Method for preparing hydrogen fluoride from a fluorosilicic acid with simultaneous alkaline hydrolysis of the components

Abstract

The present application relates to the field of anhydrous hydrogen fluoride production, and particularly relates to a method for preparing hydrogen fluoride by decomposing multi-components with fluosilicic acid and alkali. The method comprises the following steps: alkali decomposition reaction, preparation of white carbon black, preparation of calcium fluoride, recovery and circulation of anhydrous hydrogen fluoride, and regeneration and compounding of alkali decomposition agent. In the method, the fluosilicic acid is first decomposed with multi-components to convert into potassium fluoride solution, and then reacts with calcium sulfate and calcium hydroxide to generate fluorite, and the fluorite reacts with sulfuric acid solution to generate hydrogen fluoride gas, so that the calcium sulfate is completely recycled, the hydrogen fluoride is washed, condensed and rectified to obtain anhydrous hydrogen fluoride; the supercritical CO2 drying technology is introduced to co-produce high-specific-surface white carbon black, so that the agglomeration is avoided and the process flow is simplified; and the alkali decomposition agent can be recycled and regenerated for use, without by-product discharge.

Description

Technical Field

[0001] This invention relates to the field of anhydrous hydrogen fluoride production, and more particularly to a method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid and multiple components. Background Technology

[0002] Anhydrous hydrogen fluoride (AHF) is a basic raw material for the production of various fluorinated compounds. It has a wide range of applications, including the synthesis of fluorinated refrigerants, fluoroplastics, fluororubber, fluorinated pharmaceuticals and fluorinated pesticides, and the manufacture of aluminum fluoride and cryolite. In the chemical industry, it is used as a catalyst for organic synthesis such as alkylation and polymerization. In the electronics industry, it is used as a strong acid etching agent (it can be used in combination with nitric acid, acetic acid, etc.).

[0003] However, existing technologies suffer from problems such as the large amount of phosphogypsum byproducts and the ineffective utilization of silica gel. At the same time, the yield and purity of potassium fluoride are not high, making it difficult to ensure the quality of anhydrous hydrogen fluoride products, and the performance of silica is difficult to further improve. Summary of the Invention

[0004] The purpose of this invention is to propose a method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid and multiple components. This method greatly improves the yield of potassium fluoride in the reaction process, enhances the purity of potassium fluoride, ensures the quality of anhydrous hydrogen fluoride products, achieves resource recycling, significantly reduces production costs, and effectively improves the specific surface area, purity, and crystal form of silica.

[0005] The specific technical solution of the present invention is as follows: A method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid and multiple components includes the following steps: Step S1 Alkali hydrolysis reaction Fluorosilicic acid was subjected to an alkaline hydrolysis reaction with an alkaline hydrolysis agent, and the CO2 gas generated was collected. After the reaction was completed, hydrofluoric acid was added for back-conditioning. The solution after the reaction was subjected to solid-liquid separation to obtain potassium fluoride solution and solid filter cake silica gel. Step S2: Preparation of silica The solid filter cake silica gel is washed with water, filtered, and dried with supercritical CO2 to obtain the precipitated silica product. Step S3: Preparation of calcium fluoride The potassium fluoride solution in step S1 is heated, calcium sulfate and calcium hydroxide are added, the reaction is stirred, filtered and washed to obtain solid calcium fluoride and potassium sulfate solution. Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Calcium fluoride solid is dried with CO2 supercritically, prepared into a solution, and concentrated sulfuric acid is slowly added dropwise. The mixture is heated and stirred to produce calcium sulfate dihydrate wet base and fluorine-containing gas. The fluorine-containing gas is then washed and absorbed under countercurrent atmospheric pressure. The absorbed gas is condensed, and the condensate is distilled to obtain anhydrous hydrogen fluoride and bottom product. Step S5: Regeneration and compounding of the alkaline hydrolysate In step S3, a saturated calcium hydroxide solution is added to the potassium sulfate solution, and the mixture is stirred to produce a potassium hydroxide solution and a calcium sulfate precipitate. Once the reaction reaches its endpoint, the mixture is filtered at room temperature to obtain a calcium sulfate filter cake and a potassium hydroxide solution. The calcium sulfate filter cake is dried and then reused in step S3. Subsequently, the CO2 gas collected in step S1 is introduced into the potassium hydroxide solution. After the reaction is completed, the solution is transferred to concentration and crystallization. The solid obtained after centrifugation can be used as an alkaline hydrolysis agent.

[0006] As a preferred embodiment, in step S1, the alkaline hydrolysant is a solid mixture of potassium hydroxide and potassium carbonate, wherein the molar ratio of pure potassium hydroxide to potassium carbonate is 9-9.5:0.5-1; and the amount of alkaline hydrolysant added is 140-160g.

[0007] The compound alkaline hydrolysate is slowly added to the fluorosilicic acid solution and stirred at room temperature for 1-2 hours to produce a colorless, viscous potassium fluorosilicate paste. Then, the temperature is raised to 78-85°C in a water bath and stirred for 1-2 hours until the solution turns milky white. The carbon dioxide gas produced during the reaction is collected. After the reaction is completed, the pH is adjusted to 7.0-7.2 with acid.

[0008] As a preferred embodiment, in step S1, the mass percentage concentration of the fluorosilicic acid liquid is 10-16%, wherein the content of free acid impurities is 0.15-0.25%.

