JPS6242850B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing alumina sol. More specifically, the present invention relates to a method for producing an alumina sol that has excellent stability over time and a desired viscosity, or a method for producing an alumina sol that provides alumina powder having these properties and excellent redispersibility. Currently, various alumina sols and dispersible alumina powders that are used by drying and powdering the sol and redispersing the sol are commercially available.
In any of the products, if the sol has an Al ₂ O ₃ concentration of about 10% by weight or more, its stability over time is significantly poor, and it gels within a few days. Furthermore, in the case of a sol with a low Al ₂ O ₃ concentration, there are disadvantages in that a large amount of medium must be transported or a large amount of medium must be evaporated during use. Furthermore, it is difficult to obtain a product with a desired viscosity with existing commercially available products, which may lead to the problem that the viscosity must be adjusted by adding an appropriate agent during use. Alumina sol is usually produced by peptizing an alumina gel dispersion with an inorganic or organic acid. The conventional method for producing alumina sol is to react a sodium aluminate aqueous solution and a water-soluble aluminum salt solution to a pH of 9 to 10 in a short period of time to produce alumina gel, which is then aged. A method of adding an organic acid so that the acid radical/Al (molar ratio) is 0.15 or more to generate a uniform sol (Japanese Patent Publication No. 1984-8409) Carbon dioxide gas is blown into a sodium aluminate solution while stirring. A method of dispersing the produced coagulated boehmite alumina slurry in a monovalent inorganic strong acid with an acid radical/Al (molar ratio) of 0.05 to 0.2 (British Patent No.
1440194 specification) A method for producing an alumina sol having a boehmite crystal lattice and in the form of fibers by hydrothermally treating an alumina gel dispersion in the presence of an acid having an acid radical/Al (molar ratio) of 0.125 or more (Japanese Patent Publication Publication No. 1973) −
14292) etc. have been proposed. However, the powder for alumina sol obtained by this method has poor redispersibility and has an Al ₂ O ₃ concentration of 10
It has the disadvantage that it is difficult to prepare an alumina sol of less than % by weight, and its stability over time is poor. Furthermore, according to Japanese Patent Publication No. 1984-8409, water is added to the alumina gel produced by this method if the amount of acid added is less than 0.15 (acid radical/Al (molar ratio)) during peptization. However, it is stated that the dispersion of alumina gel powder is merely provided without converting it into a sol form. In this method, alumina gel obtained from a specific combination of sodium aluminate and carbon dioxide gas is turned into a sol using a strong inorganic acid, but the resulting sol is
When the Al ₂ O ₃ concentration exceeds about 10% by weight, it has the disadvantage that it is stable for only a few days. In a further method, regarding the relationship between hydrothermal treatment temperature and alumina concentration during solization, it was found that if an Al ₂ O ₃ concentration of about 15% by weight or more is used at a temperature below about 250 °C, the product will be very poor and irreversible. This seems to be because the dispersible alumina powder obtained by this method is in the form of fibers when the dispersible alumina powder is dispersed in water to prepare a liquid sol. However, there is a problem in that even when the Al ₂ O ₃ concentration is as low as about 10% by weight or less, the dispersibility is poor and a sol cannot be obtained efficiently. The molar ratio of the acid radicals of the strong basic acid used in hydrothermal treatment with a dissociation constant of 0.1 or more to the alumina concentration is set to be 0.25 or more, that is, the acid radical/Al molar ratio is 0.125 or more, but in reality, the relative This method uses a high acid concentration ratio. As mentioned above, some conventional methods have high
There is no known method for producing alumina sol that provides an alumina sol with excellent stability over time in terms of Al ₂ O ₃ concentration, or an alumina powder with excellent redispersibility. Furthermore, the viscosity of alumina sol produced by these conventional methods is unique to each production method, and there is no known method for producing alumina sol having a desired viscosity. Under such circumstances, the present inventors conducted intensive research to find a method for producing alumina sol that has extremely excellent stability over time and alumina sol that provides alumina powder with excellent redispersibility, and as a result, the method of the present invention was developed. It was completed. That is, the present invention provides an alumina gel obtained by a liquid phase neutralization reaction between an acidic substance and an alkaline substance, at least one of which is an aluminum compound, with an acid radical/Al molar ratio of 0.001 to 0.12, preferably 0.002.
