ELECTROCHEMICALLY ENHANCED PROCESS FOR NEXT GENERATION CARBON DIOXIDE CAPTURE

Abstract

Disclosed herein are methods of electrochemically enhanced amine-based CO.sub.2 capture and systems for performing the methods of amine-based CO.sub.2 capture. The present methods and systems advantageously may be carried out at ambient temperatures and allow for reusing the amine through multiple cycles.

Claims

1. A method of capturing CO.sub.2, comprising: i) reacting a CO.sub.2 source gas with a stoichiometric excess of an amine in an aqueous solution to form an amine-CO.sub.2 complex, thereby forming a solution comprising the amine-CO.sub.2 complex; ii) electrochemically adjusting the pH of the solution comprising the amine-CO.sub.2 complex to less than 7, thereby releasing CO.sub.2 from the amine-CO.sub.2 complex; and iii) collecting the released CO.sub.2 as a concentrated vapor.

2. The method of claim 1, wherein the amine-CO.sub.2 complex comprises carbamate ions.

3. The method of claim 1, wherein adjusting the pH is performed via water electrolysis.

4. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 6.

5. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 5.

6. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 4.

7. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 3.

8. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 2.

9. The method of claim 1, wherein the pH of the solution after adjustment is about 0.5 to about 1.5.

10. The method of claim 1, wherein the pH of the solution after adjustment is about 5 to about 6.

11. The method of claim 1, wherein the amine is a primary amine, a secondary amine, a tertiary amine, or a mixture thereof.

12. The method of claim 11, wherein the amine is a primary amine or a secondary amine.

13. The method of claim 11, wherein the amine has a structure of formula I:
R.sub.xNH.sub.3-x,  (I); wherein R is selected from an optionally substituted alkyl, ether, and hydroxyalkyl; x is 1, 2 or 3, and; one or more R, together with each N, optionally forms a nitrogen containing heterocycle.

14. The method of claim 11, wherein the amine is chosen from monoethanolamine, 2-ethylaminoethanol, 2-methylaminoethanol, ethylenediamine, benzylamine, diethanolamine, pyrrolidine, morpholine, 2,6-dimethylmorpholine, monoisopropanolamine, piperazine 2-(dimethylamino)ethanol, N-tert-butyldiethanolamine, 3-dimethylamino-1-propanol, 3-(dimethylamino)-1,2-propanediol, 2-diethylaminoethanol, 3-diethyl amino-1,2-propanediol, 3-diethylamino-1-propanol, triethanolamine, 1-dimethylamino-2-propanol, 1-(2-hydroxyethyl)pyrrolidine, 1-diethylamino-2-propanol, 3-pyrrolidino-1,2-propanediol, 2-(diisopropylamino)ethanol, 1-(2-hydroxyethyl)piperidine, 2-(dimethylamino)-2-methyl-1-propanol, 3-piperidino-1,2-propanediol, 3-dimethylamino-2,2-dimethyl-1-propanol, 3-hydroxy-1-methylpiperidine, N-ethyldiethanolamine, 1-ethyl-3-hydroxypiperidine, and any combination thereof.

15. The method of any one of claim 14, wherein the amine is ##STR00001## or a mixture thereof.

16. The method of claim 14, wherein the amine is: ##STR00002##

17. The method of claim 14, wherein the amine is: ##STR00003##

18. The method of claim 1, wherein the concentration of the amine in the aqueous amine solution is about 10% to about 50% v/v.

19. The method of claim 18, wherein the concentration of the amine is about 15% to about 40% v/v.

20. The method of claim 18, wherein the concentration of the amine is about 20 to about 30% v/v.

21. The method of claim 1, wherein the CO.sub.2 source gas is an effluent from an industrial source.

22. The method of claim 21, wherein the gas from the industrial source comprises about 1 to about 12% v/v CO.sub.2.

23. The method of claim 1, wherein the CO.sub.2 source gas is from an atmospheric source.

24. The method of claim 1, wherein adjusting the pH is performed at a temperature of less than 100° C.

25. The method of claim 1, further comprising regenerating and collecting the aqueous amine solution and using the regenerated amine in step (i) of the method.

