Method for preparing natural gas from biomass

Abstract

The invention belongs to the field of natural gas preparation, and particularly relates to a method for preparing natural gas from biomass, which comprises the following steps: gasifying the biomass by using steam to obtain synthesis gas; under the action of a tar pyrolysis catalyst, performing steam catalytic pyrolysis on the synthesis gas to obtain pyrolysis gas; the method comprises the following steps: capturing and separating carbon dioxide in pyrolysis gas by adopting a carbon dioxide adsorption film to obtain high-hydrogen synthesis gas, then catalytically converting the high-hydrogen synthesis gas into methane, and purifying to obtain natural gas. The method provided by the invention 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 invention belongs to the field of natural gas preparation, and particularly relates to a method for preparing natural gas from biomass. Background Art

[0002] Generating natural gas from biomass is an important way to control environmental pollution of solid organic waste and achieve reduction, harmlessness, and resource utilization of solid organic waste. With the development of social economy and the acceleration of the process of urban-rural integration and rural revitalization, the generation of organic solid waste such as livestock manure, straw, kitchen waste, organic domestic waste, and excess sludge from sewage treatment plants has increased rapidly. However, such organic waste resources have great utilization potential. Developing bio-natural gas to treat urban and rural organic solid waste such as livestock manure, crop straw, urban domestic waste, and industrial organic waste in an industrialized, large-scale, and specialized manner can solve the serious environmental pollution problems caused by the 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 defects that limit their development. First, the problem of difficult degradation of lignocellulose makes the biochemical method severely limited in the front stage of anaerobic digestion, and it is difficult to match the microbial production capacity between stages. Moreover, the catalyst in the methanation process is easily poisoned by impurities, and the hydrogen-carbon ratio needs to be strictly controlled during the process. The reaction also needs to be carried out at relatively high temperatures and pressures, and side reactions interfere severely. In the steam reforming of methane, the formation of coke will damage the catalyst structure and seriously affect its activity. When coke pyrolyzes, due to the Lewis acid adsorption of the catalyst, if the catalytic products cannot be desorbed in time, it is easy to form carbon deposits on the catalyst surface, covering the active sites of the pyrolysis catalyst. At the same time, the fine-grained active substances on the catalyst are easily sintered at high temperatures. These factors will all affect the catalytic effect, thus affecting the production efficiency and cost of natural gas. Summary of the Invention

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

[0004] A method for preparing natural gas from biomass, which uses steam to gasify biomass to obtain syngas; under the action of a tar pyrolysis catalyst, performs steam catalytic pyrolysis on the syngas to obtain pyrolysis gas; uses a carbon dioxide adsorption membrane to capture and separate carbon dioxide in the pyrolysis gas to obtain high-hydrogen syngas, and then catalytically converts the high-hydrogen syngas into methane, and purifies it to obtain natural gas.

[0005] Further, the mass ratio of the steam to the biomass is 1:1.5 - 3; the high-hydrogen syngas is converted into methane at 800 - 900 °C.

[0006] Furthermore, during steam catalytic pyrolysis, the mass flux 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; steam catalytic pyrolysis is carried out at 650 - 750 °C.

[0007] Furthermore, 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; taking tetrabutyl titanate and aluminum nitrate and fully mixing them in water, adding polyethylene glycol and fully dispersing, stirring for 0.5 - 1 h, then adding the dispersion, reacting at 70 - 85 °C for 1 - 2 h, naturally cooling to room temperature and then standing for 0.5 - 1 h; separating the precipitate, drying, and then calcining to obtain a support;

[0008] Dispersing the support, ammonium molybdate, and part of nickel nitrate in water and then adding diethanolamine, standing for 8 - 20 h after uniform dispersion; drying and then calcining at 500 - 600 °C for 4 - 6 h to obtain a primary loaded product;

[0009] Dispersing the primary loaded product and the remaining nickel nitrate in water, repeating the operations of standing and calcining to obtain the tar pyrolysis catalyst.

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

[0011] Furthermore, the mass ratio of ammonium molybdate to the support is 0.1 - 0.2:1; the mass ratio of ammonium molybdate to all nickel nitrate is 1:0.6 - 0.9; the mass ratio of the part of nickel nitrate to the remaining nickel nitrate is 2 - 5:1.

