CN109652816B - Synthesis of high-purity tungsten hexafluoride by using metal tungsten as anode to electrolyze molten salt - Google Patents
Synthesis of high-purity tungsten hexafluoride by using metal tungsten as anode to electrolyze molten salt Download PDFInfo
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Abstract
Preferably, a metal tungsten plate is used as an anode of the electrolytic cell, a raw material lithium fluoride beryllium eutectic is used as an electrolyte, the melting point range is suitable for electrolysis, no hydrogen fluoride component exists, and the pollution of harmful components such as carbon tetrafluoride and hydrogen fluoride to the finished product tungsten hexafluoride can be cut off from the source. Tungsten hexafluoride gas generated in the electrolytic cell, entrained fused salt flying dust and a small amount of fluorine gas which does not react with metal tungsten enter a gas purification tank along a gas outlet pipe of the electrolytic cell, and electrolyte micro dust entrained by the tungsten hexafluoride is removed by a flying dust filter plate and a flying dust adsorbent; and (3) completely converting a small amount of unreacted fluorine gas into tungsten hexafluoride by using the tungsten microsphere reaction layer, completely filtering out the entrained metal tungsten particles by using a microporous filter, and finally producing the high-purity tungsten hexafluoride gas. The invention realizes the direct synthesis of high-purity tungsten hexafluoride by an electrolytic method, and has the advantages of simple process route, less impurities in the finished product, high yield, extremely competitive comprehensive production cost and the like.
Description
Technical Field
The invention relates to a device for directly synthesizing high-purity tungsten hexafluoride by electrolyzing molten salt.
Background
Tungsten hexafluoride (WF)6) It is by far the only stable and industrially produced species of tungsten fluoride. The important applications are many; for example, the tungsten/rhenium composite coating prepared by the mixed metal CVD process can be used for manufacturing solar energy-absorbing materials and X-ray emitting electrodes; the production of hard tungsten carbide from tungsten on steel, copper or other metal surfaces can be used to improve the surface properties of the metal and to manufacture various shaped tungsten parts such as tungsten tubes, tungsten nozzles and tungsten crucibles. WF6It is also widely used as a raw material for semiconductor electrodes and conductive pastes in the electronics industry, particularly tungsten disilicide (WSi) made therefrom2) The conductive layer is commonly used as a contact material in microelectronics and a shunt on a polysilicon line, and has become an extremely important wiring material in the large-scale integrated circuit industry due to the enhancement of the conductivity and signal speed of the polysilicon line at high temperature.
Synthesis of WF6There are many methods of the present invention, and the industrial synthesis of WF is now mature, summarized in published reports6The process main lines comprise the following three lines;
1, with Cl22HF mixture as fluorinating agent. The metal tungsten reacts with Cl under the condition of no moisture and air2Preparation of WF by reaction of 2HF mixture6The reaction is usually carried out in Monel alloyThe reaction is carried out in an autoclave, and the reaction formula is as follows: w +3Cl2+6HF＝WF6+6 HCl. To ensure good yields of the product, Cl is required2And HF are properly excessive, the theoretical molar ratio of chlorine to tungsten hexafluoride is 3: 1, in practice, the theoretical molar ratio of chlorine to tungsten hexafluoride is 4-6: 1, in practice, the theoretical molar ratio of hydrogen fluoride to tungsten hexafluoride is 6: 1, and in practice, the theoretical molar ratio of hydrogen fluoride to tungsten hexafluoride is 7-10: 1. The reaction temperature is controlled to be 200-450 ℃, and the reaction is favorably carried out by increasing the reaction temperature (but the device is seriously corroded due to overhigh temperature). The biggest problem of the process is that the tungsten hexafluoride product has low purity and low yield, and the serious pollution is also the reason that the process route cannot be popularized in a large area.
