A method for preparing calcium metasilicate from silicon-containing biomass as a raw material

Abstract

The present invention discloses a method for preparing calcium metasilicate using silicon-containing biomass as a raw material. The method includes: mixing a mixed salt of NaCl and CaCl2 with the silicon-containing biomass, pyrolyzing, washing with water, filtering, and calcining the filter cake to obtain the calcium metasilicate. The present invention uses silicon-containing biomass as a silicon source, and by utilizing the templating effect of the natural structure of the silicon-containing biomass, calcium metasilicate nanorods can be in-situ generated at a relatively low calcination temperature, and the aspect ratio of the nanorods can reach 30-200. Compared with traditional wollastonite powder, the nanorods have more obvious anisotropy in morphology and can be used as excellent reinforcing agents and additives in many fields such as plastics, rubbers, and coatings.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparing calcium metasilicate nanorods, and specifically relates to a method for preparing calcium metasilicate using silicon-containing biomass as a raw material. Background Art

[0002] The mineralogical name of calcium metasilicate is wollastonite, which is a raw material for making ceramics. Due to its unique crystal morphology and structure, wollastonite has good insulation, dielectric properties, high heat resistance, weather resistance, etc., so it can be used as a reinforcing agent and additive in many fields such as plastics, rubber, coatings, and metallurgy. Traditional methods for artificially preparing calcium metasilicate include: high-temperature solid-phase method, hydrothermal method, chemical precipitation method, sol-gel method, and microemulsion method, etc. CN114318491A discloses a method for preparing wollastonite single crystals under high-temperature and high-pressure conditions, which solves the technical blank of preparing wollastonite single crystals with high iron content, high manganese content, and high water content in the prior art. However, the synthesis temperature required for this preparation method is as high as 1600°C, which requires high requirements for heating equipment; in addition, this patent does not involve the morphology of the wollastonite sample. CN1615272A discloses a method for preparing calcium metasilicate by heating and boiling a raw material of sodium silicate solution and lime slurry followed by calcination, but the aspect ratio of the calcium metasilicate obtained by this method is relatively short, only about 1-2.5. CN111704143A discloses a method for preparing calcium silicate composites using sodium silicate prepared from rice husk ash and quicklime as raw materials, but does not mention the morphology of the calcium silicate sample. Although silica in this synthesis method comes from natural rice husk ash, the preparation from rice husk ash to sodium silicate still inevitably uses strong alkali, which will cause certain harm to the environment. Therefore, it is urgent to find a natural biomass silicon source to replace silicon-containing chemical agents and a more environmentally friendly synthesis method to prepare calcium metasilicate with a higher aspect ratio.

[0003] It can be seen that although there are various methods for preparing calcium metasilicate nanorods in the prior art, factors such as overly harsh synthesis conditions and uncontrollable product morphology severely limit their production and application. Summary of the Invention

[0004] In order to improve the above technical problems, the present invention provides a method for preparing calcium metasilicate using silicon-containing biomass as a raw material. The method includes: mixing a mixed salt of NaCl and CaCl2 with silicon-containing biomass, pyrolyzing, washing with water, filtering, and calcining the filter cake to obtain the calcium metasilicate; recrystallizing the filtered filtrate, mixing it with silicon-containing biomass for reuse.

[0005] According to an embodiment of the present invention, in the mixed salt, the content of NaCl is 10 wt.% to 60 wt.%, and exemplarily, it is 10 wt.%, 15 wt.%, 20 wt.%, 25 wt.%, 30 wt.%, 35 wt.%, 40 wt.%, 45 wt.%, 50 wt.%, 55 wt.%, 60 wt.%.

[0006] According to an embodiment of the present invention, the silicon-containing biomass may be selected from, but not limited to, the following: rice husk, rice straw, reed leaf, bamboo pole, bamboo leaf, coconut shell, barley husk, or bracts of panicum miliaceum, millet, or barnyard grass.

