Preparation method of composite moisture-proof silica gel desiccant

Abstract

This invention relates to the field of desiccant material preparation, and discloses a method for preparing a composite moisture-proof silica gel desiccant, comprising the following steps: mixing and dispersing sodium silicate aqueous solution, sodium pyrophosphate, citric acid and bentonite to obtain an alkaline dispersion precursor slurry; slowly adding dilute sulfuric acid to lower the pH of the system to 7.8-8.2 to obtain a flowable composite sol; simultaneously pumping the composite sol and a crosslinking acid solution containing anhydrous magnesium sulfate into a static mixer for instantaneous crosslinking, controlling the transient pH at the outlet to 3.2-3.8 to form a solid gel block; aging, breaking and cyclically washing the gel block to obtain clean wet particles; immersing the wet particles in a magnesium sulfate aqueous solution for fixed-point loading, and finally dehydrating and activating them through programmed temperature rise to obtain the finished product. This invention achieves spatial decoupling between the framework construction and salt loading, effectively solving the problems of salt leakage and framework pulverization under high hygroscopic conditions.

Description

Technical Field

[0001] This invention relates to the field of desiccant material preparation technology, and in particular to a method for preparing a composite moisture-proof silica gel desiccant. Background Technology

[0002] Silica gel desiccants are used in moisture-proof packaging for food, pharmaceuticals, and precision electronic products due to their stable chemical properties and high safety. To further improve the moisture absorption capacity of conventional silica gel desiccants, existing technologies typically introduce inorganic moisture-absorbing salts into the silica polymerization system to prepare composite silica gel desiccants.

[0003] Existing composite silica gel desiccants have objective shortcomings in their preparation process and practical applications. Traditional preparation methods often employ a one-step blending process, where the hygroscopic salt component is directly mixed during the gelation stage of sodium silicate reaction with an acidic solution. This operation alters the ion concentration of the system, leading to excessively rapid local polymerization of silicic acid, resulting in an uneven distribution of pores within the final silica gel substrate. This directly limits the effective loading capacity of the hygroscopic salt within the micropores.

[0004] In practical applications, when the composite desiccant is in a high-humidity environment and absorbs a large amount of moisture, the inorganic hygroscopic salts inside will deliquesce and transform into a liquid state. Because the porous structure prepared by the one-step method lacks the ability to bind the liquid salts, the deliquesced salt solution easily seeps out from the silica gel, posing a risk of contaminating surrounding protected products. Simultaneously, the conventional pure silica framework has a rigid structure. During the alternating wet and dry process of hygroscopic deliquescence and dehydration, the volume expansion of the internal salts and the capillary contraction force generated by moisture migration create stress within the micropores. This stress cannot be effectively dissipated by the rigid framework, leading to physical cracking or even complete pulverization of the silica gel framework, causing the desiccant structure to disintegrate and lose its performance. Summary of the Invention

[0005] The technical problem solved by this invention is that existing moisture-proof silica gel desiccants are prone to structural breakage and disintegration in alternating wet and dry environments, and that the active salts added inside are prone to physical leakage under high moisture absorption load conditions.

[0006] To address the above problems, the present invention provides the following technical solution: This invention provides a method for preparing a composite moisture-proof silica gel desiccant, comprising the following steps: (1) Preparation of precursor slurry: Sodium silicate aqueous solution, sodium pyrophosphate, citric acid and bentonite are mixed and dispersed in a reactor to prepare alkaline dispersion precursor slurry; (2) Oligopolymer sol induction: Dilute sulfuric acid solution is slowly added dropwise to alkaline dispersion precursor slurry to control the pH value of the system to drop to 7.8-8.2, so as to obtain a flowable composite sol; (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) and the crosslinking acid solution are simultaneously pumped into a static mixer to carry out an instantaneous crosslinking reaction. The transient pH value at the outlet of the mixture is controlled to be 3.2 to 3.8. After the mixture flows out, it forms a solid gel block. The crosslinking acid solution contains dilute sulfuric acid solution and anhydrous magnesium sulfate. (4) Aging and washing: The solid gel block is aged at a constant temperature. After aging, it is broken into particles. The particles are then washed with desalinated water to obtain clean wet particles. (5) Active salt impregnation: The washed wet particles are impregnated in anhydrous magnesium sulfate aqueous solution for fixed-point loading; (6) Dehydration and activation: After filtering the impregnated particles, dehydration and activation are carried out by programmed heating. After cooling, composite moisture-proof silica gel desiccant is obtained.

[0007] By adopting the above technical solution, and through a stepwise gelation process combining precursor oligomerization induction with pipeline instantaneous crosslinking, and by impregnating the pure silica framework with active salt after washing, spatial decoupling of the framework network construction and the hygroscopic salt loading is achieved. Therefore, a high structural stability and leak-proof effect are obtained. The specific reaction mechanism and physicochemical processes are divided into stages as follows: The first stage involves precursor preparation and chelation masking. Sodium pyrophosphate and citric acid, after dissolution, exert a complexing effect in the alkaline sodium silicate system, coordinating and sealing the metal cations within the system to prevent premature contact between the cations and silicate ions, which could lead to localized, uneven gelation. Bentonite, relying on the hydration properties of its interlayer cations, disperses within the silicate system, constructing a mesoscopic layered dispersion phase.

[0008] The second stage involves oligomerization-induced polycondensation. Dilute sulfuric acid is added to slowly lower the pH of the system to 7.8–8.2. Under these conditions, some sodium silicate undergoes a neutralization reaction to generate oligomeric silicic acid, and the silanol groups between silicic acid molecules undergo preliminary dehydration condensation. ≡Si-OH+HO-Si≡→≡Si-O-Si≡+H2O; Due to the weakly alkaline environment, the degree of cross-linking remains at a low level, the system maintains macroscopic fluidity, and a composite sol is formed.

[0009] Secondly, the exogenously added free magnesium ions in the acid solution synergistically interact with the aforementioned endogenous cations, undergoing polynuclear hydroxyl bridge coordination and electrostatic bridging with a large number of silanol groups on the surface of oligomeric silicate: 2(≡Si-O-)+Mg 2+ →≡Si-O-Mg-O-Si≡; The reaction constructs a high-density three-dimensional cross-linked network in a very short time, causing a rheological jump in the material, transforming it from a liquid phase into a solid gel with network rigidity.

[0010] The fourth stage involves targeted loading and structural adaptation. Soluble byproduct salts from the gel pores are removed through cyclic washing to obtain a pure silica-based substrate. Subsequently, anhydrous magnesium sulfate solution is impregnated into the pure pores, embedding the active salts within the silica micropores. The bentonite component embeds itself into the silica matrix through in-situ cross-linking. During subsequent moisture absorption by the desiccant, hydration and expansion occur between the bentonite layers, forming a dynamic water-storing network together with the cross-linked silica framework. The capillary condensation of environmental water molecules on the silica hydroxyl surface synergizes with the chemical coordination of the active salts within the micropores, accommodating the liquid hygroscopic salts and preventing leakage and framework pulverization.

[0011] Preferably, in step (1), the raw materials for preparing the alkaline dispersion precursor slurry include, by weight, 100 parts of sodium silicate aqueous solution with a solid content of 25% to 35%; 1.5 to 3.0 parts of sodium pyrophosphate; 1.5 to 3.0 parts of citric acid; and 15 to 25 parts of bentonite.

[0012] By adopting the above technical solution, the ratio of sodium silicate to bentonite and chelating agent is controlled to ensure that the precursor has rheological stability and suitable ion buffering capacity.

