U.S. patent application number 12/146563 was filed with the patent office on 2008-10-30 for process for producing inorganic spheres.
This patent application is currently assigned to Asahi Glass Company, Limited. Invention is credited to Hajime Katayama, Toshiya Matsubara, Masaharu Tanaka, Kenji Yamada.
Application Number | 20080267853 12/146563 |
Document ID | / |
Family ID | 33447140 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080267853 |
Kind Code |
A1 |
Matsubara; Toshiya ; et
al. |
October 30, 2008 |
PROCESS FOR PRODUCING INORGANIC SPHERES
Abstract
To provide a process for producing inorganic spheres having a
substantially uniform particle size with high productivity. In a
process for producing inorganic spheres, which comprises a step of
injecting an alkaline aqueous liquid containing an inorganic
compound into a laminar flow of an organic liquid containing a
surfactant through micropores to form a W/O type emulsion, and a
step of solidifying droplets of the aqueous liquid containing an
inorganic compound in the W/O type emulsion by an acid to form
inorganic spheres, as the organic liquid, one which is brought into
contact with an acid in a state of the W/O type emulsion or after
separated from the W/O type emulsion, or one which is brought into
contact with the aqueous liquid and then separated and recovered,
is used.
Inventors: |
Matsubara; Toshiya;
(Ichihara-shi, JP) ; Tanaka; Masaharu;
(Kitakyushu-shi, JP) ; Katayama; Hajime;
(Ichihara-shi, JP) ; Yamada; Kenji; (Yokohama-shi,
JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Asahi Glass Company,
Limited
Tokyo
JP
|
Family ID: |
33447140 |
Appl. No.: |
12/146563 |
Filed: |
June 26, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11271905 |
Nov 14, 2005 |
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12146563 |
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PCT/JP04/06810 |
May 13, 2004 |
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11271905 |
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Current U.S.
Class: |
423/339 |
Current CPC
Class: |
B01F 5/0475 20130101;
C01B 33/193 20130101; B01J 13/02 20130101; B01J 2/06 20130101; B01F
3/0811 20130101; B01J 13/04 20130101 |
Class at
Publication: |
423/339 |
International
Class: |
C01B 33/32 20060101
C01B033/32 |
Foreign Application Data
Date |
Code |
Application Number |
May 13, 2003 |
JP |
2003-133992 |
Claims
1. A process for producing inorganic spheres, comprising: preparing
an emulsion by injecting an alkaline aqueous liquid containing an
inorganic compound into a laminar flow of an organic liquid
containing a surfactant and running at a flow rate of from 0.001 to
2 m/s in a flow path compartmentalized by at least one diaphragm
through micropores penetrating through one diaphragm in its
thickness direction to form a W/O emulsion containing droplets of
the aqueous liquid containing said inorganic compound; solidifying
said droplets of the aqueous liquid containing said inorganic
compound in said W/O emulsion by using an acid to form a liquid
containing said inorganic spheres; separating said liquid
containing said inorganic spheres into an organic liquid (A') and
said inorganic spheres, and deacidifying the organic liquid (A')
and recycling the organic liquid to the flow path for the organic
liquid.
2. The process for producing inorganic spheres according to claim
1, further comprising: separating an organic liquid (A) from the
W/O emulsion containing droplets of the aqueous liquid containing
said inorganic compound, contacting said organic liquid (A) with an
acid, deacidifying said organic liquid (A); and recycling the
organic liquid (A) to the flow path for the organic liquid.
3. The process for producing inorganic spheres according to claim
1, wherein the inorganic compound is at least one member selected
from the group consisting of potassium silicate, sodium silicate,
sodium aluminate and silica.
4. The process for producing inorganic spheres according to claim
1, wherein the surfactant is a nonionic surfactant.
5. The process for producing inorganic spheres according to claim
1, wherein the surfactant is contained in the organic liquid in an
amount of from 500 to 50,000 ppm.
6. The process for producing inorganic spheres according to claim
1, wherein at least part of the diaphragms constituting the flow
path for the organic liquid is made of a transparent material.
7. The process for producing inorganic spheres according to claim
6, wherein the preparing of the W/O emulsion is carried out while
being continuously monitored by means of a monitor provided via
said transparent material.
8. The process for producing inorganic spheres according to claim
1, wherein the organic liquid supplied to the flow path is one
which has been brought into contact with the alkaline aqueous
liquid and separated and recovered.
9. The process for producing inorganic spheres according to claim
1, comprising: separating said liquid containing said inorganic
spheres into an organic liquid (A') and said inorganic spheres.
10. The process for producing inorganic spheres according to claim
9, wherein the inorganic compound is sodium silicate; and wherein a
proportion of silicic acid to sodium in said sodium silicate is
from 2.0 to 3.8 in terms of a SiO.sub.2/Na.sub.2O molar ratio.
11. The process for producing inorganic spheres according to claim
1, wherein a concentration of alkali silicate or silica as
inorganic compound in the aqueous liquid is preferably from 5 to 30
mass % in terms of the SiO.sub.2 concentration.
12. The process for producing inorganic spheres according to claim
1, wherein said organic liquid is a C.sub.9-12 saturated
hydrocarbon.
13. The process for producing inorganic spheres according to claim
1, wherein said C.sub.9-12 saturated hydrocarbon has a flash point
of from 20 to 80.degree. C.
14. The process for producing inorganic spheres according to claim
1, wherein said surfactant is selected from the group consisting of
a polyethylene glycol fatty acid ester, a polyethylene glycol alkyl
ether, a sorbitan fatty acid ester, a polyoxyethylene sorbitan
fatty acid ester, a polyoxyethylene alkyl phenyl ether and a
polyoxyethylene alkyl ether.
15. The process for producing inorganic spheres according to claim
1, wherein a Reynolds number of the flow said organic liquid in the
flow path is at most 2,100.
16. The process for producing inorganic spheres according to claim
1, wherein said organic liquid (A') is separated from the W/O
emulsion before solidification of the droplets.
17. The process for producing inorganic spheres according to claim
1, wherein said acid for contacting said organic liquid (A') is
carbon dioxide gas or a solid acidic substance.
18. The process for producing inorganic spheres according to claim
1, wherein said acid for contacting said organic liquid (A') is a
cation exchange resin.
19. The process for producing inorganic spheres according to claim
1, wherein said acid for contacting said organic liquid (A') is
sulfuric acid, hydrochloric acid, or nitric acid.
20. The process for producing inorganic spheres according to claim
1, wherein said acid for contacting said organic liquid (A') is
carbon dioxide gas.
Description
TECHNICAL FIELD
[0001] The present invention relates to a process for producing
inorganic spheres. Particularly, it relates to a process for
producing inorganic spheres having a substantially uniform particle
size useful for chromatography supports, cosmetic applications,
catalyst supports, etc., with high productivity by a stable
continuous process.
