Ionic liquid-based absorbent composition for separating carbon dioxide contained in gaseous effluents

Abstract

The invention relates to an absorbent composition for carbon dioxide contained in a gaseous effluent, the invention relates to an aqueous composition comprising, in a predominantly non-aqueous medium: an anionic compound comprising one or more deprotonated nitrogen atoms, a cationic organic compound of the phosphonium or ammonium type, and optionally an organic additive of the organic solvent type having a boiling point greater than 100 C and a polarity index with respect to water greater than 0.3.

Description

Technical Field

[0001] This invention relates to the decarbonation of gaseous effluents. More particularly, this invention relates to non-aqueous absorbent compositions for capturing CO2 contained in gaseous effluents, especially ionic liquid-type compositions consisting of anions of heterocyclic rings containing one or more nitrogen atoms (preferably deprotonated) and phosphonium-type organic cations.

[0002] This application relates to the treatment of acidic gases, such as the capture of CO2 or the purification of gases (oxygen combustion, biogas, industrial emissions), wherein the CO2 source is anthropogenic or non-anthropogenic, biogenic or abiotic. Existing technology

[0003] Carbon dioxide is one of the greenhouse gases widely produced by various human activities, and it has a direct impact on air pollution and global warming.

[0004] To reduce the amount of carbon dioxide emitted into the atmosphere, CO2 contained in gaseous effluents can be captured.

[0005] Decarbonization of gaseous effluents (e.g., natural gas, syngas, combustion flue gas, refinery gas, tail gas from the Claus process, biomass fermentation gas, cement plant gas, and blast furnace gas) is typically carried out by washing with an absorbent solution. The physicochemical properties of the solution used are closely related to the properties of the gas being treated: the selective removal of impurities, the expected specifications of the gas being treated, and the thermal and chemical stability of the solvent relative to the various compounds present in the gas.

[0006] Commonly used solvents include, in particular, aqueous solutions of primary, secondary, or tertiary alkyl alcoholamines and optionally, organic co-solvents such as methanol. Specifically, the absorbed CO2 reacts with the alkyl alcoholamine present in the solution via a reversible exothermic reaction, a reaction well known to those skilled in the art, and results in the formation of carbamates, bicarbonates, or carbonates.

[0007] An alternative to aqueous alkanolamine solutions is to use hot solutions of alkali metal carbonates. This principle is based on the absorption of CO2 by inorganic carbonates in an aqueous solution, according to the reaction that produces inorganic bicarbonates, and on regeneration based on a reversible reaction that converts inorganic bicarbonates into inorganic carbonates.

[0008] French patent application FR 2934175 describes an absorbent composition for use in a method for capturing carbon dioxide contained in a gaseous effluent, wherein the absorbent composition comprises, in an aqueous medium, a combination of a specific base selected from carbonates and / or bicarbonates and a compound selected from thiols.

[0009] Some decarbonization methods, which involve washing with an absorbent solution such as polyethylene glycol or cold methanol, are based on the physical absorption of CO2.

[0010] Another alternative to aqueous solutions of amines or hot solutions of alkali metal carbonates is to use solutions based on ionic liquids. Ionic liquids, as generally defined, are liquid salts in ionic solution form that have melting points close to ambient temperatures and possess physicochemical properties such as non-volatility, non-flammability, and stability to water and air.

[0011] “Current Status of CO2 Capture with Ionic Liquids: Development and Progress” by Elmobarak et al. – Fuel The disclosure in 344 (2023) well demonstrates the potential versatility of ionic liquid formulations for physically and / or chemically altering their physicochemical properties and reacting with CO2.

[0012] Ionic liquid-based formulations exhibit advantages such as high solvation capability for CO2 and thermal and chemical stability, but typically exhibit high viscosity of several hundred centipoises (due to their chemical composition and the presence of numerous ionic interactions and / or hydrogen bonds between molecules, but also between the molecules of the ionic liquid and the entities formed after the reaction with CO2). Consequently, the diffusivity of both cationic and anionic entities is affected, and the reaction rate with CO2 is reduced.

[0013] Recently, Yisha Xu et al.'s paper, "Tuning Ionic Liquid-Based Functional Deep Eutectic Solvents (DES) and Other Functional Mixtures for CO2 Capture"—Chemical Engineering Journal, 463 (2023), published a series of solvents or formulations based on ionic liquids, which incorporate additives to alter their physicochemical properties. Deep eutectic solvents (DES) are solvents formed by mixing two or more compounds in proportions corresponding to their eutectic points. Several types of DES exist based on their chemical composition. Advantageously, the combination of an ionic liquid (IL) with a hydrogen-bonding agent can produce a DES that will possess properties similar to the ionic liquid, namely, chemical reactivity for CO2 capture and a near-zero saturated vapor pressure. More advantageously, the combination of an ionic liquid and a hydrogen-bonding donor can reduce the viscosity of the eutectic solvent by tens of centipoises compared to the ionic liquid itself.