26. The method of claim 1, wherein the concentrated vapor comprises about 2% to about 99% CO.sub.2.

27. A system for capturing CO.sub.2 from a CO.sub.2 source gas comprising: a CO.sub.2 absorption chamber configured to contain an aqueous amine solution, the CO.sub.2 absorption chamber having a CO.sub.2 source gas inlet, and a concentrated CO.sub.2 vapor outlet; an electrochemical cell in fluid communication with the CO.sub.2 absorption chamber and configured to receive a CO.sub.2-rich aqueous amine solution from the CO.sub.2 absorption chamber, the electrochemical cell comprising: an anode disposed in an anode chamber, a cathode disposed in a cathode chamber, a first cation exchange membrane disposed between the anode chamber and a first reservoir configured to receive a CO.sub.2-rich aqueous amine solution such that protons may flow from the anode chamber to the first reservoir, an anion exchange membrane disposed between the first reservoir and a salt reservoir such that anions from the salt reservoir may flow towards the anode chamber, a second cation exchange membrane disposed between the salt reservoir and the cathode chamber such that cations may flow from the salt reservoir toward the cathode chamber; and an anion exchange column in fluid communication with the electrochemical cell and configured to: receive a CO.sub.2-lean aqueous amine solution from the first reservoir, deliver a regenerated aqueous amine solution to the CO.sub.2-absorption chamber, and receive a catholyte from the cathode chamber.

28. The system of claim 27, further comprising a concentrated CO.sub.2 vapor outlet.

29. The system of claim 26, further comprising an H.sub.2 outlet in fluid communication with the cathode chamber, an O.sub.2 outlet in fluid communication with the anode chamber, or both.

30. The system of claim 27, wherein the electrochemical cell is configured to perform water electrolysis.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a schematic of an exemplary CO.sub.2 capture process in accordance with the present disclosure. CO.sub.2 is absorbed from a gaseous stream, such as atmospheric air or industrial process gas, into an aqueous amine solution. CO.sub.2 is then desorbed from the amine via electrochemically induced acidification. The amine solution is regenerated using a strong base anion exchange resin so that it may be used for further CO.sub.2 absorption. The strong base anion exchange resin may then be regenerated using the alkaline catholyte produced during the electrochemical step.

[0037] FIG. 2 is a schematic of an exemplary electrochemical cell 200 useful in amine-based CO.sub.2 capture comprising a cathode 201, an anode 202, a second cation exchange membrane 203, an anion exchange membrane 204, a first cation exchange membrane 205, a base solution 206, a salt solution 207, an amine solution 208, and an acid solution 209.

[0038] FIG. 3 is a graph depicting pH values (circles) and extents of CO.sub.2 desorption (triangles) at various proton to MEA ratios for 22 vol % aqueous MEA solutions with CO.sub.2 loadings of 0.25 (grey) and 0.5 (black) mol CO.sub.2 per mol MEA.

[0039] FIG. 4A shows IR spectra of CO.sub.2-rich 22% v/v MEA solutions (˜0.5 mol CO.sub.2 per mol MEA) at various pH values from an electrochemically induced acidification cell. The black line represents CO.sub.2-rich MEA prior to acidification. FIG. 4B shows regeneration extent for MEA solutions after acidification to pH ˜6-8 followed by alkalization to pH>10. In FIG. 4B, * represents the use of HCl/NaOH, # represents electrochemical acidification followed by NaOH addition, and ° represents electrochemical acidification followed by ion exchange. All experiments were carried out using a 22% v/v MEA solution with an initial loading of ˜0.5 mol CO.sub.2 per mol MEA.

[0040] FIG. 5 depicts an exemplary system for a plant design 500 comprising a CO.sub.2 absorption chamber 501, electrochemical cell 502, and anion exchange column 503. A CO.sub.2-containing source gas is brought into a CO.sub.2 absorption chamber 501 via inlet 504. CO.sub.2 absorption chamber 501 is configured to contain an aqueous amine solution, where CO.sub.2 is absorbed by the amine. The CO.sub.2-rich aqueous amine solution flows into the electrochemical cell (505), where protons generated at the anode (506) cross a first cation exchange membrane (508) to desorb the CO.sub.2. The protonated, CO.sub.2-lean amine solution next passes (515) through the anion exchange column 503, where the chlorine counter-ion is replaced with hydroxide. The regenerated amine solution completes the closed-loop and returns (518) to the CO.sub.2 absorption chamber 501 to absorb additional CO.sub.2.