2, a process using fluorine gas as a fluorinating agent. Metal tungsten directly reacts with fluorine gas to prepare WF6. The reaction formula is as follows: w +3F2＝WF6. The reaction is completed by flowing fluorine gas through a fluidized bed or a fixed bed containing metal tungsten, the reaction temperature is controlled to be about 350-450 ℃, the synthesis speed is high, the yield is high, side reactions are few, the quality of the finished tungsten hexafluoride product is high, and the quality is the most mainstream synthesis process in the world at present as long as the quality depends on the purity of the fluorine gas and the content of metal tungsten impurities. However, the purity of the raw material fluorine gas is limited (industrial fluorine gas is totally from medium-temperature electrolysis for fluorine production, and components such as carbon tetrafluoride and hydrogen fluoride which have great influence on the quality of tungsten hexafluoride), so the tungsten hexafluoride synthesized by the route is put into practical use, and either the raw material fluorine gas is refined before synthesis or the tungsten hexafluoride finished product is subjected to purification in a plurality of steps after synthesis (and the fact that the fluorine gas and the hydrogen fluoride which have close boiling points enter the tungsten hexafluoride finished product is difficult to separate the two products).
3, with nitrogen trifluoride (NF)3) As a fluorinating agent. NF (nitrogen oxide) is prepared3Into a reactor made of nickel or monel, NF3Directly reacting with metal tungsten at 200-400 ℃ to generate WF6. The reaction formula is as follows: w +2NF3＝WF6+N2. The process has the greatest characteristic of avoiding carbon tetrafluoride, hydrogen fluoride and the like carried in industrial fluorine gas as a fluorinating agentInfluence on the quality of tungsten hexafluoride. But it has to be pointed out; the mature process route for industrially producing nitrogen trifluoride is a direct conversion method of fluorine and ammonia or a plurality of methods of fluorine gas and ammonium bifluoride, fluorine gas and hydrogen fluoride and the like. If the quality of tungsten hexafluoride produced by nitrogen trifluoride is higher than that of tungsten hexafluoride produced by fluorine gas, the actual reason is that the purification of raw material fluorine gas is troublesome and is replaced by the purification of nitrogen trifluoride. But the advantages are still: although the tungsten hexafluoride produced by using nitrogen trifluoride is also subjected to subsequent refining processing, the purity of the finished tungsten hexafluoride can meet the use requirement, but the difficult-to-remove components such as carbon tetrafluoride, hydrogen fluoride and the like carried by directly synthesizing the tungsten hexafluoride by using fluorine gas are basically avoided, so that the efficiency is obviously high in the subsequent refining processing.
Because the purity requirement of the tungsten hexafluoride in the electronic gas industry is high, at least more than 99.99% (commonly called 4 to 9), and the purity of the tungsten hexafluoride industrially synthesized by the three process routes is about 99-99.9%, the tungsten hexafluoride can be really practical by various subsequent refining treatments. Tungsten hexafluoride having a purity of 99.99% or more is called high-purity tungsten hexafluoride, and by special purification, tungsten hexafluoride having a purity of 99.9999% or more (called ultra-high-purity tungsten hexafluoride) can be obtained.
In order to improve the purity of the industrially synthesized tungsten hexafluoride, scientific research institutions and production enterprises at home and abroad make a great deal of research and development work.
For example, U.S. patent No. p5324498 discloses a method for purifying tungsten hexafluoride; "tungsten hexafluoride is first evaporated to remove non-volatile residues and the evaporated product is recondensed, after which the condensed tungsten hexafluoride is frozen into solid form, its headspace is evacuated to remove volatile impurities, the solid is melted and tungsten hexafluoride is heated to a temperature above its boiling point under reduced pressure, its headspace is evacuated to remove volatile impurities therefrom, and the above steps are repeated a number of times, ultimately achieving the purpose of tungsten hexafluoride purification". The analysis shows that: the overall process is decisive for removing volatile impurities, such as nitrogen and oxygen, but is ineffective for removing hydrogen fluoride from tungsten hexafluoride because they are close in boiling point. Meanwhile, the method needs repeated thermal cycles, and is very energy-consuming and time-consuming.
Further, U.S. Pat. nos. P5328668 and 5348723 disclose integrated processes for producing semiconductor grade tungsten hexafluoride. These methods employ evaporation as a means of removing non-volatile impurities from the product, but do not provide any means of removing metallic impurities and methods of reducing the level of hydrogen fluoride.
Patent CN1281823A discloses a method for producing ultra-high-purity (UHP) tungsten hexafluoride, which comprises distilling crude tungsten hexafluoride to separate non-volatile metal impurities from tungsten hexafluoride, adsorbing with fluoride salt to remove HF, and finally separating high-purity tungsten hexafluoride product by using a bubbling system of UHP helium gas.
