Method for producing amorphous silica particles, amorphous silica particles, cosmetic containing same, and system for producing amorphous silica particles

Abstract

In order to achieve a production method for producing amorphous silica particles having a silica purity equal to or higher than that of the prior art in such a manner that the particle diameter is adjustable, a method for producing amorphous silica particles according to an aspect of the present disclosure comprises: a hot water treatment step for subjecting a plant-derived substrate to a hot water treatment; and a firing step for firing residues of the substrate obtained in the hot water treatment step.

Description

Method for producing amorphous silica particles, amorphous silica particles, cosmetics containing the same, and system for producing amorphous silica particles

[0001] The present disclosure relates to a method for producing amorphous silica particles, amorphous silica particles, cosmetics containing the same, and a system for producing amorphous silica particles.

[0002] BACKGROUND ART In order to effectively utilize plants such as agricultural crops for the purpose of environmental protection, techniques for producing silica from plants have been attracting attention in recent years.

[0003] As a technique for producing silica from plants, for example, Patent Document 1 describes a method for producing a silica raw material in which rice husk powder is treated with compressed hot water at 150 to 450° C. for at least 30 seconds. Furthermore, for example, Patent Document 2 describes a method for producing amorphous silica, which includes a step of immersing organic waste containing silicon oxide in an aqueous solution of a carboxylic acid having a hydroxyl group, and a further step of heating the organic waste in an air atmosphere.

[0004] Japanese Patent Application Publication No. 2002-265257 International Publication No. 2008 / 053711

[0005] Due to growing health consciousness, demand for plant-derived amorphous silica particles is increasing in the fields of cosmetics, food, etc. In these fields, amorphous silica particles are required to have a higher purity in order to reduce adverse effects on the human body. Furthermore, the particle size required for amorphous silica particles varies depending on the application. For example, in the fields of cosmetics, food, etc., smaller particle sizes are required to achieve a good feel on the skin.

[0006] The prior art techniques described in Patent Documents 1 and 2 leave room for improvement in terms of the purity and particle size of the amorphous silica particles produced.

[0007] An object of one aspect of the present disclosure is to realize a production method for producing amorphous silica particles having a silica purity equivalent to or higher than that of conventional techniques, with the particle size adjustable. In particular, one object of one aspect of the present disclosure is to realize a production method capable of producing amorphous silica particles having a silica purity equivalent to or higher than that of conventional techniques, but with a smaller particle size.

[0008] In order to solve the above-mentioned problems, a method for producing amorphous silica particles according to one embodiment of the present disclosure includes a hot water treatment step of treating a plant-derived substrate with hot water, and a calcination step of calcining the residue of the substrate obtained in the hot water treatment step.

[0009] Furthermore, the amorphous silica particles according to one embodiment of the present disclosure have a silicon dioxide content of 99.00 mass% or more, based on the mass of oxides in the ash, an average circularity of the particles of 0.85 or less, and an average particle diameter of the particles of 40 μm or less.

[0010] Furthermore, a system for producing amorphous silica particles according to one embodiment of the present disclosure includes a hydrothermal treatment device that hydrothermally treats a plant-derived substrate, and a calcination device that calcines a residue of the substrate obtained in the hydrothermal treatment device.

[0011] According to one aspect of the present disclosure, amorphous silica particles having a silica purity equal to or higher than that of the prior art can be produced in an adjustable particle size. Also, according to one aspect of the present disclosure, amorphous silica particles having a silica purity equal to or higher than that of the prior art and a smaller particle size can be produced.

[0012] 1 is a block diagram schematically showing the configuration of a production system according to one embodiment of the present disclosure; 2 is a diagram schematically showing the configuration of a hot water treatment device used in Example 1; 3 is a graph showing the particle size distribution of amorphous silica particles of Example 1 and Comparative Examples 1 and 2; 4 is an SEM image of the amorphous silica particles of Examples 1 and 2;

[0013] [Method for producing amorphous silica particles] As a result of extensive research, the present inventors have found that amorphous silica particles having high silica purity and a small particle size can be produced by calcining the residue of a plant-derived substrate obtained by hot water treatment, and have completed the present invention.

[0014] That is, the method for producing amorphous silica particles according to one embodiment of the present disclosure includes a hot water treatment step of treating a plant-derived substrate with hot water, and a calcination step of calcining the residue of the substrate obtained in the hot water treatment step. Hereinafter, the "method for producing amorphous silica particles according to one embodiment of the present disclosure" may be abbreviated as "the present production method."

[0015] [Hot Water Treatment Step] The present production method includes a hot water treatment step, which is a step of treating a plant-derived substrate with hot water.

[0016] (Substrate) This production method uses a plant-derived substrate as a raw material. The plant-derived substrate used here typically contains particulate amorphous silica (sometimes called plant opal). Therefore, this production method can also be described as a method for purifying particulate amorphous silica contained in the raw material.

