KR100541978B1 - Electrolyzer For High Purity Nitrogen Trifluoride Production And Manufacturing Method Of Nitrogen Trifluoride - Google Patents

Abstract

The present invention relates to an electrolytic cell for producing high purity nitrogen trifluoride (NF ₃ ) and nitrogen trifluoride (NF ₃ ). Regarding the manufacturing method, the electrolytic cell of the present invention uses a Ni electrode and electrolysis in the molten salt NH ₄ F.HF or KF-NH ₄ F-HF system ① electrolyzer body, ② bottom surface coated with fluorine resin, ③ Separator plate coated with fluorine resin, ④ electrolyte, ⑤ Ni anode, ⑥ Ni cathode, ⑦ anode connecting rod, ⑧ cathode connecting rod, ⑨ generated NF ₃ outlet, H produced H ₂ outlet, ⑪ electrolyzer cover, ⑫ cooling tube It includes, and the production method of the present invention of NF ₃ produced by a molten salt electrolytic reaction in the electrolytic cell of the present invention, wt% ratio of HF to _{NH 4 F (HF / NH 4} F) is composed of 1.0 to 2.6 NF ₃ is produced by the electrolyte.

According to the present invention, the elapsed time of dehydration electrolysis, which is an economic factor of operation, was decreased and the NF ₃ generation efficiency was increased.

Nitrogen Trifluoride, Electrolyzer

Description

Electrolyzer For High Purity Nitrogen Trifluoride Production And Manufacturing Method Of Nitrogen Trifluoride}             

1 is a cross-sectional view of an electrolytic cell for producing NF ₃ of the present invention.

* Description of the symbols for the main parts of the drawings *

1: electrolytic cell body 2: bottom surface coated with fluorocarbon resin,

       3: separator plate coated with fluorine resin 4: electrolyte,

       5: Ni anode 6: Ni cathode,

       7: anode connecting rod 8: cathode connecting rod,

9: generated NF ₃ outlet 10: generated H ₂ outlet,

      11 electrolytic cell cover 12 cooling tube

The present invention relates to an electrolytic cell for producing high purity nitrogen trifluoride (NF ₃ ) and nitrogen trifluoride (NF ₃ ). As, more particularly, to nitrogen trifluoride to reduce the dehydration electrolysis elapsed time of the boundary elements of the operation and the electron current efficiency and the NF ₃ production yield is increased (NF ₃₎ electrolytic bath and nitrogen trifluoride by preparative relates to a process for preparing (NF ₃₎ of It relates to a manufacturing method.

Recently, NF ₃ gas has been widely used as a dry etching agent for semiconductor manufacturing, as a fuel for cleaning CVD equipment, and as a propellant for rockets. The demand for NF ₃ has increased rapidly in recent years due to the activation of the semiconductor industry. The demand for NF ₃ is growing exponentially due to the increasing demand for the use of gas that is completely free of environmental problems, especially without causing warming.

As a manufacturing method, there are generally a method for direct fluorination reaction, a method using plasma, and a method for producing by electrolysis. Among these methods, molten salt electrolysis is suitable for high yield and mass production. Electrolyte to have the NH ₄ F and NH ₄ F-HF or KF-NH induced by the addition of KF in _{NH 4 F-HF 4 F-} HF or NH ₄ F-HF-LiF derived from HF can be used.

In NF ₃ gas production, NF ₃ and N ₂ gases are generated at the anode and H ₂ gas is generated at the cathode. That is, the gas generating reaction takes place simultaneously at the anode. The NF ₃ gas from the anode is mixed with the H ₂ gas from the cathode, which increases the likelihood of explosion, which requires an electrolytic cell design that improves mixing prevention and safety.

 In general, electrolytic cells are equipped with separator plates to separate the electrodes to reduce the possibility of explosion. In order to prevent corrosion of the separator and prevent the separator from functioning as an electrode, the separator is coated with fluorine resin.

