JPH0525801B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing high concentration argon by a pressure swing method using air as a raw material. Argon is known as an inert gas and is used for electrical products, welding, steel degassing, etc. Conventionally, argon is produced from air by cryogenic separation, but liquid air is rectified in a main rectification column in a liquid oxygen production plant, and the gas in the oxygen fraction with a high argon concentration is extracted. Crude argon is obtained by extraction and further rectification. Furthermore, hydrogen gas was introduced from a cylinder, oxygen was removed by an oxygen removal device equipped with a catalyst such as palladium, and the gas was purified by passing it through a rectification column again to obtain highly pure argon. Argon is chemically inert and the first
As shown in the table, its physical properties are very similar to oxygen, making it difficult to separate and requiring a large number of stages to rectify.

[Table] Separation methods using adsorbents have also been proposed.
For example, Australian patent 515010 states that argon,
In order to obtain argon from a gas mixture containing oxygen and nitrogen, the same column is filled with adsorbents A and B, which have different adsorption properties for oxygen and nitrogen, respectively, and the mixed gas is passed through this to perform adsorption, depressurization, and desorption. A method of obtaining argon of a desired purity or higher by repeating the operations of - pressure equalization - backwashing - pressure accumulation - adsorption is described. The idea is to increase the concentration of argon by adsorbing oxygen and nitrogen using two types of adsorbents, but this simply takes advantage of the difference in adsorption capacity of the adsorbents for nitrogen, oxygen, and argon. This is a method that adsorbs and removes nitrogen and oxygen from the air in order, leaving argon behind. In this method, different types of adsorbents are packed in the same adsorption tower, so it is difficult to achieve the optimum conditions for each, and it does not result in highly pure argon gas. That is, A.B.
For example, if one of the optimal conditions is adopted, oxygen will be adsorbed sufficiently, but the other adsorbent will not have the optimal conditions and will not adsorb nitrogen sufficiently. Therefore, a large amount of nitrogen comes out mixed with argon. Because of this relationship, sufficient separation is not possible. Although there is no clear description of purity in the specification, it is estimated that at most only about 50% of argon can be recovered by such a method. In view of this situation, the inventors of the present invention have conducted extensive research on the adsorption characteristics of various adsorbents, and have found that 3 Å
Carbon molecular sieves with pore diameters centered around 5 Å and zeolite molecular sieves with pore diameters centered around 5 Å have different properties at the initial stage of adsorption. It has been found that sieves lose their selective adsorption properties when adsorbed for a long period of time, such as several minutes or more. In other words, the adsorption characteristics of carbon molecular sieves are such that when adsorbed for a long time, it eventually adsorbs equal amounts of nitrogen and oxygen, but during short periods of 1 to 2 minutes, oxygen diffuses into the pores faster than nitrogen, so this adsorption is reduced. It is necessary to perform a separation operation using the speed difference. On the other hand, zeolite molecular sieves have the property of preferentially adsorbing nitrogen over oxygen, and the adsorption operation time is completely unrelated to the adsorption/separation performance of nitrogen. Therefore, the carbon molecular sieve and the zeolite molecular sieve are packed in the same adsorption tank or the same mechanism and a pressure swing (hereinafter referred to as
Abbreviated as PSA. ), it was found that the separation characteristics of each cannot be fully utilized. In the present invention, in order to take advantage of the differences in the characteristics of both adsorbents, they are not filled in the same adsorption tank or in the same mechanism, but rather in completely separate and independent PSA devices, and the optimum operating conditions for each adsorbent are used. Nitrogen and oxygen are separated and removed in stages to obtain argon. That is, the gist of the present invention is that when air is used as a raw material and pressure swing is performed independently using an adsorption device filled with a zeolite molecular sieve and an adsorption device filled with a carbon molecular sieve, the following steps are performed. The present invention relates to a method for producing high concentration argon, characterized by the following. A) A step of pressure swinging using air as a raw material using a first stage device filled with zeolite molecular sieves to obtain high concentration oxygen containing argon. B) A second stage device filled with carbon molecular sieves. A pressure swing is performed by passing the high concentration oxygen containing argon using a stage device,
a step of separating intermediate concentration argon and high purity oxygen; C) performing a pressure swing through the intermediate concentration argon using a third stage device filled with a carbon molecular sieve to obtain crude argon; and D) The crude argon is further passed through a fourth stage device filled with a zeolite molecular sieve and subjected to a pressure swing to separate nitrogen and obtain high concentration argon. Outline of the standard embodiment of the present invention (first To explain this, the first-stage PSA device is filled with zeolite molecular sieves, air is passed through as a raw material, and PSA operation is performed.For example, oxygen: 94.5%, nitrogen: 1%, argon: about 4.5% ( A high concentration of oxygen containing 3 Kg/cm ² ) of argon is obtained. Using this gas as a raw material, the second stage PSA device is filled with a carbon molecular sieve, and a short PSA operation is performed to adsorb oxygen and concentrate argon to approximately 40% concentration (intermediate argon concentration). In this process, oxygen gas with a purity of approximately 97% is obtained as a desorption gas from the raw material gas (high purity oxygen). This is done by filling each adsorbent into an independent PSA mechanism and separating the PSA separately.