Disclosure of Invention
In order to overcome the defects of the prior art, the invention provides a device for directly synthesizing high-purity tungsten hexafluoride.
In order to solve the technical problems, the invention is realized by the following scheme: the electrolytic cell comprises an electrolytic rectangular cell body (1) made of heat-resistant steel (1), wherein the whole cell body is insulated by a light refractory brick heat-insulating layer (2), an integrated sensor (8), an anode copper conducting rod (9) and a gas outlet pipe (18) are respectively installed on a heat-resistant steel cell cover (6), the cell cover is fixed above the electrolytic cell body through a mica heat-resistant sealing insulating pad, and the sensor, the conducting rod and the gas outlet pipe are respectively fixed on the cell cover through heat-resistant sealing insulating sleeves (7), (10) and (19). The metal tungsten plate (4) is fixed below the conducting rod through an electrolytic cell anode conducting rod tungsten plate fixing frame, the metal nickel plate (3) is riveted with an electrolytic cell cathode conducting rod (21), and the cathode conducting rod is fixed below the fused salt electrolytic cell body through a heat-resistant sealing insulating sleeve (20). The initial electrolyte is selected from lithium fluoride (LiF) and beryllium fluoride (BeF)2) Mixing two fluorine salts according to a molar ratio of 2:1 (then, along with electrolysis, lithium fluoride only plays a role of constructing eutectic, and only beryllium fluoride is actually consumed), heating the electrolyte to a molten state (400-500 ℃) by adopting medium-frequency electric heating devices (22) and (24), and applying 2.5-3V direct-current voltage to the cathode and the anode of the electrolytic cell in a molten salt electrolysis modeAnd the metallic beryllium is separated out from the cathode (because of the melting point, the metallic beryllium falls off from the metallic nickel cathode in a flake shape (23) to the bottom of the electrolytic bath). The fluorine gas generated by the anode reacts with the metal tungsten anode to generate tungsten hexafluoride. Tungsten hexafluoride gas, entrained molten salt flying dust and a small amount of fluorine gas which does not react with metal tungsten enter a gas purification tank (11) along an electrolytic tank gas outlet pipe (18), the electrolytic tank solid particles entrained by the molten salt and the gas are filtered and adsorbed by a flying dust filter plate (12) sintered by alkali metal and a flying dust adsorbent (17), the unreacted small amount of fluorine gas is completely reacted into tungsten hexafluoride through a tungsten microsphere support bracket (13) and a tungsten microsphere reaction layer (16), then the gas passes through a microporous filter (14) sintered by sponge nickel, the metal tungsten microparticles which are possibly entrained are completely filtered, and finally the gas is led out from a purification tank discharge pipe (15) in a high-purity tungsten hexafluoride gas state.
According to the well-known electrochemical law, when a direct current voltage is applied to an electrolyte in an electrolytic cell, oxidation reaction of electron losing and reduction reaction of electron obtaining respectively occur at the positive electrode and the negative electrode of the electrolytic cell. None of the important active metals such as sodium, potassium, lithium, aluminum, etc. is obtained by electrolysis of molten salts at the cathode portion of the electrolytic cell. The product at the anode site depends on the anion component of the molten salt, and if the molten salt is a chloride, the anode generates chlorine gas, and if the molten salt is a fluoride, the anode generates fluorine gas.
The electrolyte selected by the invention is a low-melting-point eutectic formed by beryllium fluoride and lithium fluoride. The chemical reaction formula is as follows: 2LiF + BeF2→Li2BeF4(lithium beryllium fluoride eutectic). The lithium beryllium fluoride eutectic has the characteristics of low melting point (molten state is shown at over 400 ℃ under normal pressure), low steam pressure, high hot melting and wide eutectic forming range (the ratio of two fluorides is from 1:1 to 10:1, the eutectic structure is stable, and the melting point is slightly increased). Are now widely used for heat exchange fluids such as in solar storage, fission and fusion reactors, and for the electrochemical production of beryllium metal.
Application of a dc voltage to a lithium beryllium fluoride electrolyte appears to produce two metals at the cathode (metallic beryllium and metallic lithium), but based on the electrode potentials of bothThe data is known; li++e→Li，E＝-3.040V；Be++ E → Be, E ═ 1.847V, which is far easier for beryllium than lithium, compared to both electron capabilities. The actual production result completely conforms to the electrode potential theory, the molten lithium beryllium fluoride is electrolyzed by normal direct current voltage (within 3V), and the metal generated by the cathode only contains beryllium without lithium precipitation.
