JP6795809B2 - Sodium manufacturing method - Google Patents

Description

The present invention relates to a method for producing sodium, which produces purified sodium by increasing the sodium concentration in the sodium raw material.

The sodium-sulfur battery is a secondary battery that uses sulfur for the positive electrode, sodium for the negative electrode, and β-alumina for the electrolyte. Sodium-sulfur batteries are attracting attention as batteries for storing electric power, and many are manufactured. Along with this, it is expected that a large amount of used sodium-sulfur batteries will be generated in the future. Therefore, it is required to develop a technique for reusing useful resources such as sodium contained in a used sodium-sulfur battery.

It is conceivable that impurities such as calcium, potassium, and lithium are mixed in the sodium recovered from the used sodium-sulfur battery. Therefore, in order to reuse the sodium recovered from the used sodium-sulfur battery, it is necessary to remove these impurities.

In recent years, as a method for purifying high-purity sodium from impurity-containing sodium, an electrolytic refining method using an electrolytic solution has been proposed (see, for example, Patent Documents 1 to 3).
Patent Document 1 describes an electrolytic purification method in which an impurity-containing sodium is used as an anode and a molten salt composed of an aluminum halide (AlCl ₃ ) and an alkali metal halide (NaCl or KCl) is used as an electrolytic solution.
Further, Patent Document 2 describes an electrolytic refining method in which an impurity-containing sodium is used as an anode and a solution composed of a carbonate-based organic solvent (ethylene carbonate or propylene carbonate) and a sodium salt (NaPF ₆ or the like) is used as an electrolytic solution. ..
Further, in Patent Document 3, a solution containing an impurity-containing sodium as an anode, a sodium salt of a bis (trifluoromethylsulfonyl) imide anion (hereinafter, also referred to as “TFSI”), a tetraethylammonium salt of the TFSI anion, and the like is used as an electrolytic solution. The electrolytic refining method described above is described.

Japanese Unexamined Patent Publication No. 2008-285728 Japanese Unexamined Patent Publication No. 2010-13673 Japanese Unexamined Patent Publication No. 2011-225931

In the techniques described in Patent Documents 1 to 3, high-purity purified sodium is precipitated on the cathode by applying a voltage for a certain period of time. However, it is desired to provide a method for obtaining purified sodium by a lower cost and a simple method.

The present invention has been made in view of such a problem. That is, an object of the present invention is to provide a method for producing sodium, which can obtain purified sodium by a low cost and simple method.

The present invention relates to the following method for producing sodium.
[1] The ionic liquid comprises a step of contacting a sodium raw material containing impurities with an ionic liquid containing sodium ions to increase the purity of sodium in the sodium raw material to obtain purified sodium, and the ionic liquid is bis (trifluoromethanesulfonyl). ) Sodium salt consisting of one or both of imide anion or bis (fluorosulfonyl) imide anion, and tetraethylammonium salt of bis (trifluoromethanesulfonyl) imide anion or bis (fluorosulfonyl) imide anion, tetra A method for producing sodium, which comprises at least one non-metallic salt selected from the group consisting of a butylammonium salt, a 1-ethyl-3-methylimidazole salt, and an N-methyl-N-propylpyrrolidium salt.

[2] The method for producing sodium according to [1], which comprises a step of recovering the purified sodium.
[3] The method for producing sodium according to [1] or [2], which does not include a step of electrolytically purifying the sodium raw material.
[4] The method for producing sodium according to any one of [1] to [3], wherein the sodium raw material is brought into contact with the ionic liquid at 110 ° C. or higher and 170 ° C. or lower.

[5] The method for producing sodium according to any one of [1] to [4], wherein the molar ratio of the sodium salt to the non-metal salt in the ionic liquid is 1: 9 to 3: 7.
[6] The method for producing sodium according to any one of [1] to [5], wherein the non-metal salt is a tetraethylammonium salt of a bis (trifluoromethanesulfonyl) imide anion.
[7] The method for producing sodium according to any one of [1] to [6], wherein the sodium raw material is obtained from a sodium-sulfur battery.

According to the present invention, purified sodium can be produced from a sodium raw material by a simple method at a lower cost than in the conventional technique.

