Ionic-liquid-based absorbent composition for separating the carbon dioxide contained in a gaseous effluent

Abstract

The invention relates to a composition that absorbs the carbon dioxide contained in a gaseous effluent comprising, in a predominantly non-aqueous medium, an anionic compound comprising one or more deprotonated nitrogen atoms, a phosphonium or ammonium organic cationic compound, and optionally an organic additive such as an organic solvent having a boiling point above 100°C and a water-relative polarity index higher than 0.3.

Description

[0001] ABSORBENT COMPOSITION BASED ON IONIC LIQUID FOR THE SEPARATION OF CARBON DIOXIDE CONTAINED IN A GASEOUS EFFLUENT

[0002] Technical field

[0003] The present invention relates to the decarbonation of a gaseous effluent. The invention relates more particularly to a non-aqueous absorbent composition for capturing CO2 contained in a gaseous effluent, in particular an ionic liquid type composition consisting of a heterocycle type anion containing one or more preferably deprotonated nitrogen atoms and an organic cation of phosphonium type.

[0004] The scope of application concerns the treatment of acid gases such as CO2 capture or gas purification (oxycombustion, biogas, industrial effluents) with anthropogenic or non-anthropogenic, biogenic or non-biogenic CO2 sources.

[0005] Prior art

[0006] Carbon dioxide is one of the greenhouse gases widely produced by various human activities and has a direct impact on air pollution and global warming.

[0007] In order to reduce the quantities of carbon dioxide emitted into the atmosphere, it is possible to capture the CO2 contained in a gaseous effluent.

[0008] The decarbonation of gaseous effluents such as natural gas, synthesis gas, combustion fumes, refinery gases, gases obtained at the bottom of the Claus process, biomass fermentation gases, cement gases and blast furnace gases, is generally carried out by washing with an absorbent solution. The physicochemical characteristics of the solutions used are closely linked to the nature of the gas to be treated: selective elimination of an impurity, expected specification of the treated gas, thermal and chemical stability of the solvent with respect to the different compounds present in the gas to be treated.

[0009] Solvents commonly used today include aqueous solutions of primary, secondary or tertiary alkanolamines and possibly an organic co-solvent, such as methanol for example. Indeed, the absorbed CO2 reacts with the alkanolamine present in solution according to a reversible exothermic reaction, well known to those skilled in the art and leading to the formation of carbamates, hydrogen carbonates or carbonates.

[0010] An alternative to aqueous alkanolamine solutions is the use of hot solutions of alkali metal carbonates. The principle is based on the absorption of CO2 in the aqueous solution by an inorganic carbonate in a reaction leading to an inorganic hydrogen carbonate and on regeneration by the reversible reaction transforming an inorganic hydrogen carbonate into an inorganic carbonate.

[0011] French patent application FR 2934175 describes a carbon dioxide absorbing composition, used in a process for capturing carbon dioxide contained in a gaseous effluent, comprising in an aqueous medium the association of a particular base chosen from carbonates and / or hydrogen carbonates with a compound chosen from thiols.

[0012] Some decarbonation processes by washing with an absorbent solution such as refrigerated methanol or polyethylene glycols are based on physical absorption of CO2.

[0013] Another alternative to aqueous amine solutions or hot solutions of alkali metal carbonates is the use of solutions based on ionic liquids. Ionic liquids, as commonly defined, are liquid salts in the form of ionic solutions with a melting point close to room temperature and, possessing physicochemical properties such as non-volatility, flammability, stability to water and air-,

[0014] The publication by Elmobarak et al, “Current status of CO2 capture with ionic liquids: Development and progress” - Fuel 344 (2023), illustrates well the possible versatility of ionic liquid formulations to modify their physicochemical properties and react with CO2, physically and / or chemically.

[0015] Formulations based on ionic liquids have the advantage of having a high CO2 solvation power, of being thermally and chemically stable, but often have a high viscosity, several hundred centipoises, depending on the chemical composition and the presence of numerous ionic interactions and / or hydrogen bonds between the molecules, but also between the molecules of the ionic liquid and the species formed after reaction with CO2. As a result, the diffusivity of cationic and anionic species is affected, and the reaction rate with CO2 is reduced.

[0016] More recently, the publication by Yisha Xu et al - "Tuning ionic liquid-based functional deep eutectic solvents (DES) and other functional mixtures for CO2 capture" - Chemical Engineering Journal 463 (2023), presents a range of ionic liquid-based solvents or formulations with the addition of additives to modify the physicochemical properties. Deep eutectic solvents (DES) are solvents formed by mixing two or more compounds in a proportion that corresponds to the eutectic point. There are several types of DES depending on the chemical composition. Advantageously, the combination of an ionic liquid (IL) and a hydrogen bond donor agent can generate a DES, which will have properties close to the ionic liquid, i.e., chemical reactivity for CO2 capture and a saturated vapor pressure close to 0.More advantageously, the combination of an ionic liquid and a hydrogen bond donor can reduce the viscosity of the deep eutectic solvent by several tens of centipoises compared to the ionic liquid.

