WO2025228719A1

WO2025228719A1 - Sorbent structures for co2 capture

Info

Publication number: WO2025228719A1
Application number: PCT/EP2025/060842
Authority: WO
Inventors: Anne Streb; Hannes Jacob; Niko PAVLICEK; Tobias NIEBEL; Ayoung SONG
Original assignee: Climeworks AG
Current assignee: Climeworks AG
Priority date: 2024-04-30
Filing date: 2025-04-22
Publication date: 2025-11-06
Anticipated expiration: 2026-10-30

Abstract

Method for the manufacture of a sorbent-impregnated sheet comprising the following steps: 1) providing a porous substrate (4) in the form of a sheet or a band and applying a particulate sorbent material (3) capable of reversibly binding carbon dioxide to at least one of the faces of the porous substrate (4); 2) electrostatic dry impregnation of the porous substrate (4) with the particulate sorbent material (3) to distribute said particulate sorbent material (3) within the porous substrate (4); 3) fixing the particulate sorbent material (3) within the porous substrate (4) by applying at least one of heat and pressure and radiation.

Description

TITLE

SORBENT STRUCTURES FOR CO2 CAPTURE

TECHNICAL FIELD

The present invention relates to carbon dioxide capture materials, in particular for example those provided with primary and/or secondary and/or tertiary amine carbon dioxide capture moieties, as well as to methods for preparing such capture materials, and to uses of such materials in particular in direct air capture processes.

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 32.5x10E9 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) had ratified it. The meaning of this figure is that a consensus at the time was 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 three most notable solutions currently applied, albeit being at an early stage of development, are the capturing of CO2 by means of vegetation (e.g. trees and plants, but not really permanent removal) using natural photosynthesis, by means of combining bioenergy from combustion of biomass with point source CO2 capture and subsequent permanent storage (BECCS) and by means of direct air capture (DAC, use of chemical or physical processes to extract carbon dioxide directly from the ambient air) and carbon dioxide storage technologies, which also results in permanent removal but a significantly reduced land footprint compared to BECCS.

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 potentially arable land surface to captured CO2 ratio. BECCS suffers from the same shortcoming. On the other hand, DAC coupled with carbon dioxide storage technologies 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 gas-solid interface. Such sorbents can contain different types of amino functionalization and polymers, such as immobilized aminosilane-based sorbents as reported in US-B-8834822, 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.

Several academic publications, such as Alesi et al. in Industrial & Engineering Chemistry Research 2012, 51 , 6907-6915; Veneman et al. in Energy Procedia 2014, 63, 2336; Yu et al. in Industrial & Engineering Chemistry Research 2017, 56, 3259-3269, also investigated in detail the use of cross-linked polystyrene resins functionalized with primary benzylamines as solid sorbents for DAC applications.

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-9186617). Other technologies are based on the use of solid sorbents in either a packed-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 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 using the same sorbent material without or with little loss of sorbent performance and without damaging the mechanical integrity of the adsorption unit.

More recently, structured adsorbers have also been employed for capturing CO2 from flue gas, such as the structures described by WO-A-2010096916 and WO-A-2018085927, that specify parallel passage contactors for the purpose of flue gas CO2 capture. These adsorber structures in their configuration for flue gas capture are designed for the high concentrations of CO2 present in flue gas and operate with the aim of capturing a high fraction of CChfrom the flue gas.

More specifically, WO-A-2018085927 discloses an adsorptive gas separation apparatus and method. The adsorbent structure may include a first adsorbent layer having at least a first adsorbent material, a second adsorbent layer including at least a second adsorbent material, and a barrier layer, where the barrier layer is interposed between the first adsorbent layer and the second adsorbent layer. A parallel passage contactor including a plurality of adsorbent structures each comprising a barrier layer, and arranged to form first and second fluid passages is also disclosed. An adsorption process for separating at least a first component from a multi-component fluid stream using the adsorbent structure is also provided.

US-A-2015139862 discloses a structured adsorbent sheet, including a nano-adsorbent powder, and a binder material, wherein the nano-adsorbent powder is combined with the binder material to form an adsorbent material, and a porous electrical heating substrate, wherein the adsorbent material is applied to the porous electrical heating substrate thereby forming a structured adsorbent sheet. A structured adsorbent module is provided, including a plurality of stacked structured adsorbent sheets, configured to produce a plurality of fluid passages, wherein the plurality of fluid passages have a cross-sectional shape in the direction of a fluid stream. The structured adsorbent module may have a cross-sectional shape that is trapezoidal, rectangle, square, triangular or sinusoidal. A structured adsorbent bed is provided, including a plurality of modules, stacking the modules, thereby providing a plurality of process fluid passages, and a process fluid inlet and a process fluid outlet, in fluid communication with the plurality of process fluid. 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-B-8262774 discloses a process for forming a CO2 capture element which comprises providing a mixture of a monomer or monomer blend or a polymer binder, a miscible liquid carrier for the binder and a CO2 sorbent or getter in particle form, forming the mixture into a wet film or membrane, evaporating the liquid carrier to form a film or membrane, and treating the wet film or membrane to form pores in the body of the film or membrane. Also disclosed is a process of forming a CO2 capture element which comprises the steps of applying a mixture including a sorbent material and a polymer to an underlying material; polymerizing the mixture in place on the material; and aminating the polymer-coated material.

US-A-2007217982 discloses an apparatus for capture of CO2 from the atmosphere comprising an anion exchange material formed in a matrix exposed to a flow of the air.

US-B-8999279 provides a method for removing carbon dioxide from a gas stream without consuming excess energy, wherein a solid sorbent material is used to capture the carbon dioxide. The solid sorbent material may utilize a water-swing for regeneration. Various geometric configurations are disclosed for advantageous recovery of CO2 and regeneration of the sorbent material.

US-B-7708806 and US-B-9861933 relate to a method and apparatus for extracting CO2 from air comprising an anion exchange material formed in a matrix exposed to a flow of the air, and for delivering that extracted CO2 to controlled environments. The invention contemplates the extraction of CO2 from air using conventional extraction methods or by using one of the extraction methods disclosed; e.g., humidity swing or electro dialysis. The invention also provides delivery of the CO2 to greenhouses where increased levels of CO2 will improve conditions for growth. Alternatively, the CO2 is fed to an algae culture.

US-B-8715393 discloses a method for removing carbon dioxide from a gas stream, comprising placing the gas stream in contact with a resin, wetting the resin with water, collecting water vapor and carbon dioxide from the resin, and separating the carbon dioxide from the water vapor. The resin may be placed in a chamber or a plurality of chambers connected in series wherein the first chamber contains resin that was first contacted by the gas, and each successive chamber contains resin which has been wetted and carbon dioxide collected from for a greater period of time than the previous chamber, and so on, until the last chamber. Secondary sorbents may be employed to further separate the carbon dioxide from the water vapor. US-B-9527747 provides a method and apparatus for extracting carbon dioxide (CO2) from a fluid stream and for delivering that extracted CO2 to controlled environments for utilization by a secondary process. Various extraction and delivery methods are disclosed specific to certain secondary uses, included the attraction of CO2 sensitive insects, the ripening and preservation of produce, and the neutralization of brine.

US-B-8088197 and US-B-10010829 are directed to methods for removing CO2 from air, which comprises exposing sorbent covered surfaces to the air. The invention also provides for an apparatus for exposing air to a CO2 sorbent. In another aspect, the invention provides a method and apparatus for separating carbon dioxide (CO2) bound in a sorbent.

WO-A-2024083700, not from the field of CO2 capture and not disclosing corresponding materials, discloses an installation for impregnating a porous material with powder, comprising first and second electrodes generating an electric field within an electric field zone, traversed by the porous material provided with powder, a lower conveyor capable of moving the porous material provided with powder between the first and second electrodes, and a powder distribution zone at which the powder is deposited on the porous material. The distribution zone is located upstream of the electric field zone. The installation is characterized in that it further comprises members extending perpendicularly to the plane of the lower conveyor and coming into contact with only a portion of said porous material. WO-A-2023213529 discloses an adsorption textile for adsorbing CO2, comprising at least one core layer, at least one thermally conductive layer, which is disposed on the at least one core layer, and at least one adsorber layer, which is disposed on the at least one thermally conductive layer. The at least one adsorber layer is designed to absorb CO2 from the air and/or to desorb the same. The document also relates to a method for manufacturing a textile of this kind, to a system comprising a textile of this type, and to the use of said system. The proposed approach is stated to allow CO2 to be extracted ecologically and efficiently.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide for improved carbon dioxide capture elements, preferably for direct air capture (DAC), in particular in the form of layers or sheets, which preferably are provided as self-supporting structures, in particular for example for the case without the need of an additional solid supporting layer or which are mounted on or in additional supporting elements using e.g. adhesives (glue) or other means, a fixation to a frame for hanging them or the like.

