Carbon dioxide electrolytic reduction reactor

Abstract

The invention provides a carbon dioxide electrolysis reactor, a plurality of layers of plate-shaped electrodes are arranged in the reactor, the electrode structure is a tower plate, and the plate-shaped electrodes are alternately arranged in a central opening and edge opening mode, so that an electrolyte is in a baffling flowing state, and the circulation of the electrolyte is accelerated. The electrode plate directly faces the rising direction of the bubbles, so that the lower surface of the electrode plate is covered by a carbon dioxide gas film, the concentration of carbon dioxide on the surface of the electrode is improved, a gas-liquid-solid three-phase region beneficial to mass transfer of carbon dioxide is formed, and a higher reaction rate is obtained. Compared with the existing reactor, the reactor disclosed by the invention has the following advantages: (1) the reduction electrode is formed by processing a conductive material with catalytic activity through a certain process, and has the advantages of high strength, wear resistance and capability of being manufactured in a large area; (2) large scale is easy to realize: the tower-plate-shaped electrodes are arranged in the bubble tower layer by layer to form a reactor with a plate-type tower structure; and (3) high conversion rate can be obtained.

Description

Technical Field

[0001] The invention relates to the technical field of electrolytic reduction, and in particular to a reactor for electrolytic reduction of carbon dioxide. Background Art

[0002] The electrochemical reduction of carbon dioxide is a reaction using carbon dioxide, electrons and water as raw materials. By adjusting the reduction potential, a series of products can be obtained: 16 oxygen-containing compounds and hydrocarbons such as CO, formic acid, methane, methanol and ethylene.

[0003] With the rapid development of CO2 reduction technology, new high-performance catalysts continue to emerge. Nanocatalysts of various forms (including zero-dimensional and two-dimensional sizes), metal-organic framework catalysts, nanocluster catalysts, molecular catalysts and single-atom catalysts have shown good performance. However, research on reactor development is very limited, and almost all of it is focused on the development of gas diffusion electrode reactors.

[0004] Although the use of gas diffusion electrodes greatly improves the current density, there are the following problems in engineering applications:

[0005] (1) Very sensitive to inlet pressure. When the cathode chamber contains electrolyte, if the pressure difference between the liquid phase pressure and the gas phase pressure is not equal, convection flow will occur and the reactor cannot operate normally. When the gas phase pressure is too high, the carbon dioxide gas on the back will flow into the electrolyte in a bubbling manner and react with the electrolyte (usually 1M KOH), causing carbon dioxide loss; when the liquid phase pressure is too high, the electrolyte will penetrate into the diffusion electrode, causing "flooding", so that the electrode is immersed in liquid and decomposes its structure. The most ideal situation is that the pressure difference is 0, but even so, there is still the problem of salt precipitation.

[0006] (2) Salting out problem. Salting out problem is caused by two factors: one is the capillary suction phenomenon. Since the gas diffusion electrode is a porous structure, the electrolyte will penetrate into the gas phase along the capillary path. As the water evaporates continuously, it will eventually form crystals. The other is that under high current density, the concentration of hydroxide ions at the reaction site on the electrode surface is significantly higher than that in the liquid phase, causing a series reaction of carbon dioxide conversion into bicarbonate and carbonate. The gas channel is easily blocked by salt particles produced by salting out.

[0007] (3) Catalyst shedding problem. Since the gas diffusion electrode is immersed in the electrolyte for a long time and the catalyst is bonded to the surface of the microporous layer, it is easy to fall off. Once it falls off, the thickness at the falling position is the thinnest and the resistance is the smallest, becoming the channel for carbon dioxide to pass through first, and the gas directly enters the electrolyte without reacting.

