Preparation method of white carbon black with low aluminum content and controllable specific surface area

Abstract

The invention belongs to the technical field of inorganic materials, and particularly discloses a preparation method of white carbon black with low aluminum content and controllable specific surface area, which comprises the following steps: (1) preparing high-concentration bio-based water glass by using pretreated biomass ash as a raw material; (2) diluting the obtained high-concentration bio-based water glass into two kinds of low-concentration bio-based water glass, wherein one kind of low-concentration bio-based water glass is heated under the action of a nucleating agent to generate sol reaction; and (3) adding another low-concentration bio-based water glass and a precipitant into the reaction liquid in the step (2), and continuously reacting to obtain the low-aluminum-content white carbon black with the controllable specific surface area. According to the method, the content of aluminum in the white carbon black is reduced from the source by adopting a biomass raw material, water glass with different moduli is obtained by adopting different dissolution processes, and the specific surface area regulation capability of the white carbon black is endowed by linkage control of the concentration of a reaction solution, the type / feeding proportion of a nucleating agent, the reaction temperature, the reaction time, the feeding speed of a precipitator and the like.

Description

Technical Field

[0001] This invention belongs to the field of inorganic materials technology, and relates to the preparation process of silica, specifically to a method for preparing silica with low aluminum content and controllable specific surface area. Background Technology

[0002] Silica is an ultrafine, active silica particle. Its chemical name is colloidal silica or hydrated silica, with the molecular formula SiO2·nH2O. It is a white, non-toxic, amorphous, fine powder with excellent properties such as porosity, high dispersibility, light weight, good chemical stability, high temperature resistance, non-flammability, and good electrical insulation. Its relative density is 2.319~2.653, and its melting point is 1750℃. After absorbing moisture, it forms polymeric fine particles. It has high insulation properties, is insoluble in water and acids, but soluble in caustic soda and hydrofluoric acid without decomposition at high temperatures. It exhibits chemical inertness to matrices, active ingredients, and additives, and has good compatibility with many active ingredients commonly used in vitamins, hormones, fluorides, antibiotics, enzyme preparations, and cosmetics. It is widely used in many industries, including rubber, plastics, pharmaceuticals, coatings, daily chemicals, catalyst carriers, polymer composites, electronic packaging materials, and precision ceramics.

[0003] The industrial production of precipitated silica mainly adopts two major technical routes: gas-phase method and precipitation method. Among them, the precipitation method has become the mainstream due to the availability of raw materials, simple process and cost advantages. This method uses water glass (sodium silicate) to neutralize with acidic media such as sulfuric acid / hydrochloric acid / carbon dioxide. Through patented technology optimization, a multi-path production system has been formed. For example, CN116924420A uses the carbon dioxide carbonization method, and CN102229758B has constructed a stepwise acidification process, both of which can effectively realize the large-scale production of precipitated silica.

[0004] However, at the upstream end of the precipitation process chain, both the dry and wet preparation processes of water glass, the basic raw material, rely on silica sand ore as the silicon source. Natural silica sand commonly contains impurities such as iron, aluminum, titanium, and calcium oxides (Fe2O3 content can reach 0.1-0.5%, Al2O3 about 1-3%). These metal elements are difficult to completely remove during the production of water glass through high-temperature melting or high-pressure alkaline dissolution, and ultimately remain in the water glass system in ionic or colloidal form. This leads to strict restrictions on the metal elements in silica for applications, especially in the feed, toothpaste, and pharmaceutical industries. Among them, aluminum is extremely harmful to organisms, and although there is no clear limit standard, its potential biotoxicity has raised concerns in the industry. CN111825097B specifies a method for aluminum removal by introducing calcium chloride to react with aluminum ions to form a precipitate, achieving targeted removal of impurities. However, on the one hand, the process is complex and energy consumption is increased; on the other hand, it causes silicon loss, limiting the performance range of silica and increasing costs. Alternatively, one can use low-aluminum, high-purity quartz sand, which is produced through complex processes such as material selection, crushing, flotation, purification, and drying, as used in high-end industries like photovoltaics, to ensure the low aluminum content of silica. While this method is effective, the costs from raw material processing to water glass preparation are extremely high. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a method for preparing silica with low aluminum content and controllable specific surface area. This invention is based on the plant's aluminum repulsion mechanism (Al-mediated release of organic acid anions from roots into the rhizosphere, where organic acids react with Al). 3+ (The process involves chelation to form non-toxic compounds, thus excluding Al from the roots) and plant tolerance mechanisms to aluminum (cell wall modification (most Al is bound in the cell wall) and changes in cell wall properties, as well as various Al-resistant genes and mechanisms that prevent Al absorption). 3+ Chelating low-toxicity or non-toxic complexes (stored in vacuoles or transferred to Al-insensitive areas on the ground) uses biomass raw materials to prepare bio-based water glass, and then uses bio-based water glass as raw material to obtain precipitated silica with low aluminum content under the combined action of nucleating agents and precipitants. At the same time, water glass with different moduli can be obtained by using different leaching processes. The specific surface area of ​​precipitated silica is controlled by linking the concentration of the reaction solution, the type / ratio of nucleating agent, the reaction temperature, the reaction time, and the precipitant feeding rate.