[0017] A key aspect of gas or fume treatment operations using a solvent remains the regeneration of the separation agent. Depending on the type of absorption (physical or chemical), regeneration by expansion, distillation and / or entrainment with a vaporized gas called "stripping gas", which can be water or an inert gas such as nitrogen, is generally considered.

[0018] Generally speaking, the implementation of all the absorbent solutions described above requires significant energy consumption for the regeneration of the separation agent. For example, the regeneration of an aqueous ethanolamine solution used for the capture of CO2 in a flue gas represents approximately 4GJ per tonne of CO2 captured. Such energy consumption represents a considerable operating cost for the CO2 capture process.

[0019] Summary of the invention

[0020] The Applicant has discovered that the use of ionic liquids consisting of a heterocycle-type anion with one or more deprotonated nitrogen atoms and an organic heterocycle-type cation with one or more unprotonated nitrogen, phosphonium or ammonium atoms makes it possible to obtain interesting performances for the capture of CO2 contained in a gaseous effluent.

[0021] The addition of a particular organic additive, for example a hydrogen bond donor of the polyethylene glycol type (such as ethylene glycol) or an aprotic compound (such as dimethyl sulfoxide DMSO), can also make it possible to lower the viscosity of the absorbent solution, especially in the presence of CO2. This effect is interesting for the implementation of the absorbent solution in any type of gas-liquid contactors known to those skilled in the art, such as packed columns, or for contactors aimed at process intensification, such as rotary contactors, also called Higee or Rotating Packed Bed in English.

[0022] The hydrogen bond donor additive (ethylene glycol, polyethylene glycol) allows the formation of a deep eutectic in the composition, which is very advantageous.

[0023] The organic additive advantageously has a boiling point greater than 100°C, preferably greater than 150°C and a polarity index relative to water (considering that the polarity index of water is equal to 1) greater than 0.3, preferably greater than 0.4, or even more preferably greater than 0.5. By way of non-limiting example, the organic additive may be monoethylene glycol, MEG (relative polarity index = 0.8). In this case, with ethylene glycol a deep eutectic solvent or DES is formed.

[0024] Although it is not a hydrogen donating agent, the use of an aprotic compound such as dimethyl sulfoxide DMSO, with the same boiling point (boiling temperature of 189 °C) and polarity (relative polarity index of 0.44) as an organic additive can be considered.

[0025] The invention relates to a composition for absorbing carbon dioxide contained in a gaseous effluent comprising in a predominantly non-aqueous medium:

[0026] - an anionic compound comprising one or more deprotonated nitrogen atoms,

[0027] - an organic cationic compound of heterocycle type with one or more unprotonated nitrogen, phosphonium or ammonium atoms,

[0028] - and optionally an organic additive of organic solvent type having a boiling temperature greater than 100°C, preferably greater than 150°C, and a polarity index relative to water greater than 0.3, preferably greater than 0.4, or even more preferably greater than 0.5.

[0029] The composition may comprise an organic additive selected from a glycol, preferably ethylene glycol or polyethylene glycol, or dimethyl sulfoxide or urea.

[0030] The organic additive may be present at a content of between 5 and 80% by weight, preferably between 10 and 75% by weight, inclusive, relative to the total weight of the composition. Advantageously, the content of organic additive does not exceed 50% by weight, inclusive, and is preferably between 10 and 40 or between 15 and 30% by weight of the composition.

[0031] The cation may be a quaternary compound selected from trihexyl(tetradecyl)phosphonium, tetra-n-butylphosphonium or tetradecylammonium, tetra-n-butylammonium, 1-Ethyl Pyridinium, 1-Ethyl-3-methylimidazolium, 1-Butyl-3-methylimidazolium.

[0032] The anionic compound may be an anionic nitrogen heterocycle preferably comprising an odd number of atoms and comprising at least one or at least 2 nitrogen atoms.

[0033] The anionic compound can thus be chosen from heterocycles, aromatic or not, such as imidazole, 2 methyl imidazole, 4 methyl imidazole, 2-aminoimidazole, 3-Amino- 1 ,2,4-triazole, 2-isopropylimidazole, 2-Ethyl-4-methylimidazole, 2 imidazolidone, 3, 5-Diamino-1 ,2,4-triazole, 2-ethylimidazole, 2,4-dimethylimidazole, 2,2'-biimidazole, indole, indazole, benzopyrrole, 2-hydroxypyridine, L-histidine, proline, lysine, uracyl, cytosine, piperazine, aminoethylpiperazine. Preferably, the anionic compound is chosen from imidazole, indazole, 2,2'-biimidazole, indole, 2 methyl imidazole, 4 methyl imidazole, 3-amino-1,2,4-triazole, 3,5 diamino-1,2,4-triazole.

