Method for continuously synthesizing LiFSI by using reaction-extraction technology

Abstract

The invention provides a method for continuously synthesizing LiFSI by utilizing a reaction-extraction technology. The method comprises the following steps: in the process of synthesizing LiFSI through reaction of HFSI.NEt3 and LiOH under the condition of normal temperature, adding an alkane solvent as a first extraction agent, extracting a generated by-product triethylamine into an organic phase, adding halogenated hydrocarbon as a second extraction agent, and removing residual triethylamine and unreacted HFSI.NEt3, thereby obtaining an aqueous solution of LiFSI. The conversion rate of the reaction can reach 99.5%, the hydrolysis rate of the LiFSI is controlled to be 0.1% or below, and the yield of the LiFSI can be greatly improved. According to the invention, LiFSI is synthesized by adopting a reaction-extraction technology, through simple normal-temperature extraction operation, compared with an original reaction-rectification technology, the reaction energy consumption can be reduced, the yield of LiFSI can be ensured, industrialization is easy to realize, and a new process route is provided for efficient synthesis of LiFSI.

Description

Technical Field

[0001] The present invention relates to the fields of energy chemical industry and green chemical industry, and in particular to a method for continuously synthesizing LiFSI by using a reaction-extraction technology. Background Art

[0002] With the rapid development of global industry, the demand for non-renewable energy such as oil and coal is increasing, and energy consumption has become an important topic for human survival and development today. Lithium-ion batteries are widely used in new energy vehicles, small grid energy storage, aerospace, military and industrial fields due to their advantages such as high energy density, high conversion efficiency and long cycle life. Lithium-ion batteries are composed of positive electrode, negative electrode, separator and electrolyte, among which the electrolyte is one of the most important components of lithium-ion batteries. Lithium bis(fluorosulfonyl)imide (LiFSI) is a very promising new electrolyte lithium salt with broad application prospects. Compared with the widely used electrolyte lithium hexafluorophosphate (LiPF6), LiFSI is considered to be the most likely new electrolyte to replace LiPF6 because of its better thermal stability and hydrolysis stability, higher ionic conductivity and lower aluminum corrosion potential. Therefore, the efficient synthesis of LiFSI has attracted more and more attention.

[0003] At present, the synthesis of LiFSI is commonly done by the ammonia-sulfuryl fluoride method, that is, HFSI·NEt3 is produced by the reaction of NH3, SO2F2 and triethylamine (NEt3), and then LiOH is used as a lithium source to exchange HFSI·NEt3 to obtain LiFSI, such as patents CN101980955 and WO2020099527. In addition, there are many other process reports, such as CN111620315A, which discloses the synthesis of bis(fluorosulfonyl)imide salt by the reaction of organic base and SO2F2, and then lithium oxide is added to the above intermediate in the presence of an organic solvent, and LiFSI is obtained after filtration, concentration and crystallization. However, these methods generally have problems such as low product yield, high energy consumption of the reaction process, and long reaction time.

[0004] HFSI·NEt3 undergoes ion exchange with LiOH to generate LiFSI and NEt3, which is the last step in the synthesis of LiFSI by the ammonia-sulfuryl fluoride method (as shown below). This process is a reversible reaction, and timely removal of the generated NEt3 can promote the reaction to the direction of generating LiFSI.

[0005]

[0006] In the existing industrial production of LiFSI, a reaction-distillation method is usually used to remove NEt3 produced in the reaction and improve the reaction conversion rate. The reaction-distillation temperature is usually carried out at a high temperature environment above 50°C, which causes a large amount of hydrolysis of the generated LiFSI and a low product yield.

[0007] To solve the above problems, the present invention proposes to use reaction-extraction coupling technology to continuously synthesize LiFSI, and realize the rapid removal of NEt3 during the reaction process through a low-temperature extraction process, thereby avoiding high temperature-promoted hydrolysis of LiFSI, reducing product loss, and improving the LiFSI yield. Summary of the invention

[0008] The main purpose of the present invention is to provide a method for continuously synthesizing LiFSI using a reaction-extraction technology, which improves the conversion rate of the reaction, reduces the hydrolysis rate of LiFSI, and thus effectively improves the production efficiency and product yield of LiFSI.

[0009] The method proposed by the present invention is as follows: HFSI·NEt3 and LiOH undergo a reversible chemical reaction in an aqueous solution to generate LiFSI and triethylamine (NEt3); an extractant is added to the reaction solution of HFSI·NEt3 and LiOH; the generated NEt3 is transferred to an organic phase through reaction-extraction; the organic phase is separated to obtain an aqueous phase; and LiFSI in the aqueous phase is extracted.