[0007] According to an embodiment of the present invention, the molar ratio of calcium to silicon elements in the mixed salt to the silicon-containing biomass is 2:1 to 20:1, and exemplarily, it is 2:1, 3:1, 4:1, 5:1, 6:1, 7:1, 8:1, 9:1, 10:1, 12:1, 14:1, 16:1, 18:1, 20:1.

[0008] According to an embodiment of the present invention, the pyrolysis is carried out in an inert atmosphere, and the inert atmosphere is, for example, nitrogen, argon, etc.

[0009] According to an embodiment of the present invention, during the pyrolysis process, the flow rate when the inert atmosphere is introduced is 10 - 40 mL / min, and preferably 20 - 30 mL / min.

[0010] According to an embodiment of the present invention, the temperature of the pyrolysis is 750 - 1000 °C, and the time of the pyrolysis is 1 - 14 h. Preferably, the temperature of the pyrolysis is 780 - 900 °C, and the time of the pyrolysis is 2 - 6 h. Exemplarily, the temperature of the pyrolysis is 780 °C, 800 °C, 820 °C, 840 °C, 850 °C, 860 °C, 880 °C, 900 °C.

[0011] According to an embodiment of the present invention, the method further includes cooling the pyrolyzed product, and the cooling rate is 4.5 - 10 °C / min, and preferably 5 - 7 °C / min.

[0012] According to an embodiment of the present invention, the temperature of the calcination is 450 - 700 °C, and the time of the calcination is 1 - 3 h. Preferably, the temperature of the calcination is 500 - 600 °C, and the time of the calcination is 1.5 - 2 h. Exemplarily, the temperature of the calcination is 500 °C, 520 °C, 540 °C, 560 °C, 580 °C, 600 °C.

[0013] According to an embodiment of the present invention, the calcination is carried out in an air atmosphere.

[0014] According to an embodiment of the present invention, an appropriate amount of hydrochloric acid is added to the filtrate after water washing, and then the mixed salt is recovered after evaporation and cooling crystallization. After supplementing an appropriate amount of calcium chloride, the recovered mixed salt can be used as a raw material again to be mixed and pyrolyzed with silicon-containing biomass.

[0015] According to an embodiment of the present invention, the calcium metasilicate is in the form of nanorods.

[0016] According to an embodiment of the present invention, the aspect ratio of the calcium metasilicate is 30 - 200.

[0017] As an exemplary embodiment of the present invention, the method for preparing calcium metasilicate specifically includes:

[0018] (1) Grind the mixed salt of NaCl and CaCl2 sufficiently to make it evenly mixed;

[0019] (2) Mix the mixed salt and the silicon-containing biomass evenly;

[0020] (3) Heat and pyrolyze the above mixture in a heating device;

[0021] (4) Take out the pyrolyzed product, wash it with water by suction filtration, take the filter cake and dry it to obtain an intermediate product for standby;

[0022] (5) Collect the filtrate, recover the mixed salt by evaporation and concentration, and cooling crystallization;

[0023] (6) Place the intermediate product in a heating device and calcine it in an air atmosphere to obtain the calcium metasilicate. The beneficial effects of the present invention:

[0024] The present invention uses silicon-containing biomass, including but not limited to: rice husk, rice straw, reed leaves, bamboo leaves, coconut shells, etc. as the silicon source. Utilizing the template effect of the natural structure of the silicon-containing biomass, calcium metasilicate nanorods can be in-situ generated at a relatively low calcination temperature, and the aspect ratio of the nanorods can reach 30 - 200. Compared with traditional wollastonite powder, the nanorods have more obvious anisotropy in morphology and can be used as excellent reinforcing agents and additives in many fields such as plastics, rubbers, and coatings. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is the scanning electron microscope (SEM) photograph of the calcium metasilicate prepared in Examples 1 - 3 of the present invention (a - sample 1; b - sample 2; c - sample 3).

