Method for producing electronic grade fluorine-containing hydrochloric acid from crude hydrochloric acid and electronic grade fluorine-containing hydrochloric acid

Abstract

This invention provides a method for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid and the electronic-grade fluorinated hydrochloric acid prepared by the method. The crude hydrochloric acid contains HCl, HF, and H3PO4. The method includes the following steps: (1) oxidation treatment: mixing crude hydrochloric acid and an oxidizing agent for oxidation reaction; (2) filtration: removing solid impurities after oxidation treatment using a filter; (3) distillation: distilling the filtrate obtained in step (2) to achieve concentration and purification; (4) reduction treatment: reducing the distillate from step (3) using a reducing agent; (5) filtration: removing solid impurities from the distillate after step (4) using a filter to obtain electronic-grade fluorinated hydrochloric acid. By using the preparation method of this invention, crude hydrochloric acid containing various impurities generated during the production of lithium hexafluorophosphate can be extracted and prepared into electronic-grade hydrochloric acid that meets the composition standards of electronic-grade hydrochloric acid. The component ratio can be precisely controlled, enabling the crude hydrochloric acid to be recycled and reused, saving resources and disposal costs and protecting the environment.

Description

Technical Field

[0001] This invention relates to a method for preparing fluorinated hydrochloric acid from crude hydrochloric acid and the electronic-grade fluorinated hydrochloric acid prepared by the method, particularly a method for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid obtained from waste acid generated during the production of lithium hexafluorophosphate and the electronic-grade fluorinated hydrochloric acid prepared therefrom. Technical Background

[0002] Lithium-ion batteries are widely used in energy storage fields such as batteries for new energy vehicles. Lithium-ion battery electrolytes are generally prepared by mixing lithium salt electrolytes, organic solvents, and additives in specific proportions under certain conditions. Currently, lithium hexafluorophosphate (LiPF6) is the most widely used lithium-ion battery electrolyte.

[0003] The main industrial method for preparing lithium hexafluorophosphate is the hydrogen fluoride solvent method. This involves dissolving lithium fluoride (LiF) in anhydrous hydrogen fluoride (HF) liquid, then introducing phosphorus pentafluoride (PF5) gas. The phosphorus pentafluoride reacts with the lithium fluoride to produce lithium hexafluorophosphate. The synthesis reaction takes place in the liquid phase, offering advantages such as ease of control and a fast reaction rate. However, the phosphorus pentafluoride required by this method is expensive, and phosphorus pentachloride (PCl5) is often used as a substitute in large-scale industrial production.

[0004] In industrial production, solid phosphorus pentachloride reacts with hydrogen fluoride to produce phosphorus pentafluoride. The resulting mixture of phosphorus pentafluoride, hydrogen chloride, and hydrogen fluoride gases enters a lithium hexafluorophosphate synthesis reactor. The tail gas exiting the reactor mainly contains hydrogen chloride, hydrogen fluoride, and phosphorus pentafluoride gases. This mixture enters a water absorption tower, where it is absorbed by water to obtain crude hydrochloric acid. During the absorption process, phosphorus pentafluoride undergoes a series of chemical reactions with water to form hydrogen fluoride and phosphoric acid. Therefore, the crude hydrochloric acid contains hydrogen fluoride and phosphoric acid. In the above absorption process, phosphorus pentafluoride undergoes the following series of reactions with water:

[0005] PF5 + H2O → 2HF + POF3 (1)

[0006] POF3 + H2O → HF + HPO2F2 (2)

[0007] HPO2F2 + H2O → HF + H2PO3F (3)

[0008] H2PO3F + H2O → HF + H3PO4 (4)

[0009] Furthermore, since the absorbent is usually recycled water in actual production, crude hydrochloric acid contains elements such as sodium, potassium, calcium, magnesium, iron, aluminum, sulfur, and arsenic, in addition to fluorine and phosphorus. With the continuous expansion of lithium hexafluorophosphate production, the large quantities of crude hydrochloric acid result in significant disposal costs for enterprises. Because this crude hydrochloric acid contains small amounts of hydrofluoric acid and phosphoric acid, as well as a complex mixture of various metallic and non-metallic elements, it is difficult to purify and therefore unsuitable for use as a reaction feedstock or industrial pickling material. If this crude hydrochloric acid could be recycled and reused, it would not only reduce disposal costs for enterprises but also allow for the reuse of waste products, thereby saving disposal expenses and protecting the environment.

[0010] Patent document CN113716731A discloses a calcium treatment process for lithium hexafluorophosphate industrial wastewater, characterized in that:

[0011] Includes the following steps:

[0012] Step 1: Pretreatment of lithium hexafluorophosphate wastewater. Add calcium hydroxide to the lithium hexafluorophosphate wastewater and stir to adjust the pH of the lithium hexafluorophosphate wastewater to 10-12.

