A method for the production of low-emission amorphous silicon dioxide

Abstract

This invention discloses a method for preparing low-emission amorphous silica. The method involves reacting circulating alkali with silica to obtain a high-modulus water glass solution. Flue gas containing low to medium concentrations of carbon dioxide from a process kiln is then separated from organic amine-grafted mesoporous silica to obtain approximately 99% carbon dioxide. This separation is carried out in a two-step reaction system under normal and pressure conditions. After solid-liquid separation, washing, and drying, amorphous silica powder is obtained. The sodium bicarbonate filtrate obtained from solid-liquid separation reacts directly with Ca(OH)₂ colloid to obtain light calcium carbonate and a dilute alkali solution. The dilute alkali solution is then dehydrated and concentrated through negative pressure evaporation to obtain circulating alkali with a NaOH content of over 30%. This circulating alkali reacts with silica to obtain high-modulus water glass. This production process significantly reduces the emissions of sodium sulfate wastewater and carbon dioxide during the traditional sulfuric acid process for amorphous silica production.

Description

Technical Field

[0001] This invention belongs to the field of powder preparation technology, specifically relating to a method for preparing low-emission amorphous silica. Background Technology

[0002] Amorphous silica possesses properties such as light weight, small particle size, large specific surface area, high dispersibility, good chemical stability, high temperature resistance, and good insulation. These properties enable amorphous silica powder to be widely used in many fields such as rubber, tires, papermaking, coatings, building materials, and feed, but with varying functions.

[0003] Currently, the traditional industrial process for preparing amorphous silica involves calcining quartz sand and soda ash at high temperatures to obtain high-modulus water glass. After dissolution, the water glass reacts with inorganic acids to produce amorphous silica. The production of water glass from quartz sand uses coal or natural gas as fuel. During the high-temperature preparation of water glass, the combustion of coal or natural gas and the decomposition of soda ash generate large amounts of carbon dioxide. The drying process of amorphous silica primarily involves heat exchange with flue gas from coal-fired kilns to dry the high-moisture-content amorphous silica filter cake. The acidification process primarily uses sulfuric acid as the acidifying agent, which severely corrodes equipment and generates large volumes of sodium sulfate-containing wastewater. Therefore, the emissions from the high-temperature soda ash-water glass-inorganic acid acidification process for quartz sand include carbon dioxide emissions, sodium sulfate wastewater emissions, fly ash emissions from the coal combustion process, and a small amount of alkaline slag emissions from the dissolution of water glass. The emissions of fly ash and alkaline dissolution slag can be reduced through raw material control or fuel substitution. It is estimated that using quartz sand as raw material, a process involving soda ash, high-temperature water glass, and sulfuric acid acidification can produce approximately 1 ton of amorphous silica, 12 tons of sulfate wastewater, and 2.5 tons of carbon dioxide. Utilizing recovered CO2 from the production process as an acidifying agent can not only significantly reduce CO2 emissions and minimize acid corrosion of equipment, but also achieve sodium recycling through the carbonation reaction products, sodium carbonate or sodium hydroxide, thus minimizing the amount of saline wastewater.

[0004] Patent 201110026112.0 discloses a method for preparing amorphous silica from CO2 while simultaneously evaporating, concentrating, and recovering Na2CO3. In this method, half of the sodium carbonate-containing filtrate is returned to a sodium metasilicate solution for further dissolution and precipitation of metasilicic acid, while the other half is concentrated and crystallized to obtain sodium carbonate product. However, the method does not achieve the recycling of carbon, sodium, and water throughout the entire process, and the low-emission characteristics of the process need to be further improved. Patent application 200910085908.6 discloses a process route for simultaneously preparing amorphous silica and ultrafine calcium carbonate from carbon dioxide. This route involves obtaining 5-15% sodium hydroxide through a causticization reaction, which is then reacted with quartz sand to obtain sodium silicate via a recycling process. However, the reaction of dilute sodium hydroxide with quartz sand produces sodium silicate with a modulus of 2.0-2.2, making it difficult to obtain high-modulus water glass. Furthermore, the high water content leads to high energy consumption, making it difficult to increase the water glass modulus. Additionally, the carbon dioxide flue gas generated in the process kiln is not recovered. Moreover, the addition of additives such as NaCl and Na2SO4 during the preparation of silica increases the water glass salt content, which is detrimental to the structural control of the silica product. Patent application 202310969463.8 discloses a method for preparing amorphous silica using a sodium silicate coupled carbonization process. This process involves reacting quartz sand and sodium carbonate in an oxygen-enriched kiln to produce water glass. Then, CO2 kiln gas and the water glass solution undergo a carbonization reaction to produce fumed silica and sodium carbonate filtrate. The sodium carbonate filtrate is evaporated, concentrated, and crystallized to recover sodium carbonate, thus achieving an internal cycle of sodium, carbon, and water. However, in essence, this only reduces the emissions of carbon dioxide produced by the decomposition of soda ash and the amount of saline wastewater. Summary of the Invention

