JPH06340405A - Method for removing halide in rare gas - Google Patents

Abstract

PURPOSE:To effectively remove a halide such as CF4 or SF6 from a rare gas such as krypton or xenon with a simple constitution. CONSTITUTION:Oxygen in a gaseous mixture is removed by extracting the gaseous mixture containing krypton, xenon and a halide from a krypton tower 10 and introducing to a deoxygenation tower 22. The halide contained in the remaining gas is made to react with calcium or magnesium to deposite as calcium halide or magnesium halide while heating the gas in a halide removing equipment 24. After that, the remaining gas is introduced into a separation tower 30 to rectify and high purity krypton and high purity xenon are refined.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for removing a halide from a rare gas such as krypton or xenon.

[0002]

2. Description of the Related Art Conventionally, air has been used as a raw material to purify and separate oxygen, nitrogen, argon and the like.
In addition to the above-mentioned argon, demands for other rare gases such as krypton and xenon are also increasing, and their production has been attempted. An example of the method will be described below.

A) Krypton / xenon concentration step (Fig. 4)
(See FIG. 4) In FIG. 4, krypton and xenon are concentrated in liquid oxygen at the bottom of the upper column 70 for rectification in the air separation device, and this bottom liquid is fed as a feed liquid to the middle of the first krypton column 72 through a condenser 71. Supplied.

The first krypton column 72 is a plate type rectification column which is divided into an upper part and a lower part, and a krypton-containing oxygen liquid is added to the top of the first krypton column from a part several stages above the bottom of the upper column 70. Is supplied as reflux liquid. And this first
The krypton concentrate is extracted from the reboiler 73 at the bottom of the krypton tower 72 and heated by air in the condenser 74. Here, the gasified component is returned to the central part of the first krypton column 72, and the remaining concentrated liquid is heated and gasified by the evaporator 75 and then stored in a gas holder (not shown).

This gas is boosted by the booster 76 to about 5-6 kgf /
After being compressed to cm ² G and heated to 650 ° C, heat exchanger 7
It is supplied to the first catalyst tower 78 using alumina oxide as a catalyst via 7. Here, the hydrocarbon component is catalytically burned, decomposed into carbon dioxide gas and water vapor, passes through the heat exchanger 78, and is then adsorbed and removed by the adsorption tower 81 filled with synthetic zeolite.

The remaining mixed gas is introduced into the reboiler of the second krypton column 82, which is a rectification column, as a heating source, and is cooled to about -130 ° C and then further cooled to -160 with liquid nitrogen.
It is cooled to 0 ° C. and is supplied in the liquid state to the middle part of the second krypton column 82. A concentrated mixture containing about 99% krypton and xenon is extracted from the bottom of the second krypton column 82.

B) Krypton / xenon separation / purification step (see FIG. 5) The concentrated mixture stored in the mixed solution storage tank 83 is heated by the heater 88 and then sent to the methane reaction tower 89 to remove residual hydrocarbons. Decomposed into carbon dioxide and water vapor. Furthermore, after cooling with the cooler 90, the oxygen content is removed as water by the catalytic combustion with addition of hydrogen in the deoxidizing tower 91 filled with the palladium catalyst. Through this process, krypton
The concentrations of impurities hydrocarbons and oxygen in the xenon mixture are reduced to acceptable values.

The krypton / xenon enriched gas thus obtained is introduced into the separation column 95 through the synthetic zeolite adsorption column 94, and the rectification here causes a low-boiling high-purity krypton liquid from the middle part. High-purity xenon liquid is extracted from the bottom. Each product is stored in the krypton storage tank 96 and the xenon storage tank 97, and then charged into the cylinder 99 through the heater 98.

[0009]

In the above method, a small amount of halide (CF ₄ , S
F _6, CCl _4, etc.). The content of these halides in the atmosphere is extremely small, but as the concentration increases due to the above-mentioned separation and purification, the content of halides in them also rises significantly, and finally in the product krypton and product xenon. Approximately several tens of ppm and several tens to several hundreds of pp
m will be included in the halide. On the other hand, the product krypton and the product xenon may require extremely high purity depending on the application, and in this case, removal of the above-mentioned halide is absolutely necessary.