[0013] Step 2: Add flocculant to the treated lithium hexafluorophosphate wastewater, let it stand for a period of time, and then centrifuge and filter it to obtain centrifuged mother liquor.

[0014] Step 3: Inject carbon dioxide into the centrifuged mother liquor through the aeration system, and mix the carbon dioxide with the wastewater thoroughly through the impeller in the aeration system. After aeration, let it stand and wait for the reaction to complete.

[0015] Step 4: Add flocculant to the lithium hexafluorophosphate wastewater after the reaction in Step 3, allow it to react fully, and then filter to obtain the filtrate.

[0016] The above-mentioned solutions only treat wastewater using chemical precipitation, without recycling the byproducts. This results in high disposal costs and the inability to recycle the waste. Industrial electronic-grade hydrochloric acid, with stable fluorine content, is particularly suitable for preparing electronic-grade hydrochloric acid, as the tail gas generated during lithium hexafluorophosphate production contains HF and HCl. However, this grade of hydrochloric acid has very high composition requirements, necessitating stringent treatment technologies. Solving the above problems would address both the treatment of the tail gas generated during lithium hexafluorophosphate production and its recycling, conserving resources and protecting the environment. Therefore, there is an urgent need in this field to research a treatment process that meets these requirements. Summary of the Invention

[0017] To address the problems existing in the aforementioned related technologies, the applicant of this invention has researched how to separate impurities from the crude hydrochloric acid produced in the above-mentioned production process, thereby producing fluorinated hydrochloric acid that meets the composition requirements of electronic-grade hydrochloric acid. This fundamentally solves the problem of disposing of crude hydrochloric acid as a byproduct in the production of lithium hexafluorophosphate. Furthermore, the crude hydrochloric acid can be converted into electronic-grade acid for reuse.

[0018] In view of the problems existing in the above-mentioned related technologies, the present invention aims to solve the problem of how to prepare electronic-grade hydrochloric acid from the crude hydrochloric acid after absorbing the waste gas generated in the production of lithium hexafluorophosphate.

[0019] To address the aforementioned problems, one inventive aspect of this invention is to provide a method for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid, wherein the crude hydrochloric acid comprises HCl, HF, and H3PO4, and includes the following steps:

[0020] (1) Oxidation treatment: Crude hydrochloric acid and oxidant are mixed to carry out an oxidation reaction;

[0021] (2) Filtration: Use a filter to remove solid impurities after step (1);

[0022] (3) Distillation: The filtrate obtained in step (2) is distilled to concentrate and purify it;

[0023] (4) Reduction treatment: The reduction reaction is carried out with a reducing agent and the distillate from step (3) distillation;

[0024] (5) Filtration: Use a filter to remove solid impurities from the distillate after step (4) to obtain electronic grade fluorinated hydrochloric acid.

[0025] Furthermore, the crude hydrochloric acid is a mixed acid containing hydrochloric acid obtained by absorbing water the tail gas from the production of lithium hexafluorophosphate using the hydrogen fluoride solvent method.

[0026] Further, the oxidant in step (1) is one or more of hydrogen peroxide, hypochlorous acid, perchloric acid, hypochlorite, permanganate, and perchlorate.

[0027] Furthermore, the oxidation reaction in step (1) is carried out at room temperature and pressure, and the oxidant feed ratio is 0.01 kg / m³. 3 ~10kg / m 3 The stirring speed is 100 rpm to 500 rpm, and the oxidant is added in one or more batches, either as a liquid or solid.

[0028] Furthermore, the oxidation reaction time is less than or equal to 2 hours; the reduction reaction time is less than or equal to 2 hours.

[0029] Furthermore, in step (3), the distillation pressure is atmospheric pressure and the reflux ratio is (1:5)-(10:1).

[0030] Furthermore, in step (4), the reducing agent is one or a combination of hydrazine hydrate, L-ascorbic acid, and hydrazine hydrochloride.

[0031] Furthermore, in step (4), the reduction reaction is carried out at room temperature and pressure, and the reducing agent feed ratio is 0.01 kg / m³. 3 ~1kg / m 3 The stirring speed is 100rpm to 500rpm, and the reducing agent is added in one or more batches, either as a liquid or solid.

[0032] Furthermore, the filter in steps (2) and (5) is a microporous filter.

[0033] Further, step (3) uses a distillation apparatus that is a plastic-lined packed tower; and / or a plastic-lined plate tower; the packing material of the plastic-lined packed tower is at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene; the packing shape of the plastic-lined packed tower is one or more of spherical, Raschig ring, Pall ring, stepped ring, and saddle ring. The plastic lining material is at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.

[0034] Furthermore, the obtained electronic-grade fluorinated hydrochloric acid meets one or more of the following conditions: HCl content is 30wt.% to 35wt.%, HF content is ≥3wt.%, free chlorine content is ≤500μg / L, lithium content is ≤1μg / L, sodium content is ≤100μg / L, potassium content is ≤5μg / L, calcium content is ≤50μg / L, other metal impurities content is ≤10μg / L, boron content is ≤10μg / L, arsenic content is ≤5μg / L, sulfite content is ≤1000μg / L, sulfate content is ≤1000μg / L, phosphate content is ≤1000μg / L, and residue on ignition is ≤1mg / L.