BACKGROUND ART
[0002] Heretofore, various methods have been proposed to obtain
inorganic spheres having a uniform particle size. U.S. Pat. No.
5,278,106 discloses a method for producing inorganic spheres which
comprises injecting an aqueous liquid into an organic solvent
through a microporous membrane to prepare a W/O type emulsion and
converting droplets in the resulting W/O type emulsion into
inorganic spheres.
[0003] The particle size distribution of the emulsion can be
narrowed by this method, but this method is insufficient in terms
of uniformity in the particle size of the inorganic spheres, since
the flow of the organic solvent is not controlled, which causes an
emulsion particle size distribution. Further, because a glass
microporous membrane with poor alkali resistance has problems with
its durability such as erosion of the pores to larger size by an
aqueous solution containing an alkali metal silicate as the aqueous
liquid, a W/O type emulsion having a uniform particle size can not
be obtained continuously and stably.
[0004] In recent years, U.S. Pat. No. 6,576,023 proposed a method
and an apparatus for producing a homogenous emulsion by injecting a
pressurized aqueous solution containing an inorganic compound
through distorted micropores into an organic liquid. Recently,
development of a method and an apparatus which allow long-term
efficient and stable mass production of inorganic spheres having a
uniform particle size has been desired.
DISCLOSURE OF THE INVENTION
[0005] The object of the present invention is to provide a process
for producing inorganic spheres having a highly uniform particle
size stably with high productivity, suitable for mass
production.
[0006] The present invention provides a process for producing
inorganic spheres, which comprises a step of injecting an alkaline
aqueous liquid containing an inorganic compound into a laminar flow
of an organic liquid containing a surfactant and running at a flow
rate of from 0.001 to 2 m/s in a flow path compartmentalized by
diaphragms through micropores penetrating through one diaphragm in
its thickness direction to form a W/O type emulsion, a step of
solidifying droplets of the aqueous liquid containing an inorganic
compound in the W/O type emulsion by an acid to form inorganic
spheres, and a step of recycling the organic liquid separated and
recovered from the W/O emulsion or a liquid after formation of the
inorganic spheres, to the flow path for the organic liquid, wherein
the organic liquid recycled to the flow path for the organic liquid
is one which has been brought into contact with an acid in a state
of the W/O emulsion or after separated from the W/o emulsion.
[0007] Further, the present invention provides a process for
producing inorganic spheres, which comprises a step of injecting an
alkaline aqueous liquid containing an inorganic compound into a
laminar flow of an organic liquid containing a surfactant and
running at a flow rate of from 0.001 to 2 m/s in a flow path
compartmentalized by diaphragms through micropores penetrating
through one diaphragm in its thickness direction to form a W/O type
emulsion, and a step of solidifying droplets of the aqueous liquid
containing an inorganic compound in the W/O type emulsion by an
acid to form inorganic spheres, wherein the organic liquid supplied
to the flow path for the organic liquid is one which has been
brought into contact with the alkaline aqueous liquid and then
separated and recovered.
BRIEF EXPLANATION OF THE DRAWINGS
[0008] FIG. 1 is a cross-sectional view illustrating an
emulsification apparatus used in Examples 1 and 2.
[0009] FIG. 2 is a diagram schematically illustrating production of
the inorganic spheres of the present invention.
[0010] FIG. 3 is a diagram schematically illustrating production of
the inorganic spheres of the present invention.
[0011] FIG. 4 is a cross-sectional view illustrating an
emulsification apparatus used in Examples 3 to 11.
EXPLANATION OF SYMBOLS
[0012] 1, 5, 10, 13: Acrylic resin plate [0013] 2, 11: Fluororesin
sheet [0014] 3, 12: Stainless steel plate [0015] 4: Acrylic resin
plate member [0016] 6, 7: Nozzle formed on the acrylic resin plate
1 [0017] 8: Nozzle formed on the acrylic resin plate 5 [0018] 9:
High speed camera [0019] 14, 15: Nozzle formed on the acrylic resin
plate 10 [0020] 16, 17: Nozzle formed on the acrylic resin plate 13
[0021] X: Micropores penetrating through the stainless steel plate
3 [0022] Y: Micropores penetrating through the stainless steel
plate 12
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] In the process for producing inorganic spheres of the
present invention, an alkaline aqueous liquid containing an
inorganic compound is injected through micropores into a laminar
flow of an organic liquid containing a surfactant to form an
emulsion containing the organic liquid as a dispersion medium
(continuous phase) and droplets of the aqueous solution containing
an inorganic compound as a dispersed phase in the continuous phase,
i.e. a W/O type emulsion, and then the droplets of the aqueous
liquid containing an inorganic compound in the W/O type emulsion
are solidified to form inorganic spheres.
[0024] As the alkaline aqueous liquid containing an inorganic
compound, any liquid may be used so long as it forms a precipitate
upon solidification. Not only an aqueous solution of an inorganic
compound but also a colloidal solution such as a silica sol may be
employed. As the aqueous solution of an inorganic compound,
specifically, an aqueous solution of an alkali metal silicate or
aluminate may be mentioned.
[0025] In the present invention, use of an aqueous liquid
containing as an inorganic compound at least one member selected
from the group consisting of potassium silicate, sodium silicate,
sodium aluminate and silica is preferred. Specifically, an aqueous
solution containing a water-soluble silica, an aqueous dispersion
containing a solid silica (colloidal silica) such as a silica sol
obtained by hydrolysis of an organic silicon compound or a
commercially available silica sol, and an aqueous solution of
potassium silicate or sodium silicate are preferably used. An
aqueous solution of sodium silicate is most preferred for
availability and economical reasons. The proportion of silicic acid
to sodium is preferably from 2.0 to 3.8, more preferably from 2.0
to 3.5, in terms of SiO.sub.2/Na.sub.2O molar ratio. The
concentration of the alkali silicate or silica in the aqueous
liquid is preferably from 5 to 30 mass %, particularly preferably
from 5 to 25 mass %, in terms of the SiO.sub.2 concentration.
[0026] As the organic liquid, an organic solvent having a
surfactant dissolved therein is used. As the organic solvent, a
C.sub.9-12 saturated hydrocarbon is preferred, and selection of the
organic liquid includes total consideration of ease of handling,
fire safety, ease of separation between the solidified particles
and the organic liquid, geometrical qualities of the inorganic
spherical particles, solubility of the organic liquid in water,
etc. The C.sub.9-12 saturated hydrocarbon may be used alone or as a
mixture of at least two. The C.sub.9-12 saturated hydrocarbon may
be a linear hydrocarbon or a hydrocarbon having side chains so long
as its chemical stability is good.
[0027] As the C.sub.9-12 saturated hydrocarbon, preferred is one
having a flash point of from 20 to 80.degree. C. If a saturated
hydrocarbon having a flash point below 20.degree. C. is employed as
the organic solvent, the excessively low flash point necessitates
countermeasures for fire prevention and work environment
protection. On the other hand, a hydrocarbon having a flash point
exceeding 80.degree. C. is hardly volatile and may adhere to the
resulting inorganic spheres in a large amount.
