Energy-efficient structured system for co 2 separation with high productivity for direct air capture

Abstract

A method of removing carbon dioxide from carbon dioxide-laden ambient air is provided. The method involves a) directing a flow of the carbon dioxide-laden ambient air through a carbon dioxide capture structure comprising one or more sorbent-coated substrates, wherein the sorbent is capable of binding carbon dioxide to the sorbent, so as to remove carbon dioxide from the ambient air; b) regenerating the sorbent by exposing the sorbent-coated substrates to a liquid heating medium having a temperature above at least 40 °C; c) exposing the sorbent-coated substrates to a cooling medium at a reduced temperature below about 50 °C, resulting in regenerated sorbent-coated substrates, and d) cyclically repeating exposure of the regenerated sorbent-coated substrates to carbon dioxide-laden ambient air, followed by regenerating the sorbent by repeating the process described above.

Description

ENERGY-EFFICIENT STRUCTURED SYSTEM FOR CO2SEPARATION WITH HIGH PRODUCTIVITY FOR DIRECT AIR CAPTURECROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to, and the benefit of the filing date of, United States Provisional Application No. 63 / 751,053 filed January 29, 2025, the disclosure of which is incorporated by reference herein in its entirety.FIELD OF THE INVENTION

[0002] This invention relates generally to a process for CO2 separation.BACKGROUND OF THE INVENTION

[0003] This section is intended to introduce the reader to various aspects of art that may be related to various aspects of the present invention, which are described and / or claimed below. This discussion is believed to be helpful in providing the reader with background information to facilitate a better understanding of various aspects of the present invention. Accordingly, it should be understood that these statements are to be read in this light, and not as admissions of prior art.

[0004] The CO2 emissions from distributed sources and the transportation sector in the U.S. account for -33-50% of total CO2 emissions and are very difficult to control. Currently, most direct air capture (DAC) sorbent technologies use amine-based sorbent due to high affinity toward CO2 and relatively low desorption energy requirement (-75-90 kJ / gmol CO2) than other sorbents such as alkaline mineral-based sorbents. Such amine-based sorbents are usually structured onto monolith, laminated plate, or fiber. Each structure has advantages and disadvantages. First, a monolithic structure has high surface-to-volume ratio but has poor heattransfer properties. Direct steam injection is considered to be preferred for desorption but leads to amine leaching / degradation, high desorption energy, and evaporative steam loss. Second, a metallic laminated structure has low surface-to-volume ratio relative to monolith but can utilize much better heat-transfer properties. Most designs use a combination of indirect steam injection (through tubes for conductive heat transfer to the plate) with forced convective air cooling. This approach limits the size of the plates due to the time required to reach a desired desorption temperature distribution over the plate and good desorption temperature control due to the temperature gradient developing over the plate. When forced convective air cooling isused to cool the hot plates, amine degradation is detrimental. Third, a sorbent-embedded fiber structure adds inherent external mass-transfer resistance to the sorbent phase and usually requires expensive electrical energy such as Joule heating for desorption coupled with convective air cooling. When sorbent inside the fiber reaches its lifetime, it is also difficult to regenerate the sorbent phase.SUMMARY OF THE INVENTION

[0005] Certain exemplary aspects of the invention are set forth below. It should be understood that these aspects are presented merely to provide the reader with a brief summary of certain forms the invention might take and that these aspects are not intended to limit the scope of the invention.

[0006] In an embodiment of the invention, a method of removing carbon dioxide from carbon dioxide-laden ambient air is provided. The method involves a) directing a flow of the carbon dioxide-laden ambient air through a carbon dioxide capture structure comprising one or more sorbent-coated substrates, wherein the sorbent is capable of binding carbon dioxide to the sorbent, so as to remove carbon dioxide from the ambient air; b) regenerating the sorbent by exposing said one or more sorbent-coated substrates to a liquid heating medium having a temperature above at least 40 °C, thereby causing separation of carbon dioxide from the sorbent; c) exposing said one or more sorbent-coated substrates to a cooling medium at a reduced temperature below about 50 °C, resulting in regenerated sorbent-coated substrates, and d) cyclically repeating exposure of said one or more regenerated sorbent-coated substrates to carbon dioxide-laden ambient air, followed by regenerating the sorbent by exposing said one or more sorbent-coated substrates to a heating medium at the elevated temperature and then cooling by exposing said one or more sorbent-coated substrates to a cooling medium at the reduced temperature.

[0007] In one embodiment, the sorbent comprises an amine functionalized with an epoxide chemical, the epoxide having a chemical structure selected from:

[0008] a.

[0009] wherein: R1 is a C0-C2 alkyl group; R2 is a C1-C5 alkyl group or aryl group; R3 is a C0-C1 alkyl group; R4 is a C0-C1 alkyl group or aryl group; R5 is a C0-C3 alkyl group or aryl group; R6 is a C0-C1 alkyl group or aryl group;

[0011] wherein: R1 is a C1-C4 alkyl group or aryl group; R2 is a C0-C1 alkyl group or aryl group; R3 is a C0-C1 alkyl group or aryl group; R4 is a C0-C1 alkyl group or aryl group; and

[0013] wherein: R1 is a C1-C3 alkyl group; R2 is a C0-C2 alkyl group; and R3 is a C0-C2 alkyl group.

