A device and method for producing CH4 by electrochemical reduction of CO2 using microorganisms that can be scaled up industrially

Abstract

The application discloses a device and method for producing CH4 by reducing CO2 through microbial electrochemistry, which can be amplified industrially. The device comprises a cathode chamber and a plurality of tubular anode chambers, each of which is provided with an anode electrode, and the cathode chamber is provided with a cathode electrode, and the cathode and anode electrodes are connected to form a loop through a stabilized direct-current power supply; the anode chambers and the cathode chamber are separated by a cation exchange membrane; the cathode chamber is provided with a gas circulation passage for re-introducing the generated mixed gas into the cathode chamber to realize the recycling of unreacted gas. The application realizes the proportional amplification from the laboratory scale to the pilot scale by operating in the multi-electrode parallel mode and high current density, significantly improves the CO2 reduction rate, and realizes the proportional amplification from the laboratory scale to the pilot scale; excess CO2 is introduced, the pH of the cathode chamber is stable, and external acid-base adjustment is not needed. The application solves the problems of slow CO2 reduction rate, inability to realize industrial amplification and low CH4 concentration of the existing microbial electrochemistry device, and provides an efficient and industrially amplifiable technical scheme for the resource conversion of CO2.

Description

Technical Field

[0001] This invention relates to an industrially scalable apparatus and method for the electrochemical reduction of CO2 by microorganisms to produce CH4, belonging to the field of microbial electrochemistry. Background Technology

[0002] CH4, as a renewable energy source, can be converted from CO2 through electro-methanation in a microbial electrolysis cell (MEC). This process can be divided into two pathways: direct electro-methanation and indirect electro-methanation. In direct electro-methanation, methanogenic bacteria use the electrodes as electron donors to directly reduce CO2 to CH4. Indirect electro-methanation uses H2 generated from water electrolysis as an electron medium to further drive the reduction of CO2. The H2-mediated indirect pathway does not rely on the formation of a biofilm on the cathode surface and can theoretically withstand higher current densities, thereby improving CO2 conversion efficiency.

[0003] Although microbial electrochemical reduction of CO2 to CH4 technology has shown promising application prospects in the laboratory, it still faces many bottlenecks in practical industrial applications. Existing MEC systems generally suffer from the following problems: Low CO2 conversion rate: Due to limitations in biofilm activity, electron transfer efficiency, and reactor structure, the CO2 reduction rate of existing systems is far lower than that of non-bioelectrochemical conversion technologies. The CH4 concentration is not high: The CH4 concentration in the product gas is usually below 80%, containing a large amount of unreacted H2 and CO2, making it difficult to use directly as a high-grade fuel; Scale-up difficulties: Existing devices are mostly limited to laboratory scale (<10 L) and lack structural designs suitable for pilot or industrial scale-up, which prevents their processing capacity from being increased proportionally. High operating costs: The system has poor pH stability and often requires the addition of acid / base adjusters, which increases the complexity and cost of operation.

[0004] Therefore, developing a microbial electrochemical reduction device and method for producing CH4 from CO2 that is efficient, stable, low-cost, and has industrial scale-up potential is of great practical significance and application value. Summary of the Invention

[0005] The purpose of this invention is to provide an industrially scalable device and method for the electrochemical reduction of CO2 to CH4 by microorganisms, which solves the problems of low reduction rate of CO2 to CH4, low concentration of CH4 produced gas, and inability to be applied industrially in existing electrochemical devices and methods for microorganisms, and realizes efficient and low-carbon CH4 production and simultaneous purification and recovery.

[0006] The present invention provides an industrially scalable microbial electrochemical reduction device for CO2 to CH4 production, which is an anaerobic microbial reactor comprising: A cathode chamber; Multiple anode chambers; Each of the anode chambers is provided with at least one anode electrode, and each of the cathode chambers is provided with at least one cathode electrode; The anode chamber and the cathode chamber are separated by an ion exchange membrane; The cathode electrode and the anode electrode are connected by a regulated DC power supply to form a circuit; The maximum voltage of the regulated DC power supply can be 30 V, the maximum current can be 10 A, and the current sensitivity is ≥10. -6 A; The device is provided with a gas circulation passage for reintroducing the gas generated in the cathode chamber into the cathode chamber.

