Method for efficient carbon sequestration through biomass directional pyrolysis

Abstract

The invention relates to the technical field of biomass energy conversion, in particular to a biomass oriented pyrolysis efficient carbon sequestration method which comprises the following steps: screening a porous material, selecting an MCM41 mesoporous molecular sieve with the pore size distribution of 50-150nm, bamboo powder biomass with the particle size of less than 1mm and hollow rice straw with the pore size of more than 1mm and less than 10mm, and uniformly mixing the porous material and the bamboo powder biomass; drying the screened porous material to remove free water; an aqueous solution with a certain concentration is prepared according to the water absorption characteristic of the porous material, and the modified porous material with the same loading capacity is prepared through an equivalent-volume impregnation method; placing the impregnated and modified porous material in a vacuum drying oven; the modified porous material is fully mixed with regular blocky bamboo chips, and the improvement effect of the porous material on the thermal cracking carbon yield is investigated under the same thermal cracking condition. Under the same thermal cracking condition, compared with the single biomass raw material thermal cracking process, the dry basis carbon yield of the biomass thermal cracking is obviously improved, so that the thermal cracking carbon yield of the raw material is obviously improved.

Description

Technical Field

[0001] The invention relates to the technical field of biomass energy conversion, and in particular to a method for efficient carbon fixation by directional pyrolysis of biomass. Background Art

[0002] Biochar is a carbonaceous material obtained from biomass raw materials (wood, straw, agricultural and forestry waste, etc.) through a high-temperature thermal cracking process. It has the characteristics of high porosity, high specific surface area, and high adsorption performance. It has broad applications in soil conditioners, sewage treatment, energy storage, and waste gas purification industries.

[0003] Biomass energy conversion technologies include direct combustion, biofermentation, and thermochemical conversion. Direct combustion is a simple but low-efficiency utilization technology. Biofermentation is actually a material metabolism and energy conversion process of microorganisms, with the main products being CH4 and CO2. Thermochemical conversion can be further subdivided into gasification technology, liquefaction technology, and carbonization technology according to the different products. Pyrolysis carbonization technology is to achieve incomplete thermal degradation of biomass raw materials through certain processing techniques to form biomass charcoal and pyrolysis combustible gas components.

[0004] Based on this, a method for efficient carbon fixation by directional pyrolysis of biomass is now provided, which can eliminate the drawbacks of existing devices. Summary of the invention

[0005] In view of the above problems, a method for efficient carbon fixation by directional pyrolysis of biomass is provided, which improves the charcoal yield of biomass carbon-based products by increasing the probability of secondary cracking reactions of biomass pyrolysis combustible gas.

[0006] In order to solve the problems of the prior art, the present invention provides a method for efficient carbon fixation by directional pyrolysis of biomass, comprising the following steps: S1, screening porous materials, selecting MCM41 mesoporous molecular sieve with a pore size distribution of 50-150nm, bamboo powder biomass with a particle size of less than 1mm, and hollow rice straw with a pore size greater than 1mm and less than 10mm, and drying the screened porous materials to remove free water;

[0007] S2. According to the water absorption characteristics of the porous material, an aqueous solution of a certain concentration is prepared, and a modified porous material with the same loading amount is prepared by an equal volume impregnation method, and an active site for a secondary cracking reaction is constructed inside the porous material; S3. The impregnated modified porous material is placed in a vacuum drying oven and dried at 80°C overnight to obtain a modified porous material; S4. The modified porous material is fully mixed with regular block-shaped bamboo pieces, and the mass fraction of the porous material is 10wt%-50wt% of the mass of the bamboo powder. Under the same thermal cracking conditions, the effect of the porous material on improving the carbon yield of thermal cracking is investigated.

[0008] Preferably, the drying condition of the porous material in step S1 is to place it in a forced-air drying oven at 105°C overnight.

