JPH09278430A - Production of silica - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently obtain silica hydrogel excellent in settleability at a high rate of formation by separating and collecting silica hydrogel from a liq. reactional mixture obtd. by allowing an aq. sodium silicate soln. to react with an aq. sodium hydrogencarbonate soln. SOLUTION: An aq. sodium silicate soln. having <=200g/L concn. of SiO2 is allowed to react with an aq. sodium hydrogencarbonate soln. having 164g/L concn. at 50-70 deg.C. The resultant liq. reactional mixture is filtered to separate formed silica hydrogel from a prepd. aq. sedium carbonate soln. After pH adjustment with a mineral acid, the silica hydrogel is washed, dried and pulverized to obtain silica xerogel having >=600m<2> /g BET specific surface area. Gaseous CO2 is blown and absorbed in the aq. sodium carbonate soln. to convert the sodium carbonate into sodium hydrogencarbonate and the resultant aq. sodium hydrogencarbonate soln. is used for reaction with an aq. sodium silicate soln.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a novel method for producing silica.

[0002]

2. Description of the Related Art
As a method for producing wet silica, a method using sodium silicate and a mineral acid such as sulfuric acid is generally adopted.

As a method of using carbon dioxide as a substitute for mineral acid, there is known a method of directly contacting and reacting carbon dioxide (or a boiler flue gas containing carbon dioxide) in an aqueous sodium silicate solution. However, this method has a problem that the rate of silica formation is extremely slow and it is difficult to obtain silica having a good sedimentation property.

At present, the global warming phenomenon has been pointed out as an environmental problem on a global scale. One of the causes for this is the high concentration of carbon dioxide in the atmosphere, and the reduction / fixation of carbon dioxide emissions. This method is required globally, and effective use of carbon dioxide is also desired in the production of silica.

The object of the present invention is to produce a silica hydrogel having a good sedimentation property at a high production rate and efficiently,
An object of the present invention is to provide a method for producing silica capable of effectively utilizing carbon dioxide.

[0006]

Means for Solving the Problems and Modes for Carrying Out the Invention As a result of intensive studies to achieve the above-mentioned object, the present inventor has found that by reacting an aqueous sodium hydrogen carbonate solution with an aqueous sodium silicate solution, sedimentation A silica having the same good physical properties as that of conventional silica (white carbon) can be obtained. Furthermore, by appropriately selecting the conditions for reacting an aqueous sodium hydrogen carbonate solution and an aqueous sodium silicate solution, the JIS-K-1150 method Has a specific surface area of 6
It was found that silica having a high specific surface area of 00 m ² / g or more can be obtained. Also, by reacting an aqueous solution of sodium carbonate, which is a by-product of this reaction, with carbon dioxide, fine powder crystalline sodium hydrogen carbonate can be obtained without a concentration operation in some cases. The inventors have found that the saturated aqueous solution, which is the mother liquor, is recyclable for silica synthesis, and completed the present invention.

That is, according to the present invention, (1) an aqueous solution of sodium hydrogen carbonate is added to an aqueous solution of sodium silicate to cause a reaction to produce a reaction mixture containing silica hydrogel and sodium carbonate, and then silica is prepared from the reaction mixture. A method for producing silica, characterized in that a hydrogel is separated and collected, (2) Carbon dioxide gas is introduced into the reaction mixture obtained by separating the silica hydrogel, and sodium carbonate in the reaction mixture is converted into sodium hydrogen carbonate. The method for producing silica according to (1), wherein the sodium hydrogen carbonate is used for the reaction with the sodium silicate aqueous solution, and (3) the reaction temperature between the sodium silicate aqueous solution and the sodium hydrogen carbonate aqueous solution is 50 to 70 ° C. , BET specific surface area 600
There is provided a method for producing silica according to (1) or (2), wherein a silica xerogel of m ² / g or more is obtained.

The present invention will be described in more detail below.

In the method for producing silica of the present invention, a silica slurry (reaction mixture) composed of silica hydrogel and sodium carbonate is obtained by reacting an aqueous sodium silicate solution with an aqueous sodium hydrogen carbonate solution, and the slurry is filtered to obtain silica. The silica gel is separated into a hydrogel and an aqueous solution of sodium carbonate which is a mother liquor. If necessary, the silica hydrogel is subjected to pH adjustment with a mineral acid such as sulfuric acid, and further washed, dried and pulverized by a conventional method to be manufactured as a silica xerogel. In this case, the aqueous sodium carbonate solution after silica hydrogel separation is a mother liquor after crystal precipitation by commercializing the sodium hydrogen carbonate precipitated as fine powder crystals by filtration and separation by contacting and absorbing carbon dioxide. It is preferable to adopt a series of methods in which the aqueous sodium hydrogen carbonate solution is further recycled as a starting material for silica production. The sodium hydrogencarbonate fine powder crystals can be recycled.

