Aqueous absorbent composition containing a base and an azole for separating carbon dioxide from a gaseous effluent - Patents.com

Abstract

The present invention relates to a composition for absorbing carbon dioxide contained in a gaseous effluent, comprising at least one unsaturated heterocyclic organic compound R(NH) n wherein the group R is an alicyclic, mono- or polyaromatic or heterocyclic group having at least one nitrogen atom, and n is 1 to 20, and / or the base B or the mixture of base B in an aqueous solvent Z is reacted with the compound R(NH) n The present invention also relates to a method for capturing CO2 in a gaseous effluent using said composition.

Description

[Technical field]

[0001] The present invention relates to the decarbonation of gaseous effluents, more particularly, the present invention relates to an aqueous absorbent composition for capturing CO2 contained in a gaseous effluent. [Background technology]

[0002] Carbon dioxide is one of the greenhouse gases that is widely produced by various human activities and has a direct impact on air pollution.

[0003] To reduce the amount of carbon dioxide emitted into the atmosphere, it is possible to capture the CO2 contained in the gaseous effluent.

[0004] The decarbonation of gaseous effluents, such as natural gas, synthesis gas, flue gas, refinery gas, tail gas from the Claus process, biomass fermentation gas, cement plant gas and blast furnace gas, is generally carried out by scrubbing with absorbent solutions. The physicochemical characteristics of the solutions used are closely related to the nature of the gas to be treated: selective removal of impurities, the specifications required for the treated gas, the thermal and chemical stability of the solvent towards the various compounds present in the gas to be treated.

[0005] Solvents commonly used today include aqueous solutions of primary, secondary or tertiary alkanolamines, in particular, and optionally organic cosolvents, such as methanol. Specifically, the absorbed CO2 reacts with the alkanolamines present in the solution according to reversible exothermic reactions well known to those skilled in the art, leading to the formation of carbamates, bicarbonates or carbonates. These equilibrium reactions can be depicted by the scheme shown in Figure 1: In the case of a primary alkanolamine, such as monoethanolamine, the reaction that takes place is that from FIG. 1 (top row) involving a carbamate ion, a bicarbonate ion, and a carbonate ion.

[0006] In the case of a secondary alkanolamine, such as diethanolamine, it is depicted by FIG. 1 (middle).

[0007] In addition, in the case of a tertiary alkanolamine, for example, methyldiethanolamine, etc., the procedure is as shown in FIG. 1 (lower part).

[0008] One alternative to aqueous alkanolamine solutions is the use of hot solutions of alkali metal carbonates. The principle is based on the absorption of CO2 in aqueous solution by inorganic carbonates following a reaction leading to inorganic bicarbonates and regeneration by a reversible reaction that converts the inorganic bicarbonates back to inorganic carbonates.

[0009] Certain methods of decarbonation by scrubbing with absorbent solutions, such as polyethylene glycol or chilled methanol, are based on the physical absorption of CO2.

[0010] US Pat. Nos. 5,993,333 and 5,949,623 describe the use of absorbent compositions for absorbing carbon dioxide, in which a specific base selected from amidines and guanidines or from phosphazenes, respectively, is combined with a compound containing at least one thiol or alcohol functional group and, optionally, a non-aqueous solvent.

[0011] Patent document 3 describes an absorbent composition for absorbing carbon dioxide, which is used in a method for capturing carbon dioxide contained in a gaseous effluent, and which contains, in an aqueous medium, a combination of a specific base selected from carbonates and / or hydrogen carbonates with a compound selected from thiols.

[0012] An essential aspect of the operation for the solvent treatment of gases or flue gases remains the regeneration of the separating agent. Depending on the type of absorption (physical and / or chemical), regeneration by expansion, distillation and / or entrainment of a vaporized gas known as "stripping gas" is generally envisaged.

[0013] Generally, the use of all the above mentioned absorbent solutions requires a large energy consumption for the regeneration of the separator. For example, the regeneration of the aqueous solution of ethanolamine used to capture CO2 in flue gas corresponds to about 4 GJ per tonne of captured CO2. Such energy consumption represents a significant operating cost for the CO2 capture process.

[0014] The applicant has discovered that the use of a particular absorbent composition comprising, in an aqueous medium, a combination of a base selected from carbonates and / or bicarbonates and / or hydroxides with an azole compound makes it possible to obtain advantageous performance levels for capturing CO2 contained in gaseous effluents. [Prior art documents] [Patent documents]

[0015] [Patent Document 1] French Patent Application Publication No. 2909010 [Patent Document 2] French Patent Application Publication No. 2909011 [Patent Document 3] French Patent Application Publication No. 2934175 Summary of the Invention [Means for solving the problem]

