Method of producing potassium hydroxide

Abstract

To provide a method of producing potassium hydroxide of a low sodium content.SOLUTION: There is provided a method of producing potassium hydroxide, including a process of washing a first potassium hydroxide crystal with a washing liquid, i.e., an aqueous solution of potassium hydroxide to obtain a second potassium hydroxide crystal, with the sodium concentration in the washing liquid being 100 mg / kg or more, and the sodium concentration in the second potassium hydroxide crystal being 50 mg / kg or less, in terms of a sodium concentration in a potassium hydroxide aqueous solution of a concentration of 48 mass%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a method for producing potassium hydroxide (caustic potash).

Background Art

[0002] Patent Document 1 aims to provide a production method capable of obtaining high-purity caustic potash by a simple method. Based on a caustic potash concentration of 48%, an aqueous caustic potash solution with a sodium content of 200 mg / kg or less is concentrated at a high temperature to precipitate monohydrate crystals of caustic potash, and the crystals are isolated from the slurry containing the monohydrate crystal solution. A method for producing high-purity caustic potash is described. Further, Patent Document 1 describes a production method in which the isolated crystals are rinsed with water or an aqueous caustic potash solution.

[0003] Patent Document 2 aims to provide a method for obtaining high-purity caustic potash at low cost by a simple process by removing chlorine and sodium components in caustic potash. A method for producing high-purity caustic potash is described in which an aqueous caustic potash solution with a concentration of 50 to 65 wt% is cooled to 5 to 50 °C to precipitate crystals of caustic potash. Further, Patent Document 2 describes that the caustic potash crystals were rinsed with an aqueous caustic potash solution.

[0004] Patent Document 3 aims to provide a method for obtaining high-purity caustic potash at low cost by a simple process by removing chlorine and sodium components in caustic potash. A method for producing high-purity caustic potash is described in which an aqueous caustic potash solution with a concentration of 50 to 70 wt% is maintained in a boiling state at a temperature of 70 to 90 °C to precipitate crystals of caustic potash. Further, Patent Document 3 describes that the caustic potash crystals were rinsed with an aqueous caustic potash solution.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Patent Document 3

Summary of the Invention

Problems to be Solved by the Invention

[0006] An object of the present invention is to provide a method for producing potassium hydroxide with a low sodium content.

Means for Solving the Problems

[0007] Potassium hydroxide with a low sodium content can be produced by washing potassium hydroxide crystals using an aqueous potassium hydroxide solution with a low sodium concentration as a washing liquid.

[0008] The present invention includes the following embodiments. [1] A step of washing first potassium hydroxide crystals with an aqueous potassium hydroxide solution as a washing liquid to obtain second potassium hydroxide crystals, which is a method for producing potassium hydroxide, comprising: wherein the sodium concentration of the washing liquid is 100 mg / kg or less, and the sodium concentration of the second potassium hydroxide crystals is 50 mg / kg or less when converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass. The production method. [2] The production method according to [1], wherein the sodium concentration of the second potassium hydroxide crystals is 35 mg / kg or less when converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass. [3] The following formula: Yield = [amount of second potassium hydroxide crystals (g) / amount of first potassium hydroxide crystals (g)] × 100 The production method according to [1] or [2], wherein the yield of the second potassium hydroxide crystals represented by the formula is 60 to 95%. [4] The production method according to any one of [1] to [3], wherein the usage amount of the cleaning liquid is 5 to 1000% by mass based on the mass of the first potassium hydroxide crystal. [5] The production method according to any one of [1] to [4], wherein the sodium concentration of the cleaning liquid is 0.1 to 50 mg / kg. [6] The production method according to any one of [1] to [5], wherein the potassium hydroxide concentration of the cleaning liquid is 10 to 50% by mass. [7] The production method according to any one of [1] to [6], wherein the cleaning liquid is an aqueous solution of the second potassium hydroxide crystal. [8] The production method according to any one of [1] to [7], wherein the sodium concentration of the first potassium hydroxide crystal, when converted to the sodium concentration in a 48% by mass aqueous potassium hydroxide solution, exceeds 50 mg / kg. [9] The production method according to any one of [1] to [8], wherein the sodium concentration of the first potassium hydroxide crystal, when converted to the sodium concentration in a 48% by mass aqueous potassium hydroxide solution, is 90 to 160 mg / kg.

