WO2024002881A1

WO2024002881A1 - Sorbent materials for co2 capture, uses thereof and methods for making same

Info

Publication number: WO2024002881A1
Application number: PCT/EP2023/067066
Authority: WO
Inventors: Cornelius GROPP; Davide Albani; Claudio LIMONE; Angelo VARGAS
Original assignee: Climeworks Ag
Priority date: 2022-06-28
Filing date: 2023-06-23
Publication date: 2024-01-04

Abstract

A method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material (3) capable of reversibly binding carbon dioxide and adsorbing said gaseous carbon dioxide in a unit (8), is proposed, using a sorbent material (3) comprising primary as well as secondary and/or tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene- divinylbenzene support is functionalised by secondary or tertiary benzylamine and/or secondary or tertiary α-methylbenzylamine groups substituted with at least one of ethyleneamine, propylenamine, or other branched or linear alkyldiamine systems.

Description

TITLE

SORBENT MATERIALS FOR CO2 CAPTURE, USES THEREOF AND METHODS FOR MAKING SAME

TECHNICAL FIELD

The present invention relates to carbon dioxide capture materials with primary and/or secondary amine carbon dioxide capture moieties with good capture and swelling properties, as well as methods for preparing such capture materials, uses of such capture materials and carbon dioxide capture methods involving such materials.

PRIOR ART

According to the OECD report of 2017 [Global Energy & CO2 Status Report 2017, OECD/IEA March 2018] the yearly emissions of CO2 to the atmosphere are ca 32.5 Gt (Gigatons, or 32.5x10E9 tons). As of February 2020 all but two of the 196 states that in 2016 have negotiated the Paris Agreement within the United Nations Framework Convention on Climate Change (UFCCC) have ratified it. The meaning of this figure is that a consensus is reached regarding the threat of climate change and regarding the need of a global response to keep the rise of global temperature well below 2 degrees Celsius above pre-industrial levels.

The technical and scientific community engaged in the challenge of proposing solutions to meet the target of limiting CO2 emissions to the atmosphere and to remove greenhouse gases from the atmosphere through or with a number of technologies. Flue gas capture, or the capture of CO2 from point sources, such as specific industrial processes and specific CO2 emitters, deals with a wide range of relatively high concentrations of CO2 (3-100 vol %) depending on the process that produces the flue gas. High concentrations make the separation of the CO2 from other gases thermodynamically more favorable and consequently economically favorable as compared to the separation of CO2 from sources with lower concentrations, such as ambient air, where the concentration is in the order of 400 ppm. Nonetheless, the very concept of capturing CO2 from point sources has strong limitations: it is specifically suitable to target such point sources, but is inherently linked to specific locations where the point sources are located and can at best limit emissions and support reaching carbon neutrality, while as a technical solution it will not be able to contribute to negative emissions (i.e., permanent removal of carbon dioxide from the atmosphere) and to remove historic emission. In order to achieve negative emissions (i.e., permanent removal carbon dioxide from the atmosphere), the two most notable solutions currently applied, albeit being at an early stage of development, are the capturing of CO2 by means of vegetation (i.e., trees and plants, but not truly permanent removal) using natural photosynthesis, and by means of DAC technologies, which is the only truly permanent removal.

Forestation has broad resonance with the public opinion. However, the scope and feasibility of re-forestation projects is debated and is likely to be less simple an approach as believed because it requires a large footprint in terms of occupied surface to captured CO2 ratio. On the other hand, DAC has lower land footprint and therefore it does not compete with the production of crops, can permanently remove CO2 from the atmosphere and can be deployed everywhere on the planet.

The above-described strategies to mitigate climate change all have potential and are considered as a potential part of the overall solution. The most likely future scenario is the deployment of multiple or a variety of different approaches, after undergoing further development.

Several DAC technologies were described, such as for example, the utilization of alkaline earth oxides to form calcium carbonate as described in US-A-2010034724. Different approaches comprise the utilization of solid CO2 adsorbents, hereafter named sorbents, in the form of packed beds of typically sorbent particles and where CO2 is captured at the gassolid interface. Such sorbents can contain different types of amino functionalisation and polymers, such as immobilized aminosilane-based sorbents as reported in US-B-8834822, and amine-functionalised cellulose as disclosed in WO-A-2012/168346.

WO-A-2011/049759 describes the utilization of an ion exchange material comprising an aminoalkylated bead polymer for the removal of carbon dioxide from industrial applications. WO-A-2016/037668 describes a sorbent for reversibly adsorbing CO2 from a gas mixture, where the sorbent is composed of a polymeric adsorbent having a primary amino functionality. The materials can be regenerated by applying pressure or humidity swing.

Several academic publications, such as Alesi et al. in Industrial & Engineering Chemistry Research 2012, 51 , 6907-6915; Veneman et al. in Energy Procedia 2014, 63, 2336; Yu et al. in Industrial & Engineering Chemistry Research 2017, 56, 3259-3269, also investigated in detail the use of cross-linked polystyrene resins functionalised with primary benzylamines as solid sorbents for DAC applications. Polystyrene-divinylbenzene resins have also been used as a support to impregnate amines such as tetraethylenepentamine and diethanolamine (CN 105195113A and Kim et al., Bull Chem. Soc. Jpn. 2015, 88, 1317-1322), systems that are only compatible with desorption processes that do not involve any condensation of a gas stream such as saturated or supersaturated steam. Also, WO2021136744A1 show the functionalisation of polystyrene-divynylbenzen polymers with a high variaty of amines and their use in carbon capture of gas stream with high conentration of CO2. However, the nitrogen content reported in WO2021136744A1 is between 5-10 mol/kg, which is similar to the amount that can be reached by functionalising PS-DVB with benzylamine as reported by Alesi et al. in Industrial & Engineering Chemistry Research 2012, 51 , 6907-6915. An optimal sorbent ideally should be predominant composed of active phase to be able to intensify the carbon capture process.

