Treatment method of tail gas containing phosphorus pentafluoride and preparation method and device of lithium hexafluorophosphate

Abstract

The invention provides a treatment method of tail gas containing phosphorus pentafluoride and a preparation method and device of lithium hexafluorophosphate. The treatment method of the tail gas containing phosphorus pentafluoride comprises the following steps: 1) carrying out first absorption treatment on the tail gas containing phosphorus pentafluoride by adopting a first absorption liquid containing lithium fluoride to obtain a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride; 2) carrying out first reaction on phosphorus pentachloride and the first mixed gas to obtain second mixed gas containing phosphorus pentafluoride; and 3) carrying out second absorption treatment on the second mixed gas by using a second absorption liquid containing lithium fluoride to obtain a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride. According to the treatment method of the tail gas containing phosphorus pentafluoride, provided by the invention, the content of phosphorus pentafluoride in the tail gas can be reduced, and the resource utilization rate is improved.

Description

Technical Field

[0001] This invention belongs to the field of exhaust gas treatment technology, and particularly relates to a method for treating exhaust gas containing phosphorus pentafluoride, a method for preparing lithium hexafluorophosphate, and an apparatus. Background Technology

[0002] Lithium hexafluorophosphate (LiPF6) is a core electrolyte material in lithium-ion battery electrolytes, and the exhaust gas treatment stage in its synthesis process has a significant impact on production safety, product quality, and environmental compliance. In the hydrogen fluoride solvent method for synthesizing lithium hexafluorophosphate, the exhaust gas typically contains high concentrations of phosphorus pentafluoride (PF5), hydrogen chloride (HCl), and hydrogen fluoride (HF). If these gases are not adequately absorbed and treated, they will not only corrode equipment and endanger the health of operators, but also generate phosphates (PO4) during the subsequent water absorption stage. 3- This leads to excessive phosphorus concentrations in wastewater, increasing environmental risks. Therefore, developing efficient and environmentally friendly tail gas treatment processes is a key aspect of lithium hexafluorophosphate production. Especially given the current stringent environmental policies and the growing demand for resource recycling, the deep removal and resource utilization of PF5 from tail gas has become a critical challenge that the industry urgently needs to address. Summary of the Invention

[0003] The main objective of this invention is to provide a method for treating exhaust gas containing phosphorus pentafluoride. This method can reduce the content of phosphorus pentafluoride in the exhaust gas, thereby reducing the formation of phosphates, effectively avoiding environmental risks, and improving the utilization rate of raw materials.

[0004] The present invention also provides a method for preparing lithium hexafluorophosphate, which can reduce the content of phosphorus pentafluoride in exhaust gas, thereby reducing the formation of phosphate, effectively avoiding environmental risks, and improving the utilization rate of raw materials.

[0005] The present invention also provides a treatment device for exhaust gas containing phosphorus pentafluoride. This treatment device can reduce the content of phosphorus pentafluoride in the exhaust gas, thereby reducing the formation of phosphate, effectively avoiding environmental risks, and improving the utilization rate of raw materials.

[0006] The present invention also provides an apparatus for preparing lithium hexafluorophosphate, which can reduce the content of phosphorus pentafluoride in the exhaust gas, thereby reducing the formation of phosphate, effectively avoiding environmental risks, and improving the utilization rate of raw materials.

[0007] In a first aspect, the present invention provides a method for treating exhaust gas containing phosphorus pentafluoride, comprising the following steps:

[0008] 1) The tail gas containing phosphorus pentafluoride is subjected to a first absorption treatment using a first absorbent containing lithium fluoride to obtain a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride.

[0009] 2) Phosphorus pentachloride is reacted with the first mixed gas to obtain a second mixed gas containing phosphorus pentafluoride;

[0010] 3) The second mixed gas is subjected to a second absorption treatment using a second absorbent containing lithium fluoride to obtain a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride.

[0011] As described above, the exhaust gas also contains hydrogen fluoride and hydrogen chloride.

[0012] And / or, the first mixed gas also contains phosphorus pentafluoride.

[0013] As described above, the process of reacting phosphorus pentachloride with the first mixed gas includes: the phosphorus pentachloride reacting with hydrogen fluoride in the first mixed gas to generate phosphorus pentafluoride and hydrogen chloride gas;

[0014] And / or, the pressure of the second mixed gas is greater than the pressure of the first mixed gas;

[0015] And / or, the pressure of the second mixed gas is 10-15 kPa.

[0016] The processing method described above further includes: crystallizing the first lithium hexafluorophosphate solution to obtain lithium hexafluorophosphate and mother liquor;

[0017] The mother liquor is returned as the second absorbent to participate in the second absorption process to obtain a second lithium hexafluorophosphate solution.

[0018] At least a portion of the second lithium hexafluorophosphate solution participates in the first absorption process as the first absorbent.

[0019] The processing method described above further includes: separating the third mixed gas to obtain hydrogen fluoride and hydrogen chloride.

