Electro-conversion of gaseous carbon dioxide via reduction in molten salt solution

Abstract

Sequestration and conversion of carbon dioxide via reduction in a metal-salt solution. Carbon dioxide feedstock is flowed through a reactor containing solvated electrons in a metal-salt solution. The solvated electrons react with the carbon dioxide to form various carbon products. Solvated electrons may be simultaneously regenerated for continuous operation of the metal -salt reactor.

Description

ELECTRO-CONVERSION OF GASEOUS CARBON DIOXIDE VIA REDUCTION IN MOLTEN SALT SOLUTIONCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims the benefit of and priority to United States Provisional Application No. 63 / 581,212, filed on September 7, 2023, the entire disclosure of which is hereby incorporated by reference as if set forth in its entirety herein.TECHNICAL FIELD

[0002] Embodiments herein generally relate to the capture, utilization, and sequestration of carbon dioxide and more specifically, but not exclusively, to the capture, utilization, and sequestration of carbon dioxide via reduction with solvated electrons in molten salt solutions, and the regeneration of the solvated electrons in molten salt solutions.BACKGROUND

[0003] Decarbonization requires effective, economic, and technically scalable carbon capture, utilization, and sequestration techniques. Plasma and aqueous chemical approaches are limited by low space-time yields and high activation energy kinetics, which necessitate high power consumption. Bio-sequestration through agriculture has an enormous process time and does not capture carbon emissions at the source. Geological sequestration or mineralization requires a significant quantity of calcium or other reagents which is uneconomical at the scale required to address climate change.

[0004] Therefore, a technique to reduce carbon dioxide at point sources, with regenerable catalysts and reagents, and with favorable space-time yields and activation energy kinetics, is desirable.SUMMARY

[0005] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description section. This summary is not intended to identify or exclude key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

[0006] In one aspect, embodiments relate to a method to form carbon products from carbon dioxide. The method includes flowing carbon dioxide through a solution comprising a metal that dissolves to generate solvated electrons; and regenerating the solvated electrons in the solution, wherein the solvated electrons react with the carbon dioxide to form at least one product comprising carbon.

[0007] In some embodiments, the solvated electrons are regenerated while carbon dioxide is flowed through the solution.

[0008] In some embodiments, the solvated electrons derive from the application of current to the solution.

[0009] In some embodiments, current is applied using at least one of an immersed electrode, a plasma electrode, a Tesla coil, an electron beam generator, or an X-ray generator.

[0010] In some embodiments, the solvated electrons derive from the dissolution of an electron donor.

[0011] In some embodiments, the electron donor is at least one of an alkali metal, an alkaline- earth metal, or a rare-earth metal.

[0012] In some embodiments, the electron donor is one or more of sodium or barium.

[0013] In some embodiments, the solution containing solvated electrons comprises one or more of sodium dissolved in sodium chloride, sodium dissolved in sodium bromide, sodium dissolved in sodium iodide, barium dissolved in barium chloride, barium dissolved in barium bromide, or barium dissolved in barium iodide.

[0014] In some embodiments, the current is applied using a plurality of immersed electrodes and the method further comprises monitoring the voltage between at least two of the electrodes to detect the formation of undesirable side products.

[0015] In some embodiments, the at least one product comprising carbon is one or more of carbon monoxide, amorphous carbon, graphite, graphene, diamond, carbon nanotubes, hydrocarbons, or any other allotropes of carbon or carbon and oxygen.

[0016] In some embodiments, the method further comprises forming at least one byproduct comprising oxygen.

[0017] In another aspect, embodiments of this invention include an apparatus for generating carbon products from carbon dioxide. The apparatus may comprise a reactor for a solution comprising a metal and solvated electrons; a source for the solvated electrons; and a bubbler for flowing carbon dioxide through the solution, wherein the solvated electrons react with the carbon dioxide to form at least one product comprising carbon.

[0018] In some embodiments, the source of solvated electrons is operated while carbon dioxide is flowed through the solution.

[0019] In some embodiments, the source of solvated electrons is a current source.

[0020] In some embodiments, the current source is at least one of an immersed electrode, a plasma electrode, a Tesla coil, an electron beam generator, or an X-ray generator.

