A self-assembling carbon dioxide removal structure and methods of making the same

Abstract

A carbon dioxide removal structure for separating gaseous carbon dioxide from a gas mixture containing said gaseous carbon dioxide comprises a support body having at least one attachment surface 5, a

Description

Technical Field The present invention relates to self-assembling carbon dioxide removal structures, in particular carbon dioxide removal structures that can be used in direct air carbon capture (DAC), as well as their methods of manufacture and regeneration. Background Carbon capture is a process designed to capture carbon dioxide (CO2) emissions generated from industrial processes, particularly those associated with the burning of fossil fuels. The primary goal is typically to mitigate the impact of CO2, a major greenhouse gas, on climate change. In carbon capture systems, CO2 is separated from other gases emitted during combustion or industrial activities before it is released into the atmosphere. Direct Air Carbon Capture (DAC) is a technology designed to remove carbon dioxide (CO2) directly from the ambient air, independent of its source. Unlike traditional carbon capture technologies that capture CO2 emissions from specific point sources like power plants, DAC focuses on extracting CO2 directly from the atmosphere. The captured CO2 can then be stored underground, utilized in various industrial processes, or converted into valuable products. Adsorber structures in the form of monoliths and packed beds are commonly used in carbon capture technology, specifically in the context of absorption-based processes where gases, such as carbon dioxide (CO2), are captured by a medium. Both structures provide large surface areas for efficient contact between the gas which contains CO2 and the capturing medium. Laminar sheet or plate systems can also be used, providing aspects of each of the above systems. WO2021239747A1 describes a laminar sheet or plate system for DAC. A monolith is a structured and continuous adsorbent support system designed to facilitate efficient chemical reactions. It typically consists of a single, solid piece with a highly porous structure that provides a large surface area for adsorption to take place. The key features of monoliths are: Structured Design: The monolith is engineered with a specific geometric shape, often resembling a honeycomb or a series of parallel channels. This structured design ensures uniform flow distribution and maximizes the contact between reactants and the adsorbent. Porosity: The monolith is characterized by a high degree of porosity. The walls of the channels or honeycomb-like structure are filled with an adsorbent material. This porous structure allows gas molecules to flow through the channels and come into close proximity with the adsorbent. Adsorbent Immobilization: The adsorbent material is typically immobilized within the porous structure of the monolith. Various techniques, such as impregnation, deposition, or coating, are used to ensure even distribution and fixation of the adsorbent material throughout the monolith. A packed bed for adsorption is a structured arrangement of adsorbent material, typically in the form of spheres or extrudates, within a vessel. Proper design and control of flow and regeneration processes are essential for effective adsorption and regeneration. The laminar plate or sheet system is comprised of a plurality of air collection surfaces that includes solid sheets or plates aligned in parallel to provide fluid flow channels therebetween. The channels can be used as both airflow and heated fluid flow channels, and these can be arranged such that heating channels are provided either side of air flow channels. Monoliths, laminar sheet systems and packed beds each have their own set of advantages and disadvantages. Monoliths and laminar sheet systems offer the following advantages: (1) Low Pressure Drop: Monoliths and laminar sheet systems typically offer a lower pressure drop compared to packed beds. This means that fluids can flow through a monolith or laminar sheet system with less resistance, which can be crucial in applications where maintaining a specific flow rate or minimizing energy consumption is important. (2) High Surface Area: Monoliths and laminar sheet systems often have a high surface area per unit volume, making them well-suited for processes that involve surface interactions, such as catalysis and adsorption. The increased surface area can lead to higher efficiency in these processes. (3) Uniform Flow Distribution: Monoliths and laminar sheet systems are designed to provide uniform flow distribution across their entire surface. In contrast, packed beds may suffer from channelling or uneven flow, which can result in uneven contact between the fluid and the solid phase. (4) Enhanced Mass Transfer: The structured design of monoliths and laminar sheet systems can promote efficient mass transfer. (5) Resistance to Plugging: Monoliths and laminar sheet systems are often less susceptible to particle clogging or plugging, which can be a concern in packed beds when fine particles or contaminants are present in the fluid. (6) Ease of Scale-up: Monoliths and laminar sheet systems can be more easily scaled up in size and adapted to different applications. They can be manufactured in various shapes (particularly monoliths) and sizes to accommodate specific process requirements. (7) Improved Heat Transfer: Monoliths and laminar sheet systems can facilitate efficient heat transfer due to their high surface area and uniform flow distribution. This makes them suitable for applications involving heat exchange and temperature control. (8) Reduced Material Usage: Monoliths and laminar sheet systems can be designed with thinner walls and less material compared to packed beds, making them a more resource-efficient option. (9) Ease of Cleaning and Maintenance: Cleaning and maintaining monolith structures can be simpler than packed beds, especially when dealing with fouling or contamination issues. Whilst packed beds provide the following advantages: (1) Versatility: Packed beds can accommodate a wide range of particle sizes and shapes, allowing flexibility in selecting the packing material to suit specific process requirements. (2) Scalability: Packed beds are often easier to scale up for larger industrial processes. They can be adjusted in size without major design changes, making them suitable for various production scales. (3) Simple Construction and Replacement: Packed beds are relatively straightforward to construct and replace, making them cost-effective and convenient for processes where frequent replacement or maintenance is necessary. (4) Mixing and Redistribution: Packed beds can provide better mixing of reactants or fluids when required. The random arrangement of particles in a packed bed can enhance mass transfer and chemical reactions in some cases. (5) High Porosity Options: Packed beds can be designed with high porosity, allowing for efficient permeation of gases or liquids through the bed, which can be advantageous in certain applications. (6) Cost-Effective Materials: Packing materials for packed beds are often readily available and can be cost-effective compared to the production of complex monolith structures. (7) Resistance to Fouling: Packed beds may have better resistance to fouling or clogging in some situations, as particles can be replaced or cleaned more easily compared to monoliths with intricate channels. (8) Adaptability to Non-Uniform Flow: In processes where flow rates are not uniform or where the flow pattern needs to be adjusted, packed beds can be manipulated more easily to achieve the desired flow distribution. (9) Established Design Guidelines: Packed beds have been widely used for many decades, leading to well-established design guidelines and a wealth of practical knowledge for engineers and operators. The choice between packed beds, laminar plate or sheet