PROCESS FOR CONCENTRATING CO2 FROM AIR AND DILUTE CO2 STREAMS USING MOF BASED PHYSISORBENTS

Abstract

A method for capturing CO.sub.2 from a gas stream using a metal organic framework (MOF) based physisorbent CO.sub.2 concentrator is provided. In the method, MOF material is pretreated, a gas stream is then introduced into the CO.sub.2 concentrator which comprises the pretreated MOF material. CO.sub.2 from the gas stream is captured with the CO.sub.2 concentrator to generate a CO.sub.2-free stream, which is discharged the from the CO.sub.2 concentrator into the atmosphere. Introduction of the gas stream into the CO.sub.2 concentrator is stopped when the pretreated MOF material becomes saturated with CO.sub.2. The CO.sub.2 concentrator with the saturated MOF material is then regenerated by introducing hot air, hot nitrogen, vacuum, or a combination thereof into the CO.sub.2 concentrator thereby generating a CO.sub.2-rich stream. The CO.sub.2-rich stream is diverted for purification and the regenerated CO.sub.2 concentrator is recycled for future capture of CO.sub.2.

Claims

1. A method for capturing CO.sub.2 from a gas stream containing approximately 400 ppm to 6% of CO.sub.2 using a metal organic framework (MOF) based physisorbent CO.sub.2 concentrator, comprising: pretreating a MOF material under airflow or vacuum; introducing a gas stream into the CO.sub.2 concentrator which comprises the pretreated MOF material; capturing, with the CO.sub.2 concentrator, CO.sub.2 from the gas stream to generate a CO.sub.2-free stream in the CO.sub.2 concentrator; discharging the CO.sub.2-free stream from the CO.sub.2 concentrator into the atmosphere; stopping the introduction of the gas stream into the CO.sub.2 concentrator when the pretreated MOF material becomes saturated with CO.sub.2; regenerating the CO.sub.2 concentrator from the saturated MOF material by introducing hot air, hot nitrogen, vacuum, or a combination thereof, thereby generating a CO.sub.2-rich stream; and diverting the generated CO.sub.2-rich stream for direct purification or mixing with a stream of industrial exhaust with similar CO.sub.2 concentrations for subsequent purification; and utilizing the regenerated CO.sub.2 concentrator for future capture of CO.sub.2.

2. The method of claim 1, wherein the CO.sub.2 concentrator comprises the pretreated MOF with a binder in a closed module and one or more gas valves configured to manipulate the flow of the gas stream inside the CO.sub.2 concentrator.

3. The method of claim 1, wherein the binder is an organic polymer or an inorganic binder.

4. The method of claim 1, wherein the gas stream is gas from a natural gas combined cycle (NGCC) exhaust comprising 2-6% CO.sub.2, 10-13% O.sub.2 and 2-10% H.sub.2O vapor.

5. The method of claim 1, wherein the gas stream is air.

6. The method of claim 1, wherein the MOF material has a general formula of M.sub.aM.sub.bF.sub.6-n(O/H.sub.2O).sub.w(Ligand).sub.x(solvent).sub.y].sub.z, wherein M.sub.a is selected from periodic groups IB, IIA, IIB, IIIA, IV A, IVB, VIB, VIIB, and VIII, and Mb is selected from periodic groups IIIA, MB, IVB, VB, VIB, and VIII, and wherein the ligand comprises is an organic, poly-functional, or N-donor ligand.

7. The method of claim 6, wherein the solvent is one or more of H.sub.2O, DMF, and DEF.

8. The method of claim 1, wherein the MOF material is KAUST-7.

9. The method of claim 1, further comprising cooling the gas stream to approximately 20-25° C. before introduction into the CO.sub.2 concentrator.

10. The method of claim 1, wherein the MOF material is in the form of pellets, laminates, or other structured forms.

11. The method of claim 1, wherein the MOF material is pretreated at a temperature in the range of approximately 60-150° C. under dynamic vacuum or dry inert gas.

12. The method of claim 1, wherein the pretreatment of the MOF material removes previously adsorbed molecules.

13. The method of claim 1, wherein the generated CO.sub.2-rich stream has a CO.sub.2 concentration of approximately 1-50%.

14. The method of claim 1, wherein the CO.sub.2 concentrator is regenerated by introducing hot air or hot nitrogen, and wherein the hot air or hot nitrogen is introduced at a temperature of approximately 80-150° C.

