AMINO SORBENTS FOR CAPTURING OF CO2 FROM GAS STREAMS

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, by cyclic adsorption/desorption using a sorbent material (3), 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 gaseous carbon dioxide to adsorb; (b) isolating said sorbent material (3) from said flow-through; (c) inducing an increase of the temperature of the sorbent material (3); (d) extracting at least the desorbed gaseous carbon dioxide from the unit (8) and separating gaseous carbon dioxide from steam in or downstream of the unit (8); (e) bringing the sorbent material (3) to ambient atmospheric conditions;
wherein said sorbent material (3) comprises primary and/or secondary amine moieties immobilized on a solid support, wherein the amine moieties, in the α-carbon position, are substituted by one hydrogen and one non-hydrogen substituent (R).

Claims

1. A method for separating gaseous carbon dioxide from a gas mixture, said gas mixture containing said gaseous carbon dioxide as well as further gases different from gaseous carbon dioxide, by cyclic adsorption/desorption using a sorbent material adsorbing said gaseous carbon dioxide in a unit, wherein said method comprises at least the following sequential and in this sequence repeating steps (a)-(e): (a) contacting said gas mixture with said sorbent material to allow at least said gaseous carbon dioxide to adsorb on the sorbent material by flow-through through said unit under ambient atmospheric pressure conditions and ambient atmospheric temperature conditions in an adsorption step; (b) isolating said sorbent material with adsorbed carbon dioxide in said unit from said flow-through; (c) inducing an increase of the temperature of the sorbent material to a temperature starting desorption of CO2; (d) extracting at least desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide from steam in or downstream of said unit; (e) bringing the sorbent material to ambient atmospheric temperature conditions; wherein said sorbent material comprises at least one of primary and secondary amine moieties immobilized on a solid support, wherein said amine moieties, in the α-carbon position, are substituted by one hydrogen and one non-hydrogen substituent.

2. The method according to claim 1, wherein the non-hydrogen substituent is selected from the group consisting of alkyl, alkenyl, arylalkyl, C(O)COR.sub.2, —SR.sub.2, —NR.sub.2R.sub.2, —OC(O)R.sub.2, —NR.sub.2C(O)R.sub.2, —OH, —SH, —OR.sub.2, and —C(O)NR.sub.2R.sub.2, wherein each R.sub.2 is independently H or C1 to C10 alkyl or alkenyl.

3. The method according to claim 1, wherein the non-hydrogen substituent is selected from the group of methyl or ethyl.

4. The method according to claim 1, wherein the sorbent material comprises primary α-methylbenzylamine moieties.

5. The method according to claim 1, wherein the solid support of the sorbent material is a porous or non-porous material based on an organic and/or inorganic material.

6. The method according to claim 5, wherein the sorbent material is based on a polystyrene material.

7. The method according to claim 1, wherein the primary and/or secondary amine moieties are part of a polyethyleneimine structure.

8. The method according to claim 1, wherein step (c) includes injecting a stream of saturated or superheated steam by flow-through through said unit.

9. The method according to claim 1, wherein the sorbent material takes the form of a monolith, the form of a layer or a plurality of layers, the form of hollow or solid fibres, including in woven or nonwoven (layer) structures, or the form of hollow or solid particles.

10. The method according to claim 1, wherein the sorbent material takes the form of 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.

11. The method according to claim 1, wherein 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.

12. The method according to claim 1, wherein step (d) involves extracting at least the desorbed gaseous carbon dioxide from the unit and separating gaseous carbon dioxide from steam by condensation in or downstream of the unit.

13. The method according to claim 1, wherein step (c) involves inducing an increase of the temperature of the sorbent material to a temperature between 60 and 110° C., starting the desorption of CO2.

14. A method of using a sorbent material having a solid support material functionalized on the surface with amino functionalities capable of reversibly binding carbon dioxide, for separating gaseous carbon dioxide from a gas mixture, wherein said sorbent material comprises at least one of primary and secondary amine moieties immobilized on a solid support, wherein the amine moieties, in the α-carbon position, are substituted by one hydrogen and one non-hydrogen substituent.