[0007] The main body of the device is made of acrylic glass plate with a thickness of 0.5 cm; The working volume of the cathode chamber can be 250L (Φ58 cm × 99 cm), and the working volume of the anode chamber can be 3L (Φ8 cm × 75 cm).

[0008] Preferably, the anode chambers are tubular structures, and there are 6 of them, which are evenly arranged around the cathode chamber; Each of the anode chambers contains two anode electrodes and is separated by a partition (made of acrylic glass).

[0009] Preferably, the cathode electrode is a stainless steel mesh electrode, and the anode electrode is a titanium mesh electrode coated with iridium oxide. More preferably, the cathode electrode is a 20-mesh 304 stainless steel mesh, 29 cm long, 22 cm high, and has an electrode area of ​​638 cm². 2 ; The anode electrode is 3 cm long, 30 cm high, and 0.2 cm thick, and is coated with IrO2.

[0010] The ion exchange membrane is a cation exchange membrane (such as CMI-7000S) with a thickness of 0.45 mm and a resistivity of less than 30 Ω·cm. 2 Maximum current density less than 500 A / m 2 Maximum operating temperature: 90℃; pH range: 1~10.

[0011] Preferably, the cathode chamber is equipped with a pH meter probe, a temperature control probe, and a stirring device; The cathode chamber is equipped with a water bath circulation layer to maintain the reaction temperature at 35℃~37℃.

[0012] Preferably, the gas circulation path includes a gas sampling bag, a circulating gas pump, and connecting pipes, for the purpose of recycling the gas inside the cathode chamber.

[0013] The device of this invention can be used in industrial-scale microbial electrochemical reduction of CO2 to CH4. The specific principle is as follows: CO2 enters the cathode chamber via a gas pump and is captured by methanogenic bacteria suspended in the chamber; in the anode chamber, water is electrolyzed at the anolyte to produce H2O. + And O2, O2 escapes out of the device through the top of the anode chamber, H + The electrons then pass through the cation exchange membrane into the cathode chamber; the regulated DC power supply creates a pathway between the cathode and anode electrodes, transferring electrons to the cathode electrode, where the hydrogen evolution reaction occurs, producing H2 and OH-. - H2 is captured by methanogenic bacteria and CO2 is reduced to CH4. The generated CH4 and unreacted H2 and CO2 are collected at the outlet of the cathode chamber using a gas sampling bag; the gas generated in the cathode chamber is pumped back into the cathode chamber using a gas circulation device, so that the unused H2 and CO2 are fully utilized, and CH4 is purified and recovered.

[0014] This invention further provides an industrially scalable method for the electrochemical reduction of CO2 by microorganisms to produce CH4, comprising the following steps: Add cathodic solution and methanogenic bacteria to the cathode chamber, and add anodic solution to the anode chamber; Introduce CO2 and apply an electric current; The cathode chamber gas is recycled through a gas circulation pathway. Collect and purify the generated CH4.

[0015] The current is applied in a constant current mode, with a current range of 0.5A to 3A. The CO2 intake rate is matched with the current intensity, and the H2 / CO2 ratio is controlled to be approximately 3.8:1 to 3.9:1.

[0016] The catholy solution contains a phosphate buffer system, trace elements, and vitamins; Specifically, the composition of the catholyte is as follows: 5.5 g / L Na2HPO4, 7.2 g / L KH2PO4, 0.54 g / L NH4Cl, 1 g / L NaCl, 0.2 g / L MgCl2·6H2O, 0.015 g / L CaCl2, 10 mL / L trace element solution, 0.1 mL / L vitamin solution, and adjust the pH to 6.8~7.0 using 5 mol / L NaOH; The composition of the trace element SL-10 solution is as follows: 10 mL / L HCl (25%, 7.7 mol / L), 0.1 g / L MnCl2·4H2O, 1.5 g / L FeCl2·4H2O, 0.07 g / L ZnCl2·4H2O, 0.19 g / L CoCl2·6H2O, 0.024 g / L NiCl2·6H2O, 0.002 g / LCuCl2·2H2O, 0.006 g / L H3BO3, 0.036 g / L Na2MoO4·2H2O; The vitamin solution has the following composition: 0.02 mg / L Vitamin H, 0.02 mg / L Folic Acid, 0.1 mg / L Vitamin B6 Hydrochloride, 0.05 mg / L Vitamin B1 Hydrochloride, 0.05 mg / L Vitamin B2, 0.05 mg / L Niacin, 0.05 mg / L D-Calcium Pantothenate, 0.05 mg / L Vitamin B5, 0.001 mg / L Vitamin B12, 0.05 mg / L Para-aminobenzoic Acid, 0.05 mg / L Alpha-lipoic Acid, in ultrapure water; The pH of the cathode chamber is maintained between 6.8 and 7.5; The anolyte contains a phosphate buffer system; Specifically, the composition of the anolyte is: 5.5 g / L Na2HPO4, 7.2 g / L KH2PO4.