This disclosure also relates to an innovative method of producing structured sorbent material, in particular for DAC, in the form of a sorbent-impregnated sheet, that features several advantages compared to the state of the art. This disclosure presents a novel, scalable, cheap solution for production of such structured sorbent materials at scale.

Many alternatives for making CO2 capture structured sorbent material based on loading a substrate with a particulate sorbent material rely on wet processes, thus are sensitive to changes in particulate sorbent material chemistry as a new particulate sorbent material with different particulate sorbent chemistry will mean different interactions in the liquid phase. The presented invention refers to a dry-impregnation process, that is more flexible to the change in particulate sorbent material. Moreover, in contrast to typical wet-impregnation processes, it does not need a drying step after impregnation thus reducing process complexity and cost, and it does not need an additional binder material, thus removing the associated cost, additional process steps required for adding the binder, and also eliminating the risk of the binder blocking part of the sorbent pores. Moreover, this disclosure presents a method that does not only allow to use a variety of different particulate sorbent types (including particles with different average particle sizes and/or different particle size distributions), but also different substrates that are impregnated with the particulate sorbent material. In addition, with a proper choice of substrate and process parameters, high loadings > 50 or > 60 or even > 70 or even up to 95wt% of particulate sorbent material (wt.% always being dry weight values and with respect to the total impregnated sheet weight), relative to the total weight of the loaded structured sorbent material, can be achieved in the final structure, which is at least a challenge for alternative technologies. This is important because often one works with thermal regeneration cycles, so additional dead thermal mass is to be avoided. Also, the resulting sheet of structured sorbent material can be made and shaped/formed upon application of temperature and/or pressure, thus resulting in a topologically structured element, which facilitates the building of 3D parallel-passage contactors out of the material without the need for additional material for spacing.

The method typically comprises at least the following steps:

1) Providing a porous substrate;

2) Dry impregnating the porous substrate with at least one particulate sorbent material capable of reversibly binding carbon dioxide;

3) Post-processing the dry-impregnated material using heat and/or pressure and/or radiation to fix the particulate sorbent material to the substrate resulting in a sorbent- impregnated sheet.

Particulate sorbent materials which have the property of reversibly binding carbon dioxide are particularly challenging particles for processing, because most types of treatment will negatively affect the potential of the particulate sorbent material to reversibly bind carbon dioxide. The materials are prone to oxidation, and to clogging of the porosity thereof, as well as to covering up the capture moieties, and it is a challenge to find processing conditions which do not negatively affect the pristine particulate sorbent material. It was therefore unexpected and surprising to learn that the dry-impregnation process using electrostatic particle distribution in the porous substrate and post-processing does not or only little negatively affect such particulate sorbent material.

Also, it was surprising to realize that the distribution obtained in this process optimally distributes the particles in the porous substrate. It was also unexpected to learn that the process works for impregnating and permanently fixing the required high amounts of powder and at small particle size, and that it works for the required geometries of DAC (i.e. the thickness range mentioned below). It was also unexpected to learn that by appropriately choosing the substrate, and fixation conditions, the powder can be fixed but essentially without blocking access to the sorbent porosity and also whilst leaving the overall structure porous enough for air to be able to diffuse easily into the material, i.e. without impacting the adsorption kinetics significantly, but dense enough to pack high amounts of sorbent into the sheet volume.

Without being bound to any theoretical explanation, it is suspected that the electrostatic distribution process mimics to a certain extent the air diffusion conditions in the final structure, meaning that the electrostatic distribution process distributes the particles to positions where also the accessibility is optimum.

Furthermore, it was unexpected to learn that it is possible to fix the particles, which are electrostatically distributed in the porous substrate, in a lasting way which allows to withstand the carbon dioxide adsorption and desorption cycles, also under temperature and humidity swing conditions and/or in wet conditions and/or when completely immersed in water and/or when wet-frozen, and that the corresponding fixing of the particles also does not negatively affect the capture capacity of the particles even without the need of using additional binder in addition to the particulate sorbent material and the substrate.

Particularly good results could be obtained if for the fixing of the particles to the substrate use is made of bicomponent fibers within the substrate. Without being bound to any theoretical explanation, it is suspected that the bicomponent fibers allow for fixation of the sorbent by only partially melting the fibers such that the sorbent is bound to the molten part, but the shape and porosity of the composite is retained.

In the present context the following definitions apply:

Substrate: means a material comprising porosities capable of receiving powder, in particular particulate sorbent material. It may in particular be a fibrous network, such as for example nonwoven or fabric, paper, or even open-cell foam.

Particulate sorbent material: means a particulate material which is essentially solid at room temperature and also under typical carbon dioxide capture process operating conditions, and which is provided as a loose particulate material capable of reversibly binding carbon dioxide and which features a certain flowability behavior. The particulate sorbent material may, at least partly (e.g. a shell part thereof), have the property of melting and/or softening, under the conditions of step 3). In as far as the particulate sorbent material contains further particles which are not reversibly binding carbon dioxide, also these may have the property of melting and/or softening, under the conditions of step 3). This particulate material (which includes powders) has the property of adsorbing gaseous carbon dioxide from a gas stream comprising said carbon dioxide and other gases, at a first set of environmental conditions (temperature, pressure, humidity, gas composition), and of releasing the adsorbed carbon dioxide at a second set of environmental conditions, different from the first set of environmental conditions. Typically, the particulate sorbent material is characterized by an average particle size (D50, weight average) and by a particle size distribution (PSD). Individual particles of such a particulate sorbent material can be essentially spheroidal or of different shape, and the particles may result from a grinding or sieving process or directly result from the synthesis (suspension or emulsion polymerization) without further need for grinding. The starting material for such a grinding or sieving process can be obtained in a suspension or emulsion polymerization process.

Sheet or band: Is a cohesive structure the thickness of which is at least by a factor of 5 or even 10 smaller than its length and/or width in the plane of the structure, wherein the length of the band is by at least a factor of five longer than its width.

Sorbent-impregnated sheet: means a three-dimensional structure being longer and wider than thick, including band structures, comprising or consisting of at least the substrate and the particulate sorbent material. The particulate sorbent material is embedded in and attached to the substrate such that, under both the conditions where the particulate material is adsorbing carbon dioxide and the conditions where the particulate material is releasing the adsorbed carbon dioxide, the particulate sorbent material is not or only insignificantly released from the substrate.

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 0.7 to 1.1 or 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, and a relative humidity in the range of 3-100%. However, also airwith lower relative humidity, i.e. < 3%, or with lower or higher CO2 concentration can be used as input for the process, e.g. with a concentration of 0.1 -0.5% CO2 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.

According to a first aspect of the present invention, it relates to a method for the manufacture of a sorbent-impregnated sheet comprising at least the following steps:

1) providing a porous substrate in the form of a sheet or a band and applying a particulate sorbent material capable of reversibly binding carbon dioxide to at least one of the faces of the porous substrate;

2) electrostatic dry impregnation of the porous substrate with the particulate sorbent material to distribute said particulate sorbent material within the porous substrate;

3) fixing the particulate sorbent material within the porous substrate by applying at least one of heat and pressure and radiation.

Preferably heat alone or heat and pressure are applied, where the heat in both cases can be introduced directly by contacting with hot material or by convective heat transfer, or indirectly by irradiation to generate the heat in situ. So preferably fixing the particulate sorbent material within the porous substrate takes place by applying at least one of; heat, or heat and pressure, or radiation, or radiation and pressure.

The porous substrate can be in the form of a sponge or preferably a fibrous material.

The porous material may enter the process in neutral or ionized form, and the particulate sorbent material can be applied to the sheet before or after it is located between the electrodes of step 2).

According to a preferred embodiment therefore, the porous substrate is a fibrous, woven or nonwoven band or sheet, or an open pore foam or sponge band or sheet.