15. A unit for separating gaseous carbon dioxide from a gas mixture, 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 and an outlet for said gas mixture, 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, and for contacting it with the sorbent material for an adsorption step, wherein said sorbent material comprises a solid support material functionalized on the surface with amino functionalities capable of reversibly binding carbon dioxide, wherein said sorbent material comprises primary and/or secondary amine moieties immobilized on a solid support, wherein the amine moieties, in the α-carbon position, are substituted by one hydrogen and one non-hydrogen substituent (R), at least one device, for separating carbon dioxide from water.

16. A method for preparing a sorbent material for use in a method according to claim 1, wherein the sorbent material comprises at least one of primary and secondary amine moieties immobilized on a solid support wherein the sorbent material is obtained using a phthalimide or a Blanc-Quelet reaction pathway or using a sequence of reactions that includes at least an acylation, including a Friedel-Crafts acylation and a functional group interconversion involving nucleophilic, nitrogen-based reagents including an azidation, amination, imination, or amidation step or a combination thereof.

17. A sorbent material for use in a method according to claim 1, wherein the sorbent material comprises at least one of primary and secondary amine moieties immobilized on a solid support, wherein the α-carbon position of the amine moieties is substituted by one hydrogen and one non-hydrogen substituent (R), wherein the non-hydrogen substituent is selected from the group consisting of alkyl, alkenyl, arylalkyl, C(O)COR2, —SR2, —NR2R2, —OC(O)R2, —NR2C(O)R2, —OH, —SH, —OR2, and —C(O)NR2R2, wherein each R2 is independently H or C1 to C10 alkyl or alkenyl, or wherein the sorbent material comprises primary α-methylbenzylamine moieties, and wherein the solid support of the sorbent material is a porous or non-porous material based on an organic and/or inorganic material.

18. The method according to claim 1, wherein the gas mixture is ambient atmospheric air.

19. The method according to claim 1, wherein the non-hydrogen substituent (R) is selected from the group consisting of alkyl, alkenyl, arylalkyl, with 1-12, 1-6 or 1-3 carbon atoms, —C(O)COR.sub.2, —SR.sub.2, —NR.sub.2R.sub.2, —OC(O)R.sub.2, —NR.sub.2C(O)R.sub.2, —OH, —SH, —OR.sub.2, and —C(O)NR.sub.2R.sub.2, wherein each R.sub.2 is independently H or C1-C5 or C1-C3 alkyl or alkenyl.

20. Method according to claim 1, wherein the non-hydrogen substituent (R) is the same for all primary and/or secondary amine moieties and is selected as methyl.

21. The method according to claim 1, wherein the carbon dioxide capture moieties of the sorbent material consist of primary α-methylbenzylamine moieties.

22. The method according to claim 1, wherein the solid support of the sorbent material is a porous or non-porous material organic polymer material, selected from the group of linear or branched, cross-linked or uncross-linked polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate based polymer including PMMA, or combinations thereof.

23. The method according to claim 1, wherein the solid support of the sorbent material is poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, and combinations thereof.

24. The method according to claim 5, wherein the sorbent material is based on a poly(styrene-co-divinylbenzene), which is at least partially functionalized to or contains alkylbenzylamine moieties, including α-methylbenzylamine moieties, throughout the material or at least or only on its the surface.

25. The method according to claim 24, wherein the material or the functionalization is obtained by a phthalimide or a Blanc-Quelet reaction pathway or a sequence of reactions that includes at least an acylation, including a Friedel-Crafts acylation and a functional group interconversion involving nucleophilic, nitrogen-based reagents including an azidation, amination, imination, or amidation step or a combination thereof.

26. The method according to claim 1, wherein the primary and/or secondary amine moieties are part of a polyethyleneimine structure, obtained using 2,3-dimethylaziridine, which is chemically and/or physically attached to a solid support.

27. The method according to claim 1, wherein the sorbent material, in porous form, and having specific BET surface area, in the range of 1-20 m2/g, takes the form of a monolith, the form of a layer or a plurality of layers, the form of hollow or solid fibres, including in woven or nonwoven (layer) structures, or the form of hollow or solid particles.

28. The method according to claim 1, wherein the sorbent material takes the form of essentially spherical beads with a particle size (D50) in the range of 0.30-1.25 mm.