[0021] In some embodiments, the source of solvated electrons is a dissolved electron donor.

[0022] In some embodiments, the electron donor is at least one of an alkali metal, an alkaline- earth metal, or a rare-earth metal.

[0023] In some embodiments, the electron donor is one or more of sodium or barium.

[0024] In some embodiments, the solution containing solvated electrons comprises one or more of sodium dissolved in sodium chloride, sodium dissolved in sodium bromide, sodium dissolved in sodium iodide, barium dissolved in barium chloride, barium dissolved in barium bromide, or barium dissolved in barium iodide.

[0025] In some embodiments, the current source is a plurality of immersed electrodes and the apparatus further comprises a voltmeter configured to measure the voltage between at least two of the electrodes to detect the formation of undesirable side products.

[0026] In some embodiments, the at least one product comprising carbon is one or more of carbon monoxide, amorphous carbon, graphite, graphene, diamond, carbon nanotubes, hydrocarbons, or any other allotropes of carbon or carbon and oxygen.

[0027] In some embodiments, the solvated electrons react with carbon dioxide to form at least one byproduct comprising oxygen.BRIEF DESCRIPTION OF DRAWINGS

[0028] Non-limiting and non-exhaustive embodiments of this disclosure are described with reference to the following figures, wherein like reference numerals refer to like parts throughout the various views unless otherwise specified:

[0029] Figure 1 is a flowchart describing one embodiment of a method of reducing carbon dioxide in a metal and salt solution;

[0030] Figure 2 is a block diagram presenting one embodiment of an apparatus for reducing carbon dioxide in a metal and salt solution; and

[0031] Figure 3 is a process flow diagram depicting the operation of a reactor with regeneration of solvated electrons.DETAILED DESCRIPTION

[0032] Various embodiments are described more fully below with reference to the accompanying drawings, which form a part hereof, and which show specific exemplary embodiments. However, the concepts of the present disclosure may be implemented in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided as part of a thorough and complete disclosure, to fully convey the scope of the concepts, techniques and implementations of the present disclosure to those skilled in the art. Embodiments may be practiced as methods, systems or devices. The following detailed description is, therefore, not to be taken in a limiting sense.

[0033] Reference in the specification to “one embodiment” or to “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiments is included in at least one example implementation or technique in accordance with the present disclosure. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

[0034] In addition, the language used in the specification has been principally selected for readability and instructional purposes and may not have been selected to delineate or circumscribe the disclosed subject matter. Accordingly, the present disclosure is intended to be illustrative, and not limiting, of the scope of the concepts discussed herein.Definitions

[0035] Unless otherwise specified, the following terms as used herein shall have the meanings as provided below:

[0036] The term “carbon dioxide feedstock” refers to a feedstock for the process comprising at least in part carbon dioxide (CO2). The feedstock could be a stream comprising at least in part CO2, in any phase.

[0037] The term “carbon product” or “product comprising carbon” refers to any partially reduced allotrope of carbon. This definition excludes CO2 but would include carbon monoxide (CO), carbonates, hydrocarbons, any carbon-oxygen compound or polymer with at least one hydrogen or other functional group, and allotropes of carbon including but not limited to graphite, graphene, diamonds, and carbon nanotubes.

[0038] The term “metal halide” refers to a class of salts containing at least one metallic cationic species and at least one halide anionic species. The metallic species may be selected from any group of metals on the periodic table, but particularly alkali metals, alkaline-earth metals, and rare- earth metals. Examples of the halide anionic species include but are not limited to fluoride, chloride, bromide, and iodide. The metal halide may be described with the general formula MXj, where M refers to the metallic cationic species, X refers to the halide anionic species, and the integer i is selected to balance the charge on the compound.

[0039] The term “metal-salt solution” refers to a solution formed from at least one metal halide species and at least one metal species. The solution may be heated so that it is in a liquid, or molten, state. The metal is selected to dissolve in the metal salt solution, creating free cationic metal species and solvated electrons.

[0040] The term “solvated electrons” refers to free electrons in the metal-salt solution formed from the dissolution of at least one metallic species.

