Process for continuously recovering anhydrous HF from HF-NaF waste liquid

Abstract

The invention discloses a process for continuously recovering anhydrous HF from HF-NaF waste liquid, the HF-NaF waste liquid is an aqueous solution containing HF and NaF, the anhydrous HF is a liquid phase solution with HF content not less than 95% and water content not more than 5%, the HF-NaF waste liquid and concentrated sulfuric acid continuously enter a reaction evaporation kettle for reaction evaporation, the reaction evaporation comprises the following steps: sodium fluoride and sulfuric acid react in a reaction evaporation kettle to generate hydrogen fluoride, and the hydrogen fluoride in the reaction evaporation kettle is converted into gas-phase hydrogen fluoride to be evaporated from the top in the reaction evaporation kettle; feeding gas-phase hydrogen fluoride evaporated from the reaction evaporation kettle into a rectifying tower to remove water, and extracting anhydrous HF from the top of the rectifying tower; according to the present invention, the treatment capacity is improved during the continuous operation, the HF yield of the HF is significantly improved, the recovery process and the adopted recovery device are simple and stable, the recovery amount can be improved without the arrangement of a plurality of recovery kettles, and the method is suitable for the continuous batch treatment production application.

Description

Technical Field

[0001] The invention belongs to the field of fluorobenzene preparation, and in particular relates to a process for continuously recovering anhydrous HF from HF-NaF waste liquid. Background Art

[0002] my country's fluorobenzene industry has developed rapidly and has gradually become the main supplier of the global fluorobenzene industry. It has strong market competitiveness in the global fluorobenzene industry. In order to ensure the yield, the entire production process of the fluorobenzene industry will add excessive hydrogen fluoride. After the reaction is completed, waste liquid containing hydrofluoric acid HF, sodium fluoride NaF and water (collectively referred to as "HF-NaF waste liquid" in this application) will be separated, which is highly corrosive and toxic. It is difficult for the fluorobenzene industry to treat this waste liquid and the treatment cost is high. Because the waste liquid contains fluoride ions, hydrogen ions, sodium ions, tar, etc., it will cause serious corrosion to the equipment, and the average service life of the equipment will be significantly shortened (even to 30 days). In addition, the waste liquid will cause serious pollution to the environment, destroy the ecological balance, and affect biodiversity. The fluoride ions therein will also pose a great threat to human health. Hydrofluoric acid is highly volatile and produces a large amount of white hydrogen fluoride smoke when it comes into contact with the air. Long-term contact may cause organ damage, cancer and other serious diseases. Therefore, the disposal of waste liquid is very urgent.

[0003] The commonly used methods for treating hydrofluoric acid waste liquid include concentrated sulfuric acid method, that is, adding a large amount of concentrated sulfuric acid to make the water in the hydrofluoric acid adsorbed by the concentrated sulfuric acid, and evaporating the hydrogen fluoride therein by heating at high temperature; the HF recovery method is an intermittent operation method, and the mother liquor and concentrated sulfuric acid are directly added to the recovery kettle in a certain proportion for mixing. Since the HF cannot be mixed evenly in time, the HF yield of HF is low, and multiple recovery kettles need to be set up, which occupies a large area, requires frequent personnel operation, and has a large workload, which increases the safety risk.

[0004] Therefore, the applicant hopes to seek technical solutions to solve the above technical problems. Summary of the invention

[0005] In view of this, the object of the present invention is to provide a process for continuously recovering anhydrous HF from HF-NaF waste liquid, which significantly improves the HF yield of HF while increasing the processing volume in continuous operation. The recovery process of the present invention and the recovery device used therein are simple and stable, and there is no need to increase the recovery volume by setting up multiple recovery kettles, and the process is suitable for continuous batch processing production applications.

[0006] The technical solution adopted by the present invention is as follows: A process for continuously recovering anhydrous HF from HF-NaF waste liquid, wherein the HF-NaF waste liquid is an aqueous solution containing HF and NaF, and the anhydrous HF refers to a liquid phase solution with an HF content of not less than 95% and a water content of not more than 5%. The HF-NaF waste liquid and concentrated sulfuric acid are continuously introduced into a reaction evaporator for reaction evaporation, wherein the reaction evaporation comprises: sodium fluoride and sulfuric acid react in the reaction evaporator to generate hydrogen fluoride, the hydrogen fluoride in the reaction evaporator is converted into gaseous hydrogen fluoride and evaporated from the top of the reaction evaporator; then the gaseous hydrogen fluoride evaporated from the reaction evaporator is sent into a distillation tower to remove water, and anhydrous HF is extracted from the top of the distillation tower.

