JP2651605B2 - How to remove carbon dioxide - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for removing carbon dioxide, and more particularly, to removing carbon dioxide by bringing moisture into contact with an adsorbent and bringing the gas into contact with the gas. The present invention relates to a method for removing carbon dioxide for more efficient removal.

Gases such as hydrogen, nitrogen, helium, argon and oxygen are commercially available in packed or liquefied state and are used for various industrial and academic purposes.

In recent years, with the advancement of technologies in fields such as a semiconductor manufacturing process, an optical fiber manufacturing process, a metal heat treatment process, and analysis, these gases are also required to have high purity.

[Conventional technology]

Various purification methods are known in order to obtain high-purity gas depending on the type of impurities contained in the gas and the like. For impurities such as hydrogen, hydrocarbons, carbon monoxide, etc., these are burned to produce carbon dioxide. A method has been used in which carbon and / or water is converted into carbon and / or water, and the carbon and water are mixed with the adsorbent together with the carbon and water to remove them.

As these adsorbents, synthetic zeolites are generally and widely used, for example, molecular sieve (Union Carbide, USA) is best known. The adsorbent having adsorbed impurities is repeatedly used by regenerating at high temperature.

[Problems to be solved by the invention]

Although the degree of integration of semiconductors has increased, the purity of gas has also increased, and the concentration of impurities has been decreasing.
Further, it is required to remove impurities. On the other hand, in a semiconductor process or the like, there is a strong demand for downsizing of the device due to the installation space and the like.

When the equilibrium adsorption amount of low-concentration carbon dioxide is measured for molecular sieve 5A that is currently widely used, when the concentration of carbon dioxide is as low as 1 ppm, it is about 1 / Drops to 7. That is,
In order to purify the same amount of gas, the volume of the adsorption column is reduced to only 7/10 even if the concentration is reduced to 1/10. To make the adsorption cylinder even smaller, shorten the cycle of heating and regeneration, or
Alternatively, it is necessary to increase the amount of adsorption by lowering the adsorption temperature to a low temperature such as 0 ° C. or lower.

However, shortening the heating cycle also has a design upper limit, and lowering the adsorption temperature requires installation of a chiller, a refrigerator, and the like, and thus has a drawback that it cannot meet the demand for downsizing.

On the other hand, the present inventors have previously used zinc oxide or a molded body obtained by mixing aluminum oxide and an alkali compound with zinc oxide as an adsorbent to efficiently remove carbon dioxide even at a low concentration. (Japanese Patent Application Nos. 62-318800 and 63-192104). This method has a higher adsorption performance than a method using a molecular sieve or the like, and can efficiently remove carbon dioxide without using a cooling means, and can regenerate the adsorbent at a relatively low temperature. Has advantages.

However, even if these adsorbents are used, the adsorbing performance is still not sufficient to reduce the size of the adsorption cylinder.

[Means and actions for solving the problem]

The present inventors have continued research to further enhance the adsorption performance, and as a result, using a molded body mainly composed of zinc oxide, aluminum oxide and an alkali metal compound, to make sure that an appropriate amount of moisture is present at the time of contact with a gas. As a result, the present inventors have found that the amount of adsorbed carbon dioxide can be significantly increased, and completed the present invention.

That is, the present invention relates to a method for removing carbon dioxide from a gas containing carbon dioxide as an impurity by contacting the gas with the adsorbent to remove carbon dioxide from the gas, wherein zinc oxide, aluminum oxide and an alkali metal compound are mainly used as the adsorbent. A method for removing carbon dioxide, comprising using a molded product of a composition as a component and bringing the molded product into contact with water in the presence of moisture.

The present invention is applied to the removal of carbon dioxide contained as an impurity in gases such as hydrogen, nitrogen, helium, argon and oxygen.

The adsorbent used in the present invention uses zinc oxide, aluminum oxide and an alkali metal compound.

As the zinc oxide, an appropriate one may be selected from commercially available products.Also, a precursor such as zinc carbonate, basic zinc carbonate, zinc hydroxide, and organic acid zinc, which can be changed to zinc oxide by firing or the like, may be used. May be used.

