JPH0351642B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a method for producing a high purity dry gel powder, and in particular, a method for producing a high purity dry gel powder using a metal alkoxide as a raw material. Regarding. [Prior Art] Dry gels, such as silica gel and alumina gel, are used not only as dehydrating agents, desiccant agents, and fillers for chromatography, but also as raw materials for manufacturing fine ceramics. Silica gel is also used as a raw material for multi-component optical fibers, quartz for optical glass and electronic industry, fillers for IC sealants, and new uses are being discovered. In addition, alumina gel has excellent heat resistance and is used as a raw material for high-temperature firing containers, but as the semiconductor industry has developed in recent years, there has been a strong demand for higher purity products. From the viewpoint of preventing product contamination during the firing process of products and intermediate products, it is strongly required that the material of this container has a low degree of abrasion and an extremely low content of impurities. Such requirements apply not only to silica gel and alumina gel, but also to dry gels such as zirconia and titania, and there is a strong demand for the development of a method for producing highly pure powdered dry gels. By the way, conventionally, as a method for manufacturing such dry gel, for example, silica gel, tetraalkoxysilane such as tetramethoxysilane or tetraisopropoxysilane is hydrolyzed in the presence of mineral acid or organic acid to form silanol. The first method is to obtain a dry silica gel by forming silica in a sol form, then forming it into a gel form while keeping it still, and drying it, or by preparing a tetraalkoxysilane in the presence of a sodium alcoholate such as sodium methylate or sodium ethylate. The second method is to obtain dry silica gel by hydrolyzing it with hydrous alcohol to obtain sol-like silica, then gelling it and drying it, or by reacting silicon chloride with sodium alcoholate or lithium methoxide to obtain tetrasilica. A third method is known in which, after forming an alkoxysilane, water or a hydrous alcohol is added to form a sol-like gel through a sol-gel reaction, and the resulting product is further dried to obtain a dry silica gel. [Problems to be Solved by the Invention] However, in the first method described above, although the gelled material is in the form of a lump before drying, the shape is not constant and the size is also different. In particular, the gelled product obtained when it is gelled in a stationary state has the same shape as the hydrolysis container, so the drying speed when drying such a gelled product varies depending on the size of the gelled product, and the efficiency is drying becomes difficult and takes a long time. For this reason, the dried gel is often contaminated due to abrasion during the drying process, and furthermore, the dried gel contains many particles with large particle sizes, and pulverization is required to obtain a powdered dry gel. There is also a risk of contamination during this pulverization process, so it cannot be said to be a preferred method for producing a highly pure powdered dry gel. In addition, in the second method, the caustic soda generated by hydrolysis of alcoholate is incorporated into the gelled product, and this caustic soda remains in the dried gel and reacts with the gel in the dryer or pulverizer, or causes damage to the equipment. Contact with walls may cause corrosion, etc. that is undesirable in terms of product quality. Therefore, this second method also has problems from the viewpoint of producing a highly pure powdered gel, and cannot be said to be a preferable method. By the way, it has also been proposed to wash the gelled product generated by hydrolysis with water prior to drying.
The caustic soda incorporated into the gel cannot be easily removed, and the treatment of washing wastewater (alcohol recovery and wastewater treatment) becomes complicated, which is unfavorable from the economic point of view of the process. Furthermore, the third method described above also has the same problem as the second method because caustic soda and lithium hydroxide are incorporated into the gelled product, so it is not a preferable method for producing a high-purity dry powder gel. I can't say that. [Means for Solving the Problems] The present invention was devised in view of this point of view, and consists of hydrolyzing a metal alkoxide in water in the presence of a catalyst having an acid dissociation index of 3.0 to 5.0. In the method for producing a powdered dry gel, the wet gel is dried to produce a powdered dry gel, and the above metal alkoxide hydrolysis step and/or
Alternatively, there is a method for producing a high-purity powdered dry gel in which vibration is applied during the drying process of the wet gel. The metal alkoxide used in the present invention can be synthesized by directly contacting a metal with an alcohol using mercury chloride, sodium alcoholate, etc. as a catalyst, by a reaction between a metal chloride and an alcohol, or by a method in which it is synthesized by a reaction between a metal chloride and an alcohol. It may be formed by any method such as an exchange reaction method, but from the viewpoint of producing a highly pure dry gel, it is preferably purified by a known purification process such as crystallization method or precision distillation method. Things are good. Further, the catalyst used in the present invention may be any catalyst as long as it accelerates the rate of hydrolysis of the metal alkoxide, but from the viewpoint of producing a high-purity dry gel, it is preferable to use a catalyst in the drying step that follows the hydrolysis. It is best to use something that does not remain in the dry gel.