[0010] In a preferred embodiment, the extractant includes a first extractant and a second extractant, and the first extractant is added to the aqueous reaction liquid of HFSI·NEt3 and LiOH for reaction-extraction and liquid separation; the reaction-extraction and liquid separation steps are performed at least once until the total extraction rate is ≥90%, thereby obtaining a first aqueous phase; and then the second extractant is added to the first aqueous phase, and the second aqueous phase is obtained after further extraction and liquid separation, and the obtained second aqueous phase is the LiFSI aqueous solution.

[0011] The method for continuously synthesizing LiFSI using the above reaction-extraction technology comprises the following steps: (1) adding a first extractant to the reaction solution of HFSI·NEt3 and LiOH for reaction-extraction, standing and separating the solution to obtain an aqueous phase and an organic phase, wherein the organic phase contains the by-product NEt3; (2) Repeating the above reaction-extraction and separation steps at least once with the aqueous phase reaction liquid obtained in step (1), and separating the liquids to obtain an aqueous phase and an organic phase after standing; (3) Add a second extractant to the aqueous reaction liquid obtained in step (2), stir at room temperature for 5 to 60 minutes, and separate the liquids to obtain an organic phase and an aqueous phase, wherein the organic phase contains unreacted HFSI·NEt3 and residual NEt3, and the aqueous phase is a LiFSI aqueous solution.

[0012] Furthermore, the HFSI·NEt3 and LiOH reaction solution in step (1) is a mixed solution of HFSI·NEt3 and LiOH aqueous solution; the mass fraction of the LiOH aqueous solution is 5%~11%, and the molar ratio of HFSI·NEt3 to LiOH is 1: (0.9~1.3).

[0013] Furthermore, in steps (1), (2) and (3), the volume ratio of the extractant added each time to the reaction liquid is 1: (0.3-3), and the reaction liquid in steps (2) and (3) is the aqueous phase obtained by separation.

[0014] Furthermore, the first extractant is one of cyclohexane, n-heptane, n-octane, n-hexane, isooctane, dodecane or tridecane.

[0015] Furthermore, the reaction temperature for the reaction-extraction with the first extractant is 0-50°C, and the reaction time is 5-120 min. The preferred reaction temperature is 30°C, and the preferred reaction time is 5-30 min.

[0016] Furthermore, in step (3), the second extractant is a halogenated alkane solvent.

[0017] Furthermore, the second extractant is one of dichloromethane, dichloroethane, dichloropropane or trichloroethane.

[0018] The reaction-extraction process uses a continuous extraction reactor to achieve continuous reaction at room temperature. The continuous extraction reactor includes a continuous extraction tower or a membrane separation continuous extraction device.

[0019] The first extractant is an alkane solvent, including but not limited to cyclohexane, n-heptane, n-octane, n-hexane, isooctane, dodecane, and tridecane. Such solvents have a good dissolving effect on NEt3, poor solubility in HNEt3·FSI and LiFSI, are insoluble in water and easily phase-separated, and the use of alkane solvents as the first extractant can realize the reaction-extraction synthesis of LiFSI.

[0020] The second extractant is a halogenated hydrocarbon solvent, including but not limited to dichloromethane, dichloroethane, dichloropropane, and trichloroethane. Such solvents can effectively transfer almost all free NEt3 to the organic phase, and it will also extract HFSI·NEt3 that does not participate in the reaction into the organic phase. Therefore, using it as the second extractant can completely remove NEt3 from the system to obtain a high-purity LiFSI aqueous solution.

[0021] Compared with the prior art, the advantages of the present invention are: The reaction-extraction technology is used to transfer the by-product NEt3 generated by the reaction to the extractant through a common extractant at room temperature. This not only separates the by-product, but also promotes the conversion rate of the reaction and reduces the hydrolysis rate of LiFSI under alkaline conditions, thereby effectively improving the yield of LiFSI. The process has mild reaction conditions, simple operating procedures, and environmentally friendly processes, and has good application prospects in LiFSI synthesis. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is the reaction formula of HFSI·NEt3 and LiOH.

[0023] Figure 2 FSI at 50℃ - Partial hydrolysis ion chromatogram (HFSI·NEt3: LiOH molar ratio = 1:1, mass fraction of LiOH aqueous solution 9.5%).

[0024] Figure 3 This is a process flow chart of the preferred embodiment of the present invention, that is, adding a first extractant to the reaction solution of HFSI·NEt3 and LiOH, performing three reactions-extractions and separations, and then adding a second extractant to the obtained aqueous phase for extraction, and the aqueous phase obtained after separation is the LiFSI aqueous solution.

