Sterically hindered sorbent for direct air capture

Abstract

Sorbent solutions and methods of capturing carbon dioxide may employ a hindered amino acid or amine sorbent, alone or in combination with an unhindered amino acid or amine sorbent. The sorbent solution may be aqueous. A sorbent solution comprising carbon dioxide-derived species may interact with a carbon complexing agent to regenerate a hindered amino acid or amine sorbent.

Description

STERICALLY HINDERED SORBENT FOR DIRECT AIR CAPTUREINCORPORATED BY REFERENCE

[0001] A PCT Request Form is filed concurrently with this specification as part of the present application. Each application that the present application claims benefit of or priority to as identified in the concurrently filed PCT Request Form is incorporated by reference herein in their entireties and for all purposes.TECHNIC AL FIELD

[0002] The present disclosure relates to carbon dioxide capture processes, and more particularly to a sterically hindered sorbent that is used in carbon dioxide capture, such as direct air capture.BACKGROUND

[0003] Capturing carbon dioxide (CO2) from the atmosphere is one approach to mitigating greenhouse gas emissions and slowing climate change. However, many technologies designed for CO2 capture from point sources of emissions, such as from flue gas of industrial facilities, are generally ineffective in capturing CO2 from the atmosphere due to the significantly lower CO2 concentrations and large volumes of atmospheric air required to process. In recent years, progress has been made in finding technologies better suited to capture CO2 directly from the atmosphere. Some of these direct air capture (DAC) systems use a solid sorbent where an active agent is attached to a substrate. These DAC systems typically employ a cyclic adsorption-desorption process where, after the solid sorbent is saturated with CO2, it releases the CO2 using a humidity or thermal swing and is regenerated.

[0004] Other DAC systems use a liquid sorbent (sometimes referred to as a solvent) to capture CO2 from the atmosphere. An example of such a DAC system would be one where a fan is used to draw air across a high surface area packing that is wetted with a solution comprising the liquid sorbent. CO2 in the air reacts with the liquid sorbent to generate a CO2 rich solution. The rich solution is processed to regenerate a lean solution and to release a concentrated carbon stream, for example, CO, CO2 or other carbon products.SUMMARY

[0005] Provided herein are the sorbent materials and methods of using the sorbent material for capturing carbon dioxide moieties excluding hydrogen, wherein A is a bond, a C atom,a heteroatom, a carbon chain with a backbone length of C1-C9, or a ring-containing moiety; wherein each Re, R7, Rs, R9, and Rio is, independently, H, substituted aliphatic, substituted alkyd, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkydene.

[0006] In an example implementation, a method of capturing carbon dioxide includes (a) contacting a source of impure carbon dioxide with an aqueous sorbent solution comprising at least one sterically hindered sorbent to produce a carbon-loaded sorbent solution comprising carbonate ions and / or bicarbonate ions; and (b) reacting the carbonate ions and / or the bicarbonate ions with a complexing agent to form at least one of a carbonate salt of the complexing agent or a bicarbonate salt of the complexing agent.

[0007] In some implementations, the sterically hindered sorbent has the formula:

[0008] wherein at least three of Ri, R2, R3, R4, and R5 are not hydrogen; wherein each of Ri, R2, R3, R4, and R5 is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

[0009] In some implementations, the sterically hindered sorbent has the formula:

[0010] wherein at least two of Re-Rio are moieties excluding hydrogen, wherein A is a bond, a C atom, a heteroatom, a carbon chain with a backbone length of C1-C9, or a ringcontaining moiety; wherein each Re, R7, Rs, R9, and Rio is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

[0011] In some implementations, the sterically hindered sorbent of a system has theformula:

[0012] wherein each Rn, Rn. and R13 is, independently, substituted aliphatic, substituted alkyd, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkydene.

[0013] In some implementations, at least one gas-liquid contactor comprises a plurality of gas-liquid contactors, and the system comprises at least one contactor wall comprising the plurality of gas-liquid contactors positioned side by side, the at least one contactor wall extending along a wall axis.

[0014] Some aspects of this disclosure pertain to sorbent solution for capturing carbon dioxide, which sorbent solutions may be characterized by the following features: at least one sterically hindered sorbent, and at least one sterically unhindered sorbent.

[0015] In some implementations, the sorbent solution comprises a molar concentration of between 10 mol% and 90 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

[0016] In some implementations, the sorbent solution comprises a molar concentration of between 20 mol% and 80 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

[0017] In some implementations, the sorbent solution comprises a molar concentration of between 30 mol% and 70 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

[0018] In some implementations, the sorbent solution comprises two sterically hindered sorbents and one sterically unhindered sorbent. In some implementations, the at least one sterically hindered sorbent in the sorbent solution comprises an amino acid. In some implementations, the at least one sterically hindered sorbent in the sorbent solution comprises an amine.

[0019] In some implementations, the sorbent solution comprises an inorganic base.

[0020] In some implementations, the pKa of the at least one sterically hindered sorbent is higher than the pKa of the at least one sterically unhindered sorbent. In some implementations, the at least one sterically hindered sorbent has a pKa between about 7and 14. In some implementations, the at least one sterically hindered sorbent has a pKa between about 8 and 12. In some implementations, the at least one sterically hindered sorbent has a pKa between about 8 and 11.

[0021] In some implementations, the sorbent solution has a temperature between about 10°C and 30°C.

[0022] In some implementations, the sorbent solution comprises water, thereby being an aqueous solution.

[0023] In some implementations, the sterically hindered sorbent of the sorbent solution has a solubility of at least about 0.5M at 20°C.

[0024] In some implementations, the sorbent solution comprises an alkali metal salt.

[0025] Some aspects of this disclosure pertain to carbon-loaded sorbent solutions that may be characterized by the following elements: a carbon dioxide derived species comprising: at least one of carbonates and bicarbonates, and carbamates accounting for at most 65 mol% of inorganic carbon with respect to a total number of moles of inorganic carbon in the carbon dioxide derived species.

[0026] In some implementations, a carbon-loaded sorbent solutions comprises at most 1 mol of inorganic carbon per mol of sorbent, optionally between 0.05 and 0.6 mol of inorganic carbon per mol of sorbent, further optionally between 0.075 and 0.5 mol of inorganic carbon per mol of sorbent.

[0027] In some cases, the carbamates account for at most 60 mol% of inorganic carbon with respect to the total number of moles of inorganic carbon in the carbon dioxide derived species, optionally for at most 50 mol% of inorganic carbon with respect to the total number of moles of inorganic carbon in the carbon dioxide derived species.

[0028] In some implementations, a carbon-loaded sorbent solutions has a pH between 7 and 14, optionally between 8 and 13, further optionally between 9 and 12.

[0029] Some aspects of this disclosure pertain to methods of capturing carbon dioxide from atmospheric air, and such methods may be characterized by the following operation: contacting the atmospheric air with an aqueous sorbent solution comprising at least one sterically hindered sorbent to produce a carbon-loaded sorbent solution comprising carbonate ions and / or bicarbonate ions. Such methods may be characterized by one or more additional features as described herein for the methods of capturing carbon dioxide.BRIEF DESCRIPTION OF THE DRAWINGS

[0030] FIG. 1 is a block flow diagram of a carbon dioxide capture system, such as a Direct Air Capture (DAC) system, of the present disclosure.

[0031] FIG. 2 is a graph showing a molar ratio of total inorganic carbon to sorbent using two different sorbent solutions of the present disclosure.

[0032] FIG. 3 is an illustration of a cross-section of a gas-liquid contactor according to implementations of the present disclosure.

[0033] FIG. 4 is another illustration of a cross-section of a gas-liquid contactor according to implementations of the present disclosure.

[0034] FIG. 5 is another illustration of a cross-section of a gas-liquid contactor according to implementations of the present disclosure.

[0035] FIG. 6 is another illustration of a cross-section of a gas-liquid contactor according to implementations of the present disclosure.

[0036] FIG. 7 is another illustration of a cross-section of a gas-liquid contactor according to implementations of the present disclosure.

[0037] FIG. 8 is a side elevational view of an example contactor wall of a DAC system according to implementations of the present disclosure.

[0038] FIG. 9 is a top-down view of a DAC system of the present disclosure comprising multiple contactor walls system according to implementations of the present disclosure.

[0039] FIG. 10 is a schematic block flow diagram of a control system (or controller) for units, components and subsystems system according to implementations of the present disclosure.

[0040] FIG. 11 is a schematic block flow diagram of a method for capturing carbon dioxide in accordance with certain implementations.

[0041] FIG. 12 is a schematic block flow diagram of a method for capturing carbon dioxide in accordance with certain implementations.DETAILED DESCRIPTIONTerminology and Scope

[0042] In the following descriptions, numerous specific details are set forth to provide a thorough understanding of the presented implementations. The disclosed implementations may be practiced without some or all these specific details. In other instances, well-known process operations have not been described in detail so as not to unnecessarily obscure the disclosed implementations. While the disclosed implementations will be described inconjunction with the specific implementations, it will be understood that it is not intended to limit the disclosed implementations.

[0043] As used herein, the term “sorbent” refers to an absorption compound that may be provided in solution, thereby forming an absorption solution or sorbent solution. The sorbent of the present disclosure includes compounds that may react with, complex with or otherwise facilitate absorption of carbon dioxide from an impure source such as air. The sorbent of the present disclosure includes at least one amino acid, at least one amine, or any combinations thereof.” Implementations described in relation to an amino acid as the “sorbent” can be applied mutatis mutantis to an amine as said “sorbent”. The term “sorbent” may refer to hindered and / or unhindered amines or amino acids that include at least one nitrogen. In some cases, the “sorbent” may be an amino acid or amine that is capable of complexing with carbon dioxide via a nitrogen atom to form a carbamate. In some cases, the “sorbent” may not be directly complexed with carbon dioxide. For example, a sorbent may facilitate the formation of carbonate ions and / or bicarbonate ions in a solution containing the sorbent.

[0044] As used herein a “source of impure carbon dioxide” has less than about 50 mol% CO2, or less than about 20 mol% CO2, or less than about 10 mol% CO2, or less than about 1 mol% CO2. In some implementations, the source of impure carbon dioxide is a gas phase mixture of carbon dioxide and one more other gaseous component. As examples, the source of impure carbon dioxide can be, for example, air, waste gas from an industrial or commercial process, flue gas from a power plant, exhaust from an engine, sewage or landfill gas. The source of impure carbon dioxide of the present disclosure includes a dilute gas source. The dilute gas source can include the atmosphere (e.g., ambient or atmospheric air) or another fluid source that contains dilute concentrations of CO2. Dilute concentrations of CO2, for example in the atmosphere, are in the range of 400-420 parts per million (“ppm”) or approximately 0.04-0.042% v / v, and less than 1% v / v. These dilute concentrations of CO2 are at least one order of magnitude lower than the concentration of CO2 in point-source emissions, such as flue gases, where point-source emissions can have concentrations of CO2 ranging from 1.5-15% v / v, or from 5-15% v / v depending on the source of emissions.

[0045] While some of the disclosure herein refers to DAC processes, which remove carbon dioxide from air, the associated processes, systems and apparatus of this disclosure apply more broadly to any carbon dioxide capture process that removes or captures carbon dioxide from a source of impure carbon dioxide to produce carbon dioxide-denved species.

[0046] In some contexts herein, the term “about’' means + / -10% of any recited value. As used herein, this term modifies any recited value, range of values, or endpoints of one or more ranges.

[0047] A “carbon dioxide-derived species” is a compound or ion that is not carbon dioxide but was produced directly from carbon dioxide. In many cases, the carbon dioxide-derived species is present as an ion or solute in a solution such as an aqueous solution. In some implementations, the carbon dioxide-derived species comprises a carbonate ion, a bicarbonate ion, a carbamate, or any combination thereof. In some cases, a carbon dioxide-derived species is produced by contacting carbon dioxide or a source of impure carbon dioxide such as air or flue gas with a CO2 capture species (also referred to as sorbent), such as at least one of an amine, an amino acid, or an inorganic base. As an example, the contacting may occur in a gas-liquid contactor for capturing CO2 from the source of impure carbon dioxide using the CO2 capture species to form the carbon dioxidederived species. For example, the CO2 capture species interacts with gaseous carbon dioxide from the source of impure carbon dioxide to convert the carbon dioxide to carbamate, carbonate ion, and / or bicarbonate ion, each of which is an example of a carbon dioxide-derived species.

[0048] “Carbon dioxide complexing agent” or “complexing agent” refers to any compound that can selectively interact / complex with carbon dioxide either directly or via carbon dioxide-derived species(aqueous species derived from carbon dioxide, i.e., bicarbonate ion or carbonate ion). In complexed form, a carbon dioxide complexing agent may form a salt, such as a carbonate or bicarbonate. One example of a complexing agent is an unsaturated nitrogenous compound, which could be an unsaturated chemical compound that contains a nitrogen atom. The unsaturated nitrogenous compound can be in freebase or salt form. Examples of unsaturated nitrogenous compounds include imines, amidines, guanidines, iminoguanidines, bis(imino)guanidines (e.g. glyoxal bis(imino)guanidine), and tris(imino)guanidines (e.g. benzene tris(imino)guanidine). Example iminoguanidine complexing agents are presented in U.S. Patent 11,00,1554, issued May 11, 2021, and U.S. Patent 10,633,332 issued April 28, 2020, both of which are incorporated herein by reference in their entireties. In some implementations, the carbon dioxide complexing agent is a nitrogenous acid salt such as an acid salt of an iminoguanidine (e.g., a bis(imino)guanidine or tris(imino)guanidine of the present disclosure), including but not being limited to a hydrochloric acid, a hydrobromic acid, a hydroiodic acid, a sulfuric acid, a nitric acid, a boric acid, an acetic acid, a phosphoric acid,a formic acid, a benzoic acid, a citric acid, a tartaric acid, an oxalic acid, a fumaric acid, a malonic acid, a succinic acid, a lactic acid of an iminoguanidine and analogs thereof as further defined, for example, by formula II of the present disclosure. Complexing agents may be used independently in a carbon capture process, or optionally may be used in blends. In some implementations, mixtures of at least two carbon dioxide complexing agents are used in processes and methods described herein. For example, two or more BIG compounds (e.g., BIG freebases and / or BIG acid salts) may be used to form at least one of a carbonate salt or a bicarbonate salt of the BIG compound in a crystallizer of a carbon dioxide capture system. In another example, a BIG compound is used in mixture with a tris(imino)guanidine compound as carbon complexing mixture to form at least one of a carbonate salt and / or a bicarbonate salt in a crystallizer of a carbon dioxide capture system.

[0049] In some implementations, a complexing agent is an inorganic base such as an inorganic hydroxide. Certain examples are alkaline earth hydroxides such as calcium hydroxide and magnesium hydroxide. Whether the complexing agent is organic or inorganic, it may interact with a sorbent solution comprising carbon dioxide-derived species such as carbonate and / or bicarbonate to produce insoluble organic or inorganic carbonates and / or bicarbonates.

[0050] As used herein, the term “insoluble” may encompass "sparingly soluble", i.e. being of negligible solubility in aqueous medium under the operational conditions disclosed herein, such that a dissolved amount of a compound is merely sufficient to produce a reactive concentration of dissolved species in solution. Insoluble compounds include compounds where the solubility product (Ksp) is low and the equilibrium concentration of dissolved ions remains very small, typically in the micromolar to low millimolar range.

[0051] As used herein, "soluble" may encompass "substantially soluble", i.e. being of significant solubility in an aqueous medium under the operational conditions disclosed herein, such that a dissolved amount of a compound is sufficient to produce a significant concentration of dissolved species in solution enabling consistent reactivity or analytical detectability in the intended applications disclosed herein. Soluble compounds include those with a solubility product (Ksp) or dissolution profile that allows for equilibrium concentrations typically in the millimolar range or higher.

[0052] While much of the discussion herein refers to BIG compounds when discussing processes and systems employing carbon complexing agents, this is provided for the sakeof convenience. Many of the processes and systems described with reference to BIG compounds should be understood to apply more generally to many other carbon complexing agents. Many of these other carbon complexing agents are in the class of unsaturated nitrogenous bases, with examples being imines, amidines, and iminoguanidines, which include bis(imino)guanidines and tris(imino)guani dines and their respective tautomers. Additionally, mixtures of one or more carbon complexing agents may also be employed, even where the discussion mentions only one.

[0053] As used herein, the term “freebase” refers to the neutral form of a molecule / compound. In the context of iminoguanidines, the term “freebase” refers to the neutral form of an iminoguanidine. Examples of freebases of the present disclosure may include specific BIGs (e.g., glyoxal bis(imino)guanidine). Salts are generally not freebases. Hence, BIG salts such as BIG hydrochlorides, BIG carbonates, BIG bicarbonates, BIG sulfates, BIG nitrates, etc. are not freebases. However, an unprotonated BIG without an associated anion may be a freebase.

[0054] By “amino acid salt” is meant a mixture of an amino acid and a base such as an inorganic base. For example, a mixture of glycine and sodium hydroxide.

[0055] As used herein, “precipitation”, “reactive crystallization” and similar terms refer to any reaction or process condition that drives a component or reaction product to come out of solution as a solid. The solid may be amorphous, crystalline, or some combination thereof. The solid may exhibit one or more amorphous or crystalline structures; e.g., it may have one or more distinct crystalline phases. In certain implementations, precipitation or reactive crystallization refers to a reaction involving one or more soluble reactant species (e.g., derived from solubilization of a bis(imino)guanidine) in a solvent and that produces a reaction product species (e.g., a carbonate salt and / or a bicarbonate salt of the bis(imino)guanidine) that is at least partially insoluble in the solvent and comes out of solution as a solid. As an example of precipitation or reactive crystallization, cations derived from a bis(imino)guanidine freebase react with at least one of carbonate anions or bicarbonate anions in solution to produce an insoluble bis(imino)guanidine carbonate or bicarbonate that comes out of solution as a solid during the reaction.

[0056] By “steric hindrance” is meant the chemical phenomena wherein the spatial arrangement of atoms in a chemical compound influences the relative stability or reactivity of the chemical compound. For example, upon exposure to carbon dioxide, the inventors have found that sterically hindered amines used as sorbents may be less likely to form carbamate derivatives than amines without steric hindrance.

[0057] By “aliphatic” is meant a hydrocarbon group having at least one carbon atom to 50 carbon atoms (C1-50), such as one to 25 carbon atoms (C1-25), or one to ten carbon atoms (Ci- 10), and which includes alkanes (or alkyl), alkenes (or alkenyl), alkynes (or alkynyl), including cyclic versions thereof, and further including straight- and branched-chain arrangements, and all stereo and position isomers as well. Such an aliphatic can be unsubstituted or substituted with one or more groups, such as groups described herein for an alkyl group.

[0058] By “aryl” is meant a functional group or substituent derived from an aromatic ring, inclusive of exclusively hydrocarbon rings, or rings including heteroatoms. Heteroatoms may be any non-C or non-H atom, such as nitrogen, oxygen, phosphorous, or sulfur. Exemplary aryl groups are phenyl, tolyl, pyridyl, etc. The aryl group can be substituted or unsubstituted. For example, the aryl group can be substituted with one or more substitution groups, as described herein for alkyl.

[0059] By “alkoxy” is meant -OR, where R is an optionally substituted alkyl group, as described herein. Exemplary alkoxy groups include methoxy, ethoxy, butoxy, trihaloalkoxy, such as trifluoromethoxy, etc. The alkoxy group can be substituted or unsubstituted. For example, the alkoxy group can be substituted with one or more substitution groups, as described herein for alkyl. Exemplary unsubstituted alkoxy groups include C1-3, C1-6, C1-12, C1-16, Ci-ig, C1-20, or C1-24 alkoxy groups.

[0060] By “alkoxyalkyl” is meant an alkyl group, as defined herein, which is substituted with an alkoxy group, as defined herein. Exemplary unsubstituted alkoxyalkyl groups include between 2 to 12 carbons (C2-12 alkoxy alkyl), as well as those having an alkyl group with 1 to 6 carbons and an alkoxy group with 1 to 6 carbons (i.e., C1-6 alkoxy-Ci-6 alkyl).

[0061] By “alkyl” and the prefix “alk” is meant a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. The alkyl group can be cyclic (e.g., C3-24 cycloalkyl) or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one, two, three or, in the case of alkyl groups of two carbons or more, four substituents independently selected from the group consisting of: (1) C1-6 alkoxy (e.g., -O-Ak, wherein Ak is optionally substituted C1-6 alkyl); (2) C1-6 alkylsulfinyl (e.g., -S(O)-Ak, wherein Ak is optionally substituted C1-6 alkyl); (3)Ci-6 alkylsulfonyl (e.g., -SCh-Ak, wherein Ak is optionally substituted Ci-6 alkyl); (4) amino (e.g., -NRN1RN2, where each of RN1and RN2is, independently, H or optionally substituted alkyl, or RN1and R2, taken together with the nitrogen atom to which each are attached, form a heterocyclyl group); (5) aryl; (6) arylalkoxy (e.g., -O-L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (7) aryloyl (e.g., -C(O)-Ar, wherein Ar is optionally substituted aryl); (8) azido (e.g., -N3); (9) cyano (e.g., -CN); (10) carboxyaldehyde (e.g., -C(O)H); (11) C3-8 cycloalkyl (e.g., a monovalent saturated or unsaturated non-aromatic cyclic C3-8 hydrocarbon group); (12) halo (e.g., F, Cl, Br, or I); (13) heterocyclyl (e.g., a 5-, 6- or 7-membered ring, unless otherwise specified, containing one, two, three, or four non-carbon heteroatoms, such as nitrogen, oxygen, phosphorous, sulfur, or halo); (14) heterocyclyloxy (e.g., -O-Het, wherein Het is heterocyclyl, as described herein); (15) heterocyclyloyl (e.g., -C(O)-Het, wherein Het is heterocyclyl, as described herein); (16) hydroxyl (e.g., -OH); (17) N- protected ammo; (18) nitro (e.g., -NO2); (19) oxo (e.g., =0) or hydroxyimino (e.g., =N- OH); (20) C3-8 spirocyclyl (e.g., an alkylene or heteroalkylene diradical, both ends of which are bonded to the same carbon atom of the parent group); (21) C1-6 thioalkoxy (e.g., -S-Ak, wherein Ak is optionally substituted C1-6 alkyl); (22) thiol (e.g., -SH); (23) -CO2RA, where RAis selected from the group consisting of (a) hydrogen, (b) C1-6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) Ci-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (24) -C(O)NRBRc, where each of RBand Rcis, independently, selected from the group consisting of (a) hydrogen, (b) C1-6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) C1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (25) -SO2RD, where RDis selected from the group consisting of (a) C1-6 alkyl, (b) C4-18 aryl, and (c) (C4-18 aryl) C1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (26) -SO2NRERF, where each of REand REis, independently, selected from the group consisting of (a) hydrogen, (b) Ci- 6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) C1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); and (27) -NRGRH, where each of RGand RHis, independently, selected from the group consisting of (a) hydrogen, (b) an N-protecting group, (c) C1-6 alkyl, (d) C2-6 alkenyl (e.g., optionally substituted alkyl having one or more double bonds), (e) C2-6 alkynyl (e.g., optionally substituted alkyl having one or more triple bonds), (f) C4-18 aryl, (g) (C4-18 aryl) C1-6 alkyl (e.g., L-Ar, wherein L is a bivalent form of optionally substituted alkyd group and Ar isoptionally substituted ary l), (h) C3-8 cycloalkyl, and (i) (C3-8 cycloalkyl) C1-6 alkyl (e.g., - L-Cy, wherein L is a bivalent form of optionally substituted alkyl group and Cy is optionally substituted cycloalkyl, as described herein), wherein in one implementation no two groups are bound to the nitrogen atom through a carbonyl group or a sulfonyl group. The alkyl group can be a primary, secondary, or tertiary alkyl group substituted with one or more substituents (e.g., one or more halo or alkoxy). In some implementations, the unsubstituted alkyl group is a C1-3, C1-6, C1-12, C1-16, Ci-is, C1-20, or C1-24 alkyl group.

