A method and apparatus for modifying the precursor of an ambient dry aerogel

Abstract

The application discloses a precursor modification method and device for normal-pressure dry aerogel, relates to the field of dry aerogel, and comprises the following steps: S1, precursor pretreatment; S2, composite modification; S3, solvent replacement; S4, surface modification; and S5, normal-pressure continuous drying; through the synergistic process of the accurate pretreatment of the precursor, the composite modification of the silane-alumina sol, the gradient solvent replacement, the global hydrophobic modification and the segmented gradient normal-pressure drying, the application solves the defects of the traditional normal-pressure dry aerogel, such as skeleton collapse, shrinkage and cracking.

Description

Technical Field

[0001] This invention relates to the field of dried aerogel technology, specifically to a method and apparatus for modifying precursors of atmospheric pressure dried aerogels. Background Technology

[0002] Aerogels are novel functional materials with ultra-low density, low thermal conductivity, high porosity, and excellent hydrophobic and thermal insulation properties, showing broad application prospects in fields such as thermal insulation, energy conservation, and environmental protection. Currently, the mainstream preparation methods for aerogels in the industry are divided into two categories: supercritical drying and atmospheric pressure drying. However, traditional preparation equipment and process systems have many inherent defects, restricting the large-scale, green, and high-quality industrial production of aerogels. Specific drawbacks are as follows: 1. High cost and difficulty in industrialization of supercritical drying method: Aerogels prepared by traditional supercritical drying process have excellent comprehensive properties, but the process requires special high-pressure supercritical equipment, which is expensive, difficult to obtain, and has high operation and maintenance costs. In addition, the production process conditions are harsh and the energy consumption is extremely high, which cannot be adapted to large-scale industrial mass production.

[0003] 2. Traditional atmospheric pressure drying process results in many defects and poor performance of finished products: Conventional atmospheric pressure drying technology has low threshold and low cost, but the process system is imperfect. The precursor modification is simple, the solvent replacement is incomplete, the surface modification is uneven, and the drying temperature rise method is unreasonable. This can easily lead to shrinkage, collapse and cracking of the aerogel skeleton. The finished product has low porosity, high thermal conductivity, poor mechanical strength and insufficient hydrophobicity. Its comprehensive performance is far lower than that of supercritical drying products, and the quality stability is poor.

[0004] 3. Traditional production equipment has low automation and poor production efficiency: Most existing aerogel production equipment is decentralized and independent, with poor process connection and inability to achieve integrated continuous production throughout the entire process. It relies on manual operation, has low precision and large error in process parameter control, lacks a systematic parameter recording mechanism, and has large batch quality differences and insufficient stability.

[0005] 4. Traditional processes are not environmentally friendly and have low resource utilization: Traditional preparation processes involve solvent replacement and drying, resulting in a large amount of organic solvent volatilization. There is no supporting recycling and treatment system, and the waste gas is directly emitted, polluting the environment. At the same time, the solvent cannot be recycled, resulting in serious waste of raw materials and further increasing production costs.

[0006] To address these issues, we provide a method and apparatus for modifying precursors of atmospheric pressure-dried aerogels. Summary of the Invention

[0007] To address the problems existing in the prior art, this invention provides a method and apparatus for modifying precursors of atmospheric pressure-dried aerogels. This invention solves the defects of skeleton collapse, shrinkage, and cracking of traditional atmospheric pressure-dried aerogels through a synergistic process of precise precursor pretreatment, silane-alumina sol composite modification, gradient solvent replacement, global hydrophobic modification, and segmented gradient atmospheric pressure drying.

[0008] To achieve the above objectives, the present invention employs a method for modifying the precursor of an atmospheric pressure-dried aerogel, comprising: S1: Precursor pretreatment: Select silicon source precursor, add deionized water and dispersant, and stir at 25-35℃ to obtain a uniformly dispersed precursor mixture. S2: Composite modification, adding modifier and catalyst to the precursor mixture, adjusting the pH and temperature of the system, and stirring at a constant temperature to obtain a uniform modified precursor sol. S3: Solvent replacement. The modified precursor sol is allowed to stand and gel to obtain a wet gel. The wet gel is then subjected to gradient replacement using a low-toxicity mixed solvent to remove moisture and impurities from the wet gel. The gradient replacement can be simplified according to the type of silicon source. For industrial silicate silicon sources, the 90% concentration gradient can be omitted, and only three-stage replacement of 50%, 70%, and 99% can be used. S4: Surface modification: Add surface modifier to the wet gel after displacement, soak at constant temperature to complete surface hydrophobic modification, and drain excess solvent from the surface after modification. S5: Continuous drying at atmospheric pressure. The modified wet gel is sent to a continuous drying equipment and dried to constant weight using a gradient temperature method to obtain the finished aerogel product.

[0009] As a further optimization of the above scheme, in step S1, the silicon source precursor is one or a combination of two of tetraethyl orthosilicate and industrial silicate. When tetraethyl orthosilicate and industrial silicate are combined, their volume ratio is 1:1-2:1. The dispersant is one of polyethylene glycol and sodium dodecylbenzenesulfonate. The amount of dispersant added is 0.5%-2.0% of the precursor mass. The concentration of the silicon source precursor is 0.5-1.5 mol / L. The volume ratio of deionized water to the precursor is 1:1-2:1. The mixture is stirred for 10-20 min at 25-35℃ and a stirring rate of 300-500 r / min.

