Method for preparing amorphous silicon dioxide by using waste rice husks

Abstract

The invention discloses a method for preparing amorphous silicon dioxide by using waste rice husks. According to the method, the silicon component in the rice husks is extracted under a relatively mild condition, and meanwhile waste of bio-based high-value chemicals such as cellulose and lignin is avoided. The method can be used for directly extracting amorphous silicon dioxide from rice husks, is low in process energy consumption, small in pollution and high in purity, and has high hydration activity and good compatibility when being added into concrete as a substitute of traditional silica fume.

Description

Technical Field

[0001] The invention relates to a method for preparing amorphous silicon dioxide by utilizing waste rice husks, and belongs to the field of biomass materials. Background Art

[0002] Concrete is currently the most widely used man-made building material, and cement is the key raw material that plays a bonding role in concrete. Its production process is energy-intensive and polluting. Therefore, reducing the amount of cement used in concrete production is an important measure for the industry to achieve sustainable development.

[0003] Silica has good cementing activity and is the main component of silica ash, a concrete admixture. Rice is the plant with the highest silicon content among all crops. Rice husk ash with a high silicon dioxide content can be prepared by directly incinerating discarded rice husks. Rice husk ash can be added to concrete as an admixture to reduce the amount of cement used and reduce carbon emissions. However, the current method of preparing rice husk ash mainly adopts direct incineration, which not only causes air pollution and great safety hazards, but also wastes lignin and cellulose bio-based high-value chemical raw materials. Therefore, how to convert the silicon component in rice husks into silicon dioxide under mild conditions, and recycle components such as lignin and cellulose, is a problem that needs to be solved urgently in this field. Summary of the invention

[0004] The purpose of the present invention is to overcome the shortcomings and deficiencies of the prior art and to provide a method for preparing amorphous silicon dioxide using waste rice husks, characterized in that the synthesis steps and conditions of the method are as follows, and the parts of the following raw materials are all parts by weight: (1) 1-3 parts of rice husks are crushed into 100-200 meshes by a wall breaking machine and then dispersed in 10-20 parts of a carbonate solution with a mass fraction of 15%-20%, reacted at 75-95°C for 8-16 hours, cooled and filtered after the reaction, washed the residue three times with water and dried at 50°C-70°C to constant weight to obtain a crude lignin / cellulose mixture, and the filtrate obtained is used for subsequent extraction of silica; (2) introducing carbon dioxide gas into the filtrate obtained in 1-3 parts of (1) at a gas flow rate of 1-5 mL / s, reacting for 12-16 hours and filtering to obtain a silicic acid precipitate. After filtering, drying the obtained filter residue at 120°C-150°C to constant weight to obtain amorphous silicon dioxide. The obtained filtrate mainly contains carbonate, which can be recycled; The carbonate in step (1) is one or more of sodium carbonate, potassium carbonate and ammonium carbonate.

[0005] The principle of the method involved in the present invention is: First, the waste rice husks are broken up and soaked in a carbonate solution to fully convert the silicon-containing components (silicic acid, silicon dioxide) in the rice husk residue into soluble silicates. After filtering, the main components of the filter residue are lignin and cellulose, which can be recycled; carbon dioxide gas is introduced into the filtrate to convert the sodium silicate in the solution into silicic acid precipitate, and the filter residue is filtered again. The filter residue is heated and dried, and the silicic acid precipitate is decomposed and converted into amorphous silicon dioxide. The main component of the remaining filtrate is sodium carbonate, which can be recycled.

[0006] The experiment found that when the mass fraction of sodium carbonate was between 15% and 20%, the silicon component in the rice husk was fully dissolved, and the yield of silicon dioxide after the introduction of carbon dioxide could reach more than 90%, and had a relatively high purity (see Example 1 and Example 2); when the mass fraction of sodium carbonate was less than 15%, the silicic acid in the rice husk could not be fully dissolved, and some silicon-containing components were still hidden in the xylem of the rice husk, and the final conversion rate of silicon dioxide could only reach 60% at most (see Comparative Example 1); when the mass fraction of sodium carbonate was greater than 20%, although the silicon component in the rice husk was fully dissolved and converted into silicon dioxide, the cellulose also began to hydrolyze in large quantities, resulting in a decrease in the purity of the amorphous silicon dioxide obtained in the end (see Comparative Example 1). BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1 The present invention is a process flow diagram. DETAILED DESCRIPTION

[0008] The present invention is specifically described below through embodiments, which are only used to further illustrate the present invention and cannot be understood as limiting the scope of protection of the present invention. Technical engineers in this field can make some non-essential improvements and adjustments to the present invention based on the contents of the above invention.

