JPS5964510A - Purification of argon gas - Google Patents

Abstract

PURPOSE:To recover high-purity Ar gas in high recovery, by carrying out the adsorption and desorption of N2 gas from Ar gas containing N2 using zeolite as the adsorbent under specific condition. CONSTITUTION:Ar gas containing N2 is introduced into the adsorption column packed with zeolite, and N2 is selectively adsorbed at -70-0 deg.C. The flow of the Ar gas is stopped just before the N2-adsorbed zone reaches the outlet of the adsorption column. The column is heated and the gas existing in the column is expelled from the column. Thereafter, the desorption of N2 is carried out under reduced pressure at -50-+20 deg.C to regenerate the zeolite.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for adsorptive removal of impurities in argon gas.

Since argon gas is chemically inert, it is widely used along with nitrogen etc. as an atmosphere for chemical reactions.

Particularly in recent years, with the development of the semiconductor industry, high-purity 11)' argon has been produced in large quantities for use in the synthesis or processing atmosphere of high-purity crystalline silicon, and the demand for it has increased dramatically.

Argon gas is contained in air at about 0.9 vol%, and argon with a purity of 99% or more is usually obtained by passing this air through two to six stages of low vortex distillation. Since argon is about three times more expensive than nitrogen, recovery and reuse of used argon is necessary to improve economic efficiency. Used argon contains various impurities depending on its use. Contamination with moisture or carbon dioxide gas can be removed by adsorption using silica gel, zeolite, etc., or solidified and separated by low-temperature freezing. Further, oxygen in argon can be used to generate water on the deokine catalyst by hydrogen injection, and the generated water can be removed by the method described above.

In each of the above methods, the impurity concentration is 1 vol, 1 l.
Mixed phase is used as an industrial method to reduce TIT to 1 or less. Conventionally, when the impurity contained in argon is nitrogen, a removal method using a ~j temperature reaction with a titanium sponge has been used. According to this method, nitrogen 1 v o ]
Although it is possible to easily achieve a purification level of 800°C or higher, the efficiency of using titanium as a raw material is low due to reaction inhibition by the reaction product titanium nitride, and the cost of recovering argon is high. There are disadvantages such as a significant increase in

On the other hand, a method is known in which an adsorbent is used to remove nitrogen from gas. For example, Japanese Patent Publication No. 52-20959 describes a method for removing low concentration nitrogen from oxygen obtained from an air liquefaction separation device using natural mordenite or natural clinoptilolite. The publication states that impurities in argon, which is oxidized using an air liquefaction separation device and a crude argon rectification device, are
A method of adsorption removal using zeolite at 35 kg/Cm2G is disclosed.

Although these techniques suggest the possibility of nitrogen removal or argon purification using zeolite, the purity and recovery rate of the purified 4i1J residue obtained are not necessarily sufficient to recover high-purity argon at a relatively single point. cannot operate.

The present inventors have searched for a method to obtain a high purity argon gas with a high recovery rate, and have found that this can be achieved by combining a specific adsorbent and specific operating conditions.

The present invention not only removes nitrogen mixed into argon gas with a high capture rate (adsorption rate), but also relatively sufficiently suppresses the amount of argon gas discharged from the system, thereby removing argon with a high recovery rate. It can be recovered. Industrial waste adsorption operations are generally carried out in a continuous manner, and therefore, two or more adsorption towers are used, one of which is used for the adsorption process while the other is used for capacity recovery. This capacity reversal operation is called regeneration or detachment.

An adsorption column filled with an adsorbent that selectively adsorbs nitrogen in argon has a certain argon gas capacity under conditions of 3% strength, pressure, and stability. After treating a fixed amount of the supplied gas, the adsorption tower enters a regeneration process from the adsorption culm, where the 9 adsorbed elements are desorbed (de-'41F). This desorption method includes the heat reheating method in which the temperature is increased by heating, the reduced pressure desorption method in which the pressure is lowered, and the purge desorption method in which cleaning is performed with purified argon, etc. All of these methods are used to remove the residue that remains in the column immediately after the completion of one adsorption culm. Exhaust gas (hold up). This holdup is distributed within the adsorbent particles and in the voids filled with the adsorbent particles, and not only nitrogen but also argon coexists. The volume of voids between adsorbent particles is not necessarily constant depending on the shape and size of the particles and their distribution, but generally adsorption tower volume A'~
approximately 40-50% of the adsorption properties of the particles. Therefore, it is the argon adsorption characteristics of the filled adsorbent that determines the argon content in the gas discharged outside the system in the endogenous process.