[0010] As a further optimization of the above scheme, in step S2, the organosilane is selected from methyltrimethoxysilane and methyltriethoxysilane, the solid content of alumina sol is 20%-30%, the organosilane and alumina sol are compounded in a compounding ratio of 2:1-3:1, the amount of modifier added is 5%-15% of the precursor mass, the catalyst is selected from hydrochloric acid and oxalic acid, and the amount added is 0.1%-0.5% of the precursor mixture mass. The pH value of the system is adjusted to 3.5-5.5, the temperature is raised to 40-60℃, and the reaction is carried out at a constant temperature with stirring for 30-60 min. The stirring rate is maintained at 400-600 r / min to obtain a uniform modified precursor sol.

[0011] As a further optimization of the above scheme, in step S3, the low-toxicity mixed solvent is a mixture of ethanol and propylene glycol in a volume ratio of 3:1-5:1. The volume fraction concentrations of the solvents in the gradient replacement are 50%, 70%, 90%, and 99% respectively. Fresh solvent is used after each replacement. The replacement temperature is 20-30℃, the replacement time is 2-4 hours, and the number of replacements is 3-6.

[0012] As a further optimization of the above scheme, in step S4, the surface modifier added to the replaced wet gel is one of methyltriethoxysilane and hexadecyltrimethylammonium chloride, and the addition amount is 2%-5% of the mass of the wet gel. The gel is soaked at a constant temperature of 30-40℃ for 1-2 hours to complete the surface hydrophobic modification. After modification, the excess solvent on the surface is drained.

[0013] As a further optimization of the above scheme, in step S5, a gradient heating method is adopted for drying, with a heating rate of 5-10℃ / h, and successively holding at 40-60℃ for 2-3h, 60-80℃ for 3-4h, and 80-100℃ for 1-2h, until constant weight is obtained to obtain the aerogel product. During the drying process, an inert gas is introduced with a gas flow rate of 0.5-1.0 m / s. The inert gas is either nitrogen or argon, with nitrogen being preferred, and the flow rate is controlled at 0.7-0.9 m / s.

[0014] This invention also discloses a precursor modification device for atmospheric pressure dried aerogel, applied in a method for modifying precursors of atmospheric pressure dried aerogel. The device includes a precursor pretreatment tank, a composite modification reaction tank, a gel settling tank, a multi-cavity gradient solvent displacement tank, a constant-temperature surface modification tank, and a continuous drying tunnel, all sequentially sealed and connected. Each piece of equipment is connected via sealed conveying pipelines equipped with flow regulating valves and conveying pumps. The device is also equipped with a central control system, an audible and visual fault alarm system, a waste gas treatment device, and a finished product collection bin.

[0015] As a further optimization of the above scheme, the precursor pretreatment tank is equipped with a variable frequency stirring device and a PT100 temperature sensor. The speed of the variable frequency stirring device is adjustable from 0 to 1000 r / min. The tank wall is equipped with a temperature control jacket for regulating the temperature inside the tank. The top of the tank is equipped with a feed inlet, and the bottom of the tank is equipped with a discharge outlet that is sealed to the feed inlet of the composite modification reaction tank. The precursor pretreatment tank is also equipped with a liquid level sensor for real-time monitoring of the liquid level of the material inside the tank. The composite modification reaction vessel is equipped with a frequency conversion stirring device, a pH sensor and an electric heating device. The temperature adjustment range of the electric heating device is 20-100℃. The top of the composite modification reaction vessel is equipped with a feed inlet, a modifier addition port and a catalyst addition port. The modifier addition port and the catalyst addition port adopt an adjustable and precise dripping structure with an adjustable dripping rate. The bottom outlet of the vessel is sealed to the gel settling tank. The gel settling tank is equipped with an insulation and temperature control layer and a temperature sensor to control the gel settling temperature inside the tank at 20-30℃. The discharge port at the bottom of the tank is sealed and connected to the inlet of the multi-cavity gradient solvent replacement tank.

[0016] As a further optimization of the above scheme, the multi-cavity gradient solvent replacement tank is equipped with multiple independent replacement cavities. Each cavity is equipped with a solvent inlet and outlet, a stirring device, a liquid level sensor and an independent temperature control module. The solvent inlet and outlet of the cavity are connected to an external solvent storage tank and a solvent recovery tank, respectively, which can realize continuous operation of gradient solvent replacement and solvent recycling. The temperature control module of each cavity can stably control the replacement temperature at 20-30℃. The constant temperature surface modification tank is equipped with a constant temperature heating layer on the outside and a liftable soaking support, a stirring device and a liquid level sensor inside. The temperature control accuracy is ±1℃. The bottom outlet of the tank is sealed and connected to the feed inlet of the continuous drying tunnel.

[0017] As a further optimization of the above scheme, the continuous drying tunnel has a segmented structure, which is divided into a preheating section, a medium-temperature section and a high-temperature section. Each section is equipped with an independent temperature control system and an inert gas introduction device. An adjustable speed conveyor belt is installed inside the tunnel, and the conveying speed can be adjusted within the range of 0.1-0.5 m / min. Each section is equipped with an exhaust port, and all exhaust ports are connected to a waste gas treatment device. The waste gas treatment device adopts a composite structure of activated carbon adsorption and condensation recovery. The end of the tunnel is connected to the finished product collection bin. The central control system is controlled by a PLC; the central control system is also connected to an audible and visual fault alarm system.

