A method for purifying natural gas produced from biomass

Abstract

The present application belongs to the field of biological fermentation, and particularly relates to a purification method for preparing natural gas from biomass, a porous hydrophobic carrier, and a porous particle prepared from the carrier by using a long-chain branched polymer; a hydrophilic modification is performed on the surface of the porous particle to obtain an amphiphilic carrier; then the amphiphilic carrier is stored in a hydrogen atmosphere to obtain a hydrogen-loaded particle; the hydrogen-loaded particle is mixed with an inoculum containing hydrogenotrophic methanogens, and then the mixture is used to ferment the biomass in an aqueous system to produce natural gas, thereby forming purification. The gas prepared by the method has a high content of methane and a low content of carbon dioxide, and is equivalent to natural gas in content, and can be used as natural gas.

Description

Technical Field

[0001] This invention belongs to the field of bio-fermentation, specifically relating to a purification method for biomass-to-natural gas. Background Technology

[0002] For decades, global development has relied heavily on fossil fuels. However, fossil fuels are finite and release large amounts of carbon dioxide during combustion, contributing to global warming and climate change. Developing and practically applying renewable energy sources is urgently needed to mitigate the rate of fossil fuel depletion and significantly reduce global carbon emissions. Biomass is a vast and clean renewable energy source, but most biomass exists as waste, including sewage, kitchen waste, straw, and livestock manure. Anaerobic fermentation is a widely used biological process for recovering energy from biomass, converting waste organic carbon into biogas, an important biofuel primarily composed of methane. However, biogas contains not only methane but also carbon dioxide. Methane is the most energy-rich compound in biogas, and the 15-60% carbon dioxide significantly dilutes the methane content and lowers its calorific value, limiting its use as fuel and making it suitable only for simple cooking. Furthermore, when biogas is compressed, carbon dioxide easily transforms into dry ice under high pressure, making long-distance transportation difficult.

[0003] Currently, methods such as water washing, adsorption, and membrane separation are maturely applied in industrial biogas purification. However, these methods have high operating and equipment costs, and suffer from problems such as the need for inert gases and large amounts of water, difficulty in adsorbent preparation, high regeneration costs, and the potential generation of environmentally harmful byproducts. Microbial technology offers a sustainable method for biogas purification that can be carried out under environmental conditions without the use of expensive catalysts and chemicals. Compared to raw biogas, the biogas purified by biotechnology has a higher methane concentration, reaching the concentration standards of natural gas, and can be directly injected into existing natural gas networks. Microbial purification of biogas is based on the method of hydrotrophic methanogens using hydrogen and carbon dioxide to produce methane, thereby reducing carbon dioxide and increasing methane. However, this method requires hydrogen, which has very low solubility in water compared to carbon dioxide and methane, affecting its mass transfer in the system. Methods to mitigate hydrogen gas-liquid mass transfer mainly include stirring, adding packing material to reduce bubble size, gas circulation, and increasing reactor pressure. These methods have problems such as adverse effects on the microbial community structure, high equipment requirements, and high resource and energy consumption. The low solubility of hydrogen has severely hampered the development of technologies for converting biogas into natural gas. Summary of the Invention

[0004] This invention primarily provides a method for using a carrier with high affinity for hydrogen and strong adsorption capacity to carry hydrogen, and then continuously releasing it to supply biomass fermentation for purification into natural gas. The technical solution is as follows:

[0005] A method for purifying natural gas from biomass involves preparing a porous hydrophobic carrier, which is then made into porous particles using a long-chain, branched polymer. The surface of the porous particles is hydrophilically modified to obtain an amphiphilic carrier. The amphiphilic carrier is then used to store hydrogen in a hydrogen atmosphere to obtain hydrogen-loaded particles. An inoculum containing hydrogen-nutritive methanogens is fermented with biomass in an aqueous system. After the microorganisms adapt, the hydrogen-loaded particles are added to the system for further fermentation.

[0006] Furthermore, the mass ratio of the hydrogen-loaded particles to the inoculum is 0.5–5:1; the mass ratio of the inoculum to the biomass is 1:2–4; and the thickness of the porous particles is 0.5–5 cm.

[0007] Furthermore, the inoculum contains 0.2–1 g / L nitrogen, 0.8–3.5 g / L phosphorus, and 3–6 mg / L magnesium.

