Magnetic recyclable desiccant and method of making same

Abstract

The application relates to a magnetic recyclable desiccant and a preparation method thereof, and belongs to the technical field of desiccants. The disclosed desiccant is interpenetrated with a polyacrylic acid network and a SiO2 skeleton, the rigid SiO2 network is used to limit the excessive swelling of the polyacrylic acid chain, the effect of "water absorption expansion but maintaining the overall form" is realized, the silane coupling agent is introduced on the surface of Fe3O4 to introduce a polymerizable double bond, the silane coupling agent is chemically bonded to the polymer network, the problem of loss of the magnetic component in repeated use is fundamentally solved, the magnetic heat effect of Fe3O4 is utilized to realize rapid in-situ heating in an alternating magnetic field, only the desiccant itself is heated instead of the whole environment, the regeneration efficiency is greater than 92%, and the recyclable purpose is realized.

Description

Technical Field

[0001] This invention belongs to the field of desiccant technology, and relates to a magnetic recyclable desiccant and its preparation method. Background Technology

[0002] Desiccants have a wide range of applications in compressed air drying, gas purification, electronic device protection, pharmaceutical moisture prevention, and industrial solvent dehydration. Currently, commonly used desiccant materials can be mainly divided into two categories: physical adsorption desiccants and chemical absorption desiccants.

[0003] Physical adsorption desiccants are represented by silica gel, molecular sieves, activated alumina, and silica aerogels. These materials rely on their abundant microporous / mesoporous structures to achieve physical adsorption, and have the advantages of maintaining a solid state after water absorption and good thermal stability. However, they generally suffer from low equilibrium adsorption capacity, and the regeneration process requires hot air heating, resulting in high energy consumption and long time, leading to high operating costs. In particular, silica aerogels, prepared by drying at normal pressure, are prone to irreversible collapse of their pore structure under capillary forces after water absorption, leading to a sharp decline in specific surface area and adsorption performance, limiting their recycling in environments with fluctuating humidity. Chemical adsorption desiccants are represented by superabsorbent polymeric resins (SAP) based on polyacrylic acid. These materials form hydrogen bonds with water molecules through hydrophilic groups (such as sodium carboxylate and sulfonic acid groups) on their molecular chains, and achieve highly efficient water absorption by utilizing the osmotic pressure inside and outside the network, which is far superior to that of physical adsorption materials. However, after absorbing water, SAP forms a high-water-content flowing gel, exhibiting a "water-absorbing and melting" phenomenon. It loses its original shape and mechanical strength, making it impossible to separate and recycle from the material, and easily causing secondary pollution.

[0004] To address the challenge of desiccant recovery, existing research has attempted to introduce magnetic components to impart magnetic responsiveness to materials. For example, current techniques employ co-precipitation to prepare Fe3O4 nanoparticles, which are then incorporated into silica aerogel networks through physical doping to create magnetic aerogel adsorbents. These adsorbents can achieve rapid magnetic separation and recovery under an alternating magnetic field. However, this approach still suffers from several significant drawbacks: First, Fe3O4 particles, which are only physically mixed or simply coated with the matrix, are easily detached and lost during repeated water absorption and dehydration cycles, leading to a gradual decline in magnetic responsiveness and secondary pollution. Second, the introduction of magnetic components typically results in a significant decrease in the specific surface area and pore volume of the aerogel. Third, the preparation process often relies on high-cost processes such as supercritical drying or freeze-drying, hindering large-scale production. Furthermore, existing magnetic SAP materials also fail to overcome the inherent defect of structural disintegration after water absorption. In conclusion, a magnetic desiccant material with comprehensive performance characteristics is currently lacking in the existing technology. Therefore, developing a novel magnetic regenerable desiccant that can overcome the aforementioned technical bottlenecks is of great practical significance for promoting the efficient, green, and circular application of desiccant materials. Summary of the Invention

[0005] This invention relates to a magnetic recyclable desiccant and its preparation method. The disclosed desiccant interpenetrates with a SiO2 framework through a polyacrylic acid network. The rigid SiO2 network restricts the excessive swelling of the polyacrylic acid chains, achieving the effect of "absorbing water and swelling while maintaining the overall shape". At the same time, a silane coupling agent introduces polymerizable double bonds on the Fe3O4 surface, chemically bonding them into the polymer network. This fundamentally solves the problem of magnetic component loss during repeated use. Utilizing the magnetocaloric effect of Fe3O4, rapid in-situ heating is achieved in an alternating magnetic field, heating only the desiccant itself and not the overall environment, achieving a regeneration efficiency of >92%, thereby achieving the purpose of recyclability.