[0014] In another embodiment, the epoxide chemical is selected from the group consisting of isobutylene oxide (IBO), dimethyl- 1,2-epoxybutane (DMEB), epoxy octane (EO), styrene oxide (SO), phenyl glycidyl ether (PGE), glycidyl 4-methoxyphenyl ether (GMPE), butyl glycidyl ether (BGE), glycidyl isopropyl ether (GIPE), 2- (tert-butoxymethyl oxirane) (TBGE), and neopentyl glycol diglycidyl (NGD), 2-(2,2-dimethyl propyl) oxirane, 2-(2,2-dimethylbutyl oxirane), 2,2, 3 -trimethyl oxirane, (2,3 -epoxypropyl) benzene, tert-butyl glycidyl ether, butyl glycidyl ether.

[0015] In one embodiment, the epoxide chemical is selected from the group consisting of isobutylene oxide (IBO) and glycidyl isopropyl ether (GIPE). In another embodiment, the amine is functionalized in a primary or secondary state. In one embodiment, the amine is selected from the group consisting of polyethylenimine, tetraethylenepentamine, and pentaethylenehexamine. In another embodiment, the amine of the sorbent is polyethylenimine. In one embodiment, the amine of the sorbent is tetraethylenepentamine. In another embodiment, the amine of the sorbent is pentaethylenehexamine.

[0016] In one embodiment, the one or more sorbent-coated substrates are sorbent-coated monolith. In another embodiment, the one or more sorbent-coated substrates are sorbent-coated metals. In one embodiment, the one or more sorbent-coated substrates are sorbent-coated hollow metallic structures. In another embodiment, the one or more sorbent-coated substrates further comprise a hydrophobic membrane film. In one embodiment, regenerating the sorbent-coated plates involves removing the hydrophobic membrane film from the sorbent-coated substrate. In another embodiment, the membrane film comprises a material selected from the group consisting of polydimethylsiloxane (PDMS), poly vinylidene fluoride (PVDF), surface-modified polypropylene (PP) and expanded polytetrafluoroethylene (ePTFE). In one embodiment, the one or more sorbent-coated substrates are heated and cooled under vacuum.In another embodiment, the carbon dioxide capture structure is a shell and tube heat exchanger configuration.BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing summary, as well as the following detailed description of preferred embodiments of the application, will be better understood when read in conjunction with the appended drawings.

[0018] FIG. 1 is a graph showing CO2 working capacities of unmodified PEI and 0.2 IBO-PEI monolith blocks between 80-90 °C after saturation in air at 20 °C and -50% relative humidity (RH)..

[0019] FIG. 2 is a graph showing 100 cyclic performances under 400 ppm CO2 in dry air at 30 °C (adsorption) and N2 at 90 °C (desorption) in TGA.

[0020] FIG. 3 is a graph showing in situ IR spectra of unmodified and modified PEI sorbents in air for 24 h at 80 °C. 1,670 cm'1for C=O and C=N and 1,601 cm'1for NH2 deformation.

[0021] FIG. 4 is a schematic showing a DAC system with heat exchanger design according to the present invention.

[0022] FIG. 5 A is a schematic showing a reactor set-up for performance evaluations of block (Joule heating).

[0023] FIG. 5B is a photo showing a reactor set-up for performance evaluations of block (Joule heating).

[0024] FIG. 5C is a photo showing dimensions of a monolith block.

[0025] FIG. 6A is a graph showing a performance evaluation of modified PEI-2 sorbent-coated block.

[0026] FIG. 6B is a graph showing a temperature profile.

[0027] FIG. 6C is a graph showing a CO2 purity profile.

[0028] FIG. 6D is a graph showing a CO2 volume profile.

[0029] FIG. 7 is a graph showing the cyclic performance of modified PEI-2 sorbent-coated block.

[0030] FIG. 8 is a schematic showing heating with 90 °C water at 0.5 LPM.

[0031] FIG. 9A is a schematic showing heating with 90 °C water at 0.5 LPM at 40 seconds.

[0032] FIG. 9B is a schematic showing heating with 90 °C water at 0.5 LPM at 60 seconds.

[0033] FIG. 10A is a schematic showing heating with 90 °C water at 0.5 LPM (side view on coating and plate) at 40 seconds.

[0034] FIG. 1 OB is a schematic showing heating with 90 °C water at 0.5 LPM (side view on coating and plate) at 60 seconds.

[0035] FIG. 11A is a schematic showing heating with radiator design at 90 °C water and 0.5 LPM at 0 minutes.

[0036] FIG. 1 IB is a schematic showing heating with radiator design at 90 °C water and 0.5 LPM at 10 minutes.

[0037] FIG. 12A is a schematic showing cooling down to <50 °C with 20 °C water at 0.5 LPM at 0 seconds.

[0038] FIG. 12B is a schematic showing cooling down to <50 °C with 20 °C water at 0.5 LPM at 30 seconds.

[0039] FIG. 13A is a schematic showing cooling with 20 °C water at 0.5 LPM (side view on coating and plate) at 0 seconds.

[0040] FIG. 13B is a schematic showing cooling with 20 °C water at 0.5 LPM (side view on coating and plate) at 30 seconds.

[0041] FIG. 14A is a schematic showing a first generalized structure of epoxides that are useful for functionalization of amine with a primary and / or secondary state to prepare sorbent material according to the present invention.