[0026] Figure 2 is the X-ray diffraction (XRD) pattern of the calcium metasilicate prepared in Examples 1 - 3 of the present invention.

[0027] Figure 3 is the preparation flow chart of the calcium metasilicate of the present invention. DETAILED DESCRIPTION

[0028] The technical scheme of the present invention will be further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only exemplary descriptions and explanations of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are included in the scope that the present invention is intended to protect.

[0029] Unless otherwise specified, the raw materials and reagents used in the following examples are commercially available or can be prepared by known methods.

[0030] Example 1

[0031] 9.00 g of NaCl and 17.80 g of CaCl2 were placed in an agate mortar, and after being fully ground to make the two salts evenly mixed, they were collected in a glass petri dish and placed in a 60°C oven to dry for later use.

[0032] 26.80g of the above mixed salt and 5.00g of rice husk were placed in an agate mortar, and after being fully ground and mixed, they were placed in a corundum boat, and then placed in a high-temperature tube furnace. First, the tube furnace was evacuated to replace nitrogen, the temperature was raised, and pyrolysis was carried out at 800℃ for 3h, the cooling rate was controlled to be 5℃ / min, and nitrogen was continuously introduced at a flow rate of 30mL / min during the period. The tube furnace was opened to take out the reaction product in the corundum boat, and the reaction product was filtered and washed with warm deionized water. During the period, the filtrate was tested with 1mol / L AgNO3 solution. The specific operation was as follows: 5mL of filtrate was taken into a test tube, and 3 drops of AgNO3 solution were dripped into it. If a white precipitate appeared in the solution, continue to filter and wash until the filtrate remained clear after the AgNO3 solution was dripped into it. After washing, the filter cake was taken into a glass culture dish, dried in an oven at 60℃ for 12h, and ground to obtain the intermediate product.

[0033] The intermediate product was placed back in a tube furnace, calcined at 550°C in an air atmosphere for 1 hour, and cooled naturally to room temperature, during which air was continuously introduced at a flow rate of 30 mL / min. The tube furnace was opened to take out the reaction product in the corundum boat, which was collected for later use to obtain the calcium metasilicate, which was named Sample 1.

[0034] Example 2

[0035] 13.40 g NaCl and 10.40 g CaCl2 were placed in an agate mortar, and after being fully ground to make the two salts evenly mixed, they were collected in a glass petri dish and placed in a 60°C oven to dry for later use.

[0036] 23.80g of the above mixed molten salt and 2.50g of rice husk were placed in an agate mortar, and after being fully ground and mixed, they were placed in a corundum boat and then placed in a high-temperature tube furnace. First, the tube furnace was evacuated to replace nitrogen, the temperature was raised, and pyrolysis was carried out at 850℃ for 2h. The cooling rate was controlled to be 6℃ / min, and nitrogen was continuously introduced at a flow rate of 30mL / min during the period. The reaction product in the corundum boat was opened and filtered and washed with warm deionized water. During the period, the filtrate was tested with 1mol / L AgNO3 solution. The specific operation was as follows: 5mL of filtrate was taken into a test tube, and 3 drops of AgNO3 solution were dripped into it. If a white precipitate appeared in the solution, continue to filter and wash until the filtrate remained clear after the AgNO3 solution was dripped into it. After washing, the filter cake was taken into a glass culture dish, dried in an oven at 60℃ for 12h, ground to obtain a powder product, and collected for later use.

[0037] The above product was placed back in a tube furnace, calcined at 600°C for 3h, and cooled naturally to room temperature, during which air was continuously introduced at a flow rate of 30mL / min. The tube furnace was opened to take out the reaction product in the corundum boat, and the reaction product was collected for later use to obtain the calcium metasilicate, which was named Sample 2.

[0038] Example 3

[0039] 9.00 g of NaCl and 17.80 g of CaCl2 were placed in an agate mortar, and after being fully ground to make the two salts evenly mixed, they were collected in a glass petri dish and placed in a 60°C oven to dry for later use.

