Method for removing fluorine from fluorine-containing sulfuric acid

Abstract

The invention relates to a method for removing fluorine from fluorine-containing sulfuric acid, which comprises the following steps: contacting fluorine-containing sulfuric acid with mixed gas containing a catalyst, and carrying out gas-liquid separation to obtain fluorine-free sulfuric acid. The fluorine-containing sulfuric acid is a by-product of hydrogen fluoride prepared by reaction of fluosilicic acid and concentrated sulfuric acid, the content of the sulfuric acid is 60-80 wt%, and the content of the hydrogen fluoride is 0.2-2 wt%. The catalytic removal agent is a hexafluorononmetal compound. The hexafluoro nonmetal compound is selected from sulfur hexafluoride or selenium hexafluoride. The method can be carried out under relatively mild conditions, the energy consumption is relatively low, and the fluorine content of the obtained fluorine-removed sulfuric acid is reduced to meet general industrial requirements.

Description

Technical Field

[0001] The invention belongs to the technical field of comprehensive utilization of fluorosilicic acid, and specifically relates to a method for removing fluorine from fluorine-containing sulfuric acid. Background Art

[0002] The preparation of hydrogen fluoride by the reaction of fluorosilicic acid and concentrated sulfuric acid is one of the important ways of comprehensive utilization of fluorosilicic acid resources, that is, fluorosilicic acid with a concentration of more than 40wt% reacts with concentrated sulfuric acid with a concentration of more than 98wt% to generate hydrogen fluoride and silicon tetrafluoride gas, and the two gases are separated to obtain hydrogen fluoride. The mother liquor of the reaction is stripped to separate the contained hydrogen fluoride to obtain sulfuric acid with a concentration of about 70wt%. The acid has a high yield as a by-product, and about 27 tons of 70% sulfuric acid are produced for every ton of hydrogen fluoride produced. However, because it still contains 0.2-2wt% of hydrogen fluoride, its industrial application is greatly limited, and it cannot be sold as ordinary industrial sulfuric acid, and can only be used to treat phosphate rock, which seriously limits the promotion of the hydrogen fluoride preparation method.

[0003] The existing method for treating fluorine-containing sulfuric acid mainly utilizes the difference in boiling points between hydrofluoric acid and sulfuric acid. The fluorine-containing sulfuric acid is added to a distillation tower for heating and evaporation. The evaporated gas is absorbed by pure water to obtain hydrofluoric acid, and the distillation mother liquor is fluorine-free sulfuric acid. However, this method consumes a lot of energy and has high operating costs. Chinese patent CN109795991B discloses a purification process for fluorine-containing sulfuric acid, comprising a preheating evaporation section, a mixing and removing section and a sulfuric acid concentration section; the preheating evaporation section evaporates the raw acid under vacuum conditions to increase the sulfuric acid concentration, and the concentrated sulfuric acid is sent to the mixing and removing section, and the hydrogen fluoride vapor generated during the evaporation process enters a hydrogen fluoride absorption tower; the mixing and removing section sends the sulfuric acid from the preheating evaporation section and the sulfuric acid from the sulfuric acid concentration section to a removal distillation tower to remove the hydrogen fluoride contained in the sulfuric acid by mixing, and the sulfuric acid after defluorination is sent to the sulfuric acid concentration section, and the hydrogen fluoride vapor generated during the removal process enters the hydrogen fluoride absorption tower; the sulfuric acid concentration section sends the concentrated sulfuric acid from the mixing and removing section to a sulfuric acid concentrator to increase the sulfuric acid concentration under high vacuum conditions, and a part of the obtained high-concentration sulfuric acid is continuously extracted from the system, and the other part is sent back to the mixing and removing section for mixing; its main measures are heating and vacuum, the temperature is as high as 140-160°C, and the energy consumption is still relatively high.

[0004] Therefore, it is urgent to study and develop a method for removing fluorine from fluorine-containing sulfuric acid with low energy consumption. Based on this, the present application was developed. Summary of the invention

[0005] The present invention aims to overcome the disadvantage of high energy consumption of defluorination of sulfuric acid in the above prior art and provide a method for defluorination of fluorine-containing sulfuric acid. The method can be carried out under relatively mild conditions, has low energy consumption, and the fluorine content of the defluorinated sulfuric acid obtained is reduced to meet general industrial needs.

