Carbon dioxide absorber and a method for removing carbon dioxide for gas mixtures

FIELD: gas treatment.

SUBSTANCE: invention relates to adsorption separation of gases and provides carbon dioxide absorbent, which is prepared by impregnating porous alumina with potassium carbonate, alumina having been preliminarily treated with alkali solution, in particular solution of alkali metal hydroxides and/or carbonates. Alkali treatment is carried out at temperature above 40оС. Method of removing carbon dioxide from gas mixture, including adsorption separation of carbon dioxide from atmospheric air in cyclic processes under thermal regeneration or short-cycle heating-free adsorption conditions, is characterized by that process is conducted at 20 to 200оС with above indicated absorber.

EFFECT: increased dynamic capacity of absorber and increased carbon dioxide absorption velocity.

5 cl, 2 dwg, 9 ex

 

The invention relates to the field of adsorptive gas separation.

Adsorptive removal of CO2from gas mixtures is one of the widely used techniques of chemical technology and is actively used during the purification of natural gas, thin air cleaning prior to cryogenic separation, in the preparation of protective atmospheres, etc. To the number of new applications of this method include the clearing of CO2cathode gas for alkaline fuel cells and reduction of atmospheric pollution carbon dioxide.

However, production of pure carbon dioxide for various fields of technology with the use of the above sources is also of great interest.

Existing adsorption methods for the allocation of CO2often unsuitable for wet cleaning gas mixtures, since the traditional types of sorbents (zeolites, activated carbons) have, as a rule, the affinity for water is much greater than for CO2so sharply reduce their capacity in a humid atmosphere.

So, to reduce the moisture content of the purified gas mixture and increase the capacity of the zeolites of carbon dioxide in the number of patents requested to block the preliminary drying before adsorber with zeolite (US 6309445, B 01 D 053/04, 30.10.2001; US 6106593, B 01 D 053/04, 22.08.2000). However, this method p is the solution of the problem leads to a significant complication of the process flow diagram.

In the patent (US 3865924, B 01 D 53/34, 02.11.1975) described regenerated absorber of carbon dioxide, representing a mechanical mixture of powdered aluminum oxide and potassium carbonate. This absorber offer to apply for removal of carbon dioxide in life support systems, for example, submarines. The water here does not preclude the sorption of CO2and, in contrast, is a necessary component, because the absorption of CO2is carried out by the reaction:

To2CO3+H2O+CO2=KNSO3.

In the patent (EP 1084743, 01 D 53/047, 21.03.2001) offer to remove CO2use aluminum oxide, doped with small additions of alkali metals (up to 7.25 wt.% To2About and/or Na2O). The advantage of this method of removal of CO2is that the active substance is in the pores of the matrix and does not cause corrosion of equipment, and the absorber can be produced in the form of pellets of any size and shapes or blocks. At the same time small quantities of oxides of alkali metals does not provide the high capacity of the absorber. A similar system developed for process pressure swing adsorption (US 5656064, B 01 D 53/047, 12.08.1997).

The closest is a method of removing CO2porous materials (activated carbon, alumina, zeolite, diatomaceous earth or a mixture thereof), what and who caused the hydrate of potassium carbonate and/or sodium (Carbon dioxide recovery from waste gases at low cost and the carbon dioxide adsorbents used. Hayashi, Hiroshi; Harada, Shinichi; Shigemoto, Naoya; Yamada, Shinichi (Shikoku Sogo Kenkyusho Kk; Hayashi, Hiroshi, Japan). Jpn. Kokai Tokkyo Koho, JP 08040715, A2, C 01 B 31/20; B 01 D 53/04, 13.02.1996, Heisei, 9 pp. (Japan). Regeneration of the sorbent to produce steam. The active component of the absorber, which ensures its high capacity, is dispersed in the pores of the matrix carbonate of an alkali metal. At the same time it is a highly reactive compound that can enter into irreversible chemical interaction with some matrix-carriers. This leads to the decrease of the sorption capacity of the absorber when a multicycle operation.

The present invention solves the problem of increasing the stability of the absorber while maintaining its high sorption capacity.

