Method for producing hydrogen and methane by injecting carbon dioxide to reinforce anaerobic fermentation of coal shale

Abstract

The invention discloses a method for producing hydrogen and methane by injecting carbon dioxide to reinforce anaerobic fermentation of coal-series mud shale, which comprises the following steps: adopting a stainless steel tank as an anaerobic fermentation reactor, adding a coal-series mud shale sample, injecting fermentation liquor containing indigenous flora and exogenous CO2, carrying out a fermentation experiment under the conditions of reservoir temperature and pressure, and regularly taking a gas sample and a liquid sample for detection. The method comprises the following steps of: testing the generation amount of H2 and CH4, calculating the CO2 stage and accumulated utilization amount, analyzing a liquid phase product and a flora structure, analyzing the enhancement effect of exogenous CO2 injection on H2 generation of a fermentation system and the CO2 biological methanation effect, and evaluating the enhancement effect of exogenous CO2 injection on biological methane output of the fermentation system. By adopting the method for injecting the exogenous CO2, the generation of H2 in the anaerobic fermentation system of the coal-series shale can be promoted, the CO2 conversion and the hydrogen nutrition type methane production can be enhanced, the yield of biological methane can be remarkably increased, and an efficient synergistic way is provided for the yield increase of coal-series gas and the resource utilization of CO2.

Description

Technical Field

[0001] This invention belongs to the field of coalbed methane development technology, specifically relating to a method for enhancing anaerobic fermentation of coalbed methane and shale to produce hydrogen and methane through carbon dioxide injection. Background Technology

[0002] Coal-series gas, including coalbed methane, coal-bearing shale gas, and tight gas, is a clean, unconventional natural gas that plays a crucial transitional role in energy structure adjustment. However, CO2 utilization is primarily focused on oil recovery, while resource utilization has developed slowly, making it a weak link in the CCUS (Coal-bearing Gas System) technology framework. Therefore, exploring innovative pathways for the efficient development of coal-series gas and the synergistic utilization of CO2 resources is of significant energy and environmental importance, and methanogenic microorganisms in coal-bearing reservoirs offer a feasible path for combining these two approaches.

[0003] Coal and coal-bearing shale, as important reservoirs for coalbed methane, contain abundant organic matter, providing rich substrates for methanogenic microbial metabolism. Since the 1990s, when the concept of microbial enhancement of coalbed methane production was proposed, a series of laboratory studies and engineering experiments have been conducted on anaerobic fermentation of coal for methanogenesis, verifying the effectiveness of this technology in increasing coalbed methane production. Furthermore, previous studies have confirmed that coal-bearing shale with different petrological characteristics generally possesses methanogenic capacity under microbial action, and that the addition of graphite and other methods can significantly enhance its biogenic methane production, indicating that microbial enhancement of coal-bearing shale gas production also holds great potential.

[0004] Previous studies on surface fermentation systems have found that exogenous CO2 injection can significantly increase biomethane production. However, research on underground in-situ fermentation systems is scarce, especially in coal-bearing anaerobic fermentation systems, where exploration is still in its early stages. Existing studies mainly focus on supercritical CO2 extraction of coal-bearing organic matter to enhance microbial metabolism and biomethane production, with little attention paid to CO2 bioconversion, thus limiting the development and application of this technology. Compared to surface fermentation systems, coal-bearing gas reservoirs have unique advantages such as large CO2 methanation reaction space, good system sealing, and the ability to prevent CO2 escape, making them promising candidates. Furthermore, compared to coal seams, coal-bearing shale has high modifiability, low stress sensitivity, and larger reservoir volume, making it more suitable as a reservoir for modification and providing more space for exogenous CO2 injection, biomethane conversion, and subsequent sealing. Moreover, considering that the biomethane production of coal-bearing shale is much lower than that of coal, increasing its methane production through exogenous CO2 conversion will greatly enhance its development potential. In summary, injecting CO2 into the fermentation system of coal-bearing mudstone and shale and realizing its bioconversion has the dual advantages of increasing the production of coal-bearing mudstone and shale and realizing the resource utilization of CO2.

[0005] Therefore, this application proposes a method for enhancing the anaerobic fermentation of coal-bearing shale to produce hydrogen and methane by injecting carbon dioxide, so as to increase the methane production of the coal-bearing shale fermentation system and provide an innovative path for the utilization of CO2 resources. Summary of the Invention

[0006] The purpose of this invention is to provide a method for enhancing the biogenic methane production and CO2 resource utilization of coal-bearing shale through carbon dioxide injection to produce hydrogen and methane via anaerobic fermentation. This method uses a high-pressure resistant stainless steel tank as an anaerobic fermentation reactor and conducts experimental research by injecting exogenous CO2 to simulate the temperature and pressure of coal-bearing shale reservoirs.

