Device and method for microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery

Abstract

The present invention discloses a device and method for producing CH4 by electrochemical ectopic reduction of CO2 by microorganisms and simultaneous purification and recovery. The device is an anaerobic microbial reactor; the anaerobic microbial reactor includes a dissolution chamber, a cathode chamber and an anode chamber; a partition is arranged between the dissolution chamber and the cathode chamber, and a cation exchange membrane is arranged between the anode chamber and the cathode chamber; a cathode electrode and a reference electrode are arranged in the cathode chamber, and an anode electrode is arranged in the anode chamber, and the cathode electrode, the reference electrode and the anode electrode form a loop through an electrochemical workstation. The present invention improves the dissolution rate of CO2 and maintains the stability of the pH in the system by constructing a reflux channel between the cathode chamber and the dissolution chamber, thereby ensuring the efficient operation of the device. The device and method of the present invention solve the problem that the existing microbial electrochemical devices and methods cannot obtain high-concentration CH4 and are prone to H2 escape and energy loss, thereby realizing the production and simultaneous purification and recovery of CH4, and providing a theoretical reference for the resource conversion of CO2.

Description

Technical Field

[0001] The invention relates to a device and method for microbial electrochemical ectopic reduction of CO2 to produce CH4 and synchronous purification and recovery, belonging to the field of microbial electrochemistry. Background Art

[0002] In recent years, more and more attention has been paid to the resource utilization of CO2, using CO2 to synthesize fuels, chemicals, or directly converting it into reusable products such as carbonates. However, CO2 has high stability and is not easily directly activated or decomposed. In addition, the charge center of the CO2 molecule is asymmetric, which makes it difficult to be captured by active sites during the reaction. Therefore, a large amount of energy is consumed as the driving force of the reaction in the traditional chemical conversion, electrochemical conversion, and catalytic conversion process, and the energy utilization efficiency is low. In addition, a catalyst is required in the reaction to achieve efficient and stable catalysis, but the current catalyst cost is high, and the operating cost is significantly increased. The biological capture and conversion technology of CO2 reduces carbon emissions by converting CO2 into high-value-added products such as CH4 and organic acids. It has attracted widespread attention due to its mild conditions, simple reactions, and green environmental protection. However, compared with the physical and chemical conversion technology of CO2, the conversion rate of biotechnology is relatively low, which limits the industrial application of this technology. Studies in recent years have found that Methanosarcina barkeri Extracellular electrons and hydrogen can be used to reduce CO2 to produce CH4, and the CO2 conversion efficiency is increased by dozens of times after coupling with electrochemical technology. Methanosarcina barkeri The coupled electrochemical CO2 conversion technology has the advantages of high energy utilization efficiency, low economic cost and environmental friendliness.

[0003] A Chinese patent application (CN 109022495A) discloses a method for producing CH4 by reducing CO2 with microorganisms. The method uses platinum wire as an anode electrode, prepares a nitric acid-acetic acid mixed fiber film as a cathode electrode, and fills the cathode headspace with a mixture of CO2 and N2 as an inorganic carbon source, thereby achieving the production of CH4 from CO2 and increasing the yield of CH4. However, the CH4 produced in the cathode chamber of this method will mix with the gas in the headspace, reducing the calorific value of the gas and making it impossible to directly recycle it. In addition, the generated H2 cannot be fully utilized, resulting in H2 dissipation losses and reducing energy utilization efficiency. Therefore, it is of great significance to design a microbial electrochemical device and method to achieve efficient and low-carbon CH4 production and synchronous purification and recovery. Summary of the invention

[0004] The purpose of the present invention is to provide a device and method for microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery, which solves the problem that existing microbial electrochemical devices and methods cannot obtain high-concentration CH4 and easily cause H2 escape and lead to energy loss, and realizes efficient and low-carbon CH4 production and simultaneous purification and recovery.

