CN114477196A - Method for preparing fumed silica by fluorination method - Google Patents

Abstract

The invention discloses a method for preparing fumed silica by a fluorination method. The method mainly comprises the working procedures of cooling absorption-dissolution, adsorption precipitation, washing purification, drying, fluidized decomposition and flame synthesis, and specifically comprises the following steps: taking high-quality silica powder as a raw material, cooling and absorbing smoke generated by silicon tetrafluoride flame synthesis to obtain hydrofluoric acid in solution, and carrying out dissolution reaction to obtain a fluosilicic acid solution; then, adding the fluidized decomposition powder product into a fluosilicic acid solution to enable fluosilicic acid and alkali metal fluoride to form fluosilicate precipitate and hydrofluoric acid, and circularly returning the fluosilicic acid solution for cooling, absorbing and dissolving; after being washed, purified, filtered and dried, the fluosilicate is decomposed in a fluidization way to obtain silicon tetrafluoride gas and powder products; the silicon tetrafluoride gas is purified and then synthesized into gas phase white carbon black by a hydrogen flame method, and the generated flue gas is cooled and absorbed to form hydrofluoric acid and fluosilicic acid mixed solution which is circularly used for dissolving the silica.

Description

A kind of method for preparing gas phase silica by fluorination method

technical field

The invention relates to the fields of chemical industry and materials, in particular to a method for preparing gas-phase silica by a fluorination method.

Background technique

Fumed silica (nano silica) is one of the extremely important high-tech ultra-fine inorganic new materials, because of its small particle size, large surface area, strong surface adsorption, large surface energy, high chemical purity and good dispersion performance , thermal resistance, resistance and other aspects have specific properties, with its superior stability, reinforcement, thickening and thixotropy, it has an indispensable and outstanding importance in many disciplines and fields. In industry, silicon tetrachloride is mainly used as raw material, and it is produced by high temperature flame synthesis by hydrogen flame method. For example, Chinese patent CN1282603C uses silicon tetrachloride as a raw material to synthesize fumed silica by a high-temperature flame method. However, there are problems such as high raw material cost of silicon tetrachloride and intractable by-product hydrochloric acid. Therefore, a more efficient and clean new technology of fumed silica has yet to be developed.

Among the many research and development routes, the hydrogen tetrafluoride flame synthesis method is considered to be one of the most promising routes. Silicon tetrafluoride gas can be obtained from the decomposition of fluorosilicic acid or sodium fluorosilicate by-product of the phosphate fertilizer industry, and it is easy to purify to the higher purity required for the production of silica. For example, Chinese patent CN102351150B uses crude silicon tetrafluoride produced by phosphate fertilizer as a silicon source, and after dust removal and dehumidification, it reacts with water vapor to prepare fumed silica. However, this route has the following three outstanding problems: (1) If the silicon tetrafluoride gas is obtained by decomposing sodium fluorosilicate, there is a problem that the low-temperature decomposition is incomplete and the high-temperature decomposition materials are bonded. For the method, see the relevant description of Chinese patent application CN110683548A for details; (2) the thermodynamic equilibrium conversion rate of the reaction system for preparing silica by tetrafluoride hydrogen flame method is low (only ~70% at 1500 ° C), and the powder is recovered after separation After the flue gas is absorbed and treated, it will produce a difficult-to-treat fluosilicic acid solution; (3) the flue gas generated by the decomposition of silicon tetrafluoride and the hydrogen fluoride products generated by the fluosilicic acid treatment must be purified/dehydrated before product sales, which increases the number of products sold. Silica producers' operating costs and market uncertainty risk factors.

To sum up, the existing fumed silica preparation technology has the problems of low conversion rate and high cost caused by the need to refine the emitted flue gas. Therefore, it is of great significance to develop a green, environmentally friendly and economical production technology through technological innovation.

SUMMARY OF THE INVENTION

Aiming at the problems existing in the existing technology for preparing gas-phase white body black, the present invention provides a method for preparing gas-phase white carbon black by a fluorination method. The whole process uses high-quality silica as the raw material, and effectively avoids the generation of three wastes and by-products through the circulation of fluorine medium, so as to realize the low-cost, high-efficiency and clean production of fumed silica. Therefore, the method has the characteristics of environmental friendliness, low energy consumption and high added value of products.

