WO2010010238A1

WO2010010238A1 - Aqueous extraction medium containing a carbonate and a thiol that is used in a process for separating carbon dioxide contained in a gaseous effluent

Info

Publication number: WO2010010238A1
Application number: PCT/FR2009/000810
Authority: WO
Inventors: Bruno Delfort; Pierre-Loius Carrette
Original assignee: Ifp
Priority date: 2008-07-22
Filing date: 2009-07-01
Publication date: 2010-01-28
Also published as: FR2934175A1; FR2934175B1

Abstract

The present invention describes a medium for the extraction of carbon dioxide, which is used in a process for capturing carbon dioxide contained in a gaseous effluent, comprising, in an aqueous medium, the combination of a particular base chosen from carbonates and/or hydrogen carbonates with a compound chosen from thiols. The process of capturing carbon dioxide consists in carrying out the following steps: a) bringing the gas to be treated that contains CO₂into contact with said extraction medium, so as to obtain a CO₂-depleted gas and a CO₂-rich extraction medium, b) the regeneration of the CO₂-rich extraction medium, in order to obtain an extraction medium that can be used again and to generate a gas that is very rich in CO₂.

Description

AQUEOUS EXTRACTION MEDIUM CONTAINING CARBONATE AND THIOL USED IN A METHOD OF SEPARATING CARBON DIOXIDE FROM 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 used 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 vis-à-vis the various compounds present in the gas to be treated.

The solvents commonly used today include in particular aqueous solutions of primary, secondary or tertiary alkanolamines and optionally an organic co-solvent, such as methanol for example. Indeed, the absorbed CO ₂ 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 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'NCOO ^" , ⁺ H ₂ NRR 'carbamate

hydrogen

and for a tertiary alkanolamine such as methyldiethanolamine:

RR ¹ R ¹¹ N

RR ¹ R ¹¹ N + m ₂ + H ₂ n RR ¹ R ¹¹ NHVO-C-OH _^ RR ¹ R ¹¹ NH ⁺ ^ OO ₁ ⁺ HNRR ¹ R "

II C

O M 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, by an inorganic carbonate according to a reaction leading to an inorganic hydrogencarbonate and on regeneration by the reversible reaction transforming an inorganic hydrogencarbonate into an inorganic carbonate.

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 . French patent applications FR-A-2 909 010 and FR-A-2 909 011 describe the use of a carbon dioxide extraction medium associating a particular base chosen from amidine and guanidine respectively or from phosphazenes. to a compound selected from alcohols or thiols and optionally to a non-aqueous solvent.

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 is generally envisaged by expansion, distillation and / or entrainment by a vaporized gas called "stripping gas". 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 for the capture of 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

We have now discovered the use of a carbon dioxide extraction medium comprising in aqueous medium the combination of a particular base selected from carbonates and / or hydrogenocarbonates with a compound selected from thiols.

The CO ₂ extraction medium according to the invention, used in a process for capturing carbon dioxide contained in a gaseous effluent, comprises the combination of a base B or a mixture of carbonate-type bases B corresponding to the one of the general formulas M (HCO ₃ ) _X or IVTy (CO ₃ ) with at least one compound R (SH) _n in an aqueous solvent Z and / or the product obtained by reaction of said base B or said mixture of bases with said compound R (SH) _n in said solvent Z.

The method of 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 lean gas and a CO ₂ rich extraction medium in CO _2, b) the regeneration of the medium of extraction rich in CO ₂ , to obtain a reusable extraction medium and to generate a gas rich in CO ₂ .

Detailed description of the invention.

The extraction medium according to the present invention makes it possible to capture the carbon dioxide contained in a gaseous effluent. Once loaded with carbon dioxide, said medium can also be regenerated under easier conditions than the absorbent solutions of the prior art.

