METHOD FOR ELECTROCHEMICALLY REDUCING CARBON DIOXIDE

Abstract

The invention discloses a method for in-situ extracting a reduced carbon dioxide product or product mixture in an electrochemical cell, and the use of a three-compartment electrochemical cell for in-situ extraction of organic carboxylic acids such as formic acid, acetic acid, oxalic acid, glycolic acid, tartaric acid, malonic acid, propionic acid, glyoxylic acid, and/or salts thereof for commercial use.

The method of the invention comprises introducing carbon dioxide-rich absorbent into a cathode compartment of an electrochemical cell, 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 of product mixture in the carbon dioxide-rich absorbent, thereby providing a carbon dioxide-poor absorbent, collecting reduced carbon dioxide product or product mixture via in-situ extraction into an acidic environment, and wherein the anode is separated from the cathode by more than one separator.

Claims

1. A method for electrochemically reducing carbon dioxide into a reduced carbon dioxide product or product mixture and in-situ extracting the reduced carbon dioxide product or product mixture in an electrochemical cell, comprising: a) introducing carbon dioxide-rich absorbent into a cathode compartment of an electrochemical cell; b) 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 absorbent, thereby providing a carbon dioxide-poor absorbent, and c) collecting reduced carbon dioxide product or product mixture via in-situ extraction, wherein the anode is separated from the cathode by more than one separator.

2. The method of claim 1, wherein the method further comprises contacting a carbon dioxide-containing gas stream with an absorbent, thereby absorbing carbon dioxide from the carbon dioxide-containing gas stream to form the carbon dioxide-rich absorbent.

3. The method of claim 1, wherein the method further comprises recirculating at least part of the carbon dioxide-poor absorbent to absorb carbon dioxide from the carbon dioxide-containing gas stream.

4. The method of claim 1, wherein the electrochemical cell is a three-compartment electrochemical cell comprising: a cathode compartment; an anode compartment; a cation exchange membrane; an anion exchange membrane, and a product compartment, wherein the method further comprises a step of adding at least one salt to the cathode compartment and/or anode compartment to improve electrical conductivity.

5. The method of claim 4, wherein the product compartment of the three-compartment electrochemical cell is the compartment into which reduced carbon dioxide product or product mixture is in-situ extracted.

6. The method of claim 2, wherein carbon dioxide is selectively absorbed by the absorbent.

7. The method of claim 2, wherein the absorbent comprises at least one physical solvent and/or at least one chemical solvent.

8. The method of claim 7, 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 alkylene carbonates such as propylene carbonate.

9. The method of claim 7, wherein the physical solvent is substantially non-aqueous.

10. The method of claim 7, wherein the chemical solvent comprises at least one amine, at least one alkanolamine, ammonia, or a mixture thereof.

11. The method of claim 7, wherein the chemical solvent comprises one or more selected from the group consisting of monoethanolamine, diethanolamine, N-methyldiethanolamine, dimethylethanolamine, diisopropylamine, aminomethylpropanol, ammonia, and diglycolamine.

12. The method of claim 7, wherein the chemical solvent is substantially non-aqueous.

13. The method of claim 2, wherein the contacting of the carbon dioxide-containing gas stream with the absorbent is performed at a temperature of 5 C. or higher.

14. The method of claim 1, wherein the absolute pressure is 1 bar or more and 200 bar or less.

15. (canceled)

16. (canceled)

17. 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/or salts thereof, aldehydes, or ketones.

18. The method of claim 1, wherein the reduced carbon dioxide product or product mixture comprises one or more selected from the group consisting of formic acid, acetic acid, oxalic acid, glycolic acid, tartaric acid, malonic acid, propionic acid, glyoxylic acid, and salts thereof.

19. The method of claim 4, wherein the product compartment of the three-compartment electrochemical cell comprises an acidic environment into which reduced carbon dioxide product or product mixture is extracted, and wherein the acidic environment has a pH range of 0-7.

20. The method according to claim 19, wherein the acidic environment comprises one or more ion-exchange filler(s).

21. (canceled)

22. The method of claim 20, wherein the ion-exchange filler(s) comprise at least one polymer.

23. The method of claim 20, wherein at least part of the ion-exchange filler(s) are dissolved and/S00or dispersed in the acidic environment.