[0012] Furthermore, 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, fully stirring and dispersing for 0.5 - 1 h, then reacting at 70 - 85 °C until the ethanol evaporates completely, naturally cooling and then standing for 0.5 - 1 h; removing the film layer, drying, and then calcining to obtain the carbon dioxide adsorption membrane.

[0013] Furthermore, the mass ratio of the 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; the mass ratio of 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 monomer in water, reacting at 80 °C for 10 - 20 min in a nitrogen atmosphere, adding potassium persulfate accounting for 0.5 - 1% of the monomer mass, stirring and reacting for 2 - 3 h, separating the microspheres and drying them to obtain polymethyl methacrylate microspheres.

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

[0016] Adopting the above scheme, the method of the present invention has the following advantages:

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

[0018] 2. The present invention uses polymethyl methacrylate to prepare a titanium-aluminum composite support, which protects nickel and molybdenum, inhibits high-temperature sintering and denaturation of catalytic particles, also limits the increase in the size of molybdenum and nickel catalytic particles, and inhibits carbon deposition. Moreover, the titanium-aluminum composite support uses alumina and titanium oxide to balance the acidity and basicity of the catalyst, ensuring catalytic activity and reducing the difficulty of desorption of catalytic products, avoiding secondary polymerization of pyrolysis products, and reducing carbon deposition.

[0019] 3. The nickel is loaded step by step, increasing the nickel loading amount, improving the carbon conversion rate, reducing carbon deposition on the catalyst surface, and ensuring the service life of the catalyst. Step-by-step loading can also reduce the aggregation of nickel, ensure the fineness of nickel particles, reduce the rate of carbon deposition nucleation, further reduce carbon deposition, and can also reduce the influence of large loading amounts on the surface area, thereby ensuring the gas production rate.

[0020] 4. When loading molybdenum, a templating agent is added to promote the dispersion of 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 of the present invention are used, a small amount of polyethylene glycol participates in the reaction, which can promote the dispersion of the carrier material and its combination with polymethyl methacrylate, making the carrier morphology more controllable. At the same time, polyethylene glycol itself also forms a templating effect, creating pores in the carrier and increasing the porosity of the carrier, which is beneficial to the stable loading of the catalyst.

[0022] 6. The present invention uses alumina with high temperature resistance and strong stability to form a framework under the action of polymethyl methacrylate, improving the strength of the adsorption film, defining the formation and spatial structure of calcium oxide during cyclic regeneration, and greatly extending the service life of the carbon dioxide adsorption film.

[0023] 7. The present invention uses similar raw materials and methods to prepare a tar pyrolysis catalyst and a carbon dioxide adsorption membrane. The raw materials can be prepared simultaneously, with low equipment purchase costs, quick and easy operation steps, low difficulty, and high process integration. Detailed Embodiments

[0024] The technical solutions in the embodiments of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of them. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope 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 accounting for 0.8% of the monomer mass was added and stirred for 3 h. After separating the microspheres and drying, poly(methyl methacrylate) microspheres were obtained;

[0026] (2) By mass, 4 parts of poly(methyl 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 sufficiently, stirred for 0.5 - 1 h, then the dispersion was added, and reacted at 80 °C for 1 - 2 h. After naturally cooling to room temperature, it was left standing for 0.5 - 1 h; After separating the precipitate and drying, it was calcined at 350 °C for 4 h, and then continued to be calcined at 1300 °C for 6 h to obtain a support;

[0027] (3) 4 parts of the support, 0.6 part of ammonium molybdate and part of 0.38 part of nickel nitrate were dispersed in water and then diethanolamine was added. After dispersing evenly, it was left standing for 12 h; After drying, it was calcined at 550 °C for 5 h to obtain a primary loaded product; The primary loaded product and 0.08 part of nickel nitrate were dispersed in water, and the operations of standing and calcining were repeated to obtain a tar pyrolysis catalyst;

[0028] (4) By a mass ratio of 1:15, 3 parts of poly(methyl methacrylate) microspheres were dispersed in ethanol to obtain a dispersion; 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 part of polyethylene glycol were added to the dispersion, stirred and dispersed sufficiently for 0.5 - 1 h, then reacted at 80 °C until the ethanol evaporated completely. After naturally cooling, it was left standing for 0.5 - 1 h; The film layer was removed, dried, calcined at 350 °C for 4 h, and then continued to be calcined at 1300 °C for 6 h to obtain a carbon dioxide adsorption membrane;

