JP2003226516A - Silica and method for producing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica having a large mode pore diameter, controlled pore properties, a low total content of unnecessary metal impurities and also excellent heat and water resistances, etc. <P>SOLUTION: The silica has the following properties: (a) a pore volume of the silica is 0.6-1.6 ml/g; (b) a specific surface area of the silica is 50-600 m<SP>2</SP>/g; (c) a mode pore diameter (D<SB>max</SB>) of the silica is ≥15 nm; (d) a value of Q<SP>4</SP>/Q<SP>3</SP>in a solid-state Si-NMR (nuclear magnetic resonance) spectrum of the silica is ≥3; (e) the silica is amorphous; and (f) a total content of metal impurities in the silica is ≤100 ppm. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel silica and a method for producing the same. Specifically, it relates to a novel porous silica having excellent hydrothermal resistance and having pores having a relatively large pore diameter, and a method for producing the same.

[0002]

BACKGROUND ART Silica is a porous material that has been widely used as a desiccant for a long time, but recently its use is expanding to catalyst carriers, separating agents, adsorbents, etc. Therefore, the requirements for silica performance are diversifying. The performance of silica depends on the surface area of silica,
It is determined by physical properties such as pore size, pore volume, and pore size distribution, and these properties are greatly affected by the silica production conditions.

"Silica" refers to both silicic anhydride and hydrous silicic acid. Examples of silicic acid anhydride include quartz, tridymite, cristobalite, coesite, stishovite, and quartz glass. And, as the hydrous silicic acid, obtained by gelling and drying silica hydrosol, in addition to so-called amorphous "silica gel", colloidal silica, silicate oligomer, and formed by using an organic substance as a template, for example, manufactured by Mobil Co. Examples thereof include silica of a type such as MCM-41 (so-called micelle template type silica) and the like. Further, examples of the raw material of “silica gel” include water glass and alkoxysilanes.

As a method for producing silica, which is a porous material, a method in which hydrothermal treatment of silica hydrogel is used to control pore characteristics has been widely known. As a raw material of this silica hydrogel, for example, a method using sodium silicate, so-called water glass, has been widely performed.

The most frequent pore diameter (D _max ) is, for example, 15 nm.
As described above, when producing silica having a relatively large pore diameter, generally known is a method of hydrothermally treating silica hydrogel under conditions of high temperature or high pH. Impurities such as alkali metal and alkaline earth metal of silica (hereinafter collectively referred to as “alkali metal impurities”) are mainly derived from water glass as a raw material, and the water glass is neutralized with an acid such as sulfuric acid, The hydrogel containing the neutralized salt is washed and removed by washing with water. However, it is impossible to completely remove it, and tens to hundreds of pp are contained in silica hydrogel.
Alkali metal impurities of m remain.

When the pH condition of the hydrothermal treatment for controlling the pores after the washing with water is acidic or neutral, which is a condition for obtaining silica having a relatively small pore diameter, some amount is obtained even during the hydrothermal treatment. Alkali metal impurities are removed by extraction, and the content of alkali metal impurities remaining in the product, porous silica, can be reduced to about several tens of ppm.

However, since the pH condition of hydrothermal treatment for obtaining silica having a relatively large pore diameter as described above is alkaline, alkali metal impurities in silica hydrogel are difficult to be extracted and removed. When an alkali component such as NaOH is used for pH adjustment during the hydrothermal treatment, alkali metal or alkaline earth metal is further brought into the hydrothermal treatment system, and alkali metal impurities in the porous silica product. There was a problem that the amount would be very high.
Even when a pH adjusting agent containing no alkali metal such as ammonia water is used, the dissolution and precipitation reaction on the silica surface becomes very active under hydrothermal treatment conditions of high temperature and high pH, so that it remains in the silica hydrogel. There was a problem that the micropores of silica were sealed before the alkali metal impurities derived from the raw materials were eluted from the silica hydrogel, and the alkali metal impurities remained in the product.

Even if the impurities are to be removed later by a method such as acid cleaning of the porous silica product, it is very difficult to almost completely remove the alkali metal impurities. Further, it is difficult to remove residual alkali metal impurities when a compound of alkali metal or alkaline earth metal is used as a pH adjuster during hydrothermal treatment by the same method.

As described above, conventional porous silica having a relatively large pore diameter has a problem that the amount of alkali metal impurities is larger than that of porous silica having a small pore diameter. Alkali metal impurities act as a catalyst that cleaves / recombines the siloxane bonds in the silica skeleton when porous silica is used under severe conditions such as high temperature and high pressure, and lowers sintering temperature and high hydrothermal conditions. Since it acts as a catalyst to accelerate the dissolution / precipitation of silica, and eventually changes the pore structure, silica with a large amount of alkali metal impurities is likely to change its physical properties, leading to early deterioration of the pore characteristics. was there.

On the other hand, as a method for obtaining high-purity porous silica having a low content of metal impurities, a method of hydrolyzing silicon alkoxide into silica hydrogel and subjecting it to hydrothermal treatment is known (eg, non-patent document). Reference 1).
With this method, the amount of impurities originating from the raw material can be suppressed to a low level, and therefore the influence of the alkali metal impurities as described above can be reduced. However, even with such a method for producing a porous silica derived from a silicon alkoxide, it has not been possible to obtain a porous silica with a controlled pore size, in which the spread of the pore diameter distribution is suppressed.

In addition, as a method for producing high-purity porous silica, a method using an organic or inorganic template is known. In this method, the pore distribution controllability is excellent, and the above-mentioned D _max is large. Porous silica (micelle template silica) of 15 nm or more is obtained (Example: Non-Patent Document 2). However, the porous silica obtained by this method has a fine pore distribution that is controlled and sharp, but has very thin pore walls, which poses a problem in terms of hydrothermal resistance, and further, the manufacturing process is complicated. However, there was a problem of low productivity.