[0006] To achieve the above object, the present invention adopts the following technical solution: A method for removing fluorine from fluorine-containing sulfuric acid comprises contacting the fluorine-containing sulfuric acid with a mixed gas containing a catalytic stripping agent, and separating the gas and liquid to obtain fluorine-free sulfuric acid.

[0007] Specifically, the fluorine-containing sulfuric acid is a byproduct of preparing hydrogen fluoride by reacting fluorosilicic acid with concentrated sulfuric acid, and has a sulfuric acid content of 60-80wt% and a hydrogen fluoride content of 0.2-2wt%.

[0008] Specifically, the catalytic stripping agent can be a hexafluoro non-metallic compound, and the molecular structure is octahedral. The hexafluoro non-metallic compound is usually selected from sulfur hexafluoride or selenium hexafluoride, etc. The molecular structures of sulfur hexafluoride and selenium hexafluoride are both octahedral, and they are gases at room temperature. The chemical properties are relatively stable, generally do not react with water or acid, and are almost insoluble in sulfuric acid. It is understandable that the periphery of the sulfur hexafluoride molecule is all fluorine atoms with high electronegativity, and when it comes into contact with hydrogen fluoride, it can form a F5S-FHF bond, which is similar to a hydrogen bond, so that sulfur hexafluoride and hydrogen fluoride are adsorbed together. When sulfur hexafluoride comes into contact with the surface of fluorine-containing sulfuric acid and flows, it can adsorb hydrogen fluoride and take it away.

[0009] Specifically, the mixed gas containing the catalytic stripping agent can be composed of the catalytic stripping agent and air or an inert gas (such as nitrogen, helium, argon, etc.). When it contacts with fluorine-containing sulfuric acid, the hydrogen fluoride in the sulfuric acid quickly and fully diffuses into the mixed gas, and finally there is almost no residual hydrogen fluoride in the sulfuric acid. If the mixed gas does not contain a catalytic stripping agent, hydrogen fluoride will also diffuse into the mixed gas when it contacts with fluorine-containing sulfuric acid, but the diffusion is very slow. Due to the adsorption of sulfuric acid to hydrogen fluoride, some hydrogen fluoride will remain. If only a catalytic stripping agent is used without mixing other gases, the defluorination effect of fluorine-containing sulfuric acid is also very good, but the amount of catalytic stripping agent is large, which increases the cost. It has been verified that when the weight percentage of the catalytic stripping agent in the mixed gas is 10-40wt%, the removal of hydrogen fluoride is good and the material cost is appropriate.

[0010] Specifically, the fluorine-containing sulfuric acid and the mixed gas containing the catalytic agent are countercurrently contacted in the gas stripping tower, and the weight flow ratio of the fluorine-containing sulfuric acid to the mixed gas containing the catalytic agent can be 100:5-20. In addition, increasing the temperature and increasing the pressure are both helpful to increase the defluorination effect. Therefore, when the fluorine-containing sulfuric acid is in contact with the mixed gas containing the catalytic agent, the temperature can be 30-100°C and the pressure can be 0-0.6MPa. It can also be further preferred that the weight flow ratio of the fluorine-containing sulfuric acid to the mixed gas containing the catalytic agent is 100:10-20, the temperature is 60-80°C, and the pressure is 0.1-0.4MPa.

[0011] Furthermore, when the mixed gas contacts the fluorine-containing sulfuric acid, the hydrogen fluoride leaves the sulfuric acid with the hydrogen fluoride, and is absorbed by the water; and the mixed gas without hydrogen fluoride can be reused, that is, can be reused for defluorination of the fluorine-containing sulfuric acid.

[0012] Compared with the prior art, the beneficial effects of the method of the present invention are as follows: The present application adopts a gas-liquid contact method, adds a catalytic agent to the gas, and efficiently and fully removes hydrogen fluoride from sulfuric acid at a relatively mild temperature and pressure to obtain sulfuric acid with a very low fluorine content (fluorine content is less than 10 mg / L), which can meet general industrial needs and is no longer limited to the treatment of phosphate rock. The entire process is simple and easy to operate, safe, reliable and low-cost. The catalytic agent used in the present application has stable chemical properties, and the defluorination process will not introduce new impurities into the sulfuric acid. The mixed gas can be recycled and reused after washing and purification. In addition, the hydrogen fluoride removed from the fluorine-containing sulfuric acid can be sold as a hydrofluoric acid product after collection, enrichment and impurity removal. The whole process does not produce wastewater or waste gas, which is green and environmentally friendly. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described in detail below in conjunction with the embodiments, but the protection scope of the present invention is not limited thereto.

