JPH0327485B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing spherical silica gel and an apparatus therefor. [Prior Art and Problems] Silica gel is used in various industrial fields including absorbents and catalyst supports. For example, in the past it was used as a moisture-proofing agent in processed foods and pharmaceuticals, but in recent years it has been used not only as a moisture-proofing agent inside products produced in the electronics and precision machinery industries, but also widely used in household goods. has been done. Depending on the purpose of use, silica gel is also used as a monitoring agent to detect minute amounts of water salts contained in special substances, making use of its strong absorption ability. By the way, the above-mentioned silica gel has conventionally been known to be produced by crushing semi-dry silica hydrogel, which is an intermediate step in the production of water glass, and drying it at about 250°C to produce crushed silica gel. This type of crushed silica gel is
Although it is used for some purposes, spherical silica gel is required from the background explained below. That is, the shape of crushed silica gel is not constant. For this reason, when such silica gel is used as a moisture proofing agent for processed foods or pharmaceuticals, the rough surfaces of the silica gel particles collide with each other and crush them, especially during transportation, and small crushed particles etc. are mixed into the product as impurities. As a result, it is not suitable for use as a moisture-proofing agent because it causes product defects and has a negative effect on the human body. In order to prevent such crushed particles from being mixed into the product, it is conceivable to package the crushed silica gel, but this results in an increase in packaging costs. Furthermore, the crushed silica gel requires complicated operations such as sorting and disposing of separate crushed particles during the production of silica gel. In addition, the mobilization rate of crushed silica gel is increased due to the irregular surface contact between particles.
There were also problems in terms of production efficiency and cost because the effect of mixing due to mobility was small, the reaction was reduced, and the conversion efficiency of the final product was reduced. For this reason, techniques for producing spherical silica gel have been developed. One of them is to create silica hydrosol by mixing water glass and sulfuric acid.
There is a method of injecting this into a gelling tower containing a high temperature organic solvent that is not mixed with the sol. In this method, the sol is sphericalized in a gelation tower due to the difference in surface tension, and while maintaining this spherical shape, it is transformed into a stable gel to produce a spherical silica hydrogel. In this operating process,
As is clear from Figure 5, which shows pH fluctuations and gelation time fluctuations due to changes in the molar ratio of Na ₂ O and H ₂ SO ₄ , which are the components of water glass, gelation occurs easily when the PH value is about 3 or higher. Therefore, it is possible to produce silica hydrogel at a lower pH value, but since the gelation time is less than 20 seconds, the transfer time from the silica hydrosol mixer to the injection part of the gelation tower is The transfer time must be within 20 seconds; if the transfer time is longer than this, it will gel in the transfer tube, making it difficult to produce silica hydrogel. In addition, A in FIG. 5 indicates SiO ₂ during the production of silica hydrosol.
Using water glass containing 18% by weight and 12N sulfuric acid,
The characteristic line B is obtained when the molar ratio of Na ₂ O / H ₂ SO ₄ is changed, and B is the characteristic line when the molar ratio of Na 2 O / H 2 SO 4 is changed.
Characteristic line C is obtained when the molar ratio of Na ₂ O / _{H 2} SO ₄ is changed using water glass containing 12% by weight of SiO ₂ and 7N sulfuric acid. This is a characteristic line when the molar ratio of Na ₂ O/H ₂ SO ₄ is changed using water glass containing 4.5 N sulfuric acid and 4.5 N sulfuric acid. On the other hand, it is possible to adjust the PH value of silica hydrosol to 3 or less, but this increases the time required for gelation, which takes more than 2 hours, and the sol is not stable even if it is injected into a high-temperature organic solvent. A gel cannot be formed and handling in the next washing step becomes difficult. Therefore, it is necessary to adjust the pH value of the silica hydrosol from 3 to 6 while gelling it almost instantaneously, but the mixing error of sulfuric acid and water glass must be within 2% and the pH value of water glass must be adjusted to 6.