[0035] Another inventive aspect of this invention is to provide an electronic-grade fluorinated hydrochloric acid, which is prepared by the method described above.

[0036] Compared with related technologies, the present invention has the following advantages: by using oxidation treatment, filtration, distillation, reduction treatment and filtration treatment in combination, mixed acid containing various impurities can be purified and impurities removed, so as to accurately control the component ratio and meet the requirements of electronic grade hydrochloric acid component standards. Thus, the waste acid that originally needed to be treated can be made into electronic grade hydrochloric acid, so that the above-mentioned crude hydrochloric acid can be recycled and reused, saving resources, saving disposal costs and protecting the environment.

[0037] The electronic-grade fluorinated hydrochloric acid prepared by this invention has a stable composition and can meet the needs of the electronics industry, such as the cleaning acid solution after texturing solar silicon crystal cells. It is a product that can effectively recycle and reuse resources. Attached Figure Description

[0038] Figure 1 The steps for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid according to one embodiment of the present invention Detailed Implementation

[0039] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. However, it should be understood that the description herein is merely illustrative and not intended to limit the scope of the invention.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the specification is for the purpose of describing particular embodiments only and is not intended to limit the invention. All characterization techniques mentioned herein can be found in relevant descriptions in the prior art, and will not be repeated here.

[0041] To further understand the present invention, the present invention will be described in more detail below with reference to the preferred embodiments.

[0042] Example 1

[0043] Figure 1 This embodiment of the invention describes a method for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid. The crude hydrochloric acid contains HCl, HF, and H3PO4, and includes the following steps:

[0044] (1) Oxidation treatment: Crude hydrochloric acid and oxidant are mixed to carry out an oxidation reaction;

[0045] (2) Filtration: Use a filter to remove solid impurities after step (1);

[0046] (3) Distillation: The filtrate obtained in step (2) is distilled to concentrate and purify it;

[0047] (4) Reduction treatment: The reduction reaction is carried out with a reducing agent and the distillate from step (3) distillation;

[0048] (5) Filtration: Use a filter to remove solid impurities from the distillate after step (4) to obtain electronic grade fluorinated hydrochloric acid.

[0049] The crude hydrochloric acid mentioned above is preferably a mixed acid containing hydrochloric acid obtained by absorbing water from the tail gas of lithium hexafluorophosphate production using the hydrogen fluoride solvent method. The main component of this mixed acid is hydrochloric acid, which usually accounts for 25%-45% of the mixed acid, and more commonly 30%-37%. There is also a portion of HF and H3PO4, with the HF content usually between 2%-10% and the H3PO4 content usually between 0.01%-1%. In addition, there are usually small amounts of elements such as sodium, potassium, calcium, magnesium, iron, aluminum, sulfur, and arsenic. The remaining part is basically H2O.

[0050] In this embodiment, oxidation pretreatment can treat some ions, such as oxidizing arsenic ions from low to high oxidation states and significantly reducing the content of impurities such as Li, Na, Al, Ca, K, Sn, Tl, and Bi. Filtration removes the solid impurities present in the product and those obtained after oxidation. Distillation further separates HCl and HF from the mixed acid. Reduction treatment converts free chlorine into HCl and removes some manganese and arsenic elements. Finally, filtration removes solid impurities from the effluent. Therefore, through the above-mentioned specific sequence of treatment and the cooperation of each treatment step, mixed acid containing various impurities, especially crude hydrochloric acid produced during the production of lithium hexafluorophosphate, can be purified and impurities removed. The composition ratio of the obtained product can be precisely controlled to meet the requirements of electronic-grade hydrochloric acid composition standards. This transforms the waste acid that originally needed to be treated into electronic-grade hydrochloric acid, enabling the crude hydrochloric acid to be recycled and reused, saving resources, reducing disposal costs, and protecting the environment.

[0051] Example 2

[0052] Figure 1 This embodiment of the present invention describes the steps for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid. This embodiment is a method for preparing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid. Based on embodiment 1, the oxidant in step (1) is one or more of hydrogen peroxide, hypochlorous acid, perchloric acid, hypochlorite, permanganate, and perchlorate, for example, permanganate.

[0053] In a further preferred embodiment, the oxidation reaction in step (1) is carried out at room temperature and pressure, and the oxidant feed ratio is 0.01 kg / m³. 3 ~10kg / m 3 For example, 0.01 kg / m 3 0.1kg / m 3 1kg / m 3 5kg / m 3 10kg / m 3The stirring speed is 100 rpm to 500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, etc. The oxidant is added in one or more batches, either liquid or solid. The ambient temperature typically refers to -5 to 50°C, preferably 10 to 30°C, and more preferably 15 to 25°C. The ambient pressure refers to one atmosphere, typically 100 kPa to 101 kPa. Since standard atmospheric pressure varies depending on geographical location, altitude, temperature, etc., it is not limited to the above values ​​and can be the actual local atmospheric pressure.

