Process for the production of white carbon black and ammonium fluoride from silicon tetrafluoride

Abstract

The application discloses a method for preparing white carbon black and ammonium fluoride from silicon tetrafluoride, wherein the silicon tetrafluoride gas enters an ammoniation reactor through the middle part, the carrier gas and the ammonia gas enter the ammoniation reactor through the bottom part, solid particles SiO2 and NH4F are generated, the carrier gas flows out from the top outlet of the ammoniation reactor and enters a separator, solid slurry is rapidly formed after being washed in the spray at the top inlet of the separator, and then the solid slurry is settled into the separator; inert solvents are added into the separator, and SiO2 and NH4F are separated by using the density difference. The application uses the SiF4 gas obtained by decomposing fluorosilicic acid or the by-product silicon tetrafluoride gas of phosphate fertilizer as raw materials to continuously produce high-quality white carbon black and ammonium fluoride, and the method is continuous, stable, simple, and has a long operation period, and effectively overcomes the defects of the existing intermittent process technology.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, specifically referring to a method for producing white carbon black and ammonium fluoride from silicon tetrafluoride. Background Technology

[0002] Fluorosilicic acid is a byproduct of wet-process phosphoric acid production and is typically used to produce sodium fluorosilicate. However, the market size for this product is small, and its added value is low. Another utilization route involves producing ammonium fluoride and silica through ammonolysis. Silica can be used in coatings, flame retardants, and rubber reinforcing agents, with relatively high added value. Ammonium fluoride can be used to produce ammonium bifluoride, or further converted to produce hydrogen fluoride. Hydrogen fluoride is a fundamental raw material in the fluorochemical industry, with high demand and high added value.

[0003] The production of high-quality silica by fluorosilicic acid ammoniation is an intermittent process. First, SiO2 seed crystals are prepared by fluorosilicic acid ammoniation. Then, fluorosilicic acid and ammonia are added as "seeds" to obtain silica with a high specific surface area and ammonium fluoride solution. The ammonium fluoride solution is then concentrated, crystallized, and dried to obtain solid ammonium hydrogen fluoride product.

[0004] Chinese patent CN200710065876.4 discloses a "method for producing high-reinforcing precipitated silica by ammoniation of fluorosilicic acid," which uses fluorosilicic acid and an ammonifying agent (ammonia or ammonium bicarbonate) as raw materials for a stepwise ammoniation reaction, followed by aging, filtration, washing, and drying to obtain precipitated silica. CN200610017485.0 also utilizes 10-30% ammonia and fluorosilicic acid for rapid reaction to prepare seed crystals, followed by a second ammoniation to produce precipitated silica. Both methods use ammonia for the ammoniation reaction, which has the disadvantage of introducing a large amount of water into the system with the low-concentration ammonia. This necessitates subsequent evaporation to remove a significant amount of water to prepare solid ammonium bifluoride or anhydrous hydrogen fluoride, increasing energy consumption and cost. Furthermore, the conditions and material concentration requirements for the two ammoniation steps are different, generally requiring multiple reactors connected in series and parallel for continuous production, resulting in relatively high equipment investment. Although CN201110358118.8 also uses a mixture of compressed air and ammonia as the ammonifying agent for the ammoniation reaction, which reduces the amount of water entering the system to some extent, it still achieves the production of silica through a stepwise ammoniation process via hydrolysis. CN 102351150B uses silicon tetrafluoride as a raw material, which undergoes a hydrolysis reaction with a reaction amount of water vapor at 200–800℃. The resulting products are separated into hydrogen fluoride and silica via gas-solid separation. However, it should be noted that traditional fumed silica production uses silicon tetrachloride hydrolyzed in a hydrogen-oxygen flame. This reaction produces a large amount of HCl, but HCl itself does not react with silica. Furthermore, hydrolyzing silicon tetrafluoride under fluorine-containing acidic conditions makes it difficult to obtain silica with a high specific surface area. Surface areas below 100m² are difficult to achieve. 2Low-quality silica has low market acceptance and low added value, while the SiO2 prepared in this patent has a specific surface area ranging from 45 to 400 m². 2 / g, therefore, there may be a large amount of low-value-added silica. CN 113929101 A also involves passing pretreated silicon tetrafluoride gas into dewatering water for hydrolysis, controlling the temperature between 20 and 80°C, and finally obtaining silica and fluorosilicates. Silica is also prepared by liquid-phase hydrolysis, and the product silica needs to be washed with a large amount of water to remove the fluorosilicates adsorbed in the pores. Summary of the Invention

