A method for preparing electronic-grade sulfuric acid based on low-temperature suspension crystallization and iterative balance of redox reactions

Abstract

This invention discloses a method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction, comprising the following steps: s1: adding industrial sulfuric acid as raw material to a freeze crystallization reactor for low-temperature freeze suspension crystallization; s2: adding an oxidant and / or a reducing agent and stirring; s3: performing solid-liquid separation to obtain sulfuric acid crystals and filtrate; s4: melting the sulfuric acid crystals at a set temperature to obtain electronic-grade sulfuric acid. This invention establishes a chemical field during the low-temperature suspension crystallization process by introducing oxidizing or reducing substances. The proposed method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction simplifies the production process, reduces energy consumption and costs, and offers significant economic, social, and environmental benefits, as well as promising application prospects.

Description

Technical Field

[0001] This invention relates to the field of sulfuric acid production, specifically to a method for preparing electronic-grade sulfuric acid based on the iterative equilibrium of low-temperature suspension crystallization and redox reaction. Background Technology

[0002] Electronic-grade sulfuric acid, also known as high-purity sulfuric acid or ultra-pure sulfuric acid, is a key basic chemical reagent in the microelectronics industry. In semiconductor, chip, and integrated circuit processing and assembly, it is used for cleaning and etching silicon wafers to remove impurities, inorganic residues, and carbon deposits. Therefore, the purity and cleanliness of electronic-grade sulfuric acid have a significant impact on the yield, electrical performance, and reliability of electronic components. With the rapid iteration of information technology and electronic products, the demand for electronic-grade sulfuric acid is increasing year by year.

[0003] Currently, there are two main methods for preparing electronic-grade sulfuric acid both domestically and internationally: one is the industrial sulfuric acid distillation method (which can be divided into atmospheric distillation and vacuum distillation), and the other is the direct absorption method of high-purity sulfur trioxide gas. The distillation method for preparing electronic-grade sulfuric acid includes four parts: a chemical pretreatment unit, a continuous distillation unit, an ultra-clean multi-stage filtration unit, and an ultra-clean bottling unit. The gas absorption method refers to the direct absorption of clean sulfur trioxide using ultrapure water or ultrapure sulfuric acid to prepare electronic-grade sulfuric acid. The gas absorption method mainly includes four steps: SO3 purification, SO3 absorption, sulfuric acid filtration purification, and tail gas treatment. The applicant's research has found that current high-purity sulfuric acid production processes suffer from complexities, high energy consumption, and high costs. Summary of the Invention

[0004] To overcome the aforementioned technical deficiencies and address the problems of complex production processes, high energy consumption, and high costs associated with high-purity sulfuric acid, this invention provides a method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reactions. To solve the above problems, this invention is implemented using the following technical solution:

[0005] A method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction includes the following steps:

[0006] s1: Add industrial sulfuric acid as raw material to the freeze crystallization reactor for low-temperature freeze suspension crystallization treatment;

[0007] s2: Add oxidizing agent and / or reducing agent and stir;

[0008] s3: Perform solid-liquid separation to obtain sulfuric acid crystals and filtrate;

[0009] s4: The sulfuric acid crystals are melted at a set temperature to obtain electronic-grade sulfuric acid.

[0010] Preferably, the industrial sulfuric acid in step s1 is industrial sulfuric acid with a sulfuric acid mass fraction of 95%.

[0011] Preferably, the oxidant in step s2 includes ozone and hydrogen peroxide.

[0012] Preferably, the reducing agent in step s2 is hydrogen.

[0013] Preferably, the set temperature in step s4 is greater than 25°C.

[0014] Compared with the prior art, the beneficial effects of the present invention are:

[0015] A method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction includes the following steps:

[0016] s1: Add industrial sulfuric acid as raw material to the freeze crystallization reactor for low-temperature freeze suspension crystallization treatment;

[0017] s2: Add oxidizing agent and / or reducing agent and stir;

[0018] s3: Perform solid-liquid separation to obtain sulfuric acid crystals and filtrate;

[0019] s4: The sulfuric acid crystals are melted at a set temperature to obtain electronic-grade sulfuric acid.

