Distributed direct air carbon capture in conjunction with centralized solvent regeneration

Abstract

An apparatus for directly capturing carbon dioxide from untreated air incorporates (a) an air contactor, having an untreated air inlet, a treated air outlet, a carbon dioxide-lean solvent inlet and a carbon dioxide-rich solvent outlet, (b) a carbon dioxide-lean solvent regeneration unit, having an inlet connected to the carbon dioxide-rich solvent outlet and an outlet connected to the carbon dioxide-lean solvent inlet, and (c) an alkaline solvent circulating through the air contactor and the carbon dioxide-lean solvent regeneration unit The apparatus is useful in a method of directly capturing carbon dioxide from untreated air.

Description

DISTRIBUTED DIRECT AIR CARBON CAPTURE IN CONJUNCTION WITH CENTRALIZED SOLVENT REGENERATIONRelated Applications

[0001] This application claims benefit of U.S. Provisional Patent Application Serial No. 63 / 570,048, filed March 26, 2024, the disclosure of which is incorporated herein by reference in its entirety.Statement Regarding Federally Sponsored Research or Development

[0002] This invention was made with government support under grant number FE0032125 awarded by the U.S. Department of Energy. The government has certain rights in the invention.Technical Field

[0003] This document relates generally to an apparatus for directly capturing carbon dioxide (CO2) from untreated air as well as to a method of directly capturing carbon dioxide from untreated air by means of distributed direct air carbon capture with centralized carbon-capture solvent regeneration.Background

[0004] Under the 2015 Paris Agreement, nearly 200 nations embraced the global objective of constraining the increase in average temperatures to 2.0 °C above preindustrial levels, with an even more ambitious target of 1.5 °C ideally pursued. Achieving the 1.5 C goal necessitates a 45 % reduction in global greenhouse gas emissions by 2030 and ultimately reaching net zero emissions by 2050. More and more business sectors are pledging to help mitigate climate change by reducing their CO2 gas emissions as much as possible. Nevertheless, for some sectors, the current cost of emissions reduction through available technologies can be excessively high, although these costs may become more affordable over time. Additionally, in certain industries, there are emissions sources that cannot be eliminated (e g. the large-scale production of cement, where a significant portion of CO2 emissions stems from an inherent calcination process). Due to these limitations, achieving the emissions reduction pathway to the 1.5 C target necessitates using negative emissions processes, including direct air capture (DAC), to remove CO2 from the atmosphere.

[0005] DAC technology commonly comprises solid sorbent and liquid solvent processes, and the incumbent commercially available DAC technologies capture more than 100 metric tons ofC02per year at a single geo-site. In the sorbent-based processes, porous solid sorbents, typically decorated with amine-based chemicals, are employed to capture CO2from air. After reaching saturation or desired carbon loading in capture capacity, the solid sorbent is regenerated by increasing temperature and / or decreasing pressure to liberate CO2 gas. The solvent-based processes, on the other hand, use alkaline solutions, e.g., NaOH and KOH, or other solutions containing alkaline chemical compounds, to convert CO2gas to dissolved carbon species like CO32and HCO3 and / or carbamate; and subsequently the solutions are chemically, pressure- varied and / or thermally reconditioned to release CO2gas while producing the fresh alkaline solutions. While numerous innovative methods are emerging within the DAC field, it is important to note that the sorbent-based and solvent-based DAC processes developed by Carbon Engineering, Climeworks, and Global Thermostat have made the most substantial progress in development, suggesting the potential for significant scalability in a relatively short time frame to address climate change and carbon neutral by 2050.

[0006] The operational concept of the DAC process set forth in this document is based upon both the solvent-based approach and mature technology of alkaline water electrolysis. The process involves regenerating the solvent through pH swings generated by a carbonate electrolyzer, providing an alternative to the solid sorbent and liquid solvent processes previously introduced. In contrast to those previous methods, our new approach, especially for the absorption step, can be modularized and installed at any place and variation scale from 100 kg / year to 300,000 tonnes / year where footprint is available, and / or decoupled from regeneration step at same geo-site. The regeneration step, potentially brings two significant advantages: (1) the production of hydrogen (H2) as a value-added product through water electrolysis and (2) the elimination of heat-related steps for the regeneration process.