An alumina sol with excellent stability over time and a desired viscosity by hydrothermal treatment in the presence of a monovalent inorganic acid or a water-soluble aluminum salt of these acids in an amount of ~0.10, and an alumina with excellent redispersibility. The present invention provides a method for producing an alumina sol that provides a powder. The present invention will be explained in detail below. In the present invention, the acid radical of the monovalent inorganic acid that coexists during the hydrothermal treatment of alumina gel means that there is an acid radical that can be neutralized and titrated with an alkaline substance, and is generated by neutralizing aluminum chloride with caustic soda, for example. Chlorine ions as NaCl do not correspond to acid radicals in the present invention. However, due to the use of less than the equivalent amount of caustic soda during the neutralization reaction of caustic soda, residual aluminum chloride or partially neutralized Al(OH) _x Cl _y (x+y
The chlorine ions of basic aluminum chloride such as =3) function effectively as acid radicals in the present invention. In carrying out the present invention, first, an acidic substance and an alkaline substance, at least one of which is an aluminum compound, and an alkaline substance, specifically an acidic aluminum compound and an alkaline substance, an acidic substance and an alkaline aluminum compound, or an acidic aluminum compound and an alkaline aluminum compound, are combined. Alumina gel is produced by a neutralization reaction. Acidic aluminum compounds include aluminum salts such as aluminum chloride, aluminum nitrate, aluminum sulfate, aluminum acetate, aluminum bromide, aluminum iodide, sodium alum, potassium alum, and ammonium alum, as well as basic aluminum chloride and bases. Any soluble acidic aluminum salts such as basic aluminum salts such as basic aluminum nitrate, basic aluminum sulfate, and basic aluminum acetate can be used, but in general, easily available aluminum chloride, aluminum nitrate, aluminum sulfate, It is suitable to use basic aluminum chloride, basic aluminum nitrate, basic aluminum sulfate, etc., and aluminum chloride, aluminum nitrate, basic aluminum chloride or basic aluminum nitrate are particularly suitable. Examples of alkaline aluminum compounds include water-soluble aluminates such as sodium aluminate, potassium aluminate, and ammonium aluminate. As acidic substances other than aluminum compounds, any acidic substance such as water-soluble inorganic acids and organic acids such as hydrochloric acid, nitric acid, sulfuric acid, chloric acid, perchloric acid, acetic acid, and formic acid can be used, and on the other hand, alkaline substances other than aluminum compounds can be used. Hydroxides, carbonates, bicarbonates, sulfites, borates, etc. of alkali metals, alkaline earth metals or ammonia can be used as alkali metals, especially alkali metals such as sodium carbonate, potassium carbonate, ammonium carbonate, or ammonia. carbonate is suitable. Naturally, combinations in which insoluble salts other than alumina are produced and precipitated simultaneously with alumina in the neutralization reaction are excluded. In addition, in the neutralization reaction, an acidic aluminum compound is used as the acidic substance,
Neutralizing the aluminate with an alkaline substance is more desirable as a reaction form than neutralizing the aluminate with an acidic substance. The alumina gel production reaction due to the neutralization reaction is
If the reaction is carried out at a temperature higher than 100°C, the resulting gel will crystallize and become difficult to peptize, so generally
It is carried out at a temperature below 100°C, preferably between about 5 and 50°C. The alumina gel thus produced is aged if necessary and then washed to remove impurities attached as by-products. The alumina gel after washing can be filtered and dried according to a conventional method to form a dispersion or a cake with any Al ₂ O ₃ content, and its form is appropriately adjusted depending on the purpose of use. However, if alumina gel with a low concentration is used, not only will the alumina concentration of the resulting alumina sol become low, but it will also swell and become highly viscous during hydrothermal treatment, making it difficult to obtain a homogeneous alumina sol. Also, it takes a long time to deflocculate, making it difficult to convert into a sol form. Therefore, it is effective to dry the filtered and purified alumina gel until the Al ₂ O ₃ content is about 15 to 90% by weight, preferably about 55 to 80% by weight, and then subject it to hydrothermal treatment. It is. The alumina gel dried to such an Al ₂ O ₃ content is again converted into an alumina gel slurry having a desired Al ₂ O ₃ concentration with water and hydrothermally treated according to the method of the present invention, but under appropriate drying conditions. By using the _{alumina gel} found in can be manufactured. In carrying out the present invention, the alumina gel obtained by the above method has an acid radical/Al molar ratio of 0.001.