[0042] FIG. 14B is a schematic showing a second generalized structure of epoxides that are useful for functionalization of amine with a primary and / or secondary state to prepare sorbent material according to the present invention.

[0043] FIG. 14C is a schematic showing a third generalized structure of epoxides that are useful for functionalization of amine with a primary and / or secondary state to prepare sorbent material according to the present invention.

[0044] FIG. 15A is a schematic showing the structure of unmodified 3-aminopropyltrimethoxysilane (APTMS).

[0045] FIG. 15B is a schematic showing the structure of 1.0 EB-3-APTMS.

[0046] FIG. 15C is a schematic showing the structure of 1.0 IBO-3-APTMS.

[0047] FIG. 15D is a graph showing CO2 adsorption capacities under 400 ppm CO2 in dry air at 30 °C in TGA.

[0048] FIG. 15E is a graph showing CO2 adsorption capacities under 400 ppm CO2 in dry air at 30 °C in TGA.

[0049] FIG. 16A is a schematic showing the structure of tetraethylenepentamine (TEPA).

[0050] FIG 16B is a graph showing 10 cyclic adsorption and desorption test of 50%(wt) TEPA / silica, 0.2 IBO-TEPA / silica, and 0.4 IBO-TEPA / silica sorbents under 400 ppm CO2 in dry air at 30 °C for adsorption and N2 at 70 °C for desorption in TGA.

[0051] FIG 16C is a graph showing CO2 adsorption capacities of 50%(wt) TEPA / silica, 0.2 IBO-TEPA / silica, and 0.4 IBO-TEPA / silica sorbents during the 1st and 10th cycles.

[0052] FIG 16D is a schematic showing the structure of pentaethylenehexamine (PEHA).

[0053] FIG 16E is a graph showing 10 cyclic adsorption and desorption tests of 50%(wt) PEHA / silica, 0.16 IBO-PEHA / silica, and 0.32 IBO-PEHA / silica sorbents under 400 ppm CO2 in dry air at 30 °C for adsorption and N2 at 70 °C for desorption in TGA.

[0054] FIG 16F is a graph showing CO2 adsorption capacities of 50%(wt) PEHA / silica, 0.16 IBO-PEHA / silica, and 0.32 IBO-PEHA / silica sorbents during the 1st and 10th cycles.

[0055] FIG. 17A is a schematic showing the structure of 2-(2,2-dimethylpropyl)oxirane (DPO).

[0056] FIG 17B is a graph showing 10 cyclic adsorption and desorption tests of 50%(wt) PEVsilica, 0.1 IBO-PEVsilica, and 0.1 DPO-PEVsilica sorbents under 400 ppm CO2 in dry air at 30 °C for adsorption and N2 at 90 °C for desorption in TGA.

[0057] FIG 17C is a graph showing CO2 adsorption capacities of 50%(wt) PEVsilica, 0.1 IBO-PEVsilica, and 0.1 DPO-PEVsilica sorbents during the 1st and 10th cycles.

[0058] FIG. 18 is a schematic showing the structure of a vinyl amine-based aminopolymer structure.

[0059] FIG. 19 is a graph showing CO2 working capacities obtained at various desorption temperatures and vacuum times for PEI and IBO-PEI sorb ent- washcoated monolith blocks.

[0060] FIG. 20 is a graph showing total CO2 desorption capacity including working (solid) and residual (striped) capacities obtained at various desorption temperatures and vacuum operating durations for PEI and IBO-PEI sorbent-coated blocks.

[0061] FIG. 21 is a schematic showing a typical shell and tube heat exchanger configuration.

[0062] FIG. 22 is a schematic showing how a shell and tube heat exchanger configuration with sorbent according to the present invention would operate.DETAILED DESCRIPTION OF THE INVENTION

[0063] One or more specific embodiments of the present invention will be described below. In an effort to provide a concise description of these embodiments, all features of an actual implementation may not be described in the specification. It should be appreciated that in the development of any such actual implementation, as in any engineering or design project,numerous implementation-specific decisions must be made to achieve the developers’ specific goals, such as compliance with system-related and business-related constraints, which may vary from one implementation to another. Moreover, it should be appreciated that such a development effort might be complex and time consuming, but would nevertheless be a routine undertaking of design, fabrication, and manufacture for those of ordinary skill having the benefit of this disclosure.

[0064] The present invention involves novel direct air capture (DAC) technology that takes advantage of inventive amine-based sorbents in a powdered form that can save -50% energy for desorption and also provides significant resistance to thermal and oxidative degradations. When the technology is scaled into a monolithic structure, -85-95% CO2 working capacity recovery with >~95% purity relative to its full adsorption capacity was achievable at -80-90 °C using temperature-vacuum swing adsorption (TVSA).

