Process for the preparation of fluorinated salt adsorbents for fluorine gas purification and use thereof

Abstract

The application belongs to the technical field of fluorine chemical industry, and particularly relates to a preparation method of a fluorinated salt adsorbent for fluorine gas purification and application thereof, aiming to solve the problems of low porosity, small adsorption capacity, low structural strength, and serious pulverization rate of the fluorinated salt adsorbent in the prior art, which are not conducive to industrialized continuous generation. The fluorinated salt adsorbent has a large specific surface area, high adsorption capacity, high strength, and good fluorine gas purification effect. The preparation method is simple, has small equipment corrosion, and can be popularized for industrialized production. The application adopts alkali solution reaction, fluorination etching, and calcination decomposition steps, can completely convert fluorosilicate powder into the fluorinated salt adsorbent, and is helpful to the pore-forming effect of the fluorinated salt adsorbent. The application does not need to add an organic binder, can realize granulation and molding by using the reaction of the fluorosilicate powder and the alkali solution, and has good structural strength in the preparation of the fluorinated salt adsorbent.

Description

Technical Field

[0001] This invention relates to the field of fluorochemical technology, and in particular to a method for preparing a fluoride salt adsorbent for fluorine purification and its application. Background Technology

[0002] Fluorine is the gaseous element of fluorine, which has strong oxidizing and corrosive properties. It can combine with most elements and is widely used in industries such as nuclear industry, semiconductors, synthetic rubber, electronics, solar cells, and aerospace. It plays an important role in the field of fluorochemicals.

[0003] Currently, the preparation of industrial fluorine gas generally adopts the electrolysis method. The initial concentration of fluorine gas obtained after electrolysis is about 90%, and the hydrogen fluoride content in the impurities is relatively high, about (1-8)%. How to effectively reduce the hydrogen fluoride content in fluorine gas is the key technical difficulty in purifying fluorine gas.

[0004] In existing technologies, spherical or columnar fluoride salt adsorbents are generally used in industry to remove hydrogen fluoride. Fluoride salt adsorption has many advantages, including low energy consumption, low cost, simple operation, and recyclability, and is now widely used. Patent CN114054007A, which uses a direct mixture of fluoride salt and organic binder for granulation and calcination, produces a fluoride salt adsorbent with low porosity and a small contact area with the gas, resulting in poor HF adsorption capacity. Patent CN201710557429, which uses a mixture of fluoride salt and hydrogen fluoride to prepare a porous fluoride salt adsorbent, although improving the porosity, suffers from poor forming effect, with severe pulverization of the formed adsorbent particles. Furthermore, the hydrogen fluoride generated during calcination is highly corrosive to equipment at high temperatures, posing a safety risk. Although the sodium fluoride adsorbent prepared by patent CN111085081A using nickel porous microspheres as a metal skeleton has improved adsorption effect and mechanical strength, the preparation method is complicated and costly, and the bonding strength between sodium fluoride and metal skeleton is low. Summary of the Invention

[0005] The purpose of this invention is to provide a method for preparing a fluoride salt adsorbent for fluorine purification and its application, so as to solve the problems of low porosity, small adsorption capacity, low structural strength, and serious pulverization rate of existing fluoride salt adsorbents, which are not conducive to continuous industrial production. This fluoride salt adsorbent has a large specific surface area, high adsorption capacity, high strength, better fluorine purification effect, simple preparation method, low corrosion to equipment, and can be promoted for industrial production.

[0006] To solve the above-mentioned technical problems, the technical solution provided by the present invention is as follows:

[0007] In a first aspect, the present invention provides a method for preparing a fluoride salt adsorbent for fluorine gas purification, comprising the following steps:

[0008] Step A: Mixing, mix fluorosilicate powder with alkaline solution to obtain a pre-mixed mixture;

[0009] Step B: Concentration. The pre-mixed mixture is continuously stirred at 80-100°C to concentrate the mixture and remove water. When the viscosity of the mixture increases to 4000-8000 cP, the concentration is stopped to obtain a dough-like mixture.

[0010] Step C: Granulation, using a molding process, the dough-like mixture is granulated into spherical, columnar, or olive-shaped granules;

[0011] Step D: Etching. The mixture particles are immersed in hydrofluoric acid solution for 40-60 minutes, the hydrofluoric acid concentration is 10-20 wt.%, and dried at 60-70°C for 12 hours to obtain etched mixture particles.

[0012] Step F: Calcination, the etched mixture particles are calcined at 600-800°C for 4-6 hours to prepare the fluoride salt adsorbent.

[0013] Furthermore, the fluorosilicate is one or more of sodium fluorosilicate, potassium fluorosilicate, and lithium fluorosilicate.

[0014] Furthermore, the alkali in the alkaline solution is one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

[0015] Furthermore, the ratio of the mass of fluorosilicate powder to the volume of alkali solution added is (1-6) g: 1 mL.

