A product of an alkaline non-spherical silica sol and a method for producing the same

Abstract

The application provides a preparation of alkaline non-spherical silica sol and a preparation method thereof, and relates to the technical field of silica sol, wherein the silica sol is ellipsoidal or short rod-shaped, the length-diameter ratio of the particle is 1.2-3:1, the long diameter is 30-300 nm, the short diameter is 20-100 nm, the inner core is compact, the outer shell has a mesoporous structure, the pore size is 2-5 nm, the specific surface area of the silica sol is 50-350 m 2 / g, and the pH value is 8-10. In the application, orthosilicate and methyltrimethoxysilane mixed silicate are synthesized in situ, the hydrolysis rates of the two are different, the former forms a compact inner core quickly, and the latter grafts an outer layer slowly, so that the symmetrical growth of the particle is broken, no morphology directing agent and no template residue are needed, and the purity of the finished product is higher. The organic amine is hydrolyzed mildly, the reaction is gentle and no severe polycondensation occurs, uniform size and non-agglomerated silica crystal cores can be prepared; low-speed stirring is combined with low silicon ester drop speed, the silicon source only grows on the surface of the crystal core in a directional manner, and the particle size is controllable. The outer layer of the particle is rich in methyl, and the space repulsion uniaxial extension is obtained, so that a stable shape is obtained.

Description

Technical Field

[0001] This invention relates to the field of silica sol technology, specifically to an alkaline non-spherical silica sol product and its preparation method. Background Technology

[0002] Alkaline silica sol is a stable colloidal system formed by dispersing silica particles in an alkaline aqueous solution. The particles carry a negative charge on their surface and maintain dispersion and do not agglomerate for a long time due to electrostatic repulsion. With its advantages such as stable storage, suitability for alkaline working conditions, and controllable purity, it is a key basic raw material for industries such as semiconductor chemical mechanical polishing, precision coating, composite material filling, and refractory materials.

[0003] Existing alkaline non-spherical silica sols, such as the method for preparing silica sol containing non-spherical silica using silica powder (publication number CN120736530A), have the following problems: 1. The process requires the separate purchase of special spherical silica sol seeds, which increases the cost of raw materials. Moreover, this solution relies solely on calcium ions to fine-tune the existing spherical seeds to change the shape of the particles. The range of morphology control is narrow, and fluctuations in the particle size and sphericity of the seeds themselves will be directly transmitted to the product, making it difficult to stably prepare silica with uniform shape and controllable morphology.

[0004] 2. The process uses both calcium hydroxide and sodium hydroxide, introducing a large number of calcium and sodium ions into the system. Calcium ions can damage the stability of the colloidal particles, easily causing silica sol to agglomerate and shorten the shelf life. Moreover, soluble calcium and sodium ions cannot be removed by centrifugation alone, resulting in a high content of metal impurities in the finished product. This makes it completely unsuitable for high-end fields such as semiconductor polishing, lithium battery separators, and high-purity electronic materials, which have strict requirements for low metal ion content. Summary of the Invention

[0005] This invention provides an alkaline non-spherical silica sol product and its preparation method, to solve at least one of the technical problems mentioned in the background art.

[0006] To solve the above-mentioned technical problems, this invention discloses a method for preparing alkaline non-spherical silica sol, comprising: Step S1: Add silicon powder and methanol to a high-pressure reactor at a mass ratio of 1:8 to 1:12, and add a transition metal-based catalyst at the same time; heat to 220 to 280°C with stirring, react at a pressure of 1.5 to 2.5 MPa, and react for 12 to 24 hours; after the reaction is completed, cool to room temperature and distill to obtain a mixed silicate ester. Step S2: Add the mixed silicate ester to deionized water and organic amine catalyst, and stir the reaction at 20-80°C for 1-6 hours to obtain mother liquor 1; Step S3: Maintain the reaction temperature of the mother liquor 1 obtained in step S2 at 20-80℃, and add the mixed silicate ester obtained in step S1 while stirring at a speed of 400-1000 r / min. The dropping rate of the mixed silicate ester is controlled at 0.5-2 mL / min. At the same time, add organic amine catalyst and deionized water to maintain the total amine concentration in the system at 0.05-0.2 mol / L and the molar ratio of water to silicate ester at 0.5-5:1. After the mixed silicate is added, continue stirring for 2 to 10 hours, then age for 2 hours; Step S4: The product obtained in step S3 is subjected to vacuum distillation at 60-65°C to recover methanol, and concentrated to a SiO2 mass fraction of 20-40 wt%. The product is then filtered to obtain an alkaline non-spherical silica sol.

[0007] Preferably, in S1, the molar ratio of methyl orthosilicate to methyltrimethoxysilane in the mixed silicate ester is between 1:0.3 and 1:1.5.

[0008] Preferably, in step S2, the raw materials are in the following proportions by mass: 100 parts of mixed silicate ester, 50-300 parts of deionized water, and 0.1-0.8 parts of organic amine catalyst.

[0009] Preferably, the transition metal-based catalyst is at least one of cuprous chloride, copper powder, and CuO.

[0010] Preferably, in step S1, the mass of the transition metal-based catalyst is 2 to 5% of the mass of the silicon powder.

[0011] Preferably, the organic amine catalyst includes at least one of the following: isopropylamine, tert-butylamine, 1-amino-2-propanol, diisopropylamine, triisopropylamine, cyclohexylamine, piperazine, pyridine, polyetheramine, ethanolamine, diethanolamine, triethanolamine, isopropanolamine, tetramethylguanidine, phenylguanidine, and biguanide.

