Direct air capture (DAC) process using a sorbent

Abstract

A direct air capture (DAC) process for capturing CO2 from a stream of air by passing air through a capture unit comprising a sorbent structure The sorbent structure comprises an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt% and a metal-containing support in an amount of at least 55 wt%, both based on the weight of the sorbent structure. The metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof. The method further comprises capturing the carbon dioxide by the sorbent to provide a treated stream of air with less carbon dioxide exiting the capture unit.

Description

[0001] DIRECT AIR CAPTURE (DAC) PROCESS USING A SORBENT

[0002] Field of the Invention

[0003] The present specification generally relates to the field of carbon dioxide capture, and more specifically, to a process for the capture of carbon dioxide (CO2) from air, also known as Direct Air Capture (DAC).

[0004] Background of the Invention

[0005] This section is intended to introduce various aspects of the art, which may be associated with exemplary embodiments of the present invention. This discussion is believed to assist in providing a framework to facilitate a better understanding of particular aspects of the present invention. Accordingly, it should be understood that this section should be read in this light, and not necessarily as admissions of any prior art.

[0006] The atmospheric carbon-dioxide (CO2) level is increasing at least in part due to emissions from various sources, including industrial sites like thermal power plants, oil refineries, and other processing plants such as cement, steel, aluminium, and the like. The increased level of atmospheric carbon-dioxide (CO2) has been linked to global warming. Various technologies are being used and / or developed to reduce the amount of CO2emitted into the atmosphere as one precautionary measure to address global warming. In addition, various governments have established or plan to establish programs that either provide economic incentives to reduce CO2emissions and / or regulations limiting CO2emissions, all of which encourage the development of CO2capture technologies. Processes are described in the art, for example in EP 0469781 A2, US 4952223 A and US 11198109 B2, for CO2capture from combustion exhaust gases and other waste streams.

[0007] US 11198109 B2 is directed to processes for the removal of CO2from combustion flue gas streams and sorbents for use therein. US 11198109 B2 discloses that when a sorbent comprising potassium carbonate on alumina is used as a sorbent in such processes, it deactivates due to the formation of a poison phase of potassium aluminate carbonate K2Al2O3(CO3)2.4H2O. US 11198109 B2 indicates that under hydrothermal testing conditions, there is slow conversion of slow conversion of Al2O3to boehmite, which reacts in turn with potassium carbonate to form KAlO2, resulting in weakened affinity towards CO2sorption. US 11198109 B2 notes that a similar counterpart phase does not exist with the use of sodium carbonate on alumina as a sorbent. US 111981109 B2 aims to address the formation of the poison phase when using potassium carbonate on alumina as a sorbent in processes for the removal of CO2from combustion flue gas streams. Accordingly, US 111981109 B2 describes the preparation and use of a specific mixed alkali metal sorbent made from aluminium oxide and a combination of alkali metal ions, i. e. potassium ions and at least one other type of alkali metal ions, impregnated thereon.

[0008] Processes for CO2capture from combustion exhaust gases and other waste streams are designed to capture CO2from inlet streams having typical CO2concentrations in the range of 3 to 15 volume % CO2and low concentrations of oxygen, e. g., less than 10 volume %. However, such processes do not address the problem of capturing CO2from very dilute sources such as air where the concentration of CO2is much lower (ppm levels ) than combustion exhaust gases and waste streams and the oxygen content is also higher than 10 volume %, typically around 21 volume %.

[0009] Targeted Direct air capture (DAC) processes for the removal of carbon dioxide from the air have been proposed as one way of addressing such issues. However, DAC is a capital-intensive process due to the necessity to process large amounts of air.

[0010] Typical DAC systems take in large quantities of air which is pumped as a (feed) stream through a unit containing a sorbent substance that removes the CO2from the stream under ambient conditions. The air is typically moved by fans and the energy consumption is proportional to the pressure drop across the sorbent bed. Any pressure drop above a few mbar will lead to very high energy cost.

[0011] Over time the sorbent becomes loaded with captured CO2. Next, the captured COg in the sorbent is extracted from the sorbent in a regeneration / desorption step.

[0012] Desorption may involve thermal or chemical processes depending upon the type of sorbent material that is selected for use in the DAC.

[0013] The sorbent used in DAC processes typically comprises a significant portion of the overall capital and operating costs, particularly in sorbent replacement. The performance of the sorbent, in terms of capacity and stability, has a direct economic impact. For instance, a DAC process would need less amount of a better performing (more efficient) sorbent to capture a similar amount of CO2from the same volume of air, which can result in lower capital and operating costs. Current known sorbents and processes for capturing CO2from air, however, still suffer from low efficiency and / or are too costly.

[0014] For instance, a number of sorbents employ organic amines to capture carbon dioxide, which are prone to oxidation, thereby increasing the chance of sorbent degradation and loss of COg sorption capacity over time. These sorbents are described in various documents, including WO 2010 / 027929 Al, WO 2017 / 009241 Al, WO 2010 / 091831 Al, and WO 2021 / 189042 Al.

[0015] Another set of sorbents use potassium carbonate as a sorbent for CO2, which addresses the increased chance of oxidation of amine. They, however, disclose capturing carbon dioxide from a gas stream using adsorbent particulates. For instance, the adsorbent particulates of WO 2016 / 185387 Al are transported from the adsorber to the desorber in a circulating fluidized bed. The adsorbent material comprising potassium carbonate impregnated support is crushed and sieved to form the particulates. Likewise, US 2021 / 0016220 Al discloses a plurality of fixed sorbent beds that contain an alkalized sorbent.

