Silica obtained from plant-based raw materials and a method for producing spheroidal silica from that silica.

Abstract

The present invention aims to provide a method for producing silica obtained from plant-based raw materials and spheroidal silica prepared from such silica, with the goal of reducing the number of manufacturing steps and reducing the cost. [Solution] A step (S14) of calcining bagasse (9), which is the residue of sugarcane, The process includes a grinding step (S15) for grinding the silica obtained in the calcination step, The resulting silica (10) contains Al, Si, and Fe as its main components. A method for producing silica characterized by containing Al in a mass ratio equal to or greater than that of Si, and exhibiting a skin-colored appearance.

Description

Technical Field

[0001] The present invention relates to silica efficiently produced from plant raw materials, a method for producing silica, and a method for producing spheroidized silica using said silica.

Background Art

[0002] Conventionally, silica as fine silicon dioxide has lower water absorption than general powders. Taking advantage of this property, it is used in cosmetics such as eye shadows and foundations to prevent solidification due to moisture, and is also used in creams and emulsions for purposes such as stabilization. In addition, silicon dioxide has also been used in negative electrode materials for battery materials using high-purity silicon.

[0003] Among these silicas, crystalline silica is known to be a hazardous substance, while amorphous silica is not designated as a hazardous substance, and can be used in cosmetics, foods (including supplements), or applications such as agricultural fertilizers and feeds (for livestock and pet animals).

[0004] For example, Patent Document 1 discloses a method for producing spherical silica particles, comprising the steps of: preparing an organic waste containing silica as a starting material; immersing the organic waste in a liquid to increase the purity of silica; calcining the organic waste to obtain silica powder; pulverizing the silica powder to obtain silica fine particles; and melting and spheroidizing the silica fine particles in a flame to obtain spherical silica particles.

Prior Art Literature

Patent Literature

[0005]

Patent Document 1

Disclosure of the Invention

Problem to be Solved by the Invention

[0006] Silica intended as a substitute for these microbeads has traditionally been used as a cosmetic ingredient in the form of spheroidized silica. However, silica used in foundations and other products is colored with titanium dioxide or other substances to match skin tone. Thus, a two-stage manufacturing process is necessitated after spheroidization.

[0007] This invention was made to solve the above problems and aims to provide a method for producing silica obtained from plant-based raw materials and spheroidized silica prepared from that silica, with the aim of producing it inexpensively with fewer manufacturing steps. [Means for solving the problem]

[0008] The process involves burning bagasse, which is the residue left over from extracting sugarcane juice, The process includes a grinding step of grinding the silica obtained in the calcination step, The resulting silica contains Al, Si, and Fe as its main components. A method for producing silica characterized by containing Al in a mass ratio equal to or greater than that of Si, and exhibiting a skin-colored appearance. [Effects of the Invention]

[0009] These characteristics make it possible to manufacture skin-colored silica instead of the conventional white silica. [Brief explanation of the drawing]

[0010] [Figure 1] This diagram shows a process flow illustrating the manufacturing process for producing silica as shown in Example 1 of the embodiment. [Figure 2] This is a schematic diagram showing a manufacturing apparatus for producing silica according to the embodiment. [Figure 3] This is a microscopic image showing the appearance of rice husk silica. [Figure 4] This is a microscopic image showing the appearance of rice husk silica. [Figure 5] This is a micrograph showing the appearance of silica in the embodiment. [Figure 6]This is a micrograph showing the appearance of silica in the embodiment. [Modes for carrying out the invention]

[0011] The present invention will describe in detail, with reference to the drawings, silica obtained from plant-based raw materials and a method for producing spheroidal silica made from such silica. The embodiments and drawings described below are illustrative of some embodiments of the present invention and are not intended to limit the scope to these configurations. They may be modified as appropriate without departing from the spirit of the present invention.

[0012] <Plant-based raw materials> Plant-based raw materials that contain relatively high amounts of silicon include sugarcane stalks and bagasse, which is the residue left after pressing sugarcane.

[0013] The following describes the method for producing silica in Example 1 of this embodiment. (Example 1) In Example 1, rice husks, one of the plant-based raw materials 9 of this embodiment, are used, and the method for producing silica obtained from the plant-based raw materials and spheroidized silica prepared from that silica will be explained with reference to Figure 1.

[0014] Sugarcane, a plant-based raw material 9, is pressed multiple times, from one to five times, to extract the sugar juice (S11). The bagasse residue is compressed and packaged in block form to facilitate transportation (S12). The compression step (S12) is not always necessary but is convenient for transportation. Then, the packaged bagasse is unpacked and fired using a firing apparatus described later (S13).

