White carbon black, its preparation method and application

Abstract

The application discloses white carbon black and a preparation method and application thereof, and the preparation method comprises the following steps: S1, silicon source pretreatment: mixing rice husk ash and a sodium hydroxide solution, reacting under the assistance of microwaves, adding a composite impurity removing agent for deep purification after filtration, and obtaining refined water glass solution; S2, modified precursor preparation: adding a composite modifier into the refined water glass solution, and obtaining a modified precursor solution; S3, high-pressure spray carbonization: atomizing the precursor solution, and reacting with mixed gas of CO2 and N2 in a high-pressure spray reaction tower to generate white carbon black slurry; S4, post-treatment: after washing and grinding, the white carbon black slurry is spray dried to obtain a finished product; and S5, waste liquid circulation: reacting the washing waste liquid with limestone, and recycling the alkali liquor for the step S1. The application realizes the recycling of waste resources; the product has high activation degree and excellent dispersibility, is applied to rubber reinforcement, improves processing performance, significantly enhances mechanical properties such as tensile strength, and has a good industrial application prospect.

Description

Technical Field

[0001] This invention relates to the field of silica preparation technology, and particularly to a silica preparation method and its application. Background Technology

[0002] Silica, an important inorganic functional material, is mainly composed of amorphous silica hydrate. It features a large specific surface area, strong adsorption capacity, and excellent reinforcing effect, and is widely used in rubber, coatings, adhesives, electronic materials, new energy, and other fields. With the rapid development of industries such as green tires and high-end electronic materials, the market demand for highly dispersible, high-purity, and low-production-cost silica is increasing, while simultaneously placing higher demands on the environmental friendliness of its preparation process.

[0003] Currently, the main methods for preparing precipitated silica include gas-phase methods and precipitation methods. While gas-phase precipitated silica has advantages such as high purity and good dispersibility, it suffers from problems including expensive raw materials, high reaction temperatures (>1000℃), high energy consumption, and high production costs, and also has high technological barriers. Precipitation is currently the most widely used process, and can be further divided into acid precipitation and carbonization methods. Acid precipitation involves reacting strong acids such as sulfuric acid and hydrochloric acid with sodium silicate, which results in severe equipment corrosion and the generation of large amounts of SO4. 2+ The existing silica preparation technologies suffer from several drawbacks, including difficulty in treating wastewater, significant environmental pollution, and intermittent production, limiting output and efficiency. Traditional carbonization methods often employ bubbling processes, requiring numerous reaction tanks, resulting in long reaction cycles, complex processes, and difficulty in controlling the endpoint, hindering continuous production and leading to low carbon dioxide utilization. Furthermore, precipitation methods primarily rely on quartz sand as the silicon source, a mineral resource. In summary, current silica preparation technologies still exhibit core shortcomings, such as limited silicon source selection (high cost of traditional silicon sources and difficulty and high cost of impurity removal from biomass silicon sources), low reaction efficiency, poor continuity, and low carbon dioxide utilization. It is also difficult to simultaneously achieve optimal product purity, specific surface area, and dispersibility, leading to reliance on imports for high-end products. The preparation process generates large amounts of wastewater, resulting in high environmental treatment costs and low resource utilization.

[0004] Therefore, developing a method for preparing silica that uses renewable raw materials, is environmentally friendly and energy-saving, and produces silica with high specific surface area and good dispersibility is of great practical significance and market value. Summary of the Invention

[0005] The purpose of this invention is to provide a silica, its preparation method and application, to solve the problems of high raw material cost, difficulty in impurity removal, low reaction efficiency, serious environmental pollution and poor product dispersibility in the preparation of silica in the prior art. It has the advantages of renewable raw materials, continuous process, environmental protection and energy saving, and excellent product performance.