[0017] The methanogenic bacteria are derived from anaerobic granular sludge, and the inoculation amount of anaerobic granular sludge in the cathode chamber is 100-200 mL / L.

[0018] This invention increases the number of anode chambers and electrodes on the basis of the traditional bipolar chamber, realizing the production, purification and recovery of CH4 in a multi-electrode system microbial electrochemical reactor.

[0019] Compared with the prior art, the present invention has the following beneficial technical effects: (1) The device is equipped with multiple anode chambers, and the combined action of multiple electrodes greatly increases the ability to reduce CO2 to CH4, thus realizing the scale-up of CO2 processing capacity from laboratory scale to pilot scale; (2) The gas circulation device allows the CO2 and H2 that are not fully utilized in the cathode chamber to circulate in the cathode chamber, thereby achieving the production of high-concentration CH4 biogas. (3) Using a high current mode operating device, methanogenic bacteria suspended in the cathode chamber are used as functional microorganisms, breaking through the limitations of the cathode biofilm and achieving a higher CO2 processing capacity. (4) When an excess of CO2 is introduced into the reactor at an H2 / CO2 ratio of 3.9:1, the pilot reactor can stably provide suitable growth conditions for methanogenic bacteria suspended in the cathode chamber. It is not necessary to add acid or alkali to the reactor to maintain pH, which can reduce the operating cost of the pilot plant. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of the operation of the industrially scalable microbial electrochemical reduction of CO2 to CH4 apparatus of the present invention; Figure 2 The curve showing the change in methane production in the gas collection bag of the cathode chamber of the device of the present invention as a function of current intensity and time; Figure 3 The curve showing the change of methane concentration in the gas collection bag of the cathode chamber of the device of the present invention with current intensity and time. Figure 4 This is a pH change curve over time for a pilot-scale microbial electrochemical reduction of CO2 to CH4 device based on the multi-electrode system of this invention.

[0021] Figure 1 The markings in the text are as follows: 1-Positive terminal of regulated DC power supply, 2-Negative terminal of regulated DC power supply, 3-Regulated DC power supply, 4-Stirring device, 5-Sealer, 6-Cathode chamber outlet, 7-pH meter probe and temperature probe, 8-Water bath circulation layer outlet, 9-Water bath circulation layer inlet, 10-Water bath circulation layer, 11-Cathode chamber outlet, 12-Cathode chamber inlet, 13-CO2 cylinder, 14-Gas flow meter, 15-Gas circulation pump, 16-Gas sampling bag, 17-CO2 inlet, 18-Circulating gas inlet, 19-Aeration stone, 20-Anode chamber, 21-Cathode electrode, 22-Cation exchange membrane, 23-Cathode chamber, 24-Anode electrode. Detailed Implementation

[0022] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0023] Unless otherwise specified, all materials and reagents used in the following examples are commercially available.

[0024] This invention provides an industrially scalable apparatus and method for the electrochemical reduction of CO2 by microorganisms to produce CH4, aiming to solve the problems of low CO2 conversion rate, low CH4 purity, and difficulty in achieving industrial scale-up in existing microbial electrochemical systems.

[0025] The device includes a cathode chamber and multiple tubular anode chambers arranged around the cathode chamber. Each anode chamber contains an anode electrode, and each cathode chamber contains a cathode electrode. The anode and cathode electrodes are connected by a regulated DC power supply to form a circuit. The anode chamber and the cathode chamber are separated by a cation exchange membrane. The cathode chamber is provided with a gas circulation passage for reintroducing the generated mixed gas into the cathode chamber to achieve the recycling of unreacted gas.