[0007] Preferably, a condenser is provided at the gas phase output end of the reaction evaporator, and the condensed liquid phase treated by the condenser is returned to its corresponding reaction evaporator.

[0008] Preferably, the reaction evaporator comprises at least a primary reaction evaporator and a secondary reaction evaporator, wherein the HF-NaF waste liquid and concentrated sulfuric acid are continuously introduced into the primary reaction evaporator for the reaction evaporation, and the bottom liquid phase of the primary reaction evaporator is sent into the secondary reaction evaporator for the reaction evaporation; and the operating temperature in the secondary reaction evaporator is higher than the operating temperature in the primary reaction evaporator.

[0009] Preferably, the operating temperature in the first-stage reaction evaporator is 60°C-80°C, and the operating temperature in the second-stage reaction evaporator is 70°C-110°C.

[0010] Preferably, the bottom liquid phase of the reaction evaporator at the last stage is removed from the interface; one branch of the bottom liquid phase of the distillation tower is refluxed into the tower kettle of the distillation tower after condensation treatment, and the other branch is removed from the interface or returned to the reaction evaporator.

[0011] Preferably, the reaction evaporator comprises a three-stage reaction evaporator and a four-stage reaction evaporator; wherein, the bottom liquid phase of the two-stage reaction evaporator is sent to the three-stage reaction evaporator for the reaction evaporation, and the bottom liquid phase of the three-stage reaction evaporator is sent to the four-stage reaction evaporator for the reaction evaporation; the operating temperature in the three-stage reaction evaporator is higher than the operating temperature in the two-stage reaction evaporator, and lower than the operating temperature in the four-stage reaction evaporator.

[0012] Preferably, the operating temperature in the kettle of the three-stage reaction evaporator is 110°C-130°C; the operating temperature in the kettle of the four-stage reaction evaporator is 120°C-130°C.

[0013] Preferably, the concentrated sulfuric acid refers to a sulfuric acid aqueous solution having a mass fraction of not less than 75%, and the feed mass ratio of the concentrated sulfuric acid to the HF-NaF waste liquid is 1:6-20; and the feed rate of the HF-NaF waste liquid is 60-130 kg / hour.

[0014] Preferably, the operating temperature of the top of the distillation tower is 17°C-30°C; wherein, the gas phase at the top of the distillation tower enters the liquid-phase anhydrous HF storage tank after condensation treatment, anhydrous HF is extracted from an output branch of the liquid-phase anhydrous HF storage tank, and another output branch of the liquid-phase anhydrous HF storage tank is refluxed to the upper part of the distillation tower.

[0015] Preferably, the HF-NaF waste liquid is waste liquid generated in the process of preparing fluorobenzene by anhydrous hydrogen fluoride, wherein the HF content in the HF-NaF waste liquid is 60-80%.

[0016] Compared with the prior art, the solution provided by the present invention can realize the continuous batch recovery production of anhydrous HF in HF-NaF waste liquid, and while increasing the processing volume in continuous operation, the HF yield of HF is significantly improved. The recovery process of the present invention and the recovery device used therein are simple and stable, and there is no need to increase the recovery volume by setting multiple recovery kettles, so the present invention is suitable for continuous batch processing production application. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 It is a schematic diagram of the structure of a process device for continuously recovering anhydrous HF from HF-NaF waste liquid according to a specific embodiment of the present invention. DETAILED DESCRIPTION