[0005] To address the issues of high carbon dioxide emissions and high-salinity wastewater discharge in existing amorphous silica production processes, this invention provides a method for preparing low-emission amorphous silica. This method can significantly reduce carbon dioxide emissions and sodium sulfate wastewater discharge during the amorphous silica production process.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing low-emission amorphous silica includes the following steps:

[0008] 1) The CO2 in the flue gas of the process kiln is separated and purified to more than 99% by using a CO2 recovery tower;

[0009] 2) Mix the water glass solution with a modulus of 2.3 to 4.0 with part of the filtrate A after the carbonization reaction (filtrate A after the reaction in step 2 of this invention), and introduce the CO2 gas recovered in step 1) into the atmospheric pressure-pressurized reaction system to carry out a two-step carbonization reaction. Control the gas-liquid flow field and bubble distribution of the carbonization reaction until the pH value drops below 8.8. After solid-liquid separation, washing and drying, amorphous silica powder and filtrate A containing sodium bicarbonate are obtained.

[0010] 3) React the filtrate A after carbonization reaction in step 2) with Ca(OH)2 to obtain calcium carbonate powder and dilute NaOH or Na2CO3 alkali solution. The dilute alkali solution is evaporated and concentrated under negative pressure MVR to obtain NaOH circulating alkali solution with a content of more than 30%. The condensate is returned to the washing or batching process.

[0011] 4) The NaOH circulating liquid alkali with a content of more than 30% obtained in step 3) is reacted with crystalline silicon dioxide in a pressure reactor to obtain water glass with a modulus of 2.3~4.0.

[0012] Furthermore, the flue gas used in step 1) is the process kiln flue gas from the amorphous silica production process, with a CO2 content of 8-18%, preferably 12-18%; the packing material of the CO2 recovery tower is organic amine-grafted porous amorphous silica, with an organic amine grafting amount of 10-30%, preferably 20-26%; the carbon chain length of the organic amine is C1-C4, preferably C2-C3; the pore size of the porous amorphous silica is 1.0-5.0 nm, preferably 2.0-3.5 nm; and the pore volume of the porous amorphous silica is 0.5-1.1 cm³. 3 / g, preferably with a pore volume of 0.7~1.0cm³. 3 / g.

[0013] Furthermore, the atmospheric-pressurized reaction system described in step 2) is a dual-reactor series cyclic reaction system or a single-reactor atmospheric-pressurized sequential reaction system; the reactor is a fluid self-priming forced carbon dioxide circulation pressurized reactor, where CO2 gas is carried into the bottom of the reactor by the vortex formed by the high-speed stirring blades, and the carbon dioxide bubbles are refined under the shearing action of the double-layer blades at the bottom of the reactor.

[0014] Furthermore, the reaction in step 2) is a two-step reaction under normal pressure and under pressure. Under normal pressure, water glass with a modulus of 2.3 to 4.0 is mixed with the filtrate after the carbonization reaction, and then reacted with the remaining carbon dioxide reaction gas after the end of the reaction in the pressure vessel, with a carbon dioxide partial pressure of 0.5 to 0.99. After the reaction under normal pressure is completed, the pH is 9.0 to 11.0, and water glass with a modulus of 2.3 to 4.0 is added. The carbon dioxide partial pressure in the reaction vessel is 0.3 to 0.99, and the pressure is 0.2 to 1.0 MPa. The carbon dioxide gas reacts with the water glass to achieve nucleation-induced growth and form amorphous silica elementary particles.

