JPH0930809A - Production of silica gel - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method for producing silica gel sharp in fine pore diameters, capable of controlling the BET specific surface area, fine pore volume and average fine pore diameter of the silica gel to desired ranges, respectively. SOLUTION: This method for producing silica gel comprises drying silica hydrogel. Therein, the drying of the silica hydrogel is performed by a batch type fluidized drying method. The water content of the dried silica hydrogel is preferably 50-80wt.%. The batch type fluidized drying method is preferably performed in an exhaust gas temperature ranging from 20 to 150 deg.C.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for producing silica gel from silica hydrogel, which is characterized by a drying method. According to the method of the present invention, silica gel having a desired pore volume and an average pore diameter and exhibiting a sharp pore distribution can be efficiently produced.

[0002]

2. Description of the Related Art Silica can be produced by a neutralization reaction between an aqueous solution of an alkali metal silicate and a mineral acid, and its production method is called a wet method. Further, the wet method is classified into a precipitation method in which the neutralization reaction is carried out in neutral or alkaline to obtain precipitated silica which is relatively easy to filter, and a gel method in which acidic silica is obtained to obtain gel silicic acid. . A method for producing precipitated silica is disclosed in, for example, Japanese Patent Publication No. 39-1207. According to this method, the precipitated silica is obtained by growing the primary particles so as to have a structure by the above neutralization reaction, washing the obtained precipitated silicic acid with water, drying and pulverizing. Precipitated silica is mainly used as a general-purpose rubber reinforcing agent, pesticide carrier, paint delusterant, and viscosity modifier.

A method for producing gel silica is disclosed in, for example, US
No. 2,466,842. According to this method, the neutralization reaction is carried out on the acidic side, and the obtained gel method hydrogel (hereinafter referred to as silica hydrogel) is washed with water, dried and pulverized to obtain gel method silica (hereinafter also referred to as silica gel). Is obtained. The gel method silica generally has a higher structural property than the precipitation method silica, and maintains the structural property even under a high shear. Furthermore, since gel-type silica has many pores on the surface, it is used as a coating field for synthetic leather, plastics, etc., as a beer filter, an anti-blocking agent for resin films, an adsorbent, a separating agent, and a catalyst. .

Among the physical properties of silica gel, BET specific surface area, pore volume, average pore diameter and pore diameter distribution are important. Regarding the above-mentioned physical properties of silica gel, the required range varies depending on the application. For example, when used as a beer filtering agent, the BET specific surface area is 100 to 1100 m ² / g, the pore volume is 0.2 to 2.5 ml / g, and the average pore diameter is 30 to 20.
It is preferably in the range of 0 °. Further, it is preferable that the pore size of silica gel has a sharp distribution, for example, when it is used as a beer filtering agent, an adsorbent, a separating agent, a catalyst, etc., from the viewpoint of high selectivity of adsorption and reaction.

It is known that these physical properties are somewhat changed by changing reaction conditions, washing conditions, hydrothermal treatment conditions, and drying conditions. Gel-method silica generally has a BET specific surface area in the range of 200 to 800 m ² / g. When trying to obtain silica gel having a predetermined BET specific surface area, it is extremely difficult to control the pore volume, average pore diameter and pore distribution independently of the BET specific surface area. Further, even if the pore volume and the average pore diameter can be controlled, the pore diameter distribution normally obtained is broad and it is impossible to make the pore diameter uniform. That is, it was very difficult industrially to obtain silica gel having the desired physical properties.

For example, the BET specific surface area can be changed to some extent by changing the temperature or pH of hydrothermal treatment of silica hydrogel during the production of silica gel. Further, the pore volume and the average pore diameter can be changed to some extent by changing the drying conditions of the silica hydrogel. However, the range of BET specific surface area, pore volume and average pore diameter that can be varied by changing hydrothermal treatment conditions and drying conditions is very narrow, and it is easy to obtain silica gel having desired physical properties. It's far from it.

Further, the pore size distribution can be changed to some extent by changing the drying conditions of the silica hydrogel as described above. However, it cannot be said that the pore size distribution of silica gel obtained by the conventional methods is sharp. For example, in the silica gel obtained by the conventional methods, the median diameter of the peak showing the pore size distribution is A,
When the half-width was B, B / A was 0.6 or more. On the other hand, from the viewpoint of obtaining higher adsorption selectivity and reaction selectivity, the above B / A is less than 0.6, preferably 0.5 or less.