[0006] The objective of this invention can be achieved through the following technical solutions: A magnetic recyclable desiccant, comprising the following raw materials in parts by weight: 5-20 parts modified magnetic Fe3O4 particles, 0.5-2 parts crosslinking agent, 0.3-0.8 parts initiator, 100-120 parts acrylic acid aqueous solution, and 150-200 parts SiO2 gel.

[0007] Further, the preparation method of the modified magnetic Fe3O4 particles is as follows: FeCl2·4H2O, FeCl3·6H2O are mixed with deionized water, and then ammonia water is added dropwise under nitrogen protection to adjust the pH value. The mixture is heated and then magnetically separated. The particles are washed with deionized water until neutral and then vacuum dried to constant weight to obtain pretreated particles. Subsequently, anhydrous ethanol and silane coupling agent are added and stirred. The mixture is heated and refluxed, and the product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

[0008] Further, the mass ratio of FeCl2·4H2O, FeCl3·6H2O, and deionized water is 1-2:2:5-10, the pH value is 10-11, the heating temperature is 50-60℃, the heating time is 1-1.5h, the vacuum drying temperature is 60-80℃, the mass ratio of particles, anhydrous ethanol, and silane coupling agent is 10-15:80:2-6, wherein the silane coupling agent is KH-570 coupling agent, the reflux temperature is 60-70℃, and the reflux time is 3-4h.

[0009] Further, the crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:30-45, wherein the mass fraction of sodium hydroxide solution is 60-75%.

[0010] Furthermore, the SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 5-7:10:3-4:0.1 for 2-3 hours to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.1-0.3 mol / L.

[0011] A method for preparing a magnetic recyclable desiccant, the method comprising the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred to obtain a mixture. The mixture was heated in a water bath and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel was immersed in anhydrous ethanol, then immersed in n-hexane, and finally dried in stages under normal pressure to obtain the magnetic composite desiccant. (3) The magnetic composite desiccant is immersed in the composite solvent and heated, then cooled and filtered, and vacuum dried to constant weight to obtain the magnetic recyclable desiccant.

[0012] Further, the parameters of the ultrasonic treatment in step (1) are: 500-800W, 40-50℃, 30-40min, the continuous stirring time is 30min, the water bath heating time is 3-4h, and the water bath heating temperature is 60-65℃.

[0013] Further, the immersion time in anhydrous ethanol in step (2) is 8-10h, the immersion time in n-hexane is 12h, the volume ratio of the magnetic composite hydrogel, anhydrous ethanol and n-hexane is 1-2:5:5, and the atmospheric pressure segmented drying is specifically as follows: first, heat to 60℃ and dry for 2h, then heat to 80℃ and dry for 30min, and then heat to 100℃ and dry to constant weight.

[0014] Further, in step (3), the composite solvent is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:1-3, the magnetic composite desiccant is in a mass ratio of 1-3:8 to the composite solvent, the heating treatment time is 2-3 hours, the heating treatment temperature is 60°C, and the vacuum drying temperature is 60-65°C.

[0015] The above-mentioned technical solution provides a magnesium alloy automotive anti-collision beam extrusion profile and its preparation method, which, compared with the prior art, have the following advantages: 1. The desiccant of this invention achieves the effect of "absorbing water and swelling while maintaining the overall shape" by interpenetrating a polyacrylic acid network with a SiO2 skeleton and using the rigid SiO2 network to limit the excessive swelling of the polyacrylic acid chains. At the same time, the silane coupling agent introduces polymerizable double bonds on the Fe3O4 surface, which are chemically bonded to the polymer network, fundamentally solving the problem of magnetic component loss during repeated use. Utilizing the magnetocaloric effect of Fe3O4, rapid in-situ heating is achieved in an alternating magnetic field, heating only the desiccant itself and not the overall environment, achieving a regeneration efficiency of >92%, thereby achieving the purpose of recyclability. Detailed Implementation

[0016] To further illustrate the technical means and effects of the present invention in achieving its intended purpose, the following detailed description of the specific implementation methods, structures, features and effects of the present invention, in conjunction with embodiments, is provided below.

[0017] Example 1 A magnetic recyclable desiccant, comprising the following raw materials in parts by weight: 5 parts modified magnetic Fe3O4 particles, 0.5 parts crosslinking agent, 0.3 parts initiator, 100 parts acrylic acid aqueous solution, and 150 parts SiO2 gel.