[0005] The device of the present invention mainly consists of three parts: a dissolution chamber, a cathode chamber and an anode chamber. The cathode liquid reflux path realizes water circulation and material transmission. In this way, CO2 is dissolved in the dissolution chamber and enters the cathode chamber through the partition, and is absorbed by the methanogens attached to the cathode electrode ( Methanosarcina barkeri ) capture; the anode electrolyzes water in the anode chamber to produce H + and O2, O2 escapes from the device through the top of the anode chamber, H + The electrons enter the cathode chamber through the cation exchange membrane; the electrochemical workstation forms a pathway between the cathode electrode and the anode electrode and transmits electrons to the cathode electrode; the methanogens on the cathode electrode ( Methanosarcina barkeri ) using electrons or using H + The H2 generated by the electrons reduces CO2 to produce CH4. The gas sampling bag at the cathode chamber outlet is used to collect the generated CH4 and the incompletely reacted H2 and CO2, and the mixed gas is pumped back into the dissolution chamber through the gas circulation pump to dissolve the CO2 again. Since a liquid seal plate is provided between the dissolution chamber and the cathode chamber, the CH4 in the circulating gas is prevented from escaping to the cathode chamber again. Because the solubility of CH4 in water is low, CH4 will gradually be enriched in the gas collection bag at the outlet of the dissolution chamber, thereby achieving the purification and recovery of CH4. In addition, H2 can re-enter the cathode chamber with the water flow to participate in the reduction of CO2, reducing the energy loss caused by the escape of H2. In the cathode chamber, due to H + As CO2 is continuously consumed, the pH of the cathode liquid will rise. Returning the alkaline cathode liquid to the dissolution chamber will further increase the solubility of CO2. As CO2 dissolves again, the pH of the solution will gradually drop to neutral, thereby ensuring the efficient operation of the device. There is no need to add additional acid / alkaline solution, which reduces the operating cost of the device.

[0006] Specifically, the device for microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery is an anaerobic microbial reactor;

[0007] The anaerobic microbial reactor comprises a dissolution chamber, a cathode chamber and an anode chamber;

[0008] A partition is arranged between the dissolution chamber and the cathode chamber, and a cation exchange membrane (such as CMI-7000S) is arranged between the anode chamber and the cathode chamber;

[0009] The cation exchange membrane has a thickness of 0.45 mm and a resistance of less than 30 Ω.cm 2 , the maximum current density is less than 500A / m 2 , the maximum operating temperature is 90℃, and the applicable pH range is 1~10;

[0010] A cathode electrode and a reference electrode are arranged in the cathode chamber, and an anode electrode is arranged in the anode chamber. The cathode electrode, the reference electrode and the anode electrode form a loop through an electrochemical workstation.

[0011] The main body of the device of the present invention is made of a quartz glass plate, and the thickness of the quartz glass plate is preferably 0.5 cm.

[0012] In the device of the present invention, the cathode electrode is a graphite plate, preferably with a length of 35 cm, a height of 14 cm, a thickness of 0.4 cm, and a volume density of 1.82 g / cm 3 The through-plane resistance is 9.0 μΩ.m 2 ;

[0013] The anode is a titanium plate, preferably: 35 cm long, 14 cm high, 0.5 cm thick, and coated with RuO2 and IrO2;

[0014] The reference electrode is an Ag / AgCl electrode, with a pH range of 0-14, an operating temperature of 0°C-100°C, a length of 11 cm, and a body diameter of 1.2 cm;

[0015] In the device of the present invention, a gas collection bag is provided above the dissolution chamber to collect undissolved CO2 in the device and CH4 circulating in the cathode chamber;

[0016] A gas sampling bag is provided above the cathode chamber to collect CH4 produced in the cathode chamber and incompletely reacted H2 and CO2;

[0017] The gas collection bag and the gas sampling bag are both connected to the dissolution chamber through the dissolution chamber air inlet to form a gas circulation passage for the circulation of gas in the cathode chamber and the re-dissolution of CO2 in the dissolution chamber, while achieving the purification and collection of CH4 and the reuse of H2.

[0018] In the device of the present invention, the cathode chamber is provided with a cathode chamber water outlet, and the dissolution chamber is provided with a dissolution chamber water inlet. The cathode chamber water outlet is connected to the dissolution chamber water inlet to form a cathode liquid reflux path, which is used to reflux the cathode liquid to improve the CO2 dissolution efficiency in the dissolution chamber and maintain the stability of the pH of the device.

[0019] In the device of the present invention, a water flow hole is provided at the lower part of the partition plate for water circulation and material transmission between the dissolution chamber and the cathode chamber;

[0020] A liquid sealing plate is arranged between the dissolution chamber and the cathode chamber to isolate the exchange of headspace gas between the dissolution chamber and the cathode chamber, thereby preventing CH4 in the circulating gas from escaping into the cathode chamber again.