24. (canceled)

25. The method of claim 1, wherein the anode and/or the cathode in the electrochemical cell are heated.

26. The method of claim 1, wherein the anode and/or the cathode is a zero-gap type electrode.

27. (canceled)

Description

EXAMPLE 1

[0096] FIG. 4 shows an example of an integrated monoethanolamine capture and electrochemical carbon dioxide utilisation process. A gas stream (sour gas) is fed into the absorber. Carbon dioxide-poor gas leaves the absorber from the top. The carbon dioxide-poor gas is fed through a scrubber in case impurities (e.g. liquids and/or solids) need to be removed. The scrubber, or a second scrubber, can be situated before the gas stream enters the absorber. An aqueous monoethanolamine solution of 15-35 wt. % enters the top of the absorber at 32 C. The carbon dioxide-rich monoethanolamine leaves the absorber at 58 C. The carbon dioxide-rich absorber enters an electrochemical cell (electrolyser), wherein carbon dioxide is reduced to a reduced carbon dioxide product or product mixture.

[0097] One such example reaction is given in FIG. 2. Carbon dioxide or the carbamate, RNHCO.sub.2.sup., from a CO.sub.2 reach amine stream reacts on surface of a cathode to produce formic acid and an amine. Formic acid is then selectively diffused into a middle compartment, where it is combined with protons diffused from an anode compartment to form formic acid solution in pure water in the middle compartment. On the anode an oxidation reaction takes place, for example, oxidation of water to oxygen and protons in acidic electrolyte of sulfuric acid. The carbamate preferably does not diffuse into the middle compartment, neither do amines.

Anode reaction: 2 H.sub.2O.sub.(l).fwdarw.O.sub.2(g)+4 H.sup.+.sub.(aq)+4 e.sup.

Cathode reaction: CO.sub.2(g)+2 H.sup.++2 e.sup..fwdarw.HCOO.sup..sub.(aq)

or RNHCO.sub.2.sup.+3 H.sup.+.sub.(aq)+2 e.sup..fwdarw.HCOO.sup..sub.(aq)+RNH.sub.3.sup.+

[0098] The anode and cathode are in-situ heated and/or cooled to a desirable temperature to induce local carbon dioxide release from the absorbent and to accelerate reaction rates and improve catalytic performance. The absorbent, carbon dioxide-poor absorbent, and gaseous carbon dioxide reduction product(s) are then pre-heated to 90-120 C. before being fed into the stripper, where the remainder of carbon dioxide is removed as well as the gaseous carbon dioxide reduction products are separated. The heat exchanger serves as a heat conservation device, and lowers total heat requirement of the process. The liquid reduced carbon dioxide product or product mixture is in-situ extracted in the electrochemical cell. The absorbent solution leaving the stripper is fed into a reboiler, where the remainder of all gases are removed. The resulting stripped absorbent is then fed into a mixer, wherein degraded monoethanolamine is removed. The monoethanolamine is subsequently fed into another mixer and into the absorber column.

EXAMPLE 2

[0099] Electrochemical reduction of carbon dioxide to formic acid was performed in a three-compartment electrochemical cell. Electrolysis was performed at ambient pressure in a filter-press type electrochemical reactor with plate electrodes: a Pt anode (10 cm.sup.2), a Sn cathode (10 cm.sup.2), and a Ag/AgCl reference electrode. The anode compartment was separated from the product compartment with a cation exchange membrane (Nafion) and the cathode compartment was separated from the product compartment with an anion exchange membrane (Fumatech). Aqueous ammonia (1 M) was used both as chemical solvent for carbon dioxide and as catholyte. The following environments were used in the different compartments: [0100] product compartment: 0.5 M H.sub.2SO.sub.4 (in MilliQ/Millipore water) [0101] anode compartment/anolyte: 0.5 M H.sub.2SO.sub.4 (in MilliQ/Millipore water) [0102] cathode compartment/catholyte: 1 M aqueous ammonia (in MilliQ/Millipore water), preloaded with CO.sub.2.

[0103] A constant potential of 1.8 V vs Ag/AgCl was applied to cathode during electrolysis. The anolyte was kept at ambient temperature, whereas the catholyte was kept at 15 C. The cathode was locally heated to 85 C., in order to locally release CO.sub.2 and electrochemically reduce it to formate. Formed formate-ions were in-situ extracted into the product compartment and combined with protons that were extracted from the anode compartment to form formic acid.

[0104] During the electrolysis, accumulation of formic acid was observed both in the cathode compartment and in the product compartment, and measured by HPLC. In addition, the formation of hydrogen gas at the cathode was observed. A current density of ca. 100 mA/cm.sup.2 and a total cell voltage of ca. 5 V were measured.