JPH0678593B2 - Method for producing gas by molten salt electrolysis - Google Patents

Description

The present invention relates to a method for producing nitrogen trifluoride (NF ₃ ) gas or fluorine (F ₂ ) gas. More specifically, NF ₃ by the molten salt electrolysis method
The present invention relates to a method for producing gas or F ₂ gas.

[Problems to be Solved by Conventional Techniques and Inventions] When producing NF ₃ gas or F ₂ gas by a molten salt electrolysis method, NH ₄ F ・ xHF is usually electrolyzed in a heated and molten state to produce NF ₃
In general, a method for producing F ₂ and a method for producing F ₂ by electrolyzing KF · xHF in a heated and molten state. Such methods, using such electrolytic cell shown in FIG. 8 for example, lead to crude NF ₃ gas or crude F ₂ gas generated from the anode such as collecting device shown in Figure 7, NF ₃ or F ₂ It is manufactured by the method of liquefying and collecting.

That is, the anode 2 and the cathode 4 in the electrolytic cell are separated by the partition plate 6, and the space portion (vapor phase portion) constitutes the anode chamber 3 and the cathode chamber 5, respectively. The partition plate 6 is provided to prevent the mixing because the crude NF ₃ gas or the crude F ₂ gas generated from the anode 2 and the hydrogen (H ₂ ) gas generated from the cathode 4 cause an explosion. It is what

However, since the part of the partition plate 6 that is immersed in the electrolytic solution 7 does not conduct electricity from the anode 2 to the cathode 4, the electrode of this part does not function as an electrode. Therefore, in order not to reduce the current efficiency of the electrodes, it is desirable that the liquid immersion portion of the partition plate 6 is as small as possible, and normally this liquid immersion portion is carried out at about 30 to 100 mm.

Further, during electrolysis, an inert gas such as nitrogen (N ₂ ) gas or helium (He) gas is introduced as a carrier gas into the anode chamber 3 and the cathode chamber 5, respectively.

However, a pressure difference is often generated between the anode chamber 3 and the cathode chamber 5 during electrolysis, and due to this pressure difference, the electrolyte 7 has a difference in liquid level between the anode chamber 3 and the cathode chamber 5. Then, when the above-mentioned differential pressure becomes large, one of the liquid surfaces of the anode chamber 3 and the cathode chamber 5 comes to be positioned below the lowermost portion of the partition plate 6.

In such a state, the isolation between the anode chamber 3 and the cathode chamber 5 becomes insufficient, and the NF ₃ gas or F ₂ gas generated from the anode 2 and the H ₂ gas generated from the cathode 4 are mixed with each other to cause an explosion. Become. However, the liquid immersion part of the partition plate 6 is as described above.
It is as small as about 30 to 100 mm, so the anode chamber 3 and the cathode chamber 5
Even if the differential pressure of the column is a small differential pressure of about 60 to 200 mm of water column, NF ₃ gas or F ₂ gas and H ₂ gas are mixed, and there is a possibility of explosion.Therefore, the above differential pressure must be kept as small as possible. It doesn't happen.

Since the explosion limit of the NF ₃ gas or the mixed gas of the F ₂ gas and the H ₂ gas is very wide, the mixed gas of the both has a high possibility of explosion and is dangerous.

The cause of the differential pressure between the anode chamber 3 and the cathode chamber 5 may be various factors, but is considered to be due to the following reasons. That is, 1) The amount of gas generated from the anode 2 and the amount of gas generated from the cathode 4 are different.

2) The gas generated from the anode 2 is guided to the collecting device as described above, where NF ₃ or F ₂ is cooled and liquefied and collected, so that the amount of gas in this system is significantly reduced. Therefore, the pressure in the collector 21 is lowered, and as a result, the pressure in the anode chamber 3 is changed. 3) Further, since the collection container 21 is cooled by using liquid nitrogen or the like as the refrigerant 25, the liquefaction rate of NF ₃ or F ₂ changes due to the fluctuation of the refrigerant amount in the refrigerant container 24,
As a result, exert a pressure fluctuation on the anode chamber 3.

4) The gas generated from the cathode 4 is mainly composed of H ₂ gas, but since it contains hydrogen fluoride (HF), etc., the cathode generation gas outlet pipe 20 has a cleaning process for removing it (see the figure). Not). Therefore, the pressure fluctuation in the cleaning process affects the pressure in the cathode chamber 5. And so on.