[0062] By “alkylene” is meant a multivalent (e.g., bivalent, bivalent, tetravalent, etc.) form of an alkyd group, as described herein. Exemplary alkylene groups include methylene, ethylene, propylene, butylene, etc. In some implementations, the alkydene group is a C1-3, C1-6, C1-12, C1-16, Ci-is, C1-20, C1-24, C2-3, C2-6, C2-12, C2-16, C2-18, C2-20, or C2- 24 alkylene group. The alkylene group can be branched or unbranched. The alkylene group can be saturated or unsaturated (e.g., having one or more double bonds or triple bonds). The alkylene group can also be substituted or unsubstituted. For example, the alkylene group can be substituted with one or more substitution groups, as described herein for alkyd. In one instance, a substituted alkylene group can include an optionally substituted haloalkylene (e.g., an optionally substituted alkylene substituted with one or more hydroxyl groups, as defined herein), an optionally substituted haloalkylene (e.g., an optionally substituted alkylene substituted with one or more halo groups, as defined herein), and the like.

[0063] By “alkoxy” is meant -OR, where R is an optionally substituted alkyl group, as described herein. Exemplary alkoxy groups include methoxy, ethoxy, butoxy, tnhaloalkoxy, such as trifluoromethoxy, etc. The alkoxy group can be substituted or unsubstituted. For example, the alkoxy group can be substituted with one or more substitution groups, as described herein for alkyl. Exemplary unsubstituted alkoxy groups include C1-3, C1-6, C1-12, Ci-16, Ci-is, C1-20, or C1-24 alkoxy groups.

[0064] By “alkoxyalkyl” is meant an alkyl group, as defined herein, which is substituted with an alkoxy group, as defined herein. Exemplary unsubstituted alkoxyalkyl groups include between 2 to 12 carbons (C2-12 alkoxy alkyl), as well as those having an alkyl group with 1 to 6 carbons and an alkoxy group with 1 to 6 carbons (i.e., Ci-6 alkoxy-Ci-s alkyl).

[0065] By “alkyl” and the prefix “alk” is meant a branched or unbranched saturated hydrocarbon group of 1 to 24 carbon atoms, such as methyl, ethyl, n-propyl, isopropyl, n- butyl, isobutyl, s-butyl, t-butyl, n-pentyl, isopentyl, s-pentyl, neopentyl, hexyl, heptyl, octyl, nonyl, decyl, dodecyl, tetradecyl, hexadecyl, eicosyl, tetracosyl, and the like. Thealkyl group can be cyclic (e.g., C3-24 cycloalkyl) or acyclic. The alkyl group can be branched or unbranched. The alkyl group can also be substituted or unsubstituted. For example, the alkyl group can be substituted with one, two, three or, in the case of alkyl groups of two carbons or more, four substituents independently selected from the group consisting of: (1) C1-6 alkoxy (e.g., -O-Ak, wherein Ak is optionally substituted C1-6 alkyl); (2) C1-6 alkylsulfinyl (e.g., -S(O)-Ak, wherein Ak is optionally substituted C1-6 alkyl); (3) C1-6 alkylsulfonyl (e.g., -SCh-Ak. wherein Ak is optionally substituted C1-6 alkyl); (4) amino (e.g., -NRN1RN2, where each of RN1and RN2is, independently, H or optionally substituted alkyl, or RN1and R2, taken together with the nitrogen atom to which each are attached, form a heterocyclyl group); (5) aryl; (6) arylalkoxy (e.g., -O-L-Ar, wherein L is a bivalent form of optionally substituted alkyl and Ar is optionally substituted aryl); (7) aryloyl (e.g., -C(O)-Ar, wherein Ar is optionally substituted aryl); (8) azido (e.g., -N3); (9) cyano (e.g., -CN); (10) carboxyaldehyde (e.g., -C(O)H); (11) C3-8 cycloalkyl (e.g., a monovalent saturated or unsaturated non-aromatic cyclic C3-8 hydrocarbon group); (12) halo (e.g., F, Cl, Br, or I); (13) heterocyclyl (e.g., a 5-, 6- or 7-membered ring, unless otherwise specified, containing one, two, three, or four heteroatoms, such as nitrogen, oxygen, phosphorous, sulfur, or halo); (14) heterocyclyloxy (e.g., -O-Het, wherein Het is heterocyclyl, as described herein); (15) heterocyclyloyl (e.g., -C(O)-Het, wherein Het is heterocyclyl, as described herein); (16) hydroxyl (e.g., -OH); (17) N-protected amino; (18) nitro (e.g., -NO2); (19) oxo (e.g., =0) or hydroxyimino (e.g., =N-0H); (20) C3-8 spirocyclyl (e.g., an alkylene or heteroalkylene diradical, both ends of which are bonded to the same carbon atom of the parent group); (21) Ci-6 thioalkoxy (e.g., -S-Ak, wherein Ak is optionally substituted Ci-6 alkyl); (22) thiol (e.g., -SH); (23) -CO2RA, where RAis selected from the group consisting of (a) hydrogen, (b) C1-6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) C1-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (24) -C(O)NRBRc, where each of RBand Rcis, independently, selected from the group consisting of (a) hydrogen, (b) C1-6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) Ci-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (25) -SChR.1’. where RDis selected from the group consisting of (a) Ci-6 alkyl, (b) C4-18 aryl, and (c) (C4-18 aryl) Ci-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl); (26) -SO2NRERF, where each of REand REis, independently, selected from the group consisting of (a) hydrogen, (b) Ci-6 alkyl, (c) C4-18 aryl, and (d) (C4-18 aryl) Ci-6 alkyl (e.g., -L-Ar, wherein L is a bivalent form of optionallysubstituted alkyl group and Ar is optionally substituted aryl); and (27) -NRGRH, where each of RGand RHis, independently, selected from the group consisting of (a) hydrogen, (b) an N-protecting group, (c) Ci-6 alkyl, (d) C2-6 alkenyl (e.g., optionally substituted alkyl having one or more double bonds), (e) C2-6 alkynyl (e.g., optionally substituted alkyl having one or more triple bonds), (f) C4-18 aryl, (g) (C4-is aryl) C1-6 alkyl (e.g., L-Ar, wherein L is a bivalent form of optionally substituted alkyl group and Ar is optionally substituted aryl), (h) C3-8 cycloalkyl, and (i) (C3-8 cycloalkyl) C1-6 alkyl (e.g., -L-Cy, wherein L is a bivalent form of optionally substituted alkyl group and Cy is optionally substituted cycloalkyl, as described herein), wherein in one implementation no two groups are bound to the nitrogen atom through a carbonyl group or a sulfonyl group. The alkyl group can be a primary, secondary, or tertiary alkyl group substituted with one or more substituents (e.g., one or more halo or alkoxy). In some implementations, the unsubstituted alkyl group is a C1-3, Ci-6, C1-12, Ci-16, Ci-is, C1-20, or C1-24 alkyl group.

[0066] By "alkylene" is meant a multivalent (e.g., bivalent, trivalent, tetravalent, etc.) form of an alkyd group, as described herein. Exemplary alkylene groups include methylene, ethylene, propylene, butylene, etc. In some implementations, the alkylene group is a C1-3, Ci-6, C 1-12, C1-16, Ci-is, C1-20, C1-24, C2-3, C2-6, C2-12, C2-16, C2-18, C2-20, or C2- 24 alkylene group. The alkylene group can be branched or unbranched. The alkylene group can be saturated or unsaturated (e.g., having one or more double bonds or triple bonds). The alkylene group can also be substituted or unsubstituted. For example, the alkylene group can be substituted with one or more substitution groups, as described herein for alkyl. In one instance, a substituted alkylene group can include an optionally substituted hydroxylalkylene (e.g., an optionally substituted alkylene substituted with one or more hydroxyl groups, as defined herein), an optionally substituted haloalkylene (e.g., an optionally substituted alkylene substituted with one or more halo groups, as defined herein), and the like.

[0067] By “cyclic group” is used herein to refer to either aryl groups, non-aryl groups (e.g., cycloalkyl or heterocycloalkyl groups), or both. Cyclic groups have one or more ring systems that can be substituted or unsubstituted. A cyclic group can contain one or more aryl groups, one or more non-aryl groups, or one or more aryl groups and one or more non-aryl groups.

[0068] By “halo” is meant F, Cl, Br, or I.

[0069] By “haloalkyl” is meant an alkyl group, as defined herein, substituted with one or more halo.

[0070] By “haloalkylene” is meant an alkylene group, as defined herein, substituted with one or more halo.

[0071] By “heteroaliphatic” is meant an aliphatic group, as defined herein, including at least one heteroatom to 20 heteroatoms, such as one to 15 heteroatoms, or one to 5 heteroatoms, which can be selected from, but not limited to oxygen, nitrogen, sulfur, silicon, boron, selenium, phosphorous, and oxidized forms thereof within the group.

[0072] By “heteroalkyl” is meant an alk l group, as defined herein, containing one, two, three, or four non-carbon heteroatoms (e.g., independently selected from the group consisting of nitrogen, oxygen, phosphorous, sulfur, selenium, or halo).

[0073] By “heteroalkylene” is meant an alkylene group, as defined herein, containing one, two, three, or four non-carbon heteroatoms (e.g., independently selected from the group consisting of nitrogen, oxygen, phosphorous, sulfur, selenium, or halo). The heteroalkylene group can be saturated or unsaturated (e.g., having one or more double bonds or triple bonds). The heteroalkylene group can be substituted or unsubstituted. For example, the heteroalkylene group can be substituted with one or more substitution groups, as described herein for alkyl.

[0074] By “heteroaryl” is meant a subset of heterocyclyl groups, as defined herein, which are aromatic, i.e., they contain 4n+2 pi electrons within the mono- or multi cyclic ring system.

[0075] The term “heterocycloalkyl” is a type of cycloalkyl group as defined above where at least one of the carbon atoms and its attached hydrogen atoms, if any, are replaced by O, S, N, or NH. The heterocycloalkyl group and heterocycloalkenyl group can be substituted or unsubstituted. The cycloalkenyl group and heterocycloalkenyl group can be substituted with one or more groups including, but not limited to, alkyl, alkoxy, alkenyl, alkynyl, aryl, heteroaryl, aldehyde, amino, carboxylic acid, sulfonic acid, sulfmic acid, fluoroacid, phosphonic acid, ester, ether, halide, hydroxy, ketone, nitro, cyano, azido, silyl, sulfonyl, sulfinyl, or thiol, as described herein.

[0076] By “hydroxyl” is meant an -OH group.

[0077] By “hydroxyalkyl” is meant an alkyl group, as defined herein, substituted with one or more hydroxyl.

[0078] By “hydroxyalkylene” is meant an alkylene group, as defined herein, substituted with one or more hydroxy.

[0079] By “nitro” is meant an -NO2 group.

[0080] By “phosphono” or “phosphonic acid” is meant a -P(O)(OH)2 group.

[0081] By “sulfate” is meant a group derived from sulfuric acid. One example of sulfate includes a -O-S(=O)2(ORsl) group, where RS1is H, optionally substituted alky l, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted arylalkylene.

[0082] By “sulfo” or “sulfonic acid” is meant an -S(=O)2OH group.

[0083] By “carboxyl” or “carboxylic acid” is meant a -C(O)OH group.

[0084] By “carboxylate” is meant a deprotonated “carboxylic acid”, e.g. a -C(O)O' group.

[0085] By “carbamate is meant a -N(RS1)(C(O)ORS2), where RSI is H, optionally substituted alkyd, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted arylalkylene, and RS2 is H, optionally deprotonated (i.e., the carbamate has a negative charge here), optionally substituted alkyl, optionally substituted alkenyl, optionally substituted aryl, or optionally substituted arylalkylene.Introduction and Context

[0086] The present disclosure includes descriptions of capturing carbon dioxide from a source of impure carbon dioxide (e.g., air) to form a carbon dioxide-derived species. Methods of capturing carbon dioxide from the source of impure carbon dioxide include using an amine or amino acid as the sorbent in a sorbent solution. An example of such method is a direct air capture (DAC) method that absorbs carbon dioxide from atmospheric air .

[0087] An example of a DAC system being configured to perform method implementations of the present disclosure is also disclosed. Referring to FIG. 1, a sorbent solution 6, such as an aqueous sorbent solution comprising at least one of an amino acid or an amine, is flowed (e.g., pumped or gravity -fed) through at least one gas-liquid contactor 10 being part of a gas-liquid contactor subsystem 3. The sorbent solution 6 is brought into contact with a source of impure carbon dioxide 2, such as a dilute gas source (e.g., atmospheric air), that is flowed through at least one gas-liquid contactor 10. For example, carbon dioxide in the source of impure carbon dioxide 2, such as atmospheric air, is dissolved in the sorbent solution 6 and interacts / reacts with the sorbent in the sorbent solution 6, thereby forming a carbon-loaded sorbent solution 8 comprising captured carbon dioxide in any of various forms comprising at least one of carbon dioxide and carbon dioxide-derived species, such as carbonate ions, bicarbonate ions and / or carbonates. Upon absorption of the CO2 from the source of impure carbon dioxide 2 by the sorbent solution6 in the gas-liquid contactor 10, the source of impure carbon dioxide 2 becomes depleted in CO2 and is flowed out of the gas-liquid contactor 10 as a CCh-lean gas stream 4. The CCh-lean gas stream 4 can contain compounds of the sorbent solution 6, and possibly also compounds of the carbon-loaded sorbent solution 8. The compounds of the sorbent solution 6 and possibly also of the carbon-loaded sorbent solution 8 can be in liquid and / or vapor phase when present in the flow of the CCh-lean gas stream 4.

[0088] The at least one gas-liquid contactor 10 of the gas-liquid contactor subsystem 3 may have any of various formats. The sorbent solution 6 may be distributed on contacting surfaces, such as surfaces of a packing material, as uniformly as possible, e.g., in the form of a thin film liquid. The gas-liquid contactor 10 may exhibit a low pressure drop and efficient mass transfer. FIG. 1 is not to be interpreted limiting the present disclosure to a cross-flow configuration contactor 10. The carbon dioxide capture system 1 can include any gas-liquid contactor configurations where a sorbent solution 6 is contacting a source of impure carbon dioxide 2, such as a dilute gas source. More details of example gas-liquid contactor configurations are provided below. Reference is also made to carbon capture systems and gas-liquid contactor subsystems described in U.S. Patent No. 9,095,813, U.S. Patent No. 10,421,039, U.S. Patent No. 12,239,936, U.S. Patent Application No. 18 / 865,777, U.S. Patent Application No. 17 / 558,321, U.S. Patent No. 12,214,311, U.S. Patent Application No. 17 / 742,334, U.S. Patent Application No. 18 / 691,780, U.S. Patent Application No. 18 / 717,768, PCT Patent Application No. PCT / US2024 / 039378, PCT Patent Application No. PCT / US2024 / 060124, PCT Patent Application No. PCT / US2025 / 034032, PCT Patent Application No. PCT / US2025 / 031782, PCT Patent Application No. PCT / US2025 / 025246, PCT Patent Application No. PCT / US2025 / 042410, PCT Patent Application No. PCT / US2025 / 042381 and U.S. Provisional Patent Application No. 63 / 706,421, the entire contents of all of which are incorporated herein by reference.

[0089] In some implementations, the process further includes processing the carbon- loaded sorbent solution 8 to recover the captured CO2 and to regenerate the sorbent to be reused in the sorbent solution 6 during a regeneration stage of the carbon dioxide capture system 1. Referring to FIG. 1, the carbon dioxide capture system 1 includes a regeneration subsystem 11 in fluid communication with the gas-liquid contactor 10. In the regeneration subsystem 11, one or more steps are performed to achieve extraction of CO2 from the carbon-loaded sorbent solution 8 to form a regenerated sorbent solution 22, and a CO2product stream 28. The regenerated sorbent solution 22 is flowed back to the gas-liquid contactor 10 for use in capturing CO2 from the source of impure carbon dioxide 2. Different implementations of the regeneration subsystem 11 are described in greater detail below.

[0090] For example, and referring to FIG. 1, once the aqueous sorbent solution 6 is sufficiently loaded with CO2, in any of various forms (as CCh-deri ved species), the carbon- loaded sorbent solution 8 is pumped into a solids formation subsystem 12, e.g., comprising a crystallizer, to which the complexing agent 14 (e.g., a bis(imino)guanidine or inorganic base) is added, optionally in the form of crystals. The complexing agent 14 reacts with the carbon dioxide-derived species of the carbon-loaded sorbent solution 8 and forms a precipitate being a salt (e.g., carbonate and / or bicarbonate salt) with lower solubility than that of the (uncomplexed) complexing agent 14. For example, the formed salt solids can move through the crystallizer, where the salt solids are stirred and optionally change their crystal structure (size, shape, phase, etc.) until they exit as a suspension of unloaded sorbent solution and solid carbon-containing complex. The salt solids (e.g., a carbonate and / or bicarbonate salt of the bis(imino)guanidine) precipitate out of the carbon-loaded sorbent solution 8, thereby unloading the carbon dioxide content from the carbon-loaded sorbent solution 8 and forming a slurry 16 comprising the salt solids in the unloaded sorbent solution. The salt solids can be referred to as a CCh-complexed material.

[0091] In some implementations, the carbonate and / or bicarbonate salt solids are separated from the aqueous solution (solid-liquid separation) to produce a solid phase for CO2 desorption. For example, and referring to FIG. 1, the carbon dioxide capture system 1, which can be or include a DAC process, includes separating the slurry 16 in a solidliquid separation subsystem 18, e.g., comprising a filtration unit, to recover a solid material 20 comprising the salt precipitate (e.g., carbonate and / or bicarbonate salt), and the unloaded sorbent solution 22. The unloaded sorbent solution 22 comprises the sorbent being regenerated into its active form. In some implementations, the water content of the unloaded sorbent solution 22 can be reduced using an evaporator unit 30 to produce a regenerated sorbent solution 32 that may be redirected to form the aqueous sorbent solution 6 being flowed to the gas-liquid contactor 10 for reuse in capturing CO2 from air or other low concentration gaseous source.

[0092] Referring to the example implementation of FIG. 1, the separated solid material 20 (e.g., carbonate material) is further treated in a CO2 recovery subsystem 24 to release gaseous carbon dioxide as part of the CO2 product stream 28 and regenerate theuncomplexed complexing agent in a regenerated solid material 26 (e.g., including solid BIG free base). Various techniques may be employed to release the carbon dioxide from the solid material 20 in the CO2 recovery subsytem 24. For example, the CO2 recovery subsystem 24 can heat the solid material 20 to about 40-160°C, e.g., between 80°C and 60°C, to release CO2 and to thermally regenerate the complexing agent for reuse in further carbon unloading cycles. For example, the CO2 recovery subsystem 24 can add an acid to react with the iminoguanidine bicarbonate / carbonate salt and generate an iminoguanidine acid salt.

[0093] As indicated, iminoguamdines, and BIGs more specifically, are examples of the carbon complexing agent. In many cases where the present disclosure refers to an iminoguanidine in general, or BIG specifically, their descriptions, features and advantages apply mutatis mutandis to any carbon complexing agent, such as inorganic bases and other unsaturated nitrogenous compounds in freebase or salt form, including amidines and imines (e.g., iminoguanidines).

[0094] Benefits of using an amine or amino acid containing sorbent solution may include faster kinetics of absorption of carbon dioxide than other sorbent solutions (resulting in a smaller and / or more efficient gas-contactor) and lower pH values of the solution resulting in less corrosivity in the carbon dioxide capture system, such as the DAC system of FIG. 1.

[0095] When the amino acid or amine, being used as the sorbent in the sorbent solution, is contacted with air, a significant fraction of the dissolved inorganic carbon is stored in the form of carbamates as part of the CCh-derived species. In comparison to carbonates and bicarbonates, carbamates are less or completely inaccessible for unloading via precipitation with a complexing agent (e.g., bis(imino)guanidines (BIGs) and / or one or more inorganic bases, such as alkaline earth metal hydroxides).

[0096] For example, the. when contacting a source of impure carbon dioxide with a sorbent that may be at least one amino acid in a sorbent solution , carbon dioxide can be stored in solution by reacting carbon dioxide with the amino acid, forming CCh-derived species including carbonate, bicarbonate, carbamate, and combinations thereof. In some implementations, dissolved carbon dioxide may be present in addition to the carbonate, bicarbonate, and carbamate.

