JP5685145B2 - Method for producing composite silica particles - Google Patents

Description

  The present invention relates to composite silica particles having a mesopore structure and methods for producing hollow silica particles, and composite silica particles and hollow silica particles obtained by these methods.

  Porous materials having pores in the skeleton are widely used as catalyst carriers and adsorbing materials because of their high specific surface area. Among them, those having a sharp pore size distribution have a molecular sieving effect and can be applied to selective adsorbents and separation functional materials. In particular, mesoporous silica with mesoscale pores that have the same pore size as molecules and proteins has been developed. Is attracting attention.

There are various forms of mesoporous silica such as an indefinite shape, a spherical shape, a membrane shape, and a fiber shape. One of them is a “hollow mesoporous silica particle” having a mesoporous silica membrane as an outer shell and a hollow portion inside. It has been known.
As a method for producing the hollow mesoporous silica particles, a method using an emulsion as the hollow part forming agent is useful from an industrial viewpoint.
In Patent Document 1, an organic solvent and a surfactant are mixed to obtain a W / O emulsion, and then reacted with an alkali metal silicate to synthesize hollow silica microcapsules, which are fired. A method for producing hollow silica microcapsules is disclosed.
Non-Patent Document 1 discloses a method for producing hollow mesoporous silica particles using ultrasonic irradiation. However, there is a problem that the hollow silica particles obtained by this method include non-spherical amorphous particles.
As a production method for overcoming these problems, Patent Document 2 discloses that an aqueous solution containing a quaternary ammonium salt, a silica source, a hydrophobic organic substance and water is prepared and stirred at a temperature of 10 to 100 ° C. Discloses a method for producing composite silica particles including a hydrophobic organic substance, and a method for producing hollow silica particles by firing the composite silica particles.

JP 2006-102592 A JP 2008-150229 A

Rohit K. Rana et al., Adv. Mater. , Volume 14, Page 1414 (2002)

Composite silica particles having a sharp particle size distribution are required for improving the performance of optical materials, electronic materials, and biomaterials. However, when the method of Patent Document 1 is added, mesoporous silica having a hollow structure is not formed. There is a problem that only a mixture of hollow silica particles and solid silica particles having no mesopores and mesoporous silica amorphous particles having no hollow structure can be obtained.
There is a problem that the hollow silica particles obtained by the method of Non-Patent Document 1 include non-spherical amorphous particles.
In addition, the method of Patent Document 2 has a problem that it is difficult to obtain composite silica particles having a sufficiently uniform particle size distribution because the particle size and particle size distribution change due to mechanical force and the like.
The present invention provides composite silica particles and hollow silica particles having a highly uniform mesopore structure and sharp particle size distribution, and composite silica particles and hollow silica particles obtained by these methods. This is the issue.

The present inventors have found a composite silica particle having an outer shell portion having a mesoporous structure and containing an organic compound. The composite silica particle further has a high specific surface area and a hollow having a high regularity of the mesopore structure. It has been found that silica particles can be obtained.
That is, the present invention provides the following [1] to [5].
[1] A method for producing composite silica particles having an outer shell portion having a mesoporous structure composed of a component containing silica and containing a hydrophobic organic substance inside the outer shell portion, comprising the following step (1 The manufacturing method of the composite silica particle which has (3)-(3).
Step (1): A step of obtaining an emulsified liquid containing emulsified oil droplets of a hydrophobic organic substance by combining and mixing the solution (a) containing the hydrophobic organic substance and the hydrophilic organic solvent and the aqueous medium (b). ): A silica source is added to and mixed with the emulsified liquid obtained in the step (1), and a surface of the emulsified oil droplet is provided with an outer shell portion having a mesoporous structure containing silica, and a hydrophobic organic substance is contained therein. Step of obtaining suspension containing composite silica particles containing Step (3): Step of separating composite silica particles from suspension obtained in step (2) [2] Composite produced by the method of [1] above A method for producing hollow silica particles, comprising a step of firing silica particles at a temperature of 350 to 950 ° C., comprising an outer shell portion having a mesoporous structure and having a hollow portion therein.
[3] A method for producing hollow silica particles having a hollow portion therein, comprising a step of firing the composite silica particles produced by the method of [1] above at a temperature exceeding 950 ° C.
[4] Composite silica particles produced by the method of [1].
[5] Hollow silica particles produced by the method of [2] or [3].

  According to the present invention, a composite silica particle having a highly uniform mesopore structure and a sharp particle size distribution, an industrially advantageous production method of hollow silica particles, and a composite silica particle obtained by these methods And hollow silica particles can be provided.

It is a figure which shows one embodiment of the emulsion manufacturing apparatus used for this invention. It is a cross-sectional schematic diagram which shows the embodiment of the in-tube mixer of an emulsion liquid manufacturing apparatus. It is a cross-sectional schematic diagram which shows the embodiment of the confluence | merging part of the in-pipe mixer of an emulsion manufacturing apparatus.

The method for producing composite silica particles of the present invention is a method for producing composite silica particles comprising an outer shell portion having a mesoporous structure composed of a component containing silica and containing a hydrophobic organic substance inside the outer shell portion. And it has the following process (1)-(3).
Step (1): A solution (a) containing a hydrophobic organic substance and a hydrophilic organic solvent (hereinafter, also simply referred to as “solution (a)”) and an aqueous medium (b) are combined and mixed to form a hydrophobic organic substance. Step of obtaining an emulsion containing emulsified oil droplets Step (2): A silica source is added to and mixed with the emulsion obtained in step (1), and the surface of the emulsified oil droplets has a mesoporous structure containing silica. Step of obtaining suspension containing composite silica particles including outer shell and containing hydrophobic organic substance therein Step (3): Step of separating composite silica particles from suspension obtained in step (2) In the invention, in the step (1), when the solution (a) and the aqueous medium (b) are mixed and mixed and emulsified, highly uniform emulsified oil droplets of a hydrophobic organic substance are formed, and the particle diameter In order to obtain composite silica particles having a sharp distribution, the solution (a) and the aqueous medium (b) Even without one, it is preferable to contain a quaternary ammonium salt.
In step (2), particles having a mesopore structure are formed in the outer shell, but in order to obtain composite silica particles having a highly uniform mesopore structure, emulsified oil droplets of a hydrophobic organic substance are included. The emulsion is preferably mixed with a silica source in the presence of a quaternary ammonium salt.
Hereinafter, each component used for this invention and process (1)-(3) are demonstrated sequentially.

