Device and method for separating a mixture of hydrofluoric acid and hydrochloric acid

Abstract

The invention discloses a device for separating a mixture of hydrofluoric acid and hydrochloric acid, which specifically comprises a stripping tower, a stripping reboiler, a gas-liquid separation tank, and a hydrofluoric acid recovery tower, wherein a hydrofluoric acid / hydrochloric acid raw material liquid is stripped by high-temperature nitrogen in the stripping tower, and the separated liquid is secondary recovered through the separation effect of the gas-liquid separation tank, so as to achieve effective recycling of the hydrofluoric acid. The invention constructs a stripping tower-hydrofluoric acid recovery tower double tower system, so as to effectively separate hydrogen fluoride and hydrochloric acid in a feed, achieve effective recycling of hydrogen fluoride, significantly improve the utilization efficiency of hydrofluoric acid / hydrochloric acid raw material waste liquid, and has broad market prospects.

Description

Technical Field

[0001] The invention relates to the technical field of industrial wastewater treatment, in particular to a device and a method for separating a mixture of hydrofluoric acid and hydrochloric acid. Background Art

[0002] With the continuous development and progress of the fluorine chemical industry, especially in the photovoltaic industry, fluorine chemical industry has made great progress. Among them, polycrystalline silicon substrates and glass substrates for flat panel displays contain silicon, silicon oxide and boron oxide. Based on the corrosive effect of hydrofluoric acid solution on silicon-containing substances, the photovoltaic industry needs to use high-concentration hydrofluoric acid solution for texturing and etching of substrates. A mixed solution of hydrofluoric acid and hydrochloric acid is required. In the process of treating silicon-containing materials with hydrofluoric acid-containing liquid, the activity of hydrofluoric acid will be gradually consumed, and the impurities in the mixed liquid will increase after treatment, and it will no longer meet the etching needs in the future. Therefore, in the photovoltaic industry, the hydrofluoric acid mixed liquid has a service life. After a certain number of uses, it will be treated as waste liquid. The direct discharge of fluorine-containing waste hydrochloric acid will seriously pollute the environment and is also a huge waste of resources.

[0003] At present, the main treatment methods for hydrogen-fluoride waste liquid are: chemical precipitation, adsorption, freezing and electrodialysis. The freezing and electrodialysis methods are rarely used due to their high investment cost and low efficiency. The chemical sedimentation method usually uses the addition of slaked lime to generate calcium fluoride to remove fluoride ions. However, the post-treatment of the prepared calcium fluoride is complicated and requires the addition of flocculants for flocculation, which creates new solid waste treatment problems.

[0004] CN111547682A discloses a method for removing fluorine from fluorine-containing hydrochloric acid, wherein magnesium chloride is added to the fluorine-containing hydrochloric acid, and hydrogen fluoride is absorbed by the soluble magnesium chloride to generate insoluble magnesium fluoride and hydrochloric acid. The above method can achieve the treatment of fluorine-containing waste liquid, but the treatment of the generated magnesium fluoride is a new problem.

[0005] At present, the conventional method for treating the hydrofluoric acid mixed solution produced by the photovoltaic industry is to add metal ions and treat it by forming fluoride precipitates. It is rare to explore a method of recovering the hydrofluoric acid in the hydrofluoric acid solution and reusing the hydrofluoric acid. Summary of the invention

[0006] The present invention realizes the recycling of hydrofluoric acid in a hydrofluoric acid / hydrochloric acid solution by constructing a stripping tower-absorption tower double-tower treatment system and exploring the conditions inside the stripping tower and the absorption tower. In addition, the stripping tower of the present invention abandons the traditional solution stripping method and adopts high-temperature nitrogen stripping to strip the components of the hydrofluoric acid / hydrochloric acid solution, which can not only reduce the content of hydrogen chloride in the hydrofluoric acid solution, but also effectively recover the hydrofluoric acid by re-absorption in the hydrofluoric acid absorption tower, thereby realizing the effective separation of hydrofluoric acid and hydrogen chloride.