[0016] The paper by Rodriguez-Mosqueda et al. ( Parametrical Study on COg Capture from Ambient Air Using Hydrated K2CO3 Supported on an Activated Carbon Honeycomb, Ind. Eng. Chem. Res. 2018, 57, 3628-3638, 6 ) discloses an activated carbon honeycomb monolith that was coated with K2CO3 and treated with moist N2to hydrate it.

[0017] US 2021 / 0016220 Al discloses sorbent beds that can be moved from one adsorption position to another adsorption position, and then into one regeneration position to another regeneration position, and optionally back to an adsorption position. The reference, however, only provides general disclosures around the sorbent composition.

[0018] As such, there still exists a need for improved sorbents that provide efficient capturing of CO2from air.

[0019] Summary of the Invention

[0020] Accordingly, there is provided a direct air capture (DAC) process for capturing CO2from air. The process comprises in step (i), passing air, preferably ambient air, through a capture unit comprising a sorbent structure to capture the carbon dioxide in the air. The sorbent structure comprises an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, based on the weight of the sorbent structure, and a metal-containing support in an amount of at least 55 wt%, based on the weight of the sorbent structure. The metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof. The process further comprises in step (ii), capturing the carbon dioxide by the sorbent to provide a treated stream of air with less carbon dioxide exiting the capture unit.

[0021] The process further comprises in step (iii), displacing the carbon dioxide from the sorbent by exposing it to a fluid comprising steam; and in step (iv), capturing at least a portion of the displaced carbon dioxide; and repeating the prior steps to continuously capture carbon dioxide from air passing through the capture unit.

[0022] Brief Description of the Drawings FIG. 1 illustrates a schematic representation of an exemplary DAC system in which embodiments of the sorbent structure disclosed herein can be employed.

[0023] FIG. 2 depicts an illustrative perspective view of an exemplary embodiment of a sorbent structure according to certain aspects described herein.

[0024] FIG. 3 depicts an illustrative perspective, partial cross-sectional view along the length of another exemplary embodiment of a sorbent structure according to certain aspects described herein.

[0025] FIG. 4 is a graph of COg concentration of various Examples at 7.5 wt% of a respective active component.

[0026] FIG. 5 is a bar chart of the COg utilization of various Examples at 7.5 wt% of a respective active component.

[0027] FIG. 6 is a bar chart of the COg utilization of various Examples at 5 wt% of a respective active component.

[0028] FIG. 7 is a graph of COg concentration of various Examples at 10 wt% of a respective active component.

[0029] FIG. 8 is a bar chart of the COg utilization of various Examples at 10 wt% of a respective active component.

[0030] While the present disclosure is susceptible to various modifications and alternative forms, specific embodiments have been shown in the figures and are herein described in more detail.

[0031] It should be understood, however, that the description of specific embodiments is not intended to limit the invention to the particular forms disclosed, but on the contrary, this disclosure is to cover all modifications and equivalents as illustrated, in part, by the appended claims. Detailed Description of the Invention

[0032] The present disclosure provides for sorbents and methods of using such sorbents to capture carbon dioxide from any gas stream containing CO2(such as air).

[0033] In the present invention, it has been surprisingly found that use in a sorbent structure of an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, based on the weight of the sorbent structure, is advantageous in a direct air capture process for capturing CO2from air. In particular, it has been found that the active component or a respective derivative thereof captures greater than 50%, preferably greater than 60%, more preferably greater than 75%, and most preferably greater than 90% of the total carbon dioxide being captured by the sorbent structure. That is to say, in a sorbent structure comprising (i ) an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, based on the weight of the sorbent structure, and (ii ) a metal-containing support in an amount of at least 55 wt%, based on the weight of the sorbent structure, wherein the metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, it has been found that the active component or a respective derivative thereof captures greater than 50%, preferably greater than 60%, more preferably greater than 75%, and most preferably greater than 90% of the total amount of carbon dioxide being captured by the sorbent structure as a whole.

[0034] According to another aspect, there is provided method for making a sorbent structure to capture CO2from a stream of gas comprising carbon dioxide. The method comprises providing a metal-containing support comprising a metal selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, preferably the metal-containing support consists essentially of the selected metal ( s ). The metal-containing support is in an amount of at least 55 wt% based on the weight of the sorbent structure. The method further comprises providing a solution of active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure; combining the solution and the metal-containing support for a period of time to allow the solution to provide an impregnated support; drying the impregnate support to provide a dried impregnated support; and calcining the dried impregnated support at a temperature of less than 550 °C at ambient pressure.

[0035] According to another aspect, there is provided a method for making a sorbent structure to capture CO2from a stream of gas comprising carbon dioxide. The method comprises providing a metal-containing support material comprising a metal selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, preferably the metal-containing support consists essentially of the selected metal ( s ) in an amount to provide the sorbent structure with at least 55 wt%, based on the weight of the sorbent structure. The method further comprises providing an active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure; combining the active component and the metal-containing support material to provide a sorbent mixture; conforming the sorbent mixture to a mould to provide a wet sorbent structure; drying the wet sorbent structure to provide a dried sorbent structure; and calcining the dried sorbent structure at a temperature of less than 550 °C at ambient pressure.