15. The method of claim 1, wherein the CO.sub.2-rich stream is 1-10% CO.sub.2 and wherein purification of the CO.sub.2-rich stream comprises purifying the CO.sub.2-rich stream to pure CO.sub.2 or to a stream that comprises at least 90% CO.sub.2.

16. A method for continuous capturing of CO.sub.2 from a gas stream containing approximately 400 ppm to 6% of CO.sub.2 using multiple metal organic framework (MOF) based physisorbent CO.sub.2 concentrators, comprising: pretreating MOF material under airflow or vacuum; introducing a gas stream into a first CO.sub.2 concentrator which comprises the pretreated MOF material; capturing, with the first CO.sub.2 concentrator, CO.sub.2 from the gas stream to generate a CO.sub.2-free stream in the first CO.sub.2 concentrator; discharging the CO.sub.2-free stream from the first CO.sub.2 concentrator into the atmosphere; substituting a second CO.sub.2 concentrator comprising pretreated MOF material for the first CO.sub.2 concentrator when the pretreated MOF material of the first CO.sub.2 concentrator becomes saturated with CO.sub.2; regenerating the first CO.sub.2 concentrator from the saturated MOF material by introducing hot air, hot nitrogen, vacuum, or a combination thereof, thereby generating a CO.sub.2-rich stream; and diverting the generated CO.sub.2-rich stream for direct purification or mixing with a stream of industrial exhaust with similar CO.sub.2 concentrations for subsequent purification; and recycling the regenerated first CO.sub.2 concentrator for future capture of CO.sub.2.

17. The method of claim 16, wherein the gas stream is gas from a natural gas combined cycle (NGCC) exhaust comprising 2-6% CO.sub.2, 10-13% O.sub.2 and 2-10% H.sub.2O vapor.

18. The method of claim 16, wherein the MOF material has a general formula of M.sub.aM.sub.bF.sub.6-n(O/H.sub.2O).sub.w(Ligand).sub.x(solvent).sub.y].sub.z, wherein M.sub.a is selected from periodic groups IB, IIA, IIB, IIIA, IV A, IVB, VIB, VIIB, and VIII, and Mb is selected from periodic groups IIIA, MB, IVB, VB, VIB, and VIII, and wherein the ligand comprises is an organic, poly-functional, or N-donor ligand.

19. The method of claim 16, wherein the MOF material is KAUST-7.

20. The method of claim 16, wherein the MOF material is pretreated at a temperature in the range of approximately 60-150° C. under dynamic vacuum or dry inert gas, and further comprising the step of cooling the gas stream to approximately 20-25° C. before introduction into the first CO.sub.2 concentrator.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The process of the disclosure will be described in more detail below and with reference to the attached drawings in which the same number is used for the same or similar elements.

[0029] FIG. 1A. Schematic representation of MOF-based physisorbent CO.sub.2 concentrator system involving adsorption and desorption cycles.

[0030] FIG. 1B. A flow diagram showing steps of a method for capturing CO.sub.2 from a gas stream using an MOF-based physisorbent CO.sub.2 concentrator.

[0031] FIGS. 2A-2B. 2A) Variable temperature CO.sub.2 adsorption isotherms for KAUST-7 in logarithmic scale, demonstrating high CO.sub.2 uptake at low CO.sub.2 concentration. 2B) Breakthrough experiment for KAUST-7 with 400 ppm CO.sub.2 in N.sub.2, demonstrating CO.sub.2 capture performance under dynamic conditions.

[0032] FIGS. 3A-3B. 3A) Breakthrough experiment of KAUST-7 with 1% CO.sub.2 (balance N.sub.2) under dry conditions with a flow rate of 25 cc/min. 3B) Corresponding TPD after CO.sub.2 breakthrough experiment in dry conditions.

[0033] FIGS. 4A-4B. 4A) Breakthrough experiment with KAUST-7 with 1% CO.sub.2 (balance N.sub.2) in the presence of humidity (50% RH) with a flow rate of 25 cc/min. 4B) Corresponding TPD after water breakthrough.

[0034] FIG. 5. CO.sub.2 adsorption capacity of KAUST-7 remains the same after 10 cycles of oxygen exposure at high temperatures suggesting high oxygen stability of the material. Each cycle includes exposure of the sample to hot air at 110° C. for 60 min.

DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS OF THE DISCLOSURE

[0035] Disclosed herein are metal organic framework (MOF)-based systems and processes for adsorbing CO.sub.2 from gas streams (Air, NGCC exhaust, etc.), such as dilute CO.sub.2 gas streams, and generating a CO.sub.2-rich stream (e.g., CO.sub.2 concentration ranging from 1-50%). The generated CO.sub.2-rich stream can be then purified further by existing materials or technologies. The MOF-based systems and methods can include a MOF-based physisorbent CO.sub.2 concentrator (“CO.sub.2 concentrator”). The CO.sub.2-rich stream is generated by the CO.sub.2 concentrator and can be either purified directly or can be mixed with another stream of industrial exhaust with similar concentrations before purification. The CO.sub.2 concentrator can use hot air, hot nitrogen, vacuum, or other suitable methods, or a combination thereof to recover adsorbed CO.sub.2 to produce the CO.sub.2-rich gas stream.

[0036] Direct air capture and CO.sub.2 capture from NGCC exhaust are considered very difficult compared to CO.sub.2 capture from flue gas streams (10-15% CO.sub.2). The CO.sub.2 concentrator of the present systems and methods can bridge differences in maturity between the technologies for CO.sub.2 capture from dilute (400 ppm to 5%) and concentrated streams (10-30%). The present CO.sub.2 concentrator-based technology can also expand the envelope of CO.sub.2 capture technologies to a wide concentration range and accelerate the efforts to mitigate increasing CO.sub.2 concentration in the atmosphere and accompanying global warming.

[0037] These and other aspects of the present systems and methods are described in further detail below. Further, as used in the present application, the term “approximately” when used in conjunction with a number refers to any number within about 5, 3 or 1% of the referenced number, including the referenced number.

[0038] As mentioned briefly above, in one or more embodiments, the present system includes a metal organic framework (MOF)-based physisorbent CO.sub.2 concentrator. An exemplary schematic diagram showing an exemplary MOF-based physisorbent CO.sub.2 concentrator 10 and demonstrating a method using the present MOF-based physisorbent CO.sub.2 concentrator is provided in FIG. 1A.

[0039] An MOF can include a metal-based node and an organic ligand which form a coordination network having advantageous crystalline and porous characteristics that affect structural integrity and interaction with foreign species, such as gases. The particular combination of nodes and ligands within a MOF impacts the topology and functionality of the MOF. As such, ligand modification or functionalization can be used to adjust the environment in the internal pores of the MOF to suit specific applications.

[0040] In one or more embodiments, the MOF material used in the CO.sub.2 concentrator 10 of the present application can be any existing or new MOF material with suitable CO.sub.2 capture properties. In one or more embodiments, the MOF material has a general formula of M.sub.aM.sub.bF.sub.6-n(O/H.sub.2O).sub.w(Ligand).sub.x(solvent).sub.y].sub.z. In one or more embodiments, M.sub.a comprises elements selected from periodic groups IB, IIA, IIB, IIIA, IV A, IVB, VIB, VIIB, and VIII. In one or more embodiments, M.sub.b comprises elements selected from periodic groups IIIA, MB, IVB, VB, VIB, and VIII. In one or more embodiments, M.sub.a can comprise one of the following cations: Cu.sup.2+, Zn.sup.2+, Co.sup.2+, Ni.sup.2+, Mn.sup.2+, Zr.sup.2+, Fe.sup.2+, Ca.sup.2+, Ba.sup.2+, Pb.sup.2+, Pt.sup.2+, Pd.sup.2+, Ru.sup.2+, Rh.sup.2+, Cd.sup.2+, Mg.sup.+2, Al.sup.+3, Fe.sup.+2, Fe.sup.+3, Cr.sup.2+, Cr.sup.3+, Ru.sup.2+, Ru.sup.3+ and Co.sup.3+. In some embodiments, M.sub.b can be one of the following Al.sup.+3, Fe.sup.+2, Fe.sup.+3, Cr.sup.2+, Cr.sup.3+, Ti.sup.3+, V.sup.3+, V.sup.5+, Sc.sup.3+, In.sup.3+, Nb.sup.5+, Y.sup.3+. In one or more embodiments, the ligand comprises an organic, poly-functional, or N-donor ligand. A non-limiting list of solvents can include one or more of H.sub.2O, DMF, and DEF. In one or more embodiments, the solvent can include a chemical species present after fabrication of the MOF. In at least one embodiment, the MOF material is KAUST-7 (CAS: 1973399-07-3).

