JP2005022895A - Silica and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide silica having a large mode fine pore diameter, a controlled fine pore characteristics and excellent thermal resistance, water resistance or the like. <P>SOLUTION: The silica has the following properties: (a) a fine pore volume is ≥0.6 mL/g and ≤1.6 mL/g, (b) a specific surface area is 50-600 m<SP>2</SP>/g, (c) a mode fine pore diameter (Dmax) 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 and (e) the silica is amorphous. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

【０１０７】
・結果：
表１より明らかな通り、本発明のシリカは、水熱安定性に優れており、様々な厳しい使用条件下でも比表面積の残存が多い（つまり減少が少ない）ので、安定した性能を長期に亘り維持できる。
【０１０８】
【発明の効果】
本発明のシリカは、従来からのシリカと比較して、細孔直径が大きいため、高い吸着・吸収容量を有する。また、シリコンアルコキシドを原料とした比較的簡単な工程で製造できる上に、所望の範囲に制御された望ましい物性を備えており、耐熱性や耐水性等に優れることから安定性が高い。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel silica and a method for producing the same. Specifically, the present invention 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]
[Prior art]
Silica is a porous material that has been widely used as a desiccant for a long time, but recently its use has expanded to catalyst carriers, separating agents, adsorbents, etc. The demand for is also diversifying. The performance of silica is determined by physical properties such as the surface area, pore diameter, pore volume, and pore size distribution of silica, but these physical properties are greatly influenced by the production conditions of silica.
[0003]
“Silica” refers to both silicic anhydride and hydrous silicic acid. Examples of silicic acid anhydride include quartz, tridymite, cristobalite, corsite, stishovite, and quartz glass. In addition to the so-called amorphous "silica gel" obtained by gelling and drying silica hydrosol, the hydrous silicic acid was formed using colloidal silica, silicate oligomer, and organic matter as a template, for example, manufactured by Mobil Corporation. : Silica of a type such as MCM-41 (so-called micelle template type silica). Examples of the raw material for “silica gel” include water glass and alkoxysilanes.
[0004]
As a method for producing silica as a porous material, a method of controlling pore characteristics by hydrothermally treating silica hydrogel has been widely known. For example, sodium silicate, so-called water glass, has been widely used as a raw material for this silica hydrogel.
[0005]
Most frequent pore diameter (D _max For example, when producing silica having a relatively large pore diameter of 15 nm or more, a method of hydrothermally treating silica hydrogel under high temperature or high pH conditions is generally known. Impurities such as alkali metals and alkaline earth metals of silica (hereinafter collectively referred to as “alkali metal impurities”) are mainly derived from the raw water glass, neutralize the water glass with an acid such as sulfuric acid, The hydrogel containing a neutralized salt is removed by washing with water. However, it cannot be completely removed, and tens to hundreds of ppm of alkali metal impurities remain in the silica hydrogel.
[0006]
When the pH condition of hydrothermal treatment for pore control performed after washing with water is acidic or neutral, which is a condition for obtaining silica having a relatively small pore diameter, some alkali metal is used even during hydrothermal treatment. Impurities are extracted and removed, and the content of alkali metal impurities remaining in the product porous silica can be lowered to about several tens of ppm.
[0007]
However, since the pH condition of the hydrothermal treatment for obtaining silica having a relatively large pore diameter as described above is alkaline, alkali metal impurities in the silica hydrogel are hardly extracted and removed. When an alkali component such as NaOH is used for pH adjustment during the hydrothermal treatment, an alkali metal or an alkaline earth metal is further brought into the hydrothermal treatment system, and an alkali metal impurity in the porous silica product. There was a problem that the amount became very high. Even when a pH adjuster 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. Before the alkali metal impurities derived from the raw materials were eluted from the silica hydrogel, the micropores of the silica were sealed, and there was a problem that the alkali metal impurities remained in the product.
[0008]
Note that it is very difficult to remove the alkali metal impurities almost completely even if this impurity is later removed by a method such as acid cleaning of the porous silica product. Furthermore, residual alkali metal impurities when using an alkali metal or alkaline earth metal compound as a pH adjuster during hydrothermal treatment are difficult to remove by the same method.
[0009]
As described above, the conventional porous silica having a relatively large pore diameter has a problem that the amount of alkali metal impurities is larger than that of the porous silica having a small pore diameter. Alkali metal impurities act as a catalyst to cleave and recombine siloxane bonds in the silica skeleton when porous silica is used under severe conditions such as high temperature and high pressure. It acts as a catalyst to promote silica dissolution and precipitation at the end, and eventually changes the pore structure. As a result, silica with a large amount of alkali metal impurities tends to change its physical properties, leading to early deterioration of pore characteristics. was there.
[0010]
On the other hand, as a method for obtaining high-purity porous silica having a low metal impurity content, there is known a method in which silicon alkoxide is hydrolyzed to form a silica hydrogel and hydrothermally treated (eg, Non-Patent Document 1). . With this method, the amount of impurities derived from the raw material can be kept low, so that the influence of alkali metal impurities as described above is also reduced. However, even with such a method for producing porous silica derived from silicon alkoxide, it has not been possible to obtain porous silica with controlled pores in which the spread of pore diameter distribution is suppressed.
