Classifications

• • C—CHEMISTRY; METALLURGY
  • C01—INORGANIC CHEMISTRY
  • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
  • C01B33/00—Silicon; Compounds thereof
  • C01B33/113—Silicon oxides; Hydrates thereof
  • C01B33/12—Silica; Hydrates thereof, e.g. lepidoic silicic acid
  • C01B33/18—Preparation of finely divided silica neither in sol nor in gel form; After-treatment thereof

Definitions

• the present invention relates to a novel porous spherical silica and a method for producing the same.
• Porous silica has been studied in various ways, and porous silica with various physical properties has been proposed. Taking advantage of its characteristics, porous silica is used in a wide range of applications, such as catalyst and fragrance carriers, adsorbents, cosmetic additives, abrasives for industrial products, and column packing materials for liquid chromatography. In particular, porous silica with a sharp pore size distribution is useful for applications as catalyst carriers and column packing materials for liquid chromatography.
• Porous silica with the above characteristics is manufactured, for example, by a wet synthesis method using alkoxysilane as a raw material (Patent Documents 1 and 2) or a method of spray-drying a dispersion of spherical silica particles (Patent Document 3).
• the most frequent pore size can be adjusted according to the target components to be separated and the catalyst material to be supported, thereby enabling good separation ability of the column and selective support of the catalyst material.
• porous silica with a large most frequent pore size is suitable for handling large separation components and catalyst carriers, and if it has a high pore volume, the separation efficiency of the column and the amount of catalyst supported are improved.
• Porous silica with a large modal pore size and a high pore volume can be produced, for example, by a method of gelling a fumed silica dispersion in liquid (Patent Document 4).
• the porous spherical silicas described in Patent Documents 1 to 3 all have a sharp pore size distribution, but the porous spherical silicas described in Patent Documents 1 and 2 have a small most frequent pore size, and the porous spherical silica described in Patent Document 3 has a low pore volume.
• the porous spherical silica described in Patent Document 4 has a large most frequent pore size and a high pore volume, but its pore size distribution is broad, making it unsuitable for use as a column packing material or catalyst carrier.
• the object of the present invention is therefore to provide porous spherical silica that has a large most frequent pore size, a high pore volume, and a sharp pore size distribution, and a method for producing the same.
• the present inventors have conducted extensive research to solve the above problems. As a result, they have discovered that in the manufacturing process of porous spherical silica, a fumed silica dispersion in which the particle size distribution falls within a predetermined range can be formed into spheres by an emulsion method, and then gelled, thereby making it possible to manufacture porous spherical silica that has a large most frequent pore size, a large pore volume, and a sharp pore size distribution, and have thus completed the present invention.
• the pore volume measured by mercury intrusion porosimetry is 0.5 ml/g or more and 8 ml/g or less;
• the most common pore size measured by mercury intrusion porosimetry is 5 nm or more and 50 nm or less;
• a porous spherical silica characterized in that the ratio of the volume of pores existing within a range of ⁇ 5 nm of the most frequent pore diameter to the total volume of pores is 40% or more.
• the volume-based cumulative 50% diameter (D50) of the porous spherical silica measured by a Coulter counter method is in the range of 2 to 200 ⁇ m
• a catalyst carrier comprising the porous spherical silica according to any one of [1] to [5].
• a column packing material comprising the porous spherical silica according to any one of [1] to [5].
• a cosmetic comprising the porous spherical silica according to any one of [1] to [5].
• An abrasive comprising the porous spherical silica according to any one of [1] to [5].
• a resin composition comprising the porous spherical silica according to any one of [1] to [5].
• An adsorbent comprising the porous spherical silica according to any one of [1] to [5].
• a step of preparing a W/O emulsion comprising an aqueous phase having fumed silica dispersed therein and an organic phase mainly comprising a non-aqueous solvent;
• the porous spherical silica of the present invention has a sharp pore size distribution, so when used as a column packing material, it can efficiently separate specific target components.
• it has a high pore volume, when used as a catalyst carrier, it can support a large amount of catalyst, and when used as a cosmetic additive, it can impart high oil absorption performance.