[0017] Examples of plants that can serve as a substrate source include grasses, convolvulaceous plants, legumes, etc. Examples of grasses include rice, oats (sometimes called oats), bamboo, bamboo grass, sugarcane, corn, etc.

[0018] The substrate may be the whole plant or a part thereof. Examples of plant parts include seed coats, bark, leaves, stems, roots, etc.

[0019] Among these, the substrate preferably contains a grass family plant, and more preferably contains a seed coat of a grass family plant. In grass family plants, particularly in their seed coats, the epidermal cells, motor cells, and dumbbell cells are silicified, and a large amount of amorphous silica is contained. Therefore, grass family plants are preferred as a raw material for amorphous silica particles.

[0020] The substrate may be a plant residue used to produce an article other than amorphous silica particles, such as rice husks (rice seed coats), rice straw, rice bran, wheat straw, thinnings such as bamboo, sawdust, bagasse, corn, sugarcane, cassava, or ferns. Generally, such plant residues are often incinerated as waste. However, the present production method allows the plant residue to be effectively utilized as a raw material for amorphous silica particles. Furthermore, with the recent rise in environmental awareness, the amount of smoke generated during incineration is sometimes limited to prevent air pollution. However, in the present production method, as described below, some of the combustible components of the substrate that would otherwise be removed by the calcination step are previously removed as soluble components by hot water treatment. Therefore, by using the present production method as one embodiment of a method for disposing of plant residues, the amount of smoke generated during the calcination step can be reduced compared to when the plant residues are simply incinerated. These effects will also contribute to achieving, for example, Goal 15 of the United Nations' Sustainable Development Goals (SDGs), which is to "protect and sustainably manage the life on land."

[0021] The substrate may be selected depending on the particle size desired for the amorphous silica particles to be produced. According to this production method, purified amorphous silica particles can be obtained from a substrate containing particulate amorphous silica while maintaining its particle size. Therefore, by selecting a substrate containing amorphous silica having a particle size close to the desired particle size, amorphous silica particles having the desired particle size can be produced. For example, when an average particle size of 20 μm or more and 50 μm or less is desired, it is preferable to use rice husks as the substrate.

[0022] The substrate may be pulverized before the hot water treatment, and preferably has a size that can pass through a 32 mesh sieve, for example. The finer the substrate is pulverized, the shorter the hot water treatment can be completed. Examples of the pulverization process include crushing and shredding.

[0023] (Hot Water Treatment) Hot water treatment is a treatment in which a substrate is brought into contact with water at a temperature of 100° C. or higher and in a liquid state.

[0024] The hot water treatment decomposes easily decomposable components such as xylan (or hemicellulose) in the substrate and extracts them into water, while inorganic components other than amorphous silica, such as potassium and calcium, are released into water from the substrate, which has become brittle due to hydrolysis. Therefore, the hot water treatment removes soluble components and inorganic components other than amorphous silica from the substrate. Meanwhile, unlike inorganic components such as potassium contained in trace amounts in the substrate, amorphous silica exists in the substrate in the form of silicified plant cells of a certain size, and is therefore retained in the residue of the substrate even after the hot water treatment. Therefore, the residue of the substrate obtained in the hot water treatment step has an improved silica purity compared to the substrate before the hot water treatment.

[0025] Furthermore, the hot water treatment effectively prevents aggregation of amorphous silica particles, which may cause an increase in the particle size of the produced amorphous silica particles, depending on the shear force applied to the substrate. Therefore, the hot water treatment maintains the particle size of the amorphous silica contained in the substrate and allows a residue containing the amorphous silica to be obtained.

[0026] The hydrothermal treatment can be carried out in any reaction mode, for example, a semi-flow mode (sometimes called a percolator mode or semi-batch mode), a batch mode (especially one using a stirring mechanism), or a continuous mode. The reaction mode is preferably a semi-flow mode or a batch mode using a stirring mechanism, and more preferably a semi-flow mode. By selecting the reaction mode, the shear force applied to the substrate can be adjusted, thereby making it possible to more suitably adjust the particle size of the produced amorphous silica particles.

[0027] When a semi-flow reactor is used, hydrothermal treatment can be performed by passing heated and pressurized water through a reactor filled with a substrate as a fixed bed. According to the hydrothermal treatment using a semi-flow reactor, shear force due to the flow of water is applied to the substrate, thereby preventing aggregation of amorphous silica particles. Therefore, the particle size of the amorphous silica contained in the residue becomes smaller. Furthermore, by using a semi-flow reactor, the soluble components and inorganic components removed from the substrate by the hydrothermal treatment are removed from the reactor together with the water, while the amorphous silica retained on the substrate remains in the reactor. Therefore, the silica purity in the residue of the substrate is further improved.

