JP2015533944A - Method for electrochemical reduction of carbon dioxide and high surface area electrode - Google Patents

Abstract

Methods and systems are provided for electrochemically converting carbon dioxide to organic products including formate and formic acid. This method can include steps (A)-(C) (but not limited to). Step (A) can introduce an acidic anolyte into the first compartment of the electrochemical cell. The first compartment can include an anode. Step (B) can introduce a bicarbonate-based catholyte saturated with carbon dioxide into the second compartment of the electrochemical cell. The second compartment can include a high surface area cathode comprising indium and having a void volume between about 30% and 98%. At least a portion of the bicarbonate-based catholyte is recycled. Step (C) may apply a potential between the anode and cathode sufficient to reduce carbon dioxide to at least one of a single carbon based product or a multi-carbon based product. [Selection] Figure 1

Description

  [0001] The present invention relates generally to the field of electrochemical reactions, and more particularly to a method and / or system for electrochemical reduction of carbon dioxide using high surface area electrodes.

  [0002] Combustion of fossil fuels in businesses such as power generation, transportation, and manufacturing produces billions of tons of carbon dioxide per year. Studies from the 1970s have shown that increasing concentrations of carbon dioxide in the atmosphere can cause changes in global weather, ocean pH fluctuations, and other potential damaging effects. It is shown. Countries around the world, including the United States, are looking for ways to reduce carbon dioxide emissions.

  [0003] One mechanism for reducing emissions is to convert carbon dioxide into economically valuable materials such as fuels and industrial chemicals. Converting carbon dioxide with energy from renewable sources reduces carbon dioxide emissions and converts renewable energy into a chemical form that can be stored for subsequent use. Both can be made possible.

[0004] The present invention uses high surface area electrodes and certain electrolyte solutions to incorporate single carbon (C ₁ ) chemicals, such as formic acid, and multi-carbon (C ₂₊ ) based chemicals (ie, in compounds). It relates to the production of chemical substances having two or more carbon atoms. The present invention encompasses methods, systems, and various components thereof.

  [0005] It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not necessarily restrictive of the claimed invention. The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate one aspect of the present invention and, together with the general description, serve to explain the principles of the invention.

  [0006] The numerous advantages of the present invention can be better understood by those skilled in the art by reference to the accompanying drawings.

FIG. 1 is a flow diagram of a preferred electrolyzer system for reducing carbon dioxide according to one aspect of the present invention. FIG. 2 is a flow diagram of a preferred electrochemical acidification system. FIG. 3 is a flow diagram of another preferred system for electrochemical reduction of carbon dioxide. FIG. 4 is a flow diagram of another preferred electrochemical acidification system incorporating a bipolar membrane. FIG. 5 is a flow diagram of another preferred electrochemical cell system incorporating an ion exchange section for reducing carbon dioxide. FIG. 6 is a flow diagram of a nanofiltration system according to one aspect of the present invention. FIG. 7 is a graph showing the cumulative yield of formate over time according to the embodiment described with reference to Example 1 of the present invention. FIG. 8 is a graph showing the cumulative yield of formate over time according to the embodiment described with reference to Example 2 of the present invention. FIG. 9 is a graph showing the cumulative yield of formate over time according to the embodiment described with reference to Example 3 of the present invention. FIG. 10 is a graph showing the cumulative yield of formate over time according to the embodiment described with reference to Example 4 of the present invention. FIG. 11 is a graph showing cumulative formate yield over time according to the embodiment described with reference to Example 9 of the present invention. FIG. 12 is a graph showing formate concentration vs time according to the embodiment described with reference to Example 9 of the present invention. FIG. 13 is a graph showing cumulative formate yield vs time according to the embodiment described with reference to Example 10 of the present invention. FIG. 14 is a graph showing formate concentration vs time according to the embodiment described with reference to Example 10 of the present invention. FIG. 15 is a graph showing operating cell voltage vs time according to an aspect described with reference to Example 11 of the present invention. FIG. 16 is a graph showing catholyte formate concentration vs time according to the embodiment described with reference to Example 11 of the present invention. FIG. 17 is a graph showing formate current efficiency vs time according to an embodiment described with reference to Example 11 of the present invention. FIG. 18 is a graph showing catholyte pH vs. time according to the embodiment described with reference to Example 11 of the present invention. FIG. 19 is a graph showing formate current efficiency vs time according to an embodiment described with reference to Example 12 of the present invention. FIG. 20 is a graph showing catholyte formate concentration vs time according to the embodiment described with reference to Example 12 of the present invention. FIG. 21 is a graph showing catholyte pH vs. time according to the embodiment described with reference to Example 12 of the present invention.

[0007] Reference will now be made in detail to presently preferred embodiments of the invention, examples of which are illustrated in the accompanying drawings.
[0008] According to some aspects of the invention, an electrochemical system is provided for converting carbon dioxide to organic products such as formate and formic acid. The process is facilitated by using a cathode comprising a high surface area three-dimensional material, an acidic anolyte, and a catholyte comprising bicarbonate.

  [0009] Before describing in detail aspects of the present invention, it is to be understood that the several aspects described below do not limit the scope of the claims that follow. It should also be understood that the expressions and terms used herein are for illustrative purposes and should not be considered limiting. The use of terms such as "such as", "including", or "having" and variations thereof herein is generally intended to encompass the items listed thereafter and equivalents thereof as well as further items. Is done. Furthermore, unless otherwise indicated, technical terms may be used according to conventional usage.

  [0010] Referring to FIG. 1, a flow diagram of an electrolytic cell system 100 according to one aspect of the present invention is shown. The electrolyzer system 100 can be used to electrochemically reduce carbon dioxide to an organic product or organic product intermediate. Preferably, the electrolyzer system 100 reduces carbon dioxide to an alkali metal formate such as potassium formate. The electrolyzer system 100 generally includes an electrolyzer 102, an anolyte recirculation loop 104, and a catholyte recirculation loop 106. The electrolyzer system 100 includes carbon dioxide, bicarbonate (preferably potassium bicarbonate, although other bicarbonate based compounds may be substituted for or in addition to potassium bicarbonate as process feed / input. In addition) and an acidic anolyte (preferably sulfuric acid, but other acids may be included instead of or in addition to sulfuric acid). The product of the electrolyzer system 100 is generally an alkali metal formate such as potassium formate and may contain excess catholyte, carbon dioxide, hydrogen, oxygen, and / or other unreacted process input. is there.

  [0011] The electrolytic cell 102 generally includes an anode compartment 108 and a cathode compartment 110, and can further include a cation exchange membrane 112 that separates the anode compartment 108 from the cathode compartment 110. The anode compartment 108 includes an anode 114 suitable for oxidizing water. In a preferred embodiment, anode 114 is a titanium anode with an anode electrocatalyst coating facing cation exchange membrane 112. For example, the anode 114 can include an anode mesh screen 116 that includes a folded expanded titanium screen with an anode electrocatalyst coating. The anode mesh screen 116 can provide a spacing and contact pressure between the anode 114 and the cation exchange membrane 112. The anode 114 can also include one or more current connection terminals (not shown) on the back side of the anode 114.

  The cathode compartment 110 includes a cathode 118 that is generally mounted within the cathode compartment 110. The cathode 118 preferably includes a metal electrode having an active electrocatalyst layer on the front surface of the cathode 118 facing the cation exchange membrane 112 and includes one or more current connection terminals (not shown) on the back surface of the cathode 118. be able to. The cathode 118 preferably includes a high surface area cathode structure 120. A high surface area cathode structure 120 can be mounted between the cation exchange membrane 112 and the cathode 118 to conduct current into the high surface area cathode structure 120. At the interface between the high surface area cathode structure 120 and the cation exchange membrane 112, a thin expanded plastic mesh insulator screen is used to minimize direct contact between the high surface area cathode structure 120 and the cation exchange membrane 112. An insulator screen (not shown) can be included.

[0013] The anode compartment 108 includes an anode feed stream 122 that generally contains a dilute acid anolyte solution. An anode feed stream 122 may be introduced into the bottom of the anode compartment 108 and flow through the anode mesh screen 116 along the face of the anode 114. Reactions within the anode compartment 108 can include deriving oxygen (O ₂ , ie gaseous oxygen) and hydrogen ions (H ⁺ ) or protons from the oxidation of water at an applied current and potential. Hydrogen ions or protons can generally be used for reactions in the cathode compartment 110 through the cation exchange membrane 112. Gaseous oxygen and other liquids discharged from the anode compartment 108 of the electrolytic cell 102 are discharged as an anode discharge stream 124. The anode exhaust stream 124 can be monitored by a temperature sensor 126a and can flow to an anolyte dissociator 128 suitable for separating oxygen from the anode exhaust stream 124. The anolyte dissociator 128 can process the anode discharge stream 124 into an oxygen stream 130, an anolyte recycle stream 132, and an anolyte overflow stream 134. The oxygen stream 130 can be exhausted from the anolyte dissociator 128. The anolyte stream 132 can be mixed with water (preferably deionized water) from the water source 136 and acid (preferably sulfuric acid) from the acid source 138. The anolyte acid concentration and volume for the anode feed stream 122 may be maintained by a water source 136 and an acid source 138 in the anolyte recirculation loop 104. The temperature of the anode feed stream 122 can be adjusted by a heat exchanger 140a connected to a cooling water supply 142a before being introduced into the anode compartment 108 of the electrolytic cell 102.