[0018] The modified magnetic Fe3O4 particles are prepared as follows: FeCl2·4H2O, FeCl3·6H2O and deionized water are mixed in a mass ratio of 1:2:5. Then, under nitrogen protection, ammonia water is added dropwise to adjust the pH to 10. The mixture is heated to 50°C for 1 hour, followed by magnetic separation. The particles are washed with deionized water until neutral and then vacuum dried at 60°C to constant weight to obtain pretreated particles. Subsequently, the particles, anhydrous ethanol and silane coupling agent are stirred and mixed in a mass ratio of 10:80:2. The mixture is heated to 60°C and refluxed for 3 hours. The product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

[0019] The crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:30, wherein the mass fraction of sodium hydroxide solution is 60%.

[0020] The SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 5:10:3:0.1 for 2 hours to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.1 mol / L.

[0021] A method for preparing a magnetic recyclable desiccant, the method comprising the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated at 500W, 40℃ and 30min. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred for another 30min to obtain a mixture. The mixture was heated in a water bath at 60℃ for 3h and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 1:5 for 8 hours, and then the magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 1:5 for 12 hours. Finally, the magnetic composite desiccant was obtained by first heating to 60℃ and drying for 2 hours, then heating to 80℃ and drying for 30 minutes, and then heating to 100℃ and drying to constant weight. (3) The magnetic composite desiccant and the composite solvent are mixed at a mass ratio of 1:8, heated to 60°C for 2 hours, filtered after cooling, and vacuum dried at 60°C to constant weight to obtain the magnetic recyclable desiccant. The composite solvent is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:1.

[0022] Example 2 A magnetic recyclable desiccant, comprising the following raw materials in parts by weight: 12 parts modified magnetic Fe3O4 particles, 1 part crosslinking agent, 0.5 parts initiator, 110 parts acrylic acid aqueous solution, and 180 parts SiO2 gel.

[0023] The modified magnetic Fe3O4 particles are prepared as follows: FeCl2·4H2O, FeCl3·6H2O and deionized water are mixed in a mass ratio of 1.5:2:8. Then, under nitrogen protection, ammonia water is added dropwise to adjust the pH to 10.5. The mixture is heated to 55°C for 75 minutes, then magnetically separated, washed with deionized water until neutral, and vacuum dried at 70°C to constant weight to obtain pretreated particles. Subsequently, the particles, anhydrous ethanol and silane coupling agent are stirred and mixed in a mass ratio of 13:80:4, heated at 65°C and refluxed for 3.5 hours. The product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

[0024] The crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:38, wherein the mass fraction of sodium hydroxide solution is 68%.

[0025] The SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 6:10:3.5:0.1 for 2.5 h to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.2 mol / L.

[0026] A method for preparing a magnetic recyclable desiccant, the method comprising the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated at 650W, 45℃ and 35min. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred for 30min to obtain a mixture. The mixture was heated in a water bath at 62℃ for 3.5h and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 1.5:5 for 9 hours, and then the magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 1.5:5 for 12 hours. Finally, the magnetic composite desiccant was obtained by first heating to 60℃ and drying for 2 hours, then heating to 80℃ and drying for 30 minutes, and then heating to 100℃ and drying to constant weight. (3) The magnetic composite desiccant and the composite solvent are mixed at a mass ratio of 2:8, heated to 60°C in 2.5 hours, cooled and filtered, and then vacuum dried at 62°C to constant weight to obtain the magnetic recyclable desiccant. The composite solvent is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:2.

[0027] Example 3 A magnetic recyclable desiccant, comprising the following raw materials in parts by weight: 20 parts modified magnetic Fe3O4 particles, 2 parts crosslinking agent, 0.8 parts initiator, 120 parts acrylic acid aqueous solution, and 200 parts SiO2 gel.

[0028] The modified magnetic Fe3O4 particles are prepared as follows: FeCl2·4H2O, FeCl3·6H2O and deionized water are mixed in a mass ratio of 2:2:10. Then, under nitrogen protection, ammonia water is added dropwise to adjust the pH value to 11. The mixture is heated to 60°C for 1.5 hours, followed by magnetic separation. The particles are washed with deionized water until neutral and then vacuum dried at 80°C to constant weight to obtain pretreated particles. Subsequently, the particles, anhydrous ethanol and silane coupling agent are stirred and mixed in a mass ratio of 15:80:6. The mixture is heated to 70°C and refluxed for 4 hours. The product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

[0029] The crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:45, wherein the mass fraction of sodium hydroxide solution is 75%.

[0030] The SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 7:10:4:0.1 for 3 hours to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.3 mol / L.