• the high modal pore size indicates, it has a large pore size, so it can be suitably used as a column packing material for particularly large separation components or a carrier for supporting large catalyst components.
• resin when used as an abrasive for industrial products, etc., resin can easily penetrate into the pores, making it easy to fix it to the resin on the polishing pad.
• the particle size distribution of the fumed silica dispersion is adjusted to fall within a predetermined range, and then the dispersion is gelled to synthesize porous spherical silica.
• the adjusted particle size distribution can be reflected in the pore skeleton, making it easier to obtain porous spherical silica with a sharp pore size distribution.
• the fumed silica itself has a structure, which suppresses the reduction in pore volume due to drying shrinkage, making it possible to obtain porous spherical silica with a large most frequent pore size and high pore volume without surface treatment.
• 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 mercury intrusion porosimetry. It is difficult to obtain a pore volume larger than 8 ml/g. If it is 6 ml/g or less, it is easier to produce, if it is 4 ml/g or less, it is even easier to produce, and if it is 2.5 ml/g or less, it is particularly easy to produce.
• 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. If the pore volume is within the above range, the porous spherical silica of the present invention can have a high oil absorption even when used as a cosmetic additive.
• the most frequent pore size measured by mercury porosimetry is 5 nm or more, preferably 10 nm or more, more preferably 15 nm or more.
• the upper limit is 50 nm or less, preferably 30 nm or less. If the most frequent pore size is less than 5 nm, when used as a column packing material, many pores are not used for separation, and the separation efficiency decreases. If the most frequent pore size exceeds 50 nm, the particle strength decreases, making it difficult to apply to a column packing material. If the most frequent pore size is within the above range, when used as a column packing material, it shows good separation ability and good handling properties. When the porous spherical silica having the most frequent pore size in the above range is used as an abrasive for industrial products, etc., resin easily penetrates into the pores, and it is easy to fix it to the resin on the polishing pad.
• the porous spherical silica of the present invention has a ratio of the pore volume present within ⁇ 5 nm of the most frequent pore size to the total pore volume (hereinafter, sometimes simply referred to as "pore volume ratio") of 40% or more. If the pore volume ratio is less than the above range, the amount of the catalytic substance supported will decrease, and the separation ability of the column packing will deteriorate.
• the pore volume ratio is more preferably 45% or more, and even more preferably 50% or more.
• the porous spherical silica having a pore volume ratio in the above range has a sharp pore size distribution and uniform pore sizes, when used as a catalyst carrier, it is possible to efficiently support the catalytic substance by selecting a porous spherical silica with a most frequent pore size according to the size of the catalytic substance, and when used as a column packing, it is possible to accurately separate specific substances, and therefore shows good separation ability.
• the porous spherical silica of the present invention has a spherical shape.
• spherical means that the average circularity obtained by image analysis using a scanning electron microscope (SEM) is 0.8 or more.
• the "average circularity obtained by image analysis” is the arithmetic mean value of the circularity obtained by image analysis of SEM images observed at a magnification of 1000 times with a SEM for 2000 or more porous spherical silica particles.
• the "circularity” is a value obtained by the following formula (1).
• C 4 ⁇ S/L 2 (1)
• C represents the circularity
• S represents the area (projected area) that the porous spherical silica occupies in the image
• 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.
• the porous spherical silica of the present invention has the above-mentioned properties and therefore can impart a smooth feel to the skin when used as a cosmetic additive.
• the pore volume existing within ⁇ 5 nm of the most frequent pore size is preferably 0.5 ml/g or more. More preferably, it is 0.6 ml/g or more, and even more preferably, it is 0.65 ml/g or more.
• the pore volume existing within ⁇ 5 nm of the most frequent pore size is in the above range, which means that the pore volume of the pores having a specific pore size is high, and in particular, when used as a catalyst carrier, by selecting a porous spherical silica having a most frequent pore size according to the size of the catalyst substance, it is possible to efficiently support the catalyst substance.
• there is no upper limit to the preferred range of the pore volume existing within ⁇ 5 nm of the most frequent pore size but it is technically difficult to obtain one exceeding 0.9 ml/g.
