JPH05161843A - Carbon dioxide adsorbent - Google Patents

Abstract

PURPOSE:To enhance the support amount of amines and the adsorbing and removing capacity of carbon dioxide in a carbon dioxide adsorbent. CONSTITUTION:Amines are supported on optically anisotropic porous fine granular activated carbon such as activated mesocarbon microbeads. Activated carbon has a specific surface area of about 500-4600m<2>/g and a pore volume of about 0.5-3.0ml/g and can increase the support amount of amines. The support amount of amines is about 0.1-50wt.%. As amines, aliphatic, alicyclic, aromatic and heterocyclic amines can be used and low volatile amine is pref.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an adsorbent for adsorbing carbon dioxide, more specifically, a carbon dioxide removing device in a closed space of a spacecraft, a submarine, a deep sea boat, etc. The present invention relates to a carbon dioxide gas adsorbent used in a carbon dioxide gas removal device and the like.

[0002]

2. Description of the Related Art Carbon dioxide is produced in large quantities from living organisms, combustion wastes, chemical factories, etc., and the greenhouse effect of the earth caused by carbon dioxide is now regarded as a problem. There is. In addition to the effect on the global environment, carbon dioxide poses a problem in a closed environment such as spacecraft, submarines, and deep-sea vessels. Therefore, various carbon dioxide adsorbents have been proposed. For example, a zeolite-based adsorbent such as Na-X zeolite has been proposed as an adsorbent that adsorbs and removes carbon dioxide by physical adsorption.

However, since the zeolite adsorbent has a remarkably large adsorption capacity for water, when water coexists, the adsorption of water impairs the adsorption of carbon dioxide. Therefore, the amount of carbon dioxide gas adsorbed is significantly reduced.

As an adsorbent for fixing carbon dioxide gas, an adsorbent in which amine is impregnated on activated carbon or activated carbon fiber has been proposed. Also, JP-A-61-1124
Japanese Patent Publication No. 4 proposes a carbon dioxide adsorbent in which an alkali metal salt of N-methylalaninic acid is supported on a porous carrier. In this amine impregnated activated carbon, the amount of carbon dioxide gas removed depends on the amount of impregnated amine. However, since the amount of amine impregnated is small, the amount of carbon dioxide gas adsorbed is small.

Further, a liquid amine absorbent is known which absorbs carbon dioxide by chemically reacting with carbon dioxide by gas-liquid contact with a gas containing carbon dioxide.

However, when the liquid amine absorbent is used, the equipment becomes large and the operation and maintenance of the apparatus become complicated.

Therefore, it is an object of the present invention to provide a carbon dioxide adsorbent which has a large amount of amines supported and a large ability to remove carbon dioxide.

Another object of the present invention is to provide a carbon dioxide adsorbent capable of adsorbing and removing a large amount of carbon dioxide even if the amount is small and making the apparatus compact.

[0009]

In order to achieve the above object, the present inventor has
As a result of intensive studies, the optically anisotropic porous carbon fine granular activated carbon has a remarkably large specific surface area and pore volume,
The present invention has been completed by discovering that when the above activated carbon is loaded with amines, not only the loading amount is significantly increased, but also a large amount of carbon dioxide gas can be removed even in the presence of water.

That is, the present invention provides a carbon dioxide adsorbent in which amines are supported on optically anisotropic porous carbon fine granular activated carbon. The granular activated carbon is preferably activated mesocarbon microbeads.

The activated carbon as a carrier is composed of an optically anisotropic porous carbon fine granular activated carbon (hereinafter, simply referred to as activated carbon unless otherwise specified). The activated carbon has a remarkably large specific surface area and pore volume as compared with conventional powdered activated carbon. Therefore, the amount of amines supported can be significantly increased, and the amount of carbon dioxide gas adsorbed per unit weight of the adsorbent can be significantly increased.