This is the effect of the operation, and may be caused by simply adsorbing or by combining different adsorbents together.
Such a result would not be obtained if the operation was performed. This second stage equipment can be of a multi-column type with two or more columns, but with a four-column type or more, the equipment cost is high and the yield cannot be improved, whereas with a two-column type, the yield decreases. Therefore, the three-column type is the most advantageous. For example, the flow in the case of a three-column type second stage device is shown in FIG. 2, and the sequence is shown in Table 2.

【table】

[Table] Adsorption tower in Figure 2. ．． Each is filled with a carbon molecular sieve with a pore diameter of 3 Å. Air is sent as a raw material to the PSA device filled with the first stage zeolite molecular sieve.
Highly concentrated oxygen containing argon, which is a non-adsorbable gas, obtained by performing the PSA operation is led to column 1 through compressor A, and is stored in intermediate concentration argon tank C after oxygen adsorption. On the other hand, the adsorbed oxygen is stored in a high-purity oxygen tank D via a vacuum pump B. This operation is performed by sequentially opening and closing the switching valves 1 to 16 according to Table 2. Furthermore, the third-stage PSA device is filled with the same carbon molecular sieve, and the PSA operation is performed in the same way using the intermediate concentration argon as the raw material to adsorb and remove oxygen and concentrate the argon to 85% concentration (crude argon). . During this time, nitrogen is also concentrated while maintaining approximately the same composition ratio as argon. Therefore, the ratio of argon to nitrogen remains unchanged, and in order to further reduce nitrogen, it is necessary to adsorb and remove nitrogen using a fourth stage PSA device filled with zeolite molecular sieves or to use other purification methods. This third stage device is 2
PSA is performed in a column type by switching between four steps: adsorption, pressure equalization, pressure increase, and desorption. Since the third stage desorption gas contains a considerable amount of argon, it is preferable to recover the argon by recycling it as the second stage raw material gas. Oxygen in the crude argon is removed to the extent of several percent by the PSA performed twice in the adsorption device filled with carbon molecular sieves. Furthermore, in order to increase the purity of argon to a concentration of 99% or more, if necessary, hydrogen is added twice the mole of oxygen before the fourth stage PSA device and reacted with a deoxygenation catalyst supported with palladium (deoxo device). The oxygen is removed as water. The 5th stage uses the desorption gas from the 4th stage as a raw material and is filled with zeolite molecular sieve in the same way as the 4th stage.
