EP2720778A1

EP2720778A1 - Method for absorption of co2 from a gas mixture

Info

Publication number: EP2720778A1
Application number: EP12724124.8A
Authority: EP
Inventors: Jörn Rolker; Matthias Seiler; Rolf Schneider
Original assignee: Evonik Degussa GmbH
Current assignee: Evonik Operations GmbH
Priority date: 2011-06-10
Filing date: 2012-05-25
Publication date: 2014-04-23
Also published as: EP2532413A1; WO2012168094A1; US20140120016A1

Abstract

A method for absorption of CO₂ from a gas mixture by contacting the gas mixture at an initial partial pressure of CO₂ of 0.01 to 0.6 bar with an absorption medium comprising water and an amine of the formula (I), where R is an n‑alkyl radical having 1 to 4 carbon atoms, may be operated without precipitation of a solid during the absorption of CO₂.

Description

Process for absorbing CO ₂ from a gas mixture

The invention relates to a method for the absorption of CO2 from a gas mixture, in particular from a

Combustion exhaust gas. Numerous industrial and chemical processes produce gas streams that have an undesirable level of CO2, the content of which must be reduced for further processing, transportation or avoidance of CO2 emissions.

On an industrial scale, for the absorption of CO2 from a gas mixture, usually aqueous solutions of

Alkanolamines used as absorption medium. The

loaded absorption medium is regenerated by heating, releasing to a lower pressure or stripping, whereby the carbon dioxide is desorbed. After this

Regeneration process, the absorption medium can be reused. These methods are described, for example, in Rolker, J .; Arlt, W .; "Separation of carbon dioxide from flue gases by absorption" in Chemie Ingenieur Technik 2006, 78, pages 416 to 424 and in Kohl, A.L .; Nielsen, R. B., "Gas Purification", 5th ed., Gulf Publishing,

Houston 1997 described.

However, these methods have the disadvantage that the

Separation of CO2 by absorption and subsequent

Desorption requires a relatively large amount of energy, and desorbs only part of the absorbed CO2, so that in one cycle of absorption and desorption, the capacity of the absorption medium is insufficient. No. 7,419,646 describes a process for the deacidification of waste gases, in which an absorption medium is used which forms two separable phases upon absorption of the acidic gas. As a reactive compound to Absorption of an acidic gas is mentioned in column 6 inter alia 4-amino-2, 2, 6, 6-tetramethylpiperidine. The method of US Pat. No. 7,419,646 has the disadvantage that

additional apparatus for the separation of the

Absorption incurred two phases are required.

US 2009/0199709 describes a similar process in which, after absorption of the acidic gas by heating the loaded absorption medium, two separable phases are formed and separated from one another. Again, as a suitable reactive compound for absorbing an acidic gas, other 4-amino-2,2,2,6-tetramethylpiperidine is mentioned.

FR 2900841 and US 2007/0286783 describe processes for the deacidification of exhaust gases, in which from the loaded

Absorption medium reacted with CO2 reactive

Compound is separated by extraction. As a reactive compound for absorbing an acidic gas, inter alia 4-amino-2, 2, 6, 6-tetramethylpiperidine is called.

WO 2010/089257 describes a process for the absorption of CO2 from a gas mixture with an absorption medium comprising water and a 4-amino-2,2,6,6-tetramethylpiperidine

wherein the amine may be alkylated at the 4-amino group. Absorption media containing 4-amino-2, 2, 6, 6-tetramethylpiperidine as an absorbent, however, readily absorb CO2

Precipitation of the carbamate salt. WO 2010/089257 describes the addition of solvents, such as sulfolane or ionic liquids, in order to keep the absorption medium in a single phase and to achieve a higher absorption capacity for CO 2. There is therefore still a need for one

Method of absorbing CO2 from a gas mixture suitable for the absorption of CO2 from combustion exhaust gases and with which a high absorption capacity for CO2 can be achieved, whereby in the process also without addition a solvent can be a separation into two liquid phases or the precipitation of a solid in the absorption of CO2 avoided.

It has now been found that this object can be achieved by reacting as reactive compound for the absorption of CO2, a 4-amino-2, 2, 6, 6-tetramethylpiperidine with a methyl, ethyl, n-propyl or n-butyl substituent of the

4-amino group is used and the CO 2 partial pressure of the gas mixture used in the range of 0.01 to 0.6 bar is maintained.