When a direct current voltage is applied to the lithium beryllium fluoride electrolyte, electrolysis products on the anode are not objectified if metal tungsten is not selected as the anode, and all the electrolysis products are fluorine gas (the anion of the molten salt lithium beryllium fluoride is only one kind of fluorine). But the metal tungsten is selected as the anode, which has important significance: the reactivity of the metal tungsten is greatly increased at the temperature (400-500 ℃) of the lithium beryllium fluoride molten state, and the metal tungsten reacts quickly to generate tungsten hexafluoride once encountering fluorine gas generated on the surface of the metal tungsten. Therefore, the metal tungsten plate is used as an anode to electrolyze the lithium beryllium fluoride molten salt, and the final stable product on the surface of the anode is tungsten hexafluoride gas.
The present invention ensures the elimination of the most troublesome impurities such as carbon tetrafluoride and hydrogen fluoride from tungsten hexafluoride gas (it is known that, in the preparation of industrial fluorine gas, regardless of the high, medium and low temperature electrolytic bath, the electrolyte contains hydrogen fluoride, and most of the anodes used are carbon materials, and in this environment, harmful components such as hydrogen fluoride and carbon tetrafluoride are unavoidable).
When the metal tungsten plate is used as an anode to electrolyze lithium beryllium fluoride molten salt, molten salt flying dust (namely electrolyte spray) and a small amount of fluorine gas which cannot react with metal tungsten are carried in the generated tungsten hexafluoride gas due to instantaneous fluctuation of current or overlarge electrolytic current and the like when the anode produces the tungsten hexafluoride gas. In order to solve the problem, the invention designs a set of gas purification device on the gas outlet pipe of the molten salt electrolytic cell. The device is internally provided with a dust filter plate made of sintered alkali metal and a dust adsorbent, so that the solid particles of electrolyte droplets can be prevented from passing through the device. The tungsten microsphere support bracket made of heat-resistant steel and the fine tungsten spheres (the diameter of the tungsten spheres is preferably 5-10 mm) formed by high-pressure pressing of metal tungsten powder are used, a small amount of fluorine gas carried by tungsten hexafluoride gas from an electrolytic cell is completely reacted under the condition that the fine tungsten spheres are greatly excessive, and the tungsten hexafluoride is generated. And then the gas passes through a microporous filter sintered by sponge nickel, and the dust possibly generated by the reaction of the metal tungsten balls is filtered out, so that the high-purity tungsten hexafluoride gas can be finally obtained.
The invention has the following advantages:
1, the equipment for preparing various important metals by electrolyzing molten salt is mature and stable, the core equipment, namely an electrolytic cell, and matching parts for heating, sealing, insulating and the like of the electrolytic cell form a standard system series, and the device designed by the invention is not an empty idea of space-free type, is not an idea of scale of a small beaker flask in a laboratory, and has a solid and reliable industrialized foundation.
Compared with the existing synthesis process and equipment, the device for synthesizing high-purity tungsten hexafluoride by electrolyzing molten salt by taking metal tungsten as an anode has breakthrough progress in the process of synthesizing tungsten hexafluoride: the existing tungsten hexafluoride synthesis process is complex and incomparable to control the content of carbon tetrafluoride, hydrogen fluoride and the like which are the most harmful impurities in the raw material stage: or rectifying the fluorine gas under a cryogenic condition for multiple times before reaction, or abandoning the fluorine gas in a dry and short way, and then refining to obtain nitrogen trifluoride as a fluorinating agent (if harmful impurities such as carbon tetrafluoride and hydrogen fluoride are not controlled in a raw material stage, the subsequent refining treatment process is more troublesome after the tungsten hexafluoride crude product is synthesized). The invention selects the method of electrolyzing molten salt to synthesize tungsten hexafluoride, the raw material lithium beryllium fluoride does not contain hydrogen fluoride, thus cutting off the pollution of hydrogen fluoride to the finished product tungsten hexafluoride from the source, and complex treatments such as fluorine cryogenic rectification or nitrogen trifluoride refining can be avoided.
