A high-hygroscopicity bentonite-based mineral desiccant and a method for preparing the same

Abstract

This invention relates to the field of drying technology and discloses a highly hygroscopic bentonite-based mineral desiccant and its preparation method. The desiccant prepared by this invention is composed of the following raw materials in the indicated mass percentages: 20wt%-30wt% anhydrous magnesium chloride, 8wt%-12wt% silica gel, 3wt%-8wt% sodium silicate, 4.5wt%-7.5wt% potassium silicate, 5wt%-10wt% attapulgite, with the balance being modified bentonite. The synergistic effect between the components of this desiccant imparts high hygroscopicity, making it promising for applications in electronics and precision instruments, food and pharmaceutical packaging, industrial and logistics transportation, and daily necessities and warehousing.

Description

Technical Field

[0001] This invention relates to the field of drying technology, specifically to a highly hygroscopic bentonite-based mineral desiccant and its preparation method. Background Technology

[0002] Bentonite is a layered silicate mineral with montmorillonite as its main component, possessing a unique crystalline structure. The interlayers of montmorillonite can adsorb and release water molecules, thus naturally endowing bentonite with certain hygroscopic properties. Its hygroscopic mechanism is mainly manifested in two ways: firstly, exchangeable cations in the interlayers of dehydrated montmorillonite adsorb water molecules through hydration, expanding the interlayer spacing; secondly, the negatively charged surface of the montmorillonite crystals creates an electrostatic field that promotes the directional alignment of water molecules, enhancing its ability to capture water molecules. However, the hygroscopic capacity of natural bentonite is limited. Studies show that at 25℃ and 90% relative humidity, the hygroscopic rate of pure montmorillonite is approximately 20%–30%, but the actual hygroscopic rate of natural bentonite, due to impurities such as quartz and feldspar, is only 15%–25%. At 80% relative humidity, the saturated hygroscopic capacity of unmodified bentonite is approximately 25% of its own weight. Bentonite desiccants that are simply purified or modified by sodium oxidation or acidification typically have a saturated moisture absorption rate between 16% and 25%, far lower than that of chemical desiccants such as calcium chloride. This makes it difficult to meet the moisture protection requirements of high-humidity environments such as those used in electronic components, precision instruments, and high-end pharmaceutical packaging. Therefore, introducing highly hygroscopic polymers into the bentonite interlayer is expected to significantly improve its moisture absorption capacity while maintaining the advantages of bentonite's natural structure, thereby meeting the more demanding moisture protection application scenarios. Summary of the Invention

[0003] To address the aforementioned technical problems, this invention provides a highly hygroscopic bentonite-based mineral desiccant and its preparation method.

[0004] The objective of this invention can be achieved through the following technical solutions: A highly hygroscopic bentonite-based mineral desiccant is composed of the following raw materials in weight percentage: 20wt%-30wt% anhydrous magnesium chloride, 8wt%-12wt% silica gel, 3wt%-8wt% sodium silicate, 4.5wt%-7.5wt% potassium silicate, 5wt%-10wt% attapulgite, with the balance being modified bentonite. The modified bentonite is prepared by the following steps: Step A1: Add sodium-based bentonite to deionized water and stir vigorously for 6 hours. Add 0.2 mol / L hexadecyltrimethylammonium bromide solution and heat to 50-60℃ and stir at a constant temperature for 24 hours. Centrifuge, wash, dry and grind to obtain intercalated modified bentonite. Furthermore, in step A1, the ratio of sodium bentonite, deionized water, and hexadecyltrimethylammonium bromide solution is 4.5-5 g: 100 mL: 25 mL; Step A2: Disperse the intercalated modified bentonite in deionized water and stir thoroughly. Add functionalized polyacrylamide and heat to 40-50℃. Stir at 8000-10000 rpm for 3-5 hours. Freeze dry and grind to obtain modified bentonite. Furthermore, in step A2, the amount of functionalized polyacrylamide used is 2.5-3.5 wt% of the mass of the intercalated modified bentonite; Further, the functionalized polyacrylamide described in step A2 is polymerized by initiation with an initiator using 2-acrylamido-2-methylpropanesulfonic acid, acrylamide and acrylamide functional monomers as monomers. The acrylamide functional monomers contain an imidazole ring quaternary ammonium salt structure, a phosphate ester structure and a terminal acrylamide structure.