[Hydrophobic organic matter]
Since the hydrophobic organic substance contained in the outer shell of the composite silica particle of the present invention forms emulsified oil droplets in the aqueous medium (b) in the step (1), the temperature range in the liquid state is 0. Since the aqueous medium (b) is used as the dispersion medium, the upper limit is 100 ° C. or less, preferably 90 ° C. or less, and the boiling point is 40 ° C. or more, preferably 60 Those having a temperature not lower than ° C. are preferred. In addition, when using a plurality of types of hydrophobic organic substances, for example, when mixing a liquid state having a high temperature and a low temperature, the oil droplet formation temperature and the reaction temperature are determined in consideration of their volatility. be able to. The temperature at the time of manufacture can also be determined by the compound to be included.
The hydrophobic organic substance used in the present invention is preferably a compound having low solubility in water and phase separation with the aqueous medium (b) from the viewpoint of increasing the utilization efficiency in the step (1). The hydrophobic organic material is preferably a compound that is soluble in a hydrophilic organic solvent and can be emulsified in the presence of a quaternary ammonium salt. As such a hydrophobic organic substance, a compound having a LogPow of 1 or more, preferably 2 to 25, more preferably 2 to 10 can be mentioned. Here, LogPow is a 1-octanol / water partition coefficient of a chemical substance, and refers to a value obtained by calculation by the log Kow method. Specifically, the chemical structure of a compound is decomposed into its constituents, and the hydrophobic fragment constants of each fragment are integrated (Meylan, WM and PH Howard. 1995. Atom / fragment contribution method for a reference octanol -water partition coefficients. See J. Pharm. Sci. 84: 83-92).

Examples of hydrophobic organic substances include oil agents selected from hydrocarbon compounds, ester compounds, fatty acids having 6 to 22 carbon atoms, silicone oils, and functional materials such as fragrance ingredients, agricultural chemical bases, and pharmaceutical bases. Can be mentioned. When using a fragrance | flavor component, the base material for agricultural chemicals, the base material for pharmaceuticals, etc., advantages, such as the ease of emission control of these functional materials, arise.
Examples of the hydrocarbon compound include alkane or cycloalkane having 5 to 18 carbon atoms, liquid paraffin or liquid petroleum jelly, squalane, squalene, perhydrosqualene, trimethylbenzene, xylene, toluene, benzene and the like. In these, a C5-C18 alkane or cycloalkane is preferable.
Examples of ester compounds include fats and oils such as glycerin esters of fatty acids having 6 to 22 carbon atoms. For example, mink oil, turtle oil, soybean oil, sweet almond oil, beauty leaf oil, palm oil, grape seed oil, sesame seed oil, corn oil, parrham oil, Arara oil, rapeseed oil, sunflower oil, cottonseed oil, apricot oil, Castor oil, avocado oil, jojoba oil, olive oil, cereal germ oil and the like.
Moreover, as an ester compound, the condensate of C4-C22 fatty acid and C1-C22 monohydric alcohol or the condensate of C4-C22 fatty acid and polyhydric alcohols other than glycerol can be mentioned. . Specific examples include isopropyl myristate, isopropyl palmitate, butyl stearate, hexyl laurate, isononyl isononanoate, 2-ethylhexyl palmitate, 2-hexyldecyl laurate, 2-octyldecyl palmitate, 2-octyldodecyl myristate It is mentioned in. Other ester compounds include esters of polyvalent carboxylic acid compounds and alcohols. Specific examples include diisopropyl adipate, 2-octyldodecyl lactate, di-2-ethylhexyl oxalate, diisostearyl malate, glycerol triisostearate, diglycerol tetraisostearate, and the like.

Examples of the fatty acid having 6 to 22 carbon atoms include myristic acid, palmitic acid, stearic acid, behenic acid, oleic acid, linoleic acid, linolenic acid, and isostearic acid.
Examples of the silicone oil include polydimethylsiloxane (PDMS), fatty acid, aliphatic alcohol, polysiloxane modified with polyoxyalkylene, fluorosilicone, perfluorosilicone oil, and the like.
Polydimethylsiloxane (PDMS) may be phenylated, for example phenyltrimethicone, or optionally substituted with aliphatic and / or aromatic groups. They are also hydrocarbon-based oils or silicone oils that are pendant with a silicone chain or optionally containing an alkyl or alkoxy group present at the end and containing 2 to 7 silicon atoms. Linear or cyclic silicones are preferable, and octamethylcyclotetrasiloxane, decamethylcyclopentasiloxane, hexadecamethylcyclohexasiloxane, heptamethylhexyltrisiloxane, heptamethyloctyltrisiloxane and the like are particularly preferable.
Among the above oil agents, from the viewpoint of being easily emulsified and dispersed in the presence of a quaternary ammonium salt, increasing the utilization efficiency of the hydrophobic organic substance, and forming a highly ordered mesopore structure in the outer shell. , Hydrocarbon compounds are preferred, alkanes or cycloalkanes having 5 to 18 carbon atoms, squalene are preferred, and alkanes or cycloalkanes having 5 to 10 carbon atoms are more preferred.