[0097] More particularly, when contacted, the carbamate species may be formed according to the below chemical reaction (1).AA- + CO2+ B AA -COO- + BH+(1)

[0098] The carbon dioxide (CO2) can react with the deprotonated state of the amino acid (AA‘) and any base (B) in the solution to form a sorbent-carbamate complex (AA'-COO') and conjugate acid of the base (BH+). Examples of base (B) include water (H2O), hydroxide (OH ), amino acid (AA‘), amine, or combinations thereof. In some implementations, base (B) may be any other base present in the solution, such as unsaturated nitrogenous bases, including (imino)guani dines and bis(imino)guanidines, which may be present alone or in combination with the aforementioned exemplary bases.

[0099] The carbamate anion (COO') of the carbamate complex can undergo a hydrolysis reaction to form bicarbonate (HCO3 ). The hydrolysis of the carbamate may proceed according to the below chemical reaction (2).AA'-COO' + H2O ^ AA' + HCOC (2)

[0100] In the above-described hydrolysis reach on, a carbamate complex (AA'-COO') may react with water, regenerating the deprotonated amino acid (AA ) and bicarbonate (HCO3‘ )•

[0101] In some cases, bicarbonate ions may further dissociate and form carbonate (CO?2-) ions. The dissociation of bicarbonate (HCO3) may be according to the below chemical equilibrium (3).HCO3‘ + H2O CO32' +H3O+(3)

[0102] As depicted above, some amounts of bicarbonate (HCO3‘) and carbonate (CO32') ions may be present in aqueous solution due to the equilibrium between bicarbonate (HCO3‘) and carbonate (CO32') ions.

[0103] In some implementations, dissolved carbon dioxide may participate in one or more of the following chemical reactions (4) and (5). In some implementations, reactions (4) and (5) may occur in conjunction with reactions (1) - (3).CO2 + 2H2O ^ HCO3' + H3O+(4)

[0104] As depicted in reaction (4), a small amount of dissolved carbon dioxide (CO2) may react with water (H2O) and form bicarbonate (HCO3') ions and hydronium ions (H3O+). In some implementations, some amount of bicarbonate ions may form due to a reaction between dissolved carbon dioxide and hydroxide ions (OH'), as depicted by reaction (5).

[0105] The present disclosure relates to a sterically hindered sorbent material and a method of using the sterically hindered material for capturing carbon dioxide, e.g., implemented in the DAC system of FIG. 1. Using a sterically hindered sorbent material ina carbon dioxide capture process can decrease the formation of carbamates in a gas-liquid contactor, such as gas-liquid contactor 10, and favor the formation of other CCh-derived species including inorganic carbon that is more readily available for unloading via precipitation reaction with the complexing agent, such as a bis(imino)guanidine and / or an inorganic base.

[0106] In some implementations, reaction (5) may occur at an accelerated rate compared to reaction (4). When unhindered sorbent materials are used, the reaction (5) may minorly contribute to the concentration of OH' and pH of the system. In contrast, when hindered sorbent materials are used, the reaction (5) may contribute more significantly to the concentration of OH' and pH of the system. This is because, compared to an unhindered sorbent material, a reaction rate of (5) is slower with a hindered sorbent material due to the steric hindrance of the sorbent material. Regardless of the speed and extent of contribution, hindered sorbent material can contribute to the overall concentration of the OH' and pH of the system.

[0107] In some implementations, carbon may be unloaded from a carbon-loaded solution, such as the carbon-loaded solution 8, using a BIG as a complexing agent according to the following illustrative reactions (6) - (8).

[0108] As illustrated in reaction (6), bis(imino)guanidine (BIG) is first dissolved in water to provide an aqueous solution of BIG(aq). The aqueous BIG(aq) may engage in a proton transfer reaction according to reaction (7) with an acid (AH) and form protonated BIG (BIGH22+) and a conjugate base (A'). In various implementations, the reaction (7) occurs rapidly, however, the equilibrium position may be dependent upon the relative pKa of the BIG and AH. The carbonate ions may be freely accessible in solution for precipitation or crystallization. The protonated BIG (BIGH22+) may remove carbonate (CO3‘) from the carbon-loaded sorbent solution according to the precipitation or crystallization reaction depicted by the reaction (8). As illustrated in reaction (8), carbonate may react with protonated BIG and precipitate as a BIG-carbonate complex (i.e., (BIGH22+)(CO32‘ )(H2O)X(S)), being a carbonate salt of the BIG. It is noted that a similar reactional pathway could be followed to yield a precipitate of a bicarbonate salt of BIG. Other unsaturated nitrogenous compounds, as well as inorganic bases, may react via similar pathways.

[0109] In some implementations, bicarbonate ions may engage in a precipitation reaction with protonated BIGs (similar to reaction (8)). In some implementations, carbonate and / or bicarbonate species may directly react with BIGs(aq).

[0110] When an amino acid solution is used as the sorbent solution for contacting air, a significant amount of dissolved inorganic carbon may be stored in the form of the amino acid-carbamate complex (AA'-COO ). The amino acid-carbamate complex may be less or completely inaccessible for unloading carbon via precipitation with BIGs or other carbon complexing agent, whether organic or inorganic.[OHl] In contrast with carbonate or bicarbonate being readily available to react with the BIGs, the sorbent-carbamate complex (AA'-COO') may need to first decompose to carbonate species according to reactions (2) and (3), before precipitating according to reactions (6) - (8). In some cases, sorbent-carbamate complex (AA'-COO') may first decompose to bicarbonate species according to reaction (2) and undergo precipitation reactions (6) - (8).

[0112] The sorbent-carbamate complex may lead to challenges in direct air capture using BIGs. Depending on the conditions of the sorbent solution, not all or nearly all of the sorbent-carbamate complex may be efficiently converted into carbonate (or bicarbonate) to enable reaction with BIGs. An approach to mitigate this issue is to use a larger volume of sorbent solution to capture the same amount of carbon dioxide. However, the larger volume of sorbent solution can increase the cost of the operation as well as the size of the apparatus or system for performing direct air capture.

[0113] The inventors have found that carbamate hydrolysis reactions (i.e., reactions (2) and (3)) may be slow reactions, particularly when unhindered sorbents are used. In order to maximize the amount of inorganic carbon precipitated with the BIGs, dealing with slow reactions may require the precipitation reaction to proceed for a longer period of time, often in a larger apparatus. These factors can increase the cost of the operation.

[0114] The present disclosure proposes using one or more sterically hindered sorbents to address issues associated with carbon capture leading to a carbamate complex. When used, sterically hindered sorbents, such as tertiary amines, may not directly react with carbon dioxide. Instead, a sterically hindered sorbent may act as abase, generating hydroxide ions in aqueous solution, which can react with carbon dioxide to form bicarbonate. Moreover, steric hindrance may destabilize carbamates and lead to preferential conversion into carbonate and / or bicarbonate in solution. In various implementations, most sterically hindered sorbents (e.g., 2-amino-2 -methyl- 1 -propanol) may transiently form a carbamate,where the significant portion of the transient form of carbamate quickly undergoes hydrolysis reaction according to reactions (2) to form bicarbonate species.

[0115] Using sterically hindered sorbents in sorbent solutions flowed to a carbon dioxide capture system, such as the carbon dioxide capture system 1 of FIG. 1, may offer the following advantages. When used, sterically hindered sorbent material can decrease the portions (mol%) of the inorganic carbon stored as carbamates, allowing the carbon to be more readily available for unloading via precipitation reaction with bis(imino)guanidine. When used, sterically hindered sorbents may increase the loading capacity (mol. of total inorganic carbon) / (mol. of sorbent) relative to the unhindered sorbents. Moreover, the incorporation of sterically hindered sorbents may increase the rate of carbamate hydrolysis for carbamates present in the solution, effectively decreasing the cost of operation in various downstream operations. Furthermore, the inventors have found that the rate of carbon dioxide absorption when using a mixture of sterically hindered and unhindered sorbents in the sorbent solution may be faster than the rate of carbon dioxide absorption using the unhindered sorbents alone in the sorbent solution.

[0116] Aspects of this disclosure pertain to a process for capturing carbon dioxide including (i) contacting a source of impure carbon dioxide with a sorbent solution including a sterically hindered sorbent material to produce a carbon-loaded sorbent solution comprising carbon-dioxide derived species including carbonate and / or bicarbonate ions; and (ii) reacting the carbonate and / or bicarbonate ions with a complexing agent to produce at least one of a carbonate salt or a bicarbonate salt of the complexing agent. In some implementations, the carbonate salt and / or the bicarbonate salt of the complexing agent may precipitate out of the solution.

[0117] In some implementations, the sterically hindered sorbent material comprises at least one of a sterically hindered amino acid or a sterically hindered amine. Additional details of the sterically hindered sorbents are provided below.

[0118] In some implementations, the sorbent solution includes at least one sterically hindered sorbent.

[0119] In some implementations, the sorbent solution includes two or more sorbents, where at least one of which is a sterically hindered sorbent.

[0120] In some implementations, the sorbent solution includes abase (i.e., inorganic base), such as potassium hydroxide.

[0121] In some implementations, the complexing agent comprises an unsaturated nitrogenous compound in freebase or salt form. In some implementations, the unsaturatednitrogeneous compound may be an iminoguanidine, such as a bis(imino)guanidine or tns(imino)guanidine. Examples of bis(imino)guanidine include, but are not limited to, glyoxal bis(imino)guanidine, methylglyoxal bis(imino)guanidine, diacetyl bis(imino)guanidine, diacetylbenzene bis(imino)guanidine, and pyridine bis(imino)guanidine. Further detail on bis(imino)guanidine and tris(imino)guanidine are provided below.

[0122] In some implementations, the complexing agent comprises an inorganic base. Examples of an inorganic base include, but are not limited to, alkaline earth metal hydroxides such as calcium hydroxide and magnesium hydroxide.

[0123] In some implementations, the source of impure carbon dioxide includes air, e.g., atmospheric air.

[0124] When performed, carbon loading in sterically hindered sorbents may, in some contexts, be slower compared to unhindered sorbents.Sterically hindered and unhindered sorbents

[0125] Sterically hindered sorbent may be any sterically hindered amino acid or amine compound. Compared to unhindered sorbents, the sterically hindered sorbents may resist formation of carbamates. In some implementations, a sterically hindered sorbent may be any compound represented by formula (I).where, at least three of R1-R5 are moi eties excluding hydrogen, but otherwise each Ri, R2, R3, R4, and R5 is, independently, H, optionally substituted aliphatic, optionally substituted alkyl, optionally substituted heteroaliphatic, optionally substituted heteroalkyl, optionally substituted aromatic, optionally substituted aryl, or optionally substituted arylalkylene. In some implementations, each Ri, R2, R3, R4, and R5 is, independently, H, branched or unbranched alkyl chains such as branched or unbranched Ci-6 alkyl group, branched or unbranched alkene group such as branched or unbranched Ci-6 alkene group, or branchedor unbranched alkene group such as Ci-6 alkene, or a branched or unbranched C4-7 carbon ring.

[0126] In some implementations, two or more of Ri - R5 in formula (I) are taken together to form an optionally substituted cyclic group or multi-cyclic structure (e.g., N- methylproline).

[0127] In some implementations, in formula (I), one or more Ri - R5, independently, includes one or more heteroatoms such as N, 0, S, P. In some implementations, one or more Ri - R5 is, independently, substituted or unsubstituted alcohol, substituted or unsubstituted carboxylic acid, substituted or unsubstituted carboxylates, or substituted or unsubstituted sulfonic acids.

[0128] In some implementations, in formula (I), at least three of Ri - R5 are a methyl group or larger. In some implementations, at least three of Ri - R5 are moieties excluding hydrogen. In some implementations, at least one of the Ri - Rs is, independently, methyl, ethyl, propyl, isopropyl group, carboxyl group, or sulfono group.

[0129] In some implementations, in formula (I), Ri and R2 are not part of a five-membered cyclic structure with any of R3-R5. For example, sterically hindered amino acids represented in formula (I) excludes proline.

[0130] Examples of sterically hindered sorbents include, but are not limited to, N- methylalanine, 2-aminoisobutyric acid, 2-amino-2-methyl-l-propanol, N, N- dimethylglycine, methyldiethanolamine, triethanolamine, N-methylproline.

[0131] In some implementations, the stencally hindered sorbent may be any compound represented by formula (II).Formula (II) where, A is a bond, a C atom, a heteroatom, a carbon chain with a backbone length of Ci- C9, or a ring-containing moiety, and at least two of Re-Rio are moieties excluding hydrogen, but otherwise each Re, R7, Rs, R$>, and Rio is, independently, H, optionally substituted aliphatic, optionally substituted alkyl, optionally substituted heteroaliphatic,optionally substituted heteroalkyl, optionally substituted aromatic, optionally substituted aryl, or optionally substituted arylalkylene. In some implementations, each Re, R7, Rs, R$>, and Rio is, independently, H, branched or unbranched alkyl chains such as branched or unbranched Ci-6 alkyl group, branched or unbranched alkene group such as branched or unbranched C1-6 alkene group, or branched or unbranched alkene group such as Ci-6 alkene, or a branched or unbranched C4-7 carbon ring.

[0132] In some implementations, A is a bond, a C atom, a heteroatom, a carbon chain with a backbone length of C1-C9, or a ring-containing moiety such as a benzene(phenylene) ring, which may be substituted at 1,4 (para), 1,3 (meta), or 1,2 (ortho) positions. In some implementations, a ring-containing moiety is or includes any cyclic group that includes at least one, two, three, or four carbon ring atoms. In some implementations, the ringcontaining moiety includes two sites engaged in bonds, either directly, or indirectly via a linker. In some implementations, the ring-containing moiety is or includes a monocyclic ring, i.e., a single ring not bound or fused to another ring. In some implementations, the ring-containing moiety is or includes a ring system, wherein the term ‘ring system’ refers to a polycyclic moiety (e.g., a bicyclic, or tricyclic moiety). The cyclic group can be polycyclic by either possessing a bond between at least two rings or a shared (i.e., fused) bond between at least two rings. The one or more rings in the ring-containing moiety is typically a five-membered, six-membered, or seven-membered ring. In some implementations, the ring-containing moiety can include one or more heteroatoms, such as N, 0, S, and P.

[0133] In some implementations, in formula (II), one or more Re - Rio, independently, includes one or more heteroatoms such as N, 0, S, or P. In some implementations, one or more Re - Rio is, independently, substituted or unsubstituted alcohol, substituted or unsubstituted carboxylic acid, substituted or unsubstituted carboxylates, or substituted or unsubstituted sulfonic acids.

[0134] In some implementations, in formula (II), at least three of Re - Rio are a methyl group or larger. In some implementations, at least three of Re - Rio are not hydrogen. In some implementations, at least one of the Re - Rio is, independently, methyl, ethyl, propyl, isopropyl group, carboxyl group, or sulfono group.

[0135] The unhindered sorbents may be represented by the formula (I) and the associated descriptions of the Ri - R5 above, except that at least one of Ri -R2 is hydrogen and at least three of Ri - R5 are hydrogen. Examples of unhindered sorbents include, but are not limited to, sarcosine, glycine, taurine, N-methyltaurine, arginine, histidine, lysine, asparticacid, glutamic acid, serine, threonine, asparagine, glutamine, cysteine, glycine, proline, alanine, valine, isoleucine, leucine, methionine, phenylalanine, tyrosine, tryptophan, glycineglycine, glycineglycineglycine, and other di- and tri-peptides derived from the amino acids.

[0136] In some implementations, unhindered sorbents may be represented by formula (II) and the associated descriptions of the Ks - Rio and A above, except that Rio is a hydrogen and at least four of Re - Rio are hydrogen.

[0137] In some implementations, sterically hindered sorbent may be an amine, such as tertiary amine. In some implementations, sterically hindered sorbent is any tertiary amine. In some implementations, sterically hindered sorbent may be a sterically hindered amine represented by formula (III).Formula (III) where, each Rn, R12, and Rn is, independently, substituted aliphatic, optionally substituted alkyl, optionally substituted heteroaliphatic, optionally substituted heteroalkyl, optionally substituted aromatic, optionally substituted aryl, or optionally substituted arylalkylene. In some implementations, each Rn, R12, and R13 is, independently, H, branched or unbranched alkyl chains such as branched or unbranched C1-6 alkyl group, branched or unbranched alkene group such as branched or unbranched C1-6 alkene group, or branched or unbranched alkene group such as C1-6 alkene, or a branched or unbranched C4-7 carbon ring.

[0138] In some implementations, two or more of Rn - R13 in formula (III) are taken together to form an optionally substituted cyclic group or multi-cyclic structure (e.g., N- methylproline).

[0139] In some implementations, in formula (III), one or more Rn - R13 is, independently, one or more heteroatoms such as N, 0, S, P. In some implementations, one or more Rn - R13 further include, independently, substituted or unsubstituted alcohol, substituted or unsubstituted carboxylic acid, substituted or unsubstituted carboxylates, or substituted or unsubstituted sulfonic acids.

[0140] In some implementations, the hindered amine of formula (III) includes at least one of Rn - R13 being a methyl group or larger. In some implementations, Rn - R13 is, independently, a methyl group or larger. In some implementations, at least one of the Rn - R13 is, independently, methyl, ethyl, propyl, isopropyl group, carboxyl group, or sulfono group. In some implementations, Rn - R13 is, independently, a methyl group or larger.

[0141] In some implementations, unhindered sorbent may be ammonia.Sorbent solution

[0142] The sorbent solution includes a sorbent compound (amino acid or amine) in a solvent (e.g., water). In some implementations, a sorbent compound may be a sterically hindered amino acid or a sterically hindered amine. Additional details of the sterically hindered sorbents are provided herein.

[0143] In some implementations, the sorbent solution includes at least one sterically hindered sorbent. In some implementations, the sterically hindered sorbent has formula (I). In some implementations, the sterically hindered sorbent has formula (II). In some implementations, the sterically hindered sorbent has formula (III). In some implementations, the sorbent solution includes one or more sterically hindered sorbents. In some implementations, the sorbent solution includes two or more sorbents, where at least one of which may be sterically hindered sorbent. In some implementations, the sorbent solution includes at least one sterically hindered sorbent and at least one unhindered sorbent. In some implementations, the sorbent solution includes at least three sorbents, where at least one sorbent is sterically hindered. For example, the sorbent solution may contain two sterically hindered sorbents and one sterically unhindered sorbent. In some implementations, the sorbent solution includes at least three sorbents, where all sorbents are sterically hindered sorbents.

[0144] In some implementations, the sorbent solution comprises at least one sterically unhindered sorbent, such as alanine, valine, isoleucine, leucine, methionine, phenylalanine, glycineglycine, glycineglycineglycine, sarcosine, glycine, arginine, histidine, lysine, aspartic acid, taurine, N-methyltaurine, glutamic acid, serine, threonine, asparagine, glutamine, cysteine, proline, phenylalanine, tyrosine, tryptophan or other di- and tri-peptides.

[0145] In some implementations, the sorbent solution comprises an aqueous solution. For example, the aqueous sorbent solution can comprise a hindered sorbent compound having a solubility of at least about 0.5M, at least about 0.2M, or at least about 0.1M. In someimplementations, the concentration or solubility of the hindered sorbent compound may be between about 0.1M and 8.0M, about 0.2M and 4.0M, or about 0.3M and 3.0M. All values of solubility are for water at 20 °C.

[0146] In some implementations, the sorbent solution may contain the first sorbent compound and the second sorbent compound. In some implementations, the first sorbent compound is a sterically hindered sorbent compound having formulae (I) - (III), and the second sorbent compound is an unhindered sorbent compound.

[0147] In some implementations, sorbent solution may contain 10 - 90 mol.%, 20 - 80 mol.%, or 30 - 70 mol.% of the sterically hindered sorbent compound, where mol.% represents the percentage of the total moles of sorbent. In some implementations, the relative concentration of the sterically hindered sorbent complex in solution is at least 10 mol.%, at least 20 mol.%, or at least 30 mol%.

[0148] In some implementations, sorbent solution may contain 10 - 90 mol.%, 20 - 80 mol.%, or 30 - 70 mol.% of the unhindered sorbent compound, where mol.% represents the percentage of the total moles of sorbent. In some implementations, the relative concentration of the unhindered sorbent complex in solution is at least 20 mol.%, at least 30 mol.%, or at least 40 mol%.

[0149] In some implementations, sorbent solution may have pKa between about 7 and 14, between about 8 and 12, or between about 8 and 11. In some implementations, the pKa of the sorbent solution is at least about 7, or at least about 8. In some implementations, the pKa of the sorbent solution is no more than about 11, no more than about 12, or no more than about 14.

[0150] Ammo acids have two pKa values that may be of interest. The first pKa (pKal) is associated with the carboxyl group, and the second pKa (pKa2) is associated with the amine group. In some implementations, a relatively low pKa2 of the amino acid may facilitate the protonation of BIG and the unloading of carbon. In some implementations, the pKa2 value of the amino acid-containing sorbent solution may be about 7 to 14, about 8 to 12, or about 8 to 11.

[0151] In some implementations, sorbent solution may have a pH of about 7 to 14, about 8 to 13, or about 8.3 to 12.8. In some implementations, the pH of the sorbent solution is at least about 7, at least about 8, at least about 8.3, or at least about 8.5. In some implementations, sorbent solution may have a pH of less than about 14, less than about 13, less than about 12.8, less than about 12.5, or less than about 12. In some cases, the pH of the sorbent solution may change during the loading of CO2. For example, the pH of thesorbent solution after loading of CO2 is lower than the pH of the unloaded sorbent solution. In the context of a carbon dioxide absorption apparatus such as a gas-liquid contactor 10, the pH of the sorbent solution at the liquid inlet of the apparatus is higher than the pH of the sorbent solution at the outlet of the apparatus.

[0152] In some implementations, the temperature of the sorbent solution is between about 0°C and 45°C, or between about 10°C and 30°C. In some implementations, the temperature of the sorbent solution is ambient temperature.

[0153] In some implementations, the carbon-loaded sorbent solution comprises at most 1 mol of inorganic carbon per mol of sorbent, for example between 0.05 and 0.6 mol of inorganic carbon per mol of sorbent, or for example between 0.075 and 0.5 mol of inorganic carbon per mol of sorbent.