[0006] This invention is achieved through the following technical solution: A method for preparing silica with low aluminum content and controllable specific surface area includes the following steps: (1) The pretreated biomass ash and alkaline solution are put into a high-pressure reactor, stirred evenly, and then purified after high-pressure and high-temperature reaction to obtain high-concentration bio-based water glass with a modulus of 1-4.5. (2) Dilute the high-concentration bio-based water glass obtained in step (1) into two low-concentration water glasses of different concentrations. Add a nucleating agent to one of the low-concentration water glasses and heat it to 40-95℃. Then add a precipitant at a certain rate to make it undergo a sol reaction and age it. (3) Add another low-concentration bio-based water glass and precipitant to the reaction solution after aging in step (2) at a certain rate. After the addition is complete, continue the reaction until a certain pH is reached, then stir and age. Finally, wash and dry to obtain low aluminum content silica with controllable specific surface area.

[0007] A further improvement to the present invention is as follows: The biomass ash is one or more of various types of rice husk ash, various types of straw ash, and wood fiber.

[0008] Preferably, the biomass ash is rice husk ash.

[0009] Furthermore, the alkaline solution is a 3-15 wt% aqueous solution of potassium hydroxide or sodium hydroxide.

[0010] Preferably, the alkaline solution is a 3-15 wt% aqueous solution of sodium hydroxide.

[0011] Furthermore, the pretreatment method is water washing or acid washing; Preferably, the pretreatment method is acid washing.

[0012] And / or, the high-pressure high-temperature reaction is carried out at a temperature of 80-260℃, a pressure of 0.04-4.5MPa, and a time of 4-7h.

[0013] Furthermore, the nucleating agent is one or a mixture of two or more of sodium and potassium carbonates, bicarbonates, hydroxides, sulfates, chlorides, nitrates, acetates, ammonia, urea, or tetrapropylammonium hydroxide. And / or, the precipitant is one or a mixture of two or more of sulfuric acid, hydrochloric acid, nitric acid, carbon dioxide, organic acid, and acidic salt.

[0014] Preferably, the nucleating agent is sodium carbonate; And / or, the precipitant is sulfuric acid or carbon dioxide or a mixture of both.

[0015] Furthermore, when carbon dioxide is used as the precipitant, the gas flow rate is controlled at 2-60 L / h. -1 / L represents the gas flow rate that can be accepted per liter of liquid; And / or, the silica content of the low-concentration water glass that reacts in step (2) is 3-8 wt%; And / or, the silica content of the low-concentration water glass added in step (3) is 9-15 wt%.

[0016] Furthermore, the aluminum content of the low-aluminum content silica with controllable specific surface area is no more than 0.21 wt%, and the specific surface area is 70-270 cm². 2 / g.