An inorganic compound that is gaseous or volatile at room temperature or an organic acid that evaporates under dry conditions,
It is preferable to have a certain degree of solubility in water.
To explain this point in more detail, inorganic compounds that are gaseous or volatile at room temperature have an acid dissociation index (Pka) value of 3.0 to 5.0 in water (at 25℃).
Examples of acidic compounds include hydrogen azide (HN ₃ ), hydrogen cyanide (HCN), and carbon dioxide gas (CO ₂ ). In addition, organic acids that do not volatilize during the drying process and remain in the dried gel preferably have a boiling point of 200° C. or lower at normal pressure, such as formic acid, acetic acid, propionic acid, and the like. The above catalyst has a certain degree of solubility in water and its acid dissociation index (Pka) at 25℃.
It must be within the value range of 3.0 to 5.0. If the acid dissociation index (Pka) is greater than 5, the performance as a catalyst will be significantly lowered, making it difficult for hydrolysis to proceed quantitatively, which is undesirable.
In addition, if the acid dissociation index (Pka) is less than 3.0, even if the catalyst has good performance, there is a strong tendency for it to be incorporated into the gelled product produced after hydrolysis, and it will also react with the gelled product, resulting in a product drying gel. contamination, which is undesirable in producing high-purity dry gel. Furthermore, if the boiling point of an organic acid exceeds 200°C, there is a strong tendency for it to remain in the gel during the drying process, and depending on the type of metal alkoxide, the organic acid may decompose, resulting in contamination of the dried gel product. This is not desirable as it may cause Next, hydrolysis of metal alkoxide in the present invention will be explained. The hydrolysis reaction of metal alkoxides is called the sol-gel reaction, and has been known for a long time.
Because polymerization proceeds by repeating polymerization and dehydration condensation, it becomes extremely complex, and it is difficult to completely describe it with a reaction formula. Therefore, as a result of research on hydrolysis using the above catalyst using various metal alkoxides, it was found that it is appropriate to determine the required amount of water based on the general reaction shown below. That is, M()(OR) ₄ +4H ₂ O =M()(OH) ₄ +4ROH (1) M()(OH) ₄ =M()O ₂ +2H ₂ O (2) M()(OR) ₄ +2H ₂ O = M()O ₂ +4ROH (3) (However, in the formula, MP() indicates a tetravalent metal.) In other words, if we take an alkoxide of a tetravalent metal as an example, the hydrolysis is almost quantitative. In order to proceed to the above reaction formula (1), it is necessary to add 4 times the mole of water per mole of metal alkoxide, and if it is less than this, carbon tends to be generated from the alkoxide remaining in the drying process. It was found that it became stronger. In addition, from the viewpoint of obtaining a high-purity dry gel, the water added during hydrolysis is so-called high-pure water or ultra-pure water that does not contain compounds (non-volatile compounds) and ions that do not decompose into volatile compounds during the drying process. Water is preferable, and the specific resistance value of the water is within the range of 10 to 18 MΩ·cm. By using such water, no undesirable impurities remain in the dried gel during the drying process. Further, the hydrolysis temperature is not particularly different from known methods and is usually within the range of room temperature to 80°C. Next, vibration application performed in the hydrolysis step and/or drying step of the present invention will be explained. The hydrolysis reaction of metal alkoxide utilizes the sol-gel reaction as described above, and includes a sol-forming process and a gel-forming process. Since the solization process is carried out in a suspended state, it is already known that the process is usually carried out while stirring the reactants in order to proceed efficiently. However, in the subsequent gelation step, it is a common practice to gel the sol while keeping it as stationary as possible. For this reason, a solid phase (gelled product) grows inside the hydrolysis reactor, and eventually the entire area of the reactor becomes a continuous, strong solid phase that adheres to the walls of the reactor and becomes difficult to transport as it is. Become. In addition, stirring is sometimes used during the gelation process, but as gelation occurs, the stirring power is no longer transmitted throughout the hydrolysis reactor, causing the solid phase to fragment in a very limited area. It is difficult to transport the gel as it is because it is virtually the same as a gel obtained in a static state. The surface of the gelled material near the heat source dries directly, but the dry surface inside the gelled material is thought to act as a heat insulator, making it difficult to dry homogeneously in a short time, and even if drying is possible, it will be difficult to dry. It takes a long time to process the process, which is unfavorable from a process economic point of view. Therefore, in the present invention, vibration is applied during the hydrolysis step and/or the drying step, preferably during the hydrolysis step and the drying step. When vibration is applied during the hydrolysis process, unlike the hydrolysis process using conventionally known methods, the dispersion/suspension state of the metal alkoxide in water is maintained very well during the solization process, and the solization reaction is accelerated. The process proceeds efficiently, and the gel produced during the gelation process does not adhere to the walls of the reactor, there is no continuous solid phase, and the gel is pulverized to approximately the same size, making it easier to transport. In addition, the gelled product pulverized almost homogeneously in this way is dried in the same hydrolysis reactor or transferred and shaken in a dryer for 50 to 50 minutes.