[0005] The purpose of this invention is to address the aforementioned technical deficiencies by providing a method for producing white carbon black and ammonium fluoride from silicon tetrafluoride, thereby improving product quality and reducing product costs.

[0006] To achieve the above objectives, the method for producing silica and ammonium fluoride from silicon tetrafluoride according to the present invention is as follows:

[0007] After primary cryogenic separation, the crude silicon tetrafluoride gas enters the ammoniation reactor through the middle section, while the carrier gas and ammonia gas enter the ammoniation reactor through the bottom. The two raw materials react in the ammoniation reaction tower to generate solid particles SiO2 and NH4F.

[0008] Solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor along with the carrier gas and enter the separator. After being washed in the spray at the top inlet of the separator, they quickly form a solid slurry, which then settles into the separator.

[0009] An inert solvent is added to the separator, and SiO2 and NH4F are separated by density difference. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain NH4F. The mixture at the bottom of the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain silica. The inert solvent recovered during filtration and drying is collected and returned to the separator for continued recycling.

[0010] Further, the volume ratio of SiF4:ammonia:carrier gas is 1:4:2 to 1:6.8:10.

[0011] Furthermore, the reaction temperature in the ammoniation reactor is 30–80°C and the pressure is 60–101 kPa.

[0012] Furthermore, the carrier gas is one or more of air, nitrogen, and water vapor at 100-150°C.

[0013] Furthermore, the carrier gas is a mixture of air and water vapor, and the volume ratio of air to water vapor is 1:4 to 4:1.

[0014] Furthermore, the source of the crude silicon tetrafluoride gas is: a mixture of HF and SiF4 gas generated by the decomposition of fluorosilicic acid with a mass concentration of 18-45%; or crude silicon tetrafluoride with a mass concentration of 20-80%.

[0015] Furthermore, the primary cryogenic separation degree of the crude silicon tetrafluoride gas is -80 to -5°C.

[0016] Furthermore, the inert solvent is dichloromethane, carbon tetrachloride, or glycerol.

[0017] Furthermore, the ammoniation reactor adopts an empty tower design, with a silicon tetrafluoride gas inlet distribution pipe in the middle of the side wall and a carrier gas and ammonia gas inlet distribution pipe in the lower part; the reaction temperature in the ammoniation reactor is controlled by external circulating water, and a heat exchange coil is installed in the gas phase reaction zone to further control the temperature of the reaction zone.

[0018] Compared with the prior art, the present invention has the following advantages: the present invention uses silicon tetrafluoride gas, a by-product of phosphate fertilizer, or SiF4 gas obtained by decomposing fluorosilicic acid as raw materials to continuously produce high-quality silica and ammonium fluoride. The process is continuous, stable, simple, and has a long operating cycle, effectively overcoming the shortcomings of the existing intermittent process technology. Attached Figure Description

[0019] Figure 1 A schematic diagram of the process for producing silica and ammonium fluoride from silicon tetrafluoride;

[0020] Figure 2 This is a schematic diagram of the ammoniation reactor. Detailed Implementation

[0021] The present invention will be further described in detail below through specific embodiments to facilitate a clearer understanding of the invention, but these embodiments do not constitute a limitation on the invention.