[0009] Preferably, the water absorption property of the porous material in step S2 is as follows: the water absorption rate of MCM41 is (2.0 - 2.5) mlH 2 O / g MCM41, the water absorption rate of bamboo powder is (0.5 - 0.8) mlH 2 O / g bamboo powder, and the water absorption rate of rice straw is (0.2 - 0.3) mlH 2 O / g straw, and the active component is loaded inside the porous material at a mass percentage of 2wt% - 10wt%.

[0010] Preferably, the same pyrolysis conditions in step S4 include a final pyrolysis temperature of 280°C - 380°C, a pyrolysis residence time of 15 - 45 min, and a heating rate of 2 - 10 ° / min.

[0011] The beneficial effects of the present invention compared with the prior art are as follows:

[0012] The present invention uses a porous material with modified pores to be mixed with biomass raw materials to carry out experimental research on the preparation of biochar by biomass pyrolysis. Under the same pyrolysis conditions, the dry - basis char yield of biomass pyrolysis is significantly improved compared with the pyrolysis process of a single biomass raw material. This is mainly attributed to the fact that the porous material provides abundant reaction sites for pyrolysis gas during the pyrolysis reaction process, greatly increasing the probability of secondary pyrolysis reaction of pyrolysis gas, and significantly improving the char yield of the raw material pyrolysis. Description of the Drawings

[0013] Figure 1 It is the pyrolysis data of bamboo chips and rice straw of a method for efficient carbon fixation by biomass directional pyrolysis.

[0014] Figure 2 It is the pyrolysis data of bamboo chips and bamboo powder of a method for efficient carbon fixation by biomass directional pyrolysis.

[0015] Figure 3 It is the pyrolysis data of bamboo chips and MCM41 of a method for efficient carbon fixation by biomass directional pyrolysis. Detailed Embodiments

[0016] To further understand the features, technical means, and specific purposes and functions achieved by the present invention, the following further describes the present invention in detail with reference to the drawings and specific embodiments.

[0017] Refer to Figures 1 - 3 : A method for efficient carbon fixation by biomass directional pyrolysis, including the following steps:

[0018] S1. Screen porous materials, select MCM-41 mesoporous molecular sieve with a pore size distribution of 50 - 150 nm, bamboo powder biomass with a particle size less than 1 mm, and hollow rice straw with a pore size greater than 1 mm and less than 10 mm. Dry the selected porous materials to remove free water.

[0019] S2. Prepare an aqueous solution with a certain concentration according to the water absorption characteristics of the porous materials. Use the equal - volume impregnation method to prepare modified porous materials with the same loading amount, and construct secondary pyrolysis reaction active sites inside the porous materials.

[0020] S3. Place the impregnated and modified porous materials in a vacuum drying oven and dry them at 80 °C overnight to obtain the modified porous materials.

[0021] S4. Thoroughly mix the modified porous materials with regular bamboo slices. The mass fraction of the porous materials is 10 wt% - 50 wt% of the mass of the bamboo powder. Under the same pyrolysis conditions, investigate the promotion effect of the porous materials on the char yield of pyrolysis.

[0022] In step S1, the drying condition of the porous materials is to place them in a forced - air drying oven at 105 °C overnight.

[0023] In step S2, the water absorption characteristics of the porous materials are as follows: the water absorption rate of MCM - 41 is (2.0 - 2.5) mlH 2 O / g MCM - 41, the water absorption rate of bamboo powder is (0.5 - 0.8) mlH 2 O / g bamboo powder, the water absorption rate of rice straw is (0.2 - 0.3) mlH 2 O / g straw, and the active component is loaded inside the porous materials at a mass percentage of 2 wt% - 10 wt%.

[0024] In step S4, the same pyrolysis conditions include a final pyrolysis temperature of 280 °C - 380 °C, a pyrolysis residence time of 15 - 45 min, and a heating rate of 2 - 10 ° / min.

[0025] Comparative example 1:

[0026] Select rice straw as the porous material, cut it into small sections with a length of 5 - 10 mm with scissors, and place the rice straw in a forced - air drying oven at 105 °C to dry the moisture. Weigh a certain mass of KCl and dissolve it in deionized water; the mass fraction of KCl accounts for 10 wt% of the total mass of the rice straw. Thoroughly mix the KCl solution with the rice straw, and then dry it overnight in a vacuum drying oven to remove the excess moisture in the solution, and prepare the rice - straw porous material with pore - channel modification.