[0008] Further steps include: crushing the straw and mixing it with inoculum of hydrogen-containing methanogenic bacteria, adding hydrogen-carrying granules, adding water to make the solid content of the system reach 5-25%, and anaerobic digesting at 35-38℃ for 6-24 days.

[0009] Furthermore, the preparation method of the amphiphilic vector includes the following steps:

[0010] a. Dissolve sodium aluminate in water, then add hexadecyltrimethylammonium bromide and mix thoroughly. Continue to add sodium hydroxide and silica gel, mix evenly, and obtain a mixture. Crystallize the mixture at 140-160℃ for 24-42 hours. After thoroughly washing the crystals, heat treat them at 100-150℃ for 6-12 hours to obtain a hydrophobic carrier.

[0011] b. Mix methyl methacrylate polymer, dichloromethane, carbon tetrachloride and ethanol thoroughly. After mixing evenly, pour into a mold and let stand at 40-55°C for 0.5-1 h. Then, vacuum and let stand for another 3-6 h. After taking it out, you will get porous particles.

[0012] c. Prepare an acrylic acid solution, add benzophenone and mix. Use the acrylic acid solution to wet the outer surface of the porous particles. After removing oxygen from the system, react with ultraviolet light under sealed conditions for 5-15 minutes. After removal, wash and dry thoroughly.

[0013] Furthermore, in step a, the silicon-to-aluminum ratio is 300–500; the molar ratio of silica gel to sodium hydroxide is 5–18:1; and the molar ratio of silica gel to hexadecyltrimethylammonium bromide is 2–3.5:1.

[0014] Furthermore, in step b, the mass ratio of the sum of dichloromethane and carbon tetrachloride to methyl methacrylate is 8–3:1; the mass ratio of methyl methacrylate to ethanol is 1:0.8–1.5; and the mass ratio of dichloromethane to carbon tetrachloride is 2–3:1.

[0015] Furthermore, the preparation of the methyl methacrylate includes the following steps: thoroughly mixing methyl methacrylate and a hydrophobic carrier, adding azobisisobutyronitrile, mixing evenly, and then polymerizing at 60-75°C for 2-4 hours.

[0016] Furthermore, the mass ratio of methyl methacrylate to the hydrophobic carrier is 0.5 to 5:1; the azobisisobutyronitrile accounts for 1 to 3% of the mass of methyl methacrylate.

[0017] Furthermore, the porous particles are soaked in ethanol, then rinsed with ethanol or water, dried, and placed on an acrylic acid solution; the benzophenone mentioned in step c accounts for 2-4% of the mass of the acrylic acid.

[0018] By adopting the above scheme, the method of the present invention has the following advantages:

[0019] 1. When the hydrogen-carrying particles of the present invention are placed in the aqueous fermentation broth, the pores of the carrier and the polymer have a high affinity for hydrogen, which attracts hydrogen. Meanwhile, the hydrophilic groups on the particle surface and the water in the external fermentation broth with poor affinity for hydrogen will prevent hydrogen from overflowing, thereby making the hydrogen release cycle longer and solving the problem that hydrogen is easily and quickly released into the upper gas phase.

[0020] 2. The hydrogen-carrying particles of this invention are filled with pores and gas, allowing them to float on the liquid surface under natural conditions. The gas produced during fermentation rises to the surface and combines with the hydrogen gas there, resulting in high mass transfer efficiency. This facilitates the conversion of high-concentration carbon dioxide gas at the surface by the fermenting bacteria, improving conversion efficiency. Furthermore, it prevents the hydrogen-carrying particles from falling deep into the fermentation broth and being squeezed out of the carrier under pressure, thus achieving effective storage and utilization of hydrogen.

[0021] 3. The surface of the amphiphilic carrier of the present invention is hydrophilic, which is beneficial to the interfacial bonding between the aqueous system containing hydrogen-nutritive methanogens and the carrier, thereby achieving effective utilization of hydrogen.

[0022] 4. In this invention, cetyltrimethylammonium bromide is used as a template agent. After the carrier crystal is formed, the system is thoroughly dried and heat-treated to promote the tight connection between the cetyltrimethylammonium bromide in the carrier pores and the inner wall, thereby reducing its detachment.

