A method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation

Abstract

The present invention belongs to the technical field of biomass utilization, and specifically relates to a method for preparing methane by in-situ modified biochar to strengthen anaerobic fermentation. The present invention adds biochar to the anaerobic fermentation hydrolysis and acidification system. The biochar helps to enhance the interspecies electron transfer capacity (DIET), promote hydrolysis and acidification, and utilizes the organic acids (acetic acid and butyric acid, etc.) produced by the anaerobic fermentation process to modify the biochar in situ. The in-situ modified biochar can promote the anaerobic fermentation to produce methane and improve the quality of gas production, thereby increasing the gas production and methane content, and at the same time, simply and efficiently realizes the acidification modification of biochar. The present invention makes full use of the characteristics of biochar that is easy to load and modify, combines the different characteristics of different stages of anaerobic fermentation technology, realizes the in-situ modification of biochar acidification and promotes the anaerobic fermentation to produce methane and improve the quality of gas production.

Description

Technical Field

[0001] The invention belongs to the technical field of biomass utilization, and specifically relates to a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation. Background Art

[0002] At present, one of the typical ways of domestic biomass utilization projects is to use agricultural waste such as straw and livestock and poultry manure to produce biogas through anaerobic fermentation, and then upgrade and purify it into biogas that meets the standards. Its methane concentration is above 97%, which can meet the supply requirements of natural gas. This not only handles rural non-point source pollution, but also is conducive to the sustainable green development of energy.

[0003] In the above anaerobic fermentation process, organic acids are important intermediates, such as acetic acid and butyric acid, which can be used by microorganisms as carbon sources and energy sources. Through the acetic acid and butyric acid metabolic pathways (chemical reactions are shown in formulas A and B), acetic acid and butyric acid are converted into acetyl-CoA and hydrogen, entering the TCA cycle, which can provide energy and precursor substances.

[0004] CH 3 COOH → 2H 2 +CO 2 (Formula A);

[0005] CH 3 CH 2 CH 2 COOH → 2H 2 +2CO 2 +C 2 H 4 (Formula B).

[0006] This can lower the pH value of the fermentation system and provide an acidic environment that is conducive to the growth of hydrogen-producing bacteria (such as Clostridium butyricum). However, the gas production of existing anaerobic fermentation is not ideal, and the methane content needs to be improved. Summary of the invention

[0007] The object of the present invention is to provide a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation. The method provided by the present invention improves the gas production and methane content of methane prepared by anaerobic fermentation.

[0008] In order to achieve the above object, the present invention provides the following technical solutions:

[0009] The present invention provides a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation, comprising the following steps:

[0010] The biochar is added into the anaerobic fermentation hydrolysis acidification system for in-situ modification to obtain in-situ modified biochar;

[0011] The in-situ modified biochar is added to an anaerobic fermentation methanogenetic system for anaerobic fermentation to obtain methane.

[0012] Preferably, the amount of biochar added is 5-10% of the feed volume of the anaerobic fermentation hydrolysis acidification system.

[0013] Preferably, the pH value of the in-situ modification is 5-5.5, the temperature is 36-38°C, and the total modification time is 20-60 days; the in-situ modification is carried out under stirring conditions, the stirring is interval stirring, and the interval time and stirring time of the interval stirring are independently 25-30 minutes; the stirring speed is 600-1000rpm.

[0014] Preferably, the micropore diameter of the in-situ modified biochar is 2-7 nm, the macropore diameter is 50-300 nm, the porosity is 75-85%, and the specific surface area is 200-400 m 2 / g, the functional group grafting rate is 40~60%, the polycyclic aromatic hydrocarbon structure grafting rate is 15~25%, and the graphitization degree is 15~30%.

[0015] Preferably, the mass ratio of the in-situ modified biochar to the feed amount of the anaerobic fermentation methanogenesis system is 5~10:100.

[0016] Preferably, the temperature of the anaerobic fermentation methanogenesis system is 36-38°C, and the total fermentation time is 30-60 days; the anaerobic fermentation is carried out under stirring conditions, the stirring is intermittent stirring, and the interval time and stirring time of the intermittent stirring are independently 25-30 minutes; the stirring speed is 600-1000 rpm.

[0017] Preferably, the biochar is magnetic biochar; the preparation method of the magnetic biochar is: mixing crop residues and magnetic substances and then hydrothermally carbonizing them.