[0041] The term “reactor” refers to any suitable process unit or reactor that brings the carbon dioxide feedstock in contact with the metal-salt solution for the reduction of CO2.Embodiments

[0042] Embodiments of this invention include methods and equipment configurations for the purpose of converting carbon dioxide (CO2) to a carbon product via reduction in a metal -salt solution.

[0043] Figure l is a flowchart describing one embodiment of a process 100 for reducing carbon dioxide in a metal and salt solution. In overview, a carbon dioxide feedstock is flowed through a metal-salt solution 104. Solvated electrons are generated via dissolving a metal in the same metalsalt solution 108. The solvated electrons react with the carbon dioxide to form products comprising carbon 112.

[0044] Figure 2 is a flowchart describing an apparatus 200 for the implementation of the method of Figure 1. A reactor 204 is charged with a metal-salt solution. Solvated electrons are generated in the metal-salt solution via a current source 208. An injector 212 of some type introduces the carbon dioxide feedstock to the solution. Subsequently, the reactor is held at process conditions which facilitate the reaction between the carbon dioxide feedstock and solvated electrons in the solution.

[0045] Figure 3 depicts a process flow diagram of the apparatus of Figure 2 accomplishing the reduction of carbon dioxide in a metal halide solution. The reactor 204 is charged with a metal halide solution 308 and a metal 312. A current is applied to the solution to generate solvated electrons 316 using, e.g., one or more immersed electrodes. A carbon dioxide feedstock is bubbled into the reactor 320. After reaction with the solvated electrons, the carbon dioxide is reduced to at least carbon monoxide and other carbon products 324. The metal halide solution may be recycled 328. The metal is oxidized and results in a metal oxide product 332.Feedstock

[0046] In embodiments of this process, a feedstock is selected which comprises at least in part CO2. The feedstock may be in any phase, including solid, liquid, and gaseous phases. The feedstock may be pure CO2, or a mixed stream of CO2 and other gases or liquids. For example, a gas effluent from a reactor which comprises CO2, other combustion products comprising carbon, and other gaseous species such as nitrogen are all suitable feedstocks. Optionally, the other gases and liquids may be inert and unreactive with the chemistry in the process.

[0047] In embodiments of this invention, the feedstock is charged to a reactor via some appropriate method based on the phase of the feedstock. In embodiments where the feedstock is a gas- or vapor-phase effluent, the feedstock may be bubbled through a liquid or molten metal-salt solution. In embodiments where the feedstock is liquid, it may be flowed or mixed into the metalsalt solution.Metal-Salt Solutions

[0048] In embodiments of this process, a metal-salt solution is formed by charging some quantity of suitable metal into a salt solution. Metals are suitable which at least partially dissolve in the salt solution. This dissolution generates metal cationic species and solvated free electrons, thus allowing the metal to serve as an electron donor.

[0049] In some embodiments, the electron donor metal is at least one of an alkali metal, alkaline-earth metal, or a rare-earth metal. Suitable rare-earth metals include yttrium (Y) and the lanthanons. In other embodiments, any suitable metal of the s-,p-, d-, and f- block of the periodic table may be used as an electron donor if process conditions are selected to enable the metal to dissolve in the salt solution.

[0050] In some embodiments, the electron donor metal is at least one of sodium (Na), potassium (K), calcium (Ca), barium (Ba), bismuth (Bi), strontium (Sr), lanthanum (La), praseodymium (Pr), and neodymium (Nd).

[0051] In some embodiments, the salt solution is formed by taking a metal halide salt where the metal species matches the electron donor metal, and the halide is at least one of fluoride, chloride, bromide, or iodide.

[0052] In some embodiments, the metal-salt solution may be heated so that it is in the liquid state. The operating temperature of the metal-salt solution may be selected to promote the dissolution of metal into solvated metal cations and solvated electrons. The salt may be optionally heated until it forms a liquid solution. In some embodiments, the salt solution is held under temperature and pressure process conditions so that it may be liquid or otherwise dissolve the electron donor metal. In some embodiments, the metal may be a solid dispersed in a liquid salt solution.