[0009] As a preferred option, in step S2, the supercritical CO2 drying process conditions are as follows: gas flow rate controlled at 1-9 L / min, pressure rise in the supercritical CO2 reactor at 8-10 MPa, CO2 gas volume percentage at 95%, drying temperature at 50-80℃, and drying time at 10-30 min.

[0010] As a preferred embodiment, in step S3, the temperature is raised to 80-87°C, and calcium sulfate and calcium hydroxide are added slowly in sequence according to a molar ratio of 8-9.5:0.5-2, and the mixture is stirred and reacted for 2-3 hours; the total amount of calcium sulfate and calcium hydroxide added is 150-200g.

[0011] As a preferred embodiment, in step S4, the amount of concentrated sulfuric acid added is 1.35 to 1.38 times the mass of the calcium fluoride solid, and the reaction is carried out at 82 to 85°C with stirring for 2 to 2.5 hours; the mass percentage concentration of the calcium fluoride solution prepared by adding water is 30 to 35%. The supercritical carbon dioxide drying conditions are as follows: the CO2 gas flow rate is controlled at 1-9 L / min, the pressure is first increased to 8-10 MPa in the critical storage tank, and the temperature is increased to 50-80℃ to make the CO2 in a supercritical state, with the CO2 gas volume accounting for 95%.

[0012] As a preferred embodiment, in step S4, the bottom material is absorbed by process water and then recycled to the washing absorption section. The insoluble gas generated by the process water absorption enters the tail gas absorption section and is neutralized by calcium hydroxide solution. The generated calcium sulfate dihydrate is washed with wet water and then reused.

[0013] As a preferred embodiment, in step S5, the amount of calcium hydroxide solution added is 45-55% of the mass of potassium sulfate in the filtrate, and the amount of carbon dioxide gas added is 3-6% of the mass of potassium hydroxide; the mass concentration of the calcium hydroxide solution is 30-35%; the reaction time is 30-60 min, the reaction temperature is 50-70℃, and after the reaction is completed, the mixture is transferred to concentration and crystallization at a crystallization temperature of 5-10℃. Attached Figure Description

[0014] Figure 1 This is a process flow diagram of one specific embodiment of the present invention. Detailed Implementation

[0015] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased.

[0016] Unless otherwise stated, all percentages in this invention represent mass fractions. Ratios are mass percentages, and concentrations are mass concentrations.

[0017] Unless otherwise specified, all materials, instruments, and equipment used below are conventional materials, instruments, and equipment or obtained through commercial channels; all testing methods used are existing methods unless otherwise specified.

[0018] Existing technologies suffer from problems such as the large amount of phosphogypsum byproducts and the ineffective utilization of silica gel. At the same time, the yield and purity of potassium fluoride are not high, making it difficult to ensure the quality of anhydrous hydrogen fluoride products, and the performance of silica is difficult to further improve.

[0019] Furthermore, this invention proposes a method for preparing hydrogen fluoride through the synergistic alkaline hydrolysis of fluorosilicic acid and multiple components, comprising the following steps: Step S1 Alkali hydrolysis reaction Fluorosilicic acid was subjected to an alkaline hydrolysis reaction with an alkaline hydrolysis agent (reaction I), and the CO2 gas generated by the reaction was collected. After the reaction was completed, hydrofluoric acid was added for back conditioning. The solution after the reaction was subjected to solid-liquid separation to obtain potassium fluoride solution and solid filter cake silica gel. Step S2: Preparation of silica The solid filter cake silica gel is washed with water, filtered, and dried with supercritical CO2 to obtain the precipitated silica product. Step S3: Preparation of calcium fluoride Heat the potassium fluoride solution in step S1, add calcium sulfate and calcium hydroxide, stir to react (reaction II), filter and wash to obtain solid calcium fluoride and potassium sulfate solution; Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Calcium fluoride solid is dried by supercritical CO2 to prepare a solution, and concentrated sulfuric acid is slowly added dropwise while the temperature is increased and the mixture is stirred to react (reaction III) to obtain calcium sulfate dihydrate wet base and fluorine-containing gas; the fluorine-containing gas is washed and absorbed under countercurrent atmospheric pressure, the absorbed gas is condensed, and the condensate is distilled to obtain anhydrous hydrogen fluoride and bottom product. Step S5: Regeneration and compounding of the alkaline hydrolysate In step S3, a saturated calcium hydroxide solution is added to the potassium sulfate solution, and the mixture is stirred to react (reaction IV) to generate a potassium hydroxide solution and a calcium sulfate precipitate. Once the reaction reaches its endpoint, the mixture is filtered at room temperature to obtain a calcium sulfate filter cake and a potassium hydroxide solution. The calcium sulfate filter cake is dried and then reused in step S3. Subsequently, the CO2 gas collected in step S1 is introduced into the potassium hydroxide solution. After the reaction (reaction V) is completed, the solution is transferred to a concentration and crystallization process. The solid obtained after centrifugation can be used as an alkaline hydrolysis agent.