As the aluminum oxide, alumina hydrate is usually used, and for example, commercially available alumina sol or high-concentration alumina obtained by powdering the same is suitable.

Further, as the alkali metal compound, hydroxides such as lithium, sodium and potassium, carbonates, bicarbonates and acetates are used. Among these, potassium carbonate, potassium bicarbonate, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydroxide, and mixtures thereof are preferred.

The amount of the aluminum oxide and the alkali compound with respect to the zinc oxide is usually 0.1 mol of aluminum per atom of zinc.
It is 02 to 0.60 atom, preferably 0.05 to 0.40 atom, and the amount of alkali metal is usually 0.03 to 0.50 atom, preferably 0.05 to 0.40 atom per 1 atom of zinc.

If the atomic ratio of aluminum is less than 0.02, the strength of the molded body may be reduced. On the other hand, if it is larger than 0.60, the ability to adsorb carbon dioxide gas may be reduced. When the atomic ratio of the alkali metal is less than 0.03, the effect of water on the adsorption capacity is reduced, while when it is more than 0.50, molding becomes difficult. As a method of preparing the adsorbent, for example, water is added to a mixture of zinc oxide or an oxide precursor and an alumina sol and an alkali metal compound and kneaded, or water is added to zinc oxide or a precursor thereof and an alumina sol. After kneading, there is a method of molding a cake obtained by further adding an alkali metal compound.

There are various molding methods, for example, a method of extruding a cake of the mixture obtained above, drying the obtained pellets, drying the cake, pulverizing, adding a lubricant such as graphite to the mixture, and mixing. There is a method such as tableting and molding the cake into granules using a granulator or the like.

Of these, it is generally convenient to form a pellet by extrusion molding from the viewpoint of workability, ease of selection of shape, size, etc. In addition, the pellet is rounded at its end using a marmellaizer or the like. It is preferable that the shape is a bent shape.

The molded product is heated for 180
The adsorbent is obtained by calcining at ~ 600 ° C, preferably 210-450 ° C.

Although the size and shape of the molded body are not particularly limited, spherical, cylindrical, and cylindrical shapes are typical examples. Its size is 0.5 to 10 mm in diameter if it is spherical, 0.5 to 10 mm in diameter if it is cylindrical, and about 2 to 20 mm in height.If it is irregular, such as granular, it will be 0.84 with a sieve opening
A range of about 5.66 mm is used.

The density of the molded body used in the present invention is usually 0.5 to 3.0 g / ml,
Preferably it is in the range of 0.7 to 2.5 g / ml. In the present invention, the density refers to a value obtained by dividing the weight of a molded article (particle) by the geometric volume of the molded article.

The filling density when the molded body is filled in an adsorption column is usually 0.4 to 2.0 g / ml, preferably 0.5 to 1.5 g / ml.

In the present invention, as a method for causing moisture to be present at the time of contact, for example, a method of filling an adsorbent into an adsorption column and passing a gas containing water therein, or a method of adding water to the adsorbent, and the like. Specific examples include continuously injecting a predetermined amount of water into a gas, generating water by a chemical reaction from hydrocarbons and hydrogen, etc., which are trace components in the gas, and an adsorption column without passing a raw material gas through a dehydrating agent. Or injecting a part of the source gas into water, soaking it in water and returning it to the original source gas.

To add moisture to the adsorbent, add water to the regenerated gas at the end of regeneration of the adsorbent to make it adsorb to the adsorbent, or introduce air or high humidity gas before regeneration of the adsorbent. There is.

The concentration of carbon dioxide in commercially available gases such as hydrogen, helium, and argon is typically less than a few ppm. Also, in the case of oxygen, the methane present is said to be up to 30 ppm, which is oxidatively decomposed and converted into carbon dioxide and water. It is as follows.

In the present invention, the concentration (ppm) when water is present in the gas is usually 0.2 to 20 times, preferably 0.5 to 10 times the carbon dioxide concentration.

When water is added to the adsorbent, the amount is 1 to 100 g, preferably 5 to 50 g per kg of the adsorbent.

If the water content is lower than this range, the effect is small, and if the water content is increased, not only the effect does not increase but also the strength of the adsorbent may decrease.