Typically, the material of the porous substrate, in the state as being used in step 2) and without the particulate sorbent material, has a void volume in the range of 70%-99.5%, preferably in the range of 90-99% or more preferably in the range of 95-98.5% (all vol%), with the remaining percent being the volume of the structural material (fibers, foam material). The void volume can be calculated as follows: measure the x, y and z dimensions of the porous substrate, for example with a caliper; calculate the total volume of porous substrate (including pores), measure the weight of the material, for example with a balance, determine the density of the structural material (foam material, fibers), calculate the total volume of the structural material (excluding voids), calculate the void volume by subtracting the total structural volume from the total volume. The density of the porous substrate material, i.e. the total mass divided by the total volume, is typically in the range of 5 - 200 kg/m3, preferably in the range of 10-100 kg/m3 or more preferably in the range of 15 - 50 or 20 - 35 kg/m3. Preferably, the material is a fibrous material, more preferably a non-woven material, for example a needle-punched and/or thermo-bonded and/or wet-laid and/or dry- laid and/or hydroentangled material, including meltblown and spunbond.

The porous substrate typically is a woven or non-woven polymeric material. More preferably, the porous substrate in the state as being used in step 2) and without the particulate sorbent material, has a thickness of 0.5 - 10 mm, preferably in the range of 1 - 5 mm. Moreover, preferably, the substrate in the state as being used in step 2) and without the particulate sorbent material, has an air permeability measured with an Akustron air permeability meter at 200 Pa of 1000 - 10000 l/m2/s, more preferably in the range of 1500- 5000 l/m2/s. The porous substrate can be composed of fibers, preferably of polymeric fibers, more preferably of fibers based on or made from PE or PP or Pll or PET or PA or combinations thereof. Most preferably, > 20 % or > 50 % or > 90 % of the fibers or essentially all fibers are bi-component fibers or multi-component fibers including core & sheath, side- by-side and segmented as well as reinforced fibers. Such bi-component or multi-component fibers preferably have a core with a melting point or melting range higher than the shell of the fibers, for example a PE shell and a PP core or a co-PET shell and a PET core or a PE shell and a PET core. Bi-component and multi-component fibers generally include fibers with at least one thermoplastic first component, preferably the shell, and a nonthermoplastic second component or second component with a higher Tm and/or Tg than the first component(s), preferably the core, such that during step 3) or a post-treatment essentially only the first component(s) is softened or molten. Tm (melting temperature) and Tg (glass transition temperature) are defined and to be measured according to DIN-ISO 11357.

Preferably, the porous substrate is based on fibers, which have a fiber diameter in the range of 5-50 pm, preferably in the range of 10-30 pm, and most preferably in the range of 15-25 pm.

Preferably, the porous substrate has a weight in the range of 10-400 g/m2, more preferably in the range of 20-200 g/m2 or 30-150 g/m2 and most preferably in the range of 50-120 g/m2 or 70-90 g/m2.

The process of step 2) for the electrostatic dry impregnation into the substrate, e.g. a fibrous or filamentary network with particulate sorbent material, for producing the sorbent- impregnated sheet, normally a rigid or flexible matrix with which said substrate is in intimate contact, is preferably carried out in that the particulate sorbent material and said substrate are placed between two electrodes, said electrodes being electrically insulated from each other and said electrodes being connected respectively to the oppositely charged poles of an AC voltage electrostatic generator so as to simultaneously subject said particulate sorbent material and said substrate lying between said electrodes to an electrostatic field, wherein normally the AC voltage is at least 5 kV, for a time of at least 2 seconds. An approach along these lines is disclosed in WO9922920.

During the dry-impregnation step, the particulate sorbent material penetrates the porous substrate and is distributed, preferably essentially homogeneously, throughout the thickness of the porous substrate. The dry impregnation step also partially distributes it in x/y direction, not only z direction (z direction = thickness), so that helps leveling out any inhomogeneities from the scattering step.

According to a preferred embodiment, in step 2) the porous substrate with the particulate sorbent material is placed between two electrodes preferably covered with dielectric layers on the side facing the porous substrate, and for the dry impregnation an alternating voltage of at least 5 kV, preferably at least 20 kV, or in the range of 25-60 kV is applied, preferably with a frequency in the range of 50-200 Hz, or in the range of 75-125 Hz at a spacing of the electrodes in the range of 5-30 mm, or in the range of 10-20 mm, for a time span of at least one or two seconds or 4-20 seconds (residence time in case of continuous process). Typical values are as follows 30 kV/100 Hz/10 mm/10 s or 47 kV/100 Hz/15 mm/5 s. To obtain a satisfying impregnation during a continuous treatment, it is advisable to use strip electrodes in the cross direction (as e.g. disclosed in FR-A-2933327 or in FR2402976), with phase shift between the electrodes.

Preferably, in that step 2), a device is used comprising at least a first dielectric insulating screen and first and second opposite-facing electrodes which are separated by a passage for the porous substrate provided with powder in step 1) and are capable of producing an alternating electric field in this passage after having been connected to an alternating voltage generator, with the first dielectric screen electrically insulating the first and second electrodes from each other at the level of said passage, wherein at least first electrode comprises at least two conducting strips, each of which has an internal face covered by the first dielectric screen and, overall, turned towards the second electrode, and also a longitudinal edge running along a separating slot, which strips are separated from each other by this separating slot and are electrically connected to one another. For example possible is a device and a method as described in WO2010001043 or in WO2022058696, the disclosure of which is included into this specification as concerns this aspect of the invention.

Preferably, in that step 1), an installation is used, comprising: an area for storing the powder; and a conveyor capable of coming into contact with the porous substrate and having an external surface comprising cavities; wherein the external surface of the conveyor delimits an edge of the storage area to fill said cavities with the powder; and a positioner configured to hold the porous substrate in contact with a fraction of the conveyor length, to seal cavities containing the powder along said fraction of the conveyor length; and a drive device enables to move the conveyor and the porous substrate; and an actuator configured to displace the powder and arranged opposite said fraction of the conveyor length, to at least partly displace a portion of the powder across the porous substrate. For example possible is a device and a method as described in WO2015044605, the disclosure of which is included into this specification as concerns this aspect of the invention.

Preferably, in that step 2), an apparatus is used, including a device able to generate an alternating electric field through the porous substrate, the device including a first electrode and a second electrode which are placed on either side of the porous medium, wherein the first electrode is covered with a screen coming into contact with the electrode, said screen having a dielectric strength higher than 6 kV/mm, and preferably higher than 9 kV/mm; the second electrode is covered with a protective layer, said protective layer being secured to the second electrode and having a superficial resistivity higher than 1x10¹² Ohm as surface resistivity, irrespective of the relative humidity level. For example possible is a device and a method as described in W02016092205, the disclosure of which is included into this specification as concerns this aspect of the invention.

Also it is possible to act in that prior to bringing the powder material into contact with the substrate, the substrate is exposed to a heat source with conditions of exposure intensity and time of exposure generating a gradual swelling of its thickness. For example possible is a device and a method as described in WO2016113488 the disclosure of which is included into this specification as concerns this aspect of the invention.

Also it is possible to use an application system, e.g. according to WO2022058696, which comprises means for moving the support onto which the powder is deposited. The carrier with the powder is then conveyed between electrodes connected to an AC voltage generator, the electrodes on either side of the carrier being connected to one of the terminals of a voltage generator. The electrically-charged powder is carried away by the electric field, perpendicular to the two electrodes, in particular towards the center of the substrate. The powder then impregnates the support.

Also, it is possible to use a device with transverse electrodes, such as e.g. described in FR2402976, or approaches according to FR2306243 or PCT/EP2023/078593, which latter published as WO-A-2024083700.

The particulate sorbent material may be a porous or non-porous functionalized polymer such as an ion exchange resin, a metal-organic framework (MOF, generally speaking a coordination network with organic ligands containing potential voids or porous polymers consisting of metal clusters coordinated to organic ligands to form one-, two-, or three- dimensional structures), an activated carbon, a zeolite, a functionalized porous ceramic like alumina or silica, and/or precursors thereof, and/or mixtures thereof. Particulate sorbent material can be provided for example in the form or powder or precursors thereof (functionalized or non-functionalized), most favorably it is provided in the form of powder.