[0054] The oxidant can be added entirely in solid form, entirely in liquid form, or a mixture of some oxidants in liquid form and some in solid form. The oxidant can be added all at once or in batches. When adding in batches, all the oxidant can be divided into several equal portions, with one portion added each time, or all of a portion of the oxidant can be added at a time, with all the oxidants added in multiple batches.

[0055] In a further preferred embodiment, the oxidation reaction typically lasts for 2 hours or less; the reduction reaction typically lasts for 2 hours or less. Of course, the specific oxidation and reduction reaction times need to be adjusted based on factors such as the amount of reactants, and are not entirely limited to 2 hours.

[0056] In a further preferred embodiment, the distillation pressure in step (3) is atmospheric pressure, and the reflux ratio is typically (1:5)-(10:1). Preferably, it is (1:3)-(5:1).

[0057] Wherein, reflux ratio = reflux flow rate / outflow product flow rate; calculated by mass: reflux flow rate = reflux product mass / time; outflow product flow rate = outflow product mass / time. calculated by volume: reflux flow rate = reflux product volume / time; outflow product flow rate = outflow product volume / time.

[0058] In a further preferred embodiment, the reducing agent in step (4) is one or a combination of hydrazine hydrate, L-ascorbic acid, and hydrazine hydrochloride.

[0059] In a further preferred embodiment, the reduction reaction in step (4) is carried out at room temperature and pressure, and the reducing agent feed ratio is 0.01 kg / m³. 3 ~1kg / m 3 For example, 0.01 kg / m 3 0.05kg / m 3 0.1kg / m 3 0.5kg / m 3 1kg / m 3The stirring speed is 100 rpm to 500 rpm, for example, 100 rpm, 200 rpm, 300 rpm, 400 rpm, 500 rpm, etc. The reducing agent can be added in one or multiple batches, either as a liquid or solid. The reducing agent can be added entirely in solid form, entirely in liquid form, or a mixture of some liquid and some solid forms. The reducing agent can be added all at once or in batches. When adding in batches, all the reducing agent can be divided into several equal portions, with one portion added each time, or a portion of the reducing agent can be added at a time, adding all of it in multiple batches.

[0060] In a further preferred embodiment, the reduction reaction includes the following reaction characteristics:

[0061] MnO4 - (aq)+8H + +5e - →Mn 2+ (aq) + 4H₂O E₀ = 1.51V

[0062] Cl2(g) + 2e - →2Cl - E0 = 1.36V

[0063] H3AsO4(aq) + 2H + +2e - →H3AsO3(aq)+H2O E0=0.56V

[0064]

[0065] Reducing agent + Cl2(aq) + H2O → HCl + Oxidation product

[0066] The above example uses permanganate as the oxidant. Cl2 is generated from Cl ions in the original mixed acid during distillation and mixed into the top products HCl and HF. H3AsO4 is introduced when the tail gas of lithium hexafluorophosphate is absorbed by recycled water.

[0067] Furthermore, the filters used in steps (2) and (5) are microporous filters. By using microporous filters, it is possible to achieve fast filtration speed, small adsorption capacity, large filtration area, and less susceptibility to contamination, thus enabling better filtration.

[0068] In a further preferred embodiment, step (3) uses a distillation apparatus that is a plastic-lined packed tower; and / or a plastic-lined plate tower; preferably a packed tower. The packing material of the plastic-lined packed tower is one or more of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene; the packing shape is at least one of spherical, Raschig ring, Pall ring, stepped ring, and saddle ring; the inner plastic lining material is at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene. The spherical, Raschig ring, Pall ring, stepped ring, and saddle ring are existing industrial packing shapes; the tower packing is the core component of the packed tower, providing an effective phase interface for heat and mass transfer between the gas and liquid phases. The packing performance mainly depends on the specific surface area, porosity, and packing factor. Generally speaking, saddle rings, stepped rings, and Pall rings have better performance than spherical and Raschig rings. Polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene have the advantages of fast filtration speed and small adsorption capacity.

[0069] In a further preferred embodiment, the obtained electronic-grade fluorinated hydrochloric acid meets one or more of the following conditions: HCl content 30wt.%–35wt.%, HF content ≥3wt.%, free chlorine content ≤500μg / L, lithium content ≤1μg / L, sodium content ≤100μg / L, potassium content ≤5μg / L, calcium content ≤50μg / L, other metal impurities content ≤10μg / L, boron content ≤10μg / L, arsenic content ≤5μg / L, sulfite content ≤1000μg / L, sulfate content ≤1000μg / L, phosphate content ≤1000μg / L, and residue on ignition ≤1mg / L. Generally, the method of this invention can usually meet these conditions. Therefore, this application can precisely control the component ratio of the obtained product, resulting in stable product quality and good resource utilization.