From this point of view, as a result of careful consideration of the God's adsorbent and its operating conditions, the God's zeolites described below are brought into contact with nitrogen-containing argon gas at a relatively low temperature and near atmospheric pressure to be discharged from the adsorption system. It has been discovered that the argon content in the filtrate gas can be relatively lowered.

In other words, this method allows a high rate of recovery of alcones subjected to treatment.

The adsorbent used in the present invention, that is, the zeolite, is a type A, faujasite type 1 mordenite type zeolite.

These are processed and used by conventional methods such as molding, granulation, drying, firing, and hardening with or without the addition of a binder. The shape of particles suitable for the present invention is not particularly limited, and may be spherical, 9 cylindrical, or crushed shapes thereof. The size of the adsorbent particles used in the present invention is not particularly limited, but if only nitrogen adsorption is considered in the purification operation, culms with small particle diameters are preferred. However, since the gas to be treated and the adsorbent are usually brought into contact by flowing through a fixed bed, a practical lower limit is set for the particle size of the adsorbent so as not to cause an excessive pressure loss in the flow. The lower limit of the particle size suitable for real blood of the present invention is 0.1 mm.

It has been known for a long time that sodium constituting zeolite can undergo nine ion exchanges with other cations. In the present invention, when ion-exchanged zeolite is used in this manner, favorable results can be obtained in terms of purification processing capacity. The types of ions that exchange with sodium in zeolite are potassium, lithium, calcium, strontium, and magnesium.

Barium, cobalt, nickel, silver, copper, 1ilj
lead.

These include lead and cadmium. Ion exchange is performed by a conventional method such as contacting with a solution containing cations to be introduced. Ions that are particularly effective when introduced into A-type zeolite are calcium, strontium, and magnesium. Ions that are particularly effective when introduced into faujasite zeolites such as X-type and Y-type zeolites are potassium, barium, calcium, copper, and magnesium. Also, substances that are effective when introduced into mordenite-type zeolite are carunium and strontium.

A particularly preferred adsorbent in the present invention is mordenite-type zeolite. Mordenite type zeolite usually has a silica-aluminum ratio (S'10., /1203) of 10 to
30 and, like other zeolites, contains sodium ions in an ion-exchangeable form.

In the present invention, especially 5in2/A/20. 10-15,
As a cation building, Na, Oa2. Sr2
It is a mordenite-type zeolite containing However, H
H-mordenite in which 90% or more of Na ions have been exchanged with ions has a significantly low nitrogen adsorption capacity and is not preferred in the present invention.

The degree of contact between nitrogen-containing argon (referred to as raw gas) and the adsorbent, that is, the adsorption humidity, is 0°C or lower, preferably -20°C to -70°C.

When carrying out slight additive operations in the regeneration process, the required thermal energy to reach effective desorption each time is not excessive, and the ratio of the raw gas throughput to the hold-up is sufficiently large. The temperature ranges mentioned above are advantageous.

Contact between adsorbent and raw gas? , when the adsorption temperature is lower than the water temperature, the amount of nitrogen adsorption increases.At the same time, the amount of argon adsorption increases.The increase in the amount of nitrogen adsorption increases the amount of gas purification, and the increase in the amount of argon adsorption increases again. Increase the amount of argon discharged from the system during the depressurization process. Argon adsorption 4
'+' recovery rate in J product (purified gas amount f (7'') 7 times I17 rate = (refined scum (c) → - (system Goide, 11') is determined by the temperature of not only nitrogen adsorption but also argon adsorption. It must be evaluated based on dependence.

In order to cool the adsorbent and raw gas to a predetermined temperature and maintain the adsorption temperature, ordinary heat exchange methods can be applied, but Ifi
- When mordenite-type zeolite is used as an adsorbent, this material has a concentration of 0.5 Kcal/mTeHr・℃ (
J) Since it is thermal conductivity, it is necessary to flow a cooling gas through the adsorption column to cause convective heat transfer. Preferably, this gas is pure argon, but depending on the use of the purified argon gas, hydrogen gas or other noble gases may also be used. Since these gases including alkones are expensive, it is economical to circulate them by cooling them and pumping them in after they flow out of the column. In very special cases, it is also possible to directly introduce liquefied argon into the adsorption column. This method will be described later.

The fixed bed adsorption tower used for purification is regenerated after producing a predetermined amount of purified gas. In order to desorb nitrogen adsorbed on the adsorbent, operations such as heating, depressurization, washing, etc. can be applied. Particularly in the present invention, these silk combinations are effective.

After completing the adsorption step, the adsorption tower was heated.