systems and monoliths often depends on the specific needs of the process, including factors such as the type of reaction or separation, fluid properties, space constraints, and economic considerations. Each of the structures have their unique advantages and are often selected based on the requirements of the given application. However, designing adsorbers for direct air capture (DAC), a technology used to remove carbon dioxide (CO2) directly from the atmosphere, presents several challenges including: (1) Low CO2 Concentration: Ambient air contains only a trace amount of CO2 (approximately 0.04%), making it a dilute source. Adsorbers must be highly selective to capture CO2 efficiently while minimizing the adsorption of other gases like nitrogen and oxygen. (2) Energy Requirement: DAC involves adsorbing CO2 from a large volume of air, and releasing the captured CO2 requires a significant amount of energy, typically in the form of heat. Designing energy-efficient adsorbers and optimizing energy sources are crucial challenges. (a) Adsorption: Due to the dilute nature of CO2 in the atmosphere, large volumes of air need to be processed, this typically involves passing large volumetric flow rates of air through the adsorber. Generally, for adsorption-based gas separation processes, desired configurations of the sorbent material impose little pressure drop on the gas flow in order to minimize the energy required for gas pumping and at the same time achieve maximum contact between the sorbent and the gas stream in order to maximize the mass transfer rates of the components to be removed from the gas stream. Typical configurations include packed bed columns or fluidized beds with typical lengths of several tens of centimeters to several meters, which typically impose pressure drops of several thousand Pascal up to several bars on the gas flow. This can create large pressure drops across the sorbent bed, leading to increased energy costs. For this reason, thin sorbent beds or monolith type systems are preferred. (b) Regeneration: Regenerating the adsorbent to release the captured CO2 involves heating and consuming energy. Achieving efficient and cost-effective regeneration processes while minimizing heat loss is a challenge. Effective heat management is essential to reduce energy consumption. Integrating heat recovery systems and optimizing heat exchange between different process streams are complex tasks. (3) Adsorbent Stability: Choosing the right adsorbent material is critical. The adsorbent must have high CO2 adsorption capacity, good selectivity, and the ability to withstand cyclic adsorption-desorption processes without degradation. DAC systems are intended to operate over extended periods. Adsorbents must be stable and durable, with minimal degradation overtime due to cyclic loading and regeneration. (4) Adsorption Kinetics: Achieving rapid CO2 adsorption and desorption kinetics is important for efficient DAC. Designing adsorbers that facilitate fast mass transfer of CO2 while maintaining high capacity is a challenge. (5) Contaminant Management: Ambient air contains various impurities, including dust and volatile organic compounds. These contaminants can foul or poison adsorbents, requiring effective pretreatment and filtration systems to protect the adsorbers. Overcoming these challenges can help to develop and implement effective DAC systems that can play a role in mitigating climate change by removing CO2 from the atmosphere. The present invention aims to obviate or mitigate one or more of the challenges associated with the prior art, or to provide an alternative adsorbent structure that can be use on carbon capture, particularly direct air carbon capture. It would be useful to provide an adsorber structure that can be used for direct air capture of carbon dioxide. It would be useful to provide an adsorber structure that is relatively easy and / or cost-effective to manufacture. It would be useful to provide an adsorber structure in which the sorbent is easily replaced when degraded or deactivated It would be useful to provide an adsorber structure in which heat transfer to / from the sorbent is rapid. Summary of the Invention According to the present invention, there is provided a carbon dioxide removal structure for separating gaseous carbon dioxide from a gas mixture containing said gaseous carbon dioxide comprising: a support body having at least one attachment surface, said attachment surface having a negative vacuum triboelectric surface charge density more negative than -150pc m'2; a plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide; wherein the plurality of amine-containing adsorbent particles are self-assembled on the at least one attachment surface of the support body. The capability to rapidly transfer heat to / from the sorbent is a key characteristic of this invention. It allows rapid regeneration of the sorbent (i.e. the removal of CO2 from the sorbent) as the organised, self-assembled layer of adsorbent particles, particularly when attached to the attachment surface of the support body allow very effective heat transfer, thereby significantly reducing the overall cycle time, thereby increasing the productivity of the sorbent. This contrasts with a traditional packed bed where the transfer of heat is primarily through particle to particle conduction, resulting in slow heat transfer, leading to long regeneration times. The negative vacuum triboelectric surface charge density is measured in accordance with the methodology described in Lui et al. Standardized measurement of dielectric materials' intrinsic triboelectric charge density through the suppression of air breakdown. Nature Communications. (2022) 0ct;13(l):6019. DOI: 10.1038 / s41467-022-33766-z. PMID: 36224185; PMCID: PMC9556570. Incorporated herein by reference along with the supplementary information published therewith. Preferably the said attachment surface has a negative vacuum triboelectric surface charge density more negative than -200pc m 2 Preferably the said attachment surface has a negative vacuum triboelectric surface charge density more negative than -250pc m’2 Preferably negative vacuum triboelectric surface charge density is measured in a vacuum. Preferably negative vacuum triboelectric surface charge density is measured in a in a vacuum pressure of ~5 x 10"5 Pa or less. Preferably negative vacuum triboelectric surface charge density is measured at a temperature of 400 Kelvin (400 K) or less. Induced charge density oi is independent with thickness of the material being tested tin vacuum conditions (here a vacuum is a vacuum pressure of ~5x 10^5 Pa or greater). In high vacuum condition (around 5 x 10-5 Pa), oi almost remains stable with the increasing of temperature up to 400 K. Optionally, in the measurement of the negative vacuum triboelectric surface charge density an Fe electrode is used. A carbon dioxide removal structure for separating gaseous carbon dioxide from a gas mixture containing said gaseous carbon dioxide comprising: a support body having at least one attachment surface, said attachment surface being a material selected from the group comprising: halogenated polymers; polyimide; polysulfone; polystyrene; silicon rubber; quartz glass; acetyl cellulose sheet; polyethylene; and a plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide; wherein the plurality of amine-containing adsorbent particles are self-assembled on the at least one attachment surface of the support body. Preferably the gas mixture containing said gaseous carbon dioxide is ambient air. Optionally the support body is a porous solid substrate. Optionally the support body is a non-porous solid substrate. Optionally the support body is a monolith-type structure. Optionally, at least some of the internal surfaces of the porous solid substrate or monolith comprise the at least one attachment surface. Optionally, the support body comprises one or more laminar plates or sheets. This may be referred