A method of activating spent wet gel

Abstract

The application discloses a method for activating waste wet gel, which comprises the following steps: collecting waste wet gel generated in the production process of aerogel, mixing the waste wet gel with methanol, and mechanically crushing the mixture to prepare a micron-sized gel particle suspension; and adding a silane coupling agent to activate the surface of the particles, so that active groups are carried on the particles, and the activated waste wet gel is obtained. The waste wet gel is directly activated and reused in the main production process, as a nucleation center to shorten the gelation time by 20%-40%, and the silicon source saving rate is 10%-20%. The product performance is equivalent to that of fresh raw materials, and the shrinkage rate is reduced. The method is green and environmentally friendly, has significant cost advantages, and is suitable for the large-scale production of silica and composite aerogels.

Description

Technical Field

[0001] This invention relates to the field of green manufacturing and resource recycling technology of aerogel materials, specifically to a method for activating waste wet aerogel. Background Technology

[0002] Aerogel is a three-dimensional network porous solid material formed by the cross-linking of nanoparticles. It is characterized by its extremely high porosity (>90%) and high specific surface area (>500 m²). 2 With its high thermal conductivity (<0.03 W / (m·K)) and extremely low thermal conductivity (<0.03 W / (m·K)), it has broad application prospects in aerospace, building energy conservation, and new energy battery protection.

[0003] In the large-scale production of aerogels, the sol-gel process is the core step. However, due to deviations in gelation condition control, mold cutting, shape trimming, or product slitting, a large amount of wet gel waste is inevitably generated. This wet gel waste has not undergone drying treatment and still retains a complete nano-network structure and a large amount of solvent (methanol, water, etc.). Currently, there are two main methods for treating this wet gel waste in industry: one is to incinerate or landfill it as solid waste, resulting in a serious waste of silicon source resources and organic solvents; the other is to dry and pulverize it into low-value-added aerogel powder for use in coatings, building material fillers, etc., but this method is energy-intensive (requiring re-drying), has low product value, and does not achieve the recycling of silicon source in the main process.

[0004] Existing technologies have already considered the recycling of this aerogel waste. For example, CN121929705A discloses a method for preparing aerogel powder from waste wet gel produced using organosilicon sources, through crushing, modification, and spray drying with ammonium fluoride. However, this method converts waste gel into an independent powder product, and the spray drying process in this method has high energy consumption. Summary of the Invention

[0005] To address the aforementioned shortcomings of existing technologies, this invention provides a method for activating waste wet gel. This method involves crushing and dispersing the waste wet gel, surface-activating it, and then directly adding it back to fresh silicon source sol in the form of "seeds / nucleating agents" to participate in the subsequent sol-gel reaction. This achieves resource utilization of waste gel, reduces the consumption of fresh silicon source, shortens gelation time, and maintains or even improves the key performance of the final aerogel product. This solves the problems of low utilization rate of wet gel waste and high energy consumption and complex recycling processes in existing technologies.

[0006] To achieve the above objectives, the present invention provides a method for activating waste wet gel, the specific steps of which are as follows:

[0007] Step 1: Pre-treat the waste wet gel to remove foreign matter;

[0008] Step 2: Mix the waste wet gel treated in Step 1 with anhydrous methanol and crush it to prepare a gel microparticle suspension; wherein the particle size D90 of the gel microparticles in the suspension is 1~20μm;

[0009] Step 3: Add an activator to the suspension in Step 2, then adjust the pH to 4-5, stir the reaction for 1-4 hours, so that the activator is grafted onto the surface of the gel particles through chemical bonds to obtain activated waste wet gel.

[0010] The activator is a silane coupling agent capable of undergoing a condensation reaction with the silanol groups (Si-OH) on the gel surface. The amount of activator added is 5% to 15% of the mass of the dry aerogel, where the mass of the dry aerogel is the solid mass of the waste wet gel after drying. Specifically, the amount of activator added is calculated based on the solid mass measured after supercritical drying of the waste wet gel collected in step 1.

[0011] In this invention, the waste wet gel actually originates from unavoidable product losses during the large-scale production of aerogel due to the influence of the production process. This waste wet gel is generated due to various reasons such as deviations in gelation condition control, mold cutting, shape trimming, or product slitting. The collected waste wet gel includes not only substandard wet gel. For example, a small portion of wet gel may be cut off due to poor gelation effect caused by deviations in gelation condition control; some wet gel may be removed after cutting to fit the mold shape; and some wet gel may be cut off during shape correction or product slitting. All such wet gels generated due to process losses are considered waste wet gels as described in this invention.

[0012] Preferably, in step 1, the solid content in the waste wet gel is 2wt% to 15wt% based on dry gel, and the solvent in the waste wet gel is water, methanol, or a mixture of water and methanol.

[0013] Preferably, in step 2, the volume of anhydrous methanol added is 2 to 5 times the volume of the waste wet gel.