[0009] Example 1 (1) 1 part of rice husk was crushed into 200 meshes by a wall breaking machine and then dispersed in 10 parts of 15% sodium carbonate solution by mass fraction, reacted at 80°C for 16 hours, cooled and filtered after the reaction, washed the residue with water three times and dried at 50°C to constant weight to obtain a crude lignin / cellulose mixture, and the filtrate was used for subsequent extraction of silica; (2) introducing carbon dioxide gas into the filtrate obtained in (1) at a gas flow rate of 2 mL / s, reacting for 15 hours, filtering the reaction solution to obtain silicic acid precipitate, and drying the obtained filter residue at 140°C to constant weight to obtain amorphous silicon dioxide. The main component of the obtained filtrate is carbonate, which can be recycled; X-ray photoelectron spectroscopy and X-ray diffraction results show that the yield of amorphous silicon dioxide is 90% and the purity is 95%. The recovery yield of lignin cellulose is 90%.

[0010] Example 2 (1) 3 parts of rice husks were crushed into 100 meshes by a wall breaking machine and then dispersed in 20 parts of 20% by mass sodium carbonate solution, reacted at 90°C for 16 hours, cooled and filtered after the reaction, and the residue was washed three times with water and dried at 55°C to constant weight to obtain a crude lignin / cellulose mixture. The filtrate obtained was used for the subsequent extraction of silica; (2) introducing carbon dioxide gas into the filtrate obtained in (1) at a gas flow rate of 5 mL / s, reacting for 15 hours, filtering the reaction solution to obtain silicic acid precipitate, and drying the obtained filter residue at 120° C. to constant weight to obtain amorphous silicon dioxide. The main component of the obtained filtrate is carbonate, which can be recycled; X-ray photoelectron spectroscopy and X-ray diffraction results show that the yield of amorphous silicon dioxide is 95%, the purity is 95%, and the recovery yield of lignin cellulose is 93%.

[0011] Comparative Example 1 (1) 2 parts of rice husks were crushed into 100 meshes by a wall breaking machine and then dispersed in 15 parts of 8% sodium carbonate solution by mass, reacted at 90°C for 16 hours, cooled and filtered after the reaction, washed the residue three times with water and dried at 55°C to constant weight to obtain a crude lignin / cellulose mixture, and the filtrate was used for subsequent extraction of silica; (2) introducing carbon dioxide gas into the filtrate obtained in (1) at a gas flow rate of 4 mL / s, reacting for 14 hours, filtering the reaction solution to obtain silicic acid precipitate, and drying the obtained filter residue at 125° C. to constant weight to obtain amorphous silicon dioxide. The obtained filtrate mainly contains carbonate, which can be recycled; X-ray photoelectron spectroscopy and X-ray diffraction results show that the yield of amorphous silicon dioxide is 60%, the purity is 85%, and the recovery yield of lignin cellulose is 80%.

[0012] Comparative Example 2 (1) 2 parts of rice husks were crushed into 150 meshes by a wall breaking machine and then dispersed in 15 parts of 25% by mass sodium carbonate solution. The mixture was reacted at 90°C for 16 hours. After the reaction, the mixture was cooled and filtered. The residue was washed three times with water and dried at 55°C to constant weight to obtain a crude lignin / cellulose mixture. The filtrate was used for subsequent extraction of silica. (2) introducing carbon dioxide gas into the filtrate obtained in (1) at a gas flow rate of 4 mL / s, reacting for 14 hours, filtering the reaction solution to obtain silicic acid precipitate, and drying the obtained filter residue at 125° C. to constant weight to obtain amorphous silicon dioxide. The obtained filtrate mainly contains carbonate, which can be recycled; X-ray photoelectron spectroscopy and X-ray diffraction results showed that the purity of the obtained amorphous carbon dioxide was only 40%, and the recovery yield of lignin cellulose was 75%.

Claims

1. A method for preparing amorphous silicon dioxide using waste rice husks, characterized in that The synthesis steps and conditions of the method are as follows, and the parts of the following raw materials are all parts by weight: (1) 1-3 parts of rice husks are crushed into 100-200 meshes by a wall breaking machine and then dispersed in 10-20 parts of a carbonate solution with a mass fraction of 15%-20%, reacted at 75-95°C for 8-16 hours, cooled and filtered after the reaction, washed the residue three times with water and dried at 50°C-70°C to constant weight to obtain a crude lignin / cellulose mixture, and the filtrate obtained is used for subsequent extraction of silica; (2) introducing carbon dioxide gas into the filtrate obtained in 1-3 parts of (1) at a gas flow rate of 1-5 mL / s, reacting for 12-16 hours and filtering to obtain a silicic acid precipitate. After filtering, drying the obtained filter residue at 120°C-150°C to constant weight to obtain amorphous silicon dioxide. The obtained filtrate mainly contains carbonate, which can be recycled; The carbonate in step (1) is one or more of sodium carbonate, potassium carbonate and ammonium carbonate.

Images