[0005] Furthermore, the functionalized polyacrylamide is prepared specifically by the following steps: Step B1: Add 2-imidazol-1-ethylamine to N,N-dimethylacetamide and stir until homogeneous. Transfer to an ice-water bath, then add triethylamine and stir until homogeneous. Slowly add acryloyl chloride and stir for 30 minutes. Transfer to an oil bath and heat to 65°C for 4.5-5.5 hours. Then transfer to distilled water to precipitate, vacuum filter, and dry to obtain acrylamide imidazolium. Further, in step B1, the molar ratio of 2-imidazol-1-ethylamine, acryloyl chloride, and triethylamine is 0.1:0.1-0.105:0.015-0.018; Step B2: Add acrylamide imidazole to acetonitrile and stir until homogeneous. Heat to 50-55℃ and add 4-bromo-1-butanol. Reflux for 4 hours. Remove the solvent by rotary evaporation. Remove the solvent further by vacuum distillation. Obtain acrylamide imidazole quaternary ammonium salt by vacuum distillation. Furthermore, in step B2, the molar ratio of acrylamide imidazole to 4-bromo-1-butanol is 0.1:0.105-0.12; Step B3: Add acrylamide imidazole quaternary ammonium salt to tetrahydrofuran and stir well. Add triethylamine and stir under nitrogen for 10 min. Then, under an ice-water bath, add dimethyl chlorophosphate tetrahydrofuran solution dropwise over 1 h. After the addition is complete, react at room temperature for 2 h, then heat to 40℃ and reflux for 5-6 h. Filter, rotary evaporate, wash and dry to obtain acrylamide functional monomer. Furthermore, in step B3, the molar ratio of acrylamide imidazole quaternary ammonium salt, triethylamine, and dimethyl chlorophosphate is 0.1:0.12-0.15:0.1-0.105; Furthermore, in step B3, the dimethyl chlorophosphate tetrahydrofuran solution is prepared by stirring dimethyl chlorophosphate in tetrahydrofuran; Step B4: Add 2-acrylamide-2-methylpropanesulfonic acid to deionized water and adjust the pH to 8. Then add acrylamide and acrylamide functional monomer in sequence and stir evenly. Heat to 55-65℃ and purge with nitrogen gas for 30 min while stirring. Then add azobisisobutyronitrile and react for 3.5-4.5 h. After the reaction is completed, add anhydrous ethanol to precipitate the product and dry it under vacuum to obtain functionalized polyacrylamide. Further, in step B4, the ratio of 2-acrylamide-2-methylpropanesulfonic acid, deionized water, acrylamide, acrylamide functional monomer, N-vinylpyrrolidone, and azobisisobutyronitrile is 0.01-0.03 mol: 250-300 mL: 0.08-0.12 mol: 0.005-0.01 mol: 0.01-0.03 mol: 0.02-0.04 g.

[0006] A method for preparing a highly hygroscopic bentonite-based mineral desiccant includes the following steps: Weigh the raw materials according to the weight percentage, mix anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite and modified bentonite evenly, and vacuum dry to obtain a highly hygroscopic bentonite-based mineral desiccant.

[0007] The beneficial effects of this invention are: The desiccant prepared by this invention is composed of anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite, and modified bentonite. The synergistic effect between the components gives the desiccant high hygroscopicity, making it promising for applications in electronics and precision instruments, food and pharmaceutical packaging, industrial and logistics transportation, and daily necessities and warehousing.