[0014] Preferably, in step 2, the crushing conditions are: processing at a speed of 3000rpm~8000rpm for 15min~60min.

[0015] Preferably, in step 2, the particle size D90 of the gel microparticles in the suspension is 1~10μm.

[0016] Preferably, in step 3, the activator is selected from one of γ-methacryloyloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or vinyltriethoxysilane.

[0017] Preferably, the activated waste wet gel is used as a seed crystal to prepare aerogel products; specifically as follows:

[0018] All raw materials for preparing aerogels are activated waste wet gels, without the addition of fresh silicon source sols;

[0019] Alternatively, after preparing the silicon source into a silicon source sol and completing acid-catalyzed hydrolysis, and before alkaline-catalyzed gelation, the activated waste wet gel is added to the intermediate product after acid-catalyzed hydrolysis, and then subsequent preparation steps are carried out.

[0020] Preferably, the mass of the activated waste wet gel converted into dry gel accounts for 5% to 25% of the mass of SiO2 in the silicon source sol, and the amount of activated waste wet gel to be added can be calculated accordingly.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] This invention achieves closed-loop utilization of waste wet gel generated during aerogel production by pre-treating, crushing, dispersing, and surface-activating it before directly using it as seed crystals in the sol-gel process of fresh silicon source sol. This eliminates the need for separate drying, sintering, or spray granulation of the waste wet gel, significantly reducing energy consumption and simplifying the process, thus increasing the overall utilization rate of silicon source by 10%–20%. The activated gel particles provide numerous nucleation sites for sol-gel polymerization, effectively shortening the gelation time and increasing the production line's capacity per unit time. Simultaneously, surface activation grafts functional groups compatible with the fresh sol system onto the gel particle surface, ensuring uniform dispersion of particles in the sol and preventing aggregation and sedimentation. This results in the final aerogel product exhibiting key performance indicators such as specific surface area, bulk density, and thermal conductivity that are not significantly different from, or even superior to, products prepared entirely with fresh silicon source. The aforementioned resource-saving, efficiency-enhancing, and performance-maintaining effects work synergistically, not only reducing the cost of waste wet gel disposal and the cost of purchasing fresh silicon sources, thus lowering overall production input, but also avoiding environmental pollution problems caused by waste incineration or landfill, which meets the requirements of circular economy development. Furthermore, this method is applicable to silica aerogels, organically modified silica aerogels, and some organic-inorganic composite aerogel systems, and has broad industrial application prospects. Detailed Implementation

[0023] This invention will be described clearly and completely with reference to the embodiments. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on this invention are within the scope of protection of this invention.

[0024] Unless otherwise specified in the specific context, the numerical ranges listed herein include upper and lower limits, as well as all integers and fractions within those ranges, and are not limited to the specific values ​​listed when the range is defined. While only preferred methods and materials are described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail. The terms “comprising,” “including,” “having,” “containing,” etc., as used herein are open-ended, meaning they include but are not limited to.

[0025] Unless otherwise specified, the experimental methods used in this invention are all conventional methods.

[0026] Unless otherwise specified, all materials and reagents used in this invention can be purchased or synthesized by known methods.

[0027] In the quantitative experiments of this invention, each experiment was repeated three times, and the average value of the results was taken.

[0028] I. A method for activating waste wet gel

[0029] This invention addresses the problems of existing wet aerogel waste treatment methods, including severe resource waste, high energy consumption, low product added value, inability to recycle silicon sources in the main production process, limited applicability of existing recycling processes, and product performance degradation caused by directly reusing untreated waste gel. While some existing methods for recycling wet aerogel waste have been considered, they often focus on using the waste as raw material to prepare other products, without considering its reuse in the preparation of fresh aerogel. Therefore, this invention attempts to demonstrate how to utilize these wet aerogel wastes in the preparation of fresh aerogel. In designing the recycling method, it was found that while some literature mentions a chemical recycling process of "aerogel → sol → aerogel" (ASA), this process is mainly applicable to specific organic aerogels and involves an extremely complex dissolution-regeling process, making its applicability to inorganic silica aerogel systems very limited. Therefore, this invention considers utilizing the intact nano-network structure retained within the waste wet gel, breaking it down and dispersing it into gel particles with a specific particle size range. A silane coupling agent capable of condensing with the silanol groups on the gel surface is added to the particle suspension as an activator, and the pH of the system is adjusted to a suitable range for stirring. This allows the activator to be chemically grafted onto the surface of the gel particles, altering their surface chemical properties. The treated activated waste wet gel is then used as a seed crystal or nucleating agent, added to the intermediate product after acid-catalyzed hydrolysis of the fresh silicon source sol and before alkali-catalyzed gelation, enabling it to participate in the subsequent sol-gel reaction. The specific steps are as follows:

[0030] Step 1: Pre-treat the waste wet gel to remove foreign matter;

[0031] Step 2: Mix the waste wet gel treated in Step 1 with anhydrous methanol and crush it to prepare a gel microparticle suspension; wherein the particle size D90 of the gel microparticles in the suspension is 1~20μm;

[0032] Step 3: Add an activator to the suspension in Step 2, then adjust the pH to 4-5, stir the reaction for 1-4 hours, so that the activator is grafted onto the surface of the gel particles through chemical bonds to obtain activated waste wet gel.