[0006] In a first aspect, the present invention provides a method for preparing silica, comprising the following steps:

[0007] S1. Pretreatment of silicon source: Biomass rice husk ash is mixed with sodium hydroxide solution with a concentration of 2.0~3.5mol / L at a solid-liquid ratio of 1:8~12, and reacted at 75~85℃ for 2~3h under microwave assistance. Solid impurities are removed by filtration to obtain crude water glass solution. A composite impurity removal agent is added to the crude water glass solution, and the mixture is stirred and reacted for 1~1.5h. Chelate precipitate is removed by filtration to obtain refined water glass solution with a modulus of 3.0~4.2 and a mass concentration of 10~20%.

[0008] S2. Preparation of modified precursor: Add composite modifier to refined water glass solution, stir and disperse at 50~60℃ for 30~40min to obtain modified water glass precursor solution;

[0009] S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into the high-pressure spray reaction tower and atomized into droplets by a centrifugal atomizer. At the same time, a mixture of carbon dioxide and nitrogen is introduced into the reaction tower. The pressure inside the tower is controlled at 0.1~0.5MPa and the temperature is 50~80℃. The droplets and the mixed gas react in the tower for 10~20s to generate white carbon black slurry.

[0010] S4. Post-processing: The silica slurry is washed, milled, and spray-dried in sequence to obtain the finished silica product.

[0011] S5. Waste liquid recycling: Add limestone powder to the waste liquid generated from washing in S4, stir and react at 60~70℃ for 1~2h, filter to obtain calcium carbonate byproduct and dilute sodium hydroxide solution; after the dilute sodium hydroxide solution is concentrated to a concentration of 2.0~3.5mol / L, it can be reused in the rice husk ash alkali dissolution reaction in S1.

[0012] As a preferred embodiment of the present invention, in step S1,

[0013] The microwave-assisted power is 3~8kW and the frequency is 2450MHz;

[0014] The composite impurity remover is obtained by mixing citric acid and disodium EDTA at a mass ratio of 2 to 3:1, and the amount added is 0.8 to 1.5% of the mass of the crude water glass solution.

[0015] As a preferred embodiment of the present invention, in step S2, the composite modifier is a mixture of silane coupling agent KH-550 and polyethylene glycol in a mass ratio of 3 to 5:1, and the amount added is 2 to 5% of the mass of the refined water glass solution.

[0016] As a preferred embodiment of the present invention, in step S3...

[0017] The rotation speed of the centrifugal atomizer is 15000~25000 rpm;

[0018] The volume content of carbon dioxide in the mixture of carbon dioxide and nitrogen is 70-90%.

[0019] The ratio of the feed rate of the modified water glass precursor liquid to the inlet rate of the mixed gas is 1:5~8.

[0020] As a preferred embodiment of the present invention, in step S4,

[0021] The washing process uses deionized water and involves repeated washing and filtration, with continuous monitoring until the pH of the filtrate reaches 6.5-7.5.

[0022] The grinding process involves adding washed slurry to a colloid mill and adding 15-25% (by weight) of deionized water. The grinding is carried out at a speed of 4000-6000 rpm and a grinding gap of 0.05-0.2 mm using a circulating grinding method. That is, the slurry is ground by the colloid mill and then returned to the feed end for further grinding. The particle size is monitored in real time by a laser particle size analyzer until the particle size is 8-20 nm.

[0023] The inlet air temperature of the spray dryer is 180~220℃, and the outlet air temperature is 80~100℃.

[0024] As a preferred embodiment of the present invention, in step S5, the amount of limestone powder added is calculated based on a stoichiometric ratio of sodium carbonate in the waste liquid of 1:1, and the actual amount added is 1.05 to 1.10 times the theoretical amount.

[0025] In a second aspect, the present invention provides a silica, which is prepared by the preparation method described in the first aspect.

[0026] Thirdly, the present invention also provides an application of the silica described in the second aspect, wherein the silica is used as a rubber reinforcing agent.

