A method for producing natural gas from biomass

Abstract

The application belongs to the field of natural gas preparation, and particularly relates to a method for preparing natural gas from biomass, wherein steam is used to gasify the biomass to obtain synthetic gas; the synthetic gas is subjected to steam catalytic pyrolysis under the action of a tar pyrolysis catalyst to obtain pyrolysis gas; carbon dioxide in the pyrolysis gas is captured and separated by using a carbon dioxide adsorption membrane to obtain high-hydrogen synthetic gas, which is then catalytically converted into methane, and the natural gas is obtained after purification. The method can reduce the pyrolysis temperature, avoid high-temperature deactivation of the catalyst, prolong the service life of the catalyst, reduce the production cost, increase the hydrogen-carbon ratio, and increase the methane content.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of natural gas preparation, and particularly relates to a method for preparing natural gas from biomass. BACKGROUND

[0002] Generating natural gas from biomass is an important way to treat environmental pollution of solid organic waste and realize reduction, harmlessness and resource utilization of solid organic waste. The development of social economy and the acceleration of urban-rural integration and rural revitalization process have rapidly increased the production of organic solid waste such as livestock and poultry manure, straw, kitchen waste, organic household waste and residual sludge in sewage treatment plants. However, such organic waste resources have great utilization potential. Developing bio-natural gas to treat livestock and poultry manure, crop straw, municipal solid waste and industrial organic waste in an industrialized, scaled and specialized manner can solve the problem of serious environmental pollution caused by random discharge and open burning of garbage, and accelerate the resource utilization of such organic waste. Biomass can generate methane through biochemical or thermochemical methods, but both biochemical and thermochemical methods have limitations. First, the difficulty in degrading lignocellulose seriously limits the speed of anaerobic digestion in the early stage, and it is difficult to match the production capacity of microorganisms between stages. In the process of methanation, the catalyst is easy to be poisoned by impurities, and the hydrogen-carbon ratio needs to be strictly controlled. The reaction needs to be carried out at high temperature and pressure, and the side reaction is serious. In the steam reforming of methane, the formation of coke will destroy the structure of the catalyst and seriously affect its activity. At the same time, the fine active substances on the catalyst are easy to sinter at high temperature, which will affect the catalytic effect and the production efficiency and cost of natural gas. SUMMARY

[0003] The present application mainly provides a method for preparing natural gas from biomass, which can integrally prepare catalyst and adsorbent, control the composition of synthesis gas, catalytically pyrolyze tar, and has high gas production efficiency. The technical scheme is as follows:

[0004] A method for preparing natural gas from biomass, using steam to gasify biomass to obtain synthesis gas; under the action of a tar pyrolysis catalyst, steam catalytic pyrolysis is performed on the synthesis gas to obtain pyrolysis gas; carbon dioxide in the pyrolysis gas is captured and separated by using a carbon dioxide adsorption membrane to obtain high-hydrogen synthesis gas, which is then catalytically converted into methane to obtain natural gas after purification.

[0005] Further, the mass ratio of steam to biomass is 1:1.5-3, and the high-hydrogen synthesis gas is converted into methane at 800-900℃.

[0006] Further, the mass flux ratio of steam to synthesis gas is 1:0.5-2 during the steam catalytic pyrolysis; the mass ratio of the tar pyrolysis catalyst to synthesis gas is 1:0.5-2; and the steam catalytic pyrolysis is carried out at 650-750℃.

[0007] Further, the preparation of the tar pyrolysis catalyst comprises the following steps: preparing polymethyl methacrylate microspheres; dispersing the polymethyl methacrylate microspheres in ethanol to obtain a dispersion liquid; mixing tetrabutyl titanate and aluminum nitrate in water, adding polyethylene glycol to disperse, stirring for 0.5-1h, then adding the dispersion liquid, reacting at 70-85℃ for 1-2h, naturally reducing to room temperature, and standing for 0.5-1h; separating and drying the precipitate, and calcining to obtain a carrier;

[0008] dispersing the carrier, ammonium molybdate and part of nickel nitrate in water, then adding diethanolamine, standing for 8-20h after uniform dispersion, drying, and calcining at 500-600℃ for 4-6h to obtain a primary load;

[0009] dispersing the primary load and the remaining nickel nitrate in water, repeating the standing and calcining operations to obtain the tar pyrolysis catalyst.