[0014] The cathode compartment 110 includes a cathode feed stream 144 that generally includes carbon dioxide and a catholyte. In a preferred embodiment, the catholyte is a bicarbonate compound such as potassium bicarbonate (KHCO ₃ ) saturated with carbon dioxide. Cathode feed stream 144 can be introduced into the bottom of cathode compartment 110 and flow through high surface area cathode structure 120 along the face of cathode 118. The reaction in the cathode compartment 110 can reduce carbon dioxide to formate at an applied current and potential. The reaction product and any unreacted material (eg, excess catholyte solution) can be discharged from the cathode compartment 110 as a cathode discharge stream 146. Cathode discharge stream 146 can be monitored by pH sensor 148a and temperature sensor 126b and can flow to catholyte dissociator 150, which is suitable for separating gaseous components (eg, hydrogen) from cathode discharge stream 146. Catholyte dissociator 150 can process cathode discharge stream 146 into hydrogen stream 152, product stream 154, and catholyte recycle stream 156. The hydrogen stream 152 can be exhausted from the catholyte dissociator 150. Product stream 154 preferably includes an alkali metal formate (eg, potassium formate if the electrolyte includes potassium bicarbonate) and may include excess catholyte. The catholyte stream 156 can be processed by the catholyte recirculation pump 158 and the heat exchanger 140b connected to the cooling water supply 142b. The temperature sensor 126c can monitor the catholyte stream 156 downstream of the heat exchanger 140b having the cooling water supply 142b. A new catholyte electrolyte feed stream 160 can be metered into the catholyte stream 156, where the new catholyte electrolyte feed stream 160 causes the catholyte feed stream 144 into the cathode compartment 110 of the electrolytic cell 102. The pH of the product can be adjusted, thereby controlling the final product overflow rate and determining the formate product concentration. The pH can be monitored by a pH sensor 148b. A carbon dioxide stream 162 can be metered into the cathode feed stream 144 downstream of the catholyte electrolyte feed stream 160 prior to introduction into the cathode compartment 110 of the electrolyzer 102. Preferably, the catholyte introduced into the cathode compartment is saturated with carbon dioxide.

[0015] When acidic anolyte is used (when protons are sent through the membrane into the cathode compartment), alkali metal bicarbonate and / or carbonate is used in combination with water to control the pH of the catholyte. Thus, the pH of the electrolytic cell 102 can be controlled or maintained. By controlling the catholyte pH to an optimal value, the cell produces C ₁ and C ₂ at a higher conversion than if a non-optimal pH value was maintained or if no pH control mechanism was used. Can be converted efficiently by the product. In a preferred process, the catholyte is continually recirculated to maintain a moderate and uniform carbon dioxide concentration at the cathode surface that is coated with the electrocatalyst. A new catholyte feed stream can be used to control the pH of the catholyte and to control the product concentration in the product overflow stream. The mass flow rate of the catholyte feed stream to the cathode compartment (eg, the mass flow rate of potassium bicarbonate) is preferably from the introduction of protons into the catholyte and the inefficient byproduct reaction of water separated at the cathode. Balance with the formation of hydroxide. The concentration of potassium bicarbonate is important because it gives volume to the catholyte and dilutes the product in the catholyte.

  [0016] For pH control of the catholyte, potassium bicarbonate in the concentration range of 5 to 600 g / L, or more preferably in the range of 10 to 500 g / L is preferred. If the bicarbonate feed stream concentration to the catholyte is fixed, a separate feed stream of water into the catholyte can be used to control the final product concentration. In other embodiments, potassium carbonate can be used as the feed stream for pH control. Potassium carbonate has a much higher solubility in water than potassium bicarbonate and is preferably used in a concentration range of 5-1,500 g / L.

  [0017] Referring to FIG. 2, a block diagram of an electrochemical acidification system 200 according to one aspect of the present invention is shown. Electrochemical acidification system 200 can be used to acidify product stream 154 from electrolyzer system 100. Preferably, the electrochemical acidification system 200 acidifies an alkali metal formate such as potassium formate to form an organic acid such as formic acid and co-generates an alkali metal hydroxide such as potassium hydroxide. Let Electrochemical acidification system 200 generally includes an electrochemical acidification unit 202, an anolyte recirculation loop 204, and a catholyte recirculation loop 206. Electrochemical acidification system 200 includes, as process feed / input, product stream 154 (preferably containing alkali metal formate) from electrolyzer system 100, anolyte recycle loop 204 and catholyte recycle loop. Water in each of 206 and an acidic anolyte (preferably sulfuric acid, but other acids can be included instead of or in addition to sulfuric acid) can be included. The products of electrochemical acidification system 200 are generally organic acids such as formic acid, and alkali metal hydroxides, residual alkali metal formate, bicarbonate catholyte, carbon dioxide, hydrogen, oxygen, and / or Or other unreacted process inputs.

[0018] The electrochemical acidification unit 202 is preferably a three-compartment electrochemical acidification unit or cell. The electrochemical acidification unit 202 includes an anode compartment 208, a cathode compartment 210, and a central ion exchange compartment 212 that is partitioned on each side by cation exchange membranes 214a and 214b. The anode compartment 208 includes an anode 216 suitable for oxidizing water. In a preferred embodiment, anode 216 is a titanium anode with an anode electrocatalyst coating facing cation exchange membrane 214a. Cathode compartment 210 includes a cathode 218 suitable for reducing water and producing alkali metal hydroxide. In a preferred embodiment, when a potential and current are applied to the electrochemical acidification unit 202, hydrogen ions (H ⁺ ) or protons are generated in the anode compartment 208. Hydrogen ions (H ⁺ ) or protons flow through the cation exchange membrane 214a into the central ion exchange compartment 212. The product stream 154 from the electrolyzer system 100 is preferably introduced into the electrochemical acidification unit 202 through the central ion exchange section 212 and the alkali metal ions (H ⁺ ) or protons in the product stream 154 (by protons). For example, potassium ions are replaced and the stream is acidified to produce a product stream 260 comprising an organic acid product, preferably formic acid. The substituted alkali metal ions are sent to the cathode compartment 210 through the cation exchange membrane 214b and combined with hydroxide ions (OH ⁻ ) formed by the reduction of water at the cathode 218 to form an alkali metal hydroxide, preferably Potassium hydroxide can be formed.

  [0019] The central ion exchange compartment 212 may include a plastic mesh spacer (not shown) that maintains volumetric space in the central ion exchange compartment 212 between the cation exchange membranes 214a and 214b. In one embodiment, cation ion exchange material 220 is included in a central ion exchange compartment 212 between cation exchange membranes 214a and 214b. Examples of the cation ion exchange material 220 include ion exchange resins in the form of beads, fibers and the like. The cation ion exchange material 220 can increase electrolyte conductivity in the ion exchange compartment solution, and the potential effect of carbon dioxide gas on cell voltage as bubbles are formed and pass through the central ion exchange compartment 212. Can be reduced.

  [0020] The anode compartment 208 includes an anode feed stream 222 that generally contains an acid anolyte solution (preferably a sulfuric acid solution). Gaseous oxygen and other liquids discharged from the anode compartment 208 of the electrochemical acidification unit 202 are discharged as an anode discharge stream 224. The anode exhaust stream 224 can be monitored by a temperature sensor 226a and can flow to an anolyte dissociator 228 suitable for separating oxygen from the anode exhaust stream 224. The anolyte dissociator 228 can process the anode discharge stream 224 into an oxygen stream 230, an anolyte recycle stream 232, and an anolyte overflow stream 234. The oxygen stream 230 can be exhausted from the anolyte dissociator 228. The anolyte stream 232 can be mixed with water (preferably deionized water) from the water source 236 and acid (preferably sulfuric acid) from the acid source 238. The anolyte acid concentration and volume for the anode feed stream 222 can be maintained by the water source 236 and the acid source 238 in the anolyte recirculation loop 204. The temperature of the anode feed stream 222 can be adjusted by a heat exchanger 240a connected to the cooling water source 242a prior to introduction into the anode compartment 208 of the electrochemical acidification unit 202.

  [0021] Cathode compartment 210 generally includes a catholyte feed stream 244 that includes water and may include an alkali metal hydroxide that circulates through catholyte recycle loop 206. Reaction products that may include alkali metal hydroxide and hydrogen gas may be discharged from cathode compartment 210 as cathode discharge stream 246. Cathode discharge stream 246 can be monitored by temperature sensor 226b and can be passed to a catholyte dissociator 248 suitable for separating gaseous components (eg, hydrogen) from cathode discharge stream 246. Catholyte dissociator 248 may process cathode discharge stream 246 into hydrogen stream 250, catholyte stream 252 and catholyte overflow stream 254 (which may include KOH). The hydrogen stream 250 can be exhausted from the catholyte dissociator 248. Catholyte stream 252 preferably includes an alkali metal hydroxide (eg, potassium hydroxide if product stream 154 includes potassium formate). The catholyte stream 252 can be processed by a catholyte recirculation pump 256 and a heat exchanger 240b connected to a cooling water supply 242b. A temperature sensor 226c can monitor the catholyte stream 252 downstream of the heat exchanger 240b. The catholyte stream 252 can be mixed with water (preferably deionized water) from a water source 258, where water is metered into the catholyte feed stream 244 introduced into the cathode compartment 210. The concentration of the alkali metal hydroxide can be controlled.