[0065] The significant resistance to the degradations warrants longer sorbent lifetime and also a fast switch in operations from desorption to adsorption at -50 °C. In one embodiment, the present invention advances the technology in heat exchanger design while limiting the coadsorption of water vapor using hydrophobic membrane film in conjunction with waste heat from energy-intensive industries, such as data centers, with geothermal or a high-temperature heat pump system. The low desorption temperature window can save a substantial amount of desorption energy by utilizing the sensible heat of water for heating and cooling without a need to use steam for the desorption.The CO2 emissions from distributed sources and the transportation sector in the U.S. account for -33-50% of total CO2 emissions and are very difficult to control. The present invention addresses the key impacts that the inventor’s modified amine-based sorbent technology can give for DAC. First, the technology can significantly reduce desorption energy using a low desorption temperature window of -45-90 °C for temperature-vacuum swing adsorption (TVSA) without using steam. In another embodiment, a low desorption temperature window of about 80-90 °C is used. For example, when 90 °C water is used instead of low-pressure steam at >100 °C from 20 °C, this will save -90% desorption energy relative to the use of the steam (i.e., 292 J / g water vs. 2,600 J / g water). Since the technology uses only sensible heat for desorption, potential evaporative loss of fresh water would also be reduced. Second, this technology can provide significant resistance to thermal and oxidative degradations and thus minimize amine leaching and degradations. This will result in a longer lifetime of sorbent than that of unmodified amine-based sorbent. This will also allow for a fast-operating phase switch from desorption to adsorption without significant degradations. Third, the technology willincrease the overall CO2 productivity by fast heating and cooling (in -5 min including heating, desorption with >95% CO2 purity, and cooling for a prototype shown in FIG. 4) by means of indirect heat exchange between -45-90 °C for heating. For heating temperatures from 45-55 °C, no cooling is needed. For heating temperatures above 55 °C , cooling is done at a temperature of -50 °C or less.. The small temperature difference will allow for fast operating phase change between adsorption and desorption without spending substantial energy.Sorbent Technology

[0066] The sorbent technology of the present invention significantly reduces desorption energy and resistance to degradation, which is derived from the functional groups used to modify amines. In one embodiment, the present invention uses a sorbent chemical for CO2 separation comprising an amine with a primary and / or secondary state functionalized with an epoxide chemical (EC-Amine) impregnated onto a support. In another embodiment, the present invention uses a sorbent chemical for CO2 separation comprising polyethylenimine (PEI) functionalized with an epoxide chemical (EC-PEI) impregnated onto a support. FIGs 14A-14C show generalized epoxide structures that are useful for functionalization of the PEI. Regarding FIG. 14A, Ri is a C0-C2 alkyl group; R2 is a C1-C5 alkyl group or aryl group; R3 is a C0-C1 alkyl group; R4 is a C0-C1 alkyl group or aryl group; R5 is a C0-C3 alkyl group or aryl group; and Re is a C0-C1 alkyl group or aryl group.

[0067] Regarding FIG. 14B, Ri is a C1-C4 alkyl group or aryl group; R2 is a C0-C1 alkyl group or aryl group; R3 is a C0-C1 alkyl group or aryl group; and R4 is a C0-C1 alkyl group or aryl group. Regarding FIG. 14C, Ri is a C1-C3 alkyl group; R2 is a C0-C2 alkyl group; and R3 is a C0-C2 alkyl group.

[0068] Specific examples of useful functional groups include isobutylene oxide (IBO), 3,3-Dimethyl-l,2-epoxybutane (DMEB), epoxy octane (EO), styrene oxide (SO), phenyl glycidyl ether (PGE), glycidyl 4-methoxyphenyl ether (GMPE), butyl glycidyl ether (BGE), glycidyl isopropyl ether (GIPE), 2-(tert-butoxymethyl oxirane) (TBGE), and neopentyl glycol di glycidyl (NGD), 2-(2,2-dimethyl propyl) oxirane, 2-(2,2-dimethylbutyl oxirane), 2,2,3-trimethyl oxirane, (2,3 -epoxypropyl) benzene, tert-butyl glycidyl ether, butyl glycidyl ether.

[0069] Among the 16 functional groups identified above, a fraction of the amine modification of 0.1 and 0.2 isobutylene oxide (IBO)-functionalized PEI sorbent could save -51-57% of the heat of desorption relative to unmodified PEI sorbent. This saving in the heat of desorption is much higher than the most well-known 0.1 epoxy butane (EB)-PEI sorbent that showed -23% at the same modification level (Table 2). At a higher modification level of the same 0.2 molarratio, IBO-PEI and EB-PEI sorbents showed 57% and 53% desorption energy savings, respectively.

[0070] When 0.2 IBO-PEI sorbent was coated onto a monolith, -85-95% of full CO2 adsorption capacities were recovered as CO2 working capacities at 80-90 °C by Joule heating (FIG. 1). Unmodified PEI sorbent-coated monolith showed slightly higher working capacities at 80-85 °C with an -15% higher working capacity at 90 °C. However, unmodified PEI sorbent started to show significant amine leaching and degradation over 100 cyclic evaluations in TGA at >~90 °C whereas the 0.2 IBO-PEI sorbent did not at 90 °C (FIG. 2). This significantly improved resistance was confirmed by in situ FTIR on the degradations over the 0.2 IBO-PEI and EB-PEI sorbents under extremely harsh conditions of air and 80 °C (FIG. 3). Our 100 cyclic tests at 20 °C and 50% RH with 0.2 IBO-PEI block show consistent performances without any sign of amine leaching or degradations (based on MS analysis for NH3, data not shown).