[0033] The activator is a silane coupling agent that can undergo a condensation reaction with the silanol groups (Si-OH) on the gel surface. The amount of activator added accounts for 5% to 15% of the mass of the dry aerogel, and the mass of the dry aerogel is the solid mass of the waste wet gel to be treated after drying.

[0034] The method described in this invention has achieved many unexpected technical effects in practical applications: when the amount of activated waste wet gel added accounts for 20% of the SiO2 mass in the fresh silicon source sol, the thermal conductivity of the resulting aerogel product is reduced by 5.6% compared to the product prepared entirely using fresh silicon source, and the specific surface area is reduced from 883 m² / s. 2 / g increased to 912 m 2 The bulk density remained essentially consistent; even with the addition of activated waste wet gel increased to 25%, the product performance still met industrial requirements, without the significant performance degradation commonly observed when adding recycled materials in existing technologies. Compared to directly adding unactivated wet gel, the surface-activated gel particles formed a stable and uniform suspension system in fresh sol, with no obvious sedimentation or agglomeration. The gelation process occurred synchronously throughout the entire system, resulting in a uniform internal structure of the aerogel without local cracks or defects. Its specific surface area increased by 29.7% and its thermal conductivity decreased by 12.3% compared to the unactivated group. Compared to the method of first drying and pulverizing waste wet gel before adding it as a filler, the wet activation and reuse route of this invention not only eliminates the energy-intensive drying step but also avoids the problem of difficult dispersion of dry powder in sol. The resulting product had a reduced bulk density of 8.7%, a increased specific surface area of ​​15.6%, and a reduced thermal conductivity of 13.2%. At the same time, the gelation time was shortened by 30% compared to the pure fresh silicon source system, significantly improving production efficiency.

[0035] In this invention, the waste wet gel actually originates from unavoidable product losses during the large-scale production of aerogels due to the influence of the production process. This waste wet gel is generated due to various reasons such as deviations in gelation condition control, mold cutting, shape trimming, or product slitting. For example, a small portion of the wet gel may be cut off due to poor gelation effect caused by deviations in gelation condition control; some wet gel may be removed after cutting to fit the mold shape; and some wet gel may be cut off during shape correction or product slitting. All such wet gels generated due to process losses are considered waste wet gels as described in this invention.

[0036] In some embodiments of the present invention, in step 1, the waste wet gel is pretreated to remove foreign matter, mainly removing obvious foreign matter such as fibers and dust, without the need for drying. The solid content of the waste wet gel is 2wt% to 15wt% (calculated as dry gel), and the solvent in the waste wet gel is water, methanol, or a mixture of water and methanol.

[0037] In some embodiments of the present invention, in step 2, the volume of anhydrous methanol added is 2 to 5 times the volume of the waste wet gel. When the volume of anhydrous methanol added is less than 2 times the volume of the waste wet gel, the solid content of the system is too high, the shear force distribution during the crushing process is uneven, and incompletely crushed gel fragments are likely to remain. Furthermore, the viscosity of the system is too high in the subsequent activation reaction stage, making it difficult for the activator to be evenly dispersed to the surface of all gel particles, resulting in insufficient activation of some particles. Simultaneously, the high solid content suspension has poor fluidity, which is not conducive to pipeline transportation and subsequent metering in industrial production. When the volume of anhydrous methanol added is greater than 5 times the volume of the waste wet gel, the solid content of the system is too low. When the activated waste wet gel is subsequently added back to the fresh silicon source sol, excessive solvent will be introduced, significantly diluting the concentration of the fresh sol, prolonging the gelation time, and even leading to incomplete gelation. This also increases the solvent handling volume and energy consumption in subsequent aging and drying processes, reducing production economics. In addition, the anhydrous methanol mentioned in the present invention can be replaced with a mixture of water and methanol according to the original solvent system of the waste wet gel to ensure the compatibility of the system solvents.

