WO2025120033A1

WO2025120033A1 - Sorbent material for co2 capture, uses thereof and methods for making same

Info

Publication number: WO2025120033A1
Application number: PCT/EP2024/084812
Authority: WO
Inventors: Vikram KARVE; Davide Albani; Cornelius GROPP; Tomas AZTIRIA; Stefan Diethelm; Adrian MARBERGER; Gioele MOL; Luca PORCARELLI
Original assignee: Climeworks AG
Current assignee: Climeworks AG
Priority date: 2023-12-07
Filing date: 2024-12-05
Publication date: 2025-06-12
Anticipated expiration: 2026-06-07

Abstract

Method for the preparation of sorbent material (3) for use as adsorbent for carbon dioxide separation from a gas mixture (1), said sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support, wherein said sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, is treated so as to have, after treatment, a total iron, zinc, nickel, manganese and/or chromium content above 100 ppm, as well as corresponding sorbent materials.

Description

TITLE

SORBENT MATERIAL FOR CO₂ CAPTURE, USES THEREOF AND METHODS FOR MAKING SAME

TECHNICAL FIELD

The present invention relates to carbon dioxide capture materials with primary and/or secondary amine carbon dioxide capture moieties with optimum carbon dioxide capture capacity properties, as well as methods for preparing such capture materials, uses of such capture materials and carbon dioxide capture methods involving such materials and renewal processes for such capture materials.

PRIOR ART

According to the OECD report of 2017 [Global Energy & CO₂ Status Report 2017, OECD/IEA March 2018] the yearly emissions of CO₂ to the atmosphere are ca 32.5 Gt (Gigatons, or 3x109 tons). As of February 2020, all but two of the 196 states that in 2016 have negotiated the Paris Agreement within the United Nations Framework Convention on Climate Change (UFCCC) have ratified it. The meaning of this figure is that a consensus is reached regarding the threat of climate change and regarding the need of a global response to keep the rise of global temperature well below 2 degrees Celsius above pre-industrial levels.

The technical and scientific community engaged in the challenge of proposing solutions to meet the target of limiting CO₂ emissions to the atmosphere and to remove greenhouse gases from the atmosphere has envisioned a number of technologies. Flue gas capture, or the capture of CO₂ from point sources, such as specific industrial processes and specific CO₂ emitters, deals with a wide range of relatively high concentrations of CO₂ (3-100 vol %) depending on the process that produces the flue gas. High concentrations make the separation of the CO₂ from other gases thermodynamically more favorable and consequently economically favorable as compared to the separation of CO₂ from sources with lower concentrations, such as ambient air, where the concentration is in the order of 400 ppmv. Nonetheless, the very concept of capturing CO₂ from point sources has strong limitations: it is specifically suitable to target such point sources, but is inherently linked to specific locations where the point sources are located and can at best limit emissions and support reaching carbon neutrality, while as a technical solution it will not be able to contribute to negative emissions (i.e., permanent removal of carbon dioxide from the atmosphere) and to remove emission from the past. In order to achieve negative emissions (i.e., permanent removal carbon dioxide from the atmosphere), the two most notable solutions currently applied, albeit being at an early stage of development, are the capturing of CO2 by means of vegetation (i.e., trees and plants, but not really permanent removal) using natural photosynthesis, and by means of DAC technologies, which is the only really permanent removal.

Forestation has broad resonance with the public opinion. However, the scope and feasibility of re-forestation projects is debated and is likely to be less simple an approach as believed because it requires a large footprint in terms of occupied surface to captured CO2 ratio. On the other hand, DAC has lower land footprint and therefore it does not compete with the production of crops, can permanently remove CO2 from the atmosphere and can be deployed everywhere on the planet.

The above-described strategies to mitigate climate change all have potential and are considered as a potential part of the overall solution. The most likely future scenario is the deployment of a mix of such approaches, after undergoing further development.

Several DAC technologies were described, such as for example, the utilization of alkaline earth oxides to form calcium carbonate as described in US-A-2010034724. Different approaches comprise the utilization of solid CO2 adsorbents, hereafter named sorbents, in the form of packed beds of typically sorbent particles and where CO2 is captured at the gassolid interface. Such sorbents can contain different types of amino functionalization and polymers, such as immobilized aminosilane-based sorbents as reported in US-B-8,834,822, and amine-functionalized cellulose as disclosed in WO-A-2012/168346.

WO-A-2011/049759 describes the utilization of an ion exchange material comprising an aminoalkylated bead polymer for the removal of carbon dioxide from industrial applications. WO-A-2016/037668 describes a sorbent for reversibly adsorbing CO2 from a gas mixture, where the sorbent is composed of a polymeric adsorbent having a primary amino functionality. The materials can be regenerated by applying pressure or humidity swing.

The state-of-the-art technology to capture CO2 from point sources typically uses liquid amines, as for example in industrial scrubbers, where the flue gas flows into a solution of an amine (US-B-9, 186,617). Other technologies are based on the use of solid sorbents in either a pack-bed or a flow-through structure configuration, where the sorbent is made of impregnated or covalently bound amines onto a support.

Amines react with CO2 to form of a carbamate moiety, which in a successive step can be regenerated to the original amine, for example by increasing the temperature of the sorbent bed to ca 100°C and therefore releasing the CO2. An economically viable process for carbon capture implies the ability to perform the cyclic adsorption/desorption of CO2 for hundreds or thousands of cycles over the same sorbent material, where the sorbent shall not undergo significant chemical transformations that impedes its reactivity towards CO2.

US-A-2012076711 discloses a structure containing a sorbent with amine groups that is capable of a reversible adsorption and desorption cycle for capturing CO2 from a gas mixture wherein said structure is composed of fiber filaments wherein the fiber material is carbon and/or polyacrylonitrile.

US-A-2013213229 discloses an acid-gas sorbent comprising an amine-composite. The composite may comprise a first component comprising an amine compound at a concentration of from about 1 wt % to about 75 wt %; a second component comprising a hydrophilic polymer and/or a pre-polymer compound at a concentration of from about 1 wt % to about 30 wt %; and a third component comprising a cross-linking agent, and/or a coupling agent at a concentration of from about 0.01 wt % to about 30 wt %.

US-A-2019143299 discloses a core-shell type amine-based carbon dioxide adsorbent including a chelating agent resistant to oxygen and sulfur dioxide as an adsorbent which includes a chelating agent to inhibit oxidative decomposition of amine and has, as a core, a porous support on which an amine compound is immobilized and has, as a shell, an amine layer resistant to inactivity by sulfur dioxide, and a method of preparing the same. The amine-based carbon dioxide adsorbent including a chelating agent exhibits considerably high oxidation resistance because an added chelate compound functions to directly remove a variety of transition metal impurities catalytically acting on amine oxidation. In addition, the sulfur dioxide-resistant amine layer of the shell selectively adsorbs sulfur dioxide to protect the amine compound of the core and, at the same time, the amine compound of the core selectively adsorbs only carbon dioxide. In addition, sulfur dioxide adsorbed on the shell is readily desorbed therefrom at about 110° C. and thus remarkably improved regeneration stability is obtained during the temperature-swing adsorption (TSA) process containing sulfur dioxide.

According to US-A-2023011904 porous solid amine adsorbents are prepared by bringing into contact a first (e.g., dope) solution, including a water insoluble polymer and a water- soluble amine polymer, with an aqueous solution containing a multifunctional chemical agent. The first solution can be obtained by dissolving the water insoluble polymer and the water-soluble amine polymer in a polar solvent. The adsorbents can be in the form of beads, sheets, fibers, hollow fibers, etc. and can be used in the removal of acid gases, CO2, for instance, from fluid streams.

WO-A-2023172486 discloses metal polymer complexes and metal polymer complexes adapted for capturing carbon dioxide. In accordance with one aspect, provided is a metal polymer complex comprising a polymer comprising at least one monomer having an amine group, the polymer complexed with a transition metal selected from nickel, zinc, copper, and a combination of two or more thereof. According to another aspect, provided is a method for capturing carbon dioxide comprising: providing an inlet gas comprising carbon dioxide and water; producing a carbonate, a bicarbonate, a salt thereof, or a combination thereof to remove carbon dioxide from the inlet gas by contacting the inlet gas with a polymer complex substrate; and removing the carbonate, the bicarbonate, the salt thereof, or the combination thereof from the polymer complex substrate by contacting the polymer complex substrate with a regenerant solution comprising water and at least one of a salt or an acid.

A problem associated with using particles of support material functionalised with primary and/or secondary amines as a packed bed for CO adsorption, is the formation of solid aggregates, also known as caking, in which a smaller or large number of particles adhere to each other, thereby reducing or even preventing airflow through corresponding lumps of particulate material. This can and in fact does lead to a significant reduction of the carbon dioxide capture capacity of corresponding packed beds. Without being bound to any explanation it seems the functionalisation of the particles in particular under the cyclic CO2 capture process seems to contribute significantly to the particles to firmly cling to each other and to form physical and/or chemical adherence mechanisms leading to the corresponding clogging or caking. To address this, WO-A-2024002882 proposes to use, as sorbent material, a packed bed consisting of a mixture of 82 - 98 wt.-% of first particles of support material functionalised with primary and/or secondary amines, or a combination thereof, capable of reversibly binding carbon dioxide, and 2 - 18 wt.-% of second particles of support material which are non-functionalised and/or which are functionalised but where the functionalisation is deactivated, the weight percent of the first and second particles adding up to 100% of the mixture in the packed bed.

SUMMARY OF THE INVENTION

Amino-based sorbents for cyclic continuous carbon dioxide capture from air, in particular amino-based sorbents containing primary and/or secondary amino units, preferably benzylamine units, or combinations thereof, connected for example to styrene divinylbenzene moieties, are known sorbents for carbon capture from the air and from flue gas.

