Adsorbent material

Abstract

An adsorbent material and a process for producing it adapted to capture carbon dioxide directly from a gaseous mixture comprising a carbonaceous substrate with at least one double or triple bond among carbon atoms to which at least one pyrrolidine ring is covalently bound are provided.

Description

[0001] ADSORBENT MATERIAL

[0002] Cross-Reference to Related Applications This Patent Application claims priority from Italian Patent Application No. 102024000029949 filed on December 24, 2024, the entire disclosure of which is incorporated herein by reference.

[0003] Technical Field of the Invention

[0004] The present invention relates to an adsorbent material. Preferably, the present adsorbent material is involved in the extraction of carbon dioxide directly from a gaseous mixture, in particular from atmospheric air.

[0005] The present invention also relates to a process for preparing such adsorbent material and uses thereof.

[0006] State of the Art

[0007] Over the last decades, the continuous increase in energy demand, together with concerns about climate change caused by greenhouse gas emissions, have resulted in increased efforts to promote the development of new energy technologies based on alternative sources on the one hand, and carbon dioxide capture for climate purposes on the other. Therefore, there is a strong interest in developing new adsorbent materials to be used in plats for carbon dioxide capture (Carbon Capture Utilization and Storage, CCUS).

[0008] The CCUS methods include the traditional ones, the exploitation of which is located at carbon dioxide emission points, for example in proximity to the chimneys of a steel plant, and those capturing carbon dioxide directly from the atmosphere (Direct Air Capture, DAC). The latter represent one of the most promising options in the field of engineering solutions for capturing carbon dioxide.In fact, DAC technology has the following advantages: 1 ) its implementation is not necessarily associated with the source of carbon dioxide emissions, thus reducing transport costs from the capture site to the storage or utilization site. In other words, DAC technology can be implemented anywhere, thereby promoting its dissemination;

[0009] 2 ) the captured carbon dioxide can be easily quantified, facilitating the activity of certified bodies for the generation of carbon credits.

[0010] However, compared to traditional CCUS technologies, the DAC method operates on gaseous mixtures in which carbon dioxide is highly diluted. For example, the concentration of carbon dioxide is about 420 ppm (about 0.042%) in atmospheric air. Therefore, in order to achieve significant amounts of captured carbon dioxide, comparable to those obtained by traditional CCUS technologies, the DAC mode must operate on large volumes of gaseous mixtures, for example atmospheric air, and employ highly efficient and selective adsorbent materials.

[0011] Existing DAC technologies are mainly divided into two types based on how carbon dioxide is adsorbed: adsorption via a solid adsorbent or via a liquid absorbent ( for example, via an alkaline solution or by modifying the pH).

[0012] With regard to liquid absorbents, these can be strong bases ( for example, KOH, NaOH, or Ca(OH)2) which form, by binding to carbon dioxide, carbonates or amines ( for example, NH3, ammonium salts) or amino acids.

[0013] Advantageously, liquid absorbents have a well-defined chemistry, they are involved in well-known reactions, and are easily used in industrial plants. However, the release of captured carbon dioxide and the liquid absorbentregeneration require high temperatures (above 900°C) or multi-step processes which employ intermediate substances ( for example, catalysts), with corresponding energy and economic costs.

[0014] It is precisely this limitation that has made solid adsorbents attractive in the field of DAC technologies. In fact, the regeneration of solid adsorbents can take place at lower temperatures (below 200°C), with significant energy and economic savings. For example, such temperatures can also be achieved by using heat as a by-product of industrial processes. In this case, the operational expenditure (OPEX) would be further reduced.

[0015] With regard to solid adsorbents, these can be categorized as physical type (or physiosorbents) and chemical type (or chemisorbents) adsorbents.

[0016] Physical adsorbents comprise highly porous materials which attract gaseous compounds in a poorly selective manner, which bind to their surface through weak interactions, mainly of an electrostatic type. Such adsorbents are easily synthesized, and their regeneration is also simple and inexpensive, since gaseous compounds are bound to the adsorbents by relatively weak forces. However, their capture ability, as well as their selectivity to CO2 / H2O and CO2 / other chemical species present in the gaseous mixture, is low. At the same time, reaction kinetics is also relatively slow.

[0017] Compared to physical type adsorbents, the chemical ones chemically react with gaseous compounds, forming covalent or coordination bonds between the adsorbent or, more specifically, among specific chemical groups present on the adsorbent and capable of selectively binding with some chemical species and gaseous compounds. Many chemical typeadsorbents are composed of a support provided with an adequate surface area ( for example, zeolites, silica, alumina, metal organic frameworks, also known as MOFs) that is functionalized with amines, which react with carbon dioxide by forming carbamates or ammonium salts and hydrogen carbonate, if water is present.

[0018] Advantageously, chemical type adsorbents show excellent selectivity to CO2 / other chemical species present in the gaseous mixture, good selectivity to CO2 / H2O, fast kinetics associated with the formation of chemical bonds, as well as an increase in the ability to capture carbon dioxide. However, even chemical type adsorbents are not free from drawbacks. For example, the regeneration of chemical type adsorbents requires more energy, the bonds involved being stronger than those of physical type adsorbents. Moreover, their synthesis is more complex and their stability is reduced compared to physical type adsorbents and liquid absorbents.

[0019] To date, the most widely spread solid adsorbents are those functionalized with amines, showing the best performance in terms of kinetics, stability, and selectivity.

[0020] Based on the interaction of the amine with the remaining components of the adsorbent, adsorbents are divided into: - Class I adsorbents comprising a support provided with adequate surface area incorporating amines. That is, the amine is not covalently bonded to the support, but it is trapped in the pores of the support and remains anchored thereto through electrostatic type interactions. Such Class I adsorbents can be easily synthesized. However, they exhibit amine leaching problems induced by heating, handling, or lowapplied pressures, limited recyclability, and slower kinetics due to pore saturation.