It is a schematic diagram which shows the structure of the sodium production apparatus for carrying out the sodium production method of this invention. 6 is a graph showing the relationship between the concentration of impurities (Ca and K) in the sodium raw material and the reaction time when sodium is produced at 120 ° C. in Example 1. FIG. 5 is a graph showing the relationship between the concentration of impurities (Ca and K) in the sodium raw material and the reaction time when sodium is produced at 160 ° C. in Example 1. 6 is a graph showing the relationship between the concentration of impurities (Ca and K) in the sodium raw material and the reaction time when sodium is produced by the method shown in Example 2.

The method for producing sodium of the present invention relates to a method for obtaining purified sodium by removing impurities from a sodium raw material containing impurities. Specifically, it includes a step of bringing a sodium raw material containing impurities into contact with a specific ionic liquid containing sodium ions to increase the purity of sodium in the sodium raw material and obtain purified sodium. The method may optionally include a step of recovering the purified sodium.

Here, the term "sodium raw material" as used herein means a composition containing sodium as a main component, which contains atoms other than sodium, for example, impurities such as potassium and calcium. Further, the "purified sodium" means a composition containing sodium as a main component, which has a lower content of impurities than the above-mentioned sodium raw material. Further, in the present specification, a solution of a salt containing an organic substance is referred to as an "ionic liquid".

Conventionally, when purifying a sodium raw material, it has been common to use a specific electrolytic solution and electrorefining the sodium raw material as an anode. On the other hand, the present invention has been made by finding that the concentration of sodium in the sodium raw material is increased only by bringing the sodium raw material into contact with a specific ionic liquid containing sodium ions. That is, in the method for producing sodium of the present invention, purified sodium can be obtained without electrolytic refining.

The ionization tendency of calcium, potassium, etc. with respect to the ionic liquid described later is larger than the ionization tendency of sodium with respect to the ionic liquid. Therefore, when the sodium raw material is brought into contact with an ionic liquid described later, impurities such as calcium contained in the sodium raw material become ions (for example, calcium ions) and are eluted into the ionic liquid. On the other hand, sodium in the sodium raw material is hardly dissolved. Further, sodium in the ionic liquid is replaced with calcium or the like to become metallic sodium. Then, the metallic sodium precipitates on the sodium raw material side. Therefore, as the substitution reaction proceeds, the purity of sodium in the sodium raw material gradually increases, and purified sodium having extremely high purity can be obtained.

[About ionic liquids]
The ionic liquids are: 1) a sodium salt consisting of a bis (trifluoromethylsulfonyl) imide (TFSI) anion or a bis (fluorosulfonyl) imide (FSI (hereinafter, simply referred to as "FSI")) anion and a sodium ion, and 2 ) Includes a TFSI anion or a non-metal salt consisting of an FSI anion and a particular non-metal cation.

As for the anion of TFSI and FSI, amide is correct instead of imide based on the IUPAC nomenclature, but "TFSI (bis (trifluoromethanesulfonyl) imide) widely used as a trivial name in this specification ) ”And“ FSI (bis (fluorosulfonyl) imide) ”are used.

As described above, sodium in the sodium salt is easily replaced with calcium or potassium in the sodium raw material. In addition, the sodium salt has a low vapor pressure and is nonflammable. Therefore, when these are used as ionic liquids, the handleability and safety of the ionic liquids are improved. The ionic liquid may contain only one of the sodium salt of the TFSI anion and the sodium salt of the FSI anion, or may contain both.

Here, the sodium salt has a relatively high melting point. Therefore, if only the sodium salt is used as the ionic liquid, it is necessary to raise the temperature at which the sodium raw material and the ionic liquid are brought into contact with each other. However, if the temperature at the time of contact between the sodium raw material and the ionic liquid is excessively raised, the TFSI anion and the FSI anion may be thermally decomposed and react with purified sodium. Therefore, the ionic liquid of the present invention contains a TFSI anion or a non-metal salt composed of an FSI anion and a specific non-metal cation. By including the non-metal salt, the melting point of the ionic liquid can be lowered, and thus it is possible to prevent the TFSI anion and the FSI anion from thermally decomposing and reacting with purified sodium.