[0012] Preferably, in step S3, the amount of mixed silicate ester obtained in step S1 added is 0.5 to 2 times the volume of mother liquor 1 obtained in step S2.

[0013] This invention also discloses an alkaline non-spherical silica sol product, prepared using the aforementioned method for preparing alkaline non-spherical silica sol. The alkaline non-spherical silica sol has an ellipsoidal, short rod-shaped, or worm-like morphology, with a particle aspect ratio of 1.2–3:1, a major diameter of 30–300 nm, a minor diameter of 20–100 nm, a dense core, and a mesoporous outer shell with a pore size of 2–5 nm. The alkaline non-spherical silica sol has a specific surface area of ​​50–350 m² / g. 2 / g, pH 8~10.

[0014] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments.

[0015] Compared with the prior art, the present invention has the following beneficial effects: The beneficial effects of this invention are as follows: 1. In step S1 of this invention, “methyl orthosilicate + methyltrimethoxysilane compound mixed silicate ester” (molar ratio 1:0.3 to 1:1.5) is generated in situ. There is no need to purchase two silicate esters for compounding, saving the high raw material cost of purchasing organosilicon monomers. The composite silicon source can be obtained directly by one-pot distillation, simplifying the upstream raw material process and greatly reducing the overall production cost.

[0016] The catalyst is a copper-based inexpensive inorganic catalyst. Compared with platinum and palladium precious metal catalysts, the raw materials are readily available and inexpensive. After the reaction, it can be easily separated and recovered, with no heavy metal residue pollution, making it suitable for industrial continuous production.

[0017] The hydrolysis and condensation of methyl orthosilicate readily produces regular spherical silica particles. Methyltrimethoxysilane, with its hydrophobic methyl side groups, has fewer silanol groups and greater steric hindrance after hydrolysis. The combination of the two results in a difference in hydrolysis and condensation rates: methyl orthosilicate hydrolyzes rapidly to form a dense core, while methyltrimethoxysilane slowly grafts onto the outer layer, naturally breaking the symmetrical growth trend of silica sol particles. This lays the foundation for the formation of ellipsoidal and short rod-shaped non-spherical morphologies at the molecular level, eliminating the need for additional morphology-directing agents (such as surfactants or polymer templates), avoiding template residue and post-processing removal steps, and resulting in higher product purity.

[0018] 2. In step S2, the low-concentration silicon source and mild temperature result in slow and uniform hydrolysis and condensation, and the system simultaneously generates a large number of uniform and non-agglomerated silica microcrystals. The organic amine weak base system has a slow hydrolysis rate, which will not cause crystal nucleus agglomeration and wide particle size distribution due to instantaneous and violent condensation, thus providing a uniform seed for subsequent particle growth.

[0019] 3. In step S3, the mixed silicate ester is slowly added while stirring at a constant speed of 400–1000 r / min and at an extremely low dropping rate of 0.5–2 mL / min. Simultaneously, organic amine and deionized water are continuously added, strictly maintaining the total amine concentration in the system at 0.05–0.2 mol / L and the water-silica molar ratio at 0.5–5:1. Low droplet acceleration rate controls the silicon source supply rate, avoiding local silicon source oversaturation and the generation of new impurity crystal nuclei. All silicon sources grow directionally only on the surface of the original mother liquor crystal nuclei, and the particle size is controllable. Slow catalysis by organic amine weak base enriches the methyl side groups of methyltrimethoxysilane on the outer layer of the particles. During the condensation process, the steric repulsion of methyl groups inhibits the isotropic growth of the particles, which preferentially extend along a single axis, and stably obtains ellipsoidal and short rod non-spherical particles with an aspect ratio of 1.2 to 3:1. The morphology is highly controllable and the consistency of morphology between batches is high. With precise limits on the water-to-silicon ratio and amine concentration, the outer silanol groups are not completely condensed, and 2-5 nm mesoporous pores are formed between molecules, naturally forming a dense core and mesoporous shell structure.

[0020] After the silicone ester is added, continue stirring for 2–10 hours, followed by aging for 2 hours. This allows for the slow condensation of residual silanol groups on the particle surface, eliminating internal stress and improving the sol's storage stability. Simultaneously, it helps to stabilize the mesoporous channel structure, preventing channel collapse during use and maintaining a stable specific surface area of ​​50–350 m². 2 / g.

[0021] 4. Organic amines such as ammonia, isopropylamine, tert-butylamine, 1-amino-2-propanol, diisopropylamine, and triisopropylamine are selected as catalysts. Compared with traditional strong base (NaOH, KOH) systems, organic amines are volatile weak bases. In the subsequent S4 vacuum distillation of methanol, the amines can be recovered and recycled simultaneously with the methanol, eliminating the need for NaOH. + K + Metal ion residue, suitable for high-purity applications such as electronics, catalysis, and polishing; 5. The final pH of the system is stably controlled at 8-10, which falls into the category of alkaline silica sol. It does not separate, precipitate, or gel after being stored at room temperature for several months, demonstrating excellent colloidal stability. Attached Figure Description

[0022] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 This is a transmission electron microscope (TEM) image of the product of Example 1 of the present invention; Figure 2 This is a transmission electron microscope (TEM) image of the product of Example 2 of the present invention; Figure 3 This is a transmission electron microscope (TEM) image of the product of Example 3 of the present invention; Figure 4 This is a transmission electron microscope (TEM) image of the product of Comparative Example 1 of the present invention. Figure 5 This is a transmission electron microscope (TEM) image of the product of Comparative Example 2 of the present invention. Figure 6 This is a transmission electron microscope (TEM) image of the product of Comparative Example 3 of the present invention. Detailed Implementation

[0023] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0024] Furthermore, in this invention, the use of terms such as "first" and "second" is for descriptive purposes only and does not specifically refer to any order or sequence, nor is it intended to limit the invention. They are merely used to distinguish components or operations described using the same technical terms and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions and features of the various embodiments can be combined with each other, but this must be based on the ability of those skilled in the art to implement them. If a combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by this invention.

