A biomass reducing agent for producing industrial silicon and a method for preparing the same

Abstract

The present application belongs to the field of separation and purification, and particularly relates to a biomass reducing agent for preparing industrial silicon and a preparation method thereof, which comprises the following steps: preparing rice husk carbon precursor; performing alkali treatment on the rice husk carbon precursor to obtain rice husk carbon containing sodium silicate, and separating to obtain rice husk carbon and a sodium silicate solution; modifying the rice husk carbon to convert residual sodium silicate into silicon dioxide, and obtaining modified rice husk carbon; performing hydroxyl modification on straw carbon, then mixing the modified rice husk carbon and the straw carbon, and fully mixing them in the sodium silicate solution to form, and the biomass reducing agent is obtained. The strength of the biomass reducing agent is greatly increased, and the biomass reducing agent can meet the requirements of industrial silicon production, can better replace charcoal, and realizes the resource utilization of agricultural and forestry wastes.

Description

Technical Field

[0001] This invention belongs to the field of separation and purification, specifically relating to a biomass reducing agent for preparing industrial silicon and its preparation method. Background Technology

[0002] Charcoal, with its well-balanced content of fixed carbon, ash, volatile matter, and moisture, possesses excellent physicochemical properties, making it an ideal reducing agent for the production of industrial silicon. However, charcoal originates from forest resources, and its large-scale use is detrimental to environmental protection. Importing charcoal, on the other hand, significantly increases production costs. Biomass charcoal, with its chemical and physical properties closely resembling those of charcoal, is a superior alternative raw material for carbonaceous reducing agents in industrial silicon smelting. Biomass charcoal is a highly active charcoal produced by incompletely pyrolyzing and carbonizing agricultural and forestry waste such as straw under an oxidizing atmosphere. It is primarily composed of aromatic hydrocarbons and elemental carbon or carbon with a graphite-like structure, typically containing over 60% carbon. During the charcoal production process, the fine porous structure of the primary materials, similar to that of charcoal, is well preserved in the biomass charcoal, resulting in a large specific surface area. The carbon content and ash content of biomass charcoal increase with increasing production temperature, while the hydrogen and oxygen content decreases.

[0003] However, most biomass and biochar have a relatively loose structure, low energy density, and small particle size, making them unsuitable for direct use in metal smelting and requiring shaping. During the pyrolysis preparation of biochar, the original binding components are decomposed under high temperatures, resulting in biochar lacking adhesiveness and unable to be directly extruded. Therefore, a suitable binder needs to be added. The choice of binder has a crucial impact on biochar shaping; factors such as pellet strength, resistivity, chemical reactivity, and production cost are all key indicators for evaluating practicality. Summary of the Invention

[0004] To address the problems in existing technologies where the loose structure of biochar leads to difficulties in molding and low strength of the pellets during the preparation of biomass reducing agents, this invention discloses a biomass reducing agent that is easy to mold and produces high-strength pellets, as well as a method for preparing the reducing agent. The technical solution is as follows: A biomass reducing agent for preparing industrial silicon includes the following steps: preparing a rice husk char precursor; subjecting the rice husk char precursor to alkali treatment to obtain rice husk char containing sodium silicate, and separating the rice husk char and sodium silicate solution; modifying the rice husk char to convert the residual sodium silicate into silicon dioxide to obtain modified rice husk char; hydroxylating straw char, then mixing it with the modified rice husk char, thoroughly mixing it in a sodium silicate solution, and molding it to obtain the final product.

[0005] Furthermore, the straw includes one or more of the following: grass straw, legume straw, cruciferous straw, mallow or aster family straw.

[0006] Furthermore, the mass ratio of the straw charcoal to the modified rice husk charcoal is 2~10:1.

[0007] Furthermore, this includes the following steps: a. Preparation of rice husk char precursor; prepare sodium hydroxide solution with sodium hydroxide, place the rice husk char precursor in sodium hydroxide solution, react at 80~100℃ for 5~8h to obtain rice husk char containing sodium silicate, and separate the rice husk char and sodium silicate solution. b. Prepare the epoxy coupling agent dilution solution; disperse rice husk char in water, and slowly add dilute hydrochloric acid dropwise while stirring until the pH of the system is 2-3 and the precipitation no longer increases; slowly add the epoxy coupling agent dilution solution dropwise while stirring, and react at 40-60℃ for 4-6 hours; collect the precipitate and wash it thoroughly, and then vacuum dry it to obtain modified rice husk char. c. Mix straw charcoal with hydrochloric acid and acidify for 12-24 hours. Collect the product and wash it. Then mix it with modified rice husk charcoal and place it in sodium silicate solution to mix thoroughly. Shape the mixture to obtain the final product.