[0071] However, the monolithic material, cordierite, has very poor heat-transfer properties and thus a high desorption energy demand for heating and cooling the monolith block. Direct steam injection to monolith block leads to amine leaching and degradations even if temperature management is practiced in the field. Therefore, the present invention uses a different structured system with good heat-transfer properties for fast heating, desorption with -95% CO2 recovery and purity, and cooling in order to achieve high CO2 productivity (amount of CO2 separated / (system volume x time)) and a long lifetime of the structured sorbent system. In one embodiment of the present invention, the same IBO-PEI sorbent is coated onto metal surfaces in a heat exchanger design (FIG. 4). The performance of this system during the longterm adsorption and desorption cycles is quite reliable.Inventive system

[0072] The technology of the present invention was demonstrated using a prototype with a heat exchanger design to achieve low desorption energy, long lifetime with low degradations, and high CO2 productivity. To achieve the objective, the present invention uses a system consisting of hollow heat exchanger plates coated with the sorbent inside an enclosed DAC system (FIG.4) for long-term cyclic performance evaluations (e.g., >1,000 cycles).

[0073] A monolith structure using the 0.1 and 0.2 IBO-PEI sorbents with two different modification levels showed -1.7 and -1.4 mmol CO2 / g sorbent full working capacities with >95% CO2 purity achieved by Joule heating, respectively, under 20 °C, 50% RH, and space velocity (SV) of 78,000 hr-1 (Fig. 1). The same powdered sorbent can be coated onto metalplate, which should produce similar performances based on previous results of the powdered sorbent performances.

[0074] Hydrophobic membranes can be used to affect the adsorption of water vapor and CO2 onto the sorbent phase. Useful membrane materials include polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), surface-modified polypropylene (PP) and expanded polytetrafluoroethylene (ePTFE). In one embodiment, the membrane films are coated onto the sorbent-coated metal plates. In one embodiment, the metal plates are aluminum alloy. This approach enables the membrane and sorbent-coated structure to be readily regenerated by removing the membrane film and replacing the sorbent phase. In our inventive DAC system using monolith, this evaluation is performed by real-time measurements of water vapor and CO2. Our monolith structure shows the co-adsorption molar ratio of ~4 water vapor to CO2 at 20 °C and 50% RH. Lower molar ratios under the same adsorption conditions are achievable using the different membrane materials with different pore sizes and thicknesses.

[0075] The thickness of the hollow water channel is determined based on the trade-off relationship between heating / cooling medium flow rates and pressure drop. Our preliminary model shows that heating, desorption, and cooling can be achieved in ~5 min in a prototype with a 15 cm x 15 cm plate, 0.5 LPM water flowrate of 20 and 90 °C cooling and hot water, respectively, and 1-2 mm coating thicknesses while achieving low heat of desorption.

[0076] The present invention greatly benefits from the low desorption temperatures without a need to generate steam. The system will further benefit from cost-effective and reliable sources of the desorption energy. One source of desorption energy is the waste heat generated from data centers with or without high-temperature heat pump technology.

[0077] In one embodiment, the system of the present invention is a Temperature- Vacuum Swing Adsorption (TVSA) system. A typical TVSA cycle includes: a) adsorption: ambient air or flue gas passes through the sorbent to capture CO2; b) evacuation / heating (regeneration): the bed is evacuated and then heated (vacuum applied) to release the concentrated CO2; c) cooling: the bed is cooled back to a certain temperature to prepare for the next adsorption cycle; d) pressurization: the system returns to the starting pressure.

[0078] FIGs 5 A-5C show a reactor set-up for performance evaluations of block (joule heating). Regarding FIG. 5 A, the reactor set-up 100 shows a first step with a sample bag 110, a vacuum pump 120, a cold trap 130, a DC power supplier 140, a temperature controller 150, a CO2 analyzer (0-2000 ppm) 160, a Mass Flow Controller (“MFC”) 170, compressed air 180, a rotameter 190, a humidifier 200, a reactor 210, a monolith block 220, a CO2 analyzer (0-2000ppm) 230, and a humidity sensor 240. A second step includes a sample bag 250, a Mass Flow Meter (“MFM”) 260, and a CO2analyzer (0-100%) 270.

[0079] FIGs 6A-6D show a performance evaluation of modified PEI-2 sorbent-coated block. The adsorption conditions were as follows: Flowrate: 175 LPM, SV: 77,778 hr1, Relative humidity (RH): -50%, Temperature: 20 °C. The desorption conditions (Vacuum-assisted Joule heating) were as follows: Vacuum pressure: -28.3” Hg, Initial air present inside reactor after pulling a vacuum: 5.4%, Temperature: 90 °C by Joule heating, Time to reach 90 °C: 31 min + 5 min at 90 °C, CO2recovery: 95%, CO2 purity: 95%.

[0080] FIG. 7 shows the cyclic performance of modified PEI-2 sorbent-coated block. Adsorption conditions were as follows: Temperature: 20 °C, Flowrate: 175 LPM, Relative humidity: 50%. Desorption conditions were as follows: Vacuum pressure: -28.5” Hg, Initial air present inside the reactor after pulling a vacuum: 4.7%, CO2 purity: >95%, Desorption temperature: 90 °C by Joule heating, Time to reach 90 °C: 31 min, Holding time at 90 °C: 5 min, CO2 recovery: 95%, Flowrate: 175 LPM air; SV: 77,778 hr-1; RH: -50%; Adsorption temperature: 20 °C; Desorption temperature: 90 °C; Switch from desorption to adsorption at 50 °C, Adsorption time for Cycle 1-13: 90 min for -100% adsorption capacity, Adsorption time for cycle 14-20: 30 min for -70% adsorption capacity.

