Atmospheric carbon dioxide adsorbent

Abstract

The invention relates to an atmospheric carbon dioxide adsorbent. A direct air capture (DAC) system comprising a porous sorbent structure for CO2 capture, the structure comprising nanopores of a size of 4-10 nm forming an interpenetrating network of channels for CO2 to enter the interior volume of the sorbent; a macropore for the diffusion of CO2 within the adsorbent; and nanoparticles having a size of about 4 to 10 nm and located within the network of channels.

Description

Technical Field

[0001] The present disclosure relates to sorbents for capturing atmospheric carbon dioxide (CO2) and methods of making and using the same. Background Art

[0002] Carbon dioxide is a notorious greenhouse gas, whose emissions have been rising dramatically since the start of the Industrial Revolution in the 18th century. Since then, CO2 emissions have been confirmed as a cause of climate change around the world. Recent findings from the International Panel on Climate Change have proposed that CO2 emissions should be halved by 2030 to avoid further negative impacts on the planet. Various technologies have been developed to capture atmospheric CO2, but their shortcomings have prevented the wider storage of CO2 from the air from being realized. Summary of the invention

[0003] In at least one embodiment, a direct air capture (DAC) system is disclosed. The system may include a porous adsorbent structure for CO2 capture, the structure may include nanopores of size 4-10 nm, which form an interpenetrating network of channels for CO2 to enter the internal volume of the adsorbent; macropores for CO2 diffusion within the adsorbent; and nanoparticles of size about 4-10 nm and located within the network of channels. The DAC system may include hydrophobic nanoparticles. The nanoparticles may include hydrophobic nanoparticles and hydrophilic nanoparticles. The DAC system may further include nanoparticles of substantially uniform size. The DAC system may have at least a portion of nanopores and nanoparticles of uniform size. The channel may include a localized hydrophilic region. The DAC system may further include a controller configured to adjust the relative humidity of the system.

[0004] In another embodiment, a direct air capture (DAC) system is disclosed. The system may include a compartment comprising a porous adsorbent structure for CO2 capture, the structure comprising nanopores, each having a size of at least about 4 nm, the nanopores forming a network of interwoven, interpenetrating channels, which are configured to attract a controlled amount of water less than the volume causing overflow in the channel, so that the CO2 adsorption of the adsorbent is increased and the energy demand for adsorbent regeneration is reduced; and a controller, which is programmed to adjust the relative humidity (RH) of the system. The DAC system may include at least a portion of the nanopores, which include nanopores of uniform size. The DAC system may include a majority of nanopores having a size of about 4 nm. The DAC system may further include a plurality of macropores. The relative humidity of the DAC system may be maintained at a value less than about 0.8. The DAC system may further include an exchange fluid configured to remove CO2 from the structure through the channel. The controlled amount of water in the adsorbent of the DAC system may depend on RH, temperature, and CO2 saturation of the adsorbent. The channel network of the DAC system may further include nanoparticles.

[0005] In another embodiment, a direct air capture (DAC) system is disclosed. The system may include a porous adsorbent having a network of nanopores penetrating a volume of the adsorbent, the nanopores having uniform properties in the range of about 4-10 nm, configured to allow a controlled amount of water within the network of nanopores; and nanoparticles dispersed within the network of nanopores. The controlled amount may be less than the amount of channels that cause overflow. The controlled amount may depend on relative humidity (RH), temperature, and CO2 saturation of the adsorbent. The nanoparticles may include hydrophobic nanoparticles. The DAC system may further include a controller programmed to maintain the RH of the system below a predetermined value. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 is a schematic diagram of a direct air capture (DAC) system, in which CO2 is adsorbed into a solid adsorbent and the adsorbent is regenerated;

[0007] Figure 2 A schematic diagram showing the internal structure of a prior art adsorbent including macropores and nanopores;

[0008] Figure 3 It is a schematic diagram of the water absorption state of the porous CO2 adsorbent and the change of the water saturation of the adsorbent with increasing humidity;

[0009] Figure 4A A schematic diagram showing an adsorbent structure including a network of expanded channels for CO2 transport;

[0010] Figure 4Bshows a schematic diagram of the adsorbent structure comprising a network of expanded channels and hydrophilic regions that result in partial water saturation of the network, including a dry pathway for CO2 transport;

[0011] Figure 5A is an example pore size distribution graph of a comparative example having an average pore size of 1 nm and an example embodiment having an average pore size of 4 nm; and

[0012] Figure 5B The same as the examples and comparative examples Figure 5A Graph of the pore size distribution corresponding to the water absorption curve. DETAILED DESCRIPTION

[0013] Embodiments of the present disclosure are described herein. However, it should be understood that the disclosed embodiments are merely examples, and other embodiments may take various and alternative forms. The drawings are not necessarily to scale; some features may be exaggerated or minimized to show the details of a particular component. Therefore, the specific structural and functional details disclosed herein should not be interpreted as restrictive, but only as a representative basis for teaching those skilled in the art to use the embodiments of the present invention in various ways. As will be understood by those of ordinary skill in the art, the various features illustrated and described with reference to any of the accompanying drawings may be combined with the features illustrated in one or more other drawings to produce an embodiment that is not explicitly illustrated or described. The combination of the features shown provides a representative embodiment for a typical application. However, various combinations and modifications of features consistent with the teachings of the present disclosure may be required for a specific application or implementation.