[0007] Specifically, the present invention adopts the following technical scheme, and the present invention claims protection for a device for separating a mixture of hydrofluoric acid and hydrochloric acid, comprising a stripping tower, a stripping reboiler, a gas-liquid separation tank, and a hydrofluoric acid recovery tower, characterized in that the stripping reboiler is arranged at the bottom of the stripping tower, the hydrofluoric acid / hydrochloric acid solution is fed from the top of the stripping tower, the high-temperature nitrogen is fed from the bottom of the stripping tower, a condenser is arranged between the stripping tower and the gas-liquid separation tank, the liquid of the gas-liquid separation tank returns to the stripping tower from the top of the stripping tower, the gas phase of the gas-liquid separation tank enters the hydrofluoric acid recovery tower from the bottom of the hydrofluoric acid recovery tower, and after the hydrofluoric acid is recovered by the hydrofluoric acid recovery tower, the liquid in the tower bottom re-enters the stripping tower via a delivery pump.

[0008] The present invention further provides specific parameter conditions of the stripping tower and the hydrofluoric acid recovery tower of the separation device, wherein the bottom temperature of the stripping tower is 30-70°C, the top temperature is 30-70°C, the bottom temperature of the hydrofluoric acid recovery tower is 8-30°C, and the top temperature is 1-20°C. Under the above parameter conditions, high-purity separation of hydrofluoric acid and hydrogen chloride can be achieved.

[0009] The present invention also provides a method for separating a mixture of hydrofluoric acid and hydrochloric acid using the above-mentioned device, the method comprising continuous operation or intermittent operation, characterized in that the method comprises:

[0010] 1) High temperature nitrogen is introduced into the bottom of the stripping tower;

[0011] 2) The hydrofluoric acid / hydrochloric acid solution is introduced into the stripping tower from the top of the stripping tower, the pressure of the stripping tower is 0-0.05MpaA, the bottom temperature is 38-65°C, the top temperature is 32-50°C, the theoretical plate number of the stripping tower is 15-40, the mass ratio of the hydrofluoric acid / hydrochloric acid solution feed to the nitrogen feed in the stripping tower is 1:1-5, and part of the liquid is vaporized in the reboiler and flows back into the stripping tower;

[0012] 3) The stripped gas passes through the condenser to the gas-liquid separation tank, and the condensed liquid returns to the stripping tower through the transfer pump;

[0013] 4) The uncondensed gas enters the hydrofluoric acid recovery tower from the bottom of the hydrofluoric acid recovery tower. The pressure in the hydrofluoric acid recovery tower is 0-0.05MpaA, the number of theoretical plates of the hydrofluoric acid recovery tower is 4-20, the top temperature is 3-15°C, and the bottom temperature is 10-25°C; ultrapure water is added to the top of the hydrofluoric acid recovery tower, and the recovered solution is transferred back to the stripping tower through a delivery pump to re-recover the hydrofluoric acid solution.

[0014] The above method is simple to operate and can realize repeated recovery of hydrofluoric acid. After multiple recovery and application, hydrofluoric acid and hydrogen chloride are completely separated.

[0015] Further preferably, the mass ratio of the hydrofluoric acid / hydrochloric acid solution feed amount to the nitrogen feed amount is 1:2-3.

[0016] More preferably, the stripping tower has a theoretical plate number of 18 to 33, and the hydrofluoric acid recovery tower has a theoretical plate number of 4 to 11.

[0017] Further preferably, the mass fraction of hydrochloric acid in the hydrofluoric acid / hydrochloric acid solution is 1 to 10 wt %.

[0018] Further preferably, the feed temperature of the nitrogen is 120°C-180°C.

[0019] Further preferably, the reboiler temperature in step 2) is 39-50°C, preferably 40°C.

[0020] The use of the device of the present invention and the process description:

[0021] The hydrofluoric acid / hydrochloric acid mixture is transported to the top of the stripping tower, and high-temperature nitrogen is introduced into the bottom of the tower. The nitrogen at the top of the stripping tower carries hydrofluoric acid, hydrogen chloride and water into the condenser for cooling, and then the gas-liquid mixture enters the gas-liquid separator. The liquid phase of the gas-liquid separator flows back to the stripping tower, and the gas phase enters the hydrofluoric acid recovery tower; the top of the hydrofluoric acid recovery tower enters low-temperature ultrapure water for low-temperature absorption, and the gas phase at the top of the tower is nitrogen containing hydrogen chloride, which is removed from the tail gas treatment system, and the bottom of the tower is low-concentration hydrofluoric acid solution and hydrochloric acid solution, which are transported back to the top of the stripping tower through a delivery pump to recover hydrofluoric acid.

