Materials for the direct capture of carbon dioxide from atmospheric air

Abstract

The invention relates to a method to produce a particulate activated carbon material for capturing CO.sub.2 from air, wherein the particulate activated carbon is impregnated with alkali carbonate salt such as K.sub.2CO.sub.3; and wherein the impregnated particulate activated carbon either has, determined using nitrogen adsorption methods, a pore volume of at least 0.10 cm.sup.3/g for pore sizes of at least 5 nm and a pore volume of at most 0.30 cm.sup.3/g for pore sizes of less than 2 nm or is based on a mixture of different alkali carbonate salts, or has a particular pore surface for pore sizes in the range of 2 nm-50 nm.

Claims

1. A method for making a particulate activated carbon material for capturing CO.sub.2 from air, wherein the particulate activated carbon is impregnated with two different alkali carbonate salts: K.sub.2CO.sub.3 and Na.sub.2CO.sub.3, wherein the alkali carbonate salt with the smallest weight proportion is present in an amount of at least 5 weight % with respect to the total of an impregnating mixture of the two alkali carbonate salts, wherein said two alkali carbonate salts are dissolved in a solvent, wherein pristine particulate activated carbon having a specific surface area, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and using a t-plot method, of at least 80 m.sup.2/g in the pore size range of more than 2 nm to at most 50 nm, is added to form a suspension, and wherein subsequently at least a solid fraction is isolated, dried by evaporation, or both, to obtain the impregnated particulate activated carbon.

2. The method according to claim 1, wherein the solvent is water.

3. The method according to claim 1, wherein the pristine particulate activated carbon has a pore volume of at least 0.1 cm3/g in the pore size range more than 2 nm to at most 50 nm, or wherein the pristine particulate activated carbon has a specific surface area of 80-600 m2/g, in the pore size range of more than 2 nm to at most 50 nm, in each case determined using nitrogen adsorption methods according to ISO 15901-2 and ISO 15901-3 and according to the t-plot method.

4. The method according to claim 1, wherein the suspension is subjected to at least one time period with reduced pressure, and wherein before isolation of the impregnated particulate activated carbon the suspension is returned to ambient pressure for a time period of at least 60 seconds.

5. A particulate activated carbon material for capturing CO.sub.2 from air, wherein the particulate activated carbon is impregnated with two different alkali carbonate salts: K.sub.2CO.sub.3 and Na.sub.2CO.sub.3, wherein the alkali carbonate salt with the smallest weight proportion is present in an amount of at least 5 weight % with respect to a total of an impregnating mixture of the alkali carbonate salts, wherein at least one of the following conditions applies: the impregnated particulate activated carbon has, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and according to the QSDFT calculation scheme, a) a pore volume of at least 0.10 cm.sup.3/g for pore sizes of at least 5 nm and a pore volume of at most 0.30 cm.sup.3/g for pore sizes of less than 5 nm; b) a pore volume of at least 0.04 cm.sup.3/g for pore sizes of at least 2 nm and a pore volume of at most 0.35 cm.sup.3/g for pore sizes of less than 2 nm; c) a pore surface of at least 20 m2/g for pore sizes above 2 nm or in the range of 2-50 nm.

6. The material according to claim 5, wherein the alkali carbonate salt impregnated particulate activated carbon has, a pore volume of at least 0.1 cm.sup.3/g for pore sizes above 5 nm or in the range of 5-50 nm, determined using nitrogen absorption methods as described in ISO 15901-2 and ISO 15901-3 according to the QSDFT calculation scheme, or a pore volume of at least 0.05 cm.sup.3/g for pore sizes in the range of 50-1,000 nm, as determined using mercury porosimetry analysis as described in ISO 15901-1, or a pore volume of at most 0.25 cm.sup.3/g or at most 0.2 cm.sup.3/g or in the range of 0.05-0.2 cm.sup.3/g or 0.05-0.15 cm.sup.3/g, for pore sizes of less than 5 nm, determined using nitrogen absorption methods as described in ISO 15901-2 and ISO 15901-3 according to the QSDFT calculation scheme, or wherein the alkali carbonate salt impregnated particulate activated carbon has, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and according to the QSDFT calculation scheme, a pore surface of at least 20 m.sup.2/g for pore sizes above 5 nm or in the range of 5-50 nm, or a pore surface of at most 500 m.sup.2/g or in the range of 150-500 or 100-400 m.sup.2/g for pore sizes of less than 5 nm.

7. The material according to claim 5, wherein the impregnated particulate activated carbon has a BET surface area according to ISO 9277 in the range of 100-800 m.sup.2/g, or of less than 500 m.sup.2/g or wherein the impregnated particulate activated carbon has a tapped density in the range of 300-800 kg/m.sup.3, or wherein the impregnated particulate activated carbon has a particle size in the range of 0.1-8 mm, or in the range of mesh (ASTM) 3-140.

8. The material according to claim 1, wherein the impregnated particulate activated carbon contains at least 10% by weight of alkali carbonate salt.

9. The material according to claim 5, wherein the alkali carbonate salt impregnated particulate activated carbon has an average carbon dioxide capacity, at 30° C., 60% relative humidity and 450 ppmv carbon dioxide concentration after 1000 minutes adsorption in the range of 0.5-5 mmol/g, or wherein the particles of the alkali carbonate salt impregnated particulate activated carbon are essentially spherical, extruded rods, pellets.

10. A carbon dioxide capture device comprising a material according to claim 5.

11. The carbon dioxide capture device according to claim 10, wherein it comprises a housing in which the at least one air permeable container containing the particles of the alkali carbonate salt impregnated particulate activated carbon is located, wherein the housing has at least one opening for allowing in and/or allowing out atmospheric air for adsorption and closing lids for said at least one opening to close the housing as well as means for applying a vacuum and/or temperature change for release of the adsorbed carbon dioxide as well as means for removal of said adsorbed carbon dioxide from the housing and for collecting and/or further concentrating and/or condensing the carbon dioxide.

12. A method of using a material according to claim 5 for capturing carbon dioxide from atmospheric air.

13. A method for capturing carbon dioxide from atmospheric air using the material according to claim 5, wherein a temperature swing cycle or a temperature/vacuum swing cycle, with or without steam injected, is used for adsorption and desorption of the carbon dioxide.