[0014] Except in the examples or otherwise explicitly stated, all numerical values ​​in this specification indicating the amount of material or reaction and / or use conditions should be understood as being modified by the word "about" when describing the broadest scope of the invention. It is usually preferred to practice within the specified numerical limits. In addition, unless explicitly stated to the contrary: percentages, "parts" and ratio values ​​are all by weight; describing a group or class of materials as suitable or preferred for a given purpose associated with the present invention means that mixtures of any two or more members of the group or class are also suitable or preferred; descriptions of ingredients in chemical terms refer to ingredients when added to any combination specified in the description, and do not necessarily exclude chemical interactions between ingredients of the mixture after mixing.

[0015] The first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and applies mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurements of properties are determined by the same techniques as previously or later mentioned for the same property.

[0016] It must also be noted that, as used in the specification and the appended claims, the singular forms "a," "an," and "the" include plural referents unless the context clearly dictates otherwise. For example, reference to a singular component is intended to include plural components.

[0017] As used herein, the terms "substantially", "generally" or "about" mean that the amount or value in question can be a specified specific value or some other value in its vicinity. Typically, the term "about" representing a specific value is intended to represent a range within + / - 5% of that value. As an example, the phrase "about 100" represents a range of 100+ / -5, i.e., a range from 95 to 105. Typically, when the term "about" is used, it can be expected that similar results or effects according to the present invention can be obtained within a range of + / - 5% of the value shown. The term "substantially" can modify the value or related features disclosed or claimed in the present disclosure. In such a case, "substantially" can represent that the value or related characteristics it modifies are within ± 0%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5% or 10% of the value or relative feature.

[0018] It should also be understood that integer ranges explicitly include all intermediate integers. For example, the integer range 1-10 explicitly includes 1, 2, 3, 4, 5, 6, 7, 8, 9 and 10. Similarly, the range 1 to 100 includes 1, 2, 3, 4 ... 97, 98, 99, 100. Similarly, when any range is required, the intermediate number that is the difference between the upper and lower limits divided by the increment of 10 can be taken as an alternative upper or lower limit. For example, if the range is 1.1 to 2.1, the following numbers 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9 and 2.0 can be selected as the lower or upper limit.

[0019] In the examples described herein, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) may be implemented with the values ​​provided in the examples rounded or truncated to plus or minus 50% of the values ​​indicated by two significant figures. In a refinement, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) may be implemented with the values ​​provided in the examples rounded or truncated to plus or minus 30% of the values ​​indicated by two significant figures. In another refinement, the concentrations, temperatures, and reaction conditions (e.g., pressure, pH, flow rate, etc.) may be implemented with the values ​​provided in the examples rounded or truncated to plus or minus 10% of the values ​​indicated by two significant figures.

[0020] For all compounds indicated as empirical chemical formulas with multiple letter and number subscripts (e.g., CHO), the value of the subscript may be rounded or truncated to two significant figures, plus or minus 50% of the indicated value. For example, if indicated as CHO, then the formula C (0.8-1.2) H (1.6-2.4) O (0.8-1.2)In one refinement, the value of the subscript may be plus or minus 30% of the value indicated by rounding or truncation to two significant figures. In yet another refinement, the value of the subscript may be plus or minus 20% of the value indicated by rounding or truncation to two significant figures.

[0021] As used herein, the term "and / or" means that all or only one element of the group may be present. For example, "A and / or B" means "only A, or only B, or both A and B". In the case of "only A", the term also covers the possibility that B is not present, that is, "only A, but not B".

[0022] It should also be understood that the present invention is not limited to the specific embodiments and methods described below, as specific components and / or conditions may of course vary. Furthermore, the terminology used herein is only for the purpose of describing specific embodiments of the present invention and is not intended to be limiting in any way.

[0023] The term "comprising" is synonymous with "including," "having," "containing," or "characterized by." These terms are inclusive and open-ended and do not exclude additional, unrecited elements or method steps.

[0024] The phrase "consisting of" excludes any element, step, or ingredient not specified in a claim. When the phrase appears in the body of a claim rather than immediately following the preamble, it limits only the elements set forth in that clause; other elements are not excluded from the claim as a whole.

[0025] The phrase "consisting essentially of" limits the scope of a claim to the specified materials or steps, plus those materials or steps that do not materially affect the basic and novel characteristic or characteristics of the claimed subject matter.

[0026] With respect to the terms "comprising," "consisting of," and "consisting essentially of," where one of these three terms is used herein, the presently disclosed and claimed subject matter may include the use of either of the other two terms.

[0027] The term "one or more" means "at least one," and the term "at least one" means "one or more." The terms "one or more" and "at least one" include "plurality" as a subset.