[0014] Regeneration of the separating agent remains a necessary aspect of operations for treating gases or flue gases with solvents. Depending on the type of absorption (physical or chemical), regeneration is typically considered to be achieved by pressure reduction, distillation, and / or stripping, with the stripping occurring through a vaporized gas known as the "stripping gas" (which can be water or an inert gas such as nitrogen).

[0015] In a typical manner, the use of all the aforementioned absorbent solutions requires a considerable energy consumption for regenerating the separator. For example, the regeneration of an aqueous ethanolamine solution used to capture CO2 from flue gas is equivalent to approximately 4 GJ per ton of CO2 captured. This energy consumption represents a significant operating cost for the CO2 capture process. Summary of the Invention

[0016] The applicant company has discovered that using ionic liquids composed of heterocyclic anions having one or more deprotonated nitrogen atoms and heterocyclic, phosphonium, or ammonium organic cations having one or more deprotonated nitrogen atoms enables the acquisition of advantageous performance characteristics for capturing CO2 contained in gaseous effluents.

[0017] The addition of specific organic additives (e.g., hydrogen bond donors of polyethylene glycol types (e.g., ethylene glycol) or aprotic compounds (e.g., dimethyl sulfoxide DMSO)) can further reduce the viscosity of the absorbent solution, especially in the presence of CO2. This effect facilitates the use of the absorbent solution in any type of gas-liquid contactor known to those skilled in the art (e.g., packed towers, or for contactors designed for process intensification, such as rotary contactors, also known as HiGee or rotating packed bed contactors).

[0018] Additives that provide hydrogen bonds (ethylene glycol, polyethylene glycol) enable the formation of eutectic in the composition, which is highly advantageous.

[0019] The organic additive advantageously has a boiling point greater than 100ºC, preferably greater than 150ºC, and a polarity index relative to water greater than 0.3, preferably greater than 0.4, or more preferably still greater than 0.5 (the polarity index of water is considered to be equal to 1). By way of non-limiting example, the organic additive can be monoethylene glycol, MEG (relative polarity index = 0.8). In this case, ethylene glycol is used to form a eutectic solvent or DES.

[0020] Even if it is not a hydrogen donor reagent, aprotic compounds (such as dimethyl sulfoxide DMSO) with the same boiling point (189ºC) and polarity (relative polarity index of 0.44) can be considered as organic additives.

[0021] This invention relates to an absorbent composition for carbon dioxide contained in gaseous effluents, comprising, in a predominantly non-aqueous medium: - Anionic compounds containing one or more deprotonated nitrogen atoms. -Cat organic compounds of the heterocyclic, phosphonium, or ammonium type having one or more non-protonated nitrogen atoms. - And optionally, organic additives of the type of organic solvent having a boiling point greater than 100ºC, preferably greater than 150ºC, and a polarity index relative to water greater than 0.3, preferably greater than 0.4, or more preferably still greater than 0.5.

[0022] The composition may contain an organic additive selected from glycols, preferably ethylene glycol or polyethylene glycol, or dimethyl sulfoxide or urea.

[0023] The organic additive may be present in an amount between 5% by weight and 80% by weight, preferably between 10% by weight and 75% by weight, relative to the total weight of the composition (including the limit). Advantageously, the amount of the organic additive does not exceed 50% by weight (including the limit), and it is preferably between 10% by weight and 40% by weight or between 15% by weight and 30% by weight of the composition.

[0024] The cation can be a quaternary ammonium compound selected from trihexyl(tetradecyl)phosphonium, tetra(n-butyl)phosphonium, tetradecylammonium, tetra(n-butyl)ammonium, 1-ethylpyridinium, 1-ethyl-3-methylimidazolium or 1-butyl-3-methylimidazolium.

[0025] The anionic compound may be an anionic nitrogen-containing heterocycle, preferably containing an odd number of atoms and containing at least one or at least two nitrogen atoms.

[0026] Therefore, the anionic compound can be selected from aromatic or non-aromatic heterocycles, such as imidazole, 2-methylimidazolium, 4-methylimidazolium, 2-aminoimidazolium, 3-amino-1,2,4-triazole, 2-isopropylimidazolium, 2-ethyl-4-methylimidazolium, 2-imidazolidineone, 3,5-diamino-1,2,4-triazole, 2-ethylimidazolium, 2,4-dimethylimidazolium, 2,2'-biimidazole, indole, indazole, benzopyrrole, 2-hydroxypyridine, L-histidine, proline, lysine, uracil, cytosine, piperazine, or aminoethylpiperazine.

[0027] Preferably, the anionic compound is selected from imidazole, indazole, 2,2'-biimidazole, indole, 2-methylimidazole, 4-methylimidazole, 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole.