[0053] In some embodiments, the salt solution may be comprised of alkali or alkaline-earth salts such as but not limited to at least one of NaCl, KC1, CaCh, or Nal. In other embodiments, the salt solution may be comprised of other metal halide salts such as at least one of BaCh, BiCh, and Bah. Mixtures of metal halides may be used to adjust the temperature at which the solution melts and increase the solubility of the electron donor metal. For example, at least two of a metal chloride, metal bromide, and metal iodide may be present in combination.

[0054] In other embodiments, the liquid solution may comprise ammonia (NH3) or another solvent, so long as it is compatible with the selected metal species. Compatibility is determined by whether a metal dissolves in the solvent to generate solvated electrons, and whether undesirable side products are generated by the reaction of the solvent with metal and any of the carbon feedstock or products.

[0055] In some embodiments, the metal-salt solution is comprised of metallic Na dissolved in molten NaCl, where the metallic Na dissolves into a cation Na1and solvated electrons in the solution of NaCl. In some embodiments, the metal-salt solution is comprised of metallic Ca and molten CaCh to form dissolved Ca2+and solvated electrons. In some embodiments, the metal-salt solution is comprised of metallic Bi and molten BiCh to form dissolved Bi3+and solvated electrons. In some embodiments, the metal-salt solution is comprised of metallic Ba and molten BaCh to form dissolved Ba2+and solvated electrons. In some embodiments, the metal-salt solution is comprised of metallic Na and molten Nal to form dissolved Na+and solvated electrons.Carbon Conversion

[0056] In embodiments of this invention, a carbon dioxide feedstock is flowed through a metal-salt solution containing solvated electrons.

[0057] In some embodiments, the process of flowing the carbon dioxide through the metal - salt solution involves bubbling a gas- or vapor-phase carbon dioxide feedstock through a liquid metal-salt solution. Other embodiments may include flowing the carbon dioxide over or through the metal-salt solution. In yet other embodiments, mixers or other methods to agitate and mix the carbon dioxide feedstock and metal-salt solution may be used.

[0058] In solution, the solvated electrons react with CO2 to form products comprising carbon. In some embodiments, the primary chemistry is the reduction of carbon dioxide (CO2) to carbon monoxide (CO). The oxygen is reacted with the metal cationic species to form metal oxides. Insome embodiments, the metal oxides may precipitate as a solid. Tn some embodiments, the metal oxides may be soluble.

[0059] In various embodiments, the products may comprise carbon monoxide; carbonates and any other allotropes of carbon and oxygen; and elemental carbon, including amorphous carbon, graphite, graphene, diamond, carbon nanotubes, hydrocarbons, or any other allotropes of carbon.

[0060] In some embodiments, a combination of the above products may be generated in a single pass through the reactor.

[0061] In some embodiments, these carbon products may, in turn, be intermediates and further used as feedstocks for the manufacture of other carbon products, such as graphite, graphene, carbon nanotubes, and synthetic diamonds.Byproducts

[0062] In some embodiments, byproducts may be generated from the reaction of solvated electrons with other chemical species present in the carbon dioxide feedstock or metal -salt solution. Metal oxides may be the primary byproduct, but additional intermediate products comprising oxygen may result such as metallic carbonate species.

[0063] In some embodiments, the soluble metal oxide product may redissolve into a metal cations and dissolved oxygen anions (O2). When current is applied to the solution, O2' may be converted to oxygen gas (O2) at the anode, and the metal cations may be reduced to elemental metal at the cathode.

[0064] In embodiments where water is present in the solution, byproducts including aldehydes, carboxylic acids, and other hydrocarbons may be generated.Regeneration of Solvated Electrons

[0065] In some embodiments, the solvated electrons may be regenerated while carbon dioxide is converted to enable continuous processing.

[0066] In some embodiments, metal may be continuously or periodically added during operation, and the dissolution of the metal in solution regenerates the supply of solvated electrons.

[0067] In some embodiments, solvated electrons may be regenerated through a Faradaic reaction. Current is applied to the solution at a potential greater than the activation energy requiredto reduce metal ions to metal. The potential may also be selected to be less than the activation energy of undesirable side reactions, such as the decomposition of the metal halide.

