JP2585013B2 - How to purify xenon - Google Patents

Description

The present invention relates to a method for producing high-purity xenon in a very simple yield from crude xenon produced from liquid oxygen in a main condenser of an air separation unit. About.

BACKGROUND ART Xenon, which cannot be chemically synthesized, contains only a trace amount, but there is only a method of separating it from air.
It is co-produced and separated from krypton from the liquid oxygen in the main condenser of the upper rectification column of a large air separation unit.

Conventionally, hydrocarbons, especially methane, in liquid oxygen are concentrated with the concentration of krypton, and there is a risk of explosion. Therefore, various methods considering explosion protection have been proposed.

For example, a method in which the concentration of krypton and xenon is reduced to such a degree that hydrocarbons do not cause an explosion, and after burning and removing hydrocarbons with a catalyst, krypton and xenon are concentrated by rectification (Fuji Corporation) Techno System Technical Document 1986-2
-1, pp. 430-431), an argon replacement column was installed, where oxygen and argon were replaced, and then krypton and xenon were concentrated by rectification (JP-B-47-22937). Thereafter, there is a method of concentrating krypton and xenon by rectification (JP-A-57-95583).

The liquid oxygen derived from the main condenser of the upper rectification column of the air separation unit contains xenon in the order of tens of ppm, krypton and hydrocarbons, and when krypton and xenon are produced together, As krypton is concentrated, hydrocarbons such as methane are also concentrated.

Therefore, it was necessary to suppress the concentration of krypton and xenon, burn off hydrocarbons with a catalyst, or replace oxygen with argon or nitrogen.

In addition, the concentration of krypton and xenon is suppressed from the viewpoint of preventing the explosion of hydrocarbons, so that krypton,
To purify xenon requires a multi-stage rectification operation, which requires replacement of oxygen and argon or replacement of oxygen and high-pressure nitrogen, which increases equipment costs and reduces the total xenon yield to at most 60%. There was a problem of low degree.

Furthermore, in order to purify xenon by the conventional method, a cold source, a supply line thereof, and a rectification column are required, and there has been a problem that equipment costs and production costs are high.

Object of the Invention The present invention can produce high-purity xenon in extremely high yield from crude xenon produced from liquid oxygen in the main condenser of an air separation unit with simple equipment that does not require a cryogenic cold source. It aims at a method of purifying xenon.

SUMMARY OF THE INVENTION The present invention relates to a method for introducing crude xenon into an adsorption tower under a vacuum maintained at a predetermined adsorption temperature and, when the pressure of the adsorption tower becomes equal to or higher than the atmospheric pressure, a required amount of off-gas is supplied to the head of the adsorption tower. After blowing from, the temperature of the adsorption tower is gradually raised to a predetermined purge temperature slightly higher than the adsorption temperature, and a part of the high-purity xenon obtained earlier is introduced into the adsorption tower, whereby the gas phase in the tower, Purging impurities in the xenon non-adsorbed portion and the xenon adsorbed portion, recovering off gas at that time as crude xenon, then heating the adsorption tower to a predetermined desorption recovery temperature, and vacuum or low pressure suction to remove xenon A highly purified xenon method characterized by obtaining high-purity xenon by adsorption.

In the present invention, the reason for introducing xenon into an adsorption tower under vacuum and recovering xenon by vacuum or low pressure suction at the time of xenon recovery is that the temperature swing (TS
This is because, in addition to the effective adsorption amount obtained in A), the effective adsorption amount due to pressure swing (PSA) during adsorption and desorption is also obtained.

Therefore, since the effective adsorption amount increases, after collection,
Xenon remaining in the adsorption tower can be reduced, and in the next adsorption step, a regular adsorption band can be formed in the tower, and as a result, the separation characteristics can be improved.

After the adsorption step, the temperature of the adsorption tower is gradually raised to a predetermined purge temperature, a part of the high-purity xenon obtained earlier is introduced into the adsorption tower, and the inside of the tower is purged. By gradually raising the concentration of impurities in the adsorbent can be reduced by causing an adsorption and substitution phenomenon of xenon and impurities such as oxygen and krypton adsorbed on the adsorbent, and furthermore, a part of high-purity xenon Is introduced into the adsorption tower, and the inside of the tower is purged, whereby impurities in the gas phase part in the tower and the xenon non-adsorbed part can be exhausted to the outside of the adsorption tower, and the impurity concentration in the gas phase can be reduced. This is for desorbing some impurities adsorbed on the substrate and conversely adsorbing xenon.

