A method for preparing anhydrous hydrogen fluoride using low-grade fluorite

Abstract

This invention discloses a method for preparing anhydrous hydrogen fluoride using low-grade fluorite, comprising the following steps: feeding low-grade fluorite material into a reaction kiln and heating it with concentrated sulfuric acid; extracting the high-temperature mixed gas generated from the reaction from the reaction kiln; controlling the temperature of the purification and washing zone so that the hydrogen fluoride in the mixed gas mainly escapes upward in gaseous form, while simultaneously causing the water vapor in the mixed gas to condense and initiate the hydrolysis reaction of silicon tetrafluoride. This invention features a novel design, utilizing a specific thermodynamic temperature-controlled desiliconization back-end purification system, effectively preventing the potential for silica gel blockage caused by silicon tetrafluoride hydrolysis, improving product purity, and ensuring the stability and long-term operation capability of the process system, resulting in excellent economic benefits.

Description

Technical Field

[0001] This invention relates to the field of hydrogen fluoride preparation technology, and in particular to a method for preparing anhydrous hydrogen fluoride using low-grade fluorite. Background Technology

[0002] Anhydrous hydrogen fluoride (HF), a core raw material in the modern fluorochemical industry, is traditionally produced by reacting high-grade fluorite (with a calcium fluoride content typically above 97%) with concentrated sulfuric acid or fuming sulfuric acid. However, fluorite is a non-renewable resource, and long-term over-exploitation has led to the depletion of high-quality fluorite ore resources, resulting in increasingly stringent national restrictions on its mining and approval processes. With high-grade fluorite resources becoming increasingly scarce and raw material procurement prices remaining high, how to fully utilize the fluorite-associated mineral resources widely found in the tailings of other mineral deposits has become a pressing resource and cost challenge for the entire anhydrous hydrogen fluoride industry.

[0003] In actual mineral processing, fluorite raw materials extracted from other associated minerals are generally low-grade fluorite. These raw materials have natural defects: the main component, calcium fluoride, has a low grade (usually only reaching about 80%), and the remaining components are mainly associated impurities such as carbonates and silicates.

[0004] Existing anhydrous hydrogen fluoride production processes suffer from the following serious drawbacks when processing low-grade fluorite: Silicon tetrafluoride (SiF4), generated from the reaction of silicate impurities in the ore, readily hydrolyzes during the conventional condensation and collection stage, producing large amounts of viscous silica gel. This rapidly clogs the washing and refining pipelines, rendering the production system completely unusable for long-term stable operation. These defects prevent low-grade fluorite from being used as an effective raw material in production for an extended period, resulting in significant resource waste. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies, such as the difficulty in removing silicon tetrafluoride and its tendency to clog pipelines, by proposing a method for preparing anhydrous hydrogen fluoride using low-grade fluorite.

[0006] To achieve the above objectives, the present invention adopts the following technical solution:

[0007] A method for preparing anhydrous hydrogen fluoride using low-grade fluorite includes the following steps:

[0008] S1. Low-grade fluorite material is fed into the reaction kiln and heated to react with concentrated sulfuric acid. Under negative pressure, the high-temperature mixed gas containing hydrogen fluoride, silicon tetrafluoride and water vapor generated by the reaction is extracted from the reaction kiln.

[0009] S2. Introduce the high-temperature mixed gas extracted in step S1 into the purification and washing zone, control the temperature of the purification and washing zone, so that the hydrogen fluoride in the mixed gas mainly escapes upward in the gas phase, while the water vapor in the mixed gas condenses and triggers the hydrolysis reaction of silicon tetrafluoride to generate a slurry containing solid acid.

[0010] S3. Discharge the solid acid slurry generated in step S2 from the bottom of the purification and washing zone, and draw out the desiliconized hydrogen fluoride gas from the top of the purification and washing zone. After condensation and refining, anhydrous hydrogen fluoride product is obtained.

[0011] Preferably, the low-grade fluorite contains 60% to 85% calcium fluoride by mass and contains one or more acid-consuming impurities, including calcium carbonate and magnesium carbonate, as well as siliceous impurities.

[0012] Preferably, in step S2, the operating temperature of the purification and washing zone is controlled to be 35℃~45℃ by combining the operating pressure in the purification and washing zone with the partial pressure of water vapor in the mixed gas, so as to ensure that the mixed gas reaches the dew point and undergoes condensation and hydrolysis reaction within this temperature range.

[0013] Preferably, in step S1, the temperature of the high-temperature mixed gas when it is extracted from the reaction kiln is 100℃~130℃; the negative pressure suction force maintains a gauge pressure of -0.5 kPa to -5 kPa at the gas phase outlet of the reaction kiln.

[0014] More preferably, the negative pressure suction is provided by a combination of two fans in series, an induced draft fan and a vacuum pump, an ejector, or a combination thereof.

