A recyclable covalent adaptable network for direct air capture and method for producing and using the same

Abstract

A recyclable covalent adaptable network (a sorbent polymer) for direct air capture and method for producing and using the same is disclosed. The method for using the sorbent polymer for capturing carbon dioxide includes creating a pre-polymer through controlled radical polymerization (CRP) of at least one monomer comprising a first monomer, the first monomer having a β-ketoester moiety that is reactive. The method further includes crosslinking the pre-polymer by reacting the β-ketoester moieties of the pre-polymer with a crosslinker having primary amines and secondary amines to form the sorbent polymer which is a covalent adaptable network (CAN) comprising a network of exchangeable enaminone linkages. The method also includes exposing the sorbent polymer to an airflow such that the secondary amines adsorb carbon dioxide from the airflow, and heating the sorbent polymer to release the carbon dioxide adsorbed by the secondary amines of the CAN.

Description

A RECYCLABLE COVALENT ADAPTABLE NETWORK FOR DIRECT AIR CAPTURE AND METHOD FOR PRODUCING AND USING THESAMERELATED APPLICATIONS

[0001] This application claims the benefit of U.S. provisional patent application 63 / 621,091, filed January 15, 2024 titled “A RECYCLABLE COVALENT ADAPTABLE NETWORK FOR DIRECT AIR CAPTURE AND METHOD FOR PRODUCING AND USING THE SAME,” the entirety of the disclosure of which is hereby incorporated by this reference.TECHNICAL FIELD

[0002] Aspects of this document relate generally to recyclable sorbent polymers.BACKGROUND

[0003] The need for technologies to remove carbon dioxide from ambient air has been well established. The average CO2 concentration in the atmosphere was 415 ppm in June 2021, which has been linked to elevated average global temperatures, extreme weather, wildfires, and more. The Intergovernmental Panel on Climate Change’s 2021 report predicts a 1.5 °C rise in global temperature within the next two decades, assuming global policymakers aggressively reduce emissions. Without intervention, an average temperature rise of 4.4 °C is possible, leading to catastrophic results. Current CO2 emissions are projected to reach 40 GT CCh / year. In addition to conservation, reduced-carbon processes, and on-site capture efforts, a significant amount of carbon dioxide will need to be removed from the atmosphere to avoid a looming climate change crisis. Negative emission technologies are a critical technological solution needed to reduce emissions and lead to a net-zero emission scenario.

[0004] Capture of carbon dioxide from ambient air at an affordable price could become a critical tool in managing the anthropogenic carbon cycle. Air capture technology would greatly enhance the options for developing the world’s energy infrastructure and would be a major asset in the fight against climate change. Combined with a carbon dioxide (CO2) storage technology, air capture of CO2 could compensate for CO2 emissions from any source,without requiring changes to the existing infrastructure and without requiring proximity to the point of emission. Air capture technology makes it possible for existing infrastructures to live out their natural life spans, and it permits the continued use of carbon-based fuels in distributed and mobile applications, for example in the transportation sector. With air capture technology, it is possible to continue the use of liquid hydrocarbon fuels while eliminating their climate impact. Furthermore, there are a number of applications for the captured CO2, including enhanced oil recovery and the manufacture of fuels, building materials, feedstock, and the like, providing a financial incentive in addition to the environmental.

[0005] A promising technology that is well adapted for capturing dilute atmospheric carbon dioxide in an energy efficient manner is Direct Air Capture (DAC). It is anticipated that DAC will generate a significant demand for low-cost CO2 sorbents. A typical CO2 sorbent has a capacity of <10 wt%; estimates of the amount of material needed to capture ~40 Gtons CCh / year are -10-20 Mtons sorbents. Polymeric sorbents are promising targets for scalable solutions because of the low cost, processability, the diversity of chemistries available, and a global infrastructure to manufacture megatons of material. Unfortunately, this will increase the global polymer production at a time when global society is aiming to reduce reliance on single-use plastics, increase recycling rates, and avoid polymer accumulation in the landfill. A sorbent material that is recyclable is needed to avoid solving one problem by creating another. Additionally, use for DAC demands that the CO2 sorbent have a long service life (e.g., thousands of cycles) while being exposed to sunlight, weather, and temperature fluctuations.

[0006] At present, most approaches for recycling polymers are only applicable to thermoplastics, i.e., polymers made up of distinct polymer chains such that they can be easily reshaped, reprocessed, and recycled using heat or solvents. However, thermoplastics tend to be less mechanically, thermally, and chemically durable when compared to their cross-linked thermoset counterparts. Thermosets consist of polymer chains that are largely immobilized due to their cross-linked nature. While this networked structure provides exceptional thermal and solvent resistance, it also impedes the structural dynamicity required for reprocessability and recycling.

[0007] Additionally, production at the scale needed to have an environmental impact presents a significant sustainability problem. Traditionally, these types of polymers are manufactured using petroleum sourced materials. What is needed is a sorbent material that is effective, able to withstand exposure to the operating conditions of a DAC device, recyclable, and can be produced using bio-based feedstocks.SUMMARY

[0008] According to one aspect, a method for using a sorbent polymer for capturing carbon dioxide includes creating a pre-polymer through controlled radical polymerization (CRP) of at least one monomer having a first monomer, the first monomer having a P-ketoester moiety that is reactive. The method also includes crosslinking the pre-polymer by reacting the P-ketoester moieties of the pre-polymer with a crosslinker having primary amines and secondary amines to form the sorbent polymer which is a covalent adaptable network (CAN) having a network of exchangeable enaminone linkages. The method further includes exposing the sorbent polymer to an airflow such that the secondary amines of the CAN adsorb carbon dioxide from the airflow, and heating the sorbent polymer to release the carbon dioxide adsorbed by the secondary amines of the CAN.

