Device and process for the direct carbon dioxide capture from air

Abstract

The present invention is based on the use of surface adsorption to capture CO.sub.2 molecules from air, without requiring the need for bulk absorption within the bulk of the sorbent. Since surface adsorption is a much faster process than bulk absorption, the present invention offers a greatly increased CO.sub.2 capture rate, as well as a greatly improved energy efficiency, over conventional systems. The invention involves the use of a molecular monolayer of CO.sub.2 sorbent, a process and a system for capturing CO.sub.2 from air employing such a molecular monolayer of CO.sub.2 sorbent.

Claims

1. Use of a molecular monolayer of CO.sub.2 sorbent for capturing CO.sub.2 from air, wherein the sorbent is coated onto the pore walls of a porous support.

2. Use according to claim 1, wherein CO.sub.2 sorption occurs via surface adsorption and not via bulk absorption.

3. The use according to claim 1 or 2, wherein the sorbent is coated on a microporous support.

4. The use according to any one of the preceding claims, wherein the support contains needle-shaped pores with a diameter in the range of 1-10 nm and a length in the range of 1-10 μm, wherein the surface of the pores is coated with the sorbent while the central part is free of sorbent and open to receive gaseous molecules.

5. The use according to any one of the preceding claims, wherein the porous support comprises a macroporous structure layered on top of a microporous structure, preferably wherein the macroporous structure is a sandwich of foils or a honeycomb structure.

6. The use according to claim 5, wherein air is led through the macroporous structure to enable a flow of air perpendicular to the micropores of the microporous structure and CO.sub.2 molecules diffuse into the interior of the pores where they are adsorbed onto the sorbent.

7. A process for capturing CO.sub.2 from air, comprising: (i) providing a flow of air through the sorption chamber over the surface of a microporous structure, containing a molecular monolayer of CO.sub.2 sorbent coated on the interior surface of the pores, to obtain air depleted in CO.sub.2 and a loaded CO.sub.2 sorbent; (ii) moving the microporous structure containing the loaded CO.sub.2 sorbent from the sorption chamber to a regeneration chamber; (iii) regenerating the CO.sub.2 sorbent at the regeneration chamber to obtain a product flow comprising CO.sub.2 and regenerated CO.sub.2 sorbent.

8. The process according to claim 7, wherein the process further comprises: (iv) moving the microporous structure containing the regenerated CO.sub.2 sorbent from the regeneration chamber to the sorption chamber; and wherein steps (i)-(iv) are repeated.

9. The process according to claim 7 or 8, wherein the cycle time is in the range of 0.1-60 seconds for step (i) and in the range of 0.1-60 seconds for step (iii).

10. A device for capturing CO.sub.2 from air, comprising: (a) a molecular monolayer of solid state CO.sub.2 sorbent coated on the interior surface of the pores of a microporous structure for capturing CO.sub.2 from air; (b) at least one sorption chamber; (c) at least one regeneration chamber; (d) means for transporting the microporous support structure from the sorption chamber to the regeneration chamber and back; (e) means for effecting a flow of air over the sorbent support structure through the sorption chamber; (f) at least one outlet for discharging CO.sub.2, located in the regeneration chamber; and (g) means for regenerating the sorbent in the regeneration chamber.

11. The device according to claim 10, wherein the pores have a diameter in the range of 1-10 nm and a length in the range of 1-10 μm.

12. The device according to claim 10 or 11, further comprising means for enabling close contact of the flow of air with the sorbent and/or the pores, wherein the means are selected from a sandwich of foils or a honeycomb structure.

13. The device according to any one of claims 10-12, further including transporting means to shift the sorbent from absorption to regeneration phase.

14. The device according to any one of claims 10-13, wherein means (g) are capable of heating the CO.sub.2 sorbent when positioned within the regeneration chamber to a temperature in the range of 50-180° C., preferably 60-150° C., most preferably 65-100° C.

15. The use according to any one of claims 1-6, the process according to any one of claims 7-9, or the device according to any one of claims 10-14, wherein the CO.sub.2 sorbent is selected from the group consisting of bicarbonate-based sorbents, amine-based sorbents, zeolites and metal-organic frameworks.

Description

FIGURES

[0080] FIGS. 1-2 depict preferred embodiments of the device and process according to the invention, wherein the macroporous structure is combined with the needle-shaped micropores. In FIG. 1, the “sandwich of foils” structure is depicted, and in FIG. 2 the honeycomb structure.

[0081] FIG. 3 depicts the working of the present invention with respect to the conventional CO.sub.2 capturing system. FIG. 3A shows a porous structure, wherein the pores are filled with CO.sub.2 sorbent. CO.sub.2 molecules that pass over the pores in the flow of air are adsorbed by the sorbent and diffuse into the interior of the sorbent bulk. Due to the large bulk, the sorbent has a big capacity for CO.sub.2, but the kinetics of sorption are slow. FIG. 3A shows a porous structure, wherein the interior walls of the pores are coated with a thin layer of CO.sub.2 sorbent (indicated with the arrow). CO.sub.2 molecules that pass over the pores in the flow of air diffuse into the interior of the pores, in view of the reduced partial CO.sub.2 pressure, and are then adsorbed on the surface of the sorbent. Due to the thin layer, the sorbent has a small capacity for CO.sub.2, but the kinetics of sorption are much faster, since CO.sub.2 molecules are sucked into the pores.

[0082] FIG. 4 shows the results of the CO.sub.2 capacity experiment (in g/m.sup.3), as determined using a dedicated reactor containing a mass spectrometer for online CO.sub.2 detection. The results of the conventional sorbent system (filled pores) and the sorbent system according to the invention (closed pores) are depicted.

EXAMPLE

[0083] The following example illustrates the invention.

[0084] A conventional sorbent system was prepared by depositing sorbent molecule on a porous support with a density of 250 g per m.sup.2 of material, using wet-chemical method, such as disclosed in Zeng et al, J. Phys. Chem. 2011, 115, 450-454. Success of the deposition process was measured by monitoring the weight increase of the support structure (including any deposited sorbet) in situ. The saturation of the sorbent (bulk vs. monolayer) was controlled by choosing the saturation levels of the sorbent amino-organo-silane precursor, which was applied as a toluene solution. For example, by controlling the exposure to different precursor concentrations, the inventors produced two samples, one microporous support structure largely filled with sorbent molecules and the other having a monolayer of sorbent across the available surface area. The monolayer-coated support was prepared using 0.001-0.005 mol/L amine precursor, while the comparative sorbent-filled support was prepared using a concentration of 0.01-0.05 mol/L amine precursor. The specific sample filled with sorbent exhibited a 35% weight gain, while the sorbent system according to the present invention exhibited a 5% weight gain. In other words, the convention sorbent systems contained 7 times more sorbent than the sorbent system according to the invention.

[0085] The sorbent system according to the invention contained seven times less sorbent compared to the conventional sorbent system (pores filled with sorbent), as illustrated by the weight gain of the porous support during the preparation. The samples were subjected to BET surface area measurements to show that the pores of the conventional sorbent system were indeed largely filled, while the pores of the sorbent system according to the present invention where open.

[0086] Both sorbent systems where contacted with ambient air for 24 h at ambient temperature, pressure and fixed relative humidity (60%) to test the initial capacity by initial degassing of the sorbent for CO.sub.2. The CO.sub.2 capacity of the sorbent was measured using a dedicated reactor containing a mass spectrometer for online CO.sub.2 detection. The results are depicted in FIG. 4 (CO.sub.2 sorption capacity in g/m.sup.3).