RU2798457C1 - Carbon dioxide absorber, methods for its preparation and method for cleaning gas mixtures - Google Patents

Abstract

FIELD: adsorptive separation of gases.

SUBSTANCE: invention relates to the adsorptive removal of CO₂ from gas mixtures, which is widely used in individual and collective life support systems, in the gas industry in the purification of natural gas, for deep purification of air before cryogenic separation, in preparation of protective atmospheres in metallurgy and other industries. A carbon dioxide absorber CO₂ from gas mixtures is presented, comprising an active component, potassium carbonate deposited on a carbon carrier, characterized in that it comprises multilayer carbon nanotubes in the amount of 55-87 wt.% as a carrier, the rest is potassium carbonate K₂CO₃ in the amount of 13-45 wt.%, respectively. In another embodiment, a method for preparing a carbon dioxide absorber from gas mixtures is provided, characterized in that the absorber is prepared by impregnating the moisture capacity of a powder of multilayer carbon nanotubes with an aqueous isopropanol solution of potassium carbonate, after impregnation, the resulting paste is moulded by an extruder or by shock pressing, the resulting granules are dried at a temperature 120°C for 4 hours, the resulting absorber comprises multilayer carbon nanotubes as a carrier in the amount of 55-87 wt.%, the rest is the active component potassium carbonate K₂CO₃ deposited on a carbon carrier, in the amount of 13-45 wt.% respectively, as well as a method for preparing a carbon dioxide absorber from gas mixtures, characterized in that the absorber is prepared by pelletizing the powder of multilayer carbon nanotubes in a plate granulator, whereas adding an aqueous isopropanol solution of potassium carbonate, spherical granules are obtained, the obtained granules are dried at a temperature of 120°C for 4 hours, the resulting absorber comprises multilayer carbon nanotubes as a carrier in an amount of 55-87 wt.%, the rest is the active component potassium carbonate K₂CO₃ deposited on a carbon carrier in an amount of 13-45 wt.%, respectively. A method is also provided for cleaning gas mixtures from carbon dioxide using an absorber containing an active component – potassium carbonate deposited on a carbon carrier characterized in that the specified absorber or absorber obtained by the presented methods is used, carbon dioxide is removed from mixtures with a partial pressure of carbon dioxide 10 Pa - 0.5 kPa, whereas carbon dioxide is released in the temperature range of 10-50°C, then the absorber is regenerated in the temperature range of 150-250°C.

EFFECT: production of a carbon dioxide absorber having a high and stable sorption capacity during operation.

4 cl, 2 dwg, 1 tbl, 6 ex

Description

The invention relates to the field of adsorption separation of gases. Adsorption removal of CO ₂ from gas mixtures is widely used in individual and collective life support systems, in the gas industry for natural gas purification, for deep air purification before cryogenic separation, in the preparation of protective atmospheres in metallurgy and other industries. Among the new areas of application of this method is the regulation of greenhouse gas emissions that cause irreversible changes in the Earth's climate. Today, regenerable CO ₂ absorbers are considered as promising materials for reversible carbon dioxide binding in the processes of cleaning gas emissions from industrial facilities and small mobile emitters, and CO ₂ release from the air.

For the separation of carbon dioxide from the atmosphere and gas reservoirs containing moist gas, many modern sorption methods are unsuitable, since they use traditional types of absorbers (zeolites, activated carbons), which, as a rule, have a much greater affinity for water than for CO ₂ . As a result, such absorbers are quickly saturated with water vapor, and carbon dioxide is little sorbed on their surface. To reduce the humidity of the gas mixture being cleaned and increase the capacity of zeolites and active carbons for CO ₂ , it is proposed to use a pre-drying unit installed in front of the adsorber with zeolite (US 6309445, B01D 53/02, 10/30/2001; US 6106593, B01D 53/04, 22.08. 2000). The disadvantage of this solution is a significant complication of the technological scheme of the process.

A method for the simultaneous removal of water vapor and carbon dioxide, devoid of this drawback, is described in the patent (US 3865924, B01D 53/02, 11.02.1975). The absorber proposed in this patent is a mechanical mixture of aluminum oxide and potassium carbonate. Such an absorber is proposed to be used to remove CO ₂ in life support systems. The absorption of CO ₂ is carried out according to the reaction

K ₂ CO ₃ + H ₂ O + CO ₂ \u003d 2KHCO ₃ .