[0027] Compared with the prior art, the beneficial effects of the present invention are:

[0028] 1. This invention innovates silicon source utilization by using renewable biomass rice husk ash as a silicon source, reducing raw material costs while achieving resource utilization of waste. The accompanying microwave-assisted alkali dissolution and composite impurity removal technologies specifically address the pain points of rice husk ash's high impurity content and unstable composition. Microwave technology enhances the rapid dissolution of silicon, while the combination of citric acid and EDTA precisely chelates metal ions such as iron and aluminum, improving the purity of the silicon source from the source. This combination utilizes inexpensive raw materials while ensuring that the subsequent spray carbonization reaction produces high-quality silica with uniform structure and stable performance, achieving a balance between economic efficiency and product performance.

[0029] 2. This invention breaks through the traditional step-by-step process of "preparation followed by modification" for precipitated silica by integrating modification and carbonization into an integrated process. By adding a composite modifier to the water glass solution, the carbonization reaction and surface modification are carried out simultaneously, simplifying the production process and reducing production costs. At the same time, the addition of polyethylene glycol improves the dispersibility of atomized droplets, avoids particle agglomeration, and increases the grafting rate of silane coupling agent, significantly improving the dispersibility and interfacial bonding ability of precipitated silica in the organic matrix.

[0030] 3. A closed-loop process of "alkali dissolution-carbonation-waste liquid recovery-alkali reuse" is constructed. The washing waste liquid reacts with limestone to produce calcium carbonate by-product, which can be sold as filler, creating additional revenue. The recovered dilute sodium hydroxide solution is concentrated and reused in the rice husk ash alkali dissolution step, realizing the efficient recycling of alkali resources and eliminating waste liquid discharge. The entire preparation process does not require the use of strong acid, avoiding equipment corrosion and acidic waste liquid pollution, which meets the requirements of "dual carbon" development. Attached Figure Description

[0031] Figure 1 This is a flowchart illustrating the preparation process of the silica of the present invention. Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Traditional precipitation-based silica preparation processes typically use quartz sand or industrial sodium silicate as the silicon source, neutralizing and precipitating it with inorganic acids (such as sulfuric acid) in an atmospheric pressure reactor. However, this route has significant drawbacks, such as high raw material and energy costs. Whether it's high-temperature smelting of quartz sand to produce sodium silicate or directly purchasing industrial sodium silicate, both are energy-intensive processes, and raw material costs are greatly affected by fluctuations in the mineral market. The process is also rudimentary, resulting in poor product uniformity. The batch reactor method suffers from uneven mass and heat transfer, and localized over-acidity or over-alkaliness, leading to inconsistent size and structure of the generated primary silica particles, making batch stability difficult to guarantee. The product performance also has inherent defects. Silica obtained by traditional methods is rich in silanol groups on the surface, exhibiting high polarity, and is prone to agglomeration in organic matrices such as rubber, making uniform dispersion difficult and severely limiting its reinforcing performance. Furthermore, there is significant environmental pollution, with the reaction generating large amounts of high-salt wastewater containing sodium sulfate or sodium chloride, resulting in high treatment costs and low-value byproducts, leading to poor overall atom economy.

[0034] The innovation of this invention is not an improvement in a single aspect, but rather an integration of interconnected technologies. First, by innovating the raw material route starting from waste biomass and using rice husk ash as the silicon source, the high-value utilization of agricultural waste is achieved, significantly reducing raw material costs from the source and endowing the process with distinct circular economy attributes. Second, a synergistic process chain of "pre-purification-online modification-instantaneous reaction" is designed. Through a combination of microwave-assisted alkali dissolution and composite chelation for impurity removal, the problem of high impurity content in biomass silicon sources is solved, ensuring the purity of the precursor. Innovatively, a compound modifier (KH-550 and polyethylene glycol) is added to the refined water glass before carbonization, so that the surface of the subsequently generated white carbon black primary particles is modified by organic functional groups, reducing the surface energy from the beginning and laying the foundation for excellent dispersibility. The core reaction adopts high-pressure spray carbonization technology, replacing the traditional batch sedimentation. By atomizing the precursor into micron-sized droplets and reacting them with CO2 under pressure in an instantaneous gas-liquid reaction, each droplet becomes a uniform "microreactor," thereby achieving precise and controllable construction of product particle size, pore size, and structure, and significantly improving product uniformity.