Typically and preferably, particulate sorbent material is functionalized (on the surface and/or in the bulk) with primary or secondary or tertiary amines, or a combination thereof, capable of reversibly binding carbon dioxide, and are ion exchange resin (I ER) particles, which can either be manufactured at the desired size and/or PSD or which can be ground before the sheet-manufacturing process to the desired size.

The particulate absorbent material should not adsorb water, so it is not a superabsorbent material, and it preferably has the property that it can only uptake or adsorb water up to 80% or 50% of its own mass, preferably it cannot uptake more water than 50% or not more than 40% or 30% or 25% of its own mass. Preferably to have that property, the porosity structure of the particulate absorbent material is chosen to have a specific BET surface area, preferably measured by nitrogen adsorption (BET (Brunauer, Emmett und Teller) surface area analysis is used for the determination of the specific BET surface area applying the method as described in ISO 9277), in the range of 1-20 m2/g, and/or that the sorbent material has a pore diameter distribution, measured by Mercury intrusion, such that 90%, preferably 95% of the pore volume is in the range of 50-300 nm, preferably in the range of 50-250 nm, and/or that the sorbent material has a pore volume distribution, measured by Mercury intrusion, such that the maximum pore volume is at a pore diameter in the range of 80-150 nm, preferably in the range of 100-150 nm, wherein preferably 90%, more preferably 95% of the total pore volume of the distribution is in a window of -50 nm and +150 nm, preferably of -40 and + 100 nm around the diameter of said maximum of the pore volume distribution, and/or that said sorbent material has a total pore volume, measured by Mercury intrusion, in the range 0.05-0.50 cm3/g, preferably 0.10-0.40 cm3/g, most preferably in the range of 0.15-0.35 cm3/g. Mercury porosimetry measurements can be 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 can be used:

• Mercury surface tension: 0.48 N/m

• Mercury contact angle: 150°

• Test method: PASCAL (Pressurized by Automatic Speed-up and Continuous Adjustment Logic)

• Max. pressure: 400 MPa • Increase speed: 6-19 MPa/min

• Preparation: Degassing for 130 min. (also ensured <0.03 kPa reached)

Prior to Hg intrusion, the samples can be degassed under vacuum at 70°C for 12 h.

In another embodiment, particulate sorbent material refers to a solid particulate porous substance that can adsorb CO2, in particular when used for DAC, the solid porous substance comprising amines or polyamines covalently attached to the backbone of a polymeric or copolymeric support.

In yet another embodiment, particulate sorbent material takes the form of particles of support material functionalized on the surface and/or in the bulk with primary or secondary or tertiary amines, or a combination thereof.

The support material of the particles can be an organic cross linked polymeric polystyrene- based support material, functionalised on the surface and/or in the bulk with primary or secondary amines or tertiary, or a combination thereof. Preferably the support material is based on polymeric polystyrene cross-linked by divinylbenzene, wherein further preferably the polystyrene based support material is a styrene divinylbenzene copolymer, preferably in case of said first particles to form the particulate sorbent material surface and/or in the bulk functionalised with primary amine, preferably methyl amine, most preferably benzylamine moieties, wherein the solid polymeric support material is preferably obtained in a suspension or emulsion polymerisation process.

The material of the particles can comprise primary amine moieties as well as in addition at least one of secondary amine or tertiary 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.

According to yet another preferred embodiment, the mean particle size (D50, always volume-based) of the particulate sorbent material, preferably functionalized on the surface and/or in the bulk with primary or secondary or tertiary amines, or a combination thereof, capable of reversibly binding carbon dioxide, is in the range of 1 and 300 microns, more preferably between 3 and 250 microns, or 10 and 200 microns, or 15 and 150 microns, or 20 and 120 microns, or 30 and 100 microns, or 40 and 80 microns, or 50 and 70 microns. The particulate sorbent material may comprise, in addition to actual CO2 sorbent material of a particulate type, further particulate material which is essentially not adsorbing carbon dioxide but which, under the conditions of step 3), e.g. forms an adhesive bond of the particulate sorbent material with the porous substrate. As an alternative or in addition, this further particulate material can also be an additive material providing specific properties to the sorbent impregnated sheet and/or to the particulate sorbent material, for example oxidation resistance, UV resistance, or other types of stability enhancement or for improving thermal conductivity or for improving processing. The proportion of this further particulate material is preferably in the range of 0.1-50 or 0.5-40 weight percent, preferably in the range of 1-30 or 2-20 weight percent, with respect to the total of the particulate sorbent material applied to the porous substrate, or the particulate sorbent material exclusively consists of particulate sorbent material, so actual CO2 sorbent material of a particulate type, and there is no further particulate material which is not absorbing carbon dioxide.

The particulate sorbent material may also take the form of particles of support material functionalized on the surface and/or in the bulk with primary or secondary or tertiary amines, or a combination thereof, wherein preferably the support material of the particles is an organic cross linked polymeric, preferably polystyrene based, support material.

According to yet another preferred embodiment, the weight proportion of the particulate sorbent material to the porous substrate in the sorbent-impregnated sheet is in the range of 40-90 weight percent, preferably in the range of 50-80 weight percent or 60-70 weight percent, relative to the total weight of the sorbent-impregnated sheet.

After or during or before step 3) on one or both sides of the sorbent-impregnated sheet an air permeable sheet can be applied (thermo)adhesively, and/or by crimping, sewing, and/or welding. In fact, material bonding (adhesive bonding), force fit or form fit means are possible for fastening.

So, in addition to the above-described steps, a cover sheet can be added on one or both sides of the substrate or the sorbent impregnated sheet. Such cover sheet has several advantageous effects:

- The cover sheet results in a clean, smooth and powder-free surface. This facilitates postprocessing, for example welding of the sheets if a thermoplastic cover sheet is chosen, and reduces pressure drop;

- The cover sheet prevents/reduces loss of sorbent powder, that is not sufficiently fixated within the structure, through encapsulation;

- Matching the particle size distribution (PSD) of the particulate sorbent material and the pore size distribution of the cover sheet can be important;

- The cover sheet can also improve the mechanical properties of the material; - It is possible to use a homogeneous cover sheet, or a patterned cover sheet to change the mechanical properties only in some areas, for example where post-processing should happen later-on.

The cover sheet(s) can be applied to the substrate before step 1) and/or before or after step 2), and/or after step 3). One particularly advantageous way is by attaching the cover sheet to the bottom of the substrate before applying the powder from the top, then carrying out step 2), and before or after step 3) also on the top the cover sheet is applied. In another particularly advantageous way, the cover sheet is thermo-adhesively fixed to the sorbent impregnated sheet during step 3), after it’s been applied to the substrate before step 1) or before or after step 2) and/or directly before step 3).

The cover sheet and, if applicable, an adhesive used for adhering the cover sheet, increases the thermal mass of the material, such that either more sorbent has to be dry- impregnated in step 2) compared to a configuration without cover sheet(s) to achieve the same sorbent loading, or a lower loading will be achieved (loading referring to the total particulate CO2 sorbent material weight, and typically excluding the non-CO2 sorbent particulate material weight, divided by the total impregnated sheet weight including, if applicable, cover sheet weight and, if applicable, weight of adhesive and, if applicable, weight of essentially non CO2 sorbent particulate material). The loading typically refers to the dry loading, essentially without any water contained in the impregnated sheet. If necessary, a thermoadhesive web can be used to adhere the cover sheet to the sorbent.

In the step 3), the powder is fixed through a heat and/or pressure and/or radiation treatment. Such treatment preferably takes place in a heat press or in a flat-belt calender. Other calenders or combinations of different types of calenders can be used as well.

Typically, the temperature applied during the calendering step is in the range of 50 - 300 °C, more preferably in the range of 100-240 °C or 110-220 °C or most preferably in the range of 120-200 °C or 130-180 °C or 140-160 °C.

Moreover, the pressure applied is typically in the range of 0.5-20 bars, preferably in the range of 0.7-3 bars or 1-2 bars.