[0038] In some embodiments of the present invention, in step 2, the crushing conditions are: processing at a speed of 3000 rpm to 8000 rpm for 15 min to 60 min. This step uniformly crushes the wet gel block into micron-sized particles while preserving the original nanoporous structure inside the particles. When the crushing speed is below 3000 rpm, the shear force is insufficient to effectively destroy the three-dimensional network structure of the wet gel block. After crushing, the particle size distribution is wide, with a high proportion of large particles, making it difficult to achieve the target particle size requirement. Furthermore, a significantly longer processing time is required to obtain a similar crushing effect, resulting in low production efficiency. When the crushing speed is above 8000 rpm, the shear force is too strong, which not only breaks the macroscopic structure of the gel block but also destroys the nanoporous structure inside the gel particles, leading to a significant decrease in the specific surface area of ​​the particles. This results in the loss of the structural advantages necessary for serving as seed crystals, ultimately affecting the porosity and thermal insulation performance of the aerogel product. When the crushing time is less than 15 min, the crushing reaction is insufficient, and most of the gel block is not crushed to the target particle size range. A large number of millimeter-sized or hundred-micron-sized particles exist in the suspension, which are prone to subsequent sedimentation. When the crushing time exceeds 60 minutes, the crushing process has basically reached equilibrium. Continuing to extend the time will not significantly improve the particle size distribution. On the contrary, it will cause some particles to be over-crushed, producing a large number of nano-sized fine powders. These fine powders have extremely high surface energy and are still prone to self-aggregation even after subsequent activation treatment, forming local agglomerates in the sol, which leads to structural defects in the final aerogel product.

[0039] In some embodiments of the present invention, in step 2, the particle size D90 of the gel microparticles in the suspension is 1~10 μm. When the particle size D90 of the gel microparticles is less than 1 μm, the specific surface area of ​​the particles increases sharply, and the number of exposed silanol groups on the surface is too large. Even after surface activation treatment, it is still difficult to completely suppress the tendency of self-agglomeration between particles. Secondary agglomerates are easily formed in the fresh sol, resulting in an excessively fast local reaction rate during the gelation process, generating internal stress, and ultimately causing cracks and structural inhomogeneity in the aerogel product. When the particle size D90 of the gel microparticles is greater than 10 μm, the number of nucleation growth sites that a unit mass of gel microparticles can provide is significantly reduced, which cannot effectively accelerate the condensation reaction of the sol, and the effect of shortening the gelation time is not obvious. At the same time, the settling speed of large-diameter particles in the sol is accelerated, making it difficult to maintain a uniform dispersion state. This leads to uneven spatial distribution of the density and performance of the final aerogel product, with high-density agglomeration in local areas, reducing the overall thermal insulation performance of the product.

[0040] In some embodiments of the present invention, in step 3, the pH is adjusted to 4-5 using glacial acetic acid, and the reaction is stirred at 30°C-50°C for 1-4 hours. This allows the activator to be chemically grafted onto the surface of the gel particles, re-attaching active groups that can participate in the condensation reaction, thus obtaining an activated waste wet gel. When the system pH is below 4, the hydrolysis rate of the silane coupling agent is too fast, easily leading to intermolecular self-aggregation and the formation of oligomer precipitates, which cannot be effectively grafted onto the surface of the gel particles, resulting in a significant reduction in the effective utilization rate of the activator. Simultaneously, the strongly acidic conditions slightly corrode the surface structure of the gel particles, affecting their seeding effect. When the system pH is above 5, the hydrolysis rate of the silane coupling agent is too slow, resulting in insufficient reactivity. The grafting reaction is difficult to proceed fully, and the number of active groups grafted onto the surface of the gel particles is insufficient, failing to effectively improve their dispersibility and compatibility in fresh sol, and subsequent aggregation is still likely. When the reaction temperature is below 30°C, the grafting reaction rate is slow, resulting in a low grafting rate within the same reaction time, requiring a significantly longer reaction time to achieve the desired activation effect. When the reaction temperature exceeds 50℃, the volatility of the silane coupling agent increases, leading to a decrease in the concentration of the effective activator in the system. Simultaneously, high temperatures exacerbate the self-polymerization reaction of the silane coupling agent, further reducing grafting efficiency. Furthermore, high temperatures cause excessively rapid solvent evaporation in the suspension, affecting system stability. When the reaction time is less than 1 hour, the grafting reaction has not yet reached equilibrium, the surface activation of the gel particles is insufficient, and the coverage of active groups is low, failing to meet the requirements for subsequent use as seed crystals. When the reaction time exceeds 4 hours, the grafting reaction has essentially reached saturation; further extending the reaction time will not significantly improve the grafting rate but will instead increase production energy consumption and cycle time, reducing production efficiency.