When drying is performed at 200°C under reduced pressure or normal pressure, local heating does not occur to the gelled material, and as the gelled material is crushed during the drying process, heat transfer is promoted.
A highly purified powdered dry gel with almost uniform particle size and less contamination can be produced in a short time, and furthermore, by changing the vibration conditions, the particle size and particle size distribution can be controlled. Regarding the vibration conditions given for this purpose, the optimal vibration conditions when hydrolyzing metal alkoxides using an inorganic acid compound or an organic acid with a Pka of 3.0 to 5.0 and a boiling point of 200℃ or less are as follows. Although it varies somewhat depending on the type of metal alkoxide,
The frequency is 1000 to 1300 vibrations per minute (vpm), and the amplitude is about 0.5 to 3 mm. If hydrolysis is carried out under such vibration conditions, the dispersion and suspension of the metal alkoxide in water will be very good, the solization process will proceed effectively, and the gelled product produced during the gelation process will be removed. does not become a large lumpy solid phase, but is almost uniformly crushed and pulverized. In addition, the vibration conditions applied in the drying process vary depending on the average particle size distribution of the powdered dry gel to be produced, but the vibration frequency is determined by the vibration conditions in the hydrolysis process. In many cases, by increasing the vibration frequency in this manner, uneven drying can be eliminated and the average particle size and particle size distribution of the dried gel can be shifted to the finer particle side compared to the gelled product after hydrolysis. Normally, the frequency in this drying process is 1100 to 1600 vpm, and the amplitude is 2 to 5.
mm and under such vibration conditions, a dry gel in the form of powder with an average particle size of 20 to 50 μm and a maximum particle size of 100 to 200 μm is usually obtained. Therefore, by appropriately combining the vibration conditions in the hydrolysis step and the vibration conditions in the drying step, the average particle size and particle size distribution of the finally obtained powdered dry gel can be controlled. Next, a method of maintaining the hydrolysis step and drying step in a vibrating state will be mentioned. The method of maintaining the vibration state may be any known method, such as attaching two vibration motors to the side of the hydrolysis reactor or dryer, or attaching a vibration source such as ultrasonic waves to the side of the hydrolysis reactor or dryer. A method such as attaching it directly to the bottom may be used. Performing the metal alkoxide hydrolysis process (particularly the gelling process) and the drying process of the gelled product while applying vibration imparts a type of shearing force to the solids and solid phases that are present during these processes. Therefore, the same purpose can be achieved even if a crusher or the like that applies shearing force is attached to the hydrolysis process or drying process, and these means also serve as the means for applying vibration according to the present invention. It is included in the concept. The hydrolysis reaction according to the present invention may be carried out either batchwise or continuously, but since this reaction is a type of sol-gel reaction and involves a phase transition, it is somewhat more advantageous to carry it out in a batchwise manner for better operational management. The catalyst used may be added as is into the hydrolysis reactor, or may be supplied in the form of an aqueous solution, and the addition of this catalyst usually brings the pH value during the reaction to 3.0 to 5.0. Further, the catalyst may be used alone or in a mixture of two or more. The drying process of the gelled product that follows this hydrolysis process may be either a batch process or a continuous process, but the vibration conditions include a frequency of 1000 to 1600 vpm and an amplitude of 2 to 5 mm.