[0014] In the following examples, the fluorine-containing sulfuric acid used is derived from the byproduct of the production of hydrogen fluoride from fluorosilicic acid and concentrated sulfuric acid produced by our company, with a sulfuric acid content of 71 wt % and a hydrogen fluoride content of 0.24 wt %.

[0015] Example 1 A method for defluorinating fluorine-containing sulfuric acid, specifically: preheating fluorine-containing sulfuric acid to 60°C, entering a stripping tower from an upper inlet, preheating a mixed gas of sulfur hexafluoride and air to 60°C, entering a stripping tower from a lower inlet, and the two are in countercurrent contact in the stripping tower; the mixed gas contains 30wt% sulfur hexafluoride, the temperature in the stripping tower is maintained at 60°C and the pressure is maintained at 0.1MPa, and the weight flow ratio of fluorine-containing sulfuric acid to the mixed gas is 100:15. The mixed gas discharged from the top of the stripping tower is washed with water, and the hydrogen fluoride adsorbed and carried away by the mixed gas during the washing process is absorbed by water, and the mixed gas after the hydrogen fluoride is separated is reintroduced into the stripping tower for reuse, and is reused for defluorinating fluorine-containing sulfuric acid. The defluorinated sulfuric acid is collected from the bottom of the stripping tower.

[0016] Example 2 A method for defluorinating fluorine-containing sulfuric acid, specifically: preheating fluorine-containing sulfuric acid to 80°C, entering a stripping tower from an upper inlet, preheating a mixed gas of sulfur hexafluoride and air to 80°C, entering a stripping tower from a lower inlet, and the two are in countercurrent contact in the stripping tower; the mixed gas contains 20wt% sulfur hexafluoride, the temperature in the stripping tower is maintained at 80°C and the pressure is maintained at 0.2MPa, and the weight flow ratio of fluorine-containing sulfuric acid to the mixed gas is 100:20. The mixed gas discharged from the top of the stripping tower is washed with water, and the hydrogen fluoride adsorbed and carried away by the mixed gas during the washing process is absorbed by water, and the mixed gas after the hydrogen fluoride is separated is reintroduced into the stripping tower for reuse, and is reused for defluorinating fluorine-containing sulfuric acid. The defluorinated sulfuric acid is collected from the bottom of the stripping tower.

[0017] Example 3 A method for defluorinating fluorine-containing sulfuric acid, specifically comprising: preheating fluorine-containing sulfuric acid to 32°C, entering a stripping tower from an upper inlet, preheating a mixed gas of sulfur hexafluoride and air to 32°C, entering a stripping tower from a lower inlet, and countercurrently contacting the two in the stripping tower; the mixed gas contains 10wt% sulfur hexafluoride, the temperature in the stripping tower is maintained at 32°C and the pressure is maintained at 0.6MPa, the weight flow ratio of fluorine-containing sulfuric acid to the mixed gas is 100:10, the mixed gas discharged from the top of the stripping tower is washed with water, the hydrogen fluoride adsorbed and carried away by the mixed gas during the washing process is absorbed by the water, the mixed gas after the hydrogen fluoride is separated is reintroduced into the stripping tower for reuse, and reused for defluorinating fluorine-containing sulfuric acid. The defluorinated sulfuric acid is collected from the bottom of the stripping tower.

[0018] Example 4 A method for defluorinating fluorine-containing sulfuric acid, specifically comprising: preheating fluorine-containing sulfuric acid to 96°C, entering a gas stripping tower from an upper inlet, preheating a mixed gas of selenium hexafluoride and nitrogen to 96°C, entering a gas stripping tower from a lower inlet, and countercurrently contacting the two in the gas stripping tower; the mixed gas contains 13wt% selenium hexafluoride, the temperature in the gas stripping tower is maintained at 96°C and the pressure is maintained at 0.3MPa, the weight flow ratio of fluorine-containing sulfuric acid to the mixed gas is 100:8, the mixed gas discharged from the top of the gas stripping tower is washed with water, the hydrogen fluoride adsorbed and carried away by the mixed gas during the washing process is absorbed by the water, the mixed gas after the hydrogen fluoride is separated is reintroduced into the gas stripping tower for reuse, and is reused for defluorinating fluorine-containing sulfuric acid. The defluorinated sulfuric acid is collected from the bottom of the gas stripping tower.