As for the heating method, since the thermal conductivity of the packed adsorbent is low, convective heat transfer through gas circulation is appropriate. Historically, it has been a good idea to use residual gas in the column at the end of the adsorption process as circulating waste in order to maintain a high recovery rate. is valid. In any case, is the adsorption tower not heated during the regeneration process? It is necessary to make it 1μ. In order to save the required energy, it is important to control the raw temperature to a necessary and sufficient temperature level. In the present invention, the temperature required for nitrogen desorption is -50°C to +20°C.

/! Although higher desorption demands than this can be used, this is an unnecessary condition for adsorption purification of impurity nitrogen in argon. Based on the same idea, a lower adsorption temperature is advantageous for nitrogen adsorption, and the adsorption selectivity of nitrogen to argon is also higher, but the adsorption rate and desorption rate are sufficiently high, and the heating energy required in the regeneration process is There is a lower limit of lagoon dust, -70℃~0
℃ is a suitable range.

After reaching the outer edge of the adsorption tower, the gas inside the tower is depressurized. After the raw gas has been depressurized, it is discharged outside the tower using a vacuum pump or the like in a countercurrent direction to the other direction. After the internal pressure of the column reaches a target pressure below atmospheric pressure, it is maintained at the ultimate pressure for a predetermined period of time. During this period,
The purified argon gas may be passed through the tower in a countercurrent direction to the flow direction of the raw gas for cleaning, or only vacuum degassing may be continued.

Next, pressure is increased to return the pressure inside the column to approximately the same as the bonding gas flow pressure, and cooling is performed to reach the adsorption temperature. The gas used for this pressurization is ml of purified argon or a combination of some metal gases. In order to accelerate cooling, it is effective to circulate the introduced argon gas between the condenser and the adsorption tower without allowing it to remain in the adsorption tower. Internal pressurization is more suitable.

Raw gas supply, stop, temperature rise, depressurization, and purge of the above raw gas.

In order to perform the cooling and pressurization steps in sequence and to continuously apply purified argon, two or more adsorption columns are installed and used cyclically.

Furthermore, if six or more adsorption columns are provided, the time schedule should be arranged so that when at least one column is in the pressure reduction step, at least one other column is in the pressure increase step. Efficiency is improved by conserving energy while exchanging P9 between these two towers.

Examples are shown below to specifically explain the method of the present invention and its effects.

Example 1 A column with an inner diameter of 2.76 cm and a length of 150 cnL was packed with 1,5 mm diameter columnar particles (pellets) 5501 made of Na-type mordenite with a silica to alumina molar ratio of 10, and -
Cooled to 50°C. 1000V to this adsorption column 1.
Argon gas containing ppll of nitrogen (1 at
a, and allowed to flow out from the column outlet side (first distribution step). The inflow speed is 2.5 N/min! It is.

Composition analysis of the outflow gas was conducted at the outflow port. Raw gas supply was stopped when a nitrogen leak was detected. 1νsi,
After closing both ends of the force ram with valves, reduce the column temperature to -2
The temperature was raised to 0°C. The internal pressure of the adsorption column is 2.3 to 9/
(The pressure rose to z2G.) Next, the pressure inside the column was depressurized countercurrently toward the column inlet side.

The gas flow that flowed out from the column while the pressure was lowered to 1ata was 21°C and 8.11 at Iata. Furthermore, the pressure was reduced to 50 mvrHg using a vacuum pump. The suction gas from the column by the vacuum pump is 21°C91a.
, ta was 7.5, and d. Subsequently, while maintaining the internal pressure of the λ column at 50 mmH (:t), cylinder argon gas was passed from the empty outlet side in the same direction as during depressurization, and was allowed to flow out from the column inlet side.The amount of gas flowing out was 21°C and 1at.
It was 61 at a.

Next, while continuing to feed gas from the column outlet side, the valve on the column inlet side was closed, and the pressure inside the column was increased to 1 ata. During this time, the column temperature was returned to -50°C. After the temperature inside the column reached 150°C and 1 ataK, the raw gas was fed again at 1 a,ta from the column inlet side.

It was fed at a rate of 2,63 Nl/MIN and allowed to flow out from the column outlet side (second flow culm).

The composition of the effluent gas was analyzed at regular intervals, and raw gas feeding was continued until the nitrogen concentration in the effluent gas exceeded 11-. The raw gas volume fed was 1981 at 21°C, 1a, ta.
Met.

After organizing the results, we obtained the following excellent results.