to as a laminar or laminate system or a sheet or plate system. Advantageously the laminar plates or sheets are arranged to form channels between them through which fluid can flow. Preferably the channels are a plurality of substantially parallel channels. The channels may be elongate in two dimensions. Preferably the channels are interdigitated to form an air pathway and a separate heating fluid pathway using alternating channels. Optionally there is a secondary support structure provided on the opposing side of the amine containing sorbent particles to the attachment surface. Optionally, when the support body comprises one or more laminar plates or sheets, the secondary support structure is provided as a mesh structure. The mesh structure may be in the form of a cage of substantially the same shape as the channel. Optionally the attachment surface is formed by a coating on a surface of the support body. Alternatively, the attachment surface is formed by and integral with the support body itself. Optionally, at least the attachment surface comprises, or is, a halogenated polymer. Optionally, at least the attachment surface comprises, or is, a fluorinated polymer. Optionally, the attachment surface comprises a material selected from the group: polyvinyl chloride (PVC); polytetrafluoroethylene (PTFE); polypropylene; acrylonitrile butadiene styrene; polyphenylene sulfite; acetal; polyethylene; acetyl cellulose sheet; quartz glass; polyvinyl dichloride; polyvinylidene fluoride; silicon rubber; fluorinated ethylene propylene (FEP); polystyrene; polysulfone; fluororubber; polyimide; polyether ether ketone; polytetrafluoroethylene; polyvinyl chloride; Perfluoralkoxy (PFA). In one preferred embodiment, the attachment surface is polyvinyl chloride (PVC). In another preferred embodiment, the attachment surface is polytetrafluoroethylene (PTFE). Advantageously, PTFE has a wide range of temperature stability and is very corrosion resistant. This is beneficial as the carbonic acid created from high concentrations of CO2 dissolved in water at elevated temperatures causes corrosion to typical materials of construction such as stainless steel and aluminium. In another preferred embodiment, the attachment surface is silicon rubber. In another preferred embodiment, the attachment surface is fluorinated ethylene propylene (FEP). In another preferred embodiment, the attachment surface is perfluoralkoxy (PFA). Optionally the support body is itself a halogenated polymer. In one preferred embodiment, the support body is itself polyvinyl chloride (PVC). In another preferred embodiment, the support body is itself polytetrafluoroethylene (PTFE). In another preferred embodiment, the support body is itself silicon rubber. Optionally, the amine containing sorbent particles comprise a commercial anion exchange resin. Optionally, the amine containing sorbent particles comprise metal organic frameworks (MOFs) Preferably the amine containing sorbent particles are uniformly distributed on the at least one attachment surface of the support body. Preferably, the amine containing sorbent particles are not mixed or combined with a separate chemical binder. Preferably, no chemical binder is present (or is present in di minimis quantities that does not have significant binding activity between the amine containing sorbent particles and the attachment surface of the support body). Binders are an additional cost in the manufacture of monoliths. They generally have no active function in carbon capture other than binding the active material (sorbent) to the monolith wall. They can block active carbon capture sites, impairing sorbent performance. They must be robust to temperature cycling that causes thermal expansion / contraction of the underlying monolith structure, leading to disengagement of the coating / active layer from the monolith structure. In addition, typical amine-based sorbents swell and contract with adsorption and desorption of CO2 and water vapour putting further constraints on the binder. In the present invention, the absence of binder negates or reduces the detrimental effects of expansion / contraction associated with adsorption / desorption and temperature cycles. It also negates or reduces the detrimental effect of pore / active site blocking by the binder. Optionally the support body comprises one or more tubes, with the inside of the tubes being the attachment surface. Optionally the support body comprises a monolith structure comprising a plurality of internal channels having one or more attachment surfaces. Optionally the monolith comprises multiple parallel channels. Optionally the monolith comprises a honeycomb structure. Optionally the support body comprises one or more laminar plates or sheets, with the surfaces of the plates or sheets being the attachment surface. A method of producing a carbon dioxide removal structure described above, comprising: injecting a slurry into a support body having one or more attachment surfaces, said slurry comprising a plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide and an aqueous fluid; drying the slurry present on the one or more attachment surfaces to remove a substantial portion of the aqueous fluid; such that the amine containing sorbent particles assemble on the one or more attachment surfaces. Advantageously the sorbent particles assemble on and uniformly coat the one or more attachment surfaces. The sorbent particles attach to the attachment surfaces without the need for a binder. In this manner the sorbent particles releasably bind to the attachment surfaces without the need for a binder (be releasable by a wash-through by an aqueous substance such as water). Preferably the method further includes the step of filtering the aqueous fluid from the sorbent particles. Preferably the step of filtering the aqueous fluid from the sorbent particles occurs before or concurrently with the drying step. Preferably the drying step is carried out at an elevated temperature. Preferably the drying step is carried out at 80 degrees centigrade (80°C). Optionally the drying step is carried out at 70-90 degrees centigrade (70-90“C). Preferably any excess aqueous fluid is drained from the support body prior to the drying step. Optionally, the drying step was carried out for at least 30 minutes. Optionally, the drying step was carried out for at least 2 hours. Optionally, the drying step was carried out for 3 hours or more. As the amine containing sorbent particles progressively dry, they self-bind to the attachment surface of the support body. A method of replacing the sorbent particles described above comprising the step of flushing the support body with aqueous fluid to remove any amine containing sorbent particles from the attachment surface; then carrying out the steps of producing a carbon dioxide removal structure described above. Preferably the aqueous fluid is water. A direct air carbon capture (DAC) system comprising one or more adsorber vessels, where at least one of the adsorber vessels comprises the carbon dioxide removal structure described above. Various further features and aspects of the invention are defined in the claims. 