[0020] This invention establishes a chemical field during low-temperature suspension crystallization by introducing oxidizing or reducing substances. The redox reaction allows for a more thorough transformation or removal of oxidizing and reducing substances, better ensuring the purity of sulfuric acid crystals. Based on low-temperature suspension crystallization technology, this invention proposes a technique for preparing high-purity ferrous sulfate crystals through redox potential regulation and synergistic low-temperature crystallization. By adding oxidizing or reducing agents, the redox potential of trace impurities during low-temperature crystallization is precisely controlled, leading to the removal of impurity elements through directional speciation, thus achieving efficient purification of sulfuric acid. This invention presents an electronic-grade sulfuric acid preparation method based on iterative equilibrium of low-temperature suspension crystallization and redox reactions. This simplified production process reduces energy consumption and costs, offering significant economic, social, and environmental benefits, and promising application prospects. Attached Figure Description

[0021] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, wherein:

[0022] Figure 1 This is a schematic diagram of the system structure of the present invention;

[0023] In the diagram: 1. Freezing crystallization reactor; 2. Refrigeration unit; 3. Oxidant storage tank; 4. Reducing agent storage tank; 5. Solid-liquid separation unit; 6. Wastewater storage tank; 7. Electronic sulfuric acid storage tank. Detailed Implementation

[0024] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0025] Currently, there are two main methods for preparing electronic-grade sulfuric acid both domestically and internationally: one is the industrial sulfuric acid distillation method (which can be divided into atmospheric distillation and vacuum distillation), and the other is the direct absorption method of high-purity sulfur trioxide gas.

[0026] The process for preparing electronic-grade sulfuric acid by distillation comprises four parts: a chemical pretreatment unit, a continuous distillation unit, an ultra-clean multi-stage filtration unit, and an ultra-clean bottling unit. Because industrial sulfuric acid contains light components such as sulfur dioxide and organic matter, strong oxidants (potassium permanganate, potassium dichromate, etc.) are added before distillation purification to oxidize the reducing impurities in the sulfuric acid into sulfuric acid and carbon dioxide. Then, the treated sulfuric acid is fed into a quartz distillation column for distillation to remove metallic impurities (mainly in the form of high-boiling-point sulfates) and particulate impurities. Finally, it is filtered through a microporous membrane to remove fine particulate impurities, thus obtaining high-purity sulfuric acid.

[0027] Distillation methods can be divided into atmospheric distillation and vacuum distillation. Atmospheric distillation typically involves temperatures as high as 330°C, requiring high-quality materials for the apparatus (such as quartz glass). Vacuum distillation, on the other hand, operates at temperatures of 175–190°C and pressures of 1.33–2.67 kPa, and the apparatus can be made of borosilicate glass and fluoropolymer materials.

[0028] Generally, distillation processes are difficult to control, require high operational standards, and often result in inconsistent product quality due to unstable process parameters. Furthermore, the strong corrosive and oxidizing properties of sulfuric acid at high temperatures frequently lead to corrosion of equipment components and a decrease in purity.

[0029] The gas absorption method refers to the direct absorption of clean sulfur trioxide using ultrapure water or ultrapure sulfuric acid to prepare electronic-grade sulfuric acid. The gas absorption method mainly includes four processes: SO3 purification, SO3 absorption, sulfuric acid filtration purification, and tail gas treatment. Among these, SO3 purification and precise sulfuric acid filtration are crucial for achieving product compliance.

[0030] Before absorption, sulfur dioxide in fuming sulfuric acid is typically oxidized to sulfur trioxide using hydrogen peroxide (sulfur dioxide content should be below 10 mg / kg), and then evaporated using a falling film evaporator. After further impurity removal (traces of sulfuric acid, nitrosylsulfuric acid, particulate impurities, etc.), it is directly absorbed by ultrapure water or ultrapure sulfuric acid. The ultrapure sulfuric acid is cooled in a cooler and then enters a degassing tower where SO2 is stripped using high-purity oxygen or nitrogen aeration (reducing substances to below 2 ppm). The tail gas enters a recovery system and is filtered through an ultrapure sulfuric acid liquid-phase membrane ultra-clean filter to obtain electronic-grade sulfuric acid product.

