Preparation method of amorphous silicon dioxide with controllable structure and morphology and carbonization method

Abstract

The invention discloses a preparation method of amorphous silicon dioxide with a controllable structure and morphology and a carbonization method. The method comprises the following steps: reacting carbon dioxide and a NaHCO3 solution with low-concentration water glass at normal pressure to generate a silicon dioxide core, controlling a cationic chemical environment in a growth environment, performing secondary induced growth, controlling a gas-liquid flow field in a kettle through a self-suction gas redistributor under high pressure, controlling the temperature to be 80-150 DEG C, continuing carbonization until the pH value of a reaction system is reduced to 9.0 or below, and performing vacuum drying, thereby obtaining the carbon dioxide / NaHCO3 composite material. Amorphous silicon dioxide with a specific structure is formed through nucleus-induced growth under the condition, and the amorphous silicon dioxide functional powder with adjustable specific surface area and pore volume is obtained after solid-liquid separation, washing and drying. The morphology and the pore structure of the amorphous silicon dioxide can be adjusted under the condition of no additive, the problem of sodium sulfate wastewater discharge caused by introduction of a structure regulation additive in the traditional sulfuric acid method amorphous silicon dioxide production process is avoided, and meanwhile, the particle size distribution and the powder structure morphology of the silicon dioxide powder are improved.

Description

Technical Field

[0001] The invention belongs to the technical field of powder preparation, and in particular relates to a method for preparing amorphous silicon dioxide by a carbonization method with controllable structure and morphology. Background Art

[0002] Amorphous silica is rich in surface hydroxyl groups, lightweight, has a small particle size, and has adjustable specific surface area and pore structure. It is widely used as a tire filler and carrier. Methods for preparing amorphous silica include fumed silica, acid precipitation, sol-gel, and microemulsion processes. Silica prepared by different methods also exhibits varying structures and properties. Fumed silica particles are small in size and have a large specific surface area, easily forming a large adsorption layer on rubber, enhancing the interaction between silica and silicone rubber. Consequently, it exhibits excellent reinforcing properties for silicone rubber. Fumed silica has a three-dimensional network structure, forming a composite network with silicone rubber that exhibits excellent reinforcing properties. Precipitated silica particles are larger in size and have a smaller specific surface area, resulting in a smaller adsorption layer on rubber. Consequently, its reinforcing properties for silicone rubber are relatively poor. Furthermore, silica prepared by the sol-gel process using water glass as a raw material exhibits small particles, large specific surface area, high porosity, and large pore volume, resulting in excellent physical and chemical properties. Traditional sulfuric acid method amorphous silica contains a considerable amount of two-dimensional linear structure and some three-dimensional network structure, but the structure control of silica produced by traditional preparation method usually adopts the method of adding coupling agent for modification, while the pore structure control is controlled by adding template agent.

[0003] CN 107603280 A discloses a method for preparing white carbon black, which comprises adding an aqueous solution of a carbon source, dispersing it evenly, and heating it to obtain white carbon black coated with the carbon source. CN 115286003 A discloses a method for regulating the structure of amorphous silica, which comprises adding an organic solvent and a cationic porogen during the synthesis process to increase the pore volume and porosity of the amorphous silica. CN 117208920 A discloses a method for controlling amorphous silica using a multi-reactor series process to prepare highly dispersed silica. However, due to the low absorption rate of carbon dioxide, large volumes of gas flow through the multiple reactors, resulting in high energy consumption in the reaction system and an unstable chemical environment.

[0004] Currently, there are few reports on the growth and structure regulation of carbon dioxide precipitated amorphous silica particles using existing technologies. On the one hand, the SiO2–H2O core structure in the reaction solution suffers from poor uniformity due to the unstable gas-liquid flow field. On the other hand, in the preparation process of carbon dioxide precipitated amorphous silica, the carbon dioxide absorption efficiency decreases and the bubble distribution is uneven due to the reaction in the gas-liquid-solid three-phase system, resulting in uneven silica particle size and rough particle surface. This leads to poor dispersion of silica in rubber products and uncontrollable performance in downstream applications. Summary of the Invention

