Porous spherical silica and method for producing same

Abstract

Provided are: porous spherical silica having a large modal pore diameter and large pore volume, and also having a distinct pore diameter distribution; and a method for producing the same. This porous spherical silica is characterized by having a pore volume of 0.5-8 ml / g as determined by a mercury intrusion method and having a modal pore diameter of 5-50 nm as determined by the mercury intrusion method, wherein the proportion of the volume of pores having a size in the range of ±5 nm of the modal pore diameter with respect to the total pore volume is 40% or more. The porous spherical silica can be produced by shaping a dispersion of fumed silica dispersed so as to have a particle size distribution in a prescribed range into spheres via an emulsion method and then gelling the same.

Description

Porous spherical silica and its manufacturing method

[0001] The present invention relates to a novel porous spherical silica and a method for producing the same.

[0002] Porous silica has been extensively studied, and porous silica with a variety of physical properties has been proposed. Taking advantage of its properties, porous silica is used in a wide range of applications, including as a catalyst or fragrance carrier, an adsorbent, a cosmetic additive, an abrasive for industrial products, and a column packing for liquid chromatography. In particular, porous silica with a narrow pore size distribution is useful for catalyst carriers and column packing for liquid chromatography. Porous silica with the above properties can be produced, for example, by wet synthesis using alkoxysilane as a raw material (Patent Documents 1 and 2) or by spray-drying a dispersion of spherical silica microparticles (Patent Document 3). When using the porous silica as a column packing or catalyst carrier, adjusting the modal pore size according to the target components to be separated and the catalyst material to be supported enables good column separation ability and selective support of the catalyst material. Porous silica with a large modal pore size is particularly suitable for handling large separation components or catalyst carriers, and a porous silica with a large pore volume improves column separation efficiency and catalyst loading. Porous silica having a large mode pore diameter and a high pore volume can be produced, for example, by a method of gelling a fumed silica dispersion in a liquid (Patent Document 4).

[0003] JP 2007-76941 A JP 2008-120633 A JP 2010-138021 A WO 2022 / 154014 Pamphlet

[0004] However, it is difficult to achieve both a large modal pore size and a high pore volume while having a sharp pore size distribution. All of the porous spherical silicas described in Patent Documents 1 to 3 have sharp pore size distributions, but the porous spherical silicas described in Patent Documents 1 and 2 have a small modal 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 modal pore size and a high pore volume, but its pore size distribution is broad, making it unsuitable for use as a column packing or catalyst support.

[0005] Therefore, an object of the present invention is to provide porous spherical silica having a large modal pore size, a high pore volume, and a sharp pore size distribution, and a method for producing the same.

[0006] The present inventors have conducted extensive research to solve the above-mentioned problems, and as a result have found that, in the production process of porous spherical silica, porous spherical silica having a large modal pore size, a large pore volume, and a sharp pore size distribution can be produced by forming a fumed silica dispersion, which has been dispersed so as to have a particle size distribution within a predetermined range, into spheres by an emulsion method, and then gelling the spheres, thereby completing the present invention.

[0007] [1] Porous spherical silica characterized in that it has a pore volume measured by mercury intrusion porosimetry of 0.5 ml / g or more and 8 ml / g or less, a mode pore diameter measured by mercury intrusion porosimetry of 5 nm or more and 50 nm or less, and the ratio of the volume of pores existing within a range of ±5 nm of the mode pore diameter to the total pore volume is 40% or more.

[0008] [2] The porous spherical silica according to [1], wherein the volume of pores present within a range of ±5 nm of the most frequent pore diameter as determined by mercury intrusion porosimetry is 0.5 ml / g or more.

[0009] [3] The porous spherical silica according to [1] or [2], characterized in that the volume-based cumulative 50% diameter (D50) of the porous spherical silica measured by the Coulter counter method is in the range of 2 to 200 μm, and the ratio (D10 / D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is 0.3 or more.

[0010] [4] The specific surface area of ​​the porous spherical silica measured by the BET method is 100 m ２ / g or more, 400m ２ / g or less.

[0011] [5] The porous spherical silica according to any one of [1] to [4], characterized in that the alkali metal content is 50 ppm or less.

[0012] [6] A catalyst carrier comprising the porous spherical silica according to any one of [1] to [5]. [7] A column packing material comprising the porous spherical silica according to any one of [1] to [5]. [8] A cosmetic comprising the porous spherical silica according to any one of [1] to [5].