[0028] In the present invention, the W/O type emulsion and the
organic liquid are usually subjected to liquid-liquid separation,
and the inorganic spheres and the organic liquid after
solidification of the emulsion are usually subjected to
solid-liquid separation. The organic liquid adhering to or adsorbed
in the W/O type emulsion or the inorganic spheres after separation
is preferably vaporized off by e.g. a drying operation. The organic
liquid preferably has a boiling point of at most 200.degree. C. so
that the organic liquid easily vaporizes off, and as the organic
liquid which satisfies such requirements, preferred is at least one
member selected from the group consisting of C.sub.9H.sub.2O,
C.sub.10H.sub.22 and C.sub.11H.sub.24.
[0029] As the surfactant, although an anionic surfactant or a
cationic surfactant may be employed, a nonionic surfactant is
preferred because adjustment of the balance between hydrophilicity
and lipophilicity is easy. For example, a polyethylene glycol fatty
acid ester, a polyethylene glycol alkyl ether, a sorbitan fatty
acid ester, a polyoxyethylene sorbitan fatty acid ester, a
polyoxyethylene alkyl phenyl ether and a polyoxyethylene alkyl
ether are preferred.
[0030] The amount of the surfactant varies depending upon
conditions such as the type of the surfactant, HLB
(hydrophile-lipophile balance) as an index of the degree of
hydrophilicity or hydrophobicity of the surfactant and the aimed
particle size of the inorganic spheres. However, it is preferably
contained in an amount of from 500 to 50,000 ppm, preferably from
1,000 to 20,000 ppm, in the organic liquid. If it is less than 500
ppm, an unstable emulsion which contains large droplets of the
aqueous solution may be obtained upon emulsification. On the other
hand, if it exceeds 50,000 ppm, the amount of the surfactant
adhering to the inorganic spherical particles as the product
unfavorably tends to be large.
[0031] In the present invention, by adjusting the flow rate of the
organic liquid to from 0.001 to 2 m/s, emulsion droplets having a
narrow particle size distribution are formed, and therefore, the
particle size distribution of the obtained inorganic spheres can be
narrowed. The flow rate of the organic liquid is more preferably
from 0.01 to 1 m/s.
[0032] The Reynolds number of the flow of the organic liquid in the
flow path is adjusted to at most 2,100. When the flow path has a
circular cross section, the Reynolds number is calculated from the
formula 1, and as the inner diameter D of the flow path, the
minimum diameter of the cross section of the flow path is employed.
D is the inner diameter (m) of the flow path, u is the average flow
rate (m/s), .rho. is the fluid density (kg/m.sup.3), and .mu. is
the fluid viscosity (Pas).
Reynolds number (-)=Du.rho./.mu. Formula 1
[0033] When the cross section of the flow path is not circular, the
Reynolds number is calculated from the formula 2. r is the
hydraulic radius (m) of the flow path={cross-sectional area
(m.sup.2) of the flow path}/{perimeter (m) of the cross section of
the flow path which is in contact with the fluid}, and u, .rho. and
.mu. are as defined for the formula 1.
Reynolds number (-)=4.times.ru.rho./.mu. Formula 2
[0034] If the Reynolds number is at most 2,100, the flow of is the
organic liquid is laminar and therefore stable. As a result, the
aqueous liquid containing an inorganic compound supplied through
the micropores constantly forms a W/O type emulsion having a fixed
particle size, and therefore, inorganic spheres having a
substantially uniform particle size are likely to be produced. On
the other hand, if the Reynolds number exceeds 2,100, the flow of
the organic liquid is turbulent. Therefore, the resulting W/O type
emulsion tends to have uneven particle sizes, like conventional
ones, and the resulting inorganic spheres also have uneven particle
sizes. The shape of the flow path for the organic liquid is not
particularly limited. In order to stabilize the flow of the organic
liquid, the Reynolds number of the flow of the organic liquid is
preferably at most 500. The shape of the flow path for the organic
liquid is not particularly limited.
[0035] In the present invention, the organic liquid separated and
recovered from the W/O type emulsion or a liquid after formation of
the inorganic spheres is recycled to the flow path for the organic
liquid and recycled for the emulsification step. In order to stably
produce the W/O type emulsion over a long period, it is required
that surfactant ability is stable, and according to the studies by
the present inventors, it was found that the surfactant ability
gradually decreases by the contact with an alkali. The present
inventors have found that the decrease in the surfactant ability
can be suppressed by bringing the W/O type emulsion or the organic
liquid separated and recovered from the liquid after formation of
the inorganic spheres, in a state of the W/O type emulsion or after
separated from the W/O type emulsion, into contact with an acid.
Accordingly, a W/O type emulsion having a highly uniformalized
particle size and inorganic spheres can be produced stably with
high productivity over a long period by a stable continuous
process.
[0036] Further, as a result of various studies, the present
inventors have found that the surfactant ability initially
decreases after contact with an alkali in some cases depending upon
the type of the surfactant, but by use of an organic liquid which
has been preliminarily brought into contact with an alkali and then
separated and recovered to the emulsification step, influences of
such an initial decrease of the surfactant ability can be
avoided.
[0037] Now, the embodiment of the present invention will be
explained with reference to the drawings. In FIG. 1, numerical
references 1 and 5 designate acrylic resin plates, 2 a fluororesin
sheet, 3 a stainless steel plate and 4 an acrylic resin plate
member. In FIG. 1, the aqueous liquid containing an inorganic
compound is introduced from a nozzle 8 and injected through
micropores X penetrating through the stainless steel is plate 3
into a laminar flow of an organic liquid which is introduced from a
nozzle 6 and discharged from a nozzle 7. Further, in FIG. 4,
numerical references 10 and 13 designate acrylic resin plates, 11 a
fluororesin sheet and 12 a stainless steel plate. In FIG. 4, while
an aqueous liquid containing an inorganic compound runs so that it
is introduced from a nozzle 16 and discharged from a nozzle 17, it
is injected through micropores Y penetrating through the stainless
steel plate 12 into a laminar flow of an organic liquid which is
introduced from a nozzle 14 and discharged from a nozzle 15.
[0038] The aqueous liquid injected through the micropores X or Y
grows larger than the pore size of the micropores X or Y at their
outlet due to surface tension. Then, droplets are cut off by the
flow of the organic liquid and become droplets of a W/O type
emulsion in the organic liquid.
[0039] In the present invention, it is preferred that the organic
liquid separated and recovered from the liquid obtained after the
step of forming the W/O type emulsion is brought into contact with
an acid and then recycled to the flow path for the organic liquid
and recycled for the emulsification step. Specifically, as shown in
chart of FIG. 2, a method may be mentioned wherein the W/O type
emulsion discharged from the emulsification step is introduced into
a separation apparatus and separated into an organic liquid (A) and
a W/O type emulsion (B) in which the aqueous liquid is
concentrated, (A) is brought into contact with an acid and then
recycled to the flow path for the organic liquid and recycled for
the emulsification step, and at the same time, droplets of the
aqueous liquid containing an inorganic compound in (B) are
introduced for a solidification apparatus and solidified.
