Method for utilizing byproduct fluorine-containing waste in anhydrous hydrogen fluoride production

Abstract

The invention belongs to the field of comprehensive utilization of by-product fluorine-containing waste in the process of producing anhydrous hydrogen fluoride through an IMC method, and particularly relates to a utilization method of by-product fluorine-containing waste in anhydrous hydrogen fluoride production. The utilization method comprises the following steps: (1) mixing the by-product fluorine-containing waste and a hydrofluoric acid solution to react, so that NaF in the by-product fluorine-containing waste is converted into NaHF2, and carrying out solid-liquid separation to obtain a solid and NaHF2-containing filtrate; and (2) stirring the filtrate, single cryolite and sodium hydroxide to react to prepare a cryolite or subcryolite product. According to the method, a hydrofluoric acid solution is used for reaction, then solid and filtrate are obtained through solid separation, the filtrate reacts with sodium hydroxide and single cryolite at a high temperature, a high-quality cryolite or subcryolite product is obtained by combining reaction proportion regulation and control, and finally, small-particle sodium fluoride and small-particle sodium hydrogenfluoride in the byproduct fluorine-containing waste are recycled.

Description

Technical Field

[0001] The invention belongs to the field of comprehensive utilization of by-product fluorine-containing waste materials in the process of producing anhydrous hydrogen fluoride by IMC method, and specifically relates to a method for utilizing by-product fluorine-containing waste materials in the production of anhydrous hydrogen fluoride. Background Art

[0002] As a basic fluorine chemical product, HF is mainly used in the production of refrigerants, fluorine resins, fluoride salts, fluorine rubbers, fluorine-containing intermediates and fine chemicals, and has a broad market prospect. The traditional fluorite method (CaF2+H2SO4=CaSO4+2HF) to produce HF is limited by the limited reserves of fluorite resources and cannot meet the continuous production needs of hydrogen fluoride raw materials.

[0003] Low-grade fluorosilicic acid (H2SiF6) is a byproduct of phosphate fertilizer products with large reserves at home and abroad. It can be used to produce anhydrous hydrogen fluoride industrial raw materials through the IMC method. The reaction process of the IMC method is shown in (1) to (4), where (1) to (3) all react in solution, and (4) is calcined at 150℃ to 650℃. The Chinese invention patent with the authorization announcement date of March 26, 2014 and the authorization announcement number of CN102795601B describes the working parameters and reaction conditions of these reactions.

[0004] H2SiF6+6NH3+2H2O=SiO2+6NH4F (1)

[0005] 2NH4F=NH4HF2+NH3 (2)

[0006] NH4HF2+NaF=NaHF2+NH4F (3)

[0007] NaHF2=NaF+HF (4)

[0008] From the perspective of the entire reaction system, if you want to obtain a high-yield anhydrous hydrogen fluoride product in reaction (4) by the IMC method, it is key to increase the yield and purity of NaHF2 in reaction (3). The higher the yield obtained after the reaction and the higher the proportion of NaHF2 in the yield, the higher the content of NaHF2. However, in actual production, small particles of sodium fluoride will not react completely, causing them to circulate in the system, thereby affecting the reaction conversion rate. At the same time, due to the presence of a large amount of fluoride ions in the system and the strong acidity of the system, it is bound to cause corrosion to the entire system equipment and pipes, forming various metal fluoride salts (such as sodium fluoroferrate, ammonium fluoroferrate and other complex salts). These metal fluoride salts formed by corrosion have small particles and high density, and circulate in the system with the unreacted small particles of sodium fluoride, which will seriously affect the normal occurrence of reaction (3), thereby affecting the yield of hydrogen fluoride.