[0034] According to the invention, preferably the anionic compound and the cationic compound are equimolar in the composition (because they each preferably carry a charge).

[0035] Preferably, the carbon dioxide absorbing composition described above has a viscosity at 40°C of at most 100 centipoises.

[0036] The invention also relates to a method for capturing carbon dioxide comprising a step of bringing the gaseous effluent to be treated containing CO2 into contact with the absorbent composition according to any one of the variants described so as to deplete said gaseous effluent in CO2 and to enrich said absorbent composition in CO2 and a step of regenerating said absorbent composition and generating a gas very rich in CO2.

[0037] The regeneration of the CO2-enriched absorbent composition can be carried out by steam distillation using a gas entraining carbon dioxide in the vapor phase or by heating or by expansion or by a combination of steps chosen from steam distillation using a gas entraining carbon dioxide in the vapor phase, expansion and / or heating.

[0038] The absorption step and / or the regeneration step can be carried out in a rotary contactor.

[0039] The composition according to the invention is in fact particularly suitable for the use of such equipment, in particular in its variant with the additive, the content of which can be adjusted to adjust the viscosity of the composition to make it compatible with this equipment. Thus, at most 50% by weight of organic additive can be provided, in particular between 10 and 40% by weight, so as to obtain a composition having at 40°C a viscosity of at most 100 cP. What is very advantageous is that this viscosity can be achieved with a relatively low content of additive, which makes it possible to maintain, overall, a high capture capacity of the composition (by maintaining high contents of ionic compounds in the composition).

[0040] It was also very advantageously observed that, once the composition was loaded with CO2, it remained at a sufficiently low viscosity to be able to be extracted without problem from this type of equipment, which, from an industrial point of view, is very interesting.

[0041] List of figures

[0042] Figure 1 represents the schematic diagram of the CO2 capture process with absorption and regeneration using an absorbent composition according to the invention. Figure 2 represents the evolution of the viscosity of the formulations of the virgin solutions as a function of the temperature and the ethylene glycol content (reference A, C, E and G) of example 12.

[0043] Figure 3 represents the evolution of the viscosity of formulations A and B (virgin solution and solution loaded with CO2) without ethylene glycol as a function of the temperature of example 12.

[0044] Figure 4 represents the evolution of the viscosity of formulations C and D (virgin solution and solution loaded with CO2) with 25% ethylene glycol as a function of the temperature of example 12.

[0045] Figure 5 represents the evolution of the viscosity of formulations E and F (virgin solution and solution loaded with CO2) with 50% ethylene glycol as a function of the temperature of example 12.

[0046] Figure 6 represents the evolution of the viscosity of formulations G and H (virgin solution and solution loaded with CO2) with 75% ethylene glycol as a function of the temperature of example 12.

[0047] Figure 7 represents the evolution of viscosity as a function of the shear rate of a formulation of example 13 based on 4-Methyl Imidazolure with 10% by weight of ethylene glycol, in virgin solution and loaded with CO2 as a function of temperature.

[0048] Description of the embodiments

[0049] The present invention describes a carbon dioxide extraction solvent hereinafter referred to as a carbon dioxide absorbent composition, used in a process for capturing carbon dioxide contained in a gaseous effluent, comprising in a predominantly non-aqueous medium the association of an anion chosen from compounds with one or more deprotonated nitrogen atoms associated with an organic cation of ammonium or phosphonium type.

[0050] By predominantly non-aqueous medium, it is meant that the absorbent medium may contain a small quantity of water, i.e. up to 5% by weight of water, in particular due to hydration of the composition by water from the gas to be treated or during the regeneration stage, the starting absorbent composition not containing water.

[0051] More particularly, the CO2 absorbing composition according to the invention, used in a process for capturing carbon dioxide contained in a gaseous effluent, advantageously comprises a nitrogenous heterocyclic anionic compound, and more advantageously a nitrogenous heterocycle with an odd number of atoms which, without wishing to be bound by any theory, seems to have a further improved absorption capacity. In a particular non-limiting case, it comprises an aprotic anionic nitrogenous heterocycle. Usually, the term "heterocycle" is understood to mean a cyclic molecule, aromatic or not, containing at least one heteroatom such as, for example, N, O, S, P or other.

[0052] Throughout the description, an aprotic molecule is defined as a molecule which does not contain hydrogen atoms capable of forming hydrogen bonds, that is to say, a molecule which does not contain OH, NH or FH bonds.