[0018] The present invention provides a method and apparatus for modifying precursors of atmospheric pressure-dried aerogels, which has the following beneficial effects: This invention solves the defects of traditional atmospheric pressure drying aerogel skeleton collapse, shrinkage, and cracking through a synergistic process of precise precursor pretreatment, silane-alumina sol composite modification, gradient solvent replacement, global hydrophobic modification, and segmented gradient atmospheric pressure drying. The process of this invention is adaptable to various raw material systems, including tetraethyl orthosilicate, industrial silicate single silicon source, and composite silicon source of both. It is matched with different dispersants, modifiers, catalysts, process temperature and time parameters to specifically adapt to the gelation characteristics of different silicon sources, effectively avoid molding defects in the production process of different raw materials, and has strong process versatility and industrial adaptability. This invention uses a low-toxicity ethanol-propylene glycol composite solvent for gradient replacement. Through multiple concentration gradients and multiple fresh solvent replacements, residual moisture and soluble impurities inside the wet gel are thoroughly removed, ensuring the integrity of the porous structure of the aerogel from the source, while reducing the toxicity of production. This invention employs an atmospheric pressure drying process, eliminating the need for high-pressure supercritical equipment. All raw materials used are commercially available conventional products. The process conditions are mild, energy consumption is low, and raw materials are readily available. Compared to supercritical drying processes, this reduces equipment costs, production energy consumption, and maintenance costs. The parameters of each process in this invention are precisely controllable, the modifier and catalyst are added uniformly, the hydrophobic modification is uniform throughout the entire process, and the gradient temperature rise drying avoids the problem of uneven stress.

[0019] Specific embodiments of the present invention are disclosed in detail with reference to the following description and accompanying drawings, indicating how the principles of the present invention can be adopted. It should be understood that the embodiments of the present invention are not limited in scope as a result, and that the embodiments of the present invention include many changes, modifications and equivalents within the spirit and scope of the appended claims. Attached Figure Description

[0020] Figure 1 This is a flowchart illustrating the steps of the method for modifying the precursor of the atmospheric pressure-dried aerogel according to the present invention. Figure 2 This is a schematic diagram of the precursor modification device for atmospheric pressure dried aerogel according to the present invention.

[0021] In the diagram: 1. Precursor pretreatment tank; 2. Composite modification reaction tank; 3. Gel settling tank; 4. Multi-chamber gradient solvent replacement tank; 5. Constant temperature surface modification tank; 6. Continuous drying tunnel; 7. Central control system; 8. Audible and visual fault alarm system; 9. Waste gas treatment device; 10. Finished product collection bin. Detailed Implementation

[0022] Please refer to the instruction manual appendix. Figure 1-2This invention provides a technical solution: a method and apparatus for modifying precursors of atmospheric pressure dried aerogels. The raw materials used in this embodiment are all commercially available conventional products: tetraethyl orthosilicate (AR, purity ≥98%), industrial silicates (solid content ≥30%), polyethylene glycol (PEG-6000), sodium dodecylbenzenesulfonate (AR), organosilanes (methyltrimethoxysilane, AR), alumina sol (solid content 20%), hydrochloric acid (AR, concentration 36%-38%), oxalic acid (AR), ethanol (AR, purity ≥99%), propylene glycol (AR), methyltriethoxysilane (AR), and hexadecyltrimethylammonium chloride (AR). The equipment used in this invention is all conventional industrial equipment, which can be manufactured using existing technologies. Compared to specialized equipment, the overall preparation cost is lower, the equipment is easier to obtain, and the industrial adaptability is stronger.

[0023] This invention differs from traditional single-modification atmospheric pressure drying processes by constructing an organic and inorganic composite reinforcement modification system and a multi-stage stress-relieving drying system. Traditional atmospheric pressure aerogels rely solely on hydrophobic modification with a single organosilane, which only achieves surface hydrophobicity but cannot structurally reinforce the silica gel framework. The gel network has low cross-linking degree and weak bonding force at the framework nodes, making it prone to structural collapse under the capillary tension generated by solvent evaporation.

[0024] This invention introduces an inorganic modifying component of alumina sol, which forms a synergistic modification effect with organosilane. The organosilane can perform hydrophobic grafting modification on the inner wall of the gel pores, blocking the adsorption of water molecules. The alumina sol nanoparticles can be uniformly embedded at the nodes of the three-dimensional silica network skeleton, effectively filling the micropore defects of the gel skeleton, improving the crosslinking density and structural rigidity of the skeleton, strengthening the mechanical stability of the aerogel skeleton at the microscopic level, and greatly improving the skeleton's ability to resist capillary stress deformation.

[0025] Meanwhile, this invention replaces the traditional single-concentration, short-time solvent replacement method with an ethanol-propylene glycol compound low-toxicity solvent gradient replacement system. It utilizes the differences in surface tension and evaporation rate of the two solvents to gradually replace the high surface tension aqueous solution in the gel pores, thereby gradually reducing the interfacial tension inside the pores. This avoids sudden changes in gel osmotic pressure caused by single solvent replacement, prevents problems such as pore shrinkage and skeleton distortion in wet gels, and preserves the complete porous structure in the early stage of gel formation to the greatest extent.

[0026] Furthermore, the segmented gradient heating and drying process of this invention controls the temperature according to the different solvent residue states at different drying stages of the wet gel. The low-temperature stage enables the slow evaporation of solvent, the medium-temperature stage completes the shaping of the pore structure, and the high-temperature stage completely removes residual trace solvents and functional groups. The entire process achieves stress relief and solves the problems of structural cracking and overall shrinkage caused by sudden heating and cooling in traditional atmospheric pressure drying.