[0020] Secondly, the present invention provides a method for preparing lithium hexafluorophosphate, comprising the following steps:

[0021] A second reaction is carried out with hydrogen fluoride, phosphorus pentachloride and lithium fluoride to obtain the lithium hexafluorophosphate and tail gas containing phosphorus pentafluoride;

[0022] The exhaust gas containing phosphorus pentafluoride is treated using the method described above.

[0023] The preparation method described above further includes: returning the hydrogen fluoride to participate in the second reaction.

[0024] Thirdly, the present invention provides an apparatus for treating exhaust gas for performing the treatment method described above, comprising an exhaust gas treatment unit, the exhaust gas treatment unit comprising a first absorption unit, a pressurization unit, and a second absorption unit.

[0025] The first absorption unit is used to perform a first absorption treatment on the tail gas containing phosphorus pentafluoride using a first absorbent containing lithium fluoride.

[0026] The pressurization unit is used to perform a first reaction between phosphorus pentachloride and the first mixed gas.

[0027] The second absorption unit is used to perform a second absorption treatment on the second mixed gas using a second absorption liquid containing lithium fluoride;

[0028] The gas outlet of the first absorption unit is connected to the gas inlet of the pressurization unit; the gas outlet of the pressurization unit is connected to the gas inlet of the second absorption unit.

[0029] The processing apparatus described above also includes a crystallization unit;

[0030] The liquid outlet of the first absorption unit is connected to the liquid inlet of the crystallization unit; the liquid outlet of the crystallization unit is connected to the liquid inlet of the second absorption unit.

[0031] The liquid outlet of the second absorption unit is connected to the liquid inlet of the first absorption unit.

[0032] Fourthly, the present invention provides an apparatus for preparing lithium hexafluorophosphate by performing the preparation method described above, comprising a synthesis unit and a tail gas treatment unit; the tail gas treatment unit comprises a first absorption unit, a pressurization unit, and a second absorption unit;

[0033] The synthesis unit is used to carry out a second reaction of hydrogen fluoride, phosphorus pentachloride and lithium fluoride;

[0034] The first absorption unit is used to perform a first absorption treatment on the tail gas containing phosphorus pentafluoride using a first absorbent containing lithium fluoride.

[0035] The pressurization unit is used to perform a first reaction between phosphorus pentachloride and the first mixed gas.

[0036] The second absorption unit is used to perform a second absorption treatment on the second mixed gas using a second absorption liquid containing lithium fluoride;

[0037] The gas outlet of the synthesis unit is connected to the gas inlet of the first absorption unit;

[0038] The gas outlet of the second absorption unit is connected to the gas inlet of the synthesis unit.

[0039] The present invention provides a method for treating tail gas containing phosphorus pentafluoride, which uses phosphorus pentachloride to carry out a first reaction with a first mixed gas. This can increase the pressure of the mixed gas, so that the second absorption treatment can proceed smoothly. While reducing the phosphorus pentafluoride in the tail gas, it can also improve the regeneration efficiency of lithium hexafluorophosphate, since hydrogen fluoride is eventually converted into lithium hexafluorophosphate, thus improving the utilization rate of raw materials. Attached Figure Description

[0040] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0041] Figure 1 The present invention provides a treatment device for exhaust gas containing phosphorus pentafluoride;

[0042] Figure 2 Another tail gas treatment device containing phosphorus pentafluoride is provided by the present invention.

[0043] Figure 3 An apparatus for preparing lithium hexafluorophosphate provided by the present invention;

[0044] Figure 4 Another apparatus for preparing lithium hexafluorophosphate provided by the present invention;

[0045] Figure 5 This is the apparatus for preparing lithium hexafluorophosphate, as shown in Comparative Example 1.

[0046] Explanation of reference numerals in the attached figures:

[0047] 1: First absorption unit; 2: Pressurization unit; 3: Second absorption unit; 4: Crystallization unit; 5: Synthesis unit; 51: First synthesis unit; 52: Second synthesis unit. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0049] In the lithium-ion battery industry chain, lithium hexafluorophosphate (LiPF6) is the mainstream electrolyte material, and the optimization and improvement of its synthesis process is of great significance for ensuring battery performance and production sustainability. Currently, the commonly used hydrogen fluoride solvent method in industry can effectively synthesize LiPF6, but it inevitably generates a large amount of exhaust gas during the reaction process, mainly composed of phosphorus pentafluoride (PF5), hydrogen chloride (HCl), and hydrogen fluoride (HF). These gaseous components are not only highly corrosive and toxic, posing a direct threat to production equipment and operators, but also cause secondary pollution problems during subsequent exhaust gas washing treatment. In particular, PF5 is easily hydrolyzed in water to form phosphate-containing compounds (such as PO4). 3- This leads to an increase in total phosphorus concentration in wastewater, making it difficult to meet increasingly stringent environmental emission standards. Furthermore, PF5 itself is a high-value phosphorus-fluorine compound; direct discharge or simple neutralization not only wastes resources but also increases the cost of waste treatment. Therefore, how to achieve efficient capture and resource conversion of PF5 while ensuring that exhaust gas meets emission standards has become a key technological bottleneck restricting the green manufacturing and industrial upgrading of lithium hexafluorophosphate.

