Preparation method of electronic grade potassium hydroxide and solution thereof

Abstract

The application belongs to the field of electronic grade material preparation. An electronic grade potassium hydroxide and a preparation method of an electronic grade potassium hydroxide solution are provided. The preparation method of the electronic grade potassium hydroxide solution comprises the following steps: S1. loading the crystalline and purified potassium hydroxide crystals into an alkali corrosion resistant container to form a crystal layer, the thickness of the crystal layer is L cm; S2. applying a periodically changed negative pressure at the bottom of the crystal layer; S3. continuously adding a washing liquid A at the top of the crystal layer, and collecting a daily use grade potassium hydroxide solution at the bottom of the crystal layer; when the impurity content of the solution at the outlet of the bottom of the crystal layer in step S3 is less than or equal to a set value, step S4 is performed; S4. continuously adding a washing liquid B at the top of the crystal layer, and collecting an electronic grade potassium hydroxide solution at the outlet of the bottom of the crystal layer; S5. when the thickness of the crystal layer is 1 / 4L-1 / 2, continuously adding a washing liquid C at the top of the crystal layer, and collecting a material liquid C at the bottom of the crystal layer. The method can produce electronic grade potassium hydroxide and electronic grade potassium hydroxide solution with stable quality and high yield.

Description

Technical Field

[0001] This invention belongs to the field of electronic-grade material preparation, specifically relating to a method for preparing electronic-grade potassium hydroxide and its solution. Background Technology

[0002] Electronic-grade potassium hydroxide is a type of potassium hydroxide with high purity and excellent chemical stability, and it is widely used in high-tech industries such as electronic components, semiconductor manufacturing, photovoltaics, and integrated circuits.

[0003] Currently, the most common method for producing electronic-grade potassium hydroxide is as follows: first, potassium hydroxide is prepared into a potassium hydroxide solution, then heavy metals and sodium ions are removed by ion exchange, cooling crystallization and other methods, and finally the potassium hydroxide crystals and mother liquor are separated by centrifuge, and the separated crystals are dissolved to obtain electronic-grade potassium hydroxide.

[0004] Ideally, in this method, pure KOH crystallizes out of the solution as crystals during the crystallization process, while impurity metal ions remain in the mother liquor. A centrifuge can then separate the purified potassium hydroxide crystals from the impurity-enriched mother liquor. However, in actual production, centrifuges often fail to completely separate the impurity-laden mother liquor from the potassium hydroxide crystals. The remaining mother liquor, enriched with impurity metal ions, can still lead to product defects.

[0005] To address the problem of incomplete separation between impurity-containing mother liquor and potassium hydroxide crystals, researchers proposed a method of spray washing during high-speed centrifugation (such as the preparation method of electronic-grade potassium hydroxide disclosed in Chinese Patent No. CN113860336A). However, this still cannot completely solve the problem of stable and effective removal of mother liquor or adsorbed impurities adhering to the crystal surface, resulting in large fluctuations in product quality and unstable product yield.

[0006] Furthermore, the electronics industry commonly uses 42-48 wt% potassium hydroxide solutions. Existing electronic potassium hydroxide solutions are generally prepared by mixing purified crystals with ultrapure water to achieve the required concentration, as illustrated in Chinese patent publication CN115304081A. However, due to significant batch-to-batch variations in the KOH and impurity content of electronic-grade solid potassium hydroxide crystals, the concentration and metal ion levels of the prepared crystals are prone to fluctuations. This often necessitates multiple adjustments or batch-to-batch reconstitution. Especially when the concentration is too low, additional crystals need to be added and redissolved. The entire preparation process is resource-intensive, inefficient, and detrimental to product manufacturing and quality stability.

[0007] Therefore, there is an urgent need for a method that can stably produce electronic-grade potassium hydroxide and a method for producing stable electronic-grade potassium hydroxide solutions. Summary of the Invention

[0008] The primary objective of this invention is to provide a method for preparing electronic-grade potassium hydroxide, which can produce electronic-grade potassium hydroxide with high yield and stable quality.

[0009] The second objective of this invention is to provide a method for preparing electronic-grade potassium hydroxide solution, which can produce a stable electronic-grade potassium hydroxide solution, and the preparation method is simple and the production equipment is simple.

[0010] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0011] In a first aspect, the present invention provides a method for preparing electronic-grade potassium hydroxide, comprising the following steps:

[0012] S1. The purified potassium hydroxide crystals are packed into an alkali-resistant corrosion-resistant container to form a crystal layer. The thickness of the packed crystal layer is recorded as L cm.

[0013] S2. A periodically varying negative pressure is applied to the bottom of the crystal layer. The time of each period is ts. The range of the vacuum degree P of the negative pressure during the periodic variation is denoted as P1 kPa ≥ P ≥ P2 kPa. Within each period, the negative pressure value decreases uniformly and stably from P1 to P2.

[0014] S3. Washing solution A is continuously added to the top of the crystal layer for washing, and daily chemical grade potassium hydroxide solution is collected at the bottom outlet of the crystal layer; the washing solution A is selected from at least one of ultrapure water and low potassium solution; the low potassium solution is a potassium hydroxide solution with a concentration of less than 42 wt% and an impurity content of less than a set value.

[0015] When the impurity content of the solution at the bottom outlet of the crystal layer in step S3 is less than or equal to the set value, the operation of step S4 is performed.

