JP2753189B2 - Method for purifying krypton and xenon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for purifying krypton and xenon from a mixture containing a halide.

[0002]

2. Description of the Related Art Conventionally, rectification and separation of oxygen, nitrogen, argon and the like have been carried out using air as a raw material.
In addition to the above-mentioned argon, demand for other rare gases such as krypton and xenon is also increasing, and production of such gases is being attempted. Hereinafter, an example of the method will be described.

A) Krypton / Xenon Concentration Step (See FIG. 4) In FIG. 4, krypton and xenon are concentrated in liquid oxygen at the bottom of an upper column 70 for rectification in an air separation device. The feed liquid is supplied to the center of the first krypton tower 72 through the feed 71.

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The krypton concentrate is withdrawn from the reboiler 73 at the bottom of the krypton tower 72 and is heated by air in the condenser 74.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

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

The remaining mixed gas is introduced as a heating source into a reboiler of the second krypton column 82, which is a rectification column, and after itself is cooled to about -130 ° C., it is further cooled to -160 ° C. by liquid nitrogen.
C., and supplied to the middle of the second krypton tower 82 in a liquid state. From the bottom of the second krypton tower 82, a concentrated mixture containing about 99% of krypton and xenon is extracted.

B) Krypton / Xenon Separation / Purification Step (Refer to FIG. 5) The concentrated mixture stored in the mixed liquid storage tank 83 is heated by a heater 88 and then sent to a methane reaction tower 89 to remove residual hydrocarbons. Decomposed into carbon dioxide and water vapor. Further, after cooling in the cooler 90, oxygen is removed as water by catalytic combustion in which hydrogen is added in a deoxidizing tower 91 filled with a palladium catalyst. Through these steps, 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 led to a separation column 95 through an adsorption column 94 made of synthetic zeolite, and by rectification, a high-purity krypton solution having a low boiling point is produced from the center. High purity xenon liquid is extracted from the bottom. Each product is stored in a krypton storage tank 96 and a xenon storage tank 97, respectively, and then charged into a cylinder 99 through a heater 98.

[0009]

In the above method, a small amount of a halide (CF ₄ , S
F ₆ , CCl _4, etc.). Although the content of these halides in the atmosphere is extremely small, as the concentration increases in the above-mentioned separation and purification, the content of the halide therein also increases significantly, and finally the krypton and xenon products Each have about 10 ppm, about 10 to several 100 pp
m will be included. On the other hand, the product krypton and the product xenon may be required to have extremely high purity depending on the use, and in this case, the halide must be removed.

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

When rectification is used as the separation means,
As in the case of CF ₄ or the like, the boiling point (CF ₄ is −128 ° C.) between the boiling point of krypton (−155 ° C.) and the boiling point of xenon (−112 ° C.).
C) is difficult to remove.

As a means for removing such a halide, Japanese Patent Laid-Open No. 4-149010 discloses a method for removing a halide from a rare gas by bringing the rare gas into contact with a getter metal such as calcium or magnesium. It is shown. According to this method, it is possible to remove the halide from the rare gas, but in addition to this, a method of removing the halide more efficiently or a method of removing the halide without using calcium or magnesium The development of is also desired.

[0013] In view of such circumstances, the present invention provides CF ₄
It is an object of the present invention to provide a method capable of efficiently purifying krypton and xenon from a mixture containing a halide such as krypton with a simple structure.

[0014]

As a means for solving the above problems, the present invention provides a method for purifying krypton and xenon from a mixture containing krypton, xenon, and a halide, the method comprising: At least one of calcium and magnesium is brought into contact with the halide to react with the halide, and the halide is precipitated and removed as calcium halide or magnesium halide.The remaining mixture is introduced into a rectification column to convert krypton and xenon. It is to be rectified and separated (claim 1).

In this method, it is more preferable that the mixture is subjected to a deoxidizing treatment before the halide removing operation (claim 2).

Further, the above-mentioned halide removing operation is carried out after heating the above-mentioned mixture to decompose the hydrocarbons in this mixture, and then performing the operation continuously, whereby a more excellent effect as described later can be obtained. (Claim 3).

The present invention also provides krypton and xenon by separating and removing 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. In the method of purifying, the rectification was performed by setting the 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 high-purity krypton was extracted from the top of the column. Thereafter, rectification is performed by changing the bottom temperature of the rectification column to a temperature higher than the boiling point of the halide and lower than the boiling point of xenon, thereby extracting high-purity xenon from the column bottom ( Claim 4).

