Systems and methods for electrochemical generation of syngas and other useful chemicals
Processes and apparatus for electrocatalytically converting carbon dioxide emissions and/or ambient carbon dioxide into useful chemicals are described. The process may include: removing carbon dioxide from ambient air through a carbon capture technique, supplying a carbonate or bicarbonate aqueous solution as cathode feed to a cathode of an electrolytic cell comprising a membrane electrode assembly which includes a bipolar membrane separating an anode from the cathode, and applying an electrical potential difference between the cathode and the anode of the membrane electrode assembly to electrocatalytically reduce the carbonate or bicarbonate aqueous solution to carbon monoxide or another useful chemical.
1 . A method comprising:
flowing a catholyte comprising carbonate and/or bicarbonate to an electrochemical reactor, wherein the electrochemical reactor comprises an anode, a cathode and a bipolar membrane separating the anode from the cathode, and wherein the bipolar membrane comprises a cation exchange membrane facing the cathode and an anion exchange membrane facing the anode, and wherein the catholyte has a pH above 8;
dissociating water at the bipolar membrane to generate protons and hydroxide ions, causing the protons to flow toward the cathode and causing the hydroxide ions to flow toward the anode;
reacting the carbonate and/or bicarbonate in the catholyte with the protons to yield in-situ CO 2 ;
performing a reduction reaction at the cathode, wherein the reduction reaction comprises reducing the in-situ CO 2 to generate CO and H 2 ;
performing an oxidation reaction at the anode; and
removing the CO and H 2 from the electrochemical reactor.
2 . The method of claim 1 , wherein the gaseous stream comprises ambient air, flue gas, or exhaust gas.
3 . The method of claim 1 , wherein the electrochemical reactor is maintained at a pressure of 2 atmospheres or less.
4 . The method of claim 1 , wherein the catholyte comprises the carbonate and/or the bicarbonate at a concentration of at least 3 moles/liter.
5 . The method of claim 1 , wherein the electrochemical reactor causes the oxidation and reduction reactions using power having a current density of at least 25 mA/cm 2 and at most 100 mA/cm 2 .
6 . The method of claim 1 , wherein the electrochemical reactor is operated at a temperature not exceeding 150° C.
7 . The method of claim 1 , wherein the electrochemical reactor is operated at a temperature not exceeding a boiling point of the aqueous solution.
8 . The method of claim 1 , wherein a molar ratio of the CO to the H 2 is greater than 1.
9 . The method of claim 1 , wherein a molar ratio of the CO to the H 2 is less than 1.
10 . The method of claim 1 , wherein the reduction reaction further generates CO 2 .
11 . The method of claim 1 , wherein the catholyte has a pH in the range of from 8 to 10.
12 . The method of claim 1 , wherein the cathode is spaced apart from the bipolar membrane by a distance of 100 μm or less.
13 . The method of claim 1 , wherein the anode comprises a layer of a porous metal.
14 . The method of claim 1 , wherein the cathode comprises a silver catalyst.
15 . The method of claim 1 , wherein a concentration of CO 2 in the catholyte is below 7 mM.
16 . The method of claim 1 , wherein the oxidation reaction comprises oxidizing hydroxide ions to yield water and oxygen gas.
17 . The method of claim 1 , further comprising:
flowing a gaseous stream to a contactor to contact an aqueous solution, thereby capturing CO 2 from the gaseous stream to generate the catholyte, wherein the aqueous solution comprises an enzyme catalyst for promoting the capturing of the CO 2 .
18 . The method of claim 17 , further comprising discharging a gas out of the contactor after the capturing of the CO 2 from the gaseous stream, wherein the gas discharged out of the contactor has a CO 2 concentration that is less than a CO 2 concentration of the gaseous stream.
19 . A method comprising:
in a contactor, capturing CO 2 from a gaseous stream into an aqueous solution comprising a catalyst for the capture of CO 2 to generate a catholyte comprising carbonate and/or bicarbonate;
flowing the catholyte comprising carbonate and/or bicarbonate from the contractor to an electrochemical reactor, wherein the electrochemical reactor comprises an anode, a cathode and a bipolar membrane separating the anode from the cathode, and wherein the bipolar membrane comprises a cation exchange membrane facing the cathode and an anion exchange membrane facing the anode, wherein the catholyte is directly supplied from the contactor to the electrochemical reactor;
dissociating water at the bipolar membrane to generate protons and hydroxide ions, causing the protons to flow toward the cathode and causing the hydroxide ions to flow toward the anode;
reacting the carbonate and/or bicarbonate in the catholyte with the protons to yield in-situ CO 2 ;
performing a reduction reaction at the cathode, wherein the reduction reaction comprises reducing the in-situ CO 2 to generate CO and H 2 ;
performing an oxidation reaction at the anode; and
removing the CO and H 2 from the electrochemical reactor.
20 . The method of claim 19 , wherein the catalyst comprises an enzyme catalyst.