As the SiO ₂ concentration increases, it decreases to about 0.5%, making it difficult to adjust the PH value. Another method is to produce silica hydrosol by injecting already made water glass and sulfuric acid into a nozzle placed at the top of the gelling tower and mixing them instantly, and then dispersing this sol in the gelling tower. There is a way to do it. However, this method affects the gelation time required for the PH value, so
In order to adjust the pH value and reduce the gelation time from several seconds to several tens of seconds, it is necessary to keep the error in the supply range of water glass and sulfuric acid within ±1.0%. If these conditions are not met, gelation will not occur in the gelation tower, but the injection port will become clogged, making it difficult to produce spherical silica hydrogel. Therefore,
In this method, the flow of the pump that supplies sulfuric acid, which is a PH regulator that can control the concentration of water glass or the surface area of the gel, may fluctuate, so it is impossible to produce silica gel in large quantities and it is not suitable for industrial use. It is inappropriate to do so. In addition, in the process of producing silica hydrosol, heat is generated by the acid-alkali reaction between Na ₂ O and sulfuric acid in water glass, and this heat increases the temperature of the sol, causing precipitation to occur before the sol is formed. is formed. When such precipitates occur, not only does the appearance of the final product silica gel deteriorate and the quality of the silica gel decreases, such as a decrease in hygroscopicity, but also uneven drying occurs during the drying process, resulting in the production of silica gel. cracks may develop or become prone to collapse. Conventionally, in order to prevent the formation of the above-mentioned precipitate, it is necessary to cool the product to about 5° C., but this requires cooling water at 0° C., which contributes to the increase in the manufacturing price of spherical silica gel. The present invention was made to solve the above-mentioned conventional problems, and it is possible to generate silica hydrosol at a relatively high temperature and increase the mixing ratio of water glass and sulfuric acid, which are reactants, to increase the flow rate. It is an object of the present invention to provide a method and apparatus for producing silica gel that can stably produce silica gel even when such fluctuations occur. [Means and effects for solving the problem] The first invention of the present application is based on a sulfuric acid aqueous solution of 7 to 9 N.
_PH2 ~ which does not gel for at least 24 hours by reacting water glass with SiO2 concentration of 10~16% by weight
Step 2.5 of producing a silica hydrosol, thermally aging the silica hydrosol by passing it through a heat exchanger in which heated water of 50 to 80°C is circulated so that it stays for a desired time, and gelling. A step of injecting the thermally aged silica hydrosol through a nozzle into an organic solvent contained in a column together with a water layer on the bottom side and maintained at a higher temperature than the heat exchanger to form a sphere and gel it. Then, the spherical silica hydrogel that had settled in the water layer at the bottom of the gelation tower was taken out along with the water.
This is a method for producing spherical silica gel, characterized by comprising a step of separating. The silica hydrosol needs to have a pH value in the range of 2 to 2.5 and be stable for 24 hours. In this case, as shown in FIG. 5, the mixing ratio of water glass and sulfuric acid is increased, and the PH value can be easily adjusted even if the injection amount fluctuates to some extent. The reason why the silica hydrosol is passed through a heat exchanger in which heated water of 50 to 80°C is circulated before being injected into the organic solvent is as follows. That is, the gelation time of silica hydrosol having the above-mentioned pH value is extremely slow, and even if it is directly injected into the organic solvent of the gelation tower, it will not be gelled sufficiently. For this reason,
By subjecting the silica hydrosol to thermal aging through a heat exchanger in which heated water of 50 to 80° C. is circulated, the time required for gelation becomes extremely short, and a phenomenon similar to that observed when the pH value is high is exhibited. In other words, by injecting and dispersing the thermally aged silica hydrosol into an organic solvent at a temperature higher than the aging temperature through a nozzle, the silica hydrosol is spheroidized, and
The desired silica hydrogel is obtained by gelling while maintaining the spherical shape. The temperature of the organic solvent needs to be set higher than the thermal ripening temperature from the viewpoint of sufficiently gelling the silica hydrosol after thermal ripening. In addition, the organic solvent maintains the temperature uniformly, reduces the sedimentation rate of the silica hydrogel produced in the organic solvent, provides sufficient time necessary for gelling the silica hydrosol, and further increases the strength. Upward transfer to obtain highly spherical silica hydrogels,
It is desirable to circulate. In addition, the second invention of the present application is such that a sulfuric acid aqueous solution of 7 to 9 N and water glass with a SiO ₂ concentration of 10 to 16% by weight are supplied, and a pH of 2 to 100 ml is not gelled for at least 24 hours.
