JP2009511740A - Continuous cocurrent electrochemical reduction of carbon dioxide - Google Patents

Abstract

In various embodiments, the invention provides an electrochemical method for the reduction of carbon dioxide, for example, converting carbon dioxide to formate or formic acid. In selected embodiments, operation of a continuous reactor with a three-dimensional cathode and a two-phase (gas / liquid) catholyte stream provide advantageous conditions in the electroreduction of carbon dioxide. In these embodiments, at a selected gas / liquid phase volume flow ratio, a continuous two-phase flow of catholyte solvent and gas containing carbon dioxide, along with a relatively low reactor (cell) voltage (<10V). Resulting in dynamic conditions that favor the electroreduction of CO ₂ at relatively high effective surface current densities and gas space velocities. In some embodiments, a relatively high internal gas retention in the cathode chamber (obviously a volume ratio of internal gas to liquid phase> 0.1) is greater than the equilibrium CO ₂ concentration in the liquid phase. It can be increased and can promote a relatively high effective surface current density. In some embodiments, these features can achieve a relatively low CO ₂ partial pressure (<10 bar), for example, with pH> 7 in the catholyte. In some embodiments, these features can be achieved under conditions close to adiabatic conditions, for example, with a catholyte outlet temperature of up to about 80 ° C.

Description

Detailed Description of the Invention

(Field of the Invention)
The field of the invention is electrochemistry, and the invention includes a method for electroreduction of carbon dioxide in an aqueous system and an apparatus therefor.

BACKGROUND OF THE INVENTION
Formate MHCO ₂ (where M is usually Na, K or NH ₄ ) and formic acid HCO ₂ H are produced by an industrial thermochemical method (Kirk-Othmer-Encyclopedia of Chemical Technology, 1991). To obtain commercial chemicals. For example, sodium formate is obtained by the reaction of carbon monoxide and sodium hydroxide, and then formic acid is obtained by acid decomposition with sulfuric acid.

NaOH + CO → NaHCO ₂
2NaHCO ₂ + H ₂ SO ₄ → 2HCO ₂ H + Na ₂ SO ₄
Formic acid can also be produced as a by-product in the oxidation of hydrocarbons, as well as by hydrolysis of methyl formate obtained from methanol carbonylation. A method for synthesizing formate (eg, KHCO ₂ ) by electroreduction of carbon dioxide is also known (Chaplin and Wragg, 2003; Sanchez et at., 2001; Akahori et al., 2004; Hui and Oloman, 2005).

Carbon dioxide is thought to be a cause of climate change, mainly due to humanity. Thus, there is a need for a method of sequestering CO ₂ and / or converting it to useful products.

  Oloman and Watkinson are registered in US Pat. 3,969,201 and 4,118,305 (incorporated by reference) describe a trickle bed reactor for electroreducing oxygen to alkaline peroxide. In various configurations, the electrochemical cell includes a set of spatially separated electrodes, wherein at least one electrode is in the form of a fluid permeable conductor mass separated from the counter electrode by a barrier wall. The electrode mass may be in the form of particles or a layer of a fixed porous matrix. The electron conducting material is composed of a surface that is a good electrocatalyst for performing the above reaction.

  In order to move electrolyte and gas in parallel flow through the electrode mass (eg, in a direction generally perpendicular to the direction of current between the electrodes), an inlet is provided for supplying liquid electrolyte and gas to the electrode mass. An outlet is provided to move the solution containing the reaction product from the fluid permeable conductor mass.

[Summary of the Invention]
In various embodiments, the invention provides an electrochemical method for the reduction of carbon dioxide, such as converting carbon dioxide to formate or formic acid. In selected embodiments, operation of a continuous reactor having a three-dimensional cathode and a two-phase (gas / liquid) catholyte stream provides an advantageous condition for the electroreduction of carbon dioxide. In these embodiments, a continuous two-phase flow of catholyte solvent and carbon dioxide gas at a selected gas / liquid volume ratio results in the CO ₂ at relatively high effective superficial current densities. Provide dynamic conditions that favor electrical reduction. In some embodiments, the relatively high internal gas retention in the cathode chamber (the volume ratio of gas to liquid phase in the feed stream is clearly greater than 1 or greater than 0.1 in the porous electrode. Can be supplied to be greater than the equilibrium CO ₂ concentration in the liquid phase, which can facilitate a relatively high effective surface current density. In some embodiments, these properties can be achieved, for example, at catholyte pH> 7 and relatively low CO ₂ partial pressure (<10 bar).

  As a form different from the prior art, the above invention involves continuously passing the catholyte mixture through the cathode chamber of the electrochemical reactor. The catholyte mixture may contain carbon dioxide gas and a liquid catholyte solvent containing dissolved carbon dioxide. The catholyte solvent can be, for example, an aqueous solvent. Also, dissolved alkali metal or ammonium bicarbonate may be included, and can be maintained at a desired pH, such as in the range of about 6 to about 9. The volume ratio of gas (G / L) to liquid in the catholyte can be maintained to be the ratio of the volume of carbon dioxide gas to the volume of solvent in the liquid catholyte. The G / L ratio can be maintained in the cathode chamber (eg, in the feed stream or in the porous cathode in the cathode chamber). For example, the method may be such that the G / L ratio is greater than a threshold (eg, greater than 1 in the supply or greater than 0.1 in a porous (3D) cathode). ) Can be implemented.

One form of the invention involves passing an electric current between the cathode and anode of the cathode chamber to reduce dissolved carbon dioxide to form the desired product. In some embodiments, the effective surface current density at the cathode is a threshold (eg, 1 kA / m ² (or 1.5, ² , 2.5, 3, 3.5, 4, 4.5 or The method can be carried out such that it is greater than 5 kA / m ² )). The current in the system may be, for example, a direct current driven by an electrochemical cell voltage, and in some embodiments, the method is performed at a relatively low electrochemical cell voltage (eg, less than 10V). be able to.

The various aspects of the invention are useful in some embodiments for facilitating the selection of method parameters that may improve the economic aspects of the method of the invention. In some embodiments, the above method of the invention is used with a relatively lean input gas stream. For example, the concentration of carbon dioxide gas in the supply gas may be 1% or more and 100% or less, that is, any value within this range (the partial pressure of carbon dioxide in the cathode chamber is a threshold value (eg, 3, 5, or In some embodiments, less than 10 bar)). Similarly, for example, the cathode chamber has a minimum value such as 1, 2, 3, 4 or 5 bar (1 bar = 100 kPa (abs)) and a lower maximum value such as 6, 7, 8, 9 or 10 bar. A relatively low system pressure within the range may be used. In some embodiments, the method of the invention is effective at high temperatures that do not need to be cooled (eg, cathode temperatures above desired thresholds such as 20, 25, 30, 35, 40, 45, 50 ° C., etc.). Can be done manually. In this context, it will be appreciated that the pressure and temperature of the cathode chamber can vary along the height of the cathode. For example, the inlet pressure may be greater than the outlet pressure (in some embodiments, the pressure drop is about 500, 600, 700, for example, at a minimum value such as about 10, 20, 30, 40, or 50 kPa. Up to a maximum of 800 or 900 kPa). Similarly, the outlet temperature may be greater than the inlet temperature so that the temperature rises from about 1 ° C. to 100 ° C. (ie, any value in this range) from the inlet to the outlet. It will be appreciated that the gas composition (especially the CO ₂ concentration) and total pressure determine the CO ₂ partial pressure (ie ppCO ₂ = (CO ₂ ratio) × (total pressure)).