The specific surface area of the activated carbon is, for example, 500.
~4600m ² / g, preferably 1000~4600m
² / g, more preferably 2000 to 4600 m ² / g
The total pore volume is, for example, 0.5 to 3.0 m.
1 / g, preferably 0.6 to 3 ml / g, and more preferably 0.8 to 3.0 ml / g. If the specific surface area or the total pore volume of the activated carbon is less than the above range, the amount of amines supported is not sufficient, and the carbon dioxide gas removing ability decreases.

[0013] Activated carbon has a remarkably smaller pore size than conventional activated carbon, and has a benzene adsorption capacity of about 0.2 to 1.0 g / g according to JIS K 1474.
Methylene blue adsorption capacity according to K 1470 is 100
Approximately 650 ml / g, which is more than that of conventional activated carbon.
It has a remarkably large adsorption capacity. Further, since the shape is substantially spherical and the particle size distribution is sharp, the carbon dioxide gas removing device is excellent in filling property.

The activated carbon is optically anisotropic, and usually 90% or more of the whole is composed of particles having a particle size of 80 μm or less, and 85% or more of the total pore volume is a micropore having a pore diameter of 20 Å or less. It is composed by. The average particle diameter of the activated carbon is, for example, 100 μm or less, preferably 80 μm or less, and more preferably about 5 to 30 μm.

Such activated carbon can be constituted by activated optically anisotropic porous carbon fine particles, preferably activated mesocarbon microbeads. The optically anisotropic porous carbon fine particles can be seen by forming spherulites in which carbon six-membered ring network planes are laminated in parallel in the process of heating the petroleum-based and coal-based pitches. It was issued. These spherulites form a phase different from the matrix pitch, and the antisolvent method,
It is isolated by a centrifugation method or the like. The isolated spherulite is generally called mesocarbon microbeads, is a sphere having a diameter of about 2 to 80 μm, and has an optically anisotropic structure.

The activated carbon of the present invention is obtained by activating the mesocarbon microbeads, which are the precursor particles, as they are or after applying an activation aid to the surface thereof.
The activated mesocarbon microbeads may be in the form of green powder, carbonized powder, or graphitized powder.

Examples of the activation aid include KOH and Na.
OH, CsOH, ZnCl ₂ , H ₃ PO ₄ , K ₂ S
O ₄ , K ₂ S and the like are exemplified. At least one of these activation aids is used. The amount of the activation aid applied is preferably about 1 to 10 times the weight of the mesocarbon microbeads. Since the degree of activation is approximately proportional to the amount of the activation aid applied, the specific surface area of the activated carbon can be adjusted by the amount of the activation aid. The activation aid is usually used in liquid form. That is, an activation aid that is solid at room temperature, such as KOH,
An activator that is used in the form of an aqueous solution and is liquid at room temperature, such as H ₃ PO ₄ , does not necessarily have to be an aqueous solution.

Further, in order to improve the wettability of the activation aid on the surface of the mesocarbon microbeads, a surface active agent such as acetone, methyl alcohol or ethyl alcohol may be used in combination. The amount of the surfactant used is usually preferably about 5 to 10% by weight of the total amount of the mesocarbon microbeads and the activating aid or the solution containing the activating aid.

The activation is carried out by raising the temperature of the mesocarbon microbeads with or without the activation auxiliary agent to an appropriate temperature, for example, about 400 to 1200 ° C. The rate of temperature rise and the heating and holding time are not particularly limited and can be selected within a wide range, but usually, after reaching the above temperature range, the material is cooled immediately or held within the same temperature range for up to about 3 hours. It is done by

The atmosphere at the time of activation may be an inert atmosphere such as nitrogen, helium or argon, or may be an oxidizing atmosphere in which water vapor, carbon monoxide, oxygen and the like are present. The yield is higher when activated in an inert atmosphere.

In order to activate in an inert atmosphere, an activating aid is usually used to heat at a temperature rising rate of about 300 to 600 ° C./hour to a temperature of about 400 to 1200 ° C. and at the same temperature for 3 hours.
It is preferable to hold it for 0 minutes to 1 hour.