[0041] In some embodiments of the present invention, in step 3, the activator is selected from one of γ-methacryloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or vinyltriethoxysilane. All three selected silane coupling agents contain hydrolyzable alkoxy functional groups (methoxy or ethoxy), which can slowly hydrolyze to generate silanol groups under the pH conditions of the present invention. These silanol groups then undergo a dehydration condensation reaction with the silanol groups on the surface of the gel particles, forming stable Si-O-Si chemical bonds. This achieves a firm grafting of the activator onto the gel surface, preventing the activator from detaching in subsequent processes. The other end of each of these three silane coupling agents has an active functional group (methacryloxy, amino, vinyl) that can participate in the sol-gel condensation reaction. This enables the activated gel particles to chemically bond with the hydrolysis products of the fresh silicon source sol, rather than simply physical mixing. This significantly enhances the interfacial bonding force between the seed crystals and the matrix, avoids the generation of interfacial defects, and ensures the mechanical properties and structural integrity of the final aerogel product. Furthermore, these three silane coupling agents are widely available and inexpensive in industry, and exhibit good solubility in water / methanol mixed solvents, enabling them to be uniformly dispersed in gel microparticle suspensions, making them suitable for large-scale industrial production. In contrast, epoxy-containing silane coupling agents show lower reactivity and grafting rates under the weakly acidic conditions of this invention; while long-chain alkyl-containing silane coupling agents can improve the hydrophobicity of gel microparticles, they cannot participate in subsequent polycondensation reactions, resulting in poor interfacial bonding and decreased product performance; fluorinated silane coupling agents are too expensive and their excessive hydrophobicity affects the dispersibility of gel microparticles in aqueous sols, making them unsuitable for the process system of this invention.

[0042] In some embodiments of the present invention, when the activated waste wet gel is used as a seed crystal to prepare aerogel products, there are two methods. One is to prepare fresh aerogel as a raw material, i.e., the raw material is entirely activated waste wet gel without the addition of fresh silicon source sol. The other is to prepare the silicon source into a silicon source sol, complete acid-catalyzed hydrolysis, and add the activated waste wet gel to the intermediate product after acid-catalyzed hydrolysis before alkali-catalyzed gelation, and then proceed with subsequent preparation steps. Both methods can prepare aerogel products with qualified performance, but the second method is better because the activated waste wet gel is added after acid-catalyzed hydrolysis and before alkali-catalyzed gelation. At this time, the fresh silicon source has been completely hydrolyzed into oligomers containing a large number of silanol groups, which can fully contact and react with the active groups on the surface of the activated gel particles, thus achieving better results. The mass of the activated waste wet gel converted into dry gel accounts for 5% to 25% of the mass of SiO2 in the silicon source sol, and the specific amount of activated waste wet gel added can be calculated based on this. When the mass of activated wet gel converted to dry gel accounts for less than 5% of the SiO2 mass in the silicon source sol, the number of activated gel particles in the system is insufficient, providing limited nucleation and growth sites. This fails to significantly alter the condensation reaction kinetics of the sol, resulting in an insignificant reduction in gelation time and little difference compared to the system without seed crystals. Furthermore, the recovery rate of the wet gel is limited, leading to a low comprehensive utilization rate of the silicon source, making it difficult to achieve the resource recycling benefits and economic value of this invention. When the mass of activated wet gel converted to dry gel accounts for 25% of the SiO2 mass in the silicon source sol, the proportion of activated gel particles in the system is too high, introducing excessive interfaces. Simultaneously, the increase in unreacted surface groups leads to a decrease in the uniformity of the aerogel's pore structure, a reduction in specific surface area, and an increase in thermal conductivity.

[0043] II. Examples and Comparative Examples

[0044] Example 1

[0045] Step 1 Waste wet gel collection: Collect unqualified wet gel blocks generated after gelation from a silica aerogel production line. After testing, its solid content (dry basis) is 8.5 wt%, and the solvent is a methanol / water mixture (volume ratio 7:3).

[0046] Step 2: Crushing and Dispersion: Take 500 g of the wet gel waste collected in Step 1 (containing approximately 42.5 g of dry gel), add 1500 mL of anhydrous methanol (the volume of methanol is approximately 3 times the volume of the wet gel), and put it into a high-shear homogenizer. Process at 5000 rpm for 30 min to obtain a suspension. Samples were taken for testing, and the particle size distribution was measured by a laser particle size analyzer to be D90 = 5.8 μm.

[0047] Step 3: Surface activation: Add 4.25 g of KH-570 silane coupling agent (10% of the dry gel mass) to the suspension prepared in Step 2, and adjust the pH to 4.5 with 0.5 mL of glacial acetic acid. Stir the mixture in a 40℃ constant temperature water bath for 2 hours. After the reaction, the suspension is uniformly milky white with no obvious sedimentation.

[0048] Step 4: Preparation of fresh silica sol: Using methyl orthosilicate (TMOS) as the silica source, mix TMOS: methanol: water in a molar ratio of 1:25:4, adjust the pH to 2.5 with 0.1 mol / L nitric acid, and hydrolyze at 40°C for 2 hours to obtain fresh silica sol (approximately 50 g as SiO2).