  The cathode used in the invention can have an effective thickness in the dimension of current flow, such as a porous cathode. These may be considered as three-dimensional (3D) electrodes. Such electrodes have a selected thickness, such as less than 6, 5, 4, 3, 2, 1, or 0.5 mm, and a selected porosity or porosity range, such as 5% or more and 95% or less (ie, , 30, 40, 50, 60 or 70%, etc.). The cathode of the above invention can be selectively made from a wide variety of electroactive materials. Electroactive materials include, for example, tin, lead, pewter, mercury, indium, zinc, cadmium, or electrically conductive or non-conductive materials selectively coated with electroactive materials (eg, tin plated copper, mercury And other materials such as copper (mercury amalgamated copper), tin-plated graphite, or tin-plated glass).

  The anode is in the anode chamber, which can be separated from the cathode chamber by an electrochemical cell membrane. The anolyte in the anodic chamber can be an aqueous anolyte. The anolyte contains, for example, dissolved alkali metal hydroxide, salt (including ammonium salt) or acid, and has a pH range of about 0 to about 14 (that is, any pH value or any value within the range). Range).

  The electrochemical cell membrane can be a cation permeable membrane, such as a membrane that balances the stoichiometry of the method by allowing selected ions to cross the membrane.

  Desired products of the above process include formates such as ammonium formate, potassium formate and sodium formate, or formic acid. The desired product can be separated from the catholyte solvent by various methods. For example, some catholyte solvent, recycled catholyte solvent can be recycled from the cathode chamber outlet to the cathode chamber inlet, and the desired product can be separated from the recycled catholyte solvent. Similarly, at least a portion of the anolyte can be recycled from the anolyte chamber outlet to the anolyte chamber inlet, and co-products at the anode can be separated from the recycled anolyte.

  In selected embodiments, joule heating of the anolyte can be used to provide a heated anolyte. The heated anolyte can then be used to heat the recycled catholyte, for example, by evaporation with fractional crystallization, or vacuum distillation, to separate the desired product from the recycled catholyte solvent. In some embodiments, a recycled catholyte containing formate can react with the anolyte so that the desired product is obtained by an acidolysis reaction.

Detailed Description of the Invention
In various embodiments, the invention provides a continuous reactor for an electrical reduction of CO _2. The continuous reactor can be used, for example, in a method for converting a supply of carbon dioxide added with water into formate ions (reaction 1), resulting in the production of formate or formic acid.

_{CO 2 + H 2 O + 2e} - → HCO 2 - + OH - reaction 1
In some forms, the above invention is disclosed by Oloman and Watkinson in US Pat. An electrochemical reactor similar to the trickle bed reactor described in 3,969,201 and 4,118,305 may be utilized. In such an embodiment, the invention may utilize an apparatus for performing an electrochemical reaction including a gas reaction, including an electrochemical cell having a pair of spatially separated electrodes. At least one of the electrodes is, for example, in the form of a fluid permeable conductor mass, a cathode separated from the counter electrode by an electrically insulating layer (eg a membrane or a porous diaphragm) that is ionically conductive. . The reactor can be operated in a “trickle bed” mode with cocurrent flow of reaction gas and catholyte through a 3D cathode. As illustrated in the examples, the parameters of the method of the invention described above are evident, such as the reactant feed (for example, high gas space velocity, volumetric gas feed flow ratio over the reaction vessel capacity) that this reactor favors. ), As well as mass transfer characteristics can be adjusted. The cocurrent flow at the cathode can exist in any direction with respect to gravity.

  In the reactor of the above invention, the inlet can be provided to supply liquid electrolyte and gas to the fluid-permeable conductor mass, and the outlet is provided to move the solution containing the reaction product from the conductor mass. Can do. The inlet and outlet can be arranged so that the electrolyte and gas move in parallel through the conductor mass (eg, typically perpendicular to the current flow between the electrodes). The reactor can be arranged with, for example, a cationic membrane separator (eg as described in Hui and Oloman, 2005). In other embodiments, other types of reactors may be used.

Depending on the desired product and the overall mass balance, the process can be charged with metal hydroxides and / or metal salts (eg MOH, MCl, M ₂ CO ₃ , M ₂ SO ₄ , and M ₃ PO ₄ (here And M can typically include alkali metals (Na, K, etc.) or NH ₄ ); acids such as H ₂ SO ₄ , H ₃ PO ₄ , or HCl; or ammonia (NH ₃ ).

Flow sheets, described in some detail, are provided for alternatives in FIGS. 1, 5, 6, 7, 8 and 9 illustrating the scope of embodiments encompassed by the present invention. In selected embodiments, the CO ₂ stream charged in the above method may be concentrated, for example, at a concentration greater than 80% by volume CO ₂ . Alternatively, a relatively low concentration gas stream may be used, such as, for example, a gas generated from the combustion of fossil fuels (usually containing about 10% by volume CO ₂ ). Other potential reactive components of the feed CO ₂ stream include oxygen, sulfur oxides, nitride oxides, and hydrogen sulfide. These can be processed in various ways. For example, in the feed stream entering the reactor, they can be removed in one or more initial gas scrubbing steps such that they are eliminated or have a low concentration (eg, less than about 1 volume%). The total pressure and temperature of the charged CO ₂ stream can vary over a relatively wide range (eg, about 100 kPa (abs) to 1000 kPa (abs), about 250 K to 550 K). In addition to recycling the catholyte liquid, the conversion of CO ₂ per pass through the electrochemical reactor is such that equipment for recycling unconverted CO ₂ gas can be included in the invention. It can be less than 100%.

  Steps 1-5 of the method in FIG. 5 may include several embodiments of the invention described above and can be considered briefly as follows with reference to the annotations in the figure.

  Step 1. Mix: Feed water (with optional make-up reagent added) is continuously mixed with recycled catholyte which is then continuously fed to the cathodic chamber of the reactor.

  Step 2. Reaction: [C] Cathode The reaction 1 is continuously promoted together with the reaction 2 which produces hydrogen by electroreduction of water, which is a side reaction.