[0026] The method includes: adding cathodic liquid and methanogenic bacteria to the cathode chamber, and adding anodic liquid to the anode chamber; introducing CO2 and applying a constant current of 0.5A to 3A; circulating the mixed gas of CH4, H2 and CO2 generated in the cathode chamber back through a gas circulation device to improve the utilization rate of H2 and CO2, while purifying CH4; and collecting high-concentration CH4 biogas.

[0027] This invention significantly improves the CO2 reduction rate through a multi-electrode parallel system and high current density operation, achieving proportional scale-up from laboratory to pilot-scale (250 L); the CH4 concentration is stabilized above 92%, reaching up to 95%; with an H2 / CO2 ratio of 3.9:1, excess CO2 is introduced, and the pH of the cathode chamber is stabilized between 6.8 and 7.5, eliminating the need for external acid or alkali adjustment; gas recycling reduces H2 escape and improves energy utilization efficiency.

[0028] This invention has the advantages of high conversion efficiency, high product purity, stable operation, reasonable structure, energy saving and environmental protection, and provides an efficient and industrially scalable technical solution for the resource utilization of CO2.

[0029] The cathode used in the following embodiments is a 20-mesh 304 stainless steel mesh with the following structural parameters: length 29 cm, height 22 cm, and electrode area 638 cm². 2 The anode electrode is a titanium mesh, 3 cm long, 30 cm high, and 0.2 cm thick, with an IrO2 coating. The cation exchange membrane used in the following examples is a CMI-7000S model, with a thickness of 0.45 mm and a resistivity of less than 30 Ω·cm. 2 Maximum current density less than 500 A / m 2 The maximum operating temperature is 90℃, and the pH range is 1~10. The pH meter and temperature probes are glass electrodes, 15.5 cm in length, with an operating temperature of 0℃~80℃ and an accuracy of ±0.02. The regulated DC power supply has a maximum voltage of 30 V, a maximum current of 10 A, and a current sensitivity ≥10. -6 A.

[0030] Example 1, Device Construction like Figure 1As shown, the present invention provides an industrially scalable device for the electrochemical reduction of CO2 by microorganisms to produce CH4, which is an anaerobic microbial reactor, and the main body material is an acrylic glass plate with a thickness of 0.5 cm.

[0031] The device includes a cathode chamber 23 and six tubular anode chambers 20. The working volume of the cathode chamber 23 is 250 L (Φ58 cm × 99 cm), and the working volume of each anode chamber 20 is 3 L (Φ8 cm × 75 cm). The six anode chambers 20 are evenly arranged around the cathode chamber 23, with a spacing of 5 cm between adjacent anode chambers 20.

[0032] Each anode chamber 20 contains two anode electrodes 24, and a partition (made of acrylic glass) separates the two anode electrodes 24 inside the anode chamber 20. The anode chamber 20 and the cathode chamber 23 are separated by a cation exchange membrane 22. The cation exchange membrane 22 used in this embodiment is a CMI-7000S type, with a thickness of 0.45 mm and a resistivity of less than 30 Ω·cm. 2 Maximum current density less than 500 A / m 2 Maximum operating temperature: 90℃; pH range: 1–10.

[0033] The cathode chamber 23 contains a cathode electrode 21, a pH meter probe and a temperature control probe 7, and a stirring device 4. The cathode electrode 21 is made of 20-mesh 304 stainless steel mesh, with dimensions of 29 cm in length and 22 cm in height, and a single electrode area of ​​638 cm². 2 The cathode electrodes 21 are wrapped around the surface of the anode chambers 20, with a total of 12 cathode electrodes 21 corresponding to 6 anode chambers 20. The pH meter probe and temperature control probe 7 are glass electrodes, 15.5 cm in length, with an operating temperature of 0℃~80℃ and an accuracy of ±0.02, used for real-time monitoring of the water quality characteristics of the cathode chambers 23.

[0034] The anode electrode 24 is a titanium mesh electrode with dimensions of 3 cm in length, 30 cm in height, and 0.2 cm in thickness, and its surface is coated with an IrO2 coating.