[0029] (5) At 800 °C under a nitrogen atmosphere, 100 g of corn straw powder was gasified using steam at a mass ratio of 1:2.5 to obtain syngas; at 700 °C, the mass ratio of the tar pyrolysis catalyst to the syngas was controlled at 1:1.5, and the mass flux ratio of steam to the syngas was 1:1. The syngas was subjected to steam catalytic pyrolysis to obtain pyrolysis gas; the pyrolysis gas was 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 syngas, and then at 800-900 °C and 2 MPa, the high-hydrogen syngas was catalytically converted into methane using the SCST-241 methanation catalyst of Shutai Chemical Industry, and the methane and carbon dioxide contents in the produced non-condensable gas were analyzed.

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

[0031] (2) By mass, 4 parts of polymethyl methacrylate microspheres were dispersed in ethanol to obtain a dispersion; 3 parts of tetrabutyl titanate and 6 parts of aluminum nitrate were placed in water and mixed well, 1.2 parts of polyethylene glycol was added and dispersed well, stirred for 0.5-1 h, and then the dispersion was added. The reaction was carried out at 80 °C for 1-2 h, naturally cooled to room temperature and then left standing for 0.5-1 h; after separating the precipitate and drying, it was calcined at 350 °C for 4 h, and then continued to be calcined at 1300 °C for 6 h to obtain a support.

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

[0033] (2) By mass, 4 parts of polymethyl methacrylate microspheres were dispersed in ethanol to obtain a dispersion; 3 parts of tetrabutyl titanate and 12 parts of aluminum nitrate were placed in water and mixed well, 1.2 parts of polyethylene glycol was added and dispersed well, stirred for 0.5-1 h, and then the dispersion was added. The reaction was carried out at 80 °C for 1-2 h, naturally cooled to room temperature and then left standing for 0.5-1 h; after separating the precipitate and drying, it was calcined at 350 °C for 4 h, and then continued to be calcined at 1300 °C for 6 h to obtain a support.

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

[0035] (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 well, 0.6 parts of polyethylene glycol was added and dispersed well, stirred for 0.5-1 h, and then the dispersion was added. The reaction was carried out at 80 °C for 1-2 h, naturally cooled to room temperature and then left standing for 0.5-1 h; after separating the precipitate and drying, it was calcined at 350 °C for 4 h, and then continued to be calcined at 1300 °C for 6 h to obtain a support.

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

[0037] (2) Disperse 4 parts of polymethyl methacrylate microspheres in ethanol by mass fraction to obtain a dispersion; take 3 parts of tetrabutyl titanate and 10 parts of aluminum nitrate, mix them well in water, add 1.8 parts of polyethylene glycol and disperse them fully, stir for 0.5 - 1 h, then add the dispersion, react at 80 °C for 1 - 2 h, naturally cool to room temperature and then stand for 0.5 - 1 h; separate the precipitate, dry it, calcine at 350 °C for 4 h, and then continue to calcine at 1300 °C for 6 h to obtain a support.

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

[0039] (3) Disperse 4 parts of the support, 0.6 part of ammonium molybdate and 0.3 part of nickel nitrate in water, then add 0.1 part of diethanolamine, disperse evenly and stand for 12 h; dry and calcine at 550 °C for 5 h to obtain a primary loaded product; disperse the primary loaded product and 0.15 part of nickel nitrate in water, repeat the operations of standing and calcining to obtain a tar pyrolysis catalyst.