A sol maker that produces 2.5 silica hydrosol,
An aqueous layer is disposed at the bottom, a gelling tower is placed above the gelling tower containing an organic solvent, and the gelling tower is connected to the sol manufacturer to supply the silica hydrosol and the gelling tower. a heat exchanger having a nozzle for injecting the thermally aged silica hydrosol into the organic solvent of the column; and a heat exchanger connected to the lower part of the gelation column,
This apparatus for producing spherical silica gel is characterized by comprising a transport pipe for taking out and transporting spherical silica hydrogel together with water, and means for separating the spherical silica hydrogel from the water transported by the transport pipe. Hereinafter, the first part regarding the manufacturing apparatus of the second invention of the present application will be explained.
This will be explained with reference to FIGS. FIG. 1 is a schematic diagram showing the spherical silica gel manufacturing apparatus of the present invention, FIG. 2 is an enlarged view of the main parts of the sol manufacturing device in FIG. 1, and FIG. 3 is an enlarged view of the heat exchanger in FIG. 1. FIG. 4 is an enlarged sectional view of a main part of the heat exchanger shown in FIG. 3. 1 in the figure means, for example, 96% by weight concentrated sulfuric acid
a first dilution tank for making a 9N sulfuric acid aqueous solution;
2 in the figure is, for example, a second water glass for diluting water glass with a SiO ₂ concentration of 28 to 30% by weight to a SiO ₂ concentration of 10 to 16%.
This is a dilution tank. The first dilution tank 1 is connected to a sol manufacturer 5 via a sulfuric acid supply pipe 4 in which a pump 3 is installed. This sol manufacturing device 5 has a first
As shown in FIG. 2, a water-cooled reaction tank 7 is provided with a pipe 6 through which cooling water of about 20° C. is circulated, and the supply pipe 4 is connected to the upper part.
Inside this reaction tank 7, there is a stirrer 8 having two stages of blades.
is provided. A circulation bypass pipe 10 is connected to the lower part of the reaction tank 7 via a three-way valve 9. This bypass pipe 10 is interposed with a mixing pump 13 having a stirring impeller 11 on the suction side and an injection port 12 on the discharge side.
Further, the second dilution tank 2 is connected to the mixing pump 1 via a water glass supply pipe 15 equipped with a pump 14.
It is connected to the bypass pipe 10 on the suction side of No. 3. Note that the bypass pipe 10 has an inclined structure to prevent the generated silica hydrosol from staying in the pipe. The sol manufacturing device 5 operates as follows. That is, cooling water is circulated through piping 6 to maintain the temperature of the outer wall of reaction tank 7 at around 20° C., thereby preventing an increase in reaction heat caused by the reaction between water glass and sulfuric acid aqueous solution, which will be described later. Next, the three-way valve 9 is switched to the bypass pipe 10 side, and the sulfuric acid aqueous solution in the first dilution tank 1 is supplied from the sulfuric acid supply pipe 4 to the water-cooled reaction tank 7, and the mixing pump 13 is driven to remove the sulfuric acid aqueous solution. The water glass in the second dilution tank 2 is supplied from the water glass supply pipe 15 to the bypass pipe 1 on the suction side of the mixing pump 13 while being circulated through the bypass pipe 10. The sulfuric acid aqueous solution and water glass thus supplied are instantaneously and vigorously mixed by the impeller 11 of the mixing pump 13, and are further injected into the reaction tank 7 from the injection port 12 on the discharge side of the mixing pump 13 and the two-stage impeller. More effective mixing can be achieved by stirring with the stirrer 8 having the following. Such efficient stirring and mixing prevents the formation of precipitates in the reaction tank 7, making it possible to supply highly concentrated water glass suitable for mass production. Further, the sol manufacturer 5 is connected to the upper part of a heat exchanger 18 disposed above the gelling tower 17 via the pipe 16 of the three-way valve 9. A flow meter 19 is installed in the piping 16 . The heat exchanger 18 heats and matures the silica hydrosol in the sol manufacturing device 5, and the heating is carried out in the constant temperature bath 2.
