Apparatus and method of preparing carbonate and/or formate from carbon dioxide

Abstract

The present invention relates to an apparatus and method of preparing carbonate and/or formate from carbon dioxide. The apparatus of preparing carbonate and/or formate from carbon dioxide (CO.sub.2), comprising: an electrolysis reactor comprising (i) an anode which contains an aqueous solution of a Group I metal salt as an electrolytic solution, (ii) an ion-exchange membrane through which metal cations derived from the Group I metal salt and water flow from an anode to a cathode, (iii) a cathode, and (iv) a gas diffusion layer which supplies a carbon dioxide-containing gas to the cathode; a power supply unit of applying a voltage between the anode and the cathode; a first gas-liquid separator of recovering the electrolytic solution from the products formed in the anode; a second gas-liquid separator of recovering carbonate and/or formate from the products formed in the cathode; a pH meter of measuring the pH of the electrolytic solution recovered from the first gas-liquid separator; a first reactant supply unit of supplying (a) the electrolytic solution recovered from the first gas-liquid separator and (b) the aqueous solution of the Group I metal salt with which the recovered electrolytic solution is replenished according to the pH of the electrolytic solution, to the anode; and a second reactant supply unit of supplying carbon dioxide or a mixer comprising carbon dioxide and water vapor to the cathode; wherein, when a voltage is applied between the anode and the cathode, in the anode, water undergoes electrolysis to generate hydrogen ions, oxygen, and electrons, and metal cations in the Group I metal salt are substituted with the hydrogen ions, while the generated metal cations move to the cathode through the ion-exchange membrane and the electrons move to the cathode through an external electric line; and in the cathode, carbon dioxide, water, metal cations, and electrons are reacted and produce carbonate and/or formate.

Claims

1. An apparatus for preparing carbonate and/or formate from carbon dioxide (CO.sub.2), comprising: an electrolysis reactor comprising (i) an anode which contains an aqueous solution of a Group I metal salt as an electrolytic solution, (ii) an ion-exchange membrane through which metal cations derived from the Group I metal salt and water flow from the anode to a cathode, (iii) the cathode, and (iv) a gas diffusion layer which supplies a carbon dioxide-containing gas to the cathode; a power supply unit for applying a voltage between the anode and the cathode; a first gas-liquid separator for recovering the electrolytic solution from products formed in the anode; a second gas-liquid separator for recovering carbonate and/or formate from products formed in the cathode; an ion electrode for measuring the concentration of the carbonate and/or formate recovered from the second gas-liquid separator; a pH meter for measuring a pH of the electrolytic solution recovered from the first gas-liquid separator; a first reactant supply unit for supplying (a) the electrolytic solution recovered from the first gas-liquid separator and (b) the aqueous solution of the Group I metal salt with which the recovered electrolytic solution is replenished according to the pH of the electrolytic solution, to the anode; and a second reactant supply unit for supplying carbon dioxide or a mixture comprising carbon dioxide and water vapor to the cathode; wherein, when a voltage is applied between the anode and the cathode, in the anode, water undergoes electrolysis to generate hydrogen ions, oxygen, and electrons, and the metal cations in the Group I metal salt are substituted with the hydrogen ions, while the generated metal cations move to the cathode through the ion-exchange membrane and the electrons move to the cathode through an external electric line; and in the cathode, the carbon dioxide, water, metal cations, and electrons are reacted and produce carbonate and/or formate; wherein the apparatus is configured to supply water to the cathode from the anode through the ion-exchange membrane; wherein the apparatus does not comprise a unit for supplying a cathode electrolytic solution to the cathode; wherein the electrolysis reactor comprises: (ii) the ion-exchange membrane; (i) the anode, which comprises an anode catalyst layer applied to a first surface of (ii) the ion-exchange membrane; an electrically conductive structure for providing a space for the flow of the electrolytic solution; and a current collector in which a flow path for supplying reactants of the water and metal cations and a flow path for releasing the products are formed; and (iii) the cathode, which comprises a cathode catalyst layer applied to a second surface of (ii) the ion-exchange membrane; (iv) the gas diffusion layer; and a current collector in which a flow path for supplying reactants of the carbon dioxide and a flow path for releasing the products are formed; wherein the water which moves from the anode to the cathode through the ion-exchange membrane, the water vapor in the carbon dioxide-containing gas, or both forms a water film on the surface of a cathode catalyst layer; wherein the cathode catalyst layer has a particulate structure or a porous structure, and the cathode catalyst layer is configured to promote formation of the water film on the surface of the cathode catalyst layer; wherein the electrolytic solution to be supplied to the anode is the aqueous solution of a Group I metal salt at a concentration of 0.1 M to 2 M; and wherein the concentration of the carbonate and/or formate recovered from the second gas-liquid separator is regulated by supplying additional water vapor to the cathode according to the concentration of the carbonate and/or formate recovered from the second gas-liquid separator.