[0022] Specifically, the present invention has the following beneficial effects:

[0023] The present invention realizes the recycling of hydrofluoric acid solution by constructing a double-tower treatment system of a stripping tower and a hydrofluoric acid absorption tower. The stripping tower adopts a high-temperature nitrogen stripping method, which can not only reduce the content of hydrogen chloride in the hydrofluoric acid solution, but also effectively recover the hydrofluoric acid by re-absorption in the hydrofluoric acid absorption tower. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The present invention is a flow chart for separating a mixture of hydrofluoric acid and hydrochloric acid. DETAILED DESCRIPTION

[0025] To facilitate the understanding of the present invention by those skilled in the art, the scheme of the present invention is described in detail below in conjunction with specific embodiments. The following specific embodiments are only examples and are not used as specific information to limit the scope of protection of this patent. The following process flow chart is as follows: Figure 1 shown.

[0026] Example 1

[0027] The feed rate of the mixed waste liquid raw material containing hydrofluoric acid and hydrochloric acid is 1000kg / hr (feed temperature 35°C, HF content 10.5wt%, HCl content 5.25wt%, and the rest is water), the nitrogen flow rate is 2000kg / hr (feed temperature 150°C), the theoretical plate number of the stripping tower is 20, the bottom temperature is 42°C, the top of the tower is 35°C, the pressure of the stripping tower is 0.03Mpa, and the reboiler temperature is 40°C; the ultrapure water flow rate at the top of the hydrofluoric acid recovery tower is 2000kg / hr, the feed water temperature is 5°C, the top of the hydrofluoric acid absorption tower is 5°C, the bottom temperature is 15°C, the pressure of the hydrogen fluoride recovery tower is 0.03Mpa, and the number of plates is 6. After passing through the hydrogen fluoride absorption tower, the hydrogen fluoride content is 142ppm, and the hydrogen chloride content is 0.59wt%. The hydrogen chloride content at the bottom of the stripping tower is 238ppm, and the hydrogen fluoride content is 2.5wt%. No hydrogen chloride is detected in the recovered hydrofluoric acid solution, and the final hydrogen fluoride yield is 99.81%.

[0028] Example 2

[0029] The feed flow rate of the mixed waste liquid raw material containing hydrofluoric acid and hydrochloric acid is 1000kg / hr (feed temperature 35°C, HF content 12.5wt%, HCl content 3.18wt%, and the rest is water), the nitrogen flow rate is 2500kg / hr (feed temperature 140°C), the theoretical plate number of the stripping tower is 28, the bottom temperature is 48°C, the top of the tower is 40°C, the stripping tower is at normal pressure, and the reboiler temperature is 42°C; the ultrapure water flow rate at the top of the hydrofluoric acid recovery tower is 1800kg / hr, the feed water temperature is 8°C, the top of the hydrofluoric acid absorption tower is 8°C, the bottom temperature is 20°C, and the pressure of the hydrogen fluoride recovery tower is 10. After passing through the hydrogen fluoride absorption tower, the hydrogen fluoride content is 153ppm, the hydrogen chloride content is 0.65wt%, the hydrogen chloride content at the bottom of the stripping tower is 247ppm, the hydrogen fluoride content is 3.0wt%, and no hydrogen chloride is detected in the recovered hydrofluoric acid solution, and the final hydrogen fluoride yield is 99.69%.

[0030] Example 3

[0031] The feed rate of the mixed waste liquid raw material containing hydrofluoric acid and hydrochloric acid is 1000kg / hr (feed temperature 32°C, HF content 13.2wt%, HCl content 8.25wt%, and the rest is water), the nitrogen flow rate is 3000kg / hr (feed temperature 160°C), the theoretical plate number of the stripping tower is 30, the bottom temperature is 50°C, the top temperature is 46°C, the pressure of the stripping tower is 0.05Mpa, and the reboiler temperature is 37°C; the ultrapure water flow rate at the top of the hydrofluoric acid recovery tower is 1800kg / hr, the feed water temperature is 5°C, the top of the hydrofluoric acid absorption tower is 13°C, the bottom temperature is 23°C, the pressure of the hydrogen fluoride recovery tower is 0.05Mpa, and the number of plates is 8. After passing through the hydrogen fluoride absorption tower, the hydrogen fluoride content is 152ppm, and the hydrogen chloride content is 0.87wt%. The hydrogen chloride content at the bottom of the stripping tower is 251ppm, and the hydrogen fluoride content is 2.8wt%. No hydrogen chloride is detected in the recovered hydrofluoric acid solution, and the final hydrogen fluoride yield is 99.72%.

