WO2008068411A2

WO2008068411A2 - Extraction medium used in a method for capturing carbon dioxide contained in a gaseous effluent

Info

Publication number: WO2008068411A2
Application number: PCT/FR2007/001857
Authority: WO
Inventors: Bruno Delfort; Pierre-Louis Carrette
Original assignee: Ifp
Priority date: 2006-11-27
Filing date: 2007-11-09
Publication date: 2008-06-12
Also published as: FR2909010B1; WO2008068411A3; FR2909010A1; EP2099551A2

Abstract

The invention relates to an extraction medium used in a method for capturing carbon dioxide contained in a gaseous effluent. The CO2 extraction medium used in said method comprises the product obtained from an acid-base reaction between two species B and R(ZH)n, in which B is a base or a mixture of bases selected from among amines such as amidines or guanidines and R(ZH)n is a compound or a mixture of compounds comprising at least one alcohol function or a thiol function (R being a heterocyclic, mono or polyaromatic, alicyclic or aliphatic multivalent or monovalent group, Z being an oxygen atom and/or a sulphur atom and n being between 1 and 20). The carbon dioxide capture method comprises the following steps: a) the CO2-containing gas to be treated is brought into contact with the extraction medium so as to obtain a CO2-depleted gas and a CO2-rich extraction medium, and b) the CO2-rich extraction medium is regenerated in order to obtain a reusable extraction medium and generate a gas that is very rich in CO2.

Description

EXTRACTION MEDIUM USED IN A CARBON DIOXIDE CAPTURE PROCESS CONTAINED IN A GASEOUS EFFLUENT

Field of the invention

The present invention relates to the decarbonation of a gaseous effluent.

Prior art

Carbon dioxide is one of the greenhouse gases largely produced by different human activities and has a direct impact on air pollution.

In order to reduce the quantities of carbon dioxide emitted into the atmosphere, it is possible to capture the CO ₂ contained in a gaseous effluent. Decarbonation of gaseous effluents such as for example natural gas, synthesis gases, combustion fumes, refinery gases, bottoms gases from the Claus process, biomass fermentation gases, cement gases and Blast furnace gas is usually made by washing with an absorbent solution. The physico-chemical characteristics of the solutions employed are closely related to the nature of the gas to be treated: selective removal of an impurity, specification expected on the treated gas, thermal and chemical stability of the solvent with respect to the various compounds present in the gas to be treated. treat.

The solvents commonly used today are aqueous solutions of primary, secondary or tertiary alkanolamine. Indeed, the absorbed CO ₂ reacts with Palcanolamine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of carbamates, hydrogenocarbonates or carbonates. These balanced reactions can be written according to the following diagrams:

For a primary alkanolamine such as for monoethanolamine, the reaction involved is: RNHCOO-, ⁺ H ₃ NR carbamate

hydrogen

For a secondary alkanolamine such as for diethanolamine, it is written:

RR ¹ NCOO-, ⁺ H ₂ NRR 'carbamate, H ₂ NRR

'- ** carbonate

hydrogen

and for a tertiary alkanolamine such as methyldiethanolamine:

RR ¹ R ¹¹ N

RR ¹ R ¹¹ N + CO _{2 +} H ₂ O RR ¹ R ¹¹ NHVO-C-OH _* RR ¹ R ¹¹ NH ⁺ ZO ^ 0 ^" , ⁺ HNRR ¹ R"

II C

O II carbonate hydrogen carbonate

An alternative to aqueous alkanolamine solutions is the use of hot solutions of alkali metal carbonates. The principle is based on the absorption of CO ₂ in the aqueous solution, followed by the reversible chemical reaction with the carbonates. It is known that the addition of additives makes it possible to optimize the effectiveness of the solvent.

Some decarbonation processes by washing with an absorbent solution such as chilled methanol or polyethylene glycols, are based on a physical absorption of CO ₂ .

An essential aspect of gas treatment operations or smokes by solvent remains the regeneration of the separating agent. Depending on the type of absorption (physical or chemical), regeneration by expansion, distillation and / or entrainment by a vaporized gas called "stripping gas" is generally considered.

In general, the implementation of all the absorbent solutions described above imposes a significant energy consumption for the regeneration of the separating agent. For example, the regeneration of an aqueous solution of ethanolamine used to capture CO ₂ in a smoke represents about 4GJ per tonne of CO ₂ captured. Such energy consumption represents a considerable operating cost for the CO ₂ capture process.