[0028] When a batch reactor is used, the substrate and water are added to the reactor, and the mixture is heated under pressure to perform the hydrothermal treatment. The hydrothermal treatment using a batch reactor allows for easier operation of the equipment and allows for the production of amorphous silica particles at lower cost than when a semi-flow reactor or a continuous reactor is used.

[0029] When a batch reactor is used, the reactor may be provided with a mechanism for stirring the inside of the reactor. With such a mechanism, shear force due to stirring is applied to the substrate, which effectively prevents aggregation of amorphous silica particles. As a result, the particle size of the amorphous silica contained in the residue becomes smaller.

[0030] When a batch reactor is used, it is preferable to filter the residue from the mixture of the residue of the substrate after the hot water treatment and water in the hot water treatment step, thereby removing soluble components and inorganic components that have migrated from the substrate to the water by the hot water treatment, while recovering the amorphous silica contained in the residue.

[0031] The temperature in the hot water treatment may be greater than 100°C, preferably 120°C or higher, more preferably 130°C or higher, even more preferably 140°C or higher, particularly preferably 150°C or higher, even more preferably 160°C or higher, more particularly preferably 170°C or higher, and most preferably 180°C or higher. The higher the temperature within this range, the more the silica purity can be improved. The temperature in the hot water treatment may be 370°C or lower, preferably 350°C or lower, more preferably 320°C or lower, particularly preferably 300°C or lower, even more preferably 270°C or lower, more particularly preferably 250°C or lower, and most preferably 230°C or lower. The lower the temperature within this range, the easier the operation of the hot water treatment device.

[0032] The pressure (gauge pressure) in the hot water treatment is adjusted according to the temperature so that the water is maintained in a liquid state. The pressure in the hot water treatment is preferably 0.1 MPa or higher. The higher the pressure within this range, the more the silica purity can be improved. The pressure in the hot water treatment is preferably 22.0 MPa or lower. The lower the pressure within this range, the easier it is to operate the hot water treatment device.

[0033] In the hot water treatment step, the shear force applied to the substrate is preferably 1 N or more, more preferably 500 N or more. Within this range, the larger the shear force, the more effectively the amorphous silica particles are prevented from agglomerating, resulting in a smaller particle size of the resulting amorphous silica. The shear force applied to the substrate is 25×10 ６ N or less, and 2×10 ６ It is more preferable that the shear force is not more than N. Within this range, the smaller the shear force, the easier the operation of the hot water treatment device becomes.

[0034] The shear force applied to the substrate can be calculated by a known method. For example, when a reactor in which a fluid flows inside the reactor, such as a semi-flow reactor or a continuous reactor, is used, the shear force can be calculated using the following formula: τ(N) = P(Pa) × S(m ２In the formula, τ represents the shear force applied to the substrate, P represents the pressure (gauge pressure) in the reactor, and S represents the cross-sectional area of ​​the reactor when viewed in plan along the direction of fluid flow.

[0035] The time for the hot water treatment is preferably 30 minutes or more, more preferably 1 hour or more, and even more preferably 2 hours or more.Within this range, the longer the time, the smaller the particle size of the produced amorphous silica particles tends to be.This tendency is thought to be due to the fact that secondary particles originally formed by agglomeration of amorphous silica in the substrate are separated by the hot water treatment.In addition, there is no particular upper limit to the time for the hot water treatment, but the time may be, for example, 5 hours or less.

[0036] In the hot water treatment, it is preferable not to add chemicals to the water. In the prior art, in order to remove inorganic components contained in the substrate and improve the purity of the amorphous silica particles, chemicals such as oxalic acid, which exhibit a chelating effect, have been added to the water, and the substrate has been immersed in this mixture. However, according to the present production method, amorphous silica particles with high purity can be produced without adding chemicals. Furthermore, by not adding chemicals, the product value of the amorphous silica particles is improved in the cosmetics and food industries, where there is a high demand for chemical-free materials, and the washing step for removing chemicals can be eliminated from the present production method. Note that the present production method is not limited to an embodiment in which chemicals are not added, and chemicals may be added to the water as appropriate depending on the application of the amorphous silica particles.

[0037] In the hot water treatment, the weight of water used is preferably at least three times the weight of the substrate, more preferably at least five times the weight of the substrate. The greater the weight of water within this range, the more improved the silica purity in the residue.

[0038] [Water-washing step] The present production method preferably includes a water-washing step after the hot water treatment step and before the calcination step. The water-washing step is a step of washing with water the residue of the substrate obtained in the hot water treatment step.

[0039] The water adhering to the surface of the residue after the hot water treatment and the water contained in the residue may contain water-soluble organic and inorganic components extracted or leached into the water by the hot water treatment. These remaining components may oxidize during the calcination process and become impurities in the ash of the resulting amorphous silica, which may cause a decrease in silica purity. Therefore, by washing the residue with water, the water remaining in the residue is replaced with fresh water, removing the remaining components and further improving the silica purity of the resulting amorphous silica.