[0007] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a method for enhancing anaerobic fermentation of coal-bearing shale to produce hydrogen and methane by injecting carbon dioxide, comprising the following steps: S1. Sterilize 11 high-pressure fermenters and 2 fermentation conical flasks, then add 50 g of coal-bearing mudstone and shale sample to each of the 11 high-pressure fermenters and 2 fermentation conical flasks to ensure a solid-liquid ratio of 1:10. S2. Select one high-pressure fermenter and add 500 mL of sterilized bacterial solution as a control group. After the high-pressure fermenter is evacuated to a vacuum using a vacuum pump, CO2 gas is injected into it to the reservoir pressure. Record the amount of CO2 injected. After the pressure stabilizes, disassemble the high-pressure fermenter and test the CO2 content (residual amount) remaining in the fermenter. This is used to calculate the CO2 utilization of the CO2 fermentation system experimental group. Meanwhile, the remaining 10 high-pressure fermenters and 2 fermentation conical flasks were used to construct CO2 fermentation system experimental groups and Ar fermentation system experimental groups, respectively. 500 mL of bacterial solution was added to each high-pressure fermenter and fermentation conical flask. The mudstone and shale samples were mixed evenly with the bacterial solution by shaking, and the solid-liquid ratio of 1:10 was kept constant. S3. After evacuating the 10 high-pressure fermenters in the experimental group to a vacuum using a vacuum pump, CO2 gas was injected to the reservoir pressure, and the amount of CO2 injected was recorded. At the same time, argon gas was injected into the two fermentation conical flasks to displace the air and create an anaerobic environment. S4. Conduct anaerobic fermentation experiments at the reservoir temperature. Disassemble one of the high-pressure fermenters every 3 days to collect the generated gas and fermentation liquid. At the same time, take gas and liquid samples from two conical flasks every 3 days. Test the gas composition and stage gas production of each experimental group and calculate the cumulative gas production. For the CO2 fermentation system experimental group, part of the exogenously injected CO2 was converted and utilized by microorganisms, the remaining unutilized CO2 was produced out of the fermenter, and the remaining part remained in the fermentation system in the form of dissolved state, etc. Therefore, the amount of residual CO2 under the experimental conditions was obtained through the control group, and the cumulative amount of exogenous CO2 utilized was calculated by combining the amount of CO2 injected and produced in each experimental group with the formula. S5. Every 3 days, disassemble the corresponding high-pressure fermenter and extract the fermentation broth from the conical flask of the Ar fermentation system. Collect 40 mL of fermentation broth for liquid phase product analysis and high-throughput sequencing. S6. Repeat steps S1-S5 to conduct three identical anaerobic fermentation experiments. The average value of the test results is used to analyze the biomethane production process of the fermentation system, evaluate the enhancing effect of exogenous CO2 injection on H2 generation and CO2 biomethanation in the fermentation system, and evaluate the enhancing effect of exogenous CO2 injection on biomethane production in the fermentation system.

[0008] Furthermore, the coal-bearing mudstone and shale samples in step S1 were dried to constant weight in an 80 °C drying oven before the experiment, then crushed by a ball mill and sieved to select samples with a particle size of 40-100 mesh (0.15-0.42 5 mm), which were then reduced in size and sealed for preservation.

[0009] Furthermore, the Ar fermentation system was constructed using conical flasks with a maximum graduation of 500 mL. During the experiment, the fermentation conical flasks were placed in a constant temperature incubator at the storage temperature, and the mouths of the flasks were sealed with rubber stoppers and connected to external gas collection bags. The high-pressure fermenter uses a high-pressure resistant stainless steel tank with a maximum scale of 500 mL as an anaerobic fermentation reactor to construct a CO2 fermentation system. In the CO2 fermentation system, CO2 in the high-pressure gas cylinder is connected to the high-pressure fermenter through a gas flow meter. A pressure gauge is installed on the top of the high-pressure fermenter, and the whole unit is placed in a constant temperature water bath set to the storage temperature. The other end of the high-pressure fermenter is connected in sequence to a drying tube, a gas flow meter, and a gas collection bag.

[0010] Furthermore, in step S4, the anaerobic fermentation bacteria used in the anaerobic fermentation experiment at the reservoir temperature are the original bacteria. Before the experiment, they are enriched, subcultured and domesticated, and then expanded. Bacteria in the logarithmic growth phase with OD600 values ​​that meet the bacterial growth standard curve are selected as the original bacteria for the experiment.

[0011] Furthermore, the formula for the cumulative utilization of exogenous CO2 in step S4 is as follows: the difference between the cumulative utilization of adjacent stages is the stage utilization of exogenous CO2. (1) In the formula, V P , V R, V I The figures represent the CO2 production, residual amount, and injection volume, respectively, in mL; m The amount of coal-bearing mudstone and shale sample added to the fermentation system, in g; C U The cumulative amount of exogenous CO2 utilized in the corresponding stage is expressed in mL / g.

[0012] Furthermore, gas component detection was performed by collecting gas from the gas collection bag using a 1 mL syringe and injecting it into a GC-4000A gas chromatograph (equipped with a TDX-01 gas chromatograph column (4 mm × 0.6 m)). The gas components were tested, and the production volume of each component was calculated based on the produced gas volume. The differences in the production of each gas component were analyzed to determine the impact of exogenous CO2 injection on the anaerobic fermentation of coal-bearing mudstone and shale.