[0035] This invention constructs a highly integrated, internally circulating green manufacturing system. The sodium carbonate-containing wastewater generated during post-treatment is regenerated into a sodium hydroxide solution through a causticization reaction with limestone and reused in the initial alkali-solution stage. Simultaneously, marketable calcium carbonate is produced as a byproduct. This design achieves near-zero-cost recycling of the alkali medium, eliminating the discharge problem of high-salt wastewater from traditional processes and transforming environmental burden into economic benefits. In summary, this invention, through its four-in-one innovation of "waste raw material utilization, refined reaction, product functionalization, and closed-loop process," successfully unifies the previously fragmented and even contradictory cost, quality, and environmental goals. It provides a new path for the production of precipitated silica that combines technological advancement, economic competitiveness, and environmental friendliness, and has positive significance for promoting the industry's transformation towards high-performance and sustainable development.

[0036] like Figure 1As shown, a method for preparing silica includes the following steps: S1. Silicon source pretreatment: Biomass rice husk ash is mixed with a sodium hydroxide solution with a concentration of 2.0~3.5 mol / L at a solid-liquid ratio of 1:8~12, and reacted at 75~85℃ for 2~3 h under microwave assistance. Solid impurities are removed by filtration to obtain a crude water glass solution. A composite impurity remover is added to the crude water glass solution, and the mixture is stirred and reacted for 1~1.5 h. The chelate precipitate is removed by filtration to obtain a refined water glass solution with a modulus of 3.0~4.2 and a mass concentration of 10~20%. S2. Preparation of modified precursor: A composite modifier is added to the refined water glass solution, and the mixture is stirred and dispersed at 50~60℃ for 30~40 min to obtain a modified water glass precursor solution. S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into a high-pressure spray reaction tower and atomized into droplets by a centrifugal atomizer. Simultaneously, a mixture of carbon dioxide and nitrogen is introduced into the reaction tower. The pressure inside the tower is controlled at 0.1~0.5 MPa, and the temperature at 50~80℃. The droplets and the mixed gas react in the tower for 10~20 seconds to generate precipitated silica slurry. S4. Post-treatment: The precipitated silica slurry is sequentially washed, milled, and spray-dried to obtain the finished precipitated silica product. S5. Waste liquid recycling: Limestone powder is added to the waste liquid generated from washing in S4, and the mixture is stirred and reacted at 60~70℃ for 1~2 hours. Filtration yields calcium carbonate byproduct and a dilute sodium hydroxide solution. The dilute sodium hydroxide solution is concentrated to a concentration of 2.0~3.5 mol / L and can be reused in the rice husk ash alkali dissolution reaction in S1.

[0037] All raw materials used in this invention are commercially available.

[0038] Example 1:

[0039] A method for preparing silica includes the following steps:

[0040] S1. Silicon source pretreatment: Biomass rice husk ash and sodium hydroxide solution with a concentration of 3.5 mol / L are mixed at a solid-liquid ratio of 1:12 and reacted at 85℃ for 3 hours with the assistance of microwave power of 8kW and frequency of 2450MHz. Solid impurities are removed by filtration to obtain crude water glass solution. 1.5% of a composite impurity remover (citric acid and disodium EDTA mixed at a mass ratio of 3:1) is added to the crude water glass solution and stirred for 1.5 hours. The chelate precipitate is removed by filtration to obtain a refined water glass solution with a modulus of 4.2 and a mass concentration of 20%.

[0041] S2. Preparation of modified precursor: Add 5% of composite modifier (silane coupling agent KH-550 and polyethylene glycol in a mass ratio of 5:1) to the refined water glass solution, stir and disperse at 60℃ for 40 min to obtain modified water glass precursor solution.