2. The apparatus of claim 1, wherein the pH of the electrolytic solution decreases as the metal cations contained in the electrolytic solution supplied to the anode are consumed by the reaction, and for the purpose of maintaining the concentration of the Group I metal salt in the electrolytic solution in the anode, the recovered electrolytic solution to be supplied to the anode is replenished with the aqueous solution of the Group I metal salt according to the measurement of the pH of the electrolytic solution recovered from the first gas-liquid separator.

3. The apparatus of claim 1, wherein a concentration of the carbonate and/or formate recovered from the second gas-liquid separator is regulated to 0.1 wt % to 50 wt %.

4. The apparatus of claim 1, wherein a catalyst of the cathode catalyst layer is selected from the group consisting of Sn, Pb, In, Cu, Pt, Pd, Ni Hg, Tl, Cd, Bi, Au, Ag, an oxide thereof, an alloy thereof, and an organometallic compound containing the same, and wherein a catalyst of the anode catalyst layer is selected from the group consisting of Pt, Pd, Ru, dimensionally stable anode (DSA), Au, Ir, Ag, Rh, Ni, Al, Mo, Cr, Cu, Ti, W, an oxide thereof, an alloy thereof, and a mixed metal oxide thereof.

5. The apparatus of claim 1, wherein the Group I metal in the Group I metal salt is Li, Na, K, Rb, Cs, or a mixed metal thereof, and the metal salt is hydrogen carbonate, carbonate, hydrochloride, chloride salt, sulfate, nitrate, fluoride salt, chlorate, hypochlorite, or chlorite.

6. A method of preparing carbonate and/or formate from carbon dioxide in in the apparatus of claim 1, comprising: (1) supplying the aqueous solution of the Group I metal salt as the electrolytic solution to the anode of the electrolysis reactor; (2) supplying the carbon dioxide-containing gas to the cathode of the electrolysis reactor; (3) applying the voltage between the anode and the cathode to generate the hydrogen ions, oxygen, and electrons via the electrolysis of water in the anode and substituting the metal cations in the Group I metal salt with the hydrogen ions; (4) transporting the metal cations generated in the anode to the cathode through the ion-exchange membrane and transporting the electrons to the cathode through the external electric line; and (5) reacting carbon dioxide, water, metal cations, and electrons in the cathode to produce the carbonate and/or formate; and (6) for the purpose of maintaining the concentration of the Group I metal salt in the electrolytic solution to be supplied to the anode, measuring the pH of the electrolytic solution recovered from the products formed in the anode and replenishing the recovered the electrolytic solution with the aqueous solution of the Group I metal salt according to the pH of the electrolytic solution.

7. The method of claim 6, wherein the carbonate and/or formate produced in step (5) is produced in the form of an aqueous solution.

8. The method of claim 7, wherein the concentration of the carbonate and/or formate produced in step (5) in the aqueous solution is 0.1 wt % to 50 wt %.

9. The method of claim 6, further comprising: recovering the electrolytic solution from the products produced in the anode by gas-liquid separation; and recovering the carbonate and/or formate from the products produced in the cathode by gas-liquid separation.

10. The method of claim 6, wherein the carbonate and/or formate is produced in a Faradaic efficiency of 80% or higher.

11. The method of claim 6, wherein a voltage of 2 V to 6 V is applied to both ends of the anode and the cathode.

12. The method of claim 6, wherein in Step (2), the carbon dioxide-containing gas is supplied to the cathode through the gas diffusion layer; and the water which moved from the anode to the cathode through the ion-exchange membrane, the water vapor in the carbon dioxide-containing gas, or both forms a water film on the surface of the cathode catalyst layer.