The invention therefore provides a process for absorbing CO 2 from a gas mixture by contacting the gas mixture at an initial partial pressure of CO 2 of from 0.01 to 0.6 bar with an absorption medium comprising water and an amine of the formula (I)

(I) wherein R is an n-alkyl radical having 1 to 4 carbon atoms, wherein the absorption medium comprises no amine having more than two nitrogen atoms.

The used in the process according to the invention

Absorbent medium comprises water and an amine of formula (I) wherein R is an n-alkyl radical of 1 to 4 carbon atoms. R can therefore be a methyl radical, an ethyl radical, an n-propyl radical or an n-butyl radical. Preferably, R is an n-propyl radical or an n-butyl radical, more preferably an n-butyl radical. Amines of the formula (I) can be

commercial Triacetonamin by reductive amination, ie by reaction of triacetoneamine with an amine of Formula RH ₂ and hydrogen are prepared in the presence of a hydrogenation catalyst. The

Absorbent medium preferably comprises 10 to 50 wt .-%, particularly preferably 15 to 30 wt .-% of amines of the formula (I). The absorption medium may, in addition to water and amines of the formula (I), one or more physical

Solvent included. The proportion of physical

Solvents may be up to 50 wt .-%. Suitable physical solvents are sulfolane,

aliphatic acid amides, such as N-formylmorpholine,

N-acetylmorpholine, N-alkylpyrrolidones, in particular

N-methyl-2-pyrrolidone, or N-alkylpiperidones, as well

Diethylene glycol, triethylene glycol and polyethylene glycols and their alkyl ethers, in particular

Diethylene glycol monobutyl ether. Preferably contains

Absorption medium, however, no physical solvent.

The absorption medium can additionally

Additives such as corrosion inhibitors, wetting additives and defoamers have. As corrosion inhibitors, it is possible in the absorption medium to use all substances which are known to the person skilled in the art for the absorption of CO ₂ using alkanolamines as suitable corrosion inhibitors, in particular the corrosion inhibitors described in US Pat. No. 4,714,597. The amount of corrosion inhibitors can in the inventive

Process significantly lower than in a conventional,

Ethanolamine-containing absorption medium, since the used in the process according to the invention

Absorbent medium compared to metallic materials is much less corrosive than the usual

used ethanolamine-containing absorption media.

As wetting-demanding additive are preferably from WO 2010/089257 page 11, line 18 to page 13, line 7th known nonionic surfactants, zwitterionic surfactants and cationic surfactants.

Defoamers which can be used in the absorption medium are all substances which are suitable for the person skilled in the art for the absorption of CO2 using alkanolamines

Defoamers are known.

In the process according to the invention, a CO2-containing gas mixture is brought into contact with the absorption medium at an initial partial pressure of CO 2 of from 0.01 to 0.6 bar. Preferably, the initial partial pressure of CO2 in the gas mixture is from 0.05 to 0.6 bar, more preferably from 0.1 to 0.5 bar, and most preferably from 0.1 to 0.2 bar. The total pressure of the gas mixture is preferably in the range of 0.8 to 10 bar, more preferably 0.9 to 5 bar.

The gas mixture can be a natural gas, a methane-containing biogas from a fermentation, composting or

Wastewater treatment plant, a combustion exhaust gas, an exhaust gas from a calcination reaction, such as the burning of lime or the production of cement, a residual gas from a

Blast furnace process for the production of iron or a resulting from a chemical reaction gas mixture, such as

for example, a carbon monoxide and hydrogen

containing synthesis gas or a reaction gas of a

Be hydrogen production by steam reforming.

The gas mixture is preferably a combustion exhaust gas or a gas mixture from the fermentation or composting of biomass, particularly preferably a combustion exhaust gas, for example from a power plant. The gas mixture can be more acidic in addition to CO2

Gases such as COS, H ₂ S, CH ₃ SH or S O2. In a preferred embodiment, the

Gas mixture in addition to CO2 still H2 S. One

Combustion exhaust gas is preferably desulfurized beforehand, ie SO ₂ is extracted from the gas mixture with a desulfurization process known from the prior art,

preferably by washing with lime milk, before the absorption process according to the invention

is carried out.

The gas mixture preferably has a content of CO ₂ before being brought into contact with the absorption medium

Range of 0.1 to 50% by volume, more preferably in the range of 1 to 20% by volume, and most preferably in the range of 10 to 20% by volume.