Examples of the fragrance component as the functional material include natural fragrances and synthetic fragrances.
Natural flavors include spearmint oil, peppermint oil, citronella oil, eucalyptus oil, cascalilla oil, birch oil, cinnamon oil, clove oil, garlic oil, peppermint oil, marjoram oil, nutmeg oil, palmarosa oil, perilla oil, rose oil, Examples include savory oil, rosemary oil, and lavender oil. Synthetic fragrances include amyl acetate, α-amylcinnamic aldehyde, isoamyl salicylate, anisaldehyde, benzyl acetate, benzyl alcohol, borneol, l-carvone, menthol, citral, citronellal, citronellol, coumarin, eugenol, methyl salicylate, vanillin, Examples include terpineol.
Said hydrophobic organic substance can be used individually or in mixture of 2 or more types in arbitrary ratios. Further, a compound that does not satisfy the hydrophobic condition may be dissolved in a hydrophobic organic substance. When the composite silica particles are used as a fragrance carrier, the fragrance component may be dissolved in a hydrophobic organic material and diluted.

[Hydrophilic organic solvent]
From the viewpoint of forming composite silica particles having a highly uniform mesopore structure and a sharp particle size distribution, the hydrophilic organic solvent has a dissolution amount of 50 g when dissolved in 100 g of water at 25 ° C. Preferably, it is 60 g or more, more preferably 70 g or more.
From the same viewpoint as described above, the solubility parameter (δ) of the hydrophilic organic solvent is preferably 9.5 to 16.0 (cal / cm ³ ) ^1/2 , and 10.0 to 15.0 (cal / cm). cm ³ ) ^1/2 is more preferable, and 11.0 to 15.0 (cal / cm ³ ) ^1/2 is more preferable.
Here, the solubility parameter (δ) is a value defined by the regular solution theory introduced by Hildebrand and is a scale representing intermolecular force. The solubility parameter (δ) is expressed by the parallel root of the heat of vaporization ((cal / cm ³ ) ^1/2 ) required for evaporating a 1 mol volume of liquid. The solubility parameter (δ) of various organic solvents is described in the Chemical Society, published by Ohm Co.). It can also be calculated by the Fedors method [Robert F. Fedors, Polymer Engineering and Science, 14, 147-154 (1974)].
Specific examples of the hydrophilic organic solvent include methanol (δ = 14.5), ethanol (δ = 12.7), isopropanol (δ = 11.5), n-butanol (δ = 11.4), tert- Polar organic solvents such as C1-C8 alcohols such as butanol, acetone (δ = 9.9), methyl ethyl ketone (δ = 9.3), diethyl ketone, methyl isobutyl ketone, etc. Can be mentioned. In these, C1-C3 alcohol is more preferable and methanol is especially preferable.
These hydrophilic organic solvents can be used alone or in combination of two or more.

[Aqueous medium (b)]
In the present invention, distilled water, ion exchange water, ultrapure water, or the like can be used as the aqueous medium (b). From the viewpoint of making the emulsification of the hydrophobic organic substance more uniform and stable, an organic solvent compatible with the aqueous medium (b) can be added to the aqueous medium (b) within a range not impairing the object of the present invention. .
Examples of the organic solvent that can be added include alcohols having 1 to 3 carbon atoms such as methanol, ethanol, and isopropanol, and acetone. The addition amount of the organic solvent is a range in which the aqueous medium (b) after addition of the organic solvent and the hydrophobic organic substance can be phase-separated, and is usually 100% by mass or less based on the aqueous medium (b).

[Quaternary ammonium salt]
A quaternary ammonium salt is used from the viewpoint of forming highly uniform emulsified oil droplets of a hydrophobic organic substance, having a highly uniform mesopore structure, and forming composite silica particles having a sharp particle size distribution. It is preferable. From the above viewpoint, the quaternary ammonium salt is preferably at least one selected from compounds represented by the following general formulas (1) and (2).
[R ¹ (CH ₃ ) ₃ N] ⁺ X ⁻ (1)
[R ¹ R ² (CH ₃ ) ₂ N] ⁺ X ⁻ (2)
(In the formula, R ¹ and R ² each independently represents a linear or branched alkyl group having 4 to 22 carbon atoms, and X represents a monovalent anion.)
R ¹ and R ² in the general formulas (1) and (2) are each independently a linear or branched group having 4 to 22 carbon atoms, preferably 6 to 18 carbon atoms, and more preferably 8 to 16 carbon atoms. It is an alkyl group. Examples of the alkyl group having 4 to 22 carbon atoms include various butyl groups, various pentyl groups, various hexyl groups, various heptyl groups, various octyl groups, various nonyl groups, various decyl groups, various dodecyl groups, various tetradecyl groups, and various hexadecyl groups. , Various octadecyl groups, various eicosyl groups, and the like. Here, “various” includes all isomers such as n-isomer, iso-isomer and tert-isomer.
X ⁻ in the general formulas (1) and (2) is preferably 1 such as halide ion, hydroxide ion, nitrate ion, and sulfate ion from the viewpoint of forming a highly uniform mesopore structure. One or more selected from valent anions, more preferably halide ions, still more preferably chloride ions or bromide ions, and particularly preferably bromide ions.

Examples of the alkyltrimethylammonium salt represented by the general formula (1) include butyltrimethylammonium chloride, hexyltrimethylammonium chloride, octyltrimethylammonium chloride, decyltrimethylammonium chloride, dodecyltrimethylammonium chloride, tetradecyltrimethylammonium chloride, hexadecyltrimethyl Ammonium chloride, stearyltrimethylammonium chloride, butyltrimethylammonium bromide, hexyltrimethylammonium bromide, octyltrimethylammonium bromide, decyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, hexadecyltrimethylammonium bromide Bromide, stearyl trimethyl ammonium bromide, and the like.
Examples of the dialkyldimethylammonium salt represented by the general formula (2) include dibutyldimethylammonium chloride, dihexyldimethylammonium chloride, dioctyldimethylammonium chloride, didodecyldimethylammonium chloride, ditetradecyldimethylammonium chloride, dibutyldimethylammonium bromide, dihexyl. Examples thereof include dimethylammonium bromide, dioctyldimethylammonium bromide, didodecyldimethylammonium bromide, and ditetradecyldimethylammonium bromide. Among these quaternary ammonium salts (a), from the viewpoint of forming regular mesopores, an alkyltrimethylammonium salt represented by the general formula (1) is particularly preferable, and an alkyltrimethylammonium bromide or chloride is preferable. More preferred.

