Enrichment Method

Abstract

The present invention relates to a method of carbon-13 isotope (13C) enrichment, the method comprising: (i) applying a voltage to a cathode located in a cathode chamber of an electrochemical cell; (ii) flowing a feed stream comprising CO2 to the cathode chamber, wherein the feed stream contacts the cathode causing reduction of CO2 to form one or more products; and (iii) unreacted CO2 leaving the cathode chamber, the unreacted CO2 being enriched in 13C as compared to the CO2 in the feed stream, wherein n(13CO2)/(n(13CO2)+n(12CO2)) in the unreacted CO2 is higher than n(13CO2)/(n(13CO2)+n(12CO2)) in the feed stream, n representing molar amount; wherein the voltage is about 1.5 V to about 5.5 V, and flow rate of the feed stream is selected to provide a residence time of about 0.1 seconds to about 5 seconds in the cathode chamber.

Claims

1. A method of carbon-13 isotope (.sup.13C) enrichment, the method comprising: (i) applying a voltage to a cathode located in a cathode chamber of an electrochemical cell; (ii) flowing a feed stream comprising CO.sub.2 to the cathode chamber, wherein the feed stream contacts the cathode causing reduction of CO.sub.2 to form one or more products; and (iii) unreacted CO.sub.2 leaving the cathode chamber, the unreacted CO.sub.2 being enriched in .sup.13C as compared to the CO.sub.2 in the feed stream, wherein n(.sup.13CO.sub.2)/(n(.sup.13CO.sub.2)+n(.sup.12CO.sub.2)) in the unreacted CO.sub.2 is higher than n(.sup.13CO.sub.2)/(n(.sup.13CO.sub.2)+n(.sup.12CO.sub.2)) in the feed stream, n representing molar amount; wherein the voltage is about 1.5 V to about 5.5 V, and flow rate of the feed stream is selected to provide a residence time of about 0.1 seconds to about 5 seconds in the cathode chamber.

2. The method of claim 1, wherein ?.sup.13C is at least about 0.1%, wherein ?.sup.13C is calculated as: ${?}^{13}C\left(\%\right)=x{(}^{13}{C}_{outlet})\left(\%\right)-x{(}^{13}{C}_{\mathrm{feed}})\left(\%\right)$ $\mathrm{wherein}$ $x{(}^{13}{C}_{content})\left(\%\right)=\frac{n{(}^{13}{\mathrm{CO}}_2)}{n{(}^{13}{\mathrm{CO}}_2)+n{(}^{12}{\mathrm{CO}}_2)}*100\%;$ n represents molar amount; x(.sup.13C.sub.feed) represents molar fraction of .sup.13CO.sub.2 in the CO.sub.2 in the feed stream; x(.sup.13C.sub.outlet) represents molar fraction of .sup.13CO.sub.2 in the unreacted CO.sub.2; and x(.sup.13C.sub.content) represents x(.sup.13C.sub.feed) or x(.sup.13C.sub.outlet).

3. The method of claim 2, wherein ?.sup.13C is at least about 0.2%, or at least about 0.3%, or about 0.1% to about 99%.

4. (canceled)

5. (canceled)

6. The method of claim 1, wherein the residence time is about 0.1 seconds to about 0.8 seconds.

7. The method of claim 1, wherein the voltage is about 1.5 V to about 4.5 V, or wherein a current is passed through the cathode and current density is about 0.3 A/cm.sup.2 to about 1.8 A/cm.sup.2 of cathode surface area.

8. (canceled)

9. The method of claim 1, wherein step (iii) comprises separating unreacted CO.sub.2 from product by condensation.

10. The method of claim 1, further comprising (iv) recirculating the unreacted CO.sub.2 from step (iii) to the cathode chamber.

11. The method of claim 10, wherein step (iv) is performed at least twice.

12. The method of claim 10, wherein the cathode chamber is a cathode chamber of a different electrochemical cell.

13. The method of claim 1, wherein about 5% to about 35% of CO.sub.2 in the feed stream is converted to one or more products.

14. The method of claim 1, wherein the product is selected from the group consisting of ethylene, ethanol, and acetic acid.

15. The method of claim 1, wherein the cathode chamber comprises a catholyte, wherein the catholyte is a hydroxide selected from the group consisting of NaOH, KOH, CsOH, Ca(OH).sub.2, and mixtures thereof.

16. The method of claim 15, wherein the concentration of hydroxide is about 1 M to about 10 M.

17. The method of claim 1, wherein the cathode is carbon paper, or the cathode comprises a support layered with a first layer of metal nanoparticles, a second layer of carbon nanoparticles, and a third layer of carbon microparticles, and wherein the average diameter of the carbon nanoparticles of the second layer is smaller than the average diameter of the carbon nanoparticles in the third layer, or wherein the cathode is a gas diffusion electrode (GDE).

18. The method of claim 1, wherein the concentration of metal nanoparticles is about 0.5 mg/cm.sup.2 to about 4 mg/cm.sup.2 of cathode surface area.

19. The method of claim 18, wherein the support comprises a polymeric porous membrane with a pore size in the range of about 0.1 ?m to about 0.8 ?m, or wherein the support comprises a polymeric porous membrane and the polymer of the polymeric porous membrane is PTFE or PVDF.

20. (canceled)

21. The method of claim 1, wherein the second layer comprises carbon black nanoparticles, and the third layer comprises graphite microparticles.

22. The method of claim 17, wherein the metal nanoparticles are selected from the group consisting of Cu nanoparticles, Ag nanoparticles, Ni nanoparticles, Co nanoparticles, and Au nanoparticles, or wherein the average diameter of the metal nanoparticles is in the range of about 10 nm to about 200 nm, or wherein the average diameter of the carbon nanoparticles in the second layer is in the range of about 25 nm to about 1,000 nm, or wherein the average diameter of the carbon microparticles in the third layer is in the range of about 4,000 nm to about 20,000 nm.

23. (canceled)

24. (canceled)

25. (canceled)

26. The method of claim 1, wherein the electrochemical cell further comprises an anode, wherein the anode is selected from the group consisting of Ni foam, Ni foam coated with metal oxide hydroxide, or Ni foam coated with metal oxide hydroxide selected from the group consisting of FeOOH, NiOOH, and NiCoO.sub.x(OH).sub.y.

27. (canceled)

28. (canceled)

29. .sup.13CO.sub.2 produced by the method of claim 1.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0033] The accompanying drawings illustrate disclosed embodiments and serve to explain the principles of the disclosed embodiments. It is to be understood, however, that the drawings are designed for purposes of illustration only, and not as a definition of the limits of the invention.

[0034] FIG. 1 is a diagram showing an embodiment for enriching .sup.13C from CO.sub.2 using the method of the present invention.

[0035] FIG. 2 is a diagram showing a further embodiment for enriching .sup.13C from CO.sub.2 using the method of the present invention.

[0036] FIG. 3 is a Scanning Electron Microscopy (SEM) image of a Gas Diffusion Electrode (GDE) of the present invention, with (A) indicating the carbon paper filament and (B) indicating the sprayed catalyst (metal nanoparticle)/Carbon Black/graphite layers. This GDE corresponds to GDE-1 of Table 4.

[0037] FIG. 4 is a SEM image showing the top view of GDE-1 from the graphite side.

[0038] FIG. 5a is a graph showing ?.sup.13C of the examples having an initial .sup.13C content of 1.11% in Table 5.

[0039] FIG. 5b is a graph showing ?.sup.13C over the residence time for the examples in Table 5.

[0040] FIG. 5c is a graph showing ?.sup.13C over energy consumption for the examples in Table 5.

[0041] FIG. 5d is a graph showing ?13C over the flow cell voltage at different flow rates with GDE-1.

[0042] FIG. 5e is a graph showing ?13C over the flow cell voltage at different flow rates with GDE-3.

[0043] FIG. 6a is a graph showing the flow cell voltage-dependent enrichment at higher initial .sup.13C concentration at a flow rate of 30 sccm.

[0044] FIG. 6b is a graph showing ?.sup.13C at different initial .sup.13C concentrations.

[0045] FIG. 6c is a graph showing the ?.sup.13C over residence time and energy consumption at different initial .sup.13C concentrations.

[0046] FIG. 7 is a diagram showing ?.sup.13C in Example 4f.

[0047] FIG. 8a is the gas chromatogram of the main reduction products using GDE-3.

[0048] FIG. 8b is the gas chromatogram of main reduction products using GDE-1.

DETAILED DISCLOSURE OF DRAWINGS

[0049] Referring to FIG. 1, water vapour and CO.sub.2 feed stream (10) are fed to a reactor (20) comprising a cathode chamber (21) and anode chamber (22). The cathode chamber (21) and anode chamber (22) are separated by an ion exchange membrane (23). The CO.sub.2 feed stream (10) contacts the cathode (not depicted) causing reduction of CO.sub.2 to form one or more products. Unreacted CO.sub.2 (15) and gaseous products (16) leave the cathode chamber (21). Unreacted CO.sub.2 (15a) may be recirculated as feed stream and fed to the reactor (20) a second time. This recirculation step may be repeated multiple times. Unreacted CO.sub.2 is increasingly enriched with .sup.13C with each pass. Alternatively, or after one or more recirculations, unreacted CO.sub.2 (15) and gaseous products (16) may pass through a liquid nitrogen cooling unit (100) to separate the unreacted CO.sub.2 (15) from gaseous products (16). The unreacted CO.sub.2 (15) is enriched with .sup.13C with (15) being more enriched in .sup.13C than (10). The separated gaseous products (16) may pass through a membrane unit (90a) to separate syngas components such as CO and H.sub.2 (16a) for other uses. Liquid products (18) may leave the cathode chamber (21) together with catholyte (19). Liquid products (18) (such as ethanol) may be separated from catholyte (19) via a membrane unit (90b). The separated catholyte (19a) may be removed as alkaline waste and valorized. Alternatively, the separated catholyte (19a) may be recirculated back to the cathode chamber (21) (not depicted). Catholyte (19) may also be recirculated via a catholyte line (30) to the cathode chamber (21). Anolyte may also be recirculated to the anode chamber (22) via an anolyte line (40). (50) represents a liquid pump, (60) represents a 3-way valve, and (130) represents a gas pump/compressor.

[0050] FIG. 2 shows another embodiment of the present invention. Water vapour and CO.sub.2 feed stream (10) are fed to a reactor (20a) comprising a cathode chamber (21) and anode chamber (22). The cathode chamber (21) and anode chamber (22) are separated by an ion exchange membrane (23). The CO.sub.2 feed stream (10) contacts the cathode (not depicted) causing reduction of CO.sub.2 to form one or more products. Unreacted CO.sub.2 (15) and gaseous products (16) leave the cathode chamber (21). Unreacted CO.sub.2 and gaseous products (16) may pass through a membrane unit (90a) to separate syngas components such as CO and H.sub.2 (16a) for other uses. Unreacted CO.sub.2 (15) is fed as feed stream to a second reactor (20b) where the same reaction is repeated. Unreacted CO.sub.2 (15b) and gaseous products (16b) may pass through a liquid nitrogen cooling unit (100a) to separate the unreacted CO.sub.2 (15b) from gaseous products (16b). The unreacted CO.sub.2 (15, 15b) is enriched with .sup.13C with (15) being more enriched than (10) and (15b) being more enriched than (15). The separated gaseous products (16b) may pass through a membrane unit (90c) to separate syngas components such as CO and H.sub.2 (16c) for other uses. Liquid products (18) may leave the cathode chamber together with catholyte (19). Liquid products (18) (such as ethanol) may be separated from catholyte (19) via a membrane unit (90b). The separated catholyte (19a) may be removed as alkaline waste and valorized. Alternatively, the separated catholyte (19a) may be recirculated back to the cathode chamber (21) (not depicted). Catholyte (19) may also be recirculated via a catholyte line (30) to the cathode chamber (21). Anolyte may also be recirculated to the anode chamber (22) via an anolyte line (40). (50) represents a liquid pump, (60) represents a 3-way valve, and (130) represents a gas pump/compressor.

Detailed Disclosure of Embodiments

[0051] It is known that 3 isotopes of carbon exist in nature, of which two isotopes (.sup.12C and .sup.13C) are naturally stable, while the last isotope .sup.14C is radioactive in nature. .sup.12C has a natural abundance of 98.9%, while .sup.13C has a natural abundance of 1.1%. The radioactive .sup.14C instead has a small abundance of 10.sup.?10%.

[0052] The only industrially deployed method for .sup.13C production is cryogenic distillation, a capital and operationally cost-intensive approach, resulting in a high price of .sup.13C and a barrier for many commercial applications described above. Another alternative method of .sup.13C production is based on chromatography separation. Similar to the industrial standard for .sup.13C production, this method is limited by low separation factor between .sup.12C and .sup.13C isotopes.

[0053] The cryogenic industrial process involves multistage distillation columns with heights of at least 39 m, and diameters of at least 72 mm. CO possesses the best volatility among the various carbon-containing gases, hence it is commonly chosen as the reagent for cryogenic distillation. However, in a first stage run, it would typically take about 400 hours to enrich about 5% of .sup.13CO.sub.2. In order to reach 99% enrichment, it may over a month of distillation.

[0054] The present invention generally relates to a method of .sup.13C enrichment, or improving separation efficiency of .sup.13CO.sub.2 from CO.sub.2. Enrichment or separation efficiency is improved through careful selection of one or more parameters, such as applied potential (or current density), type of electrode, residence time of CO.sub.2 in the cathode chamber (or flow rate), electrolyte type, concentration of electrolyte, and/or catalyst concentration.

[0055] The inventors have surprisingly found that in the method of the present invention, products containing one or more atoms of carbon are preferentially formed from .sup.12C and not .sup.13C. As a result, the remaining CO.sub.2 that is not converted to product (for example, ethylene, ethanol, CO, acetic acid, etc.) has a higher content of .sup.13C. This .sup.13C enriched CO.sub.2 can be used to feed a commercial process for producing .sup.13C labelled compounds and drastically reduce the processing cost for example or can be directly sold to end users such as pharmaceutical industries. Importantly, the presently disclosed method leading to enrichment of .sup.13C is very fast and can be completed, based on the desired conversion rate, in at most several hours.

[0056] Currently deployed methods for .sup.13C production are all limited by very low separation factors between .sup.12C and .sup.13C resulting from the similarity in physical properties of the two isotopes. On the contrary, the presently disclosed method explores the difference in reactivity of isotopes towards the products of electrochemical reactions, which enables fast and selective discrimination between the isotopes. Furthermore, the presently disclosed process uses an abundant and low-cost feedstock (CO.sub.2), while at the time producing value-added chemicals such as ethylene and ethanol, further improving the overall techno-economic performance.

[0057] The presently disclosed method is much simpler compared to conventional cryogenic distillation processes as the presently disclosed method does not require huge distillation columns. Additionally, the system containing the presently disclosed electrochemical cell does not require large amounts of space and heat isolation among others. The unreacted CO.sub.2 from the method may be further enriched in .sup.13C by recycling back the unreacted CO.sub.2 as the feed stream in the same electrochemical cell, or may be fed as a feed stream into a second electrochemical cell in a series of consecutive cells. The presently disclosed method also requires less time to enrich the same amount of .sup.13C when compared to cryogenic distillation as enrichment of .sup.13C in the present invention is almost immediate when CO.sub.2 contacts the cathode and selectively forms .sup.12C reduction products.

[0058] The present invention relates to a method of carbon-13 isotope (.sup.13C) enrichment, the method comprising: [0059] (i) applying a voltage to a cathode located in a cathode chamber of an electrochemical cell; [0060] (ii) flowing a feed stream comprising CO.sub.2 to the cathode chamber, wherein the feed stream contacts the cathode causing reduction of CO.sub.2 to form one or more products; and [0061] (iii) unreacted CO.sub.2 leaving the cathode chamber, the unreacted CO.sub.2 being enriched in .sup.13C as compared to the CO.sub.2 in the feed stream, wherein n(.sup.13CO.sub.2)/(n(.sup.13CO.sub.2)+n(.sup.12CO.sub.2)) in the unreacted CO.sub.2 is higher than n(.sup.13CO.sub.2)/(n(.sup.13CO.sub.2)+n(.sup.12CO.sub.2)) in the feed stream, n representing molar amount; wherein the voltage is about 1.5 V to about 5.5 V, and flow rate of the feed stream is selected to provide a residence time of about 0.1 seconds to about 5 seconds in the cathode chamber.

[0062] The unreacted CO.sub.2 may also be referred to as an outlet stream. Products produced by the reduction process may be referred to as a product stream. The product stream may be a liquid or gaseous product stream. There may be more than one product stream. The stream leaving the cathode may contain outlet stream and gaseous product stream. The stream leaving the anode may contain liquid product stream.

[0063] The feed stream may be a feed stream comprising pure CO.sub.2, or a feed stream comprising from about 0.1% CO.sub.2 to about 100% CO.sub.2. The remaining components of the feed stream may comprise a gas that is either inert to the electroreduction process like N.sub.2, Ar, Ne, He, or may comprise a gas that is a co-feed to the electro-reduction process like CO. The feed stream may be a previously processed gas stream, or taken as-is from a prior manufacturing process. The feed stream may come as a by-product stream, but is not limited to a stream resulting from natural gas extraction, biogas production, fermentation process, corn-based ethanol production, combustion process during energy production, waste incineration, ammonia production, ethylene oxide production, vinyl acetate monomer production, synthetic fuel production, hydrogen production, syngas production, or methanol-base fuel cell use.

[0064] In some embodiments, the feed stream may comprise CO.sub.2 by v/v % basis, in a range of at least about 0.1 v/v %, at least about 1 v/v %, at least about 5 v/v %, at least about 10 v/v %, at least about 20 v/v %, at least about 40 v/v %, at least about 60 v/v %, at least about 80 v/v %, at least about 100 v/v %; or from about 0.1 v/v % to about 100 v/v %, from about 0.1 v/v % to about 80 v/v %, from about 0.1 v/v % to about 60 v/v %, from about 0.1 v/v % to about 40 v/v %, from about 0.1 v/v % to about 20 v/v %, from about 0.1 v/v % to about 10 v/v %, from about 0.1 v/v % to about 5 v/v %, from about 0.1 v/v % to about 1 v/v %, from about 1 v/v % to about 100 v/v %, from about 1 v/v % to about 80 v/v %, from about 1 v/v % to about 60 v/v %, from about 1 v/v % to about 40 v/v %, from about 1 v/v % to about 20 v/v %, from about 1 v/v % to about 10 v/v %, from about 1 v/v % to about 5 v/v %, from about 5 v/v % to about 100 v/v %, from about 5 v/v % to about 80 v/v %, from about 5 v/v % to about 60 v/v %, from about 5 v/v % to about 40 v/v %, from about 5 v/v % to about 20 v/v %, from about 5 v/v % to about 10 v/v %, from about 10 v/v % to about 100 v/v %, from about 10 v/v % to about 80 v/v %, from about 10 v/v % to about 60 v/v %, from about 10 v/v % to about 40 v/v %, from about 10 v/v % to about 20 v/v %, from about 20 v/v % to about 100 v/v %, from about 20 v/v % to about 80 v/v %, from about 20 v/v % to about 60 v/v %, from about 20 v/v % to about 40 v/v %, from about 40 v/v % to about 100 v/v %, from about 40 v/v % to about 80 v/v %, from about 40 v/v % to about 60 v/v %, from about 60 v/v % to about 100 v/v %, from about 60 v/v % to about 80 v/v %, from about 80 v/v % to about 100 v/v %; or at most about 0.1 v/v %, at most about 1 v/v %, at most about 5 v/v %, at most about 10 v/v %, at most about 20 v/v %, at most about 40 v/v %, at most about 60 v/v %, at most about 80 v/v %, at most about 100 v/v %; or about 0.1 v/v %, about 1 v/v %, about 5 v/v %, about 10 v/v %, about 20 v/v %, about 40 v/v %, about 60 v/v %, about 80 v/v %, about 100 v/v %, or any ranges or values therebetween.

[0065] In some other embodiments, the feed stream may comprise CO.sub.2 with an initial .sup.13C content in a range of at least about 0.5%, at least about 1%, at least about 1.1%, at least about 5.58%, at least about 10%, at least about 30%, at least about 50%, at least about 70%, at least about 88.48%, at least about 95%, at least about 99%; or from about 0.5% to about 99%, from about 0.5% to about 95%, from about 0.5% to about 88.48%, from about 0.5% to about 70%, from about 0.5% to about 50%, from about 0.5% to about 30%, from about 0.5% to about 10%, from about 0.5% to about 5.58%, from about 0.5% to about 1%, from about 1% to about 99%, from about 1% to about 95%, from about 1% to about 88.48%, from about 1% to about 70%, from about 1% to about 50%, from about 1% to about 30%, from about 1% to about 10%, from about 1% to about 5.58%, from about 5.58% to about 99%, from about 5.58% to about 95%, from about 5.58% to about 88.48%, from about 5.58% to about 70%, from about 5.58% to about 50%, from about 5.58% to about 30%, from about 5.58% to about 10%, from about 10% to about 99%, from about 10% to about 95%, from about 10% to about 88.48%, from about 10% to about 70%, from about 10% to about 50%, from about 10% to about 30%, from about 30% to about 99%, from about 30% to about 95%, from about 30% to about 88.48%, from about 30% to about 70%, from about 30% to about 50%, from about 50% to about 99%, from about 50% to about 95%, from about 50% to about 88.48%, from about 50% to about 70%, from about 70% to about 99%, from about 70% to about 95%, from about 70% to about 88.48%, from about 88.48% to about 99%, from about 88.48% to about 95%, from about 95% to about 99%; or at most about 0.5%, at most about 1%, at most about 5.58%, at most about 10%, at most about 30%, at most about 50%, at most about 70%, at most about 88.48%, at most about 95%, at most about 99%; or about 0.5%, about 1%, about 5.58%, about 10%, about 30%, about 50%, about 70%, about 88.48%, about 95%, about 99%, or any ranges or values therebetween.

