Preparation method of electronic-grade hydrofluoric acid

Abstract

The invention belongs to the technical field of chemical engineering, and particularly relates to a preparation method of electronic-grade hydrofluoric acid. The method comprises the following steps: 1) arranging an electrolytic cell, filling a cathode region with a fluorine raw material solution, filling an anode region with an acidic raw material solution, and separating the anode region from the cathode region by an anion exchange membrane; 2) electrifying the electrolytic cell for electrolysis, and collecting gas in an anode region to obtain mixed feed gas; and (3) sequentially filtering, mixing, absorbing, cooling and recovering the mixed raw material gas to obtain the electronic-grade hydrofluoric acid. According to the method, synthesis and preliminary separation of hydrogen fluoride are achieved in one step through an electrolytic method, high-purity hydrogen fluoride can be effectively and stably obtained, ultra-high-purity electronic-grade hydrofluoric acid is rapidly prepared through aftertreatment, and the preparation process is relatively low in energy consumption, safe and environmentally friendly.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical industry, and in particular relates to a method for preparing electronic-grade hydrofluoric acid. Background Art

[0002] The core component of hydrofluoric acid is hydrogen fluoride (HF), which is a very important chemical raw material with extremely wide industrial applications, mainly covering three major areas: the synthesis of fluorine-containing compounds, such as fluororubber, PTFE and Freon; industrial processing, such as semiconductor silicon wafer etching, stainless steel pickling and catalysts in various chemical reactions; special applications, such as the atomic energy industry, the refining of rare earth elements and the preparation of rocket fuel additives.

[0003] With the development and rise of the semiconductor industry, the demand for hydrofluoric acid is increasing, but so are the quality requirements. Currently, electronic-grade hydrofluoric acid is graded into five levels: EL, UP, UPS, UPSS, and UPSSS. UPSSS is the highest-grade electronic-grade hydrofluoric acid, primarily used in semiconductor manufacturing for ultra-high-precision, ultra-small processes (such as advanced processes ≤7 nm).

[0004] However, current electronic-grade hydrofluoric acid production is severely limited by its production process. Currently, the two main methods for producing hydrofluoric acid are the sulfuric acid process (fluorspar-sulfuric acid process) and electrolysis. Electrolysis is further categorized as dry electrolysis and wet electrolysis. In addition to these primary methods, there are also less commonly used unconventional methods such as thionyl chloride dehydration and fluoride-acid displacement. However, these unconventional methods generally suffer from low efficiency and low product purity.

[0005] Of the two main methods, the sulfuric acid method is primarily used to produce high-purity industrial hydrochloric acid, with product purities generally reaching 95-99 wt%. While suitable for large-scale production and mature, it produces significant amounts of waste gas, wastewater, and solid waste, resulting in severe pollution and low material utilization (e.g., low calcium fluoride utilization). Regarding electrolysis, wet electrolysis is primarily used to produce high-purity products with purities exceeding 99.9%, but it suffers from significant halide contamination, resulting in limited purity and application. Dry electrolysis is a widely used method for producing electronic-grade hydrofluoric acid. Anhydrous potassium hydrogen fluoride (KHF2) or ammonium fluoride is placed in an electrolytic cell and electrolyzed at 100-250°C in a molten state. Fluorine gas (F2) is produced at the anode, and hydrogen (H2) is produced at the cathode. These two gases recombine outside the electrolytic cell to produce high-purity HF. This method is relatively environmentally friendly, but it also presents safety concerns regarding the fluorine gas. For industrial applications, its high energy consumption is a significant factor limiting its production capacity and output.

[0006] To meet this demand, research on the production of high-purity, electronic-grade hydrofluoric acid is increasing, but most of this research focuses on dry electrolysis. Fluorite, a highly abundant and low-cost fluorine-containing raw material, has received relatively little attention. However, its unique characteristics make it of great research and industrial value. However, existing fluorite minerals contain a large amount of it. Summary of the Invention

[0007] In order to solve the problems of existing hydrofluoric acid preparation processes such as high cost, huge energy consumption, serious three-waste pollution, and product purity failing to meet electronic grade standards, the present invention provides a method for preparing electronic grade hydrofluoric acid.

[0008] The main purpose of the present invention is: 1. It can effectively reduce the pollution of three wastes, making the preparation process more green, environmentally friendly and safe.

[0009] 2. It can ensure that the product purity reaches the electronic grade standard.

