Sorbent composition for carbon capture and methods for the production and use thereof

Abstract

The present invention relates to compositions comprising an ionic liquid and a solid support and to processes for the capture and subsequent release of carbon dioxide employing said compositions from gaseous streams comprising carbon dioxide, such as air or flue gas.

Description

[0001] SORBENT COMPOSITION FOR CARBON CAPTURE AND METHODS FOR THE PRODUCTION AND USE THEREOF

[0002] FIELD OF THE INVENTION

[0003]

[0001] The present invention relates to compositions comprising an ionic liquid and a solid support and to processes for the capture and subsequent release of carbon dioxide employing said compositions from gaseous streams comprising carbon dioxide, such as air or flue gas.

[0004] BACKGROUND

[0005]

[0002] Transportation and industrial activities are one of the major sources of carbon dioxide emissions. In this regard, about 37.4 Gt of carbon dioxide were emitted in 2023. While the concentration of carbon dioxide in air is currently of 419 ppm, the increase of the atmospheric CO2 concentration is expected to cause further global warming as result of the greenhouse effect of this gas. Several strategies have been implemented globally in order to (i) reduce the industrial emissions of carbon dioxide and (ii) reduce the atmospheric concentration of carbon dioxide. In this regard, carbon capture from both industrial processes and air represents a promising strategy in mitigating climate change by reducing the atmospheric concentration of carbon dioxide.

[0006]

[0003] Carbon dioxide is currently typically captured from a broad range of sources and specific technologies exist for each source. For instance, the power industry implements pre-combustion capture, post-combustion capture o oxy-fuel combustion capture to isolate carbon dioxide from fossil fuels, synthesis gas or flue gas. Another common source of carbon capture is air. Direct air capture (DAC) is a promising technology for mitigating climate change by removing CO2 directly from the atmosphere. However, several challenges remain to be addressed. In a first place, the low concentration of carbon dioxide in air requires that DAC treats large volumes of air, thus increasing considerably the energetic and economic costs of the process (e.g. if compared with carbon capture from flue gas). In a second place, there is a need for more performant sorbent materials with increased capture efficiency, reduced regeneration energy, and extended lifespan.

[0007]

[0004] Different systems suitable for Direct Air Capture of CO2 are known in the art. Those include solid sorbents (amine-functionalized solids, metal-organic frameworks, zeolites) and liquid sorbents (liquid amines, ionic liquids). In particular, several ionic liquids suitable for Direct Air Capture have been disclosed in the art. The CO2 absorption mechanism in ionic liquids often involves physical absorption and / or chemical reaction with the ionic liquid. However, these systems generally present a high viscosity, which somehow limits the mass transport of the gas to the binding site of carbon dioxide. Typical ionic liquids include amino-acid based ionic liquids, which possess an amino group suitable for reacting with carbon dioxide to form a carbamate group, imidazolium- based ionic liquids, such as 1-Butyl-3-methylimidazolium tetrafluoroborate ([Bmim][BF4]), 1-Butyl-3-methylimidazolium hexafluorophosphate ([Bmim][PFe]), or phophsonium-based ionic liquids, such as trihexyltetradecylphosphonium chloride ([P66614][CI]).

[0008]

[0005] US patent specification US 10 888 814 B2 discloses a method for capturing carbon dioxide which comprises contacting a gaseous stream comparting carbon dioxide with a hydrated ionic liquid comprising a cation which may be of the tetraalkylammonium or tetraalkylphosphonium type and an anion which is the conjugate base of a carboxylic acid, including oxalate. No system including oxalate is however actually tested or described - acetate and formate salts being disclosed as preferred forms. The gaseous stream may be a breathing gas. In addition, the authors are silent about the possibility to support the ionic liquid on a solid.

[0009]

[0006] In a similar approach, Anderson K. and co-workers study in Green Chem., 2015,17, 4340-4354 the solubility of carbon dioxide in a set of carboxylate ionic liquids formulated with stoichiometric amounts of water and discloses systems designed for capturing carbon dioxide from submarine sources of natural gas (having a content of 10- 90% CO2). All the reported ionic liquids are salts of monocarboxylate anions, such as formate, acetate, and aminoacids involving tetraalkylphosphonium or tetraalkyklammonium cations. According to the authors, carbon dioxide is absorbed by chemisorption as follows:

[0010] H2O + CO2+ RCO2- -> HCOT + RCO2H

[0011] In particular, it is disclosed that the basicity of the ionic liquid anion activates a reaction between water and carbon dioxide to form a hydrogencarbonate anion and the conjugate acid of the anion, which appears to exist as a complex within the ionic liquid solution. In such systems, the maximal uptake of carbon dioxide is observed when the composition comprises equimolar amounts of water and ionic liquid, which is consistent with the formation of a hydrogencarbonate anion. The regeneration of the ionic liquids and release of carbon dioxide is disclosed as requiring low energy amounts and to take place at ca. 70 °C for the formate and acetate ionic liquids.

[0012]

[0007] Hydrates of quaternary ammonium salts of carboxylate for capture of carbon dioxide have been also disclosed in the art by Quinn, R. et al. in J. Am. Chem. Soc. 1995, 117, 329-335. According to the authors, absorption capacities are inversely related to the basicity of the salt anion as measured by the pKa of its conjugate acid in dilute aqueous solutions. These systems are also described as suitable alternatives to amine sorbents for these systems exhibit lower heats required to regenerate the gas-free absorbent.

[0013]

[0008] In a slightly different approach aminoacids can be used as anions in task specific ionic liquids for carbon dioxide capture. In these systems, a possible chemisorption mechanism is one wherein carbon dioxide reacts with the amino group in the amino acid to form a carbamate. Such systems are disclosed for instance by Zhang and co-workers in Chem. Eur. J. 2006, 12, 4021 - 4026 which discloses aminoacid salts of tetrabutylphosphonium.

[0014]

[0009] Yousefe M. et al. disclose in Journal of Environmental Management 2023, 334,117469, a sorbent material consisting of tetrabutylphosphonium acetate supported on silica for the absorption of carbon dioxide from gas streams comprising carbon dioxide, in particular, flue gas. The authors do not particularly report the behaviour of this system for direct air capture nor comment on the possibility to modify the anion of the ionic liquid comprised in the sorbent material. The authors also indicate that both hydrated and non-hydrated forms of the ionic liquid are suitable for absorbing carbon dioxide. According to this document, the use of hydrated amine-free sorbent materials advantageously allows releasing a large proportion of the absorbed carbon dioxide in mild conditions, e.g. upon heating the sorbent material comprising carbon dioxide sequestered in the form of hydrogencarbonate anions at a temperature as low as 60 °C and in short periods of time (10 minutes).

[0015]

[0010] International patent application WO 2023 / 205851 A1 discloses a material designed for capturing acidic gases such as carbon dioxide, hydrogen sulfide, and sulfur dioxide from gaseous streams or the atmosphere. The invention centers on a particulate absorbent composed of swellable support hydrogel particles, which are infused with amine-functionalised ionic liquids suitable for binding acidic gases . This structure allows for efficient gas absorption while maintaining the physical properties necessary for practical deployment, such as in packed or fluidized bed reactors. The absorbent can be regenerated by heating or applying a vacuum, enabling repeated use. The capture of CO2 using this system is also disclosed.

[0016]

[0011] llehara Yusuke et al. disclose in Energy & Fuels 2018, vol. 32, 5345-5354 immobilized ionic liquids on polymeric microspheres consisting of PMMA. Amongst the disclosed ionic liquids, tetrabutylphosphonium salts of different amino acids, such as Glycine, Lysine and Histidine, are disclosed. These sorbent materials were studied in capture of carbon dioxide.

[0017]

[0012] Patent application US 2013 / 080151 A1 discloses a composite structure for capturing a gaseous electrophilic species, the composite structure comprising mesoporous refractory sorbent particles, such as silica, upon the surface of which an ionic liquid is covalently attached, wherein said ionic liquid includes an accessible functional group that is capable of binding to said gaseous electrophilic species such as carbon dioxide. This document particularly discloses ionic liquids which are tetralkylphosphonium or tetraalkylammonium salts of an anion such as borates (e.g., borate, diborate, triborate, tetraborate), phosphate, hydrogenphosphate, dihydrogenphosphate, bicarbonate, carbonate, silicate, sulfate, oxalate, malonate, glutarate and adipate.