[0017] The modulus mentioned in this invention is a term used in the water glass industry, representing the molar ratio of silicon dioxide to metal oxide salts in water glass.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows: (1) The silica obtained by the method of the present invention is a precipitated silica with a lower aluminum content; (2) By using different leaching processes to obtain water glass with different moduli, the present invention controls the concentration of the reaction solution, the type / ratio of nucleating agent, the reaction temperature, the reaction time, the feeding rate of the precipitant, etc., so as to achieve controllable specific surface area of ​​silica and a large controllable range. (3) The preparation method of the present invention has low cost, simple process, high efficiency and environmental protection. Attached Figure Description

[0019] Figure 1 The BET curve for the silica prepared in Comparative Example 5 is shown. Figure 2 The BET curve for the silica prepared in Comparative Example 6 is shown. Figure 3 The BET curve for the silica prepared in Comparative Example 12 is shown. Figure 4 The BET curve of the silica prepared in Example 2 is shown. Figure 5 The BET plot of the silica prepared in Example 6; Figure 6 The BET plot of the silica prepared in Example 8; Figure 7 The image shows the BET plot of the silica prepared in Example 9. Detailed Implementation

[0020] This invention provides a method for preparing silica with low aluminum content and controllable specific surface area. In a specific embodiment, the raw materials, reagents, and equipment used are as follows: The silicon dioxide content of rice husk ash is 60-95 wt%, the silicon dioxide content of straw ash is 40-65 wt%, the concentration of sodium hydroxide aqueous solution is 32 wt%, potassium hydroxide is AR analytical grade, sodium carbonate is AR analytical grade, sodium dodecyl sulfate is AR analytical grade, carbon dioxide is 99%, and sulfuric acid concentration is 20%.

[0021] BET testing instrument information: Jingwei Gaobo BK222.

[0022] AAS testing instrument information: PINAACLE 900F (USA).

[0023] The standard for testing the modulus of water glass is GB / T 4209-2022.

[0024] The present invention will now be described in detail with reference to specific embodiments.

[0025] Example 1:

[0026] Preparation of water glass: 600g of untreated rice husk ash with a silica content of 80% and 2560g of a 5wt% sodium hydroxide aqueous solution were placed in a high-pressure reactor and reacted at 160℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.40. This raw material was then prepared into bio-based sodium water glass with silica contents of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to the reactor, and the temperature was raised to 85℃. After stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was then stopped and the mixture was aged for 30min. 1500g of a 10% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was simultaneously introduced at a gas flow rate of 30L / h until the 10% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. The carbon dioxide introduction was then stopped, and the reaction was continued with stirring and aging for 1h. The sample was then washed and dried to obtain 249.2g of silica sample.

[0027] Example 2:

[0028] 600g of washed rice husk ash with a silica mass fraction of 83% and 2654g of sodium hydroxide aqueous solution with a concentration of 5wt% were placed in a high-pressure reactor and reacted at 160℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.51. Bio-based sodium silicate with silica mass fractions of 5% and 10% was prepared separately. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel, heated to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. After washing and drying, 249.6g of sample was obtained.

[0029] Example 3:

[0030] 600g of acid-washed rice husk ash with a silica mass fraction of 88% and 2814g of sodium hydroxide aqueous solution with a concentration of 5wt% were placed in a high-pressure reactor and reacted at 160℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.65. Bio-based sodium silicate with silica mass fractions of 5% and 10% was prepared separately. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel, heated to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. After washing and drying, 249.3g of sample was obtained.

[0031] Example 4:

[0032] 600g of acid-washed rice husk ash with a silica mass fraction of 88% and 2814g of sodium hydroxide aqueous solution with a concentration of 5wt% were placed in a high-pressure reactor and reacted at 240℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.78. Bio-based sodium silicate with silica mass fractions of 5% and 10% was prepared separately. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel, heated to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. After washing and drying, 249.5g of sample was obtained.

[0033] Example 5:

[0034] 600g of acid-washed rice husk ash with a silica mass fraction of 88% and 1760g of sodium hydroxide aqueous solution with a concentration of 8wt% were placed in a high-pressure reactor and reacted at 240℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.89. Bio-based sodium silicate with silica mass fractions of 5% and 10% was prepared separately. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel, heated to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. After washing and drying, 248.8g of sample was obtained.

