Method for synthesizing rhenium hexafluoride

Abstract

The invention relates to the technical field of fluorine chemical industry, in particular to a synthesis method of rhenium hexafluoride. The method comprises the following steps: S1, preheating fluorine-nitrogen mixed gas to 50-100 DEG C in a first temperature zone; s2, introducing the preheated fluorine-nitrogen mixed gas into a second temperature zone to react with rhenium metal to generate mixed gas containing rhenium hexafluoride, wherein the temperature of the second temperature zone is 120-180 DEG C; s3, mixed gas containing rhenium hexafluoride is introduced into a third temperature zone and continues to react with rhenium metal, and the temperature of the third temperature zone ranges from 300 DEG C to 450 DEG C; s4, introducing the gas obtained in the step S3 into a fourth temperature zone, and controlling the temperature of the fourth temperature zone to be 200-300 DEG C, and S5, carrying out low-temperature collection on the gas generated in the step S4 through a cold trap to obtain the high-purity rhenium hexafluoride. Through temperature control in multiple areas, the impurity content is reduced, and the product purity is improved.

Description

Technical Field

[0001] This application relates to the field of fluorochemical technology, specifically to a method for synthesizing rhenium hexafluoride. Background Technology

[0002] Rhenium (Re) is a rare metallic element in Group VIIB of the sixth period of the periodic table, with atomic number 75. It is a silvery-white heavy metal with extremely high melting and boiling points, as well as excellent high-temperature strength, wear resistance, and corrosion resistance. It plays a vital role in cutting-edge fields of modern industry. Particularly in the aerospace field, rhenium-containing high-temperature alloys are widely used in the manufacture of single-crystal turbine blades and combustion chamber components for high-performance aero engines, improving engine operating temperatures and thrust-to-weight ratio. Furthermore, rhenium is used as a catalyst in the petrochemical industry and in the electronics industry for manufacturing mass spectrometer filaments and high-stability electrical contact materials. Because rhenium is extremely rare in the Earth's crust and usually exists as a by-product of minerals such as molybdenite, its extraction and purification processes are complex.

[0003] Rhenium hexafluoride, a fluoride of rhenium, is a pale yellow, volatile, and chemically reactive liquid at room temperature. In traditional rhenium hexafluoride preparation processes, fluorine gas is typically used as the fluorinating agent to react directly with metallic rhenium. However, fluorine gas is highly corrosive and toxic, posing high risks to the process, imposing stringent requirements on production equipment, and making it difficult to further improve product purity. Nitrogen trifluoride, a mild fluorinating agent, has become a research hotspot in fluoride synthesis in recent years. Compared to fluorine gas, nitrogen trifluoride has lower reactivity and better safety; however, how to achieve efficient fluorination of rhenium using nitrogen trifluoride remains a pressing technical challenge. Furthermore, rhenium readily generates rhenium heptafluoride as a byproduct during the fluorination reaction. The formation of this substance not only reduces the purity of the target product, rhenium hexafluoride, but also adversely affects the separation, purification, and practical application of subsequent products. Currently, there is no mature technical solution for systems using NF3 as a fluorinating agent that can effectively inhibit the formation of ReF7 and convert it into ReF6.

[0004] Technical document CN118320717A discloses a method for synthesizing rhenium hexafluoride crystals in a diamond anvil cell. The method uses a diamond anvil cell as the reaction apparatus, xenon difluoride as the fluorinating agent, and liquid argon as the solvent to prepare rhenium hexafluoride. High-purity rhenium hexafluoride crystals are obtained by controlling the operating pressure. However, this method suffers from high equipment costs, difficult experimental operation, and small sample sizes, making large-scale production difficult. Furthermore, high-pressure operation may cause unpredictable changes in the material's structure and properties, and carries significant safety risks, requiring strict safety precautions.

[0005] CN110589893B discloses a method for preparing rhenium hexafluoride. The method involves introducing nitrogen trifluoride gas into a reactor containing rhenium powder, conducting a fluorination reaction at a temperature of 400℃~500℃ and a pressure of 0.1MPa~0.2MPa, and using a condenser to collect the generated rhenium hexafluoride and rhenium heptafluoride, causing them to sublimate into a mixed solid. Uncondensed nitrogen and nitrogen trifluoride gas are then discharged from the product. Although this patented method aims to address the poor selectivity of the direct fluorination method through a reduction step, thereby enabling the directional preparation of rhenium hexafluoride, the purity of the rhenium hexafluoride product prepared by this method is very limited.