[0008] (4) When the processing volume is large or a high conversion rate is required, the battery cells need to be used in parallel or in series (CN219793137U). Since the components are very thin and fastened together, once problems such as salt precipitation, flooding, and catalyst shedding occur, each electrolytic cell needs to be opened one by one, making maintenance work very difficult. Although the electrodes can also be made into tubular shapes (e.g., CN117448853 A), there is no report on the tubular structure so far, and large-scale production cannot be achieved by relying on a single tube. Summary of the invention

[0009] In view of the above problems, the present invention proposes a carbon dioxide electrolytic reduction reactor with a plate tower structure, and the technical solution is as follows:

[0010] A carbon dioxide electrolytic reduction reactor comprises a reaction section with a plurality of layers of plate-shaped electrodes; the plate-shaped electrodes have central openings or edge openings and are arranged alternately as a whole, so that the electrolyte is in a baffled flow state, thereby achieving a better fluid mixing function.

[0011] The reactor is a bubbling tower structure, and further comprises an upper head and a lower head respectively insulated and connected to the reaction section, wherein the lower head is an air inlet section, and the upper head is a gas-liquid separation section.

[0012] The plate-shaped electrode is made of electrode material with catalytic activity.

[0013] The wall of the reaction section is made of a porous metal material, and the metal material has electrolytic reduction catalytic activity or is an inert metal conductor.

[0014] The vessel wall is connected to the plate-shaped electrode to form a connected conductor and is connected to the negative electrode of the power supply.

[0015] The plate-shaped electrodes of all adjacent layers have central openings and edge openings, respectively.

[0016] The outer surface of the wall of the reaction section is coated with an ion exchange membrane, which is used to prevent the molecules in the cathode chamber and the anode chamber from mixing, while ensuring the ion transfer between the cathode chamber and the anode chamber.

[0017] The negative electrode of the power supply is connected to the cathode chamber, and the positive electrode of the power supply is connected to the anode chamber.

[0018] Compared with the prior art, the electrolytic reduction reactor proposed in the present invention has the following characteristics and innovations:

[0019] (1) The plate-shaped reduction electrode of the present invention is made of porous electrode materials (such as metal plates, metal meshes, metal mesh-carbon material composite plates, etc.) through a certain process, and has the advantages of high strength, wear resistance, and large-scale production. The gas diffusion electrode of the prior art is obtained by coating a slurry made of catalyst powder, conductive material, hydrophobic material, and ion polymer on carbon paper, with a total thickness of only 0.2-0.3 mm, low strength, easy to break, and difficult to prepare on a large scale.

[0020] (2) The multi-layer plate-shaped electrode of the present invention forms a reduction electrode as a whole, which has a simple structure and is easy to install. The distance between the cathode chamber and the anode chamber is short, the solution resistance is very small, and it is easy to achieve large-scale. In contrast, the gas diffusion electrode of the prior art can only use each electrode sheet as a cathode and requires an anode to correspond to it, which is extremely costly and difficult to scale up.

[0021] (3) In the electrolytic reduction reactor of the present invention, since the electrode plate is facing the rising direction of the bubbles, the lower surface of the electrode plate is covered by a carbon dioxide gas film, which increases the carbon dioxide concentration on the electrode surface and forms a gas-liquid-solid three-phase region that is conducive to carbon dioxide mass transfer. As the carbon dioxide bubbles rise layer by layer, the conversion rate will continue to increase, and finally a high conversion rate will be obtained. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a structural diagram of a reactor of the present invention;

[0023] Figure 2 is a flow state diagram of electrolyte inside the reactor of the present invention;

[0024] Figure 3 is a diagram showing the contact state between carbon dioxide gas and the electrode surface of the reactor of the present invention;

[0025] Figure 4 Schematic diagram of the beneficial effects obtained by performing hydrophobic treatment on the surface of the reactor electrode of the present invention;

[0026] Figure 5 It is a schematic diagram showing the variation of carbon dioxide conversion rate with flow rate.

[0027] Explanation of symbols:

[0028] 1 gas inlet; 2 lower end cap; 3 cathode electrolyte; 4 ion exchange membrane; 5 reaction section wall; 6 plate electrode; 7 reaction section; 8 upper end cap; 9 gas outlet; 10 anode electrolyte; 11 anode chamber; 12 anode; 13 power supply. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described below with reference to the accompanying drawings.