As described above, the carrier gas is continuously introduced into the anode chamber 3 and the cathode chamber 5 during the electrolysis in order to prevent pressure fluctuations due to these. (The anode chamber 3 and the cathode chamber 5 are provided with pressure gauges 14a and 14c, respectively, and the amount of carrier gas to be introduced is controlled by the flowmeters 12a and 12c and the valves while monitoring the pressure.
It is adjusted with 9a and 9b. However, since the differential pressure between the anode chamber 3 and the cathode chamber 5 must be suppressed to an extremely small range as described above, the introduction of the carrier gas cannot prevent the explosion.

Therefore, as shown in FIG. 9, for example, a carrier gas anode chamber introducing pipe 10 is provided with an automatic pressure control valve 17 to automatically control the introduction amount of the carrier gas to suppress the differential pressure between the anode chamber 3 and the cathode chamber 5 as much as possible. The method of doing is also adopted. However, according to this method, the pressure in the anode chamber 3 and the pressure in the cathode chamber 5 are detected, converted into an electric signal and transmitted to the automatic pressure control unit 18, and the opening / closing degree of the automatic pressure control valve 17 is automatically adjusted. It is a method of adjusting. Therefore, satisfactory results are obtained in terms of a delay (time lag) in conversion of pressure fluctuations in the anode chamber 3 and the cathode chamber 5 into an electric signal, and lack of pressure detection accuracy in the anode chamber 3 and the cathode chamber 5. In reality, the explosion has not been completely prevented in the electrolytic cell.

[Means for Solving the Problems]

In view of the above situation, the present inventors have made extensive studies in the production of gas by the molten salt electrolysis method for the purpose of completely eliminating the explosion in the electrolytic cell, and as a result, a carrier to be introduced into the anode chamber and the cathode chamber. The present invention has been completed by finding that the above object can be achieved by branching the gas introduction pipe from a single valve.

That is, the present invention, in the production of gas by the molten salt electrolysis method, the anode chamber and the cathode chamber are singular or plural, and the carrier gas introduction pipe introduced into each of the anode chamber and the cathode chamber is branched from a single valve into a plurality. The branched carrier gas introduction pipes are connected to the gas phase portions of the anode chambers and the cathode chambers via check valves, respectively, and the carrier gas is supplied to and introduced into a single valve. The present invention provides a method for producing a gas by the molten salt electrolysis method.

[Detailed Disclosure of the Invention]

 Hereinafter, the present invention will be described in detail.

When NF ₃ gas is produced by the molten salt electrolysis method, a mixed gas of NF ₃ and N ₂ is generated from the anode of the electrolytic cell, and H ₂ gas is generated from the cathode. Further, in the case of producing F ₂ gas, F ₂ gas is generated from the anode of the electrolytic cell and H ₂ gas is generated from the cathode. Then, the mixed gas of NF ₃ and N ₂ or the F ₂ gas generated from the anode is cooled, and NF ₃ or F ₂ is liquefied or solidified and collected.

A liquefied gas is usually used for the cooling, but liquid nitrogen is preferable in the case of NF ₃ gas production, liquid nitrogen or liquid helium in the case of F ₂ gas production, or a mixture of liquid nitrogen and liquid helium. Liquefied gas is suitable.

Therefore, the carrier gas used in the present invention is selected from inert gases which do not liquefy or solidify at the temperature at which NF ₃ or F ₂ liquefies. As such a carrier gas, N ₂ gas or helium gas is used in the case of NF ₃ gas production, and helium gas is used in the case of F ₂ gas production.

Examples of the electrolytic cell used in the present invention include those having a shape shown in FIG. 1 or 3. 1 and 3 are front cross-sectional views of the electrolytic cell, and FIG. 2 is a plan view showing the arrangement of electrodes (anode and cathode) and partition plates, as viewed from the direction of arrows AA ′ in FIG. FIG. 4 is a plan view similar to FIG. 2, showing the arrangement of electrodes and partition plates in FIG.

The electrolytic cell shown in FIG. 1 is a basic type of electrolytic cell in which one anode 2 and one cathode 4 form a pair. The electrolytic cell shown in Fig. 3 has two anodes (2a and 2b) and four cathodes (4a and 4b) (2 sheets each).
2), which has a shape in which the electrolytic cells having the shape shown in FIG. 1 are horizontally connected in series, and a shape in which many pairs of electrodes are connected one after another is also possible.