[0013] Preferably, step (1) specifically involves: adding sodium silicate aqueous solution to a reaction vessel equipped with a jacketed temperature control system and a stirrer, adding sodium pyrophosphate and stirring to dissolve; pre-dissolving citric acid in deionized water and then slowly dripping it into the reaction vessel; subsequently, slowly and uniformly adding bentonite, controlling the temperature inside the reaction vessel to be constant at 35℃~45℃, and continuously stirring and dispersing for 1.5~2.5 hours to obtain an alkaline dispersion precursor slurry with a pH value of 10.5~11.5.

[0014] By adopting the above technical solutions, the mixing sequence of materials and constant temperature operating conditions are standardized to prevent the agglomeration of bentonite powder and ensure that the complexing agent in the system is completely dissolved and evenly distributed.

[0015] Preferably, in step (2), the mass fraction of the dilute sulfuric acid solution is 15% to 22%; the dropping rate is controlled so that the pH value of the system decreases within 90 to 120 minutes.

[0016] By adopting the above technical solution, the droplet acceleration rate is controlled to ensure the smooth polycondensation reaction of silica monomers, generating primary silica sol particles of uniform size, and preventing excessively rapid acid-base neutralization from causing localized rapid gelation and destroying the uniformity of the final pore structure.

[0017] Preferably, in step (3), the raw materials for preparing the crosslinking acid solution include, by weight, 30 parts of dilute sulfuric acid solution with a mass fraction of 15% to 25%; 1.0 to 3.0 parts of anhydrous magnesium sulfate; the preparation method of the crosslinking acid solution is as follows: control the temperature inside the anti-corrosion reaction tank to not exceed 35°C, and add anhydrous magnesium sulfate in batches to the dilute sulfuric acid solution and stir continuously until it is dissolved and clear.

[0018] By adopting the above technical solution, an acid solution containing exogenous magnesium ions is pre-prepared to ensure that magnesium ions can enter the sol system synchronously and uniformly with free protons during the instantaneous crosslinking process, thereby improving the uniformity of the metal ion bridging crosslinking reaction.

[0019] Preferably, in step (3), the residence time of the material in the static mixer pipeline is controlled to be 1 to 5 seconds.

[0020] By adopting the above technical solution, the fluid is forced to complete molecular-level mixing in the pipeline, cutting off the dynamic path of macroscopic phase separation, and obtaining a dense hydrogel without macroscopic defects.

[0021] Preferably, in step (4), the temperature for constant temperature aging is 80℃~90℃, and the aging time is 3~5 hours; after aging, the gel block is broken into particles of 2mm~5mm; and the gel is circulated and washed until the conductivity of the washing filtrate drops to 450μS / cm~495μS / cm.

[0022] By adopting the above technical solution, the heating and aging promotes the secondary dehydration and condensation reaction of the residual silanol groups inside the skeleton, thereby improving the mechanical compressive strength of the gel; the conductivity at the washing endpoint is controlled within a low limit, and the inactive water-soluble salts in the pores are thoroughly drained, freeing up physical microporous space for subsequent high-load fixed-point loading of hygroscopic salts.

[0023] Preferably, in step (5), the mass fraction of the anhydrous magnesium sulfate aqueous solution is 10% to 20%; the immersion temperature is 55°C to 65°C; and the immersion time is 2 to 4 hours.

[0024] By adopting the above technical solution, the solution temperature is increased to reduce the surface tension and viscosity of the liquid, thereby enhancing the diffusion kinetic rate of magnesium sulfate molecules into the depth of silica micropores, and achieving deep penetration and high loading of hygroscopic salt in the three-dimensional substrate.

[0025] Preferably, in step (6), the specific implementation method of programmed temperature rise dehydration activation is as follows: first, dry at 75℃~85℃ for 1.5~2.5 hours, then heat up to 145℃~160℃ at a heating rate of 2℃ / min, and activate at a constant temperature for 3~5 hours.

[0026] By adopting the above technical solution, separate drying zones are set up. In the first stage, the free water on the surface of the particles is dried at low temperature. In the second stage, the capillary water and coordinated water inside the mesopores are discharged by slow programmed heating. This avoids the sudden increase in water vapor partial pressure in the pores caused by a single-stage rapid heating, which would lead to the physical collapse of the microstructure.

[0027] Preferably, in step (3), the composite sol is pumped into the static mixer by a screw pump, and the crosslinking acid solution is pumped into the static mixer by a side inlet metering pump; in step (4), the gel block is crushed into particles using a roller crusher; in step (6), the filtered particles are placed in a mesh belt dryer for programmed temperature rise dehydration and activation.

[0028] By adopting the above technical solutions, matching equipment with high-viscosity fluid transport capabilities with continuous heat and mass exchange drying equipment, the continuous operation of the process and the stability of material transfer between different phases are ensured.

[0029] In summary, the present invention has at least one of the following beneficial technical effects: 1. This invention achieves spatial decoupling between framework formation and salt loading by first constructing a pure silica microporous framework through washing, and then performing targeted impregnation with active salt. This process avoids the encroachment of inactive impurity salts on the microporous space in conventional one-step blending methods, significantly increases the effective loading of anhydrous magnesium sulfate, and stably locks the hygroscopic liquid salt inside the mesopores.

[0030] 2. By introducing a bentonite dispersed phase and the multinuclear coordination bridging effect of magnesium ions and silanol groups, the rigid silica skeleton and the interlayer hydration and expansion characteristics of bentonite work synergistically to construct a pore network with a certain volume self-adaptive capability. This effectively dissipates the internal stress of the skeleton caused by severe water absorption and dehydration, and ensures the structural integrity of the particles.

[0031] 3. This invention employs a stepwise process combining oligomerization-induced induction with a static mixer for inline instantaneous crosslinking. This, along with the initial masking of endogenous metal cations by a chelating agent and their subsequent instantaneous release under acidic conditions, disrupts the kinetic path of macroscopic phase separation. This avoids the inhomogeneity caused by premature local gelation, ensuring the uniformity of the micropore distribution within the product. Attached Figure Description

[0032] Figure 1 The following is an online monitoring curve of the rheology and viscosity jump point of the slurry of the present invention; wherein, (a) is a logarithmic coordinate comparison curve of the viscosity of the slurry of Example 1 and Comparative Example 1 during the alkaline dispersion and oligomerization induction stages; (b) is the viscosity jump curve of the system of Example 1 when the pH transiently drops to 3.5 due to the encounter with acid in the simulated pipeline; Figure 2 This is a comparison diagram of the mechanical load between the continuous process of this invention and the traditional in-vessel process; Figure 3The graph shows the evaluation of the material metabolism and salt loading efficiency of the washing process in this invention; (a) is the logarithmic distribution curve of the magnesium ion mass concentration in the waste liquid of Example 1 and Comparative Example 5 in six consecutive washing cycles; (b) is a bar chart comparing the effective loading of magnesium sulfate in the desiccant of the final product of the two processes. Figure 4 This is a static moisture absorption performance analysis diagram of the composite desiccant of the present invention under a gradient high humidity environment; wherein, (a) is the continuous kinetic evolution trajectory of the moisture absorption weight gain rate of the finished particles of Example 1, Example 3, Comparative Example 3 and Comparative Example 4 at 25°C and 90% relative humidity over time; (b) is a bar chart comparing the saturated moisture absorption capacity of the above four groups of test samples after reaching thermodynamic equilibrium at three gradient relative humidity levels of 40%, 60% and 90%; Figure 5 This is a quantitative comparison chart of the macroscopic anti-permeability performance of the composite desiccant under extreme water absorption conditions of the present invention; wherein, (a) is a bar chart of the actual mass of permeated salt solids retained by the bottom filter paper after the four test group samples were saturated with moisture and stood for 120 hours at 97% relative humidity; (b) is a bar chart of the absolute conductivity of the free electrolyte solution of the above-mentioned filter paper with permeated material after ultrasonic oscillation extraction with ultrapure water. Figure 6 This is a comparative graph showing the particle crushing strength and anti-powdering performance under alternating wet / dry conditions according to the present invention; wherein, (a) is a grouped bar chart of the average radial crushing strength of a single particle of the desiccant samples of Example 1, Comparative Example 3 and Comparative Example 4 when they undergo three phase change nodes: initial drying, extreme high humidity adsorption and high temperature thermal activation dehydration; (b) is a bar chart of the mass ratio of fine powder generated after the above samples have completed one complete thermodynamic adsorption-desorption cycle and undergone standard drum mechanical wear. Detailed Implementation