[0070] In a further preferred embodiment, the mass yield of the obtained electronic-grade fluorinated hydrochloric acid is ≥70%.

[0071] In this embodiment, by specifically defining the oxidant, reducing agent, and specific reaction conditions and reflux ratios, the resource utilization of hydrochloric acid generated during the production of lithium hexafluorophosphate can be better realized. The process employing oxidation, distillation, and reduction treatments ensures that the content of phosphates, sulfates, sulfites, free chlorine, boron, arsenic, and metal ions in the hydrochloric acid meets the quality standards for electronic hydrochloric acid. The method of this invention features a short process flow, high flexibility, high throughput, and stable product quality, making it easy to use in industrial production scenarios.

[0072] Example 3

[0073] An electronic-grade fluorinated hydrochloric acid, which is prepared by using the method of Example 1 or 2.

[0074] The electronic-grade fluorinated hydrochloric acid meets the following purity requirements: HCl content 30wt.%~35wt.%, HF content ≥3wt.%, free chlorine content ≤500μg / L, lithium content ≤1μg / L, sodium content ≤100μg / L, potassium content ≤5μg / L, calcium content ≤50μg / L, other metal impurities content ≤10μg / L, boron content ≤10μg / L, arsenic content ≤5μg / L, sulfite content ≤1000μg / L, sulfate content ≤1000μg / L, phosphate content ≤1000μg / L, and residue on ignition ≤1mg / L.

[0075] This invention employs a process of pre-oxidation treatment, distillation, and post-reduction treatment to ensure that the content of phosphate, sulfate, sulfite, free chlorine, boron, arsenic, and metal ions in crude hydrochloric acid meets the quality standards for electronic hydrochloric acid, achieving precise control, stable product quality, and resource utilization of hydrochloric acid generated during the production of lithium hexafluorophosphate.

[0076] Example 4

[0077] A method for producing electronic-grade fluorinated hydrochloric acid from crude hydrochloric acid generated during the production of lithium hexafluorophosphate includes pre-oxidation treatment, filtration, distillation, post-reduction treatment, and filtration unit operations.

[0078] Crude hydrochloric acid is a hydrochloric acid containing impurities such as fluorine and phosphorus, obtained by absorbing the gas generated during the production of lithium hexafluorophosphate using phosphorus pentachloride as the phosphorus source and anhydrous hydrogen fluoride solvent.

[0079] (1) Pre-oxidation treatment: Crude hydrochloric acid and oxidant are mixed and then reacted at room temperature and normal pressure. The reaction time is controlled within 2 hours. The gas produced by the reaction is sent to the waste gas treatment system.

[0080] (2) Filtration: Use a filter to separate and remove solid impurities from the crude hydrochloric acid after oxidation treatment.

[0081] (3) Distillation: The filtrate obtained in step (2) is distilled under normal pressure and the reflux ratio is controlled to be greater than 1:5. The liquid flowing out of the bottom of the column is sent to the waste liquid treatment system, and the non-condensable vapor at the top of the column is sent to the waste gas treatment system.

[0082] (4) Post-processing: Mix the top product obtained in step (3) with the reducing agent, and then react at room temperature and normal pressure. The reaction time is controlled within 2 hours. The gas produced by the reaction is sent to the waste gas treatment system.

[0083] (5) Filtration: Use a filter to separate and remove solid impurities from the top product of the reduced tower to obtain electronic grade fluorinated hydrochloric acid.

[0084] In steps (1) and (4), the reaction equipment is a stirred tank.

[0085] Preferably, the stirring vessel is a conical-bottomed container with an inner wall lined with plastic or plastic material and does not have a heat exchange jacket or coil.

[0086] The stirred tank reactor is operated in a semi-batch mode.

[0087] Preferably, in steps (1) and (4), the stirring rate is 100 rpm to 500 rpm.

[0088] In steps (2) and (5), the filtration equipment is a microporous filter.

[0089] In step (1), the oxidant is one or more of hydrogen peroxide, hypochlorous acid, perchloric acid, permanganate, hypochlorite, and perchlorate, with permanganate being preferred.

[0090] Furthermore, the reflux ratio = reflux flow rate / outflow product flow rate; calculated by mass: reflux flow rate = reflux product mass / time; outflow product flow rate = outflow product mass / time. Calculated by volume: reflux flow rate = reflux product volume / time; outflow product flow rate = outflow product volume / time.

[0091] Furthermore, the oxidant feed ratio in step (1) is 0.01 kg / m³. 3 ~10kg / m 3 .

[0092] Furthermore, the oxidant in step (1) is added to the crude hydrochloric acid in solid or liquid form.

[0093] Furthermore, the oxidant in step (1) is fed in one or several batches.