[0040] In the water washing step, the weight of water used is preferably equal to or greater than the weight of the residue. The greater the weight of water within this range, the more improved the silica purity in the residue.

[0041] [Dehydration Step] The present production method may further include a dehydration step after the water-washing step and before the calcination step. The dehydration step is a step for removing water when a large amount of water remains on the surface of the residue after the water-washing step. Removing the adhering water can improve the efficiency of the calcination step. Examples of dehydration methods include a method of applying centrifugal force to the residue to remove the adhering water (centrifugal dehydration) and a method of applying pressure to the residue to remove the adhering water (pressure dehydration), and centrifugal dehydration is preferred.

[0042] [Firing step] The present production method includes a firing step after the hot water treatment step. The firing step is a step of firing the residue of the substrate obtained in the hot water treatment step. Note that if a water washing step or a dehydration step has been performed, the washed residue or the dehydrated residue is subjected to the firing step.

[0043] In the calcination step, combustible components, including carbon, such as fibers, contained in the residue are burned and removed, and amorphous silica bound to the fibers is obtained as individual particles. Note that some of the combustible components to be removed in the calcination step have been previously removed as soluble components by hot water treatment. Therefore, the amount of combustible components to be removed in the calcination step is reduced, and the remaining combustible components are sufficiently removed in the calcination step. As a result, in this production method, amorphous silica particles with high purity are obtained as a result of the synergistic effect of the hot water treatment step and the calcination step.

[0044] The calcination temperature is preferably 600°C or higher, more preferably 650°C or higher, and even more preferably 700°C or higher. The higher the calcination temperature within this range, the more the silica purity can be improved. The calcination temperature is preferably 1000°C or lower, more preferably 950°C or lower, and even more preferably 900°C or lower. The lower the calcination temperature within this range, the easier the operation of the calcination apparatus becomes. The specific surface area can be controlled by controlling the calcination temperature, and calcining at a lower temperature can further increase the specific surface area of ​​the resulting amorphous silica particles. It is preferable to set the calcination temperature at which the desired specific surface area can be obtained depending on the application of the amorphous silica particles.

[0045] The calcination time is preferably 30 minutes or more, more preferably 1 hour or more. The longer the calcination time within this range, the more the silica purity can be improved. There is no particular upper limit to the calcination time, but the time may be, for example, 6 hours or less.

[0046] The firing can be carried out in an air atmosphere, but is not limited to this.

[0047] In the calcination step, the calcination may be carried out in one step or in two or more steps using different calcination temperatures. For example, in the calcination step, the residue may be calcined at 400°C for 1 hour and then further calcined at 700°C for 1 hour.

[0048] [Additional Steps] The present production method may further include an additional step after the calcination step. The additional step is appropriately selected depending on the application of the amorphous silica particles. As an example, if a particle size smaller than that of the amorphous silica particles obtained by the calcination step is desired, the present production method may further include a grinding step of grinding the amorphous silica particles. As another example, if coarse particles are desired, the present production method may further include a classification step of classifying the amorphous silica particles.

[0049] [Amorphous Silica Particles] Amorphous silica particles according to one embodiment of the present disclosure will be described below. For the sake of convenience, the description of members having the same functions as the members described above will not be repeated.

[0050] The amorphous silica particles according to one embodiment of the present disclosure have a silicon dioxide content of 99.00 mass% or more, based on the mass of oxides in the ash, an average circularity of the particles of 0.85 or less, and an average particle size of 40 μm or less. Hereinafter, "amorphous silica particles according to one embodiment of the present disclosure" may be abbreviated as "the present silica particles." The present silica particles are typically derived from plants and can be produced by the above-mentioned present production method.

[0051] In the present silica particles, silicon dioxide (SiO ２ ) content (i.e., silica purity) is 99.00% by mass or more, preferably 99.10% by mass or more, and more preferably 99.20% by mass or more. The higher the silicon dioxide content within this range, the more improved the whiteness of the present silica particles, making them suitable for use as ingredients in cosmetics, foods, etc. The upper limit of the silicon dioxide content is not particularly limited, but is, for example, 100.00% by mass or less. In this specification, the silicon dioxide content is expressed based on the mass of the oxide in the ash content of the present silica particles. In this specification, the silicon dioxide content is measured using X-ray fluorescence analysis (XRF).

[0052] The silica particles contain aluminum oxide (Al) in addition to silicon dioxide. ２ O ３ ), iron oxide (Fe ２ O ３ ), potassium oxide (K ２ The inorganic filler may further contain metal oxides such as calcium oxide (CaO).