The "halide" is not limited to a compound of a halogen and another element, but may be a halogen gas such as a fluorine gas or a chlorine gas.

[0019]

According to the method of the first aspect, first, calcium and magnesium are brought into contact with the mixture to react with the halide, thereby precipitating and removing the halide as calcium halide and magnesium halide, and then removing the remainder. Since the mixture of krypton and xenon is rectified and separated by introducing the mixture into a rectification column, unlike the method in which krypton and xenon are separated and then contacted with calcium or magnesium to remove halides, respectively. In a single halide removal step, krypton and xenon can be purified.

Further, in the method according to the second aspect, the mixture is previously deoxidized before contacting the mixture with calcium or magnesium to remove the halide, so that the mixture is oxidized at the time of contact with the calcium or magnesium. The generation of calcium and magnesium oxide is suppressed,
Or, it is prevented, and the removal reaction of halide, which is the reaction for producing calcium halide and magnesium halide, is accelerated accordingly. That is, by preventing the above-mentioned oxidation of calcium and magnesium, the life of these calcium and magnesium as a getter can be prevented from being shortened, and the amount of calcium and magnesium required for removing a certain amount of halide can be reduced.

The oxidation reaction of calcium and magnesium is an exothermic reaction, and the heat condition changes the temperature condition. Therefore, preventing the oxidation reaction of calcium and magnesium suppresses the change in the temperature condition. This leads to easier temperature control in the halide removal step.

In order to cause each of the above reactions to take place, heating is required. However, in the method according to the third aspect, the mixture is heated to decompose hydrocarbons as impurities in the mixture, and then continuously decomposed. (I.e., without substantially lowering the temperature of the mixture), the halide is removed by the above reaction. After heating for the decomposition of the hydrocarbon, the mixture is once returned to around normal temperature, and the halogen is removed again. The total amount of heat required for heating is smaller than in the case of performing heating for removing oxides.

Also, like oxygen, hydrocarbons react with calcium and magnesium to form calcium and magnesium carbides, which affect the halide decomposition reaction (shortening the life of calcium and magnesium as getters). Removal of the hydrocarbon in advance leads to promotion of the halide removal reaction.

According to the fourth aspect of the present invention, first, the top temperature of the rectification column is set to a temperature lower than the boiling point of the halide and higher than the boiling point of krypton (that is, almost all of the halide is contained in the bottom liquid). (Containing temperature), and high-purity krypton can be obtained at the top of the column by rectification. Then, 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 xenon (that is, the temperature at which the halide is hardly contained in the bottom liquid). By performing rectification by changing to, 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 FIG. 4 is equivalent to the second krypton tower 82 shown in FIG. 4, and the steps leading up to the second krypton tower 82 are the same as the steps described above with reference to FIG. Therefore, the description is omitted here.

In FIG. 1, krypton column 10 is supplied with oxygen containing about 600 to 2000 ppm of krypton and xenon. In the rectification in krypton column 10, the bottom of the krypton column having a purity of 99.9% or more is obtained. A xenon mixture accumulates. About 1 to about 1
After being stored for two 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 carbon dioxide and water generated by the decomposition are adsorbed and removed by the adsorption tower 20. The remaining mixed gas is supplied to the deoxidation tower 22
Where hydrogen gas is added and catalytic combustion is performed, whereby oxygen components in the gas are removed as water. After such a deoxidizing treatment, the mixed gas is introduced into the halide remover 24.

The halide remover 24 contains calcium and magnesium, and the mixed gas is introduced into the halide remover 24 and heated to a predetermined temperature, whereby the oxidation-reduction reaction is performed. Occurs. For example, when CF ₄ and SF ₆ are contained as a halide in the mixed gas, the following reaction occurs.

[0030]

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 the reaction products in these reactions are deposited in the solid phase, this is Thus, halide removal from the mixed gas is realized. That is, in the halide remover 24, calcium or magnesium reacts as a reducing agent and plays a role equivalent to a so-called getter.

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

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

As described above, in this method, a halide-containing krypton / xenon mixed gas is brought into contact with calcium and magnesium, and the halide is reliably removed with a simple structure that only causes a reaction. be able to. In addition, the above reaction can be caused by heating to a relatively low temperature, and energy consumption is low.

Further, in this embodiment method, since oxygen in the mixed gas is removed in advance in the deoxidizing tower 22 and then reacted with calcium and magnesium, these calcium and magnesium react with oxygen. The generation of calcium oxide and magnesium oxide can be prevented or largely suppressed, and the reaction of calcium halide and magnesium halide can be accelerated to thereby increase the halide removal efficiency. Such a method is particularly effective when the oxygen content in the mixed gas is large.

