Method for in-situ preparation of surface modified nano silicon dioxide by using carbon dioxide gas carrying modifier

Abstract

The invention relates to a method for in-situ preparation of surface modified nano silicon dioxide by a modifier carried by carbon dioxide gas. The method comprises the following steps: (1) melting sodium bicarbonate powder and quartz sand to prepare solid sodium silicate, wherein the step comprises collection of carbon dioxide gas; (2) adding water into solid sodium silicate, heating and dissolving to obtain a water glass solution; (3) atomizing the organic modifier, carrying the atomized organic modifier with carbon dioxide gas, and introducing the atomized organic modifier into the water glass solution to generate modified nano silicon dioxide slurry; (4) drying the by-product sodium bicarbonate solution and recovering sodium bicarbonate powder; and (5) drying the modified nano carbon dioxide slurry. Wherein the carbon dioxide gas generated in the step (1) is used for preparing silicon dioxide through hydrolysis in the step (3), and the sodium bicarbonate powder obtained in the step (4) is reused in the step (1). The method provided by the invention is green and environment-friendly, and does not discharge process wastewater and waste gas.

Description

Technical Field

[0001] This invention belongs to the field of silica preparation technology, specifically relating to a method for preparing modified nano-silica using carbon dioxide as an acidifying agent, that is, a method for preparing surface-modified nano-silica in situ using carbon dioxide gas to carry a modifier. Background Technology

[0002] Existing liquid-phase methods for preparing nano-silica often use sodium silicate, prepared by melting quartz sand with alkali (sodium hydroxide, sodium sulfate, or sodium carbonate, etc.), as raw material. After dissolving in water, it reacts with inorganic acids such as sulfuric acid and hydrochloric acid to generate nano-silica slurry. After washing and drying, hydrated silica is obtained. Sodium sulfate or sodium chloride are generated as byproducts during the washing process.

[0003] Current methods for preparing nano-silica using carbon dioxide suffer from several drawbacks. Carbon dioxide has low solubility in water and is weakly acidic, leading to significant differences in mass transfer gradients and difficulty in controlling the product's structural morphology during the reaction. Furthermore, the highly polar surface of nano-silica particles makes them prone to structural collapse and agglomeration during drying due to capillary action, resulting in poor product dispersibility and structural stability.

[0004] This invention utilizes the melting of quartz sand and sodium bicarbonate to prepare solid sodium silicate. The carbon dioxide gas generated during this process is used as an acidifying agent in the hydrolysis preparation of nano-silica. The sodium bicarbonate produced in this process can be recycled after drying to prepare sodium silicate, representing a circular preparation method of carbon dioxide-sodium bicarbonate-sodium silicate-silica. The process of this invention produces no process wastewater or exhaust gas emissions, exhibiting low-carbon and environmentally friendly characteristics. Furthermore, an in-situ surface modification method is employed. During the formation of nano-silica, organic compounds are ultrasonically atomized and carried by carbon dioxide gas for modification reactions, effectively solving the problem of product agglomeration and controlling the product's aggregation structure and surface function to obtain high-performance nano-silica. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing technologies and provide a method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carried modifiers. This method employs an in-situ surface modification approach. During the formation of nano-silica, organic compounds are ultrasonically atomized and then carried by carbon dioxide gas for modification. This effectively solves the problem of product agglomeration and regulates the product's aggregation structure and surface function, resulting in high-performance nano-silica.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: A method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carried modifiers, which achieves the preparation of silica from quartz sand → sodium silicate → silica by recycling carbon dioxide, specifically including the following steps (process route as follows). Figure 1 (as shown) (1) The step of preparing solid sodium silicate by melting sodium bicarbonate powder and quartz sand, including the collection of carbon dioxide gas; (2) The step of heating and dissolving solid sodium silicate in water to obtain a water glass solution; (3) The step of atomizing the modifier and carrying it with carbon dioxide gas, then passing it into a water glass solution to generate modified nano-silica slurry; (4) The step of drying and recovering sodium bicarbonate powder from the byproduct sodium bicarbonate solution; (5) The step of drying the modified nano silica slurry.