14. The method according to claim 13, where at least a part of the desorption of CO.sub.2 is performed at a pressure in the range of 50-400 mbar.sub.abs and at a temperature in the range of 80-150° C. or where at least a part of the desorption of CO.sub.2 is performed at a pressure in the range of 50-400 mbar.sub.abs and at a temperature of 35-80° C. and another part of the desorption of CO.sub.2 is performed at a temperature in the range of 80-150° C.

15. The method according to claim 1 wherein said pristine particulate activated carbon is at least one of dried and purified before use.

16. The method according to claim 1, wherein the solvent is deionized water, and wherein the concentration of the alkali carbonate salt is 1-8 mmol (total) alkali carbonate salt per ml water, or 1.5-4.5 mmol/m1 water, or wherein as pristine particulate activated carbon a pristine, non-oxidized, particulate activated carbon is added to the solution under stirring, at a temperature in the range of 5-40° C., or at a temperature in the range of 20-30° C., or for a time span in the range of 30 minutes-100 hours, or in the range of 6 hours-40 hours, and wherein subsequently at least the solid fraction is isolated and/or dried by evaporation, including vacuum evaporation.

17. The method according to claim 1, wherein the pristine particulate activated carbon has a pore volume of at least 0.1 cm3/g and at most 2.5 cm3/g in the pore size range more than 2 nm to at most 50 nm, or wherein the pristine particulate activated carbon has a specific surface area of 80-400 m2/g in the pore size range of more than 2 nm to at most 50 nm, in each case determined using nitrogen adsorption methods according to ISO 15901-2 and ISO 15901-3 and according to the t-plot method.

18. The method according to claim 1, wherein the suspension is subjected to at least one time period with a vacuum of at most 300 mbar, or at most 200 mbar, or in the range of 10-150 mbar, wherein that reduced pressure time period is at least 60 seconds, or at least 2 minutes, or 3-20 or 5-10 minutes, and wherein before isolation of the impregnated particulate activated carbon the suspension is returned to ambient pressure for a time period of at least 60 seconds, wherein at least two such cycles including a time period of reduced pressure of at least 60 seconds, or of at least 2 min, are used and a following time period of at least 60 seconds, or of at least 2 min, of ambient pressure is carried out, and wherein the total impregnation period before isolation can be in the range of 2-5 hours, or in the range of 2.5-3.5 hours.

19. The particulate activated carbon material according to claim 5, wherein said material is prepared using pristine particulate activated carbon, having a specific surface area, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and using a t-plot method, of at least 80 m.sup.2/g in the pore size range of more than 2 nm to at most 50 nm, added to a solution of K.sub.2CO.sub.3 and Na.sub.2CO.sub.3.

20. The particulate activated carbon material according to claim 5, wherein the impregnated particulate activated carbon has, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and according to the QSDFT calculation scheme, a pore surface in the range of 40-250 or 45-200 m2/g for pore sizes above 2 nm or in the range of 2-50 nm.

21. The particulate activated carbon material according to claim 5, wherein the alkali carbonate salt impregnated particulate activated carbon has: a pore volume in the range of 0.1-2.2 or 0.2-1.5 cm.sup.3/g for pore sizes above 5 nm or in the range of 5-50 nm, determined using nitrogen absorption methods as described in ISO 15901-2 and ISO 15901-3 according to the QSDFT calculation scheme, or a pore volume in the range of 0.05-0.2 cm.sup.3/g or 0.05-0.15 cm.sup.3/g, for pore sizes of less than 5 nm, determined using nitrogen absorption methods as described in ISO 15901-2 and ISO 15901-3 according to the QSDFT calculation scheme, or wherein the alkali carbonate salt impregnated particulate activated carbon has, determined using nitrogen adsorption methods as described in ISO 15901-2 and ISO 15901-3 and according to the QSDFT calculation scheme, a pore surface in the range of 20-500 or 50-400 m.sup.2/g for pore sizes above 5 nm or in the range of 5-50 nm, or a pore surface in the range of 150-500 or 100-400 m.sup.2/g for pore sizes of less than 5 nm.

22. The particulate activated carbon material according to claim 5, wherein the impregnated particulate activated carbon has a tapped density in the range of 400-600 kg/m.sup.3, or wherein the impregnated particulate activated carbon has a particle size in the range of 0.5-1.5 mm, or in the range of mesh (ASTM) 4-50.

23. The particulate activated carbon material according to claim 5, wherein an impregnating mixture of said two alkali carbonate salts is consisting of K.sub.2CO.sub.3 as well as Na.sub.2CO.sub.3, in a weight ratio of K.sub.2CO.sub.3 to Na.sub.2CO.sub.3 in the range of 95:5-5:95, or in the range of 90:10-10:90, or in the range of 40:60-95:5.

24. The particulate activated carbon material according to claim 1, wherein the impregnated particulate activated carbon contains at least 20% by weight or at least 30% by weight, or in the range of 25-45% by weight of K.sub.2CO.sub.3.

25. The particulate activated carbon material according to claim 5, wherein the alkali carbonate salt impregnated particulate activated carbon has an average carbon dioxide capacity, at 30° C., 60% relative humidity and 450 ppmv carbon dioxide concentration after 1000 minutes adsorption in the range of 1-2.5 mmol/g or after 180 minutes adsorption in the range of 0.5-2 mmol/g or in the range of 0.6-1.5 mmol/g or wherein the particles of the alkali carbonate salt impregnated particulate activated carbon are essentially spherical, extruded rods, or pellets.

26. A carbon dioxide capture device comprising a material according to claim 5, in the form of at least one air permeable container comprising said material in particulate form, including in the form of a multitude of layers of such containers arranged in a stack.

27. The method according to claim 12 comprising using a carbon dioxide capture device for capturing carbon dioxide from atmospheric air, in a cyclic process, said device having said particulate activated carbon material.

28. A method for capturing carbon dioxide from atmospheric air using a carbon dioxide capture device having the material according to claim 5, wherein a temperature swing cycle or a temperature/vacuum swing cycle, with or without steam injected, is used for adsorption and desorption of the carbon dioxide.