[10] The production method according to any one of [1] to [9], wherein the first potassium hydroxide crystal is obtained by a step of concentrating an aqueous solution of potassium hydroxide as a raw material at a high temperature to precipitate the first potassium hydroxide crystal.

[11] The production method according to

[10] , wherein the high temperature state exceeds 100°C.

[12] The production method according to

[10] or

[11] , wherein the sodium concentration of the potassium hydroxide as a raw material, when converted to the sodium concentration in a 48% by mass aqueous potassium hydroxide solution, exceeds 200 mg / kg.

[13] The manufacturing method according to any one of

[10] to

[12] , wherein the sodium concentration of potassium hydroxide as the raw material, when converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass, exceeds 200 mg / kg and is 1500 mg / kg or less.

Advantages of the Invention

[0009] According to the present invention, potassium hydroxide with a low sodium content can be produced.

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited thereto, and various modifications are possible without departing from the gist thereof.

[0011] <Method for Producing Potassium Hydroxide> One embodiment of the present invention is a method for producing potassium hydroxide, including a step of washing first potassium hydroxide crystals with an aqueous potassium hydroxide solution as a washing liquid to obtain second potassium hydroxide crystals, wherein the sodium concentration of the washing liquid is 100 mg / kg or less, and the sodium concentration of the second potassium hydroxide crystals, when converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass, is 50 mg / kg or less.

[0012] In the manufacturing method according to this embodiment, by using an aqueous potassium hydroxide solution with a low sodium concentration as a washing liquid to wash potassium hydroxide crystals, potassium hydroxide with a low sodium content can be produced.

[0013] In this specification, the sodium concentration is determined by atomic absorption spectrometry. When preparing an aqueous potassium hydroxide solution with a concentration of 48% by mass to determine the sodium content of potassium hydroxide, pure water is used.

[0014] In this specification, the potassium hydroxide concentration is determined by a neutralization titration method using hydrochloric acid (indicator: phenolphthalein solution).

[0015] [Washing step] The production method according to this embodiment includes a step of washing the first potassium hydroxide crystals with a washing liquid to obtain second potassium hydroxide crystals (referred to as the "washing step").

[0016] The washing method is not particularly limited, and the first potassium hydroxide crystals may be brought into contact with the washing liquid. Specific washing methods include, for example, a method of adding the washing liquid to the first potassium hydroxide crystals placed on a filter and performing suction filtration, a method of adding the washing liquid to the first potassium hydroxide crystals and performing centrifugation, a method of spraying the washing liquid in a mist form onto the first potassium hydroxide crystals and performing centrifugation, and a method of spraying the washing liquid in a mist form onto the first potassium hydroxide crystals and performing suction filtration.

[0017] (Washing liquid) As the washing liquid, an aqueous potassium hydroxide solution with a low sodium concentration is used. The sodium concentration of the washing liquid is 100 mg / kg or less, preferably 0.1 to 50 mg / kg, more preferably 0.5 to 40 mg / kg, and still more preferably 1 to 30 mg / kg. The lower the sodium concentration of the washing liquid, the lower the sodium content of the second potassium hydroxide crystals can be reduced.

[0018] The potassium hydroxide concentration of the washing liquid is preferably 10 to 50% by mass, more preferably 30 to 50% by mass. By adjusting the potassium hydroxide concentration of the washing liquid within the above range, the sodium content of the second potassium hydroxide crystals can be further reduced. By adjusting the potassium hydroxide concentration of the washing liquid within the above range, the yield of the second potassium hydroxide crystals can be improved (in other words, the amount of the first potassium hydroxide crystals dissolved in the washing step can be reduced).

[0019] The usage amount of the cleaning liquid is preferably 5 to 1000% by mass, more preferably 10 to 500% by mass, still more preferably 15 to 300% by mass, and particularly preferably 20 to 200% by mass based on the mass of the first potassium hydroxide crystal. By adjusting the usage amount of the cleaning liquid within the above range, it is possible to improve the yield of the second potassium hydroxide crystal while reducing the sodium content of the second potassium hydroxide crystal (in other words, reducing the amount of the first potassium hydroxide crystal dissolved in the cleaning step).