However, halides such as CF ₄ and SF ₆ are chemically stable and their removal is difficult,
It is desired to develop a method for removing these with a simple configuration.

When rectification is used as the separation means,
Like CF _4, etc., a boiling point between CF (−155 ° C.) and xenon (−112 ° C.) (CF ₄ is −128).
It becomes difficult to remove the halide having (.degree. C.).

As a means for removing such a halide, JP-A-4-149010 discloses a method for removing a halide from a rare gas by bringing the rare gas into contact with a getter metal of calcium or magnesium. It is shown. According to this method, it is possible to remove the halide from the rare gas. In addition to this, a more efficient method of removing the halide or a method of removing the halide without using calcium or magnesium. Development is also desired.

In view of such circumstances, it is an object of the present invention to provide a method capable of efficiently removing a halide such as CF ₄ from a rare gas such as krypton or xenon with a simple structure.

[0014]

As a means for solving the above-mentioned problems, the present invention is to add at least one of calcium and magnesium to a mixture containing a rare gas and a halide to react with the above-mentioned halide, In the method of depositing at least one of calcium halide and magnesium halide, at least one of calcium and magnesium is added to a mixture containing krypton, xenon, and the above halide to react with the above halide, and calcium halide and halogenide are added. After depositing at least one of magnesium, the above krypton and xenon are purified and separated from the remaining mixture (Claim 1).

Further, in the method of adding at least one of calcium and magnesium to the mixture containing the rare gas and the halide and reacting with the halide to precipitate at least one of calcium halide and magnesium halide, It is more effective to carry out after deoxidizing the mixture in advance before the removing operation (claim 2).

Further, in a method of adding at least one of calcium and magnesium to the mixture containing the rare gas and the halide and reacting with the above halide to precipitate at least one of calcium halide and magnesium halide, this removal is performed. The operation is performed by heating the mixture to decompose the hydrocarbons in the mixture and then continuously performing the operation, whereby a more excellent effect as described below can be obtained (claim 3).

The present invention also provides a method for separating and removing a halide in a rectification column from a mixture containing krypton, xenon, and a halide having a boiling point higher than that of krypton and lower than that of xenon. Fractionation is performed by setting the column top temperature of the rectification column to a temperature lower than the boiling point of the halide and higher than the boiling point of krypton, and after extracting high-purity krypton from the column top, the column bottom of the rectification column The temperature is changed to a temperature higher than the boiling point of the halide and lower than the boiling point of the xenon to carry out rectification to extract high-purity xenon from the column bottom (claim 4).

The "halide" is not limited to the compound of halogen and other elements, and may be halogen gas such as fluorine gas or chlorine gas.

[0019]

According to the method of claim 1, first, calcium or magnesium is added to the mixture and reacted with a halide to precipitate and remove the halide as calcium halide or magnesium halide, and then to leave the remainder. Since the above-mentioned krypton and xenon are purified and separated from the mixture, unlike the method of removing the halide by adding calcium or magnesium to each of them after separating the krypton and xenon, a single halide removal step Can purify krypton and xenon.

In the method according to the second aspect, the mixture is pre-deoxidized before calcium or magnesium is added to the mixture to remove the halide.
Generation of calcium oxide or magnesium oxide during the addition of calcium or magnesium is suppressed or prevented, and the halide removal reaction, which is a calcium halide or magnesium halide formation reaction, is accelerated by that amount. That is, by preventing the above-mentioned oxidation of calcium and magnesium, it is possible to prevent the shortening of the life of these calcium and magnesium as a getter, and it is possible to reduce the addition amount of calcium and magnesium necessary for removing the halide per a certain amount. .

Further, the oxidation reaction of these calcium and magnesium is an exothermic reaction, and this heat generation changes the temperature condition. Therefore, preventing the oxidation reaction of these calcium and magnesium suppresses the change of the temperature condition. This leads to a corresponding increase in temperature control in the halide removal step.