[0068] For example, in embodiments where a Ba-BaCh metal-salt solution with immersed electrodes is used, the reduction of CO2 to CO results in the formation of BaO as a product. BaO is soluble in BaCh, forming Ba2+cations and O2' anions. The application of current at an appropriate voltage enables the reduction of Ba2+to Ba metal at the cathode, and the oxidation of O2- to O2 gas at the anode.

[0069] In some embodiments, the current is applied using at least one of an immersed electrode, a plasma electrode, a Tesla coil, an electron beam generator, or an X-ray generator. The electrode materials may be graphite, titanium diboride, platinum, or any other chemically inert material.

[0070] In some embodiments, a pressure- swing adsorption reaction may be used to regenerate the solvated electrons.

[0071] In some embodiments, a de-gassing reaction may be used to regenerate the solvated electrons. In this embodiment, argon (Ar) or another inert gas may be bubbled through the CO product to carry CO away from the reactor and free up solvated electrons.

[0072] In some embodiments, a high-voltage electrode may be used to generate plasma through the application of a high voltage to the solution or to a gas adjacent to the solution. The plasma may generate free radicals and solvated free electrons.

[0073] In some embodiments, an electron beam of any sort would be able to introduce fresh solvated electrons to the metal-salt solution.Process Control

[0074] In some embodiments, the temperature of the solution is maintained by the heat of the effluent being bubbled into the solution.

[0075] In some embodiments, the temperature of the liquid solution is maintained by the waste heat generated from applying electrical current to the liquid solution.

[0076] In some embodiments, the current applied to the metal-salt solution is monitored, with the voltage across the electrodes being used to detect when unfavorable byproducts may be formed. The applied potential may be limited to prevent the formation of such byproducts. For example,the applied potential may be set in a range to promote metal dissolution into solvated electrons but below the applied potential necessary to decompose the metal halide which comprises the salt solution.

[0077] In some embodiments, measurements may be taken on the carbon products generated by the reactor, such as but not limited to CO. This data may be used to control the inputs to the regeneration reaction to maintain a desired concentration of solvated electrons.Miscellaneous

[0078] In some embodiments, optional catalysts, additional solvents, and other dissolved species may be present to increase solvated electron concentration. In some embodiments, optional catalysts, additional solvents, and other dissolved species may be present to facilitate the formation of particular carbon products.

[0079] Embodiments of this invention also include systems, machines, and controls to accomplish the above method.Equivalents

[0080] The methods, systems, and devices discussed above are examples. Various configurations may omit, substitute, or add various procedures or components as appropriate. For instance, in alternative configurations, the methods may be performed in an order different from that described, and that various steps may be added, omitted, or combined. Also, features described with respect to certain configurations may be combined in various other configurations. Different aspects and elements of the configurations may be combined in a similar manner. Also, technology evolves and, thus, many of the elements are examples and do not limit the scope of the disclosure or claims.

[0081] Embodiments of the present disclosure, for example, are described above with reference to block diagrams and / or operational illustrations of methods, systems, and computer program products according to embodiments of the present disclosure. The functions / acts noted in the blocks may occur out of the order as shown in any flowchart. For example, two blocks shown in succession may in fact be executed substantially concurrent or the blocks may sometimes be executed in the reverse order, depending upon the functionality / acts involved. Additionally, or alternatively, not all of the blocks shown in any flowchart need to be performed and / or executed. For example, if a given flowchart has five blocks containing functions / acts, it may be the case thatonly three of the five blocks are performed and / or executed. In this example, any of the three of the five blocks may be performed and / or executed.

[0082] A statement that a value exceeds (or is more than) a first threshold value is equivalent to a statement that the value meets or exceeds a second threshold value that is slightly greater than the first threshold value, e.g., the second threshold value being one value higher than the first threshold value in the resolution of a relevant system. A statement that a value is less than (or is within) a first threshold value is equivalent to a statement that the value is less than or equal to a second threshold value that is slightly lower than the first threshold value, e.g., the second threshold value being one value lower than the first threshold value in the resolution of the relevant system.

[0083] Specific details are given in the description to provide a thorough understanding of example configurations (including implementations). However, configurations may be practiced without these specific details. For example, well-known circuits, processes, algorithms, structures, and techniques have been shown without unnecessary detail in order to avoid obscuring the configurations. This description provides example configurations only, and does not limit the scope, applicability, or configurations of the claims. Rather, the preceding description of the configurations will provide those skilled in the art with an enabling description for implementing described techniques. Various changes may be made in the function and arrangement of elements without departing from the spirit or scope of the disclosure.