[0018]

[0013] From what is disclosed in the art, it derives that there is still a need for providing improved solid sorbent materials for direct air capture of carbon dioxide, in particular sorbents offering improved mass transport and / or improved capture capacity while maintaining a high efficiency of release of carbon dioxide.

[0019] SUMMARY OF THE INVENTION

[0020]

[0014] After exhaustive research, the inventors have developed solid sorbent materials comprising salts of tetraalkylammonium or tetraalkylphosphonium and a porous solid support. The inventors have found that these sorbent materials are particularly suitable for the capture of carbon dioxide from gas a stream whereby carbon dioxide is present in low amounts, i.e. below 1%. The use of solid sorbents advantageously promotes improved contact and mass transport between the molecules of carbon dioxide and the ionic liquid, making the chemisorption process faster and / or more efficient than liquid systems disclosed in the art. The inventors have particularly found that the capture capacity of the sorbent materials according to the invention is improved over the capacity of sorbent materials comprising analogous ionic liquids comprising acetate or formate anions of the prior art, while, at the same time, the sorbent materials according to the invention allow releasing a large portion of the absorbed carbon dioxide in a reduced amount of time and in mild conditions.

[0021]

[0015] This is particularly advantageous as it allows isolating carbon dioxide from a gaseous stream, such as air, with improved efficiency in terms of yield and energy requirement. In particular, the capture process can advantageously be carried out at atmospheric pressure. The sorbent materials of the invention thus allow capturing carbon dioxide from air in an efficient manner, since the absorbance capacity of the material is improved, which advantageously contributes to reducing atmospheric concentration of carbon dioxide, thus providing an environmental benefit. In addition, since the sorbent materials of the invention are susceptible of releasing a large portion of the captured carbon dioxide in mild conditions, this allows, on the one hand, regenerating the sorbent material for further use in carbon dioxide capture and, on the other hand, producing a gaseous stream of carbon dioxide enriched in carbon dioxide. Said stream of carbon dioxide may be used in a further industrial process, e.g. in food industry for carbonating drinks.

[0016] Thus, the first aspect of the invention relates to a composition comprising:

[0022] (i) an ionic liquid compound of formula [+XR1R2R3R4]n

[0023] (Yn-) wherein

[0024] X is P or N;

[0025] Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, hydrogencarbonate, carbonate, sulfate, silicate, aluminate and an anion of formula_OOC-(L)m-COO' wherein m is 0 or 1 and L is a diradical deriving from the abstraction of a hydrogen atom from a linear or branched (Ci-Ci2)alkyl radical that is optionally substituted at any available position with one or more groups selected from the group consisting of carboxy (-COO-) and hydroxyl; each of R1, R2, R3and R4is independently a linear or branched alkyl chain; or, alternatively wherein one of the pairs of R1and R2, R1and R3, R1and R4, R2and R3, R2and R4and R3and R4, form, together with the X atom to which they are attached, a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and from 4 to 12 carbon atoms, said ring members being optionally substituted at any available position with a (Ci-Ce)alkyl group and

[0026] (ii) a porous solid support for supporting said ionic liquid.

[0027]

[0017] A process for the preparation of the composition of the first aspect of the inventgion also forms part of the invention. Thus, a second aspect of the invention relates to a process for the preparation of a composition according to the first aspect of the invention comprising:

[0028] (i) contacting a ionic liquid as defined in the first aspect of the invention with a porous solid support for supporting said ionic liquid and as defined in the first aspect of the invention; and

[0029] (ii) optionally, contacting the ionic liquid of step (i) or the product of step (i) with a source of water or moisture.

[0030]

[0018] As mentioned above, the composition of the first aspect of the invention is useful for capturing carbon dioxide. Thus, a third aspect of the invention relates to a process for the capture of carbon dioxide from a first gaseous stream comprising carbon dioxide, said process comprising flowing said first gaseous stream through a composition according to the first aspect of the invention.

[0031]

[0019] Said process produces a composition according to the first aspect of the invention further comprising absorbed carbon dioxide. A fourth aspect of the invention thus relates to a composition obtainable by the method of the third aspect of the invention.

[0032]

[0020] The invention also encompasses the regeneration of the sorbent material and isolation of captured carbon dioxide. Thus, the fifth aspect of the invention relates to a process for preparing a second gaseous stream comprising carbon dioxide comprising heating or submitting to vacuum a composition as defined in the first aspect of the invention and further comprising hydrogencarbonate and / or carbon dioxide or a composition as defined in the fourth aspect of the invention.

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034]

[0021] Fig. 1 describes13C NMR spectra of a hydrated ionic liquid of formula [N2224][OAc] (a) before and (b) after saturation with carbon dioxide.

[0035]

[0022] Fig. 2 shows the FT-IR spectra of a hydrated ionic liquid of formula [N2224][OAc] before (dashed line) and after (plain line) saturation with carbon dioxide.

[0036]

[0023] Fig. 3 shows the experimental set-up employed to measure CO2 absorption of the prepared sorbent materials whereby a gas (1) is introduced via a gas flow meter (2) into a sorption / desorption unit (4) comprising the sorbent material (3) and the amount of CO2 in the exiting gas stream is measured with a CO2 analysis unit (5).

[0037] DETAILED DESCRIPTION

[0038]

[0024] All terms as used herein in this application, unless otherwise stated, shall be understood in their ordinary meaning as known in the art. Other more specific definitions for certain terms as used in the present application are as set forth below and are intended to apply uniformly throughout the specification and claims unless an otherwise expressly set out definition provides a broader definition.

[0039]

[0025] For the purposes of the invention, any ranges given include both the lower and the upper end-points of the range. Ranges given, such as temperatures, times, molar ratio, volume ratio and the like, should be considered approximate (i.e. with a 5% margin of variation around indicated point), unless specifically stated.

[0040]

[0026] In the context of the present invention, the term “alkyl” refers to a saturated linear or branched hydrocarbon chain. Particular embodiments of alkyl groups are those having the number of carbon atoms indicated herein, for instance, (Ci-C3o)alkyl groups having from 1 to 30 carbon atoms. Further particular embodiments of alkyl group include (C1- C2o)alkyl, (Ci-Cie)alkyl, (Ci-Ce)alkyl, (C2-C2o)alkyl, (C2-Cie)alkyl and (C2-Ce)alkyl. Alkyl groups include, in a non-limiting way, methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl, heptadecyl, octadecyl, nonadecyl and eicosyl.

[0041]

[0027] In the context of the present invention, the term “heterocycloalkyl” refers to a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and the number of carbon atoms indicated in the description and claims. In particular, the term “heterocycloal klyl” refers to a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and from 4 to 12 carbon atoms, said ring members being optionally substituted at any available position as described herein, preferably by one or more (Ci-Ce)alkyl groups.

[0042]

[0028] In the context of the present invention, the term “porous solid support” refers to a solid suitable for supporting an ionic liquid as defined in the invention. Such solids are known in the art and will become apparent to the skilled person upon reduction to practice of the invention on the basis of common general knowledge. Those include, for instance, silica, alumina, zeolites, carbon materials such as activated carbon, carbon nanotubes, graphite, graphene oxide, polymers, metal-organic frameworks, metal oxides (e.g. TiC>2, ZrCh), cellulose and derivatives thereof. The porosity of the solid support in the composition of the first aspect of the invention warrants that the gaseous stream enters in contact with the ionic liquid embedded in the material and provides for a higher contact surface for the interaction between the gas and the sorbent material.

[0043]

[0029] In the context of the present invention, the concentration of a gas is expressed as a percentage or in ppm and relates to the ratio of the volume of said gas in a mixture of gases to the total volume of the mixture of gases.

[0044]

[0030] In the context of the present invention, the term “conjugate base of boric acid” refers to an anion or mixture of anions obtainable by the treatment of an aqueous solution of boric acid with hydroxide anions. Such conjugate bases are well known in the art and are for instance disclosed in Section 6 of D. M. Schubert, Boric oxide, boric acid, and borates, Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim, (2015), and in Liu, H. et al. New J. Chem., 2023,47, 8499-8506, the content of which is incorporated herein by reference. Preferred conjugate bases of boric acid in the conttext of the invention are anions of formula [B(OH)4]', [BaOa OHjs]2'; [B4O5(OH)4]2'; [B3O3(OH)4]'; [B5O6(OH)4]' and mixtures thereof.