[0035] The cathode electrode 21 is connected to the negative terminal 2 of the regulated DC power supply 3 via a wire, and the anode electrode 24 is connected to the positive terminal 1 of the regulated DC power supply 3 via a wire. The regulated DC power supply 3 has a maximum voltage of 30 V, a maximum current of 10 A, and a current sensitivity ≥10. -6 A.

[0036] A water bath circulation layer 10 is provided outside the cathode chamber 23. The water bath circulation layer 10 is provided with a water bath circulation layer inlet 9 and a water bath circulation layer outlet 8. It is connected to the water bath circulation device through a peristaltic pump to maintain the working temperature of the cathode chamber 23 at 35℃~37℃.

[0037] The bottom of the cathode chamber 23 is equipped with a CO2 inlet 17 and a circulating gas inlet 18, both of which are connected to the aeration stone 19 to improve gas dissolution efficiency. The CO2 inlet 17 is connected to the CO2 cylinder 13 via a gas flow meter 14. The circulating gas inlet 18 is connected to the cathode chamber outlet 6 via a gas circulation pump 15, forming a gas circulation path. The cathode chamber outlet 6 is also connected to a gas sampling bag 16 for collecting the generated CH4 and unreacted H2 and CO2.

[0038] The cathode chamber 23 is also equipped with a cathode chamber inlet 12 and a cathode chamber outlet 11 for replacing and discharging the cathode solution. A sealing device 5 is provided on the top of the cathode chamber 23 to ensure the airtightness of the device.

[0039] Example 2, Material Preparation The catholy solution used in this embodiment has the following composition: 5.5 g / L Na2HPO4, 7.2 g / L KH2PO4, 0.54 g / L NH4Cl, 1 g / L NaCl, 0.2 g / L MgCl2·6H2O, 0.015 g / L CaCl2, 10 mL / L trace element solution, 0.1 mL / L vitamin solution, and adjust the pH to 6.8~7.0 using 5 mol / L NaOH; The composition of the trace element SL-10 solution is as follows: 10 mL / L HCl (25%, 7.7 mol / L), 0.1 g / L MnCl2·4H2O, 1.5 g / L FeCl2·4H2O, 0.07 g / L ZnCl2·4H2O, 0.19 g / L CoCl2·6H2O, 0.024 g / L NiCl2·6H2O, 0.002 g / LCuCl2·2H2O, 0.006 g / L H3BO3, 0.036 g / L Na2MoO4·2H2O; The vitamin solution is composed of the following: 0.02 mg / L Vitamin H, 0.02 mg / L Folic Acid, 0.1 mg / L Vitamin B6 Hydrochloride, 0.05 mg / L Vitamin B1 Hydrochloride, 0.05 mg / L Vitamin B2, 0.05 mg / L Niacin, 0.05 mg / L D-Calcium Pantothenate, 0.05 mg / L Vitamin B5, 0.001 mg / L Vitamin B12, 0.05 mg / L Para-aminobenzoic Acid, 0.05 mg / L Alpha-lipoic Acid, in ultrapure water; The anolyte used in this embodiment has the following composition: 5.5 g / L Na2HPO4 and 7.2 g / L KH2PO4.

[0040] The methanogenic bacteria used in this embodiment are derived from anaerobic granular sludge. Before use, the anaerobic granular sludge is crushed, and the inoculation amount is 100 mL / L of cathodic solution.

[0041] Example 3: Preparations before device operation Follow these steps to prepare for device operation: (1) Cut the cation exchange membrane 22 to a size of 55 cm long and 26 cm wide, soak it in deionized water for 24 h, then soak it in cathodic solution for 24 h, and then attach it to the fan-shaped window of the anode chamber 20 to ensure that the cathode chamber 23 and the anode chamber 20 are separated by the cation exchange membrane 22. (2) Place the cathode electrode 21 (stainless steel mesh) in the cathode chamber 23, wrap it around the surface of the anode chamber 20, and connect it to the negative terminal interface 2 of the regulated DC power supply 3 through a wire; place the anode electrode 24 (iridium oxide titanium mesh) in the anode chamber 20, and connect it to the positive terminal interface 1 of the regulated DC power supply 3 through a wire; (3) Constructing a gas circulation path: Connect the cathode chamber outlet 6, gas sampling bag 16, gas circulation pump 15 and circulating gas inlet 18 in sequence through pipelines to ensure that the gas can circulate in the cathode chamber 23; (4) Constructing a water bath circulation path: Connect the water inlet 9 and outlet 8 of the water bath circulation layer to the water bath circulation device through pipelines, and realize water bath circulation through a peristaltic pump; (5) Connect CO2 cylinder 13 to CO2 inlet 17 via gas flow meter 14 to control CO2 intake rate; (6) Add the prepared cathodic solution to the cathode chamber 23 and inoculate it with crushed anaerobic granular sludge at a rate of 100 mL / L cathodic solution; add the prepared anodic solution to the anode chamber 20.