[0025] The present invention provides the following embodiments: Figures 1-3 As shown, A method for preparing alkaline non-spherical silica sol, comprising: Step S1: Add silicon powder and methanol to a high-pressure reactor at a mass ratio of 1:8 to 1:12, along with a transition metal-based catalyst; heat to 220–280°C with stirring, maintain a reaction pressure of 1.5–2.5 MPa, and react for 12–24 hours; after the reaction is complete, cool to room temperature and distill to obtain a mixed silicate ester; the preferred stirring speed in step S1 is 300 r / min to 500 r / min. Step S2: Add the mixed silicate ester to deionized water and organic amine catalyst, and stir the mixture at 20-80°C for 1-6 hours to obtain mother liquor 1 (solid content approximately 10-15 wt%); the stirring speed in step S2 is 150-300 r / min. Step S3: In the mother liquor 1 obtained in step S2, the reaction temperature is maintained at 20-80℃. The mixed silicate ester obtained in step S1 is added while stirring at a speed of 400-1000 r / min. The dropping rate of the mixed silicate ester is controlled at 0.5-2 mL / min. At the same time, organic amine catalyst and deionized water are added to maintain the total amine concentration in the system at 0.05-0.2 mol / L and the molar ratio of water to silicate ester at 0.5-5:1. After the mixed silicate ester is added, stirring is continued for 2-10 hours, followed by aging for 2 hours (50-250 r / min can be used). Step S4: The product obtained in step S3 is subjected to vacuum distillation at 60-65°C to recover methanol, and concentrated to a SiO2 mass fraction of 20-40 wt%. The product is then filtered to obtain an alkaline non-spherical silica sol.

[0026] Preferably, in the silicate ester product (which also contains a small amount of dimethoxysilane and oligomers), the molar ratio of methyl orthosilicate to methyltrimethoxysilane is between 1:0.3 and 1:1.5.

[0027] In step S2, the raw materials are in the following proportions by mass: 100 parts of mixed silicate ester, 50-300 parts of deionized water, and 0.1-0.8 parts of organic amine catalyst.

[0028] Preferably, the transition metal-based catalyst is at least one of cuprous chloride, copper powder, and CuO.

[0029] Preferably, in step S1, the mass of the transition metal-based catalyst is 2 to 5% of the mass of the silicon powder.

[0030] Preferably, the organic amine catalyst includes at least one of the following: isopropylamine, tert-butylamine, 1-amino-2-propanol, diisopropylamine, triisopropylamine, cyclohexylamine, piperazine, pyridine, polyetheramine, ethanolamine, diethanolamine, triethanolamine, isopropanolamine, tetramethylguanidine, phenylguanidine, and biguanide.

[0031] Preferably, in step S3, the amount of mixed silicate ester obtained in step S1 added is 0.5 to 2 times the volume of mother liquor 1 obtained in step S2.

[0032] Preferably, the aspect ratio of the non-spherical silica particles is 1.2 to 3:1.

[0033] Example 1:

[0034] Step S1: Preparation and distillation separation of mixed silicates: 1. Feeding and reaction: Weigh 100g of industrial silicon powder with an average particle size of 50μm and a purity of ≥99%, and add it together with 1000g of industrial-grade anhydrous methanol into a 1.5L high-pressure stirred reactor. Add 3g of cuprous chloride powder as a transition metal-based catalyst.

[0035] After sealing the reactor, the air inside the reactor was replaced three times with 0.5 MPa nitrogen. The stirring was then started and the speed was controlled at 300 r / min. The temperature was increased to 250℃ at a programmed rate of 2℃ / min. The pressure inside the reactor was stabilized at 2.0 MPa, and the reaction was maintained at the same temperature and pressure for 18 hours.

[0036] 2. Distillation Separation: After the reaction is complete, the mixture is cooled to room temperature and filtered to remove unreacted silica powder and catalyst residue, yielding a crude reaction solution. The crude reaction solution is then purified by atmospheric distillation. First, collect the fraction at the top of the column at 64-66℃, which is unreacted anhydrous methanol; Once the temperature at the top of the column rises to 102°C, switch the collection container and continue to collect the fraction in the wide temperature range of 102–123°C. This fraction is the target mixed silicate ester. Distillation is terminated when the temperature at the top of the column exceeds 125°C, leaving high-polysiloxane and heavy residue in the bottom of the column.

[0037] This step ultimately yielded approximately 420g of mixed silicate ester. Gas chromatography analysis revealed that the main components of the mixed silicate ester (TMOS, Si(OCH3)4) were methyl orthosilicate and methyltrimethoxysilane (MTMS, CH3Si(OCH3)3), with a molar ratio of 1:0.8. It also contained small amounts of dimethoxysilane and siloxane oligomers, meeting the product composition requirements.

