System and method for continuously separating and absorbing tail gas from preparation of lithium hexafluorophosphate

Abstract

The invention discloses a lithium hexafluorophosphate preparation tail gas continuous separation and absorption system and method, the system comprises an absorption separation tower, an HF desorption tower, an HF absorption tower, an HCl absorption tower and a tail gas absorption tower, and efficient separation of HF and HCl and by-production of hydrofluoric acid and hydrochloric acid can be realized through the five-tower process. The five-tower separation and absorption technology is adopted, efficient separation of HF and HCl in the mixed tail gas can be achieved, the process operation is simple, the occupied area is small, and the purity of by-products hydrochloric acid and hydrofluoric acid is high.

Description

Technical Field

[0001] The present invention belongs to the technical field of chemical engineering, and particularly relates to a continuous separation and absorption system and method for the tail gas in the preparation of lithium hexafluorophosphate. Background Art

[0002] Lithium hexafluorophosphate (LiPF6), as an electrolyte for lithium-ion batteries, is mainly used in lithium-ion power batteries, lithium-ion energy storage batteries and other daily-use batteries, and is also an irreplaceable raw material for lithium-ion battery electrolytes in the near and medium terms. Lithium hexafluorophosphate (LiPF6) is a variety with relatively high scientific and technological content in the field of inorganic fluorochemical industry and has relatively high technical barriers.

[0003] The production processes of lithium hexafluorophosphate (LiPF6) include gas-solid reaction method, HF solvent method, organic solvent method and ion exchange method. Since the purity of lithium hexafluorophosphate produced by the gas-solid reaction method and the ion exchange method is relatively low, both are in the laboratory research stage and there are no industrial production examples. At present, the only mass-produced processes are the organic solvent method and the HF solvent method. Among them, the HF solvent method has become the current mainstream process because the lithium hexafluorophosphate (LiPF6) produced is solid crystal, easy to store and has high purity.

[0004] The production of lithium hexafluorophosphate (LiPF6) by the HF solvent method generally includes: reacting phosphorus pentachloride (PCl5) with anhydrous hydrofluoric acid (AHF) to prepare phosphorus pentafluoride (PF5); dissolving high-purity lithium fluoride (LiF) in anhydrous hydrofluoric acid (AHF); reacting phosphorus pentafluoride (PF5) with lithium fluoride (LiF) in an anhydrous hydrofluoric acid (AHF) solution to produce lithium hexafluorophosphate (LiPF6); intermittently crystallizing lithium hexafluorophosphate (LiPF6) from the anhydrous hydrofluoric acid (AHF) solution; filtering and drying the lithium hexafluorophosphate (LiPF6) crystal and anhydrous hydrofluoric acid (AHF); screening and packaging the dried lithium hexafluorophosphate (LiPF6) crystal;

[0005] In the currently industrialized HF solvent method for producing lithium hexafluorophosphate (LiPF6), a large amount of HCl is generated during the reaction of phosphorus pentachloride (PCl5) with anhydrous hydrofluoric acid (AHF) to prepare phosphorus pentafluoride (PF5). The reaction formula is as follows:

[0006] 5HF + PCl5 → PF5 + 5HCl

[0007] Since the boiling point of anhydrous HF is relatively low, only 19.5°C, a large amount of HF volatilizes and enters the tail gas system together with HCl. HF and HCl are both acidic gases with similar properties and are difficult to separate. Summary of the Invention

[0008] The object of the present invention is to provide a continuous separation and absorption system and method for the tail gas in the preparation of lithium hexafluorophosphate, so as to realize the continuous separation and absorption of HF and HCl in the tail gas of the preparation of lithium hexafluorophosphate and improve the production efficiency.

[0009] To achieve the above object, the present invention provides the following technical solutions:

[0010] A continuous separation and absorption system for the tail gas in the preparation of lithium hexafluorophosphate, comprising:

[0011] An absorption and separation tower, which is used for absorbing and treating the tail gas in the preparation of lithium hexafluorophosphate with a selective absorbent to obtain an absorbent containing HF and HCl gas;

[0012] An HF desorption tower, which is used for stripping the absorbent containing HF to obtain HF gas and the absorbent after desorption;

[0013] An HF absorption tower, which is used for absorbing the HF gas with water to obtain a hydrofluoric acid solution and the tail gas of the HF absorption tower;

[0014] An HCl absorption tower, which is used for absorbing the HCl gas with water to obtain a hydrochloric acid solution and the tail gas of the HCl absorption tower;

[0015] A tail gas absorption tower, which is used for absorbing the tail gas of the HF absorption tower and the tail gas of the HCl absorption tower with water to obtain a mixed acid product.