Summary of the Invention: The CO ₂ extraction medium, used in a process for capturing carbon dioxide contained in a gaseous effluent, comprises the product obtained by an acid-base reaction between two species B and R ( ZH) n, where B is a base or a mixture of bases chosen from amines such as amidines or guanidines and R (ZH) n is a compound or a mixture of compounds comprising at least one alcohol function or a thiol function ( R being is a monovalent or multivalent aliphatic, alicyclic, mono- or polyaromatic, or heterocyclic group, Z an oxygen atom and / or a sulfur atom and n being between 1 and 20).

The process for capturing carbon dioxide consists in carrying out the following steps: a) contacting the gas to be treated containing CO ₂ with said extraction medium, so as to obtain a gas depleted of CO ₂ and a medium of carbon dioxide; extraction rich in CO ₂ , b) the regeneration of the CO ₂ -rich extraction medium, to obtain an extraction medium that can be used again and to generate a gas rich in CO ₂ .

Description of the figure:

FIG. 1 represents the evolution of the regeneration rate as a function of time and compares the regeneration rate at 40 ^° C. under 20 Nl / h of nitrogen of two CO ₂ loaded extraction media (mixture A according to the invention). and reference mixture C).

Detailed description of the invention. The present invention proposes to use a CO ₂ extraction medium different from the prior art. This extraction medium makes it possible to capture CO ₂ contained in a gaseous effluent. Once loaded with CO ₂ , said medium can also be regenerated under easier conditions than the absorbent solutions of the prior art. The process for capturing carbon dioxide consists in carrying out the following steps: a) the gas to be treated containing CO ₂ is brought into contact with an extraction medium, so as to obtain a gas depleted in CO ₂ and a medium CO ₂ rich extraction medium, b) the CO ₂ -rich extraction medium is regenerated, so as to obtain a reusable extraction medium and to generate a very rich gas CO ₂ .

The extraction medium comprises the product obtained by an acid-base type reaction between two species B and R (ZH) n defined as follows:

B is a base or a mixture of bases chosen from amines such as amidines or guanidines, of general structure:

in which

- R1, R2 and R3 are independently selected from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or substituted or unsubstituted polyaromatic;

- R4 is chosen from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono- or polyaromatic substituted or unsubstituted ; or R4 is constituted by the pattern:

in which R5 and R6 are independently selected from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or not. R5 and R6 may contain, for example, one or more halogens, one or more heteroatoms or nitrile, ketone, amide or nitro groups.

When R4 represents a hydrogen atom, an aliphatic, alicyclic, heterocyclic, mono or polyaromatic hydrocarbon group, the bases B belong to the family of amidines.

R1, R2, R3 and R4 may contain, for example, one or more halogens, one or more heteroatoms or nitrile, ketone, amide or nitro groups.

In addition, R1, R2, R3 and R4 may be linked together to form rings or heterocycles. Among the amidines, mention may be made, for example, without being exhaustive, imidazoline, 2-methyl-2-imidazoline, 1, 4,5,6-tetrahydropyrimidine, N-methyltetrahydropyrimidine, 6- (dibutylamino) 1,8-diazabicyclo (5.4.0) undec-7-ene, 4-azabenzimidazole, anabasin, N'-tertbutyl-NN-dimethylformamidine, 1,5-diazabicyclo (4.3.0) non-5- ene of formula:

and 1,8-diazabicyclo (5.4.0) undec-7-ene of formula:

When R4 represents a pattern

R ₆

- N ^' R ₅

the bases B belong to the family of guanidines. R1, R2, R3, R5 and R6 can be connected together to form rings or heterocycles.

In addition, R 1, R 2, R 3, R 5 and R 6 may include, for example, one or more halogens, one or more heteroatoms or nitrile, ketone, amide or nitro groups.