DETAILED DESCRIPTION

[0041] The present disclosure generally provides methods and systems for amine-based carbon capture. More specifically, the disclosure provides in some embodiments a method of capturing CO.sub.2, comprising: reacting a CO.sub.2 source gas with an aqueous solution comprising a stoichiometric excess of an amine to form an amine-CO.sub.2 complex; adjusting the pH of the solution electrochemically to less than about 7, thereby releasing CO.sub.2 from the amine-CO.sub.2 complex; and collecting the released CO.sub.2 as a concentrated vapor. In certain embodiments, the disclosure advantageously allows for regeneration of amine solution at ambient temperatures (e.g., less than 100° C., preferably about −10 to about 50° C. and more preferably about 10 to about 40° C. and 100° C.). CO.sub.2 absorption in a basic (e.g., pH greater than about 8, greater than about 9, or preferably greater than about 10) aqueous amine solution occurs via reaction of CO.sub.2 with the amine to form stable a carbamate ion and protons/hydronium ions. The present methods advantageously electrochemically induce a pH shift to decompose the carbamate ion via acid-hydrolysis. This pH-shift to pH≤7 occurs at ambient temperature, and therefore, (1) uses simpler process equipment, (2) allows for amine regeneration and thus, maximizes working capacity and (3) reduces solvent loss. In some embodiments, the pH is adjusted to less than 7, less than 6, less than 5, less than 4, less than 3, less 2 or less than 1. In some embodiments, the pH is adjusted to about 0.5 to about 7, about 0.5 to about 6, about 0.5 to about 5, about 0.5 to about 4, about 0.5 to about 3, about 0.5 to about 2, or about 0.5 to about 1. In some embodiment, the pH is adjusted to about 5 to about 6, while in other embodiments, the pH is adjusted to about 0.5 to about 1.5.

[0042] In some embodiments, the energy intensity of the present methods is about 2× lower (e.g., 2.0 MWh per ton CO.sub.2) than current state-of-the-art amine-based CO.sub.2 capture processes (4.0 MWh per ton CO.sub.2 for KOH and >5.0 MWh per ton CO.sub.2 for MEA.sup.1-3), with reduced hazardous chemical inputs and the possibility of using renewable energy. In some embodiments, the disclosure herein provides amine-based CO.sub.2 capture processes (FIG. 1), which integrate electrochemical cells for ambient-temperature regeneration of the aqueous amine solution. In some embodiments, the amine-based processes of the present disclosure include electrochemically generated acidification to desorb the CO.sub.2, thereby reducing heat and power requirements and to increase working solvent capacity. These process improvements may advantageously lead to reduced size, and land requirements, and environmental footprints of CO.sub.2 capture systems.

Energy-Efficient Electrochemical Regeneration of Amine Solutions

[0043] Under basic conditions (pH>10), CO.sub.2 absorption occurs via the reaction of CO.sub.2 with the amine (e.g., MEA; RNH.sub.2 where R═CH.sub.2CH.sub.2OH) to form carbamate anions (RNHCOO.sup.−, RNCOO.sup.2−), protonated amines (RNH.sub.3.sup.+), and protons/hydronium ions (H.sup.+/H.sub.3O.sup.+), according to Equations 1-3, while other gases, such as N.sub.2 and O.sub.2, escape in the effluent. CO.sub.2 also forms carbonates at high pH (Equation 4).sup.4.