Although heating is required to cause each of the above reactions, in the method according to claim 3, the mixture is heated to decompose hydrocarbons as impurities in the mixture, and then continuously. Since the halogen removal by the above reaction is carried out (that is, the temperature of the mixture is hardly lowered), after heating for the decomposition of the above hydrocarbons, the mixture is once returned to room temperature and then halogenated again. The total amount of heat required for heating is small as compared with the case of performing heating for removing a compound.

Further, like oxygen, hydrocarbon reacts with calcium and magnesium to produce calcium carbide and magnesium carbide, which affects the halide decomposition reaction (shortens the life of calcium and magnesium as a getter). Removal of hydrocarbons in advance leads to promotion of the above halide removal reaction.

According to the method of claim 4, first, the temperature at the top of the rectification column is lower than the boiling point of the halide and higher than the boiling point of krypton (that is, almost all the halide is in the bottom liquid). High-purity krypton can be obtained at the top of the column by carrying out rectification by setting the content temperature). After the extraction of the high-purity krypton, the bottom temperature of the rectification column is higher than the boiling point of the halide and lower than the boiling point of the xenon (that is, the temperature at which the bottom liquid contains almost no halide). By carrying out the rectification after changing to, the high purity xenon can be obtained at the bottom of the column. That is, both krypton and xenon can be purified by a single rectification column.

[0025]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described with reference to FIG. The krypton tower 10 shown in the figure is equivalent to the second krypton tower 82 shown in FIG. 4, and the steps up to the second krypton tower 82 are the same as the steps described above with reference to FIG. Therefore, the description thereof is omitted here.

In FIG. 1, oxygen containing about 600 to 2000 ppm of krypton and xenon is supplied to the krypton column 10, and the rectification in the krypton column 10 causes the bottom of the krypton column to have a purity of 99.9% or more. The xenon mixture is accumulated. About 1 to 1 of this mixed liquid
After being stored for 2 weeks, it is transferred to the next purification step via the evaporator 14.

In this refining step, first, the mixed gas is heated to about 300 ° C. or higher (preferably 400 ° C. to 500 ° C.) in the reaction tower 16, and the hydrocarbon component mainly containing methane is thermally decomposed.

Thereafter, the mixed gas is cooled by the cooler 18, and the carbon dioxide and water produced by the above decomposition are adsorbed and removed by the adsorption tower 20. The remaining mixed gas is the deoxidizer 22
And hydrogen gas is added thereto to carry out catalytic combustion, whereby the oxygen component in the gas is removed as water. After such deoxidation treatment, the mixed gas is introduced into the halide remover 24.

Calcium and magnesium are accommodated in the halide remover 24, and the mixed gas is introduced into the halide remover 24 and heated to a predetermined temperature to carry out a redox reaction. Occurs. For example, when CF ₄ and SF ₆ are contained as halides in the mixed gas, the following reaction occurs.

[0030]

## STR1 ## 2CF ₄ + 5Ca → CaC ₂ + 4CaF ₂ 2CF ₄ + 5Mg → MgC ₂ + 4MgF ₂ SF ₆ + 4Ca → CaS + 3CaF ₂ SF ₆ + 4Mg → MgS + 3MgF ₂ Since all reaction products in these reactions are deposited in the solid phase, this This realizes halide removal from the mixed gas. That is, in the halide remover 24, calcium or magnesium reacts as a reducing agent and plays a role equivalent to what is called a getter.

The heating temperature for removing the halide is 600 ° C. when calcium (melting point 830 ° C.) is used.
To 750 ° C, and when magnesium (melting point 650 ° C) is used, it is preferably set to 500 ° C to 600 ° C.

After such removal, the remaining gas is cooled and liquefied by the cooler 26, collected in the tank 28, and then introduced into the reboiler 32 of the separation column 30 which is a rectification column. By performing a rectification operation in this separation column 30, krypton and xenon are separated, and high-purity krypton is extracted from the middle part of the separation column 30 and high-purity xenon is extracted from the bottom of the separation column 30, respectively. They are stored in the tank 34 and the xenon liquid tank 36, respectively.