[0020] The temperature of the cleaning liquid is not particularly limited and can be used in a wide temperature range. For example, the temperature of the cleaning liquid may be set to 0 to 60°C.

[0021] (The first potassium hydroxide crystal) When the sodium concentration of the first potassium hydroxide crystal is converted to the sodium concentration in a 48% by mass aqueous potassium hydroxide solution, it is preferably more than 50 mg / kg, more preferably more than 60 mg / kg, still more preferably 90 to 160 mg / kg, and particularly preferably 100 to 120 mg / kg. The lower the sodium content of the first potassium hydroxide crystal, the more the sodium content of the second potassium hydroxide crystal can be reduced. In addition, in the production method according to this embodiment, even if the sodium content of the first potassium hydroxide crystal is somewhat high, the sodium content of the second potassium hydroxide crystal can be significantly reduced by using a cleaning liquid with a low sodium concentration. Also, the first potassium hydroxide crystal with a somewhat high sodium content has the advantage of being easily available.

[0022] The sodium content of the first potassium hydroxide crystal can be adjusted by changing the conditions in the [preparation step] described later. For example, when the sodium content of potassium hydroxide as a raw material in the preparation step is decreased, the sodium content of the first potassium hydroxide crystal tends to decrease.

[0023] The first potassium hydroxide crystal may be in the form of a hydrate.

[0024] The first potassium hydroxide crystal is preferably prepared in the [Preparation Step] described below.

[0025] (Second potassium hydroxide crystal) The sodium concentration of the second potassium hydroxide crystal, when converted to the sodium concentration in a 48 mass% potassium hydroxide aqueous solution, is 50 mg / kg or less. In this technical field, even if the sodium concentration is reduced by only 1 mg / kg, it is not easy and has great significance. The lower the sodium content of the second potassium hydroxide crystal, the more preferable. The sodium concentration (the converted value) of the second potassium hydroxide crystal is preferably, for example, below the following upper limit values: 49 mg / kg, 48 mg / kg, 47 mg / kg, 46 mg / kg, 45 mg / kg, 44 mg / kg, 43 mg / kg, 42 mg / kg, 41 mg / kg, 40 mg / kg, 39 mg / kg, 38 mg / kg, 37 mg / kg, 36 mg / kg, 35 mg / kg, 34 mg / kg, 33 mg / kg, 32 mg / kg, 31 mg / kg, 30 mg / kg, 29 mg / kg, 28 mg / kg, 27 mg / kg, 26 mg / kg, 25 mg / kg, 24 mg / kg, 23 mg / kg, 22 mg / kg, 21 mg / kg, 20 mg / kg, 19 mg / kg, 18 mg / kg, 17 mg / kg, 16 mg / kg, 15 mg / kg, 14 mg / kg, 13 mg / kg, 12 mg / kg, 11 mg / kg, 10 mg / kg, 9 mg / kg, 8 mg / kg, 7 mg / kg, 6 mg / kg, 5 mg / kg, 4 mg / kg, 3 mg / kg, 2 mg / kg, or 1 mg / kg.

[0026] Since the lower the sodium content of the second potassium hydroxide crystal, the more preferable, there is no particular lower limit. However, the sodium concentration (the converted value) of the second potassium hydroxide crystal may be, for example, above the following lower limit values: 0 mg / kg, 1 mg / kg, 2 mg / kg, 3 mg / kg, 4 mg / kg, 5 mg / kg, 6 mg / kg, 7 mg / kg, 8 mg / kg, 9 mg / kg, or 10 mg / kg.

[0027] The upper and lower limit values of the sodium concentration (the converted value) of the second potassium hydroxide crystal may be appropriately combined to determine a specific numerical range. For example, the following numerical ranges may be mentioned: 0 to 50 mg / kg, 1 to 45 mg / kg, 2 to 40 mg / kg, 3 to 35 mg / kg, 4 to 30 mg / kg, 5 to 25 mg / kg, 6 to 20 mg / kg, 7 to 15 mg / kg, or 8 to 10 mg / kg.