[0015] Further, in the atmospheric pressure reaction process, a concentrated water glass solution with a modulus of 2.3~4.0 (preferably 2.4~3.5) is diluted with the filtrate after the carbonization reaction to a water glass concentration of 3~15 g / L (preferably 3~12 g / L) based on silica. The total carbon concentration in the carbonization reaction filtrate is 0.5~8.0%, preferably 1.0~4.0%. The temperature of the mixed solution is 60~95℃, preferably 70~90℃. The partial pressure of carbon dioxide in the atmospheric pressure nucleation reaction is 0.5~0.99, preferably 0.5~0.70; the reaction time is 10~90 min, preferably 30~60 min, and the prepared amorphous silica nuclei have a particle size of 2~6 nm.

[0016] Furthermore, the pressurized reaction process involves adding a water glass solution with a modulus of 2.3 to 4.0 to the reaction solution after the atmospheric pressure carbonization reaction is completed to adjust the water glass concentration in the reaction solution, making the water glass concentration, calculated as silica, 40 to 90 g / L, preferably 50 to 70 g / L. The temperature of the pressurized carbonization reaction solution is 80 to 130°C, preferably 90 to 110°C. The reactor pressure is 0.2 to 1.0 MPa, and the CO2 partial pressure is 0.1 to 0.9, preferably 0.4 to 0.8. The reaction time is 60 to 3000 min, preferably 90 to 300 min. After the reaction reaches its endpoint, the material is discharged, filtered, and washed.

[0017] Furthermore, the aforementioned fluid self-priming forced carbon dioxide circulation pressurized reactor uses the negative pressure generated by the high-speed rotating impeller at the center of the reactor to draw carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. Specifically, the central impeller rotates at 200-600 rpm, preferably 400-500 rpm; the bubbles generated by the gas redistributor are 0.1-10 mm in size, preferably 1-5 mm in diameter.

[0018] Furthermore, in step 3), when the sodium bicarbonate filtrate from step 2) reacts with Ca(OH)2, the ingredients are prepared according to the total carbon concentration in the filtrate. Ca(OH)2 colloid is added in a molar ratio of 1:0.8 to 1:0.9 based on the total carbon content in the filtrate. The reaction temperature is controlled at 50 to 100°C and the reaction time is 10 to 60 minutes.

[0019] Furthermore, the NaOH content of the dilute alkali solution before concentration is 2.0~6.0%, and the dilute alkali solution is concentrated to more than 30% by negative pressure MVR evaporation. The pressure of the negative pressure MVR evaporation chamber is controlled at -0.07~-0.02MPa (gauge pressure), preferably -0.07~-0.05MPa (gauge pressure); the temperature of the dilute alkali solution in the evaporation chamber is controlled at 50~85℃, preferably 60~80℃; the NaOH concentration of the circulating liquid alkali obtained after evaporation and concentration is more than 30%.

[0020] Furthermore, the reaction temperature in step 4) is 150~200℃, and the reaction pressure is 0.1~0.5 MPa. Preferably, the reaction temperature is 160~180℃, and the reaction pressure is 0.2~0.4 MPa. The crystalline silica is quartz sand, quartz after phase inversion, and industrial waste of crystalline silica.

[0021] Compared with the prior art, the advantages of the present invention are:

[0022] (1) This invention uses porous amorphous silica grafted with organic amine to collect and purify the low-to-medium concentration CO2 in the process kiln to more than 99%, and adopts a two-step carbonization process of atmospheric pressure and pressurized pressure to produce amorphous silica, which replaces the original inorganic acid acidification water glass amorphous silica preparation process and avoids the generation of sodium sulfate wastewater.

[0023] (2) In this invention, a dilute NaOH solution is generated by reacting Ca(OH)2 colloid with the filtrate after carbonization reaction. Then, the solution is concentrated by negative pressure MVR evaporation to generate a circulating liquid alkali of more than 30% for the preparation of high modulus water glass. The evaporation condensate is used for washing and batching circulation, which greatly reduces CO2 emissions. Compared with the existing process of preparing water glass from quartz soda ash at high temperature to produce amorphous silica, the carbon dioxide emissions are reduced by 40%, and compared with the existing soda ash recycling process, the carbon dioxide emissions are reduced by 30%. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the process flow of the present invention. Detailed Implementation Example 1

[0025] A method for preparing low-emission amorphous silica includes the following steps:

[0026] 1) After scrubbing the flue gas with a CO2 concentration of 16%, pass it through grafted porous silica filled with propylamine (propylamine grafting amount 20%, porous silica pore size 2.0 nm, pore volume 0.7 cm³). 3 A carbon dioxide recovery tower (g) was used, and the reaction was carried out at a controlled temperature of 50°C. When the absorption was saturated, the flue gas was stopped, the temperature was heated to 90°C, the gas at the top of the tower was collected, and the CO2 content was 99% after dehydration.