[0045]

[0031] As defined above, a first aspect of the invention relates to a composition comprising:

[0046] (i) an ionic liquid compound of formula [+XR1R2R3R4]n

[0047] (Yn-) wherein

[0048] X is P or N;

[0049] Yn-is an anion selected from the group consisting of a conjugate base of boric acid dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, hydrogencarbonate, carbonate, sulfate, silicate, aluminate and an anion of formula_OOC-(L)m-COO' wherein m is 0 or 1 and L is a diradical deriving from the abstraction of a hydrogen atom from a linear or branched (Ci-Ci2)alkyl radical that is optionally substituted at any available position with one or more groups selected from the group consisting of carboxy (-COO') and hydroxyl; each of R1, R2, R3and R4is independently a linear or branched alkyl chain; or, alternatively wherein one of the pairs of R1and R2, R1and R3, R1and R4, R2and R3, R2and R4and R3and R4, form, together with the X atom to which they are attached, a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and from 4 to 12 carbon atoms, said ring members being optionally substituted at any available position with a (Ci-Ce)alkyl groups; and (ii) a porous solid support for supporting said ionic liquid.

[0050]

[0032] In a preferred embodiment of the first aspect of the invention, the ionic liquid or a portion thereof is embedded in said porous solid support. In such embodiments, the ionic liquid may be located within the pores of the porous material.

[0051]

[0033] In an embodiment of the first aspect of the invention, the ionic liquid is not covalently attached to said porous solid support.

[0052]

[0034] Alternatively, the ionic liquid or a portion thereof may be located on the surface of the solid support. It is also contemplated that at least a portion of the ionic liquid is embedded in the solid support and at least a portion of the ionic liquid is located on the surface of the solid support.

[0053]

[0035] Any porous solid support suitable for supporting an ionic liquid as defined in the first aspect of the invention may be comprised in the composition of the first aspect of the invention. The function of the support is to provide a solid sorbent material, which allows improving the mass transfer conditions between the ionic liquid and the carbon dioxide, as the diffusion of the gas is believed to be faster at the gas-solid interface than in the viscous environment of a non-supported ionic liquid. As mentioned above, the porosity of the support allows for providing a higher active surface area to the support, thus providing for improved interaction with gas molecules, while improving the flow of the gas molecules through the sorbent material. Such porous solid support is preferably selected from the group consisting of silica, alumina, zeolites, metal oxides and metal organic frameworks. More preferably, the porous solid support is selected from the group consisting of silica, alumina and zeolites.

[0054]

[0036] In a preferred embodiment of the first aspect of the invention, the porous solid support is silica, preferably it is fumed silica.

[0055]

[0037] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm. Such grain size is suitable for providing interstitial voids between the grains of the support allowing for the gas to flow between the particles.

[0056]

[0038] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the porous solid support has a pore size of between 1 and 200 nm; preferably of between 50 and 100 nm. Pore size of the solid support may be determined by analysis of gas physisorption.

[0057]

[0039] another preferred embodiment, the composition of the first aspect of the invention is one wherein the porous solid support has a pore size of at least 200 nm; preferably of at least 1 .m; more preferably of at least 10 .m and no more than 800 .m. In such embodiments, the compositions of the first aspect of the invention may be foam materials.

[0058]

[0040] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the porous solid support has a pore volume of between 0.7 and 1.5 cm3per gram of the solid support; preferably of between 1.1 and 1.3 cm3per gram of the solid support. Pore volume of the solid support may be determined by analysis of gas physisorption.

[0059]

[0041] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the porous solid support has a surface area of at least 50 m2per gram of the solid support; preferably of at least 100 m2per gram of the solid support; more preferably of between 150 and 250 m2per gram of the solid support.

[0060]

[0042] In another preferred embodiment, the composition of the first aspect of the invention is one which further comprises water, i.e. a composition wherein the ionic liquid is hydrated.

[0061]

[0043] In another preferred embodiment, the composition of the first aspect of the invention is one which further comprises water in an amount of at least n moles per each mole of anion of formula Yn' in said ionic liquid, preferably between n and n+1 moles per each mole of anion of formula Yn' in said ionic liquid. More preferably, the composition of the first aspect of the invention is one which further comprises water in an amount of about n ± 10%moles per each mole of anion of formula Yn' in said ionic liquid.

[0062]

[0044] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the weight ratio of ionic liquid to solid support is comprised between 2:1 and 1 :2; preferably, it is of about 1 :1.

[0063]

[0045] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, X is P.

[0064]

[0046] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, X is N.

[0065]

[0047] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl.

[0066]

[0048] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, one of the pairs consisting of R1and R2, R1and R3, R1and R4, R2and R3, R2and R4or R3and R4, form, together with the X atom to which they are attached, a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and from 4 to 7 carbon atoms, said ring members being optionally substituted at any available position with a (Ci-Ce)alkyl groups; preferably, one of the pairs consisting of R1and R2, R1and R3, R1and R4, R2and R3, R2and R4or R3and R4, form, together with the X atom to which they are attached, a pyrrolidine ring or a phospholane ring that is optionally substituted at any available position with a (Ci-C4)alkyl chain.

[0067]

[0049] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, each of R1, R2and R3is independently a (Ci-Ce)alkyl chain; and R4is a (Ci-Cie)alkyl.

[0068]

[0050] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain.

[0069]

[0051] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl.

[0070]

[0052] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the cation of formula [+XR1R2R3R4] is selected from the group consisting of tetrabutylammonium, tetrabutylphosphonium, triethylbutylammonium and triethylbutylphosphonium.

[0071]

[0053] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the cation of formula [+XR1R2R3R4] is selected from the group consisting of tetrabutylphosphonium, triethylbutylammonium and triethylbutylphosphonium.

[0072]

[0054] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the cation of formula [+XR1R2R3R4] is selected from the group consisting of tetrabutylphosphonium, triethylbutylammonium, trimethylpropylammonium and triethylbutylphosphonium.

[0073]

[0055] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is an anion selected from the group consisting of conjugates bases of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, and an anion of formula_OOC-(L)m-COO' wherein m is 0 or 1 and L is a diradical deriving from the abstraction of a hydrogen atom from a linear or branched (Ci-Ci2)alkyl radical that is optionally substituted at any available position with one or more groups selected from the group consisting of carboxy (-COO-) and hydroxyl.

[0074]

[0056] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate.

[0075]

[0057] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenphosphate, citrate and oxalate.

[0076]

[0058] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is an anion selected from the group consisting of a conjugate base of boric acid and oxalate.

[0077]

[0059] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is a conjugate base of boric acid; preferably said conjugate base of boric acid is selected from the group consisting of the anions of formula [B(OH)4]', [BaC^OHjs]2-; [B4Os(OH)4]2'; [B3O3(OH)4]'; [B5O6(OH)4]- and mixtures thereof.

[0078]

[0060] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is oxalate.

[0079]

[0061] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, the anion of formula Yn' is hydrogenphosphate or a conjugate base of boric acid.

[0080]

[0062] In another preferred embodiment, the composition of the first aspect of the invention is one wherein said ionic liquid is not tris(tetrabutylphosphonium) citrate or is not bis(triethylbutylammonium) oxalate.

[0081]

[0063] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein X is P and the anion of formula Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, and an anion of formula_OOC-(L)m-COO' wherein m is 0 or 1 and L is a diradical deriving from the abstraction of a hydrogen atom from a linear or branched (Ci-Ci2)alkyl radical that is optionally substituted at any available position with one or more groups selected from the group consisting of carboxy (-COO-) and hydroxyl.

[0082]

[0064] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein X is P and the anion of formula Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is an anion selected from the group consisting of di hydrogenborate and oxalate; even more preferably, Yn' is an oxalate anion.

[0083]

[0065] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein X is P and each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl.

[0084]

[0066] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein X is N and each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl.

[0085]

[0067] In another preferred embodiment, the composition of the first aspect of the invention is one wherein, in said ionic liquid, X is P and Yn' is oxalate.

[0086]

[0068] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein:

[0087] - X is P;

[0088] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0089] - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is an oxalate anion.

[0090]

[0069] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein:

[0091] - X is N;

[0092] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0093] - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is an oxalate anion.

[0094]

[0070] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein: - X is N;

[0095] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0096] - - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is a conjugate base of boric acid; even more preferably said conjugate base of boric acid is selected from the group consisting of the anions of formula [B(OH)4]', [BsGh OHjs]2'; [B4Os(OH)4]2'; [B3C>3(OH)4]'; [B5O6(OH)4]- and mixtures thereof.