Further, the electrodes and the partition plates may be arranged as shown in FIG. 5 or FIG.

In short, in the present invention, the carrier gas introducing pipes 10 and 11 are provided in the gas phase portions of the anode chamber 3 and the cathode chamber 5, respectively, and the carrier gas introducing pipes 10 and 11 are provided by a single valve 9. Each of the branched carrier gas introduction pipes 10 and 11 must be connected to the gas phase portion via a check valve 13 in a branched manner.

Therefore, there are two carrier gas introduction pipes in FIGS. 1 and 2, four in FIGS. 3 and 4, and two in FIG.
In the figure, three are required respectively. It is desirable that the branched carrier gas introduction pipes 10 and 11 have the same length and diameter.

In addition, it is preferable that a flow meter 12 is provided in each of the carrier gas introduction pipes 10 and 11. The flow meter 12 does not control from the outside, and the carrier gas quickly responds to the change in the liquid level of the anode chamber and the cathode chamber of the electrolytic cell through the single valve 9 due to the change in the pressure. To do. Therefore, the flow meter 12 is rather attached to monitor the process, and may be a flow indicator such as a flow monitor. The flow meter 12 is preferably of a type in which the pressure loss at the time of introducing the carrier gas is as small as possible, for example, a rotor meter or the like.

In the present invention, as described above, each carrier gas introduction pipe 10, 11 is provided with a check valve 13, respectively, which is provided when the amount of gas generated from any of the electrodes in the electrolytic cell increases sharply.
The rapidly increased gas is mixed with the gas generated from the other electrode through the carrier gas introduction pipe (NF ₃ gas or F ₂ gas which is the gas generated from the anode 2 and H ₂ gas which is the gas generated from the cathode 4). This is to prevent (mixing).

In the present invention, the carrier gas is supplied to the single valve 9 and introduced into each of the anode chamber 3 and the cathode chamber 5. When the carrier gas is taken out from the high pressure gas cylinder, the low pressure nitrogen taken out by the PSA method is used. Is used as a carrier gas or a low-pressure carrier gas after liquid nitrogen used as a refrigerant is vaporized. When the carrier gas is taken out of the high-pressure gas cylinder and used, it is dangerous to directly supply the high-pressure carrier gas to the single valve 9, and it is difficult to control the introduction amount of the carrier gas. A pressure regulator 8 is provided on the gas inlet side of the single valve 9 so that the pressure of the carrier gas is reduced to an appropriate pressure and supplied to the single valve 9. Therefore, when low-pressure nitrogen is used as the carrier gas, it is not necessary to provide the pressure regulator 8. The pressure of the carrier gas at this time is 1 to 5 kg / in the pressure on the secondary side of the pressure regulator 8.
A cm ² -G level is preferred.

In the present invention, the amount of carrier gas introduced varies depending on the size of the electrolytic cell, the amount of gas generated from the electrodes, etc.
It is carried out at 1 to 10 Nl / min for each anode chamber 3 and cathode chamber 5.

In the present invention, the electrolytic cell is used by connecting it with a collector as shown in FIG. 7 by means of an anode generated gas outlet pipe 19, but if molten salt electrolysis is performed in such a state, a single carrier gas valve 9 is used.
Since the carrier gas anode chamber introducing pipe 10 and the carrier gas cathode chamber introducing pipe 11 are further branched, they are introduced into the respective anode chambers 3 and the cathode chambers 5, so that the pressure difference between the conventional anode chambers 3 and the cathode chambers 5 is increased. Even if a factor is generated, the amount of carrier gas introduced automatically changes in response to this, so that the pressure in each anode chamber 3 and cathode chamber 5 is maintained at the same pressure, and a differential pressure is generated. Can be prevented.

〔Example〕

Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples.

Example 1 NF ₃ gas was produced by a molten salt electrolysis method by connecting the collector shown in FIG. 7 to the electrolytic cell shown in FIG.
The electrolytic cell body 1 has a width of 300 mm, a depth of 300 mm, a height of 300 mm, and the inner surface is Teflon-lined.
The partition plate 6 is also Teflon lining and the length from the top is 120 mm.
And

Acidic ammonium fluoride (NH ₄ F · HF) and hydrogen fluoride (HF) were charged into the above electrolytic cell so that the HF / NH ₄ molar ratio would be 1.7, and then the liquid surface up to 70 mm from the top. The temperature was raised to a temperature of ~ 125 ° C to form an NH ₄ F · HF-based electrolytic solution. Further, the collection container 24 was cooled using liquid nitrogen as a refrigerant.