[0036] In the present invention, it has been surprisingly found that utilizing an active component comprising sodium aluminate in a sorbent in an amount as hereinbefore described, results in an improved CO2utilization number, wherein CO2utilization number is the ratio of uptake capacity (mole CO2 per kg sorbent) to alkali loading (mole of alkali metal to kg sorbent) as compared to other sorbents comprising different active components. The sorbent structure used in the process of the present invention preferably has a CO2utilization number of greater than 0. 11, more preferably at least 0. 15 and even more preferably greater than 0.2.

[0037] As used therein, CO2utilization % is being defined as:

[0038] CO2 Utilization[%] = Uptake capacity [mole CO2 / kg sorbent] / Alkali loading [mole alkali metal (Na,K) / kg sorbent] * 100%

[0039] mole alkali metal (Na, K) Alkali loading kg sorbent

[0040]

[0041] Optionally, the sorbent structure is a honeycomb that comprises a first end and a second end; a plurality of flow channels; and a plurality of channel walls. The flow channels are formed by at least one channel wall and extend from the first end to the second end. The metalcontaining support with the sodium aluminate deposited thereon forms the channel walls. Optionally, the sorbent structure is a monolith that comprises a cell density (CPSI) of less than 600 CPSI (less than 93 cells per cm2), preferably less than 400 CPSI (less than 62 cells per cm^ ),ancjmo repreferably les s than 200 CPSI ( less than 31 cells per cm2). Optionally, the wall thicknes s is les s than 0. 5 mm, preferably less than 0. 4 mm. Optionally, the sorbent structure is at least one of a straight channel monolith, a corrugated monolith, a stacked plate.

[0042] Optionally, the sorbent structure is selected from fibers, granules, beads, pellet s, extrudates, and any combination thereof.

[0043] Optionally, the active component comprises a molar ratio of sodium to aluminium of at lea st 1. 0.

[0044] Optionally, the sorbent structure further comprises at least one of an alkali metal carbonates ( such a s Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs2CO3), alkali metal bicarbonates, alkali metal hydroxides, the alkali salts of conj ugated bases of weak acids (gluconate, tartrate, acetate, citrate ), and any combination thereof in an amount in a range from 0. 1 wt% and up to 5. 0 wt%, preferably from 0. 5 wt% and up to 1. 5 wt%, based on the weight of the sorbent structure.

[0045] The present invention will now be described in detail with reference to embodiments thereof as illustrated in the accompanying drawings. References to "one embodiment", ''an embodiment" "an example embodiment", etc., indicate that the embodiment des cribed may include a particular feature, structure, or characteristic, but every embodiment may not neces sarily include the particular feature, structure, or characteri stic.

[0046] Moreover, such phrases are not neces sarily referring to the same embodiment. Further, when a particular feature, structure, or characteri stic is described in connection with an embodiment, it i s submitted that it is within the knowledge of one s killed in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the art, are within the spirit and scope of the invention.

[0047] Although the description herein provides numerous specific details that are set forth for a thorough understanding of illustrative embodiments, it will be apparent to one skilled in the art that embodiments may be practiced without some or all of these specific details. In other instances, well known process steps and / or structures have not been described in detail in order to not unnecessarily obscure the present invention. The features and advantages of embodiments may be better understood with reference to the drawings and discussions that follow.

[0048] In addition, when like elements are used in one or more figures, identical reference characters will be used in each figure, and a detailed description of the element will be provided only at its first occurrence. Some features or components of the systems or processes described herein may be omitted in certain depicted configurations in the interest of clarity.

[0049] FIG. 1 shows one example of a capture unit 100 (in a top or plan view) that can contain a sorbent according to aspects disclosed herein to capture carbon dioxide from air, such as ambient air. " Ambient air" refers to air that is provided from the surrounding environment, which can vary depending on the environment and season. For instance, ambient air conditions generally can include temperatures in a range from -20 °C and up to 50 °C, more commonly 10 °C and up to 40 °C, and pressures around atmospheric pressure + / - 10%. Referring to FIG. 1, the exemplary capture unit 100 comprises one or multiple rows of monolith beds or slabs that are comprised of one or more embodiments of the sorbent structure 100 disclosed herein. Preferably, the embodiment of the sorbent structure employed is a monolith where a stream of air 102 comprising carbon dioxide is drawn through flow channels (not shown in FIG. 1 ) by suitable equipment, such as impellers 103, such as fans.

[0050] The method depicted in FIG. 1 can comprise providing a stream of air 102 comprising carbon dioxide through capture unit 100 comprising a sorbent structure 104 to capture carbon dioxide present in the stream of air 102. The air stream containing CO₂ preferably comprises carbon dioxide in an amount of less than 500 ppm, more preferably from 300 and up to 500 ppm. More preferably, said stream is atmospheric air, which has its ordinary meaning, including generally a mixture of gases comprising the Earth' s atmosphere.

[0051] Optionally, air stream 102 is provided at a suitable flowrate. Examples of a suitable flow rate is provided in WO 2023 / 217740 Al, which is incorporated herein by reference. Additionally or alternatively, optionally, air stream 102 is provided under ambient conditions, which is understood by one of ordinary skill, and further information can also be found in WO 2023 / 217740 Al.