[0028] Description of a group or class of materials as suitable for a given purpose in connection with one or more embodiments means that mixtures of any two or more members of the group or class are suitable. Descriptions of ingredients in chemical terms refer to the ingredients when added to any combination specified in the specification and do not necessarily exclude chemical interactions between the ingredients of the mixture once mixed. The first definition of an acronym or other abbreviation applies to all subsequent uses of the same abbreviation herein and mutatis mutandis to normal grammatical variations of the initially defined abbreviation. Unless expressly stated to the contrary, measurements of properties are determined by the same techniques as previously or later mentioned for the same property.

[0029] Carbon dioxide or CO2 is the main greenhouse gas, accounting for about 80% of the annual greenhouse gas emissions from human activities in the United States. CO2 emissions are a recognized global problem. Greenhouse gases are gases that trap heat in the atmosphere. Heat trapping leads to changes in the Earth's radiation balance, thereby changing climate and weather patterns on a global and regional scale. CO2 is a compound composed of molecules, each of which has one carbon atom covalently double-bonded to two oxygen atoms. CO2 is found in a gaseous state at ambient temperature. In the air, CO2 is transparent to visible light, but absorbs infrared radiation, thereby acting as a greenhouse gas. CO2 enters the atmosphere through the burning of fossil fuels such as coal, natural gas and oil, solid waste, trees and other biogenic materials. CO2 further enters the atmosphere due to certain chemical reactions (such as the manufacture of cement or aluminum). In addition, when methane enters the atmosphere, it combines with oxygen to form CO2.

[0030] Due to its negative impact on the global climate, efforts have been made to reduce CO2 emissions, primarily by capturing CO2 at the source of emissions, such as the chimneys of power plants, cement plants, or aluminum plants. However, most anthropogenic CO2 emissions cannot be captured at the source, such as those originating from cars or airplanes. In addition, capturing already released CO2 (so-called legacy CO2) is highly desirable for reducing the overall impact of CO2 greenhouse gases on the climate.

[0031] Extracting CO2 from ambient air is therefore a potential way to mitigate greenhouse gas emissions and associated climate change. Direct extraction of CO2 from air via sorbents, often referred to as direct air capture (DAC), is the gold standard technology for this goal.

[0032] Typical adsorbent technologies in DAC include porous support materials functionalized with amine-containing molecules or polymers. For example, porous silica or cellulose support materials can be functionalized with amine-containing molecules or polyethyleneimine (PEI). In this type of adsorbent, the amine reacts spontaneously with CO2 to separate CO2 from the air, while the porous support material provides a high surface area for the amine / air interface, ensuring that air can flow through the adsorbent and anchoring the amine in the solid adsorbent, preventing it from volatilizing.

[0033] Non-limiting example DAC adsorption system / method includes two steps, which are Figure 1 As shown schematically in Figure 1 As shown in FIG. 1 , in a first stage or step 1 , an adsorbent 20 selected to selectively absorb CO 2 is exposed to air until it reaches a desired saturation point. Figure 1 In the first step of the process, air is passed over an amine-functionalized adsorbent 20, which separates CO2 from an input gas stream (labeled as air). In the second stage or step 2, the adsorbent is regenerated by removing the absorbed CO2 from the adsorbent 20 and storing the captured CO2 at high pressure and high purity for later use or sequestration, labeled B. In the second step, the CO2 bound to the solid adsorbent 20 is separated using a change in temperature, pressure, humidity level or other stimulus (labeled as A), regenerating the adsorbent to its original state and releasing the CO2 for storage or use. The process can then be repeated. In the schematic, the line connecting "amine" and "porous support" indicates that the amine is chemically bonded to the support.

[0034] While the first stage of the process is spontaneous, because the adsorbent chemistry is selected to react favorably with CO2, the regeneration stage requires energy input to desorb the captured CO2. The energy can come in the form of heat, external pressure changes, humidity changes, potential changes, or washing with an exchange or transfer fluid having a component with a preferential affinity for CO2, as described in U.S. Patent Application No. 18 / 162,326, which is incorporated herein by reference in its entirety.

[0035] The energy cost of the DAC process, as well as the useful life of the adsorbent material, depends largely on the efficiency of the regeneration phase, making it an important design component of any DAC process. The cost of a DAC process depends on the amount of CO2 that the adsorbent can absorb in a set amount of time and the energy input required to release the captured CO2 during the regeneration phase.

[0036] Existing adsorbent technology in DAC typically includes a porous support material functionalized with an amine-containing molecule or polymer. For example, porous silica, cellulose, or polystyrene support materials can be functionalized with amine-containing functional groups. In this type of adsorbent, the amine reacts spontaneously with CO2 to separate CO2 from air, while the porous support material provides a high surface area for the amine / air interface, ensuring that air can flow through the adsorbent, and anchoring the amine in the solid adsorbent, preventing it from volatilizing.

[0037] Porous adsorbents for CO2 capture typically have Figure 2 The multi-scale porosity is schematically shown in FIG. The structure may include a small number of macropores (20-200 nm diameter) and a large number of nanopores (1-4 nm diameter). Figure 2 In the embodiment, the adsorbent 20 includes macropores 22 and nanopores 24.