To achieve the above object, the present invention has adopted the following technical scheme:

A method for preparing fumed silica by fluorination, the method comprises the following steps: cooling absorption-dissolution step 1, adsorption precipitation step 2, washing and purification step 3, drying step 4, fluidized decomposition step 5 and The flame synthesis process 6 is specifically carried out according to the following steps:

1) The flue gas generated in the flame synthesis process 6 is sent to the cooling absorption-dissolving process 1, so that the hydrogen fluoride gas and the residual silicon tetrafluoride gas in the flue gas are dissolved and absorbed to form a solution of hydrofluoric acid and fluosilicic acid. The acid reacts with high-quality silica to form fluorosilicic acid;

2) The fluorosilicic acid solution obtained in the cooling absorption-dissolving step 1 is sent to the adsorption and precipitation step 2, and the decomposed powder product produced in the fluidized decomposition step 5 is added to make the silicon tetrafluoride and the alkali metal in the fluorosilicic acid. The fluorine salt forms an alkali metal fluorosilicate precipitate, and the hydrofluoric acid solution is circulated back to the cooling absorption-dissolving process 1;

3) the alkali metal fluorosilicate precipitation obtained in the adsorption precipitation step 2 is sent to the washing and purifying step 3, and the washing and purifying treatment is carried out, and then filtered to obtain pure alkali metal fluorosilicate powder;

4) The fluorosilicate powder obtained in the washing and purification step 3 is sent to the drying step 4, and drying and dehydration treatment is performed to obtain a dry alkali metal fluorosilicate powder;

5) The alkali metal fluorosilicate powder obtained in the drying step 4 is sent to the fluidized decomposition step 5, and the fluidized partial decomposition of the fluorosilicate is realized by using the silicon tetrafluoride circulating gas to obtain the silicon tetrafluoride gas, The decomposed powder product is sent to the adsorption precipitation process 2;

6) The silicon tetrafluoride gas obtained in the fluidized decomposition step 5 is sent to the flame synthesis step 6 after purification, and silica powder and flue gas are obtained by pyrolysis, and the hydrogen fluoride gas and residual tetrafluoride in the flue gas are obtained. The silicon gas is sent to the cooling absorption-dissolution step 1.

Preferably, the mass content of silica in the silica raw material in the absorption-dissolution step 1 is not less than 99.0%, and the particle size ranges from 0.1 to 2.0 mm.

Preferably, the alkali metal in the alkali metal fluoride salt is one or a combination of lithium, potassium, and sodium.

Preferably, the dehydration and drying process 3 adopts one or more of vacuum drying, fixed bed drying and fluidized bed drying, the dehydration drying temperature is 20-200°C, and the drying time is 0.1-36h.

Preferably, the low-temperature decomposition step 4 adopts a fluidized bed reactor, the fluidized gas is silicon tetrafluoride gas, the decomposition temperature is 400-700° C., and the residence time is 0.5-3.0 h.

Preferably, the fuel used in the flame synthesis step 5 can be hydrogen and/or carbon monoxide, or one or a combination of gaseous or liquid flammable hydrocarbons, and the temperature is 1000-2000°C, The molar ratio of silicon tetrafluoride gas, oxygen and fuel is 1:2-15:1.5-8.

In the present invention, high-quality silica powder is used as raw material, and flue gas is synthesized by flame synthesis of silicon tetrafluoride to cool and absorb to obtain hydrofluoric acid in the solution, which is dissolved and reacted to obtain a fluorosilicic acid solution; then, the fluidized decomposition powder product is added with fluorine In the silicic acid solution, fluorosilicic acid and alkali metal fluoride are formed into fluorosilicate precipitate and hydrofluoric acid, and the hydrofluoric acid solution is circulated and returned to the cooling absorption-dissolving process; the fluorosilicate is washed, purified, filtered and dried. , carry out fluidized decomposition to obtain silicon tetrafluoride gas and powder products; after the silicon tetrafluoride gas is purified, a hydrogen flame method is used to synthesize gas-phase silica products, and the generated flue gas is cooled and absorbed to form hydrofluoric acid and fluorine The silicic acid mixed solution is circulated for the dissolution of silica. The whole process uses high-quality silica as the raw material, and effectively avoids the generation of three wastes and by-products through the circulation of fluorine medium, so as to realize the low-cost, high-efficiency and clean production of fumed silica.