[0016] Optionally, the selective absorbent is at least one of 98 wt% concentrated sulfuric acid, 99.5 wt% sulfolane or 99.5 wt% diethyl ether.

[0017] Optionally, the tail gas in the preparation of lithium hexafluorophosphate enters the absorption and separation tower from the bottom of the absorption and separation tower, and counter-currently contacts with the absorbent entering from the top of the absorption and separation tower to obtain an absorbent containing HF and HCl gas;

[0018] Preferably, the absorbent containing HF enters the HF desorption tower from the bottom of the absorption and separation tower through a separation tower discharge pump.

[0019] Optionally, the absorbent containing HF enters the HF desorption tower from the top of the HF desorption tower, and counter-currently contacts with nitrogen entering from the bottom of the HF desorption tower for stripping to obtain HF gas and the absorbent after desorption;

[0020] Preferably, the absorbent after desorption enters the top of the absorption and separation tower through a desorption tower discharge pump;

[0021] Preferably, the absorbent after desorption enters the top of the absorption and separation tower through a desorption tower discharge pump and an absorbent cooler in sequence.

[0022] Optionally, the HF-containing gas desorbed in the HF desorption tower is discharged from the top of the HF desorption tower and sent to the bottom of the HF absorption tower, where it comes into countercurrent contact with water entering the HF absorption tower from the top of the HF absorption tower for absorption, obtaining a hydrofluoric acid solution and HF absorption tower tail gas;

[0023] Preferably, a part of the hydrofluoric acid solution is output as a hydrofluoric acid product, and the other part is returned to the middle of the HF absorption tower through the HF absorption tower reflux pump.

[0024] Optionally, the HCl-containing gas generated in the absorption separation tower is discharged from the top of the absorption separation tower and sent to the bottom of the HCl absorption tower, where it comes into countercurrent contact with water entering the HCl absorption tower from the top of the HCl absorption tower for absorption, obtaining a hydrochloric acid solution and HCl absorption tower tail gas;

[0025] Preferably, a part of the hydrochloric acid solution is output as a hydrochloric acid product, and the other part is returned to the middle of the HCl absorption tower through the HCl absorption tower reflux pump.

[0026] Optionally, the HF absorption tower tail gas discharged from the HF absorption tower and the HCl absorption tower tail gas discharged from the top of the HCl absorption tower are mixed and then enter the bottom of the tail gas absorption tower, where they come into countercurrent contact with water entering the bottom of the tail gas absorption tower from the top of the tail gas absorption tower for absorption, generating a mixed acid solution, and the top gas meets the standards and is discharged;

[0027] Preferably, a part of the mixed acid solution is output as a mixed acid product, and the other part is returned to the middle of the tail gas absorption tower through the tail gas absorption tower reflux pump.

[0028] A continuous separation and absorption method for the tail gas of preparing lithium hexafluorophosphate includes the following steps:

[0029] Step 1) Absorb and treat the tail gas of preparing lithium hexafluorophosphate in the absorption separation tower with a selective absorbent to obtain an HF-containing absorbent and HCl-containing gas;

[0030] Step 2) Feed the HF-containing absorbent into the HF desorption tower, and carry out stripping treatment on the HF-containing absorbent in the HF desorption tower to obtain HF-containing gas and desorbed absorbent;

[0031] Step 3) Feed the HF-containing gas into the HF absorption tower, and carry out absorption treatment on the HF-containing gas in the HF absorption tower with water to obtain a hydrofluoric acid solution and HF absorption tower tail gas;

[0032] Step 4) Feed the HCl-containing gas into the HCl absorption tower, and carry out absorption treatment on the HCl-containing gas in the HCl absorption tower with water to obtain a hydrochloric acid solution and HCl absorption tower tail gas;

[0033] Step V) Absorb the tail gas from the HF absorption tower and the tail gas from the HCl absorption tower with water to obtain a mixed acid solution.