[0020] The core of this invention lies in the efficient conversion of industrial byproduct fluorosilicic acid into high-purity anhydrous hydrogen fluoride through four consecutive reaction steps: (1) Potassium fluoride is produced by reacting potassium hydroxide or potassium carbonate with fluorosilicic acid; (2) Potassium fluoride reacts with calcium sulfate or calcium hydroxide to synthesize calcium fluoride; (3) Anhydrous hydrogen fluoride is prepared by reacting calcium fluoride with concentrated sulfuric acid; (4) The intermediate product potassium sulfate reacts sequentially with calcium hydroxide and carbon dioxide to complete the compound regeneration of the alkaline hydrolysate.

[0021] The reaction principle of this invention includes: H₂SiF₆ + 2KOH → K₂SiF₆ + 2H₂O (1) K2SiF6+4KOH→6KF+SiO2⬇+2H2O (2) K2SiF6+2K2CO3→6KF+SiO2⬇+2CO2 ⬆ (3) 2KF + CaSO4 → CaF2 + K2SO4 (4) CaF2 + H2SO4 → 2HF⬆ + CaSO4 (5) K₂SO₄ + Ca(OH)₂ → 2KOH + CaSO₄⬇ (6) 2KOH + CO2 → K2CO3 + H2O (7) It is evident that the gypsum and potassium sulfate intermediate produced by the reaction are fully utilized, and the alkaline hydrolysate can be recycled through the reaction, realizing multi-component synergistic alkaline hydrolysis and high-value conversion, as well as the endogenous cycle of potassium and calcium resources.

[0022] In this embodiment of the invention, fluorosilicic acid is first converted into potassium fluoride solution through alkaline hydrolysis of multiple components, and then reacted with calcium sulfate and calcium hydroxide to generate fluorite. Fluorite reacts with sulfuric acid in the liquid phase to generate hydrogen fluoride gas, achieving complete recycling of calcium sulfate. Hydrogen fluoride is then washed, condensed, and distilled to produce anhydrous hydrogen fluoride. By introducing supercritical CO2 drying technology, high specific surface area white carbon black can be produced simultaneously, avoiding agglomeration and simplifying the process. The alkaline hydrolysis agent can be recycled and reused, with no by-products discharged.

[0023] This invention combines the technology of producing potassium fluoride from fluorosilicic acid with the purification process of producing anhydrous hydrogen fluoride from fluorite. By using alkaline reagents to promote the release of fluorine, it achieves multi-component synergistic alkaline hydrolysis and high-value conversion, reducing the difficulty of industrialization and showing promising prospects for industrial application. At the same time, it recycles the by-product phosphogypsum, further improving resource utilization and expanding the application scenarios for phosphogypsum recycling. The by-product silica gel is converted into high-quality silica with a specific surface area greater than 200 and an average particle size of less than 30nm. The raw material potassium is recycled through alkaline hydrolysis agent, achieving efficient and high-value utilization of resources.

[0024] In one embodiment, in step S1, the alkaline hydrolysant is a mixture of potassium hydroxide liquid and potassium carbonate solid powder, with a pure molar ratio of potassium hydroxide to potassium carbonate of 9-9.5:0.5-1; the amount of alkaline hydrolysant added is 140-160g.

[0025] The compound alkaline hydrolysate is slowly added to the fluorosilicic acid solution and stirred at room temperature for 1-2 hours to produce a colorless, viscous potassium fluorosilicate paste. Then, the temperature is raised to 78-85°C in a water bath and stirred for 1-2 hours until the solution turns milky white. The carbon dioxide gas produced during the reaction is collected. After the reaction is completed, the pH is adjusted to 7.0-7.2 with acid.

[0026] Fluorosilicic acid can be directly converted into potassium fluorosilicate by reacting with a compound alkaline hydrolysant. The reaction progress is controllable, the reaction conditions are mild, and no impurities are generated during the reaction. This avoids the loss of potassium source during the washing of potassium fluorosilicate and greatly improves the yield of potassium fluoride in the reaction process.

[0027] Using potassium carbonate and potassium hydroxide as a compound alkaline hydrolysis agent can effectively control the pH value of the reaction system to maintain relative stability and promote the forward reaction. During the alkaline hydrolysis process, the potassium carbonate generates carbon dioxide after the alkaline hydrolysis reaction. The gas overflow will create microscopic channels in the reaction system, which not only helps to disturb the reaction system and accelerate the reaction between potassium fluorosilicate and the compound alkaline hydrolysis agent, thus increasing the yield of potassium fluoride, but also allows the recovery of this part of the carbon dioxide for the regeneration and preparation of the alkaline hydrolysis agent. Furthermore, a very small amount of hydrofluoric acid is used to adjust the pH value of the system, avoiding the introduction of impurity ions, improving the purity of potassium fluoride, and ensuring the quality of anhydrous hydrogen fluoride products.

[0028] In one embodiment, in step S1, the mass percentage concentration of the fluorosilicic acid liquid is 10-16%, and the content of free acid impurities is 0.15-0.25%. This ensures complete reaction of the fluorosilicic acid and that the generated carbon dioxide gas is recycled for the compound regeneration of the alkaline hydrolysate. Using this process, the expected result of complete reaction is achieved, with the fluorosilicic acid reaction volume in the reactor reaching 98%.

[0029] In one implementation method, the supercritical CO2 drying process conditions in step S2 are as follows: gas flow rate controlled at 1-9 L / min, pressure rise in the supercritical CO2 reactor at 8-10 MPa, CO2 gas volume ratio at 95%, drying temperature at 50-80℃, and drying time at 10-30 min. This allows for low-temperature drying of silica, avoiding agglomeration and simplifying the subsequent crushing process. After adopting these process parameters, the specific surface area and crystal structure of silica are significantly improved.