• the pore diameter and pore volume were measured by mercury porosimetry after pretreatment by constant temperature drying for 4 hours at 120° C.
• the pore diameter was calculated using Washburn's formula (2).
• PD -4 ⁇ cos ⁇ (2)
• P pressure [psia/absolute pressure]
• ⁇ surface tension of mercury
• D pore diameter [ ⁇ m]
• ⁇ contact angle with mercury.
• the surface tension of mercury was 480 dynes/cm
• the contact angle with mercury was 140 degrees.
• the measurement was carried out for pore diameters of 0.0036 to 200 ⁇ m, and pore diameters larger than 100 nm were considered as voids between particles, and the pore volume was calculated for pore diameters of 100 nm or less.
• the integral value of the pore volume for pore diameters of 100 nm or less obtained by the same method was differentiated, and the pore diameter that became the main peak was taken as the most frequent pore diameter.
• the porous spherical silica of the present invention preferably has a volume-based cumulative 50% diameter (D50) in the particle size distribution measured by the Coulter counter method in the range of 2 to 200 ⁇ m.
• the ratio (D10/D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is preferably 0.3 or more. If the particle size distribution of the porous spherical silica is in the above range, when it is used as a packing material for an analytical column, the column is less likely to be clogged and is easily packed.
• D50 is preferably 2 to 100 ⁇ m, particularly preferably 5 to 50 ⁇ m, and more preferably 5 to 20 ⁇ m.
• D10/D90 is preferably 0.4 or more, and more preferably 0.5 or more. Incidentally, D10/D90 cannot exceed 1.0, and is generally 0.6 or less.
• the fumed silica used as the raw material is selected so that the specific surface area of the obtained porous spherical silica falls within the above range, gelation occurs easily and it becomes easy to mold it into a sphere. Since the specific surface area of fumed silica is generally 400 m 2 /g or less, it is difficult to obtain porous spherical silica with a specific surface area exceeding 400 m 2 /g.
• the specific surface area is a value obtained by the nitrogen adsorption BET multipoint method. If the specific surface area is within the above range, when the material is used as a carrier or adsorbent for a catalyst or fragrance, the contact area with the reactants can be increased, which contributes to improving the reaction efficiency.
• the porous spherical silica of the present invention has an alkali metal content of 50 ppm or less (mass basis).
• the alkali metal content is preferably 30 ppm or less, more preferably 10 ppm or less. If the alkali metal content is within the above range, the catalyst activity is not reduced due to the inclusion of impurities, and the silica can be suitably used as a catalyst carrier, and is also extremely useful as an abrasive for semiconductors and other materials that do not like the inclusion of alkali metals.
• the porous spherical silica of the present invention may be hydrophilic or hydrophobic.
• the porous spherical silica of the present invention produced by the production method described below is hydrophilic.
• Hydrophobic porous spherical silica can be obtained by appropriately applying a silica surface treatment method after obtaining hydrophilic porous spherical silica by the production method.
• hydrophilic means that it can be dispersed in water that does not contain an organic solvent.
• the porous spherical silica of the present invention has the above-mentioned properties, it can be used as a packing material for analytical columns, a carrier for catalysts and fragrances, an adsorbent for carbon dioxide and the like, an additive for cosmetics, an abrasive for industrial products, and an additive for various resin compositions.
• the method for producing the porous spherical silica of the present invention is not particularly limited, but the high pore volume and large most frequent pore diameter can be easily achieved by using fumed silica dispersion as raw material.
• fumed silica has a structure in which fine particle silica (primary particles) are aggregated.
• fumed silica dispersion as the raw material for porous spherical silica, and gelling the fumed silica in the dispersion to form a network, the decrease in pore volume caused by drying shrinkage can be suppressed, and it is possible to obtain porous spherical silica with high pore volume and large most frequent pore diameter.
• a method of producing porous spherical silica includes preparing a fumed silica dispersion having a particle size distribution within a specified range (dispersion preparation step), preparing a W/O emulsion consisting of an aqueous phase in which the fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent (W/O emulsion preparation step), heating the emulsion to gel the aqueous phase to obtain a porous spherical silica dispersion (gelation step), and then recovering the resulting porous spherical silica from the liquid and drying it (gelled body recovery step).