[0012]

[Non-Patent Document 1] Colloids Surfaces 63, 33 (1992)

[Non-Patent Document 2] Langmuir 16 (2), 356 (2000)

[0013]

As described above, a porous material having a relatively large D _max , a narrow pore size distribution controlled, a high purity and an excellent hydrothermal resistance, particularly porous silica, and a method for producing the same are desired. However, a satisfactory porous silica and a method for producing the same have not been provided yet.

The present invention has been made in view of the above-mentioned problems, and an object thereof is to have a mode diameter (D _max ) of 15 n.
It is to provide a porous silica having a relatively large value of m or more, a controlled pore characteristic, a low content of unnecessary metal impurities, and an excellent hydrothermal resistance, and a method for producing the same.

[0015]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that Q ^{4 in} solid-state Si-NMR in a silica skeleton having specific pore characteristics.
It has been found that porous silica having a / Q ³ value of a specific value or more solves the above problems. Furthermore, silicon alkoxide is used as a raw material, and hydro obtained by hydrolyzing the silicon alkoxide is subjected to a hydrothermal treatment step under specific conditions without being substantially aged. It was found that a novel silica having the above can be industrially provided with high productivity, and the present invention has been completed.

That is, the gist of the present invention relates to silica characterized by having the following characteristics. (A) Pore volume of 0.6 ml / g or more, 1.6 ml / g
The following (b) specific surface area is 50 to 600 m ² / g (c) modal pore diameter (D _max ) is 15 nm or more (d) Q ⁴ / Q ³ value in solid Si-NMR is 3 or more (e) non- Being crystalline (f) Content of metal impurities is 100 ppm or less

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described in detail below. (1) Characteristics of silica of the present invention In the present invention, "silica" refers to hydrous silicic acid. Hydrous silicic acid is represented by a rational formula of SiO ₂ .nH ₂ O. In the present invention, as will be described later, the effect is remarkable in so-called "silica gel" and micellar template type silica among silica.

The silica of the present invention is characterized in that the pore volume and the specific surface area are present in a range larger than usual values. Specifically, the value of pore volume is usually 0.6 ml / g
Above, above all, preferably 0.7 ml / g or above, and usually below 1.6 ml / g, and above all preferably 1.5
It is less than or equal to ml / g.

The value of specific surface area is usually 50 m ² / g
Or more, more preferably 100 m ² / g or more, particularly preferably 200 m ² / g or more, usually 600 m ² / g or less, more preferably 450 m ² / g or less, particularly preferably 350 m ² / g or less, particularly preferably 290m ² / g
It is the following. These pore volume and specific surface area are measured by the BET method by nitrogen gas adsorption / desorption.

Further, the silica of the present invention was obtained from EP Barrett, LG according to the isothermal desorption curve measured by the nitrogen gas adsorption / desorption method.
Joyner, PH Haklenda, J. Amer. Chem. Soc., Vol.
73,373 (1951), the pore distribution curve calculated by the BJH method, that is, the differential nitrogen gas adsorption amount (ΔV / Δ (logd); V is the nitrogen gas adsorption volume) with respect to the pore diameter d (nm). Most frequent pore diameter (D _max ) on the plot of
Is 15 nm or more. This means that the mode diameter (D _max ) of the silica gel of the present invention is in a range larger than that of ordinary silica gel. Above all, 16 nm or more is preferable, and 17 nm or more is particularly preferable. The upper limit is not particularly limited, but is usually 50n
m or less, preferably 40 nm or less, particularly preferably 30
nm or less.

In addition, in the silica of the present invention, the total volume of pores in the range of ± 20% of the value of the mode diameter (D _max ) is usually 50% or more of the total volume of all pores, Preferably 60
% Or more, more preferably 70% or more. This means that the diameter of the pores of the silica of the present invention is uniform in the pores in the vicinity of the most frequent diameter (D _max ), that is, the pore diameter distribution is extremely narrow (sharp). . The upper limit of the value of this ratio is not particularly limited, but is usually 90% or less.

In relation to such characteristics, the silica of the present invention
Is the most frequent diameter calculated by the above BJH method
(D_max) Differential pore volume ΔV / Δ (logd)
Is usually 2 ml / g or more, especially 3 ml / g or more, especially
It is preferably 5 ml / g or more, usually 20 ml / g.
g or less, preferably 12 ml / g or less
(In the above equation, d is the pore diameter (nm),
V is the nitrogen gas adsorption volume). Differential pore volume ΔV / Δ
Those in which (logd) falls within the above range are the most frequent diameters.
(D _maxThe absolute amount of pores aligned near () is extremely large.
It can be said to be good.

The silica of the present invention has, in addition to the characteristics of the above-mentioned pore structure, a characteristic that it is amorphous, that is, no crystalline structure is observed, when looking at its three-dimensional structure. This means that the silica of the present invention corresponds to so-called "silica gel", and when analyzed by X-ray diffraction, substantially no crystalline peak is observed. In the present specification, non-amorphous silica means 6 angstroms (Å Units) in an X-ray diffraction pattern.
The peak of at least one crystal structure is shown at a position beyond d-spacing). Amorphous silica has higher thermal stability in water and is extremely excellent in productivity as compared with crystalline silica.

Further, regarding the structure of the silica of the present invention,
Characteristic results are also obtained by analysis by solid-state Si-NMR measurement. That is, in the solid Si-NMR measurement, the silica of the present invention, -OSi are three bonded Si and (Q ³⁾ -OS
Q ⁴ / Q showing the molar ratio with Si (Q ⁴ ) in which four i are bonded
The value of ³ is usually 3 or more, preferably 3.5 or more.
The upper limit value is not particularly limited, but is usually 10 or less. It is generally known that the higher this value is, the higher the thermal stability of silica is. From this, it can be seen that the silica of the present invention is extremely excellent in thermal stability. On the contrary,
Among crystalline micellar template silica, Q ⁴ / Q ³
Value is less than 1.2, and the thermal stability, especially hydrothermal stability, is low.