[0021] - Class II adsorbents, whose support provided with adequate surface area is covalently bonded to the amines. Advantageously, such adsorbents exhibit high stability, fast kinetics, and good recyclability. However, these adsorbents also exhibit issues in terms of reduced ability to capture CO2 compared to Class I adsorbents and more complex and expensive synthesis mechanisms. In this regard, these adsorbents are commonly obtained by silane chemical reactions or by reacting amines with coupling agents.

[0022] - Class III adsorbents consisting of an inorganic support and polyamines, obtained via in situ polymerization of amine-containing monomers.

[0023] These adsorbents exhibit improved stability compared to Class I adsorbents, as well as an improved capture ability compared to Class II adsorbents. However, synthesis mechanisms are very complex and raw materials are expensive.

[0024] In addition to the adsorbent materials described above, another class of materials widely used in the field of carbon dioxide capture are metal-organic frameworks (MOFs). MOFs are highly ordered nanoporous adsorbents obtained by crosslinking metal nodes with organic ligands. By modifying the length of the organic ligand, the channel size in the adsorbent material can be modulated to promote CO2 adsorption. These materials have exceptionally high surface areas, high capture ability, and low regeneration energies. However, they suffer from significant scalability problems (depending on the reagent availability), high manufacturing costs, and stability, chemistry, mechanics and CO2 / H2O selectivity problems. It should be noted that undermedium / high humidity conditions amine-modified MOFs are more chemically stable and selective than non-modified MOFs.

[0025] The recently published life cycle analyses (LCA) have highlighted the importance of developing new adsorbent materials that are more advantageous not only in terms of the operational expenditure (OPEX) of carbon capture technologies, but also in terms of the actual carbon footprint of the technology as a whole.

[0026] In this regard, the article by Leonzio et al. in Applied Sciences, 2022, 12, highlighted that a hypothetical DAC process based on state-of-the-art physiosorbents would still not lead to a carbon-negative process (namely, a process that removes more carbon dioxide than that introduced during the life cycle of the complete DAC process) due to the limited efficiency of these adsorbent materials. Furthermore, in another article (in Sustainable Production and Consumption, 2022, 32, 101-111 ), the same authors compare different CO2 adsorbents (Class II adsorbents based on silica, MOF, and cellulose) and prove that most materials do not exhibit the proper efficiency, cost-effectiveness, scalability, and recyclability to enable the development of a true large-scale carbon negative process.

[0027] With regard to solid type adsorbent material substrates, activated carbons have previously been applied to CO2 capture thanks to their wide surface area and porosity, which promotes the physisorption of the gas, and their cost-effectiveness and recyclability. Compared to other solid adsorbents, they usually exhibit lower selectivity to CO2 and a lack of stability in the presence of humidity. However, as in the examples reported above, surface functionalization of these materials with amines canimprove their selectivity towards CO2 and their stability in the presence of water.

[0028] There is therefore a need to provide an adsorbent material that is free from the drawbacks of the prior art so that this material could be implemented on a large scale, for example, in DAC technology, and thus contribute to its enhancement and dissemination.

[0029] Subject Matter and Summary of the Invention Accordingly, an obj ect of the present invention is to provide an adsorbent material, specifically a Class II chemoadsorbent, for extracting carbon dioxide CO2, which exhibits good selectivity to CO2 and greater chemical stability in the presence of humidity and, at the same time, whose preparation process is simplified and inexpensive in order to ensure large-scale implementation.

[0030] Simultaneously, the material of the present invention shows a CO2 capture ability comparable to, or even higher than, that of known adsorbent materials, while offering improved stability.

[0031] A further obj ect of the present invention is to provide a process for the preparation of the above-mentioned adsorbent material that is cost-effective, easily scalable, environmentally friendly, and compatible with a circular economy.

[0032] Consequently, the present invention relates to an adsorbent material and a process for preparing the same, as defined in independent claims 1 and 7.

[0033] The invention also relates to a system for extracting carbon dioxide where the adsorbent material is comprised, and to a plant comprising said system, as defined in claims 12 and 13, respectively.The invention also relates to the use of the abovementioned adsorbent material within the field of technologies adapted to extract carbon dioxide, preferably in DAC technology, as defined in claim 14.

[0034] Preferred and advantageous features of the invention are the subj ect matter of the dependent claims.

[0035] Briefly, the present adsorbent material comprises a carbonaceous substrate with at least one double or triple bond among carbon atoms, to which at least one pyrrolidine ring, preferably substituted with amine groups, is covalently bonded. Such substrate imparts good thermal conductivity and good mechanical strength to the present adsorbent material, and is cost-effective to produce. At the same time, the high density of substrate functionalization with amine groups leads the present adsorbent material to show good CO2 capture ability.

[0036] Although the present adsorbent material has covalent bonds between the substrate and the amine units adapted to capture CO2, this adsorbent material surprisingly shows good regeneration in kinetic and thermodynamic terms. Therefore, in addition to long-lasting chemical stability, the present adsorbent material exhibits improved kinetics of CO2 adsorption / desorption cycles overall.

[0037] Such results cannot be predicted when taking into account the teachings of the prior art.