The CO ₂ extraction medium comprises the combination of a base B or a mixture of carbonate bases B corresponding to one of the general formulas M (HCO ₃ ) _X or IVV _y (CO ₃ ) with a compound R (SH) _n in an aqueous solvent Z and / or the product obtained by reacting said base or base mixture with said compound R (SH) _n in said solvent Z, denoted by [B + α R (SH) _n ] _aq where α is a positive number, medium in which:

- B is a base B or a mixture of bases B of the carbonate type corresponding to one of the general formulas M (HCO ₃ ) _X or NT _y (CO ₃ ), M and M ', which may be identical or different, being chosen without distinction from a monovalent cation such as lithium, sodium, potassium, rubidium or cesium,

- a quaternary ammonium cation having the general formula R ₁ R ₂ R ₃ R ₄ N ⁺ _R> R _2. R ₃ and R ₄ being 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 compound containing 1 to 20 carbon atoms, R 1, R ₂ . R ₃ and R ₄ may be linked two by two by covalent bonds to form a heterocycle of 5 to 8 atoms,

a divalent cation such as magnesium, calcium or barium, and in which x and y are equal to 1 or 2; - R (SH) n is a compound or a mixture of compounds comprising at least one thiol function, R being an aliphatic, alicyclic, mono or polyaromatic or heterocyclic group, free of chemical function capable of reacting with CO ₂ and n being between 1 and 20. - Z is essentially water, or a mixture of solvents comprising water.

The group R may contain one or more halogens, one or more heteroatoms present via functions such as alcohols, ethers, thioethers, nitriles, ketones, sulfones, sulfoxides, or amides. The group R is free of chemical functions capable of reacting with CO ₂ , such as, for example, amine or phosphine functions.

Thus, it is understood that the compound R (SH) n, used alone, is not reactive with respect to CO ₂ .

The group R is bound to n -SH motifs in accordance with the rules of organic chemistry. Preferably, n is between 1 and 6 and very preferably n is 1 or 2.

Advantageously, the extraction medium according to the present invention comprises products that are readily available and easy to use.

Obtaining a high performance extraction medium in an aqueous medium has several advantages. Indeed, water is a non-toxic, inexpensive and readily available solvent.

In addition, with water, it is possible to overcome the gas purification operations very often necessary, for example when the solvent is an organic compound such as methanol. Indeed, small amounts of solvent are inevitably entrained in the gases after separation of carbon dioxide and impose additional and expensive steps of purification.

Water also has the advantage of not degrading unlike organic molecules generally used as solvents.

The water also has the advantage of being able to be vaporized in situ at the regeneration stage of the extraction medium enriched in CO ₂ . The water vapor thus generated makes it possible to heat the extraction medium and / or to carry out the stripping of the CO ₂ . The base B or the mixture of bases B of carbonate type corresponding to one of the general formulas M (HCO ₃ ) _X or IVTy (CO ₃ ) may advantageously be associated with a base of formula M "(OH) _{W 1} in which M "is defined in the same way as M or M 'and w is equal to 1 or 2.

Among the compounds B used in the extraction medium, mention may be made, for example, without being exhaustive: the lithium, sodium, potassium, cesium and rubidium, magnesium, calcium, barium and tetramethylammonium carbonates , tetraethylammonium, benzyltrimethylammonium, and decyltrimethylammonium and bicarbonates (or hydrogen carbonates) of lithium, sodium, potassium, cesium and rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium, and decyltrimethylammonium.

Most preferably, compound B is selected from potassium or sodium carbonate. Among the R (SH) _n compounds used in the extraction medium, mention may be made, for example, without being exhaustive: 1-thioglycerol, dodecanethiols, mercaptothiazoline, 2-mercapto-1-methylimidazole, 2-mercaptobenzimidazole 2-pyridylmethanethiol as well as thiosalicylic acid, thioglycolic acid, thiolactic acid and their alkali salts, for example.

The solvent Z may be essentially water. The term "essentially" in the sense of the present invention, the fact that in this case the solvent consists solely of water, without excluding the invention, the possibility of also having some inherent impurities that could be included in the water. Solvent Z may be a solvent mixture comprising water.

