JP2019019024A - Method for producing tungsten hexafluoride - Google Patents

Abstract

To provide a method for producing tungsten hexafluoride that, as compared with conventional art of giving tungsten hexafluoride through a single step from metal tungsten, is capable of giving an increased amount of tungsten hexafluoride per reactor.SOLUTION: A method for producing tungsten hexafluoride is provided which comprises a first step of giving tungstic fluoride by allowing tungsten oxide to contact a fluorine-containing gas and a second step of giving tungsten hexafluoride by allowing the tungstic fluoride to contact the fluorine-containing gas.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method for producing tungsten hexafluoride via a tungstic acid fluoride by reacting fluorine and tungsten oxide.

Tungsten hexafluoride is useful as a precursor in chemical vapor deposition of tungsten and tungsten compounds. As a method for producing tungsten hexafluoride, a method of reacting fluorine and tungsten or nitrogen trifluoride and tungsten is widely used (see, for example, Patent Documents 1 and 2). In the reaction formula (1), the standard heat of formation ΔH 298K _{, 1 atm} is −1722 kJ / _WF6 mol, and in the reaction formula (2), the standard heat of formation ΔH298K _{, 1 atm} is −1458 kJ / _WF6 mol.
W (s) + F ₂ (g) → WF ₆ (g) ... Reaction formula (1)
W (s) + 2NF ₃ (g) → WF ₆ (g) + N ₂ (g) Reaction formula (2)

Also disclosed is a method for obtaining tungsten hexafluoride from tungsten oxide molded with sodium fluoride as a molding aid and fluorine or nitrogen trifluoride (see Patent Documents 3 and 4). In the reaction formula (3), the standard heat of formation ΔH 298K _{, 1 atm} is −879 kJ / _WF6 mol, and in the reaction formula (4), the standard heat of formation ΔH298K _{, 1 atm} is −615 kJ / _WF6 mol.
WO ₃ (s) + 3F ₂ (g) → WF ₆ (g) + 3 / 2O ₂ (g) Reaction formula (3)
WO ₃ (s) + 2NF ₃ (g) → WF ₆ (g) +3/2 O ₂ (g) + N ₂ (g) ... Reaction formula (4)

JP-A-1-234301 JP-A-1-234303 JP-A-1-234302 JP-A-1-234304

However, when the present inventors reacted tungsten oxide with fluorine or nitrogen trifluoride, WOF ₄ was mainly obtained, and WF ₆ was hardly obtained. In order to produce a large amount of WF ₆ , it is necessary to make fluorine or nitrogen trifluoride excessive with respect to tungsten, the use efficiency of fluorine is poor, and the production amount of tungsten hexafluoride per reactor is increased. It was difficult.

  Also, the method of producing tungsten hexafluoride that proceeds in one step by solid-gas reaction using tungsten metal as a raw material is a solid-gas reaction that proceeds locally, so it is easy to store heat and it is difficult to increase the size of the reactor Thus, there is a problem that it is difficult to increase the production amount of tungsten hexafluoride per reactor.

  An object of the present invention is to provide a method for producing tungsten hexafluoride capable of increasing the production amount per reactor as compared with the conventional technique for obtaining tungsten hexafluoride from metallic tungsten in one step.

  As a result of intensive studies, the present inventors have adopted a two-stage reaction in which tungsten oxide is used as a raw material and tungsten hexafluoride is produced via tungstic oxyfluoride. It has been found that the reaction heat per one stage of the reaction is smaller than that of the method for producing tungsten, and the production method for tungsten hexafluoride according to the present invention has been completed.