[0009] The above-mentioned solid particles such as small particle sodium fluoride and metal fluorides exist in the form of slurry above the sodium bifluoride crystals in reaction (3). After separating the sodium bifluoride crystals, black slag (i.e., by-product fluorine-containing waste) will be obtained after separation by a plate and frame filter press or a horizontal scroll centrifuge. After analysis, in the black slag, small particle sodium fluoride accounts for 20 - 30%, small particle sodium bifluoride accounts for 5 - 10%, and metal fluorides account for 60 - 70%. Currently, most enterprises treat the above-mentioned black slag as solid waste, without realizing the recycling of valuable resources such as fluorine and sodium in it. Summary of the Invention

[0010] The object of the present invention is to provide a method for utilizing by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride, to solve the problem that the prior art does not recycle the by-product fluorine-containing waste in the process of producing anhydrous hydrogen fluoride by the IMC method, resulting in waste of resources such as fluorine and sodium.

[0011] In order to achieve the above object, the technical solution adopted by the present invention is:

[0012] A method for utilizing by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride, comprising the following steps:

[0013] (1) Mix and react the by-product fluorine-containing waste with a hydrofluoric acid solution to convert NaF in the by-product fluorine-containing waste into NaHF₂, and perform solid-liquid separation to obtain a solid and a filtrate containing NaHF₂;

[0014] (2) Stir and react the filtrate, cryolite mono and sodium hydroxide to obtain cryolite or meta-cryolite products.

[0015] The present invention belongs to a pioneering invention. It uses a hydrofluoric acid solution for reaction, then separates the solid to obtain a solid and a filtrate. The filtrate reacts with sodium hydroxide and cryolite mono at high temperature, and through adjusting the reaction ratio, high-quality cryolite or meta-cryolite products are obtained, ultimately realizing the recycling of small particle sodium fluoride and small particle sodium bifluoride in the by-product fluorine-containing waste.

[0016] This method can not only turn waste into treasure and maximize resource utilization, but also obtain high-quality meta-cryolite and cryolite products with different molecular ratios. These products can meet the needs of different manufacturers in the market, creating certain economic benefits for enterprises.

[0017] Preferably, the cryolite mono is added in an amount of 1.1 - 1.6 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and the addition amount of sodium hydroxide is determined according to the molecular ratio of the cryolite to be synthesized. Further preferably, the molecular ratio of the cryolite is 2.2 - 2.8.

[0018] Preferably, the cryolite monohydrate is added in an amount of 3.3 to 3.5 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and the sodium hydroxide is added in an amount of 1.1 to 1.3 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and then cryolite-like substance Na5Al3F is obtained through reaction. 14 .

[0019] Preferably, the sodium hydroxide is added to the reaction in the form of a sodium hydroxide solution with a mass fraction of 30-40%, the final pH of the reaction system is 3-7 when preparing cryolite, and the final pH of the reaction system is 7-8 when preparing cryolite-like substance.

[0020] Preferably, the temperature of the stirring reaction in step (2) is 60-95°C; the time is 2-6 h.

[0021] Preferably, the mass fraction of the hydrofluoric acid solution in step (1) is 2-4%. Further preferably, the hydrofluoric acid solution in step (1) is prepared by diluting the waste hydrofluoric acid generated during the production of hydrogen fluoride. In this case, comprehensive recycling of the solid waste and liquid waste by-produced during the production of anhydrous hydrogen fluoride by the IMC method can be realized, further improving the environmental protection and economy of the process for producing anhydrous hydrogen fluoride by the IMC method.

[0022] Preferably, the temperature of the mixing reaction in step (1) is 70-95°C, and the time is 2-6 h; the solid-liquid separation includes hot filtration after the mixing reaction.

[0023] Preferably, the by-product fluorine-containing waste in step (1) contains sodium fluoride and sodium hydrogen fluoride, wherein the mass content of sodium fluoride is 20-30%, and the mass content of sodium hydrogen fluoride is 5-10%. Specific Embodiments

[0024] The technical concept of the present invention is to convert sodium fluoride and sodium hydrogen fluoride in the by-product fluorine-containing waste of hydrogen fluoride into high-quality cryolite or cryolite-like substance products, so as to realize the recycling of fluorine resources in solid waste. Further, the design of the process route of this method also utilizes a hydrofluoric acid solution, which can be the waste hydrofluoric acid by-produced during the production of hydrogen fluoride, so as to realize the recycling of liquid waste in the same production process.