For example, JP-A-44-23011 discloses that
Silica hydrogel is treated with organic acid, 500 ~ 600 ℃
Discloses a method of baking to remove excess organic acid. According to this method, silica gel having extremely large pores can be obtained. However, since a step of substituting the organic acid with water is required, it is not preferable in terms of economy and safety. Also, JP-A-58-135119
Japanese Patent Publication No. 1994-242242 discloses a method of drying with a hot air dryer at about 130 ° C. for 10 to 24 hours. This method is not preferable because not only silica gel having a uniform desired pore distribution cannot be obtained, but also the drying time is long and the productivity is poor.

[0009]

[Problems to be Solved by the Invention]

An object of the present invention is a method for producing silica gel in which the BET specific surface area, pore volume and average pore diameter can be controlled to be changed within desired ranges, and silica gel having a sharp pore diameter distribution can be obtained. An object of the present invention is to provide a possible manufacturing method.

The present inventors have recognized that in the production of silica gel, the drying step is an important step for determining the physical properties of the product silica gel pores, not simply removing water. Various searches were conducted for drying methods and conditions. As a result, by adopting a specific method, it is possible to produce silica gel having a sharp peak of pore size distribution, and it is possible to arbitrarily control the BET specific surface area, pore volume, and average pore diameter of the resulting silica gel. Found and completed the present invention.

[0012]

SUMMARY OF THE INVENTION The present invention relates to a method for producing silica gel by drying silica hydrogel, which is characterized in that the silica hydrogel is dried by batch type fluidized drying. . Hereinafter, the present invention will be described in detail.

In the production method of the present invention, the gel method hydrogel to be dried is not particularly limited. For example, a gel method hydrogel obtained by a known method can be used as it is. For example, 25 wt% SiO ₂ and a sodium silicate aqueous solution having a molar ratio of 3.3, and 42 wt% H ₂ S
A method of preparing a silica hydrogel by mixing O ₄ with a pH of 0.5 to 2.0 and a temperature of 60 ° C. or less by using a mixing nozzle to prepare a silica hydrogel can be mentioned. . Gelation of the sol occurs within 10 minutes of starting mixing. Alternatively, the silica hydrogel can be prepared by the simultaneous dropping method, for example, the sodium silicate and H ₂ SO ₄ in a batch reaction tank.
Can be prepared by simultaneous dropwise addition under the conditions of pH 0.5 to 2.0.

In these silica hydrogel preparation methods, the SiO ₂ concentration of sodium silicate is preferably 10 to 29 wt%, and the H ₂ SO ₄ concentration is preferably 35 to ₄ %.
A range of 5 wt% is suitable. When the concentration is higher than the above range, the viscosity of the solution during the reaction tends to increase and the operation tends to be difficult, and when the concentration is lower than the above range, it tends to be difficult to control gelation during the reaction.

Further, in any of these reaction methods,
The pH during the reaction is preferably 0.5 to 2.0. p
When H exceeds 2.0, gelation is quick and not only handling becomes difficult, but also quality control becomes difficult. Also, p
If H is lower than 0.5, a large amount of alkali is required in the washing and hydrothermal treatment steps, which is not preferable. The reaction temperature is preferably 10 to 70 ° C, more preferably 30 to 60 ° C.
It is good to set it to ℃. When the temperature is higher than 70 ° C, the pore distribution is affected, which is not preferable, and when the temperature is 1
When the temperature is lower than 0 ° C, gelation time becomes long, which is not preferable.

The deer hydrogel obtained as described above is washed with water to remove by-product salts, and then dried according to the present invention. In addition, prior to this washing with water, it is preferable that the silica hydrogel be roughly crushed in order to perform washing with water efficiently. If the degree of crushing is too large, it will take time to wash with water,
If it is too small, it is difficult to pass the liquid, so it is preferable to set it to 1 to 30 mm.

In the preparation of silica hydrogel, in addition to the above crushing and washing with water, if necessary, an aqueous solution of sodium hydroxide or ammonia is added to the washing liquid to carry out hydrothermal treatment for controlling the specific surface area. You can also When the hydrothermal treatment is performed, the treatment temperature is 30 to 95 ° C, preferably 70 to 95 ° C. If the temperature is lower than this temperature, it takes a long time to reduce the specific surface area, which is not preferable. The pH is preferably 7-11, more preferably 8-11. If it is higher than this range, it is difficult to control the product pH after hydrothermal treatment, which is not preferable. Also,
When it is lower than the range, it takes a long time to reduce the BET specific surface area, which is not preferable. In the method for producing silica gel of the present invention, the BET specific surface area of the obtained silica gel is
The fluctuation range due to the difference in the physical properties of the silica hydrogel to be dried is larger than that under the drying conditions. Therefore, it is preferable to control the physical properties of the silica hydrogel that has been previously dried so as to obtain the desired silica gel.