Among the guanidines that may be mentioned for example, without being exhaustive, guanidine, tetramethylguanidine, pentamethylguanidine, butyltetramethylguanidine, tert-butyltetramethylguanidine, phenylguanidine, 1,5,7-triazabicyclo (4.4.0) dec-5-ene, formula :

and 7-methyl-1,5,7-triazabicyclo (4.4.0) dec-5-ene of the formula

R (ZH) n is a compound or a mixture of compounds having a structure in which:

R is chosen from a monovalent or multivalent aliphatic group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or unsubstituted. R may contain for example one or more halogens, one or more heteroatoms or functions alcoholic, thiols, ethers, thioethers, nitriles, ketones, sulfones, sulfoxides, amides, amines or nitrates. Z is an oxygen atom and / or a sulfur atom, linked on the one hand to the radical R and on the other hand to a hydrogen atom.

n is between 1 and 20, preferably between 1 and 6.

As regards the definition of R, monovalent and multivalent means that the group is substituted by at least one or more (from 1 to n) -ZH units as defined above and provided that the rules of organic chemistry.

This general structure therefore indicates that R (ZH) n has at least one alcohol function or a thiol function. When n is greater than 1, R (ZH) n can have both one or more alcohol functions with one or more thiol functions.

When Z is exclusively an oxygen atom, R (ZH) n is chosen for example, without being exhaustive, from monoalcohols such as methanol, ethanol, propanols, butanols, pentanols, hexanols, octanols, decanols, dodecanol, fatty alcohols, polyols such as ethylene glycols, propylene glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, monoethers of glycols, glycerol, C ₄ , C ₅ and C ₆ polyols. derivatives, for example, sugars, tetrahydrofurfuryl alcohol, phenol, benzyl alcohol, diglycerol, 2,2'-thiodiethanol, tetrahydrothiopyran-3-ol, 2- (methylsulfonyl) ethanol,

3-methylthio-1,2-propanediol, 3-ethylthio-1,2-propanediol, 1,4-dithiane-2,5-diol,

3,3'-thiodipropanol and 3,6-dithia-1,8-octanediol.

When Z is exclusively a sulfur atom, R (ZH) n is chosen for example, without being exhaustive, among thiols such as decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol, ethylenedithiol, 2-methyltetrahydrofuran-3- thiol, pyrimidine-2-thiol, 1H-1,2,4-triazole-3-thiol, 4-methyl-4H-1,2,4-triazole-3-thiol,

2-mercaptoethylether, phenylmercaptan, benzylmercaptan,

4-methoxybenzylmercaptan, 2-mercaptobenzothiazole, mercaptothiazoline, tert-dodecylmercaptan, tert-nonylmercaptan, 2,2 '- (ethylenedioxy) diethanethiol, 2-ethylhexanethiol and 2-furanmethanthiol. When n is greater than 1 and Z is a sulfur atom and an oxygen atom, R (ZH) n is chosen, for example, without being exhaustive, from 1-thioglycerol, 2-mercaptoethanol and 1-mercapto. 2-propanol, 2-mercapto-3-butanol, 2,3-dimercapto-1-propanol and 1,4-dithioerythritol. According to a variant of the invention, the base B and the species R (ZH) n can be linked by at least one chemical bond so as to constitute only one molecule. It may be for example 1, 4,5,6-tetrahydro-2-pyrimidinethiol, 3- (2-hydroxyethyl) -1,4,5,6-tetrahydropyrimidine, 7- (2-hydroxyethyl) - 1, 5,7-triazabicyclo [1- (4, 4)] dec-5-ene, 7- (4-hydroxybutyl) -1,5,7-triazabicyclo [4.4.0] dec-5-ene, 7- ( 2-mercaptoethyl) -1,5,7-triazabicyclo [4.4.0] dec-5-ene, 7- (2-hydroxyethoxyethyl) -1,5,7-triazabicyclo [4.4.0] dec-5-ene, (2-hydroxyethyl) tetramethylguanidine, (2-mercaptoethyl) tetramethylguanidine, (4-hydroxybutyl) tetramethylguanidine or (2-hydroxyethoxyethyl) tetramethylguanidine.

It has been found that the judicious combination, by their nature and their proportions, of the two species in the form [B + α R (ZH) n] constitutes an interesting extraction medium for carbon dioxide. Each mole of B is associated with α moles of R (ZH) n and the species thus formed has the property of reacting with CO ₂ according to the general scheme: [B + α R (ZH) n] + γ CO ₂ => [B, α R (ZHJn ₁ γ (CO ₂ )] in which γ represents the number of moles of CO ₂ chemically associated with the reactive species contained in the extraction medium [B + α R (ZH) n].

