A method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas

Abstract

This invention discloses a method for the deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas. Specifically, the lithium hexafluorophosphate synthesis tail gas, containing hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride, is passed through an Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent to deeply remove hydrogen fluoride and phosphorus pentafluoride from the tail gas. This method can effectively solve the problem of large-scale production of fluorinated HCl as a byproduct in the lithium hexafluorophosphate industry, address the bottleneck issue of waste disposal during industry capacity expansion, and increase the added value of the byproduct HCl.

Description

TECHNICAL FIELD

[0001] The present application relates to a separation method, in particular to a deep separation method of fluorine-containing HCl in lithium hexafluorophosphate synthesis tail gas. BACKGROUND

[0002] Lithium hexafluorophosphate is an important material for new energy battery electrolyte, and the market demand is growing rapidly. The reaction expression of preparing lithium hexafluorophosphate by hydrofluoric acid solvent method is as follows:

[0003] PCl5+5HF+LiF=LiPF6+5HCl

[0004] In the specific production operation process, phosphorus pentachloride and anhydrous hydrogen fluoride are first reacted to generate phosphorus pentafluoride gas, then the anhydrous hydrogen fluoride solution of lithium fluoride is introduced for reaction to obtain a synthesis liquid, and then lithium hexafluorophosphate crystal product is obtained by cooling crystallization, separation and drying. In this process, in order to make the carbon dioxide dimethyl ester insoluble (lithium fluoride) index of the final product qualified, an excess of phosphorus pentafluoride is usually added, and due to the heat released by the reaction, HF volatilizes into the tail gas during the reaction. Therefore, in addition to a large amount of hydrogen chloride, the tail gas of the reaction kettle also contains a large amount of phosphorus pentafluoride and hydrogen fluoride. Through the improvement of the synthesis process of lithium hexafluorophosphate by peers, by controlling the tail gas temperature, using double-kettle series and removing HF by rectification, the amount of phosphorus pentafluoride and hydrogen fluoride in the tail gas can be reduced, but they are still difficult to remove. Under the condition of the relatively optimal process, there are still about 0.8% of HF and 0.2% of PF5 in the tail gas.

[0005] At present, the treatment method of lithium hexafluorophosphate tail gas in the industry mostly adopts the condensation method to remove most of the hydrogen fluoride gas, and then absorbs it in water to prepare fluorine-containing waste hydrochloric acid. However, with the substantial expansion of domestic lithium hexafluorophosphate projects, the treatment of fluorine-containing waste hydrochloric acid will become an important bottleneck restricting the development of the industry in the future, and the treatment method of fluorine-containing waste hydrochloric acid is a waste of a large amount of HCl resources.

[0006] Patent CN114477114A mentions that by rectification separation of hydrogen fluoride, phosphorus pentafluoride and hydrogen chloride mixed gas, the fluorine content in the final tail gas can be reduced to below 20 ppm, but the method involves a large number of equipment, high temperature and large reflux ratio in the rectification process, resulting in huge energy consumption. Patent CN114870589A mentions that by solvent washing, fluorinated salt washing and other methods, phosphorus pentafluoride and hydrogen fluoride in lithium hexafluorophosphate tail gas can be recovered, but the defluorination effect is limited, and high-toxicity organic solvents such as benzene and carbon tetrachloride are used, which is not environmentally friendly.

[0007] To this end, the present patent provides a deep separation method of fluorine-containing HCl in lithium hexafluorophosphate synthesis tail gas, which solves the problem of resource utilization of a large amount of hydrogen chloride in lithium hexafluorophosphate tail gas. SUMMARY

[0008] To address the aforementioned technical problems, this invention proposes a method for the deep separation of fluorinated HCl from the tail gas of lithium hexafluorophosphate synthesis. This method effectively solves the problem of large-scale production of fluorinated HCl as a byproduct in the lithium hexafluorophosphate industry, addresses the bottleneck issue of waste disposal during capacity expansion, and increases the added value of the byproduct HCl.