5 Unless defined otherwise, all technical and scientific terms used herein have the meaning commonly understood by a person skilled in the art to which this invention belongs. The term 'halogenated polymer' refers to a polymer formed from polymerization of at least one halogen-containing monomer. The polymerization may include one or more non-halogen containing monomers. It would be understood by one skilled in the art that not all halogens 10 are useful in this regard and that generally a halogenated polymer contains common halogen elements such as fluorine, chlorine and bromine. Preferably, term 'halogenated polymer' refers to polymers containing one or more of fluorine, chlorine, and bromine. The term "fluoropolymer" means a halogenated polymer wherein the at least one halogen atom in the structure of the precursor halogen-containing monomer is fluorine. Brief Description of the Drawings Embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings where like parts are provided with corresponding reference numerals and in which: Figure 1 is a diagram of a monolith in accordance with an aspect of the present invention; Figure 2 is a graph showing the triboelectric charge density (TECD) of various materials in vacuum condition (i.e. the vacuum triboelectric surface charge density of said material). Error bars represent standard deviation, n = 5 independent samples. The graph is reproduced without changes under a Creative Commons Attribution 4.0 International License from Lui et al. Standardized measurement of dielectric materials' intrinsic triboelectric charge density through the suppression of air breakdown. Nature Communications. (2022) 0ct;13(l):6019. DOI: 10.1038 / s41467-022-33766-z. PMID: 36224185; PMCID: PMC9556570. The license permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. To view a copy of this license, see http: / / creativecommons.Org / licenses / by / 4.0 / ; Figure 3a is a picture of sorbent beads (~ 0.5 mm diameter) self-binding to internal surface of 6mm OD (4mm ID) PTFE tubing, made by and in accordance with the invention, and Figures 3c and 3d are pictures of sorbent beads coated on PFA tubing (6mm OD; 4mm ID), made by and in accordance with the invention; Figure 4 is a graph showing breakthrough curves for sorbent bonded to 307 mm PTFE tube (4mm ID). Mass of dry sorbent: 0.49 g; Humidity 50%; Temperature 21 °C. Figure 5 is a diagram of a laminar sheet system in accordance with the present invention which has thin plates or laminates. The thin metal sheets are coated with fluoropolymer and alternate channels are used for heating fluid, negating the need for steam regeneration. Figure 6 is a graph showing Breakthrough curves for an ion exchange resin sorbent electrostatically bonded to 150 mm FEP and PFA (4mm ID). Flowrate 0.51 L / min; Humidity 50%; Temperature 21°C; and Figure 7a is a diagram of another laminar or sheet plate system, figure 7b is the cross section a-a of Figure 7a with an inner mesh, figure 7c is the cross section a-a of Figure 7a without an inner mesh; and Figures 8a and 8b are pictures of sorbent beads coated (without binder) on 100 micron FEP sheets in accordance with the invention. Figure 8a is with an aluminium foil backing and Figure 8b without an aluminium foil backing; and Figure 9 is a diagram showing a triboelectric charge density measuring equipment and method that can be used to select material in accordance with the invention. This diagram is reproduced without changes under a Creative Commons Attribution 4.0 International License from Lui etal. Standardized measurement of dielectric materials' intrinsic triboelectric charge density through the suppression of air breakdown. Nature Communications. (2022) Oct;13(l):6019. DOI: 10.1038 / s41467-022-33766-z. PMID: 36224185; PMCID: PMC9556570. The license permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. To view a copy of this license, see http: / / creativecommons.Org / licenses / by / 4.0 / . Detailed Description A carbon dioxide removal structure 1 in accordance with the present invention, which in this embodiment the structure is in the form of a monolith 2, is generally depicted in Figure 1. In this embodiment the monolith 2 is engineered to have a series of parallel channels 3 through which air can flow. However, it would be understood that the monolith 2 could be engineered with alternative designs known in the art e.g. honeycomb design etc. The design ensures relatively uniform distribution airflow through the channels 3. The monolith body 2 is made of a ceramic material and the internal walls 4 of the channels 3 are coated in Polytetrafluoroethylene PTFE to provide an attachment surface 5. As can be seen in Figure 2, PTFE has a vacuum triboelectric surface charge density of -853.7 pCm’2. Although in this embodiment the inner walls 4 of the channels 3 are coated to provide an attachment surface 5, if the monolith 1 is made from a material with a vacuum triboelectric surface charge density which is -150 pCm-2 or greater (i.e. more densely negatively charged) - or if the surface 2 is induced to have such a vacuum triboelectric surface charge density - a separate coating is not required and the internal wall 4 is the attachment surface 5. A sorbent material comprising a plurality of sorbent particles in the form of amine containing anion exchange resin beads 6 is provided on the attachment surface 5. In this embodiment, the sorbent beads 6 are a microporous divinylbenzene crosslinked polymer in spherical bead form with primary amine groups. The sorbent material can adsorb carbon dioxide from ambient air. The anion exchange resin beads 6 are assembled on the attachment surface 5 in an organised manner without a binder. The sorbent beads 6 self-bind to the attachment surface 5 and assemble to give uniform distribution of the beads 6 on the attachment surface 5. Without wishing to be bound by theory, it is hypothesised that the difference in triboelectric charge density between the beads 6 and the attachment surface 5 results in the beads selfassembling on the attachment surface in an organised manner. It is further hypothesised that the binding forces are electrostatic (and / or Van der Waals) in nature, and in addition to binding the sorbent beads to the surface of the PTFE also tends to repel adjacent sorbent beads. This means that the beads do not clump together and tend to be isolated on the surface in a single layer with gaps between beads leading to a degree of uniformity in coating. Typically, there is 50 - 60% coverage of the surface by the anion exchange resin beads 6. In use, ambient air is flowed through the channels 3 and comes into intimate contact with the sorbent beads 6 assembled on the attachment surface 5. Carbon dioxide present in the ambient air is adsorbed by the ambient beads such that the carbon dioxide content of the air leaving the channels 3 is lower than when it entered the channels 3. An alternative embodiment of the present invention is depicted in Figure 5. In this embodiment the support body structure of the carbon dioxide removal structure 1' is formed by a plurality of parallel plates 7 held in a frame 8. Channels 3* are formed between the plates 7 and alternate channels are used for airflow (form which carbon dioxide is to be removed) and heating fluid such as steam. Effectively this means that the airflow pathway passes through each alternate channel that is formed. Gaskets can be arranged to ensure appropriate airflow pathways. This embodiment is based on a plate heat exchanger structure. In this embodiment the plates 7 are metal, and the outer planar surfaces 4' of the plates 7 are coated with PFA (or other appropriate surface coating in accordance with the invention and disclosed herein), but it would be understood that the plates could be formed by PFA (or other appropriate material). A particular benefit of the plate format is that is allows for easy, uniform coating if this is required to form an appropriate attachment surface 5'. Typically, there is 50 - 60% coverage of an attachment surface 5' by the anion exchange resin beads 6'. A sorbent material comprising a plurality of sorbent particles in the form of amine containing sorbent beads 6’ is provided on the attachment surfaces 5'. In this embodiment, the sorbent anion exchange resin beads 6 are made from a polymer, more particularly an amine functionalised polymeric resin in spherical bead form. The sorbent material can adsorb carbon dioxide from ambient air. As well as the plate format advantageously meaning the plates 7 can be readily coated with fluoropolymer it also means that alternate channels can be used for heating fluid, negating the need for steam regeneration (reducing the risk of accidental detachment of the beads from the attachment