In the patent (EP 1084743, B01D 53/02, 03/21/2001) to remove CO ₂ suggest using a more advanced absorber, in which alkali metal compounds are introduced into the pores of the aluminum oxide matrix. Due to the fact that the active component is contained in the pores of the matrix, the absorber does not cause increased corrosion of the equipment and can be produced in the form of granules of any size and shape, or in the form of blocks. At the same time, a low content of alkali metal oxides (up to 7.25 wt.% K ₂ O and/or Na ₂ O) does not provide a high capacity of the absorber. A similar system has been developed for the process of short-cycle heatless adsorption, however, the authors believe that it is advisable to introduce the active component directly into the pores of the carrier in the form of potassium carbonate (US 5656064, B01D 53/02, 12.08.1997).

The authors of the patent (JP 08040715, C01B 31/20, 02/13/1996) proposed a method for removing CO ₂ with porous materials (activated carbon, alumina, zeolite, kieselguhr or a mixture thereof) coated with potassium and/or sodium carbonate hydrate. The absorber is regenerated by blowing with superheated steam, as a result of which potassium bicarbonate is converted into potassium carbonate or potassium carbonate hydrate.

It should be noted that alkali metal carbonates are active chemical compounds capable of entering into irreversible chemical interactions with some carriers. The interaction of the active component with the carrier leads to a decrease in the sorption capacity of absorbers, therefore, in practice, they try to choose carriers in such a way that the chemical interaction of the carrier with the active component is minimal.

The authors of the patent (RU 2244586, B01D 53/02, 20.01.2005) argue that the absorber with an aluminum oxide matrix has the highest CO ₂ sorption rate, but undergoes significant deactivation during sorption/regeneration cycles. To eliminate deactivation, the authors propose to treat the original alumina with an alkaline solution, which makes it possible to remove or deactivate surface acid sites. Pretreatment leads to an increase in the stability of the sorption capacity of the absorber.

In the patent (RU 2493906, B01J 20/06, B01D 53/02, 09/27/2013) to improve the stability of the sorption capacity, it is proposed to apply potassium carbonate on a porous carrier of yttrium oxide, since yttrium oxide is less reactive with respect to potassium carbonate compared to aluminum oxide . The disadvantage of this material is the sorption capacity for carbon dioxide at the level of 2-3 wt.%. This value of the sorption capacity is due to the macroporous structure of yttrium oxide, as a result of which it is not possible to obtain a dispersed active component on the carrier surface.

Closest to the proposed invention is a patent (RU 2760325, B01D 53/56, B01J 20/06, 11/24/2021). In order to achieve a high and stable sorption capacity, this patent proposes to add potassium carbonate to the zirconium dioxide airgel matrix, which has a mesoporous structure. As a result, it is possible to obtain a material with a sorption capacity of 4-5 wt.%. The disadvantage of this invention is the high cost of production of zirconium dioxide airgel and the moderate value of the sorption capacity of 4-5 wt.% due to the high apparent density of the carrier.

The present invention solves the problem of obtaining a regenerated absorber for the selective absorption of carbon dioxide from gas mixtures, having a high sorption capacity, and developing an efficient method for removing carbon dioxide from gas mixtures.

The problem is solved using a carbon dioxide absorber from gas mixtures, which contains an active component - potassium carbonate deposited on a carrier, multi-walled carbon nanotubes (MWNTs) are used as a carrier, thus, the resulting absorber contains MWCNTs in an amount of 55-87 wt.%, the rest is potassium carbonate K ₂ CO ₃ in the amount of 13-45 wt.%, respectively.

It should be noted that multiwalled carbon nanotubes (MWNTs) form strong openwork aggregates consisting of ^entangled nanotubes with a low density, less than 0.1 g/cm , 27.11.2009). For chemical functionalization and enhancement of hydrophilic properties, MWCNTs are preliminarily oxidized by boiling in nitric acid for 2 h. (Mazov I., Kuznetsov VL, Simonova IA, Stadnichenko AI, Ishchenko AV, Romanenko AI, Tkachev EN, Anikeeva OB Different Diameters and Morphology, Applied Surface Science 2012 V.258 N17 P.6272-6280 DOI: 10.1016/j.apsusc.2012.03.021).

The developed specific surface area (up to 400 m ² /g), as well as the possibility of chemical functionalization of the surface, make it possible to use MWCNTs as a support for stabilizing finely dispersed particles (metals, oxides, salts). In addition, materials based on MWCNTs have high chemical stability in the temperature range of sorption and regeneration of potassium carbonate. These qualities make MWCNTs promising carriers for creating carbon dioxide absorbers based on K ₂ CO ₃ .

The problem is also solved by the method of preparing an absorber based on MWCNTs, according to which MWCNTs are mixed with an aqueous isopropanol solution of potassium carbonate, the resulting paste is granulated by extrusion molding, pelletizing or pressing. Next, the granules are dried in an oven at a temperature of 120°C for 4 hours. The physicochemical characteristics of the obtained absorbers and initial MWCNTs are given in the Table.