[0028] The sodium content of the second potassium hydroxide crystal can be adjusted by changing the usage amount or composition of the cleaning liquid. For example, when the usage amount of the cleaning liquid is increased, the sodium content of the second potassium hydroxide crystal tends to decrease. Also, when the sodium concentration of the cleaning liquid is decreased, the sodium content of the second potassium hydroxide crystal tends to decrease.

[0029] The yield of the second potassium hydroxide crystal in the washing step ([amount of the second potassium hydroxide crystal (g) / amount of the first potassium hydroxide crystal (g)]×100) is preferably 60 to 95%, more preferably 70 to 93%, and still more preferably 80 to 90%. By adjusting the yield of the second potassium hydroxide crystal within the above range, it is possible to reduce the sodium content of the second potassium hydroxide crystal while ensuring the amount of the second potassium hydroxide crystal.

[0030] The yield of the second potassium hydroxide crystal can be adjusted by changing the usage amount or composition of the cleaning liquid. For example, when the usage amount of the cleaning liquid is increased, the yield tends to decrease. Also, when the potassium hydroxide concentration of the cleaning liquid is decreased, the yield tends to decrease.

[0031] The second potassium hydroxide crystal may be in the form of a hydrate.

[0032] The second potassium hydroxide crystal may be used as a raw material for the cleaning solution. That is, the second potassium hydroxide crystal obtained in the cleaning step may be dissolved in water to prepare an aqueous potassium hydroxide solution, and this may be used as the cleaning solution (also referred to as the "second cleaning solution") in the next cleaning step (also referred to as the "second cleaning step"). The preferable values of the sodium concentration, potassium hydroxide concentration, and usage amount of the cleaning solution prepared from the second potassium hydroxide crystal are as described in the above (cleaning solution) column.

[0033] The water used for preparing the second cleaning solution is not particularly limited as long as it is high-purity water. Examples of the water include ion-exchanged water, ultrapure water, and reverse osmosis membrane water.

[0034] [Preparation Step] The manufacturing method according to this embodiment may include a step of preparing the first potassium hydroxide crystal (referred to as the "preparation step") before the cleaning step.

[0035] The method for preparing the first potassium hydroxide crystal is not particularly limited. For example, a method of precipitating the first potassium hydroxide crystal from an aqueous solution of potassium hydroxide as a raw material can be mentioned. As a more specific method, for example, a method of concentrating an aqueous solution of potassium hydroxide as a raw material to precipitate the first potassium hydroxide crystal (referred to as the "concentration method"), and a method of cooling an aqueous solution of potassium hydroxide as a raw material to precipitate the first potassium hydroxide crystal (referred to as the "cooling method") can be mentioned. From the viewpoint of manufacturing potassium hydroxide with a low sodium content, it is preferable to adopt the concentration method.

[0036] In the concentration method, it is preferable to concentrate the aqueous potassium hydroxide solution at a high temperature state. The high temperature state is preferably above 100°C, more preferably 100 - 150°C, and still more preferably 100 - 120°C. The high temperature state is also preferably a boiling state. The boiling state can be ensured by adjusting the temperature and pressure.

[0037] The sodium concentration of potassium hydroxide as a raw material, when converted to the sodium concentration in a 48% by mass aqueous potassium hydroxide solution, is preferably more than 200 mg / kg, more preferably more than 200 mg / kg and 1500 mg / kg or less, still more preferably 300 to 1300 mg / kg, and particularly preferably 500 to 1000 mg / kg.

[0038] The preparation step and the washing step may be carried out, for example, using the apparatus described in International Publication No. 2007 / 018203.

Examples

[0039] Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the technical scope of the present invention is not limited thereto.

[0040] Various values in the examples may be used as the preferable lower limit value or upper limit value in the embodiments of the present invention. Also, two values of the same kind in the examples may be appropriately combined to form a preferable numerical range. Note that "ppm" used hereinafter has the same meaning as "mg / kg".

