Continuous method for producing potassium hydroxide
By maintaining the temperature of the potassium hydroxide solution at 99°C or below during continuous production, the method addresses pipe clogging issues, enabling efficient and high-yield production of potassium hydroxide.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- TOAGOSEI CO LTD
- Filing Date
- 2024-12-23
- Publication Date
- 2026-07-03
AI Technical Summary
Existing methods for producing potassium hydroxide, such as those described in Patent Document 1, face challenges in achieving continuous production when temperatures exceed 100°C, leading to pipe clogging due to crystal formation.
The method involves continuously introducing an aqueous potassium hydroxide solution into a crystallization vessel at a temperature of 99°C or below, allowing for simultaneous precipitation and discharge of potassium hydroxide crystals, with specific conditions such as pressure and residence time optimized for continuous production.
This approach enables continuous, high-yield production of potassium hydroxide with reduced pipe blockage, achieving mass production and high purity.
Smart Images
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Abstract
Description
Technical Field
[0001] The present invention relates to a method for continuously producing potassium hydroxide (caustic potash).
Background Art
[0002] Potassium hydroxide is used in various fields. For example, high-purity potassium hydroxide is used for etching or cleaning silicon wafers in semiconductor manufacturing.
[0003] As a method for producing high-purity caustic potash, for example, Patent Document 1 discloses "a method for producing high-purity caustic potash, characterized in that an aqueous solution of caustic potash containing 200 mg / kg or less of sodium content and 15 mg / kg or less of chlorine content in terms of potassium chloride 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 liquid".
Prior Art Documents
Patent Documents
[0004]
Patent Document 1
Summary of the Invention
Problems to be Solved by the Invention
[0005] Specifically, Patent Document 1 performs batch production and employs 100°C as the high-temperature condition for precipitating potassium hydroxide. The inventor of the present invention has discovered the problem that potassium hydroxide cannot be continuously produced when continuous production is carried out at 100°C or higher.
[0006] An object of the present invention is to continuously produce potassium hydroxide.
Means for Solving the Problems
[0007] By adjusting the temperature of the potassium hydroxide aqueous solution in the crystallization vessel to 99°C or below, potassium hydroxide can be produced continuously.
[0008] The present invention includes the following embodiments. [1] A continuous method for producing potassium hydroxide, The crystallization process includes continuously introducing an aqueous potassium hydroxide solution into a crystallization vessel, continuously precipitating potassium hydroxide crystals from the aqueous potassium hydroxide solution within the crystallization vessel, and continuously releasing the slurry containing the potassium hydroxide crystals from the crystallization vessel. The introduction, precipitation, and release are carried out simultaneously. The temperature of the potassium hydroxide aqueous solution in the crystallization vessel is 99°C or lower. Manufacturing method. [2] The manufacturing method according to [1], wherein the temperature of the potassium hydroxide aqueous solution in the crystallization vessel is 91 to 99°C. [3] The manufacturing method according to [1] or [2], wherein the potassium hydroxide concentration of the potassium hydroxide aqueous solution is 60 to 65% by mass. [4] The manufacturing method according to any one of [1] to [3], wherein the pressure inside the crystallization vessel is 2.5 to 5.0 kPa. [5] The pressure inside the crystallization vessel is the pressure at which the potassium hydroxide aqueous solution boils. The manufacturing method according to any one of [1] to [4]. [6] The manufacturing method according to any one of [1] to [5], wherein the average residence time of the potassium hydroxide aqueous solution in the crystallization vessel is 1 to 3 hours. [7] The manufacturing method according to any one of [1] to [6], wherein the rate at which the potassium hydroxide aqueous solution is introduced into the crystallization vessel is 300 to 100,000 L / h. [8] The manufacturing method according to any one of [1] to [7], wherein the discharge rate of the slurry from the crystallization vessel is 300 to 100,000 L / h. [Effects of the Invention]
[0009] This invention allows for the continuous production of potassium hydroxide. [Modes for carrying out the invention]
[0010] The embodiments of the present invention will be described in detail below, but the present invention is not limited to these, and various modifications are possible without departing from the spirit of the invention.
[0011] <Continuous method for producing potassium hydroxide> One embodiment of the present invention is a method for the continuous production of potassium hydroxide, The crystallization process includes continuously introducing an aqueous potassium hydroxide solution into a crystallization vessel, continuously precipitating potassium hydroxide crystals from the aqueous potassium hydroxide solution within the crystallization vessel, and continuously releasing the slurry containing the potassium hydroxide crystals from the crystallization vessel. The introduction, precipitation, and release are carried out simultaneously. The temperature of the potassium hydroxide aqueous solution in the crystallization vessel is 99°C or lower. Regarding the manufacturing method.