[0066] Both the flow cell voltage applied across the electrochemical cell and the current density may affect the rate of electroreduction that happens at the cathode. As flow cells may come in different sizes, the measure of current density at the electrode is more useful than current alone for tuning the rate of electroreduction that happens at the cathode.

[0067] In some embodiments, the current density may be relative to the cathode surface area, in the range of at least about 0.1 A/cm.sup.2, at least about 0.2 A/cm.sup.2, at least about 0.3 A/cm.sup.2, at least about 0.5 A/cm.sup.2, at least about 0.75 A/cm.sup.2, at least about 1 A/cm.sup.2, at least about 1.25 A/cm.sup.2, at least about 1.5 A/cm.sup.2, at least about 1.8 A/cm.sup.2, at least about 2 A/cm.sup.2; or from about 0.1 A/cm.sup.2 to about 2 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 1 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 0.75 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 0.5 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 0.3 A/cm.sup.2, from about 0.1 A/cm.sup.2 to about 0.2 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 2 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 1 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 0.75 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 0.5 A/cm.sup.2, from about 0.2 A/cm.sup.2 to about 0.3 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 2 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 1 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 0.75 A/cm.sup.2, from about 0.3 A/cm.sup.2 to about 0.5 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 2 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 1 A/cm.sup.2, from about 0.5 A/cm.sup.2 to about 0.75 A/cm.sup.2, from about 0.75 A/cm.sup.2 to about 2 A/cm.sup.2, from about 0.75 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 0.75 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 0.75 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 0.75 A/cm.sup.2 to about 1 A/cm.sup.2, from about 1 A/cm.sup.2 to about 2 A/cm.sup.2, from about 1 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 1 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 1 A/cm.sup.2 to about 1.25 A/cm.sup.2, from about 1.25 A/cm.sup.2 to about 2 A/cm.sup.2, from about 1.25 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 1.25 A/cm.sup.2 to about 1.5 A/cm.sup.2, from about 1.5 A/cm.sup.2 to about 2 A/cm.sup.2, from about 1.5 A/cm.sup.2 to about 1.8 A/cm.sup.2, from about 1.8 A/cm.sup.2 to about 2 A/cm.sup.2; or at most about 0.1 A/cm.sup.2, at most about 0.2 A/cm.sup.2, at most about 0.3 A/cm.sup.2, at most about 0.5 A/cm.sup.2, at most about 0.75 A/cm.sup.2, at most about 1 A/cm.sup.2, at most about 1.25 A/cm.sup.2, at most about 1.5 A/cm.sup.2, at most about 1.8 A/cm.sup.2, at most about 2 A/cm.sup.2; or about 0.1 A/cm.sup.2, about 0.2 A/cm.sup.2, about 0.3 A/cm.sup.2, about 0.5 A/cm.sup.2, about 0.75 A/cm.sup.2, about 1 A/cm.sup.2, about 1.25 A/cm.sup.2, about 1.5 A/cm.sup.2, about 1.8 A/cm.sup.2, about 2 A/cm.sup.2, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein a current is passed through the cathode and current density is about 0.3 A/cm.sup.2 to about 1.8 A/cm.sup.2 of cathode surface area.

[0068] The flow rate of the feed stream is selected to provide a desired residence time. The residence time may be calculated using the formula below, wherein the internal volume of the cathode chamber is calculated by measuring the length, and depth of the channel and then subsequently calculating its volume.

[00001]$\mathrm{residence}\mathrm{time}=\frac{int\mathrm{ernal}\mathrm{volume}\mathrm{of}\mathrm{cathode}\mathrm{chamber}}{volum\mathrm{etric}\mathrm{flow}\mathrm{rate}}$

[0069] The residence time may be in the range of at least about 0.1 seconds, at least about 0.2 seconds, at least about 0.28 seconds, at least about 0.42 seconds, at least about 0.6 seconds, at least about 0.7 seconds, at least about 0.8 seconds, at least about 1 second, at least about 1.25 seconds, at least about 1.5 seconds, at least about 2 seconds, at least about 3 seconds, at least about 5 seconds, at least about 10 seconds; or from about 0.1 seconds to about 10 seconds, from about 0.1 seconds to about 5 seconds, from about 0.1 seconds to about 3 seconds, from about 0.1 seconds to about 2 seconds, from about 0.1 seconds to about 1.5 seconds, from about 0.1 seconds to about 1.25 seconds, from about 0.1 seconds to about 1 second, from about 0.1 seconds to about 0.8 seconds, from about 0.1 seconds to about 0.7 seconds, from about 0.1 seconds to about 0.6 seconds, from about 0.1 seconds to about 0.42 seconds, from about 0.1 seconds to about 0.28 seconds, from about 0.1 seconds to about 0.2 seconds, from about 0.2 seconds to about 10 seconds, from about 0.2 seconds to about 5 seconds, from about 0.2 seconds to about 3 seconds, from about 0.2 seconds to about 2 seconds, from about 0.2 seconds to about 1.5 seconds, from about 0.2 seconds to about 1.25 seconds, from about 0.2 seconds to about 1 second, from about 0.2 seconds to about 0.8 seconds, from about 0.2 seconds to about 0.7 seconds, from about 0.2 seconds to about 0.6 seconds, from about 0.2 seconds to about 0.42 seconds, from about 0.2 seconds to about 0.28 seconds, from about 0.28 seconds to about 10 seconds, from about 0.28 seconds to about 5 seconds, from about 0.28 seconds to about 3 seconds, from about 0.28 seconds to about 2 seconds, from about 0.28 seconds to about 1.5 seconds, from about 0.28 seconds to about 1.25 seconds, from about 0.28 seconds to about 1 second, from about 0.28 seconds to about 0.8 seconds, from about 0.28 seconds to about 0.7 seconds, from about 0.28 seconds to about 0.6 seconds, from about 0.28 seconds to about 0.42 seconds, from about 0.42 seconds to about 10 seconds, from about 0.42 seconds to about 5 seconds, from about 0.42 seconds to about 3 seconds, from about 0.42 seconds to about 2 seconds, from about 0.42 seconds to about 1.5 seconds, from about 0.42 seconds to about 1.25 seconds, from about 0.42 seconds to about 1 second, from about 0.42 seconds to about 0.8 seconds, from about 0.42 seconds to about 0.7 seconds, from about 0.42 seconds to about 0.6 seconds, from about 0.6 seconds to about 10 seconds, from about 0.6 seconds to about 5 seconds, from about 0.6 seconds to about 3 seconds, from about 0.6 seconds to about 2 seconds, from about 0.6 seconds to about 1.5 seconds, from about 0.6 seconds to about 1.25 seconds, from about 0.6 seconds to about 1 second, from about 0.6 seconds to about 0.8 seconds, from about 0.6 seconds to about 0.7 seconds, from about 0.7 seconds to about 10 seconds, from about 0.7 seconds to about 5 seconds, from about 0.7 seconds to about 3 seconds, from about 0.7 seconds to about 2 seconds, from about 0.7 seconds to about 1.5 seconds, from about 0.7 seconds to about 1.25 seconds, from about 0.7 seconds to about 1 second, from about 1 second to about 10 seconds, from about 1 second to about 5 seconds, from about 1 second to about 3 seconds, from about 1 second to about 2 seconds, from about 1 second to about 1.5 seconds, from about 1 second to about 1.25 seconds, from about 1.25 seconds to about 10 seconds, from about 1.25 seconds to about 5 seconds, from about 1.25 seconds to about 3 seconds, from about 1.25 seconds to about 2 seconds, from about 1.25 seconds to about 1.5 seconds, from about 1.5 seconds to about 10 seconds, from about 1.5 seconds to about 5 seconds, from about 1.5 seconds to about 3 seconds, from about 1.5 seconds to about 2 seconds, from about 2 seconds to about 10 seconds, from about 2 seconds to about 5 seconds, from about 2 seconds to about 3 seconds, from about 3 seconds to about 10 seconds, from about 3 seconds to about 5 seconds, from about 5 seconds to about 10 seconds; or at most about 0.1 seconds, at most about 0.2 seconds, at most about 0.28 seconds, at most about 0.42 seconds, at most about 0.6 seconds, at most about 0.7 seconds, at most about 0.8 seconds, at most about 1 second, at most about 1.25 seconds, at most about 1.5 seconds, at most about 2 seconds, at most about 3 seconds, at most about 5 seconds, at most about 10 seconds; or about 0.1 seconds, about 0.2 seconds, about 0.28 seconds, about 0.42 seconds, about 0.6 seconds, about 0.7 seconds, about 0.8 seconds, about 1 second, about 1.25 seconds, about 1.5 seconds, about 2 seconds, about 3 seconds, about 5 seconds, about 10 seconds, or any ranges or values therebetween. In a preferred embodiment the present disclosure discloses a method wherein the flow rate of the feed stream is selected to provide a residence time of about 0.1 seconds to about 5 seconds in the cathode chamber.

[0070] The feed stream flow rate may be broadly defined in terms of a volume of gas that passes through the internal volume of the cathode chamber in a unit of time. It is however well known in the art that the density, and consequently the pressure of the gas is affected by its temperature. Due to fluctuations in the environment and the electroreduction process, the density of the gases at the inlet, inside the cathode chamber and the outlet may deviate slightly from the norm. Hence, to better account for such deviations during the electroreduction, the feed stream and outlet stream may instead be defined in standardised volumetric flow rate, also referred to as mass flow rate.

[0071] The mass flow rate refers to the mass of gas that flows through a point and can be defined either in terms of the mass of a gas over a period of time, or the corresponding volume of a gas over the same period of time under standard temperature and pressure (STP, 25? C., 1 atm) conditions. Unless specified otherwise, all flow rates disclosed throughout the specification are intended to mean standardised volumetric flow rates.

[0072] The feed stream may thus be defined in terms of a mass flow rate, being the mass of gas that passes through the gas inlet of the cathode chamber in a unit of time. The feed stream may thus also be further defined in terms of a standardised volumetric flow rate, being the volume of a mass of gas that passes through the internal volume of the cathode chamber in a unit of time, as if it was under STP conditions.

[0073] The flow rate of CO.sub.2 in the outlet stream may be defined in terms of a mass flow rate, being the mass of CO.sub.2 that passes through the gas outlet of the cathode chamber in a unit of time. The flow rate of CO.sub.2 in the outlet stream may also be further defined in terms of a standardised volumetric flow rate, being the volume of a mass of CO.sub.2 that passes through the gas outlet of the cathode chamber in a unit of time, as if it was under STP conditions.

[0074] Using an internal volume of 0.35 cm.sup.3 as an example, the feed stream flow rate may be a standardised volumetric flow rate in standard cubic centimetres per minute (sccm or cm.sup.3/minute), in a range of at least about 5 sccm, at least about 10 sccm, at least about 20 sccm, at least about 30 sccm, at least about 40 sccm, at least about 50 sccm, at least about 60 sccm, at least about 75 sccm, at least about 100 sccm, at least about 120 sccm; or from about 5 sccm to about 120 sccm, from about 5 sccm to about 100 sccm, from about 5 sccm to about 75 sccm, from about 5 sccm to about 60 sccm, from about 5 sccm to about 50 sccm, from about 5 sccm to about 40 sccm, from about 5 sccm to about 30 sccm, from about 5 sccm to about 20 sccm, from about 5 sccm to about 10 sccm, from about 10 sccm to about 120 sccm, from about 10 sccm to about 100 sccm, from about 10 sccm to about 75 sccm, from about 10 sccm to about 60 sccm, from about 10 sccm to about 50 sccm, from about 10 sccm to about 40 sccm, from about 10 sccm to about 30 sccm, from about 10 sccm to about 20 sccm, from about 20 sccm to about 120 sccm, from about 20 sccm to about 100 sccm, from about 20 sccm to about 75 sccm, from about 20 sccm to about 60 sccm, from about 20 sccm to about 50 sccm, from about 20 sccm to about 40 sccm, from about 20 sccm to about 30 sccm, from about 30 sccm to about 120 sccm, from about 30 sccm to about 100 sccm, from about 30 sccm to about 75 sccm, from about 30 sccm to about 60 sccm, from about 30 sccm to about 50 sccm, from about 30 sccm to about 40 sccm, from about 40 sccm to about 120 sccm, from about 40 sccm to about 100 sccm, from about 40 sccm to about 75 sccm, from about 40 sccm to about 60 sccm, from about 40 sccm to about 50 sccm, from about 50 sccm to about 120 sccm, from about 50 sccm to about 100 sccm, from about 50 sccm to about 75 sccm, from about 50 sccm to about 60 sccm, from about 60 sccm to about 120 sccm, from about 60 sccm to about 100 sccm, from about 60 sccm to about 75 sccm, from about 75 sccm to about 120 sccm, from about 75 sccm to about 100 sccm, from about 100 sccm to about 120 sccm; or at most about 5 sccm, at most about 10 sccm, at most about 20 sccm, at most about 30 sccm, at most about 40 sccm, at most about 50 sccm, at most about 60 sccm, at most about 75 sccm, at most about 100 sccm, at most about 120 sccm; or about 5 sccm, about 10 sccm, about 20 sccm, about 30 sccm, about 40 sccm, about 50 sccm, about 60 sccm, about 75 sccm, about 100 sccm, about 120 sccm, or any ranges or values therebetween.

[0075] The internal volume of the cathode chamber and the flow rate determines how long the CO.sub.2 stream resides in the cathode chamber (and at the liquid-gas interface on the cathode). Generally, a longer residence time results in a better ?.sup.13C as the CO.sub.2 resides in the cathode chamber long enough for the reaction to effectively discriminate against .sup.13CO.sub.2 and favor reduction of .sup.12CO.sub.2. The residence time is inversely proportionate to the flow rate of the feed stream.

[0076] In some embodiments, to promote the electro-reduction of CO.sub.2 to useful products, the cathode chamber may comprise a liquid catholyte comprising an alkali. The alkali may be a metal hydroxide, more preferably a metal hydroxide selected from the group comprising a Group (I) hydroxide, a Group (II) hydroxide, a Group (III) hydroxide or a Group (IV) hydroxide. In some preferred embodiments, the present disclosure discloses a method wherein the cathode chamber comprises a catholyte, wherein the catholyte is a hydroxide selected from the group consisting of NaOH, KOH, CsOH, Ca(OH).sub.2, and mixtures thereof. In some further preferred embodiments, the present disclosure discloses a method wherein the cathode chamber comprises a liquid catholyte, wherein the liquid catholyte is a hydroxide selected from the group consisting of NaOH, KOH, CsOH, Ca(OH).sub.2, and mixtures thereof.

[0077] In some other embodiments, the anode chamber may comprise a liquid anolyte comprising an alkali metal hydroxide. The alkali may be a metal hydroxide, more preferably a metal hydroxide selected from the group comprising a Group (I) hydroxide, a Group (II) hydroxide, a Group (III) hydroxide or a Group (IV) hydroxide. In some preferred embodiments, the present disclosure discloses a method wherein the anode chamber comprises a liquid anolyte, wherein the liquid anolyte is a hydroxide selected from the group consisting of NaOH, KOH, CsOH, Ca(OH).sub.2, and mixtures thereof.

[0078] In some other embodiments, the present disclosure discloses a method wherein the catholyte used is the same as the anolyte.

[0079] In some embodiments, the concentration of the hydroxide in the catholyte and/or anolyte may be in the range of at least about 0.5 M, at least about 1 M, at least about 2 M, at least about 3 M, at least about 4 M, at least about 5 M, at least about 6 M, at least about 7 M, at least about 8 M, at least about 9 M, at least about 10 M, at least about 12 M; or from about 0.5 M to about 12 M, from about 0.5 M to about 10 M, from about 0.5 M to about 9 M, from about 0.5 M to about 8 M, from about 0.5 M to about 7 M, from about 0.5 M to about 6 M, from about 0.5 M to about 5 M, from about 0.5 M to about 4 M, from about 0.5 M to about 3 M, from about 0.5 M to about 2 M, from about 0.5 M to about 1 M, from about 1 M to about 12 M, from about 1 M to about 10 M, from about 1 M to about 9 M, from about 1 M to about 8 M, from about 1 M to about 7 M, from about 1 M to about 6 M, from about 1 M to about 5 M, from about 1 M to about 4 M, from about 1 M to about 3 M, from about 1 M to about 2 M, from about 2 M to about 12 M, from about 2 M to about 10 M, from about 2 M to about 9 M, from about 2 M to about 8 M, from about 2 M to about 7 M, from about 2 M to about 6 M, from about 2 M to about 5 M, from about 2 M to about 4 M, from about 2 M to about 3 M, from about 3 M to about 12 M, from about 3 M to about 10 M, from about 3 M to about 9 M, from about 3 M to about 8 M, from about 3 M to about 7 M, from about 3 M to about 6 M, from about 3 M to about 5 M, from about 3 M to about 4 M, from about 4 M to about 12 M, from about 4 M to about 10 M, from about 4 M to about 9 M, from about 4 M to about 8 M, from about 4 M to about 7 M, from about 4 M to about 6 M, from about 4 M to about 5 M, from about 5 M to about 12 M, from about 5 M to about 10 M, from about 5 M to about 9 M, from about 5 M to about 8 M, from about 5 M to about 7 M, from about 5 M to about 6 M, from about 6 M to about 12 M, from about 6 M to about 10 M, from about 6 M to about 9 M, from about 6 M to about 8 M, from about 6 M to about 7 M, from about 7 M to about 12 M, from about 7 M to about 10 M, from about 7 M to about 9 M, from about 7 M to about 8 M, from about 8 M to about 12 M, from about 8 M to about 10 M, from about 8 M to about 9 M, from about 9 M to about 12 M, from about 9 M to about 10 M, from about 10 M to about 12 M; or at most about 0.5 M, at most about 1 M, at most about 2 M, at most about 3 M, at most about 4 M, at most about 5 M, at most about 6 M, at most about 7 M, at most about 8 M, at most about 9 M, at most about 10 M, at most about 12 M; or about 0.5 M, about 1 M, about 2 M, about 3 M, about 4 M, about 5 M, about 6 M, about 7 M, about 8 M, about 9 M, about 10 M, about 12 M, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the concentration of hydroxide is about 1 M to about 10 M. In a further preferred embodiment, the present discloses a method wherein the concentration of hydroxide is from about 3 M to about 6 M.

[0080] In a further preferred embodiment, the present disclosure discloses a method wherein the concentration of KOH is from about 1 M to about 10 M, or more preferably from about 3 M to about 6 M.

[0081] The present disclosed method may be applied to a 2-electrode electrochemical cell. The presently disclosed method may also be applied to a 3-electrode electrochemical cell. In a 3-electrode electrochemical cell, the reference electrode may be a reversible hydrogen electrode (RHE). The electro-reduction of CO.sub.2 may be processed on a three-phase interface at a gas diffusion electrode working as the cathode, where it is reduced to various C.sub.2 products.