[0097]

[0071] In another preferred embodiment, the ionic liquid of the composition of the first aspect of the invention is one wherein:

[0098] - X is P;

[0099] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0100] - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is a conjugate base of boric acid; even more preferably said conjugate base of boric acid is selected from the group consisting of the anions of formula [B(OH)4]', [BaC^OHjs]2-; [B4Os(OH)4]2'; [B3C>3(OH)4]'; [B5O6(OH)4]- and mixtures thereof.

[0101]

[0072] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the ionic liquid is selected from the group consisting of tris(tetrabutylphosphonium) citrate, tris(triethylbutylphosphonium) citrate, tris(triethylbutylammonium) citrate, bis(tetrabutylphosphonium) oxalate, bis(tetrabutylammonium) oxalate, bis(triethylbutylphosphonium) oxalate, bis(triethylbutylammonium) oxalate, bis(tetrabutylphosphonium) hydrogenphosphate and a salt of tetrabutylphosphonium with a conjugate base of boric acid.

[0102]

[0073] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the ionic liquid is selected from the group consisting of tris(triethylbutylphosphonium) citrate, tris(triethylbutylammonium) citrate, bis(tetrabutylphosphonium) oxalate, bis(triethylbutylphosphonium) oxalate, bis(tetrabutylphosphonium) hydrogenphosphate, bis(triethylbutylammonium) hydrogenphosphate, tris (trimethylpropylammonium) citrate, tris(tetrabutylphosphonium) citrate, bis(triethylbutylammonium) oxalate, and a salt of tetrabutylphosphonium with a conjugate base of boric acid.

[0103]

[0074] In another preferred embodiment, the composition of the first aspect of the invention is one wherein the ionic liquid is selected from the group consisting of tris(triethylbutylphosphonium) citrate, tris(triethylbutylammonium) citrate, bis(tetrabutylphosphonium) oxalate, bis(triethylbutylphosphonium) oxalate, bis(tetrabutylphosphonium) hydrogenphosphate, bis(triethylbutylammonium) hydrogenphosphate, bis(triethylbutylammonium) oxalate, tris(trimethylpropylammonium) citrate and a salt of tetrabutylphosphonium with a conjugate base of boric acid.

[0104]

[0075] When the sorbent of the first aspect of the invention absorbs carbon dioxide, said carbon dioxide may react with water molecules comprised in the composition to form hydrogencarbonate anions. In addition to this chemisorption phenomenon, carbon dioxide may be absorbed by physisorption. Thus, in another preferred embodiment, the composition of the first aspect of the invention is one further comprising hydrogencarbonatehydrogencarbonate and / or carbon dioxide.

[0105]

[0076] In further embodiments, carbon dioxide may react in a chemisorption phenomenon with the cation of the ionic liquid comprised in the sorbent composition by formation of a zwitterion comprising a moiety of formula coo- wherein the carboxylate moiety results from the chemisorption of carbon dioxide and the wavy lines represent the attachment points to the remainder of the cation molecule. This is particularly the case when the composition of the first aspect of the invention does not comprise water.

[0106]

[0077] In particular embodiments, the composition of the first aspect of the invention comprises:

[0107] (i) an ionic liquid compound of formula [+XR1R2R3R4]n(Yn') wherein:

[0108] - X is P;

[0109] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0110] - Yn-is an anion selected from the group consisting of dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is an oxalate anion; and

[0111] (ii) a porous solid support for supporting said ionic liquid selected from the group consisting of silica, alumina and zeolites, wherein, preferably, the solid support satisfies at least one of the following conditions (a) to (d):

[0112] (a) the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm;

[0113] (b) the porous solid support has a pore size of between 1 and 20 nm; preferably of between 5 and 10 nm;

[0114] (c) the porous solid support has a pore volume of between 0.7 and 1.5 cm3per gram of the solid support; preferably of between 1.1 and 1.3 cm3per gram of the solid support;

[0115] (d) the porous solid support has a surface area of at least 50 m2per gram of the solid support; preferably of at least 100 m2per gram of the solid support; more preferably of between 150 and 250 m2per gram of the solid support.

[0116]

[0078] In another preferred embodiment, the composition of the first aspect of the invention comprises:

[0117] (i) an ionic liquid compound of formula [+XR1R2R3R4]n(Yn') wherein:

[0118] - X is N;

[0119] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0120] - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is an oxalate anion; and

[0121] (ii) a porous solid support for supporting said ionic liquid selected from the group consisting of silica, alumina and zeolites, wherein, preferably, the solid support satisfies at least one of the following conditions (a) to (d):

[0122] (a) the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm;

[0123] (b) the porous solid support has a pore size of between 1 and 20 nm; preferably of between 5 and 10 nm;

[0124] (c) the porous solid support has a pore volume of between 0.7 and 1.5 cm3per gram of the solid support; preferably of between 1.1 and 1.3 cm3per gram of the solid support;

[0125] (d) the porous solid support has a surface area of at least 50 m2per gram of the solid support; preferably of at least 100 m2per gram of the solid support; more preferably of between 150 and 250 m2per gram of the solid support.

[0079] In another preferred embodiment, the composition of the first aspect of the invention comprises:

[0126] (i) an ionic liquid compound of formula [+XR1R2R3R4]n(Yn') wherein:

[0127] - X is N;

[0128] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0129] - - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is a conjugate base of boric acid; even more preferably said conjugate base of boric acid is selected from the group consisting of the anions of formula [B(OH)4]', [BaC^OHjs]2'; [B4Os(OH)4]2'; [B3C>3(OH)4]'; [B5O6(OH)4]- and mixtures thereof; and

[0130] (ii) a porous solid support for supporting said ionic liquid selected from the group consisting of silica, alumina and zeolites, wherein, preferably, the solid support satisfies at least one of the following conditions (a) to (d):

[0131] (a) the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm;

[0132] (b) the porous solid support has a pore size of between 1 and 20 nm; preferably of between 5 and 10 nm;

[0133] (c) the porous solid support has a pore volume of between 0.7 and 1.5 cm3per gram of the solid support; preferably of between 1.1 and 1.3 cm3per gram of the solid support;

[0134] (d) the porous solid support has a surface area of at least 50 m2per gram of the solid support; preferably of at least 100 m2per gram of the solid support; more preferably of between 150 and 250 m2per gram of the solid support.

[0135]

[0080] In another preferred embodiment, the composition of the first aspect of the invention comprises:

[0136] (i) an ionic liquid compound of formula [+XR1R2R3R4]n(Yn') wherein:

[0137] - X is P;

[0138] - each of R1, R2, R3and R4is independently a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain; more preferably, each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl; and

[0139] - Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, citrate and oxalate; preferably, Yn' is an anion selected from the group consisting of dihydrogenborate, hydrogenphosphate, citrate and oxalate; more preferably, Yn' is a conjugate base of boric acid; even more preferably said conjugate base of boric acid is selected from the group consisting of the anions of formula [B(OH)4]', [BaC^OHjs]2-; [B4Os(OH)4]2'; [B3C>3(OH)4]'; [B5O6(OH)4]- and mixtures thereof; and

[0140] (ii) a porous solid support for supporting said ionic liquid selected from the group consisting of silica, alumina and zeolites, wherein, preferably, the solid support satisfies at least one of the following conditions (a) to (d):

[0141] (a) the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm;

[0142] (b) the porous solid support has a pore size of between 1 and 20 nm; preferably of between 5 and 10 nm;

[0143] (c) the porous solid support has a pore volume of between 0.7 and 1.5 cm3per gram of the solid support; preferably of between 1.1 and 1.3 cm3per gram of the solid support;

[0144] (d) the porous solid support has a surface area of at least 50 m2per gram of the solid support; preferably of at least 100 m2per gram of the solid support; more preferably of between 150 and 250 m2per gram of the solid support.

[0145]

[0081] A process for the preparation of the composition of the first aspect of the invention also forms part of the invention. As mentioned above, the second aspect of the invention relates to a process for the preparation of a composition as defined in the first aspect of the invention, said process comprising:

[0146] (i) contacting a ionic liquid as defined in the first aspect of the invention with a porous solid support for supporting said ionic liquid and as defined in the first aspect of the invention; and

[0147] (ii) optionally, contacting the ionic liquid of step (i) or the product of step (i) with a source of water or moisture.

[0148]

[0082] In preferred embodiments of the second aspect of the invention, each of the ionic liquid and solid support are independently as defined in any of the preferred and particular embodiments of the first aspect of the invention defined above.