[0033] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments and comparative examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0034] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0035] Sodium silicate aqueous solution (CAS No.: 1344-09-8), with a modulus of 3.0 to 3.3 and a silica mass fraction of 25% to 35%.

[0036] Bentonite (CAS No.: 1302-78-9), whose main mineral component is montmorillonite, has a cation exchange capacity of not less than 80 mmol / 100g, and its powder particle size passes through a 200-mesh standard sieve.

[0037] Concentrated sulfuric acid (CAS No.: 7664-93-9), with a mass fraction of 98%, should be prepared as a dilute sulfuric acid solution with a mass fraction of 15% to 25% before use.

[0038] Anhydrous magnesium sulfate (CAS No.: 7487-88-9), citric acid (CAS No.: 77-92-9), and sodium pyrophosphate (CAS No.: 7722-88-5) are all commercially available substances with known chemical structures in this field, and commercially available analytical grade products were used directly.

[0039] Preparation Example 1: This preparation example provides a method for preparing an alkaline dispersion precursor slurry, comprising the following steps: 100 kg of a sodium silicate aqueous solution with a solid content of 30% was added to a reactor equipped with a jacketed temperature control system and a stirrer. The stirrer was started and set to a speed of 400 rpm. 2.0 kg of sodium pyrophosphate was added and stirred continuously until completely dissolved. 2.0 kg of citric acid was pre-dissolved in 5.0 kg of deionized water and slowly added dropwise to the reactor through a dropping funnel. Subsequently, 20 kg of bentonite was slowly and evenly added, and the temperature inside the reactor was kept constant at 40°C. The mixture was continuously stirred and dispersed for 2.0 hours to obtain an alkaline dispersion precursor slurry with a pH of 11.0.

[0040] Preparation Example 2: This preparation example provides a method for preparing an alkaline dispersion precursor slurry, comprising the following steps: 100 kg of a sodium silicate aqueous solution with a solid content of 35% was added to a reactor equipped with a jacketed temperature control system and a stirrer. The stirrer was started and set to a speed of 500 rpm. 3.0 kg of sodium pyrophosphate was added and stirred continuously until completely dissolved. 3.0 kg of citric acid was pre-dissolved in 7.5 kg of deionized water and slowly added dropwise to the reactor through a dropping funnel. Subsequently, 25 kg of bentonite was slowly and evenly added, and the temperature inside the reactor was kept constant at 45°C. The mixture was continuously stirred and dispersed for 2.5 hours to obtain an alkaline dispersion precursor slurry with a pH of 11.5.

[0041] Preparation Example 3: This preparation example provides a method for preparing an alkaline dispersion precursor slurry, comprising the following steps: 100 kg of a sodium silicate aqueous solution with a solid content of 25% was added to a reactor equipped with a jacketed temperature control system and a stirrer. The stirrer was started and set to a speed of 300 rpm. 1.5 kg of sodium pyrophosphate was added and stirred continuously until completely dissolved. 1.5 kg of citric acid was pre-dissolved in 3.5 kg of deionized water and slowly added dropwise to the reactor through a dropping funnel. Subsequently, 15 kg of bentonite was slowly and evenly added, and the temperature inside the reactor was kept constant at 35°C. The mixture was continuously stirred and dispersed for 1.5 hours to obtain an alkaline dispersion precursor slurry with a pH of 10.5.

[0042] Preparation Example 4: This preparation example provides a method for preparing a crosslinked acid solution, including the following steps: Add 30 kg of a prepared 20% (w / w) dilute sulfuric acid solution to the corrosion-resistant reaction vessel, start stirring, and control the temperature inside the reaction vessel to not exceed 35°C. Add 2.0 kg of anhydrous magnesium sulfate in batches, stirring continuously until dissolved and clear, to obtain a homogeneous cross-linked acid solution for later use.

[0043] Preparation Example 5: This preparation example provides a method for preparing a crosslinked acid solution, including the following steps: Add 30 kg of a prepared 25% dilute sulfuric acid solution to the corrosion-resistant reaction vessel, start stirring, and control the temperature inside the reaction vessel to not exceed 35°C. Add 3.0 kg of anhydrous magnesium sulfate in batches, stirring continuously until dissolved and clear, to obtain a homogeneous cross-linked acid solution for later use.

[0044] Preparation Example 6: This preparation example provides a method for preparing a crosslinked acid solution, including the following steps: Add 30 kg of a prepared 15% dilute sulfuric acid solution to the corrosion-resistant reaction vessel, start stirring, and control the temperature inside the reaction vessel to not exceed 35°C. Add 1.0 kg of anhydrous magnesium sulfate in batches, stirring continuously until dissolved and clear, to obtain a homogeneous cross-linked acid solution for later use.

[0045] Example 1: This embodiment provides a method for preparing a composite moisture-proof silica gel desiccant, including the following steps: (1) Preparation of precursor slurry: Select the alkaline dispersion precursor slurry prepared in Preparation Example 1 and place it in the reactor. Adjust and maintain the temperature inside the reactor at 42°C and set the stirring speed to 450 rpm. (2) Oligopolymer sol induction: Slowly add a 18% by mass dilute sulfuric acid solution to the above precursor slurry, control the dropping rate, and reduce the pH value of the system from 11.0 to 8.0 within 100 minutes to obtain a fluid composite sol; (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) is pumped into the static mixer by a screw pump, and the crosslinking acid solution prepared in Preparation Example 4 is pumped into the static mixer by a side inlet metering pump. The flow rate ratio is adjusted so that the transient pH value at the outlet of the mixture is 3.5, the material stays in the pipeline for 3 seconds, and the effluent directly enters the collection tank to form a solid gel block. (4) Aging and washing: The gel block was kept at a constant temperature in an aging tank at 85°C for 4 hours. After aging, the gel block was crushed into particles of 2 mm to 5 mm by a double roller crusher and washed with deionized water until the conductivity of the washing filtrate was 480 μS / cm. (5) Active salt impregnation: The washed wet granules are put into an anhydrous magnesium sulfate aqueous solution with a mass fraction of 15% and impregnated at 60°C for 3 hours; (6) Dehydration and activation: After the impregnation, the granules are filtered dry and placed in a mesh belt dryer. They are first dried at 80°C for 2 hours, and then heated to 150°C at a heating rate of 2°C / min. They are then kept at a constant temperature for 4 hours and cooled to obtain the finished product.

