JPH0243917A - Removal of carbon dioxide - Google Patents

Abstract

PURPOSE:To enhance the removal efficiency of CO2 by bringing CO2-containing gas into contact with an adsorbent composed of a molded body formed from a composition prepared by mixing zinc oxide, aluminum oxide and an alkali compound. CONSTITUTION:Basic zinc carbonate, aluminum oxide and anhydrous potassium carbonate or sodium bicarbonate are mixed, molded, dried and baked to obtain a molded body composed of a composition wherein zinc oxide, aluminum oxide and an alkali compound are mixed. This molded body is brought into contact with CO2-containing gas as an adsorbent to adsorb and remove CO2. CO2 is desorbed from the adsorbent by heating. By using this adsorbent, CO2 removal efficiency is enhanced.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for removing carbon dioxide, and more specifically, the present invention relates to a method for removing carbon dioxide, and more specifically, a method using an adsorbent that has high carbon dioxide removal performance and excellent molded body strength. This paper relates to a method for removing carbon dioxide.

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

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

[Conventional technology]

Various purification methods are known to obtain high-purity gas depending on the type of impurities contained in the gas.
A method for removing impurities such as hydrocarbons and carbon oxides by burning them and converting them into carbon dioxide and/or water, and then contacting them with an adsorbent along with the carbon dioxide and water that were originally mixed in. is used.

Synthetic zeolites are generally widely used as these adsorbents, and for example, Molecular Sieve (Union Carbide, USA) is the most well-known. The adsorbent that has adsorbed impurities can be used repeatedly by regenerating it at high temperature.

[Problem to be solved by the invention]

As the degree of integration of semiconductors increases, the purity of gases also improves, and the concentration of impurities tends to decrease, but there is a need to further remove impurities. On the other hand, in semiconductor processes and the like, there is a strong demand for downsizing of equipment due to installation space and other considerations.

When measuring the equilibrium adsorption amount of carbon dioxide at low concentrations using Molecular Sieve 5A, which is currently widely used, it is found that when the concentration of carbon dioxide is as low as lppm, it is about 177 compared to when the carbon dioxide concentration is 10 ppm. descend. In other words, in order to purify the same amount of gas, the concentration must be 1/
Even if it is reduced to 10, the volume of the adsorption column will only be reduced to 7/10.

In order to further reduce the size of the adsorption column, it is necessary to increase the amount of adsorption by shortening the heating regeneration cycle or lowering the adsorption temperature to a low temperature below O'C.

However, there is a design upper limit for shortening the heating cycle, and lowering the adsorption temperature requires the installation of a chiller, refrigerator, etc., which has the drawback of not being able to meet demands for miniaturization.

In contrast, the present inventors have previously discovered a method of using a molded body containing zinc oxide as a main component as an adsorbent to efficiently remove carbon dioxide even at low concentrations (Japanese Patent Application No. 1983- No. 318800). This method has higher adsorption performance than methods using molecular sieves, etc.
In particular, it has the advantage that carbon dioxide can be efficiently removed without using any cooling means, and that the adsorbent can be regenerated at a relatively low temperature.

However, even if this adsorbent is used, the adsorption performance is still not sufficient to downsize the adsorption column, and the adsorbent that has adsorbed impurities is repeatedly used by heating and regenerating, but the droplets at this time are It was also discovered that dust may be generated depending on the conditions during the pressure and purge steps, and there is a risk that this dust may be mixed into the purified gas.

[Means and actions for solving problems]

The present inventors continued their research to find a removal method that has even higher adsorption performance and is free from the risk of powder contamination. As a result, they developed a molded body of a composition in which aluminum oxide and an alkali compound were added to zinc oxide. They have discovered that by using scales, no dust is generated and carbon dioxide can be removed more efficiently, and the present invention has been completed.

That is, the present invention provides a carbon dioxide removal method in which a gas containing carbon dioxide as an impurity is brought into contact with an adsorbent to remove carbon dioxide from the gas. A method for removing carbon dioxide characterized by using a molded body of a composition comprising:

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. Moreover, when moisture is contained in these gases, the moisture is also removed at the same time.

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

As zinc oxide, an appropriate one may be selected from commercially available products, and precursors such as zinc carbonate, basic zinc carbonate, zinc hydroxide, and organic acid zinc that can be converted to zinc oxide by calcination etc. May be used.

Further, as aluminum oxide, alumina hydrate is usually used, and for example, commercially available alumina sol or highly concentrated alumina made from powdered alumina sol is suitable.

Further, alkaline compounds include hydroxides, carbonates, bicarbonates, and acetates of alkali metals such as lithium, sodium, potassium, and ammonium.

Among these, potassium carbonate, potassium bicarbonate, potassium hydroxide, sodium carbonate, sodium bicarbonate, sodium hydroxide, ammonium hydroxide, and mixtures thereof are preferred.