[0041] In one or more embodiments, the MOF material is in the form of pellets, laminates, or other structured forms of the MOF such as a monolith or any other structured form to hold MOF particles in a particular shape. The MOF material can also comprise one or more appropriate binders. In at least embodiment, the one or more binders can include but are not limited to one or more of the following: organic polymers (e.g., polyethylene, polystyrene, polyethylene glycol, polyvinyl alcohol, polysulfone, polymethylmethacrylate) and inorganic binders (e.g., kaolinite, gypsum).

[0042] In one or more embodiments the CO.sub.2 concentrator 10 is a closed module that includes the MOF material and the binder in the closed module. In one or more embodiments, the CO.sub.2 concentrator 10 further includes one or more gas valves configured to manipulate the flow of the gas stream inside the module.

[0043] In one or more embodiments, a method for capturing (e.g., adsorbing) CO.sub.2 from a gas stream using a metal organic framework (MOF)-based physisorbent CO.sub.2 concentrator 10 of the present application is provided. A flow diagram showing steps of the method for capturing CO.sub.2 from a gas stream using the present MOF-based physisorbent CO.sub.2 concentrator 10 is provided in FIG. 1B.

[0044] With reference now to FIG. 1A and the flow diagram of FIG. 1B, the method 100 begin at a step S105 where the MOF material of the CO.sub.2 concentrator is pretreated at a suitable temperature under airflow, vacuum, or other methods. In one or more embodiments, pretreatment of the MOF material removes any previously adsorbed molecules such as H.sub.2O and other guest molecules before the gas stream is introduced into the CO.sub.2 concentrator. Pretreatment of the MOF material improves the MOF material's ability to adsorb target molecules (e.g. CO.sub.2) in the pores. In one or more embodiments, during pretreatment, the MOF is subjected to a temperature in the range of approximately 60-150° C. under dynamic vacuum or dry inert gas (e.g., N.sub.2, O.sub.2, Ar, He or air) flow. The pretreated MOF is incorporated into the CO.sub.2 concentrator. In one or more embodiments, pretreatment of the MOF material is performed after the MOF material has been incorporated in the CO.sub.2 concentrator.

[0045] At step S110, a gas stream is introduced into the CO.sub.2 concentrator which comprises the pretreated MOF material. In one or more embodiments, the gas stream is air or exhaust gas from a natural gas combined cycle (NGCC). In embodiments in which the gas stream is air, the air can be breathable air (e.g., atmospheric air), which can include one or more of nitrogen (N.sub.2), oxygen (O.sub.2), nitrogen (N.sub.2), and argon (Ar) in addition to CO.sub.2. In one or more embodiments, the NGCC exhaust gas is comprised of approximately 2-6% CO.sub.2 or approximately 3-5% CO.sub.2 or approximately 4% CO.sub.2. In one or more embodiments, the NGCC exhaust gas also comprises approximately 10-13% O.sub.2. In one or more embodiments, the NGCC exhaust gas further comprises 2-10% H.sub.2O vapor. In one or more embodiments, the NGCC exhaust gas can include other components such as small proportions of SO.sub.2 and NO.sub.x. In one or more embodiments, the gas stream is first cooled to a suitable temperature (e.g., approximately room temperature [20-25° C.]) before being introduced into the CO.sub.2 concentrator. In one or more embodiments, the CO.sub.2 concentrator temperature during adsorption (capture) is also recommended in the same temperature range (approximately 20-25° C.) and the temperature of the incoming gas stream helps it to maintain the similar temperature.

[0046] In at least one embodiment, the gas stream is a diluted gas stream. For example, the diluted gas stream can comprise approximately 400 ppm to 5% or 400 ppm to 6% of CO.sub.2. In one or more embodiments, the flow rate of the NGCC gas stream depends on the capacity of NGCC plant. In one or more embodiments, the present system, including the CO.sub.2 concentrator, can handle at least 80-90% of total NGCC exhaust produced by a NGCC plant.

[0047] Once the gas stream is introduced into the CO.sub.2 concentrator, at step S115 the CO.sub.2 in the gas stream is captured with the CO.sub.2 concentrator that comprises the pretreated MOF material. In one or more embodiments, the capturing of the CO.sub.2 comprises physical adsorption of the CO.sub.2 by the MOF material of the CO.sub.2 concentrator. In at least one embodiment, capturing the CO.sub.2 comprises chemisorption of the CO.sub.2 by the MOF material of the CO.sub.2 concentrator, which can occur by the CO.sub.2 chemically interacting with one or more open metal sites of the MOF material. In at least one embodiment, capturing the CO.sub.2 comprises both physical adsorption and chemisorption of the CO.sub.2 by the MOF material of the CO.sub.2 concentrator. In one or more embodiments, the MOF material has a CO.sub.2 adsorption capacity in the range of approximately 0.5 wt %-10 wt %.