[0016] The set value is the highest allowable impurity content required for the target product, electronic-grade potassium hydroxide.

[0017] S4. Stop washing. At this point, the crystal layer in the alkali-resistant container is electronic-grade potassium hydroxide.

[0018] Through research on existing technologies, the inventors discovered that existing technologies, in the process of centrifugation after crystallization, employ spray washing to separate impurities from the crystals. However, this method has the following problems:

[0019] Since the centrifugation process is carried out at high speed, and the high speed causes the washing liquid to pass through the potassium hydroxide crystal layer quickly, a single wash cannot fully remove the mother liquor from the crystal surface.

[0020] Increasing the number of washes or the amount of water used in each wash will, on the one hand, lead to the dissolution of a large amount of crystals, thereby greatly reducing the yield of the final purified potassium hydroxide product; on the other hand, since the crystal layer is fixed during the centrifugation process, a fixed mother liquor channel will be formed during the centrifugation process. After the first high-speed wash, due to the high solubility of potassium hydroxide, this fixed mother liquor channel will be strengthened. Therefore, multiple high-speed washes will further strengthen this ion channel, resulting in uneven crystal washing, large fluctuations in the metal ion index in the crystals, and unqualified products.

[0021] Based on the above findings, the inventors have creatively proposed the technical solution of this application. By applying negative pressure to continuously wash the fixed potassium hydroxide crystal layer, compared with washing under high-speed centrifugation, the residence time of the washing liquid in the fixed crystal layer is increased, allowing for sufficient contact with the crystal layer and thus making the washing more thorough. Continuous washing can also avoid excessive local crystal dissolution caused by excessive local residence time, thus avoiding substandard or highly fluctuating product quality. At the same time, by applying periodically varying negative pressure to the crystal layer, this application can effectively prevent the formation of fixed liquid flow channels in the crystal layer, making the contact between various parts of the crystal layer and the washing liquid more uniform, further avoiding substandard or highly fluctuating product quality.

[0022] Preferably, the crystal layer thickness L in step S1 and the maximum vacuum degree P1 that changes periodically in step S2 satisfy the following condition: 5P1≤L≤10P1.

[0023] A proper match between negative pressure and crystal layer thickness ensures better product quality stability. If the negative pressure and crystal layer thickness are mismatched—for example, if the crystal layer is too thin and the negative pressure is too high—the washing liquid will pass through the crystal layer too quickly, resulting in insufficient washing; if the crystal layer is too thick and the negative pressure is too low, the washing liquid will cause localized over-dissolution of the initially contacted crystals, and the washing liquid cannot pass through the crystal layer completely in a near-linear manner, thus forming new entrained impurities that are adsorbed onto the crystal surface. Both of these situations lead to insufficient washing of the crystal layer, resulting in substandard or highly fluctuating metal ion content in the final potassium hydroxide product, failing to meet the manufacturer's stringent and stable requirements.

[0024] Further preferably, in step S2, the time period t satisfies: 30s≤t≤180s; preferably 30s~90s; the maximum vacuum degree P1 satisfies: 20KPa≤P1≤30KPa; and the minimum vacuum degree P2 satisfies: 5KPa≤P2≤10KPa.

[0025] The time period for changing the negative pressure value and the range of negative pressure value changes in each period have a direct impact on the full and uniform contact between the washing liquid and the crystal in the crystal layer. Within the above time period range and negative pressure value change range, the stability, impurity content and yield of the electronic-grade potassium hydroxide prepared in this application all reach a relatively good level.

[0026] Preferably, in step S3, the addition rate of washing liquid A is C1 L / h, and C1 and the maximum vacuum degree P1 satisfy the following condition: C1 = 0.5P1 ~ 5P1.

[0027] Step S3 is the washing process, the main purpose of which is to remove impurities from the crystals while minimizing the dissolution of potassium hydroxide. Therefore, the flow rate of the washing solution A needs to be set according to this objective. Too low a flow rate will result in insufficient washing, while too high a flow rate will cause excessive potassium hydroxide dissolution. The flow rate of the washing solution A and the negative pressure together determine the final residence time of the washing solution in the crystals. Therefore, this application sets the addition rate of the washing solution A, C1 = 0.5P1 to 5P1, to maximize the yield and the removal of impurities.

[0028] On the other hand, this application also provides a method for preparing an electronic-grade potassium hydroxide solution, comprising the following steps:

[0029] S1. The purified potassium hydroxide crystals are packed into an alkali-resistant corrosion-resistant container to form a crystal layer. The thickness of the packed crystal layer is recorded as L cm.

[0030] S2. A periodically varying negative pressure is applied to the bottom of the crystal layer. The time of each period is ts. The range of the vacuum degree P of the negative pressure during the periodic variation is denoted as P1 kPa ≥ P ≥ P2 kPa. Within each period, the negative pressure value decreases uniformly and stably from P1 to P2.

[0031] S3. Washing solution A is continuously added to the top of the crystal layer for washing, and daily chemical grade potassium hydroxide solution is collected at the bottom outlet of the crystal layer; the washing solution A is selected from at least one of ultrapure water and low potassium solution; the low potassium solution is a potassium hydroxide solution with a concentration of less than 42 wt% and an impurity content of less than a set value.