[0007] Consuming OH ions toward oxygen (O2) evolution decreases the pH level at the anolyte loop, while producing OH ions resulting from splitting water causes the pH level to increase at the catholyte loop. Consequently, the reduced pH environment facilitates the release of CO2 gas from the dissolved carbon species such as CO32, whereas the elevated pH environment encourages the formation of alkaline hydroxides for carbon capture in an air absorber.Summary

[0008] In accordance with the purposes and benefits set forth herein, a new and improved apparatus is provided for directly capturing carbon dioxide from untreated air. That apparatus comprises, consists of or consists essentially of: (a) an air contactor having an untreated air inlet, a treated air outlet, a carbon dioxide-lean solvent inlet and a carbon dioxide-rich solvent outlet, (b) a carbon dioxide-lean solvent regeneration unit having an inlet connected to the carbon dioxiderich solvent outlet and an outlet connected to the carbon dioxide-lean solvent inlet, and (c) an alkaline solvent circulating through the air contactor and the carbon dioxide-lean solvent regeneration unit. The alkaline solvent may be selected from a group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof.

[0009] In at least some embodiments, the air contactor to capture CO from air and carbon dioxide-lean solvent regeneration unit may be installed at one geo-site or are installed at different geo-sites.

[0010] In at least some embodiments, the air contactor solvent regeneration unit can be connected with a hard-piped alkaline circulation loop or connected virtually via the transportation of carbon-rich solution from air contactor and carbon-lean solution from regeneration unit through road, rail and water shipment.

[0011] In at least some embodiments, the carbon dioxide-lean solvent regeneration unit is a carbonate electrolyzer. The carbonate electrolyzer may include an anolyte loop, an anode in the anolyte loop, a catholyte loop, a cathode in the catholyte loop a, a cation exchange membrane separating the anolyte loop and the catholyte loop, and a power source connected to the anode and the cathode whereby (a) carbon dioxide and oxygen are generated at the anode, (b) hydrogen is generated at the cathode and (c) the carbon dioxide-lean solvent is regenerated at the cathode.

[0012] In at least some embodiments, the apparatus further includes a first electrolyte tank in the anolyte loop and a second electrolyte tank in the catholyte loop. Alkali-metal sulfate, such as sodium sulfate, may be used as an electrolyte in the apparatus to reduce ionic resistance and achieve a lower operating voltage.

[0013] In accordance with an additional aspect, a method is provided for directly capturing carbon dioxide from untreated air. That method comprises, consists of or consists essentially of the steps of: (a) contacting untreated air containing carbon dioxide with a carbon dioxide lean solvent in an air contactor, (b) absorbing carbon dioxide from the untreated air and generating a carbon dioxide rich solvent and treated air, and (c) regenerating the carbon dioxide-lean solvent from the carbon dioxide-rich solvent by releasing carbon dioxide from the carbon dioxide-rich solvent in a carbon dioxide-lean solvent regeneration unit.

[0014] In at least some of the many possible embodiments of the method, the CO2 capture can be co-install ed at one geo-site with solvent regenerator or be installed at different geo-sites.

[0015] The method may include connecting absorption and regeneration steps via hard-piped solution loop, or transportation of carbon-rich solution from air contactor and carbon-lean solution from regeneration unit through road, rail and / or water shipments.

[0016] The method may include steps of: (a) distributing the carbon dioxide-lean solvent from a centrally located carbon dioxide-lean solvent regeneration unit to a plurality of remotely located air contactors and (b) returning carbon dioxide-rich solvent from the plurality of remotely located air contactors to the centrally located carbon dioxide-lean solvent regeneration unit.

[0017] The regenerating may include generating pH swings with a carbonate electrolyzer.

[0018] The method may include applying electricity to an anode and a cathode, generating carbon dioxide and oxygen at the anode, generating hydrogen at the cathode and regenerating the carbon dioxide-lean solvent at the cathode. The method may include using alkali-metal sulfate as an electrolyte in the carbonate electrolyzer to reduce ionic resistance and achieve a lower operating voltage.

[0019] Still further, the method may include locating the carbon dioxide-lean solvent regeneration unit adjacent at least one of (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network.