[0038] Amine-functionalized solid adsorbents are usually hydrophilic and absorb water along with CO2, where the amount and structure of absorbed water depends on environmental conditions such as humidity and temperature, as well as the type of adsorbent material used. The state of water absorption and its effect on adsorbent performance are discussed in Figure 3 As shown schematically in Figure 3 As can be seen in the figure, initially, the adsorbent is dry. As humidity increases, water is absorbed by the bulk of the material, resulting in a "wet" state. At higher humidity levels, water condenses in the nanopores of the adsorbent, resulting in an "overflowing" state. The absorbed water has a significant effect on the ability of the adsorbent to absorb CO2. In the "wet" and "overflowing" states, water improves CO2 absorption by increasing the strength and rate of CO2 adsorbent binding. But in the "overflowing" state, water prevents long-distance diffusion of CO2 into the adsorbent by blocking the nanopores. In addition, all forms of water increase the thermal mass of the adsorbent, thereby increasing the energy cost of thermal regeneration.

[0039] In some cases, water needs to be injected into and removed from the adsorbent. For example, an alternative to thermal regeneration is a process in which CO2 is removed from the adsorbent by washing it with a CO2 exchange fluid, such as a solution of ethylenediamine or an alkali metal hydroxide salt. The CO2 exchange fluid must then be removed from the adsorbent before the adsorbent can be used for the next CO2 capture cycle. The efficiency of this regeneration process is highly dependent on how effectively the adsorbent nanopores can be flooded and drained without excessive energy usage.

[0040] Therefore, the amount of CO2 absorbed in a given amount of time is highly dependent on the diffusion rate of CO2 through the adsorbent, the binding energy of CO2 to the adsorbent, and the kinetics of the binding reaction. In addition, subsequent regeneration of the adsorbent requires a large energy input to release the bound CO2 for storage or utilization. Both adsorption performance and regeneration costs are highly dependent on the adsorbent material and the amount of water absorbed with the CO2 and whether the absorbed water overflows the nanopores of the adsorbent.

[0041] Therefore, there is a need to improve the DAC system to prevent adsorbent overflow.

[0042] In one or more embodiments, solid adsorbents for DAC are disclosed. The adsorbent can be configured to control the water uptake of the solid adsorbent material to improve or maximize its CO2 adsorption performance and reduce or minimize the regeneration step energy requirements.

[0043] The adsorbent may be a solid. The adsorbent may include a porous carrier material. The porous material may be functionalized with amine-containing molecules or polymers such as polyethyleneimine (PEI). Amine-based chemicals may be attached or immobilized on the carrier. The carrier material may include mesoporous silica, cellulose, polymers such as polymethyl methacrylate (PMMA) or polystyrene (PS), etc., or a combination thereof. The porous material may form a porous body or a body having a solid structure including a plurality of pores within its internal volume. The amine may be attached by impregnation, grafting, etc.

[0044] In order to obtain the desired water absorption control, the adsorbent can have a unique structure of a porous body. The adsorbent can be configured to adjust the local water balance in the internal volume of its body. The structure can include macropores and nanopores. The macropores are configured to allow long-distance gas diffusion. The macropores can be measured to be about 20-200, 30-180 or 40-160nm. The macropores can be measured to be about, at least about or at most about 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, 160, 170, 180, 190, 200, 210 or 220nm, or any range of any two numbers mentioned here. The macropores can be randomly distributed in the adsorbent. The macropores may not form a network or be part of a network in the adsorbent. The macropores may not contact the nanopore network. Alternatively, the macropores may contact the nanopore network, providing many larger macroscopic paths through the adsorbent. At least some of the nanopores may extend away from the macropores to provide contact with a large internal surface area of ​​the adsorbent.

[0045] The nanopores may form an interwoven network. The network may be interpenetrating, in other words, a network of nanopores that penetrate a volume of the adsorbent. Thus, the nanopores may be configured to allow CO2 gas to enter the interior volume of the adsorbent.

[0046] The nanopores may have a size of about 4-10, 5-9, or 6-8 nm. The nanopores may measure about, at least about, or at most about 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5, or 10 nm. At least some of the nanopores may have a size between 10-20 nm, such as 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nm. The nanopores may have uniform characteristics, such as size, composition, shape, etc. The nanopores forming the network may have the same size. In a non-limiting example, the nanopore network may include a majority or at most 50, 60, 70, 80, 90, 99, or 100% of the total nanopores having uniform characteristics. For example, at least some of the nanopores may have the same size of about 4 nm. Deviations of about ± 1 nm are considered. Uniform characteristics, especially size, are related to the effective operation of the system. The non-uniform size can result in a wide range of relevant RHs where flooding does not occur. A wide range of humidity can lead to inefficient operation and wasteful efforts to prevent flooding events from occurring. On the other hand, the uniform size of the nanopores results in a narrow RH range, so that all water enters and leaves the adsorbent within a narrow humidity range. Therefore, controlling the narrow RH range helps the system to operate more efficiently and sustainably.

[0047] The adsorbent may be free of micropores or nanopores having a size of about 1-3 nm. Pores smaller than 4 nm tend to flood easily or at undesirably low relative humidity (RH), as demonstrated and described in the experimental section below. Flooding subsequently deactivates CO2 adsorption in the area affected by the flooding.

