Lithium fluoride manufacturing method

Abstract

To provide a novel method of producing lithium fluoride without using hydrofluoric acid.SOLUTION: There is provided a method of producing lithium fluoride by a metathesis reaction of a lithium halide and an alkali metal fluoride.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing lithium fluoride. [Background technology]

[0002] Lithium fluoride is used as a raw material for the electrolyte of lithium-ion batteries and as a bonding material for organic electroluminescence (EL). Single-crystal lithium fluoride is also used for ultraviolet spectroscopy. Known methods for producing lithium fluoride include reacting a water-soluble lithium salt such as lithium carbonate, lithium nitrate, lithium chloride, or lithium sulfate with hydrofluoric acid (see, for example, Patent Documents 1 and 2, and Non-Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2008-156190 [Patent Document 2] Japanese Patent Application Laid-Open No. 2014-189452 [Non-patent literature]

[0004] [Non-Patent Document 1] RS-Mamoory, S. Nadery and NR-Noori,Chemical Engineering Communications 2007,194,1022-1028. Summary of the Invention [Problem to be solved by the invention]

[0005] However, conventional methods for producing lithium fluoride use hydrofluoric acid, which is corrosive to stainless steel, silicon, and other materials, and therefore place limitations on the materials that can be used for the reaction vessel.

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel method for producing lithium fluoride that does not use hydrofluoric acid as a raw material. [Means for solving the problem]

[0007] In order to solve the above problems, the present invention has the following configuration. [1] A method for producing lithium fluoride by metathetic reaction between lithium halide and alkali metal fluoride. [2] The method for producing lithium fluoride according to [1], wherein the metathesis reaction is carried out using a flow reactor. [Effects of the Invention]

[0008] The present invention is a novel method for producing lithium fluoride that does not use hydrofluoric acid as a raw material. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram showing one embodiment of a manufacturing apparatus applicable to the method for manufacturing lithium fluoride of the present invention. [Figure 2] FIG. 1 is a schematic diagram showing another embodiment of a manufacturing apparatus applicable to the method for manufacturing lithium fluoride of the present invention. [Figure 3] 1 is a diagram illustrating an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] The method for producing lithium fluoride of the present invention will be described in detail below with reference to the drawings. Note that the drawings used in the following description may show characteristic portions in an enlarged scale for the sake of convenience in order to make the characteristics easier to understand, and the dimensional ratios of the respective components may not necessarily be the same as those in reality.

[0011] Furthermore, when a numerical range is indicated using "to" in this specification, the numerical values ​​before and after "to" are included as the lower limit and upper limit.

[0012] <Method for producing lithium fluoride> In the method for producing lithium fluoride of the present invention, lithium fluoride is synthesized by a metathesis reaction between a lithium halide and an alkali metal fluoride. The metathesis reaction is shown in the following reaction scheme (1). LiX + AF → LiF + NaX ···(1)

[0013] In formula (1), the halogen element X is selected from Cl, Br, and I. Lithium halides containing Br are highly hygroscopic and difficult to handle. Lithium halides containing I are oxidized in air. For these reasons, Cl is preferred as X, as it is relatively easy to handle during production.

[0014] In formula (1), the alkali metal A is selected from Na, K, Rb, and Cs. When an alkali metal fluoride containing an alkali metal other than Na is selected, the lithium fluoride particles produced are likely to have defects during the metathesis reaction. For these reasons, Na is preferred as the alkali metal A.

[0015] Specifically, the metathesis reaction is carried out by mixing a lithium halide solution and an alkali metal fluoride solution.

[0016] (lithium halide solution) A polar solvent can be used as the solvent for the lithium halide solution, and preferred polar solvents include water and methanol, which have good solubility for lithium halide.

[0017] The concentration of the lithium halide solution is preferably 0.1 M to 1 M. If the concentration is equal to or higher than the lower limit, the lithium fluoride produced does not dissolve in the solution, and solid lithium fluoride can be obtained. If the concentration is equal to or lower than the upper limit, the average particle size and bulk density of the lithium fluoride particles produced are increased, which is preferable. Note that if the average particle size of the lithium fluoride particles produced is increased, the time required for filtration and drying can be shortened, which is preferable.