[0027] 2) A SiO2 concentration of 10.0 g / L water glass solution was prepared by adding liquid water glass with a modulus of 3.0 to the filtrate after carbonization. At a temperature of 80℃, the remaining unreacted carbon dioxide from the pressurized carbonization reactor was passed into the water glass solution through a gas distribution pipe. The partial pressure of the remaining mixed gas carbon dioxide was 0.8. The reaction proceeded as follows: After h, stirring and the introduction of mixed gas were stopped, with the final pH reaching 9.5. The reaction solution was pumped into a pressurized carbonization reactor, and the SiO2 concentration in the reaction solution was adjusted to 50 g / L using water glass with a modulus of 3.0. The reaction temperature was adjusted to 90℃, and stirring was continued. The captured CO2 gas was then introduced under pressure using a booster cylinder, with the pressure inside the reactor controlled at 0.5 MPa and the CO2 partial pressure kept constant at 0.8, until the pH of the water glass solution dropped to approximately 8.7. After aging for 20 min, the mixture was filtered, washed, and pulped evenly using a plate and frame filter press before being fed into a spray drying tower. After drying, amorphous silica powder and filtrate A were obtained. The powder had a BET specific surface area of ​​160 m². 2 / g, the electron microscopy unit particle size is 40nm.

[0028] In the above steps, the negative pressure generated by the high-speed rotating blades at the center of the reactor draws carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. The central blades rotate at 600 rpm. The gas redistributor generates bubbles with a size of 0.1~10 mm.

[0029] 3) The filtrate A from the plate and frame filter press is pumped to a jacketed stirred tank with a NaHCO3 concentration of 4.5%. 37 g / L Ca(OH)2 colloid is introduced into the solution at an equal volume. The temperature is controlled at 70℃ and the reaction is carried out for 30 min to obtain solid powder CaCO3. The solution contains 1.5% NaOH. The pressure of the negative pressure MVR evaporator is controlled at -0.06 MPa (gauge pressure). After the solution is evaporated and dehydrated by 95%, the NaOH concentration of the circulating liquid reaches 30%. The condensate B is returned to the washing or batching process.

[0030] 4) After the circulating liquid alkali and crystalline silicon dioxide containing 99.5% SiO2 are stirred evenly at a ratio of 1:0.67, they are put into a pressure vessel, the temperature is controlled at 180℃, and water glass is obtained after reacting for 3 hours. The modulus of water glass is 2.83. Example 2

[0031] A method for preparing low-emission amorphous silica includes the following steps:

[0032] 1) After scrubbing the flue gas with a CO2 concentration of 10%, pass it through grafted porous silica filled with propylamine (propylamine grafting amount 25%, porous silica pore size 3.5nm, pore volume 1.0cm³). 3 A carbon dioxide recovery tower (g) was used, and the reaction was carried out at a controlled temperature of 50°C. When the absorption was saturated, the flue gas was stopped, the temperature was heated to 90°C, the gas at the top of the tower was collected, and the CO2 content was 99.5% after dehydration.

[0033] 2) A SiO2 concentration of 6.0 g / L water glass solution was prepared by adding liquid water glass with a modulus of 2.4 to the filtrate after carbonization. At a temperature of 90 ℃, the remaining unreacted carbon dioxide from the pressurized carbonization reactor was passed into the water glass solution through a gas distribution pipe. The partial pressure of the remaining mixed gas carbon dioxide was 0.8. The reaction proceeded for 1... After h, stirring and the introduction of mixed gas were stopped, with the final pH reaching 9.2. The reaction solution was pumped into a pressurized carbonization reactor, and the SiO2 concentration in the reaction solution was adjusted to 50 g / L using water glass with a modulus of 2.4. The reaction temperature was adjusted to 90℃, and stirring was continued. Collected CO2 with a purity of 99.5% was introduced under pressure, with the reactor pressure controlled at 0.4 MPa and the CO2 partial pressure kept constant at 0.75, until the pH of the water glass solution dropped to approximately 8.5. After aging for 20 min, the solution was filtered, washed, and pulped evenly using a plate and frame filter press before being fed into a spray drying tower. After drying, amorphous silica powder and filtrate A were obtained. The powder had a BET specific surface area of ​​195 m². 2 / g, the electron microscopy unit particle size is 35nm.