[0048] Figure 4A A non-limiting example adsorbent 120 having nanopores 122 is shown in FIG. 1 , which has a uniform size characteristic in the range of 4 to 10 nm. Figure 4A As can be seen in the Figure 1 , the uniform pores forming the network allow CO2 to travel through the adsorbent volume. The expanded pore size disclosed herein can inhibit flooding throughout the adsorbent, as demonstrated in the experimental section below.

[0049] The adsorbent may be a hydrophilic adsorbent. Thus, the adsorbent attracts water molecules. The adsorbent may have an affinity for water molecules. The adsorbent may wet easily and remain wet, saturated, for extended periods of time. Alternatively, the adsorbent may be more hydrophilic than hydrophobic, but contain a hydrophobic component. The hydrophobic component may be located in the nanopores, forming localized hydrophobic regions within the network. Thus, the adsorbent may be hydrophilic overall, but include hydrophobic portions, pockets, or islands.

[0050] The adsorbent structure may comprise one or more nanoparticles. The nanoparticles may be hydrophilic, hydrophobic, or a mixture of the two. Unlike hydrophilic materials that attract water molecules and maximize their contact with water molecules, hydrophobic materials such as hydrophobic nanoparticles are not attracted by water molecules and may appear to be repelled by them. Therefore, hydrophobic nanoparticles may result in the formation of water droplets, minimizing contact with water molecules.

[0051] Nanoparticles can be provided in one or more nanopores, macropores or combinations thereof. Preferably, nanoparticles can be uniformly dispersed in the nanopore network. The presence of nanoparticles in macropores is acceptable, but may not provide the desired effects described herein. Nanoparticles can form a connected network of non-overflowing, dry or anhydrous pores. Nanoparticles can also or alternatively form a network with anhydrous pores or a locally overflowing, water-rich or saturated region within the network of anhydrous pores. Anhydrous and aqueous pores can be included in a ratio of about 30:70, 40:60, 45:55, 50:50, 60:40, 70:30, 80:10 or 90:10. Anhydrous pores need to form a percolation network so that there is a continuous, uninterrupted path that passes through the adsorbent material along the anhydrous pores. Thus, the anhydrous porosity should be at least about 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, or 45% or more of the total nanopores.

[0052] Nanoparticle can have about, at least about or at most about 3,3.2,3.5,3.8,4,4.2,4.5,4.8,5,5.2,5.5,5.8,6,6.2,6.5,6.8,7,7.2,7.5,7.8,8,8.2,8.5,8.8,9,9.2,9.5,9.8 or 10nm size.Nano particle size can be about 3-10,3.2-8.8 or 3.5-7.5nm.Nano particle can have the uniform characteristic similar to pore.At least some nano particles can have uniform size so that all, most or most of nano particles included have similar or identical size, for example 4nm.Selectively, nano particles can have different sizes.

[0053] Nanoparticles can have different or uniform chemical compositions. For example, if both hydrophobic and hydrophilic nanoparticles are added, their compositions will be different. Non-limiting example materials of nanoparticles can include silicon dioxide, aluminum oxide, zinc oxide, iron oxide, titanium oxide, tin oxide, zirconium oxide, silver oxide or its combination. Nanoparticles can include coatings that impart one or more beneficial properties such as hydrophilicity or hydrophobicity. Non-limiting example hydrophobic coatings can include PDMS (polydimethylsiloxane), PTFE (polytetrafluoroethylene) or PS (polystyrene). Non-limiting example hydrophilic coatings can include PEG (polyethylene glycol), PVA (polyvinyl alcohol) or PEI (polyethyleneimine).

[0054] Thus, the nanoparticles can form a system or network of hydrophobic, water-free channels for CO2 transport connected to water-attracting hydrophilic regions that enable binding of CO2. The presence of nanoparticles in the adsorbent can create locally saturable regions while maintaining a connected network of unsaturable pores. Figure 4B A non-limiting illustrative example of an adsorbent comprising hydrophobic regions and hydrophilic regions is shown in .

[0055] exist Figure 4B 2, the porous adsorbent body 220 includes a network of pores 222 having channels 224 for transporting CO2 through the adsorbent body 120. The adsorbent body 220 may include hydrophilic nanoparticles 226, which are schematically shown with the presence of water 50 attracted to the surface of the nanoparticles. The adsorbent body 220 further includes hydrophobic portions, such as percolation channels 224 within the pores, which resist flooding due to their larger size and / or the presence of hydrophobic nanoparticles therein. The percolation network of pores 222, 224 resists flooding and allows CO2 to be transported through the adsorbent 220, while the locally saturated areas 226 provide the benefit of stronger and faster CO2 binding.

[0056] The addition of nanoparticles can affect the size of nanopores during the formation of the adsorbent. For example, during the polymerization and crosslinking of a polymer adsorbent, nanoparticles can template the formation of nanopores having a diameter similar to the size of the nanoparticles. Thus, the nanoparticles can act as a scaffold, keeping the pores open to achieve the desired size or uniform properties described herein. In addition, the hydrophilicity or hydrophobicity of the nanoparticle surface can change the local water balance in the vicinity of the nanoparticle, promoting or inhibiting flooding.