[0010] Further, the mass ratio of the polymethyl methacrylate microspheres to tetrabutyl titanate is 1-1.5:1; the mass ratio of the tetrabutyl titanate to aluminum nitrate is 1:2-4; and the mass ratio of the aluminum nitrate to polyethylene glycol is 1:0.1-0.3.

[0011] Further, the mass ratio of the ammonium molybdate to the carrier is 0.1-0.2:1; the mass ratio of the ammonium molybdate to the total nickel nitrate is 1:0.6-0.9; and the mass ratio of the part of nickel nitrate to the remaining nickel nitrate is 2-5:1.

[0012] Further, the preparation of the carbon dioxide adsorption membrane comprises the following steps: dispersing polymethyl methacrylate microspheres in ethanol at a mass ratio of 1:10-20 to obtain a dispersion liquid; adding aluminum nitrate, calcium nitrate and polyethylene glycol to the dispersion liquid, stirring and dispersing for 0.5-1h, then reacting at 70-85℃ until the ethanol is evaporated, naturally reducing the temperature, and standing for 0.5-1h; drying the membrane layer, and calcining to obtain the carbon dioxide adsorption membrane.

[0013] Further, the mass ratio of the polymethyl methacrylate microspheres to aluminum nitrate is 1:3-5; the mass ratio of the aluminum nitrate to calcium nitrate is 0.3-0.5:1; and the mass ratio of the aluminum nitrate to polyethylene glycol is 1:0.1-0.25.

[0014] Further, the preparation of the polymethyl methacrylate microspheres comprises the following steps: placing methyl methacrylate monomers in water, reacting for 10-20 min under a nitrogen atmosphere at 80 DEG C, adding 0.5-1% of potassium persulfate based on the mass of the monomers, stirring for 2-3 h, separating the microspheres, and drying to obtain the polymethyl methacrylate microspheres.

[0015] Further, calcining at 300-400 DEG C for 3-5 h, and then continuing to calcine at 1250-1400 DEG C for 5-8 h.

[0016] By using the above scheme, the method has the following advantages:

[0017] 1. The tar pyrolysis catalyst prepared by using the multiple templates and the multiple-step loading and sintering has many active sites and high catalytic activity, can reduce the pyrolysis temperature, avoid high-temperature deactivation of the catalyst, prolong the service life of the catalyst, and reduce the production cost.

[0018] 2. The titanium-aluminum composite carrier prepared by using the polymethyl methacrylate protects the nickel and the molybdenum, inhibits the high-temperature sintering deformation of the catalytic particles, limits the increase of the size of the molybdenum and nickel catalytic particles, and inhibits the carbon deposition. The titanium-aluminum composite carrier balances the acidity and alkalinity of the catalyst by using the alumina and the titanium oxide, ensures the catalytic activity, reduces the difficulty of the desorption of the catalytic products, avoids the secondary polymerization of the pyrolysis products, and reduces the carbon deposition.

[0019] 3. The step-by-step loading of the nickel increases the loading amount of the nickel, improves the carbon conversion rate, reduces the carbon deposition on the surface of the catalyst, and ensures the service life of the catalyst. The step-by-step loading can also reduce the aggregation of the nickel, ensure the small size of the nickel particles, reduce the nucleation rate of the carbon deposition, further reduce the carbon deposition, and reduce the influence of the large loading amount on the surface area, thereby ensuring the gas production rate.

[0020] 4. When the molybdenum is loaded, the template agent is added to promote the dispersion of the molybdenum and increase the porosity of the molybdenum oxide product, thereby providing more sites for the loading of the remaining nickel and ensuring the stability of the loading.

[0021] 5. When the tar pyrolysis catalyst and the carbon dioxide adsorption film are used, a small amount of polyethylene glycol is used to participate in the reaction, which can promote the dispersion of the carrier material and the combination with the polymethyl methacrylate, make the carrier form more controllable, and form a template to create pores in the carrier and increase the porosity of the carrier, which is beneficial to the stable loading of the catalyst.

[0022] 6. The alumina used in the application has high temperature resistance and high stability, forms a skeleton under the action of the polymethyl methacrylate, improves the strength of the adsorption film, limits the formation of calcium oxide and the space structure during the recycling and regeneration, and greatly prolongs the service life of the carbon dioxide adsorption film.