[0011]
In addition, as a method for producing high-purity porous silica, a method using an organic or inorganic template is known, and this method has excellent pore distribution controllability, and as described above, D _max A porous silica (micelle template silica) having a thickness of 15 nm or more is obtained (example: Non-patent document 2). However, although the porous silica obtained by this method has sharp pores with controlled pore distribution, the pore walls are very thin and there are problems in terms of hydrothermal resistance, and the manufacturing process is complicated. 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]
[Problems to be solved by the invention]
In this way, D _max Is a relatively large porous material with a narrow pore size distribution, high purity and excellent hydrothermal resistance, especially porous silica and a method for producing the same, but satisfactory porous silica and a method for producing the same are still desired. Was not provided.
[0014]
The present invention has been made in view of the above-described problems, and its purpose is to provide the most frequent pore diameter (D _max ) Is relatively large at 15 nm or more, has a controlled pore characteristic, and is excellent in hydrothermal resistance, and to provide a method for producing the same.
[0015]
[Means for Solving the Problems]
As a result of intensive studies to solve the above-mentioned problems, the present inventors have a specific pore characteristic and Q in solid Si-NMR in a silica skeleton. ⁴ / Q ³ The knowledge that the porous silica whose value is more than a specific value can solve the above-mentioned problems was obtained. Furthermore, by using a silicon alkoxide as a raw material and hydrolyzing it, the resulting hydro is subjected to a hydrothermal treatment step under specific conditions without substantially aging, thereby providing excellent properties as described above. The present inventors have found that a novel silica having the above can be industrially provided with high productivity, and have completed the present invention.
[0016]
That is, the gist of the present invention relates to silica characterized by having the following characteristics.
(A) Pore volume is 0.6 ml / g or more and 1.6 ml / g or less
(B) Specific surface area of 50 to 600 m ² / G
(C) Most frequent pore diameter (D _max ) 15nm or more
(D) Q in solid-state Si-NMR ⁴ / Q ³ Value is 3 or more
(E) Be amorphous
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail.
(1) Features of the silica of the present invention
In the present invention, “silica” refers to hydrous silicic acid. Hydrous silicic acid is SiO ₂ ・ NH ₂ It is represented by the characteristic formula of O. In the present invention, as will be described later, the effect is remarkable in so-called “silica gel” or micelle template type silica among silica.
[0018]
The silica of the present invention is characterized in that the pore volume and the specific surface area are in a range larger than usual values. Specifically, the value of the pore volume is usually 0.6 ml / g or more, preferably 0.7 ml / g or more, and usually 1.6 ml / g or less, preferably 1.5 ml / g. It is as follows.
[0019]
The specific surface area is usually 50 m. ² / G or more, more preferably 100 m ² / G or more, preferably 200 m ² / G or more, usually 600m ² / G or less, more preferably 450 m ² / G or less, preferably 350 m ² / G or less, particularly preferably 290 m ² / G or less. These pore volume and specific surface area are measured by the BET method by nitrogen gas adsorption / desorption.
[0020]
Furthermore, the silica of the present invention is obtained from the isothermal desorption curve measured by the nitrogen gas adsorption / desorption method. P. Barrett, L.M. G. Joyner, P.M. H. Hacklenda, J.H. 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)) with respect to the pore diameter d (nm); The most frequent pore diameter (D) on the plot of volume) _max ) Is 15 nm or more. This is because the mode diameter of the silica gel of the present invention (D _max ) Is larger than that of ordinary silica gel. Among these, 16 nm or more is preferable, and 17 nm or more is particularly preferable. The upper limit is not particularly limited, but is usually 50 nm or less, preferably 40 nm or less, particularly preferably 30 nm or less.
[0021]
In addition, the silica of the present invention has the above-mentioned mode diameter (D _max The total volume of pores in the range of ± 20% of the value of) is usually 50% or more, preferably 60% or more, more preferably 70% or more of the total volume of all pores. This means that the diameter of the pores of the silica of the present invention is the mode diameter (D _max ) Means that the pores in the vicinity are aligned, that is, the pore size distribution is extremely narrow (sharp). The upper limit of this ratio value is not particularly limited, but is usually 90% or less.
[0022]
In relation to such characteristics, the silica of the present invention has a mode diameter (D calculated by the above BJH method (D _max The differential pore volume ΔV / Δ (logd) is usually 2 ml / g or more, especially 3 ml / g or more, particularly preferably 5 ml / g or more, usually 20 ml / g or less, especially 12 ml / g or less. (In the above formula, d is the pore diameter (nm) and V is the nitrogen gas adsorption volume). The differential pore volume ΔV / Δ (logd) included in the above range is the mode diameter (D _max It can be said that the absolute amount of pores aligned in the vicinity of) is extremely large.
[0023]
Further, in addition to the above-described features of the pore structure, the silica of the present invention has a feature that it is amorphous, that is, a crystalline structure is not recognized in view of its three-dimensional structure. This means that the silica of the present invention corresponds to a so-called “silica gel”, and the crystallinity peak is not substantially observed when analyzed by X-ray diffraction. In the present specification, the non-amorphous silica refers to a silica having at least one crystal structure peak at a position exceeding 6 angstroms (Å Units d-spacing) in the X-ray diffraction pattern. Amorphous silica has high thermal stability in water and extremely excellent productivity compared to crystalline silica.