[0015] Preferably, in steps S2 and S3, the solid acid slurry is a mixed slurry formed by hydrated silica, silica gel, or colloidal silica and fluorinated silica droplets.

[0016] Preferably, in step S3, when the solid acid-containing slurry is discharged from the bottom, it is kept in suspension by dynamic mechanical stirring, circulating pump reflux, or gas-liquid disturbance to prevent sedimentation and blockage.

[0017] Preferably, in step S3, the hydrogen fluoride gas undergoes a demisting process before condensation to remove fluorinated silica droplets and silica gel particles entrained in the gas.

[0018] The refining process includes one or more combinations of dehydration, distillation, and demisting.

[0019] Compared with the prior art, the beneficial effects of the present invention are:

[0020] 1. In this invention, by setting a specific thermodynamic temperature control range in the purification washing and desiliconization tower, and in combination with a filler-free anti-clogging internal structure, selective condensation of water vapor and violent hydrolysis of silicon tetrafluoride are achieved, while ensuring that hydrogen fluoride escapes in gaseous form. The variable desiliconization mechanism accurately intercepts silicon impurities, fundamentally eliminating the hidden danger of silica gel and condensed liquid hydrofluoric acid mixing and clogging the distillation pipeline.

[0021] 2. In this invention, by precisely controlling the specific temperature-controlled desilication, an extremely stable reaction environment is created for the purification tower, ensuring the purity of the hydrogen fluoride product while achieving long-term continuous and stable operation of the production system.

[0022] This invention features a novel design that utilizes a specific thermodynamic temperature-controlled desiliconization back-end purification system. This effectively prevents the potential blockage of silica gel caused by the hydrolysis of silicon tetrafluoride, improves product purity, and ensures the stability and long-term operation capability of the process system. It possesses outstanding industrial application value and excellent economic benefits. Detailed Implementation

[0023] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0024] System Equipment Description: The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to this invention relies on an improved anhydrous hydrogen fluoride production system. This system sequentially includes: a rotary kiln, a negative pressure exhaust fan unit (using dual fans in series), a purification and washing desilication tower (for removing silicon tetrafluoride from the mixed gas), a bottom slurry discharge system, and a top condensation and refining tower. The purification and washing desilication tower is externally equipped with a temperature-controlled water jacket and internally features anti-clogging gas-liquid contact components (such as large-channel baffles, flow-through plates, or swirl plates). The bottom is designed as an inverted cone and incorporates a low-speed dynamic anti-wall-clogging stirring scraper. The bottom outlet is connected to a slurry pump, and the top gas outlet is connected to the condensation and refining tower.

[0025] Example 1

[0026] This embodiment uses low-grade fluorite powder with a calcium fluoride content of approximately 80%, where the main impurities are calcium carbonate and silicon dioxide.

[0027] S1. Low-grade fluorite material is fed into a rotary kiln and heated to react with fuming sulfuric acid. A dual-fan series unit is activated to maintain a negative pressure of -2.0 kPa at the gas outlet of the kiln, forcibly extracting the high-temperature mixed gas (approximately 115°C) containing hydrogen fluoride, silicon tetrafluoride, and water vapor generated in the reaction. This high-pressure extraction not only effectively overcomes system resistance and prevents the leakage and pressure buildup of corrosive, high-temperature, and toxic gases, but also provides stable fluid dynamics for the gas-liquid countercurrent flow in the subsequent scrubbing tower.

[0028] S2. The extracted high-temperature mixed gas is introduced into the purification and washing desilication tower. The gas rises through the large-channel swirl plate layer within the tower. Based on the operating pressure and water vapor partial pressure within the tower, the temperature control jacket is adjusted to strictly control the operating temperature of the purification and washing zone to 40℃. Under these conditions, the mixed gas reaches its dew point, and the water vapor condenses into liquid droplets and violently hydrolyzes with silicon tetrafluoride, generating a solid-containing acidic slurry containing hydrated silica (silica gel) and fluorosilicic acid; simultaneously, hydrogen fluoride mainly escapes upwards in gaseous form. This step utilizes thermodynamic temperature control to achieve selective phase change separation, not only trapping impurities but also allowing the condensate reflux liquid within the tower to continuously flush the anti-clogging components, fundamentally delaying silica gel scaling.

[0029] S3. Turn on the bottom dynamic stirrer to continuously discharge the generated solid acid slurry from the bottom of the tower. The desiliconized hydrogen fluoride gas is drawn from the top of the tower, and after being intercepted by the demister to remove entrained droplets, it enters the condensation and purification system to obtain anhydrous hydrogen fluoride product with qualified purity.

