Method for preparing electronic grade caustic soda from ion-exchange membrane caustic soda

Abstract

The application discloses a method for preparing electronic-grade caustic soda from ion-exchange membrane caustic soda, which comprises the following steps: sequentially performing primary cooling crystallization, primary filtration, adding a first precipitant, secondary filtration, adding a second precipitant, secondary cooling crystallization, and tertiary filtration on the ion-exchange membrane caustic soda to obtain the electronic-grade caustic soda. The ion-exchange membrane caustic soda is treated by simple chemical precipitation crystallization and physical filtration technology, so that the content of Ca²⁺ is less than or equal to 0.00042%, the content of Pb²⁺ is less than or equal to 0.0011%, the content of Fe³⁺ is less than or equal to 0.00033%, and the content of CO₃²⁻ is less than or equal to 0.39%, which meets the requirements of the electronic-grade caustic soda standard, and the cost is lower and the yield is higher compared with electrodialysis filtration.

Description

Technical Field

[0001] This invention relates to the field of chemical production technology, and in particular to a method for preparing electronic-grade caustic soda using ion-exchange membrane caustic soda. Background Technology

[0002] Ion-exchange membrane caustic soda is produced by electrolyzing brine using an ion-exchange membrane method. The main principle is based on the use of a cation exchange membrane, which has special selective permeability, allowing only cations to pass through while blocking anions and gases. Refined saturated brine enters the anode chamber, while pure water (with a certain amount of NaOH solution added) enters the cathode chamber. When electricity is applied, H₂O is discharged at the cathode surface to generate H₂, and Na₂... + It then passes through the ion-exchange membrane from the anode chamber into the cathode chamber. At this time, the catholyte introduced into the cathode chamber contains NaOH; Cl - Cl2 is generated by discharge on the anode surface. The dilute brine after electrolysis is then discharged from the anode chamber and can be recycled after adding salt to increase its concentration. However, saturated brine contains sediment and calcium. 2+ Mg 2+ Fe 3+ The caustic soda contains impurities that are far from meeting the requirements for electrolysis, thus necessitating purification and refining. The purified and refined ion-exchange membrane caustic soda is industrial-grade caustic soda, meeting the requirements of the national standard GB / T 209-2018_IL_I.

[0003] Electronic-grade caustic soda is an important raw material commonly used in the electronics industry. Meeting the requirements of enterprise standard Q / YBTY•062-2021_IL_I typically involves filtration, washing, and drying to ensure a high NaOH content per unit weight and that the solution is free of impurities and chloride ions. Specific impurity contents of electronic-grade caustic soda and ion-exchange membrane caustic soda are shown in Table 1.

[0004] Table 1. Impurity content of electronic-grade caustic soda and ion-exchange membrane caustic soda

[0005]

[0006] As shown in Table 1, electronic-grade caustic soda has more stringent requirements for impurities compared to ion-exchange membrane caustic soda. Taking ion-exchange membrane caustic soda produced by a certain company, the content of anions and cations was measured to be ω(Ca²⁺) ≤0.0062%, ω(Pb²⁺) ≤0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO₃²⁻) = 0.8%. Therefore, the ion-exchange membrane caustic soda needs to reduce the content of impurity elements to meet the standards for electronic-grade caustic soda. Currently, the main methods for purifying ultra-high purity sodium hydroxide from industrial caustic soda flakes are the anhydrous ethanol method and electrodialysis. The anhydrous ethanol method can effectively remove impurities from industrial caustic soda flakes, producing ultra-high purity sodium hydroxide reagent. However, because anhydrous ethanol has extremely low solubility in solid caustic soda, purifying a small amount of sodium hydroxide requires a large volume of anhydrous ethanol, resulting in significant ethanol evaporation losses during the production process. Electrodialysis, combined with ion-exchange membrane separation technology, purifies sodium hydroxide to produce ultra-high purity reagent. For example, Chinese invention patent application CN 111943229 A discloses a method for preparing ultra-high purity sodium hydroxide reagent using electrodialysis of industrial caustic soda flakes. This method involves dissolving industrial caustic soda flakes in water to prepare a high-concentration liquid caustic soda; filtering the high-concentration liquid caustic soda to obtain purified liquid caustic soda; purifying the purified liquid caustic soda using electrodialysis to prepare the electrodialysis product, i.e., ultra-high purity sodium hydroxide reagent; and returning the anolyte after electrodialysis, which is a low-concentration liquid caustic soda, to be filtered and used as a dissolving solution for preparing high-concentration liquid caustic soda. While this method can produce high-concentration liquid caustic soda, the use of electrodialysis technology leads to high power consumption; recycling the anolyte as a dissolving solution causes the accumulation of impurities in the solution, resulting in increased power consumption, scaling, clogging, and even damage to the electrodialysis membrane, leading to high processing costs. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a low-cost, high-yield method for preparing electronic-grade caustic soda using ion-exchange membrane caustic soda.