Specifically, the reaction formula when tungsten oxide is reacted with fluorine gas to obtain tungsten hexafluoride via tungstic acid fluoride is as follows.
WO ₃ (s) + 3F ₂ (g) → WOF ₄ + O ₂ (g) Reaction formula (3-1)
WOF ₄ + 2F ₂ (g) → WF ₆ (g) + 1 / 2O ₂ (g) Reaction formula (3-2)
The reaction formula for obtaining tungsten hexafluoride via tungsten oxyfluoride by reacting tungsten oxide with nitrogen trifluoride gas is as follows.
WO ₃ (s) + 4 / 3NF ₃ (g) → WOF ₄ + O ₂ (g) + 2 / 3N ₂ (g) Reaction formula (4-1)
WOF ₄ + 2 / 3NF ₃ (g) → WF ₆ (g) + 1 / 2O ₂ (g) + 1 / 3N ₂ (g) ... Reaction formula (4-2)
The standard heats of formation ΔH 298K _{and 1 atm} of the reaction formula (3-1) and the reaction formula (3-2) are ₋₅₆₄ kJ / _{WOF 4} mol, −315 kJ / _{WF 6} mol, the reaction formula (4-1) and the reaction formula (4- The standard heats of formation ΔH 298K _{and 1 atm} of 2) are ₋₃₈₈ kJ / _{WOF 4} mol and −227 kJ / _{WF 6} mol, respectively.

  When the present inventors produce tungsten hexafluoride using tungsten oxide and a fluorine-containing gas as raw materials, the reaction per stage of the reaction is performed by using a tungstic acid fluoride as an intermediate and a two-stage reaction. It was noted that it was possible to reduce the heat.

  Specifically, each reaction heat according to the reaction formulas (3-1) and (3-2) using tungsten oxide and fluorine as raw materials is one third of the reaction formula (1) using tungsten and fluorine as raw materials. It is as follows. Each reaction heat of reaction formulas (4-1) and (4-2) using tungsten oxide and nitrogen trifluoride as raw materials is 3 minutes of reaction formula (2) using tungsten and nitrogen trifluoride as raw materials. 1 or less.

  That is, in the present invention, tungsten hexafluoride is obtained by contacting tungsten oxide with a fluorine-containing gas, and a first step of obtaining tungsten oxyfluoride by contacting the tungsten oxide with a fluorine-containing gas. A method for producing tungsten hexafluoride, comprising: a second step.

  According to the method for producing tungsten hexafluoride of the present invention, the heat of reaction per tungsten hexafluoride for each stage of the reaction can be reduced, and the production amount per reactor can be increased.

It is explanatory drawing which showed the reaction apparatus which concerns on embodiment.

  An embodiment of the method for producing tungsten hexafluoride according to the present invention will be described in detail with reference to FIG. However, the present invention is not limited to the embodiments described below.

[Reactor]
The reaction device 01 has a first reactor 15 for reacting a fluorine-containing gas and tungsten oxide, and a second reactor 17 for reacting the fluorine-containing gas and tungstic acid fluoride. The temperature of the reaction device 01 may be controlled by a heater and a cooler (not shown), and the heating and cooling method is not particularly limited. For example, water, steam, an electric heater, air, a hot refrigerant, or the like is selected. be able to. The first reactor 15 and the second reactor 17 preferably use water and steam and air and an electric heater in combination for removing heat of reaction and raising the temperature to the reaction start temperature. preferable. Moreover, the structure inside the 1st reactor 15 and the 2nd reactor 18 is not specifically limited, For example, you may provide a fin, an empty cylinder, and a filler.

  The material of the reactor is not particularly limited, and may be appropriately selected depending on the operating temperature. When the temperature exceeds 150 ° C., nickel and nickel-based alloys (monel, hastelloy, inconel) with high corrosion resistance are preferable, and the temperature is lower than 150 ° C. Stainless steel is preferred.

  In order to prevent precipitation and condensation by reducing the diffusion of reaction heat in the reactor and reducing the partial pressure of tungsten oxyfluoride and tungsten hexafluoride, an inert gas may be supplied from the inert gas supplier 12.