[0040] Further, as shown in FIGS. 2 and 3, a method may also be
preferably employed wherein the W/O type emulsion discharged from
the emulsification step is introduced into a solidification
apparatus, droplets of the aqueous liquid containing an inorganic
compound in the W/O type emulsion are solidified by an acid, and
the obtained solid is separated into an organic liquid (A') and
inorganic spheres (C), and (A') is subjected to deacidification
treatment and then recycled for the emulsification step. In such a
case, by use of an acid as a solidifying agent, acid treatment of
(A') may be carried out simultaneously with the solidification,
whereby inorganic spheres can be produced stably for a long
term.
[0041] Further, as shown in FIG. 2, it is more preferred to carry
out separation into (A') and (C) after separation into (A) and (B),
whereby the solvent recovery rate will be more improved. The
operation of recycling (A) or (A') to the flow path for the organic
liquid and recycling it for the emulsification step is included in
the operation of supplying the organic liquid separated and
recovered from the liquid after the alkaline aqueous liquid and the
organic liquid are brought into contact with each other, to the
flow path for the organic liquid and recycling it for the
emulsification step. When the organic liquid is recycled for the
emulsification step, as shown in FIGS. 2 and 3, it is preferred to
add an organic liquid in an amount corresponding to the amount of
loss in e.g. the separation step, and the organic liquid added in
such a case is also preliminarily brought into contact with an
alkali. However, in a case where the ratio of volume of the reduced
organic liquid is 30% or less relative to the organic liquid
introduced from the nozzle 6 or 14, the organic liquid which is not
preliminarily brought into contact with an alkali may be added.
[0042] The type of the separation apparatus used for the above
separation operation is not particularly limited, but preferred is
one which separates liquids employing a difference in specific
gravity between an aqueous liquid phase and an organic liquid
phase, in view of operation efficiency and the like. The separation
into (A) and (B) is carried out by making the emulsion stay in the
separation apparatus for from 1 minute to 12 hours. If the
retention time is shorter than 1 minute, separation will be
insufficient, and part of the aqueous liquid phase may accompany
the organic liquid phase, which leads to a decrease in the yield
and dispersion of quality. Further, if the retention time exceeds
12 hours, the droplets may be united to form large particles which
deviate from a desired droplet size, and expansion of the apparatus
may increase the installation cost. The retention time is more
preferably from 3 minutes to 8 hours.
[0043] On the other hand, the separation into (A') and (C) is
carried out preferably by making the mixture stay in the separation
apparatus for from 1 minute to 5 hours. If the retention time is
less than 1 minute, separation may be insufficient, and part of the
inorganic spheres may accompany the organic liquid phase, which
leads to a decrease in the yield and dispersion of quality.
Further, if the retention time exceeds 5 hours, precipitates tend
to be deposited on the bottom of a tank and are less likely to be
discharged and in addition, expansion of the apparatus may increase
the installation cost. The retention time is more preferably from 2
minutes to 3 hours.
[0044] When the organic liquid recovered by the above separation
operation is recycled, if there is possibility of an increase in
the temperature of the organic liquid e.g. by heat input by a pump,
the organic liquid is recycled preferably by being cooled through a
cooler for the purpose of preventing loss due to an increase of a
vapor pressure.
[0045] The acid to be in contact with the organic liquid may, for
example, be an inorganic acid or an organic acid. Particularly, it
is preferred to use carbon dioxide gas or a solid acidic substance
with a view to easily carrying out deacidification treatment after
the acid treatment of the organic liquid and before recycle for the
emulsification step, and as the solid acidic substance, a cation
exchange resin may, for example, be mentioned.
[0046] Further, the acid to be used for the solidification step, an
inorganic acid, e.g., sulfuric acid, hydrochloric acid, nitric acid
or carbon dioxide is preferred. Use of carbon dioxide gas is the
simplest and the most suitable from the viewpoint of easy
operations. As the carbon dioxide gas, pure carbon dioxide gas
having a 100% concentration may be introduced, or carbon dioxide
gas diluted with air or an inert gas may be introduced.
Particularly, an organic liquid having carbon dioxide gas dissolved
in a C.sub.9-12 saturated hydrocarbon is preferred, whereby
solidification can be carried out while keeping the shape of fine
droplets, and the solidification rate can easily be controlled.
Further, other advantages can be obtained such that excellent
operation efficiency will be obtained such that separation into the
inorganic spheres and the organic liquid after solidification
becomes easy, and that the solidification will moderately proceed.
The time required for the solidification is usually preferably from
4 to 30 minutes, and the temperature at the solidification is
preferably from 5 to 30.degree. C.
[0047] In the apparatus for producing inorganic spheres of the
present invention, as a material constituting a diaphragm, one
having resistance against the aqueous liquid containing an
inorganic compound and against the organic liquid is used. One
composed mainly of a metal is preferred in view of excellent
processability and strength, and in addition, one composed mainly
of a resin is also suitably used. As a resin, it is preferred to
use at least one member selected from a polyphenylene sulfide, a
polyether ether ketone, a polyimide, a polyamide, an aromatic
polyester and a fluororesin, in view of excellent processability
and dimensional stability.
[0048] The material constituting a diaphragm having micropores
penetrating in the thickness direction preferably has affinity for
the organic liquid or water repellency. This is to facilitate
release of the aqueous liquid containing an inorganic compound
after passing through the micropores from the diaphragm. It has
been found by observation by a high speed camera that if the
diaphragm is hydrophilic, the aqueous liquid after passing through
the micropores tends to flow along the diaphragm and form uneven
droplets in the emulsion. In a case where the diaphragm is made of
a metal material, it is preferred to make it have affinity for the
organic liquid by a method of baking an oil on it, or to coat the
surface with a water repellent having a hydrophobic resin or a
silane coupling agent dissolved in a solvent. In such a case, the
hydrophobic resin is preferably a thermoplastic resin, because even
if the micropores are clogged by coating, the pores can be opened
by heat treatment. Further, it is preferred to use as the
hydrophobic resin a solvent-soluble fluororesin in view of
durability.
[0049] Further, it is preferred that at least part of the diaphragm
constituting the flow path for the organic liquid is made of a
transparent material, whereby the step of forming emulsion droplets
can be continuously monitored from outside through the transparent
material, and inorganic spheres having a substantially uniform
particle size can be stably produced. The transparent material is
not particularly limited so long as it has durability against the
organic liquid and the aqueous liquid, and an acrylic resin, a
polycarbonate or the like is preferably used.