[Silica source]
The silica source is preferably a substance that generates a silanol compound by hydrolysis of alkoxysilane or the like. Specific examples include compounds represented by the following general formulas (3) to (7).
SiY ₄ (3)
R ³ SiY ₃ (4)
R ³ ₂ SiY ₂ (5)
R ³ ₃ SiY (6)
Y ₃ Si—R ⁴ —SiY ₃ (7)
(In the formula, each R ³ independently represents an organic group in which a carbon atom is directly bonded to a silicon atom, R ⁴ represents a hydrocarbon group or a phenylene group having 1 to 4 carbon atoms, and Y represents A monovalent hydrolyzable group that becomes a hydroxy group by hydrolysis.)
In the step (2) of the present invention, from the viewpoint of forming a highly uniform mesopore structure, each R ³ in the general formulas (3) to (7) is independently a part of the hydrogen atom being a fluorine atom. It is preferable that it is a C1-C22 hydrocarbon group which may be substituted. R ³ is more preferably an alkyl group having 4 to 18 carbon atoms, more preferably 6 to 18 carbon atoms, and particularly preferably 8 to 16 carbon atoms, a phenyl group, or a benzyl group.
R ⁴ is preferably an alkanediyl group having 1 to 4 carbon atoms (methylene group, ethylene group, trimethylene group, propane-1,2-diyl group, tetramethylene group, etc.) or phenylene group, and Y is preferably An alkoxy group having 1 to 22 carbon atoms, more preferably 1 to 8 carbon atoms, still more preferably 1 to 4 carbon atoms, or a halogen group excluding fluorine.

Preferable examples of the silica source include the following compounds.
-The silane compound in which Y is a C1-C3 alkoxy group or a halogen group except a fluorine in General formula (3).
In general formula (4) or (5), R ³ is a phenyl group, a benzyl group, or a hydrogen atom in which part of the hydrogen atom is substituted with a fluorine atom, preferably 1 to 10 carbon atoms, Trialkoxysilane or dialkoxysilane which is preferably a hydrocarbon group having 1 to 5 carbon atoms.
A compound in which Y is a methoxy group and R ⁴ is a methylene group, an ethylene group or a phenylene group in the general formula (7).
Among these, tetramethoxysilane, tetraethoxysilane, phenyltriethoxysilane, and 1,1,1-trifluoropropyltriethoxysilane are particularly preferable.

[Step (1)]
Step (1) is a step in which a solution (a) containing a hydrophobic organic substance and a hydrophilic organic solvent and an aqueous medium (b) are combined and mixed to obtain an emulsion containing emulsion oil droplets of the hydrophobic organic substance. . More specifically, (i) the merging of the solution (a) and the aqueous medium (b), and (ii) the hydrophobic organic substance dissolved and contained in the solution (a) in the aqueous medium (b) In this process, an emulsion is continuously obtained by precipitation and dispersion as emulsion oil droplets.
In step (1), the solution (a) and the aqueous medium (b) are preferably continuously fed using an in-tube mixer, and the continuously supplied solution (a) and the aqueous medium (b) are mixed in the tube. It can carry out by mixing and emulsifying in a container and producing | generating the emulsion liquid containing an emulsified oil droplet continuously. At this time, when the solution (a) is mixed with the aqueous medium (b), the saturated solubility of the hydrophobic organic substance in the solution (a) is drastically lowered. As a result, the hydrophobic organic substance in the solution (a) is reduced. Becomes supersaturated, and the hydrophobic organic substance is phase-separated and deposited as emulsified oil droplets. The emulsion obtained by dispersing the hydrophobic organic substance in the aqueous medium (b) is an oil-in-water dispersion in which oil droplets are dispersed in the aqueous phase.

(Emulsion production equipment)
One embodiment of the emulsion production apparatus used in step (1) will be described with reference to FIG.
1 includes a supply tank 11 for a solution (a) containing a hydrophobic organic substance and a hydrophilic organic solvent, a supply tank 12 for an aqueous medium (b), and a solution (a) supply tank 11. An in-pipe mixer 15 to which a supply pipe 13 extending from the aqueous medium (b) supply tank 12 is coupled, and an emulsion forming unit 17 to which a mixed liquid supply pipe 16 extending from the in-pipe mixer 15 is coupled. ing. P is a pump interposed in the supply pipes 13 and 14.
FIG. 2A is a schematic diagram showing an embodiment of the in-tube mixer 15. In FIG. 2 (a), the in-pipe mixer 15 is composed of a fluid junction 18.
FIG. 2B is a schematic diagram showing another embodiment of the in-pipe mixer 15. In FIG. 2B, the in-pipe mixer 15 has a structure in which a fluid junction 18 and a mixing element 19 are connected in series. As a mixing element, a structure in which a plurality of blades are fixed in series in a straight pipe as in a general static mixer, or one or more pores on a plate partitioned so as to close the pipe Examples thereof include a structure in which one or a plurality of orifices are stacked, a continuous mixer having a rotating stirring shaft, and the like. Although the mixing of the solution (a) and the aqueous medium (b) can be performed more reliably by installing the mixing element 19 downstream of the fluid merging portion 18, the mixing may be performed only by the fluid merging portion 18. .