[0053] The average circularity of the present silica particles is 0.85 or less, preferably 0.75 or less, and more preferably 0.70 or less. In the present silica particles, the shape of the amorphous silica contained in the plant-derived substrate used as the raw material is suitably maintained. Therefore, compared with silica particles produced by wet synthesis, the present silica particles tend to have a less rounded, distorted shape, and therefore a lower average circularity. In this specification, the average circularity is determined by taking images of 7 or more amorphous silica particles, analyzing the images, determining the area (S) of each particle and the perimeter of each silica particle, and calculating the circularity of each particle using the following formula, and averaging them: Circularity = 4π x area / (perimeter) ２

[0054] The average particle size of the present silica particles is preferably 40 μm or less, more preferably 35 μm or less, and even more preferably 30 μm or less. Within this range, the smaller the average particle size, the better the feel of the present silica particles on the skin. The average particle size of the present silica particles may be, for example, 5 μm or more. In this specification, the average particle size refers to the volume average particle size, and is measured using a laser diffraction / scattering method.

[0055] The specific surface area of ​​the silica particles is 50 m ２ / g or more, and ２ / g or more. The larger the specific surface area within this range, the greater the thickening effect when the present silica particles are added to liquid products such as cosmetics or foods, and the more likely it is that the product will not drip. In addition, the specific surface area of ​​the present silica particles is, for example, 1000 m ２ / g or less.

[0056] In this specification, the specific surface area is determined by drying a sample to be measured at 200°C for 3 hours or more under a vacuum of 1 kPa or less, obtaining an adsorption isotherm for the sample only on the nitrogen adsorption side at liquid nitrogen temperature, and analyzing the adsorption isotherm by the BET method.

[0057] The oil absorption of the present silica particles is preferably 100 mL / 100 g or more, more preferably 200 mL / 100 g or more. The larger the oil absorption within this range, the more improved the wettability of the present silica particles, and when added to liquid products such as cosmetics or foods, the more easily the silica particles will blend with the product. In addition, the oil absorption of the present silica particles may be, for example, 500 mL / 100 g or less.

[0058] In this specification, the oil absorption refers to the refined linseed oil absorption measured by the test method described in JIS K5101-13-1.

[0059] [Uses of Amorphous Silica Particles] The present silica particles can be used as high-purity amorphous silica particles as materials for cosmetics, foods, pharmaceuticals, oral care products, etc. The uses of the present silica particles are not limited thereto, and the present silica particles can also be used as industrial materials for, for example, cement, tires, resins, rubber, building materials, adhesives, detergents, inks, toners, paints, etc. Cosmetics, foods, pharmaceuticals, oral care products, etc. containing the present silica particles also fall within the scope of the present disclosure.

[0060] Cosmetics containing the present silica particles can be in any known form, including powder, cake, pencil, stick, gel, mousse, liquid, and cream. Examples of cosmetics containing the present silica particles include: skin cleansers such as soap and makeup remover; skin care cosmetics intended for moisturizing, preventing rough skin, whitening, improving wrinkles and sagging, anti-aging effects, or sunscreen; makeup foundations such as powder foundation, pressed foundation, liquid foundation, cream foundation, mousse foundation, loose powder, and makeup base; and point makeup cosmetics such as eye shadow, mascara, and lipstick. The content of the present silica particles in cosmetics may be, for example, 0.1% to 30% by mass. In addition to the present silica particles, cosmetics may contain any of aqueous components, oily components, and other additives depending on the intended use of the cosmetics.

[0061] [Amorphous Silica Particle Production System] A system for producing amorphous silica particles according to one embodiment of the present disclosure includes a hydrothermal treatment device for hydrothermally treating a plant-derived substrate, and a calcination device for calcining the substrate residue obtained in the hydrothermal treatment device. Hereinafter, the "amorphous silica particle production system according to one embodiment of the present disclosure" may be abbreviated as "the present production system." The present production system is typically a system for carrying out the present production method.

[0062] The present production system will be described with reference to Fig. 1. Fig. 1 is a block diagram showing a schematic configuration of the present production system 100. As shown in Fig. 1, the present production system 100 includes a hydrothermal treatment device 11 and a calcination device 12. In the present production system 100, the hydrothermal treatment device 11 and the calcination device 12 are in communication with each other so that substrate residue in the hydrothermal treatment device 11 can be transported to the calcination device 12.

[0063] [Hot Water Treatment Apparatus] The hot water treatment apparatus 11 is an apparatus for carrying out a hot water treatment step. As the hot water treatment apparatus, for example, a combination of a reactor and a heater can be used. Furthermore, when the reactor is a semi-flow reactor or a continuous reactor, the hot water treatment apparatus may further include a water tank and a pump.

[0064] [Firing Device] The firing device 12 is a device for carrying out the firing step. A firing furnace can be used as the firing device.

[0065] [Summary] As can be understood from the above description, the present disclosure includes the following aspects.