29. The method according to claim 14, wherein it is using a temperature, vacuum, or temperature/vacuum swing process.

30. The unit according to claim 15 wherein the sorbent material takes the form of an adsorber structure comprising an array of individual adsorber elements, each adsorber element 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 material functionalized on the surface with amino functionalities capable of reversibly binding carbon dioxide, and/or wherein it comprises at least one a condenser, for separating carbon dioxide from water, and/or wherein at the gas outlet side of said device for separating carbon dioxide from water, there is at least one of a carbon dioxide concentration sensor and a gas flow sensor for controlling the desorption process.

31. The method according to claim 16, wherein the α-carbon position of the amine moieties is substituted by one hydrogen and one non-hydrogen substituent (R), wherein the non-hydrogen substituent (R) is selected from the group consisting of alkyl, alkenyl, arylalkyl, with 1-12, carbon atoms, —C(O)COR2, —SR2, —NR2R2, —OC(O)R2, —NR2C(O)R2, —OH, —SH, —OR2, and —C(O)NR2R2, wherein each R2 is independently H or C1 to C10, alkyl or alkenyl, and/or wherein the sorbent material is obtained using a phthalimide or a Blanc-Quelet reaction pathway or using a sequence of reactions that includes at least an acylation, including a Friedel-Crafts acylation and a functional group interconversion involving nucleophilic, nitrogen-based reagents including an azidation, amination, imination, or amidation step or a combination thereof, wherein poly(styrene-co-divinylbenzene) serves as a starting material.

32. The sorbent material according to claim 17, wherein the sorbent material comprises primary α-methylbenzylamine moieties, and wherein the solid support of the sorbent material is a porous material based on an organic polymer material, selected from the group of polystyrene, polyethylene, polypropylene, polyamide, polyurethane, acrylate based polymer including PMMA, or combinations thereof, wherein including poly(styrene) or poly(styrene-co-divinylbenzene) based, cellulose, or an inorganic material including silica, alumina, activated carbon, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0072] 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,

[0073] FIG. 1 shows a schematic representation of a direct air capture unit; and

[0074] FIG. 2 shows the performance in terms of carbon dioxide capture capacity of carbon dioxide capture materials according to the invention exemplified by material obtained with alpha benzylamine, as compared with material obtained with benzylamine.

DESCRIPTION OF PREFERRED EMBODIMENTS

[0075] Preferred embodiments of the invention are described in the following with reference to the schemes and examples, which are for illustrating the present preferred embodiments of the invention and not for limiting the same.

[0076] In some embodiments of the invention, cross-linked polystyrene beads are considered in which styrene residues are converted into α-methyl benzylamine (1-phenylethylamine) moieties. The product of degradation of such materials when used for the purpose of capturing CO2 from air streams can be a benzamide moiety, as shown in the scheme above. The process used to synthesize such material is an emulsion polymerization followed by the chloromethylation known as Blanc reaction involving formaldehyde or by phtalimide route. So possibilities to synthesize such material include, but are not limited to, a phthalimide or a Blanc-Quelet reaction pathway or a sequence of reactions that includes at least a Friedel-Crafts acylation and a functional group interconversion involving nucleophilic, nitrogen-based reagents such as an azidation, amination, imination, or amidation step. These reactions may be carried out on either the monomer or, preferably, the polystyrene material, which may, for example, be synthesized by a suspension polymerization of styrene and optionally a cross-linker, for example divinylbenzene. In one embodiment here described, the Blanc-Quelet reaction with acetaldehyde is used to obtain a cross-linked polystyrene containing α-methyl benzylamine moieties thus having in α-position to the amine a methyl group, as shown in Scheme 3 below. As the skilled person will understand, the α-substituted benzylamine moiety may have the following formula:

##STR00003##

wherein R is a substituted or unsubstituted alkyl or aryl group. More preferably, R is a methyl or ethyl group.

[0077] The co-polymerization of styrene and divinylbenzene followed by the Blanc Quelet reaction with acetaldehyde to form alpha-methyl benzylamine substituted cross-linked polystyrene that does not undergo the oxidation reaction leading to the formation of benzamide substituents, as do corresponding systems as claimed, is shown in Scheme 3:

##STR00004##

[0078] In another embodiment of the invention, a copolymerization of styrene and divinylbenzene is followed by a sequence of reactions that includes a Friedel-Crafts acylation, a reduction to alcohol, a chlorination, an azidation, and another reduction to amine, as shown in Scheme 4, wherein the specific reagents given are to be considered exemplary.