  [0022] Referring now to FIG. 3, a flow diagram of a preferred system 300 for electrochemical reduction of carbon dioxide to an organic acid product is shown. System 300 can include an electrolyzer system 100 (described with reference to FIG. 1) and an electrochemical acidification system 200 (described with reference to FIG. 2), preferably potassium hydroxide and A potassium hydroxide recycle loop 302 suitable for producing potassium bicarbonate from carbon dioxide is included. The system 300 can also include a carbon dioxide treatment device (eg, gas separation units 304a, 304b, 304c, 304d) for separating and recovering carbon dioxide from the process stream.

  [0023] The system 300 generally includes carbon dioxide, alkali metal hydroxide (preferably potassium hydroxide), acid (preferably sulfuric acid), and water (preferably deionized water) as process input materials, Process outputs include organic acids (preferably formic acid), oxygen gas, and hydrogen gas. The organic acid can be further processed to give the desired form and concentration. Such treatment may include evaporation, distillation, or other suitable physical separation / concentration process.

[0024] The chemical reaction of carbon dioxide reduction in the system 300 may be as follows.
[0025] As shown in equation (1), hydrogen atoms are adsorbed to the electrode from the reduction of water.

H ⁺ + e ⁻ → H _ad (1)
[0026] As shown in equation (2), carbon dioxide is reduced by adsorbed hydrogen atoms on the cathode surface to form formate, which is adsorbed on the surface.

CO ₂ + H _ad → HCOO _ad (2)
[0027] Next, as shown in equation (3), the formate salt adsorbed on the surface is reacted with other adsorbed hydrogen atoms to form formic acid, which is then released into solution.

HCOO _ad + H _ad → HCOOH (3)
[0028] As shown in equation (4), the competitive reaction at the cathode is the reduction of water, forming hydrogen gas as well as hydroxide ions.

2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ (4)
[0029] As shown in equation (5), the anodic reaction is the oxidation of water to oxygen and hydrogen ions.

2H ₂ O → 4H ⁺ + 4e ⁻ + O ₂ (5)
[0030] High surface area cathode:
[0031] As described with reference to FIG. 1, the cathode 118 preferably includes a high surface area cathode structure 120. High surface area cathode structure 120 preferably has a void volume in the range of 30% to 98%. The specific surface area of the high surface area cathode structure 120 is preferably 2 cm ² / cm ^{3 to} 500 cm ² / cm ³ or more. The surface area can also be defined as the total area compared to the current distributor / conductor backplate, the preferred range being 2 to 1000 times or more.

  [0032] The cathode 118 preferably comprises copper wire mesh, copper screen, copper fiber, and bronze coated with electroless indium on tin (Sn), others are copper-tin alloy, nickel, and stainless steel. It is. The metal can be pre-coated with other metals, such as to properly form a suitable substrate for applying indium and other preferred cathode coatings. The cathode may also include indium-Cu intermetallic compounds formed on the surface of copper fibers, wire mesh, copper foam, or copper screens. Intermetallic compounds are generally harder than soft indium metal and can provide desirable mechanical properties in addition to the usable catalytic properties. The cathode can also include coatings and / or metal structures including but not limited to Pb, Sn, Hg, Tl, In, Bi, and Cd, alloys thereof, and combinations thereof. . Among many, metals such as Ti, Nb, Cr, Mo, Ag, Cd, Hg, Tl, An, and Pb, and Cr—Ni—Mo alloy steel can be included. The cathode 118 can include a single layer or multilayer electrode coating so that the electrocatalyst coating on the cathode substrate includes one or more layers of metals and alloys. Preferred electrocatalytic coatings on the cathode include a tin coating on a high surface area copper substrate with a top layer / coating of indium. The coverage of the indium coating is preferably in the range of 5% to 100% as indium.

  [0033] When using an indium alloy on the exposed catalyst surface of the electrode, the composition of indium is preferably an alloy with other metals such as Sn, Pb, Hg, Tl, Bi, Cu, and Cd, And in the range of 5% to 99% as indium in these mixed alloys and combinations thereof. It is also contemplated that Au, Ag, Zn, and Pd are included in the coating in proportions ranging from 1% to 95%.

  [0034] Furthermore, metal oxides can be used or formed as electrocatalysts on the surface of the base cathode structure. For example, lead oxide can be formed as an electrode catalyst on the surface of the base cathode structure. Metal oxide coatings can be formed by thermal oxidation or electrodeposition followed by chemical or thermal oxidation.

  [0035] In addition, the cathode base structure may also be stepped or stepped to change the cathode density in the vertical or horizontal direction with respect to density, void volume, or specific surface area (eg, change fiber dimensions). Can do. The cathode structure can also be composed of two or more different electrocatalyst compositions that are mixed or arranged in other regions of the cathode structure within the catholyte compartment.

  [0036] During normal operation of the electrolyzer 102, system performance degradation with respect to formate yield (this is due to loss of catalyst or impurities such as other metals that may be plated on the cathode 118). May result from overcoating of the catalyst). During operation of the electrolytic cell 102, the surface of the cathode 118 can be restored by periodically adding an indium salt or a mixture of indium / tin salts in situ. Depending on the composition of the cathode 118, other metal salts or further metal salts such as Ag, Au, Mo, Cd, Sn, and other suitable metal salts may be added in situ or alone. It is intended to be possible. The electrolyzer 102 can be operated at a full rate during operation, or can be operated temporarily at a lower current density with or without the addition of carbon dioxide during metal salt injection. The conditions for restoring the cathode surface by the addition of these salts may vary depending on the desired restoration result. It is also possible to potentially restore the cathode surface using short-time current reversal at any time during operation of the electrochemical cell.

  [0037] In certain embodiments, the electrolyzer 102 operates at a pressure above atmospheric pressure, thereby providing a higher current efficiency than when operating the electrolyzer 102 at or below atmospheric pressure. In addition, the electrolytic cell 102 can be operated at a high current density.

  [0038] In the production of a cathode material to produce an organic compound, reduction may be performed on the surface of the cathode structure, such as the addition of Ag, Au, Mo, Cd, Sn, and other suitable metals. Addition of possible metal salts can also be used. The addition of such metal salts can provide a catalyst surface that can be difficult to produce directly during cathode production, or can restore the catalyst surface.

[0039] A preferred method for manufacturing the high surface area cathode structure 120 is to use an electroless plating solution, which includes an indium salt, at least one complexing agent, a reducing agent, a pH adjusting agent, and A surfactant can be included. A preferred procedure for forming an electroless indium coating on a high surface area cathode includes the following materials in stirred deionized water: trisodium citrate dihydrate (100 g / L), EDTA-disodium salt (15 g / L), mixing sodium acetate (10 g / L), InCl ₃ (anhydrous, 10 g / L), and thiodiglycolic acid (0.3 g / L, eg 3 mL of a 100 mg / mL solution) Can be made. It is also possible to use a premixed storage precipitation solution stirred (preferably several hours, eg overnight). This procedure also includes heating the mixture to about 40 ° C. This procedure also added 40 mL of TiCl ₃ (20% by weight in 2% HCl) (0.05 mM) per liter and 7M ammonia in methanol until the pH of the mixture was about 7 (about 1 liter per liter). 15 mL of ammonia solution), including adjusting the pH to between about 9.0 and 9.2 using ammonium hydroxide (28% ammonia solution) at this point. This procedure then involves heating the mixture to about 60 ° C. When the pH drops, adjust the pH to about 9.0 using ammonium hydroxide solution. This procedure then involves heating the mixture to about 75 ° C., and precipitation can begin at about 65 ° C. This procedure involves holding the mixture at 75 ° C. for about 1 hour.

  [0040] A preferred procedure for metallizing a copper substrate is to rinse the exposed copper substrate with acetone to clean the copper surface (eg, residual oil that may be present on the copper surface). Or removing the grease) and then rinsing the acetone treated copper substrate in deionized water. This procedure also includes immersing the exposed copper substrate in a 10% sulfuric acid bath for about 5 minutes and then rinsing with deionized water. This procedure also includes depositing about 25 μm of tin on the copper surface. Deposition can be performed for 15 minutes using a commercial electroless tin plating bath (Caswell, Inc.) operating at 60 ° C. After depositing tin, rinse the parts thoroughly in deionized water. This procedure also includes depositing about 1 μm of indium on the tin-plated copper surface. Deposition can be performed for 60 minutes using an electroless bath operating at 90 ° C. After depositing indium, rinse the parts thoroughly in deionized water. This procedure can also include treating the copper / tin / indium electrode in a 5 wt% nitric acid bath for 5 minutes. Such a treatment can improve the stability of the electrode compared to an untreated copper / tin / indium electrode. In other embodiments, an electroless tin-plated copper substrate can be immersed in molten indium for coating.