2H ₂ O + 2e ⁻ → H ₂ + 2OH ⁻ Reaction 2
[A] Anode Promotes a complementary anodic reaction, the nature of which depends on the desired product from the above process. For example, if the desired main product is formate and the byproduct is oxygen, anodization can be reaction 3.

2OH ⁻ → _1/2 O ₂ + H ₂ O + 2e ⁻ Reaction 3
If the desired main product is formic acid and the by-product is oxygen or chlorine, the anodic reaction can be reaction 4 or 5, respectively. Other anodic reactions can include the generation of peroxy salts of peroxy acids, such as peroxy disulfide salts (2SO ₄ ⁻ → S ₂ O ₈ ² + + 2e ⁻ ).

_{2H 2 O → O 2 + 2H} + + 2e - Reaction 4
2Cl ^- → Cl ₂ + 2e ^- reaction 5
The electrode chambers in the reactor can be separated by a membrane that selectively moves cations from the anode to the cathode in an amount that balances the desired stoichiometry. If the desired main product is a formate salt, these cations can be alkali metal ions (eg, Na ⁺ , K ⁺ or NH ₄ ⁺ supplied to the anolyte as hydroxide, salt, or NH ₃ gas. ) Here, if the desired main product is formic acid, the cations to be transported include protons (H ⁺ ) generated in reaction 4 and / or protons (H ⁺ ) supplied to the anolyte as acid. Can be.

  Step 3. Separate: The main product (formate or formic acid) and by-product (hydrogen) are continuously separated from the recycled catholyte.

  Step 4. Mix: Continuously mix the essential anodic reagent and water with the recycled anolyte.

  Step 5. Separate: Continuously separate the anode by-product from the recycled anolyte.

  In the various steps of the method, carbon dioxide and water may be consumed and / or generated in other reactions (eg, reactions 6, 7, and 8 occurring elsewhere in the reactor or process).

^{_{CO 2 + OH - → HCO 3}} - Reaction 6
HCO ₃ ⁻ + H ⁺ → H ₂ O + CO ₂ reaction 7
H ⁺ + OH ⁻ → H ₂ O Reaction 8
In some embodiments, the method provides a reactor with a relatively high surface current density (eg, greater than 0.5 kA / m ² ) and current efficiency (eg, formate production (eg, greater than 50%)). Can be included. The method of the invention includes maintaining low energy intensity while balancing the material and energy requirements in the various process steps to match the required, stoichiometric amount of the process. obtain. For example, the method of the invention was demonstrated with a current efficiency of 75% for formate at a reactor voltage of 3 V at a temperature of 300 K, a CO ₂ pressure of 200 kPa (abs), and 1.3 kPa / m ² . Water management can be important for mass balance, and it can be required that water be supplied to the cathode and / or anode path to match the rate of reaction, electroosmosis transfer, and evaporation. The energy consumption in electrochemical reactions, heating, cooling, pumping water may contribute to the cost of the method and can be kept relatively low by rationalizing the heat load in the appropriate reactor design and method. In some embodiments, non-metallic catalysts can be used. For example, US Pat. 5284563 and US5382332 disclose nickel alkyl cyclam catalysts that can be used for carbon dioxide reduction.

In some embodiments, a relatively high gas / liquid (G / L) phase feed volume flow ratio can be used in an electrochemical reactor, as can a high gas space velocity (eg,> 100 h ⁻¹ ) ( For example, G / L flow = 1 to 1000 or 10 to 200). In selected reactors of the above invention, increasing the G / L from about 5 to 100 increases the voltage by less than 10%. The optimal G / L phase capacity (shown as “G / L retention”) ratio is usually the effective catholyte conductivity (usually decreases with increasing G / L residence) and CO ₂ mass transfer capacity (usually , And increases with increasing G / L retention) and the intrinsic temperature and pH dependent reaction rates for CO ₂ conversion to non-reactive bicarbonate / carbonate species in the bulk catholyte liquid phase, and Determined by the balance between

In various embodiments, there are two separate gas / liquid (G / L) ratios that can be important.
(I) Volume G / L ratio in the reactor feed flow with a gas volume flow corrected to STP, for example, about 1 to 1000 or less, 1 to 500 or less, 10 to 200 or less, or 10 The range of 100 or less or any numerical value within these ranges can be included. For example, the gas flow rate is 1000 ml / min (corrected to STP), the liquid flow rate is 20 ml / min, and G / L [flow rate] = 1000/20 = 50.
(Ii) The volume G / L ratio in the porous cathode, that is, the ratio of the gas residence amount to the liquid residence amount in the cathode, for example, about 0.1 to 10 and about 0.2 to 2 A range from 0.2 to 4 or any numerical value or range within these ranges may be included. For example, the gas retention amount is 0.6, the liquid retention amount is (1-0.6), and G / L [retention amount] = 0.6 / 0.4 = 1.5. Here, “residence” is the fraction of the gap (in the 3D cathode) occupied by a specified phase at a certain moment. It appears to be constant during steady state operation of the reactor. At the cathode, gas has a shorter residence time than liquid, so G / L [flow rate] is not the same as G / L [retention volume] (ie, gas “exits” past the liquid). Since the above value of (ii) is determined by the above value of (i) along with the properties of the cathode (eg, porosity (or porosity), shape factor, and particle size), the supply of (i) and (ii) Flow and internal dwell values are of course related. Similarly, the value of (i) affects the value of (ii) and is also related to the CO ₂ mass transfer capacity at the cathode and the gas space velocity of the reactor.

The above conditions can be adjusted as follows (where CD is the current density):
Effective CD> 1.5 kA / m ^{2 at} CO ₂ pressure <3 bar
Effective CD = [surface CD] × [current efficiency with desired product (eg, formate)]
Formate product concentration in 1 pass> 0.5M
Voltage of all reactors at 3 kA / m ² <5V
The “surface current density” is the current passing through the cell divided by the projected surface area of the relevant component such as the cathode. The “projected surface area” of the component such as the cathode is the surface area of the protrusion of the component on the plane parallel to the component. In the case of a flat component, the projected surface area is equal to the area of the component facing the other conductive component (eg, the projected surface area of the cathode facing the anode). For a component in the form of a planar mesh, the projected surface area is the area within the outer shape of the mesh as projected onto a continuous planar surface.

  The “current efficiency” (CE) is a measure of the actual reaction rate relative to the reaction rate that would be achieved if all of the current passed through the cell consumed by the relevant reaction, such as the reduction of carbon dioxide. Usually expressed as a percentage.

In some embodiments, the invention can operate at or near thermal insulation (Tout up to about 90 ° C.). In some embodiments, increasing the temperature while simultaneously reducing the solubility of CO _{2 in} the catholyte actually favors the intrinsic rate of carbon dioxide electroreduction (ERC), and good CE is By manipulating the factors that promote mass transfer of CO ₂ in a continuous reactor, it can be obtained at higher temperatures. Since the effect of Joule heating at high CD under conditions close to adiabatic in a continuous reactor can automatically increase the reaction temperature up to about 80 ° C., in some embodiments, the ability to perform at high temperatures is possible. May be important.

