Method for preparing industrial silicon by using waste silica gel and application thereof

Abstract

The invention relates to the technical field of waste silica gel recycling, in particular to a method for preparing industrial silicon from waste silica gel and application of the method. The method provided by the invention comprises the following steps: step 1, adding collected waste silica gel into an alcoholic solution of a carburant for reaction, and then filtering; and 2, drying and removing impurities from the filter residues obtained in the step 1, heating the obtained filter residues to a melting temperature under closed and negative pressure conditions, carrying out a reaction, and cooling to obtain the product. According to the method, the added value of the waste silica gel is greatly improved, and the problems that in the existing waste silica gel treatment and industrial silicon preparation process, pollution is large, and the post-treatment procedure is complex are solved.

Description

Technical Field

[0001] The present application relates to the technical field of recycling waste silicon gel, and in particular to a method for preparing industrial silicon using waste silicon gel and its application. Background Art

[0002] Thanks to the implementation of domestic energy conservation and emission reduction policies and the rapid expansion of the economy, the silicon aerogel industry has entered a stage of rapid development. With the gradual increase in the number of domestic silicon aerogel companies and the continuous expansion of production scale, problems in the production process have become increasingly prominent. These include: silicon aerogel and its composite materials will produce solid waste during the production process. Part of the waste silicon gel comes from floating gel, especially after drying, the silicon gel cracks into small particles and falls off from the reinforcement. This part is the largest source of waste silicon gel. At present, most production units treat this part of solid waste as conventional solid waste, ignoring its value for further recycling, which results in a huge waste of materials.

[0003] Waste silica gel produced during the preparation of silica aerogel and its composite materials is rich in silicon oxide and has the potential to be reused by recycling as a silicon source and preparing higher-value silicon materials. However, there are no reports on how to recycle waste silica gel to prepare high-value silicon materials and what kind of high-value silicon materials to prepare. Developing a method for recycling silica gel waste to prepare high-value silicon materials is of high value and significance in this field.

[0004] As one of the high-value silicon materials, industrial silicon is divided into chemical grade and metallurgical grade according to its application. The chemical grade is mainly used in the production of organic silicon and polysilicon. The terminal applications of the industry involve the fields of construction, electricity, electronic appliances, automobiles, aerospace, etc. From the traditional electronics industry to the solar photovoltaic industry, industrial silicon plays an irreplaceable role. At present, the mainstream method for preparing industrial silicon is to fully mix natural silicon dioxide ore with carbon powder and then reduce it at high temperature. Specifically, it needs to go through crushing, impurity removal, mixing, reduction and refining and purification to obtain high-purity industrial silicon, as recorded in the literature "Shan Jizhou, Jiang Yuanli, Cao Guoxi. Research Progress on Production Process Conditions of Industrial Silicon [J]. Henan Chemical Industry" and "He Yunping. Industrial Silicon Production and Preparation of Solar Grade Polysilicon by Metallurgical Method [J]. New Materials Industry, 2009, (04): 52-56". However, since this type of method uses carbon powder to reduce silicon dioxide ore, both of which are solid phases, there are problems such as difficulty in mixing and poor reduction effect, which leads to low reaction degree, low efficiency and low yield. In addition, in order to improve the production efficiency of preparing industrial silicon from silicon oxide ore, the method of adding excess carbon is often adopted. This reaction will produce toxic carbon monoxide, which requires subsequent tail gas treatment and increases the preparation cost of industrial silicon. Summary of the invention

[0005] The embodiment of the present application provides a method for preparing industrial silicon using waste silica gel and its application, so as to solve the problem that the waste silica gel generated in the preparation process of silica aerogel and its composite materials in the related art cannot be well utilized as a resource.

[0006] In a first aspect, a method for preparing industrial silicon using waste silicon gel is provided, comprising the following steps:

[0007] Step 1, adding the collected waste silica gel into an alcohol solution of a carburizer to react, and then filtering;

[0008] Step 2: Dry and remove impurities from the filter residue obtained in step 1, and then heat the filter residue to the melting temperature under closed and negative pressure conditions to react, and obtain the product after cooling.

[0009] Furthermore, the recarburizer is a silane substance, and the silane substance contains an R—Si—R' group, wherein R represents a carbon-containing group.

[0010] Furthermore, the solvent in the alcohol solution of the recarburizer is an alcohol solvent, and the alcohol solvent includes but is not limited to at least one of methanol, ethanol, n-butanol and n-hexane.

