A method for preparing electronic-grade hydrofluoric acid

Abstract

This invention belongs to the field of chemical technology, and particularly relates to a method for preparing electronic-grade hydrofluoric acid. The method includes: 1) setting up an electrolytic cell, with the cathode region filled with a fluorine-based raw material solution and the anode region filled with an acidic raw material solution, the anode and cathode regions separated by an anion exchange membrane; 2) electrolyzing the electrolytic cell and collecting the gas from the anode region to obtain a mixed raw material gas; 3) sequentially passing the mixed raw material gas through filtration, mixing absorption, and cooling recovery to obtain electronic-grade hydrofluoric acid. This invention achieves the synthesis and preliminary separation of hydrogen fluoride in one step via electrolysis, effectively and stably obtaining high-purity hydrogen fluoride. Post-processing rapidly achieves the preparation of ultra-high-purity electronic-grade hydrofluoric acid, and the preparation process is relatively energy-efficient, safe, and environmentally friendly.

Description

Technical Field

[0001] This invention belongs to the field of chemical technology, and in particular relates to a method for preparing electronic-grade hydrofluoric acid. Background Technology

[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 silicon wafer etching for semiconductors, as well as pickling of stainless steel and catalysts in various chemical reactions; and special applications, such as the atomic energy industry, the refining of rare earth elements, and the preparation of rocket fuel additives.

[0003] Currently, with the development and rise of the semiconductor industry, the demand for hydrofluoric acid is increasing daily, but at the same time, the quality requirements for hydrofluoric acid are also rising. Currently, electronic-grade hydrofluoric acid is classified into five levels: EL, UP, UPS, UPSS, and UPSSS. Among them, UPSSS grade electronic-grade hydrofluoric acid is the highest level and is mainly used in the fabrication of ultra-high precision, ultra-small process semiconductors (such as advanced processes ≤7 nm).

[0004] However, the current production of electronic-grade hydrofluoric acid is severely limited by the preparation process. Currently, the main methods for preparing hydrofluoric acid are the sulfuric acid method (fluorite-sulfuric acid method) and the electrolysis method. The electrolysis method is further divided into dry electrolysis and wet electrolysis. In addition to these main methods, there are also less commonly used unconventional methods such as the thionyl chloride dehydration method and the fluoride-acid replacement method. 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 prepare high-purity industrial hydrochloric acid, with product purity generally ranging from 95 to 99 wt%. It is suitable for large-scale production and has a mature process; however, it generates extremely large amounts of waste gas, wastewater, and solid waste, causing severe pollution, and has low material utilization (especially low calcium fluoride utilization). For the electrolytic method, wet electrolysis is mainly used for high-purity products with a purity >99.9%, but it suffers from significant halide pollution, thus limiting its purity and application. Dry electrolysis is currently the most widely used method for preparing electronic-grade hydrofluoric acid. It involves placing anhydrous potassium hydrogen fluoride (KHF2) or ammonium fluoride in an electrolytic cell and electrolyzing it in a molten state at 100–250°C. Fluorine gas (F2) is produced at the anode, and hydrogen gas (H2) is produced at the cathode. The two then recombine outside the electrolytic cell to generate high-purity HF. This method is relatively more environmentally friendly, but it also presents safety concerns regarding fluorine gas. Furthermore, its extremely high energy consumption is a significant factor limiting its production capacity and output for industrial applications.

[0006] To meet demand, research on the preparation process of high-purity electronic-grade hydrofluoric acid is increasing, but most studies focus solely on dry electrolysis. Meanwhile, research on fluorite, a high-abundance and low-cost fluorine-containing raw material, remains limited, despite its significant research and industrial value due to its unique characteristics. However, fluorite contains a large amount of... Summary of the Invention

[0007] To address the problems of existing hydrofluoric acid preparation processes, such as high cost, huge energy consumption, serious pollution from waste gas, wastewater, and solid waste, or the inability to achieve electronic-grade purity, this invention provides a method for preparing electronic-grade hydrofluoric acid.

[0008] The main objectives of this invention are: 1. To effectively reduce pollution from waste gas, wastewater, and solid waste, making the preparation process greener, more environmentally friendly, and safer.