[0030] Combining supercritical CO2 drying technology with product drying can effectively improve the specific surface area, purity and crystal form of silica, while avoiding agglomeration during the drying process and reducing subsequent crushing processes, which helps to produce silica products with high added value and good microscopic properties.

[0031] In one embodiment, in step S3, the temperature is raised to 80-87°C, and calcium sulfate and calcium hydroxide are added slowly in sequence according to a molar ratio of 8-9.5:0.5-2. The mixture is stirred and reacted for 2.5-3 hours. The total amount of calcium sulfate and calcium hydroxide added is 150-200g, which can control the reaction progress and avoid the reaction rate from being too fast.

[0032] In one embodiment, in step S4, the amount of concentrated sulfuric acid added is 1.35 to 1.38 times the mass of the calcium fluoride solid, and the mixture is heated to 82 to 85°C and stirred for 2 to 2.5 hours; the mass percentage concentration of the calcium fluoride solution prepared by adding water is 30 to 35%. The supercritical carbon dioxide drying conditions are as follows: the CO2 gas flow rate is controlled at 1-9 L / min, and the pressure is first increased to 8-10 MPa and the temperature is increased to 50-80℃ in the supercritical storage tank to make the CO2 in a supercritical state, with the CO2 gas volume accounting for 95%. The calcium fluoride obtained by supercritical CO2 drying can avoid agglomeration and form a loose porous structure, which can effectively promote the subsequent reaction rate with sulfuric acid, and increase the yield of hydrogen fluoride gas by 5% compared with the ordinary drying process.

[0033] In one implementation method, in step S4, the bottom material is absorbed by process water and then recycled to the washing absorption section. The insoluble gas generated during process water absorption is neutralized with calcium hydroxide solution in the tail gas absorption section. The resulting calcium sulfate dihydrate is washed with wet-based water and then reused. The bottom material includes sulfuric acid and a small amount of gas, which is recycled to the washing absorption section to avoid resource waste.

[0034] Washing and absorption can be carried out through a concentrated sulfuric acid washing tower. The gas at the top of the washing tower enters a shell-and-tube condenser and is condensed using chilled brine. The condensate is then distilled using a high-efficiency packed tower according to conventional processes. Anhydrous hydrogen fluoride is obtained at the top of the high-efficiency packed tower, and the bottom material is absorbed by process water and then recycled to the concentrated sulfuric acid washing tower.

[0035] In one embodiment, in step S5, the amount of calcium hydroxide solution added is 45-55% of the mass of potassium sulfate in the filtrate, and the amount of carbon dioxide gas added is 3-6% of the mass of potassium hydroxide; the mass concentration of the calcium hydroxide solution is 30-35%; the reaction time is 30-60 minutes, the reaction temperature is 50-70°C, and after the reaction is completed, it is transferred to concentration and crystallization at a temperature of 5-10°C. This allows the alkaline hydrolysate to be regenerated and compounded, and is concentrated through crystallization, ensuring that no excessive water is carried in during the reuse process, and preventing the white carbon black generated by the alkaline hydrolysis reaction from hydrolyzing into silica gel.

[0036] In the preparation process of this invention, potassium fluoride reacts with calcium sulfate to produce calcium fluoride and potassium sulfate. No solid gypsum is discharged during this process, and calcium sulfate is a reaction product in the third step. The generated carbon dioxide gas is also recycled to reduce carbon emissions. Potassium sulfate participates in the endogenous cycle of the alkaline hydrolysate throughout the process, completing resource recycling and significantly reducing production costs.

[0037] During the research and development process, we encountered the following technical difficulties: (1) Adjusting the composition ratio of the compound alkaline hydrolysing agent to make the alkaline hydrolysis reaction environment mild and controllable; (2) Streamlining the process flow and simultaneously completing the regeneration and compounding of the alkaline hydrolysing agent; (3) Conventional drying process easily leads to uneven heating of materials, high temperature damages the silica gel crystal form and reduces the quality of silica gel; (4) The process easily produces by-product calcium sulfate, causing resource waste; (5) Using fluorosilicone yield and product quality as indicators, determine the optimal process conditions such as the ratio of calcium hydroxide and calcium sulfate and the amount of concentrated sulfuric acid added during the reaction process.

[0038] Furthermore, we determined the optimal ratio of potassium hydroxide and potassium carbonate in the alkaline hydrolysis agent formulation through experiments; we recovered the carbon dioxide gas generated during the alkaline hydrolysis process, and completed the regeneration and compounding of the alkaline hydrolysis agent by controlling the amount added, while ensuring no greenhouse gas emissions; we introduced supercritical carbon dioxide drying, which can achieve low-temperature, rapid and uniform drying, effectively improving the quality of silica; we reused calcium sulfate, completing resource recycling and process closed loop, with no by-product emissions from the entire process; and we determined the ratio of calcium hydroxide and calcium sulfate and the amount of concentrated sulfuric acid added through experiments to ensure that the fluorine recovery rate is ≥95% and the silicon recovery rate is ≥99%.