[0008] Furthermore, the preparation of the rice husk char precursor includes the following steps: after the dried rice husk is crushed into powder, it is placed in an oxygen-free environment and pyrolyzed at 500~750℃ for 0.5~1.5h to obtain the rice husk char precursor.

[0009] Furthermore, the mass ratio of the rice husk char precursor to sodium hydroxide in step a is 1:0.1~0.2; and the concentration of the sodium hydroxide solution is 0.8~1.2 mol / L.

[0010] Furthermore, the mass ratio of the epoxy coupling agent to the rice husk charcoal in step b is 1:0.02~0.06.

[0011] Furthermore, the slow dripping rate described in step b is 0.2~2 mL / min; the vacuum drying is carried out at 80~100℃.

[0012] Furthermore, in step c, the moisture content of the system is controlled to be 25-28%, followed by remolding.

[0013] Furthermore, the epoxy coupling agent includes one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane.

[0014] A biomass reducing agent prepared using the above method.

[0015] By adopting the above scheme, the method of the present invention has the following advantages: 1. The biomass reducing agent of the present invention has a significantly increased strength after the pellets are dried, reaching more than 2500N, which can meet the requirements of industrial silicon production, solve the problem of difficult biochar molding, can better replace wood charcoal, realize the resource utilization of agricultural and forestry waste, and the preparation method is simple and has few steps, making it suitable for industrial promotion.

[0016] 2. The method of the present invention converts the silicon present in inexpensive and readily available rice husks into water glass. On the one hand, the silicon is dissolved, thus purifying the rice husk char and increasing its porosity. On the other hand, it saves the cost of purchasing additional water glass, and has good affinity with rice husk char. Through the better integration of rice husk char with other straw char, a dense silicon-oxygen network is formed with good coating properties.

[0017] 3. This invention modifies rice husk charcoal, utilizing the residual water glass to form silicic acid through acidification, which then forms nano-silica after drying. This improves the rigidity of the reducing agent and increases the surface roughness of the charcoal, allowing it to better wet the surface of the biochar particles, enhancing the bonding force between the binder and the biochar, and reducing the probability of bonding failure.

[0018] 4. In this invention, while modifying rice husk charcoal, an epoxy silane coupling agent is added. The molecular chain of the coupling agent can be embedded in the silicon-oxygen network of water glass, increasing the toughness of the binder and reducing brittle shrinkage during drying. At the same time, the hydroxyl groups formed by the longer chain of the coupling agent can penetrate into the pores of the charcoal and form hydrogen bonds with the groups on the charcoal surface, enhancing the interfacial bonding.

[0019] 5. This invention modifies straw charcoal by acidification, increasing the hydroxyl groups on the surface of the straw charcoal, making it easier for the surface of the straw charcoal to physically adsorb with water glass binder, thus enhancing the bonding effect; and the acidification modification of straw charcoal can reduce its alkalinity, avoid the inhibitory effect of alkalinity on the hydrolysis of sodium silicate solution, and promote the coagulation and solidification of sodium silicate.

[0020] 6. The preparation method of the present invention avoids the introduction of elements such as Fe, Ca, and Al. The raw materials used are mostly controlled to contain C, O, and Si that can participate in subsequent reactions. The only byproduct generated is easily removable sodium chloride, which avoids the increase of ash content and reduces the impact on the reducing properties of the reducing agent. Detailed Implementation

[0021] 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.

[0022] Example 1: (1) After the dried rice husks were crushed into powder, they were placed in an oxygen-free environment and pyrolyzed at 600°C for 1 hour to obtain rice husk char precursor; (2) Take sodium hydroxide to prepare a 1 mol / L sodium hydroxide solution, put 8 times the mass of the rice husk char precursor into the sodium hydroxide solution, react at 90℃ for 6 h to obtain rice husk char containing sodium silicate, and separate the rice husk char and sodium silicate solution. (3) Weigh 4% of the mass of rice husk char with γ-glycidoxypropyltrimethoxysilane and dilute it with ethanol by one-fold; disperse the rice husk char in water and slowly add dilute hydrochloric acid at a rate of 1 mL / min while stirring until the pH of the system is 2.5 and the precipitation no longer increases; slowly add the diluted γ-glycidoxypropyltrimethoxysilane solution at a rate of 0.5 mL / min while stirring, and react at 50°C for 5 h; collect the precipitate and wash it thoroughly, and dry it under vacuum at 90°C to obtain modified rice husk char; (4) Mix rice straw charcoal with 3 mol / L hydrochloric acid and acidify for 20 h. Collect the product and wash it. Mix it with modified rice husk charcoal at a mass ratio of 6:1. Then mix it thoroughly in sodium silicate solution. Evaporate the solvent to make the water content of the system 27%. Then put it into a cylindrical mold with a diameter of 20 mm and cold press it with a pressure of 4 t. After demolding, dry it to constant weight to obtain biomass reducing agent.