[0082] The presently disclosed method may be performed at an flow-cell voltage range of at least about 0.5 V, at least about 0.75 V, at least about 0.8 V, at least about 0.93 V, at least about 1 V, at least about 1.1 V, at least about 1.2 V, at least about 1.25 V, at least about 1.3 V, at least about 1.5 V, at least about 1.6 V, at least about 2 V, at least about 2.5 V, at least about 2.6 V, at least about 2.8 V, at least about 3 V, at least about 3.5 V, at least about 4 V, at least about 4.1 V, at least about 4.5 V, at least about 5 V, at least about 5.5 V; or from about 0.5 V to about 5.5 V, from about 0.5 V to about 5 V, from about 0.5 V to about 4.5 V, from about 0.5 V to about 4.1 V, from about 0.5 V to about 4 V, from about 0.5 V to about 3.5 V, from about 0.5 V to about 3 V, from about 0.5 V to about 2.8 V, from about 0.5 V to about 2.6 V, from about 0.5 V to about 2.5 V, from about 0.5 V to about 2 V, from about 0.5 V to about 1.6 V, from about 0.5 V to about 1.5 V, from about 0.5 V to about 1.3 V, from about 0.5 V to about 1.25 V, from about 0.5 V to about 1.2 V, from about 0.5 V to about 1.1 V, from about 0.5 V to about 1 V, from about 0.5 V to about 0.93 V, from about 0.5 V to about 0.8 V, from about 0.5 V to about 0.75 V, from about 0.75 V to about 5.5 V, from about 0.75 V to about 5 V, from about 0.75 V to about 4.5 V, from about 0.75 V to about 4.1 V, from about 0.75 V to about 4 V, from about 0.75 V to about 3.5 V, from about 0.75 V to about 3 V, from about 0.75 V to about 2.8 V, from about 0.75 V to about 2.6 V, from about 0.75 V to about 2.5 V, from about 0.75 V to about 2 V, from about 0.75 V to about 1.6 V, from about 0.75 V to about 1.5 V, from about 0.75 V to about 1.3 V, from about 0.75 V to about 1.25 V, from about 0.75 V to about 1.1 V, from about 0.75 V to about 1 V, from about 0.75 V to about 0.93 V, from about 0.75 V to about 0.8 V, from about 0.8 V to about 5.5 V, from about 0.8 V to about 5 V, from about 0.8 V to about 4.5 V, from about 0.8 V to about 4.1 V, from about 0.8 V to about 4 V, from about 0.8 V to about 3.5 V, from about 0.8 V to about 3 V, from about 0.8 V to about 2.8 V, from about 0.8 V to about 2.6 V, from about 0.8 V to about 2.5 V, from about 0.8 V to about 2 V, from about 0.8 V to about 1.6 V, from about 0.8 V to about 1.5 V, from about 0.8 V to about 1.3 V, from about 0.8 V to about 1.25 V, from about 0.8 V to about 1.2 V, from about 0.8 V to about 1.1 V, from about 0.8 V to about 1 V, from about 0.8 V to about 0.93 V, from about 0.93 V to about 5.5 V, from about 0.93 V to about 5 V, from about 0.93 V to about 4.5 V, from about 0.93 V to about 4.1 V, from about 0.93 V to about 4 V, from about 0.93 V to about 3.5 V, from about 0.93 V to about 3 V, from about 0.93 V to about 2.8 V, from about 0.93 V to about 2.6 V, from about 0.93 V to about 2.5 V, from about 0.93 V to about 2 V, from about 0.93 V to about 1.6 V, from about 0.93 V to about 1.5 V, from about 0.93 V to about 1.3 V, from about 0.93 V to about 1.25 V, from about 0.93 V to about 1.2 V, from about 0.93 V to about 1.1 V, from about 0.93 V to about 1 V, from about 1 V to about 5.5 V, from about 1 V to about 5 V, from about 1 V to about 4.5 V, from about 1 V to about 4.1 V, from about 1 V to about 4 V, from about 1 V to about 3.5 V, from about 1 V to about 3 V, from about 1 V to about 2.8 V, from about 1 V to about 2.6 V, from about 1 V to about 2.5 V, from about 1 V to about 2 V, from about 1 V to about 1.6 V, from about 1 V to about 1.5 V, from about 1 V to about 1.3 V, from about 1 V to about 1.25 V, from about 1 V to about 1.2 V, from about 1 V to about 1.1 V, from about 1.1 V to about 5.5 V, from about 1.1 V to about 5 V, from about 1.1 V to about 4.5 V, from about 1.1 V to about 4.1 V, from about 1.1 V to about 4 V, from about 1.1 V to about 3.5 V, from about 1.1 V to about 3 V, from about 1.1 V to about 2.8 V, from about 1.1 V to about 2.6 V, from about 1.1 V to about 2.5 V, from about 1.1 V to about 2 V, from about 1.1 V to about 1.6 V, from about 1.1 V to about 1.5 V, from about 1.1 V to about 1.3 V, from about 1.1 V to about 1.25 V, from about 1.1 V to about 1.2 V, from about 1.2 V to about 5.5 V, from about 1.2 V to about 5 V, from about 1.2 V to about 4.5 V, from about 1.2 V to about 4.1 V, from about 1.2 V to about 4 V, from about 1.2 V to about 3.5 V, from about 1.2 V to about 3 V, from about 1.2 V to about 2.8 V, from about 1.2 V to about 2.6 V, from about 1.2 V to about 2.5 V, from about 1.2 V to about 2 V, from about 1.2 V to about 1.6 V, from about 1.2 V to about 1.5 V, from about 1.2 V to about 1.3 V, from about 1.2 V to about 1.25 V, from about 1.25 V to about 1.5 V, from about 1.25 V to about 1.3 V, from about 1.3 V to about 5.5 V, from about 1.3 V to about 5 V, from about 1.3 V to about 4.5 V, from about 1.3 V to about 4.1 V, from about 1.3 V to about 4 V, from about 1.3 V to about 3.5 V, from about 1.3 V to about 3 V, from about 1.3 V to about 2.8 V, from about 1.3 V to about 2.6 V, from about 1.3 V to about 2.5 V, from about 1.3 V to about 2 V, from about 1.3 V to about 1.6 V, from about 1.3 V to about 1.5 V, from about 1.5 V to about 5.5 V, from about 1.5 V to about 5 V, from about 1.5 V to about 4.5 V, from about 1.5 V to about 4.1 V, from about 1.5 V to about 4 V, from about 1.5 V to about 3.5 V, from about 1.5 V to about 3 V, from about 1.5 V to about 2.8 V, from about 1.5 V to about 2.6 V, from about 1.5 V to about 2.5 V, from about 1.5 V to about 2 V, from about 1.5 V to about 1.6 V, from about 1.6 V to about 5.5 V, from about 1.6 V to about 5 V, from about 1.6 V to about 4.5 V, from about 1.6 V to about 4.1 V, from about 1.6 V to about 4 V, from about 1.6 V to about 3.5 V, from about 1.6 V to about 3 V, from about 1.6 V to about 2.8 V, from about 1.6 V to about 2.6 V, from about 1.6 V to about 2.5 V, from about 1.6 V to about 2 V, from about 2 V to about 5.5 V, from about 2 V to about 5 V, from about 2 V to about 4.5 V, from about 2 V to about 4.1 V, from about 2 V to about 4 V, from about 2 V to about 3.5 V, from about 2 V to about 3 V, from about 2 V to about 2.8 V, from about 2 V to about 2.6 V, from about 2 V to about 2.5 V, from about 2.5 V to about 5.5 V, from about 2.5 V to about 5 V, from about 2.5 V to about 4.5 V, from about 2.5 V to about 4.1 V, from about 2.5 V to about 4 V, from about 2.5 V to about 3.5 V, from about 2.5 V to about 3 V, from about 2.5 V to about 2.8 V, from about 2.5 V to about 2.6 V, from about 2.6 V to about 5.5 V, from about 2.6 V to about 5 V, from about 2.6 V to about 4.5 V, from about 2.6 V to about 4.1 V, from about 2.6 V to about 4 V, from about 2.6 V to about 3.5 V, from about 2.6 V to about 3 V, from about 2.6 V to about 2.8 V, from about 2.8 V to about 5.5 V, from about 2.8 V to about 5 V, from about 2.8 V to about 4.5 V, from about 2.8 V to about 4.1 V, from about 2.8 V to about 4 V, from about 2.8 V to about 3.5 V, from about 2.8 V to about 3 V, from about 3 V to about 5.5 V, from about 3 V to about 5 V, from about 3 V to about 4.5 V, from about 3 V to about 4.1 V, from about 3 V to about 4 V, from about 3 V to about 3.5 V, from about 3.5 V to about 5.5 V, from about 3.5 V to about 5 V, from about 3.5 V to about 4.5 V, from about 3.5 V to about 4.1 V, from about 3.5 V to about 4 V, from about 4 V to about 5.5 V, from about 4 V to about 5 V, from about 4 V to about 4.5 V, from about 4 V to about 4.1 V, from about 4.1 V to about 5.5 V, from about 4.1 V to about 5 V, from about 4.1 V to about 4.5 V, from about 4.5 V to about 5. V, from about 4.5 V to about 5 V, from about 5 V to about 5.5 V; or at most about 0.5 V, at most about 0.75 V, at most about 0.8 V, at most about 0.93 V, at most about 1 V, at most about 1.1 V, at most about 1.2 V, at most about 1.25 V, at most about 1.3 V, at most about 1.5 V, at most about 1.6 V, at most about 2 V, at most about 2.5 V, at most about 2.6 V, at most about 2.8 V, at most about 3 V, at most about 3.5 V, at most about 4 V, at most about 4.1 V, at most about 4.5 V, at most about 5 V, at most about 5.5 V; or about 0.5 V, about 0.75 V, about 0.8 V, about 0.93 V, about 1 V, about 1.1 V, about 1.2 V, about 1.25 V, about 1.3 V, about 1.5 V, about 1.6 V, about 2 V, about 2.5 V, about 2.6 V, about 2.8 V, about 3 V, about 3.5 V, about 4 V, about 4.1 V, about 4.5 V, about 5 V, about 5.5 V, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the voltage is about 1.5 V to about 4.5 V.

[0083] The inventors have found that even with a cathode comprising purely carbon paper, the presently disclosed method can surprisingly enrich .sup.13CO.sub.2. The inventors have also found that when a cathode with a first base layer of metal nanoparticles and at least 1 layer of carbon nanoparticles are used, the effect is surprisingly improved further. It is believed that the metal nanoparticles improve the conductivity of the electrode surface to facilitate the reduction processes happening at the cathode. Additionally, the metal nanoparticles may also serve as catalysts to catalyst the electro-reduction processes. It is believed that the carbon nanoparticle layers serve to regulate the diffusion of electrolytes, supply current to the water-gas interface, as well as prevent the undesired agglomeration of the metal nanoparticles. The cathode is often found with the metal particle (or catalyst) layer on one side (in contact with the electrolyte), and hydrophobic on the other side (to be in contact with the gaseous feed stream). This allows for a gas-liquid interface to form while preventing the electrolyte from leaking into the feed stream. This is highly advantageous when a liquid electrolyte is used in the electrochemical cell. In a preferred embodiment, the present disclosure discloses a method wherein the electrolyte is a liquid electrolyte.

[0084] The support for the cathode may be made of any polymeric porous substrate suitable to provide an interface between the liquid electrolyte and the gas in the feed stream. The support may also comprise any material that is stable in alkaline or highly alkaline liquid electrolytes. In some embodiments, the support for the cathode is selected from the group comprising carbon paper, PTFE paper, PVDF paper, PTFE membrane or PVDF membrane. In a preferred embodiment, the present disclosure discloses a method wherein the cathode is carbon paper. In another preferred embodiment, the present disclosure discloses a method wherein the cathode comprises a support made of carbon paper. In yet another preferred embodiment, the present disclosure discloses a method wherein the polymer of the polymeric porous membrane is PTFE or PVDF.

[0085] In some embodiments, the cathode comprises a support layered with a layer of metal nanoparticles. When the support is coated with a first layer of metal nanoparticles, the resulting electrode becomes more highly conductive as a result. However, the surface is often not porous enough to encourage the formation of the gas-liquid interface that is required for the reaction to happen. In the absence of an extensive gas-liquid interface, other side-reactions often dominate as a result. For example, the inventors have found that when the reaction is performed with a cathode comprising only one metal nanoparticle layer, CO.sub.2 electro-reduction was hardly observed, and instead the standard hydrogen evolution reaction dominated.

[0086] Hence, by including at least one layer of carbon nanoparticles, a mesoporous network may be formed to both separate the metal nanoparticles, and also allow access of the liquid electrolyte to the gas stream, thus further improving the enrichment effect of the presently disclosed method. The inclusion of a second microparticle layer further stabilises the first two nanoparticle layers, and contributes to the enrichment effect as well. In some other embodiments, the cathode comprises a support layered with a first layer of metal nanoparticles and a second layer of carbon nanoparticles or carbon microparticles. In some further embodiments, the cathode comprises a support layered with a first layer of metal nanoparticles, a second layer of carbon nanoparticles and a third layer of carbon microparticles. In some other embodiments, the cathode comprises a support layered with a first layer of metal nanoparticles, a second layer of carbon nanoparticles and a third layer of carbon microparticles, and wherein the average diameter of the carbon nanoparticles of the second layer is smaller than the average diameter of the carbon microparticles in the third layer. In a preferred embodiment, the present disclosure discloses a method wherein the cathode is carbon paper, or the cathode comprises a support layered with a first layer of metal nanoparticles, a second layer of carbon nanoparticles, and a third layer of carbon microparticles, and wherein the average diameter of the carbon nanoparticles of the second layer is smaller than the average diameter of the carbon nanoparticles in the third layer.

[0087] The support must be naturally porous to allow the gas to be in contact with the liquid electrolyte so that the reaction may occur. In some embodiments, the support may comprise a polymeric porous membrane, with a pore size in the range of at least about 0.05 ?m, at least about 0.1 ?m, at least about 0.3 ?m, at least about 0.5 ?m, at least about 0.7 ?m, at least about 0.8 ?m, at least about 1 ?m, at least about 1.5 ?m, at least about 2 ?m, at least about 5 ?m; at least about 10 ?m; or from about 0.05 ?m to about 10 ?m, from about 0.05 ?m to about 5 ?m, from about 0.05 ?m to about 2 ?m, from about 0.05 ?m to about 1.5 ?m, from about 0.05 ?m to about 1 ?m, from about 0.05 ?m to about 0.8 ?m, from about 0.05 ?m to about 0.7 ?m, from about 0.05 ?m to about 0.5 ?m, from about 0.05 ?m to about 0.3 ?m, from about 0.05 ?m to about 0.1 ?m, from about 0.1 ?m to about 10 ?m, from about 0.1 ?m to about 5 ?m, from about 0.1 ?m to about 2 ?m, from about 0.1 ?m to about 1.5 ?m, from about 0.1 ?m to about 1 ?m, from about 0.1 ?m to about 0.8 ?m, from about 0.1 ?m to about 0.7 ?m, from about 0.1 ?m to about 0.5 ?m, from about 0.1 ?m to about 0.3 ?m, from about 0.3 ?m to about 10 ?m, from about 0.3 ?m to about 5 ?m, from about 0.3 ?m to about 2 ?m, from about 0.3 ?m to about 1.5 ?m, from about 0.3 ?m to about 1 ?m, from about 0.3 ?m to about 0.8 ?m, from about 0.3 ?m to about 0.7 ?m, from about 0.3 ?m to about 0.5 ?m, from about 0.5 ?m to about 10 ?m, from about 0.5 ?m to about 5 ?m, from about 0.5 ?m to about 2 ?m, from about 0.5 ?m to about 1.5 ?m, from about 0.5 ?m to about 1 ?m, from about 0.5 ?m to about 0.8 ?m, from about 0.5 ?m to about 0.7 ?m, from about 0.7 ?m to about 10 ?m, from about 0.7 ?m to about 5 ?m, from about 0.7 ?m to about 2 ?m, from about 0.7 ?m to about 1.5 ?m, from about 0.7 ?m to about 1 ?m, from about 0.7 ?m to about 0.8 ?m, from about 0.8 ?m to about 10 ?m, from about 0.8 ?m to about 5 ?m, from about 0.8 ?m to about 2 ?m, from about 0.8 ?m to about 1.5 ?m, from about 0.8 ?m to about 1 ?m, from about 1 ?m to about 10 ?m, from about 1 ?m to about 5 ?m, from about 1 ?m to about 2 ?m, from about 1 ?m to about 1.5 ?m, from about 1.5 ?m to about 10 ?m, from about 1.5 ?m to about 5 ?m, from about 1.5 ?m to about 2 ?m, from about 2 ?m to about 10 ?m, from about 2 ?m to about 5 ?m, from about 5 ?m to about 10 ?m; or at most about 0.05 ?m, at most about 0.1 ?m, at most about 0.3 ?m, at most about 0.5 ?m, at most about 0.7 ?m, at most about 0.8 ?m, at most about 1 ?m, at most about 1.5 ?m, at most about 2 ?m, at most about 5 ?m; at most about 10 ?m; or about 0.05 ?m, about 0.1 ?m, about 0.3 ?m, about 0.5 ?m, about 0.7 ?m, about 0.8 ?m, about 1 ?m, about 1.5 ?m, about 2 ?m, about 5 ?m, about 10 ?m, or any ranges or values therebetween. In some preferred embodiment, the present disclosure discloses a method wherein the support comprises a polymeric porous membrane with a pore size in the range of about 0.1 ?m to about 0.8 ?m.

[0088] In some embodiments, the carbon nanoparticles may comprise carbon black nanoparticles, graphite nanoparticles, graphite microparticles, graphene nanoparticles, single-walled carbon nanotubes, multi-walled carbon nanotubes, or fullerene nanoparticles. In a preferred embodiment, the present disclosure discloses a method wherein the second layer comprises carbon black nanoparticles, and the third layer comprises graphite microparticles. In another preferred embodiment, the present disclosure discloses a method wherein the second layer comprises graphene nanoparticles and the third layer comprises graphite microparticles.

[0089] In some embodiments, the metal nanoparticles may comprise Cu nanoparticles, Ag nanoparticles, Ni nanoparticles, Co nanoparticles, Au nanoparticles, Pd nanoparticles, Pt nanoparticles, Ni nanoparticles, or transition metal nanoparticles. In a preferred embodiment, the present disclosure discloses a method wherein the metal nanoparticles are selected from the group consisting of Cu nanoparticles, Ag nanoparticles, Ni nanoparticles, Co nanoparticles, and Au nanoparticles.

[0090] The size of the metal nanoparticles is important in the presently disclosed enrichment process. An overly small nanoparticle size results in over-agglomeration, and are not easy to stabilise as a result. On the other hand, larger-sized metal nanoparticles are more stable, but have a remarkedly lower enrichment effect. In some embodiments, the average diameter of the metal nanoparticles may be in the range of at least about 10 nm, at least about 20 nm, at least about 25 nm, at least about 50 nm, at least about 75 nm, at least about 100 nm, at least about 125 nm, at least about 150 nm, at least about 175 nm, at least about 200 nm, at least about 250 nm, at least about 300 nm, at least about 400 nm, at least about 500 nm; or from about 10 nm to about 500 nm, from about 10 nm to about 400 nm, from about 10 nm to about 300 nm, from about 10 nm to about 250 nm, from about 10 nm to about 200 nm, from about 10 nm to about 175 nm, from about 10 nm to about 150 nm, from about 10 nm to about 125 nm, from about 10 nm to about 100 nm, from about 10 nm to about 75 nm, from about 10 nm to about 50 nm, from about 10 nm to about 25 nm, from about 10 nm to about 20 nm, from about 20 nm to about 500 nm, from about 20 nm to about 400 nm, from about 20 nm to about 300 nm, from about 20 nm to about 250 nm, from about 20 nm to about 200 nm, from about 20 nm to about 175 nm, from about 20 nm to about 150 nm, from about 20 nm to about 125 nm, from about 20 nm to about 100 nm, from about 20 nm to about 75 nm, from about 20 nm to about 50 nm, from about 20 nm to about 25 nm, from about 25 nm to about 500 nm, from about 25 nm to about 400 nm, from about 25 nm to about 300 nm, from about 25 nm to about 250 nm, from about 25 nm to about 200 nm, from about 25 nm to about 175 nm, from about 25 nm to about 150 nm, from about 25 nm to about 125 nm, from about 25 nm to about 100 nm, from about 25 nm to about 75 nm, from about 25 nm to about 50 nm, from about 50 nm to about 500 nm, from about 50 nm to about 400 nm, from about 50 nm to about 300 nm, from about 50 nm to about 250 nm, from about 50 nm to about 200 nm, from about 50 nm to about 175 nm, from about 50 nm to about 150 nm, from about 50 nm to about 125 nm, from about 50 nm to about 100 nm, from about 50 nm to about 75 nm, from about 75 nm to about 500 nm, from about 75 nm to about 400 nm, from about 75 nm to about 300 nm, from about 75 nm to about 250 nm, from about 75 nm to about 200 nm, from about 75 nm to about 175 nm, from about 75 nm to about 150 nm, from about 75 nm to about 125 nm, from about 75 nm to about 100 nm, from about 100 nm to about 500 nm, from about 100 nm to about 400 nm, from about 100 nm to about 300 nm, from about 100 nm to about 250 nm, from about 100 nm to about 200 nm, from about 100 nm to about 175 nm, from about 100 nm to about 150 nm, from about 100 nm to about 125 nm, from about 125 nm to about 500 nm, from about 125 nm to about 400 nm, from about 125 nm to about 300 nm, from about 125 nm to about 250 nm, from about 125 nm to about 200 nm, from about 125 nm to about 175 nm, from about 125 nm to about 150 nm, from about 150 nm to about 500 nm, from about 150 nm to about 400 nm, from about 150 nm to about 300 nm, from about 150 nm to about 250 nm, from about 150 nm to about 200 nm, from about 150 nm to about 175 nm, from about 175 nm to about 500 nm, from about 175 nm to about 400 nm, from about 175 nm to about 300 nm, from about 175 nm to about 250 nm, from about 175 nm to about 200 nm, from about 200 nm to about 500 nm, from about 200 nm to about 400 nm, from about 200 nm to about 300 nm, from about 200 nm to about 250 nm, from about 250 nm to about 500 nm, from about 250 nm to about 400 nm, from about 250 nm to about 300 nm, from about 300 nm to about 500 nm, from about 300 nm to about 400 nm, from about 400 nm to about 500 nm; or at most about 10 nm, at most about 20 nm, at most about 25 nm, at most about 50 nm, at most about 75 nm, at most about 100 nm, at most about 125 nm, at most about 150 nm, at most about 175 nm, at most about 200 nm, at most about 250 nm, at most about 300 nm, at most about 400 nm, at most about 500 nm; or about 10 nm, about 20 nm, about 25 nm, about 50 nm, about 75 nm, about 100 nm, about 125 nm, about 150 nm, about 175 nm, about 200 nm, about 250 nm, about 300 nm, about 400 nm, about 500 nm, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the average diameter of the metal nanoparticles is in the range of about 10 nm to about 200 nm. In a further preferred embodiment, the present disclosure discloses a method wherein the average diameter of the metal particles is about 25 nm.