Compared with the prior art, the present invention has the following outstanding advantages:

(1) The low temperature decomposition process adopts fluidization technology to strengthen the heat and mass transfer process of the sodium fluorosilicate decomposition process, and has a faster reaction rate under lower temperature conditions, effectively avoiding melting and agglomeration;

(2) The utilization problem of the fluorosilicic acid produced in the absorption process and the solid-state decomposition product produced in the decomposition process is effectively solved, and the recycling of the fluorine medium is realized;

(3) The whole process effectively avoids the generation of three wastes and by-products.

Description of drawings

The accompanying drawings are used to provide further explanation of the present invention, and constitute a part of the specification, and are used to explain the present invention together with the embodiments of the present invention, and do not limit the present invention.

Fig. 1 is a kind of fluorination method according to the present invention to prepare the method flow schematic diagram of gas-phase silica;

Reference numerals: 1. Cooling absorption-dissolution process, 2. Adsorption precipitation process, 3. Washing and purification process, 4. Drying process, 5. Fluidized decomposition process, 6. Flame synthesis process.

Detailed ways

Any feature disclosed in this specification, unless expressly stated otherwise, may be replaced by other equivalent or alternative features serving a similar purpose. Unless stated otherwise, each feature is only one example of a series of equivalent or similar features. The description is only for helping understanding of the present invention and should not be regarded as a specific limitation of the present invention.

The present invention will be described in further detail below with the accompanying drawings and specific embodiments.

Example 1

Fig. 1 is a schematic flow diagram of a method for preparing gas-phase silica by a fluorination method according to the present invention. With reference to Fig. 1, a method for preparing fumed silica by fluorination method includes the following steps: cooling absorption-dissolution step 1, adsorption precipitation step 2, washing and purification step 3, drying step 4, fluidization decomposition step 5 And flame synthesis process 6, specifically carry out according to the following steps:

1) The flue gas generated in the flame synthesis process 6 is sent to the cooling absorption-dissolving process 1, so that the hydrogen fluoride gas and the residual silicon tetrafluoride gas in the flue gas are dissolved and absorbed to form a solution of hydrofluoric acid and fluosilicic acid. The acid reacts with high-quality silica to form fluorosilicic acid;

2) The fluorosilicic acid solution obtained in the cooling absorption-dissolving step 1 is sent to the adsorption and precipitation step 2, and the decomposed powder product produced in the fluidized decomposition step 5 is added to make the silicon tetrafluoride and the alkali metal in the fluorosilicic acid. The fluorine salt forms an alkali metal fluorosilicate precipitate, and the hydrofluoric acid solution is circulated back to the cooling absorption-dissolving process 1;

3) the alkali metal fluorosilicate precipitation obtained in the adsorption precipitation step 2 is sent to the washing and purifying step 3, and the washing and purifying treatment is carried out, and then filtered to obtain pure fluorosilicate powder;

4) sending the fluorosilicate powder obtained in the washing and purification step 3 to the drying step 4, and performing drying and dehydration treatment to obtain a dry fluorosilicate powder;

5) The fluorosilicate powder obtained in the drying step 4 is sent to the fluidized decomposition step 5, and the fluidized partial decomposition of the fluorosilicate is realized by using the silicon tetrafluoride circulating gas to obtain the silicon tetrafluoride gas. The powder product is sent to the adsorption precipitation process 2;

6) The silicon tetrafluoride gas obtained in the fluidized decomposition step 5 is sent to the flame synthesis step 6 after purification, and silica powder and flue gas are obtained by pyrolysis, and the hydrogen fluoride gas and residual tetrafluoride in the flue gas are obtained. The silicon gas is sent to the cooling absorption-dissolution step 1.