[0038] Moreover, the reagents involved in the present process for preparing said adsorbent material are widely available, cost-effective, and have a low environmental impact, making this process easily scalable. Such reagents may also be waste products from previous chemical processes, promoting the sustainability and eco-friendliness of the present process.Brief Description of the Drawings

[0039] Further features, obj ects, and advantages of the invention will be apparent from the following description, which is merely illustrative and not limiting, and supported by the annexed figures, in which:

[0040] - Figure 1 illustrates the percentage weight change (%) as a function of the temperature ( °C) to which the sample was exposed, an indicator of the degradation of the amine groups bound to three adsorbent materials according to the invention;

[0041] Figure 2 illustrates the spectroscopic characterization of two adsorbent materials according to the invention: Figures 2a) and 2b) show the percentage reflectance spectra for two adsorbent materials according to the invention (gray spectrum in Figure 2a) and Figure 2b) ) and supports thereof (black spectrum in Figure 2a) and Figure 2b) ) according to a first spectroscopic technique (KBr-FTIR), while Figure 2c) shows the percentage transmittance spectra for an adsorbent material (black spectrum) and its corresponding support (gray spectrum) according to a further spectroscopic technique (ATR-FTIR);

[0042] Figure 3 illustrates with dotted curves the temperature profile to which the adsorbent materials were subjected in accordance with the invention, while the black curves illustrate the percentage weight change (%) in the adsorbent material attributable to CO2 desorption: Figures 3a), 3b) and 3d) relate to a first adsorbent material according to the present invention synthesized in two different solvents (in Figures 3a) and 3d), the solvent is water; in Figure 3b), the solvent is DMF) and starting from two different three-dimensional structures of the support(in Figures 3a) and 3b), the support is in powder form; in Figure 3d), the support is in the form of a monolith), Figure 3c) relates to a second adsorbent material according to the invention and synthesized in the presence of DMF, and Figure 3e) relates to a third adsorbent material according to the invention;

[0043] - Figure 4 shows several steps, one step of adsorption and two steps of CO2 desorption, for a material according to the invention synthesized in water (short dotted black curve), compared to the support without functionalization (solid gray line), and as a function of temperature ( °C) (long dotted gray curve); and

[0044] - Figure 5 illustrates the relative ability, expressed as average percentage weight loss following CO2 desorption when exposing the pre-activated sample to a temperature of 120°C, to capture CO2 from a gaseous mixture (atmospheric air in this case) for four adsorbent materials according to the invention prepared with water or DMF compared to the substrate not functionalized with amine groups.

[0045] Preferred Embodiments of the Invention An obj ect of the present invention is therefore an adsorbent material having general formula ( I ) comprising a substrate S and at least one pyrrolidine ring bound to the substrate S

[0046]

[0047] In detail, S is a carbonaceous system exhibiting at least one double or triple bond among carbon atoms of the system.

[0048] Benzene rings and aromatic systems ( for example,polystyrene) do not fall within the definition of said substrate S.

[0049] Compared to other known supports that can be functionalized with amines for carbon dioxide capture, said support S based on a carbonaceous system advantageously shows good thermal conductivity.

[0050] At the same time, compared to other supports, said substrate S exhibits good mechanical strength when subjected to mechanical stress and low production costs.

[0051] According to one embodiment, S is activated carbon or carbon black.

[0052] Preferably, carbon black is derived from the incomplete combustion of oil products or plant materials and thus represents a production waste. Therefore, the use of carbon black as a substrate of the adsorbent material according to the invention meets cost-effectiveness and sustainability needs.

[0053] Preferably, the substrate S is in the form of a monolith or other three-dimensional structures ( for example, pellets; honeycomb; coil-wound structures; grid structures, such as carbon lattices and nanotubes; etc. ), showing advantageous performance, mainly when used in DAC technology. Even more preferably, the substrate S is in the form of a monolith.

[0054] At least one double or triple n bond of S participates in a 1, 3-dipolar cycloaddition reaction, described below, which leads to the synthesis of the adsorbent material of the present invention.

[0055] The derivatization degree of the substrate S, namely the number of amine groups bound to the substrate S, determined based on the percentage increase in weight of the post-derivatization sample, is preferably comprised between20% and 45%.

[0056] According to one embodiment of the invention, S has a surface area greater than 100 m2 / g. In accordance with this embodiment, the present adsorbent material is particularly favorable in DAC applications, mainly in terms of greater quantity of insaturations that can be functionalized with amine groups per unit weight and shaping possibilities to reduce pressure drop and improve mass and heat transfer.

[0057] The pyrrolidine ring has the following substituents: - R1is selected from the group consisting of hydrogen, linear or branched C1-C4 alkyl group, linear or branched polyethyleneimine with molecular weight ranging from 103,169 g·mol-1to 232,376 g·mol-1, and -COOR' ester group, wherein R' is a linear or branched C1-C4 alkyl, preferably tert-butyl ester;

[0058] - R2is selected from the group consisting of hydrogen; linear or branched C1-C4 alkyl group; hydroxyl group; primary, secondary, or tertiary amine group; -R3CORz4COH group, wherein R3and R4are a C1-C4 alkyl group, and z is 0 or 1; -MNH2 group, wherein M is a linear or branched C1-C4 alkyl; a -CnH2n-1Onmonosaccharide, with n from 3 to 6, substituted or unsubstituted with an amine; -H2X-1CX(OH)malkyl polyol with x from 1 to 6 and 2<m<2x; nitrile group; - OCyH4y-i group with y from 1 to 4; phenol group, substituted or unsubstituted with -OP, wherein P is a linear or branched C1-C4 alkyl, preferably 2 -methoxyphenol; and combinations thereof;

[0059] - A is a group corresponding to the side chain of an alphaamino acid or an alpha-amino acid derivative.

[0060] Alpha-amino acids mean amino acids in which the carboxyl group and amino group are bound to the same carbon atom,known as alpha carbon. The side chain A is also bound to the alpha carbon. As will be described below, since one of the reagents used for the formation of the pyrrolidine ring when preparing the material of formula ( I ) is an alpha-amino acid, at the end of such reaction, the pyrrolidine ring formed is substituted with the side chain A of the alpha-amino acid, which did not participate in the reaction.