The value of Q ⁴ / Q ³ can be calculated based on the result of solid-state Si-NMR measurement using the method described later in the description of the examples. The analysis of the measurement data (determination of the peak position) is performed by a method of dividing and extracting each peak by, for example, waveform separation analysis using a Gaussian function.

In the silica of the present invention, the total content of metal elements (metal impurities) excluding silicon constituting the silica skeleton is usually 100 ppm or less, preferably 50 p.
pm or less, more preferably 10 ppm or less, particularly preferably 5 ppm or less, and most preferably 1 ppm or less, which is extremely low and extremely high purity. Such a small influence of impurities is one of the major factors by which the silica of the present invention can exhibit excellent properties such as high heat resistance and water resistance.

Further, one feature of the silica of the present invention is that the change in pore characteristics is small even when it is subjected to heat treatment in water (hydrothermal resistance test). Changes in the pore characteristics of silica after the hydrothermal resistance test are observed as changes in physical properties relating to porosity such as specific surface area, pore volume, and pore size distribution. For example, in the silica of the present invention, when subjected to a hydrothermal resistance test at 280 ° C. for 24 hours, the specific surface area after the test is 20% or more (the specific surface area residual ratio is 20% or more) with respect to the specific surface area before the test. ) Is preferable. The silica of the present invention having such characteristics can be used, for example, as a catalyst carrier or the like even under long-term severe use conditions.
It is preferred because the porosity feature is not lost. The residual rate of this specific surface area is preferably 35% or more, and particularly preferably 50% or more.

Even after the hydrothermal treatment test, the silica of the present invention has a very small deterioration in the characteristics that the pore size distribution is sharp, and has a very small change in the pore volume, or has a small pore volume. The volume will increase,
It has features not found in conventional silica.

The hydrothermal resistance test in the present invention is to bring water at a specific temperature (200 ° C.) into contact with silica for a fixed time (6 hours) in a closed system. If all of them are in water, even if the closed system is completely filled with water, a part of the system has a gas phase part under pressure, and this gas phase part contains water vapor. May be. In this case, the pressure of the gas phase portion may be, for example, 60000 hPa or more, preferably 63000 hPa or more. The error of the specific temperature is usually within ± 5 ° C, preferably within ± 3 ° C, particularly preferably within ± 1 ° C.

(2) Method for producing silica of the present invention The silica of the present invention having the physical properties described above is hydrothermally treated as it is without substantially aging the silica hydrogel, and under the specific conditions as described below. It is obtained by performing hydrothermal treatment.

In producing the silica gel of the present invention, any method can be used as a method for obtaining the silica hydrogel as a raw material thereof. For example, a method obtained by hydrolyzing an alkali silicate salt or a method obtained by hydrolyzing a silicon alkoxide can be mentioned. Among them, silica hydrogel obtained by hydrolyzing silicon alkoxide is
It is preferable because the raw material silicon alkoxide can be highly purified and impurities can be easily prevented from being mixed into the silica hydrogel.

Specific examples of the silicon alkoxide used as the raw material for the silica of the present invention include trimethoxysilane, tetramethoxysilane, triethoxysilane, tetraethoxysilane, tetrapropoxysilane, tetrabutoxysilane and the like having 1 to 1 carbon atoms. Examples thereof include tri- or tetraalkoxysilanes having 4 lower alkyl groups or oligomers thereof. Among them, tetramethoxysilane, tetraethoxysilane and their oligomers, particularly tetramethoxysilane and its oligomers,
It is preferable because silica having good pore characteristics can be obtained. The main reason for this is that silicon alkoxide is easily purified by distillation to obtain a high-purity product, and thus is suitable as a raw material for high-purity silica.
The total content of metal elements (metal impurities) belonging to alkali metals or alkaline earth metals in silicon alkoxide is
It is usually 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less, and particularly preferably 1 ppm or less. The content of these metal impurities can be measured by the same method as the general method for measuring the content of impurities in silica.

In the present invention, first, in the hydrolysis / condensation step, the silicon alkoxide is hydrolyzed in the absence of a catalyst and the obtained silica hydrosol is condensed to form a silica hydrogel.

Hydrolysis of silicon alkoxide is usually 2 mol times or more with respect to 1 mol of silicon alkoxide.
Water is preferably used in an amount of 3 times or more, particularly preferably 4 times or more, and usually 20 times or less, preferably 10 times or less, particularly preferably 8 times or less. Hydrolysis of silicon alkoxide produces silica hydrogel and alcohol, and the produced silica hydrosol is sequentially condensed to form silica hydrogel.

The temperature during hydrolysis is usually room temperature or higher and 10
Although it is 0 ° C. or lower, it is also possible to carry out at a higher temperature by maintaining the liquid phase under pressure. The reaction time required for hydrolysis depends on the composition of the reaction solution (the kind of silicon alkoxide and the molar ratio with water) and the reaction temperature, and since the time until gelation differs, it is not generally specified. This reaction time is set so that the fracture stress of the hydrogel is 6MP in order to obtain silica having excellent pore characteristics like the silica of the present invention.
It is preferable that the time does not exceed a.

Incidentally, the hydrolysis can be promoted by adding an acid, an alkali, a salt or the like as a catalyst to the hydrolysis reaction system. However, the use of such additives is not very preferable in the production of the silica gel of the present invention, as it will cause aging of the hydrogel formed, as will be described later.

It is important to sufficiently stir the above-mentioned hydrolysis of the silicon alkoxide. For example, when using a stirring device equipped with a stirring blade on the rotating shaft,
The stirring speed (the number of rotations of the rotating shaft) depends on the shape of the stirring blade, the number of blades, the contact area with the liquid, etc., but is usually 30 r.
pm or higher, preferably 50 rpm or higher.