[0024]
Furthermore, regarding the structure of the silica of the present invention, a characteristic result can be obtained even by analysis by solid-state Si-NMR measurement. That is, in the solid-state Si-NMR measurement, the silica of the present invention, Si (Q ³ ) And four -OSi bonded Si (Q ⁴ Q showing the molar ratio with ⁴ / Q ³ Is usually 3 or more, preferably 3.5 or more. The upper limit is not particularly limited, but is usually 10 or less. In general, it is known that the higher this value, the higher the thermal stability of the silica. From this, it can be seen that the silica of the present invention is extremely excellent in thermal stability. In contrast, some of the crystalline micelle template silica contains Q ⁴ / Q ³ Is less than 1.2, and the thermal stability, particularly hydrothermal stability, is low.
[0025]
Q ⁴ / Q ³ The value of can be calculated based on the result of solid Si-NMR measurement using the method described later in the description of Examples. Further, analysis of measurement data (determination of peak position) is performed by a method of dividing and extracting each peak by, for example, waveform separation analysis using a Gaussian function.
[0026]
The silica of the present invention is not particularly limited in the total content of metal elements (metal impurities) excluding silicon constituting the skeleton of the silica, but is low and highly pure. It is preferable. Specifically, the range is usually 100 ppm or less, preferably 50 ppm or less, more preferably 10 ppm or less, particularly preferably 5 ppm or less, and most preferably 1 ppm or less. Thus, by suppressing the content of metal impurities to a low level and reducing the influence thereof, the silica of the present invention can further exhibit excellent properties such as high heat resistance and water resistance.
[0027]
One of the characteristics of the silica of the present invention is that there is little change in pore characteristics 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 related to porosity such as specific surface area, pore volume, and pore size distribution. For example, in the silica of the present invention, when a hydrothermal resistance test at 280 ° C. for 24 hours is performed, the specific surface area after the test is 20% or more with respect to the specific surface area before the test (the specific surface area residual ratio is 20% or more). ) Is preferable. The silica of the present invention having such characteristics is preferable because, for example, the porous characteristics are not lost even under severe use conditions for a long time as a catalyst carrier or the like. The residual ratio of the specific surface area is preferably 35% or more, particularly 50% or more.
[0028]
The silica of the present invention has very little deterioration of the characteristic that the pore diameter distribution is sharp and the change in the pore volume is very small or the pore volume is increased even after the hydrothermal treatment test. It has a characteristic that is not found in conventional silica.
[0029]
In addition, the hydrothermal resistance test in the present invention means that water at a specific temperature (200 ° C.) is brought into contact with silica for a certain time (6 hours) in a closed system. If present in water, the inside of the closed system may be completely filled with water, or a part of the system may have a gas phase part under pressure, and the gas phase part may have water vapor. . In this case, the pressure in the gas phase part 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.
[0030]
(2) Method for producing silica of the present invention
The silica of the present invention having the physical properties described above can be obtained by subjecting the silica hydrogel to hydrothermal treatment as it is without substantially aging and performing hydrothermal treatment under specific conditions as described later.
[0031]
In producing the silica gel of the present invention, any method can be used as a method for obtaining a silica hydrogel as a raw material. Examples thereof include a method obtained by hydrolyzing an alkali silicate salt, or a method obtained by hydrolyzing silicon alkoxide. Among them, silica hydrogel obtained by hydrolyzing silicon alkoxide is preferable because it can increase the purity of silicon alkoxide as a raw material and can easily prevent impurities from being mixed into silica hydrogel.
[0032]
Specific examples of the silicon alkoxide used as a raw material of the silica of the present invention include lower ones having 1 to 4 carbon atoms such as trimethoxysilane, tetramethoxysilane, triethoxysilane, tetraethoxysilane, tetrapropoxysilane, and tetrabutoxysilane. Examples thereof include tri- or tetraalkoxysilanes having an alkyl group or oligomers thereof. Among these, tetramethoxysilane, tetraethoxysilane and oligomers thereof, particularly tetramethoxysilane and oligomers thereof are preferable because silica having good pore characteristics can be obtained. The main reason is that silicon alkoxide is easily purified by distillation to obtain a high-purity product, and is therefore suitable as a raw material for high-purity silica. The total content of metal elements (metal impurities) belonging to the alkali metal or alkaline earth metal in the silicon alkoxide 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 method for measuring the impurity content in general silica.
[0033]
In the present invention, first, in the hydrolysis / condensation step, the silicon alkoxide is hydrolyzed in the absence of a catalyst and the silica hydrosol obtained is condensed to form a silica hydrogel.
[0034]
Hydrolysis of silicon alkoxide is usually 2 mol times or more, preferably 3 mol times or more, particularly preferably 4 mol times or more, and usually 20 mol times or less, preferably 10 mol times or less with respect to 1 mol of silicon alkoxide. Particularly preferably, it is carried out using 8 mol times or less of water. Hydrolysis of the silicon alkoxide produces a silica hydrogel and an alcohol, and the produced silica hydrosol is successively condensed into a silica hydrogel.
[0035]
The temperature at the time of hydrolysis is usually room temperature or higher and 100 ° C. or lower, but it can also be performed 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 (type of silicon alkoxide and molar ratio with water) and the reaction temperature, and since the time until gelation differs, it is not generally specified. This reaction time is preferably a time at which the fracture stress of the hydrogel does not exceed 6 MPa in order to obtain a silica having excellent pore characteristics such as the silica of the present invention.
[0036]
In addition, hydrolysis can be accelerated | stimulated by adding an acid, an alkali, salts, etc. to this hydrolysis reaction system as a catalyst. However, the use of such additives is not very preferable in the production of the silica gel of the present invention because it causes aging of the produced hydrogel, as will be described later.