[0020] The method may include monitoring a pH and a conductivity of the carbon dioxidelean solvent and the carbon-dioxide-rich solvent in the air contactor and adjusting circulation of(a) the carbon dioxide-lean solvent to the air contactor and (b) the carbon dioxide-rich solvent from the air contactor in response to pH and conductivity values being monitored.

[0021] The method may include monitoring carbon dioxide concentration of the treated air and adjusting circulation of (a) the carbon dioxide-lean solvent to the air contactor and (b) the carbon dioxide-rich solvent from the air contactor in response to carbon dioxide concentration being monitored.Brief Description of the Drawing Figures

[0022] Figure 1A is a schematic illustration of the new and improved apparatus for directly capturing carbon dioxide from untreated air.

[0023] Figure IB is a schematic diagram of the control module for the apparatus illustrated in Figure 1A.

[0024] Figure 2 is a schematic illustration of a carbonate electrolyzer that may be used in the apparatus illustrated in Figure 1 A to regenerate carbon dioxide-lean solvent.

[0025] Figure 3 is a schematic illustration of how the apparatus of Figure 1 A may be deployed to provide a distributed network of air contactors supported by a carbon dioxide-lean solvent unit located adjacent to (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network.Detailed Description

[0026] Reference is now made to Figure 1 A which illustrates the new and improved apparatus 10 adapted for directly capturing carbon dioxide from ambient, untreated air. As shown, the apparatus 10 includes an air contactor 12, a carbon dioxide-lean solvent regeneration unit 14 and an alkaline solvent that circulates through the air contactor and the carbon dioxide-lean solvent regeneration unit.

[0027] More specifically, the air contactor 12 includes an untreated air inlet 16, a treated air outlet 18, a carbon dioxide-lean solvent inlet 20 and a carbon dioxide-rich solvent outlet 22. The carbon dioxide-lean solvent regeneration unit 14 includes an inlet 24 connected to the carbon dioxide-rich solvent outlet 22 and an outlet 26 connected to the carbon dioxide-lean solvent inlet20. The alkaline solvent circulating through the air contactor 12 and the carbon dioxide-lean solvent regeneration unit 14 may consist of, for example, sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof.

[0028] As shown in Figure 1A, pump 28 A, connected to the outlet 22, controls the flow of carbon dioxide-rich solvent from the air contactor 12 to the inlet 24 of the carbon dioxide-lean solvent regeneration unit 14. Pump 28B, connected to the outlet 26 of the carbon dioxide-lean solvent regeneration unit 14, controls the flow of regenerated carbon dioxide-lean solvent from the carbon dioxide-lean solvent regeneration unit to the carbon dioxide-lean solvent supply source 29 where a supply of carbon dioxide-lean solvent is maintained at all times. Pump 28C controls the flow of carbon dioxide-lean solvent from the supply source 29 to the carbon dioxide-lean solvent inlet 20 of the air contactor 12.

[0029] Figure IB illustrates the control module 50 for the apparatus 10. All of the pumps 28A, 28B and 28C may be under the control of a controller 52. The controller 52 may comprise a dedicated microprocessor or an electronic control unit operating in accordance with appropriate software. The controller 52 is adapted to optimize operation of the apparatus 10, making adjustments based on the alkalinity value and / or the conductivity value of the solvent as measured in the air contactor 12 by the pH monitor 54 and the conductivity monitor 56 at the air contactor and a carbon dioxide sensor 58 at the outlet 18.

[0030] The best operating range for alkalinity of the solvent is around 3 to 4 mol per kg of solvent, in which the alkalinity also represents the alkali cations, such as Na+, K+, and / or Li+ (shown as Na+ in Figure 2). Under such a condition, the mass transfer of capturing carbon dioxide is better, meaning capturing more carbon dioxide from the air. Smaller than 3 is detrimental to the mass transfer, which is due to not sufficient OH to capture the carbon dioxide. Greater than 4 is also not as good for mass transfer, which is due to the higher viscosity of solvent. The desired mass transfer value, according to our work, is above 1.5 mmol (CO2) hr-1 m-2 Pa-1.

[0031] In at least some embodiments, the carbon dioxide-lean solvent regeneration unit 14 comprises a carbonate electrolyzer 30. The carbonate electrolyzer 30 functions (a) to generate carbon dioxide and oxygen at the anode, (b) to generate hydrogen at the cathode and (c) to regenerate the carbon dioxide-lean solvent at the cathode.