[0023] 5. The carrier of the present invention adsorbs hydrogen into the pores through van der Waals forces, and the carrier is not subjected to conventional calcination after formation. The adsorption of hydrogen in the carrier pores is improved by utilizing the long-chain characteristics of hexadecyltrimethylammonium bromide and the high affinity of hydrogen for long-chain alkanes.

[0024] 6. This invention uses polymethyl methacrylate with a high degree of branching on the main chain to connect and fix the carrier. On the one hand, the volume can be increased without affecting the adsorption of the carrier precursor, making it easier to separate and recover in practical applications. On the other hand, the highly branched main chain has a higher affinity for hydrogen, and the pores formed by the polymer itself can also adsorb hydrogen.

[0025] 7. This invention fills the amphiphilic carrier with hydrogen, and the hydrogen is released uniformly within the carrier. This solves the problems of wasted hydrogen resources and excessively high equipment and preparation costs caused by pressurization and circulating gas intake. It also solves the problem that improving mass transfer efficiency through stirring can easily affect the structure of the microbial community. Attached Figure Description

[0026] Figure 1 A comparison chart of the average carbon dioxide concentration produced in each embodiment and comparative example;

[0027] Figure 2 : Comparison of average methane concentration in gas produced by each embodiment and comparative example. Detailed Implementation

[0028] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0029] Example 1: (1) Dissolve 1 mmol sodium aluminate in water, then add 0.12 mol hexadecyltrimethylammonium bromide and mix thoroughly. Then add 30 mmol sodium hydroxide and 0.3 mol silica gel and mix evenly to obtain a mixture. Crystallize the mixture at 150°C for 36 h. After thoroughly washing the crystals, heat treat them at 120°C for 8 h to obtain a hydrophobic carrier.

[0030] (2) Mix 10g of methyl methacrylate and 25g of hydrophobic carrier thoroughly, add 0.2g of azobisisobutyronitrile, mix evenly, and then polymerize at 65℃ for 3h; mix methyl methacrylate polymer, 45mL of dichloromethane, 20mL of carbon tetrachloride and 12mL of ethanol thoroughly, and after mixing evenly, pour the mixed liquid with a thickness of 2-3cm into a mold with a pore size of 5×5cm, place it in a vacuum box, let it stand at 40℃ for 1h, and then evacuate and continue to stand for 6h to obtain porous particles;

[0031] (3) Prepare an acrylic acid solution, add 3% benzophenone by mass of acrylic acid and mix, soak the porous particles in ethanol, rinse with ethanol or water, dry, and then replace the gas adsorbed in the porous particles with nitrogen gas. Put the porous particles back into the mold, pour acrylic acid solution onto the porous particles in the mold to make the porous particles float and wet the outer surface, remove the oxygen in the system, and react under ultraviolet light for 10 min under closed conditions. After taking it out, wash and dry it thoroughly to obtain the amphiphilic carrier.

[0032] (4) Then, the amphiphilic carrier is pressurized in a hydrogen atmosphere to store hydrogen, so that the amphiphilic carrier is filled with hydrogen to obtain hydrogen-loaded particles; fresh cow manure containing 0.5-1 g / L nitrogen, 2-3 g / L phosphorus, 4-5 mg / L magnesium and rich in hydrogen-nutritive methanogens is prepared as inoculum. The inoculum and crushed straw are mixed at a mass ratio of 1:3, and water is added to make the solid content of the system reach 10%. After anaerobic digestion at 7°C for 6 days, hydrogen-loaded particles with a mass of 3 times that of the inoculum are added to the surface of the mixture, and fermentation continues for 12 days.

[0033] Example 2: The difference from Example 1 is as follows:

[0034] (1) Dissolve 1 mmol sodium aluminate in water, then add 0.15 mol cetyltrimethylammonium bromide and mix thoroughly. Then add 30 mmol sodium hydroxide and 0.3 mol silica gel and mix evenly to obtain a mixture. Crystallize the mixture at 150 °C for 36 h. After thoroughly washing the crystals, heat treat them at 120 °C for 8 h to obtain a hydrophobic carrier.