##STR00005##

[0079] In another embodiment of the invention, polyethylenimines (PEI) are considered that can be used as active phase for carbon capture. PEI is typically synthesized by cationic polymerization of aziridine, which is initiated by electrophilic addition of an acidic catalyst to aziridine to form an aziridinium cation. An additional aziridine monomer, acting as a nucleophile, ring opens the active aziridinium ion resulting in the formation of a primary amine and a new aziridinium moiety. Subsequent aziridines attack the propagating aziridinium terminus, resulting in the linear propagation of the polymer chain. However, as the secondary amine groups in the developing polymer chain are also nucleophilic, they also ring open aziridinium species leading to branching and results in branched PEI.

[0080] Using aziridine with mono- or di-substituted α-carbons to the amine group as monomers, the final product of polymerization is constituted by branched polyamines where the alpha carbon to the amine is mono- or di-substituted with a generic R group, which can be but is not limited to, a methyl group or another alkyl, aryl or alkylaryl group. As the skilled person will understand, substructures of the α-substituted PEI may have the following formula:

##STR00006##

[0081] wherein R is again a substituted or unsubstituted alkyl or aryl group. More preferably, R is a methyl or ethyl group.

[0082] The polymerization is exemplified in Scheme 5 using 2,3-dimethylaziridine as monomer to form alpha-carbon methyl substituted polyethylenimine. Such branched polyamines offer improved oxidative stability as they do not undergo oxidation at the alpha carbon.

##STR00007##

Example 1 (PS-Alphamethylbenzylamine Sorbent Beads)

[0083] 300 g of deionized water and 10 g of dispersant is added to a three-neck 1 L flask equipped with a thermometer and a reflux condenser at room temperature. To this mixture, a mixture containing 150 g of styrene, 25 g of divinylbenzene, 1.5 g of benzoyl peroxide and 90 g of pore-forming agent, which can be isooctane, toluene, wax or a mixture of thereof, is added under stirring. The temperature is increased to 70° C. for 3 h, then up to 80° C. for 4 h and completed at 95° C. for 7 h, after which the formation of the beads has occurred. The suspension is cooled down to room temperature. The poly(styrene-co-divinylbenzene) beads are filtered and are then washed three times with an equivalent volume of acetone. 100 g of poly(styrene-co-divinylbenzene) and 150 g of acetaldehyde are added to a 1 L flask. To this mixture, 3 g of zinc chloride is added and the temperature is increased to 45° C. for 16-24 h. The chloroalkylated beads are then filtered and washed three times with an equivalent volume of methyl alcohol.

[0084] To obtain the aminoalkylated polymer, the chloroalkylated beads are treated in the following way. 100 g of chloroalkylated beads and 100 g of deionized water are mixed, and then 40 g of a 200 g/L ammonia solution is added to the beads over 3 h maintaining the temperature between 3-30° C. The reaction mixture is then held for 3 h at 40° C. After cooling, 30 g of sodium hydroxide is added to the mixture. The beads are filtered and washed with water for 3 h, with acetone and finally dried.

Example 2 (PEI Based Capture Material)

[0085] In a typical polymer synthesis, 5.0 cm.sup.3 of 1,2-dimethylaziridine are dissolved in 50 cm.sup.3 distilled water a 100-cm.sup.3 glass reaction flask. Then, 0.5 cm.sup.3 of 32 vol.% hydrochloric acid are added to the mixture, the flask is closed and immersed in an oil bath heated under reflux and under magnetic stirring. The rate of polymerization is followed monitoring change in refractive index. The solution is kept at the same temperature until the refractive index remained constant for 24 hours. Sodium hydroxide is added for neutralization. Water was removed under reduced pressure (water bath 50° C., 10 mbar) and the raw polymer was dried in vacuum for 24 h. The PEI polymer was re-dissolved in 15 ml 96% (v/v) ethanol. After filtration to remove residual sodium chloride, and rinsing flask and filter with three times 5 cm.sup.3 ethanol, the polymer was recovered by precipitation in 200 cm.sup.3 diethyl ether and dried at 50° C. in vacuum for 3 weeks.

