RU2493906C1 - Absorber, method of its production (versions) and method of carbon dioxide removal from gas mixes - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to adsorption separation of gases. Proposed carbon dioxide absorber containing potassium carbonate applied on porous matrix of yttrium oxide. Invention covers two methods of absorber production. Method of carbon dioxide removal from gas mixes in implemented at 20-200°C. Proposed method can be used for adsorption separation of carbon dioxide from atmospheric air in cyclic processes under conditions of thermal regeneration or shot-cycle heatless adsorption.

EFFECT: high dynamic capacity and carbon dioxide absorption rate.

4 cl, 4 ex, 2 dwg

Description

The invention relates to the field of adsorption gas separation.

The adsorption removal of CO ₂ from gas mixtures is one of the widely used methods of chemical technology and is actively used in the purification of natural gas, fine purification of air before cryogenic separation, in the preparation of protective atmospheres, etc. Among the new applications of this method include the purification of cathode gas from CO ₂ for alkaline fuel cells.

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

Existing adsorption methods for CO ₂ emission often turn out to be unsuitable for cleaning wet gas mixtures, since traditional types of absorbers (zeolites, activated carbon), as a rule, have a much greater affinity for water than for CO ₂ , and therefore sharply reduce their capacity in a humid atmosphere.

To reduce the moisture content of the gas mixture being cleaned and increase the carbon dioxide capacity of zeolites in some patents, it is proposed to use a pre-drying unit installed in front of the adsorber with zeolite (US 6309445, B1D 53/02, 10.30.2001; US 6106593, B1D 53/04, 22.08. 2000). However, this method of solving the problem leads to a significant complication of the technological scheme of the process.

The patent (US 3865924, B1D 53/02, 02/11/1975) describes a regenerable CO ₂ absorber, which is a mechanical mixture of powders of aluminum oxide and potassium carbonate. Such an absorber is proposed to be used to remove carbon dioxide in life support systems, for example, submarines. Water here does not interfere with CO ₂ sorption, but, on the contrary, is a necessary component, because the absorption of CO _{2 is} carried out by the reaction:

K ₂ CO ₃ + H ₂ O + CO ₂ = 2KHCO ₃

In the patent (EP 1084743, B1D 53/02, 03/21/2001), alumina doped with small alkali metal additives (up to 7.25 wt.% K ₂ O and / or Na ₂ O) is proposed for CO ₂ removal. The advantage of this method of CO ₂ removal is that the active substance is located in the pores of the matrix and does not cause corrosion of the equipment, and the absorber itself can be produced in the form of granules of any size and shape or blocks. At the same time, a small content of alkali metal oxides does not provide a high absorber capacity.

A similar system has been developed for the short-cycle process of adsorption without heating (US 5656064, B1D 53/02, 08/12/1997).

The closest is the method of CO ₂ removal by porous materials (activated carbon, alumina, zeolite, kieselguhr or a mixture thereof), on which potassium carbonate and / or sodium hydrate is applied (JP 08040715, A2, 02/13/1996). The sorbent is regenerated by steam. The active component of the absorber, providing its high capacity, is alkali metal carbonate dispersed in the matrix pores. At the same time, it is a highly reactive compound capable of entering into irreversible chemical interactions with certain carriers. This leads to a decrease in the sorption capacity of the absorber in a multi-cycle operation mode.

The authors of the patent (RF No. 2244586, B1D 53/02, January 20, 2005) showed that aluminum oxide is the most preferred carrier for potassium carbonate. An absorber with an alumina matrix had the highest CO ₂ sorption rate, however, it underwent significant deactivation during sorption / regeneration cycles. To reduce the rate of formation of the KAl (CO ₃ ) ₂ × 1.5H ₂ O phase, which does not absorb carbon dioxide, it was proposed to carry out preliminary alkaline surface treatment of Al ₂ O ₃ in order to etch acid surface centers interacting with potassium carbonate. Such treatment, although significantly reduces the rate of fall of the sorption capacity, but does not completely prevent the process of decontamination of the absorber.

The present invention solves the problem of obtaining a carbon dioxide absorber with a high and stable sorption capacity.

The problem is solved by the composition of the absorber, the method of its preparation and the process of removing carbon dioxide from gas mixtures.

A carbon dioxide absorber containing an active component deposited on a carrier is proposed. As a carrier, it contains yttrium oxide in an amount of 10-90 wt.%, The rest is potassium carbonate.

For this absorber, it is proposed to use two variants of the cooking method.

The first option consists in applying the active component to the carrier, followed by drying, and differs in that during the preparation of the absorber, the carrier, which is a porous matrix of yttrium oxide, is impregnated with a solution of potassium carbonate.

