INTEGRATED ELECTROCHEMICAL CAPTURE AND CONVERSION OF CARBON DIOXIDE

Abstract

The invention is directed to a method for electrochemically reducing carbon dioxide, and an apparatus for performing the method.

The method of the invention comprises: a) contacting a carbon dioxide-containing gas stream with a capture solvent, thereby absorbing carbon dioxide from the carbon dioxide-containing gas stream to form a carbon dioxide-rich capture solvent; b) introducing at least part of the carbon dioxide-rich capture solvent into a cathode compartment of an electrochemical cell; c) applying an electrical potential between an anode and a cathode in the electrochemical cell sufficient for the cathode to reduce carbon dioxide into a reduced carbon dioxide product or product mixture in the carbon dioxide-rich capture solvent, thereby providing a carbon dioxide-poor capture solvent; and d) collecting the reduced carbon dioxide product or product mixture,
wherein the anode is separated from the cathode by a semi-permeable separator, thereby forming a cathodic compartment and an anodic compartment, and wherein the absolute pressure of the carbon dioxide-containing gas stream is 20-200 bar.

Claims

1. A method for electrochemically reducing carbon dioxide comprising: a) contacting a carbon dioxide-containing gas stream with a capture solvent, thereby absorbing carbon dioxide from the carbon dioxide-containing gas stream to form a carbon dioxide-rich capture solvent; b) introducing at least part of the carbon dioxide-rich capture solvent into a cathode compartment of an electrochemical cell; c) applying an electrical potential between an anode and a cathode in the electrochemical cell sufficient for the cathode to reduce carbon dioxide into a reduced carbon dioxide product or product mixture in the carbon dioxide-rich capture solvent, thereby providing a carbon dioxide-poor capture solvent; and d) collecting the reduced carbon dioxide product or product mixture, wherein the anode is separated from the cathode by a semi-permeable separator, thereby forming a cathodic compartment and an anodic compartment, and wherein the absolute pressure of the carbon dioxide-containing gas stream is 20-200 bar.

2. The method of claim 1, further comprising e) recirculating at least part of the carbon dioxide-poor capture solvent to an absorber unit.

3. The method of claim 1, wherein the absolute pressure in the electrochemical cell is 20 bar or more and 138 bar or less.

4. The method of claim 1, wherein the temperature in the electrochemical cell is 0 C. or more.

5. The method of claim 1, wherein the carbon dioxide-containing gas stream of a) is contacted with the capture solvent in an absorber unit, and wherein the carbon dioxide is selectively absorbed by the capture solvent.

6. The method of claim 1, wherein the capture solvent comprises at least one physical solvent.

7. The method of claim 1, wherein the capture solvent comprises at least one aqueous physical solvent.

8. The method of claim 6, wherein the physical solvent comprises one or more selected from the group consisting of dimethyl ethers of polyethylene glycol, N-methyl-2-pyrrolidone, methanol, and propylene carbonate.

9. The method of claim 6, wherein the physical solvent is a mixture of various dimethyl ethers of polyethylene glycol.

10. The method of claim 1, wherein the capture solvent comprises at least one chemical solvent.

11. The method of claim 10, wherein the chemical solvent comprises one or more selected from the group consisting of an aqueous solution of 2-amino-2-methyl-1-propanol, tertiary amine, methyldiethanolamine, and ammonia.

12. The method of claim 1, wherein the contacting of carbon dioxide-containing gas stream with capture solvent is performed at a temperature of 0 C. or higher.

13. The method of claim 1, wherein each of steps a)-d) in claim 1 is performed at an absolute pressure of 1 bar or more and 200 bar or less.

14. The method of claim 13, wherein each of steps a)-d) in claim 1 is performed at the absolute pressure is 20 bar or more and 138 bar or less.

15. The method of claim 1, wherein the reduced carbon dioxide product or product mixture comprises one or more selected from the group consisting of carbon monoxide, alkanes, alkenes, alcohols, carboxylic acids and salts thereof, such as formates, oxalates and acetates, aldehydes, and ketones.

16. The method of claim 1, wherein at least one salt in a non-aqueous solution is added to the cathodic compartment to improve electrical conductivity.

17. The method of claim 1, wherein the at least one salt in the non-aqueous solution is added to the anodic compartment to improve electrical conductivity.

18. The method of claim 1, wherein at least one salt in an aqueous solution is added to the cathodic compartment to improve electrical conductivity.

19. The method of claim 1, wherein at least one salt in an aqueous solution is added to the anodic compartment to improve electrical conductivity.

20. The method of claim 1, wherein the cathode comprises an electrically conducting metal electrocatalyst.

21. An apparatus comprising: an absorber unit, where the absorber unit is arranged to receive a carbon dioxide-containing gas stream under pressure, and an electrochemical cell connected to the absorber unit, where the electrochemical cell is arranged to electrochemically reduce carbon dioxide from the capture solvent, wherein the absorber unit, and electrochemical cell are each arranged to withstand an absolute pressure of 20-200 bar, and wherein the electrochemical cell comprises at least two compartments separated by a semi-permeable separator.

22. The apparatus of claim 21 for performing the method according to claim 1.

23. The apparatus of claim 21, wherein the absorber unit, and electrochemical cell are each arranged to withstand an absolute pressure of 20 bar or more and 138 bar or less.

24. The apparatus of claim 21, further comprising a separation unit connected to the electrochemical cell.

Description

EXAMPLE

[0092] The electrochemical reduction of carbon dioxide to carbon monoxide was performed at an elevated absolute pressure of 20 bar in a filter press type reactor. Inside the reactor, a silver plate anode (100 cm.sup.2) and a platinum plate cathode (100 cm.sup.2) were installed. Both electrodes were separated from each other by use of an activated proton exchange membrane (Nafion 117), thereby forming two compartments (i.e. an anodic and cathodic compartment). The anolyte was 0.5 liter 0.5 M H.sub.2SO.sub.4 (in MilliQ/Millipore water), whereas the catholyte was a 2 wt. % of 1-butyl-3-methylimidazolium trifluoromethanesulfonate (BMIM Otf) in propylene carbonate with traces of water. The conductivity of the catholyte was determined at 1.87 mS/cm. The electrolytes were pumped around in the setup at a flow of 16 l/h, and the setup was checked for any leakages. After finding no leakages, the absolute pressure of a carbon dioxide-containing gas stream was set at 5 bar (80 l/h carbon dioxide-flow in) on the system and the system was checked again for leakages. This procedure was continued until an absolute pressure of 20 bar was set to the system. A gas chromatography test run was performed to check whether no air was present in the system (i.e. the retention times of air/nitrogen and carbon monoxide are next to each other, thus if the air/nitrogen peak is too high no carbon monoxide can be measured). A carbon dioxide-containing gas stream with an absolute pressure of 20 bar was contacted with the catholyte to form a carbon dioxide-rich capture solvent. The carbon dioxide-rich capture solvent was introduced into the cathode compartment of the electrochemical cell. After performing a successful gas chromatography test run, a cell potential of 4.5 V was applied to the electrochemical cell and the current density measured 160 mA/cm.sup.2. The amount of carbon monoxide and hydrogen produced on the cathode was measured continuously with gas chromatography. The carbon monoxide concentration in the product stream was 3000 ppm carbon monoxide and 9700 ppm hydrogen (at 80 l/h carbon dioxide reactant feed). Oxygen was generated on the anode.