In the past, see WO-A-2023/094386, it was found that the CO2 capture performance (carbon dioxide capture capacity) of these materials can vary, notwithstanding the overall nitrogen content (an indication of the total amino content) is not changing significantly. By carrying out inductively coupled plasma optical emission spectroscopy (hereafter referred as ICP- OES) analysis it was found that the overall metal content correlates with the CO2 capture performance. In that document it was stated that to be especially apt for carbon capture, amino-based sorbents need to have a little as possible impurities that could bind to the amino group and/or block pores that would then reduce the accessibilities of the amino site with consequences on the carbon dioxide capture performance. Therefore, competitive binding to the amino groups competing with the carbon dioxide capture is to be avoided. It was found that the amino moieties provided for carbon dioxide capture can bind to a wide range of metals, and such binding impairs the carbon dioxide capture capacity of the material. Reducing the metal content of the sorbent material according to WO-A- 2023/094386 provides for a simple way to increase the carbon dioxide capture properties of the material. As the amino-based sorbent materials are typically produced using catalysts and involving washing steps, and in the steps apparently a significant number of the surface exposed amino groups are capped by metal ions from the catalysis and/or washing, from starting materials or other synthetic steps. WO-A-2023/094386 thus proposes to increase the purity level of an amino-based sorbent functionalized with primary or secondary amine, or a combination thereof, and relates to methods to remove impurities and reach a purity level acceptable for carbon capture. The proposed methods can be used for preparing sorbent materials for a carbon dioxide capture process but can also be used for refreshing sorbent materials after having been used as carbon dioxide capture materials. It is stated, that the metal content or impurity content of the material not only affects the initial carbon dioxide capture capacity of the material. It also affects the stability of the carbon dioxide capacity after aging, which means over extended time of use. It was reported that material which has been purified and which has a low metal content also shows higher stability of the carbon dioxide capture capacity.

As further background it is noted, that transition metals are known to catalyse oxidation of liquid amines used for carbon dioxide capture from flue gas as e.g. reported by Chi et al. (Ind. Eng. Chem. Res. 2002, 41 , 4178-4186). They observed that Fe(ll) and Fe(lll) species accelerate monoethanolamine oxidation at 50°C because the amount of ammonia evolved increases with the presence of such metals. In this case, the addition of ethylenediaminetetraacetic acid (EDTA) and N,N-bis(2-hydroxyethyl) glycine effectively decreased the rate of oxidation in the presence of iron by 40-50%.

As for additional background, transition metals are also known to catalyse the oxidation of supported amines on silica as reported by K. Min in Nature Communications, 2018, 9(1), 726. The authors used chelators such as EDTA for catalyst poisoning to make sure that Cu and Fe would not catalyse the degrative oxidation mechanism of the capture active amine moieties.

So, the common general knowledge at the moment provides for the firm assumption, that metal content in primary/secondary amine carbon dioxide capture materials is to be avoided, and that in particular iron but also further transition metals have a detrimental effect as concerns stability, since it appears to act like a catalyst in the oxidation of the amine functionality.

It therefore came as a complete surprise to find, that in fact increasing specifically the content in the specific metals as claimed, such as the iron (II) and/or (III) content, in such solid carbon dioxide capture capacity materials leads to an improved stability of the material, i.e. to protection from oxidation.

Another even more unexpected effect that results from increasing specifically the content in the specific metals as claimed is that one observes a very significant reduction in caking of corresponding particulate (bead) material, so impregnating the material with these metals in the claimed amounts leads to much more efficient packed bed structures less prone to caking.

The present invention therefore relates to sorbent materials comprising primary and/or secondary amine moieties immobilized on a solid support, which have an increased iron content, as well as to methods for manufacturing such sorbent materials, methods of use of such sorbent materials, and methods of operating carbon dioxide capture plants with such materials.

Specifically, according to a first aspect of the present invention, it relates to a method for the preparation of sorbent material for use as adsorbent for carbon dioxide separation from a gas mixture, said sorbent material comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support, wherein said sorbent material comprising primary amine or secondary amine moieties, or a combination thereof, or rather a starting sorbent material comprising primary amine or secondary amine moieties, is treated so as to have, after treatment, a total iron content above 100 ppm. The total iron content is measured as described in the specification, using ICP (inductively coupled plasma) measurements. The same or a similar effect can be achieved if instead or at the same time another transition metal, in particular selected from the group consisting of Mn, Zn, Cr, Ni, or a combination thereof, is loaded on the sorbent, in each case preferably in a content above 100 ppm.

Preferably the sorbent material presents a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm or below 3000 ppm, or in each case in the range of 100-3000 ppm, 100-2000 ppm, 100 - 1300 ppm, or in each case in the range of 200-1200 ppm. Preferably only one or two of iron, zinc, nickel, manganese and/or chromium are in such a proportion or range, in particular one of Fe, Mn or Ni. For Zn for certain types of substrates the content thereof is preferably above 2000 ppm.

The ppm values given here for the iron, zinc, nickel, manganese and/or chromium content are in each case given in ppm by weight. The solid support of the sorbent material is preferably a porous or non-porous material based on an organic and/or inorganic material, preferably a (organic) polymer material. A (organic) polymer carrier material is preferably selected from the group of linear or branched, cross-linked or uncross-linked polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate-based polymer including PMMA, polyacrylonitrile or combinations thereof, wherein preferably the polymer material is poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, metal organic frameworks, covalent organic frameworks and combinations thereof.

In another embodiment, a sorbent comprising polyethyleneimine either physically impregnated or chemically bound to the surface of a support, where the support can be but not limited to silica, alumina, zeolites, activated carbons, metal organic framework, covalent organic framework, presents a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, or in each case in the range of 100 - 1300 ppm, or in each case in the range of 200-1200 ppm.

In another embodiment, the iron, zinc, nickel, manganese and/or chromium used for treatment and/or in the sorbent material is in the oxidation state (II) or (III) or a mixture of iron, zinc, nickel, manganese and/or chromium in these oxidation states.

In another embodiment, said treatment is a treatment of sorbent material with a liquid solution or suspension of an iron, zinc, nickel, manganese and/or chromium salt, preferably using spray treatment or immersion.

Preferably the solution or suspension is in water.

Treatment may take place at a pH in the range of 0.5 - 10 or 4-10, preferably in the range of 0.5 to less than 7 (in particular 1-6 or 1-4) or 6-8. Surprisingly, it was found that a treatment in the acidic range, in particular when using iron but also for the other metals except Zn mentioned above, leads to increased stability of the carbon capture properties of the corresponding material. Preferably therefore the treatment takes place at a pH of below 7, preferably in an acidic range in the range of pH equal 0.5-5.5.

As for the treatment with Zn, preferably treatment takes place at a pH above 7, preferably in the range of 8 to less than 11 (in particular 8.5-11 or 9-10). Surprisingly, it was found that a treatment in the basic range is preferable for Zn treatment. Using a Zn treatment outside of these ranges leads to a material which is degrading more quickly.

The pH values given are preferably equilibrium pH values of the treatment. Normally if the metal solution is combined with the sorbent material, the pH will adapt over a certain amount of time to reach a stable value, and the values given here are preferably the values reached in the mixture in that steady state. If for example an acidic metal solution is added to the sorbent material, it will e.g. start off at an initial pH value of 1 , and then level to a final value in the range of 3-4.

Treatment may take place at a temperature in the range of 15-35°C, or in the range of 20- 30°C.

Treatment may take place over a time span in the range of 1-12 hours, or in the range of 2- 4 hours.

Note that the proposed method can be combined with a method for the preparation of sorbent material, wherein before the iron, zinc, nickel, manganese and/or chromium loading the material is treated so as to have, after treatment, a total metal impurity content below 1400 ppm and within these, an iron, zinc, nickel, manganese and/or chromium content in each case below 90 ppm (as e.g. described in WO-A-2023/094386, which is included by reference as concerns this possibility). As pointed out above, pristine amine-based capture materials due to production processes inherently comprise a large number of surface exposed amino moieties which are capped with metal ions, according to our analysis the metal impurity content in the systems is always above or around 1600 ppm. An additional pre-treatment provides for a lower metal impurity content and correspondingly provides for significantly increased carbon dioxide capture capacity, which can then be combined with the iron, zinc, nickel, manganese and/or chromium loading for improved degradation resistance.

When talking about a method for the preparation of sorbent material for use as adsorbent for carbon dioxide separation from a gas mixture, this means a treatment of sorbent material for preparing it and/or for repristinating/refreshing and/or for optimizing it for use as adsorbent for carbon dioxide separation from a gas mixture. The term preparation is thus understood as the physical and/or chemical transformation of the sorbent material to convert it into a sorbent material into one having an iron, zinc, nickel, manganese and/or chromium content as claimed.

The proposed method comprises at least one step of converting it into such an iron, zinc, nickel, manganese and/or chromium loaded sorbent material to make it (more) suitable as an adsorbent for carbon dioxide separation from a gas mixture, this step can be structured and carried out as detailed further below.

The proposed method put differently thus is a method in which a starting sorbent material is treated in an iron, zinc, nickel, manganese and/or chromium loading step (if needed preceded by a purification step as e.g. described in WO-A-2023/094386 followed by selective iron, zinc, nickel, manganese and/or chromium loading) to have, after treatment, the claimed iron, zinc, nickel, manganese and/or chromium content in particular to make it (more) suitable as a sorbent material for use as adsorbent for carbon dioxide separation from a gas mixture.

According to a first preferred embodiment of this first aspect, said sorbent material, after treatment, has a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm or below 3000ppm, or in each case in the range of 100-3000ppm, 100-2000ppm, or in each case in the range of 100 - 1300 ppm, or in each case in the range of 200-1200 ppm. Iron, zinc, nickel, manganese and/or chromium loading the sorbent material to these degrees allows to stabilize the carbon dioxide capture capacity, which is fully unexpected and an extremely significant increase of efficiency of the overall process.

The iron, zinc, nickel, manganese and/or chromium content as defined here is to be considered as the sum of all iron, zinc, nickel, manganese and/or chromium, respectively, in the sorbent material by weight, relative to the total sorbent material weight, and preferably the iron, zinc, nickel, manganese and/or chromium is in the oxidation state (II) or (III) or a mixture of iron, zinc, nickel, manganese and/or chromium in these oxidation states.

The iron, zinc, nickel, manganese and/or chromium content is measured using the following analytical method:

For the quantitative determination inductively coupled plasma optical emission spectrometry (ICP) is used. The measurements were performed using the Spectro Arcos FHM22 ICP-OES instrument (SPECTRO Analytical Instruments GmbH). The sample solution is introduced via a pneumatic atomizer system. At a temperature of 5000-7000 K in the plasma, the elements contained in the solution are atomized and excited to emit light. Since the atoms/ions emit electromagnetic radiation characteristic of the chemical element after excitation, the intensity of the light emitted at specific wavelengths is measured and used to determine the concentration of the element of interest. The concentrations in the sample are calculated using the measured intensities of the individual elements and using the functions of the recorded calibrations of the individual elements.