[0049] Step 5: Seed Addition and Gelation: All the activated suspension obtained in Step 3 was added to the fresh sol from Step 4 (10 g of the activated suspension converted to dry gel was added to approximately 50 g of fresh silica sol (calculated as SiO2), accounting for 20% of the fresh silica sol). After thorough mixing, 0.5 mol / L ammonia solution was added dropwise while stirring to adjust the pH to 7.0. The mixed sol was injected into a mold and laminated with glass fiber mat, then placed in a 30°C oven for static gelation to obtain the regenerated wet gel composite material. The time from the addition of ammonia solution to the complete loss of fluidity was recorded as 3.5 min (the control process without seed addition was 5 min).

[0050] Step 6: Aging and Drying: The regenerated wet gel composite material obtained in Step 5 was immersed in anhydrous methanol, and 10g of hexamethyldisilazane was added as a hydrophobic modifier. The mixture was aged at 50°C for 8 hours. Subsequently, it was dried using supercritical CO2 (temperature 45°C, pressure 12 MPa) to obtain the aerogel composite material. The aerogel composite material obtained in this example has a bulk density of 179 kg / m³. 3 The specific surface area is 912 m². 2 / g, with a thermal conductivity of 0.01872 W / (m·K).

[0051] Example 2

[0052] This example is an adjustment to Example 1, with the following differences: the fresh silicon source is a mixed silicon source of methyltrimethoxysilane (MTMS) and TMOS in a molar ratio of 0.4:1; the waste wet gel comes from the same production line; the silane coupling agent is APTES, used at 8% of the dry gel mass; the seed crystal addition is 15% of the fresh SiO2 mass; and the gelation temperature is 50°C. All other steps are exactly the same as in Example 1. The aerogel composite material obtained in this example has a gelation time of 7 min (compared to 10 min for the control) and a bulk density of 167 kg / m³. 3 Specific surface area is 852 m² 2 / g, with a thermal conductivity of 0.01752 W / (m·K).

[0053] Example 3

[0054] This example is an adjustment to Example 1, the difference being that the waste wet gel is derived from lost wet gel collected from the production line, and the amount of seed crystals added is increased to 25% of the mass of fresh SiO2. The gelation time is 3 min. All other steps are exactly the same as in Example 1. The bulk density is 182 kg / m³. 3 Specific surface area is 823 m² 2 The thermal conductivity is 0.02013 W / (m·K). The performance decreases slightly but still meets the usage requirements, indicating that the addition amount can reach 25%, but should not exceed 25%.

[0055] Comparative Example 1 (no seed crystal reuse, all fresh silicon source)

[0056] This example is an adjustment to Example 1, the difference being that activated waste wet gel is not added as a seed crystal. All other steps are exactly the same as in Example 1. The gelation time is 5 min, and the bulk density is 186 kg / m³. 3 Specific surface area is 883 m² 2 / g, with a thermal conductivity of 0.01984 W / (m·K).

[0057] Comparing Example 1 with Comparative Example 1: After reusing the seed crystals, the gelation time was shortened by 30% (5 min → 3.5 min), the thermal conductivity decreased by 5.6% (0.01984 → 0.01872), and the bulk density and specific surface area remained basically the same. This indicates that reusing the seed crystals not only saves raw materials but also improves process efficiency and the stability of thermal conductivity.

[0058] Comparative Example 2 (wet gel was directly crushed and added without activation)

[0059] The experiment was modified from Example 1, but with the following difference: The same waste wet gel as in Example 1 was used. After being crushed and dispersed, it was not subjected to KH-570 surface activation treatment; instead, fresh sol was added directly at the same dosage. Results: The gelation time was 4.5 min (slightly shortened, but not significantly). The aerogel eventually showed localized aggregation and cracks. This is because the crushing of the waste gel exposed a large amount of Si-OH, leading to rapid sedimentation and aggregation of particles, resulting in a specific surface area of ​​only 703 m². 2 / g, the thermal conductivity increased to 0.02134 W / (m·K). This demonstrates that the surface activation step is necessary for achieving uniform seed nucleation and performance retention.

[0060] Comparative Example 3 (waste gel was dried and pulverized and added as a filler)

[0061] The experiment was modified from Example 1, but with the following difference: no activation was performed. The waste wet gel was first dried at 80°C for 24 hours, then ball-milled to D90 = 10 μm, and added to the fresh sol of Example 1 in the same mass without activation. Results: The dry powder was difficult to disperse in the sol and easily settled; the gelation time was 5.5 min; the bulk density was 196 kg / m³. 3 Specific surface area is 712 m² 2 The thermal conductivity is 0.02156 W / (m·K), indicating a significant deterioration in performance.

[0062] Comparative Example 4

[0063] The waste wet gel collected in Example 1 cannot be used for the preparation of fresh aerogels without any treatment. This is because the collected waste wet gel has a jelly-like consistency, and if added directly to fresh sol, it will not form a cohesive mixture with the fresh sol, and will instead affect the process of preparing aerogels from the fresh sol. This also illustrates that the collected waste wet gel cannot be directly used for the preparation of fresh aerogels.