[0061] Preferably, A is a group corresponding to the side chain of the alpha-amino acid selected from the group consisting of L-lysine, D-lysine, racemic mixture thereof, L-glutamic acid, D-glutamic acid, and racemic mixture thereof.

[0062] In a preferred embodiment of the invention, A is the group corresponding to the side chain of L-lysine, D-lysine, and racemic mixture thereof.

[0063] Alpha-amino acid derivative means a chemical compound deriving from the basic structure of an a-amino acid through chemical modifications that may involve the amine group, carboxyl group, side chain A, such as, for example, substitutions, transformations, oxidations, reductions, alkylations, acylations, esterifications, or amidations.

[0064] For example, an alpha-amino acid derivative is the alpha-amino acid ( S ) -5- ( tert-butoxy) -4- ( ( tertbutoxycarbonyl ) amino ) -5-oxopentanoic acid (known by the acronym BOC-GLU-OTBU).

[0065] Preferably, A is selected from the group consisting of primary, secondary, and tertiary amine groups; -QNH2 group, wherein Q is a linear or branched C1-C4 alkyl ( for example, -C4H8NH2 group is the side chain A of lysine); -A1COOH group, wherein A1is a linear or branched C1-C3 alkyl group ( for example, the -C2H4COOH group is the side chain A of glutamic acid or BOC-GLU-OTBU); -A2CONHR5group, wherein A2is a linearor branched C1-C3 alkyl group, and R5is selected from the group consisting of hydrogen, a linear or branched C1-C3 alkyl group and polyethyleneimine with a molecular weight ranging from 103,169 g·mol-1to 232,376 g·mol-1; nucleophilic group, unmodified or modified with one or more amine groups selected from the group consisting of hydroxyl group ( for example, hydroxyl is the side chain A of serine and treonine), thiol group ( for example, the thiol group is the side chain A of cisteine), imidazole group ( for example, the imidazole group is the side chain A of histidine), phenol group ( for example, the phenol group is the side chain A of tirosine); and combinations thereof.

[0066] In other words, the alpha-amino acid can be functionalized on chain A by one or more amine groups. In this case, the adsorbent material advantageously exhibits a greater CO2 capture ability, since more CO2 molecules can bind to more amine groups. Moreover, advantageously, the side chain A comprising a group modified with one or more amine groups, even if not consecutive, increases the ability to capture CO2, thus providing greater nucleophilicity to one or more amino groups.

[0067] According to a second aspect of the present invention, a process for preparing the adsorbent material of general formula ( I ) described above is provided.

[0068] Such process of the invention comprises a step of reacting an alpha-amino acid of general formula ( II )

[0069]

[0070] (ID

[0071] wherein R1and A have the same meanings indicated above and B is a hydrogen atom or a linear or branched C1-C4 alkylgroup, preferably tert-butyl, with an aldehyde of general formula ( III )

[0072]

[0073] wherein R2has the same meanings as above, and with a carbonaceous system with at least a double or triple bond among carbon atoms of said system, except for benzene rings and aromatic systems, wherein the at least a double or triple bond participates in the step of reacting by means of a 1, 3-dipolar cycloaddition, obtaining the adsorbent material of general formula ( I ) by 1, 3-dipolar cycloaddition reaction.

[0074] In other words, substituent B of the alpha-amino acid of general formula ( II ) can make the alpha-amino acid of general formula ( II) an ester. For example, when B is tertbutyl, and thus the OB group is tert-butyl ester, being a protective group, this is detached and replaced by an -H to make it react with the support and aldehyde.

[0075] Preferably, the alpha-amino acid of general formula ( II ) is lysine.

[0076] Preferably, the aldehyde of general formula ( III ) is paraformaldehyde or vanillin.

[0077] In detail, the 1, 3-dipolar cycloaddition reaction, which participates in the step of the present process, involves an intermediate dipole (of formula ( IV), in Scheme I ), obtained preliminarily from the reaction between the alpha-amino acid of formula ( II ) and the aldehyde of formula ( III ). Said intermediate dipole subsequently reacts with the substrate S via the 1, 3-cycloaddition.

[0078] The reactions involved in the step of the present process are illustrated in Scheme 1:Scheme I

[0079] i R1p R; OR1:as H^R2...................... R2X%BR2RN^:

[0080] H OH H A

[0081] R1R1I R?.><.. A R^-N^H Rl, X y / H « R2.

[0082] ( A,?;■'■■ Y ) H A

[0083]

[0084] In a preferred embodiment of the present process, the step of the present process is carried out in the presence of a solvent selected from the group consisting of water, amide solvents, preferably N, N-dimethylformamide (DMF), DMAc, NMP; alcohols, preferably methanol, ethanol, propanol, n-butanol, benzyl alcohol, glycerol; halogenated solvents, preferably dichloromethane, chloroform, 1, 1, 1-trichloroethane; esters, ethers, hydrocarbons, heterocycles. Preferably, for clear environmental, economic, and scalability reasons, the solvent is water.

[0085] Advantageously, the alpha-amino acid and aldehyde participating in this process can be easily functionalized with amine groups (comprising primary, secondary, and / or tertiary amines) so as to increase the CO2 capture ability of the adsorbent material obtained.

[0086] For example, the side chain A of the alpha-amino acid can be easily functionalized by reacting the alpha-amino acid with compounds based on (primary, secondary, and / or tertiary) amine groups with several mechanisms, such as, for example, alkylation, acylation, diazonium salt formation, followed by a subsequent substitution ( for example with chlorine, bromine, iodine, or hydroxyl), or coupling or imineformation. At the same time, the aldehyde can also be selected so as to add additional primary, secondary, and / or tertiary amine groups to the adsorbent material, for example amino sugars, amino alkyl aldehydes ( for example, aminoacetaldehyde).