[0050] Lithium hexafluorophosphate (LiPF6) is the core electrolyte in lithium-ion battery electrolytes, and its purity and stability directly affect the overall performance of the battery. Currently, the industrial large-scale production of LiPF6 mainly adopts the hydrogen fluoride solvent method. This process typically involves first reacting phosphorus pentachloride (PCl5) with anhydrous hydrogen fluoride (AHF) to produce phosphorus pentafluoride (PF5) and hydrogen chloride (HCl). Then, PF5 gas is passed into a hydrogen fluoride solution containing dissolved lithium fluoride (LiF) to carry out the reaction, ultimately synthesizing LiPF6.

[0051] However, this synthesis process presents significant challenges in tail gas treatment. To ensure complete LiF reaction, excessive PF5 gas must be introduced into the synthesis reactor during production. This results in the tail gas emitted from the synthesis process being a complex mixture containing high concentrations of unreacted PF5, as well as byproducts HCl and AHF. These components are highly corrosive and toxic, posing a threat to production equipment and personnel safety. Improper handling could lead to serious environmental problems.

[0052] In existing technologies, an absorption vessel containing lithium fluoride (LiF) solution is commonly used to treat the aforementioned tail gas, aiming to purify the tail gas through the reaction of LiF with PF5. However, this single absorption process has significant limitations: First, the LiF in the absorption vessel is continuously consumed during the reaction, and its absorption capacity decreases continuously, making it difficult to ensure the continuous and complete removal of PF5 from the tail gas, resulting in a still high residual amount of PF5 in the outlet gas; second, the entire process system has an inherent pressure drop, forming a progressively decreasing pressure gradient from the PF5 generator (20-30 kPa) to the LiPF6 synthesis vessel (10-15 kPa), and then to the tail gas absorption vessel (approximately 5 kPa). This gradient severely restricts the feasibility of improving the PF5 removal rate by connecting multiple absorption vessels in series, because series connection would further exacerbate the system pressure drop, affecting the normal progress of the upstream reaction and gas delivery.

[0053] Due to the insufficient efficiency of the existing absorption process, a large amount of unabsorbed PF5 ultimately enters the final water scrubbing tower. PF5 readily hydrolyzes upon contact with water, generating phosphorus-containing pollutants (such as phosphate ions PO4). 3- This leads to excessive total phosphorus concentration in wastewater, greatly increasing the difficulty and cost of subsequent wastewater treatment and making it impossible to meet increasingly stringent environmental regulations.

[0054] The inventors of this application discovered through research that if the exhaust gas containing phosphorus pentafluoride is subjected to a first absorption treatment, and then phosphorus pentachloride is used to convert the hydrogen fluoride in the mixed gas into phosphorus pentafluoride before a second absorption treatment, the content of phosphorus pentafluoride in the exhaust gas can be significantly reduced, thereby reducing the formation of phosphate, effectively avoiding environmental risks, and also improving the utilization rate of raw materials.

[0055] Based on this, in a first aspect, the present invention provides a method for treating exhaust gas containing phosphorus pentafluoride, comprising the following steps:

[0056] 1) The tail gas containing phosphorus pentafluoride is subjected to a first absorption treatment using a first absorbent containing lithium fluoride to obtain a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride.

[0057] 2) Phosphorus pentachloride is reacted with the first mixed gas to produce a second mixed gas containing phosphorus pentafluoride;

[0058] 3) The second mixed gas is subjected to a second absorption treatment using a second absorbent containing lithium fluoride to obtain a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride.

[0059] Specifically, in step 1), during the first absorption treatment, lithium fluoride in the first absorbent reacts with phosphorus pentafluoride in the tail gas to generate lithium hexafluorophosphate, which dissolves in the solvent to obtain a first lithium hexafluorophosphate solution. Because the tail gas containing phosphorus pentafluoride contains hydrogen fluoride, the resulting first mixed gas contains hydrogen fluoride. Furthermore, the first mixed gas also contains hydrogen chloride. The first absorption treatment is a preliminary removal of phosphorus pentafluoride, converting most of the phosphorus pentafluoride in the tail gas into lithium hexafluorophosphate and enriching it in the solution.

[0060] In step 2), phosphorus pentachloride reacts with hydrogen fluoride in the first mixed gas to produce phosphorus pentafluoride and hydrogen chloride. Therefore, the second mixed gas contains phosphorus pentafluoride, including the phosphorus pentafluoride produced in the first reaction and the phosphorus pentafluoride not absorbed in the first absorption process. Since phosphorus pentachloride is a solid, and hydrogen fluoride, as well as the produced phosphorus pentafluoride and hydrogen chloride, are gases, according to the reaction equation: 5HF + PCl5 = 5HCl + PF5, the pressure of the system increases after the first reaction. This allows the first mixed gas to smoothly enter the next stage for the second absorption process.