Specifically, the non-metal salt is a tetraethylammonium salt, a tetrabutylammonium salt, a 1-ethyl-3-methylimidazole salt, or an N-methyl-N-propylpyrrolidium salt of a TFSI anion or an FSI anion. The ionic liquid may contain only one kind of these non-metal salts, or may contain two or more kinds of these non-metal salts. Depending on the type of TFSI anion or FSI anion, it may react with sodium or may not be mixed with the above sodium salt. On the other hand, the non-metal salt does not react with sodium and is uniformly mixed with the sodium salt. Among the above non-metal salts, a tetraethylammonium salt of a bis (trifluoromethanesulfonyl) imide anion is particularly preferable.

Here, the molar ratio of the sodium salt and the non-metal salt contained in the ionic liquid is particularly as long as the melting point of the ionic liquid is in an appropriate range and the sodium salt and the non-metal salt can be mixed without being separated. Not limited. Specifically, the molar ratio of the sodium salt to the non-metal salt is preferably 1: 9 to 3: 7, and particularly preferably 1: 4.

By setting the molar ratio within the above range, the melting point of the ionic liquid can be set to about 70 to 150 ° C. If the ratio of the non-metal salt to the sodium salt is too small, it becomes difficult to sufficiently lower the melting point of the ionic liquid. On the other hand, if the ratio of the non-metal salt to the sodium salt is too high, the sodium salt and the non-metal salt may separate. Furthermore, if the amount of the sodium salt is excessively small, the above-mentioned substitution reaction is less likely to occur, and the purity of sodium in the sodium raw material is less likely to increase.

Here, when the ionic liquid consists of a combination of a sodium salt of the TFSI anion and a tetraethylammonium salt of the TFSI anion, the molar ratio of these is particularly preferably 1: 4. Also, when the ionic liquid is composed of a combination of a sodium salt of the FSI anion and a tetraethylammonium salt of the TFSI anion, the molar ratio thereof is particularly preferably 1: 4. With such a ratio, the above-mentioned substitution reaction is likely to occur.

[About sodium raw materials]
As described above, the sodium raw material may be a composition containing sodium as a main component, which contains atoms other than sodium, for example, impurities such as potassium and calcium, and the content of impurities and the like is not particularly limited. The content of impurities is preferably 1% by mass with respect to the total amount of the sodium raw material from the viewpoint that the effects of the present invention can be sufficiently obtained.

Further, the type of impurities contained in the sodium raw material is preferably a substance having an ionization tendency toward the above-mentioned ionic liquid larger than the ionization tendency of sodium with respect to the ionic liquid, and such substances include calcium, potassium, lithium and cesium. And so on.

Here, the sodium raw material is preferably obtained from a sodium-sulfur battery. The sodium raw material recovered from the used sodium-sulfur battery usually contains calcium and the like. Then, according to the method for producing sodium of the present invention, purified sodium can be obtained from the sodium raw material.

[Contact between sodium raw material and ionic liquid]
In the method for producing sodium of the present invention, purified sodium is obtained by contacting the above-mentioned sodium raw material with an ionic liquid. The method of bringing the sodium raw material into contact with the ionic liquid is not particularly limited. FIG. 1 shows a schematic view (cross-sectional view) of a sodium production apparatus for carrying out the method for producing sodium of the present invention. The sodium production apparatus 100 of FIG. 1 has a reaction tank 110 for accommodating an ionic liquid 170 and a sodium raw material 180, and a heating unit 130 for adjusting the temperature inside the reaction tank 110. When sodium is produced using the apparatus 100, first, the ionic liquid 170 is contained in the reaction vessel 110, and the sodium raw material 180 is contained on the ionic liquid 170, so that the sodium raw material 180 and the ionic liquid 170 are brought into contact with each other. Let me.

Here, the shape and the like of the reaction tank 110 of the sodium production apparatus 100 is not particularly limited as long as it can accommodate the ionic liquid 170 and the sodium raw material 180. It is appropriately selected according to the amount of sodium to be produced and the like. The material of the reaction tank 110 is not particularly limited as long as it has heat resistance that can withstand heating and does not react with sodium and the ionic liquid 170. For example, as the reaction tank 110, a container made of resin such as polytetrafluoroethylene (PTFE), a container made of alumina ceramics, glass, or the like can be used.

The type of the heating unit 130 is not particularly limited as long as the ionic liquid 170 and the sodium raw material 180 can be heated to a desired temperature. The heating unit 130 may be a heater or the like arranged on the lower surface and / or the side surface of the reaction tank 110.