[0087] Therefore, it appears that both the reagents, such as alpha-amino acids ( for example, lysine), aldehydes ( for example, formaldehyde, paraformaldehyde, and vanillin) and the carbonaceous system ( for example, activated carbon or carbon black), and the solvent ( for example, water) are advantageously very common, abundant, non-toxic, and nonpolluting, making the present process easily scalable from an industrial viewpoint, economically affordable, environmentally friendly, sustainable, and versatile.

[0088] It should be underlined that the use of vanillin as a preferably natural origin aldehyde, further contributes to making the present adsorbent material more sustainable.

[0089] Preferably, the step of the present process is carried out at a temperature ranging from 100 to 160°C, preferably between 130 and 135°C. However, the temperature may also be lower than 100°C by introducing catalysts, for example, but not limited to, Lewis acids ( for example, zinc chloride, aluminum chloride, ferric chloride, bromine trichloride, boron trichloride) or Lewis bases ( for example, metal catalysts).

[0090] Preferably, the step of the present process is carried out at a pressure between ambient pressure and 400, 000 Pa (corresponding to 4 bar). The process can also take place in the presence of an inert gas, for example, nitrogen. In this case, the present process can take place at a pressure higher than 400, 000 Pa. With regard to the pressure at which theprocess takes place, this also depends on the selected solvent.

[0091] Preferably, the process according to the invention takes place over a period ranging from 2 to 24 hours, preferably between 2 and 8 hours. However, depending on the reaction conditions, the process may take longer than 24 hours.

[0092] Preferably, the step of the present process is followed by washing and / or drying cycles of the adsorbent material obtained. A step of freeze-drying the adsorbent material obtained may be necessary for preparations carried out in water as a solvent.

[0093] According to a third aspect of the invention, a system for extracting CO2 is also provided, preferably directly from a gaseous mixture, comprising one or more adsorption filters comprising the adsorbent material described above.

[0094] In one embodiment of the present invention, the system for extracting carbon dioxide may be, for example, the system for extracting carbon dioxide described in patent application IT102024000016588.

[0095] According to a further aspect of the present invention, a system is provided for extracting carbon dioxide directly from a gaseous mixture comprising the aforementioned system for extracting carbon dioxide, in which one or more adsorbent filters comprise the adsorbent material described above.

[0096] In a further embodiment of the present invention, the plant for extracting carbon dioxide may be, for example, the plant for extracting carbon dioxide described in patent application IT102024000019012.

[0097] According to a further aspect of the present invention, the use of the adsorbent material described above is alsoprovided for extracting carbon dioxide from a gaseous mixture, preferably for directly extracting CO2 from a gaseous mixture ( for example, atmospheric air) according to DAC technology, wherein the CO2 concentration is between 300 and 1500 ppm.

[0098] EXAMPLES

[0099] In the following some experimental examples are provided, which describe the preparation and effectiveness of the adsorbent material according to the invention.

[0100] The invention and comparative examples are provided herein for illustrative purposes and are not intended to limit the invention.

[0101] 1. Preparation of an adsorbent material according to the invention in the presence of water

[0102] In a pressure vessel ( for example, a Parr reactor), 1.75 g of lysine (LYS, corresponding to 12 mmol), 300 mg of paraformaldehyde (PFA, corresponding to 10 mmol), and 150 mg of activated carbon (AC) in powder form are mixed in 60 ml of water. The mixture is stirred at 135°C for 2 hours. The suspension is then centrifuged at 8000 rpm for 8 minutes and the supernatant is discarded. Next, two washing and centrifugation cycles are performed ( for example, washing in H2O at 8000 rpm for 8 minutes, repeated twice). The product is then freeze-dried.

[0103] The adsorbent material obtained is a 2— (4— aminobutyl ) pyrrolidine chemically bound to activated carbon, subsequently designated by the abbreviation AC-LYS-PFA-H2O.

[0104] The entire synthesis and washing process can be repeated several times to increase the amount of amine material bound to the olefinic support or with at least an unsaturated bond.

[0105] The derivatization degree of the adsorbent materialobtained after a single synthesis cycle in H2O, expressed as weight increase, is in the range of 20-28%. This data is obtained by thermogravimetric experiments.

[0106] By quadrupling the paraformaldehyde to activated carbon weight ratio, while leaving the molar ratio of lysine to paraformaldehyde unchanged, as well as the process steps, an additional material according to the invention is obtained, designated by the abbreviation AC-LYS-PFA-H2O-4.

[0107] 2. Preparation of an adsorbent material according to the invention in the presence of DMF

[0108] In a 10 ml round-bottom flask, 1, 75 g of lysine (LYS, corresponding to 12 mmol), 300 mg of paraformaldehyde (PFA, corresponding to 10 mmol) and 150 mg of activated carbon (AC) are mixed in 4 ml of DMF. The mixture is sonicated for 15 minutes to facilitate the reagent dispersion. Next, the mixture is stirred at 130°C for 2 hours.

[0109] The suspension is then centrifuged ( 8000 rpm, 8 minutes) and the supernatant is discarded. Several washing and centrifugation cycles are then performed ( for example, washing in H2O at 8000 rpm for 8 minutes, repeated three times; washing in MeOH at 8000 rpm for 8 minutes, repeated three times; washing in DCM at 8000 rpm for 8 minutes, repeated three times). The product is dried in an oven / stove at 80°C for 30 minutes.

[0110] The adsorbent material thus obtained is a 2— (4— aminobutyl ) pyrrolidine chemically bound to activated carbon, subsequently designated by the abbreviation AC-LYS-PFA-DMF.

[0111] By quadrupling the paraformaldehyde to activated carbon molar ratio, while leaving the molar ratio of lysine to paraformaldehyde unchanged, as well as the process steps, an additional material according to the invention is obtained,designated by the abbreviation AC-LYS-PFA-DMF-4.