[0154] In some implementations, the carbon-loaded sorbent solution comprises at most 65 mol% of inorganic carbon in carbamates with respect to a total number of moles of inorganic carbon in the carbon-loaded solution. For example, carbon-loaded sorbent solution comprises at most 60 mol% of inorganic carbon in carbamates with respect to a total number of moles of inorganic carbon in the carbon-loaded solution. For example, the carbon-loaded sorbent solution comprises at most 50 mol% of inorganic carbon in carbamates with respect to a total number of moles of inorganic carbon in the carbon- loaded solution.

[0155] In some implementations, the carbon-loaded solution has a pH between 7 and 14. For example, the carbon-loaded solution has a pH between 8 and 13. For example, the carbon-loaded solution has a pH between 9 and 12.

[0156] A sterically hindered sorbent solution may have favorable loading and unloading properties (i.e., increased loading capacity with the complexing agent) over the unhindered sorbents . For example, the extent of precipitation with hindered sorbents may be higher (i.e., higher crystallization yields) compared to unhindered sorbents (e.g., more utilization of BIG with hindered vs. unhindered sorbents).

[0157] In some implementations, a mixture of hindered and unhindered sorbents may provide more control in optimizing for the most economic combination of crystallizer and contactor size, while offering a balance in favoring a CO2 absorption rate and a precipitation rate.

[0158] In various implementations, the sterically hindered sorbent compound in solution may have different physical properties depending on the associated sterically hindered sorbents or blend of hindered and unhindered sorbents. Examples of these physicalproperties include but are not limited to, pKa, carbamate hydrolysis equilibrium constant, the kinetic rate constant of the carbamate hydrolysis, and volatility.

[0159] In some implementations, the rate of unhindered amine carbamate hydrolysis reaction may be accelerated when in the presence of hindered amine. In some cases, the presence of hindered amine may shift the equilibrium partitioning of the dissolved inorganic carbon away from carbamate, and towards bicarbonate and / or carbonate formation. The presence of hindered amine may allow some of the above-described equilibrium to occur in the contactor, forming the more “accessible” bicarbonate and / or carbonate. In contrast, when solely unhindered sorbents are used, significantly more of the carbamate conversion to bicarbonate and / or carbonate may occur in the downstream process or apparatus (e.g., in the crystallizer)

[0160] Additionally, combinations of hindered or unhindered sorbents where the pKa of the hindered sorbent is higher than the pKa of the unhindered sorbent may be advantageous for the CO2 capture process, for example, by increasing the rate of the CO2 capture. This may be because the hindered amine can act as the base in the reaction of the unhindered sorbent with CO2, forming the carbamate complex, allowing a larger fraction of the remaining unhindered amine in the solution to remain in the solution in the deprotonated state, which is the active species for reaction with or capturing the CO2. In some implementations, relative reaction rates between amino acids and CO2 may be as follows: Unhindered deprotonated state > hindered deprotonated state »> unhindered or hindered zwitterion or conjugate acid state (~ 0). In various implementations, the presence of hindered amine with a higher pKa compared to the unhindered amine allows more unhindered amine to remain in the deprotonated state.

[0161] Aside from chemical reactions, some unhindered sorbents (or other absorption “promoters”) may influence the physical properties of the aqueous solution (e.g., viscosity, surface tension) that can further assist the absorption of the carbon dioxide. In some implementations, the freezing point of the unhindered / hindered sorbent blend may be impacted.

[0162] In some cases, tertiary' amines (i.e., stencally hindered amines) can act as an inhibitor for the decomposition of sorbents.

[0163] In some cases, sterically hindered sorbents or a mixture of sorbents that includes at least one sterically hindered sorbent, may reduce the degradation of the BIGs or other unsaturated nitrogenous base.

[0164] In some implementations, the sorbent solution comprises a base, such as an inorganic base, e.g., potassium hydroxide, sodium hydroxide, lithium hydroxide, barium hydroxide, or any other strong base. The concentration of base may be equimolar to the amino acid sorbent in solution, but may in some cases be more or less, e.g., 10 mol% more or less.

[0165] In some implementations, a base may be added to an amino acid sorbent solution, which may convert the dissolved amino acid sorbent from the zwitterion form to a deprotonated state. As noted above, the deprotonated amino acids can react wi th carbon dioxide. In some implementations, an equimolar amount of the base relative to the sorbent (e.g., the equimolar of potassium hydroxide) may be added. In some implementations, it may be advantageous to introduce non-equimolar amounts of base. In some implementations, more than 1 equimolar of potassium hydroxide may be added to increase and expedite the CO2 absorption. In some implementations, less than 1 equimolar of potassium hydroxide may be added to improve the precipitate with the BIGs.

[0166] An alternative approach to sorbent selection involves selecting the composition of the sorbent solution to cause favorable pH levels after absorption of CO2. It has previously been demonstrated for unhindered amino acids — a form of amino carboxylic acids — that the sorbent solution unloading can be maximized by using a sorbent with a relatively low pKa. As an alternative to utilizing hindered sorbents or in combination therewith, the sorbent can include unhindered amino sulfonic acids to maximize the extent of unloading upon contact with an unsaturated nitrogenous base. Examples of such sorbents include glycineglycine, glycineglycinegylcine, taurine, and N-methyltaurine.Bis(imino)guamdmes Compounds

[0167] In some implementations, the iminoguanidine may be a bis(imino)guanidine compound (also referred to as a BIG compound) represented by the following formula (IV).Formula (IV)

[0168] The bis(imino)guanidine compound includes a central moiety (A) attached to two iminoguanidine or iminoguanidinium groups. Although formula (IV) depicts a specific tautomeric arrangement, formula (IV) is intended to include any other tautomer that can be derived from or interconvert with the tautomer shown in formula (IV). Formula (IV) is also intended to include any regioisomers that may differ in the connection points of the two aminoguanidine or aminoguanidinium groups on the central moiety (A). In the event the structure according to formula (IV) possesses one or more stereocenters, formula (IV) is intended to include all resulting stereoisomers. The stereoisomer may include one or more enantiomers and / or diastereomers. Although formula (IV) depicts a neutral molecule, it is intended to encompass salt forms of the formula (IV), for example, as depicted by formula (V)

[0169] In some implementations, iminoguanidine salt may be abis(imino)guanidine salt represented by the formula (V).Formula (V)

[0170] The salt forms may correspond to those that can be produced by the reaction of the neutral form of formula (V) with a mineral acid or alkyl halide, which results in protonation or alkylation of one or more of the shown amine or imine groups. Similarly to formula (IV), formula (V) is intended to include all possible tautomers, regioisomers, and stereoisomers of the protonated bis(immo)guanidine. Accordingly, the positive charge shown in formula (V) may be located on any of the other nitrogen atoms through tautomerization. As well as known in the case of tautomers, the positive charge is generallydistributed among all atoms capable of holding a positive charge in the various tautomers. Likewise, a partial double bond character is generally present among all the bonds capable of engaging in double bonds in the various tautomers.

[0171] In formula (V), X”1' is an anionic species with a magnitude of charge m, where m is an integer of at least 1, and n is an integer of at least 1, provided that n x m=2. The anionic species may be any anionic species that, when complexed as a salt with the bis- iminoguanidinium portion shown in formula (V), can be exchanged for another anionic species desired to be removed from an aqueous solution. As the different anionic species have different dissociation constants, any anionic species may be useful in exchanging with another anionic species to be removed from an aqueous source. The anionic species may also represent a species that has been removed from an aqueous solution wherein the resulting salt of the removed anion and bis-iminoguanidinium portion shown in Formula (II) is valuable as a precursor for producing a neutral form of formula (V) or by exchanging with another anionic species that can be used to exchange with and remove another anionic species of interest. The anionic species (X”1') can be, for example, a halide, such as fluoride, chloride, bromide, or iodide. The anionic species can alternatively be a halide equivalent (or pseudohalide), such as methanesulfonate (mesylate), tnfluoromethanesulfonate (triflate), tosylate, cyanate, thiocyanate, cyanide, or a sulfonamide anion, such as bis(trifluoromethane)sulfonamide (i.e., bistnflimide). The anionic species may alternatively be a borate anion, such as tetrafluoroborate, tetrakis(pentafluorophenyl)borate, or tetrakis[3,5-bis(trifluoromethyl)phenyl]borate. The anionic species may alternatively be hexafluorophosphate (PFe ’ ). The anionic species may alternatively be hydroxide, or an alkoxide (e.g., methoxide or ethoxide). The anionic species may alternatively be a carboxylate species, such as formate, acetate, propionate, or glycolate. In other implementations, the anionic species (Xm“ ) can be an oxyanion. As used herein, the term “oxyanion” refers to an anion having at least three or four oxygen atoms, wherein the oxygen atoms are generally all bound to a central element. Some examples of oxyanions include sulfate (e.g., SO42" ), nitrate (NO3 ’ ), chromate (e.g., CrCri2" ), selenate (e.g., SeCL2" ), phosphate (e.g., PO43" ), arsenate (AsCh3" ), carbonate(CO3 ), bicarbonate (HCO3 ' ), and perchlorate (CIO4 ' ). The oxyanions provided above may or may not also include related derivatives. For example, unless otherwise stated, the term “sulfate” may also include thiosulfate (S2O3 ), bisulfate (HSO4 ’ ), and sulfite(S032" ). Similarly, the term “chromate” may also include CVO?2" (dichromate). Similarly, the term “phosphate” may also include hydrogenphosphate (HPO4 ), dihydrogenphosphate (H2PO4 ’ ), pyrophosphate (P2O74“ ), thiosphosphates (e.g., PO3S3 ’ or PO2S23" ), and phosphite (e.g., PO33" , HPO32“ , or H2PO3 ’ ). The oxyanion may also be selected from among less common species, such as tungstate, vanadate, molybdate, tellurate, and stannate.

[0172] When Xm' is a carbonate or bicarbonate anion, m may be 1 for bicarbonate and 2 for carbonate. N is 0.5, 1, or 2.

[0173] Structures of formulae (IV) and (V), include structures having one or more of the hydrogen atoms, whether the hydrogen atoms are shown or not shown in the formula, being replaced with one or more alkyl groups (e.g., Ci-Ce alkyl groups such as methyl groups) or other substituents, respectively. For example, one or both of the terminal carbon atoms in the imino groups linked to the central moiety (A) in formulae (IV) and (V) may be bonded to an alkyl group (e.g., a Ci-Cs alkyl group such as a methyl group) or other substituent that is not part of the linkage with A. As defined, formulae (IV) and (V) are also encompassing all potential tautomers. Examples include methyglyoxal bis(imino)guanidine and diacetyl bis(imino)guanidine.

[0174] Referring to both formulae (IV) and (V), central moiety (A) may be a single bond, or it may be a linear or branched hydrocarbon (e.g., a Ci-Ce alkyl, alkenyl, or alkynyl group), optionally substituted with alcohol, amine, and / or include one or more heteroatoms.

[0175] Referring to both formulae (IV) and (V), central moiety (A) may be a ring containing moiety. The ring-containing moiety (A) is or includes any cyclic group that includes at least one, two, three, or four carbon ring atoms. Since the cyclic group is attached to two iminoguanidine or iminoguanidinium groups, the cyclic group in the ring- contaming moiety (A) necessarily includes two sites engaged in bonds, either directly, or indirectly via a linker, to the iminoguanidine or iminoguanidinium groups. Typically, the two sites in the ring (A) linked, directly or indirectly, to the iminoguanidine or iminoguanidinium groups are nng carbon atoms. In some implementations, the ringcontaining moiety is or includes a monocyclic ring, i.e., a single ring not bound or fused to another ring. In other implementations, the ring-containing moiety is or includes a ring system, wherein the term “ring system” refers to a polycyclic moiety (e.g., a bicyclic ortricyclic moiety). The cyclic group can be polycyclic by either possessing a bond between at least two rings or a shared (i.e., fused) bond between at least two rings. The one or more rings in the ring-containing moiety is typically a five-membered, six-membered, or sevenmembered ring.

[0176] In one set of implementations, the central moiety (A) is or includes a carbocyclic ring or ring system. The term “carbocyclic” indicates that the ring or ring system contains only carbon ring atoms. The carbocyclic ring or ring system can be saturated or unsaturated. Some examples of carbocyclic nngs that are monocyclic and saturated include cyclopentyl, cyclohexyl, and cycloheptyl rings. Some examples of carbocyclic rings that are monocyclic and unsaturated (which may be aliphatic or aromatic) include cyclopentenyl, cyclopentadienyl, cyclohexenyl, cyclohexadienyl, cycloheptenyl, cycloheptadienyl, and phenylene (benzene) rings. Some examples of carbocyclic rings that are polycyclic and saturated include decalin, norbomane, bicyclohexane, and 1,2- dicyclohexylethane nng systems. Some examples of carbocyclic rings that are polycyclic and unsaturated include naphthalene, anthracene, phenanthrene, phenalene, and indene ring systems.

[0177] In another set of implementations, the central moiety (A) is or includes a heterocyclic ring or ring system. The term “heterocyclic” indicates that the ring or ring system contains at least one ring heteroatom. As examples, the ring heteroatom may be selected from nitrogen, oxygen, and sulfur. The heterocyclic ring or ring system can be saturated or unsaturated. Some examples of heterocyclic saturated rings or ring systems include those containing at least one ring nitrogen atom (e.g., pyrrolidine, piperidine, piperazine, imidazolidine, azepane, and decahydroquinoline rings); those containing at least one ring oxygen atom (e.g., oxetane, tetrahydrofuran, tetrahydropyran, 1,4-dioxane, 1,3-dioxane, and 1,3-dioxepane rings); those containing at least one ring sulfur atom (e.g., tetrahydrothiophene, tetrahydrothiopyran, 1,4-dithiane, 1,3-dithiane, and 1,3 -dithiolane rings); those containing at least one ring oxygen atom and at least one ring nitrogen atom (e.g., morpholine and oxazolidine rings); and those containing at least one ring nitrogen atom and at least one ring sulfur atom (e.g., thiazolidine and thiamorphohne rings). Some examples of heterocyclic unsaturated rings or nng systems include those containing at least one ring nitrogen atom (e.g., pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, 1,3,5-tnazine, azepine, diazepine, indole, purine, benzimidazole, indazole, 2,2'-bipyridine, quinoline, isoqumohne, phenanthroline, 1,4,5,6-tetrahydropyrimidine, 1, 2,3,6-tetrahydropyridine, 1,2,3,4-tetrahydroquinoline, quinoxaline, quinazoline, pyridazine, cinnoline, and 1,8-naphthyridine rings); those containing at least one ring oxygen atom (e.g., furan, pyran, 1,4-dioxin, benzofuran, dibenzofuran, and dibenzodioxin); those containing at least one ring sulfur atom (e.g., thiophene, thianaphthene, benzothiophene, thiochroman, and thiochromene rings); those containing at least one ring oxygen atom and at least one ring nitrogen atom (e.g., oxazole, isoxazole, benzoxazole, benzisoxazole, oxazoline, 1,2,5-oxadiazole (furazan), and 1,3,4-oxadiazole rings); and those containing at least one ring nitrogen atom and at least one ring sulfur atom (e.g., thiazole, isothiazole, benzothiazole, benzoisothiazole, thiazoline, and 1,3,4-thiadiazole rings).

[0178] Some examples of compounds according to formula (IV) include the follow ing.

[0179] Some examples of compounds according to Formula (II) include the following.

[0180] Any of the above exemplary compounds may also be converted to the respective neutral analogue according to Formula (I) by removal of the two protons located onpositively charged amine groups. Moreover, in any of the above exemplary formulas, a hydrogen atom on a ring nitrogen atom may be replaced with a hydrocarbon group, such as a methyl, ethyl, n-propyl, isopropyl, in-butyl, isobutyl, sec-butyl, t-butyl, phenyl, or benzyl group. As also provided above, any one or more of the hydrogen atoms in any of the above exemplary structures, whether the hy drogen atoms are shown or not shown, may be replaced with one or more methyl (or other Ci-Ce alkyl) groups, respectively.

[0181] In some implementations, the iminoguanidine can be a bis(imino)guanidine compound in a solid phase comprising water and / or solvent molecules. The bis(imino)guanidine compound can include solvates and hydrates of the bis(imino)guanidine compounds of formula (V). For example, the bis(imino)guanidine compound can have a H2O: protonated bis(imino)guanidine molar ratio of at least 1 : 1 H2O to protonated bis(imino)guanidine.Tris(imino)guamdine Coumpounds

[0182] In some implementations, iminoguanidine is atris(imino)guanidine (TRIG). One example is 1,3,5-benzene tris(imino)guanidine.

[0183] While much of the discussion herein refers to BIG compounds when discussing processes and systems employing carbon dioxide complexing agents, this is provided for the sake of convenience. Many of the processes and systems described with reference to BIG compounds should be understood to apply more generally to any other carbon dioxide complexing agents as defined above. Many of these other carbon dioxide complexing agents are in the class of unsaturated nitrogenous compounds, with examples being imines, amidines, and iminoguanidines, the latter including bis(imino)guanidines and tns(imino)guani dines. Additionally, mixtures of one or more carbon dioxide complexing agents may also be employed, even where the discussion mentions only one.Carbon dioxide capture methods

[0184] The present disclosure relates to capturing carbon dioxide from a source of impure carbon dioxide by contact with a sorbent solution including at least one sterically hindered sorbent as disclosed herein, the contacting being performed in a contacting apparatus or gas-liquid contactor, such as the gas-liquid contactor 10 of FIG. 1. The contact may be by any means that permits the carbon dioxide in the source of impure carbon dioxide to dissolve into the sorbent solution by interaction with the sorbent. The impure source can,for example, be bubbled through the sorbent solution, with or without agitation of the sorbent solution. Alternatively, the impure source may be sprayed or misted with the sorbent solution, which may be performed in the presence of a layer of the sorbent solution under agitation to further absorb the carbon dioxide. In some implementations, the contact occurs by crossflow in a gas-liquid contactor. For example, in the contactor, the sorbent solution may drip down by gravity or otherwise and the impure source is blown through at anon-parallel angle (e.g., about 90 degrees or an acute angle). In some implementations, the contactor is configured to provide a very high surface area for the contact. For example, a very thin film of the sorbent solution may flow over a large surface area solid surface. The flow of the sorbent solution may be continuous or non-continuous (e.g., pulsed). Similarly, the flow of the source of impure carbon dioxide may be continuous or non-continuous (e.g., pulsed).

[0185] In some implementations, an aqueous sorbent solution comprising one or more sterically hindered sorbent compounds, as disclosed herein, is flowed through a gas-liquid contactor where it is brought into contact with atmospheric air flowed through by a ventilator. Dissolved carbon dioxide from the air reacts with the sorbent in the sorbent solution.

[0186] The contactor may have any of various formats. For example, it may have a structure similar to a cooling tower. The sorbent solution may be distributed in the contactor surfaces as uniformly as possible, e.g., in the form of a thin film liquid. The gasliquid contactor may exhibit a low-pressure drop and efficient mass transfer. More details on gas-liquid contactors are provided below.

[0187] In some implementations, a contactor, such as the gas-liquid contactor 10, and crystallizer, such as the crystallizer 18, are integrated into one unit operation (e.g., air is contacted with a sorbent solution comprising both the sorbent and carbon complexing agent (e.g., an unsaturated nitrogenous base or inorganic base), to form the insoluble complexed carbonate or bicarbonate salt in the unit. As an example, the integrated contactor and crystallizer may implemented as a bubble column.

[0188] In some implementations, a DAC process or other carbon dioxide capture process employing a sterically hindered sorbent compound, as disclosed herein, is configured to capture large quantities of carbon dioxide, e.g., on the order of several tons of carbon dioxide per day, in an energ -efficient and hence inexpensive manner. In some implementations, referring to FIG. 1, the CO2 capture process, such as a DAC process, of the carbon dioxide capture system 1 is a continuous process. For example, the DACprocess may employ a continuous flow air-liquid contactor as the gas-liquid contactor 10 and may continuously operate filtration of solid CCh-complexed material as the solid material 20 in the solid-liquid separation subsystem 18. For example, the DAC process can comprise reusing at least one of the unloaded sorbent solution 22 (e.g., including a sterically hindered amino acid) and a regenerated CO2 complexing compound 26 (e.g., a guanidine derivative). For example, the DAC process can comprise reusing both the unloaded sorbent solution 22 (e.g., including an amino acid) and the regenerated CO2 complexing compound 26 (e.g., a guanidine derivative). In some implementations, at least one of the gas-liquid contactor subsystem 3 and the regeneration subsystem 11 are operated batch-wise or semi-continuously. For example, the regeneration by solids formation in the solids formation subsystem 12 can be operated continuously while the solid-liquid separation subsystem 18 can be operated batch-wise or semi-continuously. For example, the solids formation subsystem 12 can be operated batch-wise or semi-continuously.

[0189] In some implementations, still refernng to FIG. 1, because CO2 is recovered from the solid material 20 (e.g., BIG carbonate / bicarbonate complex) to form part of the CO2 product stream 28, the CO2 recovery stage / step in the CO2 recovery subsystem 24 may operate on a relatively small quantity (mass and volume) of solid material 20. This batch operation can minimize the consumption of energy because, to the extent the carbon dioxide is present in a very high concentration in a low-mass vehicle, i.e. solid material 20 such as a BIG carbonate, energy is not wasted heating liquid that does not contain appreciable quantities of CO2.

[0190] Contrary to known processes involving high-temperature treatment of a carbon- loaded sorbent solution to release the CO2 therefrom, which sometimes degrades the sorbent (e.g., amine) by oxidation or thermal degradation, some implementations of the CO2 capture process of the carbon dioxide capture system 1 include a low-temperature CO2 release / recovery stage, which may be enabled by employing a guanidine derivative as the complexing agent.

[0191] As mentioned above, the CO2 in the air (or other impure CO2 source) that contacts the sorbent solution is in the form of carbamates, bicarbonates, carbonates, dissolved CO2, or any combination thereof. The inventors have found that it may be more beneficial to have the absorbed CO2 in the form of bicarbonate and carbonate to facilitate the unloading of the carbon-loaded sorbent solution via the precipitation with the complexing agent, e.g., BIGs and / or inorganic bases. The use of sterically hindered sorbents, either in isolation or combination with other sorbents, may increase the percentage of absorbed CO2 in the formof bicarbonate and carbonate, providing benefits for unloading the solution via the precipitation with, e.g., BIGs or inorganic bases during operation of a carbon dioxide capture system, such as the DAC system 1 of FIG. 1.