[0149]

[0083] Steps (i) and (ii) of the process of the second aspect of the invention may be carried out in any order. No specific orders of steps is particularly preferred - however, for commodity of the preparation process, it is preferred that step (ii) takes place before step (i).

[0150]

[0084] The ionic liquid of step (i) may be obtained from commercial sources or according to procedures known in the art that will become apparent to the skilled person. A typical procedure comprises treating a hydroxide salt of the cation of formula [+XR1R2R3R4] with an acid of formula YHn.

[0085] In preferred embodiments of the second aspect of the invention, the contacting of step (i) is an impregnation step. In particular, said impregnation step comprises contacting the solid support with a solution of the ionic liquid.

[0151]

[0086] Said solution of the ionic liquid is preferably a solution of a solvent that is polar solvent suitable for dissolving ionic liquids, such as polar protic solvents, for instance, alcohols, such as methanol, ethanol and iso-propanol. More particularly, said solvent is methanol.

[0152]

[0087] When the process of the second aspect of the invention comprises the use of a solvent, the process of the second aspect of the invention further comprises the step of eliminating said solvent, for instance by evaporation and / or under vacuum.

[0153]

[0088] When the process of the second aspect of the invention comprises contacting the ionic liquid of step (i) or the product of step (i) with a source of water or moisture, said source of water or moisture may be a solvent system comprising water or a mixture of gases comprising water or moisture.

[0154]

[0089] In particular embodiments, step (ii) of the process of the second aspect of the invention is one wherein the ionic liquid is contacted with a solvent system comprising water. Said solvent system is preferably water.

[0155]

[0090] In other particular embodiments, step (ii) of the process of the second aspect of the invention is one wherein the product of step (i) is contacted with a mixture of gases comprising water. Said mixture of gases may further comprise carbon dioxide. In this regard, it is contemplated that said mixture of gases is the first gaseous stream comprising carbon dioxide defined above in the third aspect of the invention. It is thus possible to hydrate the ionic liquid during the carbon dioxide capture process by using a gaseous stream comprising water or humidity.

[0156]

[0091] The invention also relates to the product obtainable by the process of the second aspect of the invention defined above.

[0157]

[0092] A third aspect of the invention relates to a process for the capture of carbon dioxide from a first gaseous stream comprising carbon dioxide, said process comprising flowing said first gaseous stream through a composition as defined in the first aspect of the invention.

[0158]

[0093] In preferred embodiments of the process of the third aspect of the invention, the composition is as defined in any of the particular and preferred embodiments defined above for the first aspect of the invention.

[0159]

[0094] Said first gaseous stream comprises carbon dioxide in any concentration and amount. It is contemplated that said first gaseous stream comprises less than 25% (v / v) carbon dioxide. For instance, when the first gaseous stream comprises from 1% to 25% carbon dioxide, said first gaseous stream may be a flue gas.

[0095] In preferred embodiments of the process of the third aspect of the invention, the first gaseous stream is one wherein the concentration of carbon dioxide is lower than 1 %; preferably lower than 1000 ppm; and more preferably it is of about 400 ppm. The inventors have found that the composition of the invention is particularly efficient in capturing carbon dioxide from such gaseous streams.

[0160]

[0096] In preferred embodiments of the process of the third aspect of the invention, the first gaseous stream is air. In such embodiment, the process of the third aspect of the invention is a process of direct air capture.

[0161]

[0097] Any device or reactor design suitable for flowing the first gaseous stream through the composition of the first aspect of the invention may be used. Such devices and reactor designs will become apparent to the skilled person upon reduction to practice of the invention on the basis of common general knowledge. These devices or reactor designs include, for instance, fixed-bed reactors, fluidized-bed reactors, packed bed reactors, rotary kiln reactors, membrane reactors and entrained-flow reactors.

[0162]

[0098] The flow rate of the gaseous stream mainly depends on the type of reactor employed and the amount of sorbent material in said reactor.

[0163]

[0099] It is contemplated that at least a portion of the first gaseous stream is recirculated to be further flown through the sorbent material.

[0164]

[0100] As mentioned above, the fourth aspect of the invention relates to a composition obtainable by the method of the third aspect of the invention.

[0165]

[0101] Preferred embodiments of the fourth aspect of the invention relate to a composition obtainable by the method as defined in any of the particular and preferred embodiments of the third aspect of the invention.

[0166]

[0102] As will be obvious to the skilled person, this composition comprises carbon dioxide absorbed or chemisorbed on the sorbent material, as defined above.

[0167]

[0103] As mentioned above, the sorbent compositions of the invention are particularly efficient in releasing carbon dioxide absorbed or chemisorbed within the composition. A process for the recovery of said carbon dioxide and regeneration of the sorbent material forms the fifth aspect of the invention.

[0168]

[0104] The fifth aspect of the invention relates to a process for preparing a second gaseous stream comprising carbon dioxide comprising heating or submitting to vacuum a composition as defined in the first aspect of the invention and further comprising hydrogencarbonate and / or carbon dioxide or a composition as defined in the fourth aspect of the invention.

[0169]

[0105] The process of the fifth aspect of the invention advantageously allows releasing a large portion of the captured carbon dioxide while regenerating the sorbent material for further use in a process according to the third aspect of the invention. In preferred embodiments, at least 70% of the carbon dioxide captured in a process according to the third aspect of the invention is recovered. More preferably, at least 80% of the carbon dioxide captured in a process according to the third aspect of the invention is recovered. Simultaneously, the same portion of the ionic liquid is regenerated and suitable for being re-used in a process according to the third aspect of the invention.

[0170]

[0106] In a preferred embodiment of the process of the fifth aspect of the invention, the composition is heated at a temperature of between 30 °C and 90 °C; more preferably of about 60 °C.

[0171]

[0107] In a preferred embodiment of the process of the fifth aspect of the invention, the composition is submitted to vacuum.

[0172]

[0108] In a preferred embodiment of the process of the fifth aspect of the invention, when the process comprises heating or submitting to vacuum, a composition as defined in the fourth aspect of the invention, the second gaseous stream has a higher carbon dioxide concentration than the first gaseous stream.

[0173]

[0109] Reactor designs suitable for carrying out the process of the fifth aspect of the invention will become apparent to the skilled person upon reduction to practice of the invention on the basis of common general knowledge. These devices or reactor designs include, for instance, fixed-bed reactors, fluidized-bed reactors, packed bed reactors, rotary kiln reactors, membrane reactors and entrained-flow reactors.

[0174]

[0110] Throughout the description and claims the word “comprises" and variations of the word, are not intended to exclude other technical features, additives, components or steps. Furthermore, the word “comprise” encompasses the cases of “consist of” and “consists essentially of”. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples are provided by way of illustration, and they are not intended to be limiting of the present invention.

[0175] EXAMPLES

[0176] Materials

[0177]

[0111] A model air gas mixture cylinder (CO2, 0.04%; 02, 20.9%; N2, 79.06%), pure CO2 and pure N2 were obtained from Carburos Metalicos. The suppliers of the reagents used for the synthesis of ionic liquids, characterization and preparation of sorbent materials are shown in Table 1 below.

[0178] 1P(C4H9)4OH is commercialized as a water solution of 40% in weight.

[0179] Preparative Examples

[0180] Preparation of tetrabutylphosphonium acetate [P4444][OAc] - comparative example

[0181]

[0112] Tetrabutylphosphonium hydroxide (60 mL, 40% in water, ca. 86 mmol) was added drop-wise to an equimolar amount of CH3COOH (5.2 g, ca. 86 mmol) in distilled water, up to a total volume of 100 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.11 , measured using a Metrohm pH meter. Subsequently, water was removed at 60 °C under reduced pressure (reaching ca. 15 mbar in latter stages) in a rotary evaporator until constant weight. The resulting liquid was characterized by NMR confirming the expected structure, and its water content was determined by Karl Fisher titration. Before further experiments, water amount was adjusted to the optimal ratio of 1 mol (H2O) per mol of ionic liquid and the mixture was homogenized, resulting in [P4444][AcO] H2O as a colourless viscous liquid, which was stored under N2 atmosphere. No crystallization temperature was observed by differential scanning calorimetry (DSC)for this sample. The measured glass transition temperature was of -72 °C.