[0023] 7. This invention uses similar raw materials and methods to prepare tar pyrolysis catalyst and carbon dioxide adsorption membrane. The raw materials can be prepared simultaneously, the equipment purchase cost is low, the operation steps are quick to learn, the difficulty is low, and the process integration is high. Detailed Implementation

[0024] 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.

[0025] Example 1: (1) Methyl methacrylate monomer was placed in water and reacted at 80°C for 15 min in a nitrogen atmosphere. Potassium persulfate of 0.8% of the monomer mass was added and stirred for 3 h. After separating the microspheres and drying, polymethyl methacrylate microspheres were obtained.

[0026] (2) By mass, 4 parts of polymethyl methacrylate microspheres were dispersed in ethanol to obtain a dispersion; 3 parts of tetrabutyl titanate and 10 parts of aluminum nitrate were placed in water and mixed thoroughly, 1.2 parts of polyethylene glycol were added and dispersed thoroughly, and stirred for 0.5-1 h. Then the dispersion was added and reacted at 80℃ for 1-2 h. After naturally cooling to room temperature, it was allowed to stand for 0.5-1 h; after separating the precipitate and drying it, it was calcined at 350℃ for 4 h, and then calcined at 1300℃ for 6 h to obtain the carrier;

[0027] (3) Disperse 4 parts of support, 0.6 parts of ammonium molybdate and 0.38 parts of nickel nitrate in water and then add diethanolamine. After dispersing evenly, let stand for 12 hours. After drying, calcine at 550℃ for 5 hours to obtain a primary loading. Disperse the primary loading with 0.08 parts of nickel nitrate in water and repeat the standing and calcination operations to obtain a tar pyrolysis catalyst.

[0028] (4) Disperse 3 parts of polymethyl methacrylate microspheres in ethanol at a mass ratio of 1:15 to obtain a dispersion; add 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 parts of polyethylene glycol to the dispersion, stir and disperse thoroughly for 0.5-1 h, then react at 80℃ until the ethanol evaporates to dryness, cool naturally and let stand for 0.5-1 h; remove the membrane, dry it and calcine it at 350℃ for 4 h, then continue to calcine at 1300℃ for 6 h to obtain a carbon dioxide adsorption membrane;

[0029] (5) 100 g corn stalk powder is gasified by steam with a mass ratio of 1:2.5 at 800 ℃ under a nitrogen atmosphere to obtain synthesis gas; the synthesis gas is subjected to steam catalytic pyrolysis to obtain pyrolysis gas by controlling the mass ratio of the tar pyrolysis catalyst to the synthesis gas to be 1:1.5 and the mass flux ratio of steam to synthesis gas to be 1:1 at 700 ℃; the pyrolysis gas is passed through a carbon dioxide adsorption membrane to capture and separate 50-85% of the carbon dioxide in the pyrolysis gas to obtain high-hydrogen synthesis gas; and the high-hydrogen synthesis gas is catalytically converted into methane by using SCST-241 methanation catalyst of Shueta Chemical Industry Co., Ltd. at 800-900 ℃ and 2 MPa, and the contents of methane and carbon dioxide in the non-condensable gas produced are analyzed.

[0030] Example 2: The difference from Example 1 is that:

[0031] (2) 4 parts of polymethyl methacrylate microspheres are dispersed in ethanol to obtain a dispersion liquid; 3 parts of tetrabutyl titanate and 6 parts of aluminum nitrate are fully mixed in water, 1.2 parts of polyethylene glycol is fully dispersed, stirred for 0.5-1 h, then the dispersion liquid is added, reacted at 80 ℃ for 1-2 h, naturally lowered to room temperature, and then statically placed for 0.5-1 h; after the precipitate is separated and dried, calcination is performed at 350 ℃ for 4 h, and then calcination is continued at 1300 ℃ for 6 h to obtain a carrier.

[0032] Example 3: The difference from Example 1 is that:

[0033] (2) 4 parts of polymethyl methacrylate microspheres are dispersed in ethanol to obtain a dispersion liquid; 3 parts of tetrabutyl titanate and 12 parts of aluminum nitrate are fully mixed in water, 1.2 parts of polyethylene glycol is fully dispersed, stirred for 0.5-1 h, then the dispersion liquid is added, reacted at 80 ℃ for 1-2 h, naturally lowered to room temperature, and then statically placed for 0.5-1 h; after the precipitate is separated and dried, calcination is performed at 350 ℃ for 4 h, and then calcination is continued at 1300 ℃ for 6 h to obtain a carrier.