[0008] The technical solution adopted by the present invention to solve its technical problem is: a method for preparing electronic-grade caustic soda using ion-exchange membrane caustic soda, wherein ion-exchange membrane caustic soda is subjected to a first cooling crystallization, a first filtration, the addition of a first precipitant, a second filtration, the addition of a second precipitant, a second cooling crystallization, and a third filtration to obtain electronic-grade caustic soda.

[0009] Furthermore, the concentration of the caustic soda in the ion-exchange membrane is 45-55%.

[0010] Furthermore, the first precipitant is Ca(OH)2 and the second precipitant is Na2CO3.

[0011] Furthermore, the amount of the first precipitant added is 5.5–6.5 g / L, and the amount of the second precipitant added is 1.2–1.6 g / L.

[0012] Furthermore, the temperature for the first cooling crystallization is 3–8°C, and the temperature for the second cooling crystallization is 3–8°C.

[0013] Furthermore, the temperature of the first cooling crystallization is 3-8°C, and the crystallization is allowed to stand for 10-20 minutes; the temperature of the second cooling crystallization is 3-8°C, and the crystallization is allowed to stand for 90-150 minutes.

[0014] Furthermore, the primary filtration, secondary filtration, and tertiary filtration use filter cloths with a thickness of 1–3 μm.

[0015] The beneficial effects of this invention are as follows: This invention treats caustic soda through an ion-exchange membrane using a simple chemical precipitation crystallization and physical filtration technique, achieving ω(Ca²⁺)≤0.00042%, ω(Pb²⁺)≤0.0011%, ω(Fe³⁺)≤0.00033%, and ω(CO3²⁻)≤0.39%, which meets the requirements of electronic-grade caustic soda standards. Compared to electrodialysis filtration, this method has lower costs and higher yields. Detailed Implementation

[0016] The present invention will be further described below with reference to embodiments.

[0017] Example 1:

[0018] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0019] The caustic soda ion-exchange membrane was cooled to 5°C, allowed to stand for 15 minutes, and then filtered once through a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0020] Add Ca(OH)2 to the primary filtrate and stir to dissolve it, so that the concentration of Ca(OH)2 in the primary filtrate is 5.92 g / L. Let it stand for 120 min, and then filter it a second time using a filter cloth of 1-3 μm to obtain the secondary filtrate.

[0021] Add Na2CO3 to the secondary filtrate and stir to dissolve it, so that the concentration of Na2CO3 in the secondary filtrate is 1.41 g / L. Cool it to 5℃ and let it stand for 120 min. Then filter it three times with a filter cloth of 1-3 μm to obtain the tertiary filtrate.

[0022] The tertiary filtrate was tested and found to have an alkali concentration of 52.03% and impurity content of ω(Ca²⁺)=0.00035%, ω(Pb²⁺)=0.0008%, ω(Fe³⁺)=0.00028%, and ω(CO3²⁻)=0.39%, which meets the requirements of electronic-grade caustic soda standards.

[0023] Example 2:

[0024] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0025] The caustic soda ion-exchange membrane was cooled to 3°C, allowed to stand for 15 minutes, and then filtered once through a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0026] Add Ca(OH)2 to the primary filtrate and stir to dissolve it, so that the concentration of Ca(OH)2 in the primary filtrate is 5.92 g / L. Let it stand for 120 min, and then filter it a second time using a filter cloth of 1-3 μm to obtain the secondary filtrate.

[0027] Add Na2CO3 to the secondary filtrate and stir to dissolve it, so that the concentration of Na2CO3 in the secondary filtrate is 1.41 g / L. Cool to 3℃ and let stand for 120 min. Then filter three times with a filter cloth of 1-3 μm to obtain the tertiary filtrate.

[0028] The tertiary filtrate was tested and found to have an alkali concentration of 52.03% and impurity content of ω(Ca²⁺)=0.00029%, ω(Pb²⁺)=0.0006%, ω(Fe³⁺)=0.00021%, and ω(CO3²⁻)=0.39%, which meets the requirements of electronic-grade caustic soda standards.

[0029] Example 3:

[0030] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0031] The caustic soda ion-exchange membrane was cooled to 8°C, allowed to stand for 15 minutes, and then filtered once through a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0032] Add Ca(OH)2 to the primary filtrate and stir to dissolve it, so that the concentration of Ca(OH)2 in the primary filtrate is 5.92 g / L. Let it stand for 120 min, and then filter it a second time using a filter cloth of 1-3 μm to obtain the secondary filtrate.

[0033] Add Na2CO3 to the secondary filtrate and stir to dissolve it, so that the concentration of Na2CO3 in the secondary filtrate is 1.41 g / L. Cool it to 8℃ and let it stand for 120 min. Then filter it three times with a filter cloth of 1-3 μm to obtain the tertiary filtrate.