[0053] Throughout the description, and as described in the publication by Séo et al, Chemically Tunable Ionic Liquids with Aprotic Heterocyclic Anion, J. Phys. Chem. B 2014, 118, 5740-5751, the term "anionic aprotic heterocycle" means aromatic rings containing a hetero atom, in this case a nitrogen atom that has been deprotonated by acid-base reaction with, for example, hydroxytrihexyl(tetradecyl)phosphonium.

[0054] Furthermore, the invention relates to a method for capturing carbon dioxide which consists of carrying out the following steps: a) bringing the gas to be treated containing CO2 into contact with said absorbent composition, so as to obtain a gas depleted in CO2 and an absorbent composition rich in CO2, b) regenerating the absorbent composition rich in CO2, to obtain an absorbent composition which can be used again and to generate a gas very rich in CO2.

[0055] The absorbent composition according to the present invention makes it possible to capture 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 such as aqueous amine solutions. Given its physicochemical properties, the absorbent solution is more thermally stable than the usual aqueous amine solutions and therefore more environmentally friendly by limiting degradation products.

[0056] The CO2 absorbent composition, according to the present invention, comprises at least, in a predominantly non-aqueous medium:

[0057] - an organic heterocyclic cationic compound with one or more unprotonated nitrogen, ammonium or phosphonium atoms, such as, for example, trihexyl(tetradecyl)phosphonium, 1-ethylpyridinum or 1-ethyl-3-imidazolium

[0058] - an anionic compound comprising one or more deprotonated nitrogen atoms, preferably a nitrogen heterocyclic compound, also called an anionic nitrogen heterocycle. Preferably, the cycle comprises an odd number of atoms, including at least 1 nitrogen atom, or even at least 2 nitrogen atoms. When the nitrogen atom(s) are present in the cycle, said cycle may comprise additional alkyls and / or functional groups such as aromatic cycles making it possible to increase the nucleophilic properties of the anion.

[0059] - optionally an organic additive chosen from organic solvents defined by a boiling point greater than or equal to 100°C, and preferably greater than 150°C and a polarity index relative to water (considering that the polarity index of water is equal to 1) greater than 0.3, preferably greater than 0.4, or even more preferably greater than 0.5.

[0060] Consideration may be given to the use as an organic additive of a glycol-type solvent or an aprotic solvent such as dimethyl sulfoxide, DMSO (boiling temperature of 189 °C and relative polarity index of 0.44), with the required boiling point and polarity properties.

[0061] When present, the organic additive is generally added at a content of between 5 and 80% by weight of the formulation, preferably between 10 and 75% by weight of the formulation, inclusive. Its content may, in particular, be between 10 and 40% by weight or between 15 and 30% by weight, and may be, for example, equal to or in the vicinity of 25% by weight.

[0062] Obtaining a high-performance absorbent composition in a predominantly non-aqueous environment has several advantages. Indeed, this thermally stable and very low-volatility composition allows regeneration at higher temperatures than for formulations in aqueous solutions. The composition can advantageously be used under pressure, which allows compressed CO2 to be obtained at the outlet of the regeneration stage.

[0063] Furthermore, it is possible to dispense with the gas purification operations that are very often necessary, for example, in prior art solutions when the solvent is an organic compound such as methanol. Indeed, small quantities of solvent are inevitably entrained in the gases after separation of the carbon dioxide and require additional and costly purification steps.

[0064] The nitrogenous heterocyclic compound which plays the role of the anion can be chosen, for example, without being exhaustive, from azoles such as imidazole, 2-methyl imidazole, 4-methyl imidazole, 2-aminoimidazole, 3-amino-1,2,4-triazole, 2-isopropylimidazole, 2-ethyl-4-methylimidazole, 2-imidazolidone, 2,2'-biimidazole, 3,5-diamino-1,2,4-triazole, 2-ethylimidazole, 2,4-dimethylimidazole, indole, indazole, benzopyrrole.

[0065] Preferably, the nitrogenous heterocyclic compound may be chosen from imidazole, 2-methyl imidazole, 4-methyl imidazole, indazole, 3-amino-1,2,4-triazole, 2,2'-biimidazole.

[0066] Alternatively, the nitrogenous heterocyclic compound may be selected from amino acids, for example L-histidine, proline, lysine.

[0067] Alternatively, the nitrogenous heterocyclic compound may be 2-hydroxypyridine. It may also be selected from other cyclic compounds containing multiple nitrogenous sites such as uracyl, cytosine, piperazine, aminoethylpiperazine.