[0009] The Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent used in this invention has abundant pores and a large specific surface area, providing ample adsorption sites for fluorine-containing gases. Furthermore, by loading Fe metal and sodium fluoride onto hydroxylated multi-walled carbon nanotubes and pretreating them with CO2, this invention can effectively improve the adsorption effect and adsorption capacity. The reason for this may be that CO2 combines with the acidic adsorption sites in the adsorbent, avoiding the occupation of adsorption sites and the destruction of adsorption active sites by high concentrations of hydrogen chloride, thus leaving sufficient adsorption sites for PF5 and HF, which have higher adsorption activity.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] A method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas involves passing the lithium hexafluorophosphate synthesis tail gas containing hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride into an Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent to deeply remove hydrogen fluoride and phosphorus pentafluoride from the tail gas.

[0012] As a preferred embodiment, the lithium hexafluorophosphate synthesis tail gas contains 0.8-1.0% hydrogen fluoride and 0.2-0.5% phosphorus pentafluoride, with the remainder being hydrogen chloride.

[0013] The lithium hexafluorophosphate synthesis tail gas B is obtained from the production tail gas A of lithium hexafluorophosphate prepared by the hydrofluoric acid solvent method. This tail gas, whose main component is hydrogen chloride, is obtained after preliminary reaction absorption to remove phosphorus pentafluoride and distillation to remove hydrogen fluoride. The above preliminary treatment method can refer to any technology known to those skilled in the art or any publicly disclosed technology. However, the above preliminary treatment scheme is not intended to further limit the invention. The invention scheme is also applicable to the treatment of production tail gas directly obtained by the hydrofluoric acid solvent method. Only for the purpose of saving adsorbent, the fluorine-containing gas impurities are first controlled within a certain range using conventional low-energy and low-cost methods. Then, the adsorbent described in this invention is used to further treat the fluorine-containing impurities in the hydrogen chloride to obtain high-purity hydrochloric acid, improving the applicability of the by-products.

[0014] Specifically, the production tail gas obtained directly from the hydrofluoric acid solvent method contains not only hydrogen chloride, but also 2-5% phosphorus pentafluoride and 10-20% hydrogen fluoride. In production, this tail gas is generally treated using the following methods to obtain preliminarily purified hydrogen chloride tail gas:

[0015] First, the exhaust gas is introduced into a hydrofluoric acid solution with a mass concentration of 3-5% LiF for absorption reaction. The reaction temperature is maintained at 10-15℃, the reaction pressure at 1.0-1.3 MPaG, and the reaction time at 3-5 hours. This step can further reduce the PF5 content in the production exhaust gas to 0.2-0.5%.

[0016] Secondly, the tail gas is fed into a distillation column to separate HF. The separation conditions are: 10-15 theoretical plates, pressure 1.5-1.7 MPa, top temperature -20℃ to -15℃, bottom temperature 117-122℃, and the HF content in the gas drawn from the top of the column can be reduced to 0.8-1.0%.

[0017] As a preferred embodiment, the feedstock volume hourly space velocity (VHSV) of the lithium hexafluorophosphate synthesis tail gas introduced into the adsorbent is 100-600 h⁻¹. -1 300-400h preferred -1 .

[0018] As a preferred embodiment, the treatment temperature of the lithium hexafluorophosphate synthesis tail gas introduced into the adsorbent is 20-50℃, preferably 30-35℃, and the pressure is 0.5-1.5 MPaG, preferably 0.8-1.2 MPaG.

[0019] As a preferred embodiment, the tail gas from lithium hexafluorophosphate synthesis is treated with an adsorbent to obtain high-purity HCl gas with a fluorine content of less than 10 ppm, based on the total mass of fluorine impurities in the tail gas.