Amines react with CO2 to form a carbamate moiety, which in a successive step can be regenerated to the original amine, for example by increasing the temperature of the sorbent bed to ca 100°C and therefore releasing the CO2. An economically viable process for carbon capture implies the ability of the sorbent to capture as much CO2 as possible in a very short period of time so that the throughput of the system can be increased. To this end, this feature is of course related to the amount of active amine sites able to bind CO2, thus, it is very important to develop new materials with a high CO2 capture capacity. Some materials show limits to the degree of functionalisation that can be achieved, thus new nontrivial sorbent structures are required to be invented to overcome this limitation.

Heydari-Gorji et al. (Polyethylenimine-lmpregnated Mesoporous Silica: Effect of Amine Loading and Surface Alkyl Chains on CO2 Adsorption, Langmuir 2011 , 27, 12411-12416) discuss poly(ethyleneimine) (PEI) supported on pore-expanded MCM-41 whose surface is covered with a layer of long-alkyl chains, and which was found to be a more efficient CO2 adsorbent than PEI supported on the corresponding calcined silica and all PEI-impregnated materials reported in the literature. The layer of surface alkyl chains is reported to play an important role in enhancing the dispersion of PEI, thus decreasing the diffusion resistance. It was also found that at low temperature, adsorbents with relatively low PEI contents are more efficient than their highly loaded counterparts because of the increased adsorption rate. Extensive CO2 adsorption-desorption cycling showed that the use of humidified feed and purge gases affords materials with enhanced stability, despite limited loss due to amine evaporation.

Zhang et al. (Capturing CO2 from ambient air using a polyethyleneimine-silica adsorbent in fluidized beds, Chemical Engineering Science 116 (2014) 305-316) report the performance of a mesoporous silica-supported polyethyleneimine (PEI)— silica adsorbent for CO2 capture from ambient air in a laboratory-scale Bubbling Fluidized Bed (BFB) reactor. The air capture tests lasted for between 4 and 14 days using 1 kg of the PEI-silica adsorbent in the BFB reactor. Despite the low CO2 concentration in ambient air, nearly 100% CO2 capture efficiency has been achieved with a relatively short gas-solid contact time of 7.5 s. The equilibrium CO2 adsorption capacity for air capture was found to be as high as 7.3 wt%. The proposed “PEI-CFB air capture system” mainly comprises a Circulating Fluidized Bed (CFB) adsorber and a BFB desorber with a CO2 capture capacity of 40 t-CO2/day. A large pressure drop is required to drive the air through the CFB adsorber and also to suspend and circulate the solid adsorbents within the loop, resulting in higher electricity demand than other reported air capture systems. However, the Temperature Swing Adsorption (TSA) technology adopted for the regeneration strategy in the separate BFB desorber has resulted in much smaller thermal energy requirement. The total energy required is 6.6 GJ/t-CO2 which is comparable to other reference air capture systems.

WO-A-2022013197 discloses a method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, by cyclic adsorption/desorption using a sorbent material, wherein the method comprises at least the following sequential and in this sequence repeating steps (a) - (e): (a) contacting said gas mixture with the sorbent material to allow gaseous carbon dioxide to adsorb; (b) isolating said sorbent material from said flow-through; (c) inducing an increase of the temperature of the sorbent material; (d) extracting at least the desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide from steam in or downstream of the unit; (e) bringing the sorbent material to ambient atmospheric conditions; wherein said sorbent material comprises primary and/or secondary amine moieties immobilized on a solid support, wherein the amine moieties, in the a -carbon position, are substituted by one hydrogen and one non-hydrogen substituent (R). Importantly, the treatment of chloromethylated poly(styrene-co-divinylbenzene) based starting material with hexamethylentetramine (HMTA) disclosed in that document in the experimental section leads to amination and formation of primary amines only. No secondary amines are formed. WO-A-2021239748 discloses a method for separating gaseous carbon dioxide from a gas mixture by cyclic adsorption/desorption, using a unit containing an adsorber structure with said sorbent material, wherein the method comprises the following sequential and in this sequence repeating steps: (a) contacting said gas mixture with the sorbent material to allow said gaseous carbon dioxide to adsorb under ambient atmospheric pressure and temperature conditions in an adsorption step, using a speed of the adsorption gas flow; (bO) isolating said sorbent with adsorbed carbon dioxide in said unit from said flow-through of gas mixture; (b1) injecting a stream of saturated steam essentially at ambient atmospheric pressure conditions and thereby inducing an increase of the temperature of the sorbent to a temperature between 60 and 110°C, (b2,b3) extracting at least the desorbed gaseous carbon dioxide while still injecting and/or circulating saturated steam at ambient atmospheric pressure conditions into said unit; (c) bringing the sorbent material to ambient atmospheric temperature conditions; wherein the speed of steam flow through the unit in step (b1) and/or on average in steps (b1)-(b3) is in the range of 0.5-10 times the speed of the adsorption gas flow in step (a).

GB-A-1296889 discloses how carbon dioxide is separated from mixtures with non-acid gases such as air by sorption on a weakly basic ion exchange resin followed by desorption with steam under conditions such that the steam condenses at the inlet end of the resin bed and a front of condensing steam then progressively passes through the bed displacing the carbon dioxide. Sorption is suitably conducted at 40-90 F and at a relative humidity of 75- 90%. The preferred ion exchanger is a polystyrene-divinylbenzene copolymer containing polyamino functional groups, each of which comprises at least one secondary amino nitrogen atom. In a figure, an automatically controlled single bed sorption-regeneration system is illustrated.