[0081] There are a number of differences between Monolith vs. Heat Exchanger (HE) Structures. A monolithic structure has the following characteristics: High surface to volume ratio: CO2 capacity is high with the same volume relative to other structured systems (+), Time required for desorption is longer due to poor heat-transfer property (-), Hydrophobic membrane cannot be added to the inner cell walls (-), Pressure drop is high (-), Coating thickness is limited by cell size (-), Precise T control is challenging using Joule heating (-).

[0082] A heat exchanger (HE) structure, on the other hand, has the following characteristics: Low surface to volume ratio: CO2 capacity is low relative to monolithic structure (-), Inexpensive thermal energy can be used (+), Time required for desorption is shorter due to good heat-transfer property (+), Hydrophobic membrane can be added to the walls (+), Negligible pressure drop (+), Coating thickness is readily adjustable (+), Precise T control is feasible resulting in slow degradation (+).

[0083] FIG. 8 shows heating with 90 °C water at 0.5 LPM. The schematic depicts a 15 cm x 15 cm aluminum alloy with 1 mm thickness in a 5 mm water channel with 0.5 L / min water flow rate and -1.5 cm / s water velocity. It has a 500 pm coating thickness. The Reynold number is <450. The AP in the water channel is <0.3 Pa.

[0084] FIGs 9 A and 9B show heating with 90 °C water at 0.5 LPM at different times. It takes <1 min to ramp the plate to 80-90 °C under these design and operating conditions (15 cm x 15 cm with 1 mm thickness + 90 °C and 0.5 LPM).

[0085] FIGs 10A and 10B show heating with 90 °C water at 0.5 LPM at different times.

[0086] FIGs 11 A and 1 IB show heating with a radiator design at 90 °C water and 0.5 LPM. It takes ~10 min to ramp the plate with the same dimensions (15 cm x 15 cm with 1 mm thickness) to 85-90 °C under the same operating conditions (i.e., 90 °C and 0.5 LPM).

[0087] FIGs 12A and 12B show cooling down to <50 °C with 20 °C water at 0.5 LPM at different times.

[0088] FIGs 13 A and 13B show cooling with 20 °C water at 0.5 LPM (side view on coating and plate) at different times.

[0089] FIGs 15A-15D show an example of another amine (3-APTMS) modification with only a primary amine. This shows that any amine with primary amine state can be used to functionalize with isobutylene oxide (IBO) as shown in FIG. 15C. FIG. 15B shows 1,2 epoxybutane (EB) as a functional group just to show the structure and the result for a comparison. In FIG. 15D, IBO functionalization works slightly better than EB functionalization.

[0090] FIGS 16A-16F show an example of two additional short amines (TEPA and PEHA). Both amines functionalized with IBO at different levels and show stability. This shows that any amine with primary and / or secondary amine states can be used to functionalize with isobutylene oxide (IBO).

[0091] FIGs 17A-17C show the structure and performance of 2-(2,2-dimethylpropyl)oxirane (DPO)-functionalized PEEsilica sorbent. DPO falls into the first generalized EC structure shown in FIG. 14A. It shows slightly better stability than IBO functionalization due to one more methyl group.

[0092] Another embodiment of the present uses a shell and tube heat exchanger configuration as opposed to metal plates. Referring to FIG. 21, a typical shell and tube heat exchanger configuration is shown where sorbent is coated onto the inner or outer wall of the tube bundle depending on where a gas or liquid heating medium is introduced. Referring to FIG. 22, if sorbent is coated onto the inner tubes (sorbent layer is shown in light gray), CO2 can be captured in the sorbent layer coated on the inner wall of the tubes. In this case, a gas or liquid heating medium (hot water in this schematic) can be used to desorb CO2 from the sorbent coating layer under vacuum (i.e., same temperature-vacuum swing adsorption / desorption). If the sorbent iscoated onto the outer wall of the tubes, a gas or liquid heating medium should be introduced to the inside of the tubes.

[0093] The advantage of the tubular heat exchanger system of the present invention is that it has a higher surface to volume ratio than the plate-type heat exchanger described herein. There may be additional challenges regenerating the coating layer after the sorbent layer reaches its lifetime.EXAMPLESExample 1 - CO2 Working Capacities of Monolith Blocks at Low Temperatures