• dispenser preparation step preparing a W/O emulsion consisting of an aqueous phase in which the fumed silica is dispersed and an organic phase mainly composed of a non-aqueous solvent
• gelation step heating the emulsion to gel the aqueous phase to obtain a porous spherical si
• One method for dispersing fumed silica in water is to prepare a preliminary dispersion of fumed silica in water, and then finely disperse the mixture using a crusher or the like.
• crushers that can be used for fine dispersion include ball mills, bead mills, vibration mills, pin mills, atomizers, nanomizers (product names), articulzers, colloid mills, homogenizers, high-pressure homogenizers, and ultrasonic homogenizers.
• the operating conditions of the crusher during fine dispersion are preferably adjusted according to the device so that the fumed silica dispersion liquid is in a predetermined dispersion state.
• the dispersion state of the fumed silica dispersion liquid can be confirmed by evaluating the D50 value and D90 value of the particle size distribution measured by the laser diffraction scattering method.
• the D50 value is preferably 0.15 ⁇ m or less, more preferably 0.13 ⁇ m or less, and particularly preferably 0.12 ⁇ m or less.
• the D90 value is preferably 0.20 ⁇ m or less, more preferably 0.18 ⁇ m or less, and particularly preferably 0.17 ⁇ m or less. It is preferable that both D50 and D90 satisfy the above range.
• D50 and D90 values are within the above ranges, porous spherical silica with a sharp pore size distribution can be obtained. Although there is no lower limit for the D50 and D90 values, it is difficult to obtain a fumed silica dispersion with a D50 value of 0.05 ⁇ m or less.
• the particle size distribution of the dispersion was measured using an LS 13 320 (manufactured by Beckman Coulter, Inc.).
• the refractive index of the water used as the solvent during the measurement was 1.333, and the refractive index of the particles was 1.46. From the obtained particle size distribution, the cumulative 50% diameter and cumulative 90% diameter on a volume basis were evaluated.
• Fumed silica that can be dispersed in water and can be gelled by heating, adjusting pH, etc. can be used. Such properties are achieved by having a large number of silanol groups on the silica surface, so almost any fumed silica that has not been surface-treated can be used.
• fumed silica with an upper limit of 400 m 2 /g.
• the specific surface area of the porous spherical silica obtained by the method described here is the value obtained by subtracting several tens of m2 /g from the specific surface area of the fumed silica used as the raw material. Therefore, by appropriately selecting the fumed silica used as the 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 manufacturing conditions. It is also possible to mix fumed silicas with different specific surface areas for use in the present invention.
• Fumed silica as described above is commercially available, and examples that can be used include 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.
• fumed silica is highly pure and contains almost no impurities such as alkali metals, so the alkali metal content of the porous spherical silica produced can be made extremely low.
• Water is essential as the solvent for this process, but other solvents may be included as long as they do not interfere with the formation of the emulsion or the subsequent gelation. Also, if a latent base is used to promote gelation (described below), it is a good idea to dissolve it in water before dispersing the fumed silica.
• the silica concentration in the fumed silica dispersion is preferably in the range of 10% to 30% by mass. It is more preferable that it is 15% by mass or more, and especially preferable that it is 20% by mass or more.
• the higher the silica concentration of the fumed silica dispersion the faster the gelation will proceed, but if the silica concentration is too high, it will lose fluidity and it will be difficult to make a fumed silica dispersion.
• 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 will be difficult for the W phase to become spherical in the subsequent W/O emulsion preparation process, and in extreme cases, it will be difficult to even mold the emulsion. Therefore, it is preferable to keep the liquid temperature of the fumed silica dispersion at or below room temperature (20°C) during the dispersion preparation process. When 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 lower, more preferably 12°C or lower).
• 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.
• the fumed silica dispersion which is a dispersoid, becomes spherical due to surface tension, etc., and a spherical gelled body can be obtained by gelling the fumed silica dispersion dispersed in the non-aqueous solvent in the spherical shape.