[0042] S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into a high-pressure spray reaction tower. The centrifugal atomizer rotates at 25,000 rpm to atomize it into droplets. At the same time, a mixture of carbon dioxide and nitrogen (carbon dioxide volume content is 90%) is introduced into the reaction tower. The ratio of the feed rate of the modified water glass precursor liquid to the feed rate of the mixed gas is 1:8. The pressure inside the tower is controlled at 0.5 MPa and the temperature at 80℃. The droplets and the mixed gas react in the tower for 20 seconds to generate white carbon black slurry.

[0043] S4. Post-treatment: The silica slurry is washed with deionized water, and the process is repeated by a combination of stirring, washing and filtration separation, with continuous monitoring until the pH of the filtrate reaches 7.5. Then, the washed slurry is added to a colloid mill, along with 25% of the slurry's mass of deionized water. The mill is then circulated at a speed of 6000 rpm and a grinding gap of 0.2 mm. The slurry is ground in the colloid mill and then returned to the feed end for further grinding. The particle size is monitored in real time using a laser particle size analyzer until the particle size reaches 8~20 nm. The ground silica slurry is then spray-dried at an inlet air temperature of 220℃ and an outlet air temperature of 100℃ to obtain the finished silica product.

[0044] S5. Waste liquid recycling: Limestone powder is added to the waste liquid generated from washing in S4 (the amount added is calculated based on the stoichiometric ratio of sodium carbonate in the waste liquid of 1:1, and the actual amount added is 1.10 times the theoretical amount). The mixture is stirred and reacted at 70℃ for 2 hours. After filtration, calcium carbonate byproduct and dilute sodium hydroxide solution are obtained. The dilute sodium hydroxide solution is concentrated to a concentration of 3.5 mol / L and can be reused in the rice husk ash alkali dissolution reaction in S1.

[0045] Example 2:

[0046] A method for preparing silica includes the following steps:

[0047] S1. Silicon source pretreatment: Biomass rice husk ash and sodium hydroxide solution with a concentration of 2.0 mol / L are mixed at a solid-liquid ratio of 1:8 and reacted at 75℃ for 2 hours with the assistance of microwave power of 3kW and frequency of 2450MHz. Solid impurities are removed by filtration to obtain crude water glass solution. 0.8% of the mass of the crude water glass solution is added to the crude water glass solution as a composite impurity remover (citric acid and disodium EDTA mixed at a mass ratio of 2:1). The mixture is stirred and reacted for 1 hour. The chelate precipitate is removed by filtration to obtain a refined water glass solution with a modulus of 3.0 and a mass concentration of 10%.

[0048] S2. Preparation of modified precursor: Add 2% of composite modifier (silane coupling agent KH-550 and polyethylene glycol in a mass ratio of 3:1) to the refined water glass solution, stir and disperse at 50℃ for 30 min to obtain modified water glass precursor solution.

[0049] S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into a high-pressure spray reaction tower. The centrifugal atomizer rotates at 15,000 rpm to atomize it into droplets. At the same time, a mixture of carbon dioxide and nitrogen (carbon dioxide volume content is 70%) is introduced into the reaction tower. The ratio of the feed rate of the modified water glass precursor liquid to the feed rate of the mixed gas is 1:5. The pressure inside the tower is controlled at 0.1 MPa and the temperature at 50℃. The droplets and the mixed gas react in the tower for 10 seconds to generate white carbon black slurry.

[0050] S4. Post-treatment: The silica slurry is washed with deionized water, and the process is repeated by a combination of stirring, washing and filtration separation, with continuous monitoring until the pH of the filtrate reaches 6.5. Then, the washed slurry is added to a colloid mill, along with 15% of the slurry's mass of deionized water. The mill is then circulated at a speed of 4000 rpm and a grinding gap of 0.05 mm. The slurry is ground in a circular motion, meaning it is ground by the colloid mill and then returned to the feed end for further grinding. The particle size is monitored in real time using a laser particle size analyzer until the particle size reaches 8~20 nm. The ground silica slurry is then spray-dried at an inlet air temperature of 180℃ and an outlet air temperature of 80℃ to obtain the finished silica product.