[0018] See also Figure 1 As shown, this embodiment provides a process for continuously recovering anhydrous HF from HF-NaF waste liquid, wherein the HF-NaF waste liquid is an aqueous solution containing HF and NaF, preferably, in this embodiment, specifically, the waste liquid generated in the process of preparing fluorobenzene by anhydrous hydrogen fluoride, wherein the HF content in the HF-NaF waste liquid is 60-80% (usually close to 70%), of course, it can also be other waste liquids, and this embodiment does not make the sole limitation to this; In this embodiment, anhydrous HF refers to a liquid solution having an HF content of not less than 95% and a water content of not more than 5%; HF-NaF waste liquid and concentrated sulfuric acid are continuously introduced into a reaction evaporator for reaction evaporation, wherein the reaction evaporation comprises: sodium fluoride reacts with sulfuric acid in the reaction evaporator to generate hydrogen fluoride, and the hydrogen fluoride in the reaction evaporator is converted into gaseous hydrogen fluoride and evaporated from the top of the reaction evaporator; the gaseous hydrogen fluoride evaporated from the reaction evaporator is then sent to a distillation tower to remove water, and anhydrous HF is extracted from the top of the distillation tower; it should be noted that in the reaction evaporator, hydrogen fluoride in the HF-NaF waste liquid azeotropes with water, and after the concentrated sulfuric acid is added, the relative volatility of hydrogen fluoride and water is changed, and the azeotropy between hydrogen fluoride and water is destroyed, so it can further facilitate the distillation of hydrogen fluoride; at the same time, sodium fluoride in the HF-NaF waste liquid reacts with concentrated sulfuric acid to generate hydrogen fluoride, which can further improve the yield of hydrogen fluoride; Preferably, in this embodiment, concentrated sulfuric acid refers to a sulfuric acid aqueous solution having a mass fraction of not less than 75%, and the feed mass ratio of concentrated sulfuric acid to HF-NaF waste liquid is 1:6-20, more preferably 1:8-15; the feed rate of HF-NaF waste liquid is 60-130 kg / hour, more preferably 80-110 kg / hour; Preferably, in order to improve the yield, in this embodiment, the reaction evaporator comprises at least one primary reaction evaporator ( Figure 1 Marked as "primary") and secondary reaction evaporator ( Figure 1 The HF-NaF waste liquid and the concentrated sulfuric acid are continuously introduced into the first-stage reaction evaporator for reaction evaporation, and the bottom liquid phase of the first-stage reaction evaporator is sent into the second-stage reaction evaporator for reaction evaporation; and the operating temperature in the second-stage reaction evaporator is higher than the operating temperature in the first-stage reaction evaporator; in order to further improve the yield, preferably, the reaction evaporator includes a third-stage reaction evaporator ( Figure 1 Marked as "three-stage") and four-stage reaction evaporator ( Figure 1 Marked as "fourth level"); wherein, the bottom liquid phase of the secondary reaction evaporator is sent to the third reaction evaporator for reaction evaporation, and the bottom liquid phase of the third reaction evaporator is sent to the fourth reaction evaporator for reaction evaporation; the operating temperature in the third reaction evaporator is higher than the operating temperature in the second reaction evaporator, and lower than the operating temperature in the fourth reaction evaporator; preferably, in this embodiment, the bottom liquid phase of the reaction evaporator at the last stage is removed from the interface; one branch of the bottom liquid phase of the distillation tower is transported by a pump and refluxed to the tower kettle of the distillation tower through the condenser, and the other branch is removed from the interface or returned to the first reaction evaporator; Preferably, in this embodiment, the gas phase output end of each stage of the reaction evaporator is provided with a condenser, and the condensed liquid phase processed by the condenser is returned to its corresponding reaction evaporator; further preferably, the condensers configured for each stage of the reaction evaporator use circulating water, which can reduce the consumption of chilled water and reduce energy consumption; Preferably, in this embodiment, the operating temperature in the first-stage reaction evaporator is 60°C-80°C, the operating temperature in the second-stage reaction evaporator is 70°C-110°C; the operating temperature in the third-stage reaction evaporator is 110°C-130°C; the operating temperature in the fourth-stage reaction evaporator is 120°C-130°C.

[0019] Preferably, in this embodiment, the operating temperature of the top of the distillation tower is 17°C-30°C; wherein, the gas phase at the top of the distillation tower enters the liquid-phase anhydrous HF storage tank after condensation treatment, anhydrous HF is extracted from an output branch of the liquid-phase anhydrous HF storage tank, and the other output branch of the liquid-phase anhydrous HF storage tank is pumped back to the upper part of the distillation tower.

[0020] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0021] On the basis of the above implementation contents, in order to verify the technical effects achieved by the embodiments of the present application, the present application further proposes the following embodiments and comparative examples: Example 1: HF-NaF waste liquid (waste liquid generated in the process of preparing fluorobenzene from anhydrous hydrogen fluoride, the feed rate is 90kg / hour) and concentrated sulfuric acid with a concentration of 80% (the feed rate is 10kg / hour) are continuously fed into a first-stage reaction evaporator (the operating temperature in the kettle is 70°C), react and evaporate, the gas phase enters the matching first-stage condenser, the condensed liquid phase returns to the first-stage reaction evaporator, the remaining gas phase enters the HF distillation tower, and the liquid phase continuously enters the second-stage reaction evaporator; the liquid phase successively enters the second-stage reaction evaporator (the operating temperature in the kettle is 95°C), the third-stage reaction evaporator (the operating temperature in the kettle is 120°C) and the fourth-stage reaction evaporator. The reaction evaporator of each stage (the operating temperature in the kettle is 128° C.) reacts and evaporates in the reaction evaporator of each stage, and the gas phase enters the condenser of the reaction evaporator of each stage respectively, and the condensed liquid phase returns to the corresponding distillation kettle (the operating temperature at the top of the tower is 25° C.), and the remaining gas phase enters the HF distillation tower, and the bottom liquid phase of the fourth stage reaction evaporator is removed from the interface; the HF distillation tower further removes water in the gas phase output by the evaporator of each stage, and anhydrous HF with a water content meeting the standard is produced at the top of the tower, and the water phase in the tower bottom returns to the first reaction evaporator (in other embodiments, it can also be directly produced in the boundary area); after calculation, the HF yield of this embodiment 1 reaches 98.5%.

