ACID GAS REGENERABLE BATTERY

Abstract

A method of generating electricity from an amine-based acid gas capture process using an electrolytic cell containing an anode and a cathode and an amine based electrolyte comprising: contacting a metal based redox material with an amine based electrolyte in the presence of an anode to form a metal-ammine complex in solution; adding an absorbed or absorbable acid gas to the metal-ammine complex containing electrolyte to form an acid gas absorbed electrolyte; and contacting the acid gas absorbed electrolyte with a cathode deposit, wherein the acid gas breaks up the metal-ammine complex in the metal-ammine complex containing electrolyte thereby generating a potential difference between the anode and the cathode.

Claims

1. A method of generating electricity from an amine-based acid gas capture process using an electrolytic cell containing an anode and a cathode and an amine based electrolyte comprising: contacting a metal based redox material with an amine based electrolyte in the presence of an anode to form a metal-ammine complex in solution; adding an absorbed or absorbable acid gas to the metal-ammine complex containing electrolyte to form an acid gas absorbed electrolyte; and contacting the acid gas absorbed electrolyte with a cathode deposit, wherein the acid gas breaks up the metal-ammine complex in the metal-ammine complex containing electrolyte thereby generating a potential difference between the anode and the cathode.

2. A method according to claim 1, wherein the acid gas comprises at least one of CO.sub.2, NO.sub.2, SO.sub.2, H.sub.2S, HCl, HF, or HCN or a combination thereof.

3. A method according to claim 1, wherein the acid gas comprises a flue gas.

4. A method according to claim 1, wherein the acid gas includes CO.sub.2 as a major component.

5. A method according to claim 1, wherein the metal based redox material comprises at least one of Cu, Ni, Zn, Co, Pt, Ag, Cr, Pb, Cd, Hg, Pd or a combination thereof.

6. A method according to claim 1, wherein the metal comprises Cu, Ni or Zn, preferably Cu.

7. A method according to claim 1, wherein the anode and cathode comprise the metal based redox material.

8. (canceled)

9. A method according to claim 1, wherein the metal based redox material comprises a multivalent metal ion which is in a first valence state when in solution and a second valence state when in the metal-ammine complex.

10. A method according to claim 1, wherein the amine based electrolyte comprises the general formula R.sub.1R.sub.2R.sub.3N, wherein R.sub.1, R.sub.2 and R.sub.3 comprise hydrogen, unsubstituted or substituted C1-C20 alkyl, or unsubstituted or substituted aryl.

11. A method according to claim 1, wherein the amine based electrolyte comprises at least one of ammonia, alkylamines, alkanolamines, amino-acid salts or combination thereof.

12. A method according to claim 1, wherein the amine based electrolyte comprises at least one of: an amino acid salt selected from the group consisting of L-Arginine, Taurine, L-Threonine, L-Serine, Glutamic acid, Glycine, L-Alanine, Sarcosine, and L-Proline; an alkylamine selected from the group consisting of Ammonia, Propylamine, Butylamine, Amylamine, Ethylenediamine, 1,3 Diaminopropane, hexamethylenediamine, m-Xylylenediamine, 1-(3-aminopropyl)imidazole, Piperazine, 4-methylpiperidine, Pyrrolidine, 3-(dimethylamino)-1-propylamine, and N-Methyl-1,3-diaminopropane; an alkanolamine selected from the group consisting of Triethanolamine, 2-amino-2-methyl-1,3-propanediol, Diethanolamine, bis(2-hydroxypropyl)amine, 2-(2-Aminoethoxy)ethanol, Ethanolamine, 3-Amino-1-propanol and 5-Amino-1-pentanol; or an aqueous ammonia solution.

13. (canceled)

14. A method according to claim 1, wherein the metal based redox materials comprises Cu and the amine based electrolyte comprises ammonia and the metal-ammine complex comprises [Cu(NH.sub.3).sub.4].sup.2+.

15. (canceled)

16. A method according to claim 1, wherein a gas-liquid contactor is used to form the solution of acid gas to the metal-ammine complex containing electrolyte.

17. A method according to claim 1, wherein the method further includes the step of: after contacting the acid gas absorbed electrolyte with a cathode, heating the acid gas absorbed electrolyte to release the absorbed acid gas therefrom and thermally regenerate the amine based electrolyte.

18. (canceled)

19. A method according to claim 1, wherein the electrolytic cell includes an anode chamber and a cathode chamber, and the metal based redox material is contacted with an amine based electrolyte in the anode chamber, and wherein, in use, the electrolytic cell comprises a first electrode compartment and second electrode compartment that are cyclically interchanged as the anode chamber and the cathode chamber of the electrolytic cell.

20. (canceled)

21. (canceled)

22. (canceled)

23. An acid gas regenerable electrolytic cell comprising: a first electrode compartment containing an electrode comprising at least one metal based redox material and a first electrolyte comprising an amine based electrolyte; a second electrode compartment containing an electrode comprising at least one metal based redox material and a second electrolyte comprising an amine based electrolyte; and a gas-liquid contactor located to operatively contact at least one of the first electrolyte or second electrolyte to facilitate acid gas absorption within the electrolyte, wherein, in use, the first electrode compartment and second electrode compartment are cyclically interchanged as an anode compartment and an cathode compartment of the electrolytic cell.

24. An acid gas regenerable electrolytic cell according to claim 23, wherein the first electrode compartment and second electrode compartments are fluidly separated by an anion exchange membrane.

