Method for producing amorphous silica and method for controlling mesopore volume of amorphous silica

Abstract

Provided are amorphous silica having a specific BET specific surface area and a method for producing the same, etc. Amorphous silica that is aggregated particles in which silica of nanoparticles is aggregated, the particle size (D50) of the aggregated particles being 0.5-50 μm, and the BET specific surface area being 300 m2 / g or higher. The amorphous silica can be prepared by carbonizing a pressure molded product of a silica-containing plant, mixing an alkaline solution with the carbide obtained and separating the solids to obtain a silicic acid salt solution, adjusting the solution to a pH of 0.5-2.5 to precipitate the silica, and, after 24 h, washing and drying the silica which has a pH of 0.5-2.5.

Description

[Technical Field]

[0001] This disclosure , non How to make crystalline silica Law and a method for controlling the mesopore volume of amorphous silica. [Background technology]

[0002] Silica is found in bodily fluids such as blood and saliva, as well as hair, nails, bones, and joints. It affects bone formation, collagen production, and immunity, and ingesting silica is expected to prevent osteoporosis. Reflecting this, silica-dissolved beverages and silica-containing supplements are commercially available. Furthermore, silica powder has traditionally been used to prevent cosmetics such as eye shadow and foundation from solidifying due to moisture, or to ensure the stability of creams and emulsions, and is also used as an abrasive ingredient in toothpaste.

[0003] Silica is broadly divided into crystalline silica such as quartz and amorphous silica, but it is amorphous silica that is used in food additives, health foods, and drinking water. One method for producing amorphous silica is to use discarded rice husks as raw materials (Patent Document 1). Gramineae plants are silicon-accumulating plants, and for example, approximately 20% by weight of rice husks is silica. Because some rice husks are incinerated as industrial waste, producing amorphous silica from rice husks can be considered an effective use of biomass. Furthermore, producing amorphous silica from silica sand requires an alkali fusion process at 1200°C, but has the advantage that the silica contained in rice husks can be extracted using alkali. Patent Document 1 describes a method for producing amorphous precipitated silica, or silica gel, by adding acid to the filtrate of a silicate solution obtained by alkaline digestion of rice husk ash, which does not contain unreacted silica or carbon solids, to adjust the solution to pH 8.0-9.0, aging it for 15-30 minutes, and then adding more acid to adjust the solution to pH 3.4-4.2.

[0004] There is also a method for producing a silica-containing food product, characterized by adding and mixing alkaline natural mineral water with rice husk ash obtained by burning at 500 to 800°C, and adjusting the pH to 8.0 to 8.2 (Patent Document 2). In this production method, the combustion temperature is limited in consideration of the fact that part of the silica crystallizes when burned at high temperatures, and the pH is limited to the above range in consideration of the fact that silica does not dissolve sufficiently in alkaline natural mineral water at a pH below 8.0, and that a pH above 8.2 causes severe irritation to mucous membranes, etc.

[0005] There is also a method for producing amorphous silica-containing foods using rice husk charcoal or rice straw charcoal (Patent Document 3). This method involves carbonizing rice husks or rice straw at temperatures between 500°C and 700°C in an oxygen-free atmosphere, then adding the resulting charcoal to ion-exchanged water and heating it to between 30°C and 100°C. The amorphous silica contained in the charcoal is dissolved in the ion-exchanged water and extracted. Carbonization at temperatures between 500°C and 700°C can suppress the production of crystalline silica, a carcinogenic substance. Limiting the temperature of the ion-exchanged water to this range is said to increase the Si concentration as the temperature rises. The resulting amorphous silica has excellent water solubility and is suitable for use in foods such as supplements. This method allows for the safe and inexpensive production of silica-containing foods.

[0006] Furthermore, there is also a method for producing precipitated silica, which comprises the steps of heating the ash of a silica-containing plant body in an alkaline aqueous solution to prepare aqueous alkali silicate solutions S1 and S2, adjusting the pH of the aqueous alkali silicate solution S1 to 8 to 10 to prepare a seed solution, and adding the aqueous alkali silicate solution S2 and a mineral acid dropwise to the seed solution to prepare precipitated silica (Patent Document 4). When the pH of S1 is adjusted to 8 to 10, the primary particle size tends to become smaller, and when S2 and a mineral acid are added dropwise to this, the precipitated silica has excellent dispersibility and a BET specific surface area of ​​100 to 250 m 2 / g of precipitated silica can be obtained.

[0007] The manufacturing methods in the above Patent Documents 1 to 4 are all wet methods using combustion ash, but there is also a dry method for preparing amorphous silica (Non-Patent Document 1). Non-Patent Document 1 discloses fumed silica HDK (registered trademark) manufactured by combustion hydrolysis of silicon tetrachloride. Through combustion hydrolysis, silicon dioxide is vaporized to form spherical primary particles (diameter 10 to 30 nm) in the air, and multiple particles further aggregate and fuse together in a beaded shape to form bulky aggregates with particle diameters of 100 to 400 nm. The BET specific surface area of ​​the obtained amorphous silica is 100 to 400 m. 2 / g, but because the silicon compound is vaporized by combustion hydrolysis, the shape of the primary particles is spherical and has no pores or low porosity. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] Special Publication No. 2003-529518 [Patent Document 2] Japanese Patent Application Laid-Open No. 2011-142826 [Patent Document 3] Japanese Patent Application Laid-Open No. 2014-181144 [Patent Document 4] Japanese Patent Application Publication No. 2019-38728 [Non-patent literature]

[0009] [Non-Patent Document 1] Other products: "Fumed silica", [online], Asahi Kasei Wacker Silicone Corporation website, [searched January 17, 2020], Internet<URL:http: / / www.aws-silicone.com / lineup / others.html> [Non-patent document 2] Tadayuki Akamatsu et al., "Characteristics and Applications of Gel-Method Silica", [online], Tosoh Research and Technical Report Vol. 45 (2001), [Retrieved January 17, 2020], Internet<URL:https: / / www.tosoh.co.jp / technology / assets / 2001_03_07.pdf> Summary of the Invention [Problem to be solved by the invention]

[0010] The above Patent Documents 1 to 4 all have in common that they use biomass such as rice husks as a raw material and prepare amorphous silica by a wet chemical method, but the combustion conditions, neutralization conditions, etc. are different, and the properties of the obtained amorphous silica are also different. For example, the precipitated silica prepared in the examples of Patent Document 1 has a BET surface area of ​​205 to 287 m 2 / g, and bulk density 0.337-0.472 g / cm. However, the BET specific surface area of ​​the precipitated silica obtained in Patent Document 4 is 100-250 m. 2 The BET specific surface area has a large effect on the solubility and dispersibility in an aqueous solution, and the amorphous silicas described in Patent Documents 1 to 4 all have a BET specific surface area of ​​300 m 2 / g, and therefore the dispersibility of the amorphous silica may be insufficient when added to a solution or gel.

[0011] On the other hand, when silica is dispersed in various media, it disperses in the form of aggregates without dispersing into primary particles, so the particle size of the aggregates can be said to be a factor that affects dispersibility. Fumed silica HDK (registered trademark) described in Non-Patent Document 1 is produced by a flame hydrolysis method, and the particle size of the obtained aggregates is small, ranging from 100 to 400 nm.

[0012] Non-Patent Document 2 describes methods for producing amorphous silica by the precipitation method and the gel method. Both methods synthesize silica by the neutralization reaction of sodium silicate with a mineral acid (usually sulfuric acid), and state that the size of the primary particles and the size of the aggregates can be controlled by the reaction temperature, pH, and salt concentration. Figure 2 shows a model diagram of the silica production process, illustrating the relationship between the BET specific surface area, the particle size of the primary particles, the pH during the reaction, and the shape of the aggregates. According to Figure 2, when the particle size of the primary particles grows to 60 nm, the BET specific surface area is 50 m 2 Although there is no mention of the particle size of the agglomerated particles in Figure 2, it is clear that the particle size of the primary silica particles is inversely proportional to the BET specific surface area, and that the BET specific surface area is 300 m 2 It has been shown that the particle size of primary particles of 10 nm or less is 10 nm or less.

[0013] In view of this situation, the present disclosure provides a composition having excellent water solubility and dispersibility. Non The present invention aims to provide a method for producing amorphous silica and a method for controlling the mesopore volume of amorphous silica.

[0014] Another object of the present invention is to provide cosmetics, pharmaceuticals, beverages, foods, supplements, etc., which contain such amorphous silica. [Means for solving the problem]

[0015] The present inventors have developed a nanoparticle-based nanoparticle composite that is composed of aggregated particles, the particle diameter (D50) of which is 0.5 to 50 μm and the BET specific surface area is 300 m 2 / g or more has excellent water solubility and excellent dispersibility when added to cosmetic base materials and other dispersing media, and the present disclosure has been completed based on this discovery.

[0021] Book The disclosure relates to a process for obtaining a silicate solution by mixing an alkaline solution with carbonized grass plant material and separating the solids; of the silicate solution The pH was adjusted to 0.5-2.5 and the precipitate was precipitated. washing and drying the acid-neutralized precipitate; The present invention provides a method for producing amorphous silica, which is an agglomerated particle formed by agglomeration of silica nanoparticles.

[0022] The present disclosure also provides a method for preparing a silicate solution, comprising: The aforementioned Poaceae a step of carbonizing a molded product obtained by pressure molding or extrusion molding the plant to obtain a carbonized product; and a step of mixing an alkaline solution with the carbide obtained in the above step and separating the solids to obtain a silicate solution.

[0024] The present disclosure further provides a method for controlling mesopore volume of amorphous silica, comprising: A step of mixing a carbonized material of a silica-containing plant with an alcohol-containing alkaline solution having an alcohol concentration of 2 to 35 w / w%, and separating the solids to obtain an alcohol-containing silicate solution; and a step of adjusting the pH of the alcohol-containing silicate solution obtained in the step to 0.5 to 2.5 to precipitate silica. The present invention provides a method for controlling the mesopore volume of amorphous silica, which comprises adjusting the mesopore volume of the silica according to the alcohol concentration contained in the alcohol-containing alkaline solution. [Effects of the Invention]

[0029] According to the present disclosure, the present invention provides a composition having excellent water solubility and dispersibility. Non A method for producing crystalline silica and a method for controlling the mesopore volume of amorphous silica can be provided. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 2 is a diagram showing the results of scanning electron microscopy (SEM) of amorphous silica obtained in Experimental Example 1 at hydrochloric acid drop rates of 1 g / min and 3 g / min. [Figure 2] FIG. 2 is a diagram showing the results of scanning electron microscopy (SEM) of amorphous silica obtained in Experimental Example 1 at hydrochloric acid drop rates of 6 g / min, 12 g / min, and 18 g / min. [Figure 3] FIG. 1 shows the results of the BET specific surface area, total pore volume, mesopore volume, micropore volume, particle diameter of aggregated particles (D50), and particle diameter of primary particles of the amorphous silica obtained in Experimental Example 1. [Figure 4] FIG. 2 is a graph showing the results of dropping conditions, dropping time, total amount of hydrochloric acid dropped, end point pH, pH after 24 hours, pH at the time of removal by washing, and seepage during the preparation of amorphous silica obtained in Experimental Example 1. [Figure 5] FIG. 1 is a diagram showing the results of scanning electron microscopy (SEM) of amorphous silica obtained in Experimental Example 4. [Figure 6] FIG. 1 shows the results of the BET specific surface area, total pore volume, mesopore volume, micropore volume, seepage pH, particle size of aggregated particles (D50), loss on drying (%), and bulk density (g / ml) of the amorphous silica obtained in Experimental Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0031] (1) Amorphous silica The first aspect of the present disclosure is an aggregated particle formed by aggregating silica nanoparticles, The particle diameter (D50) of the agglomerated particles is 0.5 to 50 μm, preferably 2 μm to 50 μm, more preferably 5 μm to 50 μm, and the BET specific surface area is 300 m 2 / g or more, preferably 400 to 800m 2 / g, more preferably 400 to 700m 2 / g.

[0032] In the present disclosure, the particle diameter (D50) of aggregate particles refers to the particle diameter (median diameter) corresponding to the median value of the distribution in a particle diameter distribution plotted on the horizontal axis and the number frequency on the vertical axis. For example, the particle diameter can be determined by measuring the particle diameter distribution in the particle diameter range of 0.01 μm to 3,000 μm by a wet method using a laser diffraction / scattering particle size distribution analyzer LA-950 (manufactured by HORIBA Corporation).

[0033] In the amorphous silica of the present disclosure, the size of the nanoparticles constituting the aggregated particles is not limited, but is, for example, 40 nm to 70 nm. The particle diameter of the nanoparticles can be measured, for example, by displaying a scale bar on a scanning electron microscope.

[0034] The amorphous silica of the present disclosure is porous. Pores are generally classified as mesopores, micropores, and macropores. Here, mesopores refer to pores with a pore diameter of 2 nm to 50 nm, micropores refer to pores with a pore diameter smaller than 2 nm, and macropores refer to pores with a pore diameter larger than 50 nm. The amorphous silica of the present disclosure has a micropore volume of 0.1 ml / g or more, preferably 0.1 to 0.4 ml / g, and more preferably 0.1 to 0.3 ml / g. Furthermore, the ratio of the mesopore volume to the micropore volume is 0.1 to 10 times, preferably 0.5 to 8 times. Because the micropore volume is 0.1 ml / g or more, the silica has excellent filtering properties and is expected to have activity as a catalyst, etc. Furthermore, due to the volume ratio of micropores to mesopores, the silica contains a large number of pores with different pore diameters, which results in excellent adsorption, abrasiveness, water solubility, and dispersibility of various substances.

[0035] The mesopore volume of the amorphous silica of the present disclosure is measured by the Barrett-Joyner-Halenda (BJH) method, which can be calculated by measuring a nitrogen adsorption isotherm using, for example, a 3FLEX manufactured by Micromeritics Japan LLC. The BJH method is a widely used method for analyzing pore distribution. When analyzing pore distribution based on the BJH method, first, a desorption isotherm is obtained by adsorbing and desorbing nitrogen as adsorbed molecules to and from a porous carbon material. Based on this desorption isotherm, the thickness of the adsorbed layer when the adsorbed molecules (e.g., nitrogen) are gradually adsorbed and desorbed from the pores filled with the adsorbed molecules and the inner diameter (twice the core radius) of the pores generated at that time are calculated, and the pore radius r is calculated based on the following formula (1): p The pore diameter (2r p ) to the pore volume change rate (dV p / dr p) to obtain a pore size distribution curve (see pages 85 to 88 of the manual for BELSORP-mini and BELSORP analysis software manufactured by BEL Japan Co., Ltd.).

[0036] r p =t+r k (1) V pn =R n dV n -R n ·dt n ·c·ΣA pj (2) However, R n =rp n 2 / (r kn-1 +dt n ) 2 (3)

[0037] where: r p : pore radius r k : pore radius r p The core radius (inner diameter / 2) when an adsorption layer of thickness t is adsorbed on the inner wall of a pore at that pressure. V pn : Pore volume when the nth nitrogen absorption / desorption occurs dV n : Amount of change at that time dt n : The change in thickness tn of the adsorption layer when the nth nitrogen absorption / desorption occurs rk n : Core radius at that time c: fixed value r pn : Pore radius when the nth nitrogen absorption / desorption occurs Also, ΣA pj represents the integrated value of the wall area of ​​the pores from j=1 to j=n-1.

[0038] The micropore volume of the amorphous silica of the present disclosure is measured by the HK method (Horvath-Kawazoe method). The HK method can be calculated by measuring a nitrogen adsorption isotherm using, for example, a 3FLEX (Micromeritics Japan LLC) instrument. The HK method assumes that the pores are slit-shaped, and expresses the adsorption energy in terms of the distance between the slit wall and the adsorbed molecule. This adsorption energy can be expressed thermodynamically from the adsorbed molecular weight, thereby determining the relationship between the distance between the slits, i.e., the pore diameter, and the adsorbed molecular weight. This method is applicable when the distance between the slits, i.e., the pore diameter, is sufficiently small, and is therefore used to analyze the distribution of pores with relatively small diameters of a few nanometers or less. Details of the HK method are also described in Horvath-Kawazoe, J. Chem. Eng. Jpn., 16, 470 (1983).

[0039] The total pore volume of the amorphous silica of the present disclosure is measured using a single-point method. For example, it can be measured using a 3FLEX analyzer manufactured by Micromeritics Japan LLC. If the change in the amount of adsorbed gas relative to the relative pressure (p / p0, p0: saturated vapor pressure) is considered to be the gas adsorption process, it can be assumed that the adsorbed gas exists in a liquid state in most pores when the relative pressure is sufficiently close to 1, i.e., at pressures near the saturated vapor pressure. The single-point method calculates the total pore volume by converting the amount of adsorbed gas into a liquid. Note that the upper limit of the pore size depends on the value of the relative pressure used in the calculation. Therefore, in the case of nitrogen gas adsorption at liquid nitrogen temperature, the relative pressure for pores with a diameter of up to about 30 nm is 0.931, the relative pressure for pores with a diameter of up to about 50 nm is 0.96, the relative pressure for pores with a diameter of up to about 98 nm is 0.98, and the relative pressure for pores with diameters greater than that is 1.00.

[0040] The amorphous silica of the present disclosure may be derived from plants. Gramineae plants are preferred as such silica-containing plants due to their high silica content. Examples of Gramineae plants include rice (rice), barley, wheat, rye, barnyard millet, and foxtail millet, as well as their straw, sugarcane, and bagasse. Because the silica contained in these silica-containing plants is amorphous, it can be extracted with alkali. While some of the rice husks and bagasse are discarded, using them as raw materials allows for effective utilization of biomass. Note that "silica derived from plants" does not mean that the silicon that constitutes the amorphous silica is contained in the plant, but does mean that the amorphous silica is silica extracted directly from the plant.

[0041] Based on the above properties, the amorphous silica of the present disclosure has excellent solubility in water. For example, the solubility of the amorphous silica of the present disclosure in pure water at 25°C is 50 to 300 ppm. Furthermore, when counterions for improving the solubility of amorphous silica were investigated, it was found that it dissolves in aqueous solutions of basic amino acids. In particular, it has excellent solubility in aqueous arginine solutions. It is presumed that the guanidyl group of arginine attacks the siloxane bond, cleaving the polymerization and causing dissolution. As shown in the Examples below, 30 mg of amorphous silica can be dissolved in 100 g of a 0.2% arginine solution. Furthermore, even when this solution was adjusted to a pH of 4 or less by adding citric acid, silica precipitation was suppressed. Arginine is a basic amino acid useful for the body and has been commercialized as a functional food, etc., ensuring safety. Such an arginine solution of amorphous silica can be used directly as silica-containing water or as a raw material for other applications.

[0042] (2)Applications In particular, the amorphous silica of the present disclosure is composed of aggregated particles of nanoparticles, and has a particle diameter (D50) of 0.5 to 50 μm and a BET specific surface area of ​​300 m 2 / g or more. Silica is an oxide that dissociates in water to form OH groups on its surface, which then hydrogen bond with the OH groups in the water to form a slurry. Combined with the particle size (D50) of the aggregated particles being 0.5 to 50 μm and being porous, the amorphous silica of the present disclosure is characterized by excellent water solubility. Therefore, amorphous silica can be dissolved in drinking water to prepare silica-containing drinking water. Furthermore, by utilizing the excellent water solubility of amorphous silica, it can be dissolved in water or gel to prepare pharmaceuticals, cosmetics, quasi-drugs, etc., containing amorphous silica as an active ingredient. As shown in the examples below, amorphous silica was dissolved in an arginine aqueous solution, and silica did not precipitate even when citric acid was added to this solution to make the pH acidic. By taking advantage of the properties of being soluble in water or gel and being stable to pH changes caused by citric acid and the like, amorphous silica can be used in cosmetics such as lotions, milky lotions, hand creams, and moisturizers, as well as in quasi-drugs such as toothpaste, soaps, shampoos, and conditioners, as well as in pharmaceuticals containing amorphous silica, protein adsorbents, dietary fiber adsorbents, heavy metal adsorbents, and the like.

[0043] The amorphous silica of the present disclosure can also be used as a powder. In addition to applications such as pharmaceuticals, cosmetics, and quasi-drugs similar to those described above when dissolved in water or gel, it can also be used in products such as beverages, foods, white rice, bread, mineral water, and supplements containing silica as an active ingredient. The amorphous silica of the present disclosure is highly pure, has no bitter or harsh taste, and is odorless, making it suitable for these applications. It also has excellent solubility after ingestion. It also has an excellent texture when held in the mouth, and is smooth and comfortable to the touch when applied to the skin without any roughness.

[0044] Additionally, in the fields of pharmaceuticals and cosmetics, amorphous silica has traditionally been used to improve the flowability of powders for tableting, as a coating agent, in ointments, and in emulsions. Because of its excellent dispersibility, the amorphous silica disclosed herein can be used in cosmetics such as eye shadow and foundation, formulated as a moisture-proofing agent, thickener, or other purposes, or in pharmaceuticals formulated with other ingredients during tablet processing as a flow improver, disintegrant, or other purposes. It can also be used as a food additive, filter aid, protein adsorbent, dietary fiber adsorbent, heavy metal adsorbent, or other purpose for selectively removing unwanted substances. It can also be used in nanotechnology, optics, electrodes, catalysts, filters, paper, concrete, building materials, tires, rubber, and other applications where conventional amorphous silica is used.

[0045] Furthermore, like conventional amorphous silica, it can be used in agricultural fertilizers, desiccants, humidity conditioners, surface treatment agents, antifoaming agents, etc. The blending amount and method of use can be the same as those of conventionally known methods. In particular, silicon is an essential element for paddy rice, and is used to strengthen paddy rice leaf tissue, increase disease and pest resistance, regulate water metabolism, etc. The amorphous silica of the present disclosure has excellent water solubility and is suitable for blending into agricultural fertilizers.

[0046] (3) Manufacturing method The method for producing the amorphous silica is not limited. However, the amorphous silica can be produced by the second method of the present disclosure, namely, by mixing an alkaline solution with a carbonized silica-containing plant and separating the solids to obtain a silicate solution; a step of adjusting the pH of the silicate solution obtained in the above step to 0.5 to 2.5 to precipitate silica; The method further comprises a step of washing and drying the silica obtained in the above step, which has a pH of 0.5 to 2.5 after 24 hours.

[0047] Silica-containing plants include grasses, and specific examples include the husks of rice, barley, wheat, rye, barnyard millet, and foxtail millet, as well as the straw of these grains, sugarcane, and bagasse.

[0048] As used herein, "carbonized silica-containing plants" refers to carbonized silica-containing plants. Carbonization refers to converting organic substances into carbonaceous substances through heat treatment. Here, "heat treatment" includes pyrolysis, such as gasification, combustion, and incineration, in which silica-containing plants are carbonized by applying heat. The heat treatment is carried out at a temperature of 400 to 800°C, more preferably 500 to 700°C. The heat treatment may be carried out in the presence of oxygen or air, or in an atmosphere of an inert gas such as nitrogen gas or argon gas.

[0049] The silica-containing plant may be crushed, shredded, or pulverized in advance, pressurized into a predetermined shape, and then carbonized. Pressure molding can be performed, for example, using a pelletizer commonly used for molding biomass. It is preferable to add water to the silica-containing plant and pressurize it using a pelletizer. Water-soluble components contained in the silica-containing plant are extracted, allowing the crushed silica-containing plant to adhere to each other during pressure molding. The moisture content during pressure molding is preferably 3 to 30% by mass, and more preferably 5 to 20% by mass. The moisture content can be adjusted to the above range, taking into account the inherent moisture content of the silica-containing plant. There is no limit to the weight of each pressure-molded product, and it is, for example, 0.1 to 0.5 g, more preferably 0.3 to 0.4 g. The conversion of amorphous silica to crystalline silica is suppressed, allowing for efficient production of amorphous silica.

[0050] Alternatively, if silica-containing plants are crushed, shredded, or ground beforehand and then extruded into a desired shape before carbonization, the extrusion process involves heating at 280°C to 310°C to extract water-soluble components from the silica-containing plants, bonding the crushed silica-containing plants together during extrusion. The weight of each extrusion molded product is 700 to 1000 g when extruded into a cylindrical shape with a diameter of 5 cm and a length of 36 to 37 cm, and a cavity diameter of 1.5 cm. This suppresses the conversion of amorphous silica to crystalline silica, allowing for efficient production of amorphous silica. Commercially available extrusion molded products can also be used. For example, products such as "Momigalite" manufactured by Tromso Corporation are available.

[0051] The resulting carbide is mixed with an alkaline solution, and the solid is separated to obtain a silicate solution. The alkaline solution is an aqueous solution containing a Group 1 element such as sodium or potassium. Suitable alkaline solutions include sodium hydroxide, potassium hydroxide, and sodium carbonate. The alkaline solution to be mixed with the carbide may be water such as pure water, or an alcohol-containing alkaline solution to which ethanol or an alcohol such as ethanol has been added. When alcohol is contained, the alcohol concentration is 1 to 40 w / w%, more preferably 2 to 30%, and even more preferably 3 to 20 w / w%.

[0052] Solids separation is the process of separating solids from the silicate solution obtained above, such as crystalline silica contained in the carbide; minerals such as magnesium, manganese, iron, potassium, sodium, aluminum, titanium, and calcium; and unburned carbon. This can be done by filtration, centrifugation, solid-liquid separation, ion exchange, etc. This allows for the production of a silicate solution free of solids. The silicate contained in the silicate solution is generally expressed by the molecular formula X2O·nSiO2·mH2O, where X represents a Group 1 element. The coefficient n indicates the molar ratio of X2O to SiO2, and is typically n = 3.0 to 3.3.

[0053] When an alkaline solution is added to carbide, the silica (silicon dioxide) contained in the carbide reacts with water and alkali to form silicate, which dissolves in the solution. This allows a silicate solution to be obtained. The pH of the obtained silicate solution is 8 or higher, more preferably pH 11 to 14, and even more preferably pH 12 to 14. The silicon dioxide (SiO2) content contained in the carbide is measured in advance, and an alkali is added in an amount of 1 to 4 molar times, more preferably 1.5 to 3 molar times the silicon dioxide content so that the pH of the obtained silicate solution becomes 12 to 14. Note that silicic acid is silicon dioxide added with water, and is expressed as [SiOx(OH) 4-2x]n (x is a number from 1 to 4). When preparing a silicate solution, an alkali solution may be added to the carbide, and then the solution may be heated to a temperature of 30 to 100°C, preferably 60 to 90°C. There are no limitations on the concentration of the alkali used, but in the case of sodium hydroxide, for example, it is 1% by weight or more, preferably 4 to 8% by weight, and more preferably 4 to 6% by weight.

[0054] The silicate solution is then adjusted to a pH of 0.5 to 2.5 to precipitate silica. For example, adding H2SO4 as an acid to the silicate solution causes a reaction in water: X2O·nSiO2 + H2SO4 → nSiO2 + X2O + H2O, resulting in the precipitation of amorphous silica, in which silicon and oxygen molecules are irregularly linked. Silica precipitation depends on the silicon concentration in the silicate solution. In this disclosure, the silicon (Si) concentration in the silicate solution is 0.01 to 10 mol / L, more preferably 0.05 to 5 mol / L. Therefore, prior to adjusting the pH by adding acid, it is preferable to measure the silicon (Si) content in the silicate solution, dilute and concentrate the solution as appropriate, and then adjust the pH to the above range by adding acid. Methods for measuring the silicon (Si) content include ICP emission spectroscopy, hydrogen fluoride analysis, and FT-IR.

[0055] Examples of acids to be added to the silicate solution for adjusting the pH include sulfuric acid, hydrochloric acid, phosphoric acid, acetic acid, nitric acid, and citric acid. There are no particular limitations on the concentration of the acid used, but when sulfuric acid is used, the sulfuric acid concentration is preferably 15 to 60 wt %, when hydrochloric acid is used, 10 to 35 wt %, when phosphoric acid is used, 10 to 40 wt %, when acetic acid is used, 30 to 120 wt %, when nitric acid is used, 15 to 60 wt %, and when citric acid is used, 20 to 80 wt %. In the present disclosure, sulfuric acid or hydrochloric acid is preferably used.

[0056] In the present disclosure, acid is added to adjust the pH of the solution to 0.5 to 2.5, more preferably 1.0 to 2.5, and particularly 1.5 to 2.2. As the pH decreases, primary silica particles are formed, and as the acid is further added, the primary particles aggregate to form aggregated particles. According to the present disclosure, as shown in the examples below, there is a correlation between the micropore volume and the BET specific surface area. By increasing the micropore volume, the particle diameter of the primary particles is grown while the BET specific surface area is increased to 300 m. 2 / g or more. Since the addition of acid causes silica to precipitate and the viscosity to increase, it is preferable to stir the solution to make the pH uniform. The solution may be heated to a temperature of 10 to 30°C, preferably 40 to 60°C.

[0057] In the present disclosure, when adjusting the pH by adding acid, it is preferable to add the acid gradually. Gradually lowering the pH of the silicate solution allows for sufficient neutralization and acidification, resulting in the production of large aggregated particles with nanoparticle diameters of 40 to 70 nm. While it is unclear whether micropores are formed in the primary particles, it has been found that the micropore volume increases when the nanoparticle diameter is 40 to 70 nm. Regarding the acid addition rate, for example, using hydrochloric acid, 35 wt. % hydrochloric acid is added dropwise to a silicate solution with a silicon content of 0.5 to 3 mol / L at a flow rate of 10 g / min or less, preferably 1.0 to 10.0 g / min, and more preferably 1.0 to 8.0 g / min, to precipitate silica. As shown in the Examples below, even when the pH is adjusted to 0.5 to 2.5 by adding acid dropwise and silica is precipitated, the pH fluctuates depending on the acid addition rate when the solution is allowed to stand for 24 hours and then remeasured. When hydrochloric acid was added dropwise at a rate of 10 g / min or less, the pH after 24 hours was in the range of 0.5 to 2.5. However, when the addition rate exceeded 12 g / ml, the pH after 24 hours was greater than 0.5 to 2.5 and was rather alkaline. Furthermore, it was found that the primary particle size and agglomerated particle size varied depending on the acid addition rate, and in particular, the micropore volume and BET specific surface area varied significantly. In other words, the crystalline structure of silica precipitated from the silicate solution changed depending on the acid addition rate. Therefore, in this disclosure, the pH of the solution obtained by adding acid to a silicate solution is 0.5 to 2.5, and the pH of the solution after standing for 24 hours is referred to as the "pH after 24 hours," and this pH is also defined as 0.5 to 2.5. Note that the manufacturing method of this disclosure does not require the solution obtained by adding acid to a silicate solution to stand for 24 hours. If it is possible to confirm in advance that the pH is 0.5 to 2.5 after 24 hours by controlling the acid dropping rate and other factors, leaving it for 24 hours is not necessary. Note that all pH values ​​in this disclosure are measured at a temperature of 25°C.

[0058] For example, when hydrochloric acid with a concentration of 35% by weight is added dropwise at a rate of 10 g / min or less, the primary particles grow to a particle diameter of 40 to 70 nm, and the resulting amorphous silica becomes porous with a micropore volume of 0.1 ml / g or more, as will be shown in the Examples below. Further addition of acid causes the primary particles to aggregate, growing the particle diameter (D50) to 0.5 to 50 μm and the BET specific surface area to 300 m 2 The amorphous silica has a micropore volume of 0.1 ml / g or more, and the ratio of mesopore volume to micropore volume is 0.1 to 10.

[0059] Silica precipitated by adding acid to a silicate solution forms a slurry in the cleaning solution due to hydrogen bonding between the surface OH groups and the OH groups in water. Furthermore, because the precipitated silica is porous, removing the adhering alkali is difficult. Therefore, silica with a "pH after 24 hours" of 0.5 to 2.5 is washed. Pure water or other water may be used as the washing water. The washing water used may also be heated to a temperature of 40 to 60°C. Repeated washing with pure water and filtration is performed until the pH of the cleaning solution reaches 7±1.0. The pH of the entire cleaning solution was measured after the silica precipitated by dripping acid at different rates was washed with water until the pH reached 7±1.0. The pH of the entire cleaning solution varied depending on the acid drip rate. When the drip rate exceeded 12 g / ml, the pH of the entire cleaning solution became alkaline. In this disclosure, the pH of the entire cleaning solution obtained after washing the precipitated silica to pH 7±1.0 is referred to as the "cleaning pH."

[0060] Furthermore, as shown in the examples below, it has been found that when an alcohol-containing alkaline solution with an alcohol concentration of 2 to 35 w / w% is used as the alkaline solution added to the carbonized material, the solubility of metasilicic acid and its polymers can be changed depending on the alcohol concentration, thereby controlling the physical properties of the primary silica particles and their fused secondary particles. It is believed that the fine particles that make up the amorphous silica aggregate with each other depending on the alcohol concentration, enlarging the particle size. As a result, even if the micropore volume remains constant, the mesopore volume decreases. Specifically, by mixing a carbonized silica-containing plant with an alcohol-containing alkaline solution with an alcohol concentration of 2 to 35 w / w%, separating the solids, and then adjusting the pH of the resulting alcohol-containing silicate solution to 0.5 to 2.5 to precipitate silica, the mesopore volume of the silica can be controlled depending on the alcohol concentration in the alcohol-containing alkaline solution. This is believed to be due to the controlled aggregation, which can promote the aggregation of higher-order structures such as secondary particles. According to the present disclosure, it is possible to produce silica powder having a desired mesopore volume by using an alcohol-containing alkaline solution with an alcohol concentration of 2 to 35 w / w % as the alkaline solution.

[0061] There is no limitation on the drying method after washing the precipitated amorphous silica, but for example, heating at a temperature of 100 to 150°C for 12 to 24 hours is sufficient. As a result, the nanoparticles are aggregated into agglomerated particles, and the aggregated particles have a particle diameter (D50) of 0.5 to 50 μm and a BET specific surface area of ​​300 m 2 / g or more. In the present disclosure, the dried amorphous silica may be further pulverized using a mill or ultrasonic waves, and then classified using a sieve mesh or the like.

[0062] According to the above method, even when carbonized silica-containing plants are used as the silica raw material, highly pure amorphous silica can be produced without a separate step of removing alkaline earth metals, heavy metals, etc., which are contained in trace amounts in the carbonized product. [Example]

[0063] The present disclosure will be described in more detail below with reference to examples, although the present disclosure is not limited thereto.

[0064] (Experimental Example 1) Using a grind mill (manufactured by Tromso Co., Ltd.), the ground rice husks were extruded into a cylindrical shape with a diameter of 54 cm, an inner diameter of 1.8 cm, and a length of 36 cm to 37 cm to obtain a molded product. The molded product was heated in a self-combustion mode at 700 to 800°C for 1 hour to obtain a carbonized product.

[0065] After coarsely crushing the carbide to a size of approximately 2 mm, a 10 wt.% aqueous solution of sodium hydroxide was added until the amount was three times the molar amount of silicon contained in the silicon dioxide. The mixture was then immersed at 90°C for 14 hours, and the ash was filtered off to obtain a sodium silicate solution. The pH of the sodium silicate in this solution was 13.5. The resulting sodium silicate solution was diluted to 1000 ml with pure water, and 35 wt.% hydrochloric acid was added dropwise at different concentrations to adjust the pH to 2, resulting in silica precipitation. The hydrochloric acid addition rates were 1 g / min, 3 g / min, 6 g / min, 12 g / min, and 18 g / min, respectively. Because neutralization occurs in a solid-liquid system, the final pH was confirmed to be 0.5 to 2.5 after further stirring for 1 hour.

[0066] The pH of this solution was measured after leaving it for 24 hours (pH after 24 hours). The pH of the solution when the hydrochloric acid drop rate was 1 g / min, 3 g / min, 6 g / min, 12 g / min, and 18 g / min was 2.11, 2.11, 2.13, 9.88, and 9.96, respectively.

[0067] The addition of purified water to each precipitated silica and filtration were repeated until the pH of the washing solution reached 7±1.0. The pH of all washing solutions after washing was measured. The pH values ​​(washing pH) of solutions with hydrochloric acid drop rates of 1 g / min, 3 g / min, 6 g / min, 12 g / min, and 18 g / min were 6.8, 6.01, 5.98, 8.99, and 9.05, respectively. The pH values ​​of the solutions leached from the washed crystals were measured according to JIS K1474 (2014) Activated Carbon Test Method, Section 7.11. The pH values ​​of solutions with hydrochloric acid drop rates of 1 g / min, 3 g / min, 6 g / min, 12 g / min, and 18 g / min were 7.03, 6.44, 6.12, 10.34, and 10.47, respectively. This pH is referred to as the "leaching pH."

[0068] After washing, the mixture was dried at 110°C for 12 hours or more, crushed in a crush mixer, and classified using a sieve with 106 μm openings.

[0069] The results of scanning electron microscopy (SEM) of the obtained amorphous silica are shown in Figures 1 and 2. In Figure 1, GF19020 is an example in which the hydrochloric acid dropping rate was varied in the range of 1 to 6 g / min until the final pH reached 0.5 to 2.5.

[0070] The physical properties of the amorphous silica obtained above were evaluated. The BET specific surface area, total pore volume, mesopore volume, and micropore volume were measured using a 3FLEX (Micromeritics Japan, LLC). The aggregate particle size (D50) was measured using a laser diffraction / scattering particle size distribution analyzer, and the primary particle size was measured using a scanning electron microscope (SEM). The mesopore volume of the amorphous silica was measured using 30 mg of amorphous silica by the BJH method using a 3FLEX (Micromeritics Japan, LLC) set to a relative pressure (P / P) range of 0.0000001 to 0.995. The results are shown in Figure 3.

[0071] In addition, for the production of amorphous silica obtained by dropping hydrochloric acid at a dropping rate of 1 to 18 g / min, the results of the dropping conditions, end point pH, dropping time, total amount of hydrochloric acid dropped, pH after 24 hours, pH at the time of removal by washing, and pH at the time of seepage are shown in Figure 4.

[0072] As shown in Figure 3, when hydrochloric acid is added dropwise to a sodium silicate solution at a rate of 1 to 6 g / min to neutralize it, the particle diameter (D50) of the agglomerated particles becomes 0.5 to 50 μm and the BET specific surface area becomes 300 m 2 It was found that amorphous silica having a mesopore volume of 0.1 ml / g or more, a micropore volume of 0.1 ml / g or more, and a mesopore volume to micropore volume ratio of 0.1 to 10 times could be obtained.

[0073] (Experimental Example 2) 300 mg of amorphous silica prepared in Experimental Example 1 was added to 1000 g of 0.2% arginine aqueous solution, stirred at room temperature for 1 to 3 days, and then heated to a temperature of 50 to 80°C for 2 hours to dissolve the silica (30 mg / 100 g). The pH of this solution was 10.5. Citric acid was added to this solution to adjust the pH to 3.8. As a result, silica did not precipitate in the aqueous solution, and the silica was stably dissolved in the aqueous solution.

[0074] (Experimental Example 3) A solution of 154 g of sodium hydroxide dissolved in 2 L of water was heated to 50°C. 200 g of crushed rice husk ash (rice husks from Toyama burned on farms) was added to the solution to prepare a suspension. This was heated and stirred at 70°C or higher for 3 hours. After the solution was cooled to room temperature, the black adhesive was removed using a nonwoven fabric. The liquid that passed through the nonwoven fabric was filtered using a 1 μm filter paper to obtain a light brown filtrate. This solution was made up to 2 L with water to prepare a sodium silicate solution.

[0075] To 1 L of this sodium silicate solution, 35 wt % hydrochloric acid was added dropwise at a rate of 1 g / min to neutralize the solution to a pH of 0.5 to 2, thereby precipitating silica. After leaving the solution to stand for 24 hours, the pH (pH after 24 hours) was measured, and the pH of the reaction solution after 24 hours was found to be 2.11.

[0076] The addition of purified water to each precipitated silica and filtration were repeated until the pH of the washing solution reached 7±1.0. The neutralized silica suspension was filtered through a 1 μm filter paper, and the precipitate on the filter paper was washed with purified water. The mixture was then dried at 100°C for 24 hours to obtain approximately 70 g of amorphous silica.

[0077] The amorphous silica obtained above was subjected to measurements of the BET specific surface area, total pore volume, mesopore volume, micropore volume, aggregate particle diameter (D50), and primary particle diameter in the same manner as in Experimental Example 1. The BET specific surface area was 590 m 2 / g, total pore volume was 0.41 ml / g, mesopore volume was 0.20 ml / g, micropore volume was 0.24 ml / g, agglomerated particle diameter (D50 was 14 μm), and primary particle diameter was 68 nm.

[0078] Compared with Experimental Example 1, it was found that even though the manufacturing method of sodium silicate was different, by controlling the dropping rate of hydrochloric acid, amorphous silica with similar BET specific surface area, total pore volume, mesopore volume, micropore volume, aggregate particle diameter (D50 is 14 μm), and primary particle diameter could be obtained.

[0079] (Experimental Example 4) A sodium silicate solution with a pH of 13.5 was obtained using a method similar to that used in Example 1. This solution was filtered through a 0.45 μm thread-wound filter, and 0 mL, 50 mL, 80 mL, or 100 mL of ethanol was added to the resulting sodium silicate solution to adjust the total volume to 1000 mL, yielding sodium silicate solutions with ethanol contents of 0 wt / w%, 5 wt / w%, 8 wt / w%, or 10 wt / w%. While stirring at 200 rpm, 6 mol / L sulfuric acid was added dropwise at a rate of 1 g / min to adjust the pH of the solution to 0.5 to 2.5, thereby precipitating amorphous silica. Next, the pH of the wash water from the sodium silicate solutions with ethanol contents of 0 wt / w%, 5 wt / w%, 8 wt / w%, or 10 wt / w% was measured after 24 hours and at the time of leaching, using the same procedure as in Experimental Example 1. After 24 hours, the pH was 2.38, 2.48, 2.48, and 2.49, respectively, and the seepage pH was 7.76, 7.68, 7.75, and 7.57, respectively.

[0080] The precipitated amorphous silica was dehydrated by suction filtration using No. 2 filter paper to form a cake. Water was added to the cake, and suction filtration was repeated until the washings reached approximately pH 6. The cake was then dried in a dryer at 100°C for 20 hours, crushed in a crush mixer, and classified using a 420 μm mesh sieve. The results of scanning electron microscopy (SEM) of the obtained amorphous silica are shown in Figure 5. For each alcohol concentration, the upper row shows the results of 25kΩ filtration, and the lower row shows the results of 100kΩ filtration.

[0081] The physical properties of the amorphous silica obtained above were evaluated in the same manner as in Experimental Example 1. The results are shown in Figure 6. When sulfuric acid was added dropwise at a rate of 1 to 6 g / min to a sodium silicate solution containing 0 w / w%, 5 w / w%, 8 w / w%, or 10 w / w% ethanol to neutralize the solution, the particle diameter (D50) of the aggregated particles was 0.5 to 50 μm and the BET specific surface area was 300 m. 2 / g or more, the micropore volume was 0.1 ml / g or more, and the mesopore volume was 0.39 ml / g at an ethanol concentration of 0%, 0.83 ml / g at 5 w / w%, 0.15 ml / g at 8 w / w%, and 0.06 ml / g at 10 w / w%, demonstrating that amorphous silica with different mesopore volumes can be obtained depending on the ethanol concentration.

[0082] As shown in Figure 5, the shape of the primary particles changes depending on the ethanol concentration in the sodium silicate solution, and the particles become spherical depending on the alcohol concentration. It is presumed that this sphericalization of the primary particles causes the change in mesopore volume.

[0083] The present disclosure allows various embodiments and modifications without departing from the broad spirit and scope of the present disclosure. Furthermore, the above-described embodiments and examples are intended to illustrate the present disclosure and do not limit the scope of the present disclosure. That is, the scope of the present disclosure is defined by the claims, not the embodiments and examples. Various modifications made within the scope of the claims and within the meaning of the disclosure equivalent thereto are considered to be within the scope of the present disclosure.

[0084] This application is based on Japanese Patent Application No. 2020-068471, filed on April 6, 2020. The entire specification, claims, and drawings of Japanese Patent Application No. 2020-068471 are incorporated herein by reference.

Claims

1. a step of mixing an alkaline solution with a carbonized grass plant and separating the solids to obtain a silicate solution; and a step of adjusting the pH of the silicate solution to 0.5 to 2.5 to precipitate an acid-neutralized precipitate, and washing and drying the precipitate. A method for producing amorphous silica, which is an agglomerated particle formed by the aggregation of nanoparticle silica.

2. obtaining the silicate solution, a step of carbonizing a molded product obtained by pressure molding or extrusion molding the grass family plant to obtain a carbonized product; 2. The method for producing amorphous silica according to claim 1, further comprising the steps of: mixing an alkaline solution with the carbide obtained in the above step; and separating the solids to obtain a silicate solution.

3. 1. A method for controlling mesopore volume of amorphous silica, comprising: a step of mixing a carbonized material of a silica-containing plant with an alcohol-containing alkaline solution having an alcohol concentration of 2 to 35 wt % and separating the solids to obtain an alcohol-containing silicate solution; and a step of adjusting the pH of the alcohol-containing silicate solution obtained in the step to 0.5 to 2.5 to precipitate silica. A method for controlling the mesopore volume of amorphous silica, comprising adjusting the mesopore volume of the silica in accordance with the alcohol concentration contained in the alcohol-containing alkaline solution.

Images