[0034] Optionally, the ratio of the tail gas for preparing lithium hexafluorophosphate to the selective absorbent in Step I) is 1 - 2:10 - 15;

[0035] In Step II), strip the HF-containing absorbent with nitrogen, and the ratio of nitrogen to the HF-containing absorbent is 5 - 10:1 - 2;

[0036] In Step III), the ratio of the HF-containing gas to water is 1 - 4:10 - 15;

[0037] In Step IV), the ratio of the HCl-containing gas to water is 1 - 4:10 - 15;

[0038] In Step V), the ratio of the total amount of the tail gas from the HF absorption tower and the tail gas from the HCl absorption tower to water is 1 - 3:10 - 15.

[0039] Optionally, the temperature of the absorbent in Step I) is 10 - 45 °C;

[0040] The temperature of nitrogen in Step II) is 70 - 95 °C.

[0041] Optionally, in Step III), a 10 - 35% hydrofluoric acid solution is output as the hydrofluoric acid product, and the other part is returned to the middle of the HF absorption tower through the HF absorption tower reflux pump;

[0042] In Step IV), a 10 - 35% hydrochloric acid solution is output as the hydrochloric acid product, and the other part is returned to the middle of the HCl absorption tower through the HCl absorption tower reflux pump;

[0043] In Step V), a 10 - 45% mixed acid solution is output as the mixed acid product, and the other part is returned to the middle of the tail gas absorption tower through the tail gas absorption tower reflux pump.

[0044] Preferably, desalted water is used to absorb acidic gases at the tops of the HF absorption tower, the HCl absorption tower, and the mixed gas absorption tower.

[0045] Compared with the prior art, the advantages of the present invention are:

[0046] The present invention provides a continuous separation and absorption system and method for the tail gas in the preparation of lithium hexafluorophosphate. The system includes: an absorption and separation tower, an HF desorption tower, an HF absorption tower, an HCl absorption tower, and a tail gas absorption tower. First, through the separation and desorption operations of the absorption and separation tower and the HF desorption tower, the continuous separation of HF and HCl can be achieved. Second, through the continuous absorption operations of the HF absorption tower and the HCl absorption tower, HF solution and HCl solution products can be obtained. Finally, the tail gas is absorbed and purified through the mixed gas absorption tower, and the tail gas can reach the standard for discharge. The system has a short process flow, simple equipment, low energy consumption, continuous, safe and reliable process, and has good economic and safety benefits. It meets the requirements of the continuous separation and absorption process for the tail gas containing HF and HCl in the preparation of lithium hexafluorophosphate. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below.

[0048] Figure 1 It is a schematic structural diagram of a continuous separation and absorption system for the tail gas in the preparation of lithium hexafluorophosphate in an embodiment.

[0049] Wherein the reference numerals are: 1. absorption and separation tower, 2. HF desorption tower, 3. HF absorption tower, 4. HCl absorption tower, 5. mixed gas absorption tower, 6. separation tower discharge pump, 7. desorption tower discharge pump, 8. HF absorption tower reflux pump, 9. HCl absorption tower reflux pump, 10. tail gas absorption tower reflux pump, 11. nitrogen heater, 12. absorbent cooler. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0050] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. The following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the present invention to be protected, but merely represents the embodiments of the present invention.

[0051] Embodiment 1

[0052] The present invention proposes a continuous separation and absorption system for the tail gas containing HF and HCl in the preparation of lithium hexafluorophosphate, and the structure is as Figure 1 shown, including: an absorption and separation tower 1, an HF desorption tower 2, an HF absorption tower 3, an HCl absorption tower 4, and a tail gas absorption tower 5. Through the above five-tower process, the efficient separation of HF and HCl can be achieved and hydrofluoric acid and hydrochloric acid can be by-produced, wherein:

[0053] Absorption separation tower 1 is used to absorb and treat the tail gas from the preparation of lithium hexafluorophosphate with a selective absorbent. The tail gas from the preparation of lithium hexafluorophosphate enters the absorption separation tower from the bottom of the absorption separation tower and contacts countercurrently with the absorbent entering from the top of the absorption separation tower. HF in the mixed gas is selectively absorbed by the absorbent in the tower. The solubility of HCl in the absorbent is small and it is discharged from the top of the tower to obtain an absorbent containing HF and a gas containing HCl. The selective absorbent is at least one of 98 wt% concentrated sulfuric acid, 99.5 wt% sulfolane or 99.5 wt% ether.