[0041] In certain embodiments, the cathode substrate can be treated with a catalyst material for carbon dioxide reduction. Four examples of processing are shown below.
[0042] The first treatment may include coating a conductive substrate (eg, glassy carbon or metal) in a conductive sol-gel that includes sufficient catalytic material to provide a highly active surface area. it can. The conductive component of the sol-gel may be catalytically active. After the substrate is coated with the catalytic sol gel, the sol gel is subjected to a high degree of polymerization / crosslinking. The mixed substrate / sol-gel structure can then be pyrolyzed at elevated temperatures to convert the organic material to amorphous (and potentially conductive) carbon. The pyrolyzed structure can also be subjected to a chemical treatment that selectively removes organic material or silica phase to provide a coating with a high catalyst content.

  [0043] The second treatment involves binding relatively small particles (eg, on the micron or nanometer scale) to the substrate using a binder such as an amine, thiol, or other suitable binder. Can be included. The binder is preferably electrically conductive and conducts current between the substrate and the catalyst particles. The catalyst particles preferably comprise conjugated organic molecules such as diphenylbenzene. If the substrate is also formed of a catalyst material, the binder may have a symmetric linking group, otherwise a binder having two different linking groups can be used.

  [0044] The third treatment can include coating the substrate in a slurry comprising a catalyst material (which can be in salt form) and a binder. The slurry can also include conductive additives such as carbon black, carbon nanotubes, or other suitable conductive additives. The slurry coating can then be dried to form a conformal coating on the substrate. The substrate and the dried slurry coating can be heated to fuse the various constituent materials into a mechanically strong and conductive catalyst material. In certain embodiments, heating of the substrate and the dried slurry coating is performed in a reducing atmosphere.

[0045] For the fourth treatment, the substrate is semiconducted by applying the precursor to the substrate, removing the solvent, and firing the substrate to convert the precursor material into an integral semiconductor metal chalcogenide coating. Coating with a metal chalcogenide can be included. Coating materials include Na ₄ SnS ₄ , Na ₄ Sn ₂ S ₆ , K ₄ SnTe ₄ , Na ₃ AsS ₃ , (NH ₄ ) ₄ Sn ₂ S ₆ , (NH ₄ ) ₃ AsS ₃ , and (NH ₄ ) ₂ MoS ₄ (but not limited to) can be included.

  [0046] Other coating and electrocatalyst manufacturing techniques include applying a thermal oxide on a substrate, forming an intermetallic compound with the substrate, and applying a semiconductor material on the substrate. In one aspect, thermal oxidation of various metals and various metal salts applied on ceramic substrates is preferred to form high surface area materials suitable for electrochemical reduction of carbon dioxide. Thermal oxidation may be similar to that used to form an electrocatalyst on titanium for use as an anode material in an electrochemical chlorine cell, such as iridium oxide and ruthenium oxide. In another embodiment, iridium is electroplated onto the copper foil, and then the copper foil is heated to a temperature 40 ° C. above the melting point of indium until the indium melts on the foil surface, and the gold metal with copper An intermetallic compound is formed and then cooled. Formation of the intermetallic compound can be performed in air or in an inert gas (for example, argon or helium) atmosphere, or in full or partial vacuum. Preferably, the electroplated material provides about 50% Faraday conversion efficiency and can be used as a coating on planar metal backplates and even on copper fibers. Intermetallic compounds can also be formed using tin-plated copper substrates. In further embodiments, the semiconductor material can be applied to the substrate by gas deposition, sputtering, or other suitable application. The substrate is preferably a metal substrate. The semiconductor material can be doped P-type or N-type as desired.

  [0047] In the four types of processing and other coating techniques described above, several measures may be taken to improve the quality of the bond between the substrate and the catalyst (mechanical, electrical, etc.). it can. Such means may generate functional groups on the substrate surface that can cause chemical bonding with the catalyst or binder, or create geometric features on the substrate surface that facilitate bonding with the applied catalyst coating. Can be included.

[0048] Substrates for the high surface area cathodes described herein include RVC materials such as carbon and graphite, metal foam, wire mesh, metal wool formed from fibers, sintered powder metal films and plates, Metal and ceramic beads, pellets, ceramic and metal columns and trickle bed packing materials, metal and inorganic powder shapes, metal fibers and wool, or other suitable substrate materials can be included. The specific surface area of the physical form preferably includes a specific surface area of between about ^{2 and} 2,000 cm ² / cm ³ or more.

  [0049] The electrode or high surface area structure of the electrode can include the alloy as fibers or wool, and can be coated with various compounds, followed by calcination in an oven in air or in a reducing atmosphere. Thus, a stable oxide on the surface that becomes an electrode catalyst in the reduction of carbon dioxide can be formed. Other cathode materials can include metallic glass and amorphous metal.

[0050] Referring now to FIG. 4, a particular embodiment of the acid acidification system 200 of FIG. 2 using a bipolar membrane in an electrochemical acidification unit 402 is shown. In addition to recovering potassium hydroxide, alkali metal formate (eg, potassium formate) can be acidified by using a bipolar membrane in electrochemical acidification unit 402. By using a bipolar membrane, the voltage required to acidify the alkali metal formate can be reduced, and the actual number of anodes and cathodes required for the electrochemical stack can be reduced. The bipolar membrane is preferably composed of a bonded cation membrane and anion membrane, dissociates water at the interface of the two membranes, hydrogen (H ⁺ ) ions from the cation membrane, and hydroxide ions (OH ⁻ ) from the anion membrane. It works by forming.

[0051] Referring now to FIG. 5, another embodiment of the electrochemical system 100 of FIG. 1 is shown. The electrolyzer 502 in FIG. 5 includes an ion exchange compartment 504 in addition to the anode compartment 506 and the cathode compartment 508. This ion exchange compartment 504 functions in the same manner as the acid acidification compartment 212 in the electrochemical acidification unit 202 shown in FIG. The alkali metal formate product (eg, potassium formate) from the cathode compartment and unreacted KHCO ₃ are sent through the ion exchange compartment 504 to provide the formic acid product with CO ₂ and some residual KHCO ₃ . Hydrogen ions (H ⁺ ) passing through the adjacent membrane 510a on the sides of the anode compartment replace alkali metal ions (eg, K ⁺ ) in the stream passing through the central ion exchange compartment 504, resulting in alkali metal The formate acidifies and alkali metal ions and residual hydrogen ions flow into the catholyte through the membrane 510b adjacent on the cathode compartment 508. This allows the cathode to be operated at higher pH conditions when high Faraday current efficiency is required for the cathode selected for the process.

  [0052] In indium-based cathodic systems, preferred catholytes include alkali metal bicarbonates, carbonates, sulfates, phosphates, and the like. Other preferred catholytes include borates, ammonium, and hydroxides. Other catholytes can include chlorides, bromides, and other organic and inorganic salts. Non-aqueous electrolytes such as propylene carbonate, methanesulfonic acid, methanol, and other ionic conducting liquids can be used, which can be aqueous mixtures or non-aqueous mixtures in the catholyte. By introducing carbon dioxide microbubbles into the catholyte stream, the movement of carbon dioxide to the cathode surface can be improved.

[0053] Referring now to FIG. 6, a nanofiltration system can be used between the electrolyzer system 100 shown in FIG. 1 and the electrochemical acidification system 200 shown in FIG. The nanofiltration system preferably separates the alkali metal formate (eg, potassium formate) from the bicarbonate (eg, stream 154) discharged from the electrolyzer system 100 and is introduced into the electrochemical acidification unit 202. Used to reduce the amount of carbonate. The nanofiltration system preferably uses a nanofiltration filter / membrane under pressure to selectively separate bicarbonate from alkali metal formate. The nanofiltration filter / membrane separates the monovalent anion (eg, formate) from the divalent anion (eg, carbonate) using a high pressure pump and a selected membrane suitable for separation. When using a nanofiltration system as a separation means between the electrolyzer system 100 and the electrochemical acidification system 200, formic acid is used to efficiently separate formate from carbonate using a nanofiltration filter / membrane. The bicarbonate in the salt / bicarbonate product (eg stream 154) is preferably converted to carbonate. The nanofiltration system can include a mixer, such as a mixing tank, to mix the formate / bicarbonate product stream with a potassium hydroxide (KOH) stream. The mixer can facilitate the conversion of potassium bicarbonate to potassium carbonate to facilitate separation of the formate from the carbonate. The potassium formate / carbonate stream is then routed by a high pressure pump into a nanofiltration unit comprising a nanofiltration filter / membrane. The nanofiltration unit produces a low carbonate-containing potassium formate permeate stream that is then sent to the electrochemical acidification system 200 and introduced into the electrochemical acidification unit 202 as shown as stream 154 in FIG. . The impervious stream comprising potassium carbonate discharged from the nanofiltration unit is preferably sent to the KHCO ₃ block of FIG. 3 where it is mixed with KOH and CO ₂ to convert the potassium carbonate to potassium bicarbonate. Potassium bicarbonate is preferably used as a feed stream to the cathode compartment of the electrolyzer 102 of the electrolyzer system 100. The nanofiltration separation system can be composed of multiple units connected in series flow form to increase the total separation efficiency of carbonate from formate separation. The system also uses recirculation flow to recirculate the outlet flow from one unit to the inlet of the other unit to maintain flow rate and pressure and increase formate recovery. it can.