[0039] To further illustrate the present invention, the following describes in detail, with reference to embodiments, a method for preparing hydrogen fluoride from multiple components by synergistic alkaline hydrolysis of fluorosilicic acid. Example 1

[0040] The method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid in this embodiment includes the following steps: Step S1 Alkali hydrolysis reaction Take 500g of fluorosilicic acid in a beaker. The mass percentage concentration of the fluorosilicic acid liquid is 15%, and the content of free acid impurities is 0.2%.

[0041] 154g of a compound alkaline hydrolysis agent (potassium hydroxide solid: potassium carbonate solid = 9:1, based on the molar ratio of pure substances) was added under stirring at room temperature, and the reaction was carried out for 60 min. The temperature was then raised to 78℃ in a water bath and the reaction was carried out for 120 min. During the reaction, the gas G (carbon dioxide gas) produced was collected. After 2 h of reaction, the pH was adjusted to a stable 7.0 with an appropriate amount of hydrofluoric acid, and solid-liquid separation was performed to obtain filtrate A (potassium fluoride solution) and filter cake B (silica). Filtrate A was transferred to step S3 for processing, and filter cake B was transferred to step S2 for processing.

[0042] Step S2: Preparation of silica Filter cake B was pulped and washed, then filtered using vacuum filtration at a pressure of 0.7 MPa for 30 minutes. Subsequently, supercritical CO2 gas was introduced for drying at a flow rate of 1 L / min. The pressure inside the supercritical CO2 reactor was increased to 8 MPa, the temperature was 50°C, the CO2 gas volume percentage was 95%, and the drying time was 30 minutes, yielding high-purity silica.

[0043] Step S3: Preparation of calcium fluoride Filtrate A was heated to 80°C, and calcium sulfate and calcium hydroxide were slowly added sequentially according to the theoretical molar ratio of 8:2. The mixture was stirred and reacted for 2 hours (reaction II). The amount of calcium sulfate added was 126g, and the amount of calcium hydroxide added was 31g. After filtration and washing, filtrate C (potassium sulfate solution) and filter cake D (calcium fluoride solid) were obtained. Filter cake D was transferred to step S4, and filtrate C was transferred to step S5.

[0044] Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Filter cake D is dried by supercritical CO2 drying. The gas flow rate is controlled at 1L / min, the pressure inside the supercritical CO2 reactor is increased to 8MPa, the temperature is 50℃, the volume ratio of CO2 gas is 95%, and the drying time is 30min.

[0045] After drying, calcium fluoride was prepared into a 30% solution, and 98% concentrated sulfuric acid was slowly added dropwise at a rate of 1.35 times the mass of the calcium fluoride solid. The mixture was heated to 82°C and stirred for 2 hours (reaction III). Solid E (wet calcium sulfate dihydrate) and gas F (fluorine-containing gas) were obtained.

[0046] Gas F is absorbed by countercurrent atmospheric pressure washing using 98% concentrated sulfuric acid in a concentrated sulfuric acid washing tower. The gas from the top of the concentrated sulfuric acid washing tower enters a shell-and-tube condenser and is condensed using chilled brine at a temperature of 4°C. The condensate is then distilled using a high-efficiency packed column as per conventional methods. In the high-efficiency packed column, anhydrous hydrogen fluoride is obtained at the top and bottom product is obtained at the bottom.

[0047] The bottom material is absorbed by process water and then recycled to the concentrated sulfuric acid scrubbing tower. Insoluble gases enter the tail gas absorption section and are neutralized by a 30% calcium hydroxide solution. Solid E (wet-based calcium sulfate dihydrate) is washed with process water and then reused in step S3.

[0048] Here, the process water is mainly the production recycling water, and the bottom material of the tower is mainly sulfuric acid waste gas and water vapor, which are absorbed by a small amount of process water to obtain concentrated sulfuric acid.

[0049] Step S5: Regeneration and compounding of the alkaline hydrolysate Add a 30% saturated calcium hydroxide solution (reaction IV) to the filtrate C obtained in step S3. The amount added is 45% of the mass of potassium sulfate in the filtrate. Control the pH at the end of the reaction to be 11. After the reaction is complete, filter at room temperature to obtain filter cake E (calcium sulfate) and filtrate H (potassium hydroxide solution). Filter cake E (calcium sulfate) can be dried and used for calcium sulfate in reaction II.

[0050] The gas G collected in step S1 (reaction V) is introduced into the filtrate H. 3% of the mass of potassium hydroxide is added, the reaction time is 30 min, the reaction temperature is 50℃, and after the reaction is completed, it is transferred to concentration and crystallization at 10℃. The solid obtained after centrifugation can be used to prepare compound alkaline hydrolysate. Example 2

[0051] The method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid in this embodiment includes the following steps: Step S1 Alkali hydrolysis reaction Take 500g of fluorosilicic acid in a beaker. The mass percentage concentration of the fluorosilicic acid liquid is 15%, and the content of free acid impurities is 0.2%.

[0052] 154g of a compound alkaline hydrolysis agent (potassium hydroxide solid: potassium carbonate solid = 9.3:0.7, based on the molar ratio of pure substances) was added under stirring at room temperature, and the reaction was carried out at room temperature for 120min. The temperature was then raised to 85℃ in a water bath and the reaction was carried out for 120min. During the reaction, the gas G (carbon dioxide gas) produced was collected. After 3h of reaction, the pH was adjusted to a stable 7.2 with an appropriate amount of hydrofluoric acid, and solid-liquid separation was performed to obtain filtrate A (potassium fluoride solution) and filter cake B (silica). Filtrate A was transferred to step S3 for processing, and filter cake B was transferred to step S2 for processing.