[0009] Particular embodiments may comprise one or more of the following features. The method may further include recycling the sorbent polymer through associative exchanges within the exchangeable enaminone linkages of the CAN. The recycling may be performed using melt processing. The CRP may be reversible addition-fragmentation chain transfer (RAFT). The CRP may include a chain transfer agent, a radical initiator, and / or a solvent. The chain transfer agent may be 2-((l l-mercaptoundecyl)thio)acetic acid. The radical initiator may be AIBN. The solvent may be dioxane. The first monomer may be (2- acetoacetoxy)ethyl methacrylate (AAEMA). The at least one monomer may include at least one vinyl monomer. The at least one monomer may include at least one of a methacrylate monomer and a styrenic monomer. The at least one monomer may include an alkyl methacrylate having an alkyl group that may be one of methyl, ethyl, butyl, hexyl, trifluoroethyl ( — CH2CF3), and dimethylaminoethyl ( — CH2CH2-N(CH3)2). The crosslinker may be based on linear polyethyleneimine (PEI). The sorbent polymer may be exposed to the airflow using a direct air capture (DAC) device. The sorbent polymer may be a thermoset. At least one of the crosslinker, the first monomer, and at least one monomer other than the first monomer may be derived from a natural material. The natural material may be a vegetable oil. The vegetable oil may be at least one of soybean oil, linseed oil, and castor oil. The method may further include functionalizing the vegetable oil using at least one of epoxidation, acrylation, carbonation, and hydroxylation. The crosslinker may be a polyamide derived from a natural material. The polyamide may be derived from ricinoleic acid. The polyamide may be derived from oleic acid. The at least one monomer may include an alkyl methacrylate that may be derived from fatty acid, having an alkyl chain length that may be greater than 11 carbons and less than 25 carbons.

[0010] According to another aspect of the disclosure, a method for using a sorbent polymer for capturing carbon dioxide includes crosslinking a pre-polymer having P-ketoester moieties by reacting the P-ketoester moieties of the pre-polymer with a crosslinker having primary amines and secondary amines to form the sorbent polymer which is a covalent adaptable network (CAN) having a network of exchangeable enaminone linkages. The method also includes exposing the sorbent polymer to an airflow such that the secondary amines of the CAN adsorb carbon dioxide from the airflow, and heating the sorbent polymer to release the carbon dioxide adsorbed by the secondary amines of the CAN.

[0011] Particular embodiments may comprise one or more of the following features. The method may further include creating the pre-polymer through controlled radical polymerization (CRP) of at least one monomer including a first monomer, the first monomer having a P-ketoester moiety that may be reactive. The pre-polymer may be a P-ketoester- functionalized vegetable oil having a P-ketoester moiety that may be reactive. The method may further include preparing the P-ketoester-functionalized vegetable oil by hydroxylating carbon-carbon double bonds on at least one triglyceride of a vegetable oil. The method may further include recycling the sorbent polymer through associative exchanges within the exchangeable enaminone linkages of the CAN. The recycling may be performed using melt processing. The CRP may be reversible addition-fragmentation chain transfer (RAFT). The CRP may include a chain transfer agent, a radical initiator, and / or a solvent. The chain transfer agent may be 2-((l l-mercaptoundecyl)thio)acetic acid. The radical initiator may be AIBN. The solvent may be dioxane. The first monomer may be (2-acetoacetoxy)ethyl methacrylate (AAEMA). The at least one monomer may include at least one vinyl monomer. The at least one monomer may include at least one of a methacrylate monomer and a styrenic monomer. The at least one monomer may include an alkyl methacrylate having an alkyl group that may be one of methyl, ethyl, butyl, hexyl, trifluoroethyl ( — CH2CF3), and dimethylaminoethyl ( — CH2CH2-N(CH3)2). The crosslinker may be based on linear polyethyleneimine (PEI). The sorbent polymer may be exposed to the airflow using a direct air capture (DAC) device. The sorbent polymer may be a thermoset. The crosslinker may be derived from a natural material. The natural material may be a vegetable oil. The vegetable oil may be at least one of soybean oil, linseed oil, and castor oil. The method may further include functionalizing the vegetable oil using at least one of epoxidation, acrylation, carbonation, and hydroxylation. The crosslinker may be a polyamide derived from a natural material. The polyamide may be derived from ricinoleic acid. The polyamide may be derived from oleic acid. The at least onemonomer may include an alkyl methacrylate that may be derived from fatty acid, having an alkyl chain length that may be greater than 11 carbons and less than 25 carbons.

[0012] According to yet another aspect of the disclosure, a sorbent polymer for capturing carbon dioxide includes a covalent adaptable network (CAN) having P-ketoester moieties, primary amines, and secondary amines, and also having exchangeable enaminone linkages with dynamic covalent bonds. The secondary amines adsorb carbon dioxide from an airflow. The sorbent polymer is recyclable through associative exchanges within the exchangeable enaminone linkages of the CAN.

[0013] Particular embodiments may comprise one or more of the following features. The sorbent polymer may be at least partially derived from a natural material. The natural material may be a vegetable oil. The vegetable oil may be at least one of soybean oil, linseed oil, and castor oil. The sorbent polymer may be a thermoset.

[0014] Aspects and applications of the disclosure presented here are described below in the drawings and detailed description. Unless specifically noted, it is intended that the words and phrases in the specification and the claims be given their plain, ordinary, and accustomed meaning to those of ordinary skill in the applicable arts. The inventors are fully aware that they can be their own lexicographers if desired. The inventors expressly elect, as their own lexicographers, to use only the plain and ordinary meaning of terms in the specification and claims unless they clearly state otherwise and then further, expressly set forth the “special” definition of that term and explain how it differs from the plain and ordinary meaning. Absent such clear statements of intent to apply a “special” definition, it is the inventors’ intent and desire that the simple, plain and ordinary meaning to the terms be applied to the interpretation of the specification and claims.

