Water-absorbent resin as well as preparation method and application thereof

Abstract

The invention provides water-absorbent resin and a preparation method and application thereof.The preparation method of the water-absorbent resin comprises the steps that acrylic acid and modified polyimide serve as raw materials, the acrylic acid and the modified polyimide react to obtain hydrogel, and the hydrogel is granulated and dried to obtain the water-absorbent resin, the modified polyimide is polyimide with hydroxyl. Acrylic acid and modified polyimide react to form a unique cross-linked network structure, and the structure not only endows the material with the characteristics of being hydrophobic inside and hydrophilic outside, but also remarkably improves the mechanical strength, chemical stability and rapid regeneration capacity of the material. Benefited from the special structural design, the prepared water-absorbent resin shows excellent high gel strength and water absorption capacity, and particularly shows excellent water absorption efficiency and stability in dehydration treatment of liquid lithium bis (fluorosulfonyl) imide. The invention provides a new thought for the development of the high-performance water-absorbent resin, and has a wide application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of functional polymer chemical engineering, and particularly relates to a water-absorbing resin, a preparation method thereof, and an application thereof. Background Art

[0002] Lithium bis(fluorosulfonyl)imide (LiFSI) belongs to a new type of lithium salt with excellent performance. Compared with lithium hexafluorophosphate (LiPF 6 ) commonly used in current lithium batteries, it has better electrochemical properties, hydrolysis resistance, thermal stability, and conductivity. Currently, it is mainly used as an additive in electrolytes and can also be used alone as a solute in electrolyte solutions. Due to the disadvantages of traditional lithium bis(fluorosulfonyl)imide synthesis processes, such as many side reactions, low yield, high energy consumption, and high cost, and the difficulty in achieving battery-grade purity for the synthesized lithium bis(fluorosulfonyl)imide, it is not conducive to the large-scale commercial production of lithium bis(fluorosulfonyl)imide. Liquid lithium bis(fluorosulfonyl)imide is composed of lithium bis(fluorosulfonyl)imide and an organic solvent. Its production and preparation not only simplify the cumbersome preparation process of solid lithium bis(fluorosulfonyl)imide, thereby reducing production costs, but also produce products with good quality. In addition, it saves the process of preparing the electrolyte. Therefore, battery manufacturers prefer to use liquid lithium bis(fluorosulfonyl)imide. However, lithium bis(fluorosulfonyl)imide is prone to decomposition under heating or high-temperature conditions in a water-containing environment. Therefore, lithium bis(fluorosulfonyl)imide needs to be dehydrated. Traditional methods for dehydrating lithium bis(fluorosulfonyl)imide include: (1) Low-temperature freezing dehydration: Cooling the solution of lithium bis(fluorosulfonyl)imide below the freezing point of water to freeze the water into ice, and then separating the ice crystals from the solution by filtration or centrifugation, etc., to remove moisture. For example, after passing the water-containing lithium bis(fluorosulfonyl)imide and an organic solvent into a stirring kettle and stirring to dissolve, it enters a condensation filter. Under the action of -20°C to -10°C cold brine, the water cools and freezes into ice, and after passing through a sintered filter layer, the ice crystals are precipitated. (2) Using bis(trichloromethyl) carbonate for dehydration: Under low-temperature conditions of 2°C to 20°C, adding a corresponding poor solvent, such as dichloroethane, dichloromethane, n-hexane, etc., to the water-containing lithium bis(fluorosulfonyl)imide, stirring, and then adding bis(trichloromethyl) carbonate. Bis(trichloromethyl) carbonate reacts with water to only generate HCl and CO 2 , avoiding the introduction of other impurity ions. After the reaction, the product is further purified by filtration and washing, dissolution and crystallization, washing and drying, etc. However, traditional dehydration methods have high costs and poor effects. Therefore, there is an urgent need for an efficient and low-cost method for dehydration.