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

[0041] (4) Disperse 3 parts of polymethyl methacrylate microspheres in ethanol according to a mass ratio of 1:10 to obtain a dispersion; add 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 part of polyethylene glycol to the dispersion, stir and disperse fully for 0.5 - 1 h, then react at 80 °C until the ethanol evaporates completely, naturally cool and then stand for 0.5 - 1 h; remove the film layer, dry it, calcine at 350 °C for 4 h, and then continue to calcine 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) Disperse 3 parts of polymethyl methacrylate microspheres in ethanol according to a mass ratio of 1:20 to obtain a dispersion; add 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 part of polyethylene glycol to the dispersion, stir and disperse fully for 0.5 - 1 h, then react at 80 °C until the ethanol evaporates completely, naturally cool and then stand for 0.5 - 1 h; remove the film layer, dry it, calcine at 350 °C for 4 h, and then continue to calcine 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) Disperse 4 parts of the support, 0.6 part of ammonium molybdate and 0.45 part of nickel nitrate in water, then add diethanolamine, disperse evenly and stand for 12 h; dry and calcine 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) Place 4 parts of aluminum nitrate, 10 parts of calcium nitrate and 0.8 part of polyethylene glycol in 45 parts of ethanol, stir and disperse thoroughly for 0.5 - 1 h, then react at 80 °C until the ethanol evaporates completely, let it cool naturally and then stand for 0.5 - 1 h; Remove the film layer, dry it and then calcine at 350 °C for 4 h, and then continue to calcine 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) Disperse 3 parts of polymethyl methacrylate microspheres in ethanol according to a mass ratio of 1:15 to obtain a dispersion; Add 12 parts of calcium nitrate and 0.8 part of polyethylene glycol to the dispersion, stir and disperse thoroughly for 0.5 - 1 h, then react at 80 °C until the ethanol evaporates completely, let it cool naturally and then stand for 0.5 - 1 h; Remove the film layer, dry it and then calcine at 350 °C for 4 h, and then continue to calcine at 900 °C for 6 h to obtain a carbon dioxide adsorption film.

[0050] Testing of the example samples:

[0051] Evaluate the gas production rate 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, when preparing the tar pyrolysis catalyst, the gas production rates of Example 2 and Example 3 both decreased, indicating that the proportion of alumina in the carrier has an impact on the performance of the catalyst. It may be that too much or too little alumina will affect the surface area and pores of the catalyst. The content of polyethylene glycol in Example 4 is less than that in Example 5, and the gas production rate decreased significantly, indicating that polyethylene glycol here can significantly affect the structure of the catalyst and the catalytic performance. However, the gas production rate of Example 5 did not increase compared with Example 1, while the content of carbon dioxide increased, indicating that too much polyethylene glycol will also affect the catalytic effect, possibly changing the structure of the gas. When loading nickel, in Comparative Example 1, nickel was not loaded step by step, and the gas production rate decreased significantly, indicating that step-by-step loading can significantly improve the catalytic efficiency. At the same time, in Example 6, the nickel content in the first loading was less and the nickel content in the second loading was more. The content of methane increased slightly, but the gas production rate of the produced gas decreased, indicating that the first loading plays a major role, and the nickel contents of the two loadings need to be maintained in a relatively appropriate ratio range. More nickel in the second loading may affect the protection of nickel and the tar pyrolysis effect, and the slight increase in the content of methane may be due to incomplete pyrolysis.

[0054] When preparing the carbon dioxide adsorption membrane, the ethanol content in the systems of Example 7 and Example 8 is different. The carbon dioxide content increases significantly, and the gas production rate also decreases. In particular, the gas production rate of Example 7 decreases significantly. Here, the ethanol content affects the reaction time and the formation of the structure of the adsorption membrane, thus affecting the adsorption performance of the membrane. And a low ethanol content is more unfavorable to the properties of the adsorption membrane. The carbon dioxide content of Comparative Example 2 without the participation of polymethyl methacrylate microspheres in the preparation increases significantly, indicating that 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 aluminum doping also increases significantly, indicating that the incorporation of aluminum is beneficial to improving the selective adsorption performance of the carbon dioxide adsorption membrane for carbon dioxide.

[0055] The carbon dioxide adsorption membranes of Example 1, Comparative Example 2, and Comparative Example 3 were desorbed at 850 °C, and then were respectively applied to the methods of Example 1, Comparative Example 2, and Comparative Example 3 again. The operations of adsorption and application were repeated 100 times, and the difference in methane content between the first time and the 100th time was calculated to evaluate the cyclic performance of the adsorption membrane. 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 in the gas generated after multiple cycles. As can be seen from the above table, compared with Example 1 with aluminum doping, when there is no aluminum doping in the carbon dioxide adsorption membrane, the difference in methane content after multiple cycles increases significantly, indicating that the control ability of the carbon dioxide adsorption membrane for carbon dioxide content decreases, and the methane production decreases significantly. The participation of aluminum can significantly improve the cyclic stability of the carbon dioxide adsorption membrane. The cyclic performance of Comparative Example 2 without using polymethyl methacrylate microspheres for structure shaping also decreases, indicating that the participation of polymethyl methacrylate microspheres in the preparation of the adsorption membrane is beneficial to the uniform mixing of alumina and calcium oxide and the control of crystals and structures, thus being beneficial to maintaining the cyclic stability.