[0006] Therefore, there is an urgent need to develop an efficient synthesis method for rhenium hexafluoride that has controllable reaction conditions, simple process, and is easy to industrialize, so as to solve the current problems in the preparation of rhenium hexafluoride. Summary of the Invention

[0007] To address the problems of harsh reaction conditions and difficulty in product purification in existing technologies, this application proposes a method for synthesizing rhenium hexafluoride, comprising the following steps: Step S1. Preheat the fluorine-nitrogen mixture to 50-100°C in the first temperature zone; Step S2. The preheated fluorine-nitrogen mixture is introduced into the second temperature zone to react with rhenium metal to generate a mixed gas containing rhenium hexafluoride, wherein the temperature of the second temperature zone is 120~180℃; Step S3. A mixed gas containing rhenium hexafluoride is introduced into the third temperature zone to continue the reaction with rhenium metal, wherein the temperature of the third temperature zone is 300~450℃; Step S4. Pass the gas obtained from the reaction in step S3 into the fourth temperature zone, and control the temperature of the fourth temperature zone to be 200~300℃. Step S5. The gas generated in step S4 is collected at low temperature through a cold trap to obtain high-purity rhenium hexafluoride.

[0008] Preferably, the ratio of fluorine to nitrogen in the fluorine-nitrogen mixture is 1:(0.5~2), and the flow rate of the fluorine-nitrogen mixture is 50~300 mL / min.

[0009] Preferably, the heating rate of the first temperature zone, the second temperature zone, the third temperature zone and the fourth temperature zone is 5~50°C / min, and the pressure is 0.05~0.20Mpa.

[0010] Preferably, the reaction time in the second temperature zone is 30-120 min, and the molar ratio of fluorine to rhenium in the fluorine-nitrogen mixture is (3-6):1; the gas residence time in the third temperature zone is 30-60 s, and the molar ratio of fluorine to rhenium in the fluorine-nitrogen mixture is 0.5:1.

[0011] Preferably, the reactor in the fourth temperature zone is filled with NiF2 activated carbon, with a NiF2 loading of 10~15wt%; the gas residence time is 20~40s.

[0012] Preferably, the purity of the rhenium metal is 95% or higher.

[0013] Preferably, the temperature for low-temperature collection is -80~10℃.

[0014] Preferably, the reactor material used in steps S1 to S4 is any one of stainless steel, Monel, or nickel-based alloy.

[0015] Preferably, before the reaction begins, the reaction system is evacuated to -0.1 MPa and purged with nitrogen or inert gas to a pressure of 0.005~0.15 MPa. The evacuation and purging are repeated 10~20 times.

[0016] Preferably, the inert gas is helium or argon.

[0017] The specific benefits of this application are as follows: This application utilizes multi-zone temperature control to reduce impurity content and improve product purity. First, the second temperature zone is precisely controlled between 120 and 180°C. This temperature range is compatible with the formation kinetics of rhenium hexafluoride, preferentially promoting the reaction of rhenium metal with fluorine gas to generate ReF6, while effectively inhibiting the formation of difficult-to-remove high-valence fluoride impurities such as rhenium heptafluoride. Second, the third temperature zone is raised to 300–450°C, utilizing excess rhenium metal to undergo a disproportionation reaction with trace amounts of ReF7 in the mixed gas, directly converting impurities into the target product ReF6, achieving in-situ impurity elimination without the need for additional purification units. Third, the fourth temperature zone is filled with 10–15 wt% NiF2-supported activated carbon, which can efficiently cleave trace byproducts such as fluorine oxides. Combined with the enrichment and collection by a low-temperature cold trap, this further improves product purity.

[0018] This application employs a two-stage rhenium metal ratio to maximize rhenium resource utilization: in the second temperature zone, the molar ratio of fluorine gas to metallic rhenium is controlled at 3-6:1 to ensure sufficient reaction of rhenium metal to generate ReF6, avoiding raw material waste; in the third temperature zone, excess rhenium metal is used as an impurity scavenger to convert the by-product ReF7 into the target product, achieving efficient utilization of rhenium resources, rather than the rhenium loss caused by directly discarding impurities in traditional processes. This application integrates preheating, main reaction, in-situ purification, refining, and low-temperature collection into the same reactor system, achieving continuous operation throughout the entire process and significantly shortening the production cycle. Detailed Implementation

[0019] To further illustrate the technical means and effects adopted by this application in order to achieve the intended purpose of the invention, the following detailed description of the specific implementation methods, structures, features and effects of this application, in conjunction with preferred embodiments, is provided below.