[0032] As shown in Figure 2, the carbonate electrolyzer 30 includes an anolyte loop (generally designated by reference numeral 32) and an anode 34 in the anolyte loop. The carbonate electrolyzer 30 also includes a catholyte loop (generally designated by reference numeral 36) and a cathode 38 in the catholyte loop. Still further, the carbonate electrolyzer 30 includes a cation exchange membrane 40, separating the anolyte loop 32 and the catholyte loop 36, and a power source 42 connected to the anode and the cathode. The anode 34 may be a non corrosion anode, such as titanium, and the cathode 38 may be a non corrosion cathode, such as titanium. The titanium electrode surfaces may be treated by coating with a catalytic layer containing iridium, platinum, and / or ruthenium to optimize the chemical reactions for carbon dioxide release.

[0033] The control mechanism may be adjusted based on the pH value and / or conductivity value measured from the solvent in the air contactor 12. Hydrogen gas can be utilize to upgrade carbon dioxide gas purity by reducing oxygen gas concentration through depolarization, which may simultaneously occur within the electrolyzer 30. More specifically, hydrogen gas produced (via water splitting) at the catholyte loop can be directly supplied to the anolyte electrode via gas diffuse electrode, at which hydrogen (H2) is oxidized to H+, and then H+reacts with OH to produce H2O. The benefits are (1) minimizing O2 content, since OH is neutralized by H+rather than producing O2, and (2) reducing operating voltage, since OH oxidation requires a higher voltage in comparison to H2 oxidation.

[0034] As further illustrated in Figure 2, a first electrolyte tank 44 is provided in the anolyte loop 32 and a second electrolyte tank 46 is provided in the in the catholyte loop 36. Alkali-metal sulfate, such as sodium sulfate, may be used as an electrolyte or charge carrier in the carbonate electrolyzer 30 to reduce ionic resistance and achieve a lower operating voltage for more efficient and effective operation. The carbonate electrolyzer 30 can be configured with either a single pair of electrodes or multiple pairs of electrodes.

[0035] In one possible control mechanism, (1) when the pH of the solvent decreases to 11 or the remaining carbon dioxide concentration at the outlet 18 is close to 400 ppm, the controller 52 switches on pump 28 A to move a part of carbonate-rich solvent from air contractor 12 to the lean solvent regeneration unit 14, and then turns off pump 28 A. The controller 52 also turns on pump 28C to transfer an equal volume of carbonate-lean solvent from the lean solvent supply source 29to the air contactor 12, and then turns off pump 28C. Thus, pH of the solvent in the air contactor sump will increase, and correspondingly remaining carbon dioxide concentration will drop.

[0036] Controller 52 may also activate a pump 28B to transfer water or lower alkalinity solvent from the anolyte tank 44 to the catholyte tank 46. As shown in Fig.2, 011 and CO3 are consumed to form O2 and CO2, and Na+is pushed from anode to cathode across the membrane 40. So, the remaining species in anolyte is water eventually. The solvent regeneration process can also be controlled by the pH or conductivity of anolyte. For example, when the carbonate-rich solvent enters into the anolyte loop, pH is 11-13. The regeneration process makes the anolyte pH decrease. Once anolyte pH becomes 7, the regeneration process will be stopped followed by transferring water from the anolyte loop to catholyte loop (carbon dioxide-lean solvent supply source 29).

[0037] In one possible embodiment of the apparatus 10, carbon capture performance is controlled by pH / conductivity of the solvent circulated in the air contactor 12 or by remaining carbon dioxide concentration measured at the contactor outlet 18. For example, capturing carbon dioxide from air results in pH of the solvent being reduced due to the formation of carbonate and bicarbonate. Once pH of the solvent is equal to pH 11, carbonate-rich solvent cannot capture more carbon dioxide from the air.

[0038] The apparatus 10, described above, is useful in a new and improved method of directly capturing carbon dioxide from untreated air. That method may be broadly described as including steps of: (a) contacting untreated air containing carbon dioxide with a carbon dioxide-lean solvent in an air contactor 12, (b) absorbing carbon dioxide from the untreated air and generating a carbon dioxide-rich solvent and treated air, and (c) regenerating the carbon dioxide-lean solvent from the carbon dioxide-rich solvent by releasing carbon dioxide from the carbon dioxide-rich solvent in a carbon dioxide-lean solvent regeneration unit 14.