[0094] To evaluate the potential of utilizing low-grade heat for CO2 desorption, PEI and 0.2 IBO-PEI sorbent-washcoated monolithic blocks were evaluated using the experimental set-up in FIG. 5. For each test, a sorbent-coated block was wrapped in a 25 cm * 15 cm carbon-fiber sheet, and the ends of the sheet were secured between rolled copper bus bars to establish an electrical contact. The wrapped block was then covered with a ceramic blanket to prevent a bypass air flow during adsorption and to reduce heat loss during Joule heating. Electrical connections to the reactor terminals were made using alligator clips, and thermocouple was used to monitor the real-time temperature of the monolith block. The prepared assembly was then placed into the reactor. Air supplied from the Facilities Department was used as the adsorption feed gas. The air stream was humidified to -50% RH at 20 °C and delivered to the reactor at a flow rate of -175 L / min. The CO2 concentrations at the reactor inlet and outlet were continuously monitored using two online CO2 analyzers (0 ppm to 2,000 ppm, Quantek Inc.). Once a monolith block was saturated with CO2, the reactor was isolated, and the residual gas was evacuated to -28 inches of Hg using a vacuum pump. Then, desorption was initiated by applying DC power to induce Joule heating, raising the block temperature to a desorption temperature (i.e., 45 °C, 60 °C, or 70 °C). Then, the block was held at a target temperature for the predetermined durations of 5 min, 15 min, or 60 min while the vacuum pump was continuously running. A downstream cold trap was used to condense the water vapor from the outlet stream, and high-purity CO2 gas was collected in a sampling bag. The CO2 composition and the quantity of the collected gas were determined using a CO2 analyzer coupled with a mass flow meter. After the temperature-vacuum desorption used to determine the CO2 working capacity, further desorption was run to separate the remaining CO2 in the block by ramping the temperature to 90 °C under a 10 L / min of N2 flow.

[0095] FIG. 19 presents the CO2 working capacities of the blocks containing unmodified and modified PEValumina blocks under different desorption temperatures between 45 °C-70 °Cand vacuum operating durations between 15 min and 60 min. Overall, the working capacities decreased with a decrease in desorption temperature for all the sorbent blocks. Most importantly, across the entire desorption temperatures below 70 °C, the IBO-PEI sorbent-coated blocks showed higher CO2 working capacities than the PEI sorbent-coated block. These results are different from the CO2 working capacities obtained between 80 °C and 90 °C shown in FIG. 1. These data clearly show that there is an inversion of the working capacities at ~70 °C. In addition, the block with the unmodified PEI sorbent seems to be more dependent on vacuum operation duration than that with the IBO-PEI sorbents, suggesting longer vacuum operation most likely attributed to the higher bonding strength.

[0096] The block with the PEI sorbent showed the average working capacities of (0.58 and 0.84) mmol CO2 / g sorbent at 60 °C and 70 °C, respectively. When the desorption temperature was lowered to at 45 °C, it did not show any detectable CO2 working capacity. When the block was run at 53 °C (i.e., the mid-temperature between 45 °C' and 60 °C) for 60 min, a negligible CO2 working capacity of 0.01 mmol CC>2 / g sorbent was detected. On the other hand, the blocks with the (0.1, 0.2 and 0.3) IBO-PEI sorbents showed 1.09, 1.03, and 1.20 mmol CO2 / g sorbent at 60 °C and (1.40, 1.20, and 1.20) mmol CO2 / g sorbent at 70 °C, respectively. When the blocks in the same order were evaluated at 45 °C, the average working capacities were (0.58, 0.57 and 0.80) mmol CO2 / g sorbent, respectively.

[0097] It is interesting to note that the block with the 0.1 IBO-PEI sorbent shows higher CO2 working capacities than those with the (0.2 and 0.3) IBO-PEI sorbents at ~60 °C to 70 °C. However, the 0.3 IBO-PEI sorbent-coated block showed higher CO2 working capacities than the other two sorbents-coated blocks below 60 °C. These findings suggest that low level of amine modification (e.g., 0.1 IBO-PEI) with less reduced bonding strength results in high CO2 working capacities at ~60 °C to 70 °C. However, at low desorption temperatures (e.g., below 60 °C), the less reduced bonding strength does not seem to allow for the desorption. As the level of the amine modification increases, the bonding strengths between adsorbed CO2 molecules and modified amine sites become reduced and thus give low CO2 working capacities at ~60 °C to 70 °C. However, the reduced bonding strengths can benefit from the low desorption temperatures (i.e., below 60 °C) which can show high CO2 working capacities. These results clearly underscore that the modified amine-based sorbent technology of the present invention has potential to utilize low desorption temperatures that would also provide higher resistance to thermal and oxidative degradations.Example 2

[0098] Complete desorption was enabled each time by ramping the block temperature to 90 °C under a nitrogen gas flow. The residual CO2 was determined from the resulting CO2 concentration profiles. FIG. 20 shows the combined CO2 working and residual capacities under each desorption condition for all the blocks. The CO2 desorption recovery is defined here as the amount of CO2 working capacity under a vacuum at a specific desorption temperature (45 °C, 60 °C, or 70 °C) expressed as a percentage relative to the total CO2 capacity (= working capacity + residual capacity under N2). As expected, the CO2 recovery at all temperatures was in the order of unmodified PEI < 0.1 IBO-PEI < 0.2 IBO-PEI < 0.3 IBO-PEI, indicating weaker bonding strength with an increase in the level of the PEI modification. Additionally, a more interesting result can be seen from the variation of desorption time. For the unmodified PEI sorbent-coated block at 60 °C, there was a significant increase in the CO2 recovery from 29% to 36% when the N2 desorption time changed from 5 min to 15 min and a further increase to 41% at 60 mins. Similarly, at the same temperature, the recovery from the block with the 0.1 IBO-PEI sorbent was 51, 57, and 61% from 5-min, 15-min and 60-min desorption durations, respectively. However, it is interesting to note that the recovery was fairly similar for 0.2 IBO-PEI (i.e., 70-73%) and 0.3 IBO-PEI (i.e., 82%-85%) across all vacuum operating durations. These results again highlight the fast desorption kinetics from the blocks with the IBO-PEI sorbent with an increase in the level of the modification. A similar conclusion can be made from the result at 70 °C. However, at 45 °C, the CO2 recovery moderately increased with N2 desorption time for all the IBO-PEI sorbent-coated blocks (i.e., 0.1 IBO-PEI: 31%-38%; 0.2 IBO-PEI: 38%-46%; and 0.3 IBO-PEI: 60%-66%). As shown before, CO2 recovery was not detected at this temperature for the block with the unmodified PEI sorbent.