[0016] Furthermore, the ratio of the mass of fluorosilicate powder to the volume of alkali solution added is (4-6) g: 1 mL.

[0017] Furthermore, the molar ratio of fluorosilicate powder to alkali is (1-15):1, preferably (5-10):1.

[0018] Furthermore, the molar ratio of fluorosilicate powder to alkali is (5-10):1.

[0019] Furthermore, the molding process in step C is compression molding, extrusion granulation, and shot blasting.

[0020] The molding process employs conventional molding processes in this field, such as compression molding, extrusion granulation, and shot blasting.

[0021] Furthermore, in step C, the dough-like mixture is granulated and then dried for 10 hours.

[0022] Secondly, the present invention provides an application of the method for preparing a fluoride salt adsorbent for fluorine purification as described above in the preparation of fluoride salt adsorbents.

[0023] In summary, the technical effects achieved by this invention are as follows:

[0024] 1. In step A, fluorosilicate (MeSiF6) reacts in an alkaline environment to form fluoride (MeF), and the reaction equation is as follows:

[0025] Me2SiF6+4MeOH→6MeF+SiO2+2H2O;

[0026] Typically, fluoride salt (MeF) or acidic fluoride salt (MeHF2) powder raw materials have poor viscosity. To improve the molding effect of the powder raw materials, a certain amount of organic binder needs to be added during the mixing process to enhance the structural strength of the adsorbent. However, if the aforementioned organic binders, such as carboxymethyl cellulose, starch, and chitosan, are not completely oxidized and decomposed during subsequent calcination, the residual organic binders in the fluoride salt adsorbent will react with fluorine gas, thereby affecting the purity of the fluorine gas. In this invention, SiO2 generated by the reaction of fluorosilicates in an alkaline solution can be used as a binder to increase the viscosity of the fluorosilicate mixture. Through further concentration, the molding effect of the fluorosilicate mixture can be significantly improved. The molding of the fluorosilicate mixture can be achieved solely through the reaction of fluorosilicates with alkaline solution without the addition of organic binders.

[0027] 2. In step D, the mixture particles are placed in a hydrofluoric acid solution. The SiO2 in the mixture particles will react with the hydrofluoric acid, and the reaction equation is as follows:

[0028] SiO2 + 4HF → SiF4 + 2H2O;

[0029] The fluorination etching reaction with hydrofluoric acid can not only remove the binder SiO2 generated in step A, but also further improve the specific surface area and porosity of the mixed particles after the fluorination etching reaction.

[0030] 3. In step E, during the high-temperature calcination process, the fluorosilicates in the etching mixture particles will further decompose, undergoing the following reaction:

[0031] Me2SiF6→2MeF+SiF4;

[0032] High-temperature calcination not only completely transforms the etched mixture particles into fluoride salt adsorbents, but also, during the overflow process, the silicon tetrafluoride gas generated by the reaction further forms a large number of pore structures on the surface or inside of the fluoride salt adsorbent, thereby increasing the specific surface area and porosity of the fluoride salt adsorbent.

[0033] Unlike existing conventional methods that use the high-temperature decomposition of acidic fluoride salts to generate hydrogen fluoride for pore creation, the reaction process is as follows:

[0034] MeHF2→MeF+HF;

[0035] Hydrogen fluoride produced by the decomposition of acidic fluoride salts during calcination is highly corrosive to metal equipment. The high-temperature decomposition and pore-forming method of fluorosilicate mixture used in this invention has a weaker corrosive effect on metal equipment and will not cause significant corrosion, making it easy to achieve large-scale industrial production.

[0036] Unlike existing conventional inventions, this invention does not require external organic binders. Granulation and molding can be achieved through the reaction of fluorosilicate powder and alkaline solution. The prepared fluoride salt adsorbent has good structural strength, with a mechanical strength as high as 4.1 MPa / m. 2 .

[0037] Unlike existing conventional inventions, this invention employs steps such as alkaline reaction, fluorination etching, and calcination decomposition. This not only completely converts fluorosilicate powder into fluoride salt adsorbents but also enhances the pore-forming effect of the fluoride salt adsorbents, resulting in a fluoride salt adsorbent with a specific surface area as high as 3.8 m². 2 / g, with a porosity as high as 58%. Attached Figure Description

[0038] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0039] Figure 1 This is a schematic flowchart of the preparation method of the fluoride salt adsorbent in this invention;

[0040] Figure 2 The XRD pattern of the fluoride salt adsorbent prepared in Example 1 is shown below.

[0041] Figure 3 This is a SEM image of the fluoride salt adsorbent prepared in Example 1. Detailed Implementation

[0042] The present invention will be further described below with reference to specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention.