[0066] Aspect 1: A method for producing amorphous silica particles, comprising: a hot water treatment step of treating a plant-derived substrate with hot water; and a calcination step of calcining a residue of the substrate obtained in the hot water treatment step.

[0067] Aspect 2: The method for producing amorphous silica particles according to Aspect 1, wherein the hot water treatment in the hot water treatment step is carried out in a semi-flow system, a batch system using a stirring mechanism, or a continuous system.

[0068] Aspect 3: The method for producing amorphous silica particles according to Aspect 1 or 2, wherein the hot water treatment in the hot water treatment step is carried out at a temperature of 120° C. or higher and 350° C. or lower and a pressure of 0.1 MPa or higher and 20 MPa or lower.

[0069] Aspect 4: In the hot water treatment step, 1N or more and 25 × 10 ６ A method for producing amorphous silica particles according to any one of Aspects 1 to 3, wherein a shear force of N or less is applied to the substrate.

[0070] Aspect 5: The method for producing amorphous silica particles according to any one of Aspects 1 to 4, wherein the calcination in the calcination step is carried out at a temperature of 600° C. or higher and 1000° C. or lower.

[0071] Aspect 6: The method for producing amorphous silica particles according to any one of Aspects 1 to 5, further comprising, after the hot water treatment step and before the calcination step, a water washing step of washing with water the residue of the substrate obtained in the hot water treatment step.

[0072] Aspect 7: The method for producing amorphous silica particles according to any one of Aspects 1 to 6, wherein the substrate comprises a grass plant.

[0073] Aspect 8: Amorphous silica particles produced by the method for producing amorphous silica particles according to any one of Aspects 1 to 7.

[0074] Aspect 9: Amorphous silica particles having a silicon dioxide content of 99.00% by mass or more, based on the mass of the oxide in the ash, an average circularity of the particles of 0.85 or less, and an average particle size of the particles of 40 μm or less.

[0075] Aspect 10: The specific surface area of ​​the particles is 50 m ２ / g or more, and the oil absorption of the particles is 100 mL / 100 g or more.

[0076] Aspect 11: A cosmetic product comprising the amorphous silica particles of aspect 9 or 10.

[0077] Aspect 12: A system for producing amorphous silica particles, comprising: a hydrothermal treatment device that hydrothermally treats a plant-derived substrate; and a calcination device that calcines a residue of the substrate obtained in the hydrothermal treatment device.

[0078] [Additional Notes] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0079] Comparative Example 1 Rice husks (rice seed coats) were used as the raw plant substrate. The rice husks were calcined at 700° C. for 1 hour in a calcination furnace to obtain amorphous silica particles of Comparative Example 1.

[0080] Comparative Example 2 Rice husks were immersed in a 0.5 M aqueous oxalic acid solution overnight, washed with water, and dried. The dried rice husks were calcined at 700° C. for 1 hour to obtain amorphous silica particles of Comparative Example 2.

[0081] Example 1: Hot water treatment was carried out using the hot water treatment device shown in Figure 2. First, 15 g of rice husks was packed into a 180 mL semi-flow reactor equipped with a thermocouple and a downstream SUS filter (pore size 10 μm). Next, water heated to 180°C in a preheater was passed through the semi-flow reactor. The water temperature in the reactor was 180°C, the pressure was 2.0 MPa, the flow rate was 33 mL / min, and the flow time was 2.5 hours. The water discharged from the reactor was collected in a collection tank.

[0082] The rice husk residue recovered from the reactor was dried and then calcined at 700° C. for 1 hour to obtain amorphous silica particles of Example 1.

[0083] Example 2 Amorphous silica particles of Example 2 were obtained using the same method as in Example 1, except that bamboo thinnings were used instead of rice husks as the plant substrate.

[0084] Example 3 A batch-type autoclave (volume 300 mL) was used as a container, and 10 g of rice husks and 100 g of water were charged into the container. The container was heated while stirring the contents of the container at 120 rpm with a propeller-type stirring blade. After the liquid temperature reached 180°C, the temperature was maintained for 30 minutes. During this time, the pressure was 0.9 MPa. The rice husk residue recovered from the container was washed with 100 g of ion-exchanged water, and then the residue was thoroughly dried in a dryer maintained at 110°C. The dried residue was calcined in an electric furnace at 600°C for 1 hour to obtain amorphous silica particles of Example 3. The resulting amorphous silica particles had a specific surface area of ​​173 m2 as measured by the BET method. ２ / g.

[0085] Example 4 A batch-type autoclave (volume 300 mL) was used as a container, and 10 g of rice husks and 100 g of water were filled into the container. The container was heated without stirring. After the liquid temperature reached 180°C, the temperature was maintained for 30 minutes. During this time, the pressure was 0.9 MPa. The rice husk residue recovered from the container was washed with 100 g of ion-exchanged water, and then the residue was thoroughly dried in a dryer maintained at 110°C. The dried residue was fired in an electric furnace at 850°C for 3 hours to obtain amorphous silica particles of Example 4. The obtained amorphous silica particles had a specific surface area of ​​62 m2 as measured by the BET method. ２ The oil absorption of the obtained amorphous silica particles, measured in accordance with JIS K5101-13-1, was 130 mL / 100 g.