[0015] Next, in the firing process (S4), the plant-based raw material 9 is placed in the furnace, the furnace is brought to atmospheric pressure, oxygen is supplied, the furnace temperature is raised to 300°C, and the temperature is maintained at a constant temperature between 300°C and 500°C for about 1 to 3 hours. The best temperature to maintain for a constant period is around 300°C.

[0016] Thereafter, the system is placed in a state where oxygen can be supplied, and the temperature is held constant for a certain period of about 1 to 3 hours at any temperature between 500°C and 700°C. The most preferable temperature for holding the temperature for the certain period is around 500°C.

[0017] Thereafter, the system is placed in a state where oxygen can be supplied, and the temperature is held constant for a certain period of about 1 to 3 hours at any temperature between 700°C and 900°C. The most preferable temperature for holding the temperature for the certain period is around 700°C. After the holding time, the total calcination time is set to about one day by natural self-calcination of the rice husks themselves, and the most preferable natural calcination time is 10 to 13 hours.

[0018] Thereafter, after the fire is naturally extinguished, the calcined silica 10 is taken out from the furnace. Since calcination is performed by self-calcination of the rice husks after the holding time, no energy is required after the holding time, which results in cost reduction. By holding the temperatures of 300°C and 500°C, which require the most energy when calcining rice husks, for a certain period of time, complete calcination can be achieved, thus improving purity.

[0019] [Table 1]

[0020] An example of the components of the calcined silica 10 is shown in Table 1. A 1.1 mg sample was dissolved in 11 ml of 5% HNO₃ to prepare a 100 ppm sample solution. Qualitative measurement of the silica 10 sample was performed by ICP-OES. Then, Al, Ca, Cr, Fe, K, Mg, Mn, P, S, Si, and Na were detected. Mixed solutions of 10, 5, 1, 0.5, 0.1, 0.05, and 0.01 ppm were prepared using metal element standard solutions other than Na. Additionally, standard solutions of 10, 5, 1, 0.1, and 0.01 ppm were prepared using only the Na standard solution. 5% HNO₃ was used for dilution.

[0021] Na was measured alone because it can interfere with the detection of other metal ions. 5% HNO₃ was used as a blank. ICP-OES (quantitative) measurements were performed on silica sample solutions, mixed metal element standard solutions, and Na standard solutions using three different wavelengths for each element. The concentrations (ppm) within the sample were as follows: Al 4.344, Ca 0.879, Cr 0.024, Fe 0.283, K 2.015, Mg 0.626, Mn 0.0018, P 0.821, S 0.247, Si 2.885, Na 1.306, and Ca 0.879.

[0022] The mass (μg) per 1 mg of sample was as follows: Al 43.44, Ca 8.79, Cr 0.24, Fe 2.83, K 20.15, Mg 6.26, Mn 0.18, P 8.21, S 2.47, Si 28.85, and Na 13.06.

[0023] [Table 2]

[0024] In particular, with bagasse, the plant-based raw material 9, it was possible to produce silica 10 in colors similar to skin tone, such as skin color or reddish-brown, as indicated by the color codes above. The most noticeable color differences were observed with bagasse from Tokunoshima, while the silica from Okinawa Island was white.

[0025] These differences are thought to be due to differences in soil type, with dark red soil, fine-grained dark red soil, red soil, fine-grained red soil, yellow soil, and fine-grained yellow soil exhibiting colors close to the skin tone described above. These soils are very similar in composition to bauxite and contain a large amount of Al. The elemental composition combinations closest to the foundation color were Al at 30%-60% by mass, Si at 10%-40%, and Fe at 1%-5%.

[0026] Figure 3 is an electron microscope image of typical rice husk silica at 500x magnification. Figure 4 is an electron microscope image of typical rice husk silica at 2000x magnification. Figure 5 is a 500x electron microscope image of the calcined bagasse silica-10. Figure 6 is a 2000x electron microscope image of the calcined bagasse. The appearance of the calcined bagasse silica-10 was turtle shell-like.

[0027] Next, the silica 10 is pulverized (S14). The pulverized silica 10 has a particle size distribution that is mostly between 5 μm and 20 μm. The pulverization method may be a jet mill, ball mill, bead mill, or other pulverization method.

[0028] Next, molten silica spheroidization is performed (S15). Plasma or gas spraying is a method in which crushed silica powder is supplied into a flame at a high temperature of 2000°C or higher to melt the silica, and spherical silica particles are obtained by rapidly cooling the molten silica that has been sphericalized by surface tension. Because the molten silica is rapidly cooled, the resulting spherical silica particles are amorphous.