[0052] Referring to FIG. 1, sorbent structure 104 comprises an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, based on the weight of sorbent structure, and a metal-containing support in an amount of at least 55 wt%, based on the weight of sorbent structure. The phrase "an active component comprising sodium aluminate" means the active component comprises sodium aluminate only. The metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof. In the present invention, preferred metal-containing supports comprise one or more metal oxides. Preferred metal oxides for use as the metal-containing support may be selected from titania, alumina, zirconia, amorphous silica-alumina, cordierite, and combinations thereof. A most preferred metal-containing support is alumina. As used herein, the term "sorbent" or "sorbent structure" includes both the salt component or "active component" ( sodium aluminate ) and the metal-containing support or carrier.

[0053] The method further comprises capturing the carbon dioxide in air stream 102 by sorbent structure 104 to provide treated air stream 106 with less carbon dioxide exiting capture unit 100. Greater than 50% (preferably greater than 60%, more preferably greater than 75%, and most preferably greater than 90% ) of the carbon dioxide captured by sorbent structure 104 is captured by the sodium aluminate or a respective derivative of the sodium aluminate.

[0054] The Examples herein demonstrate that the maj ority (greater than 50% ) of the carbon dioxide captured by sorbent structure 104 is done by the active component of sodium aluminate and / or its respective derivative, rather than the metal-containing support.

[0055] Optionally, the active component of sorbent structure 104 can further comprise a molar ratio of sodium to aluminium of at least 1. 0. Optionally, in instances where sorbent structure 104 is produced via a process where a solution of the active component is used, additives may be present to stabilize the solution. For example, the sorbent may further comprise at least one of an alkali metal carbonates ( such as Li₂CO₃, Na₂CO₃, K₂CO₃₃, Rb₂CO₃, Cs₂CO₃, alkali metal bicarbonates, alkali metal hydroxides, the alkali salts of conj ugated bases of weak acids (gluconate, tartrate, acetate, citrate), and any combination thereof in an amount in a range from 0. 1 wt% and up to 5. 0 wt%, preferably from 0.5 wt% and up to 1.5 wt%, based on the total weight of the sorbent. The additives may be in the form of organic acids, such as acetic acid, tartaric acid, gluconic acid and citric acid.

[0056] As air stream 102 continues to flow through capture unit 100, carbon dioxide continues to be captured by sorbent structure 104. Eventually, sorbent structure 104 approaches a selected saturation level with captured carbon dioxide, which can be displaced from sorbent to recover the displaced carbon dioxide and to allow sorbent structure 104 to capture additional carbon dioxide.

[0057] The capture unit 100 can include a movable regenerator unit 101 that is able to move along a track (not shown) and encompasses an adj acent pair of monolith blocks at any given time whilst allowing neighbouring monolith blocks to continue to adsorb carbon dioxide. In this way the cycle of adsorption and regeneration within the capture unit can occur continuously without interruption and significant downtime. It will be appreciated that the configuration of a movable regenerator unit 101 depicted in FIG. 1 is merely exemplary and alternative assemblies of monoliths and regenerator units are possible. For example, US 10512880 Bl describes an arrangement whereby monolith beds are arranged in a rotating drum around a static regeneration unit. Displacing the captured carbon dioxide can also be known as regenerating of sorbent structure 104, which can be done by contacting sorbent structure 104 with fluid 108 comprising steam. Additional detailed examples of suitable ways to regenerate the sorbent (also known as desorbing) can be found in WO 2023 / 217740 Al.

[0058] Optionally, for the regenerating, fluid 108 comprising steam can be provided to sorbent structure 104 via suitable means such as a vacuum or at or near atmospheric pressure or has a slightly elevated pressure j ust above atmospheric pressure (e. g. >1 bar), suitably around 1.3 bar / 130 KPa (around 18. 9 psi), and at a temperature in a range from 70 °C and up to 200 °C. If the regenerating temperature is less than 100 °C, then the regenerating pressure (which is the total operation pressure for the regenerating step) is preferably (but not necessarily) at or below the saturation vapor pressure of water to avoid condensation. For instance, if the regenerating temperature (operation temperature for the regenerating step) is 100 °C (the saturation pressure of water is 1 bar ( 1 atm) ), then the regenerating pressure is preferably at or below 1 bar. If the regenerating temperature is less than 100 °C, for instance 90 °C, the saturation pressure of water is less than 1 bar, approximately 0.7 bar. The regenerating pressure is preferably at or below 0.7 bar. Optionally, fluid 108 consists essentially of steam. Preferably, fluid 108 consists of steam, i. e. fluid 108 is steam.

[0059] Fluid 108 can be provided to sorbent structure 104 by suitable means, such as those disclosed in WO 2023 / 217740 Al. Contact with fluid 108 moves the captured carbon dioxide from sorbent structure 104 into fluid 108, which allows the carbon dioxide to be removed as part of exit fluid 110, which comprises fluid 108 and the carbon dioxide captured from air stream 102 by the sorbent.

[0060] These steps can be repeated to capture carbon dioxide from air as desired.

[0061] Other references, such as US 9504955 B2, generally disclose that a sorbent can be formed from alkali metals such as Li, Na, K, Rb, Cs, and Fr, as well as alkaline-earth metals, on a support like alumina to capture CO₂, suggesting that all listed alkali and alkaline-earth metals function essentially the same as one another.