[0020] As a preferred embodiment, the method for preparing the adsorbent includes the following steps:

[0021] 1) Dissolve hydroxylated multi-walled carbon nanotubes, NaF, and Fe salt in water to obtain a mixed solution, and stir at 40-60℃, preferably 50-55℃ for 30-80 min, preferably 40-50 min;

[0022] 2) The water in the mixed solution is rapidly evaporated under reduced pressure and heating conditions to complete the loading of the active component and obtain the adsorbent precursor;

[0023] 3) The adsorbent precursor was packed into the adsorption column and pretreated with CO2 to prepare Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent.

[0024] As a preferred embodiment, in step 1), the amount of NaF added is 4-10 wt% of the hydroxylated multi-walled carbon nanotubes; the amount of Fe salt added is 0.5-8 wt% of the hydroxylated multi-walled carbon nanotubes, based on the mass of Fe element.

[0025] Preferably, the mass ratio of hydroxylated multi-walled carbon nanotubes to water is (6-14):200.

[0026] As a preferred embodiment, in step 1), the Fe salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate.

[0027] As a preferred embodiment, in step 2), the pressure reduction heating conditions are specifically: the evaporation pressure is 2-20 kPaA, preferably 5-8 kPaA, and the temperature is 70-90℃, preferably 75-80℃.

[0028] As a preferred embodiment, in step 3) CO2 pretreatment, the temperature inside the adsorption column is controlled at 10-30℃, preferably 20-25℃; the CO2 inlet pressure is 0.3-1 MPaG, preferably 0.5-0.7 MPaG, and then the column is allowed to stand under pressure; the CO2 pretreatment time is 1-5 hours, preferably 2-3 hours.

[0029] The method of this invention has advantages such as mild process conditions, high defluorination efficiency, and easy recycling of the adsorbent. Using this method, the fluoride content in fluorinated HCl can be reduced to below 10 ppm. Detailed Implementation

[0030] The present invention will be further illustrated below with specific embodiments. These embodiments are merely illustrative and do not limit the scope of the invention.

[0031] I. The main raw material information in the following embodiments of the present invention is as follows:

[0032] Anhydrous hydrogen fluoride was purchased from Zibo Feixiang Chemical Co., Ltd.; hydroxylated multi-walled carbon nanotubes were purchased from Nanjing Xianfeng Nanomaterials Co., Ltd. (diameter: 1-2 nm, length: 1-3 μm, purity: >90%, hydroxyl content: 3.96%, specific surface area: >380 m²). 2 / g, tap density: 0.14g / cm³ 3 True density: 2.1 g / cm³ 3 Concentrated sulfuric acid and concentrated nitric acid were purchased from Beijing Innocare Technology Co., Ltd.; ferric chloride, ferric nitrate nonahydrate, ferric sulfate, and sodium fluoride were all purchased from Beijing Innocare Technology Co., Ltd.; phosphorus pentachloride was purchased from Admas Reagent Co., Ltd. (>99%).

[0033] Unless otherwise specified, all other raw materials and reagents were purchased through commercial channels.

[0034] II. The following test methods are used in the various examples of the present invention:

[0035] After the exhaust gas is absorbed by alkaline solution, it is sampled and then analyzed by ion chromatography to obtain the contents of chloride ions, fluoride ions and phosphate ions, thereby obtaining the contents of HCl, PF5 and HF in the exhaust gas.

[0036] Ion chromatography analysis method: Ion analysis was performed using a DIONX ICS-1500 ion chromatograph (USA), equipped with an AG14 anion guard column, an AS14 anion separation column, an ULTRA II anion auto-regeneration suppressor, and a DS6 heatable conductivity cell. The eluent was a mixture of 3.5 mmol / L Na₂CO₃ and 1.0 mmol / L NaHCO₃, with a flow rate of 1.2 mL / min, a column temperature of 30 °C, and a conductivity cell temperature of 30 °C.

[0037] To provide the production tail gas A in the following preparation embodiment, lithium hexafluorophosphate was prepared with reference to the scheme in Example 5 of patent CN105600809B, and a production tail gas with a composition of 5% PF5, 10% HF and 85% HCl was obtained simultaneously.