The heat is typically applied for a duration of 5-300 s, more preferably for a duration of 20- 200 s and most preferably for 30-90 s. Shorter exposure times can be partially compensated with higher temperatures. In particular when using fibers with different melting points including also bi- and multicomponent fibers where the components feature a different melting point, heating the material only to below the melting point of at least one of the higher melting fibers or fiber components allows to bind the particulate sorbent material to the fiber component with the lower melting point whilst maintaining porosity of the sorbent-impregnated sheet. The heat/pressure treatment moreover compacts the material. The particulate sorbent material is thus fixed a) through adhesion to the partially molten fibers and b) through interlocking within the structure and c) if applicable through the non- CO2 sorbent particulate material and d) if applicable through the cover sheet.

The conditions during this calendering can turn out to be important for achieving key properties of the final structure. Adapting the calendering conditions properly can surprisingly make sure that the corresponding final structure provides for the optimum porosity and corresponding equilibrium capture capacity and quick carbon dioxide uptake and release properties, but also low water uptake properties (not only relevant for the sorbent material as such as pointed out above, but equally or even more so for the final sorbent impregnated sheet structure), for providing a low pressure drop in capture structures comprising the corresponding sorbent impregnated sheet structures, and for (making sure that the particulate sorbent material is not released during further processing and/or during CO2 capture cycling (also termed "powder loss"), and to avoid delamination of the sorbent impregnated sheet, or a combination of these properties.

Note that water uptake is an important parameter for the sorbent-impregnated sheet in particular if the sorbent-impregnated sheets are used in a CO2 capture process using steam desorption. If water is absorbed by the sorbent-impregnated sheets and not released in the other parts of the cycle, absorbed water will accumulate and can negatively impact adsorption and desorption performance (uptake and kinetics) and also lead to swelling and/or deformation of the sorbent-impregnated sheets, leading to a pressure drop which will impair the efficiency of adsorption and desorption in the CO2 cycle.

So, it is important to adapt the calendering conditions to avoid complete compression and to thereby destroy the porosity of the sorbent impregnated sheet, to avoid heating so that the particulate sorbent material is harmed by the calendering process e.g. by losing porosity and/or capture active amine moieties (e.g. by oxidation of the amine moieties), and to make sure that the particulate sorbent material is nevertheless as much as possible adhering to the fibers of the sorbent impregnated sheet.

In particular for the situation of using organic polymeric (bicomponent) fibers based on unsaturated hydrocarbon starting materials, such as polyethylene, polypropylene, polybutylene or combinations thereof, and in particular for the situation of using particulate sorbent material based on organic polymeric backbone structures, for example comprising styrene building blocks, of the types as described above, it turns out that the temperature during the calendering is preferably adapted to be below 160 °C or below 150 °C, preferably below 140 °C and preferably in the window of 125 °C - 135 °C (temperature that the sheet reaches on its surface or in its core is relevant here, the temperature setpoint of the device used for calendaring may differ), alone or this in combination with a duration of applying this heat in the range of 5-150 seconds or preferably 20-70 seconds depending on the heat capacity, heat transfer properties and grammage of the materials used. Also, high pressures can be applied using these conditions, so the pressure applied can under these conditions but also more generally be in the range of 0.5-50 bars, preferably 1-20 or 2-10 or 3-6 bars. Pressure, in particular in these ranges, can be applied independently of and separate from the heat treatment in a subsequent step and/or during at least part of the heat treatment and/or at the end of the heat treatment or combinations thereof.

The thickness of the final sorbent impregnated sheet after the calendering can then, but also more generally, go down to 0.2-2 mm or preferably 0.3-1.5 mm or 0.4-1.2 mm.

Normally, increasing the pressure and/or temperature and/or residence time leads to a sheet with a higher density, lower thickness, lower water uptake, lower powder-loss and less delamination, which are all beneficial properties as described in more detail below. However, when increasing either of these parameters too much, the CO2 capture properties of the material can suffer either because of degradation of the CO2 capture amine moieties (for example oxidation) or loosing porosity of the sorbent or of the sorbent impregnated structure (for example by completely melting the polymeric substrate this encapsulating all sorbent without and porosity for air/CO2 flow and diffusion; measuring the air permeability through the sheet allows for a quick check if there is still some porosity retained but that lower air permeability does not directly translate to lower kinetics for CO2 uptake), shrinkage of the sheets, clogging of pores, densifying the material too much thus reduce diffusion of CO2 into and out of the structure, etc. For example, a higher grammage of substrate with a high sorbent loading may need a longer residence time to heat through the whole impregnated sheet than a low grammage substrate impregnated with low sorbent loading. Or a more conductive material may need less residence time compared to a less conductive material.

In general, when talking about substrate materials made from bi-component or multicomponent fibers, the temperature window within which to optimize is typically quite narrow as the melting points of the different fiber types tend to be not very far apart for good processability. A good heat treatment is characterized by having a temperature that is above the melting point (range) of the material(s) with the lower melting point and below the melting point (range) of the material(s) with the higher melting point, thus it is preferred to operate in a rather narrow temperature range defined by these boundaries. For typical bi-component fibers made from PE/PP, for example, temperatures in the range of ~130°C and ~150°C are beneficial, as they allow for completely melting the PE which leads to a good adherence of the powder to the fibers and the fibers to each other, but are low enough to prevent melting of the PP component or substantial shrinkage. These temperature ranges may vary for different polymers/polymer mixtures, and the values given are the temperatures that the impregnated parts of the core of the sheets should reach and no part of the sheets should exceed; the actual settings of the heating device (heat press, laminating press, calender) may differ from these temperature, i.e. be higher in case of slow heat transfer or short residence times. Typically, longer residence times are required for lower temperatures and vice versa.

Lower thickness and correspondingly higher density of the sorbent impregnated sheets that can be achieved with optimized calendering parameters is beneficial for the CO2 capture process in particular as it allows to fit a higher sorbent impregnated sheet mass into the same volume of capture structure comprising the corresponding sorbent impregnated sheet structures, whilst still allowing for the same low pressure drop, i.e. the same extra-sheet void fraction for air to flow through, thus increasing the amount of CO2 that can be captured per volume of capture structure. As an alternative, a capture structure with a higher extrasheet void fraction and thus lower pressure drop that nonetheless contains the same sheet mass can be build from higher density sheets, thus reducing the energy needed for flowing air through the capture structure.

Moreover, such sorbent impregnated sheet that has undergone optimized heat/pressure treatment will take up substantially (e.g. 30-50% less or up to or -50%) less water, measured for example as weight increase compared to a fully dry sheet after immersion in water for a sufficient time to be fully soaked, compared to a sorbent impregnated sheet that has undergone no or a non-optimized heat/pressure treatment. This may be related to the lower void fraction of the sheet itself available for water entrainment and the lack of delamination. Such lower water uptake is particularly beneficial for carbon capture processes, especially such processes where heat is used for regeneration, as all water adsorbed or entrained within the structure will have to be heated up as well thus leading to additional energy needs.

The residence time at heat and/or pressure is preferably optimized to make sure that the material is completely heated through such that also the sorbent material in the middle/core of the sorbent-impregnated sheet is bonded to the fibers, and not only the sorbent on one or both outer sides. Applying heat from both sides can be beneficial, because the overall residence time at a given temperature can be reduced compared to a setup where heat is applied only on one side, which may in addition induce stress and deformation in the material. Cooling directly after the heat treatment can be beneficial to further reduce exposure time at high temperature. In case the material is not completely heated through, delamination in the middle is possible. Such delamination can be visible directly after the manufacturing of the dry impregnated sheet, or only after further processing/handling (additional stress/strain/deformation causes the already instable middle section to delaminate) or when using the material in a direct air capture process. This is not only undesirable because it may increase powder loss, but also because it can lead to an increase in thickness and thus increase in pressure drop when air flows between two sheets, or may lead to additional water uptake.

Another alternative combines the step 3) or follows up on it with a forming step, for example an embossing step, either by integrating the forming step in the calendering step, or by adding a forming step after the calendering step. Such forming step can form embosses into the sheet or corrugate or pleat the structure to facilitate the use in a parallel-passage contactor for DAC. Embosses can for example be used to a) space two sheets apart or b) stiffen specific parts of the sheets by compressing them more, whereas other parts stay softer. Methods as disclosed in the application EP 24 161 426.2 can be used for such three- dimensional structuring, the disclosure of this application is included into the present application as concerns this structuring aspect.