[0011] Furthermore, the concentration of the recarburizer in the alcohol solution of the recarburizer is 0.005-0.017 kg / L.

[0012] Furthermore, the mass ratio of the recarburizer to the waste silica gel is (0.006-0.02):1.

[0013] The carbon-containing groups are introduced by the recarburizer, and are pyrolyzed into C in an oxygen-free high-temperature environment to participate in the silicon oxide reduction reaction. The reduction reaction formula is: SiO2+2C→Si+2CO.

[0014] Furthermore, the silane substance is at least one of trimethylchlorosilane and triethylchlorosilane.

[0015] Furthermore, the silane substance is methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, trimethylethoxysilane, and ethyltriethoxysilane.

[0016] Furthermore, the method further comprises the step of adding a catalyst.

[0017] Furthermore, the catalyst is ammonium fluoride.

[0018] Furthermore, the mass ratio of the added amount of the catalyst to the recarburizer is (0.1-1.0):1.

[0019] Furthermore, the silica gel in step 1 includes wet silica gel or dry silica gel or a combination of the two; the method provided by the present invention is applicable to waste gels such as wet gel and dry gel;

[0020] Furthermore, the drying and impurity removal process in step 2 is heating at 90-450° C. for 2-16 hours.

[0021] Furthermore, the negative pressure condition is -0.03 to -0.1 MPa.

[0022] Furthermore, the reaction temperature in step 2 is 1100-1300° C., and the reaction time is 50-80 hours.

[0023] Furthermore, the cooling temperature is 0-200°C.

[0024] In a second aspect, there is provided industrial silicon prepared by the above-mentioned method.

[0025] The beneficial effects of the technical solution provided by this application include:

[0026] 1. The present application adds a recarburizer to the waste silica gel so that a certain amount of carbon-containing groups are grafted onto the surface of the waste silica gel, and the carbon-containing groups are pyrolyzed into C and H2 during the high-temperature reduction process, which can react with SiO2 in the waste silica gel to generate industrial silicon Si and pollution-free CO2 and H2O, thereby solving the problems of low purity, low yield, and complex process in the existing industrial silicon production method for preparing industrial silicon; in addition, the waste silica gel contains SiO2 that is not hydrophobically modified, and the addition of a recarburizer can increase the carbon content of the system, ensure that the reduction reaction of silicon oxide is sufficient, and avoid partial silicon oxide residue due to too low carbon content; and the addition of a recarburizer generates carbon in situ, and the carbon generated after pyrolysis is evenly distributed on the surface and inside of the waste silica gel, and can react at multiple sites at the same time, greatly improving the reaction efficiency;

[0027] 2. In the traditional method of preparing industrial silicon, carbon powder is often added for reduction. Since carbon powder is a solid granule, dry mixing or wet mixing after solution dispersion to form a suspension and then mixing has the disadvantages of low mixing uniformity, small contact surface and low reaction efficiency. Compared with the traditional method of adding carbon powder for reduction, the method of adding a recarburizer for reduction in the present invention has the advantages of easy mixing, large contact area, high reaction efficiency and small dosage.

[0028] 3. By preparing waste silicon gel into industrial silicon materials with higher value, compared with the traditional method of directly treating waste silicon gel as solid waste, the resource utilization of waste silicon gel is realized, and the added value of waste silicon gel is greatly improved;

[0029] 4. The method of the present application uses waste silica gel as raw material, and its structural composition is silicon dioxide. After recovery, high-purity silicon oxide raw material can be obtained by simple impurity removal. Compared with the traditional method of preparing industrial silicon from silicon ore, this method greatly simplifies the impurity removal process and has the advantages of simple process flow and high purity of finished products;

[0030] 5. During use, the method of the present application does not produce toxic or harmful gases or pollutants, which is beneficial to environmental protection and solves the problems of large pollution, complex post-processing procedures, and high processing costs in the existing waste silica gel treatment and industrial silicon preparation process. DETAILED DESCRIPTION

[0031] The technical solution of the present application will be clearly and completely described below in conjunction with the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

[0032] Example 1

[0033] A method for preparing industrial silicon using waste silicon gel:

[0034] Step 1, adding the collected waste silica gel to an ethanol solution of trimethylchlorosilane (carburizer concentration 0.010 kg / L) at a mass ratio of waste silica gel to carburizer of 1:0.01 to react, and then filtering;

[0035] Step 2: Heat the filter residue obtained in step 1 at 300°C for 8 hours, then heat the solid obtained in step 2 to 1200°C in a sealed state at a negative pressure of -0.10 MPa for 65 hours, and then cool down to below 200°C to obtain the product.