[0018] (alkali metal fluoride solution) A polar solvent can be used as the solvent for the alkali metal fluoride solution, and preferred polar solvents include water and methanol, which have good solubility for alkali metal fluorides.

[0019] The concentration of the alkali metal fluoride solution is preferably 0.1 M to 1 M. If the concentration is equal to or greater than the lower limit, the lithium fluoride produced does not dissolve in the solution, and solid lithium fluoride can be obtained. If the concentration is equal to or less than the upper limit, the average particle size and bulk density of the lithium fluoride particles produced are increased, which is preferable. Note that if the average particle size of the lithium fluoride particles produced is increased, the time required for filtration and drying can be shortened, which is preferable.

[0020] (Reaction temperature) The reaction temperature for the metathesis reaction is not particularly limited as long as it is within a temperature range in which the solvent of the lithium halide solution or alkali metal fluoride solution used in the reaction does not solidify or vaporize. Such a reaction temperature may be, for example, about 0 to 100°C, and room temperature (15 to 25°C) is preferred.

[0021] (residence time) The metathesis reaction proceeds instantaneously when two solutions, a lithium halide solution and an alkali metal fluoride solution, are mixed. When the metathesis reaction is carried out using a flow reactor (described later), if the residence time in the liquid feed path L3 in the reactor is too short, the solution will be discharged from the reactor before mixing is complete, which is undesirable. Furthermore, if the residence time in the liquid feed path L3 is too long, the device will become large, and the resulting lithium fluoride will accumulate, easily clogging the piping that makes up the flow path, which is undesirable. The residence time in the liquid feed path L3 may be, for example, about 1 to 60 seconds, and preferably 1 to 20 seconds.

[0022] In the method for producing lithium fluoride of the present invention, either a flow reactor or a batch reactor can be used as a synthesis apparatus for the metathesis reaction. Among these, a flow reactor (flow reactor) is preferred because it can produce monodisperse lithium fluoride particles. Note that, in the present invention, monodisperse lithium fluoride particles refer to lithium fluoride particles having a Cv value, which indicates the degree of dispersion of the particles, of 5% or less.

[0023] <Flow reactor> Next, the configuration of a flow reactor as a synthesis apparatus applicable to the method for producing lithium fluoride of the present invention will be described. Figure 1 is a schematic diagram showing the configuration of a flow reactor applicable to the method for producing lithium fluoride of the present invention.

[0024] As shown in FIG. 1, a flow reactor 1 applicable to the method for producing lithium fluoride of the present invention includes a supply path L1 for a lithium halide solution, a supply path L2 for an alkali metal fluoride solution, a mixer 2, a liquid transfer path L3 for a mixed solution, and a recovery container 3.

[0025] The supply path L1 for the lithium halide solution is a flow path that introduces the lithium halide solution into the mixer 2. One end of the supply path L1 is connected to a supply source of the lithium halide solution (not shown), and the other end is connected to the mixer 2. On the other hand, the supply path L2 for the alkali metal fluoride solution is a flow path that introduces the alkali metal fluoride solution into the mixer 2. One end of the supply path L2 is connected to a supply source of the alkali metal fluoride solution (not shown), and the other end is connected to the mixer 2.

[0026] The material of the supply path L1 and the supply path L2 is not particularly limited as long as it is not corroded by the solvents used in the lithium halide solution and the alkali metal fluoride solution, and examples of such materials include silicone rubber.

[0027] A liquid feed pump 4 is located in each of the supply path L1 and the supply path L2. The liquid-sending pump 4 is not particularly limited, and may be a tube pump, a diaphragm pump, a plunger pump, a syringe pump, etc. Among these examples, it is particularly preferable to use a pump that generates pulsation during liquid sending (for example, a tube pump) because this can prevent the lithium fluoride particles that are generated from depositing inside the piping.