[0034] Example 4: The difference from Example 1 is that:

[0035] (2) 4 parts of polymethyl methacrylate microspheres are dispersed in ethanol to obtain a dispersion liquid; 3 parts of tetrabutyl titanate and 10 parts of aluminum nitrate are fully mixed in water, 0.6 parts of polyethylene glycol is fully dispersed, stirred for 0.5-1 h, then the dispersion liquid is added, reacted at 80 ℃ for 1-2 h, naturally lowered to room temperature, and then statically placed for 0.5-1 h; after the precipitate is separated and dried, calcination is performed at 350 ℃ for 4 h, and then calcination is continued at 1300 ℃ for 6 h to obtain a carrier.

[0036] Example 5: The difference from Example 1 is that:

[0037] (2) 4 parts of polymethyl methacrylate microspheres were dispersed in ethanol to obtain a dispersion liquid; 3 parts of tetrabutyl titanate and 10 parts of aluminum nitrate were mixed in water, 1.8 parts of polyethylene glycol was added and dispersed, stirred for 0.5-1 h, then the dispersion liquid was added, reacted at 80°C for 1-2 h, naturally cooled to room temperature, and then stood for 0.5-1 h; the precipitate was separated and dried, then calcined at 350°C for 4 h, and then calcined at 1300°C for 6 h to obtain a carrier.

[0038] Example 6: The difference from Example 1 is that:

[0039] (3) 4 parts of the carrier, 0.6 parts of ammonium molybdate and part of 0.3 parts of nickel nitrate were dispersed in water, then 0.1 parts of diethanolamine was added, uniformly dispersed, and stood for 12 h; dried and calcined at 550°C for 5 h to obtain a primary loading; the primary loading was dispersed in water with 0.15 parts of nickel nitrate, and the standing and calcining operations were repeated to obtain a tar pyrolysis catalyst.

[0040] Example 7: The difference from Example 1 is that:

[0041] (4) 3 parts of polymethyl methacrylate microspheres were dispersed in ethanol at a mass ratio of 1:10 to obtain a dispersion liquid; 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 parts of polyethylene glycol were added to the dispersion liquid, stirred and dispersed for 0.5-1 h, then reacted at 80°C until the ethanol was evaporated, naturally cooled, and then stood for 0.5-1 h; the membrane layer was taken out, dried, calcined at 350°C for 4 h, and then calcined at 1300°C for 6 h to obtain a carbon dioxide adsorption membrane.

[0042] Example 8: The difference from Example 1 is that:

[0043] (4) 3 parts of polymethyl methacrylate microspheres were dispersed in ethanol at a mass ratio of 1:20 to obtain a dispersion liquid; 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 parts of polyethylene glycol were added to the dispersion liquid, stirred and dispersed for 0.5-1 h, then reacted at 80°C until the ethanol was evaporated, naturally cooled, and then stood for 0.5-1 h; the membrane layer was taken out, dried, calcined at 350°C for 4 h, and then calcined at 1300°C for 6 h to obtain a carbon dioxide adsorption membrane.

[0044] Comparative Example 1: The difference from Example 1 is that:

[0045] (3) 4 parts of the carrier, 0.6 parts of ammonium molybdate and part of 0.45 parts of nickel nitrate were dispersed in water, then diethanolamine was added, uniformly dispersed, and stood for 12 h; dried and calcined at 550°C for 5 h to obtain a tar pyrolysis catalyst.

[0046] Comparative Example 2: The difference from Example 1 is that:

[0047] (4) 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 parts of polyethylene glycol were placed in 45 parts of ethanol, and dispersed by stirring for 0.5-1 h, then reacted at 80°C until the ethanol was evaporated, and then naturally cooled and stood for 0.5-1 h; the film layer was taken out, dried, calcined at 350°C for 4 h, and then calcined at 1300°C for 6 h to obtain a carbon dioxide adsorption film.

