JPH0422415A - Method for adsorbing and removing carbon dioxide - Google Patents

Abstract

PURPOSE:To drastically enhance adsorption performance by previously allowing ammonia to be adsorbed to an adsorbent or previously adding ammonia to a gaseous raw material, in a method for removing the trace quantity of carbon dioxide contained in the gaseous raw material utilized for the producing process of a semiconductor, while using the adsorbent. CONSTITUTION:An adsorbent which selectively adsorbs carbon dioxide and ammonia is equipped to the insides of main adsorption towers 11, 12. Gaseous ammonia is passed through an ammonia circulation passage 30 from an ammonia storage tank 34 and introduced into the main adsorption tower 11, and adsorbed to the adsorbent. Thereafter, a gaseous raw material such as air is introduced into the reactor 10 of a copper oxide catalyst and the combustible components contained therein are converted into carbon dioxide and water. Thereafter, these are introduced into the main adsorption tower 11 at normal temp. and brought into contact with the adsorbent. Thereby carbon dioxide contained in the gaseous raw material is selectively adsorbed to the adsorbent. The concn. of carbon dioxide in the outlet side of the adsorption tower 11 is stably held at low concn. Thereafter, ammonia is desorbed from the adsorbent in an auxiliary adsorption tower 21 and recovered into the ammonia storage tank 34. Further purification and recovery of gas can be continuously performed by alternately utilizing two sets of adsorption towers in this equipment.

Description

Detailed Description of the Invention [Field of Industrial Application] The present invention is applicable to He, Ar, N2.02, H2, air, C
This relates to a method for removing trace amounts of carbon dioxide contained in pure H4 gas, etc. using an adsorbent, and is particularly effective for applications in fields that require ultra-high purity gas, such as semiconductor manufacturing processes. It is related to.

[Conventional technology]

Conventionally, when removing carbon dioxide from a raw material gas containing carbon dioxide, especially a low concentration gas such as air, the following methods have been used:
An adsorption method using synthetic zeolite as shown in Japanese Patent Publication No. 57-27380 has been adopted. In addition, when the raw material gas contains trace amounts of combustible components, a method is also known in which these combustible components are burned on a noble metal catalyst or copper oxide catalyst, converted into carbon dioxide and moisture, and then adsorbed and removed (especially (Refer to JP-A-61-225568).

Furthermore, in recent years, a method has been proposed in which the adsorption is performed at low temperatures of about 0°C to -70°C to increase the adsorption capacity of carbon dioxide in the adsorbent and lower the concentration at the outlet of the adsorption tower. (1971 Atomic Energy Society of Japan Autumn Subcommittee Material G-35).

FIG. 3 shows an example of an adsorption/removal apparatus for carrying out the above method. In this apparatus, first, combustible gas in the raw material gas is oxidized in a copper oxide catalyst reactor 90 and converted into carbon dioxide and moisture, and then this gas is introduced into a zeolite adsorption tower 91 (92), and the carbon dioxide and adsorbs and removes moisture. Then, the adsorption operation is stopped before the breakthrough of carbon dioxide and moisture begins.
Carbon dioxide and water adsorbed in the adsorption tower 91 (92) are desorbed by circulating a part of the purified gas through the regeneration gas passage 95 while heating the adsorption tower 91 (92) with the heater 93 (94). and discard. During this desorption operation, purified gas can be continuously obtained by performing adsorption in another adsorption tower 92 (91).

According to such a method, for example, synthetic zeolite (typically Molecular Sieve 5A) is used as an adsorbent, and carbon dioxide is adsorbed at room temperature and carbon dioxide is desorbed at about 150°C to 250°C, thereby reducing the amount of carbon dioxide at the outlet of the adsorption tower. It is possible to reduce the carbon concentration to 1-2 ppm.