[0046] Example 2: This embodiment provides a method for preparing a composite moisture-proof silica gel desiccant, including the following steps: (1) Preparation of precursor slurry: Select the alkaline dispersion precursor slurry prepared in Preparation Example 2, maintain the temperature inside the reactor at 45°C and the stirring speed at 500 rpm; (2) Oligopolymer sol induction: A 22% by mass dilute sulfuric acid solution was slowly added dropwise to the above precursor slurry, and the dropping rate was controlled. The pH value of the system was reduced from 11.5 to 8.2 within 120 minutes to obtain a composite sol. (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) is pumped into the static mixer by a screw pump, and the crosslinking acid solution prepared in Preparation Example 5 is pumped into the static mixer by a side inlet metering pump. The flow rate ratio is adjusted so that the transient pH value at the outlet of the mixture is 3.8, the material stays in the pipeline for 1 second, and the effluent enters the collection tank to form a solid gel block. (4) Aging and washing: The gel block was kept at a constant temperature in an aging tank at 90°C for 5 hours. After aging, the gel block was broken into particles of 2 mm to 5 mm and washed with deionized water until the conductivity of the washing filtrate was 450 μS / cm. (5) Active salt impregnation: The washed wet granules are put into an anhydrous magnesium sulfate aqueous solution with a mass fraction of 20% and impregnated at 65°C for 4 hours; (6) Dehydration and activation: After the impregnation, the granules are filtered dry and placed in a mesh belt dryer. They are first dried at 85°C for 2.5 hours, and then heated to 160°C at a heating rate of 2°C / min. They are then kept at a constant temperature for 5 hours and cooled to obtain the finished product.

[0047] Example 3: This embodiment provides a method for preparing a composite moisture-proof silica gel desiccant, including the following steps: (1) Preparation of precursor slurry: Select the alkaline dispersion precursor slurry prepared in Preparation Example 3, maintain the temperature inside the reactor at 35°C and the stirring speed at 300 rpm; (2) Oligopolymer sol induction: Slowly add a 15% by mass dilute sulfuric acid solution to the above precursor slurry, control the dropping rate, and reduce the pH value of the system from 10.5 to 7.8 within 90 minutes to obtain a composite sol; (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) is pumped into the static mixer by a screw pump, and the crosslinking acid solution prepared in Preparation Example 6 is pumped into the static mixer by a side inlet metering pump. The flow rate ratio is adjusted so that the transient pH value at the outlet of the mixture is 3.2, the material stays in the pipeline for 5 seconds, and the effluent enters the collection tank to form a solid gel block. (4) Aging and washing: The gel block was kept at a constant temperature in an aging tank at 80°C for 3 hours. After aging, the gel block was broken into particles of 2 mm to 5 mm and washed with deionized water until the conductivity of the washing filtrate was 495 μS / cm. (5) Active salt impregnation: The washed wet granules are put into an anhydrous magnesium sulfate aqueous solution with a mass fraction of 10% and impregnated at 55°C for 2 hours; (6) Dehydration and activation: After the impregnation, the granules are filtered dry and placed in a mesh belt dryer. They are first dried at 75°C for 1.5 hours, and then heated to 145°C at a heating rate of 2°C / min. They are then kept at a constant temperature for 3 hours and cooled to obtain the finished product.

[0048] Example 4: This embodiment provides a method for preparing a composite moisture-proof silica gel desiccant, including the following steps: (1) Preparation of precursor slurry: Select the alkaline dispersion precursor slurry prepared in Preparation Example 1, maintain the temperature inside the reactor at 42°C and the stirring speed at 450 rpm; (2) Oligopolymer sol induction: Slowly add a 20% by mass dilute sulfuric acid solution to the above precursor slurry, control the dropping rate, and reduce the pH value of the system from 11.0 to 8.0 within 110 minutes to obtain a composite sol; (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) is pumped into the static mixer by a screw pump, and the crosslinking acid solution prepared in Preparation Example 4 is pumped into the static mixer by a side inlet metering pump. The flow rate ratio is adjusted so that the transient pH value at the outlet of the mixture is 3.5, the material stays in the pipeline for 2 seconds, and the effluent enters the collection tank to form a solid gel block. (4) Aging and washing: The gel block was kept at a constant temperature in an aging tank at 85°C for 4.5 hours. After aging, the gel block was broken into particles of 2 mm to 5 mm and washed with deionized water until the conductivity of the washing filtrate was 470 μS / cm. (5) Active salt impregnation: The washed wet granules are put into an 18% anhydrous magnesium sulfate aqueous solution and impregnated at 60°C for 3.5 hours; (6) Dehydration and activation: After the impregnation, the granules are filtered dry and placed in a mesh belt dryer. They are first dried at 80°C for 2 hours, and then heated to 155°C at a heating rate of 2°C / min. They are then kept at a constant temperature for 4 hours and cooled to obtain the finished product.

[0049] Comparative Example 1: Compared with Example 1, the difference is that sodium pyrophosphate and citric acid were not added in step (1) precursor slurry preparation, but all other aspects are the same.

[0050] Comparative Example 2: Compared with Example 1, the difference is that the pipeline instantaneous crosslinking in step (3) is omitted, the composite sol obtained in step (2) is kept in the reactor, and the crosslinking acid solution prepared in Example 4 is added dropwise to directly reduce the pH value of the system to 3.5 in the reactor for in-reactor gelation. The rest are the same.

[0051] Comparative Example 3: Compared with Example 1, the difference is that bentonite was not added in step (1) of precursor slurry preparation, but the rest are the same.

[0052] Comparative Example 4: Compared with Example 1, the difference is that commercially available conventional macroporous silica gel particles are directly used to replace the sodium-free composite gel particles obtained in steps (1) to (4), and the active salt impregnation in step (5) and the dehydration activation in step (6) are directly carried out. The rest are the same.

[0053] Comparative Example 5: Compared with Example 1, the difference is that all the anhydrous magnesium sulfate required in step (5) is added directly to the reactor in the oligomeric sol induction stage of step (2) in advance, and the high-concentration active salt impregnation process in the subsequent step (5) is omitted, while the rest are the same.

[0054] Test Example 1: The experimental steps are as follows: (1) The operation process of step (1) of Example 1 and Comparative Example 1 were used as the monitoring objects. The ingredients were prepared according to their respective formulas in a reaction vessel equipped with jacket temperature control and constant speed stirring (set to 400 rpm). Using a digital rotational viscometer, the probe was fixed at a specific depth below the liquid surface in the reaction vessel, and the online viscosity acquisition program was started, with the sampling frequency set to record data once per minute. During the alkaline dispersion stage (0 to 120 minutes) after the ingredients were added, the viscosity evolution and pH fluctuation of the system were continuously monitored.

[0055] (2) After the alkaline dispersion is complete, dilute sulfuric acid is slowly added dropwise to the reactor using a peristaltic pump according to the parameters in step (2) of Example 1. During the 100-minute dropwise addition cycle, the rheological data changes during the transition from strongly alkaline to slightly alkaline (approximately pH 8.0) are continuously recorded synchronously. The same acid addition operation is performed on Comparative Example 1. Since no chelating agent is added, it is necessary to observe and stop data acquisition when the system exhibits severe binding or gel hardening that causes the viscometer to exceed its range.