29. The method according to claim 13, where at least a part of the desorption of CO.sub.2 is performed at a pressure in the range of 100-300 mbar.sub.abs and at a temperature in the range of 80-150° C., or where at least a part of the desorption of CO.sub.2 is performed at a pressure in the range of 100-300 mbar.sub.abs and at a temperature of 45-80° C. and another part of the desorption of CO.sub.2 is performed at a temperature in the range of 90-135° C.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) 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,

(2) FIGS. 1(a)-1(d) show N.sub.2 adsorption isotherms for (a) AC mesh 20-40-, (b) AC mesh 4-12, (c) AC extruded, (d) K.sub.2CO.sub.3/AC V (mesh 20-40);

(3) FIG. 2 shows the pore size distributions for AC mesh 20-40 batch 1, AC mesh 4-12, AC extruded;

(4) FIG. 3 shows a BJH plot for AC 1: AC mesh 20-40 batch 1, AC 2: AC mesh 20-40 batch 2, AC 3: AC mesh 4-12 and AC 4: AC extruded;

(5) FIG. 4 shows pore size vs. pore volume for AC mesh 20-40 batch 1;

(6) FIG. 5 shows pore size vs. pore volume for AC mesh 20-40 batch 2;

(7) FIG. 6 shows pore size vs. pore volume for AC mesh 4-12;

(8) FIG. 7 shows pore size vs. pore volume for extruded AC;

(9) FIG. 8 shows pore size vs. pore volume for K.sub.2CO.sub.3/AC V;

(10) FIG. 9 shows pore size distributions for AC mesh 20-40 and K.sub.2CO.sub.3/AC mesh 20-40;

(11) FIG. 10 shows CO.sub.2 adsorption curves for samples K.sub.2CO.sub.3/AC IV, V, VII, VIII, IX, XI;

(12) FIG. 11 shows CO.sub.2 adsorption curves for K.sub.2CO.sub.3/AC IV after different desorption conditions;

(13) FIG. 12 shows CO.sub.2 desorption flow during TVS desorption of 40 g of K.sub.2CO.sub.3/AC V at 100 mbar and 150° C.

(14) FIG. 13 shows pore size distributions of AC 3:AC mesh 4-12 and AC 7: K.sub.2CO.sub.3/AC mesh 4-12 obtained by mercury porosimetry analysis

(15) FIG. 14 shows pore size distributions of AC2: mesh 20-40 batch 2, AC 3: mesh 4-12 and AC 4: AC extruded obtained with mercury porosimetry analysis

(16) FIG. 15 shows the correlation between mesopore surface and mesopore volume of the AC support and the capacity to capture CO.sub.2 of the K.sub.2CO.sub.3/AC sorbent material. AC supports with mesopore surface ≥80 m.sup.2/g and mesopore volume ≥0.1 cm.sup.3/g are the most apt for formulating the sorbent material

(17) FIG. 16 shows an exemplary adsorption breakthrough curve of the demonstration plant at an airflow of approximately 1000 m3/h, yielding an uptake of 1.15 kg of CO.sub.2

(18) FIG. 17 shows an exemplary desorption sorbent and steam temperatures of the demonstration plant during desorption by method 1

(19) FIG. 18 shows an exemplary desorption chamber pressure of the demonstration plant during desorption by method 1

(20) FIG. 19 shows an exemplary concentration and flow of the CO.sub.2-product gas during desorption on the demonstration plant by method 1

(21) FIG. 20 shows the correlation between the mesopore surface of the pristine activated carbon ingredient and the CO.sub.2 adsorption capacity of the sorbent

(22) FIG. 21 shows the cumulative CO.sub.2 adsorption curves for the examined sorbents

(23) FIG. 22 shows the breakthrough curves for the examined sorbents.

DESCRIPTION OF PREFERRED EMBODIMENTS

Example 1. Synthesis of Different Activated Carbon/K.SUB.2.CO.SUB.3 .Sorbents

(24) Utilized chemicals and materials:

(25) Granular activated carbon, mesh size 20-40 (0.841-0.420 mm) CAS no.: 7440-44-0, Sigma Aldrich, DARCO®;

(26) Granular activated carbon mesh size 4-12 (4.76-1.68 mm), CAS no.: 7440-44-0, Sigma Aldrich, DARCO®;

(27) Extruded activated carbon 3 mm, CAS no.: 7440-44-0, Cabotcorp, Norit®;

(28) K.sub.2CO.sub.3, CAS no.: 584-08-7, Sigma Aldrich Potassium Cabonate Anhydrous.

(29) Description of the Synthesis of Particulate Activated Carbon/K.sub.2CO.sub.3 Sorbents:

(30) K.sub.2CO.sub.3/AC 20-40 Mesh

(31) Method 1: (Batch IV) K.sub.2CO.sub.3 (10.31 g, 0.075 mol) was added to deionized water (30 cm.sup.3). Granular, mesh 20-40 activated carbon (20.07 g) was added to the mixture while stirring. The mixture was left stirring at room temperature for 24 hours. The mixture was placed on a tray in an oven and heated to 105° C. The material was dried at 105° C. for 3 hours.

(32) Method 2: K.sub.2CO.sub.3 (10.0355 g) was added to 60 cm.sup.3 of deionized water. Activated carbon 20-40 mesh (20.0577 g) was added to the solution. The mixture was placed in a rotary evaporator and was mixed at room temperature for 24 hours. The water was removed at 60° C.

(33) K.sub.2CO.sub.3/AC (Batches V, VII, VIII, IX, XI) were all prepared in the same way as K.sub.2CO.sub.3/AC IV. Below in Table 1 are the exact amounts of K.sub.2CO.sub.3 and granular mesh 20-40 activated carbon that were used. K.sub.2CO.sub.3/AC IV, V and VII were produced with activated carbon taken from one supplier batch and K.sub.2CO.sub.3 AC VIII, IX, and XI were taken from a second supplier batch in order to check reproducibility.

(34) TABLE-US-00001 TABLE 1 Mass of K.sub.2CO.sub.3 and AC used in the synthesis of the composite sorbent Batch K.sub.2CO.sub.3 (g) 20-40 mesh activated carbon (g) IV 10.31 20.07 V 10.19 20.14 VII 10.13 20.44 VIII 10.12 20.07 IX 10.03 20.09 XI 10.02 20.09

(35) K.sub.2CO.sub.3/AC 4-12 mesh: K.sub.2CO.sub.3 (10.05 g, 0.073 mol) was added to deionized water (30 cm.sup.3). Granular, mesh 4-12 activated carbon (20.01 g) was added to the mixture while stirring. The mixture was left stirring at room temperature for 24 hours. The mixture was placed on a tray in an oven and heated to 105° C. The material was dried at 105° C. for 3 hours.