25. (canceled)

26. An acid gas regenerable electrolytic cell according to claim 23, wherein at least the first or second electrolyte comprises an amine based electrolyte having the general formula R.sub.1R.sub.2R.sub.3N, wherein R.sub.1, R.sub.2 and R.sub.2 comprise hydrogen, unsubstituted or substituted C1-C20 alkyl, or unsubstituted or substituted aryl.

27. An acid gas regenerable electrolytic cell according to claim 23, wherein the metal based redox material comprises at least one of Cu, Ni, Zn, Co, Pt, Ag, Cr, Pb, Cd, Hg, Pd or a combination thereof.

28. (canceled)

29. (canceled)

30. An acid gas regenerable electrolytic cell according to claim 23, wherein the first electrode compartment and second electrode compartment are cyclically interchanged as an anode compartment and an cathode compartment of the electrolytic cell when at least one of: a specified amount of metal based redox material is removed from the electrode; the potential difference/voltage between the anode and cathode falls below a specified level/voltage; a specified amount of amine based electrolyte is reacted; or the metal based redox material has contacted the amine based electrolyte is reacted for a specified amount of time.

31. (canceled)

32. (canceled)

33. (canceled)

34. (canceled)

35. (canceled)

36. (canceled)

37. (canceled)

38. (canceled)

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0089] The present invention will now be described with reference to the figures of the accompanying drawings, which illustrate particular preferred embodiments of the present invention, wherein:

[0090] FIG. 1 provides a general schematic of one embodiment an acid gas regenerable electrolytic cell incorporated into an acid gas capture process.

[0091] FIG. 2 provides a more detailed schematic of one embodiment of a regenerative electrolytic cell integrated post-combustion CO.sub.2 capture process according to the present invention.

[0092] FIG. 3 provides a perspective view of an experimental an acid gas regenerable electrolytic cell according to one embodiment of the present invention.

[0093] FIG. 4 provides an open circuit potential vs time plot for the experimental acid gas regenerable electrolytic cell shown in FIG. 3 discharging against a 1.2 ohm resistor.

[0094] FIG. 5 provides absorption spectra of the spent and regenerated solution using the experimental acid gas regenerable electrolytic cell shown in FIG. 3.

DETAILED DESCRIPTION

[0095] The present invention provides a method of generating electricity and an associated regenerable battery in which an amine-based acid gas-capture process can be utilised to generate electricity.

[0096] Capturing acid gasessuch as the greenhouse gas carbon dioxide (CO.sub.2) from coal-fired power station flue gasis extremely important in mitigating global warming and climate change. Post-combustion carbon capture technology using chemical absorbents is often considered as the most cost effective and feasible option for large-scale removal of CO.sub.2 from flue gases emitted from power plants and other industry facilities. One chemical absorbent of interest is aqueous ammonia-based CO.sub.2 capture technology due to its high CO.sub.2 absorption capacity, low regeneration energy, no sorbent degradation, cheap chemical cost, and simultaneous capture of multiple pollutants (including CO.sub.2, SO.sub.x, NO.sub.x, HCl and HF). Several pilot and demonstration plants have been constructed and operated to test the technical and economic feasibility of this technology by industry and research organisations such as Alstom, Powerspan, Commonwealth Scientific and Industrial Research Organisation (CSIRO), Korea Institute of Energy Research (KIER) and Research Institute of Industrial Science & Technology (RIST), implying promising industrial applications.

[0097] Amine-based capture processes, such as ammonia based CO.sub.2-capture processes require large amounts of (thermal) energy for regeneration of the amine solutions which have absorbed the CO.sub.2. The process economics must therefore account for a high parasitic energy penalty to regenerate the absorbent.

[0098] The present invention relates to the utilisation of captured acid gases such as CO.sub.2, NO.sub.2, SO.sub.2 and H.sub.2S to break up a metal-ammine complex formed between the anode metal and amine based electrolyte for electricity generation within an electrochemical energy conversion system utilising cyclic formation and destruction of that metal-ammine complex in aqueous solution. The concept is based on the formation and controllable break down of metal complexes in an aqueous solution using the captured acid gas.

[0099] Whilst not wishing to be limited to any one theory, the Inventors have found that a metal-ammine complex such as the Cu-ammine complex aCu(NH.sub.3).sub.41.sup.2) formed in reaction 1 can also be broken up by the addition of acid gases introduced into the solution by gas-liquid contact, producing free NH.sub.4.sup.+. Captured acid gases such as CO.sub.2, NO.sub.2, SO.sub.2 and H.sub.2S can therefore be used to break up the metal-ammine complex (for example [Cu(NH.sub.3).sub.4].sup.2) for electricity generation within an electrochemical energy conversion systems utilising cyclic formation and destruction of metal-ammine complexes in aqueous solutions.

[0100] The process of the present invention enables the recovery of part of the required thermal energy requirement as electrochemical energy. In some embodiments, the energy generated can be close to or in some cases equivalent to the parasitic energy penalty due to capture. In such embodiments, this could result in a small to zero energy penalties for CO.sub.2 capture.

