Porous Adsorbent Structure for Adsorption of CO2 from a Gas Mixture

Abstract

A porous adsorbent structure that is capable of a reversible adsorption and desorption cycle for capturing CO.sub.2 from a gas mixture comprises a support matrix formed by a web of surface modified cellulose nanofibers. The support matrix has a porosity of at least 20%. The surface modified cellulose nanofibers consist of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 100 nm to 1 mm that are covered with a coupling agent being covalently bound to the surface thereof. The coupling agent comprises at least one monoalkyldialkoxyaminosilane.

Claims

1-15. (canceled)

16. A method for producing a porous adsorbent structure that is capable of a reversible adsorption and desorption cycle for capturing CO.sub.2 from a gas mixture, said structure comprising a support matrix of surface modified cellulose nanofibers, said surface modified cellulose nanofibers consisting of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 100 nm to 1 mm covered with a coupling agent being covalently bound to the surface thereof, characterized in that: i) said support matrix is a web of nanofibers with a porosity of at least 20%, and ii) said coupling agent comprises at least one monoalkyldialkoxyaminosilane, wherein the method comprises the steps of: a) providing a first amount of a homogenized suspension of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 1.00 nm to 1 mm in a solvent; b) adding thereto a second amount of a coupling agent comprising at least one monoalkyldialkoxyaminosilane, thereby allowing formation of a homogeneous suspension of surface modified cellulose nanofibers in said solvent; c) mechanically concentrating said suspension through centrifugation, filtration or pressing, thereby obtaining a wet slurry; d) optionally washing said wet slurry with said solvent; e) removing said solvent by a drying operation, said drying operation being selected from freeze drying, atmospheric freeze drying, or a combination thereof, thereby obtaining a dried material; and f) subjecting said dried material to a heating process in an inert atmosphere, thereby obtaining said porous adsorbent structure.

17. The method according to claim 16, wherein said solvent is an aqueous medium which is preferably acidified, preferably with acetic acid or CO.sub.2, more preferably with CO.sub.2.

18. The method according to claim 16, wherein each one of said monoalkyldialkoxyaminosilanes is selected from the group consisting of: 3-aminoproplmethyldiethoxysilane, N-(2-Aminoethyl)-3-aminopropyl-methyldimethoxysilane, and N-(3-Methyldimethoxysilylpropyl)diethylenetriamine.

19. The method according to claim 16, wherein said coupling agent further comprises a trialkoxyaminosilane in an amount of up to 60% by weight with respect to the total coupling agent weight.

20. The method according to claim 19, wherein said trialkoxyaminosilane is selected from the group consisting of: 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, N-(2-Aminoethyl)-3-aminopropyl-trimethoxysilane, N-(2-Aminoethyl)-3-aminopropyl-triethoxysilane, and N-(3-Trimethoxysilylpropyl)diethylenetriamine.

21. The method according to claim 17, wherein each one of said monoalkyldialkoxyaminosilanes is selected from the group consisting of: 3-aminopropylmethyldiethoxysilane, N-(2-Aminoethyl)-3-aminopropyl-methyldimethoxysilane, and N-(3-Methyldimethoxysilylpropyl)diethylenetriamine.

22. The method according to claim 17, wherein said coupling agent further comprises a trialkoxyaminosilane in an amount of up to 60% by weight with respect to the total coupling agent weight.

23. The method according to claim 17 for producing a porous adsorbent structure, wherein said homogenized suspension of cellulose nanofibers or said first amount of cellulose nanofibers provided in step a) further comprises an admixture of large cellulose fibers, said large cellulose fibers having a diameter of more than 1 m and/or a length exceeding 1 mm, and wherein said drying operation comprises freeze drying, atmospheric freeze drying, air drying, vacuum drying, heating or a combination thereof.