[0032] When the impurity content of the solution at the bottom outlet of the crystal layer in step S3 is less than or equal to the set value, the operation of step S4 is performed.

[0033] The set value is the highest allowable impurity content required for the target product, electronic-grade potassium hydroxide.

[0034] S4. Washing solution B is continuously added to the top of the crystal layer for washing, and electronic grade potassium hydroxide solution is collected at the outlet at the bottom of the crystal layer.

[0035] The washing solution B is selected from at least one of ultrapure water and low potassium solution; the low potassium solution in step S4 is a potassium hydroxide solution with a concentration of less than 42 wt% and an impurity content of less than a set value.

[0036] S5. When the thickness of the crystal layer is 1 / 4L to 1 / 2L, wash solution C is continuously added to the top of the crystal layer for washing, and the liquid C is collected at the bottom of the crystal layer.

[0037] In the preparation methods of electronic-grade potassium hydroxide solution and electronic-grade potassium hydroxide of this application, the selection of crystal layer thickness L, negative pressure periodic change time t, and vacuum degree magnitudes P1 and P2 in steps S1 to S3 are the same.

[0038] In addition, it should be noted that, through long-term work in this industry, the inventors not only discovered the problem that the mother liquor and potassium hydroxide crystals are difficult to separate completely by centrifugation and that washing is difficult during the preparation of electronic-grade potassium hydroxide, but also found that the existing technology has problems such as complicated preparation process, time-consuming preparation and unstable solution performance when preparing electronic-grade potassium hydroxide solution. In order to solve the washing problem in the preparation process of electronic-grade potassium hydroxide, the inventors thought of continuing to use the same equipment and method to prepare electronic-grade potassium hydroxide solution after washing to obtain electronic-grade potassium hydroxide, so that the obtained electronic-grade potassium hydroxide solution is a stable and uniform dissolution process, and can prepare electronic-grade potassium hydroxide solution with stable quality.

[0039] Further preferably, this application also includes step S6. Repeating steps S1-S5 to carry out a continuous reaction; and the washing liquid C in step S5 is ultrapure water, and the feed liquid C is a low potassium solution; when repeating steps S1-S5, the feed liquid C in step S5 is used as the low potassium solution in steps S3 and S4.

[0040] As the crystal layer dissolves, steps S1-S5 are repeated, and the low-potassium solution prepared in step S5 is directly used for all or part of the washing solution in step S3 or S4, thus realizing the circulation and continuity of the entire system and greatly improving the yield and preparation efficiency of the final electronic-grade potassium hydroxide solution.

[0041] Preferably, the addition rate of washing liquid B in step S4 is C2 L / h, and C2 and the maximum vacuum degree P1 satisfy the following condition: C2 = 5P1 ~ 10P1.

[0042] After washing in step S3, a large amount of impurities in the crystals have been removed, and the impurity content meets the requirements for electronic-grade potassium hydroxide (i.e., less than or equal to a set value). Therefore, in step S4, the main task is to dissolve the qualified electronic-grade potassium hydroxide crystals into a stable potassium hydroxide solution. Washing solution B mainly acts as a solvent for dissolution. To achieve this, the addition rate C2 of washing solution B needs to satisfy C2 = 5P1 to 10P1. If the flow rate of washing solution B is too low, it will result in insufficient dissolution, while if the flow rate is too high, it will increase the difficulty of process control.

[0043] More preferably, in step S5, the addition rate of the washing liquid C is C3 L / h, and C3 and the maximum vacuum degree P1 satisfy the following relationship: C3 = 5P1 ~ 10P1.

[0044] When the thickness of the crystal layer reaches 1 / 4L to 1 / 2L, preferably 1 / 3L, and the washing solution B is used to continue washing and dissolving at the flow rate of C2, the potassium hydroxide concentration of the washing solution C will not reach 42w due to insufficient crystal layer thickness, which cannot meet the application requirements of the electronics industry. At this time, the addition rate C3 of the washing solution C can be adjusted so that the dissolving solution C can still meet the requirements. Alternatively, the same or higher addition rate C2 as in step S4 can be used to continue washing. The collected solution is not used as the electronic grade potassium hydroxide solution for the product, but as a potassium hydroxide solution with a lower concentration and lower impurity content (i.e., low potassium solution).

[0045] This application selects the same washing liquid addition rate as in step S4, returning the collected low-concentration, low-impurity potassium hydroxide solution, i.e., the low-potassium solution of this application, to steps S3 and S4 as all or part of the washing liquid. This low-potassium solution can achieve the washing function of ultrapure water, while also ensuring that more potassium hydroxide from the system enters the target product (electronic-grade potassium hydroxide solution), thereby improving the yield of potassium hydroxide. Therefore, using the preparation method of this application, not only can a high-purity and stable electronic-grade potassium hydroxide product be obtained, but the product yield is also high, the production process can be carried out continuously, ensuring production efficiency and improving benefits.

[0046] In the above preparation method of this application, the low potassium solution obtained in step S5 is an electronic grade KOH solution with a concentration of less than 42w%, sodium ions not exceeding 5ppm, calcium ions not exceeding 50ppb, and other non-potassium and sodium metal ions not exceeding 10ppb.

[0047] In the preparation method described above in this application, in step S3, the impurity content in the solution at the outlet below the crystal layer is detected online by ICP-MS. When the impurity content is less than or equal to a set value, washing can be stopped to obtain electronic-grade potassium hydroxide crystals; or the washing solution B can be used for washing, and the electronic-grade potassium hydroxide solution can be collected.