[0053] Step S2: Preparation of silica Filter cake B was pulped and washed, then filtered using vacuum filtration at a pressure of 0.7 MPa for 30 minutes. Subsequently, supercritical CO2 gas was introduced for drying at a flow rate of 5 L / min. The pressure inside the supercritical CO2 reactor was increased to 9 MPa, the temperature was 65℃, the CO2 gas volume percentage was 95%, and the drying time was 15 minutes, yielding high-purity silica.

[0054] Step S3: Preparation of calcium fluoride Filtrate A is heated to 85℃, and calcium sulfate and calcium hydroxide are slowly added in sequence according to the theoretical molar ratio of 9:1. The amount of calcium sulfate added is 153g and the amount of calcium hydroxide added is 17g.

[0055] The reaction was stirred for 2.5 hours. After filtration and washing, filtrate C (potassium sulfate solution) and filter cake D (calcium fluoride solid) were obtained. Filter cake D was transferred to step S4, and filtrate C was transferred to step S5.

[0056] Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Filter cake D is dried by supercritical CO2 drying. The gas flow rate is controlled at 5 L / min, the pressure inside the supercritical CO2 reactor is increased to 9 MPa, the temperature is 65℃, the volume of CO2 gas is 95%, and the drying time is 15 min.

[0057] After drying, calcium fluoride was prepared into a 30% solution, and 98% concentrated sulfuric acid was slowly added dropwise at a rate of 1.36 times the mass of the solid calcium fluoride. The mixture was heated to 85°C and stirred for 2.5 hours. Solid E (wet calcium sulfate dihydrate) and gas F (fluorine-containing gas) were obtained.

[0058] Gas F is absorbed by countercurrent atmospheric pressure washing using 98% concentrated sulfuric acid in a concentrated sulfuric acid washing tower. The gas from the top of the concentrated sulfuric acid washing tower enters a shell-and-tube condenser and is condensed using chilled brine at a temperature of 4°C. The condensate is then distilled using a high-efficiency packed column as per conventional methods. In the high-efficiency packed column, anhydrous hydrogen fluoride is obtained at the top and bottom product is obtained at the bottom.

[0059] The bottom material is absorbed by process water and then recycled to the concentrated sulfuric acid scrubbing tower. Insoluble gases enter the tail gas absorption section and are neutralized by a 30% calcium hydroxide solution. Solid E (wet-based calcium sulfate dihydrate) is washed with process water and then reused in step S3.

[0060] Step S5: Regeneration and compounding of the alkaline hydrolysate Add a saturated calcium hydroxide solution with a concentration of about 30% to the filtrate C obtained in step S3. The amount added is 50% of the mass of potassium sulfate in the filtrate. Control the pH at the end of the reaction to be 12. After the reaction is completed, filter at room temperature to obtain filter cake E (calcium sulfate) and filtrate H (potassium hydroxide solution).

[0061] The gas G collected in step S1 is introduced into the filtrate H, and 4.5% of the mass of potassium hydroxide is added. The reaction time is 45 min and the reaction temperature is 60℃. After the reaction is completed, the mixture is transferred to concentration and crystallization at 8℃. The solid obtained after centrifugation can be used to prepare compound alkaline hydrolysate. Example 3

[0062] The method for preparing hydrogen fluoride by synergistic alkaline hydrolysis of fluorosilicic acid in this embodiment includes the following steps: Step S1 Alkali hydrolysis reaction Take 500g of fluorosilicic acid in a beaker. The mass percentage concentration of the fluorosilicic acid liquid is 15%, and the content of free acid impurities is 0.2%.

[0063] 154g of a compound alkaline hydrolysis agent (potassium hydroxide solid: potassium carbonate solid = 9.5:0.5, based on the molar ratio of pure substances) was added under stirring at room temperature. After stirring at room temperature for 1 hour, a colorless, viscous potassium fluorosilicate paste was formed. The mixture was then heated to 85℃ in a water bath and reacted for 120 minutes. During the reaction, the gas G (carbon dioxide gas) produced was collected. After 3 hours of reaction, the pH was adjusted to a stable 7.2 with an appropriate amount of hydrofluoric acid. Solid-liquid separation was then performed to obtain filtrate A (potassium fluoride solution) and filter cake B (silica). Filtrate A was transferred to step S3 for further processing, and filter cake B was transferred to step S2 for further processing.

[0064] Step S2: Preparation of silica Filter cake B was pulped and washed, then filtered using vacuum filtration at a pressure of 0.7 MPa for 30 minutes. Subsequently, supercritical CO2 gas was introduced for drying at a flow rate of 9 L / min. The pressure inside the supercritical CO2 reactor was increased to 10 MPa, the temperature was 80℃, the CO2 gas volume percentage was 95%, and the drying time was 10 minutes, yielding high-purity silica.

[0065] Step S3: Preparation of calcium fluoride Filtrate A was heated to 87°C, and calcium sulfate and calcium hydroxide were slowly added sequentially according to the theoretical molar ratio of 9.5:0.5. The amount of calcium sulfate added was 168g, and the amount of calcium hydroxide added was 9g.