[0035] Example 6:

[0036] 600g of acid-washed rice husk ash with a silica mass fraction of 88% and 1173g of sodium hydroxide aqueous solution with a concentration of 12wt% were placed in a high-pressure reactor and reacted at 240℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 3.15. Bio-based sodium silicate with silica mass fractions of 5% and 10% was prepared separately. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel, heated to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. After washing and drying, 249.1g of sample was obtained.

[0037] Example 7:

[0038] Bio-based sodium silicate with a modulus of 3.15 was prepared using the process described in Example 6. Bio-based sodium silicate solutions with silica mass fractions of 5% and 10% were prepared. 2000g of the 5% solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 60L / h until the sol reaction was complete. The reaction was stopped and the solution was aged for 30 minutes. Then, 1500g of the 10% solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 60L / h until the 10% solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was continued with stirring for 1 hour. After washing and drying, 249.5g of sample was obtained.

[0039] Example 8:

[0040] Bio-based sodium silicate with a modulus of 3.15 was prepared using the process described in Example 6. Bio-based sodium silicate solutions with silica mass fractions of 5.65% and 10% were prepared. 2000g of the 5.65% bio-based sodium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and allowed to age for 30 minutes. Then, 1500g of the 10% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1 hour. After washing and drying, 262.1g of sample was obtained.

[0041] Example 9:

[0042] Bio-based sodium silicate with a modulus of 3.15 was prepared using the process described in Example 6. Bio-based sodium silicate solutions with silica mass fractions of 6.53% and 10% were prepared. 2000g of the 6.53% bio-based sodium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and allowed to age for 30 minutes. Then, 1500g of the 10% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1 hour. After washing and drying, 280.0g of sample was obtained.

[0043] Example 10: Bio-based sodium silicate with a modulus of 3.15 was prepared using the process described in Example 6. Bio-based sodium silicate solutions with silica mass fractions of 7.21% and 10% were prepared. 2000g of the 7.21% bio-based sodium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol-gel reaction was complete. The reaction was stopped and the solution was aged for 30min. Then, 1500g of the 10% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1h. After washing and drying, 293.6g of sample was obtained.

[0044] Example 11: Bio-based sodium silicate with a modulus of 3.15 was prepared using the process described in Example 6. Bio-based sodium silicate solutions with silica mass fractions of 5.65% and 12% were prepared. 2000g of the 5.65% bio-based sodium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol-gel reaction was complete. The reaction was stopped and allowed to age for 30 minutes. Then, 1500g of the 12% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 12% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1 hour. After washing and drying, 293.1g of sample was obtained.

[0045] Example 12: 600g of acid-washed rice husk ash with a silica mass fraction of 88% and 1173g of potassium hydroxide aqueous solution with a concentration of 12wt% were placed in a high-pressure reactor and reacted at 240℃ for 5h. The resulting water glass was purified to obtain a bio-based potassium water glass raw material with a modulus of 3.20. Bio-based potassium silicate solutions with silica mass fractions of 5% and 10% were prepared. 2000g of the 5% bio-based potassium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and the mixture was aged for 30min. Then, 1500g of the 10% bio-based potassium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% bio-based potassium silicate solution was completely added and the final pH reached 8.5. The carbon dioxide introduction was stopped, and the reaction was stirred for another 1h. After washing and drying, 249.1g of sample was obtained.

[0046] Comparative Example 1: Mineral-based sodium silicate with a modulus of 3.2 was prepared into mineral-based sodium silicate solutions with a silica mass fraction of 5% and 10%. 2000g of the 5% mineral-based sodium silicate solution and 3g of sodium carbonate were added to a reaction vessel. The temperature was raised to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and the mixture was aged for 30min. Then, 1500g of the 10% silica mineral-based sodium silicate solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica mineral-based sodium silicate solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1h. The mixture was washed and dried to obtain 249.1g of sample.