[0022] like Figure 1 The flowchart shown illustrates the specific methods for producing white carbon black and ammonium fluoride from silicon tetrafluoride:

[0023] The crude silicon tetrafluoride gas is subjected to primary cryogenic separation to remove most of the HCl, HF, water and organic matter to obtain silicon tetrafluoride gas. The separation temperature is -80 to -5℃, preferably -25 to -10℃.

[0024] Silicon tetrafluoride gas enters the ammoniation reactor through the middle section, while carrier gas and ammonia gas enter the ammoniation reactor through the bottom. The two raw materials react in the ammoniation reaction tower, and the volume ratio of the reacting gases is SiF4:ammonia:carrier gas = 1:4:2 to 1:6.8:10, preferably SiF4:ammonia:carrier gas = 1:4.8:4. The reaction temperature is 30–80℃, preferably 40–60℃, and the pressure is 60–101 kPa, preferably 80–101 kPa.

[0025] The source of crude silicon tetrafluoride gas is: a mixture of HF and SiF4 gas produced by the decomposition of fluorosilicic acid with a mass concentration of 18-45%, wherein the mass concentration of fluorosilicic acid is preferably 20-40%; or crude silicon tetrafluoride with a mass concentration of 20-80%, preferably 40-60%.

[0026] The carrier gas is one or more of air, nitrogen, and water vapor at 100-150°C, preferably a mixture of air and water vapor, with a volume ratio of air to water vapor of 1:4 to 4:1, preferably 2:3. The ammonia source is liquid ammonia or ammonia water.

[0027] Two raw materials react in the ammoniation reaction tower to produce solid particles SiO2 and NH4F. The solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor with the carrier gas and enter the separator. After being washed in the spray at the top inlet of the separator, they quickly form a solid slurry, which then settles into the separator.

[0028] An inert solvent is added to the separator, and SiO2 and NH4F are separated by density difference, with SiO2 at the bottom and NH4F at the top. The inert solvent can be dichloromethane, carbon tetrachloride, or glycerol, with carbon tetrachloride being preferred. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain NH4F. The bottom mixture in the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain silica. The inert solvent recovered during filtration and drying is collected and returned to the separator for reuse.

[0029] This invention uses silicon tetrafluoride gas, a byproduct of phosphate fertilizer production, or SiF4 gas obtained by decomposing fluorosilicic acid, as raw materials. It employs a gas-phase reaction method to continuously prepare silica and ammonium fluoride under alkaline conditions, thereby effectively improving product quality and reducing product costs.

[0030] SiF4 + 4NH3 + 2H2O → SiO2 + 4NH4F

[0031] The key to this invention lies in using gas-phase raw materials to prepare SiO2 and NH4F solids through reaction. Currently, the preparation of silica from fluorosilicic acid via ammonolysis involves a liquid-phase reaction of fluorosilicic acid solution with ammonia or liquid ammonia. The main drawback is that the reaction products are SiO2 and NH4F solution. Separating the SiO2 solid requires extensive washing with water, and the NH4F solution needs to be evaporated and concentrated to obtain the solid product. Both processes are energy-intensive and costly. By using a gas-phase reaction, an appropriate amount of water can be added as a raw material as needed, reducing the introduction of other moisture at the source and thus lowering the energy consumption for product separation.

[0032] Secondly, compared with liquid phase reaction, gas phase reaction reduces liquid film mass transfer resistance, has a faster reaction rate, and can reduce reactor size by about 40%, reducing equipment investment. By controlling the concentration of SiF4 and ammonia by carrier gas, both the reaction temperature and the material concentration can be maintained within the optimal range.