[0013] Furthermore, the liquid phase product analysis in step S5 includes pH value and HCO3. - The detection methods for small molecule organic matter in the liquid phase are as follows: The pH value of the fermentation broth was measured using a Shanghai Leici PHS-3C pH meter; HCO3 was tested by titration according to industry standard DZ / T0064.49-93. - Concentration; After adding methyl orange indicator to the fermentation broth, titration was performed using standard hydrochloric acid solution. The amount of hydrochloric acid used was recorded based on the color change of the liquid, and the HCO3 in the fermentation broth was calculated according to formula (2). - Concentration; The content of small molecule organic matter in the liquid phase at each stage was tested using a GC-MS3100 gas chromatography-mass spectrometry system (equipped with an Agilent Hp-Innowax Gc Column (0.25mm*0.25um*60m)); The centrifuged and filtered fermentation broth was mixed with acetone at a ratio of 1:9, thoroughly shaken, and then 2 μL was injected through a microsyringe. Helium was used as the carrier gas for the test to clarify the differences in liquid phase products of each fermentation system under different gas atmospheres (CO2 and Ar), and to explain the effect of exogenous CO2 on the hydrolysis metabolism of coal-series shale fermentation system; (2) In the formula, HCO3 - The ion content is mg / L; c is the concentration of the hydrochloric acid standard solution, which is 0.05 mol / L; V MO The volume of standard hydrochloric acid solution consumed in titration using methyl orange as an indicator, in mL; HCO3 - The molar mass is 61.02 g / mol; V is the volume of the supernatant, mL.

[0014] Furthermore, the specific method for high-throughput sequencing in step S5 is as follows: After the fermentation broth is centrifuged at a high speed of 10,000 r / min, the bottom precipitate is collected for testing; firstly, DNA is extracted from the sample using the EZNA Soil NDA Kit (Omega, USA), and after PCR amplification, a sequencing library is constructed. Finally, sequencing is performed using the NovaSeq6000 system (Illumina MiSeq, USA) to analyze the evolution of the microbial community structure and the characteristics of biological enzymes in the anaerobic fermentation system, and to identify the differences in microbial community structure in the anaerobic fermentation system of coal-bearing shale under different gas atmospheres.

[0015] Compared with related technologies, the present invention has the following beneficial effects by adopting the above technical solution: This invention uses coal-bearing mudstone and shale samples from the Yima area of ​​Henan Province as the research object. The samples were collected from the roof of the Middle Jurassic 21 coal seam in the Yima coalfield, Henan Province, at a burial depth of 780-790 m. Based on the geothermal gradient (1.77 °C / 100 m) and pressure gradient (0.70 MPa / 100 m), the reservoir temperature and pressure were estimated to be approximately 35 °C and 5.5 MPa, respectively. The total organic carbon (TOC) content was 3.16%, and the organic matter maturity was (…). R o The percentage was 0.68%.

[0016] This invention establishes two control systems: an Ar fermentation system and a CO2 fermentation system. Using these two systems, the influence of exogenous CO2 on biomethane production in an anaerobic fermentation system of coal-bearing shale is investigated. The results show that H2 produced after exogenous CO2 injection... + Under the mediation of hydrogenase, a large amount of H2 is generated, thereby realizing the endogenous supply of H2 within the fermentation system. At the same time, the external injection of CO2 effectively prolongs the methanogenesis cycle of the fermentation system and significantly increases the biomethane production, with the cumulative biomethane production being 2.12 times that of the Ar fermentation system.

[0017] This invention relates to a method for enhancing H2 generation and methane production in anaerobic fermentation of coal-bearing shale using exogenous CO2 injection. Research has found that coal-bearing shale, in addition to possessing coalbed methane reservoir properties and anaerobic fermentation methanogenesis substrate properties, can also drive CO2-induced biomethanogenesis. The effects of exogenous CO2 injection on biomethane production in a coal-bearing shale anaerobic fermentation system were investigated through in-situ thermo-barrier anaerobic fermentation experiments. Results showed that the microbial community structure and metabolic function of the coal-bearing shale anaerobic fermentation system were significantly altered after exogenous CO2 injection. Biomethane production consistently prioritized the hydrogen-trophic methanogenesis pathway, and the acetic acid produced from organic matter degradation in the later stages of fermentation was utilized, effectively prolonging the methanogenesis cycle. Within the fermentation system... Clostridium_sensu_stricto_1 Under the mediation of predominantly hydrogen-producing bacteria, H2 is produced after the injection of exogenous CO2. +By utilizing the "catalytic electrode" effect of hydrogenases such as ferroredoxin hydrogenase, a large amount of H2 was generated through electron binding, achieving an endogenous supply of H2 and providing abundant substrates for hydrogen-trophic methanogenesis. With the injection of exogenous CO2, the biogenic methane production of the fermentation system was significantly increased, reaching 2.12 times that of the Ar fermentation system, demonstrating a remarkable increase in production. The method of injecting exogenous CO2 according to this invention can effectively enhance H2 generation and methane production in coal-bearing shale anaerobic fermentation systems, providing an efficient and synergistic pathway for increasing coalbed methane production and utilizing CO2 resources. Attached Figure Description

[0018] Figure 1 A diagram showing the gas production characteristics of an Ar anaerobic fermentation system; Figure 2 This is a diagram showing the changes in liquid phase matter in an Ar anaerobic fermentation system. Figure 3 A diagram showing the characteristics of microbial community changes in an Ar anaerobic fermentation system; Figure 4 A diagram showing the gas production characteristics of a CO2 anaerobic fermentation system; Figure 5 This is a diagram showing the changes in liquid phase matter in a CO2 anaerobic fermentation system. Figure 6 This is a diagram showing the characteristics of microbial community changes in a CO2 anaerobic fermentation system. Detailed Implementation