[0061] In step 3), during the second absorption process, lithium fluoride in the second absorbent reacts with phosphorus pentafluoride in the second mixed gas to generate lithium hexafluorophosphate, which dissolves in the solvent to obtain a second lithium hexafluorophosphate solution. The resulting third mixed gas includes hydrogen fluoride and hydrogen chloride.

[0062] Therefore, the tail gas treatment method containing phosphorus pentafluoride provided by the present invention uses phosphorus pentachloride to carry out a first reaction with a first mixed gas, which can increase the pressure of the mixed gas, so that the second absorption treatment can proceed smoothly. While reducing phosphorus pentafluoride in the tail gas, it can improve the regeneration efficiency of lithium hexafluorophosphate, because hydrogen fluoride is eventually converted into lithium hexafluorophosphate, the raw material utilization rate is improved, and the formation of phosphate can be reduced, effectively avoiding environmental risks.

[0063] In some embodiments of the present invention, the exhaust gas also contains hydrogen fluoride and hydrogen chloride.

[0064] In one embodiment, the tail gas containing phosphorus pentafluoride is obtained during the production of lithium hexafluorophosphate using the hydrogen fluoride solvent method. Therefore, the tail gas contains unreacted hydrogen fluoride and generated hydrogen chloride. This portion of hydrogen fluoride is converted into lithium hexafluorophosphate in subsequent treatment, which can improve the regeneration efficiency of lithium hexafluorophosphate.

[0065] In some embodiments, the first mixed gas further contains phosphorus pentafluoride.

[0066] Initially, the concentration of lithium fluoride in the first absorbent is high, allowing for efficient absorption of large amounts of phosphorus pentafluoride in the exhaust gas. As the first absorption process progresses, the lithium fluoride concentration gradually decreases, resulting in incomplete absorption of phosphorus pentafluoride and leaving a small amount of phosphorus pentafluoride in the first mixed gas. This portion of phosphorus pentafluoride will be converted into lithium hexafluorophosphate in the subsequent second absorption process, further improving the regeneration efficiency of lithium hexafluorophosphate.

[0067] In some embodiments of the present invention, the process of carrying out a first reaction with phosphorus pentachloride and a first mixed gas includes: phosphorus pentachloride reacting with hydrogen fluoride in the first mixed gas to generate phosphorus pentafluoride and hydrogen chloride gas.

[0068] Because the first mixed gas contains hydrogen fluoride, phosphorus pentachloride reacts with the hydrogen fluoride in the first mixed gas to generate phosphorus pentafluoride and hydrogen chloride gas, which can further increase the pressure of the system, so that the second absorption treatment can proceed smoothly, thereby further reducing the content of phosphorus pentafluoride in the tail gas and improving the regeneration efficiency of lithium hexafluorophosphate.

[0069] In some embodiments, the pressure of the second mixed gas is greater than that of the first mixed gas, which allows the second absorption process to proceed smoothly, thereby further reducing the content of phosphorus pentafluoride in the exhaust gas and improving the regeneration efficiency of lithium hexafluorophosphate.

[0070] In some embodiments, the pressure of the second mixed gas is 10-15 kPa, for example, it can be a range of 10 kPa, 11 kPa, 12 kPa, 13 kPa, 14 kPa, 15 kPa, or any combination thereof. The pressure of the second mixed gas within the above range allows it to be higher than the pressure of the first mixed gas (approximately 5 kPa), facilitating the smooth operation of the second absorption process and further reducing the phosphorus pentafluoride content in the exhaust gas, thereby improving the regeneration efficiency of lithium hexafluorophosphate.

[0071] In some embodiments of the present invention, the method further includes: crystallizing the first lithium hexafluorophosphate solution to obtain lithium hexafluorophosphate and mother liquor; returning the mother liquor as a second absorbent to participate in the second absorption process to obtain a second lithium hexafluorophosphate solution; and at least a portion of the second lithium hexafluorophosphate solution participating in the first absorption process as a first absorbent.

[0072] The mother liquor (which still contains uncrystallized lithium hexafluorophosphate and excess lithium fluoride) generated after the first lithium hexafluorophosphate solution crystallizes can be reused as the second absorbent, which can reduce the consumption of lithium fluoride.

[0073] Part of the second lithium hexafluorophosphate solution is returned as the first absorbent, realizing a closed-loop flow of the absorbent, avoiding the discharge of the absorbent as waste liquid, reducing wastewater treatment costs, and making full use of the residual lithium fluoride and lithium hexafluorophosphate in the solution (as a medium to improve absorption efficiency).

[0074] The lithium hexafluorophosphate generated in the first absorbent is crystallized to obtain the product, while the uncrystallized lithium hexafluorophosphate enters the second absorption process with the mother liquor, where it is enriched together with the second lithium hexafluorophosphate. It is then recycled back to the first absorption process, which can reduce the loss of product in solution and significantly improve the overall yield.