[0003] In the prior art, adsorption materials prepared from raw materials such as acrylic acid are usually applied to sewage treatment. Utilizing the rich sulfonic groups, carboxyl groups, and amino groups, for Cu 2+Heavy metal ions such as have excellent complexation and adsorption properties, achieving excellent adsorption effects. However, in the case of lithium bis(fluorosulfonyl)imide in liquid, only water removal is required for lithium bis(fluorosulfonyl)imide in liquid, and there is no need to adsorb heavy metal ions. Therefore, those skilled in the art have no motivation to use an adsorption material prepared from raw materials such as acrylic acid to remove the water in lithium bis(fluorosulfonyl)imide in liquid.

[0004] In addition, usually, after the water-absorbing resin absorbs water, its surface becomes wet and it cannot be quickly dried and reused.

[0005] Therefore, the existing technology needs to be further developed. Summary of the Invention

[0006] In view of the various deficiencies of the existing technology, to solve the above problems, a water-absorbing resin, its preparation method and application are now proposed, and the following technical solutions are provided: A preparation method of a water-absorbing resin, the preparation method includes: using acrylic acid and modified polyimide as raw materials, reacting acrylic acid and modified polyimide to obtain a hydrogel, and granulating and drying the hydrogel to obtain the water-absorbing resin, wherein the modified polyimide is a polyimide with hydroxyl groups.

[0007] Further, the mass ratio of the modified polyimide to acrylic acid is (10 - 30):(70 - 90).

[0008] Further, the modified polyimide is an aromatic polyimide.

[0009] Further, the molecular weight of the modified polyimide is 2 × 10 5 g / mol −1 ~ 3 × 10 5 g / mol −1 , and the structural formula is as follows: .

[0010] Further, the modified polyimide is prepared according to the following steps: Dissolve 3, 3'-dihydroxy diphenylamine and biphenyl-3, 3', 4, 4'-tetracarboxylic dianhydride in N-methylpyrrolidone to obtain a mixed solution, stir the mixed solution, add triethylamine, pyridine and toluene, and then heat at 160 - 200 °C for 2 - 8 h. After cooling, pour the mixed solution into absolute ethanol, and carry out centrifugal washing and drying in a vacuum oven.

[0011] Further, the reaction temperature for the reaction of acrylic acid and modified polyimide is 50 - 80 °C, and the reaction time is 2 - 6 h.

[0012] Further, before the reaction of acrylic acid and modified polyimide, the modified polyimide is dissolved in acetone to form a mixed solution A; acrylic acid is added to water to prepare a 40% solution B. The mixed solution A is added to solution B, and then an initiator and a crosslinking agent are added, and the reaction is carried out under vacuum conditions.

[0013] Further, the crosslinking agent is one or more of N, N-methylenebisacrylamide, glutaraldehyde, vinyltriethoxysilane, and diisocyanate; the initiator is one or more of potassium persulfate, ammonium persulfate, and hydrogen peroxide.

[0014] In addition, the present invention also provides a water-absorbing resin prepared by the above-mentioned preparation method of the water-absorbing resin.

[0015] The present invention also provides an application of the water-absorbing resin, and the application of the water-absorbing resin in removing water from liquid lithium bis(fluorosulfonyl)imide.

[0016] Beneficial effects: 1. The present invention relates to a novel water-absorbing resin, which forms a unique crosslinked network structure through the reaction of acrylic acid and modified polyimide. This structure is hydrophobic inside and hydrophilic outside, endowing the water-absorbing resin with excellent water absorption performance, stability, and rapid drying and reusability. In the treatment of removing water from liquid lithium bis(fluorosulfonyl)imide, this resin exhibits excellent water absorption efficiency.

[0017] 2. The present invention precisely controls the dosage ratio of modified polyimide and acrylic acid to achieve the balance between hydrophobic and hydrophilic parts, so that the water-absorbing resin reaches the best balance among water absorption performance, drying and reusability, and mechanical properties.

[0018] 3. The present invention prepares the water-absorbing resin by a two-step method of polymerization and esterification reaction. The synthesis process is simple and efficient, with low requirements for experimental conditions and technology. No catalysts such as copper chloride or cuprous chloride need to be added during the reaction process, and no post-treatment of the catalyst is required. Description of the drawings

[0019] Figure 1 is a schematic diagram of the reaction process of acrylic acid and modified polyimide of the present invention.