[0009] Second, it can ensure that the purity of the product meets electronic grade standards.

[0010] Third, it can significantly reduce the energy consumption in the production of electronic-grade hydrofluoric acid.

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

[0012] A method for preparing electronic-grade hydrofluoric acid, the method comprising: 1) setting up an electrolytic cell, wherein the cathode region is filled with fluorine raw material solution, the anode region is filled with acidic raw material solution, and the anode region and the cathode region are separated by anion exchange membrane.

[0013] 2) Electrolysis is performed by energizing the electrolytic cell, and the gas in the anode area is collected to obtain a mixed raw material gas.

[0014] 3) The mixed raw material gas is sequentially filtered, mixed and absorbed, and cooled for recovery to obtain electronic-grade hydrofluoric acid.

[0015] Preferably, the fluorine feedstock solution in step 1) is an aqueous suspension of calcium fluoride; the concentration of calcium fluoride in the aqueous suspension of calcium fluoride 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 solution in step 1) is an oxalic acid aqueous solution, and the concentration of oxalic acid in the oxalic acid aqueous solution is 0.12-0.18 mol / L.

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

[0018] Preferably, during the electrolysis process in step 2), the electrolysis voltage is controlled to be 2.0 to 2.2V.

[0019] Preferably, during the electrolysis process in step 2), the cathode region remains continuously flowing.

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

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

[0022] Preferably, condensation and re-evaporation can be carried out between the filtration and mixing absorption processes in step 3); the condensation and re-evaporation involves condensing at 2-10°C and then heating to 25°C to evaporate and transform into a gaseous state.

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

[0024] This invention utilizes a fluorite pathway for the synthesis of electronic-grade hydrofluoric acid. Unlike traditional fluorite utilization methods, this invention innovatively leverages the low solubility and high stability of fluorite, employing a completely different wet electrolysis process.

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

[0026] The anode region is primarily composed of an oxalic acid aqueous solution. During electrolysis, the oxalic acid solution forms carbon dioxide, a byproduct that readily separates from the target substance, hydrogen fluoride, and the two do not have a direct reaction pathway. Compared to the large amounts of waste or intermediate fluorine gas generated in traditional processes, carbon dioxide is neither a pollutant in the traditional sense nor a hazardous substance; it is merely a regulated emission component and can actually be used for other industrial purposes and transformed into other industrial products, thus possessing significant safety and environmental friendliness. In this process, as oxalate ions are oxidized to carbon dioxide, anions in the cathode region enter the anode region through the anion exchange membrane. During electrolysis, the anions in the cathode region are mainly hydroxide ions and fluoride ions, which compete to enter the anode region. Hydroxide ions form water molecules upon entering the anode region, while fluoride ions form hydrogen fluoride.

[0027] However, hydrogen fluoride differs from conventional inorganic acids; it readily forms aggregates (HF) in solution. n), such as dimers (HF)2, or anionic aggregates, such as HF·F - Anionic aggregates such as difluoride ions can theoretically pass through conventional anion exchange membranes. However, this invention utilizes a 3.5 Å pore size fluoride-resistant anion exchange membrane customized from Fujifilm. Similar exchange membranes can be customized by most exchange membrane manufacturers without technical obstacles, and the size of hydrogen fluoride aggregates generally reaches 4 Å or more. Therefore, it achieves a certain degree of fixation of fluoride ions, enabling fluoride ions to be effectively fixed in the anode region after entering the anode region through the anion exchange membrane and unable to re-enter the cathode region, thus achieving control over the directional migration of ions.