Example 2

In this example, the method for preparing gas-phase silica by a fluorination method described in Example 1 is adopted. The silica powder with a mass content of 99.0% and a particle size of 0.5 mm is used as a raw material, which is sent to the cooling-absorption and dissolution process 1, and reacts with the hydrofluoric acid solution obtained from the flue gas in the absorption flame synthesis process 6 to form fluorine. silicic acid; then send the fluorosilicic acid to the adsorption precipitation step 2, and react with the solid decomposition product of the low-temperature decomposition step 4 to obtain sodium fluorosilicate; send the sodium fluorosilicate to the drying step 3, in a fixed bed at 100 ° C Dry for 5 hours to obtain dry sodium fluorosilicate powder; send the dried sodium fluorosilicate powder to fluidization reaction step 5, react at 400°C for 3.0 hours, and send the obtained solid reaction product to the adsorption precipitation step 2. The silicon tetrafluoride gas generated by the decomposition enters the flame synthesis process 6 after dust removal and purification, and is decomposed and oxidized under the conditions that the temperature is 1500 ° C and the molar ratio of silicon tetrafluoride, oxygen and fuel is 1:5:5, The fumed silica is obtained, and the generated flue gas enters the cooling absorption-dissolution process 1.

Example 3

In this example, the method for preparing gas-phase silica by a fluorination method described in Example 1 is adopted. The silica powder with a mass content of 99.4% and a particle size of 2.0 mm is used as a raw material, which is sent to the cooling-absorption and dissolution process 1, and reacts with the hydrofluoric acid solution obtained from the flue gas in the absorption flame synthesis process 6 to form fluorine. silicic acid; then send the fluorosilicic acid to the adsorption precipitation step 2, and react with the solid decomposition product of the low-temperature decomposition step 4 to obtain sodium fluorosilicate; send the sodium fluorosilicate to the drying step 3, in a fluidized bed for 200 ℃ drying treatment for 0.1h to obtain dry sodium fluorosilicate powder; the dried sodium fluorosilicate powder is sent to fluidized reaction step 5, reacted at 500 ℃ for 2.0h, and the obtained solid reaction product is sent to adsorption Precipitation process 2, and the silicon tetrafluoride gas generated by the decomposition enters the flame synthesis process 6 after dust removal and purification, and decomposes under the conditions that the temperature is 1000 ° C and the molar ratio of silicon tetrafluoride, oxygen and fuel is 1:10:8 Oxidation to obtain fumed silica, and the generated flue gas enters the cooling absorption-dissolution process 1.

Example 4

In this example, the method for preparing gas-phase silica by a fluorination method described in Example 1 is adopted. The silica powder with a mass content of 99.5% and a particle size of 0.1 mm is used as a raw material, which is sent to the cooling-absorption and dissolution process 1, and reacts with the hydrofluoric acid solution obtained from the flue gas in the absorption flame synthesis process 6 to form fluorine. silicic acid; then send the fluorosilicic acid to the adsorption precipitation step 2, and react with the solid decomposition product of the low-temperature decomposition step 4 to obtain sodium fluorosilicate; send the sodium fluorosilicate to the drying step 3, and put it in a vacuum drying oven for 20 ℃ drying for 36h to obtain dry sodium fluorosilicate powder; the dried sodium fluorosilicate powder is sent to fluidized reaction step 5, reacted at 400 ℃ for 3.0h, and the obtained solid reaction product is sent to adsorption precipitation In step 2, the silicon tetrafluoride gas generated by the decomposition enters into the flame synthesis step 6 after dedusting and purification, and decomposes and oxidizes under the condition that the temperature is 2000°C and the molar ratio of silicon tetrafluoride, oxygen and fuel is 1:4:2 , to obtain fumed silica, and the generated flue gas enters the cooling absorption-dissolution process 1.

Example 5

In this example, the method for preparing gas-phase silica by a fluorination method described in Example 1 is adopted. The silica powder with a mass content of 99.0% and a particle size of 1.0 mm is used as a raw material, which is sent to the cooling-absorbing and dissolving process 1, and reacts with the hydrofluoric acid solution obtained from the flue gas in the absorption flame synthesis process 6 to form fluorine. silicic acid; then send the fluorosilicic acid to the adsorption and precipitation step 2, and react with the solid decomposition product of the low-temperature decomposition step 4 to obtain sodium fluorosilicate; ℃ dry for 24h to obtain dry sodium fluorosilicate powder; send the dry sodium fluorosilicate powder to fluidized reaction step 5, react at 700 ℃ for 0.5h, and send the obtained solid reaction product to adsorption precipitation Step 2, and the silicon tetrafluoride gas generated by the decomposition enters the flame synthesis step 6 after dedusting and purification, and decomposes and oxidizes under the conditions that the temperature is 1500 ° C and the molar ratio of silicon tetrafluoride, oxygen and fuel is 1:15:8 , to obtain fumed silica, and the generated flue gas enters the cooling absorption-dissolution process 1.