[0047] Comparative Example 2: 600g of untreated rice husk ash with 80% silica (by mass) and 6400g of a 2wt% sodium hydroxide aqueous solution were placed in a high-pressure reactor and reacted at 160℃ for 5h. The resulting water glass was purified to obtain a low-concentration bio-based sodium water glass raw material with a modulus of 0.7. This was then concentrated into bio-based sodium water glass with 5% and 10% silica (by mass) concentrations, respectively. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to the reactor, and the temperature was raised to 85℃. After stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and the mixture was aged for 30min. Then, 1500g of the 10% silica (by mass) bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica (by mass) bio-based sodium water glass solution was completely added and the final pH reached 8.5. During this process, the reaction was violently exothermic, the system boiled, and the experiment failed.

[0048] Comparative Example 3: When 600g of untreated rice husk ash with a silica mass fraction of 80% and 640g of a sodium hydroxide aqueous solution with a concentration of 20wt% were placed in a high-pressure reactor, they could not be dispersed and could not form a fluid, resulting in experimental failure.

[0049] Comparative Example 4: 600g of untreated rice husk ash with 80% silica (by mass) and 2580g of a 5wt% sodium hydroxide aqueous solution were placed in a high-pressure reactor and reacted at 60℃ for 5h. The resulting water glass was purified to obtain a low-concentration bio-based sodium water glass raw material with a modulus of 0.8. This was then concentrated into bio-based sodium water glass with 5% and 10% silica (by mass) concentrations, respectively. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to the reactor, and the temperature was raised to 85℃. After stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and the mixture was aged for 30min. Then, 1500g of the 10% silica (by mass) bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica (by mass) bio-based sodium water glass solution was completely added and the final pH reached 8.5. During this process, the reaction was violently exothermic, the system boiled, and the experiment failed.

[0050] Comparative Example 5: 600g of untreated rice husk ash with a silica mass fraction of 80% and 2580g of sodium hydroxide aqueous solution with a concentration of 5wt% were placed in a high-pressure reactor and reacted at 300℃ for 5h. The resulting water glass was purified to obtain a low-concentration bio-based sodium water glass raw material with a modulus of 2.21. The solution was concentrated into bio-based sodium silicate with a silica mass fraction of 5% and 10%, respectively. 2000g of the 5% bio-based sodium silicate solution and 3g of sodium carbonate were added to the reaction vessel. The temperature was raised to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was completed. The reaction was stopped and aged for 30min. Then, 1500g of the 10% bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% bio-based sodium silicate solution was added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for 1h. The sample was washed and dried to obtain 249.3g of sample.

[0051] Comparative Example 6: 600g of untreated straw ash with a silica mass fraction of 64% and 2048g of sodium hydroxide aqueous solution with a concentration of 5wt% were placed in a high-pressure reactor and reacted at 160℃ for 5h. The resulting water glass was purified to obtain a bio-based sodium water glass raw material with a modulus of 2.04. It was then partially concentrated to obtain a bio-based sodium water glass with a mass fraction of more than 10%. The solution was then prepared as a bio-based sodium silicate with a silica mass fraction of 5% and 10%. 2000g of the 5% silica bio-based sodium silicate solution and 3g of sodium carbonate were added to the reactor. The temperature was raised to 85℃, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and aged for 30min. Then, 1500g of the 10% silica bio-based sodium silicate solution was added dropwise at a rate of 15ml / min, while carbon dioxide was introduced at a gas flow rate of 30L / h until the 10% silica bio-based sodium silicate solution was completely added and the final pH reached 8.5. The carbon dioxide was then stopped, and the reaction was stirred for another 1h. The mixture was washed and dried to obtain 249.1g of sample.

[0052] Comparative Example 7: Bio-based water glass with a modulus of 3.15, prepared using the process of Example 6, was further prepared into bio-based sodium water glass with silica mass fractions of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to a reaction vessel, heated to 30°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. The reaction was stopped and aged for 30min. Then, 1500g of the 10% silica bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica bio-based sodium water glass solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1h. After washing and drying, 249.2g of sample was obtained.