[0021] In the device of the present invention, the device is connected to a heating belt to maintain the temperature of the device at 35°C to 37°C;

[0022] The cathode chamber is provided with a pH meter probe and a temperature control probe for real-time monitoring of water quality characteristics of the cathode chamber.

[0023] The pH meter probe is a glass electrode with a length of 15.5 cm, an operating temperature of 0°C to 80°C, and an accuracy of ±0.02;

[0024] The temperature control probe is made of 304 stainless steel, with a probe diameter of 0.7 cm, a length of 15 cm, and a measurement range of -50°C to 150°C.

[0025] When the device of the present invention is used, the cathode liquid reflux path maintains the water circulation and material transport of the device. CO2 enters the dissolution chamber from the air inlet of the dissolution chamber, dissolves, and is transported to the cathode chamber by the water flow; the anode electrode electrolyzes water in the anode chamber to produce H + , H + It enters the cathode chamber through the cation exchange membrane; the methanogens in the cathode chamber use electrons and H2 to reduce CO2 to produce CH4. The CH4 produced in the cathode chamber and the incompletely utilized CO2 and H2 are collected by the gas sampling bag and transported to the dissolution chamber through the gas circulation path. After multiple cycles, the CH4 is purified and finally collected by the gas collection bag in the dissolution chamber.

[0026] Specifically, the method for producing CH4 by electrochemical ex situ reduction of CO2 by microorganisms and simultaneous purification and recovery provided by the present invention comprises the following steps:

[0027] S1, connecting the cathode electrode in the device to the working electrode interface of the electrochemical workstation, connecting the reference electrode to the reference electrode interface of the electrochemical workstation, and connecting the anode electrode to the auxiliary electrode interface of the electrochemical workstation;

[0028] S2, constructing a gas circulation passage between the gas collecting port of the dissolution chamber, the gas outlet of the cathode chamber and the gas inlet of the dissolution chamber, and realizing the circulation flow of the gas through a gas circulation pump;

[0029] S3, constructing a cathode liquid reflux passage between the water outlet of the cathode chamber and the water inlet of the dissolution chamber, and realizing the reflux of the cathode liquid by a peristaltic pump;

[0030] S4, adding cathode liquid and methanogens to the cathode chamber, and adding anolyte to the anode chamber;

[0031] S5, introducing CO2 into the dissolution chamber, turning on the electrochemical workstation, applying a constant potential of -0.4V~-0.8V to the cathode electrode, reducing CO2 to produce CH4 by methanogens in the cathode chamber, and collecting the CH4 at the cathode chamber outlet to participate in the gas circulation, thereby purifying and collecting the CH4;

[0032] The maximum voltage range of the electrochemical workstation is ±10 V, the potential accuracy is ±1 mV, and the current sensitivity is ≥10 -6 A.

[0033] The composition of the catholyte is as follows:

[0034] 6 g / L K2HPO4, 3 g / L KH2PO4, 0.5 g / L NH4Cl, 2 g / L NaCl, 0.45 g / L MgSO4·7H2O, 0.22 g / L CaCl2, 1 mL / L trace element solution, 0.1 mL / L vitamin solution, 1 mL / L FeSO4·6H2O (0.2% w / v H2SO4), pH adjusted to 6.8-7.0 with 5 mol / L NaOH;

[0035] The composition of the trace element SL-10 solution is as follows:

[0036] 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 solvent is ultrapure water;

[0037] The composition of the vitamin solution is as follows:

[0038] 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 p-aminobenzoic acid, 0.05 mg / L lipoic acid, the solvent is ultrapure water;

[0039] The composition of the anolyte is: 6 g / L K2HPO4, 3 g / L KH2PO4;

[0040] The methanogens are Methanosarcina barkeri , 10 mL to 20 mL of methanogens are inoculated per 100 mL of the cathode liquid;

[0041] In step S5, CO2 is introduced intermittently, and the reaction cycle is 15 to 20 days. Then, CO2 is replenished, and the anolyte and 70% to 90% of the catholyte are replaced.

[0042] The present invention adds a dissolution chamber on the basis of the traditional bipolar chamber, and directly realizes the production, purification and recovery of CH4 in a three-chamber microbial electrochemical reactor.