By hydrothermal treatment in the presence of a monovalent inorganic acid or a water-soluble aluminum salt of these acids in an amount of ~0.12, an alumina sol with a high Al ₂ O ₃ concentration and excellent stability over time can be obtained. The monovalent inorganic acids used in the hydrothermal treatment of the method of the present invention include hydrochloric acid, nitric acid, chloric acid, perchloric acid, hydrobromic acid, and hydroiodic acid, but hydrofluoric acid is not suitable. do not have. As water-soluble aluminum salts of these acids, basic aluminum chloride, basic aluminum nitrate, aluminum chloride, aluminum nitrate, etc. can be used, but hydrochloric acid, nitric acid, basic aluminum chloride, aluminum chloride, aluminum nitrate, etc., which are easily available, can be used. etc. are appropriate. Of course, these acid radicals may be used in combination without causing any inconvenience. Furthermore, by appropriately changing the acid radical/Al molar ratio within the range, it is possible to adjust the viscosity of the obtained alumina sol. The amount of acid radicals to be present during hydrothermal treatment is such that the molar ratio of acid radicals/Al to Al ₂ O ₃ in the alumina gel is 0.001.
~0.12, but in the form of the alumina sol to be obtained, for example, when producing an alumina sol with a high Al ₂ O ₃ concentration and extremely excellent stability over time, the acid radical/Al molar ratio is approximately 0.002 to 0.02. It is preferable that the molar ratio of acid radicals _{/ Al} be approximately It is appropriate to control it within the range of 0.02 to 0.10. The molar ratio of acid radical/Al is approximately 0.02.
In the above case, almost 100% of the alumina gel is easily peptized, the resulting sol is extremely clear, and there is no need to over-manipulate the residue. The alumina sol obtained after hydrothermal treatment by appropriately changing the molar ratio of acid radicals/Al within the above range has different viscosity even at the same Al ₂ O ₃ concentration, and in general, the higher the molar ratio of acid radicals/Al, the higher the viscosity of the alumina sol. will rise. As described above, by hydrothermal treatment using a monovalent inorganic acid and the molar ratio of acid group/Al, an alumina sol having a desired viscosity with a higher concentration of Al ₂ O ₃ than conventional products and excellent stability over time can be produced. However, the expected effect of the present invention cannot be obtained by using hydrofluoric acid or divalent or higher acid radicals.
If the molar ratio of Al is less than 0.001, peptization becomes extremely difficult, and it is also difficult to separate the sol from the residue after hydrothermal treatment, resulting in a decrease in productivity and a low conversion rate to alumina sol. Furthermore, when the molar ratio of acid radical/Al exceeds 0.12, it is thought that fibrous alumina is formed.
During hydrothermal treatment, even if it is peptized, it immediately turns into a gel, and even if a sol is obtained, its stability over time is extremely poor. Monovalent inorganic acids or water-soluble aluminum salts of these acids to coexist during the hydrothermal treatment of the alumina gel slurry may be added in the necessary amount when preparing the alumina gel slurry before the hydrothermal treatment, or during the process of obtaining the raw material alumina, i.e. An aluminum compound, which is a monovalent inorganic acid used in hydrothermal treatment, is used as an acidic substance, and is neutralized with an equivalent amount of an alkaline substance to produce an alumina gel with an appropriate amount of monovalent acid groups bound. As long as a predetermined amount of residual acid radicals are present during the subsequent hydrothermal treatment, no new acid radicals are added.