[0012] According to the manufacturing method of this embodiment, potassium hydroxide can be produced continuously. Preferably, the manufacturing method of this embodiment can achieve continuous production, mass production, and high yield of aqueous potassium hydroxide solution.
[0013] When potassium hydroxide crystals are precipitated from an aqueous potassium hydroxide solution, monohydrate or dihydrate crystals are mainly obtained. Because dihydrate crystals have a high water content, it is more difficult to remove the impurity Na compared to monohydrate crystals, and they tend to adhere to the piping of the manufacturing equipment. Therefore, from the viewpoint of continuously producing high-purity potassium hydroxide, it is expected that it is preferable to preferentially produce monohydrate crystals.
[0014] The monohydrate crystals are likely to be formed under high-temperature conditions (100 °C or higher), and the dihydrate crystals are likely to be formed under lower-temperature conditions. Therefore, in Patent Document 1 (batch production), a condition of 100 °C was adopted for the crystallization of potassium hydroxide. However, when adopting conditions of 100 °C or higher during the continuous production of potassium hydroxide, problems such as clogging of the pipes of the production apparatus with potassium hydroxide crystals occurred. In contrast, by adopting conditions of 99 °C or lower, potassium hydroxide could be continuously produced. This is a result contrary to what is expected from conventional knowledge and is surprising.
[0015] Hereinafter, the method for producing potassium hydroxide will be described step by step. In addition, in order to assist in understanding the production flow of potassium hydroxide, various steps other than the crystallization step will also be described, but the present invention is not limited by these steps in any way.
[0016] The method for producing potassium hydroxide includes, for example, a raw material supply step, a pre-concentration step, a crystallization step, a separation step, a washing step, and a dissolution step.
[0017] [Raw Material Supply Step] The raw material supply step is a step of supplying an aqueous potassium hydroxide solution (hereinafter also referred to as "the first KOH aqueous solution") as a raw material to a production apparatus for potassium hydroxide equipped with a crystallization vessel.
[0018] The sodium concentration of the first KOH aqueous solution is not particularly limited, but in terms of the sodium concentration in an aqueous potassium hydroxide solution with a concentration of 48.5% by mass, it may be, for example, 500 to 2,000 mg / kg, 600 to 1,500 mg / kg, or 800 to 1,000 mg / kg.
[0019] In this specification, the sodium concentration is determined by atomic absorption spectrometry. When preparing an aqueous potassium hydroxide solution with a concentration of 48.5% by mass for determining the sodium concentration, pure water is used.
[0020] The potassium hydroxide concentration of the first KOH aqueous solution is not particularly limited, but may be, for example, 35-65% by mass, 40-60% by mass, or 45-55% by mass.
[0021] In this specification, the potassium hydroxide concentration is determined by a neutralization titration method using hydrochloric acid (indicator: phenolphthalein solution).
[0022] The supply rate of the first KOH aqueous solution is not particularly limited, but it may be, for example, 500-100,000 L / h, 700-5,000 L / h, or 900-1,100 L / h when converted to the amount of 48.5% by mass potassium hydroxide aqueous solution.
[0023] [Pre-concentration process] The pre-concentration step is a process of concentrating the first KOH aqueous solution to increase the potassium hydroxide concentration.
[0024] By performing a pre-concentration step, the precipitation efficiency of potassium hydroxide crystals in the subsequent crystallization step can be increased. However, if the potassium hydroxide concentration of the first KOH aqueous solution is already high, the pre-concentration step may be omitted.
[0025] In the pre-concentration step, the potassium hydroxide concentration is increased to preferably 60-65% by mass, more preferably 60-63% by mass, and even more preferably 60-62% by mass.
[0026] The method of concentration is not particularly limited, but one example is to heat a concentrator with high-temperature steam and evaporate the water from the first KOH aqueous solution. Concentration is preferably carried out under reduced pressure.
[0027] [Crystallization process] The crystallization process involves continuously introducing an aqueous potassium hydroxide solution into a crystallization vessel, continuously precipitating potassium hydroxide crystals from the aqueous solution within the crystallization vessel, and continuously releasing the slurry containing the potassium hydroxide crystals from the crystallization vessel.
[0028] In the crystallization process, the continuous introduction, continuous precipitation, and continuous discharge described above are carried out simultaneously. This enables the continuous production of potassium hydroxide. "Carried out simultaneously" means that the operation of continuously introducing the potassium hydroxide aqueous solution into the crystallization vessel (hereinafter referred to as the "introduction operation"), the operation of continuously precipitating potassium hydroxide crystals from the potassium hydroxide aqueous solution in the crystallization vessel (hereinafter referred to as the "precipitation operation"), and the operation of continuously discharging the slurry containing potassium hydroxide crystals from the crystallization vessel (hereinafter referred to as the "discharge operation") are carried out at the same time. In other words, in a crystallization vessel where the precipitation operation is being carried out, the potassium hydroxide aqueous solution is continuously introduced while the slurry containing potassium hydroxide crystals is continuously discharged at the same time. Therefore, for example, an embodiment in which the precipitation operation is started after the completion of the introduction operation and the discharge operation is started after the completion of the precipitation operation is not "carried out simultaneously".