To solve the problem absorber of carbon dioxide is prepared by impregnation with potassium carbonate porous aluminum oxide, the aluminum oxide pre-treated with an alkaline solution, and then into the pores of the thus prepared aluminum oxide impregnation contribute potassium carbonate. I.e. the problem is solved by chemical treatment of the surface of the matrix carrier.

As a solution having an alkaline reaction, use a solution of hydroxides or carbonates of alkali metals or any mixture. Processing walochnik solution is carried out at temperatures above 40° C.

The quantity of applied potassium carbonate SOS is to place 5-30 wt.%.

The task is also solved by a method of removing carbon dioxide from gas mixtures at a temperature of 20-200° including for the adsorption of carbon dioxide from atmospheric air in cyclic processes in conditions of thermal regeneration or pressure swing adsorption. The proposed method is characterized by the fact that they use the absorber, prepared as described above.

We found that the sorption rate and the dynamic capacity of the sorbents potassium carbonate in a porous matrix substantially depends on the matrix, and a crucial role is played by non-porous structure or specific surface area, and its chemical nature. Thus, the silica and exfoliated vermiculite due to the acidity of the surface capable of irreversible reaction with potassium carbonate with the formation of active silicates. The surface hydrophobicity of activated charcoal does not allow to achieve high dispersion of potassium carbonate and, consequently, the sorption rate is quite low. As follows from the examples 1-4, the highest sorption rate and the dynamic capacity show sorbents on the basis of gamma-aluminum oxide.

It turned out that when conducting multi-cycle tests the dynamic capacity of the absorber on the basis of gamma-aluminium oxide is gradually reduced to stationary values, as is evident from the example is 6. The main reason for this effect is the high reactivity of the surface of aluminum oxide with respect to potassium carbonate. We found that when high-cycle regeneration in large quantities formed lookabout potassium, incapable of reversible absorption of carbon dioxide l(CO3)2·N2O. Thus, for increasing the dynamic capacity of the absorber required to reduce the chemical activity of matrix-carrier, possibly removing or deaktivirovav surface acid centers.

We offer for reduction (attenuation) of the reaction between the surface of gamma-alumina and potassium carbonate to carry out chemical treatment of the carrier with an alkaline solution of a carbonate or hydroxide of an alkali metal or mixtures thereof. Such processing leads to etching of the most active acidic centers of the surface and turn them into soluble aluminates. It turned out that this treatment really helps to increase the dynamic capacity of the absorber by 50-80% and does not affect the sorption rate and the residual concentration of carbon dioxide.

For the preparation of scavengers potassium carbonate or gamma-aluminum oxide as the alkali is most appropriate to take hydroxide or potassium carbonate or a mixture thereof. To increase the speed of the process trawl the of the recommended at an elevated temperature, in boiling water or in an autoclave. Increased pH also helps speed up the process.

Later in the pores of the thus prepared aluminum oxide contribute potassium carbonate in the amount of 5-30 wt.%. The best way to make salt is a single impregnation of the alumina with an aqueous solution followed by drying.

The proposed method of application of this absorber is the removal of carbon dioxide from wet gas mixtures, including emissions of carbon dioxide from atmospheric air and fine cleaning of the cathode gas for alkaline fuel cells.

The invention is illustrated by the following examples.

Example 1. 3 g of silica gel KSK, a fraction of 0.5-1 mm, soaked in water capacity 40% solution To2CO3and dried on a rotary evaporator until a water content of 1.5 mol per 1 mol To2CO3. The resulting sorbent loaded into a flow adsorber, the inlet of which serves a mixture of saturated at 20° With water vapor the air with 2% vol. CO2, the volumetric feed rate of 150 NCM3/min. Dynamic capacity is defined as the ratio of the number of absorbed until breakthrough of carbon dioxide to the mass of sorbent and she is about 0 mg/g

Example 2. Analogously to example 1, but as a matrix using porous carbon media Sibunit. Dynamic capacity status is made about 8 mg/g

Example 3. Analogously to example 1, but as a matrix using natural clay - expanded vermiculite. The dynamic capacity is about 0 mg/g

Example 4. Analogously to example 1, but as a matrix using gamma-alumina. The dynamic capacity is about 70 mg/g, the residual concentration of carbon dioxide at the outlet is less than 20 ppm during the entire retention period.