[0062] Surprisingly, it has been determined that sorbents comprising sodium aluminate in an amount from 5 wt% and up to 40 wt% and a metal-containing support according to aspects disclosed herein in an amount of at least 55 wt%, both based on the total weight of the sorbent, have improved performance, at least over other alkali salts, such as Na₂CO₃ or K₂CO₃.

[0063] As further shown in the Examples, which provide comparative examples of CO₂ uptake capacity and utilization of a sorbent structure according to aspects disclosed versus reference sorbents, with the same amounts of sodium carbonate, respectively, on the same type of metal-containing support. As can be seen, the examples of the sorbents according to aspects disclosed herein has a higher CO₂ uptake capacity as compared to the reference samples. For the Examples, the "CO₂ utilization" indicates the number of moles of CO₂ that is captured per mole of the respective sorbent sample. A sorbent with a higher CO₂ utilization number means that one mole of that sorbent can capture more CO₂ than one mole of a sorbent with a lower CO₂ utilization number. In particular, CO₂ utilization is preferably defined in the equation below as a %. As defined herein, the maximum theoretical CO₂ utilization number is 0.5 (or 50% as a % in according with the equation below) because stoichiometrically, it requires two moles of alkali metal to capture one mole of CO₂.

[0064] CO2 Utilization[%] = (CO2 Uptake capacity [mole CO2 / kg sorbent]) / (Alkali loading [mole alkali metal (Na,K) / kg sorbent]) * 100%

[0065]

[0066] kg sorbent

[0067] "CO₂ uptake capacity" can be determined by integration of the particular CO₂ concentration profiles shown in FIGS. 4 and 7, which gives the total amount of CC>2 captured by a particular sorbent structure for a particular Example. The unit for COg uptake capacity reported in Table 1 is liters of COg captured per kg of sorbent structure (L / kg), which can be converted to mol / kg by one of ordinary skill for calculating utilization. The alkali loading can be determined by knowing the wt% of the active component for and mass of the particular sorbent structure. For instance, one of ordinary skill can convert the wt% to mole of alkali metal through standard stoichiometric calculations. The mass of the sorbent structure for both CO₂ uptake capacity and alkali loading are based on the dry mass of that sample. A sorbent structure with a higher CO₂ uptake capacity number means it has captured more CO₂ under similar testing conditions. The CO₂ utilization number (and % ) accounts for any differences in mass and amount of sorbent material that can contribute to the total amount of CO₂ captured (CO₂ uptake capacity), which allows for the effectiveness of CO₂ captured per mol of sorbent material to be compared. As can be seen in the Examples, the sorbents comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, and a metalcontaining support in an amount of at least 55 wt% have higher CO₂ capacity and CO₂ utilization.

[0068] Sorbent structure 104 can have any suitable solid form for use in suitable sorbent beds, including moving solid sorbents, or solid sorbents contained in packed beds, which suitable forms include pellets or extrudates as known to one of ordinary skill. Additionally or alternatively, sorbent structure 104 can also be a form a sorbent structure, such as a monolith as disclosed in WO 2024 / 160605 Al, which provides parallel channels through which gas stream 102 can flow for the carbon dioxide to be captured. The disclosures of WO 2024 / 160605 Al are incorporated herein in its entirety by reference. The sorbent structure can also be moving and / or stationary. The sorbent can be in the form of granules, pellets, monoliths, powders that are collected on filters, or combinations thereof. If the sorbent structure is a monolith, it can be of any suitable form, such as straight channel monoliths, corrugated monoliths, stacked plates, sheets, wire mesh, including materials that are directly extruded or coated on an inert substrate (e. g. cordierite, ceramic fiber, metal).

[0069] For instance, FIG. 2 schematically depicts exemplary sorbent structure 200, and FIG. 3 schematically depicts another exemplary sorbent structure 300. Sorbent structures 200 and 300 can have any suitable crosssection shape, such as geometrical shapes including trapezoidal, triangular, rectangular, square, sinusoidal, hexagonal, oval, circular, and the like. The sorbent structure 200 in FIG. 2 has a depth (D) 210 and a length (L) 212. Sorbent structures 200 and 300 comprise respective first ends 202 and 302 and second ends 204 and 304, as well as flow channels ( see, for example, 306 formed by channel walls 308 in FIG. 3 ).

[0070] In instances where sorbent structure 104 is a monolith, it is preferred that the monolith comprises a cell density (CPSI ) of less than 600 CPSI (less than 93 cells per cm2), preferably less than 400 CPSI (less than 62 cells per cm2), and more preferably less than 200 CPSI (less than 31 cells per cm2). Optionally, the wall thickness of the monolith is less than 0.5 mm, preferably less than 0. 4 mm.

[0071] According to another aspect, the present disclosure also provides methods of making a sorbent structure as described herein for capturing carbon dioxide from a CO₂-containing gas. In embodiments wherein the metalcontaining support is produced separately (such as through extrusion or 3D printing), the active component can be applied to the metal-containing substrate using impregnation. In addition, wash-coating can be used to apply the active component on top of the surface of the metal-containing support.