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

[0029] Furthermore, the acidic raw material solution selected for the anode region in this invention is an aqueous solution of oxalic acid, also because oxalic acid has specific properties for the technical solution system of this invention. Calcium fluoride is a raw material with extremely low solubility; in the cathode region, calcium fluoride can only dissolve a small amount of fluoride ions. As fluoride ions migrate, the increased concentration of calcium ions inhibits further dissolution of calcium fluoride, leading to reaction termination. This invention uses a special oxalic acid solution as the raw material for the anode region because the solubility of calcium oxalate is even lower than that of calcium fluoride. The selected special anion exchange membrane also meets the conditions for the passage of oxalate ions. Driven by concentration gradient, oxalate ions in the anode region can slowly and in small quantities enter the cathode region to perform secondary reaction on calcium ions. Fixing the ions not only prevents reaction termination but also enhances the solubility of calcium fluoride by suppressing and weakening the common ion effect, thus accelerating the dissolution of fluoride ions. Therefore, oxalic acid and calcium fluoride serve as the main raw materials for the anode and cathode regions, respectively. They can not only effectively synthesize hydrogen fluoride through electrolysis but also work synergistically to positively promote the electrolytic synthesis of hydrogen fluoride. This is the secondary ion and reaction migration pathway in the technical solution system of this invention. This process promotes the synthesis of hydrogen fluoride from fluoride ions from the cathode region to the anode region, and the two complement each other.

[0030] Regarding the selection of raw materials, calcium fluoride has many advantages, including high abundance, low cost, easy purification, and excellent stability. For the technical solution of this invention, the impurities in the calcium fluoride raw material ore, fluorite, can be largely ignored. In the existing preparation process 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 factor limiting the purity of the existing sulfuric acid process (fluorite-sulfuric acid process). The technical solution of this invention can almost completely eliminate the interference of such impurities through anion exchange. Therefore, the selection of calcium fluoride is the best result from the perspective of industrialization, considering factors such as cost and difficulty of acquisition. However, oxalic acid is currently the only feasible acid component after testing. If non-volatile acids such as sulfuric acid are used, their anions may also pass through the anion exchange membrane into the cathode region. However, unlike oxalate ions, they cannot promote the precipitation of calcium ions, thereby indirectly increasing the solubility of calcium fluoride. Therefore, the problem of reaction termination still exists. Volatile acids, on the other hand, will co-evaporate with the target product, hydrogen fluoride, in the anode region, forming impurities with similar boiling points, leading to increased separation costs and a more complex preparation process, thus weakening their applicability. Experiments have confirmed the above situation, and based on current research results, oxalic acid has an irreplaceable and unique characteristic.

[0031] Based on the above, after the synthesis of hydrogen fluoride in the anode region by ion exchange, the present invention can actually be directly released together with the carbon dioxide produced by the anode reaction by means of the heat of electrolysis (the heat generated in the electrolysis process). However, the present invention is preferably able to control the temperature of the electrolyte in the anode region to a certain extent, controlling it at 30-40 °C, so as to avoid excessive heating and the removal of a large number of water molecules. At temperatures above 30 °C, HF can be evaporated relatively effectively. 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. Through simple conventional post-processing, extremely high purity electronic-grade hydrofluoric acid products can be obtained.

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

[0033] The beneficial effects of this invention are as follows: This invention achieves the synthesis and preliminary separation of hydrogen fluoride in one step through electrolysis, which can effectively and stably obtain high-purity hydrogen fluoride. Through post-processing, it can quickly achieve the preparation of ultra-high purity electronic-grade hydrofluoric acid. Moreover, the preparation process has relatively low energy consumption, is safe and environmentally friendly. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the electrolysis reaction of the present invention. Detailed Implementation

[0035] The present invention will be further described clearly and 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 some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained 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, all raw materials used in the embodiments of the present invention are commercially available or obtainable by those skilled in the art; unless otherwise specified, all methods used in the embodiments of the present invention are methods mastered by those skilled in the art.

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

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

[0039] Cathode: Platinum-titanium electrode (purchased from Baoji Olympic bid).

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

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

[0042] Anion exchange membrane: FUJIFILM (Fujifilm) custom-made fluoride-resistant anion exchange membrane with a pore size of 35 Å (this anion exchange membrane is custom-made by the laboratory and does not have a 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 anion exchange membranes.

[0044] 2) The electrolytic cell is energized to perform constant voltage electrolysis at 2.2 V. During the electrolysis process, the rotor in the cathode area is continuously stirred and the anode area is controlled at a constant temperature of 32±1 ℃. The gas in the anode area is collected to obtain mixed raw material gas.