(36) K.sub.2CO.sub.3/AC Extruded AC:

(37) Method 1: K.sub.2CO.sub.3 (10.08 g, 0.073 mol) was dissolved in 30 cm.sup.3 of deionized water. Carbon rods (20.13 g) were placed in a flat beaker and the aqueous K.sub.2CO.sub.3 solution was pipetted onto it. The activated carbon was left to soak for 24 hours at room temperature and was then dried in the oven for two hours at 150° C.

(38) Method 2: K.sub.2CO.sub.3 (10.10 g, 0.073 mol) was dissolved in 30 cm.sup.3 of deionized water. Activated carbon rods (19.99 g) were added to the solution. The rods were left to soak for 24 hours at room temperature. The mixture was filtered using gravity filtration and then dried in the oven at 150° C. for two hours. 10 cm.sup.3 of the 24 cm.sup.3 of filtrate was dropped onto the dried activated carbon. The mixture was left at room temperature for a further 24 hours and was then dried in the oven at 150° C. for two hours.

Example 2. Measurement of Tapped Density of Adsorbents

(39) Method for the tapped density measurements: 1. A graduated cylinder was placed on a PCE (Mettler Toledo) analytical scale and tarred. 2. The graduated cylinder was filled with sorbent particles using a funnel. 3. As the cylinder was filled, it was tapped manually with a spatula in order to compact the material. The cylinder was tapped between 10 and 20 times by tapping different parts of the cylinder, including the base. 4. Once the cylinder was filled with 5 cm.sup.3 of material, the weight (g) was recorded. 5. The density was calculated by dividing the weight, w by the volume, V of 5 ml, d=w/V. The error associated with the measurement is ±0.01 g/ml.

(40) Results for tapped density measurements:

(41) TABLE-US-00002 TABLE 2 Tapped densities of AC pure and loaded with K.sub.2CO.sub.3 AC granular 20-40 AC granular 20-40 AC granular mesh batch 1/ mesh batch 2/ 4-12 mesh/ kg m.sup.−3 kg m.sup.−3 kg m.sup.−3 Pure AC — 403 ± 10 432 ± 10 AC loaded with 558 ± 10 592 ± 10 539 ± 10 33 w % K.sub.2CO.sub.3

Example 3. Pore Size, Pore Volume and Specific Surface Area of Adsorbents

(42) Method for the specific surface area measurements of the sorbents:

(43) Nitrogen adsorption measurements were performed at 77 K on a Quantachrome Autosorb iQ and post-processed using ASiQWin. The mass of the sample used was 100 mg, the samples were degassed at 130° C. under vacuum for four hours before measurement.

(44) BET (Brunauer, Emmett and Teller) surface area analysis was done using the method described in ISO 9277.

(45) Method for the pore volume and pore size calculations:

(46) The experimental characterization of micro- and macropores is described in ISO 15901-2 and ISO 15901-3. Micropore and mesopore volume and surface distributions were calculated using the QSDFT method (quenched solid density functional theory) as referred to in Iupac Technical Report, Pure Appl. Chem. 2015; 87(9-10): 1051-1069.

(47) The applied calculation tools were: “QSDFT—N.sub.2—carbon adsorption branch kernel at 77 K based on a slit-pore model (pore diameter <2 nm) and cylindrical pore model (pore diameter >2 nm)” which has an upper calculation limit for a pore size of 33 nm. “N.sub.2 @ 77K on carbon (slit/cyl./spher. pore)” which contains in comparison to the kernel above additionally a spherical pore model for pore sizes above 5 nm and in such allows calculations up to 50 nm.

(48) The adsorption curves were used instead of the desorption curves due to tensile-strength effects.

(49) Results for the specific surface area measurements are given in FIG. 1.

(50) According to IUPAC definitions micropores are defined as being <2 nm in diameter, mesopores are defined as being 2<x<50 nm in diameter and macropores are >50 nm. From FIG. 1 (a) it can be seen that AC mesh 20-40 has both micro- and mesopores. The knee at low partial pressures shows strong adsorbate-adsorbent interactions typical of micropores. The hysteresis indicates the presence of mesopores. K.sub.2CO.sub.3/AC V in FIG. 1 (d) has the same adsorption isotherm with a lower volume, which indicates that both micro- and mesopores were filled with K.sub.2CO.sub.3. The AC mesh 4-12 also has a similar isotherm showing that this material too has micro- and mesopores. From FIG. 1 (c) it can be seen that the extruded AC has predominantly micropores and few mesopores with small size featuring a typical type 1 adsorption isotherm. From the pore size distribution analysis below (see FIG. 2) one can see that the extruded AC has predominantly pores in the size range of <2 nm or <5 nm of pore diameter.

(51) The specific surface areas are summarized in Table 3 below:

(52) TABLE-US-00003 TABLE 3 BET surface areas of pristine AC supports and K.sub.2CO.sub.3/AC V AC 20-40 AC 20-40 AC 4-12 mesh batch 1/ mesh batch 2/ mesh AC extruded/ m.sup.2 g.sup.−1 m.sup.2 g.sup.−1 m.sup.2 g.sup.−1 m.sup.2 g.sup.−1 Pure AC 585 650 448 757 AC loaded with 304 — — — 33 w % K.sub.2CO.sub.3

(53) The AC extruded has the highest surface area as this material has predominantly micropores and small mesopores below 5 nm or below 2 nm. AC mesh 4-12 has the lowest surface area indicating that it presumably has the largest pore sizes. As shown below the extruded AC has the lowest CO.sub.2 capacity for CO.sub.2 capture from air and AC mesh 4-12 has the highest, so that the AC support with the lowest specific surface area performs best. This is contrary to prior art, where it is largely claimed that the specific surface area of the support needs to be maximized, but no indications with respect to pore size are given.

(54) The surface area for the two AC mesh 20-40 supplier batches differ by 10%. The fact that the surface area in batch 1 is lower than that of batch 2 could indicate that it has larger pore sizes, e.g. more pore volume in size above 30 nm.