If the stirring speed is generally too fast, the droplets generated in the tank may block various gas lines, or may adhere to the inner wall of the reactor to deteriorate heat conduction, which may cause physical property control. It may affect important temperature control. Further, the adhered substance on the inner wall may be peeled off and mixed into the product to deteriorate the quality. For this reason, the stirring speed is preferably 2000 rpm or less, and more preferably 1000 rpm or less.

In the present invention, the stirring method of the separated two liquid phases (aqueous phase and silicon alkoxide phase) may be any stirring method as long as it accelerates the reaction. Among these, examples of an apparatus for further mixing the two liquid phases include the following.

A device having a stirring blade in which the rotating shaft is inserted perpendicularly or at a slight angle to the liquid surface and in which the liquid flows vertically. : A stirrer having a stirring blade provided with a rotation axis direction substantially parallel to an interface between the two liquid phases and stirring the two liquid phases.

The rotation speed of the stirring blade when using the above-mentioned apparatus is the peripheral speed of the stirring blade (the speed of the stirring blade tip).
, 0.05-10 m / s, especially 0.1-5 m / s,
Further, it is preferably 0.1 to 3 m / s.

The shape and length of the stirring blade are arbitrary, and examples of the stirring blade include propeller type, flat blade type, angled flat blade type, pitched flat blade type, flat blade disc turbine type, curved blade type, Examples include the Faudler type and the bull margin type.

The width of the blades, the number of blades, the angle of inclination, etc., depend on the shape of the reactor,
It may be appropriately selected according to the size and the target stirring power. For example, the ratio (b / D) of the blade width (blade length in the rotation axis direction) to the inner diameter of the reactor (the longest diameter of the liquid phase surface forming a plane perpendicular to the rotation axis direction) is 0.05 to 0.2,
A preferable example is a stirrer having an inclination angle (θ) of 90 ° ± 10 ° and 3 to 10 blades.

Above all, a structure in which the above-mentioned rotating shaft is provided above the liquid level in the reaction vessel and a stirring blade is provided at the tip of the shaft extended from this rotating shaft is suitable from the viewpoint of stirring efficiency and equipment maintenance. used.

Silica having a crystal structure tends to have poor thermal stability in water, and hydrolyzes silicon alkoxide in the presence of a template such as a surfactant used to form pores in the gel. Then, the gel easily contains a crystal structure. Therefore, in the present invention, it is preferable to hydrolyze in the absence of a template such as a surfactant, that is, under the condition that they do not exist in an amount sufficient to exert the function as a template.

In the above-mentioned hydrolysis reaction of silicon alkoxide, the silicon alkoxide is hydrolyzed to produce silica hydrosol, and subsequently, the condensation reaction of the silica hydrosol occurs, the viscosity of the reaction solution increases, and It gelates into silica hydrogel.

Then, in the present invention, as a physical property adjusting step, the silica hydrogel produced by the above hydrolysis is not aged so that the hardness does not increase,
Hydrothermal treatment of silica hydrogel is performed. Hydrolysis of silicon alkoxides produces soft silica hydrogels. As in the prior art, it is difficult to produce the silica of the present invention by a method of aging or drying and then subjecting to hydrothermal treatment in order to stabilize the physical properties of the hydrogel.

Immediately performing hydrothermal treatment on the silica hydrogel produced by hydrolysis as described above, without substantially aging, means that the soft state immediately after the formation of the silica hydrogel is maintained. It means to be subjected to the hydrothermal treatment of.

Specifically, it is preferable that the hydrothermal treatment is generally carried out within 10 hours from the time when the silica hydrogel is formed, and especially within 8 hours, more preferably within 6 hours, and especially within 4 hours. Hydrothermal treatment is preferred.

In an industrial plant or the like, a large amount of silica hydrogel once stored in a silo or the like,
It may be possible that hydrothermal treatment is performed thereafter. In such a case, in the silica hydrogel, the time from the production of the silica hydrogel to the hydrothermal treatment, that is, the so-called standing time may exceed the above range. In such a case, the liquid component in, for example, the silica hydrogel may not be dried during the standing in the silo so that the aging does not substantially occur.

Specifically, for example, the inside of the silo may be sealed or the humidity may be adjusted. Further, the silica hydrogel may be left standing while the silica hydrogel is immersed in water or another solvent.

It is preferable that the temperature during standing is as low as possible, for example, 50 ° C. or lower, especially 35 ° C. or lower,
In particular, it is preferable to stand at 30 ° C. or lower. Further, as another method of preventing aging substantially, there is a method of preparing the silica hydrogel by controlling the raw material composition in advance so that the silica concentration in the silica hydrogel becomes low.

Considering the effect obtained by the hydrothermal treatment without substantially aging the silica hydrogel and the reason why this effect is obtained, the following can be considered.

First, when the silica hydrogel is aged,
It is considered that a macroscopic network structure of —Si—O—Si— bonds is formed in the entire silica hydrogel. Since this network structure is present in the entire silica hydrogel, it is considered that this network structure becomes an obstacle during hydrothermal treatment, making it difficult to form mesoporous materials. Further, the silica hydrogel obtained by controlling the raw material composition in advance so that the silica concentration in the silica hydrogel becomes low can suppress the progress of crosslinking in the silica hydrogel that occurs during standing. Therefore, it is considered that the silica hydrogel does not age.

Therefore, in the present invention, it is important to carry out hydrothermal treatment without aging the silica hydrogel.

It is not preferable to add an acid, an alkali, a salt or the like to the hydrolysis reaction system of the silicon alkoxide, or to make the temperature of the hydrolysis reaction too strict, in order to accelerate the aging of the hydrogel. Also,
Washing with water, drying, and leaving in the post-treatment after hydrolysis should not be performed at an unnecessarily high temperature or time.

