DE102022123491A1 - Thermally reversibly crosslinkable polymers for use as sorbent materials in the area of carbon capture - Google Patents

Abstract

The invention relates to a method for the reversible storage of CO2 (carbon dioxide) using the Diels-Alder reaction and retro-Diels-Alder reaction. The invention also relates to the two starting compounds and their use for this purpose. It is envisaged that the following two starting compounds are used as a mixture at a temperature of <70 ° C, so that a thermoreversible sorbent material is formed by means of the Diels-Alder reaction :• 1,3-diene compound and a• dienophile compound, each of these two compounds comprising a polymer chain containing amine groups. When it comes into contact with CO2, it is reversibly stored in the thermoreversible sorbent material.

Description

The invention relates to a method for the reversible storage of CO ₂ (carbon dioxide) using the Diels-Alder reaction and retro-Diels-Alder reaction.

The need to slow global climate change caused by greenhouse gas emissions is very urgent. Above all, the increase in atmospheric CO ₂ levels must be sustainably avoided. In addition to avoiding and reducing CO _2, technologies for adsorbing CO ₂ from the ambient air, called “Direct Air Capture” (DAC), are suitable for reducing the proportion of CO ₂ in the atmospheric air through “negative carbon emissions”. The development of suitable adsorption materials should enable efficient and energetically sensible CO ₂ capture. A challenge is the development of efficient sorption materials/sorbent materials that have a high CO ₂ adsorption capacity and require little energy for desorption, as this is particularly important in large-scale industrial environments.

Classic sorbent materials for storing CO ₂ include, for example, the groups of metal organic frameworks (MOFs), amine-functionalized adsorbers, functionalized activated carbon materials, zeolites and other polymers. Polymer-based adsorbers in particular offer a good opportunity to combine high adsorption capacity with economic advantages.

KR 2017009796 A discloses a CO ₂ absorber made of 3d porous graphene nanoribbon, in which the CO ₂ is trapped in the carbon network. Using a Diels-Alder reaction, a nanoribbon with defined 3D pores is built from carbon repeat units. During the Dies-Alder reaction, CO ₂ is released from one of the starting compounds and escapes. As a result, this Diels-Alder reaction is irreversible and irreversible. The disadvantage is that CO ₂ release occurs at elevated temperatures, which leads to degradation processes.

Describes for dissolved substances, such as active pharmaceutical ingredients US 2013/0048853 A1 a heterocyclic copolymer adsorber. The copolymers are made up of divinylbenzene and triallyl cyanurate.

WO 2019/101160 A1 discloses a gas adsorber made from 2,5-furandiimine guanidine, as an acidic gas adsorber and as an anionic precipitant. The disadvantage is that the chemical compound has to be dissolved in a solvent in order to be able to separate a yellow CO ₂ adduct (carbonate 2,5-furan-guanidine tetrahydrate) later. This can later release CO ₂ and H ₂ O again with great effort. The method disclosed is not suitable for large-scale storage of CO ₂ because it is very complicated in terms of process technology.

Polyethyleneimine polymers (PEI), which are branched and cross-linked, are also established in order to ensure good adsorption capacity using intermolecular interactions between the carbon dioxide and the aminic polymer. However, a major disadvantage of these materials is their tendency to degrade over time. The mechanisms of aging include, for example, oxidative degradation at elevated temperatures with the formation of ammonium salts, hydroxylamine structures, amine oxides, nitroso compounds and nitro compounds. Other degradation mechanisms include, for example, aminic degradation with the formation of urea derivatives and the formation of cyclic urea structures from the polymer chain. However, for CO ₂ storage in polymers, the most significant degradation mechanism is thermal degradation, as this occurs during the temperature-induced CO ₂ desorption process. In this type of degradation, for example, Hofmann elimination (Hofmann degradation) occurs with the formation of quaternary ammonium compounds. Further thermal degradation leads to the formation of cyclic imidazole structures as well as the formation of numerous urea derivatives with the breaking of the linear chain structure in the polymer chain. The breaking of the polymer chains and the associated removal of amine structures leads to a reduction in the amine density of the polymer and thus to a constant reduction in the adsorption capacity for CO ₂ .