[0018] Preferably, the mass ratio of the crop residues to the magnetic substance is 1-5:1.

[0019] Preferably, the hydrothermal carbonization includes a heating stage and a heat preservation stage in sequence; the heating rate of the heating stage is 5-10°C / min; the temperature of the heat preservation stage is 180-300°C, and the heat preservation time is 1-3h.

[0020] Preferably, the anaerobic fermentation further includes post-treatment, wherein the post-treatment is: separating the in-situ modified biochar and reusing it as biochar.

[0021] The present invention provides a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation. The present invention adds biochar to the anaerobic fermentation hydrolysis and acidification system. The biochar helps to enhance the interspecies electron transfer capacity (DIET), promote hydrolysis and acidification, and utilizes the organic acids (acetic acid and butyric acid, etc.) produced by the anaerobic fermentation process to modify the biochar in situ. The in-situ modified biochar can promote the anaerobic fermentation to produce methane and improve the quality of gas production, thereby increasing the gas production and methane content, and at the same time, simply and efficiently realizes the acidified modified biochar. The present invention makes full use of the characteristics of biochar that is easy to load and modify, combines the different characteristics of different stages of anaerobic fermentation technology, realizes the in-situ modification of biochar acidification and promotes the anaerobic fermentation to produce methane and improve the quality of gas production. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 This is a process flow chart for preparing methane by in-situ modified biochar enhanced anaerobic fermentation provided by the present invention. DETAILED DESCRIPTION

[0024] The present invention provides a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation, comprising the following steps:

[0025] The biochar is added into the anaerobic fermentation hydrolysis acidification system for in-situ modification to obtain in-situ modified biochar;

[0026] The in-situ modified biochar is added to an anaerobic fermentation methanogenetic system for anaerobic fermentation to obtain methane.

[0027] The present invention adds biochar to an anaerobic fermentation hydrolysis acidification system for in-situ modification to obtain in-situ modified biochar. In the present invention, the biochar is preferably magnetic biochar; the method for preparing the magnetic biochar is preferably: mixing crop residues and magnetic substances (recorded as the first mixing) and then hydrothermally carbonizing them. The present invention uses magnetic biochar, and the introduced magnetic elements are uniformly distributed in the matrix of the biochar in the form of nanoparticles, which is convenient for separating and collecting them using their magnetism. During the production process, the biogas slurry and sludge discharged from the anaerobic fermentation hydrolysis acidification system every day will contain magnetic biochar, which should be separated and re-added to the anaerobic fermentation hydrolysis acidification system to complete the in-situ acidification modification.

[0028] In the present invention, the crop residues preferably include one or more of food crop residues and cash crop residues; the food crop residues are preferably food crop straws; the food crop straws preferably include one or more of wheat straws, corn straws and rice straws; the cash crop residues preferably include one or more of peanut straws, cotton straws and vegetable residues.

[0029] In the present invention, the magnetic material preferably includes one or more of iron, cobalt, nickel, iron compounds, cobalt compounds and nickel compounds, and is more preferably an iron compound; the iron compound is preferably ferroferric oxide (Fe 3 O 4 ).

[0030] In the present invention, the mass ratio of the crop residues to the magnetic substance is preferably 1-5:1, specifically 1:1, 2:1, 3:1, 4:1 or 5:1.

[0031] In the present invention, the first mixing is preferably performed in sequence by crushing mixing and grinding mixing; the grinding mixing is preferably performed by ball milling mixing; the ball milling mixing is preferably performed by ball milling the product obtained by crushing mixing for 2 minutes and then standing for 20 minutes, and repeating the above operation for more than 6 times; the rotation speed of the ball milling mixing is preferably 300-950 rpm, more preferably 300, 600 rpm, 900 rpm or 950 rpm.

[0032] In the present invention, the hydrothermal carbonization preferably includes a heating stage and a heat preservation stage in sequence; the heating rate of the heating stage is preferably 3-10 ℃ / min, specifically 3 ℃ / min, 5 ℃ / min, 7 ℃ / min, 9 ℃ / min or 10 ℃ / min; the temperature of the heat preservation stage is preferably 180-300 ℃, specifically 180 ℃, 200 ℃, 220 ℃, 240 ℃, 260 ℃, 280 ℃ or 300 ℃, and the heat preservation time is preferably 3-12 h, specifically 3 h, 6 h, 7.5 h, 10 h or 12 h.