[0043] Compared with the prior art, the present invention has the following beneficial technical effects:

[0044] (1) Methanogens can reduce CO2 through multiple pathways (electrode electrons and H2), which improves the efficiency of CO2 reduction to produce CH4;

[0045] (2) A gas circulation passage constructed between the cathode chamber and the dissolution chamber allows the CH4 produced in the cathode chamber and the CO2 and H2 that are not completely reacted to circulate within the device, thereby achieving purification and recovery of the CH4 by utilizing the differences in the dissolution characteristics of different gases;

[0046] (3) The circulation of H2 in the device increases the residence time of H2, improves the utilization efficiency of H2, and avoids the energy loss caused by H2 escape, thus improving the energy utilization efficiency;

[0047] (4) The cathode liquid reflux path returns the alkaline cathode liquid to the dissolution chamber, thereby improving the CO2 dissolution efficiency, reducing the pH fluctuation caused by CO2 dissolution, keeping the pH in the device stable, and maintaining the efficient operation of the reaction. This eliminates the need to add additional acid / base solution to the reactor, thereby reducing the operating cost of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Figure 1 It is a schematic diagram of the operation of the microbial electrochemical ex situ reduction of CO2 to produce CH4 and the simultaneous purification and recovery device of the present invention;

[0049] Figure 2 The curve of the methane content and output in the gas collecting bag of the dissolution chamber of the device of the present invention changing with time;

[0050] Figure 3 This is a curve showing the change of pH over time in the device for producing CH4 with simultaneous purification and recovery using microbial electrochemical ectopic reduction of CO2.

[0051] Figure 1 The marks are as follows:

[0052] 1-reference electrode interface, 2-working electrode interface, 3-auxiliary electrode interface, 4-cathode electrode, 5-anode electrode, 6-reference electrode, 7-pH probe, 8-temperature control probe, 9-cation exchange membrane, 10-partition, 11-liquid seal plate, 12-dissolution chamber air inlet, 13-dissolution chamber water inlet, 14-dissolution chamber gas collecting port, 15-gas collection bag, 16-cathode chamber air outlet, 17-gas sampling bag, 18-cathode chamber water outlet, 19-peristaltic pump, 20-gas circulation pump, 21-gas circulation pump, 22-CO2 gas cylinder, 23-dissolution chamber, 24-cathode chamber, 25-anode chamber, 26-electrochemical workstation. DETAILED DESCRIPTION

[0053] Unless otherwise specified, the experimental methods used in the following examples are conventional methods.

[0054] Unless otherwise specified, the materials and reagents used in the following examples can be obtained from commercial sources.

[0055] The cathode used in the following examples is a graphite plate with the following structural parameters: length 35 cm, height 14 cm, thickness 0.4 cm, and volume density 1.82 g / cm 3 The through-plane resistance is 9.0 μΩ.m 2 ; The anode electrode is a titanium plate, 35 cm long, 14 cm high, 0.5 cm thick, with a coating of RuO2 and IrO2; the reference electrode is an Ag / AgCl electrode, with a pH range of 0-14, an operating temperature of 0℃-100℃, a length of 11 cm, and a body diameter of 1.2 cm;

[0056] The cation exchange membrane used in the following examples is CMI-7000S, with a thickness of 0.45 mm and a resistance of less than 30 Ω.cm. 2 , the maximum current density is less than 500 A / m 2 , the maximum operating temperature is 90℃, the pH applicable range is 1~10; the pH meter probe is a glass electrode, the length is 15.5 cm, the working temperature is 0℃~80℃, the accuracy is ±0.02; the temperature control probe is made of 304 stainless steel, the probe diameter is 0.7 cm, the length is 15 cm, and the measurement range is -50℃~150℃; the maximum voltage range of the electrochemical workstation is ±10V, the potential accuracy is ±1 mV, and the current sensitivity is ≥10 -6 A.

[0057] like Figure 1As shown, the device for microbial electrochemical ectopic reduction of CO2 to produce CH4 and synchronous purification and recovery provided by the present invention is an anaerobic reactor, including a dissolution chamber 23, a cathode chamber 24, an anode chamber 25, a cathode electrode 4, an anode electrode 5, a reference electrode 6, a cation exchange membrane 9, a partition 10, a liquid sealing plate 11, a dissolution chamber air inlet 12, a dissolution chamber water inlet 13, a dissolution chamber gas collection port 14, a cathode chamber air outlet 16, a cathode chamber water outlet 18, etc.