[0068] The composition may comprise an organic additive as described above such as for example a glycol, for example polyethylene glycol-200 or ethylene glycol, to lower the viscosity in a suitable range [in particular 1-100 cP] for use, for example, in RPB (Rotating Packed Bed) type reactors. The solvents which can be used as an additive are preferably chosen from glycols, polyethylene glycols, polypropylene glycols, ethylene glycol-propylene glycol copolymers, glycol ethers, thioglycols.

[0069] Another family of solvents considered are polar aprotic solvents such as DMSO.

[0070] The organic additive makes it possible in particular to adjust the viscosity of the formulation in a viscosity range which is compatible with that admissible for a gravity flow [1-5 cP] or for implementation in a rotating contactor of the RPB (Rotating Packed Bed) type [1-100 cP],

[0071] The choice of the organic cationic compound, the nitrogenous heterocyclic anionic compound, and the possible organic additive in the absorbent composition according to the invention is made by a person skilled in the art according to the desired physical properties, in particular viscosity, and the specifications on the treated gas, in particular CO2 partial pressure.

[0072] The system for capturing CO2 according to the invention can be implemented in a process for treating gas containing CO2.

[0073] The process for capturing carbon dioxide according to the invention schematically comprises the following steps: a) the gas to be treated containing CO2 is brought into contact with an absorbent composition according to the invention, so as to obtain a gas depleted in CO2 and an absorbent composition rich in CO2, b) the absorbent composition rich in CO2 is regenerated, so as to obtain a regenerated and usable absorbent composition, and to generate a gas very rich in CO2.

[0074] More specifically, in a carbon dioxide capture process (Figure 1), the gas to be treated (1) is introduced into a gas-liquid contactor (A) where it is brought into contact with a regenerated liquid absorbent composition (10). This results in a treated gas depleted in CO2 (2) and a separation medium rich in CO2 (11). The absorbent composition rich in CO2 is introduced into a heat exchange device (E) so as to produce an absorbent composition rich in heated CO2 (12). The heat is provided by the cooling of the absorbent composition poor in hot CO2 (13). This also results in a stream of cooled absorbent composition poor in CO2 (10). External hot and cold sources, not shown, can be used to adapt the temperature of the streams (10) and (12) to the operating conditions of the elements (A) and (C) respectively.The heated CO2-rich absorbent composition (12) is introduced into a gas-liquid separation equipment (C) where the separation medium is regenerated. The driving force for this separation is heat supplied by a hot source (20) by means of a heat exchange device (D). This results in a cooled hot source (21). Alternatively, this hot source can be supplemented in whole or in part by a stripping gas, water vapor, inert gas such as N2, not shown. The regeneration of the separation medium produces a hot CO2-poor separation medium (13) and a CO2-rich gas stream (3). Depending on the regeneration method chosen, the CO2 in the stream (3) can be mixed with a stripping gas. Alternatively, the stream (3) can be connected to a device intended to cause the expansion of the CO2-rich separation medium and thus constitute in whole or in part the driving force for the regeneration.The hot CO2-poor separation stream (13) releases its heat in the device (E) described previously to provide the device (A) with a cooled CO2-poor separation medium (10) at the temperature adapted to the operating conditions of (A).

[0075] The temperature during step (A) may advantageously be between 20 and 80°C and preferably between 30 and 70°C.

[0076] The gas-liquid contactor can be a rotary contactor.

[0077] Examples

[0078] The examples presented below illustrate the technical interest of the present invention without limiting its scope. They present in particular the CO2 absorption capacity of different absorption media.

[0079] Example 1. Synthesis of a salt solution [PG6614][OH] in ethanol by anion exchange from [P666i4][Br],

[0080] [PB6614][OH] / trihexyl(tetradecyl)phosphonium hydroxide and [P666 ][Br] trihexyl(tetradecyl)phosphonium bromide.

[0081] 45.3 g of trihexyl(tetradecyl)phosphonium bromide [Pe66i4][Br] (M=563.76 g / mol) or 0.080 mol are dissolved in 100 ml of ethanol dried on a 3A sieve. This solution is brought into contact with 1 OH- equivalent of Amberlite IRN78 type resin, or 0.080 mol. DOWEX monospheres 550A type resin can also be used. Since the resin is at 1.1 eq OH / L, 0.072 liters of resin or 78 g (d(resin)=1.08 g / ml) will be required. The resin is added to the solution of [P666i4][Br] in ethanol dried on a 3A sieve, then the mixture is stirred for 24 hours. This operation is repeated a second time. The resin is removed by Büchner filtration.

[0082] Example 2. Synthesis of the salt [P666i4][indazolide].