[0086] The prepared PEI with methyl groups substituted in alpha can be either physically impregnated or chemically bound to the surface of a support. In the case of the physical impregnation, 18 g of PEI and 150 g of water are added to a round bottom flask. To this mixture, 42 g of silica is added under stirring. The flask is then connected to a rotary evaporator setting a rotation speed of 20-30 rpm. The flask is left under stirring for 3 h at room temperature, and then the temperature is increased to 50° C. and a vacuum level of ca 150 mbar is applied. After 1 h at 50° C., to completely remove the solvent, the temperature is increased to 90° C. for 2 h. The flask is left under vacuum until room temperature is reached. The sorbent is then removed from the flask and placed in a container for storage.

Example 3 (PS-Alphamethylbenzylamine Sorbent Beads)

[0087] Step a. 20 g of poly(styrene-co-divinylbenzene) beads and 150 mL of 1,2-dichloroethane (DCE) are loaded into a reactor and stirred at RT for 5 minutes. To this suspension, 34.5 g of AlCl.sub.3 is added. The resulting suspension is cooled to 0° C. A solution of 19.6 g acetyl chloride in 50 mL of DCE is added dropwise to the reaction mixture. When the addition is complete, the suspension is stirred at 50° C. for 4 hours. The reaction mixture is quenched with iso-propanol, and the acetylated PS beads thus made are filtered off, washed with water, 1M aqueous HCl, water again (until pH 5), and then dried.

[0088] Step b. The acetylated PS beads are dispersed in 200 mL of ethanol. To this mixture, 21.2 g of solid NaBH4 is added in portions, while the mixture is stirred at room temperature. After the addition is complete, the reaction mixture is stirred at room temperature for 4 hours. The hydroxy-functionalized PS beads thus made are filtered off, washed with water, 1M HCl, water, and are subsequently dried.

[0089] Step c. The hydroxy-functionalized PS beads are suspended in 175 mL of dichloromethane, and the suspension is cooled to 0° C. To this mixture, a solution of 57.7 g of PCIS in 175 mL of dichloromethane is added drop-wise while the reaction mixture is stirred at 0° C. The resulting suspension is then stirred at room temperature for 3 hours, after which the reaction is quenched by adding iso-propanol. The chlorine-functionalized PS beads thus made are filtered off, washed with acetone, pentane, and are subsequently dried.

[0090] Step d. The chlorine-functionalized PS beads are suspended in 250 mL of DMF and stirred for 5 minutes. 27.2 g of solid NaN.sub.3 is added in portions while the reaction mixture is stirred at ambient temperature. The resulting suspension is then heated to 100° C. and stirred at 100° C. for 3 hours, after which it is cooled to RT. The azide-functionalized PS beads thus made are filtered off, washed with water, methanol, acetone, pentane, and are subsequently dried.

[0091] Step e. Under an inert atmosphere, 10 g of the azide-functionalized PS beads are dispersed in 80 mL of dry THF at 0° C. To this suspension, 3.3 g of solid LiAIH.sub.4 is added in portions, while the reaction mixture was stirred at 0° C. After the addition was complete, the reaction mixture was stirred at 0° C. for one hour, and then for an additional 12 h at ambient temperature. The reaction is quenched by drop-wise addition of iso-propanol, water, and 1M aqueous NH.sub.4Cl. Each addition is performed until no more gas evolution is observed. The suspension is then washed with a 1M aqueous HCl, and the α-methylated, amine-functionalized PS beads thus made are filtered off. The beads are washed with water (until neutral pH), methanol, acetone, pentane, and are finally dried.

Example 4 (PS-Benzylamine Sorbent Beads)

[0092] 300 g of deionized water and 10 g of dispersant is added to a three-neck 1 L flask equipped with a thermometer and a reflux condenser at room temperature. To this mixture, a mixture containing 150 g of styrene, 25 g of divinylbenzene, 1.5 g of benzoyl peroxide and 90 g of pore-forming agent, which can be isooctane, toluene, wax or a mixture of thereof, is added under stirring. The temperature is increased to 70° C. for 3 h, then up to 80° C. for 4 h and completed at 95° C. for 7 h, after which the formation of the beads has occurred. The suspension is cooled down to room temperature. The poly(styrene-co-divinylbenzene) beads are filtered and are then washed three times with an equivalent volume of acetone. To obtain the chloromethylated beads, the poly(styrene-co-divinylbenzene) beads are treated in the following way. 600 g of chloromethyl methyl ether is added to 100 g of poly(styrene-co-divinylbenzene) in a flask equipped with a thermometer and a reflux condenser. The mixture is then heated to 50° C. for 1 h, after that 60 g of ZnCl2 is added to the mixture. After 5 h of reaction, the mixture is cooled down to room temperature, the beads are separated by filtration. To quench the excess of chloromethyl methyl ether, the beads are washed with water until pH neutral, then with acetone, and dried.