[0182] Preparation of triethylbutylphosphonium acetate [P2224 OAC] - comparative example

[0183]

[0113] The synthesis of triethylbutylphosphonium acetate involved a three-step synthetic pathway. In the first step, the synthesis of triethylbutylphosphonium bromide [P2224][Br] was cairred out. In the second step, the synthesis of triethylbutylphosphonium hydroxide [P2224][OH] was performed, and in the third step, the synthesis of triethylbutylphosphonium acetate was carried out. [P2224][Br] was synthesised via alkylation of triethylphosphine (25.0 g, ca. 212 mmol) with excess 1-bromobutane (32.2 g, ca. 235 mmol) in acetonitrile (200 mL) at room temperature with vigorous stirring for 24 h, under argon atmosphere. After reaction, the unreacted reagents and the solvent were removed at 50 °C under reduced pressure in a rotary evaporator until constant weight. The resulting solid was characterized by NMR confirming the expected structure. [P2224][OH] was synthesised from [P2224][Br] by ion-exchange resin (Amberlite IRN-78). A mixture of the resin (400 mL) and Milli-Q® water was placed in a chromatography column. [P2224][Br] (25.7 g) was dissolved in Milli-Q® water (500 mL) and it was passed through the resin with the speed of 1 drop every 20-30s. The concentration of [P2224][OH] was determined by titration with an aqueous HCI solution known concentration. Triethylbutylphosphonium hydroxide (500 mL, 1.89% in water, ca. 49 mmol) was added drop-wise to an equimolar amount of CH3COOH (2.9 g, ca. 49 mmol) in distilled water, up to a total volume of 500 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.77, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed as indicated for IL1 , resulting in [P2224][AcO] H2O as a orange viscous liquid, which was stored under N2 atmosphere. No crystallization or glass transition temperature was observed by DSC for this sample.

[0184] Preparation of triethylbutylammonium acetate [N2224][OAc] - comparative example

[0185]

[0114] [N2224][Br] was synthesised via alkylation of triethylamine (70.0 g,-692 mmol) with 1-bromobutane (95.0 g, -692 mmol) in ethanol (200 mL) under reflux (83 °C), vigorous stirring for 21 h, and under N2 atmosphere. After reaction, the unreacted reagents and the solvent were removed at 60 °C under reduced pressure in a rotary evaporator until constant weight. The resulting solid was characterized by NMR confirming the expected structure. [N2224][OH] was synthesised from [N2224][Br] by ion-exchange resin (Amberlite IRN-78). A mixture of the resin (400 mL) and Milli-Q® water was placed in a chromatography column. [N2224][Br] (30 g) was dissolved in Milli-Q® water (500 mL) and it was passed through the resin with the speed of 1 drop every 20-30s. Triethylbutylammonium hydroxide (350 mL, 2.88% in water, ca. 57 mmol) was added drop-wise to an equimolar amount of CH3COOH (3.4 g, ca. 57 mmol) in distilled water, up to a total volume of 350 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.87, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [N2224][AcO] H2O as a yellow viscous liquid, which was stored under N2 atmosphere. No crystallization temperature was observed by DSC for this sample. The measured glass transition temperature was of -69°C.

[0186] Preparation of trimethylbutylammonium acetate [Nn ][0Ac] - comparative example

[0187]

[0115] The synthesis of n-butyltrimethylammonium acetate involved a two-step synthetic pathway. [N1 1 1 4][OH] was synthesised from commercially available [N1 1 1 4][CI] by ionexchange resin (Amberlite IRN-78). A mixture of the resin (250 mL) and Milli-Q® water was placed in a chromatography column. [N1 1 1 4][CI] (15 g) was dissolved in Milli-Q® water (500 mL) and it was passed through the resin with the speed of 1 drop every 20- 30s. The concentration of [N1 1 14][OH] was determined by titration with an aqueous HCI solution of known concentration. n-Butylltrimethylammonium hydroxide (150 mL, 0.1837 M in water, ca. 28 mmol) was added drop-wise to an equimolar amount of CH3COOH (1 .7 g, ca. 28 mmol) in distilled water, up to a total volume of 200 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.83, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [N1 1 14][AcO] H2O as, colourless liquid, which was stored under N2 atmosphere.

[0188] Preparation of trihexyl(tetradecyl)phosphonium acetate [P666 ][AcO] - comparative example

[0189]

[0116] The synthesis of trihexyl(tetradecyl)phosphonium acetate involved a two-step synthetic pathway. [Pe66 i4][OH] was synthesised from [Pe66 i4][CI] by ion-exchange resin (Amberlite IRN-78). The mixture of the resin (400 mL) and methanol was placed in a chromatography column. [Pe 66 i4][CI] (80 g) was dissolved in methanol (500 mL) and it was passed through the resin with the speed of 1 drop every 20-30s. The concentration of [Pe 66 14][OH] was determined by titration with known concentration of HCI solution. Trihexyl(tetradecyl)phosphonium hydroxide (200 mL, 0.23M in methanol, ca. 46 mmol) was added drop-wise to an equimolar amount of CH3COOH (2.7 g, ca. 46 mmol) in methanol, up to a total volume of 400 mL, in a round bottom flask. Subsequently, methanol was removed at 50 °C under reduced pressure (reaching ca. 15 mbar in latter stage) in a rotary evaporator until constant weight. The resulting liquid was characterized by NMR confirming the expected structure, and its water content was determined by Karl Fisher titration. Before further experiments, [Pe66 i4][AcO] as a dark orange viscous liquid was stored under N2 atmosphere.

[0190] Preparation of n-Propyltrimethylammonium acetate [Nm3][AcO] - comparative example

[0191]

[0117] A 100 mL round bottom flask was charged with 1 -bromopropane (5.8 mL, 63.8 mmol), trimethylamine (45% in H2O, 20 mL, 126 mmol), and 20 mL acetonitrile. The reaction was heated at 40 °C for 5 h and then cooled to room temperature. The solvent was removed via rotary evaporation to leave an oily residue. Diethyl ether was added to precipitate the product, which was filtered and washed with additional ether. The product was dried in rotary evaporator at 50 °C until constant weight. The resulting solid was characterized by NMR confirming the expected structure. [Nm3][0H] was synthesised from [Nm3][Br] by ion-exchange resin (Amberlite IRN-78). A mixture of the resin (250 mL) and Milli-Q® water was placed in a chromatography column. [N 3][Br] (25 g) was dissolved in Milli-Q® water (500 mL) and it was passed through the resin with the speed of 1 drop every 20-30s. The concentration of [Nm3][0H] was determined by titration with an aqueous HCI solution of known concentration. n-Propyltrimethylammonium hydroxide (500 mL, 0.1655 M in water, ca. 82 mmol) was added drop-wise to an equimolar amount of CH3COOH (4.9 g, ca. 82 mmol) in distilled water, up to a total volume of 350 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.87, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [Nm3][AcO] H2O as a pinkish liquid, which was stored under N2 atmosphere. No crystallization temperature was observed by DSC for this sample. The measured glass transition temperature was of -

[0192] 70 °C.

[0193] Preparation of tetrabutylphosphonium oxalate [P4444]2[Oxalate]

[0194]

[0118] Tetrabutylphosphonium hydroxide (20 mL, 40% in water, ca.28 mmol) was added drop-wise to oxalic acid (1.8 g, ca. 14 mmol) in the molar ratio 2 to 1 , respectively, in distilled water, up to a total volume of 100 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.44, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [P4444]2[Oxalate] H2O as a colourless viscous liquid, which was stored under N2 atmosphere. A measured crystallization temperature of -18 °C was observed by DSC for this sample. The measured glass transition temperature was of -

[0195] 71 °C.

[0196] Preparation of Tetrabutylphosphonium citrate [P4444]3[Citrate]

[0197]

[0119] Tetrabutylphosphonium hydroxide (20 mL, 40% in water, ca. 28 mmol) was added drop-wise to citric acid (1.8 g, ca. 9.6 mmol) in distilled water, up to a total volume of 100 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.28, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [P4444]3 [Citrate] H2O as an extremely viscous colourless liquid, which was stored under N2 atmosphere.

[0198] Preparation of n-Propyltrimethylammonium citrate [NmsMCitrate]

[0199]

[0120] n-Propyltrimethylammonium hydroxide (300 mL, 0.1655M in water, -50 mmol), prepared as described above, was added drop-wise to citric acid (3.2 g,-ca. 16 mmol) in distilled water, up to a total volume of 340 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.14, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [Minsk [Citrate] -3.00 H2O, as a colourless liquid, which was stored under N2 atmosphere.