[0015] The inventors are also aware of the normal precepts of English grammar. Thus, if a noun, term, or phrase is intended to be further characterized, specified, or narrowed in some way, then such noun, term, or phrase will expressly include additional adjectives, descriptive terms, or other modifiers in accordance with the normal precepts of English grammar. Absent the use of such adjectives, descriptive terms, or modifiers, it is the intent that such nouns, terms, or phrases be given their plain, and ordinary English meaning to those skilled in the applicable arts as set forth above.

[0016] Further, the inventors are fully informed of the standards and application of the special provisions of 35 U.S.C. § 112(f). Thus, the use of the words “function,” “means” or “step” in the Detailed Description or Description of the Drawings or claims is not intended to somehow indicate a desire to invoke the special provisions of 35 U.S.C. § 112(f), to definethe invention. To the contrary, if the provisions of 35 U.S. C. § 112(f) are sought to be invoked to define the inventions, the claims will specifically and expressly state the exact phrases “means for” or “step for”, and will also recite the word “function” (i.e., will state “means for performing the function of [insert function]”), without also reciting in such phrases any structure, material or act in support of the function. Thus, even when the claims recite a “means for performing the function of . . . “ or “step for performing the function of . . . ,” if the claims also recite any structure, material or acts in support of that means or step, or that perform the recited function, then it is the clear intention of the inventors not to invoke the provisions of 35 U.S.C. § 112(f). Moreover, even if the provisions of 35 U.S.C. § 112(f) are invoked to define the claimed aspects, it is intended that these aspects not be limited only to the specific structure, material or acts that are described in the preferred embodiments, but in addition, include any and all structures, materials or acts that perform the claimed function as described in alternative embodiments or forms of the disclosure, or that are well known present or later-developed, equivalent structures, material or acts for performing the claimed function.

[0017] The foregoing and other aspects, features, and advantages will be apparent to those artisans of ordinary skill in the art from the DESCRIPTION and DRAWINGS, and from the CLAIMS.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The disclosure will hereinafter be described in conjunction with the appended drawings, where like designations denote like elements, and:

[0019] FIG. 1 is a schematic view of the synthesis of a direct air capture covalent adaptable network (DAC CAN) sorbent polymer from synthetic starting materials;

[0020] FIG. 2 is a schematic view of the usage cycle of a DAC CAN sorbent polymer;

[0021] FIG. 3 A is a schematic view of a sorbent polymer after reprocessing;

[0022] FIGs. 3B-3E show various properties of embodiments of the sorbent polymer;

[0023] FIGs. 4A-4C are compounds derived from natural materials that may be substituted into the synthesis of a DAC CAN sorbent polymer; and

[0024] FIG. 5 shows the CO2 sorption capacity of various embodiments of the contemplated DAC CAN sorbent polymer.DETAILED DESCRIPTION

[0025] This disclosure, its aspects and implementations, are not limited to the specific material types, components, methods, or other examples disclosed herein. Many additional material types, components, methods, and procedures known in the art are contemplated for use with particular implementations from this disclosure. Accordingly, for example, although particular implementations are disclosed, such implementations and implementing components may comprise any components, models, types, materials, versions, quantities, and / or the like as is known in the art for such systems and implementing components, consistent with the intended operation.

[0026] The word "exemplary," "example," or various forms thereof are used herein to mean serving as an example, instance, or illustration. Any aspect or design described herein as "exemplary" or as an “example” is not necessarily to be construed as preferred or advantageous over other aspects or designs. Furthermore, examples are provided solely for purposes of clarity and understanding and are not meant to limit or restrict the disclosed subject matter or relevant portions of this disclosure in any manner. It is to be appreciated that a myriad of additional or alternate examples of varying scope could have been presented, but have been omitted for purposes of brevity.

[0027] While this disclosure includes a number of embodiments in many different forms, there is shown in the drawings and will herein be described in detail particular embodiments with the understanding that the present disclosure is to be considered as an exemplification of the principles of the disclosed methods and systems, and is not intended to limit the broad aspect of the disclosed concepts to the embodiments illustrated.

[0028] The need for technologies to remove carbon dioxide from ambient air has been well established. The average CO2 concentration in the atmosphere was 415 ppm in June 2021, which has been linked to elevated average global temperatures, extreme weather, wildfires, and more. The Intergovernmental Panel on Climate Change’s 2021 report predicts a 1.5 °C rise in global temperature within the next two decades, assuming global policymakers aggressively reduce emissions. Without intervention, an average temperature rise of 4.4 °C is possible, leading to catastrophic results. Current CO2 emissions are projected to reach 40 GT CCh / year. In addition to conservation, reduced-carbon processes, and on-site capture efforts, a significant amount of carbon dioxide will need to be removed from the atmosphere to avoid a looming climate change crisis. Negative emission technologies are a critical technological solution needed to reduce emissions and lead to a net-zero emission scenario.

[0029] Capture of carbon dioxide from ambient air at an affordable price could become a critical tool in managing the anthropogenic carbon cycle. Air capture technology would greatly enhance the options for developing the world’s energy infrastructure and would be a major asset in the fight against climate change. Combined with a carbon dioxide (CO2) storage technology, air capture of CO2 could compensate for CO2 emissions from any source, without requiring changes to the existing infrastructure and without requiring proximity to the point of emission. Air capture technology makes it possible for existing infrastructures to live out their natural life spans, and it permits the continued use of carbon-based fuels in distributed and mobile applications, for example in the transportation sector. With air capture technology, it is possible to continue the use of liquid hydrocarbon fuels while eliminating their climate impact. Furthermore, there are a number of applications for the captured CO2, including enhanced oil recovery and the manufacture of fuels, building materials, feedstock, and the like, providing a financial incentive in addition to the environmental.