[0007] Specifically, in step (1), the molar ratio of sodium bicarbonate to quartz sand during melting is 1:2.3 to 1:3.5, and the melting temperature is 1000 to 1600℃; the method for collecting carbon dioxide gas includes, but is not limited to, at least one of membrane separation, low-temperature distillation separation, etc.

[0008] Specifically, in step (2), the solid sodium silicate is heated and dissolved in water to obtain a water glass solution. The solid content of the water glass solution is 30%~43%, the dissolution temperature is 150~170℃, and the dissolution pressure is 5~8MPa. It can be heated by superheated steam or electric heating.

[0009] Specifically, in step (3), the water glass solution is diluted with water to a SiO2 concentration of 2% to 10%. The modifier is atomized and carried by carbon dioxide gas and introduced into the water glass solution for reaction. The reaction pressure is 0.1 to 0.7 MPa, the reaction temperature is 40 to 170°C, and the carbon dioxide is stopped when the pH is 8 to 10. The reaction continues for 1 to 12 hours at a temperature of 40 to 170°C. The slurry is filtered and washed through a plate and frame or ceramic membrane to make the conductivity of the filtrate reach below 500 μs / m.

[0010] Furthermore, in step (3), the filter cake is mixed with water and dried; or a modifier is added for a secondary modification reaction. The reaction conditions are: pH 3~8, reaction temperature 40~80℃, and reaction time 0.5~5 hours.

[0011] Furthermore, the modifier in step (3) includes organosilicon and / or polymers, etc.; the organosilicon includes, but is not limited to, at least one of silane coupling agents, chlorosilanes, silazanes or siloxanes, etc.; the polymer includes, but is not limited to, at least one of polyvinyl alcohol, natural rubber adhesive, polyvinyl chloride paste resin, ethylene-vinyl acetate copolymer (EVA), polyurethane, unsaturated polyester, epoxy resin, polymethacrylic acid, polydimethylsiloxane, etc.; the amount of modifier added is 5% to 40% of the mass of silica, preferably 7% to 25%.

[0012] Furthermore, the sodium bicarbonate filtrate generated from the filtration and washing of the reaction slurry in step (3) is dried and recovered as sodium bicarbonate powder in step (4) by multi-effect evaporation or mechanical vapor recompression evaporation (MVR).

[0013] Specifically, in step (5), the modified nano-dioxide slurry is dried by flash drying or spray drying, with an inlet temperature of 300~600℃ and an outlet temperature of 80~140℃; the flash drying uses filter cake directly, with a filter cake solid content of 18%~45%; the spray drying uses slurry with a solid content of 10%~25%.

[0014] More preferably, the sodium bicarbonate powder dried and recovered in step (4) is recycled for step (1), the water vapor is reused in step (2) or step (3), and the released carbon dioxide gas is recovered for step (3) to achieve the recycling of carbon dioxide.

[0015] Compared with the prior art, the advantages and beneficial effects of the method of the present invention are as follows: 1) This invention employs a carbon dioxide recycling method, which is a green and carbon-reducing preparation method; 2) This invention uses organic compounds, including polymer-modified nano-silica, which can not only change the size and morphology of the original particles, but also obtain highly dispersed, large-pore-volume, and highly branched nano-silica by reducing surface polarity. 3) This invention uses ultrasonic atomization of the modifier and adds it to the reaction system with carbon dioxide gas as a carrier, which can disperse the modifier in a finer state, improve the solid-liquid-gas mass transfer state during the reaction process, and obtain a uniform reaction system. Attached Figure Description

[0016] Figure 1 A schematic diagram of the process for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carried modifiers according to the present invention; Figure 2 Transmission electron microscopy (TEM) image of unmodified nano-silica obtained from the blank control group (scale bar 50 nm). Figure 3 Transmission electron microscopy (TEM) image of the modified nano-silica obtained in Example 1 (scale bar 50 nm). Figure 4 Transmission electron microscopy (TEM) image of the modified nano-silica obtained in Example 2 (scale bar 50 nm). Figure 5 The image shows a transmission electron microscope (TEM) image (scale bar 50 nm) of the modified nano-silica obtained in Example 3. Detailed Implementation

[0017] The technical solution of the present invention will be further described in detail below with reference to the embodiments, but the scope of protection of the present invention is not limited thereto.