[0054] HF desorption tower 2 is used to strip the absorbent containing HF. The absorbent containing HF enters HF desorption tower 2 from the top of HF desorption tower after passing through the separation tower discharge pump 6 from the bottom of absorption separation tower 1 and contacts countercurrently with the nitrogen entering from the bottom of HF desorption tower 2 for stripping to obtain a gas containing HF and a desorbed absorbent. The desorbed absorbent enters the top of the absorption separation tower through the desorption tower discharge pump 7 and the absorbent cooler 12. To improve the absorption efficiency of the absorption separation tower, the absorbent cooler 12 uses circulating water to cool down the absorbent. To improve the desorption efficiency of the HF desorption tower, the nitrogen heater 11 heats the nitrogen entering the bottom of the HF desorption tower by using steam.

[0055] HF absorption tower 3 is used to absorb and treat the gas containing HF with water. The gas containing HF desorbed in the HF desorption tower is discharged from the top of the HF desorption tower and sent to the bottom of the HF absorption tower, and contacts countercurrently with the water entering the HF absorption tower from the top of the HF absorption tower for absorption to obtain a hydrofluoric acid solution and the tail gas of the HF absorption tower. A part of the hydrofluoric acid solution is output as a hydrofluoric acid product, and the other part returns to the middle of the HF desorption tower through the HF absorption tower reflux pump 8.

[0056] HCl absorption tower 4 is used to absorb and treat the gas containing HCl with water. The gas containing HCl generated in the absorption separation tower 1 is discharged from the top of the absorption separation tower 1 and sent to the bottom of the HCl absorption tower 4, and contacts countercurrently with the water entering the HCl absorption tower 4 from the top of the HCl absorption tower 4 for absorption to obtain a hydrochloric acid solution and the tail gas of the HCl absorption tower. A part of the hydrochloric acid solution is output as a hydrochloric acid product, and the other part returns to the middle of the HCl absorption tower through the HCl absorption tower reflux pump 9.

[0057] The tail gas absorption tower 5 is used to absorb the tail gas from the HF absorption tower and the HCl absorption tower with water. The tail gas from the HF absorption tower discharged from the HF absorption tower and the tail gas from the top of the HCl absorption tower discharged from the HCl absorption tower are mixed and then enter the bottom of the tail gas absorption tower. After counter-current contact absorption with the water entering the bottom of the tail gas absorption tower from the top of the bottom of the tail gas absorption tower, a mixed acid solution is generated, and the gas at the top of the tower meets the standard and is discharged. A part of the mixed acid solution is output as a mixed acid product, and the other part is returned to the middle of the tail gas absorption tower through the tail gas absorption tower reflux pump 10.

[0058] Example 2

[0059] A continuous separation and absorption process for HF- and HCl-containing tail gas in the preparation of lithium hexafluorophosphate. In this example, the volume fraction of HF in the HF- and HCl-containing tail gas is 65%, and the volume fraction of HCl is 34%. This example includes the following steps:

[0060] Step 1): Send the tail gas to be treated to the absorption and separation tower. After HF is selectively absorbed by the selective absorbent, it is discharged from the bottom of the tower, and the HCl-containing gas not absorbed is discharged from the top of the tower. The absorbent used is 98wt% concentrated sulfuric acid, and the temperature of the absorbent is 30°C to improve the absorption efficiency of the absorbent in the absorption and separation tower. The mass ratio of the tail gas to be treated to the absorbent is 1:10.

[0061] Step 2): Send the absorbent after absorbing HF in Step 1) to the top of the HF desorption tower through the absorption tower discharge pump, and make counter-current contact with N2 fed from the bottom of the tower. The HF in the absorbent is desorbed by N2, and the mixed gas exits from the top of the tower. After the desorbed absorbent is cooled by the absorbent cooler, it is sent to the top of the absorption and separation tower for continuous recycling. The temperature of the nitrogen gas is about 90°C after being heated by the nitrogen gas heater to improve the desorption efficiency of N2 in the HF desorption tower. The mass ratio of nitrogen gas to the absorbent containing HF is 5:1.