[0038] Step S2: Preparation of hydrolysis mother liquor 1: Take 100g of the above mixed silicate ester and 100g of deionized water and add them to a 1L three-necked flask equipped with a paddle stirrer, reflux condenser and constant temperature water bath. Prepare 1mol / L tert-butylamine as an organic amine catalyst, and slowly add 2.4mL of tert-butylamine to the system; turn on the stirrer, control the speed at 400r / min, raise the water bath temperature to 50℃, and stir the reaction at a constant temperature for 4 hours to obtain a homogeneous and transparent hydrolysis mother liquor 1.

[0039] Step S3: Particle Growth and Aging: Transfer all of the mother liquor 1 obtained in Step S2 into a 1L jacketed reactor, start stirring and control the rotation speed at 800 r / min, and maintain a constant temperature of 50±1℃; add the mixed silicate ester prepared in Step S1 to the mother liquor 1 at a constant dropping rate of 1.0 mL / min, with a total addition volume of 270 mL, which is 1.35 times the volume of the mother liquor 1. During the addition of silicate ester, 0.5 mol / L tert-butylamine and deionized water are added simultaneously. The amine concentration of the system is sampled and titrated every 30 min. The tert-butylamine addition rate is adjusted to maintain the total amine concentration of the system at 0.10±0.01 mol / L, and the amount of deionized water added is simultaneously controlled to keep the molar ratio of water to total silicate in the system stable at 3.8:1.

[0040] After the silicate ester was added, the mixture was stirred continuously at 50℃±1℃ and 800r / min for 6 hours. Then the stirring speed was reduced to 100r / min, and the mixture was allowed to stand for 2 hours to age. The system was then allowed to cool naturally to room temperature.

[0041] Step S4: Vacuum Concentration and Product Filtration: The aged reaction solution is transferred to a rotary evaporator, the water bath temperature is set to 62℃, and the system vacuum degree is -0.09MPa (gauge pressure) for vacuum distillation. 1. The distillate is a methanol-water mixture. Distillation continues until no obvious droplets fall from the end of the condenser. The recovered methanol can be purified and reused in the upstream process. 2. Sampling and testing the SiO2 mass fraction in the system; distillation is stopped when it reaches 25 wt%. 3. The concentrated solution was filtered through a 0.45μm microporous membrane to remove trace amounts of large particle agglomerates, yielding a clear alkaline non-spherical silica sol product with the following parameters: worm-like shape, short diameter 20nm, long diameter 60nm, aspect ratio 3:1, mesopore size 2.1nm, and specific surface area 242m². 2 / g, pH 9.2, no aggregation, clear and stable sol. Figure 1 As shown.

[0042] Example 2

[0043] Step S1: 100g silicon powder, 1100g methanol (mass ratio 1:11), add 2.5g copper powder (2.5% of silicon powder mass); react at 255℃ and 1.8MPa for 16h; distill to obtain mixed silicate ester, TMOS:MTMS=1:1.0.

[0044] Step S2: Take 100g of mixed silicate ester, 140g of deionized water, and 2.8mL of 1mol / L cyclohexylamine, and react at a constant temperature of 52℃ for 3.5h at 400r / min to obtain hydrolysis mother liquor 1.

[0045] Step S3: The mother liquor 1 is kept at a constant temperature of 52℃ and stirred at 750r / min. 240mL of mixed silicate ester (1.2 times the volume of the mother liquor) is added dropwise at a rate of 0.9mL / min. Cyclohexylamine and deionized water are added simultaneously to maintain the amine concentration at 0.09mol / L and the water-silica molar ratio at 3.5:1. After the addition is completed, the mixture is stirred for 7h and aged for 2h with a gradient decrease in stirring rate.

[0046] Step S4: Distill at 62℃ and -0.09MPa under reduced pressure to concentrate to a SiO2 solid content of 28wt%, filter through a 0.22μm filter membrane to obtain the finished product.

[0047] Measured finished product parameters: morphology: potato-shaped; minor axis: 45 nm; major axis: 90 nm; aspect ratio: 2:1; mesopore size: 3.1 nm; specific surface area: 165 m². 2 / g, pH 9.1, intact core-shell structure, uniform mesoporous channels. For example... Figure 2 As shown.

[0048] Example 3

[0049] Step S1: 100g silicon powder, 900g methanol (mass ratio 1:9), add 4g cuprous chloride (4% of silicon powder mass); react at 240℃ and 2.2MPa for 20h; distill to obtain mixed silicate ester, TMOS:MTMS=1:1.2.

[0050] Step S2: Take 100g of mixed silicate ester, 180g of deionized water, and 3.0mL of 1mol / L triethanolamine, and react at a constant temperature of 400r / min and 55℃ for 3h to obtain hydrolysis mother liquor 1.

[0051] Step S3: The mother liquor 1 is kept at a constant temperature of 55℃ and stirred at 700r / min. 300mL of mixed silicate ester (1.5 times the volume of the mother liquor) is added dropwise at a rate of 1.2mL / min. Triethanolamine and deionized water are added simultaneously to maintain the amine concentration at 0.12mol / L and the water-silica molar ratio at 3.0:1. After the addition is completed, the mixture is stirred for 5h and aged for 2h with a gradient decrease in stirring rate.