[0101] The overall reactions in the electrochemical cell for the present invention when used to capture carbon dioxide are as follows:

Anode

Me(s)+nR.sub.1R.sub.2R.sub.3N(aq).fwdarw.[Me(R.sub.1R.sub.2R.sub.3N).sub.n].sup.z+(aq)+ze.sup.(3)

Addition of CO.sub.2 directly from flue gas

mCO.sub.2(aq)+[Me(R.sub.1R.sub.2R.sub.3N).sub.n].sup.z+(aq).fwdarw.nR.sub.1R.sub.2R.sub.3N(CO.sub.2).sub.m(aq)+Me.sup.z+(aq)(4)

Cathode

Me.sup.z+(aq)+ze.sup..fwdarw.Me(s)(5)

[0102] Reaction 4 and 5 might be integrated in the cathode compartment when the absorption of CO.sub.2 occurs in the electrode compartment:

mCO.sub.2(aq)+[Me(R.sub.1R.sub.2R.sub.3N).sub.n].sup.z+(aq)+ze.sup..fwdarw.nR.sub.1R.sub.2R.sub.3N(CO.sub.2).sub.m(aq)+Me(s)(6)

[0103] Where R (i.e. R.sub.1 R.sub.2 R.sub.3) typically represents groups taken from or a combination of H, or CH.sub.2, and/or CH.sub.3, or CH.sub.2OH, or CH.sub.2NH.sub.2, or SO.sub.3.sup., or COO.sup.. More generally, in these reactions (and as discussed above) R.sub.1, R.sub.2 and R.sub.3 can comprise hydrogen, unsubstituted or substituted C1-C20 alkyl, or unsubstituted or substituted aryl, and Me is a metal selected from at least one of Cu, Ni, Zn, Co, Pt, Ag, Cr, Pb or a combination thereof, and more preferably one of Cu, Ni or Zn. z corresponds to the valancy/cation charge of the respective metal Me. For primary/secondary monoamines, m=0.5; for primary/secondary diamines, m=1; for tertiary amine or sterically hindered amine or diamines, m=1. As defined previously, the unsubstituted or substituted C1-C20 alkyl, or unsubstituted or substituted aryl, can contain a variety of one or more substituents selected from C1-C6 alkyl which is unsubstituted (to form an aralkyl group), aryl which is unsubstituted, cyano, amino, C1-C10 alkylamino, di(C1-C10)alkylamino, arylamino, diarylamino, arylalkylamino, amido, acylamido, hydroxy, halo, carboxy, alcohol (i.e. OH), ester, acyl, acyloxy, C1-C20 alkoxy, aryloxy, haloalkyl, sulfhydryl (i.e. thiol, SH), C1-10 alkylthio, arylthio, sulfonic acid, phosphoric acid, phosphate ester, phosphonic acid and phosphonate ester and sulfonyl. It should be appreciated that in embodiments, at least one of R.sub.1, R.sub.2 and R.sub.3 may include alcohol group substituents.

[0104] One specific example is where Cu-ammine complex can be used for CO.sub.2-absorption and using the reaction products in an electro-chemical cell provides a pathway towards generation of electricity. Apart from ammonia other amines will have a similar propensity to form complexes with metal ions.

[0105] The following reactions will take place on the electrodes:

Anode

Cu(s)+4NH.sub.3(aq).fwdarw.[Cu(NH.sub.3).sub.4].sup.2+(aq)+2e.sup.(7)

Addition of CO.sub.2 directly from flue gas

2CO.sub.2(aq)+[Cu(NH.sub.3).sub.4].sup.2+(aq).fwdarw.2NH.sub.4.sup.+(aq)+2NH.sub.2COO.sup.(aq)+Cu.sup.2+(aq)(8)

Cathode

Cu.sup.2+(aq)+2e.sup..fwdarw.Cu(s)(9)

[0106] Reactions 8 and 9 might be integrated in the cathode compartment when the absorption of CO.sub.2 occurs in the electrode compartment:

2CO.sub.2(aq)+[Cu(NH.sub.3).sub.4].sup.2+(aq)+2e.sup..fwdarw.2NH.sub.4+(aq)+2NH.sub.2COO.sup.(aq)+Cu(s)(10)

[0107] After deposition of Cu on the cathode, the aqueous mixture containing the carbamate and ammonium ion can be thermally regenerated in which CO.sub.2 is released from the solution and the recovered ammonia is reused for Cu-dissolution in the anode compartment.

[0108] The overall reaction stoichiometry involves 2 mole of CO.sub.2 per mole of Cu being dissolved or deposited.

[0109] It should be appreciated that the above reaction scheme could be equally applied to other acid gases, such as SO.sub.2, H.sub.2S, HCl, HF, HCN, in which case the carbamate formation does not take place and a simple acid-base reaction takes place. Reaction 11 gives the example for SO.sub.2:

4SO.sub.2(aq)+[Cu(NH.sub.3).sub.4].sup.2+(aq)+4H.sub.2O(aq).fwdarw.4NH.sub.4.sup.+(aq)+4HSO.sub.3.sup.(aq)+Cu.sup.2+(aq)(11)

[0110] Reaction 11 and 9 might be integrated in the cathode compartment when the absorption of SO.sub.2 occurs in the electrode compartment:

4SO.sub.2(aq)+[Cu(NH.sub.3).sub.4].sup.2+(aq)+4H.sub.2O(aq)+2e.sup..fwdarw.4NH.sub.4.sup.+(aq)+4HSO.sub.3.sup.(aq)+Cu(s)(12)

[0111] The overall reaction stoichiometry involves 4 mole of SO.sub.2 per mole of Cu being dissolved or deposited.

[0112] It should be appreciated that reactions 11 and 12 are also applicable to CO.sub.2 interactions with tertiary amines or sterically hindered amines, i.e. where CO.sub.2 reacts to form bicarbonate instead of carbamate.