RNH.sub.2+CO.sub.2.fwdarw.H.sup.++RNHCOO.sup.−  (1)

RNHCOO.sup.−+RNH.sub.2.fwdarw.RNH.sub.3.sup.++RNCOO.sup.2−  (2)

RNHCOO.sup.−+H.sub.2O.fwdarw.H.sub.3O.sup.++RNCOO.sup.2−  (3)

CO.sub.2+H.sub.2O.fwdarw.CO.sub.3.sup.2−+2H.sup.+  (4)

[0044] Electrochemically shifting the pH of the solution to acidic conditions (e.g., pH≤7) favors the decomposition of the carbamate ions via acid-hydrolysis according to the reverse of Equations (1) and (3). Water electrolysis generates the protons for carbamate ion hydrolysis, thereby converting a CO.sub.2-rich amine solution to a CO.sub.2-lean solution, and hydroxide ions that are used to increase the pH of the CO.sub.2-lean solution for subsequent cycles of CO.sub.2 absorption.

[0045] In certain embodiments, protons are generated from an aqueous solution at the anode with hydroxide ions generated at the cathode in an electrochemical cell (FIG. 2) according to equations 5 and 6:

2H.sub.2O(l).fwdarw.O.sub.2(g)+4H.sup.+(aq)+4e.sup.−;E.sub.0=1.23V vs. SHE  (5)

4H.sub.2O(l)+4e.sup.−.fwdarw.2H.sub.2(g)+4OH.sup.−(aq);E.sub.0=−0.83V vs. SHE  (6)

[0046] In certain embodiments, the protons diffuse into the CO.sub.2-rich amine solution across a cation exchange membrane (CEM) resulting in a decrease in the pH which leads to the decomposition of carbamate ions and release of CO.sub.2. In certain embodiments, the CEM prevents diffusion of carbamate anions into the anode chamber, thereby preventing electrooxidation of carbamates/amine. In certain embodiments, a concentrated salt solution (e.g., NaCl or NaNO.sub.3) provides counter anions to the amine solution and cations to the catholyte to maintain electroneutrality. In certain embodiments, an anion exchange membrane (AEM) prevents the diffusion of the salt solution cations into the aqueous amine chamber. In certain embodiments, after CO.sub.2 is released, the CO.sub.2-lean amine solution is restored to high pH using a strong base anion exchange resin (see FIG. 1). In certain embodiments, this resin exchanges the counterions (Cl.sup.− or NO.sub.3.sup.−) from the salt reservoir that have accumulated in the amine solution with hydroxide ions to increase the pH of the CO.sub.2-lean aqueous amine solution to its original basic value. The strong base anion exchange resin is then regenerated using the hydroxide rich solution from the cathode chamber of the electrochemical cell, thereby recovering the anions used in the salt solution chamber. In certain embodiments, the regeneration process allows efficient recycling of the aqueous amine solution, thereby minimizing operating costs and preventing waste generation.

[0047] Accordingly, the present electrochemically-induced pH-swing process of the present disclosure has the advantages of replacing hazardous, expensive, and carbon-intensive reagents (e.g., mineral acids) with an abundant and benign proton source (e.g., water), while optionally leveraging renewable energy to facilitate the process.

[0048] While not being bound by theory, using water electrolysis for amine regeneration according to the present methods has at least two significant advantages. First, performing water electrolysis in isolated anode/cathode cell chambers allows for localized generation of protons without using stoichiometric or expensive/exotic regents, catalysts, or materials, and with reduced risk of electrochemical degradation of the amines/electrodes. Second, water electrolysis at the cathode generates H.sub.2, thereby providing an opportunity for realistic energy requirements of 2.0 MWh/tonne CO.sub.2 by capturing and using the evolved H.sub.2. An additional benefit of using electrochemical processes is that up to 100% of the required energy can be supplied from renewable sources. These features impact both the process equipment and energy efficiencies. Complete or near complete regeneration of the amine molecules at ambient temperature can be achieved via acid-mediated carbamate decomposition. This impacts process equipment by (1) reducing the amount of amine used by an amount that is proportional to the CO.sub.2 working capacity increase and (2) replacing complex distillation towers with simpler, modular electrochemical cells and, in some embodiments, separate anion exchange columns. Simpler process equipment has the potential for reducing CAPEX (e.g., less than the >$60 million investment cost for an amine stripper column.sup.7) and increasing the flexibility and modularity of the system, both of which would allow for the use of the process in a wider array of applications including concentrated and dilute CO.sub.2 streams (e.g., capture from industrial process and directly from air). In some embodiments, the concentration of the absorbed CO.sub.2 may range from 300 ppm to 250,000 ppm. In certain such embodiments, the concentration of the absorbed CO.sub.2 may range from 350 ppm to 20,000 ppm. In certain embodiments, preferably wherein the method of the disclosure is being used for direct air capture of CO.sub.2, the concentration of CO.sub.2 may range from 400 ppm to 1,000 ppm.