  The pressure of the gas phase in the first reactor 15, the second reactor 18, and the conduit during the reaction is preferably 10 kPa or more and 300 kPa or less, more preferably 30 kPa or more and 200 kPa or less in absolute pressure. If the pressure is less than 10 kPa, the load of incidental equipment for maintaining the pressure, for example, a decompression pump, is increased. When the pressure exceeds 300 kPa, the reactor must be structured to withstand pressure and corrosion.

<First reactor>
In the first reactor 15, the tungsten oxide filling portion 14 in which solid tungsten oxide supplied from the tungsten oxide supplier 13 is filled as a fixed layer and the fluorine-containing gas supplied from the fluorine-containing gas supplier 11 are in contact with each other. As a result, the reaction of reaction formula (3-1) or (4-1) proceeds to produce tungstic acid fluoride. The produced WOF ₄ flows into the second reactor 17 in a gaseous state.

  The reaction in the first reactor 15 can be carried out by a continuous method, a semi-batch method, or a batch method depending on the supply method of the tungsten oxide supplier 13 and the fluorine-containing gas supplier 11. The continuous type is a method for continuously supplying tungsten oxide and fluorine-containing gas, the semi-batch type is for supplying tungsten oxide intermittently while the semi-batch type is for intermittently supplying tungsten oxide, and the batch type is for In this method, tungsten oxide and fluorine-containing gas are supplied intermittently. In the case of the continuous type, there is a risk of clogging between the tungsten oxide supplier 11 and the first reactor 15 when supplying solid tungsten oxide. In the case of the batch type, intermittent supply of gaseous fluorine-containing gas reduces the production amount per unit time. The reaction in the first reactor 15 is preferably a semi-batch type.

  The conversion rate of the fluorine-containing gas which is the ratio used for the reaction with tungsten oxide in the introduced fluorine-containing gas in the first reactor 15 is not particularly limited, but the conversion rate is 80% or more, more preferably conversion. The rate is preferably 98% or more. When the conversion rate is less than 80%, the fluorine-containing gas becomes excessive. Therefore, it is possible to increase the proportion of tungsten hexafluoride at the outlet of the first reactor 15, but the conversion rate depends on the remaining amount of tungsten oxide. It is difficult to stabilize the operation because of the change, unreacted tungstic fluoride may be deposited in the reactor, and the total flow rate increases due to the unreacted fluorine-containing gas, increasing the burden on the second reactor. There is a fear. In particular, since it affects the flow rate of tungstic acid fluoride flowing into the second reactor 17, the reaction in the first reactor 15 needs to be stable. For example, a conversion rate of 98% or more is preferable.

  The temperature of the first reactor 15 is determined by the process pressure, the heat exchange method, and the material of the reactor, and is not particularly limited, but the temperature at the start of the reaction is preferably 50 ° C. or higher and 400 ° C. or lower. . If the temperature is lower than 50 ° C., the reaction may not proceed. If the temperature exceeds 400 ° C., when the reaction starts, the increase in the reactor temperature cannot be stopped and the reactor may be damaged. The temperature when the reaction is stabilized is preferably 80 ° C. or higher and 400 ° C. or lower, particularly preferably 100 ° C. or higher and 350 ° C. or lower. If it is less than 80 ° C., the produced tungstic acid fluoride may be deposited in the first reactor 15 and clogged. At temperatures above 400 ° C, the reactor may be damaged.

  The heat exchange method may be changed between when the reaction starts and when it is stable, for example, when the reaction starts, it may be heated with steam and an electric heater, and when the reaction is stable, it may be cooled with water and air.

In the first reactor 15, tungsten hexafluoride may be generated by the reaction formulas (3), (4), (3-2), and (4-2), but it is generated by the following reaction formula (5). All or most of the tungsten hexafluoride converted is converted to tungstic acid fluoride. The standard heat of formation ΔH 298K _{and 1 atm in the} reaction formula (5) are ₊₂₂ kJ / _{WOF 4} mol.
2WF ₆ + WO ₃ → 3WOF ₄ ... Reaction formula (5)

<Second reactor>
In the second reactor 17, the gaseous tungstic acid fluoride flowing from the first reactor 15, the fluorine-containing gas that was not consumed in the first reactor 15, and the fluorine-containing gas supplier 16 were supplied. By contacting the fluorine-containing gas, the reactions of the reaction formulas (3-2) and (4-2) proceed to generate tungsten hexafluoride.