When activating in an oxidizing atmosphere, an activating aid is usually unnecessary, but it may be used in combination. When activating without using an activating aid, usually, when activating with an activating aid at a temperature of about 600 to 900 ° C., it is usually 30.
Temperature rising rate of 0-900 ℃, temperature rising rate of 300-600 ℃
It is preferable to heat for about 3 hours / hour and to maintain the same temperature for about 2 to 3 hours. It should be noted that when an activation aid is used, bumping may occur.

There is an optimum activation temperature depending on the type of activation aid. The optimum activation temperature is, for example, KOH,
In the case of K ₂ SO ₄ and K ₂ S, about 800 to 1000 ° C., in the case of NaOH and CsOH, about 600 ° C., Zn
In the case of Cl ₂ , the temperature is about 450 ° C. After cooling the activated mesocarbon microbeads to room temperature, the unreacted activation aid and the activation aid reaction product are removed by washing with water as necessary, and the activated carbon used in the present invention is dried. can get.

It is speculated that the above-mentioned activation aid promotes gasification by oxidation of carbon in the mesocarbon microbeads. That is, the activation aid reacts with the carbon atoms of the carbon six-membered ring network surface forming the mesocarbon microbeads,
It is assumed that the generated carbon monoxide or carbon dioxide is discharged out of the system.

When activated in an inert atmosphere, carbonization proceeds in the portion not involved in the reaction, so that the structural difference between the reacted portion and the unreacted portion becomes large and pores are formed. In this case, the mesocarbon microbeads have a regular layered structure, and the generated pores have many micropores of less than 20 angstrom. Further, when the reaction atmosphere is an inert atmosphere, the selectivity of the surface gas reaction is high and the yield is significantly high.

Since the reaction between the activation aid and carbon proceeds extremely violently, when carbon fibers are used instead of the mesocarbon microbeads and activation is performed in the same manner as described above, the shape thereof does not remain in its original shape. It is deformed and the strength is significantly reduced. On the other hand, in the case of mesocarbon microbeads, the spherical shape thereof is substantially maintained even after activation, and no remarkable decrease in strength is observed.

The activated carbon obtained as described above has substantially the same size and shape as the mesocarbon microbeads used as a raw material, and exhibits the above-mentioned excellent properties.

The activated carbon is not limited to a powder form, and can be used by an ordinary method, for example, using a resin binder or the like to be formed into an appropriate shape such as a granular form, a paper form, a honeycomb form, or a fibrous form. In molding, in addition to the binder,
Fibers such as pulp can also be used. As a molding method,
For example, a suction molding method of sucking and molding the slurry containing the activated carbon using a suction molding die, an extrusion molding method of extruding and molding a composition containing the activated carbon, and the like can be adopted.

As the amines supported on the activated carbon, any of aliphatic, alicyclic, aromatic and heterocyclic amines can be used. The amines may be any of primary amines, secondary amines and tertiary amines, but primary amines and secondary amines are preferred. Examples of amines include dibutylamine, tributylamine, monoethanolamine, diethanolamine, triethanolamine, diethylenetriamine,
Aliphatic amines such as triethylenetetramine and hexamethylenediamine; Alicyclic amines such as cyclohexylamine; Aromatic amines such as aniline, N, N-dimethylaniline, N-ethylaniline, aminophenol, benzylamine and phenylenediamine; Morpholine, N-
Heterocyclic amines such as methylpyrrolidone are exemplified. These amines can be used alone or in combination of two or more.

Preferred amines are those with low volatility, preferably non-volatility, especially those having a vapor pressure at 20 ° C. of not more than 20 mmHg.

The supported amount of amines is, for example, 0.1 to 7
It is about 5% by weight, preferably about 1 to 60% by weight, and more preferably about 2.5 to 50% by weight. If the supported amount of amines is less than 0.1% by weight, the ability to adsorb and remove carbon dioxide is small, and if it exceeds 75% by weight, an excess amount tends to occur.