[0013] [9] An abrasive comprising the porous spherical silica according to any one of [1] to [5].

[10] A resin composition comprising the porous spherical silica according to any one of [1] to [5].

[11] An adsorbent comprising the porous spherical silica according to any one of [1] to [5].

[0014]

[12] A method for producing porous spherical silica according to any one of [1] to [5], comprising: preparing a fumed silica dispersion so that the particle size distribution of the fumed silica dispersion has a D50 value of 0.15 μm or less and a D90 value of 0.2 μm or less; 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; heating the emulsion to gel the aqueous phase to obtain a gelled dispersion; and recovering and drying the resulting gelled material from the liquid.

[0015] The porous spherical silica of the present invention has a sharp pore size distribution, and therefore, when used as a column packing material, it can efficiently separate specific target components. Furthermore, because it has a large pore volume, when used as a catalyst support, it can support a large amount of catalyst, and when used as a cosmetic additive, it can impart high oil absorption performance. In addition, as indicated by the high modal pore size, it has a large pore size, making it suitable for use as a column packing material for particularly large separation components or a support for supporting large catalyst components. Furthermore, when used as an abrasive for industrial products, etc., it facilitates the penetration of resin into the pores, facilitating fixation to the resin on the polishing pad.

[0016] In the manufacturing method of the present invention, porous spherical silica is synthesized by adjusting the particle size distribution of a fumed silica dispersion to fall within a predetermined range and then gelling the dispersion. By undergoing the gelling step as described above, the adjusted particle size distribution can be reflected in the pore skeleton, making it easy to obtain porous spherical silica with a sharp pore size distribution. Additionally, by using fumed silica as a raw material, the fumed silica itself has a structure that suppresses the reduction in pore volume due to drying shrinkage, making it possible to obtain porous spherical silica with a large modal pore size and a high pore volume without surface treatment.

[0017] The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0018] <Porous Spherical Silica> (Pore Volume) 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 porous spherical silica having a pore volume exceeding 8 ml / g. If the pore volume is 6 ml / g or less, production is easier, if it is 4 ml / g or less, it is even easier, and if it is 2.5 ml / g or less, it is particularly easy to produce. In particular, when the porous spherical silica of the present invention is used as a catalyst support, in order to achieve a high loading amount, 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.

[0019] (Modular pore diameter) The modal pore diameter measured by mercury intrusion porosimetry is 5 nm or more, preferably 10 nm or more, and more preferably 15 nm or more. The upper limit is 50 nm or less, preferably 30 nm or less. If the modal pore diameter is less than 5 nm, when used as a column packing material, many pores will not be used for separation, resulting in a decrease in separation efficiency. If the modal pore diameter exceeds 50 nm, the particle strength will decrease, making it difficult to apply to a column packing material. If the modal pore diameter is within the above range, the porous spherical silica will exhibit good separation ability and good handleability when used as a column packing material. When used as an abrasive for industrial products, etc., the porous spherical silica having a modal pore diameter within the above range allows resin to easily penetrate into the pores, making it easy to fix to the resin on the polishing pad.

[0020] (Proportion of pore volume within ±5 nm of the mode pore diameter to the total pore volume) The porous spherical silica of the present invention has a ratio of the volume of pores within ±5 nm of the mode pore diameter to the total pore volume (hereinafter sometimes simply referred to as "pore volume ratio") of 40% or more. A pore volume ratio below the above range can result in a decrease in the amount of catalytic substance supported and a deterioration in the separation ability of the column packing. The pore volume ratio is more preferably 45% or more, and even more preferably 50% or more. Porous spherical silica having a pore volume ratio within the above range has a sharp pore size distribution and uniform pore sizes. Therefore, when used as a catalyst support, efficient support of the catalytic substance can be achieved by selecting porous spherical silica with a mode pore diameter appropriate to the size of the catalytic substance. When used as a column packing, specific substances can be separated with high precision, resulting in good separation ability. Although there is no upper limit to the preferred range of the pore volume ratio, the upper limit is determined by the silica concentration of the fumed silica dispersion used as the raw material, and it is technically difficult to obtain one exceeding 90%.