[0051] S5. Waste liquid recycling: Add limestone powder to the waste liquid generated from washing in S4 (the amount added is calculated based on the stoichiometric ratio of sodium carbonate in the waste liquid as 1:1, and the actual amount added is 1.05 times the theoretical amount), stir and react at 60℃ for 1 hour, filter to obtain calcium carbonate byproduct and dilute sodium hydroxide solution; after the dilute sodium hydroxide solution is concentrated to a concentration of 2.0 mol / L, it can be reused in the rice husk ash alkali dissolution reaction in S1.

[0052] Example 3:

[0053] A method for preparing silica includes the following steps:

[0054] S1. Silicon source pretreatment: Biomass rice husk ash and sodium hydroxide solution with a concentration of 2.7 mol / L were mixed at a solid-liquid ratio of 1:10 and reacted at 80℃ for 2.5 h with the assistance of microwave power of 5 kW and frequency of 2450 MHz. Solid impurities were removed by filtration to obtain a crude water glass solution. 1.2% of a composite impurity remover (citric acid and disodium EDTA mixed at a mass ratio of 2.5:1) was added to the crude water glass solution and stirred for 1.2 h. The chelate precipitate was removed by filtration to obtain a refined water glass solution with a modulus of 3.6 and a mass concentration of 15%.

[0055] S2. Preparation of modified precursor: Add 3.5% of the mass of the refined water glass solution as a composite modifier (silane coupling agent KH-550 and polyethylene glycol are compounded in a mass ratio of 4:1) to the refined water glass solution, stir and disperse at 55℃ for 35 min to obtain the modified water glass precursor solution.

[0056] S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into the high-pressure spray reaction tower. The centrifugal atomizer rotates at 20,000 rpm to atomize it into droplets. At the same time, a mixture of carbon dioxide and nitrogen (carbon dioxide volume content is 80%) is introduced into the reaction tower. The pressure inside the tower is controlled at 0.3 MPa and the temperature at 65℃. The droplets and the mixed gas react in the tower for 15 seconds to generate white carbon black slurry.

[0057] S4. Post-treatment: The silica slurry is washed with deionized water, and the process is repeated by a combination of stirring, washing and filtration separation, with continuous monitoring until the pH of the filtrate reaches 7.0. Then, the washed slurry is added to a colloid mill, along with 20% of the slurry's mass of deionized water. The mill is then circulated at a speed of 5000 rpm and a grinding gap of 0.1 mm. The slurry is ground in the colloid mill and then returned to the feed end for further grinding. The particle size is monitored in real time using a laser particle size analyzer until the particle size reaches 8~20 nm. The ground silica slurry is then spray-dried at an inlet air temperature of 200℃ and an outlet air temperature of 90℃ to obtain the finished silica product.

[0058] S5. Waste liquid recycling: Limestone powder is added to the waste liquid generated from washing in S4 (the amount added is calculated based on the stoichiometric ratio of sodium carbonate in the waste liquid of 1:1, and the actual amount added is 1.07 times the theoretical amount). The mixture is stirred and reacted at 65℃ for 1.5h. After filtration, calcium carbonate byproduct and dilute sodium hydroxide solution are obtained. The dilute sodium hydroxide solution is concentrated to a concentration of 2.7mol / L and can be reused in the rice husk ash alkali dissolution reaction in S1.

[0059] Comparative Example 1:

[0060] The difference from Example 1 is that the refined water glass solution obtained in S1 is reacted with a sulfuric acid solution with a concentration of 2~4 mol / L, the reaction temperature is controlled at 80℃ and the pH is 4.0, and after 2 hours of reaction, a silica slurry is obtained, which is then washed, ground and spray-dried to obtain the silica product.

[0061] Comparative Example 2:

[0062] The difference from Example 1 is that step S2 is removed and no composite modifier is added.

[0063] Comparative Example 3:

[0064] The difference from Example 1 is that the microwave-assisted processing in step S1 is removed.