The calibration of the instrument is done in the following manner:

Merck’s multi-element standard solutions for ICP (MISA-04-1 , MISA-05-1 , MISA-06-1) were used for preparing working standards. Deionized water acidified with HNO3 (Merck) was used as the calibration blank.

The samples are prepared in the following manner:

Sorbent dissolution is achieved by microwave digestion. The sorbent is dried under N2 flow for 1 h at 94°C and then cooled to room temperature. 0.5 g of sample is weighed and placed in a 100 mL sample holder. To the sample, 10 mL of 65% HNO3 and 0.4 mL of 48% HF is added, and then the mixture is left to react for 10 min before the sample holder is closed. The sample holder is then placed in a microwave oven (StarT, MWS GmbH) until the sample has completely dissolved. The following temperature profile is used: heating to 240°C at 3°C/ min, holding for 1 h, followed by cooling down to 50°C before removing the sample from the oven. The sample is then filtered with Whatman 42 (2.5 pm particle retention) filter paper. 2 mL of deionized water is used to wash the inner walls of the beaker to prevent the loss of the sample. Then, deionized water is added to make a final volume up to 50 mL.

The concentration of the iron, zinc, nickel, manganese and/or chromium in the sorbent material is determined in the following manner: The concentrations in the sample are calculated using the measured intensities of the individual elements and using the functions of the recorded calibrations of the individual elements. The iron, zinc, nickel, manganese and/or chromium concentration is expressed as the mean of three measurements. The concentration of the iron, zinc, nickel, manganese and/or chromium is expressed in mg iron, zinc, nickel, manganese and/or chromium per kg sorbent, so in ppm by weight.

According to yet another preferred embodiment, said treatment is with a liquid solution of a sulfate, chloride, nitrate, acetate, oxalate, phosphate, or a combination thereof (including mixed salts), of iron (II) and/or iron (III).

Preferably an aqueous solution of iron (III) nitrate, iron (III) nitrate nonahydrate, iron (III) sulfate, iron (III) sulfate hydrate, iron (III) cloride, iron (III) chloride tetrahydrate, iron (II) nitrate, iron (II) hexa nitrate, iron (II) sulfate, iron (II) sulfate hepta hydrate, iron (II) chloride, iron (II) chloride tetra hydrate, or a combination thereof, or respective systems of zinc, nickel, manganese and/or chromium, is used. Preferably iron, zinc, nickel, manganese and/or chromium are used as nitrates.

The concentration of iron, zinc, nickel, manganese and/or chromium in the liquid solution can be, in each case at least 400 or at least 500 ppm (by weight), preferably in each case at least 700 ppm, or in each case in the range of 400-25'000ppm or 500-10'OOOppm, 700- 5000ppm or 700-2'000 ppm or 800-1'500 ppm.

The sorbent material typically takes the form of sorbent particles, sorbent powder, a porous monolithic structure, or the form of an essentially contiguous adsorbent layer, or a combination thereof.

The amine moieties in the a-carbon position are preferably substituted by two hydrogen substituents or one hydrogen and one alkyl group (preferably having up to ten carbon atoms, preferably selected as methyl or ethyl) which can be linear or branched and can contain further amino moieties in the branching, or two alkyl groups (preferably having up to ten carbon atoms, preferably selected as methyl or ethyl) which can be linear or branched and can contain further amino moieties in the branching , or one hydrogen and an amino group, or one hydrogen and alkyl amino moieties where the alkyl group (up to ten carbon atoms, preferably methyl or ethyl) can be linear or branched and contain further amino moieties in the branching, preferably the sorbent material comprises primary and/or secondary benzylamine moieties. Most preferably the carbon dioxide capture moieties of the sorbent material consist of primary benzylamine moieties.

Also possible are systems, where the sorbent material comprises primary amine moieties as well as in addition at least one of secondary amine moieties and tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene- divinylbenzene support is functionalised by at least one of secondary benzylamine groups, tertiary benzylamine groups, secondary a-methylbenzylamine groups, and tertiary a- methylbenzylamine groups, wherein in each case the secondary or tertiary amine groups are substituted with at least one of ethyleneamine, branched or linear polyethyleneimine, branched or linear propyleneamine, branched or linear polypropyleneimine, branched or linear polyethylenepropyleneimine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine.

Also possible are systems, where the sorbent material comprises: primary amine moieties as well as at least one of secondary amine, and/or ether, amide, and amidine moieties, immobilized on a solid support, wherein they are obtained in that a solid support precursor is provided, having at least one of a primary amine, secondary amine, and alcohol functionality, and wherein this solid support precursor is reacted with at least one reactant selected from the following group:

wherein PG is a protecting group, with the proviso that PG may also be a cyclic group with one branch of the cycle replacing the hydrogen bound to the protected secondary amine moiety of the reactant, X is a leaving group, i is in the range of 0-5, and wherein the resulting material is converted into said sorbent material by removing said protecting group.

Also possible are systems, where the sorbent material is a particulate copolymeric material based on at least one of amino mono allyl and amino mono vinyl monomeric building blocks or precursors thereof copolymerized and cross-linked with divinyl building blocks, wherein the at least one of amino mono allyl and amino mono vinyl monomeric building blocks or precursors thereof are non-aromatic monomeric building blocks with 2 - 4 carbon atoms, and wherein the molar proportion of the divinyl building blocks to the sum of the divinyl building blocks and the at least one of amino mono allyl and amino mono vinyl monomeric building blocks or precursors thereof and, if present, further building blocks, is in the range of 8-30%.

The solid support of the sorbent material can be a porous or non-porous material based on an organic and/or inorganic material, preferably a polymer material. Preferably this is selected from the group of linear or branched, cross-linked or uncross-linked polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate-based polymer including PMMA, polyacrylonitrile or combinations thereof, wherein preferably the polymer material is poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, metal organic frameworks, covalent organic frameworks, and combinations thereof.

Preferably, the sorbent material is based on a polystyrene material, preferably cross-linked polystyrene material and most preferably poly(styrene-co-divinylbenzene), which is at least partially functionalized with (primary or secondary) amino moieties or contains benzylamine moieties, preferably throughout the material or at least or only on its surface. The material or the functionalization can e.g. be obtained by amidomethylation or phthalimide or chloromethylation reaction pathways or a combination thereof.

The primary and/or secondary amine moieties can also be part of a polyethyleneimine structure, preferably obtained using aziridine, which is preferably chemically and/or physically attached to a solid support.

The sorbent material, preferably in porous form, and having specific BET surface area, in the range of 0.5-4000 m²/g or 1-2000, preferably 1-1000 m²/g, preferably takes the form of a monolith, the form of a layer or a plurality of layers, the form of hollow or solid fibres, including in woven or nonwoven (layer) structures, or the form of hollow or solid particles.

The sorbent material according to yet another preferred embodiment takes the form of preferably essentially spherical beads with a particle size (D50) in the range of 0.002 - 4 mm, 0.005 - 2 mm, 0.002 - 1.5 mm, 0.005 - 1.6 mm or 0.01-1.5 mm, preferably in the range of 0.30-1.25 mm.

According to a second aspect of the present invention, it relates to a method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using such a sorbent material adsorbing said gaseous carbon dioxide in a unit.

The method comprises at least the following sequential and in this sequence repeating steps (a) - (e):

(a) contacting said gas mixture with the sorbent material to allow at least said gaseous carbon dioxide to adsorb on the sorbent material by flow-through through said unit under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step (if ambient atmospheric air is pushed through the device using a ventilator for the like, this is still considered ambient atmospheric pressure conditions in line with this application, even if the air which is pushed through the reactor by the ventilator has a pressure slightly above the surrounding ambient atmospheric pressure, and the pressures to is in the ranges as detailed above in the definition of "ambient atmospheric pressures") ;

(b) isolating said sorbent material with adsorbed carbon dioxide in said unit from said flow- through, preferably while maintaining the temperature in the sorbent;

(c) inducing an increase of the temperature of the sorbent material, preferably to a temperature between 60 and 110°C, starting the desorption of CO2 (this is e.g. possible by heat exchangers or by injecting a stream of saturated or superheated steam by flow-through through the unit and thereby inducing an increase of the temperature of the sorbent material to a temperature between 60 and 110°C, starting the desorption of CO2);

(d) extracting at least the desorbed gaseous carbon dioxide from the unit and preferably separating gaseous carbon dioxide from steam, preferably by condensation, in or downstream of the unit;

(e) bringing the sorbent material to ambient atmospheric temperature conditions (if the sorbent material is not cooled in this step down to exactly the surrounding ambient atmospheric temperature conditions, this is still considered to be according to this step, preferably the ambient atmospheric temperature established in this step (e) is in the range of the surrounding ambient atmospheric temperature +25°C, preferably +10°C or +5°C). According to the invention, the sorbent material regenerated for use or used in such a repeating cycle comprises primary and/or secondary amine moieties immobilized on a solid support. Specifically, a sorbent material comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support, is used as adsorbent for carbon dioxide separation from a gas mixture, which sorbent material has a total iron, zinc, nickel, manganese and/or chromium content in each case above 100 ppm, preferably a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, or in each case in the range of 100 - 1300 ppm, or in each case in the range of 200-1200 ppm, preferably prepared in a method as described above before being used as adsorbent for carbon dioxide separation from a gas mixture. Preferably the sorbent material presents a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm or below 3000 ppm, or in each case in the range of 100-3000 ppm, 100-2000 ppm, 100 - 1300 ppm, or in each case in the range of 200-1200 ppm.

In the context of this disclosure, the expressions “ambient atmospheric pressure” and “ambient atmospheric temperature” refer to the pressure and temperature conditions to that a plant that is operated outdoors is exposed to, i.e. typically ambient atmospheric pressure stands for pressures in the range of 0.8 to 1.1 barabs and typically ambient atmospheric temperature refers to temperatures in the range of -40 to 60° C, more typically -30 to 45°C. The gas mixture used as input for the process is preferably ambient atmospheric air, i.e. air at ambient atmospheric pressure and at ambient atmospheric temperature, which normally implies a CO2 concentration in the range of 0.03-0.06% by volume. However, also air with lower or higher CO2 concentration can be used as input for the process, e.g. with a concentration of 0.1-0.5% by volume, so generally speaking, preferably the input CO2 concentration of the input gas mixture is in the range of 0.01-0.5% by volume. However, also flue gas can be the source, in this case the input CO2 concentration of the input gas mixture is typically in the range of up to 20% or up to 12% by volume, preferably in the range of 1-20% or 1 - 12% by volume.