In yet another alternative embodiment particulate sorbent material is deposited on the substrate together with one or multiple additional preferably powder material(s), preferably after prior mixing of the different materials, and/or the additional material(s) are deposited on the porous material before and/or after the particulate sorbent material is deposited. Such additional powders may for example be a binder powder, a powder to add thermoformability, a powder to reduce oxidation, increase stability, make it conductive, etc. Also an application of two or more different sorbent materials is possible.

In yet another embodiment, a heat treatment can be applied to the porous support structure, preferably prior to powder deposition, to increase the thickness of the material, as described in patent application WO2016113488.

In yet another embodiment, the porous substrate is inhomogeneous across its thickness, for example the nonwoven features a denser side and a less dense side, whereas the denser side is difficult for the particulate sorbent material to penetrate during dry impregnation thus preventing powder loss from this denser side. Such material can make the use of a cover sheet unnecessary. Another embodiment uses substrates with a steady decrease in density from bottom to the top, such that fine particles can easily penetrate to the bottom during dry impregnation, whereas coarser particles would be held back at the top. Moreover, this invention also refers to an embodiment where two such sheets are adhered together back-to-back to result in a combined sheet that has coarser particles at the outside and smaller particles at the inside, which can be beneficial for mass transfer. A similar configuration can also be achieved with varying dry-impregnation settings. Such configuration can be beneficial for direct air capture, as the larger outside particulate sorbent material is easier to adhere thus limiting loss of particles, but at the same time would be in best contact with the airflow thus counteracting possibly slower mass transfer due to the larger particle size.

Another alternative is the use of a porous substrate that is non-homogeneous in x/y direction, thus creating also a non-homogeneous pattern in the sorbent-impregnated sheet. For example, a substrate can feature denser and less dense parts, which would lead to the dense parts being impregnated with a lot of powder, whereas the less dense parts would hold less powder. Such parts with less powder would be thinner and could be more mechanically stable after the heat/pressure treatment, thus increasing the mechanical stability of the sheet. Moreover, they could also be put in places where post-processing will require e.g. cutting/removing/welding of material to avoid unnecessary waste of particulate sorbent material.

Moreover, the present invention relates to an adsorber structure made from sorbent impregnated sheets arranged in a parallel passage contactor to allow flow over the structure. Such parallel-passage contactors can be built by adding spacing elements. In a different embodiment, such parallel-passage contactors can be spaced by thermoformed embosses that are formed into the sheet either as part of the heat treatment, or in a subsequent step. It is possible to subject the sheet after step 3) or also during such step 3) to a temperature in the range of 50-300 °C, preferably 60-240 °C and embossing at least one protrusion into said thermoplastic sheet to form an embossed sorbent sheet. Methods as disclosed in the application EP 24 161 426.2 can be used for such three-dimensional structuring, the disclosure of this application is included into the present application as concerns this structuring aspect.

In yet another embodiment, a parallel passage contactor consists of corrugated or pleated sheets, that can be alternated with flat sheets, to form a honeycomb-like structure with triangular (pleated), sinusoidal, rhombus-shaped, or similar parallel, essentially identical channels. A rolled configuration is possible as well. Sheets in a contactor may be arranged horizontally or vertically.

In order to achieve homogeneous impregnation, high sorbent loadings (wt%) as required in DAC processes with a heat-up step to reduce parasitic thermal energy, and good powder fixation, sorbent particle size and the characteristics of the porous substrate have to be matched such that a) the particulate sorbent material can penetrate through the porous substrate upon dry-impregnation and b) the particulate sorbent material is fixated within the porous substrate after step 3. For a coarse porous material as substrate and fine powder as particulate sorbent material, the particulate sorbent material is not held back by the porous substrate and thus cannot be impregnated homogeneously; for a coarse powder and very fine porous substrate the powder cannot penetrate throughout the material, and for very coarse fibers and fine powder, the powder is not well fixated. The optimal particle size distribution for a specific substrate ensures a good penetration of the porous substrate, a good fixation afterwards, good mechanical stability. Moreover, the particle size impacts the adsorption kinetics, such that different particle sizes may be preferred for particulate sorbent materials with different intrinsic kinetics, which may require the choice of a different substrate for different sorbent types and sorbent particle size distributions.

According to yet another aspect of the present invention, it relates to a sorbent- impregnated sheet obtainable or obtained using such a method.

The final sorbent impregnated sheet typically has a thickness in the range of 0.2-3 mm, more preferably in the range of 0.5-2 mm and most preferably in the range of 0.6-1 .5 mm . Moreover, the sorbent impregnated sheet typically has a density in the range of 0.2 - 1 g/cc, more preferably in the range of 0.3 - 0.6 g/cc or 0.4-0.5 g/cc. In addition, the final sorbent impregnated sheet typically features a much lower air permeability than the porous substrate.

The sorbent impregnated sheet typically features a particulate sorbent material content (by mass, dry w%) in the range of 30-95 w%, more preferably of 50-90 w% and most preferably of 60-80 w%. Lower sorbent loadings are easy to achieve, but not preferred due to the additional thermal mass of the porous substrate. Higher particulate sorbent material loadings are challenging to achieve whilst maintaining good mechanical properties and fixation of particulate sorbent material.

Moreover, the sorbent impregnated sheet typically features a lower air permeability, than the sheet before fixation, in the range of 5 - 500 l/m2/s, more typically in the range of IQ- 400 or 50-300 l/m2/s. Moreover, if a cover sheet is applied on one or both sides of the material, the air permeability is reduced further featuring final air permeabilities typically in the range of 5 - 300l/m2/s.

According to yet another aspect of the present invention, it relates to a use of such a sorbent-impregnated sheet for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas (e.g. including off-gas from other carbon capture system or CO2 capture for closed environments or mixes thereof or off-gas from DAC systems), containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide.

According to another 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 at least one such sorbent-impregnated sheet adsorbing said gaseous carbon dioxide in a containment unit, wherein the method comprises at least the following sequential and in this sequence repeating steps (a) - (e):

(a) contacting said gas mixture with at least one sorbent-impregnated sheet to allow at least said gaseous carbon dioxide to adsorb on (including in the porosity thereof) the sorbent- impregnated sheet by flow-through through said unit (and over/into the sheets) essentially under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step;

(b) isolating said sorbent-impregnated sheet with adsorbed carbon dioxide in said unit from said flow-through;

(c) inducing an increase of the temperature of the sorbent-impregnated sheet, preferably to a temperature between 60 and 110 °C, starting the desorption of CO2;

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

(e) optionally bringing the sorbent-impregnated sheet essentially to ambient atmospheric temperature conditions and ambient atmospheric pressure conditions.

According to another aspect of the present invention, it relates to a carbon dioxide capture, preferably direct air capture system comprising at least one such sorbent impregnated sheet.

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 a schematic of a dry-impregnation step;

Fig. 2 shows carbon dioxide uptake curves for the materials according to Example 2 normalized by the equilibrium CO2 uptake of the particulate sorbent before dry impregnation;

Fig. 3 shows carbon dioxide uptake curves for the materials according to Example 3 and Example 4 normalized by the equilibrium CO2 uptake of the particulate sorbent before dry impregnation;

Fig. 4 shows equilibrium carbon dioxide capacity for the materials according to Example 3 normalized by the equilibrium carbon dioxide capacity for the flat sheet; Fig. 5 shows carbon dioxide mass transfer for the materials according to Example 3 normalized by the carbon dioxide mass transfer coefficient for the flat sheet.

DESCRIPTION OF PREFERRED EMBODIMENTS

As mentioned above, the proposed method typically comprises at least the following steps

1) Providing a porous substrate;

2) Dry impregnating the porous substrate with at least a particulate sorbent material;

3) Post-processing the dry-impregnated material using heat and/or pressure and/or radiation to fix the particulate sorbent material resulting in a sorbent-impregnated sheet.

In the second step, particulate sorbent material is added to the porous substrate and dry impregnated. A scattering unit can be used for powder deposition, and a schematic of such a dry-impregnation step is shown in Fig. 1. The principle is described for example in the following patent applications: WO2010001043; WO2015044605, WO2016092205, WO2016113488, WO2022058696 which for the method and for the dry impregnating device are included into this disclosure.

The application system which can be used, e.g. according to WO2022058696, may comprise means for moving the support onto which the powder is deposited. The carrier with the powder is then conveyed between electrodes connected to an AC voltage generator, the electrodes on either side of the carrier being connected to one of the terminals of a voltage generator. The electrically-charged powder is carried away by the electric field, perpendicular to the two electrodes, in particular towards the center of the substrate. The powder then impregnates the support.