The deer hydrogel prepared by the above-mentioned crushing, washing with water and, if necessary, hydrothermal treatment is subjected to batch type fluidized drying. In the present invention, fluidized drying is performed in a batch system. By carrying out the batch method, silica gel having a sharp peak of pore size distribution can be obtained. In continuous fluidized drying, the residence time has a wide range, and as a result, the pore size distribution tends to be broad.

Fluidized drying is a drying method using a gas-solid type fluidized bed. Hot air is blown from below the granular material layer to bring the granular material into a suspended suspension state so that the water content in the granular material is increased. Is a method of evaporating and separating. In fluidized drying, the mixing of hot air and powder is very good and the effective contact area is large, so even if a small device is used, the processing amount per device capacity is large, and the mixing of powder in the layer is difficult. Since it is almost perfect, it is characterized in that the temperature and moisture of the entire layer can be controlled to be uniform. Fluidized drying of the present invention,
It can be performed using a commercially available fluid dryer. Furthermore, in the method of the present invention, the silica hydrogel is dried with constant flow. By drying while flowing, uniform drying can be performed in a relatively short drying time.

In carrying out fluidized drying, the exhaust temperature is very important for controlling the physical properties. The exhaust temperature is suitably in the range of 20 to 150 ° C. Preferably, it is in the range of 50 to 120 ° C. By drying within this range, various pores can be controlled. For example, when the exhaust temperature is lowered, the pores are kept large, and the pore volume and average pore diameter become very large. Further, when the exhaust temperature is raised, the pores contract due to the surface tension of water, and the pore volume and average pore diameter decrease.

If the exhaust temperature is lower than the above range, the drying time becomes very long, which is not preferable in practice. Further, if it is higher than the above range, it is possible to further reduce the pore volume and the average pore diameter, but it is necessary to maintain the temperature of the hot air blown into the fluidized dryer to be extremely high, so that the drying cost is increased. . The fluid used for fluidized drying may include, for example, compressed air, heated air, heated steam, inert gas and the like. However, it is not limited to these.

The drying time can be appropriately selected so that the water content of silica gel falls within a predetermined range. The time until the water content of silica gel reaches a predetermined value varies depending on the amount of silica hydrogel charged in the fluidized dryer and the temperature and flow rate of the fluid supplied to the fluidized dryer. Therefore, by appropriately changing these conditions, the drying time can be 1-2.
It is appropriate that the range is 00 minutes. Preferably,
2 to 150 minutes. If it is longer than this range, the drying cost will be high.

The water content of the silica hydrogel subjected to fluidized drying is preferably in the range of, for example, 50 to 80 wt% from the viewpoint of obtaining silica gel having a large pore volume and a large average pore diameter. The larger the water content, the larger the pore volume tends to be. However, considering the drying efficiency and the like, the range is more preferably 60 to 75 wt%.
After washing with water, silica hydrogel usually has a water content of 60 to 75 wt%. Therefore, it is possible to make an adjustment to obtain a desired water content.

The average particle size of the silica hydrogel used for fluidized drying is, for example, 1 to 30 m from the viewpoint that the drying rate can be easily controlled and uniform drying can be performed.
It is preferably in the range of m. More preferably, 1 to
It is in the range of 20 mm. If the average particle size of the silica hydrogel is too small, it will be difficult to control the drying rate, and if it is too large, uneven drying will occur easily.

In the silica hydrogel, the space (that is, the pore volume) of the three-dimensional network structure of colloidal particles is completely filled with water, and the space, that is, the pore volume shrinks as the dehydration by drying progresses ( Decrease). This phenomenon occurs because the packed state of the colloidal particles changes due to the contracting force based on the surface tension at the gas-liquid interface during the evaporation of water. Therefore, the degree of contraction due to this drying depends on the balance between the structural force of the three-dimensional network structure of colloidal particles and the contractive force based on the surface tension. That is, this balance can be controlled by controlling the exhaust temperature and the drying time by batch type fluidized drying, and products having various pore volumes and average pore diameters can be efficiently produced.

As a drying device used for drying the granular material, an airflow dryer, an aeration band dryer, a turbo type dryer, a fluidized dryer and the like are generally used industrially. A flash dryer has a very large processing capacity and a low equipment cost.
The thermal efficiency is poor, and the ventilation band dryer and the turbo-type dryer have a problem that the processing capacity is very large, but the equipment cost is high and the thermal efficiency is poor. Further, there arises a problem that silica gel having a uniform and desired pore volume and average pore diameter cannot be obtained. On the other hand, the present invention has the following effects by performing the batch type fluidized drying.