[0041] [Example 1] An aqueous potassium hydroxide solution (raw material) (KOH concentration: 48.5% by mass, Na concentration: 800 ppm) was concentrated until the KOH concentration reached 61% by mass and placed in a tank lined with a nickel material equipped with a stirrer. This aqueous potassium hydroxide solution was concentrated by adjusting the pressure to a boiling state at 100 °C to obtain a slurry containing potassium hydroxide monohydrate crystals. The crystals were taken out from this slurry by a centrifuge. Using an aqueous potassium hydroxide solution (washing liquid) (KOH concentration: 48.5% by mass, Na concentration: 5 ppm or less) in an amount of 100% by mass based on the mass of the crystals, the crystals were washed. Specifically, the washing was performed by placing the crystals taken out by the centrifuge on a membrane filter, adding the washing liquid from above, and performing suction filtration. The Na concentrations of the crystals before washing and after washing (converted to the Na concentration in a 48 mass% potassium hydroxide aqueous solution) were 110 ppm and 10 ppm, respectively. Also, the yield of the crystals after washing ([amount of crystals after washing / amount of crystals before washing] × 100) was 81%.

[0042] [Example 2] The same operations as in Example 1 were carried out except that the Na concentration of the washing solution was changed to 30 ppm.

[0043] [Example 3] The same operations as in Example 2 were carried out except that the amount of the washing solution was changed to 20 mass% based on the mass of the crystals.

[0044] [Comparative Example 1] The same operations as in Example 1 were carried out except that the Na concentration of the washing solution was changed to 800 ppm.

[0045] [Comparative Example 2] The same operations as in Example 1 were carried out except that pure water (Na concentration: 0.1 ppm or less) was used as the washing solution.

[0046] [Comparative Example 3] The same operations as in Example 2 were carried out except that the amount of the washing solution was changed to 1 mass% based on the mass of the crystals.

[0047] [Comparative Example 4] The same operations as in Example 2 were carried out except that the amount of the washing solution was changed to 4 mass% based on the mass of the crystals.

[0048] The results of each example and each comparative example are shown in Table 1.

Table 1

Claims

1. A step of washing the first potassium hydroxide crystal with an aqueous potassium hydroxide solution as a cleaning liquid to obtain a second potassium hydroxide crystal, A method for producing potassium hydroxide, comprising: The sodium concentration of the cleaning liquid is 100 mg / kg or less, When the sodium concentration of the second potassium hydroxide crystal is converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass, it is 50 mg / kg or less. The production method.

2. When the sodium concentration of the second potassium hydroxide crystal is converted to the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48% by mass, it is 35 mg / kg or less. The production method according to Claim 1.

3. The following formula: Yield = [amount of the second potassium hydroxide crystal (g) / amount of the first potassium hydroxide crystal (g)] × 100 The yield of the second potassium hydroxide crystal represented by this is 60 to 95%. The production method according to Claim 1.

4. The usage amount of the cleaning liquid is 5 to 1000% by mass based on the mass of the first potassium hydroxide crystal. The production method according to Claim 1.

5. The sodium concentration of the cleaning liquid is 0.1 to 50 mg / kg. The production method according to Claim 1.

6. The potassium hydroxide concentration of the cleaning liquid is 10 to 50% by mass. The production method according to Claim 1.

7. The cleaning liquid is an aqueous solution of the second potassium hydroxide crystal. The production method according to Claim 1.

8. When the sodium concentration of the first potassium hydroxide crystal is converted to the sodium concentration in a 48% by mass potassium hydroxide aqueous solution, it exceeds 50 mg / kg. The production method according to claim 1.

9. When the sodium concentration of the first potassium hydroxide crystal is converted to the sodium concentration in a 48% by mass potassium hydroxide aqueous solution, it is 90 to 160 mg / kg. The production method according to claim 1.

10. The first potassium hydroxide crystal is obtained by a step of concentrating an aqueous solution of potassium hydroxide as a raw material at a high temperature to precipitate the first potassium hydroxide crystal. The production method according to claim 1.

11. The high temperature state exceeds 100°C. The production method according to claim 10.

12. When the sodium concentration of the potassium hydroxide as a raw material is converted to the sodium concentration in a 48% by mass potassium hydroxide aqueous solution, it exceeds 200 mg / kg. The production method according to claim 10.

13. When the sodium concentration of the potassium hydroxide as a raw material is converted to the sodium concentration in a 48% by mass potassium hydroxide aqueous solution, it exceeds 200 mg / kg and is 1500 mg / kg or less. The production method according to claim 10.

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