• the non-aqueous solvent used in this manufacturing method may be any solvent that is hydrophobic enough to form an emulsion with the fumed silica dispersion.
• 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 can be mentioned. Among these, hexane, heptane, and decane, which have appropriate viscosities, can be preferably used. If necessary, multiple solvents may be mixed and used. Also, it is possible to use hydrophilic solvents such as lower alcohols in combination (as a mixed solvent) as long as they can form an emulsion with the fumed silica dispersion.
• the amount of non-water-soluble solvent used is not particularly limited as long as it is within the range that allows the formation of a W/O emulsion, but generally, about 1 to 10 parts by volume of non-water-soluble solvent is used per 1 part by volume of fumed silica dispersion.
• the surfactant to be used can be any known surfactant used in forming a W/O emulsion, and any of anionic surfactants, cationic surfactants, and nonionic surfactants can be used. Among these, nonionic surfactants are preferred because they are easy to form a W/O emulsion and are less likely to be contaminated with alkali metals.
• Surfactants with an HLB value which indicates the degree of hydrophilicity and hydrophobicity, of 3 or more and 5 or less are particularly suitable for use.
• HLB value means the HLB value according to the Griffin method.
• Specific examples of surfactants that can be used preferably include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate.
• the amount of surfactant used is the same as the amount generally used when forming a W/O emulsion. Specifically, a range of 0.05 g to 10 g per 100 ml of fumed silica dispersion can be suitably used.
• a known method for forming a W/O emulsion can be used as a method for dispersing the fumed silica dispersion in a non-aqueous solvent.
• emulsion formation by mechanical emulsification is preferred, and specific examples include methods using a mixer, homogenizer, etc.
• a homogenizer can be preferably used. This emulsification process produces an emulsion with a sharp particle size distribution of the aqueous phase droplets, and therefore the particle size distribution of the spherical porous silica finally obtained is also sharp.
• the gelation step is a step following the W/O emulsion preparation step, in which the fumed silica dispersion is gelled while the droplets of the fumed silica dispersion are dispersed in a non-aqueous solvent.
• the gelation can be carried out by a known method.
• the gelation can be easily promoted by a method of heating to a high temperature or a method of adjusting the pH of the fumed silica dispersion to a weak acidic or basic state.
• the above-mentioned methods are preferred in that the reaction can be controlled independently.
• the pH of the fumed silica dispersion prepared by the above-mentioned method and not subjected to pH adjustment is generally in the range of 3.0 to 4.5.
• the temperature should not exceed the boiling point of each solvent used.
• the lower limit of the gelling temperature is preferably 50°C or higher, and more preferably 60°C or higher.
• the upper limit is preferably 100°C or lower, and more preferably 90°C or lower.
• the above pH adjustment can be easily performed by mixing the fumed silica dispersion with a substance (called a "latent base") that becomes basic when thermally decomposed by heating, such as urea, and then heating the mixture during gelation to increase the pH, or by adding a base to the emulsion while maintaining the W/O emulsion state by stirring the mixture with a mixer or the like.
• a substance such as urea
• 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.
• TMAH tetraalkylammonium hydroxides
• amines such as trimethylamine
• alkali hydroxides such as sodium hydroxide
• alkali metal carbonates such as sodium carbonate and sodium bicarbonate
• alkali metal silicates alkali metal silicates.
• 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, since they do not involve the contamination of metal elements.
• ammonia When ammonia is used to adjust the pH, it may be blown in as a gas or added as aqueous ammonia. It is particularly preferred to employ pH adjustment using urea, since it allows for uniform pH adjustment throughout the solution by heating.
• the specific amount added is preferably 1% by mass or more relative to the fumed silica dispersion, and particularly preferably 2% by mass or more.
• the upper limit is preferably 7% by mass or less, and more preferably 5% by mass or less.
• the dispersoid changes from liquid to 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.
• the gelled body produced as described above is collected from the liquid.
• a general solid-liquid separation method such as filtration or centrifugation can be used, but WO phase separation may be performed prior to the collection.
• 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 also called demulsification.