[0028] The mixer 2 is a mixing section for the lithium halide solution and the alkali metal fluoride solution. The shape of the mixer 2 is not particularly limited as long as it can mix two solutions. For example, a T-type mixer can be used as such a mixer 2. The material of the mixer 2 is not particularly limited as long as it is not corroded by the solvents used in the lithium halide solution and the alkali metal fluoride solution, and an example of such a material is polypropylene resin. The diameter of the mixer 2 is not particularly limited as long as it is large enough not to be clogged with the lithium fluoride produced. As such a mixer 2, for example, a mixer with an inner diameter of 4 mm and an outer diameter of 6 mm can be used.

[0029] The mixed solution sending path L3 is a flow path through which the mixed solution of the lithium halide solution and the alkali metal fluoride solution flows. The material of the liquid supply path L3 is not particularly limited as long as it is not corroded by the solvents used in the lithium halide solution and the alkali metal fluoride solution, and examples of such materials include silicone rubber.

[0030] The diameter of the liquid transfer path L3 is not particularly limited as long as it is large enough to prevent the lithium fluoride produced from accumulating therein. As such a liquid transfer path L3, for example, a pipe having an inner diameter of 6 mm and an outer diameter of 8 mm can be used.

[0031] The liquid supply path L3 may extend horizontally, but is preferably vertically. By extending the liquid supply path L3 (i.e., the flow direction of the mixed solution) vertically, it is possible to prevent the lithium fluoride particles produced from accumulating in the flow path.

[0032] The liquid sending path L3 may be straight, but is preferably spiral, which can improve the efficiency of stirring the mixed liquid in the flow path.

[0033] The recovery container 3 is a container for recovering the mixed liquid of lithium fluoride and the solvent that is delivered from the liquid delivery path L3. The recovery container 3 is provided with a stirring device 5 for stirring the mixed liquid.

[0034] (Method for producing lithium fluoride using a flow reactor) In the lithium halide solution supply source (not shown) and the alkali metal fluoride solution supply source (not shown), the standing time of each solution from the preparation of the lithium halide solution and the alkali metal fluoride solution until the start of the reaction affects the particle size of the lithium fluoride particles produced. Specifically, the longer the standing time, the larger the particle size of the lithium fluoride particles produced.

[0035] Therefore, when a flow reactor is used, the method for producing lithium fluoride of the present invention preferably involves allowing the lithium halide solution and alkali metal fluoride solution to stand for 40 minutes or longer after preparation before carrying out the metathesis reaction. By allowing a sufficient standing time, the raw material solutions during the reaction become homogeneous, and the difference in particle size between the lithium fluoride particles obtained in the early stage of the reaction and those obtained in the later stage of the reaction becomes small, which is preferable.

[0036] The residence time in the liquid supply path L3 is not particularly limited, but is preferably, for example, 1 to 60 seconds, particularly 1 to 20 seconds, because the metathesis reaction proceeds immediately after the solutions are mixed. A long residence time is undesirable because the resulting lithium fluoride particles tend to remain in the liquid supply path L3, leading to clogging of the reactor. On the other hand, a residence time that is too short is undesirable because the solution is discharged from the liquid supply path L3 before the mixing of the solutions is complete.

[0037] The method for producing lithium fluoride of the present invention uses a flow reactor, which makes it possible to maintain constant the nucleation and growth rates of lithium fluoride crystals, thereby obtaining monodisperse lithium fluoride microparticles.

[0038] <Batch type reactor> Next, the configuration of a batch reaction apparatus as a synthesis apparatus applicable to the method for producing lithium fluoride of the present invention will be described. Figure 2 is a schematic diagram showing the configuration of a batch reaction apparatus applicable to the method for producing lithium fluoride of the present invention.

[0039] As shown in FIG. 2, a batch reaction apparatus 21 applicable to the method for producing lithium fluoride of the present invention includes a lithium halide solution supply source 22, a lithium halide solution supply path L21, and a reaction vessel 23 for storing an alkali metal fluoride solution.

[0040] The lithium halide solution supply source 22 stores the lithium halide solution, which is one of the raw materials. The supply source 22 is not particularly limited as long as it can store the required amount of lithium halide solution. For example, a syringe can be used as such supply source 22.

[0041] The supply path L21 for the lithium halide solution is a flow path for introducing the lithium halide solution into the reaction vessel 23. One end of the supply path L21 is connected to a supply source 22 for the lithium halide solution, and the other end opens into the reaction vessel 23. This allows a required amount of lithium halide solution supplied from the supply source 22 to be dropped into the reaction vessel 23.

