FR2909010A1 - Medium for extraction of carbon dioxide from a gaseous effluent, comprises a product of acid base reaction between a base of amidine or guanidine compound and a hydroxyl/thiol compound - Google Patents

Abstract

Medium for extraction of carbon dioxide from a gaseous effluent, comprises a product of acid base reaction between a base (mixture) (I) of amidine or guanidine and a hydroxyl/thiol compound (mixture) (II). Medium for extraction of carbon dioxide from a gaseous effluent, comprises a product of acid base reaction between a base (mixture) (I) of amidine or guanidine compound of formula R 2R 3N-C(R 4)=NR 1 and a hydroxyl/thiol compound (mixture) (II) of formula R(ZH) n. R 1-R 3, R 5, R 6alicyclic, heterocyclic, (mono or poly)aromatic hydrocarbon (all optionally substituted), aliphatic hydrocarbon or H; R 4alicyclic, heterocyclic, (mono or poly)aromatic hydrocarbon (all optionally substituted), aliphatic hydrocarbon, H or -NR 5R 6; R : mono or multivalent aliphatic, alicyclic or optionally substituted heterocyclic or (mono or poly)aromatic; Z : O and/or S; and n : 1-20, preferably 1-6. An independent claim is included for capturing carbon dioxide, comprising contacting gas effluent to be treated containing carbon dioxide with the extraction medium, to impoverish the effluent gas of carbon dioxide and to enrich the extraction medium in carbon dioxide and a regenerating the extraction medium and generating carbon dioxide rich gas.

Description

Field of the Invention The present invention relates to decarbonation

  a gaseous effluent. Background Art Carbon dioxide is one of the greenhouse gases largely produced by various 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 CO2 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 CO2 reacts with the alkanolamine 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 equilibrium reactions can be written according to the following schemes: For a primary alkanolamine such as for monoethanolamine, the reaction involved is: RNHCOO-, + H3NR carbamate 1 H2O RNH3 +, ## STR2 ## RNH2 O hydrogen carbonate RNH3 +, + H3NR IIO carbonate 2 RNH2 + CO2 2909010 2 For a secondary alkanolamine such as for diethanolamine, it is written: RR'NCOO-, + H2NRR 'carbamate RR'NH2 +, whereCuOH + RR'NH II 0 hydrogen carbonate RR'NH2 +; ), For a tertiary alkanolamine such as, for example, methyldiethanolamine: RR'R " ## STR1 ## wherein an alternative to aqueous alkanolamine solutions is the use of hot solutions of alkali metal carbonates. The principle is based on the absorption of CO2 10 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 solulion such as chilled methanol or polyethylene glycols, are based on a physical absorption of CO2.

An essential aspect of the gas treatment or solvent smoked operations is the regeneration of the separating agent. Depending on the type of absorption (physical or chemical), regeneration is generally envisaged by expansion, distillation and / or entrainment by a vaporized gas called "stripping gas". In general, the use 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 CO2 in a smoke represents about 4GJ per tonne of CO2 captured. Such energy consumption represents a considerable operating cost for the CO2 capture process.

SUMMARY OF THE INVENTION: The CO2 extraction medium, used in a process for capturing carbon dioxide contained in a gaseous effluent, comprises the product obtained by an acid-base type reaction between two species B and R ( ZH) n, where B is a base or a mixture of bases selected from amines such as amidines or guaridines 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 is an oxygen atom and / or a sulfur atom and n is 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 002 with said extraction medium, so as to obtain a gas depleted in 002 and a medium of extraction rich in 002, b) the regeneration of the extraction medium rich in 002, to obtain a usable extraction medium and generate a very rich gas in 002. Description of the figure: Figure 1 represents the evolution the regeneration rate as a function of time and compares the regeneration rate at 40 C under 20 Nl / h of nitrogen of two extraction media loaded in 002 (mixture A according to the invention and reference mixture C). Detailed description of the invention. The present invention proposes to use a 002 extraction medium different from the prior art. This extraction medium makes it possible to capture CO2 contained in a gaseous effluent. Once loaded at 002, said medium can be further 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 002 is brought into contact with an extraction medium, so as to obtain a CO2-depleted gas and a carbon dioxide medium; CO2-rich extraction b) the CO2-rich extraction medium is regenerated, so as to obtain an extractable extraction medium and to generate a gas rich in CO2. The extraction medium comprises the product obtained by an acid-base 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 - R 1, R 2 and R 3 are independently 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; 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, substituted mono or polyaromatic, or no ; or R4 is constituted by the unit: R6-N. Wherein R5 and R6 are independently selected from hydrogen, 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 include, for example, one or more halogens, one or more heteroatoms or nitrile, ketone, amide or nitro groups. When R.sub.4 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 include, 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-N, N-dimethylformamidine, 1,5-diazabicyclo (4.3.0) non-5-diazabicyclo -ene of formula: and 1,8-diazabicyclo (5.4.0) undec-7-ene of formula: When R4 represents a R5 unit, the B bases 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 of the formula: 1 H 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.