[0049] Realistic energy requirements for the electrochemically enhanced amine process can be estimated based on the number of protons required to desorb CO.sub.2 and on electrolyzers operating at ˜80% efficiency (e.g., 68 kWh per kg H.sub.2 produced.sup.18 assuming a thermodynamic demand of 54.8 kWh/kg for the stoichiometric hydrogen evolution reaction and oxygen evolution reaction as shown in equations (5) and (6).sup.19). For example, titration of a 22% MEA solution at various CO.sub.2 loadings (FIG. 3; 0.25 and 0.5 mol CO.sub.2 per mol MEA) shows that ˜1.0 mol of H.sup.+ per mol of amine is used for a pH decrease from 12 to 0.6, at which point all of the CO.sub.2 is desorbed. From this information, energy requirements can be estimated for certain embodiments of disclosure: (1) Direct Air Capture with an initial MEA loading is 0.25 mol CO.sub.2 per mol MEA.sup.20 and (2) industrial effluents containing between 1-12% CO.sub.2 (initial loading of 0.5 mol CO.sub.2 per mol MEA).

[0050] In some embodiments, the ratio of protons to CO.sub.2 is ˜4 for complete desorption in a Direct Air Capture application. In some such embodiments, using currently available electrolyzers, the process would require 6.3 MWh/tonne CO.sub.2 removed. In certain embodiments, if ˜70% of the H.sub.2 energy is recovered, this value decreases to 3.8 MWh/tonne CO.sub.2 removed. At 95% cell efficiency, the energy requirements may be 5.3 and 2.8 MWh/tonne CO.sub.2 without and with H.sub.2 recovery, respectively. By comparison, for a traditional thermal swing process, the reboiler duty required to desorb CO.sub.2 from a loading of 0.30 to 0.25 mol CO.sub.2 per mol MEA is ˜5.0 MWh/tonne CO.sub.2.sup.3, and the duty required for complete desorption would be >25 MWh/tonne CO.sub.2.sup.3, 20. This preliminary energy analysis indicates that, in certain embodiments, the methods or apparatuses of the disclosure could not only currently be carried out at much lower energy requirements than traditional thermal swing processes (6.3 versus 25.0 MWh/tonne CO.sub.2), but could also potentially achieve a factor of 5× higher working capacity (0.25 versus 0.05 mol CO.sub.2/mol MEA).

[0051] For applications with effluents containing >1% CO.sub.2, the energy requirements decrease. In certain embodiments, e.g., assuming that the initial MEA loading is about 0.5 mol CO.sub.2 per mol MEA, the ratio of protons to CO.sub.2 is ˜2 for complete desorption. At an 80% efficiency, the methods of certain embodiments of the disclosure would require about 3.1 MWh/tonne CO.sub.2 removed. If ˜70% of the H.sub.2 energy is recovered, this value decreases to about 1.9 MWh/tonne CO.sub.2 removed. In certain embodiments, at 95% cell efficiency, the energy requirements are about 2.6 and about 1.4 MWh/tonne CO.sub.2 without and with H.sub.2 recovery, respectively. By comparison for a traditional thermal swing process, the reboiler duty required to desorb CO.sub.2 from a loading of 0.5 to 0.25 mol CO.sub.2 per mol MEA is ˜1.3 MWh/tonne CO.sub.2.sup.5. This duty increases to >2.2 MWh/tonne CO.sub.2 for desorption to less than 0.20 mol CO.sub.2 per mol MEA and is >5 MWh/tonne CO.sub.2 for desorption from less concentrated amines (i.e., from 0.3 to 0.2 mol CO.sub.2 per mol MEA).sup.5. Based on these studies, the duty required for complete desorption would be >25 MWh/tonne CO.sub.2 because CO.sub.2 desorption is thermodynamically un-favored at low CO.sub.2 loadings.sup.5. This preliminary energy analysis indicates that the process could currently be carried out at comparable energy requirements as traditional thermal swing processes (1.9 versus 1.3 MWh/tonne CO.sub.2) but could potentially achieve a factor of 2 higher working capacity (0.5 versus 0.25 mol CO.sub.2 per mol MEA).