[0066] The reaction was stirred for 2.5 hours. After filtration and washing, filtrate C (potassium sulfate solution) and filter cake D (calcium fluoride solid) were obtained. Filter cake D was transferred to step S4, and filtrate C was transferred to step S5.

[0067] Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Filter cake D is dried by supercritical CO2 drying. The gas flow rate is controlled at 9 L / min, the pressure inside the supercritical CO2 reactor is increased to 10 MPa, the temperature is 80℃, the volume ratio of CO2 gas is 95%, and the drying time is 10 min.

[0068] After drying, calcium fluoride was prepared into a 35% solution, and 98% concentrated sulfuric acid was slowly added dropwise at a rate of 1.38 times the mass of the solid calcium fluoride. The mixture was heated to 85°C and stirred for 2.5 hours. This yielded solid E (wet-based calcium sulfate dihydrate) and gas F (fluorine-containing gas). Gas F was absorbed by countercurrent atmospheric pressure washing with 98% concentrated sulfuric acid in a concentrated sulfuric acid washing tower. The gas from the top of the washing tower entered a shell-and-tube condenser and was condensed using chilled brine at 4°C. The condensate was then distilled using a high-efficiency packed column according to conventional methods. In the high-efficiency packed column, anhydrous hydrogen fluoride was obtained at the top, and the bottom product was obtained at the bottom.

[0069] The bottom material is absorbed by process water and then recycled to the concentrated sulfuric acid scrubbing tower. Insoluble gases enter the tail gas absorption section and are neutralized by a 30% calcium hydroxide solution. Solid E (wet-based calcium sulfate dihydrate) is washed with process water and then reused in step S3.

[0070] Step S5: Regeneration and compounding of the alkaline hydrolysate Add a saturated calcium hydroxide solution with a concentration of about 30% to the filtrate C obtained in step S3. The amount added is 55% of the mass of potassium sulfate in the filtrate. Control the pH at the end of the reaction to be 12. After the reaction is completed, filter at room temperature to obtain filter cake E (calcium sulfate) and filtrate H (potassium hydroxide solution).

[0071] The gas G collected in step S1 is introduced into the filtrate H, and 6% of the mass of potassium hydroxide is added. The reaction time is 60 min and the reaction temperature is 70℃. After the reaction is completed, the mixture is transferred to concentration and crystallization at 5℃. The solid obtained after centrifugation can be used to prepare compound alkaline hydrolysate.

[0072] Comparative Example 1 (Conventional Drying Comparative Example) The difference from Example 2 is that: Step S2: Preparation of silica Filter cake B was pulped and washed, then filtered using vacuum filtration at a pressure of 0.7 MPa for 30 minutes. It was then sent to an oven for drying at a temperature of 110°C for 30 minutes. Finally, it was crushed and passed through a 200-mesh sieve to obtain silica.

[0073] Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling The filter cake D was then sent to an oven for drying at 110°C for 30 minutes. After drying, it was crushed and passed through a 200-mesh sieve to obtain calcium fluoride powder.

[0074] Comparative Example 2 (Comparative Example under Abnormal Operating Conditions) The difference from Example 2 is that: Step S1 Alkali hydrolysis reaction After reacting for 2 hours, the pH was adjusted to a stable 8.0 with an appropriate amount of hydrofluoric acid.

[0075] Step S5: Regeneration and compounding of the alkaline hydrolysate The gas G collected in step S1 is introduced into the filtrate H, and 7% of the mass of potassium hydroxide is added.

[0076] Comparative Example 3 (Comparison of Single Alkali Hydrolysate) The difference from Example 2 is that: Step S1 Alkali hydrolysis reaction Add 154g of potassium hydroxide unit alkaline hydrolysate under stirring at room temperature.

[0077] Step S5: Regeneration of the alkaline hydrolysate Without adding gas G to the filtrate H, directly transfer it to the concentration and crystallization process at a temperature of 10℃. The solid obtained after centrifugation is the unit alkaline hydrolysate.

[0078] The purity of anhydrous hydrogen fluoride and potassium fluoride, as well as the particle size of high-activity silica, were determined according to HG / T 3061-2021 "Precipitated Hydrated Silica in Rubber Compounding Agents" and GB 7746-2011 "Industrial Anhydrous Hydrogen Fluoride". The results are shown in Table 1.

[0079] Table 1. Particle size distribution of anhydrous hydrogen fluoride, fluoride salts, and highly reactive silica in the examples and comparative examples. As shown in Tables 1-3, the anhydrous hydrogen fluoride prepared within the specified process parameters all meet the Class II Grade 1 requirements of the national standard for industrial anhydrous hydrogen fluoride (GB7746-2011). In addition, the purity of the by-product silica exceeds 95%, which also meets the high activity requirements and conforms to the standard for precipitated hydrated silica in rubber compounding agents (HG / T 3061-2021).

[0080] As shown in Comparative Example 1 in Table 1, the supercritical CO2 drying process, being a low-temperature gas-phase drying method, can preserve the microscopic properties of the material. Therefore, compared to the conventional direct heating drying process, the supercritical CO2 drying process improves the specific surface area, bulk density, and particle size of the silica. Furthermore, it is less prone to agglomeration during the drying process, eliminating the need for subsequent crushing steps. As shown in Comparative Examples 2 and 3 in Table 1, deviations from the process parameter range and the use of a single alkaline hydrolysate can easily lead to incomplete reactions, resulting in a decline in product quality.