(55) The results for the pore volume and pore size calculations using the two different kernels are shown in Table 4a and Table 4b below:

(56) TABLE-US-00004 TABLE 4a Surface area and pore volumes for micropores and mesopores as determined by QSDFT calculations with kernel “QSDFT - N2 - carbon adsorption branch kernel at 77K based on a slit-pore model (pore diameter < 2 nm) and cylindrical pore model (pore diameter > 2 nm)” Micropores Mesopores Micropore Micropore Mesopore Mesopore surface area/ volume/ surface area/ volume/ Sample ID m.sup.2 g.sup.−1 cm.sup.3 g.sup.−1 m.sup.2 g.sup.−1 cm.sup.3 g.sup.−1 AC mesh 375 0.144 210 0.408 20-40 batch 1 AC mesh 402 0.163 248 0.498 20-40 batch 2 AC mesh 4-12 315 0.130 133 0.274 AC extruded 660 0.270 97 0.076 K.sub.2CO.sub.3/AC V 188 0.073 116 0.258

(57) TABLE-US-00005 TABLE 4b Surface area and pore volumes for pore sizes as determined by QSDFT calculations with kernel “N2 @ 77K on carbon (slit/cyl./spher. pore)” Micropores Mesopores Micropore Micropore Mesopore Mesopore surface area/ volume/ surface area/ volume/ Sample ID m.sup.2 g.sup.−1 cm.sup.3 g.sup.−1 m.sup.2 g.sup.−1 cm.sup.3 g.sup.−1 AC mesh 381 0.146 191 0.383 20-40 batch 1 AC mesh 401 0.163 215 0.471 20-40 batch 2 AC mesh 4-12 304 0.121 126 0.261 AC extruded 661 0.271 59 0.073 K.sub.2CO.sub.3/AC V 188 0.073 299 0.243

(58) Analysis of Table 4a and Table 4b shows that both kernels yielded comparable results which is why in the following analysis is limited to results obtained with kernel “QSDFT—N.sub.2—carbon adsorption branch kernel at 77 K based on a slit-pore model (pore diameter <2 nm) and cylindrical pore model (pore diameter >2 nm)” (except for BJH calculation below).

(59) By comparing the pore volume of pristine AC mesh 20-40 batch 1 and K.sub.2CO.sub.3/AC V it can be seen that roughly 50% of the micropore volume was filled with K.sub.2CO.sub.3 as well as around 35% of the mesopore volume, hence, both pore regimes contribute to K.sub.2CO.sub.3 modification, as further explained below. Due to the much higher specific surface area of the micropore volume (375 m.sup.2/g) than the mesopore volume (210 m.sup.2/g) in AC mesh 20-40 batch 1 it can be assumed that the K.sub.2CO.sub.3 filling is distributed on a bigger surface in the micropores and in such offering higher mass transfer area compared to the mesopore volume. However, as described below especially the pore volume available at pore size above 5 nm, hence, medium to large size mesopores as well as small macropores, contribute to a favourable K.sub.2CO.sub.3 modified sorbent for CO.sub.2 capture from air. This finding has not been described in prior art, rather the opposite.

(60) As described further below K.sub.2CO.sub.3/AC V (AC mesh 40-20 batch 1) and K.sub.2CO.sub.3/AC 4-12 mesh feature high CO.sub.2 capacities where K.sub.2CO.sub.3/AC extruded shows very little capacity for CO.sub.2 capture from air.

(61) From the adsorption isotherms, specific surface area, pore volume and pore size distributions data (see FIG. 2) it can be seen that AC extruded is predominantly microporous and has few pores in the small range below 2 nm or below 5 nm. This support did not work for CO.sub.2 capture from air and so it can be concluded that pore sizes >2 nm or >5 nm are needed to provide feasible supports for CO.sub.2 capture from air.

(62) In addition to the BET and DFT calculations BJH (Barrett-Joyner-Halenda) calculations were made. The comparisons for AC mesh 20-40 batch 1, AC mesh 20-40 batch 2, AC mesh 4-12 and AC extruded are shown in FIG. 3. It can be seen that AC mesh 20-40 batch 2 has the highest pore volume followed by AC mesh 20-40 batch 1 and then AC mesh 4-12. There seems to be a peak at approximately 35 nm for the materials AC mesh 20-40 batch 1 and mesh 20-40 batch 2. AC mesh 4-12 has a peak of pore volume around 45 nm. FIG. 3 seems to indicate that the best performing materials do have mesopores.

(63) FIGS. 4-8 show the detailed measurement results of the cumulative pore volume versus the pore size (given as half pore width), and FIG. 9 gives the pore size distribution for the pristine AC mesh 20-40 batch 1 and the K.sub.2CO.sub.3/AC V.

(64) From FIG. 9 it can be seen that the pores in the range 5<x<30 nm are all filled approximately equally with K.sub.2CO.sub.3. There isn't a specific range that seems to take up more K.sub.2CO.sub.3.

Example 4. CO.SUB.2 .Adsorption/Desorption Capacities of Adsorbents

(65) The method used to determine the CO.sub.2 adsorption/desorption capacity was as follows: 1. The as synthesized material was weighed. It was placed on a tray and heated to 150° C. in a Binder natural convection oven. 2. The material was desorbed for 2 hours once the oven reached 150° C. 3. After two hours the oven was cooled and once a temperature of 80° C. was reached the material was removed and weighed. 4. 6 g of desorbed sample was filled into a cylinder with an inner diameter of 40 mm and a height of 40 mm and placed into a CO.sub.2 adsorption/desorption device, where it was exposed to a flow of 2.0 NL/min of air at 30° C. containing 450 ppmv CO.sub.2, having a relative humidity of 60% corresponding to a temperature of 30° C. for a duration of 1000 min. The amount of CO.sub.2 adsorbed on the adsorbent was determined by integration of the signal of an infrared sensor measuring the CO.sub.2 content of the air stream leaving the cylinder. After CO.sub.2 adsorption the adsorbent was weighed again.

(66) The results of the CO.sub.2 adsorption/desorption measurements are summarized in the FIGS. 10 and 11 and Table 5.

(67) TABLE-US-00006 TABLE 5 CO.sub.2 capacities after 1000 min. and 180 min. for different batches of K.sub.2CO.sub.3/AC CO.sub.2 capacity after CO.sub.2 capacity after 1000 min. adsorption/ 180 min. adsorption/ mmol g.sup.−1 mmol g.sup.−1 AC mesh 20-40 batch 1 IV 1.350 0.641 V 1.528 0.760 VII 1.330 0.673 AC mesh 20-40 batch 2 VIII 1.215 0.676 IX 1.382 0.739 XI 1.328 0.586 Average 1.4 ± 0.1 0.68 ± 0.06

(68) The average CO.sub.2 capacity at 30° C., 60% relative humidity (at 30° C.) and 450 ppmv CO.sub.2 concentration after 1000 min. adsorption measured across six samples produced from two activated carbon mesh 20-40 batches was found to be 1.4±0.1 mmol/g. The average capacity after 180 min. adsorption was found to be 0.68±0.06 mmol/g.