[Problem to be solved by the invention]

As mentioned above, in the method of adsorbing carbon dioxide and water at room temperature, the concentration at the outlet of the adsorption tower is always kept stable and low (1 to 2
ppm) and cannot be purified to a lower concentration. In addition, in such a low concentration region, as adsorption progresses and the carbon dioxide concentration decreases, the adsorption capacity of the adsorbent decreases approximately in proportion to this, so it is necessary to try to lower the outlet concentration slightly. Even with only this,
The amount of adsorbent required for this will increase rapidly.

On the other hand, compared to such room temperature adsorption methods, if adsorption is performed at low temperatures, the adsorption capacity of the adsorbent can be greatly improved. Alternatively, since a refrigerator is required and the adsorption/desorption cycle is inevitably lengthened, it is inevitable that the device becomes larger and the cost increases. In particular, this method is uneconomical when processing a small flow rate of raw material gas, and cannot be called an advantageous method.

In view of these circumstances, an object of the present invention is to provide a method that can sufficiently remove carbon dioxide from raw material gas with a simple configuration.

[Means to solve the problem]

The present invention is a carbon dioxide adsorption/removal method in which carbon dioxide is removed by bringing a raw material gas containing carbon dioxide into contact with an adsorbent and selectively adsorbing carbon dioxide onto the adsorbent. and then bring the raw material gas into contact with the adsorbent (Claim 1)
.

The same effect can also be obtained by adding ammonia to the raw material gas in advance and then bringing the raw material gas into contact with an adsorbent (Claim 2).

Furthermore, after bringing the raw material gas into contact with the adsorbent, the adsorption operation is stopped before carbon dioxide breakthrough begins, and then after carbon dioxide and ammonia are desorbed, this desorption gas is mixed with ammonia in the desorption gas. More preferably, the ammonia is brought into contact with a sub-adsorbent that selectively adsorbs the ammonia, and then the ammonia is desorbed and recovered from the sub-adsorbent (Claim 3).

[For production]

According to the methods described in claims 1 and 2, by adsorbing ammonia and carbon dioxide in the coexistence, the amount of carbon dioxide adsorbed is significantly increased compared to the case where carbon dioxide is adsorbed alone. This is because ammonium carbamate NH2COONH4 is generated within the adsorbent due to the coexistence of both molecules.
Or ammonium carbonate (NH4) in the presence of water.
This is presumed to be due to the fact that 2C03 is generated, the polarity becomes stronger, and high-density adsorption is realized.

Furthermore, according to the method of claim 3, ammonia used for removing carbon dioxide is recovered after use, and can be reused.

〔Example〕

FIG. 1 shows an example of an apparatus for carrying out the method of the present invention.

In the figure, 10 is a copper oxide catalyst reactor, and two main adsorption towers 11 and 12 are arranged in parallel on the downstream side thereof. These copper oxide catalyst reactor 10 and each main adsorption tower 11.
12 is equipped with electric heaters 14 to 16 for heating, respectively.

Each main adsorption tower 11.12 is internally equipped with an adsorbent (5A type synthetic zeolite) that selectively adsorbs carbon dioxide and ammonia. A regeneration gas passage 18 for reflux is provided.

In addition, in this example apparatus, sub-adsorption towers 21.22 are provided separately from the main adsorption towers 11 and 12, and each sub-adsorption tower 21.2
2 is provided with electric heaters 25 and 26, and
Inside, an eye-opening adhesive is provided that selectively adsorbs only ammonia without adsorbing carbon dioxide. As this eye opening adhesive, for example, 3A type synthetic zeolite is suitable. If such an adsorbent is used, carbon dioxide whose molecules are too large will not be adsorbed, but only ammonia will be adsorbed.

The adsorption towers 2122 on both sides are connected to the main adsorption tower 11.12 via the waste gas passage 28, and are connected to the copper oxide catalyst reactor 10 and each main adsorption tower 11.12 via the ammonia circulation passage 30. A vacuum pump 32 and an ammonia storage tank 34 are provided in the middle of this ammonia circulation passage 30.