[0005] In order to overcome the structural control problem of the existing carbonization method for producing amorphous silicon dioxide, the present inventors provide a method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: A method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology is a two-step reaction of normal pressure and pressurized pressure, comprising the following steps: 1) In a normal pressure-pressurized reaction apparatus, a dilute water glass solution with a modulus of 2.3-3.8 and a NaHCO3 solution or CO2 gas are mixed to obtain a mixed solution having a SiO2 content of less than 20 g / L. The reaction temperature is controlled at 60-100°C, and a mixture of CO2 and a diluent gas is introduced at normal pressure. The pH of the reaction system is adjusted to ≤10.3 to obtain a solution A containing induced SiO2–H2O nuclei. 2) Mix a water glass solution with a modulus of 2.3-3.8 with solution A, adjust the SiO2 content in the reaction solution to 40-70 g / L to obtain reaction solution B, stir and heat to 80-150°C, and close the gas outlet of the pressure reactor; 3) CO2 gas is introduced to cause carbonization reaction, and the gauge pressure is increased to 0~0.5MPa. Water glass reacts with CO2 until the pH value of the system drops below 9.0; 4) After the reaction is completed, the reaction solution is stirred and aged for 10 to 150 minutes, discharged, and subjected to solid-liquid separation, deionized water washing, weak acid leaching, slurrying, and drying to obtain silica powder.

[0007] Furthermore, the present invention adopts a normal pressure-pressurized reaction device, the reaction system is a single kettle internal circulation system with an intermediate gas cabinet or a double kettle circulation reaction system, the reactor stirring device is equipped with a self-priming gas redistributor, and the process flow is as follows: Figure 1 shown.

[0008] Furthermore, the SiO2 content in the dilute water glass solution in step 1) is 4.0~16.0g / L, preferably 6.0~12.0g / L; the water glass modulus is preferably 2.8~3.50; and the amount of sodium bicarbonate added is 0~20g / L, preferably 4.0~12g / L.

[0009] Furthermore, in the normal pressure reaction adopted in the preparation method of solution A for inducing SiO2–H2O nuclei in step 1), the initial structure of the induced SiO2–H2O nuclei is controlled by the concentration of the NaHCO3 solution in the pre-reaction liquid, and the temperature of the pre-reaction liquid is controlled at 60–100°C, preferably at 60–80°C; a mixed gas consisting of CO2 and diluent gas is introduced from the intermediate gas cabinet, and the partial pressure of CO2 in the mixed gas is 0.3–0.8, preferably at 0.4–1.0; the diluent gas is one or two of air, nitrogen, and argon; and the pH is controlled at 9.0–10.3, preferably at 9.5–10.0.

[0010] Furthermore, in step 2), the SiO2 content in the reaction solution is adjusted to 50-60 g / L, and after the temperature is raised to the set temperature by self-priming stirring, the outlet valve of the reactor is closed.

[0011] Furthermore, in step 3), the gauge pressure is increased to 0-0.5 MPa (gauge pressure) by CO2 or a diluent gas, preferably 0.1-0.4 MPa (gauge pressure). After the reaction, the pH is not greater than 9.0, preferably 8.1-8.8; the reaction temperature is 80-150°C, preferably 85-95°C; and the reaction time is 60-600 min, preferably 100-240 min.

[0012] Furthermore, the reaction liquid B is stirred by a stirring paddle of a self-priming gas redistributor, and a fully mixed flow field is formed in the reactor. The gas at the top of the reactor is redispersed in the reaction liquid in the form of bubbles under the strong shearing action of the gas redistributor impeller. The gas redistributor rotates at high speed to shear and produces bubbles with a size of 0.08 to 10 mm, preferably 0.5 to 5.0 mm, thereby increasing the contact area between the carbon dioxide gas and the liquid.

[0013] Furthermore, the self-priming stirring system used in the present invention is as follows Figure 2 As shown, the self-priming stirring paddle is divided into two parts, namely the stirring blade and the bottom impeller. The stirring blade realizes the stirring function, and the bottom impeller realizes self-priming and secondary bubbling of CO2.

[0014] Furthermore, the stirring shaft is a hollow shaft with a small hole at the upper end of the shaft, which is connected to the gas phase at the top of the reactor (such as Figure 2 As shown in 1-1 and 2-2); the bottom of the stirring shaft has internal teeth, connected to a three-leaf or five-leaf impeller, which is driven by gears and increases the impeller speed (as shown in Figure 2 The high-speed impeller increases the flow rate of the fluid at the bottom of the agitator, forming a negative pressure near the impeller. The unreacted CO2 in the upper space of the reactor circulates through the hollow agitator shaft to the negative pressure zone at the bottom of the agitator shaft. Under the action of the high-speed rotating impeller, bubbles are formed again and react again in the water glass fluid.