[0008] The desiccant of this invention incorporates modified bentonite, which is based on sodium-based bentonite and undergoes two intercalation modifications to significantly enhance its moisture absorption performance. The first modification uses hexadecyltrimethylammonium bromide as an intercalating agent to increase the interlayer spacing of the bentonite, providing favorable space for the subsequent entry of functionalized polyacrylamide molecules. This transforms the surface of the bentonite interlayers from a hydrophilic to a hydrophobic organic phase, greatly reducing the resistance to the entry of large-molecule functionalized polyacrylamide. The second modification uses functionalized polyacrylamide as an intercalating agent to create a chemically stable microenvironment with a unique charge and hydrophilic network within the bentonite interlayers, thereby improving the desiccant's water absorption rate. The functionalized polyacrylamide is synthesized from 2-acrylamido-2-methylpropanesulfonic acid, acrylamide, and acrylamide functional monomers via initiation polymerization. The acrylamide functional monomers contain imidazole ring quaternary ammonium salt structures, phosphate ester structures, and terminal acrylamide structures. Among them, the functional monomer containing the imidazole ring quaternary ammonium salt structure plays a key "pathfinder" role. As a cationic intercalating agent, it can undergo ion exchange reactions with sodium and calcium ions in the bentonite interlayer. The unique conjugated imidazole ring structure endows the intercalating agent with excellent thermal stability, preventing it from decomposing and failing at high temperatures. The imidazole ring quaternary ammonium salt is firmly anchored to the negatively charged interlayer surface through strong electrostatic interaction. This binding method solves the problem that traditional nonionic polyacrylamide is difficult to effectively enter and fix in the interlayer due to its lack of charge. The introduction of phosphate ester functional groups can synergistically regulate the hydrophilicity and charge density of the interlayer microenvironment. The oxygen atoms contained therein can act as coordination sites for metal ions, helping to complex polyvalent cations (especially Ca2+) in the solution. 2+ Mg 2+ This mitigates their destructive effects on the network structure. Furthermore, the numerous hydrophilic groups on the polymer backbone, as well as the imidazole rings and phosphate groups on the functional monomers, can capture water molecules through strong hydrogen bonding. The expanded bentonite layers provide a vast nanoscale space for the aforementioned hydrophilic network to exert its water absorption capacity. The large sulfonic acid groups on the 2-acrylamide-2-methylpropanesulfonic acid unit can further expand and stabilize this space like pillars, thus endowing the modified bentonite with high hygroscopicity.

[0009] In addition, due to the moisture reversion phenomenon of anhydrous magnesium chloride, modified bentonite can effectively inhibit the moisture reversion behavior of magnesium chloride by forming multiple physical barriers; the sulfonic acid groups, amide groups, phosphate groups and quaternary ammonium salt cations carried by the polymer between the modified bentonite layers can effectively adsorb and bind chloride ions and magnesium ions in the polymer network through electrostatic attraction or complexation, preventing them from migrating freely in the moisture, thereby inhibiting deliquescence. Detailed Implementation

[0010] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0011] Example 1: Functionalized polyacrylamide, specifically prepared by the following steps: Step B1: Add 0.1 mol of 2-imidazol-1-ethylamine to 200 mL of N,N-dimethylacetamide and stir until homogeneous. Transfer the mixture to an ice-water bath, then add 0.1 mol of triethylamine and stir until homogeneous. Slowly add 0.015 mol of acryloyl chloride and stir for 30 min. Transfer the mixture to an oil bath and heat to 65 °C for 4.5 h. Then transfer the mixture to distilled water to precipitate the precipitate. Filter under vacuum and dry to obtain acrylamide imidazolium. Step B2: Add 0.1 mol acrylamide imidazole to 100 mL acetonitrile and stir until homogeneous. Heat to 50 °C and add 0.105 mol 4-bromo-1-butanol. Reflux for 4 h. Remove the solvent by rotary evaporation, remove the solvent further by vacuum distillation, and obtain acrylamide imidazole quaternary ammonium salt by vacuum distillation. Step B3: Add 0.1 mol of acrylamide imidazole quaternary ammonium salt to 50 mL of tetrahydrofuran and stir well. Add 0.12 mol of triethylamine and stir under nitrogen for 10 min. Then, under an ice-water bath, add dimethyl chlorophosphate tetrahydrofuran solution dropwise over 1 h. After the addition is complete, react at room temperature for 2 h, then heat to 40 °C and reflux for 5 h. Filter, rotary evaporate, wash, and dry to obtain the acrylamide functional monomer. The dimethyl chlorophosphate tetrahydrofuran solution is prepared by stirring 0.1 mol of dimethyl chlorophosphate in 50 mL of tetrahydrofuran. Step B4: Add 0.01 mol of 2-acrylamide-2-methylpropanesulfonic acid to 250 mL of deionized water and adjust the pH to 8. Then add 0.08 mol of acrylamide and 0.005 mol of acrylamide functional monomer in sequence and stir until homogeneous. Heat to 55 °C and purge with nitrogen gas for 30 min while stirring. Then add 0.02 g of azobisisobutyronitrile and react for 3.5 h. After the reaction is complete, add anhydrous ethanol to precipitate the product and dry under vacuum to obtain functionalized polyacrylamide.