SUMMARY OF THE INVENTION

Amines react with CO2 to form of a carbamate moiety, which in a successive step can be regenerated to the original amine, for example by increasing the temperature of the sorbent bed to ca. 100°C and therefore releasing the CO2. An economically viable process for carbon capture implies the ability to perform the cyclic adsorption/desorption of 002 for hundreds or thousands of cycles over the same sorbent material, where the sorbent shall not undergo any or if at all only insignificant chemical transformations that impedes its reactivity towards 002.

The co-polymerization of styrene and divinylbenzene is shown in Scheme 1 :

Scheme 1

For converting such systems, e.g. in particulate form, into materials suitable for carbon dioxide capture, they can be chloromethylated in a first step under formation of a chloromethylated styrene-divinylbenzene resin and then aminated to form primary benzylamine groups which are then providing the primary amines for carbon dioxide capture. Amination can e.g. be carried out by reacting the chloromethylated styrene- divinylbenzene resin with hexamethylenetetramine followed by hydrolysis typically under acidic conditions.

While such primary amine systems perform well for carbon dioxide capture purposes, including direct air capture, still higher capture capacity is needed for a more efficient carbon dioxide removal process.

According to the present invention this object is achieved by a new method for separating gaseous carbon dioxide from a gas mixture using a new sorbent material according to claim 1.

It is noted that in the document WO 2022/013197 mentioned above, in the experimental section reacting chloromethylated poly(styrene-co-divinylbenzene) based starting material with hexamethylentetramine (HMTA) is disclosed, which leads to a simple amination, so the resulting product is a primary amine poly(styrene-co-divinylbenzene) system.

Furthermore it is noted that in the document GB 1 296 889 also mentioned above reacting chloromethylated poly(styrene-co-divinylbenzene) based starting material with diamine systems is disclosed, however only with polyamine systems, such as diethylenetriamine or diethylenetdiamine. The focus there is on using polyfunctional amine systems, so obtaining predominantly secondary amine functionality in the resulting system due to the polyamine chains attached to the divinylbenzene backbone structure.

In contrast, the present invention focuses on and claims systems where single linear or branched alkyl diamine systems with 2-5 carbon atoms are attached to the divinylbenzene backbone structure, so there are no polyamine polyalkyl systems attached to the backbone. Defined differently, what is claimed are systems in which the divinylbenzene is substituted with linear or branched alkylamine where for essentially each substituted system there is only one secondary amine or tertiary and a minimum of one primary amine functionality available for carbon dioxide capture purposes. So, the substitution of the divinylbenzene is free from alkyldiamine moieties which are attached to one or more further alkyldiamine moieties.

Surprisingly, as will be detailed and evidenced further below, the claimed systems show superior properties compared with the polyamine systems known in the prior art, in particular if the chain length of the diamine system is chosen to have 3-4 carbon atoms. In fact what is observed is an increase in carbon dioxide capture capacity, which surprisingly is not observed in parallel as concerns the exchange capacity behavior, so surprisingly the advantage is only to be seen for the carbon dioxide capture property but not for the exchange capacity for the usual exchange applications of corresponding resins (in particular under wet/immersion conditions for example in water). Also, there is a significant increase in the kinetic of carbon dioxide capture uptake and an increase in amine efficiency.

One possible synthetic pathway to obtain the corresponding systems for the example of 1 ,3-propylene diamine as a reactant is given in the following Scheme 2:

Scheme 2

More specifically, the present invention according to a first aspect thereof relates to a method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material capable of reversibly binding carbon dioxide and adsorbing said gaseous carbon dioxide in a unit, wherein the method comprises at least the following sequential and in this sequence repeating steps (a) - (e):

(a) contacting said gas mixture with the sorbent material to allow at least said gaseous carbon dioxide (parts thereof or essentially all of the CO2) to adsorb on the sorbent material by flow-through through said unit (and thus through and/or over the sorbent material adsorbing at least part of said gaseous carbon dioxide) under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step (if ambient atmospheric air is pushed/pulled through the device using a ventilator for the like, this is still considered ambient atmospheric pressure conditions in line with this application, even if the air which is pushed/pulled through the reactor by the ventilator has a pressure slightly above or below the surrounding ambient atmospheric pressure, and the pressure is in the ranges as detailed below in the definition of "ambient atmospheric pressures");

(b) isolating said sorbent material with adsorbed carbon dioxide in said unit from said flow- through, preferably while essentially maintaining the temperature in the sorbent;

(c) inducing an increase of the temperature of the sorbent material, preferably to a temperature between 60 and 110°C, starting the desorption of CO2. This is e.g. possible by injecting a stream of saturated or superheated steam, preferably by flow-through through the unit and over/through the sorbent, and thereby inducing an increase of the temperature of the sorbent material to a temperature between 60 and 110°C, starting the desorption of CO2; (d) extracting at least the desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide, preferably by condensation, in or downstream of the unit;

(e) bringing the sorbent material to ambient atmospheric temperature conditions and ambient atmospheric pressure conditions (if the sorbent material is not cooled in this step down to exactly the surrounding ambient atmospheric temperature conditions, this is still considered to be according to this step, preferably the ambient atmospheric temperature established in this step (e) is in the range of the surrounding ambient atmospheric temperature +25°C, preferably +10°C or +5°C).

According to one aspect of the invention said sorbent material comprises primary amine moieties as well as in addition at least one of secondary amine moieties and tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene- divinylbenzene support is functionalised (on the surface and/or in the bulk) by at least one of secondary benzylamine groups, tertiary benzylamine groups, secondary a- methylbenzylamine groups, and tertiary a-methylbenzylamine groups, wherein in each case the secondary or tertiary amine is substituted with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine.