[0091] The metal and carbon layers may be formed by spraying the nanoparticle/microparticle dispersions onto the support. The concentration of the metal and/or carbon nanoparticles in the layers formed on the support are affected by a few factors, e.g., the concentration of the nanoparticle dispersion used, the volume of the dispersion sprayed per surface area of the support, and the loss that typically occurs during the spraying process. In some embodiments, the metal nanoparticle (catalyst) loading may be in the range of at least about 0.25 mg/cm.sup.2, at least about 0.5 mg/cm.sup.2, at least about 1 mg/cm.sup.2, at least about 2 mg/cm.sup.2, at least about 2.5 mg/cm.sup.2, at least about 4 mg/cm.sup.2, at least about 5 mg/cm.sup.2, at least about 7.5 mg/cm.sup.2, at least about 10 mg/cm.sup.2, at least about 15 mg/cm.sup.2; or from about 0.25 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 4 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 2.5 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 2 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 1 mg/cm.sup.2, from about 0.25 mg/cm.sup.2 to about 0.5 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 4 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 2.5 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 2 mg/cm.sup.2, from about 0.5 mg/cm.sup.2 to about 1 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 4 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 2.5 mg/cm.sup.2, from about 1 mg/cm.sup.2 to about 2 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 4 mg/cm.sup.2, from about 2 mg/cm.sup.2 to about 2.5 mg/cm.sup.2, from about 2.5 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 2.5 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 2.5 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 2.5 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 2.5 mg/cm.sup.2 to about 4 mg/cm.sup.2, from about 4 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 4 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 4 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 4 mg/cm.sup.2 to about 5 mg/cm.sup.2, from about 5 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 5 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 5 mg/cm.sup.2 to about 7.5 mg/cm.sup.2, from about 7.5 mg/cm.sup.2 to about 15 mg/cm.sup.2, from about 7.5 mg/cm.sup.2 to about 10 mg/cm.sup.2, from about 10 mg/cm.sup.2 to about 15 mg/cm.sup.2; or at most about 0.25 mg/cm.sup.2, at most about 0.5 mg/cm.sup.2, at most about 1 mg/cm.sup.2, at most about 2 mg/cm.sup.2, at most about 2.5 mg/cm.sup.2, at most about 4 mg/cm.sup.2, at most about 5 mg/cm.sup.2, at most about 7.5 mg/cm.sup.2, at most about 10 mg/cm.sup.2, at most about 15 mg/cm.sup.2; or about 0.25 mg/cm.sup.2, about 0.5 mg/cm.sup.2, about 1 mg/cm.sup.2, about 2 mg/cm.sup.2, about 2.5 mg/cm.sup.2, about 4 mg/cm.sup.2, about 5 mg/cm.sup.2, about 7.5 mg/cm.sup.2, about 10 mg/cm.sup.2, about 15 mg/cm.sup.2, or any ranges or values therebetween. In a preferred embodiment, the metal nanoparticle loading and/or the carbon nanoparticle loading is from about 0.5 mg/cm.sup.2 to about 10 mg/cm.sup.2, or more preferably from about 1 mg/cm.sup.2 to about 5 mg/cm.sup.2. In a preferred embodiment, the catalyst loading is from about 0.5 mg/cm.sup.2 to about 10 mg/cm.sup.2, or more preferably from about 1 mg/cm.sup.2 to about 5 mg/cm.sup.2. In a further preferred embodiment, the present disclosure discloses a method wherein the metal nanoparticle loading and/or the carbon nanoparticle loading is from about 0.5 mg/cm.sup.2 to about 4 mg/cm.sup.2, or about 1 mg/cm.sup.2 to about 3 mg/cm.sup.2. In a further preferred embodiment, the present disclosure discloses a method wherein the catalyst loading is from about 0.5 mg/cm.sup.2 to about 4 mg/cm.sup.2, or about 1 mg/cm.sup.2 to about 3 mg/cm.sup.2. In a further preferred embodiment, the present disclosure discloses a method wherein the concentration of metal nanoparticles is about 0.5 mg/cm.sup.2 to about 4 mg/cm.sup.2 of cathode surface area.

[0092] In some embodiments, the average diameter of the carbon nanoparticles in the second layer may be in the range of at least about 10 nm, at least about 20 nm, at least about 25 nm, at least about 50 nm, at least about 100 nm, at least about 250 nm, at least about 500 nm, at least about 1000 nm, at least about 1500 nm, at least about 2000 nm, at least about 3000 nm, at least about 4000 nm, at least about 5000 nm; or from about 10 nm to about 5000 nm, from about 10 nm to about 4000 nm, from about 10 nm to about 3000 nm, from about 10 nm to about 2000 nm, from about 10 nm to about 1500 nm, from about 10 nm to about 1000 nm, from about 10 nm to about 500 nm, from about 10 nm to about 250 nm, from about 10 nm to about 100 nm, from about 10 nm to about 50 nm, from about 10 nm to about 25 nm, from about 10 nm to about 20 nm, from about 20 nm to about 5000 nm, from about 20 nm to about 4000 nm, from about 20 nm to about 3000 nm, from about 20 nm to about 2000 nm, from about 20 nm to about 1500 nm, from about 20 nm to about 1000 nm, from about 20 nm to about 500 nm, from about 20 nm to about 250 nm, from about 20 nm to about 100 nm, from about 20 nm to about 50 nm, from about 20 nm to about 25 nm, from about 25 nm to about 5000 nm, from about 25 nm to about 4000 nm, from about 25 nm to about 3000 nm, from about 25 nm to about 2000 nm, from about 25 nm to about 1500 nm, from about 25 nm to about 1000 nm, from about 25 nm to about 500 nm, from about 25 nm to about 250 nm, from about 25 nm to about 100 nm, from about 25 nm to about 50 nm, from about 50 nm to about 5000 nm, from about 50 nm to about 4000 nm, from about 50 nm to about 3000 nm, from about 50 nm to about 2000 nm, from about 50 nm to about 1500 nm, from about 50 nm to about 1000 nm, from about 50 nm to about 500 nm, from about 50 nm to about 250 nm, from about 50 nm to about 100 nm, from about 100 nm to about 5000 nm, from about 100 nm to about 4000 nm, from about 100 nm to about 3000 nm, from about 100 nm to about 2000 nm, from about 100 nm to about 1500 nm, from about 100 nm to about 1000 nm, from about 100 nm to about 500 nm, from about 100 nm to about 250 nm, from about 250 nm to about 5000 nm, from about 250 nm to about 4000 nm, from about 250 nm to about 3000 nm, from about 250 nm to about 2000 nm, from about 250 nm to about 1500 nm, from about 250 nm to about 1000 nm, from about 250 nm to about 500 nm, from about 500 nm to about 5000 nm, from about 500 nm to about 4000 nm, from about 500 nm to about 3000 nm, from about 500 nm to about 2000 nm, from about 500 nm to about 1500 nm, from about 500 nm to about 1000 nm, from about 1000 nm to about 5000 nm, from about 1000 nm to about 4000 nm, from about 1000 nm to about 3000 nm, from about 1000 nm to about 2000 nm, from about 1000 nm to about 1500 nm, from about 1500 nm to about 5000 nm, from about 1500 nm to about 4000 nm, from about 1500 nm to about 3000 nm, from about 1500 nm to about 2000 nm, from about 2000 nm to about 5000 nm, from about 2000 nm to about 4000 nm, from about 2000 nm to about 3000 nm, from about 3000 nm to about 5000 nm, from about 3000 nm to about 4000 nm, from about 4000 nm to about 5000 nm; or at most about 10 nm, at most about 20 nm, at most about 25 nm, at most about 50 nm, at most about 100 nm, at most about 250 nm, at most about 500 nm, at most about 1000 nm, at most about 1500 nm, at most about 2000 nm, at most about 3000 nm, at most about 4000 nm, at about 5000 nm; or about 10 nm, about 20 nm, about 25 nm, about 50 nm, about 100 nm, about 250 nm, about 500 nm, about 1000 nm, about 1500 nm, about 2000 nm, about 3000 nm, about 4000 nm, about 5000 nm, or any ranges values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon nanoparticles in the second layer is in the range of about 25 nm to about 1,000 nm. In a further preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon nanoparticles in the second layer is about 100 nm.

[0093] In some embodiments, the average diameter of the carbon microparticles in the third layer may be in the range of at least about 1 ?m, at least about 2.5 ?m, at least about 4 ?m, at least about 5 ?m, at least about 7.5 ?m, at least about 10 ?m, at least about 12.5 ?m, at least about 15 ?m, at least about 17.5 ?m, at least about 20 ?m, at least about 30 ?m, at least about 40 ?m, at least about 50 ?m; or from about 1 ?m to about 50 ?m, from about 1 ?m to about 40 ?m, from about 1 ?m to about 30 ?m, from about 1 ?m to about 20 ?m, from about 1 ?m to about 17.5 ?m, from about 1 ?m to about 15 ?m, from about 1 ?m to about 12.5 ?m, from about 1 ?m to about 10 ?m, from about 1 ?m to about 7.5 ?m, from about 1 ?m to about 5 ?m, from about 1 ?m to about 4 ?m, from about 1 ?m to about 2.5 ?m, from about 2.5 ?m to about 50 ?m, from about 2.5 ?m to about 40 ?m, from about 2.5 ?m to about 30 ?m, from about 2.5 ?m to about 20 ?m, from about 2.5 ?m to about 17.5 ?m, from about 2.5 ?m to about 15 ?m, from about 2.5 ?m to about 12.5 ?m, from about 2.5 ?m to about 10 ?m, from about 2.5 ?m to about 7.5 ?m, from about 2.5 ?m to about 5 ?m, from about 2.5 ?m to about 4 ?m, from about 4 ?m to about 50 ?m, from about 4 ?m to about 40 ?m, from about 4 ?m to about 30 ?m, from about 4 ?m to about 20 ?m, from about 4 ?m to about 17.5 ?m, from about 4 ?m to about 15 ?m, from about 4 ?m to about 12.5 ?m, from about 4 ?m to about 10 ?m, from about 4 ?m to about 7.5 ?m, from about 4 ?m to about 5 ?m, from about 5 ?m to about 50 ?m, from about 5 ?m to about 40 ?m, from about 5 ?m to about 30 ?m, from about 5 ?m to about 20 ?m, from about 5 ?m to about 17.5 ?m, from about 5 ?m to about 15 ?m, from about 5 ?m to about 12.5 ?m, from about 5 ?m to about 10 ?m, from about 5 ?m to about 7.5 ?m, from about 7.5 ?m to about 50 ?m, from about 7.5 ?m to about 40 ?m, from about 7.5 ?m to about 30 ?m, from about 7.5 ?m to about 20 ?m, from about 7.5 ?m to about 17.5 ?m, from about 7.5 ?m to about 15 ?m, from about 7.5 ?m to about 12.5 ?m, from about 7.5 ?m to about 10 ?m, from about 10 ?m to about 50 ?m, from about 10 ?m to about 40 ?m, from about 10 ?m to about 30 ?m, from about 10 ?m to about 20 ?m, from about 10 ?m to about 17.5 ?m, from about 10 ?m to about 15 ?m, from about 10 ?m to about 12.5 ?m, from about 12.5 ?m to about 50 ?m, from about 12.5 ?m to about 40 ?m, from about 12.5 ?m to about 30 ?m, from about 12.5 ?m to about 20 ?m, from about 12.5 ?m to about 17.5 ?m, from about 12.5 ?m to about 15 ?m, from about 15 ?m to about 50 ?m, from about 15 ?m to about 40 ?m, from about 15 ?m to about 30 ?m, from about 15 ?m to about 20 ?m, from about 15 ?m to about 17.5 ?m, from about 17.5 ?m to about 50 ?m, from about 17.5 ?m to about 40 ?m, from about 17.5 ?m to about 30 ?m, from about 17.5 ?m to about 20 ?m, from about 20 ?m to about 50 ?m, from about 20 ?m to about 40 ?m, from about 20 ?m to about 30 ?m, from about 30 ?m to about 50 ?m, from about 30 ?m to about 40 ?m, from about 40 ?m to about 50 ?m; or at most about 1 ?m, at most about 2.5 ?m, at most about 4 ?m, at most about 5 ?m, at most about 7.5 ?m, at most about 10 ?m, at most about 12.5 ?m, at most about 15 ?m, at most about 17.5 ?m, at most about 20 ?m, at most about 30 ?m, at most about 40 ?m, at most about 50 ?m; or about 1 ?m, about 2.5 ?m, about 4 ?m, about 5 ?m, about 7.5 ?m, about 10 ?m, about 12.5 ?m, about 15 ?m, about 17.5 ?m, about 20 ?m, about 30 ?m, about 40 ?m, about 50 ?m, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon microparticles in the third layer is in the range of about 4 ?m to about 20 ?m. In a further preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon microparticles in the third layer is in the range of about 5 ?m to about 20 ?m.

[0094] In some embodiments, the average diameter of the carbon microparticles in the third layer may be in the range of at least about 1000 nm, at least about 2500 nm, at least about 4000 nm, at least about 5000 nm, at least about 7500 nm, at least about 10000 nm, at least about 12500 nm, at least about 15000 nm, at least about 17500 nm, at least about 20000 nm, at least about 30000 nm, at least about 40000 nm, at least about 50000 nm; or from about 1000 nm to about 50000 nm, from about 1000 nm to about 40000 nm, from about 1000 nm to about 30000 nm, from about 1000 nm to about 20000 nm, from about 1000 nm to about 17500 nm, from about 1000 nm to about 15000 nm, from about 1000 nm to about 12500 nm, from about 1000 nm to about 10000 nm, from about 1000 nm to about 7500 nm, from about 1000 nm to about 5000 nm, from about 1000 nm to about 4000 nm, from about 1000 nm to about 2500 nm, from about 2500 nm to about 50000 nm, from about 2500 nm to about 40000 nm, from about 2500 nm to about 30000 nm, from about 2500 nm to about 20000 nm, from about 2500 nm to about 17500 nm, from about 2500 nm to about 15000 nm, from about 2500 nm to about 12500 nm, from about 2500 nm to about 10000 nm, from about 2500 nm to about 7500 nm, from about 2500 nm to about 5000 nm, from about 2500 nm to about 4000 nm, from about 4000 nm to about 50000 nm, from about 4000 nm to about 40000 nm, from about 4000 nm to about 30000 nm, from about 4000 nm to about 20000 nm, from about 4000 nm to about 17500 nm, from about 4000 nm to about 15000 nm, from about 4000 nm to about 12500 nm, from about 4000 nm to about 10000 nm, from about 4000 nm to about 7500 nm, from about 4000 nm to about 5000 nm, from about 5000 nm to about 50000 nm, from about 5000 nm to about 40000 nm, from about 5000 nm to about 30000 nm, from about 5000 nm to about 20000 nm, from about 5000 nm to about 17500 nm, from about 5000 nm to about 15000 nm, from about 5000 nm to about 12500 nm, from about 5000 nm to about 10000 nm, from about 5000 nm to about 7500 nm, from about 7500 nm to about 50000 nm, from about 7500 nm to about 40000 nm, from about 7500 nm to about 30000 nm, from about 7500 nm to about 20000 nm, from about 7500 nm to about 17500 nm, from about 7500 nm to about 15000 nm, from about 7500 nm to about 12500 nm, from about 7500 nm to about 10000 nm, from about 10000 nm to about 50000 nm, from about 10000 nm to about 40000 nm, from about 10000 nm to about 30000 nm, from about 10000 nm to about 20000 nm, from about 10000 nm to about 17500 nm, from about 10000 nm to about 15000 nm, from about 10000 nm to about 12500 nm, from about 12500 nm to about 50000 nm, from about 12500 nm to about 40000 nm, from about 12500 nm to about 30000 nm, from about 12500 nm to about 20000 nm, from about 12500 nm to about 17500 nm, from about 12500 nm to about 15000 nm, from about 15000 nm to about 50000 nm, from about 15000 nm to about 40000 nm, from about 15000 nm to about 30000 nm, from about 15000 nm to about 20000 nm, from about 15000 nm to about 17500 nm, from about 17500 nm to about 50000 nm, from about 17500 nm to about 40000 nm, from about 17500 nm to about 30000 nm, from about 17500 nm to about 20000 nm, from about 20000 nm to about 50000 nm, from about 20000 nm to about 40000 nm, from about 20000 nm to about 30000 nm, from about 30000 nm to about 50000 nm, from about 30000 nm to about 40000 nm, from about 40000 nm to about 50000 nm; or at most about 1000 nm, at most about 2500 nm, at most about 4000 nm, at most about 5000 nm, at most about 7500 nm, at most about 10000 nm, at most about 12500 nm, at most about 15000 nm, at most about 17500 nm, at most about 20000 nm, at most about 30000 nm, at most about 40000 nm, at most about 50000 nm; or about 1000 nm, about 2500 nm, about 4000 nm, about 5000 nm, about 7500 nm, about 10000 nm, about 12500 nm, about 15000 nm, about 17500 nm, about 20000 nm, about 30000 nm, about 40000 nm, about 50000 nm, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon microparticles in the third layer is in the range of about 4000 nm to about 20000 nm. In a further preferred embodiment, the present disclosure discloses a method wherein the average diameter of the carbon microparticles in the third layer is in the range of about 5000 nm to about 20000 nm.

[0095] The anode may comprise materials that are stable in alkaline or highly alkaline liquid electrolytes, such as Ni foam, Ni foam coated with various metal oxide-hydroxides such as FeOOH, NiOOH, or NiCoO.sub.x(OH).sub.y. In a preferred embodiment, the present disclosure discloses a method wherein the electrochemical cell further comprises an anode, wherein the anode is selected from the group consisting of Ni foam, and Ni foam coated with metal oxide hydroxide. In a further preferred embodiment, the present disclosure discloses a method wherein the Ni foam is coated with metal oxide hydroxide selected from the group consisting of FeOOH, NiOOH, and NiCoO.sub.x(OH).sub.y.

[0096] In a preferred embodiment, the present disclosure discloses a method wherein the cathode is a gas diffusion electrode (GDE).

[0097] The electrochemical cell may also comprise an ion-exchange membrane to separate the liquid catholyte from the liquid anolyte, while allowing ions to flow through easily. Examples of suitable ion-exchange membranes may comprise anion exchange membranes, or polymer backbone structures like polysulfone, polyphenol, polyester, PTFE, polypropylene, PVDF, polyester ketone, or mixtures thereof, or polymer backbone structures modified with ion conducting channels formed by tertiary amine groups such as trimethylamine, 1,4-diazabicyclo[2.2.2]octane (DABCO), hexamethylenetetramine, N,N,N,N-tetramethyl-1,6-diaminohexane, or N,N,N,N-tetramethyl-1,2-diaminoethylene or mixtures thereof. In some embodiments, the ion-exchange membrane is a polysulfone-based membrane, preferentially doped with selenium, bromide or similar compounds.

[0098] The presently disclosed method may be used in an electrochemical cell comprising a flat membrane cell.

[0099] In some embodiments, the unreacted CO.sub.2 may be channeled as a feed stream into either the same cathode chamber, or into the cathode chamber of another reactor. This advantageously allows the same volume of CO.sub.2 to be continuously enriched over multiple cycles. The recirculating process can allow the enrichment of .sup.13CO.sub.2 to stack, eventually resulting in a highly enriched .sup.13CO.sub.2 stream. The unreacted CO.sub.2 may be directly fed as the feed stream to the cathode chamber, or may first be processed to separate the CO.sub.2 from the liquid products being recirculated as a feed stream to the cathode chamber. In a preferred embodiment, the present disclosure discloses a method wherein the method further comprises recirculating the unreacted CO.sub.2 as a feed stream to the cathode chamber. In a further preferred embodiment, the present disclosure discloses a method wherein the recirculation is performed at least twice. In another preferred embodiment, the present disclosure discloses a method wherein the cathode chamber is a cathode chamber of a different electrochemical cell. In a preferred embodiment, the present disclosure discloses a method further comprising (iv) recirculating the unreacted CO.sub.2 from step (iii) to the cathode chamber. In a further preferred embodiment, the present disclosure discloses a method wherein step (iv) is performed at least twice. In another preferred embodiment, the present disclosure discloses a method wherein the cathode chamber is a cathode chamber of a different electrochemical cell.