[0033] Finally, the process of producing fluorosilicic acid as a byproduct of phosphate fertilizer production also utilizes water to absorb fluorine-containing HF and SiF4 gases to obtain approximately 10 wt% dilute fluorosilicic acid. This dilute fluorosilicic acid is then reacted with liquid ammonia or ammonia water to produce ammonium fluoride and silica. Using this invention reduces the need for absorption equipment, saving investment. Simultaneously, it directly utilizes fluorine-containing gas to react with ammonia in a gas-phase reaction within an ammoniation reactor to directly obtain ammonium fluoride and silica, thus reducing the overall amount of water added and evaporation energy consumption. Furthermore, although the 10 wt% concentration can be concentrated to obtain 20–40 wt% concentrated fluorosilicic acid for ammoniation to reduce water carryover, fluorosilicic acid concentrations exceeding 20 wt% are unstable and easily decompose into HF and SiF4.

[0034] like Figure 2 The ammoniation reactor shown adopts an empty tower design. A silicon tetrafluoride gas inlet distribution pipe is installed in the middle of the side wall of the ammoniation reactor, and a carrier gas and ammonia gas inlet distribution pipe is installed at the bottom. The reaction temperature in the ammoniation reactor is controlled by external circulating water, and a heat exchange coil is installed in the gas phase reaction zone to further control the temperature of the reaction zone.

[0035] Example 1

[0036] The feedstock SiF4 gas, with a flow rate of 1000 L / h and a mass concentration of 20%, is fed into the middle of the ammoniation reactor after being cooled and purified at -10℃. The carrier gas (air / water vapor = 50 / 50) has a flow rate of 4000 L / h. Liquid ammonia, after vaporization, has a flow rate of 800 L / h. Both the carrier gas and ammonia are fed into the bottom of the ammoniation reactor. The reaction operation pressure is 70 kPa and the temperature is 40℃. The two feedstocks react in the ammoniation reactor to produce solid particles SiO2 and NH4F. The solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor with the carrier gas and enter the separator. After being washed in a spray at the top inlet of the separator, they quickly form a solid slurry, which then settles and separates. The solvent used for washing is carbon tetrachloride. The washed carrier gas is treated and then discharged into the atmosphere. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain 1280g of NH4F. The bottom mixture in the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain 498g of silica. The main economic indicator of silica is a specific surface area of ​​150m². 2 / g; DBP absorbance value 2.80.

[0037] Example 2

[0038] The feedstock SiF4 gas, with a flow rate of 1000 L / h and a mass concentration of 80%, is fed into the middle of the ammoniation reactor after being cooled and purified at -25°C. The carrier gas (air / water vapor = 40 / 60) has a flow rate of 2000 L / h. Liquid ammonia, after vaporization, has a flow rate of 5440 L / h. Both the carrier gas and ammonia are fed into the bottom of the ammoniation reactor. The reaction operation pressure is 60 kPa and the temperature is 80°C. The two feedstocks react in the ammoniation reactor to produce solid particles SiO2 and NH4F. The solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor with the carrier gas and enter the separator. After being washed in a spray at the top inlet of the separator, they quickly form a solid slurry, which then settles and separates. The solvent used for washing is carbon tetrachloride. The washed carrier gas is treated and then discharged into the atmosphere. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain 5200g of NH4F. The bottom mixture in the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain 2100g of silica. The main economic indicator of silica is a specific surface area of ​​110m². 2 / g; DBP absorbance value 2.30.

[0039] Example 3

[0040] The raw material, 18% fluorosilicic acid, is thermally decomposed to obtain a mixed gas of SiF4 and HF at a flow rate of 1000 L / h. The SiF4 mass concentration is 40%. After being cooled and purified at -15℃, the mixture is fed into the middle of the ammoniation reactor. The carrier gas (air / water vapor = 60 / 40) has a flow rate of 7000 L / h. 15% ammonia water is stripped by the carrier gas to obtain ammonia gas. A mixed gas of ammonia gas, air, and water vapor is fed into the reactor at a flow rate of 11800 L / h. The carrier gas and ammonia gas are fed into the reactor from the bottom. The reaction operation pressure is 80 kPa and the temperature is 80℃. The two raw materials react in the ammoniation reactor to produce solid particles SiO2 and NH4F. The solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor with the carrier gas and enter the separator. After being washed in a spray at the top inlet of the separator, they quickly form a solid slurry, which then settles and separates. The washing solvent is dichloromethane. The washed carrier gas is treated and then discharged. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain 2588g of NH4F. The bottom mixture in the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain 982g of silica. The main economic indicator of silica is a specific surface area of ​​120m². 2 / g; DBP absorbance value 2.60.