(69) In order to identify the threshold desorption temperature the material was desorbed at different temperatures. Once the set temperature was reached, the material was left desorbing for two hours. After two hours the oven was left to cool until it reached 80° C. The material was then removed and tested with above described CO.sub.2 adsorption protocol for CO.sub.2 adsorption capacity.

(70) The threshold temperature is concluded to be 115° C. because after desorbing at this temperature the total CO.sub.2 capacity as described above is reached. When the material is desorbed at 110° C., the adsorption capacity was 1.02 mmol g.sup.−1, indicating it was not fully desorbed.

(71) The CO.sub.2 capacity at the CO.sub.2 adsorption conditions described above for the K.sub.2CO.sub.3 impregnated on 4-12 mesh activated carbon was found to be 1.687 mmol/g.

(72) The CO.sub.2 capacity at the CO.sub.2 adsorption conditions described above for the K.sub.2CO.sub.3 impregnated extruded carbon was found to be 0.100 and 0.219 mmol/g for the two syntheses, hence, it is too little to qualify as feasible adsorbent for CO.sub.2 capture from air.

Example 5. Temperature-Vacuum-Swing Desorption of Adsorbents

(73) For commercial application of the adsorbents described herein desorption methods are required which produce a concentrated stream of CO.sub.2 during desorption. Temperature-vacuum-swing (TVS) desorption is a desorption technique used mainly for amine-modified adsorbents for their regeneration. In this example we tested whether TVS desorption is also feasible for desorption of K.sub.2CO.sub.3 modified activated carbons.

(74) The method for the TVS desorption was as follows: 1. The adsorbent was desorbed in the oven at 150° C. and 40 grams were weighed out for the experiment. 2. The 40 g of dry mass was filled into a rectangular CO.sub.2 adsorption/desorption chamber having inner dimensions of 62 mm×62 mm×72 mm. 3. For TVS desorption the chamber containing the adsorbent was heated by an external source to 150° C. and the pressure was reduced to 100 mbar with a vacuum pump for a duration of 300 min. 4. After the desorption, the chamber is cooled to 30° C. and once this temperature was reached CO.sub.2 adsorption was performed with air at a temperature of 30° C., a flow rate of 15.0 NL/min, a CO.sub.2 concentration of 450 ppmv, a relative humidity of 60% at 30° C. for a duration of 1000 min. 5. The adsorption and desorption were repeated for 5 consecutive cycles.

(75) FIG. 12 shows the CO.sub.2 desorption flow during TVS desorption of 40 g of K.sub.2CO.sub.3/AC V at 100 mbar and 150° C. Integration of the signal of the flow measurement device yielded a CO.sub.2 desorption capacity of 1.3 mmol CO.sub.2/g and subsequent CO.sub.2 adsorption yielded 1.2 mmol CO.sub.2/g, consequently confirming that the adsorbent can be regenerated with TVS desorption.

Example 6. Mercury Porosimetry Measurements

(76) Mercury porosimetry measurements were performed to analyze the pore sizes and pore volumes not accessible through N.sub.2 adsorption measurements (see Example 3). In order to perform mercury porosimetry measurements the ISO 15901-1 measurement standard was followed and the following parameters were used: Mercury surface tension: 0.48 N/m Mercury contact angle: 150° Test method: PASCAL (Pressurized by Automatic Speed-up and Continuous Adjustment Logic) Max. pressure: 400 MPa Increase speed: 6-19 MPa/min Preparation: Degassing for 30 min. (also ensured <0.03 kPa reached)

(77) The results of Hg porosimetry analysis are summarized the following table:

(78) TABLE-US-00007 TABLE 6 Results obtained with Hg porosimetry analysis Total pore volume/ Pore volume Sample ID cm.sup.3 g.sup.−1 50-1′000 nm/cm.sup.3 g.sup.−1 AC mesh 20-40 batch 2 0.65 0.23 AC mesh 4-12 0.62 0.25 AC extruded 0.29 0.03 K.sub.2CO.sub.3/AC mesh 20-40 0.38 0.06 batch 2 K.sub.2CO.sub.3/AC mesh 4-12/ 0.29 0.08 K.sub.2CO.sub.3 K.sub.2CO.sub.3/AC extruded/ 0.24 0.03 K.sub.2CO.sub.3

(79) FIG. 13 shows the pore size distributions for AC mesh 4-12 and K.sub.2CO.sub.3/AC mesh 4-12. It can be seen that the pore volume over the complete measurement range 3-120'000 nm is reduced for the material modified with K.sub.2CO.sub.3, indicating that all pores sizes contribute to K.sub.2CO.sub.3 modification. It can be further seen that the pore volume reduction after K.sub.2CO.sub.3 impregnation in the pore size range of 20-1'000 nm is the largest, indicating that this is the most feasible pore size range for activated carbon adsorbents modified with K.sub.2CO.sub.3 used for CO.sub.2 capture from air.

(80) FIG. 14 summarizes the pore size distributions for AC mesh 20-40, AC mesh 4-12 and AC extruded. It can be seen that AC mesh 20-40 and AC mesh 4-12 have very different pore size distributions than AC extruded. AC extruded contains mostly micropores and macropores in the size range above 1000 nm. Such pore sizes are not favourable for activated carbons modified with K.sub.2CO.sub.3 for CO.sub.2 capture from air. In turn pore sizes in the range of 5-1'000 nm, as present in AC mesh 20-40 and AC mesh 4-12 are suitable for activated carbons modified with K.sub.2CO.sub.3 to be used for CO.sub.2 capture from air.

Example 7: Synthesis of Activated Carbon/Na.SUB.2.CO.SUB.3./K.SUB.2.CO.SUB.3 .Sorbents (See Also More Detailed Sorbent Production Further Below)

(81) Utilized chemicals and materials:

(82) Extruded activated carbon, AC 12 (Table 10).