[0192] The benefits of using sterically hindered sorbent compounds may include any one or more of the following.

[0193] During CO2 absorption, the rate of CO2 absorption when sterically hindered sorbents are used in combination with unhindered sorbents may be increased, relative to unhindered sorbents alone. At increasing concentrations, unhindered sorbents increase the rate of CO2 absorption. However, due to the changes in speciation at increasing concentrations for unhindered sorbents, the additional CO2 absorbed is largely inaccessible for precipitation. In contrast, combinations of unhindered and hindered sorbents will have faster rates of CO2 absorption than when just unhindered sorbents are used (maintaining the concentration of unhindered sorbent), while the additional CO2 absorbed will be more accessible for precipitation. The synergy in combinations of sorbents may be optimized.

[0194] During CO2 absorption, sterically hindered sorbents may increase the maximum CO2 loading level (mol CO2 I mol sorbent), in either isolation or in combination with other sorbents. The speciation is also believed to favor bicarbonate and carbonate over carbamate, relative to unhindered sorbents alone.

[0195] During precipitation with the complexing agent, e.g., BIGs and / or inorganic bases, sterically hindered sorbents can be unloaded to a lower CO2 loading level (mol CO2 / mol sorbent). Unloading more CO2 translates to a higher working capacity for the carbon dioxide capture system 1, reducing the amount of aqueous solution required.

[0196] When sterically hindered sorbents are used in combination with unhindered sorbents, the rate of unhindered sorbent carbamate decomposition may be faster than carbamate decomposition when unhindered sorbents are used in isolation. This can potentially decrease the amount of time required in the crystallizer to remove a given amount of inorganic carbon from the solution, decreasing the crystallizer size.

[0197] In certain implementations, a carbon dioxide capture system is configured to load carbon dioxide into an aqueous sorbent solution as described herein, such as sorbent solution 6. The loaded carbon dioxide may take the form of carbon dioxide-derived species. The carbon dioxide system can be configured to use an organic base (e.g., an unsaturated nitrogenous base) and / or an inorganic base (e.g., Ca(OH)2, Mg(OH)2, etc..) to unload the carbon dioxide derived species.

[0198] In some examples, an aqueous sorbent solution is produced from one or more hindered amino acids and alkali metal hydroxide (optionally equimolar KOH and the amino acid(s)). Alternatively, the sorbent solution is produced by adding an alkali metal salt (e.g., K-AA) directly to water to create the sorbent solution.

[0199] The carbon dioxide loaded into the sorbent solution may be from the atmosphere or other source of impure carbon dioxide.

[0200] As explained, a sorbent solution reacts with the carbon dioxide to form any of multiple carbon dioxide-derived species such as bicarbonate (HCOT) or carbonate (CO?2-)•

[0201] The carbon dioxide capture system 1 is also configured to react the carbon dioxide derived species with an inorganic base (e.g., Ca(OH)2 and / or Mg(OH)2) to form an insoluble inorganic carbonate (e.g., CaCCh and / or MgCCh) and water. The inorganic base may be provided in addition to the at least one sterically hindered sorbent or any other sorbent disclosed herein. The insoluble inorganic carbonate may be separated and heated to release pure CO2.

[0202] In some implementations, the inorganic base is provided in a pure form (e.g., pure CaO or Ca(OH)2). In some implementations, the inorganic base is provided as a blend (e.g., a blend of Ca(OH) 2 and Mg(OH) 2). In other implementations, the inorganic base is provided from alkali waste material; for example, from mining waste or concrete / construct on waste. In some implementations, the inorganic base is produced from an inorganic silicate such as calcium silicate (CaSiCh), which can react with water to form calcium hydroxide and silicon dioxide.

[0203] In some implementations, the carbon dioxide capture and release are performed in separate loops. For example, the carbon dioxide capture loop may comprise: (a) contacting carbon dioxide with a nominally pure sorbent solution in a gas-liquid contactor to produce carbon dioxide-derived species in what is now a carbon dioxide loaded sorbent solution, (b) in a precipitation unit, contacting the carbon loaded sorbent solution with an inorganic base to produce an insoluble inorganic carbonate and to recreate the nominally pure sorbent solution, and (c) returning the nominally pure sorbent solution to the gas-liquid contactor. Optionally, the precipitated inorganic carbonate and the nominally pure sorbent solution are separated in a solid-liquid separation unit. This separation would be performed between operations (b) and (c).

[0204] The carbon dioxide release loop may comprise: (a) providing the inorganic base to the precipitation unit, (b) in the precipitation unit, allowing the carbon dioxide loadedsorbent solution to react with the inorganic base to produce the insoluble inorganic carbonate and to recreate the nominally pure sorbent solution, (c) treating the insoluble inorganic carbonate to expel pure carbon dioxide and regenerate the inorganic base, and (d) making the regenerated inorganic base available for delivery to the precipitation unit (per operation (a)). Optionally, the precipitated inorganic carbonate is separated from nominally pure sorbent solution in a solid-liquid separation unit. This separation would be performed between operations (b) and (c).

[0205] FIG. 11 illustrates example operations in a method 1100 for capturing carbon dioxide according to certain implementations. In certain implementations, the method 1100 begins with operation 1103 including contacting a source of impure carbon dioxide with an aqueous sorbent solution having at least one stencally hindered sorbent to produce a carbon-loaded sorbent solution. The carbon-loaded sorbent solution may include carbonate ions and / or bicarbonate ions. The method 1100 further includes operation 1105 including reacting the carbonate ions and / or the bicarbonate ions with a complexing agent to form at least one of a carbonate salt of the complexing agent or a bicarbonate salt of the complexing agent.

[0206] FIG. 12 illustrates example operations in a method 1200 for capturing carbon dioxide according to certain implementations. In certain implementations, the method 1200 begins with operation 1203 including contacting atmospheric air with an aqueous sorbent solution comprising at least one sterically hindered sorbent to produce a carbon- loaded sorbent solution comprising carbonate ions and / or bicarbonate ions. The method 1200 may further optionally include operation 1205 including reacting the carbonate ions and / or the bicarbonate ions with a complexing agent to form at least one of a carbonate salt of the complexing agent or a bicarbonate salt of the complexing agent.Gas-liquid contactor subsystem

[0207] The gas-liquid contactor subsystem includes at least one gas-liquid contactor, such as gas-liquid contactor 10, 103, 03 shown in FIGS. 10 to 25, that can have various implementations including those shown in FIGS. 3 to 7 and described as follows. Although reference numbers may differ, it is noted that the description, units, componentry, features, streams and advantages of the gas-liquid contactor 10, 103, 03 apply mutatis mutandis to the gas-liquid contactor 200, 200A, 200B, 200C, 200D of FIGS. 3 to 7. For example, the description, features and advantages of the sorbent solution 6 and the carbon-loadedsorbent solution 8 described herein apply mutatis mutandis to the sorbent solution 214 and the carbon-loaded sorbent solution 211 of FIGS. 3 to 7. For example, the description, features and advantages of the dilute gas source 2 and the CO2 lean gas stream 4 described herein apply mutatis mutandis to the CCF-laden air 201 and the CO2 lean gas 205 of FIGS. 3 to 7.

[0208] Referring to FIG. 3, the gas-liquid contactor 200 includes a housing 202. The housing 202 defines part of the corpus of the gas-liquid contactor 200 and provides structure thereto. The housing 202 includes exterior structure or walls that partially enclose any combination of interconnected structural members 215. The structural members 215 provide structural support and stability to the gas-liquid contactor 200, and provide a body for supporting components of the gas-liquid contactor 200 within the housing 202 or surrounding the housing 202. The structural members 215 can include, but are not limited to, walls, panels, beams and frames. For example, the structural members 215 can define a plenum 208 of the housing 202 and support other elements extending from the housing 202, such as a fan stack 207. As depicted in FIG. 3, the structural members 215 can further support one or more sections of packing 206 that provide a gas-liquid contact surface. The structural members 215 of the housing 202 may define internal or external framing, such as a structural frame and a plenum structure, by including interconnecting members. It is noted that, when an element is said herein to be supported by the housing 202, such element can be fastened to, mounted on, operatively connected to and / or contacting one or more structural members 215 of the housing 102. In some implementations, the housing 202 can include other components as well, such as cladding and / or panels, which help to close off parts of the housing 202 and define the enclosure of the housing 202.

[0209] Still referring to FIG. 3, the housing 202 at least partially encloses and defines an interior 213 of the housing 202. The interior 213 of the housing 202 is an inner volume or inner space (e.g., a void) in which components of the gas-liquid contactor 200 are positioned. As used herein, the term “vertical” refers to a direction or an orientation that is parallel or substantially parallel with the force of gravity and the term “horizontal” refers to a direction or an orientation that is perpendicular or substantially perpendicular to the force of gravity.

[0210] Still referring to FIG. 3, the gas-liquid contactor 200 also includes openings 203 that allow for movement of gases into and out of the gas-liquid contactor 200. For example, the housing 202 has one or more inlet(s) 2031. In some implementations, the one or more inlet(s) 2031 are formed by some of the openings 203, such that the inlet(s) 2031may be referred to herein as one or more inlet opening(s) 2031 through which the CO2- laden air 201 enters the interior 213 of the housing 202. For example, the gas-liquid contactor 200 has one or more outlet(s) 2030. In some implementations, the one or more outlet(s) 2030 are formed by remaining openings 203, such that the outlet(s) 2030 may be referred to herein as one or more outlet opening(s) 2030 through which the CO2-lean gas 205 exits the interior 213 of the housing 202 through the fan stack 207.

[0211] In the example implementation of the gas-liquid contactor 200 of FIG. 3, the housing 202 defines two inlets 2031 and one outlet 2030. The outlet 2030 can be defined by a component of the gas-liquid contactor 200. For example, in the implementation of the gas-liquid contactor 200 of FIG. 3, the gas-liquid contactor 200 has a fan stack 207 with an upright orientation. The fan stack 207 extends upwardly from the housing 202 and helps to discharge a CCh-lean gas 205. The outlet 2030 is positioned along the fan stack 207. In such an implementation, the CO2-laden air 201 enters the interior 213 of the housing 202 along a substantially horizontal direction through one or both of the inlets 2031, and the CO2-lean gas 205 exits the interior 213 along a substantially vertical direction through the outlet 2030. The outlet 2030 is located at the upper extremity of the fan stack 207. In implementations of the gas-liquid contactor 200 without a fan stack 207, the outlet 2030 can be located elsewhere. Other configurations for the inlets 2031 and outlets 2030 of the housing 202 are possible.

[0212] The housing 202 at least partially encloses and protects components of the gasliquid contactor 200 positioned in the interior 213 of the housing 102. One example of such a component is a packing section 206, which is protected from the surrounding atmosphere by the housing 202. As can be seen in FIG. 3, one or more packing sections 206, which are sometimes referred to herein collectively as “fill 206” or “packing 206,” are located within the interior 213 in a position adjacent to the one or more inlets 2031. In this position, the one or more packing sections 206 receive the CCh-laden air 201 which enters the interior 213 via the one or more inlets 2031. The one or more packing sections 206 function to increase transfer of CO2 present in the CC -laden air 201 to a flow of the sorbent solution 214, in that the one or more packing sections 206 provide a large surface area for the sorbent solution 214 to disperse on, thereby increasing the reactive area between the CCh-laden air 201 and the sorbent solution 214. The sorbent solution 214 transforms the CCh-laden air 201 into the CCh-lean gas 205 which is discharged from the one or more outlet(s) 2030 of the gas-liquid contactor 200. The packing sections 206 receive the sorbent solution 214 and facilitates absorption of the CO2 present in the CO2-laden air 201 into the sorbent solution 214 on the packing sections 206, as described in greater detail below.

[0213] Referring to FIG. 3, one possible arrangement of the packing sections 206 includes two or more packing sections 206A, 206B. Each packing section 206A, 206B is positioned adj acent to and downstream of one of the inlets 2031, relative to a flow direction of the CO2-laden air 201 through the inlets 2031. The packing sections 206A, 206B are spaced apart from each other within the housing 202. The direction along which the packing sections 206A, 206B are spaced apart is parallel to the direction along which the CO - laden air 201 flows through the packing sections 206A, 206B. The space or volume defined between the packing sections 206A, 206B and / or one or more structural members of the housing 202 is a plenum 208. The plenum 208 is flanked by the packing sections 206A, 206B. The plenum 208 is a void or space within the housing 202 into which gases flow from the packing sections 206A, 206B (e.g., the CCE-lean gas 205), and from which the CCh-lean gas 205 flows out of the housing 202 through the outlet 2030. The plenum 208 is part of the interior 213 of the housing 202. The volume of the plenum 208 is less than a volume of the interior 213. In example implementations, the volume of the interior 213 of the housing 202 is approximately equal to the combined volume of the packing sections 206 A, 206B and the plenum 208.

[0214] Referring to FIG. 3, the packing sections 206A, 206B are positioned along the same level, or are positioned along the same lower horizontal plane, as the plenum 208. The plenum 208 can include an upper plenum portion 208U that is an uppermost portion of the plenum 208, and a lower plenum portion 208L that is a lowermost portion of the plenum 208. A total height of the plenum 208 is defined as the height of the upper plenum portion 208U plus the height of the lower plenum portion 208L. Part of the upper plenum portion 208U is defined by housing plenum walls 202W of the housing 202, and a remainder of the upper plenum portion 208U is defined by the portion of the fan stack 207 positioned beneath the fan 221, The housing plenum walls 202W extend upwardly from a remainder of the housing 202. In some embodiments, and referring to FIG. 3, the housing plenum walls 202W are the uppermost portion of the housing 202. The height of the upper plenum portion 208U includes a lower height portion defined by the housing plenum walls 202W, and an upper height portion defined by the portion of the fan stack 207 positioned beneath the fan 221. The plenum 208 is beneath the fan 221.

[0215] Referring to FIG. 3, part of the upper plenum portion 208U, and thus part of the plenum 208, extends into the fan stack 207 or cowling. After the CCh-laden air 201 flowsthrough the packing sections 206A, 206B, the CCh-lean gas 205 flows through the plenum 208 before being discharged to the ambient environment. In other implementations of the gas-liquid contactor 200, the plenum is absent.

[0216] In the example implementation of the gas-liquid contactor 200 of FIG. 3, the CO2-laden air 201 enters the interior 213 of the housing 202 along a substantially horizontal direction through both of the inlets 2031. The CCh-laden air 201 then flows through the packing sections 206A, 206B along a substantially horizontal direction, where the CO2 present in the CCF-laden air 201 contacts the sorbent solution 214 present on the packing sections 206A, 206B and / or flowing in a substantially downward direction over the packing sections 206A, 206B. The exposed surface of the liquid film on the packing sections 206A, 206B is a gas-hquid interface between the CCh-laden air 201 and the CO2 capture solution 214. CO2 from the CCh-laden air 201 is absorbed into the liquid film to form the CCL-laden capture solution 211 and the CCL-lean gas 205. The CCh-laden capture solution 211 flows downwardly off the packing sections 206A, 206B in a mixed solution with unreacted CO2 capture solution 214 and is collected. The CO2- laden air 201 treated by the packing sections 206A, 206B exits the packing sections 206A, 206B as the CO2- lean gas 205. The CCh-lean gas 205 from both packing sections 206A, 206B converges in the plenum 208, and then flows in a vertically upward direction out of the plenum 208 through the outlet 2030. The gas-hquid contactor 200 of FIG. 3 can be considered a dualcell, cross-flow air contactor, where each cell is defined as the portion of the gas-hquid contactor 200 having one of the packing sections 206A, 206B. Other configurations of a gas-hquid contactor are possible, as described in greater detail below.

[0217] Referring to FIG. 3, each packing section 206 includes one or more structured packings 216. In the implementation of the packing sections 206 of FIG. 3, each packing section 206 includes multiple structured packings 216. Within one of the packing sections 206, each structured packing 216 is arranged adjacent to another structured packing 216. The structured packings 216 of each packing section 206 can be arranged adjacent to each other in the direction of one or more of the packing depth 206D, the packing LTD 206L, and a direction perpendicular to both of the packing depth 206D and the packing LTD 206L. Within one of the packing sections 206, in example implementations one structured packing 216 is attached to another structured packing 216. Within one of the packing sections 206, in example implementations the structured packings 216 of each packing section 206 are arranged next to one another with minimal separation or gaps along one or more of the packing depth 206D, the packing LTD 206L, and a direction perpendicular toboth of the packing depth 206D and the packing LTD 206L.

[0218] Referring to FIG. 3, some of the structured packings 216 of each packing section 206 are mounted to one or both of 1) a structural member 215 of the housing 102, and 2) at least one other structured packing 216. This support of the structured packings 216 reinforces their arrangement within each packing section 206, helps to rigidity each packing section 206, and can also help each structured packing 216 resist or support loads acting upon it during operation of the gas-liquid contactor 200. For example, in mounting the structured packings 216 as described above, the structured packings 216 become constrained which can result in an increase in the overall strength (e.g., crush strength) of each structured packing 216 and of each packing section 206, compared to a packing structure that is unconstrained.

[0219] Referring to FIG. 3, each structured packing 216 includes, or is composed of, multiple packing sheets 230 attached together to form a three-dimensional structured packing 216. The packing sheets 230 of each structured packing 216 can be made of any suitable material, or have any suitable configuration, to achieve the function ascribed to the packing sections 206 herein. Some or all of the packing sheets 230 can be made from PVC, which is relatively light, moldable, affordable, and resists degradation caused by many chemicals. The packing sheets 230 are arranged, constructed, treated or otherwise configured to promote spreading of the liquid sorbent solution 214 into a thin film on the surfaces of the packing sheets 230, which can enable maximum exposure of the liquid sorbent solution 214 to the CO2 present in the CCh-laden air 201. For example, the liquidgas interface surface of one or more of the packing sheets 230 can be treated with a coating, have shapes or formations, and / or be made of a material that vary the surface energy (e.g., increase the surface energy) of portions of the packing sheet 230 and / or lower the contact angle of the liquid sorbent solution 214. For example, the hydrophilicity of the liquid-gas interface surface of one or more of the packing sheets 230 can be increased by applying a coating to increase the surface free energy. Coatings can be applied to some or all of the structured packing 216 to make the structured packing 216 even more suitable for low liquid loading rates ranging from 0.5 L / m2s to 2.5 L / m2s. In this regard, reference is made to such surface treatments and modifications described in U.S. Patent Application Publication No. 2022 / 0176312, the entire contents of which are incorporated herein by reference. Such “film-type” packing sheets 230 are suitable for DAC applications since they have the capacity for effective mass transfer per unit volume of fill space. For example, film-type fill offers a relatively high ratio of specific surface area to volume, theratio defined in units of m2 / m3. A high specific surface area helps to expose more CO2 to the surface of the sorbent solution 214. and also has cost and structural implications. Each packing sheet 230 supports and directs the sorbent solution 214 as it flows along the packing sheet 230. Each packing sheet 230 is shaped, sized, formed, and configured to assist with the transfer of CO2 from the CCh-laden air 201 to the sorbent solution 214. Each packing sheet 230 is thus a medium intended to optimise CO2 from the flowing atmospheric air being absorbed into the flowing sorbent solution 214. Other fill sheets, for example, those used in water cooling tower applications, function primarily to transfer heat between water and atmospheric air, with little or no mass transfer occurring between the constituent gases of the air flow and the water being cooled. By optimizing for the mass transfer of CO2, the packing sheet 230 can be able to achieve lower pressure losses of air flowing across the packing sheet 230 and more optimal distribution of the sorbent solution 214, compared to if the mass transfer of CO2 was attempted with a fill sheet optimised for heat transfer. The packing sheet 230 can be referred to using other terms similar to "sheet." such as panel, pane, plate, and layer. The packing sheet 230 in some cross-flow implementations is also shaped, sized, formed, and configured to assist with the transfer of CO2 from the CCh-laden air 201 to the sorbent solution 214 at low liquid loading rates (e.g., 0.5 L / m2s to 2.5 L / m2s) compared to the higher liquid loading rates (often greater than 15 L / m2s) of cross-flow water cooling tower applications.

[0220] In the structured packing 216 of FIG. 3, all the packing sheets 230 are identical. In example implementations, one or more of the packing sheets 230 of the structured packing 216 is different from another packing sheet 230 of the structured packing 216. In an example implementation, one or more of the packing sheets 230 is optimised for minimal pressure drop across the packing sheet 230, while another one of the packing sheets 230 is optimised for stiffening or being resistant to crushing. Features of the packing sheet 230 can be selected to optimise for mass-transfer capture efficiency, reduced pressure drop, and improved surface wetting, among other possible parameters.

[0221] Different, or additional, componentry to the structured packing 216 can be used to form each packing section 206. For example, in some implementations, one or more of the packing sections 206 are formed of random packing (also referred to as dumped or non-structured packing). In some implementations, one or more of the packing sections 206 includes both structured packing and random packing. In some implementations, one or more of the packing sections 206 is formed of one or more styles of random packing that are positioned in tiers of packing. In some implementations, one or more of thepacking sections 206 includes corrugated packing. In some implementations, one or more of the packing sections 206 includes non-corrugated packing. In some implementations, one or more of the packing sections 206 includes cross-fluted, parallel plate packing.

[0222] The gas-liquid contactor 200 may include other configurations of the one or more packing section(s) 206 in addition to, or separate from, the packing sections 206 described above. Non-limiting examples of other types of packing, fill, and gas-sorbent interfaces 229 include splash fill, film fill, random packing, mesh, panels, etc. The packing section(s) 206 may include corrugated sheets arranged in a crisscrossing relationship to create flow channels for the vapour phase. The packing section(s) 206 may include any material that fills a space and facilitates the contact between the CCh-laden air 201 and a sorbent (liquid and / or solid). The packing section(s) 206 may include: a cross flow geometry designed to limit or minimize the pressure drop in the CCh-laden air 201; can be efficiently wetted by intermittent liquid flows; and, has a liquid hold up enabling intermittent operation with long time durations between wetting.