A further disadvantage of such known polyethyleneimine polymer networks, in which the polyethyleneimines themselves are irreversibly cross-linked, is the presence of tertiary and quaternary alkyl amine groups formed during the cross-linking between the polyethyleneimine chains (ie those nitrogen atoms to which hydrogen is no longer bonded ). In particular, the quaternary alkyl amine groups no longer have a free pair of electrons available on the nitrogen. This leads to a low sorption capacity for CO ₂ .

Another disadvantage is that this cross-linking in the polyethyleneimine polymers leads to a lower mobility of these polymer chains and thus tends to lead to longer diffusion times for the CO ₂ .

The object of the invention is to provide a process or starting materials so that reversible storage of gaseous CO ₂ by means of sorption is possible. The process should be simple and the starting materials should be easy to use. What is also important is applicability on an industrial scale. The sorbent material should have a long shelf life and should not be subject to strong degradation processes, because the capacity for CO ₂ absorption should be consistently high over a long period of time.

The invention relates to a 1,3-diene compound and a dienophile compound, each comprising a polymer chain which has amine groups. In particular, the repeating units of the polymer chain have the amine groups. Of course, it is also included that both compounds each comprise several such polymer chains.

oder auch Furan mit der folgenden Formel:

As is well known, “1,3-diene compound” means that within this chemical compound two CC double bonds are arranged next to each other, as is the case, for example, with 1,3-butadiene, which has the following formula:

or furan with the following formula:

oder auch Maleinsäureimid mit der folgenden Formel:

The “dienophile compound” is a chemical compound that is an alkene, i.e. comprises at least one double bond, the compound being a suitable reactant for 1,3-dienes in a Diels-Alder reaction. It is known that electron-withdrawing substituents on the double bond withdraw electrons. This enables the reaction with a 1,3-diene compound. The person skilled in the art recognizes these electronic properties from the double bond and knows which compounds are suitable or could be suitable. A well-known representative of the dienophiles is, for example, maleic anhydride, which has the following formula:

or maleimide with the following formula:

“Polymer chain” in the sense of the invention includes both linear and branched polymers, because it is known to those skilled in the art that amine groups can interact with CO ₂ and the degree of branching of the polymer chain containing the amine groups can be variable. However, the branched polymers as a polymer chain are not completely cross-linked. This means they are still soluble in solvents, such as water. In particular, the amine groups are secondary and tertiary amine groups, ie those that still have a free pair of electrons on the nitrogen atom, which can interact with the CO ₂ . In particular, a polymer chain is recommended as a homopolymer, ie made up of the same repeating units, with each repeating unit having such an amine group. However, copolymers are also possible, in which case at least one of the monomers used is an amine group pen has. For the purposes of the invention, it is also included that coupling groups are contained between the polymer chain and the respective compound, which can be different, depending on whether the polymer chain has been linked to the 1,3-diene compound or to the dienophile compound.

The invention utilizes the concept of the Diels-Alder reaction of a 1,3-diene with a dienophile. The concept was modified to form a thermoreversible polymeric sorbent material for CO ₂ at low temperatures and the possibility of initiating a retro-Diels-Alder reaction by increasing the temperature. The CO ₂ that is to be bound interacts with the amine groups. However, it can only be stored for a longer period of time if the 1,3-diene compound according to the invention and the dienophile compound have been linked via the Diels-Alder reaction, with at least one polymer chain with the amine groups attached to each of the compounds, and a 3D network is created from the polymer chains (i.e. a cross-linked polymer network). This is the only way the CO ₂ can be stored for a long time. The invention allows the cross-linked polymer network to dissolve by increasing the temperature above 70 ° C, which leads to the separation of the polymer chains according to the invention, so that the CO ₂ is released again over time.

1. a) Bereitstellen einer Mischung enthaltend eine
   • • 1 ,3-Dien-Verbindung und eine
   • • Dienophil-Verbindung,

wobei jede dieser beiden Verbindungen (mindestens) eine Polymerkette, aufweisend Amin-Gruppen, umfasst, bei einer Temperatur von <70 °C, zur Bildung eines thermoreversiblen Sorbentmaterials,

• b) Kontaktieren von CO₂ mit dem thermoreversiblen Sorbentmaterial aus Schritt a).

The invention furthermore relates to a method for the reversible storage of CO ₂ with the steps:

1. a) Providing a mixture containing a
   • • 1,3-Diene compound and a
   • • Dienophile compound,

wherein each of these two compounds comprises (at least) one polymer chain containing amine groups, at a temperature of <70 ° C, to form a thermoreversible sorbent material,

• b) contacting CO ₂ with the thermoreversible sorbent material from step a).