As shown in FIG. 1, when the sodium raw material 180 containing impurities and the ionic liquid 170 are brought into contact with each other in the reaction vessel 110 and held at a predetermined temperature for a certain period of time, the calcium and potassium contained in the sodium raw material 180 become ions and become ions. It elutes into liquid 170. On the other hand, the sodium salt in the ionic liquid 170 is replaced with calcium, potassium and the like, and precipitates on the sodium raw material 180 side. By this reaction, impurities (calcium and potassium) in the sodium raw material 180 decrease with the passage of time, and the concentration of sodium in the sodium raw material 180 increases with the passage of time. Therefore, after a lapse of a certain period of time, by recovering the sodium (purified sodium) on the ionic liquid 170, sodium having a desired impurity concentration can be obtained.

Here, the temperature of the ionic liquid 170 or the sodium raw material 180 when the ionic liquid 170 and the sodium raw material 180 are brought into contact with each other is not particularly limited as long as the temperature is equal to or higher than the melting point of the ionic liquid 170. Normally, at that temperature, the sodium raw material 180 is also melted into a liquid state. Here, when the temperature of the ionic liquid 170 is high, the diffusion rate of each component in the ionic liquid 170 becomes high, and the substitution reaction between calcium and the like and sodium tends to proceed. That is, it is easy to increase the sodium concentration in the sodium raw material 180 in a short time. On the other hand, if the temperature of the ionic liquid 170 is excessively high, a part of the ionic liquid 170 may be decomposed and the decomposed product may react with the purified sodium. Therefore, from the viewpoint of promoting the substitution reaction between calcium and the like and sodium and preventing side reactions, the temperature of the ionic liquid 170 and the sodium raw material 180 is preferably 110 to 170 ° C, preferably 120 to 170 ° C. More preferred.

The mass ratio of the sodium raw material 180 and the ionic liquid 170 contained in the reaction tank 110 is preferably 1: 3 to 1: 5. When the mass ratio of the sodium raw material 180 and the ionic liquid 170 is within the above range, the impurities in the sodium raw material 170 can be sufficiently replaced with the sodium in the ionic liquid 170, and the purity of the sodium in the obtained purified sodium is high. It will be high enough.

The time for contacting the ionic liquid 170 with the sodium raw material 180 is not particularly limited, but is preferably 15 to 25 hours from the viewpoint of sufficiently causing the above-mentioned substitution reaction.

On the other hand, the method for recovering sodium (purified sodium) on the ionic liquid 170 is not particularly limited, and may be recovered from, for example, a discharge port (not shown) provided on the upper part of the reaction tank 110, or by suction or the like. You may collect it.

As described above, the method for producing sodium of the present invention uses an ionic liquid composed of a mixture of a sodium salt of TFSI or FSI, which is excellent in operability and safety, and a non-metal salt of TFSI or FSI to produce purified sodium. obtain. Therefore, purified sodium can be obtained from a sodium raw material containing impurities more easily and safely than in the conventional technique.

Hereinafter, the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

(Example 1)
In a glove box filled with Ar gas, a sodium salt of TFSI (manufactured by Mitsubishi Materials Corporation (hereinafter, also referred to as "NaTFSI")) and a tetraethylammonium salt of TFSI (hereinafter, also referred to as "tetraethylammonium TFSI") 99.0 %; (Manufactured by Iolitech) was placed in a glass beaker and heated to obtain an ionic liquid A composed of NaTFSI and tetraethylammonium TFSI. The molar ratio of NaTFSI to tetraethylammonium TFSI was 20:80.

Subsequently, 400 g of the above-mentioned ionic liquid A was placed in a glass beaker. Then, 80 g of a sodium raw material (purity 99.95%, manufactured by Aldrich) containing impurities (Ca and K) was added onto the ionic liquid A. Then, the temperature of the ionic liquid was maintained at 120 ° C. or 160 ° C. for 12 hours, and Ca and K in the sodium raw material were subjected to a substitution reaction with Na in the ionic liquid. Sodium on the ionic liquid was collected at regular time intervals and the concentrations of Ca and K in the sodium were quantified. The concentrations of Ca and K were quantified by dissolving the collected sodium in pure water and analyzing the aqueous solution with an ICP emission spectroscopic analyzer.