[Example 1]
FIG. 1 shows a flow diagram of a method reflecting this embodiment of carbon dioxide electroreduction (ERC). Pure CO ₂ or a mixture of CO ₂ (gas) and N ₂ (gas) is mixed with catholyte (liquid) at the T junction (mixer), and the gas and liquid from the mixture are It was advanced as a slag flow to enter the cathode chamber. Thus, the electrochemical reactor was operated with a cocurrent and upward multiphase (G / L) flow on the cathode side. The anolyte, which is a KOH aqueous solution, also flowed upward through the anode chamber and was recycled to the anolyte storage tank. All gases and liquids were passed through individual rotameters. The liquid flow was controlled by a pump and the gas flow was controlled by a manual valve to ensure proper gas and liquid charge in the reactor. The reactor inlet and outlet pressures and temperatures were measured by visual instruments at the points indicated in the flow sheet. In operation where the catholyte product temperature was controlled during operation, precooling or preheating of both the anolyte and catholyte was employed to keep the temperature at the desired level. The liquid product was recovered from the sampling point and analyzed for formic acid concentration. Gaseous products from gas / liquid separators (graphite felt packed beds) can be used for post-hoc hydrocarbon analysis with an Orsat gas analyzer for CO ₂ and CO analysis, a wet gas flow meter for flow measurement, or a gas chromatograph. Controlled by a 3-way valve to either of the Tedlar sampling bags.

The constant current electrolysis of CO ₂ was performed with a DC power source connected across the anode and cathode. The voltmeter was connected to the structural unit that measures the reactor voltage. All voltages included anodic potential, cathodic potential and IR drop. Individual electrode potentials were not measured.

  An automatic pressure regulating valve was used in the anolyte product line to balance the pressure in the anode chamber against the pressure in the cathode chamber. Such pressure equilibrium requires that the catholyte be bypassed by a 3-D cathode and / or prevent rupture of the membrane that can occur when the cathode pressure exceeds the anode pressure. Is done.

  Most operations take place at the cathode outlet at atmospheric pressure. In some operations in reactor B, a manual back pressure control valve and pressure gauge were installed in the catholyte product line to maintain superatmospheric pressure at the catholyte outlet.

  The above inventive process was carried out first in reactor A (small reactor) and then in 7 times larger reactor B (large reactor) to demonstrate the effect of scale-up. Both reactors have the structure shown in FIG. The reactor comprises a cathode feeder plate and a 3-D cathode, a Nafion cation exchange membrane separator, an anode spacer / membrane support, an anode feeder plate, and a gasket. The cathode mesh, anode mesh, and anode spacer are closed at their ends with silicone adhesive, and the cell assembly is sandwiched between insulated mild steel sheets to create a balanced fluid distribution. Compressed by SS bolt.

FIG. 3 shows a cut front view of single cell reactor A. FIG. The “flow-by” cathode dimensions of the reactor were 30 mm wide and 150 mm high (geometric surface). The thickness of the cathode was determined by the 3-D cathode material used. In a copper mesh cathode coated with tin, a single layer or multiple layers of mesh are placed between the membrane and the cathode feeder, the thickness of the cathode being the thickness of all these layers, 0.38 mm or more 1.83 mm or less. In graphite felt and metal granules or shots, the cathode material was incorporated into two layers of neoprene gasket in contact with the cathode feeder and integrated with the back of the cathode. Therefore, the thickness of the cathode was that of the gasket, i.e. 3.2 mm. The geometric (also known as apparent) cathode area perpendicular to the current was 4.5 × 10 ⁻³ m ² (150 mm × about 30 mm). In the reactor A, the applied current was in the range of 1 A to 14 A, and the corresponding surface current density was 0.22 kAm ^{−2 to} 3.11 kAm ⁻² .

In reactor B, a copper mesh cathode or tin granule cathode coated with tin was used. FIG. 4 shows a dimensioned front view and the corresponding dimensions of reactor B with a tin granule fixed layer cathode. In order to minimize catholyte bypass formation at the edge of the cathode layer, the gasket was intentionally made of five triangles on each side that directed the flow towards the center of the cathode. The apparent cathode area minus the area taken by these triangles was 3.22 × 10 ⁻² m ² , about 7 times that of reactor A (4.5 × 10 ⁻³ m ² ). The current applied to reactor B ranged from 20 A to 101 A, and the corresponding surface current density was from 0.62 kAm ^{-2 to} 3.20 kAm ^-2 .

Reactor B was assembled with a tin granule fixed layer cathode according to the following procedure.
(1) A sanded tin plate (99.99 wt% Sn, 3 mm thick) cathode feeder was placed on the neoprene gasket.
(2) The pretreated tin granules were uniformly spread on a durable gasket (thickness 3.2 mm) on the tin plate. A layer of netron screen was inserted into the inlet and outlet regions of the catholyte stream to deliver fluid and support the membrane.
(3) A wet Nafion 117 membrane was placed on the surface of the tin granule layer, and a PVC screen spacer, anode SS mesh, and anode feeder (SS plate) were placed on top of each other in this order.
(4) Finally, the cell body was installed and sandwiched using 24 3/8 inch bolts to uniformly compress the cell.

  Various cathode materials are available for use in other situations of the present invention. Carbon dioxide can be electrochemically reduced on almost all metal groups in the periodic table, resulting in different products with different levels of selectivity. In particular, the following cathode materials may be suitable for certain embodiments. Cu with nanostructures deposited on graphite felt; Cu / Sn alloy deposited on graphite felt; Sn with nanostructure, Sn-coated plastic mesh on Cu mesh, Cu mesh; on graphite felt Deposited Sn; Sn coated copper mesh; Pb plates, shots, granules, grids and Pb-C particulates; Sn shots and granules. The last five of the above materials were used in another embodiment for the current example. In some embodiments, a deposit having a high (specific) surface area micro- or nanostructure on a 3D substrate is desirable. Other potential cathodes are instead of Pb, In or Hg as electroactive surfaces, Cu with nanostructures on Cu mesh, Sn with nanostructures on Sn mesh, or Sn-coated plastic It is a mesh.

Reactor A using a granular tin cathode (99.9 wt% Sn) and a feed gas of 100% CO ₂ performed slightly better than that of a tin plated copper mesh cathode. Reactor B, scaled up 7-fold, supplied a 100% CO ₂ feed gas with a water-soluble catholyte and an anolyte [0.5M KHCO ₃ + 2MKCl] and 2MKOH, respectively, from 350 kPa (abs) to 600 kPa (abs). And an outlet temperature of 295K to 325K. At a surface current density of 0.6 kAm ^{−2 to} 3.1 kAm ⁻² , the reactor B has a reactor voltage in the same range as that in the reactor A (2.7 V or more and 4.3 V or less), and 91% to 63%. % Corresponding formate current efficiency was achieved. In one pass of reactor B, a maximum of 1M formate was obtained as the catholyte product.