[0048] Additionally, in one or more embodiments, capturing the CO.sub.2 can comprise wholly or partially containing the CO.sub.2 within pores of the MOF material. The capturing of the CO.sub.2 results in the generation of a CO.sub.2-free (or substantially CO.sub.2-free) stream (i.e., the remainder of the gas stream from which the CO.sub.2 was captured) in the CO.sub.2 concentrator. Once the MOF material is saturated with CO.sub.2, at step S120, the CO.sub.2-free gas stream is discharged from the CO.sub.2 concentrator into the atmosphere (see FIG. 1A), or optionally subjected to additional treatment, for example, to remove other components such as SO.sub.2 and NO.sub.x.

[0049] By the capturing the CO.sub.2 via adsorption, the MOF material of the CO.sub.2 concentrator becomes saturated. Once the MOF material is saturated with CO.sub.2, at step S125 the gas stream (e.g., Air, NGCC exhaust, etc.) is stopped from entering the CO.sub.2 concentrator. In one or more embodiments, the CO.sub.2 concentrator is a closed module with one or more gas valves for receiving and dispersing of gas streams. The gas valves are configured to manipulate the flow of the gas stream inside the CO.sub.2 concentrator. Thus, in one or more embodiments, the gas stream is stopped from entering the CO.sub.2 concentrator upon saturation of the MOF material by closing one or more valves of the CO.sub.2 concentrator. In at least one embodiment, the gas stream is stopped from entire the CO.sub.2 concentrator by closing one or more valves of the NGCC exhaust unit.

[0050] At step S130, the CO.sub.2 concentrator is regenerated. More specifically, the CO.sub.2 saturated MOF material of the CO.sub.2 concentrator is regenerated by introducing a stream of hot air, hot nitrogen, vacuum or a combination of thereof into the CO.sub.2 concentrator. In one or more embodiments, the stream of hot air or hot nitrogen is introduced to the CO.sub.2 concentrator at a temperature of approximately 80-150° C. As shown in FIG. 1A, as the CO.sub.2 concentrator is regenerated via the introduction of a stream of hot air or hot nitrogen, said stream or hot air or hot nitrogen or vacuum removes the CO.sub.2 from the MOF material of the CO.sub.2 concentrator (e.g., the CO.sub.2 is desorbed from the MOF material), and exits the CO.sub.2 concentrator as a part of a CO.sub.2-rich gas stream.

[0051] In one or more embodiments, the desorption of CO.sub.2 from the MOF material is a thermal desorption, a chemical desorption (result of a chemical reaction), or a combination of both. The flow rate of the stream of hot air or hot nitrogen depends upon the amount of MOF material used and the overall process parameters. In one or more embodiments, the flow rate of the stream of hot air or hot nitrogen can be optimized to provide as high as possible a CO.sub.2 concentration in the desorbed stream (i.e., CO.sub.2-rich gas stream) while keeping the regeneration/desorption step as fast as possible.

[0052] At step S135, the generated CO.sub.2-rich stream exits the CO.sub.2 concentrator and is diverted for further processing, such as a purification step. More specifically, in one or more embodiments, the generated CO.sub.2-rich stream can be diverted for direct purification or can be mixed with another stream of industrial exhaust with similar concentrations before purification. For example, in one or more embodiments the generated CO.sub.2-rich stream (e.g., 1-10% CO.sub.2 stream) is subsequently purified to result in a pure or substantial pure (at least 90%) CO.sub.2 stream. Purification of the CO.sub.2-rich stream can be done via a CO.sub.2 purification unit or via other technologies as known in the art.

[0053] At step S140, the regenerated CO.sub.2 concentrator is utilized in a future CO.sub.2 capture process. For example, in one or more embodiments, the CO.sub.2 capture process is not continuous, and thus the regenerated CO.sub.2 concentrator can be used for the next CO.sub.2 capture cycle. In the case of a continuous CO.sub.2 capturing process, two or more CO.sub.2 concentrator units can be used alternatively, such that once a first CO.sub.2 concentrator becomes saturated with CO.sub.2, the first CO.sub.2 concentrator is swapped out for a second, unsaturated CO.sub.2 concentrator for further CO.sub.2 capture, in a swing mode of operation. In this embodiment, after saturation of the first CO.sub.2 concentrator, the first CO.sub.2 concentrator is regenerated as described above, and once the second CO.sub.2 concentrator become saturated with CO.sub.2, the second CO.sub.2 concentrator is swapped out for the regenerated CO.sub.2 concentrator to allow the CO.sub.2 capture process to continue. In a continuous CO.sub.2 capturing process, this swapping and recycling process for the two or more CO.sub.2 concentrators can continue indefinitely. Additionally, in a continuous CO.sub.2 capturing process, multiple CO.sub.2 concentrators comprising the MOFs can be pretreated prior to the beginning of the process such that a pretreated, unsaturated MOF-based CO.sub.2 concentrator can be quickly substituted for a saturated MOF-based CO.sub.2 concentrator.