[0100] In some embodiments, the present disclosure discloses a method wherein the recirculation is performed at least about 1 time, at least about 2 times, at least about 3 times, at least about 4 times, at least about 5 times, at least about 10 times, at least about 20 times, at least about 30 times, at least about 50 times, at least about 100 times, at least about 200 times, at least about 300 times, at least about 500 times, at least about 750 times, at least about 1000 times; or from about 1 time to about 1000 times, from about 1 time to about 750 times, from about 1 time to about 500 times, from about 1 time to about 300 times, from about 1 time to about 200 times, from about 1 time to about 100 times, from about 1 time to about 50 times, from about 1 time to about 30 times, from about 1 time to about 20 times, from about 1 time to about 10 times, from about 1 time to about 5 times, from about 1 time to about 4 times, from about 1 time to about 3 times, from about 1 time to about 2 times, from about 2 times to about 1000 times, from about 2 times to about 750 times, from about 2 times to about 500 times, from about 2 times to about 300 times, from about 2 times to about 200 times, from about 2 times to about 100 times, from about 2 times to about 50 times, from about 2 times to about 30 times, from about 2 times to about 20 times, from about 2 times to about 10 times, from about 2 times to about 5 times, from about 2 times to about 4 times, from about 2 times to about 3 times, from about 3 times to about 1000 times, from about 3 times to about 750 times, from about 3 times to about 500 times, from about 3 times to about 300 times, from about 3 times to about 200 times, from about 3 times to about 100 times, from about 3 times to about 50 times, from about 3 times to about 30 times, from about 3 times to about 20 times, from about 3 times to about 10 times, from about 3 times to about 5 times, from about 3 times to about 4 times, from about 4 times to about 1000 times, from about 4 times to about 750 times, from about 4 times to about 500 times, from about 4 times to about 300 times, from about 4 times to about 200 times, from about 4 times to about 100 times, from about 4 times to about 50 times, from about 4 times to about 30 times, from about 4 times to about 20 times, from about 4 times to about 10 times, from about 4 times to about 5 times, from about 5 times to about 1000 times, from about 5 times to about 750 times, from about 5 times to about 500 times, from about 5 times to about 300 times, from about 5 times to about 200 times, from about 5 times to about 100 times, from about 5 times to about 50 times, from about 5 times to about 30 times, from about 5 times to about 20 times, from about 5 times to about 10 times, from about 10 times to about 1000 times, from about 10 times to about 750 times, from about 10 times to about 500 times, from about 10 times to about 300 times, from about 10 times to about 200 times, from about 10 times to about 100 times, from about 10 times to about 50 times, from about 10 times to about 30 times, from about 10 times to about 20 times, from about 20 times to about 1000 times, from about 20 times to about 750 times, from about 20 times to about 500 times, from about 20 times to about 300 times, from about 20 times to about 200 times, from about 20 times to about 100 times, from about 20 times to about 50 times, from about 20 times to about 30 times, from about 30 times to about 1000 times, from about 30 times to about 750 times, from about 30 times to about 500 times, from about 30 times to about 300 times, from about 30 times to about 200 times, from about 30 times to about 100 times, from about 30 times to about 50 times, from about 30 times to about 40 times, from about 40 times to about 1000 times, from about 40 times to about 750 times, from about 40 times to about 500 times, from about 40 times to about 300 times, from about 40 times to about 200 times, from about 40 times to about 100 times, from about 40 times to about 50 times, from about 50 times to about 1000 times, from about 50 times to about 750 times, from about 50 times to about 500 times, from about 50 times to about 300 times, from about 50 times to about 200 times, from about 50 times to about 100 times, from about 100 times to about 1000 times, from about 100 times to about 750 times, from about 100 times to about 500 times, from about 100 times to about 300 times, from about 100 times to about 200 times, from about 200 times to about 1000 times, from about 200 times to about 750 times, from about 200 times to about 500 times, from about 200 times to about 300 times, from about 300 times to about 1000 times, from about 300 times to about 750 times, from about 300 times to about 500 times, from about 500 times to about 1000 times, from about 500 times to about 750 times, from about 750 times to about 1000 times; or at most about 1 time, at most about 2 times, at most about 3 times, at most about 4 times, at most about 5 times, at most about 10 times, at most about 20 times, at most about 30 times, at most about 50 times, at most about 100 times, at most about 200 times, at most about 300 times, at most about 500 times, at most about 750 times, at most about 1000 times; or about 1 time, about 2 times, about 3 times, about 4 times, about 5 times, about 10 times, about 20 times, about 30 times, about 50 times, about 100 times, about 200 times, about 300 times, about 500 times, about 750 times, about 1000 times, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein the recirculation is performed at least twice.

[0101] The presently disclosed method can produce a highly enriched .sup.13CO.sub.2 stream. The presently disclosed method is also capable of producing one or more product streams comprising reduction products, like carbon monoxide, ethanol, ethane, ethene, acetic acid, among others. In a preferred embodiment, the present disclosure discloses .sup.13CO.sub.2 produced by the method disclosed herein. In a further preferred embodiment, the present disclosure discloses a product produced by the method disclosed herein, wherein the product comprises ethanol, ethane, ethene and acetic acid. In another preferred embodiment, the present disclosure discloses a product produced by the method disclosed herein, wherein the product comprises CO, ethylene, propene and ethanol. In a further preferred embodiment, the present disclosure discloses a product produced by the method disclosed herein, wherein the product is selected from the group consisting of ethylene, ethanol, and acetic acid.

[0102] The presently disclosed method can produce a highly enriched .sup.13CO.sub.2 stream. The presently disclosed method is also capable of producing one or more product streams comprising reduction products, like formic acid, methane, acetone, propyl aldehyde, propylene and propanol, amongst others. The present disclosed method can also produce various reduction products like syngas, CO and H.sub.2. In some other embodiments, the presently disclosed method is capable of producing C.sub.2 products comprising ethanol, ethane, ethene, acetic acid or acetaldehyde. In other embodiments, the presently disclosed method is capable of producing products comprising formic acid, methane, acetone, propyl aldehyde, propylene, propanol, CO, H.sub.2, C.sub.2 products comprising ethanol, ethane, ethene, acetic acid, or acetaldehyde. In a preferred embodiment, the present disclosure discloses .sup.13CO.sub.2 produced by the method disclosed herein. In a further preferred embodiment, the present disclosure discloses a product produced by the method disclosed herein, wherein the product comprises CO, H.sub.2, formic acid, methane, ethanol, ethane, ethene, acetic acid, acetaldehyde, acetone, propyl aldehyde, propylene and propanol. In another preferred embodiment, the present disclosure discloses CO, ethylene, propene and ethanol mainly produced by the method disclosed herein. In another preferred embodiment, the present disclosure discloses CO, ethylene, propene and ethanol produced by the method disclosed herein. In a further preferred embodiment, the present disclosure discloses CO mainly produced by the method disclosed herein. In a further preferred embodiment, the present disclosure discloses CO produced by the method disclosed herein.

[0103] In some embodiments, the presently disclosed method can reduce a portion of CO.sub.2 in the feed stream to products, in a range of at least about 0.5%, at least about 0.68%, at least about 0.7%, at least about 1%, at least about 2%, at least about 2.2%, at least about 2.64%, at least about 2.78%, at least about 3.51%, at least about 5%, at least about 8%, at least about 10%, at least about 12%, at least about 20%, at least about 25%, at least about 28%, at least about 31%, at least about 35%, at least about 40%, at least about 50% at least about 70%, at least about 90%; or from about 0.5% to about 90%, from about 0.5% to about 70%, from about 0.5% to about 50%, from about 0.5% to about 40%, from about 0.5% to about 35%, from about 0.5% to about 31%, from about 0.5% to about 28%, from about 0.5% to about 25%, from about 0.5% to about 20%, from about 0.5% to about 12%, from about 0.5% to about 10%, from about 0.5% to about 8%, from about 0.5% to about 5%, from about 0.5% to about 3.51%, from about 0.5% to about 2.78%, from about 0.5% to about 2.64%, from about 0.5% to about 2.2%, from about 0.5% to about 2%, from about 0.5% to about 1%, from about 0.5% to about 0.7%, from about 0.5% to about 0.68%, from about 0.68% to about 90%, from about 0.68% to about 70%, from about 0.68% to about 50%, from about 0.68% to about 40%, from about 0.68% to about 31%, from about 0.68% to about 28%, from about 0.68% to about 25%, from about 0.68% to about 20%, from about 0.68% to about 12%, from about 0.68% to about 10%, from about 0.68% to about 8%, from about 0.68% to about 5%, from about 0.68% to about 3.51%, from about 0.68% to about 2.78%, from about 0.68% to about 2.64%, from about 0.68% to about 2.2%, from about 0.68% to about 2%, from about 0.68% to about 1%, from about 0.68% to about 0.7%, from about 0.7% to about 90%, from about 0.7% to about 70%, from about 0.7% to about 50%, from about 0.7% to about 40%, from about 0.7% to about 31%, from about 0.7% to about 28%, from about 0.7% to about 25%, from about 0.7% to about 20%, from about 0.7% to about 12%, from about 0.7% to about 10%, from about 0.7% to about 8%, from about 0.7% to about 5%, from about 0.7% to about 3.51%, from about 0.7% to about 2.78%, from about 0.7% to about 2.64%, from about 0.7% to about 2.2%, from about 0.7% to about 2%, from about 0.7% to about 1%, from about 1% to about 90%, from about 1% to about 70%, from about 1% to about 50%, from about 1% to about 40%, from about 1% to about 31%, from about 1% to about 28%, from about 1% to about 25%, from about 1% to about 20%, from about 1% to about 12%, from about 1% to about 10%, from about 1% to about 8%, from about 1% to about 5%, from about 1% to about 3.51%, from about 1% to about 2.78%, from about 1% to about 2.64%, from about 1% to about 2.2%, from about 1% to about 2%, from about 2% to about 90%, from about 2% to about 70%, from about 2% to about 50%, from about 2% to about 40%, from about 2% to about 31%, from about 2% to about 28%, from about 2% to about 25%, from about 2% to about 20%, from about 2% to about 12%, from about 2% to about 10%, from about 2% to about 8%, from about 2% to about 5%, from about 2% to about 3.51%, from about 2% to about 2.78%, from about 2% to about 2.64%, from about 2% to about 2.2%, from about 2.2% to about 90%, from about 2.2% to about 70%, from about 2.2% to about 50%, from about 2.2% to about 40%, from about 2.2% to about 31%, from about 2.2% to about 28%, from about 2.2% to about 25%, from about 2.2% to about 20%, from about 2.2% to about 12%, from about 2.2% to about 10%, from about 2.2% to about 8%, from about 2.2% to about 5%, from about 2.2% to about 3.51%, from about 2.2% to about 2.78%, from about 2.2% to about 2.64%, from about 2.64% to about 90%, from about 2.64% to about 70%, from about 2.64% to about 50%, from about 2.64% to about 40%, from about 2.64% to about 31%, from about 2.64% to about 28%, from about 2.64% to about 25%, from about 2.64% to about 20%, from about 2.64% to about 12%, from about 2.64% to about 10%, from about 2.64% to about 8%, from about 2.64% to about 5%, from about 2.64% to about 3.51%, from about 2.64% to about 2.78%, from about 2.78% to about 90%, from about 2.78% to about 70%, from about 2.78% to about 50%, from about 2.78% to about 40%, from about 2.78% to about 31%, from about 2.78% to about 28%, from about 2.78% to about 25%, from about 2.78% to about 20%, from about 2.78% to about 12%, from about 2.78% to about 10%, from about 2.78% to about 8%, from about 2.78% to about 5%, from about 2.78% to about 3.51%, from about 3.51% to about 90%, from about 3.51% to about 70%, from about 3.51% to about 50%, from about 3.51% to about 40%, from about 3.51% to about 31%, from about 3.51% to about 28%, from about 3.51% to about 25%, from about 3.51% to about 20%, from about 3.51% to about 12%, from about 3.51% to about 10%, from about 3.51% to about 8%, from about 3.51% to about 5%, from about 5% to about 90%, from about 5% to about 70%, from about 5% to about 50%, from about 5% to about 40%, from about 5% to about 31%, from about 5% to about 28%, from about 5% to about 25%, from about 5% to about 20%, from about 5% to about 12%, from about 5% to about 10%, from about 5% to about 8%, from about 8% to about 90%, from about 8% to about 70%, from about 8% to about 50%, from about 8% to about 40%, from about 8% to about 31%, from about 8% to about 28%, from about 8% to about 25%, from about 8% to about 20%, from about 8% to about 12%, from about 8% to about 10%, from about 10% to about 90%, from about 10% to about 70%, from about 10% to about 50%, from about 10% to about 40%, from about 10% to about 31%, from about 10% to about 28%, from about 10% to about 25%, from about 10% to about 20%, from about 10% to about 12%, from about 12% to about 90%, from about 12% to about 70%, from about 12% to about 50%, from about 12% to about 40%, from about 12% to about 31%, from about 12% to about 28%, from about 12% to about 25%, from about 12% to about 20%, from about 20% to about 90%, from about 20% to about 70%, from about 20% to about 50%, from about 20% to about 40%, from about 20% to about 31%, from about 20% to about 28%, from about 20% to about 25%, from about 25% to about 90%, from about 25% to about 70%, from about 25% to about 50%, from about 25% to about 40%, from about 25% to about 31%, from about 25% to about 28%, from about 28% to about 50%, from about 28% to about 40%, from about 28% to about 31%, from about 31% to about 50%, from about 31% to about 40%, from about 40% to about 90%, from about 40% to about 70%, from about 40% to about 50%, from about 50% to about 90%, from about 50% to about 70%, from about 70% to about 90%; or at most about 0.5%, at most about 0.68%, at most about 0.7%, at most about 1%, at most about 2%, at most about 2.2%, at most about 2.64%, at most about 2.78%, at most about 3.51%, at most about 5%, at most about 8%, at most about 10%, at most about 12%, at most about 20%, at most about 25%, at most about 28%, at most about 31%, at most about 40%, at most about 50%, at most about 70%, at most about 90%; or about 0.5%, about 0.68%, about 0.7%, about 1%, about 2%, about 2.2%, about 2.64%, about 2.78%, about 3.51%, about 5%, about 8%, about 10%, about 12%, about 20%, about 25%, about 28%, about 31%, about 35%, about 40%, about 50%, about 70%, about 90%, or any ranges or values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein about 5% to about 35% of CO.sub.2 in the feed stream is converted to one or more products. In a further preferred embodiment, the present disclosure discloses a method wherein about 5% to about 35% of CO.sub.2 in the feed stream is converted to one or more products, wherein the product is selected from the group consisting of ethylene, ethanol, and acetic acid.

[0104] In some embodiments, the unreacted CO.sub.2 may have a .sup.13C isotope concentration in the range of at least about 1.112%, at least about 1.114%, at least about 1.115%, at least about 1.119%, at least about 1.12%, at least about 1.121%, at least about 1.124%, at least about 1.125%, at least about 1.13%, at least about 1.15%, at least about 1.23%, at least about 1.27%, at least about 1.47%, at least about 2.5%, at least about 5.76%, at least about 10%, at least about 30%, at least about 50%, at least about 70%, at least about 88.7%, at least about 90%, at least about 95%, at least about 99%, at least about 99.9%, at least about 99.99%; or from about 1.112% to about 99.99%, from about 1.112% to about 99.9%, from about 1.112% to about 99%, from about 1.112% to about 95%, from about 1.112% to about 90%, from about 1.112% to about 88.7%, from about 1.112% to about 70%, from about 1.112% to about 50%, from about 1.112% to about 30%, from about 1.112% to about 10%, from about 1.112% to about 5.76%, from about 1.112% to about 2.5%, from about 1.112% to about 1.47%, from about 1.112% to about 1.27%, from about 1.112% to about 1.23%, from about 1.112% to about 1.15%, from about 1.112% to about 1.13%, from about 1.112% to about 1.125%, from about 1.112% to about 1.124%, from about 1.112% to about 1.121%, from about 1.112% to about 1.12%, from about 1.112% to about 1.119%, from about 1.112% to about 1.115%, from about 1.112% to about 1.114%, from about 1.114% to about 99.99%, from about 1.114% to about 99.9%, from about 1.114% to about 99%, from about 1.114% to about 95%, from about 1.114% to about 90%, from about 1.114% to about 88.7%, from about 1.114% to about 70%, from about 1.114% to about 50%, from about 1.114% to about 30%, from about 1.114% to about 10%, from about 1.114% to about 5.76%, from about 1.114% to about 2.5%, from about 1.114% to about 1.47%, from about 1.114% to about 1.27%, from about 1.114% to about 1.23%, from about 1.114% to about 1.15%, from about 1.114% to about 1.13%, from about 1.114% to about 1.125%, from about 1.114% to about 1.124%, from about 1.114% to about 1.121%, from about 1.114% to about 1.12%, from about 1.114% to about 1.119%, from about 1.114% to about 1.115%, from about 1.115% to about 99.99%, from about 1.115% to about 99.9%, from about 1.115% to about 99%, from about 1.115% to about 95%, from about 1.115% to about 90%, from about 1.115% to about 88.7%, from about 1.115% to about 70%, from about 1.115% to about 50%, from about 1.115% to about 30%, from about 1.115% to about 10%, from about 1.115% to about 5.76%, from about 1.115% to about 2.5%, from about 1.115% to about 1.47%, from about 1.115% to about 1.27%, from about 1.115% to about 1.23%, from about 1.115% to about 1.15%, from about 1.115% to about 1.13%, from about 1.115% to about 1.125%, from about 1.115% to about 1.124%, from about 1.115% to about 1.121%, from about 1.115% to about 1.12%, from about 1.115% to about 1.119%, from about 1.119% to about 99.99%, from about 1.119% to about 99.9%, from about 1.119% to about 99%, from about 1.119% to about 95%, from about 1.119% to about 90%, from about 1.119% to about 88.7%, from about 1.119% to about 70%, from about 1.119% to about 50%, from about 1.119% to about 30%, from about 1.119% to about 10%, from about 1.119% to about 5.76%, from about 1.119% to about 2.5%, from about 1.119% to about 1.47%, from about 1.119% to about 1.27%, from about 1.119% to about 1.23%, from about 1.119% to about 1.15%, from about 1.119% to about 1.13%, from about 1.119% to about 1.125%, from about 1.119% to about 1.124%, from about 1.119% to about 1.121%, from about 1.119% to about 1.12%, from about 1.12% to about 99.99%, from about 1.12% to about 99.9%, from about 1.12% to about 99%, from about 1.12% to about 95%, from about 1.12% to about 90%, from about 1.12% to about 88.7%, from about 1.12% to about 70%, from about 1.12% to about 50%, from about 1.12% to about 30%, from about 1.12% to about 10%, from about 1.12% to about 5.76%, from about 1.12% to about 2.5%, from about 1.12% to about 1.47%, from about 1.12% to about 1.27%, from about 1.12% to about 1.23%, from about 1.12% to about 1.15%, from about 1.12% to about 1.13%, from about 1.12% to about 1.125%, from about 1.12% to about 1.124%, from about 1.12% to about 1.121%, from about 1.121% to about 99.99%, from about 1.121% to about 99.9%, from about 1.121% to about 99%, from about 1.121% to about 95%, from about 1.121% to about 90%, from about 1.121% to about 88.7%, from about 1.121% to about 70%, from about 1.121% to about 50%, from about 1.121% to about 30%, from about 1.121% to about 10%, from about 1.121% to about 5.76%, from about 1.121% to about 2.5%, from about 1.121% to about 1.47%, from about 1.121% to about 1.27%, from about 1.121% to about 1.23%, from about 1.121% to about 1.15%, from about 1.121% to about 1.13%, from about 1.121% to about 1.125%, from about 1.121% to about 1.124%, from about 1.124% to about 99.99%, from about 1.124% to about 99.9%, from about 1.124% to about 99%, from about 1.124% to about 95%, from about 1.124% to about 90%, from about 1.124% to about 88.7%, from about 1.124% to about 70%, from about 1.124% to about 50%, from about 1.124% to about 30%, from about 1.124% to about 10%, from about 1.124% to about 5.76%, from about 1.124% to about 2.5%, from about 1.124% to about 1.47%, from about 1.124% to about 1.27%, from about 1.124% to about 1.23%, from about 1.124% to about 1.15%, from about 1.124% to about 1.13%, from about 1.124% to about 1.125%, from about 1.125% to about 99.99%, from about 1.125% to about 99.9%, from about 1.125% to about 99%, from about 1.125% to about 95%, from about 1.125% to about 90%, from about 1.125% to about 88.7%, from about 1.125% to about 70%, from about 1.125% to about 50%, from about 1.125% to about 30%, from about 1.125% to about 10%, from about 1.125% to about 5.76%, from about 1.125% to about 2.5%, from about 1.125% to about 1.47%, from about 1.125% to about 1.27%, from about 1.125% to about 1.23%, from about 1.125% to about 1.15%, from about 1.125% to about 1.13%, from about 1.13% to about 99.99%, from about 1.13% to about 99.9%, from about 1.13% to about 99%, from about 1.13% to about 95%, from about 1.13% to about 90%, from about 1.13% to about 88.7%, from about 1.13% to about 70%, from about 1.13% to about 50%, from about 1.13% to about 30%, from about 1.13% to about 10%, from about 1.13% to about 5.76%, from about 1.13% to about 2.5%, from about 1.13% to about 1.47%, from about 1.13% to about 1.27%, from about 1.13% to about 1.23%, from about 1.13% to about 1.15%, from about 1.15% to about 99.99%, from about 1.15% to about 99.9%, from about 1.15% to about 99%, from about 1.15% to about 95%, from about 1.15% to about 90%, from about 1.15% to about 88.7%, from about 1.15% to about 70%, from about 1.15% to about 50%, from about 1.15% to about 30%, from about 1.15% to about 10%, from about 1.15% to about 2.76%, from about 1.15% to about 2.5%, from about 1.15% to about 1.47%, from about 1.15% to about 1.27%, from about 1.15% to about 1.23%, from about 1.23% to about 99.99%, from about 1.23% to about 99.9%, from about 1.23% to about 99%, from about 1.23% to about 95%, from about 1.23% to about 90%, from about 1.23% to about 88.7%, from about 1.23% to about 70%, from about 1.23% to about 50%, from about 1.23% to about 30%, from about 1.23% to about 10%, from about 1.23% to about 5.76%, from about 1.23% to about 2.5%, from about 1.23% to about 1.47%, from about 1.23% to about 1.27%, from about 1.27% to about 99.99%, from about 1.27% to about 99.9%, from about 1.27% to about 99%, from about 1.27% to about 95%, from about 1.27% to about 90%, from about 1.27% to about 88.7%, from about 1.27% to about 70%, from about 1.27% to about 50%, from about 1.27% to about 30%, from about 1.27% to about 10%, from about 1.27% to about 5.76%, from about 1.27% to about 2.5%, from about 1.27% to about 1.47%, from about 1.47% to about 99.99%, from about 1.47% to about 99.9%, from about 1.47% to about 99%, from about 1.47% to about 95%, from about 1.47% to about 90%, from about 1.47% to about 88.7%, from about 1.47% to about 70%, from about 1.47% to about 50%, from about 1.47% to about 30%, from about 1.47% to about 10%, from about 1.47% to about 5.76%, from about 1.47% to about 2.5%, from about 2.5% to about 99.99%, from about 2.5% to about 99.9%, from about 2.5% to about 99%, from about 2.5% to about 95%, from about 2.5% to about 90%, from about 2.5% to about 88.7%, from about 2.5% to about 70%, from about 2.5% to about 50%, from about 2.5% to about 30%, from about 2.5% to about 10%, from about 2.5% to about 5.76%, from about 5.76% to about 99.99%, from about 5.76% to about 99.9%, from about 5.76% to about 99%, from about 5.76% to about 95%, from about 5.76% to about 90%, from about 5.76% to about 88.7%, from about 5.76% to about 70%, from about 5.76% to about 50%, from about 5.76% to about 30%, from about 5.76% to about 10%, from about 10% to about 99.99%, from about 10% to about 99.9%, from about 10% to about 99%, from about 10% to about 95%, from about 10% to about 90%, from about 10% to about 88.7%, from about 10% to about 70%, from about 10% to about 50%, from about 10% to about 30%, from about 30% to about 99.99%, from about 30% to about 99.9%, from about 30% to about 99%, from about 30% to about 95%, from about 30% to about 90%, from about 30% to about 88.7%, from about 30% to about 70%, from about 30% to about 50%, from about 50% to about 99.99%, from about 50% to about 99.9%, from about 50% to about 99%, from about 50% to about 95%, from about 50% to about 90%, from about 50% to about 88.7%, from about 50% to about 70%, from about 70% to about 99.99%, from about 70% to about 99.9%, from about 70% to about 99%, from about 70% to about 95%, from about 70% to about 90%, from about 70% to about 88.7%, from about 88.7% to about 99.99%, from about 88.7% to about 99.9%, from about 88.7% to about 99%, from about 88.7% to about 95%, from about 88.7% to about 90%, from about 90% to about 99.99%, from about 90% to about 99.9%, from about 90% to about 99%, from about 90% to about 95%, from about 95% to about 99.99%, from about 95% to about 99.9%, from about 95% to about 99%, from about 99% to about 99.99%, from about 99% to about 99.9%, from about 99.9% to about 99.99%; or at most about 1.112%, at most about 1.114%, at most about 1.115%, at most about 1.119%, at most about 1.12%, at most about 1.121%, at most about 1.124%, at most about 1.125%, at most about 1.13%, at most about 1.15%, at most about 1.23%, at most about 1.27%, at most about 1.47%, at most about 2.5%, at most about 5.76%, at most about 10%, at most about 30%, at most about 50%, at most about 70%, at most about 88.7%, at most about 90%, at most about 95%, at most about 99%, at most about 99.9%, at most about 99.99%; or about 1.112%, about 1.114%, about 1.115%, about 1.119%, about 1.12%, about 1.121%, about 1.124%, about 1.125%, about 1.13%, about 1.15%, about 1.23%, about 1.27%, about 1.47%, about 2.5%, about 5.76%, about 10%, about 30%, about 50%, about 70%, about 88.7%, about 90%, about 95%, about 99%, about 99.9%, about 99.99%; or any ranges or values therebetween.