[0083] To 50 ml of a 0.8 M (0.040 mol) solution of [Pe66i4][OH], 1.1 equivalents of indazole are added, i.e. 0.044 mol. The mixture is stirred overnight. The ethanol is then evaporated on a rotary evaporator. The resulting yellow-orange fluid liquid is then dried under vacuum in a water bath at 60°C for 24 hours. NMR spectra 1 H and NMR 13 These are made in dmso-d6.

[0084] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(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).

[0085] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(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.

[0086] Example 3. Synthesis of the salt [P666i4][prolinate].

[0087] The synthesis is carried out under the same conditions as Example 2 but using 0.044 mol of proline as anion precursor. The yellow oil obtained is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are done in the dmso-de.

[0088] 1 H NMR (300 MHz, dmso-d6, 25 °C), 5 (ppm) = 0.86 (m, 12H; CH3); 1.14-1.54 (m, 48H; CH2); 1.59 and 1.72 (2m, 4H; CH2-3 and 4); 2.22 (m, 8H; PCH2); 2.88 (m, 2H; CH2-5); 3.01 (m, 1 H; CH-2).

[0089] 13 C NMR (75 MHz, dmso-d6, 25 °C), 5 (ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 47.0; 62.5; 175.5.

[0090] Example 4. Synthesis of the salt [P666i4][pyndine-2-olate].

[0091] The synthesis is carried out under the same conditions as Example 2, but using 0.044 mol of 2-hydroxypyridine as anion precursor. The orange oil obtained is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are done in the dmso-de.

[0092] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(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, 1 H, Py CH-3); 7.56 (m, 1 H, Py CH-6).

[0093] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 103.6; 114.5; 136.1; 147.7; 172.4. Example 5. Synthesis of the salt [P666i4][benzimidazolide].

[0094] The synthesis is carried out under the same conditions as Example 2 but using 0.044 mol of benzimidazole as anion precursor. The resulting brown fluid liquid is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are made in dmso-d6.

[0095] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(ppm) = 0.87 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.21 (m, 8H, PCH2); 6.71 (m, 2H, CH-4.7); 7.31 (m, 2H, CH-5.6); 7.66 (s, 1H, CH-2).

[0096] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(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.

[0097] Examples 6 to 8: Synthesis of the salt [P666i4][lndazolide] added with ethylene glycol

[0098] Following the synthesis described in example 2, formulations are produced by adding ethylene glycol according to the mass concentrations presented below.

[0099] Examples 9 to 11: Synthesis of the salt [P666i4][Prolinate] added with ethylene glycol

[0100] Example 12. Synthesis of the salt [P666i4][imidazolide].

[0101] The synthesis is carried out under the same conditions as Example 2, but using 0.044 mol of imidazole as anion precursor. The resulting orange fluid liquid is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are done in the dmso-de.

[0102] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(ppm) = 0.92 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.22 (m, 8H, PCH2); 6.86 (s, 2H, CH-4.5); 7.37 (s, 1 H, CH-2);. 13C-NMR (75 MHz, dmso-d6, 25 °C), 5(ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 123.04(C4.5); 138.89 (C2).

[0103] Example 13. Synthesis of the salt [P666i4][4-methylimidazolide].

[0104] The synthesis is carried out under the same conditions as Example 2 but using 0.044 mol of 4-methylimidazole as anion precursor. The resulting red fluid liquid is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are made in dmso-d6.

[0105] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(ppm) = 0.92 (m, 12H, CH3); 1.24-1.48 (m, 48H, CH2); 2.10 (s, 3H, lmz-CH3); 2.22 (m, 8H, PCH2); 6.42 (s, 2H, CH-5); 7.02 (s, 1H, CH-2).

[0106] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(ppm) = 13.0 (lmz-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).

[0107] Example 14. Synthesis of the salt [P666i4]2[2,2'-biimidazolide].

[0108] The synthesis is carried out under the same conditions as Example 2 but using 0.022 mol of 2,2'-biimidazole as anion precursor. The resulting red viscous liquid is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are done in the dmso-de.

[0109] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(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',5.5').

[0110] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 123.73 (C4.4',5.5').

[0111] Example 15. Synthesis of the salt [P666][lndolure].

[0112] The synthesis is carried out under the same conditions as Example 2 but using 0.044 mol of indole as anion precursor. The orange fluid liquid obtained is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectrum 1 H is realized in dmso-d6.

[0113] 1 H-NMR (300 MHz, dmso-d6, 25 °C), 5(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, 6); 7.30 (m, 2H, CH-3.4); 7.40 (d.1 H, CH-7). Example 16. Synthesis of the salt [P666i4][3-amino-1, 2, 4-triazide],

[0114] The synthesis is carried out under the same conditions as Example 2, but using 0.044 mol of 3-amino-1,2,4-triazole as anion precursor. The resulting orange fluid liquid is then dried under vacuum in a water bath at 60°C for 24 hours. The NMR spectra 1 H and NMR 13 These are made in dmso-d6.