[0030] A promising technology that is well adapted for capturing dilute atmospheric carbon dioxide in an energy efficient manner is Direct Air Capture (DAC). It is anticipated that DAC will generate a significant demand for low-cost CO2 sorbents. A typical CO2 sorbent has a capacity of <10 wt%; estimates of the amount of material needed to capture ~40 Gtons CCh / year are -10-20 Mtons sorbents. Polymeric sorbents are promising targets for scalable solutions because of the low cost, processability, the diversity of chemistries available, and a global infrastructure to manufacture megatons of material. Unfortunately, this will increase the global polymer production at a time when global society is aiming to reduce reliance on single-use plastics, increase recycling rates, and avoid polymer accumulation in the landfill. A sorbent material that is recyclable is needed to avoid solving one problem by creating another. Additionally, use for DAC demands that the CO2 sorbent have a long service life (e.g., thousands of cycles) while being exposed to sunlight, weather, and temperature fluctuations.

[0031] At present, most approaches for recycling polymers are only applicable to thermoplastics, i.e., polymers made up of distinct polymer chains such that they can be easily reshaped, reprocessed, and recycled using heat or solvents. However, thermoplastics tend to be less mechanically, thermally, and chemically durable when compared to their cross-linked thermoset counterparts. Thermosets consist of polymer chains that are largely immobilized due to their cross-linked nature. While this networked structure provides exceptional thermal and solvent resistance, it also impedes the structural dynamicity required for reprocessability and recycling.

[0032] Additionally, production at the scale needed to have an environmental impact presents a significant sustainability problem. Traditionally, these types of polymers are manufactured using petroleum sourced materials. What is needed is a sorbent material that is effective, able to withstand exposure to the operating conditions of a DAC device, recyclable, and can be produced using bio-based feedstocks.

[0033] Contemplated herein is a recyclable covalent adaptable network (CAN) that acts as a sorbent material well adapted for use in the direct air capture of carbon dioxide, and methods for producing and using the same. The contemplated direct air capture covalent adaptable networks (hereinafter DAC CAN or simply sorbent polymer) is a thermoset with covalent cross-link reversibility, yielding materials that retain their network structure while providing routes for reprocessing. CANs (or vitrimers) are cross-linked polymers with reversible covalent connectivity between chains that advantageously combine the thermal, chemical, and solvent resistance of thermosets with the dynamicity of thermoplastics.

[0034] Most CANs rely on bond exchange that proceeds by an “associative” process in which a pendent reactive group within the network undergoes a substitution reaction with an existing cross-link to form a new cross-link and regenerate a reactive group capable of further exchange. A key advantage of associative exchange is that the crosslink density remains constant, even at very high temperatures or in the presence of solvent.

[0035] The contemplated DAC CAN materials are sorbents that reversibly adsorb carbon dioxide upon exposure. This is made possible by the use of amine-rich components. According to various embodiments, these amine-rich components can be derived from synthetic or natural polymers, easing the sustainability problems posed by usage at the scale needed to combat climate change. Covalent adaptable networks can enable a circular polymer economy. The sorbent polymer contemplated herein can efficiently capture CO2 from ambient air and then avoid the landfill at the end of its service life. Additionally, these materials may be less expensive to produce than traditional sorbent materials with similar properties.

[0036] It should be noted that while the following discussion of DAC CAN materials is done in the context of use in a passive DAC device (i.e., capturing CO2 from natural air flows), it should not be viewed as a limitation. The contemplated materials may also be used in active DAC systems (e.g., mechanically driven air, exhaust systems, etc.), and may also be adapted for use in other CO2 capture technologies, both known in the art and not yet existing. Those skilled in the art will recognize that an inexpensive, durable, recyclable and reprocessable polymeric sorbent material will have a wide range of applications. The exemplary implementations discussed herein should not be taken as limitations.

[0037] FIG. 1 is a schematic view of a non-limiting example of the synthesis of a direct air capture covalent adaptable network (hereinafter sorbent polymer 100) from synthetic starting materials. The DAC CAN materials contemplated herein demonstrate the CO2 capture capacity, kinetics, and longevity needed for efficient and effective extraction of atmospheric carbon dioxide while being designed from the outset with consideration for recyclability and sustainability. According to various embodiments, this is achieved by incorporating amine-rich components capable of CO2 capture within covalent adaptable networks. Although the resulting materials will be crosslinked thermosets, recyclability and reprocessability are made possible by the associative exchange chemistry of enaminone networks. According to various embodiments, the amine-containing components can be derived from either synthetic or natural resources, provided that multiple primary amines 112 are present to enable crosslinking and a high density of secondary amines 114 exist for CO2 capture.

[0038] While the embodiments discussed in the context of FIG. 1 are composed of synthetic materials, it should be noted that in some embodiment, the contemplated sorbent polymer 100 may be derived, at least in part, from natural materials. The use of natural materials will be discussed in greater detail with respect to FIGs. 4A-4C, below.

[0039] According to various embodiments, the synthesis begins with a pre-polymer 108 having pendent P-ketoester moieties 106, as shown in FIG. 1. In some embodiments, this pre-polymer 108 may be created through controlled radical polymerization 122 (CRP) of at least one monomer 102 that includes, but is not limited to, a first monomer 104 having a P- ketoester moiety 106 that is reactive. As a specific example, in some embodiments including the non-limiting example shown in FIG. 1, the first monomer 104 is (2-acetoacetoxy)ethyl methacrylate (AAEMA), an inexpensive and commercially available monomer 102 containing a reactive P-ketoester moiety 106.