[Example 2] [Regeneration of cathode activity]
The electrochemical reactor described in Example 1 was configured and operated as follows.
・ Anode feeder = 316 stainless steel plate ・ Anode = 304 stainless steel, number 10 mesh (10 mesh / inch)
-Anode spacer = PVC "fly screen" 10 mesh-Separator = Nafion 117 cationic membrane-Cathode = Tin granule of about 50 mesh (height 150 mm, width 32 mm, thickness 3 mm)
-Cathode surface area = 45E-4m ²
Cathode feeder = Tin foil supported on a copper plate Operating conditions:
-Current = 6A (eg 1.3 kA / m ² )
Catholyte = 0.45M KHCO ₃ + 2M KCl, anolyte = 1M KOH, anolyte flow = 40 ml / min CO ₂ gas flow = 364 ml (STP) / min, catholyte flow = 20 ml / min Temperature = 300K, Pressure = 140 kPa (abs) or more and 170 kPa (abs) or less The current efficiency (CE) of formate using a cathode of unused tin granules is about 60% at 30 minutes operating time to 50% at 250 minutes operating time. Fell to. The regeneration of the current efficiency was achieved by the following.

  (I) Cathodic chemical treatment and recycling: The used cathode tin granules were treated with 11 wt% nitric acid for 2 minutes at room temperature, washed with deionized water and reused in the reactor. Table 1 shows that this treatment regenerated the cathode activity at 30 minutes operating time.

使用したスズ顆粒の塩酸及び／又は水酸化カリウムでの処理によっても、陰極再生について同様の結果が得られた。

Similar results for cathodic regeneration were obtained by treatment of the used tin granules with hydrochloric acid and / or potassium hydroxide.

  (Ii) Polarity reversal: Under the same conditions as above, unused tin granules reduced the formate current efficiency from about 65% at 30 minutes operating time to 48% at 360 minutes operating time. Polarity reversal was applied to the reactor at 1A for 5 minutes. The formate current efficiency then increased and returned to 65% at 400 minutes operating time.

[Example 3] [Scale-up]
The electrochemical reactor described in Example 1 was configured and operated as follows.
・ Anode feeder = 316 stainless steel plate ・ Anode = 304 stainless steel, number 10 mesh (10 mesh / inch)
-Anode spacer = PVC "fly screen", 10 mesh-Separator = Nafion 117 cationic membrane-Cathode = approx. 50 mesh tin granules (height 680 mm, width 50 mm, thickness 3 mm)
-Cathode surface area = 340E-4m ²
-Cathode feeder = 2 mm thick tin plate operating conditions:
Catholyte = 0.45M KHCO ₃ + 2MKCl, anolyte = 2M KOH, anolyte flow rate = 60 ml / min CO ₂ gas flow rate = 1600 ml (STP) / min to 2200 ml (STP) / min, catholyte flow rate = 20 ml / min / temperature in-out = 300 K or more and 314 K or less, pressure in-out = 600 kPa (abs) or less and 100 kPa (abs) or more Table 2 shows the performance of this reactor.

〔実施例４〕［酸性陽極液］
反応器を実施例１のように構成し、動作は実施例２のように行った。但し、陽極液は以下のような酸性の硫酸ナトリウム溶液に置き換えた。
動作条件：
・陰極液＝０．４５Ｍ ＫＨＣＯ_３ ＋ ２Ｍ ＫＣｌ
・陽極液＝０．５Ｍ以上２Ｍ以下のＮａ_２ＳＯ_４ ＋ ０．５Ｍ以上４Ｍ以下のＨ_２ＳＯ_４、陽極液流量＝４０ｍｌ／分
・ＣＯ_２ガス流量＝５００ｍｌ（ＳＴＰ）／分、陰極液流量＝２０ｍｌ／分
・温度＝３００Ｋ、圧力＝１４０ｋＰａ（ａｂｓ）以上１７０ｋＰａ（ａｂｓ）以下
上記反応器は、１Ａ〜１４Ａ（０．２ｋＡ／ｍ^２〜３．１ｋＡ／ｍ^２）の電流で、８０％〜３０％の対応するギ酸塩ＣＥ、３．５Ｖ〜８．０Ｖの反応器電圧で動作させた。

[Example 4] [Acid anolyte]
The reactor was configured as in Example 1 and the operation was performed as in Example 2. However, the anolyte was replaced with an acidic sodium sulfate solution as follows.
Operating conditions:
Catholyte = 0.45M KHCO ₃ + 2M KCl
・ Anolyte = 0.5M or more and 2M or less Na ₂ SO ₄ + 0.5M or more and 4M or less H ₂ SO ₄ , anolyte flow = 40 ml / min ・ CO ₂ gas flow = 500 ml (STP) / min, catholyte Flow rate = 20 ml / min, temperature = 300 K, pressure = 140 kPa (abs) or more and 170 kPa (abs) or less The above reactor has a current of 1 A to 14 A (0.2 kA / m ^{2 to} 3.1 kA / m ² ), 80 % -30% of the corresponding formate CE, operated at a reactor voltage of 3.5V-8.0V.

This result shows that the method can be carried out with an acidic anolyte. Various ratios of Na ⁺ / H ⁺ in the anolyte gave different formate current efficiencies, indicating that formate CE can be improved by manipulating the anolyte composition.

[Example 5] [Ammonium cation]
In some embodiments, the invention can utilize an ammonium cation to produce an ammonium formate salt.

The reactor was configured in the same manner as in Example 1 as in Example 4 except that the potassium cation in the catholyte was replaced with ammonium and the anolyte was replaced with an acidic ammonium sulfate solution. It was made to work.
Operating conditions:
Current = 4A (ie 0.89kA / m ² )
Catholyte = 0.45M NH ₄ HCO ₃ + 2M NH ₄ Cl
Catholyte = 0.93M (NH ₄ ) ₂ SO ₄ + 0.754MH ₂ SO ₄ , anolyte flow rate = 40 ml / min CO ₂ gas flow rate = 500 ml (STP) / min, catholyte flow rate = 20 ml / min Temperature = 300K, pressure = 140 kPa (abs) or more and 170 kPa (abs) or less The above reactor is in the range of 35% or more and 70% or less formate CE, with a reactor voltage of 4.6V or more and 5.2V or less, 2 Operated for more than an hour.

  This result revealed that the above method can use the ammonium cation alone in the catholyte. The ability to use ammonium cations is illustrated in process flow sheets B and C for the production of formic acid or ammonium formate.