[0020] Figure 2 is a schematic diagram of the preparation process of modified polyimide. Specific embodiments

[0021] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the following combines the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Based on the embodiments in this application, other similar embodiments obtained by those of ordinary skill in the art without creative efforts shall all fall within the scope of protection of this application.

[0022] According to an embodiment of the present invention, a water-absorbing resin, a preparation method thereof and an application are provided. The preparation method includes: using acrylic acid and modified polyimide as raw materials, reacting acrylic acid and modified polyimide to obtain a hydrogel, granulating and drying the hydrogel to obtain the water-absorbing resin, and the modified polyimide is a polyimide with hydroxyl groups. The hydroxyl functional groups in the modified polyimide undergo an esterification reaction with the carboxyl groups in the acrylic acid monomers. At the same time, these acrylic acid monomers further polymerize along the modified polyimide chain through a free radical polymerization mechanism, thereby forming a polymer network with a hydrophobic interior and a hydrophilic exterior. This unique cross-linking strategy significantly improves the water absorption performance, stability and rapid drying and reuse ability of the material. The prepared water-absorbing resin thus exhibits excellent stability and water absorption. Especially in the dehydration treatment of liquid lithium bis(fluorosulfonyl)imide, the resin shows extraordinary water absorption efficiency.

[0023] The structural formula of the modified polyimide is as follows: The reaction process of acrylic acid and modified polyimide is as Figure 1 shown.

[0024] The mass ratio of the modified polyimide to acrylic acid is (10 - 30):(70 - 90). This application explores the dosage ratio of the two raw materials of modified polyimide and acrylic acid, realizes the balance between the hydrophobic and hydrophilic parts, so that the water-absorbing resin reaches the best balance among water absorption performance, drying and regeneration ability and mechanical properties.

[0025] Specifically, in this three-dimensional network of polyimide and polyacrylic acid, the hydrophobic group ester group is inside, and the water-absorbing carboxyl group is outside, forming a material with a hydrophobic interior and a hydrophilic exterior. The hydrophilic outer layer can quickly absorb water, and the hydrophobic inner layer prevents water penetration, ensuring that the material can still remain dry after absorbing water. The hydrophobic inner layer can avoid swelling or deformation caused by water and maintain the structural integrity of the material; due to the internal hydrophobicity, water only stays on the surface, the evaporation speed is accelerated, and the material can be quickly dried and reused.

[0026] Polyimide can be functionalized by grafting various groups. In this application, based on chemical stability, reactivity and experimental verification, polyimide with hydroxyl groups is finally selected. The hydroxyl group can undergo an esterification reaction with the carboxyl group to form an ester group, and under the experimental conditions of this application, the hydroxyl group will not have a significant impact on the quality of lithium bis(fluorosulfonyl)imide.

[0027] Before the reaction of acrylic acid and modified polyimide, the modified polyimide is dissolved in acetone to form a mixed solution A; acrylic acid is added to water to prepare a 40% solution B. After adding the mixed solution A to solution B, an initiator and a cross-linking agent are added, and the reaction is carried out under vacuum conditions.

[0028] The dosage of the crosslinking agent is 1%-5% of acrylic acid, and the dosage of the initiator is 0.2%-1% of acrylic acid.

[0029] Specifically, the preparation process of the modified polyimide is as Figure 2 shown.

[0030] Dissolve 3,3'-dihydroxydiphenylamine and biphenyl-3,3',4,4'-tetracarboxylic dianhydride in N-methylpyrrolidone to obtain a mixed solution. After stirring the mixed solution, add triethylamine, pyridine and toluene, and then heat at 160-200 °C for 2-8 h. After cooling, pour the mixed solution into absolute ethanol, wash by centrifugation and dry in a vacuum oven to obtain the modified polyimide denoted as polyimide-hydroxy (PI-OH).

[0031] Example 1 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine and 12 mL of toluene, and then heat at 180 °C for 5 h. After cooling, pour the mixture into absolute ethanol, wash by centrifugation and dry in a vacuum oven to obtain polyimide-hydroxy (PI-OH). The number-average molecular weight (M n ) of PI-OH is confirmed to be 2.86 × 10 5 g / mol −1 .