[0016] (Summary of the invention) The present invention relates to an absorbent composition for absorbing carbon dioxide contained in a gaseous effluent, comprising at least one compound R(NH) of a base B or a mixture of bases B in an aqueous solvent Z. n and / or said mixture of said salt B or base B in said aqueous solvent Z, n and wherein - B has the general formula M(HCO3) x or M' y (CO3) or M''(OH) wwhere M, M', M'' are identical or different and can be independently selected from the following: - monovalent cations, such as lithium, sodium, potassium, rubidium or cesium, - General formula R1R2R3R4N + wherein R1, R2, R3 and R4 are independently selected from a hydrogen atom, a branched or unbranched, saturated or unsaturated aliphatic, substituted or unsubstituted, saturated or unsaturated alicyclic, substituted or unsubstituted, saturated or unsaturated heterocyclic, substituted or unsubstituted, monoaromatic or polyaromatic hydrocarbon-based group containing 1 to 20 carbon atoms, and R1, R2, R3 and R4 can be linked in pairs by covalent bonds to form a heterocycle having 5 to 8 atoms, - divalent cations, e.g. magnesium, calcium or barium Selected from x, y, w equal 1 or 2; - R(NH) n is an unsaturated heterocyclic organic compound or a mixture of unsaturated heterocyclic organic compounds, in which the group R is an alicyclic, mono- or polyaromatic or heterocyclic group having at least one nitrogen atom, and n is between 1 and 20, preferably between 1 and 6, and highly preferably n is equal to 2 or 3; Z is essentially water or a mixture of solvents including water.

[0017] The base B or mixture of bases B is selected from the carbonates of lithium, sodium, potassium, cesium, rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium, the bicarbonates (or hydrogen carbonates) of lithium, sodium, potassium, cesium, rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium, the hydroxides of lithium, sodium, potassium, cesium and rubidium, magnesium, calcium and barium, alone or as a mixture.

[0018] The compound R(NH) n may be an unsaturated heterocyclic organic compound containing at least 2, 3 or 4 nitrogen atoms in a ring of 5 or more atoms, the ring containing at least 3, 2 or 1 carbon atoms, respectively, and preferably the compound R(NH) n is an organic compound that includes an unsaturated heterocycle containing five atoms and having at least one nitrogen atom for every four carbon atoms.

[0019] The group R may contain one or more heteroatoms present by way of functional groups such as alcohols, ethers, thioethers, nitriles, ketones, sulfones, sulfoxides, amides or amines.

[0020] Compound R(NH) nmay be selected from azoles such as imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole, 3-amino-1,2,4-triazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 2-imidazolidone, 3,5-diamino-1,2,4-triazole, L-histidine, adenine, barbituric acid, methyl-1H-1,2,4-triazole-3-carboxylate, 2-ethylimidazole, 4-methyl-5-imidazolecarboxaldehyde, 2,4-dimethylimidazole, and highly preferably selected from imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole and 3-amino-1,2,4-triazole.

[0021] Preferably, the compound R(NH) n is selected from imidazole, 2-methylimidazole, 4(5)-methylimidazole, 1,2,4-triazole, and 3-amino-1,2,4-triazole.

[0022] In one embodiment, solvent Z consists essentially of water.

[0023] In another embodiment, solvent Z is water in combination with another solvent or mixture of solvents that is miscible with water.

[0024] In this case, water represents at least 30% by weight, preferably at least 50% by weight and highly preferably at least 60% by weight, relative to the total amount of solvent Z.

[0025] The other solvent may be selected from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulfones, sulfoxides, alcohols, ureas, lactams, N-alkylpyrrolidones, N-alkylpiperidones, cyclotetramethylene sulfones, N-alkylformamides, N-alkylacetamides, ether ketones, alkyl phosphates, alkylene carbonates, dialkyl carbonates, and derivatives thereof.

[0026] Said other solvent may be selected from inter alia tetraethylene glycol dimethyl ether, sulfolane, dimethyl sulfoxide, ethanol, polyethylene glycol-200 / 400 / 600, N-methylpyrrolidone, 1,3-dioxan-2-one, dimethylformamide, dimethylacetamide, formamide, acetamide, 2-methoxy-2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethyl thiodipropionate, bis(2-hydroxyethyl)sulfone or tributyl phosphate.

[0027] In the absorbent composition according to the invention, α moles of R(NH) n may be combined with each mole of B, and α is of the formula R(NH) n is a positive number defined to satisfy the condition that at least one hydrogen atom bonded to N in must be bonded to a basic group provided by B.

[0028] The present invention also relates to a method for capturing carbon dioxide, comprising the steps of contacting a CO2-containing gaseous effluent to be treated with an absorbent composition according to any one of the previous variations, so as to deplete the gaseous effluent of CO2 and enrich the absorbent composition with CO2, and regenerating said absorbent composition to produce a gas highly enriched in CO2.

[0029] Regeneration of the CO2-rich absorbent composition may be carried out by a combination of steps selected from steam entrainment, heating or expansion with a gas entraining carbon dioxide in the vapor phase, or steam entrainment, expansion and / or heating with a gas entraining carbon dioxide in the vapor phase. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0030] (List of Drawings) FIG. 1 shows, for primary (1a), secondary (1b) and tertiary (1c) alkanolamines, that the absorbed CO2 reacts with the alkanolamines present in the absorbent solution in a reversible exothermic reaction leading to the formation of carbamates, bicarbonates or carbonates.

[0031] FIG. 2 shows a diagram of a method for capturing CO2 by absorption and regeneration using a sorbent composition according to the present invention.

[0032] FIG. 3 shows the amount of captured CO per unit of the amount of scavenger available in the absorbent composition (1) according to the present invention (imidazole and KOH) as a function of the equilibrium pressure of the system at the measurement temperature (in order: cross indicates 40° C., triple cross indicates 60° C., + indicates 70° C., dash indicates 80° C., and filled square indicates 90° C.).