As described above, according to this method, the halide is surely removed with a simple structure in which calcium and magnesium are added to the mixed gas of krypton / xenon containing the halide to cause the reaction. can do. Further, the above reaction can be caused by heating to a relatively low temperature, and energy consumption is small.

Furthermore, in the method of this embodiment, oxygen in the mixed gas is removed in advance in the deoxidizing tower 20 and then reacted with calcium and magnesium, so that these calcium and magnesium react with oxygen. Generation of calcium oxide or magnesium oxide can be prevented or significantly suppressed, and the reaction of calcium halide or magnesium halide can be promoted by that much, and the efficiency of removing halides can be increased. Such a method is especially effective when the oxygen content in the mixed gas is high.

Specifically, if the deoxidizing step is not performed before the halide removing step, the following reaction occurs when calcium and magnesium are added, which wastes calcium and magnesium and thus the life as a getter thereof. May decrease.

[0036]

## STR00002 ## Ca + (1/2) O ₂ → CaO Mg + (1/2) O ₂ → MgO Moreover, since this reaction is an exothermic reaction, the temperature condition in the halide removal step is not satisfied due to the occurrence of this reaction. There is a possibility that the temperature will change deterministically and the temperature control will become difficult. Therefore, by performing the above deoxidation step in advance to prevent the occurrence of the reaction of (Chemical Formula 2), it is possible to reduce the amount of calcium and magnesium required to remove a certain amount of halide, and to reduce the temperature in the step of removing halide It becomes possible to facilitate control.

If the hydrocarbon removing step is not performed before the halide removing step, the following reaction may occur when calcium and magnesium are added.

[0038]

## STR00003 ## Ca + C _n H _m → CaC ₂ + C _(n-2) H _m Mg + C _n H _m → MgC ₂ + C _(n-2) H _m However, in the method of this example, after removing hydrocarbons in advance, Since the halide removal process is being performed,
It is possible to prevent the generation reaction of calcium carbide or magnesium carbide as described above from occurring, and the amount of calcium or magnesium required to remove a certain amount of halide can be reduced accordingly.

Next, a second embodiment will be described with reference to FIG.

In this embodiment, a halide remover 24 is arranged immediately downstream of the reactor 16 in the first embodiment, and the hydrocarbon content is burned and removed by heating the mixed gas in the reactor 16. After that, the halide removal reaction is continuously carried out as it is (that is, without cooling).

According to such a method, the mixed gas is introduced into the halide remover 24 in a state of being heated to about 400 to 500 ° C. in advance in the reactor 16, so that in the halide remover 24, For example, when calcium is used as a getter, the temperature of the mixed gas is 100 ° C to 350 ° C.
It is only necessary to increase it additionally. Therefore, the total amount of heat required for causing both reactions can be further reduced, and energy saving can be achieved, as compared with the method in which the decomposition reaction of the hydrocarbon component and the reaction of removing the halide are performed separately. it can.

Specifically, the amount of heat required to heat the mixture from room temperature to the temperature required for hydrocarbon decomposition (eg, 400 ° C.) is Q1 (kcal), and the temperature required for removing the halide from room temperature (eg, 700 ° C.). Assuming that the amount of heat required to heat up to Q2 (kcal) is (Q1 + Q2) (kca) in the method of heating for decomposition of hydrocarbons, returning the mixture to room temperature and then heating for halide removal again.
While the heat quantity of l) is required, according to the method of this embodiment, Q
It is possible to cause both reactions with a calorific value of 2 (kcal).

Further, since the hydrocarbon is removed before the step of removing the halide, it is possible to prevent the getter life from being shortened due to the reaction between the hydrocarbon and calcium or magnesium as in the first embodiment.

Next, a third embodiment will be described. In this embodiment, the halide remover 24 is omitted in the apparatus shown in FIG.
With the separation of xenon, the boiling point of krypton (−155
Halides having a boiling point between ° C.) and xenon boiling point (-112 ° C.), for example, CF ₄ (so that the removal of the boiling point -128 ° C.). Specifically, the following batch processing is performed.