[0032] Dissolve 10 g of PI-OH with a molecular weight of 2.86 × 10 5 g / mol −1 in 80 mL of acetone to prepare a solution, denoted as Solution A. Add 90 g of acrylic acid to 135 mL of purified water to prepare a 40% acrylic acid solution, denoted as Solution B. Add Solution B to Solution A and stir evenly. Then add 0.9 g of N,N-methylenebisacrylamide and 0.18 g of potassium persulfate to the mixed solution and stir evenly. Then introduce nitrogen to completely exhaust the air and immediately seal it, and continue to react at 80 °C for 2 h. After the reaction, a hydrogel is obtained. Extrude and granulate the hydrogel, dry it at 80 °C for 6 h and then pulverize and screen it to obtain particulate water-absorbing resin with a particle size of 120-400 μm.

[0033] Example 2 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine, and 12 mL of toluene, then heat at 180 °C for 5 h. After cooling, pour the mixture into absolute ethanol, and obtain polyimide-hydroxy (PI-OH) after centrifugal washing and drying in a vacuum oven. The number-average molecular weight (M n ) of PI-OH is confirmed by GPC to be 2.86 × 10 5 g / mol −1 .

[0034] Dissolve 20 g of PI-OH with a molecular weight of 2.86 × 10 5 g / mol −1 in 80 mL of acetone to prepare a solution, denoted as solution A. Add 80 g of acrylic acid to 120 mL of purified water to prepare a 40% acrylic acid solution, denoted as solution B. Add solution B to solution A and stir evenly. Then, add 1.8 g of N,N'-methylenebisacrylamide and 0.36 g of potassium persulfate to the mixed solution and stir evenly. Then, introduce nitrogen to completely expel the air and immediately seal it, and continue to react at 60 °C for 4 h. After the reaction, a hydrogel is obtained. Extrude and granulate the hydrogel, dry it at 80 °C for 6 h, and then crush and screen it to obtain particulate water-absorbing resin with a particle size of 120 - 400 μm.

[0035] Example 3 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine, and 12 mL of toluene, then heat at 180 °C for 5 h. After cooling, pour the mixture into absolute ethanol, and obtain polyimide-hydroxy (PI-OH) after centrifugal washing and drying in a vacuum oven. The number-average molecular weight (M n ) of PI-OH is confirmed by GPC to be 2.86 × 10 5 g / mol −1 .

[0036] Dissolve 30 g of PI-OH with a molecular weight of 2.86 × 10 5 g / mol −1PI-OH was dissolved in 80 mL of acetone to prepare a solution, denoted as Solution A. 70 g of acrylic acid was added to 105 mL of purified water to prepare a 40% acrylic acid solution, denoted as Solution B. Solution B was added to Solution A and stirred evenly. Subsequently, 2.7 g of N, N-methylenebisacrylamide and 0.54 g of potassium persulfate were added to the mixed solution and stirred evenly. Then, nitrogen was introduced to completely expel the air and immediately sealed. The reaction continued at 60 °C for 4 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then pulverized and sieved to obtain granular water-absorbing resin with a particle size of 120 - 400 μm.

[0037] Example 4 10.8 g of 3, 3'-dihydroxybenzidine and 14.7 g of biphenyl-3, 3', 4, 4'-tetracarboxylic dianhydride (BPDA) were dissolved in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. The mixed solution was stirred at room temperature, and 3 mL of triethylamine, 3 mL of pyridine, and 12 mL of toluene were slowly added. Subsequently, it was heated at 200 °C for 2 h. After cooling, the mixture was poured into absolute ethanol, centrifuged and washed, and dried in a vacuum oven to obtain polyimide-hydroxy (PI-OH). The number-average molecular weight (M n ) of PI-OH was confirmed by GPC to be 2.15 × 10 5 g / mol −1 .