Argon gas purity 1<99.9999 vol, % argon gas recovery rate 90.0% Example 2 The same procedure as in Example 1 was performed up to the first distribution step. Next, the gas inside the column was suctioned from the column inlet side using a vacuum pump while maintaining the column viewing angle at -50°C.

Ten minutes after the start of suction, the pressure inside the column fell below im+l (g), but vacuum suction was continued for another 50 minutes.Next, argon gas was introduced from the column outlet side, and the pressure inside the column was lowered to 1
The pressure was increased to ATA.

After confirming that the temperature inside the column was 1 a, ta, -50°C, a second circulation process was performed in which raw gas was introduced from the column inlet side for one month. The feeding conditions are the same as in Example 1: 1 a t a + 263 N l Δ correction N.

When the composition of the outflow gas was analyzed, leakage of 50 voLll-glue cable was observed 20 minutes after the start of raw gas flow.

Example 6 The procedure up to the first flow-tracing culm was carried out in exactly the same manner as in Example 1, and then the column vortex layer was valved to 0°C. At this time, the pressure inside the column is 5.9 kl? / cnL”G was shown.

Next, the gas in the column was extracted from the column inlet side in a self-current manner, and after reaching atmospheric pressure, the pressure was further reduced to 1 Hg using a vacuum pump. After stopping supply of raw gas, the total volume of gas extracted from the column was 21°C.

Ivy at 16.5/ at 1a, t, and a.

Next, argon gas not containing nitrogen was introduced from the column inner inlet side 1, and the column was cooled to -50°C to bring the inside of the column to -50°C and 1 ata. Then 1 ata.

Raw gas was introduced at 2,65 N7/MIN (second distribution step). As a result of analysis of the effluent gas, it was found that argon with a nitrogen content of less than 'r 1 vol, pI'' was obtained from the flow-tracing direct bond, and the concentration of 9 elements remained unchanged in the city where 220 nitric acid leaked out at 21°C and 1 ata. In other words, the gas purity was 99,9
999 vol.% of argon was recovered with an excellent result of 93%.

Example 4 The same operation as in Example 1 except that 1.5 mm diameter columnar particles made of mordenite in which 98% of the exchangeable sodium ions in sodium mordenite crystals with a silica to alumina molar ratio of 10 were replaced with calcium ions were used. The volume of purified argon obtained was 1901 (2
Nitrogen concentration in argon is 1 vo at 1°C, 1 ata)
l, ρ was below the wall plate.

The total volume of gas discharged in the regeneration process performed between the first flow mill and the second flow mill scale was 2001. That is, the argon recovery rate was 90%.

Example 5 550 g of 1,5-φ columnar particle layer pellets made of type A zeolite in which 80% of sodium ions were converted into 9 by calcium ions were packed into a column with an inner diameter of 2.76 CM and a length of 150 mm. , and cooled to -50'c.

Argon gas (original gas) containing 1000 vol, III"m of nitrogen was fed into this adsorption column at -50°C and 1 ata, and was allowed to flow out from the empty outlet side (first flow).
nj process. The inlet velocity is 2.5 N/min. Marine composition analysis of the outflow gas was performed at the outflow port using gas chromatography. The concentration of nitrogen in the flowing argon is 5 vol. Raw gas supply was stopped when this was detected.

After closing both ends of the adsorption column with valves, reduce the muddyness of the column to 12
The temperature rose to 0°C. Adsorption column internal pressure is 2.0 kg/c
It rose to m2G. Next, the internal pressure of the column became demineralized in a self-current manner toward the column inlet side. The gas band flowing out from the column while the pressure was lowered to 1 ata was 21°G, 1 at
It was 6.21 in a. Furthermore, 50i by vacuum pump
The pressure was reduced to mHg. The suction gas from the column by the vacuum pump was 5.01 at 21°C and 1 ata.

Subsequently, while maintaining the column internal pressure at 50 mmHg, cylinder argon gas was passed from the column outlet side in the same direction as when the pressure was reduced, and was allowed to flow out from the column inlet side 1. The effluent gas volume was 61 at 21°C and 1 ata. Next, while continuing to feed gas from the column outlet 0111, the valve on the column inlet side was closed, and the pressure inside the column was increased to 1 ata.

This first column was then cooled to -50°C.

After the temperature inside the column reaches -50°C and 1 ata, the raw gas is again heated to -50°G and 1at from the column inlet side.
a.

2.65 Nl/MT, N was introduced into the column [E (i
It was allowed to flow out from IIl (second distribution step). The composition of the effluent gas is analyzed at regular intervals and the nitrogen concentration in the effluent gas is 1.
Raw gas was continued to be fed until it passed the throat. The raw gas volume fed was 951 at 21° and 1 ata.