In addition, when there is a concern that water may be mixed into the outlet gas of the adsorption column due to the inflow of water of a predetermined amount or more, the water is completely removed by filling the downstream side of the adsorbent with an adsorbent having a stronger dehydration ability. be able to.

In general, the adsorption temperature is preferably lower, but may be about 80 ° C. or lower, and usually has sufficient adsorption performance at room temperature of 60 ° C. or lower, and does not particularly require cooling.

The velocity of the gas at the time of contact may be the same as that in the case of using synthetic zeolite, and is usually 150 cm / sec or less, preferably 1 to 70 cm / sec in linear velocity of the cylinder. The pressure at the time of contact is not particularly limited, but practically, the pressure is often in the range of 1 to 10 kg / cm ² G.

In the present invention, usually, two adsorption columns are used, and the adsorption and purification of the gas and the heat regeneration of the adsorbent are alternately switched. The adsorbent that has adsorbed carbon dioxide flows at 200 to 500 ° C, preferably 300 to 400 ° C while flowing purified gas through the adsorption column.
, Impurities such as carbon dioxide and water are desorbed and removed and regenerated, and are repeatedly used for gas adsorption purification.

〔The invention's effect〕

The present invention relates to a method using a synthetic zeolite or the like which has been conventionally used by using a molded body of a composition containing zinc oxide, aluminum oxide and an alkali metal compound as main components as an adsorbent and contacting it in the presence of moisture. In comparison, the adsorption performance is remarkably high, and carbon dioxide can be efficiently removed.

Moreover, since the adsorbent is regenerated by a relatively low temperature, it can be used repeatedly.

Thus, the adsorbent shows a high adsorption capacity even when using the same system as before, so that the device can be greatly reduced in size compared to the conventional method, and it can be easily installed in a limited space such as a semiconductor manufacturing process. became.

〔Example〕

The breakthrough time of the adsorption column with carbon dioxide was measured by the following method, and the adsorption performance was evaluated based on the measurement.

A stainless steel adsorption tube having an inner diameter of 7.53 mm and a length of 300 mm was filled with an adsorbent to a filling length of 100 mm, and regenerated at 350 ° C. for 2 hours while flowing a purified gas (base gas used for measurement) at 80 ml / min.

The raw material gas containing carbon dioxide is pressurized in this adsorption tube.
5Kg / cm ² G, temperature 35 ℃, flow at a flow rate of 1.08 Nl / min, contact with the adsorbent in the presence of moisture, analyze the carbon dioxide in the outlet gas, carbon dioxide concentration is 30 pp after starting to flow the gas
b is measured and the breakthrough time (hereinafter T
B)).

Using FID gas chromatograph for analysis, carbon dioxide emitted from the gas chromatograph separation tube was converted to methane by contacting it with nickel catalyst at 600 ° C in the presence of hydrogen, and then converted to FID (hydrogen flame ionization detector). The methane concentration was detected.

Example 1 Basic zinc carbonate 500 g, Cataloid AP (Catalyst Chemical Co., Ltd.)
(High-concentration alumina) was mixed in a kneader for 3 minutes in a kneader, and 280 g of water was added and kneaded for 1 hour. Add 30.8 g of anhydrous potassium carbonate (Z
K0.10 atom (n1 atom) was added, and the mixture was further kneaded for 20 minutes. The cake was extruded from a 1.6φ nozzle plate by a small extruder, and the obtained pellet was rounded by a marmellaizer and dried at 110 ° C. for 2 hours. This was placed in a muffle furnace and fired at 350 ° C for 1 hour to obtain a density of 1.3
An adsorbent having a packing density of 5 g / ml and a packing density of 0.89 g / ml was obtained.

Fill the adsorption tube with 3.69 g of adsorbent crushed to 20 to 30 mesh, add 36.9 mg of water (10 mg of water per 1 g of adsorbent) to the inlet of the adsorption tube, and add TB
(Breakthrough time) was measured. The result was 623 min.

Similarly, TB was measured when 184.5 mg of water (50 mg of water per 1 g of adsorbent) was added. The result was 950 min.