[0038]

Preparation of Example 1

[0039] First, the production tail gas A was passed into a 4% LiF hydrofluoric acid solution for absorption reaction. The reaction temperature was maintained at 15℃, the reaction pressure at 1.3 MPaG, and the reaction time at 4 hours. The gas after the reaction was collected and passed into a distillation column for further separation of HF. The distillation separation conditions were: 15 theoretical plates, pressure at 1.7 MPa, top temperature at -15℃, and bottom temperature at 122℃. The gas collected from the top of the column was analyzed for its composition, which contained 0.82% hydrogen fluoride, 0.24% phosphorus pentafluoride, and 98.94% hydrogen chloride. This gas was used as tail gas B1 for the synthesis of lithium hexafluorophosphate.

[0040]

Preparation of Example 2

[0041] First, the production tail gas A was passed into a 5% LiF hydrofluoric acid solution for absorption reaction. The reaction temperature was maintained at 13℃, the reaction pressure at 1.2 MPaG, and the reaction time at 3 hours. The gas after the reaction was collected and passed into a distillation column for further separation of HF. The distillation separation conditions were: 10 theoretical plates, pressure at 1.5 MPa, top temperature at -20℃, and bottom temperature at 118℃. The gas collected from the top of the column was analyzed for its composition, which contained 0.93% hydrogen fluoride, 0.41% phosphorus pentafluoride, and 98.66% hydrogen chloride. This gas was used as tail gas B2 for lithium hexafluorophosphate synthesis.

[0042] [Preparation Example 3]

[0043] First, the production tail gas A was passed into a 3.5% LiF hydrofluoric acid solution for absorption reaction. The reaction temperature was maintained at 11℃, the reaction pressure at 1.1 MPaG, and the reaction time at 4 hours. The gas after the reaction was collected and passed into a distillation column for further separation of HF. The distillation separation conditions were: 14 theoretical plates, pressure at 1.6 MPa, top temperature at -17℃, and bottom temperature at 120℃. The gas collected from the top of the column was analyzed for its composition, which contained 0.87% hydrogen fluoride, 0.33% phosphorus pentafluoride, and 98.80% hydrogen chloride. This gas was used as tail gas B3 for the synthesis of lithium hexafluorophosphate.

[0044]

Example 1

[0045] (1) Preparation of Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent

[0046] Take 200g of deionized water and place it in a three-necked flask. Add 8.0g of hydroxylated multi-walled carbon nanotubes and stir well. Then add 0.70g of ferric chloride and 0.56g of sodium fluoride. Then heat to 50℃ and stir for 45min. After that, heat the mixture to 80℃ and control the system pressure to 5kpa (absolute pressure) for evaporation until the sample is dry. Then take the dried sample and place it in an oven at 70℃ for 6h to obtain the adsorbent precursor.

[0047] An adsorption column with a specification of DN10mm×600mm was filled with 45mL of adsorbent precursor prepared by the above method, connected to a CO2 cylinder for CO2 pretreatment, and the temperature inside the adsorption column was controlled at 20℃; the CO2 inlet pressure was 0.5MPaG, and then the column was allowed to stand under pressure for 3h. After the pretreatment was completed, the gas inside the adsorption column was released to atmospheric pressure to obtain adsorbent a for the adsorption and removal of fluorine-containing HCl.

[0048] (2) Deep separation of fluorinated HCl

[0049] The tail gas B1 from the synthesis of lithium hexafluorophosphate was driven at a space velocity of 300 h⁻¹ -1 The adsorption column containing adsorbent a prepared by the above method is filled with the gas. The temperature of the adsorption column is controlled at 35°C and the adsorption pressure is 1.2 MPaG. The amount of fluorine gas is detected when the tail gas treatment volume reaches 10L (0°C, 101 kPa standard conditions), and it is <1.0 ppm.