[0036] Example 2

[0037] A method for preparing industrial silicon using waste silicon gel:

[0038] Step 1, adding the collected waste silica gel to an ethanol solution of triethylchlorosilane (carburizer concentration 0.005 kg / L) at a mass ratio of waste silica gel to carburizer of 1:0.006 for reaction, and then filtering;

[0039] Step 2: Heat the filter residue obtained in step 1 at 90°C for 16 hours, then heat the solid obtained in step 2 to 1100°C in a sealed state at a negative pressure of -0.03 MPa for 80 hours, and then cool down to below 200°C to obtain the product.

[0040] Example 3

[0041] A method for preparing industrial silicon using waste silicon gel:

[0042] Step 1, adding the collected waste silica gel to an ethanol solution of trimethylchlorosilane (carburizer concentration 0.017 kg / L) at a mass ratio of waste silica gel to carburizer of 1:0.02 for reaction, and then filtering;

[0043] Step 2: Heat the filter residue obtained in step 1 at 450°C for 2 hours, then heat the solid obtained in step 2 to 1300°C in a sealed state and at a negative pressure of -0.1 MPa for 50 hours, and then cool down to below 200°C to obtain the product.

[0044] Example 4

[0045] A method for preparing industrial silicon using waste silicon gel:

[0046] Step 1, according to the mass ratio of waste silica gel, recarburizer and ammonium fluoride being 1:0.01:0.005, the collected waste silica gel is added to an ethanol solution of methyltrimethoxysilane (recarburizer concentration 0.017 kg / L) and ammonium fluoride for reaction, and then filtered;

[0047] Step 2: Heat the filter residue obtained in step 1 at 250° C. for 8 h, then heat the solid obtained in step 2 to 1200° C. in a sealed state at a negative pressure of -0.07 MPa for 60 h, and then cool down to below 200° C. to obtain the product.

[0048] Example 5

[0049] A method for preparing industrial silicon using waste silicon gel:

[0050] Step 1, according to the mass ratio of waste silica gel, carburizer and ammonium fluoride being 1:0.01:0.001, the collected waste silica gel is added to an ethanol solution of methyltriethoxysilane (carburizer concentration 0.005 kg / L) and ammonium fluoride for reaction, and then filtered;

[0051] Step 2: Heat the filter residue obtained in step 1 at 90°C for 16 hours, then heat the solid obtained in step 2 to 1100°C in a sealed state at a negative pressure of -0.03 MPa for 80 hours, and then cool down to below 200°C to obtain the product.

[0052] Example 6

[0053] A method for preparing industrial silicon using waste silicon gel:

[0054] Step 1, according to the mass ratio of waste silica gel, carburizer and ammonium fluoride being 1:0.01:0.01, the collected waste silica gel is added to an ethanol solution of ethyltriethoxysilane (carburizer concentration 0.014 kg / L) and ammonium fluoride for reaction, and then filtered;

[0055] Step 2: Heat the filter residue obtained in step 1 at 450°C for 2 hours, then heat the solid obtained in step 2 to 1300°C in a sealed state and at a negative pressure of -0.1 MPa for 50 hours, and then cool down to below 200°C to obtain the product.

[0056] Comparative Example 1

[0057] In this comparative example, the conventional carbon powder reduction method is adopted, and the carbon enhancer in Example 1 is replaced by carbon powder. Other features are the same as those in Example 1.

[0058] Comparative Example 2

[0059] A method for preparing industrial silicon using waste silicon gel:

[0060] Step 1, adding the collected waste silica gel to an ethanol solution of trimethylchlorosilane (carburizer concentration 0.003 kg / L) at a mass ratio of waste silica gel to carburizer of 1:0.005 to react, and then filtering;

[0061] Step 2: Heat the filter residue obtained in step 1 at 250° C. for 8 h, then heat the solid obtained in step 2 to 1200° C. in a sealed state at a negative pressure of -0.07 MPa for 65 h, and then cool down to below 200° C. to obtain the product.

[0062] Comparative Example 3

[0063] The amount of the recarburizer used is greater than the upper limit of the given range, and other features are the same as those in Example 1.