[0081] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-disclosed technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing hydrogen fluoride from multiple components through synergistic alkaline hydrolysis of fluorosilicic acid, characterized in that: Includes the following steps: Step S1 Alkali hydrolysis reaction Fluorosilicic acid was subjected to an alkaline hydrolysis reaction with an alkaline hydrolysis agent, and the CO2 gas generated was collected. After the reaction was completed, hydrofluoric acid was added for back-conditioning. The solution after the reaction was subjected to solid-liquid separation to obtain potassium fluoride solution and solid filter cake silica gel. Step S2: Preparation of silica The solid filter cake silica gel is washed with water, filtered, and dried with supercritical CO2 to obtain the precipitated silica product. Step S3: Preparation of calcium fluoride The potassium fluoride solution in step S1 is heated, calcium sulfate and calcium hydroxide are added, the reaction is stirred, filtered and washed to obtain solid calcium fluoride and potassium sulfate solution. Step S4: Anhydrous Hydrogen Fluoride Recovery and Recycling Calcium fluoride solid is dried with CO2 supercritically, prepared into a solution, and concentrated sulfuric acid is slowly added dropwise. The mixture is heated and stirred to produce calcium sulfate dihydrate wet base and fluorine-containing gas. The fluorine-containing gas is then washed and absorbed under countercurrent atmospheric pressure. The absorbed gas is condensed, and the condensate is distilled to obtain anhydrous hydrogen fluoride and bottom product. Step S5: Regeneration and compounding of the alkaline hydrolysate In step S3, a saturated calcium hydroxide solution is added to the potassium sulfate solution, and the mixture is stirred to produce a potassium hydroxide solution and a calcium sulfate precipitate. Once the reaction reaches its endpoint, the mixture is filtered at room temperature to obtain a calcium sulfate filter cake and a potassium hydroxide solution. The calcium sulfate filter cake is dried and then reused in step S3. Subsequently, the CO2 gas collected in step S1 is introduced into the potassium hydroxide solution. After the reaction is completed, the solution is transferred to concentration and crystallization. The solid obtained after centrifugation can be used as an alkaline hydrolysis agent.

2. The method according to claim 1, characterized in that, In step S1, the alkaline hydrolysant is a solid mixture of potassium hydroxide and potassium carbonate, wherein the molar ratio of pure potassium hydroxide to potassium carbonate is 9-9.5:0.5-1; and the amount of alkaline hydrolysant added is 140-160g. The alkaline hydrolysate is slowly added to the fluorosilicic acid solution and stirred at room temperature for 1-2 hours to produce a colorless, viscous potassium fluorosilicate paste. Then, the temperature is raised to 78-85°C in a water bath and stirred for 1-2 hours until the solution turns milky white. The carbon dioxide gas produced during the reaction is collected, and the pH is adjusted to 7.0-7.2 with acid after the reaction is completed.

3. The method according to claim 2, characterized in that, In step S1, the mass percentage concentration of the fluorosilicic acid liquid is 10-16%, and the content of free acid impurities is 0.15-0.25%.

4. The method according to claim 1, characterized in that, In step S2, the supercritical CO2 drying process conditions are as follows: gas flow rate is controlled at 1-9 L / min, pressure rise in the supercritical CO2 reactor is 8-10 MPa, CO2 gas volume percentage is 95%, drying temperature is 50-80℃, and drying time is 10-30 min.

5. The method according to claim 1, characterized in that, In step S3, the temperature is raised to 80-87℃, and calcium sulfate and calcium hydroxide are added slowly in sequence according to a molar ratio of 8-9.5:0.5-2, and the mixture is stirred and reacted for 2-3 hours; the total amount of calcium sulfate and calcium hydroxide added is 150-200g.

6. The method according to claim 1, characterized in that, In step S4, the amount of concentrated sulfuric acid added is 1.35 to 1.38 times the mass of the calcium fluoride solid, and the mixture is heated to 82 to 85°C and stirred for 2 to 2.5 hours; the mass percentage concentration of the calcium fluoride solution prepared by adding water is 30 to 35%. The supercritical carbon dioxide drying conditions are as follows: the CO2 gas flow rate is controlled at 1-9 L / min, the pressure is first increased to 8-10 MPa in the critical storage tank, and the temperature is increased to 50-80℃ to make the CO2 in a supercritical state, with the CO2 gas volume accounting for 95%.

7. The method according to claim 1, characterized in that, In step S4, the bottom material is absorbed by process water and then recycled to the washing absorption. The insoluble gas generated by the process water absorption enters the tail gas absorption section and is neutralized by calcium hydroxide solution. The generated calcium sulfate dihydrate is washed with wet water and then reused.

8. The method according to claim 1, characterized in that, In step S5, the amount of calcium hydroxide solution added is 45-55% of the mass of potassium sulfate in the filtrate, and the amount of carbon dioxide gas added is 3-6% of the mass of potassium hydroxide; the mass concentration of the calcium hydroxide solution is 30-35%; the reaction time is 30-60 min, the reaction temperature is 50-70℃, and after the reaction is completed, it is transferred to concentration and crystallization, and the crystallization temperature is 5-10℃.

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