[0019] The method for enhancing hydrogen and methane production through carbon dioxide injection in anaerobic fermentation of coal-bearing shale includes the following steps: S1. Sterilize 11 high-pressure fermenters and 2 fermentation conical flasks, then add 50 g of coal-bearing mudstone and shale sample to each of the 11 high-pressure fermenters and the two fermentation conical flasks to ensure a solid-liquid ratio of 1:10. S2. Select one high-pressure fermenter and add 500 mL of sterilized bacterial solution as a control group. After the high-pressure fermenter is evacuated to a vacuum using a vacuum pump, CO2 gas is injected into it to 5.5 MPa. Record the amount of CO2 injected. After the pressure stabilizes, disassemble the high-pressure fermenter and test the CO2 content (residual amount) remaining in the fermenter. This is used to calculate the CO2 utilization of the CO2 fermentation system experimental group. Meanwhile, the remaining 10 high-pressure fermenters and 2 fermentation conical flasks were used to construct CO2 fermentation system experimental groups and Ar fermentation system experimental groups. 500 mL of bacterial solution was added to each high-pressure fermenter and each fermentation conical flask. The mudstone and shale samples were mixed evenly with the bacterial solution by shaking, and the solid-liquid ratio of 1:10 was kept constant. S3. After evacuating the 10 high-pressure fermenters in the experimental group to a vacuum using a vacuum pump, CO2 gas was injected to 5.5 MPa, and the amount of CO2 injected was recorded. At the same time, argon gas was injected into two fermentation conical flasks to displace the air and create an anaerobic environment. S4. Conduct anaerobic fermentation experiments at 35 °C. Disassemble one of the high-pressure fermenters every 3 days to collect the generated gas and fermentation liquid. At the same time, take gas and liquid samples from two conical flasks every 3 days. Test the gas composition and stage gas production of each experimental group and calculate the cumulative gas production. For the CO2 fermentation system experimental group, part of the exogenously injected CO2 was converted and utilized by microorganisms, the remaining unutilized CO2 was produced out of the fermenter, and the remaining part remained in the fermentation system in the form of dissolved state, etc. Therefore, the amount of residual CO2 under the experimental conditions was obtained through the control group, and the cumulative amount of exogenous CO2 utilized was calculated by combining the amount of CO2 injected and produced in each experimental group with the formula. S5. Every 3 days, disassemble the corresponding high-pressure fermenter and extract the fermentation broth from the conical flask of the Ar fermentation system. Collect 40 mL of fermentation broth for liquid phase product analysis and high-throughput sequencing. S6. Repeat steps S1-S5 to conduct three identical anaerobic fermentation experiments. The average value of the test results is used to analyze the biomethane production process of the fermentation system, evaluate the enhancing effect of exogenous CO2 injection on H2 generation and CO2 biomethanation in the fermentation system, and evaluate the enhancing effect of exogenous CO2 injection on biomethane production in the fermentation system.

[0020] Furthermore, the coal-bearing mudstone and shale samples in step S1 were dried to constant weight in an 80 °C drying oven before the experiment, then crushed by a ball mill and sieved to select samples with a particle size of 40-100 mesh (0.15-0.42 5 mm), which were then reduced in size and sealed for preservation.

[0021] Furthermore, the Ar fermentation system was constructed using Erlenmeyer flasks with a maximum graduation of 500 mL. During the experiment, the Erlenmeyer flasks were placed in a 35 °C constant temperature incubator, and the mouths of the flasks were sealed with rubber stoppers and connected to external gas collection bags. The high-pressure fermenter uses a high-pressure resistant stainless steel tank with a maximum scale of 500 mL as an anaerobic fermentation reactor to construct a CO2 fermentation system. In the CO2 fermentation system, CO2 in the high-pressure gas cylinder is connected to the high-pressure fermenter through a gas flow meter. A pressure gauge is installed on the top of the high-pressure fermenter, and the whole unit is placed in a constant temperature water bath set to the storage temperature (35 °C). The other end of the high-pressure fermenter is connected in sequence to a drying tube, a gas flow meter, and a gas collection bag.

[0022] Furthermore, in step S4, the anaerobic fermentation bacteria used in the anaerobic fermentation experiment at 35 °C are the original bacteria. Before the experiment, they are enriched, subcultured and domesticated, and then expanded. Bacteria in the logarithmic growth phase with OD600 values ​​that meet the bacterial growth standard curve are selected as the original bacteria for the experiment.

[0023] Furthermore, the formula for the cumulative utilization of exogenous CO2 in step S4 is as follows: the difference between the cumulative utilization of adjacent stages is the stage utilization of exogenous CO2. (1) In the formula, V P , V R , V I The figures represent the CO2 production, residual amount, and injection volume, respectively, in mL; m The amount of coal-bearing mudstone and shale sample added to the fermentation system, in g; C U The cumulative amount of exogenous CO2 utilized in the corresponding stage is expressed in mL / g.