[0033] FIG. 4 depicts the amount of captured CO2 per unit of the amount of scavenger available in the absorbent composition (2) according to the invention (1,2,4-triazole and KOH) and shows the role of temperature (in the above order: 40° C., 60° C., 70° C., 80° C. and 90° C.) on the equilibrium pressure achieved and therefore the amount of captured CO2.

[0034] FIG. 5 represents the amount of captured CO2 per unit of the amount of capture agent available in the comparative absorbent composition (3), considered as a reference for the prior art (monoethanolamine), as a function of the equilibrium pressure of the system at the measurement temperatures (in the order given above: 40° C., 60° C., 70° C., 80° C. and 90° C.).

[0035] FIG. 6 depicts the amount of CO captured per unit of the amount of scavenger available in the comparative absorbent composition (4) (KOH alone) (adsorption isotherms, in the order listed above: 40° C., 60° C., 70° C., 80° C., and 90° C.) over the range of experimental CO equilibrium pressures.

[0036] FIG. 7 depicts the amount of CO2 captured per unit of the amount of scavenger available in the absorbent composition (5) according to the invention (2-methylimidazole and KOH) and shows the role of temperature (in the above order: 40° C., 60° C., 70° C., 80° C. and 90° C.) on the equilibrium pressure achieved and therefore the amount of CO2 captured.

[0037] FIG. 8 represents the amount of captured CO2 per unit of the amount of capture agent available in the absorbent composition (6) according to the invention (4(5)-methylimidazole and KOH) as a function of the equilibrium pressure of the system at the measurement temperatures (in the above order: 40° C., 60° C., 70° C., 80° C. and 90° C.).

[0038] FIG. 9 depicts the amount of CO2 captured per unit of the amount of scavenger available in the absorbent composition (7) according to the invention (3-aminotriazole and KOH) and shows the role of temperature (in the above order: 40° C., 60° C., 70° C., 80° C. and 90° C.) on the equilibrium pressure achieved and therefore the amount of CO2 captured.

[0039] (Description of the embodiment) The present invention describes a medium for extracting carbon dioxide, more specifically an absorbent composition, for use in a method for capturing carbon dioxide contained in a gaseous effluent, the method comprising the combination, in an aqueous medium, of a specific base selected from carbonates and / or bicarbonates and / or hydroxides with a compound selected from azole type compounds.

[0040] More specifically, the absorbent composition for absorbing CO2 according to the invention is used in a method for capturing carbon dioxide contained in a gaseous effluent, and comprises at least one compound R(NH) of a base B or a mixture of bases B of the (hydrogen)carbonate or hydroxide type in an aqueous solvent Z. n and / or the compound R(NH) of the base B or the mixture of base B in an aqueous solvent Z. n This includes products obtained by reaction with

[0041] The present invention further relates to a method for capturing carbon dioxide, comprising the steps of: a) contacting a CO2-containing gas to be treated with said absorbent composition to obtain a CO2-depleted gas and a CO2-rich absorbent composition; and b) regenerating the CO2-rich absorbent composition to obtain an absorbent composition that can be used again and to produce a gas highly enriched in CO2.

[0042] The absorbent composition according to the invention makes it possible to capture the carbon dioxide contained in the gaseous effluent. Once loaded with carbon dioxide, the absorption medium can further be regenerated under easier conditions than the absorbent solutions from the prior art.

[0043] The absorbent composition for absorbing CO2 according to the invention is a sorbent of the general formula M(HCO3) of the carbonate (hydrogen) salt or hydroxide type in an aqueous solvent Z. x or M' y (CO3) or M''(Oh)W w Compound R(NH) of base B or mixture of bases B corresponding to one of n and / or the compound R(NH) of the base B or the mixture of base B in an aqueous solvent Z n and wherein - B is the general formula M(HCO3) of the carbonate (hydrogen) salt type x or M' y (CO3), where M and M' are identical or different and can be any of the following: - monovalent cations, such as lithium, sodium, potassium, rubidium or cesium, - General formula R1R2R3R4N + R1, R2, R3 and R4 are independently selected from a hydrogen atom, a branched or unbranched, saturated or unsaturated aliphatic, a substituted or unsubstituted saturated or unsaturated alicyclic, a substituted or unsubstituted saturated or unsaturated heterocyclic, or a substituted or unsubstituted monoaromatic or polyaromatic hydrocarbon-based group containing 1 to 20 carbon atoms, and R1, R2, R3 and R4 can be covalently bonded in pairs to form a heterocyclic ring having 5 to 8 atoms. - divalent cations, e.g. magnesium, calcium or barium Selected from x and y are equal to 1 or 2; and / or B is a hydroxide type of general formula M''(OH) w where M″ is defined as M or M′, and w is equal to 1 or 2, - R(NH) n is an unsaturated heterocyclic organic compound or a mixture of unsaturated heterocyclic organic compounds, where the group R is an alicyclic group, a monoaromatic or polyaromatic group, or a nitrogen-containing (i.e., containing at least one nitrogen atom) heterocyclic group, and n is 1 to 20; The aqueous solution Z is a mixture of solvents that essentially contains water or that mainly contains water.

[0044] The group R is bonded to the n -NH units according to the rules of organic chemistry.

[0045] Preferably, the number of -NH units (n) is from 1 to 6, and highly preferably, n is equal to 2 or 3.