This means that the amine functionality of the benzylamine groups or a-methylbenzylamine groups takes the form of a secondary or tertiary amine which is functionalised with one of the listed alkylamine groups, the terminal primary amine groups of these alkylamine groups forming the mentioned primary amine moieties. In any case, these primary amine moieties contribute to the carbon dioxide capture process, but also the secondary and/or tertiary amine of the functionalised benzylamine groups or a-methylbenzylamine groups may contribute to the carbon dioxide capture process.

As for the terminology of "branched and/or linear" systems, this includes on the one hand linear or branched structures of the alkyl chains of the alkylamine moieties or building blocks (e.g. also including isopropylamine moieties and the like).

Generally speaking therefore, the sorbent material comprising primary amine moieties as well as in addition at least one of secondary amine moieties and tertiary amine moieties immobilized on a solid styrene-divinylbenzene support takes the form of the following structures (wherein for the case of a-methylbenzylamine a methyl group has to be added in at the carbon atom between the N and aromatic ring):

wherein typically the value of m is in the range of 1-100, or 10 - 100 preferably in the range of 20-90, more preferably in the range of 50-80, and/or wherein the value of n is in the range of 1-100, preferably in the range of 20-90, more preferably in the range of 50-80. In these structures, R¹ and R² can be the same or different, wherein preferably R¹ and R² are the same. The same at least in so far as the corresponding functionalisation by way of the specific alkylamine groups is the same. So the means of functionalisation is preferably the same, but the actual structure of the R¹ and R² groups in such a system in this case can still be different in the individual systems due to different types of branching, different types of mixtures of secondary and tertiary functionalisations, as well as due to amine rearrangements.

Generally speaking, the R¹ and R² groups in the above structure take the following form:

(I) (II) wherein i in the structures (I) and/or (IV) and j in the structure (IV) independently from each other take a value in the range of 2-6, more preferably 3-4, or preferably take the same value in this range.

Examples for the residues R¹ and R² are as follows:

In the context of this disclosure, the expressions “ambient atmospheric pressure” and “ambient atmospheric temperature” refer to the pressure and temperature conditions to that a plant that is operated outdoors is exposed to, i.e. typically ambient atmospheric pressure stands for pressures in the range of 0.8 to 1.1 barabs and typically ambient atmospheric temperature refers to temperatures in the range of -40 to 60° C, more typically -30 to 45°C. The gas mixture used as input for the process is preferably ambient atmospheric air, i.e. air at ambient atmospheric pressure and at ambient atmospheric temperature, which normally implies a CO2 concentration in the range of 0.03-0.06% by volume. However, also air with lower or higher CO2 concentration can be used as input for the process, e.g. with a concentration of 0.1 -0.5% by volume, so generally speaking, preferably the input CO2 concentration of the input gas mixture is in the range of 0.01-0.5% by volume.

Typically and preferably, the solid styrene-divinylbenzene support is functionalised by secondary benzylamine or secondary a-methylbenzylamine groups is the result of a reaction of halogenmethylated styrene-divinylbenzene, preferably chloromethylated styrene-divinylbenzene, with at least one of 1 ,2-ethylenediamine, 1 ,3-propylenediamine, 1 ,4-butylenediamine, 1 ,5-pentanediamine, 1 ,6-hexylenediamine , or a combination thereof, preferably 1 ,3-propylenediamine, 1 ,4-butylenediamine, or a combination thereof.

According to yet another preferred embodiment, the styrene-divinylbenzene based support material is in the form of at least one of monolith, layer or sheet, hollow or solid fibres, preferably in woven or nonwoven structures, hollow or solid particles, or extrudates, wherein preferably it takes the form of preferably essentially spherical beads with a particle size (D50, e.g. determined by laser diffraction with a Mastersizer 3000, e.g. according to ISO 13320 (2020)) in the range of 0.002 - 4 mm or 0.01-1 .5 mm, preferably in the range of 0.30- 1.25 mm.

The styrene-divinylbenzene based support material may also take the form of solid particles embedded in a porous or non-porous matrix.

Preferably said polystyrene based support material has a nitrogen content in the range 8- 50 wt.%, preferably in the range or 9 - 30 wt.% or 12 - 25 wt.%, in each case for dry sorbent material.

Said polystyrene based support material further may have a swelling of less than 30%, preferably of less than 25%, most preferably of less than 20%.

The gas mixture preferably is ambient atmospheric air.

The above method can be carried out in different ways.

Preferably step (b) involves isolating said sorbent material with adsorbed carbon dioxide in said unit from said flow-through while maintaining the temperature in the sorbent.

Alternatively and/or additionally, step (c) may involve inducing an increase of the temperature of the sorbent material to a temperature between 60 and 110°C, starting the desorption of CO2.

According to another preferred embodiment, step (d) involves extracting at least the desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide from steam, preferably by condensation, in or downstream of the unit.

Also it is possible to carry out the method in that step (d) is carried out by still contacting the sorbent material with steam by injecting and/or circulating saturated or superheated steam into said unit, thereby flushing and purging both steam and CO2 from the unit, preferably while regulating the extraction and/or steam supply to essentially maintain the temperature in the sorbent at the end of the preceding step (c) and/or to further preferably essentially maintain the pressure in the sorbent at the end of the preceding step (c).

According to yet another aspect of the present invention, it relates to the use of such a sorbent material. More specifically, it relates to the use of a sorbent material capable of reversibly binding carbon dioxide, for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, preferably for direct air capture, in particular using a temperature, vacuum, or temperature/vacuum swing process, wherein said sorbent material. According to this aspect of the invention, said sorbent material comprises primary amine moieties as well as in addition secondary and/or tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene- divinylbenzene support is functionalised by secondary and/or tertiary benzylamine or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentaneamine, branched or linear hexyleneamine, preferably, as detailed above and in particular with at least one of branched and/or linear propyleneamine, and branched and/or linear butyleneamine.