[0058] For those skilled in the art, according to the technical solutions and concepts described above, various corresponding changes and deformations can be made, and all these changes and deformations should fall within the protection scope of the claims of the present invention.

Claims

1. A method for preparing natural gas from biomass, characterized in that, Gasify biomass using steam to obtain syngas; under the action of a tar pyrolysis catalyst, perform steam catalytic pyrolysis on the syngas to obtain pyrolysis gas; use a carbon dioxide adsorption membrane to capture and separate carbon dioxide in the pyrolysis gas to obtain high-hydrogen syngas, and then catalytically convert the high-hydrogen syngas into methane, and obtain natural gas after purification.

2. The method for preparing natural gas from biomass according to claim 1, wherein The mass ratio of the steam to the biomass is 1:1.5 - 3; convert the high-hydrogen syngas into methane at 800 - 900 °C.

3. The method for preparing natural gas from biomass according to claim 1, characterized in that, During steam catalytic pyrolysis, the mass flux ratio of the steam to the syngas is 1:0.5 - 2; the mass ratio of the tar pyrolysis catalyst to the syngas is 1:0.5 - 2; perform steam catalytic pyrolysis at 650 - 750 °C.

4. The method for preparing natural gas from biomass according to claim 1, wherein The preparation of the tar pyrolysis catalyst includes the following steps: prepare polymethyl methacrylate microspheres; disperse the polymethyl methacrylate microspheres in ethanol to obtain a dispersion; take tetrabutyl titanate and aluminum nitrate and place them in water and mix well, add polyethylene glycol and disperse fully, stir for 0.5 - 1 h, then add the dispersion, react at 70 - 85 °C for 1 - 2 h, naturally cool to room temperature and then stand for 0.5 - 1 h; separate the precipitate, dry it, and then calcine to obtain a support; Disperse the support, ammonium molybdate, and part of nickel nitrate in water and then add diethanolamine, disperse evenly and then stand for 8 - 20 h; dry and then calcine at 500 - 600 °C for 4 - 6 h to obtain a primary loaded product; Disperse the primary loaded product and the remaining nickel nitrate in water, repeat the operations of standing and calcining to obtain the tar pyrolysis catalyst.

5. The method for preparing natural gas from biomass according to claim 4, wherein, The mass ratio of the polymethyl methacrylate microspheres to tetrabutyl titanate is 1 - 1.5:1; the mass ratio of tetrabutyl titanate to aluminum nitrate is 1:2 - 4; the mass ratio of aluminum nitrate to polyethylene glycol is 1:0.1 - 0.

3.

6. The method for preparing natural gas from biomass according to claim 4, characterized in that, The mass ratio of ammonium molybdate to the support is 0.1 - 0.2:1; the mass ratio of ammonium molybdate to all nickel nitrate is 1:0.6 - 0.9; the mass ratio of the part of nickel nitrate to the remaining nickel nitrate is 2 - 5:

1.

7. The method for preparing natural gas from biomass according to claim 1, wherein, The preparation of the carbon dioxide adsorption membrane includes the following steps: disperse polymethyl methacrylate microspheres in ethanol at a mass ratio of 1:10 - 20 to obtain a dispersion; add aluminum nitrate, calcium nitrate, and polyethylene glycol to the dispersion, stir and disperse fully for 0.5 - 1 h, then react at 70 - 85 °C until the ethanol evaporates completely, naturally cool and then stand for 0.5 - 1 h; remove the membrane layer, dry it, and then calcine to obtain the carbon dioxide adsorption membrane.

8. The method for preparing natural gas from biomass according to claim 7, wherein The mass ratio of the 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; the mass ratio of aluminum nitrate to polyethylene glycol is 1:0.1 - 0.

25.

9. The method for preparing natural gas from biomass according to claim 4 or 7, characterized in that, The preparation of the polymethyl methacrylate microspheres includes the following steps: place methyl methacrylate monomer in water, react at 80 °C for 10 - 20 min in a nitrogen atmosphere, add potassium persulfate accounting for 0.5 - 1% of the monomer mass and stir and react for 2 - 3 h, separate the microspheres and dry them to obtain polymethyl methacrylate microspheres.

10. The method for preparing natural gas from biomass according to claim 4 or 7, characterized in that, Calcine at 300 - 400 °C for 3 - 5 h, and then continue to calcine at 1250 - 1400 °C for 5 - 8 h.

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