[0062] Step 3): Send the HF-containing gas desorbed in Step 2) to the bottom of the HF absorption tower. The HF in the HF-containing gas makes counter-current contact with the demineralized water at the top of the HF absorption tower and is absorbed. The mass ratio of the HF-containing gas to the demineralized water is 1:15. The generated HF solution is pressurized by the HF absorption tower reflux pump and 90wt% is sent to the top for reflux absorption, and the remaining 10wt% is sent out of the boundary area as hydrofluoric acid product. The unabsorbed tail gas (containing N2 and trace amounts of HF) from the HF absorption tower in the mixed gas is discharged from the top of the tower.

[0063] Step 4) Send the HCl-containing gas discharged from the top of the self-absorption separation tower in Step 1) to the bottom of the HCl absorption tower, where it contacts the demineralized water flowing countercurrently from the top of the HCl absorption tower and is absorbed. The mass ratio of the HCl-containing gas to the demineralized water is 1:15. The generated HCl solution is pressurized by the HCl absorption tower reflux pump and 90 wt% of it is sent to the top for reflux absorption, and 10 wt% is sent out of the battery limit as hydrochloric acid product. The unabsorbed HCl absorption tower tail gas (containing trace amounts of HCl) in the mixed gas is discharged from the top of the tower.

[0064] Step 5) After the HF absorption tower tail gas discharged from the top of the HF absorption tower in Step 3) and the HCl absorption tower tail gas from the top of the HCl absorption tower in Step 4) are combined, they are sent to the bottom of the mixed gas absorption tower, where they contact the demineralized water flowing countercurrently from the top of the mixed gas absorption tower and are absorbed. The total mass ratio of the HF absorption tower tail gas and the HCl absorption tower tail gas to water is 1:15. The generated mixed acid solution is pressurized by the mixed gas absorption tower reflux pump and 90 wt% of it is sent to the top for reflux absorption, and 10 wt% is sent out of the battery limit as the mixed acid product. The unabsorbed N2 in the mixed gas is discharged from the top of the tower.

[0065] Through the above embodiments, three products can be continuously obtained, namely HCl product, HF product and mixed acid product solution.

[0066] Among them, the content of HF in the HF product is 31 wt%, and the content of HCl is 0.1 wt%;

[0067] The content of HCl in the HCl product is 30 wt%; the content of HF is 0.15 wt%;

[0068] The content of HF in the mixed acid product is 12 wt%, and the content of HCl is 11 wt%.

[0069] The recovery rate of HF in the tail gas is 99.9%, and the recovery rate of HCl is 99.5%.

[0070] Example 3

[0071] A continuous separation and absorption process for HF- and HCl-containing tail gas in the preparation of lithium hexafluorophosphate. In this example, the volume fraction of HF in the HF- and HCl-containing tail gas is 65%, and the volume fraction of HCl is 34%. This example includes the following steps:

[0072] Step 1) Send the tail gas to be treated to the absorption separation tower. After HF is selectively absorbed by the selective absorbent, it is discharged from the bottom of the tower, and the unabsorbed HCl is discharged from the top of the tower; among them, the absorbent is 98 wt% concentrated sulfuric acid, and the temperature of the absorbent is 30 °C to improve the absorption efficiency of the absorbent in the absorption separation tower. The mass ratio of the tail gas to be treated to the absorbent is 1:5.

[0073] Step 2) The absorbent after absorbing HF obtained in Step 1) is sent to the top of the HF desorption tower through the absorbent tower discharge pump, and contacts countercurrently with the N2 fed into the bottom of the tower. The HF in the absorbent is desorbed by N2, and the mixed gas exits from the top of the tower. After the desorbed absorbent is cooled by the absorbent cooler, it is sent to the top of the absorption and separation tower for continuous recycling. The nitrogen gas is heated by the nitrogen heater to a temperature of about 90 °C to improve the desorption efficiency of N2 in the HF desorption tower. The mass ratio of nitrogen gas to the absorbent containing HF is 10:1.