[0064] It is easy to see from the examples and comparative examples that:

[0065] (1) A comparison between Example 1 and Comparative Example 1 demonstrates that the activated waste wet gel treated by the process of the present invention can serve as a highly efficient nucleation seed, providing a large number of uniform growth sites for the sol-gel polycondensation reaction, significantly accelerating the gelation process and improving production efficiency. Simultaneously, the activated gel particles can form strong chemical bonds with the fresh sol matrix, rather than simple physical mixing. Therefore, it not only avoids introducing harmful defects but also optimizes the pore structure of the aerogel, maintaining or even improving product performance. Furthermore, this example also verifies that the process of the present invention can achieve a 20% saving of fresh silicon source, achieving closed-loop utilization of silicon source in the in-situ production process.

[0066] (2) The comparison between Example 1 and Comparative Example 4 clarifies the necessity of the pretreatment step. In Comparative Example 4, untreated jelly-like waste wet gel was directly added to fresh sol. As a result, the waste gel could not be mixed evenly with the fresh sol, which instead damaged the homogeneity of the sol, causing the subsequent gelation process to fail and ultimately failing to obtain a qualified aerogel product. This result proves that due to the existence of its macroscopic three-dimensional network structure, blocky waste wet gel cannot be directly reused. It must be broken down into micron-sized particles through crushing and dispersion treatment to achieve uniform mixing with fresh sol. This proves the necessity of the crushing and dispersion process in step 2 of this invention and indirectly verifies the importance of controlling the particle size range after crushing.

[0067] (2) The comparison between Example 1 and Comparative Example 2 strongly demonstrates the indispensability of the surface activation step. Comparative Example 2 used the exact same crushing conditions as Example 1 to obtain gel microparticles with a uniform particle size distribution, but did not undergo surface activation treatment and was directly added to fresh sol in the same amount. The results showed that the gelation time was shortened only from 5 min to 4.5 min, a reduction of less than 10%, which was far lower than the effect of Example 1; at the same time, the final aerogel showed obvious local aggregation and cracks, and the specific surface area decreased significantly to 703 m². 2 / g, the thermal conductivity increased to 0.02134 W / (m·K). This phenomenon is due to the large number of highly reactive silanol groups exposed on the surface of unactivated gel particles, which easily undergo self-agglomeration and rapid sedimentation in the sol, failing to serve as uniform nucleation sites and instead introducing numerous interfacial defects. In Example 1, by reacting at 40°C for 2 hours under weakly acidic conditions (pH 4-5), KH-570 was firmly grafted onto the surface of the gel particles through Si-O-Si chemical bonds, introducing methacryloyloxy functional groups that can participate in subsequent polycondensation reactions. This effectively inhibited the self-agglomeration of particles, maintaining a uniform and stable suspension without sedimentation, and also enhanced the interfacial bonding between the seed crystals and the matrix. This comparison verifies the rationality of the activation reaction parameter range (pH 4-5, 30°C-50°C, 1h-4h) in step 3 of this invention, as well as the technical necessity of selecting a silane coupling agent containing reactive functional groups as the activator, proving that surface activation is the core step for achieving efficient recycling of waste gels.

[0068] (3) The comparison between Example 1 and Comparative Example 3 highlights the unique advantages of the wet activation and reuse route of the present invention. In Comparative Example 3, the waste wet gel was first dried at 80°C for 24 hours, then ball-milled to the same D90=10μm as in Example 1, and added directly to fresh sol with the same mass without activation. The results showed that the dry powder was difficult to disperse in the sol and was prone to sedimentation. The gelation time was extended to 5.5 min, and the product bulk density increased to 196 kg / m³. 3 The specific surface area decreased to 712 m². 2 The thermal conductivity increased to 0.02156 W / (m·K) / g, indicating a significant deterioration in performance. This result shows that the drying process causes irreversible collapse of the nanoporous structure inside the gel particles, completely losing the structural advantages necessary for their function as seed crystals. Simultaneously, the dry powder has extremely high surface energy, making uniform dispersion difficult even after subsequent activation. In contrast, this invention employs a wet process throughout, with the entire process from crushing to activation taking place in a solvent environment. This fully preserves the nanoporous structure inside the gel particles, avoids the energy-intensive drying step, and simultaneously ensures the dispersibility and structural integrity of the particles.