Typical micrographs of the initial MWCNT powder and the 60%-K ₂ CO ₃ /MWNT carbon dioxide scavenger prepared on its basis after its use in CO ₂ adsorption/regeneration cycles, obtained using a scanning electron microscope, are shown in Fig. 1.

The problem is also solved by the method of cleaning gas mixtures from CO ₂ , in which atmospheric air or a gas (flue) mixture is passed through a fixed absorber layer, which contains a porous matrix of MWCNTs in an amount of 55-87 wt.%, the rest is potassium carbonate K ₂ CO ₃ in the amount of 13-45 wt.%, respectively, at a temperature of 10-50°C, a partial pressure of CO ₂ in a gas mixture of 10 Pa - 0.5 kPa.

After the absorber is saturated with carbon dioxide, it is regenerated by heating in the temperature range of 150-250°C in a stream of air or an inert gas.

This method can be used for the adsorptive separation of carbon dioxide from atmospheric air and flue gases, from air flows in ventilation systems in rooms and in closed life support systems.

EFFECT: high and stable sorption capacity of the regenerated absorber during operation. The sorption capacity of K ₂ CO ₃ /MWNT absorbers with different potassium carbonate content in successive sorption/regeneration cycles is shown in FIG. 2.

The essence of the invention is illustrated by the following examples, table and figures 1-2.

Example 1

To prepare the absorber, MWCNTs are first synthesized in accordance with the procedure given in the patent (RU 2373995, B01J 37/00, 11/27/2009). To enhance the hydrophilic properties, MWCNTs are oxidized by boiling in nitric acid for 2 h. , Applied Surface Science 2012 V.258 N17 P.6272-6280 DOI: 10.1016/j.apsusc.2012.03.021).

An SEM microimage of the MWCNT powder is shown in FIG. 1(A).

MWCNT powder is divided into 4 parts, each part is impregnated according to moisture capacity with water-isopropanol solutions of potassium carbonate with different concentrations. After impregnation, the resulting paste is molded by an extruder, granules of the required shape are obtained. The resulting granules are dried in an oven at a temperature of 120°C for 4 hours. According to elemental analysis, the content of K ₂ CO ₃ in the prepared samples of absorbers is 13, 24, 40, 45 wt.%, the rest is 87, 76, 60, 55 wt.% MWCNT, respectively.

The study of the porous structure of the obtained absorbers is carried out using the method of low-temperature nitrogen adsorption. According to nitrogen porosimetry, the granules of the absorber samples have a pore volume of 0.19–1.3 ml/g, a developed mesoporous structure with a specific surface area of 36–201 m ² /g (Table). Scanning electron microscopy images of the original MWCNTs and the K ₂ CO ₃ /MWCNT absorber are shown in FIG. 1, (A) and (B), respectively.

The obtained samples of absorbers are alternately loaded into a flow-through adsorber, and sorption experiments are carried out. Each sorption experiment includes the following stages:

1) Sorption of CO ₂ from atmospheric air (partial pressure of CO ₂ in a mixture of 40-45 Pa) for 6 hours at room temperature (15-25 ° C) and a fixed relative humidity of 25%, air supply rate 2.3 l / min. In the process of sorption, the absorbers are completely saturated with carbon dioxide, which is determined from the breakthrough curve of the CO ₂ concentration at the outlet of the reactor;

2) Thermal regeneration of the absorber at a temperature of 200°C in an argon atmosphere (Ar flow rate 50 ml/min).

During the regeneration process, CO ₂ is desorbed from the absorber. At the desorption stage, the dependence of the values of the output concentration of carbon dioxide on time is recorded, from which the value of the sorption capacity of the material for CO ₂ is calculated using the formula

where: (с(t)) is the dependence of the values of the output concentration of carbon dioxide (in vol. %) on time (in minutes); U ₀ is the input flow rate of argon (0.05 l / min), m is the mass of the absorber (g), M is the molar mass of CO ₂ (44 g / mol), V _m is the molar volume of an ideal gas (24.4 l / mol at standard conditions: T = 298 K and P = 1 bar).

Sorption/regeneration cycles are carried out several times. The change in sorption capacity during the tests is shown in Fig. 2. Sorption capacity of K ₂ CO ₃ /MWNT absorbers containing potassium carbonate 13, 24, 40, 45 wt.% is 2.5, 4.9, 6.9, 7.9 wt.%, respectively, at a regeneration temperature of 200°C after 10 successive sorption/regeneration cycles. .

Example 2

According to example 1 get the absorber, which contains 14 wt.% potassium carbonate, 86 wt.% MWCNT.