[0033] The present invention has no special requirements for the anaerobic fermentation hydrolysis acidification system. In a specific embodiment of the present invention, the anaerobic fermentation hydrolysis acidification system preferably includes silage straw and distiller's grains; the silage straw is preferably corn silage straw; the solid content of the distiller's grains is preferably 15wt%; the mass ratio of the silage straw to the distiller's grains is preferably 4:1.

[0034] In the present invention, the addition amount of the biochar is preferably 5-10% of the feed volume of the anaerobic fermentation hydrolysis acidification system, specifically 5%, 6%, 7%, 8%, 9% or 10%.

[0035] In the present invention, the pH value of the in-situ modification is preferably 5-5.5, specifically 5, 5.1, 5.2, 5.3, 5.4 or 5.5, and the temperature is preferably 36-38°C, specifically 37°C.

[0036] In the present invention, the in-situ modification is preferably carried out under stirring conditions; the stirring is preferably intermittent stirring, and the interval time of the intermittent stirring and the stirring time are independently preferably 25 to 30 min; the stirring speed is preferably 600 to 1000 rpm, specifically 600 rpm, 800 rpm, 900 rpm or 1000 rpm. The present invention generates medium-chain fatty acids (with 8 to 10 carbon atoms) in the system through stirring.

[0037] In the present invention, the total modification time (hydraulic cycle) of the in-situ modification is preferably 20 to 60 days, specifically 20 days, 30 days, 40 days, 50 days or 60 days; the in-situ modification equipment is preferably an acidification reactor. The present invention increases the porosity and specific surface area of ​​the biochar in structure through in-situ modification, and has abundant micropores and macropores with uniform pore size distribution. In terms of composition, organic acids enter the pore structure of the biochar and partially fill it, so that new hydroxyl, carboxyl, phenolic hydroxyl and ester functional groups and polycyclic aromatic hydrocarbon structures are formed on the surface of the biochar.

[0038] In the present invention, the micropore diameter of the in-situ modified biochar is 2-7 nm, the macropore diameter is 50-300 nm, the porosity is 75-85%, and the specific surface area is 200-400 m 2 / g, the functional group grafting rate is 40~60%, the polycyclic aromatic hydrocarbon structure grafting rate is 15~25%, and the graphitization degree is 15~30%.

[0039] After obtaining the in-situ modified biochar, the present invention adds the in-situ modified biochar to the anaerobic fermentation methanogenesis system for anaerobic fermentation to obtain methane. In the present invention, the in-situ modified biochar is preferably in-situ modified magnetic biochar; the mass ratio of the feed amount of the in-situ modified biochar to the anaerobic fermentation methanogenesis system is preferably 5 to 10:100, specifically 5:100, 5.5:100, 6:100, 6.5:100, 7:100, 7.5:100, 8:100, 8.5:100, 9:100 or 10:100.

[0040] In the present invention, the equipment of the anaerobic fermentation methanogenesis system is preferably an anaerobic fermentation methanogenesis reactor (CSTR reactor). In a specific embodiment of the present invention, the reaction substrate of the anaerobic fermentation methanogenesis system preferably includes corn stalks; the corn stalks are preferably dried and then crushed before use.

[0041] In the present invention, the temperature of the anaerobic fermentation methanogenesis system is preferably 36-38°C, specifically 37°C; the anaerobic fermentation is preferably carried out under stirring conditions; the stirring is preferably intermittent stirring, and the interval time and stirring time of the intermittent stirring are independently preferably 25-30 min; the stirring speed is preferably 600-1000 rpm, specifically 600 rpm, 800 rpm, 900 rpm or 1000 rpm.

[0042] In the present invention, the total fermentation time (hydraulic cycle) of the anaerobic fermentation is preferably 30 to 60 days, specifically 30 days, 40 days, 50 days or 60 days.

[0043] In the present invention, the anaerobic fermentation preferably further includes post-treatment; the post-treatment is preferably: separating the in-situ modified biochar and reusing it as biochar, and preparing methane through in-situ modification and anaerobic fermentation; when the in-situ modified biochar is in-situ modified magnetic biochar, the separation is preferably magnetic separation.