[0025] Figure 4 Schematic diagram of the steps for continuous synthesis of LiFSI by multi-stage dual-solvent tandem extraction. DETAILED DESCRIPTION

[0026] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0027] The HFSI·NEt3 in the following examples was purchased from Shidai Sikang New Materials Co., Ltd. with a concentration of 88 wt.% HFSI·NEt3 (12 wt.% water); the LiOH aqueous solution was prepared by adding LiOH·H2O and water to obtain a LiOH aqueous solution with a mass fraction of 9.5 wt.%.

[0028] The ion exchange reaction equilibrium and hydrolysis behavior of HFSI·NEt3 and LiOH were systematically studied. Figure 1As shown in the figure, the reaction is a reversible reaction. NEt3 reacts with LiFSI to generate HFSI·NEt3 and LiOH, consuming LiFSI and thus reducing the yield. Therefore, removing NEt3 from the reaction system is an effective method to promote the reaction to continue in the direction of generating LiFSI. At the same time, the hydrolysis behavior of the lithiation reaction was studied. 10 mL of the reaction solution of HFSI·NEt3 and 9.5 wt.% LiOH aqueous solution was placed in 50 o The reaction was carried out in a constant temperature stirring bath at C, wherein the molar ratio of HFSI·NEt3: LiOH was 1:1, and the mass fraction of LiOH aqueous solution was 9.5%. The ion chromatography analysis results were obtained ( Figure 2 ), indicating that at 50 °C and strong alkaline conditions (pH ≥ 12), the hydrolysis products of LiFSI include FSO2NSO3 2- 、SO3NHSO3 2- and F - In this regard, the present invention proposes a reaction-extraction method to synthesize LiFSI.

[0029] The analysis method in the embodiment is as follows: Quantitative analysis was performed on Qingdao Shenghan's ion chromatograph (IC-D150) and Shimadzu's gas chromatograph (GC-2014). The ion chromatograph used an anion chromatographic column model SH-AC-3 (4×250 mm), with a conductivity detector, KOH aqueous solution as the mobile phase, and a gradient elution method. The specific program settings are as follows: 0~10 min, KOH concentration maintained at 3mmol / L, 10~30 min, KOH concentration maintained at 30 mmol / L, 30~45 min, KOH concentration maintained at 55 mmol / L, 45~55min, KOH concentration maintained at 3 mmol / L. The gas chromatograph used a SH-I-17 (30.0 m× 0.25 mm× 0.25µm) column. The data results were corrected by the external standard method. The extraction rate of triethylamine, the conversion rate of HFSI·NEt3 and the hydrolysis rate of LiFSI were calculated as follows:

[0030]

[0031]

[0032] The following describes the embodiments 2-3 of the present application, and the process is as follows: Figure 3 The embodiments described below are exemplary and are only used to explain the present application, and should not be construed as limiting the present application.

[0033] Example 1 Effect of the number of extraction stages of the first extractant The reaction solution was a mixed solution of 500 mL HFSI·NEt3 and LiOH aqueous solution, the molar ratio of HFSI·NEt3 to LiOH was 1:1, the mass fraction of LiOH aqueous solution was 9.5%, and n-octane was used as the first extractant for one to four extractions. The volume ratio of n-octane added at each stage to the aqueous phase reaction solution was 1:1, and each stage of extraction was carried out at 30 o The reaction was carried out at 40 °C and the extraction was carried out for 20 min. The extraction rate results are shown in Table 1.

[0034] Table 1 Extraction rate of different extraction stages

[0035] The results show that the total extraction rate increases with the increase of the number of extraction stages, but the subsequent single-stage extraction rate decreases. Most of the NEt3 has been removed in the three-stage extraction process. When the extraction stage reaches the fourth stage, the NEt3 content in the aqueous phase is low, and the mass transfer between the two phases is affected by the equilibrium. The extraction rate of the fourth stage extraction is only 0.56%, indicating that the effect of the fourth stage extraction is very limited. In order to avoid the waste of the extractant, the extraction stage is set to three after comprehensive consideration, and the total extraction rate is 93.64%.

[0036] Example 2 Effect of Extraction Agent In the reaction-extraction process, the extractant should have significant characteristics such as chemical stability, excellent product solubility, and insolubility in water and raw materials. After analyzing the solubility of various solvents, alkane solvents were screened as suitable extractants. Furthermore, different alkane solvents were selected for experiments.