When the fluorine-containing gas and tungstic acid fluoride are reacted in the second reactor 17, the form of tungstic acid fluoride (melting point 107 ° C., boiling point 186 ° C. in the case of WOF ₄ ) depends on the temperature and process pressure of the second reactor 17. Can be selected from solids, liquids, and gases. When the tungstic acid fluoride is a solid, the temperature for maintaining the solid state is lower than the temperature for the reaction, which is not preferable because the production amount per hour becomes small. When the tungstic acid fluoride is liquid, it is not preferable because temperature control for maintaining the liquid state is difficult. When the tungstic acid fluoride is a gas, it is preferable because air-gas mixing with the fluorine-containing gas is facilitated and the production amount per hour can be increased.

The fluid flowing into the second reactor 17 from the first reactor 15 is a fluorine-containing gas, a tungstic acid fluoride which is a reaction product in the first reactor 15, oxygen, nitrogen (nitrogen trifluoride as a fluorine-containing gas). And an inert gas.
The supply of the fluorine-containing gas to the second reactor 17 is determined by the supply method of tungsten oxide and fluorine-containing gas in the first reactor 15. When tungsten oxide and raw materials are supplied in the first reactor 15 in a continuous and semi-batch manner, the temperature of the second reactor is preferably 80 ° C. or higher and 400 ° C. or lower, particularly 100 ° C. or higher and 350 ° C. or lower. preferable. If it is less than 80 ° C., the reaction rate between the tungstic acid fluoride and the fluorine-containing gas may decrease, and the amount of tungsten hexafluoride produced per unit time may be small, and the inflowed tungstic acid fluoride may precipitate and condense. There is. If the reaction temperature exceeds 400 ° C, the reactor may be damaged.

  The flow rate of the fluorine-containing gas introduced into the second reactor 17 is determined by the flow rate of the tungstic acid fluoride flowing from the first reactor 15, and is not particularly limited. Less than 3 is preferred. When the reaction equivalence ratio is less than 1, tungsten hexafluoride can be produced, but it is not preferable because unreacted tungsten oxyfluoride may be precipitated in the subsequent stage of the second reactor. A reaction equivalence ratio of less than 3 is not preferable because the equipment for reusing unreacted fluorine-containing gas is enlarged.

[Materials used for reaction]
Examples of the inert gas supplied from the inert gas supplier 12 include gases that do not react with fluorine, nitrogen trifluoride, tungsten oxide, tungsten oxyfluoride, and tungsten hexafluoride, such as nitrogen gas, argon gas, and helium gas. And oxygen gas. Nitrogen gas that is easily available is preferable.
As the fluorine-containing gas supplied from the fluorine-containing gas supply devices 11 and 16, fluorine gas, nitrogen trifluoride gas, or a mixed gas thereof, or a gas obtained by diluting these gases with an inert gas can be used. . The purity of the fluorine-containing gas is preferably 95% or more in consideration of collection of reaction products and separation of impurities.

Tungsten oxide supplied from the tungsten oxide supplier 13 is preferably YTO (Yellow Tungsten Oxide) or BTO (Blue Tungsten Oxide) composed of WO _x (x = 2 to 4). The purity of tungsten oxide is not particularly limited, but it is preferably 95% or more, more preferably 99% or more in consideration of collection of reaction products and separation of impurities. The shape of tungsten oxide is not particularly limited, and a powder and a powdered powder can be used.

  In the method for producing tungsten hexafluoride according to the present invention, the reaction of converting tungsten oxide into tungsten oxyfluoride in the first reactor is a solid-gas reaction, but the reaction heat is higher than the reaction of converting metal tungsten into tungsten hexafluoride. Therefore, the reactor can be easily cooled, and overheating of the solid raw material can be prevented.