[0072] In various embodiments, the metal-containing support material and the carbonate material may be combined, for example into a paste, and extruded through or inj ected into a mould (cast or die) to form the sorbent structure. In this embodiment, the carbonate may be dispersed throughout the metal-containing support when the combined paste is extruded into a monolithic form to achieve the desired physical and structural properties. One advantage of combining the metal-containing support material and the carbonate material in one single step is that fewer process steps are required. A further advantage is that it is easier to obtain a good mixing and distribution of the metal-containing support material and the carbonate material when they are combined and formed together ( such as via extrusion or 3D printing).

[0073] Accordingly, one method of making a sorbent structure of the present disclosure comprises providing a metalcontaining support selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, wherein the metal-containing support is provided in an amount of at least 55 wt% based on the total weight of the sorbent structure. The metal-containing support, if in the form of a monolith or honeycomb, may be produced separately, such as through extrusion, pressing, or 3D printing.

[0074] Such suitable methods to produce the metal-containing support are known to one of ordinary skill ( such as extrusion, 3D printing, and wash coating, casting or rolling in at least cases where a second material, such as alumina, is applied on top). The method can further comprise providing a solution of active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the total weight of the sorbent structure. The solution and metal-containing support can be combined and for a period of time to allow the solution to impregnate the support to provide an impregnated support. Preferably, after the desired contact time, the impregnated support is removed from the solution and excess solution remaining on the support is removed to facilitate drying and minimize precipitation of excess salt that can impede CO₂ uptake. Suitable methods to remove excess solution are known to one of ordinary skill, such as air knifing. The impregnated support is then dried to provide a dried impregnated support. The drying can be done through suitable means known to one of ordinary skill, such as evaporation at room temperature or in an oven at elevated temperature ( such as in a range from 50 °C and up to 150 °C) and atmospheric pressure. Preferably, air flow through the sorbent structure is provided during the drying step to facilitate even spatial distribution of the salt. The method can further comprise a subsequent thermal treatment in addition to the initial drying step that provides the dried impregnated support. The subsequent thermal treatment may be referred to calcining for the purposes of this disclosure to distinguish from the initial drying step. Calcining the dried impregnated support can be carried out at a temperature of less than 550 °C, preferably less than 450 °C, including at 300 °C. Surprisingly, it has been found (and the Examples show) that calcining at a temperature that is at or above 550 °C reduces the capacity and efficiency of the sorbent structure.

[0075] Also, another method of making a sorbent structure of the present disclosure comprises providing a metalcontaining support material selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof. Preferably, the metal-containing support is present in an amount of at least 55 wt%, based on the weight of the sorbent structure. The method further comprises providing an active component comprising sodium aluminate in an amount that provides the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure. The method further comprises combining the active component and the metalcontaining support material to provide a sorbent mixture, conforming the sorbent mixture to a mould or die to provide a wet sorbent structure; drying the wet sorbent structure to provide a dried sorbent structure; and calcining the dried sorbent structure at a temperature of less than 550 °C at ambient pressure.

[0076] Examples

[0077] For all the Examples, Table 1 below provides the amount and type of sorbent material that was dissolved in demineralized water to obtain a solution volume of 10 ml.

[0078] 31.2 g of either titania granulate with 250 - 600 micron particle size, a porosity of 0. 50 and an average pore size of 22 nm or trilobe-shaped alumina extrudates with a diameter of 1.3 mm, a porosity of 0.70 and an average pore size of 12 nm was added to a 125 ml polypropylene bottle and the sorbent solution was added to it. Then the sample was mixed on a roller mixer for 60 min in a sealed bottle, allowing the solution to impregnate the carrier. The sample was dried at 120 °C for 2 hours and subsequently at 300 °C or 550 °C or none (as indicated by Table 1 ) for 2 hours. There are methods known to one of ordinary skill to calculate the wt% of the sorbent material that has been loaded onto the support. In addition, a compositional analysis using a portion of a particular sorbent structure sample can also be conducted to determine or confirm the wt%, as calculated. The samples of various sorbent structures were then subj ected to COg capacity testing. For Examples 9 and 10, samples of the particular support materials were provided for COg capacity testing as references to show that the supports per se do not contribute to the COg capture. Those samples were also dried at 120 degrees C and calcined at 300 degrees C prior to testing. Table 1 provides the results of the testing, and the details of such testing are provided below Table 1.

[0079] As noted above, COg capacity can be determined by integration of the particular COg concentration profiles shown in FIGS. 4 and 7, which gives the total amount of CC>2 captured by a particular sorbent structure for a particular Example. The unit for COg capacity reported in Table 1 is liters of COg captured per kg of sorbent structure (L / kg), which can be converted to mol / kg by one of ordinary skill for calculating utilization. The sorbent material loading number can be determined by knowing the wt% of the sorbent material and mass of the particular sorbent structure. The mass of the sorbent structure for both COg capacity and loading are based on the dry mass of that sample. A sorbent structure with a higher CO₂ capacity number means it has captured more COg under similar testing conditions. The CO₂ utilization number and % accounts for any differences in mass and amount of sorbent material that can contribute to the total amount of COg captured (COg capacity), which allows for the effectiveness of COg capture per mol of sorbent material to be compared.

[0080] As can be seen in Examples 1 - 8 as compared to Examples 11 - 14, the sorbent structures with sodium aluminate has a higher CO₂ utilization % than the sorbent structures with sodium or potassium carbonate. Examples 9 and 10 show that the support materials did not capture any CO₂ during the CO₂ capacity testing. Examples 1 - 14 thus confirms at least that the active component or a respective derivative of the active component captures greater than 50%, preferably at least 90%, or more preferably at least 99% of the carbon dioxide actually captured by the respective sorbent structure.