[0099] Although not described in detail herein, other steps which are readily interpreted from or incorporated along with the disclosed embodiments shall be included as part of the invention. The embodiments that have been described herein provide specific examples to portray inventive elements, but will not necessarily cover all possible embodiments commonly known to those skilled in the art.

Claims

What is claimed is:

1. A method of removing carbon dioxide from carbon dioxide-laden ambient air, the method comprising:a. directing a flow of the carbon dioxide-laden ambient air through a carbon dioxide capture structure comprising one or more sorbent-coated substrates, wherein the sorbent is capable of binding carbon dioxide to the sorbent, so as to remove carbon dioxide from the ambient air,b. regenerating the sorbent by exposing said one or more sorbent-coated substrates to a liquid heating medium having a temperature above at least 40 °C, thereby causing separation of carbon dioxide from the sorbent,c. exposing said one or more sorbent-coated substrates to a cooling medium at a reduced temperature below about 50 °C, resulting in regenerated sorbent-coated substrates, andd. cyclically repeating exposure of said one or more regenerated sorbent-coated substrates to carbon dioxide-laden ambient air, followed by regenerating the sorbent by exposing said one or more sorbent-coated substrates to a heating medium at the elevated temperature and then cooling by exposing said one or more sorbent-coated substrates to a cooling medium at the reduced temperature.

2. The method of claim 1 wherein the sorbent comprises an amine functionalized with an epoxide chemical, the epoxide having a chemical structure selected from the group consisting of:wherein:Ri is a C0-C2 alkyl group;R2 is a C1-C5 alkyl group or aryl group;R3 is a C0-C1 alkyl group;R4 is a C0-C1 alkyl group or aryl group;R5 is a C0-C3 alkyl group or aryl group;Re is a Co-Ci alkyl group or aryl group;wherein:Ri is a C1-C4 alkyl group or aryl group;R2 is a C0-C1 alkyl group or aryl group;R3 is a C0-C1 alkyl group or aryl group;R4 is a C0-C1 alkyl group or aryl group; andwherein:Ri is a C1-C3 alkyl group;R2 is a C0-C2 alkyl group; andR3 is a C0-C2 alkyl group.

3. The method of claim 2 wherein the epoxide chemical is selected from the group consisting of isobutylene oxide (IBO), dimethyl- 1 ,2-epoxybutane (DMEB), epoxy octane (EO), styrene oxide (SO), phenyl glycidyl ether (PGE), glycidyl 4-methoxyphenyl ether (GMPE), butyl glycidyl ether (BGE), glycidyl isopropyl ether (GIPE), 2- (tertbutoxymethyl oxirane) (TBGE), and neopentyl glycol diglycidyl (NGD), 2-(2,2-dimethyl propyl) oxirane, 2-(2,2-dimethylbutyl oxirane), 2, 2, 3 -trimethyl oxirane, (2,3- epoxypropyl) benzene, tert-butyl glycidyl ether, butyl glycidyl ether.

4. The method of claim 2 wherein the epoxide chemical is selected from the group consisting of isobutylene oxide (IBO) and glycidyl isopropyl ether (GIPE).

5. The method of claim 2 wherein the amine is functionalized in a primary or secondary state.

6. The method of claim 2 wherein the amine is selected from the group consisting of polyethylenimine, tetraethylenepentamine, and pentaethylenehexamine.

7. The method of claim 2 wherein the amine of the sorbent is polyethylenimine.

8. The method of claim 2 wherein the amine of the sorbent is tetraethylenepentamine.

9. The method of claim 2 wherein the amine of the sorbent is pentaethylenehexamine.

10. The method of claim 1 where the one or more sorbent-coated substrates are sorbent- coated monolith.

11. The method of claim 1 where the one or more sorbent-coated substrates are sorbent- coated metals.

12. The method of claim 1 wherein the one or more sorbent-coated substrates are sorbent- coated hollow metallic structures.

13. The method of claim 1 wherein the one or more sorbent-coated substrates further comprise a hydrophobic membrane film.

14. The method of claim 13 wherein regenerating the sorbent-coated plates comprises removing the hydrophobic membrane film from the sorbent-coated substrate.

15. The method of claim 13 wherein the membrane film comprises a material selected from the group consisting of polydimethylsiloxane (PDMS), polyvinylidene fluoride (PVDF), surface-modified polypropylene (PP) and expanded polytetrafluoroethylene (ePTFE).

16. The method of claim 1 wherein the one or more sorbent-coated substrates are heated and cooled under vacuum.

17. The method of claim 1 wherein the carbon dioxide capture structure is a shell and tube heat exchanger configuration.

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