[0048] Comparative Example 3: The difference from Example 1 is that:

[0049] (4) 3 parts of polymethyl methacrylate microspheres were dispersed in ethanol at a mass ratio of 1:15 to obtain a dispersion liquid; 12 parts of calcium nitrate and 0.8 parts of polyethylene glycol were added to the dispersion liquid, and dispersed by stirring for 0.5-1 h, then reacted at 80°C until the ethanol was evaporated, and then naturally cooled and stood for 0.5-1 h; the film layer was taken out, dried, calcined at 350°C for 4 h, and then calcined at 900°C for 6 h to obtain a carbon dioxide adsorption film.

[0050] Example sample test:

[0051] The gas production rate was evaluated according to the mass ratio of gas to corn straw powder. The results are as follows:

[0052]

[0053] As can be seen from the above table, the gas production rate of Example 2 and Example 3 both decreased when preparing the tar pyrolysis catalyst, indicating that the proportion of aluminum oxide in the carrier affects the performance of the catalyst, and too much or too little aluminum oxide can affect the surface area and pores of the catalyst. The gas production rate of Example 4 decreased significantly compared to Example 5 due to the lower polyethylene glycol content, indicating that the polyethylene glycol can significantly affect the structure of the catalyst and affect the catalytic performance. However, the gas production rate of Example 5 did not increase compared to Example 1, and the carbon dioxide content increased, indicating that too much polyethylene glycol can also affect the catalytic effect, which may change the structure of the gas. In the loading of nickel, Comparative Example 1 did not load nickel in steps, and the gas production rate decreased significantly, indicating that stepwise loading can significantly improve the catalytic efficiency. At the same time, Example 6 has less nickel content in the first loading and more nickel content in the second loading, and the methane content slightly increases, but the gas production rate of the prepared gas decreases, indicating that the first loading plays a major role, and the nickel content of the two loadings needs to be maintained in a relatively appropriate proportion range. More nickel in the second loading may affect the protection of nickel and affect the tar pyrolysis effect, and the slight increase in the methane content may be affected by the insufficient pyrolysis.

[0054] In the preparation of carbon dioxide adsorption membrane, the carbon dioxide content of the system of Example 7 and Example 8 is obviously increased, and the gas production rate is also decreased, especially the gas production rate of Example 7 is decreased obviously. Here, the content of ethanol affects the reaction time and the structure formation of the adsorption membrane, thereby affecting the adsorption performance of the membrane, and low ethanol content is more detrimental to the properties of the adsorption membrane. The carbon dioxide content of Comparative Example 2 without the participation of polymethyl methacrylate microspheres in preparation is obviously increased, indicating that the polymethyl methacrylate microspheres can significantly affect the adsorption effect of the carbon dioxide adsorption membrane. At the same time, the carbon dioxide content of Comparative Example 3 without the addition of aluminum is also obviously increased, indicating that the addition of aluminum is beneficial to improve the selective adsorption performance of the carbon dioxide adsorption membrane to carbon dioxide.

[0055] The carbon dioxide adsorption membranes of Example 1, Comparative Example 2 and Comparative Example 3 are desorbed at 850°C, and then continue to be applied to the methods of Example 1, Comparative Example 2 and Comparative Example 3 respectively, and the adsorption and application operations are repeated 100 times, the difference in methane content between the first time and the 100th time is calculated, and the cycle performance of the adsorption membrane is evaluated. The results are as follows.

[0056] Methane content difference (%) Example 1 6.35 Comparative Example 2 8.86 Comparative Example 3 12.74

[0057] The greater the difference in methane content, the greater the change in the methane content of the gas produced after multiple cycles. As can be seen from the above table, compared with Example 1 with aluminum, when no aluminum is added to the carbon dioxide adsorption membrane, the difference in methane content after multiple cycles is obviously increased, indicating that the control ability of the carbon dioxide adsorption membrane to the carbon dioxide content is decreased, and the methane production is obviously reduced. The participation of aluminum can significantly improve the cycle stability of the carbon dioxide adsorption membrane. The cycle performance of Comparative Example 2 without the use of polymethyl methacrylate microspheres for structure shaping is also decreased, indicating that the participation of polymethyl methacrylate microspheres in the preparation of the adsorption membrane is beneficial to the uniform mixing of aluminum oxide and calcium oxide and the control of the crystal and structure, thereby being beneficial to maintaining the stability of the cycle.

[0058] For those skilled in the art, based on the technical solutions and concepts described above, various corresponding changes and modifications can be made, and all of these changes and modifications should belong to the protection scope of the claims of the present application.