[0086] [Evaluation Example 1] Composition Analysis The compositions of the amorphous silica particles of Examples 1, 3, and 4 and Comparative Examples 1 and 2 were analyzed by XRF using a ZSX Primus IV (manufactured by Rigaku Corporation). The analysis results are shown in Table 1.

[0087] As shown in Table 1, Example 1 exhibited higher silica purity than Comparative Examples 1 and 2. Example 1 exhibited a higher silica purity than Comparative Examples 1 and 2. ２ The contents of O and CaO were particularly reduced, which is thought to have improved the silica purity. Examples 3 and 4 showed silica purity at the same level as Comparative Example 2, which used chemicals.

[0088] [Evaluation Example 2] Particle size analysis The particle size distributions of the amorphous silica particles of Examples 1 to 4 and Comparative Examples 1 and 2 were analyzed using an LS-230 (manufactured by Beckman Coulter). The particle size distributions (volume basis) obtained for Example 1 and Comparative Examples 1 and 2 are shown in Figure 3. The volume-based average particle sizes calculated from the particle size distributions are also shown in Table 1.

[0089] As shown in Figure 3, in Example 1, the distribution peak shifted to a smaller value compared to Comparative Examples 1 and 2. In particular, particles with a particle diameter of 100 µm or more, which are considered to have an unpleasant feel on the skin, were not detected in Example 1. Furthermore, as shown in Table 1, in Examples 1 and 3, which used a semi-flow system or a batch system with a stirring mechanism, respectively, the average particle diameter was smaller compared to Comparative Examples 1 and 2. In Example 4, which used a batch system without a stirring mechanism, the average particle diameter was larger compared to Example 3. The average particle diameter in Example 2 was about 20 µm.

[0090] [Evaluation Example 3] Circularity Analysis The circularity of the amorphous silica particles of Examples 1 to 4 was analyzed as follows. Specifically, an SEM image of the amorphous silica particles was obtained using an electron microscope JSM-7800F Prime (JEOL) under conditions of an acceleration voltage of 10.0 kV and a magnification of 300x. Next, seven particles were selected from the SEM image, and the area and perimeter of each particle were analyzed using image analysis software ImageJ. The circularity was calculated using the following formula, and the number average of the circularities of the seven particles was calculated as the average circularity. The SEM images obtained for Examples 1 and 2 are shown in Figure 4. The calculated average circularity is shown in Table 1. Circularity = 4π × area / (perimeter) ２

[0091]

[0092] In Table 1, "-" means that the measurement was not performed.

[0093] As shown in Table 1, the amorphous silica particles of Examples 1, 3, and 4 had a high silica purity of 98.4 mass% or more, and their average particle diameters were adjustable over a wide range. These results demonstrate that the method for producing amorphous silica particles according to one embodiment of the present disclosure, which involves a hot water treatment step and a calcination step, makes it possible to produce amorphous silica particles having silica purities comparable to or higher than those of conventional techniques, with adjustable particle diameters.

[0094] A comparison between Example 3 and Example 4 shows that the average particle size of the resulting amorphous silica particles can be made smaller by selecting a reaction mode in which shear force is applied to the substrate in the hot water treatment step, such as a batch process using a stirring mechanism.The above results show that the method for producing amorphous silica particles according to one embodiment of the present disclosure can produce amorphous silica particles having a silica purity equal to or greater than that of the conventional technology and a smaller particle size.

[0095] Example 5: An autoclave (volume 120 L) was used as a container. 2 kg of rice husks and 20 kg of water were filled into the container, and the container was heated without stirring. After the liquid temperature reached 190°C, the temperature was maintained for 30 minutes. During this time, the pressure was 0.9 MPa. The rice husk residue recovered from the container was placed in a net and washed with 20 kg of ion-exchanged water. The net was then pressurized and dehydrated (pressurized dehydration). The weight of the rice husk residue after dehydration was 6.04 kg. The moisture content of the rice husk residue was 77% before dehydration and 76% after dehydration, remaining almost unchanged. The rice husk residue was then thoroughly dried in a dryer maintained at 110°C. The dried residue was calcined in an electric furnace at 850°C for 3 hours to obtain amorphous silica particles of Example 5. The specific surface area of ​​the resulting amorphous silica particles measured by the BET method was 57 m. ２ The oil absorption of the obtained amorphous silica particles, measured in accordance with JIS K5101-13-1, was 123 mL / 100 g. The results of Evaluation Examples 1 and 2 are shown in Table 2.