[0027]

EFFECTS OF THE INVENTION According to the present invention, a method for producing silica gel in which the BET specific surface area, pore volume and average pore diameter can be controlled to be changed within desired ranges, and silica gel having a sharp pore diameter distribution is obtained. It is possible to provide a manufacturing method capable of performing the above. That is, according to the production method of the present invention, it is possible to obtain a silica gel having a sharp pore size distribution with B / A of less than 0.6, preferably 0.5 or less.

[0028]

EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples. Various test methods used in the examples are described below. (A) BET specific surface area After measuring the adsorption and desorption isotherms of nitrogen using ASAP-2400 manufactured by Shimadzu Corporation, S. Brunauer, PHEmett, E. Tel
It was measured using the method described by J. Am. Chem. Soc., 60309 (1938) by the Ler method.

(B) Pore Volume, Average Pore Diameter, and Pore Distribution After measuring the adsorption and desorption isotherm of nitrogen using ASAP-2400 manufactured by Shimadzu Corporation, Barrett-Joyner-Halenda method, J.
Am.Chem.Soc., 73, 373 (1951) was used for the measurement. (C) Water Content It was measured at 150 ° C. for 60 minutes using a KETT water content meter. (D) The average particle size was measured using a sieve having a diameter of 10 mm.

Example 1 A silica hydrosol was obtained by reacting a 20 wt% sodium silicate aqueous solution with a 35 wt% sulfuric acid aqueous solution using a mixing nozzle. The silica hydrosol was gelated in about 5 minutes to obtain a silica hydrogel. The silica hydrogel is sieved to about 1
After crushing to 0 mm, it was hydrothermally treated for 4 hours at 90 ° C. and pH 9.5, and then washed. The washed silica hydrogel (water content 72.5 wt%) was dried in a batch manner using a fluid dryer. The silica gel of the present invention was obtained under the three drying conditions shown in Table 1 [exhaust temperature and drying time of silica hydrogel]. Table 1 shows the physical properties of the obtained silica gel. Further, FIGS. 1 to 3 show the pore distribution of the obtained silica gel.

Comparative Example 1 Silica hydrogel (water content 72.5 wt%) obtained by performing the same operation as in Example 1 was continuously dried using a rotary kiln. As the drying condition, the furnace temperature is 15
It was set at 0 ° C. and operated for 1 hour. Samples were taken during continuous operation and physical properties were measured. Table 1 shows the physical properties of the obtained silica gel. The pore distribution of the silica gel sample having a drying time of 30 minutes is shown in FIG.

Comparative Example 2 In the same operation as in Comparative Example 1, the drying temperature was set to the furnace temperature of 250 ° C. and the operation was carried out for 1 hour. Samples were taken during continuous operation and physical properties were measured. Table 1 shows the physical properties of the obtained silica gel. The pore distribution of the silica gel sample having a drying time of 30 minutes is shown in FIG.

[0033]

[Table 1]

From the results shown in Table 1, it is not possible to obtain silica gel having a large pore volume and a large average pore diameter in the continuous rotary kiln used in the comparative example, and the pore volume and the average pore diameter change with time. You can see that it changes and is unstable. On the other hand, according to the production method of the present invention, the pore volume and average pore diameter of silica gel can be changed by selecting the conditions, and the silica gel obtained has a B / A of 0.5 or less. It can be seen that it has a sharp pore distribution.

[Brief description of drawings]

FIG. 1 Pore distribution of silica gel of the present invention.

FIG. 2 is a pore distribution of the silica gel of the present invention.

FIG. 3 Pore distribution of the silica gel of the present invention.

FIG. 4 Pore distribution of silica gel of Comparative Example 1 (drying time 30 minutes).

FIG. 5: Pore distribution of silica gel of Comparative Example 2 (drying time 30 minutes).

Claims (5)

[Claims] 1. A method for producing silica gel by drying silica hydrogel, wherein the silica hydrogel is dried by batch type fluidized drying. 2. The method according to claim 1, wherein the silica hydrogel having a water content in the range of 50 to 80 wt% is dried. 3. An exhaust gas temperature of 2 is used for batch type fluidized drying.
The method according to claim 1 or 2, wherein the temperature is in the range of 0 to 150 ° C.
The manufacturing method as described. 4. The production method according to claim 1, wherein the batch type fluidized drying time is in the range of 1 to 200 minutes. 5. The production method according to claim 1, wherein the hydrogel having an average particle size in the range of 1 to 20 mm is dried.