  In the method for producing tungsten hexafluoride according to the present invention, the reaction for converting tungsten oxyfluoride to tungsten hexafluoride in the second reactor requires less reaction heat than the reaction for converting tungsten metal to tungsten hexafluoride. In addition to easy cooling of the reactor, particularly when performing an air-gas reaction in which tungsten oxyfluoride is reacted with gas in the second reactor, the cooling rate is particularly easy and the reaction rate can be increased. .

  As described above, the method for producing tungsten hexafluoride according to the present invention makes it easier to increase the size of the reactor than the reaction in which tungsten metal is converted to tungsten hexafluoride, and the production amount per reactor can be increased.

  The method for producing tungsten hexafluoride according to the present invention will be described with reference to specific examples. However, the method for producing tungsten hexafluoride according to the present invention is not limited to the following examples.

Example 1
As shown in FIG. 1, a Ni-made first reactor 15 having an inner diameter of 28.4 mm and a length of 500 mm is filled with 500 g of tungsten oxide (YTO) by weight from a tungsten oxide supplier 13, and an electric heater (not shown) is used. Heated to 180 ° C. A second Ni reactor 17 having an inner diameter of 28.4 mm and a length of 500 mm was heated to 230 ° C. with an electric heater (not shown). Fluorine gas was introduced from the fluorine-containing gas supply 11 to 1.2 SLM (volume flow rate L / min at 0 ° C., 1 atm), and fluorine gas was introduced from the fluorine-containing gas supply 16 to 0.66 SLM, and the process pressure was absolute. Holding at 50 kPa, fluorine gas and tungsten oxide, and fluorine gas and tungstic acid fluoride were reacted.

  As a result of extracting a part of the latter stage gas of the first reactor 15 and analyzing the concentration of the fluorine gas with an ultraviolet spectrophotometer, the conversion rate of the fluorine gas is 99% or more, and the tungstic acid fluoride in the second reactor 17 is obtained. The reaction equivalent ratio of fluorine gas to the fluoride was 1.1. As a result of extracting a part of the gas after the second reactor 17 and analyzing the concentration of tungsten hexafluoride with an infrared spectrophotometer, the conversion rate of tungstic acid fluoride in the second reactor 17 was 99% or more. It was. The calorific values based on the standard conditions (25 ° C., 1 atm) in the first reactor and the second reactor are 252 W and 141 W, respectively, but the temperature of each reactor remains constant and stable for 60 minutes. Thus, tungsten hexafluoride could be produced at 0.6 SLM.

Example 2
Nitrogen trifluoride gas and tungsten oxide, and nitrogen trifluoride gas and tungsten as in Example 1, except that the nitrogen trifluoride gas is changed to 0.8 SLM and 0.44 SLM from the fluorine-containing gas supplies 11 and 16, respectively. The acid fluoride was reacted.
As a result of extracting a part of the rear gas of the first reactor 15 and analyzing the concentration of nitrogen trifluoride gas with an infrared spectrophotometer, the conversion rate of nitrogen trifluoride gas is 99% or more, and the second reaction The reaction equivalent ratio of fluorine gas to tungstic acid fluoride in the vessel 17 was 1.1. As a result of extracting a part of the gas after the second reactor 17 and analyzing the concentration of tungsten hexafluoride with an infrared spectrophotometer, the conversion rate of tungstic acid fluoride in the second reactor 17 was 99% or more. It was. The calorific values based on the standard conditions (25 ° C., 1 atm) in the first reactor and the second reactor are 173 W and 101 W, respectively, but the temperature of each reactor remains constant and stable for 60 minutes. Thus, tungsten hexafluoride could be produced at 0.6 SLM.