[0028] According to the present invention, it is preferred that the anionic compound and the cationic compound are in equimolar amounts in the composition (because each preferably carries a charge).

[0029] Preferably, the above-described absorbent composition for carbon dioxide exhibits a viscosity of up to 100 centipoise at 40ºC.

[0030] The present invention also relates to a method for capturing carbon dioxide, the method comprising a stage of contacting a gaseous effluent containing CO2 to be treated with an absorbent composition according to any of the alternative forms described, so as to deplete the CO2 in the gaseous effluent and enrich the absorbent composition with CO2, and a stage of regenerating the absorbent composition to produce a gas very rich in CO2.

[0031] Regeneration of the CO2 enriched absorbent composition can be carried out by steam stripping with a gas entrained with carbon dioxide in the gas phase, or by heating, or by pressure reduction, or by a combination of stages selected from steam stripping with a gas entrained with carbon dioxide in the gas phase, pressure reduction and / or heating.

[0032] The absorption and / or regeneration phases can be carried out in a rotary contactor.

[0033] This is because the compositions according to the invention are particularly suitable for use with such devices, especially in their alternative forms using additives, the content of which can be adjusted to modify the viscosity of the composition to make it compatible with the device. Thus, it is contemplated that up to 50% by weight of organic additives, particularly between 10% and 40% by weight, can yield a composition exhibiting a viscosity of up to 100 cP at 40ºC. It is highly advantageous that this viscosity can be achieved with relatively low amounts of additives, which allows maintaining a high overall trapping capacity of the composition (while simultaneously maintaining a high content of ionic compounds in the composition).

[0034] It has also been very advantageous to observe that once the composition is loaded with CO2, it remains at a sufficiently low viscosity to be extracted without problems arising from this type of equipment, which is very advantageous on an industrial scale. Attached Figure Description

[0035] Figure 1 A diagram is shown illustrating a CO2 capture method employing the absorbent composition according to the invention, which involves absorption and regeneration.

[0036] Figure 2 The viscosity of the formulation of the original solution of Example 12 is shown as a function of temperature and ethylene glycol content (refer to A, C, E and G).

[0037] Figure 3 The viscosity of formulations A and B (original solution and CO2-loaded solution) without ethylene glycol in Example 12 is shown as a function of temperature.

[0038] Figure 4 The viscosity of formulations C and D (the original solution and the CO2-loaded solution) of Example 12 with 25% ethylene glycol is shown as a function of temperature.

[0039] Figure 5 The viscosity of formulations E and F (the original solution and the CO2-loaded solution) of Example 12 with 50% ethylene glycol is shown as a function of temperature.

[0040] Figure 6 The viscosity of formulations G and H (original solution and CO2-loaded solution) of Example 12 with 75% ethylene glycol is shown as a function of temperature.

[0041] Figure 7 The viscosity in the original solution and the CO2-loaded solution is shown to vary with the shear rate and temperature of the formulation of Example 13 (which is based on 4-methylimidazolide and has 10% by weight ethylene glycol). Detailed Implementation

[0042] This invention describes a solvent for extracting carbon dioxide, hereinafter referred to as an absorbent composition for carbon dioxide, in a method for capturing carbon dioxide contained in a gaseous effluent, wherein the absorbent composition comprises a combination of anions (selected from compounds having one or more deprotonated nitrogen atoms) associated with ammonium or phosphonium-type organic cations in a predominantly non-aqueous medium.

[0043] The term “primarily non-aqueous medium” is understood to mean that the absorbent medium may contain a small amount of water (that is, up to 5% by weight of water, especially due to the hydration of the composition by water generated from the gas to be treated) or that the initial absorbent composition is water-free during the regeneration phase.

[0044] More specifically, the CO2 absorbent composition according to the invention used in methods for capturing carbon dioxide contained in gaseous effluents advantageously comprises anionic nitrogen-containing heterocyclic compounds, and more advantageously comprises nitrogen-containing heterocycles having an odd number of atoms, without being bound by any theory, which appear to exhibit further enhanced absorption capacity. In certain non-limiting cases, it comprises aprotic anionic nitrogen-containing heterocycles.

[0045] The term "heterocyclic" is generally understood to refer to an aromatic or non-aromatic cyclic molecule containing at least one heteroatom, such as N, O, S, P or others.

[0046] Throughout the specification, the term "aprotic molecule" refers to a molecule that does not contain hydrogen atoms capable of forming hydrogen bonds, i.e., a molecule that does not contain OH, NH, or FH bonds.

[0047] Throughout this specification, and as described in Séo et al.’s publication “Chemically Tunable Ionic Liquids with Aprotic Heterocyclic Anion”, J. Phys. Chem. B, 2014, 118, 5740–5751, the term “aprotic anionic heterocycle” is understood to mean an aromatic ring containing a heteroatom (in this case, a nitrogen atom that has been deprotonated by, for example, an acid-base reaction with trihexyl(tetradecyl)phosphonium hydroxide).