[0012] Modified bentonite is prepared by the following steps: Step A1: Add 5g of sodium-based bentonite to 100mL of deionized water and stir vigorously for 6h. Add 25mL of 0.2mol / L hexadecyltrimethylammonium bromide solution and heat to 50℃ and stir for 24h. Centrifuge, wash, dry and grind to obtain intercalated modified bentonite. Step A2: Disperse 5g of intercalated modified bentonite in 50mL of deionized water and stir thoroughly. Add 0.125g of functionalized polyacrylamide and heat to 40℃. Stir at 8000rpm for 4 hours, freeze dry, and grind to obtain modified bentonite.

[0013] Example 2: Functionalized polyacrylamide, specifically prepared by the following steps: Step B1: Add 0.1 mol of 2-imidazol-1-ethylamine to 200 mL of N,N-dimethylacetamide and stir until homogeneous. Transfer the solution to an ice-water bath, then add 0.103 mol of triethylamine and stir until homogeneous. Slowly add 0.017 mol of acryloyl chloride and stir for 30 min. Transfer the solution to an oil bath and heat to 65 °C for 5 h. Then transfer the solution to distilled water to precipitate the precipitate. Filter under vacuum and dry to obtain acrylamide imidazolium. Step B2: Add 0.1 mol acrylamide imidazole to 100 mL acetonitrile and stir until homogeneous. Heat to 55 °C and add 0.11 mol 4-bromo-1-butanol. Reflux for 4 h. Remove the solvent by rotary evaporation, remove the solvent further by vacuum distillation, and obtain acrylamide imidazole quaternary ammonium salt by vacuum distillation. Step B3: Add 0.1 mol of acrylamide imidazole quaternary ammonium salt to 50 mL of tetrahydrofuran and stir well. Add 0.135 mol of triethylamine and stir under nitrogen for 10 min. Then, add dimethyl chlorophosphate tetrahydrofuran solution dropwise over 1 h in an ice-water bath. After the addition is complete, react at room temperature for 2 h, then heat to 40 °C and reflux for 5.5 h. Filter, rotary evaporate, wash, and dry to obtain the acrylamide functional monomer. The dimethyl chlorophosphate tetrahydrofuran solution is prepared by stirring 0.103 mol of dimethyl chlorophosphate in 50 mL of tetrahydrofuran. Step B4: Add 0.02 mol of 2-acrylamide-2-methylpropanesulfonic acid to 280 mL of deionized water and adjust the pH to 8. Then add 0.1 mol of acrylamide and 0.0075 mol of acrylamide functional monomer in sequence and stir until homogeneous. Heat to 60 °C and purge with nitrogen gas for 30 min while stirring. Then add 0.03 g of azobisisobutyronitrile and react for 4 h. After the reaction is complete, add anhydrous ethanol to precipitate the product and dry it under vacuum to obtain functionalized polyacrylamide.