3, the important innovation of the device for synthesizing the high-purity tungsten hexafluoride by electrolyzing the molten salt is also in the selection of the anode material of the electrolytic cell; at present, all fluorine-making electrolytic cells, whether low-temperature, medium-temperature or high-temperature ones, are known, the anodes are mostly made of carbon materials (amorphous carbon in low-temperature and medium-temperature cells and graphite in high-temperature cells), and metallic nickel plates are rarely used. The carbon material selected by the electrolytic cell has the advantages of durability, low cost and obvious defects; carbon is used as an anode, so that the carbon can not participate in oxidation reaction of electron loss, and finally, fluorocarbon impurities such as carbon tetrafluoride in anode gas are difficult to avoid. As such, in order to produce a gas without fluorocarbon impurities, most enterprises select nickel metal as the anode material. The metal nickel as the anode has obvious advantages (no fluorine carbon impurities are generated), but has the disadvantages of headache; besides the cost is not so high, the anode metal nickel cannot generate gaseous compounds like carbon tetrafluoride or tungsten hexafluoride after losing electrons and only can enter the electrolyte. Too much nickel ions enter the electrolyte, which causes a series of problems of increased viscosity of the electrolyte, low current efficiency and the like. The invention selects tungsten as anode when electrolyzing fused salt, which is also thought; the general fluorine-making electrolytic cell can not solve the problem that hydrogen fluoride is carried in anode gas even if the anode is made of metal tungsten (because the standard electrolyte must contain hydrogen fluoride). If the general graphite anode is adopted in the molten salt electrolysis, tungsten hexafluoride can be produced smoothly, and the hydrogen fluoride component can be avoided. But entrainment of fluorocarbons is not avoided. Comprehensively considering, the electrolytic molten salt selects metal tungsten as the anode, and reacts with fluorine gas generated on the surface of the anode at any time to generate high-purity tungsten hexafluoride with few impurities, and various defects caused by using other materials as the anode are avoided, so that the electrolytic molten salt is really an innovation.
4, the metal tungsten of the invention is used as the anode to electrolyze molten salt to synthesize high-purity tungsten hexafluoride, and is also characterized in electrolyte selection; the lithium fluoride beryllium eutectic formed by lithium fluoride and beryllium fluoride is taken as the electrolyte by careful consideration. Such eutectic crystals are characterized by a low melting point (i.e., melt at temperatures above 400 ℃ C. at atmospheric pressure), relative to the melting point of other fluoride salts (e.g., melting point of lithium fluoride 842 ℃, melting point of potassium fluoride 846 ℃, melting point of sodium fluoride 995 ℃, melting point of magnesium fluoride 1270 ℃, melting point of calcium fluoride 1478 ℃ C., etc.). Due to the fact that lithium beryllium fluoride eutectic is selected, electrolysis can be carried out at the temperature of 400-500 ℃, energy consumption is greatly reduced, more importantly, reliability and durability of the device are greatly improved, and mass production is possible.
Compared with the current general synthetic process route, the method for synthesizing high-purity tungsten hexafluoride by electrolyzing molten salt by using metal tungsten as an anode has the advantages of equivalent product quality and competitive production cost; since not only is tungsten hexafluoride produced at the anode, but also valuable beryllium scrap is produced at the cathode (not to be unduly limited herein with respect to the recovery and refining of beryllium scrap, as described in the metallurgical specialties).
Drawings
FIG. 1 is a general view of a production apparatus for synthesizing high-purity tungsten hexafluoride by electrolyzing molten salt using metal tungsten as an anode.
FIG. 2 is a schematic diagram of the cell body structure of the molten salt electrolyzer in the production apparatus.
FIG. 3 is a schematic diagram of a gas purification tank in a production plant.