Alternatively, the insufficient amount can be replenished and hydrothermal treatment can be performed. The latter method is more advantageous than the former method because the alumina gel, which is obtained by the neutralization reaction and in which acid groups remain, is not washed out or removed during the washing and drying process and is also advantageous in terms of peptizing properties. This is a preferred embodiment because the operation is simple. The hydrothermal treatment of the present invention is carried out at a temperature of about 120-300°C, preferably about 140-200°C, for about 15 minutes to 7 hours, preferably about 30 minutes to 4 hours. The processing temperature is approx.
Temperatures lower than 120°C are undesirable because peptization takes a long time, and temperatures higher than about 300°C require rapid cooling equipment, high-pressure containers, etc. When hydrothermally treated under the above conditions, the alumina gel slurry gradually peptizes and changes from milky white to opalescent translucent, and it is possible to produce an alumina sol with any alumina concentration up to about 30% by weight and any viscosity. Can be done. The viscosity of the alumina sol obtained by the above is
Approximately 50 cp at 20℃ for a sol with Al ₂ O ₃ concentration of 25% by weight
(centipoise) to a high viscosity of several 100 cp, and in the case of a sol with an Al ₂ O ₃ concentration of 10% by weight, a few cp
It is possible to produce alumina sols with any desired viscosity, from extremely low viscosity of about 100cp to relatively high viscosity of about 100cp.Moreover, these sols do not gel even after being left for more than 3 months and are very stable. It is stable. As a result of X-ray diffraction and electron microscopy, this alumina sol has a boehmite crystal lattice.
Plate-like materials with a size of 0.1 to 0.02 μ are in a dispersed or aggregated state and are not in a fibrous state. The alumina sol produced in this way can be used as it is as a dispersion liquid, or it can be dried and powdered by means such as spray drying or evaporation, and then redispersed in water and converted into a sol. It can also be used as a powder or as a powder. As detailed above, according to the method of the present invention, compared to known methods, a milky-colored translucent alumina sol with a high viscosity, a high Al ₂ O ₃ concentration, and excellent stability over time can be produced. Furthermore, it is possible to produce an alumina sol that provides alumina powder with excellent redispersibility. The alumina sol produced according to the present invention can be
Heat-resistant binders in the electronics industry, ceramics, and foundry industries, soft compounding bases in cosmetics and pharmaceuticals, aerosol products, texture improvement in the textile industry, anti-pilling, emulsifiers, stabilizers, and adhesive properties in paints, pigments, and printing inks. It is particularly useful as an improver, a resin, a surface coating agent for paper, a sizing agent, a catalyst carrier in the petroleum industry, etc. The method of the present invention will be explained in more detail with reference to Examples below, but the method of the present invention is not limited thereto. Example 1 100 parts by weight of a basic aluminum chloride aqueous solution containing 10.2% by weight of Al ₂ O ₃ and Cl/Al (equivalent ratio) of 0.547 was added with unreacted chlorine radicals in an amount to give the acid radical/Al molar ratio shown in Table 1. React the required amount of 4.0% by weight aqueous sodium carbonate solution at 20℃ so that
The resulting alumina gel was aged at the same temperature for about 1 hour, then washed and filtered, and the resulting cake was dried in an air bath at 120°C to obtain a dry gel. The Al ₂ O ₃ content of the resulting dry gel is shown in Table 1.

[Table] Subsequently, the obtained dried gel was adjusted with water to an alumina gel slurry having the concentration shown in Table 2, and each adjusted alumina gel slurry was transferred to an autoclave and soaked in water at a temperature of 150 to 160°C for 2 hours. Heat treated. The properties of the alumina sol obtained as a result are shown in Table 2.