[0037]
In the hydrolysis of the above-mentioned silicon alkoxide, it is important to sufficiently stir. For example, when a stirrer equipped with a stirring blade on the rotating shaft is used, the stirring speed (the number of rotations of the rotating shaft) depends on the shape, the number of the stirring blades, the contact area with the liquid, etc. 30 rpm or more, preferably 50 rpm or more.
[0038]
In general, if the stirring speed is too high, droplets generated in the tank block various gas lines or adhere to the inner wall of the reactor to deteriorate the heat conduction, which is an important temperature control property. It may affect management. Furthermore, the deposits on the inner wall may be peeled off and mixed into the product to deteriorate the quality. For these reasons, the stirring speed is preferably 2000 rpm or less, and more preferably 1000 rpm or less.
[0039]
In the present invention, any stirring method can be used as the stirring method for the two liquid phases (aqueous phase and silicon alkoxide phase) which are separated, as long as the method promotes the reaction. Among them, examples of the apparatus for further mixing the two liquid phases include the following (1) and (2).
[0040]
{Circle around (1)} A device having an agitating blade in which a rotating shaft is inserted perpendicularly or slightly at an angle with respect to the liquid surface and the liquid flows up and down.
{Circle around (2)} A stirrer having a stirring blade provided with a rotation axis direction substantially parallel to the interface between the two liquid phases and causing stirring between the two liquid phases.
[0041]
The rotational speed of the stirring blade when using the devices as described in (1) and (2) above is 0.05 to 10 m / s, especially the peripheral speed (stirring blade tip speed) of the stirring blade. -5 m / s, more preferably 0.1-3 m / s.
[0042]
The shape and length of the agitating blade is arbitrary, and examples of the agitating blade include a propeller type, a flat blade type, an angled flat blade type, a pitched flat blade type, a flat blade disk turbine type, a curved blade type, a fiddler type, Examples include a bull margin type.
[0043]
The width, number of blades, inclination angle, etc. of the blades may be appropriately selected according to the shape and size of the reactor and the target stirring power. For example, the ratio (b / D) of the blade width (blade length in the rotation axis direction) to the tank inner diameter (the longest diameter of the liquid phase surface forming a plane perpendicular to the rotation axis direction) of the reactor is 0.05 to A suitable example is 0.2, an inclination angle (θ) of 90 ° ± 10 °, and a stirring device of 3 to 10 blades.
[0044]
Among these, the structure in which the above-described rotating shaft is provided above the liquid level in the reaction vessel and the stirring blade is provided at the tip of the shaft extending from the rotating shaft is preferably used from the viewpoint of stirring efficiency and equipment maintenance. .
[0045]
In addition, silica having a crystal structure tends to have poor thermal stability in water. When silicon alkoxide is hydrolyzed in the presence of a template such as a surfactant used to form pores in the gel, the gel Easily includes 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, in a condition where there is no such an amount that it functions as a template.
[0046]
In the above hydrolysis reaction of silicon alkoxide, silicon alkoxide is hydrolyzed to form silica hydrosol. Subsequently, condensation reaction of the silica hydrosol occurs, the viscosity of the reaction solution increases, and finally gelation occurs. Silica hydrogel.
[0047]
Next, in the present invention, as a physical property adjusting step, hydrothermal treatment of the silica hydrogel is performed without substantially aging so that the hardness of the silica hydrogel generated by the above hydrolysis does not increase. Hydrolysis of silicon alkoxide produces a soft silica hydrogel. 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 hydrothermal treatment to stabilize the physical properties of the hydrogel.
[0048]
The hydrothermal treatment immediately performed without substantially aging the silica hydrogel produced by hydrolysis as described above means that the next hydrothermal treatment is performed while maintaining the soft state immediately after the silica hydrogel is produced. It means to be used for.
[0049]
Specifically, it is preferable that the hydrothermal treatment is generally performed within 10 hours from the time when the silica hydrogel is formed, and the hydrothermal treatment is preferably performed within 8 hours, more preferably within 6 hours, particularly within 4 hours. It is preferable.
[0050]
Moreover, in an industrial plant etc., the case where the silica hydrogel produced | generated in large quantities is once stored in a silo etc. and hydrothermal treatment is performed after that can be considered. In such a case, the silica hydrogel is considered to have a case where the time from when the silica hydrogel is formed to when it is subjected to hydrothermal treatment, the so-called standing time, exceeds the above range. In such a case, for example, the liquid component in the silica hydrogel may be prevented from drying during standing in the silo so that aging does not substantially occur.
[0051]
Specifically, for example, the inside of the silo may be sealed or the humidity may be adjusted. Alternatively, the silica hydrogel may be allowed to stand in a state where the silica hydrogel is immersed in water or another solvent.
[0052]
The temperature at the time of standing is preferably as low as possible, for example, 50 ° C. or less, particularly 35 ° C. or less, particularly preferably 30 ° C. or less. Further, as another method for preventing aging substantially from occurring, there is a method of preparing a silica hydrogel by controlling the raw material composition in advance so that the silica concentration in the silica hydrogel is lowered.
[0053]
Considering the effect obtained by hydrothermal treatment without substantially aging the silica hydrogel and the reason why this effect is obtained, the following can be considered.