[0029] In addition, silica-10 may be spheroidized by a molten flame method, with a flame treatment temperature of 1750°C to 2500°C. Furthermore, spray drying may also be used as another method of spheroidization.

[0030] Furthermore, in plasma melting, a large volume of thermal plasma can be generated and melted at high temperatures exceeding 10,000°C using the high-frequency induction plasma method to produce highly spherical silica 10 powder. The final product is amorphous spherical silica particles 11 (S16).

[0031] Next, the manufacturing apparatus used for firing silica 10 will be explained with reference to Figure 2. Figure 2 is a schematic diagram of the mesh-type continuous firing furnace 100. Figure 2(A) is a schematic diagram showing the internal structure of the mesh-type continuous firing furnace 100 as viewed from the side. The mesh-type continuous firing furnace 100 is equipped with a drive motor 106 and a drive belt on rollers 107, and a mesh-type conveyor belt 102 is provided. The mesh-type continuous firing furnace 100 can reach temperatures from room temperature up to 1000°C, and it is possible to adjust the temperature gradient and temperature holding time.

[0032] The mesh-type continuous firing furnace 100 loads plant-based raw materials 9 into multiple mesh-type storage containers 110, which are transported from the inlet 101 to the outlet 109. A mesh-type conveyor belt 102 transports the multiple mesh-type storage containers 110 from the inlet 101 to the outlet 109.

[0033] Since the plant-based raw material 9 generates gas when burned, the mesh-type continuous firing furnace 100 is equipped with a waste intake port 105 and an exhaust port 104 for external discharge, taking gas exhaust into consideration. This ensures that combustible gases are discharged to the outside, reducing the amount of tar remaining inside the furnace.

[0034] Figure 2(B) is a plan view of the mesh conveyor belt 102. The mesh conveyor belt facilitates combustion of the plant-based raw materials 9 by supplying air to the material through its mesh structure.

[0035] Figure 2(C) is a schematic diagram of the mesh-type storage container 110. The mesh-type storage container 110 has a housing 114 with a certain height, and a metal mesh (116) made of stainless steel or the like is provided on the bottom surface to facilitate the transfer of heat from the heaters 103 from both the top and bottom, and to facilitate the intake of air. The mesh-type storage container 110 also has handles 112 on the sides of the housing 114 for easy carrying.

[0036] Although the explanation used a mesh-type conveyor belt, it does not necessarily have to be mesh-type. Also, the storage container does not have to be mesh-type; a ceramic container is also acceptable. In the case of metal storage containers, metal residues tend to remain as impurities, so a ceramic container is a good alternative.

[0037] (Technical features) The following are examples of the technical features of this embodiment, shown in parentheses, but these are not limiting and are merely illustrative. The effects that can be expected from these features are also described.

[0038] <Feature 1> The process of burning bagasse, which is the residue left over from sugarcane extraction (S14), The process includes a grinding step (S15) for grinding the silica obtained in the calcination step, The resulting silica contains Al, Si, and Fe as its main components. A method for producing silica characterized by containing Al in a mass ratio equal to or greater than that of Si, and exhibiting a skin-colored appearance.

[0039] These characteristics make it possible to manufacture skin-colored silica instead of the conventional white silica.

[0040] <Feature 2> The method is characterized by including a spheroidizing step in which the obtained silica is melted and spheroidized, thereby producing amorphous spheroidized silica.

[0041] Based on the above characteristics, amorphous, spherical silica can be obtained. [Explanation of symbols]

[0042] 9 Plant-based raw materials 10 Silica 11 Amorphous spherical silica particles 100-mesh continuous firing furnace 102 Mesh conveyor belt 103 Heater 104 Exhaust port 110 Mesh Storage Containers S11 Grinding process for plant-based raw materials S12 Sugarcane pressing process S13 Bagasse Compression Process S14 Firing process S15 Spheroidization process S16 Spheroidized silica extraction process.

Claims

1. The process involves burning bagasse, which is the residue left over from extracting sugarcane juice, The process includes a grinding step of grinding the silica obtained in the calcination step, The resulting silica contains Al, Si, and Fe as its main components. A method for producing silica characterized by containing Al in a mass ratio equal to or greater than that of Si, and exhibiting a skin-colored appearance.

2. The process includes a spheroidizing step in which the obtained silica is melted and formed into spheres, A method for producing silica according to claim 1, characterized by producing amorphous spheroidized silica.

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