[0046] The group R may contain one or more heteroatoms present by way of functional groups such as alcohols, ethers, thioethers, nitriles, ketones, sulfones, sulfoxides, amides or amines.

[0047] When (NH) is present in a ring, it may contain alkyl and / or further functional groups.

[0048] In one embodiment, R(NH) n is a heterocyclic organic compound or mixture of heterocyclic organic compounds containing at least 2, 3 or 4 nitrogen atoms in a ring of 5 or more atoms, the ring containing at least 3, 2 or 1 carbon atom, respectively.

[0049] Preferably, the compound R(NH) n is an organic compound having an unsaturated heterocycle containing five atoms, the heterocycle having at least one nitrogen atom for every four carbon atoms.

[0050] R highly preferably represents a ring containing 3, 2 or 1 carbon atoms.

[0051] Advantageously, said ring contains at least two nitrogen atoms, or even at least three or at least four nitrogen atoms.

[0052] Advantageously, absorbent compositions according to the present invention contain ingredients that are readily available and easy to use.

[0053] The fact that the effective absorbent composition is obtained in an aqueous medium has several advantages: in particular, water is a non-toxic, inexpensive and readily available solvent.

[0054] Moreover, water makes it possible to dispense with gas purification operations, which are very often necessary, for example, when the solvent is an organic compound, such as methanol: in particular, small amounts of solvent are inevitably entrained in the gas after separation of the carbon dioxide, necessitating expensive further purification steps.

[0055] Water also has the advantage that it does not degrade, unlike the organic molecules commonly used as solvents.

[0056] Water has the further advantage that it can be vaporized in situ in the process of regenerating the CO2-rich absorbent composition, the steam thus produced making it possible to heat the absorbent composition and / or to strip the CO2 (steam entrainment).

[0057] A base B of carbonate or hydroxide type or a mixture of bases B has the general formula M(HCO3) x or M' y (CO3) or M''(OH) w where M, M', and M'' are the same or different and can be any of the following: - monovalent cations, such as lithium, sodium, potassium, rubidium or cesium, - General formula R1R2R3R4N + R1, R2, R3 and R4 are independently selected from a hydrogen atom, a branched or unbranched, saturated or unsaturated aliphatic, a substituted or unsubstituted, saturated or unsaturated alicyclic, a substituted or unsubstituted, saturated or unsaturated heterocyclic, or a substituted or unsubstituted monoaromatic or polyaromatic hydrocarbon-based group containing 1 to 20 carbon atoms, and R1, R2, R3 and R4 can be covalently linked in pairs to form a heterocyclic ring having 5 to 8 atoms. - divalent cations, e.g. magnesium, calcium or barium Selected from x, y, and w are independently equal to 1 or 2.

[0058] Among the bases B of carbonate or bicarbonate type or mixtures of bases B used in the absorbent composition according to the invention, mention may be made, for example and without being exhaustive, of the following, used alone or as mixtures: carbonates of lithium, sodium, potassium, caesium and rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium and bicarbonates (or bicarbonates) of lithium, sodium, potassium, caesium and rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium.

[0059] In this case, the base B is highly preferably selected from potassium or sodium carbonates.

[0060] Among the bases B of hydroxide type or mixtures of bases B used in the absorbent composition according to the invention, mention may be made, for example and without being exhaustive, of the following, used alone or as mixtures: hydroxides of lithium, sodium, potassium, cesium and rubidium, magnesium, calcium and barium. Preferably, base B is a hydroxide of sodium or potassium, and highly preferably, base B is potassium hydroxide.

[0061] Formula R(NH) n may be selected, for example, without being exhaustive, from azoles such as imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole, 3-amino-1,2,4-triazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 2-imidazolidone, 3,5-diamino-1,2,4-triazole, L-histidine, adenine, barbituric acid, methyl-1H-1,2,4-triazole-3-carboxylate, 2-ethylimidazole, 4-methyl-5-imidazolecarboxaldehyde and 2,4-dimethylimidazole.

[0062] Preferably, the compound R(NH) n may be selected from imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole and 3-amino-1,2,4-triazole.

[0063] Highly preferred is the compound R(NH) n is imidazole or 1,2,4-triazole or 2-methylimidazole or 4(5)-methylimidazole or 3-amino-1,2,4-triazole, since these compounds allow a good compromise between the loading rate and the enthalpy of absorption.

[0064] Even more preferably, the compound R(NH) n may be selected from imidazole, 2-methylimidazole, 4(5)-methylimidazole.

[0065] Solvent Z may be essentially water. The term "essentially" is understood to mean, for the purposes of the present invention, that the solvent consists in this case only of water, but does not exclude the possibility of having certain inherent impurities that may be contained in water.

[0066] Solvent Z may be a mixture of solvents including water.

[0067] Preferably, when solvent Z consists of a mixture of solvents, water remains the main component. Preferentially, depending on the number of constituents of solvent Z, water may therefore be present in a content of at least 30% by weight relative to the total amount of solvent. Highly preferably, the mixture of solvents may contain at least 50% by weight of water, and more highly preferentially at least 60% by weight of water.

[0068] In this case, the solvent is water combined with another water-miscible solvent or mixture of solvents, selected from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols, thioalcohols, sulfones, sulfoxides, alcohols, ureas, lactams, N-alkylpyrrolidones, N-alkylpiperidones, cyclotetramethylene sulfones, N-alkylformamides, N-alkylacetamides, ether-ketones, alkyl phosphates, alkylene carbonates, dialkyl carbonates and derivatives thereof.