[0021] (Circularity) 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 circularities obtained by image analysis of SEM images of 2000 or more porous spherical silica particles observed at 1000x magnification using an SEM. Here, "circularity" is a value determined by the following formula (1):

[0022] 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. Because the porous spherical silica of the present invention has the above properties, it can impart a smooth feel when used as a cosmetic additive.

[0023] (Pore volume within ±5 nm of the most common pore size) The pore volume within ±5 nm of the most common 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 within ±5 nm of the most common pore size being within the above range means that the pore volume of pores having a specific pore size is high. In particular, when used as a catalyst support, by selecting porous spherical silica having a most common pore size according to the size of the catalyst substance, it becomes possible to efficiently support the catalyst substance. Note that there is no upper limit to the preferred range of the pore volume within ±5 nm of the most common pore size, but it is technically difficult to obtain one exceeding 0.9 ml / g.

[0024] The pore diameter and pore volume were measured by mercury porosimetry after pretreatment by constant temperature drying at 120 ° C for 4 hours. The pore diameter was calculated using Washburn's formula (2): PD = -4σ cos θ (2) where P is pressure [psia / absolute pressure], σ is the surface tension of mercury, D is the pore diameter [μm], and θ is the contact angle with mercury. The surface tension of mercury was 480 dynes / cm, and the contact angle with mercury was 140 degrees. Measurements were performed on pore diameters of 0.0036 to 200 μm, and pore diameters larger than 100 nm were considered to be voids between particles, and the pore volume was calculated for pore diameters of 100 nm or less. In addition, the integrated 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 formed the main peak was taken as the most frequent pore diameter.

[0025] (Particle Size Distribution) 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 μm. Similarly, the ratio (D10 / D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is preferably 0.3 or greater. When the particle size distribution of the porous spherical silica is within 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 to 100 μm, particularly preferably 5 to 50 μm, and even more preferably 5 to 20 μm. 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.

[0026] (Specific Surface Area by BET Method) The porous spherical silica of the present invention has a specific surface area of ​​100 m2 by BET method. ２ / g or more, 400m ２ / g or less. The specific surface area is preferably 150 m ２ / g or more, and ２ / g or more, 350m ２ It is particularly preferable that the specific surface area of ​​the porous spherical silica obtained by the production method of the present invention is within a range of several tens of square meters from the specific surface area of ​​the fumed silica used as the raw material. ２If the fumed silica used as the raw material is selected so that the specific surface area of ​​the resulting porous spherical silica falls within the above range, gelation occurs easily and shaping into a spherical shape becomes easy. Generally, the specific surface area of ​​fumed silica is 400 m ２ / g or less, the specific surface area is 400m ２ It is difficult to obtain porous spherical silica having a specific surface area exceeding 1 / g. Here, the specific surface area is a value measured by the nitrogen adsorption BET multipoint method. If the specific surface area is within the above range, when the silica is used as a carrier or adsorbent for a catalyst or fragrance, the contact area with the reactant can be increased, which contributes to improving the reaction efficiency.

[0027] (Alkali Metal Content) The porous spherical silica of the present invention has an alkali metal content of 50 ppm or less (by mass). The alkali metal content is preferably 30 ppm or less, and 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 support. It is also extremely useful as an abrasive for semiconductors and other materials that should not contain alkali metals.

[0028] 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 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.

[0029] Because 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 the like, and an additive for various resin compositions.

[0030] <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 large modal pore diameter 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 and a large modal pore diameter can be obtained.

[0031] In addition, by dispersing the fumed silica dispersion so that the particle size distribution falls within a predetermined range and then gelling the dispersion, it becomes easy to reflect the dispersion state of the dispersion in the skeletal structure of the porous spherical silica, and porous spherical silica having a sharp pore size distribution can be obtained.

[0032] More specifically, a method for producing porous spherical silica includes preparing a fumed silica dispersion having a particle size distribution within a predetermined 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 (gel recovery step). Each step will be described in detail below.

[0033] (Dispersion Preparation Step) The dispersion preparation step is a step of dispersing fumed silica in water to prepare a dispersion.

[0034] A method for dispersing fumed silica in water includes a method in which fumed silica is preliminarily dispersed in water to prepare a dispersion, and then the dispersion is finely dispersed using a crusher, etc. Specific examples of crushers that can be used for fine dispersion include a ball mill, a bead mill, a vibration mill, a pin mill, an atomizer, a Nanomizer (trade name), an Ultimizer, a colloid mill, a homogenizer, a high-pressure homogenizer, and an ultrasonic homogenizer.