[0025] The above design of the comprehensive utilization plan is of great significance for reducing the waste generated during the production of hydrogen fluoride and improving the resource utilization rate.

[0026] Now, the comprehensive utilization method of the present invention for the by-product waste in the production of anhydrous hydrogen fluoride is described as follows:

[0027] S1. The slag material (black slag) containing sodium fluoride and sodium hydrogen fluoride as by-products is mixed with dilute hydrofluoric acid at high temperature, and then solid A and filtrate A are obtained after solid-liquid separation; solid A is treated as chemical industrial waste, and filtrate A enters the next step for treatment.

[0028] The main reaction equations involved in this step are as follows:

[0029] NaF + HF = NaHF2 (1-1)

[0030] The reaction temperature is preferably 70-95 °C, and the time is 2-6 h. Reacting at this temperature can not only accelerate the reaction but also make NaHF2 have higher solubility, facilitating the separation from solid A. The separation is carried out in a hot solid-liquid separation form, taking advantage of the high solubility of NaHF2, and the heat-carrying filtrate can reduce the energy consumption of the next-step reaction. The amount of dilute hydrofluoric acid used should be appropriate to fully convert the NaF in the black residue. For example, the molar ratio of HF to NaF can be controlled at 1.0-1.2:1.

[0031] S2. Heat the filtrate A to 60-95 °C, add cryolite monohydrate and 30-40% sodium hydroxide solution, and continuously stir and react for 2-6 h.

[0032] The reaction equations involved in this step are as follows:

[0033] NaAlF4 + NaHF2 + NaOH = Na3AlF6 + H2O (1-2)

[0034] 3NaAlF4 + NaHF2+ NaOH = Na5Al3F 14 + H2O (1-3)

[0035] In this step, by adjusting the molar ratio of raw materials, cryolite or meta-cryolite (Na5Al3F 14 ) products can be obtained.

[0036] The feeding time of cryolite monohydrate can be controlled at 10-30 min to avoid overflow caused by too fast feeding. The feeding time of sodium hydroxide can be 10-30 min.

[0037] Typical ways to adjust the molar ratio of raw materials are as follows:

[0038] When the molar number of sodium hydroxide fed in step S2 is in a ratio of 1.1:1 to the molar number of sodium fluoride in the black residue in step S1, and the molar number of cryolite monohydrate fed is in a ratio of 3.3:1 to the molar number of sodium fluoride in the black residue in step S1, high-quality meta-cryolite products can be obtained.

[0039] When the molar number of sodium hydroxide fed in step S2 is in a ratio of 1:4 to the molar number of sodium fluoride in the black residue in step S1, and the molar number of cryolite monohydrate fed is in a ratio of 1.1:1 to the molar number of sodium fluoride in the black residue in step S1, high-quality cryolite products with a minimum molecular ratio of 2.2 can be obtained.

[0040] When the molar ratio of the sodium hydroxide added in step S2 to the molar ratio of the sodium fluoride in the black slag in step S1 is 1:1.05-1.1, and the molar ratio of the cryolite added to the molar ratio of the sodium fluoride in the black slag in step S1 is 1.1:1, a high-quality cryolite product with a maximum molecular ratio of 2.8 can be obtained.

[0041] Furthermore, the molar number of sodium hydroxide added can be adjusted according to actual production, so that the molecular ratio of sodium to aluminum in the cryolite product obtained by the reaction is between 2.2-2.8:1, for example, the molecular ratio is 2.5.

[0042] S3. The slurry obtained in step S2 is subjected to solid-liquid separation while hot, and the filter cake is washed with pure water and then dried to obtain cryolite or sub-cryosite product; the mother liquor (still containing elements such as fluorine and Na) is used to produce other fluoride salt products or discharged after neutralization with lime, and the washing water is reused in S1 to dilute the hydrogen fluoride solution.