[0065] Comparative Example 4:

[0066] The difference from Example 1 is that the composite impurity remover in step S1 is removed.

[0067] The silica prepared in Examples 1, 2, and 3 and Comparative Examples 1, 2, 3, and 4 were subjected to relevant performance tests.

[0068] The activation degree of the silica prepared in Examples 1, 2, and 3, and Comparative Examples 1, 2, 3, and 4 was determined. The activation degree was determined by measuring 50 mL of distilled water into a 100 mL beaker, adding 1 g of silica, stirring for 30 min, and letting it stand for 24 h. The silica that sank to the bottom was separated, dried, and weighed. The activation degree was then calculated according to the following formula: Activation degree = [(Total mass of silica (g) - Mass of silica that sank to the bottom (g)) / Total mass of silica (g)] × 100%. The rubber compounding properties of the silica prepared in the above examples and comparative examples were tested, referring to HG / T2404-2008 "Precipitated hydrated silica in styrene-butadiene rubber". The silica-styrene-butadiene rubber compound was prepared according to the "Identification of Silica in Rubber" standard, and then vulcanized at 160℃ using a flat vulcanizing agent. The Mooney viscosity and stress-strain characteristics were then tested. The Mooney viscosity was tested according to GB / T1232 "Determination of Unvulcanized Rubber Using a Disk Shear Viscometer - Part 1: Determination of Mooney Viscosity"; the stress-strain characteristics were tested according to GB / T528-2009 "Determination of Tensile Stress-Strain Properties of Vulcanized Rubber or Thermoplastic Rubber"; and the dispersibility of silica was determined using GB / T6030-2006 "Rapid Comparative Method for Evaluating the Dispersibility of Carbon Black and Carbon Black Silica in Rubber". The test results are shown in Table 1.

[0069] Table 1: Performance tests of silica prepared in the example group and the comparative group

[0070] As can be seen from Table 1, the silica prepared by the method of the present invention has high activation, is not prone to agglomeration, and has high dispersibility in rubber; when used in rubber products, it significantly improves the processing and mechanical properties of rubber.

[0071] Microwave-assisted processing significantly accelerates the dissolution rate and efficiency of silicon in rice husk ash, resulting in a more active water glass precursor. The composite impurity remover deeply chelates and removes metallic impurities such as iron and aluminum, preventing them from damaging subsequent carbonization reactions and the final product structure, thus ensuring chemical purity – the foundation of high activity. The core composite modifier is introduced before carbonization, causing the silica surface to be instantly coated and modified by the organic functional groups of the silane coupling agent and the hydrophilic chains of polyethylene glycol. This greatly reduces the surface energy of the native particles, fundamentally inhibiting hard agglomeration and achieving "in-situ modification," which is key to obtaining excellent dispersibility. High-pressure spray atomization creates a massive number of homogeneous microreactors, producing native particles with small particle size, narrow distribution, and loose structure, providing a huge specific surface area and abundant surface active sites (high activation). Simultaneously, its loose structure is easily opened by mechanical force. When this highly active and highly dispersible silica is applied to rubber, it is easier to mix in the rubber compound, has good flowability, and an ideal Mooney viscosity, facilitating extrusion and molding. Its high specific surface area and organic surface modification enable it to form more and stronger physical adsorption and chemical bonding with rubber molecules (such as through the bridging of KH-550), thereby more effectively transferring stress and making the vulcanizate exhibit higher tensile strength, tear strength and abrasion resistance, significantly improving the reinforcement effect.

[0072] In summary, the silica prepared by this invention uses renewable biomass rice husk ash as the silicon source. Through synergistic composite impurity removal and modification, continuous high-pressure spray carbonization reaction, and waste liquid recycling, the efficient and green preparation of silica is achieved, while improving the purity, specific surface area, and dispersibility of the product, thus meeting the application needs of high-end fields.