(83) K.sub.2CO.sub.3, CAS no.: 584-08-7, Sigma Aldrich Potassium Cabonate Anhydrous

(84) Na.sub.2CO.sub.3, Cas no: 497-19-8, Sigma Aldrich, Sodium Carbonate Anhydrous

(85) Description of the Synthesis of Extruded Activated Carbon Impregnated with Na.sub.2CO.sub.3/K.sub.2CO.sub.3

(86) K.sub.2CO.sub.3 and Na.sub.2CO.sub.3 (total 20 g) were dissolved in 120 ml of water, and 40 g of activated carbon was added to the solution and soaked overnight, after which the water was removed at 100 mbar and 60° C. The resulting samples were dried in oven at 150° C. for 2 hours. The synthesis was repeated by using different relative weight proportions of the sodium and potassium salts. The materials thus prepared contained 10, 30 and 50% wt. of the sodium salt with respect to the potassium salt.

Example 8: Temperature Swing Adsorption Desorption Cycles with Air Purge Using AC/Na.SUB.2.CO.SUB.3./K.SUB.2.CO.SUB.3 .Sorbents

(87) The samples prepared in example 7 were tested using five cycles of adsorption-desorption as described in the following: 6 g of each material where placed in a steel vessel delimited by a steel net through which a controlled air flow of 2 l/min was passed. The air flowed through the samples had a controlled CO.sub.2 concentration of 450 ppmv. The outgoing air flow was controlled for the CO.sub.2 concentration using a CO.sub.2 infrared sensor. During desorption, the desorption bed temperature was set to 94° C., and a constant air flow of 2 l/min was applied. Adsorption and desorption times were 300 minutes and 120 minutes respectively. Surprisingly cyclic adsorption capacities increased up to four times by using a mixture of Na and K carbonates, with respect to the adsorption capacities of the pure potassium carbonate salt, as shown in table

(88) TABLE-US-00008 TABLE 7 Cyclic air purge adsorption capacities using mixed Na and K carbonates Mixture ratio Cyclic air purge adsorption capacity [% wt. Na.sub.2CO.sub.3:K.sub.2CO.sub.3] [mmol/g]  0:100 0.12 10:90 0.31 30:70 0.39 50:50 0.49

Example 9: Temperature-Vacuum-Swing Adsorption Desorption Cycle with AC/Na.SUB.2.CO.SUB.3./K.SUB.2.CO.SUB.3 .Sorbents

(89) The TVS experiment of example 5 was repeated, with the following modifications: 120° C. of jacket temperature during the desorption phase; adsorption and desorption times of 300 minutes; material as prepared in Example 7; four consecutives adsorption and desorption cycles were applied. The results in table 8 show an increase of 50% of cyclic capacity of CO.sub.2 for the material prepared with the combination 30-70 w % Na.sub.2CO.sub.3—K.sub.2CO.sub.3 as compared to the same material but only impregnated with K.sub.2CO.sub.3 in the same total weight proportion.

(90) TABLE-US-00009 TABLE 8 cyclic TVS adsorption capacities using mixed Na and K carbonates Mixture ratio Cyclic TVS adsorption capacity [% wt. Na.sub.2CO.sub.3:K.sub.2CO.sub.3] [mmol/g]  0:100 0.40 10:90 0.49 30:70 0.60 50:50 0.42

Example 10: Use of Na/K Carbonate Mixtures to Decrease the Regeneration Temperature of a Sorbent System

(91) The TVS experiment of example 9 was repeated with the modifications described in the following. The material described in example 7 was impregnated with K.sub.2CO.sub.3 and used in a TVS experiment applying a desorption (jacket) temperature of 140° C.; another experiment was carried out using the material described in example 7 impregnated with a mixture of 30:70% wt. of Na/K carbonates, and using a desorption (jacket) temperature of 120° C. The results shown in table 9 show that the material impregnated with a mixture of Na and K carbonates afford a 20% increase in cyclic capacity at 20° C. lower (jacket) temperature with respect to the same material impregnated with the pure K.sub.2CO.sub.3.

(92) TABLE-US-00010 TABLE 9 cyclic TVS adsorption capacities using pure and mixed Na and K carbonates at two different desorption temperatures Cyclic TVS adsorption Cyclic TVS adsorption capacity [mmol/g] at capacity [mmol/g] at Mixture ratio 140° C. desorption 120° C. desorption [% wt. Na.sub.2CO.sub.3:K.sub.2CO.sub.3] temperature temperature  0:100 0.50 0.40 30:70 0.60 0.60

Example 11: Correlation Between Mesopore Volume and Mesopore Surface of the AC and the CO.SUB.2 .Capture Capacity of the K.SUB.2.CO.SUB.3./AC Sorbent

(93) K.sub.2CO.sub.3/AC sorbents were prepared according to method described in Example 1, method 2, using as ingredients the activated carbons AC 1 to AC 18 listed in table 10. The pores size distribution and the mesopore volume and mesopore surface of the ACs were measured by nitrogen physisorption according to the method described in Example 3 and with the following specificities: prior to the analysis, the samples were outgassed at 150° C. for 12 hours under vacuum. For the calculation of the micro- and mesopore surface area contributions, the t-plot method was applied according to ISO 15901-3. The adsorption branch of the isotherm was used for the calculation. The CO.sub.2 capture capacities of the resulting K.sub.2CO.sub.3/AC sorbents were measured according to the method already described in Example 4. The CO.sub.2 capture capacities of the sorbents were plotted against the mesopore volume and the mesopore surface, revealing that the sorbents that were prepared using AC that had a mesopore volume ≥0.1 cm.sup.3/g, and/or a mesopore surface ≥80 m.sup.2/g showed superior capacities of CO.sub.2 capture, measurable as ≥0.8 mmol/g within the experimental setup already described, while the sorbent materials that were prepared using ACs that had a mesopore volume ≤0.1 cm.sup.3/g, and/or a mesopore surface ≤80 m.sup.2/g showed less pronounced capacities of CO.sub.2 capture, measurable as ≤0.8 mmol/g, and more often ≤0.4 mmol/g within the experimental setup already described. The plot of reference is shown in FIG. 15. The optimal loading of the sorbent was not optimized, nonetheless a clear trend can be read in the plotted values.