[0112] The entire synthesis and washing process can be repeated several times to increase the amount of amine material bound to activated carbon.

[0113] The derivatization degree of the adsorbent material AC-LYS-PFA-DMF, obtained after a single synthesis cycle in DMF, expressed as weight increase, is in the range of 18-25%.

[0114] The same procedure is followed in the event carbon black (CB) is the substrate, obtaining the adsorbent material subsequently designated by NB-LYS-PFA-DMF.

[0115] 3. Side chain A functionalization of an alpha-amino acid derivative with amine groups, obtaining a functionalized reagent, and preparation of an adsorbent material with said functionalized reagent.

[0116] The alpha-amino acid derivative, namely BOC-GLU-OTBU, is activated in the presence of N, N' -dichloroisopropylcarbodiimide or l-ethyl-3 (3-dimethylaminopropyl ) carbodiimide.

[0117] The solution is then slowly dripped into a flask containing the solvent ( for example, water) with an excess of amines ( for example, tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), etc. ).

[0118] Once the amide is formed as the reaction product, the BOC-protected amine and the carboxyl group protected in the form of tert-butyl ester are released from the protective groups by adding trifluoroacetic acid (TFA). The functionalized reagent thus obtained is reacted with paraformaldehyde (PFA), activated carbon (AC) in DMF or H2O, according to the process in accordance with the invention and described in Examples 1 and 2, obtaining the adsorbent material of general formula ( la).

[0119]

[0120] Similarly, glutamic acid (GLU), functionalized with tetraethylenepentamine (TEPA) to give GLU: TEPA, reacts with paraformaldehyde (PEA) and activated carbon (AC) in DMF or H20, according to the processes described in Examples 1 and 2. The adsorbent material is thus obtained, designated with AC-GLU: TEPA-PFA-DMF or AC-GLU: TEPA-PFA-H20.

[0121] 4. Preparation of an adsorbent material according to the invention in the presence of DMF and by using vanillin as an aldehyde.

[0122] In a 10 ml round-bottom flask, 1, 75 g of lysine (LYS, corresponding to 12 mmol), 1, 52 g of vanillin (VAN, corresponding to 10 mmol) and 150 mg of activated carbon (AC) are mixed in 4 ml of DMF. The mixture is sonicated for 15 minutes to facilitate the reagent dispersion. Next, the mixture is stirred at 130°C for 2 hours.

[0123] The suspension is then centrifuged ( 8000 rpm, 8 minutes) and the supernatant is discarded. Several washing and centrifugation cycles are then performed ( for example, washing in H2O at 8000 rpm for 8 minutes, repeated three times; washing in MeOH at 8000 rpm for 8 minutes, repeated three times; washing in DCM at 8000 rpm for 8 minutes, repeated three times). The product is dried in an oven / stove at 80°C for 30 minutes.

[0124] The adsorbent material obtained is a 2— (4— aminobutyl ) pyrrolidine chemically bound to activated carbon, subsequently designated by the abbreviation AC -LYS -VAN- DMF, of general formula ( Ila).

[0125]

[0126] ( Ila) The entire synthesis and washing process can be repeated several times to increase the amount of amine material bound to the olefinic support or with at least an unsaturated bond.

[0127] The derivatization degree of the adsorbent material obtained after a single synthesis cycle in DMF, expressed as weight increase, is in the range of 18-25%. This data is obtained by thermogravimetric experiments.

[0128] 5. Characterization of the adsorbent materials in accordance with the invention.

[0129] The adsorbent materials according to the invention, obtained according to the procedures described in Examples 1-4, were thermogravimetrically analyzed by inducing controlled pyrolysis of the samples so as to quantify the loss of amine groups bound to the substrate expressed in terms of percentage weight loss of the adsorbent material as temperature changes.

[0130] Indeed, Figure 1 shows the results of this analysis for the AC-LYS-PFA-DMF-4 material (Figure la) and for the NC-LYS-PFA-DMF material (Figure lb). Both Figure la) and Figure lb) depict the degradation between 150 and 450°C of the amines present on the two materials.For the AC-LYS-PFA-DMF-4 material, a percentage weight loss of amine groups equal to 43.01% is recorded, while for the NC-LYS-PFA-DMF-2 material, a loss of amine groups equal to 33.12% occurs. These percentage values provide an indication of the functionalization degree of the two materials obtained according to the present invention, and they are in line with, if not higher than, the values reported in the literature for 1, 3-dipolar cycloaddition reactions.

[0131] Referring to Figure 1c), this shows the results for the AC-LYS-VAN-DMF material, revealing a percentage weight loss of amine groups equal to 19.45%.

[0132] Some materials according to the invention were also characterized with spectroscopic techniques. Specifically, such characterization occurred by means of two Fourier transform infrared spectroscopy (FT-IR) techniques: according to a first technique, designated as KBr-FTIR, the sample was previously blended with an IR-transparent matrix, such as potassium bromide (KBr), while in a second technique, designated as ATR-FTIR, the sample was kept as such.

[0133] Figures 2a) and 2b) show the results of the KBr-FTIR analysis expressed as percentage reflectance, while Figure 2c) shows the results of the ATR-FTIR analysis as percentage transmittance.

[0134] Furthermore, Figures 2a) and 2c) relate to the AC-LYS-PFA-DMF material, while Figure 2b) relates to the AC-GLU: TEPA-PFA-DMF material. All the spectra of the materials according to the invention are compared with the simple substrate, namely with activated carbon (AC) not bound to any functionalized pyrrolidine ring.

[0135] It should be noted that the characteristic bandattributed to the stretching of the double C=C bond between 1600 and 1680 cm-1is always reduced in the adsorbent materials according to the invention compared to the relative substrates, confirming that the double bonds of the substrate have reacted to form the pyrrolidine ring.