[0030] Example 2

[0031] This embodiment is basically the same as Embodiment 1, except that:

[0032] In control step S1, the gas outlet is maintained at a negative pressure of -0.5 kPa, and the extraction temperature is 100℃; in control step S2, the operating temperature of the purification and washing zone is 35℃.

[0033] Example 3

[0034] This embodiment is basically the same as Embodiment 1, except that:

[0035] In control step S1, the gas phase outlet is maintained at a negative pressure of -5.0 kPa, and the extraction temperature is 130℃; in control step S2, the operating temperature of the purification and washing zone is 45℃.

[0036] Comparative Example 1

[0037] The steps of this comparative example are basically the same as those of Example 1, except that...

[0038] In step S2, the temperature of the purification and washing area is not controlled between 35°C and 45°C. Instead, conventional cryogenic spraying is used to keep the temperature below 20°C in an attempt to condense the hydrogen fluoride and water together.

[0039] To verify the synergistic beneficial effects of the combined process of the present invention, the key indicators of the above embodiments and comparative examples in experimental production were statistically analyzed, and the specific data are shown in Table 1.

[0040] Test benchmark description: All tests were conducted using low-grade fluorite from the same batch containing 80% calcium fluoride.

[0041] Table 1. Statistics of Key Indicators in Experimental Production

[0042] Example 1 28ppm ≥99.98% Example 2 45ppm 99.90% Example 3 38ppm 99.95% Comparative Example 1 The colloids are mixed and cannot be detected. Extraction failed, product scrapped.

[0043] The data from Comparative Example 1 and the Examples show that, using conventional cryogenic operation, the silica gel generated from the hydrolysis of silicon tetrafluoride and the large amount of condensed liquid hydrofluoric acid form an extremely viscous colloid, causing complete failure of gas-liquid separation and direct product scrapping. However, Example 1, by setting a specific temperature control range of 35℃ to 45℃ under negative pressure, achieved selective condensation and hydrolysis of water vapor and upward escape of hydrogen fluoride gas. Data from Examples 1 to 3 show that the silicon content of the crude gas before condensation was suppressed to below 45 ppm, which is crucial for achieving a final product purity of 99.90% to 99.98% (Grade 1, Chinese standard GB / T 7746-2023).

[0044] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing anhydrous hydrogen fluoride using low-grade fluorite, characterized in that, Includes the following steps: S1. Low-grade fluorite material is fed into the reaction kiln and heated to react with concentrated sulfuric acid. Under negative pressure, the high-temperature mixed gas containing hydrogen fluoride, silicon tetrafluoride and water vapor generated by the reaction is extracted from the reaction kiln. S2. Introduce the high-temperature mixed gas extracted in step S1 into the purification and washing zone, control the temperature of the purification and washing zone, so that the hydrogen fluoride in the mixed gas mainly escapes upward in the gas phase, while the water vapor in the mixed gas condenses and triggers the hydrolysis reaction of silicon tetrafluoride to generate a slurry containing solid acid. S3. Discharge the solid acid slurry generated in step S2 from the bottom of the purification and washing zone, and draw out the desiliconized hydrogen fluoride gas from the top of the purification and washing zone. After condensation and refining, anhydrous hydrogen fluoride product is obtained.

2. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, The low-grade fluorite contains 60% to 85% calcium fluoride by mass, and also contains one or more acid-consuming impurities, including calcium carbonate and magnesium carbonate, as well as siliceous impurities.

3. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, In step S2, the operating temperature of the purification and washing zone is controlled to be 35℃~45℃, based on the operating pressure in the purification and washing zone and the partial pressure of water vapor in the mixed gas, so as to ensure that the mixed gas reaches the dew point and undergoes condensation and hydrolysis reaction within this temperature range.

4. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, In step S1, the temperature of the high-temperature mixed gas when it is extracted from the reaction kiln is 100℃~130℃; the negative pressure suction force maintains a gauge pressure of -0.5 kPa to -5 kPa at the gas phase outlet of the reaction kiln.

5. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 4, characterized in that, The negative pressure suction is provided by a combination of two fans in series, an induced draft fan and a vacuum pump, an ejector, or a combination thereof.

6. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, In steps S2 and S3, the solid acid slurry is a mixed slurry formed by hydrated silica, silica gel or colloidal silica and fluorinated silica droplets.

7. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, In step S3, when the solid acid slurry is discharged from the bottom, it is kept in suspension by dynamic mechanical stirring, circulating pump reflux or gas-liquid disturbance to prevent sedimentation and blockage.

8. The method for preparing anhydrous hydrogen fluoride using low-grade fluorite according to claim 1, characterized in that, In step S3, the hydrogen fluoride gas undergoes a demisting process before condensation to remove fluorinated silica droplets and silica gel particles entrained in the gas. The refining process includes one or more combinations of dehydration, distillation, and demisting.