[0031] A method for preparing a magnetic recyclable desiccant, the method comprising the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated at 800W, 50℃ and 40min. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred for 30min to obtain a mixture. The mixture was heated in a water bath at 65℃ for 4h and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 2:5 for 10 hours, and then the magnetic composite hydrogel and anhydrous ethanol were immersed in each other at a volume ratio of 2:5 for 12 hours. Finally, the magnetic composite desiccant was obtained by first heating to 60℃ and drying for 2 hours, then heating to 80℃ and drying for 30 minutes, and then heating to 100℃ and drying to constant weight. (3) The magnetic composite desiccant and the composite solvent are mixed in a mass ratio of 3:8, heated to 60°C in 3 hours, filtered after cooling, and vacuum dried to constant weight at 65°C to obtain the magnetic recyclable desiccant. The composite solvent is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:3.

[0032] Comparative Example 1 Based on Example 2, the SiO2 gel and its preparation method in the raw materials were removed, while other conditions remained the same as in Example 2.

[0033] Comparative Example 2 Based on Example 2, the silane coupling agent in the process of preparing modified magnetic Fe3O4 particles was removed, while other conditions remained the same as in Example 2.

[0034] Comparative Example 3 Based on Example 2, a magnetic recyclable desiccant is provided, comprising the following raw materials in parts by weight: 12 parts modified magnetic Fe3O4 particles, 1 part crosslinking agent, 0.5 parts initiator, 110 parts acrylic acid aqueous solution, and 180 parts SiO2 gel.

[0035] The modified magnetic Fe3O4 particles are prepared as follows: FeCl2·4H2O, FeCl3·6H2O and deionized water are mixed in a mass ratio of 1.5:2:8. Then, under nitrogen protection, ammonia water is added dropwise to adjust the pH to 10.5. The mixture is heated to 55°C for 75 minutes, then magnetically separated, washed with deionized water until neutral, and vacuum dried at 70°C to constant weight to obtain pretreated particles. Subsequently, the particles, anhydrous ethanol and silane coupling agent are stirred and mixed in a mass ratio of 13:80:4, heated at 65°C and refluxed for 3.5 hours. The product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

[0036] The crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:38, wherein the mass fraction of sodium hydroxide solution is 68%.

[0037] The SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 6:10:3.5:0.1 for 2.5 h to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.2 mol / L.

[0038] A method for preparing a magnetic recyclable desiccant, the method comprising the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated at 650W, 45℃ and 35min. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred for 30min to obtain a mixture. The mixture was heated in a water bath at 62℃ for 3.5h and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel was first heated to 60℃ and dried for 2 hours, then heated to 80℃ and dried for 30 minutes, and then heated to 100℃ and dried to constant weight to obtain the magnetic composite desiccant. (3) The magnetic composite desiccant and the composite solvent are mixed at a mass ratio of 2:8, heated to 60°C in 2.5 hours, cooled and filtered, and then vacuum dried at 62°C to constant weight to obtain the magnetic recyclable desiccant. The composite solvent is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:2.

[0039] Comparative Example 4 Based on Example 2, the atmospheric pressure segmented drying in step (2) of the preparation process of the magnetic recyclable desiccant was carried out by constant temperature drying at 100°C in an oven until constant weight, while other conditions remained the same as in Example 2.

[0040] Performance testing The magnetic recyclable desiccants prepared in Examples 1-3 and Comparative Examples 1-4 were used as samples. The particle size of the samples was 5 mm. The water absorption rate of the samples was tested according to GB / T 22875-2018 "Super Absorbent Resins". The water-saturated samples were placed in a test tube with a diameter of 2 cm and a length of 15 cm. After standing for 10 min, the test tube was inverted to determine the integrity of the shape (if the sample plastically flows and slides due to its own weight, it is judged as "melted (unqualified)"; if it remains intact and cylindrical and does not fall off, it is judged as "solid retention (qualified)"). Regeneration efficiency was determined: the samples in the dry state and the water-saturated state after 20 cycles were placed in an alternating magnetic field generator (frequency 300 kHz, current 100 A). The surface temperature was increased from 20 °C to 200 °C. The regeneration efficiency % = water absorption rate after the 20th regeneration / water absorption rate after the first regeneration × 100%; The test results are shown in Table 1.

[0041] Table 1 Test Results

[0042] A comprehensive analysis of the data in Table 1 shows that Examples 1-3 exhibit high water absorption and do not melt, while maintaining a regeneration efficiency of over 92% after 20 cycles. Therefore, this invention relies on a SiO2 interpenetrating network to provide a rigid, anti-swelling framework and chemically anchored magnetic particles. Comparative Examples 1-4 demonstrate that removing the rigid framework, modifying with a silane coupling agent, omitting the "solvent replacement (ethanol / n-hexane)" process in step four, and directly drying the hydrogel and performing segmented drying at atmospheric pressure are prerequisites for ensuring the mesoporous structure and maximizing the magnetocaloric effect. Abandoning this process would compromise the physical basis for rapid regeneration.