[0054] Finally, at step S145, the method ends.

[0055] The aforementioned features and aspects of the present system and methods are further described in the following examples with reference to FIGS. 2-5. These examples utilize an exemplary MOF material of the present system and method, KAUST-7. As exemplified in FIGS. 2-5, KAUST-7 provides excellent CO.sub.2 capture properties from dilute streams and excellent oxygen stability.

[0056] FIG. 2A display variable temperature CO.sub.2 adsorption isotherms for KAUST-7 (FIG. 2A) in logarithmic scale. The graph of FIG. 2A demonstrates that KAUST-7 displays high CO.sub.2 uptake at low CO.sub.2 concentration. FIG. 2B displays results of a breakthrough experiment for KAUST-7 with as gas stream of 400 ppm CO.sub.2 in N.sub.2. The graph of FIG. 2B demonstrates excellent CO.sub.2 capture performance for KAUST-7 under dynamic conditions.

[0057] FIG. 3A displays the results of a breakthrough experiment of KAUST-7 with a gas stream comprising 1% CO.sub.2 (balance N.sub.2) under dry conditions with a flow rate of 25 cc/min. FIG. 3B displays the corresponding temperature programmed desorption (TPD) after the CO.sub.2 breakthrough experiment in dry conditions.

[0058] Similarly, FIG. 4A displays the result of a breakthrough experiment of KAUST-7 with a gas stream comprising 1% CO.sub.2 (balance N.sub.2) in the presence of humidity (50% relative humidity [RH]) with a flow rate of 25 cc/min. FIG. 4B displays the corresponding TPD after water breakthrough.

[0059] FIG. 5 displays the CO.sub.2 adsorption capacity of KAUST-7 over 10 cycles of oxygen exposure at high temperatures. Each cycle includes exposure of the sample to hot air at 110° C. for 60 min. As shown in the bar graph of FIG. 5, the CO.sub.2 adsorption capacity of KAUST-7 remains the same after 10 cycles of oxygen exposure at high temperatures suggesting high oxygen stability of the KAUST-7 material.

[0060] In accordance with one or more embodiments, exemplary methods are set out in the following items:

[0061] Item 1. A method for capturing CO.sub.2 from a gas stream containing approximately 400 ppm to 6% of CO.sub.2 using a metal organic framework (MOF) based physisorbent CO.sub.2 concentrator, comprising: [0062] pretreating a MOF material under airflow or vacuum; [0063] introducing a gas stream into the CO.sub.2 concentrator which comprises the pretreated MOF material; [0064] capturing, with the CO.sub.2 concentrator, CO.sub.2 from the gas stream to generate a CO.sub.2-free stream in the CO.sub.2 concentrator; [0065] discharging the CO.sub.2-free stream from the CO.sub.2 concentrator into the atmosphere; [0066] stopping the introduction of the gas stream into the CO.sub.2 concentrator when the pretreated MOF material becomes saturated with CO.sub.2; [0067] regenerating the CO.sub.2 concentrator from the saturated MOF material by introducing hot air, hot nitrogen, vacuum, or a combination thereof, thereby generating a CO.sub.2-rich stream; and [0068] diverting the generated CO.sub.2-rich stream for direct purification or mixing with a stream of industrial exhaust with similar CO.sub.2 concentrations for subsequent purification; and [0069] utilizing the regenerated CO.sub.2 concentrator for future capture of CO.sub.2.

[0070] Item 2. The method of item 1, wherein the CO.sub.2 concentrator comprises the pretreated MOF with a binder in a closed module and one or more gas valves configured to manipulate the flow of the gas stream inside the CO.sub.2 concentrator.

[0071] Item 3. The method of item 2, wherein the binder is an organic polymer or an inorganic binder.