• the gelled body obtained by the gelling step is present on the separated W phase side. By separating this from the O phase, it becomes easier to collect the gelled body by solid-liquid separation such as filtration.
• the WO phase separation method can be carried out by appropriately selecting a method known as a demulsification method, but is preferably carried out by adding a certain amount of water-soluble organic solvent normally used in demulsification to the gel dispersion and heating it to separate it into O and W phases.
• 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).
• the above-mentioned water-soluble organic solvents include acetone, methanol, ethanol, isopropyl alcohol, etc. Of these, isopropyl alcohol is particularly suitable for use.
• 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 or more and 5 or less used when forming the emulsion.
• the water-soluble organic solvent is added in an amount of about 1/6 to 1/2 times 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 allowing the mixture to demulsify suitably.
• the surfactant migrates (extracts) to the O phase, so by removing the O phase, it is possible to obtain porous spherical silica that is free of surfactant impurities.
• the heating temperature range is 50°C or higher, preferably 50 to 80°C, and more preferably 60 to 70°C.
• the water-soluble organic solvent is added to the gel dispersion as described above, it is preferable to stir the mixture to prevent the gel dispersion from agglomerating.
• a known method is generally used for stirring, and a specific example is a mixer equipped with stirring blades.
• the degree of mixing is not particularly limited as long as the liquid surface rotates due to stirring.
• the stirring power using a mixer is 0.1 to 3.0 kW/m 3 , preferably 0.5 to 1.5 kW/m 3 .
• the appropriate stirring time is 0.5 to 24 hours, and preferably 0.5 to 1 hour.
• the W phase containing the gel is recovered.
• the O phase upper layer
• the O phase can be separated and removed by decantation or the like.
• the gelled body contained in the recovered W phase is collected by solid-liquid separation and dried to obtain the porous spherical silica of the present invention.
• a known method can be used to collect the gelled body, and specific examples include suction filtration and centrifugation.
• a general method can be used for drying, but it is preferable to adopt a fluid drying method in order to suppress the aggregation of particles. Specific examples include vibration drying, air flow drying, and spray drying.
• the aggregation of particles can be suppressed by replacing the solvent with an organic solvent with a low surface tension, or by rinsing the cake after solid-liquid separation with such an organic solvent.
• the organic solvent is preferably water-soluble, since it is easy to replace the water remaining inside the pores. Specific examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol.
• the drying shrinkage inside the pores can also be adjusted by solvent replacement or rinsing, making it possible to control the pore volume by appropriate drying shrinkage.
• solvent replacement the concentration of the water-soluble organic solvent is reduced and the proportion of water is increased, making drying shrinkage more likely to occur and reducing the pore volume.
• increasing the concentration of the water-soluble organic solvent suppresses drying shrinkage and tends to increase the pore volume.
• rinsing the pore volume can be reduced by reducing the amount of water-soluble organic solvent used.
• the temperature during drying is preferably equal to or higher than the boiling point of the solvent with the highest boiling point among the various solvents used from the preparation of the fumed silica dispersion to drying, and the pressure is preferably normal pressure or reduced pressure. Note that "equal to or higher than the boiling point" above means equal to or higher than the boiling point of the solvent under the pressure used during drying.
• the porous spherical silica of the present invention may be further calcined after drying. Calcination can remove organic matter and adjust the compressive strength. If the purpose is to remove organic matter, the calcination temperature should be equal to or higher than the boiling point of each organic matter used in the manufacturing method of the present invention. If the purpose is to adjust the compressive strength, the calcination conditions can be adjusted so that the target value is obtained; generally, the longer the calcination time and the higher the calcination temperature, the higher the compressive strength.
• Any known method can be used for firing, and a typical method is to place dried porous spherical silica in a crucible or quartz tray and heat it in an electric furnace.
• the atmosphere during firing is not particularly limited, and firing can be performed under an inert gas such as argon or nitrogen, or in the air.
• the heating rate during firing should be within a range that can be followed by the temperature rise of the heating device, such as an electric furnace.
• the slower the heating rate the lower the efficiency of the firing process, so it is preferable not to make it too slow.