[0115] 1H-NMR (300 MHz, dmso-d6, 25 °C), 5(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).

[0116] 13 C-NMR (75 MHz, dmso-d6, 25 °C), 5(ppm) = 14.3; 17.7; 18.3; 21.1; 22.3; 22.6; 28.6-31.2; 147.78 (C5); 162.06 (C3).

[0117] The CO2 absorption tests in the different absorbent compositions are carried out according to the following procedure:

[0118] The mixture composed of at least one ionic liquid and possibly a hydrogen bond donor type additive is first degassed under vacuum in the reactor in order to desorb the residual gases including CO2, then stirred and at the desired temperature, in our examples 40°C, until the saturated vapor pressure of the mixture is reached at the temperature of interest.

[0119] Then, volumes of pure CO2 are injected into the reactor by discharging calibrated ballast in order to reach the different pressure setpoints between 0 and 3 bars defined by an automaton. At each pressure setpoint reached in the reactor following the injection of CO2, a 40 min hold is carried out in order to obtain liquid vapor equilibrium. Thus, by monitoring the pressure within the reactor as a function of time, a series of points is obtained, corresponding to the quantity of CO2 injected into the reactor. Knowing the volumes of the empty reactor and the volume of the inserted mixture, the volume of the gas phase can be calculated, and therefore the number of moles of CO2 in the gas phase and that captured can be deduced. When the CO2 absorption step is complete, the loading rate is determined. The loading rate is defined by those skilled in the art as being the number of moles of CO2 captured divided by the number of moles of the reactive compound present in the absorbent composition.

[0120] Table 1 shows the absorption capacities for the different absorbent compositions (ionic liquids without the addition of organic additives) under different CO2 partial pressures (30, 100 and 250 mbar). They are classified by decreasing performance under the CO2 pressure of 30 mbar and compared to the reference, an aqueous solution of MEA at 30% by weight. Table 1

[0121] As observed, for all CO2 partial pressures of 30 mbar, 100 mbar, 250 mbar, the ionic liquid formulations based on 2-Hydroxy pyridine, proline, indazole, benzimidazole according to the invention have molar absorption capacities equivalent to or greater than the aqueous formulation based on MEA. At a CO2 partial pressure of 250 mbar, the absorption capacity of the formulations according to the invention is significantly greater than the absorption capacity of the reference solution.

[0122] Table 2 shows the absorption capacities for the different absorbent compositions with ethylene glycol additives under different CO2 partial pressures (30, 100 and 250 mbar) and compared to the reference, a 30% by weight aqueous MEA solution. The capacities are expressed in mol CCh / mol of Ll without taking into account the added ethylene glycol.

[0123] Table 2 nd: not determined

[0124] These examples show that absorbent compositions according to the invention, in the presence of ethylene glycol or not, capture as much or even more CO2 than the reference solution, in particular for high partial pressures of CO2. If the molar capacity is relatively constant in the case of indazole (Examples 2, 6, 7 and 8), this is not the case for proline where a non-monotonic variation of the loading rate is observed as a function of the concentration of EG added. Without wishing to be bound by any theory, the differences in results may indicate that ethylene glycol could intervene in the reaction with CO2, and this in a variable manner depending on the anion used.

[0125] Table 3 lists the dynamic viscosity values ​​measured, with the addition of ethylene glycol to the ionic liquid, in virgin solution or loaded with CO2 (expressed in mol of CC>2 / mol of reactive species). The compositions tested, in % by mass of ethylene glycol, are 0%, 25%, 50% and 75%. The formulation is that based on indazole of examples 2, 6, 7, 8. The CO2 loading rate is measured by calcimetry.

[0126] Table 3

[0127] In virgin solution, the addition of ethylene glycol decreases, as expected, the dynamic viscosity p of the solution (Fig.2).

[0128] Unexpectedly, in the presence of CO2, a "buffering effect" of the presence of ethylene glycol on the viscosity of the loaded solutions is observed compared to those obtained without ethylene glycol, i.e. the viscosity of the loaded solutions is unexpectedly lower than the viscosity of the virgin solutions (Fig. 3, Fig.4, Fig.5 and Fig.6).

[0129] Indeed, in the presence of ethylene glycol, we observe in the figures that the difference between the viscosity curves decreases and that, at iso concentration of ethylene glycol, the viscosity of the loaded solutions is surprisingly lower than that of the virgin solutions, which facilitates the implementation of the process (kinetics, transfer of matter).

[0130] Table 4 shows, for the different absorbent compositions with 10% by weight of ethylene glycol, the molar absorption capacity under different partial pressures of CO2 (30, 100 and 250 mbar). They are classified by decreasing performance for a CO2 pressure of 30 mbar and compared to the reference, an aqueous solution of MEA at 30% by weight. All these formulations contain 10% by weight of ethylene glycol.