[0048] In the preparation method described above in this application, the set values ​​are: sodium ions 5 ppm, calcium ions 50 ppb, and other non-sodium and non-potassium metal ions 10 ppb. That is, the impurity content in the target product, electronic-grade potassium hydroxide or electronic-grade potassium hydroxide solution, of this application satisfies the following conditions: sodium ions not exceeding 5 ppm, calcium ions not exceeding 50 ppb, and other non-potassium and non-sodium metal ions not exceeding 10 ppb.

[0049] In the above preparation method, the potassium hydroxide crystals after crystallization and purification in step S1 refer to potassium hydroxide crystals purified by crystallization purification or ion exchange, or potassium hydroxide crystals purified by other purification methods not mentioned in this application. The impurity content meets the following requirements: after sampling and dissolving to a KOH concentration of 48w%, sodium ions are not higher than 50ppm, calcium ions are not higher than 90ppb, and other non-potassium and sodium metal ions are all <30ppb.

[0050] Reactions S1-S6 of this application are all carried out at 15-30°C, preferably at room temperature.

[0051] In the above preparation method, washing liquid A, washing liquid B and washing liquid C are preferably added by spraying.

[0052] The beneficial effects of this invention are:

[0053] (1) The present invention achieves high yield of electronic grade potassium hydroxide with stable quality and impurity content by applying a periodically varying negative pressure below a fixed crystal layer and adding a washing liquid above the crystal layer to wash the purified potassium hydroxide crystals.

[0054] (2) This invention achieves the preparation of electronic-grade potassium hydroxide solution with stable quality, low impurity content, and high yield by applying a periodically varying negative pressure below a fixed crystal layer and adding a washing liquid above the crystal layer to dissolve the electronic-grade potassium hydroxide crystals. The preparation method is simple, improves the efficiency of solution preparation, and saves costs.

[0055] (3) By collecting the low-potassium solution in the later stage of dissolution and recycling the low-potassium solution for washing liquid in the process of preparing electronic-grade potassium hydroxide or washing liquid in the process of preparing electronic-grade potassium hydroxide solution, the system can be continuously circulated and the yield of electronic-grade potassium hydroxide is as high as 82% or more. Detailed Implementation

[0056] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the present invention will be further described below in conjunction with specific embodiments. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents used, or any products for which the manufacturer is not specified, are all commercially available conventional products. All features disclosed in this specification, except for mutually exclusive features and / or steps, may be combined in any manner.

[0057] Example 1

[0058] This embodiment provides a method for preparing electronic-grade potassium hydroxide, including the following steps:

[0059] S1. 220 kg of purified potassium hydroxide dihydrate crystals (60.50% KOH, Na = 36 ppm, Ca = 60 ppb, Fe = 22 ppb, Cu = 5 ppb, Zn = 8 ppb, and other non-sodium and potassium metal ions < 20 ppb) were packed into a PFA material container with a height-to-diameter ratio of 5, and the crystal layer was packed to a height of 160 cm.

[0060] S2. Turn on the vacuum system and apply a periodic negative pressure of 20KPa≥P≥5KPa to the crystal layer inside the container. In each cycle, the vacuum level changes periodically from 20KPa to 5KPa, and the cycle time is 90S.

[0061] S3. Introduce ultrapure water from the top of the crystal layer at a rate of 100 L / h, and continuously collect daily chemical grade potassium hydroxide solution (48 w% KOH) at the bottom feed outlet. Analyze the impurity content of the outlet solution online using ICP-MS. When the impurity content of the outlet solution is less than or equal to the set value (5 ppm for sodium ions, 30 ppb for calcium ions, and 10 ppb for other non-sodium potassium metal ions), i.e., when the impurity content of the outlet solution meets the requirements for electronic grade potassium hydroxide (sodium ions not higher than 5 ppm, calcium ions not higher than 30 ppb, and other non-sodium potassium metal ions not higher than 10 ppb), proceed to step S4.

[0062] S4. Stop washing. The crystals in the container are the electronic-grade potassium hydroxide of this application.

[0063] Final recycling:

[0064] Chemical grade potassium hydroxide solution: 47.92 kg; concentration 48 wt%, Na = 123 ppm, Ca = 162 ppb, Fe = 52 ppb, Cu = 22 ppb, Zn = 9 ppb; other non-sodium and non-potassium metal ions are all <20 ppb; product yield percentage: 17.29%;

[0065] Electronic grade potassium hydroxide: 184.98 kg: KOH content in crystals 59.5 wt%, Na = 5 ppm, Ca = 23 ppb, Fe = 8 ppb, Cu = 2 ppb, Zn = 5 ppb, other non-sodium and potassium metal ions are all <10 ppb; product yield: 82.69%.

[0066] Example 2

[0067] This embodiment provides a method for preparing electronic-grade potassium hydroxide solution, whose steps S1-S3 are exactly the same as in Example 1, and further includes:

[0068] S4. Introduce ultrapure water from the top of the crystal layer at a rate of 200 L / h, and continuously collect electronic-grade potassium hydroxide solution at the bottom feed outlet.