Carbon and nickel electrodes are used as anode materials, and nickel electrodes are generally used as anodes to reduce the amount of CF ₄ . However, there is a problem that the nickel used is easily dissolved. Some of the dissolved nickel is deposited on the cathode.

In this case, the long distance operation decreases the distance between the cathode and the separator, and as a result, the gap between the cathode and the separator becomes narrow, which is close to the explosion limit due to the mixing of NF ₃ and H ₂ .

Very small NF ₃ bubbles generated in the nickel electrode do not rise vertically along the electrode, but diffuse upwardly at an angle. The amount of NF ₃ gas generated per cross-sectional area of the anode nickel electrode is increased, and the diffusion of NF ₃ causes the reaction of the cathode portion to be severe.

In addition, when nickel is used, NiF is deposited on the bottom of the electrolytic cell, and the distance between the electrode tip and the deposit becomes gradually closer. After the reaction proceeds, the electrode tip close to the bottom of the electrolytic cell is buried in NiF. The tip of the NiF-embedded electrode can no longer function as an electrode, resulting in an increase in current density, an increase in voltage in the electrolyzer, and a decrease in yield. In severe cases, there may be a short curcit or explosion.

Therefore, eliminating the heat of reaction generated between the two electrodes by electrolysis, keeping the temperature distribution of the electrolytic cell uniform, and maintaining the distance between the bottom and the electrode tip are very important factors for safe operation. Cooling the upper end of the electrolyzer while heating the lower end is preferred.

In molten salt electrolysis, the temperature of molten salt is preferably 100 to 130 ° C., because it is easy to operate, has good electrical conductivity, and has good electric current efficiency.

NH ₄ F-HF: when the molten salt temperature at (melting point 126 ℃) system is one 100~130 ℃, NH ₄ F-HF that is the ones adversely the deposition in the electrolytic bath temperature lower than the temperature of vaporization. As a result of operation, NH ₄ F-HF is deposited in the Lid of the electrolytic cell, which blocks the product gas outlet.

As a result, the difference in pressure between the anode chamber with NF ₃ and the cathode chamber with H ₂ and the cathode chamber with H ₂ will change the height of the electrolyte interface.

For example, if the outlet is blocked by the NF ₃ produced at the anode, the internal pressure rises because it cannot be discharged from the anode chamber. As a result, the interface of the electrolyte is pressed and the interface of the cathode chamber rises. In this case, when the pressure is increased and the interface is lower than the separator, NF ₃ is introduced into the cathode chamber.

As a result, NF ₃ and H ₂ are mixed to cause an explosion in the worst case. The present invention has been studied to solve this problem.

In the present invention, the electrolytic cell for producing NF ₃ by molten salt electrolysis is composed of an electrode, a separator, an electrolytic cell bottom, a solution surface, and Lid. The present invention sets the relationship therebetween to produce NF ₃ by molten salt electrolysis and The purpose of the present invention is to improve NF ₃ production rate by inducing local high temperature phenomena by preventing electrolytic cell explosion and controlling temperature caused by reaction by improving material design to improve electrolytic cell design and corrosion of separator.

The configuration of the electrolytic cell of the present invention, as shown in Figure 1,

1 electrolyzer body, 2 fluororesin-coated bottom, 3 fluororesin-coated separator, 4 electrolyte, 5 Ni anode, 6 Ni cathode, 7 anode connecting rod, 8 cathode connecting rod, 9 generated NF ₃ outlet, 10 generation H ₂ outlet, 11 electrolyzer cover, 12 cooling tubes.

In the electrolytic cell is configured as in the above production method of the present invention of NF ₃ produced by the molten salt electrolysis reaction, the electrolyte wt% ratio (HF / NH ₄ F) of HF to NH ₄ F is composed of 1.0 to 2.6 It is characterized by producing NF ₃ .

Hereinafter, the present invention will be described in detail.