According to a further aspect of the present invention, it relates to a unit for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air, flue gas and biogas, preferably direct air capture unit, comprising at least one reactor unit containing sorbent material suitable and adapted for flow-through of said gas mixture, wherein the reactor unit comprises an inlet for said gas mixture, preferably for ambient air, and an outlet for said gas mixture, preferably for ambient air during adsorption, wherein the reactor unit is heatable to a temperature of at least 60°C for the desorption of at least said gaseous carbon dioxide and the reactor unit being openable to flow-through of the gas mixture, preferably of the ambient atmospheric air, and for contacting it with the sorbent material for an adsorption step, wherein preferably the reactor unit is further evacuable to a vacuum pressure of 400 mbar(abs) or less, wherein the sorbent material preferably takes the form of an adsorber structure comprising an array of individual adsorber elements, each adsorber element preferably comprising at least one support layer and at least one sorbent material layer comprising or consisting of at least one sorbent material.

Again, according to the invention, said sorbent material comprises a solid, polymeric support comprising primary amine moieties as well as secondary and/or tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene- divinylbenzene support is functionalised by secondary and/or tertiary benzylamine or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propyleneamine, branched or linear butyleneamine, branched or linear pentaneamine, branched or linear hexyleneamine, preferably, as detailed above and in particular branched or linear propyleneamine, and/or branched or linear butyleneamine , wherein preferably the adsorber elements in the array are arranged essentially parallel to each other and spaced apart from each other forming parallel fluid passages for flow-through of said gas mixture, preferably of ambient atmospheric air and/or steam.

The device further comprises at least one device, preferably a condenser, for separating carbon dioxide from water.

Preferably at the gas outlet side of said device for separating carbon dioxide from water, preferably said condenser, there is at least one of, preferably both of a carbon dioxide concentration sensor and a gas flow sensor for controlling the desorption process.

Finally, in yet another aspect the present invention relates to a method for preparing a sorbent material for use in a as defined above.

Again, the sorbent material comprises primary and secondary amine moieties immobilized on a solid polystyrene based support.

According to the proposed method, monomeric styrene is provided and reacted with a cross-linker, preferably selected as divinylbenzene, in a solvent, wherein the cross-linker is preferably used in an amount of more than 10% by weight relative to the weight of styrene, and wherein subsequently the resulting solid material, preferably but not exclusively in the form of beads, is functionalised to form secondary and/or tertiary benzylamine and/or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propyleneamine, branched or linear butyleneamine, branched or linear pentaneamine, branched or linear hexyleneamine, preferably, as detailed above and in particular with at least one of branched or linear propyleneamine, and/or branched or linear butyleneamine on the surface and/or in the bulk.

This functionalisation is preferably implemented by using a chloromethylation reaction followed by amination with at least one of ethylenediamine, branched or linear propylenediamine, branched or linear butylenediamine, branched or linear pentanediamine, branched or linear hexylenediamine, preferably with at least one of 1 ,3-propylendiamine, 1 ,4-butylenediamine, or a combination thereof.

Further embodiments of the invention are laid down in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred embodiments of the invention are described in the following with reference to the drawings, which are for the purpose of illustrating the present preferred embodiments of the invention and not for the purpose of limiting the same. In the drawings, Fig. 1 shows a schematic representation of a direct air capture unit; Fig. 2 shows the equilibrium carbon dioxide capture capacity as a function of the chain length of the alkylamine substitution including the value for unsubstituted benzyl amine DVB backbone for two different basic divinylbenzene systems, in each case relative to the value of unsubstituted benzyl amine taken as 100%;

Fig. 3 shows the values according to Fig. 2 for the sorbent A compared with the exchange capacity of the same material as a function of the chain length of the alkylamine substitution;

Fig. 4 shows the improvement of the carbon dioxide capture kinetics for 180 minutes and 600 minutes as a function of the chain length of the alkylamine substitution, in each case relative to unsubstituted benzylamine systems for propylenediamine substitution taken as 100%;

Fig. 5 shows the amine efficiency for benzylamine and for propylenediamine substituted systems in each case relative to theoretical equilibrium capacity based on the nitrogen content.

DESCRIPTION OF PREFERRED EMBODIMENTS

Synthesis procedure of chloromethylated styrene-divinylbenzene resin

In a 1 L reactor, 1 % (mass ratio) of gelatin and 2% (mass ratio) of sodium chloride are dissolved in 300 mL of water at 45°C for 1 h. In another flask, 1 g of benzoyl peroxide is dissolved in a mixture of 54 g of styrene, 10 g of divinylbenzene (content 80%), 68 g of heptane and 22 g of toluene. The resulting mixture is then added to the reactor. After that the reaction mixture is stirred and heated up to 70°C maintaining the temperature for 2 h, then the temperature is raised to 80°C and kept it for 16 h. The temperature is then raised to 100°C for 3 h to distill out the porogen. The reaction mixture is cooled down to room temperature and the beads are filtered off using a funnel glass filter and vacuum suction. The beads are dried in rotavapor.

The polystyrene-divinylbenzene beads are functionalised using the chloromethylation reaction. 5 g of so obtained beads are added to a 3-neck flask containing 30 mL of chloromethyl methyl ether. 3.5 g of zinc chloride is added to the mixture over 2 h and heated for an additional 4 h to 60°C. After that, the mixture is cooled to room temperature and 25% HCI in water is added to quench chloromethyl methyl ether. The chloromethylated beads are washed until neutral with water, filtered off, and dried.