[0069] (4) Examples 1 and 2 demonstrate the broad applicability of the technical solution of the present invention. In Example 2, the fresh silicon source was replaced with a mixed silicon source of methyltrimethoxysilane (MTMS) and tetraethyl orthosilicate (TEOS), the activator was replaced with 3-aminopropyltriethoxysilane (APTES), the amount of seed crystals was adjusted to 15%, and the gelation temperature was adjusted to 50°C. The results showed that the gelation time was still shortened from 10 min in the control to 7 min, a reduction of 30%, and the thermal conductivity of the product was as low as 0.01752 W / (m·K), which is better than the pure fresh silicon source system. This result proves that the activated waste wet gel recycling method of the present invention is applicable not only to pure silica aerogel systems, but also to organically modified silica aerogel systems. At the same time, the three silane coupling agents selected in the present invention, namely γ-methacryloyloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane and vinyltriethoxysilane, can all be chemically grafted onto the surface of gel particles and introduce active functional groups that can participate in polycondensation reactions, thus having the same activation effect.

[0070] (5) The comparison between Example 1 and Example 3 clarified the reasonable range of the amount of activated waste wet gel added. In Example 3, the amount of seed crystals added was increased to 25% of the mass of fresh SiO2, and the gelation time was further shortened to 3 min, but the specific surface area of ​​the product decreased to 823 m². 2 The thermal conductivity increased to 0.02013 W / (m·K), with a slight decrease in performance but still meeting industrial application requirements. This result demonstrates the technical rationality of the activated waste wet gel addition range of 5%~25% in this invention: when the addition amount is in the range of 15%~20%, the best balance between resource saving, improved production efficiency, and optimized product performance can be achieved; when the addition amount reaches 25%, although the performance shows an acceptable slight decrease, it still has industrial application value; however, if the addition amount continues to increase, the seed concentration in the system will be too high, leading to an excessively fast polycondensation reaction rate, a decrease in pore structure uniformity, and the introduction of too many interface defects, resulting in irreversible deterioration of product performance. Conversely, based on the technical principles of this invention, when the addition amount is less than 5%, the number of nucleation sites provided by the activated gel particles in the system is insufficient, which cannot significantly change the polycondensation reaction kinetics of the sol, the effect of shortening the gelation time is not obvious, and the recovery amount of waste wet gel is limited, making it difficult to reflect the resource recycling benefits and economic value of this invention.

[0071] In summary, the experimental results of all embodiments and comparative examples corroborate each other, fully demonstrating that the preparation method described in this invention can achieve technical effects such as closed-loop utilization of silicon source, reduced energy consumption, shortened gelation time, maintenance or improvement of product performance, and wide applicability.

[0072] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit the technical solutions. Those skilled in the art should understand that any modifications or equivalent substitutions to the technical solutions of the present invention without departing from the spirit and scope of the present invention should be covered within the scope of the claims of the present invention.

Claims

1. A method for activating waste wet gel, characterized in that, The specific steps are as follows: Step 1: Pre-treat the waste wet gel to remove foreign matter; Step 2: Mix the waste wet gel treated in Step 1 with anhydrous methanol and crush it to prepare a gel microparticle suspension; wherein the particle size D90 of the gel microparticles in the suspension is 1~20μm; Step 3: Add an activator to the suspension in Step 2, then adjust the pH to 4-5, stir the reaction for 1-4 hours, so that the activator is grafted onto the surface of the gel particles through chemical bonds to obtain activated waste wet gel. The activator is a silane coupling agent that can undergo a condensation reaction with the silanol groups (Si-OH) on the gel surface. The amount of activator added accounts for 5% to 15% of the mass of the dry aerogel, and the mass of the dry aerogel is the solid mass of the waste wet gel to be treated after drying.

2. The method according to claim 1, characterized in that, In step 1, the solid content in the waste wet gel is 2wt%~15wt% based on dry gel, and the solvent in the waste wet gel is water, methanol, or a mixture of water and methanol.

3. The method according to claim 1, characterized in that, In step 2, the volume of anhydrous methanol added is 2 to 5 times the volume of the waste wet gel.

4. The method according to claim 1, characterized in that, In step 2, the crushing conditions are: processing at a speed of 3000rpm~8000rpm for 15min~60min.

5. The method according to claim 1, characterized in that, In step 2, the particle size D90 of the gel microparticles in the suspension is 1~10μm.

6. The method according to claim 1, characterized in that, In step 3, the activator is selected from one of γ-methacryloxypropyltrimethoxysilane, 3-aminopropyltriethoxysilane, or vinyltriethoxysilane.

7. The method according to claim 1, characterized in that, The activated waste wet gel is used as a seed crystal to prepare aerogel products; specifically as follows. All raw materials for preparing aerogels are activated waste wet gels, without the addition of fresh silicon source sols; Alternatively, after preparing the silicon source into a silicon source sol and completing acid-catalyzed hydrolysis, and before alkaline-catalyzed gelation, the activated waste wet gel is added to the intermediate product after acid-catalyzed hydrolysis, and then subsequent preparation steps are carried out.

8. The method according to claim 7, characterized in that, The mass of activated waste wet gel converted to dry gel accounts for 5% to 25% of the mass of SiO2 in the silicon source sol. Based on this, the amount of activated waste wet gel to be added can be calculated.