[0015] Furthermore, under the action of the internal circulation device, the rotation of the high-speed impeller throws the fluid carrying CO2 bubbles toward the reactor wall and rises along the reactor wall. Under the control of the stirring slurry, the fluid descends from the top along the stirring shaft to the bottom.

[0016] Furthermore, the aging time in step 4) is 10 to 150 minutes, preferably 20 to 40 minutes; the unreacted residual CO2 gas enters the intermediate gas cabinet 4 to provide CO2 for the formation of SiO2·nH2O nuclei in the next reaction; the slurry is filtered and washed with deionized water, and at the end of washing, a weak acid is used for washing, and the weak acid is one of acetic acid, citric acid, and formic acid to remove the residual NaHCO3 on the surface.

[0017] The present invention adopts the above technical scheme, first reacting carbon dioxide, NaHCO3 solution and low-concentration water glass at normal pressure to produce silica particle nuclei, controlling the cationic chemical environment in the growth environment, and secondary induced growth under high pressure. The gas-liquid-solid three-phase flow field and bubble diameter in the kettle are controlled by a self-priming gas redistributor, the carbon dioxide absorption rate is enhanced, the temperature is controlled at 80-150°C, and carbonization is continued until the pH value of the reaction system drops below 9.0. Under these conditions, amorphous silica with a specific structure is formed by induced growth through the particle nuclei. After solid-liquid separation, washing and drying, amorphous silica functional powder with adjustable specific surface area and pore volume is obtained.

[0018] Compared with the prior art, the advantages of the present invention are: The present invention provides an amorphous silica core structure and a gas-liquid flow field control method regulated by sodium bicarbonate and carbon dioxide. A uniform particle size core is obtained through a uniform flow field. At the same time, a special reaction device structure design is adopted to realize the secondary bubbling of unreacted CO2 in a pressurized reactor, increase the gas-liquid contact area, and improve the mass transfer rate and reaction rate. It can not only greatly improve the overall reaction rate and the utilization rate of CO2, but also improve the current situation of uneven gas-liquid contact and difficult reaction control in the traditional carbonization method, improve the powder structure and powder morphology of silica, and the morphology, particle size distribution, specific surface area, porosity and pore volume of amorphous silica can be controlled over a large range through this process. The particle size of the elementary particles of the product produced by the present invention is adjustable from 30 to 100 nm, and the BET specific surface area is between 80 and 400 m 2 / g, pore volume adjustable from 0.2 to 0.6 ml / g.

[0019] The production process technology of the present invention can solve the problems of secondary bubbling of carbon dioxide in the reactor and increasing the reaction rate of carbon dioxide, regulate the morphology and pore structure of carbon dioxide-processed amorphous silica particles, and at the same time solve the problem of sodium sulfate wastewater discharge generated by the introduction of structure-regulating additives in the production process of traditional sulfuric acid-processed amorphous silica. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 This is a flow chart of a pressure reaction with a self-priming gas redistribution agitator used in an embodiment of the present invention; 1-Reactor, 2-Roots blower, 3-Reactor, 4-Gas cabinet.

[0021] Figure 2 This is a structural diagram of the self-priming stirring system of the present invention; 1-1 is a cross-sectional view of the hollow structure of the upper part of the stirring shaft, 2-2 is a cross-sectional view of the lower structure of the stirring shaft, A is a top view of the speed change gear coupling, and B is a top view of the bottom high-speed impeller.

[0022] Figure 3 This is an SEM image of the spherical silica product prepared in Example 1 of the present invention.

[0023] Figure 4 This is an SEM image of the spherical silica product prepared in Example 2 of the present invention.

[0024] Figure 5 This is an SEM image of the spherical silica product prepared in Example 3 of the present invention.

[0025] Figure 6 This is an SEM image of the spherical silica product prepared in Example 4 of the present invention. DETAILED DESCRIPTION Example 1