After that, the pressure of 2 as carrier gas is applied to the single valve 9.
N ₂ gas of kg / cm ² -G was supplied at a flow rate of 1 Nl / min and introduced into the anode chamber 3 and the cathode chamber 5. In this state, the amount of N ₂ gas introduced into the anode chamber 3 is 450 Nml / min, and the amount introduced into the cathode chamber 5 is
The pressure was 550 Nml / min, the pressure inside the anode chamber 3 and the pressure inside the cathode chamber 5 were both 3 × 10 ⁻³ kg / cm ² -G, and there was no differential pressure.

In this state, a direct current of 50 ampere was passed from the anode 2 to the cathode 4 to carry out electrolysis for 50 hours.

About 70 Nml / min of NF ₃ gas and about 30 Nm from anode 2 by electrolysis.
l / min H ₂ gas is generated, and about 300 Nml / min H ₂ is emitted from the cathode 4.
₂ gas was generated. The amount of carrier gas introduced during electrolysis was 650 to 700 Nml / min into the anode chamber 3 and 300 to 350 Nml / min into the cathode chamber 5. The pressure in the anode chamber 3 is 4 × 10 ^{−3 to} 5 × 10 ⁻³ kg / cm ² −G, and the pressure in the cathode chamber 5 is 5 × 10 ^{−3 to} 6 × 10 ⁻³ kg / cm ³ −. It fluctuated in the range of G, and almost no differential pressure was generated.

Example 2 Using the apparatus used in Example 1, the molten salt electrolysis method was used.
F ₂ gas was produced. However, the electrolytic cell body 1 and the partition plate 6 were made of nickel.

HF / K of acidic potassium fluoride (KF ・ HF) and HF in the above electrolyzer
After the liquid surface was charged to 70 mm from the top so that the F molar ratio was 2.0, this was heated to a temperature of 90 to 100 ° C. to form a KF · HF electrolyte.

After that, the pressure of 2 as carrier gas is applied to the single valve 9.
Ne gas of kg / cm ² -G was supplied at a flow rate of ² Nl / min and introduced into the anode chamber 3 and the cathode chamber 5. In this state, the amount of He gas introduced into the anode chamber 3 is 900 Nml / min, and the amount introduced into the cathode chamber 5 is
The pressure in the anode chamber 3 and the cathode chamber 5 were both 4 × 10 ⁻³ kg / cm ² -G and there was no differential pressure.

In this state, a direct current of 30 amps was passed from the anode 2 to the cathode 4 to carry out electrolysis for 50 hours.

About 200 Nml / min of F ₃ gas is generated from the anode 2 by electrolysis,
About 220 Nml / min of H ₂ gas was generated from the cathode 4. The amount of carrier gas introduced during electrolysis is 850 in the anode chamber 3.
~ 1050 Nml / min, and cathode chamber 5 950 ~ 1150 Nml / min
Met. Moreover, the pressure in the anode chamber 3 is 3 × 10 ^{−3 to} 5 × 10 5.
^-3 kg / cm ² -G, the pressure in the cathode chamber 5 is 3 × 10 ^{-3 to} 5 × 10
It fluctuated within the range of ^-3 kg / cm ² -G, and almost no differential pressure occurred.

Comparative Example 1 NF ₃ gas was produced in the same manner as in Example 1 except that the method of introducing the carrier gas was changed as shown in FIG.

That is, N ₂ gas as a carrier gas is delivered to the anode chamber 3 by 450N.
The valve 9a is adjusted and introduced at a flow rate of ml / min, and 55 is introduced into the cathode chamber 5.
The valve 9b was adjusted and introduced at a flow rate of 0 Nml / min. The pressure in the anode chamber 3 and the cathode chamber 5 at this time are both 3 × 10 ^-3 kg / cm 2.
^{There was 2-} G and there was no differential pressure.

In this state, in the same manner as in Example 1, a direct current of 50 ampere was passed from the anode 2 to the cathode 4 to start electrolysis. After the electrolysis was started, the electrolysis was performed while adjusting the amount of carrier gas introduced into the anode chamber 3 so that a pressure difference between the pressure in the anode chamber 3 and the pressure in the cathode chamber 5 did not occur. After 10 minutes, the differential pressure became 7 × 10 ⁻³ , and there was a danger of explosion, so the electrolysis had to be stopped.