[0043] Example 1:

[0044] Mix 500g of sodium fluorosilicate powder with 100mL of sodium hydroxide solution, wherein the molar ratio of sodium fluorosilicate to sodium hydroxide is 8:1. Stir continuously at 80-100℃. When the viscosity of the mixture reaches 6000cp, stop heating to obtain a dough-like mixture.

[0045] The dough-like mixture was transferred to an extruder to obtain columnar mixture particles with a diameter of 4*8mm, and then placed in the sun to dry for 12 hours.

[0046] The columnar mixture particles were immersed in a 20wt% hydrofluoric acid solution for 60 minutes and then dried in a forced-air drying oven at 60°C for 12 hours to obtain the etched mixture particles.

[0047] The etched mixture particles were placed in a muffle furnace and sintered at 800℃ for 6 hours to obtain sodium fluoride adsorbent. The XRD and SEM images of the prepared adsorbent are shown below. Figure 1 and Figure 2 .

[0048] from Figure 1 It can be seen that the prepared sodium fluoride adsorbent exhibits obvious diffraction peaks of sodium fluoride crystals, with no other impurity peaks observed, indicating high purity that meets the requirements for fluorine purification. Figure 2 It can be seen that the sodium fluoride adsorbent has a microscopic rough surface and a rich pore structure, which gives it good adsorption performance for hydrogen fluoride.

[0049] Example 2:

[0050] Mix 500g of sodium fluorosilicate powder with 100mL of sodium hydroxide solution, wherein the molar ratio of sodium fluorosilicate to sodium hydroxide is 5:1. Stir continuously at 80-100℃. When the viscosity of the mixture reaches 5000cp, stop heating to obtain a dough-like mixture.

[0051] The dough-like mixture was transferred to a roller granulator to granulate into spherical particles of Φ8mm, and then placed in the sun to dry for 12 hours.

[0052] The above spherical mixture particles were immersed in a 20wt% hydrofluoric acid solution for 60 minutes and then dried in a forced-air drying oven at 60°C for 12 hours to obtain etched mixture particles.

[0053] The etched mixture particles were placed in a muffle furnace and sintered at 800°C for 4 hours to obtain sodium fluoride adsorbent.

[0054] The strength and specific surface area of ​​the prepared sodium fluoride adsorbent were tested using a strength tester and a BET specific surface area analyzer. The relevant data are shown in Table 1.

[0055] 100g of sodium fluoride adsorbent was loaded into the adsorption tower. After passing the pressure test, 95% fluorine gas (hydrogen fluoride content of 5%) was continuously introduced, and the fluorine gas flow rate was controlled at 0.5m / s. The purity of fluorine gas and the hydrogen fluoride content at the outlet of the adsorption tower were tested. The test results are shown in Table 2.

[0056] Comparative Example 1:

[0057] 500g of sodium fluorosilicate powder was mixed evenly with 20mL of water and then transferred to a roller granulator to granulate into spherical particles with a diameter of 8mm. These particles were then dried in the sun for 12 hours. Finally, they were placed in a muffle furnace and sintered at 800℃ for 4 hours to obtain sodium fluoride adsorbent.

[0058] The strength and specific surface area of ​​the prepared sodium fluoride adsorbent were tested using a strength tester and a BET specific surface area analyzer. The relevant data are shown in Table 1.

[0059] 100g of sodium fluoride adsorbent was loaded into the adsorption tower. After passing the pressure test, 95% fluorine gas (hydrogen fluoride content of 5%) was continuously introduced, and the fluorine gas flow rate was controlled at 0.5m / s. The purity of fluorine gas and the hydrogen fluoride content at the outlet of the adsorption tower were tested. The test results are shown in Table 2.

[0060] Comparative Example 2:

[0061] 500g of sodium fluoride powder was mixed evenly with 20mL of water and then transferred to a roller granulator to granulate into spherical particles with a diameter of 8mm. These particles were then dried in the sun for 12 hours. Finally, they were placed in a muffle furnace and sintered at 800℃ for 4 hours to obtain sodium fluoride adsorbent.

[0062] The strength and specific surface area of ​​the prepared sodium fluoride adsorbent were tested using a strength tester and a BET specific surface area analyzer. The relevant data are shown in Table 1.

[0063] 100g of sodium fluoride adsorbent was loaded into the adsorption tower. After passing the pressure test, 95% fluorine gas (hydrogen fluoride content of 5%) was continuously introduced, and the fluorine gas flow rate was controlled at 0.5m / s. The purity of fluorine gas and the hydrogen fluoride content at the outlet of the adsorption tower were tested. The test results are shown in Table 2.

[0064] Comparative Example 3:

[0065] 500g of acidic sodium fluoride powder was mixed evenly with 20mL of water and then transferred to a roller granulator to granulate into spherical particles with a diameter of 8mm. These particles were then dried in the sun for 12 hours. Finally, they were placed in a muffle furnace and sintered at 800℃ for 4 hours to obtain sodium fluoride adsorbent.