[0027] Example 1 A method for modifying the precursor of an atmospheric pressure-dried aerogel, the specific steps of which are as follows: S1: Precursor pretreatment: Tetraethyl orthosilicate was selected as the silicon source precursor. A precursor solution with a concentration of 1.0 mol / L was prepared. Deionized water was added, and the volume ratio of deionized water to precursor was 1.5:1. Polyethylene glycol with a mass of 1.0% of the precursor was added as a dispersant. The mixture was stirred at 30℃ and 400 r / min for 15 min to obtain a uniformly dispersed precursor mixture. S2: Composite modification: A modifier composed of methyltrimethoxysilane and alumina sol with a solid content of 20% in a ratio of 2.5:1 is added to the precursor mixture. The amount of modifier added is 10% of the precursor mass. Then, 0.3% of hydrochloric acid by mass of the precursor mixture is added as a catalyst. The pH value of the system is adjusted to 4.5, the temperature is raised to 50℃, and the mixture is stirred at a constant temperature and stirring rate of 500r / min for 45min to obtain a modified precursor sol with uniform composition and sufficient reaction. S3: Solvent replacement. The modified precursor sol was allowed to stand for 2 hours to complete natural gelation, resulting in a structurally complete wet gel. A low-toxicity mixed solvent of ethanol and propylene glycol in a volume ratio of 4:1 was used to perform gradient replacement on the wet gel at a constant temperature of 25°C. The volume fraction concentrations of the solvents in the gradient replacement were 50%, 70%, 90%, and 99% respectively. Each replacement lasted for 3 hours, and a total of 4 replacements were performed. After each replacement, a completely fresh solvent was used to thoroughly remove residual moisture and soluble impurities from the wet gel. S4: Surface modification. 3.5% of the wet gel mass of methyltriethoxysilane was added to the wet gel after displacement treatment as a surface modifier. The system was immersed at a constant temperature of 35°C for 1.5 h to complete the global hydrophobic modification of the wet gel. After immersion, the excess solvent adhering to the surface of the wet gel was drained. S5: Continuous drying at atmospheric pressure. The wet gel with completed surface modification is sent into the continuous drying tunnel 6. Nitrogen gas with a flow rate of 0.8 m / s is continuously introduced as a protective gas. Gradual heating drying is carried out at a heating rate of 8℃ / h. The sample is then subjected to segmented heat treatments of 50℃ for 2.5h, 70℃ for 3.5h, and 90℃ for 1.5h until it is dried to constant weight, and finally a high-performance hydrophobic aerogel product is obtained.

[0028] The aerogel product prepared in this embodiment exhibits excellent performance indicators, with a porosity of 92%, a thermal conductivity of 0.018 W / (m·K), and a density of 0.05 g / cm³. 3 It has a compressive strength of 0.18 MPa and a hydrophobic angle of 135°. The finished product has no skeleton shrinkage or collapse defects, and its comprehensive performance is close to that of aerogel products prepared by supercritical drying.

[0029] Example 2 A method for modifying the precursor of an atmospheric pressure-dried aerogel, the specific steps of which are as follows: S1: Precursor pretreatment: Industrial silicate was selected as the silicon source precursor. A precursor solution with a concentration of 0.8 mol / L was prepared. Deionized water was added, and the volume ratio of deionized water to precursor was 1:1. Sodium dodecylbenzenesulfonate with a mass of 0.8% of the precursor was added as a dispersant. The mixture was stirred at 28℃ and 350 r / min for 12 min to obtain a uniform and stable precursor mixture. S2: Composite modification: A modifier composed of methyltrimethoxysilane and alumina sol with a solid content of 20% in a 2:1 ratio is added to the precursor mixture. The amount of modifier added is 8% of the precursor mass. Then, 0.2% of oxalic acid is added as a catalyst. The pH of the system is adjusted to 4.0, the temperature is raised to 45℃, and the mixture is stirred at a constant temperature for 35 minutes at a stirring rate of 450r / min to obtain a homogeneous and transparent modified precursor sol. S3: Solvent replacement. The modified precursor sol was allowed to stand for 1.5 hours to complete natural gelation, resulting in a complete wet gel. A low-toxicity mixed solvent of ethanol and propylene glycol in a volume ratio of 3:1 was used to perform gradient replacement on the wet gel at a constant temperature of 22°C. The volume fraction concentrations of the solvents in the gradient replacement were 50%, 70%, and 99% respectively. Each replacement lasted 2.5 hours, and a total of 3 replacements were performed. Fresh solvent was used after each replacement to adapt to the gel characteristics of industrial silicate precursors, thoroughly remove internal impurities and moisture, and avoid the risk of skeleton collapse. S4: Surface modification: 2.5% of hexadecyltrimethylammonium chloride by weight of the wet gel was added to the replaced wet gel as a surface modifier. The system was immersed at a constant temperature of 32℃ for 1.2h to complete the hydrophobic modification of the wet gel. After modification, excess solvent on the surface was drained. S5: Continuous drying at atmospheric pressure. The modified wet gel is sent into the continuous drying tunnel 6, and argon gas with a flow rate of 0.6 m / s is continuously introduced as a protective gas. Gradual heating is carried out at a heating rate of 6℃ / h. The gel is then subjected to segmented heating treatments of 45℃ for 2 h, 65℃ for 3 h, and 85℃ for 1.2 h. After drying to constant weight, the aerogel product is obtained.