[0010] 3. It can significantly reduce the production energy consumption of electronic-grade hydrofluoric acid.

[0011] To achieve the above objectives, the present invention adopts the following technical solutions.

[0012] A method for preparing electronic-grade hydrofluoric acid comprises: 1) providing an electrolytic cell, filling the cathode region with a fluorine raw material solution, filling the anode region with an acidic raw material solution, and separating the anode region and the cathode region with an anion exchange membrane.

[0013] 2) Power the electrolytic cell to perform electrolysis, collect the gas in the anode area, and obtain the mixed raw gas.

[0014] 3) The mixed raw gas is filtered, mixed absorbed and cooled and recovered in sequence to obtain electronic grade hydrofluoric acid.

[0015] Preferably, the fluorine raw material liquid in step 1) is an aqueous suspension of calcium fluoride; the concentration of calcium fluoride in the aqueous suspension is 5.5-6.5 wt%, and the aqueous suspension of calcium fluoride contains 0.08-0.12 mol / L ethylenediamine.

[0016] Preferably, the acidic raw material liquid in step 1) is an oxalic acid aqueous solution, and the oxalic acid concentration in the oxalic acid aqueous solution is 0.12-0.18 mol / L.

[0017] Preferably, the pore size of the anion exchange membrane in step 1) is 3.2 to 3.5 Å.

[0018] Preferably, in step 2), during the electrolysis process of the electrolytic cell being energized, the electrolysis voltage is controlled to be 2.0-2.2V.

[0019] Preferably, in step 2), during the process of energizing the electrolytic cell for electrolysis, the cathode region continuously maintains flow.

[0020] Preferably, in step 3), the filtration is performed using a PTFE / PFA lined filter with a pore size of 3 to 12 nm; in step 3), the mixed absorption is performed by spraying and absorbing ultrapure water with a resistivity of ≥18.25 MΩ·cm; and in step 3), the cooling and recovery is performed by cooling the hydrofluoric acid after mixed absorption to ≤10°C and then recovering and storing it.

[0021] Preferably, after the cooling and recovery in step 3) is completed, the concentration of the product hydrogen fluoride is detected by an online density meter and / or conductivity meter, and the amount of ultrapure water used in the mixed absorption process is adjusted based on the comparison between the product concentration and the target concentration.

[0022] Preferably, in step 3), condensation and re-evaporation may be performed between the filtering and the mixed absorption process; the condensation and re-evaporation is performed by condensing at 2-10°C and then heating to 25°C to evaporate and convert into gaseous state.

[0023] When high-purity hydrofluoric acid with a high target concentration and low water content is required, this process can be used to achieve preliminary water removal to more accurately control the water content of the hydrofluoric acid.

[0024] This invention uses a fluorite pathway to synthesize electronic-grade hydrofluoric acid. Unlike traditional fluorite utilization, this invention pioneered the use of fluorite's low solubility and high stability, using a completely different wet electrolysis process for preparation.

[0025] Specifically, the present invention constructs a special anode region and a special cathode region.

[0026] The anode region is mainly composed of an oxalic acid aqueous solution. During the electrolysis process, the oxalic acid aqueous solution forms a byproduct, carbon dioxide, which is very easy to separate from the target substance, hydrogen fluoride, and the two do not have a direct reaction pathway. Compared with the large amount of three wastes or intermediate fluorine gas generated in traditional processes, carbon dioxide is neither a pollutant in the traditional sense nor a hazardous substance. It is only a regulated emission component and can actually be used for other industrial purposes and converted into other industrial products. Therefore, it has significant safety and environmental protection. In this process, as the oxalate ions are oxidized to carbon dioxide, the anions in the cathode region will enter the anode region through the anion exchange membrane. During the electrolysis process, the anions in the cathode region are mainly hydroxide ions and fluoride ions. The two compete to enter the anode region. After entering the anode region, the hydroxide ions form water molecules, while the fluoride ions form hydrogen fluoride after entering the anode region.

[0027] However, hydrogen fluoride is different from conventional inorganic acids and is prone to form aggregates in a solution environment (HF). n), such as dimer (HF)2, or anionic aggregates, such as HF·F - In theory, anionic aggregates such as (hydrogen difluoride ions) can pass through conventional anion exchange membranes. However, the present invention customizes a 3.5 Å pore-diameter fluoride-resistant anion exchange membrane from Fujifilm. Similar exchange membranes can be customized by most exchange membrane manufacturers without technical barriers, and the size of hydrogen fluoride aggregates generally reaches more than 4 Å. Therefore, to a certain extent, the fluoride ions are fixed, so that after the fluoride ions enter the anode area through the anion exchange membrane, they can be effectively fixed in the anode area and cannot enter the cathode area again, realizing the control of the directional migration of ions.