The value of the coefficient α depends on the nature of the two chemical species involved. Α is a positive number. Preferably, α must satisfy the condition that a basic function provided by B must be associated with at least one hydrogen atom bonded to Z in the formula R (ZH) n. In the case of a monobase B associated with a monohydric alcohol or a monothiol RZH, α is preferably greater than or equal to 1.

In this way, the gas containing CO ₂ to be treated after contact with the extraction medium will be depleted in CO ₂ . Carbon dioxide may be in excess or in default with respect to

[B + α R (ZH) n], which means that after CO ₂ capture the extraction medium can contain, in addition to the CO ₂ capture product [B, α R (ZH) n, γ (CO ₂ )], an excess amount of CO ₂ or an amount of [B + α R (ZH) n] in excess.

This reaction is reversible. The inverse reaction can be represented by the general scheme: [B, α R (ZH) n, γ (CO ₂ )] => [B + α R (ZH) n] + γ CO ₂

Thus, on the extraction medium, there will be an operation to restore [B + α R (ZH) n] and CO ₂ . This operation will generate a gas rich in CO ₂ and regenerate the extraction medium.

The operation of regeneration of the extraction medium can be carried out under conditions that require little energy and in particular less energy than the operation that would be necessary to regenerate the same amount of CO ₂ when it is extracted. by means of one or more primary, secondary or tertiary amines or a composition of them leading to carbamates, hydrogencarbonates or carbonates according to the balanced reactions previously presented as known to those skilled in the art and conventionally used to capture CO ₂ .

Similarly, this operation of regeneration of the extraction medium can be carried out under conditions that require little energy and in particular less energy than the operation that would be necessary to regenerate the same amount of CO ₂ when the latter is extracted using species B when used alone in the absence of R (ZH) n.

It has been noted that the only use of R (ZH) n does not make it possible to capture as much CO ₂ present in a gas as the mixture [B + α R (ZH) n].

It is the combination of B and R (ZH) n according to a judicious choice and in optimized proportions which defines the CO ₂ extraction process and the regeneration process of the extraction medium according to the invention.

According to a variant of the invention, the extraction medium comprises a mixture of bases B in combination with a mixture of compounds R (ZH) n.

The extraction medium may further comprise one or more solvents, defined as having the property of dissolving one or more species present in the extraction medium before and / or after capture of CO ₂ . The solvents may be chosen, for example, from aliphatic hydrocarbons, saturated or unsaturated, branched or otherwise, alicyclic, saturated or unsaturated, substituted or unsubstituted, mono- or polyaromatic substituted or unsubstituted, saturated or unsaturated heterocyclic, branched or unbranched, glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulfones, sulfoxides, alcohols, thiols, ureas, lactams, N-alkylated pyrrolidones, N-piperidones, alkylated cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl phosphates, alkylene carbonates, dialkyl carbonates and derivatives thereof. By way of example and in a nonlimiting manner, mention may be made without being exhaustive of hexanes, decanes, dodecanes, cyclohexane, decalin, tetralin, toluene, xylenes, ethylbenzene, dodecylbenzene and nitrobenzenes. chlorobenzenes, fluorobenzenes, perfluoroalkanes such as perfluorohexanes, perfluorodecanes, perfluorododecanes, perfluorohexadecane, tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2-one, propylene carbonate, ethylene carbonate, diethyl carbonate, diisobutyl carbonate, diphenyl carbonate, glycerol carbonate, dimethylpropyleneurea, N-methylcaprolactam, dimethylformamide, dimethylacetamide, formamide, acetamide, 2-methoxy -2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethylthiodipropionate, bis (2-hydroxyethyl) sulfone, 3-mercapto-1, 2-propanediol and 2,3-dimercapto-1-propanol or tributylphosphate.

The system for capturing CO ₂ according to the invention can be implemented according to a gas treatment process containing CO ₂ , which according to the invention can be represented schematically as follows:

treated gas depleted in CO2 [B + αR (ZH) n]

gas to be treated

[B, α R (ZH) n, γ (CO2)] containing CO2 +

[B + αR (ZH) n]

The method for capturing CO ₂ according to the invention comprises a step of bringing the gaseous effluent to be treated into contact with the extraction medium as described above and a step of regenerating said extraction and generation medium. a gas rich in CO ₂ .