[0075] During the cycle, the concentration of lithium hexafluorophosphate in the solution accumulates through repeated absorption, resulting in a higher purity product during crystallization (impurities are gradually diluted or separated during the cycle), thus reducing the energy and reagent consumption for subsequent purification.

[0076] In some embodiments of the present invention, the third mixed gas is further separated to obtain hydrogen fluoride and hydrogen chloride.

[0077] The separated hydrogen chloride has a high purity and can be recycled as a byproduct. The separated hydrogen fluoride can be recycled back to the production system.

[0078] Secondly, the present invention provides a method for preparing lithium hexafluorophosphate, comprising the following steps:

[0079] A second reaction is carried out with hydrogen fluoride, phosphorus pentachloride and lithium fluoride to obtain lithium hexafluorophosphate and tail gas containing phosphorus pentafluoride;

[0080] The exhaust gas containing phosphorus pentafluoride was treated using the method described above.

[0081] Specifically, hydrogen fluoride and phosphorus pentachloride first react to produce phosphorus pentafluoride and hydrogen chloride. Then, phosphorus pentafluoride reacts with lithium fluoride to produce lithium hexafluorophosphate, while simultaneously producing tail gas containing phosphorus pentafluoride.

[0082] Using the treatment method for phosphorus pentafluoride-containing tail gas provided in the first aspect to treat the tail gas containing phosphorus pentafluoride can reduce the phosphorus pentafluoride content in the tail gas while improving the regeneration efficiency of lithium hexafluorophosphate. Since hydrogen fluoride is ultimately converted into lithium hexafluorophosphate, the utilization rate of raw materials is improved, and the formation of phosphate can be reduced, effectively avoiding environmental risks.

[0083] In some embodiments of the present invention, the method further includes returning hydrogen fluoride to participate in a second reaction.

[0084] In this invention, the hydrogen fluoride obtained from separating the third mixed gas is returned to participate in the second reaction, thereby converting the fluorine resources that might otherwise be wasted back into components of the target product, significantly reducing raw material costs and improving raw material utilization.

[0085] Thirdly, the present invention provides an apparatus for treating exhaust gas for performing the treatment method described above, such as... Figure 1As shown, the device includes an exhaust gas treatment unit, which comprises a first absorption unit 1, a pressurization unit 2, and a second absorption unit 3. The first absorption unit 1 is used to perform a first absorption treatment on the exhaust gas containing phosphorus pentafluoride using a first absorbent containing lithium fluoride. The pressurization unit 2 is used to perform a first reaction with phosphorus pentachloride and a first mixed gas. The second absorption unit 3 is used to perform a second absorption treatment on a second mixed gas using a second absorbent containing lithium fluoride. The gas outlet of the first absorption unit 1 is connected to the gas inlet of the pressurization unit 2. The gas outlet of the pressurization unit 2 is connected to the gas inlet of the second absorption unit 3.

[0086] Specifically, the exhaust gas treatment unit can be the aforementioned treatment device for exhaust gas containing phosphorus pentafluoride.

[0087] Specifically, the tail gas containing phosphorus pentafluoride is subjected to a first absorption treatment in the first absorption unit 1 by a first absorbent containing lithium fluoride, yielding a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride. The first mixed gas exits from the gas outlet of the first absorption unit 1 and enters the pressurization unit 2 through the gas inlet. In the pressurization unit 2, phosphorus pentachloride reacts with the hydrogen fluoride in the first mixed gas to yield a second mixed gas containing phosphorus pentafluoride and hydrogen chloride. The second mixed gas exits from the gas outlet of the pressurization unit 2 and enters the second absorption unit 3 through the gas inlet. In the second absorption unit 3, a second absorbent containing lithium fluoride performs a second absorption treatment on the phosphorus pentafluoride in the second mixed gas, yielding a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride. The third mixed gas is separated to obtain hydrogen fluoride and hydrogen chloride. The hydrogen chloride has high purity and can be recycled as a byproduct.

[0088] The device for treating exhaust gas containing phosphorus pentafluoride provided by this invention involves a first reaction in the pressurization unit 2, where phosphorus pentachloride reacts with hydrogen fluoride in the first mixed gas to obtain a second mixed gas containing phosphorus pentafluoride. This increases the pressure of the mixed gas, allowing the second absorption treatment to proceed smoothly. While reducing the phosphorus pentafluoride in the exhaust gas, it also improves the regeneration efficiency of lithium hexafluorophosphate, as hydrogen fluoride is ultimately converted into lithium hexafluorophosphate. This improves the utilization rate of raw materials and reduces the formation of phosphates, effectively mitigating environmental risks.

[0089] In some embodiments of the present invention, such as Figure 2 As shown, it also includes a crystallization unit 4; the liquid outlet of the first absorption unit 1 is connected to the liquid inlet of the crystallization unit 4; the liquid outlet of the crystallization unit 4 is connected to the liquid inlet of the second absorption unit 3; and the liquid outlet of the second absorption unit 3 is connected to the liquid inlet of the first absorption unit 1.