Further, the silica hydrogel obtained by the hydrolysis of silicon alkoxide is preferably subjected to a crushing treatment or the like before the hydrothermal treatment so that the average particle diameter becomes 1 mm or less, especially 0.5 mm or less. .

If the particle size of the silica hydrogel to be subjected to the hydrothermal treatment is too large, the hydrothermal treatment may not proceed uniformly and the pore size distribution may become broad or the pore volume may become small.

On the contrary, if the particle size is too small, the uniform structure of the silica hydrogel is destroyed by pulverization.
In some cases, the appropriate effect of hydrothermal treatment cannot be obtained, and the pore size distribution becomes broad or the pore volume becomes small.

For example, a column or a tube is filled with the silica gel of the present invention, and when used as an adsorbent or a catalyst for harmful substances, the particle size is 1 m.
Particles of m or more are preferable because they do not hinder the flow when a gas or liquid is circulated inside a tower or a pipe, and can reduce pressure loss in the case of a gas, for example.

When silica gel having such a large particle size is desired, it is preferable that the particle size after crushing is set to a desired size by the crushing treatment of the silica hydrogel described above, and then this is subjected to hydrothermal treatment. .

As described above, as the method for producing silica of the present invention, it is important to immediately hydrothermally treat the silica hydrogel immediately after it is produced. However, in the production method of the present invention, since the silica hydrogel to be subjected to hydrothermal treatment need not be aged, for example, hydrothermal treatment is performed after standing still at a low temperature for a while. Does not require hydrothermal treatment.

As described above, if the hydrothermal treatment is not performed immediately after the silica hydrogel is produced, for example, the hydrothermal treatment may be performed after specifically confirming the aging state of the silica hydrogel. The means for specifically confirming the aging state of the hydrogel is arbitrary, and for example, there is a method in which the hardness of the hydrogel measured by the method as described in the examples below is referred to. That is, as described above, by hydrothermally treating a hydrogel having a fracture stress of 6 MPa or less, preferably 3 MPa or less, and particularly preferably 2 MPa or less in a soft state, silica having physical properties defined in the present invention can be obtained. .

The condition of the hydrothermal treatment may be either a liquid state or a gas state. Among them, liquid water is preferably used, and the hydrothermal treatment is carried out in the form of slurry in addition to silica hydrogel. In the hydrothermal treatment, first, the silica hydrogel to be treated is usually 0.1 times by weight or more, preferably 0.5 times or more the weight of the silica hydrogel.
Water is added in an amount of not less than 1 times by weight, particularly preferably not more than 1 times by weight, usually not more than 5 times by weight, particularly preferably not more than 3 times by weight, to form a slurry. Then, this slurry is usually heated to 150 ° C or higher, preferably 20 ° C.
0 ° C or higher, usually 250 ° C or lower, preferably 240
The hydrothermal treatment is carried out at a temperature of not higher than 0 ° C. for usually 0.1 hour or longer, preferably 1 hour or longer, and usually 100 hours or shorter, preferably 10 hours or shorter. If the temperature of the hydrothermal treatment is too low, the distribution of pore size may not be sharp, and it may be difficult to increase the pore size.

In the present invention, in order to increase the pore size of silica, the water concentration around silica (water concentration in the hydrothermal treatment liquid) is set as a condition for hydrothermal treatment.
It is important to carry out hydrothermal treatment with a high temperature.

As the hydrothermal treatment conditions for obtaining the silica of the present invention, the water concentration around the silica is usually 80% or more, preferably 85% or more, more preferably 90% or more, particularly preferably 95% or more, It is preferable to set the value higher than usual.

For example, when a hydrogel obtained by using a silicon alkoxide is subjected to hydrothermal treatment, alcohols produced by hydrolysis of the silicon alkoxide exist in the hydrogel in such a hydrogel. Therefore, when hydrothermally treating such a hydrogel, it is preferable to remove these alcohols before hydrothermal treatment. Specifically, such a hydrogel may be washed with water and then subjected to hydrothermal treatment.

Although the reason why the pore size becomes large when the water concentration of the hydrothermal treatment liquid is high is not clear, it can be roughly considered as follows. The hydrothermal treatment causes the silica components in the hydrogel to aggregate and condense. The role of water in this change is to phase separate the silica and liquid components. Water has a function of binding silicas together by a strong hydrogen bond and bringing them closer to each other, and in addition, water tends to collect together. It is presumed that the action of such water forms pores having a large diameter.

However, since alcohol has a function of inhibiting such a function of water, it is preferable that such alcohols are not present in the hydrothermal treatment liquid as much as possible.

This hydrothermal treatment method can also be applied to a material in which silica is formed in a film or layer form on a substrate such as particles, a substrate, or a tube for the purpose of producing a membrane reactor or the like. It is also possible to carry out hydrothermal treatment by changing the temperature conditions using a hydrolysis reaction reactor, but the optimum conditions are usually different between the hydrolysis reaction and the subsequent hydrothermal treatment. In general, it is difficult to obtain the silica of the present invention by the method performed without adding water.

Under the above hydrothermal treatment conditions, increasing the temperature tends to increase the diameter and pore volume of the obtained silica. The hydrothermal treatment temperature is 100 to 200 ° C.
It is preferably in the range of. Further, with the treatment time, the specific surface area of the obtained silica tends to gradually decrease after reaching the maximum once. Based on the above tendency, it is necessary to appropriately select the conditions according to the desired physical property values, but hydrothermal treatment is for the purpose of changing the physical properties of silica, and therefore, it is usually higher temperature conditions than the above hydrolysis reaction conditions. Preferably.