Select a general-purpose model that can ensure the following conditions, and dry the gelled product by setting the drying conditions (temperature, pressure) according to the type of alcohol produced by hydrolysis of metal alkoxide. Drying temperature is usually 50-200℃
It is. The maximum temperature of 200°C is determined by the thermal stability of the organic acid used as a catalyst during drying. The highly pure powdered dry gel obtained by the present invention is
By selecting the vibration conditions in the manufacturing process, particles with arbitrary average particle size and particle size distribution can be extracted, making them easy to handle.Furthermore, they are used as raw materials for high-purity containers, raw materials for high thermal conductivity ceramics, and various fillings. It has an extremely wide range of fields including materials, IC package materials, etc. [Example] Hereinafter, the method of the present invention will be specifically explained based on Examples and Comparative Examples. Example 1 Methyl orthosilicate 100 synthesized by a known method in a SUS304 hydrolysis container equipped with a vibration source
parts by weight and 15 parts of methanol were charged, and further 47 parts by weight of ultrapure water (specific resistance value 15 MΩ cm) were charged, and then hydrogen cyanide water with an acid dissociation index Pka of 3.32 was added to adjust the pH to 4.0. did. After charging, frequency 1000vpm,
Hydrolysis was carried out at a reaction temperature of 20 to 25° C. for 3 hours while applying vibration under vibration conditions with an amplitude of 2 mm. When the inside of the hydrolysis reaction vessel was observed after the hydrolysis was completed, it was found that the gelled product did not adhere to the vessel wall, was not a continuous solid phase, and was crushed into pieces of several mm or less. The gelled product thus obtained was transferred to a vibration dryer made of SUS304, and dried for 2 hours at a drying temperature of 50 to 150°C, a degree of vacuum of 100 to 300 Torr, a vibration frequency of 1200 per minute, and an amplitude of 2 mm. A dry gel was obtained.
The average particle size and impurities of the obtained dried gel were measured. The results are shown in Table 1. Example 2 Formic acid (acid dissociation index Pka: 3.76, boiling point
100.8℃), the pH was set to 4.0, the vibration conditions during hydrolysis were a frequency of 1000 vpm and an amplitude of 1 mm, and the vibration conditions during drying were a frequency of 1000 vpm and an amplitude of 2 mm, and the dried gel was dried in the same manner as in the example. Parts by weight were obtained. The average particle size and impurities of the obtained dried gel were measured. The results are shown in Table 1. Comparative Example 1 39.5 parts by weight of a dry gel was obtained in the same manner as in Example 1 except that the pH was adjusted to 4.0 using hydrochloric acid (acid dissociation index Pka: 7.0) as a catalyst. The average particle size and impurities of the obtained dried gel were measured. The results are shown in Table 1.

【table】

[Table] Comparative Example 2 Hydrolysis was carried out in the same manner as in Example 1, using hydrochloric acid (acid dissociation index Pka: -7.0) as a catalyst to adjust the pH to 3.0, and stirring instead of vibration. When the inside of the hydrolysis container was observed after the hydrolysis was completed, a continuous solid phase was formed near the wall of the container where stirring power could not reach. It is necessary to apply vibration or shear force, and as a result of analysis,
It became clear that hydrolysis of methyl silicate did not proceed quantitatively during the reaction time of 3 hours. [Effects of the Invention] According to the present invention, there is no contamination of impurities in the hydrolysis step and/or drying step, and the resulting dry gel is in the form of a powder, which is extremely easy to handle and transport, and has high purity. Therefore, its uses are extremely wide, and since the manufacturing process is simple, it is easy to operate.

Claims (1)

[Claims] 1. Powder drying in which a metal alkoxide is hydrolyzed in water in the presence of a catalyst with an acid dissociation index of 3.0 to 5.0, and the resulting wet gel is dried to produce a powdered dry gel. A method for producing a high-purity dry gel powder, characterized in that vibration is applied during the metal alkoxide hydrolysis step and/or the wet gel drying step. 2. The method for producing a high purity powdered dry gel according to claim 1, which uses an organic acid having a boiling point of 200° C. or less as a catalyst.