[0090] In this invention, a first lithium hexafluorophosphate solution is output from the liquid outlet of the first absorption unit 1, enters the crystallization unit 4 through the liquid inlet of the crystallization unit 4 for crystallization treatment, and obtains lithium hexafluorophosphate and mother liquor. The mother liquor is output from the liquid outlet of the crystallization unit 4, enters the second absorption unit 3 through the liquid inlet of the second absorption unit 3, and returns as the second absorbent to participate in the second absorption treatment, obtaining a second lithium hexafluorophosphate solution. At least a portion of the second lithium hexafluorophosphate solution is output from the liquid outlet of the second absorption unit 3, enters the first absorption unit 1 through the liquid inlet of the first absorption unit 1, and participates in the first absorption treatment as the first absorbent.

[0091] The lithium hexafluorophosphate generated in the first absorption solution is crystallized to obtain the product, while the uncrystallized lithium hexafluorophosphate enters the second absorption process with the mother liquor, where it is enriched together with the second lithium hexafluorophosphate. This is then recycled back to the first absorption process, reducing product loss in solution and significantly improving the overall yield. During the recycling process, the concentration of lithium hexafluorophosphate in the solution accumulates through multiple absorptions, resulting in a higher purity product during crystallization (impurities are gradually diluted or separated during the cycle), reducing energy and reagent consumption in subsequent purification.

[0092] Fourthly, the present invention provides an apparatus for preparing lithium hexafluorophosphate by performing the preparation method described above, such as... Figure 3 As shown, the system includes a synthesis unit 5 and a tail gas treatment unit. The tail gas treatment unit includes a first absorption unit 1, a pressurization unit 2, and a second absorption unit 3. The synthesis unit 5 is used to carry out a second reaction of hydrogen fluoride, phosphorus pentachloride, and lithium fluoride. The first absorption unit 1 is used to perform a first absorption treatment on the tail gas containing phosphorus pentafluoride using a first absorbent containing lithium fluoride. The pressurization unit 2 is used to carry out a first reaction of phosphorus pentachloride with a first mixed gas. The second absorption unit 3 is used to perform a second absorption treatment on a second mixed gas using a second absorbent containing lithium fluoride. The gas outlet of the synthesis unit 5 is connected to the gas inlet of the first absorption unit 1. The gas outlet of the second absorption unit 3 is connected to the gas inlet of the synthesis unit 5.

[0093] In one embodiment, hydrogen fluoride, phosphorus pentachloride, and lithium fluoride undergo a second reaction in synthesis unit 5 to obtain lithium hexafluorophosphate and a tail gas containing phosphorus pentafluoride. The tail gas containing phosphorus pentafluoride is output from the gas outlet of synthesis unit 5 and enters the first absorption unit 1 through the gas inlet of the first absorption unit 1. The tail gas containing phosphorus pentafluoride is subjected to a first absorption treatment in the first absorption unit 1 by a first absorbent containing lithium fluoride to obtain a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride. The first mixed gas exits from the gas outlet of the first absorption unit 1 and enters the pressurization unit 2 through the gas inlet. In the pressurization unit 2, phosphorus pentachloride reacts with hydrogen fluoride in the first mixed gas to produce a second mixed gas containing phosphorus pentafluoride and hydrogen chloride. The second mixed gas exits from the gas outlet of the pressurization unit 2 and enters the second absorption unit 3 through the gas inlet. In the second absorption unit 3, a second absorbent containing lithium fluoride performs a second absorption treatment on the phosphorus pentafluoride in the second mixed gas to produce a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride. The third mixed gas is separated to obtain hydrogen fluoride and hydrogen chloride. The hydrogen fluoride exits from the gas outlet of the second absorption unit 3 and enters the synthesis unit 5 through the gas inlet to participate in a second reaction.

[0094] In another implementation, such as Figure 4 As shown, the synthesis unit 5 includes a first synthesis unit 51 and a second synthesis unit 52. The gas outlet of the first synthesis unit 51 is connected to the gas inlet of the second synthesis unit 52. The gas outlet of the second synthesis unit 52 is connected to the gas inlet of the first absorption unit 1. The gas outlet of the second absorption unit 3 is connected to the gas inlet of the first synthesis unit 51.

[0095] Hydrogen fluoride and phosphorus pentachloride react in the first synthesis unit 51 to produce phosphorus pentafluoride and hydrogen chloride. Phosphorus pentafluoride exits from the gas outlet of the first synthesis unit 51 and enters the second synthesis unit 52 through the gas inlet, where it reacts with lithium fluoride to produce lithium hexafluorophosphate and a tail gas containing phosphorus pentafluoride. The tail gas containing phosphorus pentafluoride exits from the gas outlet of the second synthesis unit 52 and enters the first absorption unit 1 through the gas inlet for first absorption treatment. Hydrogen fluoride exits from the gas outlet of the second absorption unit 3 and enters the first synthesis unit 51 through the gas inlet to participate in the second reaction.