surface). Beneficially, by incorporating heating fluid on one side of the plate, this may also impart a charge on the gas / air side of the plate that will act to further strengthen the adherence of the beads 6' to the attachment surface 5'. In use, ambient air is flowed through alternate channels 3', whilst heating fluid (steam or hot water) is flowable through the remaining channels. The ambient air comes into intimate contact with the sorbent beads 6' assembled on the attachment surface 5'. The steam or hot water does not come into intimate or direct contact with the beads 6' assembled on the attachment surface 5' as the plate structure allows the heating of the beads 6'. Carbon dioxide present in the ambient air is adsorbed by the ambient beads such that the carbon dioxide content of the air leaving the channels 3' is lower than when it entered the channels 3'. Another, similar embodiment is depicted in Figures 7a-c. Again, this is a laminar or sheet plate system. The support body structure of the carbon dioxide removal structure 1" is formed by a plurality of parallel plates 7". The plates 7" are arranged to provide two interlocking or interdigitated fluid flow pathways. As can be seen more clearly in figure 7c, spacer elements 10" can be included between the plates to maintain the gap between surfaces (in this case 3mm). One pathway formed by the interdigitated channels 3a" forms an airflow pathway which allows air to flow into the structure 1" and to travel through alternate channels. The other set of interdigitated channels 3b" form a heating / cooling pathway which can have fluid such as steam or hot water flowed through. This is shown more clearly by the arrows in Figure 7a which show how the fluid flow paths can be arranged such that heating / cooling fluid flows through alternate channels. As the airflow pathway and heating pathway are interdigitated channels 3a",3b" (i.e. alternating parallel channels are either for airflow or heating) this means the plates 7" can have sorbent 6" on one side and be heated from the other. As the plates conduct heat well (in this case they are a 0.4mm thickness metal plate with a fluoropolymer coating of 0.1mm) and the sorbent beads 6" are assembled in a layer (held electrostatically to the fluoropolymer coating) on one surface of the plate (such that the majority of sorbent is in contact with the plate 7" via the attachment surface 5"), the sorbent can be easily and quickly heated by flowing a heated fluid through the heating pathway, without having direct contact with heating fluid such as steam or hot water. Heat is conducted from the heated fluid, e.g. steam, in contact with one surface of the plate 7", via the plate 7", to the layer of sorbent beads 6" arranged on the opposing surface of the plate 7". In this embodiment the plates 7" are metal, and the outer planar surfaces 4" of the plates 7" are coated with FEP (or other appropriate surface coating in accordance with the invention and disclosed herein), but it would be understood that the plates could be formed by FEP (or other appropriate material). A particular benefit of the plate format is that it allows for easy, uniform coating if this is required to form an appropriate attachment surface 5". A sorbent material comprising a plurality of sorbent particles in the form of positively charged ion exchange beads 6' is provided on the attachment surfaces 5'. In this embodiment, the sorbent beads 6 are made from a polymer, more particularly an amine functionalised polymeric resin in spherical bead form. The sorbent material can adsorb carbon dioxide from ambient air. As can be seen in Figure 7b, a fine mesh cage 8" can be used to provide a secondary supporting structure for the beads. This can further assist to retain the sorbent particles on the supporting surface, in this case amine functionalised ion exchange resin beads, if the system is to be used in challenging environments. The mesh cage 8" in this embodiment is removable to allow for easy removal and replacement of the beads. A mesh cap 9" can also be provided at the ends of the elongate channels. The mesh cap 9" can be useful during production of the plate system 1” as discussed further below. Notably, the secondary supporting structure could be used in other embodiments. The mesh cage 8" which forms an optional secondary support 8", could also be positively charged. Without wishing to be bound by theory, this may induce a stronger attachment to the attachment surfaces. Laminar or sheet plate systems are themselves known in the art, for example WO2021239747A1 describes such a structure that could be adapted in accordance with the present invention and is incorporated herein by way of reference. Sorbent Amine containing sorbent particulates are known in the art and are able to react with and bind carbon dioxide. They may be adapted or even optimised for direct air capture (DAC). Surface modification can be provided by impregnation, grafting and / or bonding of amine functionalities, in particular primary and / or secondary amine functionalities. The sorbent material can be an amine-functionalized solid adsorbent. For example, the material can be a weak-base ion exchange resin and / or amine-functionalized cellulose and / or amine-functionalized silica and / or amine-functionalized carbons and / or amine-functionalized metal organic frameworks and / or other amine-functionalized polymeric adsorbents. Another sorbent material suitable for use with this invention can be amine-functionalized cellulose. The solid inorganic or organic, non- polymeric or polymeric base of the particle can be an organic or inorganic polymeric support, preferably an organic polymeric support, in particular a polystyrene based material, preferably a styrene divinylbenzene copolymer, preferably to form the sorbent material surface functionalized with primary amine, such as methyl amine or benzylamine moieties. Polymer resins with amine functionalities can be formed into bead shapes. Production An exemplary method of producing a monolith 2 carbon dioxide removal structure 1 described above is as follows. Sorbent anion exchange resin beads 6 are loaded into the monolith 1 by injecting them as a sorbent bead 6 / water slurry. Excess water is drained from the tube and the monolith 1, and the beads 6 are dried in a vacuum oven at 80 °C. As the beads progressively dry, they self-bind to the attachment surface 5 of the monolith 2. After approximately 3 hours of drying, the monolith 2 is removed from the oven and agitated gently, resulting in an even coating of sorbent beads 6 on the internal walls 4 of the monolith 2. Agitation of the beads could be by vibrating the monolith or also by dispersion using airflow through the channels. A similar exemplary method can be used to produce the plurality of parallel plates for the laminar sheet or plate systems. In a preferred embodiment the plates form two interlocking or interdigitated fluid flow pathways. Sorbent anion exchange resin beads 6 are coated onto plates as a sorbent bead 67water slurry. Excess water is drained from plate 7,7" and the plate 7,7" and anion exchange resin beads 6' are dried. In a preferred embodiment, a mesh cap 9" is present at one end of a channel that is to be an airflow channel and have sorbent beads present on the walls of the plates 7". A slurry of beads and water is loaded into the airflow channels. The mesh cap 9" retains the beads based on size and allows water to flow through, such that the channel can be filled with the bead mixture. The retained bead mixture can then be dried by raising the temperature to 80 °C. In a preferred version of the method, a heat transfer fluid present in alternate heating channels can itself be used to dry the beads (in a similar mannerthan is used for regeneration). Such a system may be preferred as, unlike with many monolith systems, the laminar sheet or plate system does not require steam regeneration where steam is in direct contact with the