[0028] That is Figure 1 As shown, the most important process in the preparation system of the present invention is to realize the directional migration of fluoride ions and the synthesis and fixation of hydrogen fluoride by constructing a special electrolysis system and coordinating it with a special anion exchange membrane. This is the main path of fluoride ion migration and hydrogen fluoride synthesis in the present invention.

[0029] In addition, the present invention uses oxalic acid aqueous solution as the acidic raw material liquid in the anode area, which is also because oxalic acid has a special feature for the technical solution system of the present invention. Because calcium fluoride is a raw material with extremely low solubility, in the cathode area, calcium fluoride can only dissolve a small amount of fluoride ions. As the fluoride ions migrate, the concentration of calcium ions increases, which will inhibit the continued dissolution of calcium fluoride and cause the reaction to terminate. The present invention uses a special oxalic acid solution as the raw material in the anode area because the solubility of calcium oxalate is lower than that of calcium fluoride, and the special anion exchange membrane selected also meets the conditions for the passage of oxalate ions. Through the concentration driving force, the oxalate ions in the anode area can also slowly and in small amounts enter the cathode area for secondary treatment of calcium ions. Fixation can avoid the termination of the reaction. Secondly, it can improve the solubility of calcium fluoride and accelerate the dissolution of fluoride ions by inhibiting and weakening the common ion effect. Therefore, oxalic acid and calcium fluoride are used as the main raw materials of the anode region and the cathode region respectively. The two can not only effectively synthesize hydrogen fluoride by electrolysis, but also cooperate with each other to produce a positive promoting effect on the electrolytic synthesis of hydrogen fluoride. This is the secondary ion and reaction migration path in the technical solution system of the present invention. This process promotes the process of fluoride ions synthesizing hydrogen fluoride from the cathode region to the anode region, and the two complement each other.

[0030] As for the selection of raw materials, calcium fluoride has many advantages, such as high abundance, low cost, easy purification, and excellent stability. In addition, the technical solution of the present invention can actually largely ignore impurities in the calcium fluoride raw material ore, fluorite. For example, in the existing preparation of electronic-grade hydrofluoric acid, the main difficulty lies in the removal of impurities, especially the deep removal of key impurities such as arsenic (As), boron (B), phosphorus (P), iron (Fe), and calcium (Ca), rather than the removal of water. Most of these impurities are present in fluorite ore, which is the key to limiting the purity of the product of the existing sulfuric acid method (fluorite-sulfuric acid method). The technical solution of the present invention can almost completely eliminate such impurity interference through anion exchange. Therefore, the selection of calcium fluoride is the best result based on multiple industrial considerations such as cost and difficulty of acquisition. However, for oxalic acid, it is the only feasible acid component currently tested. If a non-volatile acid such as sulfuric acid is used, its acid radical ions may also pass through the anion exchange membrane and enter the cathode region. However, they cannot promote the precipitation of calcium ions like oxalate ions, thereby indirectly increasing the solubility of calcium fluoride. Therefore, the problem of reaction termination still exists. Volatile acids will volatilize with the target product hydrogen fluoride in the anode region to form impurities with similar boiling points, resulting in increased separation costs and more complicated preparation processes, thus weakening the applicability. Experiments have also confirmed the above situation. Based on current research results, oxalic acid has irreplaceable uniqueness.

[0031] Based on the above, after hydrogen fluoride is synthesized in the anode region by ion exchange in the present invention, the carbon dioxide produced by the anode reaction can actually be directly released by electrolytic heat (heat generated during the electrolysis process). However, the present invention preferably controls the temperature of the electrolyte in the anode region to a certain extent, controlling it at 30-40°C to avoid excessive temperature rise that would remove a large amount of water molecules. HF can be relatively effectively evaporated at temperatures above 30°C. Therefore, the technical solution of the present invention can actually achieve the synthesis and preliminary separation of the target component hydrogen fluoride in a simple electrolysis process, and through simple conventional post-processing, an extremely high-purity electronic-grade hydrofluoric acid product can be obtained.

[0032] In addition, although the present invention is also an electrolysis method, compared with dry electrolysis, the present invention does not require heating and melting, has lower requirements for raw materials, and the raw materials are more abundant, easy to obtain and convenient to store, which significantly reduces the industrialization cost of the technical solution of the present invention and has a very significant cost advantage.