[0105] In some other embodiments the unreacted CO.sub.2 may be further enriched in .sup.13C relative to the feed stream, having a ?.sup.13C in a range of at least about 4%, wherein

[00002]${?}^{13}C=\left(\frac{{{(}^{13}C{/}^{12}C)}_{\mathrm{sample}}}{{{(}^{13}C{/}^{12}C)}_{\mathrm{standard}}}-1\right)?1000\%$

wherein (.sup.13C/.sup.12C).sub.sample is measured isotopes ratio after reaction and (.sup.13C/.sup.12C).sub.standard is initial isotopes ratio before reaction.

[0106] ?.sup.13C may be at least about 4%, at least about 6%, at least about 6.76%, at least about 10.5%, at least about 11.33%, at least about 12%, at least about 14.8%, at least about 16%, at least about 18.22%, at least about 22%, at least about 34.23%, at least about 36.46%, at least about 50%, at least about 109.45%, at least about 146%, at least about 200%, at least about 329.16%, at least about 400%, at least about 500%; or from about 4% to about 500%, from about 4% to about 400%, from about 4% to about 329.16%, from about 4% to about 200%, from about 4% to about 146%, from about 4% to about 109.45%, from about 4% to about 50%, from about 4% to about 36.46%, from about 4% to about 34.23%, from about 4% to about 22%, from about 4% to about 18.22%, from about 4% to about 16%, from about 4% to about 14.8%, from about 4% to about 12%, from about 4% to about 11.33%, from about 4% to about 10.5%, from about 4% to about 6.76%, from about 4% to about 6%, from about 6% to about 500%, from about 6% to about 400%, from about 6% to about 329.16%, from about 6% to about 200%, from about 6% to about 146%, from about 6% to about 109.45%, from about 6% to about 50%, from about 6% to about 36.46%, from about 6% to about 34.23%, from about 6% to about 22%, from about 6% to about 18.22%, from about 6% to about 16%, from about 6% to about 14.8%, from about 6% to about 12%, from about 6% to about 11.33%, from about 6% to about 10.5%, from about 6% to about 6.76%, from about 6.76% to about 500%, from about 6.76% to about 400%, from about 6.76% to about 329.16%, from about 6.76% to about 200%, from about 6.76% to about 146%, from about 6.76% to about 109.45%, from about 6.76% to about 50%, from about 6.76% to about 36.46%, from about 6.76% to about 34.23%, from about 6.76% to about 22%, from about 6.76% to about 18.22%, from about 6.76% to about 16%, from about 6.76% to about 14.8%, from about 6.76% to about 12%, from about 6.76% to about 11.330%, from about 6.76% to about 10.5%, from about 10.5% to about 500%, from about 10.5% to about 400%, from about 10.5% to about 329.16%, from about 10.5% to about 200%, from about 10.5% to about 146%, from about 10.5% to about 109.45%, from about 10.5% to about 50%, from about 10.5% to about 36.46%, from about 10.5% to about 34.23%, from about 10.5% to about 22%, from about 10.5% to about 18.22%, from about 10.5% to about 16%, from about 10.5% to about 14.8%, from about 10.5% to about 12%, from about 10.5% to about 11.33%, from about 11.33% to about 500%, from about 11.33% to about 400%, from about 11.33% to about 329.16%, from about 11.33% to about 200%, from about 11.33% to about 146%, from about 11.33% to about 109.45%, from about 11.33% to about 50%, from about 11.33% to about 36.46%, from about 11.33% to about 34.23%, from about 11.33% to about 22%, from about 11.33% to about 18.22%, from about 11.33% to about 16%, from about 11.33% to about 14.8%, from about 11.33% to about 12%, from about 12% to about 500%, from about 12% to about 400%, from about 12% to about 329.16%, from about 12% to about 200%, from about 12% to about 146%, from about 12% to about 109.45%, from about 12% to about 50%, from about 12% to about 36.46%, from about 12% to about 34.23%, from about 12% to about 22%, from about 12% to about 18.22%, from about 12% to about 16%, from about 12% to about 14.8%, from about 14.8% to about 500%, from about 14.8% to about 400%, from about 14.8% to about 329.16%, from about 14.8% to about 200%, from about 14.8% to about 146%, from about 14.8% to about 109.45%, from about 14.8% to about 50%, from about 14.8% to about 36.46%, from about 14.8% to about 34.23%, from about 14.8% to about 22%, from about 140.8% to about 18.22%, from about 14.8% to about 16%, from about 16% to about 500%, from about 16% to about 400%, from about 16% to about 329.16%, from about 16% to about 200%, from about 16% to about 146%, from about 16% to about 109.45%, from about 16% to about 50%, from about 16% to about 36.46%, from about 16% to about 34.23%, from about 16% to about 22%, from about 16% to about 18.22%, from about 18.22% to about 500%, from about 180.22% to about 400%, from about 180.22% to about 329.16%, from about 18.22% to about 200%, from about 18.22% to about 146%, from about 18.22% to about 109.45%, from about 18.22% to about 50%, from about 18.22% to about 36.46%, from about 18.22% to about 34.23%, from about 18.22% to about 22%, from about 22% to about 500%, from about 22% to about 400%, from about 22% to about 329.16%, from about 22% to about 200%, from about 22% to about 146%, from about 22% to about 109.45%, from about 22% to about 50%, from about 22% to about 36.46%, from about 22% to about 34.23%, from about 34.23% to about 500%, from about 34.23% to about 400%, from about 34.23% to about 329.16%, from about 34.23% to about 200%, from about 34.23% to about 146%, from about 340.23% to about 109.45%, from about 34.23% to about 50%, from about 34.23% to about 36.46%, from about 36.46% to about 500%, from about 36.46% to about 400%, from about 36.46% to about 329.16%, from about 36.46% to about 200%, from about 36.46% to about 146%, from about 36.46% to about 109.45%, from about 36.46% to about 50%, from about 50% to about 500%, from about 50% to about 400%, from about 50% to about 329.16%, from about 50% to about 200%, from about 50% to about 146%, from about 50% to about 109.45%, from about 109.45% to about 500%, from about 109.45% to about 400%, from about 109.45% to about 329.16%, from about 109.45% to about 200%, from about 109.45% to about 146%, from about 146% to about 500%, from about 146% to about 400%, from about 146% to about 329.16%, from about 146% to about 200%, from about 1090.45% to about 146%, from about 200% to about 500%, from about 200% to about 400%, from about 200% to about 329.16%, from about 329.16% to about 500%, from about 329.16% to about 400%, from about 400% to about 400%; or at most about 4%, at most about 6%, at most about 6.76%, at most about 10.5%, at most about 11.33%, at most about 12%, at most about 14.8%, at most about 16%, at most about 18.22%, at most about 22%, at most about 34.23%, at most about 36.46%, at most about 50%, at most about 109.45%, at most about 146%, at most about 200%, at most about 329.16%, at most about 400%, at most about 500%; or about 4%, about 6%, about 6.76%, about 10.5%, about 11.33%, about 12%, about 14.8%, about 16%, about 18.22%, about 22%, about 34.23%, about 36.46%, about 50%, about 109.45%, about 146%, about 200%, about 329.16%, about 400%, about 500%, or any ranges or values therebetween.

[0107] In some other embodiments the unreacted CO.sub.2 may be further enriched in .sup.13C relative to the feed stream, having a ?.sup.13C in a range of at least about 0.001%, wherein:

[00003]${?}^{13}C\left(\%\right)=x{(}^{13}{C}_{outlet})\left(\%\right)-x{(}^{13}{C}_{\mathrm{feed}})\left(\%\right)$$\mathrm{wherein}$$x{(}^{13}{C}_{content})\left(\%\right)=\frac{n{(}^{13}{\mathrm{CO}}_2)}{n{(}^{13}{\mathrm{CO}}_2)+n{(}^{12}{\mathrm{CO}}_2)}*100\%;$ [0108] n represents molar amount; [0109] x(.sup.13C.sub.feed) represents molar fraction of .sup.13CO.sub.2 in the CO.sub.2 in the feed stream; [0110] x(.sup.13C.sub.outlet) represents molar fraction of .sup.13CO.sub.2 in the unreacted CO.sub.2; and [0111] x(.sup.13C.sub.content) represents x(.sup.13C.sub.feed) or x(.sup.13C.sub.outlet).