Preferably, in the case where the solvent Z consists of a mixture of solvents, the water remains the main constituent. Preferably, according to the number of constituents of the solvent Z, the water is present at a content of at least 30% by weight relative to the total amount of solvent. Very preferably, the solvent mixture comprises at least 50% by weight of water and even more preferably at least 60% by weight of water. In this case, the solvent is water associated with another solvent or a mixture of solvents miscible with water. These solvents are chosen from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulphones, sulphoxides, alcohols, ureas, lactams and N-pyrrolidones. alkylated, N-alkylated piperidones, 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 tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2-one, 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 or tributylphosphate.

In general, the extraction medium may contain from 1 to 90% by weight of water and preferably from 20 to 80% by weight of water.

It has been discovered that the judicious combination, by their nature and by their proportions, of the two species in the form [B + α R (SH) _n ] in an aqueous medium denoted by [B + α R (SH) _n ] _aq is an interesting extraction medium for carbon dioxide. Each mole of B is associated with moles of R (SH) _n and the species thus formed has the property of reacting with CO ₂ in an aqueous medium according to the general scheme:

[B + α R (SH) _n ] _aq + γ CO ₂ => [B, α R (SH) n, γ (CO ₂ )] _aq 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 (SH) _n ] _aq .

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 S in the formula R (SH) _n . For example, in the case of a monobase B = MOH monothiol RSH ₁ 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 .

The carbon dioxide may be in excess or in defect with respect to [B + α R (SH) _n ] _aq , which means that after capture of CO ₂ the extraction medium may contain, in addition to the capture product CO ₂ [B, α R (SH) _n , γ (CO ₂ )] _aq , a quantity of CO ₂ in excess or a quantity of [B + α R (SH) _n ] _aq in excess.

This reaction is reversible. The opposite reaction can be represented by the general scheme:

[B, α R (SH) _n , γ (CO ₂ )] _aq => [B + α R (SH) _n ] _aq + γ CO ₂ Thus, on the extraction medium, an operation will be carried out in order to restore [B + α R (SH) _n ] _aq 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, hydrogenocarbonates or carbonates according to the balanced reactions presented previously 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 (SH) _n in an aqueous medium.

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

It is the combination of B and R (SH) _n in an aqueous medium according to a judicious choice and in optimized proportions which defines the process of CO ₂ extraction and the process of regeneration of the extraction medium according to the invention. 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 _aqueous C02 [B + αR (SH) n]

gas to be treated containing

[B + αR (SH) n] _aqueous

The method 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 temperature during step a) is between 20 and 80 ^° C. and preferably between 30 and 70 ^° C.

According to the invention, the regeneration of the extraction medium according to the reaction: [B, α R (SH) _n , γ (CO ₂ )] _aq => [B + α R (SH) _n ] _aq + γ CO ₂ can be done:

or 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: can be one of the compounds defined according to the invention but it can also be a compound from the gas to be treated that would have been absorbed with 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.

- by heating

- either by relaxation

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

Examples:

The examples presented below illustrate the technical interest of the present invention without limiting its scope. In particular, they exhibit the CO ₂ absorption capacity of different absorption media and the regeneration capacity of the various extraction media under the conditions of implementation of the examples.

The CO ₂ absorption and desorption tests in the various extraction media are carried out according to the following procedure:

The extraction medium consists of a mixture of compounds. A stream of nitrogen is saturated with water by bubbling in acidified water and heated to 40 ^° C. This flow of nitrogen thus saturated with water is brought into contact with the extraction medium at atmospheric pressure and at a rate of 30 Nl / h in a double-jacketed glass bubble column thermostated at 40 ⁰ C for 180 minutes to condition the extraction medium.

Then, a gaseous CO ₂ / N ₂ mixture containing 10% CO ₂ volume is saturated with water by bubbling in acidified water and heated to 40 ^° C. The gaseous mixture thus saturated with water is brought into contact with the medium. extraction at atmospheric pressure and at a flow rate of 20 Nl / h in the same equipment at 40 ° C for 180 minutes. The gas at the outlet of the column is analyzed online by gas chromatography. This analysis makes it possible to determine over time the number of moles of CO ₂ absorbed by the extraction medium. When the CO ₂ absorption step is complete, the charge rate is determined. The charge rate is defined by those skilled in the art as being the number of moles of captured CO ₂ divided by the number of moles of the basic compound B present in the extraction medium.