The amount of aluminum oxide and alkali compounds relative to zinc oxide is usually 0% aluminum per 1 atomic number of zinc oxide.
．． 02-0.60 atoms, preferably 0.05-0.40
and the amount of alkali compound is usually 0.02 to 0.70 atoms, preferably 0.05 to 0.50 atoms of alkali metal or ammonium groups.

If the atomic ratio of aluminum is less than 0.02, the strength of the molded product may decrease, while if it exceeds 0.60, the carbon dioxide adsorption ability may decrease.

Also, the atomic ratio of alkali metal or ammonium groups is 0
．． If it is smaller than 0.02, the strength and adsorption capacity of the molded product will decrease, and if it is larger than 0.70, it will be difficult to mold. The adsorbent can be prepared by, for example, adding water to a mixture of zinc oxide or oxide precursor, alumina sol, and an alkali compound and kneading it, or adding water to zinc oxide or its precursor and alumina sol and kneading it. After that, an alkaline compound is further added to form a fine cake.

There are various molding methods, such as: ■ extrusion molding the cake of the mixture obtained above and drying the resulting pellets, ■ drying the cake, then crushing it, and adding a lubricant such as graphite to it. There are two methods: 1) forming a mixture into tablets, and 2) forming a cake into granules using a granulator.

Among these, it is generally convenient to make pellets by extrusion molding for ease of processing and selection of shape and size. It is preferable to have a shape.

The molded body is heated at 180°C while flowing air or the target purified gas.
It is made into an adsorbent by firing at ~600°C, preferably 210~450°C.

There are no particular restrictions on the size and shape of the molded body, but representative examples include spherical, cylindrical, and cylindrical shapes. The size is 0.5 to 10 mm in diameter if spherical, 0.5 to 10 mm in diameter and 2 to 20 mm in height if cylindrical.
If the material is irregularly shaped, such as granules, a sieve with an opening of about 0.84 to 5.66 mm is used.

The density of the molded product used in the present invention is usually 0.5 to 3.0 g.
/vtΩ, preferably in the range of 0.7 to 2.5 g/yyd2. In the present invention, density refers to the weight of a molded body (grains) divided by the geometric volume of the molded body.

In addition, the packing density when the molded body is packed into an adsorption column is usually 0.4 to 2.0 g/- preferably 0.5 to 15 g/-
It is said that

In the present invention, the adsorbent is usually packed in an adsorption column, and by passing a gas containing carbon dioxide through the adsorbent and bringing them into contact, carbon dioxide in the gas is adsorbed and removed. At this time, if water is contained in the gas, this water is also removed at the same time to obtain purified gas with a low dew point.

Although the lower the adsorption temperature, the lower the adsorption temperature is generally preferred, it is sufficient as long as it is about 80°C or less, and usually has sufficient adsorption performance at room temperature of 60°C or less, and does not particularly require cooling.

The gas velocity at the time of contact may be about the same as when using synthetic zeolite, and usually the cylinder linear velocity is 150 cm/sec or less, preferably 1 to 70 cm/sec. In addition, there is no particular limit to the pressure at the time of contact, but in practice it is 1 to 10K.
It is often carried out in the range of g/cm2G.

In the present invention, two adsorption cylinders are normally used, and gas adsorption purification and adsorbent heating regeneration are alternately performed. The adsorbent that has adsorbed carbon dioxide, water, etc. is regenerated by desorbing and removing impurities such as carbon dioxide and water by heating it at 200 to 500°C, preferably 300 to 400°C while flowing purified gas through the adsorption column. , repeatedly used for adsorption purification of gases.

〔Effect of the invention〕

The present invention uses a molded composition made of a mixture of zinc oxide, aluminum oxide, and an alkali compound as an adsorbent, so that the adsorption performance is extremely high compared to the conventional method using synthetic zeolite. Furthermore, the amount of adsorption is higher than when using a molded body containing only zinc oxide as a main component, and carbon dioxide can be removed efficiently.

Furthermore, the adsorbent can be regenerated at relatively low temperatures and thus can be used repeatedly.

In addition, since the molded product has sufficient strength, it is possible to rapidly reduce the pressure from high pressure to atmospheric pressure while filling the adsorption cylinder.
It will not turn into powder even when used under harsh conditions such as increasing or decreasing the temperature.

In this way, there is no risk of powder being mixed into the purified gas, and
Because it has a high adsorption capacity, the device can be made much smaller than conventional methods, and it can be easily installed in limited spaces such as in semiconductor manufacturing processes.