Comparative Example 1
The total production amount of tungsten hexafluoride in Example 1 is 0.6 SLM, and the ratio of the total calorific value is 64% in the first reactor. Tungsten and fluorine were reacted so that the production amount of tungsten hexafluoride in the first reactor was 0.384 SLM, which is 64% of 0.6 SLM.
The first reactor 15 was charged with 400 g of metallic tungsten by weight, and 1.15 SLM of fluorine gas was introduced from the fluorine-containing gas supply device 11.
As a result of extracting each part of the latter stage gas of the first reactor 15 and analyzing the concentration of tungsten hexafluoride with an infrared spectrophotometer, the conversion rate of the fluorine gas was 99% or more. The calorific value based on the standard condition (25 ° C., 1 atm) in the first reactor is 493 W, but the temperature of the first reactor gradually increases with time, and particularly the temperature rise of the metallic tungsten as a raw material The production of tungsten hexafluoride was stopped because it was remarkable.

Comparative Example 2
The total production amount of tungsten hexafluoride in Example 2 is 0.6 SLM, and the ratio of the total calorific value is 63% in the first reactor. Tungsten and nitrogen trifluoride gas were reacted so that the production amount of tungsten hexafluoride in the first reactor was 0.378 SLM, which is 63% of 0.6 SLM.
The first reactor 15 was charged with 400 g of tungsten metal by weight, and 0.76 SLM of nitrogen trifluoride gas was introduced from the fluorine-containing gas supply 11.
As a result of extracting each part of the latter stage gas of the first reactor 15 and analyzing the concentration of tungsten hexafluoride with an infrared spectrophotometer, the conversion rate of the fluorine gas was 99% or more. The calorific value based on the standard condition (25 ° C., 1 atm) in the first reactor is 410 W, but the temperature of the first reactor gradually increases with time, and in particular, the temperature rise of the metallic tungsten as a raw material The production of tungsten hexafluoride was stopped because it was remarkable.

The production conditions and results for each example are shown in Table 1.
In Examples 1 and 2 of the present invention, tungsten hexafluoride could be stably produced, whereas in Comparative Examples 1 and 2 using the conventional technique, this corresponds to Examples 1 and 2 per reactor. When it was going to manufacture quantity, since the emitted-heat amount was large, manufacturing had to be stopped. In addition, when the first reactor of Comparative Examples 1 and 2 is operated with the same calorific value as the first reactor of Examples 1 and 2, the production amount of tungsten hexafluoride is 0.25 to 0.3 SLM. Therefore, even if the presence of the second reactor is taken into consideration, the production amount of tungsten hexafluoride per reactor is larger in Examples 1 and 2 than in Comparative Examples 1 and 2.

01 Reactor 11 Fluorine Gas Supply Unit 12 Inert Gas Supply Unit 13 Tungsten Oxide Supply Unit 14 Tungsten Oxide Filler 15 First Reactor 16 Fluorine-Containing Gas Supply Unit 17 Second Reactor 18 Exhaust Ports 21, 22, 23, 25 , 26 Valve

Claims (5)

A first step of obtaining tungsten oxyfluoride by contacting tungsten oxide with a fluorine-containing gas;
A second step of obtaining tungsten hexafluoride by contacting the tungstic acid fluoride with a fluorine-containing gas;
A process for producing tungsten hexafluoride, comprising: The fluorine-containing gas in the first step and the fluorine-containing gas in the second step are each independently a fluorine-containing gas selected from the group consisting of F ₂ gas and NF ₃ gas. Item 2. A method for producing tungsten hexafluoride according to Item 1.   The method for producing tungsten hexafluoride according to claim 1 or 2, wherein in the first step, the conversion rate of the fluorine-containing gas is 80% or more.   The method for producing tungsten hexafluoride according to any one of claims 1 to 3, wherein in the first step, the reaction temperature is 50 ° C or higher and 400 ° C or lower. 5. The method for producing tungsten hexafluoride according to claim 1, wherein, in the second step, the reaction temperature is 80 to 400 ° C. 5.

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