[0022] Embodiment 2: The remaining technical scheme of this embodiment 2 is the same as that of embodiment 1, except that, in this embodiment 2, the operating temperature in the kettle of the primary reaction evaporator is 60°C; the operating temperature in the kettle of the secondary reaction evaporator is 70°C; the operating temperature in the kettle of the tertiary reaction evaporator is 110°C; the operating temperature in the kettle of the quaternary reaction evaporator is 120°C; after calculation, the HF yield of this embodiment 2 reaches 97.6%.

[0023] Embodiment 3: The remaining technical scheme of this embodiment 3 is the same as that of embodiment 1, except that, in this embodiment 3, the operating temperature in the kettle of the primary reaction evaporator is 80°C; the operating temperature in the kettle of the secondary reaction evaporator is 110°C; the operating temperature in the kettle of the tertiary reaction evaporator is 130°C; the operating temperature in the kettle of the quaternary reaction evaporator is 130°C; after calculation, the HF yield of this embodiment 3 reaches 98.1%.

[0024] Embodiment 4: The remaining technical scheme of this embodiment 4 is the same as that of embodiment 1, except that, in this embodiment 4, the operating temperature in the kettle of the primary reaction evaporator is 70°C; the operating temperature in the kettle of the secondary reaction evaporator is 70°C; the operating temperature in the kettle of the tertiary reaction evaporator is 130°C; the operating temperature in the kettle of the quaternary reaction evaporator is 130°C; after calculation, the HF yield of this embodiment 4 reaches 95.5%.

[0025] Embodiment 5: The remaining technical scheme of this embodiment 5 is the same as that of embodiment 1, except that, in this embodiment 5, the secondary reaction evaporator is cancelled, and the bottom liquid phase of the primary reaction evaporator is sent to the tertiary reaction evaporator; after calculation, the HF yield of this embodiment 5 is 94.3%.

[0026] Embodiment 6: The remaining technical scheme of this embodiment 6 is the same as that of embodiment 1, except that, in this embodiment 6, the secondary reaction evaporator and the tertiary reaction evaporator are cancelled, and the bottom liquid phase of the primary reaction evaporator is sent to the quaternary reaction evaporator; after calculation, the HF yield of this embodiment 6 is 93.5%.

[0027] Embodiment 7: The remaining technical scheme of this embodiment 7 is the same as that of embodiment 1, except that, in this embodiment 7, the secondary reaction evaporator, the tertiary reaction evaporator and the quaternary reaction evaporator are eliminated, and the bottom liquid phase of the primary reaction evaporator is directly moved out of the interface; after calculation, the HF yield of this embodiment 7 is 91.7%.

[0028] Comparative Example 1: The remaining technical solutions of this comparative example 1 are the same as those of Example 1, except that, in this comparative example 1, concentrated sulfuric acid is replaced by a sulfuric acid solution having a concentration of 35%; after calculation, the HF yield of this comparative example 1 is less than 70%.

[0029] Comparative Example 2: The remaining technical solutions of this Comparative Example 2 are the same as those of Example 1, except that, in this Comparative Example 2, concentrated sulfuric acid is replaced by a sulfuric acid solution having a concentration of 65%; after calculation, the HF yield of this Comparative Example 2 is less than 82%.

[0030] Comparative Example 3: The remaining technical solutions of this Comparative Example 3 are the same as those of Example 1, except that, in this Comparative Example 3, concentrated sulfuric acid is replaced by a sulfuric acid solution having a concentration of 70%; after calculation, the HF yield of this Comparative Example 3 is less than 85%.

[0031] Comparative Example 4: The remaining technical scheme of this comparative example 4 is the same as that of Example 1, except that, in this comparative example 4, HF-NaF waste liquid and concentrated sulfuric acid are fed to the recovery kettle (the operating temperature in the kettle is 85° C.) respectively, and after mixing, the hydrogen fluoride therein is evaporated by heating at high temperature; after calculation, the HF yield of this comparative example 4 is less than 75%.