[0053] Comparative Example 8: The bio-based water glass with a modulus of 3.15 prepared using the process in Example 6 was further prepared into bio-based sodium water glass with a silica mass fraction of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to a reaction vessel, heated to 85°C, and after stabilization, 20% sulfuric acid was added dropwise at a rate of 10ml / min until the pH dropped to 8.5. The reaction was stopped and aged for 30min. Then, 20% sulfuric acid was added dropwise at a rate of 5ml / min, and simultaneously 1500g of the 10% bio-based sodium water glass was added dropwise at a rate of 15ml / min until the pH dropped to 4.0. The addition of sulfuric acid was stopped, and the reaction was stirred for 1h. After washing and drying, 249.6g of sample was obtained.

[0054] Comparative Example 9: Bio-based water glass with a modulus of 3.15, prepared using the process of Example 6, was further prepared into bio-based sodium water glass with silica mass fractions of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to a reaction vessel, heated to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 2L / h until the sol reaction was complete. The reaction was stopped and aged for 30 minutes. Then, 1500g of the 10% silica bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 2L / h until the 10% silica bio-based sodium water glass solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was stopped, and the reaction was stirred for another 1 hour. After washing and drying, 249.2g of sample was obtained.

[0055] Comparative Example 10: The bio-based water glass with a modulus of 3.15 prepared using the process in Example 6 was further prepared into bio-based sodium water glass with a silica mass fraction of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution and 3g of sodium carbonate were added to the reactor, and the temperature was raised to 85°C. After stabilization, carbon dioxide was introduced at a gas flow rate of 300L / h. However, the gas flow rate was too high, causing material splashing and resulting in experimental failure.

[0056] Comparative Example 11: Bio-based water glass with a modulus of 3.15, prepared using the process in Example 6, was further prepared into bio-based sodium water glass with silica mass fractions of 1% and 6%. 2000g of the 1% bio-based sodium water glass solution and 3g of sodium carbonate were added to a reaction vessel, and the temperature was raised to 85°C. After stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h. During this period, the system only became turbid with no change in viscosity, and a sol reaction did not form. After reacting for 30 minutes, the reaction was stopped and allowed to age for another 30 minutes. Then, 1500g of the 6% silica bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 6% silica bio-based sodium water glass solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was then stopped. At this point, the system was a sol and no gel had formed. The reaction was continued for 1 hour, but the system still failed to form a gel, and the experiment failed.

[0057] Comparative Example 12: Bio-based water glass with a modulus of 3.15, prepared using the process of Example 6, was further prepared into bio-based sodium water glass with silica mass fractions of 10% and 20%. 2000g of the 10% bio-based sodium water glass solution and 3g of sodium carbonate were added to a reaction vessel, heated to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h. The sol reaction quickly completed and continued until the gel stage. After stopping the reaction and aging for 30 minutes, 1500g of the 20% silica bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 20% silica bio-based sodium water glass solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was then stopped, and the reaction was stirred for another 1 hour. After washing and drying, 249.1g of sample was obtained.

[0058] Comparative Example 13: (without sodium carbonate) Bio-based water glass with a modulus of 3.15, prepared using the process of Example 6, was further prepared into bio-based sodium water glass with silica mass fractions of 5% and 10%. 2000g of the 5% bio-based sodium water glass solution was added to a reaction vessel, heated to 85°C, and after stabilization, carbon dioxide was introduced at a gas flow rate of 30L / h until the sol reaction was complete. After reacting for 30 minutes, the reaction was stopped and aged for 30 minutes. Then, 1500g of the 10% silica bio-based sodium water glass solution was added dropwise at a rate of 15ml / min, while simultaneously introducing carbon dioxide at a gas flow rate of 30L / h until the 10% silica bio-based sodium water glass solution was completely added and the final pH reached 8.5. Carbon dioxide introduction was then stopped, and the reaction was stirred for another 1 hour. After washing and drying, 249.4g of sample was obtained.