[0048] Furthermore, the present invention relates to a method for capturing carbon dioxide, the method comprising the following steps: a) Contact the CO2-containing gas to be treated with the absorbent composition to obtain a CO2-depleted gas and a CO2-rich absorbent composition. b) Regenerate the CO2-rich absorbent composition to obtain a reusable absorbent composition and generate a very CO2-rich gas.

[0049] The absorbent composition according to the invention can capture carbon dioxide contained in gaseous effluents. Once loaded with carbon dioxide, the medium can be further regenerated under conditions easier than prior art absorbent solutions, such as aqueous amine solutions. The absorbent solution is more thermally stable than typical aqueous amine solutions due to its physicochemical properties, and is therefore more environmentally friendly by limiting degradation products.

[0050] The CO2 absorbent composition according to the present invention comprises, at least in the primary non-aqueous medium: - Cationic heterocyclic organic compounds, cationic ammonium compounds, or cationic phosphonium compounds having one or more nonprotonated nitrogen atoms, such as trihexyl(tetradecyl)phosphonium, 1-ethylpyridinium, or 1-ethyl-3-imidazolium. - An anionic compound containing one or more deprotonated nitrogen atoms, preferably a nitrogen-containing heterocyclic compound, also known as anionic nitrogen-containing heterocycles. Preferably, the ring contains an odd number of atoms, including at least one nitrogen atom, and practically even at least two nitrogen atoms. When one or more nitrogen atoms are present in the ring, the ring may contain additional alkyl and / or functional groups, such as aromatic rings, to increase the nucleophilic properties of the anion.

[0051] -Optional organic additives are selected from organic solvents defined as follows: boiling point greater than or equal to 100ºC, and preferably greater than 150ºC, and polarity index relative to water (considered to be equal to 1) greater than 0.3, preferably greater than 0.4 or more preferably greater than 0.5.

[0052] Solvents such as ethylene glycol or aprotic solvents, which are organic additives, can be considered, such as dimethyl sulfoxide or DMSO (boiling point 189ºC and relative polarity index 0.44), which have the desired boiling point and polarity properties.

[0053] When present, organic additives are typically added at a concentration of 5% to 80% by weight, preferably 10% to 75% by weight, of the formulation, including limits. In particular, their concentration may be between 10% and 40% by weight or between 15% and 30% by weight, and may, for example, be equal to or near 25% by weight.

[0054] The fact that an effective absorbent composition is obtained in a primarily non-aqueous medium presents several advantages. This is because this thermally stable composition with very low volatility makes regeneration possible at temperatures higher than those of formulations used as aqueous solutions. The composition can advantageously be used under pressure, which makes it possible to have compressed CO2 at the outlet during the regeneration stage.

[0055] Furthermore, it is possible to eliminate the need for gas purification steps, which are often necessary in existing solutions when the solvent is an organic compound (such as methanol). This is because a small amount of solvent is inevitably entrained in the gas after carbon dioxide separation, requiring an additional and expensive purification stage.

[0056] The nitrogen-containing heterocyclic compound that acts as the anion can be selected from, for example (non-exhaustive list) azoles, such as imidazole, 2-methylimidazolium, 4-methylimidazolium, 2-aminoimidazolium, 3-amino-1,2,4-triazole, 2-isopropylimidazolium, 2-ethyl-4-methylimidazolium, 2-imidazolidineone, 2,2'-biimidazole, 3,5-diamino-1,2,4-triazole, 2-ethylimidazolium, 2,4-dimethylimidazolium, indole, indazole, or benzopyrrole.

[0057] Preferably, the nitrogen-containing heterocyclic compound may be selected from imidazole, 2-methylimidazolium, 4-methylimidazolium, indazole, 3-amino-1,2,4-triazole or 2,2'-biimidazole.

[0058] Alternatively, nitrogen-containing heterocyclic compounds can be selected from amino acids, such as L-histidine, proline, or lysine.

[0059] Alternatively, the nitrogen-containing heterocyclic compound could be 2-hydroxypyridine.

[0060] It can also be selected from other cyclic compounds containing several nitrogen-containing sites, such as uracil, cytosine, piperazine, or aminoethylpiperazine.

[0061] The composition may contain organic additives as described above, such as glycols, for example polyethylene glycol-200 or ethylene glycol, to reduce the viscosity to a suitable range [particularly 1-100 cP] for use in reactors of, for example, rotating packed bed (RPB) type. Solvents that can be used as additives are preferably selected from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, or thioglycols.

[0062] Another class of solvents to consider are polar aprotic solvents, such as DMSO.