[0038] 30 g of PI-OH with a molecular weight of 2.15 × 10 5 g / mol −1 was dissolved in 80 mL of acetone to prepare a solution, denoted as Solution A. 70 g of acrylic acid was added to 105 mL of purified water to prepare a 40% acrylic acid solution, denoted as Solution B. Solution B was added to Solution A and stirred evenly. Subsequently, 3.6 g of N, N-methylenebisacrylamide and 0.72 g of potassium persulfate were added to the mixed solution and stirred evenly. Then, nitrogen was introduced to completely expel the air and immediately sealed. The reaction continued at 50 °C for 6 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then pulverized and sieved to obtain granular water-absorbing resin with a particle size of 120 - 400 μm.

[0039] Example 5 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine, and 12 mL of toluene, and then heat at 160 °C for 8 h. After cooling, pour the mixture into absolute ethanol, wash by centrifugation, and dry in a vacuum oven to obtain polyimide-hydroxy (PI-OH). The number-average molecular weight (M n ) of PI-OH was confirmed by GPC to be 3.06 × 10 5 g / mol −1 .

[0040] Dissolve 30 g of PI-OH with a molecular weight of 3.06 × 10 5 g / mol −1 in 80 mL of acetone to prepare a solution, denoted as solution A. Add 70 g of acrylic acid to 105 mL of purified water to prepare a 40% acrylic acid solution, denoted as solution B. Add solution B to solution A and stir evenly. Then add 4.5 g of N,N'-methylenebisacrylamide and 0.9 g of potassium persulfate to the mixed solution and stir evenly. Then pass nitrogen to completely expel the air and immediately seal it, and continue to react at 60 °C for 4 h. After the reaction, a hydrogel is obtained. Extrude and granulate the hydrogel, dry it at 80 °C for 6 h, and then crush and screen it to obtain particulate water-absorbing resin with a particle size of 120 - 400 μm.

[0041] Comparative Example 1 A polyacrylic acid water-absorbing resin was prepared as follows: Add 70 g of acrylic acid to 105 mL of purified water to prepare a 40% acrylic acid solution. Add 0.9 g of N,N'-methylenebisacrylamide and 0.18 g of potassium persulfate to the solution and stir evenly. Then pass nitrogen to completely expel the air and immediately seal it, and raise the temperature to 60 °C and react for 4 h. After the reaction, a hydrogel is obtained. Extrude and granulate the hydrogel, dry it at 80 °C for 6 h, and then crush and screen it to obtain particulate water-absorbing resin with a particle size of 120 - 400 μm. The number-average molecular weight (M n ) of polyacrylic acid was confirmed by GPC to be 712000 g / mol -1 .

[0042] Comparative Example 2 70 g of acrylic acid was added to 105 mL of purified water to prepare a 40% acrylic acid solution. 1.8 g of N, N-methylenebisacrylamide and 0.36 g of potassium persulfate were added to the solution and stirred evenly. Subsequently, nitrogen was introduced to completely expel the air, and then it was immediately sealed. The temperature was raised to 60 °C and reacted for 6 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then pulverized and sieved to obtain granular water-absorbing resin with a particle size of 120 - 400 μm. The number-average molecular weight (M n ) of polyacrylic acid was confirmed to be 745000 g mol -1 by GPC.

[0043] Comparative Example 3 70 g of acrylic acid was added to 105 mL of purified water to prepare a 40% acrylic acid solution. 2.7 g of N, N-methylenebisacrylamide and 0.54 g of potassium persulfate were added to the solution and stirred evenly. Subsequently, nitrogen was introduced to completely expel the air, and then it was immediately sealed. The temperature was raised to 60 °C and reacted for 8 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then pulverized and sieved to obtain granular water-absorbing resin with a particle size of 120 - 400 μm. The number-average molecular weight (M n ) of polyacrylic acid was confirmed to be 761000 g mol -1 by GPC.

[0044] Comparative Example 4 30 g of 3, 3'-dihydroxybenzidine was dissolved in 50 mL of NMP to prepare a solution, denoted as Solution A. 70 g of acrylic acid was added to 105 mL of purified water to prepare a 40% acrylic acid solution, denoted as Solution B. Solution B was added to Solution A and stirred evenly. Subsequently, 3.6 g of N, N-methylenebisacrylamide and 0.72 g of potassium persulfate were added to the mixed solution and stirred evenly. Then, nitrogen was introduced to completely expel the air, and it was immediately sealed and reacted at 60 °C for another 4 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then pulverized and sieved to obtain granular water-absorbing resin with a particle size of 120 - 400 μm.