The process parameters (such as temperature, time, etc.) of the present invention can implement the method by setting the upper and lower limits of the interval and the interval value, and the embodiments are not listed one by one here.

For the content not described in detail in the present invention, conventional technical knowledge in the field can be used.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention will not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the present invention. within the scope of the claims.

Claims (6)

1. A method for preparing fumed silica by a fluorination method comprises the following steps: the method comprises a cooling absorption-dissolution process (1), an adsorption precipitation process (2), a washing and purification process (3), a drying process (4), a fluidization decomposition process (5) and a flame synthesis process (6), and specifically comprises the following steps:

1) sending the flue gas generated in the flame synthesis process (6) into a cooling absorption-dissolution process (1) to dissolve and absorb hydrogen fluoride gas and residual silicon tetrafluoride gas in the flue gas to form hydrofluoric acid and fluorosilicic acid solution, wherein the hydrofluoric acid reacts with added silica to form fluorosilicic acid;

2) sending the fluosilicic acid solution obtained in the cooling absorption-dissolution process (1) into an adsorption precipitation process (2), adding a decomposition powder product generated in a fluidization decomposition process (5), so that silicon tetrafluoride and alkali metal fluoride in the fluosilicic acid form alkali metal fluosilicate precipitate, and circularly returning the hydrofluoric acid solution to the cooling absorption-dissolution process (1);

3) sending the alkali metal fluosilicate precipitate obtained in the adsorption precipitation step (2) into a washing and purification step (3), carrying out washing and purification treatment, and then filtering to obtain pure alkali metal fluosilicate powder;

4) feeding the alkali metal fluorosilicate powder obtained in the washing and purifying step (3) to a drying step (4), and drying and dehydrating to obtain dry alkali metal fluorosilicate powder;

5) feeding the alkali metal fluosilicate powder obtained in the drying step (4) into a fluidized decomposition step (5), realizing fluidized decomposition of fluosilicate by using silicon tetrafluoride circulating gas to obtain silicon tetrafluoride gas, and feeding the decomposed powder product into an adsorption precipitation step (2);

6) and (3) purifying the silicon tetrafluoride gas obtained in the fluidized decomposition step (5), then sending the silicon tetrafluoride gas into a flame synthesis step (6), obtaining white carbon black powder and flue gas through pyrolysis, and sending the hydrogen fluoride gas and the residual silicon tetrafluoride gas in the flue gas into a cooling absorption-dissolution step (1).

2. The method for preparing fumed silica according to claim 1, wherein the silica has a silicon dioxide content of not less than 98.0% by mass and a particle size of 0.01-2.0 mm.

3. The method for preparing fumed silica according to claim 1, wherein the alkali metal of the alkali metal fluoride is selected from one or more of lithium, potassium and sodium.

4. The method for preparing fumed silica by fluorination according to claim 1, wherein one or more of vacuum drying, fixed bed drying and fluidized bed drying is adopted in the drying step (4), the dehydration drying temperature is 0-200 ℃, and the drying time is 0.1-36 h.

5. The method for preparing fumed silica by fluorination according to claim 1, wherein the fluidized decomposition step (5) adopts a fluidized bed reactor, the fluidized gas is silicon tetrafluoride gas, the decomposition temperature is 400-700 ℃, and the retention time is 0.5-3.0 h.

6. The method for preparing fumed silica by fluorination according to claim 1, wherein the fuel used in the flame synthesis step (5) is one or a combination of hydrogen and gaseous or liquid combustible hydrocarbon, the temperature is 1200-2000 ℃, and the molar ratio of silicon tetrafluoride gas, oxygen and fuel is 1: 2-15: 1.5-8.

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