[0042] The reaction vessel 23 is a vessel for storing an alkali metal fluoride solution, which is one of the raw materials, and for stirring and mixing the alkali metal fluoride solution with the lithium halide solution dropped from the liquid supply line L21 to cause a metathesis reaction. The recovery vessel 23 is provided with a stirring device 25 for stirring the mixed solution.

[0043] (Method for producing lithium fluoride using a batch reactor) When a batch-type reaction apparatus is used, the method for producing lithium fluoride of the present invention can be carried out by stirring and mixing an alkali metal fluoride solution and a lithium halide solution in the reaction vessel 23. Although the mixing method is not particularly limited, it is preferable to dropwise add the lithium halide solution to the alkali metal fluoride solution stored in the reaction vessel 23. This is to prevent precipitation in the reaction vessel 23, since the solubility of the alkali metal fluoride is smaller than that of the lithium halide.

[0044] In the method for producing lithium fluoride of the present invention, a batch-type reaction apparatus is used, and therefore the concentration of alkali fluoride in the reaction vessel 23 differs between the start and end of the reaction, and therefore the nucleation concentration and the crystal growth rate are variable, and lithium fluoride microparticles having a certain degree of dispersion can be obtained.

[0045] As described above, the method for producing lithium fluoride of the present invention is a novel method that does not use hydrofluoric acid as a raw material. Specifically, the method for producing lithium fluoride of the present invention utilizes a metathesis reaction between a lithium halide and an alkali metal fluoride, which eliminates the need for highly corrosive hydrofluoric acid and increases the freedom in selecting materials for constructing the synthesis apparatus.

[0046] Furthermore, in the method for producing lithium fluoride of the present invention, by using a flow reactor as a synthesis apparatus, it is possible to obtain monodisperse lithium fluoride microparticles compared to when a batch reactor is used.

[0047] The technical scope of the present invention is not limited to the above-described embodiments, but includes designs within the scope that do not deviate from the gist of the present invention. [Example]

[0048] The present invention will be specifically explained below with reference to test examples, but the present invention is not limited to the following description.

[0049] (Test Example 1) Using a flow reactor 1 shown in FIG. 1, lithium fluoride was synthesized according to the following procedure. Specifically, 11.02 g (0.2625 mol) of sodium fluoride and 11.13 g (0.2625 mol) of lithium chloride were added to a 500 ml measuring flask. Pure water was added to the flask to bring the volume up to 500 ml, preparing a 0.525 M sodium fluoride aqueous solution and a 0.525 M lithium chloride aqueous solution. The prepared solutions were irradiated with ultrasound to completely dissolve the solids, and then allowed to stand for 40 minutes. Each solution was transferred to a 500 ml Erlenmeyer flask, and the pump inlet was placed inside the solution. Each solution was pumped at 100 ml / min using a tube pump to carry out the reaction (residence time: 20 seconds). The reaction solution was then discharged into a 1 L beaker, and the contents of the beaker were stirred using a stirrer. After 5 minutes, the liquid was stopped from being pumped, and stirring was continued for 1 hour. The slurry in the beaker was then filtered and washed with 100 ml of pure water. The filtered solid was dried overnight in a vacuum dryer to obtain lithium fluoride as a white powder (yield: 3.13 g, 46%). Table 1 below shows the raw materials, yield, and amount of the product.

[0050] [Relationship between raw material solution concentration and average particle size] The relationship between the concentration of the raw material solution and the average particle size of the lithium fluoride particles produced was confirmed. The synthesis conditions for lithium fluoride were the same as those in Test Example 1, except that 0.465 M and 0.6 M aqueous sodium fluoride solutions and a lithium chloride solution were used. The average particle size of the produced lithium fluoride particles was measured using a scanning electron microscope (manufactured by Hitachi High-Technologies Corporation: trade name "Miniscope TM3000"). Here, FIG. 3 is a diagram showing the relationship between the solution concentration and the average particle size of the lithium fluoride particles produced in the range of 0.46 to 0.60M.