[0031] However, this process requires high-purity reagents, and to ensure the purity of the electronic-grade sulfuric acid product, the hydrogen peroxide and pure water used must also be electronic-grade, making the production cost of such electronic-grade sulfuric acid high. Furthermore, sulfur trioxide itself has relatively unstable physicochemical properties and is highly corrosive; pipeline leaks can cause serious environmental accidents. During purification and preparation, the temperature required to maintain the liquid or gas phase of sulfur trioxide must also be considered, especially in winter, when the heating of equipment and pipelines consumes a large amount of heat.

[0032] To address the problems of complex, energy-intensive, and costly current high-purity sulfuric acid production processes, this paper proposes several measures, including ozone-based alternative aeration for sulfur dioxide removal, development of a vertical tube bundle SO2 generator, and the development of multi-cycle evaporation and absorption. These measures demonstrate potential in mitigating environmental hazards and reducing process costs.

[0033] In addition, a method for producing electronic-grade sulfuric acid through vacuum distillation and falling film crystallization was proposed. This process includes four steps: vacuum distillation (pre-preparation of high-purity distilled sulfuric acid), cooling crystallization (film growth), sweating purification, and melt liquefaction. Vacuum distillation can remove most impurities from industrial sulfuric acid. By controlling the falling film crystallization conditions, electronic-grade sulfuric acid ranging from MOS to BV-III can be produced. However, the core steps of these improved processes are still distillation and gas absorption, which present the following problems: firstly, these core technologies are still controlled by foreign companies; secondly, they still cannot produce the BV-IV and BV-V grade sulfuric acid urgently needed in my country.

[0034] To effectively solve the above-mentioned technical problems, this invention provides a method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction, comprising the following steps:

[0035] s1: Add industrial sulfuric acid as raw material to the freeze crystallization reactor for low-temperature freeze suspension crystallization treatment;

[0036] s2: Add oxidizing agent and / or reducing agent and stir;

[0037] s3: Perform solid-liquid separation to obtain sulfuric acid crystals and filtrate;

[0038] s4: Sulfuric acid crystals are melted at a set temperature to obtain electronic-grade sulfuric acid.

[0039] Furthermore, the industrial sulfuric acid in step s1 is industrial sulfuric acid with a sulfuric acid mass fraction of 95%.

[0040] Furthermore, the oxidant in step s2 includes ozone and hydrogen peroxide.

[0041] Furthermore, the reducing agent in step s2 is hydrogen gas.

[0042] Furthermore, the set temperature in step s4 is greater than 25°C.

[0043] Low-temperature suspension crystallization utilizes the differences in solubility of components in a mixture under hot and cold conditions, and employs a gradual cooling method to transform the target substance into a solid crystal through crystallization, thereby achieving separation and purification.

[0044] During crystal growth, molecules with the same lattice structure continuously accumulate on the crystal nucleus, causing the crystal to grow. Impurities are left in the liquid phase and purified through solid-liquid separation. Under low-temperature conditions, excessively rapid crystal growth can lead to entrainment phenomena such as surface adhesion, embedding, and liquid cells, as interfacial impurities do not have enough time to diffuse.

[0045] Stirring causes the crystals to remain suspended within the crystallizer, while forced convection accelerates the solute diffusion and mass transfer rate at the crystal interface, reducing impurity entrainment. Furthermore, by controlling the crystal nucleation and growth process, combined with ripening, washing, and recrystallization, the impurity entrainment caused by adhesion and encapsulation can be mitigated, resulting in large-size, high-purity crystals.

[0046] Currently, it is known that low-temperature suspension crystallization has been applied to remove and separate impurities such as organic matter, heavy metals, and inorganic salts from mixed components, and has shown excellent performance.

[0047] Studies have found that purifying phosphoric acid using a low-temperature suspension crystallization method, with a H3PO4 feed mass fraction of 84%-86% and a washing tower stirring rate of 10-20 r / min, reduces the percentage content of impurities such as arsenic, lead, and fluorine in phosphoric acid to below the order of 10⁻⁹. Subsequently, high-purity NiSO₄ and CoSO₄ hydrates can be separated from aqueous solutions of metal sulfates and dilute sulfuric acid solutions using the low-temperature crystallization method.

[0048] Although low-temperature suspension crystallization appears to have great potential for substance purification, there are still cases where impurities cannot be completely removed. For example, the effect of impurity ions on the purification of urea phosphate by low-temperature suspension crystallization was investigated, and it was found that Al... 3+ Fe 3+ Mg 2+ and SO4 2- Both will decrease the yield of urea phosphate.