[0112] ?.sup.13C may be about 0.001%, at least about 0.002%, at least about 0.004%, at least about 0.005%, at least about 0.009%, at least about 0.01%, at least about 0.011%, at least about 0.014%, at least about 0.015%, at least about 0.02%, at least about 0.04%, at least about 0.12%, at least about 0.16%, at least about 0.18%, at least about 0.2%, at least about 0.22%, at least about 0.3%, at least about 0.36%, at least about 0.4%, at least about 0.5%, at least about 1%, at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 50%, at least about 70%, at least about 90%, at least about 95%, at least about 99%, at least about 99.9%; or from about 0.001% to about 99.9%, from about 0.001% to about 99%, from about 0.001% to about 95%, from about 0.001% to about 90%, from about 0.001% to about 70%, from about 0.001% to about 50%, from about 0.001% to about 30%, from about 0.001% to about 20%, from about 0.001% to about 10%, from about 0.001% to about 5%, from about 0.001% to about 1%, from about 0.001% to about 0.5%, from about 0.001% to about 0.4%, from about 0.001% to about 0.36%, from about 0.001% to about 0.3%, from about 0.001% to about 0.22%, from about 0.001% to about 0.2%, from about 0.001% to about 0.18%, from about 0.001% to about 0.16%, from about 0.001% to about 0.12%, from about 0.001% to about 0.04%, from about 0.001% to about 0.02%, from about 0.001% to about 0.015%, from about 0.001% to about 0.014%, from about 0.001% to about 0.011%, from about 0.001% to about 0.01%, from about 0.001% to about 0.009%, from about 0.001% to about 0.005%, from about 0.001% to about 0.004%, from about 0.001% to about 0.002%, from about 0.002% to about 99.9%, from about 0.002% to about 99%, from about 0.002% to about 95%, from about 0.002% to about 90%, from about 0.002% to about 70%, from about 0.002% to about 50%, from about 0.002% to about 30%, from about 0.002% to about 20%, from about 0.002% to about 10%, from about 0.002% to about 5%, from about 0.002% to about 1%, from about 0.002% to about 0.5%, from about 0.002% to about 0.4%, from about 0.002% to about 0.36%, from about 0.002% to about 0.3%, from about 0.002% to about 0.22%, from about 0.002% to about 0.2%, from about 0.002% to about 0.18%, from about 0.002% to about 0.16%, from about 0.002% to about 0.12%, from about 0.002% to about 0.04%, from about 0.002% to about 0.02%, from about 0.002% to about 0.015%, from about 0.002% to about 0.014%, from about 0.002% to about 0.011%, from about 0.002% to about 0.01%, from about 0.002% to about 0.009%, from about 0.002% to about 0.005%, from about 0.002% to about 0.004%, from about 0.004% to about 99.9%, from about 0.004% to about 99%, from about 0.004% to about 95%, from about 0.004% to about 90%, from about 0.004% to about 70%, from about 0.004% to about 50%, from about 0.004% to about 30%, from about 0.004% to about 20%, from about 0.004% to about 10%, from about 0.004% to about 5%, from about 0.004% to about 1%, from about 0.004% to about 0.5%, from about 0.004% to about 0.4%, from about 0.004% to about 0.36%, from about 0.004% to about 0.3%, from about 0.004% to about 0.22%, from about 0.004% to about 0.2%, from about 0.004% to about 0.18%, from about 0.004% to about 0.16%, from about 0.004% to about 0.12%, from about 0.004% to about 0.04%, from about 0.004% to about 0.02%, from about 0.004% to about 0.015%, from about 0.004% to about 0.014%, from about 0.004% to about 0.011%, from about 0.004% to about 0.01%, from about 0.004% to about 0.009%, from about 0.004% to about 0.005%, from about 0.005% to about 99.9%, from about 0.005% to about 99%, from about 0.005% to about 95%, from about 0.005% to about 90%, from about 0.005% to about 70%, from about 0.005% to about 50%, from about 0.005% to about 30%, from about 0.005% to about 20%, from about 0.005% to about 10%, from about 0.005% to about 5%, from about 0.005% to about 1%, from about 0.005% to about 0.5%, from about 0.005% to about 0.4%, from about 0.005% to about 0.36%, from about 0.005% to about 0.3%, from about 0.005% to about 0.22%, from about 0.005% to about 0.2%, from about 0.005% to about 0.18%, from about 0.005% to about 0.16%, from about 0.005% to about 0.12%, from about 0.005% to about 0.04%, from about 0.005% to about 0.02%, from about 0.005% to about 0.015%, from about 0.005% to about 0.014%, from about 0.005% to about 0.011%, from about 0.005% to about 0.01%, from about 0.005% to about 0.009%, from about 0.009% to about 99.9%, from about 0.009% to about 99%, from about 0.009% to about 95%, from about 0.009% to about 90%, from about 0.009% to about 70%, from about 0.009% to about 50%, from about 0.009% to about 30%, from about 0.009% to about 20%, from about 0.009% to about 10%, from about 0.009% to about 5%, from about 0.009% to about 1%, from about 0.009% to about 0.5%, from about 0.009% to about 0.4%, from about 0.009% to about 0.36%, from about 0.009% to about 0.3%, from about 0.009% to about 0.22%, from about 0.009% to about 0.2%, from about 0.009% to about 0.18%, from about 0.009% to about 0.16%, from about 0.009% to about 0.12%, from about 0.009% to about 0.04%, from about 0.009% to about 0.02%, from about 0.009% to about 0.015%, from about 0.009% to about 0.014%, from about 0.009% to about 0.011%, from about 0.009% to about 0.01%, from about 0.01% to about 99.9%, from about 0.01% to about 99%, from about 0.01% to about 95%, from about 0.01% to about 90%, from about 0.01% to about 70%, from about 0.01% to about 50%, from about 0.01% to about 30%, from about 0.01% to about 20%, from about 0.01% to about 10%, from about 0.01% to about 5%, from about 0.01% to about 1%, from about 0.01% to about 0.5%, from about 0.01% to about 0.4%, from about 0.01% to about 0.36%, from about 0.01% to about 0.3%, from about 0.01% to about 0.22%, from about 0.01% to about 0.2%, from about 0.01% to about 0.18%, from about 0.01% to about 0.16%, from about 0.01% to about 0.12%, from about 0.01% to about 0.04%, from about 0.01% to about 0.02%, from about 0.01% to about 0.015%, from about 0.01% to about 0.014%, from about 0.01% to about 0.011%, from about 0.011% to about 99.9%, from about 0.011% to about 99%, from about 0.011% to about 95%, from about 0.011% to about 90%, from about 0.011% to about 70%, from about 0.011% to about 50%, from about 0.011% to about 30%, from about 0.011% to about 20%, from about 0.011% to about 10%, from about 0.011% to about 5%, from about 0.011% to about 1%, from about 0.011% to about 0.5%, from about 0.011% to about 0.4%, from about 0.011% to about 0.36%, from about 0.011% to about 0.3%, from about 0.011% to about 0.22%, from about 0.011% to about 0.2%, from about 0.011% to about 0.18%, from about 0.011% to about 0.16%, from about 0.011% to about 0.12%, from about 0.011% to about 0.04%, from about 0.011% to about 0.02%, from about 0.011% to about 0.015%, from about 0.011% to about 0.014%, from about 0.014% to about 99.9%, from about 0.014% to about 99%, from about 0.014% to about 95%, from about 0.014% to about 90%, from about 0.014% to about 70%, from about 0.014% to about 50%, from about 0.014% to about 30%, from about 0.014% to about 20%, from about 0.014% to about 10%, from about 0.014% to about 5%, from about 0.014% to about 1%, from about 0.014% to about 0.5%, from about 0.014% to about 0.4%, from about 0.014% to about 0.36%, from about 0.014% to about 0.3%, from about 0.014% to about 0.22%, from about 0.014% to about 0.2%, from about 0.014% to about 0.18%, from about 0.014% to about 0.16%, from about 0.014% to about 0.12%, from about 0.014% to about 0.04%, from about 0.014% to about 0.02%, from about 0.014% to about 0.015%, from about 0.015% to about 99.9%, from about 0.015% to about 99%, from about 0.015% to about 95%, from about 0.015% to about 90%, from about 0.015% to about 70%, from about 0.015% to about 50%, from about 0.015% to about 30%, from about 0.015% to about 20%, from about 0.015% to about 10%, from about 0.015% to about 5%, from about 0.015% to about 1%, from about 0.015% to about 0.5%, from about 0.015% to about 0.4%, from about 0.015% to about 0.36%, from about 0.015% to about 0.3%, from about 0.015% to about 0.22%, from about 0.015% to about 0.2%, from about 0.015% to about 0.18%, from about 0.015% to about 0.16%, from about 0.015% to about 0.12%, from about 0.015% to about 0.04%, from about 0.015% to about 0.02%, from about 0.02% to about 99.9%, from about 0.02% to about 99%, from about 0.02% to about 95%, from about 0.02% to about 90%, from about 0.02% to about 70%, from about 0.02% to about 50%, from about 0.02% to about 30%, from about 0.02% to about 20%, from about 0.02% to about 10%, from about 0.02% to about 5%, from about 0.02% to about 1%, from about 0.02% to about 0.5%, from about 0.02% to about 0.4%, from about 0.02% to about 0.36%, from about 0.02% to about 0.3%, from about 0.02% to about 0.22%, from about 0.02% to about 0.2%, from about 0.02% to about 0.18%, from about 0.02% to about 0.16%, from about 0.02% to about 0.12%, from about 0.02% to about 0.04%, from about 0.04% to about 99.9%, from about 0.04% to about 99%, from about 0.04% to about 95%, from about 0.04% to about 90%, from about 0.04% to about 70%, from about 0.04% to about 50%, from about 0.04% to about 30%, from about 0.04% to about 20%, from about 0.04% to about 10%, from about 0.04% to about 5%, from about 0.04% to about 1%, from about 0.04% to about 0.5%, from about 0.04% to about 0.4%, from about 0.04% to about 0.36%, from about 0.04% to about 0.3%, from about 0.04% to about 0.22%, from about 0.04% to about 0.2%, from about 0.04% to about 0.18%, from about 0.04% to about 0.16%, from about 0.04% to about 0.12%, from about 0.12% to about 99.9%, from about 0.12% to about 99%, from about 0.12% to about 95%, from about 0.12% to about 90%, from about 0.12% to about 70%, from about 0.12% to about 50%, from about 0.12% to about 30%, from about 0.12% to about 20%, from about 0.12% to about 10%, from about 0.12% to about 5%, from about 0.12% to about 1%, from about 0.12% to about 0.5%, from about 0.12% to about 0.4%, from about 0.12% to about 0.36%, from about 0.12% to about 0.3%, from about 0.12% to about 0.22%, from about 0.12% to about 0.2%, from about 0.12% to about 0.18%, from about 0.12% to about 0.16%, from about 0.16% to about 99.9%, from about 0.16% to about 95%, from about 0.16% to about 90%, from about 0.16% to about 70%, from about 0.16% to about 50%, from about 0.16% to about 30%, from about 0.16% to about 20%, from about 0.16% to about 10%, from about 0.16% to about 5%, from about 0.16% to about 1%, from about 0.16% to about 0.5%, from about 0.16% to about 0.4%, from about 0.16% to about 0.36%, from about 0.16% to about 0.3%, from about 0.16% to about 0.22%, from about 0.16% to about 0.2%, from about 0.16% to about 0.18%, from about 0.18% to about 99.9%, from about 0.18% to about 99%, from about 0.18% to about 95%, from about 0.18% to about 90%, from about 0.18% to about 70%, from about 0.18% to about 50%, from about 0.18% to about 30%, from about 0.18% to about 20%, from about 0.18% to about 10%, from about 0.18% to about 5%, from about 0.18% to about 1%, from about 0.18% to about 0.5%, from about 0.18% to about 0.4%, from about 0.18% to about 0.36%, from about 0.18% to about 0.3%, from about 0.18% to about 0.22%, from about 0.02% to about 0.2%, from about 0.02% to about 99.9%, from about 0.02% to about 99%, from about 0.02% to about 95%, from about 0.02% to about 90%, from about 0.02% to about 70%, from about 0.02% to about 50%, from about 0.02% to about 30%, from about 0.02% to about 20%, from about 0.02% to about 10%, from about 0.02% to about 5%, from about 0.02% to about 1%, from about 0.02% to about 0.5%, from about 0.02% to about 0.4%, from about 0.02% to about 0.36%, from about 0.02% to about 0.3%, from about 0.02% to about 0.22%, from about 0.22% to about 99.9%, from about 0.22% to about 99%, from about 0.22% to about 95%, from about 0.22% to about 90%, from about 0.22% to about 70%, from about 0.22% to about 50%, from about 0.22% to about 30%, from about 0.22% to about 20%, from about 0.22% to about 10%, from about 0.22% to about 5%, from about 0.22% to about 1%, from about 0.22% to about 0.5%, from about 0.22% to about 0.4%, from about 0.22% to about 0.36%, from about 0.22% to about 0.3%, from about 0.3% to about 99.9%, from about 0.3% to about 99%, from about 0.3% to about 95%, from about 0.3% to about 90%, from about 0.3% to about 70%, from about 0.3% to about 50%, from about 0.3% to about 30%, from about 0.3% to about 20%, from about 0.3% to about 10%, from about 0.3% to about 5%, from about 0.3% to about 1%, from about 0.3% to about 0.5%, from about 0.3% to about 0.4%, from about 0.3% to about 0.36%, from about 0.36% to about 99.9%, from about 0.36% to about 99%, from about 0.36% to about 95%, from about 0.36% to about 90%, from about 0.36% to about 70%, from about 0.36% to about 50%, from about 0.36% to about 30%, from about 0.36% to about 20%, from about 0.36% to about 10%, from about 0.36% to about 5%, from about 0.36% to about 1%, from about 0.36% to about 0.5%, from about 0.36% to about 0.4%, from about 0.4% to about 99.9%, from about 0.4% to about 99%, from about 0.4% to about 95%, from about 0.4% to about 90%, from about 0.4% to about 70%, from about 0.4% to about 50%, from about 0.4% to about 30%, from about 0.4% to about 20%, from about 0.4% to about 10%, from about 0.4% to about 5%, from about 0.4% to about 1%, from about 0.4% to about 0.5%, from about 0.5% to about 99.9%, from about 0.5% to about 99%, from about 0.5% to about 95%, from about 0.5% to about 90%, from about 0.5% to about 70%, from about 0.5% to about 50%, from about 0.5% to about 30%, from about 0.5% to about 20%, from about 0.5% to about 10%, from about 0.5% to about 5%, from about 0.5% to about 1%, from about 1% to about 99.9%, from about 1% to about 99%, from about 1% to about 95%, from about 1% to about 90%, from about 1% to about 70%, from about 1% to about 50%, from about 1% to about 30%, from about 1% to about 20%, from about 1% to about 10%, from about 1% to about 5%, from about 5% to about 99.9%, from about 5% to about 99%, from about 5% to about 95%, from about 5% to about 90%, from about 5% to about 70%, from about 5% to about 50%, from about 5% to about 30%, from about 5% to about 20%, from about 5% to about 10%, from about 10% to about 99.9%, from about 10% to about 99%, from about 10% to about 95%, from about 10% to about 90%, from about 10% to about 70%, from about 10% to about 50%, from about 10% to about 30%, from about 10% to about 20%, from about 20% to about 99.9%, from about 20% to about 99%, from about 20% to about 95%, from about 20% to about 90%, from about 20% to about 70%, from about 20% to about 50%, from about 20% to about 30%, from about 30% to about 99.9%, from about 30% to about 99%, from about 30% to about 95%, from about 30% to about 90%, from about 30% to about 70%, from about 30% to about 50%, from about 50% to about 99.9%, from about 50% to about 99%, from about 50% to about 95%, from about 50% to about 90%, from about 50% to about 70%, from about 70% to about 99.9%, from about 70% to about 99%, from about 70% to about 95%, from about 70% to about 90%, from about 90% to about 99.9%, from about 90% to about 99%, from about 90% to about 95%, from about 95% to about 99.9%, from about 95% to about 99%, from about 99% to about 99.9%; or at most about 0.001%, at most about 0.002%, at most about 0.004%, at most about 0.005%, at most about 0.009%, at most about 0.01%, at most about 0.011%, at most about 0.014%, at most about 0.015%, at most about 0.02%, at most about 0.04%, at most about 0.12%, at most about 0.16%, at most about 0.18%, at most about 0.2%, at most about 0.22%, at most about 0.3%, at most about 0.36%, at most about 0.4%, at most about 0.5%, at least about 1%, at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 50%, at least about 70%, at least about 90%, at least about 95%, at least about 99%, at least about 99.9%; or about 0.001%, about 0.002%, about 0.004%, about 0.005%, about 0.009%, about 0.01%, about 0.011%, about 0.014%, about 0.015%, about 0.02%, about 0.04%, about 0.12%, about 0.16%, about 0.18%, about 0.2%, about 0.22%, about 0.3%, about 0.36%, about 0.4%, about 0.5%, at least about 1%, at least about 5%, at least about 10%, at least about 20%, at least about 30%, at least about 50%, at least about 70%, at least about 90%, at least about 95%, at least about 99%, at least about 99.9%, or any ranges and values therebetween. In a preferred embodiment, the present disclosure discloses a method wherein ?.sup.13C is at least about 0.1%. In a further preferred embodiment, the present disclosure discloses a method wherein ?.sup.13C is at least about 0.2%. In a further preferred embodiment, the present disclosure discloses a method wherein ?.sup.13C is at least about 0.3%. In yet another preferred embodiment, the present disclosure discloses a method wherein ?.sup.13C is about 0.1% to about 99%.

[0113] The unreacted CO.sub.2 in the outlet stream may be separated from gaseous reduction products by various means, for example by condensation. Condensation serves to remove the compound with the highest boiling point. Examples of by-products that can be removed are CO, H.sub.2, syngas, or CH.sub.4. The condensation may be performed at a certain pressure and temperature and may be further or subsequently separated on a membrane in a membrane distillation process, for example a polysulfone membrane, or more preferentially a polysulfone membrane doped with selenium, bromide or similar compounds. The membrane distillation after the condensation step may comprise a flat membrane cell in a cross-flow, counter-current flow or a co-current flow configuration. In a preferred embodiment, the present disclosure discloses a method, wherein step (iii) comprises separating unreacted CO.sub.2 from product by condensation.

[0114] In some embodiments, the condensation may be performed at a pressure range of at least about 0.5 bar, at least about 1 bar, at least about 2 bar, at least about 4 bar, at least about 6 bar, at least about 8 bar, at least about 10 bar, at least about 12 bar; or from about 0.5 bar to about 12 bar, from about 0.5 bar to about 10 bar, from about 0.5 bar to about 8 bar, from about 0.5 bar to about 6 bar, from about 0.5 bar to about 4 bar, from about 0.5 bar to about 2 bar, from about 0.5 bar to about 1 bar, from about 1 bar to about 12 bar, from about 1 bar to about 10 bar, from about 1 bar to about 8 bar, from about 1 bar to about 6 bar, from about 1 bar to about 4 bar, from about 1 bar to about 2 bar, from about 2 bar to about 12 bar, from about 2 bar to about 10 bar, from about 2 bar to about 8 bar, from about 2 bar to about 6 bar, from about 2 bar to about 4 bar, from about 4 bar to about 12 bar, from about 4 bar to about 10 bar, from about 4 bar to about 8 bar, from about 4 bar to about 6 bar, from about 6 bar to about 12 bar, from about 6 bar to about 10 bar, from about 6 bar to about 8 bar, from about 8 bar to about 12 bar, from about 8 bar to about 10 bar, from about 10 bar to about 12 bar; or at most about 0.5 bar, at most about 1 bar, at most about 2 bar, at most about 4 bar, at most about 6 bar, at most about 8 bar, at most about 10 bar, at most about 12 bar; or about 0.5 bar, about 1 bar, about 2 bar, about 4 bar, about 6 bar, about 8 bar, about 10 bar, about 12 bar, or any ranges or values therebetween.

[0115] In some other embodiments, the condensation may be performed a temperature range of at least about ?10? C., at least about ?30? C., at least about ?50? C., at least about ?70? C., at least about ?90? C., at least about ?110? C., at least about ?130? C.; or from about ?10? C. to about ?130? C., from about ?10? C. to about ?110? C., from about ?10? C. to about ?90? C., from about ?10? C. to about ?70? C., from about ?10? C. to about ?50? C., from about ?10? C. to about ?30? C., from about ?30? C. to about ?130? C., from about ?30? C. to about ?110? C., from about ?30? C. to about ?90? C., from about ?30? C. to about ?70? C., from about ?30? C. to about ?50? C., from about ?50? C. to about ?130? C., from about ?50? C. to about ?110? C., from about ?50? C. to about ?90? C., from about ?50? C. to about ?70? C., from about ?70? C. to about ?130? C., from about ?70? C. to about ?110? C., from about ?70? C. to about ?90? C., from about ?90? C. to about ?130? C., from about ?90? C. to about ?110? C., from about ?110? C. to about ?130? C.; or at most about ?10? C., at most about ?30? C., at most about ?50? C., at most about ?70? C., at most about ?90? C., at most about ?110? C., at most about ?130? C.; or about ?10? C., about ?30? C., about ?50? C., about ?70? C., about ?90? C., about ?110? C., about ?130? C., or any ranges or values therebetween.

[0116] The liquid products may be separated from the catholyte by various means, for example by membrane distillation. The membrane distillation may be performed at a certain pressure and temperature, while the membrane used may comprise PTFE, PP, PVDF or mixtures thereof. The membrane distillation setup may also comprise a flat membrane cell in a cross-flow, counter-current flow or a co-current flow configuration.

[0117] In some embodiments, the membrane distillation may be performed in a pressure range of at least about 0.01 bar, at least about 0.02 bar, at least about 0.05 bar, at least about 0.1 bar, at least about 0.25 bar, at least about 0.5 bar, at least about 0.75 bar, at least about 1 bar, at least about 2 bar, at least about 3 bar; or from about 0.01 bar to about 3 bar, from about 0.01 bar to about 2 bar, from about 0.01 bar to about 1 bar, from about 0.01 bar to about 0.75 bar, from about 0.01 bar to about 0.5 bar, from about 0.01 bar to about 0.25 bar, from about 0.01 bar to about 0.1 bar, from about 0.01 bar to about 0.05 bar, from about 0.01 bar to about 0.02 bar, from about 0.02 bar to about 3 bar, from about 0.02 bar to about 2 bar, from about 0.02 bar to about 1 bar, from about 0.02 bar to about 0.75 bar, from about 0.02 bar to about 0.5 bar, from about 0.02 bar to about 0.25 bar, from about 0.02 bar to about 0.1 bar, from about 0.02 bar to about 0.05 bar, from about 0.05 bar to about 3 bar, from about 0.05 bar to about 2 bar, from about 0.05 bar to about 1 bar, from about 0.05 bar to about 0.75 bar, from about 0.05 bar to about 0.5 bar, from about 0.05 bar to about 0.25 bar, from about 0.05 bar to about 0.1 bar, from about 0.1 bar to about 3 bar, from about 0.1 bar to about 2 bar, from about 0.1 bar to about 1 bar, from about 0.1 bar to about 0.75 bar, from about 0.1 bar to about 0.5 bar, from about 0.1 bar to about 0.25 bar, from about 0.25 bar to about 3 bar, from about 0.25 bar to about 2 bar, from about 0.25 bar to about 1 bar, from about 0.25 bar to about 0.75 bar, from about 0.25 bar to about 0.5 bar, from about 0.5 bar to about 3 bar, from about 0.5 bar to about 2 bar, from about 0.5 bar to about 1 bar, from about 0.5 bar to about 0.75 bar, from about 0.75 bar to about 3 bar, from about 0.75 bar to about 2 bar, from about 0.75 bar to about 1 bar, from about 1 bar to about 3 bar, from about 1 bar to about 2 bar, from about 2 bar to about 3 bar; or at most about 0.01 bar, at most about 0.02 bar, at most about 0.05 bar, at most about 0.1 bar, at most about 0.25 bar, at most about 0.5 bar, at most about 0.75 bar, at most about 1 bar, at most about 2 bar, at most about 3 bar; or about 0.01 bar, about 0.02 bar, about 0.05 bar, about 0.1 bar, about 0.25 bar, about 0.5 bar, about 0.75 bar, about 1 bar, about 2 bar, about 3 bar, or any ranges or values therebetween. In a preferred embodiment, the membrane distillation is performed in a range from about 0.02 bar to about 1 bar.

[0118] In some other embodiments, the membrane distillation may be performed at a temperature range of at least about 10? C., at least about 20? C., at least about 40? C., at least about 60? C., at least about 80? C., at least about 90? C.; or from about 10? C. to about 90? C., from about 10? C. to about 80? C., from about 10? C. to about 60? C., from about 10? C. to about 40? C., from about 10? C. to about 20? C., from about 20? C. to about 90? C., from about 20? C. to about 80? C., from about 20? C. to about 60? C., from about 20? C. to about 40? C., from about 40? C. to about 90? C., from about 40? C. to about 80? C., from about 40? C. to about 60? C., from about 60? C. to about 90? C., from about 60? C. to about 80? C., from about 80? C. to about 90? C.; or at most about 10? C., at most about 20? C., at most about 40? C., at most about 60? C., at most about 80? C., at most about 90? C.; or about 10? C., about 20? C., about 40? C., about 60? C., about 80? C., about 90? C., or any ranges or values therebetween.

[0119] The present disclosure also provides for a system for electrochemical .sup.13C-isotope enrichment by electrochemical reduction, comprising: [0120] an electrochemical station with a gas diffusion cathode, a porous metal anode, an ion exchange membrane and an electrolyte; [0121] a product separation station membrane for separation of CO.sub.2 or distillation; and [0122] a recirculation station or chain of consecutive reactors.

[0123] The gas diffusion cathode may comprise porous carbon paper coated with catalyst layer on one side and hydrophobic layer on the other side that allows a diffusion of CO.sub.2 and electrolyte to catalyst with products diffusing back to the gas phase while preventing leakage of electrolyte into a gas phase.

[0124] The porous metal anode may comprise porous Nickel foam coated with Nickel-Iron oxide-hydroxide for greater stability.

[0125] The ion exchange membrane may comprise an anion exchange membrane that prevents the mixing cathode and anode electrolyte.

[0126] The electrolyte may comprise potassium hydroxide water solution where the concentration of KOH can be from 1 to 10 mol/L.

[0127] The catalyst may comprise copper nanoparticles with size from 10 to 200 nm more preferably from 20 to 100 nm.

[0128] The catalyst loading may be from 0.5 to 10 mg per cm.sup.2, more preferably from 1 to 5 mg per cm.sup.2.

[0129] The gas products separation station may comprise a heat exchanger for partial condensation of the gas stream, under the pressure between 1 and 10 bar, preferably between ?70? C. and ?90? C., and subsequent separation on polysulfone based membrane, preferentially doped with Selenium, Bromide or alike compounds, under the pressure between 1 and 10 bar and in temperature between 20? C. and 50? C.

[0130] The liquid products separation station may comprise a membrane distillation device, operating under the pressure between 0.02 and 1 bar, preferably between 20? C. and 80? C., and uses a membrane composed of PTFE, PP, PVDF or mixture of polymers.

[0131] The device used for membrane separation may comprise a flat membrane cell, in a cross-flow, counter-current or co-current flow.

EXAMPLES

[0132] Non-limiting examples of the invention and comparative examples will be further described in greater detail by reference to specific examples, which should not be construed as in any way limiting the scope of the invention.

Material and Methods

[0133] Copper nanoparticles (25 nm and 60 nm, 99.99%), silver-copper alloy nanopowder (<100 nm, 98% Ag, 2% Cu), graphite powder (<20 m) and Nafion 117 solution for GDE fabrication, nickel foam, and potassium hydroxide flakes used as electrolyte were acquired from Sigma Aldrich. The Fumasep FAA anionic exchange membrane (AEM) utilized to partition cathode and anode chambers of the cell, carbon black (Vulcan XC-72R) and carbon paper (Freudenberg H14C9) for GDE fabrication were obtained from The Fuel Cell Store. MC-series mass flow controllers and MS-series mass flow meters were obtained from Alicat Scientific, Inc.

[0134] The feed stream flow rates in the following Examples were controlled using an Alicat MC-series mass flow controller set to standard temperature and pressure (STP, 25? C., 1 atm) conditions, while the outlet stream flow rates in the following Examples were measured using an Alicat MS-series mass flow-meter set to standard temperature and pressure (STP, 25? C., 1 atm) conditions.

Example 1: Process for .SUP.13.C Enrichment

[0135] A general process for .sup.13C enrichment is shown in FIG. 1 and FIG. 2 and described in detail in the Detailed Disclosure of Drawings section above. The main reactions taking place within the described cell are given in Table 1.

[0136] In one embodiment, potassium-hydroxide-based electrolytes are deployed, and the cathode is a GDE electrode based on copper (Cu) or silver (Ag), while the anode is primarily nickel (Ni). The gaseous stream leaving the reactor consists of gaseous products and unreacted CO.sub.2. The unreacted CO.sub.2 may be recirculated and is enriched with .sup.13C in every pass. The unreacted CO.sub.2 may first be separated from the other products by means of liquid condensation with liquid nitrogen, while the remaining components may be further separated on a polysulfone based membrane into its separate components. The separation of liquid products is achieved by vacuum membrane distillation process. A minor part of the catholyte may be removed and valorized as e.g. cleaning medium for the food processing industry.