[0041] Example 4

[0042] The raw material, 45% fluorosilicic acid, is thermally decomposed to obtain a mixed gas of SiF4 and HF at a flow rate of 1000 L / h. The SiF4 mass concentration is 60%. After being cooled and purified at -25℃, the mixture is fed into the middle of the ammoniation reactor. The carrier gas (air / water vapor = 50 / 50) has a flow rate of 10000 L / h. 30% ammonia water is stripped by the carrier gas to obtain ammonia gas. A mixed gas of ammonia, air, and water vapor is fed into the reactor at a flow rate of 12400 L / h. The carrier gas and ammonia gas are fed into the reactor from the bottom. The reaction operation pressure is 90 kPa and the temperature is 90℃. The two raw materials react in the ammoniation reactor to produce solid particles SiO2 and NH4F. The solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor with the carrier gas and enter the separator. After being washed in a spray at the top inlet of the separator, they quickly form a solid slurry, which then settles and separates. The washing solvent is dichloromethane. The washed carrier gas is treated and then discharged. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain 3860g of NH4F. The bottom mixture in the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain 1580g of silica. The main economic indicator of silica is a specific surface area of ​​130m². 2 / g; DBP absorbance value 2.68.

Claims

1. A method for preparing silica and ammonium fluoride from silicon tetrafluoride, characterized in that: The preparation method is as follows: After primary cryogenic separation, the crude silicon tetrafluoride gas enters the ammoniation reactor through the middle section, while the carrier gas and ammonia gas enter the ammoniation reactor through the bottom. The two raw materials react in the ammoniation reaction tower to generate solid particles SiO2 and NH4F. Solid particles SiO2 and NH4F flow out from the top outlet of the ammoniation reactor along with the carrier gas and enter the separator. After being washed in the spray at the top inlet of the separator, they quickly form a solid slurry and then settle into the separator. An inert solvent is added to the separator, and SiO2 and NH4F are separated by density difference. The upper mixture in the separator is filtered to obtain an NH4F filter cake, which is then dried to obtain NH4F. The mixture at the bottom of the separator is filtered to obtain a SiO2 filter cake, which is then dried to obtain silica. The inert solvent recovered during filtration and drying is collected and returned to the separator for continued recycling. The carrier gas is a mixture of air and water vapor, and the volume ratio of air to water vapor is 1:4 to 4:

1.

2. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The volume ratio of SiF4:ammonia:carrier gas is 1:4:2~1:6.8:

10.

3. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The reaction temperature in the ammoniation reactor is 30~80℃ and the pressure is 60~101kPa.

4. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The source of the crude silicon tetrafluoride gas is: a mixture of HF and SiF4 gas produced by the decomposition of fluorosilicic acid with a mass concentration of 18-45%; or crude silicon tetrafluoride with a mass concentration of 20-80%.

5. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The primary cryogenic separation degree of the crude silicon tetrafluoride gas is -80~-5℃.

6. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The inert solvent is dichloromethane, carbon tetrachloride, or glycerol.

7. The method for producing white carbon black and ammonium fluoride from silicon tetrafluoride according to claim 1, characterized in that: The ammoniation reactor adopts an empty tower design. A silicon tetrafluoride gas inlet distribution pipe is installed in the middle of the side wall of the ammoniation reactor, and a carrier gas and ammonia gas inlet distribution pipe is installed at the bottom. The reaction temperature in the ammoniation reactor is controlled by external circulating water, and a heat exchange coil is installed in the gas phase reaction zone.

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