[0069] S5. When the dissolved thickness of the potassium hydroxide crystal layer in the container exceeds 110 cm, continue to introduce ultrapure water from the top of the crystal layer at a rate of 200 L / h, switch the collection container of the liquid outlet, and continuously collect the low potassium solution at the bottom liquid outlet.

[0070] Final recycling:

[0071] Chemical grade potassium hydroxide solution: 47.92 kg; concentration 48 wt%, Na = 123 ppm, Ca = 162 ppb, Fe = 52 ppb, Cu = 22 ppb, Zn = 9 ppb; other non-sodium and non-potassium metal ions are all <20 ppb; product yield percentage: 17.29%;

[0072] Electronic grade potassium hydroxide solution: 146.52 kg; concentration 48 wt%, Na = 5 ppm, Ca = 23 ppb, Fe = 8 ppb, Cu = 2 ppb, Zn = 5 ppb, other non-sodium and potassium metal ions <10 ppb; product yield percentage: 52.87%.

[0073] Low-potassium solution: 104.39 kg; concentration 38%, Na = 3 ppm, Ca = 19 ppb, Fe = 6 ppb, Cu = 2 ppb, Zn = 4 ppb, other non-sodium and potassium metal ions are all <10 ppb; product yield percentage: 29.83%;

[0074] In summary, in Example 2, the yield of daily chemical grade potassium hydroxide was 17.29%, and the yield of electronic grade potassium hydroxide (including low potassium solution) was 82.60%.

[0075] Example 3

[0076] This embodiment provides a method for preparing electronic-grade potassium hydroxide, including the following steps:

[0077] S1. 220 kg of purified potassium hydroxide dihydrate crystals (60.23% KOH, Na = 23 ppm, Ca = 36 ppb, Fe = 13 ppb, Cu = 6 ppb, Zn = 6 ppb, and other non-sodium and potassium metal ions < 20 ppb) were packed into a PFA material container with a height-to-diameter ratio of 5, and the crystal layer was packed to a height of 160 cm.

[0078] S2. Turn on the vacuum system and apply a periodic negative pressure of 20KPa≥P≥5KPa to the crystal layer inside the container. In each cycle, the vacuum level changes periodically from 20KPa to 5KPa, and the cycle time is 90S.

[0079] S3. Introduce the low-potassium solution (KOH content 38%) from Example 2 from the top of the crystal layer at a rate of 100 L / h. Continuously collect the daily chemical grade potassium hydroxide solution (48 w% KOH) at the bottom liquid outlet and continuously analyze the impurity content of the outlet solution online using ICP-MS. When the impurity content of the outlet solution is less than or equal to the set value (sodium ions 5 ppm, calcium ions 30 ppb, and other non-sodium potassium metal ions 10 ppb), that is, when the impurity content of the outlet solution meets the requirements of electronic grade potassium hydroxide solution (sodium ions not higher than 5 ppm, calcium ions not higher than 30 ppb, and other non-sodium potassium metal ions not higher than 10 ppb), proceed to step S4.

[0080] S4. Stop washing. The crystals in the container are the electronic-grade potassium hydroxide of this application.

[0081] Final recycling:

[0082] Daily chemical grade potassium hydroxide solution: 58.31 kg; concentration 48 wt%, Na = 72 ppm, Ca = 164 ppb, Fe = 32 ppb, Cu = 11 ppb, Zn = 8 ppb; other non-sodium potassium metal ions are all <20 ppb;

[0083] Electronic grade potassium hydroxide: 190.2 kg; KOH content in crystals 60.06%, Na = 4 ppm, Ca = 23 ppb, Fe = 7 ppb, Cu = 3 ppb, Zn = 3 ppb, and other non-sodium potassium metal ions are all <10 ppb.

[0084] Dosage of 38% KOH low potassium solution: 25.5 kg (Na = 3 ppm, Ca = 19 ppb, Fe = 6 ppb, Cu = 2 ppb, Zn = 4 ppb, other non-sodium and potassium metal ions are all <10 ppb).

[0085] The yield of electronic-grade KOH crystals reached 80.3%.

[0086] Example 4

[0087] This embodiment provides a method for preparing electronic-grade potassium hydroxide solution, whose steps S1-S3 are exactly the same as those in Example 3, and further include:

[0088] S4. Low potassium solution and ultrapure water (preferably the low potassium solution prepared in Example 2, and ultrapure water if the low potassium solution is insufficient) are introduced from the top of the crystal layer at a rate of 200 L / h, and electronic grade potassium hydroxide solution is continuously collected at the bottom liquid outlet.

[0089] S5. When the dissolved thickness of the potassium hydroxide crystal layer in the container exceeds 110 cm, continue to introduce ultrapure water from the top of the crystal layer at a rate of 200 L / h, switch the collection container of the liquid outlet, and continuously collect the low potassium solution at the bottom liquid outlet.

[0090] Final recycling:

[0091] Daily chemical grade potassium hydroxide solution: 58.31 kg; concentration 48 wt%, Na = 72 ppm, Ca = 164 ppb, Fe = 32 ppb, Cu = 11 ppb, Zn = 8 ppb; other non-sodium potassium metal ions are all <20 ppb;

[0092] Electronic grade potassium hydroxide solution: 218.75 kg; concentration 48 wt%, Na = 4 ppm, Ca = 23 ppb, Fe = 7 ppb, Cu = 3 ppb, Zn = 3 ppb, other non-sodium potassium metal ions are all <10 ppb;

[0093] Low potassium solution 99.60 kg; concentration 40 wt%, Na = 4 ppm, Ca = 21 ppb, Fe = 7 ppb, Cu = 2 ppb, Zn = 4 ppb, other non-sodium and potassium metal ions are all <10 ppb.