[0035] The operating conditions of the crusher or the like during fine dispersion are preferably adjusted depending on the device so that the fumed silica dispersion achieves a predetermined dispersion state. The dispersion state of the fumed silica dispersion can be confirmed by evaluating the D50 and D90 values ​​of the particle size distribution measured by laser diffraction scattering. The D50 value is preferably 0.15 μm or less, more preferably 0.13 μm or less, and particularly preferably 0.12 μm or less. The D90 value is preferably 0.20 μm or less, more preferably 0.18 μm or less, and particularly preferably 0.17 μm or less. It is preferable that both D50 and D90 satisfy the above ranges. If the 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 limit to the lower limits of the D50 and D90 values, it is difficult to obtain a fumed silica dispersion with a D50 value of 0.05 μm or less.

[0036] The particle size distribution of the dispersion was measured using an LS 13 320 (manufactured by Beckman Coulter, Inc.) The refractive index of water used as a 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.

[0037] Fumed silica that can be dispersed in water and can be gelled by heating, adjusting the 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 undergone surface treatment can be used. In addition, due to the ease of gelling, the specific surface area of ​​fumed silica is preferably 100 m. ２ / g or more, especially 200m ２ It is preferable to use one having a molecular weight of 250m / g or more. ２ 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. ２ It is preferable to use one having a molecular weight of 1 / g.

[0038] The specific surface area of ​​the porous spherical silica obtained by the method described here is several tens of square meters smaller than the specific surface area of ​​the fumed silica used as the raw material. ２ / g is subtracted from the specific surface area of ​​the porous spherical silica. Therefore, by appropriately selecting the fumed silica to be used as the raw material depending on the specific surface area of ​​the target porous spherical silica, the specific surface area of ​​the porous spherical silica can be controlled as desired without changing the production conditions. Note that the fumed silica used in the present invention can also be a mixture of silicas with different specific surface areas.

[0039] 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.

[0040] Generally, fumed silica is highly pure and contains almost no impurities such as alkali metals, so the alkali metal content of the produced porous spherical silica can be made extremely low.

[0041] 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, as described below, it is advisable to dissolve the base in water before dispersing the fumed silica.

[0042] The silica concentration in the fumed silica dispersion is preferably in the range of 10% by mass to 30% by mass, 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, but if the silica concentration is too high, the fluidity is lost and it becomes difficult to obtain a fumed silica dispersion.

[0043] The gelation of the fumed silica dispersion is accelerated by heating. If the gelation of the fumed silica dispersion progresses during the dispersion preparation step, the W phase will be less likely to become spherical in the subsequent W / O emulsion preparation step, and in extreme cases, the emulsion formation itself will be difficult. 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 step. 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 below, more preferably 12°C or below).

[0044] (W / O emulsion preparation step) 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.

[0045] 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.

[0046] The amount of the non-aqueous solvent used is not particularly limited as long as it is within a range that allows formation of a W / O emulsion, but generally, the non-aqueous solvent is used in an amount of about 1 to 10 parts by volume per part by volume of the fumed silica dispersion.

[0047] In this production method, it is preferable to add a surfactant when forming the W / O emulsion. Known surfactants used in forming W / O emulsions can be used without limitation, including anionic surfactants, cationic surfactants, and nonionic surfactants. Among these, nonionic surfactants are preferred because they facilitate the formation of W / O emulsions 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. Here, "HLB value" refers to the HLB value determined by the Griffin method. Specific examples of surfactants that can be used include sorbitan monooleate, sorbitan monostearate, and sorbitan monosesquioleate.

[0048] The amount of surfactant used is the same as that generally used when forming 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.

[0049] When forming a W / O emulsion, a known method for forming a W / O emulsion can be used as a method for dispersing a fumed silica dispersion in a non-aqueous solvent. From the viewpoint of ease of industrial production, emulsion formation by mechanical emulsification is preferred, and specific examples include methods using a mixer, homogenizer, etc. Preferably, a homogenizer can be used. This emulsification process produces an emulsion with a sharp particle size distribution of droplets in the aqueous phase, and therefore the particle size distribution of the spherical porous silica finally obtained is also sharp.

[0050] (Gelation Step) 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, 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 weakly acidic or basic state. The above-mentioned methods are preferred in that they allow the reaction to be controlled independently. The pH of a 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.