[0064] A method for preparing industrial silicon using waste silicon gel:

[0065] Step 1, adding the collected waste silica gel to an ethanol solution of trimethylchlorosilane (carburizer concentration 0.03 kg / L) at a mass ratio of waste silica gel to carburizer of 1:0.03 to react, and then filtering;

[0066] Step 2: Heat the filter residue obtained in step 1 at 250° C. for 8 h, then heat the solid obtained in step 2 to 1200° C. in a sealed state at a negative pressure of -0.07 MPa for 65 h, and then cool down to below 200° C. to obtain the product.

[0067] Comparative Example 4

[0068] A method for preparing industrial silicon using waste silicon gel:

[0069] Step 1, according to the mass ratio of waste silica gel to carburizer of 1:0.01, the collected waste silica gel is added to an ethanol solution of methyltrimethoxysilane (carburizer concentration 0.017 kg / L) and ammonium fluoride for reaction, and then filtered;

[0070] Step 2: Heat the filter residue obtained in step 1 at 250° C. for 8 h, then heat the solid obtained in step 2 to 1200° C. in a sealed state at a negative pressure of -0.07 MPa for 60 h, and then cool down to below 200° C. to obtain the product.

[0071] Performance Testing

[0072] The testing method of industrial silicon shall refer to GB / T 14849-2020 standard, and the classification method shall refer to GB / T2881-2023 standard;

[0073] Table 1 Performance parameters of industrial silicon prepared by the method of the present invention

[0074]

[0075] Note: The above nominal silicon content is 100% minus the sum of the iron, aluminum and calcium contents.

[0076] As can be seen from Table 1, the industrial silicon prepared by the method of the present invention meets the requirements of GB / T 2881-2023, has a significant yield advantage over the carbon powder treatment process, and has good application prospects. In addition, the market price of industrial silicon is 12,000-15,000 yuan / ton, and the existing waste silica gel treatment cost is 2,000-5,000 yuan / ton. Under the premise that the energy consumption cost is basically the same as that of the traditional method, the preparation cost of the method of the present invention also has the advantages of low raw material cost and low three waste treatment cost, which is mainly due to the simple acquisition of raw materials (no need to screen ore), small amount of recarburizer, high yield, and environmental friendliness. Therefore, it can be seen that the method of the present invention not only reduces the cost of waste silica gel treatment, but also improves the additional economic value of waste silica gel.

Claims

1. A method for preparing industrial silicon using waste silicon gel, characterized in that: The following steps are involved: Step 1, adding the collected waste silica gel into an alcohol solution of a carburizer to react, and then filtering; Step 2: drying and removing impurities from the filter residue obtained in step 1, and then heating the filter residue to the melting temperature under closed and negative pressure conditions to react, and obtaining the product after cooling.

2. The method for preparing industrial silicon using waste silicon gel according to claim 1, characterized in that: The recarburizer solution is a silane substance, and the silane substance contains an R—Si—R' group, wherein R represents a carbon-containing group.

3. The method for preparing industrial silicon using waste silicon gel according to claim 2, characterized in that: The silane substance is at least one of trimethylchlorosilane and triethylchlorosilane.

4. The method for preparing industrial silicon using waste silicon gel according to claim 2, characterized in that: The silane substance is at least one of methyltrimethoxysilane, methyltriethoxysilane, ethyltriethoxysilane, dimethyldiethoxysilane, trimethylmethoxysilane and trimethylethoxysilane.

5. The method for preparing industrial silicon using waste silicon gel according to claim 4, characterized in that: The step of adding a catalyst is also included.

6. The method for preparing industrial silicon using waste silicon gel according to claim 5, characterized in that: The catalyst is ammonium fluoride.

7. The method for preparing industrial silicon using waste silicon gel according to claim 6, characterized in that: The mass ratio of the added amount of the catalyst to the added recarburizer is (0.1-1.0):

1.

8. The method for preparing industrial silicon using waste silicon gel according to claim 1, characterized in that: The drying and impurity removal process in step 2 is heating at 90-450° C. for 2-16 hours.

9. The method for preparing industrial silicon using waste silicon gel according to claim 1, characterized in that: The reaction temperature in step 2 is 1100-1300° C., and the reaction time is 50-80 hours.

10. An industrial silicon, characterized in that: The invention is prepared by the method according to any one of claims 1 to 9.

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