【table】

[Table] Example 2 Add NH ₃ to 100 parts by weight of a basic aluminum nitrate aqueous solution containing 4.46% by weight of Al ₂ O ₃ and NO ₃ /Al (equivalence ratio) of 0.637.
2.43% by weight ammonium carbonate aqueous solution as 123
The alumina gel produced by gradually adding and reacting parts by weight at about 10°C with stirring was aged for about 1 hour, washed until no nitrate radicals were found to flow out, and the resulting cake was then filtered at 100°C. It was dried in an air bath to obtain a dry gel containing 64.1% by weight of Al ₂ O ₃ . This dried gel was divided into portions and added to dilute nitric acid at the acid radical/Al (molar ratio) and Al ₂ O ₃ concentrations shown in Table 3 to prepare an alumina gel slurry. These alumina gel slurries were then transferred into a glass autoclave and incubated at a temperature of 150-160°C for 3
Hydrothermal treatment was carried out for an hour. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 3 100 parts by weight of an aluminum nitrate aqueous solution containing 10.36% by weight of Al ₂ O ₃ and 1.01 NO ₃ /Al (equivalent ratio) was added with an amount of unreacted to give the acid group/Al (molar ratio) shown in Table 4. Required amounts of 10.18% by weight potassium carbonate aqueous solution were reacted at 30°C so that the nitrate radicals remained, and the resulting alumina gel was aged at the same temperature for about 1 hour, then washed and filtered, and the resulting cake was filtered. A dry gel was obtained by drying in an air bath at 120°C. The required amount of potassium carbonate as well as the Al ₂ O ₃ content of the dry gel is shown in Table 4.

[Table] Each of the subsequently obtained dried gels was prepared with water to give an alumina gel slurry with an Al ₂ O ₃ concentration of 10%, and then transferred to an autoclave for 150 min.
Hydrothermal treatment was carried out at a temperature of ~160 °C for 1.5 h. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 4 119 parts by weight of a 16.03% by weight potassium carbonate aqueous solution was gradually added to 100 parts by weight of an aqueous aluminum chloride solution containing 4.38% by weight of Al ₂ O ₃ and Cl/Al (equivalent ratio) of 1.02 while stirring at approximately 40°C. After aging the resulting alumina gel for about 1 hour, it was washed until no chlorine radicals were observed to flow out, and the resulting cake was dried in an air bath at 110°C to remove Al ₂ O ₃ . 68.41
% dry gel was obtained. This dry gel was divided into acid groups/Al (molar ratio) shown in Table 6 and
An alumina gel slurry was prepared by adding it to dilute hydrochloric acid so that the Al ₂ O ₃ concentration was 10% by weight. These alumina gel slurries were then transferred into a glass autoclave at a temperature of 150-160°C.
Hydrothermal treatment was performed for 1.5 hours. Table 6 shows the properties of the alumina sol obtained as a result.

[Table] Based on the results of Examples 1 to 4, specific acid groups/
It is clear that the alumina sol has excellent stability over time in terms of Al (molar ratio) and that it is possible to adjust an alumina sol of any viscosity. Example 5 The alkaline substances shown in Table 7 were added to each 100 parts by weight of the basic aluminum nitrate aqueous solution used in Example 2 so that unreacted nitrate radicals remained in an amount giving an acid radical/Al (molar ratio) of 0.03. The required amount was gradually added and reacted at 30°C with stirring, and the resulting alumina gel was aged for about 1 hour, washed, filtered, and the resulting cake was dried in an air bath at 110°C. Got the gel. The Al ₂ O ₃ content of the dried gel is shown in Table 7.