In the above carbon dioxide capture method step sequence (a)-(e), in steps (a) and (e) reference is made to ambient atmospheric pressure conditions and ambient atmospheric temperature conditions. This only applies if the supplied gas mixture is provided under these conditions, for example in case of direct air capture, where the source of the gas mixture is atmospheric air. If, however the source of gas mixture is a different source, it may well be that the supply conditions are not ambient atmospheric pressure and/or are not ambient atmospheric temperature conditions. In particular, in case of flue gas the gas mixture can be and normally will be at an elevated temperature, for example at a temperature above room temperature, it may even be at a temperature above 50°C. The temperature may even go up to 70°C, and in that case normally the setup is adapted such that the temperature to desorb the carbon dioxide in step (c) is at least 10°C, preferably at least 20°C higher than that temperature of the supply gas. So, under these non-atmospheric temperature and pressure conditions in step (a) and in step (e) normally the pressure and temperature conditions are different, specifically contacting in step (a) takes place under temperature and pressure conditions of the supplied gas mixture, and in step (e) the sorbent is brought to the temperature and pressure conditions of the supplied gas mixture.

According to the second aspect of the invention, in such a process either material prepared as described above is used as the sorbent material, or, after having repeated said sequence of steps (a)-(e) a number of times having led to deterioration of the sorbent material in the form of a reduced carbon dioxide capture capacity, the sorbent material is treated so as to have, after treatment, a total iron, zinc, nickel, manganese and/or chromium content in each case above 100 ppm, preferably above 200 ppm, or in each case in the range of 100 - 1300 ppm, or in the range of 200-1200 ppm, preferably using a method as described above. Preferably, the sorbent material presents a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm or below 3000 ppm, or in each case in the range of 100-3000 ppm, 100-2000 ppm, 100 - 1300 ppm, or in each case in the range of 200-1200 ppm.

Said unit is preferably evacuable to a vacuum pressure of 400 mbar(abs) or less, and step (b) may include isolating said sorbent with adsorbed carbon dioxide in said unit from said flow-through while maintaining the temperature in the sorbent and then evacuating said unit to a pressure in the range of 20-400 mbar(abs), wherein in step (c) injecting a stream of saturated or superheated steam is also inducing an increase in internal pressure of the reactor unit, and wherein step (e) includes bringing the sorbent material to ambient atmospheric pressure conditions and ambient atmospheric temperature conditions.

Preferably, after step (d) and before step (e) the following step is carried out:

(d1) ceasing the injection and, if used, circulation of steam, and evacuation of the unit to pressure values between 20 - 500 mbar(abs), preferably in the range of 50-250 mbar(abs) in the unit, thereby causing evaporation of water from the sorbent and both drying and cooling the sorbent.

Step (e) is preferably carried out exclusively by contacting said ambient atmospheric air with the sorbent material under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions to evaporate and carry away water in the unit and to bring the sorbent material to ambient atmospheric temperature conditions.

After step (b) and before step (c) the following step can be carried out:

(b1) flushing the unit of non-condensable gases by a stream of non-condensable steam while essentially holding the pressure of step (b), preferably holding the pressure of step (b) in a window of ± 50 mbar, preferably in a window of ± 20 mbar and/or holding the temperature below 75°C or 70°C or below 60°C, preferably below 50°C.

In a further embodiment of the step b1 , the temperature of the adsorber structure rises from the conditions of step (a) to 80-110°C preferably in the range of 95-105°C.

In step (b1) the unit can preferably be flushed with saturated steam or steam overheated by at most 20°C in a ratio of 1 kg/h to 10 kg/h of steam per liter volume of the adsorber structure, while remaining at the pressure of step (b1), to purge the reactor of remaining gas mixture/ambient air. The purpose of removing this portion of ambient air is to improve the purity of the captured CO2.

In step (c), steam can be injected in the form of steam introduced by way of a corresponding inlet of said unit, and steam can be (partly or completely) recirculated from an outlet of said unit to said inlet, preferably involving reheating of recirculated steam, or by the re-use of steam from a different reactor. It should be noted that heating for desorption according to this process in step (c) is preferably only affected by this steam injection and there is no additional external or internal heating e.g. by way of tubing with a heat fluid.

In step (c) furthermore preferably the sorbent can be heated to a temperature in the range of 80-110°C or 80-100°C, preferably to a temperature in the range of 85-98°C.

According to yet another preferred embodiment, in step (c) the pressure in the unit is in the range of 700-950 mbar(abs), preferably in the range of 750-900 mbar(abs).

According to a first preferred embodiment of the second aspect of the invention, treatment to increase the total iron, zinc, nickel, manganese and/or chromium content is carried out in situ in the device for separating gaseous carbon dioxide from a gas mixture, preferably by wash or spraying or a combination thereof. In fact, it can be carried out in situ using any of the schemes as described in the context of the above method for preparing sorbent material for use as adsorbent for carbon dioxide separation from a gas mixture.

Alternatively, the second aspect of the invention can be implemented in that the treatment is carried out by taking the sorbent material out of the device for separating gaseous carbon dioxide from a gas mixture, the sorbent material is treated to increase the iron, zinc, nickel, manganese and/or chromium content, and then reintroduced into the device for separating gaseous carbon dioxide to continue the separation process.

According to a third aspect of the present invention it relates to a use of a material produced as described above for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material adsorbing said gaseous carbon dioxide in a unit.

According to a fourth aspect of the present invention, it relates to a sorbent material for use as adsorbent for carbon dioxide separation from a gas mixture, which has a total iron, zinc, nickel, manganese and/or chromium content in each case above 100 ppm, preferably above 200 ppm, or in each case in the range of 100 - 1300 ppm, or in the range of 200-1200 ppm, in particular one prepared using a method as described above. Preferably, the sorbent material presents a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm or below 3000 ppm, or in each case in the range of 100-3000 ppm, 100-2000 ppm, 100 - 1300 ppm, or in each case in the range of 200-1200 ppm.

The sorbent preferably is one comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support.

The present invention according to a fifth aspect, and this also independent of the above- mentioned metal impregnation, so generally in relation with sorbent material comprising primary amine or secondary amine moieties or a combination thereof, immobilised on a solid support, relates also to a method of washing such sorbents in particular after their production. Washing processes applied to sorbents as such are known in the state of art to be applied for cleaning a batch of such sorbents from any remaining parts or substances of the production process. The influence of the washing process after production on the degradation behavior of carbon capture capacity of the sorbents was studied and uncovered unexpected effects. The washing process can be realized by placing e.g. 100 g of sorbent beads in e.g. a 1 L flask equipped with overhead stirrer and condenser. In a first stage, e.g. 700 g water can be added to the beads, and the suspension can be allowed to stir for a specific duration at a constant temperature. After the stirring process, the beads can be filtered and washed with e.g. two 200 mL portions of water and subsequently dried. The washing can be carried out for a stirring or flow through process duration between 2 to 24 hours. The temperature for the stirring or flow through process can be chosen to be in the range of 10°C to 90°C wherein preferably the temperature is kept constant throughout the stirring/flow through process. In a comparative stage, surfactants were added to the water which again was added to the beads. The surfactants added to the water can be found in the table in Fig. 11 . The performance of the sorbent is defined by the degradation behavior of its carbon capture capacity. The degradation behavior of the sorbents coming out of the washing process were tested in a degradation test. The procedure of the degradation test is described below.

Surprisingly, a beneficial behavior for the carbon capture capacity degradation of the sorbents is reached only by using water without surfactants in the washing process. This effect was achieved already starting by a washing process with a duration of 2 hours or more at a temperature of at least 10°C.

The sorbent material for the washing may take the form of sorbent particles, sorbent powder, a porous monolithic structure, or the form of an essentially contiguous adsorbent layer, or a combination thereof.

The amine moieties in the a-carbon position of the material to be washed can be substituted by hydrogen and/or alkyl, preferably by one methyl and one hydrogen substituent or by two hydrogen substituents, wherein preferably the sorbent material comprises primary and/or secondary benzylamine moieties, wherein most preferably the carbon dioxide capture moieties of the sorbent material consist of primary benzylamine moieties.

The solid support of the sorbent material to be washed can be a porous or non-porous material based on an organic and/or inorganic material, preferably a polymer material, preferably selected from the group of linear or branched, cross-linked or uncross-linked polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate-based polymer including PMMA, polyacrylonitrile or combinations thereof, wherein preferably the polymer material is poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, metal organic frameworks, covalent organic frameworks, and combinations thereof. Preferably the sorbent material for the washing is based on a polystyrene material, preferably cross-linked polystyrene material and most preferably poly(styrene-co-divinylbenzene), which is at least partially functionalized with amino moieties or contains benzylamine moieties, preferably throughout the material or at least or only on its surface, wherein preferably the material or the functionalization is obtained by amidomethylation or phthalimide or chloromethylation reaction pathways or a combination thereof.

The primary and/or secondary amine moieties of the washed sorbent can be part of a polyethyleneimine structure, preferably obtained using aziridine, which is preferably chemically and/or physically attached to a solid support.

The sorbent material, preferably in porous form, before and/or after the washing has preferably a specific BET surface area, in the range of 0.5-4000 m2/g or 1-2000, preferably 1-1000 m2/g, may take the form of a monolith, the form of a layer or a plurality of layers, the form of hollow or solid fibres, including in woven or nonwoven (layer) structures, or the form of hollow or solid particles.

The sorbent material may take the form of preferably essentially spherical beads with a particle size (D50) in the range of 0.002 - 4 mm, 0.005 - 2 mm, 0.002 - 1.5 mm, 0.005 - 1.6 mm or 0.01-1.5 mm, preferably in the range of 0.30-1.25 mm.

Further embodiments of the invention are laid down in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings,

Fig. 1 shows the normalized CO2 capture capacity of the resins as a function of time of aging; improved resistance to degradation for the samples containing iron (III) salts (Diamonds: Sorbent A + Fe (III) nitrate; Triangles: Sorbent A + Fe (III); sulphate; Circles: Sorbent A + Fe (III) chloride) and an iron (II) salt (Stars: Sorbent A + Fe (II) sulphate) as compared to the non-iron loaded resin beads (Squares: Sorbent A); conditions: 02 containing gas at 100% RH;

Fig. 2 shows the improved resistance to degradation for the samples containing iron (III) nitrate salt (Diamonds: Sorbent A + Fe (III) nitrate), samples washed with DI water (Triangles: Sorbent A + water wash) and sodium nitrate (Circles: Sorbent A + Na nitrate) as compared to the non-iron loaded resin beads (Squares: Sorbent A); as is evident, the iron salts lead to improved degradation performance as compared to the others.

