Porous spherical silica, catalyst carrier, cosmetics, analytical column, abrasive, resin composition, and method for producing porous spherical silica

Abstract

To provide: porous spherical silica which is reduced in the content of alkali metal, has high particle hardness, is reduced in the number of fragmentary particles, and has independent spherical shapes; and a method for producing the porous spherical silica.SOLUTION: With respect to the porous spherical silica, the volume-based cumulative 50% diameter (D50) is from 2 μm to 200 μm inclusive; the ratio (D10 / D90) of a cumulative 10% diameter (D10) to a cumulative 90% diameter (D90) is 0.3 or more; the pore volume is from 0.5 ml / g to 8 ml / g inclusive; the most frequent pore radius is from 5 nm to 50 nm inclusive; the specific surface area is from 50 m2 / g to 400 m2 / g inclusive; the arithmetic mean value of "test forces obtained when the fracture of a specimen is observed" determined in accordance with the method prescribed in JIS Z8844 is from 1.0×101 mN to 2.0×101 mN inclusive; the number of particles having circularity of 0.7 or less is 20 or less; and the content of alkali metal is 50 ppm or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to novel porous spherical silica, catalyst supports, cosmetics, analytical columns, abrasives, resin compositions, and methods for producing porous spherical silica. [Background technology]

[0002] Porous silica has been extensively studied, and porous silica with a variety of physical properties has been proposed. Porous silica can be produced, for example, by adding a mineral acid to an aqueous alkali metal silicate solution to neutralize it, followed by separation and recovery of the resulting particles (Patent Document 1), spray-drying a fumed silica dispersion (Patent Document 2), or gelling a fumed silica dispersion in liquid (Patent Document 3). Porous silica produced by these methods has distinctive pore volumes and pore diameters, making it promising for use as a catalyst support or analytical column packing. Furthermore, when used as an abrasive in industrial products, resin penetration into the pores facilitates fixation to the resin on the polishing pad. Using spherical silica for these applications offers the advantage of easily adjusting particle size and improving packing density. Additionally, porous spherical silica possesses a smooth texture due to its shape, making it useful as a cosmetic additive. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2004 / 101139 Pamphlet [Patent Document 2] International Publication No. 2019 / 131873 Brochure [Patent Document 3] International Publication No. 2022 / 154014 Brochure [Non-patent literature]

[0004] [Non-Patent Document 1] "Sintering of Fine Ceramics", Journal of the Society of Powder Technology, Vol. 25, No. 12, (1988), pp. 805-811 Summary of the Invention [Problem to be solved by the invention]

[0005] However, due to its porous structure, porous silica has a tendency to easily disintegrate, posing durability issues when used as a catalyst support for long periods of time or as a packing material for analytical columns used in fluids. Furthermore, when used as an abrasive in industrial products, the process of kneading with resin can cause distortion of particle shape or particle breakage, resulting in poor handling. While calcination is generally used as a method for increasing the hardness of inorganic materials (Non-Patent Document 1), the porous silica described in Patent Document 1, which uses sodium silicate as a raw material, has pores that are blocked by high-temperature calcination due to a melting point drop caused by the sodium contained in the raw material, making it impossible to maintain its porous structure.

[0006] The porous silica described in Patent Document 2, which is obtained by spray-drying a fumed silica dispersion, has low compressive strength after calcination, making it impossible to obtain silica with high hardness. The porous silica described in Patent Document 3, which is obtained by gelling a fumed silica dispersion in liquid, causes particles to aggregate upon calcination, necessitating a crushing process. This process generates fine, fragmented powder, which reduces the overall circularity of the particles. The inclusion of this fine powder can cause column blockage when the porous spherical silica is used as a packing material for an analytical column, and also deteriorates the texture when the porous spherical silica is used as a cosmetic additive.

[0007] Therefore, an object of the present invention is to provide porous spherical silica particles having a reduced alkali metal content, high particle hardness, and a reduced number of fragmented particles, and to provide a method for producing the same. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that, in the process of producing porous spherical silica, by gelling a fumed silica dispersion in a liquid to obtain a gel, spray-drying the gel and then calcining the gel, it is possible to produce porous spherical silica having a reduced alkali metal content, high particle hardness, and a reduced number of fragmented particles, which has a closed sphere shape, and which has led to the completion of the present invention.

[0009] [1] The cumulative 50% diameter (D50) of the volume basis measured by the Coulter counter method is in the range of 2 μm to 200 μm, Similarly, the ratio (D10 / D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is 0.3 or more, The pore volume measured by the BJH method is 0.5 ml / g or more and 8 ml / g or less, The most frequent value of the pore radius according to the BJH method is 5 nm or more and 50 nm or less, The specific surface area by BET method is 50m 2 / g or more, 400m 2 / g or less, According to the method specified in JIS Z8844, the arithmetic mean value of the "test force at which the specimen breaks" for 10 particles, calculated at a loading rate of 0.4462 mN / sec, is 1.0 x 10 1 mN or more 2.0×10 1 mN or less, Of 200 particles observed in an SEM image, 20 or fewer particles have a circularity of 0.7 or less, Porous spherical silica characterized by having an alkali metal content of 50 ppm or less.

[0010] [2] A catalyst carrier comprising the porous spherical silica described in [1]. [3] A cosmetic product containing the porous spherical silica described in [1]. [4] An analytical column comprising the porous spherical silica according to [1].

[0011] [5] An abrasive containing the porous spherical silica described in [1]. [6] A resin composition containing the porous spherical silica described in [1].

[0012] [7] A step of preparing a W / O emulsion comprising an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent; a step of heating the emulsion to gel the aqueous phase and obtain a gelled dispersion; A step of recovering the resulting gelled body from the liquid and spray-drying it; and and calcining the obtained porous spherical silica at a temperature of 900 to 1500°C for 10 to 25 hours. [8] The method for producing porous spherical silica according to [7], characterized in that the spraying method for spray drying is a two-fluid nozzle method. [Effects of the Invention]

[0013] The porous spherical silica of the present invention has a high pore volume and high hardness, as indicated by the high "test force at which sample destruction is observed." Therefore, even when used for a long period of time or in a fluid, the porous structure can be maintained without particle collapse or pore blockage. Therefore, the use of the porous spherical silica of the present invention can improve the durability required for catalyst supports, adsorbents for carbon dioxide, etc., and analytical column packings. Furthermore, when used as an abrasive in industrial products, etc., the particle strength is strong enough to withstand mixing with resins, improving handleability during the manufacturing process.

[0014] In addition, as indicated by the high D10 / D90, the particle size distribution is narrow, so when used as a packing material for an analytical column, clogging due to fine particles entering the gaps between particles is unlikely to occur.

[0015] Furthermore, out of 200 particles observed in the SEM image, there were 20 or fewer particles with a circularity of 0.7 or less, reducing the number of fragmented particles. Because the particles are independent spheres, their use as a cosmetic additive can impart a smooth feel to the skin. Furthermore, the purity is high, with an alkali metal content of 50 ppm or less, making it extremely useful as a polishing agent for semiconductors and other materials that must be free from alkali metals.

[0016] In the production method of the present invention, the raw material is spray-dried and then calcined, thereby suppressing particle aggregation and enabling production without a crushing step. This makes it possible to suppress the generation of fragmented particles that would occur if a crushing step were carried out, and to produce porous spherical silica having the above characteristics without generating fine powder or reducing the circularity of the particles as a whole.

[0017] Furthermore, the manufacturing method of the present invention improves the bond strength between primary particles by firing under specific conditions, thereby making it possible to obtain porous spherical silica with high particle hardness. DETAILED DESCRIPTION OF THE INVENTION

[0018] The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0019] <Porous spherical silica> The porous spherical silica of the present invention has a volume-based cumulative 50% diameter (D50) in the particle size distribution measured by the Coulter counter method in the range of 2 μm to 200 μm, and the ratio of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) (D10 / D90) is 0.3 or greater. When the porous spherical silica is in the above range, when used as a packing material for an analytical column, the column is less likely to clog and is easier to pack. D50 is preferably 2 μm to 100 μm, particularly preferably 5 μm to 50 μm, and even more preferably 5 μm to 20 μm. Furthermore, D10 / D90 is preferably 0.4 or greater, and even more preferably 0.5 or greater. D10 / D90 cannot exceed 1.0 and is generally 0.6 or less.

[0020] The porous spherical silica of the present invention has a pore volume of 0.5 ml / g or more and 8 ml / g or less, as measured by the BJH method described below. It is difficult to obtain a pore volume greater than 8 ml / g. A pore volume of 6 ml / g or less is easier to produce, 4 ml / g or less is even easier to produce, and 2.5 ml / g or less is particularly easy to produce. In particular, when the porous spherical silica of the present invention is used as a catalyst support or an adsorbent for carbon dioxide or the like, in order to achieve a high loading or adsorption capacity, the pore volume is preferably 0.6 ml / g or more, more preferably 0.7 ml / g or more, and even more preferably 1.0 ml / g or more.

[0021] The mode of the pore radius measured by the BJH method is 5 nm or more, preferably 10 nm or more, and more preferably 15 nm or more, and the upper limit is 50 nm or less, and preferably 30 nm or less.

[0022] The pore volume and pore radius measured by the BJH method were obtained by drying the sample to be measured at 200°C for 3 hours or more under a vacuum of 1 kPa or less, obtaining an adsorption isotherm only for the nitrogen adsorption side at liquid nitrogen temperature, and analyzing the resulting isotherm by the BJH method (Barrett, EP; Joyner, LG; Halenda, PP, J. Am. Chem. Soc. 73, 373 (1951)). The "mode of pore radius measured by the BJH method" refers to the pore radius value at the maximum value on a pore distribution curve (volume distribution curve) obtained by analysis by the BJH method, which is plotted with the differential of the cumulative pore volume with respect to the logarithm of the pore radius on the vertical axis and the pore radius on the horizontal axis.

[0023] The porous spherical silica of the present invention has a specific surface area of ​​50 m2 by the BET method. 2 / g or more, 400m 2 / g or less. The specific surface area is preferably 100 m 2 / g or more, and 120m 2 / g or more, 350m 2It is particularly preferable that the specific surface area of ​​the porous spherical silica is in the range of 400 m / g or less. The higher the specific surface area of ​​the fumed silica used as the raw material, the higher the specific surface area of ​​the porous spherical silica. Also, the higher the specific surface area of ​​the fumed silica, the more likely it is to gel and the easier it is to mold it into a spherical shape. Generally, the specific surface area of ​​fumed silica is 400 m / g or less. 2 / g or less, so the specific surface area is 400m 2 It is difficult to obtain porous spherical silica having a specific surface area exceeding 1 / g. The specific surface area is a value measured by the nitrogen adsorption BET multipoint method.

[0024] The porous spherical silica of the present invention has an arithmetic mean value of the "test force at which specimen breakage was observed" (hereinafter referred to as "test force at breakage") of 1.0 × 10 for 10 particles, determined at a loading rate of 0.4462 mN / sec according to the method specified in JIS Z8844:2019. 1 ~2.0×10 1 The test force at break is 2.0×10 1 If the particle size exceeds 1.0×10 mN, it becomes difficult to obtain porous spherical silica having a pore volume of 0.5 ml / g or more. 1 ~1.8×10 1 If the test force at the time of breaking is within the above range, the particles will have high hardness and will be porous spherical silica with the desired durability.

[0025] The porous spherical silica of the present invention has an alkali metal content of 50 ppm or less (by mass), preferably 40 ppm or less, and more preferably 30 ppm or less.

[0026] The porous spherical silica of the present invention has a spherical shape. Here, "spherical" means that the average circularity determined by image analysis using a scanning electron microscope (SEM) is 0.8 or more. The "average circularity determined by image analysis" is the arithmetic mean value of the circularity obtained by image analysis of SEM images of 2000 or more porous spherical silica particles observed at 1000x magnification with an SEM. Here, "circularity" is a value determined by the following formula (1):

[0027] C=4πS / L 2 (1) In the above formula (1), C represents the circularity, S represents the area (projected area) occupied by the porous spherical silica in the image, and L represents the length (perimeter) of the outer periphery of the porous spherical silica in the image. The average circularity is particularly preferably 0.85 or more.

[0028] In the porous spherical silica of the present invention, the number of shard particles out of 200 particles observed in an SEM image is 20 or less. Here, shard particles refer to particles having a circularity of 0.7 or less as calculated according to the above definition. The number of shard particles is preferably 15 or less, and more preferably 10 or less.

[0029] The porous spherical silica of the present invention may be either hydrophilic or hydrophobic. The porous spherical silica of the present invention produced by the production method described below is hydrophilic. Hydrophobic silica can be obtained by appropriately applying a silica surface treatment method after obtaining hydrophilic porous spherical silica by the production method. Here, "hydrophilic" means that it can be dispersed in water that does not contain an organic solvent.

[0030] Because the porous spherical silica of the present invention has the above-mentioned properties, it can be used as a carrier for catalysts and fragrances, an adsorbent for carbon dioxide and the like, a filler for analytical columns, an additive for cosmetics, an abrasive for industrial products and the like, and an additive for various resin compositions.

[0031] <Method for producing porous spherical silica> The method for producing the porous spherical silica of the present invention is not particularly limited, but the high pore volume and the most frequent pore radius can be easily achieved by using a fumed silica dispersion as a raw material. Generally, fumed silica has a structure in which fine silica particles (primary particles) are aggregated. Therefore, by using a fumed silica dispersion as a raw material for porous spherical silica and gelling the fumed silica in the dispersion to form a network, the decrease in pore volume due to drying shrinkage can be suppressed, and porous spherical silica with a high pore volume can be obtained.

[0032] More specifically, a W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent is prepared (W / O emulsion preparation step), the emulsion is then heated to gel the aqueous phase to obtain a porous spherical silica dispersion (gelation step), and the resulting porous spherical silica is recovered from the liquid (gel recovery step), spray-dried (drying step), and calcined (calcination step) to produce porous spherical silica. Each step is described in detail below.

[0033] (W / O emulsion preparation process) A particularly preferred method for preparing a W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent is to first prepare a dispersion in which fumed silica is dispersed in an aqueous phase (dispersion preparation step), and then prepare an emulsion using this and an organic solvent according to a standard method (emulsification step). These methods are further described below.

[0034] (Dispersion liquid preparation process) The dispersion preparation step is a step of dispersing fumed silica in water to prepare a dispersion.

[0035] The fumed silica used is water-dispersible and can be gelled by heating, adjusting the pH, etc. These properties are achieved by having a large number of silanol groups on the silica surface, so almost any fumed silica that has not undergone surface treatment can be used. Furthermore, due to the ease with which gelling can proceed, the specific surface area of ​​the fumed silica is set to 100 m. 2 / g or more, especially 200m 2 It is preferable to use a material with a molecular weight of 250m / g or more. 2 / g or more is more preferable. The larger the specific surface area, the faster the gelation proceeds, and the easier it is to gel the droplets (W phase) in which the fumed silica is dispersed. From the viewpoint of availability, the upper limit is 400 m 2 It is preferable to use one having a specific surface area of ​​1 / g. The specific surface area is a value measured by the nitrogen adsorption BET multipoint method.

[0036] Furthermore, the specific surface area of ​​the porous spherical silica obtained by the method described here increases as the specific surface area of ​​the fumed silica used as raw material increases.Therefore, by appropriately selecting the fumed silica used as raw material according to the specific surface area of ​​the target porous spherical silica, the specific surface area of ​​the porous spherical silica can be arbitrarily controlled without changing the production conditions.In addition, the fumed silica used in the present invention can also be used by mixing fumed silicas with different specific surface areas.

[0037] The above-mentioned fumed silica is commercially available, and for example, various hydrophilic grades of Reolosil from Tokuyama Corporation, various hydrophilic grades of Aerosil from Nippon Aerosil Co., Ltd., and various hydrophilic grades of dry silica HDK from Asahi Kasei Wacker Silicone Co., Ltd. can be used.

[0038] Furthermore, since fumed silica is generally highly pure and contains almost no impurities such as alkali metals, the alkali metal content of the produced porous spherical silica can be made extremely low.

[0039] Although water is essential as the solvent in this step, other solvents may be included as long as they do not inhibit emulsion formation or subsequent gelation. In addition, when a latent base is used to promote gelation (described later), it is advisable to dissolve the base in water before dispersing the fumed silica.

[0040] A preferred method for dispersing fumed silica in a solvent is to prepare a dispersion by preliminarily dispersing fumed silica in a solvent, and then finely disperse the resulting mixture using a crusher or the like. Specific examples of crushers that can be used for finely dispersing include a ball mill, a bead mill, a vibration mill, a pin mill, an atomizer, a colloid mill, a homogenizer, a high-pressure homogenizer, and an ultrasonic homogenizer. Regarding the degree of dispersion after fine dispersion, it is preferred that the D90 value be 0.5 μm or less when the particle size distribution of the dispersion is measured by a laser diffraction scattering method.

[0041] The silica concentration in the fumed silica dispersion is preferably in the range of 10% by mass to 30% by mass. It is more preferably 15% by mass or more, and particularly preferably 20% by mass or more. The higher the silica concentration in the fumed silica dispersion, the faster the gelation proceeds. However, if the silica concentration is too high, the fluidity is lost, making it difficult to obtain a fumed silica dispersion.

[0042] The gelation of the fumed silica dispersion is accelerated by heating. If the gelation of the fumed silica dispersion progresses during the dispersion preparation process, it becomes difficult for the W phase to become spherical in the subsequent emulsification process, and in extreme cases, it becomes difficult to even form the emulsion. Therefore, it is preferable to keep the liquid temperature of the fumed silica dispersion at about room temperature (20°C) or below during the dispersion preparation process. In cases where the specific surface area or concentration of the fumed silica is high and gelation is likely to progress, it is also effective to cool it to a temperature lower than room temperature (preferably 15°C or below, more preferably 12°C or below).

[0043] (Emulsification process) The W / O emulsion preparation step is a step of dispersing the fumed silica dispersion obtained in the dispersion preparation step in a non-aqueous solvent to form a W / O emulsion. By forming such a W / O emulsion, the fumed silica dispersion, which is a dispersoid, becomes spherical due to surface tension, etc., and by gelling the fumed silica dispersion dispersed in the non-aqueous solvent in this spherical shape, a spherical gel can be obtained.

[0044] The non-aqueous solvent used in this production method may be any solvent that is hydrophobic enough to form an emulsion with the fumed silica dispersion. Examples of such solvents include organic solvents such as hydrocarbons and halogenated hydrocarbons. More specifically, non-aqueous solvents such as hexane, heptane, octane, nonane, decane, liquid paraffin, dichloromethane, chloroform, carbon tetrachloride, and dichloropropane are examples. Among these, hexane, heptane, and decane, which have appropriate viscosities, are preferred. If necessary, multiple solvents may be mixed and used. Furthermore, hydrophilic solvents such as lower alcohols may also be used in combination (as a mixed solvent) as long as they can form an emulsion with the fumed silica dispersion.

[0045] The amount of the non-water-soluble solvent used is not particularly limited as long as it is within a range that allows the formation of a W / O emulsion, but generally, the amount used is about 1 to 10 parts by volume of the non-water-soluble solvent per 1 part by volume of the fumed silica dispersion.

[0046] In this production method, it is preferable to add a surfactant when forming the W / O emulsion. Known surfactants used in W / O emulsion formation can be used without limitation, including anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred because they facilitate W / O emulsion formation and are less likely to be contaminated with alkali metals. In particular, surfactants with an HLB value of 3 to 5, which indicates the degree of hydrophilicity and hydrophobicity of a surfactant, are preferably used. Here, "HLB value" refers to the HLB value determined by the Griffin method. Specific examples of surfactants that can be preferably used include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate.

[0047] The amount of surfactant used is the same as that generally used to form a W / O emulsion, and specifically, a range of 0.05 g to 10 g per 100 ml of fumed silica dispersion can be suitably used.

[0048] When forming a W / O emulsion, known methods for forming W / O emulsions can be used to disperse the fumed silica dispersion in a non-aqueous solvent. From the perspective of ease of industrial production, mechanical emulsification is preferred, specifically, methods using a mixer, homogenizer, etc. are exemplified. A homogenizer is preferably used. This emulsification process produces an emulsion with a sharp particle size distribution of the aqueous phase droplets, thereby resulting in a sharp particle size distribution of the final spherical porous silica. To obtain particles of preferably 1 μm or more but less than 100 μm, and more preferably 8 μm or more but less than 90 μm, the homogenizer rotation speed is preferably 1,000 rpm or more but 15,000 rpm or less, more preferably 2,000 rpm or more but 12,000 rpm or less, and even more preferably 4,000 rpm or more but 9,000 rpm or less. The stirring time is preferably 30 seconds or more but 1 hour or less, more preferably 1 minute or more but 30 minutes or less.

[0049] (Gelling process) The gelation step is a step following the W / O emulsion preparation step in which the fumed silica dispersion is gelled while droplets of the fumed silica dispersion are dispersed in a non-aqueous solvent. The gelation can be carried out by a known method. For example, the gelation can be easily promoted by heating to a high temperature or by adjusting the pH of the fumed silica dispersion to a weakly acidic or basic state. These methods are preferred because they allow the reaction to be controlled independently. The pH of the fumed silica dispersion prepared by the above-described method and without pH adjustment is generally in the range of 3.0 to 4.5.

[0050] When heating is performed, the temperature should not exceed the boiling point of each solvent used, and the lower limit of the gelling temperature is preferably 50° C., more preferably 60° C. The upper limit is preferably 100° C. or lower, more preferably 90° C. or lower.

[0051] The pH adjustment can be easily carried out by a method in which a substance that exhibits basicity when thermally decomposed by heating, such as urea, is mixed with the fumed silica dispersion in advance, and the pH is increased by heating during gelation, or by a method in which a base is added to the emulsion while maintaining the W / O emulsion state by stirring with a mixer or the like.

[0052] Specific examples of the base include ammonia, tetraalkylammonium hydroxides such as tetramethylammonium hydroxide (TMAH), amines such as trimethylamine, alkali hydroxides such as sodium hydroxide, alkali metal carbonates such as sodium carbonate and sodium bicarbonate, and alkali metal silicates. The stirring intensity may be strong enough to mix the W / O emulsion with the base.

[0053] Among the above pH adjustment methods, the method of thermal decomposition of a latent base such as urea, or the method of using ammonia, tetraalkylammonium hydroxides, or amines as a base are preferred because they do not involve the inclusion of metal elements. When ammonia is used to adjust the pH, the ammonia may be blown in as a gas or added as aqueous ammonia. pH adjustment using urea is particularly preferred because it allows for uniform pH adjustment throughout the solution by heating.

[0054] When adjusting the pH to promote gelation, it is particularly preferable to adjust the amount added so that the pH value of the fumed silica dispersion rises to about 4.5 to 8.0. The same applies to the case where a latent base is used, but a specific amount added when using urea, for example, is preferably 1% by mass or more, and particularly preferably 2% by mass or more, relative to the fumed silica dispersion. The upper limit is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0055] When the above heating or pH adjustment is performed, stirring is preferably performed to prevent the gel from agglomerating. A known stirring method is generally used, but a specific example is a mixer equipped with stirring blades.

[0056] Furthermore, after gelation, the dispersoid changes from a liquid to a solid, so the system is no longer a W / O emulsion, but a dispersion (suspension) in which a solid (gelled body) is dispersed in a hydrophobic solvent.

[0057] (Gelated body recovery process) In this production method, the gelled body produced as described above is recovered from the liquid. Typical solid-liquid separation methods, such as filtration and centrifugation, can be used to recover the gelled body, but WO phase separation may be performed prior to the recovery. WO phase separation is a process in which the gelled body dispersion is separated into two layers, an O phase and a W phase, and is generally known as demulsification. The gelled body obtained by the gelling step is present in the separated W phase. Separating this from the O phase facilitates recovery of the gelled body by solid-liquid separation, such as by filtration.

[0058] The WO phase separation method can be carried out by appropriately selecting a known method for demulsification, but is preferably carried out by adding a certain amount of a water-soluble organic solvent commonly used in demulsification to the gel dispersion and heating it to separate it into an O phase and a W phase. After this process, the upper layer is generally the O phase (a layer mainly containing the organic solvent) and the lower layer is the W phase (a water layer containing the aqueous organic solvent and the gel).

[0059] Examples of the water-soluble organic solvent include acetone, methanol, ethanol, isopropyl alcohol, etc. Among these, isopropyl alcohol is particularly suitable.

[0060] The amount of the water-soluble organic solvent added is preferably adjusted depending on the type and amount of the surfactant with an HLB of 3 to 5 used during emulsion formation. For example, when sorbitan monooleate is used as the surfactant, the water-soluble organic solvent is added in an amount of about 1 / 6 to 1 / 2 times by mass the mass of the water-insoluble organic solvent (water-soluble organic solvent / water-insoluble organic solvent), and the mixture is stirred as necessary and then allowed to stand, thereby enabling the demulsification to be carried out suitably.

[0061] In WO phase separation, the surfactant migrates (extracts) to the O phase, so by removing the O phase, porous spherical silica free of surfactant impurities can be obtained.

[0062] The heating temperature range is 50°C or higher, preferably about 50 to 80°C, and more preferably about 60 to 70°C.

[0063] After adding the water-soluble organic solvent to the gel dispersion as described above, it is preferable to stir the mixture to prevent the gel from agglomerating. A known method is generally used for stirring, but a specific example is a mixer equipped with a stirring blade. The degree of mixing is not particularly limited, but it is sufficient as long as the liquid surface rotates due to stirring. For example, stirring with a mixer is performed at a speed of 0.1 to 3.0 kW / m. 3 , preferably 0.5 to 1.5 kW / m 3 The stirring time is preferably 0.5 to 24 hours, and more preferably 0.5 to 1 hour.

[0064] After the WO phase separation, the W phase containing the gel is recovered. Specifically, the O phase (upper layer) can be separated and removed by decantation or the like.

[0065] (drying process) The gel contained in the recovered W phase is preferably recovered from the W phase. A known method can be used for recovery, and specific examples include suction filtration and centrifugation. In this case, it is preferable that the solvent is removed so that the recovered gel is in the form of a cake.

[0066] The recovered gel is dried by spray drying. When producing a gel by a wet process, such as the manufacturing method of the present invention, capillary forces of the solvent are generated between the particles of the gel when the gel is removed from the liquid and dried. This causes the particles to aggregate, and agglomeration also occurs in the dried powder, particularly when the particles are left to dry. On the other hand, drying by spray drying allows the solvent droplet size during drying to approach the particle size of the porous spherical silica particles. Ideally, if the solvent droplet size is equal to the particle size of the porous spherical silica particles, each porous spherical silica particle will be contained in the solvent droplet during drying. In this state, the porous spherical silica particles are not adjacent to each other during drying, allowing drying without capillary forces due to the solvent between the particles, making it easier to obtain particles without agglomeration. The spray drying method is not particularly limited, and known methods such as a rotary atomizer method or a nozzle method can be used. However, it is preferable to select a method in which the particle size of the target porous spherical silica particles is equal to the droplet size of the sprayed solvent. In general, the nozzle type tends to produce finer droplets than the rotary atomizer type. The two-fluid nozzle type is particularly preferred from the viewpoint that it can produce finer droplets and is less likely to aggregate during drying.

[0067] The gel is preferably dispersed in a water-soluble organic solvent to prevent aggregation during spray drying. Specific examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol. The use of a solvent with a lower boiling point can improve drying efficiency.

[0068] The water-soluble organic solvent may contain water or a non-water-soluble solvent. To suppress aggregation during drying, the concentration of the water-soluble organic solvent in the solvent is preferably 60% by mass or more, more preferably 65% ​​by mass or more, and particularly preferably 70% by mass or more. When the concentration of the water-soluble organic solvent is within the above range, aggregation due to insufficient drying during spray drying is less likely to occur. Note that drying shrinkage inside the pores can be adjusted by the concentration of the water-soluble solvent during drying, so adjusting the concentration of the water-soluble organic solvent can cause appropriate drying shrinkage and control the pore volume. Specifically, increasing the proportion of water contained in the solvent and decreasing the concentration of the water-soluble organic solvent makes drying shrinkage more likely to occur and reduces the pore volume. Conversely, reducing the proportion of water contained in the solvent and increasing the concentration of the water-soluble organic solvent suppresses drying shrinkage and increases the pore volume.

[0069] The water-soluble organic solvent (slurry) in which the gel is dispersed is preferably stirred to prevent particles from agglomerating in the liquid. Generally known stirring methods can be used, and specific examples include a stirrer, a mixer with a stirring blade, and the like. The degree of mixing may be such that the particles do not settle in the liquid and are not destroyed. The slurry may be charged into the spray dryer while stirring, or may be charged into the spray dryer after stirring for a certain period of time. From the viewpoint of preventing particle settling, charging while stirring is more preferable.

[0070] The inlet temperature during spray drying is preferably adjusted to be equal to or higher than the boiling point of the solvent in the slurry, and is preferably adjusted so that the porous spherical silica is not in the form of a slurry or cake at the outlet of the spray dryer but is a dry powder. Note that "equal to or higher than the boiling point" means equal to or higher than the boiling point of the solvent under pressure during drying. It is more preferable that the inlet temperature be adjusted to a value approximately 20 to 50°C higher than the boiling point of the solvent in the slurry, and that the temperature difference between the inlet temperature and the outlet temperature be adjusted to be within a range of 10 to 70°C. Generally, a spray dryer is equipped with a heating device only at the inlet (inlet), and the outlet temperature does not exceed the inlet temperature. The temperature difference between the inlet temperature and the outlet temperature is more preferably within a range of 20 to 70°C, and particularly preferably within a range of 20 to 60°C. When the inlet temperature and the outlet temperature are within the above range, the drying state during spray drying is good, and porous spherical silica without aggregation can be obtained.

[0071] The circulating air volume during spray drying may be adjusted so as to stabilize the temperature inside the drying chamber, and is preferably adjusted according to the scale of the spray dryer. When collecting dried porous spherical silica using a cyclone, the circulating air volume affects the collection efficiency under the cyclone, and the greater the circulating air volume, the higher the collection efficiency under the cyclone.

[0072] The concentration of the gelled material in the slurry should be adjusted to such an extent that the slurry containing the dispersed gelled material has fluidity and can be fed to a spray dryer without clogging. Specifically, the silica solids concentration (by mass) after drying is preferably 60% by mass or less, more preferably 50% by mass or less, and even more preferably 40% by mass or less. There is no particular lower limit for the concentration of the gelled material, but since the lower the concentration, the lower the drying efficiency becomes, it is preferable that the concentration not be too low, and more preferably 5% by mass or more.

[0073] The slurry feed rate during spray drying may be adjusted so that spraying is stable and the inlet and outlet temperatures are within the above-mentioned ranges, and is preferably adjusted according to the scale of the spray dryer. The slurry feed rate affects the temperature difference between the inlet and outlet temperatures, and as the feed rate increases, the temperature difference between the inlet and outlet temperatures increases.

[0074] As a method for collecting the dried porous spherical silica, a generally known method can be used. Specific examples include a single-point collection method and a two-point collection method. Furthermore, a general collector can be used, specifically a cyclone or a bag filter. From the viewpoint of removing coarse particles, collection by the two-point collection method using a cyclone is preferred.

[0075] (Firing process) The porous spherical silica of the present invention is further calcined after drying. Calcination can increase the test force at break. The calcination conditions can be adjusted so that the test force at break reaches the desired value; the longer the calcination time and the higher the calcination temperature, the higher the test force at break. The calcination temperature is 900 to 1500°C, preferably 1400°C or less, and more preferably 1300°C or less. The calcination time is 10 to 25 hours, preferably 12 to 23 hours, and more preferably 12 to 20 hours. If the calcination temperature and calcination time are within the above ranges, the particles dried by spray drying without agglomeration will not agglomerate again, and the pores will not be clogged, resulting in porous spherical silica having a test force at break within the desired range.

[0076] As the firing method, known methods can be used, and a typical method is to place dried porous spherical silica in a crucible or quartz vat and heat it in an electric furnace.

[0077] The atmosphere during firing is not particularly limited, and firing can be carried out in an inert gas atmosphere such as argon or nitrogen, or in the air.

[0078] The temperature rise rate during firing may be within a range that can be followed by the temperature rise of a heating device such as an electric furnace. The slower the temperature rise rate, the lower the firing processing efficiency, so it is preferable not to make the rate too low. When using a general electric furnace, a temperature rise rate of 2 to 10°C / min is suitable.

[0079] In the above-described production method, the particle size of the resulting porous spherical silica roughly corresponds to the droplet (W phase) diameter of the fumed silica dispersion in the W / O emulsion prepared in the emulsification step. Therefore, it is necessary to set the dispersion conditions so that the droplet size falls within the desired range. Various methods for controlling the droplet size in W / O emulsions are known, and these techniques can be appropriately selected and applied. Known methods can be used to adjust the droplet size, including adjusting the amount of surfactant added and adjusting the shear force applied during emulsification by the rotation speed, flow rate, etc. When adjusting the amount of surfactant added, using a large amount of surfactant tends to result in finer droplets, while using a small amount tends to result in larger droplets. When adjusting the shear force, the greater the applied shear force, the more likely the droplets are to be finer, and the smaller the shear force, the more likely the droplets are to be large.

[0080] The pore volume can also be controlled by drying shrinkage. Known methods for controlling drying shrinkage can be used, specifically, by adjusting the concentration of the water-soluble solvent before drying. The pore volume can also be controlled by the calcination conditions; the higher the calcination temperature and the longer the calcination time, the smaller the pore volume. Furthermore, by using fumed silica as a raw material, as in the manufacturing method of the present invention, the fumed silica has an aggregated structure, resulting in the mode of the high pore radius. The specific surface area can be adjusted by appropriately selecting the specific surface area of ​​the fumed silica used as a raw material, and can also be adjusted by the gelation time. The shorter the gelation time, the higher the specific surface area. The specific surface area can also be adjusted by the calcination conditions. Generally, the higher the calcination temperature and the longer the calcination time, the lower the specific surface area.

[0081] The alkali metal content can be easily reduced by using, as a raw material, fumed silica that is substantially free of alkali metals, as described above, and other raw materials that are also substantially free of alkali metals, and by those skilled in the art paying sufficient attention to the production process to avoid contamination (the inclusion of impurities). Furthermore, when aiming to reduce the alkali metal content, the cake may be washed with water, an organic solvent, or the like after solid-liquid separation and before drying. The number of fragmented particles can be reduced by suppressing particle aggregation during the manufacturing process and eliminating the crushing step, as in the manufacturing method of the present invention. Furthermore, care must be taken throughout the manufacturing process to avoid applying excessive stress to the particles so as not to break them. [Example]

[0082] Examples are given below to specifically explain the present invention, but the present invention is not limited to these examples.

[0083] <Evaluation method> The produced porous spherical silica was evaluated for the following items.

[0084] (Measurement of particle size distribution and cumulative diameter by volume using a Coulter counter) 0.1 g of porous spherical silica was added to 40 ml of ion-exchanged water and dispersed for 30 minutes using an ultrasonic cleaner (BRANSON BRANSONIC1510J-DTH). The particle size distribution of the dispersion was measured using a Beckman Coulter Multisizer III. An aperture with a diameter of 100 μm was used for the measurement. From the obtained particle size distribution, the cumulative 50%, 10%, and 90% diameters on a volume basis were evaluated.

[0085] (Measurement of BJH pore volume, pore radius (mode) and BET specific surface area) The BJH pore volume, pore radius (mode), and BET specific surface area were measured using a BELSORP-mini (manufactured by BEL Japan Co., Ltd.) according to the above-mentioned definitions.

[0086] (Test force when specimen breakage is observed) The "test force at which the specimen broke" was measured according to the definition above using a micro-compression testing machine (Shimadzu Corporation, MCT-W510-J). The loading rate during measurement was 0.4462 mN / sec, and the load holding time was 10 sec. An indenter with a diameter of 200 μm was used for the measurement.

[0087] (alkali metal content) 10 ml of nitric acid and 10 ml of hydrofluoric acid were added to 1 g of porous spherical silica and dissolved. The solution was heated at 180°C for 4 hours and evaporated to dryness. After cooling to room temperature, 2 ml of nitric acid and 18 ml of ultrapure water were added, and the total volume was adjusted to 20 ml to obtain a measurement sample. The alkali metal content of the obtained measurement sample was measured using an inductively coupled plasma optical emission spectrometer (Thermo Scientific, ICAP650DUO).

[0088] (average circularity) More than 2000 porous silica particles were observed at 1000x magnification using an SEM (Hitachi High-Technologies S-5500, accelerating voltage 3.0 kV, secondary electron detection), and the SEM images were analyzed to calculate the average circularity according to the definition above.

[0089] (Number of fragmented particles (number of particles with a circularity of 0.7 or less)) More than 200 porous silica particles were observed at 800x magnification using an SEM (Hitachi High-Technologies S-5500, accelerating voltage 3.0 kV, secondary electron detection) and the SEM images were analyzed. The circularity of each particle was calculated according to the definition above, and the number of particles with a circularity of 0.7 or less was counted.

[0090] Example 1 (Dispersion liquid preparation process) To 200 ml of ion-exchanged water containing 6.65 g of urea, 66 g of Reolosil QS-30 (Tokuyama Corporation) was added while stirring with a homogenizer (IKA, T25BS1). The fumed silica was pre-dispersed, and then finely dispersed using an ultrasonic homogenizer (BRANSON, Sonifier SFX250), to obtain a fumed silica dispersion. The particle size distribution of the dispersed liquid was measured using a laser diffraction scattering method, and the D90 value was 0.19 μm. The dispersion preparation process was carried out in a chiller cooled to 10°C.

[0091] (W / O emulsion preparation process) A 65.5 g aliquot was taken from the fumed silica dispersion prepared by the above method, and 129 g of decane in which 0.75 g of sorbitan monooleate (Kao Corporation, Rheodol SP-010V) had been dispersed was added. The mixture was then stirred for 3 minutes at 8600 rpm using a homogenizer to obtain a W / O emulsion.

[0092] (Gelling process) The resulting W / O emulsion was gelled by stirring it at 200 rpm using a four-paddle impeller with a blade diameter of 60 mm, a blade width of 20 mm, and an oblique angle of 45 degrees in a water bath at 80°C for 3 hours.

[0093] (Gelated body recovery process) 77 g of isopropyl alcohol and 52 g of water were added, and the mixture was stirred with a stirring blade while maintaining the temperature at 70° C. for 30 minutes. After that, the mixture was allowed to stand, whereby it separated into two layers: an upper O phase and a lower W phase.

[0094] Then, the O phase and the W phase were separated by decantation, and the W phase was recovered.

[0095] The W phase was filtered by suction, and the gel was separated from the W phase by filtration.

[0096] (drying process) The gel cake obtained was dispersed in 60 g of isopropyl alcohol and, while stirring with a stirrer, was introduced into a spray dryer (BUCHI, Mini Spray Dryer B-290). At this time, the silica solid content in the slurry after drying was 10% by mass. The inlet temperature of the spray dryer was 120°C, and the outlet temperature was 85°C. The liquid feed rate was 15 ml / min, and the circulating air volume was 35 m 3 / h.

[0097] (Firing process) The obtained dried powder was placed in a crucible and fired in an electric furnace (Advantec, FUS722PB) at a temperature increase rate of 5°C / min at 1000°C for 20 hours. The firing atmosphere was not adjusted, and the firing was carried out in an air atmosphere.

[0098] The physical properties of the porous spherical silica thus obtained are shown in Table 1. (The physical properties of the porous spherical silica obtained in the following Examples and Comparative Examples are also shown in Table 1.)

[0099] <Example 2> Porous spherical silica was obtained in the same manner as in Example 1, except that the firing conditions were changed to 900°C for 17 hours. The outlet temperature during spray drying was 85°C.

[0100] Example 3 Porous spherical silica was obtained in the same manner as in Example 1, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 3000 rpm. The outlet temperature during spray drying was 85°C.

[0101] Example 4 Porous spherical silica was obtained in the same manner as in Example 1, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 10,000 rpm. The outlet temperature during spray drying was 85°C.

[0102] <Example 5> Porous spherical silica was obtained in the same manner as in Example 1, except that the firing conditions were changed to 1200°C for 15 hours. The outlet temperature during spray drying was 85°C.

[0103] Example 6 Porous spherical silica was obtained in the same manner as in Example 1, except that the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 6000 rpm and the firing conditions were changed to 1200°C for 10 hours. The outlet temperature during spray drying was 85°C.