[0081] In addition, Examples 2 - 4 show that calcining at a high temperature of 550 °C negatively impacts the % CO₂ utilization, about 1 / 3 between Examples 3 and 4, signifying about 33% capacity loss. Examples 2 - 3 also shows the benefit of having a calcining step where the CO₂ utilization is higher in Example 3 (calcining at 300 °C) as compared to Example 2 where no calcining took place (only dried at a temperature of 120 °C). Active component (wt% ) and Calcining CO2 CO2 Active

[0082] No. type of metal-containing temperature upta ke utilization component capacity

[0083] support ( ° C )

[0084] ( L / kg )

[0085] 1 1. 64 g NaA102 5. 0 wt% NaA102 on TiO2 300 2. 47 18 %

[0086] 2 2. 53 g NaA102 7. 5 wt% wt% NaA102 on TiO2 None * 3. 14 15%

[0087] 3 2. 53 g NaA102 7. 5 wt% wt% NaA102 on TiO2 300 3. 36 16%

[0088] 4 2. 53 g NaA102 7. 5 wt% wt% NaA102 on TiO2 550 2. 24 11%

[0089] 5 2. 90 g NaA102 8. 5 wt% wt% NaA102 on TiO2 300 4. 03 17 %

[0090] 6 3. 47 g NaA102 10. 0 Wt% NaA102 on TiO2 300 4. 48 16% 7 3. 47 g NaA102 10. 0 Wt% NaA102 on Al2O3300 7. 62 28 %

[0091]

[0092] 8 5. 51 g NaA102 15. 0 Wt% NaA102 on Al2O3300 9. 19 22 %

[0093] 9 ( Ref. ) 0 TiO2 300 0. 00 - 10 ( Ref. ) 0 Al2O3300 0. 05 - 11 ( Ref. ) 1. 64 g Na2CO3 5. 0 Wt% Na2 CO3 on TiO2300 2. 02 10%

[0094] 12 ( Ref. ) 2. 53 g Na2CO3 7. 5 Wt% Na2CO3on TiO2300 2. 02 6%

[0095] 13 ( Ref. ) 3. 47 g Na2CO3 10. 0 Wt% Na2CO3on TiO2300 2. 24 5%

[0096] 14 ( Ref. ) 2. 53 g K2CO3 7. 5 Wt% K2CO3on TiO2300 1. 57 6%

[0097]

[0098] *Temperature = 120 °C.

[0099] CO₂ capacity testing

[0100] Sorption capacity was tested over 5 adsorptiondesorption cycles in a fixed bed setup with a sorbent volume of 5 cm3. The setup was equipped with calibrated mass flow controllers to control gas flow (air, nitrogen) and a membrane vapor generator to humidify the gasses. Prior to the adsorption and desorption cycles, the sample was dried in argon at 120 °C for 2 hours. Then the bed was cooled to 30 °C and the sorbent and humid nitrogen gas with 70% RH at 30 °C was passed over the sorbent bed for 75 minutes. Maintaining a bed temperature of 30 °C the flow was switched to air containing 380 - 420 ppm CO₂ with a relative humidity of 70% at 30 °C. Humid air was passed through the sorbent bed for 2 hours at a gas hourly space velocity of 24,000 h-1. Then the flow was switched to nitrogen and the bed was flushed for 15 minutes to remove any physisorbed water. The sorbent sample was then heated to 120 °C in nitrogen for 30 minutes followed by 45 minutes in a mixture of 5% steam with balance nitrogen to regenerate the sorbent and desorb CO₂. Afterwards, the sorbent sample was cooled to 30 °C to complete the first adsorption-desorption cycle. Subsequent cycles were carried out according to the same protocol. Gas lines were heated to prevent condensation of water. After the 5thcycle, the samples were desorbed (or regenerated) to remove the CO₂. The off gas from regeneration was passed through an IR analyzer to measure at least the CO₂ concentration throughout the regeneration process. FIGS. 4 and 7 illustrate the CO₂ concentrations of the various Examples overtime throughout the regeneration. As can be seen in FIGS. 4 and 7, the metal-containing support reference samples (Examples 9 and 10 ) did not have any CO₂ uptake capacity so the CO₂ concentration remains at the maximum, around 400 ppm starting at time 0 and for the remainder of the time. The sample of Examples 2 - 4 remains active in capturing CO₂ longer than the reference samples where other alkali salts are the active components (Examples 12 and 14). That is, the respective CO₂ concentration curve of Examples 2 - 4 reaches the max ppm (around 400 ) at a later time than the reference samples.

[0101] The higher COg uptake capacity translates to higher CC>2 utilization set forth in Table 1 and depicted in graph form in FIGS. 5, 6, and 8. For instance, in FIG.

[0102] 5, Examples 2 - 4 have higher utilization than the reference Examples 9 (carrier only), 12 ( sodium carbonate), and 14 (potassium carbonate), with the sorbent structures that were calcined at lower than 550 °C (or none at all) having the best utilization in FIG. 5. FIGS. 6 and 8 show similar superior utilization of Examples 1 and 6 as compared to their respective references at 5 wt% and 10 wt%, respectively.