Fig. 3 shows the rig measuring the CO2 capture capacity;

Fig. 4 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure in accelerated oxidative degradation conditions for sorbent B experiments;

Fig. 5 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure in accelerated oxidative degradation conditions for sorbent for Sorbent C experiments;

Fig. 6 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure in accelerated oxidative degradation conditions for sorbent for Sorbent D experiments;

Fig. 7 shows normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure in accelerated oxidative degradation conditions at 100 % RH for Sorbent A with different metal ions;

Fig. 8 shows normalized equilibrium CO2 adsorption capacity measured after variable time of exposure in accelerated oxidative degradation conditions for Sorbent A with different metal ions;

Fig. 9 shows normalized equilibrium CO2 adsorption capacity measured after variable time of exposure with 0 % RH for Sorbent A with different metal ions;

Fig. 10 shows the results of cake compression tests for the two samples given;

Fig. 11 shows the relative results of the degradation behaviour between various washing agent mixtures used in the washing process.

DESCRIPTION OF PREFERRED EMBODIMENTS

In the following working examples, cross-linked polystyrene beads (essentially spherical beads with a particle size (D50) in the range of 0.30-1.2 mm) functionalized with benzylamine units were used.

Synthesis of Sorbent A

A glass reactor is charged with 300 mL of water, 1g of gelatin and 2g of sodium chloride and the solids are dissolved at 45°C for 1h. In another flask, 1 g of benzoyl peroxide is dissolved in a mixture of 54 g of styrene, 5g of divinylbenzene (80% purity, 68 g of heptane and 22 g of toluene. The resulting mixture is then added to the reactor. After that the reaction mixture is stirred and heated up to 70°C maintaining the temperature for 2 h, then the temperature is raised to 80°C and kept it for 16 h. The temperature is then raised to 100°C for 3 h to distill out the organic solvents. The reaction mixture is cooled down to room temperature and the beads are filtered off using a funnel glass filter and vacuum suction. The beads are dried in rotavapor.

The polystyrene-divinylbenzene beads are functionalised using the chloromethylation reaction. 5 g of so obtained beads are added to a 3-neck flask containing 30 mL of chloromethyl methyl ether. 3.5 g of zinc chloride is added to the mixture over 2 h and heated for an additional 4 h to 60°C. After that, the mixture is cooled to room temperature and 25% HCI in water is added to quench chloromethyl methyl ether. The chloromethylated beads are washed until neutral with water, filtered off, and dried.

To afford the benzylamine: the chloromethyl-functionalized polystyrene-divinylbenzene beads are aminated using the benzylamine-amination reaction:

The chloromethylated beads are added to a three-necked flask with 27 g of methylal and the mixture is stirred for 1 h at 25°C (room temperature). To this mixture, 9 g of hexamethylenetetramine and 12 g of water are added and kept under gentle reflux for 6 h. The beads are filtered off and washed with water. To have a primary amine, a hydrolysis step followed by a treatment with a base are required. The beads are placed in a 3-neck flask containing 140 mL of a solution of hydrochloric acid (30%) - ethanol (95%) (volume ratio of 1 :3), the reaction mixture is heated to 80°C and kept at this temperature for 20 h. After that, the beads are filtered off and washed with water. At this stage the amine is protonated and to free the base, the beads are treated with 50 mL of an NaOH solution 2 M, and stirred for 1 h at 50°C. The aminated beads are filter off and washed to neutral pH with demineralized water.

The resultant particles had an average particle size of 500 urn and an average pore diameter in the range of 50-300nm. These values remained unchanged by the Fe treatment in the examples according to the invention.

The resulting Sorbent A, after further washing, was analyzed using ICP and was shown to have the following levels of elemental contents in ppm (mg/kg): Ag<1 ; Al = 50; As<1 ;Ba<1 ;Be<1 ;Bi<5;Ca = 460; Cd<1 ; Co<1 ; Cr<1 ; Cu<2; Fe=11 ; Ga<3; Ge<7; Hf<3; ln<8; K< 10; Li<10; Mg=48; Mn=2; Mo<2; Na=290; Nb<4; Ni<1 ; P=10; Pb<2; Re<1 ; S=1500; Sb<2; Sn<2; Se<5; Sr=2; Ta<3; Ti=1 ; TK15; V<2; Zn<1 ; Zr<1.

Synthesis of Sorbent B

In a 1 L reactor, 1% (mass ratio) of gelatin and 2% (mass ratio) of sodium chloride are dissolved in 340 mL of water at 45°C for 1h. In another flask, 1 g of benzoyl peroxide is dissolved in a mixture of 59.7 g of styrene, 3.9 g of divinylbenzene (content 80%) and 65.3 g of C11-C13 iso-paraffin. The resulting mixture is then added to the reactor. After that the reaction mixture is stirred and heated up to 70°C maintaining the temperature for 2 h, then the temperature is raised to 80°C and kept it for 3 h, and then raised to 90°C for 6 h. The reaction mixture is cooled down to room temperature and the beads are filtered off using a funnel glass filter and vacuum suction. The beads are washed with toluene and dried in rotavapor.

The polystyrene-divinylbenzene beads are functionalized using the chloromethylation reaction. 5 g of so obtained beads are added to a 3-neck flask containing 50 mL of chloromethyl methyl ether. The mixture is stirred for 1 h, 2 g of zinc chloride is added and is heated to 40°C and kept it for 24 h. After that, the beads are filtered off and wash with 25% HCI and water to obtain chloromethylated beads. To obtain benzylamine units, the chloromethylated beads are aminated using the following procedure. The chloromethylated beads are added to a three-necked flask with 27 g of methylal and the mixture is stirred for 1 h. To this mixture, 16 g of hexamethylenetetramine and 13 g of water are added and kept under gentle reflux for 24 h. The beads are filtered off and washed with water. To have a primary amine, a hydrolysis step followed by a treatment with a bases are required. The beads are placed in a 3-neck flask containing 140 mL of a solution of hydrochloric acid (30%) - ethanol (95%) (volume ratio of 1 :3), the reaction mixture is heated to 80°C and kept at this temperature for 20 h. After that, the beads are filtered off and washed with water. At this stage the amine is protonated and to free the base, the beads are treated with 50 mL of an NaOH solution 2 M, and stirred with 1 h at 80°C. The aminated beads are filter off and washed to neutral pH with demineralized water.

Synthesis of Sorbent C

Sorbent C was made according to PCT/EP 2024/068540, which for this sorbent and the method of making is included into the specification, and which was made as follows:

10 gdry of Sorbent A beads were suspended in 60 g of water. 15 g of a 30wt% aqueous NaOH solution was added, and the mixture was stirred at ambient temperature for 30 min. To this mixture was added a premixed solution of 10 g 3-chloropropylamine hydrochloride in 25 g water. The mixture is heated to 65 °C and stirred for 6 hours. The solvent was decanted off, and the beads were washed with 100 g of water, 100 g 1 M NaOH and again with water until neutral pH.

Synthesis of Sorbent D

Sorbent D was made according to PCT/EP 2024/068540, which for this sorbent and the method of making is included into the specification, and which was made as follows: 10 gdry of Sorbent B beads were suspended in 60 g of water. 15 g of a 30wt% aqueous NaOH solution was added, and the mixture was stirred at ambient temperature for 30 min. To this mixture was added a premixed solution of 10 g 3-chloropropylamine hydrochloride in 25 g water. The mixture is heated to 65 °C and stirred for 6 hours. The solvent was decanted off, and the beads were washed with 100 g of water, 100 g 1 M NaOH and again with water until neutral pH.

Synthesis of iron-loaded Sorbents:

Example Sorbent A + FefNCh

In a 1 L beaker, 500 g of DI water and 500 mg of iron (III) nitrate nonahydrate (Fe(NOa)3 ■ 9H2O) were mixed till full dissolution of the iron salt. The nominal concentration of iron in this solution is 1000 ppm iron (III) nitrate nonahydrate per weight of solvent. Next, 40 gdry of Sorbent Awas added to the iron nitrate solution. The mixture was stirred using a magnetic stirring plate at room temperature (20-30°C) for 3 hours. The pH of this mixture was in the range of 8 (steady-state value). After 3 hours, the beads were separated from the solution by vacuum filtration and washed with 100 g of water. The resin beads were then air dried at room temperature. Alternatively, the resin beads were dried under vacuum at 50°C.

The final concentration of iron in the beads measured by ICP was around 250 ppm Fe per weight dry sorbent.

Example Sorbent A + Fe^SC

In a 1 L beaker, 500 g of DI water and 500 mg of iron (III) sulfate hydrate (Fe2(SC>4)3 ■ H2O) were mixed till full dissolution of the iron salt. The nominal concentration of iron in this solution is 1000 ppm iron (III) sulfate hydrate per weight of solvent. Next, 40 gdry of Sorbent A was added to the iron sulfate solution. The mixture was stirred using a magnetic stirring plate at room temperature (20-30°C) for 3 hours. The pH of this mixture was in the range of 8 (steady-state value). After 3 hours, the resin beads were separated from the solution by vacuum filtration and washed with 100 g of water. The resin beads were then air dried at room temperature. Alternatively, the resin beads were dried under vacuum at 50°C.

The final concentration of iron in the beads measured by ICP was around 1000 ppm Fe per weight dry sorbent.

Similar procedures as outlined above were used for different iron containing salts. In particular, the method was applied also using iron (III) sulfate heptahydrate, iron (III) chloride, iron (II) sulfate heptahydrate. Example Sorbent A + water wash

A 1 L beaker is charged with 500 g of DI water and 40 gdry of Sorbent A. The mixture was stirred using a magnetic stirring plate at room temperature (20-30°C) for 3 hours. The pH of this mixture was 8 (steady-state value).

After 3 hours, the resin beads were separated from the solution by vacuum filtration and washed with 100 g of water. The resin beads were then air dried at room temperature. Alternatively, the resin beads were dried under vacuum at 50°C.

After water wash the concentration of iron in Sorbent A + water wash measured by ICP was around 50 ppm Fe per weight dry sorbent.