[0045] 3) The mixed raw gas is sequentially filtered, mixed and absorbed, and cooled and recovered; Filtration: The mixed raw gas is filtered by passing through an industrial gas filter with a 5 nm pore size and a PTFE / PFA lining.

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

[0047] Cooling and recovery: The absorbent is passed into a mixing cooling tank and cooled to 5 °C to completely fix HF, yielding electronic-grade hydrofluoric acid.

[0048] The hydrogen fluoride concentration of electronic-grade hydrofluoric acid was characterized using a conductivity meter. The amount of ultrapure water used in the atomizing spray of the mixed absorption process was adjusted until the characterization results showed that the HF concentration in electronic-grade hydrofluoric acid reached the target concentration (50±1% in this example). At this point, the amount of ultrapure water used in the atomizing spray 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, and the laboratory energy consumption of step 1) was calculated and compared with that of the laboratory simulated wet electrolysis (KF·2HF molten salt electrolysis method) for the preparation of electronic-grade hydrogen fluoride (equivalent to step 1 in this example). The total amount of metal 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] The characterization results in Table 1 clearly demonstrate that this invention can directly achieve the preparation of electronic-grade hydrofluoric acid. The resulting product at least meets the standards for UP-grade electronic-grade hydrofluoric acid, with the total amount of metal impurities reaching UPSS-grade standards, and the chloride and particulate content both meeting UPS-grade standards. Furthermore, the non-target components generated during the preparation process mainly include incompletely reacted calcium fluoride, calcium oxalate (a secondary precipitate of calcium), and harmless carbon dioxide emissions. The overall process is safe and environmentally friendly. In terms of energy consumption, this invention achieves an energy reduction of approximately 70.74% compared to traditional wet electrolysis. The entire preparation process is conducted within a controllable temperature range, ensuring safety and energy efficiency.

[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 rest of the preparation process and preparation parameters are the same as in Example 1, and the product is characterized in the same way as in Example 1.

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

[0055] Table 2:

[0056] As can be clearly seen from Table 2 above, the concentration of calcium fluoride in the calcium fluoride aqueous suspension has no significant impact on the product quality. The main factor affecting quality is the fluorosilicic acid content. The fluorosilicic acid content is limited by the conditions of the research and development laboratory. In the subsequent industrialization process, it can be further controlled by avoiding equipment and / or pipelines containing hydrogen fluoride and silicon. However, the most significant change is in energy consumption. Compared with wet electrolysis, the preparation efficiency of this invention is limited (due to the solubility and dissolution rate of calcium fluoride, it is lower than that of wet electrolysis), while energy consumption and safety and environmental protection are process advantages. However, as shown in Table 2 above, when the concentration of calcium fluoride in the calcium fluoride aqueous suspension is 5.0 wt%, the dissolution efficiency decreases, leading to competition for hydroxide ions and a significant decrease in fluoride ion mobility, resulting in a significant increase in ineffective energy consumption. At high concentrations, a deposited film, which is a calcium oxalate deposit, is found on the cathode side surface of the ion exchange membrane after preparation. High concentrations of calcium fluoride will form calcium oxalate deposits on the cathode surface of the cathode ion exchange membrane in the early and short period of time, thereby slowing down the ion exchange rate and increasing the overall resistance, increasing ineffective energy consumption, and thus 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 rest of the preparation process and parameters are the same as in Example 1. The product is characterized and the reaction process is recorded in the same way as in Example 1.

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

[0059] Table 3:

[0060] As can be clearly seen from Table 3 above, the main purpose of adding ethylenediamine to the electrolyte in the cathode region of this invention is 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 some extent, excessively high concentrations of ethylenediamine will lead to increased solution viscosity, accelerated particle sedimentation, and inability to maintain a uniform suspension state during stirring, resulting in increased ineffective energy consumption, and even the formation of a gel state, making electrolysis impossible.

[0061] Example 4: A method for preparing electronic-grade hydrofluoric acid. This example is based on Example 1, except that the concentration of oxalic acid aqueous solution in the anode region is adjusted. 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 way as in Example 1.