[0104] <Comparative Example 1> 500 mL of silica sol was prepared by adding 10 g / 100 mL of sulfuric acid to an aqueous sodium silicate solution with a SiO2 / Na2O molar ratio of 3.1 (9 g / 100 mL) to adjust the pH to 2.9. 66.5 g of this silica sol was sampled, and the W / O emulsion preparation step, gelation step, and gelled body recovery step were carried out in the same manner as in Example 1, except that the fumed silica dispersion in Example 1 was replaced with this silica sol, to obtain a gelled body. The obtained gelled body was dried in a vacuum dryer and calcined at 1000°C for 20 hours to obtain porous spherical silica.

[0105] <Comparative Example 2> A fumed silica dispersion prepared in the same manner as in the dispersion preparation step of Example 1 was spray-dried and then calcined at 1000° C. for 20 hours to obtain porous spherical silica.

[0106] <Comparative Example 3> In Example 1, the rotation speed of the homogenizer in the W / O emulsion preparation step was changed to 5500 rpm, and the gelation step and gelled body recovery step were carried out to obtain a gelled body. The obtained gelled body was dried in a vacuum dryer and calcined at 1000°C for 20 hours. After calcination, the gelled body was crushed using a jet mill to obtain porous spherical silica.

[0107] <Comparative Example 4> Porous spherical silica was obtained in the same manner as in Example 1, except that the calcination step was not carried out.

[0108] <Comparative Example 5> Porous spherical silica was obtained in the same manner as in Example 6, except that the calcination was carried out at 800° C. for 10 hours.

[0109] [Table 1]

[0110] <Evaluation results> Examples 1 to 6 As shown in Table 1, in Examples 1 to 6, the arithmetic mean value of the "test force at which the specimen was broken" for 10 particles, calculated at a loading rate of 0.4462 mN / sec according to the method specified in JIS Z8844, was 1.0 × 10 1 ~2.0×10 1 The hardness was high, with a circularity of 0.7 mN, and out of 200 particles observed in an SEM image, 20 or fewer particles had a circularity of 0.7, indicating a reduced number of fragmented particles. This can be achieved by the production method of the present invention, in which a gel obtained by gelling a fumed silica dispersion in a liquid is dried by spray drying under appropriate drying conditions to suppress particle aggregation, and then the gel is fired under appropriate firing conditions.

[0111] In addition, all of the porous spherical silica obtained in Examples 1 to 6 had a D50 in the range of 2 to 200 μm, a D10 / D90 of 0.3 or more, a pore volume measured by the BJH method in the range of 0.5 to 8 ml / g, a mode of the pore radius measured by the BJH method in the range of 5 nm or more and 50 nm or less, and a specific surface area measured by the BET method of 50 m 2 / g or more, 400m 2 / g or less, and the alkali metal content was 50 ppm or less.

[0112] In Examples 1 to 6, porous spherical silica with various D50 values ​​was obtained, all of which were controlled by adjusting the droplet size of the W / O emulsion by changing the rotation speed during emulsification. The production method of the present invention makes it possible to easily control the D50 value of porous spherical silica without making major changes to the production process.

[0113] (Comparative Example 1) The porous spherical silica of Comparative Example 1, which used sodium silicate as a raw material, had a small pore volume. This was because the residual sodium from the raw material caused a drop in melting point during firing, resulting in pore blockage. Thus, when sodium silicate is used as a raw material, it is difficult to obtain porous spherical silica with high hardness while maintaining the pore volume.

[0114] (Comparative Example 2) The porous spherical silica of Comparative Example 2 obtained by spray-drying the fumed silica dispersion had a low breaking strength. This was due to the low strength of the bonds between the primary particles of the raw material before calcination. Thus, it is difficult to obtain porous spherical silica with the desired hardness when granulated by spray drying.

[0115] (Comparative Example 3) The porous spherical silica of Comparative Example 3, which was recovered from the gel and then dried by standing in a vacuum dryer, had a large number of fragmented particles. This is because the particles had aggregated during standing drying, and the fragmented particles were generated by the crushing step. Thus, it is difficult to obtain porous spherical silica with a reduced number of fragmented particles by standing drying.

[0116] Comparative Example 4 The porous spherical silica of Comparative Example 4, which was not subjected to a calcination step, had a low test force at break. As such, it is difficult to obtain porous spherical silica with high hardness without performing a calcination step.

[0117] (Comparative Example 5) The porous spherical silica of Comparative Example 5 had a low breaking test force. As such, unless the firing conditions are appropriate, it is difficult to obtain porous spherical silica with high hardness.

Claims

1. a volume-based cumulative 50% diameter (D50) measured by a Coulter counter method in the range of 2 μm or more and 200 μm or less; Similarly, the ratio (D10 / D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is 0.3 or more, The pore volume according to the BJH method is 0.5 ml / g or more and 8 ml / g or less, The most frequent value of the pore radius measured by the BJH method is 5 nm or more and 50 nm or less, The specific surface area measured by the BET method is 50m ２ / g or more, 400m ２ / g or less, According to the method specified in JIS Z8844, the arithmetic mean value of the "test force at which the specimen breakage was observed" for 10 particles was calculated at a loading rate of 0.4462 mN / sec and was 1.0 x 10 １ mN or more 2.0 x 10 １ mN or less, Porous spherical silica having an alkali metal content of 50 ppm or less.

2. A catalyst carrier comprising the porous spherical silica of claim 1.

3. A cosmetic comprising the porous spherical silica according to claim 1.

4. An analytical column comprising the porous spherical silica of claim 1.

5. An abrasive comprising the porous spherical silica of claim 1.

6. A resin composition comprising the porous spherical silica according to claim 1.

7. A step of preparing a W / O emulsion comprising an aqueous phase in which fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent; a step of heating the emulsion to gel the aqueous phase and obtain a gelled dispersion; A step of recovering the resulting gelled body from the liquid; and a step of calcining the obtained porous spherical silica at a temperature of 900 to 1500°C for 10 to 25 hours; A method for producing porous spherical silica comprising the steps of:

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