[0094] Example 5

[0095] This embodiment provides a method for preparing electronic-grade potassium hydroxide solution, including the following steps:

[0096] S1. 290 kg of purified potassium hydroxide dihydrate crystals (59.50% KOH, Na = 38 ppm, Ca = 51 ppb, Fe = 15 ppb, Cu = 2 ppb, Zn = 8 ppb, and other non-sodium and potassium metal ions < 20 ppb) were packed into a PFA material container with a height-to-diameter ratio of 5, and the crystal layer was packed to a height of 210 cm.

[0097] S2. Turn on the vacuum system and apply a periodic negative pressure of 30KPa≥P≥5KPa to the crystal layer inside the container. In each cycle, the vacuum level changes periodically from 30KPa to 5KPa, and the cycle time is 60S.

[0098] S3. Introduce ultrapure water from the top of the crystal layer at a rate of 90 L / h, and continuously collect daily chemical grade potassium hydroxide solution (48 w% KOH) at the bottom feed outlet. Analyze the impurity content of the outlet solution online using ICP-MS. When the impurity content of the outlet solution is less than or equal to the set value (5 ppm for sodium ions, 30 ppb for calcium ions, and 10 ppb for other non-sodium potassium metal ions), i.e., the impurity content of the outlet solution meets the requirements for electronic grade potassium hydroxide solution (sodium ions not higher than 5 ppm, calcium ions not higher than 30 ppb, and other non-sodium potassium metal ions not higher than 10 ppb), proceed to step S4.

[0099] S4. Introduce ultrapure water from the top of the crystal layer at a rate of 150 L / h, and continuously collect electronic-grade potassium hydroxide solution at the bottom feed outlet.

[0100] S5. When the dissolved thickness of the potassium hydroxide crystal layer in the container exceeds 140cm (two-thirds of the original thickness of the potassium hydroxide crystal layer), continue to introduce ultrapure water from the top of the crystal layer at a rate of 150L / h, switch the liquid outlet collection container, and continuously collect low potassium solution at the bottom liquid outlet.

[0101] Final recycling:

[0102] Daily chemical grade potassium hydroxide solution: 47.92 kg; concentration 48 wt%, Na = 123 ppm, Ca = 98 ppb, Fe = 52 ppb, Cu = 22 ppb, other non-sodium potassium metal ions are all <20 ppb;

[0103] Electronic grade potassium hydroxide solution: 167.79 kg; concentration 42 wt%, Na = 5 ppm, Ca = 26 ppb, Fe = 6 ppb, Cu = 2 ppb, other non-sodium potassium metal ions are all <10 ppb;

[0104] Low potassium solution 104.39 kg; concentration 39 wt%, Na = 3 ppm, Ca = 28 ppb, Fe = 6 ppb, Cu = 2 ppb, other non-sodium and potassium metal ions are all <10 ppb.

[0105] Example 6

[0106] This embodiment provides a method for preparing electronic-grade potassium hydroxide solution, including the following steps:

[0107] S1. 247 kg of purified potassium hydroxide monohydrate crystals (72% KOH, Na = 23 ppm, Ca = 38 ppb, Fe = 18 ppb, Cu = 8 ppb, Zn = 4 ppb, and other non-sodium and potassium metal ions < 20 ppb) were packed into an HDPE container with a height-to-diameter ratio of 5, and the crystal layer was filled to a height of 150 cm.

[0108] S2. Turn on the vacuum system and apply a periodic negative pressure of 30KPa≥P≥10KPa to the crystal layer inside the container. In each cycle, the vacuum level changes periodically from 30KPa to 10KPa, and the cycle time is 30S.

[0109] S3. Introduce ultrapure water from the top of the crystal layer at a rate of 15 L / h, and continuously collect daily chemical grade potassium hydroxide solution (48 w% KOH) at the bottom feed outlet. Analyze the impurity content of the outlet solution online using ICP-MS. When the impurity content of the outlet solution is less than or equal to the set value (5 ppm for sodium ions, 30 ppb for calcium ions, and 10 ppb for other non-sodium potassium metal ions), i.e., the impurity content of the outlet solution meets the requirements for electronic grade potassium hydroxide solution (sodium ions not higher than 5 ppm, calcium ions not higher than 30 ppb, and other non-sodium potassium metal ions not higher than 10 ppb), proceed to step S4.

[0110] S4. Introduce ultrapure water from the top of the crystal layer at a rate of 150 L / h, and continuously collect electronic-grade potassium hydroxide solution at the bottom feed outlet.

[0111] S5. When the dissolved thickness of the potassium hydroxide crystal layer in the container exceeds 100cm (two-thirds of the original thickness of the original potassium hydroxide crystal layer), switch the liquid outlet collection container and continuously collect low potassium solution at the bottom liquid outlet.