A further improvement of such a device/method in particular with transverse electrodes can alternatively be used, such as e.g. described in PCT/EP2023/078593 filed on October 16, 2023, which published as WO-A-2024083700, or FR2306243 filed on June 17, 2023, or FR 2402976 filed on March 25, 2024.

More specifically, a porous substrate 4 is provided, in this case schematically illustrated as a woven, and on one or both sides it is provided with a layer or impregnation of particulate sorbent material 3. This application may take place by spraying or pouring or scattering, for example using a scattering roller with needle covering and a brush belt to transfer the corresponding powder from a dispenser onto the surface of the substrate. In addition, the powder may be scattered through a mesh to improve the homogeneity of the distribution. One possibility to do this is to apply the powder by way of a slot dispenser where the slot direction is perpendicular to the paper layer in the illustration of Fig 1 when the substrate is transported from left to right or the opposite way, and applying the powder to the upper surface while shifting the porous substrate 4 between the two electrodes 1. These electrodes 1 are arranged essentially parallel to each other and during insertion there is no potential applied. In the space between the two electrodes 1 and adjacent or essentially adjacent to each of the electrodes a dielectric layer 2 is provided to avoid contact of the electrodes 1 with the powder and the substrate. Once the powder covered substrate is placed between the two electrodes and dielectric layers, an alternating voltage 5 is applied, leading to the distribution of the powder within the porosity of the substrate, i.e. leading to an essentially homogeneous distribution of the particles in the porosity of the sorbent- impregnated sheet before post-processing 6. This is then followed by the post processing which leads to attachment of the powder particles to the substrate forming the final sorbent- impregnated sheet. The post processing can take place within the same device or in another device (for example a calender, preferably a flat-belt calender). The process as illustrated in this figure can be a batch process or a continuous process.

Example 1 :

A sheet was produced from ~70wt% particulate sorbent material (particulate sorbent material in this example being composed of ~40 w% non-CO2 sorbent particulate material) and ~30 wt% porous substrate as follows:

I ER beads were synthesized as follows: 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 1 h. 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 for 24 h. After that, the beads are filtered off and washed 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 filtered off and washed to neutral pH with demineralized water.

The I ER beads were then milled in a jet mill to obtain particulate sorbent material powder at -3 microns and ~40 microns (D50). Each sorbent powder was mixed -60:40 w/w (60 w% sorbent) with co-polyester binder powder with a melting point of -130 °C and a particle size in the range of 50-80 microns (D50) and using a thermomixer heating from 100 °C to 130 °C, a 5 °C gap was set every 5 minutes until 130 °C, then 10 minutes at this temperature.

The resulting mixed powder was then scattered on top of a PET/co-PET nonwoven with, 150g/m2, 2.05 mm thickness, and 2000 l/m2/s air permeability (measured at 200 Pa) in a ratio of -70:30 w/w (70 w% sorbent-binder mixture, i.e. mixture of CO2 adsorbing particulate material and essentially non CO2-adsorbing particulate material), dry impregnated in a dryimpregnation device as described above and heat treated in a flat belt calender pneumatic heat press at 147 °C, a speed of 2 m/min, a pressure of 10 N/cm2 and 2 mm distance between the belts.

Both particle sizes of sorbent result in a homogeneous impregnation, but the 3-micron powder results in a poorer attachment.

Example 2:

A PE/PP nonwoven with a high amount of bi-component fibers (fiber diameter about 25 pm), 70 g/m2 weight, 2.5 mm thickness and 2800 l/m2/s air permeability at 200 Pa was provided, particulate sorbent powder produced as in Example 1 with 40 microns size (D50) and dry-impregnated.

The dry-impregnated sheet was then heat-treated at 130°C/4 bars for 60 s and at 140 °C / 2 bars also for 60 s. The application of less pressure results in a 25% thicker sorbent- impregnated sheet with lower density.

A final sheet with 70 wt% sorbent and a thickness of 0.2-3 mm.

A key advantage compared to Example 1 is the higher particulate sorbent material loadings that can be achieved in this process due to the omission of binder powder. One important parameter enabling the binding of the sorbent even without binder powder is the amount of bi-component fibers in the nonwoven. The bicomponent fibers feature a component (PE) with lower melting point and another one with higher melting point (PP). During the heat treatment at 130 °C/3 bars, the PE component of the bicomponent fibers melts thus fixating the sorbent powder. PE is a particularly suitable component for such bicomponent fibers, as the melting point is higher than the typical desorption temperature of low-T adsorption based DAC processes as described with a maximum typically around 100 °C, but at the same time allows to carry out the heat treatment at low temperatures, thus resulting in limited degradation (oxidation) of the temperature-sensitive particulate sorbent material and reduced heat demand compared to materials with a higher melting point.

After fixing the powder in the substrate, a PES (20 g/m2, >3100 l/m2/s air permeability) spunbound cover sheet was laminated to both sides of the base sheet applying the same heat treatment as before, but for 20 s only.

This results in a sorbent-impregnated sheet with slightly higher thickness, and approx. 65 wt% sorbent. The resulting sheets have an air permeability of roughly 10 l/m2/s and can be steamed and soaked in hot and cold water without significantly changing their shape or loosing powder.

The adsorption performance of both sorbent-impregnated sheets was tested by stacking 8 sheets in parallel in a small contactor and placing them in an CO2 adsorption desorption device and no difference was found between the sheets with and without cover sheet regarding CO2 uptake (normalized by sorbent mass) and kinetics. The uptake (normalized by sorbent mass) was found to be in line (within the range of uncertainty) with the uptake of the sorbent before dry-impregnation as shown in Fig. 2. which shows the CO2 uptake of the sheets per g of dry sorbent within the sheet normalized by the CO2 uptake per g of dry sorbent before dry-impregnation. For both cases, the CO2 uptake curves were measured in a CO2 adsorption-desorption device on a mini-module made from 8 sheets stacked in parallel and operated as a parallel-passage contactor with air flowing in between the channels, and the behavior is shown in Fig. 2. The measurement was made with steambased desorption, at 20 °C/65 %RH, each sheet 20 mm x 40 mm.

Thus, importantly, the dry-impregnation with subsequent fixing does not limit the access of CO2 to the sorbent pores and active sites. This is an advantage compared to wet- impregnated or coated material, that typically uses a binder, that will at least partially block sorbent pores and thus limit the CO2 access to the active sites, resulting in a reduction in equilibrium uptake and/or kinetics.

Example 3:

PE/PP nonwoven with 100% bi-component fibers (fiber diameter about 18 pm), an air permeability of 2300 l/m2/s and ~3 mm thickness and 80 g/m2 was provided. Particulate sorbent material prepared as described above at a mean particle size of ~50 microns (D50) was scattered on top to reach a weight percentage of ~75 w% particulate sorbent material. Afterwards, the particulate sorbent material was dry impregnated in a laboratory dryimpregnation device.

The powder was then fixed in a first heat treatment at 130 °C using a flat-belt calender and 10 N/cm2 pressure with 0.9 mm distance between the belts.

Subsequently, a PET spunbound cover-sheet with a weight of 20 g/m2 was fixed to both sides of the sorbent-impregnated sheet using a thermoadhesive web made from co-PET with a weight of 8 g/m2 at a temperature of 150 °C, a pressure of 10 N/cm2 and 0.7 mm distance between the belt.

The resulting sheets have a sorbent content of 67 w%. The air permeability is roughly 85 l/m2/s.

The sheets were then characterized in the same adsorption-desorption device as in Example 2. A mini-module made from 8 sheets stacked in parallel to form a parallel-passage contactor was tested. The uptake (normalized by sorbent mass) was found to be in-line (within the range of uncertainty) with the uptake of the sorbent before dry-impregnation as shown in Fig. 3.

The sorbent-impregnated sheets were then corrugated using a hair crimper with the medium crimping plates attached. A temperature of 140 °C was selected and sheets of 4 cm height were crimped for ~1 minute heat treatment duration per sheet, which resulted in good and permanent deformation of the sheets with a total pleat height of approximately 4 mm.