[0040] In some embodiments, AAEMA (i.e., the first monomer 104) may be copolymerized with at least one vinyl monomer. In other embodiments, the at least one monomer 102 may comprise at least one of a methacrylate monomer and a styrenic monomer, in addition to the first monomer 104 (e.g., AAEMA, etc.). In still other embodiments, the at least one monomer 102 comprises an alkyl methacrylate. Specific alkyl groups include, but are not limited to, methyl, ethyl, butyl, hexyl, trifluoroethyl ( — CH2CF3), and dimethylaminoethyl ( — CH2CH2-N(CH3)2).

[0041] The alkyl group may be chosen depending on desired characteristics of the pre-polymer 108 and ultimately the sorbent polymer 100. For example, according to various embodiments, methyl, ethyl, butyl, or hexyl may be chosen to better tune Tg. Trifluoroethylmay be chosen to tune surface energy / polarity, while dimethylaminoethyl may be chosen to add tertiary amine character, according to various embodiments. In some embodiments, comonomers in the range of C2-6-alkyl methacrylates may selected based on their ability to result in prepolymers with Tgranging from -5 - 65 °C. A tunable Tgwill have a direct effect on the mobility and diffusion coefficient of CO2 (DC02) through the networks.

[0042] In some embodiments, the synthesis of the contemplated sorbent polymer 100 may begin with a crosslinking crosslinking a pre-polymer 108 having P-ketoester moi eties 106. In some embodiments, the pre-polymer 108 may be derived from natural materials, as will be discussed in the context of FIGs. 4A-4C, below. In other embodiments, the synthesis may begin with the creation of the pre-polymer 108.

[0043] According to various embodiments, this copolymerization may be performed using controlled radical polymerization 122 (CRP), which permits a degree of control over the resulting molecular weighs and architectures, and results in a pre-polymer 108. As shown in FIG. 1, variations in the copolymerization can modify the length of different parts of the pre-polymer 108 (i.e., / / , m). According to various embodiments, the ratio of n:m (e.g., 25:75, 50:50, 75:25, etc.) can be used to tune the crosslink density / Tg. As m increases relative to / / , the crosslink density increases, as well as Tg.

[0044] The sum of n+m (e.g. 50, 100, 500, 1000, etc.) may also be used to tune the rheology and activation energy for flow, according to various embodiments. As molecular weight (i.e., n+m goes up, the viscosity and activation energy for flow increase as well.

[0045] According to various embodiments, the CRP used is reversible additionfragmentation chain transfer 124 (RAFT 124). As shown in FIG. 1, and continuing with the previous specific example, in one embodiment the RAFT 124 process makes use of a chain transfer agent 126 (e.g., 2-((l l-mercaptoundecyl)thio)acetic acid), a radical initiator 128 (e.g., AIBN), and a solvent 130 (e.g., dioxane). In this specific example, the RAFT polymerization is carried out at 70 °C.

[0046] According to various embodiments, the resulting pre-polymers 108 are P ketoester functionalized. In some embodiments, the pre-polymer 108 is random, while in others it is block. The resulting pre-polymers 108 will be crosslinked by the reaction of the polymer-bound P ketoester groups with primary amine-containing reagents to result in networks having dynamic, exchangeable enaminone linkages 118, according to various embodiments. Specifically, the crosslinking reagent comprises primary amines 112, which form the exchangeable enaminone linkages 118, and secondary amines 114, which are responsible for the sorbent polymer's ability to adsorb carbon dioxide. In some embodiments,this conversion of the pre-polymers 108 into covalent adaptable networks 116 may be performed in a single step with no catalyst, through treatment with a trifunctional amine.

[0047] According to various embodiments, the crosslinking of the pre-polymer 108 by reacting the P-ketoester moi eties 106 of the pre-polymer 108 with a crosslinker 110 comprising primary amines 112 and secondary amines 114 results in covalent adaptable networks 116 comprising P-ketoester moieties 106, primary amines 112, and secondary amines 114, and further comprising a network of exchangeable enaminone linkages 118 having dynamic covalent bonds 120.

[0048] In some embodiments, including the non-limiting example shown in FIG. 1, the crosslinker 110 may be based on linear polyethyleneimine (PEI) oligomers or polymers, which are available either commercially or by controlled polymerization methods that lead to well-defined linear PEI. PEI-based crosslinkers 110 contain the primary amine groups 112 needed for crosslinking and subsequent associative exchange and the high density of secondary amine groups 114 required for CO2 capture. While PEI has been demonstrated to be particularly effective for DAC, the traditional methods used to prepare PEI and its derivatives, along with many other polymers with high amine content, typically lead to ill-defined polymers that are highly branched and / or crosslinked. Immobilization of the amine-rich polymer to a heterogeneous support can partially alleviate the difficulty of handling these materials, but this approach dilutes the amine component and CO2 capture is limited by the surface area of the support.

[0049] It should be noted that there is a wide range of embodiments of the contemplated method. The alkyl substituents, copolymer composition, and free amine content in the pre-polymer will all influence the performance. For example, the length of the PEI crosslinker 110 directly affects processability by determining the molecular weight between crosslinks, CAN flow behavior at elevated temperatures, and the ratio of primary to secondary amines 114, according to various embodiments. Furthermore, the ratio of excess primary amine 112 to exchangeable enaminone linkages 118 (e.g., 1 : 1, 1 :2, 1 :4, etc.) can be used to tune the exchange rate, according to various embodiments.