Functionalisation of the chloromethylated styrene-divinylbenzene beads with primary and/or secondary amines:

6 g of chloromethylated beads are added to a three-neck flask with 23 g of methylal and the mixture is stirred for 1 h at 40°C. To this mixture, depending on the final functional group of the amino-based sorbent either of the following amounts of amines are added:

12 g of ethylenediamine;

15 of 1 ,3-propylendiamine;

18 g of 1 ,4-butanediamine;

21 g of 1 ,5-pentanediamine;

23 g of 1 ,6-hexanediamine.

The mixture containing chloromethylated beads, methylal and one of the above amine is kept under stirring at 50°C for 12 h. The beads are filtered off and washed with methanol and water. The aminated beads are then dried in the vacuum oven at 60°C for 12h.

Swelling properties:

The sorbent is dried to reach a water content of ca 10 wt.% in a convection oven at 40°C. 12 g of sorbent is then placed in a 50 cm3 cylinder. The sorbent is tapped by using an Autotap machine from Anton Paar until the volume change between 250 consecutive taps is less than 0.5 cm3, this represents the starting volume of the material in the unswollen state. The cylinder containing the sorbent is filled with deionised water. The sorbent is left to swell for 1 h or until no more volume changes are evidenced. To have the value of the final volume, the sorbent in the swollen state is tapped until the volume change between 250 consecutive taps is less than 0.5 cm3.

Exchange Capacity properties:

Exchange capacity determination: To measure exchange capacity around 2g of wet material is added to a beaker with 50mL of 1M NaOH solution and stirred at room temperature for 40min. The solution is then filtered on a Buchner funnel with a filter mesh size of 40pm, the beads are washed to neutral with deionized water and collected. Around half of the beads are transferred to a graduated flask, the weight is noted down and 100mL of 0.1 M HCI solution is added to the flask. The flask is closed and left in the oven at 70°C for 1 h. The solid content of the remaining half is determined following the method below.

The flask is then removed from the oven and let cool down to room temperature. 25mL of the supernatant are titrated with 0.1M NaOH solution (to inflection point, with an SI Analytics Titrator TitroLine 5000). The exchange capacity is calculated through the following equation: 0.4

Solid Content measurements:

Solid content is measured with a Halogen Moisture Analyzer (Adam Equipment PMB Moisture Analyzer); measurement temperature is 110°C, the measurement stops automatically at constant weight (0.002g/15s).

Nitrogen content measurements:

Elemental analysis of the materials was carried out using a LECO CHN-900 combustion furnace. Prior to the measurement, the samples were treated under N2 flow (2 L/min) at 90°C for 2 h. Alternatively, the sample were treated in a vacuum oven at 60°C for 6 h.

Method for the specific surface area measurements:

Nitrogen adsorption measurements were performed at 77 K on a Quantachrome ASiQ. The mass of the sample used was between 0.2-1.0 g. Since the samples contain a significant amount of water, it is important to use a treatment that does not alter their intrinsic porosity and pore structure. Therefore, prior to degassing, the samples were treated using the elutropic row method, which comprises removing water and replacing it with organic solvents with lower boiling point in the following order: methanol, acetone, and n-heptane. 2 g of samples was place in a chromatography column with a frit and flushed with 20 cm3 of each solvent in decreasing polarity order. The sample was then spread out on a petri dish and placed in a vacuum oven at40°C for 24 hours. After that, the sample was degassed at 70 °C under vacuum for twelve hours before measurement.

BET (Brunauer, Emmett und Teller) surface area analysis was used applying the method ISO 9277.

Mercury Porosimetry Measurements:

Mercury porosimetry measurements were performed to analyze the pore sizes and pore volumes not accessible through N2 adsorption measurements. In order to perform mercury porosimetry measurements the following parameters were used:

• Mercury surface tension: 0.48 N/m

• Mercury contact angle: 150°

• Max. pressure: 400 MPa

• Increase speed: 6-19 MPa/min

Prior to Hg porosimetry, the samples were degassed under vacuum at 70°C for 12 h.

Carbon dioxide capture capacity properties:

The beads according to the above examples were tested in an experimental rig in which the beads were contained in a packed-bed reactor or in air permeable layers. The rig is schematically illustrated in Fig. 1. There is an ambient air inflow structure 1 and the actual reactor unit 8 comprises a container or wall 7 within which the layers of sorbent material 3 are located. There is an inflow structure 4 for desorption, if for example steam is used for desorption, and there is a reactor outlet 5 for extraction. Further, there is a vacuum unit 6 for evacuating the reactor.

For the adsorption measurements, 6 g of dry sample was filled into a cylinder with an inner diameter of 40 mm and a height of 40 mm and placed into a CO2adsorption/desorption device, where it was exposed to a flow of 2.0 NL/min of air at 30°C containing 450 ppmv CO2, having a relative humidity of 60% corresponding to a temperature of 30°C for a duration of 600 min. Prior to adsorption, the sorbent bed was desorbed by heating the sorbent to 94°C under an air flow of 2.0 NL/min. The amount of CO2adsorbed on the sorbent was determined by integration of the signal of an infrared sensor measuring the CO2content of the air stream leaving the cylinder.

The adsorber structure can alternatively be operated using a temperature/vacuum swing direct air capture process involving temperatures up to and vacuum pressures in the range of 50-250 mbar(abs) and heating the sorbent to a temperature between 60 and 110°C. In addition, experiments involving steam were carried out, with or without vacuum.