[0072] Item 4. The method of any one of items 1-3, wherein the gas stream is gas from a natural gas combined cycle (NGCC) exhaust comprising 2-6% CO.sub.2, 10-13% O.sub.2 and 2-10% H.sub.2O vapor.

[0073] Item 5. The method of any one of items 1-3, wherein the gas stream is air.

[0074] Item 6. The method of any one of items 1-5, wherein the MOF material has a general formula of M.sub.aM.sub.bF.sub.6-n(O/H.sub.2O).sub.w(Ligand).sub.x(solvent).sub.y].sub.z, wherein M.sub.a is selected from periodic groups IB, IIA, IIB, IIIA, IV A, IVB, VIB, VIIB, and VIII, and Mb is selected from periodic groups IIIA, MB, IVB, VB, VIB, and VIII, and wherein the ligand comprises is an organic, poly-functional, or N-donor ligand.

[0075] Item 7. The method of item 6, wherein the solvent is one or more of H.sub.2O, DMF, and DEF.

[0076] Item 8. The method of any one of items 1-7, wherein the MOF material is KAUST-7.

[0077] Item 9. The method of any one of items 1-8, further comprising cooling the gas stream to approximately 20-25° C. before introduction into the CO.sub.2 concentrator.

[0078] Item 10. The method of any one of items 1-9, wherein the MOF material is in the form of pellets, laminates, or other structured forms.

[0079] Item 11. The method of any one of items 1-10, wherein the MOF material is pretreated at a temperature in the range of approximately 60-150° C. under dynamic vacuum or dry inert gas.

[0080] Item 12. The method of any one of items 1-11, wherein the pretreatment of the MOF material removes previously adsorbed molecules.

[0081] Item 13. The method of any one of items 1-12, wherein the generated CO.sub.2-rich stream has a CO.sub.2 concentration of approximately 1-50%.

[0082] Item 14. The method any one of items 1-13, wherein the CO.sub.2 concentrator is regenerated by introducing hot air or hot nitrogen, and wherein the hot air or hot nitrogen is introduced at a temperature of approximately 80-150° C.

[0083] Item 15. The method any one of items 1-14, wherein the CO.sub.2-rich stream is 1-10% CO.sub.2 and wherein purification of the CO.sub.2-rich stream comprises purifying the CO.sub.2-rich stream to pure CO.sub.2 or to a stream that comprises at least 90% CO.sub.2.

[0084] Item 16. A method for continuous capturing of CO.sub.2 from a gas stream containing approximately 400 ppm to 6% of CO.sub.2 using multiple metal organic framework (MOF) based physisorbent CO.sub.2 concentrators, comprising: [0085] pretreating MOF material under airflow or vacuum; [0086] introducing a gas stream into a first CO.sub.2 concentrator which comprises the pretreated MOF material; [0087] capturing, with the first CO.sub.2 concentrator, CO.sub.2 from the gas stream to generate a CO.sub.2-free stream in the first CO.sub.2 concentrator; [0088] discharging the CO.sub.2-free stream from the first CO.sub.2 concentrator into the atmosphere; [0089] substituting a second CO.sub.2 concentrator comprising pretreated MOF material for the first CO.sub.2 concentrator when the pretreated MOF material of the first CO.sub.2 concentrator becomes saturated with CO.sub.2; [0090] regenerating the first CO.sub.2 concentrator from the saturated MOF material by introducing hot air, hot nitrogen, vacuum, or a combination thereof, thereby generating a CO.sub.2-rich stream; and [0091] diverting the generated CO.sub.2-rich stream for direct purification or mixing with a stream of industrial exhaust with similar CO.sub.2 concentrations for subsequent purification; and [0092] recycling the regenerated first CO.sub.2 concentrator for future capture of CO.sub.2.

[0093] Item 17. The method of item 16, wherein the first and second CO.sub.2 concentrators each comprise the pretreated MOF with a binder in a closed module and one or more gas valves configured to manipulate the flow of the gas stream inside the first and second CO.sub.2 concentrators.

[0094] Item 18. The method of item 17, wherein the binder is an organic polymer or an inorganic binder.

[0095] Item 19. The method of any one of items 16-18, wherein the gas stream is gas from a natural gas combined cycle (NGCC) exhaust comprising 2-6% CO.sub.2, 10-13% O.sub.2 and 2-10% H.sub.2O vapor.

[0096] Item 20. The method of any one of items 16-18, wherein the gas stream is air.