13. The method of claim 6, wherein the electrolysis reactor comprises: the ion-exchange membrane; the anode, which comprises the anode catalyst layer applied to the first surface of the ion-exchange membrane; the electrically conductive structure for providing the space for the flow of the electrolytic solution; and the current collector in which a flow path for supplying reactants and a flow path for releasing products are formed; and the cathode, which comprises the cathode catalyst layer applied to the second surface of the ion-exchange membrane; the gas diffusion layer; and the current collector in which the flow path for supplying reactants and the flow path for releasing products are formed.

14. The method of claim 6, wherein the electrolytic solution supplied to the anode is an aqueous solution of a Group I metal salt at a concentration of 0.1 M to 2 M.

15. The method of claim 6, wherein the apparatus further comprises the ion electrode for measuring the concentration of the carbonate and/or formate recovered from the second gas-liquid separator, wherein the concentration of the carbonate and/or formate recovered from the second gas-liquid separator is regulated by supplying additional water vapor to the cathode according to the concentration of the carbonate and/or formate recovered from the second gas-liquid separator.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1A is a schematic diagram that thermodynamically explains the limit of the gas-phase reaction of existing carbon dioxide.

(2) The top two graphs in FIG. 1B show the concentrations and Faradaic efficiencies of products in the liquid-phase reaction, and the two bottom graphs show the concentrations and Faradaic efficiencies of products in the gas-phase reaction.

(3) FIG. 2 is a conceptual diagram schematically illustrating the reaction of carbon dioxide occurring in an apparatus and each part of the apparatus according to an embodiment of the present invention.

(4) FIG. 3 is a schematic diagram of an apparatus of preparing formate and carbonate by electrochemically reducing carbon dioxide (CO.sub.2) according to an embodiment of the present invention.

(5) FIG. 4 shows the measurement results of concentrations and Faradaic efficiencies according to the amount of water vapor supplied in preparing formate and carbonate by electrochemical reduction of carbon dioxide (CO.sub.2) according to the method of the present invention.

BEST MODE

(6) The following Examples are for illustrative purposes only, and the scope of the present invention is not limited by these Examples.

Example 1: Manufacture of Apparatus of Preparing Carbonate and/or Formate by Electrochemical Reduction of Carbon Dioxide According to the Present Invention

(7) As illustrated in FIGS. 2 and 3, an apparatus of preparing carbonate (M.sub.2CO.sub.3 or MHCO.sub.3) and/or formate (HCOOM) by electrochemical reduction of carbon dioxide was manufactured.

(8) An anode electrode was manufactured by spray coating particles of platinum (Pt) catalyst powder on one side of an ion-exchange membrane (Nafion 115) while particulate tin (Sn) powders were coated on the other side to prepare a cathode electrode. A 0.2 mm-thick titanium gauze was inserted into the prepared anode so that the electrolytic solution can be filled with the electrolytic solution, whereas a 0.2 mm-thick water-repellent carbon paper was inserted into a gas diffusion layer and a current collector was bonded thereto. For the current collector, a graphite or brass plate with good electrical conductivity was used to generate a potential difference between the two electrodes when voltage was applied to an electrolysis reactor and the reactant was supplied to the anode and the cathode, and a flow path was formed to discharge the products.

Experimental Example 1: Examination of Efficiency with Regard to Method of Preparing Carbon Dioxide According to the Present Invention

(9) The concentrations of carbonate and formate were measured by changing the rate of water vapor supply from 0 mg/min to 502.3 mg/min by applying a 3.0 V voltage at a reactor temperature of 25° C., while supplying CO.sub.2 gas at 300 sccm using a apparatus of preparing carbonate and/or formate by electrochemically reducing the carbon dioxide (CO.sub.2) produced in Example 1 above.

(10) Specifically, the experimental conditions were as follows:

(11) Applied voltage: 3.0 V

(12) Reaction temperature: 25° C.

(13) Ion-exchange membrane: Nafion 115

(14) Anode electrode catalyst: Spray-coated Pt powder

(15) Cathode electrode catalyst: Spray-coated Sn powder

(16) Electrolytic solution supplied to anode: 0.5 M KHCO.sub.3 (aqueous solution)

(17) Gas supplied to cathode: Mixed gas of CO.sub.2 water vapor

(18) Amount of water vapor supply: 0 mg/min to 196 mg/min

(19) As a result of the analysis of the products using HPLC, it was confirmed that 1% to 2% of carbonate and 3% to 7% of formate were prepared at a Faradaic efficiency of 80% or higher according to the amount of water vapor introduced (FIG. 4).