The PSA can recover argon, and the recovered argon can be recycled as feedstock for the fourth stage. The desorption gas of this fifth stage PSA is an argon mixed gas containing nitrogen as a main component, and is used as an inert gas. Further, if argon is liquefied using a low temperature liquefaction device instead of the fourth stage PSA device and argon having a high boiling point is separated and removed, even higher purity argon can be obtained. The zeolite molecular sieve used in the present invention suitably has a pore diameter of 5 Å, and the carbon molecular sieve suitably has a pore diameter of 3 Å. Adsorption pressure is 0.3~10Kg/ ^cm2
A range of 1 to 3 kg/kg is appropriate, and more preferably 1 to 3 kg/
It is economical to carry out the process at about cm ² . On the other hand, the lower the desorption pressure, the better the efficiency, and desorption is usually carried out at a reduced pressure of 400 Torr or less, preferably 200 Torr or less. Theoretically, adsorption and desorption are more efficient when adsorption is performed at a lower temperature and desorption at a higher temperature due to the amount of adsorption, but PSA is an adiabatic operation, and the heat of adsorption (heat generation) turns into the heat of desorption (endotherm). Because it is utilized, it is effectively carried out at room temperature. In the present invention, high concentration argon is defined as having a purity of at least
Refers to 98% argon gas. Although it is possible to obtain high-purity products such as 99.9% purity or higher, such as the argon gas for welding specified by JIS, the yield is low. For example, in applications such as steel degassing, even if the purity is not as high as this, a purity of about 98% is sufficient, so the method of the present invention is particularly effective from an economic standpoint in such cases. In the method of the present invention,
Although each of the first, second, and third stage PSA devices can be operated using one adsorption tower, each stage is usually equipped with multiple adsorption towers for adsorption, pressure equalization, pressure release, and reduced pressure desorption. - It is preferable to perform each operation of pressure equalization, pressure accumulation, and adsorption by switching between each column. In PSA operation, there is a correlation between composition and yield, and as purity increases, yield decreases, so select operating conditions (adsorption pressure, desorption pressure, time cycle, etc.) appropriately according to the required product purity. do. The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited thereto. Example 1 (Production of intermediate concentration argon) A carbon molecular sieve was used as the adsorbent, and an adsorption tower of 40 mmφ x 500 mmh was constructed as shown in Figure 2.
The tower is assembled, the first stage PSA device is filled with zeolite molecular sieve, and air is used as the raw material.
Highly concentrated oxygen containing argon (4.5% argon, 93.6% oxygen, 1.9% nitrogen) obtained through PSA operation
%) was used as the raw material for second stage PSA separation.
The adsorption pressure (maximum) is 3.0Kg/cm ² , the desorption pressure is 150 Torr, and the time cycle is shown in Table 2.
Adsorption time was 38.5 seconds, pressure release to desorption was 38.5 seconds, and pressure equalization was 1.5 seconds (1 cycle total 120 seconds). When the non-adsorptive gas extraction rate is 0.8N/min, the intermediate concentration argon gas composition is 33.0% argon, 52.3% oxygen, and nitrogen.
The yield of argon was 69%. Pressure release and desorption gas (high purity oxygen) at this time
The composition is argon 1.5%, oxygen 97.9%, nitrogen 0.5%
The oxygen yield was 94.7%. Example 2 (Method for producing crude argon) Third-stage PSA separation was performed using intermediate concentration argon gas obtained in the same manner as in Example 1 as a raw material gas.