[0097] Item 21. The method of any one of items 16-20, wherein the MOF material has a general formula of M.sub.aM.sub.bF.sub.6-n(O/H.sub.2O).sub.w(Ligand).sub.x(solvent).sub.y].sub.z, wherein M.sub.a is selected from periodic groups IB, IIA, IIB, IIIA, IV A, IVB, VIB, VIIB, and VIII, and Mb is selected from periodic groups IIIA, MB, IVB, VB, VIB, and VIII, and wherein the ligand comprises is an organic, poly-functional, or N-donor ligand.

[0098] Item 22. The method of item 21, wherein the solvent is one or more of H.sub.2O, DMF, and DEF.

[0099] Item 23. The method of any one of items 16-22, wherein the MOF material is KAUST-7.

[0100] Item 24. The method of any one of items 16-23, further comprising cooling the gas stream to approximately 20-25° C. before introduction into the first CO.sub.2 concentrator.

[0101] Item 25. The method of any one of items 16-24, wherein the MOF material is in the form of pellets, laminates, or other structured forms.

[0102] Item 26. The method of any one of items 16-25, wherein the MOF material is pretreated at a temperature in the range of approximately 60-150° C. under dynamic vacuum or dry inert gas.

[0103] Item 27. The method of any one of items 16-26, wherein the pretreatment of the MOF material removes previously adsorbed molecules.

[0104] Item 28. The method of any one of items 16-27, wherein the generated CO.sub.2-rich stream has a CO.sub.2 concentration of approximately 1-50%.

[0105] Item 29. The method any one of items 16-28, wherein the first CO.sub.2 concentrator is regenerated by introducing hot air or hot nitrogen, and wherein the hot air or hot nitrogen is introduced at a temperature of approximately 80-150° C.

[0106] Item 30. The method any one of items 16-29, wherein the CO.sub.2-rich stream is 1-10% CO.sub.2 and wherein purification of the CO.sub.2-rich stream comprises purifying the CO.sub.2-rich stream to pure CO.sub.2 or to a stream that comprises at least 90% CO.sub.2.

[0107] It is to be understood that like numerals in the drawings represent like elements through the several figures, and that not all components and/or steps described and illustrated with reference to the figures are required for all embodiments or arrangements. Further, the terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “including,” “comprising,” or “having,” “containing,” “involving,” and variations thereof herein, when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

[0108] It should be noted that use of ordinal terms such as “first,” “second,” “third,” etc., in the claims to modify a claim element does not by itself connote any priority, precedence, or order of one claim element over another or the temporal order in which acts of a method are performed, but are used merely as labels to distinguish one claim element having a certain name from another element having a same name (but for use of the ordinal term) to distinguish the claim elements.

[0109] Notably, the figures and examples above are not meant to limit the scope of the present disclosure to a single implementation, as other implementations are possible by way of interchange of some or all the described or illustrated elements. Moreover, where certain elements of the present disclosure can be partially or fully implemented using known components, only those portions of such known components that are necessary for an understanding of the present disclosure are described, and detailed descriptions of other portions of such known components are omitted so as not to obscure the disclosure. In the present specification, an implementation showing a singular component should not necessarily be limited to other implementations including a plurality of the same component, and vice-versa, unless explicitly stated otherwise herein. Moreover, applicants do not intend for any term in the specification or claims to be ascribed an uncommon or special meaning unless explicitly set forth as such. Further, the present disclosure encompasses present and future known equivalents to the known components referred to herein by way of illustration.

[0110] The foregoing description of the specific implementations will so fully reveal the general nature of the disclosure that others can, by applying knowledge within the skill of the relevant art(s), readily modify and/or adapt for various applications such specific implementations, without undue experimentation, without departing from the general concept of the present disclosure. Such adaptations and modifications are therefore intended to be within the meaning and range of equivalents of the disclosed implementations, based on the teaching and guidance presented herein. It is to be understood that the phraseology or terminology herein is for the purpose of description and not of limitation, such that the terminology or phraseology of the present specification is to be interpreted by the skilled artisan in light of the teachings and guidance presented herein, in combination with the knowledge of one skilled in the relevant art(s). It is to be understood that dimensions discussed or shown are drawings accordingly to one example and other dimensions can be used without departing from the disclosure.

[0111] The subject matter described above is provided by way of illustration only and should not be construed as limiting. Various modifications and changes can be made to the subject matter described herein without following the example embodiments and applications illustrated and described, and without departing from the true spirit and scope of the invention encompassed by the present disclosure, which is defined by the set of recitations in the following claims and by structures and functions or steps which are equivalent to these recitations.