[0113] A number of redox suitable metals can be used in the process and electrochemical cell of the present invention include Cu, Ni, Zn, Co, Pt, Ag, Cr, Pb or the like. The overall suitability of these metals depends on the electrode potential and the ability for amines to form complexes with these metals. The solubility of metals salts in aqueous solutions might pose a limit on the concentrations at which these metals can be used.

[0114] Advantageously, the use of metal ions can suppress volatilisation of selected amine based electrolytes in embodiments of the present invention. For example, ammonia has an intrinsically high volatility, which results in high ammonia loss during absorption and regeneration processes. The recovery of ammonia requires extra energy and facilities, adding costs to the CO.sub.2 capture process. Moreover, vaporised ammonia can react with CO.sub.2 in the gas phase in the presence of moisture and generate crystalline deposits which are predominantly comprised of ammonium bicarbonate capable of scale formation on associated surfaces of equipment. Reference 3 teaches that the addition of Me(II) ions (Ni, Cu and Zn) in ammonia based electrolytes significantly reduced ammonia loss in absorption and regeneration processes, and only slightly decreased the rate of CO.sub.2 absorption. The order of ammonia suppression efficiency found was Ni(II)>Cu(II)>Zn(II). The regeneration result also showed that metal additives can accelerate the CO.sub.2 desorption rate.

[0115] Apart from ammonia, other amines such as alkylamines, alkanolamines, amino-acid salts have the capability to form complexes with metal ions. For CO.sub.2, the reaction for primary amines and secondary amines which form carbamates when in contact with CO.sub.2 would be identical to the ones described for ammonia shown above (reactions 7 to 12).

[0116] The acid gas absorbed electrolyte can be thermally regenerated to enable reuse in the process. Here, the acid gas absorbed electrolyte is heated to release the absorbed acid gas therefrom and leaving a substantially acid gas free amine based electrolyte. For example, where the acid gas comprises CO.sub.2 and the amine based electrolyte comprises ammonia, the regeneration reaction comprises the recovering ammonia and CO.sub.2 from the carbamate and ammonium ion:

2NH.sub.4.sup.++2NH.sub.2COO.sup.+heat.fwdarw.4NH.sub.3+2CO.sub.2(13)

[0117] The regenerated amine based electrolyte (e.g. recovered ammonia) is recycled for use in the step of contacting the anode metal with the amine based electrolyte in the anode compartment or chamber of the electrolytic cell.

[0118] The above reactions can be utilised to harvest the enthalpy released by the reaction of the acid gas with the amine based electrolyte. In current acid gas (for example CO.sub.2) treatment processes this enthalpy is simply cooled away as the temperature levels are too low to be of practical use. Given that electrochemical energy conversion is not limited by the Carnot efficiency, the conversion efficiency can be quite high and be similar to flow batteries (0.75).

[0119] FIG. 1 shows an acid gas capture absorption enthalpy conversion process 100 according to one embodiment of the present invention. This process 100 includes the following fluidly linked process units: [0120] Absorber 110, a gas-liquid contactor in which an acid gas rich feed 120 is fed into and contacted with a lean amine solution 127, typically the amine based electrolyte to absorb the acid gas, to produce a rich amine solution 128 comprising the acid gas absorbed electrolyte. An acid gas lean stream 122 is emitted from the absorber 110; [0121] Absorption enthalpy converter 110 (typically in the form of a regenerable flow battery 210see FIG. 2 and description below for more details) comprises an electrolytic cell in which the above described reactions are undertaken to generate power. Electrolyte stream 126 and 127 flow out from (stream 126) and into (stream 127) the absorption enthalpy converter 110. [0122] Heat exchanger 114 used to exchange or transfer heat from electrolyte input stream 127 (higher temperature stream which flows from the desorber 116 where the electrolyte is heated) to electrolyte output stream 126 (lower temperature stream which flows from the absorption enthalpy converter 110); and [0123] Desorber 116, preferably a stripping unit which is used to strip the acid gas from the electrolyte. As shown in FIG. 2, this typically uses a reboiler heated from a suitable heat source 123 (thermal, solar, waste heat, geothermal or the like) to strip the acid gas from the electrolyte. The acid gas product stream 124 exits the desorber 116, whilst the electrolyte is recycled back into the absorption enthalpy converter 110.

[0124] The schematic details of one form of absorption enthalpy converter 110 are shown in FIG. 2. It should be appreciated that components in FIG. 2 which correspond to components illustrated in FIG. 1 have been given the same reference numeral PLUS 100.

[0125] The process described above in relation to FIG. 1 can be implemented using an acid gas regenerable electrolytic cell 210 as shown in FIG. 2. The illustrated electrolytic cell 210 is constructed with at least a pair of electrode compartments, being an anode electrode compartment 240 and a cathode electrode compartment 242 which each contain an electrode 244, 246 formed from the metal based redox material, such as Cu or the like and an electrolyte comprising the amine based electrolyte discussed above. Each of the electrode compartments 240 and 242 contain an amine based electrolyte, and are separated by an anion-exchange membrane 248. The anion-exchange membrane 248 localises the electrolyte reactions to the relevant electrodes. The absorber 210 is fluidly connected to the anode compartment 240, with electrolyte flowing from the anode compartment 240 to the absorber 210 to absorb fed acid gas 220 therein. The rich solvent 228 is then fed into the cathode compartment 242 where reaction 4 occurs. The desorber/stripper 210 are fluidly connected to the cathode compartment 246, with electrolyte flowing from the cathode compartment 242 to the stripper 216 to desorb or strip the absorbed acid gas content from the rich electrolyte. Reboiler 223 is used to heat the electrolyte to a suitable stripping temperature. A condenser 225 is used to condense any electrolyte vapour near a gas exit of the stripper 216 to ensure that electrolyte is not emitted with the acid gas flow 224 exiting the stripper 216. The resulting lean electrolyte 227A from the stripper 216 is then fed into the anode compartment 240. A heat exchanger 214 is used to transfer heat from the lean electrolyte stream 227A fed from stripper 216 to the rich solvent stream 228A being flowing from the cathode compartment 242. Ideally, the amount of electrolyte flowing from each of the anode and cathode compartments 240 and 242 to the absorber 210 and stripper 216 respectively are substantially the same, preferably the same, so as to maintain the volume of electrolyte in each of these compartments 240 and 242.