FIG. 3A is a schematic cross-sectional view showing an embodiment of a merging portion of the solution (a) and the aqueous medium (b) in the fluid merging portion 18. In FIG. 3A, the supply pipes 13 and 14 are arranged so as to face each other and form the same straight line, and the liquid from the supply pipes 13 and 14 is mixed and emulsified at the joining part of the fluid joining part 18. The mixed liquid flows out of a supply pipe 16 extending in a direction substantially orthogonal to the straight line formed by the supply pipes 13 and 14 and is supplied to the emulsion forming device 17 or emulsified through the mixing element 19. It is structured to be supplied to the liquid former 17.
FIGS. 3B to 3E are schematic cross-sectional views of other modes illustrating the inflow and outflow paths of the liquid in the fluid junction 18. 3B to 3D, the supply pipes 13 and 14 are disposed so as to form a V shape. In FIG. 3E, the supply pipes 13 and 14 are arranged in parallel to each other.
The maximum flow rate when the solution (a) and the aqueous medium (b) are joined and mixed in the in-pipe mixer 15 is improved in mixing, emulsification and dispersion efficiency, has a highly uniform mesopore structure, and particles From the viewpoint of forming composite silica particles having a sharp diameter distribution, 0.1 to 50 m / sec is preferable, 0.2 to 30 m / sec is more preferable, and 0.3 to 15 m / sec is still more preferable. In addition, the maximum flow velocity is generated in the flow channel having the smallest flow channel diameter after the solution (a) and the aqueous medium (b) merge in the in-tube mixer 15, and the flow channel diameter is 0.1 to 100 mm. Preferably, 0.2-30 mm is more preferable, and 0.4-25 mm is more preferable.

The in-tube mixer 15 can continuously mix the solution (a) from the supply pipe 13 and the aqueous medium (b) from the supply pipe 14 in one pass. When the solution (a) and the aqueous medium (b) join together in the in-pipe mixer 15, the hydrophobic organic matter in the solution (a) becomes supersaturated and phase-separates and precipitates as emulsified oil droplets. Since this phenomenon occurs over the entire liquid flowing through the in-pipe mixer 15, precipitation of the emulsified oil droplets having a substantially uniform diameter is completed in a very short time (about 0.001 to 1 second).
In conventional batch mixing with a mixing tank, it takes a long time (several tens of seconds to several minutes on an actual production scale) to complete the precipitation of emulsified oil droplets throughout the mixing tank. The difference in oil droplet size became large, and the resulting composite silica particles had to have a wide particle size distribution.
However, according to the present invention, compared to the batch method, the capital investment, the operation load is greatly reduced, and the emulsified oil droplet size distribution is narrowed, resulting in a highly uniform mesopore structure, Composite silica particles having a sharp particle size distribution can be produced with high productivity.

As the mixing element 19 shown in FIG. 2 (b), for example, a line homomixer (TK Pipeline homomixer manufactured by PRIMIX Co., Ltd.) or a milder (manufactured by Taihei Kiko Co., Ltd., Matsubo Co., Ltd.) Rotating mixers such as Ebara Manufacturing Co., Ltd., static mixers (manufactured by Noritake Co., Ltd.), high mixers (Hi-Mixer manufactured by Toray Engineering Co., Ltd.), static mixers such as micromixers, and dispersion-kun (Fujikin) Or an orifice type mixer such as
Among these, a static mixer and an orifice type mixer are preferable from the viewpoint of uniform mixing and emulsification.
A static mixer is a tube-type mixer that does not have a drive unit. As a typical example, a rectangular plate is twisted 180 degrees in a narrow pipe line, and the right element depends on the direction of twist. The left element is housed, and when the two liquids to be emulsified pass through the element, they are mixed by the three actions of division, inversion, and conversion. Is a mixer configured to move (convert) and mix along the twisted surface of the element from the center to the wall and from the wall to the center.
In the embodiment of FIG. 1, the supply pipes 13 and 14 are coupled to the in-tube mixer 15. However, the present invention is not limited to this, and the supply pipes 13 and 14 are disposed immediately before the in-tube mixer 15. The solution (a) and the aqueous medium (b) may be joined together and supplied to the in-tube mixer 15.

(Control of emulsion oil droplet size)
The size of the emulsified oil droplets immediately after precipitation is affected by the degree of supersaturation, as in general crystallization operations. Since the supersaturation degree of the hydrophobic organic substance immediately after mixing varies depending on the mixing ratio of the solution (a) and the aqueous medium (b) at the time of continuous mixing, the average diameter of the emulsified oil droplets is controlled by controlling the mixing ratio. be able to. The relationship between the mixing ratio and the average diameter of the emulsified oil droplets is influenced by the composition, type, temperature, etc. of the solution (a) and aqueous medium (b) to be used. When the supply amount of the solution (a) and the aqueous medium (b) to the in-pipe mixer changes with time, the emulsion oil droplet diameter that precipitates changes with time, and the composite silica particles finally obtained The particle size distribution is wide.
Therefore, in the step (1), the composite silica particles having a highly uniform mesopore structure and a sharp particle size distribution are not greatly changed in the mixing ratio of the solution (a) and the aqueous medium (b). Is important to get. From such a viewpoint, if the mixing ratio to be set is a, the mixing ratio during operation is preferably 0.66a to 1.5a, more preferably 0.75a to 1.35a, and still more preferably 0.8a to It is desirable to maintain it in the range of 1.25a, more preferably in the range of 0.9a to 1.1a.
The volume ratio of [water in aqueous medium (b) / hydrophobic organic substance in solution (a)] when solution (a) and aqueous medium (b) merge is preferably 20 to 800. 30 to 600 is more preferable.
In addition, from the viewpoint of adjusting the concentration of the hydrophobic organic substance and causing the silica raw material to react uniformly, the solution (a) and the aqueous medium (b) may be further mixed and further diluted with an aqueous medium.

The average particle diameter of the composite silica particles is preferably 0.01 to 10 μm from the viewpoint of availability. In order to obtain such composite silica particles, the average diameter of the emulsified oil droplets of the hydrophobic organic substance in the emulsion is 0. 0.001 to 10 μm is preferable, and 0.005 to 8.5 μm is more preferable.
Control of the emulsified oil droplet diameter of the hydrophobic organic substance can be performed by adjusting the mixing temperature of the solution (a) and the aqueous medium (b) in the step (1). The temperature is preferably 10 to 100 ° C, more preferably 10 to 80 ° C.
In addition, the emulsion oil droplet size can be controlled by adjusting the number of rotations and selecting the clearance when using a rotary mixer, and by adjusting the flow velocity and selecting the channel diameter when using a static mixer. In addition, the average diameter of the emulsified oil droplets of the hydrophobic organic substance can be measured by a conventional method such as a dynamic light scattering method or a laser diffraction scattering method.