[0052] Some embodiments of the disclosure include a method of capturing CO.sub.2, comprising: reacting CO.sub.2 with a solvent capable of forming an anionic complex; adjusting the pH of the solution electrochemically to less than about 7; collecting the CO.sub.2 as a concentrated vapor that is released during or after the pH adjusting step; and optionally collecting the regenerated solvent. In some embodiments, the anionic complex comprises carbamate ions and/or a hydroxide (e.g., sodium hydroxide, potassium hydroxide). In some embodiments, the solvent is an amine. In some embodiments, the amine is R.sub.xNH.sub.3-x, wherein R is selected from an optionally substituted alkyl, ether, or alcohol.

[0053] Exemplary embodiments of amines include Primary Amines (e.g., monoethanolamine (MEA), 2-ethylaminoethanol, 2-methylaminoethanol, ethylenediamine, benzylamine); Secondary Amines (e.g., diethanolamine (DEA), pyrrolidine, morpholine, 2,6-dimethylmorpholine, monoisopropanolamine, piperazine (PZ)); Tertiary Amines (e.g., 2-(dimethylamino)ethanol (DMAE), N-tert-butyldiethanolamine (tBDEA), 3-dimethylamino-1-propanol (DMA-1P), 3-(dimethylamino)-1,2-propanediol (DMA-1,2-PD), 2-diethylaminoethanol (DEAE), 3-diethylamino-1,2-propanediol (DEA-1,2-PD), 3-diethylamino-1-propanol (DEA-1P), triethanolamine (TEA), 1-dimethylamino-2-propanol (DMA-2P), 1-(2-hydroxyethyl)pyrrolidine [1-(2HE)PRLD], 1-diethylamino-2-propanol (DEA-2P), 3-pyrrolidino-1,2-propanediol (PRLD-1,2-PD), 2-(diisopropylamino)ethanol (DIPAE), 1-(2-hydroxyethyl)piperidine [1-(2HE)PP], 2-(dimethylamino)-2-methyl-1-propanol (DMA-2M-1P), 3-piperidino-1,2-propanediol (3PP-1,2-PD), 3-dimethylamino-2,2-dimethyl-1-propanol (DMA-2,2-DM-1P), 3-hydroxy-1-methylpiperidine (3H-1MPP), N-ethyldiethanolamine, 1-ethyl-3-hydroxypiperidine), and mixtures thereof.

[0054] In certain embodiments, the pH adjusting step is performed via water electrolysis. In certain embodiments, the CO.sub.2 source gas is an effluent from an industrial source. In some embodiments, the pH adjusting step is performed at a temperature of less than 100° C. In some embodiments, the regenerated amine is collected and used for the same process again. In some embodiments, the CO.sub.2 source gas is from an atmospheric source. In further embodiments, the CO.sub.2 source gas is a mixture of industrial and atmospheric sources.