[0042] Example 4: Equipment Operation and CH4 Production After completing the above preparations, start the device by following these steps: (1) Turn on the water bath circulation device to continuously circulate 40°C hot water to the water bath circulation layer 10 to maintain the working temperature of the cathode chamber 23 at 35°C to 37°C. (2) Turn on the regulated DC power supply 3 and apply a constant current to the cathode electrode 21. In this embodiment, four current intensity conditions of 0.5A, 1.0A, 2.0A and 3.0A were tested respectively. (3) Open CO2 cylinder 13 and control the CO2 intake rate through gas flow meter 14. Introduce excess CO2 into cathode chamber 23 at a ratio of H2 / CO2 of 3.9:1. The rate of CO2 introduction varies under different current intensities. When the current is 3A, the CO2 flow rate is 73 mL / min. (4) Turn on the gas circulation pump 15 to reintroduce the mixed gas (CH2, H2 and CO2) generated in the cathode chamber 23 through the gas circulation path to realize the recycling of gas; (5) Each reaction cycle is 24 hours. After the cycle ends, replace the gas sampling bag 16 and replenish CO2. (6) The contents of CH4, H2 and CO2 in gas sampling bag 16 were determined by gas chromatograph (GC 7900). The chromatographic conditions were: carrier gas N2, injection port temperature 140℃, column oven temperature 120℃, detector temperature 150℃, and current 50 mA. The total volume of gas in gas sampling bag 16 was determined by direct measurement method, and the average yield and concentration of CH4 were calculated.

[0043] Example 5, Execution Results The device was operated under different current intensities according to the method in Example 4, and the results are as follows: Figures 2-4 As shown.

[0044] Figure 2 This is a curve showing the change in methane production in the gas collecting bag of the cathode chamber of the device of the present invention as a function of current intensity and time. Figure 2 It can be seen that under high current conditions, the CH4 generated in the cathode chamber gradually accumulates in the gas collection bag. The CH4 production rate increases accordingly with increasing current, and the pilot-scale device exhibits stable CH4 production performance under various current conditions. At a current of 3A, the CH4 production rate reaches 100 L / d.

[0045] Figure 3 This is a curve showing the change in methane concentration in the gas collecting bag of the cathode chamber of the device of the present invention as a function of current intensity and time. Figure 3 It can be seen that when the CH4 production performance of the pilot device reaches stability under various current conditions, the CH4 concentration in the gas collection bag remains stable at over 92%, reaching a maximum of 95%. This indicates that the pilot device can rapidly reduce CO2 to produce CH4 under high current conditions while simultaneously generating biogas with a high CH4 concentration. The generated biogas can be directly used for combustion power generation, further reducing the operating cost of the device.

[0046] Figure 4 This is a pH change curve over time in a pilot-scale microbial electrochemical reduction of CO2 to CH4 device using the multi-electrode system of this invention. Figure 4 It can be seen that the pH of the reactor catholyte remained stable between 6.8 and 7.25, providing favorable survival conditions for the functional microorganisms in the cathode zone. This indicates that introducing excess CO2 with an H2 / CO2 ratio of 3.9:1 can effectively maintain pH stability within the device without the need for additional acid / alkali solutions, thus reducing the operating costs of the device.

[0047] Example 6: Verification of Gas Circulation Effect To verify the effectiveness of the gas circulation device, a comparative experiment was set up in this embodiment.