[Step (2)]
In step (2), a silica source is added to and mixed with the emulsion obtained in step (1), and an outer shell portion having a mesoporous structure containing silica is provided on the surface of the emulsion oil droplets. This is a step of obtaining a suspension containing composite silica particles containing a hydrophobic organic substance.
In the emulsion forming device 17 of FIG. 1, the silica source is added to the emulsion obtained in the step (1) (not shown), mixed, and then left to stand, so that the emulsion oil droplets of hydrophobic organic matter A mesopore structure is formed on the surface by a quaternary ammonium salt and a silica source, and composite silica particles including a hydrophobic organic substance inside can be deposited.
Mixing in the emulsion forming device 17 is usually performed at 10 to 100 ° C., preferably at 10 to 80 ° C. for 0.1 to 24 hours, so that the outer shell portion having a mesoporous structure is provided. Composite silica particles containing a hydrophobic organic substance inside are formed.
In step (2), the contents of the hydrophobic organic substance, the silica source, and the quaternary ammonium salt in the aqueous solution of the emulsion former 17 are as follows.
The hydrophobic organic material is preferably contained at 0.1 to 100 mmol / L, more preferably 1 to 100 mmol / L, and even more preferably 5 to 80 mmol / L, and the silica source is preferably 0.1 to 100 mmol / L. When the quaternary ammonium salt is added, it is preferably 0.1 to 100 mmol / L, more preferably 1 to 100 mmol / L, more preferably 1 to 100 mmol / L, and even more preferably 5 to 80 mmol / L. The content is preferably 1 to 100 mmol / L, more preferably 5 to 80 mmol / L.
The obtained composite silica particles are obtained in a state suspended in the aqueous medium (b). Depending on the application, it can be used as it is.

In the aqueous solution containing the hydrophobic organic substance, silica source, and quaternary ammonium salt, as long as the formation of the composite silica particles of the present invention is not hindered, other components such as organic compounds such as methanol and other inorganic compounds Ingredients may be added.
When it is desired to carry elements other than silica, metal raw materials such as alkoxy salts and halogenated salts containing these metals can be added during or after production. When an organic group having an organic group is used as the silica source, an outer shell of a silica structure having an organic group is obtained. In addition to the silica source, other elements such as Al, Ti, V, Cr, Co, Ni, By adding a metal such as Cu, Zn, Zr, Mn, Fe or an alkoxy salt or a halogenated salt containing a non-metallic element such as B, P, N, S or the like during or after production, the metal or non-metal Metal elements can be present in the outer shell of the silica particles. The structure of the outer shell part is preferably manufactured from tetramethoxysilane or tetraethoxysilane as a silica source from the viewpoint of stability, and the silica wall is substantially composed of silicon oxide.

[Step (3)]
Step (3) is a step of concentrating the suspension obtained in step (2) as necessary to separate the composite silica particles from the suspension.
In the present invention, the method for concentrating and separating the suspension is not particularly limited, and examples thereof include centrifugation, filter filtration, and dialysis using a porous membrane.
When a cationic surfactant is used in the production process of the obtained composite silica particle, the cationic surfactant may remain inside the composite silica particle, in the mesopores, or on the surface of the silica particle. . If there is no problem even if the cationic surfactant remains, it is not necessary to remove it, but if it is desired to remove the remaining cationic surfactant, the composite silica particles should be removed by contacting with an acidic solution. Can do.
For example, after removing the cationic surfactant by mixing the composite silica particles in an acidic aqueous solution, if necessary, it is washed with water and dried at a temperature at which the hydrophobic organic substance does not volatilize too much. Composite silica particles can be obtained. Examples of the acidic solution used include inorganic acids such as hydrochloric acid, nitric acid, and sulfuric acid; organic acids such as acetic acid and citric acid; and solutions obtained by adding a cation exchange resin or the like to water or ethanol. Hydrochloric acid is particularly preferable. The pH is usually adjusted to 1.5 to 5.0.
The composite silica particles of the present invention are obtained by the steps (1) to (3).

[Composite silica particles]
The composite silica particles obtained by the method of the present invention have an outer shell portion having a mesoporous structure composed of a component containing silica, and a hydrophobic organic substance or a hydrophobic organic substance inside the outer shell portion. Composite silica particles containing an ionic liquid composition.
The average particle diameter of the composite silica particles is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm.
The particle size distribution of the composite silica particles of the present invention is sharp, and the coefficient of variation (CV value,%) of the average particle size (volume median particle size: D ₅₀ ) is preferably 35% or less, preferably 30% or less. More preferably, it is 25% or less. The coefficient of variation (%) is expressed by the following equation, and can be obtained by the method described in the examples described later.
Coefficient of variation (%) = [standard deviation (μm) / average particle size (μm)] × 100
The average particle size of the composite silica particles can be adjusted by the kind and concentration of the hydrophobic organic substance or the cationic surfactant, the flow rate when the solution (a) and the aqueous medium (b) merge, the temperature, and the like. it can.

The ratio of [thickness of outer shell / average particle diameter] is preferably 0.01 to 0.6, more preferably 0.05 to 0.5, and 0.075 to 0.4. It is particularly preferred.
The mesopore structure of the composite silica particle of the present invention is one of the features that the mesopore diameter is uniform, and usually 70% or more of the mesopores of the composite silica particle are within an average pore diameter of ± 30%. to go into. The average pore diameter of mesopores in the present invention is a value obtained by nitrogen adsorption measurement and determined from the nitrogen adsorption isotherm by the BJH method.
The average particle size of the composite silica particles and the degree of distribution thereof can be measured by observation with a scanning electron microscope (SEM), and the thickness of the outer shell can be measured by observation with a transmission electron microscope (TEM). it can. Specifically, the diameter of all particles in a visual field containing 100 to 500 particles is measured under a scanning electron microscope, and this operation is performed by changing the visual field multiple times. Deviation can be obtained. In addition, under observation with a transmission electron microscope, the outer shell thickness of all particles in the visual field including 20 to 30 particles is measured on a photograph. The average outer shell thickness can be obtained by performing this operation by changing the field of view a plurality of times.