[0026] A method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization 1) Liquid water glass with a modulus of 3.0 was added with water to prepare a water glass solution with a SiO2 content of 6.0 g / L. Sodium bicarbonate solution was added to 5.0 g / L and introduced into pressure reactor 1. The reactor temperature was set at 60°C. A mixture of CO2 and air was introduced into the water glass solution through a gas distribution pipe. The volume concentration of CO2 was 45%. After reacting for 2 h, stirring and the introduction of the mixed gas were stopped to obtain solution A. The pH value of solution A was 9.5. 2) Mix liquid water glass with a modulus of 3.0 and solution A, adjust the SiO2 content of the reaction solution to 50 g / L, stir again at a stirring speed of 250 rpm and a bottom impeller speed of 500 rpm, and raise the temperature to 90°C; 3) Introduce CO2 gas, adjust the gas pressure to 0.45 MPa, react until the pH value of the reaction liquid drops to about 8.7, then reduce the pressure, and transport the remaining CO2 to gas cabinet 4 via a Roots pump; 4) After the reaction is completed, the reaction solution is stirred and aged for 30 minutes, filtered, washed with deionized water, rinsed with citric acid, and slurried evenly before being passed into a spray drying tower. The solution is classified by a cyclone classifier, collected, and bagged to obtain the silica product.

[0027] After testing, the obtained silica product has a primary particle size of 30nm and a specific surface area of ​​272.4 m 2 / g, pore volume 0.65cm 3 / g. Example 2

[0028] A method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization 1) Liquid water glass with a modulus of 3.4 was added with water to prepare a water glass solution with a SiO2 content of 10.0 g / L. Sodium bicarbonate solution was added to 10.0 g / L and introduced into a pressure reactor 1. The reactor temperature was set at 80°C. A mixture of CO2 and air was introduced into the water glass solution through a gas distribution pipe. The volume concentration of CO2 was 80%. After reacting for 2 h, stirring and the introduction of the mixed gas were stopped to obtain solution A. The pH value of solution A was 9.8. 2) Mix liquid water glass with a modulus of 3.4 and solution A, adjust the SiO2 content of the reaction solution to 60 g / L, stir again at a stirring speed of 200 rpm and a bottom impeller speed of 400 rpm, and raise the temperature to 90°C; 3) Introduce CO2 gas, adjust the gas pressure to 0.5 MPa, react until the pH value of the reaction liquid drops to about 8.7, then reduce the pressure, and transport the remaining CO2 to gas cabinet 4 through a Roots pump; 4) After the reaction is completed, the reaction solution is stirred and aged for 30 minutes, filtered, washed with deionized water, rinsed with citric acid, and slurried evenly before being passed into a spray drying tower. The solution is classified by a cyclone classifier, collected, and bagged to obtain the silica product.

[0029] After testing, the obtained silica product has a primary particle size of 40nm and a specific surface area of ​​120.0 m 2 / g, pore volume 0.25cm 3 / g. Example 3

[0030] A method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization 1) Liquid water glass with a modulus of 3.0 was added with water to prepare a water glass solution with a SiO2 content of 6.0 g / L. The solution was added to a pressure reactor. The reactor temperature was set at 90°C. A mixture of CO2 and air was introduced into the water glass solution through a gas distribution pipe. The volume concentration of CO2 was 60%. After reacting for 2 h, stirring and the introduction of the mixed gas were stopped to obtain Solution A. The pH value of Solution A was 9.8. 2) Mix liquid water glass with a modulus of 3.4 and solution A, adjust the SiO2 content of the reaction solution to 50 g / L, stir again at a stirring speed of 150 rpm and a bottom impeller speed of 300 rpm; and heat to 95°C. 3) Introduce CO2 gas, adjust the gas pressure to 0.5 MPa, react until the pH value of the reaction liquid drops to about 8.3, reduce the pressure, and transport the remaining CO2 to the gas cabinet through a Roots pump; 4) After the reaction is completed, the reaction solution is stirred and aged for 30 minutes, filtered, rinsed with deionized water and citric acid, and then slurried evenly and passed into a spray drying tower. The mixture is classified by a cyclone classifier, collected and bagged to obtain the silica product.

[0031] After testing, the obtained silica product has a primary particle size of 35nm and a BET specific surface area of ​​142.4 m 2 / g, pore volume 0.35cm 3 / g. Example 4