  [0054] Depending on the chemistry of the electrochemical system described herein, the pH of the catholyte is preferably in the range of 3-12. The desired pH of the catholyte may be a function of the catholyte operating conditions and the catalyst used in the cathode compartment with limited or no corrosion in the electrochemical cell.

[0055] Preferred catholyte cross-sectional area flow rates may include a range of ^{2 to} 3000 gpm / ft ² or more (0.0076 to 11.36 m ³ / m ² ), with a flow rate range of 0. 002 to 20 feet / second (0.0006 to 6.1 m / second).

  [0056] Preferably, a homogeneous heterocyclic catalyst is used in the catholyte. Examples of the homogeneous heterocyclic catalyst include 4-hydroxypyridine, adenine, sulfur-containing heterocyclic amine, oxygen-containing heterocyclic amine, azoles, benzimidazoles, bipyridines, furan, imidazoles, at least 1 Imidazoles related species having two 5-membered rings, indoles, lutidines, methylimidazole, oxazoles, phenanthroline, pterin, pteridine, pyridines, pyridines related species having at least one 6-membered ring, pyrrole, quinoline, or Mention may be made of one or more of thiazoles and mixtures thereof.

  [0057] Preferred anolytes for this system are alkali metal hydroxides such as KOH, NaOH, LiOH; ammonium hydroxide; inorganic acids such as sulfuric acid, phosphoric acid, etc .; organic acids such as methanesulfonic acid. Non-aqueous and aqueous solutions; chloride, bromide, and iodine type alkali halide salts such as NaCl, NaBr, LiBr, and NaI; and halide acids such as HCl, HBr, and HI; Halide acids and alkali halide salts produce, for example, chlorine, bromine, or iodine as a halide gas or dissolved aqueous product from the anolyte compartment. Methanol or other hydrocarbon non-aqueous liquids can also be used, which form some oxidized organic products from the anolyte. The choice of anolyte is dictated by the process chemistry products and the requirements for lowering the total operating cell voltage. For example, when bromine is formed at the anode, a much lower anode potential is required than with chlorine, and iodine is even lower than bromine. This allows for significant power cost savings in the operation of both electrochemical units when bromine is produced in the anolyte. The formation of a halogen such as bromine in the anolyte is then used in an external reaction such as a reaction with an alkane forming bromoethane to produce another compound, which is then an alcohol such as ethanol. Or a halogen acid byproduct from the reaction can be recycled back to the electrochemical cell anolyte.

[0058] Manipulating the electrolyzer catholyte at higher operating pressures can allow more carbon dioxide to be dissolved in the aqueous electrolyte than at lower pressures (eg, atmospheric pressure). Electrochemical cells can be operated at pressures up to about 20-30 psig in multi-cell laminate designs, but can be operated at pressures up to 100 psig with modification. The electrolyzer anolyte can also be operated in the same pressure range to minimize the pressure differential over the membrane separating the two electrode compartments. In order to operate the electrochemical unit at higher operating pressures up to about 60-100 atmospheres or more, which is the liquid CO ₂ and supercritical CO ₂ operating range, special electrochemical designs are required.

[0059] In certain embodiments, a portion of the catholyte recycle stream, while injecting the CO _2, pressurized separately with or pump using flow restriction by back pressure, then the pressurized fluid It can be injected into the catholyte compartment of the electrolytic cell. With such a configuration, the conversion rate can be improved by increasing the amount of dissolved CO _{2 in} the aqueous solution.

[0060] The operating temperature of the catholyte and anolyte is preferably in the range of -10 to 95 ° C, more preferably 5 to 60 ° C. The minimum operating temperature is limited to the electrolytes used and their freezing points. In general, the lower the temperature, the higher the solubility of CO ₂ in the aqueous solution phase of the electrolyte, which is useful for obtaining higher conversion and current efficiency. Considerations for lower operating temperatures may result in higher cell voltages in the operating cell, which may need to be optimized to produce chemicals at the lowest operating cost Is that there is.

  [0061] Electrochemical cell designs can include zero-gap inflow designs using recirculating catholyte electrolytes with various high surface area cathode materials. Other designs include full cocurrent packed bed and trickle bed designs using various high surface area cathode materials, bipolar stacked cell designs, and high pressure cell designs.

  [0062] The anode used in an electrochemical system may depend on various system conditions. For acidic anolytes, to oxidize water to produce oxygen and hydrogen ions, the anode can include a coating, and preferred electrocatalyst coatings include noble metal oxides such as ruthenium and iridium oxides, and Including platinum, rhodium, and gold as metals and oxides deposited on valve metal substrates such as titanium, tantalum, zirconium, and niobium, and combinations thereof. For other anolytes, such as alkaline or hydroxide electrolytes, the anode produced can be stable as a suitable anode under alkaline conditions, carbon, cobalt oxide, stainless steel, nickel, and These alloys and combinations are included.

  [0063] As described herein, in an electrochemical system, a membrane disposed between the anode and cathode compartments can be used. Cation ion exchange type membranes, especially those with high blocking efficiency against anions such as DuPont Nafion® brand non-reinforced N117 and N120 series, more preferred PTFE fiber reinforced N324 and N424 types, and Flemion ( Preferred are perfluorinated sulfonic acid based ion exchange membranes such as similar related membranes manufactured by Japanese companies under the trade name of the supplier such as. Other multilayer perfluorinated ion exchange membranes used in the chlor-alkali industry have a bilayer structure of sulfonic acid based membrane layers bonded to a carboxylic acid based membrane layer, which is about 2 or more. It operates efficiently using anolyte and catholyte at a pH higher than pH. These membranes have much higher anion blocking efficiency. These are sold by DuPont under the N900 series, such as N90209, N966, N982, and the 2000 series, such as N2010, N2020, and N2030, and their Nafion registered trademarks such as all of these multiple types and subtypes. Has been. Also, if anion blocking is not important, among those available on the market, Ionac® under the trade name by Sybron, and under the Selemion® name by AGC Engineering (Asahi Glass), And hydrocarbon-based membranes made from a variety of cation ion exchange materials, such as those sold by Tokuyama Soda.

[0064] Examples of electrolytic cell designs:
[0065] The electrolyzer design used in the experimental examples can include various thicknesses of high surface area cathode structures using additional spacer frames, and physical for electrical contact to the cathode current conductor backplate. Contact pressure can also be applied.

[0066] For most of the bench scale test examples, a bench scale electrochemical cell having an electrode projected area of about 108 cm ² was used. An electrochemical cell composed of two electrode compartments machined from 1.0 inch (2.54 cm) thick raw polypropylene was assembled. The dimensions of the anode and cathode compartments are 8 inches (20.32 cm) × 5 inches (12.70 cm), 0.375 inches (0.9525 cm) deep, 3.0 inches (7.62 cm) wide × The inside of the 6-inch (15.24 cm) height had a machined recess, and the sealing area of the flat gasket was 1.0 inch (2.52 cm) wide. Two holes are drilled at equal intervals in the recessed area to receive two electrode conductor terminals penetrating the section thickness, giving two 0.25 inch (0.635 cm) drilling screw holes, and 0 A plastic part that passes through and seals around a 25 inch (0.635 cm) conductor terminal was received to prevent liquid from leaking out of the electrode compartment. Perforate the electrode frame to give top and bottom flow distribution holes, give 0.25 inch pipe screw holes, give plastic parts attached to the outside of the cell frame at the top and bottom of the cell, in and out of the cell frame The surface of the flat electrode was created by providing outflow and drilling twelve 0.125 inch (0.3175 cm) holes into the upper and lower flow distribution holes at a 45 ° bevel at the end of the recessed area. And the same amount of flow distribution through the thickness of the high surface area electrode of the compartment was given.

  [0067] For the anode compartment cell frame, a thickness of 0.060 inches (0.1524 cm) with two titanium conductor terminals 0.25 inches (0.635 cm) in diameter welded on the back surface; An anode having a width of 875 inches (7.303025 cm) and a length of 5.875 inches (14.9225 cm) was inserted into two holes drilled in the recessed area of the electrode compartment. The position depth of the anode in the recess depth was adjusted by adding a plastic spacer behind the anode, and the end of the anode relative to the recess in the cell frame was sealed using medical grade epoxy. The electrocatalytic coating on the anode is Water Star WS-32, an iridium oxide based coating on a 0.060 inch (0.1524 cm) thick titanium substrate suitable for generating oxygen in acid. there were. Further, in the anode compartment, a 0.010 inch (0.0254 cm) thick titanium expanded metal material (EC626) from DeNora North America with an iridium oxide based oxygen generating coating disposed between the anode and the membrane. An anode folding screen (3-fold folding) is also used to provide a zero-gap anode configuration (with the anode in contact with the membrane), and also has pressure on the membrane from the anode side (also contact pressure from the cathode side) ) Was given.