[0032] It will be apparent to those skilled in the art that the invention is not limited to the details of the exemplary embodiments described above and that the invention can be implemented in other specific forms without departing from the spirit or essential features of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description, and it is intended that all variations falling within the meaning and scope of the equivalent elements of the claims be included in the invention. Any reference numeral in a claim should not be considered as limiting the claim to which it relates.

[0033] In addition, it should be understood that although the present specification is described according to implementation modes, not every implementation mode contains only one independent technical solution. This description of the specification is only for the sake of clarity. Those skilled in the art should regard the specification as a whole. The technical solutions in each embodiment may also be appropriately combined to form other implementation modes that can be understood by those skilled in the art.

Claims

1. A process for continuously recovering anhydrous HF from HF-NaF waste liquid, wherein the HF-NaF waste liquid is an aqueous solution containing HF and NaF, and the anhydrous HF refers to a liquid phase solution with an HF content of not less than 95% and a water content of not more than 5%, characterized in that: The HF-NaF waste liquid and concentrated sulfuric acid are continuously introduced into a reaction evaporator for reaction evaporation, wherein the reaction evaporation comprises: sodium fluoride and sulfuric acid react in the reaction evaporator to generate hydrogen fluoride, the hydrogen fluoride in the reaction evaporator is converted into gaseous hydrogen fluoride and evaporated from the top of the reaction evaporator; then the gaseous hydrogen fluoride evaporated from the reaction evaporator is sent to a distillation tower to remove water, and anhydrous HF is extracted from the top of the distillation tower.

2. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: A condenser is provided at the gas phase output end of the reaction evaporator, and the condensed liquid phase treated by the condenser is returned to its corresponding reaction evaporator.

3. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: The reaction evaporator at least comprises a primary reaction evaporator and a secondary reaction evaporator, wherein the HF-NaF waste liquid and concentrated sulfuric acid are continuously introduced into the primary reaction evaporator for the reaction evaporation, and the bottom liquid phase of the primary reaction evaporator is sent into the secondary reaction evaporator for the reaction evaporation; and the operating temperature in the secondary reaction evaporator is higher than the operating temperature in the primary reaction evaporator.

4. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 3, characterized in that: The operating temperature in the first-stage reaction evaporator is 60°C-80°C, and the operating temperature in the second-stage reaction evaporator is 70°C-110°C.

5. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: The bottom liquid phase of the last stage reaction evaporator is removed from the interface; one branch of the bottom liquid phase of the distillation tower is refluxed into the tower kettle of the distillation tower after condensation treatment, and the other branch is removed from the interface or returned to the reaction evaporator.

6. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 3, 4 or 5, characterized in that: The reaction evaporator comprises a three-stage reaction evaporator and a four-stage reaction evaporator; wherein the bottom liquid phase of the two-stage reaction evaporator is sent to the three-stage reaction evaporator for the reaction evaporation, and the bottom liquid phase of the three-stage reaction evaporator is sent to the four-stage reaction evaporator for the reaction evaporation; the operating temperature in the three-stage reaction evaporator is higher than the operating temperature in the two-stage reaction evaporator, and lower than the operating temperature in the four-stage reaction evaporator.

7. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 6, characterized in that: The operating temperature in the kettle of the three-stage reaction evaporator is 110°C-130°C; the operating temperature in the kettle of the four-stage reaction evaporator is 120°C-130°C.

8. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: The concentrated sulfuric acid refers to a sulfuric acid aqueous solution with a mass fraction of not less than 75%, and the feed mass ratio of the concentrated sulfuric acid to the HF-NaF waste liquid is 1:6-20; the feed rate of the HF-NaF waste liquid is 60-130 kg / hour.

9. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: The top operating temperature of the distillation tower is 17°C-30°C; wherein, the top gas phase of the distillation tower enters the liquid phase anhydrous HF storage tank after condensation treatment, anhydrous HF is extracted from an output branch of the liquid phase anhydrous HF storage tank, and another output branch of the liquid phase anhydrous HF storage tank is refluxed to the upper part of the distillation tower.

10. The process for continuously recovering anhydrous HF from HF-NaF waste liquid according to claim 1, characterized in that: The HF-NaF waste liquid is waste liquid generated in the process of preparing fluorobenzene by using anhydrous hydrogen fluoride, wherein the HF content in the HF-NaF waste liquid is 60-80%.

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