[0043] The implementation process of the present invention is described in detail below in conjunction with specific examples. In the following examples, unless otherwise specified, the substances involved are all commercially available conventional substances. "%" is mass percentage unless otherwise specified.

[0044] 1. Specific embodiment of the method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride of the present invention

[0045] Example 1

[0046] The method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride in this embodiment specifically comprises the following steps:

[0047] 1) Prepare 600g of 2.3% dilute hydrofluoric acid solution, then slowly add 100g of black slag containing 29% sodium fluoride and 5% sodium bifluoride to the solution, heat and stir to react for 3h, the reaction temperature is 95°C, the stirring speed is 200rpm, and after the reaction is completed, filter while hot to obtain a filter cake and a filtrate.

[0048] 2) After the filtrate is heated to 95° C., 95.6 g of cryolite powder (1.1 times the molar amount of sodium fluoride in the by-product fluorine-containing waste) is slowly added thereto, and the feeding time is controlled to be 10 min to avoid overflow caused by too fast feeding. The reaction is stirred for 30 min. After the solution is dissolved and no bubbles are generated (the raw material cryolite in this step is derived from the by-product obtained when producing silicone, which contains some aluminum element, which will react with hydrogen fluoride and sodium bifluoride in the system to produce hydrogen. The bubbles are hydrogen, and the relevant chemical reaction equation is 2NaHF2+4HF+2Al=2NaAlF4+3H2↑), 23 g of 30% sodium hydroxide solution is dripped into the solution. The dripping time is 10 min. The reaction is stirred for 2 h. After the reaction, the pH value of the system is 3.

[0049] 3) Subsequently, solid-liquid separation is carried out. The filter cake is washed with pure water, and the solid obtained by filtration can be dried to obtain 140.8 g of pure cryolite (molecular ratio is about 2.2). The mother liquor is used for producing other fluoride products or discharged after being neutralized with lime, and the washing water is reused to dilute the hydrogen fluoride solution in step 1).

[0050] Example 2

[0051] The utilization method of the fluorine-containing waste produced as a by-product in the production of anhydrous hydrogen fluoride in this example specifically includes the following steps:

[0052] 1) Prepare 600 g of 2.3% dilute hydrofluoric acid solution. Subsequently, slowly add 100 g of black slag containing 29% sodium fluoride and 8% sodium bifluoride to the solution, heat up and stir for reaction for 3 h. The reaction temperature is 90 °C, and the stirring speed is 200 rpm. After the reaction, filter while it is hot to obtain a filter cake and a filtrate.

[0053] 2) Then heat the filtrate to 95 °C and slowly add 95.7 g of monocrystal cryolite powder (1.1 times the molar amount of sodium fluoride in the by-product fluorine-containing waste) to it. Control the feeding time to be 15 min to avoid overflow caused by too fast feeding. Stir and react for 30 min. After the solution becomes clear, dropwise add 88 g of 30% sodium hydroxide solution to the solution, with the dropping time being 30 min, and continuously stir and react for 2 h. After the reaction, the pH value of the system is 6 - 7.

[0054] 3) Subsequently, solid-liquid separation is carried out. The filter cake is washed with pure water, and the solid obtained by filtration can be dried to obtain 112.3 g of pure cryolite (molecular ratio is 2.8). The mother liquor is used for producing other fluoride products or discharged after being neutralized with lime, and the washing water is reused to dilute the hydrogen fluoride solution in step 1).

[0055] Example 3

[0056] The utilization method of the fluorine-containing waste produced as a by-product in the production of anhydrous hydrogen fluoride in this example specifically includes the following steps:

[0057] 1) Prepare 600 g of 2.3% dilute hydrofluoric acid solution. Subsequently, slowly add 100 g of black slag containing 30% sodium fluoride and 8% sodium bifluoride to the solution, heat up and stir for reaction for 6 h. The reaction temperature is 95 °C, and the stirring speed is 250 rpm. After the reaction, filter while it is hot to obtain a filter cake and a filtrate.