The results were summarized and the following excellent results were obtained.

Argon gas purity 99.9999vol. % Argon gas recovery rate 84.6% Example 6 The same procedure as in Example 5 was performed up to the first flow tracing process. Next, while maintaining the column temperature at -50° C., the gas inside the column was sucked from the column inlet side using a vacuum pump. One minute after the start of suction, the pressure inside the column became 1 mm and 13 g or less.

Vacuum suction was continued for an additional 50 minutes. Next, argon gas was introduced from the column outlet side to increase the column internal pressure to 1 ata. After the inside of the column reached 1 ata and -50°C,
A second circulation step was performed in which raw gas was again introduced from the column inlet side. The feeding conditions were the same as in Example 5: -50°C, 1
ata, 2.65 Nt/MIN.

An analysis of the composition of the outflow gas revealed that 50 vol, pFl of nitrogen leaked 7 minutes after the raw gas started flowing.

Example 7 After carrying out exactly the same procedure as in Example 5 up to the first distribution culm,
The column temperature was raised to 0°C. At this time, the pressure inside the column was 3.0 k! ? /Crn2G was shown. Next, the gas in the column was extracted countercurrently from the column inlet side, and after reaching atmospheric pressure, the pressure was reduced to 1+vI++) (g) using a vacuum pump.After the supply of raw gas was stopped, the gas was extracted from the column. The total volume of gas was IAO 7 at 21°C and Lata.

Next, argon gas that does not contain nitrogen is introduced from the column outlet side, and the inside of the column is cooled to 150°C.
The temperature was 0°C and 1ata. Then -50℃, 1 at
a. Gas was introduced at 2.65 Nl/kA (second distribution process). As a result of analyzing the outflow gas, argon with a nitrogen content of less than 1 vol and PI of 1 m was obtained immediately after the flow, and the nitrogen concentration remained unchanged until 751 outflow at 21° C. and 1 ata. i.e. gas purity 9'9
．． 9999 vow,% argon recovery rate 84.9
I was able to get a score that was 5% aided.

Example 8 75% of sodium ions in A'1llI zeolite
When the same operation as in Example 5 was carried out except that a 1.5 mm diameter beret made of A was replaced with strontium (Sr, Na) as the adsorbent, the volume of the trapped treetop H7 was 8.4. .8 l (21°C, 1at
In a), the nitrogen concentration in argon is 1 vol, 1) 1111
It was below.

The volume of gas discharged in the regeneration process performed between the first distribution process and the second distribution process is 21°0°1 ata
It was a good result with an argon recovery rate of 85%.

Example 9 Sodium x (sample A) as an adsorbent, potassium X (sample B) in which the sodium was exchanged with potassium ions, calcium )
, sodium Y (E material E), copper Y (specimen F) in which this sodium was exchanged with copper ions, and barium Y (sample G) in which the sodium was exchanged with barium ions were tested in the same manner as in Example 5. The results are listed in Table-1.

It can be seen that each adsorbent exhibits excellent performance in removing nitrogen from argon.

Examples 10-20 10001'1ll using the device used once a month in Example 1
Argon gas containing 1 liter of desired elements was heated to -19°C, Iata
, the nitrogen concentration in the effluent gas was analyzed by gas chromatography at the empty outlet, and the amount of gas that had flowed out was 1 ppm or higher. Converted to base adhesive amount (Nl/(9)
B, Ir when using each god zeolite shown in each leg-2
The capacity of the product was determined. The results are shown in Table-2.

Table-2 65-

Claims (1)

[Claims] An adsorption step in which argon gas containing nitrogen is introduced into an adsorption tower filled with zeolite, and nitrogen is selectively adsorbed in a temperature range of -70°C to 0°C. Immediately before reaching the nitrogen adsorption zone or the outlet of the adsorption tower, the flow of the gas is stopped, the adsorption tower is added, the gas inside the adsorption tower is discharged to the outside, and the pressure is below atmospheric pressure and -50 ℃～20℃
An argon gas purification method consisting of two desorption steps at a temperature range of . 2) Type A and forujazite type adsorbents. The method according to claim 1, wherein one or more types of mordenite type zeolite are used. 3) The exchangeable cations of zeolite are sodium, potassium, lithium, and calcium. Strontium, Magnesium, Barium. The method according to claim 1 or 2, wherein zeolite exchanged with one or more ions selected from the group consisting of cobalt, nickel, silver, copper, zinc, lead, and cadmium is used.