[0126] The electrode compartments 240 and 242 are used as transposable Anode and Cathodes (reversible polarity) where they can be interchanged from functioning as a cathode compartment and an anode compartment. Therefore, in use, the illustrated anode compartment 240 and cathode compartment 242 are selectively interchanged, preferably periodically interchanged to function as an anode compartment and a cathode compartment of the battery. The absorber 210 therefore feeds the electrolyte in the respective anode compartment a solution of absorbed or absorbable acid gas to form an acid gas absorbed electrolyte.

[0127] For example, for the Cu-ammonia system shown in reactions 7 to 10, following initial formation of the Cu-ammine complex in the anode compartment, CO.sub.2 is captured, forming the ammonium carbamate and releasing copper(II) ions into solution. This is a spontaneous process. The anode compartment is then transposed, to become the cathode compartment for the next discharge. Another batch of ammonia is injected into the other compartment (anode side). NH.sub.3+CO.sub.2 are regenerated using the stripper for ammonia consumption reasons. This interposes CO.sub.2 capture in the NH.sub.3-processing side of the electrolytic cell.

[0128] The amine based electrolyte is therefore only used as an anolyte (electrolyte surrounding an anode) that reacts with the copper electrode as waste heat warms the electrolyte, generating electricity. When the reaction uses up the amine component of the electrolyte or depletes the metal ions in the electrolyte near the cathode the reaction stops. The addition of the acid gas then is used to distil the amine component of the electrolyte from the used anolyte. The regenerated electrolyte is then added to the cathode chamber. The electrolytic cell/battery's polarity reverses and the anode becomes the cathode and vice versa.

[0129] It should be appreciated that the process could be operated as an integrated gas/liquid contactor and electrochemical reactor, with the acid gas absorption and both anode and cathode integrated in the same compartment or stack. In this embodiment, the amine based electrolyte could react in the anode compartment with the metal based redox material, typically the metal anode, to form the metal-ammine complex. The cathode compartment includes a gas-liquid contacting arrangement, for example a porous gas-liquid contacting membrane, which enables an acid gas to be directly absorbed into the electrolyte in the anode compartment. In this arrangement, the metal-ammine complex undergoes direct reduction in the presence of an acid gas. Metal is then deposited on the cathode, as shown in reaction (14).

2CO.sub.2+[Cu(NH.sub.3).sub.4].sup.2++2e.fwdarw.2NH.sub.4.sup.++2NH.sub.2COO.sup.+Cu(14)

[0130] The electrolyte can then be regenerated using a heating process, or flow to a separate regenerative process, such as a stripper 216 shown in FIG. 2 to desorb the acid gas therefrom. In this way, the acid gas is intimately involved in the electrochemistry and, may provide an energy gain and a process intensification, depending on its effect on the reduction potential for copper.

[0131] In some embodiments, the acid gas, such as high purity CO.sub.2 could also be recycled back into the electrolyte in the anode compartment. In this way, the gas could be used to generate electricity in a similar cycle as a heat engine such as an Organic Rankine Cycle.

EXAMPLES

Example 1: Cu(NO.SUB.3.).SUB.2 .and NH.SUB.4.NO.SUB.3 .Battery

[0132] A Cu-ammonia CO.sub.2 regenerative battery was prepared according to one embodiment of the present invention.

[0133] Two cells were prepared with solutions of 0.1 M Cu(NO.sub.3).sub.2 and 5 M NH.sub.4NO.sub.3 in 50 ml beakers. One cell was charged to 2 M NH.sub.4OH from a 5M solution, the other cell was topped up with water to balance the concentrations. Adding the NH.sub.4OH changes the colour from light blue to dark blue (Cu(NO.sub.3).sub.2 to Cu(NH.sub.3).sub.4) A salt bridge filled with 5 M NH.sub.4NO.sub.3 was used to complete the circuit and copper electrodes were cut from copper film supplied by Sigma Aldrich.

[0134] The potential difference between the two cells was 0.34 V. Various current and power density measurements were recorded before running the battery down. The spent anolyte (containing Cu(NH.sub.3).sub.4) was taken and exposed to CO.sub.2 for more than an hour. No colour change from the disruption of the Cu(NH.sub.3).sub.4 was apparent by eye. However, the pH changed from 8.6 to 6.9 after this CO.sub.2 exposure.

Example 2: Alternate Cu(NO.SUB.3.).SUB.2 .and NH.SUB.4.NO.SUB.3 .Battery

[0135] A further experiment was conducted using a larger cell constructed from two 3d printed polycarbonate half cells as shown in FIG. 3. An ion selective membrane was used as supplied by Selemion. Two equal sized electrodes were cut from 1 mm thick copper foam supplied by Gelon Lib group.