[0027] Using bamboo slices with a regular morphology after drying moisture as raw materials, the bamboo slices and the modified rice straw are mixed evenly at a mass ratio of 1:1. Under the reaction atmosphere with a final pyrolysis temperature of 280°C, a residence time of 15 min, a heating rate of 10 / °C / min, and an N2 flow rate of 100 ml / min, the char yields and product calorific values of single bamboo slices and bamboo slices + rice straw during pyrolysis are investigated respectively. The results are as follows Figure 1 shown. For single bamboo slices, at the investigated test temperatures, the char yield during pyrolysis is 43.2%, and the air-dried basis gross calorific value of the corresponding char product is 5684.7 kcal / kg. After adding the modified rice straw material to the bamboo slices, the char yield of biomass pyrolysis increases significantly to 51.3%, and the air-dried basis gross calorific value of the corresponding biomass char product basically remains unchanged at about 5600 kcal. The significant increase in the char yield during pyrolysis is mainly attributed to the significantly enhanced secondary pyrolysis process of pyrolysis gas: the pyrolysis gas formed by the pyrolysis of bamboo slices comes into full contact with the abundant pore structure of rice straw during the diffusion process, resulting in a significant secondary pyrolysis process. Moreover, the pore structure of rice straw is rich in K ion catalytic active sites, which further improves the secondary pyrolysis reaction of pyrolysis gas. Therefore, the char yield of bamboo slice pyrolysis increases significantly.

[0028] Comparative Example 2:

[0029] Bamboo powder with a particle size less than 1 mm is selected as the porous material, and the bamboo powder is placed in a forced-air drying oven at 105°C and dried overnight to remove moisture. Weigh a certain mass of KCl + H3PO4 (m(K):m(P) = 1:1), and dissolve it in deionized water; the mass fraction of K + P accounts for 10 wt% of the total mass of bamboo powder. The mixed solution of KCl + H3PO4 is fully mixed with the bamboo powder (equal-volume impregnation), and then dried overnight in a vacuum drying oven to remove the excess moisture in the solution, and a pore-modified bamboo powder material is prepared.

[0030] Using bamboo slices with a regular morphology after drying moisture as raw materials, the bamboo slices and the modified bamboo powder are mixed evenly at a mass ratio of 1:1. Under the reaction atmosphere with a final pyrolysis temperature of 280°C, a residence time of 15 min, a heating rate of 10 / °C / min, and an N2 flow rate of 100 ml / min, the char yields and product calorific values of single bamboo slices and bamboo slices + bamboo powder during pyrolysis are investigated respectively. The results are as follows Figure 2As shown in the figure. For a single bamboo slice, at the tested experimental temperature, the char yield of pyrolysis is 43.2%, and the gross calorific value of the corresponding char product on an air-dried basis is 5684.7 kcal / kg. After adding the modified bamboo powder to the bamboo slice, the char yield of biomass pyrolysis significantly increases to 48.4%, and the gross calorific value of the corresponding biomass char product on an air-dried basis is 5680 kcal, which is basically unchanged compared with the bamboo slice char. The significant increase in the char yield of pyrolysis is mainly attributed to the addition of bamboo powder, which constructs a large number of stacked pore structures around the bamboo slice, increasing the probability of secondary pyrolysis reaction of pyrolysis gas during the external diffusion process: the pyrolysis gas formed by the pyrolysis of the bamboo slice is adsorbed by the stacked pores formed by the accumulation of bamboo powder during the diffusion process and undergoes a secondary pyrolysis reaction process; moreover, the surface of the bamboo powder contains abundant K and P active sites, further increasing the probability of secondary pyrolysis reaction of pyrolysis gas, so the char yield of bamboo slice pyrolysis significantly increases.