[0029] The sodium concentration of the potassium hydroxide aqueous solution introduced into the crystallization vessel is essentially the same as the sodium concentration of the first KOH aqueous solution when converted to the sodium concentration of a 48.5% by mass potassium hydroxide aqueous solution. However, when the recovered solution obtained in the isolation process described later is returned to the crystallization vessel, the sodium from the first KOH aqueous solution and the sodium from the recovered solution combine, and the overall sodium concentration increases. In that case, the sodium concentration of the potassium hydroxide aqueous solution introduced into the crystallization vessel can be converted to the sodium concentration of a 48.5% by mass potassium hydroxide aqueous solution, for example, 500-10,000 mg / kg, 600-7,000 mg / kg, or 800-4,000 mg / kg.
[0030] The rate at which the potassium hydroxide aqueous solution is introduced into the crystallization vessel is preferably 300 to 100,000 L / h, more preferably 500 to 10,000 L / h, and even more preferably 600 to 5,000 L / h.
[0031] The temperature of the potassium hydroxide aqueous solution in the crystallization vessel is preferably 99°C or lower, more preferably 91-99°C, even more preferably 93-99°C, particularly preferably 95-99°C, and most preferably 96-99°C. By keeping the temperature below 99°C, it becomes possible to achieve high purity and continuous production of potassium hydroxide. Maintaining a temperature of 91°C or higher tends to suppress blockage of pipes due to crystal formation.
[0032] The temperature of the potassium hydroxide aqueous solution can be adjusted, for example, by heating the crystallization vessel with high-temperature steam.
[0033] The pressure inside the crystallization vessel is preferably the pressure at which the potassium hydroxide aqueous solution boils.
[0034] The pressure inside the crystallization vessel is preferably 2.5 to 5.0 kPa, more preferably 2.5 to 4.0 kPa, and even more preferably 3.0 to 4.0 kPa.
[0035] It is preferable that the potassium hydroxide aqueous solution in the crystallization vessel is stirred.
[0036] The average residence time of the potassium hydroxide aqueous solution in the crystallization vessel is preferably 1 to 6 hours, more preferably 1 to 5 hours, and even more preferably 1 to 3 hours. The average residence time is the value obtained by dividing the amount of slurry maintained at a constant level within the crystallization vessel by the discharge rate of the slurry released from the crystallization vessel. Average residence time (h) = Amount of slurry maintained in the crystallization vessel (L) / Slurry discharge rate (L / h)
[0037] The discharge rate of slurry from the crystallization vessel is preferably 300 to 100,000 L / h, more preferably 500 to 10,000 L / h, and even more preferably 600 to 5,000 L / h.
[0038] [Isolation process] The isolation step is the process of isolating potassium hydroxide crystals from the slurry.
[0039] The isolation method is not particularly limited, but one example is to separate the aqueous solution from the crystals by letting the slurry stand or by centrifugation.
[0040] The potassium hydroxide aqueous solution separated from the crystals (hereinafter also referred to as the "recovered solution") may be reused in the crystallization process.
[0041] [Washing process] The washing process involves washing the isolated potassium hydroxide crystals.
[0042] The cleaning method is not particularly limited, but one example is washing the surface of the crystal with high-purity water.
[0043] [Dissolution process] The dissolution process involves dissolving the isolated potassium hydroxide crystals in water to obtain an aqueous potassium hydroxide solution (hereinafter also referred to as the "second aqueous KOH solution").
[0044] The production rate of the second KOH aqueous solution is preferably 300 to 50,000 L / h, more preferably 500 to 5,000 L / h, and even more preferably 600 to 700 L / h, when converted to a 48.5% by mass potassium hydroxide aqueous solution.
[0045] The yield of potassium hydroxide crystals represented by the following formula is preferably 60% or more, more preferably 70% or more, and even more preferably 80% or more. While a higher yield is preferable, there is no upper limit; however, for example, 100%, 90%, or 80% may be set as upper limits. Crystallization yield = (Amount of second KOH aqueous solution / Amount of first KOH aqueous solution) × 100 [The amounts of the second KOH aqueous solution and the first KOH aqueous solution are converted to 48.5% by mass potassium hydroxide aqueous solution amounts.] [Examples]
[0046] The present invention will be described in more detail below using examples and comparative examples, but the technical scope of the present invention is not limited thereto.