FIG. 4 is a schematic view showing the structure of an anode of a molten salt electrolytic cell in a production apparatus
FIG. 5 is a schematic view showing the structure of a cathode of a molten salt electrolytic cell in a production apparatus
Description of the symbols
1 molten salt electrolytic tank heat-resistant steel tank body
2 molten salt electrolytic bath light refractory brick heat insulation layer
3 molten salt electrolytic bath nickel plate cathode
Tungsten plate anode of 4 fused salt electrolytic cell
Heat-resistant sealing insulating pad for cover of 5 fused salt electrolytic bath
Heat-resistant steel upper cover of 6 fused salt electrolytic cell
Heat-resisting sealing insulating sleeve of 7 fused salt electrolytic cell integrated sensor
8 fused salt electrolytic bath integrated sensor
9 fused salt electrolysis trough positive pole conducting rod
Heat-resistant sealing insulating sleeve for 10 anode conducting rod tungsten plate fixing frame
11 gas purification jar fused salt electrolysis trough gas eduction tube
12 gas purification jar sintering alkali metal material raise dust filter
13 tungsten microsphere support bracket of gas purification tank
14 gas purification jar sintering sponge nickel material microporous filter
15 gas outlet of gas purification tank
16 gas purification tank tungsten microsphere reaction layer
17 gas purification tank electrolyte sintered alkali metal dust adsorbent
18 gas outlet pipe of fused salt electrolytic tank (used as electrolyte inlet when feeding)
Heat-resistant sealing insulating sleeve for gas outlet pipe of 19 molten salt electrolytic cell
Heat-resistant sealing insulating sleeve for cathode conducting rod of 20 fused salt electrolytic cell
Cathode conducting rod of 21 fused salt electrolytic cell
Medium-frequency electric heating coil of 22 fused salt electrolytic bath
Crushed scale-shaped beryllium metal precipitated from cathode of 23 molten salt electrolytic cell
Controller for 24 intermediate frequency electric heating device
Detailed Description
The invention will be described in more detail hereinafter with reference to an embodiment of the drawing to which, however, the invention is not restricted.
Example (b):
the method for synthesizing the high-purity tungsten hexafluoride by electrolyzing molten salt by using metal tungsten as an anode comprises the following steps:
selecting DYD-100-0.5 type beryllium-making electrolytic cell as core equipment prototype (basic parameter: electrolytic cell volume 0.8M)3The power of the medium-frequency heating device is 100Kw, the whole material 3010 heat-resistant stainless steel of the electrolytic cell, the thickness of the cover plate of the electrolytic cell is 30mm, the thickness of the cell body plate is 18mm, the thickness of the light refractory brick heat insulation layer outside the cell body is 200mm, and the normal working temperature of the electrolytic cell is as follows: the highest heat resistance of the short time period is 800 ℃, the long-term work is within 600 ℃, and the size of the cathode nickel plate of the electrolytic cell is as follows: 400 x 300 x 6 x 9, cell anode tungsten plate size: 400*300*20*8,).
Cleaning, deoiling, assembling a cathode, an anode, an electrolytic cell, a gas purification tank and other components according to the requirements of the tool, sealing the tank before feeding, vacuumizing and testing pressure for electrolysis through a gas outlet pipe, starting medium-frequency electric heating in a no-load state, and testing whether the device is normal or not through an integrated sensor.
The assembly of the gas purification tank takes care of the sequence, the purification tank upper lid is opened and the insert is started from the very bottom. Sequentially comprises the following steps: the dust filter comprises a dust filter plate made of sintered alkali metal, a spherical dust adsorbent made of sintered alkali metal, a tungsten microsphere support bracket made of heat-resistant steel, a tungsten microsphere reaction layer and a microporous filter made of sintered sponge nickel. And finally, sealing the upper cover of the tank body, and adding and extracting inert gas through a gas delivery pipe to test the gas resistance of the purification tank (the normal pressure drop is between 0.01 and 0.012 MPa).
600Kg of molten lithium beryllium fluoride is transferred from a gas outlet of the electrolytic cell by a special feeding container (the initial electrolyte lithium fluoride and the beryllium fluoride are fed according to the mol ratio of 2:1, the mol ratio of the initial electrolyte lithium fluoride to the beryllium fluoride is not more than 10:1 before the end of electrolysis), and the gas purification tank is reset after the feeding is finished.
And vacuumizing the electrolytic cell to more than-0.098 Mpa by using a gas purification tank conduit, and controlling the temperature of the electrolytic cell to be 460-480 ℃ according to the data of the integrated sensor.
And (3) switching on an external direct-current electrolysis power supply, selecting a constant-current variable-voltage mode, increasing the operation from 100A to 1000A in the first 1 hour, and stabilizing the current of the subsequent electrolysis time within 1100-1200A.