[0057] The combination of structural features disclosed herein, in particular the presence of nanoparticles, the pore size distribution of nanopores of about 4-10 nm, or both, can result in the presence of a controlled amount of water in the pores or adsorbent, but allow gas to move through the adsorbent material. Overflow is thus avoided and CO2 is allowed to diffuse through the adsorbent. Adsorbents that partially attract and partially repel water combine the advantages of water absorption (stronger and faster CO2 binding) without incurring the losses (poor gas transport and excess thermal mass). Therefore, a local water balance can be achieved in the body of the adsorbent, preventing excessive water absorption in the DAC and ensuring that the CO2 adsorbent can operate effectively.

[0058] The controlled amount of water may depend on the relative humidity (RH). To prevent overflow, the ambient or relative humidity (RH) should be kept below about 0.8-0.9. RH is a measure of how much water vapor is present in a water-air mixture compared to the maximum amount possible. RH is the ratio of the amount of atmospheric moisture present relative to the amount that would be present if the air were saturated. RH is a function of moisture content and temperature. The controlled amount may be less than the amount of the channel that causes overflow. Overflow or overflowing channels involve saturation of the channels, network, or both with water such that CO2 is prevented from moving through the adsorbent.

[0059] As shown in the experimental section below, water absorption curves demonstrate that with increasing pore size of about 4-10 nm, RH triggered flooding is in the range of about 0.8-0.9 and higher. The addition of hydrophobic nanoparticles can push the RH range even further to values ​​greater than about 0.8-0.9.

[0060] Thus, controlled saturation can occur suddenly at high RH, rather than gradually over a wide range of conditions. Thus, RH can be used to initiate and / or terminate saturation events within the adsorbent. In other words, the adsorbent can switch between a water-saturated state and an anhydrous state or an unsaturated state, the switch being triggered by fluctuations or changes in RH. Fluctuations or changes in RH can be controlled, for example, by a central controller. Thus, the adsorbent can exhibit a controlled presence of water within the adsorbent, which is adjusted to the desired operating conditions of the DAC adsorbent.

[0061] The sorbent disclosed herein may be part of a system configured to sequester CO2 from a dilute source. The system may be a DAC system. The system is arranged to capture CO2 from air, atmosphere. The capture may be direct capture. The CO2 may be anthropogenic CO2, legacy CO2, naturally occurring CO2, CO2 from various sources such as decomposition CO2, ocean release CO2, respiratory CO2, industrial source CO2, deforestation CO2, fossil fuel combustion CO2, transportation CO2, fuel combustion CO2, exhaust CO2, etc., or a combination thereof.

[0062] The system includes several components that cooperate mechanically, physically, chemically, fluidically, or in combination thereof. The system may include one or more compartments containing the porous adsorbent described herein, one or more mechanisms configured to regenerate the adsorbent, one or more devices for storing captured CO2, one or more components for releasing exhaust air having a CO2 concentration lower than that of the incoming air, and the like, or a combination thereof. The compartment may be a can, a vessel, a container, a canister, a capsule, a basin, a chamber, a water tank, a flask, a receptacle, and the like. The container may be a closed, closable, openable, sealable, and / or resealable container.

[0063] The compartment may include one or more air inputs configured as resealable or closable openings, one or more conduits connecting one or more parts of the system and arranged to conduct one or more fluids between the various parts of the system. The fluid may be air, exchange fluid, electrolytes, etc.

[0064] The system may use a solid porous adsorbent in combination with liquid exchange of a transfer fluid having a chemical composition with a preferential affinity for CO2, the system being configured to regenerate the adsorbent after CO2 binds to the adsorbent to a predetermined saturation point. Regeneration is achieved by mediated transfer of CO2 from the adsorbent, which is achieved by removing, desorbing, stripping or displacing CO2 absorbed onto the adsorbent and binding CO2. Alternatively, the system may use heat, changes in external pressure, changes in RH to regenerate the porous adsorbent. Thus, the system may include a heat source, a pressure regulator, a humidity control system, and the like.

[0065] The system may further include one or more controllers, sensors, or both, receiving or providing inputs and outputs to trigger the binding of CO2, the release of CO2 from the adsorbent, the regeneration of the adsorbent, or a combination thereof. Thus, the controller may monitor, regulate, initiate, terminate, or facilitate the binding and / or release of the adsorbent, for example by controlling, regulating, monitoring the RH of the system, subsystem, or unit in which the adsorbent is present. Alternatively, controlled flooding may be ensured by structural features of the adsorbent disclosed herein, and may not require the assistance of a controller. Figure 1 A non-limiting example of a controller 90 and a sensor 92 is schematically depicted in the system shown in FIG. The placement and configuration are schematic only and may be different from Figure 1 Different from what is described in .

[0066] Disclosed herein is a method for preparing an adsorbent for a DAC system. The method may include forming a porous adsorbent comprising a functional group configured to capture or bind CO2 from air, and fixing the functional group on a support material comprising pores. The method may include polymerizing, cross-linking a base component, or both to form a porous support material. The method may include tailoring the porosity of the material to achieve a balanced pore size distribution of nanopores having a size in the range of about 4-10 nm or any value within the range. The method may include checking, adjusting, confirming that the nanopores have substantially uniform properties of shape, size, composition, or a combination thereof. For example, the method may include providing the adsorbent with a majority of nanopores having a size of 4 nm. The method may include providing nanoparticles of a certain size to keep the pores open and / or expand the pores throughout the polymerization, cross-linking, or both.