[0056] (3) The composite sol sample obtained in Example 1 at the end of the acid dropping phase (i.e., at the end of the 120 to 220 minute stage) was placed in a beaker equipped with a high-speed variable frequency stirrer. A crosslinked acid solution was injected into the beaker at an extremely high flow rate using a precision syringe pump to simulate the fluid conditions in a static mixer. The amount of acid injected was controlled to cause the pH of the system to drop sharply to 3.5 within seconds. During this period, the sampling frequency of the viscometer was increased to once every 0.5 seconds to capture the viscosity mutation behavior triggered by the sudden drop in pH.

[0057] The experimental results are shown in Table 1.

[0058] Table 1. Online monitoring data of slurry viscosity changes with time and pH:

[0059] According to Table 1 and Figure 1The data showed that the rheological characteristics of the system during the precursor dispersion stage differed significantly. In Comparative Example 1, without sodium pyrophosphate and citric acid, the viscosity of the slurry rapidly increased from the low viscosity range to over 3000 mPa·s upon the addition of bentonite powder, and then deteriorated uncontrollably during subsequent dispersion and acid addition. Instrument measurements showed that the rotor load was nearing its limit in the later stages, and in laboratory operations, a sharp increase in the running resistance of the stirring paddle and the accompanying hardening and agglomeration of local materials could be visually observed. The chemical reason for this early abnormal viscosity change was that the calcium, aluminum, and other metal cations with empty orbitals released from the edge of the bentonite lattice under strong alkaline conditions directly coordinated and neutralized the high concentration of polysilicate ions in the water glass solution without any masking, inducing disordered and irreversible bridging flocculation. In Example 1, which introduced a multi-stage chelating agent, the viscosity remained stable at an extremely low level below 200 mPa·s throughout the 120-minute strongly alkaline dispersion period. This data confirms that the highly negatively charged anionic groups dissociated from the multi-stage chelating agent effectively encapsulate and electrostatically isolate free multivalent metal ions, forcibly blocking the initial cross-linking side reactions, and providing a sufficient low-viscosity hydrodynamic window for the sodium silicate solution to thoroughly penetrate the bentonite interlayer for electrode stripping.

[0060] As the system gradually entered the oligomeric sol induction phase, in Example 1, with the continuous addition of acid, the pH dropped to 8.03 after more than 100 minutes, and the viscosity showed a controlled, gentle increase to 514 mPa·s. At this time, although the silica molecules in the system began to condense, the overall material still maintained good liquid flowability because the multivalent crosslinking agent was still blocked, which could meet the engineering requirements for continuous pressurized transportation by screw pump. The key node that truly triggered the macroscopic phase change occurred during the transient acid addition operation inside the simulated pipeline. When the external crosslinking acid was rapidly injected, bringing the pH close to 3.5, the system underwent a violent kinetic response within just 3 seconds, and the viscosity measurement value jumped sharply from 514 to 50,000, forming a gel state. This extreme rheological leap stems from the influx of hydrogen ions disrupting the previous coordination equilibrium. The protonation of pyrophosphate and citrate ions leads to a precipitous drop in their chelation constants, releasing previously accumulated and blocked endogenous metal cations in situ. These cations, along with free magnesium ions introduced from the acid solution, form a high-density three-dimensional cross-linked network with the highly reactive oligomeric silicate surface and silanol groups through polynuclear hydroxyl bridge coordination and electrostatic bridging. The results reproduce the physicochemical process of the transformation from a viscous fluid to a highly rigid solid network, demonstrating that the spatial decoupling design using pH as a chemical switch effectively avoids the reaction lock-up problem that easily occurs in traditional in-reactor synthesis, providing a reliable process route for the continuous large-scale production of porous network structures.

[0061] Test Example 2: The experimental steps are as follows: (1) The continuous conveying and gelling section using a combination of screw pump and static mixer in Example 1, and the traditional batch gelling section using an anchored stirring tank in Comparative Example 2 were selected as engineering monitoring and comparison objects. Contact-type dynamic torque sensors were installed on the stirring shaft of the reactor in Comparative Example 2 and the material conveying pump drive shaft in Example 1, respectively. The system data acquisition frequency was set to twice per second to track the changes in mechanical load of the equipment under different hydrodynamic conditions in real time.

[0062] (2) The gelation and crosslinking processes of the two sets of experiments were started simultaneously. In Example 1, the composite sol and crosslinking acid solution were continuously pumped into the static mixer pipeline through a metering pump at a set volume ratio; in Comparative Example 2, the crosslinking acid solution was added dropwise into the reactor with constant-speed stirring at the same overall flow rate ratio. The torque parameter evolution of the system from pH 8.0 to 3.5 was continuously recorded until the process ended or the equipment was shut down due to mechanical overload.

[0063] (3) Collect the final gel solid material produced by both systems. In Example 1, the gel was continuously collected directly from the collection tank at the end of the pipeline; in Comparative Example 2, the unreacted liquid phase was drained after forced shutdown, and the gel blocks were manually removed from the reactor wall and stirring blades. The collected nascent gel blocks were cross-sectionally inspected and physically sieved to remove soft gel masses containing unreacted free acid and dead zone clumps that were hardened due to excessively high local concentrations. The mass of the qualified gel blocks with uniform texture after sieving was accurately weighed, and its mass percentage of the total theoretical gel yield was calculated.

[0064] The experimental results are shown in Table 2.

[0065] Table 2. Statistics on mechanical load and gel yield during the transient crosslinking stage:

[0066] According to Table 2 and Figure 2The data shows that, in Comparative Example 2, when acid was added to form a gel in a traditional reactor, the mechanical load on the stirring spindle exhibited a destructive exponential increase. This phenomenon is frequently observed in actual engineering scale-up operations. When the pH of the mixed system crosses the highest activity zone of the silica polycondensation reaction (around pH 5.0–7.0) and rapidly approaches 3.5, the polymerization and cross-linking rate of silica molecules suddenly jumps by orders of magnitude. Combined with the unique pH-sensitive ion shielding mechanism of this invention, a large number of previously masked polyvalent metal cations are instantly released at this acidity, acting as highly active chemical cross-linking nodes. This drastic reconstruction of the microscopic network structure directly leads to the macroscopic material completing a phase transition from liquid to high-rigidity solid in less than two minutes. The rotor gets trapped in the viscoelastic dead zone, causing a stall and triggering the frequency converter to cut off the power. Because the shear field inside the reactor completely fails at this point, the residual acid cannot continue to transfer mass with the unreacted sol on the outside. This not only creates a destructive torque peak of up to 1000 N·m, but also results in the system being filled with unreacted liquid pockets and over-crosslinked hard lumps. The yield of qualified gel blocks can only be barely maintained at around 34%. This inherent contradiction between laboratory bench and industrial reactor scale-up is the core engineering barrier restricting the large-scale mass production of multifunctional composite materials.

[0067] In contrast, the system in Example 1 exhibited fluid dynamics characteristics where the pump torque remained consistently low and stable around 13 N·m throughout a full 300-second operating cycle. This data confirms the feasibility of the reaction space decoupling mechanism, which delivers highly intense oligomerization condensation and in-situ cation release into the pipeline of the static mixer. The high-intensity micro-turbulence generated by the internal components forces proton transfer and concentration homogenization between fluid elements within milliseconds. During the brief few seconds the material resides in the pipeline, it is merely in a critical state of the induction precursor phase and does not form a macroscopic three-dimensional rigid framework that hinders macroscopic flow. True bulk solidification only occurs after the homogeneous mixture with sufficient kinetic energy leaves the pipeline and enters the collection tank. This operational logic, which completely separates the physical mixing zone from the chemical solidification zone, fundamentally avoids the hard interference between mechanical agitators and high-viscosity rheosomes. Flow field drive replaces mechanical shearing, ensuring absolute homogeneity of the gelation environment throughout the batch, resulting in an extremely complete internal micro-crosslinking network and ultimately achieving an effective gelation yield of over 96%. This test confirms the decisive role of introducing pipeline-type continuous transient control in material uniformity and production continuity in a highly reactive coordination crosslinking system.