[0035] Example 3: The difference from Example 1 is as follows:

[0036] (1) Dissolve 1 mmol sodium aluminate in water, then add 0.085 mol cetyltrimethylammonium bromide and mix thoroughly. Then add 30 mmol sodium hydroxide and 0.3 mol silica gel and mix evenly to obtain a mixture. Crystallize the mixture at 150 °C for 36 h. After thoroughly washing the crystals, heat treat them at 120 °C for 8 h to obtain a hydrophobic carrier.

[0037] Example 4: The difference from Example 1 is as follows:

[0038] (2) Mix 10g of methyl methacrylate and 5g of hydrophobic carrier thoroughly, add 0.2g of azobisisobutyronitrile, mix evenly, and then polymerize at 65℃ for 3h; mix methyl methacrylate polymer, 45mL of dichloromethane, 20mL of carbon tetrachloride and 12mL of ethanol thoroughly, and after mixing evenly, pour the mixed liquid with a thickness of 2-3cm into a mold with a pore size of 5×5cm, place it in a vacuum box, let it stand at 40℃ for 1h, and then evacuate and continue to stand for 6h to obtain porous particles.

[0039] Example 5: The difference from Example 1 is as follows:

[0040] (2) Mix 10g of methyl methacrylate and 50g of hydrophobic carrier thoroughly, add 0.2g of azobisisobutyronitrile, mix evenly, and then polymerize at 65℃ for 3h; mix methyl methacrylate polymer, 45mL of dichloromethane, 20mL of carbon tetrachloride and 12mL of ethanol thoroughly, and after mixing evenly, pour the mixed liquid with a thickness of 2-3cm into a mold with a pore size of 5×5cm, place it in a vacuum box, let it stand at 40℃ for 1h, and then evacuate and continue to stand for 6h to obtain porous particles.

[0041] Example 6: The difference from Example 1 is as follows:

[0042] (2) Mix 10g of methyl methacrylate and 25g of hydrophobic carrier thoroughly, add 0.2g of azobisisobutyronitrile, mix evenly, and then polymerize at 65℃ for 3h; mix methyl methacrylate polymer, 60mL of dichloromethane, 20mL of carbon tetrachloride and 12mL of ethanol thoroughly, and after mixing evenly, pour the mixed liquid with a thickness of 2-3cm into a mold with a pore size of 5×5cm, place it in a vacuum box, let it stand at 40℃ for 1h, and then evacuate and continue to stand for 6h to obtain porous particles.

[0043] Example 7: The difference from Example 1 is as follows:

[0044] (2) Mix 10g of methyl methacrylate and 25g of hydrophobic carrier thoroughly, add 0.2g of azobisisobutyronitrile, mix evenly, and then polymerize at 65℃ for 3h; mix methyl methacrylate polymer, 20mL of dichloromethane, 10mL of carbon tetrachloride and 12mL of ethanol thoroughly, and after mixing evenly, pour the mixed liquid with a thickness of 2-3cm into a mold with a pore size of 5×5cm, place it in a vacuum box, let it stand at 40℃ for 1h, and then evacuate and continue to stand for 6h to obtain porous particles.

[0045] Example 8: The difference from Example 1 is as follows:

[0046] (4) Then, the amphiphilic carrier is pressurized in a hydrogen atmosphere to store hydrogen, so that the amphiphilic carrier is filled with hydrogen to obtain hydrogen-loaded particles; fresh cow manure containing 0.5-1 g / L nitrogen, 2-3 g / L phosphorus, 4-5 mg / L magnesium and rich in hydrogen-nutritive methanogens is prepared as inoculum. The inoculum and crushed straw are mixed at a mass ratio of 1:3, and water is added to make the solid content of the system reach 10%. After anaerobic digestion at 7°C for 6 days, hydrogen-loaded particles with a mass of 5 times that of the inoculum are added to the surface of the mixture, and fermentation continues for 12 days.

[0047] Example 9: The difference from Example 1 is as follows:

[0048] (4) Then, the amphiphilic carrier is pressurized in a hydrogen atmosphere to store hydrogen, so that the amphiphilic carrier is filled with hydrogen to obtain hydrogen-loaded particles; fresh cow manure containing 0.5-1 g / L nitrogen, 2-3 g / L phosphorus, 4-5 mg / L magnesium and rich in hydrogen-nutritive methanogens is prepared as inoculum. The inoculum and crushed straw are mixed at a mass ratio of 1:3, and water is added to make the solid content of the system reach 10%. After anaerobic digestion at 7°C for 6 days, 0.5 times the mass of the inoculum hydrogen-loaded particles are added to the surface of the mixture, and fermentation continues for 12 days.