Examples 1-4 show that the decisive role belongs to the chemical nature of the matrix carrier.

Example 5. 3 g of aluminum oxide, a fraction of 0.5-1 mm, soaked in water capacity 40% solution To2CO3and dried on a rotary evaporator until a water content of 1.5 mol per 1 mol To2CO3. The resulting sorbent loaded into a flow adsorber, the inlet of which serves a mixture of saturated at 20° With water vapor the air with 2% vol. CO2, the volumetric feed rate of 150 NCM3/min. Dynamic capacity is defined as the ratio of the number of absorbed until breakthrough of carbon dioxide gas to the mass of sorbent and she is about 0 mg/year Then regenerate the sorbent calcination in a stream of water vapor and repeat the experiment. Changing dynamic capacity during the tests is shown in figure 1, curve 1.

Example 6. Analogously to example 1, but as a matrix take sustained 45 minutes in a boiling 5%solution of KOH gamma-alumina. A plot of the change in dynamic capacity is shown in figure 1, curve 2.

Example 7. In running the adsorber loaded 6 g of sorbent on the basis of gamma-alumina, prepared as in example 1. Within 23 hours after the adsorber purge air at a rate of about 500 ml/min, followed by regeneration, as described in example 6. The amount of emitted CO2determined using a gas cylinder. A plot of the changes in the capacitance are shown in figure 2, curve 1.

Example 8. Analogously to example 8, but as the matrix used soaked 15 minutes in boiling 30% solution of K2CO3gamma-alumina. A plot of the changes in the capacitance are shown in figure 2, curve 2.

Example 9. Sorbents, in which media use pure gamma-alumina and gamma-alumina, pre-soaked for 20 minutes at a temperature of 100° With a 15% solution of K2CO3and washed with water, research method, differential dissolution. After 15 cycles “sorption-regeneration” in the sorbent on the basis of pure gamma-alumina, about 50 mol.% potassium is contained in the form of lookabout, whereas in the sorbent on the basis of pre-activated gamma-alumina of lookabout not observed.

Thus, as seen from the above examples, the proposed method allows yet get regenerated absorber of carbon dioxide CO 2suitable for removal of carbon dioxide from wet gases having a high dynamic capacity and speed of absorption of CO2. The absorber according to the invention may find wide application for separation of carbon dioxide from atmospheric air, as well as for fine purification of gases in alkaline fuel cells, for the adsorption of carbon dioxide from atmospheric air in cyclic processes in conditions of thermal regeneration or pressure swing adsorption, etc.

1. The absorber of carbon dioxide from gaseous mixtures obtained by impregnation with potassium carbonate porous alumina, wherein the alumina pretreated with an alkaline solution, and then into the pores of the thus prepared aluminum oxide impregnation contribute potassium carbonate.

2. The absorber according to claim 1, characterized in that as a solution having an alkaline reaction, use a solution of hydroxides or carbonates of alkali metals, or any mixture.

3. The absorber according to any one of claims 1 and 2, characterized in that the alkaline processing solution is carried out at temperatures above 40°C.

4. The absorber according to claim 1, characterized in that the quantity of applied potassium carbonate is 5-30 wt.%.

5. Method of removing carbon dioxide from gas mixtures, including adcor the covers emissions of carbon dioxide from atmospheric air in cyclic processes in conditions of thermal regeneration or pressure swing adsorption, characterized in that it is carried out at a temperature of 20-200°and use the absorber according to any one of claims 1 to 4.



 

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FIELD: gas treatment.

SUBSTANCE: invention relates to adsorption separation of gases and provides carbon dioxide absorbent, which is prepared by impregnating porous alumina with potassium carbonate, alumina having been preliminarily treated with alkali solution, in particular solution of alkali metal hydroxides and/or carbonates. Alkali treatment is carried out at temperature above 40оС. Method of removing carbon dioxide from gas mixture, including adsorption separation of carbon dioxide from atmospheric air in cyclic processes under thermal regeneration or short-cycle heating-free adsorption conditions, is characterized by that process is conducted at 20 to 200оС with above indicated absorber.

EFFECT: increased dynamic capacity of absorber and increased carbon dioxide absorption velocity.

5 cl, 2 dwg, 9 ex

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