• a heating rate of 2 to 10°C/min is suitable.
• the dried porous spherical silica, or the dried and calcined porous spherical silica may be further crushed.
• Crushing can be carried out using a general grinding machine, and specifically, methods using a ball mill, pin mill, vibration mill, bead mill, jet mill, Masscolloider (trade name), etc. are known. It is desirable to adjust the crushing conditions as desired depending on the equipment used, and it is sufficient that the particles are not destroyed and agglomerations are broken down.
• the particle size of the porous spherical silica obtained is almost the same as the droplet (W phase) diameter of the fumed silica dispersion in the W/O emulsion prepared in the emulsification process. Therefore, the dispersion conditions may be set so that the diameter is within the desired range.
• Various methods for controlling the droplet size in W/O emulsions are known, and these techniques may be appropriately selected and applied.
• known methods may be used, specifically, a method for adjusting the amount of surfactant added, or a method for adjusting the shear force applied during emulsification by the rotation speed, flow rate, etc.
• the droplets When adjusting by the amount of surfactant added, the droplets tend to become finer when a large amount of surfactant is used, and the droplets tend to become larger when a small amount is used.
• the droplets When adjusting by shear force, the droplets tend to become finer as the applied shear force increases, and the droplets tend to become larger as the applied shear force decreases.
• the pore volume can be controlled by drying shrinkage.
• a known method can be used to control drying shrinkage, specifically, a method of adjusting the concentration of the water-soluble solvent before drying.
• the pore volume can also be controlled by the firing conditions, and the higher the firing temperature and the longer the firing time, the smaller the pore volume.
• 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 high most frequent pore size.
• the specific surface area can be adjusted by appropriately selecting the specific surface area of the fumed silica used as the 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 firing conditions. In general, the higher the firing temperature and the longer the firing time, the lower the specific surface area.
• the alkali metal content can be easily reduced by using fumed silica, which is substantially free of alkali metals as a raw material as described above, and other raw materials that are also substantially free of alkali metals, and by taking sufficient care to avoid contamination (mixing in impurities) when manufacturing the product. If the aim is to further reduce the alkali metal content, the cake may be washed with water or an organic solvent after solid-liquid separation and before drying.
• BET specific surface area The BET specific surface area was measured using a BELSORP-miniX (manufactured by BEL Japan Co., Ltd.). The sample to be measured was dried at a temperature of 200° C. for 3 hours or more under a vacuum of 1 kPa or less, and an adsorption isotherm only on the nitrogen adsorption side at liquid nitrogen temperature was obtained, and the BET specific surface area was calculated by analyzing it using the BET method (Stephen Brunauer, P. H. Emmett and Edward Teller, J. Am. Chem. Soc. 60, 309 (1938)).
• Example 1 (Dispersion preparation process) To 200 ml of ion-exchanged water in which 6.65 g of urea was dissolved, 66 g of Reolosil QS-30 (manufactured by Tokuyama Corporation) was added while stirring with a homogenizer (manufactured by IKA, T25BS1) to pre-disperse the fumed silica. Next, using an ultrasonic homogenizer (manufactured by BRANSON, Sonifier SFX250), dispersion was performed twice for 2 minutes at 60% output to perform fine dispersion, thereby obtaining a fumed silica dispersion. The D50 value of the obtained dispersion was 0.12 ⁇ m and the D90 value was 0.16 ⁇ m.
• the dispersion preparation step was performed in a chiller cooled to 10° C.
• LS 13 320 manufactured by Beckman Coulter, Inc.
• the refractive index of water used as the solvent in the measurement was 1.333, and the refractive index of the particles was 1.46. From the obtained particle size distribution, the cumulative 50% diameter (D50 value) and cumulative 90% diameter (D90 value) on a volume basis were evaluated.
• the obtained W/O emulsion was gelled by being kept in a water bath at 80° C. for 3 hours while being stirred at 300 rpm using a four-paddle impeller having a blade diameter of 60 mm, a blade width of 20 mm and an oblique angle of 45 degrees.
• the resulting gel was filtered from the W phase using a suction filter.