[0051] 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. or higher, more preferably 60° C. or higher. The upper limit is preferably 100° C. or lower, more preferably 90° C. or lower.

[0052] 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.

[0053] 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 intensity of the stirring may be strong enough to mix the W / O emulsion with the base.

[0054] 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 for pH adjustment, 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 entire solution by heating.

[0055] 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 when 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.

[0056] When the above heating or pH adjustment is carried out, stirring is preferably carried out to prevent the gel from agglomerating. A known stirring method is generally used, and a specific example is a mixer equipped with stirring blades.

[0057] Furthermore, after gelation, the dispersoid changes from a liquid state to a solid state, so the system is no longer a W / O emulsion but becomes a dispersion (suspension) in which a solid (gelled substance) is dispersed in a hydrophobic solvent.

[0058] (Gelated body recovery step) 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 carried out 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 also generally called demulsification. Here, the gelled body obtained by the gelling step is present in the separated W phase. By separating this from the O phase, the gelled body can be easily recovered by solid-liquid separation such as filtration.

[0059] 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 the mixture to separate it into an O phase and a W phase. After this process, the upper layer generally becomes the O phase (a layer mainly containing the organic solvent) and the lower layer becomes the W phase (a water layer containing the aqueous organic solvent and the gel).

[0060] Examples of the water-soluble organic solvent include acetone, methanol, ethanol, isopropyl alcohol, etc. Among these, isopropyl alcohol is particularly suitable.

[0061] The amount of the water-soluble organic solvent added is preferably adjusted depending on the type and amount of the surfactant used during emulsion formation and having an HLB of 3 or more and 5 or less. 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 suitably carried out.

[0062] In the WO phase separation, the surfactant is transferred (extracted) to the O phase side, and therefore, by removing the O phase, porous spherical silica free of surfactant impurities can be obtained.

[0063] The heating temperature range is 50°C or higher, preferably about 50 to 80°C, and more preferably about 60 to 70°C.

[0064] 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 power 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.

[0065] 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.

[0066] The gelled material contained in the recovered W phase is recovered by solid-liquid separation and dried to obtain the porous spherical silica of the present invention. Known methods can be used to recover the gelled material, and specific examples include suction filtration and centrifugation. While conventional drying methods can be used, fluidized drying methods are preferred to suppress particle aggregation. Specific examples include vibration drying, flash drying, and spray drying. Particle aggregation can also be suppressed by replacing the solvent with an organic solvent with low surface tension before drying, or by rinsing the cake after solid-liquid separation with such an organic solvent. The organic solvent is preferably water-soluble, as this facilitates replacement with water remaining in the pores. Specific examples of water-soluble organic solvents include acetone, methanol, ethanol, and isopropyl alcohol.

[0067] Since drying shrinkage inside the pores can be adjusted by solvent substitution or rinsing, it is possible to control the pore volume by appropriate drying shrinkage. When solvent substitution is performed, the concentration of the water-soluble organic solvent is reduced and the proportion of water is increased, which makes drying shrinkage more likely to occur and reduces the pore volume. Conversely, increasing the concentration of the water-soluble organic solvent suppresses drying shrinkage and increases the pore volume. When rinsing is performed, the pore volume is reduced by reducing the amount of water-soluble organic solvent used.

[0068] 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 the drying, and the pressure is preferably normal pressure or reduced pressure. Note that the above-mentioned "equal to or higher than the boiling point" means equal to or higher than the boiling point of the solvent under the pressure during drying.

[0069] The porous spherical silica of the present invention may be further calcined after drying. Calcination can remove organic substances and adjust the compressive strength. When the purpose is to remove organic substances, the calcination temperature should be equal to or higher than the boiling point of each organic substance used in the manufacturing method of the present invention. When the purpose is to adjust the compressive strength, the calcination conditions should 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.

[0070] 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.

[0071] 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.

[0072] 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 it too slow. When using a general electric furnace, a temperature rise rate of 2 to 10°C / min is suitable.

[0073] 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 crusher or the like, and specifically, methods using a ball mill, pin mill, vibration mill, bead mill, jet mill, Mass Colloider (trade name), etc. are known. The crushing conditions are desirably adjusted as needed depending on the equipment used, and may be such that the particles are not destroyed and agglomerations are broken down.