[0050] In FIG. 1, continuous monitoring is carried out by providing
a high speed camera 9 via an acrylic resin plate 1. It is preferred
that while image information obtained by the high speed camera 9 is
analyzed by image processing, emulsification conditions are
adjusted based on results of the analysis. The adjustment may be
carried out by manual or automatic control, but is carried out
preferably by automatic control in view of quick adjustment of the
emulsification conditions. Further, it is preferred to provide a
sliding guide so that the high speed camera 9 can move from side to
side and up and down, whereby dispersion of the emulsion droplet
size among the micropores can be observed.
[0051] In the present invention, the micropores preferably have a
circular cross section, but may have a cross section other than a
circular shape. The micropores preferably have at least one cross
section selected from the group consisting of a rectangular, an
ellipse and a triangle, which does not form a convex shape into the
inside, whereby processing will relatively easily be carried out,
and inorganic spheres having a uniform particle size can be stably
produced. However, it is essential that all the pores are pores
smaller than the width of the flow path for the organic liquid. The
method of forming the micropores may be a processing method
employing a laser such as an excimer laser or pressing, but is not
particularly limited.
[0052] In a case where the micropores have a cross section other
than a circular shape, it is estimated that droplets which become
droplets at the outlet of the pores have a curvature distribution,
and are spontaneously separated off at a relatively early stage and
become droplets in the organic liquid. Accordingly, there is such
an advantage that droplets having a relatively small emulsion
particle size tend to be easily obtained as compared with a case of
using circular pores. Further, the ratio of the diameter of a
circle which is circumscribed about the cross-sectional shape to
the diameter of a circle which is inscribed in the cross-sectional
shape is preferably at most 20, more preferably at most 10. If it
exceeds 20, the droplets tend to be divided in the major axis
direction and resultingly, uneven emulsion particles tend to be
obtained. It is particularly preferred that the diameter of a
circle which is inscribed in the cross-sectional shape is at least
1 .mu.m and that the diameter of a circle which is circumscribed
about the cross-sectional shape is at most 80 .mu.m.
[0053] The quadruple of the hydraulic radius r of the cross section
of the micropores is preferably from 0.1 to 100 .mu.m. It is more
preferably from 1 to 80 .mu.m. r is, in the same manner as for the
formula 2, the hydraulic radius (m) of the cross
section={cross-sectional area (m.sup.2) of micropore}/{perimeter
(m) of the cross section of the micropore which is in contact with
the fluid}. Accordingly, when the micropores have a circular cross
section, the hydraulic radius r=(the inner diameter D of the
circle)/4, and thus the quadruple of the hydraulic radius r
corresponds to the inner diameter D of the circle. If the quadruple
of the hydraulic radius r of the cross section of the micropores is
less than 0.1 .mu.m, the supply amount of the aqueous liquid
containing an inorganic compound tends to be small, such being
unfavorable in view of productivity. If it is larger than 100
.mu.m, emulsion particles having particle sizes which deviate from
the aimed particle size are likely to form.
[0054] In the present invention, it is preferred that a plurality
of micropores X or Y which supply the aqueous liquid containing an
inorganic compound are formed so that they penetrate through the
stainless steel plate 3 or 12 on the flow path for the organic
liquid in its thickness direction, in view of productivity. It is
preferred that 100 or more, particularly preferably 1,000 or more
micropores are formed, whereby sufficient productivity will be
obtained.
[0055] Further, although the arrangement of the micropores X or Y
is not particularly limited, in view of productivity and
processability, preferred is a parallel arrangement wherein a
plurality of micropores are formed at constant pitches in the width
direction (width direction of the flow path for the organic liquid)
and in the length direction (direction of the flow of the organic
liquid), respectively, on the stainless steel plate 3 or 12, or a
zigzag arrangement wherein among micropores arranged in parallel,
two micropores adjacent to each other in the width direction and
two micropores adjacent to each other in the length direction are
selected, and another micropore is formed on the center of
diagonals of a rectangular formed by connecting centers of these
pores. The zigzag arrangement is particularly preferred in view of
improvement of productivity, since the micropores can be densely
arranged, whereby the open area ratio can be increased.
[0056] On this occasion, the open area ratio of the stainless steel
plate 3 or 12 is preferably from 1 to 35%. If the open area ratio
is 1% or low, the productivity tends to be low, and the
installation cost tends to be comparatively high. On the other
hand, if the open area ratio is 35% or higher, droplets of the
emulsion formed by injecting the aqueous liquid through the
micropores may be united and as a result, uneven droplets are
likely to form. The open area ratio is more preferably from 2 to
25%.
[0057] The open area ratio when a plurality of micropores having a
constant area are arranged in a constant arrangement is calculated
from the formula 3. S is the cross-sectional area (m.sup.2) of the
micropores, P.sub.1 is the pitch (m) in the width direction and
P.sub.2 is the pitch (m) in the length direction.
Open area ratio (%)=100.times.S/(P.sub.1.times.P.sub.2) Formula
3
[0058] The open area ratio when circular micropores are formed in a
parallel arrangement can be calculated from the formula 4. D is the
diameter (m) of the micropores, and P.sub.1 and P.sub.2 are as
defined for the formula 3.
Open area ratio (%)=78.5.times.D.sup.2/(P.sub.1.times.P.sub.2)
Formula 4
[0059] Further, when circular micropores are formed in a zigzag
arrangement, the open area ratio when the angle formed by the
above-defined two diagonals is 90.degree. (square zigzag
arrangement) can be calculated from the formula 5, and the open
area ratio when the angle is 60.degree. (60.degree. zigzag
arrangement) can be calculated from the formula 6. D is as defined
for the formula 4, and P is the pitch (m). P in the formula 6
represents the shorter pitch (m) between the pitches in the width
direction and in the length direction.
Open area ratio (%)=157.times.D.sup.2/P.sup.2 Formula 5
Open area ratio (%)=91.times.D.sup.2/P.sup.2 Formula 6
[0060] The micropores X or Y are formed on the stainless steel
plate 3 or 12 with a distance of at least half the diameter of a
circle which is circumscribed about the cross-sectional shape of
the micropores. They are formed more preferably with a distance of
at least the diameter of a circle which is circumscribed about the
cross-sectional shape of the micropores. If the micropores are
formed only with a distance shorter than a half of the diameter of
the circumscribed circle, droplets of the emulsion are likely to be
united and as a result, uneven droplets may form. However, the
micropores are formed preferably as closely as possible within a
range where the droplets will not be united, so as to improve
productivity.
[0061] Further, with a view to efficiently obtaining inorganic
spheres having an aimed particle size, in the present invention,
the ratio of the average particle size of the inorganic spheres to
the quadruple of the hydraulic radius r of the cross section of the
micropores is preferably from 0.1 to 5.0, more preferably from 0.3
to 3.0. If this ratio is less than 0.1, the productivity tends to
be low, and it is highly possible that the average particle size of
the obtained inorganic spheres is larger than the aimed value. On
the other hand, if it exceeds 5.0, the particle size is less likely
to be controlled, and it is highly possible that particulate
particles having particle sizes which largely deviate from the
aimed particle size are formed as by-products.