Examples Sorbent A + other metal salts

40 gdry (ca. 70 % SC) sorbent A was added to a mixture of 500 mg of Zinc nitrate hexahydrate (Zn(NOa)2 6H2O, Sigma-Aldrich, 98%), or Nickel(ll) nitrate hexahydrate (Ni(NOa)2 ■ 6H2O, Sigma-Aldrich, >97%), or Copper(ll) nitrate trihydrate (Cu(NOa)2 ■ 3H2O, Sigma-Aldrich, 98.0-103%), or Manganese(ll) nitrate tetrahydrate (Mn(NC>3)2 ■ 4H2O, Sigma-Aldrich, >97%), or Chromium(lll) nitrate nonahydrate (Cr(NO3)3'9H2O, Sigma- Aldrich, 99%) in 500 g of water, which yields a nominal salt concentration in each case of 1000 ppm metal salt per solvent weight.

The suspension was stirred at ambient temperature for 3 hours (the pH of the mixture was 8-9 (steady-state value)) and then filtered to isolate the solids. Subsequently, the solids were dried to a solid content of around 80% to yield the final material.

To vary the loading of metal within the sorbent, the concentration of amount of the metal salt was simply changed to the desired value, by keeping constant the amount of solvent at 500 g of water. Therefore, to prepare a nominal salt concentration of 100 ppm and 500 ppm, 50 mg and 250 mg of salt were used, respectively.

Background art information:

As for the materials disclosed in WO-A-2023/094386, these are characterized as follows: The Fe content of the samples reported there is 77 ppm and drops to 54 ppm after 3x acid base wash, 44 ppm after EDTA wash, 31 ppm after eluotropic row, 49 ppm after acid base wash. Zn, Ni, Mn and Cr contents of the materials are in each case in the range below 70 ppm. Zn and Ni are below 2 ppm for samples after 3x acid base wash, after EDTA and after eluotropic row. Cr is below 3 ppm for samples after 3x acid base wash, after EDTA and after eluotropic row. Mn is below 1 ppm for samples after 3x acid base wash, after EDTA, after eluotropic row and acid base wash. Example Sorbent B + Fe:

40 gdry (ca. 90% SC) of sorbent B was suspended in 100 g water and stirred for 18 hours (suspension A). In a separate container 80 g water was mixed with 1.29 g iron (III) nitrate nonahydrate (solution B). This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 8.5 (steady-state value).

The solvent was decanted off, and the sorbent was washed with 200 g of water.

The sorbent was suspended in 200 g 1M aq. NaOH and stirred for 1 hour at ambient temperature. The solution was removed, and the sorbent was washed with water until a neutral pH was reached and dried under vacuum at 50 °C.

Example Sorbent B + Fe + HCI:

40 gdry of wet (ca. 90% SC) sorbent B was suspended in 100 g water and stirred for 18 hours (suspension A). 20.8 mL HCI (25% in water) was added. In a separate container 80 g water was mixed with 2.63 g iron (III) nitrate nonahydrate (solution B).

This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 6.1 (steady-state value).

The solvent was decanted off, and the sorbent was washed with 200 g of water. The sorbent was suspended in 200 g 1 M aq. NaOH and stirred for 1 hour at ambient temperature. The solution was removed, and the sorbent is washed with water until a neutral pH is reached and dried under vacuum at 50 °C.

Examples Sorbent C + Fe + HCI:

40 gdry of wet (ca. 38% SC) sorbent C was suspended in 100 g water and stirred for 10 min (suspension A). 26 mL HCI (25% in water) is added. In a separate container 80 g water was mixed with 2 g iron (III) nitrate nonahydrate (solution B).

This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 6 (steady-state value).

The solvent was decanted off, and the sorbent was washed with 200 g water. The sorbent was suspended in 200 g 1 M aq. NaOH and stirred for 1 hour at ambient temperature. The solution was removed, and the sorbent is washed with water until a neutral pH is reached and dried under vacuum at 50 °C.

Reduction of the iron salt amount to 1g of iron (III) nitrate nonahydrate or exchange of iron (III) nitrate nonahydrate by 0.8 g of iron (III) chloride did not have a significant impact on performance of the final material. Example Sorbent D + Fe:

40 gdry of wet (ca. 45% SC) sorbent D was suspended in 100 g water and stirred for 10 min (suspension A). In a separate container 84 g water was mixed with 2 g iron (III) nitrate nonahydrate (solution B).

This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 7.8 (steady-state value).

The solvent was decanted off, and the sorbent was washed with 200 g of water.

The final concentration of iron in the beads measured by ICP was around 2’600 ppm Fe per weight dry sorbent.

Example Sorbent D + Fe + NaOH:

40 gdry of wet (ca. 45% SC) sorbent D was suspended in 100 g 1 M aq. NaOH and stirred for 10 min (suspension A). In a separate container 84 g 1M aq. NaOH was mixed with 2 g iron (III) nitrate nonahydrate (solution B).

This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was >12 (steady-state value).

The solvent was decanted off, and the sorbent was washed with 200 g water. The sorbent was suspended in 200 g 1 M aq. NaOH and stirred for 1 hour at ambient temperature. The solution was removed, and the sorbent was washed with water until a neutral pH was reached and dried under vacuum at 50 °C.

The final concentration of iron in the beads measured by ICP was around 11 ppm Fe per weight dry sorbent.

Example Sorbent D + Fe + HCI:

40 gdry of wet (ca. 45% SC) sorbent D was suspended in 100 g water and stirred for 10 min (suspension A). 5.2 mL HCI (25% in water) was added. In a separate container 84 g water was mixed with 16.3 mL HCI (25% in water) and 2 g iron (III) nitrate nonahydrate (solution B).

This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 8 (steady-state value).

The final concentration of iron in the beads measured by ICP was around 2’800 ppm Fe per weight dry sorbent.

Examples for sorbent on woven or nonwoven structures or monoliths:

Sorbent material, for instance sorbent A or B or C or D, milled and on woven or nonwoven (layer) structures or monoliths are immersed in water (500 wt%). Sorbent material such as s sorbent A or B or C or D, milled and on woven or nonwoven (layer) structures or monoliths is immersed in water (500 wt%). Optionally, 25% aq. HCI (50 mol%) can be added. Solid metal salt such as iron (III) nitrate nonahydrate or zinc (II) nitrate hexahydrate is added (preferentially 0.1 g - 5 g salt per gram dry sorbent), and the structured sorbent is shaken in the reaction solution for 3h at ambient temperature. The solvent is decanted off and the structured sorbent is washed with 1M aq. NaOH for 1h. The structure sorbent is washed with water and dried.

Preparation of the samples for the cake compression tests:

Sorbent A and sorbent C beads were used for preparation of the material for cake compression tests. 40 gdry of wet (ca. 45% SC) sorbent A or C was suspended in 100 g water and stirred for 10 min (suspension A). In a separate container 84 g water was mixed with 2 g zinc (II) nitrate hexahydrate (solution B). This solution B was transferred to suspension A and the mixture was stirred at ambient temperature for 3 hours. The pH of this mixture was 7.8 (steady-state value). The solvent was decanted off, and the sorbent was washed with 200 g of water. The sorbent was suspended in 200 g 1M aq. NaOH and stirred for 1 hour at ambient temperature. The solution was removed, and the sorbent was washed with water until a neutral pH was reached and dried under vacuum at 50 °C.

The Zn loading within the sorbent was estimated to be between 3500-5000 mg of Zn/kg of dry sorbent A or C.

Subsequently, the dried sorbent beads (sorbent A + Zn or sorbent C + Zn) were placed into a cylindrical container and sealed from both sides. This container was subsequently soaked with water to mimic the change in wetness the sorbent experiences during the desorption phase. The wet container with the sorbent inside was then placed in a sealed vessel at 90°C again to mimic the temperature expected in the process for 18 hours. Finally, the so-formed cake was isolated from the cylindrical container and tested in terms of its breaking strength using a Universal Testing Machine (UTM)

Characterization: Solid Content: Solid content is measured with a Halogen Moisture Analyzer (Adam Equipment PMB Moisture Analyzer); measurement temperature is 110°C, the measurement stops automatically at constant weight (0.002 g/15 s).

Nitrogen content measurements: Elemental analysis of the materials was carried out using a LEGO CHN-900 combustion furnace. Prior to the measurement, the samples were treated under N2 flow (2 L/min) at 90°C for 2 h. Alternatively, the sample were treated in a vacuum oven at 60°C for 6 h.

Inductively coupled plasma (ICP) measurements: Iron content within the resin beads was determined using ICP measurements. Prior to the measurement, the samples were treated with a mixture of nitric acid and hydrofluoric acid to digest the resin beads. This solution was then analyzed by ICP-OES using a standard device.

The measurements were performed using the Spectro Arcos FHM22 ICP-OES instrument (SPECTRO Analytical Instruments GmbH). The sample solution is introduced via a pneumatic atomizer system. At a temperature of 5000-7000 K in the plasma, the elements contained in the solution are atomized and excited to emit light. Since the atoms/ions emit electromagnetic radiation characteristic of the chemical element after excitation, the intensity of the light emitted at specific wavelengths is measured and used to determine the concentration of the element of interest. The concentrations in the sample are calculated using the measured intensities of the individual elements and using the functions of the recorded calibrations of the individual elements.

The calibration of the instrument is done in the following manner:

The samples for the determination of the metal content thereof are prepared in the following manner:

Degradation test: The degradation tests are conducted in flow through reactors. The gas flow rate is controlled by a flow meter. The gas stream is saturated with water at 90 °C (100% RH). The water saturated 02 containing gas mixture is then fed to the reactors at 90 °C. Samples are taken out at regular intervals and their CO2 capture capacity values are measured using a breakthrough analyzer.

CO2 capacity measurement: The beads according to the above examples were tested in an experimental rig in which the beads were contained in a packed-bed reactor or in air permeable layers. The rig is schematically illustrated in Fig. 3. There is an ambient air inflow structure 1 and the actual reactor unit 8 comprises a container or wall 7 within which the layers of sorbent material 3 are located. There is an inflow structure 4 for desorption, if for example steam is used for desorption, and there is a reactor outlet 5 for extraction. Further, there is a vacuum unit 6 for evacuating the reactor.

6 g of dry sample was filled into a cylinder with an inner diameter of 40 mm and a height of 40 mm and placed into a CO2 adsorption/desorption device, where it was exposed to a flow of 2.0 NL/min of air at 30°C containing 450 ppmv CO2, having a relative humidity of 60% corresponding to a temperature of 30°C for a duration of 600 min. Prior to adsorption, the sorbent bed was desorbed by heating the sorbent to 94°C under an N2 flow of 2.0 NL/min. The amount of CO2 adsorbed on the sorbent was determined by integrating the signal of an infrared sensor which measures the CO2 content of the air stream leaving the reactor.