I) First step: Fractionation is carried out by setting the bottom temperature of the separation column 30 to a temperature lower than the boiling point of the halide and higher than the boiling point of krypton. As a result, almost all of the halide is contained in the bottom liquid, so that high-purity krypton is extracted from the top of the column.

II) Second step: After the krypton extraction, the bottom temperature of the same separation column 30 is changed to a temperature higher than the boiling point of the halide and lower than the boiling point of the xenon to carry out rectification. As a result, almost no halide is contained in the bottom liquid, so that high-purity xenon is extracted from the bottom.

According to such a method, even if the krypton-xenon mixed gas contains a halide having a boiling point between the two, a single rectification is performed without using a plurality of rectification columns. The above halide can be easily removed in the tower.

The present invention is not limited to the above embodiments, and the following modes can be adopted as examples.

(1) In the first and second embodiments described above, the krypton and the xenon are separated after the halide is removed from the mixed gas. However, as shown in FIG. 3, the mixed gas is a halide. Separation tower 3 while containing
0, a krypton liquid tank 34 and a xenon liquid tank 36
Separation of krypton and xenon is also possible by separately removing the halide from the krypton solution and the xenon solution stored in the reactor by the halide remover 24. However, it is possible to purify both krypton and xenon by a single halide removal operation by carrying out the methods of the first and second embodiments.

(2) In the first and second embodiments,
The halide to be removed is not limited to the above-mentioned CF ₄ and SF ₆ , but may be a halogen gas such as F ₂ or Cl ₂ , a hydrogen halide such as HF or HCl, or NF _3.
And OF ₂ such as nitrogen halide and oxygen halide,
Other halogenated carbon such as CCl ₄ and CF ₃ , S
It is applicable to other sulfur halides such as F ₅ . Among them, the method of the third embodiment is a halide having a boiling point higher than that of krypton and lower than that of xenon,
That is, NF ₃ (boiling point −129 ° C.) and OF ₂ (boiling point −144.9)
℃) is effective in removing.

(3) Although both calcium and magnesium are used in the above-mentioned first and second embodiments, it is possible to remove the halide in either of them in the present invention.

[0052]

As described above, according to the present invention, the following effects can be obtained.

In each of the methods described in claims 1 to 3, by adding at least one of calcium and magnesium to a mixture of a rare gas and a halide and reacting the mixture, the halogen in the halide is converted into calcium halide or magnesium halide. The above halide can be effectively removed from the rare gas.

Moreover, in the method of claim 1, when separating both the krypton and the xenon from the mixture, first, calcium and magnesium are added to the mixture to remove the halide in the same manner as described above, and thereafter, Since the above krypton and xenon are purified and separated from the rest of the mixture, unlike the method of removing the halide by adding calcium or magnesium to each of them after separating the krypton and xenon, one time of the halide There is an effect that both the krypton and the xenon can be purified at a lower cost in the removal step.

Further, in the method according to claim 2, when the halide is removed, the mixture is previously deoxidized before the addition of the calcium or magnesium. Therefore, the calcium oxide at the time of the addition of the calcium or magnesium is By suppressing or preventing the formation of magnesium oxide and magnesium oxide, it is possible to prevent the shortening of the life of calcium and magnesium as a getter, and it is possible to accelerate the halide removal reaction that is the formation reaction of calcium halide and magnesium halide. As a result, it is possible to reduce the amount of calcium or magnesium required to remove a certain amount of halide. In addition, since the oxidation reaction of calcium and magnesium is an exothermic reaction, preventing this reaction has the effect of facilitating temperature control during halide removal.

In the method according to the third aspect, when the mixture contains a hydrocarbon component as an impurity, the mixture is first heated to decompose the hydrocarbon, and then continuously. Since the halide removal by the above reaction is carried out, when the decomposition reaction of the hydrocarbon and the halide removal reaction are carried out independently, that is, the temperature of the mixture is kept at room temperature after heating for the decomposition of the hydrocarbon. As compared with the case of returning to the same temperature and further heating for removing the halide, the total amount of heat required for heating can be further reduced, and energy saving can be achieved. Further, since the above-mentioned hydrocarbon reacts with calcium or magnesium to produce calcium carbide or magnesium carbide and shortens the life of calcium or magnesium as a getter, it is necessary to remove halide after removing this hydrocarbon from the mixture. As a result, it is possible to reduce the amount of calcium or magnesium required to remove a certain amount of halide.