[0063] In particular, organic additives enable the viscosity of the formulation to be adjusted to a range compatible with the viscosity of gravity flow [1-5 cP] or rotary contactors for rotating packed bed (RPB) type [1-100 cP].

[0064] The selection of cationic organic compounds, anionic nitrogen-containing heterocyclic compounds, and optional organic additives in the absorbent compositions according to the invention is made by those skilled in the art based on the desired physical properties (especially viscosity) and the specifications of the gas being treated (especially the partial pressure of CO2).

[0065] The CO2 capture system according to the present invention can be used in methods for treating gases containing CO2.

[0066] The method for capturing carbon dioxide according to the present invention schematically includes the following stages: a) Contact the CO2-containing gas to be treated with the absorbent composition according to the invention to obtain a CO2-depleted gas and a CO2-rich absorbent composition. b) Regenerate the CO2-rich absorbent composition to obtain a regenerated and reusable absorbent composition and generate a gas that is very rich in CO2.

[0067] More specifically, in the capture of carbon dioxide (CCO2) Figure 1In this method, 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 produces a CO2-lean treatment gas (2) and a CO2-rich separation medium (11). The CO2-rich absorbent composition is introduced into a heat exchanger (B) to produce a heated CO2-rich absorbent composition (12). Heat is provided by cooling the heated CO2-lean absorbent composition (13). This also produces a stream of cooled CO2-lean absorbent composition (10). External heat and cold sources (not shown) can be used to adjust the temperatures of the streams (10) and (12) to the operating conditions of elements (A) and (C), respectively. The heated CO2-rich absorbent composition (12) is introduced into a gas-liquid separation device (C), where the separation medium is regenerated. The driving force for this separation is heat provided by a heat source (20) via a heat exchanger (D). This produces a cooled heat source (21). Alternatively, the heat source can be supplemented wholly or partially by stripping gas, steam, or an inert gas such as N2 (not shown). Regeneration of the separation medium produces a CO2-lean thermal separation medium (13) and a CO2-rich gas stream (3). Depending on the chosen regeneration method, the CO2 in the stream (3) can be a mixture with the stripping gas. Alternatively, the stream (3) can be connected to a device intended to reduce the pressure of the CO2-rich separation medium, thereby constituting wholly or partially the driving force for the regeneration. The CO2-lean thermal separation stream (13) transfers its heat in the aforementioned device (B) to provide cooled CO2-lean separation medium (10) to the device (A) at a temperature suitable for the operating conditions of (A).

[0068] The temperature during stage (A) can advantageously be between 20ºC and 80ºC, and preferably between 30ºC and 70ºC.

[0069] Gas-liquid contactors can be rotary contactors. Example

[0070] The embodiments presented below illustrate the technical advantages of the invention without limiting its scope. They particularly demonstrate the absorption capacity of different absorbent media for CO2.

[0071] Example 1. [P] in ethanol 66614 [OH] salts are transferred from [P] salts via anion exchange. 66614 Synthesis starting with ][Br] [P 66614 [OH] is understood to refer to trihexyl(tetradecyl)phosphonium hydroxide, and [P] 66614 [Br] is understood to refer to trihexyl(tetradecyl)phosphonium bromide.

[0072] 45.3 g of trihexyl(tetradecyl)phosphonium bromide [P] 66614 [Br] (M = 563.76 g / mol), i.e., 0.080 mol, is dissolved in 100 ml of ethanol dried through a 3A sieve. This solution is then reacted with 1OH... - The equivalent of Amberlite IRN78 resin is 0.080 mol contact. Dowex Monosphere 550A resin can also be used. This resin requires 0.072 liters (78 g) at 1.1 OH eq / l (d(resin) = 1.08 g / ml). Add this resin to [P 66614 A solution of [Br] was prepared in ethanol (dried through a 3A sieve), and the mixture was stirred for 24 hours. This operation was repeated once more. The resin was removed by filtration through a Büchner funnel.

[0073] Example 2. [P] 66614 Synthesis of [indazole] salts 1.1 equivalents of indazole (i.e., 0.044 mol) were added to 50 ml of 0.8 M (0.040 mol) [P] 66614 The mixture was stirred overnight in a [OH] solution. Ethanol was then evaporated on a rotary evaporator. The resulting orange-yellow liquid was subsequently dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum.

[0074] 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.87 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.21 (m, 8H, PCH2); 6.72 (t, 1H, CH-5); 6.90 (t, 1H, CH-6); 7.43 (d, 1H, CH-7); 7.53 (d, 1H, CH-4); 7.87 (s, 1H, CH-3).

[0075] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 113.9; 116.6; 119.4; 121.0; 124.0; 130.9; 147.3.

[0076] Example 3. [P] 66614 Synthesis of [proline] salts The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of proline as the anionic precursor. The resulting yellow oil was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum.