[0014] Modified bentonite is prepared by the following steps: Step A1: Add 4.8g of sodium-based bentonite to 100mL of deionized water and stir vigorously for 6h. Add 25mL of 0.2mol / L hexadecyltrimethylammonium bromide solution and heat to 55℃ and stir for 24h. Centrifuge, wash, dry and grind to obtain intercalated modified bentonite. Step A2: Disperse 5g of intercalated modified bentonite in 50mL of deionized water and stir thoroughly. Add 0.145g of functionalized polyacrylamide and heat to 45℃. Stir at 9000rpm for 4.5h, freeze dry, and grind to obtain modified bentonite.

[0015] Example 3: Functionalized polyacrylamide, specifically prepared by the following steps: Step B1: Add 0.1 mol of 2-imidazol-1-ethylamine to 200 mL of N,N-dimethylacetamide and stir until homogeneous. Transfer the solution to an ice-water bath, then add 0.105 mol of triethylamine and stir until homogeneous. Slowly add 0.018 mol of acryloyl chloride and stir for 30 min. Transfer the solution to an oil bath and heat to 65 °C for 5.5 h. Then transfer the solution to distilled water to precipitate the precipitate. Filter under vacuum and dry to obtain acrylamide imidazolium. Step B2: Add 0.1 mol acrylamide imidazole to 100 mL acetonitrile and stir until homogeneous. Heat to 55 °C and add 0.12 mol 4-bromo-1-butanol. Reflux for 4 h. Remove the solvent by rotary evaporation, remove the solvent further by vacuum distillation, and obtain acrylamide imidazole quaternary ammonium salt by vacuum distillation. Step B3: Add 0.1 mol of acrylamide imidazole quaternary ammonium salt to 50 mL of tetrahydrofuran and stir well. Add 0.15 mol of triethylamine and stir under nitrogen for 10 min. Then, under an ice-water bath, add dimethyl chlorophosphate tetrahydrofuran solution dropwise over 1 h. After the addition is complete, react at room temperature for 2 h, then heat to 40 °C and reflux for 6 h. Filter, rotary evaporate, wash, and dry to obtain the acrylamide functional monomer. The dimethyl chlorophosphate tetrahydrofuran solution is prepared by stirring 0.105 mol of dimethyl chlorophosphate in 50 mL of tetrahydrofuran. Step B4: Add 0.03 mol of 2-acrylamide-2-methylpropanesulfonic acid to 300 mL of deionized water and adjust the pH to 8. Then add 0.12 mol of acrylamide and 0.01 mol of acrylamide functional monomer in sequence and stir until homogeneous. Heat to 65 °C and purge with nitrogen gas for 30 min while stirring. Then add 0.04 g of azobisisobutyronitrile and react for 4.5 h. After the reaction is complete, add anhydrous ethanol to precipitate the product and dry it under vacuum to obtain functionalized polyacrylamide.

[0016] Modified bentonite is prepared by the following steps: Step A1: Add 4.5g of sodium-based bentonite to 100mL of deionized water and stir vigorously for 6h. Add 25mL of 0.2mol / L hexadecyltrimethylammonium bromide solution and heat to 60℃ and stir for 24h. Centrifuge, wash, dry and grind to obtain intercalated modified bentonite. Step A2: Disperse 4.5g of intercalated modified bentonite in 50mL of deionized water and stir thoroughly. Add 0.175g of functionalized polyacrylamide and heat to 50℃. Stir at 10000rpm for 5h, freeze dry, and grind to obtain modified bentonite.

[0017] Example 4: A method for preparing a highly hygroscopic bentonite-based mineral desiccant includes the following steps: 26wt% anhydrous magnesium chloride, 12wt% silica gel, 5.5wt% sodium silicate, 7.5wt% potassium silicate, 8wt% attapulgite, with the balance being the modified bentonite prepared in Example 1; Weigh the raw materials according to the weight percentage, mix anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite and the modified bentonite prepared in Example 1 evenly, and vacuum dry to obtain a highly hygroscopic bentonite-based mineral desiccant.