According to the method of claim 4, rectification is carried out by setting the column top temperature of the rectification column to a temperature lower than the boiling point of the halide and higher than the boiling point of krypton to obtain high-purity krypton from the column top. After extraction, the bottom temperature of the rectification column is changed to a temperature higher than the boiling point of the halide and lower than the boiling point of the xenon to carry out rectification to extract high-purity xenon from the bottom. Therefore, even if the mixture contains a halide having a boiling point between the boiling point of krypton and the boiling point of xenon, it is possible to obtain a high purity while removing the above-mentioned halide with an inexpensive equipment consisting of a single rectification column. There is an effect that both krypton and high-purity xenon can be purified.

[Brief description of drawings]

FIG. 1 is a flow sheet showing a first embodiment of the present invention.

FIG. 2 is a flow sheet showing a second embodiment of the present invention.

FIG. 3 is a flow sheet showing a third embodiment of the present invention.

FIG. 4 is a flow sheet showing a krypton / xenon concentration step in a conventional krypton / xenon production method.

FIG. 5 is a flow sheet showing a krypton / xenon separation and purification step in the above method.

[Explanation of symbols]

 10 Krypton tower 16 Reaction tower 20 Adsorption tower 22 Deoxidation tower 24 Halide remover 30 Separation tower (rectification tower)

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Keiichi Ishiyama 1-3-18 Wakihamacho, Chuo-ku, Kobe City Kobe Steel, Ltd. Kobe Head Office (72) Inventor Takashi Oyama 1-3, Wakihamacho, Chuo-ku, Kobe No. 18 Kobe Steel, Ltd. Kobe Head Office (72) Inventor Satoshi Morimoto 1-33 Wakihamacho, Chuo-ku, Kobe City Kobe Steel Co., Ltd. Kobe Head Office

Claims (4)

[Claims] 1. A calcium halide, which is obtained by adding at least one of calcium and magnesium to a mixture containing a rare gas and a halide and reacting the mixture with the halide.
In the method for removing a halide in a rare gas for precipitating at least one of magnesium halides, krypton,
At least one of calcium and magnesium is added to a mixture containing xenon and the above halide to react with the above halide, and after depositing at least one of calcium halide and magnesium halide, the remaining mixture is subjected to the above krypton and xenon. And a method for removing a halide in a rare gas, characterized in that and are purified and separated. 2. A calcium halide, which is obtained by adding at least one of calcium and magnesium to a mixture containing a rare gas and a halide and reacting the mixture with the halide.
In the method of removing a halide in a rare gas for precipitating at least one of magnesium halides, a rare gas characterized in that the mixture is deoxidized in advance before adding at least one of magnesium and magnesium to the mixture. Method for removing halides inside. 3. A calcium halide, which is obtained by adding at least one of calcium and magnesium to a mixture containing a rare gas and a halide and reacting the mixture with the halide.
In the method of removing a halide in a rare gas for precipitating at least one of magnesium halides, the mixture is heated in advance to decompose hydrocarbons in the mixture, and subsequently, in succession thereto, calcium and magnesium are added to the mixture. At least one of the above is added to react with the above halide to precipitate at least one of calcium halide and magnesium halide, and a method for removing a halide in a rare gas. 4. A method for separating and removing the halide from a mixture containing krypton, xenon, and a halide having a boiling point higher than the boiling point of krypton and lower than the boiling point of xenon in a rectification column. The column top temperature of the column is set to a temperature lower than the boiling point of the halide and higher than the boiling point of krypton to carry out rectification, and after extracting high-purity krypton from the column top, the column bottom temperature of the rectification column is set. A method for removing a halide in a rare gas, characterized by changing the temperature to a temperature higher than the boiling point of the halide and lower than the boiling point of the xenon to carry out rectification to extract high-purity xenon from the column bottom.