[0069] By way of example, and without being exhaustive, there may be mentioned, but is not limited to, tetraethylene glycol dimethyl ether, sulfolane, dimethyl sulfoxide, ethanol, polyethylene glycol-200 / 400 / 600, N-methylpyrrolidone, 1,3-dioxan-2-one, dimethylformamide, dimethylacetamide, formamide, acetamide, 2-methoxy-2-methyl-3-butanone, 2-methoxy-2-methyl-4-pentanone, tetrahydropyrimidone, dimethyl thiodipropionate, bis(2-hydroxyethyl)sulfone or tributyl phosphate.

[0070] Generally, the absorbent composition may contain from 1% to 90% water by weight, preferably from 20% to 80% water by weight, more preferably at least 50% water by weight.

[0071] In aqueous media, [B+αR(NH) n ] aq It is written as, [B+αR(NH) n It has been found that a judicious combination of the two, in the form of ], according to their nature and their proportions, constitutes an advantageous absorbent composition for carbon dioxide. n is bound and the chemical species thus formed has the property of reacting with CO2 in aqueous media according to the following general scheme:

[0072] [ka]

[0073] where γ is the absorbent composition [B + αR(NH) n ] aq It represents the number of moles of CO2 chemically bound to reactive species contained within the gas.

[0074] The value of the coefficient α depends on the nature of the two chemical species involved. α is a positive number. Preferably, α is a function of the formula R(NH) n The condition must be met that at least one hydrogen atom bonded to N in must be bonded to a basic group provided by B. For example, in the case of a bond between a monobase B=M″OH and a compound RNH, α is preferably 1 or greater.

[0075] In this manner, the CO2-containing gas to be treated is subjected to contact with the absorbent composition. Later, CO2 will run out.

[0076] Carbon dioxide is [B+αR(NH) n ] aq , because after capturing CO2, the absorbent composition is converted to the CO2 capture product [B,αR(NH) n ,γ(CO2)] aq In addition to excess CO2 or excess [B+αR(NH) n ] aq This means that it may contain

[0077] This reaction is reversible. The reverse reaction can be represented by the following general scheme:

[0078] [ka]

[0079] Therefore, for the absorbent composition, [B + αR(NH) n ] aqand an operation aimed at recovering the CO2, which makes it possible to generate a gas very rich in CO2 and to regenerate the sorbent composition.

[0080] The operations to regenerate the absorbent composition require little energy and, in particular, may be carried out under conditions requiring less energy than operations that would be required to regenerate the same amount of CO2 if the CO2 was extracted using one or more primary, secondary or tertiary amines or compositions thereof that yield carbamates, bicarbonates or carbonates according to the equilibrium reactions presented above as known to those skilled in the art (Figure 1) and conventionally used to capture CO2.

[0081] Likewise, this operation, through the regeneration of the absorbent composition, requires little energy, in particular in aqueous media, R(NH) n The extraction may be carried out under conditions requiring less energy than would be required to regenerate the same amount of CO2 if the CO2 were extracted with base B used alone in the absence of

[0082] R(NH) in aqueous media n Even if only the mixture [B + αR(NH) n ] aq It has been observed that the CO2 present in the gas cannot be captured as effectively as the base B or a mixture of base B and compound R(NH) in an aqueous medium in a ratio that is wisely chosen and preferably optimized. n This combination makes it possible to carry out the steps of extraction of CO2 and regeneration of the absorbent composition according to the invention.

[0083] The system for capturing CO2 according to the invention may be used in a method for treating a gas containing CO2.

[0084] The method for capturing carbon dioxide generally comprises the steps of: a) contacting a CO2-containing gas to be treated with an absorbent composition to obtain a CO2-depleted gas and a CO2-rich absorbent composition; and b) regenerating the CO2-rich absorbent composition to obtain a regenerated absorbent composition that can be used again, producing a gas highly enriched in CO2.

[0085] More specifically, as depicted in FIG. 2, in a method for capturing carbon dioxide, the gas to be treated (1) is introduced into a gas-liquid contactor (A) where it is contacted with a regenerated liquid absorbent composition (10). This results in a CO2-depleted treated gas (2) and a CO2-rich separation medium (11). The CO2-rich absorbent composition is introduced into a heat exchange device (E) to produce a CO2-rich heated absorbent composition (12). Heat is provided by cooling the CO2-lean hot absorbent composition (13). This also results in a CO2-lean cooled absorbent composition stream (10). External hot and cold sources (not shown) may be used to adapt the temperatures of streams (10) and (12) to the operating conditions of components (A) and (C), respectively. The heated absorbent composition (12) rich in CO2 is introduced into a gas-liquid separation facility (C) where the separation medium is regenerated. The driving force for this separation is heat provided by a heat source (20) by means of a heat exchange device (D). This results in a cooled heat source (21). Alternatively, this heat source can be supplemented, completely or partially, by a stripping gas, not shown. The regeneration of the separation medium results in a hot separation medium (13) lean in CO2 and a gas stream (3) rich in CO2. Depending on the regeneration method chosen, the CO2 of stream (3) can be mixed with the stripping gas. Alternatively, stream (3) can be connected to a device intended to cause an expansion of the CO2-rich separation medium, thus constituting, completely or partially, the driving force for the regeneration. The hot CO2 lean separation stream (13) transfers its heat to the above-mentioned device (E) so as to provide device (A) with a cooled CO2 lean separation medium (10) at a temperature suitable for the operating conditions of (A).