[0049] The applicant studied the interaction between crystals and organic impurities at the molecular level and found that during low-temperature suspension crystallization, the functional groups of organic matter form hydrogen bonds with the crystals, adsorbing onto the crystal surface or entering the crystal interior, resulting in low crystal purity. Therefore, low-temperature suspension crystallization, similar to distillation technology, can significantly improve the purity of products such as acids and salts; however, the simple low-temperature suspension crystallization process often fails to guarantee the production of high-purity crystals.

[0050] Further research revealed that introducing a redox reaction significantly improved impurity removal during the distillation and gas absorption methods for producing electronic-grade sulfuric acid. The introduction of a chemical reaction field during freeze-drying crystallization was also proven to effectively improve crystal purity.

[0051] Supporting technologies for this research include: Yoolim Ahn et al. discovered that a spontaneous redox reaction between tetrathiofulvalene (TTF) and iron ions can produce morphology-preserving TTF mixed-valence (MV) salt crystals through solid-state transformation, indicating that the redox reaction occurs not only on the crystal surface but also inside the crystal, and that it is mainly accomplished through the penetration of oxidizing agents. Alexander McPherson et al. pointed out that by adding reducing agents (such as ascorbic acid or disulfide) or oxidizing agents (such as H2O2) to the crystal mother liquor, redox-sensitive dyes can be stained, demonstrating that ions can diffuse within the crystal. Furthermore, Kim Jungwon's research group at Hallym University discovered that the concentration phenomenon caused by crystallization can promote redox reactions that are almost unchanged at room temperature, inducing chemical transformations such as Fe2+ reduction of Cr(VI) and oxidation of As(III) to As(VI) at the ice crystal interface.

[0052] In practical applications, the corresponding system structure diagram of the electronic-grade sulfuric acid preparation method based on low-temperature suspension crystallization and redox reaction iterative equilibrium of the present invention is shown below. Figure 1 As shown, the system includes a cryogenic crystallization reactor 1, a refrigeration unit 2, an oxidant storage tank 3, a reducing agent storage tank 4, a solid-liquid separation unit 5, a wastewater storage tank 6, and an electronic sulfuric acid storage tank 7.

[0053] Combination Figure 1 The principle of the electronic-grade sulfuric acid preparation method of the present invention is as follows: Raw industrial sulfuric acid undergoes low-temperature freeze-suspension crystallization treatment in a freeze-crystallization reactor 1, followed by a cooling source provided by a refrigeration device 2. Then, the oxidant from the oxidant storage tank 3 and the reducing agent from the reducing agent storage tank 4 are added to the freeze-crystallization reactor 1 to regulate the redox potential. Solid-liquid separation is achieved through a solid-liquid separation device 5, yielding filter residue (sulfuric acid crystals) and filtrate. The filtrate is stored in a wastewater storage tank 6, which can be used as wastewater or incorporated into the industrial sulfuric acid product. The filter residue, i.e., sulfuric acid crystals, is stored in an electronic sulfuric acid storage tank 7, thus obtaining electronic-grade sulfuric acid. Several specific embodiments of the present invention are listed below.

[0054] Example 1

[0055] Procedure: Take 500 ml of 95% industrial sulfuric acid and place it in a low-temperature freezing tank for freezing and suspension crystallization, maintaining the crystallization temperature at 0-5℃. Introduce 5 ml / min of 10% ozone and stir at 500 rpm for 2 hours. Then, use a vacuum filtration device for solid-liquid separation. Melt the obtained solid at 30℃ (greater than 25℃) to prepare electronic-grade sulfuric acid.

[0056] Result: The purified sulfuric acid met all the standards of E4 grade in the national standard for electronic grade sulfuric acid (GB / T41881—2022).

[0057] Example 2

[0058] Procedure: Take 500 ml of 95% industrial sulfuric acid and place it in a low-temperature freezing tank for freezing and crystallization, maintaining the crystallization temperature at 0-5℃. Add 5 ml of hydrogen peroxide and stir at 500 rpm for 2 hours. Then, use a vacuum filtration device to separate the solid and liquid. Melt the obtained solid at 28℃ (above 25℃) to prepare electronic-grade sulfuric acid.