In order to produce the silica of the present invention having excellent microstructural homogeneity, the temperature in the reaction system is raised rapidly during hydrothermal treatment so that the temperature in the reaction system reaches the target temperature within 5 hours. The speed condition is preferable. Specifically, in the case of being filled in a tank and processed, the average temperature increase rate from the start of temperature increase to reaching the target temperature is 0.1 to 100 ° C./min,
Among them, 0.1 to 30 ° C / min, particularly 0.2 to 10 ° C / min
It is preferable to adopt a value in the range of min.

A temperature raising method using a heat exchanger or the like, or a temperature raising method of charging hot water prepared in advance is preferable because the temperature raising rate can be shortened. Further, if the temperature raising rate is within the above range, the temperature may be raised stepwise.
When it takes a long time for the temperature in the reaction system to reach the target temperature, the aging of the silica hydrogel proceeds while the temperature is rising,
Microstructural homogeneity may be reduced.

The temperature rising time to reach the above target temperature is preferably within 4 hours, more preferably within 3 hours. The water used for the hydrothermal treatment can be preheated to shorten the temperature raising time.

If the temperature and time of hydrothermal treatment are set outside the above ranges, it will be difficult to obtain the silica of the present invention. For example, if the temperature of the hydrothermal treatment is too high, the pore diameter and pore volume of silica become too large, and the pore distribution also widens. Conversely, if the temperature of the hydrothermal treatment is too low, the silica produced will be
The degree of cross-linking is low, the thermal stability is poor, the pore distribution does not have a peak, and the Q ⁴ / Q ³ value in the solid-state Si-NMR is extremely small.

In the present invention, a silica hydrogel obtained by hydrolyzing a silicon alkoxide as a raw material under conditions without a catalyst such as hydrochloric acid (in the absence of a catalyst) is added to ammonia water. Even by hydrothermal treatment
As described above, the silica gel of the present invention having a large pore size can be obtained.

When the hydrothermal treatment is performed in ammonia water, the same effect can be obtained at a lower temperature than that in pure water.
Further, when hydrothermal treatment is performed in ammonia water, the silica finally obtained is generally hydrophobic as compared with the hydrothermal treatment using ammonia-free water. At this time, the temperature of the hydrothermal treatment is 30 ° C. or higher, preferably 40 ° C. or higher, and 25
At a relatively high temperature of 0 ° C. or lower, preferably 200 ° C. or lower, the hydrophobicity becomes particularly high. The ammonia concentration of the ammonia water here is preferably 0.001% or more, particularly preferably 0.005% or more, preferably 10% or less, particularly preferably 5%.

The obtained silica is usually dried at 40 ° C. or higher, preferably 60 ° C. or higher, and usually 200 ° C. or lower, preferably 120 ° C. or lower. The drying method is not particularly limited, and may be a batch type or a continuous type, and can be dried under normal pressure or reduced pressure. Among them, vacuum drying is preferable because not only drying can be carried out rapidly, but also the pore volume and specific surface area of the obtained silica are increased.

If necessary, if the carbon content derived from the silicon alkoxide of the raw material is contained, it is usually 400.
It can be removed by firing at ~ 600 ° C. Further, in order to control the surface condition, firing may be performed at a temperature of up to 900 ° C. Furthermore, the silica of the present invention finally obtained is obtained by pulverizing and classifying as required.

(3) Uses of the silica of the present invention The novel silica of the present invention is superior in heat resistance and water resistance to conventional silica and thus has high stability and high purity. Further, according to the method for producing silica of the present invention,
It is possible to manufacture silica in which a silicon alkoxide is used as a raw material in a relatively simple process and which is controlled in a desired physical property range.

The silica of the present invention can be used in various applications of conventional silica, but particularly when it is used as a catalyst carrier, a membrane reactor, etc., its performance is less deteriorated and it can be used more stably for a long time.

The silica of the present invention can be used for any purpose other than the conventional use of silica. Among them, the conventional uses include the following.

For example, in the field of application used for manufacturing and treating products in industrial facilities, various catalysts and catalyst carriers (acid-base catalysts, photocatalysts, precious metal catalysts, etc.), waste water / waste oil treatment agents, odor treatment agents, gases Examples of applications include separating agents, industrial desiccants, bioreactors, bioseparators, membrane reactors, and the like. Examples of building materials include humidity control agents, soundproofing / sound absorbing materials, refractories, and heat insulating materials. In the air conditioning field, desiccant air conditioner humidity control agents,
Examples include heat storage agents for heat pumps. In the application field of paints / inks, examples include matting agents, viscosity adjusting agents, chromaticity adjusting agents, anti-settling agents, antifoaming agents, ink strike-through preventing agents, stamping foils, and wallpaper. In the application field of additives for resins, anti-blocking agents for films (polyolefin films, etc.), plate-out prevention agents, reinforcing agents for silicone resins, reinforcing agents for rubber (for tires / general rubber, etc.), fluidity improvers, Powder resin anti-caking agent, printability improving agent, matting agent for synthetic leather and coating film, adhesive / adhesive tape filler, translucency adjusting agent, anti-glare adjusting agent, porous polymer sheet Applications include fillers for use. In the field of papermaking applications, thermal paper fillers (such as dust adhesion preventives), ink jet paper image improving fillers (ink absorbing agents, etc.), diazo photosensitive paper fillers (photosensitive density improving agents, etc.), tracing papers. Examples thereof include writability improvers, coated paper fillers (writability, ink absorbability, antiblocking property improvers, etc.), electrostatic recording fillers, and the like. In the field of food applications, filter aids for beer, hanging agents for fermented products such as soy sauce, sake, and wine, stabilizers for various fermented beverages (removal of turbidity factor protein and yeast, etc.), food additives, powdered food products, etc. Applications include anti-caking agents. In the field of medicines and agricultural chemicals, tableting aids for medicines, crushing aids, dispersion / pharmaceutical carriers (dispersion / sustained release / improved delivery, etc.), pesticide carriers (oil pesticide carrier / hydrated dispersibility improved, sustained release)・ Improvement of delivery property, etc., pharmaceutical additives (anti-caking agent, graininess improving agent, etc.), agricultural chemical additives (anti-caking agent, anti-settling agent, etc.) and the like. In the field of separation materials,
Examples thereof include packing materials for chromatography, separating agents, fullerene separating agents, adsorbents (proteins, dyes, odors, etc.), dehumidifying agents, and the like. In the field of agriculture, feed additives and fertilizer additives can be mentioned. As other uses, in the field of daily life, humidity control agents, desiccants, cosmetic additives, antibacterial agents, deodorant / deodorant / fragrance agents, detergent additives (surfactant powdering, etc.), abrasives (toothpaste) Etc.), powder fire extinguishing agents (powder graininess improving agents, anti-caking agents, etc.), antifoaming agents, battery separators and the like.