[0223] The structured packings 216 can be arranged to form packing sections 206 of any desired shape or configuration. For example, and referring to FIG. 3, the structured packings 216 are arranged such that each packing section 206 A, 206B includes at least one arrangement 218 of the structured packings 216. In FIG. 3, each packing section 206A, 206B includes two arrangements 218 of the structured packing 216 - an upper arrangement 218U and a lower arrangement 218L. The structured packings 216 of each arrangement 218 can be arranged adjacent to each other in the direction of one or more of the packing depth 206D, the packing LTD 206L, and the direction perpendicular to both of the packing depth 206D and the packing LTD 206L. All the structured packings 216 of each upper arrangement 218U are positioned above all the structured packings 216 of each lower arrangement 218L. Each arrangement 218 can be considered a “slab” of packing. Other configurations of each arrangement 218, and of the positioning of the arrangements 218 of each packing section 206, are possible. The packing sections 206A, 206B of FIG. 3 are thus vertically sectioned, and include one or more arrangements 218 of structured packings 216 positioned one above another.

[0224] In the example implementation of the packing sections 206 of FIG. 3, each packing section 206 A, 206B has a respective packing section height that is substantially equal to a height of the inlets 2031. Providing the packing sections 206 with substantially the same height as the height of the inlet 2031 can help to prevent or reduce the ability ofthe CCh-laden air 201 to bypass the packing sections 206 (e.g., flow around the packing sections 206), thereby helping to ensure that the greatest possible volume of CCh-laden air201 is treated by the packing sections 206. By “substantially equal” or “substantially the same,” it is understood that the heights are approximately equal in value, with any differences being minimal compared to the overall height dimension, where said differences can result from manufacturing tolerances, packing installation requirements, and / or adjustments in dimensions to allow for seals, baffles or other features. Other configurations for the packing sections 206 are possible. For example, in another implementation, the heights of the packing sections 206A, 206B are less than the height of the inlet 2031, and any gaps between the packing sections 206A, 206B and the housing202 are sealed using suitable techniques.

[0225] The gas-liquid contactor 200 has a gas-circulating device which functions to move gas flows into and out of the gas-liquid contactor 200. In the implementation of the gas-liquid contactor of FIG. 3, the gas-circulating device of the gas-liquid contactor 200 is a fan 221. The fan 221 functions to flow gases like ambient air, such that the CCh-laden air 201 is caused by the fan 221 to flow into the gas-liquid contactor 200, and such that the CCh-lean gas 205 is caused by the fan 221 to be discharged from the gas-liquid contactor 200. The fan 221 thus functions to circulate the CCh-laden air 201 and the CCh-lean gas 205 in the manner described herein. Referring to FIG. 3, the fan 221 is rotatable about a fan axis defined by a fan shaft. In the implementation of the fan 221 depicted in FIG. 3, the fan axis has an upright or vertical orientation. Other orientations for the shaft and for the fan axis are possible, as described in greater detail below. Referring to FIG. 3, the fan 221 is positioned upstream of the end of the fan stack 207 that defines the outlet 2030 relative to a flow direction of the CO2-lean gas 205. The fan 221 functions to induce a flow of the CO2-lean gas 205 through the outlet 2030. In another possible configuration, the fan 221 is positioned elsewhere between the vertically-opposite ends of the fan stack 207 and upstream of the outlet 2030, such that the fan 221 flows the CO2-lean gas 205 through the outlet 2030. Referring to FIG. 3, the fan 221 is positioned downstream of, and above, the upper plenum portion 108U, relative to a flow direction of the CO2-lean gas 205. Rotation of the fan 221 about the fan axis causes gases to flow into the inlets 2031, through the first packing section 206A and the second packing section 206B simultaneously along predominantly horizontal, and opposite, flow directions, and through the gas-liquid contactor 200. For example, in the implementation of the gas-liquid contactor of FIG. 3, rotation of the fan 221 causes the CCh-laden air 201 to be drawn into the gas-liquidcontactor 200 and causes the CCh-lean gas 205 to be discharged from the gas-liquid contactor 200. The fan 221 can cause the C Ch- laden air 201 to enter the packing sections 206 at airspeeds below 5 m / s. The fan 221 can cause the CCh-laden air 201 to enter the packing sections 206 at airspeeds between 0.1 m / s and 5 m / s.

[0226] Referring to FIG. 3, the gas-liquid contactor 200 has, includes components of, or is functionally linked to, a liquid distribution system 220. The liquid distribution system 220 operates to move, collect and distribute the sorbent solution 214 and / or the carbon- loaded sorbent solution 211. At least some of the features of the liquid distribution system 220 are supported by the housing 202 and / or structural members 215. In the example implementation of FIG. 3, the support is such that components of the liquid distribution system 220 are structurally supported by the housing 202 and / or by structural members 215, so that loads generated by these components are supported. Some or all of the features of the liquid distribution system 220 can be part of the gas-liquid contactor 200, or part of a DAC system of the present disclosure.

[0227] Referring to FIG. 3, the liquid distribution system 220 includes one or more liquid collection devices 109. Each liquid collection device 209 is configured to receive one or both of the sorbent solution 214 and the carbon-loaded sorbent solution 211 and to hold a volume thereof temporarily or for a longer duration, thereby serving as a source of the sorbent solution 214 and / or of the carbon-loaded sorbent solution 211. Each liquid collection device 209 can have any configuration or be made of any material suitable to achieve the function ascribed to it in the present description. For example, one or more of the liquid collection devices 209 can be open-topped, or partially or fully covered. In FIG. 3, one or more of the liquid collection devices 209 include, or are in the form of, basins. Other configurations of the liquid collection device 209 are possible, such as a reservoir, a bed, a sheet, a culvert, a pan, a container, a receptacle, a network of pressurized pipes with openings or spray nozzles, or any other device capable of retaining liquid.

[0228] The liquid collection devices 209 of the liquid distribution system 220 include one or more top basins 204 and one or more bottom basins 210. The top basins 204 are supported by the housing 202 and / or by the structural members 215. In example implementations, the top basins 204 are formed from portions of the housing 202. The top basins 204 are configured to at least partially enclose or store the sorbent solution 214. Referring to FIG. 3, the top basins 204 are each positioned at least partially above the packing sections 206. Referring to FIG. 3, the top basins 204 are positioned above the inlets 2031. Referring to FIG. 3, the top basins 204 are positioned beneath the upper plenumportion 208U. Part of the plenum 208 (e.g., the upper plenum portion 208U) thus extends beyond or above the top basins 204. When stored (at least transiently) within the top basins 204, the sorbent solution 214 is positioned to be circulated (e.g., through pumping, gravity flow or both) predominantly vertically downward, through each of the packing sections 206A, 206B at the same time, and ultimately into the bottom basin 210. As the sorbent solution 214 flows through the packing sections 206, the CCh-laden air 201 is flowed through the packing sections 206 to contact the sorbent solution 214, then through the plenum 208, and ultimately to an ambient environment as the CCh-lean gas 205. A process stream is formed by contacting the CCh-laden air 201 and the liquid sorbent solution 214, where the process stream is or includes the carbon-loaded sorbent solution 211 having CO2 absorbed from the CCh-laden air 201 by the sorbent solution 214. The top basins 204 can each have any suitable form or feature for distributing the sorbent solution 214 over the packing sections 206. In the example implementation of the gas-liquid contactor 200 of FIG. 3, the liquid collection devices 209 include two top basins 204. Each top basin 204 is positioned above one of the packing sections 206A, 206B to distribute the sorbent solution 214 to the respective packing section 206A, 206B. The top basins 204 of FIG. 3 are fluidly isolated from one another (e.g., no fluid communication between the two top basins 204). Other configurations and numbers of the top basins 204 are possible. Other configurations for the distribution of the sorbent solution 214 over the packing sections 206 is possible. In one such possible configuration, the one or more of the liquid collection devices 209 include, or are in the form of, a network of pressurized pipes with openings or spray nozzles which distribute the sorbent solution 214 over the uppermost portions of the packing sections 206.

[0229] Referring to FIG. 3, the one or more bottom basins 210 are positioned at the bottom of the gas-liquid contactor 200 opposite the top basins 204. As can be seen in FIG. 3, the bottom basin 210 is positioned below the packing sections 206. The bottom basin 210 acts as a collection tank for the process stream (e.g., the carbon-loaded sorbent solution 211). The carbon-loaded sorbent solution 211 including absorbed CO2, as well as unreacted sorbent solution 214, collects in the bottom basin 110, and can then be pumped or otherwise moved out of the bottom basin 210 for further processing. For example, at least a portion of the liquids collected in the bottom basin 210 can be processed and then pumped for redistribution over the packing sections 206 for use in CO2 capture. In another possible implementation, some or all of the liquids collected in the bottom basin 210 is pumped to the top basins 204 without being processed, for redistribution over the packingsections 206 for CO2 capture. In another possible implementation, some or all of the liquids collected in the bottom basin 210 are pumped to components of a DAC system, such as DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902, for further processing, as described in greater detail below. The bottom basin 210 can be compatible with a containment structure and prevent loss of various sorbent solutions 214, some of which might have corrosive, caustic or high pH properties. In some aspects, the bottom basin 210 can be lined or coated with one or more materials that are resistant to caustic induced corrosion or degradation. In example implementations of the gas-liquid contactor 200, components can be kept out of the bottom basin 210 holding the sorbent solution 214. Additionally, the gas-liquid contactor 200 can be designed to keep most or all the structural components out of the wettable area of the gas-liquid contactor 200, e.g., any portion of the gas-liquid contactor 200 that is in contact with the sorbent solution 214. Examples of wettable areas of the gas-liquid contactor 200 includes components supporting the packing sections 206. FIG. 3 depicts a single bottom basin 210. However, other configurations and numbers of bottom basins 210 are possible. One or both of the top and bottom basins 204, 210 can include liquid-manipulation componentry such as weirs, valves, piping, manifolds, and spray nozzles.

[0230] In example implementations, the gas-liquid contactor 200 includes vertically sectioned packing sections 206 with redistribution of the sorbent solution 214between the vertically-spaced apart packing. For example, and referring to FIG. 3, the liquid collection devices 209 of the liquid distribution system 220 include one or more redistribution basins 219. The one or more redistribution basins 119 are each positioned in a redistribution spacing that is defined between the upper and lower arrangements 218U, 218L of each packing section 206A, 206B. The redistribution spacing is a vertically-extending gap defined between the upper and lower arrangements 218U, 218L of each packing section 206A, 206B. Each packing section 206A, 206B includes a redistribution basin 219, which is positioned in the redistribution spacing of that packing section 206 A, 206B. Thus, in the configuration of packing sections 206A, 206B of FIG. 3, each redistribution basin 219 divides each packing section 206A, 206B into at least a top section (e.g., the upper arrangement 218U of structured packings 216) and a bottom section (e.g., the lower arrangement 218L of structured packings 216). Each redistribution basin 219 is located vertically between the one or more top basins 204 and the bottom basin 210. During operation of the gas-liquid contactor 200, a process stream including the carbon-loaded sorbent solution 211 including absorbed CO2 as well as unreacted sorbent solution 214flows from each upper arrangement 218U of structured packings 216 and collects in each redistribution basin 219. When stored (at least transiently) within the redistribution basins 219, the process stream is positioned to be redistributed (e.g., through pumping, gravity flow or both) downwards, through the remaining structured packings 216 of the lower arrangement 218L and eventually into the bottom basin 210. In example implementations, the process stream is pumped into the redistribution basins 219 from the bottom basin 210. The redistribution basins 219 can each have any suitable form or feature for redistributing the process stream over the structured packings 216 of the of the lower arrangement 218L. Non-limiting examples of features of the redistribution basins 219 include basin walls, redistribution apertures, and redistribution nozzles. Thus, in the gas-liquid contactor 200, there can be a collector / distributor system between vertical sections of packing that collects fluid flowing from above and redistnbutes it evenly to the packing below. The description and one, some, or all of the advantages, and functions of features of the top basins 204 and of the bottom basin 210 apply mutatis mutandis to the redistribution basins 219.

[0231] In example implementations of redistribution of the sorbent solution 214 between the vertically-spaced apart packing, the packing sections 206 themselves include redistribution features. The redistribution features can be part of redistribution packing that is different from the structured packings 216. The redistribution packing can have a vertical extent and be positioned between arrangements 218U, 218L of structured packings 216, for example mid-way up the packing LTD 206L. Alternatively, the redistribution packing can include multiple redistribution packing portions alternating with arrangements 218U, 218L of structured packings 216. The redistribution features promote redistribution of the sorbent solution 214 to lower portions of the packing sections 206. In example implementations of the gas-liquid contactor 200, the gas-liquid contactor 200 does not include vertically-sectioned packing or redistribution.

[0232] The gas-liquid contactor 200 can include supports positioned within the packing sections 206 between the top basins 204 and bottom basin 210. For example, the packing sections 206 can include additional support, such as one or more structural members 215, for a specific portion of the packing sections 206, such as for an upper portion of the packing sections 206, so that the loads (e.g., the weight of the portion of structured packings 216 when dry plus the weight of the liquid hold up of the sorbent solution 214 on the portion of the structured packings 216) do not bear upon another portion of thepacking sections 206 (e.g., a bottom portion of the packing sections 206). In some implementations, the packing sections 206 do not include the support. In some implementations, at least one structural support can be positioned between the structured packings 216 of the packing sections 206.

[0233] The liquid distribution system 220 can include any suitable componentry, such as piping, weir(s), pump(s), valve(s), manifold(s), etc., fluidly coupled in any suitable arrangement, to achieve the functionality ascribed to the liquid distribution system 220 herein. One non-limiting example of such componentry is one or more pump(s) 222, an example of which is shown in FIG. 3. The pumps 222 function to move liquids under pressure, such as the sorbent solution 214and / or the carbon-loaded sorbent solution 211, from their source to where they are used or processed. Some non-limiting examples of possible functions of the pumps 222 include moving the sorbent solution 214 to the top basins 204, moving the process streams from the bottom basin 210 to the redistribution basins 219, moving the sorbent solution 214 and / or the carbon-loaded sorbent solution 211 from the bottom basin 210 to the top basins 204 for redistribution over the packing sections 206, moving the sorbent solution 214 and / or the carbon-loaded sorbent solution 211 from the bottom basin 210 to components of the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 for further processing, and any combination of the preceding flows. The pumps 222 can thus be used to move liquid to, from and within the gas-liquid contactor 200.

[0234] A control system (e.g., control system 999 shown in FIG. 3) can be used to control the flow of fluid by the pumps 222 of the liquid distribution system 220. For example, a control system can be used to control the pumps 222 in order to pump the sorbent solution 214 from the bottom basin 210 to the top basins 204. The pumps 222 can also be controlled such that a constant velocity of flow is provided to the liquid distribution system 220 regardless of changes of liquid flow throughout the gas-liquid contactor 200.

[0235] The pumps 222 can help to distribute the sorbent solution 214 over the packing sections 206 at relatively low liquid flow rates, which can help to reduce costs associated with pumping or moving the sorbent solution 214. Further, low liquid flow rates of the sorbent solution 214 over the packing sections 206 can result in a lower pressure drop of the CO2-laden air 201 as it flows through the packing sections 206, which reduces the energy requirements of the device used for moving the C Ch-laden air 201 across the packing sections 206 (e.g., a fan 221 described below). The pumps 222 can be configuredto generate intermittent or pulsed flow of the sorbent solution 214 over the packing sections 206, which can allow for intermittent wetting of the packing sections 206 using relatively low liquid flows. The sorbent solution 214 sprayed, flowed, or otherwise distributed over the packing sections 206 is collected in the bottom basin 210 and can then be moved by the pumps 222 back to the top basin 204, or sent elsewhere for processing.

[0236] In example implementations, and referring to FIG. 3, the one or more pump(s) 222 of the liquid distribution system are operable to flow the sorbent solution 214 over each packing section 206 at a liquid loading rate ranging from 0.5 L / m2s to 10 L / m2s. In example implementations, the liquid loading rate is between 2 L / m2s and 6 L / m2s. The units L / m2s of the liquid loading rate refer to a given volume of the sorbent solution 214 covering a given area of the packing section 206, each second. The given area of the packing section 206 can refer to a plane area of a top of the packing section 206, such as the area of the packing section 206 underneath the top basin 204 (e.g., looking down on the top part of the packing section 206 from the top basin 104). When determined using the plane area, a liquid loading rate of 2 L / m2s means that the pump(s) 222 is configured to flow the sorbent solution 214 over each packing section 206 such that every second each square meter of the plane area of the packing section 206 receives 2 L of the sorbent solution 214. The given area of the liquid loading rate may not refer to the area of a surface of the structured packing 216. The liquid loading rate can refer to, or be reflective of, an initial flow condition where the sorbent solution 214 is applied to the top of the packing section 206. The liquid loading rate may not reflect subsequent flow conditions present lower down the packing section 206.

[0237] In example implementations, and referring to FIG. 3, the CCh-lean gas stream 205 can contain components of the CO2 capture solution 214, and possibly also components of the CC -laden capture solution 211. The components of the CO2 capture solution 214 and possibly also of the CC -laden capture solution 211 can be in liquid and / or vapour phase, and may be present in the flow of the CCh-lean gas stream 205 such that they can flow with the CCh-lean gas stream 205 out of the gas-liquid contactor 200. The components in the CCh-lean gas stream 205 can include, but are not limited to, alkali hydroxides, carbonic anhydrase, amines (primary, secondary, tertiary), amino acids, carbonates, bicarbonates and any combinations thereof. The size and phase of the components can vary based on numerous factors, non-limiting examples of which include the physical and / or chemical properties of the CO2 capture solution 214, ambient and / or solution temperature, and the relative humidity of ambient and / or of the CCh-laden air 201.For example, in implementations where the capture species of the CO2 capture solution 214 includes one or more amine species, the components can include volatilized amine components which are in vapour or gas phase and are in equilibrium with the CCh-lean gas stream 205, due to the volatility of the amine species resulting from its high vapour pressure at most ambient conditions. In some examples, in implementations of the present disclosure where the capture species of the CO2 capture solution 214 includes one or more alkali hydroxides species, the components can be in liquid phase as liquid airborne particles and can be entrained by, or suspended in, the CCh-lean gas stream 205, due to the comparatively low volatility of the alkali hydroxide species resulting from its relatively low vapour pressure at most ambient conditions. In some examples, in implementations of the present disclosure where the capture species of the CO2 capture solution 214 includes two or more species which have both high and low volatilities, the components can be in both vapour phase, and liquid phase as liquid airborne particles. In such examples of liquid airborne particles, the airborne particles can be liquid aerosol particles of the CO2 capture solution 214 that are suspended in the CCh-lean gas stream 205 and can range in size from less than 1 micron to over 70 microns. In such examples of liquid aerosol particles, the liquid aerosol particles of the CO2 capture solution 214 that are suspended in the CCh-lean gas stream 205 can have a size less than 2.5 microns.

[0238] Solid airborne particles can also be entrained in the CCh-lean gas stream 205. Depending on such non-limiting factors as the physical and / or chemical properties of the CO2 capture solution 214, the reaction products of the CO2 capture solution 214 with CO2 (carbon dioxide derived species), the solids present in liquid flows returning to the gasliquid contactor 200, and the environment in which the gas-liquid contactor 200 is operating, solid airborne particles can be suspended in the CC -lean gas stream 205 flowing from the gas-liquid contactor 200. Such solid airborne particles can be, or can include non-process elements (NPEs) which are desirable to remove from the gas flows exiting the gas-liquid contactor 200. The present disclosure describes measures to reduce or eliminate these solid airborne particles, as described in greater detail below.

[0239] Referring to FIG. 3, the gas-liquid contactor 200 can include one or more portions of drift eliminators 217 to remove or reduce one or more of the sorbent solution 214, the CCh-laden capture solution 211 and solid airborne particles that may be entrained in the CCh-lean gas 205 and exhausted from the outlet 2030. The CO2 capture solution 214 and / or the CO2-laden capture solution 211 entrained in the CO2-lean gas 205 can be referred to as “drift” or “mist”, and can be in liquid aerosol form or as volatilizedcomponents. The drift eliminators 217 (sometimes referred to as “mist eliminators”) are positioned downstream of the packing 206 relative to a flow direction of the CCh-laden air 201, and function to eliminate drift (z.e., remove 100% of aerosolized or volatilized particles) or to reduce the amount of drift (z.e., remove less than 100% of aerosolized or volatilized particles) exiting the gas-liquid contactor 200 through the outlet 2030. For example, in implementations where the capture species of the CO2 capture solution 214 includes one or more amine species, the drift eliminators 217 help to remove or reduce the aerosolized and / or volatilized amine components from the CO2-lean gas stream 205. The drift eliminators 217 may include componentry of the passive type, of the active type, or both. Non-limiting examples of passive componentry for the drift eliminators 217 include baffles, vanes, slats, and packing material. Non-limiting examples of active componentry for the drift eliminators 217 include wash or scrubbing componentry, and electrostatic componentry. The drift eliminators 217 can include both passive and active componentry, in any combination. In some implementations, the drift eliminator 217 can be provided horizontally across the plenum 208 and upstream of the fan 221.

[0240] If not processed, referring to FIG. 3, the produced CCh-lean gas 205 can contain volatilized compounds and / or aerosolized particles of at least one of the (unloaded) sorbent solution 214 and the loaded sorbent solution 211. In some implementations, makeup water can be supplied to the gas-liquid contactor subsystem 200, e.g., to at least one wash section that would scrub entrained sorbent from the CCh-lean gas 205 before exiting the gas-liquid contactor subsystem 200. Scrubbing the CCh-lean gas 205 can reduce a sorbent solution makeup rate and reduce sorbent (e.g., BIG freebase) makeup costs accordingly.