[0055] In certain embodiments, the disclosure provides system, such as the one shown in FIG. 5. FIG. 5 depicts an exemplary system for a plant design 500 comprising a CO.sub.2 absorption chamber 501, electrochemical cell 502, and anion exchange column 503. A CO.sub.2-containing source gas is brought into a CO.sub.2 absorption chamber 501 via CO.sub.2 source gas inlet 504. CO.sub.2 absorption chamber 501 is configured to contain an aqueous amine solution, where CO.sub.2 is absorbed by the amine, and further includes a scrubbed gas outlet (519). The CO.sub.2-rich aqueous amine solution flows (505) into a first reservoir 523 in the electrochemical cell (502). Protons generated at the anode (506) are disposed in anode chamber 522 and can pass a first cation exchange membrane (508) and into the first reservoir to desorb the CO.sub.2, thereby producing a CO.sub.2-lean amine solution. Anode chamber further includes an O outlet 512. The first reservoir is further in fluid communication with a salt reservoir 524 via an anionic exchange membrane 511, such that anions can flow into the first reservoir. Electrochemical cell 502 further includes concentrated CO.sub.2 vapor outlet 514. Salt reservoir 524 is in fluid communication with cathode chamber 525 via a second cation exchange membrane 510, such that cations can flow into the cathode chamber towards cathode 507. Cathode chamber 525 further includes H.sub.2 outlet 513. The CO.sub.2-lean amine solution is delivered (515) through the anion exchange column 503, where the chlorine counter-ion is replaced with hydroxide. A salt solution flows (516) back to salt reservoir 524, and catholyte flows from the cathode chamber to the anion exchange column. The regenerated amine solution completes the closed-loop and returns (518) to the CO.sub.2 absorption chamber 501 to absorb additional CO.sub.2. A sweep gas also may be provided to the system via inlet 519 to aid the desorbed gas flow. Finally, one-way (520) and two-way (521) valves can control flow in and out of anion exchange column 503.

[0056] The terms “a,” “an,” and “the” include plural referents unless the context clearly dictates otherwise. Thus, for example, reference to an object can include multiple objects unless the context clearly dictates otherwise.

[0057] As used herein, the terms “substantially,” “substantial,” “approximately,” and “about,” and the symbol “˜,” are used to describe and account for small variations. When used in conjunction with an event or circumstance, the terms can refer to instances in which the event or circumstance occurs precisely as well as instances in which the event or circumstance occurs to a close approximation. When used in conjunction with a numerical value, the terms can refer to a range of variation of less than or equal to ±10% of that numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. For example, a first numerical value can be deemed to be “substantially” the same or equal to a second numerical value if the first numerical value is within a range of variation of less than or equal to ±10% of the second numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%.

[0058] Additionally, amounts, ratios, and other numerical values are sometimes presented herein in a range format. It is to be understood that such range format is used for convenience and brevity and should be understood flexibly to include numerical values explicitly specified as limits of a range, but also to include all individual numerical values or sub-ranges encompassed within that range as if each numerical value and sub-range is explicitly specified. For example, a ratio in the range of about 1 to about 200 should be understood to include the explicitly recited limits of about 1 and about 200, but also to include individual ratios such as about 2, about 3, and about 4, and sub-ranges such as about 10 to about 50, about 20 to about 100, and so forth.

EXAMPLES

[0059] A proof-of-concept of the electrochemical pH-swing system was performed using a modified electrochemical cell containing four chambers (FIG. 2). The dimensions of the cell were ˜20 cmט14 cmט5.0 cm. The anode (˜8 cm.sup.2 of platinum immersed in ˜0.5 M Na.sub.2SO.sub.4; ˜2.9 cm thickness) and cathode (—8 cm.sup.2 of 316 stainless steel in ˜0.5 M NaCl; ˜0.7 cm thickness) chambers were separated from a saturated salt (NaNO.sub.3) solution (˜0.7 cm thickness) and a CO.sub.2-rich MEA solution (˜0.5 mol CO.sub.2 per mol MEA; ˜0.7 cm thickness) using cation (˜160 cm.sup.2; Fuel cell store, FAS-PET-130) and anion exchange membranes (˜160 cm.sup.2; Fuel cell store, FAA-3-PK-75).