Fig. 2 shows the results of the carbon dioxide capture capacity properties of the newly synthesised materials, given relative to 100% benzyl amine as a reference. Data is given for two different basic DVB systems designated as Sorbent A and B in the following table:

As one can see from that Fig. 2, there is an unexpected and significant increase of the equilibrium carbon dioxide capture capacity associated with single alkylamine substitution. In fact, the equilibrium carbon dioxide capture capacity increases as a function of the number of carbon atoms in the alkyl chain, reaching a maximum for 4 or 5 carbon atoms, and then decreases again. Surprisingly there is a maximum for propylenediamine and butylenediamine form most systems, where the increase is almost 50% compared with unsubstituted benzylamine.

Fig. 3 shows that a different behavior is obtained for the exchange capacity measured in water; there, there is - if at all - only an insignificant increase of exchange capacity as a function of alkyl chain length. So the mechanisms for carbon dioxide capture and for exchange properties in water are significantly different and the effect is only pronounced for the carbon dioxide capture capacity Predictions and extrapolation based on exchange property considerations measured in water are therefore essentially impossible.

As illustrated in Fig. 4, not only the equilibrium carbon dioxide capture capacity as illustrated in the preceding figures, but also the kinetics are significantly improved with the substitution. The effect here is the same or even more pronounced than for the equilibrium carbon dioxide capture capacity. An increase of up to more than 30% is already available at 180 minutes and goes up to more than 45% at 600 minutes for the optimum system.

Fig. 5 illustrates how the proposed approach improves amine efficiency which would be expected based on theoretical capacity calculations from the total nitrogen content found in the elemental analysis, compared to the actual experimental equilibrium carbon dioxide capture capacity. Amine efficiency is defined as the ratio of CO2 in mmol/g captured per amine mmol/g and given in percent. The total amount of amines are calculated from the total nitrogen content found in the elemental analysis. The amine efficiency is thus one measure of the efficiency of a material to capture CO2. The amine efficiency is increased from about 20% for benzylamine to 30-35% for propylenediamine.

Summary of Results:

The PS-DVB sorbents synthesised according to the invention consistently show swelling properties which are either similar or at least equally low as the ones for the PS-DVB sorbents which are only aminated with primary amines, i.e. the PS-DVB with primary benzylamine moieties.

The PS-DVB sorbents synthesised according to the invention furthermore show a significantly higher amine content than PS-DVB with primary benzylamine moieties produced using the same chloromethylated PS-DVB material as starting material, and also an improved amine efficiency, so the load with capture active amino groups can be increased as well as its effect for capture using the proposed approach.

The PS-DVB sorbents synthesised according to the invention in particular show very good carbon dioxide capture capacity properties (equilibrium and kinetics), which are superior to the ones according to the prior art, i.e. the PS-DVB with primary benzylamine moieties.

Also the PS-DVB sorbents synthesised according to the invention show improved stability over a large number of cycles compared with the PS-DVB with primary benzylamine moieties according to the prior art.

LIST OF REFERENCE SIGNS

1 ambient air, ambient air 2 outflow of ambient air behind inflow structure adsorption unit in adsorption flow-through mode 5 reactor outlet for extraction sorbent material 6 vacuum unit/separator steam, steam inflow structure 7 wall for desorption 8 reactor unit

Claims

1. A method for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material (3) capable of reversibly binding carbon dioxide and adsorbing said gaseous carbon dioxide in a unit (8), wherein the method comprises at least the following sequential and in this sequence repeating steps (a) - (e):

(a) contacting said gas mixture (1) with the sorbent material (3) to allow at least said gaseous carbon dioxide to adsorb on the sorbent material (3) by flow-through through said unit (8) essentially under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step;

(b) isolating said sorbent material (3) with adsorbed carbon dioxide in said unit (8) from said flow-through;

(c) inducing an increase of the temperature of the sorbent material (3) to a temperature starting the desorption of carbon dioxide;

(d) extracting at least the desorbed gaseous carbon dioxide from the unit (8) and separating gaseous carbon dioxide in or downstream of the unit (8);

(e) bringing the sorbent material (3) essentially to ambient atmospheric temperature conditions and ambient atmospheric pressure conditions; wherein said sorbent material (3) comprises primary amine moieties as well as in addition at least one of secondary amine moieties and tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene-divinylbenzene support is functionalised by at least one of secondary benzylamine groups, tertiary benzylamine groups, secondary a-methylbenzylamine groups, and tertiary a-methylbenzylamine groups, wherein in each case the secondary or tertiary amine groups are substituted with at least one of ethyleneamine, branched or linear propyleneamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine.

2. The method according to claim 1 , wherein the solid styrene-divinylbenzene support is functionalised by secondary benzylamine or secondary a-methylbenzylamine groups is the result of a reaction of halogenmethylated styrene-divinylbenzene, preferably chloromethylated styrene-divinylbenzene, with at least one of ethylenediamine, 1 ,3- propylendiamine, 1 ,4-butylenediamine, 1 ,5-pentanediamine, 1 ,6-hexylenediamineor a combination thereof, preferably 1 ,3-propylenediamine, 1 ,4-butylenediamine, or a combination thereof.

3. The method according to any of the preceding claims, wherein in each case the secondary or tertiary amine are substituted with at least one of branched or linear propyleneamine, preferably linear propyleneamine, branched or linear butylenediamine, preferably linear butyleneamine, or a combination thereof.

4. The method according to any of the preceding claims, wherein the styrene- divinylbenzene based support material is in the form of at least one of monolith, layer or sheet, hollow or solid fibres, preferably in woven or nonwoven structures, hollow or solid particles, or extrudates, wherein preferably it takes the form of preferably essentially spherical beads,

5. The method according to any of the preceding claims, wherein the styrene- divinylbenzene based support material is in the form of solid particles embedded in a porous or non-porous matrix.