Regarding the definition of R, monovalent and multivalent is understood to mean that the group is substituted by at least one or more (from 1 to n) units ùZH as defined above and provided that the rules are respected. 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 ethylenic glycols, propylene glycols, polyethylene glycols, polypropylene glycols, ethylene glycolpropylene glycol copolymers, monoethers of glycols, glycerol, C4, C5 and C6 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. When Z is exclusively a sulfur atom, R (ZH) n is chosen, for example, without being exhaustive, among the thiols such as decanethiol, dodecanethiol, hexadecanethiol, octadecanethiol, ethylenedithiol, 2-methyltetrahydrofuran and the like. 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, tertdodecylmercaptan, 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 selected, for example, without being exhaustive, from 1-thioglycerol, 2-mercaptoethanol, 1- 2-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- (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- ethene, (2-hydroxyethyl) tetramethylguanicyl, (2-mercaptoethyl) tetramethylguanidine, (4-hydroxybutyl) tetramethylguaridine 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 + a R (ZH) n] constitutes an interesting extraction medium for carbon dioxide. Each mole of B is associated with moles of R (ZH) n and the species thus formed has the property of reacting with CO2 according to the general scheme: [B + a R (ZH) n] + y CO2 [B, in which y represents the number of moles of CO2 chemically associated with the reactive species contained in the extraction medium [B + a R (ZH) n]. The value of coefficient a depends on the nature of the two chemical species involved. A is a positive number. Preferably, a 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, a 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 CO2. Carbon dioxide may be in excess or in default with respect to [B + a. R (ZH) n], which means that after capture of CO2 the extraction medium can contain, in addition to the product of the capture of CO2 [B, a R (ZH) n, y (CO2)], a amount of excess CO2 or excess amount of [B + a R (ZH) n].

This reaction is reversible. The reverse reaction can be represented by the general scheme: [B, a R (ZH) n, y (CO2)] [B + a R (ZH) n] + y CO2. Thus, on the extraction medium, we will proceed an operation to restore [B + a R (ZH) n] and CO2. This operation will make it possible to generate a gas that is very rich in CO2 and to regenerate the extraction medium.

The regeneration operation of the extraction medium can be carried out under conditions that require little energy and especially less energy than the operation that would be necessary to regenerate the same amount of CO2 when it is extracted by means of one or more primary, secondary or tertiary amines or a composition of them leading to carbamates, hydrogenocarbonates or carbonates according to the balanced reactions previously presented as known to those skilled in the art and conventionally used to capture CO2. 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 CO2 when the latter is extracted using species B when used alone in the absence of R (ZH) n. It was noticed that the only use of R (ZH) n did not allow to capture as much CO2 present in a gas as the mixture [B + a 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 CO2 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 CO2. 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 alkyl-cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl phosphates, alkylene carbonates, dialkyl carbonates and their derivatives.