[0062] The particle size of the droplets in the resulting W/O type
emulsion is affected not only by the above-defined conditions of
forming the micropores but also by the ratio of the linear velocity
of the organic liquid to the linear velocity of the aqueous liquid
in the flow direction. The linear velocity of the aqueous liquid in
the flow direction is measured at the micropore portion. The linear
velocity ratio is preferably from 1 to 500, more preferably from 10
to 300. It is not economically preferable that the ratio exceeds
500 because the organic liquid is likely to be overspent. It is
unfavorable that the ratio is less than 1, because the flow of the
organic liquid can not carry away the droplets effectively, and is
uneven emulsion droplets are likely to be formed.
[0063] In the present invention, when the inorganic compound in the
aqueous liquid containing an inorganic compound is an alkali
silicate or silica, gelation of the W/O type emulsion by an acid
allows the dispersed spherical droplets of the aqueous solution to
gel in the same shape and gives a spherical silica hydrogel. For
gelation, it is preferred to introduce a gelling agent to the
emulsion.
[0064] After completion of the gelation, it is preferred to keep
the reaction system still so that the emulsion separates into two
phases, the organic liquid phase and the aqueous phase containing a
silica hydrogel, and then isolate the silica gel. When a saturated
hydrocarbon is used as the organic liquid, the phase of the organic
liquid separates out as the upper layer, while the phase of the
aqueous liquid containing a silica hydrogel separates out as the
lower layer, and then they are separated by a known means,
preferably by means of a separation apparatus as mentioned
above.
[0065] If necessary, an acid such as sulfuric acid is added to the
aqueous slurry of the silica hydrogel to a pH of about from 1 to
about 5 to complete the gelation, and then the aqueous slurry is
subjected to steam distillation at a temperature of from 60 to
150.degree. C., preferably from 80 to 120.degree. C. to evaporate
any slight amount of the saturated hydrocarbon remaining in the
aqueous slurry. Further, the aqueous slurry is heated at an
appropriate pH of from about 7 to about 9 to age the silica
hydrogel.
[0066] After the aging as the cases requires, the aqueous slurry is
filtered to recover the silica hydrogel, and the silica hydrogel is
dried at a temperature of from about 100 to about 150.degree. C.
for from about 1 to about 30 hours to give porous silica spherical
particles.
[0067] When an alkali silicate aqueous solution is used as the
aqueous liquid, it is preferred to adequately wash the silica
hydrogel recovered by filtration (wet cake) with water in order to
prevent an alkali metal salt (e.g., sodium carbonate when the
gelling agent is carbon dioxide) formed as a by-product by gelation
from contaminating the porous silica spheres. If necessary, water
may be added to the washed wet cake to make a slurry again, and
filtration and washing with water are repeated again. In this case,
pH adjustment of the slurry to from about 1 to about 5 and aging of
the silica hydrogel may be carried out again, if necessary.
EXAMPLE 1
(1) Preparation of Solutions
[0068] A sodium silicate aqueous solution having a SiO.sub.2
concentration of 24.4 mass % and a Na.sub.2O concentration of 8.14
mass % (SiO.sub.2/Na.sub.2O molar ratio=3.09, density: 1,320
kg/m.sup.3) was prepared. As the organic solvent, isononane
(C.sub.9H.sub.2O, density: 730 kg/m.sup.3) was employed, and
sorbitan monooleate as a surfactant was preliminarily dissolved in
an amount of 5,000 ppm in isononane.
(2) Assembly of Emulsification Apparatus
[0069] A cross-sectional view of an emulsification apparatus is
shown in FIG. 1. On a 50 mm-square acrylic resin plate 1 having a
thickness of 2 mm, two pores having an inner diameter of 3.2 mm
were formed, and rubber tube pipes (TYGON tube R-3603, manufactured
by Norton) having an outer diameter of 3.2 mm were connected to the
two pores to make nozzles 6 and 7 so that a liquid could be
supplied through the nozzle 6, and the liquid could be discharged
through the nozzle 7. At the center of another 50 mm-square acrylic
resin plate 5 having a thickness of 2 mm, a pore having an inner
diameter of 3 mm was opened, and a tetrafluoroethylene tube pipe
having an inner diameter of 1 mm was connected via a joint member
to make a nozzle 8 so that a liquid could be supplied through the
nozzle 8. A 30 mm square was hollowed out at the center of another
50 mm-square acrylic resin plate having a thickness of 2 mm with a
margin of 10 mm from the periphery left to prepare an acrylic resin
plate member 4. Further, a slit with a width of 3 mm and a length
of 35 mm was formed on a 50 mm-square fluororesin sheet having a
thickness of 400 .mu.m to prepare a fluororesin sheet 2. Then, at a
center portion of a 50 mm-square stainless steel plate 3 having a
thickness of 50 .mu.m, 28 pores with a pitch of 100 .mu.m in the
width direction and 230 pores with a pitch of 100 .mu.m in the
length direction in a parallel arrangement, totally 6,440 pores,
each pore having an inner diameter 4r=30 .mu.m and a circular
cross-sectional shape, were opened to prepare micropores X by an
excimer laser. The open area ratio of the stainless steel plate 3
was 7.1% in a range surrounded by lines connecting centers of the
outermost pores in the width direction and in the length
direction.
[0070] The acrylic resin plate 1, the fluororesin sheet 2, the
stainless steel plate 3, the acrylic resin plate member 4 and the
acrylic resin plate 5 were laminated in this order, and four sides
were clamped with equal forces. On this occasion, the width
direction and the length direction of the pores opened on the
stainless steel plate 3 were fitted to the width direction and the
length direction of the slit formed on the fluororesin sheet 2,
respectively, so that the pores were located at the center portion
of the slit and the pore of the nozzle 6 and the pore of the nozzle
7 of the acrylic resin plate 1 were located on the slit of the
fluororesin sheet 2. Further, the assembled apparatus was checked
for leaks by preliminarily supplying water.
[0071] A high speed camera 9 was disposed in front of the acrylic
resin plate 1 to continuously monitor the shape and the particle
size of emulsion droplets to be formed employing illumination.
(3) Emulsification
[0072] The emulsification apparatus assembled in (2) was
horizontally placed, and the isononane having a surfactant
dissolved therein prepared in (1) was supplied from the nozzle 6,
while the sodium silicate aqueous solution prepared in (1) was
supplied from the nozzle 8 to continuously produce a W/O type
emulsion in which the sodium silicate aqueous solution was
dispersed in the isononane having a surfactant dissolved therein.
The isononane having a surfactant dissolved therein was supplied at
a rate of 1,350 mL/h. The experiment was carried out at room
temperature for 2 hours.