[Method for producing hollow silica particles]
The hollow silica particle of the present invention is a hollow silica particle having a hollow portion therein, and the step (A) of firing the composite silica particle produced by the above method at a temperature of 350 to 950 ° C., or 950 It can obtain by attaching | subjecting to the process (B) baked at the temperature exceeding degreeC.
In the step (A), it is preferably baked in an electric furnace or the like at a temperature of preferably 350 to 800 ° C., more preferably 450 to 700 ° C., preferably for 1 to 10 hours, to remove the hydrophobic organic substance contained in the composite silica particles. To do. The hollow silica particles (A) thus obtained have a mesopore structure without changing the basic structure of the outer shell, but the encapsulated hydrophobic organic substances and cationic surfactants are removed by calcination.
In the step (B), the temperature is preferably 960 to 1500 ° C., more preferably 970 to 1300 ° C., further preferably 980 to 1200 ° C., preferably 0.5 to 100 hours, using an electric furnace or the like. More preferably, baking is performed for 1 to 72 hours. By performing this step (B), the mesopore structure of the outer shell portion of the obtained hollow silica particles (B) can be baked to make the BET specific surface area less than 30 m ² / g.

[Hollow silica particles]
The hollow silica particles of the present invention have a sharp particle size distribution.
The average particle diameter of the hollow silica particles (A) of the present invention is preferably 0.01 to 10 μm, more preferably 0.02 to 5 μm, still more preferably 0.02 to 3 μm. The average particle diameter of the hollow silica particles (B) is preferably 0.02 μm or more and less than 3 μm, more preferably 0.02 to 2 μm, still more preferably 0.02 to 1 μm.
Further, the average particle size distribution of the hollow silica particles (A) and (B) of the present invention is sharp, the average thickness of the outer shell, the ratio of [thickness of outer shell / average particle size], The average pore diameter is the same as that of the composite silica particles.
The BET specific surface area of the hollow silica particles (A) is less than 200 to 2000 m ² / g, and the BET specific surface area of the hollow silica particles (B) is less than 30 m ² / g.

Various measurements of the silica particles obtained in Examples and Comparative Examples were performed by the following methods.
(1) Measurement of average particle diameter and coefficient of variation Using a scanning electron microscope (SEM) S-4000 manufactured by Hitachi, Ltd., measurement is carried out at an acceleration voltage of 10 kV, and there are 5 visual fields each containing 100 to 500 particles. The diameters of all the particles were measured on a photograph, and the average particle diameter and standard deviation were measured. The coefficient of variation was calculated by the following formula. Coefficient of variation (%) = standard deviation (μm) / average particle diameter (μm) × 100
(2) Measurement of BET specific surface area and average pore diameter The specific surface area / pore distribution measuring device manufactured by Shimadzu Corporation, trade name “ASAP2020” is used, and the BET specific surface area is determined by a multipoint method using liquid nitrogen. Measurements were made and values were derived in the range where parameter C was positive. The BJH method described above was employed, and the peak top was defined as the average pore diameter. The pretreatment was performed at 250 ° C. for 5 hours.

Example 1
91 parts by weight of Cathogen TML (Daiichi Kogyo Seiyaku Co., Ltd.), 17 parts by weight of tetramethylammonium hydroxide (Seychem Co.), hexane (Japanese) A solution phase A containing a hydrophobic organic material and a hydrophilic organic solvent was prepared by adding and stirring 20 parts by weight of Kojun Pharmaceutical Co., Ltd. (special grade). Ion-exchanged water is allowed to flow out simultaneously at a ratio of 1 volume part with respect to 1 volume part of the solution phase, and the structure shown in FIG. 3 (b) has a fluid confluence part with an inner diameter of 9.6 mm and a static mixer (Toray Engineering) Emulsified liquid was obtained by mixing using a product name, Hi-Mixer). The maximum flow rate in the mixer was 0.83 m / s, the minimum part of the flow path was parallel to 2 flow paths, the inner diameter was 8 mm, and the flow path length was 80 mm in total for 5 elements in series. 7 parts by volume of ion exchange water was added to 10 parts by volume of the emulsion obtained by collecting the emulsion for 6 minutes. Tetramethoxysilane 0.5 part was added with respect to 100 volume part of emulsion after adding water, and it stirred at 25 degreeC for 10 minutes. The resulting cloudy solution was filtered off with 5C filter paper and dried at 100 ° C. to obtain composite silica particles. The obtained composite silica particles were heated up to 600 ° C. at a rate of 1 ° C./min with an air flow (3 L / min) using a high-temperature heating electric furnace (manufactured by Motoyama Co., Ltd., trade name: SK-2535E). The organic component was removed by heating and baking at 600 ° C. for 2 hours to obtain hollow silica particles (A). 50 g of the hollow silica particles were transferred to an alumina crucible and calcined at 1000 ° C. for 38 hours in the air using the electric furnace to obtain hollow silica (B). The results are shown in Table 1.

Example 2
Solution phase A was prepared in the same manner as in Example 1. Ion exchange water was simultaneously allowed to flow out at a ratio of 7 parts by volume with respect to 5 parts by volume of the solution phase, and mixed using the fluid merging part and Hi-Mixer used in Example 1 to obtain an emulsion. The maximum flow rate in the mixer was 0.99 m / s. 5 parts by volume of ion-exchanged water was added to 12 parts by volume of the emulsion obtained by collecting the emulsion for 6 minutes. Tetramethoxysilane 0.5 part was added with respect to 100 volume part of emulsion after adding water, and it stirred at 25 degreeC for 10 minutes. The resulting cloudy solution was filtered off with 5C filter paper and dried at 100 ° C. to obtain composite silica particles. The results are shown in Table 1.

Example 3
In Example 1, composite silica particles were obtained under the same conditions except that the scale was reduced to 1/3, that is, the maximum flow rate in the mixer was 0.28 m / s. The results are shown in Table 1.

Example 4
Solution phase A was prepared in the same manner as in Example 1. Ion-exchanged water is simultaneously flowed out at a ratio of 1 volume part with respect to 1 volume part of the solution phase, and mixed using a fluid confluence section having an inner diameter of 2 mm and a static mixer in series with the structure shown in FIG. An emulsion was obtained. The static mixer uses a Hi-Mixer with a pipe diameter different from that used in Example 1, the maximum flow velocity in the mixer is 2.38 m / s, and the flow paths are two flow paths in parallel. The inner diameter was 0.7 mm, and the flow path length was 14 mm in total for 5 elements in series. Immediately thereafter, 7 parts by volume of ion-exchanged water was continuously mixed with 10 parts by volume of the emulsified liquid using a T-shaped tube. Furthermore, 0.5 parts of tetramethoxysilane was continuously mixed with a double tube with respect to 100 parts by volume of the emulsified liquid after adding water, and reacted in the line at 25 ° C. for 10 minutes. The resulting cloudy solution was filtered off with 5C filter paper and dried at 100 ° C. to obtain composite silica particles. The results are shown in Table 1.

Example 5
In Example 4, a fluid merging portion having an inner diameter of 4 mm was used as the fluid merging portion with the structure shown in FIG. 3A, and an orifice type mixer “Dispersion-kun” manufactured by Fujikin Co., Ltd. was used as the stationary mixer. Except for the above, composite silica particles were obtained in the same manner as in Example 4. The orifice-type mixer has a structure in which four orifices having four holes are stacked on a plate partitioned so as to close the pipe, each hole diameter is 0.5 mm, and the maximum flow velocity in the hole is the flow velocity. Was 2.33 m / s. The results are shown in Table 1.

Comparative Example 1
6000 parts by weight of ion-exchanged water, 2000 parts by weight of methanol (made by Wako Pure Chemical Industries, Ltd., special grade), 91 parts by weight of Cathogen TML (made by Daiichi Kogyo Seiyaku Co., Ltd.), tetramethylammonium hydroxide (made by Seychem) 17 parts by weight and 20 parts by weight of hexane (made by Wako Pure Chemical Industries, Ltd., special grade) were added and stirred to prepare an emulsion. To 100 parts by volume of the obtained emulsion, 0.5 part of tetramethoxysilane was added and stirred at 25 ° C. for 10 minutes. The resulting cloudy solution was filtered off with 5C filter paper and dried at 100 ° C. to obtain composite silica particles. The obtained composite silica particles were heated up to 600 ° C. at a rate of 1 ° C./min with an air flow (3 L / min) using a high-temperature heating electric furnace (manufactured by Motoyama Co., Ltd., trade name: SK-2535E). The organic component was removed by heating and baking at 600 ° C. for 2 hours to obtain hollow silica particles (A). 50 g of the hollow silica particles were transferred to an alumina crucible and calcined at 1000 ° C. for 38 hours in the air using the electric furnace to obtain hollow silica (B). The results are shown in Table 1.

According to the production method of the present invention, composite silica particles and hollow silica particles having a highly uniform mesopore structure and a sharp particle size distribution can be advantageously produced industrially.
The obtained composite silica particles and hollow silica particles can be effectively used as, for example, a structure-selective catalyst carrier, adsorbent, substance separation agent, enzyme or functional organic compound immobilization carrier.

DESCRIPTION OF SYMBOLS 10: Emulsified liquid manufacturing apparatus 11: Solution (a) supply tank 12: Aqueous medium (b) supply tank 13: Solution (a) supply pipe 14: Aqueous medium (b) supply pipe 15: In-pipe mixer 16: Mixed liquid supply Tube 17: Emulsifier (tank)
18: Fluid junction 19: Mixing element

Claims (8)

A method for producing composite silica particles comprising an outer shell portion having a mesoporous structure composed of a component containing silica and containing a hydrophobic organic substance inside the outer shell portion,
The manufacturing method of the composite silica particle which has the following process (1)-(3).
Step (1): The solution (a) containing the hydrophobic organic substance and the hydrophilic organic solvent and the aqueous medium (b) are continuously merged and mixed at a maximum flow rate of 0.1 to 50 m / sec. Step of obtaining an emulsion containing emulsified oil droplets Step (2): A silica source is added to and mixed with the emulsion obtained in step (1) to form a mesopore structure containing silica on the surface of the emulsified oil droplets. Step of obtaining a suspension containing composite silica particles including an outer shell portion having a hydrophobic organic substance therein Step (3): Step of separating composite silica particles from the suspension obtained in step (2)   In the step (1), when the solution (a) containing the hydrophobic organic substance and the aqueous organic solvent and the aqueous medium (b) join together [the hydrophobic organic substance in the water / solution (a) in the aqueous medium (b) ] Is a volume ratio of 20-1000, The manufacturing method of the composite silica particle of Claim 1. The method for producing composite silica particles according to claim 1 or 2 , wherein in the step (2), a silica source is continuously joined to the emulsion and mixed. The method for producing composite silica particles according to claim 1, wherein the composite silica particles have an average particle diameter of 0.01 to 3 μm and a coefficient of variation of less than 35%. An outer shell portion having a mesoporous structure, comprising a step of firing the composite silica particles produced by the method according to any one of claims 1 to 4 at a temperature of 350 to 950 ° C, and a hollow portion therein A method for producing hollow silica particles comprising: The manufacturing method of the hollow silica particle which provided the hollow part inside with the process of baking the composite silica particle manufactured by the method in any one of Claims 1-4 at the temperature exceeding 950 degreeC. The composite silica particle whose coefficient of variation manufactured by the method in any one of Claims 1-4 is 25% or less . Hollow silica particles having a coefficient of variation of 25% or less produced by the method according to claim 5 or 6 .

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