In addition, flashing solenoid valves for passage switching are provided at appropriate locations in each passage.

Next, a method for adsorbing and removing carbon dioxide performed in this apparatus will be explained. In addition, this apparatus is capable of continuously obtaining purified gas by alternately adsorbing carbon dioxide and ammonia in the main adsorption towers 11 and 12, and alternately adsorbing ammonia in the sub-adsorption towers 21 and 22. However, in the following explanation, for convenience, only the steps performed in the main column 1 11 and the sub-adsorption column 21 on one side will be discussed.

First, from the ammonia storage tank 34 to the ammonia circulation passage 30
Ammonia gas is fed into the main adsorption tower 11 through the main adsorption tower 11 and adsorbed by the adsorbent. The amount of ammonia adsorbed at this time is desirably set so that the molar ratio to carbon dioxide to be adsorbed is 21, as will be explained in detail later.

Thereafter, a raw material gas such as air is fed into the copper oxide catalytic reactor 10 to convert the combustible components therein into carbon dioxide and water, and then fed into the main adsorption tower 11 at room temperature to contact with the adsorbent. Thereby, carbon dioxide in the raw material gas is selectively adsorbed by the adsorbent and removed from the raw material gas.

The amount of carbon dioxide adsorbed at this time will be described in detail later;
This significantly increases the carbon dioxide concentration compared to the case where ammonia does not exist, and the carbon dioxide concentration at the outlet side of the adsorption tower 11 is stably maintained at a low concentration.

As the adsorption operation progresses in this way, the main adsorption tower 11
The adsorption operation is terminated at a point before breakthrough begins within the reactor, and the supply of raw material gas is stopped. Next, while heating the main adsorption tower 11 to 150°C to 250°C with the electric heater 15, a part of the purified gas is refluxed through the regeneration gas passage 18, thereby removing the carbon dioxide and ammonia adsorbed in the main adsorption tower 11. is desorbed and the mixed gas is sent into the sub-adsorption tower 21 through the waste gas passage 28. In this sub-adsorption tower 21, carbon dioxide is not adsorbed, but only ammonia is adsorbed.

Thereafter, by operating the vacuum pump 32 while heating the sub-adsorption tower 21 with the electric heater 25, the sub-adsorption tower 21 is heated.
Ammonia is desorbed from the adsorbent inside and collected in the ammonia storage tank 34. At this time, the purge gas for regeneration may be supplied into the sub-adsorption tower 21.

According to the method described above, as is clear from the experimental results shown below, the carbon dioxide adsorption performance can be significantly improved simply by adsorbing ammonia in advance in the adsorption tower 11.

FIG. 2 shows the experimental steps carried out to confirm the effects obtained by the above method.

The operating conditions in each step are as follows.

Adsorption temperature: Room temperature (27-29℃) Adsorption pressure + 5Nm Regeneration temperature = 250℃ (After keeping the temperature inside the adsorption tower at 250℃ for 1 hour under dry N2 flow at atmospheric pressure, cooling and adsorption) Adsorbent: 5A type Synthetic zeolite adsorption gas I: C02350ppm/N2 balance gas Gas II: NH370G 911111/N2 balance gas To explain each step in detail, first, the adsorption tower 11 is heated to regenerate the adsorbent inside it, step P1); Next, gas, which is a balance gas of carbon dioxide and nitrogen, is sent into the main adsorption tower 11. As a result, carbon dioxide is adsorbed onto the adsorbent (step P2).

Thereafter, regeneration is performed again (step P3), and this time gas (2), which is a balance gas of ammonia and nitrogen, is sent into the adsorption tower 11 to adsorb ammonia (step P4). Further, after the regeneration (step P5), the gas (2) is adsorbed, and immediately after that, the gas I is adsorbed (step Pa), followed by regeneration (step P7).

By performing the above series of operations, it was possible to obtain adsorption amounts and concentrations at the outlet of the adsorption tower in each step as shown in the following table.