〔Example〕

Example 1 Basic zinc carbonate 500g, Cataloid AP (Catalyst Chemical ■
52.4 g of high-concentration alumina (0.16 atom of AI per 1 atom of Zn), 30 g of anhydrous potassium carbonate.
2g (KO, 10 atoms per Znl atom) was placed in a small kneader and mixed for 3 minutes, then 280g of water was added and 1
Kneaded for hours. This cake is processed using a small extruder.1.
The pellets obtained by extrusion through a 9φ nozzle plate were rolled into balls using a marmerizer and dried at 110° C. for 2 hours. This material was placed in a Matsufuru furnace and fired at 350°C for 1 hour, resulting in a density of 1.14 g/mQ and a packing density of 0.74 g/mQ.
- Obtain an adsorbent.

First, the powderization rate of this product was measured.

The pulverization rate was calculated by accurately weighing the adsorbent of approximately Log, placing it in a 20 mesh sieve with a diameter of 80 mm, attaching a saucer and a lid, and using a stroke length of 55 mm and 280 strokes/min for 5
The powder was shaken horizontally for a minute, the weight of the powder that fell into the saucer was weighed, and the powderization rate was determined using the following formula.

As a result, the powdering rate was 0.6%.

Next, the adsorption capacity was measured.

Crush the molded body to 20-32 mesh and then add Ig.

A stainless steel adsorption column with an inner diameter of 7.53 mm and a length of 300 mm was filled with purified nitrogen at 50 mQ/
Regenerate at 350°C for 2 hours while running at min.

In this adsorption cylinder, raw nitrogen containing 10 ppm of carbon dioxide and having a dew point of 161°C (9 ppm as water) was
Pressure 5Kg/cm2G, temperature 35℃, flow jt1.8NZ
/min until the carbon dioxide concentration at the outlet reached 0.95 times the concentration in the raw material gas.

The amount of carbon dioxide adsorbed was determined as follows, and the gas discharged from the outlet of the adsorption column was analyzed using an FID gas chromatograph. The carbon dioxide coming out of the separation tube of the gas chromatograph is brought into contact with a nickel catalyst at 600° C. in the presence of hydrogen to convert it into methane, and then introduced to an FID (Flame Ionization Detector) to detect the methane concentration. The carbon dioxide concentration at the outlet determined in this way is plotted against the time axis, the amount of carbon dioxide released from the outlet of the adsorption column is determined, and the value is calculated by subtracting this amount from the amount of carbon dioxide in the raw material nitrogen. It was taken as the amount of carbon dioxide adsorbed. Further, the dew point was measured using a Hamada dew point meter.

As a result, the amount of carbon dioxide adsorbed was 5.3 mg/g of adsorbent, and the dew point of the outlet gas was -76°C (1 as moisture).
ppm).

Subsequently, a heating regeneration test of this adsorbent was conducted. While heating the above carbon dioxide adsorbing cylinder to 350°C, purified nitrogen gas was supplied at a flow rate of 50rd/min under normal pressure.
The amount of carbon dioxide desorbed from the adsorbent was determined using the measurement method described above and was 5.1 mg/g of the absorbent.

Furthermore, when this regenerated adsorbent was again subjected to an adsorption experiment under the same conditions as above by passing raw nitrogen through it, the amount of carbon dioxide adsorbed was 5.2 mg/g of the adsorbent.

Example 2 The amount of carbon dioxide adsorbed, the amount of desorption during regeneration, and the amount of re-adsorption were measured in the same manner as in Example 1, except that the concentration of carbon dioxide in the raw material nitrogen gas in Example 1 was changed to 30.2 ppm. Na.

As a result, the adsorption amount was 5.7 mg/g adsorbent, and the desorption amount was 5.7 mg/g adsorbent.
．． 7 mg/g adsorbent, and the re-adsorption amount was 5.6 mg/g adsorbent.

Example 3 An experiment was conducted in the same manner as in Example 1, except that the adsorption temperature and re-adsorption temperature in Example 1, 35°C, were changed to 55°C.

As a result, the adsorption amount was 4.9 mg/g adsorbent, and the desorption amount was 4.9 mg/g adsorbent.
．． 8 mg/g adsorbent, and the re-adsorption amount was 4.6 mg/g adsorbent.

Examples 4 and 5 Hydrogen gas was used instead of nitrogen gas in Example 1. Experiments were conducted in the same manner as in Example 1 for hydrogen gas containing 0.2 ppm (Example 4) and 2.7 ppm (Example 5) of carbon dioxide], respectively.

As a result, for Example 4, the adsorption amount was 8.2 mg/g.
Adsorbent, desorption amount is 8.0 mg/g adsorbent, re-adsorption amount is 8.
．． In Example 5, the amount of adsorption was 9.8 mg/g adsorbent, the amount of desorption was 9.5 mg/g adsorbent, and the amount of re-adsorption was 9.6 mg/g adsorbent.

Example 6 Oxygen gas was used instead of nitrogen gas in Example 1. An experiment was conducted in the same manner as in Example 1 using oxygen gas containing 30 ppm of carbon dioxide.