[0112] Final recycling:

[0113] Daily chemical grade potassium hydroxide solution: 78.75 kg; concentration 48 wt%, Na = 98 ppm, Ca = 104 ppb, Fe = 68 ppb, other non-sodium and potassium metal ions are all <20 ppb;

[0114] Electronic grade potassium hydroxide solution: 202.85 kg; concentration 46 wt%, Na = 2 ppm, Ca = 17 ppb, Fe = 3 ppb, other non-sodium potassium metal ions <10 ppb;

[0115] Low potassium solution 119.74 kg; concentration 39%, Na = 3 ppm, Ca = 16 ppb, Fe = 2 ppb, other non-sodium and potassium metal ions are all <10 ppb.

[0116] Comparative Example 1

[0117] This comparative example provides a method for preparing electronic-grade potassium hydroxide, which removes impurities by centrifugation and spraying ultrapure water as washing water during the centrifugation process. The specific operation is as follows:

[0118] 200 kg of purified potassium hydroxide dihydrate crystals (60.50% KOH, Na = 36 ppm, Ca = 66 ppb, Fe = 22 ppb, Cu = 5 ppb, Zn = 8 ppb, and other non-sodium and potassium metal ions < 20 ppb) were divided into four batches and placed into an internal and external fluorine-spraying centrifuge. The centrifuges were washed by spraying the crystals at a speed of 3000 r / min. The washing water for the four batches was 2 w%, 5 w%, 5 w%, and 8 w% of the added crystals, respectively. The washing mother liquor was combined with the crystallization mother liquor and used as industrial alkali for recovery.

[0119] The following are the results of preparing a 48% KOH solution from the four batches of recovered crystals:

[0120] First centrifugal washing: 50 kg of crystals were added, 1 kg of washing water was added, and 43.2 kg of crystals were recovered (yield 86.4%). After the crystals were dissolved (48 w%): Na: 18 ppm, Ca: 32 ppb, Fe: 12 ppb, and other non-sodium and potassium metal ions were all <10 ppb.

[0121] Second centrifugal washing: 50 kg of crystals were added, 2.5 kg of washing water was added, and 38.7 kg of crystals were recovered (yield 77.4%). After crystal dissolution (48 w%): Na: 4 ppm, Ca: 23 ppm, Fe: 8 ppb, and other non-sodium and potassium metal ions were all <10 ppb.

[0122] Third centrifugal washing: 50 kg of crystals were added, 2.5 kg of washing water was added, and 37.2 kg of crystals were recovered (yield 74.4%). After the crystals were dissolved (48 w%): Na: 7 ppm, Ca: 26 ppb, Fe: 11 ppb, and other non-sodium and potassium metal ions were all <10 ppb.

[0123] Fourth centrifugal washing: 50 kg of crystals were added, 4 kg of washing water was added, and 31.1 kg of crystals were recovered (yield 62.2%). After crystal dissolution (48 w%): Na: 3 ppm, Ca: 26 ppb, Fe: 10 ppb, and other non-sodium and potassium metal ions were all <10 ppb.

[0124] As shown in Comparative Example 1, when traditional crystal washing meets the requirements of electronic-grade potassium hydroxide solution (sodium ions not higher than 5 ppm, calcium ions not higher than 30 ppb, and other non-sodium potassium metal ions not higher than 10 ppb), 5w% to 8w% of washing water is required (for the second and fourth washes), and the crystal yield is only 62% to 77% (for the second and fourth washes).

[0125] Meanwhile, this method may result in quality fluctuations. For example, during the second and third centrifugal washing, using the same amount of washing water under the same conditions, the impurity content in the resulting products varies greatly.

[0126] Moreover, the traditional centrifugal washing method results in the washing mother liquor being incorporated into the crystallization mother liquor for industrial alkali recovery, which reduces the overall system yield.

[0127] Comparative Example 2

[0128] The only difference between this comparative example and Example 2 is that: instead of applying a periodically varying negative pressure, a fixed vacuum of 20 kPa is applied only at the bottom of the crystal layer.

[0129] Final recycling:

[0130] Chemical grade potassium hydroxide solution: 152.88 kg; concentration 48 wt%, Na = 62 ppm, Ca = 87 ppb, Fe = 32 ppb, Cu = 7 ppb, Zn = 10 ppb; other non-sodium and non-potassium metal ions are all <20 ppb; yield percentage: 55.17%;

[0131] Electronic grade potassium hydroxide solution: 41.52 kg; concentration 48 wt%, Na = 5 ppm, Ca = 28 ppb, Fe = 9 ppb, Cu = 3 ppb, Zn = 4 ppb, other non-sodium and potassium metal ions are all <10 ppb; product percentage: 14.98%;

[0132] Low potassium solution: 97.56 kg; concentration 41 wt%, Na = 5 ppm, Ca = 21 ppb, Fe = 8 ppb, Cu = 2 ppb, Zn = 4 ppb, other non-sodium and potassium metal ions are all <10 ppb; product percentage 34.08%;

[0133] Results of Comparative Example 2: Yield of chemical grade potassium hydroxide: 55.17%, Yield of electronic grade potassium hydroxide (including low potassium solution): 49.06%.

[0134] The comparison between Comparative Example 2 and Example 2 shows that when potassium hydroxide crystals are washed without periodically varying negative pressure, the time required to reach the electronic grade potassium hydroxide requirement is extended, the amount of electronic grade potassium hydroxide obtained is reduced, and the yield is decreased.