[0044] The present invention provides a method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation. The main process flow is as follows: Figure 1 As shown: first, biochar is prepared, and then the obtained biochar is added to an acidification reactor for in situ modification to obtain in situ modified biochar, and then the in situ modified biochar is separated and collected from the acidification reactor, and then the obtained in situ modified biochar is added to an anaerobic fermentation and methanogenesis reactor for anaerobic fermentation to prepare methane, and then the sludge and sludge are discharged, and the biochar therein is separated and collected, and recycled for the next in situ modified biochar enhanced anaerobic fermentation to prepare methane.

[0045] In order to further illustrate the present invention, the scheme of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments, but they should not be understood as limiting the protection scope of the present invention.

[0046] Example 1

[0047] (1) Preparation of magnetic biochar

[0048] Corn straw and ferrous oxide (Fe 3 O 4 ) were used as raw materials with a mass ratio of 1:1. After mixing, they were ball milled at 300 rpm for 2 min, paused for 20 min, and repeated 6 times. Hydrothermal carbonization was performed at a temperature of 230 ℃, a heating rate of 3 ℃ / min, and a hydrothermal time of 12 h to obtain magnetic biochar.

[0049] (2) In-situ acidification modification

[0050] The acidification reactor was used, the pH value of the system was 5.5, the temperature was 38 ℃, the stirring interval was 30 min, the speed was 600 rpm, the main purpose was to produce medium-chain fatty acids, one hydraulic cycle was 30 d, and it was operated continuously. The use volume of the acidification reactor was 2.5 L, the hydraulic load was 12%, and the amount of magnetic biochar added was 5% of the daily feed volume of the acidification reactor. After the daily discharge, the biochar was separated and collected by magnetism and re-added to the acidification reactor to obtain in-situ modified biochar.

[0051] (3) Anaerobic fermentation to produce methane

[0052] The anaerobic fermentation methanogen reactor was used, with a temperature of 38 °C, stirring for 30 min at intervals of 30 min, a rotation speed of 600 rpm, a hydraulic cycle of 30 d, and continuous operation. The amount of in-situ modified biochar added was 10wt% of the daily feed amount, and the biochar in the discharge was collected by magnetic separation every day. The changes in biogas production (wet gas flow meter), biogas content (methane, carbon dioxide, hydrogen content, determined by gas chromatography) and pH value (pH meter) were monitored every 3 days of anaerobic fermentation, and the results are shown in Table 1.

[0053] Example 2

[0054] (1) Preparation of magnetic biochar

[0055] Rice straw and ferric oxide (Fe 3 O 4 ) were used as raw materials with a mass ratio of 1:1. After mixing, they were ball milled at 300 rpm for 2 min, paused for 20 min, and repeated 6 times. Hydrothermal carbonization was performed at a temperature of 230 ℃, a heating rate of 3 ℃ / min, and a hydrothermal time of 12 h to obtain magnetic biochar.

[0056] (2) In-situ acidification modification

[0057] The acidification reactor was used, the pH value of the system was 5.0, the temperature was 38 ℃, the stirring interval was 30 min, the speed was 600 rpm, the main purpose was to produce medium-chain fatty acids, one hydraulic cycle was 30 d, and it was operated continuously. The use volume of the acidification reactor was 2.5 L, the hydraulic load was 12%, and the amount of magnetic biochar added was 5% of the daily feed volume of the acidification reactor. After the daily discharge, the biochar was separated and collected by magnetism and re-added to the acidification reactor to obtain in-situ modified biochar.

[0058] (3) Anaerobic fermentation to produce methane

[0059] The anaerobic fermentation methanogen reactor was used, with a temperature of 38 °C, stirring for 30 min at intervals of 30 min, a rotation speed of 600 rpm, a hydraulic cycle of 30 d, and continuous operation. The amount of in-situ modified biochar added was 5wt% of the daily feed amount, and the biochar in the discharge was collected by magnetic separation every day. The changes in biogas production (wet gas flowmeter) and methane content (determination method was gas chromatography) of anaerobic fermentation were monitored every 3 days, and the results are shown in Table 1.

[0060] Comparative Example 1

[0061] (1) Preparation of magnetic biochar

[0062] Rice straw and ferric oxide (Fe 3 O 4 ) were used as raw materials with a mass ratio of 1:1. After mixing, they were ball milled at 300 rpm for 2 min, paused for 20 min, and repeated 6 times. Hydrothermal carbonization was performed at a temperature of 230 ℃, a heating rate of 3 ℃ / min, and a hydrothermal time of 12 h to obtain magnetic biochar.