Comparative Example 1 The TB was measured in the same manner as in Example 1 except that water was not added to the adsorbent, and it was 327 minutes.

Examples 2 and 3 Two kinds of adsorbents were prepared in the same manner as in Example 1 except that the mixing amount of anhydrous potassium carbonate was changed to 15.4 g (Example 2) and 61.6 g (Example 3). K is 0.05 and 0.2 atoms for Zn1 atom, respectively.

1 g of adsorbent at the entrance of the adsorption tube for each of these adsorbents
Per 10 mg of water per 10
TB was measured by flowing nitrogen containing ppm. The result is 343mi
n (Example 2) and 695 min (Example 3).

Comparative Examples 2 and 3 TB was measured in the same manner as in Examples 2 and 3 except that water was not added to the adsorbent.
And 306 min (Comparative Example 3).

Example 4 Cataloid AP, 67.9 g (0.20 atom of Al with respect to 1 atom of Zn), 44.7 g of potassium bicarbonate as an alkali metal compound
An adsorbent was prepared using 293 g of water (K0.10 atom per 1 atom of Zn), 10 mg of water was added per 1 g of the adsorbent, and nitrogen containing 10 ppm of carbon dioxide was flowed in the same manner as in Example 1 to remove TB. It was measured. As a result, TB was 580 min.

Comparative Example 4 The TB was measured in the same manner as in Example 4 except that water was not added to the adsorbent, and it was 298 minutes.

Example 5 23.6 g of anhydrous sodium carbonate as an alkali metal compound
An adsorbent was prepared in the same manner as in Example 1 except that (0.10 atom of Na for 1 atom of Zn) was used, 10 mg of water was added per 1 g of the adsorbent, and TB was measured in the same manner as in Example 1. did. As a result, TB was 570 min.

Comparative Example 5 TB was measured in the same manner as in Example 5 except that water was not added to the adsorbent, and it was 312 min.

Example 6 The same 20-32 mesh adsorbent as used in Example 1 was filled with 7.4 g of a 200 mm-filled adsorbent, and 30 ppm of carbon dioxide and oxygen containing 52 ppm of water instead of adding water to the adsorbent were passed therethrough. TB was measured in the same manner as in Example 1. As a result TB
Was 590min.

Comparative Example 6 30 ppm of carbon dioxide instead of oxygen used in Example 6
When TB containing water was passed through oxygen containing 3 ppm, the TB was measured in the same manner.

Comparative Example 7 27 g of aqueous ammonia (28%) instead of the alkali metal compound in Example 1 (0.10 mol of NH ₃ per Zn atom)
The adsorbent was prepared using
TB was measured by flowing nitrogen containing 10 ppm.

The TB when adding 10 mg of water per 1 g of the adsorbent was 34 min, and when not adding water was 204 min, and the TB was significantly shortened by adding water.

Comparative Example 8 An adsorbent was prepared using 81.4 g of alumina cement instead of the cataloid AP in Example 1 without adding an alkali metal compound (0.18 atom of Al and 0.13 atom of Ca based on 1 atom of Zn).

This adsorbent was treated with 10 carbon dioxide in the same manner as in Example 1.
The TB was measured by flowing nitrogen containing ppm. Per 1g of adsorbent
TB when adding 2.3 mg and 11.8 mg of water is 103 respectively
min and 18min, and TB when water is not added
It was 176min, and TB was shortened by adding water.

Comparative Example 9 In place of the adsorbent used in Example 1, 3.45 g of a crushed product of molecular sieve 5A of 20 to 32 mesh was filled, and 10 mg of water per 1 g of the adsorbent was added thereto. TB was measured by flowing nitrogen containing 10 ppm of carbon dioxide, and it was 45 minutes. Also, when no water was added, the TB was measured to be 24 minutes.

Claims (1)

(57) [Claims] 1. A method for removing carbon dioxide from a gas containing carbon dioxide as an impurity by contacting the gas with an adsorbent, wherein zinc oxide, aluminum oxide and an alkali metal compound are mainly used as the adsorbent. A method for removing carbon dioxide, comprising using a molded body of a composition as a component and bringing the molded body into contact with water.