anion exchange resin beads. As the beads progressively dry, they self-bind to the attachment surface 5', 5" of the plate 7, 7". After approximately 30 minutes of drying, the plates 7, 7" have an even coating of sorbent beads 6', 6" on the attachment surfaces 5', 5" of the plates 7, 7". It would be understood that a higher temperature could be used, and the drying time reduced. Similarly, a lower temperature could be used and the drying time increased. A vacuum oven assists with the process but is not essential. Sorbent replacement Chemical binders are an additional cost in the manufacture of traditional carbon dioxide removal structures such as monoliths, or laminar sheet / plate systems. The binders generally have no active function in carbon capture other than binding the active material (sorbent) to the wall over which gas will pass. Furthermore, chemical binders can block active carbon capture sites, impairing sorbent performance. Binders can also cause problems as they must be robust to temperature cycling which can cause thermal expansion / contraction of the underlying structure, leading to disengagement of the sorbent and binder layer from the monolith structure. In addition, typical amine-based sorbents swell and contract with adsorption and desorption of CO2 and water vapour putting further constraints on the binder. In the present invention, the absence of chemical binder negates the detrimental effects of expansion / contraction associated with adsorption / desorption and temperature cycles. It also negates the detrimental effect of pore / active site blocking by the binder. The absence of chemical binder also allows deactivated sorbent to be readily replaced by simple flushing of the channels with water. This removes the active component (sorbent) leaving the carbon dioxide removal structure e.g. the monolith, bed, or sheet / plate structure intact. In typical monolith structures, the whole monolith structure must either be replaced when the active component deactivates, or the active component can be combusted by high temperature treatment of the monolith. Similar regeneration challenges apply to sheet / plate systems. This adds cost, increased operational downtime and additional waste. The present invention allows the underlaying carbon dioxide renewal support structure to be reutilised many times by simple flushing with water to remove old sorbent particles and then a replenishment with new sorbent particles, for example using the production method described above. There are examples of laminar sheets / monoliths that are composed entirely of the sorbent. However, these can suffer from stresses due to expansion / contraction that can cause the laminates / monoliths to crack and degrade. In the present invention, the sorbent particles, which are preferably spherical sorbent beads can expand and contract without causing structural damage to the beads. Selection of the material for the attachment surface The material selected for the attachment surface (on which the amine containing sorbent particles will self-assemble even in the absence of a binder) is selected based on the triboelectric charge density as measured in vacuum conditions (referred to herein as the 'vacuum triboelectric charge density' or 'vacuum TECD'). As identified in the paper by Lui et al fLui et al. Standardized measurement of dielectric materials' intrinsic triboelectric charge density through the suppression of air breakdown. Nature Communications. (2022) Oct;13(l):6019. DOI: 10.1038 / s41467-022-33766-z. PMID: 36224185; PMCID: PMC9556570. Incorporated herein by reference along with associated supplementary information), the triboelectric density is measured under vacuum conditions (preferably being a vacuum pressure of ~5 x 10-5 Pa or lower). Vacuum TECD of a material can be measured by incorporating the material into a contact separation triboelectric generator (TENG) and then measuring triboelectric charge density under vacuum conditions as follows: Part I: cut a round shape of said material (e.g. diameter: 20mm; thickness: 3mm), for example by using a laser cutter (PLS6.75, Universal Laser System). An Fe plate (diameter: 20mm; thickness: 0.1mm) is adhered on the surface of the as the electrode layer (the Fe electrode shows high-temperature stability and high hardness which can reduce materials transfer as much as possible). Part II: Cut a round shape of material (diameter: 15mm; thickness: 3mm). An Fe plate (diameter: 15mm; thickness: 0.1mm) is adhered on the surface of the substrate material as the electrode layer. The substrate material is adhered on the surface of the electrode layer as the triboelectric layer. The Fe electrode can be obtained by tailoring the Fe plate and treating with sandpaper. Both metal plates are connected by high-temperature resistant wires for electrical measurement. A high vacuum system with a heater is used to give a stable working environment. A mechanical pump can be used for realizing a low atmosphere pressure, and an adjustable air intake is combined to achieve pressure regulation. A molecular pump is used for realizing a high vacuum condition (the ultimate vacuum of the molecular pump is around 5x 10-5Pa). Before testing, samples are placed in the high vacuum system until the ultimate vacuum of the molecular pump, and are kept 2 h for steady state with the vacuum gauge closed (the vacuum gauge can produce little ions affecting the environmental conditions). When temperature changes, there will be 2 h for realizing equilibrium state. The vacuum is monitored by a vacuum ionization gauge. The temperature is monitored by a vacuum thermocouple gauge. The output charges and voltage of the substrate materials are measured by an electrostatic electrometer (such as a Keithley 6514). The energy density is calculated by the ratio of output energy to the geometric area. The induced charge (oi) measured in vacuum represents TECD (ot). The charge density measuring equipment and method are shown in Figure 9. By avoiding charge loss from air breakdown and thermionic emission effects, the standardized strategy was used in Lui et al to test more than forty dielectric materials' TECD with the counterpart of Fe electrode, because the Fe electrode shows high-temperature stability and high hardness which can reduce materials transfer as much as possible. The initial surface charges on triboelectric layers are removed by absolute ethyl alcohol. Five materials with different thicknesses were tested, and this further demonstrated that ot has no relationship with substrate material thickness in this method. Moreover, to eliminate occasionality of testing a single sample, every kind of material was tested with five different samples, and the corresponding values were recorded and plotted in Figure 2. The negative and positive charge density indicates that this material will be negatively or positively charged when it contacts with Fe electrode. For example, polyvinyl chloride (PVC) and PTFE tend to obtain electrons while polyurethane (Pll) and cellulose tend to lose electrons. This is different from the conventional triboelectric series which only considers the polarity of materials, as both of polarity and amounts of transferred charges are considered. One skilled in the art would also appreciate that the material selected for the attachment surface must also be suitable for use as an attachment surface in a DAC system For example it must be able to structurally withstand temperatures appropriate for sorbent regeneration (typically temperature in the range of 80-120 °C). Experimental work Taking the triboelectric charge density chart in Figure 2 as a reference, a set of tests were done to show the suitability of different materials as an attachment surface (either as a coating on or forming one or more elements of a support body) for DAC. It would be understood that the material would also need to be suitable for inclusion into the structure either as a structural