[0074] In the above-described production method, the particle size of the resulting porous spherical silica is approximately equal to the droplet (W phase) diameter of the fumed silica dispersion in the W / O emulsion prepared in the emulsification step. Therefore, dispersion conditions can be set to achieve the desired diameter 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.

[0075] The pore volume can 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 high modal pore size. 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.

[0076] 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.

[0077] Examples are given below to specifically explain the present invention, but the present invention is not limited to these examples.

[0078] <Evaluation Method> The produced porous spherical silica was evaluated for the following items.

[0079] (Measurement of particle size distribution and cumulative diameter on a volume basis 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 resulting dispersion was measured using a Multisizer III manufactured by Beckman Coulter, Inc. An aperture with a diameter of 100 μm was used for the measurement. From the obtained particle size distribution, the cumulative 50% diameter, cumulative 10% diameter, and cumulative 90% diameter on a volume basis were evaluated.

[0080] (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. The BET specific surface area was then analyzed and calculated by the BET method (Stephen Brunauer, P.H. Emmett and Edward Teller, J. Am. Chem. Soc. 60, 309 (1938)).

[0081] (Pore Volume and Pore Size Distribution) The pore volume and pore size distribution were measured using Autopore V9620 (manufactured by Micromeritics) in accordance with the above definitions.

[0082] (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, and the solution was heated at 180°C for 4 hours to evaporate 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 emission spectrometer (ICAP650DUO, manufactured by Thermo Scientific).

[0083] (Circularity) For 2000 or more porous spherical silica particles, SEM images were observed at a magnification of 1000 times using an SEM (S-5500 manufactured by Hitachi High-Technologies Corporation, accelerating voltage 3.0 kV, secondary electron detection), and the average circularity was calculated according to the above-mentioned definition.

[0084] Example 1 (Dispersion Preparation Step) To 200 ml of ion-exchanged water containing 6.65 g of urea dissolved therein, 66 g of Reolosil QS-30 (manufactured by Tokuyama Corporation) was added while stirring with a homogenizer (manufactured by IKA, model T25BS1), thereby pre-dispersing fumed silica. Next, using an ultrasonic homogenizer (manufactured by BRANSON, model Sonifier SFX250), dispersion was performed twice for 2 minutes at 60% output power to finely disperse the mixture, thereby obtaining a fumed silica dispersion. The D50 value of the obtained dispersion was 0.12 μm, and the D90 value was 0.16 μm. The dispersion preparation step was carried out in a chiller cooled to 10°C. An LS 13 320 (manufactured by Beckman Coulter, Inc.) was used to measure the particle size distribution of the obtained fumed silica dispersion. The refractive index of 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 (D50 value) and cumulative 90% diameter (D90 value) on a volume basis were evaluated.

[0085] (W / O emulsion preparation step) 65.5 g of the fumed silica dispersion prepared by the above method was taken out, and 129 g of decane in which 0.75 g of sorbitan monooleate (Rheodol SP-010V, manufactured by Kao Corporation) had been dispersed was added, followed by stirring for 3 minutes at 8,600 rpm using a homogenizer to obtain a W / O emulsion.

[0086] (Gelling Step) The obtained W / O emulsion was 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, and was kept in a water bath at 80°C for 3 hours to cause gelation.

[0087] (Gelation recovery step) 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 the mixture was separated into two layers, with the O phase as the upper layer and the W phase as the lower layer.

[0088] Then, the O phase and the W phase were separated by decantation, and the W phase was recovered.

[0089] The resulting gel was separated from the W phase using a suction filter. The recovered 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.

[0090] 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 μm and a D90 value of 0.15 μm.

[0091] 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 Corporation) at a treatment pressure of 150 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 0.09 μm and a D90 value of 0.12 μm.

[0092] Comparative Example 1 Porous spherical silica was obtained in the same manner as in Example 1, except that the micro-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 μm and a D90 value of 0.25 μm. Comparative Example 2 Porous spherical silica was obtained in the same manner as in Example 1, except that the micro-dispersion conditions in the dispersion preparation step were changed to one minute of 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 μm and a D90 value of 0.30 μm.

[0093] Comparative Example 3 A fumed silica dispersion prepared in the same manner as in 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 µm and a D90 value of 0.14 µm.