[0068] Test Example 3: The experimental steps are as follows: (1) The wet gel particles prepared in Example 1 and the nascent gel particles prepared by the pre-addition of salts in Comparative Example 5 were selected as experimental comparison objects. Both groups of materials were treated in parallel in the washing process of step (4), and were circulated and rinsed using washing columns of the same specifications and deionized water with a constant flow rate. The washing cycle was set to 6 times, and the rinsing ratio for each wash was water:gel = 2:1 (volume ratio). After each washing cycle, the washing waste liquid of that batch was accurately collected.

[0069] (2) The mass concentration of magnesium ions in each stage of the washing wastewater was determined by EDTA complexometric titration. A 50 mL sample of wastewater was taken, and the pH was adjusted to 10.0 with ammonia-ammonium chloride buffer solution. Using Chrome Black T as an indicator, the solution was titrated with standard EDTA solution until it changed from purple to pure blue. The amount of magnesium lost from the wastewater was calculated based on the amount consumed. This process was used to assess in real time the stripping effect of washing intensity on the active ingredients.

[0070] (3) After all washing cycles are completed and the dehydration and activation in step (6) are finished, desiccant particles from each component are randomly sampled. A certain mass of the finished product is weighed and crushed and dissolved. The actual mass percentage of magnesium sulfate loaded inside the final product is determined again by titration. At the same time, the content of residual sodium sulfate impurities in the finished product is detected by ion chromatography to verify the thoroughness of the washing process in removing by-products, and to calculate the effectiveness of the process of this invention in resolving the elution contradiction.

[0071] The experimental results are shown in Table 3.

[0072] Table 3. Evolution of magnesium ion concentration in washing wastewater and statistics of finished product salt loading rate:

[0073] According to Table 3 and Figure 3 Based on the data, the step-by-step processing strategy proposed in this invention demonstrates significant technical advantages in addressing the inherent paradox of "washing and impurity removal" versus "activity retention" in chemical production. In the test data of Comparative Example 5, it can be observed that while adding the hygroscopic active salt magnesium sulfate in advance during the gel formation stage simplifies the process, a large amount of magnesium ions are drastically lost with the wastewater during the subsequent washing process to remove the byproduct sodium sulfate. The magnesium ion concentration in the first-stage washing wastewater reached as high as 8452.7 mg / L, meaning that the vast majority of the active salt was stripped from the silica gel pores before it could function. Even though both sets of experiments ultimately reduced the residual sodium sulfate to an extremely low level below 0.01%, the magnesium sulfate loading rate of the finished product in Comparative Example 5 was only 2.16%, almost losing its practical value as a high-performance composite desiccant.

[0074] In contrast, Example 1 exhibited minimal ion loss during the washing stage, with the trace magnesium in the waste liquid originating solely from the minimal auxiliary crosslinking agent used in Preparation Examples 4-6 for transient crosslinking. This phenomenon demonstrates that the present invention, through process decoupling, first thoroughly removes sodium sulfate impurities affecting porosity using high-intensity washing in a state without active salt loading, thus constructing a pure silicon-oxygen-mineral composite framework. Since the main hygroscopic salt, magnesium sulfate, is subsequently impregnated in a constant-temperature liquid phase at a specific concentration in step (5), it is precisely embedded in the already cleaned aged pores. From the final analysis results in Table 3, the salt loading of the finished product in Example 1 is stable at 17.84%, approximately 8 times higher than that of Comparative Example 5. Through this material decoupling mechanism, this scheme not only ensures the desiccant possesses extremely high chemical purity, avoiding the potential decrease in hygroscopic kinetics caused by residual sodium salt, but also maximizes the retention of active salt concentration, thereby fundamentally guaranteeing the product's strong water molecule capture ability and thermodynamic stability under high humidity conditions.

[0075] Test Example 4: The experimental steps are as follows: (1) The dehydrated and activated finished products of Examples 1, 3, Comparative Example 3 (without bentonite) and Comparative Example 4 (commercially available silica gel substrate) were selected as the subjects for hygroscopic kinetic evaluation. All test samples were placed in a vacuum drying oven at 150°C for 2 hours to eliminate the interference of background moisture. After cooling to room temperature, approximately 10.00 g of particle sample was accurately weighed using an analytical balance with an accuracy of 0.0001 g and evenly spread in a petri dish with a pre-calibrated basic mass.

[0076] (2) Start the programmable temperature and humidity test chamber, keep the internal ambient temperature constant at 25°C, and set three independently running humidity gradient test batches with relative humidity (RH) set to 40%, 60% and 90% respectively. After the temperature and humidity field inside the chamber reaches a balanced and stable state, quickly move the petri dish containing the sample into the same horizontal rack in the test chamber.

[0077] (3) The petri dishes were removed and weighed rapidly at set logarithmic time intervals (i.e., 2, 4, 8, 12, and 24 hours in the initial stage of moisture absorption, and 48, 72, 96, 120, and 144 hours in the middle and later stages). Each weighing operation was completed within 15 seconds to avoid external environmental disturbances. Based on the difference in mass increase at different time points, the percentage of moisture gain under corresponding conditions for each group of samples was calculated until the mass fluctuation after three consecutive weighings was less than 0.5%, at which point the system was considered to have reached the static adsorption thermodynamic saturation point.

[0078] The experimental results are shown in Table 4.

[0079] Table 4. Hygroscopic kinetics and other humidity saturation capacity data of the composite desiccant at 25℃ / 90% RH:

[0080] According to Table 4 and Figure 4 The data shows that the microporous structure constructed in this invention exhibits significant mass transfer advantages under gradient water vapor partial pressure. In a test environment with a relative humidity of 90%, the sample of Example 1 showed a steep moisture absorption climb trajectory within the initial 24 hours, reaching a limit moisture absorption mass fraction of 86.1% at approximately 144 hours. Conventional physical mixing processes often clog external pores due to premature crystallization and hydration of salts when facing high-concentration water vapor interface diffusion. This mass transfer resistance blocking phenomenon was confirmed in the data evolution of Comparative Example 4. The critical threshold for capillary condensation of commercially available macroporous silica gel as a carrier is limited by the pore size distribution. The magnesium sulfate hydrate liquid film precipitated on its surface constitutes an insulating layer at the gas-solid interface, causing it to fall into an adsorption lag state after 72 hours, and ultimately the macroscopic saturated moisture absorption is physically cut off at around 60%.

[0081] A thorough comparison of the hygroscopic kinetics between Example 1 and Comparative Example 3 (lacking a two-dimensional flexible component) reveals the underlying mechanisms of pore evolution in the composite material. Comparative Example 3 even slightly outperformed Example 1 in the initial adsorption rate, likely due to the higher initial specific surface area of ​​the pure silica-oxygen framework providing more apparent physical adsorption sites. However, after 72 hours and entering the deep hydration stage, the hygroscopic curve of Comparative Example 3 exhibited an abnormally flattened passivation, ultimately stalling at 76.4% capacity. This subsequent weakness stemmed from the microscopic volume repulsion caused by the phase transition expansion of anhydrous magnesium sulfate within the pores. In Example 1, the bentonite layered electrode, through in-situ cross-linking and embedding into the silica matrix, did not significantly encroach on the micropore space. Instead, utilizing the hydration and expansion characteristics of its interlayer cations, it collaborated with the silica-oxygen framework to construct a dynamically adaptive mesoscopic elastic water storage network. During the rapid increase in ambient humidity, the capillary condensation kinetics of water molecules on the silanol surface and the chemical coordination process of the deep active salts achieved a spatially coordinated alternation. The aforementioned dynamic adaptive regulation at the structural level breaks through the inherent pore volume limit of traditional rigid carriers, enabling the composite matrix to not only maintain a rapid transient response speed, but also release extremely high water storage potential energy under extreme conditions.