material or a coating and will need to be able to withstand the temperatures used in DAC i.e. be stable at temperatures up to 100°C. PTFE Experiments were conducted by loading a single length of PTFE tubing with sorbent beads. Commercially, multiple parallel channels could be used in a monolith type structure. The results obtained on a single channel are linearly scalable for application in a range of structures such as monoliths, or laminar sheet / plate systems. Sorbent beads (commercially available amine loaded anion exchange resin) were loaded into the polytetrafluoroethylene (PTFE) tubing (307 mm) by injecting them as a sorbent bead / water slurry. The excess water was drained from the tube and the beads were dried in a vacuum oven at 80 °C. As the beads progressively dried, they self-bound to the interior surface of the tubing. Upon completion of drying (3 h), the PTFE tube was removed from the oven and shaken gently, resulting in an even coating of sorbent on the internal walls of the tubing (Figure 3a). The same experiment was carried out using perfluoroaloxy alkane (PFA) tubing (6mm OD; 4mm ID) with the results shown in Figures 3b and 3c. The binding force appears to be electrostatic (and / or Van der Waals) in nature and in addition to binding the sorbent particles to the surface of the PTFE also tends to repel adjacent sorbent particles. This means that the beads do not clump together and tend to be isolated on the surface in a single layer with gaps between beads leading to a degree of uniformity in coating. Images are shown in Figure 3. The PTFE tubing was connected to a flow of humid air (0.25 L / min, 410 ppm CO2, 50% RH) and the exhaust from the bed measured for CO2 concentration (Figure 4). The sorbent bed was regenerated in the vacuum oven and the experiment repeated with a doubling of the flow rate of air (0.51 L / min). Following completion of the adsorption tests, the sorbent was readily removed from the tube by flushing with water. Table 1 summarises the results. CO2 uptake (to 100% breakthrough) was similar for both flowrates, indicating an equilibrium uptake of 1.71 mol / kg at 21 °C and 50% RH. Table 1: Summary of Breakthrough Experiments Air Flow rate (L / min) 0.25 0.51 Specific Air Flow Rate (m3 / h / kg(sorbent)) 31 62 CO2 Uptake (full breakthrough) (mol / kg(sorbent)) 1.69 1.71 CO2 Uptake (at 40 min) (mol / kg(sorbent)) 0.38 0.75 FEP (Fluoroethylenepropylene) and PFA (Perfluoroalkoxy alkane) As in the previous experiment, sorbent material comprising anion exchange resin particles was loaded into tubing which mimics the internal walls of a monolith, bed, or laminate / sheet. Anion exchange resin sorbent with primary amine functional groups (more specifically, a 5 macroporous polystyrene crosslinked with dwinylbenzene) was charged in its fresh 'wet' form (i.e. combined with water) into 170mm of 6mm outside diameter (OD) (4 mm inside diameter (ID)) FEP tubing. Glass wool was used at the at the top and bottom of the tube to prevent loss of sorbent from the tube. Excluding the glass wool, the available tube length for the sorbent coating was 150mm. After drying in a vacuum oven at 80 °C and Imbar (for 3 hours), the 10 sorbent beads dispersed to form an evenly formed coating of sorbent beads on the inner surface of the FEP tubes. The same experiment was carried out with a PFA tube. 15 After regeneration, the tubes containing the sorbent were tested in adsorption using a humid stream of 420 ppm CO2 in Air. A summary of the experimental conditions and results are shown in Table 2: Table 2: Substrate material screening results at 21°C and 50% RH. Substrate material ofthe tube FEP PFA Dry sorbent after regeneration (g) 0.18 0.17 CO2 Uptake (full breakthrough) (mol / kg) 1.60 1.66 CO2 Uptake (40 min) (mol / kg) 1.01 1.06 Experimental conditions: 150 mm length of tube, 6mm OD (4 mm ID) Airflow: 0.51 L / min Average COZ concentration (ppm): 420 ppm Breakthrough curves for the anion exchange resin are shown in Figure 6. The flowrate of the air containing carbon dioxide at 420ppm was 0.51 L / min; Humidity 50%; Temperature 2rc. Notably, it can be seen that as the sorbent beads are arranged on the attachment surface this has allowed efficient heating which allows regeneration to take place in 40 mins (or less) as opposed to the typical 3 or 4 hours required in a packed bed system. Similar experiments were also carried out on sheets of FEP rather than with tubes to show that the beads also self-assemble on a substantially flat or planar surface (although said surface may have variations in surface roughness). Amine functionalised sorbent beads were coated (without a chemical binder) on 100 micron FEP sheets. The excess water was drained and the beads were dried at 80 °C. As the beads progressively dried, they self-bound to the surface of the sheet. The results can be seen in figure 8a where the sheet has an aluminium foil backing and in figure 8b where the FEP sheet was without a backing. This shows that the methods are equally applicable to a laminate / laminar or sheet system. All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and / or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and / or steps are mutually exclusive. Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent, or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features. The invention is not restricted to the details of the foregoing embodiment(s). The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed. With respect to the use of substantially any plural and / or singular terms herein, those having skill in the art can translate from the plural to the singular and / or from the singular to the plural as is appropriate to the context and / or application. The various singular / plural permutations may be expressly set forth herein for sake of clarity. It will be understood by those within the art that, in general, terms used herein, and especially in the appended claims are generally intended as "open" terms (e.g., the term "including" or "comprising" should be interpreted as "including but not limited to," the term "having" should be interpreted as "having at least," the term "includes" should be interpreted as "includes but is not limited to," etc.). It will be further understood by those within the art that if a specific number of an introduced claim recitation is intended, such an intent will be explicitly recited in the claim, and in the absence of such recitation no such intent is present. For example, as an aid to understanding, the following appended claims may contain usage of the introductory phrases "at least one" and "one or more" to introduce claim recitations. However, the use of such phrases should not be construed to imply that the introduction of a claim recitation by the indefinite articles "a" or "an" limits any particular claim containing such introduced claim recitation to embodiments containing only one such recitation, even when the same claim includes the introductory phrases "one or more" or "at least one" and indefinite articles such as "a" or "an" (e.g., "a" and / or "an" should be interpreted to mean "at least one" or "one or more"); the same holds true for the use of definite articles used to introduce claim recitations. In addition, even if a specific number of an introduced claim recitation is explicitly recited, those skilled in the art will recognize that such recitation should be interpreted to mean at least the recited number (e.g., the bare recitation of "two recitations," without other modifiers, means at least two recitations, or two or more recitations). It will be appreciated that various embodiments of the present disclosure have been described herein for purposes of illustration, and that various modifications may be made without departing from the scope of the present disclosure. Accordingly, the various embodiments disclosed herein are not intended to be limiting, with the true scope being indicated by the following claims.