[0074] Step 3) The gas containing HF desorbed in Step 2) is sent to the bottom of the HF absorption tower. The HF in the gas containing HF contacts countercurrently with the demineralized water at the top of the HF absorption tower and is absorbed. The mass ratio of the gas containing HF to the demineralized water is 1:10. The generated HF solution is pressurized by the HF absorption tower reflux pump and 80 wt% is sent to the top for reflux absorption, and the remaining 20 wt% is sent out of the battery limit as hydrofluoric acid product. The unabsorbed HF absorption tower tail gas (containing N2 and trace HF) in the mixed gas is discharged from the top of the tower.

[0075] Step 4) The gas containing HCl discharged from the top of the absorption and separation tower in Step 1) is sent to the bottom of the HCl absorption tower, and contacts countercurrently with the demineralized water at the top of the HCl absorption tower and is absorbed. The mass ratio of the gas containing HCl to the demineralized water is 1:10. The generated HCl solution is pressurized by the HCl absorption tower reflux pump and 80 wt% is sent to the top for reflux absorption, and 20 wt% is sent out of the battery limit as hydrochloric acid product. The unabsorbed HCl absorption tower tail gas (containing trace HCl) in the mixed gas is discharged from the top of the tower.

[0076] Step 5) The HF absorption tower tail gas discharged from the top of the HF absorption tower in Step 3) and the HCl absorption tower tail gas discharged from the top of the HCl absorption tower in Step 4) are merged and sent to the bottom of the mixed gas absorption tower, and contact countercurrently with the demineralized water at the top of the mixed gas absorption tower and are absorbed. The total amount of the HF absorption tower tail gas and the HCl absorption tower tail gas and the mass ratio of water is 1:10. The generated mixed acid solution is pressurized by the mixed gas absorption tower reflux pump and 80 wt% is sent to the top for reflux absorption, and 20 wt% is sent out of the battery limit as mixed acid product. The unabsorbed N2 in the mixed gas is discharged from the top of the tower.

[0077] Through the above embodiments, three products can be continuously obtained, namely HCl product, HF product and mixed acid product solution.

[0078] Among them, the content of HF in the HF product is 30.5 wt%, and the content of HCl is 0.12 wt%;

[0079] The content of HCl in the HCl product is 29.7 wt%; the content of HF is 0.13 wt%;

[0080] The content of HF in the mixed acid product is 11.3 wt%, and the content of HCl is 11.7 wt%.

[0081] The recovery rate of HF in the tail gas is 99.2%, and the recovery rate of HCl is 99.0%.

[0082] Example 4

[0083] A continuous separation and absorption process for tail gas containing HF and HCl in the preparation of lithium hexafluorophosphate. In this example, the volume fraction of HF in the tail gas containing HF and HCl is 65%, and the volume fraction of HCl is 34%. This example includes the following steps:

[0084] Step 1) Send the tail gas to be treated to the absorption and separation tower. After HF is selectively absorbed by the selective absorbent, it is discharged from the bottom of the tower, and the unabsorbed HCl is discharged from the top of the tower. The absorbent used is 99.5 wt% sulfolane, and the temperature of the absorbent is 30 °C to improve the absorption efficiency of the absorbent in the absorption and separation tower. The mass ratio of the tail gas to be treated to the absorbent is 1:15.

[0085] Step 2) Send the absorbent after absorbing HF in Step 1) to the top of the HF desorption tower through the absorbent discharge pump, and make it flow countercurrently with N2 fed from the bottom of the tower. The HF in the absorbent is desorbed by N2, and the mixed gas exits from the top of the tower. After the desorbed absorbent is cooled by the absorbent cooler, it is sent to the top of the absorption and separation tower for continuous recycling. The temperature of the nitrogen gas is about 90 °C after being heated by the nitrogen gas heater to improve the desorption efficiency of N2 in the HF desorption tower. The mass ratio of nitrogen gas to the absorbent containing HF is 5:2.