(94) TABLE-US-00011 TABLE 10 Properties of the activated carbons used for example 11 Corre- V.sub.pore ≥ S ≥ 2- sponding CO.sub.2 V.sub.pore < 2-50 S < 2 50 capacity of V.sub.pore 2 nm nm nm nm S.sub.BET Particle size modified AC No. [cm.sup.3/g] [cm.sup.3/g] [cm.sup.3/g] [m.sup.2/g] [m.sup.2/g] [m.sup.2/g] and type [mmol/g] AC 1 0.38 0.34 0.04 878 33 911 3 mm, 0.15 extruded AC 2 0.358 0.323 0.035 798 13 811 3 mm, 0.47 extruded AC 3 0.683 0.578 0.105 1256 53 1309 4 mm, 0.48 extruded AC 4 0.425 0.383 0.042 973 39 1012 3 mm, 0.39 extruded AC 5 0.388 0.339 0.049 798 31 829 3 mm, 0.38 extruded AC 6 0.355 0.31 0.045 704 26 730 4 mm, pellet 0.09 AC 7 0.413 0.371 0.042 909 22 931 3 mm, 0.14 extruded AC 8 0.673 0.538 0.135 1128 107 1235 4 mm, 0.9 extruded AC 9 0.312 0.083 0.229 172 100 272 2 mm, 0.86 pellets AC 0.526 0.114 0.412 272 185 457 4-12 mesh, 1.4 10 granular AC 0.944 0.155 0.789 367 390 757 20-40 mesh, 1.9 11 granular AC 0.712 0.588 0.124 1425 98 1523 0.8 mm, 1.1 12 extruded AC 0.788 0.639 0.149 1531 134 1665 0.8 mm, 1.46 13 extruded AC 0.629 0.406 0.223 874 129 1003 8-30 US 1.49 14 mesh, granular (0.6-2.36 mm) AC 0.604 0.503 0.101 1245 79 1324 0.5-0.8 mm, 1.4 15 spherical AC 0.445 0.289 0.156 723 119 842 8-30 US 1.57 16 mesh, granular (0.6-2.36 mm) AC 0.606 0.292 0.314 711 207 918 8-30 US 1.53 17 mesh, granular (0.6-2.36 mm) AC 0.496 0.32 0.176 770 106 876 12-40 US 1.95 18 mesh, granular (0.425-1.7 mm)

Example 12. Sorbent and its Production

(95) FIG. 20 shows the correlation between the mesopore surface of the pristine activated carbon ingredient and the CO.sub.2 adsorption capacity of the sorbent.

(96) We hereby show that for activated carbon supports impregnated with K.sub.2CO.sub.3 the CO.sub.2 adsorption capacities from ambient air increases with increasing mesopore surface. In particular activated carbons having mesopore surfaces above 80 m2/g are especially apt as formulation ingredient. The range of 80-600 m2/g, and most preferably 80-400 m2 g, is optimum for the mesopore surface of the activated carbon ingredient used in the formulation of the sorbent as described further below.

(97) To obtain a good sorbent it is important that the K.sub.2CO.sub.3-solution enters the pores of the support and infiltrates the large internal surface area. Capillary forces can be assumed to be a major driving force for this process. However, before the infiltration the pores are usually filled with air that needs to be replaced and that takes time to diffuse out of the porous support. Usually, rather long soaking times >12 h are used for the impregnation of activated carbon with K.sub.2CO.sub.3. The infiltration can be accelerated by the application of vacuum to remove the entrapped air followed by a return to atmospheric pressure to push the solution into the pores.

(98) The application of a vacuum of 100 mbar for 2 times 5 min followed by a return to ambient pressure at the beginning of a 3 h impregnation period allowed improving the CO.sub.2-adsorption capacity of the sorbent by a factor of 2.4 for a 180-min adsorption experiment. To be specific the capacity raised from 0.37 mmol/g to 0.88 mmol/g. The performance of the sorbent produced within 3 h with initial vacuum is similar to a sorbent produced by impregnating 18 h without initial vacuum. The latter one showed an adsorption capacity of 0.84 mmol/g. The differences between the two can be regarded to be within the experimental error.

(99) FIG. 21 shows the cumulative CO.sub.2 adsorption curves for the examined sorbents

(100) The same trend can be observed in the break through curves shown in FIG. 22. The two curves of the sorbent prepared in 3 h with initial vacuum and the one of the sorbent prepared in 18 h without initial vacuum are almost identical and did not reach breakthrough within 180 min adsorption time. In contrast, the sorbent prepared in 3 h without initial vacuum showed a much steeper breakthrough curve reaching 90% of the inlet CO.sub.2 concentration already in less than 2 h.

(101) FIG. 22 shows the breakthrough curves for the examined sorbents

(102) From the data shown it can be concluded that applying vacuum for a short period of time followed by returning to ambient pressure at the beginning of the impregnation of a porous support material with a solution of an active phase is effective in drastically reducing the necessary impregnation time. For a sorbent based on activated carbon and K.sub.2CO.sub.3 we could realize a reduction of the soaking time by a factor of six. This is highly improving the state-of-the art preparation of such materials, reducing drastically the production time and costs and simultaneously increasing the production capacity of a given facility.

(103) Sorbent Preparation:

(104) To prepare 30 g dry sorbent 10 g K.sub.2CO.sub.3 (Sigma Aldrich, analytical grade) were dissolved in a 11 pear flask in 60 ml de-ionized water by mildly shaking it. To the clear solution 20 g activated carbon (Sigma Aldrich, DARCO 20-40 mesh) were added. The flask was mounted on a rotary evaporator (Heidolph) and rotated at approx. 30 rpm for 3 or 18 h as required. For the sample with initial vacuum the apparatus was evacuated to approx. 100 mbar followed by venting to ambient pressure with air. This step was repeated once. The soaking was done in any case at ambient pressure. After the required impregnation time, the flask was lowered in a water bath at 60° C. and vacuum was applied at approx. 100 mbar to evaporate the water. After 30-45 min the dried sorbent was collected from the flask and stored in a plastic bottle until further use.

(105) Sorbent Characterization:

(106) Prior to the measurement of the adsorption characteristics the sorbent was spread on a tray and placed in an oven (Binder) at 150° C. for at least 2 h to desorb any pre-adsorbed CO2 or H2O.

(107) Immediately afterwards 6 g of the sorbent (assumed solid content: 100%) were weighed into the measurement cell and transferred into the reactor of the RC testing unit. The reactor was sealed immediately to avoid CO.sub.2 or H.sub.2O take-up from air and the adsorption measurement was started using the following parameters:

(108) Adsorption flow: 2 Nl/min; Adsorption temperature: 30° C.; CO.sub.2 concentration adsorption gas: 450 ppm; Relative Humidity: 60% rH (30° C.).