Furthermore, the reason for purging the inside of the column and collecting the off-gas at that time as crude xenon is to minimize xenon released to the outside of the system and to improve the xenon yield.

Next, in the present invention, a phenomenon in which xenon is adsorbed and replaced with oxygen and krypton and other impurities adsorbed on the adsorbent by gradually increasing the temperature of the adsorption tower to the purge temperature will be described in detail.

First, crude xenon, for example, a gas having a purity of about 90% and containing oxygen and krypton as impurities is supplied to an adsorption tower filled with an adsorbent for selectively adsorbing xenon to the adsorption tower, and then a required amount of gas is supplied from the head of the adsorption tower. By blowing off gas and then gradually raising the temperature of the adsorption tower to the purge temperature, the adsorbed xenon and impurities are desorbed,
The xenon concentration in the gas phase increases. As a result, xenon is re-adsorbed and the xenon ratio in the adsorbent increases. Conversely, the impurity concentration in the gas phase becomes higher than before the temperature rise. Further, a gas amount commensurate with the decrease in the adsorption capacity due to the temperature rise is exhausted from the tower top together with the purge gas.

Further, in the present invention, after gradually raising the temperature of the adsorption tower to a predetermined purge temperature, a part of the high-purity xenon obtained earlier is introduced into the adsorption tower to purify the inside of the tower, After the adsorption step, the same effect can be obtained by simultaneously introducing the heated purge gas into the tower to raise the temperature of the adsorption tower to the purge temperature and simultaneously purging the inside of the tower with high-purity xenon. Can be

In the present invention, crude xenon is produced and refined by a conventional method such as the above-mentioned rectification method.In addition, xenon-containing liquid oxygen derived from the main condenser of the upper rectification column of the air separation device is converted to xenon. The xenon is sequentially concentrated by introducing and adsorbing and desorbing into a plurality of adsorption towers filled with an adsorbent that selectively adsorbs, and high-concentration xenon is obtained by burning off hydrocarbons with a catalyst to improve xenon purity. By using the method of producing xenon, xenon can be produced safely, with high purity, with high yield, and at low cost from xenon-containing liquid oxygen derived from the main condenser of the upper rectification column of the air separation device.

Further, in the present invention, the configuration of the adsorption tower is not limited to the configuration of the embodiment, but may be a configuration in which the adsorbent charged in the column can be controlled to a required temperature and brought into contact with crude xenon, and a vacuum or low pressure suction can be performed. Any configuration may be used, and silica gel, activated carbon, zeolite having a molecular sieve effect, or the like may be used as an adsorbent for selectively adsorbing xenon.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a circuit configuration diagram of an apparatus used in a purification method according to the present invention.

Here, a heat medium line for cooling and heating in the tower (2)
An example using an adsorption tower (1) having a configuration in which a winding tube is arranged and filled with activated carbon as an adsorbent is shown.

At the bottom of the adsorption tower (1), an introduction line (4) is provided so that crude xenon having a concentration of, for example, about 90% can be introduced from the crude xenon tank (3). The suction line (5) and the collection line (6) of the crude xenon tank (3) are connected.

Further, a purge line (8) from a highly purified xenon tank (7) containing highly purified xenon of the product is connected to the bottom of the adsorption tower (1), and a purification line (9) for recovering the highly purified xenon. Is connected.

In the apparatus having the above-described configuration, the purification method according to the present invention will be described. First, a refrigerant is passed through a heat medium line (2) of an adsorption tower (1) to, for example, 20 ° C. to −80
Cool to ° C.

Next, crude xenon is introduced into the adsorption tower (1) from the crude xenon tank (4), and further blown with a required amount of off-gas.

By returning the blow gas to a process for producing crude xenon or a process before that, the yield of xenon is improved.