[0030] The aerogel product prepared in this embodiment was tested and found to have a porosity of 91%, a thermal conductivity of 0.019 W / (m·K), and a density of 0.06 g / cm³. 3 The compressive strength is 0.16MPa, the hydrophobic angle is 132°, and the finished product has a complete structure without collapse or cracking.

[0031] Example 3 A method for modifying the precursor of an atmospheric pressure-dried aerogel, the specific steps of which are as follows: S1: Precursor pretreatment: Tetraethyl orthosilicate and industrial silicate were selected as composite silicon source precursors in a volume ratio of 1:1. A precursor solution with a concentration of 1.2 mol / L was prepared, and deionized water was added with a volume ratio of 2:1 between deionized water and precursor. Then, 1.5% of polyethylene glycol by mass of the precursor was added as a dispersant. The mixture was stirred at 32℃ and 450 r / min for 18 min to obtain a uniformly dispersed precursor mixture. S2: Composite modification: A modifier composed of methyltrimethoxysilane and alumina sol with a solid content of 20% in a 3:1 ratio is added to the precursor mixture. The amount of modifier added is 12% of the precursor mass. Then, 0.4% of hydrochloric acid by mass of the precursor mixture is added as a catalyst. The pH value of the system is adjusted to 5.0, the temperature is raised to 55℃, and the mixture is stirred at a constant temperature and stirring rate of 550r / min for 50min to obtain a modified precursor sol with stable performance. S3: Solvent replacement. The modified precursor sol was allowed to stand for 2.5 h to complete natural gelation, resulting in a dense wet gel. A low-toxicity mixed solvent of ethanol and propylene glycol in a volume ratio of 5:1 was used to perform gradient replacement on the wet gel at a constant temperature of 28℃. The volume fraction concentrations of the solvents in the gradient replacement were 50%, 70%, 90%, and 99% respectively. Each replacement lasted 3.5 h, and a total of 4 replacements were performed. After each replacement, fresh solvent was used to completely remove the moisture and residual impurities inside the wet gel. S4: Surface modification: 4% of the wet gel mass of methyltriethoxysilane was added to the replaced wet gel as a surface modifier. The system was immersed at a constant temperature of 38℃ for 1.8h to complete the uniform hydrophobic modification of the whole area. After immersion, excess modification solvent on the surface of the wet gel was drained. S5: Continuous drying at atmospheric pressure. The modified wet gel is sent into the continuous drying tunnel 6, and nitrogen gas with a flow rate of 0.9 m / s is continuously introduced as a protective gas. Gradual heating is carried out at a heating rate of 9℃ / h. The gel undergoes segmented heat treatment, including holding at 55℃ for 3h, 75℃ for 4h, and 95℃ for 1.8h. After drying to constant weight, a high-quality aerogel product is obtained.

[0032] The aerogel product prepared in this embodiment was tested and found to have a porosity of 93%, a thermal conductivity of 0.017 W / (m·K), and a density of 0.04 g / cm³. 3 It has a compressive strength of 0.20MPa, a hydrophobic angle of 138°, and the finished product has no collapse or shrinkage defects, exhibiting the best overall performance.

[0033] Example 4 A production apparatus adapted to any of the atmospheric pressure drying aerogel precursor modification methods in Examples 1-3 includes a precursor pretreatment tank 1, a composite modification reaction tank 2, a gel settling tank 3, a multi-cavity gradient solvent replacement tank 4, a constant temperature surface modification tank 5, and a continuous drying tunnel 6, all sealed and connected in sequence. Each piece of equipment is connected via a sealed conveying pipeline, which is equipped with a flow regulating valve and a conveying pump. The apparatus is equipped with a central control system 7, an audible and visual fault alarm system 8, a waste gas treatment device 9, a solvent storage tank, a solvent recovery tank, and a finished product collection bin 10. This allows for fully integrated, automated, and green production of the entire process, from aerogel precursor modification, solvent replacement, surface modification, atmospheric pressure drying, to finished product collection. This addresses the shortcomings of traditional decentralized equipment, such as poor process connections, low production efficiency, poor parameter accuracy, and insufficient environmental friendliness.

[0034] The precursor pretreatment tank 1 has a volume of 1000L. The tank is equipped with a variable frequency stirring device and a PT100 temperature sensor. The speed of the variable frequency stirring device is adjustable from 0-1000 r / min. A temperature control jacket is installed on the side wall of the tank, using steam heating to stably regulate the internal temperature, with a temperature adjustment range of 20-100℃. A raw material inlet is located at the top of the tank, and a sealed outlet is located at the bottom. The bottom outlet is sealed to the inlet of the composite modification reaction tank 2, effectively preventing leakage of the precursor mixture and uneven modification caused by the introduction of external impurities. A liquid level sensor is installed inside the tank to dynamically monitor the liquid level in real time, ensuring accurate raw material feeding ratios and fully meeting the process parameter requirements of the precursor pretreatment process.