6. The method according to any of the preceding claims, wherein the sorbent material takes the form of preferably essentially spherical beads with a particle size (D50) in the range of 0.002 - 4 mm, 0.005 - 2 mm, 0.002 - 1.5 mm, 0.005 - 1.6 mm or 0.01-1 .5 mm, preferably in the range of 0.30-1.25 mm.

7. The method according to any of the preceding claims, wherein said polystyrene-based support material has a nitrogen content in the range 8-50 wt.%, preferably in the range or 9 - 30 wt.% or 12 - 25 wt.%, in each case for dry sorbent material.

8. The method according to any of the preceding claims, wherein said polystyrene-based support material has a swelling of less than 30%, preferably of less than 25%, most preferably of less than 20%.

9. The method according to any of the preceding claims, wherein the gas mixture is ambient atmospheric air.

10. The method according to any of the preceding claims, wherein step (b) involves isolating said sorbent material (3) with adsorbed carbon dioxide in said unit (8) from said flow-through while maintaining the temperature in the sorbent; and/or wherein step (c) involves inducing an increase of the temperature of the sorbent material (3) to a temperature between 60 and 110°C, starting the desorption of carbon dioxide; and/or wherein step (d) involves extracting at least the desorbed gaseous carbon dioxide from the unit (8) and separating gaseous carbon dioxide from steam, preferably by condensation, in or downstream of the unit (8) and/or wherein step (d) is carried out by still contacting the sorbent material (3) with steam by injecting and/or circulating saturated or superheated steam into said unit, thereby flushing and purging both steam and carbon dioxide from the unit, preferably while regulating the extraction and/or steam supply to essentially maintain the temperature in the sorbent at the end of the preceding step (c) and/or to further preferably essentially maintain the pressure in the sorbent at the end of the preceding step (c).

11. Use of a sorbent material (3) capable of reversibly binding carbon dioxide, for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, preferably for direct air capture, in particular using a temperature, vacuum, or temperature/vacuum swing process, wherein said sorbent material (3), wherein said sorbent material comprises primary amine moieties as well as in addition secondary and/or tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene-divinylbenzene support is functionalised by secondary and/or tertiary benzylamine and/or secondary and/or tertiary a- methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine.

12. Use according to claim 11 , wherein said solid styrene-divinylbenzene support is functionalised by secondary and/or tertiary benzylamine and/or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propylenamine, preferably lienar propylenamine, and branched or linear butyleneamine, preferably linear butyleneamine.

13. Unit for separating gaseous carbon dioxide from a gas mixture, preferably from at least one of ambient atmospheric air (1), flue gas and biogas, preferably direct air capture unit, comprising at least one reactor unit (8) containing sorbent material (3) suitable and adapted for flow-through of said gas mixture (1), wherein the reactor unit comprises an inlet for said gas mixture, preferably for ambient air (1), and an outlet (2) for said gas mixture, preferably for ambient air during adsorption, wherein the reactor unit is heatable to a temperature of at least 60°C for the desorption of at least said gaseous carbon dioxide and the reactor unit being openable to flow-through of the gas mixture, preferably of the ambient atmospheric air, and for contacting it with the sorbent material for an adsorption step, wherein preferably the reactor unit is further evacuable to a vacuum pressure of 400 mbar(abs) or less, wherein the sorbent material (3) preferably takes the form of an adsorber structure comprising an array of individual adsorber elements, each adsorber element preferably comprising at least one support layer and at least one sorbent material layer comprising or consisting of at least one sorbent material, where said sorbent material comprises a solid, polymeric support comprising primary amine moieties as well as and secondary and/or tertiary amine moieties immobilized on a solid styrene-divinylbenzene support, wherein said solid styrene-divinylbenzene support is functionalised by secondary and/or tertiary benzylamine and/or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine, preferably with branched or linear propylenamine, and/or branched or linear polybutyleneamine, wherein preferably the adsorber elements in the array are arranged essentially parallel to each other and spaced apart from each other forming parallel fluid passages for flow-through of said gas mixture, preferably of ambient atmospheric air and/or steam, at least one device, preferably a condenser, for separating carbon dioxide from water, wherein preferably at the gas outlet side of said device for separating carbon dioxide from water, preferably said condenser, there is at least one of, preferably both of a carbon dioxide concentration sensor and a gas flow sensor for controlling the desorption process.

14. A method for preparing a sorbent material (3) for use in a method according to any of claims 1-10, wherein the sorbent material (3) comprises primary and secondary amine moieties immobilized on a solid polystyrene based support, wherein monomeric styrene is provided and reacted with a cross-linker, preferably selected as divinylbenzene, in a solvent, wherein the cross-linker is preferably used in an amount of more than 10% by weight relative to the weight of styrene, and wherein subsequently the resulting solid material, preferably in the form of beads, is functionalised to form secondary and/or tertiary benzylamine and/or secondary and/or tertiary a-methylbenzylamine groups substituted with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine, preferably with branched or linear propylenamine, and/or butyleneamine on the surface and/or in the bulk, preferably using a chloromethylation reaction followed by amination with at least one of ethyleneamine, branched or linear propylenamine, branched or linear butyleneamine, branched or linear pentanamine, branched or linear hexyleneamine.

15. The method according to claim 14, wherein the resulting solid material, in the form of beads, is functionalised to form secondary and/or tertiary benzylamine and/or secondary and/or tertiary a-methylbenzylamine groups substituted by way of reaction with at least one of ethylenediamine, 1 ,3-propylendiamine, 1,4-butylenediamine, 1 ,5- pentanediamine, 1 ,6-hexylenediamine, or a combination thereof, preferably using a chloromethylation reaction followed by amination with at least one of ethylenediamine, 1,3- propylendiamine, 1,4-butylenediamine, 1 ,5-pentanediamine, 1 ,6-hexylenediamine , or a combination thereof.