[0077] 1 ¹H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.86 (m, 12H, CH3); 1.14–1.54 (m, 48H, CH2); 1.59 and 1.72 (2 m, 4H, CH2-3 and -4); 2.22 (m, 8H, PCH2); 2.88 (m, 2H, CH2-5); 3.01 (m, 1H, CH-2).

[0078] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 47.0; 62.5; 175.5.

[0079] Example 4. [P] 66614 Synthesis of [pyridin-2-olate] salt The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of 2-hydroxypyridine as the anionic precursor. The resulting orange oil was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 HNMR and 13 C NMR spectrum.

[0080] 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.88 (m, 12H, CH3); 1.25-1.46 (m, 48H, CH2); 2.19 (m, 8H, PCH2); 5.74 (m, 2H, Py CH-4 and CH-5); 6.90 (m,1H, Py CH-3); 7.56 (m, 1H, Py CH-6).

[0081] 13C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2;

[0082] Example 5. [P] 66614 Synthesis of [benzimidazole] salt The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of benzimidazole as the anionic precursor. The resulting brown fluid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 HNMR and 13 C NMR spectrum.

[0083] 1 ¹H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.87 (m, 12H, CH3); 1.24–1.48 (m, 48H, CH2); 2.21 (m, 8H, PCH2); 6.71 (m, 2H, CH-4 and -7); 7.31 (m, 2H, CH-5 and -6); 7.66 (s, 1H, CH-2).

[0084] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 116.1; 116.6; 146.5; 152.2.

[0085] Examples 6 to 8: [P] with added ethylene glycol 66614 Synthesis of [indazole] salts: At the end of the synthesis described in Example 2, the formulation was prepared by adding ethylene glycol at the concentrations presented below by weight. Formulation (weight %) according to IL(g) Ethylene glycol (g) standalone IL Example 2 50 0 IL / EG(75 / 25) Example 6 33 17 IL / EG(50 / 50) Example 7 25 25 IL / EG(25 / 75) Example 8 17 33

[0086] Examples 9 to 11: [P] with added ethylene glycol 66614 Synthesis of [proline] salts Formulation (weight %) according to IL(g) Ethylene glycol (g) standalone IL Example 3 50 0 IL / EG(75 / 25) Example 9 33 17 IL / EG(50 / 50) Example 10 25 25 IL / EG(25 / 75) Example 11 17 33

[0087] Example 12. [P] 66614 Synthesis of [imidazolium] salts The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol imidazole as the anionic precursor. The resulting orange fluid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum.

[0088] 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.92 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.22 (m, 8H, PCH2); 6.86 (s, 2H, CH-4 and -5); 7.37 (s, 1H,CH-2).

[0089] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6–31.2; 123.04 (C4 and C5); 138.89 (C2).

[0090] Example 13. [P] 66614 Synthesis of [4-methylimidazole] salt The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of 4-methylimidazole as the anionic precursor. The resulting red fluid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum.

[0091] 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.92 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.10 (s, 3H, Imz-CH3); 2.22 (m, 8H, PCH2); 6.42 (s, 1H,CH-5); 7.02 (s, 1H, CH-2).

[0092] 13C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 13.0 (Imz-CH3), 14.3; 17.7;18.3; 21.1; 22.3; 22.6; 28.6-31.2; 122.28 (C5); 132.81 (C4); 140.93 (C2).

[0093] Example 14. [P] 66614 Synthesis of 2,2'-Bimidazole Salt The synthesis was carried out under the same conditions as in Example 2, but using 0.022 mol of 2,2'-biimidazole as the anionic precursor. The resulting red, viscous liquid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum.

[0094] 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.92 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.22 (m, 8H, PCH2); 7.02 (s, 2H, CH-4, -4', -5 and -5').

[0095] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 123.73 (C4, C4', C5, C5').

[0096] Example 15. [P] 66614 Synthesis of [indole] salts The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of indole as the anionic precursor. The resulting orange fluid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR spectrum.

[0097] 1¹H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.92 (m, 12H, CH3); 1.24–1.48 (m, 48H, CH2); 2.22 (m, 8H, PCH2); 6.25 (b, 1H, CH-2); 6.78 (m, 2H, CH-5 and -6); 7.30 (m, 2H, CH-3 and -4); 7.40 (d, 1H, CH-7).

[0098] Example 16. [P] 66614 Synthesis of [3-amino-1,2,4-triazole] salt The synthesis was carried out under the same conditions as in Example 2, but using 0.044 mol of 3-amino-1,2,4-triazole as the anionic precursor. The resulting orange fluid was then dried under vacuum in a 60ºC water bath for 24 hours. The solution was recorded in d6-DMSO. 1 H NMR and 13 C NMR spectrum. 1 H NMR (300 MHz, d6-DMSO, 25ºC), δ (ppm) = 0.92 (m,12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.22 (m, 8H, PCH2); 4.50 (b, 2H, NH2);7.15 (s, 1H, CH-5).