The main difference of the proposed second cooking option is that potassium hydroxide is preliminarily added to the pores of the carrier, yttrium oxide, and then the absorber is aged in a carbon dioxide atmosphere at a temperature of 40-60 ° C. As a result of this treatment, potassium hydroxide localized in the pores is converted to potassium carbonate. This method allows you to make potassium carbonate in the pores of yttrium oxide in an amount of up to 90 wt.%.

To use these absorbers, a method for removing carbon dioxide from gas mixtures at a temperature of 20-200 ° C, including for the adsorption of carbon dioxide from atmospheric air in cyclic processes under conditions of thermal regeneration or short-cycle heating without adsorption. Thus, the main difference of this method of removing CO ₂ is the use of the proposed absorber for binding carbon dioxide.

The proposed method of using this absorber is to remove carbon dioxide from wet gas mixtures, including carbon dioxide emission from atmospheric air and fine purification of cathode gas for alkaline fuel cells.

The invention is illustrated by the following examples.

Example 1. (Comparative).

3 g of a granular gamma-alumina support is impregnated with a moisture capacity of 40% K ₂ CO ₃ and dried on a rotary evaporator to a water content of 1.5 mol per 1 mol of K ₂ CO ₃ . The resulting sorbent is loaded into a flow adsorber, to the inlet of which a mixture of air saturated with water vapor with 2 vol.% CO ₂ is fed at 20 ° C, the volumetric feed rate is 150 ncm ³ / min. Dynamic capacity is defined as the ratio of the amount of gas absorbed until the breakthrough of carbon dioxide gas to the mass of the sorbent and in the first cycle it is about 40 mg / g. Then the sorbent is regenerated by calcination in a stream of water vapor and the experiment is repeated. The composition of the absorber is represented by two components: alumina in an amount of 10-90 wt.%, Potassium carbonate 90-10 wt.%.

The change in dynamic capacity during the tests shown in figure 1, curve 1.

Example 2

Analogously to example 1, but as a carrier take granular yttrium oxide.

The dependence of the dynamic capacitance is shown in figure 1, curve 2.

Example 3. (Comparative).

6 g of a sorbent based on gamma-alumina prepared analogously to Example 1 is loaded into a flow adsorber. Air is blown through the adsorber for 23 hours at a rate of about 500 ml / min, then steam regeneration is carried out. The amount of CO ₂ emitted is determined using a gas cylinder.

The dependence of the change in capacity is shown in Figure 2, curve 1.

Example 4

Analogously to example 3, but use an absorber prepared by impregnating a porous carrier from yttrium oxide with a 30% potassium hydroxide solution, followed by carbonization of the absorber in an atmosphere of carbon dioxide at a temperature of 40-60 ° C. The composition of the absorber: yttrium oxide in an amount of 10-90 wt.%, The rest is potassium carbonate.

The graph of the dependence of capacity changes is shown in Figure 2, curve 2.

Sorbents in which gamma-alumina and yttrium oxide are used as a carrier are examined by x-ray phase analysis.

After 15 cycles of sorption-regeneration, peaks corresponding to the formation of the mixed phase KAl (CO ₃ ) ₂ × 1.5H ₂ O appear on the diffractogram of the sorbent with an alumina support.

On the diffraction pattern of the sorbent with the yttrium oxide support, the formation of peaks of the mixed potassium – yttrium phase is not observed.

Thus, as can be seen from the above examples and illustrations, the proposed method allows to obtain a regenerable absorber suitable for removing CO ₂ from moist gases, having a high dynamic capacity and absorption rate of carbon dioxide.

The absorber according to the invention can be widely used for the emission of CO ₂ from atmospheric air, as well as for fine purification of gases in alkaline fuel cells.

Claims (4)

1. The carbon dioxide absorber containing the active component is potassium carbonate deposited on a carrier, characterized in that it contains a porous matrix of yttrium oxide in an amount of 10-90 wt.%, The rest is potassium carbonate. 2. A method of preparing a carbon dioxide absorber by applying an active component of potassium carbonate to a carrier, followed by drying, characterized in that during the preparation of the carrier, which is a porous matrix of yttrium oxide, impregnated with a solution of potassium carbonate, the result is an absorber containing yttrium oxide in the amount of 10-90 wt.%, the rest is potassium carbonate. 3. A method of preparing a carbon dioxide absorber by applying an active component of potassium carbonate to a carrier, followed by drying, characterized in that during the preparation process, potassium hydroxide is preliminarily added to the pores of the carrier, which is a porous matrix of yttrium oxide, and then the absorber is aged in a carbon dioxide atmosphere at a temperature of 40-60 ° C, the result is an absorber containing yttrium oxide in an amount of 10-90 wt.%, the rest is potassium carbonate. 4. The method of removing carbon dioxide from gas mixtures at a temperature of 20-200 ° C, including for the adsorption of carbon dioxide from atmospheric air in cyclic processes in the conditions of thermal regeneration or short-cycle heating without adsorption, characterized in that the absorber according to claim 1 or prepared according to any one of paragraphs.2 and 3.

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