[0073] The Reynolds number of the flow of the isononane was about
213 as calculated from a hydraulic radius of the flow path of 176.5
.mu.m, a linear velocity of 0.31 m/s and a viscosity of
7.5.times.10.sup.-4 Pas, and the flow of the isononane was laminar.
The supply of the sodium silicate aqueous solution was 32.2 mL/h,
and the linear velocity in the flow direction at the pores was
2.0.times.10.sup.-3 m/s.
[0074] The ratio of the linear velocity of the isononane in the
flow direction to the linear velocity of the sodium silicate
aqueous solution supplied through the pores in the flow direction
at the pore portion was 159. The state of emulsification was
confirmed by the high speed camera, whereupon the sodium silicate
aqueous solution was formed into droplets at the outlet of the
pores, and the emulsion particles had a substantially uniform
particle size of about 60 .mu.m.
(4) Phase Separation
[0075] The W/O type emulsion taken out from the emulsification
apparatus was separated into an isononane phase and an emulsion
phase utilizing a difference in specific gravity in a separation
tank (diameter: 120 mm, height: 300 mm) having an effective volume
of about 3 L. The retention time in the separation tank was 2.2
hours. The isononane phase after separation was supplied to the
nozzle 6 and recycled for the emulsification operation.
(5) Gelation
[0076] While the emulsion phase separated in (4) was continuously
supplied to a container (diameter: 100 mm, height: 650 mm) having a
volume of about 5 L, carbon dioxide gas was blown into it at a
supply rate of 300 mL/min for preliminary gelation to obtain an
aqueous silica hydrogel slurry. The aqueous silica hydrogel slurry
was adjusted to pH 9 at 25.degree. C. with a 0.1 N aqueous sulfuric
acid solution and aged at 80.degree. C. for 1 hour. Then, it was
allowed to cool to room temperature, adjusted to pH 2 with a 20
mass % aqueous sulfuric acid solution, allowed to stand still for 3
hours and filtered. The filter cake was washed with water and dried
at 120.degree. C. for 20 hours to give porous silica spheres. The
yield of the obtained porous silica spheres was 19.7 g.
(6) Geometrical Analysis
[0077] It was confirmed by scanning electron microphotography that
the obtained porous silica spheres were almost completely
spherical. The particle size distribution was calculated by
actually measuring the particle sizes of a total of more than 1,000
spheres in several photographs. The arithmetical mean particle size
was 50 .mu.m with a standard deviation of 6.4 .mu.m. The value
obtained by dividing the standard deviation in the particle size
distribution by the arithmetical mean particle size was 0.128,
which indicates that the porous silica spheres had a substantially
uniform particle size.
EXAMPLE 2
[0078] A W/O type emulsion was continuously produced in the same
manner as in Example 1. Isononane having a surfactant dissolved
therein was put in a container (diameter: 100 mm, height: 650 mm)
having a volume of about 5 L, and while carbon dioxide gas was
blown into the solution at a supply rate of 300 mL/min, the
above-obtained W/O type emulsion was continuously supplied to the
container for gelation. The formed silica hydrogel was separated
into an isononane phase and an aqueous liquid phase utilizing a
difference in specific gravity in a separation tank (diameter: 110
mm, height: 240 mm) having an effective volume of about 2 L to
obtain an aqueous silica hydrogel slurry. The retention time was
1.4 hours. The obtained aqueous slurry was aged and filtered, and
the filter cake was washed with water and dried in the same manner
as in Example 1 to obtain porous silica spheres. The yield of the
obtained porous silica spheres was 19.5 g. The isononane phase
after separation was supplied to the nozzle 6 and recycled for the
emulsification operation.
[0079] It was confirmed by scanning electron microphotography that
the obtained porous silica spheres were almost completely
spherical. The arithmetical mean particle size was 51 .mu.m with a
standard deviation of 6.8 .mu.m. The value obtained by dividing the
standard deviation in the particle size distribution by the
arithmetical mean particle size was 0.133, which indicates that the
porous silica spheres had a substantially uniform particle
size.
EXAMPLE 3
(1) Assembly of Emulsification Apparatus
[0080] A cross-sectional view of an emulsification apparatus is
shown in FIG. 4. Two pores having an inner diameter of 3.2 mm were
formed on a 50.times.120 mm rectangular acrylic resin plate 10
having a thickness of 20 .mu.m, and rubber tube pipes (TYGON tube
R-3603, manufactured by Norton) having an outer diameter of 3.2 mm
were connected to make nozzles 14 and 15 so that a liquid could be
supplied through the nozzle 14, and the liquid could be discharged
through the nozzle 15. At the center of another 5.times.120 mm
rectangular acrylic resin plate 13 having a thickness of 20 mm, a
linear channel with a width of 5 mm and a depth of 2 mm was formed,
pores having an inner diameter of 3 mm were opened at both ends,
and tetrafluoroethylene tube pipes having an inner diameter of 1 mm
were connected to the pores via a joint member to make nozzles 16
and 17 so that a liquid could be supplied through the nozzle 16 and
a liquid could be discharged through the nozzle 17. Then, on a
50.times.120 mm rectangular fluororesin sheet having a thickness of
400 .mu.m, a slit with a width of 3 mm and a length of 70 mm was
formed to prepare a fluororesin sheet 11. Further, at the center
portion of a 50.times.100 mm rectangular stainless steel plate 12
having a thickness of 50 .mu.m, 26 pores with a pitch of 100 .mu.m
in the width direction and 301 pores with a pitch of 100 .mu.m in
the length direction in a parallel arrangement, totally 13,026
pores, each pore having an inner diameter 4r=30 .mu.m and a
circular cross-sectional shape, were opened to make micropores Y by
an excimer laser. Then, the stainless steel plate 12 was treated
with a solution having a solvent-soluble fluororesin (CYTOP,
manufactured by Asahi Glass Company, Limited) dissolved in a
solvent (CT-solv100, manufactured by Asahi Glass Company, Limited)
to form a fluororesin layer in a thickness of 0.1 .mu.m. The open
area ratio of the stainless steel plate 12 measured in the same
manner as in Example 1 was 7.1%.
[0081] The acrylic resin plate 10, the fluororesin sheet 11, the
stainless steel plate 12 and the acrylic resin plate 13 were
laminated in this order, and top and bottom two sides were clamped
with equal forces. On that occasion, the width direction and the
length direction of the pores opened on the stainless steel plate
12 were fitted to the width direction and the length direction of
the slit formed on the fluororesin sheet 11, respectively, so that
the pores were located at the center portion of the slit and the
pore of the nozzle 14 and the pore of the nozzle 15 of the acrylic
resin plate 10 were located on the slit of the fluororesin sheet
11. Further, the assembled apparatus was checked for leaks by
preliminarily supplying water.