[0093] To obtain the aminoalkylated beads, the chloroalkylated beads are treated in the following way. 100 g of chloroalkylated beads are added to 1000 mL of dimethoxymethane. To this suspension, 100 g of hexamethylentetramine is added. The reaction mixture is heated up to 40° C. then held at this temperature for 24 h. After cooling, the beads are filtered off and washed with water. To free the amino groups, the beads undergo a hydrolysis step followed by a treatment with sodium hydroxide. The beads are suspended in a solution containing HCl and ethanol in a 1:3 volume ratio and are left under stirring overnight. After that, the beads are separated by filtration and washed with water until pH neutral. The beads are then suspended in sodium hydroxide solution for 3 h, filtered, washed with water until pH neutral, and finally dried.

Carbon Dioxide Capture Properties and Oxidation Resistance:

[0094] The beads according to example 3 can be 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.

[0095] For the adsorption measurements the results of which are illustrated further below, 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 CO2 adsorption/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 CO2 adsorbed on the sorbent was determined by integration of the signal of an infrared sensor measuring the CO2 content of the air stream leaving the cylinder.

[0096] 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.

[0097] From the experiments one can see that unexpectedly the adsorption characteristics are not significantly changed due to the methyl substitution in the α-position compared with the beads having primary benzylamine according to the prior art. Some experiments even show better carbon dioxide capture properties but only so for a small number of cycle. For a high number of cycles, only the systems according to the claimed invention can maintain high carbon dioxide capture properties.

[0098] Importantly, and as an example, the methyl substituted benzylamine beads in the experiments show essentially no degradation (in the sense of decrease of adsorption characteristics over time) even if comparably high temperatures are used and/or long time spans involving high temperatures.

[0099] The experiments for this example therefore unexpectedly show that while not impairing the adsorption characteristics, the new sorbent materials, and this applies to not only this example but to the materials as claimed in the process as claimed, allow for much higher resistance to oxidative degradation and to corresponding decrease of the adsorption characteristics.

[0100] FIG. 2 illustrates, how unexpectedly the carbon dioxide capture capacity of materials according to the present invention, exemplified by carbon dioxide capture material based on benzylamine and produced according to example 4 as compared to carbon dioxide capture material based on alpha methyl benzylamine, so according to the invention, produced according to example 3 just by replacing the benzylamine by alpha methylbenzylamine.

[0101] Again, beads according to example 4 and according to this modified example 3 with alpha methylbenzylamine as starting material were tested in an experimental rig in which the beads were contained in a packed-bed reactor. The adsorber structure was operated using a temperature swing direct air capture process as detailed above heating the sorbent to a temperature between 60 and 110° C.

[0102] What is given in FIG. 2 is the results of a degradation test used to assess the stability to oxidation of the sorbents. Specifically, as an example, the alpha methyl benzylamine and the benzylamine sorbents were placed in a convection oven at 95° C. under air atmosphere for 10 days. This specific treatment is a stress test used to assess sorbent stability in a relatively short time and based on comparative experiments it is equivalent to more than 10000 adsorption/desorption cycles. After the treatment, the sorbents were tested in the rig and the carbon dioxide capture capacity was compared to the initial carbon dioxide capture capacity, i.e. before the degradation test. As one can see impressively from that representation, the oxidation of the material based on benzylamine is highly significant and leads to a dramatic reduction of the carbon dioxide capture capacity after the degradation test corresponding to an extended number of cycles compared with alpha methylbenzylamine based systems for the same number of cycles.

[0103] The same behavior is observed for materials based on PEI as compared with materials based on PEI with methyl groups substituted in alpha position.

LIST OF REFERENCE SIGNS

[0104]

TABLE-US-00001 1 ambient air, ambient air 2 outflow of ambient air behind adsorption unit in adsorption flow-through mode 3 sorbent material 4 steam, steam inflow structure inflow structure for desorption 5 reactor outlet for extraction 6 vacuum unit/separator 7 wall 8 reactor unit