Referring to the structure of the electrolytic cell of the present invention in detail, the height difference between the end of the electrode and the end of the separator plate is 200-2000mm, more preferably 500-800mm, the distance between the electrode end and the bottom of the electrolytic cell is 100-1000mm, More preferably, the distance between the electrolytic cell lid and the electrolyte interface, which is installed for the evaporation of the electrolyzer and the space configuration for collecting the generated gas, is 500 to 2000 mm, more preferably 500 to 1000 mm. It is possible to continuously maintain the optimum nitrogen trifluoride generation rate within a short time through the structure change between the electrodes in the electrolyte.

The bottom and the separator are made of fluorine resin to prevent corrosion. Examples of the material used may include polytetrafluoroethylen, polychlorotrifluorethylen, polyvinylidene fluoride, polyvinyl fluoride, tetrafluoroethylenehexafluoropropylene copolymer, tetrafluoroethylene ethylene copolymer, and the like. Polytetrafluoroethylen and tetrafluoroethylene-perfluoroalkly vinyl ether copolymers are mainly used because they have acid and heat resistance.

In this case, an electrode made of Ni is used. The electrolyte uses NH ₄ F-HF, and the composition ratio of the electrolyte in the NF ₃ electrolyzer is such that the wt% ratio of HF to NH ₄ F is 1.0 to 2.6. If the wt% ratio of HF exceeds 2.6, it will cause not only economic loss but also corrosion due to excessive HF content, whereas if it is less than 1.0, the formation efficiency of NF ₃ is increased due to the increase of viscosity and side reaction of electrolyte. This decreases.

When the temperature of the electrolytic bath to increase more than 130 ℃ side reactions because due to (the generation of N ₂₎ to fall, the efficiency, the operating temperature of the electrolytic cell is installed a thermal couple into the electrolytic bath and the electrode to enable operation at a temperature rise 100~130 ℃ In order to prevent a sudden temperature rise and maintain a constant temperature, a cooling tube is installed outside the upper part of the electrolyzer.

In order to analyze the gas generated after the reaction, gas chromatograph with TCD and DID detector was installed at the NF ₃ outlet side of the anode and H ₂ outlet side of the cathode, whereby Enable analysis. IR allows observation of the presence of CF ₄ .

First, before performing this reaction, the electrolytic cell is hygroscopic, so dehydration electrolysis is performed at low current. 50A flows at low current and the average current density is 2A / dm ² for 200 hours to operate this reaction. The electrolytic reaction was performed at 250A with an average current density of 10A / dm ² for 4000 hours to analyze H ₂ and NF ₃ and other by-products.

An embodiment of the present invention is as follows.

<Example>

The height difference between the tip of the electrode and the tip of the separator is 500mm, the distance between the tip of the electrode and the bottom of the electrolytic cell is 300mm, and the electrolytic cell cap and the electrolyte interface installed for space configuration for evaporation of the electrolytic cell and capture of generated gas. And the distance was produced electrolytic cell having a structure of 500mm.

The bottom surface and the separator were made of fluorine resin to prevent corrosion and the electrode was made of Ni material. The electrolyte used NH ₄ F-HF, the composition ratio of the electrolyte in the NF ₃ electrolytic cell was composed of HF wt% ratio of 2.0 to NH ₄ F, the operation temperature of the electrolytic cell and the electrode so that it can be operated at 100 ~ 130 ℃ Thermal couples were installed in the system to observe the temperature according to the conditions.

In order to analyze the gas generated after the reaction, gas chromatograph with TCD and DID detector was installed at the NF ₃ outlet side of the anode and H ₂ outlet side of the cathode, whereby The analysis was made possible.

Prior to carrying out this reaction, the electrolytic cell was hygroscopic and dehydration electrolysis was carried out at low current.

The dehydration electrolysis was terminated by flowing 40-50A at low current and operating for 200 hours at an average current density of 1-2A / dm ² when the concentration of O ₂ produced at the anode was kept constant at 2%. The electrolytic reaction was performed at 250 to 500 A with an average current density of 10 to 20 A / dm ² at 4000 hours for analysis of H ₂ , NF ₃ and other by-products. The results are shown in Table 1 below.

<Comparative Example 1>

In the same manner as in Example, the structure and dehydration electrolysis of the electrolytic cell were changed as shown in Table 1 below. The generation efficiency of NF ₃ was shown in Table 1 below.