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

[0063] Table 4:

[0064] As can be clearly seen from Table 3 above, low concentrations of oxalic acid lead to increased energy consumption due to conductivity issues. To ensure energy efficiency, an oxalic acid aqueous solution of 0.12–0.18 mol / L should be used. However, when the concentration of oxalic acid 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, which increases resistance and leads to 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 the acidic raw material solution in the anode region is replaced, and hydrogen is used to replace it with an equivalent amount of other acids. 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 way 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, due to the solubility difference between calcium oxalate and calcium fluoride, with calcium oxalate being less soluble than calcium fluoride, oxalic acid not only enhances the conductivity of the electrolyte in the anolyte and acts as a reducing agent in the anolyte, but also synergistically regulates the concentration of free calcium ions in the cathode. Through the spontaneous diffusion of oxalate ions, it promotes the precipitation of free calcium ions in the cathode, preventing the common ion effect caused by the decrease in fluoride ion concentration and the increase in calcium ion concentration during electrolysis. This indirectly increases the solubility of calcium fluoride and ensures the effective and continuous electrolysis process. Other common industrial inorganic acids do not possess this property, and therefore the electrolysis reaction spontaneously terminates because the common ion effect significantly inhibits the trace dissolution of calcium fluoride, preventing the re-dissolution and migration of fluoride ions. Furthermore, the hydrogen chloride in hydrochloric acid is volatile, which can easily introduce more new impurities into the product. Therefore, due to various factors, oxalic acid is currently the only known acid that can be used to prepare the acidic raw material solution for the anolyte region of this invention.

Claims

1. A method for preparing electronic-grade hydrofluoric acid, characterized in that, The method includes: 1) Set up an electrolytic cell, with the cathode area filled with fluorine feed solution and the anode area filled with acidic feed solution, and the anode and cathode areas separated by anion exchange membrane; 2) Electrolysis is performed by energizing the electrolytic cell, and the gas in the anode area is collected to obtain a mixed raw material gas; 3) The mixed raw material gas is sequentially filtered, mixed and absorbed, and cooled for recovery to obtain electronic-grade hydrofluoric acid; Step 1) The fluorine feedstock solution is an aqueous suspension of calcium fluoride; The calcium fluoride aqueous suspension contains 5.5–6.5 wt% calcium fluoride and 0.08–0.12 mol / L ethylenediamine. Step 1) The acidic raw material solution is an oxalic acid aqueous solution, and the concentration of oxalic acid in the oxalic acid aqueous solution is 0.12-0.18 mol / L; Step 1) The anion exchange membrane has a pore size of 3.2–3.5 Å.

2. The method for preparing electronic-grade hydrofluoric acid according to claim 1, characterized in that, In step 2), during the electrolysis process of the electrolytic cell being energized, the electrolysis voltage is controlled to be 2.0 to 2.2 V.

3. The method for preparing electronic-grade hydrofluoric acid according to claim 1 or 2, characterized in that, Step 2) During the electrolysis process of the electrolytic cell being energized: the cathode region continues to flow.

4. The method for preparing electronic-grade hydrofluoric acid according to claim 1, characterized in that, Step 3) The filtration is performed using a PTFE / PFA lined filter with a pore size of 3–12 nm; Step 3) The mixed absorption is carried out by spraying with ultrapure water with a resistivity ≥18.25 MΩ·cm; Step 3) Cooling and recycling involves cooling the hydrofluoric acid after mixing and absorption to ≤10 ℃ and then recycling and storing it.

5. The method for preparing electronic-grade hydrofluoric acid according to claim 4, characterized in that, Step 3) After the cooling and recovery process is completed, the concentration of hydrogen fluoride in the product is detected by an online density meter and / or conductivity meter, and the amount of ultrapure water used in the mixing and absorption process is adjusted according to the comparison between the product concentration and the target concentration.

6. A method for preparing electronic-grade hydrofluoric acid according to claim 1, 4, or 5, characterized in that, Step 3) involves condensation and re-evaporation between the filtration and mixing absorption processes; the condensation and re-evaporation involves condensing at 2-10°C and then heating to 25°C to evaporate and transform into a gaseous state.

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