[0241] Referring to FIGS. 4 to 7, in some implementations, the gas-liquid contactor 200A, 200B, 200C and 200D include at least one wash section 303, 403, 503, 603. The wash section 303, 403, 503, 603 help to reduce or eliminate emissions (e.g., the drift described above) from the gas-liquid contactor 200A, 200B, 200C, 200D. The emissions reduced or eliminated from the gas-liquid contactor 200A, 200B, 200C, 200D can include one or more of: volatilized components of the sorbent solution, and aerosolized / airbome particles of the sorbent solution, as described in greater detail below. The at least one wash section 303, 403, 503, 603 is positioned adjacent to and in fluid communication with the packing section 306, 406, 506. In example implementations, the at least one wash section 303, 403, 503, 603 includes one or more sections of wash section packing. The one or more sections of wash section packing can be positioned lower than the fan 321, 421, 521.In the wash section 303, 403, 503, 603, the CCh-lean gas stream including volatilized components and / or airborne particles of the CO2 capture solution 206 is contacted with a wash water stream. The wash water stream can flow along or through the wash section packing helping to scrub the volatilized components and / or the airborne particles from the CCh-lean gas stream to form a washed CCh-lean gas stream 234 and a used wash water stream. The presence of the volatilized components and / or the airborne particles in the washed CCh-lean gas stream 234 is reduced as a result of washing the CCh-lean gas stream with the wash water stream. In example implementations, the volatilized components and / or the airborne particles are eliminated from the washed CCh-lean gas stream 234. In example implementations, the volatilized components and / or the airborne particles are reduced in the washed CCh-lean gas stream 234 to such an extent that their potential emission from the gas-liquid contactor 200B, 200C, 200D and 200E complies with applicable air emission standards or regulations.

[0242] The flow rates of the wash water stream provided to the wash section packing of the at least one wash section 303, 403, 503, 603 can vary. For example, in some implementations, the flow rate of the wash water stream is between 1% and 500% of the flow rate of the sorbent solution 206 provided to the capture section packing 306, 406, 506. In some implementations where the sorbent solution 214 includes an amine or amino acid, as the at least one capture species (sorbent), the flow rate of the wash water stream provided to the wash section packing is between 40% and 80% of the flow rate of the sorbent solution 206. The flow rate of the wash water stream provided to the wash section packing can be dependent on numerous factors, non-limiting examples of which include the volatility of the capture molecule in the solvent, and the concentration of the capture molecule in the solvent.

[0243] The gas-liquid contactor can include a wash section liquid distribution system including one or more liquid collection devices as defined herein.

[0244] Referring to FIGS. 4 to 7, the at least one wash section 303, 403, 503, 603 allows for the gas-liquid contactor subsystem 200B, 200C, 200D, 200E to use a variety of sorbent solutions 206, and help to broaden the choice of suitable sorbent solutions 206 beyond those whose air emissions can only be managed using conventional techniques. For example, the at least one wash section 303, 403, 503, 603 allow for amine or amino acid capture species to be used in the sorbent solution 206 despite the potential volatility of these capture species and associated health and environmental issues, because the washsection 303, 403, 503, 603 allows for reducing or eliminating the volatile amine to acceptable levels.

[0245] Referring to FIG.4, the flow of the sorbent solution 206 through the packing 306 is counter-current (or counterflow) to the flow of the CCF- laden air 204 through the packing 306. The packing liquid travel dimension along which the CO2 capture solution 206 flows through the packing 306 is defined along the vertical direction and is the same as the packing depth along which the CCh-laden air 204 flows upwardly through the packing 306. A portion of the CO2 within the CCh-laden air 204 is transferred to (e.g., absorbed by) the CO2 capture solution 206, and the fan 321 moves the CO2 lean gas 234 out of the gas-liquid contactor subsystem 200A to an ambient environment through the wash section 303. The wash section is positioned downstream of the packing 306 and upstream of the fan 321.

[0246] In the configuration of FIG. 5, the gas-liquid contactor subsy stem 200B has only one section of packing 406 and may therefore be referred to as a “single cell” gas-liquid contactor subsystem 200B. The CO2 capture solution 206 circulates downwards by, for example, gravity flow, uniform or laminar flow, etc., within the packing 406 and eventually flows into one or more bottom basins 410. As the CO2 capture solution 206 circulates through the packing 406, the CCh-laden air 204 is flowing (e.g., by action of the fan 421) substantially horizontally through the packing 406 to thereby contact the CO2 capture solution 206. Thus, the flow of CO2 capture solution 206 through the packing 406 in FIG. 5 is substantially perpendicular to the flow of the CO2-laden air 204 through the packing 406. Such a configuration of the flows may be referred to as a “cross flow” configuration. The packing liquid travel dimension along which the CO2 capture solution 206 flows through the packing 406 is defined along the vertical direction, and is perpendicular to the packing depth along which the CCh-laden air 204 flows horizontally through the packing 406. A portion of the CO2 within the CCh-laden air 204 is transferred to the CO2 capture solution 206, and the fan 421 moves the CCh-lean gas 234 out of the gas-liquid contactor subsystem 200B to an ambient environment through the wash section 403. The wash section 403 is positioned downstream of the packing 406 and upstream of the fan 421. The CO2 rich solution flows into the at least one bottom basin 410.

[0247] Referring to FIG. 6, another possible configuration of a gas-liquid contactor subsystem 200C has an upright body and an air inlet 505 along atop portion through which the CO2-laden air 204 is admitted into the gas-liquid contactor subsystem 200C. The fan 521 rotates to push the CO2- laden air 204 into the gas-liquid contactor subsystem 200Cand contact the packing section 506. In the configuration of FIG. 6, the gas-liquid contactor subsystem 200C has only one packing section 506 and can therefore be referred to as a “single cell” gas-liquid contactor. The CO2 capture solution 206 circulates downwards by, for example, gravity flow, uniform or laminar flow, etc., within the packing 506 and eventually flows into one or more bottom basins 510. As the CO2 capture solution 206 circulates downward through and over the packing 506, the C Ch-laden air 204 (e.g., by action of the fan 521) also flows downward through the packing 506 to contact the CO2 capture solution 206. Thus, the flow of the CO2 capture solution 206 through the packing 506 in FIG. 6 is co-current to the flow of the CC -laden air 204 through the packing 506. The packing liquid travel dimension along which the CO2 capture solution 206 flows through the packing 506 is defined along the vertical direction, and is the same as the packing depth along which the CCh-laden air 204 flows downwardly through the packing 506. At least a portion of the CO2 within the CCh-laden air 204 is transferred to (e.g., absorbed by) the CO2 capture solution 206, and the fan 521 pushes the CCh-lean gas 234 through the wash section 503 and out of the gas-liquid contactor subsystem 200C to an ambient environment. The wash section 303 is positioned downstream of the packing 506.

[0248] In implementations as illustrated in FIG. 7, the wash section 603 is positioned adjacent an outlet 302 of the gas-liquid contactor subsystem 200D. Some non-limiting examples of possible configurations for the gas-liquid contactor subsystem 200D include being a modular unit, being rounded or circular, being a cell of an array or train of gasliquid contactor subsystems 200D being a cell of a rounded or circular gas-liquid contactor subsystem 200D and being a component of a heating, ventilation, and air conditioning (HVAC) system. The gas-liquid contactor subsystem 200D may include, or be fluidly coupled to, devices for managing liquid levels in the gas-liquid contactor subsystem 200D. These devices may include, but are not limited to, evaporators to reduce liquid levels and / or maintain concentrations of the CO2 capture solution 206. These devices may include, but are not limited to, water make-up tanks or sources to manage liquid levels and / or maintain concentrations of the CO2 capture solution 206. The description, units, componentry, features, streams, reference numbers and advantages of the gas-liquid contactor 200 provided in relation to FIG. 3 apply mutatis mutandis to the gas-liquid contactor subsystems 200A, 200B, 200C, 200D of FIGS. 4 to 7. The positioning and the orientation of the wash section 303 may vary. The wash section 303 may have a horizontal orientation. In some implementations, and referring to FIG. 3 for example, the gas-liquid contactor subsystem 200 can be adapted to include at least one wash section in each “cell”that may have a vertical orientation and being positioned upstream of the fan 221.

[0249] In some implementations, the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 includes a control system 999 communicably coupled to the components (illustrated or otherwise). The liquid process streams in the at least one gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D, as well as process streams within any downstream processes with which the at least one gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D is fluidly coupled, can be flowed using one or more flow control systems (e.g., control system 999). A flow control system can include one or more flow pumps (including or in addition to the pumps 222), fans, blowers, or solids conveyors to move the process streams, one or more flow pipes through which the process streams are flowed and one or more valves to regulate the flow of streams through the pipes. Each of the configurations described herein can include at least one variable frequency drive (VFD) coupled to a respective pump that is capable of controlling at least one liquid flow rate. In example implementations, liquid flow rates are controlled by at least one flow control valve. For example, the control system 999 shown in FIG. 4 can be used to control the speed and / or blade pitch of the fan 321. The control system 999 of FIG. 4 can be communicatively coupled to one or more sensors of the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 to help process information received from such sensors, and to communicate commands to componentry whose functions are linked to the such sensors.

[0250] In some implementations, the control system 999 comprises a flow control system that can be operated manually. For example, an operator can set a flow rate for each pump or transfer device and set valve open or closed positions to regulate the flow of the process streams through the pipes in the flow control system. Once the operator has set the flow rates and the valve open or closed positions for all flow control systems distributed across the DAC system, the flow control system can flow the streams under constant flow conditions, for example, constant volumetric rate or other flow conditions. To change the flow conditions, the operator can manually operate the flow control system, for example, by changing the pump flow rate or the valve open or closed position.

[0251] In some implementations, the control system 999 comprises at least one flow control system that can be operated automatically. For example, the control system 999 can include one or more processors and a computer-readable medium storing instructions (such as flow control instructions and other instructions) executable by the one or more processors to perform operations (such as flow control operations) by the flow controlsystem. An operator can set the flow rates and the valve open or closed positions for all flow control systems distributed across the facility using the control system. In such embodiments, the operator can manually change the flow conditions by providing inputs through the control system 999. Also, in such embodiments, the control system 999 can automatically (that is, without manual intervention) control one or more of the flow control systems, for example, using feedback systems connected to the control system. For example, a sensor (such as a pressure sensor, temperature sensor or other sensor described herein) can be connected to a pipe through which a process stream flows. The sensor can monitor and provide a flow condition (such as a pressure, temperature, or other flow condition) of the process stream to the control system. In response to the flow condition exceeding a threshold (such as a threshold pressure value, a threshold temperature value, or other threshold value), the control system can automatically perform operations. For example, if the pressure or temperature in the pipe exceeds the threshold pressure value or the threshold temperature value, respectively, the control system can provide a signal to the pump to decrease a flow rate, a signal to open a valve to relieve the pressure, a signal to shut down process stream flow, or other signals.

[0252] Although reference numbers may differ, it is noted that the description, units, componentry, features, streams and advantages of the gas-liquid contactor 103, 03, 200, 200A, 200B, 200C, 200D provided herein apply mutatis mutandis to the carbon dioxide capture system 1 of FIGS. 10.

[0253] Referring to FIGS. 8 and 9, each gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D can be grouped together with one or more other gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D to provide the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 with one or more wall(s), array (s) or train(s), where each wall, array or train has multiple gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D. For example, and referring to FIGS. 8 and 9, multiple gas-liquid contactors 10, 103, 03, 200, 200 A, 200B, 200C, 200D are arranged next to one another to form a contactor wall 1502. The number of gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D composing the contactor wall 1502 may vary (as represented by the ellipsis symbol “[... ]” in FIG. 8). The contactor wall 1502 may include a large number of gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D, for example between 10 and 100 gas-hquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D. In some implementations, the number of gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D in the contactor wall 1502 is greater than 1,000. The numberof gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D in the contactor wall 1502 may be determined based on a variety of factors, such as a plume of CCh-lean gas205 generated by the contactor wall 1502 during operation of the gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D. The contactor wall 1502 extends along its own wall axis 1509. The wall axis 1509 extends along a direction that is perpendicular to the packing depth of the packing 206 of the gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D, and perpendicular to the packing LTD of the packing 206 of the gasliquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D.

[0254] In implementations where the gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D are positioned (e.g., directly) adjacent each other, and referring to FIG. 8, they may be abutted along a dividing wall 1525 which fluidly separates components of one gas-liquid contactor 10, 103, 03, 200, 200 A, 200B, 200C, 200D from an adjacent gasliquid contactor 10, 103, 03, 200, 200 A, 200B, 200C, 200D. The dividing wall 1525 helps to ensure that the CCh-laden air 201 flowing through the air inlet 2031 of a gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D flows through the packing section(s)206 of that gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D, rather than into an adjacent gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D. The dividing walls 1525 extend in an upright or vertical direction, and along a direction parallel to the packing depth 206D. In example implementations, the vertical extent of one or more of the dividing walls 1525 begins at, or below, the liquid level in the bottom basin 210. This configuration of the dividing walls 1525 can help to minimise or eliminate air bypassing the dividing walls 1525. The plenum 208 of each gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D is separated from the plenum 208 of an adjacent gasliquid contactor 10, 103, 03, 200, 200 A, 200B, 200C, 200D by one or more dividing walls 1525. At least some of the dividing walls 1525 are internal to the contactor wall 1502. Each dividing wall 1525 forms a barrier to airflow between the adjacent plenums 208 delimited by that dividing wall 1525, so as to prevent air from flowing between the plenums 208. The dividing walls 1525 may allow for multiple gas-liquid contactors 10, 103, 03, 200, 200 A, 200B, 200C, 200D of the contactor wall 1502 to remain operational if one of the gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D or its fan 221 is deactivated. The dividing walls 1525 of FIG. 8 are internal to the contactor wall 1502, and it will be appreciated that the contactor wall 1502 can have externally-applied dividing walls 1525 at opposite longitudinal ends of the contactor wall 1502. The plenums 208 are arranged adjacent each other along the length of the contactor wall 1502 definedalong the wall axis 1509. In other implementations, the contactor wall 1502 includes a single plenum 208 that is continuous along its length defined parallel to the wall axis 1509, such that the contactor wall 1502 is free of internal dividing walls 1525. In other implementations, the contactor wall 1502 includes multiple plenums 208 delineated by the dividing walls 1525, where two or more gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D of the contactor wall 1502 share a common plenum 208. In some implementations, the dividing walls 1525 include doors or closeable openings, to provide access to the interior 213 of adjacent gas-liquid contactors 10, 103, 03, 200, 200A, 200B, 200C, 200D. In example implementations, and referring to FIG. 8, the contactor wall 1502 includes multiple plenums 208, where each gas-liquid contactor 10, 103, 03, 200, 200A, 200B, 200C, 200D forming the contactor wall 1502 has one plenum 208. Each plenum 208 is separated from an adjacent plenum 208 by one or more dividing walls 1525. In the example implementation of FIG. 8, each dividing wall 1525 shown is located between two fan stacks 207, and forms a barrier to airflow between two plenums 208 delimited by that dividing wall 1525, where each plenum 208 is in fluid communication with a respective one of the fan stacks 207.

[0255] The contactor wall 1502 can be part of a carbon dioxide capture system, such as the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902. Referring to FIG. 9, each DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 can include multiple contactor walls 1502 arranged on a plot of land 1505. Each contactor wall 1502 is spaced apart from another contactor wall 1502. In this disclosure, the terms “train”, “array” and “wall” may be used interchangeably. The DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 of FIG. 9 is shown with multiple contactor walls 1502 for the purposes of illustration. The DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 can alternatively have only one contactor wall 1502. Referring to FIG. 9, the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902 includes a regeneration subsystem 11, 180 including one or more units such as one or more of those described above, in fluid communication with the contactor walls 1502. The regeneration subsystem 11, 180 functions to regenerate the carbon-loaded sorbent solution and the complexing agent, the carbon-loaded sorbent solution being received from the contactor walls 1502, or from other componentry that treats the carbon-loaded sorbent solution from the contactor walls 1502. The regeneration subsystem 11 forms a regenerated sorbent (e.g., in unloaded sorbent solution) that is conveyed back to the contactor walls 1502. Theregeneration system 11, 180 can also function to release CO2 from the carbonate / bicarbonate salt of the iminoguanidine compound (unsaturated nitrogenous compound), to produce the CO2 product stream and regenerate the complexing agent (e.g., imininoguanidine in freebase or salt form according to formula (I) or (II)). In example implementations, and referring to FIG. 9, each contactor wall 1502 has a single or common bottom basin 210. In such implementations, the bottom basin 210 of each contactor wall 1502 is in fluid communication with the regeneration system 11, 180. In example implementations, the process streams from the bottom basin 210 of a contactor wall 1502 flows, or is flowed, to the bottom basin 210 of another contactor wall 1502.

[0256] Many of the methods described herein can be implemented in systems comprising one or more units / subsystems such as illustrated in FIGS. 3 to 9. Many of these units and subsystems may have one or more controllers (as per the control system of the present disclosure) or other logic for controlling the operations they perform. As examples, the one or more controllers may control the operation of crystallizers, reactors, separators, contactors, regenerators, as well as associated pumps, flow controllers, filters, heaters, and / or other components of a system or subsystem. The at least one controller or logic may employ program instructions such as executable instructions on computer- readable medium. The instructions may be executed by computer-executable components such as those integrated with a communication system. The computer-readable medium may be stored on any suitable computer readable media such as RAMs, ROMs, flash memory, EEPROMs, optical devices, hard dnves, or any suitable device. The controller may also have one or more processors such as microprocessors, microcontrollers, programmable logic devices, etc. In some embodiments, the executable instructions are alternatively or additionally be embedded in a dedicated hardware device such as any of the one or more processors.

[0257] FIG. 10 is a schematic diagram of a control system, such as control system 999(or controller), which may be used for example with the DAC system 1, 100, 102, 104, 106, 108, 110, 112, 700, 702, 704, 706, 800, 802, 900, 902, at least one gas-liquid contactor 10, 103, 03, 200, 200 A, 200B, 200C, 200D and the capture solution regeneration subsystem 11, 180. The control system 999 can be used for the operations described in association with any of the computer-implemented methods described previously, for example as or as part of controllers described herein.

[0258] The control system 999 is intended to include various forms of digital computers, such as laptops, desktops, workstations, personal digital assistants, servers, blade servers,mainframes, and other appropriate computers. The control system 999 can also include mobile devices, such as personal digital assistants, cellular telephones, smartphones, and other similar computing devices. Additionally, the control system can include portable storage media, such as, Universal Serial Bus (USB) flash drives. For example, the USB flash drives may store operating systems and other applications. The USB flash drives can include input / output components, such as a wireless transmitter or USB connector that may be inserted into a USB port of another computing device.

[0259] The control system 999 includes aprocessor 910, amemory 920, astorage device 930, and an input / output device 940. Each of the components 910, 920, 930 and 940 are interconnected using a system bus 950. The processor 910 is capable of processing instructions for execution within the control system 999. The processor may be designed using any of a number of architectures. For example, the processor 910 may be a CISC (Complex Instruction Set Computers) processor, a RISC (Reduced Instruction Set Computer) processor, or a MISC (Minimal Instruction Set Computer) processor.

[0260] In one implementation, the processor 910 is a single-threaded processor. In example implementations, the processor 910 is a multi-threaded processor. The processor 910 is capable of processing instructions stored in the memory 920 or on the storage device 930 to display graphical information for a user interface on the input / output device 940.

[0261] The memory 920 stores information within the control system 999. In one implementation, the memory 920 is a computer-readable medium. In one implementation, the memory 920 is a volatile memory unit. In example implementations, the memory 920 is a non-volatile memory unit.

[0262] The storage device 930 is capable of providing mass storage for the control system 999. In one implementation, the storage device 930 is a computer-readable medium. In various different implementations, the storage device 930 may be a floppy disk device, a hard disk device, an optical disk device, or a tape device.

[0263] The input / output device 940 provides input / output operations for the control system 999. In one implementation, the input / output device 940 includes a keyboard and / or pointing device. In example implementations, the input / output device 940 includes a display unit for displaying graphical user interfaces.

[0264] In example implementations, the processor 910 is configured to execute a machine learning model (e.g., an artificial intelligence model) that employs multiple layers of models to generate an output for a received input. A deep neural network is a deep machine learning model that includes an output layer and one or more hidden layers thateach apply a non-linear transformation to a received input to generate an output. In some cases, the neural network may be a recurrent neural network. A recurrent neural network is a neural network that receives an input sequence and generates an output sequence from the input sequence. In particular, a recurrent neural network uses some or all of the internal state of the network after processing a previous input in the input sequence to generate an output from the current input in the input sequence. The machine learning model executed by the processor 910 can be, for example, a deep-leaming neural network or a "very" deep learning neural network. For example, the machine learning model executed by the processor 910 can be a convolutional neural network or a recurrent network. The machine learning model can have residual connections or dense connections.

[0265] In example implementations, the machine learning model executed by the processor 910 is an ensemble of models that may include all or a subset of the architectures described above.

[0266] In example implementations, the machine learning model executed by the processor 910 is a graph neural network (GNN). GNNs are a designed to process data that can be represented in a graph form and feature pairwise message passing to enable iterative updating of node representation of the graph data.

[0267] In example implementations, the machine learning model executed by the processor 910 can be a feedforward auto-encoder neural network. For example, the machine learning model executed by the processor 910 can be a three-layer auto-encoder neural network. The machine learning model executed by the processor 910 may include an input layer, a hidden layer, and an output layer. In example implementations, the neural network has no recurrent connections between layers. Each layer of the neural network may be fully connected to the next, e.g., there may be no pruning between the layers. The neural network may include an optimizer for training the network and computing updated layer weights. In example implementations, the neural network may apply a mathematical transformation, e.g., a convolutional transformation or factor analysis to input data prior to feeding the input data to the network.

[0268] In example implementations, the machine learning model executed by the processor 910 can be a supervised model. For example, for each input provided to the model during training, the machine learning model can be instructed as to what the correct output should be. The machine learning model executed by the processor 910 can use batch training, e.g., training on a subset of examples before each adjustment, instead of theentire available set of examples. This may improve the efficiency of training the model and may improve the generalizability of the model. In example implementations, the machine learning model executed by the processor 910 may be an unsupervised model. For example, the model may adjust itself based on mathematical distances between examples rather than based on feedback on its performance. In example implementations, the machine learning model executed by the processor 910 can provide suggested additional data that could further improve the output of the machine learning model.