[0059] Result: The purified sulfuric acid met all the standards of E4 grade in the national standard for electronic grade sulfuric acid (GB / T41881—2022).

[0060] Example 3

[0061] Procedure: Take 500 ml of 95% industrial sulfuric acid and place it in a low-temperature freezing bath for freeze-suspended crystallization, maintaining the crystallization temperature at 0-5℃. Introduce 10 ml / min of 10% ozone and stir at 500 rpm for 1 hour, then introduce 5 ml / min of high-purity hydrogen and continue stirring at 500 rpm for 1 hour. Separate the solid and liquid using a vacuum filtration device. Melt the resulting solid at 35℃ (above 25℃) to prepare electronic-grade sulfuric acid.

[0062] Results: The purified sulfuric acid met all the standards of E1 grade in the national standard for electronic grade sulfuric acid (GB / T41881—2022).

[0063] Example 4

[0064] Procedure: Take 500 ml of 95% industrial sulfuric acid and place it in a low-temperature freezing bath for freeze-suspended crystallization, maintaining the crystallization temperature at 0-5℃. Add 10 ml of hydrogen peroxide and stir at 500 rpm for 1 hour. Then, introduce high-purity hydrogen gas at 5 ml / min and continue stirring at 500 rpm for 1 hour. Use a vacuum filtration device for solid-liquid separation. Melt the obtained solid at 35℃ (above 25℃) to prepare electronic-grade sulfuric acid.

[0065] Results: The purified sulfuric acid met all the standards of E1 grade in the national standard for electronic grade sulfuric acid (GB / T41881—2022).

[0066] The purpose of this invention is to alter the redox potential of the sulfuric acid system in a cryogenic crystallization reactor by introducing a chemical field, thereby influencing the nucleation, growth, and energy balance of sulfuric acid crystals. Conversely, the sulfuric acid crystallization process also affects the redox reaction. These two processes interact, resulting in an iterative and synergistic purification method for preparing electronic-grade sulfuric acid.

[0067] This invention establishes a chemical field during low-temperature suspension crystallization by introducing oxidizing or reducing substances. The redox reaction allows for a more thorough transformation or removal of oxidizing and reducing substances, better ensuring the purity of sulfuric acid crystals. Based on low-temperature suspension crystallization technology, this invention proposes a technique for preparing high-purity ferrous sulfate crystals through redox potential regulation and synergistic low-temperature crystallization. By adding oxidizing or reducing agents, the redox potential of trace impurities during low-temperature crystallization is precisely controlled, leading to the removal of impurity elements through directional speciation, thus achieving efficient purification of sulfuric acid. This invention presents an electronic-grade sulfuric acid preparation method based on iterative equilibrium of low-temperature suspension crystallization and redox reactions. This simplified production process reduces energy consumption and costs, offering significant economic, social, and environmental benefits, and promising application prospects.

[0068] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Therefore, any modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction, characterized in that, Includes the following steps: s1: Add industrial sulfuric acid as raw material to the freeze crystallization reactor for low-temperature freeze suspension crystallization treatment, maintaining the crystallization temperature at 0-5℃; s2: Add oxidant and / or reducing agent and stir. Adding oxidant or reducing agent precisely controls the redox potential of trace impurities during low-temperature crystallization, and the impurity elements undergo directional transformation to be removed; s3: Perform solid-liquid separation to obtain sulfuric acid crystals and filtrate; s4: The sulfuric acid crystals are melted at a set temperature to obtain electronic-grade sulfuric acid; In step s2, the redox reaction interacts with the sulfuric acid crystallization process to achieve iterative synergistic purification.

2. The method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction according to claim 1, characterized in that: The industrial sulfuric acid used in step s1 is industrial sulfuric acid with a mass fraction of 95%.

3. The method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction according to claim 1, characterized in that: The oxidant in step s2 includes ozone and hydrogen peroxide.

4. The method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction according to claim 1, characterized in that: The reducing agent in step s2 is hydrogen.

5. The method for preparing electronic-grade sulfuric acid based on iterative equilibrium of low-temperature suspension crystallization and redox reaction according to claim 1, characterized in that: The set temperature in step s4 is greater than 25°C.

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