[0084] Having described several example configurations, various modifications, alternative constructions, and equivalents may be used without departing from the spirit of the disclosure. For example, the above elements may be components of a larger system, wherein other rules may take precedence over or otherwise modify the application of various implementations or techniques of the present disclosure. Also, a number of steps may be undertaken before, during, or after the above elements are considered.

Claims

CLAIMSWhat is claimed is:

1. A method to form carbon products from carbon dioxide, the method comprising: flowing carbon dioxide through a solution comprising a metal that dissolves to generate solvated electrons; and regenerating the solvated electrons in the solution, wherein the solvated electrons react with the carbon dioxide to form at least one product comprising carbon.

2. The method of claim 1 wherein the solvated electrons are regenerated while carbon dioxide is flowed through the solution.

3. The method of claim 1 wherein the solvated electrons derive from the application of current to the solution.4 The method of claim 3, wherein current is applied using at least one of an immersed electrode, a plasma electrode, a Tesla coil, an electron beam generator, or an X-ray generator.

5. The method of claim 1 wherein the solvated electrons derive from the dissolution of an electron donor.

6. The method of claim 5 wherein the electron donor is at least one of an alkali metal, an alkaline-earth metal, or a rare-earth metal.

7. The method of claim 5 wherein the electron donor is one or more of sodium or barium.

8. The method of claim 7 wherein the solution containing solvated electrons comprises one or more of sodium dissolved in sodium chloride, sodium dissolved in sodium bromide, sodium dissolved in sodium iodide, barium dissolved in barium chloride, barium dissolved in barium bromide, or barium dissolved in barium iodide.

9. The method of claim 4 wherein the current is applied using a plurality of immersed electrodes and the method further comprises monitoring the voltage between at least two of the electrodes to detect the formation of undesirable side products.

10. The method of claim 1 wherein the at least one product comprising carbon is one or more of carbon monoxide, amorphous carbon, graphite, graphene, diamond, carbon nanotubes, hydrocarbons, or any other allotropes of carbon or carbon and oxygen.

11. The method of claim 1, further comprising forming at least one byproduct comprising oxygen.

12. An apparatus for generating carbon products from carbon dioxide, the apparatus comprising: a reactor for a solution comprising a metal and solvated electrons; a source for the solvated electrons; and a bubbler for flowing carbon dioxide through the solution, wherein the solvated electrons react with the carbon dioxide to form at least one product comprising carbon.

13. The apparatus of claim 12 wherein the source of solvated electrons is operated while carbon dioxide is flowed through the solution.

14. The apparatus of claim 12 wherein the source of solvated electrons is a current source.

15. The apparatus of claim 14, wherein the current source is at least one of an immersed electrode, a plasma electrode, a Tesla coil, an electron beam generator, or an X-ray generator.

16. The apparatus of claim 12 wherein the source of solvated electrons is a dissolved electron donor.

17. The apparatus of claim 16 wherein the electron donor is at least one of an alkali metal, an alkaline-earth metal, or a rare-earth metal.

18. The apparatus of claim 16 wherein the electron donor is one or more of sodium or barium.

19. The method of claim 18 wherein the solution containing solvated electrons comprises one or more of sodium dissolved in sodium chloride, sodium dissolved in sodium bromide, sodium dissolved in sodium iodide, barium dissolved in barium chloride, barium dissolved in barium bromide, or barium dissolved in barium iodide.

20. The apparatus of claim 15 wherein the current source is a plurality of immersed electrodes and the apparatus further comprises a voltmeter configured to measure the voltage between at least two of the electrodes to detect the formation of undesirable side products.

21. The apparatus of claim 12 wherein the at least one product comprising carbon is one or more of carbon monoxide, amorphous carbon, graphite, graphene, diamond, carbon nanotubes, hydrocarbons, or any other allotropes of carbon or carbon and oxygen.

22. The apparatus of claim 12, wherein the solvated electrons react with carbon dioxide to form at least one byproduct comprising oxygen.

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