[0063] (2) Anaerobic fermentation to produce methane

[0064] The anaerobic fermentation methanogen reactor was used, with a temperature of 38 °C, stirring for 30 min at intervals of 30 min, a rotation speed of 600 rpm, a hydraulic cycle of 30 d, and continuous operation. The amount of biochar added was 5wt% of the daily feed amount, and the biochar in the discharge was collected by magnetic separation every day. The changes in biogas production (wet gas flow meter) and methane content (determination method was gas chromatography) of anaerobic fermentation were monitored every 3 days, and the results are shown in Table 1.

[0065] Comparative Example 2

[0066] (1) Anaerobic fermentation to produce methane

[0067] The anaerobic fermentation methanogen reactor was used, with a temperature of 38 °C, stirring for 30 min at intervals of 30 min, a rotation speed of 600 rpm, and a hydraulic cycle of 30 d, and continuous operation. No biochar was added to enhance anaerobic fermentation, and the changes in biogas production (wet gas flow meter) and methane content (determination method: gas chromatography) were monitored every 3 days of anaerobic fermentation. The results are shown in Table 1.

[0068] Table 1 Acidity and gas production data of Examples 1-2 and Comparative Examples 1-2

[0069]

[0070] According to Table 1, the gas production of Examples 1-2 of the present invention is significantly higher than that of Comparative Examples 1-2, and the methane content is also significantly higher than that of Comparative Examples 1-2, proving that the method provided by the present invention successfully improves the gas production and methane content of methane produced by anaerobic fermentation. By monitoring the gas production and methane yield, it can be verified that the catalytic effect of biochar is enhanced, thereby proving the successful acidification modification of biochar.

[0071] It can be seen from the above examples that the method provided by the present invention can increase the gas production and methane content of anaerobic fermentation to produce methane.

[0072] Although the above embodiment describes the present invention in detail, it is only a part of the embodiments of the present invention, not all of the embodiments. Other embodiments can be obtained based on this embodiment without creativity, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing methane by in-situ modified biochar enhanced anaerobic fermentation, characterized in that: The following steps are involved: The biochar is added into the anaerobic fermentation hydrolysis acidification system for in-situ modification to obtain in-situ modified biochar; Adding the in-situ modified biochar to an anaerobic fermentation methanogen system for anaerobic fermentation to obtain methane; The amount of biochar added is 5-10% of the feed volume of the anaerobic fermentation hydrolysis acidification system; The in-situ modified biochar has a micropore size of 2-7 nm, a macropore size of 50-300 nm, a porosity of 75-85%, and a specific surface area of ​​200-400 m 2 / g, the functional group grafting rate is 40~60%, the polycyclic aromatic hydrocarbon structure grafting rate is 15~25%, and the graphitization degree is 15~30%; The mass ratio of the in-situ modified biochar to the feed amount of the anaerobic fermentation methanogenesis system is 5-10:100; The biochar is magnetic biochar; the preparation method of the magnetic biochar is: mixing crop residues and magnetic substances and then hydrothermally carbonizing them.

2. The method according to claim 1, characterized in that The pH value of the in-situ modification is 5-5.5, the temperature is 36-38°C, and the total modification time is 20-60 days; the in-situ modification is carried out under stirring conditions, the stirring is interval stirring, and the interval time and stirring time of the interval stirring are independently 25-30 minutes; the stirring speed is 600-1000 rpm.

3. The method according to claim 1, characterized in that The temperature of the anaerobic fermentation methanogenesis system is 36-38°C, and the total fermentation time is 30-60 days; the anaerobic fermentation is carried out under stirring conditions, the stirring is intermittent stirring, and the interval time and stirring time of the intermittent stirring are independently 25-30 minutes; the stirring speed is 600-1000 rpm.

4. The method according to claim 1, characterized in that: The mass ratio of the crop residues to the magnetic material is 1-5:

1.

5. The method according to claim 1, characterized in that The hydrothermal carbonization includes a heating stage and a heat preservation stage in sequence; the heating rate of the heating stage is 5-10°C / min; the temperature of the heat preservation stage is 180-300°C, and the heat preservation time is 1-3 h.

6. The method according to claim 1 or 3, characterized in that: The anaerobic fermentation further includes post-processing, wherein the post-processing is to separate the in-situ modified biochar and reuse it as biochar.

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