[Example 6] [Lead cathode]
The electrochemical reactor described in Example 1 was constructed and operated as follows.
・ Anode feeder = 316 stainless steel plate ・ Anode = 304 stainless steel, number 10 mesh (10 mesh / inch)
-Anode spacer = PVC "fly screen" 10 mesh-Separator = Nafion 117 cationic membrane-Cathode = lead shot with a diameter of 0.5 mm (height 150 mm, width 32 mm, thickness 3 mm)
-Cathode surface area = 45E-4m ²
・ Cathode feeder = Lead plate Operating conditions:
Current = 6A (ie 1.3 kA / m ² )
Catholyte = 0.45M KHCO ₃ + 2M KCl, anolyte = 1M KOH, anolyte flow = 40 ml / min. CO ₂ gas flow = 364 ml (STP) / min, catholyte flow = 20 ml / min. Temperature = 300K Pressure = 140 kPa (abs) or more and 180 kPa (abs) or less The operation of the reactor for 2 hours or more and 6 hours or less showed a constant formate current efficiency of 31 +/− 1%.

[Example 7] [Process Flow Sheet A]
The method of this example is illustrated in FIG. 6 and shows the electrosynthesis of sodium formate from carbon dioxide, water and sodium hydroxide.

Based on the concept of FIG. 5, this method (FIG. 6) converts CO ₂ to NaHCO ₂ (sodium formate) and NaHCO ₃ (sodium bicarbonate), by-products of H ₂ (hydrogen) and O ₂ (oxygen). Convert with by-products. The feed plus recycled CO ₂ is compressed to about 300 kPa (abs) and fed to the cathode of the electrochemical reaction along with the recycled catholyte, NaHCO ₂ and NaHCO ₃ aqueous solutions. The cathode outlet goes to a gas / liquid separator where the liquid from the gas / liquid separator is separated directly into a recycle and stream, and the NaHCO ₂ and NaHCO ₃ from the stream are the main cathode products (NaHCO ₂ and NaHCO 3). ₃ ) separated by evaporation and fractional crystallization to give. The cathode outlet gas proceeds to a gas separation system (eg, pressure swing adsorption) that regenerates hydrogen and sends unconverted CO ₂ to recycle. On the anode side of this method, the sodium amount of NaOH (Na ⁺ ) moves across the cation membrane while NaOH (sodium hydroxide) is converted to oxygen regenerated as a by-product from the gas / liquid separator. , NaOH supply is included. The recycle flow in this process includes the necessary compressors and pumps, as well as heat exchangers (eg, C1, C2, C3) that control the reactor temperature to a range of about 300K to 350K.

FIG. 7 illustrates process flow sheet A and shows a steady state mass balance flow table based on 600 tons / day CO ₂ . Formate current efficiency = 77%, CO ₂ conversion / pass = 72%.

〔実施例８〕［プロセスフローシートＢ］
図８は、二酸化炭素及び水からギ酸の電気合成を説明する。例示された方法では、ＣＯ_２を、Ｈ_２（水素）の副生物及びＯ_２（酸素）の副産物と共に、ＨＣＯ_２Ｈ（ギ酸）へ変換する。リサイクルＣＯ_２を加えた供給は、約３００ｋＰａ（ａｂｓ）に圧縮され、（必要に応じて）ＮＨ_４Ｃｌ若しくは（ＮＨ_４）_２ＳＯ_４等の支持電解質を加えた、リサイクル陰極液、ＮＨ_４ＨＣＯ_２及びＮＨ_４ＨＣＯ_３の水溶液と共に、電気化学反応器（Ｕ１）の陰極へ供給される。上記陰極出口の流れは、ガス／液体セパレータ（Ｕ３）へ進行し、Ｕ３からの液体は、熱化学的酸分解反応器／セパレータ（Ｕ６、Ｕ７）へ通過する直接リサイクル及び流れの中へ分配される（Ｕ５）。ここで、ギ酸が硫酸（陽極液で生成）との反応９により得られ、部分減圧下で蒸留され、ギ酸水溶液のオーバーヘッド生成物と、混合器Ｕ８を経て陽極へリサイクルされる（ＮＨ_４）_２ＳＯ_４のボトム溶液とが得られる。Ｕ３からのガスの流れは、Ｈ_２が再生され、ＣＯ_２が混合器Ｕ２を経て、原料が送り込まれる反応器へリサイクルされるセパレータ（Ｕ４）を、酸分解反応器での副反応７により生成するＣＯ_２と共に通る。

[Example 8] [Process Flow Sheet B]
FIG. 8 illustrates the electrosynthesis of formic acid from carbon dioxide and water. In the illustrated method, CO ₂ is converted to HCO ₂ H (formic acid) along with by-products of H ₂ (hydrogen) and by-products of O ₂ (oxygen). The supply with recycled CO ₂ is compressed to about 300 kPa (abs) and, if necessary, recycled catholyte, NH ₄ HCO with support electrolyte such as NH ₄ Cl or (NH ₄ ) ₂ SO ₄ added. Together with an aqueous solution of ₂ and NH ₄ HCO ₃ , it is fed to the cathode of the electrochemical reactor (U1). The cathode exit stream proceeds to the gas / liquid separator (U3), and the liquid from U3 is distributed into the direct recycle and stream passing to the thermochemical acidolysis reactor / separator (U6, U7). (U5). Here, formic acid is obtained by reaction 9 with sulfuric acid (generated with anolyte), distilled under partial vacuum, and recycled to the anode via an overhead product of aqueous formic acid and a mixer U8 (NH ₄ ) ₂ A bottom solution of SO ₄ is obtained. The gas flow from U3 is produced by side reaction 7 in the acidolysis reactor where H ₂ is regenerated and CO ₂ is recycled to the reactor through which the raw material is fed through the mixer U2. through with CO ₂ to.

An aqueous solution of (NH ₄ ) ₂ SO ₄ and H ₂ SO ₄ is recycled via the anodic route to supply NH ₄ ⁺ and H ⁺ cations that are transported to the catholyte via the cation membrane. The by-product O ₂ gas is produced together with protons (H ⁺ ) at the anode by reaction 4 and is regenerated from the gas / liquid separator (U9). The recycled acidic anolyte is separated (U10) to supply H ₂ SO ₄ for the acid decomposition reaction (U6), and the spent reactants from the acid decomposition reaction are mixed again with the anolyte ( U8).

2NaHCO ₂ + H ₂ SO ₄ → 2HCO ₂ H + Na ₂ SO ₄ reaction 9
The raw material and energy (M & E) balance operated in steady state in Flow Sheet B is shown in the following flow table. This M & E balance is based on the assumption that the formate current efficiency is 80% and the CO ₂ conversion per pass through the electrochemical reactor is 80%.