[0136] It should also be noted that the characteristic band attributed to the amine groups at 3000 cm-1, which should be predominant in the materials according to the invention, is obscured by the type of material having a low reflectance. However, a weak signal at this frequency is observed, confirming the presence of amine groups in the adsorbent materials.

[0137] 6. Carbon dioxide capture ability of the adsorbent materials in accordance with the invention

[0138] Figures 3 to 5 show the results of carbon dioxide capture ability by thermogravimetric analysis.

[0139] Indeed, these results show the percentage weight change in the adsorbent material due to carbon dioxide desorption when heat is applied to the adsorbent material. Since a preactivation step of the adsorbent material and subsequent saturation with pure CO2 in the gas phase were carried out, this change is assumed to be associated only with CO2 desorption.

[0140] In detail, Figures 3a), 3b), 3c), and 3d) show the temperature profile (dotted curve) to which the material is subjected. In these characterization tests, desorption is preceded by a pre-activation step at 120°C for 1 hour in an inert atmosphere (N2) and an adsorption step in which a flow of 99% pure CO2 is contacted with the adsorbent material for 1 hour at room temperature (25°C). This is followed by the desorption phase by exposing the sample to a first step oftemperature increase up to 80°C, maintained for 10-20 minutes, and after that a second step of increase in order to reach 120°C, maintained until the weight stabilizes, in the presence of N2. The weight loss induced by desorption and expressed as a weight percentage is represented by the solid black curve. The pressure inside the reactor, where the thermogravimetric analysis takes place, is 1000 mbar.

[0141] Figure 3 a) relates to the AC-LYS-PFA-H2O-4 material and shows an overall percentage weight loss of 9. 61%, while Figure 3b) relates to the AC-LYS-PFA-DMF-4 material and shows an overall loss of 9.41%. It should be noted that CO2 desorption starts at 60-65°C and ends at 120°C.

[0142] Figure 3c) relates to the NC-LYS-PFA-DMF material and shows a total percentage weight loss of 3.08%.

[0143] Figure 3d) refers to the same material as in Figure 3a), namely AC-LYS-PFA-H2O-4, the difference being that the activated carbon-based support is in the three-dimensional form of a monolith. Also in this case, the desorption step takes place in two steps characterized by two temperatures, 80°C and 120°C, and with a pressure of 1000 mbar in the reactor. Moreover, unlike the material in Figure 3a), the desorption step shown in Figure 3d) is preceded by an activation step at 120°C in the presence of N2 for 2 hours, and then a one-hour adsorption step in ambient conditions, with an average temperature of 23.1 °C and in the presence of atmospheric air, with an average CO2 concentration equal to 496 ppm and an average relative humidity equal to 24.7%. Finally, the material is passed through a flow of pure N2 for 2 hours at room temperature so that physisorbed H2O and CO2 molecules are removed, and then desorption is tested in an inert atmosphere inside the reactor. The results in Figure3 d) are intended to simulate the operating conditions for direct air carbon capture applications.

[0144] Figure 3d) depicts an overall weight loss equal to 7.37%, 67% of which corresponds to CO2 desorption and 33% to H2O desorption, and thus a CO2 capture ability of 1.12 mmolg-1. It can be noted that the monolith substrate provides the best trade-off in terms of DAC applications between efficient mass transfer, low pressure drop, and higher thermal conductivity compared to other monoliths ( for example, ceramic monoliths). Furthermore, the activated carbon in the three-dimensional form of a monolith has a thermal conductivity coefficient higher than that of other known monoliths ( for example, ceramic monoliths).

[0145] Referring to Figure 3e), this shows the results for the AC-LYS-VAN-DMF material, where an overall weight loss equal to 3.51% and thus a CO2 capture ability of 0.8 mmolg-1is revealed.

[0146] Table 1 shows the isothermal analysis for the AC-LYS- PFA-H2O-4 material using pure CO2 ( 99.9%) at a temperature of 25°C for the adsorption step.

[0147] Table 1

[0148] Adsorption Adsorbed Adsorbed Adsorption

[0149] Pressure Quantity Quantity Pressure (bar)

[0150] (mmHG) (cm3 / g) (mmol / g) 4, 596 0, 006 49, 92 2, 05 7, 664 0, 010 50, 15 2, 06 13, 223 0, 018 50, 35 2, 07 18, 966 0, 025 50, 60 2, 08 29, 556 0, 039 50, 95 2, 09

[0151]

[0152] 48, 322 0, 064 51, 28 2, 1176, 164 0, 102 51, 55 2, 12 121, 016 0, 161 51, 85 2, 13 193, 140 0, 257 52, 15 2, 14 307, 781 0, 410 52, 51 2, 16 486, 823 0, 649 52, 92 2, 17

[0153]

[0154] 791,133 1,055 53,48 2,20

[0155] Figure 4 shows instead the trend in CO2 loss during multiple adsorption / desorption steps for the AC-LYS-PFA-H2O- 4 material (short dotted black curve) compared to the substrate alone (solid gray curve). Instead, the long gray dotted curve denotes the temperature profile. The analysis starts by activating the AC-LYS-PFA-H2O-4 material at 120°C in the presence of N2 for 30 minutes. The temperature is then returned to 25°C and at this point, the adsorption step starts by introducing pure CO2, resulting in a weight increase of the AC-LYS-PFA-H2O-4 material. After 30 minutes at 25°C, the CO2 flow is stopped and N2 is introduced, followed by a temperature increase to 120°C, which corresponds to the desorption step.

[0156] From the thermogravimetric results, Figure 5 is obtained, showing the relative ability to capture CO2, designated as weight loss resulting from the desorption of the AC-LYS-PFA-H2O / DMF-4, AC-LYS-VAN-H2O / DMF, NC-LYS-PFA- H2O / DMF, AC-GLU: TEPA-PFA-H2O / DMF materials, compared to the non-functionalized substrate, denoted as AC / NC.