[0058] like Figure 1 As shown, the dissolution chamber 23 is separated from the cathode chamber 24 by a partition 10 and a liquid sealing plate 11, and the cathode chamber 24 is separated from the anode chamber 25 by a cation exchange membrane 9. The electrodes include a cathode electrode 4, an anode electrode 5 and a reference electrode 6, wherein the cathode electrode 4 is placed in the cathode chamber 24 and connected to the working electrode terminal 2 of the electrochemical workstation 26, the reference electrode 6 is placed in the cathode chamber 24 and connected to the reference electrode terminal 1 of the electrochemical workstation 26, and the anode electrode 5 is placed in the anode chamber 25 and connected to the auxiliary electrode terminal 3 of the electrochemical workstation 26.

[0059] like Figure 1 As shown, the pH probe 7 and the temperature control probe 8 are placed in the cathode chamber 24 to detect the water quality characteristics of the cathode liquid.

[0060] like Figure 1 As shown, a partition 10 is arranged between the dissolution chamber 23 and the cathode chamber 24 to slow down the flow of water and improve the CO2 dissolution efficiency; a water flow hole is arranged below the partition 10 for water circulation and material transfer between the dissolution chamber 23 and the cathode chamber 24.

[0061] like Figure 1 As shown, the cathode chamber gas outlet 16 is connected to a gas sampling bag 17 for collecting generated CH4 and incompletely utilized CO2 and H2; the dissolution chamber gas collecting port 14 is connected to a gas collecting bag 15 for collecting undissolved CO2 and purified CH4.

[0062] like Figure 1 As shown, the cathode chamber gas outlet 16 and the dissolution chamber gas collecting port 14 respectively form a gas circulation passage with the dissolution chamber gas inlet 12 through gas circulation pumps 20 and 21, which is used for the circulation of cathode chamber gas and the re-dissolution of CO2 in the dissolution chamber, and a liquid sealing plate 11 is provided between the dissolution chamber 23 and the cathode chamber 24 to prevent CH4 in the circulating gas from escaping into the cathode chamber 24 again, thereby realizing the purification and collection of CH4 and the reuse of H2.

[0063] like Figure 1As shown, a cathode liquid reflux passage is provided between the cathode chamber water outlet 18 and the dissolution chamber water inlet 13 to maintain the water circulation and material transport of the reactor, and the reflux cathode liquid can improve the CO2 dissolution efficiency in the dissolution chamber and maintain the stability of the reactor pH.

[0064] When using the device of the present invention to carry out microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery, the following steps can be followed:

[0065] (1) A graphite plate with a length of 35 cm, a height of 14 cm, and a thickness of 0.4 cm was soaked in deionized water for 12 h and then dried, then soaked in a 1 mol / L HCl solution for 12 h, then rinsed with deionized water and then soaked in a 1 mol / L NaOH solution for 12 h, finally rinsed with deionized water and dried for later use;

[0066] (2) A titanium plate with a length of 35 cm, a height of 14 cm, and a thickness of 0.5 cm was rinsed with deionized water and then soaked in a 1 mol / L HCl solution for 12 h. After the acid soaking, it was rinsed with deionized water and then soaked in a 1 mol / L NaOH solution for 12 h. It was then rinsed with deionized water and dried for later use.

[0067] (3) A cation exchange membrane 9 with a length of 35 cm and a width of 26 cm was soaked in deionized water for 24 h, then soaked in cathode liquid for 24 h, and then adhered to both sides of the anode chamber 25;

[0068] (4) The cathode electrode 4 (graphite plate) is placed in the cathode chamber 24 and connected to the working electrode interface 2 of the electrochemical workstation 26, the Ag / AgCl reference electrode 6 is connected to the reference electrode interface 1 of the electrochemical workstation 26, and the anode electrode titanium plate 5 is placed in the anode chamber 25 and connected to the auxiliary electrode interface 3 of the electrochemical workstation 26;