[0035] The composite modification reaction vessel 2 has a volume of 1500L. Inside, it is equipped with a variable frequency stirring device, a high-precision pH sensor, and an electric heating device. The pH sensor has a measurement range of 0-14 and an accuracy of ±0.1, while the electric heating device has a temperature adjustment range of 20-100℃. This allows for real-time monitoring and precise control of the pH and temperature of the reaction system within the vessel. The top of the vessel features a material inlet, a dedicated modifier addition port, and a dedicated catalyst addition port. Both the modifier and catalyst addition ports employ an adjustable, precise dripping structure with a dripping rate adjustable from 0.1-1.0L / min. This ensures uniform and consistent addition of the modifier and catalyst, preventing aerogel skeleton defects caused by excessively high local material concentrations and vigorous reactions. The bottom of the vessel has a sealed outlet that is sealed to the inlet of the gel settling tank 3, ensuring a closed-loop transport of the modified sol and meeting the precise reaction requirements of the composite modification process.

[0036] The gel settling tank 3 has a volume of 2000L and an internal insulation and temperature control layer to stably control the settling temperature within the optimal gelation temperature range of 20-30℃. The tank is equipped with a temperature sensor to monitor the settling environment temperature in real time, ensuring a uniform and stable sol-gel process for the modified precursor and avoiding gelation defects. A sealed outlet is located at the bottom of the tank, which is sealed to the inlet of the multi-cavity gradient solvent replacement tank 4 to achieve closed-loop transport of the formed wet gel.

[0037] The multi-chamber gradient solvent replacement tank 4 is equipped with four independent replacement chambers, each with a volume of 500L. Each independent chamber is equipped with a solvent inlet, a solvent outlet, a small stirring device, and a liquid level sensor. The solvent inlet of each chamber is connected to a solvent storage tank, and the solvent outlet is connected to a solvent recovery tank, enabling the recycling and reuse of the replacement solvent. Each chamber is equipped with an independent temperature control module, which can stably control the replacement temperature at 20-30℃, precisely adapting to the requirements of the gradient solvent replacement process. It can complete solvent replacement operations with different concentration gradients of 50%, 70%, 90%, and 99% in stages, ensuring thorough replacement of moisture and impurities inside the wet gel. A discharge port is uniformly set at the bottom of the tank, which is sealed and connected to the inlet of the constant temperature surface modification tank 5.

[0038] The constant-temperature surface modification tank 5 has a volume of 1000L. The tank body is wrapped with a constant-temperature heating layer, and the temperature adjustment range is 20-50℃ with a temperature control accuracy of ±1℃. The tank body is equipped with a height-adjustable soaking rack inside, which facilitates the neat placement and removal of wet gel and improves the convenience of loading and unloading. The top of the tank body is equipped with a material inlet and a modifier addition port. The internal stirring device can realize the rapid and uniform dispersion of surface modifier, avoiding the problem of insufficient or uneven modification of wet gel caused by uneven local modifier concentration. The tank body is equipped with a liquid level sensor to accurately control the amount of modifier added. The bottom outlet of the tank body is sealed and connected to the inlet of the continuous drying tunnel 6.

[0039] The continuous drying tunnel 6 has a total length of 10m and is divided into three sections according to its process function: a 2m long preheating section, a 5m long medium-temperature section, and a 3m long high-temperature section. Each section is equipped with an independent electric heating device, a temperature control system, and an inert gas introduction device. The temperature adjustment range of each section covers 40-100℃, fully adapting to the gradient temperature rise drying process. An adjustable-speed stainless steel conveyor belt is laid inside the tunnel, with a conveying speed adjustment range of 0.1-0.5m / min, which can precisely match the drying time requirements. Each section of the tunnel has an exhaust vent at the top, and all exhaust vents are connected to the exhaust gas treatment device 9. The exhaust gas treatment device 9 adopts a composite treatment structure of activated carbon adsorption + solvent condensation recovery, with an exhaust gas treatment capacity of 400-600m³. 3 / h, can efficiently recover the organic solvents volatilized during the drying process, with an overall solvent recovery rate of ≥80%; the tunnel end docking finished product collection chamber 10 is used for the orderly collection of the dried aerogel finished product.

[0040] The central control system 7 adopts a PLC programmable control system, which can monitor and regulate the operating parameters of each device in the whole process, including system temperature, stirring speed, material conveying flow rate, reagent drop acceleration rate, etc. It supports custom parameter setting and real-time data recording and storage. The system is equipped with an integrated audible and visual fault alarm system 8, with an equipment fault alarm response time of ≤1s, which can quickly troubleshoot equipment abnormalities. The system data storage time is ≥1 year, realizing the traceability of parameters throughout the entire production process, and completely solving the problems of large errors, no recording of process parameters, and poor product quality stability in traditional manual control.

[0041] All material conveying pipelines in this unit are made of 304 stainless steel. The pipeline docking points adopt flange sealing connection. The flange connection is equipped with PTFE sealing gaskets, which are corrosion resistant, have strong sealing performance, and can solve the risk of organic solvent leakage. The flow regulating valves of the pipeline have an adjustment accuracy of ±5%, and the material conveying flow control is precise, which can ensure the stability of the entire production process.

[0042] This device enables integrated, continuous, and automated production of aerogel precursors, including modification, solvent replacement, surface modification, and atmospheric pressure drying. It boasts a daily production capacity of 500 kg, a solvent recovery rate of ≥80%, and exhaust emissions that fully comply with national environmental standards. The equipment is stable, easy to maintain, and adaptable to the industrial-scale production needs of aerogels at various scales. It effectively addresses the industry pain points of traditional production equipment, such as fragmented processes, low production efficiency, poor environmental performance, and unstable product quality. This contributes to the large-scale and green development of the atmospheric pressure dried aerogel industry. Compared to traditional equipment, it offers advantages in production efficiency, environmental performance, parameter control precision, and product stability.