[0024] Furthermore, gas component detection was performed by collecting gas from the gas collection bag using a 1 mL syringe and injecting it into a GC-4000A gas chromatograph (equipped with a TDX-01 gas chromatograph column (4 mm × 0.6 m)). The gas components were tested, and the production volume of each component was calculated based on the produced gas volume. The differences in the production of each gas component were analyzed to determine the impact of exogenous CO2 injection on the anaerobic fermentation of coal-bearing mudstone and shale.

[0025] Furthermore, the liquid phase product analysis in step S5 includes pH value and HCO3. - The detection methods for small molecule organic matter in the liquid phase are as follows: The pH value of the fermentation broth was measured using a Shanghai Leici PHS-3C pH meter; HCO3 was tested by titration according to industry standard DZ / T0064.49-93. - Concentration; After adding methyl orange indicator to the fermentation broth, titration was performed using standard hydrochloric acid solution. The amount of hydrochloric acid used was recorded based on the color change of the liquid, and the HCO3 in the fermentation broth was calculated according to formula (2). -Concentration; The content of small molecule organic matter in the liquid phase at each stage was tested using a GC-MS3100 gas chromatography-mass spectrometry system (equipped with an Agilent Hp-Innowax Gc Column (0.25mm*0.25um*60m)); The centrifuged and filtered fermentation broth was mixed with acetone at a ratio of 1:9, thoroughly shaken, and then 2 μL was injected through a microsyringe. Helium was used as the carrier gas for the test to clarify the differences in liquid phase products of each fermentation system under different gas atmospheres (CO2 and Ar), and to explain the effect of exogenous CO2 on the hydrolysis metabolism of coal-series shale fermentation system; (2) In the formula, HCO3 - The ion content is mg / L; c is the concentration of the hydrochloric acid standard solution, which is 0.05 mol / L; V MO The volume of standard hydrochloric acid solution consumed in titration using methyl orange as an indicator, in mL; HCO3 - The molar mass is 61.02 g / mol; V is the volume of the supernatant, mL.

[0026] Furthermore, the specific method for high-throughput sequencing in step S5 is as follows: After the fermentation broth is centrifuged at a high speed of 10,000 r / min, the bottom precipitate is collected for testing; firstly, DNA is extracted from the sample using the EZNA Soil NDA Kit (Omega, USA), and after PCR amplification, a sequencing library is constructed. Finally, sequencing is performed using the NovaSeq6000 system (Illumina MiSeq, USA) to analyze the evolution of the microbial community structure and the characteristics of biological enzymes in the anaerobic fermentation system, and to identify the differences in microbial community structure in the anaerobic fermentation system of coal-bearing shale under different gas atmospheres.

[0027] The specific experimental procedures for the control group and the fermentation system experimental group are described in detail below: I. Experimental Control Group (1) Gas production of Ar fermentation system Coal-bearing shale from the Yima area was selected as the fermentation substrate, and the original microbial community enriched and cultured in the laboratory was used as the fermentation microbial community. Experiments were conducted using 500 mL Erlenmeyer flasks. The methane production cycle of the Ar fermentation system was 15 days. During the first 3 days of reaction, the methane yield was only 0.04 mL / g; from days 3 to 9, the methane yield increased rapidly, reaching 0.52 mL / g from days 3 to 6 and 0.92 mL / g from days 6 to 9, respectively; thereafter, the methane yield decreased rapidly, dropping to 0.02 mL / g from days 9 to 12 and 0.003 mL / g from days 12 to 15, respectively. The cumulative biogenic methane yield over the entire reaction cycle was 1.50 mL / g. Figure 1 (As shown in a). The methane concentration in the produced gas followed the same pattern as the stage yield, reaching a peak (73.27%) between 6 and 9 days. Furthermore, the CO2 production and concentration followed the same pattern, both peaking between 3 and 6 days, at 0.14 mL / g and 13.54%, respectively, before continuously decreasing. H2 production and concentration remained at low levels throughout, showing a trend of first increasing and then decreasing, peaking between 3 and 6 days of reaction, at 0.026 mL / g and 2.52%, respectively. Figure 1 (as shown in b).

[0028] (2) Liquid phase substance content of Ar fermentation system The pH value in the Ar fermentation system fluctuated and increased as the reaction progressed, rising from 7.40 on day 0 to 7.43 on day 15, with relatively small pH fluctuations. Figure 2 (as shown in a). HCO3 in the Ar fermentation system within 0-15 days. - The ion concentration exhibits a fluctuating upward trend. In the anaerobic fermentation process, HCO3- in the Ar fermentation system... - The lowest concentration was 915.3 mg / L on day 3, the highest concentration was 1006.83 mg / L on day 12, and the average concentration was 956.5 mg / L. Figure 2 (as shown in a).

[0029] In the Ar fermentation system, the main small-molecule organic compounds in the liquid phase are volatile fatty acids and alcohols, with the former accounting for 48.56%-68.08%. The content of small-molecule organic compounds in the liquid phase of the Ar fermentation system is highest on day 3 of the reaction, at 84.38 mg / L. During days 3-9, when biomethane production rapidly increases, its content rapidly decreases to 68.86 mg / L. Afterward, the rate of decrease significantly slows and tends to stabilize, reaching 64.16 mg / L 15 days after the end of methanogenesis. Figure 2 (as shown in b).