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 and dodecylbenzene. nitrobenzenes, chlorobenzenes, fluorobenzenes, perfluoroalkanes such as perfluorohexanes, perfluorodecanes, perfluorododecanes, perfluorohexadecane, tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2-one, carbonate, propylene, ethylene carbonate, diethyl carbonate, diisobuloyl carbonate, diphenyl carbonate, glycerol carbonate, dimethylpropyleneurea, N-methylcaprolactam, dimethylformamide, dimethylacetamide, formamide, and the like. 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 CO2 according to the invention can be implemented according to a CO 2 gas-treatment process, which according to the invention can be schematically represented as follows: treated gas depleted in CO 2 gas to be treated [B, a R (ZH) n, y (CO2)] containing CO2 + [B + aR (ZH) n] [B + aR (ZH) n] CO2 The CO2 capture method according to the invention comprises a step of contacting the gaseous effluent to be treated with the extraction medium as described above and a step of regenerating said extraction medium and generating a gas rich in CO2. According to the invention, the regeneration of the extraction medium according to the reaction: [B, a R (ZH) n, y (CO2)] = [B + a R (ZH) n] + y CO2 2909010 can be carried out 1. by stripping by means of a gas which vaporises 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 that would have been absorbed with CO2, 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 portion of the treated gas from the absorption stage. 2. either by heating 3. or by expansion 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 the 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 CO2 / N2 gaseous mixture containing 10% volume of CO2 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. column outlet is analyzed online by gas chromatography. When the capture is complete, the number of moles of CO2 captured divided by the number of moles of DBN is equal to 0.38.

The 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 as the ratio of the amount of CO2 released by regeneration divided by the amount of CO2 captured, of the mixture A is 90% 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) of hexanol. A CO2 / N2 gas mixture containing 10% volume of CO2 is brought into contact 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 CO2 captured divided by the number of moles of DBU is equal to 0.52. 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. Experience shows that, under these regeneration conditions (22 C), the regeneration rate, defined by the ratio of the amount of CO2 released by regeneration divided by the amount of CO2 captured, of the mixture B reaches 100%.

Example 3 (Comparative): This example shows the absorption and 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 the capture of CO2 in fumes. The extraction medium consists of 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 gaseous mixture CO 2 / N 2 containing 10% volume of CO 2 is brought into contact with the mixture C at atmospheric pressure and at a temperature of 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 column outlet is analyzed online by gas chromatography. When the capture is complete, the number of moles of CO2 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 as the ratio of the amount of 002 released by regeneration divided by the amount of CO2 captured, of the mixture C is 19. % 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. 1.

Claims (24)

  A 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: 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 unit: ## STR2 ## in which R5 and R6 are independently 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; and a species R (ZH) n which is a compound or a mixture of compounds where 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 not, substituted or unsubstituted mono or polyaromatic and wherein Z is an 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 10 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, Ndimethylformamidine, 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 selected from guanidine, tetramethylguanidine, pentamethylguanidine, butyltetramethylguanidine, tert-butyltetramethylguanidine, phenylguanidine, 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, and C4, C5 and C6 polyols derived therefrom. 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.   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 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, a 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 selected from 1,4,5,6-tetrahydro-2-pyrimidinethiol, 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 5 (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, heterocyclic. saturated or unsaturated, branched or unbranched, glycols, polyethylene glycols, polypropylene glycols, ethylene glycolpropylene 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, doclecylbenzene, nitrobenzenes, chlorobenzenes, fluorobenzenes, perfluoroalkanes such as perfluorohexanes, perfluorodecanes, perfluorododecanes, perfluorohexadecane, tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2- propylene carbonate, ethylene carbonate, diethyl carbonate, diisobutyl carbonate, diphenyl carbonate, glycerol carbonate, dimethylpropyleneurea, N-methylcaprolactam, dimethylformamide, dimethylacetamide, formamide and the like. acetamide, 2-methoxy-2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethylthiodipropionate, bis (2-hy- droxyethyl) sulfone, 3-mercapto-1,2-propanediol, 2,3-dimercapto-1-propanol and tributylphosphate. 2909010 18   18. A process for capturing carbon dioxide comprising a step of contacting the gaseous effluent to be treated containing CO2 with the extraction medium as defined in claims 1 to 17 so as to deplete said gaseous effluent with CO2. and enriching said CO2 extraction medium and a regeneration step of said extraction medium and generating a very CO2-rich gas.   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. 10   21. Method according to one of claims 18 to 20 characterized in that the regeneration of the CO2 enriched extraction medium is by stripping by means of a gas vapor phase-driving carbon dioxide.   22. Method according to one of claims 18 to 20 characterized in that the regeneration of the extraction medium enriched in CO2 is by heating. 15   23. Method according to one of claims 18 to 20 characterized in that the regeneration of the CO2 enriched extraction medium is by expansion.   24. Process according to one of Claims 18 to 20, characterized in that the regeneration of the CO2-enriched extraction medium is carried out by various combinations chosen from stripping by means of a gas which, in the vapor phase, causes the carbon dioxide to be vaporised. , relaxation and heating.