[0050] The CO2 capacity of the networks is largely dictated by the surface area to volume ratio (i.e., access to amines at the surface of the sorbent polymer 100). However, in some embodiments, the use of rubbery networks allows CO2 to diffuse and find secondary amines 114 within the sorbent polymer 100, as will be discussed below. Small improvements in CO2 capacity can have a large impact. An increase in CO2 capacity by even 5-10% couldmean that 1 kg of sorbent only has to cycle 90,000 times instead of 100,000 times to capture 1 ton of CO2.

[0051] FIG. 2 is a schematic view of the usage cycle of a non-limiting example of the contemplated sorbent polymer 100. According to various embodiments, the sorbent polymer 100 may be used with a direct air capture (DAC) device 200, which is configured to cycle the sorbent polymer 100 between a collection state, where it is exposed to an airflow 202 (e.g., wind, etc.) such that the secondary amines 114 of the CAN 116 adsorb carbon dioxide 204, and a release or harvest state, where the sorbent polymer 100 is enclosed within the device 200 and exposed to heat 206, causing the sorbent polymer 100 to release the carbon dioxide 204 adsorbed by the secondary amines 114. According to various embodiments, the carbon dioxide 204 released within the device 200 may be removed for a wide range of downstream activities (e.g., purification, compression, sequestration, use as feedstock, etc.).

[0052] It should be noted that the schematic representation of the DAC device 200 shown in FIG. 2 is non-limiting. DAC devices 200 may have many different architectures that may be configured for various use environments. The particular design used in this schematic representation was chosen to emphasize the exposed and enclosed natures of the collection and release states, respectively. Those skilled in the art will recognize that the contemplated recyclable sorbent polymer 100 may be used in a wide range of devices, including but not limited to direct air capture devices, passive or otherwise.

[0053] FIG. 3 A is a schematic view of the sorbent polymer 100 after reprocessing. According to various embodiments, the contemplated sorbent polymer 100 may be recycled or reprocessed, even though it is a thermoset. This is accomplished through associative exchanges within the exchangeable enaminone linkages 118 of the covalent adaptable network 116. In some embodiments, the sorbent polymer 100 may be reprocessed through melt processing. The sorbent polymer 100 is heated and undergoes shear which results in bond rearrangement, allowing the polymer to be mechanically recycled.

[0054] As a specific example, embodiments of sorbent polymers 100 were prepared from vinyl-derived commodity polymers, yielding sorbent polymers 100 of varying MW. Specifically, a variety of methacrylate and styrenic monomers were copolymerized with (2- acetoacetoxy)ethyl methacrylate (AAEMA). The resulting prepolymers were converted into CANs in a single step with no catalyst by treatment with a trifunctional amine. The resulting exchangeable enaminone linkages 118 allowed these materials to display the characteristic features and reprocessability of CANs over as many as six catalyst- and solvent-free reprocessing cycles. Because the prepolymers are readily synthesized by controlled radicalpolymerization 122, it is possible to prepare CANs from block copolymers capable of microphase separating into morphologies that determine reprocessability, transport, and the like, according to various embodiments.

[0055] FIGs. 3B-3E show various properties of non-limiting examples of the contemplated sorbent polymer 100. FIG. 3B shows the stress relaxation of the resulting sorbent polymers 100 as a function of MW. FIG. 3C shows Arrhenius plots and Eavalues for the sorbent polymers 100 as a function of MW. FIG. 3D shows SAXS profile for sorbent polymers 100 prepared from statistical and block copolymers. Finally, FIG. 3E shows an AFM phase image of a non-limiting example of a block copolymer sorbent polymer 100.

[0056] FIGs. 4A-4C are non-limiting examples of compounds at least partially derived from natural materials that may be substituted into the synthesis of a sorbent polymer 100 sorbent polymer. Specifically, FIG. 4 A shows fatty acid-derived alkyl methycrylate 400 (i.e., a monomer 102 for the pre-polymer 108), FIG. 4B shows a P-ketoester-functionalized vegetable oil 402 that is a bio-based pre-polymer 108 for the contemplated methods discussed above, and FIG. 4C shows a crosslinker 110 that is a polyamide 404 derived from a natural material.

[0057] According to various embodiments, there are various methods of incorporating vegetable oil-based components into the contemplated sorbent polymer 100 design. In some embodiments, some components of the contemplated sorbent polymer 100 may be replaced with materials derived from a bio-based source, like vegetable oil. Vegetable oils and their fatty acids are beneficial bio-based sources for polymers due to low costs, lack of toxicity, global availability, and ease of functionalization. Vegetable oils such as soybean oil, linseed oil, and castor oil have been used in the preparation of sorbent polymers 100 through functionalization routes including epoxidation, acrylation, carbonation, and hydroxylation, according to various embodiments. The flexibility of the long alkyl chains on the fatty acids of vegetable oils leads to more flexible CANs with elastomeric properties. Such rubbery networks are beneficial in the mobility and diffusion of CO2 through the network, as previously mentioned.

[0058] According to various embodiments, the design strategy presented in FIG. 1 can be modified such that at least one component of the sorbent polymer 100 is replaced with a vegetable oil derivative. A host of monomers, P ketoesters and polymeric amines can be made to include components from natural materials like vegetable oil. Three specific, nonlimiting examples will be discussed with respect to FIGs. 4A-4C.

[0059] In some embodiments, long-chain poly(meth)acrylates may be derived from fatty acids. Other embodiments may employ fatty acid-based alkyl methacrylate monomers, with alkyl chain lengths C12-C24, for the synthesis of the P ketoester-functionalized pre-polymers 108, as shown in FIG. 4 A.