[0086] The temperature during step (A) may advantageously be between 20°C and 80°C, preferably between 30°C and 70°C.

[0087] According to the present invention,

[0088] [ka]

[0089] The regeneration of the absorbent composition according to the reaction of is carried out by either: - steam entrainment (or stripping) by a gas which entrains in the vapour phase the carbon dioxide contained in the solvent to be regenerated. The stripping gas may for example be formed in situ by vaporisation of one or more compounds present in the absorbent composition: it may be one of the compounds defined according to the invention, but it may also be a compound originating from the gas to be treated which may have been absorbed together with the CO2, for example water in the case of flue gas. The stripping gas may be added to the regeneration step: it may for example be nitrogen, steam or part of the treated gas obtained from the absorption step; or - Heating; or - Inflation, or - Various combinations of the three mentioned playback methods.

[0090] (Example) The examples presented below illustrate the technical advantages of the present invention, but do not limit the scope of the present invention. They particularly present the CO2 absorption capacity of various absorption media and the absorption energy of the target species of various absorbent compositions under the conditions of the implementation of the examples.

[0091] Testing of CO2 absorption in various absorbent compositions is carried out according to the following procedure.

[0092] The absorbent composition is formed from a mixture of compounds. The mixture is first degassed under vacuum with controlled agitation and controlled temperature to degas residual gases including CO2. A known mass of the mixture is then injected into a closed reactor under an inert atmosphere to avoid any contamination with ambient CO2. A vacuum is then applied in the reactor until the saturated vapor pressure of the mixture at the desired temperature is reached.

[0093] Then, at 40°C, 60°C, 70°C, 80°C and 90°C, a large amount of high purity CO2 is injected into the reactor by a calibrated ballast discharge to achieve various pressure setpoints between 0 and 3 bar defined by the automaton. Once each pressure setpoint is reached in the reactor after the injection of CO2, a 40 minute hold is performed to obtain liquid-vapor equilibrium. In this way, by monitoring the pressure in the reactor as a function of time, a series of points is obtained for each temperature corresponding to the amount of CO2 injected into the reactor. Knowing the volume of the vacuum reactor and the volume of the mixture inserted, the volume of the gas phase can be calculated and therefore the number of moles of CO2 in the gas phase and the number of moles of CO2 captured can be deduced therefrom. At the end of the CO2 absorption step, the loading factor is determined. The loading factor is defined by those skilled in the art as the number of moles of CO2 captured divided by the number of moles of basic compound (base or mixture of bases) B present in the absorbent composition.

[0094] Through a series of isotherms from 40°C to 90°C, it is possible to determine the enthalpy of reaction of CO2 in the mixture as a function of the loading factor α, by applying the Gibbs-Helmholtz equation, known to those skilled in the art as the relationship between the temperature of the mixture, the partial pressure of CO2 and the enthalpy of reaction.

[0095] In addition, the typical partial pressures found at the outlet of the emission plant (e.g., P CO2 =10 kPa) may be recorded to observe the packing ratio that may be achieved by the mixture.

[0096] The following mixtures were evaluated:

[0097] The absorbent composition (1) (according to the invention) is obtained by mixing 0.14 mol of KOH with 0.14 mol of imidazole and 70 g of water.

[0098] The absorbent composition (2) (according to the invention) is obtained by mixing 0.14 mol of KOH with 0.14 mol of 1,2,4-triazole and 70 g of water.

[0099] The absorbent composition (3) (comparative example) is obtained by mixing 30 g (0.49 mol) of monoethanolamine (MEA) with 40 g of water. This absorbent composition corresponds to a 30% by weight aqueous solution of ethanolamine (MEA), which is a standard solvent well known to those skilled in the art for capturing CO2 in flue gases.

[0100] The absorbent composition (4) (comparative example) is obtained by mixing 0.14 mol of KOH and 70 g of water. This absorbent composition contains a hydroxide base, but does not contain the compound R(NH) n Does not contain.

[0101] The absorbent composition (5) (according to the invention) is obtained by mixing 0.14 mol of KOH with 0.14 mol of 2-methylimidazole and 70 g of water.

[0102] The absorbent composition (6) (according to the invention) is obtained by mixing 0.14 mol of KOH with 0.14 mol of 4(5)-methylimidazole and 70 g of water.

[0103] The absorbent composition (7) (according to the invention) is obtained by mixing 0.14 mol of KOH with 0.14 mol of 3-amino-1,2,4-triazole and 70 g of water.

[0104] Figures 3, 4, 5, 6, 7, 8 and 9 present the absorption isotherms of CO2 for mixtures (1), (2), (3), (4), (5), (6) and (7) at 40, 60, 70, 80 and 90 °C.

[0105] As can be seen in Figures 3, 4 and 8, in comparison with Figure 5, the capacities achieved by equilibration of CO2 at low partial pressures, for example 5 kPa (40 ° C.), are greater than or at least equal to those of the compounds from the prior art in the absorbent composition of the extraction medium (3), where [α:medium (1): 5 kPa] = 0.48 mol CO2 / mol B, [α:medium (2): 5 kPa] = 0.58 mol CO2 / mol B and α:medium (7): 5 kPa] = 0.56 mol CO2 / mol B, whereas [α:medium (3): 5 kPa] = 0.48 mol CO2 / mol B. For CO2 10 kPa and thermodynamic equilibrium, the capacities achieved are all greater than those achieved by the mixture (3) representative of the prior art (see Table 1).