[0052] Step S4: Distill at 63℃ and -0.09MPa under reduced pressure to concentrate to a SiO2 solid content of 30wt%, filter through a 0.22μm filter membrane to obtain the finished product.

[0053] Measured finished product parameters: morphology ellipsoidal, minor axis 100nm, major axis 160nm, aspect ratio 1.6:1, mesopore diameter 5nm, specific surface area 116m² 2 / g, pH 8.9, uniform particle size, and excellent dispersibility. For example... Figure 3 As shown.

[0054] Comparative Example 1 Process conditions: completely consistent with Example 1, except that the mixed silicate ester was replaced with pure methyl silicate (TMOS), no MTMS was added, and tert-butylamine was used as the organic amine.

[0055] Experimental results: The particles are regular spherical, without ellipsoidal or worm-like non-spherical structures; the particle size is about 30 nm, with no core-shell differentiation; the mesoporous structure disappears, and the specific surface area is 95 m². 2 / g. For example... Figure 4 As shown.

[0056] Conclusion: The isotropic hydrolytic condensation of a single TMOS cannot break the symmetric growth and cannot form a non-spherical morphology and mesoporous shell, proving that MTMS is a necessary condition for constructing non-spherical morphologies and mesoporous structures.

[0057] Comparative Example 2 Process conditions: completely consistent with Example 2, except that the organic amine cyclohexylamine was replaced with an equal amount of ammonia (inorganic strong base), and the TMOS:MTMS ratio was fixed at 1:1.0.

[0058] Experimental results: The particles changed from a regular worm-like shape to a spherical shape with a diameter of about 50 nm. The non-spherical characteristics disappeared, and the specific surface area decreased to 62 m². 2 / g. For example... Figure 5 As shown.

[0059] Conclusion: The weak basicity and steric hindrance effect of organic amines can precisely regulate the difference in hydrolysis rate of disilyl esters and stabilize the non-spherical anisotropic growth; the hydrolysis rate of inorganic strong bases is too fast and the selectivity is poor, which cannot maintain the target morphology and mesoporous structure, proving the key regulatory role of the type of organic amine on morphology.

[0060] Comparative Example 3 Process conditions: completely consistent with Example 3, except that the silicon ester molar ratio TMOS:MTMS=1:1.6 was adjusted, and triethanolamine was selected as the organic amine.

[0061] Experimental results: The particles exhibited disordered morphology, collapsed ellipsoidal structures, and numerous irregular aggregates; the sol showed poor storage stability and was prone to stratification and sedimentation. Figure 6 As shown.

[0062] Conclusion: An excessively high proportion of MTMS will disrupt the synergistic polycondensation mechanism of the two silicone esters, leading to uncontrolled morphology. This verifies the rationality and necessity of the 1:0.3 to 1:1.5 ratio range of the present invention.

[0063] The beneficial effects of this invention are as follows: 1. In step S1 of this invention, “methyl orthosilicate + methyltrimethoxysilane compound mixed silicate ester” (molar ratio 1:0.3 to 1:1.5) is generated in situ. There is no need to purchase two silicate esters for compounding, saving the high raw material cost of purchasing organosilicon monomers. The composite silicon source can be obtained directly by one-pot distillation, simplifying the upstream raw material process and greatly reducing the overall production cost.

[0064] The catalyst is a copper-based inexpensive inorganic catalyst. Compared with platinum and palladium precious metal catalysts, the raw materials are readily available and inexpensive. After the reaction, it can be easily separated and recovered, with no heavy metal residue pollution, making it suitable for industrial continuous production.

[0065] The hydrolysis and condensation of methyl orthosilicate readily produces regular spherical silica particles. Methyltrimethoxysilane, with its hydrophobic methyl side groups, has fewer silanol groups and greater steric hindrance after hydrolysis. The combination of the two results in a difference in hydrolysis and condensation rates: methyl orthosilicate hydrolyzes rapidly to form a dense core, while methyltrimethoxysilane slowly grafts onto the outer layer, naturally breaking the symmetrical growth trend of silica sol particles. This lays the foundation for the formation of ellipsoidal and short rod-shaped non-spherical morphologies at the molecular level, eliminating the need for additional morphology-directing agents (such as surfactants or polymer templates), avoiding template residue and post-processing removal steps, and resulting in higher product purity.

[0066] 2. In step S2, the low-concentration silicon source and mild temperature result in slow and uniform hydrolysis and condensation, and the system simultaneously generates a large number of uniform and non-agglomerated silica microcrystals. The organic amine weak base system has a slow hydrolysis rate, which will not cause crystal nucleus agglomeration and wide particle size distribution due to instantaneous and violent condensation, thus providing a uniform seed for subsequent particle growth.

[0067] 3. In step S3, the mixed silicate ester is slowly added while stirring at a constant speed of 400–1000 r / min and at an extremely low dropping rate of 0.5–2 mL / min. Simultaneously, organic amine and deionized water are continuously added, strictly maintaining the total amine concentration in the system at 0.05–0.2 mol / L and the water-silica molar ratio at 0.5–5:1. Low droplet acceleration rate controls the silicon source supply rate, avoiding local silicon source oversaturation and the generation of new impurity crystal nuclei. All silicon sources grow directionally only on the surface of the original mother liquor crystal nuclei, and the particle size is controllable. Slow catalysis by organic amine weak base enriches the methyl side groups of methyltrimethoxysilane on the outer layer of the particles. During the condensation process, the steric repulsion of methyl groups inhibits the isotropic growth of the particles, which preferentially extend along a single axis, and stably obtains non-spherical particles with an aspect ratio of 1.2 to 3:1, such as ellipsoids, short rods or worms. The morphology is highly controllable and the consistency of morphology between batches is high. With precise limits on the water-to-silicon ratio and amine concentration, the outer silanol groups are not completely condensed, and there are 2-5 nm mesoporous pores between molecules, naturally forming a dense core and mesoporous shell structure.