Further, by purging the inside of the adsorption tower (1) with the highly purified xenon from the highly purified xenon tank (7) while gradually increasing the temperature of the adsorption tower (1) by, for example, 10 ° C., the adsorption tower (1) An adsorption displacement phenomenon in which the adsorbent is purged as well as the gaseous phase inside is obtained.

The off-gas at this time is recovered from the recovery line (6) to the crude xenon tank (3).

Next, a heat medium is passed through a heat medium line (2) of the adsorption tower (1), and the adsorbent is heated to, for example, 120 ° C. or less to desorb xenon, and recovered from the purification line (9). can get.

Advantageous Effects of Invention According to the high-purification method of the present invention, xenon can be highly purified at normal pressure and room temperature or in a low temperature range where xenon does not liquefy, and only in an adsorption tower. And the equipment is simple, the equipment cost is low and the production cost can be reduced.
High purity xenon of 99.99% or more can be manufactured.

Further, since the operating temperature and pressure are close to normal temperature and normal pressure, there is an advantage that so-called running cost and equipment cost for high purification can be reduced to about 1/3 of the conventional one.

EXAMPLE oxygen generation amount xenon containing upon withdrawal gasifying liquid oxygen 150 Nm ³ / Hr from the main condenser of the rectification column of the total low pressure air separation apparatus 15000 nm ³ / Hr is 31 ppm, krypton 70 ppm, methane Was 38 ppm and other hydrocarbons were very small.

After flowing the above gas through a silica gel packed adsorption tower cooled to -170 ° C until xenon breaks through, it is heated to 120 ° C and depressurized to 100 Torr, where xenon is 1.4%, krypton is 0.14%, and hydrocarbons are 0.066%. % Concentration. At this time, the concentration of hydrocarbons is below the explosion limit.

The concentrated gas is introduced into the catalyst tower, and water produced by removing hydrocarbons and carbon dioxide gas are removed by the removal tower.Then, the xenon gas is passed through the adsorption tower filled with silica gel at -150 ° C until xenon breaks through. After the mixture was heated to -100 ° C and discharged with a low xenon concentration from the outlet of the adsorption tower, the temperature was lowered to -100 ° C.
A part of the gas was flowed from the crude xenon tank to the adsorption tower, and after krypton and oxygen in the adsorption tower were purged, the mixture was heated to room temperature to collect xenon.

The thus obtained crude xenon having a concentration of 90% is subjected to 0 ° C.
, 700 l was introduced into an adsorption tower under a vacuum filled with activated carbon, and blown with 80 l of off-gas.

After that, air at 15 ° C was passed through the heating medium line (2),
The temperature of the adsorption tower was raised to 10 ° C. by heating at a rate of ° C./hr, 315 l of high-purity xenon was supplied to the adsorption tower and purged, and the off-gas at this time was collected in a crude xenon tank.

Next, the activated carbon was heated to 90 ° C, and 620 l of purified xenon was added.
Collected.

At this time, the pressure in the adsorption tower was 100 Torr, the purity of xenon obtained was 99.99% or more, and the yield was 98%.

[Brief description of the drawings]

FIG. 1 is a circuit configuration diagram of an apparatus used in the purification method according to the present invention. DESCRIPTION OF SYMBOLS 1 ... Adsorption tower, 2 ... Heat medium line, 3 ... Crude xenon tank, 4 ... Introduction line tower, 5 ... Suction line, 6 ...
… Recovery line, 7… Purified xenon tank, 8… Purge line, 9… Purification line.

Claims (1)

(57) [Claims] 1. Crude xenon is introduced into an adsorption tower under a vacuum maintained at a predetermined adsorption temperature, and when the pressure of the adsorption tower becomes higher than the atmospheric pressure, a required amount of off-gas is blown from the head of the adsorption tower. After that, the temperature of the adsorption tower is gradually raised to a predetermined purge temperature slightly higher than the adsorption temperature, and a part of the high-purity xenon obtained earlier is introduced into the adsorption tower, so that the gas phase in the tower and the xenon gas are removed. Purging impurities in the adsorption section and the xenon adsorption section, recovering off gas at that time as crude xenon, then heating the adsorption tower to a predetermined desorption recovery temperature, and vacuum or low pressure suction to desorb xenon A highly pure xenon purification method characterized by obtaining high-purity xenon.