[0050]

Example 2

[0051] (1) Preparation of Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent

[0052] Take 200g of deionized water and place it in a three-necked flask. Add 6.0g of hydroxylated multi-walled carbon nanotubes and stir well. Then add 2.90g of ferric nitrate nonahydrate and 0.40g of sodium fluoride. Then heat to 60℃ and stir for 55min. After that, heat the mixture to 70℃ and control the system pressure at 15kpa (absolute pressure) for evaporation until the sample is dry. Then take the dried sample and place it in an oven at 70℃ for 6h to obtain the adsorbent precursor.

[0053] An adsorption column with a specification of DN10mm×600mm was filled with 45mL of adsorbent precursor prepared by the above method, connected to a CO2 cylinder for CO2 pretreatment, and the temperature inside the adsorption column was controlled at 10℃; the CO2 inlet pressure was 0.3MPaG, and then the column was allowed to stand under pressure for 1h. After the pretreatment was completed, the gas inside the adsorption column was released to atmospheric pressure to obtain adsorbent b for the adsorption and removal of fluorine-containing HCl.

[0054] (2) Deep separation of fluorinated HCl

[0055] The tail gas B2 from the synthesis of lithium hexafluorophosphate was driven at a space velocity of 400 h⁻¹ -1 The adsorption column containing adsorbent b prepared by the above method is filled with the gas. The temperature of the adsorption column is controlled at 50°C and the adsorption pressure is 0.6 MPaG. The amount of fluorine gas is detected when the tail gas treatment volume reaches 10L (0°C, 101 kPa standard conditions), and it is 6.5 ppm.

[0056]

Example 3

[0057] (1) Preparation of Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent

[0058] Take 200g of deionized water and place it in a three-necked flask. Add 14.0g of hydroxylated multi-walled carbon nanotubes and stir well. Then add 0.72g of ferric sulfate and 0.70g of sodium fluoride. Then heat to 40℃ and stir for 30min. After that, heat the mixture to 90℃ and control the system pressure to 2kpa (absolute pressure) for evaporation until the sample is dry. Then take the dried sample and place it in an oven at 70℃ for 6h to obtain the adsorbent precursor.

[0059] An adsorption column with specifications of DN10mm×600mm was filled with 45mL of adsorbent precursor prepared by the above method, connected to a CO2 cylinder for CO2 pretreatment, and the temperature inside the adsorption column was controlled at 25℃; the CO2 inlet pressure was 0.6MPaG, and then the column was allowed to stand under pressure for 4 hours. After the pretreatment was completed, the gas inside the adsorption column was released to atmospheric pressure to obtain adsorbent c for the adsorption and removal of fluorine-containing HCl.

[0060] (2) Deep separation of fluorinated HCl

[0061] The tail gas B3 from the synthesis of lithium hexafluorophosphate was driven at a space velocity of 150 h⁻¹-1 The adsorption column containing adsorbent c prepared by the above method was filled with the gas. The temperature of the adsorption column was controlled at 25°C and the adsorption pressure was 1.3 MPaG. The amount of fluorine gas was measured when the tail gas treatment volume reached 10L (0°C, 101 kPa standard conditions), and it was 4.7 ppm.

[0062]

Example 4

[0063] (1) Preparation of Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent

[0064] Take 200g of deionized water and place it in a three-necked flask. Add 10.0g of hydroxylated multi-walled carbon nanotubes and stir well. Then add 1.23g of ferric nitrate nonahydrate and 0.90g of sodium fluoride. Then heat to 55℃ and stir for 70min. After that, heat the mixture to 85℃ and control the system pressure at 10kpa (absolute pressure) for evaporation until the sample is dry. Then take the dried sample and place it in an oven at 70℃ for 6h to obtain the adsorbent precursor.