[0136] The cells were charged in the same way as described in Example 1 using 0.1 M Cu(NO.sub.3).sub.2 and 5 M NH.sub.4NO.sub.3 and 2 M NH.sub.4OH for the anolyte and 0.1 M Cu(NO.sub.3).sub.2 and 5 M NH.sub.4NO.sub.3 for the catholyte, an open circuit potential of 0.5 V was recorded. Chronopotentiometry was recorded for the cell discharging against a 1.2 ohm resistor and is shown in FIG. 4. The consumed NH.sub.3 solution was treated with solid CO.sub.2 to regenerate the solution without evaporating NH.sub.3. This time, the original NH.sub.3 free solution was charged with NH.sub.3 and run against the CO.sub.2 regenerated solution, an open circuit potential of 0.19 V was recorded along with chronopotentiometry as shown in the figure. The potential recorded demonstrates the possibility of using a CO.sub.2 or other acid gas to disrupt the Cu[NH.sub.3].sub.x complex and thereby recharge the battery.

[0137] The absorption spectra of the spent and regenerated solution were are shown in the FIG. 5. A15 nm blue shift in the absorption peak of the CO.sub.2 sample was observed. This is consistent with a change in the solution from the dominant species in solution being Cu(NH.sub.3).sub.5 to the dominant species being Cu(NH.sub.3).sub.4, as seen in literature data (for example Bjerrum, j., Nielsen, E. J., Acta Chemica Scandinavica, 2 (1948) 297-318). This also fits with modelling data using the stability constants that show as the pH is decreased from >11 to pH<8 Cu(NH.sub.3).sub.5 is replaced as the dominant species by Cu(NH.sub.3).sub.4 (International Journal of Greenhouse Gas Control, (2014), 54-63).

Example 3: Applicable Metals

[0138] Several metals could potentially be used for the process. For aqueous ammonia solutions data on metal-amine equilibria is commonly available. Table 1 provides examples of the metals that could be used in combination with ammonia as the complexing agent and the open circuit potential determined from the equilibrium constants. The acid gas carbon dioxide (CO.sub.2) will react with ammonia via the carbamate formation step:

CO.sub.2+2NH.sub.3->NH.sub.4.sup.++NH.sub.2COO.sup.(15)

and bicarbonate formation step:

CO.sub.2+NH.sub.3+H.sub.2O->NH.sub.4.sup.++HCO.sub.3.sup.(16)

[0139] The maximum of energy (or work) that could be produced by the reactions of the ammonia complexes with carbon dioxide can be determined by the Gibbs free energy difference for the redox reactions as determined by:

G=W.sub.max=zFE

where z is the charge transferred, F equals the Faraday constant (96485 C/mol) and E is the open circuit voltage.

TABLE-US-00001 TABLE 1 Open circuit voltage for a range of metals with ammonia [1] Maximum Cathode Anode work * reaction and reaction and Open circuit [KJ/mol potential potential potential, V CO.sub.2] Co.sup.2+ + [Co(NH.sub.3).sub.4].sup.2+ + +0.145 14.00 2e .fwdarw. Co(s) 2e .fwdarw. Co(s) + 4NH.sub.3 E = 0.277 V E = 0.422 V Cd.sup.2+ + [Cd(NH.sub.3).sub.4].sup.2+ + +0.219 21.12 2e .fwdarw. Cd(s) 2e .fwdarw. Cd(s) + 4NH.sub.3 E = 0.403 V E = 0.622 V Ni.sup.2+ + [Ni(NH.sub.3).sub.6].sup.2+ + +0.233 14.98 2e .fwdarw. Ni(s) 2e .fwdarw. Ni(s) + 6NH.sub.3 E = 0.257 V E = 0.49 V Zn.sup.2+ + [Zn(NH.sub.3).sub.4].sup.2+ + +0.277 26.72 2e .fwdarw. Zn(s) 2e .fwdarw.Zn(s) + 4NH.sub.3 E = 0.763 V E = 1.04 V Cu.sup.2+ + [Cu(NH.sub.3).sub.4].sup.2+ + +0.380 36.67 2e .fwdarw. Cu(s) 2e .fwdarw.Cu(s) + 4NH.sub.3 E = +0.34 V E = 0.04 V Ag.sup.+ + [Ag(NH.sub.3).sub.2].sup.+ + +0.430 41.48 e .fwdarw. Ag(s) e .fwdarw. Ag(s) + 2NH.sub.3 E = +0.80 V E = +0.37 Hg.sup.2+ + [Hg(NH.sub.3).sub.4].sup.2+ + +0.570 55.00 2e .fwdarw. Hg(l) 2e .fwdarw. Hg(l) + 4NH.sub.3 E = +0.8535 V E = +0.283 V Pd.sup.2+ + [Pd(NH.sub.3).sub.4].sup.2+ + +0.915 88.28 2e .fwdarw. Pd(s) 2e .fwdarw. Pd(s) + 4NH.sub.3 E = +0.915 V E = 0.0 V Pt.sup.2+ + [Pt(NH.sub.3).sub.6].sup.2+ + +1.044 67.16 2e .fwdarw. Pt(s) 2e .fwdarw. Pt(s) + 6NH.sub.3 E = +1.188 V E = +0.144 V Note: * maximum work calculation based on the CO.sub.2 reacting with ammonia via carbamate formation to completely release free metal ions from the complex. [1] Speight, J. G., 2005. Lange's Handbook of Chemistry, 16th edition. McGraw-Hill Companies, Inc, Laramie, Wyoming, Table 1.358 and 1.380

Example 4: Applicable Amines

[0140] A wide range of amines can be applied in the process in the amine base electrolyte, including alkanolamines, alkylamines and amino-acid salts solutions.