The sodium silicate aqueous solution used in the reaction for obtaining the silica hydrogel is any sodium silicate, for example, the formula Na ₂ O.nSiO ₂ (where n is a number from 1 to 3.8). An aqueous solution of sodium silicate can be used. From the economical point of view, it is desirable to use so-called No. 3 sodium silicate in which n is in the range of 3.0 to 3.4. The concentration of the aqueous sodium silicate solution used in the reaction is not particularly limited, but generally the SiO ₂ concentration is 200 g /
Those of 1 or less are operationally advantageous.

Further, the sodium hydrogen carbonate aqueous solution is at 60 ° C.
The following saturated aqueous solution (concentration of 164 g / l or less) is preferable, and more preferably 40 to 50 ° C. saturated aqueous solution (127
˜145 g / l). In this case, when the temperature of the aqueous sodium hydrogen carbonate solution is raised, the sodium hydrogen carbonate is thermally decomposed, so that the loss of sodium hydrogen carbonate may occur and the reproducibility of the reaction may be deteriorated.

In the production of silica, a silica slurry is obtained by pouring an aqueous sodium hydrogen carbonate solution into a stirring sodium silicate aqueous solution. The reaction temperature is not particularly limited, but it is preferably 95 ° C or lower, particularly 80 ° C or lower. In addition, it may be desirable to age for a suitable time after the particulate amorphous silica has been deposited.

Further, the silica xerogel having a high specific surface area of the present invention can be effectively obtained by setting the reaction temperature at the time of obtaining the silica hydrogel to 50 to 70 ° C.

On the other hand, the aqueous sodium carbonate solution of the mother liquor obtained by separating the silica hydrogel from the above silica slurry is
By introducing carbon dioxide into this and contact absorption,
Sodium carbonate can be converted to sodium hydrogen carbonate. In this case, as the carbon dioxide, it is possible to use a normal carbon dioxide gas, but a flue gas of a boiler which is a gas containing carbon dioxide and an exhaust gas of a lime firing furnace (in some cases, carbon dioxide is contained in these gases). A gas obtained by concentrating the gas) may be used.

As described above, the production method of the present invention is one of the practical methods for preventing global warming, since carbon dioxide, which is a kind of global warming gas, can be recovered and utilized as sodium hydrogen carbonate. Since it is possible to efficiently produce silica because the reaction rate is increased as compared with the conventional method of directly reacting an aqueous solution of sodium silicate with carbon dioxide, and the silica obtained by this production method has a high specific surface area. It has excellent properties as a carrier for pharmaceuticals and agricultural chemicals, a powdering agent, and various adsorbents, and is preferably used.

[0016]

EXAMPLES The present invention will be specifically described below with reference to Examples and Comparative Examples, but the present invention is not limited to the following Examples.

Example 1 Commercially available sodium silicate No. 3 was diluted with water to adjust the SiO ₂ concentration to 76 g / l, and 1 liter of an aqueous solution was maintained at 60 ° C. Concentration 145g / l) 0.19
5 liters were added. Next, after aging at the same temperature for 30 minutes, an aqueous sodium hydrogencarbonate solution of the same concentration 0.2
24 liters were added. This reaction takes about 1
It was time.

The obtained silica slurry was separated into silica hydrogel and an aqueous sodium carbonate solution by filtration. The silica hydrogel was resuspended in water, adjusted to pH 5 with sulfuric acid, filtered, and washed with water. After further resuspending this in water, the pH was adjusted to 4 with sulfuric acid, and filtration and washing with water were performed to remove by-products sodium carbonate and sodium sulfate. The obtained silica hydrogel was dried with hot air at 140 ° C. for 1 hour to obtain 70 g of silica xerogel (yield 9
2%). The properties are shown in Table 1.

On the other hand, the aqueous sodium carbonate solution obtained above was concentrated twice and brought into contact with carbon dioxide at room temperature (20 ° C.) to precipitate fine powdery crystalline sodium hydrogen carbonate. This was filtered and air dried at room temperature to obtain 27 g of sodium hydrogen carbonate (yield 53%). The obtained sodium hydrogencarbonate was white fine powder crystals and had JIS-K
The purity according to -8622 was 105%, which was almost pure.

An aqueous sodium hydrogen carbonate solution whose concentration was adjusted by adding the obtained sodium hydrogen carbonate to the saturated sodium hydrogen carbonate aqueous solution of the mother liquor from which the fine powdery crystalline sodium hydrogen carbonate had been separated and removed was prepared in the same manner as above. When reacted with, a silica slurry similar to the above was obtained.

Example 2 Commercially available sodium silicate No. 3 was diluted with water to adjust the SiO ₂ concentration to 76 g / l. Concentration 145g / l) 0.19
5 liters were added. Next, after aging at the same temperature for 30 minutes, an aqueous sodium hydrogencarbonate solution of the same concentration 0.2
24 liters were added. This reaction takes about 1
It was time.