[0094] In step (3), the distillation equipment is a packed tower or a plate tower lined with plastic, preferably a packed tower.

[0095] Furthermore, the packing material of the packed tower in step (3) includes polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene, with polytetrafluoroethylene being the preferred material.

[0096] In step (3), the packing shape of the packed tower is spherical, Raschig ring, Pall ring, stepped ring, or saddle ring, with Pall ring being the preferred choice.

[0097] The inner lining plastic material is at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.

[0098] In step (4), the reducing agent is one or more combinations of hydrazine hydrate, L-ascorbic acid, and hydrazine hydrochloride, preferably hydrazine hydrate.

[0099] Furthermore, the reducing agent feed ratio in step (4) is 0.01 kg / m³. 3~1kg / m 3 .

[0100] The reducing agent in step (4) is added to the top product of the distillation column in step (3) in either solid or liquid form. The reducing agent can be added entirely in solid form, entirely in liquid form, or a mixture of some liquid and some solid reducing agents can be added.

[0101] The reducing agent in step (4) is added once or in batches.

[0102] The electronic-grade fluorinated hydrochloric acid prepared by the method of preparing fluorinated hydrochloric acid using crude hydrochloric acid.

[0103] The method of this invention achieves the following: 1. Improves the traditional utilization of crude hydrochloric acid, a byproduct of lithium hexafluorophosphate, thereby increasing raw material utilization efficiency. 2. The electronic-grade fluorinated hydrochloric acid prepared from the crude hydrochloric acid generated during lithium hexafluorophosphate production can be used in some special applications, such as as a cleaning acid solution after texturing solar silicon wafers. 3. The process described in this invention is short, highly flexible, has a large throughput, and produces stable product quality, making it easy to promote and industrialize.

[0104] Example 5

[0105] This embodiment is based on the method of embodiment 4, and the specific steps are as follows:

[0106] The crude hydrochloric acid produced during the production of lithium hexafluorophosphate (100L) was placed into a plastic conical reactor equipped with a stirrer, and 100g of chemically pure hypochlorous acid was added at once. The stirring was started at room temperature and atmospheric pressure at a stirring speed of 250rpm. After reacting for 1.5 hours, the mixture was filtered to remove solid impurities from the liquid.

[0107] The liquid, after solid impurities have been removed, is pumped by a peristaltic pump into a polyethylene-lined distillation column. The distillation column is filled with polyethylene Pall rings, and the bottom temperature is controlled at 110°C with a reflux ratio of 1:2.

[0108] The contents of 11 impurity ions in the top product of the distillation column are listed in Table 1.

[0109] 100 L of the obtained fluorinated hydrochloric acid was placed in a plastic conical reactor equipped with a stirrer, and 10 g of a mixture of hydrazine hydrochloride hydrate and L-ascorbic acid was added at once. The mixture was stirred at 250 rpm at room temperature and atmospheric pressure for 45 minutes, and then filtered to remove solid impurities from the liquid.

[0110] The free chlorine content in the fluorinated hydrochloric acid after removing solid impurities is less than 500 ppb.

[0111] Example 6

[0112] This embodiment is based on the method of embodiment 4, and the specific steps are as follows:

[0113] The crude hydrochloric acid produced during the production of lithium hexafluorophosphate (100L) was placed into a plastic conical reactor equipped with a stirrer, and 250g of chemically pure potassium permanganate powder was added at once. The stirring was started at room temperature and atmospheric pressure at a stirring speed of 220rpm. After reacting for 1 hour, the mixture was filtered to remove solid impurities from the liquid.

[0114] The liquid, after solid impurities have been removed, is pumped by a peristaltic pump into a polypropylene-lined distillation column. The distillation column is filled with polypropylene Pall rings, and the bottom temperature is controlled at 110°C with a reflux ratio of 1.

[0115] The contents of 11 impurity ions in the top product of the distillation column are listed in Table 1.

[0116] 100 L of the obtained fluorinated hydrochloric acid was placed in a plastic conical reactor equipped with a stirrer, and a mixture of 20 g of hydrazine hydrate solution and L-ascorbic acid was added at once. The mixture was stirred at 350 rpm at room temperature and atmospheric pressure for 30 minutes, and then filtered to remove solid impurities from the liquid.

[0117] The free chlorine content in the fluorinated hydrochloric acid after removing solid impurities is less than 500 ppb.

[0118] Example 7

[0119] This embodiment is based on the method of embodiment 4, and the specific steps are as follows:

[0120] The crude hydrochloric acid produced during the production of lithium hexafluorophosphate (100L) was placed into a plastic conical reactor equipped with a stirrer, and 500g of chemically pure perchloric acid powder was added at once. The stirring was started at room temperature and atmospheric pressure at a stirring speed of 150rpm, and the reaction was carried out for 30 minutes. After that, the solid impurities in the liquid were removed by filtration.