The thermoreversible sorbent material therefore comprises the adduct of 1,3-diene compound and dienophile compound with the respective polymer chains which have amine groups. It is also included that other substances are included; In particular, unavoidable substances such as solvents, catalysts, etc. in amounts of a maximum of 10% by weight, in particular with a maximum of 2% by weight, or even <1% by weight, at best <0.3% by weight. %. Contacting with CO ₂ can take place simultaneously with step a) or downstream of the step. If downstream, the temperature in step b) is the same as in step a).

Finally, the invention also relates to the use of a 1,3-diene compound and/or a dienophile compound, each comprising a polymer chain containing amine groups, for the reversible storage of CO ₂ , in particular the use of the two compounds according to the invention in the invention Procedure.

The advantage of the invention is that the low temperatures in the Diels-Alder reaction (that is the reaction that takes place in step a) and when contacting the 1,3-diene compound with the dienophile compound at <70 ° C) and also The still relatively low temperature of the retro-Diels-Alder reaction (which is the optional reaction that can be carried out to release the CO ₂ from the sorbent material again at temperatures >70 °C) prevents the sorbent material from being broken down. There is therefore advantageously no or only slight degradation of the sorbent material, in particular of the polymer chains containing the amine groups.

Another advantage of the invention is that the “limit temperature” in step b) of 70 ° C is low, which means that a particularly high temperature is not necessary for a later desired desorption. The invention is therefore suitable for the reversible storage of CO ₂ on a large industrial scale.

The advantage of the invention is that the polymer chains with the amine groups do not have to be irreversibly cross-linked in order to absorb the CO ₂ , because the CO ₂ is produced by the Diels-Alder reaction of the two compounds according to the invention (1,3-diene and dienophile). bound, in which the actual polymer network first forms, due to which the CO ₂ remains bound. The amine groups can therefore remain free, ie they retain at least one free pair of electrons, and better even an H substituent, so that the capacity of CO ₂ sorption does not necessarily have to be reduced.

In this context, a significant advantage is that due to the possibility of keeping the amine groups in the polymer chain free, the diffusion of the CO ₂ into the sorbent material formed can occur more quickly than if the polymer chains themselves had to be irreversibly cross-linked via the amine groups to bind the CO ₂ .

An important advantage of the invention is that it makes it possible to reversibly store and release CO ₂ in a simple manner, simply through the step of changing the temperature, which is very easy to implement on an industrial scale. No solvent change is necessary.

In a preferred embodiment of the invention, the polymer chain is a branched polymer chain with at least 5% branched repeating units. This means that a maximum of 95% of the repeating units in the polymer chain are unbranched. However, the polymer chain is not yet cross-linked in a way that would prevent the polymer chains from being dissolved in a solvent. This means that the branched polymer chains in this embodiment are still soluble in a solvent, in particular in water. Particularly preferably at least 20% is branched, in particular even at least 70%. This is particularly effective for the reversible storage of CO ₂ . In particular, this degree of branching allows a balance between effective storage in the (reversibly cross-linked) sorbent material and rapid CO ₂ release upon “dewetting” of the sorbent material by increasing the temperature (via the retro-Diels-Alder reaction).

In one embodiment, where the polymer chain is polyethyleneimine, the branching is in a range obtained when ethyleneimine (aziridine) is polymerized to polyethyleneimine by ring-opening polymerization. This degree of branching is difficult to measure, but is very characteristic and uniform in this production variant.

In one embodiment, the temperature in step a), that is, when the thermoreversible sorbent material is formed, is even ≤ 65 ° C, in particular also ≤ 60 ° C.

• c) Erhitzen des thermoreversiblen Sorbentmaterials (nach Schritt b) des Verfahrens) auf eine Temperatur von > 70 °C zur Freisetzung des CO₂ (bevorzugt ≥ 75 °C, insbesondere sogar ≥ 80 °C). Sinnvoller Weise übersteigt diese Temperatur nicht die 90 °C, besser sie bleibt unterhalb von oder gleich 85 °C, denn das Sorbentmaterial soll keinen oder nur geringen thermischen Abbau erleiden.