The amines can be supported by a conventional method, for example, a method of spraying the activated carbon with amines or a solution thereof, and a method of immersing the activated carbon in a solution of amines and drying.

The adsorption capacity of such a carbon dioxide adsorbent is equivalent to 10 to 50% by weight of the activated carbon, which is about four times as high as that of the conventional carbon dioxide adsorbent using activated carbon. Indicates. Therefore, the adsorbent of the present invention can adsorb and remove a large amount of carbon dioxide even if the adsorbent is a small amount.

[0034]

The carbon dioxide adsorbent of the present invention uses activated carbon as a carrier, which has a remarkably large specific surface area and a large pore volume, and therefore has a large amount of amines supported and can remarkably enhance the adsorption and removal ability for carbon dioxide. it can. Further, since the carbon dioxide adsorbent of the present invention has a high ability to adsorb and remove carbon dioxide, a large amount of carbon dioxide can be adsorbed and removed even in a small amount,
The device can be made compact.

[0035]

EXAMPLES The present invention will be described in more detail based on the following examples.

Example 1 To a mixture of 100 parts by weight of mesocarbon micro beads and 1200 parts by weight of a potassium hydroxide solution (400 parts by weight of potassium hydroxide and 800 parts by weight of water), 50 parts by weight of acetone was added to homogenize the mixture. Mix to form a slurry. Then, the slurry is heated from room temperature to 850 ° C. under a nitrogen gas atmosphere.
After heating at a temperature rising rate of 10 ° C./min for 1 hour to activate at that temperature, the reaction mixture is cooled to 100 ° C. or lower, washed with water, and dried to obtain optically anisotropic porous fine particles. Activated carbon was obtained. The specific surface area of this activated carbon after drying is 2800 m.
It was ² / g.

The obtained activated carbon (180 parts by weight) and wood pulp (120 parts by weight) were dispersed in water (50,000 parts by weight) and beaten until the fiber diameter of the pulp became 0.1 to 5 mm.
100 parts by weight of a 5% by weight polyvinyl alcohol aqueous solution was added to prepare a uniform slurry. Then the inner frame is 1
The slurry was poured into a molding frame of 00 mm × 100 mm × 10 mm and mixed, suctioned from the inside to remove water, and the sheet-shaped molded body remaining in the molding frame was taken out from the molding frame.
It was heated and dried at 0 ° C. for 120 minutes to obtain molded activated carbon. The dimensions of the obtained molded activated carbon are 100 mm in length and 100 mm in width.
And the thickness was 10 mm.

The shaped activated carbon was immersed in a 30% by weight benzylamine ethanol solution and air-dried to obtain a shaped adsorbent having an amine loading of 45% by weight.

Air containing 2% by volume of carbon dioxide gas was passed from one surface of the obtained sheet-shaped molded adsorbent to the other surface, and the saturated adsorption amount of carbon dioxide gas was measured. As a result, the weight of the shaped adsorbent increased by 11% by weight due to the adsorption of carbon dioxide gas. When this weight increase is converted into a saturated adsorption amount with respect to the activated carbon weight, it corresponds to 34% by weight.

Example 2 The saturated adsorption amount of carbon dioxide gas was measured in the same manner as in Example 1 except that diethanolamine was used instead of benzylamine of Example 1, and the weight of the shaped adsorbent due to the adsorption of carbon dioxide gas was measured. Was increased by 8% by weight. Converting this weight increase into a saturated adsorption amount with respect to the activated carbon weight, it corresponds to 24% by weight.

Claims (2)

[Claims] 1. A carbon dioxide gas adsorbent in which amines are supported on optically anisotropic porous carbon fine granular activated carbon. 2. The carbon dioxide adsorbent according to claim 1, wherein the optically anisotropic porous carbon fine granular activated carbon is activated mesocarbon microbeads.