[0018] Example 5: A method for preparing a highly hygroscopic bentonite-based mineral desiccant includes the following steps: 28wt% anhydrous magnesium chloride, 10wt% silica gel, 7.5wt% sodium silicate, 6wt% potassium silicate, 5.5wt% attapulgite, with the balance being the modified bentonite prepared in Example 2; Weigh the raw materials according to the weight percentage, mix anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite and the modified bentonite prepared in Example 2 evenly, and vacuum dry to obtain a highly hygroscopic bentonite-based mineral desiccant.

[0019] Example 6: A method for preparing a highly hygroscopic bentonite-based mineral desiccant includes the following steps: 25wt% anhydrous magnesium chloride, 8wt% silica gel, 4wt% sodium silicate, 7.5wt% potassium silicate, 9wt% attapulgite, with the balance being the modified bentonite prepared in Example 3; Weigh the raw materials according to the weight percentage, mix anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite and the modified bentonite prepared in Example 3 evenly, and vacuum dry to obtain a highly hygroscopic bentonite-based mineral desiccant.

[0020] Comparative Example 1: This comparative example is a desiccant. The difference between this example and Example 6 is that bentonite is used instead of the modified bentonite prepared in Example 3. All other aspects are the same.

[0021] Comparative Example 2: This comparative example is a desiccant. The difference between this example and Example 6 is that pure anhydrous magnesium chloride is used as the desiccant, while the rest are the same.

[0022] Performance testing: The desiccants provided in Examples 4-6 and Comparative Examples 1-2 were placed in the same sealed environment to simulate a high-humidity sealed environment downhole. After standing for 24 hours at 90% RH and 40°C, samples were obtained. Hygroscopicity test: The ability of the above sample to absorb water vapor was tested. The total weight of the desiccant before and after moisture absorption was measured. Each test was performed 5 times, and the average value was taken to calculate the moisture absorption rate. Moisture absorption rate / % = [(total weight of desiccant after water absorption saturation)] [Total weight of desiccant before water absorption] / Total weight of desiccant before water absorption × 100%.

[0023] Deliquescence resistance test: The deliquescence performance of the desiccant after the above test was evaluated by observation. Observation included whether the surface of the desiccant was damp or had water droplets. Five parallel samples were set up for each group of samples. The number and severity of the above deliquescence phenomena were used to comprehensively judge the anti-moisture effect. The less deliquescence and the drier the surface, the better the inhibitory effect of modified bentonite on the moisture reversion behavior of magnesium chloride.

[0024] The test results are shown in Table 1: Table 1: Performance Test Results

[0025] As can be seen from Table 1, the desiccant prepared by this invention has high hygroscopicity and deliquescence resistance, and has good application prospects in high humidity environments.

[0026] The above content is merely an example and illustration of the concept of the present invention. Those skilled in the art can make various modifications or additions to the specific embodiments described or use similar methods to replace them, as long as they do not deviate from the scope defined by the inventive concept, they should all fall within the protection scope of the present invention.

Claims

1. A high hygroscopic swelling bentonite-based mineral desiccant, characterized in that, It is composed of the following raw materials by weight percentage: 20wt%-30wt% anhydrous magnesium chloride, 8wt%-12wt% silica gel, 3wt%-8wt% sodium silicate, 4.5wt%-7.5wt% potassium silicate, 5wt%-10wt% attapulgite, and the balance is modified bentonite. The modified bentonite is prepared by the following steps: Step A1: Add sodium-based bentonite to deionized water and stir vigorously for 6 hours. Add 0.2 mol / L hexadecyltrimethylammonium bromide solution and heat to 50-60℃ and stir at a constant temperature for 24 hours. Centrifuge, wash, dry and grind to obtain intercalated modified bentonite. Step A2: Disperse the intercalated modified bentonite in deionized water and stir thoroughly. Add functionalized polyacrylamide and heat to 40-50℃. Stir at 8000-10000 rpm for 3-5 hours. Freeze dry and grind to obtain modified bentonite. The functionalized polyacrylamide is polymerized by initiation with an initiator using 2-acrylamido-2-methylpropanesulfonic acid, acrylamide and acrylamide functional monomers as monomers. The acrylamide functional monomers contain an imidazole ring quaternary ammonium salt structure, a phosphate ester structure and a terminal acrylamide structure.