[0082] Test Example 5: The experimental steps are as follows: (1) Particle samples from Examples 1, 4, Comparative Examples 3, and 4, which had reached thermodynamic saturation after 144 hours of moisture absorption at 25°C and 90% relative humidity, were extracted from Test Example 4 as experimental subjects. Standard quantitative slow qualitative filter paper was prepared, pre-dried in an oven at 105°C for 2 hours, cooled in a desiccator, and its initial dry weight was weighed using a high-precision balance of 0.01% and marked accordingly.

[0083] (2) The particle samples that have reached hygroscopic saturation are evenly spread in a single layer in the central area of ​​the corresponding numbered quantitative filter paper, ensuring that there is a small gap between the particles to avoid capillary liquid bridge effect. Then, the filter paper carrying the sample is transferred into a sealed glass desiccator containing a supersaturated potassium sulfate solution (which can provide a constant relative humidity of about 97% at 25°C). The desiccator is then left to stand continuously in a constant temperature room at 25°C for 120 hours to artificially create an extreme high humidity overload environment to stimulate potential capillary permeation behavior.

[0084] (3) After the set time is reached, carefully remove the filter paper and use plastic tweezers to remove all test particles from the surface. Observe and record the macroscopic wetting state of the filter paper surface, and place the damp filter paper after particle removal into a 105℃ oven to dry it thoroughly to constant weight. By calculating the difference between the mass of the dried filter paper and the initial dry weight, the mass of salt solids that leaked from the inside of the desiccant into the external environment can be accurately quantified.

[0085] (4) To further verify the ion concentration of trace exudates, each dried filter paper was cut into small pieces and immersed in an Erlenmeyer flask containing 50.0 mL of ultrapure water (basic conductivity less than 0.1 μS / cm). The mixture was extracted by shaking in an ultrasonic water bath for 30 minutes, and the absolute conductivity of the extract was measured using a high-precision portable conductivity meter. Electrochemical parameters were used to indirectly verify the performance of the antipermeability solution.

[0086] The experimental results are shown in Table 5.

[0087] Table 5. Quantitative assessment data of macroscopic permeate from desiccant under saturated hygroscopic conditions:

[0088] According to Table 5 and Figure 5 According to the data, the internally flexible and externally rigid microreactor structure constructed in this invention plays a decisive physical isolation role in blocking the deliquescent seepage of inorganic salts. A very typical structural failure phenomenon was observed when measuring the quantitative filter paper of Comparative Example 4. Before drying, the filter paper exhibited a large area of ​​semi-transparent, wet, and sticky state, ultimately retaining a seepage salt mass as high as 234.3 mg, and the conductivity of the extract soared to 2874.6 μS / cm. Commercially available conventional silica gel carriers rely solely on physical capillary pores to accommodate magnesium sulfate. When the salt absorbs a large number of water molecules and undergoes a transformation from anhydrous to heptahydrate crystal form, its volume expands dramatically by more than 100%. This microscopic phase transition-induced local crystallization stress directly exceeds the mechanical yield limit of the pure silicon-oxygen framework, causing the originally dense pore network to expand with microcracks or even macroscopically pulverize and break apart. Without the framework's constraint, the high-concentration salt solution, driven by both concentration difference and gravity, leaks without resistance into the external environment along the cracks. This is a fatal liquid leakage contamination accident in the moisture-proof packaging of precision electronic or optical instruments.

[0089] Comparative Example 3, which removed the flexible bentonite component, also exhibited leakage defects, with obvious spot-like water stains left on its filter paper surface and an exudate mass close to 38 mg. Although its chemically cross-linked silica matrix had slightly stronger tensile strength than commercially available physically doped silica, the purely rigid network still could not effectively absorb the continuously accumulated crystal expansion energy under 120 hours of extreme overload and high humidity pressure. The forced deformation of the micropores eventually evolved into structural leakage points. The data from Examples 1 and 4, however, fully met our design expectations for spatial decoupling and buffering mechanisms. Even under extreme conditions where the particles had completely reached their thermodynamic hydration saturation point, the surface of the supporting filter paper remained dry, and the exudate mass was firmly suppressed to the edge of the extremely low detection limit of 1.4 to 2.2 mg, with the extract conductivity only showing slight fluctuations relative to the background environment. This result confirms that the flexible volume buffer pool established by the two-dimensional bentonite nanosheets in the three-dimensional silica framework is truly effective. When highly hydrated magnesium sulfate crystals encounter physical constraints from an external rigid network during expansion, the resulting directional stress is absorbed by the slippage of bentonite plates with extremely high ductility between the layers. Free water molecules within the system are forcibly bound within the mineral layers, transforming into bound water or gel water, thus severing the seepage pathway of macroscopic liquid water. This achieves a blockage against deliquescent leakage from both thermodynamic and hydrodynamic perspectives.

[0090] Test Example 6: The experimental steps are as follows: (1) The finished particles from Example 1, Comparative Example 3, and Comparative Example 4 were selected as the test objects for mechanical property evolution. To eliminate data bias caused by size effect, all samples were pre-screened using standard test sieves, and spherical or near-spherical particles with a particle size distribution in the range of 3.0 mm to 4.0 mm were uniformly collected. Each group of screened particles was divided into three test batches, corresponding to the mechanical determination of "initial dry state", "fully hygroscopic saturated state" and "thermally activated regeneration state", respectively.

[0091] (2) For the "initial dry state" batch, fresh samples were directly taken from the dehydrated and activated samples at 150℃ for testing. For the "fully hygroscopic saturated state" batch, the particles were placed in a constant temperature and humidity chamber at 25℃ and 90% relative humidity for 144 hours for continuous exposure to confirm that their mass no longer increased and that they reached hygroscopic thermodynamic equilibrium. For the "thermally activated and regenerated state" batch, the particles that had reached the aforementioned hygroscopic saturation state were extracted and transferred back into a 150℃ forced-air drying oven for 4 hours of constant temperature deep dehydration to simulate a complete adsorption-desorption cycle in industrial applications.

[0092] (3) An intelligent particle strength tester equipped with a high-precision micro force sensor was used to test the average radial crushing strength of the three batches of samples. During the test, the probe displacement rate was set to 1.0 mm / min. 50 intact particles were measured in parallel for each group. After removing obvious outliers, the arithmetic mean was taken as the final crushing strength (N / particle). After the strength test was completed, the crushed particle fragments from the "thermally activated regeneration state" batch were collected and combined with the remaining samples into a standard drum crushability tester, which was run at 25 rpm for 10 minutes. Subsequently, the material inside the drum was collected and manually sieved using a 60-mesh metal standard sieve. The mass of the fine powder that passed through the sieve was accurately weighed, and the macroscopic pulverization and breakage rate of the sample was calculated accordingly.

[0093] The experimental results are shown in Table 6.