[0045] Comparative Example 5 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine and 12 mL of toluene, then heat at 180 °C for 5 h. After cooling, pour the mixture into absolute ethanol, wash by centrifugation and dry in a vacuum oven to obtain polyimide-hydroxy (PI-OH). The number-average molecular weight (M n ) of PI-OH is confirmed by GPC to be 2.86 × 10 5 g / mol −1 .

[0046] Dissolve 40 g of PI-OH with a molecular weight of 2.86 × 10 5 g / mol −1 in 80 mL of acetone to prepare a solution, denoted as solution A. Add 60 g of acrylic acid to 90 mL of purified water to prepare a 40% acrylic acid solution, denoted as solution B. Add solution B to solution A and stir evenly, then add 4.5 g of N,N-methylenebisacrylamide and 0.9 g of potassium persulfate to the mixed solution and stir evenly. Then, pass nitrogen to completely expel the air and seal immediately, and continue to react at 60 °C for 4 h. After the reaction, a hydrogel is obtained. Extrude and granulate the hydrogel, dry it at 80 °C for 6 h and then crush and screen it to obtain granular water-absorbing resin with a particle size of 120 - 400 μm.

[0047] Comparative Example 6 Dissolve 10.8 g of 3,3'-dihydroxybenzidine and 14.7 g of biphenyl-3,3',4,4'-tetracarboxylic dianhydride (BPDA) in 50 mL of N-methylpyrrolidone (NMP) to obtain a mixed solution. Stir the mixed solution at room temperature, slowly add 3 mL of triethylamine, 3 mL of pyridine and 12 mL of toluene, then heat at 180 °C for 5 h. After cooling, pour the mixture into absolute ethanol, wash by centrifugation and dry in a vacuum oven to obtain polyimide-hydroxy (PI-OH). The number-average molecular weight (M n ) of PI-OH is confirmed by GPC to be 2.86 × 10 5 g / mol −1 .

[0048] Dissolve 50 g of PI-OH with a molecular weight of 2.86 × 10 5 g / mol −1PI-OH was dissolved in 80 mL of acetone to prepare a solution, denoted as Solution A. 50 g of acrylic acid was added to 75 mL of purified water to prepare a 40% acrylic acid solution, denoted as Solution B. Solution B was added to Solution A and stirred evenly. Subsequently, 4.5 g of N, N-methylenebisacrylamide and 0.9 g of potassium persulfate were added to the mixed solution and stirred evenly. Then, nitrogen was introduced to completely expel the air and immediately sealed, and the reaction was continued at 60 °C for 4 h. After the reaction, a hydrogel was obtained. The hydrogel was extruded and granulated, dried at 80 °C for 6 h, and then crushed and screened to obtain granular water-absorbing resin with a particle size of 120 - 400 μm.

[0049] The water-absorbing properties of the water-absorbing resins obtained in Examples 1 - 5 and Comparative Examples 1 - 6 were tested for liquid lithium bis(fluorosulfonyl)imide. The specific operations were as follows.

[0050] The same amounts of the water-absorbing resins prepared in Examples 1 - 5 and Comparative Examples 1 - 6 were taken respectively, and a water absorption experiment was carried out according to the mass ratio of resin to liquid lithium bis(fluorosulfonyl)imide (with 1 - 2% water) of 1:500. Samples were taken every 10 min to test the moisture content until the moisture content was below the index requirement (moisture requirement < 20 ppm). The compression properties of the water-absorbing resins in Examples 1 - 5 and Comparative Examples 1 - 6 were tested using a GC-WD-500D universal material testing machine, and the test standard was GB / T 1040 - 2006. After water absorption, it was dried in a 60 °C forced-air oven, and the complete drying time was recorded. The test results are shown in Tables 1 - 2.