[0121] The liquid, after solid impurities have been removed, is pumped by a peristaltic pump into a distillation column lined with polytetrafluoroethylene (PTFE). The distillation column is filled with PTFE Pall rings, and the bottom temperature is controlled at 110°C with a reflux ratio of 2.

[0122] The contents of 11 impurity ions in the top product (fluorinated hydrochloric acid) of the distillation column are listed in Table 1.

[0123] 100 L of the obtained fluorinated hydrochloric acid was placed in a plastic conical reactor equipped with a stirrer, and 30 g of L-ascorbic acid was added at once. The stirring was started at room temperature and atmospheric pressure at a stirring speed of 450 rpm. After reacting for 1 hour, the mixture was filtered to remove solid impurities from the liquid.

[0124] The free chlorine content in the fluorinated hydrochloric acid after removing solid impurities is less than 500 ppb.

[0125] Comparative Example 1

[0126] Based on Example 7, without the oxidation treatment step in Example 7, i.e. without step (1), the crude hydrochloric acid after removing solid impurities is directly pumped into a distillation column lined with PTFE using a peristaltic pump. The distillation column is filled with PTFE Pall rings, the bottom temperature of the column is controlled at 110°C, and the reflux ratio is 2.

[0127] The contents of 11 impurity ions in the top product of the distillation column are listed in Table 1.

[0128] Other methods are based on Example 7.

[0129] Table 1 Content of 11 impurity ions in fluorinated hydrochloric acid

[0130]

[0131] The results in the table above show that the content of 11 impurity ions in the top product of the distillation column was well controlled in Examples 5-7. Examples 5-7, by designing different amounts of oxidant, showed different effects, achieving optimized selection of the oxidant dosage. Comparative Example 1 is based on the method of Example 7, except that it does not include an oxidation treatment step and directly enters the distillation step. It can be seen that the impurity ion content in Comparative Example 1 is significantly higher than that in Example 7, demonstrating the importance of oxidation treatment.

[0132] Example 8

[0133] The crude hydrochloric acid produced during the lithium hexafluorophosphate production process is placed in a plastic conical reactor equipped with a stirrer, and then added at a concentration of 1.5 kg oxidant / m³. 3 The crude hydrochloric acid was added in one batch, consisting of chemically pure potassium permanganate granules. Stirring was started at room temperature and atmospheric pressure at a speed of 200 rpm. After reacting for 30 minutes, the mixture was filtered to remove solid impurities from the liquid.

[0134] The liquid, after solid impurities have been removed, is pumped by a peristaltic pump into a PTFE-lined distillation column. The distillation column is filled with PTFE Pall rings, and the bottom temperature is controlled at 110°C with a reflux ratio of 1:2.

[0135] The top product from the distillation column was transferred to a plastic conical reactor equipped with a stirrer, and then reacted with 30g of reducing agent per cubic meter of water. 3 The product from the top of the column was fed dropwise with analytical grade hydrazine hydrate solution. Stirring was started at room temperature and atmospheric pressure at a stirring rate of 250 rpm, and the reaction was carried out for 45 minutes. After that, the liquid was filtered to remove solid impurities.

[0136] The product yield of the distillation column top after removing solid impurities was 71%, and the product color was 5 PHA. The product contained 31.5 wt.% hydrogen chloride, 4.2 wt.% hydrogen fluoride, and <1 mg / L residue on ignition. The impurity content is listed in Table 2.

[0137] Table 2. Impurity ion content in fluorinated hydrochloric acid

[0138]

[0139] Example 9

[0140] The crude hydrochloric acid produced during the lithium hexafluorophosphate production process is placed in a plastic conical reactor equipped with a stirrer, and then added at a concentration of 1.5 kg oxidant / m³. 3 The crude hydrochloric acid was added in one batch, consisting of chemically pure potassium permanganate granules. Stirring was started at room temperature and atmospheric pressure at a speed of 200 rpm. After reacting for 30 minutes, the mixture was filtered to remove solid impurities from the liquid.

[0141] The liquid, after solid impurities have been removed, is pumped by a peristaltic pump into a distillation column lined with polytetrafluoroethylene (PTFE). The distillation column is filled with PTFE Pall rings, and the bottom temperature is controlled at 110°C with a reflux ratio of 5:1.

[0142] The top product from the distillation column was transferred to a plastic conical reactor equipped with a stirrer, and then reacted at a ratio of 300g reducing agent / m³. 3 The product from the top of the column was fed dropwise with analytical grade L-ascorbic acid solution. Stirring was started at room temperature and atmospheric pressure at a stirring rate of 350 rpm, and the reaction was carried out for 45 minutes. After that, the liquid was filtered to remove solid impurities.

[0143] The product yield of the top product of the distillation column after removing solid impurities was 70%, and the product color was 5 PHA. The product contained 32.0 wt.% hydrogen chloride, 4.2 wt.% hydrogen fluoride, and <1 mg / L residue on ignition. The impurity content is listed in Table 3.