[0131] Table 4 nd: not determined

[0132] These examples show that the formulations according to the invention have a higher absorption capacity than the reference formulation regardless of the CO2 pressure.

[0133] On the 4-methyl Imidazole-based formulation, viscosity measurements as a function of shear rate in virgin and loaded solutions were carried out (Fig. 7).

[0134] Figure 7 clearly shows that the ionic liquid has Newtonian behavior, the dynamic viscosity does not vary with the loading rate. As in the previous examples, unexpectedly, the addition of ethylene glycol at a content of 10% by weight shows that the viscosity decreases in the presence of CO2 and is relatively constant for two loading rate values, in the example, a = 0.7 and a = 0.8.

[0135] Example 8 was made with a composition comprising P6614, 4-methyl imidazolide (4 MelM) in equimolar amounts, as for the previous examples, and examples 9, 10 and 11 which add to the composition of example 8 an organic additive in the form of dimethylsulfoxide DMSO in different contents (% weight of the composition).

[0136] Table 5 below shows the % weight contents of the compositions in this series of examples, the viscosity at 40°C of the composition expressed in centipoises, and the molar capacity of CO2 per mole of ionic liquid, with a CO2 pressure of 100 mbar at a temperature of 40°C:

[0137] Table 5

[0138] It is found that the presence of DMSO in the composition allows its viscosity to be reduced, without adversely impacting the molar CO2 capture capacity of the composition. It is thus possible to lower the viscosity of the composition below 100 cP with only 25% by weight of DMSO.

Claims

Claims 1. Composition for absorbing carbon dioxide contained in a gaseous effluent comprising in a predominantly non-aqueous medium: an anionic compound comprising one or more deprotonated nitrogen atoms, an organic cationic compound of heterocycle type with one or more non-protonated nitrogen atoms, phosphonium or ammonium, 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 relative to water greater than 0.3, preferably greater than 0.4, or even more preferably greater than 0.

5.

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

3. Absorbent composition according to one of claims 1 or 2, in which the organic additive is present at 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, limits included, relative to the total weight of the composition.

4. Carbon dioxide absorbing composition according to one of claims 1 to 3, in which the cation is chosen from a quaternary compound chosen from Trihexyl(tetradecyl)phosphonium, tetra-n-butylphosphonium or tetradecylammonium, tetra-n-butylammonium, 1-Butyl-3-methylimidazolium, 1-ethylpyridinum or 1-ethyl-3-imidazolium 5. Carbon dioxide absorbing composition according to one of claims 1 to 4, in which the anionic compound is an anionic nitrogen heterocycle preferably comprising an odd number of atoms and comprising at least one or at least 2 nitrogen atoms.

6. Carbon dioxide absorbing composition according to claim 5, in which the anionic compound is chosen from heterocycles, aromatic or not, such as imidazole, 2 methyl imidazole, 4 methyl imidazole, 2-aminoimidazole, 3-Amino- 1 ,2,4-triazole, 2-isopropylimidazole, 2-Ethyl-4-methylimidazole, 2 imidazolidone, 3,5-Diamino-1 ,2,4-triazole, 2-ethylimidazole, 2,4-dimethylimidazole, 2,2'- biimidazole, indole, indazole, benzopyrrole, 2-hydroxypyridine, L-histidine, proline, lysine, uracyl, cytosine, piperazine, aminoethylpiperazine.

7. Carbon dioxide absorbing composition according to claim 6, wherein the anionic compound is selected from imidazole, indazole, 2,2'-biimidazole, indole, 2 methyl imidazole, 4 methyl imidazole, 3-amino-1,2,4-triazole, 3,5 diamino-1,2,4-triazole.

8. Carbon dioxide absorbent composition according to one of the preceding claims, the viscosity of which at 40°C is at most 100 centipoise.

9. A method for capturing carbon dioxide comprising a step of bringing the gaseous effluent to be treated containing CO2 into contact with the absorbent composition according to any one of the preceding claims, so as to deplete said gaseous effluent in CO2 and to enrich said absorbent composition in CO2 and a step of regenerating said absorbent composition and generating a gas very rich in CO2.

10. Method according to the preceding claim, characterized in that the regeneration of the CO2-enriched absorbent composition is carried out by steam entrainment using a gas entraining carbon dioxide in the vapor phase or by heating or by expansion or by a combination of steps chosen from steam entrainment using a gas entraining carbon dioxide in the vapor phase, expansion and / or heating.

11. Method according to one of claims 9 or 10, in which the absorption step and / or the regeneration step is (are) carried out in a rotary contactor.

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