[0051] Table 1 Water Absorption Performance Test of Water-Absorbing Resins in Examples 1 - 5 and Comparative Examples 1 - 6 Table 2 Processing and Molding, Mechanical Properties, and Rapid Drying Ability Performance Test of Water-Absorbing Resins in Examples 1 - 5 and Comparative Examples 1 - 6 As can be seen from Table 1 and Table 2, compared with Comparative Examples 1-6, the water-absorbing resins prepared in Examples 1-5 of the present invention show significant advantages in terms of water absorption performance, processability and mechanical properties. Specifically, in Examples 1-5, by adjusting the ratio of polyimide to polyacrylic acid, a network structure with internal hydrophobic - external hydrophilic characteristics was successfully constructed. This unique structural design not only endows the material with excellent water absorption capacity and stability, but also enables it to rapidly dehydrate and regenerate at a relatively low temperature, significantly improving the reuse efficiency of the material. Further research found that too high a proportion of polyimide would lead to difficulties in processing and molding, and the brittleness of the molded resin increased, making it prone to cracking. This indicates that the optimization of the ratio of polyimide to polyacrylic acid is the key to achieving a balance of material properties. In the present invention, polyacrylic acid was in-situ polymerized on the crosslinkable polyimide - hydroxyl (PI-OH) chain to form a special internal hydrophobic - external hydrophilic network structure. This structure not only significantly improves the mechanical strength and stability of the water-absorbing resin, but also enables it to exhibit excellent water absorption performance in the removal of lithium bis(fluorosulfonyl)imide in liquid, while maintaining the integrity and stability of the material structure.

[0052] In addition, it should be understood that although this specification is described according to embodiments, not every embodiment only contains an independent technical solution. This narrative way of the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for preparing a water-absorbing resin, characterized in that: The preparation method comprises: using acrylic acid and modified polyimide as raw materials, reacting the acrylic acid and the modified polyimide to obtain hydrogel, granulating and drying the hydrogel to obtain water-absorbing resin, wherein the modified polyimide is a polyimide with hydroxyl groups.

2. The method for preparing a water-absorbing resin according to claim 1, characterized in that: The mass ratio of the modified polyimide to acrylic acid is (10-30):(70-90).

3. The method for preparing a water-absorbing resin according to claim 1, characterized in that: The modified polyimide is an aromatic polyimide.

4. The method for preparing a water-absorbing resin according to claim 3, characterized in that: The molecular weight of the modified polyimide is 2 × 10 5 g mol −1 ~ 3 × 10 5 g mol −1 , the structural formula is as follows: 。 5. The method for preparing a water-absorbing resin according to claim 4, characterized in that: The modified polyimide is prepared according to the following steps: 3, 3'-dihydroxydiphenylamine and biphenyl-3, 3', 4, 4'-tetracarboxylic dianhydride are dissolved in N-methylpyrrolidone to obtain a mixed solution, triethylamine, pyridine and toluene are added after stirring the mixed solution, and then heated at 160-200°C for 2-8 h. After cooling, the mixed solution is poured into anhydrous ethanol, washed by centrifugation and dried in a vacuum oven.

6. The method for preparing a water-absorbing resin according to claim 1, characterized in that: The reaction temperature of acrylic acid and modified polyimide is 50-80°C, and the reaction time is 2-6 h.

7. The method for preparing a water-absorbing resin according to claim 1, characterized in that: Before the reaction of acrylic acid and modified polyimide, the modified polyimide is dissolved in acetone to form a mixed solution A; acrylic acid is added to water to prepare a 40% solution B, and the mixed solution A is added to the solution B, and then an initiator and a cross-linking agent are added to react under vacuum conditions.

8. The method for preparing a water-absorbing resin according to claim 7, characterized in that: The crosslinking agent is one or more of N, N-methylenebisacrylamide, glutaraldehyde, vinyl triethoxysilane, and diisocyanate; the initiator is one or more of potassium persulfate, ammonium persulfate, and hydrogen peroxide.

9. A water-absorbing resin, characterized in that: The water-absorbing resin is prepared by the preparation method of the water-absorbing resin according to any one of claims 1 to 8.

10. Use of the water-absorbing resin according to claim 9, characterized in that: The water-absorbing resin is used in dewatering of liquid lithium bis(fluorosulfonyl)imide.

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