[0054]
First, when the silica hydrogel is aged, a macroscopic network structure due to —Si—O—Si— bonds is considered to be formed in the entire silica hydrogel. It is considered that this network structure is present in the entire silica hydrogel, so that this network structure becomes an obstacle during hydrothermal treatment, and it becomes difficult to form mesoporous materials. Moreover, the silica hydrogel obtained by previously controlling the raw material composition so that the silica concentration in the silica hydrogel is 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.
[0055]
Therefore, in the present invention, it is important to perform hydrothermal treatment without aging the silica hydrogel.
[0056]
Adding an acid, alkali, salt, or the like to the silicon alkoxide hydrolysis reaction system or making the temperature of the hydrolysis reaction too strict is not preferable from the standpoint of aging the hydrogel. Also, temperature and time should not be taken more than necessary in washing, drying, leaving, etc. in post-treatment after hydrolysis.
[0057]
Further, the silica hydrogel obtained by hydrolysis of silicon alkoxide is preferably subjected to a pulverization treatment or the like so as to have an average particle size of 1 mm or less, particularly 0.5 mm or less, before hydrothermal treatment.
[0058]
If the particle size of the silica hydrogel subjected to the hydrothermal treatment is too large, the hydrothermal treatment does not proceed uniformly, and the pore size distribution may be broadened or the pore volume may be reduced.
[0059]
On the other hand, if the particle size is too small, the uniform structure of the silica hydrogel is destroyed by pulverization, so the appropriate effect of hydrothermal treatment cannot be obtained, the pore size distribution becomes broad, and the pore volume becomes small. Sometimes.
[0060]
For example, when the silica gel of the present invention is packed in a tower or a tube, and a harmful substance adsorbent or a catalyst is used, a particle having a particle size of 1 mm or more flows when a gas or liquid is circulated inside the tower or the tube. For example, in the case of gas or the like, the pressure loss can be reduced.
[0061]
When silica gel having such a large particle size is desired, it is preferable to set the particle size after pulverization to a desired size by the above-described pulverization treatment of silica hydrogel, and then hydrothermally treat it.
[0062]
As described above, as a method for producing the silica of the present invention, a method of immediately hydrothermally treating the silica hydrogel immediately after the production of the silica hydrogel is important. However, in the production method of the present invention, it is sufficient that the hydrothermally-treated silica hydrogel is not aged. Does not require hydrothermal treatment.
[0063]
As described above, when the hydrothermal treatment is not performed immediately after the formation of the silica hydrogel, the hydrothermal treatment may be performed after specifically confirming the aging state of the silica hydrogel. The means for specifically confirming the ripening state of the hydrogel is arbitrary, and examples thereof include a method of referring to the hardness of the hydrogel measured by a method as shown in Examples described later. That is, as described above, silica having a physical property range defined in the present invention can be obtained by hydrothermally treating a soft hydrogel having a fracture stress of usually 6 MPa or less, preferably 3 MPa or less, particularly preferably 2 MPa or less. .
[0064]
As conditions for this hydrothermal treatment, the state of water may be either liquid or gas, but it is preferable to perform hydrothermal treatment using liquid water as a slurry in addition to silica hydrogel. In the hydrothermal treatment, first, the silica hydrogel to be treated is usually 0.1 times or more, preferably 0.5 times or more, particularly preferably 1 or more times, and usually 10 times the weight of the silica hydrogel. Double or less, preferably 5 times or less, particularly preferably 3 times or less of water is added to form a slurry. The slurry is usually 150 ° C. or higher, preferably 200 ° C. or higher, and usually 250 ° C. or lower, preferably 240 ° C. or lower, usually 0.1 hour or longer, preferably 1 hour or longer, and usually 100 hours. Hereinafter, hydrothermal treatment is preferably performed for 10 hours or less. If the temperature of the hydrothermal treatment is too low, the pore size distribution is difficult to be sharp, and it may be difficult to increase the pore size.
[0065]
In the present invention, in order to increase the pore diameter of silica, it is important to perform hydrothermal treatment by increasing the water concentration around the silica (water concentration in the hydrothermal treatment liquid) as a condition for performing hydrothermal treatment. It becomes.
[0066]
As 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, and particularly preferably 95% or more. A high value is preferable.
[0067]
For example, when a hydrogel obtained using silicon alkoxide is hydrothermally treated, in such a hydrogel, alcohols produced by hydrolysis of silicon alkoxide are present in the 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.
[0068]
The reason why the pore diameter increases when the water concentration of the hydrothermal treatment liquid is high is not clear, but can be considered as follows.
The silica component in the hydrogel is aggregated and condensed by hydrothermal treatment. The action of water in this change is to phase separate silica and liquid components. In addition to having the function of bringing silica together by strong hydrogen bonds, water tends to gather together. It is presumed that pores having a large diameter are formed by the action of such water.
[0069]
However, since alcohol has a function of inhibiting the function of water, it is preferable that such alcohols are not present in the hydrothermal treatment liquid as much as possible. Specifically, the alcohol is preferably 20% or less, particularly preferably 15% or less.
[0070]
The hydrothermal treatment method is also applied to a material in which silica is formed on a substrate such as a particle, a substrate, or a tube in the form of a film or a layer for the purpose of making a membrane reactor or the like. It is also possible to perform 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 a method carried out without newly adding water.