[0060] In some embodiments, the P ketoester-functionalized pre-polymers 108 may be replaced with p ketoester-functionalized vegetable oils 402, as shown in FIG. 4B. To tune the network properties, the number of ketoester groups per vegetable oil triglyceride can be increased to beyond 3 through a thiol-ene coupling approach (i.e., using the unsaturated carboncarbon double bonds on the fatty acids), in which the hydroxyl functionality is increased prior to conversion to ketoester groups, according to various embodiments. . This approach has previously been used to prepare CANs from ketoester-functionalized castor oil, though the resulting CANs did not contain secondary amine groups required for CO2 sorption.

[0061] Furthermore, those prior studies emphasized the use of castor oil as the feedstock (which naturally contains hydroxyl groups). Toxicity issues and lack of global availability of castor oil may limit applicability of these embodiments. Soybean oil, a highly available vegetable oil in the US, does not suffer these limitations. Some embodiments make use of ketoester-functionalized soybean oil, which can be prepared by hydroxylating the carbon-carbon double bonds on the triglyceride.

[0062] In some embodiments, the PEI crosslinker 110 of FIG. 1 may be replaced with a polyamide 404 derived from a natural material. There are two important requirements for the polyamine crosslinker 110: primary amine end-groups that can participate in the CAN formation and secondary amines 114 distributed along the polymer chain to enhance CO2 sorption. Polyamides 404 are polymers prepared from step-growth polymerization that can meet these two requirements if an excess of an amine monomer 102 is used in their synthesis, leading to the presence of primary amine end-groups. In one embodiment, a polyamide 404 is derived from ricinoleic acid (the fatty acid found in castor oil), as shown in FIG. 4C. In another embodiment, a polyamide 404 is derived from oleic acid (a fatty acid found in many oils such as soybean and linseed oils).

[0063] FIG. 5 shows preliminary performance data for various non-limiting examples of the contemplated sorbent polymer 100 prepared using the contemplated method. Specifically, FIG. 5 shows the CO2 sorption capacity of various embodiments of the sorbent polymer 100. The samples were regenerated by exposure to steam at 95-100 °C for 1 h before being loaded into an open-flow test chamber. Compressed air with a fixed CO2 concentration was passed over the sample, and the outlet CO2 concentration was measured over time. Thereduction in outlet CO2 concentration was attributed to sorption by the sample. It should be noted that while the monolithic forms are unoptimized, they show that polymer composition and architecture affect performance.

[0064] As shown, the p(AAEMA) homopolymer has the highest amine concentration, but one of the lower sorption capacities ~25 pmol CCh / g polymer. The three p(BMA-co-AAEMA) copolymers have roughly the same AAEMA concentration (48-51%) and the same ratio of AAEMA:amine, but display CO2 sorption capacities that range from ~5- 150 pmol CO2 / g polymer. The copolymer films vary in molecular weight and molecular weight distribution. Finally, the p(BMA-co-AAEMA) block polymer shows the highest capacity of -250 pmol CO2 / g polymer. This sample has a 2° amine density (and theoretical CO2 capacity) of 3.87 mmol / g polymer, suggesting that the capacity of the sorbent can be increased dramatically. According to various embodiments, controlling the surface area to volume ratio via form factor design using the microphase separation behavior of block polymers to preferentially present amines at the surface and / or tuning other molecular properties can improve the capacity and (de)sorption rates of the contemplated materials.

[0065] It will be understood that implementations are not limited to the specific components disclosed herein, as virtually any components consistent with the intended operation of a recyclable covalent adaptable network for direct air capture and method for producing and using the same may be utilized. Accordingly, for example, although particular covalent adaptable networks may be disclosed, such components may comprise any shape, size, style, type, model, version, class, grade, measurement, concentration, material, weight, quantity, and / or the like consistent with the intended operation of a recyclable covalent adaptable network for direct air capture and method for producing the same may be used. In places where the description above refers to particular implementations of a recyclable covalent adaptable network for direct air capture, it should be readily apparent that a number of modifications may be made without departing from the spirit thereof and that these implementations may be applied to other air capture and / or polymer recycling technologies.

Claims

CLAIMSWhat is claimed is:

1. A method for using a sorbent polymer for capturing carbon dioxide, comprising: creating a pre-polymer through controlled radical polymerization (CRP) of at least one monomer comprising a first monomer, the first monomer having a P-ketoester moiety that is reactive; crosslinking the pre-polymer by reacting the P-ketoester moieties of the pre-polymer with a crosslinker comprising primary amines and secondary amines to form the sorbent polymer which is a covalent adaptable network (CAN) comprising a network of exchangeable enaminone linkages; exposing the sorbent polymer to an airflow such that the secondary amines of the CAN adsorb carbon dioxide from the airflow; and heating the sorbent polymer to release the carbon dioxide adsorbed by the secondary amines of the CAN.

2. The method of claim 1, further comprising recycling the sorbent polymer through associative exchanges within the exchangeable enaminone linkages of the CAN.

3. The method of claim 2, wherein the recycling is performed using melt processing.

4. The method of claim 1, wherein the CRP is reversible addition-fragmentation chain transfer (RAFT).

5. The method of claim 1, wherein the CRP comprises a chain transfer agent, a radical initiator, and a solvent.

6. The method of claim 5, wherein the chain transfer agent is 2-((l 1- mercaptoundecy 1 )thi o)aceti c aci d .

7. The method of claim 5, wherein the radical initiator is AIBN.

8. The method of claim 5, wherein the solvent is dioxane.

9. The method of claim 1, wherein the first monomer is (2-acetoacetoxy)ethyl methacrylate (AAEMA).

10. The method of claim 1, wherein the at least one monomer comprises at least one vinyl monomer.

11. The method of claim 1, wherein the at least one monomer comprises at least one of a methacrylate monomer and a styrenic monomer.