Specifically, if the deoxidizing step is not performed before the halide removing step, the following reaction occurs when calcium and magnesium come into contact with each other, so that calcium and magnesium are wasted and the life as a getter is lost. May be reduced.

[0036]

## STR2 ## _{Ca + (1/2) O 2 →} CaO Mg + (1/2) O 2 → MgO Moreover, since the reaction is an exothermic reaction, the temperature conditions in the halide-removing step is not selected by this reaction occurs It may change deterministically, making temperature control difficult. Therefore, by performing the deoxidation step in advance and preventing the occurrence of the reaction of (Chemical Formula 2), the amount of calcium and magnesium required for removing a certain amount of halide can be reduced, and the temperature in the halide removal step can be reduced. Control can be facilitated.

If the hydrocarbon removal step is not performed before the halide removal step, the following reaction may occur when calcium and magnesium come into contact.

[0038]

## STR3 ## _{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, later in this example method, performing the pre-hydrocarbon removal Since the halide removal process is performed,
It is possible to prevent the above-described generation reaction of calcium carbide and magnesium carbide from occurring, and accordingly, it is possible to reduce the amount of calcium and magnesium required for removing a certain amount of halide.

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

In this embodiment, the halide remover 24 is disposed immediately downstream of the reactor 16 in the first embodiment, and the reactor 16 burns and removes hydrocarbons by heating the mixed gas. Thereafter, the halide removal reaction is continuously performed (that is, without cooling).

According to such a method, the mixed gas is introduced into the halide remover 24 while being heated to about 400 to 500 ° C. in the reactor 16 in advance. For example, when calcium is used as a getter, the temperature of the mixed gas is further increased by 100 ° C. to 350 ° C.
The only thing we need to do is add extra. Therefore, the total amount of heat required to cause both the hydrocarbon decomposition reaction and the halide removal reaction can be further reduced as compared with the method in which the two reactions are separately performed, thereby achieving energy saving. it can.

Specifically, the amount of heat required to heat the mixture from room temperature to a temperature required for hydrocarbon decomposition (eg, 400 ° C.) is Q1 (kcal), and the mixture is heated from room temperature to a temperature required for removing halides (eg, 700 ° C.). Assuming that the amount of heat required for heating up to Q2 is k2 (kcal), in a method in which heating for hydrocarbon decomposition is performed, the mixture is once returned to normal temperature, and heating is performed again for halide removal, (Q1 + Q2) (kca)
l), the method according to this embodiment requires Q.
It is possible to cause both reactions with a calorific value of 2 (kcal).

Further, since the hydrocarbons are removed before the halide removing step, similarly to the first embodiment, it is possible to prevent the getter life from being shortened by the reaction between the hydrocarbons and calcium or magnesium.

Next, a third embodiment will be described. In this embodiment, in the apparatus shown in FIG. 1 described above, the halide remover 24 is omitted, and a single separation tower 30 is used.
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: The rectification is performed 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 the halide is contained in the bottom liquid, and high-purity krypton is extracted from the top of the tower.

II) Second step: After the krypton extraction, the rectification is performed by changing the bottom temperature of the same separation column 30 to a temperature higher than the boiling point of the halide and lower than the boiling point of xenon. Thereby, almost no halide is contained in the bottom liquid, and high-purity xenon is extracted from the bottom.

According to such a method, even if a krypton / xenon mixed gas contains a halide having a boiling point between both boiling points, a single rectification can be performed without using a plurality of rectification columns. The halide can be easily removed in a column.

In the first and second embodiments according to the present invention, krypton and xenon are separated after the halide is removed from the mixed gas. On the other hand, as shown in FIG. The mixed gas is introduced into the separation tower 30 in a state of containing the halide, and the halide remover 2 is individually separated from the krypton liquid and the xenon liquid stored in the krypton liquid tank 34 and the xenon liquid tank 36, respectively.
Although krypton and xenon can be separated by reacting and removing the halide in Step 4, the first and second kneads can be separated.
By carrying out the method of the example, it becomes possible to purify both krypton and xenon in one halide removal operation.

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 halogen gas such as F ₂ or Cl ₂ , H ₂
Hydrogen halides such as F and HCl, nitrogen halides and oxygen halides such as NF ₃ and OF ₂ , CCl ₄ ,
It is applicable to other halogenated carbons such as CF _{3 and} other sulfur halides such as SF ₅ . Among them, the method of the third embodiment is based on a halide higher than the boiling point of krypton and lower than the boiling point of xenon, that is, N 2
It is effective for removing F ₃ (boiling point −129 ° C.) and OF ₂ (boiling point −144.9 ° C.).