24. A method for producing a porous adsorbent structure that is capable of a reversible adsorption and desorption cycle for capturing CO.sub.2 from a gas mixture, said structure comprising a support matrix of surface modified cellulose nanofibers, said surface modified cellulose nanofibers consisting of cellulose nanofibers having a diameter of about 4 mu to about 1000 nm and a length of 100 nm to 1 mm covered with a coupling agent being covalently bound to the surface thereof, characterized in that: i) said support matrix is a web of nanofibers with a porosity of at least 20%, and ii) said coupling agent comprises at least one monoalkyldialkoxyaminosilane, wherein the method comprises the steps of: a) providing a first amount of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 100 nm to 1 mm formed as a dry web of cellulose nanofibers with a porosity of at least 20%; b) forming a solution by adding a second amount of a coupling agent comprising at least one monoalkyldialkoxyaminosilane to a solvent, said solvent being an organic solvent with a water content not exceeding 5% by weight; c) immersing said dry cellulose nanofibers web in said solution, thereby allowing formation of a solvent covered cellulose nanofibers web; d) after a pretermined immersion time, removing said solvent by filtering, thereby obtaining a residue containing cellulose nanofibers coated with said coupling agent; e) optionally washing said residue with said solvent; f) subjecting said residue to a drying operation, said drying operation being selected from air drying, vacuum drying, heating or a combination thereof, thereby obtaining a dried material; g) subjecting said dried material to a heating process in an inert atmosphere, thereby obtaining said porous adsorbent structure; and, wherein said homogenized suspension of cellulose nanofibers or said first amount of cellulose nanofibers provided in step a) further comprises an admixture of large cellulose fibers, said large cellulose fibers having a diameter of more than 1 m and/or a length exceeding 1 mm, and wherein said drying operation comprises freeze drying, atmospheric freeze drying, air drying, vacuum drying, heating or a combination thereof.

25. A method for producing a porous adsorbent structure that is capable of a reversible adsorption and desorption cycle for capturing CO.sub.2 from a gas mixture, said structure comprising a support matrix of surface modified cellulose nanofibers, said surface modified cellulose nanofibers consisting of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 100 nm to 1 mm covered with a coupling agent being covalently bound to the surface thereof, characterized in that: i) said support matrix is a web of nanofibers with a porosity of at least 20%, ii) said coupling agent comprises at least one monoalkyldialkoxyaminosilane, and, iii) wherein said support matrix further comprises an admixture of large cellulose fibers, said large cellulose fibers having a diameter of more than 1 m and/or a length exceeding 1 mm, wherein the method comprises the steps of: a) providing a first amount of a homogenized suspension of cellulose nanofibers having a diameter of about 4 nm to about 1000 nm and a length of 1.00 nm to 1 mm in a solvent, wherein said homogenized suspension of cellulose nanofibers further comprises an admixture of large cellulose fibers, said large cellulose fibers having a diameter of more than 1 m and/or a length exceeding 1 mm; b) adding thereto a second amount of a coupling agent comprising at least one monoalkyldialkoxyaminosilane, thereby allowing formation of a homogeneous suspension of surface modified cellulose nanofibers in said solvent; c) mechanically concentrating said suspension through centrifugation, filtration or pressing, thereby obtaining a wet slurry; d) optionally washing said wet slurry with said solvent; e) removing said solvent by air drying at room temperature, thereby obtaining a dried material; and f) subjecting said dried material to a heating process in an inert atmosphere, thereby obtaining said porous adsorbent structure.

26. The method according to claim 25, wherein each one of said monoalkyldialkoxyaminosilanes is selected from the group consisting of: 3-aminopropylmethyldiethoxysilane, N-(2-Aminoethyl)-3-aminopropyl-methyldimethoxysilane, and N-(3-Methyldimethoxysilylpropyl)diethylenetriamine.

27. The method according to claim 25, wherein said coupling agent further comprises a trialkoxyaminosilane in an amount of up to 60% by weight with respect to the total coupling agent weight.

28. The method according to claim 25, wherein said solvent is an aqueous medium which is preferably acidified, preferably with acetic acid or CO.sub.2, more preferably with CO.sub.2.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0064] The above mentioned and other features and objects of this invention and the manner of achieving them will become more apparent and this invention itself will be better understood by reference to the following description of various embodiments of this invention taken in conjunction with the accompanying drawings. Each figure shows the CO.sub.2 adsorption/desorption mass balance for a certain number of cycles under specified adsorption and desorption conditions, which include the gas medium and flow rate, the temperature, the relative humidity (RH) expressed at a given temperature and the cycle time. In all these measurements the desorbed amount in the first cycle was higher than the adsorbed amount in the first cycle, which was particularly pronounced in the measurements of FIG. 2 and FIG. 4. This effect is attributed to the fact that the samples were stored in ambient air for a certain time before starting the experiments and thus had already adsorbed a certain quantity of CO.sub.2.