According to the invention, the regeneration of the extraction medium according to the reaction:

[B, α R (ZH) n, γ (CO ₂ )] => [B + α R (ZH) n] + γ CO ₂ can be carried out: 1. either by stripping with a gas causing vapor phase the carbon dioxide contained in the solvent to be regenerated. The stripping gas may, for example, be formed in situ by vaporization of one or more compounds present in the extraction medium: it may be one of the compounds defined according to the invention, but it may also be a compound from the gas to be treated which would have been absorbed with the CO ₂ , such as water for example in the case of a smoke. The stripping gas may also be supplied to the regeneration step: it may be, for example, nitrogen, water vapor or a part of the treated gas resulting from the absorption step.

2. either by heating 3. or by relaxing

4. or by different combinations of the 3 regeneration modes mentioned.

The examples presented below illustrate the technical interest of the present invention without limiting its scope. Example 1 (according to the invention):

The extraction medium consists of mixture A, obtained by mixing 10.01 g (81 mmol) of 1,5-diazabicyclo (4.3.0) non-5-ene (DBN) with 16.65 g (82 mmol). of dodecanethiol. A CCVN ₂ gas mixture containing 10% volume of CO ₂ is brought into contact with the mixture A at atmospheric pressure and at a flow rate of 20 Nl / h in a double-jacketed glass bubble column thermostated at 40 ^° C. The gas in FIG. column outlet is analyzed online by gas chromatography. When the capture is complete, the number of moles of CO ₂ captured divided by the number of moles of DBN is equal to 0.38. Regeneration of the extraction medium is then carried out by stripping under a stream of nitrogen at 20 Nl / h at 40 ° C. in the same equipment at atmospheric pressure. The gas at the outlet of the column is analyzed online by gas chromatography.

The experiment shows that, under these regeneration conditions (40 ^° C.), the regeneration rate, defined by the ratio of the quantity of CO ₂ released by regeneration divided by the quantity of CO ₂ captured, of the mixture A is 90 ^° C. % after 45 minutes and 100% after 60 minutes.

Example 2 (according to the invention):

The extraction medium consists of mixture B, obtained by mixing 30.5 g (200 mmol) of 1,8-diazabicyclo (5.4.0) undec-7-ene (DBU) with 21.6 g (211 mmol). hexanol. A CO ₂ / N ₂ gas mixture containing 10% CO ₂ volume is contacted with the mixture B at atmospheric pressure and at a flow rate of 30 Nl / h in a glass bubble column at 22 ° C. The gas at the outlet of the column is analyzed online by gas chromatography. When the capture is complete, the number of moles of captured CO ₂ divided by the number of moles of DBU is equal to 0.52. The regeneration of the extraction medium is then carried out by stripping under a stream of nitrogen at 20 Nl / h at 22 ° C. in the same equipment at atmospheric pressure. The gas at the outlet of the column is analyzed online by gas chromatography.

The experiment shows that, under these regeneration conditions (22 ° C.), the regeneration rate, defined as the ratio of the amount of CO ₂ released by regeneration divided by the amount of CO ₂ captured, of the mixture B reaches 100%. . Example 3 (comparative):

This example shows the absorption and the regeneration of an aqueous solution of ethanolamine (MEA) at 30% by weight for comparison with an extraction medium according to the invention. It is a reference solvent for capturing CO ₂ in fumes. The extraction medium consists of the mixture C, obtained by mixing 4.92 g

(81 mmol) of ethanolamine and 11.48 g of water. The number of moles of MEA introduced is the same as the number of moles of DBN used in Example 1. A CO ₂ / N ₂ gas mixture containing 10% CO ₂ volume is brought into contact with the mixture C at atmospheric pressure. and at a flow rate of 20 Nl / h in a double-jacketed glass bubble column thermostated at 40 ° C. The experimental conditions are the same as in Example 1. The gas at the outlet of the column is analyzed online by gas chromatography. When the capture is complete, the number of moles of CO ₂ captured divided by the number of moles of MEA, is equal to 0.48.

Regeneration of the extraction medium is then carried out by stripping under a stream of nitrogen at 20 Nl / h at 40 ^° C. in the same equipment at atmospheric pressure as in Example 1. The gas at the outlet of the column is analyzed in line by gas chromatography.