[0069] (5) constructing a gas circulation passage between the gas collecting port 14 of the dissolution chamber, the gas outlet 16 of the cathode chamber and the gas inlet 12 of the dissolution chamber, and realizing the circulation flow of the gas through the gas circulation pumps 20 and 21;

[0070] (6) constructing a cathode liquid reflux passage between the cathode chamber water outlet 18 and the dissolution chamber water inlet 13, and realizing the reflux of the cathode liquid through a peristaltic pump 19;

[0071] (7) Add cathode liquid to cathode chamber 24 and inoculate Methanosarcina barkeri , inoculate 10 mL~20 mL of methanogens per 100 mL of cathode liquid;

[0072] The composition of the cathodic solution was: 6 g / L K2HPO4, 3 g / L KH2PO4, 0.5 g / L NH4Cl, 2 g / L NaCl, 0.45 g / L MgSO4·7H2O, 0.22 g / L CaCl2, 1 mL / L trace element solution, 0.1 mL / L vitamin solution, 1 mL / L FeSO4·6H2O (0.2% w / v H2SO4), and the pH was adjusted to 6.8-7.0 using 5 mol / L NaOH;

[0073] The composition of the anolyte was: 6 g / L K2HPO4, 3 g / L KH2PO4;

[0074] (8) Wrap the heating tape around the outer surface of the reactor at intervals to maintain the temperature of the reactor between 35°C and 37°C;

[0075] (9) Turn on the electrochemical workstation 26 and apply a potential of -0.7 V (vs. Ag / AgCl) to the cathode electrode 4;

[0076] (10) Use the CO2 cylinder 22 to pass CO2 (99.99%) into the dissolution chamber 23 of the device at a flow rate of 100 mL / min for 10 h. The reaction period is 20 d. CO2 is replenished every 20 days, and the anolyte and 80% of the cathode liquid are replaced. The CH4 content in the gas collection bag 15 is measured every 24 h. When the CH4 content is higher than 90%, the gas collection bag 15 is replaced.

[0077] (11) The CH4 content in the gas collection bag was determined by gas chromatograph (GC 7900) with N2 as the carrier gas, 140°C as the injection port temperature, 120°C as the column box temperature, 150°C as the detector temperature, and 50 mA as the current. The total volume of the gas in the gas collection bag 15 was determined by direct measurement, and the average CH4 production was calculated.

[0078] Through the method of the present invention, the mixed gas of CH4, CO2 and H2 produced in the cathode chamber circulates in the device through the gas passage, and due to the difference in the solubility characteristics of different gases, CH4 will gradually accumulate in the gas collection bag, realizing the coupling of CH4 production, purification and collection. The circulation of H2 in the device can increase the retention time of H2, thereby improving the utilization efficiency of H2, and avoiding the energy loss caused by the escape of H2, thereby improving the energy utilization efficiency.

[0079] Another feature of the device of the present invention is that the cathode liquid reflux passage returns the alkaline cathode liquid to the dissolution chamber, which increases the CO2 dissolution rate while reducing the pH fluctuation caused by the CO2 dissolution, keeps the pH in the device stable, maintains the efficient operation of the reaction, eliminates the need for additional acid / alkaline solution to be added to the reactor, and reduces the operating cost of the device.

[0080] The results are as follows Figure 2 As shown, the CH4 produced in the cathode chamber gradually accumulated in the gas collection bag. On the 12th day, the CH4 content in the gas collection bag was measured to be 90.6%. At this time, the total CH4 production within 12 days was 808.93 mmol, and the average CH4 production was 67.4 mmol / d. After replacing the gas sampling bag, the CH4 content in the gas collection bag was measured to be 92.8% on the 20th day. At this time, the total CH4 production within 8 days was 828.57 mmol, and the average CH4 production was 103.6 mmol / d. And by Figure 3 It can be seen that the pH of the reactor always maintains a dynamic balance between 6.8 and 7.5.