[0073] The above are merely specific embodiments of the present invention, but the technical features of the present invention are not limited thereto. Any simple changes, equivalent substitutions, or modifications made based on the present invention to solve essentially the same technical problems and achieve essentially the same technical effects are all covered within the protection scope of the present invention.

Claims

1. A method for preparing silica, characterized in that, Includes the following steps: S1. Pretreatment of silicon source: Biomass rice husk ash is mixed with sodium hydroxide solution with a concentration of 2.0~3.5mol / L at a solid-liquid ratio of 1:8~12, and reacted at 75~85℃ for 2~3h under microwave assistance. Solid impurities are removed by filtration to obtain crude water glass solution. A composite impurity removal agent is added to the crude water glass solution, and the mixture is stirred and reacted for 1~1.5h. Chelate precipitate is removed by filtration to obtain refined water glass solution with a modulus of 3.0~4.2 and a mass concentration of 10~20%. S2. Preparation of modified precursor: Add composite modifier to refined water glass solution, stir and disperse at 50~60℃ for 30~40min to obtain modified water glass precursor solution; S3. High-pressure spray carbonization reaction: The modified water glass precursor liquid is introduced into the high-pressure spray reaction tower and atomized into droplets by a centrifugal atomizer. At the same time, a mixture of carbon dioxide and nitrogen is introduced into the reaction tower. The pressure inside the tower is controlled at 0.1~0.5MPa and the temperature is 50~80℃. The droplets and the mixed gas react in the tower for 10~20s to generate white carbon black slurry. S4. Post-processing: The silica slurry is washed, milled, and spray-dried in sequence to obtain the finished silica product. S5. Waste liquid recycling: Add limestone powder to the waste liquid generated from washing in S4, stir and react at 60~70℃ for 1~2h, filter to obtain calcium carbonate by-product and dilute sodium hydroxide solution; after the dilute sodium hydroxide solution is concentrated to a concentration of 2.0~3.5mol / L, it can be reused in the rice husk ash alkali dissolution reaction in S1. The composite impurity remover is obtained by mixing citric acid and disodium EDTA at a mass ratio of 2-3:1, and the amount added is 0.8-1.5% of the mass of the crude water glass solution. The composite modifier is a mixture of silane coupling agent KH-550 and polyethylene glycol in a mass ratio of 3~5:1, and the amount added is 2~5% of the mass of the refined water glass solution.

2. The method for preparing silica according to claim 1, characterized in that, In S1, the power of the microwave-assisted power is 3~8kW and the frequency is 2450MHz.

3. The method for preparing silica according to claim 1, characterized in that, In S3, The rotation speed of the centrifugal atomizer is 15000~25000 rpm; The volume content of carbon dioxide in the mixture of carbon dioxide and nitrogen is 70-90%. The ratio of the feed rate of the modified water glass precursor liquid to the inlet rate of the mixed gas is 1:5~8.

4. The method for preparing silica according to claim 1, characterized in that, In S4, The washing process uses deionized water and involves repeated washing and filtration, with continuous monitoring until the pH of the filtrate reaches 6.5-7.

5. The grinding process involves adding washed slurry to a colloid mill and adding 15-25% (by weight) of deionized water. The grinding is carried out at a speed of 4000-6000 rpm and a grinding gap of 0.05-0.2 mm using a circulating grinding method. That is, the slurry is ground by the colloid mill and then returned to the feed end for further grinding. The particle size is monitored in real time by a laser particle size analyzer until the particle size is 8-20 nm. The inlet air temperature of the spray dryer is 180~220℃, and the outlet air temperature is 80~100℃.

5. The method for preparing silica according to claim 1, characterized in that, In step S5, the amount of limestone powder added is calculated based on a stoichiometric ratio of 1:1 to sodium carbonate in the waste liquid, and the actual amount added is 1.05 to 1.10 times the theoretical amount.

6. A type of silica, characterized in that, The silica is prepared by the preparation method according to any one of claims 1 to 5.

7. An application of silica according to claim 6, characterized in that, Used in rubber reinforcing agents.

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