12. The method of claim 1, wherein the at least one monomer comprises an alkyl methacrylate having an alkyl group that is one of methyl, ethyl, butyl, hexyl, trifluoroethyl ( — CH2CF3), and dimethylaminoethyl ( — CH2CH2-N(CH3)2).

13. The method of claim 1, wherein the crosslinker is based on linear polyethyleneimine (PEI).

14. The method of claim 1, wherein the sorbent polymer is exposed to the airflow using a direct air capture (DAC) device.

15. The method of claim 1, wherein the sorbent polymer is a thermoset.

16. The method of claim 1, wherein at least one of the crosslinker, the first monomer, and at least one monomer other than the first monomer are derived from a natural material.

17. The method of claim 16, wherein the natural material is a vegetable oil.

18. The method of claim 17, wherein the vegetable oil is at least one of soybean oil, linseed oil, and castor oil.

19. The method of claim 17, further comprising functionalizing the vegetable oil using at least one of epoxidation, acrylation, carbonation, and hydroxylation.

20. The method of claim 16, wherein the crosslinker is a polyamide derived from a natural material.

21. The method of claim 20, wherein the polyamide is derived from ricinoleic acid.

22. The method of claim 20, wherein the polyamide is derived from oleic acid.

23. The method of claim 1, wherein the at least one monomer comprises an alkyl methacrylate that is derived from fatty acid, having an alkyl chain length that is greater than 11 carbons and less than 25 carbons.

24. A method for using a sorbent polymer for capturing carbon dioxide, comprising: crosslinking a pre-polymer having P-ketoester moieties by reacting the P-ketoester moieties of the pre-polymer with a crosslinker comprising primary amines and secondary amines to form the sorbent polymer which is a covalent adaptable network (CAN) comprising a network of exchangeable enaminone linkages; exposing the sorbent polymer to an airflow such that the secondary amines of the CAN adsorb carbon dioxide from the airflow; and heating the sorbent polymer to release the carbon dioxide adsorbed by the secondary amines of the CAN.

25. The method of claim 24, further comprising creating the pre-polymer through controlled radical polymerization (CRP) of at least one monomer comprising a first monomer, the first monomer having a P-ketoester moiety that is reactive.

26. The method of claim 24, wherein the pre-polymer is a P-ketoester-functionalized vegetable oil having a P-ketoester moiety that is reactive.

27. The method of claim 26, further comprising preparing the P-ketoester-functionalized vegetable oil by hydroxylating carbon-carbon double bonds on at least one triglyceride of a vegetable oil.

28. The method of claim 24, further comprising recycling the sorbent polymer through associative exchanges within the exchangeable enaminone linkages of the CAN.

29. The method of claim 28, wherein the recycling is performed using melt processing.

30. The method of claim 25, wherein the CRP is reversible addition-fragmentation chain transfer (RAFT).

31. The method of claim 25, wherein the CRP comprises a chain transfer agent, a radical initiator, and a solvent.

32. The method of claim 31, wherein the chain transfer agent is 2-(( 11- mer c aptoun decyl )thi o)aceti c aci d .

33. The method of claim 31, wherein the radical initiator is AIBN.

34. The method of claim 31, wherein the solvent is dioxane.

35. The method of claim 25, wherein the first monomer is (2-acetoacetoxy)ethyl methacrylate (AAEMA).

36. The method of claim 25, wherein the at least one monomer comprises at least one vinyl monomer.

37. The method of claim 25, wherein the at least one monomer comprises at least one of a methacrylate monomer and a styrenic monomer.

38. The method of claim 25, wherein the at least one monomer comprises an alkyl methacrylate having an alkyl group that is one of methyl, ethyl, butyl, hexyl, trifluoroethyl ( — CH2CF3), and dimethylaminoethyl ( — CH2CH2-N(CH3)2).

39. The method of claim 24, wherein the crosslinker is based on linear polyethyleneimine (PEI).

40. The method of claim 24, wherein the sorbent polymer is exposed to the airflow using a direct air capture (DAC) device.

41. The method of claim 24, wherein the sorbent polymer is a thermoset.

42. The method of claim 24, wherein the crosslinker is derived from a natural material.

43. The method of claim 42, wherein the natural material is a vegetable oil.

44. The method of claim 43, wherein the vegetable oil is at least one of soybean oil, linseed oil, and castor oil.

45. The method of claim 44, further comprising functionalizing the vegetable oil using at least one of epoxidation, acrylation, carbonation, and hydroxylation.

46. The method of claim 24, wherein the crosslinker is a polyamide derived from a natural material.

47. The method of claim 46, wherein the polyamide is derived from ricinoleic acid.

48. The method of claim 46, wherein the polyamide is derived from oleic acid.

49. The method of claim 25, wherein the at least one monomer comprises an alkyl methacrylate that is derived from fatty acid, having an alkyl chain length that is greater than 11 carbons and less than 25 carbons.

50. A sorbent polymer for capturing carbon dioxide, comprising: a covalent adaptable network (CAN) comprising P-ketoester moieties, primary amines, and secondary amines, and further comprising exchangeable enaminone linkages having dynamic covalent bonds; wherein the secondary amines adsorb carbon dioxide from an airflow; wherein the sorbent polymer is recyclable through associative exchanges within the exchangeable enaminone linkages of the CAN.

51. The sorbent polymer of claim 50, wherein the sorbent polymer is at least partially derived from a natural material.

52. The sorbent polymer of claim 51, wherein the natural material is a vegetable oil.

53. The sorbent polymer of claim 52, wherein the vegetable oil is at least one of soybean oil, linseed oil, and castor oil.

54. The sorbent polymer of claim 50, wherein the sorbent polymer is a thermoset.

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