Claims

1. A method for producing natural gas from biomass, characterized in that, Biomass is gasified with steam to obtain syngas; the syngas is then subjected to steam catalytic pyrolysis in the presence of a tar pyrolysis catalyst to obtain pyrolysis gas; carbon dioxide is captured and separated from the pyrolysis gas using a carbon dioxide adsorption membrane to obtain high-hydrogen syngas, which is then catalytically converted into methane and purified to obtain natural gas. The preparation of the tar pyrolysis catalyst includes the following steps: preparing polymethyl methacrylate microspheres; dispersing the polymethyl methacrylate microspheres in ethanol to obtain a dispersion; mixing tetrabutyl titanate and aluminum nitrate thoroughly in water, adding polyethylene glycol for thorough dispersion, stirring for 0.5-1 h, then adding the dispersion, reacting at 70-85℃ for 1-2 h, allowing it to cool naturally to room temperature and stand for 0.5-1 h; separating the precipitate and drying it, then calcining it to obtain the support; The carrier, ammonium molybdate, and a portion of nickel nitrate were dispersed in water, and then diethanolamine was added. After the dispersion was uniform, the mixture was allowed to stand for 8-20 hours. After drying, it was calcined at 500-600℃ for 4-6 hours to obtain the primary loaded material. The primary loading material and the remaining nickel nitrate were dispersed in water, and the process of settling and calcining was repeated to obtain the tar pyrolysis catalyst.

2. The method for producing natural gas from biomass according to claim 1, characterized in that, The mass ratio of steam to biomass is 1:1.5~3; the high-hydrogen synthesis gas is converted into methane at 800~900℃.

3. The method for producing natural gas from biomass according to claim 1, characterized in that, During steam catalytic pyrolysis, the mass flow ratio of steam to syngas is 1:0.5~2; the mass ratio of the tar pyrolysis catalyst to syngas is 1:0.5~2; and steam catalytic pyrolysis is carried out at 650~750℃.

4. The method for producing natural gas from biomass according to claim 1, characterized in that, The mass ratio of polymethyl methacrylate microspheres to tetrabutyl titanate is 1~1.5:1; the mass ratio of tetrabutyl titanate to aluminum nitrate is 1:2~4; and the mass ratio of aluminum nitrate to polyethylene glycol is 1:0.1~0.

3.

5. The method for producing natural gas from biomass according to claim 1, characterized in that, The mass ratio of ammonium molybdate to the carrier is 0.1~0.2:1; the mass ratio of ammonium molybdate to all nickel nitrate is 1:0.6~0.9; and the mass ratio of some nickel nitrate to the remaining nickel nitrate is 2~5:

1.

6. The method for producing natural gas from biomass according to claim 1, characterized in that, The preparation of the carbon dioxide adsorption membrane includes the following steps: dispersing polymethyl methacrylate microspheres in ethanol at a mass ratio of 1:10~20 to obtain a dispersion; adding aluminum nitrate, calcium nitrate and polyethylene glycol to the dispersion, stirring and dispersing thoroughly for 0.5~1h, then reacting at 70~85℃ until the ethanol evaporates to dryness, allowing it to cool naturally and stand for 0.5~1h; removing the membrane layer, drying it, and calcining it to obtain the carbon dioxide adsorption membrane.

7. The method for producing natural gas from biomass according to claim 6, characterized in that, The mass ratio of polymethyl methacrylate microspheres to aluminum nitrate is 1:3~5; the mass ratio of aluminum nitrate to calcium nitrate is 0.3~0.5:1; and the mass ratio of aluminum nitrate to polyethylene glycol is 1:0.1~0.

25.

8. The method for producing natural gas from biomass according to claim 1 or 6, characterized in that, The preparation of the polymethyl methacrylate microspheres includes the following steps: placing methyl methacrylate monomer in water, reacting at 80°C for 10-20 min in a nitrogen atmosphere, adding potassium persulfate at 0.5-1% of the monomer mass and stirring for 2-3 h, separating the microspheres and drying them to obtain polymethyl methacrylate microspheres.

9. The method for producing natural gas from biomass according to claim 1 or 6, characterized in that, The calcination refers to calcining at 300~400℃ for 3~5 hours, and then continuing to calcine at 1250~1400℃ for 5~8 hours.

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