(2) Emulsification
[0082] The emulsification apparatus assembled in (1) was placed at
a right angle to a horizontal plane as shown in FIG. 4. The
isononane prepared in the same manner as in Example 1 except that
the concentration of the surfactant was 20,000 ppm was supplied
from the nozzle 14, and the sodium silicate aqueous solution
prepared in the same manner as in Example 1 was supplied from the
nozzle 16 to continuously produce a W/O type emulsion. The
isononane having a surfactant dissolved therein was supplied at a
rate of 900 mL/h. The experiment was carried out at room
temperature for 1 hour.
[0083] The Reynolds number of the flow of the isononane was about
137 as calculated from a hydraulic radius of the flow path of 176.5
.mu.m, a linear velocity of 0.20 m/s and a viscosity of
7.5.times.10.sup.-4 Pas, and the flow of the isononane was laminar.
The supply of the sodium silicate aqueous solution was 29 mL/h, and
the linear velocity in the flow direction at the pores was
8.7.times.10.sup.-4 m/s.
[0084] The ratio of the linear velocity of the isononane in the
flow direction to the linear velocity of the sodium silicate
aqueous solution supplied through the pores in the flow direction
at the pore portion was 238.
[0085] The W/O type emulsion taken out from the emulsification
apparatus was separated into an isononane phase and an emulsion
phase utilizing a difference in specific gravity in a separation
tank (diameter: 120 mm, height: 300 mm) having an effective volume
of about 3 L. The separated isononane phase was supplied to the
nozzle 14 and recycled for the emulsification operation. This
recycle was repeated four times.
[0086] Part of the emulsion phase obtained after each separation
operation was sampled, and the average emulsion size (.mu.m) was
observed by an optical microscope, and results shown in Table 1
were obtained (in Table 1, n (time) represents the number of time
isononane used). Using FT-IR, the concentration of the surfactant
was quantitatively analyzed from carbonyl absorption intensity, and
no change in concentration was confirmed among the respective
samples.
TABLE-US-00001 TABLE 1 n Emulsion size 1 55 2 100 3 120 4 120 5 110
6 120
[0087] It is judged from the results shown in Table 1 that although
the surfactant ability of the organic liquid initially decreases by
the contact with the aqueous liquid, it is relatively stable after
the third use of the isononane.
EXAMPLES 4 to 10
[0088] 10 L of isononane was prepared in the same manner as in
Example 1 except that the concentration of the surfactant was
20,000 ppm, and 1.2 L thereof was put in a 2 L beaker, and a liquid
containing an alkali as identified in Table 2 was added, followed
by mixing for 10 minutes with a stirrer. A W/O type emulsion was
prepared in the same manner as in Example 3 except that the above
liquid was left to stand overnight and then about 1 L of the
isononane phase as an upper phase was collected and used as an
organic liquid. Part of the obtained emulsion was sampled, and it
was observed by an optical microscope whether an emulsion was
formed or not. Further, a change in the emulsion size after left to
stand overnight was observed by an optical microscope, to examine
stability of the emulsion. The results are shown in Table 2.
TABLE-US-00002 TABLE 2 Treatment method NaOH aqueous Sodium Amount
of solution silicate sodium added Emulsion concentration aqueous
Addition per solvent formation Emulsion (N) solution amount *2)
(g/L) ability stability Ex. 4 5 -- 3.5 0.40 X -- Ex. 5 1 -- 3.5
0.081 .largecircle. X Ex. 6 0.5 -- 0.14 0.002 .largecircle.
.largecircle. Ex. 7 0.5 -- 0.7 0.008 .largecircle. .largecircle.
Ex. 8 0.5 -- 3.5 0.040 .largecircle. .largecircle. Ex. 9 0.05 -- 70
0.081 .largecircle. .largecircle. Ex. 10 -- *1) 0.5 0.040
.largecircle. .largecircle. *1) Prepared in the same manner as in
Example 1 *2) Addition amount (mL) per liter of the organic
liquid
[0089] It is found from the results shown in Table 2 that the
surfactant ability of the organic liquid remarkably decreases by
the contact with a strongly alkaline aqueous solution.
EXAMPLE 11
[0090] An emulsification apparatus was assembled in the same manner
as in Example 3 except that one having a thickness of 200 .mu.m was
used for the fluororesin sheet 2, and the inner diameter of the
pores opened on the stainless steel plate 3 was 20 .mu.m. Using the
assembled emulsification apparatus, a W/O type emulsion was
prepared in the same manner as in Example 10. The amount of
isononane used was 950 mL/time. The loss of isononane and the like
in one emulsification operation was roughly estimated at 100 mL/n,
and the recycle was repeatedly carried out while the organic liquid
prepared in the same manner as in Example 10 was added in an amount
of 100 mL/time to the isononane phase obtained after each
separation operation to continuously prepare a W/O type
emulsion.
[0091] To the separated emulsion, isononane containing 7,000 ppm of
a surfactant was added so that the total amount would be 900 mL,
and carbon dioxide gas was blown for 30 minutes at a rate of 200
mL/min to solidify droplets. The resulting solid was separated,
washed and dried to obtain porous silica spheres. The particle size
distribution of the obtained porous silica spheres was measured by
means of an electrical sensing zone method (Multisizer 3,
manufactured by Beckman Coulter, Inc.) using an aperture of 140
.mu.m. The results are shown in Table 3.
TABLE-US-00003 TABLE 3 average particle n size (.mu.m)
D.sub.25/D.sub.75 1 47.7 1.15 6 47.1 1.14 11 49.0 1.17 17 48.4 1.16
24 49.6 1.16 49 52.4 1.18 55 56.3 1.18 60 55.1 1.26 66 51.2 1.22 85
57.2 1.23 After carbon 48.3 1.16 dioxide treatment
[0092] It is found from the results shown in Table 3 that both
average particle size and particle size distribution width
gradually increase with time by repeated use of isononane.
[0093] Then, into the organic liquid (about 800 mL) used 85 times,
carbon dioxide gas was blown for 30 minutes at a rate of 200
mL/min, and then the air was blown for 15 minutes at a rate of 200
mL/min to carry out decarboxylation treatment, and the isononane
solution prepared in the same manner as in Example 10 was added
thereto so that the total amount would be 950 mL, and the resulting
liquid was used again as the organic liquid to prepare a W/O type
emulsion, which was subjected to solidification treatment in the
same manner as mentioned above to obtain porous silica spheres. The
average particle size and the particle size distribution of the
porous silica spheres measured in the same manner as mentioned
above are shown in Table 3.
[0094] It is found from the results shown in Table 3 that the
surfactant ability of the organic liquid recovers by acid treatment
(carbon dioxide gas treatment).
INDUSTRIAL APPLICABILITY
[0095] According to the present invention, inorganic spheres having
a substantially uniform particle size can be produced with high
productivity by a stable continuous process.
[0096] The entire disclosure of Japanese Patent Application No.
2003-133992 filed on May 13, 2003 including specification, claims,
drawings and summary is incorporated herein by reference in its
entirety.
* * * * *