[0033] The beneficial effects of the present invention are: the present invention realizes the synthesis and preliminary separation of hydrogen fluoride in one step through electrolysis, can effectively and stably obtain high-purity hydrogen fluoride, and can quickly realize the preparation of ultra-high-purity electronic-grade hydrofluoric acid through post-processing, and the preparation process has relatively low energy consumption, is safe and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 Schematic diagram of the electrolysis reaction of the present invention. DETAILED DESCRIPTION

[0035] The present invention is further described in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only a portion of the embodiments of the present invention, rather than all of the embodiments. Therefore, all other embodiments derived by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0036] Unless otherwise specified, the raw materials used in the examples of the present invention are all commercially available or available to those skilled in the art; unless otherwise specified, the methods used in the examples of the present invention are all methods known to those skilled in the art.

[0037] Unless otherwise specified, the calcium fluoride used to prepare the calcium fluoride aqueous suspension in the embodiments of the present invention is 3N purity calcium fluoride powder with a mesh size of 120 mesh.

[0038] Example 1: A method for preparing electronic-grade hydrofluoric acid, comprising: 1) providing an electrolytic cell: an anode: a platinum electrode (purchased from Baoji Shenao).

[0039] Cathode: platinum-titanium electrode (purchased from Baoji Shenao).

[0040] Cathode zone: 6 wt% calcium fluoride aqueous suspension containing 0.10 mol / L ethylenediamine. The cathode zone is continuously stirred at 20 rpm using a PTFE-encapsulated magnetic rotor to maintain the suspension and prevent calcium oxalate from depositing on the ion exchange membrane.

[0041] Anode area: 0.15 mol / L oxalic acid aqueous solution. During the preparation process, analytical pure oxalic acid was added at a ratio of 0.01 mol / L every five minutes to basically maintain a stable oxalic acid concentration in the oxalic acid aqueous solution in the anode area.

[0042] Anion exchange membrane: FUJIFILM customized 35Å pore size fluoride-resistant anion exchange membrane (this anion exchange membrane is customized by the laboratory and has no specific product name or brand, but it can be customized by any anion exchange membrane manufacturer on the market).

[0043] The anode and cathode regions are separated by an anion exchange membrane.

[0044] 2) The electrolytic cell was powered to perform constant voltage electrolysis at 2.2 V. During the electrolysis process, the rotor in the cathode region was continuously stirred and the anode region was controlled at a constant temperature of 32±1°C. The gas in the anode region was collected to obtain a mixed feed gas.

[0045] 3) The mixed raw gas is recovered in sequence through filtration, mixed absorption and cooling; Filtration: The mixed raw gas is passed through an industrial gas filter with a pore size of 5 nm and a PTFE / PFA lining to obtain filtered gas.

[0046] Mixed absorption: Ultrapure water with a resistivity of ≥18.25 MΩ·cm is sprayed in an atomized manner to absorb and fix the hydrogen fluoride in the filtered gas to obtain an absorption liquid.

[0047] Cooling recovery: The absorption liquid is passed into a mixing cooling tank to cool down to 5°C to completely fix the HF and obtain the product electronic grade hydrofluoric acid.

[0048] The hydrogen fluoride concentration of electronic-grade hydrofluoric acid was characterized using a conductivity meter, and the amount of ultrapure water used in the atomization spray during the mixed absorption process was adjusted until the characterization results showed that the HF concentration in the electronic-grade hydrofluoric acid reached the target concentration (in this case, the target concentration was 50±1%). The amount of ultrapure water used in the atomization spray at this point was fixed, and electronic-grade hydrofluoric acid was continuously produced.

[0049] The purity and impurity content of the continuously produced electronic-grade hydrofluoric acid were characterized. The laboratory energy consumption for step 1) was calculated and compared with the energy consumption of a laboratory simulated wet electrolysis (KF·2HF molten salt electrolysis) process for producing electronic-grade hydrogen fluoride (equivalent to step 1) in this example). The total amount of metallic impurities was determined by ICP-MS, the fluorosilicic acid content by UV spectrophotometry, the chloride (chloride ion) concentration by ion chromatography, and the particulate matter content by a laser particle counter.

[0050] The characterization results are shown in Table 1 below.