[0071]
In the above hydrothermal treatment conditions, when the temperature is increased, the diameter and pore volume of the resulting silica tend to increase. The hydrothermal treatment temperature is preferably in the range of 100 to 200 ° C. Further, with the treatment time, the specific surface area of the obtained silica tends to gradually decrease after reaching a maximum once. Based on the above tendency, it is necessary to appropriately select the conditions according to the desired physical property values, but since hydrothermal treatment is the purpose of changing the physical properties of silica, it is usually at a higher temperature than the hydrolysis reaction conditions described above. It is preferable to do.
[0072]
In order to produce the silica of the present invention having excellent microstructural homogeneity, a fast heating rate condition is set so that the temperature in the reaction system reaches the target temperature within 5 hours during the hydrothermal treatment. It is preferable to do. Specifically, when the tank is filled and processed, the average rate of temperature increase from the start of temperature increase until reaching the target temperature is 0.1 to 100 ° C./min, especially 0.1 to 30 ° C./min. A value in the range of 0.2 to 10 ° C./min is preferably adopted.
[0073]
A temperature raising method using a heat exchanger or the like or a temperature raising method in which hot water prepared in advance is used is preferable because the temperature raising rate can be shortened. Moreover, if the temperature increase rate is in the above range, the temperature may be increased 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 progresses during the temperature rise, which may reduce the microstructural homogeneity.
[0074]
The temperature raising time until the above target temperature is reached is preferably within 4 hours, more preferably within 3 hours. In order to shorten the temperature raising time, the water used for the hydrothermal treatment can be preheated.
[0075]
When the hydrothermal treatment temperature and time are set outside the above ranges, it is difficult to obtain the silica of the present invention. For example, if the hydrothermal treatment temperature is too high, the pore diameter and pore volume of silica become too large, and the pore distribution is also widened. On the other hand, when the temperature of the hydrothermal treatment is too low, the generated silica has a low degree of cross-linking, poor thermal stability, no peak in the pore distribution, or Q in the above-described solid Si-NMR. ⁴ / Q ³ The value becomes extremely small.
[0076]
In the present invention, a silica hydrogel obtained by hydrolyzing silicon alkoxide as a raw material and using no catalyst such as hydrochloric acid (in the absence of a catalyst) is hydrothermally treated in aqueous ammonia. By doing so, the silica gel of the present invention having a large pore diameter as described above can be obtained.
[0077]
When the hydrothermal treatment is performed in ammonia water, the same effect can be obtained at a lower temperature than in pure water. In addition, when hydrothermal treatment is performed in ammonia water, the finally obtained silica generally becomes hydrophobic as compared with hydrothermal treatment using water not containing ammonia. At this time, when the temperature of the hydrothermal treatment is a relatively high temperature of 30 ° C. or higher, preferably 40 ° C. or higher, 250 ° C. or lower, preferably 200 ° C. or lower, the hydrophobicity is particularly high. The ammonia concentration here is preferably 0.001% or more, particularly preferably 0.005% or more, and preferably 10% or less, particularly preferably 5%.
[0078]
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 it may be a batch type or a continuous type, and can be dried under normal pressure or reduced pressure. Among these, vacuum drying is preferable because not only drying can be performed quickly, but also the pore volume and specific surface area of the resulting silica are increased.
[0079]
If necessary, when carbon content derived from the raw material silicon alkoxide is contained, it can be usually removed by baking at 400 to 600 ° C. Moreover, in order to control a surface state, it may bake at the temperature of a maximum of 900 degreeC. Furthermore, the final silica of the present invention is obtained by pulverizing and classifying as necessary.
[0080]
(3) Use of the silica of the present invention
The novel silica of the present invention is superior in heat resistance and water resistance compared to conventional silica, and thus has high stability and preferably high purity. Further, according to the method for producing silica of the present invention, it is possible to produce silica controlled in a desired physical property range by a relatively simple process using silicon alkoxide as a raw material.
[0081]
The silica of the present invention can be used in various applications of conventional silica, but particularly when used as a catalyst carrier, a membrane reactor, etc., performance degradation is small and it can be used more stably for a long time.
[0082]
The silica of the present invention can be used in any application other than the conventional use of silica. Among these, conventional applications include the following.