[0067] The method may include using an initially non-porous support material and creating a desired volume and size of nanopores within the volume of the support. The method may include forming macropores and nanopores, as disclosed herein.

[0068] Alternatively, the method may include using a porous support adsorbent material and adjusting, increasing or decreasing the pore size. For example, the adjustment may include changing the size of the pores from about 1-3 nm to about 4-10 nm. The method may include expanding existing pores, for example, by high strain rate tensile deformation or polymer crazing. Polymer crazing involves polymer fracture. Crazing may be triggered by applying excessive tensile stress to the support material, forming microvoids in a plane perpendicular to the stress.

[0069] Alternatively, the pores may be expanded by adding a pore expansion fluid. In a non-limiting example, the material may be saturated with CO2 at high pressure and temperature. The temperature and / or pressure may then be brought closer to ambient conditions, causing the CO2 to suddenly expand and push open the pores of the material. The treatment may additionally be performed above the glass transition temperature of the adsorbent material to facilitate deformation of the polymer material. At the end of the treatment step, the polymer may be returned to below its glass transition temperature to lock in the pore-expanded structure.

[0070] Another alternative approach may include blending the polymer with a phase separating copolymer such as dextran, where the characteristic length scale of the phase separation is equal to the desired pore size. The method may include subsequent removal of the copolymer by selective dissolution and leaching.

[0071] In addition to expanding or forming nanopores of a desired size distribution, the method may include adding a nanoparticle additive. Alternatively, the method may include adding nanoparticles without expanding the pore size. The method may include providing nanoparticles during the formation of the support material, as described above. The method may include forming hydrophilic regions, hydrophobic regions, or both within the support material of the adsorbent by including nanoparticles modified to be hydrophilic or hydrophobic, such as by having a relevant coating. The nanoparticles may be added after the pores are formed or expanded to the desired size.

[0072] Disclosed herein are methods of using the adsorbent disclosed herein. The method may include providing the adsorbent in a DAC system. The method may include absorbing CO2 in the adsorbent until a predetermined CO2 saturation point, saturation value, or saturation range. The method may include regenerating the adsorbent by using an exchange fluid having an affinity for CO2, heat, or other means.

[0073] The method may include controlling the amount of water absorbed by the adsorbent by maintaining, keeping or adjusting the RH of the system. The control may include receiving input from one or more sensors in the adsorbent through one or more controllers. The control may include processing the input through a controller and providing output to one or more additional components of the system such as a humidifier release valve, an air input valve, a dehumidifier, etc. The method may include removing water from the adsorbent, releasing water into the adsorbent, triggering saturation of the network, and changing the overflow degree of the network. The method may include preventing excess water from reaching the channel by pausing or stopping the flow of water / steam, air or both into the adsorbent. The method may include adjusting RH through a controller based on the input. The method may include maintaining RH at or below a predetermined value based on the size, hydrophobicity, hydrophilicity or a combination of nanopores in the network. The method may include maintaining RH at a value less than about 0.8.

[0074] Experimental Section

[0075] The water absorption by porous adsorbents disclosed herein can be described by the sum of two mechanisms. The first mechanism is the absorption of water by the bulk of the adsorbent material, which is characterized by the hydrophilicity of the dense regions of the adsorbent. The second mechanism is the condensation of liquid water in the nanopores of the material. The formation of liquid water in the nanopores of the material can be described by a capillary mechanism, where the relative humidity at which condensation occurs is defined by the interfacial energy between the pore walls and the liquid water and the characteristic diameter of the pores. For pores with diameter d and interfacial energy γ, the critical relative humidity (RH) for condensation (pore overflow) is crit ) is given by the equation:

[0076]

[0077] where ρ H2Ois the density of water, R is the ideal gas constant, and T is the temperature. For macroscopic materials, the size of the pores in the material can be described by the pore size distribution, e.g. Figure 5A The lognormal distribution shown in . Combining the above equations, we can get Figure 5B Representative water absorption curves of the adsorbents were constructed from the various pore size distributions shown in FIG.

[0078] As from Figure 5A , 5B As can be seen in the graphs, when the relative humidity increases from 0 to 100%, the material with 1 nm nanopores (Comparative Example) representing the prior art adsorbent continuously absorbs water, with some pore overflow occurring as early as relative humidity (RH) = 0.2. In contrast, the adsorbent with 4 nm nanopores (Example) disclosed herein does not show significant pore overflow until RH = 0.8, and absorbs water within a narrow relative humidity range.

[0079] Figure 5B The water absorption curves corresponding to the pore size distribution of the comparative example and the embodiment are shown. Figure 5A , 5B As can be seen in Figure 5, changing the pore size distribution of the adsorbent from the 1 nm case to the 4 nm case enables more precise control over the water uptake of the adsorbent. Figure 5B The water absorption curve of the 4nm embodiment shown in Figure 1 prevents diffusion barrier overflow from occurring until the ambient humidity exceeds about 0.8-0.9. The bottom dashed line of the 4nm embodiment shows the lack of continuous overflow, showing no overflow, consistently remaining at or near 0 until a RH of about 0.8. On the other hand, the comparative example line shows continuous water absorption starting at a RH of about 0.1, rising consistently with increasing RH.