[0049] Comparative Example 1: The difference from Example 1 is that:

[0050] (1) Dissolve 1 mmol sodium aluminate in water, then add 0.12 mol hexadecyltrimethylammonium bromide and mix thoroughly. Then add 30 mmol sodium hydroxide and 0.3 mol silica gel and mix evenly to obtain a mixture. Crystallize the mixture at 150 °C for 36 h. After thoroughly washing the crystals, calcine them at 550 °C for 3 h to obtain a hydrophobic support.

[0051] Comparative Example 2: The difference from Example 1 is that:

[0052] No acrylic acid is used for hydrophilic modification.

[0053] Example Sample Testing:

[0054] The daily gas production was measured using the water displacement gas collection method from day 12 to day 18 of the overall fermentation process. Gas chromatography was used to determine the carbon dioxide and methane content in the gases. The carbon dioxide and methane concentrations were calculated based on the gas production, and the average values ​​for days 12 to 18 were calculated. The results are as follows:

[0055]

[0056] As can be seen from the table above, the carbon dioxide content in each embodiment is significantly lower than that in the comparative example, while the methane content is significantly higher. Furthermore, the methane content in most embodiments is greater than 90%, indicating that the hydrogen-carrying particles of the present invention have a significant promoting effect on the conversion of carbon dioxide to methane. Compared to Example 1, the average carbon dioxide content in Examples 2 and 3, which added more and less hexadecyltrimethylammonium bromide respectively, increased, while the average methane content decreased. This indicates that more hexadecyltrimethylammonium bromide is beneficial for hydrogen adsorption, but excessive amounts may affect the formation of carrier pores, and excessively large pores are also detrimental to hydrogen adsorption. In Comparative Example 1, where the carrier was calcined to remove hexadecyltrimethylammonium bromide, the carbon dioxide content reached 10.4%, and the methane content was only 81.7%, indicating that the presence of hexadecyltrimethylammonium bromide has a significant impact on hydrogen loading.

[0057] In Example 4, the carbon dioxide content increased significantly while the methane content decreased. In Example 5, the carbon dioxide content decreased while the methane content increased, indicating that when preparing porous particles, a higher polymer-loaded support is beneficial for hydrogen adsorption, thereby promoting the conversion of carbon dioxide to methane. However, the decrease in carbon dioxide content in Example 5 did not match the increase in the hydrophobic support, resulting in a relative increase in cost. Moreover, an excessive amount of hydrophobic support can easily affect the structural integrity of the porous particles. In the preparation of porous particles, the dichloromethane content increased and the carbon tetrachloride content relatively decreased in Example 6. In Example 7, the amount of dichloromethane and carbon tetrachloride added decreased, but the proportion of carbon tetrachloride in dichloromethane and carbon tetrachloride increased. However, the carbon dioxide content in Examples 6 and 7 increased compared to Example 1, indicating that maintaining the content of dichloromethane, carbon tetrachloride, and polymer within a relatively balanced ratio range is beneficial for promoting the adsorption of hydrogen-loaded particles.

[0058] Comparative Example 2 did not undergo hydrophilic modification of the porous particles, resulting in a strong hydrophobic surface. This made it difficult for the aqueous fermentation broth to directly contact the porous particles, hindering the mass transfer of hydrogen to the fermentation broth. Consequently, it affected the rate at which microorganisms directly consumed carbon dioxide and hydrogen at the liquid surface, thus impacting the concentration difference of hydrogen generated by the liquid surface and microbial consumption, and the rate at which hydrogen continuously dissolved into the fermentation broth. Therefore, the carbon dioxide content of Comparative Example 2 was significantly increased, while the methane content dropped to below 80%.

[0059] In actual fermentation, compared to Example 1, Example 8, which incorporated more hydrogen-loaded particles, showed a significant decrease in carbon dioxide content and a significant increase in methane content, while Example 9, with less hydrogen-loaded particles, showed the opposite. This indicates that the content of hydrogen-loaded particles directly affects the efficiency of carbon dioxide to methane conversion. The method of this invention can significantly purify biogas produced by biomass fermentation, enabling the production of natural gas from biomass.