[0058] 2) Then, heat the filtrate to 95°C and slowly add 95.7 g of single cryolite powder (1.1 times the molar amount of sodium fluoride in the by-product fluorine-containing waste) thereto, control the feeding time to 15 min to avoid overflow caused by too fast feeding, stir and react for 30 min. After the solution becomes clear, add 53.3 g of 30% sodium hydroxide solution dropwise to the solution, with the dropping time being 20 min, continuously stir and react for 2 h, and the pH value of the system is 5 - 6 after the reaction ends.

[0059] 3) Subsequently, perform solid-liquid separation, wash the filter cake with pure water, and the solid obtained by filtration can be dried to obtain 108.3 g of pure cryolite (molecular ratio is 2.5). The mother liquor is used for producing other fluorinated salt products or discharged after being neutralized with lime, and the washing water is reused in step 1) to dilute the hydrogen fluoride solution.

[0060] Example 4

[0061] The method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride in this example specifically includes the following steps:

[0062] 1) Prepare 500 g of 4% dilute hydrofluoric acid solution, and then slowly add 80 g of black slag containing 20% sodium fluoride and 8% sodium bifluoride thereto, heat up and stir and react for 6 h, with the reaction temperature being 70°C and the stirring speed being 200 rpm. After the reaction ends, filter while it is hot to obtain a filter cake and a filtrate.

[0063] 2) Then, keep the filtrate at 60°C and slowly add 76.21 g of single cryolite powder (1.6 times the molar amount of sodium fluoride in the by-product fluorine-containing waste) thereto, control the feeding time to 30 min to avoid overflow caused by too fast feeding, stir and react for 30 min. After the solution becomes clear, add 40.3 g of 30% sodium hydroxide solution dropwise to the solution, with the dropping time being 15 min, continuously stir and react for 6 h, and the pH value of the system is 3 - 4 after the reaction ends.

[0064] 3) Subsequently, perform solid-liquid separation, wash the filter cake with pure water, and the solid obtained by filtration can be dried to obtain 115 g of pure cryolite (molecular ratio is 2.5). The mother liquor is used for producing other fluorinated salt products or discharged after being neutralized with lime, and the washing water is reused in step 1) to dilute the hydrogen fluoride solution.

[0065] Example 5

[0066] The method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride in this example specifically includes the following steps:

[0067] 1) Prepare 600 g of 2% dilute hydrofluoric acid solution. Then, slowly add 100 g of black slag containing 25% sodium fluoride and 6% sodium bifluoride to the solution. Heat up and stir for reaction for 2 h. The reaction temperature is 90 °C, and the stirring speed is 200 rpm. After the reaction, filter while it is hot to obtain a filter cake and a filtrate.

[0068] 2) Then, heat the filtrate to 90 °C and slowly add 249.3 g of synthetic cryolite powder (3.3 times the molar amount of sodium fluoride in the by-product fluorine-containing waste). Control the feeding time to 30 min to avoid overflow caused by too fast feeding. Stir and react for 30 min. After the solution becomes clear, dropwise add 66 g of 40% sodium hydroxide solution (sodium hydroxide is 1.1 times the molar amount of sodium fluoride in the by-product fluorine-containing waste) to the solution. The dropping time is 20 min, and continue to stir and react for 2 h. After the reaction, the pH value of the system is 7 - 8.

[0069] 3) Then, separate the solid and liquid. Wash the filter cake with pure water. The solid obtained by filtration can be dried to obtain 316.5 g of pure cryolite. The mother liquor is used to produce other fluorinated salt products or discharged after being neutralized with lime. The washing water is reused in step 1) to dilute the hydrofluoric acid solution.

[0070] II. Experimental Examples

[0071] This experimental example illustrates the quality inspection results of the cryolite or synthetic cryolite prepared in each example. Among them, the inspection of cryolite is carried out with reference to the provisions of "GB / T 4291 - 2017 Cryolite", and the test results of synthetic cryolite are given with reference to this standard, as shown in Table 1 specifically.