[0060] Next, to demonstrate the effectiveness of the electrochemical cells of some embodiments of the disclosure, ˜50 mL of 22% v/v aqueous MEA solution was saturated with CO.sub.2 via bubbling CO.sub.2 until a liquid phase loading of ˜0.5 mol CO.sub.2 per mol MEA was achieved. The liquid phase loading was quantified by continuously measuring, via gas phase infrared (IR) spectroscopy, the CO.sub.2 concentration in the gas phase effluent from the bubbling chamber, and then numerically integrating the resulting concentration versus time curve. The CO.sub.2-rich MEA solution was loaded into the amine chamber with ˜1 M NaNO.sub.3 in the salt reservoir chamber and an overpotential was applied. CO.sub.2 desorption was confirmed via infrared (IR) spectroscopy of MEA samples collected at various pH values. FIG. 4A shows that the presence of carbamate ions (with characteristic peaks at 1568, 1486, 1320 cm.sup.−1) decreases with a concomitant increase in the amount of protonated MEA (characteristic peak at 1517 cm.sup.−1) as the experiment proceeds (and as the pH decreases). Furthermore, the peak at 1340 cm.sup.−1 indicates the presence of nitrate ions (NO.sub.3.sup.−) accumulating in the amine solution via migration from the salt reservoir to maintain electroneutrality.

[0061] The extent of CO.sub.2 desorption at pH=˜6, ˜7, and ˜8 was quantified by shifting the pH of these amine solutions (using NaOH) to ˜10 followed by contacting with the gaseous CO.sub.2 stream. This method indicated that a pH decrease from ˜10 to ˜6 corresponded to a >80% extent of desorption/regeneration (FIG. 4B, Blue bars) at ambient temperature (˜25° C.). This regeneration extent was similar to that achieved by adding aliquots of ˜5 M HCl followed by ˜1M NaOH to achieve a similar pH shift (i.e., HCl addition to decrease from ˜10 to ˜6, ˜7, or ˜8 followed by NaOH addition to increase back to ˜10; FIG. 4B, *). To demonstrate the effectiveness of anion exchange resins to complete the pH-swing process, in certain embodiments, electrochemically acidified MEA (at pH=˜6, ˜7, and ˜8) was mixed with a commercial anion exchange resin (˜200 ml of IRN78-OH) in a batch reactor for ˜5 min. The solutions were then filtered to recover the resin and to test the MEA solution for CO.sub.2 absorption. The pH of MEA solutions after exposure to the resin increased to ˜11, and their capacities for CO.sub.2 reabsorption were similar to those of the previous experiments (FIG. 4B, #). Specifically, electrochemically acidifying a CO.sub.2-rich MEA solution to pH=˜6 followed by exchange with IRN78-OH to pH=˜11 resulted in recovery of >80% of the initial absorption capacity. These results clearly demonstrate the effectiveness of the electrochemical-ion exchange pH-swing process for MEA regeneration at ambient temperature without capacity loss.

[0062] While the disclosure has been described with reference to the specific embodiments thereof, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the true spirit and scope of the disclosure as defined by the appended claim(s). In addition, many modifications may be made to adapt a particular situation, material, composition of matter, method, operation or operations, to the objective, spirit and scope of the disclosure. All such modifications are intended to be within the scope of the claim(s) appended hereto. In particular, while certain methods may have been described with reference to particular operations performed in a particular order, it will be understood that these operations may be combined, sub-divided, or re-ordered to form an equivalent method without departing from the teachings of the disclosure. Accordingly, unless specifically indicated herein, the order and grouping of the operations are not a limitation of the disclosure. As will be apparent to those of skill in the art upon reading this disclosure, each of the individual embodiments described and illustrated herein has discrete components and features which may be readily separated from or combined with the features of any of the other several embodiments without departing from the scope or spirit of the present invention. Any recited method can be carried out in the order of events recited or in any other order which is logically possible.

[0063] All publications and patents cited in this specification are herein incorporated by reference as if each individual publication or patent were specifically and individually indicated to be incorporated by reference and are incorporated herein by reference to disclose and describe the methods and/or materials in connection with which the publications are cited. The citation of any publication is for its disclosure prior to the filing date and should not be construed as an admission that the present invention is not entitled to antedate such publication by virtue of prior invention. Further, the dates of publication provided may be different from the actual publication dates which may need to be independently confirmed.

[0064] This invention is not limited to particular embodiments described, as such may, of course, vary. It is also to be understood that the terminology used herein is for the purpose of describing particular embodiments only, and is not intended to be limiting, since the scope of the present invention will be limited only by the appended claims.

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