[0039] More specifically, in at least some embodiments, the regenerating step includes generating pH swings with a carbonate electrolyzer 30. This includes (a) applying electricity to the anode 34 and the cathode 38 at, for example, a current density (ratio of current to membrane geometric surface area) of 500 to 3,000 A / m2, (b) generating carbon dioxide and oxygen at the anode, (c) generating hydrogen at the cathode, and (d) regenerating the carbon dioxide-lean solventat the cathode. The method may also include using alkali-metal sulfate as an electrolyte in the carbonate electrolyzer to reduce ionic resistance and achieve a lower operating voltage.

[0040] Still further, the method includes the steps of: (a) distributing the carbon dioxide-lean solvent from a centrally located carbon dioxide-lean solvent regeneration unit 14 to a plurality of remotely located air contactors 12 and (b) returning carbon dioxide-rich solvent from the plurality of remotely located air contactors to the centrally located carbon dioxide-lean solvent regeneration unit. Still more specifically, the method includes locating the carbon dioxide-lean solvent regeneration unit 14 adjacent at least one of (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network. See Figure 3. The locating of the air contactors 12 at various, spaced locations remote from the carbon dioxide-lean solvent regeneration unit 14 adjacent at least one of (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network provides for more efficient and effective system operation and carbon dioxide capture from the ambient air. In some embodiments, the carbon-dioxide-lean solvent regeneration unit 14 is located 5 kilometers, 10 kilometers, 25 kilometers, 50 kilometers, 75 kilometers, 100 kilometers or more from each of the air contactors 12.

[0041] This document relates to the following aspects.Aspect 1. An apparatus for directly capturing carbon dioxide from untreated air, comprising: an air contactor having an untreated air inlet, a treated air outlet, a carbon dioxide-lean solvent inlet and a carbon dioxide-rich solvent outlet; a carbon dioxide-lean solvent regeneration unit having an inlet connected to the carbon dioxide-rich solvent outlet and an outlet connected to the carbon dioxide-lean solvent inlet; and an alkaline solvent circulating through the air contactor and the carbon dioxide-lean solvent regeneration unit.Aspect 2. The apparatus of aspect 1, wherein the alkaline solvent is selected from a group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof.Aspect 3. The apparatus of aspect 1 or aspect 2, wherein the air contactor may be coinstalled at one geo-site with solution regenerator or be installed at different geo-sites.Aspect 4. The apparatus of aspect 1 or aspect 2, wherein the air contactor and solvent regenerator may be connected by a hard-piped solution loop, or virtually connected via at least one of road, rail and water shipment.Aspect 5. The apparatus of aspect 1 or aspect 2, wherein the carbon dioxide-lean solvent regeneration unit is a carbonate electrolyzer.Aspect 6. The apparatus of aspect 5, wherein the carbonate electrolyzer includes an anolyte loop, an anode in the anolyte loop, a catholyte loop, a cathode in the catholyte loop, a cation exchange membrane separating the anolyte loop and the catholyte loop, and a power source connected to the anode and the cathode whereby (a) carbon dioxide and oxygen are generated at the anode, (b) hydrogen is generated at the cathode and (c) the carbon dioxide-lean solvent is regenerated at the cathode.Aspect 7. The apparatus of aspect 6, further including a first electrolyte tank in the anolyte loop and a second electrolyte tank in the catholyte loop.Aspect 8. The apparatus of aspect 7, including alkali-metal sulfate as an electrolyte to reduce ionic resistance and achieve a lower operating voltage.Aspect 9. The apparatus of aspect 1, wherein the air contactor includes a plurality of remotely located air contactors.Aspect 10. The apparatus of aspect 1, wherein the air contactor includes a plurality of air contactors co-hosted at a single processing site.Aspect 11. The apparatus of aspect 1, further including a control module including a controller connected to a pH monitor and a conductivity monitor whereby pH and conductivity of the alkaline solvent are monitored and the controller is adapted to adjust circulation of the alkaline solvent through the air contactor and the carbon dioxide-lean solvent regeneration unit for more efficient operation.Aspect 12. A method of directly capturing carbon dioxide from untreated air, comprising: contacting untreated air containing carbon dioxide with a carbon dioxide-lean solvent in an air contactor;absorbing, by air contactor, carbon dioxide from the untreated air and generating a carbon dioxide-rich solvent and treated air; and regenerating, by solvent regeneration unit, the carbon dioxide-lean solvent from the carbon dioxide-rich solvent by releasing carbon dioxide from the carbon dioxide-rich solvent in a carbon dioxide-lean solvent regeneration unit at same geo-site with air contactor or different geo-sites.Aspect 13. The method of aspect 12, including connecting the air contactors and solvent regeneration unit by a hard-piped solution loop at a geo-site.Aspect 14. The method of aspect 12, including transporting a capture solvent from a centrally located regeneration location to a plurality of remotely located air contactors via at least one of road, rail and water shipment.Aspect 15. The method of aspect 12, including locating the solvent regeneration unit adjacent at least one of (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network.Aspect 16. The method of aspect 12, wherein the regenerating includes generating pH swings with a carbonate electrolyzer.Aspect 17. The method of aspect 16, including applying electricity to an anode and a cathode, generating carbon dioxide and oxygen at the anode, generating hydrogen at the cathode and regenerating the carbon dioxide-lean solvent at the cathode.Aspect 18. The method of aspect 17, including using alkali-metal sulfate as an electrolyte in the carbonate electrolyzer to reduce ionic resistance and achieve a lower operating voltage.Aspect 19. The method of aspect 12, including monitoring a pH and a conductivity of the carbon dioxide-lean solvent and the carbon-dioxide-rich solvent in the air contactor and adjusting circulation of (a) the carbon dioxide-lean solvent to the air contactor and (b) the carbon dioxiderich solvent from the air contactor in response to pH and conductivity values being monitored.Aspect 20. The method of aspect 12, including monitoring carbon dioxide concentration of the treated air and adjusting circulation of (a) the carbon dioxide-lean solvent to the aircontactor and (b) the carbon dioxide-rich solvent from the air contactor in response to carbon dioxide concentration being monitored.