[0141] An electrochemical cell was designed and manufactured using a 3-D printer. It was subsequently operated to evaluate the battery energy performance using different metals and amines by connecting the Potentiostat Electrochemical Systems (Autolab PGSTAT12, Metrohm). The cell consists of anode and cathode compartments separated by an anion exchange membrane (AEM, Selemion AMV, Japan) with surface area 6.96 cm.sup.2. The distance of two electrodes is 1.0 cm to decrease the solution resistance. Ag/AgCI reference electrodes (199 my versus Standard Hydrogen Electrode, Pine research) was used to monitor the potential changes for anode and cathode electrode. Table 2 and Table 3 provide the experimental results of power generation performance using different amine base electrolytes and metals at room temperature (20-22 C.). The catholyte is CO.sub.2-loaded which is representative of the solution after CO.sub.2 absorption, while the anolyte is non CO.sub.2-loaded representative of the solution after CO.sub.2 desorption. Each catholyte and anolyte contains 2M amines, 0.1 M Cu(II) and 1 M NH.sub.4NO.sub.3 or 1 M KNO.sub.3 as supporting electrolyte.

Example 5

[0142] Using the procedure described in Example 4, experiments were carried for Zn as the metal active in the electrochemical cell. Each catholyte and anolyte contains 2M amines, 0.1 M Zn(II) and 1 M NH.sub.4NO.sub.3 or 1 M KNO.sub.3 as supporting electrolyte.

[0143] Table 3 provides the experimental results of power generation performance using different amines at room temperature (20-22 C.).

TABLE-US-00002 TABLE 2 Results summary of energy performance using different amines and Cu/Cu.sup.2+ as the redox couple Measured Open maximum circuit power CO.sub.2 loading potential, density, No. Solvent Structure pKa in cathode v W/m.sup.2* Amino acid salts (neutralised by KOH) 1 L-Arginine [00001] 8.99 1.28 0.09 0.15 2 Taurine [00002] 9.06 0.42 (solid) 0.24 2.52 3 L-Threonine [00003] 9.1 0.45 0.096 0.79 4 L-Serine [00004] 9.15 0.48 0.092 0.49 5 Glutamic acid [00005] 9.47 0.28 0.11 0.27 6 Glycine [00006] 9.6 0.50 0.144 1.21 7 L-Alanine [00007] 9.69 0.51 0.20 1.48 8 Sarcosine [00008] 10.05 0.48 0.145 0.52 9 L-Proline [00009] 10.6 0.59 0.182 0.91 Alkylamines 1 Ammonia NH.sub.3 9.24 0.5 0.09 0.96 2 Propylamine [00010] 10.93 0.61 0.22 3.52 3 Butylamine [00011] 10.65 0.5 0.19 2.37 4 Amylamine [00012] 10.81 0.5 (volatile) 0.27 4.83 5 Ethylenediamine [00013] 9.93 0.96 0.24 2.93 6 1,3 Diaminopropane [00014] 10.4 1.0 0.25 3.23 7 hexamethylenediamine [00015] 10.9 1.1 0.24 2.88 8 m-Xylylenediamine [00016] 9.2 0.81 (precipitation) 0.28 4.20 9 1-(3-aminopropyl)- imidazole [00017] 9.6 0.75 0.12 0.81 10 Piperazine [00018] 9.73 0.84 0.21 2.88 11 4-methylpiperidine [00019] 11.27 0.56 0.13 0.91 12 Pyrrolidine [00020] 11.35 0.61 0.2 1.05 13 3-(dimethylamino)-1- propylamine [00021] 1.03 0.21 2.6 14 N-Methyl-1,3- diaminopropane [00022] 1.03 0.20 1.39 Alkanolamines 1 Triethanolamine [00023] 7.76 0.56 0.09 0.38 2 2-amino-2-methyl-1 3- propanediol [00024] 8.8 0.63 0.14 1.25 3 Diethanolamine [00025] 8.88 0.55 0.14 1.56 4 bis(2-hydroxypropyl)- amine [00026] 9.1 0.47 0.12 0.76 5 2-(2-Aminoethoxy)- ethanol [00027] 9.3 0.52 0.22 3.34 6 Ethanolamine [00028] 9.5 0.49 0.214 2.17 7 3-Amino-1-propanol [00029] 10 0.64 0.268 2.73 8 5-Amino-1-pentanol [00030] 10.5 0.56 0.218 2.82 Note: * the power density is calculated based on the effective membrane area.

TABLE-US-00003 TABLE 3 Results summary of energy performance using different amines and Zn/Zn.sup.2+ as the redox couple Measured CO.sub.2 Open maximum loading circuit power in potential, density, No. Solvent Structure pKa cathode V W/m.sup.2* 1 Ammonia NH.sub.3 9.24 0.5 0.11 2.57 2 Propylamine [00031] 10.93 0.53 0.133 0.53 3 3-Amino-1-propanol [00032] 10 0.55 0.24 0.52 4 5-Amino-1-pentanol [00033] 10.5 0.51 0.09 2.50 5 Piperazine [00034] 9.73 0.815 0.15 0.79 6 Ethylenediamine [00035] 9.93 0.96 0.15 1.64 7 1,3 Diaminopropane [00036] 10.4 1.0 0.21 3.5 8 hexamethylenediamine [00037] 10.9 1.09 0.142 1.06 Note: * the power density is calculated based on the effective membrane area

Example 6

[0144] Using the procedure described in example 4, an experiment was conducted for Co.sup.2+/Co.sup.3+ representing a valence changeable metal for the redox couple in the electrochemical cell. The use of multi-valence metals enables the full flow battery without alternating the metal electrode used in Examples 4 and 5, as the electrodes are not affected by metal dissolution or deposition. Graphite was used as the electrode material for the electron transfer. Each catholyte and anolyte contained 1 M NH.sub.4NO.sub.3 as supporting electrolyte. Table 4 provides the experimental open circuit potential at room temperature (20-22 C.).