In particular, the silica of the present invention has a large pore diameter as compared with conventional silica, and therefore has a high adsorption / absorption capacity. Therefore, among the above-mentioned applications, it is particularly preferable in fields in which large pore diameters and excellent hydrothermal resistance are required, and controlled pore characteristics and small changes in physical properties are required over a long period of time. Can be used.

[0085]

EXAMPLES The present invention will be described in more detail with reference to examples below, but the present invention is not limited to the following examples as long as the gist thereof is not exceeded.

(1) Silica analysis method: 1-1) Pore volume, specific surface area, differential pore volume: BET nitrogen adsorption isotherm was measured with AS-1 manufactured by Kantachrome Co.,
The pore volume and specific surface area were determined. Specifically, the pore volume adopts a value when the relative pressure P / P ₀ = 0.98, and the specific surface area is 3 points of P / P ₀ = 0.1, 0.2, 0.3. It was calculated from the nitrogen adsorption amount using the BET multipoint method. Also, BJH
The pore distribution curve and the differential pore volume at the most frequent diameter (D _max ) were determined by the method. The interval between the relative pressure points to be measured is 0.
It was set to 025.

1-2) Powder X-ray diffraction: RAD- manufactured by Rigaku Denki Co., Ltd.
Using an RB device, measurement was performed using CuKα as a radiation source. Divergence slit 1/2 deg, scattering slit 1/2 d
and the light-receiving slit is 0.15 mm.

1-3) Content of metallic impurities: 2.5 g of sample
Hydrofluoric acid was added to and heated to dryness, and then water was added to make 50 ml. ICP emission analysis was performed using this aqueous solution. In addition, sodium and potassium were analyzed by the flame flame method.

1-4) Solid-state Si-NMR measurement: Bruke
CP / MAS using a 7 mm sample tube with a resonance frequency of 59.2 MHz (7.05 Tesla) while using a solid state NMR device (“MSL300”) manufactured by r company.
(Cross Polarization / Magic Angle Spinning) Measurement was performed under probe conditions. Sample rotation speed is 5000 rp
s.

The analysis of the measurement data (determination of the Q ⁴ peak position) is performed by a method of extracting each peak by peak division. Specifically, waveform separation analysis using a Gaussian function is performed. For this analysis, Thermo Galatec (Thermo
Galatic) waveform processing software "GRAMS386"
Can be used.

Using the areas of the respective peaks of Q ⁴ and Q ³ thus obtained by peak division, the ratio (Q ⁴ / Q ³ ) was obtained.

1-5) Average particle size Laser type particle size distribution measuring apparatus (LM manufactured by Seishin Enterprise Co., Ltd.
S-30).

1-6) Thermal stability test in water: Pure water was added to the sample to prepare a 40% by weight slurry. About 40 ml of the slurry prepared above was placed in a stainless steel micro bomb having a volume of 60 ml, sealed, and immersed in an oil bath of 280 ± 1 ° C. for 24 hours. A part of the slurry was extracted from the micro bomb and filtered with a filter paper (No. 5A). After the filter cake was vacuum dried at 100 ° C. for 5 hours, the specific surface area of the remaining sample was measured.

(2) Production and evaluation of silica: Example 1: <Hydrolysis / gelation reaction> In a 5 L separable flask (with a jacket) made of glass, and equipped with a water-cooled condenser open to the atmosphere, 1000 g of pure water was charged. As for the stirring speed, while stirring at a stirring blade tip speed of 2.5 m / s, 1400 g of tetramethoxysilane was added to this.
Was charged for 3 minutes. The number of moles of water (molar ratio of water / tetramethoxysilane) to 1 mole of tetramethoxysilane used was 6. Hot water at 50 ° C was passed through the jacket of the separable flask. The stirring was continued, and when the contents reached the boiling point, the stirring was stopped.
Subsequently, warm water of 50 ° C. was passed through the jacket for about 0.5 hours to gelate the sol produced.

<Pulverization reaction> After that, the gel was quickly taken out and pulverized through a nylon net having openings of 600 microns to obtain a powdery wet gel (silica hydrogel) having a predetermined average particle diameter.

<Hydrothermal Treatment of Silica Hydrogel> 450 g of this silica hydrogel and 450 g of 0.56% ammonia water were charged into a 1 L glass autoclave, and 2
A closed system hydrothermal treatment was carried out at 00 ° C. for 3 hours. The silica thus obtained was filtered through a filter paper (No. 5A), and the filter cake was dried under reduced pressure at 100 ° C. until a constant weight was obtained, without washing the filter cake, to obtain silica of Example 1.

The total amount of metal impurities in the silica of Example 1 was 0.5 ppm (of which: Na: 0.2, calcium (Ca): 0.2, potassium (K): 0.1, all in ppm). Met.

Example 2: <Hydrolysis / gelation reaction / pulverization step> After a silica hydrogel was produced by the same procedure as in Example 1, the same procedure as in Example 1 was performed.
The silica hydrogel was pulverized by the same procedure as in (1) to obtain a powdery silica hydrogel having a predetermined average particle diameter.