[0030] Example 1

[0031] The carbon dioxide electrolytic reduction reactor of this embodiment includes: a cathode chamber containing a cathode electrolyte 3 and an anode chamber 11 containing an anode 12 and an anode electrolyte 10, and the carbon dioxide electrolytic reduction reaction is completed in the cathode chamber. Figure 1 As shown, carbon dioxide enters the cathode chamber (or carbon dioxide reduction reactor) from the gas inlet 1, mixes with the cathode electrolyte 3 in the lower head 2, and dissolves into the electrolyte. Carbon dioxide gas moves upward by bubbling, contacts the plate electrodes 6 at different installation heights, undergoes a reduction reaction, and generates carbon monoxide. Each plate electrode 6 is connected to the reaction section wall 5 to form a conductor. The area between the bottom plate electrode 6 and the top plate electrode 6 constitutes the reaction section 7. After leaving the reaction section 7, carbon dioxide gas enters the upper head 8 and is finally discharged through the gas outlet 9. The electrolyte level in the upper head 8 accounts for 1 / 3 to 1 / 2 of the height of the upper head 8. The surface of the reaction section wall 5 is wrapped with an ion exchange membrane 4, which separates the anode chamber 11 from the cathode chamber to avoid mixing of substances between the two chambers, thereby allowing only ions to pass through. The negative pole of the power supply 13 is connected to the cathode chamber, and the positive pole is connected to the anode chamber 11.

[0032] Example 2

[0033] The method for manufacturing the electrolytic reduction reactor of Example 1 includes the following steps:

[0034] Step 1: Cut metals with carbon dioxide catalytic reduction activity such as zinc plates, copper plates, copper mesh, etc. into tower plate shapes (round or square). Open a large hole in the center of 1 / 2 of the tower plates, and open several small holes on the edges of the remaining tower plates. Cut a section of metal plate or mesh, roll it into a cylinder or cut it into a quadrilateral to make the reactor tower wall. Place the two types of tower plates alternately in the height direction, according to Figure 1 Install it in the middle section of the reactor, and wrap a layer of Nafion117 cation exchange membrane on the outside of the middle section wall to form the reaction section. Fix the upper and lower heads to the middle section through insulating gaskets to complete the assembly of the entire reactor. Add a certain amount of water to the reactor until the water level reaches 1 / 2 of the height of the upper head. Open the carbon dioxide inlet pipe at the lower head and the exhaust pipe valve at the upper head, let in air, and observe whether the reactor has any leakage or gas leakage. Finally, use a multimeter to measure whether the connection between each layer of tower plates and the wall is normal, and whether the upper and lower heads are insulated.

[0035] Step 2: Figure 1A certain amount of electrolyte is added to the carbon dioxide reduction reactor shown, and the liquid level reaches half of the upper head space. The electrolyte can be an alkali metal salt aqueous solution, preferably a 0.1M KHCO3 solution, which has a certain buffering capacity and is close to neutral (pH = 6.81), does not consume carbon dioxide, and potassium ions can promote the activation of carbon dioxide molecules on the electrode surface. Figure 1 0.1M KHCO3 solution is added into the anode chamber shown, and the electrode is a platinum mesh. The positive and negative electrodes of the power supply are connected to the platinum mesh of the anode chamber and the wall of the reactor in the cathode chamber respectively to form an electrolytic reaction working circuit.

[0036] Example 3

[0037] A certain flow of carbon dioxide gas is introduced into the electrolytic reduction reactor of Example 1 from the inlet pipe, and carbon dioxide can bubble and flow in the tower. Since the multi-layer plate-shaped electrodes have a baffle effect, the circulation of the electrolyte is promoted. The flow condition is as follows: Figure 2 As shown. During the upward flow, carbon dioxide bubbles are hindered by the plate electrode, and thus gather at the bottom of the electrode to form a gas covering layer (referred to as a gas film), while the upper surface of the plate electrode is completely covered by the electrolyte, as shown. Figure 3 This gas film is very favorable for the reaction, allowing carbon dioxide to directly penetrate into the electrode and react in the presence of electrons, water, and carbon dioxide.