[0042] Each of the following terms written in singular grammatical form: “a”, “an”, and “the”, as used herein, means “at least one”, or “one or more”. Use of the phrase “One or more” herein does not alter this intended meaning of “a”, “an”, or “the”. Accordingly, the terms “a”, “an”, and “the”, as used herein, may also refer to, and encompass, a plurality of the stated entity or object, unless otherwise specifically defined or stated herein, or, unless the context clearly dictates otherwise. For example, the phrase: “an air contactor”, as used herein, may also refer to, and encompass, a plurality of air contactors.

[0043] Each of the following terms: “includes”, “including”, “has”, “having”, “comprises”, and “comprising”, and, their linguistic / grammatical variants, derivatives, or / and conjugates, as used herein, means “including, but not limited to”, and is to be taken as specifying the stated component(s), feature(s), characteristic(s), parameter(s), integer(s), or step(s), and does not preclude addition of one or more additional component(s), feature(s), characteristic(s), parameter(s), integer(s), step(s), or groups thereof.

[0044] The phrase “consisting of’, as used herein, is closed-ended and excludes any element, step, or ingredient not specifically mentioned. The phrase “consisting essentially of’, as used herein, is a semi-closed term indicating that an item is limited to the components specified and those that do not materially affect the basic and novel character! stic(s) of what is specified.

[0045] Terms of approximation, such as the terms about, substantially, approximately, etc., as used herein, refers to ± 10 % of the stated numerical value.

[0046] Although the apparatus and method of this disclosure have been illustratively described and presented by way of specific exemplary embodiments, and examples thereof, it is evident that many alternatives, modifications, or / and variations, thereof, will be apparent to those skilled in the art. Accordingly, it is intended that all such alternatives, modifications, or / and variations, fall within the spirit of, and are encompassed by, the broad scope of the appended claims.

Claims

What is claimed:

1. An apparatus for directly capturing carbon dioxide from untreated air, comprising: an air contactor having an untreated air inlet, a treated air outlet, a carbon dioxide-lean solvent inlet and a carbon dioxide-rich solvent outlet; a carbon dioxide-lean solvent regeneration unit having an inlet connected to the carbon dioxide-rich solvent outlet and an outlet connected to the carbon dioxide-lean solvent inlet; and an alkaline solvent circulating through the air contactor and the carbon dioxide-lean solvent regeneration unit.