[0034] In the above steps, the negative pressure generated by the high-speed rotating blades at the center of the reactor draws carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. The central blades rotate at 200 rpm. The gas redistributor generates bubbles with a size of 0.1~10 mm.

[0035] 3) The filtrate A from the plate and frame filter press is pumped to the jacketed stirred tank with a NaHCO3 concentration of 5.8%. 100 g / L of Ca(OH)2 colloid is introduced and the temperature is controlled at 50℃. The reaction is carried out for 60 min to obtain solid powder CaCO3. The solution has a NaOH content of 2.5%. The pressure of the negative pressure MVR evaporator is controlled at -0.06 MPa (gauge pressure). After the solution is evaporated and dehydrated by 92%, the NaOH concentration of the circulating liquid reaches 32%. The condensate B is returned to the washing or batching process.

[0036] 4) After the circulating liquid alkali containing 32% NaOH and crystalline silicon dioxide containing 99.5% SiO2 are stirred evenly at a ratio of 1:0.60, the mixture is put into a pressure vessel, the temperature is controlled at 160℃, and the reaction is carried out for 2 hours to obtain water glass with a modulus of 2.45. Example 3

[0037] A method for preparing low-emission amorphous silica includes the following steps:

[0038] 1) After scrubbing the flue gas with a CO2 concentration of 16%, pass it through grafted porous silica filled with ethylamine (20% ethylamine grafting, pore size of 2.5 nm, pore volume of 0.6 cm³). 3 A carbon dioxide recovery tower ( / g) was used, with the reaction temperature controlled at 45℃. When the absorption was saturated, the flue gas was stopped, and the temperature was heated to 80℃. After the gas at the top of the tower was collected and dehydrated, the CO2 content was 99.2%.

[0039] 2) A SiO2 concentration of 4.0 g / L water glass solution was prepared by adding liquid water glass with a modulus of 2.45 to the filtrate after carbonization. At a temperature of 90 ℃, the remaining unreacted carbon dioxide from the pressurized carbonization reactor was passed into the water glass solution through a gas distribution pipe. The partial pressure of the remaining mixed gas carbon dioxide was 0.8. The reaction proceeded for 1... After h, stirring and the introduction of mixed gas were stopped, with the final pH reaching 9.0. The reaction solution was then pumped into a pressurized carbonization reactor, and the SiO2 concentration in the reaction solution was adjusted to 70 g / L. The reaction temperature was adjusted to 100℃, and stirring was continued. Collected CO2 with a purity of 99.2% was introduced under pressure using a booster cylinder, with the reactor pressure controlled at 0.5 MPa and the CO2 partial pressure kept constant at 0.7, until the pH of the water glass solution dropped to approximately 8.8. After aging for 20 min, the solution was filtered, washed, and pulped evenly using a plate and frame filter press before being fed into a spray drying tower. After drying, amorphous silica powder and filtrate A were obtained. The powder had a BET specific surface area of ​​240 m². 2 / g, with an electron microscopy unit particle size of 30~35nm.

[0040] In the above steps, the negative pressure generated by the high-speed rotating blades at the center of the reactor draws carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. The central blades rotate at 350 rpm. The gas redistributor generates bubbles with a size of 0.1~10 mm.

[0041] 3) The filtrate A from the plate and frame filter press is pumped to a jacketed stirred tank with a NaHCO3 concentration of 8%. 100 g / L Ca(OH)2 colloid is introduced into the same volume of the solution. The temperature is controlled at 80℃ and the reaction is carried out for 30 min to obtain solid powder CaCO3. The NaOH content of the solution is 4.5%. The pressure of the negative pressure MVR evaporator is controlled at -0.06 MPa (gauge pressure). After the solution is evaporated and dehydrated by 88%, the NaOH concentration of the circulating liquid reaches 37.5%. The condensate B is returned to the washing or batching process.