[0048] The experimental group was run according to the method in Example 4 (with the gas circulation pump turned on), while the control group was exactly the same as the experimental group except that the gas circulation pump was not turned on. Both experiments were run at a current of 3A for a reaction period of 7 days, and the CH4 concentration in the gas sampling bag was measured daily.

[0049] The results showed that the CH4 concentration in the experimental group reached over 88% on day 3 and stabilized at 89.5%–92% after day 5; while the CH4 concentration in the control group remained below 80%, with a maximum of only 79.9%. This indicates that the gas circulation pathway can effectively reintroduce unreacted H2 and CO2 into the cathode chamber, improving their utilization rate and thus achieving CH4 purification.

[0050] Example 7: Scale-up Verification of Multi-Electrode System To verify the scale-up effect of the multi-electrode system, this embodiment compares the device of this invention (250 L) with a laboratory-scale device (5 L). The laboratory-scale device uses a single anode chamber and a single pair of electrodes, with other operating conditions identical to the device of this invention (current density remains the same). Both devices operate at a current density of 0.5 A / m. 2 Under the same conditions, the CH4 yield per unit volume was compared.

[0051] The results show that the CH4 yield per unit volume of the device of the present invention is 0.42 L / L·d, and the CH4 yield per unit volume of the laboratory-scale device is 0.45 L / L·d, which is basically the same. This indicates that the device of the present invention, through a multi-electrode parallel mode, successfully achieves a proportional scale-up of the CO2 reduction CH4 production performance from the laboratory scale to the pilot-scale.

[0052] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Those skilled in the art can make various improvements and modifications without departing from the spirit and principles of the invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An industrially scalable apparatus for the electrochemical reduction of CO2 to CH4 by microorganisms, comprising an anaerobic microbial reactor, including: A cathode chamber; Multiple anode chambers; Each of the anode chambers is provided with at least one anode electrode, and each of the cathode chambers is provided with at least one cathode electrode; The anode chamber and the cathode chamber are separated by an ion exchange membrane; The cathode electrode and the anode electrode are connected by a regulated DC power supply to form a circuit; The device is provided with a gas circulation passage for reintroducing the gas generated in the cathode chamber into the cathode chamber.

2. The apparatus according to claim 1, characterized in that: The anode chamber is a tubular structure, and there are 6 of them, which are evenly arranged around the cathode chamber; Each of the anode chambers is provided with two anode electrodes, separated by a partition.

3. The apparatus according to claim 1 or 2, characterized in that: The cathode electrode is a stainless steel mesh electrode, and the anode electrode is a titanium mesh electrode coated with iridium oxide. The ion exchange membrane is a cation exchange membrane.

4. The apparatus according to claim 1 or 2, characterized in that: The cathode chamber is equipped with a pH meter probe, a temperature control probe, and a stirring device; The cathode chamber is equipped with a water bath circulation layer to maintain the reaction temperature at 35℃~37℃.

5. The apparatus according to claim 1 or 2, characterized in that: The gas circulation pathway includes a gas sampling bag, a circulating gas pump, and connecting pipes, which are used to recycle the gas inside the cathode chamber.

6. The application of the apparatus according to any one of claims 1-5 in industrial-scale microbial electrochemical reduction of CO2 to CH4.

7. A method for industrially scalable microbial electrochemical reduction of CO2 to CH4, comprising the following steps: Provide the apparatus according to any one of claims 1-5; Add cathodic solution and methanogenic bacteria to the cathode chamber, and add anodic solution to the anode chamber; Introduce CO2 and apply an electric current; The cathode chamber gas is recycled through a gas circulation pathway. Collect and purify the generated CH4.

8. The method according to claim 7, characterized in that: The current is applied in a constant current mode, with a current range of 0.5A to 3A. The CO2 intake rate is matched with the current intensity, and the H2 / CO2 ratio is controlled at 3.8:1 to 3.9:

1.

9. The method according to claim 7 or 8, characterized in that: The catholy solution contains a phosphate buffer system, trace elements, and vitamins; The pH of the cathode chamber is maintained between 6.8 and 7.5; The anolyte contains a phosphate buffer system.

10. The method according to claim 7 or 8, characterized in that: The methanogenic bacteria are derived from anaerobic granular sludge, and the inoculation amount of anaerobic granular sludge in the cathode chamber is 100-200 mL / L.

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