  The first and second substantial reactions in flow sheet B are reactions 10 and 11, respectively.

CO ₂ + H ₂ O → HCO ₂ H + 1 / 2O ₂ reaction 10
H ₂ O → H ₂ + 1 / 2O ₂ reaction 11
The conditions of this process can be selected to promote the main substantial reaction 10. The properties of this example method that promote reaction 10 can be selected as follows.
i. Appropriate electrode materials, current density, fluid composition, fluid load, pressure and temperature in electrochemical reactors
ii. With respect to acids and salts that provide cation transport across the membrane at the exact ratio (eg, H ⁺ / NH ₄ ⁺ ) that balances the ratio of cathodic reactions 1 and 2 and maintains the catholyte pH in the desired range. Maintaining liquid composition
iii. Bulk catholyte pH in the range of about 4 to 10 (preferably 6 to 8)
iv. Flow to provide protons for acidolysis reactions that maintain the anolyte composition and produce HCO ₂ H at U6 and allow the aqueous formic acid to be regenerated by evaporation at U7. Catholyte acid (eg, H ₂ SO ₄ ) concentration above 1M
vi. Maintain the formate concentration of the catholyte high enough to allow the formation and separation of HCO ₂ H at U6.
vii. Formate (HCO ₂ ⁻ ) concentration in recycled catholyte higher than about 1M, preferably higher than about 5M
viii. Supply water to the cathode and / or anode path at an appropriate ratio to maintain water balance and electrolyte concentration that facilitates both electrochemical and thermochemical methods at U1, U6 and U7.
ix. Maintaining recycle anolyte flow and temperature high enough to utilize Joule heating of the electrochemical reactor for evaporation of formic acid at U6 x. At the same time as the anolyte flow determined by the energy balance that reduces the need for heating utilized in the above method, the recycle anolyte temperature above about 320 K. The implementation of the above method is usually performed under the conditions i to x listed above. It depends on the mutual influence between them. The modeling of this embodiment provides a steady state feed and energy balance based on 105 tons / day CO ₂ that yields 80% current efficiency and 80% CO ₂ conversion / pass. The raw material and energy balance flow table corresponding to process flow sheet B is shown below with a table that continues over three dependent tables.

〔実施例９〕［プロセスフローシートＣ］
図９は、二酸化炭素、アンモニア及び水からのギ酸アンモニウムの電気合成を説明する。この方法は、ＣＯ_２及びＮＨ_３をＮＨ_４ＨＣＯ_２（ギ酸アンモニウム）へ、Ｈ_２（水素）の副生物及びＯ_２（酸素）の副産物と共に変換する。

[Example 9] [Process Flow Sheet C]
FIG. 9 illustrates the electrosynthesis of ammonium formate from carbon dioxide, ammonia and water. This method converts CO ₂ and NH ₃ to NH ₄ HCO ₂ (ammonium formate), with by-products of H ₂ (hydrogen) and by-products of O ₂ (oxygen).

Feed with recycled CO ₂ is compressed and electrochemical reactor with recycled catholyte, NH ₄ HCO ₂ aqueous solution (eg> 1M) with a small amount of NH ₄ HCO ₃ (ammonium bicarbonate, eg 0.1M) To the cathode. The cathode outlet flow proceeds to a separation system that recovers NH ₄ HCO ₂ solution, plus by-product hydrogen, and recycles the spent catholyte.

Ammonia (NH ₃ gas or aqueous solution) is supplied to the anolyte path, which mixes to form (NH ₄ ) ₂ SO ₄ (ammonium sulfate). The aqueous solution of (NH ₄ ) ₂ SO ₄ and H ₂ SO ₄ is then recycled via the anodic pathway and supplies NH ₄ ⁺ and H ⁺ cations for transport to the catholyte via the cation membrane. The co-product O ₂ gas is generated with protons (H ⁺ ) at the anode by reaction 4 and regenerated from the gas / liquid separator. The ratio of [NH ₄ ⁺ ] / [H ⁺ ] is in the pH range of about 4 or more and 8 or less, balancing the stoichiometry of Reactions 1 and 2 to produce most of the ammonium formate catholyte solution. In the anolyte so that these species are fed to the catholyte at a ratio.

  The first and second substantial reactions in the flow sheet C are reactions 12 and 13, respectively.

CO ₂ + H ₂ O + NH ₃ → NH ₄ HCO ₂ + 1 / 2O ₂ reaction 12
H ₂ O → H 2 + 1 / 2O ₂ reaction 13
The various schemes can include, for example, exchange of (NH ₄ ) ₂ SO ₄ and H ₂ SO _{4 in} the anolyte with (NH ₄ ) ₃ PO ₄ and H ₃ PO ₄ or NH ₄ Cl and HCl. . In the latter case, the anode by-product can be Cl _{2 from} reaction 5. Anode by-products can include peroxy compounds, such as ammonium persulfate (NH ₄ ) ₂ S ₂ O ₈ , or persulfate H ₂ S ₂ O ₈ , from reaction 14.

^{_{2SO 4 - → S 2 O 8}} - + 2e - reaction 14
[References]
Kirk-Othmer-Encyclopedia of Chemical Technology. John Wiley, NewYork, 1991
R. Chaplin and A. Wragg. "Effects of process conditions and electrode material on reaction pathways for carbon dioxide electroreduction with particular reference to formate formation". J. Appl. Electrochem. 33: 1107-1123 (2003)
CMSanchez et al. "Electrochemical approaches to alleviation of the problem of carbon dioxide accumulation". Pure Appl. Chem. 73 (12), 1917-1927, 2001
Y. Akahori et al. "New electrochemical process for CO ₂ reduction to formic acid from combustion flue gases" .Denki Kagaku (Electrochemistry) 72 (4) 266-270 (2004)
Li Hui and C. Oloman. "The electro-reduction of carbon dioxide in a continuous reactor". J. Appl. Electrochem. 35, 955-965, (2005)
K. Hara and T. Sakata. "Electrocatlytic formation of CH ₄ from CO ₂ on a Pt gas diffusion electrode". J. EIectrochem. Soc. 144 (2), 539-545 (1997)
MN Mahmood, D.Masheder and CJHarty. "Use of gas-diffusion electrodes for high rate electrochemical reduction of carbon dioxide". J. Appl. Electrochem. 17: 1159-1170 (1987)
KS Udupa, GS Subramamian and HVK Udupa. Electrochim Acta 16, 1593, 1976
While various embodiments of the above invention have been disclosed herein, various adaptations and modifications can be made within the scope of the invention based on the general knowledge of those skilled in the art. Such modifications also include the substitution of known equivalents in any feature of the invention described above to achieve the same result in substantially the same way. The numerical range includes a number defining the above range. The word “comprising” is used herein as an unrestricted word and is substantially the same as the phrase “including” but is not limited and the word “comprising” Has meaning. As used herein, the singular forms “a”, “an”, and “the” clearly include plural support objects unless the context indicates otherwise. Thus, for example, reference to “a thing” includes one or more such things. Reference herein to a cited document is not an admission that such a cited document is prior art to the present invention. Any conventional literature and all publications, including but not limited to the patents and patent applications mentioned in this specification, are individually and individually incorporated by reference in their entirety. Is incorporated herein by reference as if implied and as if fully set forth herein. The invention described above substantially includes all embodiments and variations as referred to above by way of example and drawings.