[0051] Table 1:

[0052] It is obvious from the above-mentioned Table 1 characterization results that the present invention can directly realize the preparation of electronic-grade hydrofluoric acid, and the product obtained by preparing at least meets the standard of UP electronic-grade hydrofluoric acid, wherein the total amount of metal impurities reaches the UPSS level standard, and the chloride content and particle content both reach the UPS level standard. In addition, the non-target components produced by the preparation process mainly include incompletely reacted calcium fluoride, calcium oxalate, a secondary precipitate of calcium, and harmless exhaust gas carbon dioxide. The overall process is safe and environmentally friendly. From the perspective of energy consumption comparison, the technical solution of the present invention can achieve an energy consumption reduction of up to about 70.74% compared to traditional wet electrolysis, and the overall preparation process is all in an easily controllable temperature range, which is safe and energy-saving.

[0053] Example 2: A method for preparing electronic-grade hydrofluoric acid. This example is based on Example 1, except that the concentration of the aqueous suspension of calcium fluoride in the cathode region is adjusted. The remaining preparation processes and parameters are the same as those in Example 1, and the product is characterized in the same manner as in Example 1.

[0054] The characterization results are shown in Table 2 below.

[0055] Table 2:

[0056] As can be clearly seen in Table 2 above, the calcium fluoride concentration in the calcium fluoride aqueous suspension has no significant impact on product quality. The primary factor affecting quality is the fluorosilicic acid content, which is limited by R&D laboratory conditions. This content can be further controlled during subsequent industrialization by avoiding silicon-containing hydrogen fluoride equipment and / or pipelines. However, the most significant change is the change in energy consumption. While the preparation efficiency of the present invention is limited compared to wet electrolysis (due to the solubility and dissolution rate of calcium fluoride, which is lower than that of wet electrolysis), energy efficiency and safety and environmental protection are the process advantages. However, it can be seen from Table 2 above that when the calcium fluoride concentration in the calcium fluoride aqueous suspension is 5.0 wt%, the fluoride ion mobility is significantly decreased due to competition with hydroxide ions due to the decreased dissolution efficiency, resulting in a significant increase in ineffective energy consumption. At high concentrations, a deposited film is found on the cathode side surface of the ion exchange membrane after preparation. The deposited film is a calcium oxalate deposited film. High concentrations of calcium fluoride will form calcium oxalate deposits on the cathode side of the cathode ion exchange membrane in the early stage for a short period of time, thereby slowing down the ion exchange rate, increasing the overall resistance, and increasing ineffective energy consumption, thereby significantly increasing energy consumption.

[0057] Example 3: A method for preparing electronic-grade hydrofluoric acid. This example is based on Example 1, except that the concentration of ethylenediamine in the aqueous suspension of calcium fluoride in the cathode region is adjusted. The remaining preparation process and preparation parameters are the same as those in Example 1. The product is characterized and the reaction process is recorded in the same manner as in Example 1.

[0058] The characterization and recording results are shown in Table 3 below.

[0059] Table 3:

[0060] It can be clearly seen from Table 3 above that the addition of ethylenediamine to the cathode electrolyte in the present invention is mainly to enhance the conductivity of the electrolyte, thereby achieving electrolysis. However, ethylenediamine has a complexing effect on calcium ions. Although this can improve the solubility of calcium fluoride to a certain extent, an excessively high concentration of ethylenediamine will cause the solution viscosity to increase, accelerate particle sedimentation, and make it impossible to maintain a uniform suspension state during stirring, resulting in increased ineffective energy consumption and even formation of a gel state, which makes electrolysis impossible.

[0061] Example 4: A method for preparing electronic-grade hydrofluoric acid. This example is based on Example 1, except that only the concentration of the aqueous oxalic acid solution in the anode region is adjusted. The remaining preparation processes and parameters are the same as those in Example 1. The product is characterized and the reaction process is recorded in the same manner as in Example 1.

[0062] The characterization and recording results are shown in Table 4 below.

[0063] Table 4:

[0064] It can be clearly seen from Table 3 above that low concentrations of oxalic acid increase energy consumption due to the influence of conductivity. In order to ensure energy consumption advantages, 0.12-0.18 mol / L oxalic acid aqueous solution should be used. When the oxalic acid concentration is further increased, the spontaneous migration rate of oxalate ions is higher, resulting in the formation of a deposited film on the surface of the ion exchange membrane, increasing the resistance and causing a significant increase in preparation energy consumption.