[0037] The molar ratio of HFSI·NEt3 to LiOH is 1:1, and the mass fraction of LiOH aqueous solution is 9.5%. Under room temperature, 570 mL of the first extractant is added to the reaction solution of 500 mL HFSI·NEt3 and LiOH aqueous solution, stirred for 20 min, and then allowed to stand for stratification, and the aqueous phase and the organic phase are obtained by separation; 500 mL of the first extractant is continued to be added to the aqueous phase, stirred for 5 min, and then allowed to stand for stratification, and the aqueous phase and the organic phase are obtained by separation; 430 mL of the first extractant is continued to be added to the aqueous phase obtained after separation, stirred for 5 min, and then allowed to stand for stratification, and the aqueous phase and the organic phase are obtained by separation; 350 mL of dichloromethane is added to the aqueous phase, stirred for 10 min, and then allowed to stand for stratification, and the aqueous phase obtained by separation is the LiFSI aqueous solution. The effects of different extractants on the HFSI·NEt3 conversion rate, NEt3 extraction rate and LiFSI hydrolysis rate are analyzed, as shown in Table 2.

[0038] Table 2 HFSI·NEt3 conversion rate, NEt3 extraction rate, LiFSI hydrolysis rate of different first extractants

[0039] The results show that alkane extractants have good extraction performance for NEt3, and water is almost insoluble in alkane solvents, which can effectively avoid introducing new impurities into the LiFSI solution.

[0040] Example 3 Effect of extraction temperature The reaction solution was a mixed solution of 500 mL HFSI·NEt3 and LiOH aqueous solution. The molar ratio of HFSI·NEt3 to LiOH was 1:1, the mass fraction of LiOH aqueous solution was 9.5%, n-octane was used as the extractant, the volume ratio of the extractant added in each stage to the volume of the reaction solution was 1:1, the reaction-extraction time in each stage was 20 min, and the three-stage extraction experiment was carried out at 0~40℃. The HFSI·NEt3 conversion rate, NEt3 extraction rate, and LiFSI hydrolysis rate at different extraction temperatures are shown in Table 3. The results show that with the increase of temperature, the two-phase mass transfer effect is better, the solubility of NEt3 in the organic phase increases, the extraction rate increases, and NEt3 can be more effectively removed from the reaction system, thereby promoting the forward reaction and improving the conversion rate. At 20℃ and 30℃, the hydrolysis rate remained at a low level, but compared with 20℃, the conversion rate at 30℃ was significantly improved. As the temperature increased, the hydrolysis rate of LiFSI in the reaction system increased, but the reaction equilibrium shifted to the right, and the conversion rate increased. Therefore, it is more reasonable to set the reaction temperature to 30°C.

[0041] Table 3 HFSI·NEt3 conversion rate, NEt3 extraction rate, and LiFSI hydrolysis rate at different temperatures

[0042] Example 4 Continuous synthesis of LiFSI by multi-stage dual solvent series extraction The present invention realizes the reaction of continuous synthesis of LiFSI by adopting a continuous extraction reactor. This embodiment adopts a Zaiput membrane separator for multi-stage continuous extraction. The multi-stage continuous extraction experiment was carried out in a modular continuous flow device, which consists of a multi-stage extraction platform (Zaiput flow Technologies, USA), a four-channel independently controlled injection pump and two collection containers. The multi-stage extraction platform has 5 stages of countercurrent extraction, each stage includes a mass transfer tube, a membrane separator, interstage pumping and a pressure sensor. The interstage pumping is regulated by a pressure sensor. All tubings are PFA, 1 / 8-in and 1 / 16-in. The flow channel of the separator is a perfluoropolymer with a volume of 400 μL. Taking into account all tubings and pressure sensors, the total volume of each stage is 2 mL. Figure 4As shown, the reaction liquid and the extractant are simultaneously added to the system from different feed positions through the injection pump for multi-stage countercurrent extraction, and the reaction liquid and the extractant flow in opposite directions; after the first extractant performs primary, secondary, and tertiary reaction-extraction on the reaction liquid, the first extractant and the NEt3 extracted are separated from the system by the membrane separator; the reaction liquid after reaction-extraction continues to flow into the next module, and is separated by the membrane separator after extraction by the second extractant to obtain LiFSI aqueous solution, and the second extractant and the HFSI·NEt3 and NEt3 extracted by it flow out from another outlet. The startup procedure is as follows: 9.5 wt.% LiOH aqueous solution, HFSI·NEt3 aqueous solution and extractant are injected into 50 mL syringes respectively. LiOH aqueous solution and HFSI·NEt3 are mixed in the front pipeline before entering the membrane separator. The flow rate of each phase is controlled by changing the injection pump flow rate. The interstage pump is controlled by a pressure sensor to balance the pressure of each module. The separated phases flow out of the device and enter the corresponding collection container. After 20 min of feeding, water samples were taken from the outlet to detect the concentrations of NEt3 and HFSI·NEt3; the organic phase was taken to analyze the NEt3 content. All experiments were carried out at room temperature.