[0099] 13 C NMR (75 MHz, d6-DMSO, 25ºC), δ (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 147.78 (C5); 162.06 (C3).

[0100] The CO2 absorption tests in various absorbent compositions were conducted according to the following procedure.

[0101] The mixture, consisting of at least an ionic liquid and an additive of optional hydrogen bond donor type, is first completely degassed in a reactor under vacuum to desorb residual gases (including CO2), and then stirred at the desired temperature, 40ºC in the discussed examples, until the saturated vapor pressure of the mixture at the temperature of interest is reached.

[0102] Subsequently, a certain volume of pure CO2 is injected into the reactor via calibrated ballast discharge to achieve various pressure setpoints between 0 and 3 bar, defined by an automated device. At each pressure setpoint achieved in the reactor after CO2 injection, a 40-minute stationary phase is performed to achieve liquid-vapor equilibrium. Therefore, by monitoring the pressure within the reactor over time, a series of points corresponding to the amount of CO2 injected into the reactor are obtained. Knowing the volume of the vacuum reactor and the volume of the injected mixture, the volume of the gas phase can be calculated, and thus the number of moles of CO2 in the gas phase and the number captured can be inferred. When the CO2 absorption phase ends, the loading rate is determined. Those skilled in the art define the loading rate as the number of moles of captured CO2 divided by the number of moles of reactive compounds present in the absorbent composition.

[0103] The absorption capacities of different absorbent compositions (ionic liquids without organic additives) at different CO2 partial pressures (30, 100, and 250 mbar) are shown in Table 1. They were classified by decreasing performance at a CO2 pressure of 30 mbar and compared with a reference (30 wt% aqueous MEA solution).

[0104] Table 1

[0105] As observed, for all CO2 partial pressures of 30 mbar, 100 mbar, and 250 mbar, the formulations based on the ionic liquids of 2-hydroxypyridine, proline, indazole, and benzimidazole according to the invention exhibited molar absorbance equal to or greater than that of the MEA-based aqueous formulations. At a CO2 partial pressure of 250 mbar, the absorbance of the formulations according to the invention was significantly greater than that of the reference solution.

[0106] Table 2 shows the absorption capacity of different absorbent compositions with added ethylene glycol at different partial pressures of CO2 (30, 100, and 250 mbar) and compares them with a reference (30 wt% aqueous MEA solution). The capacity per liter (IL) is expressed as mol CO2 / mol, without considering the addition of ethylene glycol.

[0107] Table 2 nd: Undetermined.

[0108] These examples demonstrate that, with or without ethylene glycol, the absorbent compositions according to the invention capture as much, and indeed even more, CO2 as the reference solution, especially at high CO2 partial pressures. While the molar capacity is relatively constant in the case of indazole (Examples 2, 6, 7, and 8), this is not the case with proline, where a non-monotonic change in loading rate with the concentration of added EG is observed. Without wishing to be bound by any single theory, the differences in results may indicate that ethylene glycol may be involved in the reaction with CO2, and this depends on the anion used and how it occurs.

[0109] When ethylene glycol is added to an ionic liquid, the dynamic viscosity values ​​(expressed as mol CO2 / mol reactive entity) measured in the original solution or CO2-loaded solution are summarized in Table 3. The tested compositions contained 0%, 25%, 50%, and 75% ethylene glycol by weight. This formulation is based on indazoles from Examples 2, 6, 7, and 8. CO2 loading was measured using a calcium carbonate calcimetry method.

[0110] Table 3

[0111] In the original solution, the addition of ethylene glycol reduced the dynamic viscosity µ(t / t) of the solution in the expected manner. Figure 2 ).

[0112] Surprisingly, in the presence of CO2, a "buffering effect" of ethylene glycol on the viscosity of the loaded solution was observed, meaning that the viscosity of the loaded solution was unexpectedly lower than that of the original solution compared to those obtained without ethylene glycol. Figure 3 , Figure 4 , Figure 5 and Figure 6 ).

[0113] Specifically, in the presence of ethylene glycol, the difference between the viscosity curves was reduced as shown in the attached figures, and at the same ethylene glycol concentration, the viscosity of the loaded solution was surprisingly lower than that of the original solution, which facilitates the implementation of the method (kinetics, mass transfer).

[0114] The molar absorption capacities of different absorbent compositions containing 10% ethylene glycol at different CO2 partial pressures (30, 100, and 250 mbar) are presented in Table 4. They are classified by decreasing performance at a CO2 pressure of 30 mbar and compared with a reference (30% by weight aqueous MEA solution). All these formulations contain 10% by weight ethylene glycol.

[0115] Table 4 nd: Undetermined.

[0116] These examples demonstrate that the formulations according to the invention exhibit higher absorption capacity than the reference formulations, regardless of CO2 pressure.