TABLE-US-00001 TABLE 1 Primary reactions occurring in the electrochemical cell Cathode reactions Anode reactions CO.sub.2 + 2H.sup.+ + 2e.sup.? .Math. CO + H.sub.2O 4OH.sup.? .Math. O.sub.2 + 2H.sub.2O + 2e.sup.? 2CO.sub.2 + 12H.sup.+ + 12e.sup.? .Math. C.sub.2H.sub.4 + 4H.sub.2O 2CO.sub.2 + 12H.sup.+ + 12e.sup.? .Math. C.sub.2H.sub.5OH + 3H.sub.2O 2CO.sub.2 + 8H.sup.+ + 8e.sup.? .Math. CH.sub.3COOH + 2H.sub.2O 2H.sup.+ + 2e.sup.? .Math. H.sub.2

Example 2: Cathode Preparation

Example 2a: Metal Nanoparticle Dispersion

[0137] Metal nanoparticles (50-150 mg) were dispersed in a water-isopropanol mixture (10 ml) in a ratio of 1:3. To homogenize the dispersion, Nafion 117 solution (0.5 ml) was further added and the mixture was sonicated by ultrasonic homogenizer for 2 minutes. The type of metal nanoparticles and their average particle size are given in Table 2.

TABLE-US-00002 TABLE 2 Metal nanoparticles (M-NP) dispersion preparations M-NP Dispersions Metal Average size/nm M-1 Cu 25 M-2 Cu 60 M-3 Ag 100

Example 2b: Carbon Nanoparticle Dispersion

[0138] Carbon nanoparticle dispersions were used to form a gas dispersion layer.

[0139] To form the dispersions, carbon particles (100 mg) were dispersed in a water-isopropanol mixture in a ratio of 1:3. To homogenize the dispersion, Nafion 117 solution (0.5 ml) was added and the mixture sonicated by ultrasonic homogenizer for 2 minutes. The type of carbon nanoparticles and their average particle sizes are given in Table 3.

TABLE-US-00003 TABLE 3 Carbon nanoparticles (C-NP) dispersion preparations C-NP Dispersions Carbon Average size/nm C-1 Carbon black XC-72 25 C-2 Graphene 100 C-3 Graphite 5000-20000

Example 2c: GDE Fabrication

[0140]

TABLE-US-00004 TABLE 4 Prepared GDE cathodes Cathode no. Layer 1 Layer 2 Layer 3 GDE-1 M-1 C-1 C-3 GDE-2 M-2 C-1 C-3 GDE-3 M-3 C-1 C-3 GDE-4 M-1 C-2 C-3 GDE-5 M-2 C-2 C-3 GDE-6 M-3 C-2 C-3 GDE-7.sup.1 .sup.1Carbon paper was used as-is for the electrode.

[0141] Gas diffusion electrodes (GDEs) were prepared by spray-casting each layer on porous carbon paper substrate. 1 ml of material was sprayed per 4 cm.sup.2 of cathode surface area to form each layer. As up to 30% of the dispersion is lost during the spraying process, the final metal loading was estimated to be from 1 mg/cm.sup.2 to 3 mg/cm.sup.2. Similar losses are expected when spraying the carbon nanoparticles onto the porous carbon paper substrate. The layer order and materials sprayed are given in Table 4. GDE-7 does not have contain any sprayed material and thus consists purely of carbon paper.

Example 3: Characterising the GDE Cathode

[0142] The SEM images of the as-prepared GDE-1 are shown in FIGS. 3 and 4.

[0143] The SEM images in FIGS. 3 and 4 show the formation of the gas diffusion layer (GDL) on top of the carbon paper filaments of the porous carbon paper substrate. However, it was noted that the layers formed were much thinner compared to the carbon paper filaments and hence, the three layers of nanoparticles could not be distinguished from each other.

[0144] FIG. 4 also shows the rough surface of the GDL formed by layering a first carbon nanoparticle layer and a second carbon microparticle layer on top of the base metal nanoparticle layer.

Example 4: Results of enrichment

[0145] The results of the electrochemical reduction and .sup.13C isotope enrichment after a single pass of CO.sub.2 through the flow-cell are given in Table 5. The cathode surface area was 1 cm.sup.2 in all tests and the internal volume of the cathode chamber is 0.35 cm.sup.3.

[0146] To detect the unreacted CO.sub.2 in the outlet stream and liquid products in the product stream, a proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) was used. A PTR-TOF-MS Qi8000 from IONICON Inc (Austria) from multiple supply reactive ions tube was utilized where H.sub.3O.sup.+ ions were used to ionize outgassing species. The drift tube settings were found to be optimal at 114 Td to achieve good sensitivity and resolution. The outlet stream was split and 1.5 sccm of it was mixed with pure nitrogen and directed into the PTR-TOF-MS. Isotope contents and ?.sup.13C was evaluated based on H.sub.3CO.sub.3+/H.sub.3.sup.13CO.sub.3+ ions for CO.sub.2.

[0147] To determine the .sup.12CO.sub.2 and .sup.13CO.sub.2 concentrations in the outlet stream during the process, 10 sccm of the outlet stream was split and sampled into a Hiden analytical QGA mass-spectrometer (UK) to monitor changes in the concentration in real time.

Example 4a: Calculations

[0148] Carbon isotope compositions (?.sup.13C) were calculated for each test according to the following formula wherein (.sup.13C/.sup.12C).sub.sample is measured isotopes ratio after reaction and (.sup.13C/.sup.12C).sub.standard is initial isotopes ratio before reaction:

[00004]${?}^{13}C=\left(\frac{{{(}^{13}C{/}^{12}C)}_{sample}}{{{(}^{13}C{/}^{12}C)}_{\mathrm{standard}}}-1\right)?1000\%.$

[0149] The percent amount of .sup.13C was estimated from mass spectra with following formula, wherein n is the amount of the isotope, and x is the molar fraction of .sup.13CO.sub.2 in the sample:

[00005]$x{(}^{13}{C}_{content})\left(\%\right)=\frac{n{(}^{13}{\mathrm{CO}}_2)}{n{(}^{13}{\mathrm{CO}}_2)+n{(}^{12}{\mathrm{CO}}_2)}*100\%.$

[0150] The change of the .sup.13C concentration (?.sup.13C) between feed and outlet was calculated using the following formula:

[00006]${?}^{13}C\left(\%\right)=x{(}^{13}{C}_{outlet})\left(\%\right)-x{(}^{13}{C}_{\mathrm{feed}})\left(\%\right)$

[0151] The residence time was calculated using the formula below, wherein the internal volume of the cathode chamber is calculated by measuring the length, and depth of the channel and then subsequently calculating its volume. In subsequent examples, the internal volume of the cathode chamber was measured as 0.35 cm.sup.3:

[00007]$\mathrm{residence}\mathrm{time}=\frac{int\mathrm{ernal}\mathrm{volume}\mathrm{of}\mathrm{cathode}\mathrm{chamber}}{volum\mathrm{etric}\mathrm{flow}\mathrm{rate}}.$

Example 4b: ?.SUP.13.C

[0152] As shown from the results in Table 5 and FIG. 5a, E-18 gave the best ?.sup.13C of 0.36% compared to all the other GDE tests. When comparing E-16 to E-18 with the same GDE used, the results indicate that by increasing the current density while keeping the flow rate constant, the best ?.sup.13C may be achieved. This indicates that a higher current density is important in producing CO.sub.2 enriched in carbon-13.

[0153] Additionally, further tests using GDE-1 comprising Cu nanoparticles as a catalyst layer (first layer) (E-7 to E-9) and tests using GDE-3 comprising Ag nanoparticles as a catalyst layer (first layer) (E-16 to E-18) indicate that Ag was better in enriching .sup.13C. At the same flow cell voltage, it was observed that the enrichment for E-18 was 0.36%, as compared to E-9 with a Cu GDE cathode with the same parameters (0.12%).

TABLE-US-00005 TABLE 5 Electrochemical enrichment of .sup.13CO.sub.2 .sup.13C in Flow rate CO.sub.2 in Feed of CO.sub.2 Total Catalyst Flow cell Current feed flow detected conversion GDE loading, voltage, density, stream, rate, at outlet, to products, Tests Cathode mg/cm.sup.2 V A/cm.sup.2 % sccm sccm % E-1 GDE-1 2 2.6 0.5 1.11 50 41 3.51 E-2 GDE-2 2 2.6 0.5 1.11 50 41 2.64 E-3 GDE-3 2 2.6 0.5 1.11 50 41 0.7 E-4 GDE-4 1 2.6 0.5 1.11 50 41 2.78 E-5 GDE-5 1 2.6 0.5 1.11 50 41 2.2 E-6 GDE-6 1 2.6 0.5 1.11 50 41 0.68 E-7 GDE-1 3 2.6 0.5 1.11 30 25 8 E-8 GDE-1 3 2.8 1.0 1.11 30 20 20 E-9 GDE-1 3 4.1 1.5 1.11 30 17 28 E-10 GDE-1 3 1.6 0.5 1.11 30 25 8 E-11 GDE-1 3 2.8 1 1.11 30 20 20 E-12 GDE-1 3 4.1 1.5 1.11 30 17 28 E-13 GDE-1 3 1.6 0.5 1.11 50 43 9 E-14 GDE-1 3 2.8 1 1.11 50 36 5.2 E-15 GDE-1 3 4.1 1.5 1.11 50 30 23 E-16 GDE-3 2 1.6 0.5 1.11 30 19 12 E-17 GDE-3 2 2.8 1.0 1.11 30 15.3 25 E-18 GDE-3 2 4.1 1.5 1.11 30 15.2 31 E-19 GDE-3 2 1.6 0.5 1.11 50 39.5 11 E-20 GDE-3 2 2.8 1 1.11 50 26 9 E-21 GDE-3 2 4.1 1.5 1.11 50 19 21 E-22 GDE-3 2 1.6 0.5 1.11 75 64 17 E-23 GDE-3 2 2.8 1 1.11 75 55.3 25 E-24 GDE-3 2 4.1 1.5 1.11 75 51 19 E-25 GDE-3 2 2.8 1.0 5.58 30 15.4 25 E-26 GDE-3 2 2.8 1.0 88.48 30 15.4 25 E-27 GDE-7 0 2.8 1.0 1.11 30 20 1.0 E-28 GDE-7 0 4.1 1.5 1.11 30 15.4 1.5 .sup.13C in CO.sub.2 .sup.13C in Energy ? .sup.13C/s ?.sup.13C/J in outlet products, ?.sup.13C, ?.sup.13C, time, input, (per (per Tests stream, % % % s J time) energy) E-1 1.125 1.041 16 0.015 0.42 0.546 0.036 0.028 E-2 1.121 1.061 12 0.011 0.42 0.546 0.026 0.020 E-3 1.114 1.091 6 0.004 0.42 0.546 0.010 0.008 E-4 1.124 1.047 14.8 0.014 0.42 0.546 0.033 0.025 E-5 1.119 1.069 10.5 0.009 0.42 0.546 0.022 0.017 E-6 1.112 1.101 4 0.002 0.42 0.546 0.005 0.004 E-7 1.130 1.010 18.22 0.02 0.7 0.56 0.029 0.036 E-8 1.150 1.030 36.46 0.04 0.7 1.96 0.057 0.020 E-9 1.230 0.953 109.45 0.12 0.7 4.305 0.171 0.028 E-10 1.130 1.010 18.22 0.02 0.7 0.56 0.029 0.036 E-11 1.150 1.030 36.46 0.04 0.7 1.96 0.057 0.020 E-12 1.230 0.953 109.45 0.12 0.7 4.305 0.171 0.028 E-13 1.115 1.079 6.76 0.005 0.42 0.336 0.012 0.015 E-14 1.120 1.084 11.33 0.01 0.42 1.176 0.024 0.009 E-15 1.150 1.050 38.73 0.04 0.42 2.583 0.095 0.015 E-16 1.150 1.041 36.46 0.04 0.7 0.56 0.057 0.071 E-17 1.270 0.943 146.00 0.16 0.7 1.96 0.229 0.082 E-18 1.470 0.740 329.16 0.36 0.7 4.305 0.514 0.084 E-19 1.130 1.035 20.46 0.02 0.42 0.336 0.048 0.060 E-20 1.190 1.023 75.30 0.08 0.42 1.176 0.190 0.068 E-21 1.240 1.030 121.04 0.13 0.42 2.583 0.310 0.050 E-22 1.120 1.052 11.33 0.01 0.28 0.224 0.036 0.045 E-23 1.150 0.998 38.73 0.04 0.28 0.784 0.143 0.051 E-24 1.190 0.940 75.30 0.08 0.28 1.722 0.286 0.046 E-25 5.760 5.390 34.23 0.18 0.7 1.96 0.257 0.092 E-26 88.700 88.248 22.00 0.22 0.7 1.96 0.314 0.112 E-27 1.115 1.100 6.76 0.005 0.7 1.96 0.007 0.003 E-28 1.120 1.099 11.33 0.01 0.7 4.305 0.014 0.002

[0154] Generally, a larger change in ?.sup.13C is observed to correlate with a bigger conversion rate of CO.sub.2 to products. This is likely due to discrimination against the heavy .sup.13C isotope when undergoing electroreduction. As noted in Table 5, the .sup.13C content of the CO.sub.2 in the outlet stream was observed to increase across all tests, while the .sup.13C content of the reduction products were observed to have a lower .sup.13C content as compared to the .sup.13C content in the initial feed stream.

Example 4c: Flow Cell Potential and Current Density

[0155] The effect of the flow cell voltage was studied, with the results being shown amongst at least E-7 to E-9 and E-16 to E-18. As shown in Table 5 and FIG. 5a, ?.sup.13C was observed to increase when a higher voltage was applied. Thus a higher voltage results in more enrichment. Additionally, the method was effective at higher voltages with no significant side reactions, which is an important consideration when performing the method on an industrial scale.

[0156] Current is proportionate to the voltage applied, and hence a higher current also directly translates to more enrichment as more energy is provided to the electrode for the electroreduction. To account for different electrode sizes, current density may be used in place of current. Hence as shown in Table 5, current density also directly translates to more enrichment.

Example 4d: Flow Rate and Residence Time

[0157] The flow rate was also studied with results being shown in FIGS. 5d and 5e. The flow rate may be used interchangeably with residence time, as they are inversely proportionate to each other.

[0158] FIG. 5d relates to E-7 to E-15, while FIG. 5e relates to E-16 to E-24. The same parameters were used, except that the flow rates were varied between 30 sccm, 50 sccm and 75 sccm (residence times of 0.7 seconds, 0.42 seconds and 0.28 seconds).

[0159] As shown in the results, a lower flow rate and a corresponding larger residence time increases ?.sup.13C across all tests. At lower flow cell voltages, ?.sup.13C was similar between the three tested flow rates, however the differences were quite small. At higher voltages (4.1 V), enrichment was observed at all tested residence times, with the test at 30 sccm having the highest ?.sup.13C. Thus a low flow rate is important to increasing the enrichment rate of the present method.

Example 4e: Efficiency

[0160] ?.sup.13C was plotted against the residence time (FIG. 5b) and energy input (FIG. 5c) for E-7 to E-9, E-16 to E-18 and E-27 to E-28.

[0161] As shown in FIG. 5b, at the same residence time of 0.7 seconds, all tests were found to produce .sup.13CO.sub.2 enriched CO.sub.2. E-9 and E-18 in particular had the highest enrichment rate over time.

[0162] Comparison of ?.sup.13C over energy input (FIG. 5c) indicates both the Ag cathode GDE-3 and Cu cathode GDE-1 are energy-efficient and produced good enrichment rates. E-18 in particular had an enrichment rate of about 0.084% per Joule of energy input, as compared to E-9 having an enrichment rate of 0.028% per Joule of energy input.

Example 4f: Further enrichment

[0163] The method discussed in the previous Examples has been shown to produce .sup.13CO.sub.2 enriched stream in a single pass. To further obtain higher enrichment content, the method may be repeated either with recirculation or in a series of electrochemical cells. FIG. 1 demonstrates a recirculation process for producing a .sup.13CO.sub.2 enriched stream, while FIG. 2 demonstrates a proposed series of electrochemical cells for producing a .sup.13CO.sub.2 enriched stream.

[0164] As mentioned, prolonged enrichment may be performed in a single-pass reactor, recirculating reactor (FIG. 1), or in tandem reactors (FIG. 2). To show robustness of the method in this aspect, additional experiments were designed with higher initial .sup.13C content in mind (see E-25 and E-26 of Table 5).

[0165] Both E-25 and E-26 have higher initial .sup.13C abundances (5.58% and 88.48% respectively) in the feed stream as compared to the natural .sup.13C abundance of 1.11% in E-17 as shown in FIG. 6b. As shown in the results in FIG. 6b, substantial enrichment was still observed at higher initial .sup.13C abundances, showing that the method can still enrich .sup.13C from a higher initial .sup.13CO.sub.2 content. Even in E-26 with an initial .sup.13C content of 88.48%, a recorded ?.sup.13C value of 0.22% was still comparable to the E-25 (0.18%) with a far lower initial .sup.13C content at 5.58%.

[0166] The enrichment rates were also plotted against the residence time and energy input and shown in FIG. 6c. As shown, the enrichment rate was comparable across all the initial .sup.13C content, with E-26 showing the highest enrichment rate. Additionally, energy efficiency was similarly comparable at all initial .sup.13C content tested, with E-26 (initial .sup.13C content of 88.48%) being the most efficient. Thus the method of the present invention can be applied to feed streams of all .sup.13C content. Additionally this also implies that the method can be further applied to a recirculation process, or a tandem process, as discussed in the further Examples.

[0167] Additionally, the effect of voltage was also studied on a feed stream of higher .sup.13C abundance (5.58%) with the results being shown in FIG. 6a. As shown in FIG. 6a, enrichment was observed at all applied voltages, showing that the presently disclosed enrichment method can be applied to a feed stream with higher .sup.13C content at different voltages. Furthermore, the example E-26 shows that the enrichment is still going on even for concentration of .sup.13C at 88.48% with the same electrolyte and feed residence time as previous example E-7. These results indicate that tested voltage ranges and parameters are applicable across all feed streams with any level of .sup.13C content.

Example 5: Reduction Products

[0168] GC results of all major isolated products are shown in FIGS. 8a and 8b.

[0169] When GDE-3 was used, CO was the major reduced product observed (see FIG. 8a). On the other hand, when GDE-1 was used, a mixture of CO, ethylene, propene and ethanol were observed (see FIG. 8b). The results indicate that the Cu GDE cathode was able to further reduce the CO.sub.2 from the +4 oxidation states to the ?2 oxidation state (as in ethylene), or ?3 (as in propene and ethanol). Hence, if the liquid products are desired, the Cu cathode may be used in place of the Ag cathode. Otherwise, the Ag cathode may be used to only produce CO as the only by-product. This is advantageous as the liquid electrolyte would not need to undergo purification to remove side-products, which also translates to lower maintenance costs as well as easier operation.

Example 6: Recirculation Process

[0170]

TABLE-US-00006 TABLE 6 Recirculation test with E-1 Cycle number ?.sup.13C, .sup.13C in unreacted CO.sub.2, % 1 16 1.115 2 9 1.123 3 10 1.131 4 10 1.140 5 10 1.149

[0171] To demonstrate a recirculation electrochemical cell, CO.sub.2 was introduced to the cathode chamber of an electrochemical cell using the same parameters as that of Test E-1. For E-1, the outlet stream was re-directed to the inlet of the same cathode chamber similar to FIG. 1. Results for E-1 are shown in Table 6 and FIG. 7.

[0172] As shown from the FIG. 7, an increase in carbon-13 content was observed with the completion of each cycle. At the completion of cycle 5, a ?.sup.13C percentage of about 60% was observed relative to the .sup.13CO.sub.2 content in the initial feed stream. It has also been amply demonstrated in Example 4f that the present method can enrich CO.sub.2 with a higher initial .sup.13C content. Thus, the presently disclosed method can be easily adjusted to accommodate a recirculation electrochemical cell for further enrichment of .sup.13CO.sub.2.

Example 7: Industrial Enrichment

[0173] In order to further demonstrate the industrial scalability of the method, a study was prepared to determine whether .sup.13CO.sub.2 could be enriched to about 5% in a feasible timeframe. In conclusion, higher ?.sup.13C is achievable by firstly deploying the optimum process conditions as discussed in the previous examples, and secondly, increasing the size of the GDE cathode. To achieve 5% of .sup.13C content in the outlet stream, the electrode surface should preferably be increased by a factor of about ten (while keeping other process parameters constant).

INDUSTRIAL APPLICABILITY

[0174] The present invention relates to a method of enriching .sup.13C. The presently disclosed method is cost efficient at only about $0.001 per litre of .sup.13CO.sub.2 enriched as compared to current cryogenic processes costing about $16 per litre of .sup.13CO enriched. The presently disclosed method is also more energy-efficient, space efficient and more time-efficient compared to conventional process for enriching .sup.13C, for example cryogenic distillation. The .sup.13C-enriched product can also be applied to many different areas, for example, in drug discovery and validation, reaction mechanism studies, .sup.13C-MRI radiology and medical diagnosis. The other products, for example syngas, CO, ethanol, acetic acid or CH.sub.4, may also be applied and used in many different areas, for example in plastics manufacture, fermentation, combustion, or to be further processed into other useful products. Thus this invention is capable of industrial applicability.

[0175] It will be apparent that various other modifications and adaptations of the invention will be apparent to the person skilled in the art after reading the foregoing disclosure without departing from the spirit and scope of the invention and it is intended that all such modifications and adaptations come within the scope of the appended claims.