[Table] Subsequently, the obtained dried gel was prepared with water to an alumina gel slurry with an Al ₂ O ₃ concentration of 10% by weight, and each prepared alumina gel slurry was transferred to an autoclave and heated at 150 to 160°C. Hydrothermal treatment was carried out for 2 hours at temperature. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 6 Aluminum chloride aqueous solution used in Example 4 100
Gradually add 119.5 parts by weight of ammonium carbonate (3.71% by weight as NH ₃ ) while stirring at about 30°C so that an amount of unreacted chlorine radicals remains in the weight part to give an acid radical/Al (molar ratio) of 0.03. After aging the resulting alumina gel for about 1 hour, the resulting cake was washed and filtered and dried in an air bath at 95°C.
A dry gel containing 60.5% by weight of Al ₂ O ₃ was obtained. Subsequently, the obtained dry gel was prepared with water to an alumina gel slurry with an Al ₂ O ₃ concentration of 15% by weight, and then transferred to an autoclave and gradually heated to 150 ~
Hydrothermal treatment was performed at a temperature of 160°C for 2 hours. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 7 3.86% by weight of Al 2 O 3 and 3.86% by weight of K ₂ O ₃ and 4.67% by weight of K 2 O 3 were added so that an amount of unreacted chlorine radicals remained in 94.0 parts by weight of 4.05% by weight hydrochloric acid so that the acid radical/Al (mole ratio) _was 0.07. 100 parts by weight of potassium aluminate was gradually added at 40°C with stirring, and the resulting alumina gel was aged for about 2 hours, then washed and filtered.
It was dried in an air bath at 0.degree. C. to obtain a dry gel with 57.3% by weight _{of Al.sub.2O.sub.3} . Subsequently, the obtained dried gel was prepared with water to give an alumina gel slurry having an Al ₂ O ₃ concentration of 10% by weight, and then transferred to an autoclave and subjected to hydrothermal treatment at a temperature of 150 to 160° C. for 1 hour. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 8 108 parts by weight of a 13.03% by weight potassium bicarbonate aqueous solution were stirred at 30°C into 100 parts by weight of a basic aluminum chloride aqueous solution containing 4.16% by weight of Al ₂ O ₃ and Cl/Al (equivalent ratio) of 0.547. The resulting alumina gel was aged for about 1 hour, washed until no chlorine radicals were observed to flow out, and the resulting cake was dried in an air bath at 120°C.
A dry gel containing 72.4% by weight of Al ₂ O ₃ was obtained. Next, this dry gel was divided into acid groups/Al (molar ratio) 0.03,
The acids shown in Table 11 to give an Al ₂ O ₃ concentration of 15%,
Or, after preparing an alumina gel by adding it to an aluminum salt of the acid, it was transferred to an autoclave and subjected to hydrothermal treatment at a temperature of 150 to 160°C for 2 hours. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 9 NH ₃ was added to 100 parts by weight of an aluminum sulfate aqueous solution containing 4.31% by weight of Al ₂ O ₃ and SO ₄ /Al (equivalent ratio) of 1.01.
115.5 parts by weight of 3.97% ammonium carbonate was gradually added and reacted at 50°C with stirring, and the resulting alumina gel was aged for about 2 hours and washed until no sulfuric acid radicals were observed to flow out. was dried in an air bath at 100° C. to obtain 6.7 parts by weight of a dry gel containing 63.9% by weight of Al ₂ O ₃ . Next, 6.7 parts by weight of _this dry gel was added to 37.1 parts by weight of an aluminum chloride aqueous solution containing 0.31 _{% by weight of Al 2 O 3} and 1.02% by weight of Cl/Al (equivalent ratio). ) After preparing an alumina gel slurry of 0.08, it was transferred to an autoclave and subjected to hydrothermal treatment at a temperature of 150 to 160°C for 1 hour. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 10 Al ₂ O ₃ 4.58% by weight, acetic acid radical/Al (equivalent ratio) 1.01
Add 129 parts by weight of ammonium hydroxide (3.77% by weight as _NH3) to 100 parts by weight of an aqueous solution of aluminum acetate.