[0096] The technical solution of the present invention will be further described below with reference to specific embodiments.

[0097] Example 1

[0098] The apparatus in this embodiment is a lithium hexafluorophosphate preparation apparatus, such as... Figure 4As shown, it includes a first absorption unit 1 (first absorption tower); a pressurization unit 2 (pressurization vessel); a second absorption unit 3 (second absorption tower); a crystallization unit 4 (crystallization vessel); a first synthesis unit 51 (first reaction vessel); and a second synthesis unit 52 (second reaction vessel).

[0099] Specifically, the gas outlet of the first synthesis unit 51 is connected to the gas inlet of the second synthesis unit 52, and the gas outlet of the second synthesis unit 52 is connected to the gas inlet of the first absorption unit 1; the gas outlet of the first absorption unit 1 is connected to the gas inlet of the pressurization unit 2; the gas outlet of the pressurization unit 2 is connected to the gas inlet of the second absorption unit 3; the gas outlet of the second absorption unit 3 is connected to the gas inlet of the first synthesis unit 51; the liquid outlet of the first absorption unit 1 is connected to the liquid inlet of the crystallization unit 4; the liquid outlet of the crystallization unit 4 is connected to the liquid inlet of the second absorption unit 3; and the liquid outlet of the second absorption unit 3 is connected to the liquid inlet of the first absorption unit 1.

[0100] Specifically, hydrogen fluoride and phosphorus pentachloride react in the first synthesis unit 51 to produce phosphorus pentafluoride and hydrogen chloride, and also include unreacted hydrogen fluoride. The molar ratio of phosphorus pentafluoride to hydrogen chloride is 1:5, and the molar ratio of hydrogen fluoride to hydrogen chloride is 1:3. Phosphorus pentafluoride is output from the gas outlet of the first synthesis unit 51 and enters the second synthesis unit 52 through the gas inlet of the second synthesis unit 52, where it reacts with lithium fluoride to produce lithium hexafluorophosphate and tail gas containing phosphorus pentafluoride (the conversion rate of phosphorus pentafluoride is 60%). The tail gas containing phosphorus pentafluoride is output from the gas outlet of the second synthesis unit 52, enters the first absorption unit 1 through the gas inlet, and undergoes a first absorption treatment with a first absorbent containing lithium fluoride, yielding a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride (phosphorus pentafluoride conversion rate 70%). The first mixed gas is output from the gas outlet of the first absorption unit 1, enters the pressurization unit 2 through the gas inlet, and undergoes a first reaction with the hydrogen fluoride in the first mixed gas, yielding a second mixed gas containing phosphorus pentafluoride and hydrogen chloride. The second mixed gas is output from the gas outlet of the pressurization unit 2, enters the second absorption unit 3 through the gas inlet, and undergoes a second absorption treatment with a second absorbent containing lithium fluoride, yielding a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride (phosphorus pentafluoride conversion rate 80%). The third mixed gas is then separated to obtain hydrogen fluoride and hydrogen chloride. Hydrogen chloride has high purity and can be recycled as a byproduct. Hydrogen fluoride is output from the gas outlet of the second absorption unit 3 and enters the first synthesis unit 51 through the gas inlet to participate in the second reaction.

[0101] The first lithium hexafluorophosphate solution is output from the liquid outlet of the first absorption unit 1, enters the crystallization unit 4 through the liquid inlet of the crystallization unit 4 for crystallization treatment, and obtains lithium hexafluorophosphate and mother liquor. The mother liquor is output from the liquid outlet of the crystallization unit 4, enters the second absorption unit 3 through the liquid inlet of the second absorption unit 3, and is returned as the second absorbent to participate in the second absorption treatment, obtaining the second lithium hexafluorophosphate solution. At least a portion of the second lithium hexafluorophosphate solution is output from the liquid outlet of the second absorption unit 3, enters the first absorption unit 1 through the liquid inlet of the first absorption unit 1, and participates in the first absorption treatment as the first absorbent.

[0102] Ultimately, the molar concentration of phosphorus pentafluoride in the third gas mixture is 1%.

[0103] Comparative Example 1

[0104] The preparation method and apparatus for lithium hexafluorophosphate in Comparative Example 1 and Example 1 are basically the same, except that, for example... Figure 5 As shown, excluding pressurization unit 2, the first reaction between phosphorus pentachloride and hydrogen fluoride in the first mixed gas was not carried out. Ultimately, the molar concentration of phosphorus pentafluoride in the third mixed gas is 1.6%.

[0105] Compared to Comparative Example 1, the molar concentration of phosphorus pentafluoride in Example 1 decreased by 37.5%.