[0018] Preparation of solid sodium silicate (Na2O·nSiO2): Sodium bicarbonate powder and quartz sand are mixed at a molar ratio of 1:3 and melted. The melting temperature is controlled at 1200℃. The prepared sodium silicate melt is cooled to obtain solid sodium silicate (Na2O·nSiO2). The carbon dioxide gas generated during the reaction is collected.

[0019] Preparation of water glass: Solid sodium silicate was mixed with water to achieve a solid content of 35%, and then heated to 170°C with superheated steam at a dissolution pressure of 6 MPa to obtain a water glass solution. The sodium silicate modulus was approximately 1.0. This water glass solution was used as the raw material for synthesizing modified nano-silica in the following examples.

[0020] Blank control group: Unmodified nano-silica A water glass solution with a modulus of 1 was added to a 50L reactor, followed by pure water until the silica concentration reached 6%. Stirring was started, and the temperature was maintained at 60℃ and the reaction pressure at 0.5MPa. Carbon dioxide gas was introduced into the reactor until the pH value was below 8.5, for approximately 3 hours (the time may vary depending on the scale and pressure). Gas introduction was stopped, the temperature was raised to 80℃, and the reaction continued for 1 hour. The material was fed into a plate and frame filter press, filtered, and washed until the conductivity of the filtrate reached below 500μs / m. The filter cake was mixed with water and slurried (solid content 18%), then spray-dried (inlet temperature 400℃, outlet temperature 110℃) to obtain the final product.

[0021] The product has a primary particle size of 10-13 nm, and some particles exhibit non-uniform agglomeration (see transmission electron microscope images). Figure 2 ).

[0022] Example 1: Preparation of nano-silica using hexamethyldisilazane as a modifier A water glass solution with a modulus of 1 was added to a 50L reactor, followed by pure water until the silica concentration reached 6%. Stirring was started, and the temperature was maintained at 60℃. Hexamethyldisilazane (10% of the silica content) was atomized using an atomizer and carried into the reactor by carbon dioxide gas. The reaction pressure was 0.5MPa, and the induction time was approximately 3.5 hours, until the pH value was below 8.5. Gas induction was stopped, the temperature was raised to 80℃, and the reaction continued for 1 hour. The material was fed into a plate and frame filter press, filtered, and washed until the conductivity of the filtrate reached below 500μs / m. The filter cake was mixed with water to form a slurry (solid content 20%), which was then spray-dried (inlet temperature 400℃, outlet temperature 110℃) to obtain the product.

[0023] The product has a primary particle size of 13-15 nm and exhibits good dispersion uniformity (see transmission electron microscopy image). Figure 3 ).

[0024] Example 2: Preparation of nano-silica using methacryloyloxypropyltrimethoxysilane (KH-570) / polyvinyl alcohol A water glass solution with a modulus of 1 was added to a 50L reactor, followed by pure water until the silica concentration reached 4.5%. Stirring was started, and the temperature was maintained at 40℃ and the reaction pressure at 0.5MPa. Silane coupling agent KH-570 (17% of the silica content) was atomized and carried into the reactor by carbon dioxide gas at a pressure of 0.3 MPa for approximately 2.5 hours, until the pH value fell below 8.5. Gas flow was stopped, and the temperature was raised to 80℃, with the reaction continuing for 1 hour. The material was fed into a plate and frame filter press, filtered, and washed until the conductivity of the filtrate reached below 500 μS / m. The filter cake was slurried with water (solid content 15%), and polyvinyl alcohol (3% of the silica content) was added. The reaction was continued at 80℃ for 1 hour. The product was then spray-dried (inlet temperature 400℃, outlet temperature 110℃) to obtain a reactive nano-silica product containing double bonds.

[0025] The product has a primary particle size of 5-6 nm and a well-developed network structure (see transmission electron microscope image). Figure 4 ).