[0042] 4) After the circulating liquid alkali containing 37.5% NaOH and crystalline silicon dioxide containing 99.5% SiO2 are stirred evenly in a ratio of 1:1.90, the mixture is put into a pressure vessel, the temperature is controlled at 200℃, and the reaction is carried out for 4 hours to obtain water glass with a modulus of 4.0. Example 4

[0043] A method for preparing low-emission amorphous silica includes the following steps:

[0044] 1) After scrubbing the flue gas with a CO2 concentration of 16%, pass it through grafted porous silica filled with ethylamine (ethylamine content 20%, porous silica pore size 4.0 nm, pore volume 0.8 cm³). 3 A carbon dioxide recovery tower ( / g) was used, with the reaction temperature controlled at 45℃. When the absorption was saturated, the flue gas was stopped, and the temperature was heated to 80℃. After the gas at the top of the tower was collected and dehydrated, the CO2 content was 99.2%.

[0045] 2) Prepare a SiO2 concentration of 6.0 g / L water glass solution by adding the carbonized filtrate to liquid water glass with a modulus of 3.45. Under conditions of 90 ℃, the remaining unreacted carbon dioxide from pressurized carbonization is introduced into the water glass solution through an intermediate gas holder. The partial pressure of carbon dioxide in the remaining mixed gas is 0.8. The reaction proceeds for 1... After h, stirring and the introduction of mixed gas were stopped, with the final pH being 9.3. The SiO2 concentration in the reaction solution was adjusted to 70 g / L using a concentrated water glass solution with a modulus of 3.45. The reaction temperature was maintained at 90℃, the outlet valve of the reactor was closed, and stirring continued. Collected CO2 with a purity of 99.2% was introduced under pressure using a booster cylinder, with the internal pressure controlled at 0.5 MPa and the partial pressure of CO2 kept constant at 0.7, until the pH of the water glass solution dropped to approximately 8.8. After aging for 20 min, the mixture was filtered, washed, and pulped evenly using a plate and frame filter press before being fed into a spray drying tower. After drying, amorphous silica powder and filtrate A were obtained. The powder had a BET specific surface area of ​​200 m². 2 / g, with electron microscopy unit particle size of 32~36nm.

[0046] In the above steps, the negative pressure generated by the high-speed rotating blades at the center of the reactor draws carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. The central blade rotation speed is 450 rpm. The gas redistributor shears and generates bubbles with a size of 0.1~10 mm.

[0047] 3) The filtrate A from the plate and frame filter press is pumped to the jacketed stirred tank with a total carbon concentration of 8%. 100 g / L Ca(OH)2 colloid is introduced into the solution at an equal volume. The temperature is controlled at 80℃ and the reaction is carried out for 30 min to obtain solid powder CaCO3. The solution contains 4.5% NaOH. The pressure of the negative pressure MVR evaporator is controlled at -0.06 MPa (gauge pressure). After evaporation and dehydration of 90%, the NaOH concentration of the circulating liquid reaches 35.0%. The condensate B is returned to the washing or batching process.

[0048] 4) After the circulating liquid alkali containing 35.0% NaOH and crystalline silicon dioxide containing 99.5% SiO2 are stirred evenly in a ratio of 1:1.90, the mixture is put into a pressure vessel, the temperature is controlled at 200℃, and the reaction is carried out for 3 hours to obtain water glass with a modulus of 4.0.

Claims

1. A method for preparing low-emission amorphous silica, characterized in that, Includes the following steps: 1) The CO2 in the flue gas from the process kiln is separated and purified to over 99% using a CO2 recovery tower; 2) Mix the water glass solution with a modulus of 2.3~4.0 and the filtrate A after the carbonization reaction. In the atmospheric pressure-pressurized reaction system, the CO2 gas recovered in step 1) is introduced to carry out a two-step carbonization reaction until the pH value drops below 8.