Specific surface area measurements: Nitrogen adsorption measurements were performed at 77 K on a Quantachrome ASiQ. The mass of the sample used was between 0.2-1.0 g. Since the samples contain a significant amount of water, it is important to use a treatment that does not alter their intrinsic porosity and pore structure. Therefore, prior to degassing, the samples were treated using the elutropic row method, which comprises removing water and replacing it with organic solvents with lower boiling point in the following order: methanol, acetone, and n-heptane. 2 g of samples was place in a chromatography column with a frit and flushed with 20 cm3 of each solvent in decreasing polarity order. The sample was then spread out on a petri dish and placed in a vacuum oven at 40°C for 24 hours. After that, the sample was degassed at 70 °C under vacuum for twelve hours before measurement.

BET (Brunauer, Emmett und Teller) surface area analysis was used applying the method ISO 9277.

Mercury Porosimetry Measurements-. Mercury porosimetry measurements were performed to analyze the pore sizes and pore volumes not accessible through N2 adsorption measurements. In order to perform mercury porosimetry measurements the following parameters were used:

• Mercury surface tension: 0.48 N/m

• Mercury contact angle: 150°

• Max. pressure: 400 MPa

• Increase speed: 6-19 MPa/min

Prior to Hg porosimetry, the samples were degassed under vacuum at 70°C for 12 h. A sample is placed into a measuring assembly with an empty glass sample cell. Using the Washburn equation, the data set is converted into a cumulative curve of the amount intruded as a function of pore size. The derivative of this curve provides a pore size distribution of the pores accessible via the exterior of the material.

Cake compression tests.

Sorbent beads with a solid content of 91 ,5±1 .0% were placed inside cylindrical steel inserts with inner dimensions of 30 mm in diameter and 25 mm in height. Both ends of the inserts were sealed with metallic mesh. Water was added until the solid content of the sorbents reached 45±5%. The inserts were then sealed in glass jars and conditioned in an oven at 90 °C for 18 hours. After conditioning, cylindrical sorbent cakes formed, matching the inner dimensions of the steel inserts. The cakes were removed from the inserts after taking off the metallic meshes. A TA.XTplusC Texture Analyser was used to measure the force needed to break the cakes using a compression test, with the following settings: 0.2 mm/sec test speed, 20 mm target mode, 0.020 kg force auto trigger mode, and 20 g/s rate break mode. The compression tests were repeated at least twice for each sample. The results of the cake compression tests are given in Fig. 10 after normalizing the data. Data normalization is carried out by using the compressive force of the non-metal modified sorbent as the normalization factor. For the samples given in the figure, there is a huge reduction in cake strength of 80% in case of the first sample, and of about 60% in case of the second sample.

Sorbent material washing tests.

The washing process is realized by placing 100 g of sorbent beads of the given type in a 1 L flask equipped with overhead stirrer and condenser. In a first stage, 700 g water is added to the beads, and the suspension is allowed to stir for a specific duration at a constant temperature. After the stirring process, the beads are filtered and washed with two 200 mL portions of water and subsequently dried. The experiments are carried out for a stirring process duration between 2 to 24 hours. The temperature for the stirring process is chosen to be between 10°C to 90°C whereas the temperature is kept constant throughout the stirring process. In a second stage, surfactants are added to the water which again is added to the beads.

The surfactants added to the water can be found in the table in Fig. 11. The performance of the sorbent is defined by the degradation behavior of its carbon capture capacity. Fig. 11 shows the influence of the washing process on the degradation behavior for Sorbent A, Sorbent A2 and Sorbent B. Sorbent A2 is another batch of Sorbent A. The framed in each case upper bars indicate the difference in equilibrium carbon dioxide capture capacity loss to pristine material, and the non-framed in each case lower bars indicate the loss in equilibrium capacity after wet stream tests.

Sorbent A shows a degradation of its carbon capture capacity of around 28% from its starting value. Sorbent A2 as a different batch of the same sorbent shows a slightly lower degradation of 25%. Sorbent B experiences a degradation of its carbon capture capacity compared to its starting by 32%. The behavior of the sorbents without experiencing a washing process are shown by only one horizontal bar in the figure. The results of the water washing process are represented by two horizontal bars. The lower bar shows the degradation behavior of the carbon capture capacity of the according sorbent whereas the upper bar shows the difference to the non-washed Sorbent. If the upper bar is extending to the right-hand side in direction of the positive values this sorbent provides better degradation behavior thanks to the washing process. In turn, if the upper bar is extending to the left-hand side in direction of the negative values this sorbent provides worse degradation behavior due to the washing process.

Surprisingly, the washing process with only water leads to the biggest improvement of the degradation behavior of the sorbent. Sorbent A shows an improvement of 11 - 13 % on the reduced degradation of the sorbent thanks to the washing process. The improvement of the reduced degradation for Sorbent B is around 8%.

A minimum washing time of two hours at a temperature of at least 10°C is necessary for the effect using water as washing agent to be considerable.

Results:

The results of the characterization are summarized in Table 1 below:

Table 1 : characterization of the materials used.

^a: measured by N2 adsorption/desorption; ^b measured by Hg porosimetry; nd: not determined; * metal content reported here is not the total metal content, but just the content of the metal added to the sorbent as indicated in the leftmost column; values in bracket, where available, are metal content after degradation with steam

Fig. 1 shows the degradation of various sorbents. When compared to a benchmark material without the iron treatment (Squares: Sorbent A, untreated), the Fe containing samples degrade significantly slower. This slower degradation is independent of the iron salt used for the loading (Diamonds: Sorbent A + Fe (III) nitrate; Triangles: Sorbent A + Fe (III); sulphate; Circles: Sorbent A + Fe (III) chloride) as well as the oxidation state of the iron species in solution (Stars: Sorbent A + Fe (II) sulphate). This clearly shows the impact of iron in stabilizing the sorbent against degradation.

The concentration of iron in the sorbent ranges from 250-1100 ppm and we see stabilization across this range of concentrations.

Without delving into and being bound by any theoretical explanation, the iron oxidation state might not be playing a role because iron might oxidize under the conditions used for the degradation test.

Other amine-based sorbents were modified with Fe salts and the same improvement was seen similar to what is shown in Fig. 1.

Fig. 2 shows the degradation of various further sorbents. When compared to a benchmark material (Squares: Sorbent A, untreated), the Fe containing samples degrade significantly slower (Diamonds: Sorbent A + Fe (III) nitrate). This slower degradation is caused by the presence of iron as 2 blank samples washed with DI water (Triangles: Sorbent A + water wash) and sodium nitrate (Circles: Sorbent A + Na nitrate) do not show slower degradation. Hence, the impact of iron on improving degradation performance is clear.

Fig. 4 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure to an 02 containing gas saturated with water at 90 °C for sorbent B and the given Examples with iron loading. All are normalized to the capacity of the respective sample at time zero. Adsorption conditions: T = 30 °C, RH = 60 %; desorption conditions: T = 94 °C. Untreated Sorbent B shows much higher degradation (ca. 30%) as compared to Sorbent B doped with Fe(lll) (ca. 2%). For Sorbent B doped with Fe (III) following the pH modulated acid recipe (ca. 4%), there is no big difference in degradation behaviour as compared to the non-acid modulated recipe.

Fig. 5 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure to an 02 containing gas saturated with water at 90 °C for sorbent C and Examples with iron loading. All are normalized to the capacity of the respective sample at time zero. Adsorption conditions: T = 30 °C, RH = 60 %; desorption conditions: T = 94 °C.

Untreated Sorbent C shows much higher degradation (ca. 70%) as compared to Sorbent C doped with Fe(lll) (ca. 20%). For Sorbent C doped with Fe (III) following the pH modulated acid recipe there is a significant difference in degradation behaviour (ca. 2%) as compared to the non-acid modulated recipe.

Fig. 6 shows the normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure to an 02 containing gas saturated with water at 90 °C for sorbent D and Examples with iron loading. All are normalized to the capacity of the respective sample at time zero. Adsorption conditions: T = 30 °C, RH = 60 %; desorption conditions: T = 94 °C.

Untreated Sorbent D shows much higher degradation (ca. 70%) as compared to Sorbent D doped with Fe(lll) (ca. 30%). For Sorbent D doped with Fe (III) following the pH modulated acid recipe there is a significant difference in degradation behaviour (ca. 6%) as compared to the non-acid modulated recipe. Interestingly, when the pH is modulated to basic conditions, the stabilization is worsened and is in the range of sorbent D with no Fe doping (ca. 40%)

Fig. 7 shows normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure to an 02 containing gas saturated with water at 90 °C for Sorbent A with different metal loadings as given in the Table 1 . All are normalized to the capacity of the respective sample at time zero. Adsorption conditions: T = 30 °C, RH = 60 %; desorption conditions: T = 94 °C.

On the other hand, as shown in this Figure, the impregnation of metals on sorbent A shows to bring beneficial effects on the stability of the sorbent under wet conditions. This applies to all metals according to this invention.

As one can see from the values in brackets in Table 1 , the metal is not washed out in the wet process.

For copper e.g. no beneficial effect is observed. In fact, normalized equilibrium CO2 adsorption capacity measured after 7 days of exposure to an 02 containing gas saturated with water at 90 °C for Sample A and Sample A + Cu(ll) prepared with 100, 500, and 1000 ppm nominal concentration, all normalized to the capacity of the respective sample at time zero (Adsorption conditions: 2 L/min, t = 600 min, T = 30 °C, RH = 60 %; desorption conditions: 2 L/min, t = 75 min, T = 94 °C, RH = 60 %) shows that even changing Cu loading on the sorbent, the degradation of the sorbent gets worse than that of pristine sorbent A. This confirms over a larger spectrum of concentrations that Cu has a negative impact on stability.

Fig. 8 shows normalized equilibrium CO2 adsorption capacity measured after variable time of wet exposure to an O2 containing gas saturated with water at 90 °C for a styrene DVB benzylamine bead system + Metal prepared with 1000 ppm nominal concentration (Sorbent A). All are normalized to the capacity of the respective sample at time zero. Adsorption conditions: T = 30 °C, RH = 60 %; desorption conditions: T = 94 °C. Metal washed sorbent material was made by stirring pristine sorbent material in a solution of 1000 ppm of Zinc (II) nitrate hexahydrate, Nickel (II) nitrate hexahydrate, Manganese (II) nitrate tetrahydrate, and Chromium (III) nitrate nonahydrate in DI water. Example of final loading of Zn species in Sorbent = 1300 mg/kg (ICP). Degradation test conditions: The material was loaded into a reactor, placed in an oven at 90°C and exposed to an O2 gas saturated with H2O at 1 bara. Sampling of the material was done after defined exposure times and the adsorption capacity for CO2 was measured using a breakthrough analyzer. Interestingly, Zn, Ni, Mn, and Cr loaded samples show slower degradation compared to pristine sorbent in wet conditions.