[0065] An adsorption column with specifications of DN10mm×600mm was filled with 45mL of adsorbent precursor prepared by the above method, connected to a CO2 cylinder for CO2 pretreatment, and the temperature inside the adsorption column was controlled at 30℃; the CO2 inlet pressure was 0.8MPaG, and then it was allowed to stand under pressure for 5h. After the pretreatment was completed, the gas inside the adsorption column was released to atmospheric pressure to obtain adsorbent d for the adsorption and removal of fluorine-containing HCl.

[0066] (2) Deep separation of fluorinated HCl

[0067] The tail gas B1 from the synthesis of lithium hexafluorophosphate was driven at a space velocity of 200 h⁻¹. -1 The adsorbent d prepared by the above method is introduced into an adsorption column, the temperature of the adsorption column is controlled at 20℃ and the adsorption pressure is 1.0 MPaG, and the amount of fluorine gas is detected when the tail gas treatment volume reaches 10L (0℃, 101kpa standard conditions), which is <1.0ppm.

[0068]

Example 5

[0069] (1) Preparation of Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent

[0070] Take 200g of deionized water and place it in a three-necked flask. Add 12.0g of hydroxylated multi-walled carbon nanotubes and stir well. Then add 0.87g of ferric chloride and 0.52g of sodium fluoride. Then heat to 45℃ and stir for 80min. After that, heat the mixture to 75℃ and control the system pressure at 20kpa (absolute pressure) for evaporation until the sample is dry. Then take the dried sample and place it in an oven at 70℃ for 6h to obtain the adsorbent precursor.

[0071] An adsorption column with a specification of DN10mm×600mm was filled with 45mL of adsorbent precursor prepared by the above method, connected to a CO2 cylinder for CO2 pretreatment, and the temperature inside the adsorption column was controlled at 15℃. The CO2 inlet pressure was 1.0MPaG, and then the column was allowed to stand under pressure for 2 hours. After the pretreatment was completed, the gas inside the adsorption column was released to atmospheric pressure to obtain adsorbent e for the adsorption and removal of fluorine-containing HCl.

[0072] (2) Deep separation of fluorinated HCl

[0073] The tail gas B2 from the synthesis of lithium hexafluorophosphate was driven at a space velocity of 500 h⁻¹ -1 The adsorbent e prepared by the above method is introduced into an adsorption column, the temperature of the adsorption column is controlled at 40℃, the adsorption pressure is 1.5 MPaG, and the amount of fluorine gas is detected when the tail gas treatment volume reaches 10L (0℃, 101 kPa standard conditions), which is 5.6 ppm.

[0074] Comparative Example 1

[0075] The deep separation of fluorinated HCl was performed using essentially the same method as in Example 1, except that the adsorbent packed in the adsorption column was replaced with hydroxylated carbon nanotubes. The amount of fluorinated gas was measured to be 56.9 ppm when the exhaust gas treatment volume reached 10 L (0°C, 101 kPa standard conditions).

[0076] Comparative Example 2

[0077] The modified hydroxylated multi-walled carbon nanotube adsorbent was prepared using essentially the same method as in Example 1, except that ferric chloride was not added to the raw materials. This adsorbent was then used for deep separation of fluorinated HCl according to the method described in Example 1. The amount of fluorinated gas was measured to be 25.8 ppm when the exhaust gas treatment volume reached 10 L (0°C, 101 kPa standard conditions).

[0078] Comparative Example 3

[0079] The modified hydroxylated multi-walled carbon nanotube adsorbent was prepared using essentially the same method as in Example 1, except that sodium fluoride was not added to the raw materials. This adsorbent was then used for deep separation of fluorinated HCl according to the method described in Example 1. The amount of fluorinated gas was measured to be 43.5 ppm when the exhaust gas volume reached 10 L (0°C, 101 kPa standard conditions).

[0080] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and additions without departing from the method of the present invention, and these improvements and additions should also be considered within the scope of protection of the present invention.