2. The apparatus of claim 1, wherein the alkaline solvent is selected from a group consisting of sodium hydroxide, potassium hydroxide, lithium hydroxide and mixtures thereof.

3. The apparatus of claim 1 or claim 2, wherein the air contactor may be co-installed at one geosite with solution regenerator or be installed at different geo-sites.

4. The apparatus of claim 1 or claim 2, wherein the air contactor and solvent regenerator may be connected by a hard-piped solution loop, or virtually connected via at least one of road, rail and water shipment.

5. The apparatus of claim 1 or claim 2, wherein the carbon dioxide-lean solvent regeneration unit is a carbonate electrolyzer.

6. The apparatus of claim 5, wherein the carbonate electrolyzer includes an anolyte loop, an anode in the anolyte loop, a catholyte loop, a cathode in the catholyte loop, a cation exchange membrane separating the anolyte loop and the catholyte loop, and a power source connected to the anode and the cathode whereby (a) carbon dioxide and oxygen are generated at the anode, (b) hydrogen is generated at the cathode and (c) the carbon dioxide-lean solvent is regenerated at the cathode.

7. The apparatus of claim 6, further including a first electrolyte tank in the anolyte loop and a second electrolyte tank in the catholyte loop.

8. The apparatus of claim 7, including alkali-metal sulfate as an electrolyte to reduce ionic resistance and achieve a lower operating voltage.

9. The apparatus of claim 1, wherein the air contactor comprises a plurality of remotely located air contactors.

10. The apparatus of claim 1, wherein the air contactor comprises a plurality of air contactors cohosted at a single processing site.

11. The apparatus of claim 1, further including a control module including a controller connected to a pH monitor, a conductivity monitor and a carbon dioxide monitor whereby pH and conductivity of the alkaline solvent and carbon dioxide concentration at the treated air outlet are monitored and the controller is adapted to adjust circulation of the alkaline solvent through the air contactor and the carbon dioxide-lean solvent regeneration unit for more efficient operation.

12. A method of directly capturing carbon dioxide from untreated air, comprising: contacting untreated air containing carbon dioxide with a carbon dioxide-lean solvent in an air contactor; absorbing, by air contactor, carbon dioxide from the untreated air and generating a carbon dioxide-rich solvent and treated air; and regenerating, by solvent regeneration unit, the carbon dioxide-lean solvent from the carbon dioxide-rich solvent by releasing carbon dioxide from the carbon dioxide-rich solvent in a carbon dioxide-lean solvent regeneration unit at same geo-site with air contactor or different geosites.

13. The method of claim 12, including connecting the air contactors and solvent regeneration unit by a hard-piped solution loop at a geo-site.

14. The method of claim 12, including transporting a capture solvent from a centrally located regeneration location to a plurality of remotely located air contactors via at least one of road, rail and water shipment.

15. The method of claim 12, including locating the solvent regeneration unit adjacent at least one of (a) a geologic underground storage site, (b) a carbon dioxide utilization site and (c) a carbon dioxide transportation network.

16. The method of claim 12, wherein the regenerating includes generating pH swings with a carbonate electrolyzer.

17. The method of claim 16, including applying electricity to an anode and a cathode, generating carbon dioxide and oxygen at the anode, generating hydrogen at the cathode and regenerating the carbon dioxide-lean solvent at the cathode.

18. The method of claim 17, including using alkali-metal sulfate as an electrolyte in the carbonate electrolyzer to reduce ionic resistance and achieve a lower operating voltage.

19. The method of claim 12, including monitoring a pH and a conductivity of the carbon dioxidelean solvent and the carbon-dioxide-rich solvent in the air contactor and adjusting circulation of (a) the carbon dioxide-lean solvent to the air contactor and (b) the carbon dioxide-rich solvent from the air contactor in response to pH and conductivity values being monitored.

20. The method of claim 12, including monitoring carbon dioxide concentration of the treated air and adjusting circulation of (a) the carbon dioxide-lean solvent to the air contactor and (b) the carbon dioxide-rich solvent from the air contactor in response to carbon dioxide concentration being monitored.

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