The experiment shows that, under these regeneration conditions (40 ^° C.), the regeneration rate, defined by the ratio of the quantity of CO ₂ released by regeneration divided by the quantity of CO ₂ captured, of the mixture C is 19 ° C. % after 45 minutes, 21% after 60 minutes and 30% after 180 minutes.

These results show that the regeneration of the mixture C according to the prior art is much more difficult than that of the mixture A according to the invention under the same conditions as illustrated in FIG.

Claims

1. Medium for extracting carbon dioxide contained in a gaseous effluent characterized in that it comprises the product of an acid-base reaction between

- a species B, which is a base or a mixture of bases of general structure:

R ₁ N

in which

R1, R2 and R3 are independently selected from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or unsubstituted;

R4 is chosen from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or unsubstituted; or R4 is constituted by the pattern:

- No. R ₅

in which R5 and R6 are independently selected from a hydrogen atom, an aliphatic hydrocarbon group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or unsubstituted;

and a species R (ZH) n which is a compound or a mixture of compounds in which R is chosen from a monovalent or multivalent aliphatic group, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic substituted or unsubstituted and where Z is a oxygen atom and / or a sulfur atom and n is between 1 and 20, preferably between 1 and 6.

2. Carbon dioxide extraction medium according to claim 1 characterized in that R1, R2, R3, R4, R5 and R6 contain one or more halogens, one or more heteroatoms or nitrile, ketone, amide or nitro groups.

3. carbon dioxide extraction medium according to claim 1 or 2 characterized in that R1, R2, R3 and R4 are connected together to form rings or heterocycles.

4. extraction medium according to one of claims 1 to 3 characterized in that the base B belongs to the family of amidines.

5. extraction medium according to claim 4 characterized in that the base B is selected from imidazoline, 2-methyl-2-imidazoline, 1, 4,5,6-tetrahydropyrimidine, N-methyltetrahydropyrimidine 6- (dibutylamino) -1,8-diazabicyclo- (5.4.0) undec-7-ene, 4-azabenzimidazole, anabasin, N'-tertbutyl-N, N-dimethylformamidine, 1,5 -diazabicyclo (4.3.0) non-5-ene and 1,8-diazabicyclo

(5.4.0) undec-7-ene

6. extraction medium according to one of claims 1 to 3 characterized in that the base B belongs to the family of guanidines.

7. Extraction medium according to claim 6, characterized in that the base B is chosen from guanidine, tetramethylguanidine, pentamethylguanidine, butyltetramethylguanidine, tert-butyltetramethylguanidine, phenylguanidine and 1,5,7-triazabicyclo (4.4.0). ) dec-5-ene and 7-methyl-1,5,7-triazabicyclo (4.4.0) dec-5-ene

8. extraction medium according to one of claims 1 to 7 characterized in that the R group contains one or more halogens, one or more heteroatoms or functions alcohol, thiols, ethers, thioethers, nitriles, ketones, sulfones, sulfoxides , amides, amines or nitrates.

9. extraction medium according to one of claims 1 to 8 characterized in that R (ZH) n is selected from monoalcohols such as methanol, ethanol, propanols, butanols, pentanols, hexanols, octanols, decanols, dodecanol, fatty alcohols, polyols such as ethylene glycols, propylene glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, monoethers of glycols, glycerol , C ₄ , C ₅ and C ₆ polyols derived for example from sugars, tetrahydrofurfuryl alcohol, phenol, benzyl alcohol, diglycerol, 2,2'-thiodiethanol, tetrahydrothiopyran-3-ol, 2- (methylsulfonyl) ethanol, 3-methylthio-1,2-propanediol, 3-ethylthio-1,2-propanediol, 1,4-dithiane-2,5-diol, 3,3'-thiodipropanol and 3,6-dithia-1,8-octanediol.

10. extraction medium according to one of claims 1 to 8 characterized in that R (ZH) n is selected from thiols such as decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol, ethylenedithiol, 2 3-methyltetrahydrofuran-3-thiol, pyrimidine-2-thiol, 1H-1,2,4-triazole-3-thiol, 4-methyl-4H-1,2,4-triazole-3-thiol, 2-mercaptoethylether, phenylmercaptan, benzylmercaptan, 4-methoxybenzylmercaptan, 2-mercaptobenzothiazole, mercaptothiazoline, tert-dodecylmercaptan, tert-nonylmercaptan, 2,2 '- (ethylenedioxy) diethanethiol, 2-ethylhexanethiol and 2-furanméthanthiol.