In a preferred embodiment of the invention, a re-release of the CO ₂ is achieved by the step:

• c) heating the thermoreversible sorbent material (after step b) of the process) to a temperature of >70 °C to release the CO ₂ (preferably ≥ 75 °C, in particular even ≥ 80 °C). It makes sense that this temperature does not exceed 90 °C, it is better that it remains below or equal to 85 °C, because the sorbent material should suffer little or no thermal degradation.

Advantageously, this temperature for desorption of the CO ₂ is relatively low, so that on the one hand the sorbent material is not subject to thermal degradation even when CO ₂ is released and on the other hand the operating costs remain manageable on a large industrial scale.

It has been shown that the entire thermoreversible sorbent material does not have to break down into its individual parts, but that it is sufficient if the pores expand due to the dissolution of individual crosslinking points. Advantageously, a temperature of >70 °C (up to a maximum of 90 °C) is sufficient to achieve this and the associated re-release of CO ₂ in an effective manner, without initiating any significant thermal degradation.

In a preferred variant of this embodiment with a release step by heating the thermoreversible sorbent material after step b), the temperature in step a) is ≤ 65 ° C and that in the release step c) is then ≥ 75 ° C. Even more preferably, the temperature in step a) is ≤ 60 ° C and in the release step ≥ 80 ° C.

In a special variant of the above-mentioned embodiment with step c), a vacuum is also applied in addition to the heating in order to accelerate the release of the CO ₂ .

In a preferred embodiment of the invention, the 1,3-diene compound is a furan compound, that is, it comprises a furyl unit. It is preferably a furfuryl alcohol, with the polymer chain according to the invention particularly preferably being attached to the alcohol group of the furfuryl alcohol. Advantageously, such compounds are easily available on an industrial scale and are therefore inexpensive and available in large quantities. In addition, furfuryl alcohol can advantageously be produced entirely from renewable raw materials (starting from furfural from agricultural residues).

oder Hydrate oder Salze davon mit der Polymerkette, aufweisend die Amin-Gruppen, an einem der beiden Kohlenstoffatome der Epoxid-Einheit.In a preferred embodiment of the invention, the 1,3-diene compound is a compound obtained by substitution of 2-[(oxiranyl-methoxy)methyl]furan (also called 2,3-epoxypropyl 2-furylmethyl ether), i.e the following chemical structure

or hydrates or salts thereof with the polymer chain containing the amine groups on one of the two carbon atoms of the epoxide unit.

wobei R₂ die Polymerkette, aufweisend die Amin-Gruppen, bedeutet.In a preferred embodiment of the invention, the dienophile compound is a maleimide compound, such as maleimide, which has been functionalized on the nitrogen atom with the polymer chain containing the amine groups, or such as N-hydroxymaleimide, which has been functionalized on the OH group with the Polymer chain was functionalized. For example, in the case of maleimide, this corresponds to the structure:

where R ₂ means the polymer chain containing the amine groups.

The N-hydroxymaleimide is usefully linked to the polymer chain at the OH group.

In a preferred embodiment of the invention, the 1,3-diene compound is a compound according to formula I and/or the dienophile compound is a compound according to formula II, in which R ¹ and R ² are each the polymer chain containing amine groups :

This is particularly suitable for the reversible storage of CO ₂ . In particular, the -CH ₂ -O- joint in the compound according to formula I is advantageous in order to gain a certain flexibility in the (reversibly cross-linked) sorbent material according to the invention, which improves CO ₂ storage.

In a further embodiment of the invention, the polymer chain has a chain length of at least 5 repeating units, each of the repeating units having at least one of the amine groups. This means that in particular the polymer chain according to the invention also has at least this number of amine groups. In the case of a copolymer, these repeating units with the amine groups can also be present distributed throughout the entire copolymer. This is particularly effective for the reversible storage of CO ₂ . In particular, this minimum polymer size allows a balance between effective storage in the (reversibly cross-linked) sorbent material and rapid CO ₂ release upon “dewetting” of the sorbent material by increasing the temperature (via the retro-Diels-Alder reaction). The polymer chain particularly preferably has at least 10 repeating units, very particularly preferably at least 300, in particular 300 - 600, or even 400 - 500. Here too, the polymer chain preferably has this as the minimum number of amine groups.

In a preferred embodiment of the invention, the polymer chain is a polyethyleneimine chain. It is particularly preferred to be branched polyethyleneimine. This has a particularly strong interaction with CO ₂ , which has proven to be particularly favorable for reversible storage using the Diels-Alder and retro-Diels-Alder reactions.