[0080] Furthermore, the modified pore size distribution of this embodiment allows condensed water to be removed from the adsorbent with only a small decrease in ambient humidity, enabling lower cost adsorbent regeneration.

[0081] The process, method or algorithm disclosed herein can be delivered to or implemented by a processing device, a controller or a computer, and the processing device, the controller or the computer can include any existing programmable electronic control unit or a dedicated electronic control unit. Similarly, the process, method or algorithm can be stored in many forms as data and instructions that can be executed by a controller or a computer, including but not limited to information permanently stored on a non-writable storage medium such as a ROM device and information that can be modified and stored on a writable storage medium such as a floppy disk, a tape, a CD, a RAM device and other magnetic media and optical media. The process, method or algorithm can also be implemented in a software executable object. Alternatively, suitable hardware components, such as application specific integrated circuits (ASICs), field programmable gate arrays (FPGAs), state machines, controllers or other hardware components or devices, or a combination of hardware, software and firmware components, can be used to implement the process, method or algorithm in whole or in part.

[0082] Although exemplary embodiments are described above, it is not meant that these embodiments describe all possible forms covered by the claims. The words used in the specification are descriptive rather than restrictive, and it should be understood that various changes can be made without departing from the spirit and scope of the present disclosure. As previously mentioned, the features of various embodiments can be combined to form further embodiments of the present invention that may not be clearly described or illustrated. Although various embodiments may have been described as providing advantages or being superior to other embodiments or prior art implementations relative to one or more required characteristics, it is recognized by those of ordinary skill in the art that one or more features or characteristics can be compromised to achieve the desired overall system properties, depending on the specific application and implementation. These properties may include, but are not limited to, cost, strength, durability, life cycle cost, marketability, appearance, packaging, size, applicability, weight, manufacturability, ease of assembly, etc. Therefore, although it is not as ideal as other embodiments or prior art implementations in terms of one or more characteristics within the scope of describing any embodiment, these embodiments do not exceed the scope of the present disclosure and may be desirable for specific applications.

Claims

1. A direct air capture (DAC) system comprising: A porous adsorbent structure for CO2 capture, the structure comprising Nanopores with a size of 4-10 nm that form an interpenetrating network of channels for CO2 to enter the interior volume of the sorbent; macropores for CO2 diffusion within the adsorbent; and Nanoparticles are approximately 4-10 nm in size and are located within the network of channels.

2. The DAC system of claim 1, wherein the nanoparticles are hydrophobic. 3 . The DAC system of claim 1 , wherein the nanoparticles include hydrophobic nanoparticles and hydrophilic nanoparticles. The DAC system of claim 1 , wherein the nanoparticles comprise nanoparticles of substantially uniform size.

5. The DAC system of claim 1, wherein at least a portion of the nanopores and nanoparticles have a uniform size. The DAC system of claim 1 , wherein the channel comprises a locally hydrophilic region.

7. The DAC system of claim 1, wherein the system further comprises a controller configured to adjust relative humidity of the system.

8. A direct air capture (DAC) system comprising: A compartment comprising a porous adsorbent structure for CO2 capture, the structure comprising nanopores, each having a dimension of at least about 4 nm, the nanopores forming a network of interwoven, interpenetrating channels configured to attract a controlled amount of water less than a volume causing flooding within the channels, such that CO2 adsorption by the adsorbent is increased and energy requirements for regeneration of the adsorbent are reduced; and A controller is programmed to regulate the relative humidity (RH) of the system.

9. The DAC system of claim 8, wherein at least a portion of the nanopores comprise nanopores of uniform size.

10. The DAC system of claim 8, wherein a majority of the nanopores have a size of about 4 nm.

11. The DAC system of claim 8, wherein the structure further comprises a plurality of macropores.

12. The DAC system of claim 8, wherein the relative humidity is maintained at a value less than about 0.

8.

13. The DAC system of claim 8, wherein the system further comprises an exchange fluid configured to remove CO2 from the structure through the channel.

14. The DAC system of claim 8, wherein the controlled amount of water in the sorbent depends on RH, temperature, and CO2 saturation of the sorbent.

15. The DAC system of claim 8, wherein the network of channels further comprises nanoparticles.

16. A direct air capture (DAC) system comprising: A porous adsorbent comprising a network of nanopores penetrating a volume of an adsorbent, the nanopores having uniform characteristics in the range of about 4-10 nm configured to allow a controlled amount of water within the network of nanopores; and Nanoparticles are dispersed within the network of nanopores.

17. The DAC system of claim 16, wherein the controlled amount is less than an amount of the channel causing overflow.

18. The DAC system of claim 16, wherein the controlled amount depends on relative humidity (RH), temperature, and CO2 saturation of the adsorbent.

19. The DAC system of claim 16, wherein the nanoparticles comprise hydrophobic nanoparticles.

20. The DAC system of claim 16, further comprising a controller programmed to maintain the RH of the system below a predetermined value.

Images