[0144] Table 3. Impurity ion content in fluorinated hydrochloric acid

[0145]

[0146]

[0147] Comparative Example 2

[0148] The method is based on Example 8, except that it does not include a post-reduction processing step.

[0149] The free chlorine content in the fluorinated hydrochloric acid after removing solid impurities is approximately 0.01%. The reduction treatment is primarily to convert the free chlorine into HCl. It is evident that without reduction treatment, the free chlorine content is higher than the requirements for electronic-grade hydrochloric acid. Therefore, the reduction step is essential.

[0150] Furthermore, without the filtration step, solid impurities in the mixed acid cannot be removed. Without the distillation step, HF and HCl cannot be separated from other impurities. Therefore, it can be seen that each step of this invention plays a crucial role in the successful preparation of electronic-grade fluorinated hydrochloric acid; none can be omitted, forming an inseparable organic whole. In addition, through experiments with different oxidants and reducing agents, and experiments with distillation ratios, the inventors have identified preferred types of oxidants, reducing agents, their addition methods and proportions, and a preferred distillation ratio, further ensuring the stability of the component content of the product and guaranteeing that the content of each component meets the requirements for electronic-grade hydrochloric acid.

[0151] In embodiments of the present invention, the method of the present invention is used to extract electronic-grade hydrochloric acid from crude hydrochloric acid produced in the production of lithium hexafluorophosphate. It is understood that the method of the present invention is not limited to the above application. The method of the present invention can be used for any product that needs to be extracted from crude hydrochloric acid containing elements such as sodium, potassium, calcium, magnesium, iron, aluminum, sulfur, and arsenic in addition to fluorine and phosphorus, and has a stable fluorine and HCl content.

[0152] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions or improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A process for the production of electronic grade hydrofluoric acid from crude hydrochloric acid, characterized in that, The crude hydrochloric acid is a mixed acid containing HCl, HF, and H3PO4 obtained by absorbing water from the tail gas of lithium hexafluorophosphate produced by the hydrogen fluoride solvent method; it includes the following steps: (1) Oxidation treatment: Crude hydrochloric acid and oxidant are mixed to carry out an oxidation reaction; (2) Filtration: Use a filter to remove the solid impurities after step (1); (3) Distillation: The filtrate obtained in step (2) is distilled under atmospheric pressure and a reflux ratio of (1:5)-(10:1) to achieve concentration and purification; (4) Reduction treatment: The reduction reaction is carried out using a reducing agent and the distillate from step (3) distillation; (5) Filtration: Use a filter to remove solid impurities from the distillate after step (4) to obtain electronic grade fluorinated hydrochloric acid; The obtained electronic-grade fluorinated hydrochloric acid meets one or more of the following conditions: HCl content is 30wt.%~35wt.%, HF content is ≥3wt.%, free chlorine content is ≤500μg / L, lithium content is ≤1μg / L, sodium content is ≤100μg / L, potassium content is ≤5μg / L, calcium content is ≤50μg / L, other metal impurities content is ≤10μg / L, boron content is ≤10μg / L, arsenic content is ≤5μg / L, sulfite content is ≤1000μg / L, sulfate content is ≤1000μg / L, phosphate content is ≤1000μg / L, and residue on ignition is ≤1mg / L.

2. The method of claim 1, wherein: The oxidant in step (1) is one or more of hydrogen peroxide, hypochlorous acid, perchloric acid, hypochlorite, permanganate, and perchlorate.

3. The method of claim 1, wherein: The oxidation reaction in step (1) is carried out at room temperature and pressure, and the oxidant feed ratio is 0.01 kg / m³. 3 ~10kg / m 3 The stirring speed is 100 rpm to 500 rpm, and the oxidant is added in one or more batches, either as a liquid or solid.

4. The method of claim 1, wherein: In step (4), the reducing agent is one or a combination of hydrazine hydrate, L-ascorbic acid, and hydrazine hydrochloride.

5. The method of claim 1, wherein: In step (4), the reduction reaction is carried out at room temperature and pressure, and the reducing agent feed ratio is 0.01 kg / m³. 3 ~1kg / m 3 The stirring speed is 100 rpm to 500 rpm, and the reducing agent is added in one or more batches, either as a liquid or solid.

6. The method as described in claim 1, characterized in that: The filters used in steps (2) and (5) are microporous filters; Step (3) Use distillation equipment for plastic-lined packed towers and / or plastic-lined plate towers; The packing material of the plastic-lined packed tower is at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene; The packing shape of the plastic-lined packed tower is at least one of the following: spherical, Raschig ring, Pall ring, stepped ring, and saddle ring. The inner lining plastic is made of at least one of polypropylene, polyethylene, polyvinyl chloride, and polytetrafluoroethylene.

7. An electronic-grade fluorinated hydrochloric acid, characterized in that: It is prepared by the method described in any one of claims 1-6.

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