As a result, the amount of adsorption was 4.9 mg/g adsorbent, the amount of desorption was 4.9+ng/g adsorbent, and the amount of re-adsorption was 5.0 mg/g adsorbent.
g adsorbent.

Example 7 Basic zinc carbonate 782g, Cataloid AP 85.2
g (0.16 atoms of AI per 1 atom of Zn), water 34
After adding 1g and kneading for 90 minutes, add 28% ammonia water 2
2.7 g (0,047 atoms of N84 groups per 1 atom of Zn) was added and kneaded for an additional 30 minutes. The pellets obtained by extrusion molding this cake were rolled with a marmerizer, and then the same conditions as in Example 1 were applied. The adsorbent was dried and fired to obtain an adsorbent having a density of 1.23 g/d and a packing density of 0.80 g/d.

The pulverization rate of this product was measured and found to be 0.1%.

Using this adsorbent, an experiment was conducted in the same manner as in Example 1 using nitrogen gas containing 10 ppm of carbon dioxide.

As a result, the adsorption amount was 3.5 mg/g adsorbent, and the desorption amount was 3.5 mg/g adsorbent.
．． 4 mg/g adsorbent, and the re-adsorption amount was 3.3 mg/g adsorbent.

Example 8 Active Zinc Oxide 79, 9g, Cataloid AP I2.
2g (0.16 atom of AI per 1 atom of Zn), 4g of water
After adding 9.8 g and kneading for 60 minutes, 8.4 g of sodium bicarbonate (0.10 atom of Na per 1 atom of Zn) was added and kneading was further continued for 30 minutes. The pellets obtained by extrusion molding this cake were rounded with a marmerizer, dried under the same conditions as in Example 1, and baked to a density of 1.
An adsorbent with a packing density of 36 g/ml and a packing density of 0.88 g/yd was obtained.

The powdering rate of this product was measured and found to be 0.3%.

Using this adsorbent, an experiment was conducted in the same manner as in Example 1 using nitrogen gas containing 10 ppm of carbon dioxide.

As a result, the amount of adsorption was 5.0 mg/g adsorbent, and the amount of desorption was 4.
．． 8 mg/g adsorbent, and the re-adsorption amount was 4.9 mg/g adsorbent.

Example 9 Basic zinc carbonate 782g, Cataloid AP I27.
8g (10.24 atoms of A per 1 atom of Zn), 37% of water
After adding 5.4 g and kneading for 50 minutes, 213 g of 28% ammonia water (0.05 atom of NH4 group per 1 atom of Zn) was added and kneading for 20 minutes, and then 210 g of potassium bicarbonate was added.
．． 2 g (K 2 O, 30 atoms per 1 atom of Zn) was added and kneaded for an additional 20 minutes. Example 1
After drying and firing under the same conditions as in
An adsorbent with a packing density of 1.25 g/d and a packing density of 1.25 g/d was obtained.

The pulverization rate of this product was measured and was 0.2%.

Using this adsorbent, an experiment was conducted in the same manner as in Example 1 using nitrogen gas containing 10 ppm of carbon dioxide.

As a result, the adsorption amount was 3.2 mg/g adsorbent, and the desorption amount was 2.
．． The adsorption amount was 8 mg/g adsorbent and the re-adsorption amount was 2.9 mg/g adsorbent.

Comparative Example 1 A test was conducted in the same manner as in Example 1 using an adsorbent made by crushing Molecular Sieve 5A (manufactured by Union Carbide) into 20 to 32 mesh pieces, and the adsorption amount of carbon dioxide was 0, 65 mg/g adsorbent. , the carbon dioxide desorbed by regeneration is 59 mg/g of adsorbent, and the amount of re-adsorption is 6
1 mg/g adsorbent.

Comparative Example 2 82 g of commercially available activated zinc oxide prepared by baking basic zinc carbonate at 300°C and 18 g of alumina cement were mixed, 51 g of water was added and kneaded, and the pellet obtained by extrusion molding was rolled with a marmerizer. It was dried and fired under the same conditions as in Example 1 to obtain a molded body.

The powdering rate of this product was 1.2%.

This molded body was crushed into 20 to 32 meshes, and an experiment was conducted in the same manner as in Example 1.

As a result, the amount of adsorption was 2.6 mg/g, and the amount of desorption was 2.7.
mg/g, and the readsorption amount was 2.3 mg/g.

Patent applicant: Japan Bionics Co., Ltd. Representative Patent attorney: Sadafumi Kobori

Claims (1)

[Claims] In a method for removing carbon dioxide in which a gas containing carbon dioxide as an impurity is brought into contact with an adsorbent to remove carbon dioxide from the gas, a composition comprising a mixture of zinc oxide, aluminum oxide and an alkaline compound as an adsorbent is used. A method for removing carbon dioxide, characterized by using a molded body.