<Washing Step of Silica Hydrogel> 450 g of this pulverized silica hydrogel and 675 g of water were placed in a beaker, stirred for 10 minutes, and then solid-liquid separated by decantation. After repeating this operation a total of two times, the same amount of water was added and the mixture was allowed to stand at room temperature for one day, and solid-liquid separation was performed by decantation.

<Hydrothermal Treatment Step> This silica hydrogel and 500 g of water were charged into a 1 L glass autoclave and subjected to a closed system hydrothermal treatment at 200 ° C. for 3 hours. The slurry after the hydrothermal treatment was decanted to perform solid-liquid separation, and the methanol concentration in the liquid was analyzed by gas chromatography.

<Drying Process> After hydrothermal treatment, No. It was filtered with a 5A filter paper, and the filter cake was dried under reduced pressure at 100 ° C. without washing with water until a constant weight was obtained, to obtain the silica of Example 2. The total amount of metallic impurities in this silica is 0.9 p
pm {of which: Na: 0.2, calcium (Ca): 0.
2, iron (Fe) 0.4, potassium (K): 0.1, all in ppm}.

Example 3: Silica (silica of Example 3) was obtained by the same procedure as in Example 2 except that the nylon mesh was opened to 8 mm in the crushing step of Example 2. The total amount of metal impurities in this silica is 0.3 ppm {of which:
Na: 0.1, calcium (Ca): 0.1, potassium (K): 0.1, and the unit was ppm}.

Example 4 Silica (implemented in the same manner as in Example 2 except that the number of moles of water relative to 1 mole of tetramethoxysilane was 10 times in the hydrolysis / gelation step of Example 2) The silica of Example 4) was obtained. The total amount of metal impurities in this silica was 0.8 ppm {of which: Na: 0.
2, calcium (Ca): 0.2, iron (Fe): 0.
4, the unit was ppm}.

Regarding the obtained silicas of Examples 1 to 4,
Table 1 shows the physical properties measured by the above-mentioned analysis methods. No peak of crystallinity appeared in the powder X-ray diffraction pattern of any of the silicas, and the low angle side (2θ ≦ 2 due to the periodic structure was observed.
No peak of 5 deg) was also observed.

Comparative Example 1: Commercially available silica gel [manufactured by Mizusawa Chemical Co., Ltd .: gel type silica gel P-707, the total amount of metal impurities is 626 ppm {of which: Na: 120, magnesium (Mg): 26, aluminum (Al): 38. , K:
10, Ca: 78, titanium (Ti): 260, chromium (Cr): 3, iron (Fe): 61, zirconium (Z
r): 30, each unit is ppm}, and there is no crystalline peak in the powder X-ray diffraction pattern. The low-angle peak due to the periodic structure was not observed either. ]] Was used to perform a thermal stability test in water in the same manner as in Example 1. Table 1 shows the results.

[0106]

[Table 1]

Results: As is clear from Table 1, the silica of the present invention is excellent in hydrothermal stability and has a large residual specific surface area (that is, a small decrease) even under various harsh conditions of use, and thus is stable. It is possible to maintain the above performance for a long time.

[0108]

EFFECTS OF THE INVENTION The silica of the present invention has a large pore diameter as compared with conventional silica, and thus has a high adsorption / absorption capacity. In addition, it can be manufactured by a relatively simple process using silicon alkoxide as a raw material, and it has desirable physical properties controlled in a desired range, and it has high heat resistance and water resistance. It is pure.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takayuki Yoshimori             1-1 Kurosaki Shiroishi, Hachiman Nishi Ward, Kitakyushu City, Fukuoka Prefecture               Within Mitsubishi Chemical Corporation (72) Inventor Takashi Yamaguchi             1-1 Kurosaki Shiroishi, Hachiman Nishi Ward, Kitakyushu City, Fukuoka Prefecture               Within Mitsubishi Chemical Corporation F term (reference) 4G072 AA25 AA27 AA28 BB13 BB15                       CC10 GG01 GG03 HH30 JJ11                       LL06 MM01 RR05 RR12 RR19                       TT05 TT08 TT09 TT19 UU17

Claims (9)

[Claims] 1. The following characteristics are provided,
silica. (A) Pore volume of 0.6 ml / g or more, 1.6 ml / g
The following (b) specific surface area is 50 to 600 m ² / g (c) modal pore diameter (D _max ) is 15 nm or more (d) Q ⁴ / Q ³ value in solid Si-NMR is 3 or more (e) non- Being crystalline (f) Content of metal impurities is 100 ppm or less 2. A specific surface area of 100 m ² / g or more, 450
The silica according to claim 1, wherein the silica is m ² / g or less. 3. The silica according to claim 1, wherein the most frequent pore diameter (D _max ) is 50 nm or less. 4. The pore diameter is ± of the mode pore diameter (D _max ).
The volume of pores present in the range of 20% is 5% of the total pore volume.
Silica according to any one of claims 1 to 3, characterized in that it is 0% or more. 5. The silica according to claim 1, wherein the content of metallic impurities is 10 ppm or less. 6. The differential pore volume in the most frequent pore diameter (D _max ) is 2 ml / g or more and 20 ml / g or less, according to claim 1. silica. 7. The silica according to claim 1, wherein the residual specific surface area after heat treatment in closed water under conditions of 280 ° C. and 24 hours is 20% or more. . 8. A method for producing silica according to claim 1, wherein the silicon alkoxide is hydrolyzed, and the resulting hydrogel is hydrothermally treated without substantially aging. A method for producing silica, characterized in that the hydrothermal treatment is carried out under conditions of an alcohol concentration of 20% or less and 200% or more. 9. The silica according to claim 1, wherein the silicon alkoxide is hydrolyzed in the absence of a catalyst, and the resulting hydrogel is hydrothermally treated with aqueous ammonia. A method for producing silica, comprising: