Porous spherical silica and method for producing same

Abstract

Provided are: a porous spherical silica having a large number of pore diameters, a high pore volume, and a narrow pore diameter distribution; and a method for producing the porous spherical silica. [Solution] A porous spherical silica characterized by having a pore volume as determined by mercury intrusion method of 0.5-8 ml / g, a mode pore diameter as determined by mercury intrusion method of 5-50 nm, and a ratio of a pore volume in the range of + / -5 nm of the mode pore diameter to the total pore volume of 40% or more. A fumed silica dispersion, which is dispersed so that the particle size distribution reaches a prescribed range, is formed into a spherical shape by an emulsion method and then gelled, thereby being able to be produced.

Description

Technical Field

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

[0002] Various studies have been conducted on porous silica, and porous silica with a variety of physical properties has been proposed. Porous silica is used in a wide range of applications such as carriers of catalysts or spices, adsorbents, cosmetic additives, grinding agents for industrial products, and column fillers for liquid chromatography due to its characteristics. In particular, porous silica with a narrow pore size distribution is useful in the use of catalyst supports and column fillers for liquid chromatography. Porous silica with the above-mentioned characteristics is manufactured, for example, by a method for wet synthesis using alkoxysilane as a raw material (patent documents 1, 2) and a method for spray drying a dispersion of spherical silica particles (patent document 3). When the above-mentioned porous silica is used as a column filler or catalyst support, the mode pore size is adjusted according to the target component to be separated and the catalyst substance to be supported, thereby achieving good separation ability of the column and selective support of the catalyst substance. In particular, porous silica with a large mode pore size is suitable when processing larger separation components or catalyst supports. If it has a higher pore volume, the separation efficiency of the column and the supported amount of the catalyst are improved. Porous silica having a large numerical pore diameter and a high pore volume is produced, for example, by a method of gelling a fumed silica dispersion in a liquid (Patent Document 4).

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 2007-76941

[0006] Patent Document 2: Japanese Patent Application Laid-Open No. 2008-120633

[0007] Patent Document 3: Japanese Patent Application Laid-Open No. 2010-138021

[0008] Patent Document 4: International Publication No. 2022 / 154014 Pamphlet Summary of the Invention

[0009] Problems to be solved by the invention

[0010] However, it is difficult to achieve both a high mode pore size and a high pore volume while having a narrow pore size distribution. The porous spherical silicas described in Patent Documents 1 to 3 all have a narrow pore size distribution, but there are problems such as the small mode pore size of the porous spherical silicas described in Patent Documents 1 and 2, and the low pore volume of the porous spherical silica described in Patent Document 3. The porous spherical silica described in Patent Document 4, while having a large mode pore size and a high pore volume, has a wide pore size distribution, making it unsuitable for use as a column filler or catalyst support.

[0011] Therefore, an object of the present invention is to provide porous spherical silica having a large numerical pore diameter, a high pore volume, and a narrow pore diameter distribution, and a method for producing the same.

[0012] Solutions for solving problems

[0013] The present inventors have conducted extensive research to address the above-mentioned issues. As a result, they have discovered that, in the production process of porous spherical silica, by forming a fumed silica dispersion into spherical shapes using an emulsion method and then gelling the spherical shapes, porous spherical silica having a high numerical pore diameter, a high pore volume, and a narrow pore size distribution can be produced. This has led to the completion of the present invention described below.

[0014] [1] A porous spherical silica, characterized in that:

[0015] The pore volume based on mercury intrusion porosimetry is 0.5 ml / g or more and 8 ml / g or less,

[0016] The mode pore diameter based on mercury intrusion porosimetry is 5 nm or more and 50 nm or less.

[0017] The proportion of the pore volume existing in the range of ±5 nm of the aforementioned mode pore diameter relative to the total pore volume is 40% or more.

[0018] [2] The porous spherical silica according to [1], characterized in that the pore volume of the porous spherical silica within the range of ±5 nm of the mode pore diameter based on mercury intrusion porosimetry is 0.5 ml / g or more.

[0019] [3] The porous spherical silica according to [1] or [2], wherein the volume-based cumulative 50% particle size (D50) of the porous spherical silica measured by the Coulter counter method is in the range of 2 to 200 μm,

[0020] Likewise, the ratio (D10 / D90) of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) obtained was 0.3 or more.

[0021] [4] The porous spherical silica according to any one of [1] to [3], wherein the porous spherical silica has a specific surface area of 100 m 2 / g and above and 400m 2 / g or less.

[0022] [5] The porous spherical silica according to any one of [1] to [4], wherein the alkali metal content is 50 ppm or less.

[0023] [6] A catalyst support comprising the porous spherical silica according to any one of [1] to [5].

[0024] [7] A column packing material comprising the porous spherical silica according to any one of [1] to [5].

[0025] [8] A cosmetic comprising the porous spherical silica according to any one of [1] to [5].

[0026] [9] A polishing agent comprising the porous spherical silica according to any one of [1] to [5].

[0027]

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

[0028]

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

[0029]

[12] A method for producing porous spherical silica according to any one of [1] to [5], comprising the following steps:

[0030] A step of preparing a fumed silica dispersion so that the D50 value of the fumed silica dispersion in the particle size distribution is 0.15 μm or less and the D90 value is 0.2 μm or less;

[0031] A process for preparing a W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase containing a non-water-soluble solvent as a main component;

[0032] heating the emulsion to gel the aqueous phase to obtain a gel dispersion; and

[0033] The process of recovering the generated gel from the liquid and drying it.

[0034] Effects of the Invention

[0035] Porous spherical silica of the present invention has narrow pore size distribution, therefore can carry out the separation of specific target composition efficiently when using as column packing agent.In addition, owing to having high pore volume, therefore can increase the carrying capacity of catalyst when using as catalyst carrier, can give high oil absorption performance when being used for the purposes of cosmetic additive.In addition, as shown in high mode pore diameter, have large pore diameter equally, therefore, particularly can be suitable as the column packing agent with larger separation component as object, with the carrier that carries larger catalyst component as target and use.In addition, when using as the abrasive of industrial products etc., resin easily immerses hole inside, makes resin easily fixed on the grinding pad.

[0036] The manufacturing method of the present invention is to gel the dispersion after adjusting the particle size distribution of the fumed silica dispersion to a specified range, thereby synthesizing porous spherical silica. Through the process of gelation as described above, the adjusted particle size distribution can be reflected in the pore skeleton, and porous spherical silica with a narrow pore size distribution can be easily obtained. In addition, by using fumed silica as a raw material, since the fumed silica itself has a structure, the pore volume reduction caused by drying shrinkage can be suppressed, and even without surface treatment, porous spherical silica with a large pore size and a high pore volume can be obtained. DETAILED DESCRIPTION

[0037] The following embodiments are examples of the present invention, and the present invention is not limited to these embodiments.

[0038] <Porous spherical silica>

[0039] (Kong Rong)

[0040] For the porous spherical silica of the present invention, the pore volume measured by mercury intrusion is 0.5 ml / g or more and 8 ml / g or less. It is difficult to obtain a porous spherical silica with a pore volume as large as more than 8 ml / g. If it is 6 ml / g or less, it is easier to manufacture, if it is 4 ml / or less, it is easier to manufacture, and if it is 2.5 ml / g or less, it is particularly easy to manufacture. In particular, when the porous spherical silica of the present invention is used as a catalyst carrier, in order to have a high loading amount, the pore volume is preferably 0.6 ml / g or more, more preferably 0.7 ml / g or more, and 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 also have a high oil absorption when used as a cosmetic additive.

[0041] (Mode Aperture)

[0042] In addition, the mode pore size measured by mercury intrusion is more than 5nm, preferably more than 10nm, more preferably more than 15nm. In addition, the upper limit is below 50nm, preferably below 30nm. If the mode pore size is less than 5nm, then when used as a column packing agent, the holes that cannot be utilized in the separation increase, and the separation efficiency decreases. In addition, if the mode pore size exceeds 50nm, the reduction of particle strength occurs, and it is difficult to be applied to the column packing agent. If the mode pore size is the above-mentioned range, then when used as a column packing agent, good separating power is demonstrated, and operability is also good. When the porous spherical silica whose mode pore size is the above-mentioned range is used as an abrasive as an industrial product, resin is easily immersed in the hole interior, and resin is easily fixed on the grinding pad.

[0043] (Ratio of pore volume within the range of ±5 nm of the mode pore diameter to the total pore volume)

[0044] For the porous spherical silica of the present invention, the ratio of the pore volume within the range of the aforementioned mode pore diameter ± 5 nm relative to the total pore volume (hereinafter sometimes referred to as "pore volume") is 40% or more. When the pore volume is less than the above range, it will become the main reason for the reduction in the amount of catalyst material supported or the deterioration of the separation ability of the column filler. The pore volume is more preferably 45% or more, and further preferably 50% or more. The porous spherical silica with a pore volume in the above range has a narrow pore size distribution and a uniform pore size. Therefore, when used as a catalyst support, by selecting a porous spherical silica with a mode pore diameter corresponding to the size of the catalyst material, efficient support of the catalyst material can be achieved. When used as a column filler, specific substances can be separated with high precision, thereby showing good separation ability. It should be noted that there is no upper limit to the suitable range of the pore volume, and its upper limit is determined according to the silica concentration of the fumed silica dispersion used as a raw material, but it is technically difficult to obtain a pore volume of more than 90%.

[0045] (Circularity)

[0046] The shape of the porous spherical silica of the present invention is spherical. Here, spherical refers to that the average circularity obtained by image analysis using a scanning electron microscope (SEM) is more than 0.8. "Average circularity obtained by image analysis" refers to the sum of the circularity obtained by observing more than 2000 porous spherical silicas with a magnification of 1000 times using SEM and performing image analysis on the SEM image. Here, "circularity" is the value obtained by the following formula (1).

[0047] C=4πS / L 2 (1)

[0048] In the above formula (1), C represents 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 greater.

[0049] Since the porous spherical silica of the present invention has the above-mentioned properties, it can impart a smooth touch when used as a cosmetic additive.

[0050] (Pore volume within the range of ±5nm of the mode pore diameter)

[0051] The pore volume present in the range of the aforementioned mode pore size ± 5nm is preferably 0.5ml / g or more. More preferably 0.6ml / g or more, further preferably 0.65ml / g or more. The pore volume present in the range of the mode pore size ± 5nm represents a high pore volume of holes with a specific pore size in the above range, particularly when used as a catalyst support, by selecting a porous spherical silica with a mode pore size corresponding to the size of the catalyst substance, the catalyst substance can be efficiently supported. It should be noted that there is no upper limit to the suitable range of the pore volume present in the range of the mode pore size ± 5nm, but it is technically difficult to obtain a pore volume exceeding 0.9ml / g.

[0052] The pore diameter and pore volume are values measured by mercury intrusion porosimetry after pretreatment by constant temperature drying at 120° C. for 4 hours. The pore diameter was calculated using Washburn's formula (2).

[0053] PD=―4σcosθ (2)

[0054] Here, 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 is set to 480 dynes / cm, and the contact angle with mercury is set to 140 degrees. The measurement is carried out for pore diameters of 0.0036 to 200 μm. Pore diameters greater than 100 nm are considered to be interparticle spaces, and the pore volume is calculated for pore diameters below 100 nm. In addition, the integrated value of the pore volume relative to pore diameters below 100 nm, obtained by the same method, is differentiated, and the pore diameter of the main peak is used as the mode pore diameter.

[0055] (Particle size distribution)

[0056] The porous spherical silica of the present invention preferably has a volume-based cumulative 50% particle size (D50) in the range of 2 to 200 μm in the particle size distribution measured by the Coulter counter method. In addition, the ratio (D10 / D90) of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) obtained in the same manner is preferably 0.3 or more. If the particle size distribution of the porous spherical silica is within the above range, column clogging is unlikely to occur when used as a filler for an analytical column, making it easier to fill. D50 is preferably 2 to 100 μm, particularly preferably 5 to 50 μm, and more preferably 5 to 20 μm. D10 / D90 is preferably 0.4 or more, and more preferably 0.5 or more. It should be noted that D10 / D90 will not exceed 1.0 and is generally 0.6 or less.

[0057] (Specific surface area based on BET method)

[0058] The porous spherical silica of the present invention preferably has a specific surface area of 100 m2 based on the BET method. 2 / g and above and 400m 2 / g or less. The specific surface area is preferably 150m 2 / g or more, particularly preferably at 200m 2 / g and above and 350m 2 The specific surface area of the porous spherical silica obtained by the production method of the present invention is the specific surface area of the fumed silica used as a raw material minus several tenths of m2. 2 If the fumed silica used as the raw material is selected so that the specific surface area of the obtained porous spherical silica reaches the above range, it is easy to gel and be formed into a spherical shape. Usually, the specific surface area of fumed silica is 400m 2 / g or less, so it is difficult to obtain a specific surface area exceeding 400m 2 / g of porous spherical silica. Here, 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, it can increase the contact area with the reactants when used as a catalyst or fragrance carrier or adsorbent, which helps improve the reaction efficiency.

[0059] (Alkali metal content)

[0060] The alkali metal content of the porous spherical silica of the present invention is 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 catalytic activity will not be reduced due to the presence of impurities, and the porous spherical silica can be suitably used as a catalyst carrier. In addition, it is extremely useful as an abrasive for materials such as semiconductors that are not suitable for containing alkali metals.

[0061] The porous spherical silica of the present invention can be either hydrophilic or hydrophobic. The porous spherical silica of the present invention produced by the manufacturing method described below is hydrophilic. After obtaining the hydrophilic porous spherical silica by the manufacturing method, a method for appropriately applying the silica surface treatment can be used to obtain a hydrophobic porous spherical silica. Here, "hydrophilic" means that it can be dispersed in water without an organic solvent.

[0062] The porous spherical silica of the present invention has the above-mentioned properties and can be used as a filler for analytical columns, a carrier for catalysts or fragrances, an adsorbent for carbon dioxide, etc., a cosmetic additive, a polishing agent for industrial products, etc., and an additive for various resin compositions.

[0063] <Method for producing porous spherical silica>

[0064] The method for manufacturing the porous spherical silica of the present invention is not particularly limited, but by using a fumed silica dispersion as a raw material, it is easy to achieve the aforementioned high pore volume and the majority number pore diameter. Typically, fumed silica has a structure formed by the aggregation of particulate silica (primary particles). Therefore, a fumed silica dispersion is used as the raw material of the porous spherical silica, and the fumed silica in the dispersion is gelled to form a network, thereby being able to suppress the pore volume reduction caused by drying shrinkage, and a porous spherical silica with a high pore volume and the majority number pore diameter can be obtained.

[0065] Furthermore, by dispersing the fumed silica dispersion so that the particle size distribution falls within a predetermined range and then gelling it, the dispersion state of the dispersion is easily reflected in the skeleton structure of the porous spherical silica, and porous spherical silica having a narrow pore size distribution can be obtained.

[0066] More specifically, the following method can be cited: preparing a fumed silica dispersion so that the particle size distribution falls within a predetermined range (dispersion preparation step); preparing a W / O emulsion composed of an aqueous phase in which the fumed silica is dispersed and an organic phase containing a non-water-soluble solvent as a main component (W / O emulsion preparation step); then, heating the emulsion to gel the aqueous phase to obtain a porous spherical silica dispersion (gelation step); and then, recovering the generated porous spherical silica from the liquid and drying it (gel recovery step), thereby producing porous spherical silica. Each step is described in detail below.

[0067] (Dispersion Preparation Step)

[0068] The dispersion preparation step is a step of dispersing fumed silica in water to prepare a dispersion.

[0069] Examples of methods for dispersing fumed silica in water include preparing a dispersion in which fumed silica is preliminarily dispersed in water, and finely dispersing the dispersion using a crusher or the like. Specifically, examples of crushers that can be used for fine dispersion include ball mills, bead mills, vibration mills, pin mills, atomizers, Nanomizer (trade name), Ultimizers, colloid mills, homogenizers, high-pressure homogenizers, and ultrasonic homogenizers.

[0070] The operating conditions of the crusher, etc. during micro-dispersion are preferably adjusted according to the device to achieve a specified dispersion state of the fumed silica dispersion. The dispersion state of the fumed silica dispersion 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 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 should be noted that preferably both D50 and D90 meet the above ranges.

[0071] If the D50 and D90 values are within the above ranges, porous spherical silica with a narrow pore size distribution can be obtained. There is no lower limit for the D50 and D90 values, but it is difficult to obtain a fumed silica dispersion with a D50 value of 0.05 μm or less.

[0072] The particle size distribution of the dispersion was measured using LS13 320 (manufactured by Beckman Coulter, Inc.) The volume-based cumulative 50% and 90% particle sizes were evaluated based on the obtained particle size distribution, using the refractive index of water used as the solvent at 1.333 and the refractive index of the particles at 1.46.

[0073] As fumed silica, fumed silica that can be dispersed in water and can be gelled by heating, adjusting pH, etc. can be used. This property is achieved by having a large number of silanol groups on the surface of the silica. Therefore, as long as it is fumed silica that has not been so-called surface treated, most fumed silica can be used. In addition, from the perspective of facilitating gelation, it is preferred to use a specific surface area of 100 m 2 / g or above, especially 200m 2 / g or more. More preferably 250m 2 / g or more. The larger the specific surface area, the faster the gelation process, and the easier it is to gel the droplets (W phase) dispersed with the fumed silica. From the perspective of easy availability, it is preferred to use 400m 2 / g as the upper limit.

[0074] The specific surface area of the porous spherical silica obtained by the method described here is the specific surface area of the fumed silica used as a raw material minus several tenths of a micron. 2 The value obtained by % / g. 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 should be noted that the fumed silica used in the present invention can also be used by mixing those with different specific surface areas.

[0075] The above-mentioned fumed silica is commercially available. For example, various hydrophilic grades of Reolosil from Tokuyama Co., Ltd., 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.

[0076] Generally, fumed silica is of high purity and contains almost no impurities such as alkali metals. Therefore, the alkali metal content of the produced porous spherical silica can be made extremely low.

[0077] Water is essential as a solvent for this step, but other solvents may be included within the range that does not hinder emulsion formation and subsequent gelation. In addition, when a latent base is used to promote gelation described later, the fumed silica may be dissolved in water before dispersing it.

[0078] The silica concentration in the fumed silica dispersion is preferably in the range of 10% to 30% by mass. It is more preferably 15% by mass or greater, and particularly preferably 20% by mass or greater. The higher the silica concentration in the fumed silica dispersion, the faster the gelation rate. However, if the silica concentration is too high, the dispersion loses fluidity, making it difficult to prepare the fumed silica dispersion.

[0079] Heating accelerates the gelation of the fumed silica dispersion. When the gelation of the fumed silica dispersion is carried out in the dispersion preparation step described above, it is difficult for the W phase to form a spherical shape in the subsequent W / O emulsion preparation step. In extreme cases, the formation of the emulsion itself becomes difficult. Therefore, in the dispersion preparation step, the liquid temperature of the fumed silica dispersion is preferably maintained below room temperature (20°C). When the specific surface area or concentration of the fumed silica is high and gelation is easy to proceed, cooling to a temperature below room temperature (preferably below 15°C, more preferably below 12°C) is also effective.

[0080] (W / O emulsion preparation process)

[0081] The W / O emulsion preparation step involves dispersing the fumed silica dispersion obtained in the dispersion preparation step in a non-aqueous solvent to form a W / O emulsion. Forming this W / O emulsion causes the fumed silica dispersion, serving as the dispersoid, to become spherical due to surface tension and other factors. Consequently, the spherical fumed silica dispersion dispersed in the non-aqueous solvent is gelled, yielding a spherical gel.

[0082] As the non-water-soluble solvent used in this manufacture method, any solvent having a hydrophobicity that can form an emulsion with the fumed silica dispersion can be used. As such a solvent, for example, organic solvents such as hydrocarbons and halogenated hydrocarbons can be used. More specifically, non-water-soluble solvents such as hexane, heptane, octane, nonane, decane, liquid paraffin, methylene chloride, chloroform, carbon tetrachloride, and dichloropropane can be mentioned. Among them, hexane, heptane, and decane with appropriate viscosity can be suitably used. It should be noted that, as required, a variety of solvents can also be mixed and used. In addition, as long as an emulsion can be formed with the fumed silica dispersion, hydrophilic solvents such as lower alcohols (used as a mixed solvent) can also be used.

[0083] The amount of the water-insoluble solvent used is not particularly limited as long as it can form a W / O emulsion. Generally, the water-insoluble solvent is used in an amount of about 1 to 10 parts by volume per 1 part by volume of the fumed silica dispersion.

[0084] In the present manufacturing method, when forming the above-mentioned W / O emulsion, a surfactant is preferably added. As the surfactant used, known surfactants that can be used for the formation of W / O emulsions can be used without limitation, and anionic surfactants, cationic surfactants and nonionic surfactants can all be used. Among them, nonionic surfactants are preferred from the viewpoint of easy formation of W / O emulsions and less likely to be mixed with alkali metals. Surfactants having an HLB value of 3 or more and 5 or less, which represents the degree of hydrophilicity and hydrophobicity, are particularly suitable. It should be noted that the "HLB value" here refers to the HLB value obtained based on the Griffin method. Specific examples of surfactants that can be used include: sorbitan monooleate, sorbitan monostearate, sorbitan monosesquioleate, etc.

[0085] The amount of surfactant used is not different from the conventional amount used in forming a W / O emulsion. Specifically, it is preferably in the range of 0.05 g to 10 g per 100 ml of the fumed silica dispersion.

[0086] As a method for making the fumed silica dispersion liquid be dispersed in a non-water-soluble solvent when forming a W / O emulsion, the known formation method of the W / O emulsion can be adopted. From the viewpoints such as being easy to industrial manufacturing, it is preferred to utilize mechanical emulsification to form the emulsion. Specifically, a method using a mixer, a homogenizer, etc. can be exemplified. Preferably, a homogenizer can be used. By this emulsification process, an emulsion with a narrow particle size distribution of the droplets of the aqueous phase can be obtained. Therefore, the particle size distribution of the spherical porous silica finally obtained is also narrow.

[0087] (Gelation process)

[0088] The gelation process is a process for gelling the fumed silica dispersion in a state where the droplets of the fumed silica dispersion are dispersed in a non-water-soluble solvent after the W / O emulsion preparation process. The gelation can be carried out using a known method. For example, gelation can be easily carried out by heating to a high temperature or adjusting the pH of the fumed silica dispersion to a weak acid or even alkaline state. From the viewpoint of being able to mainly control the reaction, the above method is preferred. It should be noted that the pH of the fumed silica dispersion prepared by the above method and not pH-adjusted is generally in the range of 3.0 to 4.5.

[0089] When heating is performed, the boiling point of each solvent used should not be exceeded, and the lower limit of the gelation temperature is preferably 50°C or higher, more preferably 60°C or higher, and the upper limit is preferably 100°C or lower, more preferably 90°C or lower.

[0090] The pH adjustment can be easily performed by the following methods: a method in which a substance such as urea, which decomposes upon heating and becomes alkaline (called a "latent base") is pre-mixed with the fumed silica dispersion and then heated during gelation to raise the pH; or a method in which a base is added to the emulsion while stirring it with a mixer or the like and maintaining the W / O emulsion in a formed state.

[0091] Specific examples of the base include ammonia; tetraalkylammonium hydroxides such as tetramethylammonium hydroxide (TMAH); amines such as trimethylamine; alkali metal hydroxides such as sodium hydroxide; alkali metal carbonates such as sodium carbonate and sodium bicarbonate; and alkali metal silicates. The stirring intensity should be strong enough to cause mixing of the W / O emulsion and the base.

[0092] Among the aforementioned pH adjustment methods, methods utilizing thermal decomposition of a latent base such as urea are preferred from the perspective of preventing contamination of metallic elements, or methods using ammonia, tetraalkylammonium hydroxides, or amines as the base. When ammonia is used for pH adjustment, it can be injected as a gas or added as aqueous ammonia. Urea is particularly preferred for pH adjustment because it allows for uniform pH adjustment across the entire system by heating.

[0093] When adjusting the pH to promote gelation, it is particularly preferred to adjust the amount added so that the pH of the fumed silica dispersion is raised to approximately 4.5 to 8.0. The same applies to the use of a latent base. For example, when urea is used, the specific amount added is preferably 1% by mass or greater, particularly preferably 2% by mass or greater, relative to the fumed silica dispersion. The upper limit is preferably 7% by mass or less, and more preferably 5% by mass or less.

[0094] During the heating and pH adjustment, stirring is preferably performed to prevent the gel from agglomerating. A known method is generally used for stirring, and a mixer equipped with a stirring blade can be used as a specific example.

[0095] In addition, after gelation, the dispersoid changes from a liquid to a solid state. Therefore, the system forms a dispersion (suspension) in which a solid (gel) is dispersed in a hydrophobic solvent, and is no longer a W / O emulsion.

[0096] (Gel recovery process)

[0097] In this production method, the gel produced as described above is recovered from the liquid. Conventional solid-liquid separation methods such as filtration and centrifugation can be used to recover the gel, but W-O phase separation can also be performed before recovery. W-O phase separation refers to the separation of the gel dispersion into two layers: the O phase and the W phase. This operation is also commonly referred to as demulsification. The gel obtained from the gelation step is present on the W phase side after separation. By separating this from the O phase, solid-liquid separation using filtration or the like is facilitated for recovery of the gel.

[0098] The WO phase separation method can be appropriately selected from known methods for demulsification. Preferably, the method is as follows: a certain amount of a water-soluble organic solvent, typically used for demulsification, is added to a gel dispersion and heated to separate the phases O and W. This process typically results in an upper layer consisting of the O phase (a layer primarily composed of the organic solvent) and a lower layer consisting of the W phase (a water layer containing the aqueous organic solvent and the gel).

[0099] Examples of the water-soluble organic solvent include acetone, methanol, ethanol, and isopropyl alcohol, among which isopropyl alcohol can be particularly preferably used.

[0100] The amount of the water-soluble organic solvent added is preferably adjusted according to the type and amount of the surfactant having an HLB of 3 or higher and 5 or lower used to form the emulsion. For example, when sorbitan monooleate is used as the surfactant, demulsification can be suitably achieved by adding a water-soluble organic solvent at a mass ratio of approximately 1 / 6 to 1 / 2 (water-soluble organic solvent / water-insoluble organic solvent) relative to the mass of the water-insoluble organic solvent, stirring as needed, and then allowing the mixture to stand.

[0101] During the WO phase separation, the surfactant migrates to the O phase side (extraction). Therefore, by removing the O phase, porous spherical silica free of impurities due to the surfactant can be obtained.

[0102] The heating temperature range is 50°C or higher, preferably about 50 to 80°C, and more preferably about 60 to 70°C.

[0103] As described above, after the water-soluble organic solvent is added to the gel dispersion, it is preferably stirred to prevent the gels from agglomerating. A known method is generally used for stirring. Specifically, a mixer equipped with a stirring blade can be used. The degree of mixing is not particularly limited, as long as the liquid surface is rotated by stirring. For example, stirring using a mixer is 0.1 to 3.0 kW / m 3 , preferably 0.5~1.5kW / m 3 The stirring time is suitably 0.5 to 24 hours, preferably about 0.5 to 1 hour.

[0104] 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.

[0105] The gel contained in the recovered W phase is subjected to solid-liquid separation and recovered and dried to obtain the porous spherical silica of the present invention. As a recovery method for the gel, known methods can be used. If specific examples are given, suction filtration and centrifugation are available. As a drying method, general methods can be used, but it is preferred to adopt a fluidized drying method to suppress the aggregation of particles. Specifically, vibration drying, airflow drying, spray drying, etc. can be mentioned. In addition, before drying, the solvent can be replaced with an organic solvent having low surface tension or the filter cake after solid-liquid separation can be rinsed with these organic solvents to suppress the aggregation of particles. As the above-mentioned organic solvent, it is preferably water-soluble from the viewpoint of easily replacing the water remaining in the pore interior. As a specific example of a water-soluble organic solvent, there are acetone, methanol, ethanol, isopropanol, etc.

[0106] Solvent replacement and rinsing can also be used to adjust drying shrinkage within the pores. Therefore, by adjusting drying shrinkage appropriately, pore volume can be controlled. When performing solvent replacement, reducing the concentration of the water-soluble organic solvent and increasing the proportion of water tends to induce drying shrinkage, resulting in a decrease in pore volume. Conversely, increasing the concentration of the water-soluble organic solvent suppresses drying shrinkage and increases pore volume. When performing rinsing, reducing the amount of water-soluble organic solvent used reduces pore volume.

[0107] The drying temperature is preferably at least 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 process, and the drying process is preferably carried out under normal pressure or reduced pressure. It should be noted that the term "at least the boiling point" refers to the boiling point of the solvent under the pressure used during drying.

[0108] The porous spherical silica of the present invention can also be further calcined after drying. By calcining, the removal of organic matter and the adjustment of compressive strength can be carried out. In the case of removing organic matter for the purpose, the calcining temperature is as long as it is above the boiling point of each organic matter used in the manufacture method of the present invention. In addition, in the case of adjusting the compressive strength for the purpose, the calcining conditions can be adjusted in a way that the target value can be obtained, and the general direction is that the longer the calcining time is, the higher the calcining temperature is, the higher the compressive strength is.

[0109] As the firing method, a known method can be used. Generally, a method in which dried porous spherical silica is placed in a crucible, a quartz pot, or the like and heated in an electric furnace is exemplified.

[0110] The atmosphere during firing is not particularly limited, and the firing can be performed under an inert gas such as argon or nitrogen, or in an air atmosphere.

[0111] The heating rate during firing can be adjusted to a range that allows the temperature rise of a heating device such as an electric furnace to be maintained. Slower heating rates reduce the efficiency of the firing process, so it is best not to be extremely slow. When using a conventional electric furnace, a heating rate of 2 to 10°C / minute is suitable.

[0112] The porous spherical silica after drying or the porous spherical silica after drying and firing can also be further crushed. Crushing can be carried out using a general pulverizer, and specifically, it is known that there are methods for processing using a ball mill, a pin mill, a vibration mill, a bead mill, a jet mill, a Masscolloider (trade name, attritor) etc. Crushing conditions are expected to be arbitrarily adjusted according to the equipment used, as long as the particles are not destroyed to the extent of dissolving the aggregation.

[0113] In the above-mentioned manufacturing method, the particle size of the obtained porous spherical silica is substantially consistent with the diameter of the droplets (W phase) of the fumed silica dispersion in the W / O emulsion prepared in the emulsification process. Therefore, the dispersion conditions can be set in a manner to achieve the target diameter range. There are many known methods for controlling the diameter of droplets in W / O emulsions, and these techniques can be appropriately selected and applied. As a method for adjusting the droplet particle size, known methods can be used, specifically: a method for adjusting the amount of surfactant added; a method for adjusting the shear force applied during emulsification by rotating speed, flow rate, etc. When adjusting based on the amount of surfactant added, if the amount of surfactant used is large, the droplets tend to become fine, and if the amount used is small, the droplets tend to become larger. In addition, when adjusting based on shear force, the greater the shear force applied, the easier it is for the droplets to become fine, and the smaller the shear force, the easier it is for the droplets to become larger.

[0114] The pore volume can be controlled by drying shrinkage. The method for controlling drying shrinkage can use a known method, specifically, a method for adjusting the concentration of the water-soluble solvent before drying. The pore volume can also be controlled by the firing conditions, and the direction is that the higher the firing temperature and the longer the firing time, the smaller the pore volume. In addition, by using fumed silica as a raw material as in the manufacturing method of the present invention, the aforementioned high mode pore diameter is achieved because the fumed silica has an aggregated structure. The specific surface area can be adjusted by appropriately selecting the specific surface area of the fumed silica used as the raw material. In addition, it can also be adjusted by the gelation time. The direction is that the shorter the gelation time, the higher the specific surface area. The specific surface area can also be adjusted by firing conditions. Generally speaking, the direction is that the higher the firing temperature and the longer the firing time, the lower the specific surface area.

[0115] As described above, as long as fumed silica that is substantially free of alkali metals is used as the raw material, and other raw materials that are also substantially free of alkali metals are used, and those skilled in the art pay sufficient attention to avoid contamination (impurity mixing) during production, the alkali metal content can be easily reduced. In addition, when the goal is to reduce the alkali metal content, the filter cake can be washed with water, an organic solvent, etc. after solid-liquid separation and before drying.

[0116] Example

[0117] Hereinafter, examples are shown for specifically explaining the present invention, but the present invention is not limited to these examples.

[0118] Evaluation Method

[0119] The produced porous spherical silica was evaluated with respect to the following items.

[0120] (Particle size distribution and volume-based cumulative particle size were measured using a Coulter counter)

[0121] 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 IC1510J-DTH). The particle size distribution of the resulting dispersion was measured using a Multisizer III manufactured by Beckman Coulter, Inc. A pore size of 100 μm was used for the measurement. Based on the obtained particle size distribution, the cumulative 50% particle size, the cumulative 10% particle size, and the cumulative 90% particle size based on volume were evaluated.

[0122] (BET specific surface area)

[0123] 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 200°C for at least 3 hours under a vacuum of 1 kPa or less. An adsorption isotherm was obtained for the nitrogen adsorption side at liquid nitrogen temperature. The surface area was calculated by analysis using the BET method (Stephen Brunauer, P.H. Emmett and Edward Teller, J. Am. Chem. Soc. 60, 309 (1938)).

[0124] (Pore volume and pore size distribution)

[0125] The pore volume and pore size distribution were measured according to the above definitions using AutoPore V9620 (manufactured by Micromeritics).

[0126] (Alkali metal content)

[0127] To 1 g of porous spherical silica, 10 ml of nitric acid and 10 ml of hydrofluoric acid were added and dissolved, and the mixture 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 volume was fixed 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 (Thermo Scientific, ICAP650DUO).

[0128] (Circularity)

[0129] At least 2,000 porous spherical silica particles were observed at 1,000x magnification using a SEM (S-5500 manufactured by Hitachi High Technologies, accelerating voltage 3.0 kV, secondary electron detection). The observed SEM images were analyzed and the average circularity was calculated according to the above definition.

[0130] <Example 1>

[0131] (Dispersion Preparation Step)

[0132] In 200 ml of ion exchange water in which 6.65 g of urea was dissolved, 66 g of Reolosil QS-30 (manufactured by Tokuyama Co., Ltd.) was added while stirring with a homogenizer (manufactured by IKA, T25BS1) to pre-disperse the fumed silica. Subsequently, an ultrasonic homogenizer (manufactured by BRANSON, Sonifier SFX250) was used to disperse the mixture twice for 2 minutes at an output power of 60% to obtain a fumed silica dispersion. The D50 value of the obtained dispersion was 0.12 μm, and the D90 value was 0.16 μm. It should be noted that the dispersion preparation process was carried out in a cooler cooled to 10° C. LS13 320 (manufactured by Beckman Coulter, Inc.) was used in the particle size distribution measurement of the obtained fumed silica dispersion. The refractive index of water used as a solvent in the measurement was set to 1.333, and the refractive index of the particles was set to 1.46. Based on the obtained particle size distribution, the cumulative 50% particle size (D50 value) and the cumulative 90% particle size (D90 value) on a volume basis were evaluated.

[0133] (W / O emulsion preparation process)

[0134] 65.5 g of the fumed silica dispersion prepared by the above method was separated, and 129 g of decane in which 0.75 g of sorbitan monooleate (Rheodol SP-010V, manufactured by Kao Corporation) was dispersed was added. The mixture was then stirred at 8600 rpm for 3 minutes using a homogenizer to obtain a W / O emulsion.

[0135] (Gelation process)

[0136] The obtained W / O emulsion was kept in a water bath at 80° C. for 3 hours while being stirred at 300 rpm using four paddles having a blade diameter of 60 mm, a blade width of 20 mm, and an inclination angle of 45 degrees to cause gelation.

[0137] (Gel recovery process)

[0138] 77 g of isopropyl alcohol and 52 g of water were added, and the mixture was stirred with a stirring blade while being maintained at 70° C. for 30 minutes. The mixture was then allowed to stand to separate into two layers, with the O phase as the upper layer and the W phase as the lower layer.

[0139] Next, the O phase and the W phase were separated by decantation, and the W phase was recovered.

[0140] The obtained gel was filtered out 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.

[0141] <Example 2>

[0142] 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 (manufactured by Nanomizer Co., Ltd., NMS-200L D10) 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.

[0143] <Example 3>

[0144] Porous spherical silica was obtained in the same manner as in Example 1, except that the fine dispersion in the dispersion preparation step was performed using an Ultimizer (HJP-25005, manufactured by SUGINO MACHINE LIMITED CO., LTD.) 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.

[0145] Comparative Example 1

[0146] In 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 μm and a D90 value of 0.25 μm.

[0147] Comparative Example 2

[0148] In 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 a dispersion cycle of 1 minute. 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.

[0149] Comparative Example 3

[0150] The fumed silica dispersion prepared in the same manner as in the dispersion preparation step of Example 1 was spray-dried and granulated, 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.

[0151] [Table 1]

[0152]

[0153] <Evaluation Results>

[0154] (Examples 1 to 3)

[0155] As shown in Table 1, Examples 1 to 3 have a pore volume of 0.5 ml / g or greater as measured by mercury intrusion porosimetry, indicating a high pore volume. Furthermore, the mode pore diameter as measured by mercury intrusion porosimetry is 5 nm or greater, indicating a large mode pore diameter for the porous spherical silica. Furthermore, the proportion of pore volume within the range of ±5 nm of the mode pore diameter as measured by mercury intrusion porosimetry relative to the total pore volume (pore volume fraction) is 40% or greater, indicating a narrow pore size distribution. This can be achieved by adjusting the dispersion conditions in the production method of the present invention so that the particle size distribution of the fumed silica dispersion falls within a specified range and causing the dispersion to gel.

[0156] Furthermore, in Examples 1-3, various apparatuses and operating conditions were used to microdisperse the fumed silica dispersion, but the resulting porous spherical silica all had a majority pore diameter, high pore volume, and a narrow pore size distribution. This demonstrates that, in the production method of the present invention, the dispersion method of the fumed silica dispersion is not limited; as long as the particle size distribution of the dispersion is within a specified range, porous spherical silica with a narrow pore size distribution can be obtained.

[0157] (Comparative Example 1)

[0158] The D50 value of the fumed silica dispersion prepared in Comparative Example 1 was 0.20 μm, and the D90 value was 0.25 μm, both exceeding the specified ranges. The resulting porous spherical silica had a porosity of 19% and a wide pore size distribution. This is due to insufficient dispersing force. This demonstrates that it is difficult to obtain the porous spherical silica of the present invention if the dispersion state of the fumed silica dispersion is inappropriate.

[0159] (Comparative Example 2)

[0160] The D50 value of the fumed silica dispersion prepared in Comparative Example 2 was 0.15 μm, within the specified range, but the D90 value was 0.30 μm, exceeding the specified range. The resulting porous spherical silica had a porosity of 18% and a wide pore size distribution. This was due to insufficient dispersion time. This demonstrates that it is difficult to obtain the porous spherical silica of the present invention if the dispersion state of the fumed silica dispersion is not appropriate.

[0161] (Comparative Example 3)

[0162] The D50 and D90 values of the fumed silica dispersion prepared in Comparative Example 3 were both within the specified ranges, but the resulting porous spherical silica had a pore volume of 22% and a wide pore size distribution. This is because the fumed silica dispersion was granulated using spray drying. This indicates that even if the dispersion is properly dispersed, the particle size distribution of the dispersion cannot be reflected in the porous skeleton without gelling the fumed silica dispersion, making it difficult to obtain the porous spherical silica of the present invention.

Claims

1. A porous spherical silica, characterized in that The pore volume based on mercury intrusion porosimetry is 0.5 ml / g or more and 8 ml / g or less, The mode pore diameter based on mercury intrusion porosimetry is 5 nm or more and 50 nm or less. The proportion of the pore volume existing in the range of ±5 nm of the mode pore diameter relative to the total pore volume is 40% or more.

2. The porous spherical silica according to claim 1, characterized in that The porous spherical silica has a pore volume within a range of ±5 nm from a mode pore diameter determined by mercury intrusion porosimetry of 0.5 ml / g or more.

3. The porous spherical silica according to claim 1, characterized in that The porous spherical silica has a volume-based cumulative 50% particle size (D50) in the range of 2 to 200 μm as measured by a Coulter counter method. Likewise, the ratio (D10 / D90) of the cumulative 10% particle size (D10) to the cumulative 90% particle size (D90) obtained was 0.3 or more.

4. The porous spherical silica according to claim 1, characterized in that The specific surface area of the porous spherical silica based on the BET method is 100 m 2 / g and above and 400m 2 / g or less.

5. The porous spherical silica according to claim 1, characterized in that The alkali metal content is 50 ppm or less. A catalyst support 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 claim 1 . 8 . A cosmetic comprising the porous spherical silica according to claim 1 . 9 . An abrasive comprising the porous spherical silica according to claim 1 . 10 . A resin composition comprising the porous spherical silica according to claim 1 . 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 following steps: A step of preparing a fumed silica dispersion so that the D50 value of the fumed silica dispersion in the particle size distribution is 0.15 μm or less and the D90 value is 0.2 μm or less; A process for preparing a W / O emulsion consisting of an aqueous phase in which fumed silica is dispersed and an organic phase containing a non-water-soluble solvent as a main component; The step of heating the emulsion to gel the aqueous phase to obtain a gel dispersion; and The process of recovering the generated gel from the liquid and drying it.

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