[0083]
For example, in application fields used for manufacturing and processing products in industrial facilities, various catalysts and catalyst carriers (acid-base catalysts, photocatalysts, noble metal catalysts, etc.), wastewater / waste oil treatment agents, odor treatment agents, gas separation agents, Applications include industrial desiccants, bioreactors, bioseparators, membrane reactors and the like. Examples of building materials include humidity control agents, soundproofing / absorbing materials, refractories, and heat insulating materials. Moreover, in applications in the air conditioning field, desiccant air conditioners, heat pump heat storage agents, and the like. In the paint / ink application field, matting agents, viscosity adjusting agents, chromaticity adjusting agents, anti-settling agents, antifoaming agents, ink back-through preventing agents, stamping foils, and wallpapering applications may be mentioned. In the field of resin additives, anti-blocking agents for films (polyolefin films, etc.), plate-out inhibitors, silicone resin reinforcing agents, rubber reinforcing agents (for tires, general rubbers, etc.), fluidity improvers, Anti-caking agent for powdered resin, printability improver, matting agent for synthetic leather and coating film, filler for adhesive / adhesive tape, translucency adjuster, antiglare adjuster, porous polymer sheet Uses for fillers and the like. In the papermaking field, thermal paper fillers (such as residue adhesion inhibitors), ink jet paper image enhancement fillers (ink absorbers, etc.), diazo photosensitive paper fillers (photosensitive density improvers, etc.), and tracing paper Uses such as a writing property improving agent, a filler for coated paper (writing property, ink absorbability, anti-blocking property improving agent, etc.), a filler for electrostatic recording and the like can be mentioned. In food applications, beer filter aids, soy sauce, sake, wine and other fermented product lowering agents, various fermented beverage stabilizers (such as turbidity factor protein and yeast removal), food additives, and powdered foods Uses such as anti-caking agents are mentioned. In the medical and agrochemical field, tableting aids for pharmaceuticals, grinding aids, dispersion / pharmaceutical carriers (dispersion, sustained release, improved delivery, etc.), agrochemical carriers (oily agrochemical carrier, improved hydration dispersibility, sustained release) -Delivery improvement etc.), Additives for medicine (anti-caking agent / powdering improver, etc.), additives for agricultural chemicals (anti-caking agent, anti-settling agent, etc.), etc. In the field of separation materials, there are applications such as chromatographic fillers, separation agents, fullerene separation agents, adsorbents (proteins, dyes, odors, etc.), and dehumidifiers. In the agricultural field, feed additives and fertilizer additives can be mentioned. As other applications, in life-related fields, humidity control agent, desiccant, cosmetic additive, antibacterial agent, deodorant / deodorant / fragrance, detergent additive (surfactant powder, etc.), abrasive (toothpaste) Etc.), powder fire extinguishing agents (powdering property improver, anti-caking agent, etc.), antifoaming agents, battery separators and the like.
[0084]
In particular, since the silica of the present invention has a larger pore diameter than conventional silica, it has a high adsorption / absorption capacity. Therefore, among the applications listed above, particularly in fields where large pore diameters and excellent hydrothermal resistance are required, controlled pore characteristics, and changes in physical properties over a long period are required. Can be used.
[0085]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention still in detail, this invention is not restrict | limited to a following example, unless the summary is exceeded.
[0086]
(1) Analysis method of silica:
1-1) Pore volume, specific surface area, differential pore volume:
The BET nitrogen adsorption isotherm was measured with AS-1 manufactured by Cantachrome, and the pore volume and specific surface area were determined. Specifically, the pore volume is relative pressure P / P ₀ = 0.98 is adopted, and the specific surface area is P / P ₀ = Calculated using the BET multipoint method from three points of nitrogen adsorption amounts of 0.1, 0.2, and 0.3. Also, pore distribution curve and mode diameter (D _max ) Differential pore volume was determined. The interval between each point of the relative pressure to be measured was 0.025.
[0087]
1-2) Powder X-ray diffraction:
Using a RAD-RB apparatus manufactured by Rigaku Corporation, measurement was performed using CuKα as a radiation source. The divergence slit was ½ deg, the scattering slit was ½ deg, and the light receiving slit was 0.15 mm.
[0088]
1-3) Content of metal impurities:
Hydrofluoric acid was added to 2.5 g of the sample and heated to dryness, and then water was added to make 50 ml. ICP emission analysis was performed using this aqueous solution. Sodium and potassium were analyzed by flame flame light method.
[0089]
1-4) Solid Si-NMR measurement:
Conditions of CP / MAS (Cross Polarization / Magic Angle Spinning) probe using a Bruker solid-state NMR apparatus (“MSL300”) and a resonance frequency of 59.2 MHz (7.05 Tesla) and a 7 mm sample tube Measured with The rotation speed of the sample was 5000 rps.
[0090]
Analysis of measurement data (Q ⁴ The determination of the 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, waveform processing software “GRAMS386” manufactured by Thermogalatic can be used.
[0091]
Q obtained by peak division in this way ⁴ And Q ³ Using the area of each peak, and the ratio (Q ⁴ / Q ³ )
[0092]
1-5) Average particle diameter
It measured with the laser type particle size distribution analyzer (LMS-30 by Seishin Enterprise Co., Ltd.).
[0093]
1-6) Underwater thermal stability test:
Pure water was added to the sample to prepare a 40 wt% slurry. About 40 ml of the slurry prepared above was sealed in a stainless steel microbomb having a capacity of 60 ml, and immersed in an oil bath at 280 ± 1 ° C. for 24 hours. A part of the slurry was extracted from the microbomb and filtered with a filter paper (No. 5A). The filter cake was vacuum-dried at 100 ° C. for 5 hours, and then the specific surface area of the remaining sample was measured.
[0094]
(2) Production and evaluation of silica:
Example 1:
<Hydrolysis / gelation reaction>
1000 g of pure water was charged into a 5 L separable flask (with a jacket) made of glass and fitted with a water-cooled condenser open to the atmosphere at the top. As the stirring speed, 1400 g of tetramethoxysilane was charged over 3 minutes while stirring at a stirring blade tip speed of 2.5 m / s. The number of moles of water relative to 1 mole of tetramethoxysilane used (water / tetramethoxysilane molar ratio) is 6. Warm water at 50 ° C. was passed through the jacket of the separable flask. Stirring was continued, and the stirring was stopped when the contents reached the boiling point. Subsequently, hot water of 50 ° C. was passed through the jacket for about 0.5 hour to gel the sol produced.
[0095]
<Crushing reaction>
Thereafter, the gel was quickly taken out, and the gel was pulverized through a nylon net having an opening of 600 microns to obtain a powdery wet gel (silica hydrogel) having a predetermined average particle size.