[0157] Ultimately, it is understood that further modifications and variations may be made to the process and plant described herein without departing from the scope of the appended claims.

Claims

CLAIMS1. An adsorbent material having general formula ( I ) comprising a substrate S and at least one pyrrolidine ring bound to the substrate SR1whereinS represents a carbonaceous system with at least a double or triple bond among carbon atoms of said system, except for benzene rings and aromatic systems;R1is selected from the group consisting of hydrogen; linear or branched C1-C4 alkyl group; linear or branched polyethyleneimine with molecular weight ranging from 103,169 g·mol-1to 232,376 g·mol-1; and -COOR' ester group, wherein R' is a linear or branched C1-C4 alkyl, preferably tert-butyl ester;R2is selected from the group consisting of hydrogen; linear or branched C1-C3 alkyl group; hydroxyl group; primary, secondary, or tertiary amine group; -R3CORz4COH group, wherein R3and R4are a C1-C4 alkyl group, and z is 0 or 1; -MNH2 group, wherein M is a linear or branched Ci-C4 alkyl; a -CnH2n-1Onmonosaccharide, with n from 3 to 6, substituted or unsubstituted with an amine; -H2x-1Cx(OH)malkyl polyol group with x from 1 to 6 and 2≤m≤2x; nitrile group; -OCyH4y-1group with y from 1 to 4; phenol group, substituted or unsubstituted with -OP, wherein P is a linear or branched C1-C4 alkyl; and combinations thereof; andA is a group corresponding to the side chain of an alphaamino acid or derivative thereof.

2. The adsorbent material according to claim 1, wherein S is activated carbon or carbon black.

3. The adsorbent material according to claim 1 or 2, wherein S is in the form of a monolith.

4. The adsorbent material according to any one of claims 1-3, wherein R2is hydrogen or 2 -methoxyphenol.

5. The adsorbent material according to any one of claims 1-4, wherein A is selected from the group consisting of primary, secondary, and tertiary amine groups; -QNH2 group, wherein Q is a linear or branched Ci-C4 alkyl; a -A1COOH group, wherein A1is a linear or branched C1-C3 alkyl group; -A2CONHR5group, wherein A2is a linear or branched C1-C3 group, and R5is selected from the group consisting of hydrogen, a linear or branched C1-C3 alkyl group and polyethyleneimine with a molecular weight ranging from 103,169 g·mol-1to 232,376 g·mol-1; nucleophilic group, unmodified or modified with one or more amine groups selected from the group consisting of hydroxyl group, thiol group, imidazole group, phenol group; and combinations thereof.

6. The adsorbent material according to any one of claims 1-5, wherein A is the group corresponding to the side chain of L-lysine, D-lysine, and racemic mixture thereof.

7. A process for preparing an adsorbent material having general formula ( I ) according to any one of claims 1-6, comprising the step of reacting an alpha-amino acid of general formula ( II )R\N-( I DwhereinR1is selected from the group consisting of hydrogen, linear or branched C1-C4 alkyl group, linear or branched polyethyleneimine with molecular weight ranging from 103,169 g·mol-1to 232,376 g·mol-1, -COOR' ester group, wherein R' is a linear or branched C1-C4 alkyl, preferably tert-butyl ester;A is a group corresponding to the side chain of an alphaamino acid or derivative thereof; andB is a hydrogen atom or a linear or branched C1-C4 alkyl group, preferably it is tert-butyl,with an aldehyde of general formula ( III )oA( III )whereinR2is selected from the group consisting of hydrogen; linear or branched C1-C3 alkyl group; hydroxyl group; primary, secondary, or tertiary amine group; -R3CORz4COH group, wherein R3and R4are a C1-C4 alkyl group, and z is 0 or 1; -MNH2 group, wherein M is a linear or branched Ci-C4 alkyl; a -CnH2n-1Onmonosaccharide, with n from 3 to 6, substituted or unsubstituted with an amine; -H2X-1CX(OH)malkyl polyol group with x from 1 to 6 and 2<m<2x; nitrile group; -OCyH4y-1group with y from 1 to 4; phenol group, substituted or unsubstituted with -OP, wherein P is a linear or branched C1-C4 alkyl, and combinations thereof; andwith a carbonaceous system with at least a double or triple bond among carbon atoms of said system, except for benzene rings and aromatic systems, wherein the at least a double or triple bond participates in the step of reacting by means of a 1, 3-dipolar cycloaddition for obtaining the adsorbent mat ' '8. The process according to claim 7, wherein the alpha-amino acid of general formula ( II ) is lysine.

9. The process according to claim 7, wherein an aldehyde of general formula ( III ) is paraformaldehyde or vanillin.

10. The process according to one of claims 7-9, wherein the step is conducted in the presence of a solvent selected from the group consisting of water, amide solvents, alcohols, halogenated solvents, esters, ethers, hydrocarbons and heterocycles.

11. The process according to claim 10, wherein the solvent is water or N, N-dimethylformamide.

12. The process according to any one of claims 7-11, wherein the step is conducted at a temperature ranging from 100 to 160°C, preferably between 130 and 135°C.

13. The process according to any one of claims 7-12, wherein the step is conducted in the presence of a catalyst selected from the group consisting of Lewis acids and Lewis bases.

14. A system for extracting carbon dioxide comprising one or more adsorption filters comprising an adsorbent material according to any one of claims 1-6.

15. A plant for extracting carbon dioxide from a gaseous mixture comprising a system for extracting carbon dioxide according to claim 14.

16. A use of the adsorbent material according to any one of claims 1-6 for extracting carbon dioxide from a gaseous mixture.

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