[0020] Example 1 This embodiment provides a method for synthesizing rhenium hexafluoride, the specific operation of which is as follows: First, the reaction system was pretreated, and the reactor material used was Monel alloy. The reaction system was evacuated to -0.1 MPa using a vacuum pump, and then purged with nitrogen until the system pressure reached 0.01 MPa. This vacuuming-purging operation was repeated 15 times to thoroughly remove air, moisture, and other impurities from the system, preventing moisture from reacting with fluorine to form harmful hydrogen fluoride products. It also prevented moisture from causing the hydrolysis of rhenium hexafluoride subsequently generated, ensuring reaction safety and product purity.

[0021] Step S1: Prepare a fluorine-nitrogen mixture with a fluorine to nitrogen volume ratio of 1:1. Introduce this mixture into the first temperature zone and heat it to 70°C at a rate of 20°C / min, maintaining this temperature for preheating. Control the system pressure at 0.1 MPa, and maintain the flow rate of the fluorine-nitrogen mixture at 150 mL / min. In this step, the preheating temperature ensures a uniform and stable temperature of the mixture, close to the subsequent reaction temperature, thus preventing temperature fluctuations caused by the low-temperature mixture entering the reaction zone.

[0022] Step S2: The preheated fluorine-nitrogen mixture is introduced into the second temperature zone, where 95.4% pure block rhenium is placed. The temperature in the second temperature zone is increased to 150°C at a rate of 20°C / min, the system pressure is maintained at 0.1 MPa, the reaction time is adjusted to 60 min, and the molar ratio of fluorine to metallic rhenium in the fluorine-nitrogen mixture is controlled at 4:1. At this temperature, rhenium reacts with fluorine to form rhenium hexafluoride, and the formation of rhenium heptafluoride is suppressed.

[0023] Step S3: The rhenium hexafluoride-containing mixed gas generated in the second temperature zone is introduced into the third temperature zone. In this zone, 95.4% pure rhenium of the same specification is placed. The third temperature zone is heated to 380°C at a rate of 25°C / min, maintaining a system pressure of 0.1 MPa and a gas residence time of 45 s. The molar ratio of fluorine to metallic rhenium in the fluorine-nitrogen mixed gas is 0.5:1. Excess metallic rhenium will undergo a disproportionation reaction with trace amounts of rhenium heptafluoride in the mixed gas, efficiently converting the impurity rhenium heptafluoride into the target product rhenium hexafluoride.

[0024] Step S4: The gas reacted in the third temperature zone is introduced into the fourth temperature zone, which is filled with a 12wt% NiF2 / activated carbon catalyst. The fourth temperature zone is heated to 240℃ at a rate of 20℃ / min, maintaining a system pressure of 0.1MPa and adjusting the gas residence time to 30s. The NiF2 catalyst can efficiently catalyze the cracking of trace impurities such as fluorine oxides in the mixed gas, decomposing them into harmless small molecules or easily separable components. This step achieves deep impurity removal, eliminating trace impurities not removed in previous steps, ensuring the high purity of the final product.

[0025] Step S5: The gas processed in the fourth temperature zone is introduced into the cold trap, and the temperature of the cold trap is controlled at -50℃ for low-temperature collection. Rhenium hexafluoride can rapidly condense into solid crystals at this temperature, while non-condensable gases such as nitrogen can be directly discharged, achieving efficient separation of rhenium hexafluoride from other gases. The low-temperature collection process does not introduce additional impurities and can reduce the volatilization loss of rhenium hexafluoride.

[0026] After collection, the product was tested, and the results showed that the purity of rhenium hexafluoride reached 99.92%, of which the content of rhenium heptafluoride was 0.04%, the content of fluorine oxide impurities was less than 0.03%, and the rhenium atom utilization rate reached 98.3%.

[0027] Example 2 This embodiment provides a method for synthesizing rhenium hexafluoride, the specific operation of which is as follows: First, the reaction system was pretreated, and the reactor material was selected from 316L stainless steel. The reaction system was evacuated to -0.1MPa using a vacuum pump, and then purged with argon gas until the system pressure reached 0.005MPa. The above evacuation-purging operation was repeated 10 times.

[0028] Step S1: Prepare a fluorine-nitrogen mixture with a volume ratio of fluorine to nitrogen of 1:0.5, introduce it into the first temperature zone, heat it to 50°C at a low heating rate of 5°C / min and hold it at that temperature for preheating, control the system pressure to maintain at 0.05MPa, and the flow rate of the fluorine-nitrogen mixture is 50mL / min.