Table Here, gas chromatography is used to measure carbon dioxide concentration, and spectrophotometry is used to measure ammonia concentration. The amount of adsorption is determined by integrating the change curve of the outlet concentration, that is, the breakthrough curve.

From the above experimental results, the following considerations can be made.

i) Improving carbon dioxide adsorption performance In step P2 in which carbon dioxide is adsorbed alone, the adsorption amount of carbon dioxide is 2.7v1%, and the outlet side concentration is 1.7p.
pm, whereas in step P6 where it is adsorbed in the coexistence with ammonia, the amount of carbon dioxide adsorbed is 12.0w1%.
, the outlet side concentration is 0. It is less than ippm. That is, by allowing ammonia to coexist, the amount of carbon dioxide adsorbed becomes four times or more, and the outlet concentration is also reduced to an unmeasurable range. In other words, by implementing this method, it is possible to reduce the amount of adsorbent to 1/4 compared to the conventional method.

In addition, the partial pressure of carbon dioxide in the raw material gas is kept the same, and only the adsorption temperature is lowered from -73°C to -53°C in the above step P2.
It has been experimentally confirmed that an adsorption amount of approximately 18.0 wt% can be obtained when using It can be seen that an adsorption amount that is 2/3 of the adsorption amount during low-temperature adsorption can be obtained.

Therefore, according to this method, it is possible to obtain a sufficient amount of carbon dioxide adsorbed at room temperature and with a small amount of adsorbent, without particularly performing low-temperature adsorption.

Moreover, by comparing the adsorption amounts in the above steps P4 and P6, it is clearly seen that the adsorption amount of ammonia also increases significantly due to coexistence with carbon dioxide.

) Relationship between adsorption amount of carbon dioxide and ammonia In step P6, the adsorption amounts of carbon dioxide and ammonia are each 12
．． Ovt% and 9.4v1%, and the molar ratio of both is 1:2.

When both molecules coexist, ammonium carbamate NH2C○ONH4 is produced within the adsorbent, or ammonium carbonate (NH4) is produced in the coexistence of water.
) 2 This suggests that COa is generated. Since such products have strong polarity, they tend to be strongly adsorbed, and it can be inferred that this allows high-density adsorption to be achieved, resulting in a significant increase in the amount of adsorption.

Therefore, in this method, by mixing carbon dioxide and ammonia at a molar ratio of 1.2, carbon dioxide can be adsorbed in just the right amount, and the amount of carbon dioxide is small relative to this ratio. If the amount of ammonia is too small, carbon dioxide will not be adsorbed sufficiently and breakthrough will occur early.

In other words, it can be said that in this method, it is most ideal to set the molar ratio to 1:2.

For example, as in step P2, the amount of carbon dioxide adsorbed is
2.7 vt% and to maintain the outlet concentration at the same level as the concentration in step P6, add 2.7 vt% of ammonia in advance.
．． It would be ideal if lvt% was adsorbed. Further, if ammonia is used in an amount equal to or more than the amount corresponding to this molar ratio, there will be a surplus of ammonia, but the carbon dioxide adsorption performance will be completely improved.

Note that the desorbed ammonia may be disposed of as is or may be disposed of after being subjected to appropriate removal treatment, but as in the above method, the desorbed gas is sent to the sub-adsorption tower 21 and only ammonia is removed. If the ammonia is adsorbed and desorbed, the used ammonia can be recovered without being disposed of and thus effectively reused.

Typical operating conditions for this method are shown below.

Raw material gas pressure 5a1m or less Temperature of copper oxide catalytic reactor 10: 250℃ or less Main adsorption focus 1.12 Adsorption temperature: room temperature adsorption pressure/5a1m or less Regeneration temperature 150 to 250°C Regeneration pressure Crab atmospheric pressure adsorbent: 5A type zeolite Sub-adsorption tower 21.22 Adsorption temperature Normal temperature Adsorption pressure 1 atm or less Regeneration temperature: 150 to 250°C Regeneration pressure/negative pressure (when using vacuum pump 30) Adsorbent: 3A type synthetic zeolite Note that sub-adsorption tower 2], , 22 can be raised to about 12 (m) by using purge gas. Conversely, by using vacuum pump 32, the amount of purge gas used can be lowered and the regeneration pressure can be lowered.