[0068] After the silicone ester is added, continue stirring for 2–10 hours, followed by aging for 2 hours. This allows for the slow condensation of residual silanol groups on the particle surface, eliminating internal stress and improving the sol's storage stability. Simultaneously, it helps to stabilize the mesoporous channel structure, preventing channel collapse during use and maintaining a stable specific surface area of ​​50–350 m². 2 / g.

[0069] 4. Organic amines such as isopropylamine, tert-butylamine, 1-amino-2-propanol, diisopropylamine, triisopropylamine, cyclohexylamine, piperazine, pyridine, polyetheramine, ethanolamine, diethanolamine, triethanolamine, isopropanolamine, tetramethylguanidine, phenylguanidine, and biguanide are selected as catalysts. Compared with traditional strong base (NaOH, KOH) systems, organic amines are volatile weak bases. During the subsequent S4 vacuum distillation of methanol, the amines can be recovered and recycled along with the methanol, eliminating the need for NaOH. + K + Metal ion residue, suitable for high-purity applications such as electronics, catalysis, and polishing; 5. The final pH of the system is stably controlled at 8-10, which falls into the category of alkaline silica sol. It does not separate, precipitate, or gel after being stored at room temperature for several months, demonstrating excellent colloidal stability.

[0070] In silicate ester products, the molar ratio of methyl orthosilicate to methyltrimethoxysilane is between 1:0.3 and 1:1.5. Before mass production, it is necessary to select a corresponding sub-molar ratio range (e.g., a sub-molar ratio range commonly used in industrial production) based on the actual needs of downstream products, and determine the appropriate range for each parameter in step S1 corresponding to this sub-molar ratio range through experiments. That is, after selecting a more precise sub-molar ratio range, the criteria for evaluation are that the molar ratio of the internal components of the mixed silicate ester meets the standard (satisfies the sub-molar ratio range) and the product quality is qualified, within the predetermined process range of step S1 (silicon powder to methanol mass ratio 1:8 to 1:12, reaction temperature 220 to 280℃, reaction pressure 1.5 to 2.5). Within a range of MPa, reaction time of 12–24 hours, stirring speed of 300–500 r / min, and transition metal-based catalyst mass of 2–5% of silicon powder mass, a set of specific process parameter ranges (referred to as the suitable process parameter ranges for the selected sub-molar ratio ranges; suitable mass ratio range; suitable reaction temperature range; suitable reaction pressure range; suitable reaction time range; suitable stirring speed range; and suitable ratio range where the transition metal-based catalyst mass is equal to the silicon powder mass) was selected through experiments to stably achieve the product quality requirements (the final quality requirements of the product prepared within the sub-molar ratio range). This ensures that the molar ratio of the two substances in the product is stably controlled within the selected sub-range, meeting the production requirements for subsequent preparation of alkaline non-spherical silica sol.

[0071] Preferred embodiment 1: Step S1 for the selected target sub-moole interval includes: Step S11: Add silicon powder and methanol to the high-pressure reactor according to the selected value in the suitable mass ratio range of the selected target molar range, and add a transition metal-based catalyst at the same time, wherein the mass of the transition metal-based catalyst is the selected value in the suitable mass ratio range corresponding to the mass of silicon powder. Step S12: Select a stirring speed within the suitable stirring speed range of the selected target sub-molar range and continue stirring; first, replace the air in the reactor and pre-charge nitrogen to 50% to 60% of the lower limit of the suitable reaction pressure range (this pressure is suitable for all target sub-molar ranges, all particle size micron-sized silicon powder and all methanol feeding ratios of this invention; relying on the superposition law of nitrogen partial pressure and methanol high-temperature vapor pressure, adopting a pre-charged nitrogen base partial pressure higher than the industry's conventional ratio can significantly reduce the gas phase pressure fluctuation during the heating stage, without the need for large-scale nitrogen replenishment and pressure relief operations, effectively reducing methanol gas phase loss and stabilizing the product silicate molar ratio), then heat to the midpoint of the suitable reaction temperature range, and simultaneously rely on the methanol saturated vapor pressure in conjunction with nitrogen replenishment or micro-release of gas phase pressure adjustment during the heating process, before entering the midpoint of the suitable reaction temperature range, pre-adjust and stabilize the reaction pressure in the reactor to the midpoint of the suitable reaction pressure range; The reaction pressure stabilizes at the midpoint of the suitable reaction pressure range ([P1, P2]), meaning the reaction pressure inside the reactor is maintained at the midpoint of the suitable reaction pressure range (midpoint of the suitable reaction pressure range ± 0.05 MPa). Step S13: Control the reaction temperature to maintain the corresponding suitable reaction temperature range, and detect the gas pressure inside the high-pressure reactor until the gas pressure inside the high-pressure reactor exceeds the preset gas pressure range for the first time, and detect the gas pressure inside the high-pressure reactor multiple times. The preset air pressure range is [ , M is set to 5-6 (the fluctuation window is moderate, which not only provides sufficient buffer to prevent ratio deviation, but also matches the auto-control accuracy of the autoclave). To fit the median of the reaction pressure range ([P1, P2]); Step S14: Determine the average pressure change rate based on the pressure detection value in step S13; Average pressure change rate = (P1 - P2) ÷ t; P1 is the gas pressure inside the reactor during the last test in step S13; P2 is the gas pressure measured when the gas pressure inside the reactor was in the midpoint of the adaptive reaction pressure range for the last time; t is "the gas pressure measurement time corresponding to P1 - the gas pressure measurement time corresponding to P2"; When the average pressure change rate exceeds the preset pressure change rate threshold, it indicates that hydrogen production continues at the interface, the proportion of gaseous hydrogen gradually increases, the effective methanol gas phase partial pressure is diluted, and the trend of side reaction formation intensifies; with the first pressure range [P1, ], First stirring speed range [adapted to the median of the stirring speed range, adapted to the upper limit of the stirring speed range], adapted to the reaction temperature range to continue controlling the reaction; The preset pressure change rate threshold is determined by fully executing the entire set of small-scale tests from S11 to S14, with the target silicate ester molar ratio being qualified (meaning that in the mixed silicate product, the molar ratio of methyl orthosilicate to methyltrimethoxysilane falls within a pre-selected, precise range of 1:0.3 to 1:1.5, meeting the material requirements for downstream alkaline non-spherical silica sol production, which is considered a qualified product). Through multiple sets of experiments, repeated adjustment of reaction conditions, and actual measurement verification, the maximum permissible comprehensive pressure increase rate that can stably ensure product qualification was determined. Comparative Example 01: The difference from Preferred Example 1 is that the pre-charged nitrogen gas adopts the industry-standard fixed low-pressure pre-charge of 0.4 to 0.6 MPa, and is not linked to the lower limit of the adaptive reaction pressure range corresponding to the target sub-molar ratio; the other basic process conditions such as the adaptive mass ratio, adaptive reaction temperature range, adaptive reaction pressure range, and reaction time that match the target sub-molar ratio are consistent with those of Preferred Example 1.