[0135] This indicates that while applying a stable negative pressure to a fixed crystal layer can increase the contact between the washing liquid and the crystal layer to some extent compared to centrifugal washing, it still cannot avoid the problem of the washing liquid forming a fixed liquid flow gap (short circuit) in the crystal layer. Therefore, it cannot solve the problem of insufficient washing and cannot achieve the effect of obtaining a stable quality product with a high yield.

[0136] In summary, the method of the present invention enables potassium hydroxide crystals to be thoroughly and effectively washed, and the product obtained after washing has stable quality and high yield. It also produces a stable electronic-grade potassium hydroxide solution, avoiding the problems of time-consuming and laborious solution preparation caused by the unstable quality of each batch of electronic-grade potassium hydroxide during use.

[0137] This invention is not limited to the above-described embodiments. Anyone should know that any structural changes made under the guidance of this invention, and any technical solutions that are the same as or similar to this invention, fall within the protection scope of this invention.

Claims

1. A method for preparing electronic-grade potassium hydroxide, characterized in that, Includes the following steps: S1. The purified potassium hydroxide crystals are packed into an alkali-resistant corrosion-resistant container to form a crystal layer. The thickness of the packed crystal layer is recorded as L cm. S2. A periodically varying negative pressure is applied to the bottom of the crystal layer. The time of each variation period is ts. The periodic variation range of the vacuum degree P is denoted as P1 kPa ≥ P ≥ P2 kPa. Within each variation period, the negative pressure value decreases uniformly and stably from P1 to P2. S3. Washing solution A is continuously added to the top of the crystal layer for washing, and daily chemical grade potassium hydroxide solution is collected at the bottom outlet of the crystal layer; the washing solution A is selected from at least one of ultrapure water and low potassium solution; the low potassium solution is a potassium hydroxide solution with a concentration of less than 42 wt% and an impurity content of less than a set value. When the impurity content of the solution at the bottom outlet of the crystal layer in step S3 is less than or equal to the set value, proceed to step S4. The set value is the highest allowable impurity content required for the target product, electronic-grade potassium hydroxide. S4. Stop washing. At this point, the crystal layer in the alkali-resistant container is electronic-grade potassium hydroxide.

2. The method for preparing electronic-grade potassium hydroxide according to claim 1, characterized in that, The crystal layer thickness L in step S1 and the maximum vacuum degree P1 that changes periodically in step S2 satisfy the following condition: 5P1≤L≤10P1.

3. The method for preparing electronic-grade potassium hydroxide according to claim 1 or 2, characterized in that, In step S2, the cycle time t satisfies: 30s≤t≤180s; the maximum vacuum degree P1 satisfies: 20KPa≤P1≤30KPa; and the minimum vacuum degree P2 satisfies: 5KPa≤P2≤10KPa.

4. The method for preparing electronic-grade potassium hydroxide according to claim 3, characterized in that, In step S3, the rate at which the washing liquid A is added is C1 L / h, and C1 and the maximum vacuum degree P1 satisfy the following condition: C1 = 0.5P1 ~ 5P1.

5. The method for preparing electronic-grade potassium hydroxide according to claim 1, characterized in that, The purified potassium hydroxide crystals obtained in step S1 refer to potassium hydroxide crystals purified by a purification method, whose impurity content meets the following requirements: after sampling and dissolving to a KOH concentration of 48w%, sodium ions are not higher than 50ppm, calcium ions are not higher than 90ppb, and other non-potassium and sodium metal ions are all <30ppb.

6. The method for preparing electronic-grade potassium hydroxide according to claim 1, characterized in that, In step S4, the set values ​​are: sodium ions 5 ppm, calcium ions 50 ppb, and other non-sodium and non-potassium metal ions 10 ppb.

7. A method for preparing an electronic-grade potassium hydroxide solution, characterized in that, Includes the following steps: Steps S1 to S3 are performed using steps S1 to S3 of any of the methods described in claims 1-6; S4. Washing solution B is continuously added to the top of the crystal layer for washing, and electronic grade potassium hydroxide solution is collected at the bottom outlet of the crystal layer; the washing solution B is selected from at least one of ultrapure water and low potassium solution; the low potassium solution in step S4 is a potassium hydroxide solution with a concentration of less than 42 wt% and an impurity content of less than a set value. S5. When the thickness of the crystal layer is 1 / 4L to 1 / 2L, wash solution C is continuously added to the top of the crystal layer for washing, and the liquid C is collected at the bottom of the crystal layer.

8. The method for preparing electronic-grade potassium hydroxide solution according to claim 7, characterized in that, Also includes: Step S6. Repeat steps S1-S5 to carry out a continuous reaction; and the washing liquid C in step S5 is ultrapure water, and the feed liquid C is a low potassium solution; when repeating steps S1-S5, the feed liquid C in step S5 is used as the low potassium solution in steps S3 and S4.

9. The method for preparing electronic-grade potassium hydroxide solution according to claim 7, characterized in that, In step S4, the addition rate of washing liquid B is C2 L / h, and C2 and the maximum vacuum degree P1 satisfy the following relationship: C2 = 5P1 ~ 10P1.

10. The method for preparing electronic-grade potassium hydroxide solution according to claim 7, characterized in that, In step S5, the addition rate of the washing liquid C is C3 L / h, and C3 and the maximum vacuum degree P1 satisfy the following relationship: C3 = 5P1 ~ 10P1.