In the first hour after the beginning of electrolysis, the gas in the tank is not collected (the amount of a single tank is small, the gas can be discharged to a leaching tower to decompose harmful components, the waste gas reaches the standard and is emptied, and the waste liquid is recycled in a centralized way). And (3) carrying out subsequent stable electrolysis and simultaneously detecting the product quality on line, and collecting tungsten hexafluoride gas after the requirements are stably met (the tungsten hexafluoride gas in the electrolytic cell is continuously led to an external tungsten hexafluoride liquefaction tank from the gas purification tank).
During normal electrolysis, because the synthesis of the tungsten hexafluoride is an exothermic reaction, the medium-frequency electric heating device enters a temperature maintaining mode according to the set bath temperature. Meanwhile, as tungsten hexafluoride is continuously generated, the metal tungsten plate anode is continuously consumed (according to the Law's law of electrolysis, it can be known by simple calculation that when 10000 ampere is electrified, 11.4Kg of tungsten anode is consumed, 18.5Kg of tungsten hexafluoride can be produced, and simultaneously 1.69Kg of scaly beryllium is produced at the cathode).
In this embodiment, the total installation amount of the anode tungsten plate is 19.25g/cm according to the pure tungsten density3The calculation was 369.6 Kg. Theoretically, the mass of the anode tungsten plate can be continuously electrolyzed for 32 ten thousand amperes, practically, the electrolysis efficiency is considered, the power is generally electrified to 75 percent of the theoretical quantity (namely the electrified quantity is 25 ten thousand amperes), namely, the consideration is further consideredAnd (6) changing the anode.
During actual production, the replacement of the anode of the electrolytic cell is very simple; and (4) assembling a spare anode on a spare electrolytic tank cover, and integrally hoisting and replacing (after the suspended tank cover is cleaned according to rules in a disassembling process, detaching the anode residual tungsten plate, and reprocessing the anode residual tungsten plate into a tungsten plate with a specified size by a professional metallurgy unit).
In this example, when the current was supplied to 25 ten thousand amperes, 420.8Kg of high-purity tungsten hexafluoride was collected in total, and the yield was 91% by theoretical amount.
In the embodiment, when the power is supplied to 25 ten thousand amperes, 40.5Kg of crushed flaky metallic beryllium is collected from the bottom of the electrolytic cell in total, and the yield is 95.7 percent calculated according to theoretical quantity.
In the embodiment, when the power is supplied to 25 kiloamperes, the molar ratio of the lithium beryllium fluoride in the electrolyte is changed from 2:1 in the initial feeding stage to 8.9:1 (according to the property of a lithium beryllium fluoride eutectic, the melting point is increased from 400 ℃ to 454 ℃, and the melting point is still below the normal set temperature of the electrolytic cell, so that the method is very safe). When the power is on for 25 ten thousand amperes, the anode is replaced, and the crushed scaly beryllium metal is fished out, 219Kg of powdery beryllium fluoride is put into the electrolytic cell according to the feeding procedure of the electrolytic cell, the cover of the electrolytic cell is closed, the electrolytic cell is normally heated until the powdery beryllium fluoride is completely dissolved, and the powdery beryllium fluoride and the original electrolyte are restored to lithium fluoride: the molar ratio of beryllium fluoride is 2: 1.
According to the actual measurement of GB/T32386-2015 tungsten hexafluoride standard for gas in the electronic industry, the tungsten hexafluoride (WF) produced by the device for synthesizing high-purity tungsten hexafluoride by using the metal tungsten as the anode to electrolyze molten salt is adopted as the anode6) Purity [ (volume fraction/10)-2)]Not less than 99.99; standard limiting value [ (volume fraction)/10 ] of Hydrogen Fluoride (HF) as main impurity-6]Is 5, the measured value is less than 1; carbon tetrafluoride (CF)4) Standard limit [ (volume fraction)/10%-6]Is 0.5, and the measured value is not detected. The conclusion is very satisfactory in the core problem of targeted elimination of the major deleterious impurities of tungsten hexafluoride.