The specified absorber is loaded into a flow-through adsorber, a sorption experiment is carried out analogously to example 1 with the difference that the sorption is carried out at a temperature of 10°C and a partial pressure of CO ₂ in a mixture of 10 Pa. After completion of the stage of sorption spend regeneration of the absorber at a temperature of 200°C. The sorption capacity of the absorber is 2.1 wt.%.

Example 3

According to example 1 get the absorber, which contains 14 wt.% potassium carbonate, 86 wt.% MWCNT.

The specified absorber is loaded into a flow-through adsorber, a sorption experiment is carried out analogously to example 1, with the difference that the sorption is carried out at a temperature of 15°C and a partial pressure of CO ₂ in a mixture of 20 Pa. After completion of the stage of sorption spend regeneration of the absorber at a temperature of 150°C. The sorption capacity of the absorber is 2.0 wt.%.

Example 4

According to example 1 get the absorber, which contains 45 wt.% potassium carbonate, 55 wt.% MWCNT.

The specified absorber is loaded into the flow adsorber, carry out the sorption experiment analogously to example 1 with the difference that the sorption is carried out at a temperature of 50°C and a partial pressure of CO ₂ in the mixture of 0.5 kPa. After completion of the stage of sorption spend regeneration of the absorber at a temperature of 250°C. The sorption capacity of the absorber is 8.3 wt.%.

Example 5

MWCNT powder obtained according to example 1, impregnated by moisture capacity with water-isopropanol solution of potassium carbonate. After impregnation, the resulting paste is molded by shock pressing in a tablet machine, and granules of the required shape are obtained. The obtained granules are dried in an oven at a temperature of 120°C for 4 hours. The resulting absorber contains 41 wt.% potassium carbonate, 59 wt.% MWCNT.

The absorber is loaded into a flow-through adsorber, a sorption experiment is carried out analogously to example 1 with the difference that the sorption is carried out at a temperature of 30°C and a partial pressure of CO ₂ in a mixture of 0.5 kPa. After completion of the stage of sorption spend regeneration of the absorber at a temperature of 200°C. The sorption capacity of the absorber is 6.5 wt.%.

Example 6

An aqueous isopropanol solution of potassium carbonate is added to the MWCNT powder obtained according to example 1, and the mixture is simultaneously rolled in a plate granulator, spherical granules of the required size are obtained. The resulting granules are dried in an oven at a temperature of 120°C for 4 hours The resulting absorber contains 43 wt.% potassium carbonate, 57 wt.% MWCNT.

The absorber is loaded into the flow adsorber, carry out the sorption experiment analogously to example 4 with the difference that the sorption is carried out at a temperature of 50°C. After completion of the stage of sorption spend regeneration of the absorber at a temperature of 200°C. The sorption capacity of the absorber is 7.8 wt.%.

Table - Textural characteristics of absorbers and MWNTs.

Claims (4)

1. Carbon dioxide absorber CO ₂ from gas mixtures containing an active component - potassium carbonate deposited on a carbon carrier, characterized in that it contains multilayer carbon nanotubes in the amount of 55-87 wt.% as a carrier, the rest is potassium carbonate K ₂ CO ₃ in the amount of 13-45 wt.%, respectively. 2. A method for preparing a carbon dioxide absorber from gas mixtures, characterized in that the absorber is prepared by impregnating the moisture capacity of the powder of multilayer carbon nanotubes with an aqueous isopropanol solution of potassium carbonate, after impregnation the resulting paste is molded by an extruder or by shock pressing, the resulting granules are dried at a temperature of 120 ° C for 4 hours, the resulting absorber contains multilayer carbon nanotubes as a carrier in the amount of 55-87 wt.%, the rest is the active component potassium carbonate K₂CO₃deposited on a carbon carrier, in the amount of 13-45 wt.%, respectively. 3. A method for preparing a carbon dioxide absorber from gas mixtures, characterized in that the absorber is prepared by pelletizing the powder of multilayer carbon nanotubes in a plate granulator, while adding an aqueous isopropanol solution of potassium carbonate, spherical granules are obtained, the obtained granules are dried at a temperature of 120 ° C in for 4 hours, the resulting absorber contains multilayer carbon nanotubes as a carrier in the amount of 55-87 wt.%, the rest is the active component potassium carbonate K₂CO₃deposited on a carbon carrier, in the amount of 13-45 wt.%, respectively. 4. A method for cleaning gas mixtures from carbon dioxide using an absorber containing an active component - potassium carbonate deposited on a carbon carrier, characterized in that the absorber according to claim 1 is used or obtained by the method according to claim 2 or 3, the removal of carbon dioxide is carried out from mixtures with a partial pressure of carbon dioxide 10 Pa - 0.5 kPa, while the release of carbon dioxide is carried out in the temperature range of 10-50°C, then the absorber is regenerated in the temperature range of 150-250°C.

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