As adsorption towers, two towers of 40 mmφ×500 mmh filled with carbon molecular sieves were used. The raw material gas composition was 35.5% argon, 50% oxygen, and 14.5% nitrogen. The adsorption pressure (maximum) was 2.0 Kg/cm ² and the desorption pressure was 100 Torr. Time cycle: adsorption 45 seconds, desorption 48.5 seconds, pressure equalization
The pressure was increased for 1.5 seconds, and the pressure was increased for 3.5 seconds (total of 100 seconds for one cycle). When the non-adsorptive gas withdrawal rate is 1.0N/min, the crude argon gas composition is 71.1% argon,
Oxygen 2.67%, nitrogen 26.2%, and argon yield is
It was 53%. Desorption gas composition is argon 22.7%,
The content was 66.7% oxygen and 10.6% nitrogen. Example 3 (Method for producing crude argon) Highly concentrated oxygen containing argon (argon 4.35%, oxygen 93.5%, nitrogen
2.15%) was used. Three adsorption towers were used in the second stage, and two adsorption towers were used in the third stage. The adsorption pressure (maximum) was 3 Kg/cm ² , the second stage desorption pressure was 150 Torr, and the third stage desorption pressure was 100 Torr. The third stage PSA desorption gas was recycled to the second stage PSA feed gas. The third stage product gas composition (crude argon) is argon
71.8%, oxygen 2.5%, nitrogen 25.6%, and the argon yield was 56%. Second stage desorption gas (high purity oxygen) composition is argon
2.0%, oxygen 96.6%, nitrogen 1.3%, and the oxygen yield was 99.9%. Example 4 (Method for producing high concentration argon) The third stage PSA product gas (crude argon) is deoxidized using a deoxo device, and then nitrogen is separated using the fourth stage zeolite molecular sieve PSA to produce high concentration argon gas. Obtained. That is, nitrogen was further adsorbed and separated from the 4th stage desorbed gas by the 5th stage zeolite molecular sieve PSA, and the 5th stage non-adsorbable gas was recycled to the raw material supply line of the 4th stage PSA. The fourth stage inlet gas was combined with the fifth stage non-adsorbent (recycle) gas and had a composition of 78.1% argon and 21.9% nitrogen. The purity of highly concentrated argon, which is the non-adsorptive gas in the fourth stage, is 99%, and the argon yield with respect to the inlet gas is
55%, and that from the third stage was 79.8%. The fourth stage and the fifth stage were both three-column type, and the sequence was such that pressure was accumulated in the column during the adsorption stage and after the desorption stage. Time cycle is 60 adsorption for both 4th stage and 5th stage
50 seconds for desorption, 10 seconds for equalizing pressure, and 50 seconds for accumulating pressure. The adsorption pressure in the fourth stage was 1.5 Kg/cm ² and the desorption pressure was 50 Torr. The fifth stage adsorption pressure was 1.2 Kg/cm ² and the desorption pressure was 50 Torr. The 5th stage desorption gas composition is argon 36.4%, nitrogen
It was 63.6%.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an overview of an embodiment.
FIG. 2 is a flow sheet of a second stage device showing an embodiment of the present invention.

Claims (1)

[Claims] 1. When pressure swinging is performed independently using air as a raw material and using an adsorption device filled with zeolite molecular sieve and an adsorption device filled with carbon molecular sieve, the following steps are performed. A method for producing highly concentrated argon, characterized by comprising the following steps: A) A step of pressure swinging using air as a raw material using a first stage device filled with zeolite molecular sieves to obtain high concentration oxygen containing argon. B) A second stage device filled with carbon molecular sieves. A pressure swing is performed by passing the high concentration oxygen containing argon using a stage device,
a step of separating intermediate concentration argon and high purity oxygen; C) performing a pressure swing through the intermediate concentration argon using a third stage device filled with a carbon molecular sieve to obtain crude argon; and D) The crude argon is further passed through a fourth stage device filled with a zeolite molecular sieve and subjected to pressure swing to separate nitrogen and obtain highly concentrated argon. 2. The method according to claim 1, wherein the second stage device is a three-column type, the third stage device is a two-column type, and the third stage desorption gas is mixed and circulated with the second stage inlet gas. 3. The method according to claim 1 or 2, in which high concentration argon is obtained by adding hydrogen to the crude argon to deoxidize it. 4 Using the desorption gas of the fourth stage device filled with zeolite molecular sieve as a raw material, argon is recovered by the fifth stage device filled with zeolite molecular sieve, and the recovered argon is used as the raw material gas of the fourth stage device. A method according to claim 1, 2 or 3 for recycling. 5. The method according to claim 4, wherein each of the fourth stage device and the fifth stage device is of a three-column type. 6 Adsorption pressure in pressure swing is
The method according to claims 1 to 5, wherein the amount is 0.3 to 10 Kg/ ^cm2 . 7 The desorption pressure in the pressure swing is
Claims 1 to 760 Torr or less of reduced pressure
5. The method described in 5.