FIG. 2 shows the relationship between the reaction time when the reaction was carried out at 120 ° C. and the quantified Ca and K concentrations, and the reaction time when the reaction was carried out at 160 ° C. and the quantified Ca and K concentrations. The relationship between the above is shown in FIG.

(Example 2)
In the same manner as above, in a glove box filled with Ar gas, sodium salt of FSI (manufactured by Solvionic (hereinafter, also referred to as "NaFSI")) and tetraethylammonium TFSI (99.0%; Kishida Chemical Co., Ltd.) are mixed. The mixture was placed in a glass beaker and heated to obtain an ionic liquid B composed of NaFSI and tetraethylammonium TFSI. The molar ratio of NaFSI to tetraethylammonium TFSI was 20:80.

Subsequently, 400 g of the above-mentioned ionic liquid B was placed in a glass beaker. Then, 80 g of a sodium raw material (purity 99.95%, manufactured by Aldrich) containing impurities (Ca and K) was added onto the ionic liquid B. Then, the temperature of the ionic liquid was maintained at 160 ° C. for 12 hours, and Ca and K in the sodium raw material were subjected to a substitution reaction with Na in the ionic liquid. Sodium on the ionic liquid was collected at regular time intervals and the concentrations of Ca and K in the sodium were quantified. The concentrations of Ca and K were quantified by purely dissolving the collected sodium and analyzing the aqueous solution with an ICP emission spectrophotometer. The relationship between the reaction time at this time and the quantified Ca and K concentrations is shown in FIG.

(Evaluation)
As shown in FIGS. 2 to 4, the initial sodium raw materials contained 341 ppm of Ca and 118 ppm of K. When the sodium raw material is brought into contact with either the ionic liquid A (mixed solution of NaTFSI and tetraethylammonium TFSI) or the ionic liquid B (mixed solution of NaFSI and tetraethylammonium TFSI), the Ca concentration and The K concentration decreased sharply up to 120 minutes and then gradually decreased. Moreover, in any of the examples, the sodium concentration in the sodium raw material was increased from 99.95% to 99.99%.

Comparing the case of reacting at 120 ° C. (FIG. 2) and the case of reacting at 160 ° C. (FIG. 3) in Example 1, the Ca concentration and Ca concentration and the reaction at 160 ° C. were shorter. The K concentration was likely to decrease. It is considered that this is because the higher the temperature, the faster the substitution reaction rate and the faster the diffusion rate of each component in the ionic liquid.

According to the present invention, purified sodium can be produced from a sodium raw material at low cost and by a simple method. Therefore, the method for producing sodium of the present invention is useful for recycling sodium recovered from a used sodium-sulfur battery.

100 Sodium production equipment 110 Reaction tank 120 Separation member 130 Heating unit 170 Ionic liquid 180 Sodium raw material

Claims (6)

And the sodium source material containing impurities, by contacting the ionic liquid containing sodium ions, Ru enhance sodium purity of the sodium in the raw material step,
A step of recovering the sodium raw material in contact with the ionic liquid as purified sodium,
Including
The ionic liquid
A sodium salt consisting of one or both of a bis (trifluoromethanesulfonyl) imide anion or a bis (fluorosulfonyl) imide anion,
A group consisting of tetraethylammonium salt, tetrabutylammonium salt, 1-ethyl-3-methylimidazole salt, and N-methyl-N-propylpyrrolidium salt of bis (trifluoromethanesulfonyl) imide anion or bis (fluorosulfonyl) imide anion. only containing at least a kind of non-metallic salt, the selected from the group consisting of,
The impurity is a substance that has a greater ionization tendency than sodium.
How to make sodium. Does not include the step of electrolytically purifying the sodium raw material.
The method for producing sodium according to claim 1 . The sodium raw material is brought into contact with the ionic liquid at 110 ° C. or higher and 170 ° C. or lower.
The method for producing sodium according to claim 1 or 2 . The molar ratio of the sodium salt to the non-metal salt in the ionic liquid is 1: 9 to 3: 7.
The method for producing sodium according to any one of claims 1 to 3 . The non-metal salt is a tetraethylammonium salt of a bis (trifluoromethanesulfonyl) imide anion.
The method for producing sodium according to any one of claims 1 to 4 . The sodium raw material is obtained from a sodium-sulfur battery.
The method for producing sodium according to any one of claims 1 to 5 .

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