[0086] Step 3) Send the HF-containing gas desorbed in Step 2) to the bottom of the HF absorption tower. The HF in the HF-containing gas contacts and is absorbed by the demineralized water flowing countercurrently from the top of the HF absorption tower. The mass ratio of the HF-containing gas to the demineralized water is 2:5. The generated HF solution is pressurized by the HF absorption tower reflux pump and 65 wt% is sent to the top for reflux absorption, and the remaining 35 wt% is sent out of the battery limit as hydrofluoric acid product. The unabsorbed tail gas of the HF absorption tower (containing N2 and trace HF) in the mixed gas is discharged from the top of the tower.

[0087] Step 4) Send the HCl-containing gas discharged from the top of the absorption and separation tower in Step 1) to the bottom of the HCl absorption tower, and make it contact and be absorbed by the demineralized water flowing countercurrently from the top of the HCl absorption tower. The mass ratio of the HCl-containing gas to the demineralized water is 2:5. The generated HCl solution is pressurized by the HCl absorption tower reflux pump and 65 wt% is sent to the top for reflux absorption, and 35 wt% is sent out of the battery limit as hydrochloric acid product. The unabsorbed tail gas of the HCl absorption tower (containing trace HCl) in the mixed gas is discharged from the top of the tower.

[0088] Step (5): After combining the HF absorption tower tail gas discharged from the top of the HF absorption tower in Step (3) and the HCl absorption tower tail gas from the top of the HCl absorption tower in Step (4), it is sent to the bottom of the mixed gas absorption tower and countercurrently contacts with the demineralized water at the top of the mixed gas absorption tower for absorption. The total mass ratio of the HF absorption tower tail gas and the HCl absorption tower tail gas to water is 1:5. The generated mixed acid solution is pressurized by the reflux pump of the mixed gas absorption tower, 55 wt% is sent to the top for reflux absorption, and 45 wt% is sent out of the boundary as the mixed acid product. The unabsorbed N2 in the mixed gas is discharged from the top of the tower.

[0089] Through the above embodiments, three products can be continuously obtained, namely HCl product, HF product, and mixed acid product solution.

[0090] Among them, the content of HF in the HF product is 29.8 wt%, and the content of HCl is 0.1 wt%.

[0091] The content of HCl in the HCl product is 29.2 wt%; the content of HF is 0.2 wt%.

[0092] The content of HF in the mixed acid product is 11.5 wt%, and the content of HCl is 10.8 wt%.

[0093] The recovery rate of HF in the tail gas is 98.8%, and the recovery rate of HCl is 98.6%.

[0094] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all the implementation manners here. And the obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A continuous separation and absorption system for tail gas in the preparation of lithium hexafluorophosphate, characterized in that: include: An absorption and separation tower, used for absorbing the tail gas from the preparation of lithium hexafluorophosphate using a selective absorbent to obtain an absorbent containing HF and a gas containing HCl; An HF desorption tower is used to perform a stripping treatment on the HF-containing absorbent to obtain a HF-containing gas and a desorbed absorbent; An HF absorption tower is used to absorb the HF-containing gas with desalted water to obtain a hydrofluoric acid solution and HF absorption tower tail gas; An HCl absorption tower, used to absorb the HCl-containing gas with desalted water to obtain a hydrochloric acid solution and an HCl absorption tower tail gas; The tail gas absorption tower is used to absorb the tail gas from the HF absorption tower and the tail gas from the HCl absorption tower with water to obtain a mixed acid product.

2. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The selective absorbent is at least one of 98 wt % concentrated sulfuric acid, 99.5 wt % sulfolane or 99.5 wt % ether.

3. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The tail gas for preparing lithium hexafluorophosphate enters the absorption separation tower from the bottom of the absorption separation tower, and countercurrently contacts with the absorbent entering from the top of the absorption separation tower to obtain the HF-containing absorbent and the HCl-containing gas; Preferably, the HF-containing absorbent enters the HF desorption tower from the bottom of the absorption separation tower through a separation tower discharge pump.

4. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The HF-containing absorbent enters the HF desorption tower from the top of the HF desorption tower, and is countercurrently contacted with the nitrogen entering from the bottom of the HF desorption tower to perform stripping, thereby obtaining a HF-containing gas and a desorbed absorbent; Preferably, the desorbed absorbent enters the top of the absorption and separation tower through a desorption tower discharge pump; Preferably, after desorption, the absorbent passes through the desorption tower discharge pump and the absorbent cooler in sequence and enters the top of the absorption separation tower.

5. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The HF-containing gas desorbed in the HF desorption tower is discharged from the top of the HF desorption tower and sent to the bottom of the HF absorption tower, and is countercurrently contacted and absorbed with the water entering the HF absorption tower from the top of the HF absorption tower to obtain a hydrofluoric acid solution and a HF absorption tower tail gas; Preferably, a portion of the hydrofluoric acid solution is output as a hydrofluoric acid product, and the other portion is returned to the middle of the HF absorption tower through a HF absorption tower reflux pump.

6. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The HCl-containing gas generated in the absorption and separation tower is discharged from the top of the absorption and separation tower and then sent to the bottom of the HCl absorption tower, and is countercurrently contacted and absorbed with the water entering the HCl absorption tower from the top of the HCl absorption tower to obtain a hydrochloric acid solution and an HCl absorption tower tail gas; Preferably, a portion of the hydrochloric acid solution is output as a hydrochloric acid product, and the other portion is returned to the middle of the HCl absorption tower through the HCl absorption tower reflux pump.

7. The continuous separation and absorption system for tail gas from the preparation of lithium hexafluorophosphate according to claim 1, characterized in that: The HF absorption tower tail gas discharged from the HF absorption tower and the HCl absorption tower tail gas discharged from the top of the HCl absorption tower are mixed and enter the bottom of the tail gas absorption tower, and are countercurrently contacted and absorbed with the water entering the bottom of the tail gas absorption tower from the top of the tail gas absorption tower to generate a mixed acid solution, and the top gas is discharged when it meets the standards; Preferably, a portion of the mixed acid solution is output as a mixed acid product, and the other portion is returned to the middle of the tail gas absorption tower through a tail gas absorption tower reflux pump.

8. A method for continuous separation and absorption of tail gas for preparing lithium hexafluorophosphate, characterized in that: The steps include: Step 1) In an absorption and separation tower, the tail gas from the preparation of lithium hexafluorophosphate is absorbed by a selective absorbent to obtain an absorbent containing HF and a gas containing HCl; Step 2) sending the HF-containing absorbent to an HF desorption tower, and performing a stripping treatment on the HF-containing absorbent in the HF desorption tower to obtain a HF-containing gas and a desorbed absorbent; Step 3) sending the HF-containing gas to an HF absorption tower, where the HF-containing gas is absorbed by water to obtain a hydrofluoric acid solution and HF absorption tower tail gas; Step 4) sending the HCl-containing gas to an HCl absorption tower, where the HCl-containing gas is absorbed by water to obtain a hydrochloric acid solution and an HCl absorption tower tail gas; Step 5) The tail gas from the HF absorption tower and the tail gas from the HCl absorption tower are absorbed by water to obtain a mixed acid solution.

9. The method for continuous separation and absorption of tail gas for preparing lithium hexafluorophosphate according to claim 8, characterized in that: The mass ratio of tail gas and selective absorbent used to prepare lithium hexafluorophosphate in step 1) is 1-2:10-15; In the step 2), nitrogen is used to strip the HF-containing absorbent, and the mass ratio of nitrogen to the HF-containing absorbent is 5-10:1-2; The mass ratio of the gas containing HF to water in the step 3) is 1-4:10-15; the mass ratio of the gas containing HCl to water in the step 4) is 1-4:10-15; In the step 5), the total amount of the HF absorption tower tail gas and the HCl absorption tower tail gas and the water mass ratio is 1-3:10-15; Preferably, the temperature of the absorbent in step 1) is 10-45°C; The temperature of the nitrogen in step 2) is 70-95°C.

10. The method for continuous separation and absorption of tail gas for preparing lithium hexafluorophosphate according to claim 8, characterized in that: In the step 3), 10-35% of the hydrofluoric acid solution is output as a hydrofluoric acid product, and the other part is returned to the middle of the HF absorption tower through the HF absorption tower reflux pump; In the step 4), 10-35% of the hydrochloric acid solution is output as a hydrochloric acid product, and the other part is returned to the middle of the HCl absorption tower through the HCl absorption tower reflux pump; In the step 5), 10-40% of the mixed acid solution is output as a mixed acid product, and the other part is returned to the middle of the tail gas absorption tower through the tail gas absorption tower reflux pump.

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