[0072] Comparative Example 02: The difference from Preferred Example 1 is that the narrow-range control mechanism of adapting to the median range of reaction pressure and matching the preset gas pressure range is cancelled. The pressure inside the reactor is allowed to fluctuate freely within the adapted reaction pressure range. It is impossible to calculate the actual reaction activity of silicon powder under the corresponding target sub-molar ratio based on the median of the adapted pressure range, and no layered control buffer window is reserved. All other process steps and adaptation parameter ranges that are associated with the target sub-molar ratio are the same as those in Preferred Example 1.

[0073] Comparative Example 03: The difference from Preferred Example 1 is that the average pressure change rate quantification judgment mechanism based on the target molar ratio qualification threshold established in step S14 is cancelled, as well as the pressure-stirring layered hierarchical linkage control process. The entire process only maintains the initially selected adaptive pressure and adaptive stirring speed at a constant speed, without adaptive correction operation for hydrogen production side reaction; the other pre-charge nitrogen gas, temperature rise and pressure stabilization and other pre-supporting operations are the same as those in Preferred Example 1.

[0074] Test Example: Three batches of industrially produced micron-sized silicon powder were selected. Due to inherent differences in particle size distribution and surface oxide layer thickness, the reactivity of each batch of silicon powder naturally fluctuates from batch to batch. Mixed silicates adapted to the same target molar ratio range were prepared using the complete layered control process of this invention and the processes of Comparative Examples 1 to 3, respectively. Three sets of repeated tests were carried out in parallel for each batch of silicon powder, and the following performance indicators were uniformly tested: 1. First-pass yield of product molar ratio: refers to the percentage of test batches in which the molar ratio of methyl orthosilicate to methyltrimethoxysilane falls within the preset target molar ratio range; 2. Maximum fluctuation of molar ratio in a single batch: The maximum deviation of the molar ratio test results of the two components in the product obtained by repeated tests of the same batch of silicon powder; 3. Fluctuation in pass rate across batches: The maximum difference in pass rate between the corresponding molar ratios of the three batches of silicon powder with different activities.

[0075]

[0076] The beneficial effects of the above technical solution are as follows: This invention employs a comprehensive graded control process, including pre-charge nitrogen partial pressure regulation, constant temperature and pressure operation within a steady-state range, online determination of the pressure increase rate, and pressure-stirring stratified step-by-step linkage control. The effects are reflected in the following: Step S12 limits the pre-charged nitrogen to 50% to 60% of the lower limit of the reaction pressure range, which is different from the industry's common fixed low-pressure pre-charge scheme. It establishes a medium-to-high stable gas phase base based on the superposition law of nitrogen and methanol vapor pressure, which greatly reduces the fluctuation range of gas phase pressure during the heating stage. It eliminates the need for frequent and large-scale nitrogen replenishment and depressurization, reduces methanol vapor phase loss during the heating process, and avoids the ratio deviation caused by raw material loss from the beginning of the heating process.

