrane, characterized in that: The preparation method comprises: (1) freezing a mixture containing alkali, urea, cellulose and water to obtain an alkali-urea solution of cellulose; (2) mixing the cellulose alkali-urea solution and the cross-linking agent and stirring to obtain a cellulose solution mixed with the cross-linking agent; (3) Adding a polydiallyldimethylammonium chloride aqueous solution to the cellulose solution mixed with a cross-linking agent and mixing them evenly; then, casting and dehydrating the mixed solution to obtain a cross-linked hydrogel membrane; then, removing inorganic ions from the cross-linked hydrogel membrane and drying it to obtain a halogen-type anion exchange membrane; finally, exchanging ions between the halogen-type anion exchange membrane and an alkaline solution to obtain the anion exchange membrane.

2. The preparation method according to claim 1, wherein In step (1), the alkali includes sodium hydroxide and / or potassium hydroxide.

3. The preparation method according to claim 1, wherein In step (1), the mass ratio of the alkali, urea and cellulose is (0.7-1.2): (1.2-2): 0.3; The solid-liquid ratio of the cellulose to water is 0.3:(7.8-10) g / mL.

4. The preparation method according to claim 1, wherein In step (1), the freezing temperature is -20°C to -60°C, and the freezing time is 4 to 12 hours.

5. The preparation method according to claim 1, wherein In step (2), the cross-linking agent is epichlorohydrin; The solid-liquid ratio of the cellulose to the cross-linking agent is 0.3:(1-2) g / mL.

6. The preparation method according to claim 1, wherein In step (2), the stirring temperature is 5°C to 15°C, and the stirring time is 2 to 4 hours.

7. The preparation method according to claim 1, wherein In step (3), the mass fraction of the polydiallyldimethylammonium chloride aqueous solution is 20% to 40%; The mass dosage ratio of the cellulose to the polydiallyldimethylammonium chloride aqueous solution is 0.3:(0.3-2.5).

8. The preparation method according to claim 1, wherein In step (3), the cellulose solution mixed with the crosslinking agent and the polydiallyldimethylammonium chloride aqueous solution are mixed at a temperature of 5° C. to 15° C. for a time of 4 to 6 hours; The temperature of dehydration is 40° C. to 55° C., and the relative humidity of dehydration is 40% to 60%.

9. The preparation method according to claim 1, wherein In step (3), the drying temperature is 40°C to 55°C and the drying time is 4 to 6 hours; The alkaline solution includes a NaOH aqueous solution and / or a KOH aqueous solution, and the concentration of the alkaline solution is 0.5-2.0 mol / L.

10. A cellulose-based anion exchange membrane prepared by the preparation method according to any one of claims 1 to 9.

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