This is done by circulating heated water of 0.0 liters using the pump 21. The heat exchanger 18 includes a main body container 22 through which the heated water is circulated, as shown in FIGS. 3 and 4. This main container 22 includes
A plurality of heat exchange tubes 23 through which the silica hydrosol of the sol manufacturing device 5 circulates are penetrated in the vertical direction, and near the entrance and exit of the tubes 23 of the container 22, there are holes for sealing and fixing the tubes 23 in a liquid-tight manner. Jigs 24a and 24b are provided. A joint 25 is attached to the lower end of each heat exchange tube 23, and a ring-shaped rubber gasket 26 is interposed in each joint 25, respectively. A rubber tube 27 is fitted into each joint 25,
At the lower ends of these rubber tubes 27 are nozzles 2.
8 are inserted respectively. These nozzles 28 are
Fixing plate 2 disposed above the gelling tower 17, respectively
It is inserted into the connecting portion 30 of No. 9. Furthermore, an aqueous layer 31 is provided at the bottom of the gelling tower 17.
However, an organic solvent 32 is accommodated on the aqueous layer 31, respectively. One end of a circulation pipe 33 is connected to the side wall portion of the gelation tower 17 above the water layer 31, and the other end of the circulation pipe 33 is connected to the upper side wall of the gelation tower 17. A pump 34 and a heater 35 are interposed in this circulation pipe 33. By providing such a circulation pipe 33, the organic solvent 32 in the gelling tower 17 is transported upward and circulated, and
Heated to 90-100℃. In addition, the gelling tower 1
The gelling tower 1 is connected to the lower part of the gelling tower 7 via a three-way joint 36.
A transport pipe 37 for transporting the aqueous layer 31 in 7 together with the silica hydrogel is connected. This transport pipe 37
A storage tank 38 is attached to one end, and a collection net 39 is arranged above the storage tank 38. The other end of the transport pipe 37 extends to the collection net 39. The storage tank 38 and the three-way joint 36
A pump 40 is interposed in the transport pipe 37 between the two. The water transported along with the silica hydrogel through the transport pipe 37 is collected in the storage tank 38 during separation in the silica hydrogel collection network 39, and is returned to the gelling tower 17 through the transport pipe 37. According to the present invention, a sulfuric acid aqueous solution with a predetermined concentration and water glass with a predetermined SiO ₂ concentration are reacted to produce a silica hydrosol with a pH of 2 to 2.5 that does not gel for at least 24 hours. After gradually heating and thermally ripening the sol while flowing through a heat exchanger, this sol is directly injected into the organic solvent in the gelation tower through a nozzle, thereby easily gelling it and forming it into a spherical shape. can be converted into The relationship between the temperature of the heated water supplied to the heat exchanger, the molar ratio of Na ₂ O and sulfuric acid in the water glass, the gelation time, and the gelation temperature is shown in Table 1 below. .

[Table] As is clear from Table 1 above, the temperature of the heated water is
For a constant case, the molar ratio of Na ₂ O / H ₂ SO ₄ is from 0.93 to
Even though it was changed up to 1.0, the time required for gelation remained approximately constant and correlated with the gelation temperature. This means that even if the mixing molar ratio is changed to about 7%, if it is thermally aged, gelation will occur for approximately the same time and at the same temperature. Therefore, the mixing range,
In other words, there is no need to control the PH value extremely accurately,
It is easily gelled by thermal aging at a certain temperature for a certain period of time. Taking advantage of this effect, the silica hydrosol is thermally aged for a period slightly shorter than the time required for gelation, and then the aged silica hydrosol is injected into an organic solvent at a temperature higher than the aging temperature through a nozzle to form spheres. It can be gelled while maintaining its shape. At this time, the range of mixing ratios is considerably expanded, making industrial use easier. Thereafter, by washing and drying the obtained drogel, a spherical silica gel having sufficient strength can be obtained. Furthermore, the present invention can provide a manufacturing apparatus with a simple structure that can manufacture such spherical silica gel. [Embodiments of the Invention] Hereinafter, the embodiments of the present invention will be described with reference to FIGS. 1 to 4.