[0077] Steps S12 and S13 set the adaptive reaction pressure median range (median ± 0.05 MPa) and match the preset gas pressure range. , Furthermore, with M set to 5-6, the entire narrow-range buffer window uses the median pressure as the core benchmark, matching the auto-control precision of the high-pressure reactor while reserving sufficient buffer margin for ratio deviation. Under normal operating conditions, the reaction is stably constrained within a narrow pressure range close to the median pressure for isothermal operation, establishing a statically stable reaction base with a fixed temperature range and a centrally located narrow pressure range. Simultaneously, relying on operating conditions close to the median, pressure data is accurately collected to quickly calculate the actual reactivity and real-time pressure rise rate corresponding to different silicon powder raw materials, predicting reaction trends in advance and reserving sufficient dynamic control buffer time. Regardless of the reactivity of the raw materials, this central operating mode can maintain a stable and controllable methanol vapor phase partial pressure baseline, stably locking the competitive selectivity of the main reaction, avoiding drastic fluctuations in reaction rate caused by different active raw materials from the source, and reserving sufficient operating window for subsequent S14 layered stepwise correction control.

[0078] Step S14 introduces a quantitative judgment mechanism for the average pressure change rate. By accurately calculating the gas phase pressure rise amplitude per unit time, it identifies abnormal operating conditions such as continuous hydrogen production at the interface and intensified side reactions in real time. Once the pressure rise rate exceeds the preset threshold determined by multiple small-scale experiments, it immediately initiates hierarchical control: the reaction pressure is lowered to the first gas pressure range and the first stirring speed range. Under the premise of not exceeding the process safety pressure limit, the total system pressure is reduced to increase the proportion of methanol gas phase. At the same time, stirring is strengthened to renew the gas-liquid interface and break the hydrogen stagnation layer, thereby bidirectionally weakening the competitive advantage of side reactions and strengthening the positive progress of the main reaction.

[0079] Overall, the first layer of pre-charged nitrogen gas stabilizes the gaseous environment from the source of temperature rise, offsetting initial differences in raw material properties. The second layer locks in the selectivity of the basic reaction within a narrow temperature and pressure static range, resisting conventional activity fluctuations. The third layer features online monitoring of the pressurization rate and dynamic correction through pressure-stirring linkage, providing real-time adaptive adjustment for extreme conditions such as large-scale hydrogen production from highly active silicon powder and sudden increases in side reactions. This fundamentally reduces the rate of substandard products caused by fluctuations in raw material activity, significantly improving batch production stability and first-pass yield, and addressing the industry shortcomings of traditional narrow-window alcoholysis processes, which can only passively stabilize pressure, lack fine-tuning capabilities, and have poor raw material adaptability.

[0080] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A method for preparing an alkaline non-spherical silica sol, characterized in that: include: Step S1: Add silicon powder and methanol to a high-pressure reactor at a mass ratio of 1:8 to 1:12, and add a transition metal-based catalyst at the same time; The mixture was heated to 220–280 °C with stirring, the reaction pressure was 1.5–2.5 MPa, and the reaction time was 12–24 hours. After the reaction was completed, it was cooled to room temperature and distilled to obtain a mixed silicate ester. Step S2: Add the mixed silicate ester to deionized water and organic amine catalyst, and stir the reaction at 20-80°C for 1-6 hours to obtain mother liquor 1; Step S3: Maintain the reaction temperature of the mother liquor 1 obtained in step S2 at 20-80℃, and add the mixed silicate ester obtained in step S1 while stirring at a speed of 400-1000 r / min. The dropping rate of the mixed silicate ester is controlled at 0.5-2 mL / min. At the same time, add organic amine catalyst and deionized water to maintain the total amine concentration in the system at 0.05-0.2 mol / L and the molar ratio of water to silicate ester at 0.5-5:

1. After the mixed silicate is added, continue stirring for 2 to 10 hours, then age for 2 hours; Step S4: The product obtained in step S3 is subjected to vacuum distillation at 60-65°C to recover methanol, and concentrated to a SiO2 mass fraction of 20-40 wt%. The product is then filtered to obtain an alkaline non-spherical silica sol.

2. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: In S1, the molar ratio of methyl orthosilicate to methyltrimethoxysilane in the mixed silicate ester is between 1:0.3 and 1:1.

5.

3. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: In step S2, the raw materials are in the following proportions by mass: 100 parts of mixed silicate ester, 50-300 parts of deionized water, and 0.1-0.8 parts of organic amine catalyst.

4. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: The transition metal-based catalyst is at least one of cuprous chloride, copper powder, and CuO.

5. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: In step S1, the mass of the transition metal-based catalyst is 2 to 5% of the mass of the silicon powder.

6. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: Organic amine catalysts include at least one of the following: isopropylamine, tert-butylamine, 1-amino-2-propanol, diisopropylamine, triisopropylamine, cyclohexylamine, piperazine, pyridine, polyetheramine, ethanolamine, diethanolamine, triethanolamine, isopropanolamine, tetramethylguanidine, phenylguanidine, and biguanide.

7. The method for preparing an alkaline non-spherical silica sol according to claim 1, characterized in that: In step S3, the amount of mixed silicate ester obtained in step S1 is 0.5 to 2 times the volume of mother liquor 1 obtained in step S2.

8. An alkaline non-spherical silica sol product, characterized in that: The alkaline non-spherical silica sol is prepared using any one of the preparation methods described in claims 1-7. The alkaline non-spherical silica sol has an ellipsoidal, short rod-shaped, or worm-like morphology, with a particle aspect ratio of 1.2–3:1, a major diameter of 30–300 nm, a minor diameter of 20–100 nm, a dense core, and a mesoporous outer shell with a pore size of 2–5 nm. The specific surface area of ​​the alkaline non-spherical silica sol is 50–350 m² / g. 2 / g, pH 8~10.

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