The adsorption performance of both flat sorbent-impregnated sheets and corrugated sorbent-impregnated sheets was tested in an adsorption-desorption device by stacking 8 sheets in parallel with 3-7 mm spacing between flat sheets, the spacing between the corrugated sheets is defined by the pleat height. No significant difference was seen between the resulting equilibrium capacity and kinetics of flat and corrugated sheets. This shows that the corrugating did not measurably change the adsorption performance, see Fig. 4 and Fig.

5.

Example 4:

A sorbent-impregnated sheet was produced according to Example 3, but without application of cover sheet. The air permeability was measured to be roughly 350 l/m2/s without cover sheet. Subsequently, the tensile strength of the sorbent-impregnated sheet was determined in a universal testing machine according to DIN EN ISO 29073-3 but with a sample size of 20 mm x 150 mm and a clamping length of 100 mm. The tensile strength was determined both a 65%RH and 20 °C, and at 95 °C. The samples were tested wet after conditioning for 5 min in a water bath at the same temperature as the tensile strength testing took place. The tear strength of the samples at 95 °C is approximately 55 N with an elongation at break of > 30 % and -20% lower at higher temperature compared to 20 °C. This high stability is due to the fibrous substrate material, that provides stability to the sample.

Example 5:

Several sorbent-impregnated sheets were produced according to Example 3 both with and without cover sheets. The resulting sheets were then cut in three pieces each, the dry mass was recorded. Then the sheets were soaked in demineralized water for 5 minutes, drained, and frozen for at least 18 h. Then the sheets were defrosted, one at room temperature, one by boiling in demineralized water, and one by placing onto a steaming insert. These cycles were repeated 38 times. No mass decrease was measured even after 38 cycles of freezing and thawing.

LIST OF REFERENCE SIGNS

1 electrodes

2 dielectric layers

3 particulate sorbent material, powder

4 porous substrate, textile

5 alternating voltage

6 sorbent-impregnated sheet before post- processing

Claims

1. Method for the manufacture of a sorbent-impregnated sheet comprising at least the following steps:

1) providing a porous substrate (4) in the form of a sheet or a band and applying a particulate sorbent material (3) to at least part of one of the faces of the porous substrate (4), wherein the particulate sorbent material (3) is a material capable of reversibly binding carbon dioxide;

2) electrostatic dry impregnation of the porous substrate (4) with the particulate sorbent material (3) to distribute said particulate sorbent material (3) within the porous substrate (4);

3) fixing the particulate sorbent material (3) within the porous substrate (4) by applying at least one of heat and pressure and radiation.

2. Method according to claim 1 , wherein the porous substrate (4) is a fibrous, woven or nonwoven band or sheet, or an open pore foam or sponge band or sheet, and/or wherein the porous substrate (4) has an air permeability measured at 200 Pa of 1000-10000 l/m2/s, more preferably in the range of 1500-5000 l/m2/s, and/or wherein the porous substrate (4) is based on or consists of polymeric, preferably at least partly or fully thermoplastic fibers, and/or wherein the porous substrate (4) has a base weight in the range of 10-400 g/m2, preferably in the range of 20-200 g/m2 or 30-150 g/m2 or in the range of 50-120 g/m2.

3. Method according to any of the preceding claims, wherein the porous substrate (4) is a fibrous, woven or nonwoven band or sheet, and wherein at least 20 or at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent, or all of the fibers are bi- or multicomponent fibers, preferably with a core with a melting point or melting range higher than the shell of the fibers, and preferably having at least one component with a melting or softening temperature which is below the temperature in step 3), but which is above the temperature, at which the particulate sorbent material (3) desorbs carbon dioxide.

4. Method according to any of the preceding claims, wherein in step 2) the porous substrate (4) with the particulate sorbent material (3) is placed between two electrodes (1) preferably covered with dielectric layers (2) on the side facing the porous substrate (4), and wherein for the dry impregnation an alternating voltage of at least 5 kV, preferably at least 20 kV, or in the range of 25-60 kV is applied, preferably with a frequency in the range of 50-200 Hz, or in the range of 75-125 Hz at a spacing of the electrodes (1) in the range of 5-30 mm, or in the range of 10-20 mm, for a time span of at least two seconds or 4-20 seconds.

5. Method according to any of the preceding claims, wherein the particulate sorbent material comprises, in addition to sorbent material, further preferably particulate material which is not absorbing carbon dioxide, wherein preferably such further material, under the conditions of step 3), forms an adhesive bond of the particulate sorbent material with the porous substrate, and/or wherein preferably such material provides specific desirable properties to the sorbent impregnated sheet and/or to the particulate sorbent material, wherein the proportion of this further particulate material preferably is in the range of 0.1-50 or 0.5-40 weight percent, more preferably in the range of 2-20 weight percent, with respect to the total of the particulate material applied to the porous substrate, or wherein the particulate sorbent material exclusively consists of particulate sorbent material, and/or wherein the particulate sorbent material takes the form of particles of support material functionalized on the surface and/or in the bulk with primary or secondary or tertiary amines, or a combination thereof, wherein preferably the support material of the particles is an organic cross linked polymeric, preferably polystyrene based, support material.

6. Method according to any of the preceding claims, wherein the particulate sorbent material has a mean particle size of the particulate sorbent material, preferably functionalized on the surface and/or in the bulk with primary or secondary or tertiary amines, or a combination thereof, is in the range of 1 and 300 microns, more preferably between 3 and 250 microns, or 10 and 200 microns, or 15 and 150 microns, or 20 and 120 microns, or 30 and 100 microns, or 40 and 80 microns, or 50 and 70 microns.

7. Method according to any of the preceding claims, wherein the weight proportion of the particulate sorbent material to the porous substrate in the sorbent- impregnated sheet is in the range of 40 - 95 or 40-90 weight percent, preferably in the range of 50-80 weight percent or 60-70 weight percent, relative to the total weight of the sorbent- impregnated sheet.

8. Method according to any of the preceding claims, wherein an air permeable cover sheet is added to the sorbent-impregnated sheet, preferably before, during or after step 2) or during or after step 3), and preferably fixed to the sorbent-impregnated sheet, preferably during step 3, on one or both sides of the sorbent-impregnated sheet.

9. Method according to any of the preceding claims, wherein in step 3) and/or during step 3) a temperature in the range of more than 50 °C or more than 80 °C, preferably more than 100 °C, or in the range of 50-300 °C, preferably 60-240 °C or 120-200 °C, is applied, preferably for a time span of at least 1 or at least 2 or at least 5 or 10 seconds, preferably at least 20 seconds, or in the range of 30-200 seconds, and/or wherein in step 3) a pressure in the range of at least 150 kPa, or in the range of 180-300 kPa is applied preferably for a time span of at least 10 seconds, preferably at least 20 seconds, or in the range of 30-200 seconds.

10. Sorbent-impregnated sheet obtainable or obtained using a method according to any of the preceding claims.

11. Sorbent-impregnated sheet according to claim 10, wherein the porous substrate thereof is a fibrous, woven or nonwoven band or sheet, and wherein at least 50 weight percent, at least 70 weight percent, or at least 90 weight percent, or all of the fibers are multicomponent, preferably bicomponent, fibers, preferably having at least one component with a melting or softening temperature which is below the temperature in step 3), but which is above the temperature, at which the particulate sorbent material desorbs carbon dioxide, and/or wherein the sorbent-impregnated sheet has a thickness in the range of 0.2- 3 mm, more preferably in the range of 0.5-2 mm and most preferably in the range of 0.6-1.5 mm.

12. A contactor unit, preferably parallel-passage or multi-channel contactor unit, comprising at least one sorbent-impregnated sheet according to any of claims 10 or 11 , in particular for direct air capture, or a direct air capture unit comprising at least one such contactor unit.

13. Use of a sorbent-impregnated sheet 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.

14. 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 at least one sorbent-impregnated sheet according to any of claims 10 or 11 adsorbing said gaseous carbon dioxide in a containment unit, wherein the method comprises at least the following sequential and, in this sequence, repeating steps (a) - (e):

(a) contacting said gas mixture with at least one sorbent-impregnated sheet to allow at least part of said gaseous carbon dioxide to adsorb on the sorbent-impregnated sheet by flow-through over/through said unit essentially under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step;

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

15. Carbon dioxide capture, preferably direct air capture system comprising at least one sorbent impregnated sheet according to any of the preceding claims 10 or 11 or a contactor unit according to claim 12.