[0117] Viscosities of 4-methylimidazole-based formulations as a function of shear rate were measured in both the original solution and the loaded solution. Figure 7 ).

[0118] Figure 7 This clearly demonstrates that the ionic liquid exhibits Newtonian behavior; the dynamic viscosity does not change with the loading rate. As with the previous examples, unexpectedly, the addition of ethylene glycol at a content of 10% by weight showed a decrease in viscosity in the presence of CO2 and a relatively constant viscosity for both loading rates (α = 0.7 and α = 0.8 in the examples).

[0119] Example 8 uses P in equimolar amounts 66614 The composition of 4-methylimidazole (4MeIm) salt was prepared as in the foregoing examples, as well as Examples 9, 10 and 11, in which organic additives were added to the composition of Example 8 in different amounts (weight %) of the composition in the form of dimethyl sulfoxide (DMSO).

[0120] The composition of this series of embodiments is shown in Table 5 below, with its content in weight percent, viscosity in centipoise at 40°C, and molar CO2 capacity per mole of ionic liquid (with CO2 pressure at 100 mbar at 40°C): Table 5

[0121] The presence of DMSO in the composition was found to reduce its viscosity without adversely affecting the composition's molar CO2 trapping capacity. Therefore, the viscosity of the composition can be reduced to below 100 cP with only 25% by weight of DMSO.

Claims

1. Absorbent composition for carbon dioxide contained in a gaseous effluent, comprising in a mainly non-aqueous medium: - an anionic compound comprising one or more deprotonated nitrogen atoms, - a cationic organic compound of heterocyclic, phosphonium or ammonium type having one or more non-deprotonated nitrogen atoms, - and optionally an organic additive of organic solvent type having a boiling point greater than 100°C, preferably greater than 150°C and a polarity index with respect to water greater than 0.3, preferably greater than 0.4 or more preferably still greater than 0.

5.

2. Absorbent composition according to claim 1, wherein the composition comprises an organic additive chosen from glycols, preferably ethylene glycol or polyethylene glycol, or dimethyl sulfoxide or urea.

3. Absorbent composition according to either of claims 1 and 2, wherein the organic additive is present in a content of between 5 and 80% by weight, preferably between 10 and 75% by weight, in particular between 10 and 40% by weight or between 15 and 30% by weight, relative to the total weight of the composition.

4. Absorbent composition for carbon dioxide according to any one of claims 1 to 3, wherein the cation is chosen from quaternary ammonium compounds chosen from trihexyl(tetradecyl)phosphonium, tetra(n-butyl)phosphonium, tetradecylammonium, tetra(n-butyl)ammonium, 1 -butyl-3-methylimidazolium, 1 -ethylpyridinium or 1 -ethyl-3- imidazolium.

5. Absorbent composition for carbon dioxide according to any one of claims 1 to 4, wherein the anionic compound is an anionic nitrogen-containing heterocycle, preferably comprising an odd number of atoms and comprising at least one or at least two nitrogen atoms.

6. Absorbent composition for carbon dioxide according to claim 5, wherein the anionic compound is chosen from aromatic or non-aromatic heterocycles, such as imidazole, 2-methylimidazole, 4-methylimidazole, 2-aminoimidazole, 3-amino-1,2,4-triazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 2-imidazolidinone, 3,5-diamino-1,2,4-triazole, 2- ethylimidazole, 2,4-dimethylimidazole, 2,2'-biimidazole, indole, indazole, benzopyrrole, 2- hydroxypyridine, L-histidine, proline, lysine, uracil, cytosine, piperazine or aminoethylpiperazine.

7. Absorbent composition for carbon dioxide according to claim 6, wherein the anionic compound is chosen from imidazole, indazole, 2,2'-biimidazole, indole, 2-methylimidazole, 4- methylimidazole, 3-amino-1,2,4-triazole or 3,5-diamino-1,2,4-triazole.

8. Absorbent composition for carbon dioxide according to any one of the preceding claims, wherein the viscosity at 40°C is at most 100 centipoises.

9. Process for capturing carbon dioxide comprising a stage of contacting a gaseous effluent to be treated containing CO2 with an absorbent composition according to any one of the preceding claims, so as to deplete the gaseous effluent in CO2 and enrich the absorbent composition in CO2, and a stage of regeneration of the absorbent composition and production of a gas very rich in CO2.

10. The method according to any of the preceding claims, characterized in that The regeneration of the absorbent composition enriched in CO2 is carried out by steam stripping with a gas entraining carbon dioxide in the gas phase or by heating or by pressure reduction, or by a combination of stages chosen from steam stripping with a gas entraining carbon dioxide in the gas phase, pressure reduction and / or heating.

11. Process according to either of Claims 9 and 10, wherein the absorption stage and / or the regeneration stage is carried out in a rotating contactor.

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