8. After solid-liquid separation, washing and drying, amorphous silica powder and filtrate A are obtained. The atmospheric-pressurized reaction system is either a dual-reactor series cyclic reaction system or a single-reactor atmospheric-pressurized sequential reaction system. The reaction system is a fluid self-priming forced carbon dioxide circulation pressurized reactor. The negative pressure generated by the high-speed rotating blades at the center of the reactor draws carbon dioxide from the top of the reactor to the bottom. The carbon dioxide is then sheared into small bubbles by the bottom gas redistributor and rises with the reaction liquid, increasing the contact area between the carbon dioxide gas and the liquid and enhancing the carbonization reaction rate. Step 2) involves a two-step reaction: one under normal pressure and the other under pressure. Under normal pressure, water glass is mixed with filtrate A from the carbonization reaction, with a carbon dioxide partial pressure of 0.5–0.

99. After the normal pressure reaction is complete, the final pH is 9.0–11.0, yielding amorphous silica growth nuclei. Under pressure, the carbon dioxide source partial pressure is 0.9–1.0, the reactor pressure is 0.2 MPa–1.0 MPa, and the carbon dioxide partial pressure inside the reactor is 0.3–0.

99. The reaction of carbon dioxide gas with water glass induces nucleus-induced growth into amorphous silica elementary particles. During the atmospheric pressure reaction process, the concentration of water glass in the reaction solution, calculated as silica, is 3~15 g / L, and the total carbon concentration of filtrate A is 0.5~8.0%. The temperature of the solution is 60-95℃, and the reaction time is 10~90 min. The resulting amorphous silica cores have a particle size of 2~6 nm. The pressurized reaction process involves adding a water glass solution with a modulus of 2.3 to 4.0 to the reaction solution after the atmospheric pressure carbonization reaction is completed to adjust the water glass concentration in the reaction solution to 40 to 90 g / L based on silica; the temperature of the reaction solution is 80-130℃, the pressure of the reactor is 0.2 to 1.0 MPa, and the reaction time is 60 to 3000 min. 3) React the filtrate A obtained after the carbonization reaction in step 2) with Ca(OH)2 to obtain calcium carbonate powder and dilute NaOH alkali solution. The dilute alkali solution is evaporated and concentrated under negative pressure MVR to obtain NaOH circulating alkali solution with a concentration of more than 30%. The condensate B is returned to the washing or batching process. 4) React the NaOH circulating liquid alkali with a concentration of more than 30% obtained in step 3) with crystalline silicon dioxide in a pressure reactor to obtain water glass with a modulus of 2.3~4.

0.

2. The method for preparing low-emission amorphous silica according to claim 1, characterized in that, Step 1) uses flue gas from the kiln during the amorphous silica production process, with a CO2 content of 8-18%. The packing material for the CO2 recovery tower is organic amine-grafted porous amorphous silica, with a grafting amount of 10-30% and a carbon chain length of C1-C4 for the organic amine. The pore size of the porous amorphous silica is 1.0-5.0 nm, and the pore volume is 0.5-1.1 cm³. 3 / g.

3. The method for preparing low-emission amorphous silica according to claim 1, characterized in that, The blade rotation speed is 200~600 rpm; the size of the bubbles generated by the gas redistributor shearing is 0.1~10 mm.

4. The method for preparing low-emission amorphous silica according to claim 1, characterized in that, Step 3) When reacting sodium bicarbonate filtrate A after the reaction in step 2) with Ca(OH)2, the ingredients are prepared according to the total carbon concentration in filtrate A. Ca(OH)2 colloid is added according to the total carbon content in filtrate A at a molar ratio of 1:0.8 to 1:0.

9. The reaction temperature is controlled at 50 to 100°C and the reaction time is 10 to 60 minutes.

5. The method for preparing low-emission amorphous silica according to claim 1, characterized in that, Before concentration, the NaOH content of the dilute alkali solution is 2.0~6.0%. The dilute alkali solution is concentrated to more than 30% by negative pressure MVR evaporation. The pressure of the negative pressure MVR evaporation chamber is controlled at a gauge pressure of -0.07~-0.02MPa. The temperature of the dilute alkali solution in the evaporation chamber is controlled at 50~85℃. The condensate B after steam condensation is returned to the batching or washing.

6. The method for preparing low-emission amorphous silica according to claim 1, characterized in that, The reaction temperature in step 4) is 150~200℃ and the reaction pressure is 0.1~0.5MPa; silica includes quartz sand and quartz after phase inversion.

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