FIG. 1 is a process flow sheet for explaining the characteristics of the method of Example 1, where A = ammeter, P = pressure gauge, T = thermometer, V = voltmeter, W = wet gas flow meter, PC = pressure. It is a control. FIG. 2 is a schematic diagram of the electrochemical cell of the invention described in Example 1, wherein the reference numerals in the figure refer to the following components: 1 and 2: cell body, 2, 7 and 9: gasket, 3: anode Feeder, 4: anode spacer, 5: membrane, 6: 3-D cathode (tin coated copper mesh, tin shot / granule, and Pb shot / granule), 8: cathode feeder. FIG. 3 shows a front view in cross section of a single cell reactor of the invention as reactor A described in more detail in Example 1. FIG. 4 shows a front view in section of a single cell reactor of the invention as reactor B described in more detail in Example 1. FIG. 5 is a process flow sheet illustrating various features of a continuous process for the conversion of CO ₂ to formate or formic acid, including the recycling of catholyte and anolyte. FIG. 6 illustrates the implementation of a method for converting CO ₂ to NaHCO ₂ (sodium formate) and NaHCO ₃ (sodium bicarbonate), along with by-products of H ₂ (hydrogen) and co-products of O ₂ (oxygen). It is a process flow sheet (flow sheet “A”) for explaining the form. FIG. 7 is a formalized version of process flow sheet A made on the basis of a steady state mass balance flow chart for a method of converting about 600 tons / day of carbon dioxide gas to sodium formate. FIG. 8 illustrates the process flow sheet B, and is a corresponding material and energy balance flow table in the above embodiment for the process flow sheet B. FIG. 9 illustrates the process flow sheet C of the above embodiment.

Claims (33)

An electrochemical method for reducing carbon dioxide,
a) passing the catholyte mixture continuously through the cathodic chamber of the electrochemical reactor, the catholyte mixture containing carbon dioxide gas and a liquid catholyte solvent containing dissolved carbon dioxide;
b) maintaining a volumetric retention ratio of gas to catholyte liquid such that the ratio of the volume of gas to the volume of liquid catholyte solvent in the cathode chamber is greater than about 0.1;
c) passing an electric current between the cathode and the anode in the cathode chamber so as to reduce the dissolved carbon dioxide to form the desired product;
Including methods.   The method of claim 1, wherein a volumetric supply rate of the gas (modified to STP) to the liquid to the cathode chamber is greater than about one. Effective surface current density at the cathode is greater than 1 kA / m ^2, The method of claim 1 or 2.   The method according to claim 1, 2 or 3, wherein the partial pressure of carbon dioxide gas in the cathode chamber is less than 10 bar.   The method according to claim 1, wherein the current is a direct current driven by an electrochemical cell voltage.   The method of claim 5, wherein the electrochemical cell voltage is less than 10V.   The method according to any one of claims 1 to 6, wherein the fluid in the cathode chamber is maintained at a cathode temperature higher than 20 ° C. The cathode chamber is maintained at cathode pressure;
The method according to any one of claims 1 to 7, wherein the cathode pressure is in a range of 1 bar (100 kPa (abs)) to 10 bar (1000 kPa (abs)).   The method according to any one of claims 1 to 8, wherein the catholyte is an aqueous solution.   10. The method of claim 9, wherein the catholyte solvent comprises dissolved alkali metal bicarbonate or formate, or dissolved ammonium bicarbonate or formate.   The method according to claim 9, wherein the bulk pH of the catholyte solvent is in the range of 4 to 10.   The method of claim 9, wherein the catholyte solvent comprises an ammonium cation.   The method according to any one of claims 1 to 12, wherein the thickness of the cathode in the dimension of current flow is 0.5 mm or more and 10 mm or less.   The method of claim 13, wherein the cathode has a porosity or porosity of about 5% or more and about 95% or less.   15. A method according to any one of claims 1 to 14, wherein the cathode comprises tin or lead. The anode is in the anode chamber,
The method according to claim 1, wherein the anode chamber is separated from the cathode chamber by an electrochemical cell membrane.   The method of claim 16, wherein the anodic chamber comprises an anolyte.   The method of claim 17, wherein the anolyte is an aqueous anolyte. The anolyte is
a) dissolved alkali metal hydroxide,
b) dissolved alkali metal or ammonium salt,
c) a dissolved acid that becomes H ₂ SO ₄ , HCl, or H ₃ PO ₄ ;
d) dissolved sulfuric acid and ammonium sulfate, or e) dissolved sulfuric acid and sodium sulfate,
The method of claim 18 comprising:   The method of claim 18, wherein the anolyte comprises ammonium ions.   The method of claim 16, wherein the electrochemical cell membrane is a cation permeable membrane.   The method of claim 16, wherein the electrochemical cell membrane causes selected ions to traverse the membrane so as to balance the stoichiometry of the method.   23. A method according to any one of claims 1-22, wherein the desired product comprises formate or formic acid.   24. The method of claim 23, wherein the formate salt is ammonium formate.   25. A method according to any one of the preceding claims, further comprising the step of separating the desired product from the catholyte solvent.   The method according to any one of claims 1 to 24, further comprising a step of recycling at least a part of the catholyte solvent and the recycled catholyte solvent from the cathode chamber outlet to the cathode chamber inlet.   27. The method of claim 26, further comprising separating the desired product from the recycled catholyte solvent.   The method according to any one of claims 1 to 27, further comprising a step of recycling at least part of the anolyte and the recycled anolyte from the anolyte chamber outlet to the anolyte chamber inlet.   30. The method of claim 28, further comprising separating an anode byproduct from the recycled anolyte.   30. A method according to any one of claims 1 to 29, further comprising Joule heating the anolyte to provide a heated anolyte. Further comprising the step of joule heating the anolyte, resulting in a heated anolyte,
28. The method of claim 27, wherein the heated anolyte is used to heat the recycled catholyte solvent to separate water or the desired product from the recycled catholyte solvent by evaporation.   27. The method of claim 26, further comprising reacting a recycled catholyte containing formate with the anolyte to obtain the desired product by an acidolysis reaction. Recycling at least part of the anolyte and recycle anolyte from the anolyte chamber outlet to the anolyte chamber inlet,
The method of claim 32, wherein the anolyte used to obtain the desired product is part of the recycled anolyte.

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