Fig. 9 shows normalized equilibrium CO2 adsorption capacity measured after variable time of dry exposure to an O2 containing gas at 90 °C for a styrene DVB benzylamine bead system (Sorbent A) + Metal prepared with 1000 ppm nominal concentration. Metal washed sorbent was made by stirring pristine sorbent in a solution of 1000 ppm of Zinc(ll) nitrate hexahydrate, Nickel(ll) nitrate hexahydrate, Manganese(ll) nitrate tetrahydrate in DI water. Example of final loading of Zn species in sorbent = 1300 mg/kg (ICP). Degradation test conditions: The material was loaded into a reactor, placed in an oven at 90°C and exposed to a gas containing 21% 02, 79% N2, at 1 bara. Sampling of the material was done after defined exposure times and the adsorption capacity for CO2 was measured using a breakthrough analyzer. Interestingly, Zn, Ni, and Mn loaded samples show slower degradation compared to Fe-loaded sorbent in dry conditions.

The figure shows that adding metals to Sorbent A is accelerating sorbent oxidation under dry conditions, which is in line with the results reported in WO-A-2023/094386. This is also in line with the catalytic effects of metals on oxidation of organic compounds.

LIST OF REFERENCE SIGNS

1 ambient air, ambient air inflow structure

2 outflow of ambient air behind adsorption unit in adsorption flow-through mode

3 sorbent material

4 steam, steam inflow structure for desorption

5 reactor outlet for extraction

6 vacuum unit/separator

7 wall

8 reactor unit

Claims

1. Method for the preparation of sorbent material (3) for use as adsorbent for carbon dioxide separation from a gas mixture (1), said sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support, wherein said sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, is treated so as to have, after treatment, at least one of: a total iron content above 100 ppm, a total zinc content above 100 ppm, a total nickel content above 100 ppm, a total manganese content above 100 ppm, and a total chromium content above 100 ppm.

2. Method according to claim 1 , wherein said sorbent material (3), after treatment, has a total iron, zinc, nickel, manganese and/or chromium content in each case above 200 ppm, typically in each case below 5000 ppm, or in each case in the range of 100-3000 ppm or 100 - 1300 ppm, or in each case in the range of 200-1200 ppm, wherein preferably only one or two of iron, zinc, nickel, manganese and/or chromium are in such a proportion or range.

3. Method according to any of the preceding claims, wherein the iron used for treatment and/or in the sorbent material (3) is in the oxidation state (II) or (III) or a mixture of iron in these oxidation states and/or wherein zinc used for treatment and/or in the sorbent material (3) is in the oxidation state (II), and/or wherein nickel used for treatment and/or in the sorbent material (3) is in the oxidation state (II) or (III) or a mixture of nickel in these oxidation states, and/or wherein manganese used for treatment and/or in the sorbent material (3) is in the oxidation state (II) or (III) of (IV) or a mixture of manganese in these oxidation states, and/or wherein chromium used for treatment and/or in the sorbent material (3) is in the oxidation state (II) or (III) or a mixture of chromium in these oxidation states.

4. Method according to any of the preceding claims, wherein said treatment is a treatment of sorbent material (3) with a liquid solution or suspension of an iron, zinc, nickel, manganese and/or chromium salt, preferably using spray treatment or immersion, and wherein preferably the solution or suspension is in water, wherein preferably treatment takes place at a pH in the range of 0.5 - 10 or 4-10, preferably in the range of 1-6 or 6-8, and/or at a temperature in the range of 15-35°C, or in the range of 20-30°C, and/or over a time span in the range of 1-12 hours, or in the range of 2-4 hours.

5. Method according to the preceding claim, wherein the treatment is with a liquid solution of a sulfate, chloride, nitrate, or a combination thereof, of iron (II) and/or iron (III), zinc, nickel, manganese and/or chromium, wherein preferably an aqueous solution of iron (III) nitrate, iron (III) nitrate nonahydrate, iron (III) sulfate, iron (III) sulfate hydrate, iron (III) cloride, iron (III) chloride tetrahydrate, iron (II) nitrate, iron (II) hexa nitrate, iron (II) sulfate, iron (II) sulfate hepta hydrate, iron (II) cloride, iron (II) chloride tetra hydrate, or a combination thereof, or respective systems of zinc, nickel, manganese and/or chromium, is used, and/or wherein the concentration of iron, zinc, nickel, manganese and/or chromium in the liquid solution is at least 400ppm or 500 ppm (by weight), preferably in each case at least 700 ppm, or in each case in the range of 400-25'000ppm or 500-10'OOOppm, or 700- 5000ppm, or 700-2000 ppm or 800-1500 ppm.

6. Method according to any of the preceding claims, wherein the sorbent material (3) takes the form of sorbent particles, sorbent powder, a porous monolithic structure, or the form of an essentially contiguous adsorbent layer, or a combination thereof.

7. Method according to any of the preceding claims, wherein the amine moieties in the a-carbon position are substituted by hydrogen and/or alkyl, preferably by one methyl and one hydrogen substituent or by two hydrogen substituents, wherein preferably the sorbent material (3) comprises primary and/or secondary benzylamine moieties, wherein most preferably the carbon dioxide capture moieties of the sorbent material consist of primary benzylamine moieties.

8. Method according to any of the preceding claims, wherein the solid support of the sorbent material (3) is a porous or non-porous material based on an organic and/or inorganic material, preferably a polymer material, preferably selected from the group of linear or branched, cross-linked or uncross-linked polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate-based polymer including PMMA, polyacrylonitrile or combinations thereof, wherein preferably the polymer material is poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, metal organic frameworks, covalent organic frameworks, and combinations thereof, wherein preferably the sorbent material (3) is based on a polystyrene material, preferably cross-linked polystyrene material and most preferably poly(styrene-co- divinylbenzene), which is at least partially functionalized with amino moieties or contains benzylamine moieties, preferably throughout the material or at least or only on its surface, wherein preferably the material or the functionalization is obtained by amidomethylation or phthalimide or chloromethylation reaction pathways or a combination thereof, and/or wherein the primary and/or secondary amine moieties are part of a polyethyleneimine structure, preferably obtained using aziridine, which is preferably chemically and/or physically attached to a solid support.

9. Method according to any of the preceding claims, wherein the sorbent material (3), preferably in porous form, and having specific BET surface area, in the range of 0.5-4000 m2/g or 1-2000, preferably 1-1000 m2/g, takes the form of a monolith, the form of a layer or a plurality of layers, the form of hollow or solid fibres, including in woven or nonwoven (layer) structures, or the form of hollow or solid particles.

10. Method according to any of the preceding claims, wherein the sorbent material takes the form of preferably essentially spherical beads with a particle size (D50) in the range of 0.002 - 4 mm, 0.005 - 2 mm, 0.002 - 1.5 mm, 0.005 - 1.6 mm or 0.01-1.5 mm, preferably in the range of 0.30-1.25 mm.

11. A method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material (3) adsorbing said gaseous carbon dioxide in a unit (8), wherein the method comprises at least the following sequential and in this sequence repeating steps (a) - (e):

(a) contacting said gas mixture (1) with the sorbent material (3) to allow at least said gaseous carbon dioxide to adsorb on the sorbent material (3) by flow-through through said unit (8), in case of ambient atmospheric air as gas mixture under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions and in other cases under temperature and pressure conditions of the supplied gas mixture, in an adsorption step; (b) isolating said sorbent material (3) with adsorbed carbon dioxide in said unit (8) from said flow-through;

(c) inducing an increase of the temperature of the sorbent material (3) to a temperature starting the desorption of CO2, preferably by heat exchangers or by injecting a stream of saturated or superheated steam by flow-through through the unit (8) and thereby inducing an increase of the temperature of the sorbent material to a temperature between 60 and 110°C, starting the desorption of CO2;

(d) extracting at least the desorbed gaseous carbon dioxide from the unit (8) and preferably separating gaseous carbon dioxide from steam in or downstream of the unit (8);

(e) bringing the sorbent material (3), in case of ambient atmospheric air as gas mixture, to ambient atmospheric temperature conditions, and in other cases to the temperature and pressure conditions of the supplied gas mixture; wherein said sorbent material (3) comprises primary and/or secondary amine moieties or a combination thereof immobilized on a solid support, and wherein either material prepared according to any of the preceding claims or a material according to claim 15 is used as the sorbent material (3), or, after having repeated said sequence of steps a number of times having led to deterioration of the sorbent material in the form of a reduced carbon dioxide capture capacity , the sorbent material (3) is treated so as to have, after treatment, a total metal impurity content below 1400 ppm, preferably below 1200 ppm, more preferably below 1100 ppm, most preferably in the range of 200-1000 ppm, preferably using a method according to any of the preceding claims.

12. Method according to claim 11 , wherein treatment to achieve the total iron, zinc, nickel, manganese and/or chromium content is carried out in situ in the device for separating gaseous carbon dioxide from a gas mixture, preferably by wash or spraying or a combination thereof, or is carried out by taking the sorbent material/support material out of the device for separating gaseous carbon dioxide from a gas mixture, is treated to achieve the total iron, zinc, nickel, manganese and/or chromium content, and then reintroduced into the device for separating gaseous carbon dioxide to continue the separation process.

13. Method according to any of the preceding claims, wherein said sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, is treated so as to have, after treatment, a total iron content above 100 ppm.

14. Use of a material produced or treated according to any of claims 1-10 or a material according to claim 15 for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material (3) adsorbing said gaseous carbon dioxide in a unit (8).

15. Sorbent material (3) comprising primary amine or secondary amine moieties, or a combination thereof, immobilised on a solid support, for use as adsorbent for carbon dioxide separation from a gas mixture (1), which sorbent material (3) has a total iron, zinc, nickel, manganese and/or chromium content of in each case above 100 ppm, preferably a total iron, zinc, nickel, manganese and/or chromium content of in each case above 200 ppm, or of in each case in the range of 100 - 1300 ppm, or in the range of 200-1200 ppm, preferably prepared or treated using a method according to any of claims 1-10.