[0038] After carbon dioxide is introduced into the reactor for 10 minutes, the fluid mechanics state in the reactor is basically stable, and the power supply can be turned on to start the electrolysis reaction. In order to illustrate whether the gas film covering the lower surface of the electrode is conducive to the reaction, this example conducted a comparative experiment of hydrophilic and hydrophobic electrode surfaces, in which the hydrophobic surface is conducive to gas enrichment.

[0039] At a current density of -5 mA cm -2 、-15mA·cm -2 、-25mA·cm -2 and -35mA·cm -2 During the electrolysis process, there is a significant difference between the zinc foam with a hydrophilic surface (liquid-solid contact angle of 28.3°) and the zinc foam with a polytetrafluoroethylene-treated lower surface (liquid-solid contact angle of 102.1°), indicating that increasing the hydrophobicity of the electrode surface can increase the carbon dioxide enrichment capacity, promote carbon dioxide mass transfer, and facilitate the electroreduction reaction. Figure 4 It can be seen that when hydrophilic zinc foam trays are used, the carbon monoxide Faraday efficiency (FE CO ) changes in a volcano-shaped curve, at -5 mA·cm -2 86.5% at -15 mA·cm -2 When the current density continues to increase, FE COStart to decrease from -25mA·cm -2 83.4% of the time was reduced to -35 mA·cm -2 In contrast, the hydrophobic zinc foam plate at -5 mA·cm -2 A high Faradaic efficiency of 96.5% is achieved at -15mA·cm -2 When the -2 When the -2 It can still reach 87.6%.

[0040] The above two types of zinc foam are made into single blocks with an area of ​​25cm 2 The four-layer electrode plate was inserted into the cathode chamber and carbon dioxide was introduced to conduct electrolysis test. The test was conducted at five gas flow rates of 30, 60, 90, 120, and 150 ml / min. The carbon dioxide conversion rate was as follows: Figure 5 When hydrophilic zinc foam is used, the carbon dioxide conversion rates under five gas flow rates are 59.7%, 29.8%, 19.9%, 14.9%, and 11.9%, respectively, and the CO selectivity is between 71% and 73%; when hydrophobic zinc foam is used, the carbon dioxide conversion rates under five gas flow rates are 71.3%, 35.6%, 23.7%, 17.8%, and 14.2%, respectively, and the CO selectivity is between 84% and 86%.

[0041] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A carbon dioxide electrolytic reduction reactor, characterized in that: The reactor comprises a reaction section with multiple layers of plate-shaped electrodes; the plate-shaped electrodes have central openings or edge openings and are arranged alternately as a whole.

2. The reactor according to claim 1, characterized in that The reactor is a bubbling tower structure, and further comprises an upper head and a lower head respectively insulated and connected to the reaction section, wherein the lower head is an air inlet section, and the upper head is a gas-liquid separation section.

3. The reactor according to claim 1, characterized in that The plate-shaped electrode is made of electrode material with catalytic activity.

4. The reactor according to claim 1, characterized in that The wall of the reaction section is made of a porous metal material, and the metal material has electrolytic reduction catalytic activity or is an inert metal conductor.

5. The reactor according to claim 4, characterized in that The vessel wall is connected to the plate-shaped electrode to form a connected conductor and is connected to the negative electrode of the power supply.

6. The reactor according to claim 1, characterized in that The plate-shaped electrodes of all adjacent layers have central openings and edge openings, respectively.

7. The reactor according to claim 1, characterized in that The outer surface of the wall of the reaction section is coated with an ion exchange membrane.

8. The reactor according to claim 5, characterized in that The negative electrode of the power supply is connected to the cathode chamber, and the positive electrode of the power supply is connected to the anode chamber.

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