In the first and second embodiments, both calcium and magnesium are used, but in the present invention, any one of them can remove the halide.

[0051]

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

The method according to claim 1 is characterized in that krypton,
Xenon and a mixture containing a halide are contacted with calcium or magnesium to remove the halide, and then the remaining mixture is introduced into a rectification column to rectify and separate krypton and xenon. Unlike the method of separating krypton and xenon and then contacting calcium and magnesium with each other to remove halide, purification of both krypton and xenon can be performed at a lower cost in a single halide removal step. effective.

Further, in the method according to the second aspect, when the halide is removed, the mixture is pre-deoxidized before the contact with the calcium or magnesium. By suppressing or preventing the generation of calcium and magnesium oxide, it is possible to prevent a decrease in the life of the calcium and magnesium as a getter, and to promote a halide removal reaction which is a generation reaction of calcium halide and magnesium halide, Thereby, the amount of calcium and magnesium required for removing a certain amount of halide can be reduced. Moreover, since the oxidation reaction of calcium and magnesium is an exothermic reaction, by preventing this reaction beforehand, there is an effect that the temperature control at the time of removing the halide can be more easily performed.

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 performed, when the hydrocarbon decomposition reaction and the halide removal reaction are each performed independently, that is, after heating for hydrocarbon decomposition, the temperature of the mixture is set to room temperature. And the like, and the total amount of heat required for heating can be further reduced as compared with the case of performing heating for removing halides. In addition, the hydrocarbons react with calcium and magnesium to produce calcium carbide and magnesium carbide, and to reduce the life of the calcium and magnesium as getters, it is necessary to remove halides after removing the hydrocarbons from the mixture. Thereby, the amount of calcium and magnesium required for removing a certain amount of halide can be reduced.

According to a fourth aspect of the present invention, the rectification is performed by setting the 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. After extraction, rectification is performed by changing the bottom temperature of the rectification column to a temperature higher than the boiling point of the halide and lower than the boiling point of xenon, and extracting high-purity xenon from the bottom. Therefore, even if the mixture contains a halide having a boiling point between the boiling points of krypton and xenon, the inexpensive equipment consisting of a single rectification column can be used to remove the halide and achieve high purity. There is an effect that both krypton and high-purity xenon can be purified.

[Brief description of the 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 an example different from the present invention.

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

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

[Explanation of symbols]

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

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Keiichi Ishiyama 1-3-18 Wakihamacho, Chuo-ku, Kobe Kobe Steel, Ltd. Kobe Head Office (72) Inventor Takashi Oyama 1-chome, Wakihamacho, Chuo-ku, Kobe-shi No. 3-18 Kobe Steel, Ltd.Kobe Head Office (72) Inventor Satoshi Morimoto 1-3-18 Wakihama-cho, Chuo-ku, Kobe Kobe Steel Co., Ltd.Kobe Head Office (56) References JP4 149010 (JP, A) JP-A-6-122508 (JP, A) JP-A-62-266381 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C01B 23/00

Claims (4)

(57) [Claims] 1. Krypton, xenon, and halogenated
Of krypton and xenon from mixtures containing waste
A method for calcium to the above mixture, is brought into contact with at least one of magnesium is reacted with the halide, calcium halide this halide
Or after precipitation and removal as magnesium halide,
Krypton and xenon, wherein the remaining mixture is introduced into a rectification column to rectify and separate krypton and xenon.
Non purification method. 2. Krypton and xenon according to claim 1.
In the purification method , krypton characterized in that the mixture is pre-deoxidized before contacting the mixture with at least one of calcium and magnesium.
Xenon purification method. 3. Krypton according to claim 1 or 2, and
In the method of purifying xenon, the mixture is heated in advance to decompose hydrocarbons in the mixture, and subsequently, the mixture is contacted with at least one of calcium and magnesium to react with the halide. ,
The halide is precipitated and removed as calcium halide or magnesium halide.
A method for purifying krypton and xenon. 4. Krypton and xenon are separated 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 rectifying column to remove krypton and xenon.
A method for purification, wherein rectification is performed by setting the 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 extracting high-purity krypton from the top of the column. Rectifying the bottom temperature of the rectification column to a temperature higher than the boiling point of the halide and lower than the boiling point of the xenon, and extracting high-purity xenon from the bottom. Of krypton and xenon
Purification method.