This will be explained with reference to the manufacturing apparatus shown in the figure. Example 1 First, cooling water was circulated through the piping 6 of the sol manufacturer 5 to bring the temperature of the outer wall of the cooling reaction tank 7 to around 20°C, and then the three-way valve 9 was switched to the bypass pipe 10 side, and the first dilution was carried out. The 9N sulfuric acid aqueous solution 50 in the tank 1 is supplied from the sulfuric acid supply pipe 4 to the water-cooled reaction tank 7, and while the mixing pump 13 is driven to circulate the sulfuric acid aqueous solution through the bypass pipe 10, the sulfuric acid aqueous solution 50 in the second dilution tank 2 is supplied. Water glass with a SiO ₂ concentration of 12% by weight (component weight ratio SiO ₂ :Na ₂ O=28:9) 240 was supplied from the water glass supply pipe 15 to the bypass pipe 10 on the suction side of the mixing pump 13 . The sulfuric acid aqueous solution and water glass thus supplied are instantaneously and vigorously mixed by the impeller 11 of the mixing pump 13, and are further injected into the reaction tank 7 from the injection port 12 on the discharge side of the mixing pump 13 and the two-stage impeller. The silica hydrosol was prepared by mixing more effectively by stirring with the stirrer 8 having the following. The silica hydrosol had a pH of 2.3 with a Na ₂ O/H ₂ SO ₄ molar ratio of 0.984 and a gelation time of at least 24 hours. Next, switch the three-way valve 9 to turn on the sol maker 5.
The silica hydrosol in the reaction tank 7 was supplied through piping 16 to each heat exchange tube 23 of a heat exchanger 18 at a temperature of 75° C. through which heated water was circulated from a constant temperature bath 20. At this time, the inner diameter of the heat exchange tube 23 was set to 5 cm, and the silica hydrosol Reynolds No. 550~
2000, and the length of the tube 23 is set to 2 m in order to make the residence time of the silica hydrosol 5 to 40 minutes.
The number of silica hydrosols inserted into the chamber was 7, and the overall silica hydrosol processing rate was set at 6, 12, 25, 30, and 40/hr. Subsequently, the organic solvent 32 at a temperature of 80°C in the gelling tower 17, which is transferred upward and circulated by the circulation pipe 33, pump 34 and heater 45, is injected through the nozzle 28 connected at the lower end of each heat exchange tube 23. The mixture was formed into a sphere and gelled in an organic solvent 32. After this, the silica hydrogel precipitated in the water layer 31 at the bottom of the gelling tower 17 is transferred to the three-way joint 3 together with water.
6 into the transport pipe 37, and by operating the pump 40, the water containing the silica hydrogel was sent to the collection net 39, where the silica hydrogel was separated from the water. The solidity and gel state of the silica hydrogels obtained by changing the treatment rate of silica hydrosol into the heat exchanger to 6, 12, 25, 30, and 40/hr were observed. The results are shown in Table 2 below.

[Table] When the silica hydrogel No. 2 in Table 2 above was washed with water and dried, the spherical silica hydrogel was not crushed during these steps, and a spherical silica gel with good strength could be obtained. Ta. Furthermore, when observing the solidity of silica hydrogel accompanying gelation at a pH of 1.5 to 2 with a molar ratio of 0.931 or less, the gelation phenomenon did not appear within 40 minutes at a heating temperature of 65°C, and at 90°C. In the vicinity, the sol boils and becomes gelatinous even when cooled, and sufficient gelation is not achieved. Example 2 The temperature of the heated water in the heat exchanger was set to 75°C, Na ₂ O/
The silica hydrogel was prepared in the same manner as in Example 1, except that the molar ratio of H ₂ SO ₄ was 0.984, the processing rate of the silica hydrosol to the heat exchanger was 12, 18, 25, and 30/hr, and the view of the nozzle was changed. was manufactured. The average particle size of each silica hydrogel obtained was examined. The results are shown in Table 3 below.