Regeneration of the extraction medium is then carried out by stripping under a stream of nitrogen at 30 Nl / h saturated with water as previously described in the same equipment at 40 ^° C. and at atmospheric pressure. The gas at the outlet of the column is analyzed online by gas chromatography. This analysis makes it possible to determine the number of moles of CO ₂ desorbed from the extraction medium over time.

The regeneration rate is defined as the ratio of the number of moles of CO ₂ released during the regeneration operation divided by the number of moles of CO ₂ captured. It is established for different regeneration times: 45, 60 and 180 minutes. The post-regeneration charge rate is defined as the number of moles of non-regenerated CO ₂ divided by the number of moles of compound B after 180 minutes of regeneration. The difference between the charge rate after absorption and the charge rate after regeneration is known to those skilled in the art to represent the absorption capacity of CO ₂ by the absorbent solution. This value must be as high as possible.

The following mixtures were evaluated:

The extraction medium 1 according to the invention is obtained by mixing 4.97 g (59 mmol) of NaHCO ₃ with 6.51 g (60 mmol) of 1-thioglycerol and 25 g of water.

The extraction medium 2 according to the invention is obtained by mixing 8.16 g (59 mmol) of K ₂ CO ₃ with 6.51 g (60 mmol) of 1-thioglycerol and 25 g of water.

• The extraction medium 3 is obtained by mixing 3.61 g (59 mmol) of monoethanolamine (MEA) with 8.41 g of water. This extraction medium corresponds to an aqueous solution of ethanolamine (MEA) at 30% by weight which is a reference solvent well known to those skilled in the art for the capture of CO ₂ in the fumes. Extraction medium 4 is obtained by mixing 8.16 g (59 mmol) of K ₂ CO ₃ and

25 g of water. This extraction medium does not contain the compound R (SH) _n required by the definition of the extraction medium according to the invention.

• The extraction medium 5 is obtained by mixing 6.51 g (60 mmol) of 1-thioglycerol and 25 g of water. This extraction medium does not contain the compound B required by the definition of the extraction medium according to the invention. The following table shows for the various extraction media the CO ₂ loading rate after absorption and after regeneration and the difference of these charge rates as well as the regeneration rate as a function of the regeneration time.

These examples show that the extraction media 1 and 2 according to the invention capture more CO ₂ and are regenerated more easily than the extraction medium 3 according to the prior art.

In addition, the comparisons of the results obtained with the extraction media 4 and 5 not in accordance with the invention with the extraction media 1 or 2 according to the invention clearly show that it is the combination of the compound R ( SH) _n with the compound B in an aqueous medium according to the invention which allows a facilitated regeneration of the extraction medium having absorbed CO ₂ and not the compound B used alone in solution in water or the compound R (SH) n used alone in solution in water.

Claims

1. Carbon dioxide extraction medium contained in a gaseous effluent characterized in that it comprises the combination of a base B or a mixture of carbonate-type bases B corresponding to one of the general formulas M (HCO ₃ ) _X or IVT _y (CO ₃ ) with at least one compound R (SH) _n in an aqueous solvent Z and / or the product obtained by reacting said base B or the mixture of bases with said compound R (SH) _n in said solvent Z ₁ denoted [B + α R (SH) _n ] _aq where α is a positive number, medium in which:

B is a base or a mixture of bases corresponding to one of the general formulas M (HCO ₃ ) _X or IvVy (CO ₃ ) in which M and M ', which are identical or different, are indifferently chosen from:

a monovalent cation such as lithium, sodium, potassium, rubidium or cesium,

a quaternary ammonium cation having the general formula R ₁ R ₂ R ₃ R ₄ N ⁺ R ₁ , R ₂ , R ₃ and R ₄ being independently chosen from a hydrogen atom, a saturated or unsaturated aliphatic hydrocarbon group, branched or unbranched, alicyclic, saturated or unsaturated, substituted or unsubstituted, heterocyclic, saturated or unsaturated, substituted or unsubstituted, mono or polyaromatic, substituted or unsubstituted, containing 1 to 20 carbon atoms, R 1. R ₂ . R 3 and R ₄ may be linked pairwise by covalent bonds to form a 5- to 8 atoms,

a divalent cation such as magnesium, calcium or barium, and in which x and y are equal to 1 or 2;

R (SH) n is a compound or a mixture of compounds comprising at least one thiol function, R being an aliphatic, alicyclic, mono or polyaromatic, or heterocyclic group, free of chemical function capable of reacting with CO ₂ and n being between 1 and 20.

Z is essentially water or a mixture of solvents comprising water.

2. Extraction medium according to claim 1, in which the compound B is chosen from lithium, sodium, potassium, cesium, rubidium, magnesium, calcium, barium, tetramethylammonium, carbonates and tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium and bicarbonates (or hydrogen carbonates) of lithium, sodium, potassium, cesium and rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium, and decyltrimethylammonium .

3. Medium according to one of the preceding claims wherein the compound R (SH) _n is selected from 1-thioglycerol, dodecanethiols, mercaptothiazoline, 2-mercapto-1-methylimidazole, 2-mercaptobenzimidazole, 2- pyridylmethanethiol and thiosalicylic acid, thioglycolic acid, thiolactic acid and their salts, for example alkali.

4. Medium according to one of the preceding claims wherein the solvent Z is essentially water.

5. Medium according to one of claims 1 to 3 wherein the solvent Z is water associated with another solvent or a mixture of solvents miscible with water.

The medium of claim 5 wherein the water is the main constituent of the solvent Z.

7. Medium according to one of claims 5 or 6 wherein said other solvent is selected from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulfones, sulfoxides, alcohols, ureas, lactams, N-alkylated pyrrolidones, N-alkylated piperidones, cyclotetramethylenesulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl phosphates, carbonates, alkylenes, dialkyl carbonates and their derivatives.

8. Medium according to claim 7 wherein said other solvent is selected from tetraethyleneglycoldimethylether, sulfolane, N-methylpyrrolidone, 1,3-dioxan-2-one, dimethylformamide, dimethylacetamide, formamide, acetamide, 2-methoxy-2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethylthiodipropionate, bis (2-hydroxyethyl) sulfone or tributylphosphate.

9. Medium according to one of the preceding claims wherein the base B or the mixture of bases B of the carbonate type corresponding to one of the general formulas M (HCO ₃ ) _X or IW _y (CO ₃ ) is associated with a base of formula M "(OH) _w , wherein M" is defined in the same way as M or M 'and w is 1 or 2.

10. Medium according to one of the preceding claims wherein each mole of B is associated with α moles of R (SH) _n , α being a positive number preferably defined, to satisfy the condition that a basic function provided by B must be associated with at least one hydrogen bonded to S in the formula R (SH) _n .

11. 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 10 so as to deplete said gaseous effluent CO ₂ and enriching said CO2 extraction medium and a regeneration step of said extraction medium and generating a very CO ₂ rich gas.

12. Method according to one of claims 1 to 11 characterized in that the regeneration of the CO ₂ enriched extraction medium is by stripping by means of a gas vapor phase driving carbon dioxide.

13. Method according to one of claims 1 to 11 characterized in that the regeneration of the extraction medium enriched in CO ₂ is by heating.

14. Method according to one of claims 1 to 11 characterized in that the regeneration of CO ₂ enriched extraction medium is by expansion.

15. Method according to one of claims 1 to 11 characterized in that the regeneration of CO ₂ enriched extraction medium is by various combinations selected from stripping by means of a vapor phase-driving gas carbon dioxide , relaxation and / or heating.