[0106] Particular attention may be paid to the even better performance obtained with the absorbent compositions of extraction media (5) and (6), where for a partial pressure of CO2 at equilibrium at a low pressure of 5 kPa (40°C), the achieved capacities are even higher: [α:medium (5): 5 kPa] = 0.67 mol CO2 / mol B, [α:medium (6): 5 kPa] = 0.65 mol CO2 / mol B and [α:medium (7): 5 kPa] = 0.56 mol CO2 / mol B, whereas [α:medium (3): 5 kPa] = 0.48 mol CO2 / mol B.

[0107] Table 1 below presents the absorption enthalpy for various absorbent compositions at different loading rates of CO2 after absorption at 40°C and 10 kPa, as well as the absorption enthalpy at the same loading rates for comparison.

[0108] [Table 1]

[0109] These examples show that the absorbent compositions (1) and (2), as well as (5), (6) and (7) according to the invention capture more CO2 than the prior art absorbent composition (3) due to the lower enthalpy of absorption of CO2 and are more easily regenerated. The regeneration is achieved by reacting the compound R(NH) n This is particularly easy in comparison with the mixture (4) which does not contain

[0110] Furthermore, a comparison of the results of the absorbent composition (4) with the absorbent compositions (1), (2), (5), (6) and (7) according to the invention shows that it is the presence of the compound R(NH) in the aqueous medium according to the invention that allows for easier regeneration of the absorbent composition for an equivalent amount of absorbed CO2. n This clearly shows that this was in combination with compound B and not compound B used alone in an aqueous solution. [Brief description of the drawings]

[0111] [Figure 1] For primary (1a), secondary (1b) and tertiary (1c) alkanolamines, the absorbed CO2 reacts with the alkanolamines present in the absorbent solution in a reversible exothermic reaction leading to the formation of carbamates, bicarbonates or carbonates. [Diagram 2] FIG. 1 shows a diagram of a method for capturing CO2 by absorption and regeneration using a sorbent composition according to the present invention. [Diagram 3] The amount of captured CO2 per unit of the amount of capture agent available in the absorbent composition (1) according to the present invention (imidazole and KOH) as a function of the equilibrium pressure of the system at the measurement temperature (in order, x indicates 40°C, triple cross indicates 60°C, + indicates 70°C, dash indicates 80°C, and filled square indicates 90°C). [Figure 4] It represents the amount of CO2 captured per unit of the amount of scavenger available in the absorbent composition (2) according to the present invention (1,2,4-triazole and KOH). [Diagram 5]It represents the amount of captured CO2 per unit of the amount of capture agent available in the comparative absorbent composition (3), considered as a reference for the prior art (monoethanolamine), as a function of the equilibrium pressure of the system at the measurement temperatures (in the above order: 40°C, 60°C, 70°C, 80°C and 90°C). [Figure 6] The amount of CO captured per unit of the amount of scavenger available in the comparative absorbent composition (4) (KOH alone) (adsorption isotherms, in the order given above: 40° C., 60° C., 70° C., 80° C. and 90° C.) is shown over the range of experimental CO equilibrium pressures. [Figure 7] 4 represents the amount of CO2 captured per unit of the amount of scavenger available in the absorbent composition (5) according to the present invention (2-methylimidazole and KOH). [Figure 8] It represents the amount of captured CO2 per unit of the amount of capture agent available in the absorbent composition (6) according to the present invention (4(5)-methylimidazole and KOH) as a function of the equilibrium pressure of the system at the measurement temperatures (in the above order: 40°C, 60°C, 70°C, 80°C and 90°C). [Figure 9] 4 represents the amount of CO2 captured per unit of the amount of scavenger available in the absorbent composition (7) according to the present invention (3-aminotriazole and KOH).

Claims

1. An absorbent composition for absorbing carbon dioxide contained in a gaseous effluent, comprising at least one compound R(NH) of a base B or a mixture of bases B in an aqueous solvent Z ｎ in combination with and / or a product obtained by the reaction of said compound R(NH) of said base B or said mixture of bases B in said aqueous solvent Z ｎ composition: wherein - B is a base corresponding to one of the general formulas M(HCO ３ ), M'(CO ｘ ), or M''(OH) ｙ ), where M, M', and M'' are the same or different and, without distinction, are as follows: ３ ), or M''(OH) ｗ ), where M, M', and M'' are the same or different and, without distinction, are as follows: - Monovalent cations, such as lithium, sodium, potassium, rubidium or cesium, - General formula R １ R ２ R ３ R ４ N ＋ corresponding quaternary ammonium cation, wherein R １ 、R ２ 、R ３ and R ４ are independently selected from a hydrogen atom, a branched or unbranched saturated or unsaturated aliphatic, a substituted or unsubstituted saturated or unsaturated alicyclic, a substituted or unsubstituted saturated or unsaturated heterocyclic, a substituted or unsubstituted monoaromatic or polyaromatic hydrocarbon-based group containing 1 to 20 carbon atoms, and R １ 、R ２ 、R ３ and R ４ can be covalently paired to form a heterocycle having 5 to 8 atoms. - Divalent cations, such as magnesium, calcium or barium selected from, x, y, w are equal to 1 or 2; -R(NH) ｎ is an unsaturated heterocyclic organic compound, where the group R is an alicyclic, monoaromatic or polyaromatic, or heterocyclic group having at least one nitrogen atom, n is from 1 to 20, preferably from 1 to 6, and most preferably, n is equal to 2 or 3; - Z is essentially water or a mixture of solvents containing water.