[0047] The various values in the examples may be preferred lower or upper limits in the embodiments of the present invention. Alternatively, two similar values in the examples may be combined as appropriate to form a preferred numerical range. Note that "ppm" as used below is synonymous with "mg / kg".
[0048] [Measurement method] (Measurement of KOH concentration) The concentration of potassium hydroxide was measured by a neutralization titration method using hydrochloric acid (indicator: phenolphthalein solution).
[0049] [Example 1] A potassium hydroxide aqueous solution ("first KOH aqueous solution") (KOH concentration: 48.5% by mass) was concentrated to a KOH concentration of 61% by mass and continuously introduced into a crystallization tank lined with nickel material and equipped with a stirrer. The temperature of the potassium hydroxide aqueous solution was measured 325 mm inside the tank wall using a resistance thermometer, and the pressure was adjusted to 3.3 kPa so that it boiled at 96°C, thereby concentrating the potassium hydroxide aqueous solution and continuously precipitating potassium hydroxide crystals. The slurry containing potassium hydroxide crystals was continuously discharged from the tank. Potassium hydroxide crystals were removed from the slurry using a centrifuge. These crystals were washed and dissolved in water to prepare a potassium hydroxide aqueous solution with a KOH concentration of 48.5% by mass ("second KOH aqueous solution").
[0050] When crystallization conditions of 96°C were adopted, the piping did not become clogged with crystals, and continuous production was possible.
[0051] The crystallization yield, expressed by the following formula, was 72%. Crystallization yield = (Amount of second KOH aqueous solution / Amount of first KOH aqueous solution) × 100
[0052] [Example 2] The procedure was the same as in Example 1, except that the temperature inside the crystallization tank was adjusted to 98°C and the pressure to 3.5kPa to maintain a boiling state, and other conditions were changed as shown in Table 1 below.
[0053] [Example 3] The procedure was the same as in Example 1, except that the temperature inside the crystallization tank was adjusted to 99°C and the pressure to 2.9kPa to maintain a boiling state, and other conditions were changed as shown in Table 1 below.
[0054] [Comparative Example 1] The procedure was the same as in Example 1, except that the temperature inside the crystallization tank was adjusted to 100°C and the pressure to 3.1 kPa to maintain a boiling state, and other conditions were changed as shown in Table 1 below.
[0055] [Comparative Example 2] The procedure was the same as in Example 1, except that the temperature inside the crystallization tank was adjusted to 101°C and the pressure to 3.2 kPa to maintain a boiling state, and other conditions were changed as shown in Table 1 below.
[0056] [Table 1]
[0057] In Examples 1-3, by adjusting the temperature of the potassium hydroxide aqueous solution in the crystallization tank to 99°C or below, it was possible to achieve continuous production, mass production, and high yield of potassium hydroxide aqueous solution simultaneously.
[0058] On the other hand, in Comparative Examples 1 and 2, where the temperature was adjusted to 100°C or higher, continuous production, mass production, and high yield of potassium hydroxide aqueous solution could not be achieved.
Claims
1. A continuous method for producing potassium hydroxide, The crystallization process includes continuously introducing an aqueous potassium hydroxide solution into a crystallization vessel, continuously precipitating potassium hydroxide crystals from the aqueous potassium hydroxide solution within the crystallization vessel, and continuously releasing the slurry containing the potassium hydroxide crystals from the crystallization vessel. The introduction, precipitation, and release are carried out simultaneously. The temperature of the potassium hydroxide aqueous solution in the crystallization container is 99°C or lower. Manufacturing method.
2. The temperature of the potassium hydroxide aqueous solution in the crystallization vessel is 91 to 99°C. The manufacturing method according to claim 1.
3. The potassium hydroxide concentration in the aforementioned potassium hydroxide aqueous solution is 60 to 65% by mass. The manufacturing method according to claim 1 or 2.
4. The pressure inside the crystallization vessel is 2.5 to 5.0 kPa. The manufacturing method according to claim 1 or 2.
5. The pressure inside the crystallization vessel is the pressure at which the potassium hydroxide aqueous solution boils. The manufacturing method according to claim 1 or 2.
6. The average residence time of the potassium hydroxide aqueous solution in the crystallization vessel is 1 to 3 hours. The manufacturing method according to claim 1 or 2.
7. The rate at which the potassium hydroxide aqueous solution is introduced into the crystallization vessel is 300 to 100,000 L / h. The manufacturing method according to claim 1 or 2.
8. The discharge rate of the slurry from the crystallization container is 300 to 100,000 L / h. The manufacturing method according to claim 1 or 2.