[0269] Certain features described herein can be implemented in digital electronic circuitry, or in computer hardware, firmware, software, or in combinations of them. The apparatus can be implemented in a computer program product tangibly embodied in an information carrier, e.g., in a machine-readable storage device for execution by a programmable processor; and method steps can be performed by a programmable processor executing a program of instructions to perform functions of the described implementations by operating on input data and generating output. The described features can be implemented advantageously in one or more computer programs that are executable on a programmable system including at least one programmable processor coupled to receive data and instructions from, and to transmit data and instructions to, a data storage system, at least one input device, and at least one output device. A computer program is a set of instructions that can be used, directly or indirectly, in a computer to perform a certain activity or bring about a certain result. A computer program can be written in any form of programming language, including compiled or interpreted languages, and it can be deployed in any form, including as a stand-alone program or as a module, component, subroutine, or other unit suitable for use in a computing environment.

[0270] Suitable processors for the execution of a program of instructions include, by way of example, both general and special purpose microprocessors, and the sole processor or one of multiple processors of any kind of computer. Generally, a processor will receive instructions and data from a read-only memory or a random-access memory or both. The essential elements of a computer are a processor for executing instructions and one or more memories for storing instructions and data. Generally, a computer will also include, or be operatively coupled to communicate with, one or more mass storage devices for storing data files; such devices include magnetic disks, such as internal hard disks and removable disks; magneto-optical disks; and optical disks. Storage devices suitable for tangibly embodying computer program instructions and data include all forms of non-volatilememory, including by way of example semiconductor memory devices, such as EPROM, EEPROM, and flash memory devices; magnetic disks such as internal hard disks and removable disks; magneto-optical disks; and CD-ROM and DVD-ROM disks. The processor and the memory can be supplemented by, or incorporated in, ASICs (application-specific integrated circuits).

[0271] To provide for interaction with a user, the features can be implemented on a computer having a display device such as a CRT (cathode ray tube) or LCD (liquid crystal display) monitor for displaying information to the user and a keyboard and a pointing device such as a mouse or a trackball by which the user can provide input to the computer. Additionally, such activities can be implemented via touchscreen flat panel displays and other appropriate mechanisms.

[0272] The features can be implemented in a control system (such as control system 999) that includes a back-end component, such as a data server, or that includes a middleware component, such as an application server or an Internet server, or that includes a front-end component, such as a client computer having a graphical user interface or an Internet browser, or any combination of them. The components of the control system can be connected by any form or medium of digital data communication such as a communication network. Examples of communication networks include a local area network (“LAN”), a wide area network (“WAN”), peer-to-peer networks (having ad-hoc or static members), grid computing infrastructures, and the Internet.EXPERIMENTAL RESULTS AND EXAMPLES

[0273] Comparative Example 1

[0274] A 2L aqueous solution of Unhindered Sorbent A was prepared by dissolving 2 mol of Unhindered Sorbent A and 2 mol of KOH in deionized water to prepare the aqueous sorbent solution. After Unhindered Sorbent A and KOH were fully dissolved, the solution was placed into a laboratory-scale gas-liquid contactor. While the aqueous sorbent solution was circulating in the system, air was blown through the contactor for approximately 3 hours. To account for water losses, water was continuously added to the contactor throughout the experiment to maintain the sorbent concentration. Samples of the aqueous sorbent solution were periodically collected and analyzed by 1H NMR and total inorganic carbon (TIC).

[0275] Example 1

[0276] A 2L aqueous solution of Hindered Sorbent A was prepared by dissolving 2 mol of Hindered Sorbent A and 2 mol of KOH in deionized water to prepare the aqueous sorbent solution. After Hindered Sorbent A and KOH were fully dissolved, the solution was placed into a laboratory-scale gas-liquid contactor. While the aqueous sorbent solution was circulating in the system, air was blown through the contactor for approximately 6 hours. To account for water losses, water was continuously added to the contactor throughout the experiment to maintain the sorbent concentration. Samples of the aqueous sorbent solution were periodically collected and analyzed by 1H NMR and total inorganic carbon (TIC). The loading of the solution - in mole of TIC per mole of Hindered Sorbent A - over the experiment can be seen in FIG. 2.

[0277] Example 2

[0278] A 2L aqueous solution of a blend of Unhindered Sorbent A and Hindered Sorbent A was prepared by dissolving 1 mol of Unhindered Sorbent A, 1 mol of Hindered Sorbent A, and 2 mol of KOH in deionized water to prepare the aqueous sorbent solution. After Unhindered Sorbent A, Hindered Sorbent A, and KOH were fully dissolved, the solution was placed into a laboratory-scale gas-liquid contactor, wherein the gas flow is orthogonal to the gravity -driven downward flow of the liquid. While the aqueous sorbent solution was circulating in the system, air was blown through the contactor for approximately 4.5 hours. To account for water losses, water was continuously added to the contactor throughout the experiment to maintain the sorbent concentration. Samples of the aqueous sorbent solution were periodically collected and analyzed by 1H NMR and total inorganic carbon (TIC). The loading of the solution - in mole of TIC per mole of (Unhindered Sorbent A + Hindered Sorbent A) - over the experiment can be seen in FIG. 2.

[0279] Comparative Example 2

[0280] The CO2 loaded sorbent solution from Comparative Example 1 - with IM Unhindered Sorbent A - was treated with BIG A in a ratio of 2 moles of BIG A per mol of total inorganic carbon measured in the CO2 loaded sorbent solution. The mixture was allowed to stir overnight. The mixture was filtered, and the TIC and pH of the filtrate was measured. The results can be seen in Table 1.

[0281] Example 3

[0282] The CO2 loaded sorbent solution from Example 1 - with IM Hindered Sorbent A - was treated with BIG A in a ratio of 1.5 moles of BIG A per mol of total inorganic carbon measured in the CO2 loaded sorbent solution. The mixture was allowed to stir overnight. The mixture was filtered, and the TIC and pH of the filtrate was measured. The results can be seen in Table 1.

[0283] Example 4

[0284] The CO2 loaded sorbent solution from Example 2 - with 0.5M Hindered SorbentA and 0.5M Unhindered Sorbent A - was treated with BIG A in a ratio of 1.5 moles of BIG A per mol of total inorganic carbon measured in the CO2 loaded sorbent solution.The mixture was allowed to stir overnight. The mixture was filtered, and the TIC and pH of the filtrate was measured. The results can be seen in Table 1.

[0285] In FIG. 2, the CO2 loading of the solution - in mol of TIC per mol of Sorbent - forExamples 1 and 2 is shown. It can be seen that a blend of Unhindered Sorbent A and Hindered Sorbent A has a faster rate of CO2 absorption than Hindered Sorbent A alone.

[0286] Comparative Example 5

[0287] A 25 mL simulated solution of carbon loaded Unhindered Sorbent A was prepared by mixing Unhindered Sorbent A, KOH, KHCO3, and deionized water such that the nominal concentration of Unhindered Sorbent A was IM, the concentration of potassium ions was IM, and the concentration of inorganic carbon was 0.5M. The solution was allowed to equilibrate for more than 14 hours. The concentration of Unhindered Sorbent A was confirmed by quantitative 1H NMR, the concentration of inorganic carbon was calculated from the amount of KHCO3 added to the solution, the concentration of carbamate was measured by quantitative 1H NMR. The mol percentage of inorganic carbon in the form of the carbamate was calculated from the measured carbamate concentration and the calculated concentration of inorganic carbon. The results can be seen in Table 2.

[0288] Example 6

[0289] A 25 mL simulated solution of carbon loaded Hindered Sorbent A was prepared by mixing Hindered Sorbent A, KOH, KHCO3, and deionized water such that the nominal concentration of Hindered Sorbent A was IM, the concentration of potassium ions was IM, and the concentration of inorganic carbon was 0.5M. The solution was allowed to equilibrate for more than 14 hours. The concentration of Hindered Sorbent A was confirmed by quantitative 1H NMR, the concentration of inorganic carbon was calculated from the amount of KHCO3 added to the solution, the concentration of carbamate was measured by quantitative 1H NMR. The mol percentage of inorganic carbon in the form of the carbamate was calculated from the measured carbamate concentration and the calculated concentration of inorganic carbon. The results can be seen in Table 2. Note that the Hindered Sorbent A has less of the inorganic carbon in the form of carbamate.

[0290] Although the foregoing implementations have been described in some detail for purposes of clarity of understanding, it will be apparent that certain changes and modifications may be practiced within the scope of the appended claims. It should be noted that there are many alternative ways of implementing the processes, systems, and apparatus of the present implementations. Accordingly, the present implementations are to be considered as illustrative and not restrictive, and the implementations are not to be limited to the details given herein.

Claims

CLAIMSWhat is claimed is: A method of capturing carbon dioxide, the method comprising:(a) contacting a source of impure carbon dioxide with an aqueous sorbent solution comprising at least one stencally hindered sorbent to produce a carbon-loaded sorbent solution compnsing carbonate ions and / or bicarbonate ions; and(b) reacting the carbonate ions and / or the bicarbonate ions with a complexing agent to form at least one of a carbonate salt of the complexing agent or a bicarbonate salt of the complexing agent.

2. The method of claim 1, wherein the at least one sterically hindered sorbent comprises an amine, an amino acid or a combination thereof.

3. The method of claim 1 or 2, wherein the sterically hindered sorbent has the formula:wherein at least three of Ri, R2, Rs, R4, and R5 are not hydrogen; wherein each of Ri, R2, R3, R4, and R5 is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

4. The method of claim 3, wherein each Ri, R2, R3, R4, and R5 is or comprise, independently, H, an unbranched or branched C1-6 alkyl group, an unbranched or branched C1-6 carbon alkene group, an unbranched or branched C1-6 carbon alkyne group, a C4-C7 carbon ring, wherein two or more of non-hydrogen Ri - R5 may form a cyclic or a multi-cyclic structure,an alcohol, a carboxylic acid, a carboxylate, or a sulfonic acid.

5. The method of claim 3, wherein one or more Ri - R5 is, independently, substituted with or comprises one or more heteroatoms.

6. The method of claim 4, wherein at least three of Ri - R5 that exclude hydrogen are independently methyl, ethyl, propyl, isopropyl, carboxyl, or sulfo.

7. The method of claim 1 or 2, wherein the sterically hindered sorbent has the formula:wherein at least two of Re-Rio are moieties excluding hydrogen, wherein A is a bond, a C atom, a heteroatom, a carbon chain with a backbone length of C1-C9, or a ring-containing moiety; wherein each Re, R7, Rs, R$>, and Rio is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

8. The method of claim 1 or 2, wherein the sterically hindered sorbent has the formula:wherein each Rn, R12, and R13 is, independently, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

9. The method of any one of claims 1 to 8, wherein the at least one sterically hindered sorbent is selected from the group consisting of 2-aminoisobutyric acid, 2-amino-2- methyl-1 -propanol, N-methylalanine, N,N-dimethylglycine, methyldi ethanol amine, triethanol amine, N-methylproline, and any combinations thereof.

10. The method of any one of claims 1 to 9, wherein the sorbent solution further comprises a second sorbent being a sterically hindered sorbent having the formula as defined in any one of claims 3 to 7.

11. The method of claim 10, wherein the second sorbent compound is selected from the group consisting of sarcosine, glycine, taurine, N-methyltaurine, arginine, histidine, lysine, aspartic acid, glutamic acid, serine, threonine, asparagine, glutamine, cysteine, glycine, proline, alanine, valine, isoleucine, leucine, methionine, phenylalanine, tyrosine, tryptophan, glycineglycine, glycineglycineglycine, other di- and tri-peptides derived from the amino acids listed above, monoethanol amine, piperazine, and piperazine derivatives.

12. The method of claim 10, wherein the second sorbent comprises ammonia.

13. The method of any one of claims 1 to 12, wherein the sorbent solution has a molar concentration of between 10 mol% and 90 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

14. The method of any one of claims 1 to 13, wherein the at least one sterically hindered comprises a first sorbent, a second sorbent and a third sorbent, each one of the first sorbent, the second sorbent and the third sorbent independently having a formula as defined in any one of claims 3 to 8.

15. The method of any one of claims 1 to 14, wherein the at least one sterically hindered sorbent has a solubility of at least about 0.5M in water at 20 °C.

16. The method of any one of claims 1 to 15, wherein the sorbent solution has a pH of about 7 to 14.

17. The method of any one of claims 1 to 16, wherein the at least one sterically hindered sorbent is an amine having a pKa of about 7 to 14 or an amino acid having a pKa2 of about 7 to 14.

18. The method of any one of claims 1 to 17. wherein the at least one sterically hindered sorbent has a concentration of about 0.1 M to 8 M in the sorbent solution.

19. The method of any one of claims 1 to 18, wherein the sorbent solution comprises an inorganic base.

20. The method of claim 19, wherein the inorganic base comprises potassium hydroxide, sodium hydroxide, lithium hydroxide, barium hydroxide, calcium hydroxide, strontium hydroxide, or any combinations thereof.

21. The method of any one of claim 1 to 20, wherein the complexing agent comprises at least one of an inorganic base, at least one of an unsaturated nitrogenous compound in freebase form, at least one of an unsaturated nitrogenous compound in salt form, or any combinations thereof.

22. The method of claim 21, wherein the unsaturated nitrogenous compound is an imine or an amidine.

23. The method of claim 22, wherein the unsaturated nitrogenous compound is an iminoguanidine.

24. The method of claim 23, wherein the unsaturated nitrogenous compound is a bis(imino)guanidine.

25. The method of claim 24, wherein the bis(imino)guanidine is selected from the group consisting of glyoxyl bis(imino)guamdine, methyl glyoxyl bis(immo)guanidine, diacetyl bis(imino)guanidine, pyridine bis(imino)guanidine, diacetylbenzene bis(imino)guanidine and any combinations thereof.

26. The method of any one of claims 1 to 25, wherein reacting the carbonate ions and / or the bicarbonate ions with the complexing agent comprises reacting the carbonate ions and / or the bicarbonate ions with at least two different immoguanidine compounds.

27. The method of claim 1, comprising precipitating and / or crystallizing the carbonate salt and / or the bicarbonate salt of the complexing agent when reacting the carbonate ions and / or the bicarbonate ions with the complexing agent, thereby forming a suspension comprising solids being suspended in an unloaded sorbent solution, the solids comprising at least one of a carbonate salt solid or a bicarbonate salt solid.

28. The method of claim 27, comprising separating the suspension into the solids and the unloaded sorbent solution downstream of the reacting, and reusing the unloaded sorbent solution as the sorbent solution.

29. The method of claim 27 or 28, comprising decomposing the carbonate salt solid and / or the bicarbonate salt solid to form carbon dioxide and the complexing agent.

30. The method of claim 29, comprising providing the complexing agent to a reactor configured to perform the reacting operation.

31. The method of any one of claims 1 to 30, wherein the contacting and the reacting are performed together in a single unit.

32. The method of any one of claims 1 to 31, wherein at least one of the contacting and reacting is performed in a batch-wise manner, semi-continuous manner, continuous manner or any combinations thereof.

33. The method of any one of claims 1 to 32, wherein the sorbent solution comprises the at least sterically hindered sorbent and at least one sterically unhindered sorbent.

34. The method of claim 33, wherein the pKa of the at least one sterically hindered sorbent is higher than the pKa of the sterically unhindered sorbent.

35. The method of any one of claims 1 to 34, wherein the source of impure carbon dioxide comprises a dilute gas source.

36. The method of claim 35, wherein the dilute gas source is air.

37. A system comprising:(a) at least one gas-liquid contactor comprising at least one capture section configured to contact a source of impure carbon dioxide with an aqueous sorbent solution comprising at least one sterically hindered sorbent to form a CO2 lean gas stream and a carbon loaded sorbent solution comprising carbonate ions and / or bicarbonate ions; and(b) a solids formation unit configured to react the carbonate ions and / or the bicarbonate ions with a complexing agent to precipitate at least one of a carbonate salt of the complexing agent or a bicarbonate salt of the complexing agent.

38. The system of claim 37, wherein the gas-liquid contactor and the solids formation unit are in the same unit.

39. The system of claim 37 or 38, wherein the solids formation unit comprises a reaction vessel configured to perform precipitation or reactive crystallization.

40. The system of any one of claims 37 to 39, comprising a CO2 recovery unit being configured to at least partially decompose the carbonate salt and / or bicarbonate salt of the complexing agent into the complexing agent and gaseous CO2.

41. The system of any one of claims 37 to 40, wherein the carbonate salt and / or bicarbonate salt of the complexing agent is produced in suspension in the unloaded sorbent solution, and the capture solution regeneration subsystem comprises a solidliquid separation unit being configured to separate the suspension into the unloaded sorbent solution and a solid comprising the carbonate salt and / or bicarbonate salt of the unsaturated nitrogenous compound.

42. The system of any one of claims 37 to 41, comprising an evaporator being fluidly coupled to the solids formation unit to evaporate at least a portion of a liquid from the unloaded sorbent solution.

43. The system of any one of claims 37 to 42, wherein the gas-liquid contactor comprises a wash section positioned adjacent the capture section and configured to contact the CCh-lean gas stream with a wash water stream to remove the at least one of aerosolized particles or volatilized components of the CCh-lean gas stream and to form a washed CCL-lean gas stream flowable from the wash section and a used wash water stream.

44. The system of any one of claims 37 to 43, wherein the at least one sterically hindered sorbent comprises an amine, an amino acid or a combination thereof.

45. The system of claim 44, wherein the sterically hindered sorbent has the formula:wherein at least three of Ri, R2, R3, 4, and R5 are not hydrogen; wherein each of Ri, R2, R3, R4, and Rs is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

46. The system of claim 45, wherein each Ri, R2, R3, R4, and R5 is or comprise, independently, H, an unbranched or branched Ci-Ce alkyl group, an unbranched or branched Ci-Ce carbon alkene group, an unbranched or branched Ci-Ce carbon alkyne group, a C4-C7 carbon ring, wherein two or more of non-hydrogen Ri - R5 may form a cyclic or a multi-cyclic structure, an alcohol, a carboxylic acid, a carboxylate, or a sulfonic acid.

47. The system of claim 45, wherein one or more Ri - R5 is, independently , substituted with or comprises one or more heteroatoms.

48. The system of claim 45, wherein at least three of Ri - Rs that are not hydrogen are independently methyl, ethyl, propyl, isopropyl, carboxyl, or sulfo.

49. The system of claim 44, wherein the sterically hindered sorbent has the formula:wherein at least two of Re-Rio are moieties excluding hydrogen, wherein A is a bond, a C atom, a heteroatom, a carbon chain with a backbone length of C1-C9, or a ring-containing moiety; wherein each Re, R7, Rs, R$>, and Rio is, independently, H, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyd, substituted aromatic, substituted aryl, or substituted arylalkylene.

50. The system of claim 44, wherein the sterically hindered sorbent has the formula:wherein each Rn, Rn, and Ria is, independently, substituted aliphatic, substituted alkyl, substituted heteroaliphatic, substituted heteroalkyl, substituted aromatic, substituted aryl, or substituted arylalkylene.

51. The system of any one of claims 1 to 50, wherein the at least one gas-liquid contactor comprises a plurality of gas-liquid contactors, and the system comprises at least one contactor wall comprising the plurality of gas-liquid contactors positioned side by side, the at least one contactor wall extending along a wall axis.

52. A sorbent solution for capturing carbon dioxide, the sorbent solution comprising: at least one sterically hindered sorbent, and at least one sterically unhindered sorbent.

53. The sorbent solution of claim 52, comprising a molar concentration of between 10 mol% and 90 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

54. The sorbent solution of claim 52, comprising a molar concentration of between 20 mol% and 80 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

55. The sorbent solution of claim 52, comprising a molar concentration of between 30 mol% and 70 mol% of the at least one sterically hindered sorbent with respect to a total number of moles of sorbent.

56. The sorbent solution of any one of claims 52 to 55, comprising two sterically hindered sorbents and one sterically unhindered sorbent.

57. The sorbent solution of any one of claims 52 to 56, wherein the at least one sterically hindered sorbent comprises an amino acid.

58. The sorbent solution of any one of claims 52 to 57, wherein the at least one sterically hindered sorbent comprises an amine.

59. The sorbent solution of any one of claims 52 to 57, comprising an inorganic base.

60. The sorbent solution of any one of claims 52 to 59, wherein the pKa of the at least one sterically hindered sorbent is higher than the pKa of the at least one sterically unhindered sorbent.

61. The sorbent solution of any one of claims 52 to 60, wherein the at least one sterically hindered sorbent has a pKa between about 7 and 14.

62. The sorbent solution of any one of claims 52 to 60, wherein the at least one sterically hindered sorbent has a pKa between about 8 and 12.

63. The sorbent solution of any one of claims 52 to 60, wherein the at least one sterically hindered sorbent has a pKa between about 8 and 11.

64. The sorbent solution of any one of claims 52 to 63, having a temperature between about 10°C and 30°C.

65. The sorbent solution of any one of claims 52 to 64, comprising water, thereby being an aqueous solution.

66. The sorbent solution of claim 65, wherein the sterically hindered sorbent has a solubility of at least about 0.5M at 20 °C.

67. The sorbent solution of any one of claims 52 to 66, comprising an alkali metal salt.

68. A carbon 4 oaded sorbent solution, comprising: a carbon dioxide derived species comprising: at least one of carbonates and bicarbonates, and carbamates accounting for at most 65 mol% of inorganic carbon with respect to a total number of moles of inorganic carbon in the carbon dioxide derived species.

69. The carbon-loaded sorbent solution of claim 68, comprising at most 1 mol of inorganic carbon per mol of sorbent, optionally between 0.05 and 0.6 mol of inorganic carbon per mol of sorbent, further optionally between 0.075 and 0.5 mol of inorganic carbon per mol of sorbent.

70. The carbon-loaded sorbent solution of claim 68 or 69, wherein the carbamates account for at most 60 mol% of inorganic carbon with respect to the total number ofmoles of inorganic carbon in the carbon dioxide derived species, optionally for at most 50 mol% of inorganic carbon with respect to the total number of moles of inorganic carbon in the carbon dioxide derived species.

71. The carbon-loaded sorbent solution of any one of claims 68 to 70, having a pH between 7 and 14, optionally between 8 and 13, further optionally between 9 and 12.

72. A method of capturing carbon dioxide from atmospheric air, the method comprising: contacting the atmospheric air with an aqueous sorbent solution comprising at least one sterically hindered sorbent to produce a carbon-loaded sorbent solution comprising carbonate ions and / or bicarbonate ions.

73. The method of claim 72, comprising at least one additional feature defined in any one of claims 1 to 36.

Images