[0030] (3) Characteristics of microbial community changes in the Ar fermentation system Within the bacterial community of the Ar fermentation system, Romboutsia and Clostridium_sensu_stricto_1 The abundance of methanogens was high in the early stages of methanogenesis, at 12.8% and 10.0%, respectively, before decreasing rapidly. The abundance dropped to 2.5% and 1.2% at the peak of methanogenesis, respectively, and to 4.9% and 0.9% at the end of the reaction. Macellibacteroides The abundance increased from 10.0% in the initial stage to 21.5% and 18.6% in the peak and late stages, respectively, making it the bacterial genus with the highest proportion. Terrisporobacter The abundance remained consistently low, ranging from 1.8% to 4.4%. Additionally, BRH-c20a Abundance fluctuated slightly within the range of 10-12.5%. Figure 3(As shown in a). In the archaic community, the Ar fermentation system always... Methanosaeta Primarily. On day 3 of the reaction, Methanosaeta and Methanoculleus The abundances of the two bacteria were 55.0% and 5.9%, respectively. On day 9 of the reaction, they increased to 78.8% and 16.4%, respectively. On day 15 of the reaction, the bacterial community structure remained essentially unchanged, with the abundances of the two bacteria being 77.8% and 15.2%, respectively. Figure 3 (as shown in b).

[0031] II. Examples of Experimental Groups (1) Gas production of CO2 fermentation system In the laboratory, coal-bearing shale from the Yima area was used as the fermentation substrate, and enriched native microbial communities were used as the fermentation microbiota. A custom-made high-pressure resistant stainless steel tank was used as the reaction vessel. CO2 was introduced through a gas flow meter to reach the pressure of the coal-bearing shale reservoir before experimental research was conducted. The biomethane generation cycle of the CO2 fermentation system was extended to 30 days. During the first 9 days of the reaction, methane production increased slowly, ranging from 0.13 to 0.21 mL / g, with an average of 0.18 mL / g. From days 9-12, 12-15, and 15-18, production increased rapidly, reaching 0.36, 0.72, and 0.83 mL / g, respectively. Afterward, production decreased, but the decrease was significantly smaller compared to the Ar fermentation system. Production was 0.36 and 0.25 mL / g from days 18-21 and 21-24, respectively. From days 24-27 and 27-30, production decreased to 0.08 and 0.05 mL / g, respectively, with a cumulative methane production of 3.18 mL / g, 2.12 times that of the Ar fermentation system. Figure 4 (as shown in a).

[0032] CO2 was continuously utilized over the 30 days of the reaction, with the utilization peaking between days 15 and 18. Specifically, the utilization rate increased slowly during the first 9 days, ranging from 0.09 to 0.13 mL / g, with an average of 0.11 mL / g. During days 9-12 and 12-15, when methane production increased rapidly, CO2 utilization reached 0.37 and 0.50 mL / g, respectively. The utilization rate reached its maximum of 0.70 mL / g between days 15 and 18. Between days 18-21 and 21-24, the utilization rate decreased to 0.41 mL / g and 0.31 mL / g, respectively, before rapidly decreasing and approaching zero. The cumulative CO2 utilization during the entire reaction was 2.80 mL / g. Figure 4 (as shown in a).

[0033] The H2 yield in the system peaked at 1.09 mL / g during the first 3 days of reaction, after which the yield decreased significantly and remained below 0.5 mL / g. Specifically, the yields decreased to 0.16 and 0.10 mL / g during days 3-6 and 6-9, respectively, but maintained relatively high yields of 0.30, 0.47, and 0.37 mL / g during days 9-12, 12-15, and 15-18, respectively; the yields decreased to 0.09 mL / g during days 18-21 and 21-24, and further decreased to 0.04 and 0.03 mL / g during days 24-27 and 27-30. The cumulative H2 yield over the entire reaction cycle reached 2.75 mL / g, significantly higher than that of the Ar fermentation system (…). Figure 4 (as shown in b).

[0034] (2) Liquid phase substance content of CO2 fermentation system The pH value of the CO2 fermentation system showed a fluctuating downward trend within 0-30 days, decreasing from 7.4 on day 0 to 6.58 on day 30, with a relatively large pH variation. Figure 5 a) Exogenous CO2 and HCO3 injected into the fermentation broth - There is a dynamic transformation relationship; due to the large amount of CO2 in the fermentation system, it dissolves in water to form HCO3. - Ions, therefore, HCO3 in CO2 fermentation systems - The ion content is much higher than in the Ar fermentation system. In anaerobic fermentation, HCO3- in the CO2 fermentation system... - The lowest concentration was 1040.8 mg / L on day 0, the highest was 3783.24 mg / L on day 24, and the average was 2928.17 mg / L. Figure 5 (as shown in a).

[0035] The concentration of small-molecule organic matter in the liquid phase of the CO2 fermentation system showed opposite trends, reaching its lowest point on day 3 at 59.65 mg / L, and then continuously increasing, especially during days 9-18 when biomethane was produced in large quantities, increasing from 69.09 mg / L to 91.42 mg / L. It then tended to stabilize, reaching 95.55 mg / L on day 30 of the reaction. Figure 5 (as shown in b).