Claims

1. A method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas, characterized in that, The tail gas from the synthesis of lithium hexafluorophosphate, which contains hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride, is passed into Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent to deeply remove hydrogen fluoride and phosphorus pentafluoride from the tail gas. The method for preparing the adsorbent includes the following steps: 1) Dissolve hydroxylated multi-walled carbon nanotubes, NaF, and Fe salt in water to obtain a mixed solution, and stir at 40-60℃ for 30-80 min; 2) The water in the mixed solution is rapidly evaporated under reduced pressure and heating conditions to complete the loading of the active component and obtain the adsorbent precursor; 3) The adsorbent precursor was packed into the adsorption column and pretreated with CO2 to prepare Fe / NaF@hydroxylated multi-walled carbon nanotube adsorbent.

2. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 1, characterized in that, The tail gas from the synthesis of lithium hexafluorophosphate contains 0.8-1.0% hydrogen fluoride and 0.2-0.5% phosphorus pentafluoride, with the remainder being hydrogen chloride.

3. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 2, characterized in that, The feedstock volume hourly space velocity (VHSV) of the tail gas from lithium hexafluorophosphate synthesis introduced into the adsorbent is 100-600 h⁻¹. -1 .

4. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 3, characterized in that, The feedstock volume hourly space velocity (VHSV) of the tail gas from lithium hexafluorophosphate synthesis introduced into the adsorbent is 300-400 h⁻¹. -1 .

5. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 3, characterized in that, The treatment temperature of the tail gas from lithium hexafluorophosphate synthesis is 20-50℃, and the pressure is 0.5-1.5 MPaG.

6. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 5, characterized in that, The treatment temperature of the tail gas from lithium hexafluorophosphate synthesis in the adsorbent is 30-35℃, and the pressure is 0.8-1.2 MPaG.

7. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to any one of claims 1-6, characterized in that, After being treated with an adsorbent, the tail gas from the synthesis of lithium hexafluorophosphate yields high-purity HCl gas with a fluorine content of less than 10 ppm, calculated based on the total mass of fluorine impurities in the tail gas.

8. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to any one of claims 1-6, characterized in that, In the preparation method of the adsorbent, step 1) involves dissolving hydroxylated multi-walled carbon nanotubes, NaF, and Fe salt in water to obtain a mixed solution, and then heating it at 50-55°C for 40-50 minutes.

9. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 1, characterized in that, In step 1) of the preparation method of the adsorbent, the amount of NaF added is 4-10 wt% of the hydroxylated multi-walled carbon nanotubes; the amount of Fe salt added is 0.5-8 wt% of the hydroxylated multi-walled carbon nanotubes, based on the mass of Fe element.

10. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 9, characterized in that, The mass ratio of hydroxylated multi-walled carbon nanotubes to water was (6-14):

200.

11. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 9, characterized in that, In step 1) of the preparation method of the adsorbent, the Fe salt is selected from one or more of ferric chloride, ferric nitrate, and ferric sulfate.

12. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 1, characterized in that, In step 2) of the preparation method of the adsorbent, the specific conditions for reduced pressure heating are: evaporation pressure of 2-20 kPaA and temperature of 70-90℃.

13. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 12, characterized in that, In step 2) of the preparation method of the adsorbent, the specific conditions for reduced pressure heating are: evaporation pressure of 5-8 kPaA and temperature of 75-80℃.

14. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 1, characterized in that, In step 3) of the preparation method of the adsorbent, during CO2 pretreatment, the temperature inside the adsorption column is controlled at 10-30℃; the CO2 inlet pressure is 0.3-1 MPaG, and then the column is allowed to stand under pressure; the CO2 pretreatment time is 1-5 h.

15. The method for deep separation of fluorinated HCl from lithium hexafluorophosphate synthesis tail gas according to claim 14, characterized in that, In step 3) of the preparation method of the adsorbent, during CO2 pretreatment, the temperature inside the adsorption column is controlled at 20-25℃; the CO2 inlet pressure is 0.5-0.7 MPaG, and then the column is allowed to stand under pressure for treatment; the CO2 pretreatment time is 2-3 hours.