[Table] * indicates turbulent flow, and the difference in gel morphology and size is significant.
When the silica hydrogels Nos. 1 to 3 in Table 3 above were washed with water and dried, the spherical silica hydrogels were not crushed during these steps, and spherical silica gels with good strength could be obtained. . [Effects of the Invention] As detailed above, according to the present invention, it is possible to generate silica hydrosol at a relatively high temperature, and by increasing the mixing ratio of water glass and sulfuric acid, which are reactants, fluctuations in flow rate, etc. Silica hydrogel can be produced stably in the gelation tower even when water is generated, and by separating, washing, and drying the silica hydrogel taken out from the bottom of the gelation tower together with water, it is possible to produce spherical silica gel with stable dimensions and high strength. It is possible to provide a method that can be easily and mass-produced, and an apparatus with a simple structure that can easily manufacture such spherical silica gel.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the spherical silica gel manufacturing apparatus of the present invention, FIG. 2 is an enlarged view of the main parts of the sol manufacturing device in FIG. 1, and FIG. 3 is an enlarged view of the heat exchanger in FIG. 1. Figure 4 is an enlarged cross-sectional view of the main parts of the heat exchanger in Figure 3;
The figure is a characteristic diagram showing the relationship between the molar ratio of Na ₂ O/H ₂ SO ₄ and PH and gelation time. 1... First dilution tank, 2... Second dilution tank, 5... Sol manufacturer, 7... Cooling reaction tank, 8... Stirrer, 10
...Bypass pipe, 11...Agitating impeller, 12...
Injection port, 13...Mixing pump, 17...Gelification tower, 1
8... Heat exchanger, 20... Constant temperature bath, 22... Main container,
23... Heat exchange tube, 25... Joint, 28... Nozzle, 31... Water layer, 32... Organic solvent, 33... Circulation pipe, 35... Heater, 37... Transport pipe, 39... Collection network.

Claims (1)

[Claims] 1 7-9 normal sulfuric acid aqueous solution and SiO ₂ concentration 10-9
reacting 16% by weight of water glass to produce a silica hydrosol with a pH of 2 to 2.5 that does not gel for at least 24 hours;
A step of thermally ripening the heated water at 50 to 80° C. by passing it through a circulating heat exchanger so as to stay there for a desired period of time; A process of injecting the thermally aged silica hydrosol through a nozzle into an organic soot maintained at a higher temperature to form a sphere and gel it, and a process of forming a sphere and gelling it into an aqueous layer at the bottom of the gelation tower. A method for producing spherical silica gel, comprising a step of taking out silica hydrogel together with water and separating it. 2 7-9 normal sulfuric acid aqueous solution and SiO ₂ concentration 10-16
A sol maker that is supplied with % water glass and produces a silica hydrosol with a pH of 2 to 2.5 that does not gel for at least 24 hours, and a gelling tower that contains an aqueous layer at the bottom and an organic solvent above it. and a nozzle disposed above the gelling tower, connected to the sol manufacturer to supply the silica hydrosol, and injecting the thermally aged silica hydrosol into the organic solvent of the gelling tower. a heat exchanger having a heat exchanger; a transport pipe connected to the lower part of the gelling tower for taking out and transporting the spherical silica hydrogel together with water; and means for separating the spherical silica hydrogel from the water transported by the transport pipe. An apparatus for producing spherical silica gel, characterized by the following: 3. The sol manufacturer consists of a water-cooled reaction tank with a sulfuric acid supply pipe connected to the upper part, a stirrer installed in the reaction tank, and a circulation bypass connected to the lower part of the reaction tank via a three-way valve. a mixing pump installed in the bypass pipe and having a stirring impeller on the suction side and an injection port on the discharge side, and a water glass supply connected to the bypass pipe on the suction side of the mixing pump. 3. The apparatus for producing spherical silica gel according to claim 2, characterized in that the apparatus is comprised of a tube.