The resulting silica slurry was separated into silica hydrogel and an aqueous sodium carbonate solution by filtration. The silica hydrogel was resuspended in water, adjusted to pH 5 with sulfuric acid, filtered, and washed with water. This was further resuspended in water, the pH was adjusted to 4 with sulfuric acid, and filtration and washing with water were performed to remove by-products sodium carbonate and sodium sulfate. The obtained silica hydrogel was dried with hot air at 140 ° C. for 1 hour to obtain 68 g of silica xerogel (yield 8
9%). The properties are shown in Table 1.

On the other hand, the aqueous sodium carbonate solution obtained above was concentrated twice and brought into contact with carbon dioxide at room temperature (20 ° C.) to precipitate fine powdery crystalline sodium hydrogen carbonate. This was filtered and air dried at room temperature to obtain 25 g of sodium hydrogen carbonate (yield 50%). The obtained sodium hydrogencarbonate was white fine powder crystals and had JIS-K
The purity according to -8622 was 104%, which was almost pure.

An aqueous sodium hydrogen carbonate solution whose concentration was adjusted by adding the obtained sodium hydrogen carbonate to the saturated aqueous sodium hydrogen carbonate solution of the mother liquor from which the fine powdery crystalline sodium hydrogen carbonate had been separated and removed was prepared in the same manner as above. When reacted with, a silica slurry similar to the above was obtained.

Example 3 Commercially available sodium silicate No. 3 was diluted with water to adjust the SiO ₂ concentration to 192 g / l. Concentration 145g / l) 0.4
88 liters were added. Then, after aging at the same temperature for 30 minutes, an aqueous sodium hydrogen carbonate solution having the same concentration was further added.
558 liters were added, and the mixture was aged at 97 ° C. for 30 minutes. The time required for this reaction was about 1.5 hours.

The obtained silica slurry was separated into silica hydrogel and an aqueous sodium carbonate solution by filtration. The silica hydrogel was resuspended in water, adjusted to pH 5 with sulfuric acid, filtered, and washed with water. This was further resuspended in water, the pH was adjusted to 4 with sulfuric acid, and filtration and washing with water were performed to remove by-products sodium carbonate and sodium sulfate. The obtained silica hydrogel was dried with hot air at 140 ° C. for 1 hour to obtain 173 g of silica xerogel (yield 90%). The properties are shown in Table 1.

On the other hand, the aqueous sodium carbonate solution obtained above was not concentrated, but was brought into contact with carbon dioxide at room temperature (20 ° C.) to precipitate fine powdery crystalline sodium hydrogen carbonate. This is filtered and air dried at room temperature,
53 g of sodium hydrogen carbonate was obtained (yield 50%). The obtained sodium hydrogen carbonate was white fine powder crystals,
The purity according to SK-8622 was 103%, which was almost pure.

An aqueous sodium hydrogen carbonate solution whose concentration was adjusted by adding the obtained sodium hydrogen carbonate to the saturated aqueous sodium hydrogen carbonate solution of the mother liquor from which the fine powdery crystalline sodium hydrogen carbonate had been separated and removed was prepared in the same manner as above. When reacted with, a silica slurry similar to the above was obtained.

[Comparative Example 1] A commercially available sodium silicate No. 3 was diluted with water to adjust the SiO ₂ concentration to 76 g / l. Was contacted and reacted. The time required for this reaction was about 24 hours.

Next, the properties of the silica xerogel obtained in Examples 1, 2, 3 and Comparative Example 1 were measured. The results are shown in Table 1. In addition, Table 1 also shows properties of commercially available wet silica.

[0031]

[Table 1]

[0032]

EFFECTS OF THE INVENTION According to the present invention, silica having a good sedimentation property can be efficiently produced at a reaction rate equivalent to that of the conventional method for producing silica by the reaction of sodium silicate and mineral acid. By introducing and contacting carbon dioxide into the separated reaction mixture, sodium carbonate in the reaction mixture can be converted into sodium hydrogen carbonate, so that carbon dioxide can be effectively used.

Claims (3)

[Claims] 1. A method for producing a reaction mixture containing silica hydrogel and sodium carbonate by adding an aqueous solution of sodium hydrogen carbonate to an aqueous solution of sodium silicate to cause a reaction, and then separating and collecting the silica hydrogel from the reaction mixture. A method for producing silica, comprising: 2. Carbon dioxide gas is introduced into the reaction mixture from which silica hydrogel has been separated, sodium carbonate in the reaction mixture is converted into sodium hydrogen carbonate, and the sodium hydrogen carbonate is reacted with an aqueous sodium silicate solution. The method for producing silica according to claim 1, wherein the method is used. 3. The reaction temperature between the sodium silicate aqueous solution and the sodium hydrogen carbonate aqueous solution is 50 to 70 ° C., and BET
The method for producing silica according to claim 1 or 2, wherein a silica xerogel having a specific surface area of 600 m ² / g or more is obtained by the method.