[0106] Compared with the comparative example, the tail gas treatment method containing phosphorus pentafluoride provided by the present invention uses phosphorus pentachloride to carry out a first reaction with a first mixed gas, which can increase the pressure of the mixed gas, so that the second absorption treatment can proceed smoothly. While reducing phosphorus pentafluoride in the tail gas, it can improve the regeneration efficiency of lithium hexafluorophosphate, because hydrogen fluoride is eventually converted into lithium hexafluorophosphate, thus improving the utilization rate of raw materials.

[0107] Finally, it should be noted that other embodiments of the invention will readily occur to those skilled in the art upon consideration of the specification and practice of the invention disclosed herein. This invention is intended to cover any variations, uses, or adaptations of the invention that follow the general principles of the invention and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of the invention is limited only by the appended claims.

Claims

1. A method for treating a phosphorus pentafluoride-containing tail gas, characterized by, The method comprises the following steps: 1) using a first absorption solution containing lithium fluoride to perform first absorption treatment on the tail gas containing phosphorus pentafluoride, to obtain a first lithium hexafluorophosphate solution and a first mixed gas containing hydrogen fluoride; 2) using phosphorus pentachloride to perform first reaction with the first mixed gas, to obtain a second mixed gas containing phosphorus pentafluoride; 3) using a second absorption solution containing lithium fluoride to perform second absorption treatment on the second mixed gas, to obtain a second lithium hexafluorophosphate solution and a third mixed gas containing hydrogen fluoride and hydrogen chloride.

2. The treatment method according to claim 1, characterized in that, The tail gas further contains hydrogen fluoride and hydrogen chloride; And / or, the first mixed gas further contains phosphorus pentafluoride.

3. The treatment method according to claim 1 or 2, characterized in that, The process of using phosphorus pentachloride to perform first reaction with the first mixed gas comprises: the phosphorus pentachloride reacts with the hydrogen fluoride in the first mixed gas to generate phosphorus pentafluoride and hydrogen chloride gas; And / or, the pressure of the second mixed gas is greater than the pressure of the first mixed gas; And / or, the pressure of the second mixed gas is 10-15 kPa.

4. The treatment method according to any one of claims 1 to 3, characterized in that, Further comprising: performing crystallization treatment on the first lithium hexafluorophosphate solution to obtain lithium hexafluorophosphate and a mother liquor; the mother liquor is returned as a second absorption solution to participate in the second absorption treatment to obtain a second lithium hexafluorophosphate solution; at least part of the second lithium hexafluorophosphate solution participates in the first absorption treatment as a first absorption solution.

5. The treatment method according to any one of claims 1 to 4, characterized in that, Further comprising: separating the third mixed gas to obtain hydrogen fluoride and hydrogen chloride.

6. A method for producing lithium hexafluorophosphate, characterized by, The method comprises the following steps: making hydrogen fluoride, phosphorus pentachloride and lithium fluoride perform second reaction to obtain the lithium hexafluorophosphate and the tail gas containing phosphorus pentafluoride; using the treatment method in any one of claims 1-5 to treat the tail gas containing phosphorus pentafluoride.

7. The production method according to claim 6, characterized by, Further comprising: making the hydrogen fluoride return to participate in the second reaction.

8. An apparatus for performing the treatment method of any one of claims 1 to 5, characterized in that The tail gas treatment unit comprises a first absorption unit, a pressurization unit and a second absorption unit; the first absorption unit is used to perform first absorption treatment on the tail gas containing phosphorus pentafluoride using a first absorption solution containing lithium fluoride; the pressurization unit is used to perform first reaction with the first mixed gas using phosphorus pentachloride; the second absorption unit is used to perform second absorption treatment on the second mixed gas using a second absorption solution containing lithium fluoride; the gas outlet of the first absorption unit is in communication with the gas inlet of the pressurization unit; the gas outlet of the pressurization unit is in communication with the gas inlet of the second absorption unit.

9. The processing device of claim 8, wherein, Further comprising a crystallization unit; the liquid outlet of the first absorption unit is in communication with the liquid inlet of the crystallization unit; the liquid outlet of the crystallization unit is in communication with the liquid inlet of the second absorption unit; the liquid outlet of the second absorption unit is in communication with the liquid inlet of the first absorption unit.

10. An apparatus for producing lithium hexafluorophosphate for carrying out the production method according to claim 6 or 7, characterized in that, The method comprises the following steps: the synthesis unit is used to make hydrogen fluoride, phosphorus pentachloride and lithium fluoride perform second reaction; the first absorption unit is used to perform first absorption treatment on the tail gas containing phosphorus pentafluoride using a first absorption solution containing lithium fluoride; the pressurization unit is used to perform first reaction with the first mixed gas using phosphorus pentachloride; The pressurizing unit is used for carrying out a first reaction with phosphorus pentachloride and the first mixed gas; The second absorption unit is used for carrying out a second absorption treatment on the second mixed gas by using a second absorption liquid containing lithium fluoride; The gas outlet of the synthesis unit is communicated with the gas inlet of the first absorption unit; The gas outlet of the second absorption unit is communicated with the gas inlet of the synthesis unit.

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