Comparative Example 2 NF ₃ gas was produced in the same manner as in Example 1 except that the method of introducing the carrier gas was changed as shown in FIG.

That is, 550 Nml of N ₂ gas as a carrier gas to the cathode chamber 5.
Adjust the valve 9b at a flow rate of / min to introduce a fixed amount, and operate the automatic pressure control unit 18 and adjust the automatic pressure control valve 17 so that the pressure in the anode chamber 3 becomes the same as the pressure in the cathode chamber 5. Then, N ₂ gas was introduced. In this state, the pressure in the anode chamber 3 and the pressure in the cathode chamber 5 were both 3 × 10 ⁻³ kg / cm ² -G.

In this state, in the same manner as in Example 1, a direct current of 50 ampere was passed from the anode 2 to the cathode 4 to start electrolysis. After the start of electrolysis, electrolysis was performed while automatically adjusting the amount of carrier gas introduced into the anode chamber 3 by the automatic pressure control unit 18 so that a pressure difference between the pressure in the anode chamber 3 and the pressure in the cathode chamber 5 did not occur. However, due to the time lag of the electric signal of the automatic pressure control unit 18, a differential pressure is generated, and the differential pressure becomes 7 × 10 ^-3 kg / cm ² -G about 2 hours after the start of electrolysis, and there is a danger of explosion. I had no choice but to stop electrolysis.

〔The invention's effect〕

As described in detail above, the present invention relates to the production of gas by a molten salt electrolysis method, and the introduction of carrier gas into each anode chamber and cathode chamber is performed from a carrier gas introducing pipe branched from a single valve into a plurality of branches. This is a very simple method of introducing into the respective anode chamber and cathode chamber. In the conventional method, a pressure difference is generated between the anode chamber and the cathode chamber, and as a result, the gas generated from the anode and the gas generated from the cathode are mixed, which causes a serious problem of causing an explosion during electrolysis. there were. On the other hand, if the method of the present invention is adopted, the problem of explosion during electrolysis can be completely solved. Especially, the amount of gas generated at the anode and cathode is different NF ₃
It is effective in molten salt electrolysis such as manufacturing.

Moreover, the method of the present invention is an extremely simple method as described above, and it is not necessary to use an automatic pressure control unit, an automatic pressure control valve, etc., which have been used to prevent differential pressure.

[Brief description of drawings]

1 and 3 are front cross-sectional views of an electrolytic cell used in the present invention, and FIG. 2 is an arrangement of electrodes (anode and cathode) and a partition plate taken along the line AA 'in FIG. FIG. 4 is a plan view similar to FIG. 2, showing the arrangement of electrodes and partition plates in FIG. 5 and 6 show another embodiment of the arrangement of electrodes and diaphragms, FIG.
It is a top view similar to FIG. And FIG. FIG. 7 is a diagram showing an example of an apparatus for collecting NF ₃ or F ₂ in crude NF ₃ gas or crude F ₂ gas generated from the anode of the electrolytic cell. FIG. 8 and FIG. 9 are front sectional views of a conventional electrolytic cell. In the figure, 1 ... Electrolyzer body, 2 ... Anode 3 ... Anode chamber, 4 ... Cathode 5 ... Cathode chamber, 6 ... Separator plate 7 ... Electrolyte solution, 8 ... Pressure regulator 9 ... Single valve, 9a, 9b …… Valve 10 …… Carrier gas anode chamber inlet pipe 11 …… Carrier gas cathode chamber inlet pipe 12 …… Flowmeter, 13 …… Check valve 14 …… Pressure gauge 17 …… Pressure Automatic control valve 18 …… Automatic pressure control unit 19 …… Anode generated gas outlet pipe 20 …… Cathode generated gas outlet pipe 21 …… Collection container, 22,23 …… Valve 24 …… Refrigerant container, 25 …… Refrigerant 26 …… Indicates an exhaust pipe.

Claims (1)

[Claims] 1. In the production of gas by a molten salt electrolysis method,
The number of the anode chamber and the cathode chamber is one or more, and the carrier gas introducing pipes to be introduced into each anode chamber and the cathode chamber are branched from a single valve into a plurality, and each branched carrier gas introducing pipe is passed through a check valve. A method for producing gas by a molten salt electrolysis method, which is connected to a gas phase portion of each of the anode chamber and the cathode chamber, and supplies the carrier gas by supplying it to a single valve.