• the collected gel was dried in a vacuum dryer at 150°C for 12 hours, and then calcined at 800°C for 1 hour.
• the physical properties of the porous spherical silica thus obtained are shown in Table 1.
• Example 2 Porous spherical silica was obtained in the same manner as in Example 1, except that the fine dispersion in the dispersion preparation step was carried out using a Nanomizer (NMS-200L D10, manufactured by Nanomizer Co., Ltd.) at a treatment pressure of 125 MPa.
• the physical properties of the obtained porous spherical silica are shown in Table 1.
• the dispersion obtained in the dispersion preparation step had a D50 value of 0.10 ⁇ m and a D90 value of 0.15 ⁇ m.
• Example 3 Porous spherical silica was obtained in the same manner as in Example 1, except that the fine dispersion in the dispersion preparation step was carried out using an Ultimizer (HJP-25005, manufactured by Sugino Machine Ltd.) at a treatment pressure of 150 MPa.
• Ultimizer HJP-25005, manufactured by Sugino Machine Ltd.
• the physical properties of the obtained porous spherical silica are shown in Table 1.
• the dispersion obtained in the dispersion preparation step had a D50 value of 0.09 ⁇ m and a D90 value of 0.12 ⁇ m.
• ⁇ Comparative Example 1> Porous spherical silica was obtained in the same manner as in Example 1, except that the fine dispersion conditions in the dispersion preparation step were changed to an output of 20%.
• the physical properties of the obtained porous spherical silica are shown in Table 1.
• the dispersion obtained in the dispersion preparation step had a D50 value of 0.20 ⁇ m and a D90 value of 0.25 ⁇ m.
• ⁇ Comparative Example 2> Porous spherical silica was obtained in the same manner as in Example 1, except that the microdispersion conditions in the dispersion preparation step were changed to one minute dispersion once.
• the physical properties of the obtained porous spherical silica are shown in Table 1.
• the dispersion obtained in the dispersion preparation step had a D50 value of 0.15 ⁇ m and a D90 value of 0.30 ⁇ m.
• Example 3 A fumed silica dispersion prepared in the same manner as in the dispersion preparation step of Example 1 was spray-dried to form granules, and then calcined at 800° C. for 1 hour to obtain porous spherical silica.
• the physical properties of the obtained porous spherical silica are shown in Table 1.
• the dispersion obtained in the dispersion preparation step had a D50 value of 0.11 ⁇ m and a D90 value of 0.14 ⁇ m.
• Example 3 As shown in Table 1, in Examples 1 to 3, the porous spherical silica had a high pore volume (pore volume measured by mercury intrusion porosimetry: 0.5 ml/g or more) and a mode pore diameter measured by mercury intrusion porosimetry: 5 nm or more, and thus had a large mode pore diameter, but the ratio of the pore volume present within ⁇ 5 nm of the mode pore diameter measured by mercury intrusion to the total pore volume (pore volume ratio) was 40% or more, and thus the pore diameter distribution was sharp. This can be achieved by adjusting the dispersion conditions so that the particle size distribution of the fumed silica dispersion falls within a predetermined range, and gelling the dispersion, according to the production method of the present invention.
• Comparative Example 1 The fumed silica dispersion prepared in Comparative Example 1 had a D50 value of 0.20 ⁇ m and a D90 value of 0.25 ⁇ m, both of which are larger than the specified range, and the pore volume fraction of the obtained porous spherical silica was 19%, with a broad pore size distribution. This was due to insufficient dispersion power, and when the dispersion state of the fumed silica dispersion is not appropriate, it is difficult to obtain the porous spherical silica of the present invention.
• Comparative Example 2 The fumed silica dispersion prepared in Comparative Example 2 had a D50 value of 0.15 ⁇ m, which was within the specified range, but a D90 value of 0.30 ⁇ m, which was larger than the specified range, and the pore volume fraction of the obtained porous spherical silica was 18%, with a broad pore size distribution. This is due to an insufficient dispersion time, and when the dispersion state of the fumed silica dispersion is not appropriate, it is difficult to obtain the porous spherical silica of the present invention.

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