[0059] Table 1 Comparison of bio-based water glass preparation processes in some comparative examples and embodiments

[0060] Table 2 Comparison of silica preparation processes in some comparative examples and embodiments

[0061] Table 1 shows the preparation methods of water glass used in each embodiment. As can be seen from Table 1, water glass with different moduli can be obtained by using different leaching conditions, thus realizing the controllable adjustment of the water glass modulus.

[0062] As shown in Table 2, the aluminum content of silica prepared using bio-based raw materials is lower than that of silica prepared using mineral-based raw materials. The specific surface area of ​​silica can be regularly controlled by adjusting the modulus of bio-based water glass, the concentration of the reaction solution, the type / ratio of nucleating agent, the reaction temperature, the reaction time, and the feeding rate of the precipitant.

[0063] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing silica with low aluminum content and controllable specific surface area, characterized in that, Includes the following steps: (1) The pretreated biomass ash and alkaline solution are put into a high-pressure reactor, stirred evenly, and then purified by high-pressure and high-temperature reaction to obtain high-concentration water glass with a modulus of 1-4.

5. (2) Dilute the high-concentration water glass obtained in step (1) into two low-concentration water glasses of different concentrations. Add a nucleating agent to one of the low-concentration water glasses and heat it to 40-95℃. Then add a precipitant at a certain rate to make it undergo a sol-gel reaction. After the reaction is completed, age it. (3) Add another type of low-concentration water glass and precipitant to the reaction solution after aging in step (2) at a certain rate. After the addition is complete, continue the reaction until a certain pH is reached. Continue stirring and aging. Finally, wash and dry to obtain low aluminum content silica with controllable specific surface area.

2. The method for preparing low-aluminum-content and controllable specific surface area silica according to claim 1, characterized in that: The biomass ash is one or more of various types of rice husk ash, various types of straw ash, and wood fiber.

3. The method for preparing a low-aluminum-content and controllable specific surface area silica according to claim 2, characterized in that: The biomass ash is rice husk ash.

4. The method for preparing low-aluminum-content and controllable specific surface area silica according to claim 1, characterized in that: The alkaline solution is an aqueous solution of sodium hydroxide or potassium hydroxide, and the concentration of the alkaline solution is 3-15 wt%.

5. The method for preparing a low-aluminum-content and controllable specific surface area silica according to claim 4, characterized in that: The alkaline solution is a 3-15 wt% aqueous solution of sodium hydroxide.

6. The method for preparing low-aluminum-content and controllable specific surface area silica according to claim 1, characterized in that: The pretreatment method is water washing or acid washing; And / or, the high-pressure high-temperature reaction is carried out at a temperature of 80-260℃, a pressure of 0.04-4.5MPa, and a time of 4-6h.

7. The method for preparing a low-aluminum-content and controllable specific surface area silica according to claim 1, characterized in that: The nucleating agent is one or a mixture of two or more of the following: sodium or potassium carbonates, bicarbonates, hydroxides, sulfates, chlorides, nitrates, acetates, ammonia, urea, or tetrapropylammonium hydroxide. And / or, the precipitant is one or a mixture of two or more of sulfuric acid, hydrochloric acid, nitric acid, carbon dioxide, organic acid, and acidic salt.

8. The method for preparing low-aluminum-content and controllable specific surface area silica according to claim 7, characterized in that: The nucleating agent is sodium carbonate; And / or, the precipitant is sulfuric acid or carbon dioxide or a mixture of both.

9. A method for preparing low-aluminum-content silica with controllable specific surface area according to claim 1, 7, or 8, characterized in that: When carbon dioxide is used as the precipitant, the gas flow rate is controlled at 2-60 L / h. -1 / L represents the gas flow rate that can be accepted per liter of liquid; And / or, the silica content of the low-concentration water glass that reacts in step (2) is 3-8 wt%; And / or, the silica content of the low-concentration water glass added in step (3) is 9-15 wt%.

10. The method for preparing a low-aluminum-content and controllable specific surface area silica according to claim 1, characterized in that: The low-aluminum content silica with controllable specific surface area has an aluminum content of no more than 0.21 wt% and a specific surface area of ​​70-270 cm². 2 / g.

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