[0072] Table 1 Quality inspection results of the cryolite or synthetic cryolite products obtained in Examples 1 - 5

[0073]

[0074] From the results in Table 1, it can be seen that the quality of the cryolite or synthetic cryolite products prepared in this example is relatively high, and the molecular ratio is between 2.2 and 2.8, which can meet the requirements of cryolite manufacturers with high or low molecular ratios in the market. It not only realizes the utilization of waste materials from hydrogen fluoride production enterprises but also can create good economic benefits for the enterprises.

[0075] Finally, it should be noted that the above are only the preferred embodiments of the present invention and are not used to limit the present invention. Although the present invention has been described in detail with reference to the foregoing embodiments, for those skilled in the art, they can still modify the technical solutions recorded in the foregoing embodiments or perform equivalent replacements for some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for utilizing by - product fluorine - containing waste in the production of anhydrous hydrogen fluoride, characterized in that, It includes the following steps: (1) Mix and react the by-product fluorine-containing waste and hydrofluoric acid solution to convert NaF in the by-product fluorine-containing waste into NaHF2, and perform solid-liquid separation to obtain a solid and a filtrate containing NaHF2; (2) Stir and react the filtrate, synthetic cryolite and sodium hydroxide to obtain a cryolite or meta-cryolite product.

2. The method for utilizing by - product fluorine - containing waste in the production of anhydrous hydrogen fluoride according to claim 1, characterized in that, Add the synthetic cryolite in an amount of 1.1 - 1.6 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and determine the addition amount of sodium hydroxide according to the molecular ratio of the cryolite to be synthesized.

3. The method for utilizing the fluorine-containing waste by-product in the production of anhydrous hydrogen fluoride according to claim 2, characterized in that, The molecular ratio of the cryolite is 2.2 - 2.

8.

4. The method for utilizing the fluorine-containing waste by-produced in the production of anhydrous hydrogen fluoride according to claim 1, characterized in that, Add the single cryolite in an amount of 3.3 to 3.5 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and add the sodium hydroxide in an amount of 1.1 to 1.3 times the molar amount of sodium fluoride in the by-product fluorine-containing waste, and react to obtain cryolite Na5Al3F 14 .

5. The method for utilizing fluorine-containing waste by-products in the production of anhydrous hydrogen fluoride as claimed in claim 1 or 2 or 3 or 4, characterized in that, The sodium hydroxide is added to the reaction in the form of a sodium hydroxide solution with a mass fraction of 30 - 40%. The final pH of the reaction system is 3 - 7 when preparing cryolite, and the final pH of the reaction system is 7 - 8 when preparing meta-cryolite.

6. The method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride as claimed in claim 1, wherein, The temperature of the stirring reaction in step (2) is 60 - 95 °C; the time is 2 - 6 h.

7. The method for utilizing the by-product fluorine-containing waste in the production of anhydrous hydrogen fluoride according to claim 1, characterized in that, The mass fraction of the hydrofluoric acid solution in step (1) is 2 - 4%.

8. The method for utilizing the fluorine-containing waste by-product in the production of anhydrous hydrogen fluoride according to claim 7, characterized in that, The hydrofluoric acid solution in step (1) is prepared by diluting the waste hydrofluoric acid generated in the production process of hydrogen fluoride.

9. The method for utilizing fluorine-containing waste by-products in the production of anhydrous hydrogen fluoride according to claim 1 or 7, characterized in that, The temperature of the mixing reaction in step (1) is 70 - 95 °C, and the time is 2 - 6 h; the solid-liquid separation includes hot filtration after the mixing reaction.

10. The method for utilizing the fluorine-containing waste by-product in the production of anhydrous hydrogen fluoride as claimed in claim 1 or 7, characterized in that, The by-product fluorine-containing waste in step (1) contains sodium fluoride and sodium bifluoride, wherein the mass content of sodium fluoride is 20 - 30%, and the mass content of sodium bifluoride is 5 - 10%.

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