  [0068] For the cathode compartment cell frame, with a thickness of 0.080 inches (0.2032 cm), with two 316L-SS conductor terminals of 0.25 inches (0.635 cm) in diameter welded on the backside, and A 316L stainless steel cathode having a width of 2.875 inches (7.303025 cm) and a length of 5.875 inches (14.9225 cm) was inserted into two holes drilled in the recessed area of the electrode compartment. The position depth of the cathode in the depth of the recess was adjusted by adding a plastic spacer behind the cathode, and the end of the cathode relative to the cell frame recess was sealed using fast-curing medical grade epoxy.

  [0069] A copper rod was connected between the two anode and cathode terminals to distribute the current to the electrode backplate. The cell was assembled and clamped using 0.25 inch (0.635 cm) bolts and nuts with a compressive force of about 60 inches and pounds by weight. A neoprene elastomer gasket (thickness 0.0625 inch (0.159 cm)) was used as a sealing gasket between the cell frame, frame spacer, and membrane.

[0070] Example 1:
[0071] The above cell was assembled using 0.010 inch (0.0254 cm) thick indium foil mounted on a 316L-SS back conductor plate using conductive silver epoxy. A multilayer, high surface area cathode comprising an electrolessly applied indium layer having a thickness of about 1 micron deposited on a layer of electroless tin having a thickness of about 25 microns on a reticulated copper fiber substrate. The base copper fiber structure was a copper wire mesh obtained from PestMall.com (Anteater Pest Control Inc.), an online internet supplier. The dimensions of the copper fibers in the wire mesh had a thickness of 0.0025 inches (0.00635 cm) and a width of 0.010 inches (0.0254 cm). The prepared high surface area cathode material is folded into a 1.25 inch (3.175 cm) thick and 6 inch (15.24 cm) high and 3 inch (7.62 cm) wide pad, which is 0.875 inch. The dimensions of the cathode compartment, which is (2.225 cm) × about 0.25 inches (0.635 cm), were filled and made larger than the adjusted compartment thickness (plus a spacer). The prepared cathode has a calculated surface area of about 3,171 cm ² , which is about 31 times the area of the flat cathode plate, 91% void volume, and a ratio of 12.3 cm ² / cm ³ . It had a surface area. The cathode pad was compressible, thereby providing a spring force to make contact with the cathode plate and membrane. Two layers of a very thin (0.002 inch thick) plastic screen with large 0.125 inch holes were placed between the cathode mesh and the Nafion® 314 membrane. A neoprene gasket (thickness 0.0625 inch (0.159 cm)) was used as a sealing gasket between the cell frame and the membrane. The electrocatalytic coating on the anode in the anolyte compartment was Water Star WS-32, which is a suitable iridium oxide based coating for generating oxygen in acid. In addition, the anode compartment also includes a titanium expanded metal material from DeNora North America 0.010 inch (0.0254 cm) thick DeNora North America with an iridium oxide based oxygen generating coating disposed between the anode and the membrane. EC626) is used to provide a zero-gap anode structure (where the anode is in contact with the membrane) and a pressure on the membrane from the anode side (which also has a contact pressure from the cathode side). It was.

  [0072] The cell assembly is clamped using stainless steel bolts, together with the catholyte dissociator, centrifugal catholyte circulation pump, inlet cell pH and outlet cell pH sensors, temperature sensor for outlet solution flow, and in FIG. Placed in a cell station having the same structure as shown. Using a 5 micron stainless steel frit filter, carbon dioxide was sparged into the solution in the catholyte dissociator volume and fed dissolved carbon dioxide into the recycle stream back to the catholyte cell inlet.

[0073] The anolyte used was a dilute 5% by volume sulfuric acid solution formed from reagent grade 98% sulfuric acid and deionized water.
[0074] In this test run, a catholyte composition comprising a 0.4 molar aqueous potassium sulfate solution supplemented with 2 g / L potassium bicarbonate was used, and carbon dioxide was sparged onto it to give a final 6.60. The system was operated at pH.

[0075] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 0.4 M-K ₂ SO ₄ , 0.14 mM-KHCO ₃ ;
Catholyte flow rate: 2.5 LPM;
Catholyte flow rate: 0.08 ft / sec;
Applied cell current: 6 amps (6,000 mA);
Catholyte pH range: 5.5-6.6; controlled by periodically adding potassium bicarbonate to the catholyte solution recirculation loop;
The pH of the catholyte decreased with time and was controlled by adding potassium bicarbonate.

[0076] Results:
Cell voltage range: 3.39 to 3.55 volts (slightly lower voltage when the catholyte pH drops);
Driving time: 6 hours;
Formate Faraday yield: constant between 32 and 35%; calculated by taking samples periodically; see FIG.
Final formate concentration: 9,845 ppm.

[0077] Example 2:
[0078] The same cell as in Example 1 was used, and the same cathode was used, but was used for this operation after rinsing with water in the electrochemical cell after completing the operation.

  [0079] In this test run, a catholyte composition containing a 0.375 molar aqueous potassium sulfate solution with 40 g / L potassium bicarbonate added was used, and carbon dioxide was sparged onto the final composition of 7.05. The system was operated at pH.

[0080] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 0.4M-K ₂ SO ₄ , 0.4M-KHCO ₃ ;
Catholyte flow rate: 2.5 LPM;
Catholyte flow rate: 0.08 ft / sec;
Applied cell current: 6 amps (6,000 mA);
Catholyte pH range: linearly decreased from 7.5 to 6.75 over time during operation.

[0081] Results:
Cell voltage range: 3.40-3.45 volts;
Operation time: 5.5 hours;
Formate Faraday yield: constant at 52% and slowly decreased to 44% over time as the pH of the catholyte decreased; see FIG.
Final formate concentration: 13,078 ppm.

[0082] Example 3:
[0083] The same cell as in Examples 1 and 2 was used, and the same cathode was used, but was used for this operation only after rinsing with water in the electrochemical cell after completing the operation.

  [0084] In this test run, a catholyte composition comprising a 0.200 molar potassium sulfate aqueous solution with 40 g / L potassium bicarbonate added was used, and carbon dioxide was sparged over to a final 7.10. The system was operated at pH.

[0085] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 0.2M-K ₂ SO ₄ , 0.4M-KHCO ₃ ;
Catholyte flow rate: 2.5 LPM;
Catholyte flow rate: 0.08 ft / sec;
Applied cell current: 9 amps (9,000 mA);
Catholyte pH range: linearly drops from 7.5 to 6.65 over time during operation, then 10 g increments of additional solid KHCO ₃ into the catholyte loop at 210, 252 and 290 minutes And the pH was returned to about 7 for the last part of the run.

[0086] Results:
Cell voltage range: 3.98-3.80 volts;
Operation time: 6.2 hours;
Formate Faraday yield: dropped from 75% to 60% at a pH of 6.65, then solid potassium bicarbonate into catholyte to catholyte loop at 210, 252 and 290 minutes in 10 g increments The addition increased to 75% and slowly decreased to 68% over time as the catholyte pH decreased to 6.90; see FIG.

Final formate concentration: 31,809 ppm.
[0087] Example 4:
[0088] The same cell as in Examples 1, 2, and 3 was used, and the same cathode was used, but was used for this run only after rinsing with water in the electrochemical cell after the run was completed.

[0089] In this test run, a catholyte composition containing 1.40 molar potassium bicarbonate (120 g / L KHCO ₃ ) was used, and carbon dioxide was sparged onto it to a final pH of 7.8. And operated the system.

[0090] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 2.6 LPM;
Catholyte flow rate: 0.09 ft / sec;
Applied cell current: 11 amp (11,000 mA);
Catholyte pH range: linearly dropped to a final pH of about 7.8 to 7.48 over time during operation.

[0091] Results:
Cell voltage range: 3.98 to 3.82 volts;
Driving time: 6 hours;
Formate Faraday yield: 63%, decreased to about 54-55%; see FIG. 10;
Final formate concentration: 29,987 ppm.

[0092] Theoretical Example 5:
[0093] This example is intended to separate the product potassium formate from the carbonate / potassium bicarbonate supporting electrolyte by membrane nanofiltration (NF) (Figure 10). The test uses two commercially available NF membranes. The feed solution contains 1.2M-KHCO ₃ + 0.6M-K-formate, and its pH is adjusted to 7, 9, and 11 for three separate experiments (for each membrane).

[0094] All NF tests are performed in a GE-Osmonic Sepa permeator (active membrane area of 0.0137 m ² ) at an applied pressure of 40 bar (580 psig) and 50 ° C. During each experiment, 3 liters of feed solution is run and the permeate is collected in a graduated cylinder (to measure volume) and the elapsed time is recorded. The permeate is then analyzed for total carbonate (HCO ₃ ⁻ + CO ₃ ²⁻ ) and formate. From such data, the transmittance (L / m ² · hour · bar) and the solute rejection (%) are calculated as follows.

Here, [S] indicates the molar concentration of the solute which can be either formate or total carbonate.
[0095] The expected results are summarized below.