[0043] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A magnetically recyclable desiccant, characterized in that, The magnetic recyclable desiccant comprises the following raw materials in parts by weight: 5-20 parts modified magnetic Fe3O4 particles, 0.5-2 parts crosslinking agent, 0.3-0.8 parts initiator, 100-120 parts acrylic acid aqueous solution, and 150-200 parts SiO2 gel.

2. The magnetic recyclable desiccant according to claim 1, characterized in that, The method for preparing the modified magnetic Fe3O4 particles is as follows: FeCl2·4H2O, FeCl3·6H2O are mixed with deionized water, and then ammonia is added dropwise under nitrogen protection to adjust the pH value. The mixture is heated and then magnetically separated. The particles are washed with deionized water until neutral and then vacuum dried to constant weight to obtain pretreated particles. Subsequently, anhydrous ethanol and silane coupling agent are added and stirred. The mixture is heated and refluxed, and the product at the bottom of the reactor is the modified magnetic Fe3O4 particles.

3. The magnetic recyclable desiccant according to claim 2, characterized in that, The mass ratio of FeCl2·4H2O, FeCl3·6H2O, and deionized water is 1-2:2:5-10; the pH value is 10-11; the heating temperature is 50-60℃; the heating time is 1-1.5h; the vacuum drying temperature is 60-80℃; the mass ratio of particles, anhydrous ethanol, and silane coupling agent is 10-15:80:2-6; the silane coupling agent is KH-570; the reflux temperature is 60-70℃; and the reflux time is 3-4h.

4. The magnetic recyclable desiccant according to claim 1, characterized in that, The crosslinking agent is N,N′-methylenebisacrylamide, the initiator is ammonium persulfate, and the acrylic acid aqueous solution is a mixture of acrylic acid and sodium hydroxide solution in a mass ratio of 100:30-45, wherein the mass fraction of sodium hydroxide solution is 60-75%.

5. The magnetic recyclable desiccant according to claim 1, characterized in that, The SiO2 gel is prepared by mixing tetraethyl orthosilicate, anhydrous ethanol, deionized water and hydrochloric acid solution in a volume ratio of 5-7:10:3-4:0.1 for 2-3 hours to obtain SiO2 gel, wherein the concentration of hydrochloric acid solution is 0.1-0.3 mol / L.

6. A method for preparing the magnetic recyclable desiccant as described in claim 1, characterized in that, The preparation method of the magnetic recyclable desiccant includes the following steps: (1) The modified magnetic Fe3O4 particles were dispersed in an acrylic acid aqueous solution and ultrasonically treated. Then, a crosslinking agent and an initiator were added and stirred. Then, SiO2 gel was added and stirred to obtain a mixture. The mixture was heated in a water bath and then cooled to room temperature to obtain a magnetic composite hydrogel. (2) The magnetic composite hydrogel was immersed in anhydrous ethanol, then immersed in n-hexane, and finally dried in stages under normal pressure to obtain the magnetic composite desiccant. (3) The magnetic composite desiccant is immersed in the composite solvent and heated. After cooling, it is filtered and vacuum dried to constant weight to obtain the magnetic recyclable desiccant.

7. A method for preparing a magnetic recyclable desiccant according to claim 6, characterized in that, The parameters for ultrasonic treatment in step (1) are: 500-800W, 40-50℃, 30-40min, the continuous stirring time is 30min, the water bath heating time is 3-4h, and the water bath heating temperature is 60-65℃.

8. The method for preparing a magnetic recyclable desiccant according to claim 6, characterized in that, The immersion time in anhydrous ethanol in step (2) is 8-10 hours, the immersion time in n-hexane is 12 hours, the volume ratio of the magnetic composite hydrogel, anhydrous ethanol and n-hexane is 1-2:5:5, and the atmospheric pressure segmented drying is as follows: first heat to 60℃ and dry for 2 hours, then heat to 80℃ and dry for 30 minutes, and then heat to 100℃ and dry to constant weight.

9. The method for preparing a magnetic recyclable desiccant according to claim 6, characterized in that, The composite solvent in step (3) is composed of hexamethyldisilazane and n-hexane in a mass ratio of 1:1-3. The mass ratio of the magnetic composite desiccant to the composite solvent is 1-3:

8. The heating treatment time is 2-3 hours. The heating treatment temperature is 60°C. The vacuum drying temperature is 60-65°C.

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