[0019] Comparative Example A method for defluorinating fluorine-containing sulfuric acid, specifically: preheating fluorine-containing sulfuric acid to 60°C, entering a stripping tower from an upper inlet, preheating air to 60°C, entering a stripping tower from a lower inlet, and the two are in countercurrent contact in the stripping tower; the air does not contain a defluoridating agent, the temperature in the stripping tower is maintained at 60°C, the pressure is maintained at 0.1MPa, and the weight flow ratio of fluorine-containing sulfuric acid to air is 100:15. The gas discharged from the top of the stripping tower is washed with water and then reintroduced into the stripping tower for reuse, and is reused for defluorinating fluorine-containing sulfuric acid. The defluorinated sulfuric acid is collected from the bottom of the stripping tower.

[0020] Test Case The defluorinated sulfuric acid products prepared by the above examples and comparative examples were sampled and the hydrogen fluoride content was tested according to the standard GB / T7484-1987. The results are listed in the following table: (unit: mg / L) It can be seen from the data in the table that the fluorine content in the defluorinated sulfuric acid prepared in Examples 1-4 is very low, all less than 10 mg / L, which can meet the general industrial sulfuric acid demand, while the fluorine content in the defluorinated sulfuric acid prepared in the comparative example is still very high, up to 860 mg / L, which cannot meet the general industrial sulfuric acid demand.

[0021] In summary, the present application adopts a gas-liquid contact method, adds a catalyst to the gas, and efficiently and fully removes hydrogen fluoride from sulfuric acid at a relatively mild temperature and pressure to obtain sulfuric acid with a fluorine content of less than 10 mg / L, which can meet the general industrial sulfuric acid needs. The entire process is simple and easy to operate, safe, reliable and low-cost, and has great value for promotion and application.

Claims

1. A method for defluorination of fluorine-containing sulfuric acid, characterized in that: The fluorine-containing sulfuric acid is brought into contact with a mixed gas containing a catalytic agent, and the gas and liquid are separated to obtain fluorine-free sulfuric acid.

2. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: The fluorine-containing sulfuric acid is a byproduct of the reaction of fluorosilicic acid and concentrated sulfuric acid to prepare hydrogen fluoride, with a sulfuric acid content of 60-80wt% and a hydrogen fluoride content of 0.2-2wt%.

3. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: The stripping agent is a hexafluoro non-metal compound.

4. The method for defluorination of fluorine-containing sulfuric acid according to claim 3, characterized in that: The hexafluoro non-metal compound is selected from sulfur hexafluoride or selenium hexafluoride.

5. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: The mixed gas containing the stripping agent consists of the stripping agent and air or an inert gas.

6. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: The weight percentage of the stripping agent in the mixed gas is 10-40wt%.

7. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: The fluorine-containing sulfuric acid and the mixed gas containing the catalytic stripping agent are countercurrently contacted in a gas stripping tower, and the weight flow ratio of the fluorine-containing sulfuric acid to the mixed gas containing the catalytic stripping agent is 100:5-20.

8. The method for defluorination of fluorine-containing sulfuric acid according to claim 7, characterized in that: When the fluorine-containing sulfuric acid contacts the mixed gas containing the catalytic agent, the temperature is 30-100°C and the pressure is 0-0.6MPa.

9. The method for defluorination of fluorine-containing sulfuric acid according to claim 8, characterized in that: During countercurrent contact, the weight flow ratio of the fluorine-containing sulfuric acid to the mixed gas containing the catalytic stripping agent is 100:10-20, the temperature is 60-80°C, and the pressure is 0.1-0.4MPa.

10. The method for defluorination of fluorine-containing sulfuric acid according to claim 1, characterized in that: After the mixed gas contacts the fluorine-containing sulfuric acid, it carries hydrogen fluoride away from the sulfuric acid and then passes into water where the hydrogen fluoride is absorbed; the mixed gas that does not contain hydrogen fluoride is reused and then returned to the fluorine-containing sulfuric acid for defluorination.

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