[0066] The strength and specific surface area of ​​the prepared sodium fluoride adsorbent were tested using a strength tester and a BET specific surface area analyzer. The relevant data are shown in Table 1.

[0067] 100g of sodium fluoride adsorbent was loaded into the adsorption tower. After passing the pressure test, 95% fluorine gas (hydrogen fluoride content of 5%) was continuously introduced, and the fluorine gas flow rate was controlled at 0.5m / s. The purity of fluorine gas and the hydrogen fluoride content at the outlet of the adsorption tower were tested. The test results are shown in Table 2.

[0068] Comparative Example 4:

[0069] Mix 500g of acidic sodium fluoride powder with 20g of sodium carboxymethyl cellulose, add about 100mL of water, and stir continuously at 80-100℃. When the viscosity of the mixture reaches 5000cp, stop heating to obtain a dough-like mixture.

[0070] The mixture was then transferred to a roller granulator to granulate into spherical particles of Φ8mm, and then sun-dried for 12 hours. It was then placed in a muffle furnace and sintered at 800℃ for 4 hours to obtain sodium fluoride adsorbent.

[0071] The strength and specific surface area of ​​the prepared sodium fluoride adsorbent were tested using a strength tester and a BET specific surface area analyzer. The relevant data are shown in Table 1.

[0072] 100g of sodium fluoride adsorbent was loaded into the adsorption tower. After passing the pressure test, 95% fluorine gas (hydrogen fluoride content of 5%) was continuously introduced, and the fluorine gas flow rate was controlled at 0.5m / s. The purity of fluorine gas and the hydrogen fluoride content at the outlet of the adsorption tower were tested. The test results are shown in Table 2.

[0073] Table 1. Test data of adsorbent strength, specific surface area and porosity

[0074]

[0075] Table 2. Test data on fluorine purity and hydrogen fluoride content at the adsorption tower outlet.

[0076] sample Fluorine purity (%) Hydrogen fluoride content (%) Example 2 99.9 0.1 Comparative Example 1 99.2 0.8 Comparative Example 2 98.5 1.5 Comparative Example 3 99.0 1.0 Comparative Example 4 99.3 0.7

[0077] The raw materials for Comparative Example 1 include sodium fluorosilicate, the raw materials for Comparative Example 2 include sodium fluoride, and the raw materials for Comparative Example 3 include acidic sodium fluoride and sodium carboxymethyl cellulose as an organic binder. As can be seen from the data in Tables 1 and 2, the fluoride salt adsorbent prepared by the preparation method provided by the present invention has higher structural strength, specific surface area and porosity than the comparative examples, and the purity of fluorine gas is higher, and the hydrogen fluoride content detected at the outlet of the adsorption tower is lower.

[0078] 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 foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a fluoride salt adsorbent for fluorine gas purification, characterized in that, Includes the following steps: Step A: Mixing, mix fluorosilicate powder with alkaline solution to obtain a pre-mixed mixture; Step B: Concentration. The pre-mixed mixture is continuously stirred at 80-100°C to concentrate the mixture and remove water. When the viscosity of the mixture increases to 4000-8000 cP, the concentration is stopped to obtain a dough-like mixture. Step C: Granulation, using a molding process, to form the dough-like mixture into spherical, cylindrical, or olive-shaped granules; Step D: Etching. The mixture particles are immersed in hydrofluoric acid solution for 40-60 minutes, the hydrofluoric acid concentration is 10-20 wt.%, and dried at 60-70°C for 12 hours to obtain etched mixture particles. Step F: Calcination, the etched mixture particles are calcined at 600-800°C for 4-6 hours to prepare the fluoride salt adsorbent.

2. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The fluorosilicate is one or a mixture of sodium fluorosilicate, potassium fluorosilicate, and lithium fluorosilicate.

3. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The alkali in the alkaline solution is one or a mixture of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

4. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The ratio of the mass of fluorosilicate powder to the volume of alkali solution added is (1-6) g: 1 mL.

5. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The ratio of the mass of fluorosilicate powder to the volume of alkali solution added is (4-6) g: 1 mL.

6. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The molar ratio of fluorosilicate powder to alkali is (1-15):

1.

7. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The molar ratio of fluorosilicate powder to alkali is (5-10):

1.

8. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, The molding process in step C is compression molding, extrusion granulation, or shot blasting.

9. The method for preparing the fluoride salt adsorbent for fluorine purification according to claim 1, characterized in that, In step C, the dough-like mixture is granulated and then dried for 10 hours.

10. The application of the method for preparing a fluoride salt adsorbent for fluorine purification as described in any one of claims 1-9 in the preparation of fluoride salt adsorbents.

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