[0060] For those skilled in the art, various other corresponding changes and modifications can be made based on the technical solutions and concepts described above, and all such changes and modifications should fall within the protection scope of the claims of this invention.

Claims

1. A method for purifying natural gas from biomass, characterized in that, A porous hydrophobic carrier is prepared by using a long-chain, branched polymer to form porous particles; the surface of the porous particles is hydrophilically modified to obtain an amphiphilic carrier; then, the amphiphilic carrier is subjected to hydrogen storage in a hydrogen atmosphere to obtain hydrogen-loaded particles; an inoculum containing hydrogen-nutritive methanogens is fermented with biomass in an aqueous system; after the microorganisms have adapted, hydrogen-loaded particles are added to the system for continued fermentation; the preparation method of the amphiphilic carrier includes the following steps: a. Dissolve sodium aluminate in water, then add hexadecyltrimethylammonium bromide and mix thoroughly. Continue to add sodium hydroxide and silica gel, mix evenly to obtain a mixture. Crystallize the mixture at 140~160℃ for 24~42h. After thoroughly washing the obtained crystals, heat treat them at 100~150℃ for 6~12h to obtain a hydrophobic carrier. b. Mix methyl methacrylate polymer, dichloromethane, carbon tetrachloride and ethanol thoroughly. After mixing evenly, pour into a mold and let stand at 40~55℃ for 0.5~1h. Then, vacuum and let stand for another 3~6h. After taking it out, you will get porous particles. c. Prepare an acrylic acid solution, add benzophenone and mix. Use the acrylic acid solution to wet the outer surface of the porous particles. After removing oxygen from the system, react with ultraviolet light under sealed conditions for 5-15 minutes. After removal, wash and dry thoroughly.

2. The method for purifying natural gas from biomass according to claim 1, characterized in that, The mass ratio of hydrogen-loaded particles to inoculum is 0.5~5:1; the mass ratio of inoculum to biomass is 1:2~4; and the thickness of the porous particles is 0.5~5cm.

3. The method for purifying natural gas from biomass according to claim 1, characterized in that, The inoculum contains 0.2-1 g / L nitrogen, 0.8-3.5 g / L phosphorus, and 3-6 mg / L magnesium.

4. The method for purifying biomass-to-natural gas according to claim 1, characterized in that, The process includes the following steps: crushing the straw and mixing it with inoculum of hydrogen-containing methanogenic bacteria, adding hydrogen-carrying granules, adding water to make the solid content of the system reach 5-25%, and anaerobic digesting at 35-38℃ for 6-24 days.

5. The method for purifying natural gas from biomass according to claim 1, characterized in that, In step a, the silicon-to-aluminum ratio is 300-500; the molar ratio of silica gel to sodium hydroxide is 5-18:1; and the molar ratio of silica gel to hexadecyltrimethylammonium bromide is 2-3.5:

1.

6. The method for purifying natural gas from biomass according to claim 1, characterized in that, In step b, the mass ratio of the sum of dichloromethane and carbon tetrachloride to methyl methacrylate is 8-3:1; the mass ratio of methyl methacrylate to ethanol is 1:0.8-1.5; and the mass ratio of dichloromethane to carbon tetrachloride is 2-3:

1.

7. The method for purifying natural gas from biomass according to claim 1, characterized in that, The preparation of the methyl methacrylate includes the following steps: Methyl methacrylate and a hydrophobic carrier are thoroughly mixed, then azobisisobutyronitrile is added and mixed evenly. The mixture is then polymerized at 60-75°C for 2-4 hours.

8. The method for purifying natural gas from biomass according to claim 7, characterized in that, The mass ratio of methyl methacrylate to hydrophobic carrier is 0.5~5:1; the azobisisobutyronitrile accounts for 1~3% of the mass of methyl methacrylate.

9. The method for purifying natural gas from biomass according to claim 1, characterized in that, The porous particles are soaked in ethanol, then rinsed with ethanol or water, dried, and placed on an acrylic acid solution; the benzophenone mentioned in step c accounts for 2-4% of the mass of the acrylic acid.

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