[0200] Preparation of triethylbutylammonium citrate [N2224]3[Citrate]

[0201]

[0121] Triethylbutylammonium hydroxide (60 mL, 0.15M in water, 5 mmol), prepared as described above, was added drop-wise to citric acid (0.6 g,-ca. 3 mmol) in distilled water, up to a total volume of 100 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.10, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [N2224]3 [Citrate] 4.26 H2O, an extremely viscous colourless liquid, which was stored under N2 atmosphere. No crystallization temperature was observed by DSC for this sample. The measured glass transition temperature was of -47 °C.

[0202] Preparation of triethylbutylphosphonium citrate [P2224]3[Citrate]

[0203]

[0122] Triethylbutylphosphonium hydroxide (100 mL, 0.097 M in water, ca. 10 mmol) , prepared as described above, was added drop-wise to citric acid (0.6 g, ca. 3 mmol) in the molar ratio 3 to 1 , respectively, in distilled water, up to a total volume of 150 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.01 , measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [P2224]3 [Citrate] H2O as a colourless extremely viscous liquid, which was stored under N2 atmosphere. . No crystallization temperature was observed by DSC for this sample. The measured glass transition temperature was of -59 °C.

[0204] Preparation of tetrabutylphosphonium hydrogenphosphate [P4444 HPO4]

[0205]

[0123] Tetrabutylphosphonium hydroxide (25 mL, 40% in water, -37 mmol) was added drop-wise to phosphoric acid solution (2.74 mL, ca.18 mmol) in the molar ratio 2 to 1 , respectively, in distilled water, up to a total volume of 100 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.22, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [P4444]2]n[HPC>4]-2.70 H2O, a colourless viscous liquid, which was stored under N2 atmosphere.

[0206] Preparation of triethylbutylammonium hydrogenphosphate [N2224 HPO4]

[0207]

[0124] Triethylbutylammonium hydroxide (90 mL, 0.15M in water, -14 mmol), prepared as described above, was added drop-wise to phosphoric acid solution (0.508 mL, ca.7 mmol) in the molar ratio 2 to 1 , respectively, in distilled water, up to a total volume of 91.015 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 9.25, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [N2224]2[HPO4] 6.90 H2O, a colourless viscous liquid, which was stored under N2 atmosphere. No crystallization temperature was observed by DSC for this sample. The measured glass transition temperature was of -57 °C.

[0208] Preparation of triethylbutylphosphonium oxalate [P2224]2[Oxalate]

[0209]

[0125] Triethylbutylphosphonium hydroxide (100 mL, 0.097 M in water, ca. 10 mmol) was added drop-wise to oxalic acid dihydrate (0.6 g, ca. 4.8 mmol) in distilled water, up to a total volume of 150 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.17, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [P2224]2[Oxalate] 4.38H2O as a colourless viscous liquid, which was stored under N2 atmosphere.

[0210] Preparation of triethylbutylammonium oxalate [N2224]2[Oxalate]

[0211]

[0126] Triethylbutylammonium hydroxide (100 mL, 0.15 M in water, ca. 15 mmol), prepared as described above, was added drop-wise to oxalic acid dihydrate (0.9 g, ca. 8 mmol) in distilled water, up to a total volume of 150 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 8.25, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed, resulting in [N2224]2[Oxalate] 5.76H2O, an extremely viscous colourless liquid, which was stored under N2 atmosphere.

[0212] Preparation of a tetrabutylphosphonium salt of a conjugate base of boric acid “[P4444][H2BO3]”

[0127] Tetrabutylphosphonium hydroxide (10 mL, 40% in water, -14.4 mmol) was added drop-wise to boric acid solution (0.8945 g, ~14.4 mmol) in the molar ratio 1 to 1 , respectively, in distilled water, up to a total volume of 500 mL, in a round bottom flask. The addition was carefully performed until the calculated final molar equivalence point at pH = 10.63, measured using a Metrohm pH meter. Ionic liquid hydrate isolation and characterisation was performed as indicated below, resulting in “[P4444][H2BC>3] H2O”, a colourless viscous liquid, which was stored under N2 atmosphere.

[0213] General Procedures

[0214] Characterization of ionic liquids

[0215]

[0128] The synthesized ionic liquids were characterized by NMR spectroscopy (1H,13C and31P NMR) on a Varian Gemini 400 spectrometer (400 MHz), either dissolved in DMSO-de or as neat liquid using DMSO-de in a sealed capillary tube as an external standard. Thermal behaviour and stability studies were performed by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) on DSC 3 + STARe System and TGA 2 STARe System, respectively, Mettler Toledo instruments. The DSC analysis (2 cycles) were performed from 25 to 60 °C, then from 60 to -80 °C, -80 to 60 °C, 60 to -80 °C, and then from -80 to 60 °C. Cooling and heating cycles were done at 5 °C min-1, under N2 (50 mL min-1). The TGA profiles were recorded from 30 to 600 °C, at 10 °C min-1, under air atmosphere (50 mL min-1). Fourier-transform infrared (FTIR) spectra were recorded on Jasco FT / IR instrument and processed using the Spectra ManagerTM Suite Spectroscopy Software by Jasco Corporation.

[0216] Impregnation of ionic liquids on solid support

[0217]

[0129] The silica-supported CO2 sorbents were prepared by impregnation. The fumed silica powder was compacted by a hydraulic press into cakes, and then crushed and sieved. The fraction composed of pellets between 0.25 and 0.50 mm in size were separated and employed as solid support. The amount of hydrated ionic liquid was dissolved in methanol in a Schlenk flask and then the SiO2 pellets (the same amount as IL) were added. The mixture was gently shaken and dried off under a gentle N2 flow at 50 °C until constant weight. The solid-supported sorbents were stored under N2 atmosphere until used for CO2 capture experiments.

[0218] CO2 sorption-desorption experiments with model air gas and model flue gas

[0219]

[0130] Before CO2 sorption-desorption experiments sorbents were placed in a custom- designed glass U-tube and were dried at 60 °C with flow of N2 > 500 mL min-1. In typical sorption experiment, the U-tube containing the desired solid-supported sorbent (ca. 2.0 g) was connected into the system. Optionally, the sorbent was subsequently moisturized overnight by passing N2 at a defined relative humidity (for example, 5%). The next day, the direct air capture CO2 sorption-desorption experiment was carried out. Model air gas was flowed (c(CC>2) = 400 ppm, 300 mL min-1, dry or at a defined relative humidity) at nearly atmospheric pressure and room temperature (25.0 ± 0.5 °C) through the solid- supported sorbents in the ll-tube glass container. The concentration of CO2 in the gas exiting the ll-tube fixed-bed was monitored in real time by using non-dispersive infrared gas analyzer (HORIBA VA-5001), and the data recorded every second. The CO2 sorption was considered to be completed when the CO2 concentration of the outlet stream was equal to the inlet one (maximum time: 1 hour). Afterwards, the glass ll-tube was immersed in the recirculation cryo-thermostat filled with thermal bath fluid. The temperature of the fluid was -30 °C and N2 was flowed (300 mL min-1), in order to remove any CO2 in the gas-phase remaining in the system, while avoiding any possible regeneration that could happen at room temperature. Figure 3 shows a set-up of the system employed.

[0220]

[0131] Desorption of CO2 from saturated sorbents was carried out by monitoring the CO2 concentration in the same way as described for the sorption method. However, in desorption experiments the sorbents were regenerated by heating at moderate temperature. For this purpose, the ll-tube glass container was immersed in a water bath at 60 °C. Immediately afterwards, N2 flow at nearly atmospheric pressure (300 mL min-1) was passed through the CCh-saturated sorbents in the glass container. In this stage, CO2 was released and increases in CO2 concentration were observed. The CO2 desorption was considered to be completed when the CO2 concentration reading returned down to 0 ppm CO2 concentration, or no change in CO2 concentration was observed (maximum time of 15 minutes).

[0221]

[0132] After this first sorption-desorption (direct air capture) cycle, a second cycle was analogously carried out as described above, but a model flue gas was used instead of a model air gas (CCO2 = 15%, dry or Relative Humidity = 5%) as the capture stream.