Gradual addition reaction was allowed to occur with stirring at 10°C, and the resulting alumina gel was aged for about 1 hour, washed until no acetic acid radicals were observed to flow out, and the resulting cake was filtered in an air bath at 90°C. dry with
8.0 parts by weight of a dry gel containing 56.9% by weight of Al ₂ O ₃ was obtained. Next, 8.0 parts by weight of this dry gel was mixed with 2.93% by weight of Al ₂ O ₃ and
It was added to 53 parts by weight of an aqueous solution of aluminum nitrate with NO ₃ /Al (equivalence ratio) 1.01 to produce 10% by weight of Al ₂ O ₃ and acid radicals/
After preparing an alumina gel slurry with Al (molar ratio) of 0.1, it was transferred to an autoclave and subjected to hydrothermal treatment at a temperature of 150 to 160°C for 30 minutes. As a result, the properties of the obtained alumina sol were
Shown in the table.

[Table] Example 11 The alumina sol obtained in No. 2 of Example 3 was spray-dried at an inlet gas temperature of 130°C and an outlet gas temperature of 55°C to produce alumina powder. The properties of the alumina powder obtained as a result were as follows. Al ₂ O ₃ content: 63.7% by weight Shape: Spherical Average particle size: 20 μ These alumina powders were added to water at 15°C to give an Al ₂ O ₃ concentration of 15% by weight, and stirred for 5 minutes.
redispersed. As a result, the properties of the obtained alumina sol and the results obtained by re-dispersing commercially available dispersible alumina powder to form an alumina sol in the same manner as above are also shown in Table 14 for comparison.

[Table] From Table 14, it is clear that the products of the present invention have superior dispersion rates compared to commercially available products, and also have superior sol stability over time.

Claims (1)

[Claims] 1. A monovalent alumina gel obtained by a liquid phase neutralization reaction between an acidic substance and an alkaline substance, at least one of which is an aluminum compound, in an amount such that the acid radical/Al molar ratio is 0.001 to 0.12. A method for producing an alumina sol, comprising hydrothermal treatment in the presence of an inorganic acid or a water-soluble aluminum salt of these acids. 2. The method according to claim 1, which comprises neutralizing an acidic aluminum compound with an alkaline substance. 3. The method according to claim 2, wherein the acidic aluminum compound is any one of aluminum chloride, aluminum nitrate, basic aluminum chloride, and basic aluminum nitrate. 4. The method according to claim 2, wherein the alkaline substance is a hydroxide, carbonate, bicarbonate, sulfite, or borate of an alkali metal, alkaline earth metal, or ammonia. 5. According to any one of claims 1 to 4, wherein the alumina gel obtained by liquid phase neutralization reaction is once dried and hydrothermally treated so that the Al ₂ O ₃ content becomes 15 to 90% by weight. Method described. 6 Alumina gel with Al ₂ O ₃ content of 55-80% by weight
6. The method according to claim 5, wherein the drying process is carried out to obtain a drying process. 7 The molar ratio of acid radicals/Al during hydrothermal treatment is 0.002~
7. The method according to any one of claims 1 to 6, wherein the 0.10. 8. The method according to any one of claims 1 to 7, wherein the hydrothermal treatment is carried out at a temperature of 120 to 300°C. 9. The method according to any one of claims 1 to 8, wherein the monovalent inorganic acid is hydrochloric acid or nitric acid. 10. The method according to any one of claims 1 to 8, wherein the water-soluble aluminum salt of a monovalent inorganic acid is basic aluminum chloride, basic aluminum nitrate, aluminum chloride, or aluminum nitrate. 11 Neutralize the aluminum compound of the monovalent inorganic acid with an alkaline substance in an equivalent amount or less to obtain an alumina gel in which the monovalent acid radical remains in an amount required or less than that required for subsequent hydrothermal treatment. 2. The method according to claim 1, wherein the hydrothermal treatment is carried out without adding the inorganic acid or the water-soluble aluminum salt of such acid, or with supplementary addition of the necessary amount.