The above explanation is about a method in which ammonia is adsorbed on an adsorbent in advance and then carbon dioxide is adsorbed, but the method is not limited to this, and if ammonia and carbon dioxide coexist in the adsorbent, the above results can be obtained. is obtained. Therefore, even if an appropriate amount of ammonia is added to the raw material gas in advance and the raw material gas is brought into contact with the adsorbent, good adsorption of carbon dioxide can be achieved in the same way as described above.

In this case as well, the molar ratio of carbon dioxide and ammonia is 1.2
For example, when the concentration of carbon dioxide in the raw material gas is 10 ppm, it is best to add ammonia until the concentration of ammonia in the gas reaches 20 ppm. Also in this method, after desorbing carbon dioxide and ammonia, this gas is sent to the sub-adsorption tower 21, 22, thereby making it possible to recover and reuse ammonia.

〔Effect of the invention〕

As described above, in the present invention, ammonia is adsorbed on an adsorbent in advance, or ammonia is added to a raw material gas in advance, and then the raw material gas is brought into contact with an adsorbent. Compared to the case of adsorption, the adsorption performance can be greatly improved, and for this reason,
A sufficient amount of adsorption can be obtained with a small amount of adsorbent at room temperature, and the carbon dioxide concentration after passing through the adsorbent can be stably maintained at a low concentration.

Furthermore, carbon dioxide and ammonia adsorbed by the above-mentioned adsorbent are desorbed, this desorbed gas is brought into contact with an adsorbent that selectively adsorbs only ammonia in the same gas, and then ammonia is desorbed from this adsorbent. By doing so, the used ammonia can be recovered and effectively reused without being discarded, and further cost reduction can be achieved.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram showing an example of an apparatus for carrying out the method of the present invention, Fig. 2 is a flowchart showing the experimental steps carried out in the same apparatus, and Fig. 3 is a diagram of a conventional carbon dioxide adsorption/removal apparatus. FIG. 1 is an overall configuration diagram showing an example. 11.12... Main adsorption tower, 21.22... Sub-adsorption tower, 30... Ammonia circulation passage, 34... Ammonia storage tank. Patent Applicant: Kobe Steel Orisyoshi Co., Ltd. Patent Attorney: Etsushi Kotani Patent Attorney: Chief 1) Positive Diagram

Claims (1)

[Claims] 1. In a carbon dioxide adsorption/removal method in which carbon dioxide is removed by bringing a raw material gas containing carbon dioxide into contact with an adsorbent and allowing the adsorbent to selectively adsorb carbon dioxide, A method for adsorbing and removing carbon dioxide, which comprises adsorbing ammonia onto a carbon dioxide, and then bringing a raw material gas into contact with the adsorbent. 2. In a carbon dioxide adsorption removal method in which carbon dioxide is removed by bringing a raw material gas containing carbon dioxide into contact with an adsorbent and selectively adsorbing carbon dioxide on the adsorbent, ammonia is added to the raw material gas in advance, A method for adsorption and removal of carbon dioxide, which comprises subsequently bringing this raw material gas into contact with an adsorbent. 3. In the method for adsorption and removal of carbon dioxide according to claim 1 or 2, the adsorption operation is stopped after bringing the raw material gas into contact with the adsorbent and before carbon dioxide breakthrough begins, and then carbon dioxide and ammonia are desorbed. After that, this desorption gas is brought into contact with a sub-adsorbent that selectively adsorbs only ammonia in the desorption gas, and then ammonia is desorbed and recovered from this sub-adsorption agent. .