[0034] The tertiary filtrate was tested and found to have an alkali concentration of 52.05% and impurity content of ω(Ca²⁺)=0.00042%, ω(Pb²⁺)=0.0011%, ω(Fe³⁺)=0.00033%, and ω(CO3²⁻)=0.39%, which meets the requirements of electronic-grade caustic soda standards.

[0035] Comparative Example 1: (No single cooling crystallization, otherwise the same as Example 3)

[0036] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0037] Add Ca(OH)2 to the ion-exchange membrane caustic soda and stir to dissolve, so that the concentration of Ca(OH)2 in the ion-exchange membrane caustic soda is 5.92 g / L. Let it stand for 120 min, and then filter it once with a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0038] Add Na2CO3 to the primary filtrate and stir to dissolve, so that the concentration of Na2CO3 in the secondary filtrate is 1.41 g / L. Cool to 8℃ and let stand for 120 min. Then filter a second time using a 1-3 μm filter cloth to obtain the secondary filtrate.

[0039] The secondary filtrate was found to have an alkali concentration of 52.01% and impurity content of ω(Ca²⁺)=0.00063%, ω(Pb²⁺)=0.0028%, ω(Fe³⁺)=0.0018%, and ω(CO3²⁻)=0.39%, which does not meet the requirements of the electronic grade caustic soda standard.

[0040] Comparative Example 2: (No Na2CO3 added, otherwise the same as Example 1)

[0041] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0042] The caustic soda ion-exchange membrane was cooled to 5°C, allowed to stand for 15 minutes, and then filtered once through a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0043] Add Ca(OH)2 to the primary filtrate and stir to dissolve it, so that the concentration of Ca(OH)2 in the primary filtrate is 5.92 g / L. Let it stand for 120 min, and then filter it a second time using a filter cloth of 1-3 μm to obtain the secondary filtrate.

[0044] The secondary filtrate was cooled to 5°C and allowed to stand for 120 minutes. Then, it was filtered three times with a 1-3 μm filter cloth to obtain the tertiary filtrate.

[0045] The tertiary filtrate was tested and found to have an alkali concentration of 52.04%, and impurity contents of ω(Ca²⁺)=0.14053%, ω(Pb²⁺)=0.0008%, ω(Fe³⁺)=0.00028%, and ω(CO3²⁻)=0.12%, which does not meet the requirements of the electronic grade caustic soda standard.

[0046] Comparative Example 3: (No Ca(OH)2 added, otherwise the same as Example 1)

[0047] A sample of ion-exchange membrane caustic soda produced by a certain company was measured to have a concentration of 52.01%, ω(Ca²⁺) = 0.0062%, ω(Pb²⁺) = 0.0032%, ω(Fe³⁺) = 0.0032%, and ω(CO³⁻) = 0.8%.

[0048] The caustic soda ion-exchange membrane was cooled to 5°C, allowed to stand for 15 minutes, and then filtered once through a 1-3 μm filter cloth to obtain the first-stage filtrate.

[0049] Add Na2CO3 to the primary filtrate and stir to dissolve it, so that the concentration of Na2CO3 in the primary filtrate is 1.41 g / L. Cool to 5℃ and let stand for 120 min. Then filter it a second time using a 1-3 μm filter cloth to obtain the secondary filtrate.

[0050] The secondary filtrate was found to have an alkali concentration of 58.32% and impurity content of ω(Ca²⁺)=0.00021%, ω(Pb²⁺)=0.0008%, ω(Fe³⁺)=0.00026%, and ω(CO3²⁻)=0.88%, which does not meet the requirements of the electronic grade caustic soda standard.

Claims

1. A method for preparing electronic-grade caustic soda using an ion-exchange membrane, characterized in that: The ion-exchange membrane caustic soda was subjected to a series of processes: first cooling and crystallization, first filtration, addition of a first precipitant, second filtration, addition of a second precipitant, second cooling and crystallization, and third filtration to obtain electronic-grade caustic soda.

2. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 1, characterized in that: The concentration of the caustic soda in the ion-exchange membrane is 45-55%.

3. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 1, characterized in that: The first precipitant is Ca(OH)2 and the second precipitant is Na2CO3.

4. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 3, characterized in that: The amount of the first precipitant added is 5.5–6.5 g / L, and the amount of the second precipitant added is 1.2–1.6 g / L.

5. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 1, characterized in that: The temperature for the first cooling crystallization is 3–8°C, and the temperature for the second cooling crystallization is 3–8°C.

6. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 5, characterized in that: The temperature for the first cooling crystallization is 3-8℃, and the crystallization is allowed to stand for 10-20 minutes; the temperature for the second cooling crystallization is 3-8℃, and the crystallization is allowed to stand for 90-150 minutes.

7. The method for preparing electronic-grade caustic soda using an ion-exchange membrane according to claim 1, characterized in that: The primary, secondary, and tertiary filtration processes use filter cloths with a diameter of 1–3 μm.

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