<Comparative Example 2>

In the same manner as in Example, the structure and dehydration electrolysis of the electrolytic cell were changed as shown in Table 1 below. The generation efficiency of NF ₃ was shown in Table 1 below.

<Comparative Example 3>

In the same manner as in Example, the structure and dehydration electrolysis of the electrolytic cell were changed as shown in Table 1 below. The generation efficiency of NF ₃ was shown in Table 1 below.

Example Comparative Example 1 Comparative Example 2 Comparative Example 3 Cooling pipe operation status behavior Non-operational Separator end and electrode tip height (mm) 500 800 900 500 Distance between electrode tip and bottom of electrolyzer (mm) 300 100 300 300 Distance between electrolytic cell cap and electrolyte interface (mm) 500 500 250 250 dehydration electrolysis (hour) 200 250 300 250 NF ₃ generation efficiency (%) 45 40 35 30

From the results of the above Examples and Comparative Examples 1 to 3, it can be seen that when the size of the electrolytic cell becomes too large, the time required for dehydration electrolysis becomes longer and the efficiency decreases. On the contrary, if the distance is shorter than 300mm, the NF ₃ gas from the Ni anode diffuses at an angle and passes through the end of the separator to be mixed in the cathode, which increases the possibility of explosion.

In addition, it was found that there is a large difference in production efficiency depending on whether the cooling tube is running. In other words, by constantly removing / adjusting the heat generated in the outer and the inner of the electrolytic cell it was confirmed that the reactivity is greatly improved, the production rate of the desired material is higher.

In the present invention, the electrolytic cell for manufacturing NF ₃ by molten salt electrolysis is composed of an electrode, a separator, an electrolytic cell bottom, a solution surface, and an electrolytic cell cover, and a cooling tube is installed at the upper outer part of the electrolytic cell, and the relationship between them is established. Improvement of NF ₃ production by molten salt electrolysis and the design of electrolytic cell used in this process and the elapsed time of dehydration electrolysis, an economic factor of operation, were reduced and NF ₃ production efficiency was increased.

Claims (6)

In the molten salt NH ₄ F.HF or KF-NH ₄ F-HF system using Ni electrode and electrolysis, ① electrolyzer body, ② bottom surface coated with fluorine resin, ③ separator plate coated with fluorine resin, ④ electrolyte ⑤ Ni anode, ⑥ Ni cathode, ⑦ anode connecting rod, ⑧ cathode connecting rod, ⑨ generated NF ₃ outlet, 생성 produced H ₂ outlet, ⑪ electrolyzer cover, ⑫ cooling tube, In the molten salt NH ₄ F.HF system or KF-NH ₄ F-HF system, the height difference between the electrode tip and the bottom end of the separator plate is 200-1500mm, and the distance between the electrode tip and the bottom of the electrolytic cell is 100-1000mm. and an NF ₃ and H ₂ generated 500~2000mm distance between the lid and the electrolytic cell electrolyte interface is provided for a configuration space for collecting the gas produced in the, thereby containing the cooling pipe between the electrolytic cell body NF ₃ through the molten salt electrolysis reaction An electrolytic cell for producing nitrogen trifluoride (NF ₃ ), characterized in that the temperature of the electrolyte can be adjusted to 100 to 130 ° C. during the production reaction. delete delete The method of claim 1, wherein nitrogen trifluoride is characterized in that the NF ₃ with the electrolytic cell body is connected to the outlet H ₂ generated in the electrolytic cell comprises an upper distribution plate / the electrolytic cell bottom coated with a fluorine resin (NF ₃₎ for producing the electrolytic cell. delete The manufacture of NF ₃ by the molten salt electrolysis reaction in the electrolytic cell according to claim 1, for producing the NF ₃ as an electrolyte wt% ratio of HF to _{NH 4 F (HF / NH 4} F) it is composed of 1.0 to 2.6 Method for producing nitrogen trifluoride (NF ₃ ) characterized in that.

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