[0026] Example 3: Preparation of nano-silica using hydroxyl silicone oil as a modifier A water glass solution with a modulus of 1 was added to a 50L reactor, followed by pure water until the silica concentration reached 5.2%. Stirring was started, and the temperature was maintained at 50℃. Hydroxysilicone oil was dissolved in ethanol (15% of the silica content) and atomized using an atomizer. The solution was then carried into the reactor by carbon dioxide gas at a pressure of 0.5 MPa for approximately 2.5 hours, until the pH value fell below 9. Gas flow was stopped, and the temperature was raised to 80℃, with the reaction continuing for 2 hours. The material was then fed into a plate and frame filter press, filtered, and washed until the conductivity of the filtrate reached below 500 μS / m. The filter cake was mixed with water and slurried (solid content 12%), then spray-dried (inlet temperature 400℃, outlet temperature 110℃) to obtain the final product.

[0027] The product has a primary particle size of 19-22 nm and is a hydrophobic network structure of nano-silica (see transmission electron microscope image). Figure 5 ).

[0028] Table 1 Quality indicators of modified nano-silica obtained from different embodiments As can be seen from the data in Table 1 above, when carbon dioxide is used as the acidifying agent, by selecting different surface modifiers to modify silica in situ, a specific surface area (140-300 m²) can be obtained. 2 The product contains nano-silica with a density of / g, and its pore volume and surface wettability can be effectively controlled according to requirements.

Claims

1. A method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carried modifiers, characterized in that, Includes the following steps: (1) The step of preparing solid sodium silicate by melting sodium bicarbonate powder and quartz sand, including the collection of carbon dioxide gas; (2) The step of heating and dissolving solid sodium silicate in water to obtain a water glass solution; (3) The step of atomizing the modifier and carrying it with carbon dioxide gas, then passing it into a water glass solution to generate modified nano-silica slurry; (4) The step of drying and recovering sodium bicarbonate powder from the byproduct sodium bicarbonate solution; (5) The step of drying the modified nano silica slurry.

2. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that, In step (1), the molar ratio of sodium bicarbonate to quartz sand during melting is 1:2.3~1:3.5, and the melting temperature is 1000~1600℃.

3. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that... In step (2), the solid sodium silicate is dissolved in water by heating to obtain a water glass solution. The solid content of the water glass solution is 30%~43%, the dissolution temperature is 150~170℃, and the dissolution pressure is 5~8MPa.

4. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that... Step (3) Dilute the water glass solution with water to a SiO2 concentration of 2% to 10%, atomize the modifier and carry it through carbon dioxide gas, and pass it into the water glass solution for reaction; the reaction pressure is 0.1 to 0.7 MPa, the reaction temperature is 40 to 170℃, and the carbon dioxide is stopped when the pH is 8 to 10; continue the reaction for 1 to 12 hours; filter and wash the slurry so that the conductivity of the filtrate reaches below 500 μs / m.

5. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 4, characterized in that... In step (3), the filter cake is mixed with water and dried; or a modifier is added for a secondary modification reaction. The reaction conditions are: pH 3~8, reaction temperature 40~80℃, and reaction time 0.5~5 hours.

6. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that, In step (3), the modifier includes organosilicon and / or polymer; the organosilicon includes at least one of silane coupling agent, chlorosilane, silazane, and siloxane; the polymer includes at least one of polyvinyl alcohol, natural rubber adhesive, polyvinyl chloride paste resin, EVA, polyurethane, unsaturated polyester, epoxy resin, polymethacrylic acid, and polydimethylsiloxane; the amount of modifier added is 5% to 40% of the mass of silica.

7. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that, The sodium bicarbonate filtrate generated from the filtration and washing of the reaction slurry in step (3) is dried and recovered as sodium bicarbonate powder in step (4) by multi-effect evaporation or steam mechanical recompression evaporation.

8. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that, Step (5) The modified nano-carbon dioxide slurry is dried by flash drying or spray drying, with an inlet temperature of 300~600℃ and an outlet temperature of 80~140℃; for flash drying, filter cake is used directly, with a solid content of 18%~45%; for spray drying, slurry is used, with a solid content of 10%~25%.

9. The method for in-situ preparation of surface-modified nano-silica using carbon dioxide gas-carrying modifiers as described in claim 1, characterized in that, The sodium bicarbonate powder dried and recovered in step (4) is recycled for step (1), and the water vapor is reused in step (2) or step (3); the released carbon dioxide gas is recovered for step (3) to achieve the recycling of carbon dioxide.

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