[0051] As shown in Figure 3, it was found that lithium fluoride particles with small particle sizes were obtained when the raw material solution concentration was high, and lithium fluoride particles with large particle sizes were obtained when the concentration was low. It was also shown that the average particle size could be controlled within the range of 1 to 10 μm by using the approximation curve shown in Figure 3.

[0052] (Test Example 2) Using the batch reaction apparatus 21 shown in FIG. 2, lithium fluoride was synthesized according to the following procedure. Specifically, 4.989 g (0.1188 mol) of sodium fluoride and 5.040 g (0.1189 mol) of lithium chloride were added to a 200 mL volumetric flask. Pure water was added to the flask to bring the volume up to 200 mL, preparing a 0.594 M sodium fluoride aqueous solution and a 0.594 M lithium chloride aqueous solution. The resulting solution was irradiated with ultrasound to completely dissolve the solid, and then allowed to stand for 60 minutes. The sodium fluoride solution was transferred to a 500 mL beaker and stirred using a stirrer. The lithium chloride solution was loaded into a syringe and added dropwise to the sodium fluoride solution at 10 mL / min using a syringe pump. The resulting solution was stirred for 1 hour. The slurry in the beaker was then filtered and washed with 100 mL of pure water. The filtered solid was dried overnight in a vacuum dryer, yielding lithium fluoride as a white powder (yield: 2.35 g, 76%). Table 1 below shows the raw materials, yields, and yields.

[0053] (Test Example 3) Using a flow reactor 1 shown in FIG. 1, lithium fluoride was synthesized according to the following procedure. Specifically, 6.899 g (0.1187 mol) of potassium fluoride and 5.040 g (0.1189 mol) of lithium chloride were added to a 200 mL volumetric flask. Pure water was added to the flask to bring the volume up to 200 mL, preparing a 0.594 M potassium fluoride aqueous solution and a 0.594 M lithium chloride aqueous solution. The resulting solution was irradiated with ultrasound to completely dissolve the solid, and then allowed to stand for 60 minutes. The potassium fluoride solution was transferred to a 500 mL beaker and stirred using a stirrer. The lithium chloride solution was loaded into a syringe and added dropwise to the potassium fluoride solution at 10 mL / min using a syringe pump. The resulting solution was stirred for 1 hour. The slurry in the beaker was then filtered and washed with 100 mL of pure water. The filtered solid was dried overnight in a vacuum dryer, yielding lithium fluoride as a white powder (yield: 2.32 g, 75%). Table 1 below shows the raw materials, yields, and yields.

[0054] [Table 1]

[0055] (particle size measurement) Using the lithium fluoride synthesized in Test Examples 1 and 2, 0.25 wt% ethanol solutions were prepared. Specifically, the particles were dispersed by irradiating them with ultrasound using an ultrasonicator (Branson: Sonifier 450) under three conditions: frequency: 20 kHz, time: 0, 2.5, and 5 min. Next, the particle size distribution of the particles contained in each solution was measured using a particle size distribution analyzer (Shimadzu Corporation: particle size distribution analyzer "SALD-7100"). The dispersity of particle size distribution (Cv value = standard deviation / number average particle size) calculated from the measurement results of the particle size distribution measuring instrument is shown in Table 2 below.

[0056] [Table 2]

[0057] As shown in Table 2, it was confirmed that the Cv value, which indicates the degree of dispersion, was smaller in Test Example 1, which used a flow reactor, compared to Test Example 2, which used a batch reactor. In other words, it was confirmed that monodisperse lithium fluoride can be obtained by synthesis using a flow reactor. [Explanation of symbols]

[0058] 1...Flow reactor 2. Mixer 3. Collection container 4...Liquid transfer pump 5,25...Mixing device 21...Batch reactor 22...Source of lithium halide solution 23...Reaction vessel L1, L21...Lithium halide solution supply route L2: Alkali metal fluoride solution supply path L3: Mixed solution delivery path

Claims

[Claim 1] Lithium fluoride is obtained by a metathesis reaction between lithium halide and an alkali metal fluoride, A method for producing lithium fluoride, wherein the metathesis reaction is carried out using a flow reactor.

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