The gas mixture may contain oxygen in addition to CO ₂ , preferably in a proportion of 0.1 to

25% by volume, and more preferably in a proportion of 0.1 to 10% by volume. Any apparatus suitable for contacting a gaseous phase with a liquid phase may be used in the method of the present invention to contact the gas mixture with the absorption medium.

Preference is given to using gas scrubbers or absorption columns known from the prior art,

For example, membrane contactors, radial flow scrubber, jet scrubber, venturi scrubber, rotary scrubber packed columns, packed columns or tray columns. Particular preference is given to absorption columns in the

Countercurrent operation used.

In the method according to the invention, the absorption of CO _{2 is} preferably carried out at a temperature of the absorption medium in the range of 10 to 80 ° C, particularly preferably 20 to 50 ° C. When using an absorption column in countercurrent operation, the temperature of

Absorption medium particularly preferably 30 to 60 ° C when entering the column and 35 to 70 ° C when leaving the column. In a preferred embodiment of the method according to the invention, CO2 absorbed in the absorption medium is desorbed again by increasing the temperature and / or reducing the pressure, and the absorption medium is used again for the absorption of CO2 after this desorption of CO2. Desorption is preferably carried out by increasing the

Temperature. By such a cyclic process of absorption and desorption, CO2 can be separated from the gas mixture completely or partially and separated from others

Components of the gas mixture can be obtained.

As an alternative to increasing the temperature or decreasing the pressure, or in addition to increasing and / or decreasing the pressure, desorption can also be achieved by stripping the CO2 laden absorption medium with an inert gas, such as air or nitrogen.

be performed.

If water is also removed from the absorption medium during the desorption of CO2, the

Absorption medium may be added to water before reuse for absorption if necessary.

For the desorption, it is possible to use all apparatus known from the prior art for the desorption of a gas from a liquid. Desorption is preferably carried out in a desorption column.

Alternatively, the desorption of CO2 can also be carried out in one or more flash evaporation stages.

The desorption is preferably carried out at a temperature in the range of 30 to 180 ° C. In a desorption by increasing the temperature, the desorption of CO2 is preferably carried out at a temperature of the absorption medium in the range of 50 to 180 ° C, particularly preferably 80 to 150 ° C. The temperature during the desorption is preferably at least 20 ° C., more preferably at least 50 ° C, above the temperature at the

Absorption.

As used in the process according to the invention

Absorbent medium has a high absorption capacity for CO2 at a sufficiently high for a technical application absorption rate and is present in the process according to the invention as a homogeneous solution without the precipitation of a solid occurs upon absorption of CO2, the inventive method can be used in simple systems and achieved thereby an improved absorption capacity for CO2 compared to ethanolamine.

At the same time, much less energy is needed to desorb CO2 than ethanolamine.

In a preferred embodiment of the process according to the invention, the desorption is carried out by stripping with an inert gas, such as air or nitrogen, in a desorption column. Stripping in the desorption column is preferably carried out at a temperature of

Absorption medium in the range of 60 to 100 ° C. By stripping a low residual content of the absorption medium of CO2 after desorption can be achieved with low energy consumption.

In a further embodiment, the composition of the absorption medium is selected so that in a

Temperature increase for desorption a demixing of the CO2-loaded absorbent in an aqueous

C02 ~ rich and an organic C02 ~ poor liquid phase takes place. This allows regeneration at lower temperatures and energy savings

Regeneration by regenerating only the C02-rich phase and the C02-poor directly into the absorption

is returned. In these cases, an energetically favorable flash may already be sufficient to regenerate the CO2-laden absorbent. The following examples illustrate the invention, but without limiting the scope of the invention.

EXAMPLES The absorption media investigated are summarized in Table 1.