[0096]
<Hydrothermal treatment process 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 subjected to a closed hydrothermal treatment at 200 ° C. for 3 hours. The obtained silica was filtered with a filter paper (No. 5A), and the filter cake was dried under reduced pressure at 100 ° C. until it became a constant weight without washing the filter cake with water to obtain the silica of Example 1.
[0097]
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). .
[0098]
Example 2:
<Hydrolysis / gelation reaction / grinding process>
After producing a silica hydrogel by the same procedure as in Example 1, the silica hydrogel was pulverized by the same procedure as in Example 1 to obtain a powdery silica hydrogel having a predetermined average particle size.
[0099]
<Washing process of silica hydrogel>
450 g of this crushed silica hydrogel and 675 g of water were placed in a beaker and stirred for 10 minutes, and then solid-liquid separation was performed by decantation. After repeating this operation twice in total, the same amount of water was added, and the mixture was allowed to stand at room temperature for a whole day and night, followed by solid-liquid separation by decantation.
[0100]
<Hydrothermal treatment process>
This silica hydrogel and 500 g of water were charged into a 1 L glass autoclave and subjected to a closed hydrothermal treatment at 200 ° C. for 3 hours. The slurry after hydrothermal treatment was decanted and separated into solid and liquid, and the methanol concentration in the liquid was analyzed by gas chromatography.
[0101]
<Drying process>
After hydrothermal treatment, no. The resultant was filtered through 5A filter paper, and dried under reduced pressure at 100 ° C. until it became a constant weight without washing the filter cake with water, whereby the silica of Example 2 was obtained. The total amount of metal impurities in this silica is 0.9 ppm {of which: Na: 0.2, calcium (Ca): 0.2, iron (Fe) 0.4, potassium (K): 0.1, all units are ppm}.
[0102]
Example 3:
In the crushing step of Example 2, silica (silica of Example 3) was obtained in the same procedure as Example 2 except that the opening of the nylon mesh was 8 mm. The total amount of metal impurities in the silica was 0.3 ppm (of which Na: 0.1, calcium (Ca): 0.1, potassium (K): 0.1, all in ppm).
[0103]
Example 4:
In the hydrolysis / gelation step of Example 2, silica (silica of Example 4) was obtained in the same procedure as Example 2 except that the number of moles of water relative to 1 mole of tetramethoxysilane was 10 times. . The total amount of metal impurities in the silica was 0.8 ppm (of which Na: 0.2, calcium (Ca): 0.2, iron (Fe): 0.4, all in ppm).
[0104]
Table 1 shows various physical properties of the obtained silicas of Examples 1 to 4 measured by the above analytical methods. In any of the silicas, no crystalline peak appeared in the powder X-ray diffraction pattern, and no peak on the low angle side (2θ ≦ 5 deg) due to the periodic structure was observed.
[0105]
Comparative example 1:
Commercially available silica gel [manufactured by Mizusawa Chemical Co., Ltd .: gel type silica gel P-707, 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 (Zr): 30, all in ppm}, no crystallinity peak in the powder X-ray diffraction diagram. There is no low-angle peak due to the periodic structure. Table 1 shows the results of a hydrothermal stability test conducted in the same manner as in Example 1.
[0106]
[Table 1]

[0107]
·result:
As is apparent from Table 1, the silica of the present invention is excellent in hydrothermal stability, and the residual specific surface area remains large (that is, the decrease is small) even under various severe use conditions. Can be maintained.
[0108]
【The invention's effect】
The silica of the present invention has a high adsorption / absorption capacity because it has a larger pore diameter than conventional silica. In addition, it can be produced by a relatively simple process using silicon alkoxide as a raw material, and has desirable physical properties controlled within a desired range, and is excellent in heat resistance, water resistance and the like, and thus has high stability.

Claims (9)

Silica having the following characteristics:
(A) The pore volume is 0.6 ml / g or more and 1.6 ml / g or less (b) The specific surface area is 50 to 600 m ² / g
(C) The most frequent pore diameter (D _max ) is 15 nm or more. (D) The Q ⁴ / Q ³ value in solid Si-NMR is 3 or more. (E) It is amorphous. ^2. The silica according to claim 1, wherein the specific surface area is 100 m ² / g or more and 450 m ² / g or less. Silica according to claim 1 or 2, characterized in that the mode pore diameter ( _Dmax ) is 50 nm or less. The volume of the pores having a pore diameter in the range of ± 20% of the mode pore diameter (D _max ) is 50% or more of the total pore volume, Silica as described in any one. The silica according to any one of claims 1 to 4, wherein the metal impurity content is 100 ppm or less. The silica according to any one of claims 1 to 5, wherein the differential pore volume at the most frequent pore diameter ( _Dmax ) is 2 ml / g or more and 20 ml / g or less. The silica according to any one of claims 1 to 6, wherein the residual ratio of specific surface area after heat treatment in sealed water under conditions of 280 ° C and 24 hours is 20% or more. A method for producing silica according to any one of claims 1 to 7, comprising hydrolyzing silicon alkoxide and subjecting the resulting hydrogel to hydrothermal treatment without substantially aging. A method for producing silica, wherein the heat treatment is performed under conditions of an alcohol concentration of 20% or less and 150 ° C or more. The silica according to any one of claims 1 to 7 is produced by hydrolyzing a silicon alkoxide in the absence of a catalyst and hydrothermally treating the resulting hydrogel with aqueous ammonia. A method for producing silica.