[0043] To fully verify the technical gains of the core processes of composite modification, gradient replacement, and segmented drying in this invention, three sets of traditional process comparison examples were set up. Aerogels were prepared using industry-standard conventional atmospheric pressure drying processes and compared with the products of the embodiments of this invention in a comprehensive performance benchmarking to ensure that the experimental data are objective and the conclusions are reliable.

[0044] Comparative Example 1: The traditional single silane modification process uses only methyltrimethoxysilane as a single modifier, without adding alumina sol inorganic reinforcing components. The other precursor pretreatment parameters are consistent with those of Example 1 of this invention. Solvent replacement is carried out by single replacement with a single ethanol solvent, without gradient concentration replacement process. Drying adopts the traditional constant temperature drying mode, and the entire process is carried out at a constant temperature of 80°C until constant weight.

[0045] Comparative Example 2: The process of solvent replacement without gradients uses only 99% single-concentration ethanol solvent for one-time replacement. It does not use ethanol-propylene glycol compound solvent, does not have multi-concentration gradient transition, skips the multi-concentration gradient transition replacement process, and only uses 99% high-concentration ethanol for one-time replacement. The remaining composite modification and drying processes are the same as in Example 1.

[0046] Comparative Example 3: Conventional atmospheric pressure rapid heating and drying process, retaining the composite modification and gradient replacement process of this invention, adopts a direct heating to 90°C rapid drying mode in the drying stage, without segmented gradient heat preservation and inert gas protection, simulating the traditional extensive drying process.

[0047] Three sets of differential comparison examples were used to verify the effects of composite modification on skeleton strength, gradient replacement on pore integrity, and gradient inert drying on finished product appearance and hydrophobic stability.

[0048] Parallel experiments comparing the three sets of examples and three sets of comparative examples reveal that aerogels prepared using traditional atmospheric pressure drying processes generally exhibit significant structural defects and performance shortcomings. Comparative Example 1 shows visibly significant shrinkage, surface cracking, and severe pore collapse, with a porosity of only about 75%, a thermal conductivity as high as 0.028 W / (m·K), a hydrophobic angle of less than 95°, and extremely poor mechanical strength, making it easily breakable under stress. This demonstrates that single organic modification cannot effectively strengthen the gel skeleton and cannot resist capillary damage during the drying process. Comparative Example 2 shows no obvious cracking, but its overall shrinkage rate is as high as 18%, with an uneven pore structure, severe densification, and a significantly increased thermal conductivity. This indicates that non-gradient replacement causes drastic fluctuations in the internal osmotic pressure of the gel, leading to irreversible collapse of the micropores and severely affecting its thermal insulation performance. Comparative Example 3 showed localized cracking and poor hydrophobicity uniformity in the finished product. After long-term storage, the hydrophobic properties significantly deteriorated, proving that rapid heating and drying would cause a large amount of solvent to evaporate instantly, leading to stress concentration and damage in the pores. Furthermore, the lack of inert gas protection would cause the functional groups on the gel surface to oxidize and fail, resulting in a significant decrease in stability.

Claims

1. A method for modifying the precursor of an atmospheric pressure-dried aerogel, characterized in that, include: S1: Precursor pretreatment: Select silicon source precursor, add deionized water and dispersant, and stir at 25-35℃ to obtain a uniformly dispersed precursor mixture. S2: Composite modification, adding modifier and catalyst to the precursor mixture, adjusting the pH and temperature of the system, and stirring at a constant temperature to obtain a uniform modified precursor sol. S3: Solvent replacement. The modified precursor sol is allowed to stand and gel to obtain a wet gel. A low-toxicity mixed solvent is used to perform gradient replacement on the wet gel to remove moisture and impurities inside the wet gel. S4: Surface modification: Add surface modifier to the wet gel after displacement, soak at constant temperature to complete surface hydrophobic modification, and drain excess solvent from the surface after modification. S5: Continuous drying at atmospheric pressure. The modified wet gel is sent to a continuous drying equipment and dried to constant weight using a gradient temperature method to obtain the finished aerogel product.

2. The method for modifying the precursor of an atmospheric pressure-dried aerogel according to claim 1, characterized in that: In step S1, the silicon source precursor is one or a combination of two of tetraethyl orthosilicate and industrial silicate. When tetraethyl orthosilicate and industrial silicate are combined, their volume ratio is 1:1-2:

1. The dispersant is one of polyethylene glycol and sodium dodecylbenzenesulfonate. The amount of dispersant added is 0.5%-2.0% of the precursor mass. The concentration of the silicon source precursor is 0.5-1.5 mol / L. The volume ratio of deionized water to the precursor is 1:1-2:

1. The mixture is stirred for 10-20 min at 25-35℃ and a stirring rate of 300-500 r / min.

3. The method for modifying the precursor of an atmospheric pressure-dried aerogel according to claim 1, characterized in that: In step S2, the organosilane is selected from methyltrimethoxysilane and methyltriethoxysilane. The solid content of the alumina sol is 20%-30%. The organosilane and alumina sol are compounded in a ratio of 2:1-3:

1. The amount of modifier added is 5%-15% of the precursor mass. The catalyst is selected from hydrochloric acid and oxalic acid. The amount added is 0.1%-0.5% of the precursor mixture mass. The pH of the system is adjusted to 3.5-5.

5. The temperature is raised to 40-60℃ and the reaction is carried out under constant temperature stirring for 30-60 minutes. The stirring rate is maintained at 400-600 r / min to obtain a uniform modified precursor sol.

4. The method for modifying the precursor of an atmospheric pressure-dried aerogel according to claim 1, characterized in that: In step S3, the low-toxicity mixed solvent is a mixture of ethanol and propylene glycol in a volume ratio of 3:1 to 5:

1. The volume fraction concentrations of the solvents in the gradient replacement are 50%, 70%, 90%, and 99% respectively. Fresh solvent is used after each replacement. The replacement temperature is 20-30℃, the replacement time is 2-4 hours, and the number of replacements is 3-6.

5. The method for modifying the precursor of an atmospheric pressure-dried aerogel according to claim 1, characterized in that: In step S4, the surface modifier added to the replaced wet gel is one of methyltriethoxysilane and hexadecyltrimethylammonium chloride, and the amount added is 2%-5% of the mass of the wet gel. The gel is soaked at a constant temperature of 30-40℃ for 1-2 hours to complete the surface hydrophobic modification. After modification, excess solvent on the surface is drained.

6. The method for modifying the precursor of an atmospheric pressure-dried aerogel according to claim 1, characterized in that: In step S5, a gradient heating method is used for drying, with a heating rate of 5-10℃ / h. The temperature is successively maintained at 40-60℃ for 2-3h, 60-80℃ for 3-4h, and 80-100℃ for 1-2h until constant weight is achieved, resulting in the aerogel product. During the drying process, an inert gas is introduced at a flow rate of 0.5-1.0 m / s. The inert gas is either nitrogen or argon, with nitrogen being the preferred inert gas. The flow rate is controlled at 0.7-0.9 m / s.

7. A device for modifying precursors of atmospheric pressure-dried aerogels, characterized in that: The method for modifying the precursor of an atmospheric pressure dry aerogel according to any one of claims 1-6 includes a precursor pretreatment tank (1), a composite modification reaction tank (2), a gel settling tank (3), a multi-cavity gradient solvent replacement tank (4), a constant temperature surface modification tank (5), and a continuous drying tunnel (6) connected in sequence and sealed. The devices are connected by sealed conveying pipelines, and flow regulating valves and conveying pumps are installed on the pipelines. The device is also equipped with a central control system (7), an audible and visual fault alarm system (8), a waste gas treatment device (9), and a finished product collection bin (10).

8. The apparatus for modifying a precursor of an atmospheric pressure-dried aerogel according to claim 7, characterized in that: The precursor pretreatment tank (1) is equipped with a variable frequency stirring device and a PT100 temperature sensor. The speed of the variable frequency stirring device can be adjusted from 0 to 1000 r / min. The tank wall is equipped with a temperature control jacket for regulating the temperature inside the tank. The top of the tank is equipped with a feed inlet, and the bottom of the tank is equipped with a discharge outlet that is sealed to the feed inlet of the composite modification reaction tank (2). The precursor pretreatment tank (1) is also equipped with a liquid level sensor for real-time monitoring of the liquid level of the material inside the tank. The composite modified reaction vessel (2) is equipped with a frequency conversion stirring device, a pH sensor and an electric heating device. The temperature adjustment range of the electric heating device is 20-100℃. The top of the composite modified reaction vessel (2) is equipped with a feed inlet, a modifier addition port and a catalyst addition port. The modifier addition port and the catalyst addition port adopt an adjustable and precise dripping structure. The dripping rate can be adjusted. The bottom outlet of the vessel is sealed to the gel settling tank (3). The gel settling tank (3) is equipped with a heat-insulating temperature control layer and a temperature sensor to control the gel settling temperature in the tank at 20-30℃. The bottom outlet of the tank is sealed and connected to the inlet of the multi-cavity gradient solvent replacement tank (4).

9. The apparatus for modifying a precursor of an atmospheric pressure-dried aerogel according to claim 7, characterized in that: The multi-cavity gradient solvent replacement tank (4) is equipped with multiple independent replacement cavities. Each cavity is equipped with a solvent inlet and outlet, a stirring device, a liquid level sensor and an independent temperature control module. The solvent inlet and outlet of the cavity are connected to an external solvent storage tank and a solvent recovery tank, respectively. It can realize continuous operation of gradient solvent replacement and solvent recycling. The temperature control module of each cavity can stably control the replacement temperature at 20-30℃. The constant temperature surface modification tank (5) is provided with a constant temperature heating layer on the outside and a liftable soaking support, stirring device and liquid level sensor inside. The temperature control accuracy is ±1℃. The bottom outlet of the tank is sealed and connected to the inlet of the continuous drying tunnel (6).

10. The apparatus for modifying a precursor of an atmospheric pressure-dried aerogel according to claim 7, characterized in that: The continuous drying tunnel (6) is a segmented structure, which is divided into a preheating section, a medium-temperature section and a high-temperature section. Each section is equipped with an independent temperature control system and an inert gas inlet device. The tunnel is equipped with an adjustable speed conveyor belt with a conveying speed adjustment range of 0.1-0.5 m / min. Each section is equipped with an exhaust port, and all exhaust ports are connected to the waste gas treatment device (9). The waste gas treatment device (9) adopts a composite structure of activated carbon adsorption and condensation recovery. The end of the tunnel is connected to the finished product collection bin (10). The central control system (7) is controlled by a PLC; the central control system (7) is connected to an audible and visual fault alarm system (8).

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