[0103] While specific embodiments have been described herein, it is understood that such descriptions are not intended to limit the described embodiments. Instead, any combination of the features and elements provided above, whether related to different embodiments or not, is contemplated to implement and practice contemplated embodiments. Furthermore, although embodiments disclosed herein may achieve advantages over other possible solutions or over the prior art, whether or not a particular advantage is achieved by a given embodiment is not limiting of the scope of the present disclosure. Thus, the aspects, features, embodiments and advantages described herein are merely illustrative and are not considered elements or limitations of the appended claims except where explicitly recited in a claim (s ).

Claims

C L A I M S1. A direct air capture (DAC) process for capturing CO2from air, comprising:(i) passing air, preferably ambient air, through a capture unit comprising a sorbent structure to capture the carbon dioxide in the air;wherein the sorbent structure comprises (i ) an active component comprising sodium aluminate in an amount from 5 wt% and up to 40 wt%, based on the weight of the sorbent structure, and (ii ) a metal-containing support in an amount of at least 55 wt%, based on the weight of the sorbent structure;wherein the metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metalnon-metal alloy, a ceramic material, and any combination thereof;(ii) capturing the carbon dioxide by the sorbent to provide a treated stream of air with less carbon dioxide exiting the capture unit;(iii ) displacing the carbon dioxide from the sorbent by exposing it to a fluid comprising steam;(iv) capturing at least a portion of the displaced carbon dioxide; and(v) repeating steps (i ) - (iv).

2. Process according to Claim 1, wherein the sorbent structure is made by a method comprising:providing a metal-containing support selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, wherein the metal-containing supportis provided in an amount of at least 55 wt% based on the weight of the sorbent structure; andadding to said support an active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure.

3. Process according to Claim 1 or 2, wherein the sorbent structure is made by a method comprising:providing a metal-containing support selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, wherein the metal-containing support is provided in an amount of at least 55 wt% based on the weight of the sorbent structure;providing a solution of active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure;combining the solution and the metal-containing support for a period of time to allow the solution to provide an impregnated support;drying the impregnate support to provide a dried impregnated support; andcalcining the dried impregnated support at a temperature of less than 550 °C at ambient pressure.

4. Process according to Claim 1 or 2, wherein the sorbent structure is made by a method comprising:providing a metal-containing support material selected from the group consisting of a metal alloy, metal oxide, metal-non-metal alloy, a ceramic material, and any combination thereof, wherein the metal-containingsupport is provided in an amount of at least 55 wt%, based on the weight of the sorbent structure;providing an active component comprising sodium aluminate in an amount to provide the sorbent structure with 5 wt% and up to 40 wt% of the active component, based on the weight of the sorbent structure;combining the active component and the metalcontaining support material to provide a sorbent mixture;conforming the sorbent mixture to a mould to provide a wet sorbent structure;drying the wet sorbent structure to provide a dried sorbent structure; andcalcining the dried sorbent structure at a temperature of less than 550 °C at ambient pressure.

5. Process according to any of the preceding Claims, wherein the sorbent structure is a honeycomb comprising:• a first end and a second end;• a plurality of flow channels; and• a plurality of channel walls,wherein the flow channels are formed by at least one channel wall,wherein the flow channels extend from the first end to the second end, andwherein the metal-containing support with the sodium aluminate deposited thereon forms the channel walls.

6. Process according to Claim 5, wherein the sorbent structure is a monolith comprising a cell density (CPSI) of less than 600 CPSI (less than 93 cells per cm2), preferably less than 400 CPSI (less than 62 cells per cm2),ancjmorepreferably less than 200 CPSI (less than 31cells per cm2).

7. Process according to of any of Claims 5 to 6, wherein the wall thickness is less than 0.5 mm, preferably less than 0.4 mm.

8. Process according to any of Claims 5 to 7, wherein the sorbent structure is at least one of a straight channel monolith, a corrugated monolith, a stacked plate.

9. Process according to any of Claims 1 to 5, wherein the sorbent structure is selected from fibers, granules, beads, pellets, extrudates, and any combination thereof.

10. Process according to any of the preceding Claims, wherein the active component comprises a molar ratio of sodium to aluminium of at least 1. 0.

11. Process according to any of the preceding Claims, wherein the metal-containing support is selected from the group consisting of a metal alloy, metal oxide, metalnon-metal alloy, a ceramic material, and any combination thereof.

12. Process according to any of the preceding Claims, wherein the metal-containing support comprises one or more metal oxides.

13. Process according to any of the preceding Claims, wherein the metal-containing support is selected from titania, alumina, zirconia, amorphous silica-alumina, cordierite, and combinations thereof.

14. Process according to any of the preceding Claims, wherein the metal-containing support is alumina.

15. Process according to any of the preceding Claims, wherein the sorbent structure further comprises at least one of an alkali metal carbonates (such as Li2CO3, Na2CO3, K2CO3, Rb2CO3, Cs2CO3), alkali metal bicarbonates, alkali metal hydroxides, the alkali salts of conjugated bases of weak acids (gluconate, tartrate, acetate, citrate), and any combination thereof in an amount in a range from 0.1 wt% and up to 5.0 wt%, preferably from 0.5 wt% and up to 1.5 wt%, based on the weight of the sorbent structure.

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