[0096] Example 6: An autoclave (volume 120 L) was used as a container. 2 kg of rice husks and 20 kg of water were charged into the container, and the container was heated without stirring. After the liquid temperature reached 190°C, the temperature was maintained for 30 minutes. During this time, the pressure was 0.9 MPa. The rice husk residue recovered from the container was placed in a net and washed with 20 kg of ion-exchanged water. The net was then placed in a washing machine and dehydrated by centrifugal force (centrifugal dehydration). The weight of the rice husk residue after dehydration was 2.96 kg. The moisture content of the rice husk residue was 77% before dehydration and 53% after dehydration, indicating a decrease. The rice husk residue was then thoroughly dried in a dryer maintained at 110°C. The dried residue was calcined in an electric furnace at 700°C for 3 hours to obtain amorphous silica particles of Example 6. The resulting amorphous silica particles had a specific surface area of ​​140 m2 measured by the BET method. ２ The oil absorption of the obtained amorphous silica particles, measured in accordance with JIS K5101-13-1, was 137 mL / 100 g. The results of Evaluation Examples 1 and 2 are shown in Table 2.

[0097]

[0098] The difference in moisture content after dehydration between pressurized and centrifugal dehydration is likely due to the fact that the plant-derived substrate is a hard solid containing a large amount of silica. With pressurized dehydration, the shape of the hard substrate remains unchanged even when pressure is applied, making it impossible to remove the moisture between particles. However, centrifugal dehydration removes moisture between particles regardless of the substrate shape or hardness, presumably resulting in a high dehydration effect. The reduction in moisture content due to dehydration is thought to contribute to shorter drying times and reduced energy requirements, potentially enabling the efficient production of plant-derived amorphous silica particles. Furthermore, when the water used for washing is removed from the substrate by evaporation, impurities dissolved in the washing water remain in the substrate. However, removing the washing water by dehydration removes the impurities from the substrate along with the wastewater, potentially resulting in amorphous silica particles of higher purity.

[0099] Furthermore, the specific surface area of ​​the amorphous silica particles obtained in Example 5 differs by approximately 2.5 times from that in Example 6. This result is thought to be due to the difference in calcination temperature. As shown in Table 2, plant-derived amorphous silica contains small amounts of potassium and sulfur, which give it a lower melting point than simple silica. Therefore, even at temperatures of around 600 to 900°C, some of the silica surface melts, causing a change in the specific surface area. Because the degree of melting differs depending on the calcination temperature, it is possible to produce amorphous silica particles with a controlled specific surface area by adjusting the calcination temperature setting.

[0100] The present invention can be used to produce amorphous silica particles.

[0101] 11 Hot water treatment device 12 Calcination device 100 Manufacturing system

Claims

1. A method for producing amorphous silica particles, comprising: a hot water treatment step of treating a plant-derived substrate with hot water; and a calcination step of calcining a residue of the substrate obtained in the hot water treatment step.

2. The method for producing amorphous silica particles according to claim 1, wherein the hot water treatment in the hot water treatment step is carried out in a semi-flow system, a batch system using a stirring mechanism, or a continuous system.

3. The method for producing amorphous silica particles according to claim 1 or 2, wherein the hot water treatment in the hot water treatment step is carried out at a temperature of 120°C or higher and 350°C or lower and a pressure of 0.1 MPa or higher and 20 MPa or lower.

4. In the hot water treatment step, 1N or more 25 x 10 ６ The method for producing amorphous silica particles according to claim 1 or 2, wherein a shear force of N or less is applied to the substrate.

5. The method for producing amorphous silica particles according to claim 1 or 2, wherein the firing in the firing step is carried out at a temperature of 600°C or higher and 1000°C or lower.

6. The method for producing amorphous silica particles according to claim 1 or 2, further comprising, after the hot water treatment step and before the calcination step, a water washing step of washing the residue of the substrate obtained in the hot water treatment step with water.

7. The method for producing amorphous silica particles according to claim 1 or 2, wherein the substrate comprises a grass plant.

8. Amorphous silica particles produced by the method for producing amorphous silica particles according to claim 1 or 2.

9. Amorphous silica particles having a silicon dioxide content of 99.00 mass% or more, based on the mass of oxides in the ash, an average circularity of the particles of 0.85 or less, and an average particle size of 40 μm or less.

10. The specific surface area of ​​the particles is 50 m ２ 10. The amorphous silica particles according to claim 9, wherein the particle has an oil absorption of 100 mL / 100 g or more.

11. A cosmetic product comprising the amorphous silica particles according to claim 9 or 10.

12. A system for producing amorphous silica particles, comprising: a hydrothermal treatment device for hydrothermally treating a plant-derived substrate; and a calcination device for calcining a residue of the substrate obtained in the hydrothermal treatment device.

Images