In a particularly preferred variant of this embodiment of the invention, the polyethyleneimine chain has a molecular weight of 14,000 g/mol to 21,000 g/mol. The molar mass is determined using gel permeation chromatography and a light scattering detector as the average of the number-average molar mass Mn and the weight-average molar mass Mw. Mn is in particular 8,000-12,000 g/mol (very particularly preferably 10,000 ± 500 g/mol) and Mw is 20,000-30,000 g/mol (very particularly preferably 25,000 ± 1000 g/mol). The polydispersity is therefore particularly preferably (Mw/Mn) 2.5 (±20%), or also 2.2-2.8. Finally, the molar mass (as the average of Mn and Mw) is preferably 14,000 - 21,000 g/mol, in particular 17,500 ± 2,500 g/mol or even 17,000 - 18,000 g/mol. These molecular weights have proven to be particularly effective for the reversible storage of CO ₂ because the molecular distance of the polymer chains between the crosslinking points (which result from the two compounds: 1,3-diene compound and dienophile compound) is so favorable designed so that penetration through the carbon dioxide is possible and interactions with the amine groups can take place.

Further preferred embodiments of the invention result from the remaining features mentioned in the subclaims.

The various embodiments of the invention mentioned in this application can be advantageously combined with one another, unless stated otherwise in individual cases.

The invention is explained below in exemplary embodiments using the associated drawing.

1 shows schematically the operation of the invention, where R ₁ and R ₂ are the polymer chains which have the amine groups. The sorption of CO ₂ when the temperature T ₁ falls below 70 °C is illustrated (because a cross-linked polymer network has formed due to the Diels-Alder reaction) and the desorption of CO ₂ when the temperature T ₂ is exceeded, which is also 70 °C due to the retro-Diels-Alder reaction.

Example 1:

The two starting materials PEI-functionalized maleimide (maleimide) and PEI-functionalized 2-[(oxiranyl-methoxy)methyl]furan were used to absorb CO ₂ .

Both substances were dissolved in suitable solvents. CO ₂ was bubbled through the solution at room temperature (15 °C - 45 °C). To release the liquid solution, it was heated to 82 °C and treated under a slight vacuum of 500 mbar for 1 hour.

The polymer chains used on the two starting materials were PEI (polyethyleneimine) (branched) with 25 kDa (Mw) with Mw at approx. 25,000 (determined with a light scattering detector) and Mn at approx. 10,000 determined by GPC. The calculated degree of polymerization is approximately 43.

QUOTES INCLUDED IN THE DESCRIPTION

This list of documents listed by the applicant was generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• KR 2017009796 A [0004]
• US 2013/0048853 A1 [0005]
• WO 2019/101160 A1 [0006]

Claims (10)

1,3-Diene compound or dienophile compound, each comprising a polymer chain containing amine groups. Method for the reversible storage of CO ₂ with the steps: a) providing a mixture containing a • 1,3-diene compound and a • dienophile compound, each of these two compounds comprising a polymer chain containing amine groups, at a Temperature of <70 ° C, to form a thermoreversible sorbent material, b) contacting CO ₂ with the thermoreversible sorbent material from step a). Procedure according to Claim 2 , wherein the release of the CO ₂ is achieved by the step: c) heating the thermoreversible sorbent material after step b) to a temperature of > 70 ° C to release the CO ₂ . Procedure according to one of the Claims 2 or 3 , where the 1,3-diene compound is a furan compound. Procedure according to one of the Claims 2 until 4 , where the dienophile compound is a maleimide compound. Procedure according to one of the Claims 2 until 5 , where the 1,3-diene compound is a compound according to formula I and/or the dienophile compound is a compound according to formula II, in which R ¹ and R ² are each the polymer chain containing amine groups:

Procedure according to one of the Claims 2 until 6 , wherein the polymer chain has a chain length of at least 5 repeating units, each of the repeating units having at least one of the amine groups. Procedure according to one of the Claims 2 until 7 , where the polymer chain is a polyethyleneimine chain. Procedure according to Claim 8 , where the polyethyleneimine chain has a molecular weight of 14,000 g/mol to 21,000 g/mol. Use of a 1,3-diene compound and/or a dienophile compound, each comprising a polymer chain containing amine groups, for the reversible storage of CO ₂ .

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