Claims

1. A device for microbial electrochemical ectopic reduction of CO2 to produce CH4 and simultaneous purification and recovery, which is an anaerobic microbial reactor; The anaerobic microbial reactor comprises a dissolution chamber, a cathode chamber and an anode chamber; A partition is arranged between the dissolution chamber and the cathode chamber, and a cation exchange membrane is arranged between the anode chamber and the cathode chamber; A cathode electrode and a reference electrode are arranged in the cathode chamber, an anode electrode is arranged in the anode chamber, and the cathode electrode, the reference electrode and the anode electrode form a loop through an electrochemical workstation; A gas collection bag is provided above the dissolution chamber to collect undissolved CO2 in the device and CH4 circulating in the cathode chamber; A gas sampling bag is provided above the cathode chamber to collect CH4 produced in the cathode chamber and incompletely reacted H2 and CO2; The gas collection bag and the gas sampling bag are both connected to the dissolution chamber through the dissolution chamber air inlet to form a gas circulation passage for the circulation of the gas in the cathode chamber and the re-dissolution of CO2 in the dissolution chamber; The cathode chamber is provided with a cathode chamber water outlet, and the dissolution chamber is provided with a dissolution chamber water inlet. The cathode chamber water outlet is connected to the dissolution chamber water inlet to form a cathode liquid reflux path, which is used to reflux the cathode liquid to improve the CO2 dissolution efficiency in the dissolution chamber and maintain the stability of the pH of the device.

2. The device according to claim 1, characterized in that: The cathode electrode is a graphite plate; the anode is a titanium plate; and the reference electrode is an Ag / AgCl electrode.

3. The device according to claim 1 or 2, characterized in that: The lower part of the partition is provided with a water flow hole for water circulation and material transmission between the dissolution chamber and the cathode chamber; A liquid sealing plate is arranged between the dissolution chamber and the cathode chamber to isolate the exchange of headspace gas between the dissolution chamber and the cathode chamber.

4. The device according to claim 1 or 2, characterized in that: The device is connected to a heating tape; The cathode chamber is provided with a pH meter probe and a temperature control probe for real-time monitoring of water quality characteristics of the cathode chamber.

5. Use of the device according to any one of claims 1 to 4 in microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery.

6. A method for microbial electrochemical ex situ reduction of CO2 to produce CH4 and simultaneous purification and recovery, comprising the following steps: S1. Connecting the cathode electrode in the device according to any one of claims 1 to 4 to the working electrode interface of an electrochemical workstation, connecting the reference electrode to the reference electrode interface of the electrochemical workstation, and connecting the anode electrode to the auxiliary electrode interface of the electrochemical workstation; S2, constructing a gas circulation passage between the gas collecting port of the dissolution chamber, the gas outlet of the cathode chamber and the gas inlet of the dissolution chamber, and realizing the circulation flow of the gas through a gas circulation pump; S3, constructing a cathode liquid reflux passage between the water outlet of the cathode chamber and the water inlet of the dissolution chamber, and realizing the reflux of the cathode liquid by a peristaltic pump; S4, adding cathode liquid and methanogens to the cathode chamber, and adding anolyte to the anode chamber; S5, introducing CO2 into the dissolution chamber, turning on the electrochemical workstation, applying a constant potential of -0.4 V to -0.8 V to the cathode electrode, reducing CO2 to produce CH4 by methanogens in the cathode chamber, and collecting the CH4 at the cathode chamber outlet to participate in the gas circulation, thereby purifying and collecting the CH4; The methanogens are Methanosarcina barkeri , 10 mL to 20 mL of methanogens are inoculated per 100 mL of the cathode liquid; CO2 is introduced intermittently, with a reaction period of 15 to 20 days, followed by replenishment of CO2, replacement of the anode liquid and 70% to 90% of the cathode liquid.

7. The method according to claim 6, characterized in that: The composition of the catholyte is as follows: 6 g / L K2HPO4, 3 g / L KH2PO4, 0.5 g / L NH4Cl, 2 g / L NaCl, 0.45⋅g / L MgSO4⋅7H2O, 0.22g / L CaCl2, 1 mL / L trace element solution, 0.1 mL / L vitamin solution, 1 mL / L FeSO4·6H2O, use 5 mol / LNaOH to adjust the pH to 6.8~7.0; The composition of the trace element solution is as follows: 10 mL / L HCl, 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 / L CuCl2·2H2O, 0.006 g / L H3BO3, 0.036 g / L Na2MoO4·2H2O, the solvent is ultrapure water; The composition of the vitamin solution is as follows: 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 p-aminobenzoic acid, 0.05 mg / L lipoic acid, the solvent is ultrapure water; The composition of the anolyte is: 6 g / L K2HPO4, 3 g / L KH2PO4.

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