[0065] Example 5: A method for preparing electronic-grade hydrofluoric acid. This example is based on Example 1, except that only the acidic raw material liquid in the anode area is replaced, and an equivalent amount of other acid is replaced based on hydrogen. The rest of the preparation process and preparation parameters are the same as in Example 1. The product is characterized and the reaction process is recorded in the same manner as in Example 1.

[0066] The characterization and recording results are shown in Table 5 below.

[0067] Table 5:

[0068] As shown in Table 5, the oxalic acid of the present invention has a lower solubility than calcium fluoride due to the solubility difference between calcium oxalate and calcium fluoride. As a result, oxalic acid not only plays a role in enhancing the conductivity of the electrolyte in the anode region and the role of a reducing agent in the anode region, but also plays a role in synergistically regulating the concentration of free calcium ions in the cathode region. The spontaneous diffusion of oxalate ions can promote the precipitation of free calcium ions in the cathode region, so as to avoid the common ion effect caused by the decrease in fluoride ion concentration and the increase in calcium ion concentration in the cathode region during the electrolysis process, indirectly improving the solubility of calcium fluoride and ensuring that the electrolysis process can be effectively carried out continuously. The rest of the common industrial inorganic acids do not have this property, so the electrolysis process reaction will terminate spontaneously, because the common ion effect will significantly inhibit the trace dissolution process of calcium fluoride, resulting in the inability of fluoride ions to dissolve and migrate, and the hydrogen chloride of hydrochloric acid is also volatile, which can easily lead to the introduction of more new impurities into the product. It can be seen that various factors have led to oxalic acid being a currently known acid that can be used to prepare the anode region of the present invention as an acidic raw material liquid.

Claims

1. A method for preparing electronic grade hydrofluoric acid, characterized in that: The method comprises: 1) setting up an electrolytic cell, filling a cathode region with a fluorine raw material liquid, filling an anode region with an acidic raw material liquid, and separating the anode region and the cathode region with an anion exchange membrane; 2) energizing the electrolytic cell for electrolysis, collecting gas from the anode region to obtain a mixed raw material gas; and 3) recovering the mixed raw material gas through filtering, mixed absorption, and cooling in sequence to obtain electronic-grade hydrofluoric acid.

2. The method for preparing electronic grade hydrofluoric acid according to claim 1, wherein Step 1) The fluorine raw material liquid is an aqueous suspension of calcium fluoride; the calcium fluoride concentration in the aqueous suspension is 5.5-6.5 wt%, and the aqueous suspension of calcium fluoride contains 0.08-0.12 mol / L ethylenediamine.

3. The method for preparing electronic grade hydrofluoric acid according to claim 1, wherein In step 1), the acidic raw material liquid is an oxalic acid aqueous solution, and the oxalic acid concentration in the oxalic acid aqueous solution is 0.12-0.18 mol / L.

4. The method for preparing electronic grade hydrofluoric acid according to claim 1 or 2, wherein: In step 1), the pore size of the anion exchange membrane is 3.2 to 3.5 Å.

5. The method for preparing electronic grade hydrofluoric acid according to claim 1, wherein: Step 2) During the electrolysis process of the electrolytic cell being energized, the electrolysis voltage is controlled to be 2.0-2.2 V.

6. The method for preparing electronic grade hydrofluoric acid according to claim 1 or 5, wherein: Step 2) During the electrolysis process of the electrolytic cell being energized: the cathode region continuously maintains flow.

7. The method for preparing electronic grade hydrofluoric acid according to claim 1, wherein: In step 3), the filtration is performed using a PTFE / PFA lined filter with a pore size of 3 to 12 nm. In step 3), the mixed absorption is performed using ultrapure water with a resistivity of ≥18.25 MΩ·cm for spray absorption. In step 3), the cooling recovery is performed by cooling the hydrofluoric acid after mixed absorption to ≤10°C before recovery and storage.

8. The method for preparing electronic grade hydrofluoric acid according to claim 7, wherein: Step 3) After the cooling and recovery is completed, the concentration of the product hydrogen fluoride is detected by an online density meter and / or conductivity meter, and the amount of ultrapure water used in the mixed absorption process is adjusted based on the comparison between the product concentration and the target concentration.

9. The method for preparing electronic grade hydrofluoric acid according to claim 1, 7 or 8, wherein: Step 3) Condensation and re-evaporation can be performed between the filtering and mixed absorption processes; the condensation and re-evaporation is performed by condensing at 2-10°C and then heating to 25°C to evaporate and transform into gaseous state.

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