[0029] Step S2: The preheated fluorine-nitrogen mixture is introduced into the second temperature zone, where 95% pure rhenium metal powder is placed. The second temperature zone is heated to 120°C at a heating rate of 5°C / min, the system pressure is maintained at 0.05MPa, the reaction time is adjusted to 120min, and the molar ratio of fluorine gas to rhenium metal is controlled at 3:1.

[0030] Step S3: Introduce the mixed gas generated in the second temperature zone into the third temperature zone, place rhenium metal particles of the same purity in this zone, control the third temperature zone to heat up to 300°C at a heating rate of 15°C / min, maintain the system pressure at 0.05MPa, adjust the gas residence time to 60s, and the molar ratio of fluorine gas to rhenium metal to 0.5:1.

[0031] Step S4: The gas reacted in the third temperature zone is introduced into the fourth temperature zone, which is filled with a NiF2 / activated carbon catalyst with a loading of 10wt%. The fourth temperature zone is heated to 200℃ at a heating rate of 5℃ / min, the system pressure is maintained at 0.05MPa, and the gas residence time is adjusted to 40s.

[0032] Step S5: The gas processed in the fourth temperature zone is introduced into the cold trap, and the temperature of the cold trap is controlled at -80℃ for low-temperature collection.

[0033] After collection, the product was tested, and the results showed that the purity of rhenium hexafluoride reached 99.90%, of which the content of rhenium heptafluoride was 0.05%, the content of fluorine oxide impurities was 0.03%, and the rhenium atom utilization rate reached 98.0%.

[0034] Example 3 This embodiment provides a method for synthesizing rhenium hexafluoride, the specific operation of which is as follows: First, the reaction system was pretreated, and the reactor material used was Monel alloy. The reaction system was evacuated to -0.1 MPa using a vacuum pump, and then purged with nitrogen until the system pressure reached 0.15 MPa. This evacuation-purging operation was repeated 20 times.

[0035] Step S1: Prepare a fluorine-nitrogen mixture with a volume ratio of fluorine to nitrogen of 1:2, introduce it into the first temperature zone, heat it to 100°C at a high heating rate of 50°C / min and hold it at that temperature for preheating, control the system pressure to maintain at 0.20 MPa, and the flow rate of the fluorine-nitrogen mixture is 300 mL / min.

[0036] Step S2: The preheated fluorine-nitrogen mixture is introduced into the second temperature zone, in which a rhenium mesh with a purity of 99.5% is placed. The second temperature zone is heated to 180°C at a heating rate of 50°C / min, the system pressure is maintained at 0.20 MPa, the reaction time is adjusted to 30 min, and the molar ratio of fluorine gas to rhenium metal is controlled at 6:1.

[0037] Step S3: Introduce the mixed gas generated in the second temperature zone into the third temperature zone, place rhenium metal particles in this zone, control the third temperature zone to heat up to 450°C at a heating rate of 50°C / min, maintain the system pressure at 0.20MPa, adjust the gas residence time to 30s, and the molar ratio of fluorine gas to rhenium metal to 0.5:1.

[0038] Step S4: The gas reacted in the third temperature zone is introduced into the fourth temperature zone, which is filled with a NiF2 / activated carbon catalyst with a loading of 15wt%. The fourth temperature zone is heated to 300℃ at a heating rate of 50℃ / min, the system pressure is maintained at 0.20MPa, and the gas residence time is adjusted to 20s.

[0039] Step S5: The gas processed in the fourth temperature zone is introduced into the cold trap, and the temperature of the cold trap is controlled at 10°C for low-temperature collection.

[0040] After collection, the product was tested, and the results showed that the purity of rhenium hexafluoride reached 99.93%, of which the content of rhenium heptafluoride was 0.03%, the content of fluorine oxide impurities was less than 0.02%, and the rhenium atom utilization rate reached 98.5%.

[0041] Comparative Example 1 The difference between this comparative example and Example 1 is that this comparative example did not perform the preheating step S1.

[0042] The purity of rhenium hexafluoride decreased to 99.25%, the impurity content of rhenium heptafluoride increased to 0.58%, the impurity content of fluorine oxides was 0.17%, and the rhenium atom utilization rate decreased to 92.1%. This difference is due to the temperature fluctuation in the second temperature zone caused by the unheated fluorine-nitrogen mixture, resulting in poor mixing uniformity, which in turn promotes impurity formation and reduces the degree of reaction completion.