[0094]

[0095] <Evaluation Results> (Examples 1 to 3) As shown in Table 1, in Examples 1 to 3, the porous spherical silica had a high pore volume (measured by mercury intrusion porosimetry) of 0.5 ml / g or more, and a modal pore diameter (measured by mercury intrusion porosimetry) of 5 nm or more, and the modal pore diameter was large, but the ratio of the volume of pores existing within ±5 nm of the modal pore diameter (measured by mercury intrusion) to the total pore volume (pore volume ratio) was 40% or more, and 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 using the production method of the present invention.

[0096] Furthermore, in Examples 1 to 3, various apparatuses were used to finely disperse the fumed silica dispersion, and the operating conditions were also varied, but the resulting porous spherical silica all had a large modal pore size, a high pore volume, and a sharp pore size distribution. Thus, in the production method of the present invention, the dispersion method for the fumed silica dispersion is not limited, and porous spherical silica with a sharp pore size distribution can be obtained as long as the particle size distribution of the dispersion is within a predetermined range.

[0097] The fumed silica dispersion prepared in Comparative Example 1 had a D50 value of 0.20 μm and a D90 value of 0.25 μm, both of which were larger than the predetermined ranges, and the resulting porous spherical silica had a pore volume fraction of 19% and a broad pore size distribution. This was due to insufficient dispersing power; if the dispersion state of the fumed silica dispersion is not appropriate, it is difficult to obtain the porous spherical silica of the present invention.

[0098] (Comparative Example 2) The fumed silica dispersion prepared in Comparative Example 2 had a D50 value of 0.15 μm, which was within the specified range, but a D90 value of 0.30 μm, 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 was due to an insufficient dispersion time; if the dispersion state of the fumed silica dispersion is thus inappropriate, it is difficult to obtain the porous spherical silica of the present invention.

[0099] (Comparative Example 3) The D50 and D90 values ​​of the fumed silica dispersion prepared in Comparative Example 3 were both within the specified ranges, but the pore volume fraction of the obtained porous spherical silica was 22%, and its pore size distribution was broad. This was because the fumed silica dispersion was granulated by spray drying. Thus, even if the dispersion state of the dispersion is appropriate, the particle size distribution of the dispersion cannot be reflected in the pore skeleton unless the fumed silica dispersion is subjected to a step of gelling, making it difficult to obtain the porous spherical silica of the present invention.

Claims

1. Porous spherical silica characterized in that the pore volume measured by mercury intrusion porosimetry is 0.5 ml / g or more and 8 ml / g or less, the most frequent pore diameter measured by mercury intrusion porosimetry is 5 nm or more and 50 nm or less, and the ratio of the pore volume existing within a range of ±5 nm of the most frequent pore diameter to the total pore volume is 40% or more.

2. The porous spherical silica according to claim 1, characterized in that the volume of pores existing within a range of ±5 nm of the most frequent pore size as determined by mercury intrusion porosimetry is 0.5 ml / g or more.

3. The porous spherical silica according to claim 1, characterized in that the volume-based cumulative 50% diameter (D50) of the porous spherical silica measured by the Coulter counter method is in the range of 2 to 200 μm, and the ratio (D10 / D90) of the cumulative 10% diameter (D10) to the cumulative 90% diameter (D90) is 0.3 or more.

4. The specific surface area of ​​the porous spherical silica measured by the BET method is 100 m ２ / g or more, 400m ２ 2. The porous spherical silica according to claim 1, wherein the molecular weight of the porous spherical silica is 1 / g or less.

5. The porous spherical silica according to claim 1, characterized in that the alkali metal content is 50 ppm or less.

6. A catalyst carrier comprising the porous spherical silica according to any one of claims 1 to 5.

7. A column packing material comprising the porous spherical silica according to any one of claims 1 to 5.

8. A cosmetic product comprising the porous spherical silica according to any one of claims 1 to 5.

9. An abrasive comprising the porous spherical silica according to any one of claims 1 to 5.

10. A resin composition comprising the porous spherical silica according to any one of claims 1 to 5.

11. An adsorbent comprising the porous spherical silica according to any one of claims 1 to 5.

12. A method for producing the porous spherical silica according to claim 1, comprising the steps of: preparing a fumed silica dispersion so that the particle size distribution of the fumed silica dispersion has a D50 value of 0.15 μm or less and a D90 value of 0.2 μm or less; 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-water-soluble solvent; heating the emulsion to gel the aqueous phase to obtain a gelled body dispersion; and recovering and drying the resulting gelled body from the liquid.

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