[0036] (3) Characteristics of microbial community changes in CO2 fermentation system In the bacterial community of the CO2 fermentation system, on day 3 of the reaction... Romboutsia and Clostridium_sensu_stricto_ 1The abundances were initially low, at 9.3% and 7.5%, respectively, increasing to 18.8% and 15.2% on day 9 of the reaction. On day 18, when methane production peaked, the abundances were 16.8% and 12.8%, respectively, and reached 33.4% and 12.7% at the end of the reaction. Unlike Ar fermentation systems, Macellibacteroides The abundance remained low within the CO2 fermentation system. Terrisporobacter The abundance was only 3.1% and 10.9% on day 3 and day 9, respectively, but it increased to 62.2% during the peak of methanogenesis, becoming absolutely dominant, before decreasing to 43.7% at the end. Additionally, BRH-c20a The abundance was high only on day 3 of the reaction, at 23.7%, decreasing to 2.5% on day 9, and then falling below 1%. Figure 6 (As shown in a). In the archaea community, the reaction occurred on day 3. Methanoculleus Abundance lower than Methanosaeta The rates were 30.0% and 43.5%, respectively. However, on days 9 and 18 of the response, Methanoculleus The abundance significantly increased and became dominant, reaching 87.5% and 85.6% respectively, while Methanosaeta The abundance remained low, at only 9.6% and 6.0%. On day 30 of the reaction, the abundances of the two archaea were 54.5% and 33.0%, respectively. Figure 6 (as shown in b).

[0037] The anaerobic fermentation system for injecting exogenous CO2 provided by this invention utilizes enriched and expanded native bacterial communities to conduct experimental research simulating reservoir pressure and temperature conditions in coal-bearing shale. The results show that injecting exogenous CO2 achieves an endogenous supply of H2, and the H2 generated after the exogenous CO2 dissolves... + Under the mediation of hydrogenase, a large amount of H2 was generated, with a cumulative H2 yield of 2.75 mL / g, significantly higher than that of the Ar fermentation system. At the same time, the injection of exogenous CO2 prolonged the methanogenesis cycle and increased methane production, with a cumulative methane yield of 3.18 mL / g, which was 2.12 times that of the Ar fermentation system.

[0038] The above embodiments illustrate the basic principles and features of the present invention, but are merely preferred embodiments and are not limited to these embodiments. Those skilled in the art, inspired by this patent, can make many modifications and improvements without departing from the spirit and scope of the claims, all of which fall within the scope of protection of the present invention. Therefore, the scope of this patent and its protection should be determined by the appended claims.

Claims

1. A method for enhancing hydrogen and methane production from anaerobic fermentation of coal measures shale by injecting carbon dioxide, characterized in that: The method comprises the following steps: S1, sterilize 11 high-pressure fermentation tanks and 2 fermentation conical flasks, then add 50 g of coal measure shale samples to each of the 11 high-pressure fermentation tanks and 2 fermentation conical flasks to ensure a solid-liquid ratio of 1:10; S2, select one of the high-pressure fermentation tanks to add 500 mL of sterilized bacterial liquid as a control group, use a vacuum pump to draw the high-pressure fermentation tank to vacuum, then inject CO2 gas into the high-pressure fermentation tank to the reservoir pressure, record the CO2 injection amount, and after the pressure is stable, disassemble the high-pressure tank and test the CO2 content (residual amount) remaining in the fermentation tank, which is used for calculating the CO2 utilization amount of the CO2 fermentation system experimental group; Meanwhile, the remaining 10 high-pressure fermentation tanks and 2 fermentation conical flasks are used to construct a CO2 fermentation system experimental group and an Ar fermentation system experimental group respectively, 500 mL of bacterial liquid is added to each high-pressure fermentation tank and fermentation conical flask, the shale sample is mixed with the bacterial liquid uniformly by oscillation, and the solid-liquid ratio of 1:10 is kept unchanged; S3, use a vacuum pump to draw the 10 high-pressure fermentation tanks of the experimental group to vacuum respectively, then inject CO2 gas into the high-pressure fermentation tanks to the reservoir pressure, and record the CO2 injection amount; at the same time, fill argon gas into the two fermentation conical flasks respectively to replace the air to form an anaerobic environment; S4, carry out anaerobic fermentation experiment at reservoir temperature, disassemble one of the high-pressure fermentation tanks every 3 days, and collect the generated gas and fermentation liquid; at the same time, take gas and liquid from the two conical flasks every 3 days; test the gas components and stage gas production of each experimental group and calculate the cumulative gas production; For the CO2 fermentation system experimental group, part of the exogenous CO2 is converted and utilized by microorganisms, the remaining part of the CO2 that is not utilized is discharged from the fermentation tank, and part of the CO2 remains in the fermentation system in the form of dissolution; therefore, the residual amount of CO2 under the experimental condition is obtained by the control group, combined with the injection amount and output amount of CO2 of each experimental group, and the cumulative utilization amount of exogenous CO2 is calculated by the formula; S5, disassemble the corresponding high-pressure fermentation tank and extract the fermentation liquid in the Ar fermentation system conical flask every 3 days, collect 40 mL of fermentation liquid respectively, and perform liquid product analysis and high-throughput sequencing; S6, repeat steps S1-S5 to carry out three identical anaerobic fermentation experiments, and the test results are averaged for analysis of the biological methane production process of the fermentation system, evaluation of the strengthening effect of exogenous CO2 injection on H2 generation of the fermentation system and the CO2 biomethanation effect, and evaluation of the strengthening effect of exogenous CO2 injection on biological methane production of the fermentation system.

2. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 1, characterized in that: The coal measure shale sample in step S1 is dried to constant weight in an 80 °C drying oven before the experiment, then crushed by a ball mill and sieved, and the sample with a particle size of 40-100 mesh (0.15-0.42 5 mm) is selected and sealed for storage after reduction.

3. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 2, characterized in that: The Ar fermentation system is constructed by using a conical flask with a maximum scale of 500 mL, and the fermentation conical flask is placed in a constant temperature incubator at reservoir temperature during the experiment, the bottle mouth is sealed with a rubber plug and connected with a gas collection bag. The high-pressure fermentation tank adopts a high-pressure stainless steel tank with a maximum scale of 500 mL as an anaerobic fermentation reactor to construct a CO2 fermentation system; in the CO2 fermentation system, CO2 in the high-pressure gas cylinder is connected to the high-pressure fermentation tank through a gas flow meter, a pressure gauge is installed at the top of the high-pressure fermentation tank, and the whole is placed in a constant-temperature water bath box set to the reservoir temperature; the other end of the high-pressure fermentation tank is sequentially connected to a drying tube, a gas flow meter and a gas collection bag.

4. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 1, characterized in that: The anaerobic fermentation bacteria used in the anaerobic fermentation experiment at the reservoir temperature in step S4 are original bacteria, which are enriched and cultured, step-by-step acclimated and then expanded before the experiment, and the bacteria in the logarithmic growth phase and with OD600 values meeting the standard curve of bacterial growth are selected as the original bacteria for the experiment.

5. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 1, characterized in that: The cumulative utilization amount of the exogenous CO2 in step S4 is as follows, and the difference between the cumulative utilization amounts of adjacent stages is the stage utilization amount of the exogenous CO2. (1) wherein, V P , V R , V I are the output, residual and injection amounts of CO2, respectively, mL; m is the amount of coal-bearing shale sample added to the fermentation system, g; C U is the cumulative amount of exogenous CO2 used at the corresponding stage, mL / g.

6. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 3, characterized in that: Gas component detection is performed by collecting the gas in the gas collection bag through a 1 mL syringe and injecting it into a GC-4000A type gas chromatograph (with a TDX-01 type gas chromatographic column (4 mm x 0.6 m)), testing the gas components, and combining the gas volume to calculate the gas output volume of each component, analyze the yield difference of each gas component, and identify the effect of exogenous CO2 injection on coal shale anaerobic fermentation.

7. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production according to claim 1, characterized in that: The liquid phase product analysis in step S5 includes pH value, HCO3 - , and detection of small molecule organic matter in liquid phase. The specific detection method is as follows: a PHS-3C acidity meter from Shanghai Ray Magnet is used to measure the pH value of the fermentation liquor; according to the industry standard DZ / T0064.49-93, a titration method is used to test the HCO3 - concentration; after methyl orange indicator is added to the fermentation liquor, a hydrochloric acid standard solution is used for titration, the amount of hydrochloric acid used for titration is recorded according to the color change of the liquid, and the HCO3 - concentration in the fermentation liquor is calculated according to formula (2); a GC-MS3100 gas chromatography-mass spectrometry instrument (with Agilent Hp-Innowax Gc Column (0.25 mm*0.25 um*60 m)) is used to test the content of small molecule organic matter in liquid phase at each stage; after the centrifuged and filtered fermentation liquor is mixed with acetone at a ratio of 1:9, it is fully shaken and uniformly mixed, then 2 μL of the mixed solution is introduced into the liquid through a micro-sampler, and helium is used as the carrier gas for testing, so as to clarify the differences of liquid phase products of each fermentation system under different gas atmospheres (CO2 and Ar) and explain the influence of exogenous CO2 on the hydrolysis and metabolism of the coal shale fermentation system. (2) wherein, is the ion content of HCO3 - MO is the volume of standard hydrochloric acid consumed in the titration with methyl orange as indicator, mL; is the ion content of HCO3 - MO is the volume of standard hydrochloric acid consumed in the titration with methyl orange as indicator, mL; is the ion content of HCO3 - MO is the volume of standard hydrochloric acid consumed in the titration with methyl orange as indicator, mL; is the ion content of HCO3 - MO is the volume of standard hydrochloric acid consumed in the titration with methyl orange as indicator, mL; is the ion content of HCO3 - MO is the volume of standard hydrochloric acid consumed in the titration with methyl orange as indicator, mL; 8. The process for carbon dioxide injected enhanced coal measures shale anaerobic fermentation hydrogen and methane production of claim 1, characterized in that: In step S5, the high-throughput sequencing method is as follows: after the fermentation liquid is treated by high-speed centrifugation (10000 r / min), the bottom sediment is collected for testing; first, the DNA in the sample is extracted using an E.Z.N.A. soil NDA kit (Omega, USA), and after PCR amplification, a sequencing library is constructed, and finally, NovaSeq6000 system (Illumina MiSeq, USA) is used for sequencing to analyze the evolution of the bacterial community structure and the characteristics of the biological enzymes in the anaerobic fermentation system, and identify the differences in the bacterial community structure in the coal shale anaerobic fermentation system under different gas atmospheres.

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