[0094] Table 6. Test data on mechanical strength and pulverization rate of desiccant particles under alternating wet and dry conditions:

[0095] According to Table 6 and Figure 6 Data shows that conventional inorganic salt composite materials face extremely stringent structural mechanical challenges when switching between dry and wet states. The industry has long observed that pure silica skeletons are highly susceptible to fracture after being loaded with hygroscopic salts, a phenomenon fully confirmed by the basic data of Comparative Example 3. Because this comparative example uses a pure silica network for in-situ crosslinking, it exhibits a crushing strength as high as 92.3 N in the initial dry state, demonstrating the high modulus rigidity characteristics typical of inorganic non-metallic materials. When the anhydrous magnesium sulfate embedded within the pores absorbs water vapor and undergoes a hydration reaction to form polyhydrate crystals, its volume irreversibly expands several times. The crystallization stress generated by this micro-phase transition acts directly on the inelastic silica pore walls, causing the strength of Comparative Example 3 to plummet to 31.8 N after moisture saturation, with a decay rate exceeding 65%. Subsequent thermal dehydration at 150°C, coupled with the violent vaporization and dissipation of water molecules and the pre-existing microcrack network, caused the skeleton to completely collapse, ultimately resulting in a pulverization and breakage rate approaching 23%. Comparative Example 4, a commercially available physically doped substrate, performed even worse. Its large-pore, thin-walled structure, under the dual tearing of crystal expansion and thermal stress, had a strength of only 6.8 N after cycling, with nearly half of the material turning into dust, making it unsuitable as a packaging moisture-proof and protective material.

[0096] The stress buffering mechanism constructed in this scheme demonstrated a decisive intervention effect under the aforementioned harsh boundary conditions. The compressive strength of Example 1 was slightly lower than that of Comparative Example 3 in the initial stage, but this was precisely because the introduction of flexible bentonite appropriately reduced the overall brittle modulus of the system. After undergoing the same 144 hours of extreme high-humidity expansion compression, Example 1 still retained a high strength level of 73.2 N, with the attenuation effectively controlled within 15%. More importantly, after high-temperature regeneration, its mechanical strength exhibited a significant self-healing rebound phenomenon, recovering to 82.7 N. During continuous phase transformation and mechanical wear, the final pulverization and breakage rate of Example 1 was only 2.14%, maintaining extremely high macroscopic integrity. The underlying mechanism for this excellent mechanical stability lies in the semi-rigid interpenetrating network formed between the two-dimensional bentonite nanosheets and the three-dimensional rigid silica matrix. The anisotropic stress generated by the volume expansion of the crystalline salt is absorbed by the interlayer slippage of a large number of parallel-oriented bentonite plates in this multi-level structure. The flexible buffer actively provides space to absorb the geometric deformation of crystal growth, avoiding the concentrated burst of stress at the nodes of the silicon-oxygen backbone. This mesoscopic mechanical design, which combines rigidity and flexibility, fundamentally resolves the intrinsic contradiction between salt phase transformation and carrier stiffness, ensuring the long-term structural service life of porous hygroscopic materials under complex environmental conditions.

[0097] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a composite moisture-proof silica gel desiccant, characterized in that, Includes the following steps: (1) Preparation of precursor slurry: Sodium silicate aqueous solution, sodium pyrophosphate, citric acid and bentonite are mixed and dispersed in a reactor to prepare alkaline dispersion precursor slurry; (2) Oligopolymer sol induction: Dilute sulfuric acid solution is slowly added dropwise to the alkaline dispersion precursor slurry to control the pH value of the system to drop to 7.8-8.2, so as to obtain a flowable composite sol; (3) In-line instantaneous crosslinking: The composite sol obtained in step (2) and the crosslinking acid solution are simultaneously pumped into a static mixer to carry out an instantaneous crosslinking reaction. The transient pH value at the outlet of the mixture is controlled to be 3.2 to 3.

8. After the mixture flows out, a solid gel block is formed. The crosslinking acid solution contains dilute sulfuric acid solution and anhydrous magnesium sulfate. (4) Aging and washing: The solid gel block is aged at a constant temperature. After aging, it is broken into particles. The particles are then washed with desalinated water to obtain clean wet particles. (5) Active salt impregnation: The washed wet particles are impregnated in anhydrous magnesium sulfate aqueous solution for fixed-point loading; (6) Dehydration and activation: After filtering the impregnated particles, dehydration and activation are carried out by programmed temperature rise. After cooling, the composite moisture-proof silica gel desiccant is obtained.

2. The method of claim 1, wherein the moisture absorbing silica gel is prepared by mixing 100 parts by weight of silica gel, 0.1 to 10 parts by weight of the moisture absorbing agent, and 0.1 to 10 parts by weight of the moisture absorbing auxiliary agent. In step (1), the raw materials for preparing the alkaline dispersion precursor slurry, by weight, include: 100 parts of a sodium silicate aqueous solution with a solid content of 25%–35%; Sodium pyrophosphate 1.5–3.0 parts; Citric acid 1.5–3.0 parts; 15-25 parts of bentonite.

3. The preparation method of the composite moisture-proof silica gel desiccant according to claim 2, characterized in that, Step (1) is as follows: The sodium silicate aqueous solution was added to a reaction vessel equipped with a jacketed temperature control system and a stirrer, and sodium pyrophosphate was added and stirred to dissolve. The citric acid was pre-dissolved in deionized water and then slowly dripped into the reaction vessel. The bentonite was then slowly and uniformly added, and the temperature inside the reactor was kept constant at 35℃~45℃. The mixture was continuously stirred and dispersed for 1.5~2.5 hours to obtain an alkaline dispersion precursor slurry with a pH value of 10.5~11.

5.

4. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (2), the mass fraction of the dilute sulfuric acid solution is 15% to 22%; the dropping rate is controlled so that the pH value of the system decreases within 90 to 120 minutes.

5. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (3), the raw materials for preparing the crosslinking acid solution, by weight, include: 30 portions of a dilute sulfuric acid solution with a mass fraction of 15%–25%; 1.0–3.0 parts of anhydrous magnesium sulfate; The preparation method of the crosslinked acid solution is as follows: control the temperature inside the anti-corrosion reaction tank to not exceed 35°C, and add the anhydrous magnesium sulfate in batches to the dilute sulfuric acid solution and stir continuously until it is clear.

6. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (3), the residence time of the material in the static mixer pipeline is controlled to be 1 to 5 seconds.

7. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (4), the constant temperature aging temperature is 80℃~90℃ and the aging time is 3~5 hours; after aging, the gel block is broken into particles of 2mm~5mm; and the gel is circulated and washed until the conductivity of the washing filtrate drops to 450μS / cm~495μS / cm.

8. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (5), the mass fraction of the anhydrous magnesium sulfate aqueous solution is 10% to 20%; the immersion temperature is 55℃ to 65℃; and the immersion time is 2 to 4 hours.

9. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (6), the specific implementation method of the programmed temperature rise dehydration activation is as follows: first, dry at 75℃~85℃ for 1.5~2.5 hours, then heat to 145℃~160℃ at a heating rate of 2℃ / min, and activate at a constant temperature for 3~5 hours.

10. The preparation method of the composite moisture-proof silica gel desiccant according to claim 1, characterized in that, In step (3), the composite sol is pumped into the static mixer by a screw pump, and the crosslinking acid solution is simultaneously pumped into the static mixer by a side inlet metering pump. In step (4), the gel block is crushed into particles using a double-roll crusher; In step (6), the filtered particles are placed in a mesh belt dryer for the programmed temperature rise dehydration and activation.

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