TABLE-US-00004 TABLE 4 Experimental results of open circuit potential using Co.sup.2+/Co.sup.3+ as redox couple Anolyte Catholyte Open circuit No. Solvent composition composition potential, V 1 Ammonia 2M NH.sub.3 2M NH.sub.3; 0.01 .sup.a (NH.sub.3) 0.5 CO.sub.2 loading 2 Ammonia 2M NH.sub.3, 2M NH.sub.3; .sup.0.16 .sup.b (NH.sub.3) 0.2M Co.sup.2+/ 0.5 CO.sub.2 loading; 0.2M Co.sup.3+ 0.2M Co.sup.2+/0.2M Co.sup.3+ 3 Ethanolamine 4M MEA; 4M MEA; 0.25 (MEA) 0.1M Co.sup.2+/ 0.35 CO.sub.2 loading; 0.1M Co.sup.3+ 0.1M Co.sup.2+/0.1M Co.sup.3+ Note: .sup.a The open circuit potential of the test without the redox couple; .sup.b Fine particle were observed in the cathode compartment.

[0145] A non-exhaustive list of applications for the process and the electrolytic cell of the present invention are as follows: [0146] Acid gas treatment: Power can be generated from the separation of acid gas in conventional gas treatment. The present invention could for example supply part of the electrical energy requirement of an LNG train or a compression process. [0147] Biogas treatment: The production of methane from biogas using an amine based process could provide electricity as well. The need to remove CO.sub.2 to produce sales gas quality could be used beneficially to generate power, in addition to the high quality methane product. [0148] CO.sub.2-capture from air: CO.sub.2 capture from air could be used to generate power directly with regeneration of the liquid absorbents being carried e.g. by solar thermal energy. In some forms, a small scale system could be utilised to generate electricity through CO.sub.2 capture from air (for example during night time) when power is needed for lighting etc. with regeneration of the liquid absorbents occurring during the day. In particular, amino-acid salt solution could be used for this purpose as they have no vapour pressure and hence no losses to the atmosphere. [0149] CO.sub.2-capture from flue gas (Post Combustion CapturePCC): A PCC process with the present invention could have an energy consumption close to its thermodynamic minimum. [0150] Regenerative desulphurisation: Apart from CO.sub.2, other gases like SO.sub.2 can be utilised in the process of the present invention as described above. In one example, the present invention could be used as part of the CANSOLV processan amine based desulphurisation process. [0151] Coal seam gas conditioning: Coal seam gas has relatively low CO.sub.2 content (<1%) which is removed in a central unit before the liquefaction. The present invention could be used to generate power from decentralised CO.sub.2-separation processes with the power used for gas compression processes. [0152] Miscellaneous CO.sub.2-removal applications: Other CO.sub.2-removal applications may include use in submarines, space-crafts and greenhouses where amine based scrubbing processes are used, and can include the present invention. Again, in some forms the capture of CO.sub.2 from a combustion facility (or maybe from air) at night could provide electricity for use in lighting or other power applications. The CO.sub.2-stored in the liquid absorbent can be released during the day using solar thermal energy. This can be particularly relevant to greenhouse applications, where CO.sub.2 is injected into the greenhouse during daytime to promote plant growth and crop production. At night light is required to sustain the photo-synthesis processes in the plants. Using the process of this invention the electricity required could be generated through the absorption of CO.sub.2. [0153] Operation with pure CO.sub.2 (or other acid gas), where CO.sub.2 released from the liquid absorbent regeneration would be fed back to the metal-ammine solution and re-absorbed. The system will work as a heat engine with the heat of regeneration converted into electricity.

[0154] Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is understood that the invention includes all such variations and modifications which fall within the spirit and scope of the present invention.

[0155] Where the terms comprise, comprises, comprised or comprising are used in this specification (including the claims) they are to be interpreted as specifying the presence of the stated features, integers, steps or components, but not precluding the presence of one or more other feature, integer, step, component or group thereof.

REFERENCES

[0156] 1. Enhancing Low-Grade Thermal Energy Recovery in a Thermally Regenerative Ammonia Battery Using Elevated Temperatures, Fang Zhang, Nicole LaBarge, Wulin Yang, Jia Liu and Bruce E. Logan, ChemSusChem 2015, 8, 1043-1048. [0157] 2. A thermally regenerative ammonia-based battery for efficient harvesting of low-grade thermal energy as electrical power, Fang Zhang, Nicole LaBarge, Wulin Yang, Jia Liu and Bruce E. Logan Energy Environ. Sci., 2015, 8, 343-349. [0158] 3. Theoretical and experimental study of NH.sub.3 suppression by addition of Me (II) ions (Ni, Cu and Zn) in an ammonia based CO.sub.2 capture process, Kangkang Li, Hai Y, Moses Tade, Paul Feron, International Journal of Greenhouse Gas Control 24 (2014) 54-63.