[0043] Under the conditions that the volume of the extractant is 1.5 times that of the aqueous phase, n-octane is used as the first extractant and dichloromethane is used as the second extractant, the device is used to carry out an experimental study on the three-stage countercurrent extraction of n-octane coupled with the first-stage extraction of dichloromethane. The feed rate of HFSI·NEt3 is set to 0.50 mL / min, the feed rate of 9.5 wt.% LiOH aqueous solution is set to 0.39 mL / min, and the feed rates of n-octane and dichloromethane are both 1.34 mL / min. After feeding for 20 min at room temperature, water samples are taken from the water outlet to detect the concentrations of NEt3 and HFSI·NEt3, and the organic phase is taken to analyze the NEt3 content. It is calculated that the conversion rate obtained by the multi-stage dual solvent continuous reaction-extraction can reach 99.73%, which is close to complete conversion, which is a significant improvement compared with the conversion rate of less than 90% of reactive distillation. At the same time, the hydrolysis rate is only 0.05%, which is also much smaller than the hydrolysis rate of 5% in the current industrial process, proving that the present invention has prospects for industrial application.

[0044] Comparative Example 1 Vacuum distillation comparison experiment 500 ml of the reaction solution of HFSI·NEt3 and LiOH aqueous solution was added to a flask for reduced pressure distillation, wherein the molar ratio of HFSI·NEt3 to LiOH was 1:1, the mass fraction of LiOH aqueous solution was 9.5%, and distilled at 50°C and 20 kPa for 1 h to obtain LiFSI aqueous solution. Analysis showed that the reaction conversion rate was 92% and the hydrolysis rate of LiFSI was 4%.

[0045] The above description is only a preferred specific implementation method of the invention, but the protection scope of the invention is not limited thereto. Any technician familiar with the technical field can make equivalent replacements or changes according to the technical solutions and inventive concepts of the invention within the technical scope disclosed by the invention, which should be covered by the protection scope of the invention.

Claims

1. A method for continuously synthesizing LiFSI using reaction-extraction technology, characterized in that: An extractant is added to the aqueous phase reaction liquid of HFSI·NEt3 and LiOH for reaction-extraction, and an aqueous phase and an organic phase are obtained after separation; the reaction-extraction and separation steps are performed at least once; and the obtained aqueous phase is the LiFSI aqueous solution.

2. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 1, characterized in that: The extractant includes a first extractant and a second extractant, and the specific operation includes the following steps: (1) adding a first extractant to the reaction solution of HFSI·NEt3 and LiOH to carry out reaction-extraction, standing and then separating the liquids to obtain an aqueous phase and an organic phase, wherein the organic phase contains triethylamine as a by-product; (2) Repeating the above reaction-extraction and separation steps at least once with the aqueous phase obtained in step (1), and separating the aqueous phase and the organic phase after standing; (3) Add a second extractant to the aqueous phase obtained in step (2), stir at room temperature for 5 to 60 minutes, stand and separate the liquids to obtain an organic phase and an aqueous phase, wherein the organic phase contains unreacted HFSI·NEt3 and residual triethylamine, and the aqueous phase is a LiFSI aqueous solution.

3. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: The reaction solution of HFSI·NEt3 and LiOH in step (1) is a mixed solution of HFSI·NEt3 and LiOH aqueous solution; the mass fraction of the LiOH aqueous solution is 5%~11%, and the molar ratio of HFSI·NEt3 to LiOH is 1: (0.9~1.3).

4. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: The volume ratio of the extractant added each time to the reaction solution is 1: (0.3~3).

5. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: In step (1), the first extractant is one of cyclohexane, n-heptane, n-octane, n-hexane, isooctane, dodecane or tridecane.

6. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: The reaction temperature of the reaction-extraction with the first extractant is 0-50°C and the reaction time is 5-120 min.

7. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: In step (3), the second extractant is a halogenated alkane solvent.

8. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 7, characterized in that: The second extracting agent is one of dichloromethane, dichloroethane, dichloropropane or trichloroethane.

9. The method for continuously synthesizing LiFSI using reaction-extraction technology according to claim 2, characterized in that: The reaction-extraction process adopts a continuous extraction reactor to carry out continuous reaction at room temperature, and the continuous extraction reactor includes a continuous extraction tower or a membrane separation continuous extraction device.

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