11. extraction medium according to one of claims 1 to 8 characterized in that R (ZH) n is selected from 1-thioglycerol, 2-mercaptoethanol, 1-mercapto-2-propanol, 2-mercapto 3-butanol, 2,3-dimercapto-1-propanol and 1,4-dithioerythritol.

12. extraction medium according to one of claims 1 to 11 characterized in that each mole of B is associated with moles of R (ZH) n, α being a positive number preferably defined so that a function basic provided by B is associated with at least one hydrogen bonded to Z in the formula R (ZH) n.

13. Extraction medium according to one of claims 1 to 11 characterized in that the base B and the species R (ZH) n are connected by at least one chemical bond so as to constitute a single molecule.

14. Extraction medium according to claim 13, characterized in that said molecule is chosen from 1α, 5α-tetrahydro-pyrimidinethiol and 3- (2-hydroxyethyl)

1, 4,5,6-tetrahydropyrimidine, 7- (2-hydroxyethyl) -1,5,7-triazabicyclo (4.4.0) dec-5- ene, 7- (4-hydroxybutyl) -1,5,7-triazabicyclo (4.4.0) dec-5-ene, 7- (2-mercaptoethyl) -1,5,7-triazabicyclo (4.4.0) dec-5-ene, 7- (2-hydroxyethoxyethyl) -1,5,7-triazabicyclo (4.4.0) dec-5-ene, (2-hydroxyethyl) tetramethylguanidine, (2-mercaptoethyl) tetramethylguanidine, (4-hydroxybutyl) tetramethylguanidine and (2-hydroxyethoxyethyl) tetramethylguanidine.

15. Extraction medium according to one of claims 1 to 14 characterized in that it comprises a solvent or a solvent composition.

16. Extraction medium according to claim 15, characterized in that the solvent is chosen from aliphatic hydrocarbons, saturated or unsaturated, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, mono- or polyaromatic substituted or unsubstituted, saturated heterocyclic or not, branched or unbranched, glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulphones, sulphoxides, alcohols, thiols, ureas, lactams , N-alkylated pyrrolidones, N-alkylated piperidones, cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl phosphates, alkylene carbonates, dialkyl carbonates and their derivatives .

17. extraction medium according to one of claims 15 and 16 characterized in that the solvent is selected from hexanes, decanes, dodecanes, cyclohexane, decalin, tetralin, toluene, xylenes, ethylbenzene, dodecylbenzene, nitrobenzenes, chlorobenzenes, fluorobenzenes, perfluoroalkanes such as perfluorohexanes, perfluorodecanes, perfluorododecanes, perfluorohexadecane, tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2-one propylene carbonate, ethylene carbonate, diethyl carbonate, diisobutyl carbonate, diphenyl carbonate, glycerol carbonate, dimethylpropyleneurea, N-methylcaprolactam, dimethylformamide, dimethylacetamide, formamide, acetamide, 2-methoxy-2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethylthiodipropionate, bis (2-hydroxyl) yethyl) sulfone, 3-mercapto-1,2-propanediol, 2,3-dimercapto-1-propanol and tributylphosphate.

18. A process for capturing carbon dioxide comprising a step of contacting the gaseous effluent to be treated containing CO ₂ with the extraction medium as defined in claims 1 to 17 so as to deplete said gaseous effluent by CO ₂ and enriching said CO ₂ extraction medium and a regeneration step of said medium for extracting and generating a gas rich in CO ₂ .

19. The method of claim 18 characterized in that the carbon dioxide is in excess relative to said extraction medium.

20. The method of claim 18 characterized in that the carbon dioxide is in default with respect to said extraction medium.

21. Method according to one of claims 18 to 20 characterized in that the regeneration of the CO ₂ -rich extraction medium is by stripping by means of a gas which vapor phase entrainment of carbon dioxide.

22. Method according to one of claims 18 to 20 characterized in that the regeneration of CO ₂ enriched extraction medium is by heating.

23. Method according to one of claims 18 to 20 characterized in that the regeneration of CO ₂ enriched extraction medium is by relaxation.

24. Method according to one of claims 18 to 20 characterized in that the regeneration of CO ₂ enriched extraction medium is done by various combinations selected from stripping by means of a vapor phase-driving gas carbon dioxide , relaxation and heating.