[0040] 26.80g of the above mixed molten salt and 5.00g of rice husk were placed in an agate mortar, and after being fully ground and mixed, they were placed in a corundum boat and then placed in a high-temperature tube furnace. First, the tube furnace was evacuated to replace nitrogen, the temperature was raised, and pyrolysis was carried out at 780℃ for 3h. The cooling rate was controlled to be 7℃ / min, and nitrogen was continuously introduced at a flow rate of 30mL / min during the period. The reaction product in the corundum boat was opened and filtered and washed with warm deionized water. During the period, the filtrate was tested with 1mol / L AgNO3 solution. The specific operation was as follows: 5mL of filtrate was taken into a test tube, and 3 drops of AgNO3 solution were added. If a white precipitate appeared in the solution, the filtration and washing were continued until the filtrate remained clear after the AgNO3 solution was added. After washing, the filter cake was taken into a glass culture dish, dried in an oven at 60℃ for 12h, and the intermediate product was ground.

[0041] The above product was placed back in a tube furnace, calcined at 500°C for 2h, and cooled naturally to room temperature, during which air was continuously introduced at a flow rate of 30mL / min. The tube furnace was opened to take out the reaction product in the corundum boat, and the reaction product was collected for later use to obtain the calcium metasilicate, which was named Sample 3.

[0042] The samples 1-3 in Examples 1-3 were subjected to scanning electron microscopy tests, and Figure 1 . A relatively smooth nanorod morphology appeared in the SEM photos of all three samples. The aspect ratios of the nanorods were all greater than 30, and some aspect ratios could be as high as 200.

[0043] The samples 1-3 in Examples 1-3 were subjected to X-ray diffraction tests, and Figure 2 . The main peaks of all three samples could be considered to belong to the diffraction of CaSiO3 (PDF#27-0088). Since there were differences in the heat treatment processes of the three samples, it might lead to different peak intensities of the three samples in the XRD pattern.

[0044] Above, the embodiments of the present invention have been exemplarily described. However, the protection scope of the present invention is not limited to the above embodiments. Any modifications, equivalent replacements, improvements, etc. made by those skilled in the art within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for preparing calcium metasilicate using silicon-containing biomass as a raw material, characterized in that, The method includes: mixing a mixed salt of NaCl and CaCl2 with a silicon-containing biomass, subjecting it to pyrolysis, washing with water, filtering, and calcining the filter cake to obtain the calcium metasilicate; Recrystallizing the filtered filtrate and mixing it with the silicon-containing biomass for reuse; The silicon-containing biomass is selected from at least one of the following substances: rice husk, rice straw, reed leaf, bamboo pole, bamboo leaf, coconut shell, barley husk, or bracts of panicum miliaceum, millet, or barnyard grass; The pyrolysis is carried out in an inert atmosphere, and the temperature of the pyrolysis is 750-1000 °C; the method also includes cooling the pyrolyzed product, and the cooling rate is 4.5-10 °C / min; The temperature of the calcination is 450-600 °C, and the time of the calcination is 1-3 h; the calcination is carried out in an air atmosphere.

2. The method according to claim 1, characterized in that, In the mixed salt, the content of NaCl is 10 wt.% - 60 wt.%.

3. The method according to claim 1, characterized in that, The molar ratio of calcium to silicon elements in the mixed salt and the silicon-containing biomass is 2:1 - 20:

1.

4. The method according to claim 1, wherein The inert atmosphere is nitrogen or argon; During the pyrolysis process, the flow rate when the inert atmosphere is introduced is 10-40 mL / min.

5. The method according to claim 1, characterized in that, The time of the pyrolysis is 1-14 h.

6. The method according to claim 1, characterized in that, The calcium metasilicate is in the form of nanorods.

7. The method according to claim 1, wherein The aspect ratio of the calcium metasilicate is 30-200.

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