[0096] Theoretical Example 6:
[0097] A single permeation test can be performed with a DK membrane using a formate-enriched feed solution containing 1.2M-KHCO ₃ + 1.2M-K-formate. The test can be performed at pH 11 and all other conditions are the same as in Example 1 above.

[0098] This test appears to give a rejection of 79.9% and -33.8% for total carbonate and formate, respectively. The transmittance is 0.32 L / m ² · hr · bar.
[0099] Example 7:
[00100] The same cell as in Examples 1, 2, and 3 was used, except that 701 g of tin shot (0.3-0.6 mm diameter) media with an electroless plated indium coating was used as the cathode. The thickness of the cathode compartment was 0.875 inches.

[00101] In this test run, a catholyte composition containing 1.40 molar concentration of potassium bicarbonate (120 g / L KHCO ₃ ) was used and sparged with carbon dioxide to a final pH of 8.0. And operated the system.

  [00102] The cell operates in batch conditions and does not overflow for the first 7.3 hours, then a 1.40 molar potassium bicarbonate feed stream at a rate of about 1.4 mL / min in the catholyte. The overflow was collected and measured, and a sample of the loop was collected for formate concentration analysis.

[00103] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 3.2 LPM;
Applied cell current: 6 amps (6,000 mA);
Catholyte pH range: linearly and slowly dropped to a final pH of about 8 to 7.50 over time during operation.

[00104] Results:
Cell voltage range: 3.98 to 3.82 volts;
Operation time: Batch mode: 7.3 hours;
Feed stream and product overflow: 7.3 hours by the end of 47 hours of operation;
[00105] The formate Faraday efficiency was between 42% and 52% during the batch run time, and the formate concentration increased to 10,490 ppm. During the feed and overflow times, the efficiency calculated periodically varied between 32% and 49%. The average conversion efficiency was about 44%. The formate concentration varied between 10,490 and 48,000 ppm during the feed and overflow times. The cell voltage started at about 4.05 volts and ended at 3.80 volts.

[00106] Example 8:
[00107] Electrolysis was performed using a three-compartment glass cell with a total volume of approximately 80 mL. The cell was hermetically constructed with a Teflon bushing. The compartments were separated by two glass frits. A three electrode assembly was used. A working and reference electrode (Accumet silver / silver chloride) was housed in one compartment containing the aqueous electrolyte and catalyst described above. Moreover, the above-mentioned electrolyte solution and catalyst solution were included in the central compartment. The third compartment is filled with 0.5 molar aqueous K ₂ SO ₄ electrolyte solution having a pH of about 4.5 by sprinkling CO ₂ and counter electrode (TELPRO (Stafford, TX) -mixed metal oxidation). A material electrode). Carbon dioxide was sprayed on the working electrode section during the experiment. The solution was measured for formic acid by ion chromatography and the solution was analyzed before (blank) and after electrolysis. The test was conducted for about 1.5 hours using a 6-channel Arbin Instruments MSTAT operating at -1.46 or -1.90 volts (SCE reference electrode standard) under potentiometric titration conditions.

[00108] Example 9:
[00109] The same cell as in Examples 1, 2, and 3 was used, except that 890.5 g of tin shot (3 mm diameter) media with a tin foil coating as the cathode was used. The cathode compartment thickness was 1.25 inches and the system was operated in batch mode with no feed input. In the catholyte dissociator, carbon dioxide was sparged to saturate the solution.

[00110] Filled tin floor cathode details:
Weight: 890.5g tin shot;
Tin shot: 3 mm average dimension;
Total compartment volume: 369 cm ³ ;
Calculated tin bead surface area: 4,498 cm ² ;
Calculated packed bed cathode specific surface area: 12.2 cm ² / cm ³ ;
Calculated packed bed void volume: 34.6%.

[00111] In this test run, a catholyte composition comprising 1.40 molar potassium bicarbonate (120 g / L KHCO ₃ ) was used, which was sparged with CO ₂ to a final pH of about 8.0. And operated the system.

[00112] The cell was operated in batch conditions, did not overflow, and samples of the catholyte loop were collected periodically for formate concentration analysis.
[00113] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 3.0 LPM (upflow);
Catholyte flow rate: 0.068 ft / sec;
Applied cell current: 6 amps (6,000 mA);
Catholyte pH range: During operation, it slowly slowly increased linearly from a pH of about 7.62 to a final pH of 7.73.

[00114] Results:
Cell voltage range: started at 3.84 volts and slowly dropped to 3.42 volts.
Operation time: Batch mode: 19 hours;
[00115] Formate Faraday efficiency started at about 65% and dropped to 36% after 10 hours and to about 18.3% after 19 hours. The final formate concentration ended at 20,500 ppm at the end of 19 hours of operation. See Figures 11 and 12.

[00116] Example 10:
[00117] 805 g indium-coated tin shot (3 mm diameter) with 0.010 inch (0.0254 cm) indium foil mounted on a 316L-SS back conductor plate using conductive silver epoxy as the cathode The same cell as in Examples 1, 2, and 3 was used except that the medium was used. The cathode compartment thickness was 1.25 inches and the system was operated in batch mode with no feed input. In the catholyte dissociator, carbon dioxide was sparged to saturate the solution. The tin shot was electrolessly plated with indium on the tin-coated copper mesh in the same manner as used in Examples 1-4. The indium coating was measured to be about 0.5 to 1.0 microns thick.

[00118] Details of indium coated tin shot packed bed cathode:
Weight: 890.5 g; indium coating on tin shot;
Indium-coated tin shot: average dimension of 3 mm;
Total compartment volume: 369 cm ³ ;
Calculated tin bead surface area: 4498 cm ² ;
Packed bed cathode specific surface area: 12.2 cm ² / cm ³ ;
Packed bed void volume: 34.6%.

[00119] In this test run, a catholyte composition containing 1.40 molar potassium bicarbonate (120 g / L KHCO ₃ ) was used, which was sparged with CO ₂ to a final pH of about 8.0. And operated the system.

[00120] The cell was operated in batch conditions, did not overflow, and samples of the catholyte loop were collected periodically for formate concentration analysis.
[00121] Operating conditions:
Batch catholyte recirculation operation:
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 3.0 LPM (upflow);
Catholyte flow rate: 0.068 ft / sec;
Applied cell current: 6 amps (6,000 mA);
Catholyte pH range: During operation, it slowly and linearly decreased over time from a pH of about 7.86 to a final pH of 5.51.

[00122] Results:
Cell voltage range: started at 3.68 volts and slowly dropped to 3.18 volts.
Operation time: batch mode; 24 hours;
[00123] Formate Faraday efficiency started at about 100%, varied between 60% and 85%, and ended at about 60% after 24 hours. The final formate concentration ended at about 60,000 ppm at the end of the 24 hour run. Sample dilution errors at high formate concentrations may have given the variability seen in yield numbers. See FIGS. 13 and 14.

[00124] Example 11:
[00125] The same cell as in Examples 1, 2, and 3 was used with indium on a tin electrocatalyst coating on a newly prepared copper mesh cathode. The prepared cathode has a calculated surface area of about 3,171 cm ² , which is about 31 times the area of the flat cathode plate, 91% void volume, and 12.3 cm ² / cm ³ . It had a specific surface area.

[00126] In this test run, a catholyte composition containing 1.40 M potassium bicarbonate (120 g / L KHCO ₃ ) was used and sparged with CO ₂ before use to achieve a final of 7.8. The system was operated at pH.

  [00127] The cell is operated in recycle batch conditions for the first 8 hours of operation to give a catholyte formate ion concentration of about 20,000 ppm or less, and then a new feed stream of 1.4 M potassium bicarbonate. Was metered into the catholyte at a feed rate of about 1.2 mL / min. The amount of overflow was collected, the volume was recorded, and overflow and catholyte loop samples were taken and analyzed for formate by ion chromatography.

[00128] Operating conditions:
Cathode: electroless indium on tin on copper mesh substrate;
Continuous supply with catholyte recirculation operation: 11.5 days;
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 3.2 LPM;
Catholyte flow rate: 0.09 ft / sec;
Applied cell current: 6 amps (6,000 mA);
[00129] Results:
Cell Voltage vs Time: FIG. 15 shows the cell voltage vs time results, showing a stable operating voltage of about 3.45 volts over 11.5 days after initial start-up.

Continuous operation time: 11.5 days;
Formate concentration vs time: FIG. 16 shows the results of formate concentration vs time.
Formate Faraday Efficiency: FIG. 17 shows the calculated formate current efficiency vs time, whereby the formate yield from the recovered sample is determined.

Final formate concentration: about 28,000 ppm.
Catholyte pH: FIG. 18 shows the pH change of the catholyte over 11.5 days, slowly decreasing from a pH of 7.8 to a pH value of 7.5. The feed rate was not changed during operation, but may have been slowly increased or decreased to maintain a constant catholyte pH within the optimum operating pH range.

[00130] Example 12:
[00131] The same cell as in Examples 1, 2, and 3 was used with indium on a tin electrocatalyst coating on a newly prepared copper mesh cathode. The prepared cathode has a calculated surface area of about 3,171 cm ² , which is about 31 times the area of the flat cathode plate, 91% void volume, and 12.3 cm ² / cm ³ . It had a specific surface area.