[0065] FIG. 1 Example 3, adsorbent mass 0.8 g, [0066] Adsorption: 1l/min air, 25C, RH 0% @ 25C, 60 min, [0067] Desorption: 0.8l/min argon, 90 C., RH 0% @ 25 C., 30 min;

[0068] FIG. 2 Example 3, adsorbent mass 0.8 g, [0069] Adsorption: 1l/min air, 25 C., RH 40% @ 25 C., 60 min, [0070] Desorption: 0.8l/min argon, 90 C., RH 0% @ 25 C., 60 min;

[0071] FIG. 3 Example 5, adsorbent mass 1.2 g, [0072] Adsorption: 1l/min air, 25 C., RH 40% @ 25 C., 60 min, [0073] Desorption: 0.8l/min argon, 90 C., RH 40% @ 25C, 60 min;

[0074] FIG. 4 Example 8, adsorbent mass 1.1 g, [0075] Adsorption: 1l/min air, 25 C., RH 40% @ 25 C., 60 min, [0076] Desorption: 0.8/min argon, 90 C., RH 40% @ 25 C., 45 min;

[0077] FIG. 5 Example 9, adsorbent mass 0.8 g, [0078] Adsorption: 1l/min air, 25 C., RH 40% @ 25C., 60 min, [0079] Desorption: 0.8/min argon, 90 C., RH 40% @ 25 C., 60 min;

[0080] FIG. 6 Example 10, adsorbent mass 1.0 g, [0081] Adsorption: 1/min air, 25 C., RH 40% @ 25 C., 60 min, [0082] Desorption: 0.8l/min argon, 90 C., RH 40% @ 25 C., 60 min,

[0083] The time required to reach the maximum CO.sub.2 capture capacity under the above conditions is typically in the order of 12 hours, which is clearly longer than the above indicated adsorption time of 60 min. However, using shorter cycles in the order of 1 h will often be more viable from an industrial scale process. Therefore, the results presented in the figures are considered important indicators for the practical performance of the investigated systems.

DETAILED DESCRIPTION OF THE INVENTION

1. Isolation of Cellulose Nanofibers

[0084] 1.2 kg refined fibrous beech wood pulp suspension having a dry material content of 13.5% w/w (Arbocel P10111 obtained from Rettenmeier & Shne GmbH & Co. KG, Germany) was placed in a 10 liter thermostatic glass reactor kept at 15 C. and diluted with 8.8 kg of deionized water. The starting material is considered as a mixture of cellulose nanofibers and large cellulose fibers. The resulting suspension was stirred at 148 rpm for 21 h to allow swelling, Thereafter the suspension was homogenized for 170 min through an inline Ultra-Turrax system (Megatron MT 3000, Kinematica AG, Switzerland) at 15000 rpm, which was connected to the glass reactor, The homogenized suspension was subjected to high shearing-stress generated through a high-shear homogenizer (Microfluidizer Type M-110Y, Microfluidics Corporation, USA). Thereby the suspension was pumped for 10 passes through a sequence of 400 m and 200 pm interaction chambers and subsequently for 5 passes through a sequence of 200 m and 75 m interaction chambers at a flow rate of 9.75 g/s.

2. Production of Dried Porous Cellulose Nanofibers

[0085] Water was removed from the cellulose nanofiber suspension obtained according to Example 1 through centrifugation at 3600 rpm for 20 min and subsequent freeze drying. For freeze drying, 25 ml of solution were poured in a copper cylinder, having a diameter of 40 mm. The copper cylinder was then immersed in liquid nitrogen and the frozen sample was dried in a freeze dryer without heating and/or cooling.

3. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension

[0086] 0.96g of 3-aminoproplymethyldiethoxysilane were hydrolyzed in 7.5g of demineralized water for 2h under stirring. To 25 g of cellulose nanofibers having a dry mass content of 3.2% w/w in a beaker, the hydrolyzed silane-H2O mixture was added and completed with demineralized water to 40.8 g. The resulting mixture was homogenized for 5 min at 12000 rpm using an Ultra-Turrax blender device. The homogenized mixture was stirred for 2h. Thereafter the mixture was poured in a copper form that was immersed in liquid nitrogen. The frozen mixture was dried for 48 h in a freeze dryer. After freeze drying the sample was thermally treated at 120 C. in an argon atmosphere.

[0087] The porous structure thus produced had a CO.sub.2 capture capacity of 1.15 mmol CO.sub.2/g adsorbent and a CO.sub.2 uptake rate of around 10 mol CO.sub.2/ g adsorbent/min during the first 60 min of CO.sub.2 adsorption. The BET surface was 22.9 m.sup.2/g. The cyclic adsorption/desorption performance is given in FIGS. 1 and 2 for two different conditions, namely adsorption of dry air and a short desorption cycle in FIG. 1, and adsorption of humid air and a longer desorption cycle in FIG. 2.

4. Incorporation of a Reinforcing Structure

[0088] In a variant of the procedure described in Example 3, the solution was poured into a tray-like copper mold in which a reinforcing web of polyurethane fibers with a mesh size of 10 mm had been laid out. This was followed by freeze drying as in Section 2.

5. Production of a Porous Adsorbent Structure Starting from Dried Porous Cellulose Nanofibers

[0089] 1 g of a dry porous cellulose nanofiber web product as obtained according to Example 2 was immersed in a solution containing 4 g of 3-aminopropylmethyldiethoxysilane in 100 g ethanol and kept for 24 h. Subsequently, the solution was removed by filtering and the resulting residue was dried in air so as to obtain a silane coated cellulose nanofiber specimen. This specimen was cured at 120 C. for 2 h in an inert atmosphere, thereby yielding a porous adsorbent structure.

[0090] The CO.sub.2 uptake rate was 10 mol CO.sub.2/g adsorbent/min during the first 60 min of CO.sub.2 adsorption. The BET surface area was 8.8 m.sup.2/g. The cyclic adsorption/ desorption performance is given in FIG. 3.

6. Production of an Adsorbent Structure Starting from Cellulose Nanofiber Suspension Containing an Admixture of Large Cellulose Fibers (without Freeze Drying)

[0091] 3.09 g of N-(2-Aminoethyl)-3-aminopropyl-methyldimethoxysilane were hydrolyzed in 7.5 g of demineralized H.sub.2O for 2 h under stirring.

[0092] 6 g of refined fibrous beech wood pulp suspension as described in Example 1 (13.5% w/w) was solvent exchanged (3 times) with an EtOH/H.sub.2O mixture (95/5, w/w), with ultra turrax homogenization for 1 min before each exchange.

[0093] The solvent exchanged cellulose nanofibers, the silane-H.sub.2O mixture and 142.5 g of EtOH were transferred to a beaker and were completed to 162 g with an EtOH/H.sub.2O mixture (95/5, w/w).

[0094] The resulting mixture was blended with an ultra turrax for 1 min, thereafter stirred for 2 h and then poured completely on a Nutsche filter (=11 cm) and filtered by gravitation. The retentate was dried at room temperature for several days and subsequently cured at 60 C. for 3 h. The porous structure thus produced had a CO.sub.2 capture capacity of 1.1 mmol CO.sub.2/g adsorbent.

7. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension (Only Trialkoxy Silane)

[0095] For the present and the following examples, the experimental procedure is given in a short list form. [0096] Into a beaker 46.2 g of cellulose nanofiber suspension (@ 3.2 wt. %) were added and completed with demineralized H.sub.2O to 288 g [0097] Ultra turraxed for several minutes between 12 k and 17 k rpm [0098] Added 12 g of 3-aminopropyltriethoxysilane [0099] Stirred mixture for 24 h at 500 rpm [0100] Centrifuged for 20 min @ 3600 rpm [0101] Frozen in liquid N.sub.2 [0102] Evacuated frozen sample in freeze drier for 48 h [0103] Cured at 120 C. for 2 h in Argon

[0104] The CO.sub.2 capture capacity after 12 h of CO.sub.2 exposure was 0.32 mmol/g, and the BET surface area was 15.9 m.sup.2/g.

8. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension (Similar to 7 but Dialkoxy) [0105] Into a beaker were added 46.2 g of cellulose nanofiber suspension (@ 3.2 wt. %) and completed with demineralized H.sub.2O to 288 g [0106] Ultra turraxed for several minutes between 12 k and 17 k rpm [0107] Added 12 g of 3-aminopropylmethyldiethoxysilane [0108] Stirred mixture for 24 h at 500 rpm [0109] Centrifuged for 20 min @ 3600 rpm [0110] Frozen in liquid N.sub.2 [0111] Evacuated frozen sample in freeze drier for 48 h [0112] Cured at 60 C. for 180 minutes

[0113] The CO.sub.2 capture capacity after 12 h of CO.sub.2 exposure was 1.277 mmol/g and the BET surface area was 9.6 m.sup.2/g. The cyclic adsorption/ desorption performance is given in FIG. 4.

9. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension (Dialkoxy CO.sub.2 Acidification) [0114] Into a beaker were added 46.2 g of cellulose nanofiber suspension (@ 3.2 wt. %) and completed with demineralized H.sub.2O to 288 g [0115] Ultra turraxed for several minutes between 12 k and 17 k rpm [0116] Started bubbling 100% CO.sub.2 until the pH reached a value of roughly 3.8 [0117] Added 6 g of 3-aminopropylmethyldiethoxysilane step by step so that pH never exceeded 7 [0118] Stirred mixture for 24 h at 500 rpm under bubbling of CO.sub.2 [0119] Centrifuged for 20 min @ 3600 rpm [0120] Frozen in liquid N.sub.2 [0121] Evacuated frozen sample in freeze drier for 48 h [0122] Cured at 120 C. for 2 h in argon

[0123] The BET surface area of the adsorbent was 16.5 m.sup.2/g, and the cyclic adsorption/desorption performance is given in FIG. 5.

10. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension (Similar to 9 without CO.sub.2) [0124] Into a beaker were added 46.2 g of cellulose nanofiber suspension 3.2 wt. %) and completed with demineralized H.sub.2O to 294 g [0125] Ultra turraxed for several minutes between 12 k and 17 k rpm [0126] Added 6 g of 3-aminopropylmethyldiethoxysilane [0127] Stirred mixture for 24 h at 500 rpm [0128] Centrifuged for 20 min @ 3600 rpm [0129] Frozen in liquid N.sub.2 [0130] Evacuated frozen sample in freeze drier for 48 h [0131] Cured at 120 C. for 2 h in argon atmosphere
The BET surface area of the adsorbent was 29.8 m.sup.2/g, and the cyclic adsorption/desorption performance is given in FIG. 6.
11. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension Containing an Admixture of Large Cellulose Fibers (without Freeze Drying) [0132] Hydrolyzed 2.87 g of 3-aminopropylmethyldiethoxysilane in 7.5 g of demineralized H.sub.2O for 2 h under stirring [0133] Solvent exchanged 6 g of refined fibrous beech wood pulp (13.5% w/w) with EtOH/H.sub.2O mixture (95/5, w/w) 3 times (ultra turraxed 1 min before each exchange) [0134] Into a beaker were added 142.5 g of EtOH, the solvent exchanged cellulose nanofibers containing an admixture of large cellulose fibers, the silane-H.sub.2O mixture and completed with a EtOH/H.sub.2O mixture (95/5, w/w) to 162 g [0135] Ultra turraxed for 1 min [0136] Stirred mixture for 2 h [0137] Poured solution completely on Nutsche filter [0138] Filtered by gravitation and dried at room temperature for several days [0139] Cured at 60 C. for 3 h
The CO.sub.2 capture capacity was 0.8 mmol/g.
12. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension Containing an Admixture of Large Cellulose Fibers (Mixture Dialkoxy/Trialkoxy without Freeze Drying) [0140] Hydrolyzed 0.76 g of 3-aminopropyltrimethoxysilane and 2.15 g of 3aminopropylmethyldiethoxysilane in 7.5 g of demineralized H.sub.2O for 2 h under stirring [0141] Solvent exchanged 6 g of refined fibrous beech wood pulp (13.5% w/w) with EtOH/H.sub.2O mixture (95/5, w/w) 3 times (ultra turraxed 1 min before each exchange) [0142] Into a beaker were added 142.5 g of EtOH, the solvent exchanged cellulose nanofibers containing an admixture of large cellulose fibers, the silane-H.sub.2O mixture and completed with a EtOH/H.sub.2O mixture (95/5, w/w) to 162 g [0143] Ultra turraxed for 1 min [0144] Stirred mixture for 2 h [0145] Poured solution completely on Nutsche filter [0146] Filtered by gravitation and dried at room temperature for several days [0147] Cured at 60 C. for 3 h
The CO.sub.2 capture capacity was 0.87 mmol/g.
13. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension Containing an Admixture of Large Cellulose Fibers [0148] Added 2.87 g of 3-aminopropyldiethoxysilane to sealable glass bottle and completed with H.sub.2Oto 71.75 g and left closed for roughly 1 week [0149] Into a beaker were added 6 g of refined fibrous beech wood pulp (13.5% w/w) the hydrolyzed silane solution and completed with H.sub.2O to 162 g [0150] Ultra turraxed for 1 min [0151] Stirred mixture for 2 h [0152] Poured solution on Nutsche filter [0153] Filtered by gravitation and dried at room temperature for several days [0154] Cured at 60 C. for 3 h
The CO.sub.2 capture capacity was 0.34 mmol/g.
14. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension (Differing Pulp Feedstock) [0155] Into a beaker were added 120.84 g of cellulose nanofiber suspension (@ 1.2 wt. %) and completed with demineralized H.sub.2O to 288 g [0156] Ultra turrax for several minutes between 12 k and 17 k rpm [0157] Add 12 g of 3-aminopropylmethyldiethoxysilane [0158] Stir mixture for 24 h at 500 rpm [0159] Centrifuge for 20 min @ 3600 rpm [0160] Freeze in liquid N.sub.2 [0161] Evacuate freezed sample in freeze drier for 48 h [0162] Cure at 120 C. for 2 h in an inert atmosphere
The CO.sub.2 capture capacity after 12 h of CO.sub.2 exposure was 1.56 mmol/g, and the BET surface area was 6.5 m.sup.2/g. The CO.sub.2 uptake rate during the first 60 minutes of CO.sub.2 adsorption was 10 mol/g/min.
15. Production of a Porous Adsorbent Structure Starting from Cellulose Nanofiber Suspension Without an Admixture of Large Cellulose Fibers [0163] Into a beaker were added 120.84 g of cellulose nanofiber suspension (@ 1.2 wt. %) and completed with demineralized H.sub.2O to 288 g [0164] Ultra turrax for several minutes between 12 k and 17 k rpm [0165] Add 12 g of 3-aminopropylmethyldiethoxysilane [0166] Stir mixture for 24 h at 500 rpm [0167] Poured solution on Nutsche filter [0168] Filtered by gravitation and dried at room temperature for several days [0169] Cure at 120 C. for 2 h in an inert atmosphere
The CO.sub.2 capture capacity was 0.06 mmol/g.
16. Process for CO.sub.2 Capture from Air Using a Porous Adsorbent Structure Made from Cellulose Nanofibers

[0170] A mat-shaped adsorbent structure made from cellulose nanofibers is inserted into a flow-through container. During the first process step (adsorption) it is exposed to an air flow for 0.1 to 24 hours at 10-40 C. and atmospheric pressure (0.7 to 1.3 bar-.sub.abs). During this time, CO.sub.2 or CO.sub.2 and water vapor is adsorbed by the sorbent structure from the air stream. In the following, the second process step (desorption) is initiated and the container is evacuated to 1-250 mbar.sub.abs by a vacuum pump/vacuum line and the sorbent is heated to 50-110 C. during 5-240 minutes, The gas stream leaving the container is being sucked off by the vacuum pump/vacuum line (the desorption stream) and contains 0.5 to 100% carbon dioxide, the remainder being air and/or water vapor. The air content of the desorption stream is caused by air remainders in the system volume after evacuation and air penetrating the container through leaks and/or intended openings during desorption. After completion of the desorption step, the sorbent is cooled down to desorption temperature and the next adsorption cycle is initiated.