To determine the CO 2 loading, the CO 2 stroke and the relative absorption rate, 150 g of absorption medium were placed in a thermostatable container with a reflux condenser which was mounted and cooled to 3 ° C. After heating to 40 ° C or 100 ° C, a gas mixture of 14 vol% CO2, 80% by volume of nitrogen and 6% by volume of oxygen was passed through the absorption medium via a frit on the container bottom at a flow rate of 59 1 / h the CO 2 concentration in the gas stream leaving the reflux condenser over the

IR absorption determined with a C02 analyzer. By integration of the difference of the C02 content in the introduced gas stream and in the exiting gas stream, the

recorded C02 ~ amount and the

Equilibrium loading of the absorption medium calculated with CO2. The CO 2 stroke was calculated as the difference between the CO 2 levels recorded at 40 ° C and 100 ° C. From the slope of the curve of C02 concentration in the exiting gas stream for the concentration increase from 1% by volume to 12% by volume, a relative absorption rate of CO2 in the

Absorption medium determined. The so determined

Equilibrium loadings at 40 and 100 ° C. in mol CO 2 / mol amine, the CO 2 lift in mol CO 2 / kg absorption medium and the CO 2 relative absorption rate of CO 2 given in Example 1 are listed in Table 1.

In Example 2, when charged with CO2 at 40 ° C, precipitation of the carbamate salt of TAD (4-amino-2,2,6,6-tetramethylpiperidine) occurred. Table 1

* not according to the invention

** when gassing fell solid

MEA: ethanolamine

TAD: 4-amino-2, 2, 6, 6-tetramethylpiperidine

Me-TAD: 4-methylamino-2, 2, 6, 6-tetramethylpiperidine

Pr-TAD: 4- (n-propylamino) -2,2,6,6-tetramethylpiperidine

Bu-TAD: 4- (n-butylamino) -2,2,6,6-tetramethylpiperidine

The examples carried out at a C0 ₂ partial pressure of 0.14 bar show that with the inventive Method to achieve a higher C02 ~ stroke, than at

Process containing ethanolamine or TAD for absorption

deploy .

To determine the CO 2 partial pressure, from which it comes to the precipitation of a solid in the absorption, absorption medium was with that listed in Table 2

Composition in a thermostatable container with attached and cooled to 3 ° C reflux condenser

submitted. After heating to 40 ° C, a gas mixture of CO2 and nitrogen was passed through a frit at 1 bar for 2 h through the absorption medium, gas mixtures were used with 20, 40, 60 and 80% by volume of CO2

Adjust C02 partial pressures in the supplied gas mixture from 0.2 to 0.8 bar. In Table 2 is summarized in which of the experiments a precipitation of solid

was observed.

With the working medium of Example 2, an experiment was also carried out in which 250 g of working medium at 40 ° C was placed in a thermostated 500 ml autoclave and evacuated after CO2 pressure controlled to the

Saturation was added, which was gradually increased by C02 partial pressures of 75 mbar, 90 mbar and

100 mbar. At a CO 2 partial pressure of

100 mbar, the precipitation of solid was observed.

Table 2

* not according to the invention

Claims

Claims:

Process for absorbing CO ₂ from a gas mixture by contacting the gas mixture at an initial partial pressure of CO ₂ of 0.01 to 0.6 bar with an absorption medium comprising water and an amine of the formula (I)

2. The method according to claim 1,

characterized,

that R is an n-butyl radical.

3. The method according to claim 1 or 2,

characterized,

that the initial partial pressure of CO ₂ in the

Gas mixture of 0.1 to 0.5 bar.

4. The method according to any one of claims 1 to 3,

characterized,

the initial fraction of CO ₂ in the gas mixture is from 0.1 to 50% by volume.

5. The method according to any one of claims 1 to 4,

characterized,

that the gas mixture contains from 0.1 to 25% by volume of oxygen.

6. The method according to any one of claims 1 to 5, characterized

the gas mixture is a combustion exhaust gas.

7. The method according to any one of claims 1 to 5,

characterized,

that the gas mixture from the fermentation or

Composting of biomass comes.

8. The method according to any one of claims 1 to 7,

characterized,

the absorption medium comprises from 10 to 50% by weight of an amine of the formula (I).

9. The method according to any one of claims 1 to 8,

characterized,

the absorption medium contains no solvent.

10. The method according to any one of claims 1 to 9,

characterized,

that absorbed in the absorption medium CO ₂ is desorbed by increasing the temperature and / or reducing the pressure and the absorption medium after this desorption of CO ₂ again for the absorption of CO ₂

is used.

11. The method according to claim 10,

characterized,

that the absorption at a temperature in the range of 10 to 80 ° C and the desorption at a temperature in the

Range of 30 to 180 ° C is performed.

12. The method according to claim 10 or 11,

characterized,

that CO ₂ loaded absorption medium is stripped with an inert gas for desorption.