Claims (15)
1. An apparatus for synthesizing high-purity tungsten hexafluoride by electrolyzing molten salt by using metal tungsten as an anode, wherein the apparatus comprises: an electrolytic rectangular tank body (1) made of heat-resistant steel and a light refractory brick heat insulation layer (2) used outside the whole tank body, a heat-resistant steel tank cover (6) and an integrated sensor (8), an anode copper conducting rod (9) and a gas outlet pipe (18) which are configured, wherein the tank cover is fixed above the electrolytic tank body through a mica heat-resistant sealing insulation pad, the sensor, the conducting rod and the gas outlet pipe are respectively fixed on the tank cover through heat-resistant sealing insulation sleeves (7), (10) and (19), a metal tungsten electrode (4) is fixed below the conducting rod through an electrolytic tank anode conducting rod tungsten plate fixing frame, a metal nickel plate (3) is fixedly connected with an electrolytic tank cathode conducting rod (21) in a riveting way and is fixed below the molten salt electrolytic tank body through a heat-resistant sealing insulation sleeve (20), medium-frequency electric heating devices (22) and (24) are used as a molten salt electrolytic tank heat source, a gas outlet pipe (11) of a gas purification molten salt tank is arranged on the gas, the purification tank is internally provided with a sintered alkali metal dust filter plate (12), a sintered alkali metal spherical dust adsorbent (17), a tungsten microsphere support bracket (13), a tungsten microsphere reaction layer (16) and a sintered sponge nickel microporous filter (14) from bottom to top in sequence, and the highest point of the gas purification tank is provided with a gas outlet pipe (15).
2. The device for electrolyzing molten salt to synthesize high-purity tungsten hexafluoride as claimed in claim 1, wherein the anode plate of the molten salt electrolyzer is made of tungsten.
3. The device for electrolyzing molten salt to synthesize high-purity tungsten hexafluoride as claimed in claim 2, wherein the tungsten electrode is fixed below the anode conductive rod by bolts.
4. The device for electrolyzing molten salt to synthesize high-purity tungsten hexafluoride as claimed in claim 3, wherein the anode conductive rod of the molten salt electrolyzer is made of pure copper.
5. The device for synthesizing high-purity tungsten hexafluoride through molten salt electrolysis by using metal tungsten as an anode according to claim 1, wherein a metal nickel plate is selected as a cathode of the molten salt electrolysis cell.
6. The device for electrolyzing molten salt to synthesize high-purity tungsten hexafluoride as claimed in claim 5, wherein the metal nickel plate is connected to the cathode conductive rod by riveting.
7. The device of claim 6, wherein the cathode conductive rod of the molten salt electrolyzer is made of heat-resistant steel.
8. The device for synthesizing high-purity tungsten hexafluoride through molten salt electrolysis by using metal tungsten as the anode according to claim 1, wherein the cell body of the molten salt electrolysis cell is made of heat-resistant steel.
9. The device for synthesizing high-purity tungsten hexafluoride through molten salt electrolysis by using metal tungsten as an anode according to claim 1, wherein the heat-insulating layer of the bath body of the molten salt electrolysis bath is made of light silicate refractory bricks.
10. The device for synthesizing high-purity tungsten hexafluoride through molten salt electrolysis by using metal tungsten as the anode according to claim 1, wherein a medium-frequency electric heating device is selected as a heat source of the molten salt electrolysis bath.
11. The device for synthesizing high-purity tungsten hexafluoride through molten salt electrolysis by using metal tungsten as an anode according to claim 1, wherein a gas purification tank is arranged on a gas outlet pipe of a cover of the molten salt electrolysis cell.
12. The apparatus of claim 11, wherein the gas purification tank is made of stainless steel.
13. The apparatus for the electrolysis of molten salt to synthesize high purity tungsten hexafluoride as claimed in claim 11, wherein the gas purification tank is provided with an integrated gas purification component.
14. The apparatus according to claim 13, wherein the gas purifying member in the purifying tank comprises a dust filter plate, a dust adsorbent, a tungsten microsphere support bracket, a tungsten microsphere reaction layer, and a microporous filter.
15. The apparatus of claim 14, wherein the gas purification unit is integrated in the purification tank, the dust filter plate and the dust adsorbent are made of sintered alkali metal, the tungsten microsphere support bracket is made of heat-resistant steel, the tungsten microsphere reaction layer is made of tungsten powder and pressed under high pressure, and the microporous filter is made of sintered sponge nickel.
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| SG80671A1 (en) * | 1999-02-10 | 2001-05-22 | Mitsui Chemicals Inc | A process for producing high-purity nitrogen trifluoride gas |
| CN101428858A (en) * | 2008-11-07 | 2009-05-13 | 黎明化工研究院 | Method for producing high-purity tungsten hexafluoride with fluidized bed and equipment thereof |
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