2. A high hygroscopic swelling bentonite based mineral desiccant according to claim 1, characterized in that, In step A1, the ratio of sodium bentonite, deionized water, and hexadecyltrimethylammonium bromide solution is 4.5-5 g: 100 mL: 25 mL.

3. A high hygroscopic swelling bentonite based mineral desiccant according to claim 1, characterized in that, In step A2, the amount of functionalized polyacrylamide used is 2.5-3.5 wt% of the mass of the intercalated modified bentonite.

4. The highly hygroscopic bentonite-based mineral desiccant according to claim 1, characterized in that, The functionalized polyacrylamide is prepared by the following steps: Step B1: Add 2-imidazol-1-ethylamine to N,N-dimethylacetamide and stir until homogeneous. Transfer to an ice-water bath, then add triethylamine and stir until homogeneous. Slowly add acryloyl chloride and stir for 30 minutes. Transfer to an oil bath and heat to 65°C for 4.5-5.5 hours. Then transfer to distilled water to precipitate, vacuum filter, and dry to obtain acrylamide imidazolium. Step B2: Add acrylamide imidazole to acetonitrile and stir until homogeneous. Heat to 50-55℃ and add 4-bromo-1-butanol. Reflux for 4 hours. Remove the solvent by rotary evaporation. Remove the solvent further by vacuum distillation. Obtain acrylamide imidazole quaternary ammonium salt by vacuum distillation. Step B3: Add acrylamide imidazole quaternary ammonium salt to tetrahydrofuran and stir well. Add triethylamine and stir under nitrogen for 10 min. Then, under an ice-water bath, add dimethyl chlorophosphate tetrahydrofuran solution dropwise over 1 h. After the addition is complete, react at room temperature for 2 h, then heat to 40℃ and reflux for 5-6 h. Filter, rotary evaporate, wash and dry to obtain acrylamide functional monomer. Step B4: Add 2-acrylamido-2-methylpropanesulfonic acid to deionized water and adjust the pH to 8. Then add acrylamide and acrylamide functional monomer in sequence and stir until homogeneous. Heat to 55-65℃ and purge with nitrogen gas for 30 minutes while stirring. Then add azobisisobutyronitrile and react for 3.5-4.5 hours. After the reaction is complete, add anhydrous ethanol to precipitate the product and dry it under vacuum to obtain functionalized polyacrylamide.

5. The highly hygroscopic bentonite-based mineral desiccant according to claim 4, characterized in that, In step B1, the molar ratio of 2-imidazol-1-ethylamine, acryloyl chloride, and triethylamine is 0.1:0.1-0.105:0.015-0.

018.

6. The highly hygroscopic bentonite-based mineral desiccant according to claim 4, characterized in that, In step B2, the molar ratio of acrylamide imidazole to 4-bromo-1-butanol is 0.1:0.105-0.

12.

7. The highly hygroscopic bentonite-based mineral desiccant according to claim 4, characterized in that, In step B3, the molar ratio of acrylamide imidazole quaternary ammonium salt, triethylamine, and dimethyl chlorophosphate is 0.1:0.12-0.15:0.1-0.

105.

8. The highly hygroscopic bentonite-based mineral desiccant according to claim 4, characterized in that, In step B4, the ratio of 2-acrylamide-2-methylpropanesulfonic acid, deionized water, acrylamide, acrylamide functional monomer, N-vinylpyrrolidone, and azobisisobutyronitrile is 0.01-0.03 mol: 250-300 mL: 0.08-0.12 mol: 0.005-0.01 mol: 0.01-0.03 mol: 0.02-0.04 g.

9. A method for preparing the highly hygroscopic bentonite-based mineral desiccant according to any one of claims 1-8, characterized in that, Includes the following steps: Weigh the raw materials according to the weight percentage, mix anhydrous magnesium chloride, silica gel, sodium silicate, potassium silicate, attapulgite and modified bentonite evenly, and vacuum dry to obtain a highly hygroscopic bentonite-based mineral desiccant.

Images