[0032] Comparative Example 1

[0033] The feed rate of the mixed waste liquid raw material containing hydrofluoric acid and hydrochloric acid is 1000kg / hr (feed temperature 35°C, HF content 10.5wt%, HCl content 5.25wt%, and the rest is water), the nitrogen flow rate is 2000kg / hr (feed temperature 150°C), the theoretical plate number of the stripping tower is 40, the bottom temperature is 80°C, the top of the tower is 60°C, the pressure of the stripping tower is 0.07Mpa, and the reboiler temperature is 40°C; the ultrapure water flow rate at the top of the hydrofluoric acid recovery tower is 2000kg / hr, the feed water temperature is 5°C, the top of the hydrofluoric acid absorption tower is 18°C, the bottom temperature is 30°C, the pressure of the hydrogen fluoride recovery tower is 0.07Mpa, and the number of plates is 15. After passing through the hydrogen fluoride absorption tower, the hydrogen chloride content is 3.75wt%, the hydrogen fluoride content is 5.35wt%, and the recovered hydrofluoric acid solution contains 3.18% hydrogen chloride. Hydrogen fluoride and hydrogen chloride are not effectively separated, and the final hydrogen fluoride yield is 67.2%.

[0034] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "specific examples", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, unless they are contradictory.

[0035] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. A device for separating a mixture of hydrofluoric acid and hydrochloric acid, comprising a stripping tower, a stripping reboiler, a gas-liquid separation tank, and a hydrofluoric acid recovery tower, characterized in that: The stripping reboiler is arranged at the bottom of the stripping tower, the hydrofluoric acid / hydrochloric acid solution is fed from the top of the stripping tower, the high-temperature nitrogen is fed from the bottom of the stripping tower, a condenser is arranged between the stripping tower and the gas-liquid separation tank, the liquid of the gas-liquid separation tank returns to the stripping tower from the top of the stripping tower, the gas phase of the gas-liquid separation tank enters the hydrofluoric acid recovery tower from the bottom of the hydrofluoric acid recovery tower, and after the hydrofluoric acid is recovered by the hydrofluoric acid recovery tower, the liquid in the tower bottom re-enters the stripping tower through a delivery pump.

2. The device according to claim 1, characterized in that The bottom temperature of the stripping tower is 30-70°C, and the top temperature is 30-70°C. The bottom temperature of the hydrofluoric acid recovery tower is 8-30°C, and the top temperature is 1-20°C.

3. A method for separating a mixture of hydrofluoric acid and hydrochloric acid using the device of claim 1, the method comprising continuous operation or intermittent operation, characterized in that: The method comprises: 1) High temperature nitrogen is introduced into the bottom of the stripping tower; 2) The hydrofluoric acid / hydrochloric acid solution is introduced into the stripping tower from the top of the stripping tower. The pressure of the stripping tower is 0-0.05MPa, wherein the tower bottom temperature is 38-65°C, the tower top temperature is 32-50°C, the theoretical plate number of the stripping tower is 15-40, and the mass ratio of the hydrofluoric acid / hydrochloric acid solution feed amount to the nitrogen feed of the stripping tower is 1:1-5. Part of the liquid is vaporized by the reboiler and flows back into the stripping tower; 3) The stripped gas passes through the condenser to the gas-liquid separation tank, and the condensed liquid returns to the stripping tower through the transfer pump; 4) The uncondensed gas enters the hydrofluoric acid recovery tower from the bottom of the hydrofluoric acid recovery tower. The pressure in the hydrofluoric acid recovery tower is 0~0.05MPa, the theoretical plate number of the hydrofluoric acid recovery tower is 4~20, the top temperature is 3-15℃, and the bottom temperature is 10-25℃; ultrapure water is added to the top of the hydrofluoric acid recovery tower, and the recovered solution is transported back to the stripping tower through a delivery pump to re-recover the hydrofluoric acid solution.

4. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The mass ratio of the hydrofluoric acid / hydrochloric acid solution feed amount to the nitrogen feed amount is 1:2-3.

5. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The number of theoretical plates of the stripping tower is 18 to 33, and the number of theoretical plates of the hydrofluoric acid recovery tower is 4 to 11.

6. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The mass fraction of hydrochloric acid in the hydrofluoric acid / hydrochloric acid solution is 1-10 wt %.

7. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The feed temperature of the nitrogen is 120°C-180°C.

8. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The reboiler temperature is 39-50°C.

9. The method for separating a mixture of hydrofluoric acid and hydrochloric acid according to claim 3, characterized in that: The reboiler temperature was 40°C.

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