[0031] Comparative Example 3:

[0032] MCM41 is a commercial mesoporous molecular sieve, which contains abundant mesopores and micropores inside. Using MCM41 as the porous material, it is dried in a forced-air drying oven at 105°C to remove moisture. Weigh a certain mass of KCl and dissolve it in deionized water; the mass fraction of KCl accounts for 10 wt% of the total mass of MCM41. The KCl solution is fully mixed with the mesoporous molecular sieve, and then dried overnight in a vacuum drying oven to remove the excess moisture in the solution, and the modified MCM41 porous material is prepared.

[0033] Using the regular-shaped bamboo slices with dried moisture as the raw material, the modified MCM41 accounts for 10 wt% of the total mass of the bamboo slices. The two are mixed evenly. Under the reaction atmosphere with a final pyrolysis temperature of 280°C, a residence time of 15 min, a heating rate of 10 / °C / min, and an N2 flow rate of 100 ml / min, the char yields and product calorific values of single bamboo slices and bamboo slices + MCM41 are respectively investigated. The results are as follows Figure 3 As shown in the figure. For a single bamboo slice, at the tested experimental temperature, the char yield of pyrolysis is 43.2%, and the gross calorific value of the corresponding char product on an air-dried basis is 5684.7 kcal / kg. After adding the modified MCM41 porous material to the bamboo slice, the char yield of biomass pyrolysis significantly increases to 51.7%, and the gross calorific value of the corresponding biomass char product on an air-dried basis slightly decreases to 5558 kcal / kg. The decrease in the char yield of pyrolysis is mainly attributed to the non-combustibility of the MCM41 pores. The significant increase in the char yield of pyrolysis is due to two reasons: on the one hand, the abundant mesopores and micropores of MCM41 have a significant adsorption effect on the pyrolysis gas released by the pyrolysis of bamboo slices; secondly, the inner pores of MCM41 are modified with K ion active sites, which have a significant catalytic promotion effect on the secondary pyrolysis process of pyrolysis gas, so the char yield of bamboo slice pyrolysis significantly increases.

[0034] The above embodiments merely represent one or several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the appended claims.

Claims

1. A method for efficient carbon fixation by directional pyrolysis of biomass, characterized in that: The steps include: S1. Screening porous materials, selecting MCM41 mesoporous molecular sieve with a pore size distribution of 50-150 nm, bamboo powder biomass with a particle size of less than 1 mm, and hollow rice straw with a pore size greater than 1 mm and less than 10 mm, and drying the screened porous materials to remove free water; S2. According to the water absorption characteristics of the porous material, a certain concentration of aqueous solution is prepared, and the modified porous material with the same loading amount is prepared by an equal volume impregnation method, and a secondary cracking reaction active site is constructed inside the porous material; S3, placing the impregnated modified porous material in a vacuum drying oven and drying at 80° C. overnight to obtain a modified porous material; S4. The modified porous material is fully mixed with regular block-shaped bamboo chips, wherein the mass fraction of the porous material is 10wt%-50wt% of the mass of the bamboo powder. Under the same thermal cracking conditions, the effect of the porous material on the carbon yield of thermal cracking is investigated.

2. The method for efficient carbon fixation by directional pyrolysis of biomass according to claim 1, characterized in that: The drying condition of the porous material in step S1 is to place it in a forced air drying oven at 105° C. overnight.

3. The method for efficient carbon fixation by directional pyrolysis of biomass according to claim 1, characterized in that: The water absorption characteristics of the porous material in step S2 are: the water absorption rate of MCM41 is (2.0-2.5) mlH2O / gMCM41, the water absorption rate of bamboo powder is (0.5-0.8) mlH2O / gbamboo powder, and the water absorption rate of rice straw is (0.2-0.3) mlH2O / gstraw, and the active component is loaded inside the porous material at a mass percentage of 2wt%-10wt%.

4. The method for efficient carbon fixation by directional pyrolysis of biomass according to claim 1, characterized in that: The same thermal cracking conditions in step S4 include a thermal cracking final temperature of 280°C-380°C, a thermal cracking residence time of 15-45min, and a heating rate of 2-10° / min.

Images