2. The base B is selected from lithium, sodium, potassium, cesium, rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium carbonates, lithium, sodium, potassium, cesium, rubidium, magnesium, calcium, barium, tetramethylammonium, tetraethylammonium, benzyltrimethylammonium and decyltrimethylammonium bicarbonates (or hydrogen carbonates), lithium, sodium, potassium, cesium and rubidium, magnesium, calcium and barium hydroxides, either alone or as a mixture, the absorbent composition for absorbing carbon dioxide according to claim 1.

3. Compound R(NH) ｎ is an unsaturated heterocyclic organic compound, and the unsaturated heterocyclic organic compound contains at least 2, 3 or 4 nitrogen atoms in a ring of 5 or more atoms, and the ring contains at least 3, 2 or 1 carbon atom respectively. Preferably, the compound R(NH) ｎ is an organic compound having an unsaturated heterocyclic ring containing 5 atoms, and the organic compound has at least 1 nitrogen atom per 4 carbon atoms. The absorbent composition for absorbing carbon dioxide according to claim 1 or 2.

4. The group R contains one or more heteroatoms, and the one or more heteroatoms are present by functional groups, such as alcohol, ether, thioether, nitrile, ketone, sulfone, sulfoxide, amide or amine, the absorbent composition for absorbing carbon dioxide according to claim 1.

5. Compound R(NH) ｎ is selected from azoles such as imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole, 3-amino-1,2,4-triazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 2-imidazolidone, 3,5-diamino-1,2,4-triazole, L-histidine, adenine, barbituric acid, methyl-1H-1,2,4-triazole-3-carboxylate, 2-ethylimidazole, 4-methyl-5-imidazolecarboxaldehyde, 2,4-dimethylimidazole, and most preferably is selected from imidazole, 1,2,4-triazole, 2-methylimidazole, 1,2,3-triazole, 4(5)-methylimidazole, and 3-amino-1,2,4-triazole, the absorbent composition for absorbing carbon dioxide according to claim 1.

6. Compound R(NH) ｎ is an absorbent composition for absorbing carbon dioxide according to claim 5, selected from imidazole, 2-methylimidazole, 4(5)-methylimidazole, 1,2,4-triazole, 3-amino-1,2,4-triazole.

7. The solvent Z is essentially water, the absorbent composition for absorbing carbon dioxide according to claim 1.

8. The solvent Z is a combination of water and another solvent or a mixture of solvents miscible with water, the absorbent composition for absorbing carbon dioxide according to claim 1.

9. Water occupies at least 30% by weight, preferably at least 50% by weight, most preferably at least 60% by weight relative to the total amount of the solvent Z, the absorbent composition for absorbing carbon dioxide according to claim 8.

10. The other solvent is selected from glycol, polyethylene glycol, polypropylene glycol, copolymers of ethylene glycol - propylene glycol, glycol ether, thioglycol, thioalcohol, sulfone, sulfoxide, alcohol, urea, lactam, N - alkylpyrrolidone, N - alkylpiperidone, cyclotetramethylene sulfone, N - alkylformamide, N - alkylacetamide, ether - ketone, alkyl phosphate, alkylene carbonate, dialkyl carbonate and their derivatives, and is an absorbent composition for absorbing carbon dioxide according to claim 8 or 9.

11. The other solvent is selected from tetraethylene glycol dimethyl ether, sulfolane, dimethyl sulfoxide, ethanol, polyethylene glycol - 200 / 400 / 600, N - methylpyrrolidone, 1,3 - dioxan - 2 - one, dimethylformamide, dimethylacetamide, formamide, acetamide, 2 - methoxy - 2 - methyl - 3 - butanone, 2 - methoxy - 2 - methyl - 4 - pentanone, tetrahydropyrimidone, dimethyl thiodipropionate, bis(2 - hydroxyethyl) sulfone or tributyl phosphate, and is an absorbent composition for absorbing carbon dioxide according to claim 10.

12. α moles of R(NH) ｎ is combined with each mole of B, and α is such that at least one hydrogen atom bonded to N in the formula R(NH) ｎ satisfies the condition that it must be combined with a basic group provided by B, and is a positive number defined as such. The absorbent composition for absorbing carbon dioxide according to claim 1

13. A method for capturing carbon dioxide, the CO to be treated ２ Contacting the gas-containing effluent described in claim 1 with the absorbent composition to deplete the gaseous effluent of CO ２ and enriching the absorbent composition with CO ２ A step of regenerating the absorbent composition to produce a gas highly enriched in CO ２ A method comprising the steps of:

14. CO ２ The regeneration of the absorbent composition rich in CO is carried out by a combination of steps selected from steam entrainment or heating or expansion with a gas entraining carbon dioxide in the vapor phase or steam entrainment, expansion and / or heating with a gas entraining carbon dioxide in the vapor phase, according to the method of claim 13.

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