[0043] Comparative Example 2 The difference between this comparative example and Example 1 is that rhenium metal was not placed in the third temperature zone in this comparative example.

[0044] The purity of rhenium hexafluoride was only 98.10%, the impurity content of rhenium heptafluoride was as high as 1.72%, the impurity content of fluorine oxide was 0.18%, and the rhenium atom utilization rate dropped sharply to 85.5%. This was because the lack of rhenium metal prevented the neutralization reaction from taking place. The rhenium heptafluoride impurity generated in the second temperature zone could not be converted into the target product, and the rhenium resources could not be recovered, resulting in a double decrease in purity and atom utilization rate.

[0045] Comparative Example 3 The difference between this comparative example and Example 1 is that no catalyst was placed in this comparative example in the fourth temperature zone.

[0046] The rhenium hexafluoride purity is 99.55%, the rhenium heptafluoride impurity content is 0.05%, the fluorine oxide impurity content is 0.40%, and the rhenium atom utilization rate is 97.8%. Since there is no catalyst, the fluorine oxide impurities cannot be cracked, which only affects the fluorine oxide content and has little impact on the rhenium heptafluoride conversion and rhenium utilization rate. Therefore, the data differences are mainly concentrated on the fluorine oxide index.

[0047] Comparative Example 4 The difference between this comparative example and Example 1 is that this comparative example is in the third temperature zone, with a temperature of 260°C.

[0048] The rhenium hexafluoride purity is 99.30%, the rhenium heptafluoride impurity content is 0.52%, the fluoride oxide impurity content is 0.18%, and the rhenium atom utilization rate is 93.0%. Due to insufficient temperature, the disproportionation reaction rate is slowed down, the rhenium heptafluoride conversion is incomplete, the impurity residue is increased, and the rhenium metal activity is reduced, thus affecting the product purity and atom utilization rate. The above description is only a preferred embodiment of this application and is not intended to limit this application in any way. Although this application has disclosed the preferred embodiment as above, it is not intended to limit this application. 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 technical solution of this application. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of this application without departing from the scope of the technical solution of this application shall still fall within the scope of the technical solution of this application.

Claims

1. A method for synthesizing rhenium hexafluoride, characterized in that, Includes the following steps: Step S1. Preheat the fluorine-nitrogen mixture to 50-100°C in the first temperature zone; Step S2. The preheated fluorine-nitrogen mixture is introduced into the second temperature zone to react with rhenium metal to generate a mixed gas containing rhenium hexafluoride, wherein the temperature of the second temperature zone is 120~180℃; Step S3. A mixed gas containing rhenium hexafluoride is introduced into the third temperature zone to continue the reaction with rhenium metal, wherein the temperature of the third temperature zone is 300~450℃; Step S4. Pass the gas obtained from the reaction in step S3 into the fourth temperature zone and control the temperature of the fourth temperature zone to be 200~300℃; Step S5. The gas generated in step S4 is collected at low temperature through a cold trap to obtain high-purity rhenium hexafluoride.

2. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The ratio of fluorine to nitrogen in the fluorine-nitrogen mixture is 1:(0.5~2), and the flow rate of the fluorine-nitrogen mixture is 50~300 mL / min.

3. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The heating rate of the first, second, third, and fourth temperature zones is 5~50°C / min, and the pressure is 0.05~0.20 MPa.

4. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The reaction time in the second temperature zone is 30-120 min, and the molar ratio of fluorine to rhenium in the fluorine-nitrogen mixture is (3-6):1; the gas residence time in the third temperature zone is 30-60 s, and the molar ratio of fluorine to rhenium in the fluorine-nitrogen mixture is 0.5:

1.

5. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The reactor in the fourth temperature zone is filled with NiF2 activated carbon, with a NiF2 loading of 10~15wt%; the gas residence time is 20~40s.

6. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The purity of the rhenium metal is above 95%.

7. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The temperature for the low-temperature collection is -80~10℃.

8. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, The reactors used in steps S1 to S4 are made of any one of stainless steel, Monel, or nickel-based alloys.

9. The method for synthesizing rhenium hexafluoride according to claim 1, characterized in that, Before the reaction begins, the reaction system is evacuated to -0.1 MPa and purged with nitrogen or inert gas to a pressure of 0.005~0.15 MPa. The evacuation and purging process is repeated 10~20 times.

10. The method for synthesizing rhenium hexafluoride according to claim 9, characterized in that, The inert gas is helium or argon.