Claims

1. A carbon dioxide removal structure for separating gaseous carbon dioxide from a gas mixture containing said gaseous carbon dioxide comprising:a support body having at least one attachment surface with a negative vacuum triboelectric surface charge density more negative than -150pC m'2;a plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide;wherein the plurality of amine-containing adsorbent particles are self-assembled on the at least one attachment surface of the support body.

2. A carbon dioxide removal structure as in Claim 1 wherein negative vacuum triboelectric surface charge density is measured in a vacuum.

3. A carbon dioxide removal structure as in Claim 1 or 2 wherein negative vacuum triboelectric surface charge density is measured at a temperature of 400 Kelvin (400 K) or less.

4. A carbon dioxide removal structure as in any of the previous Claims wherein for the measurement of the negative vacuum triboelectric surface charge density an Fe electrode is used.

5. A carbon dioxide removal structure for separating gaseous carbon dioxide from a gas mixture containing said gaseous carbon dioxide comprising:a support body having at least one attachment surface, said attachment surface being a material selected from the group comprising:halogenated polymers;polyimide;polysulfone;polystyrene;silicon rubber;quartz glass;acetyl cellulose sheet;polyethylene; anda plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide;wherein the plurality of amine-containing adsorbent particles are self-assembled on the at least one attachment surface of the support body.

6. A carbon dioxide removal structure as in any of the previous Claims wherein the gas mixture containing said gaseous carbon dioxide is ambient air.

7. A carbon dioxide removal structure as in any of the previous Claims wherein the support body is a solid substrate such as a monolith or wherein the support body comprises one or more laminar plates or sheets.

8. A carbon dioxide removal structure as in any of the previous Claims wherein the attachment surface is a coating.

9. A carbon dioxide removal structure as in any of the previous Claims wherein at least the attachment surface comprises or is a halogenated polymer.

10. A carbon dioxide removal structure as in any of the previous Claims wherein the attachment surface comprises a material selected from the group: polyvinyl chloride (PVC);polytetrafluoroethylene (PTFE);polypropylene;acrylonitrile butadiene styrene;polyphenylene sulfite;acetal;polyethylene;acetyl cellulose sheet;quartz glass;polyvinyl dichloride;polyvinylidene fluoride;silicon rubber;fluorinated ethylene propylene (FEP);polystyrene;polysulfone;fluororubber;polyimide;polyether ether ketone;polytetrafluoroethylene;polyvinyl chloride;Perfluoralkoxy (PFA).

11. A carbon dioxide removal structure as in any of the previous Claims wherein the attachment surface is polytetrafluoroethylene (PTFE).

12. A carbon dioxide removal structure as in any of the previous Claims the attachment surface is fluorinated ethylene propylene (FEP).

13. A carbon dioxide removal structure as in any of the previous Claims the attachment surface is perfluoralkoxy (PFA).

14. A carbon dioxide removal structure as in any of the previous Claims wherein the amine containing sorbent particles comprise a commercial anion exchange resin and / or metal organic frameworks (MOFs)15. A carbon dioxide removal structure as in any of the previous Claims wherein the amine containing sorbent particles are uniformly distributed on the at least one attachment surface of the support body.

16. A carbon dioxide removal structure as in any of the previous Claims wherein no chemical binder is present (or it is present in di minimis quantities that do not havesignificant binding activity between the amine containing sorbent particles and the attachment surface of the support body).

17. A carbon dioxide removal structure as in any of the previous Claims wherein the support body comprises a plurality of plates, with at least part of a surface of a plate being the attachment surface and with a plurality of channels formed between said plates.

18. A carbon dioxide removal structure as in Claim 17 wherein the channels are interdigitated to form an air pathway and a separate heating fluid pathway using alternating channels.

19. A carbon dioxide removal structure as in Claim 17 or 18 wherein there is a secondary support structure provided on the opposing side of the amine containing sorbent particles to the attachment surface.

20. A carbon dioxide removal structure as in any of Claims 17 to 19 wherein the secondary support structure is provided as a mesh structure which may be a mesh cage.

21. A method of producing a carbon dioxide removal structure in accordance with any of claims 1 to 20, comprising:injecting a slurry into a support body having one or more attachment surfaces, said slurry comprising a plurality of amine containing sorbent particles capable of adsorbing or binding to carbon dioxide and an aqueous fluid;drying the slurry to remove a substantial portion of the aqueous fluid;such that the amine containing sorbent particles coat the one or more attachment surfaces.

22. A method of producing a carbon dioxide removal structure as in claim 21 wherein the drying step is carried out at an elevated temperature which is preferably 80 degrees centigrade (80°C).

23. A method of producing a carbon dioxide removal structure as in claims 21 or 22 wherein any excess aqueous fluid is drained from the support body prior to the drying step.5 24. A method of replacing sorbent in the carbon dioxide removal structure described inany of claims 1 to 20 comprising the step of flushing the support body with aqueous fluid to remove any amine containing sorbent particles from the attachment surface; then carrying out the steps for producing a carbon dioxide removal structure as in any of claims 21 to 23.1025. A method of replacing sorbent in the carbon dioxide removal structure as in claim 24 wherein the aqueous fluid is water.

26. A direct air carbon capture (DAC) system comprising one or more adsorber vessels, 15 where at least one of the adsorber vessels comprises the carbon dioxide removalstructure described in any of claims 1 to 20.

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