[0222] Results

[0223]

[0133] In order to confirm if the molecular mechanisms of CO2 capture in the sorbents takes place as expected by formation of hydrogencarbonate, NMR and FTIR analyses before and after CO2 capture were performed. Figure 1 presents13C NMR spectra of hydrated [N2224][AcO] before and after CO2 capture. In both spectra, before and after CO2 capture, peak at around 26 ppm corresponds to carbon from acetate anion. The rest of peaks between 0 and 60 ppm are associated to the carbons from cations and peak around 175 ppm corresponds to carboxylate from anion. After CO2 capture, a bicarbonate peak is observed around 160 ppm, thus proving that CO2 was absorbed by the ionic liquid by formation of hydrogencarbonate.

[0224]

[0134] Figure 2 presents FTIR spectra of fresh hydrated [N1 1 1 a][AcO] (dotted black line) and the ionic liquid after saturation with CO2 (solid black line). The signals observed at 1640 cm-1and at 1340 cm-1after saturation with CO2 are attributed to the asymmetric and symmetric stretching of the COO- moiety of the bicarbonate anion formed by chemical sorption of CO2 by the hydrated acetate ionic liquid. The carboxylate stretching signals of the acetate anion are observed on both spectra.

[0225] Sorption / Desorption experiments of model air gas

[0226]

[0135] Table 3 below reports the measured amount of CO2, expressed in mg of CO2 per gram of sorbent material, absorbed and released by the material when a model air gas stream (400 ppm CO2) having a relative humidity of 5% is flown through the sorbent material. Table 3 also reports the release efficiency, expressed as a percentage, and calculated as the ratio of released carbon dioxide to absorbed carbon dioxide.

[0227] Table 3 aRelative Humidity of model air gas: 50%, 400 ppm CO2- H2BO3 refers to a conjugate base of boric acid in “[P4444]H2BC>3”

[0228] *Relative Humidity of model air gas: 12%, 400 ppm CO2

[0229] ** Relative Humidity of model air gas: 10%, 400 ppm CO2 ***possible solidification of the sorbent under these conditions.

[0230] **** substantially complete release

[0231]

[0136] The results of Table 3 show that the sorbents according to the invention advantageously allow increasing the capture capacity of the sorbent while maintaining a high release capacity of the captured carbon dioxide. It is particularly surprising that sorbent materials comprising oxalate anions release carbon dioxide in a fast manner, i.e. at a comparable rate as observed for acetate-based sorbent materials.

[0232]

[0137] Table 4 below reports the measured amount of CO2, expressed in mg of CO2 per gram of sorbent material, absorbed and released by the material when a dry model air gas stream (400 ppm CO2) is flown through the sorbent material. Table 4 also reports the release efficiency, expressed as a percentage, and calculated as the ratio of released carbon dioxide to absorbed carbon dioxide.

[0233] Table 4

[0234] **** substantially complete release

[0235]

[0138] The results of Table 4 show that the sorbents according to the invention are suitable for capturing carbon dioxide from dry air even when they are not hydrated. It is surprising as the presence of water is known in the art to promote the absorption of carbon dioxide by formation of hydrogencarbonate via reaction between a water molecule and a CO2 molecule; said hydrogencarbonate ion being further stabilized via hydrogen bonding by the anion of the ionic liquid.

[0236]

[0139] The sorbent materials according to the invention are thus particularly suitable for producing carbon dioxide by capture for carbon dioxide from air followed by release upon heating at 60 °C. This represents a low energetically demanding process, which can be operated at atmospheric pressure, employing air as CO2 source and promoting the release of carbon dioxide in mild conditions.

[0237] Sorption / Desorption experiments of model flue gas

[0238]

[0140] Table 5 below reports the measured amount of CO2, expressed in mg of CO2 per gram of sorbent material, absorbed and released by the material when a model flue gas stream (15% CO2) having a relative humidity of 5% is flown through the sorbent material. Table 5 also reports the release efficiency, expressed as a percentage, and calculated as the ratio of released carbon dioxide to absorbed carbon dioxide.

[0239] Table 5

[0240] * Relative Humidity of model flue gas: 12%, 15.01% CO2

[0241] ** Relative Humidity of model flue gas: 8%, 15.01% CO2

[0242] *** Relative Humidity of model flue gas: 50%, 15.01% CO2

[0243]

[0141] Table 6 below reports the measured amount of CO2, expressed in mg of CO2 per gram of sorbent material, absorbed and released by the material when a dry model flue gas stream (15% CO2) is flown through the sorbent material. Table 6 also reports the release efficiency, expressed as a percentage, and calculated as the ratio of released carbon dioxide to absorbed carbon dioxide.

[0244] Table 6

Claims

CLAIMS1. Composition comprising:(i) an ionic liquid compound of formula [+XR1R2R3R4]n(Yn') whereinX is P or N;Yn-is an anion selected from the group consisting of a conjugate base of boric acid, dihydrogenborate, hydrogenborate, borate, dihydrogenphosphate, hydrogenphosphate, phosphate, hydrogencarbonate, carbonate, sulfate, silicate, aluminate and an anion of formula_OOC-(L)m-COO' wherein m is 0 or 1 and L is a diradical deriving from the abstraction of a hydrogen atom from a linear or branched (Ci-Ci2)alkyl radical that is optionally substituted at any available position with one or more groups selected from the group consisting of carboxy (-COO') and hydroxyl; each of R1, R2, R3and R4is independently a linear or branched alkyl chain; or, alternatively wherein one of the pairs of R1and R2, R1and R3, R1and R4, R2and R3, R2and R4and R3and R4, form, together with the X atom to which they are attached, a cyclic saturated hydrocarbon group whose ring members consist of a heteroatom that is either nitrogen or phosphorous and from 4 to 12 carbon atoms, said ring members being optionally substituted at any available position with a (Ci-Ce)alkyl groups; and(ii) a porous solid support for supporting said ionic liquid.

2. Composition according to claim 1 wherein Yn' is selected from the group consisting of citrate, oxalate, a conjugate base of boric acid, and hydrogenphosphate; preferably, Yn' is selected from the group consisting of oxalate and a conjugate base of boric acid.

3. Composition according to any of claims 1 to 2 wherein the porous solid support is silica.

4. Composition according to any of claims 1 to 3 wherein the porous solid support has a grain size of between 0.1 to 1 mm; preferably of from 0.25 to 0.50 mm.

5. Composition according to any of claims 1 to 4 wherein the ionic liquid is hydrated.

6. Composition according to any of claims 1 to 5 wherein each of R1, R2and R3is independently a (Ci-Ce)alkyl chain; and R4is a (Ci-Cie)alkyl; preferably, each of R1, R2, R3and R4is independently a (Ci-Ce)alkyl chain.

7. Composition according to any of claims 1 to 6 wherein each of R1, R2, R3and R4is selected from the group consisting of ethyl and butyl.

8. Composition according to any of claims 1 to 7 wherein:- the weight ratio of ionic liquid to solid support is comprised between 2:1 and 1 :2; preferably, it is of about 1 :1 ; and / or- the composition further comprises water in an amount of at least n moles per each mole of anion of formula Yn' in said ionic liquid.

9. Composition according to any of claims 1 to 8 wherein the cation of formula [+XR1R2R3R4] is selected from the group consisting of tetrabutylammonium, tetrabutylphosphonium, triethylbutylammonium and triethylbutylphosphonium.

10. Composition according to any of claims 1 to 11 further comprising hydrogencarbonate and / or carbon dioxide.

11. A process for the preparation of a composition according to any of claims 1 to 10 comprising:(i) contacting an ionic liquid as defined in any of claims 1 to 10 with a porous solid support for supporting said ionic liquid and as defined in any of claims 1 to 10; preferably, said contacting is made by impregnation; and(ii) optionally, contacting the ionic liquid of step (i) or the product of step (i) with a source of water or moisture.

12. A process for the capture of carbon dioxide from a first gaseous stream comprising carbon dioxide, said process comprising flowing said first gaseous stream through a composition according to any of claims 1 to 10, wherein the concentration of carbon dioxide in said first gaseous stream is preferably lower than 1000 ppm; more preferably it is of about 400 ppm.

13. Composition obtainable by the method of claim 12.

14. Process for preparing a second gaseous stream comprising carbon dioxide comprising heating or submitting to vacuum a composition as defined in claim 10 or in claim 13; preferably, wherein the composition is heated at a temperature of between 30 °C and 90 °C; more preferably of about 60 °C.

15. Process according to claim 14 comprising heating or submitting to vacuum a composition as defined in claim 13 whereby the second gaseous stream has a higher carbon dioxide concentration than the first gaseous stream.

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