[00132] In this test run, a catholyte composition containing 1.40 M potassium bicarbonate (120 g / L KHCO ₃ ) was used and sparged with CO ₂ before use to achieve a final of 7.8. The system was operated at pH.

  [00133] The cell is operated in recirculation batch mode for the first 8 hours of operation to provide a catholyte formate ion concentration of about 20,000 ppm or less, and then a new feed stream of 1.4 M potassium bicarbonate. Was metered into the catholyte at a feed rate of about 1.2 mL / min. The amount of overflow was collected, the volume was recorded, and overflow and catholyte loop samples were taken and analyzed for formate by ion chromatography.

[00134] Operating conditions:
Cathode: electroless indium on tin on copper mesh substrate;
Continuous supply with catholyte recirculation operation: 21 days;
Anolyte solution: _0.92M-H 2 _SO 4;
Catholyte solution: 1.4M-KHCO ₃ ;
Catholyte flow rate: 3.2 LPM;
Catholyte flow rate: 0.09 ft / sec;
[00135] Applied cell current: 6 amps (6,000 mA).

[00136] Results:
Cell voltage vs time: The cell exhibited a higher operating voltage of about 4.40 volts, higher than all other cells of the present invention due to inadequate electrical contact pressure of the cathode to the indium foil conductor backplate. . The cell was kept in operation for a long time.

Continuous operation time: 21 days.
[00137] Formate Faraday Yield: FIG. 19 shows the calculated formate current efficiency vs time, which determines the formate yield from the collected sample. The formate Faraday current efficiency fell to the range of 20% after 16 days.

  [00138] Formate concentration vs time: FIG. 20 shows the results of formate concentration vs time. On the 21st day, 0.5 g of indium (III) carbonate was added to the catholyte while the cell was further operated at 6 amps utilization. The formate concentration in the catholyte operating loop was 11,330 ppm before the indium addition, increased to 13,400 ppm 8 hours after the unit was shut down 21 days after operation, and increased to 14,100 ppm after 16 hours.

  [00139] pH of the catholyte: FIG. 21 shows the cathode over a continuous operating time operating in the pH range of 7.6 to 7.7, except for an abnormal data point near the 16th day when pumping of the feed pump was stopped. The pH change of a liquid is shown. The feed rate was not changed during operation, but may have been increased or decreased to maintain a constant pH operation within the optimum range.

  [00140] The present invention and many of the attendant advantages will be understood by the foregoing description, without departing from the scope and spirit of the invention or without sacrificing all of its significant advantages. It will be apparent that various changes in the form, configuration, and arrangement of the components can be made. The forms described herein above are merely exemplary embodiments, and it is the intent of the claims to encompass and embrace such modifications.

Claims (30)

(A) introducing an acidic anolyte into the first compartment of the electrochemical cell containing the anode;
(B) A bicarbonate-based catholyte saturated with carbon dioxide is introduced into a second compartment of an electrochemical cell containing a high surface area cathode, the high surface area cathode comprising an indium coating, and about 30% to 98% Recycle at least a portion of the bicarbonate-based catholyte with a void volume between; and (C) reduce carbon dioxide to at least one of a single carbon-based product or a multi-carbon based product A potential sufficient to do so is applied between the anode and the cathode;
A method of electrochemically reducing carbon dioxide to a product. Applying a potential between the anode and cathode sufficient to reduce carbon dioxide to at least one of a single carbon based product or a multi carbon based product;
Applying a potential between the anode and cathode sufficient to reduce carbon dioxide to a single carbon based product comprising alkali metal formate;
The method of claim 1, comprising: Introducing an alkali metal formate into the second electrochemical cell; and applying a potential to the second electrochemical cell to convert the alkali metal formate into at least formic acid;
The method of claim 2 further comprising:   The method of claim 1, wherein the cathode compartment further comprises a homogeneous heterocyclic amine catalyst.   Homogeneous heterocyclic amine catalyst is 4-hydroxypyridine, adenine, sulfur containing heterocyclic amine, oxygen containing heterocyclic amine, azoles, benzimidazoles, bipyridines, furans, imidazoles, at least one Imidazoles related species having a 5-membered ring, indoles, lutidines, methylimidazoles, oxazoles, phenanthrolines, pterins, pteridines, pyridine, pyridines related species having at least one 6-membered ring, pyrroles, 5. The method of claim 4, wherein the method is selected from the group consisting of quinolines or thiazoles, and mixtures thereof.   The method of claim 1, wherein the high surface area cathode comprises indium deposited on tin.   The method of claim 6, wherein the high surface area cathode further comprises a copper substrate and the tin is laminated onto the copper substrate. Operating the electrochemical cell at a pressure higher than atmospheric pressure;
The method of claim 1 further comprising:   The method of claim 1, wherein the anode comprises an electrocatalytic coating comprising at least one of ruthenium oxide, iridium oxide, platinum, platinum oxide, gold, or gold oxide.   The method of claim 1, wherein the electrochemical cell comprises a membrane configured to selectively control ion flow between the first compartment and the second compartment. (A) introducing an acidic anolyte into the first compartment of the electrochemical cell containing the anode;
(B) introducing a catholyte saturated with carbon dioxide into the second compartment of the electrochemical cell, the catholyte being alkali metal bicarbonate, alkali metal carbonate, alkali metal sulfate, alkali metal chloride, and these The second compartment comprises a high surface area cathode, the high surface area cathode comprises an indium coating and has a void volume between about 30% and 98%;
(C) removing at least a portion of the catholyte from the second compartment;
(D) recirculating at least a portion of the catholyte back into the second compartment; and (E) (i) transferring a new catholyte stream to at least a portion of the catholyte or at least one of the second compartments. Or (ii) introducing water into the second compartment; controlling the pH of the second compartment by at least one of:
Controlling the pH in the cathode compartment of an electrochemical system having an acidic anolyte.   The method of claim 11, wherein the catholyte comprises an alkali metal bicarbonate.   13. The method of claim 12, wherein the alkali metal bicarbonate is potassium bicarbonate.   14. The method of claim 13, wherein the potassium bicarbonate has a concentration range between about 5 and 600 grams / liter.   The method of claim 11, wherein the catholyte comprises an alkali metal carbonate.   The method of claim 15, wherein the alkali metal carbonate is potassium carbonate.   17. The method of claim 16, wherein the potassium carbonate has a concentration range between about 5 and 1500 grams / liter. (A) introducing an acidic anolyte into the first compartment of the first electrochemical cell containing the anode;
(B) introducing a catholyte containing alkali metal bicarbonate into the second compartment of the first electrochemical cell, the catholyte being saturated with carbon dioxide, the second compartment comprising a high surface area cathode; The high surface area cathode includes an indium coating, has a void volume between about 30% and 98%, and recycles at least a portion of the bicarbonate-based catholyte;
(C) applying a potential sufficient between the anode and cathode to reduce carbon dioxide to alkali metal formate;
(D) introducing an alkali metal formate into the ion exchange compartment of the second electrochemical cell;
(E) a potential sufficient to generate at least formic acid and an alkali metal hydroxide is applied between the anode of the second electrochemical cell and the cathode of the second electrochemical cell; and (F) the alkali metal Introducing a hydroxide with carbon dioxide to produce at least a portion of the alkali metal bicarbonate introduced into the second compartment of the first electrochemical cell;
A method of electrochemically reducing carbon dioxide to a product. Separating the alkali metal formate from the alkali metal bicarbonate of the catholyte of the first electrochemical cell using a nanofiltration system;
The method of claim 18 further comprising: Separating the alkali metal formate from the alkali metal bicarbonate of the catholyte of the first electrochemical cell using a nanofiltration system;
Catholyte alkali metal bicarbonate is introduced into the alkali metal hydroxide to convert at least a portion of the alkali metal bicarbonate to alkali metal carbonate; and using a nanofiltration unit, the alkali metal formate to alkali Separating the metal carbonate;
20. The method of claim 19, comprising: Introducing an alkali metal carbonate with an alkali metal hydroxide and carbon dioxide to produce at least a portion of the alkali metal bicarbonate that is introduced into the second compartment of the first electrochemical cell;
21. The method of claim 20, further comprising:   19. The method of claim 18, wherein at least a portion of the alkali metal hydroxide is derived from one or more of the first electrochemical cell and the second electrochemical cell.   The method of claim 18, wherein formic acid is generated in the ion exchange compartment of the second electrochemical cell.   The method of claim 18, wherein the alkali metal hydroxide is generated in the cathode compartment of the second electrochemical cell. The method of claim 18, wherein the high surface area cathode has a specific surface area greater than 2 cm ² / cm ³ .   The method of claim 18, wherein the acidic anolyte comprises sulfuric acid. A halogen selected from the group consisting of F ₂ , Cl ₂ , Br ₂ , and I ₂ in at least one of the first compartment of the first electrochemical cell and the first compartment of the second electrochemical cell; To generate
The method of claim 18 further comprising: Reacting halogen with an organic compound to form a halogenated product;
28. The method of claim 27, further comprising:   28. The method of claim 27, wherein the halogen is bromine.   30. The method of claim 28, wherein the halogen is bromine.

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