[0023] Example 2: The difference from Example 1 is as follows: (2) Prepare a 1 mol / L sodium hydroxide solution by taking sodium hydroxide, and place 5 times the mass of the rice husk char precursor into the sodium hydroxide solution. React at 90°C for 6 h to obtain rice husk char containing sodium silicate. Separate the rice husk char and sodium silicate solution.

[0024] Example 3: The difference from Example 1 is as follows: (2) Prepare a 1 mol / L sodium hydroxide solution by taking sodium hydroxide, and place 10 times the mass of the rice husk char precursor into the sodium hydroxide solution. React at 90°C for 6 h to obtain rice husk char containing sodium silicate. Separate the rice husk char and sodium silicate solution.

[0025] Example 4: The difference from Example 1 is as follows: (3) Weigh 2% of the mass of rice husk char with γ-glycidoxypropyltrimethoxysilane and dilute it with ethanol by one-time; disperse the rice husk char in water, and slowly add dilute hydrochloric acid at a rate of 1 mL / min while stirring until the pH of the system is 2.5 and the precipitation no longer increases; slowly add the diluted γ-glycidoxypropyltrimethoxysilane solution at a rate of 0.5 mL / min while stirring, and react at 50℃ for 5 h; collect the precipitate and wash it thoroughly, and dry it under vacuum at 90℃ to obtain modified rice husk char.

[0026] Example 5: The difference from Example 1 is as follows: (3) Weigh 6% of the mass of rice husk char with γ-glycidoxypropyltrimethoxysilane and dilute it with ethanol by one-time; disperse the rice husk char in water, and slowly add dilute hydrochloric acid at a rate of 1 mL / min while stirring until the pH of the system is 2.5 and the precipitation no longer increases; slowly add the diluted γ-glycidoxypropyltrimethoxysilane solution at a rate of 0.5 mL / min while stirring, and react at 50℃ for 5 h; collect the precipitate and wash it thoroughly, and dry it under vacuum at 90℃ to obtain modified rice husk char.

[0027] Example 6: The difference from Example 1 is as follows: (3) Weigh 4% of the mass of rice husk char with γ-glycidoxypropyltrimethoxysilane and dilute it with ethanol by one-time; disperse the rice husk char in water, and slowly add dilute hydrochloric acid at a rate of 1 mL / min while stirring until the pH of the system is 2.5 and the precipitation no longer increases; slowly add the diluted γ-glycidoxypropyltrimethoxysilane solution at a rate of 2 mL / min while stirring, and react at 50℃ for 5 h; collect the precipitate and wash it thoroughly, and dry it under vacuum at 90℃ to obtain modified rice husk char.

[0028] Example 7: The difference from Example 1 is as follows: (4) Mix rice straw charcoal with 3 mol / L hydrochloric acid and acidify for 20 h. Collect the product and wash it. Mix it with modified rice husk charcoal at a mass ratio of 10:1. Then mix it thoroughly in sodium silicate solution. Evaporate the solvent to make the water content of the system 27%. Then put it into a cylindrical mold with a diameter of 20 mm and cold press it with a pressure of 4 t. After demolding, dry it to constant weight to obtain biomass reducing agent.

[0029] Comparative Example 1: Rice straw charcoal was thoroughly mixed in a sodium silicate solution, and the mass of sodium silicate was controlled to be 10% of that of rice straw charcoal. The solvent was evaporated to make the water content of the system 27%. The mixture was then placed in a cylindrical mold with a diameter of 20 mm and cold-pressed at a pressure of 4 t. After demolding, it was dried to constant weight to obtain a biomass reducing agent.

[0030] Example Sample Testing: The dry and wet strengths of the demolded pellets before and after drying were measured using a cold compressive strength tester, with the force applied in the axial direction of the pellets. The compressive strength of the wet pellets was measured immediately after demolding, and the strength of the dry pellets was measured after the pellets were completely dry. The pellets were placed directly into a muffle furnace at 1000 °C, and the furnace temperature was raised to 1000 °C within 8 minutes. After holding at this temperature for 30 minutes, the pellets were removed and cooled to room temperature. The pellets were then dropped once from 2 m onto a 3 mm thick steel plate. The sample was passed through a 13 mm sieve, and the hot drop strength was calculated as the ratio of the mass of the residue on the sieve to the initial mass. The results are as follows:

[0031] As shown in the table above, the strength of the biomass reducing agent of the present invention is significantly higher than that of the comparative example, especially the dry strength and hot drop strength, indicating that the method of the present invention can effectively solve the problem of water glass as a binder easily debonding after drying. After heat treatment, the skeleton formed by silica in the system can ensure the mechanical strength of the sample. Compared with Example 1, the dry, wet strength and hot drop strength of the biomass reducing agents prepared in Examples 2 and 3, which have less or more sodium hydroxide content, are all reduced. This may be because the change in sodium ion content in the system affects the modulus of sodium silicate, and the decrease in modulus affects the bonding effect. In the process of modifying rice husk charcoal, the coupling agent content in Example 4 is less, and the sample strength is significantly reduced. This indicates that adding coupling agent to the system can promote the uniform loading of silica on rice husk charcoal, improve the loading strength, and thus improve the strength of rice husk charcoal. Subsequently, after mixing rice husk charcoal and rice straw charcoal, a skeleton effect is formed, which significantly enhances the strength of the pellets. However, the strength of Example 5, which had a higher coupling agent content, also decreased. This may be because excessive coupling agent content can lead to self-aggregation, resulting in free aggregation in the system. This aggregation, when mixed with rice straw charcoal and sodium silicate, forms ineffective bonds, wasting active sites. In Example 6, the coupling agent was added at a faster rate, and the sample strength also decreased, indicating that an excessively fast addition rate affects the controllability of the reaction and reduces the modification effect. In Example 7, the rice straw charcoal content was higher than in Example 1, while the rice husk charcoal content was lower, resulting in a decrease in sample strength. This indicates that the key to improving the strength of the biomass reducing agent of this invention lies in rice husk charcoal. However, excessive rice husk charcoal content can also affect the ash content, so strength should not be pursued at the expense of other properties.

[0032] 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 preparing a biomass reducing agent for industrial silicon, characterized in that, Includes the following steps: Prepare rice husk char precursor; treat the rice husk char precursor with alkali to obtain rice husk char containing sodium silicate, and separate the rice husk char and sodium silicate solution; modify the rice husk char to convert the residual sodium silicate into silicon dioxide, and add an epoxy silane coupling agent to obtain modified rice husk char; hydroxylate the straw char, then mix it with the modified rice husk char, place it in a sodium silicate solution and mix thoroughly, and then shape it to obtain the final product.

2. The method for preparing a biomass reducing agent for industrial silicon according to claim 1, characterized in that, The straw includes one or more of the following: grass straw, legume straw, cruciferous straw, mallow or aster family straw.

3. The method for preparing a biomass reducing agent for industrial silicon according to claim 1, characterized in that, The mass ratio of straw charcoal to modified rice husk charcoal is 2~10:

1.

4. The method for preparing a biomass reducing agent for industrial silicon according to claim 1, characterized in that, Includes the following steps: a. Preparation of rice husk char precursor; Sodium hydroxide solution was prepared by taking sodium hydroxide, and the rice husk char precursor was placed in the sodium hydroxide solution and reacted at 80~100℃ for 5~8h to obtain rice husk char containing sodium silicate. The rice husk char and sodium silicate solution were then separated. b. Prepare the epoxy coupling agent dilution solution; disperse rice husk char in water, and slowly add dilute hydrochloric acid dropwise while stirring until the pH of the system is 2-3 and the precipitation no longer increases; slowly add the epoxy coupling agent dilution solution dropwise while stirring, and react at 40-60℃ for 4-6 hours; collect the precipitate and wash it thoroughly, and then vacuum dry it to obtain modified rice husk char. c. Mix straw charcoal with hydrochloric acid and acidify for 12-24 hours. Collect the product and wash it. Then mix it with modified rice husk charcoal and place it in sodium silicate solution to mix thoroughly. Shape the mixture to obtain the final product.

5. The method for preparing a biomass reducing agent for industrial silicon according to claim 4, characterized in that, The preparation of the rice husk char precursor includes the following steps: After the dried rice husks are crushed into powder, they are placed in an oxygen-free environment and pyrolyzed at 500~750℃ for 0.5~1.5h to obtain rice husk char precursor.

6. The method for preparing a biomass reducing agent for industrial silicon according to claim 4, characterized in that, The mass ratio of the rice husk char precursor to sodium hydroxide in step a is 1:0.1~0.2; the concentration of the sodium hydroxide solution is 0.8~1.2 mol / L.

7. The method for preparing a biomass reducing agent for industrial silicon according to claim 4, characterized in that, The mass ratio of the epoxy coupling agent to the rice husk charcoal in step b is 1:0.02~0.

06.

8. The method for preparing a biomass reducing agent for industrial silicon according to claim 4, characterized in that, The dripping rate described in step b is 0.2~2 mL / min; the vacuum drying is carried out at 80~100℃.

9. The method for preparing a biomass reducing agent for industrial silicon according to claim 4, characterized in that, The epoxy coupling agent includes one or more of γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane, γ-glycidoxypropylmethyldimethoxysilane, and γ-glycidoxypropylmethyldiethoxysilane.

10. A biomass reducing agent prepared by the method according to any one of claims 1 to 9.

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