[0032] A method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization 1) Liquid water glass with a modulus of 3.3 was added with water to prepare a water glass solution with a SiO2 content of 6.0 g / L. Sodium bicarbonate solution was added to 5.0 g / L and introduced into a pressure reactor. The reactor temperature was set at 60°C, and a mixture of CO2 and air from a gas cabinet was introduced into the water glass solution through a gas distribution pipe. The partial pressure of CO2 was 0.45. After reacting for 2 h, stirring and the introduction of the mixed gas were stopped to obtain Solution A. The pH value of Solution A was 9.5. 2) Mix liquid water glass with a modulus of 3.3 and solution A, adjust the SiO2 content of the reaction solution to 50 g / L, stir again at a stirring speed of 300 rpm and a bottom impeller speed of 600 rpm, and raise the temperature to 95°C; 3) Introduce CO2 gas, adjust the gas pressure to 0.45 MPa, react until the pH value of the reaction liquid drops to about 8.9, reduce the pressure, and transport the remaining CO2 to the gas cabinet through a Roots pump; 4) After the reaction is completed, the reaction solution is stirred and aged for 30 minutes, filtered, rinsed with deionized water and citric acid, and then slurried evenly and passed into a spray drying tower. The mixture is classified by a cyclone classifier, collected and bagged to obtain the silica product.

[0033] After testing, the silica product obtained has a primary particle size of 30nm and a specific surface area of ​​342.4 m 2 / g, pore volume 1.14cm 3 / g.

Claims

1. A method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology, characterized in that: The following steps are involved: 1) In a normal pressure-pressurized reaction apparatus, a dilute water glass solution with a modulus of 2.3-3.8 and a NaHCO3 solution or CO2 gas are mixed to obtain a mixed solution having a SiO2 content of less than 20 g / L. The reaction temperature is controlled at 60-100°C, and a mixture of CO2 and a diluent gas is introduced at normal pressure. The pH of the reaction system is adjusted to ≤10.3 to obtain a solution A containing induced SiO2–H2O nuclei. 2) Mix a water glass solution with a modulus of 2.3-3.8 with solution A, adjust the SiO2 content in the reaction solution to 40-70 g / L to obtain reaction solution B, and heat the mixture to 80-150°C while stirring. 3) Introduce CO2 gas to cause carbonization reaction, increase the gauge pressure to 0~0.5MPa, and react with water glass and CO2 until the pH value of the system drops below 9.0; 4) After the reaction is completed, the reaction solution is stirred and aged for 10 to 150 minutes, and then subjected to solid-liquid separation, washing, pulping and drying to obtain silica powder.

2. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 1, wherein: The SiO2 content in the dilute water glass solution in step 1) is 4.0-16.0 g / L, the water glass modulus is 2.8-3.50, and the amount of NaHCO3 added is 0-20 g / L.

3. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 1, wherein: A normal pressure-pressurized reaction device is used, and the reaction system is a single-kettle internal circulation system with an intermediate gas cabinet or a double-kettle circulation reaction system. The reaction kettle stirring device is equipped with a self-priming gas redistributor.

4. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 3, characterized in that: The reaction liquid B is stirred by the stirring paddle of the self-priming gas redistributor, and a fully mixed flow field is formed in the reactor. The gas at the top of the reaction device is redispersed in the reaction liquid in the form of bubbles under the shearing action of the gas redistributor impeller. The bubble size generated by the shearing of the gas redistributor is 0.08~10mm.

5. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 3, characterized in that: In the normal pressure reaction adopted in the preparation method of step 1) solution A containing induced SiO2–H2O nuclei, the initial structure of the induced SiO2–H2O nuclei is controlled by the concentration of the NaHCO3 solution in the pre-reaction liquid, the temperature of the pre-reaction liquid is controlled at 60–80°C, a mixed gas consisting of CO2 and diluent gas is introduced from the intermediate gas cabinet, and the pH is controlled at 9.0–10.

3.

6. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 5, characterized in that: The dilution gas is one or two of air, nitrogen, and argon. The partial pressure of CO2 in the mixed gas is 0.3~0.8, and the pH is controlled at 9.0~10.

3.

7. The method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization according to claim 1, characterized in that: Step 2) Adjust the SiO2 content in the reaction solution to 50-60 g / L.

8. The method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization according to claim 1, characterized in that: Step 3) The gauge pressure is increased to 0.1-0.4 MPa by CO2 or diluent gas. After the reaction, the pH value of the system is 8.1-8.

8. The reaction temperature is 80-150°C, and the reaction time is 60-600 min.

9. The method for preparing amorphous silicon dioxide by carbonization with controllable structure and morphology according to claim 8, characterized in that: The reaction temperature of step 3) is 85-95°C, and the reaction time is 100-240 min.

10. The method for preparing amorphous silicon dioxide with controllable structure and morphology by carbonization according to claim 8, characterized in that: The aging time in step 4) is 10 to 150 minutes. The washing is first performed with deionized water and then with acid to remove the remaining NaHCO3. The weak acid is one of acetic acid, citric acid, and formic acid.

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